Vehicular drive system

• US 20050209760A1
• Filed: 12/23/2004
• Published: 09/22/2005
• Est. Priority Date: 12/26/2003
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Tabata, Atsushi, Taga, Yutaka
• Granted Patent: US 7,822,524 B2
• Time in Patent Office: Days
• US Class Current: 701/53
• CPC Class Codes: B60K 1/02 comprising more than one electric motor
• CPC Class Codes: B60K 6/365 with the gears having orbital motion
• CPC Class Codes: B60K 6/445 Differential gearing distribution type
• CPC Class Codes: B60K 6/48 Parallel type
• CPC Class Codes: B60K 6/485 Motor-assist type
• CPC Class Codes: B60K 6/547 the transmission being a stepped gearing
• CPC Class Codes: B60W 10/02 including control of driveline clutches
• CPC Class Codes: B60W 10/06 including control of combustion engines
• CPC Class Codes: B60W 10/08 including control of electric propulsion units, e.g. motors or generators
• CPC Class Codes: B60W 10/10 including control of change-speed gearings
• CPC Class Codes: B60W 10/18 including control of braking systems
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60W 20/30 Control strategies involving selection of transmission gear ratio control of change speed gearings, together with other vehicle sub-units B60W10/10; HEV transmission gearing B60K6/36; gearings and control thereof F16H
• CPC Class Codes: B60W 2520/10 Longitudinal speed
• CPC Class Codes: F16H 2061/0223 Generating of new shift maps, i.e. methods for determining shift points for a schedule by taking into account driveline and vehicle conditions
• CPC Class Codes: F16H 2061/6603 characterised by changing ratio in the mechanical gearing
• CPC Class Codes: F16H 2200/0008 specially adapted for front-wheel-driven vehicles
• CPC Class Codes: F16H 2200/0034 the gear ratios comprising two forward speeds
• CPC Class Codes: F16H 2200/0039 the gear ratios comprising three forward speeds
• CPC Class Codes: F16H 2200/0043 the gear ratios comprising four forward speeds
• CPC Class Codes: F16H 2200/0047 : the gear ratios comprising five forward speeds
• CPC Class Codes: F16H 2200/0056 : the gear ratios comprising seven forward speeds
• CPC Class Codes: F16H 2200/006 : the gear ratios comprising eight forward speeds
• CPC Class Codes: F16H 2200/0086 : the gear ratios comprising two reverse speeds
• CPC Class Codes: F16H 2200/2005 : with one sets of orbital gears
• CPC Class Codes: F16H 2200/2007 : with two sets of orbital gears
• CPC Class Codes: F16H 2200/201 : with three sets of orbital gears
• CPC Class Codes: F16H 3/666 : with compound planetary gear units, e.g. two intermeshing orbital gears F16H3/663 takes precedence
• CPC Class Codes: F16H 3/728 : with means to change ratio in the mechanical gearing
• CPC Class Codes: Y02T 10/40 : Engine management systems
• CPC Class Codes: Y02T 10/62 : Hybrid vehicles
• CPC Class Codes: Y10S 903/903 : having energy storing means, e.g. battery, capacitor
• CPC Class Codes: Y10S 903/904 : Component specially adapted for hev
• CPC Class Codes: Y10S 903/906 : Motor or generator
• CPC Class Codes: Y10S 903/909 : Gearing
• CPC Class Codes: Y10S 903/91 : Orbital, e.g. planetary gears

Abstract

Vehicular drive system which is small-sized and/or improved in its fuel economy.

A power distributing mechanism 16, which is provided with a differential-state switching device in the form of a switching clutch C0 and a switching brake B0, is switchable by the switching device between a differential state (continuously-variable shifting state) in which the mechanism is operable as an electrically controlled continuously variable transmission, and a fixed-speed-ratio shifting state in which the mechanism is operable as a transmission having a fixed speed ratio or ratios. The power distributing mechanism 16 is placed in the fixed-speed-ratio shifting state during a high-speed running of the vehicle or a high-speed operation of engine 8, so that the output of the engine 8 is transmitted to drive wheels 38 primarily through a mechanical power transmitting path, whereby fuel economy of the vehicle is improved owing to reduction of a loss of conversion of a mechanical energy into an electric energy. The mechanism 16 is also placed in the fixed-speed-ratio shifting state during a high-output operation of the engine 8, so that the required electric reaction of first electric motor M1 can be reduced, whereby the required size of the first electric motor M1, and the required size of the drive system 10 including the electric motor M1 can be reduced.

Claims

1. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed between the power transmitting member and a drive wheel of a vehicle, characterized by comprising:

a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission.

2. A vehicular drive system according to claim 1, wherein said power distributing mechanism includes a first element fixed to said engine, a second element fixed to said first electric motor, and a third element fixed to said power transmitting member, and said differential-state switching device is operable to permit said first, second and third elements to be rotated relative to each other, for thereby placing the power distributing mechanism in said differential state, and to connect at least two of said first, second and third elements to each other or to hold said second element stationary, for thereby placing the power distributing mechanism in said locked state.

5. A vehicular drive system according to claim 2, wherein said power distributing mechanism is a planetary gear set,

and wherein said first element is a carrier of said planetary gear set, and said second element is a sun gear of said planetary gear set, while said third element is a ring gear of said planetary gear set,

said differential-state switching device including a clutch operable to connect selected two of said carrier, sun gear and ring gear to each other, and/or a brake operable to fix said sun gear to a stationary member.

6. A vehicular drive system according to claim 5, wherein said planetary gear set is a planetary gear set of single-pinion type.

7. A vehicular drive system according to claim 6, wherein said differential-state switching device is operable to connect said carrier and sun gear of said planetary gear set of single-pinion type, for enabling said planetary gear set to operate as a transmission having a speed ratio of 1, or to hold said sun gear stationary, for enabling the planetary gear set as a speed-increasing transmission having a speed ratio lower than 1.

8. A vehicular drive system according to claim 5, wherein said planetary gear set is a planetary gear set of double-pinion type.

9. A vehicular drive system according to claim 8, wherein said differential-state switching device is operable to connect said carrier and sun gear of said planetary gear set of double-pinion type, for enabling said planetary gear set to operate as a transmission having a speed ratio of 1, or to hold said sun gear stationary, for enabling the planetary gear set to operate as a speed-reducing transmission having a speed ratio higher than 1.

10. A vehicular drive system according to claim 1, further comprising an automatic transmission disposed between said power transmitting member and said drive wheel,

and wherein a speed ratio of said drive system is determined by a speed ratio of said automatic transmission.

11. A vehicular drive system according to claim 1, further comprising an automatic transmission disposed between said power transmitting member and said drive wheel, and wherein an overall speed ratio of said drive system is determined by a speed ratio of said power distributing mechanism and a speed ratio of said automatic transmission.

12. A vehicular drive system according to claim 10, wherein said automatic transmission is a step-variable automatic transmission.

25. A vehicular drive system according to claim 10, wherein said power distributing mechanism is disposed on a first axis, and said automatic transmission is disposed on a second axis parallel to said first axis, said power transmitting member being constituted by a pair of members which are disposed on said fist and second axes, respectively, said power distributing mechanism and said automatic transmission being connected to each other through said power transmitting member, so as to transit a drive force therebetween.

26. A vehicular drive system according to claim 25, wherein said second electric motor is disposed on said first axis.

27. A vehicular drive system according to claim 25, wherein said second electric motor is disposed on said second axis.

28. A vehicular drive system according to claim 25, wherein said power transmitting member is located on one side of said power distributing mechanism which is remote from said engine.

29. A vehicular drive system according to claim 25, wherein said automatic transmission includes a differential drive gear as an output rotary member thereof, said differential drive gear being located at one end of said automatic transmission which is remote from said power transmitting member.

3. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed between the power transmitting member and a drive wheel of a vehicle, characterized by comprising:

a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a fixed-speed-ratio shifting state in which the power distributing mechanism is operable as a transmission having a single speed ratio or a plurality of speed ratios.

4. A vehicular drive system according to claim 3, wherein said power distributing mechanism include a first element fixed to said engine, a second element fixed to said first electric motor, and a third element fixed to said power transmitting member, and said differential-state switching device is operable to permit said first, second and third elements to be rotated relative to each other, for thereby placing the power distributing mechanism in said differential state, and to connect at least two of said first, second and third elements to each other or to hold said second element stationary, for thereby placing the power distributing mechanism in said fixed-speed-ratio shifting state.

13. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a first element and a third element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

said step-variable automatic transmission includes a second planetary gear set, a third planetary gear set and a fourth planetary gear set, and has five rotary elements each of which is constituted by at least one of sun gears, carriers and ring gears of said second, third and fourth planetary gear sets, rotating speeds of said five rotary elements being indicated along respective straight lines in a collinear chart in which said five rotary elements are arranged as a fourth element, a fifth element, a sixth element, a seventh element and an eighth element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said fifth element being selectively fixed through a second brake to the stationary member, while said sixth element being selectively fixed through a third brake to the stationary member, said seventh element being fixed to an output rotary member of said step-variable automatic transmission, said eighth element being selectively connected through a first clutch to said power transmitting member, said step-variable automatic transmission having a plurality of operating positions that are established by engaging actions of respective combinations of said first clutch, second clutch, first brake, second brake and third brake.

14. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set of single-pinion type having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, and said first sun gear being fixed to said first electric motor, while said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable to fix said first sun gear to a stationary member; and

said step-variable automatic transmission includes a second planetary gear set of single-pinion type, a third planetary gear set of single-pinion type and a fourth planetary gear set of single-pinion type, said second planetary gear set having a second sun gear, a second carrier and a second ring gear, and said third planetary gear set having a third sun gear, a third carrier and a third ring gear, while said fourth planetary gear set having a fourth sun gear, a fourth carrier and a fourth ring gear, said second sun gear and said third sun gear being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said second carrier being selectively fixed through a second brake to the stationary member, while said fourth ring gear being selectively fixed through a third brake to the stationary member, and wherein said second ring gear, said third carrier and said fourth carrier are fixed to an output rotary member of said step-variable automatic transmission, and said third ring gear and said fourth sun gear are selectively connected through a first clutch to said power transmitting member.

15. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a first element and a third element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

said step-variable automatic transmission includes a second planetary gear set and a third planetary gear set, and has four rotary elements each of which is constituted by at least one of sun gears, carriers and ring gears of said second and third planetary gear sets, rotating speeds of said fourth rotary elements being indicated along respective straight lines in a collinear chart in which said four rotary elements are arranged as a fourth element, a fifth element, a sixth element and a seventh element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member; and

said fifth element being selectively fixed through a second brake to the stationary member, while said sixth element being fixed to an output rotary member of said step-variable automatic transmission, said seventh element being selectively connected through a first clutch to said power transmitting member, said step-variable automatic transmission having a plurality of operating positions that are established by engaging actions of respective combinations of said first clutch, second clutch, first brake and second brake.

16. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set of single-pinion type having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, and said first sun gear being fixed to said first electric motor, while said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable to fix said first sun gear to a stationary member; and

said step-variable automatic transmission includes a second planetary gear set of single-pinion type and a third planetary gear set of single-pinion type, said second planetary gear set having a second sun gear, a second carrier and a second ring gear, and said third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said third carrier being selectively fixed through a second brake to the stationary member, while said second carrier and said third ring gear being fixed to an output rotary element of said step-variable automatic transmission, said second ring gear being selectively connected through a first clutch to said power transmitting member.

17. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a first element and a third element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

said step-variable automatic transmission includes a second planetary gear set and a third planetary gear set, and has four rotary elements each of which is constituted by at least one of sun gears, carriers and ring gears of said second and third planetary gear sets, rotating speeds of said fourth rotary elements being indicated along respective straight lines in a collinear chart in which said four rotary elements are arranged as a fourth element, a fifth element, a sixth element and a seventh element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected through a second clutch to said power transmitting member and selectively connected through a fourth brake to said engine, and said fifth element being selectively connected through a third clutch to said engine and selectively fixed through a second brake to the stationary member, while said sixth element being fixed to an output rotary member of said step-variable automatic transmission, said seventh element being selectively connected through a first clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, said step-variable automatic transmission having a plurality of operating positions that are established by engaging actions of respective combinations of said first clutch, second clutch, third clutch and fourth clutch, first brake and second brake.

18. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set of single-pinion type having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, and said first sun gear being fixed to said first electric motor, while said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable to fix said first sun gear to a stationary member; and

said step-variable automatic transmission includes a second planetary gear set of double-pinion type and a third planetary gear set of single-pinion type, said second planetary gear set having a second sun gear, a second carrier and a second ring gear, and said third planetary gear set having a third sun gear, a third carrier and a third ring gear, said third sun gear being selectively connected through a second clutch to said power transmitting member and selectively connected through a fourth clutch to said engine, said second carrier and said third carrier being selectively connected through a third clutch to said engine and selectively fixed through a second brake to the stationary member, while said second ring gear and said third ring gear being fixed to an output rotary element of said step-variable automatic transmission, said second sun gear being selectively connected through a first clutch to said power transmitting member and selectively fixed through a first brake to the stationary member.

19. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a third element and a first element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

said step-variable automatic transmission includes a second planetary gear set and a third planetary gear set, and has four rotary elements each of which is constituted by at least one of sun gears, carriers and ring gears of said second and third planetary gear sets, rotating speeds of said fourth rotary elements being indicated along respective straight lines in a collinear chart in which said four rotary elements are arranged as a fourth element, a fifth element, a sixth element and a seventh element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected through a third clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said fifth element being selectively connected through a second clutch to said engine and selectively fixed through a second brake to the stationary member, while said sixth element being fixed to an output rotary member of said step-variable automatic transmission, said seventh element being selectively connected through a first clutch to said power transmitting member, said step-variable automatic transmission having a plurality of operating positions that are established by engaging actions of respective combinations of said first clutch, second clutch, third clutch, first brake and second brake.

20. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set of double-pinion type having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, and said first sun gear being fixed to said first electric motor, while said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable to fix said first sun gear to a stationary member; and

said step-variable automatic transmission includes a second planetary gear set of single-pinion type and a third planetary gear set of double-pinion type, said second planetary gear set having a second sun gear, a second carrier and a second ring gear, and said third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected through a third clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, said second carrier and said third carrier being selectively connected through a second clutch to said engine and selectively fixed through a second brake to the stationary member, while said second ring gear and said third ring gear being fixed to an output rotary element of said step-variable automatic transmission, said third sun gear being selectively connected through a first clutch to said power transmitting member.

21. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a first element and a third element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

said step-variable automatic transmission includes a second planetary gear set, a third planetary gear set and a fourth planetary gear set, and has five rotary elements each of which is constituted by at least one of sun gears, carriers and ring gears of said second, third and fourth planetary gear sets, rotating speeds of said five rotary elements being indicated along respective straight lines in a collinear chart in which said five rotary elements are arranged as a fourth element, a fifth element, a sixth element, a seventh element and an eighth element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said fifth element being selectively fixed through a second brake to the stationary member, while said sixth element being selectively fixed through a third brake to the stationary member, said seventh element being fixed to an output rotary member of said step-variable automatic transmission, said eighth element being fixed to said power transmitting member, said step-variable automatic transmission having a plurality of operating positions that are established by engaging actions of respective combinations of said second clutch, first brake, second brake and third brake.

30. A vehicular drive system according to claim 21, wherein a direction of an output rotary motion of said power distributing mechanism transmitted to said automatic transmission is reversed with respect to that of an input rotary motion of said power distributing mechanism, said drive system having a rear-drive position established by engaging said third brake.

32. A vehicular drive system according to claim 21, wherein a direction of an output rotary motion of said power distributing mechanism to be transmitted to said automatic transmission is reversed with respect to that of an input rotary motion of said power distributing mechanism, said drive system having a rear-drive position established by engaging said second clutch.

22. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set of single-pinion type having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, and said first sun gear being fixed to said first electric motor, while said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable to fix said first sun gear to a stationary member; and

said step-variable automatic transmission includes a second planetary gear set of single-pinion type, a third planetary gear set of single-pinion type and a fourth planetary gear set of single-pinion type, said second planetary gear set having a second sun gear, a second carrier and a second ring gear, and said third planetary gear set having a third sun gear, a third carrier and a third ring gear, while said fourth planetary gear set having a fourth sun gear, a fourth carrier and a fourth ring gear, said second sun gear and said third sun gear being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said second carrier being selectively fixed through a second brake to the stationary member, while said fourth ring gear being selectively fixed through a third brake to the stationary member, and wherein said second ring gear, said third carrier and said fourth carrier are fixed to an output rotary member of said step-variable automatic transmission, and said third ring gear and said fourth sun gear are fixed to said power transmitting member.

23. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a first element and a third element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

said step-variable automatic transmission includes a second planetary gear set and a third planetary gear set, and has four rotary elements each of which is constituted by at least one of sun gears, carriers and ring gears of said second and third planetary gear sets, rotating speeds of said fourth rotary elements being indicated along respective straight lines in a collinear chart in which said four rotary elements are arranged as a fourth element, a fifth element, a sixth element and a seventh element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, and said fifth element being selectively fixed through a second brake to the stationary member, while said sixth element being fixed to an output rotary member of said step-variable automatic transmission, said seventh element being fixed to said power transmitting member, said step-variable automatic transmission having a plurality of operating positions that are established by engaging actions of respective combinations of said second clutch, first brake and second brake.

31. A vehicular drive system according to claim 23, wherein a direction of an output rotary motion of said power distributing mechanism to be transmitted to said automatic transmission is reversed with respect to that of an input rotary motion of said power distributing mechanism, said drive system having a rear-drive position established by engaging said second brake.

24. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set of single-pinion type having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, and said first sun gear being fixed to said first electric motor, while said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable to fix said first sun gear to a stationary member; and

said step-variable automatic transmission includes a second planetary gear set of single-pinion type and a third planetary gear set of single-pinion type, and said second planetary gear set having a second sun gear, a second carrier and a second ring gear, said third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected through a second clutch to said power transmitting member and selectively fixed through a first brake to the stationary member, said third carrier being selectively fixed through a second brake to the stationary member, while said second carrier and said third ring gear being fixed to an output rotary element of said step-variable automatic transmission, said second ring gear being fixed to said power transmitting member.

33. A method of controlling a vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed between the power transmitting member and a drive wheel of a vehicle, characterized by comprising:

placing said power distributing mechanism selectively, on the basis of a condition of the vehicle, in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission.

35. A method according to claim 33 or 34, wherein the drive system further includes an automatic transmission disposed between the power transmitting member and the drive wheel, and an overall speed ratio of the drive system is determined by a speed ratio of the power distributing mechanism and a speed ratio of the automatic transmission, and wherein said overall speed ratio is controlled by controlling the speed ratio of the power distributing mechanism and the speed ratio of the automatic transmission, on the basis of the condition of the vehicle.

36. A method according to claim 33, wherein said condition of the vehicle is represented by a value relating to a drive force of the vehicle.

37. A method according to claim 33, wherein said condition of the vehicle is represented by a running speed of the vehicle.

34. A method controlling a vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed between the power transmitting member and a drive wheel of a vehicle, characterized by comprising:

placing said power distributing mechanism selectively, on the basis of a condition of the vehicle, in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a fixed-speed-ratio shifting state in which the power distributing mechanism is operable as a transmission having a single speed ratio or a plurality of speed ratios.

38. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear set having three elements consisting of a sun gear, a carrier and a ring gear rotating speeds of which are indicated along respective straight lines in a collinear chart in which said three elements are arranged as a second element, a first element and a third element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said first element being fixed to said engine, said second element being fixed to said first electric motor, while said third element being fixed to said power transmitting member, said power distributing mechanism further including a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to a stationary member, said power distributing mechanism being placed in a differential state by releasing said switching clutch and/or said switching brake, and in a fixed-speed-ratio shifting state in which said power distributing mechanism has a fixed speed ratio, by engaging said switching clutch and/or said switching brake; and

a direction of a rotary motion of said power transmitting member to be transmitted to said automatic transmission in a rear-drive position of the drive system is reversed by said power distributing mechanism, with respect to that in forward-drive positions of the drive system.

39. A vehicular drive system according to claim 38, wherein said step-variable automatic transmission includes a planetary gear set having a sun gear, a carrier and a ring gear which mesh with each other and constitute at least three rotary elements rotating speeds of which are indicated along respective straight lines in a collinear chart in which said at least three rotary elements are arranged as a fourth element, a fifth element and a sixth element, respectively, in the order of description, in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being fixed to said power transmitting member such that a drive force can be transmitted to the power transmitting member, and said fifth element being fixed to an output rotary element of said automatic transmission such that the drive force can be transmitted to the output rotary element, while said sixth element is selectively fixed through a brake to a stationary member,

and wherein a rear-drive position of the drive system is established by engaging said brake.

40. A vehicular drive system according to claim 38, wherein said step-variable automatic transmission includes a planetary gear set having a sun gear, a carrier and a ring gear which mesh with each other and constitute at least three rotary elements, said fourth element being fixed to said power transmitting member such that a drive force can be transmitted to the power transmitting member, and said fifth element being fixed to an output rotary element of said automatic transmission such that the drive force can be transmitted to the output rotary element,

and wherein said automatic transmission further includes a clutch operable to rotate the rotary elements as a unit, and a rear-drive position of the drive system is established by engaging said clutch.

41. A control device for a vehicular drive system arranged to transmit an output of an engine to a drive wheel of a vehicle, characterized by comprising:

a transmission mechanism of switchable type switchable between a continuously-variable shifting state in which the transmission mechanism is operable as an electrically controlled continuously variable transmission, and a step-variable shifting state in which the transmission mechanism is operable as a step-variable transmission; and

switching control means for placing said transmission mechanism of switchable type selectively in one of said continuously-variable shifting state and said step-variable shifting state, on the basis of a predetermined condition of the vehicle.

42. A control device according claim 41, wherein said transmission mechanism of switchable type includes a power distributing mechanism having a first element fixed to said engine, a second element fixed to a first electric motor, and a third element fixed to a power transmitting member,

and wherein said power distributing mechanism includes a differential-state switching device operable to place said transmission mechanism of switchable type selectively in said continuously-variable shifting state and said step-variable shifting state,

said switching control means being operable to control said differential-state switching device, so as to place said transmission mechanism selectively in said continuously-variable shifting state and said step-variable shifting state.

43. A control device according to claim 42, wherein said differential-state switching device is operable not only to place said transmission mechanism of switchable type selectively in said continuously-variable shifting state and said step-variable shifting state, and but also to place said transmission mechanism placed in said step-variable shifting state, in one of a plurality of operating positions thereof,

said switching control means being operable to control said differential-state switching device on the basis of the predetermined condition of the vehicle, to place the transmission mechanism in one of said plurality of operating positions after the transmission mechanism is switched from said continuously-variable shifting state to said step-variable shifting state.

44. A control device according to claim 41, wherein said predetermined condition of the vehicle includes a predetermined upper limit of a running speed of the vehicle,

and wherein said switching control means is operable to place the transmission mechanism of switchable type in said step-variable shifting state, when an actual value of the running speed of the vehicle has exceeded said predetermined upper limit.

45. A control device according to claim 41, wherein said predetermined condition of the vehicle includes a predetermined upper limit of a running speed of the vehicle,

and wherein said switching control means is operable to inhibit the transmission mechanism of switchable type from being placed in said continuously-variable shifting state, when an actual value of the running speed of the vehicle has exceeded said predetermined upper limit.

46. A control device according to claim 41, wherein said predetermined condition of the vehicle includes a predetermined upper limit of an output of the vehicle,

and wherein said switching control means is operable to place the transmission mechanism of switchable type in said step-variable shifting state, when a drive-force-related value of the vehicle has exceeded said upper limit.

47. A control device according to claim 41, wherein said predetermined condition of the vehicle includes a predetermined upper limit of an output of the vehicle,

and wherein said switching control means is operable to inhibit the transmission mechanism of switchable type from being placed in said continuously-variable shifting state, when a drive-force-related value of the vehicle has exceeded said upper limit.

48. A control device according to claim 44, wherein said predetermined condition of the vehicle is represented by a stored switching boundary line map including an upper vehicle-speed limit line and an upper output limit line that respectively represent the upper limit of the running speed and an upper limit of a drive-force-related value of the vehicle, with which actual values of the running speed and the drive-force-related value are compared.

49. A control device according to claim 41, wherein said predetermined condition of the vehicle includes a predetermined diagnosing condition for determining whether control components operable to place said transmission mechanism of switchable type in said continuously-variable shifting state have a deteriorated function,

and wherein said switching control means is operable to place said transmission mechanism in said step-variable shifting state, when said predetermined diagnosing condition is satisfied.

50. A control device according to claim 41, wherein said predetermined condition of the vehicle includes said predetermined diagnosing condition,

and wherein said switching control means is operable to inhibit said transmission mechanism of switchable type from being placed in said continuously-variable shifting state, when said predetermined diagnosing condition is satisfied.

51. A control device according to claim 42, wherein said differential-state switching device includes a coupling device operable to connect selected two of said first through third elements to each other, and/or fix said second element to a stationary member,

and where said switching control means places said transmission mechanism in said continuously-variable shifting state by releasing said engaging device to permit said first, second and third elements to be rotatable relative to each other, and places said transmission mechanism in said step-variable shifting state by engaging said coupling device to connect at least two of said first, second and third elements to each other or fix said second element to the stationary member.

52. A control device according to claim 51, wherein said predetermined condition of the vehicle includes a predetermined upper limit of a running speed of the vehicle,

and wherein said switching control means is operable to control said coupling device, so as to fix said second element to the stationary member when an actual value of the running speed of the vehicle has exceeded said predetermined upper limit.

53. A control device according to claim 51, wherein said predetermined condition of the vehicle includes a predetermined upper limit of an output of the vehicle,

and wherein said switching control means is operable to control said coupling device, so as to connect at least two of said first, second and third elements to each other, when said drive-force-related value of the vehicle has exceeded said upper limit.

54. A control device according to claim 51, wherein said power distributing mechanism is a planetary gear set,

and wherein said first element is a carrier of said planetary gear set, and said second element is a sun gear of said planetary gear set, while said third element is a ring gear of said planetary gear set,

said differential-state switching device including a clutch operable to connect selected two of said carrier, sun gear and ring gear to each other, and/or a brake operable to fix said sun gear to the stationary member.

55. A control device according to claim 54, wherein said planetary gear set is a planetary gear set of single-pinion type.

56. A vehicular drive system according to claim 55, wherein said switching control means is operable to control said coupling device, so as to connect said carrier and sun gear of said planetary gear set of single-pinion type, for enabling said planetary gear set to operate as a transmission having a speed ratio of 1, or to hold said sun gear stationary, for enabling the planetary gear set as a speed-increasing transmission having a speed ratio lower than 1.

57. A vehicular drive system according to claim 54, wherein said planetary gear set is a planetary gear set of double-pinion type.

58. A vehicular drive system according to claim 57, wherein said differential-state switching device is operable to control said coupling device, so as to connect said carrier and sun gear of said planetary gear set of double-pinion type, for enabling said planetary gear set to operate as a transmission having a speed ratio of 1, or to hold said sun gear stationary, for enabling the planetary gear set to operate as a speed-reducing transmission having a speed ratio higher than 1.

59. A vehicular drive system according to claim 42, wherein said transmission mechanism of switchable type further comprises an automatic transmission disposed between said power transmitting member and said drive wheel and connected in series to said power distributing mechanism,

and wherein a speed ratio of said transmission mechanism of switchable type is determined by a speed ratio of said automatic transmission.

60. A vehicular drive system according to claim 59, wherein an overall speed ratio of said transmission mechanism of switchable type is determined by a speed ratio of said power distributing mechanism and a speed ratio of said automatic transmission.

61. A control device according to claim 59, wherein said automatic transmission is a step-variable transmission, and said step-variable transmission is shifted according to a stored shifting boundary line map.

62. A control device according to claim 41, wherein said switching control means places said transmission mechanism in said continuously-variable shifting state when the vehicle is in a predetermined running state, and does not place said transmission mechanism in said continuously-variable shifting state when the vehicle is in the other running state.

63. A control device for a vehicular drive system arranged to transmit outputs of a plurality of drive power sources to a drive wheel of a vehicle, characterized by comprising:

a differential gear device of switchable type disposed in a power transmitting path between said plurality of drive power sources and the drive wheel and switchable between a locked state and a non-locked state; and

switching control means for placing said differential gear device of switchable type selectively in one of said locked state and said non-locked state, on the basis of a predetermined condition of the vehicle.

64. A control device according to claim 63, wherein said switching control means places said differential gear device in said non-locked state when the vehicle is in a predetermined running state, and does not place said differential gear device in said non-locked state when the vehicle is in the other running state.

65. A control device for a vehicular drive system arranged to transmit an output of an engine to a drive wheel of a vehicle, characterized by comprising:

a transmission mechanism of switchable type switchable between a continuously-variable shifting state in which the transmission mechanism is operable as an electrically controlled continuously variable transmission, and a fixed-speed-ratio shifting state; and

switching control means for placing said transmission mechanism of switchable type selectively in one of said continuously-variable shifting state and said fixed-speed-ratio shifting state, on the basis of a running speed of the vehicle, and a load of the vehicle or an output torque of the vehicular drive system, and according to a predetermined relationship.

66. A control device for a vehicular drive system arranged to transmit an output of an engine to a drive wheel of a vehicle, characterized by comprising:

a transmission mechanism of switchable type switchable between a continuously-variable shifting state in which the transmission mechanism is operable as an electrically controlled continuously variable transmission, and a step-variable shifting state in which the transmission mechanism is operable as a step-variable transmission; and

switching control means for placing said transmission mechanism of switchable type selectively in one of said continuously-variable shifting state and said step-variable shifting state, on the basis of a running speed of the vehicle, and a load of the vehicle or an output torque of the vehicular drive system, and according to a predetermined relationship.

67. A control device for a vehicular drive system arranged to transmit an output of an engine to a drive wheel of a vehicle, characterized by comprising:

a transmission mechanism of switchable type switchable between a continuously-variable shifting state in which the transmission mechanism is operable as an electrically controlled continuously variable transmission, and a fixed-speed-ratio shifting state;

a control map which defines, with control parameters consisting of a running speed of the vehicle and a load of the vehicle or an output torque of the vehicular drive system, a first region in which said transmission mechanism of switchable type is placed in said continuously-variable shifting state, and a second region in which the transmission mechanism is placed in said fixed-speed-ratio shifting state; and

switching control means for placing said transmission mechanism of switchable type selectively in one of said continuously-variable shifting state and said fixed-speed-ratio shifting state, according to said control map.

68. A control device for a vehicular drive system arranged to transmit an output of an engine to a drive wheel of a vehicle, characterized by comprising:

a transmission mechanism of switchable type switchable between a continuously-variable shifting state in which the transmission mechanism is operable as an electrically controlled continuously variable transmission, and a step-variable shifting state;

a control map which defines, with control parameters consisting of a running speed of the vehicle and a load of the vehicle or an output torque of the vehicular drive system, a first region in which said transmission mechanism of switchable type is placed in said continuously-variable shifting state, and a second region in which the transmission mechanism is placed in said step-variable shifting state; and

switching control means for placing said transmission mechanism of switchable type selectively in one of said continuously-variable shifting state and said step-variable shifting state, according to said control map.

69. A control device for a vehicular drive system including a continuously-variable shifting portion which functions as a continuously variable transmission and which has a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, said vehicular drive system further including a step-variable shifting portion which constitutes a part of said power transmitting path and which functions as a step-variable automatic transmission, characterized by comprising:

a differential-state switching device provided in said differential mechanism and operable to place said continuously-variable shifting portion selectively in a differential state in which the differential mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the differential mechanism is in a non-differential state;

a first control map which defines, with predetermined control parameters, shifting lines for effecting a shifting control of said step-variable automatic transmission; and

a second control map which defines, with the same control parameters as used for said first control map, a differential region in which said differential mechanism is placed in said differential state by said differential-state switching device, and a non-differential state in which the differential mechanism is placed in said non-differential state by said differential-state switching device.

72. A control device according to claim 69, wherein said predetermined control parameters consist of a running speed of the vehicle, and a load of the vehicle or an output torque of said vehicular drive system.

70. A control device for a vehicular drive system including a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, characterized by comprising:

a differential-state switching device operable to place said differential mechanism selectively in a differential state in which the differential mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the differential mechanism is in a non-differential state;

a first control map which defines, with predetermined control parameters, a plurality of regions for effecting a drive-power-source selection control to select at least one drive power source to be operated to generate a drive force, from among said engine, said first electric motor and said second electric motor; and

a second control map which defines, with the same control parameters used for said first control map, a differential region in which the differential mechanism is placed in said differential state by said differential-state switching device, and a non-differential region in which the differential mechanism is placed in said non-differential state by said differential-state switching device.

71. A control device for a vehicular drive system including a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, characterized by comprising:

a differential-state switching device operable to place said differential mechanism selectively in a differential state in which the differential mechanism is operable as an electrically controlled continuously variable transmission, and a step-variable shifting state in which the differential mechanism is operable as a step-variable transmission;

a first control map which defines, with predetermined control parameters, a plurality of regions for effecting a drive-power-source selection control to select at least one drive power source to be operated to generate a drive force, from among said engine, said first electric motor and said second electric motor; and

a second control map which defines, with the same control parameters used for said first control map, a differential region in which the differential mechanism is placed in said differential state by said differential-state switching device, and a non-differential region in which the differential mechanism is placed in said non-differential state by said differential-state switching device.

73. A control device for a vehicular drive system arranged to transmit an output of an engine to a drive wheel of a vehicle, characterized by comprising:

a transmission mechanism of switchable type switchable between an electrically established continuously-variable shifting state in which the transmission mechanism is operable as an electrically controlled continuously variable transmission, and a step-variable shifting state in which the transmission mechanism is operable as a step-variable transmission; and

switching control means operable to place said transmission mechanism of switchable type selectively in one of said continuously-variable shifting state and said step-variable shifting state in which a fuel consumption ratio of the vehicle is lower.

74. A control device according to claim 73, wherein said fuel consumption ratio is calculated from time to time, on the basis of a condition of the vehicle.

75. A control device according to claim 74, wherein said fuel consumption ratio which is calculated from time to time on the basis of the condition of the vehicle is calculated on the basis of a fuel consumption ratio of the engine obtained according to a stored relationship.

76. A control device according to claim 74, wherein said fuel consumption ratio which is calculated from time to time on the basis of the condition of the vehicle is obtained by taking account of an efficiency of power transmission from the engine to the drive wheel.

77. A control device according to claim 76, wherein said efficiency of power transmission changes with a running resistance of the vehicle.

78. A control device according to claim 76, wherein said efficiency of power transmission changes with a running speed of the vehicle.

79. A control device according to claim 76, wherein said efficiency of power transmission changes with a drive-force-related value of the vehicle.

80. A control device according to claim 73, wherein said transmission mechanism of switchable type is placed selectively in one of said continuously-variable shifting state and said step-variable shifting state, on the basis of a condition of the vehicle, and according to a stored relationship which defines shifting regions corresponding to said continuously-variable and step-variable shifting states such that said transmission mechanism is placed in one of said continuously-variable and step-variable shifting states in which the fuel consumption ratio is lower.

81. A control device according to claim 73, wherein said switching control means is operable to place said transmission mechanism of switchable type in said step-variable shifting state when an actual speed of the vehicle has exceeded a predetermined upper limit.

82. A control device according to claim 73, wherein said switching control means is operable to place said transmission mechanism of switchable type in said step-variable shifting state when a drive-force-related value of the vehicle has exceeded a predetermined upper limit.

83. A control device according to claim 73, wherein said switching control means is operable to place said transmission mechanism of switchable type in said step-variable shifting state when it is determined that a predetermined diagnosing condition indicative of functional deterioration of control components that are operable to place the transmission mechanism in said electrically established continuously-variable shifting state is satisfied.

84. A control device according to claim 73, wherein said transmission mechanism of switchable type includes a power distributing mechanism having a first element fixed to said engine, a second element fixed to a first electric motor, and a third element fixed to a second electric motor and a power transmitting member,

said power distributing mechanism including a differential-state switching device operable to place said transmission mechanism selectively in one of said continuously-variable shifting state and said step-variable shifting states,

said switching control means controlling said differential-state switching device to place said transmission mechanism selectively in one of said continuously-variable shifting state and said step-variable shifting state.

85. A control device according to claim 84, wherein said differential-state switching device includes a coupling device operable to connect selected two of said first, second and third elements to each other, and/or fix said second element to a stationary member,

said switching control means being operable to release said coupling device to permit said first, second and third elements to be rotated relative to each other, for thereby placing said transmission mechanism in said continuously-variable shifting state, and to engage said coupling device to connect at least two of said first, second and third elements to each other or fix said second element to said stationary member, for thereby placing said transmission mechanism in said step-variable shifting state.

86. A control device according to claim 85, wherein said power distributing mechanism is a planetary gear set,

and wherein said first element is a carrier of said planetary gear set, and said second element is a sun gear of said planetary gear set, while said third element is a ring gear of said planetary gear set,

said differential-state switching device including a clutch operable to connect selected two of said carrier, sun gear and ring gear to each other, and/or a brake operable to fix said sun gear to said stationary member.

87. A control device according to claim 86, wherein said planetary gear set is a planetary gear set of single-pinion type.

88. A control device according to claim 87, wherein said switching control device is operable to control said coupling device, so as to connect said carrier and said sun gear of said planetary gear set of single-pinion type, for enabling said planetary gear set to operate as a transmission having a speed ratio of 1, or to hold said sun ear stationary, for enabling the planetary gear set as a speed-increasing transmission having a speed ratio lower than 1.

89. A control device according to claim 84, wherein said transmission mechanism of switchable type further comprises an automatic transmission disposed in series between said power transmitting member and said drive wheel,

and wherein a speed ration of said transmission mechanism of switchable type is determined by a speed ratio of said automatic transmission.

90. A control device according to claim 89, wherein an overall speed ratio of said transmission mechanism of switchable type is determined by a speed ratio of said power distributing mechanism and the speed ratio of said automatic transmission.

91. A control device according to claim 89, wherein said automatic transmission is a step-variable automatic transmission, which is shifted according to a stored shifting control map.

92. A control device for a vehicular drive system including a continuously-variable shifting portion operable in an electrically established continuously-variable shifting state, and a step-variable shifting portion operable as a step-variable shifting state, said continuously-variable shifting portion including a differential gear device having three elements consisting of a first element fixed to a first electric motor, a second element fixed to an engine and a third element fixed to an output shaft, said continuously-variable shifting portion further including a second electric motor operatively connected to a power transmitting path between said output shaft and a drive wheel of a vehicle, said step-variable shifting portion being disposed in said power transmitting path, characterized by comprising:

speed-ratio control means operable in said continuously-variable shifting state of said continuously-variable shifting portion, for controlling a speed ratio of said step-variable shifting portion and a speed ratio of said continuously-variable shifting portion, so as to maximize a fuel economy of the vehicle.

94. A control device according to claim 92, wherein said speed-ratio control means is operable to control the speed ratio of said step-variable shifting portion and the speed ratio of said continuously-variable shifting portion, on the basis of an efficiency of said first electric motor of said continuously-variable shifting portion and an efficiency of said second electric motor of said continuously-variable shifting portion.

95. A control device according to claim 92, wherein said speed-ratio control means is operable to change a rotating speed of said output shaft of said continuously-variable shifting portion, by adjusting the speed ratio of said step-variable shifting portion.

96. A control device according to claim 92, further comprising:

a switching device operable to switch said continuously-variable shifting portion between said continuously-variable shifting portion in which the speed ratio is continuously variable, and said step-variable shifting portion in which the speed ratio is held constant; and

continuously-variable-shifting-run determining means operable for determining that said continuously-variable shifting portion has been switched by said switching device to said step-variable shifting state,

and wherein said speed-ratio control means is operable, upon determination by said continuously-variable-shifting run determining means that said continuously-variable shifting portion has been switched by said switching device to said continuously-variable shifting state, to control the speed ratio of said step-variable shifting portion and the speed ratio of said continuously-variable shifting portion, so as to maximize the fuel economy of the vehicle.

93. A control device for a vehicular drive system including a continuously-variable shifting portion operable in an electrically established continuously-variable shifting state, and a step-variable shifting portion operable in a step-variable shifting state, said continuously-variable shifting portion including a differential gear device having three elements consisting of a first element fixed to a first electric motor, a second element fixed to an engine and a third element fixed to an output shaft, said continuously-variable shifting portion further including a second electric motor operatively connected to a power transmitting path between said output shaft and a drive wheel of a vehicle, said step-variable shifting portion being disposed in said power transmitting path, characterized by comprising:

speed-ratio control means operable in said continuously-variable shifting state of said continuously-variable shifting portion, for controlling a speed ratio of said continuously-variable shifting portion, depending upon a speed ratio of said step-variable shifting portion.

97. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear device having as three elements a sun gear, a carrier and a ring gear, said three elements consisting of a first element, a second element and a third element which are arranged in the order of said second element, said first element and said third elements in a direction from one of opposite ends of a collinear chart toward the other end, said collinear chart having straight lines indicating rotating speeds of said three elements, said first element being fixed to said engine, said second element being fixed to said first electric motor, and said third element being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a second planetary gear set and a third planetary gear set, said second and third planetary gear sets having sun gears, carriers and ring gears selected ones of which are fixed to each other to constitute four elements consisting of a fourth element, a fifth element, a sixth element and a seventh elements rotating speeds of which are indicated by straight lines of a collinear chart in which said four elements are arranged in the order of said fourth element, said fifth element, said sixth element and said seventh element in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said fifth element being selectively connected to said power transmitting member through a third clutch and selectively fixed to said stationary member through a second brake, said sixth element being fixed to an output rotary member of said automatic transmission, and said seventh element being selectively connected to said power transmitting member through a first clutch, said automatic transmission having a plurality of gear positions which are established by engaging respective combinations of said first, second and third clutches and said first and second brakes.

98. A vehicular drive system according to claim 97, wherein said differential-state switching device includes a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to said stationary member, said first planetary gear set being placed in said differential state by releasing said switching clutch and/or said switching brake, and in said locked state by engaging said switching clutch and/or said switching brake.

99. A vehicular drive system according to claim 98, wherein said plurality of gear positions includes:

a first-gear position which has a highest speed ratio and which is established by engaging said switching clutch, said first clutch and said second brake;

a second-gear position which has a speed ratio lower than that of said first-gear position and which is established by engaging said switching clutch, said first clutch and said first brake;

a third-gear position which has a speed ratio lower than that of said second-gear position and which is established by engaging said switching clutch, said first clutch and said third clutch;

a fourth-gear position which has a speed ratio lower than that of said third-gear position and which is established by engaging said switching clutch, said third clutch and said first brake; and

a fifth-gear position which has a speed ratio lower than that of said fourth-gear position and which is established by engaging said third clutch, said switching brake and said first brake.

100. A vehicular drive system according to claim 97, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said second carrier and said third carrier functioning as said fifth element, said second ring gear and said third ring gear functioning as said sixth element, and said third sun gear functioning as said seventh element.

101. A vehicular drive system according to claim 97, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second carrier and said third sun gear functioning as said fourth element, said second ring gear and said third carrier functioning as said fifth element, said third ring gear functioning as said sixth element, and said third ring gear functioning as said seventh element.

102. A vehicular drive system according to claim 97, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear and said third sun gear functioning as said fourth element, said second ring gear functioning as said fifth element, said third carrier functioning as said sixth element, and said second carrier and said third ring gear functioning as said seventh element.

103. A vehicular drive system according to claim 97, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said second ring gear and said third ring gear functioning as said fifth element, said third carrier functioning as said sixth element, and said second carrier and said third sun gear functioning as said seventh element.

104. A vehicular drive system according to claim 97, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said third sun gear functioning as said fourth element, said second ring gear functioning as said fifth element, said second carrier and said third ring gear functioning as said sixth element, and said second sun gear and said third carrier functioning as said seventh element.

105. A vehicular drive system according to claim 97, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said second carrier and third ring gear functioning as said fifth element, said second ring gear and said third carrier functioning as said sixth element, and said third sun gear functioning as said seventh element.

106. A vehicular drive system according to claim 97, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said third sun gear functioning as said fourth element, said second ring gear functioning as said fifth element, said second carrier and said third carrier functioning as said sixth element, and said second sun gear and said third ring gear functioning as said seventh element.

107. A vehicular drive system according to claim 97, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear and said third sun gear functioning as said fourth element, said third carrier functioning as said fifth element, said second carrier and said third ring gear functioning as said sixth element, and said second ring gear functioning as said seventh element.

108. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second carrier and said third carrier being selectively connected to said power transmitting member through a third clutch and selectively fixed to said stationary member through a second brake, said second ring gear and said third ring gear being fixed to an output rotary member of said automatic transmission, and said third sun gear being selectively connected to said power transmitting member through a first clutch.

116. A vehicular drive system according to claim 108, wherein said shifting-state switching device includes a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable fix said first sun gear to said stationary member.

109. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a first clutch, said second carrier and said third sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second ring gear and said third carrier being selectively connected to said power transmitting member through a third clutch and selectively fixed to said stationary member through a second brake, and said third ring gear being fixed an output rotary member of said automatic transmission.

110. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second carrier and said third ring gear being selectively connected to said power transmitting member through a first clutch, said second ring gear being selectively connected to said power transmitting member through a third clutch and selectively fixed to said stationary member through a second brake, and said third carrier being fixed to an output rotary member of said automatic transmission.

111. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second carrier and said third sun gear being selectively connected to said power transmitting member through a first clutch, said second ring gear and said third ring gear being selectively connected to said power transmitting member through a third clutch and selectively fixed to said stationary member through a second brake, and said third carrier being fixed to an output rotary member of said automatic transmission.

112. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third carrier being selectively connected to said power transmitting member through a second clutch, said second carrier and said third ring gear being integrally fixed to each other for rotation as a unit and fixed to an output rotary member of said automatic transmission, said second ring gear being selectively connected to said power transmitting member through a third clutch and selectively fixed to a stationary member through a second brake, and said third sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a first brake.

113. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second carrier and said third ring gear being selectively connected to said power transmitting member through a third clutch and selectively fixed to a stationary member through a second brake, said second ring gear and said third carrier being fixed to an output rotary member of said automatic transmission, and said third sun gear being selectively connected to said power transmitting member through a first clutch.

114. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third ring gear being selectively connected to said power transmitting member through a second clutch, said second carrier and said third carrier being fixed to an output rotary member of said automatic transmission, said second ring gear being selectively connected to said power transmitting member through a third clutch and selectively fixed to a stationary member through a second brake, and said third sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a first brake.

115. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively fixed to a stationary member through a first brake, said second carrier and said third ring gear being fixed to an output rotary member of said automatic transmission, said second ring gear being selectively connected to said power transmitting member through a first clutch, and said third carrier being selectively connected to said power transmitting member through a third clutch and selectively fixed to said stationary member through a second brake.

117. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, an automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said automatic transmission includes a plurality of input clutches selectively connected to an output shaft of said power distributing mechanism; and

said automatic transmission has a plurality of gear positions which are established by selectively engaging and releasing said plurality of input clutches.

118. A vehicular drive system according to claim 117, wherein said power distributing mechanism includes a first planetary gear set having as three elements a sun gear, a carrier and a ring gear, said three elements consisting of a first element, a second element and a third element which are arranged in the order of said second element, said first element and said third elements in a direction from one of opposite ends of a collinear chart toward the other end, said collinear chart having straight lines indicating rotating speeds of said three elements, said first element being fixed to said engine, said second element being fixed to said first electric motor, and said third element being fixed to said power transmitting member.

119. A vehicular drive system according to claim 118, wherein said power distributing mechanism further includes a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission

120. A vehicular drive system according to claim 117, wherein said automatic transmission is a step-variable automatic transmission.

121. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a first planetary gear device having as three elements a sun gear, a carrier and a ring gear, said three elements consisting of a first element, a second element and a third element which are arranged in the order of said second element, said first element and said third elements in a direction from one of opposite ends of a collinear chart toward the other end, said collinear chart having straight lines indicating rotating speeds of said three elements, said first element being fixed to said engine, said second element being fixed to said first electric motor, and said third element being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a second planetary gear set and a third planetary gear set, said second and third planetary gear sets having sun gears, carriers and ring gears selected ones of which are fixed to each other to constitute four elements consisting of a fourth element, a fifth element, a sixth element and a seventh elements rotating speeds of which are indicated by straight lines of a collinear chart in which said four elements are arranged in the order of said fourth element, said fifth element, said sixth element and said seventh element in a direction from one of opposite ends of the collinear chart toward the other end, said fourth element being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said fifth element being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said sixth element being fixed to an output rotary member of said automatic transmission, and said seventh element being selectively fixed to said stationary member through a first brake, said automatic transmission having a plurality of gear positions which are established by engaging respective combinations of said first and second clutches and said first, second and third brakes.

122. A vehicular drive system according to claim 121, wherein said differential-state switching device includes a switching clutch operable to connect said second element to said first element, and/or a switching brake operable to fix said second element to said stationary member, said first planetary gear set being placed in said differential state by releasing said switching clutch and/or said switching brake, and in said locked state by engaging said switching clutch and/or said switching brake.

123. A vehicular drive system according to claim 122, wherein said plurality of gear positions includes:

a first-gear position which has a highest speed ratio and which is established by engaging said switching clutch, said first clutch and said first brake;

a second-gear position which has a speed ratio lower than that of said first-gear position and which is established by engaging said switching clutch, said second clutch and said first brake;

a third-gear position which has a speed ratio lower than that of said second-gear position and which is established by engaging said switching clutch, said first clutch and said second clutch;

a fourth-gear position which has a speed ratio lower than that of said third-gear position and which is established by engaging said switching clutch, said second clutch and said second brake; and

a fifth-gear position which has a speed ratio lower than that of said fourth-gear position and which is established by engaging said second clutch, said switching brake and said second brake.

124. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second carrier and said third sun gear functioning as said fourth element, said second ring gear functioning as said fifth element, said third carrier functioning as said sixth element, and said second sun gear and said third ring gear functioning as said seventh element.

125. A vehicular drive system according to claim 121, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second carrier and said third sun gear functioning as said fourth element, said second ring gear and said third carrier functioning as said fifth element, said third ring gear functioning as said sixth element, and said second sun gear functioning as said seventh element.

126. A vehicular drive system according to claim 121, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear and said third sun gear functioning as said fourth element, said second ring gear and said third carrier functioning as said fifth element, said third ring gear functioning as said sixth element, and said second carrier functioning as said seventh element.

127. A vehicular drive system according to claim 121, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear and said third sun gear functioning as said fourth element, said second ring gear functioning as said fifth element, said third carrier functioning as said sixth element, and said second carrier and said third ring gear functioning as said seventh element.

128. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said third sun gear functioning as said fourth element, said second carrier functioning as said fifth element, said second ring gear and said third carrier functioning as said sixth element, and said second sun gear and said third ring gear functioning as said seventh element.

129. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear and said third sun gear functioning as said fourth element, said second carrier functioning as said fifth element, said second ring gear and said third ring gear functioning as said sixth element, and said third carrier functioning as said seventh element.

130. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said second carrier and said third carrier functioning as said fifth element, said second ring gear and said third ring gear functioning as said sixth element, and said third sun gear functioning as said seventh element.

131. A vehicular drive system according to claim 121, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said second ring gear and said third ring gear functioning as said fifth element, said third carrier functioning as said sixth element, and said second carrier and said third sun gear functioning as said seventh element.

132. A vehicular drive system according to claim 121, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second carrier functioning as said fourth element, said second ring gear and said third ring gear functioning as said fifth element, said third carrier functioning as said sixth element, and said second sun gear and said third sun gear functioning as said seventh element.

133. A vehicular drive system according to claim 121, wherein said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said third ring gear and said third ring gear functioning as said fifth element, said second ring gear and said third carrier functioning as said sixth element, and said second carrier and said third sun gear functioning as said seventh element.

134. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear and said third sun gear functioning as said fourth element, said second carrier functioning as said fifth element, said second ring gear and said third carrier functioning as said sixth element, and said third ring gear functioning as said seventh element.

135. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said second sun gear functioning as said fourth element, said second carrier and said third ring gear functioning as said fifth element, said second ring gear and said third carrier functioning as said sixth element, and said third sun gear functioning as said seventh element.

136. A vehicular drive system according to claim 121, wherein said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear,

said third sun gear functioning as said fourth element, said second ring gear functioning as said fifth element, said second carrier and said third carrier functioning as said sixth element, and said second sun gear and said third ring gear functioning as said seventh element.

137. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third ring gear being selectively fixed to a stationary member through a first brake, said second carrier and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to said stationary member through a second brake, said second ring gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said third carrier being fixed to an output rotary member of said automatic transmission.

150. A vehicular drive system according to claim 137, wherein said shifting-state switching device includes a switching clutch operable to connect said first carrier and said first sun gear to each other, and/or a switching brake operable fix said first sun gear to said stationary member.

138. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a first clutch, said second carrier and said third sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second sun gear being selectively fixed to a stationary member through a first brake, said second carrier and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to said stationary member through a second brake, said second ring gear and said third carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, and said third ring gear being fixed an output rotary member of said automatic transmission.

139. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to a stationary member through a first brake, said second sun gear and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier being selectively fixed to said stationary member through a first brake, said second ring gear and said third carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, and said third ring gear being fixed to an output rotary member of said automatic transmission.

140. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said second ring gear and said third ring gear being fixed to an output rotary member of said automatic transmission, and said third carrier being selectively fixed to said stationary member through a first brake.

141. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third ring gear being selectively fixed to a stationary member through a first brake, said second carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said second ring gear and said third carrier being fixed to an output rotary member of said automatic transmission, said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to said stationary member through a second brake.

142. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary.gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said second ring gear and said third ring gear being fixed to an output rotary member of said automatic transmission, and said. third carrier selectively fixed to said stationary member through a first brake.

143. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a double-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier and said third carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said second ring gear and said third ring gear being fixed to an output rotary member of said automatic transmission, said third sun gear being selectively fixed to said stationary member through a first brake.

144. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier and said third sun gear being selectively fixed to said stationary member through a first brake, said second ring gear and said third ring gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said third carrier being fixed an output rotary member of said automatic transmission.

145. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively fixed to a stationary member through a first brake, said second carrier being selectively connected to said power transmitting member through a first clutch and selectively fixed to said stationary member through a second brake, said second ring gear and said third ring being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said third carrier being fixed an output rotary member of said automatic transmission.

146. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a double-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier and said third sun gear being selectively fixed to said stationary member through a first brake, said second ring gear and said third carrier being fixed to an output rotary member of said automatic transmission, and said third ring gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake.

147. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said second ring gear and said third carrier being fixed to an output rotary member of said automatic transmission, and said third ring gear being selectively fixed to said stationary member through a first brake.

148. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to a stationary member through a second brake, said second carrier and said third ring gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, said second ring gear and said third carrier being fixed to an output rotary member of said automatic transmission, and said third sun gear being selectively fixed to said stationary member through a first brake.

149. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, a step-variable automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a single-pinion type first planetary gear device having a first sun gear, a first carrier and a first ring gear, said first carrier being fixed to said engine, said first sun being fixed to said first electric motor, and said first ring gear being fixed to said power transmitting member, said power distributing mechanism further including a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission; and

said automatic transmission includes a single-pinion type second planetary gear set having a second sun gear, a second carrier and a second ring gear, and a single-pinion type third planetary gear set having a third sun gear, a third carrier and a third ring gear, said second sun gear and said third ring gear being selectively fixed to a stationary member through a first brake, said second carrier and said third carrier being fixed to an output rotary member of said automatic transmission, and said second ring gear being selectively connected to said power transmitting member through a second clutch and selectively fixed to said stationary member through a third brake, and said third sun gear being selectively connected to said power transmitting member through a first clutch and selectively fixed to said stationary member through a second brake.

151. A vehicular drive system including a power distributing mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, an automatic transmission disposed between said power transmitting member and a drive wheel of a vehicle, and a second electric motor disposed between said power transmitting member and said drive wheel, characterized in that:

said power distributing mechanism includes a planetary gear device having as three elements a sun gear, a carrier and a ring gear, said three elements consisting of a first element, a second element and a third element which are arranged in the order of said second element, said first element and said third elements in a direction from one of opposite ends of a collinear chart toward the other end, said collinear chart having straight lines indicating rotating speeds of said three elements, said first element being fixed to said engine, said second element being fixed to said first electric motor, and said third element being fixed to said power transmitting member; and

said automatic transmission is arranged to increase a rotating speed of said power transmitting member.

152. A vehicular drive system according to claim 151, wherein said power distributing mechanism further includes a differential-state switching device operable to place said power distributing mechanism selectively in a differential state in which the power distributing mechanism is operable as an electrically controlled continuously variable transmission, and a locked state in which the power distributing mechanism is not operable as the electrically controlled continuously variable transmission