VEHICLE POWER TRANSMISSION DEVICE

• US 20120028749A1
• Filed: 07/29/2011
• Published: 02/02/2012
• Est. Priority Date: 07/30/2010
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc. (DENSO Corporation)
• Original Assignee: DENSO Corporation, Nippon Soken, Inc. (DENSO Corporation)
• Inventors: KAWASAKI, Koji, Matsue, Takenori
• Granted Patent: US 8,900,080 B2
• Time in Patent Office: Days
• US Class Current: 475/211
• CPC Class Codes: B60K 2006/4816 Electric machine connected or connectable to gearbox internal shaft
• CPC Class Codes: B60K 6/42 characterised by the architecture of the hybrid electric vehicle
• CPC Class Codes: B60K 6/48 Parallel type
• CPC Class Codes: B60K 6/543 the transmission being a continuously variable transmission
• 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 10/11 Stepped gearings
• CPC Class Codes: B60W 20/10 Controlling the power contribution of each of the prime movers to meet required power demand
• CPC Class Codes: F16H 3/725 with means to change ratio in the mechanical gearing
• CPC Class Codes: Y02T 10/62 Hybrid vehicles
• CPC Class Codes: Y10S 903/902 Prime movers comprising electrical and internal combustion motors
• CPC Class Codes: Y10S 903/918 Continuously variable

Abstract

A power transmission apparatus for a vehicle is provided which is equipped with a power split device and a speed variator. The power transmission device is designed to set a speed ratio of speed of rotation of an output of a power source to speed of rotation of a driven wheel in a power circulation mode of a power split device to lie within one of a positive range in which a sign of the speed ratio is positive and a negative range in which a sign of the speed ratio is negative. This results in a decrease in degree of torque acting on the speed variator such as a continuously variable transmission, thus permitting a required degree of durability of the speed variator to be reduced.

Claims

1. A power transmission apparatus for a vehicle comprising:

a power split device which includes a first, a second, and a third rotor which rotate in conjunction with each other to split power among the first, second, and third rotors, the third rotor being coupled mechanically to a driven wheel of a vehicle; and

a speed variator joined mechanically to the power split device,

wherein the power split device is placed in a power transmission mode in which power, as produced by the power source, is transmitted to the third rotor through the second rotor and then to the driven wheel as torque,

wherein in the power transmission mode, the power split device is also placed in a power circulation mode wherein the power is circulated between the first and second rotors, and

wherein a speed ratio of a speed of rotation of an output of the power source to a speed of rotation of the driven wheel in the power circulation mode is set to lie within one of a positive range in which a sign of the speed ratio is positive and a negative range in which a sign of the speed ratio is negative.

2. A power transmission apparatus as set forth in claim 1, further comprising a controller which controls the speed ratio to lie within one of the positive range and the negative range.

3. A power transmission apparatus as set forth in claim 2, wherein the power source is an electric rotating machine.

4. A power transmission apparatus as set forth in claim 3, wherein the controller works to switch rotation of the electric rotating machine in opposite directions.

5. A power transmission apparatus as set forth in claim 2, further comprising a reversing mechanism which changes between mechanical connections of at least one of the power source and the driven wheel to the first, second, and third rotors of the power split device to reverse a sign of the speed ratio.

6. A power transmission apparatus as set forth in claim 2, wherein the controller keeps an absolute value of a minimum value of the speed ratio above zero in the one of the positive and negative ranges.

7. A power transmission apparatus as set forth in claim 1, wherein the speed variator is a continuously variable transmission equipped with pulleys and a belt, and wherein the continuously variable transmission is so designed that an absolute value of a minimum value of the speed ratio is kept away from zero in the one of the positive and negative ranges for compensating for a change in the speed ratio arising from aging of the continuously variable transmission.

8. A power transmission apparatus as set forth in claim 1, wherein an absolute value of a minimum value of the speed ratio is so determined as to be away from zero by a given margin which is equivalent to a change in the speed ratio arising from aging of the speed variator.

9. A power transmission apparatus as set forth in claim 1, wherein the power source is an electric rotating machine, wherein the first rotor is coupled mechanically to an internal combustion engine working as a power source, and further comprising a power transmission control mechanism which selectively establishes and blocks transmission of power between the first rotor and the internal combustion engine.

10. A power transmission apparatus as set forth in claim 9, wherein the power transmission control mechanism includes an electronically-controlled breaker which breaks the transmission of power between the third rotor and the internal combustion engine.

11. A power transmission apparatus as set forth in claim 10, wherein the power transmission control mechanism also includes a one-way transmission mechanism which achieves the transmission of power between the first rotor and the internal combustion engine in a condition that a speed of an input of the one-way transmission mechanism which leads to the first rotor is not lower than that of an output of the one-way transmission mechanism which leads to the internal combustion engine.

12. A power transmission apparatus as set forth in claim 9, wherein the power transmission control mechanism which selectively establishes and blocks the transmission of power between the first rotor and the internal combustion engine functions as a first power transmission control mechanism, further comprising a second power transmission control mechanism which selectively establishes and blocks transmission of power between the second rotor and the internal combustion.

13. A power transmission apparatus as set forth in claim 1, wherein the power split device includes a planetary gear set equipped with a sun gear, a carrier, and a ring gear which work as the first, second, and third rotors.

14. A power transmission apparatus as set forth in claim 1, further comprising a power transmission path in which the speed variator is disposed and through which the first and second rotors are so linked without the third rotor as to rotate in conjunction with each other, and wherein the power source is coupled mechanically to the power transmission path.

15. A power transmission apparatus as set forth in claim 14, wherein the power source which are coupled mechanically to the first and second rotors is an electric rotating machine, wherein an internal combustion engine working as a power source is joined mechanically to one of the first and second rotors, and further comprising a first-to-second operation mode switching mechanism which switches between a first operation mode in which the speed varator is connected mechanically to both the first and second rotors and a second operation mode in which the speed variator is connected mechanically to the second and third rotors, and wherein a derivative value of a function, in which the speed ratio is expressed by a dependent variable, and a gear ratio of the speed variator is expressed by an independent variable, with respect to the independent variable in the second operation mode is opposite in sign to that in the first operation mode.

16. A power transmission apparatus for a vehicle comprising:

an electric rotating machine working as a power source;

a power split device which includes a first, a second, and a third rotor which rotate in conjunction with each other to split power among the first, second, and third rotors, the third rotor being coupled mechanically to a driven wheel of a vehicle;

a speed variator joined mechanically to the power split device;

setting means for setting signs of power, as outputted from the first and second rotors, opposite each other to establish a power circulation mode in which the power is circulated between the first and second rotors in a power transmission mode in which power, as produced by the power source, is transmitted to the third rotor through the second rotor and then to the driven wheel; and

bidirectional switching means for switching rotation of the electric rotating machine between opposite directions.

17. A power transmission apparatus as set forth in claim 16, further comprising a controller which controls a speed ratio of a speed of rotation of an output of the power source to a speed of rotation of the driven wheel to lie within one of a positive range in which a sign of the speed ratio is positive and a negative range in which a sign of the speed ratio is negative.

18. A power transmission apparatus as set forth in claim 16, wherein the second rotor becomes rotatable when a speed of the third rotor coupled to the driven wheel is zero, and wherein the second rotor is also coupled to an accessory of the vehicle.

19. A power transmission apparatus as set forth in claim 16, wherein a speed ratio of a speed of rotation of an output of the power source to a speed of rotation of the driven wheel in the power circulation mode is determined to lie within a range extending from a positive range in which a sign of the speed ratio is positive and a negative range in which a sign of the speed ratio is negative across zero (0).

20. A power transmission apparatus as set forth in claim 16, wherein the power source is an electric rotating machine, wherein the first rotor is coupled mechanically to an internal combustion engine working as a power source, and further comprising a power transmission control mechanism which selectively establishes and blocks transmission of power between the first rotor and the internal combustion engine.

21. A power transmission apparatus as set forth in claim 20, wherein the power transmission control mechanism includes an electronically-controlled breaker which breaks the transmission of power between the third rotor and the internal combustion engine.

22. A power transmission apparatus as set forth in claim 21, wherein the power transmission control mechanism also includes a one-way transmission mechanism which achieves the transmission of power between the first rotor and the internal combustion engine in a condition that a speed of an input of the one-way transmission mechanism which leads to the first rotor is not lower than that of an output of the one-way transmission mechanism which leads to the internal combustion engine.

23. A power transmission apparatus as set forth in claim 20, wherein the power transmission control mechanism which selectively establishes and blocks the transmission of power between the first rotor and the internal combustion engine functions as a first power transmission control mechanism, further comprising a second power transmission control mechanism which selectively establishes and blocks transmission of power between the second rotor and the internal combustion.

24. A power transmission apparatus as set forth in claim 16 wherein the power split device includes a planetary gear set equipped with a sun gear, a carrier, and a ring gear which work as the first, second, and third rotors.

25. A power transmission apparatus as set forth in claim 16, further comprising a power transmission path in which the speed variator is disposed and through which the first and second rotors are so linked without the third rotor as to rotate in conjunction with each other, and wherein the power source is coupled mechanically to the power transmission path.

26. A power transmission apparatus as set forth in claim 25, wherein the power source which are coupled mechanically to the first and second rotors is an electric rotating machine, wherein an internal combustion engine working as a power source is joined mechanically to one of the first and second rotors, and further comprising a first-to-second operation mode switching mechanism which switches between a first operation mode in which the speed varator is connected mechanically to both the first and second rotors and a second operation mode in which the speed variator is connected mechanically to the second and third rotors, and wherein a derivative value of a function, in which the speed ratio is expressed by a dependent variable, and a gear ratio of the speed variator is expressed by an independent variable, with respect to the independent variable in the second operation mode is opposite in sign to that in the first operation mode.

27. A power transmission apparatus for a vehicle comprising:

a power split device which includes a first, a second, and a third rotor which rotate in conjunction with each other to split power among the first, second, and third rotors, the third rotor being coupled mechanically to a driven wheel of a vehicle;

a speed variator joined mechanically to the power split device;

setting means for setting signs of power, as outputted from the first and second rotors, opposite each other to establish a power circulation mode in which the power is circulated between the first and second rotors in a power transmission mode in which power, as produced by the power source, is transmitted to the third rotor through the second rotor and then to the driven wheel; and

a reversing mechanism which works to change between mechanical connections of at least one of the power source and the driven wheel to the first, second, and third rotors of the power split device to reverse a sign of a speed ratio of a speed of rotation of an output of the power source to a speed of rotation of the driven wheel.

28. A power transmission apparatus as set forth in claim 27, wherein the power source is an electric rotating machine.

29. A power transmission apparatus as set forth in claim 27, further comprising a controller which controls a speed ratio of a speed of rotation of an output of the power source to a speed of rotation of the driven wheel to lie within one of a positive range in which a sign of the speed ratio is positive and a negative range in which a sign of the speed ratio is negative.

30. A power transmission apparatus as set forth in claim 27, wherein the second rotor becomes rotatable when a speed of the third rotor coupled to the driven wheel is zero, and wherein the second rotor is also coupled to an accessory of the vehicle.

31. A power transmission apparatus as set forth in claim 27, wherein a speed ratio of a speed of rotation of an output of the power source to a speed of rotation of the driven wheel in the power circulation mode is determined to lie within a range extending from a positive range in which a sign of the speed ratio is positive and a negative range in which a sign of the speed ratio is negative across zero (0).

32. A power transmission apparatus as set forth in claim 27, wherein the power source is an electric rotating machine, wherein the first rotor is coupled mechanically to an internal combustion engine working as a power source, and further comprising a power transmission control mechanism which selectively establishes and blocks transmission of power between the first rotor and the internal combustion engine.

33. A power transmission apparatus as set forth in claim 32, wherein the power transmission control mechanism includes an electronically-controlled breaker which breaks the transmission of power between the third rotor and the internal combustion engine.

34. A power transmission apparatus as set forth in claim 33, wherein the power transmission control mechanism also includes a one-way transmission mechanism which achieves the transmission of power between the first rotor and the internal combustion engine in a condition that a speed of an input of the one-way transmission mechanism which leads to the first rotor is not lower than that of an output of the one-way transmission mechanism which leads to the internal combustion engine.

35. A power transmission apparatus as set forth in claim 32, wherein the power transmission control mechanism which selectively establishes and blocks the transmission of power between the first rotor and the internal combustion engine functions as a first power transmission control mechanism, further comprising a second power transmission control mechanism which selectively establishes and blocks transmission of power between the second rotor and the internal combustion.

36. A power transmission apparatus as set forth in claim 27 wherein the power split device includes a planetary gear set equipped with a sun gear, a carrier, and a ring gear which work as the first, second, and third rotors.

37. A power transmission apparatus as set forth in claim 27, further comprising a power transmission path in which the speed variator is disposed and through which the first and second rotors are so linked without the third rotor as to rotate in conjunction with each other, and wherein the power source is coupled mechanically to the power transmission path.

38. A power transmission apparatus as set forth in claim 37, wherein the power source which are coupled mechanically to the first and second rotors is an electric rotating machine, wherein an internal combustion engine working as a power source is joined mechanically to one of the first and second rotors, and further comprising a first-to-second operation mode switching mechanism which switches between a first operation mode in which the speed varator is connected mechanically to both the first and second rotors and a second operation mode in which the speed variator is connected mechanically to the second and third rotors, and wherein a derivative value of a function, in which the speed ratio is expressed by a dependent variable, and a gear ratio of the speed variator is expressed by an independent variable, with respect to the independent variable in the second operation mode is opposite in sign to that in the first operation mode.

39. A power transmission apparatus for a vehicle comprising:

a power split device which is to be coupled to a power source and includes power split rotors that are a first, a second, and a third rotor which rotate in conjunction with each other to split power among the first, second, and third rotors, the first rotor being coupled mechanically to a driven wheel of a vehicle, the first, second, and third rotor being so linked as to have rotational speeds thereof arrayed on a straight line in a nomographic chart;

a continuously variable transmission joined mechanically to the power split device;

a power circulation path through which power is to be circulated between the second and third rotors through the continuously variable transmission in a power transmission mode in which power, as produced by the power source, is transmitted to the first rotor through the second rotor; and

fixing means for fixing a speed ratio of a speed of the second rotor to a speed of the third rotor without use of the continuously variable transmission by establishing either one of a given mechanical connection among the power split rotors and a mechanical connection of one of the power split rotors to a given member when the continuously variable transmission is determined to be failing in operation to transmit the power therethrough.

40. A power transmission apparatus as set forth in claim 39, further comprising a driving power transmission path through which the second rotor is to be connected mechanically to the first rotor through the continuously variable transmission and a driven wheel-side power transmission control mechanism which is disposed in the driving power transmission path and selectively establishes and blocks transmission of power between the first and second rotors, and wherein the fixing means includes dual path establishing controlling means for controlling an operation of the driven wheel-side power transmission control mechanism to establish transmission of power through both the power circulation path and the driving power transmission path when the continuously variable transmission is determined to be failing in operation to transmit the power therethrough.

41. A power transmission apparatus as set forth in claim 40, further comprising a circulation establishing power transmission control mechanism which selectively establishes and blocks transmission of power between the second and third rotors through the power circulation path, and wherein the dual path establishing controlling means controls operations of the driven wheel-side power transmission control mechanism and the circulation establishing power transmission control mechanism to establish the transmission of power through the power circulation path and the driving power transmission path when the continuously variable transmission is determined to be failing in operation to transmit the power therethrough.

42. A power transmission apparatus as set forth in claim 40, wherein the power source is connected mechanically between the continuously variable transmission and the second rotor.

43. A power transmission apparatus as set forth in claim 42, further comprising diagnosing means for diagnosing whether the continuously variable transmission is failing in operation to transmit the power therethrough or not, and wherein the dual path establishing controlling means establishes the transmission of power through both the power circulation path and the driving power transmission path when the continuously variable transmission is determined to be failing in operation to transmit the power therethrough.

44. A power transmission apparatus as set forth in claim 43, wherein the power source includes an internal combustion engine and an electric rotating machine, the internal combustion engine being joined mechanically to one of an input and an output of the continuously variable transmission leading to the second rotor, the electric rotating machine being joined mechanically to the other of the input and the output of the continuously variable transmission.

45. A power transmission apparatus as set forth in claim 44, further comprising a starting power transmission control mechanism which selectively establishes and blocks transmission of power between the third rotor and a rotating shaft of the internal combustion engine.

46. A power transmission apparatus as set forth in claim 45, wherein the starting power transmission control mechanism includes an electrically-controlled fastener which selectively establishes engagement and disengagement between the third rotor and the rotating shaft of the internal combustion engine.

47. A power transmission apparatus as set forth in claim 45, wherein the starting power transmission control mechanism includes a one-way transmission mechanism which establishes the transmission of power between the third rotor and a rotating shaft of the internal combustion engine in a condition that a speed of rotation of an input of the one-way transmission mechanism leading to the third rotor is not lower than that of an output of the one-way transmission mechanism leading to the internal combustion engine.

48. A power transmission apparatus as set forth in claim 45, further comprising a driving power transmission control mechanism which selectively establishes and blocks transmission of power between the second rotor and the internal combustion engine.

49. A power transmission apparatus as set forth in claim 42, wherein the continuously variable transmission is of a belt type, further comprising transmission blocking means for loosening a belt of the continuously variable transmission to block the transmission of power through the continuously variable transmission, and wherein when the transmission blocking means blocks the transmission of power through the continuously variable transmission, the dual path establishing controlling means establishes the transmission of power through both the power circulation path and the driving power transmission path.

50. A power transmission apparatus as set forth in claim 39, wherein the power source is connected mechanically between the continuously variable transmission and the second rotor, further comprising holding means for holding the third rotor from rotating, and wherein said fixing means operates the holding means to hold the third rotor from rotating.

51. A power transmission apparatus for a vehicle comprising:

a power split device which is to be coupled to a power source and includes power split rotors that are a first, a second, and a third rotor which rotate in conjunction with each other to split power among the first, second, and third rotors, the first rotor being coupled mechanically to a driven wheel of a vehicle;

a continuously variable transmission joined mechanically to the power split device;

a power circulation path which is established by connecting the second and third rotors through the continuously variable transmission and through which power is to be circulated between the second and third rotors in a power transmission mode in which power, as produced by the power source, is transmitted to the first rotor through the second rotor;

a driving power transmission path through which the second rotor is to be connected mechanically to the first rotor through the continuously variable transmission;

a driven wheel-side power transmission control mechanism which is disposed in the driving power transmission path and selectively establishes and blocks transmission of power between the first and second rotors; and

dual path establishing controlling means for controlling an operation of the driven wheel-side power transmission control mechanism to establish transmission of power through both the power circulation path and the driving power transmission path when the continuously variable transmission is determined to be failing in operation to transmit the power therethrough.

52. A power transmission apparatus as set forth in claim 51, further comprising efficiency determining means for determining that the continuously variable transmission has decreased in efficiency in transmitting the power therethrough when a degree of torque acting on the continuously variable transmission increases, and wherein when the efficiency determining means determines that the continuously variable transmission has decreased in efficiency in transmitting the power therethrough, the dual path establishing controlling means setting speeds of an input and an output of the driven wheel-side power transmission control mechanism to be different from each other so as to decrease a degree to which the power is to be transmitted through the driven wheel-side transmission control mechanism.

53. A power transmission apparatus for a vehicle comprising:

a power split device which is to be coupled to a power source and includes a plurality of power split rotors that are so linked as to rotate in conjunction with each other to split power between the power split rotors;

a speed variator which is coupled mechanically to the power split device and has a variable gear ratio;

an in-direct transmission path which is established to transmit power, as produced by the power source, to the driven wheel through the speed variator;

a direct transmission path which is established to transmit the power, as produced by the power source, to the driven wheel without using the speed variator; and

switching means for between an in-direction transmission mode in which the in-direction transmission path is established and a direct transmission mode in which the direct transmission path is established.

54. A power transmission apparatus as set forth in claim 53, wherein the power split rotors includes a first, a second, and a third rotor, the first rotor being coupled mechanically to the driven wheel, wherein in the in-direct transmission mode, the second and third rotors are coupled mechanically to each other through the speed variator to transmit the power, as produced by the power source, to the first rotor through one of the second and third rotors, and further comprising a power circulation path through which power is to be circulated between the second and third rotors in the in-direct power transmission mode.

55. A power transmission apparatus as set forth in claim 53, wherein the power split rotors includes a first, a second, and a third rotor, the first rotor being coupled mechanically to the driven wheel, further comprising a driving power transmission path through which the first rotor is to be connected mechanically to the second rotor through the speed variator, an in-direct power transmission control mechanism which selectively establishes and blocks transmission of power between one of an input and an output of the speed variator which is connected mechanically to the second rotor and the power source, and a direct power transmission control mechanism which selectively establishes and blocks transmission of power between one of the input and the output of the speed variator which is coupled mechanically to the first rotor and the power source.

56. A power transmission apparatus as set forth in claim 55, wherein the direct power transmission control mechanism includes an electronically-controlled fastener which has a first axis leading to the power source and a second axis leading to the speed varaitor and which selectively establishes engagement and disengagement between the first and second axes.

57. A power transmission apparatus as set forth in claim 55, wherein the direct power transmission control mechanism includes a one-way transmission mechanism which transmits power therethrough in a condition that a speed of an input of the one-way transmission mechanism which leads to the power source is not lower than that of an output of the one-way transmission mechanism which leads to the speed variator.

58. A power transmission apparatus as set forth in claim 55, wherein the direct power transmission control mechanism is implemented by an electronically-controlled fastener which has a first axis leading to the power source and a second axis leading to the speed varaitor and which selectively establishes engagement and disengagement between the first and second axes, and the in-direct power transmission control mechanism is implemented by a one-way transmission mechanism which transmits power therethrough in a condition that a speed of an input of the one-way transmission mechanism which leads to the power source is not lower than that of an output of the one-way transmission mechanism which leads to the speed variator, or wherein the direct power transmission control mechanism is implemented by a one-way transmission mechanism which transmits power therethrough in a condition that a speed of an input of the one-way transmission mechanism which leads to the power source is not lower than that of an output of the one-way transmission mechanism which leads to the speed variator, and the indirect power transmission control mechanism is implemented by an electronically-controlled fastener which has a first axis leading to the power source and a second axis leading to the speed varaitor and which selectively establishes engagement and disengagement between the first and second axes, and further comprising controlling means for controlling an operation of the speed variator in the direct power transmission mode so that a speed of rotation of the output of the one-way transmission mechanism is not low or equal to that of the input of the one-way transmission mechanism.

59. A power transmission apparatus as set forth in claim 55, wherein the direct power transmission control mechanism is implemented by a one-way transmission mechanism which transmits power therethrough in a condition that a speed of an input of the one-way transmission mechanism which leads to the power source is not lower than that of an output of the one-way transmission mechanism which leads to the speed variator, and wherein the indirect power transmission control mechanism is implemented by a one-way transmission mechanism which transmits power therethrough in a condition that a speed of an input of the one-way transmission mechanism which leads to the power source is not lower than that of an output of the one-way transmission mechanism which leads to the speed variator.

60. A power transmission apparatus as set forth in claim 55, further comprising a power circulation path which is established by connecting the second and third rotors through the speed variator and through which power is to be circulated between the second and third rotors in a power transmission mode in which power, as produced by the power source, is transmitted to the first rotor through one of the second rotor and the third rotor, a circulation establishing power transmission control mechanism which selectively establishes and blocks transmission of the power between the second and third rotors through the power circulation path, and a driven wheel-side power transmission control mechanism which is disposed in the driving power transmission path and selectively establishes and blocks transmission of the power between one of the output and the input of the speed variator which is coupled mechanically to the first rotor and the first rotor.

61. A power transmission apparatus as set forth in claim 60, wherein the power source producing the power which is to be transmitted selectively through the in-direct power transmission control mechanism and the direct power transmission control mechanism is an internal combustion engine, and wherein the second rotor is coupled mechanically to an electric rotating machine.

62. A power transmission apparatus as set forth in claim 61, further comprising a starting power transmission control mechanism which selectively establishes and blocks transmission of power between the third rotor and the internal combustion engine.

63. A power transmission apparatus as set forth in claim 62, wherein the starting power transmission control mechanism includes an electrically-controlled fastener which selectively establishes engagement and disengagement between the third rotor and the internal combustion engine.

64. A power transmission apparatus as set forth in claim 62, wherein the starting power transmission control mechanism includes a one-way transmission mechanism which establishes the transmission of power between the third rotor and the internal combustion engine in a condition that a speed of rotation of an input of the one-way transmission mechanism leading to the third rotor is not lower than that of an output of the one-way transmission mechanism leading to the internal combustion engine.

65. A power transmission apparatus as set forth in claim 62, wherein when the circulation establishing power transmission control mechanism blocks the transmission of the power between the second and third rotors, the driven wheel-side power transmission control mechanism establishes the transmission of the power between the one of the output and the input of the speed variator and the first rotor, and the starting power transmission control mechanism establishes the transmission of power between the third rotor and the internal combustion engine, the power is circulated between the first and second rotors through the driven wheel-side power transmission control mechanism.

66. A power transmission apparatus as set forth in claim 53, further comprising direct transmission mode establishing means for establishing the direct transmission mode when a speed of the driven wheel lies within a given range.

67. A power transmission apparatus as set forth in claim 53, wherein the speed variator is of a belt type continuously variable transmission, further comprising diagnosing means for diagnosing whether the continuously variable transmission is failing in operation to transmit the power therethrough or not and direct transmission mode establishing means for establishing the direct transmission mode when the continuously variable transmission is determined to be failing in operation to transmit the power therethrough.

68. A power transmission apparatus as set forth in claim 62, wherein the electric rotating machine is coupled mechanically to the second rotor through the speed variator, and further comprising power conversion means for converting the power, as produced by the internal combustion engine, into electric energy, and wherein when the driven wheel is stopped, the power conversion means blocks the transmission of the power between the second and third rotors and the transmission of the power between the one of the output and the input of the speed variator and the first rotor through the circulation establishing power transmission control mechanism and the driven wheel-side power transmission control mechanism, and converts the power into the electric energy.

69. A power transmission apparatus as set forth in claim 54, further comprising a driving power transmission path through which the first rotor is to be connected mechanically to the second rotor through the speed variator, a driven wheel-side power transmission control mechanism which is disposed in the driving power transmission path and selectively establishes and blocks transmission of the power between one of the output and the input of the speed variator which is coupled mechanically to the first rotor and the first rotor, and a circulation establishing power transmission control mechanism which selectively establishes and blocks transmission of the power between the second and third rotors through the power circulation path, wherein the switching means includes the driven wheel-side power transmission control mechanism and the circulation establishing power transmission control mechanism, and wherein when the driven wheel-side power transmission control mechanism establishes the transmission of the power between one of the output and the input of the speed variator and the first rotor, and the circulation establishing power transmission control mechanism blocks the transmission of the power between the second and third rotors, the direct transmission mode is established.