Coast downshift control apparatus for a vehicular automatic transmission

• US 6,090,008 A
• Filed: 03/15/1999
• Issued: 07/18/2000
• Est. Priority Date: 03/31/1998
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Endo, Hiroatsu, Oba, Hidehiro, Hoshiya, Kazumi
• Primary Examiner(s): Marmor, Charles A
• Assistant Examiner(s): HO, HA DINH
• Application Number:
  US09/267,777
• Time in Patent Office: 491 Days
• Field of Search: 477/118, 477/83, 477/84, 477/99, 477/109, 477/180, 477/120, 477/123, 477/124, 477/156
• US Class Current: 477/84
• CPC Class Codes: F16H 2059/186 Coasting
• CPC Class Codes: F16H 2061/0078 Linear control, e.g. PID, state feedback or Kalman
• CPC Class Codes: F16H 2061/0087 Adaptive control, e.g. the control parameters adapted by learning
• CPC Class Codes: F16H 3/006 power being selectively transmitted by either one of the parallel flow paths
• CPC Class Codes: F16H 59/40 Output shaft speed
• CPC Class Codes: F16H 59/42 Input shaft speed
• CPC Class Codes: F16H 59/46 dependent on a comparison between speeds
• CPC Class Codes: F16H 61/061 using electric control means
• CPC Class Codes: F16H 61/21 Providing engine brake control

Abstract

In a vehicular automatic transmission, a coast downshift is executed in an appropriate engine-braking state and with a light gearshift shock. While predetermined conditions for the execution of the downshift are met, an oil pressure to be fed to a clutch (c12 in FIG. 1) on the side of a gearshift output stage (a lower speed stage) is controlled, for example, in order that the input shaft speed (turbine speed01 in FIG. 1) of the automatic transmission may agree with a desired value adapted to keep the weak engine-braking state.

Claims

1. A coast downshift control apparatus in a vehicular automatic transmission in a motor vehicle, the automatic transmission having a plurality of clutches, wherein a coast downshift is executed under predetermined conditions by a clutch-to-clutch gearshift which is achieved by engagement of a gearshift output stage side clutch and release of a preceding gearshift stage side clutch, comprising:

means for judging whether or not said predetermined conditions for executing the coast downshift are satisfied;

means for setting a desired value for a predetermined parameter in order that a motor vehicle furnished with said automatic transmission will be kept in a substantially constant engine-braking state; and

means for performing during said coast conditions a coast control in which an oil pressure to be fed to said gearshift-output-stage side clutch is feedback controlled so that said predetermined parameter will substantially agree with the desired value.

2. A coast downshift control apparatus in for a vehicular automatic transmission as defined in claim 1, wherein after a state where said desired value is unattainable has been reached, said coast control based on said desired value is continued as long as said coast conditions continue.

3. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein input shaft speed of said automatic transmission is employed as said predetermined parameter, and a value which is higher than a speed of an engine of the motor vehicle by a predetermined value is set as said desired value of the input shaft speed.

4. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein input shaft speed of said automatic transmission is employed as said predetermined parameter, and a value which is lower than synchronous speed of the gearshift output stage by a predetermined value is set as said desired value of the input shaft speed, said synchronous speed being calculated in accordance with (Output shaft speed of Automatic transmission)×

(Gear ratio of Gearshift output stage).

5. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein a speed ratio of a torque converter of said automatic transmission is employed as said predetermined parameter, and a predetermined value which is larger than 1 (one) is set as said desired value of the speed ratio.

6. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein a coast control based on said desired value is performed by said preceding-gearshift-stage side clutch since issue of a gearshift output of said automatic transmission until said gearshift-output-stage side clutch comes to have a predetermined transmission torque capacity, and the coast control is thereafter performed by said gearshift-output-stage side clutch.

7. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein when said predetermined conditions are not satisfied any longer on account of pressing an accelerator pedal of the motor vehicle, a gearshift is executed to the gearshift stage of either the current gearshift output stage or (said current gearshift output stage+one stage) whose synchronous speed exhibits a smaller difference from the current input shaft speed of said automatic transmission.

8. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein when said predetermined conditions are not satisfied any longer because of a new upshift having occurred, an engagement timing is learnt as to the higher-speed-stage side clutch which has been in its released state as the preceding-gearshift-stage side clutch till then and which is to be engaged again anew.

9. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 1, wherein standby pressures concerning the engagement and release of said clutch are learnt on the basis of a duty ratio of said gearshift-output-stage side clutch which is under said coast control based on said desired value.

10. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 3, said automatic transmission having a synchro mechanism, wherein when synchronous speed of the current gearshift stage, which is calculated in accordance with (Output shaft r.p.m. of Automatic transmission)×

(Gear ratio of Current gearshift output stage), has become less than said desired value with a predetermined magnitude added thereto, because of a delay of switchover of said synchro mechanism due to a rapid deceleration, said desired value is temporarily changed over to another desired value with which the automatic transmission falls into a neutral state.

11. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 4, said automatic transmission having a synchro mechanism, wherein when synchronous speed of the current gearshift stage, which is calculated in accordance with (Output shaft r.p.m. of Automatic transmission)×

(Gear ratio of Current gearshift output stage), has become less than said desired value with a predetermined magnitude added thereto, because of a delay of switchover of said synchro mechanism due to a rapid deceleration, said desired value is temporarily changed over to another desired value with which the automatic transmission falls into a neutral state.

12. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 3, said automatic transmission having a synchro mechanism, wherein when synchronous speed of a first speed stage, which is calculated in accordance with (Output shaft speed of Automatic transmission)×

(Gear ratio of First speed stage), has become less than said desired value in a gearshift output state toward the first speed stage, because of a delay of switchover of the synchro mechanism due to a rapid deceleration, said desired value is changed over to a desired value with which a decreasing rate of said input shaft speed of said automatic transmission can be reduced.

13. A coast downshift control apparatus in a vehicular automatic transmission as defined in claim 4, said automatic transmission having a synchro mechanism, wherein when synchronous speed of a first speed stage, which is calculated in accordance with (Output shaft speed of Automatic transmission)×

(Gear ratio of First speed stage), has become less than said desired value in a gearshift output state toward the first speed stage, because of a delay of switchover of the synchro mechanism due to a rapid deceleration, said desired value is changed over to a desired value with which a decreasing rate of said input shaft speed of said automatic transmission can be reduced.