Shift control system for continuously variable transmissions

• US 6,405,115 B2
• Filed: 05/15/2001
• Issued: 06/11/2002
• Est. Priority Date: 05/16/2000
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Yamamoto, Yoshiaki, Inoue, Daisuke, Tamura, Tadashi, Hattori, Yuji, Habuchi, Ryoji, Morioka, Hiroshi, Matsuo, Kenji, Kondo, Hiroki, Taniguchi, Hiroji, Yasue, Hideki, Kono, Katsumi
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Hernandez, Olga
• Application Number:
  US09/854,471
• Publication Number:
  US 20010044686A1
• Time in Patent Office: 392 Days
• Field of Search: 701/51, 701/54, 701/65, 180/170, 477/34, 477/63, 477/64, 477/65
• US Class Current: 701/51
• CPC Class Codes: F16H 61/66259 using electrical or electronical sensing or control means

Abstract

A shift control system for a continuously variable transmission, in which a road load on a vehicle is detected, the lower limit speed is set according to the detected road load, in which a target input speed, as set according to the running state of a vehicle, is restricted with the set lower limit speed, and in which the gear ratio of the continuously variable transmission is controlled so that the actual input speed may be equal to the target input speed restricted. The target input speed is restricted after the actual input speed is more than the lower limit value, when the road load is light, and said target input speed is restricted irrespective of the actual input speed when the road load is heavy.

Claims

1. A shift control system for a continuously variable transmission to control a gear ratio so that an actual input speed may be equal to a target input speed, comprising:

road load detector for detecting a road load on a vehicle;

lower limit speed setter for setting a lower limit speed according to a detected road load;

restrictor for restricting said target input speed on condition that the actual input speed is more than said lower limit speed, when said road load is light, and for restricting said target input speed irrespective of said condition when said road load is heavy; and

gear ratio controller for controlling the gear ratio of the continuously variable transmission so that the actual input speed may be equal to the target input speed restricted.

2. A shift control system for a continuously variable transmission according to claim 1,

wherein said lower limit speed setter includes a unit for changing and setting said lower limit speed to a value according to the road load detected and a vehicle speed, and for setting said lower limit speed to a value higher than the road load value under the road load at least in a low vehicle speed range, when said road load is heavy.

3. A shift control system for a continuously variable transmission according to claim 2, further comprising:

shift position selecting device for selecting a shift position for an ordinary run and a brake position for causing a braking action by a prime mover more than the case in which the vehicle runs at said shift position,

wherein said restrictor includes a unit for releasing the restriction on said target input speed on condition that said road load is light, when a shift operation is made from said brake position to said shift position for the ordinary run.

4. A shift control system for a continuously variable transmission according to claim 1, further comprising:

shift position selecting device for selecting a shift position for an ordinary run and a brake position for causing a braking action by a prime mover more than the case in which the vehicle runs at said shift position,

wherein said restrictor includes a unit for releasing the restriction on said target input speed on condition that said road load is light, when a shift operation is made from said brake position to said shift position for the ordinary run.

5. A shift control system for a continuously variable transmission according to claim 1,

wherein said restrictor includes a unit for setting a restriction speed of said target input speed when said road load is heavy, to a larger value than the restriction value of said target input speed when said road load is light.

6. A shift control system for a continuously variable transmission according to claim 1, further comprising:

a shift mechanism capable of making an upshift manually for lowering the gear ratio,

wherein said restrictor includes a unit for releasing the restriction on said target input speed on condition that said road load is light, when the upshift is manipulated.

7. A shift control system for a continuously variable transmission according to claim 1,

wherein said road load detector includes a unit for computing the road load from a reference acceleration, computed on the basis of a demanded drive quantity, and an actual acceleration detected.

8. A shift control system for a continuously variable transmission according to claim 1,

wherein said road load detector includes a unit for computing a gradient of a road from a reference acceleration, as computed on the basis of the demanded drive quantity, and an actual acceleration detected, to decide that the road load is heavy, when the road gradient computed is larger than a predetermined reference value.

9. A shift control system for a continuously variable transmission according to claim 1, further comprising:

a decider for deciding whether the condition that the actual input speed is more than said lower limit speed is satisfied, on the basis of the fact that a target value of the input speed is larger than said lower limit value.

10. A shift control system for a continuously variable transmission according to claim 1,

wherein said lower limit speed setter includes means for setting the lower limit speed to a larger value of the target input speed, as computed on the basis of the demanded drive quantity, and a predetermined lower limit speed.

11. A shift control system for a continuously variable transmission to control a gear ratio so that an actual input speed may be equal to a target input speed, comprising a controller which executes controls of:

detecting a road load on a vehicle;

setting a lower limit speed according to a detected road load;

restricting said target input speed on condition that the actual input speed is more than said lower limit speed, when said road load is light, and for restricting said target input speed irrespective of said condition when said road load is heavy; and

controlling the gear ratio of the continuously variable transmission so that the actual input speed may be equal to the target input speed restricted.

12. A shift control system for a continuously variable transmission according to claim 11, further comprising a step of judging whether the condition that the actual input speed is more than said lower limit speed is satisfied, on the basis of the fact that a target value of the input speed is larger than said lower limit value.

13. A shift control system for a continuously variable transmission according to claim 11, further comprising:

shift position selecting device for selecting a shift position for an ordinary run and a brake position for causing a braking action by a prime mover more than the case in which the vehicle runs at said shift position,

wherein the controller further executes a control for releasing the restriction on said target input speed on condition that said road load is light, when a shift operation is made from said brake position to said shift position for the ordinary run.

14. A shift control system for a continuously variable transmission according to claim 11, further comprising:

a shift mechanism capable of making an upshift manually for lowering the gear ratio,

wherein the controller further executes a control for releasing the restriction on said target input speed on condition that said road load is light, when the upshift is manipulated.

15. A shift control system for a continuously variable transmission according to claim 11,

wherein the controller executes judging whether the condition that the actual input speed is more than said lower limit speed is satisfied, on the basis of the fact that a target value of the input speed is larger than said lower limit value.

16. A shift control method for a continuously variable transmission to control a gear ratio so that an actual input speed may be equal to a target input speed, comprising steps of:

detecting a road load on a vehicle;

setting a lower limit speed according to a detected road load;

restricting said target input speed on condition that the actual input speed is more than said lower limit speed, when said road load is light, and for restricting said target input speed irrespective of said condition when said road load is heavy; and

controlling the gear ratio of the continuously variable transmission so that the actual input speed may be equal to the target input speed restricted.

17. A shift control method for a continuously variable transmission according to claim 16, further comprising:

a step of releasing the restriction on said target input speed on condition that said road load is light, when a shift operation is made from a brake position for causing a braking action by a prime mover to a shift position for causing a lower braking action than the braking action at the brake position.

18. A shift control method for a continuously variable transmission according to claim 16, further comprising a step of releasing the restriction on said target input speed on condition that said road load is light, when the upshift is manually operated.