Control device for continuously variable transmission

Abstract

Safety as well as the minimum driving performance is secured by preventing abrupt down-shifting if a line pressure valve or a primary pressure control valve fails. A line pressure path connected to an oil pump is connected with a line pressure control valve. A first primary pressure path branched from the line pressure path is connected with a hydraulic fluid chamber through a fail-safe valve, and a secondary pressure path branched from the line pressure path is connected to a hydraulic fluid chamber. The line pressure control valve is connected with a second primary pressure path in communication with a hydraulic fluid chamber, and this secondary primary pressure path is provided with a primary pressure control valve and a limiter valve. When the line pressure control valve and the primary pressure control valve fail and excess line pressure or primary pressure is output, the pressure in the hydraulic fluid chamber is reduced by the fail-safe valve, so that the pressure in the hydraulic fluid chamber is reduced by the limiter valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a skeleton view of a continuously variable transmission that is controlled by a control device according to one embodiment of the invention;

FIG. 2 schematically shows a hydraulic control system and an electronic control system for the continuously variable transmission;

FIG. 3 is a block diagram of a transmission control system for a CVT control unit;

FIG. 4 is a characteristic line graph representing the relation between a speed ratio, a clamp force ratio, and a torque ratio;

FIG. 5 schematically shows a hydraulic supply state when the speed change ratio is controlled to the low state;

FIG. 6 schematically shows a hydraulic supply state when the speed change ratio is controlled to the overdrive state; and

FIG. 7 schematically shows a hydraulic supply state when the line pressure control valve and the primary pressure control valve attain a failed state.

Claims

1. A control device for a continuously variable transmission having a variable speed pulley including first and second variable speed pressure chambers that control the groove width of the pulley, a tightening pulley including a tightening pressure chamber that controls the groove width of the pulley, and a power transmission element wound around the variable speed pulley and the tightening pulley, the control device comprising: a line pressure control valve provided between a hydraulic pressure supply source and the tightening pulley to regulate line pressure supplied to the first variable speed pressure chamber and the tightening pressure chamber;a speed ratio control valve provided between the line pressure control valve and the variable speed pulley to regulate variable speed control pressure supplied to the second variable speed pressure chamber;a first reducing valve provided between the line pressure control valve and the variable speed pulley to reduce the line pressure when the line pressure exceeds first limit pressure; anda second reducing valve provided between the speed ratio control valve and the variable speed pulley to reduce the variable speed control pressure when the variable speed control pressure exceeds second limit pressure.

2. The control device for a continuously variable transmission according to claim 1, wherein the first reducing valve is provided between the line pressure control valve and the first variable speed pressure chamber to reduce the line pressure supplied to the first variable speed pressure chamber.

3. The control device for a continuously variable transmission according to claim 1, wherein the second reducing valve is provided between the speed ratio control valve and the second variable speed pressure chamber and reduces the variable speed control pressure supplied to the second variable speed pressure chamber.

4. The control device for a continuously variable transmission according to claim 1, wherein the size of the first variable speed pressure chamber relative to the tightening pressure chamber is set based on a shift speed requested upon down-shifting.

5. The control device for a continuously variable transmission according to claim 1, wherein the sizes of the first and second variable speed pressure chambers relative to the tightening pressure chamber are set based on a shift speed requested upon up-shifting.

6. The control device for a continuously variable transmission according to claim 1, wherein the first limit pressure is the maximum line pressure regulated by the line pressure control valve.

7. The control device for a continuously variable transmission according to claim 1, wherein the line pressure control valve and the speed ratio control valve set the second limit pressure based on a target speed ratio when the line pressure control valve and the speed ratio control valve fail.

8. The control device for a continuously variable transmission according to claim 2, wherein the second reducing valve is provided between the speed ratio control valve and the second variable speed pressure chamber and reduces the variable speed control pressure supplied to the second variable speed pressure chamber.

9. The control device for a continuously variable transmission according to claim 2, wherein the size of the first variable speed pressure chamber relative to the tightening pressure chamber is set based on a shift speed requested upon down-shifting.

10. The control device for a continuously variable transmission according to claim 3, wherein the size of the first variable speed pressure chamber relative to the tightening pressure chamber is set based on a shift speed requested upon down-shifting.

11. The control device for a continuously variable transmission according to claim 2, wherein the sizes of the first and second variable speed pressure chambers relative to the tightening pressure chamber are set based on a shift speed requested upon up-shifting.

12. The control device for a continuously variable transmission according to claim 3, wherein the sizes of the first and second variable speed pressure chambers relative to the tightening pressure chamber are set based on a shift speed requested upon up-shifting.

13. The control device for a continuously variable transmission according to claim 4, wherein the sizes of the first and second variable speed pressure chambers relative to the tightening pressure chamber are set based on a shift speed requested upon up-shifting.

14. The control device for a continuously variable transmission according to claim 2, wherein the first limit pressure is the maximum line pressure regulated by the line pressure control valve.

15. The control device for a continuously variable transmission according to claim 3, wherein the first limit pressure is the maximum line pressure regulated by the line pressure control valve.

16. The control device for a continuously variable transmission according to claim 4, wherein the first limit pressure is the maximum line pressure regulated by the line pressure control valve.

17. The control device for a continuously variable transmission according to claim 5, wherein the first limit pressure is the maximum line pressure regulated by the line pressure control valve.

18. The control device for a continuously variable transmission according to claim 2, wherein the line pressure control valve and the speed ratio control valve set the second limit pressure based on a target speed ratio when the line pressure control valve and the speed ratio control valve fail.

19. The control device for a continuously variable transmission according to claim 3, wherein the line pressure control valve and the speed ratio control valve set the second limit pressure based on a target speed ratio when the line pressure control valve and the speed ratio control valve fail.

20. The control device for a continuously variable transmission according to claim 4, wherein the line pressure control valve and the speed ratio control valve set the second limit pressure based on a target speed ratio when the line pressure control valve and the speed ratio control valve fail.

21. The control device for a continuously variable transmission according to claim 5, wherein the line pressure control valve and the speed ratio control valve set the second limit pressure based on a target speed ratio when the line pressure control valve and the speed ratio control valve fail.

22. The control device for a continuously variable transmission according to claim 6, wherein the line pressure control valve and the speed ratio control valve set the second limit pressure based on a target speed ratio when the line pressure control valve and the speed ratio control valve fail.