Control system and method for continuously variable transmission with variator speed ratio closed-loop feedback

1. A method of controlling a continuously variable transmission in a vehicle which is responsive to driver and vehicle inputs and which has a variator including at least one roller operatively positioned between an input disk and an output disk so that a variator speed ratio (VSR) is defined as a ratio of a speed of the output disk to a speed of the input disk, and a motor to adjust a position of the roller, comprising:

determining a desired VSR based on at least one of the driver and vehicle inputs;

determining a motor position adjustment needed to adjust the position of the roller to achieve the desired VSR;

driving the motor based on the determined motor position adjustment needed;

sensing a transmission output speed as the motor is being driven;

determining an actual VSR as the motor is being driven; and

providing closed-loop feedback corresponding to any difference between the actual VSR and the desired VSR and driving the motor to eliminate the difference between the actual VSR and the desired VSR, thereby achieving the desired VSR.

2. The method of claim 1 wherein the motor is a DC servo motor.

3. The method of claim 1 wherein determining the motor position adjustment needed uses a proportional-integral-derivative (PID) algorithm.

4. The method of claim 1 including using a feedback signal of a speed of the vehicle for determining the desired VSR.

5. The method of claim 1 wherein determining the actual VSR further includes sensing the output disk speed and the input disk speed as the motor is driven and calculating the actual variator speed as a ratio of the sensed output disk speed and the sensed input disk speed.

6. The method of claim 1 further including sensing a transmission input speed and wherein determining the actual VSR is determined using the ratio of the sensed transmission output speed and the sensed transmission input speed.

7. A system for controlling a continuously variable transmission in a vehicle which is responsive to driver and vehicle inputs comprising:

a variator including at least one roller operatively positioned between an input disk and an output disk so that a variator speed ratio (VSR) is defined as a ratio of a speed of the output disk to a speed of the input disk;

a motor to adjust a position of the roller; and

a controller for controlling the variator and the motor by determining a desired VSR based on at least one of the driver and vehicle inputs, determining a motor position adjustment needed to adjust the position of the roller to achieve the desired VSR, driving the motor based on the determined motor position adjustment needed, sensing a transmission output speed as the motor is being driven, determining an actual VSR as the motor is being driven, and providing closed-loop feedback corresponding to any difference between the actual VSR and the desired VSR and driving the motor to eliminate the difference between the actual VSR and the desired VSR, thereby achieving the desired VSR.

8. The system of claim 7 wherein the motor is a DC servo motor.

9. The system of claim 7 wherein the controller determines the motor position adjustment needed using a proportional-integral-derivative (PID) algorithm.

10. The system of claim 7 wherein the controller further provides feedback of a speed of the vehicle for determining the desired VSR.

11. The system of claim 7 wherein the controller determines the actual VSR by sensing the output disk speed and the input disk speed as the motor is driven and calculating the actual variator speed as a ratio of the sensed output disk speed and the sensed input disk speed.

12. The system of claim 7 wherein the controller senses a transmission input speed and determines the actual VSR using a ratio of the sensed transmission output speed and the sensed transmission input speed.

13. A vehicle including a continuously variable transmission (CVT) which is responsive to driver and vehicle inputs comprising:

an engine for driving an input shaft;

a wheel being propelled by an output shaft; and

a system having:

a variator including at least one roller operatively positioned between an input disk and an output disk so that a variator speed ratio (VSR) is defined as a ratio of a speed of the output disk to a speed of the input disk;

a motor to adjust a position of the roller; and

a controller for controlling the variator and the motor by determining a desired VSR based on at least one of the driver and vehicle inputs, determining a motor position adjustment needed to adjust the position of the roller to achieve the desired VSR, driving the motor based on the determined motor position adjustment needed, sensing a transmission output speed as the motor is being driven, determining an actual VSR as the motor is being driven, and providing closed-loop feedback corresponding to any difference between the actual VSR and the desired VSR and driving the motor to eliminate the difference between the actual VSR and the desired VSR, thereby achieving the desired VSR;

wherein the input shaft is coupled to the input disk and the output shaft is coupled to the output disk.

14. The vehicle of claim 13 wherein the motor is a DC servo motor.

15. The vehicle of claim 13 wherein the controller determines the motor position adjustment needed using a proportional-integral-derivative (PID) algorithm.

16. The vehicle of claim 13 wherein the controller further provides feedback of a speed of the vehicle for determining the desired VSR.

17. The vehicle of claim 13 wherein the controller determines the actual VSR by sensing the output disk speed and the input disk speed as the motor is driven and calculating the actual variator speed as a ratio of the sensed output disk speed and the sensed input disk speed.

18. The vehicle of claim 13 wherein the controller senses a transmission input speed and determines the actual VSR using the ratio of the sensed transmission output speed and the sensed transmission input speed.