System and method for controlling engine torque to prevent driveline bump during a downshift when a throttle valve is closed

1. A system comprising:

a downshift determination module that determines when a closed-throttle downshift occurs and that generates a signal indicating when the closed-throttle downshift occurs, wherein the closed-throttle downshift is a downshift of a transmission when a throttle valve of an engine is closed; and

a speed control module that receives the signal and that controls engine speed based on turbine speed during the closed-throttle downshift while the throttle valve is closed, wherein the turbine speed is a speed of a turbine in a torque converter that couples the engine to the transmission.

2. The system of claim 1 , wherein the speed control module:

(i) maintains the engine speed less than the turbine speed during the closed-throttle downshift when the engine speed is less than the turbine speed when the closed-throttle downshift starts; and

(ii) maintains the engine speed greater than the turbine speed during the closed-throttle downshift when the engine speed is greater than the turbine speed when the closed-throttle downshift starts.

3. A system comprising:

a downshift determination module that determines when a closed-throttle downshift occurs, wherein the closed-throttle downshift is a downshift of a transmission when a throttle valve of an engine is closed;

a speed control module that controls engine speed based on turbine speed during the closed-throttle downshift, wherein the turbine speed is a speed of a turbine in a torque converter that couples the engine to the transmission, and wherein the speed control module:

(i) maintains the engine speed less than the turbine speed during the closed-throttle downshift when the engine speed is less than the turbine speed when the closed-throttle downshift starts; and

(ii) maintains the engine speed greater than the turbine speed during the closed-throttle downshift when the engine speed is greater than the turbine speed when the closed-throttle downshift starts; and

a desired speed determination module that determines a desired speed of the engine during a vehicle coastdown based on a maximum of a first speed and a second speed, wherein the first speed is an idle speed and the second speed is equal to a sum of the turbine speed and a first offset.

4. The system of claim 3 , wherein the speed control module maintains the engine speed greater than a third speed during the vehicle coastdown, wherein the third speed is equal to a difference between the desired speed and a second offset.

5. The system of claim 3 , further comprising:

a torque determination module that determines a torque request based on the desired speed, wherein the torque determination module limits a change in the torque request during the closed-throttle downshift based on a vehicle deceleration rate; and

a torque control module that controls engine torque based on the torque request during the vehicle coastdown.

6. The system of claim 5 , wherein the torque control module controls the engine torque independent from the torque request during the vehicle coastdown:

when the torque converter is locked and slip of the torque converter is less than a first threshold;

when the slip is controlled and the slip is less than a second threshold; and

when fuel delivery to at least one cylinder of the engine is stopped.

7. The system of claim 5 , wherein the torque determination module determines the torque request based on a sum of an open-loop torque, an integral gain, and a proportional gain, wherein the open-loop torque is based on a maximum of:

(i) a minimum torque that prevents engine stall; and

(ii) a sum of a coast torque and a transmission load.

8. The system of claim 7 , wherein the torque determination module sets the integral gain equal to a difference between a previous torque request and the open-loop torque when the torque control module starts to control the engine torque based on the torque request.

9. The system of claim 7 , wherein the torque request includes a predicted torque request and an immediate torque request, and the torque determination module limits the predicted torque request based on the minimum torque and a maximum torque without limiting the immediate torque request.

10. The system of claim 7 , wherein the torque determination module determines the torque request further based on a torque reserve and determines the torque reserve and the transmission load based on the vehicle deceleration rate.

11. A method comprising:

determining when a closed-throttle downshift occurs, wherein the closed-throttle downshift is a downshift of a transmission when a throttle valve of an engine is closed; and

controlling engine speed based on turbine speed during the closed-throttle downshift while the throttle valve is closed, wherein the turbine speed is a speed of a turbine in a torque converter that couples the engine to the transmission.

12. The method of claim 11 , further comprising:

maintaining the engine speed less than the turbine speed during the closed-throttle downshift when the engine speed is less than the turbine speed when the closed-throttle downshift starts; and

maintaining the engine speed greater than the turbine speed during the closed-throttle downshift when the engine speed is greater than the turbine speed when the closed-throttle downshift starts.

13. A method comprising:

determining when a closed-throttle downshift occurs, wherein the closed-throttle downshift is a downshift of a transmission when a throttle valve of an engine is closed;

controlling engine speed based on turbine speed during the closed-throttle downshift, wherein the turbine speed is a speed of a turbine in a torque converter that couples the engine to the transmission;

maintaining the engine speed less than the turbine speed during the closed-throttle downshift when the engine speed is less than the turbine speed when the closed-throttle downshift starts;

maintaining the engine speed greater than the turbine speed during the closed-throttle downshift when the engine speed is greater than the turbine speed when the closed-throttle downshift starts; and

determining a desired speed of the engine during a vehicle coastdown based on a maximum of a first speed and a second speed, wherein the first speed is an idle speed and the second speed is equal to a sum of the turbine speed and a first offset.

14. The method of claim 13 , further comprising maintaining the engine speed greater than a third speed during the vehicle coastdown, wherein the third speed is equal to a difference between the desired speed and a second offset.

15. The method of claim 13 , further comprising:

determining a torque request based on the desired speed;

limiting a change in the torque request during the closed-throttle downshift based on a vehicle deceleration rate; and

controlling engine torque based on the torque request during the vehicle coastdown.

16. The method of claim 15 , further comprising controlling the engine torque independent from the torque request during the vehicle coastdown:

when the torque converter is locked and slip of the torque converter is less than a first threshold;

when the slip is controlled and the slip is less than a second threshold; and

when fuel delivery to at least one cylinder of the engine is stopped.

17. The method of claim 15 , further comprising determining the torque request based on a sum of an open-loop torque, an integral gain, and a proportional gain, wherein the open-loop torque is based on a maximum of:

(i) a minimum torque that prevents engine stall; and

(ii) a sum of a coast torque and a transmission load.

18. The method of claim 17 , further comprising setting the integral gain equal to a difference between a previous torque request and the open-loop torque when starting to control the engine torque based on the torque request.

19. The method of claim 17 , wherein the torque request includes a predicted torque request and an immediate torque request, the method further comprising limiting the predicted torque request based on the minimum torque and a maximum torque without limiting the immediate torque request.

20. The method of claim 17 , further comprising determining the torque request further based on a torque reserve and determining the torque reserve and the transmission load based on the vehicle deceleration rate.