Hybrid powertrain speed control
A vehicle powertrain includes a controller, a torque converter, and an engine and electric machine coupled by a clutch. The torque converter may be configured to couple the electric machine to an output shaft. The controller may be programed to generate a command for the electric machine to output torque to drive the torque converter toward a desired rotational speed, and to modify the command according to a difference between the desired rotational speed and an actual rotational speed to reduce the difference, wherein values of the difference are limited by thresholds that change with powertrain operation.
1. A vehicle powertrain comprising:
an engine and electric machine coupled by a clutch;
a torque converter configured to couple the electric machine to an output shaft; and
a controller configured to
alter torque output of the electric machine to reduce a difference between a desired rotational speed and an actual rotational speed of the torque converter, and
change thresholds that limit a maximum value of the difference according to powertrain operation.
2. The vehicle powertrain of claim 1 , wherein the controller is further configured to, in response to the powertrain operation being an imminent start event of the engine, change the thresholds to a maximum range and command the electric machine to increase the torque output.
3. The vehicle powertrain of claim 1 , wherein the controller is further configured to, in response to the powertrain operation being an imminent vehicle stop, change the thresholds to a minimum range and command the electric machine to decrease the torque output.
4. The vehicle powertrain of claim 1 , wherein the controller is further configured to, in response to the powertrain operation being propulsion via the electric machine only, change the thresholds to a minimum range.
5. The vehicle powertrain of claim 1 , wherein the controller is further configured to, in response to a downshift of a transmission, change the thresholds to a nominal range and command the electric machine to output torque to drive the torque converter toward a predetermined rotational speed during disengagement of the clutch.
6. The vehicle powertrain of claim 1 , wherein the controller is further configured to limit a desired torque, derived from the desired rotational speed, to a range that is based on the powertrain operation.
7. The vehicle powertrain of claim 6 , wherein the controller is further configured to, in response to the powertrain operation being an imminent engine start event, change the range to a maximum range.
8. The vehicle powertrain of claim 6 , wherein the controller is further configured to, during vehicle travel propelled by the electric machine only, change the range to a minimum range.
9. A hybrid powertrain control method comprising:
by a controller,
operating an electric machine to output a desired rotational speed that is based on a torque estimate; and
altering the output responsive to a difference between the desired rotational speed and an actual rotational speed such that the difference is reduced; and
changing thresholds that limit a range of the difference according to an operational mode.
10. The method of claim 9 further comprising, in response to the operational mode being an imminent engine start event, changing the range to a maximum.
11. The method of claim 9 further comprising, in response to the operational mode being an imminent vehicle stop, changing the range to a minimum.
12. The method of claim 9 further comprising, during vehicle travel propelled by the electric machine only, changing the range to a minimum.
13. The method of claim 9 further comprising, in response to the operational mode being transitioning from a non-motive gear to a motive gear, changing the range to a nominal range.
14. A control system for a vehicle powertrain comprising:
a controller configured to
operate an electric machine responsive to a difference between a desired rotational speed and an actual rotational speed of a torque converter coupled with the electric machine such that the difference is reduced, and
change thresholds that limit a maximum value of the difference according to an operational mode of the vehicle powertrain.
15. The control system of claim 14 , wherein the controller is further programmed to, in response to a downshift of a transmission while vehicle speed is less than a speed threshold, change the thresholds to a nominal range.
16. The control system of claim 15 , wherein the controller is further programmed to, in response to a shift of the transmission from a non-motive gear to a motive gear, changing the thresholds to a minimum range.
17. The control system of claim 14 , wherein the controller is further programmed to, during vehicle travel propelled by the electric machine only, changing the thresholds to a minimum range.