Torque control strategy for management of rollback in a wheeled vehicle whose powertrain includes a rotary electric machine

In a motor vehicle comprising:

• road-engaging wheels;
• a powertrain comprising a rotary electric machine that is operatively coupled through a drivetrain to the road-engaging wheels and that is capable both of delivering traction torque to the wheels and of imposing regenerative braking torque on the wheels;
• friction brakes for applying friction brake torque to the wheels;
• a throttle request source that is selectively operable by a driver of the vehicle to request traction torque for accelerating the vehicle;
• a brake request source that is selectively operable by the driver to request brake torque for braking the vehicle;
• at least one processor for providing a motor torque request to the rotary electric machine and a friction brake torque request to the friction brakes by processing data that includes a request from the throttle request source and a request from the brake request source to develop a torque modification that defines an appropriate regeneration torque component of the motor torque request to the electric machine, and by also processing data that includes a request from the throttle request source and a request from the brake request source, data that defines a regeneration limit, and data that distinguishes between the vehicle being in a non-rollback state wherein the direction of vehicle motion is not contrary to that selected by a selector mechanism associated with the powertrain and the vehicle being in an incipient rollback state wherein the direction of vehicle motion is contrary to that selected by the selector mechanism, to develop the torque modification, the friction brake torque request, and a total torque that is used in subsequent processing that develops the motor torque request;
• wherein certain change in the request from the throttle request source calling for a decrease in traction torque is effective to create corresponding compression regenerative braking torque simulating the compression braking that would occur in an internal combustion when a depressed throttle of such an engine is released;
• a method that comprises distinct processes for rollback and non-rollback states of the vehicle, including;
• in both the rollback and non-rollback states, assigning the same algebraic sign to the brake torque request from the brake request source, a compression regenerative braking torque request resulting from change in the request from the throttle request source calling for a decrease in traction torque from the throttle, and the torque modification, and assigning an opposite algebraic sign to a request from the throttle request source calling for traction torque;
• in the non-rollback state, developing the total torque by algebraically summing the request from the brake request source and the request from the throttle request source;
• in the rollback state, developing the total torque by subtracting the request from the brake request source from the request from the throttle request source;
• and
• in the rollback state, setting the regeneration limit equal to the request from the throttle request source.