Patent ID: 7217221

Claim:
A method of providing an active engine stop mode of operation for a vehicle powertrain system comprising an electric machine that is operatively and selectively coupled to an engine and transmission, the system having a system controller for controlling the vehicle powertrain system which is in signal communication with and adapted to provide an output torque command to an engine controller for controlling the output torque of the engine, wherein the electric machine is adapted to provide an output torque to oppose rotation of the engine and provide and active engine stop, comprising: initiating an active engine stop request; defueling the engine in response to the active engine stop request and maintaining the rotation of the engine and a predetermined engine speed using the electric machine; determining a desired rate of reduction of the engine speed from the predetermined engine speed, wherein determining the desired rate of reduction comprises calculating an engine speed reduction trajectory for the engine; determining an electric machine output torque command necessary to obtain the engine speed reduction trajectory as a function of a plurality of vehicle dynamic parameters; applying the opposing torque using the electric machine to oppose the rotation of the engine and reduce the engine speed consistent with the desired rate of reduction of the engine speed; controlling the electric machine output torque using the electric machine output torque command; calculating an engine speed trajectory error using the engine speed trajectory reduction and an actual engine speed; determining an electric machine output torque command correction based on the trajectory error; and applying the electric machine output torque command correction to the electric machine output torque command.