Patent ID: 7197382

Claim:
A method for controlling on/off states of an engine in a hybrid electric vehicle powertrain, the method comprising the steps of: generating a plurality of request state variables based on a comparison of vehicle operating conditions and requirements, each variable indicating an active or inactive status of a plurality of engine requests; prioritizing the active request state variables according to a predetermined schedule; selecting at least two active request state variables of higher priority than other request state variables in the plurality of request state variables; combining the at least two request state variables to form a combined request state variable that contains active requests in the at least two request state variables; simplifying the combined request state variable to eliminate any redundant requests and to resolve any conflicting requests; providing a final request state variable; evaluating the final request state variable to determine whether a change in engine state is desirable; the step of evaluating the final request state variable comprising: transitioning a state machine from an engine on state to an engine off state in accordance with a first predetermined relationship of engine request variables fpu, pu, ipu and fpd and otherwise maintaining the state machine in an engine on state; and transitioning the state machine from an engine off state to an engine on state in accordance with a second predetermined relationship of engine request variables fpu, pu, ipu and fpd and otherwise maintaining the state machine in an engine off state, where fpd, pd, fpu, ipd, pu and ipu are engine request variables, which identify the active or inactive status of engine requests.