A hybrid drive system for a combine includes a control wherein the hybrid system control determines a battery pack state-of-charge of the battery pack, and the hybrid system control also receives the current engine load estimate and engine speed from the engine control. Depending upon these variables, the hybrid control sends a torque command to a motor/generator control to provide a desired composite speed-torque curve from the engine and the motor/generator. In cases where the battery pack can be charged, an engine fuel curve is set by engine control to provide maximum engine power at isochronous speed, and when the battery pack is fully charged, the engine fuel curve is reduced to be shaped so that battery electric assist is not engaged until engine speed falls.
