Patent ID: 8875819

Claim:
A hybrid drive system for a vehicle, the hybrid drive system comprising: a primary drive sub-system having: a front-most drive axle located at a forward position of the vehicle, a middle drive axle positioned at a distance behind the front-most drive axle, an internal combustion engine dimensioned for providing the primary source of motive power, the internal combustion engine having an internal coupling to the front-most drive axle, and a first drive shaft in mechanical communication with the internal combustion engine and the middle drive axle; a supplemental drive sub-system electrically and mechanically isolated from the primary drive sub-system, the supplemental drive sub-system having: an electric motor dimensioned for providing supplemental motive power, an energy storage unit for storing electric energy supplied to the electric motor, a clutch assembly for selectively engaging and disengaging the electric motor, a rear-most drive axle positioned at a distance behind the middle drive axle, and a second driveshaft in mechanical communication between the clutch assembly and the rear-most drive axle; and a drive controller for controlling the electric motor and the clutch assembly, the drive controller controlling engagement of the clutch assembly only: when supplemental motive power is demanded to supplement primary motive power generated by the internal combustion engine to transfer power from the electric motor to the rear-most drive axle, and when the vehicle is decelerating to transfer motive power from the rear-most drive axle to the electric motor to recharge the energy storage unit, and the drive controller is configured to control disengagement of the clutch assembly at other times including when the primary drive sub-system satisfies a demanded motive power during cruising or acceleration of the vehicle in order to isolate the electric motor from the rear-most drive axle.