A vehicle drive train and drive train system is provided to simplify wire harness including power cables and reduce power loss in an engine-motor hybrid vehicle drive train system. The drive train and system includes some wheels driven by an engine, and other wheels driven by a motorized machine. When the running load is large, for example, starting a vehicle or running on a climbing lane, the motorized machine is activated for driving wheels in order to assist the engine. When no motor assistances is needed (for example, in low to medium load running or deceleration), the motorized machine functions as a generator to convert mechanical energy from the wheels into electric energy. The motorized machine, inverter, capacitor device and controller are integrated into a unit and the unit is attached to a differential gear.