Hybrid vehicle drive system

The invention relates to a vehicle drive train system intended to simplify wire harness including power cables and reduce power loss in an engine-motor hybrid vehicle drive train system. Some wheels (1; 2) are driven by an engine (3). Wheels (1; 2) other than the wheels (1; 2) are driven by the engine (3) are driven by a motorized machine (4). When the running load is large, for example, in starting a vehicle or running it on a climbing lane, the motorized machine (4) is activated as a motor for driving wheels (1; 2) in order to assist the engine drive system. While a vehicle runs, there is a range in which no motor assistance is needed (for example, in low to medium load running or deceleration). While no motor assistance is needed, the motorized machine (4) functions as a generator to convert mechanical energy from the wheels (1; 2) into electric energy. The motorized machine (4), inverter (7), capacitor device (11) and controller (18) are integrated into a unit (10) and the unit (10) is attached to a differential gear (5).