In such a hybrid vehicle, the layout for an engine, a generator/motor, and a transmission that is conventionally employed is in general of a so-called sandwiched generator/motor type in which a thin generator/motor is sandwiched between the engine and the transmission. In the layout of the sandwiched generator/motor type, since the generator/motor is joined to a crankshaft of the engine and an input shaft of the transmission and always rotates integrally therewith, when the generator/motor carries out regenerative braking during deceleration of the vehicle, there are the problems that friction in the engine and the transmission might degrade the energy recovery efficiency, and the friction of the engine is a load on the generator/motor when traveling by means of the generator/motor, thus increasing the power consumption.
A so-called leg shaft drive system hybrid vehicle is known from, for example, Patent Publication 1 below in which the above-mentioned problems have been solved by enabling a generator/motor to be isolated from a crankshaft of an engine and an input shaft of a transmission, and enabling the driving force of the generator/motor to be transmitted to a driven wheel side rather than an output shaft of the transmission.
In this hybrid vehicle, the generator/motor is connected in series via a clutch to an end of the input shaft of the transmission on the side opposite to the engine, and by isolating the generator/motor from the input shaft of the transmission and the crankshaft of the engine by disengaging the clutch, the driving force of the generator/motor can be transmitted directly to the output shaft of the transmission. Patent Publication 1: Japanese Patent Application Laid-open No. 2002-188716