Hybrid vehicle driving system

A hybrid vehicle driving system adapted to be used in a hybrid vehicle including an internal combustion engine that can be switched to an all cylinder activated operation where all cylinders are activated for operation and a cylinder deactivated operation where at least part of the cylinders is deactivated for rest, an electric motor and a transmission, as drive sources, the hybrid vehicle driving system comprising:

• a battery that supplies electric power to the electric motor;
• a first change-speed mechanism where mechanical power from an output shaft of the internal combustion engine and the electric motor is borne by a first input shaft that engages with the electric motor and any of a plurality of change-speed gears is engaged so that the first input shaft is engaged with driven wheels;
• a second change-speed mechanism where mechanical power from the output shaft of the internal combustion engine is borne by a second input shaft and any of a plurality of change-speed gears is engaged so that the second input shaft is engaged with the driven wheels;
• a first engaging and disengaging portion that can engage the output shaft of the internal combustion engine with the first input shaft;
• and
• a second engaging and disengaging portion that can engage the output shaft of the internal combustion engine with the second input shaft, wherein:
• the hybrid vehicle can be driven in an EV mode only by a driving force of the electric motor via the first input shaft, the hybrid vehicle driving system characterized by further comprising a cylinder deactivated operation necessity determination unit for determining on the necessity of the internal combustion engine running in the cylinder deactivated operation when a required driving force required on the vehicle is smaller than a driving force resulting when the internal combustion engine runs in the cylinder deactivated operation;
• when a quick response is required, and when the cylinder deactivated operation is determined to be unnecessary by the cylinder deactivated operation necessity determination unit, the vehicle is configured to operate in the EV mode by disengaging the first engaging and disengaging portion and the second engaging and disengaging portion;
• and
• when the cylinder deactivated operation is determined to be necessary by the cylinder deactivated operation necessity determination unit, the internal combustion engine runs in the cylinder deactivated operation and at least one of the first engaging and disengaging portion and the second engaging and disengaging portion is engaged.