Hybrid drive system of vehicle

A hybrid electric drive system for a vehicle comprising:

• a combustion engine,
• a transmission comprising an input shaft and an output shaft and transmitting rotational torque between the input shaft and the output shaft;
• a first clutch adapted to connect the engine to the input shaft of the transmission and to disconnect the engine from the input shaft of the transmission;
• a rotating electric machine which serves as a motor as well as a generator;
• a second clutch which can connect the rotating electric machine to the input shaft of the transmission and disconnect the rotating electric machine from the input shaft of the transmission;
• a storage device which stores electric power generated by the rotating electric machine;
• a control unit programmed to:
• control a rotational speed of the rotating electric machine when the second clutch is commanded to connect the rotating electric machine to the input shaft of the transmission, so as to decrease the difference between the rotational speed of the rotating electric machine and a rotational speed of the input shaft of the transmission;
• and
• cause the second clutch to connect the rotating electric machine to the input shaft of the transmission only after the difference decreases to a value within a predetermined allowable range.