Hybrid vehicle drive system

A drive system of a hybrid vehicle, comprising:

• an internal combustion engine;
• a first motor-generator;
• a power transmission path including a first power transmission path and a second power transmission path connected with each other in series;
• a power division mechanism connected to the internal combustion engine to divide a power generated by the internal combustion engine to the first motor-generator and the first power transmission path;
• a second motor-generator connected to the second power transmission path;
• a clutch portion including friction elements engageable and disengageable with each other to connect or disconnect so as to make or break the first power transmission path in accordance with an engagement and an disengagement of the friction elements;
• and
• an electronic control unit including a microprocessor and a memory and configured to perform controlling the internal combustion engine, the first motor-generator, the second motor-generator and the clutch portion, wherein
• the microprocessor is configured to perform determining whether a drive in a region exceeding a characteristic curve of a driving force defined by a sum of a driving force output through the first power transmission path and a driving force of the second motor-generator at a range of a vehicle speed smaller than or equal to a predetermined vehicle speed is necessary, and
• the controlling including controlling the clutch portion to a half-clutch state when determining that the drive in the region is necessary, while connecting or disconnecting the clutch portion when determining that the drive in the region is not necessary.