Vehicle driving system, control apparatus for vehicle driving system, and control method for vehicle driving system

A control method for a vehicle driving system, the vehicle driving system including a continuously variable transmission mechanism, a transmission mechanism, a clutch mechanism, and an electronic control unit, the continuously variable transmission mechanism and the transmission mechanism being provided in parallel with each other in a power transmission path between an input shaft and an output shaft, torque output from an internal combustion engine being transmitted to the input shaft, the output shaft being coupled to a drive wheel so as to transmit power, the transmission mechanism having at least one gear ratio, the clutch mechanism being configured to selectively change between a first power transmission path and a second power transmission path, the first power transmission path being configured to transmit the torque to the output shaft via the transmission mechanism, the second power transmission path being configured to transmit the torque to the output shaft via the continuously variable transmission mechanism, the control method comprising:

• (a) selectively changing, by the electronic control unit, the power transmission path during traveling to one of the first power transmission path and the second power transmission path by controlling the clutch mechanism;
• and
• (b) in changing the power transmission path by controlling the clutch mechanism, controlling, by the electronic control unit, an operating point of the internal combustion engine during a change of the power transmission path so that the operating point crosses over an optimum fuel consumption line of the internal combustion engine.

A vehicle driving system comprising:

• an input shaft to which torque from an internal combustion engine is transmitted;
• an output shaft coupled to a drive wheel so as to transmit power;
• a continuously variable transmission mechanism and a transmission mechanism provided in parallel with each other in a power transmission path between the input shaft and the output shaft, the transmission mechanism having at least one gear ratio;
• a clutch mechanism configured to selectively change between a first power transmission path and a second power transmission path, the first power transmission path being configured to transmit the torque to the output shaft via the transmission mechanism, the second power transmission path being configured to transmit the torque to the output shaft via the continuously variable transmission mechanism;
• and
• an electronic control unit configured to:
• (a) selectively change the power transmission path during traveling to one of the first power transmission path and the second power transmission path by controlling the clutch mechanism;
• and
• (b) in changing the power transmission path by controlling the clutch mechanism, control an operating point of the internal combustion engine during a change of the power transmission path so that the operating point crosses over an optimum fuel consumption line of the internal combustion engine.