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Toyota has developed and confirmed the efficiency of a hybrid system using a continuously variable transmission (CVT) for relatively large vehicles like minivans. The fuel economy is double that of vans of the same class (in the Japan 10-15 test mode), and the system meets the emissions requirements for the U-LEV category. The hybrid system is configured for four-wheel drive. The front drive unit has a gasoline engine and an electric motor that are connected to a power-switching device, the output from which is conveyed to the CVT. The rear drive unit has an electric motor and a reduction gear that are independent of the front unit.

In hybrid electric vehicles, engine starting and stopping occur frequently to provide better fuel economy. Specifically, the structure of the series-parallel hybrid system transmits engine torque pulsations to the driving wheels during engine starting and stopping, which may degrade the quality of the ride. In addition, the quick response of the electric motor can easily cause drivetrain vibration. This paper presents a motor control system for a series-parallel hybrid vehicle designed to reduce these vibrations. The proposed motor control system consists of two parts; one controller functions to compensate the engine torque pulsation during engine starts, and the other controller functions to control torsional vibration of the propeller shaft and drive shaft generated by rapid increases or decreases in driving torque. The proposed vibration reduction motor control method was added to the motor controller on the first rear wheel drive hybrid vehicle (Lexus GS450h).