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This paper presents a new hybrid propulsion system that has been developed to address environmental issues related to the automotive powertrain, based on the view that such systems will be a core automotive technology in the future. To achieve market acceptance, it is essential that hybrid systems do not compromise engine performance or driving performance. The following target performance characteristics were considered to be important in the development of this hybrid propulsion system for the Japanese market. First, driving performance should not be sacrificed for the mere reason that it is a hybrid car. Second, fuel economy should be twice that of gasoline-powered vehicles in the same class under 10-15 test mode operation, or even better. Further, performance in other areas should be comparable to conventional vehicles. The system presented here has two motors for propulsion and energy regeneration. Both are inverter type permanent magnetic synchronous motors.

Attenuation of fore and after vehicle vibration caused by transient throttle pedal maneuvering is a key factor in achieving a good drivability. The dynamics of this vibration is analyzed considering torque generated by combustion as the exciting force. The relationship between vibration attenuation and improvement of drivability is determined using a subjective, low frequency vibration test. Through these analyses and tests, a new vibration control system is developed which controls the above noted torque by providing optimum adjustment of ignition timing. Decreasing fore and after vehicle vibration without adversely affecting vehicle performance, this control system improves drivability in both FF and FR cars by more than 1.0 evaluation point.