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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.

This paper presents the results of several studies conducted on a natural gas vehicle. In one study of engine-out emissions performance, the exhaust emissions of the CNG engine were lower than those of the base gasoline engine. In another study of the conversion characteristics of three-way catalysts, it was found that the conversion efficiency of total hydrocarbons (THCs) was much lower in the lean-mixture region for the NGV. The reduced efficiency was traced to lower conversion and poor reactivity of low-end hydrocarbons and to a higher concentration of H2O.