The development of power-assisted hybrid propulsion system for city-SUV application

Taiwan Government has devoted lots of efforts to improve the air quality in the metropolitan area since early 1970. The efforts include the implementation of the more stringent emission standard each stages, the enhancement of the motor-vehicle technologies, and the education of public environmental awareness. To continuously support this never-ending good-will social policy, ITRI has also devoted its long-term technical commitment to advance its clean propulsion development to a cost-effective parallel hybrid propulsion system for the light-duty vehicle and the power assisted HEV for the SUV applications. In Taiwan, the market share of the City-SUV is growing obviously and up to 25% in those years. To improve the poor fuel-economy of City-SUV, ITRI has developed a power-assisted hybrid equipped with 100kW of the power and it consists of a 2.2L engine and an 18kW motor/generator with a high power Ni-MH battery system. This power plant has matched it into the new-developed 2,200kg t-car for 25% of fuel-economy improvement than the conventional engine power plant in FTP testing driving cycle. The step achievement shows 19% improvement and average 12.85km/l of fuel economy. The key systems of this hybrid propulsion system are the efficient electronic fuel injection engine with smart cooling control, the brush-less motor control based motor/generator with crankshaft direct mounted design, the hybrid power and energy management for the high power Ni-MH batteries system, and the overall vehicle control system. There are two types of high efficient transmission adapted for the tight packaging, including the 6-speed with 4-shift designed manual transmission and the high efficient metal belt type CVT. With the expertise of the engine calibration and the whole range of the power-electronic mapping, the power-assisted hybrid propulsion system performed well high efficient operation function, including Idle off, fast crank to drive, motor power-assisted driving and motor power-regulated generating, and brake regeneration. This article will describe these key technical aspects and development results of this hybrid propulsion system.