Emission characteristics of parallel hybrid electric bus as a function of the instantaneous degree of hybridization

Based on the importance of hybridization degree control of real-time electric machine to fuel economy and emission control, we put forward the concept of instantaneous degree of hybridization for parallel hybrid electric vehicle and make a research to instantaneous degree of hybridization of parallel hybrid electric vehicle. Through the research to real-time power, motor power, state of charge and vehicle speed of engine variation relations with the instantaneous degree of hybridization, we analyze the variation trend of pollutant emission rate with instantaneous degree of hybridization. The result shows that when |IDOH| >0.1, as the increase of the absolute value of IDOH, motor power will increase, motor of engine will decrease. As the changing of IDOH, vehicle speed and state of charge will have a trade-off variation trend. During the emission control, we should avoid the state of 0<IDOH<0.2 and -0.35<IDOH<0; When we charge the power battery pack, we should control the state of IDOH at about -0.55. When HEV drives, we should control the degree of hybridization at above 0.2 to get the strong accelerating ability and in the mean time to decrease the emission. Based on the load and emission characteristics of engine and at the same time according to the variation relationship of pollutant with the instantaneous degree of hybridization, we coordinate and control the run of motor and engine and output power to reduce emissions and increase the fuel economy. This will provide a technical support for the research of HE and low emission control of HEV.