Start and acceleration optimization of a parallel hybrid electric vehicle

The main issues relating to hybrid electric vehicle (HEV) emissions are starting and transient air-fuel ratio (AFR) control. The idle-cancelling function of an HEV will postpone the catalyst activation at cold start. So it is vital to confine the start emission to a much lower level. The conventional transient fuel also dramatically deteriorates emissions. The start and transient acceleration control strategies were developed on a uni-axis integrated starter-generator (ISG) parallel HEV. The optimization of each stage of the start process was realized. The start parameters of the engine controller (ECU) and vehicle controller (VCU) were determined by analysing unsuccessful starts. The results show that the engine starts smoothly without much speed overshoot. The AFR is superior to that of the prototype vehicle. At warming-up start and hot start there is also a smooth transition from ambient oxygen ratio to stoichiometric AFR. The concept is introduced of 'fast' and 'slow' torque to ISG boost acceleration. The conventional engine fuel wetting effect is overcome by ISG boost. The engine transient fuel and acceleration fuel compensation (AFC) for vehicle acceleration were replaced by ISG transient torque and continuous torque. The ISG boost acceleration calibration was completed and validated the result that the transient AFR was optimized without sacrificing vehicle drivability or acceleration performance. Both ISG start and ISG boost acceleration are effective approaches to solve the problem of HEV emission.