Research On Torque Distribution Strategy Of Four-wheel Drive Plug-in Hybrid Electric Vehicle

Plug-in hybrid electric vehicles(PHEV)have become a hotspot because it have the advantages of long driving range of HEV and low fuel consumption and zero discharge of EV.Two energy sources drive and electro-mechanical brake are the generic technologies of the powertrains for PHEV,and the flexibility of the driving energy forms and the power flows highlight the necessity for vehicle energy management.It is the core problem of vehicle energy management to realize the optimization of vehicle energy efficiency and the reasonable torque distribution.under the premise of satisfying the dynamic condition,considering the difference between the efficient range of engine and motor.This paper focus on torque distribution strategy of Four-wheel drive(4WD)PHEV.The structural characteristics of the power system of 4WD PHEV is analysed as the reaearch object.According to the main parts model of the power system,build a vehicle model based on CRUISE.The rule-based torque distribution strategy is studied for the characteristics of 4WD PHEV.According to the driver's intention,the working mode is switched and then the torque distribution among three power source is performed taking into account the engine,motor and battery efficient range.Hybrid control unit based on the rule-based strategy on the modeling platform of Matlab/Simulink is built.At the same time,the key problems such as two-wheel drive torque distribution,the braking torque distribution and the torque distribution in 4WD mode are studied.In order to make the rule-based strategy have a better fuel economy,the method which optimize logic threshold in rule-based strategy based on ISIGHT is proposed.The ISIGHT can integrated with CRUISE and MATLAB to optimize logic threshold in rule-based control strategy.The optimized simulation results have a better fuel economy compared with the traditional oil vehicle and unoptimized simulation results which illustrates the effectiveness of the optimized strategy based on the ISIGHT.In order to futher improve the optimization effect,the Equivalent Consumption Minimization Strategy(ECMS)specifically for 4WD PHEV is proposed.Calculate the equivalent coefficient which can maintain the balance of SOC in ECMS according to the SOC of battery.Design the strategy of torque distribution in ECMS between the three power source.The HCU of ECMS is designed in Matlab/Simulink and the simulation results show that the proposed strategy can possess better fuel economy as well as keep balance of SOC compared with the rule-based strategy.and optimized strategy based on ISIGHT.