Power Distribution Strategy For An Axle-Split Hybrid Electric Vehicle

An axle-split hybrid electric vehicle,the front-axle and rear-axle of which are driven by the internal combustion engine(with a 6-speed transmission)and electric motor separately,attaches great importance for excellent economy and driving performance.The main challenge of power distribution control of this axle-split hybrid electric vehicle is that both power balance and torque distribution should be considered to satisfy the driving requirement of both axles.The split structure leads to that the equivalent torque of motor and engine generates different effect of driving force at wheels,and this makes it inconvenient to allocate torque between motor and engine when the energy management strategy is designed.This thesis proposes an energy management strategy based on power.The hybrid vehicle model,which is built based on the IFP Drive model library in AMEsim environment,includes engine,DCT,motor,battery,electric fittings and dynamic model.The co-simulation between the vehicle model and the strategy in MATLAB/SIMULINK is operated for verifying the models in the loop after predefining I/O ports.This thesis proposes an energy management strategy,which firstly detects the power distribution based on engine efficiency map.It converts the required torque at wheels to the power of engine and motor,and then finds out the optimal engine power according to the optimal economy at current engine speed on engine efficiency map of which abscissa is engine speed and coordinate is engine power to design the economy shifting rules and allocate the optimal power of engine and motor.Detailed analysis and optimization are carried out aiming at key parameters about the threshold value of vehicle mode switching,the value of power distribution and the threshold value of engine start-stop,including introducing the principles and the calculation process about the parametric curves.Equivalent efficiency line of engine and motor is drawn as the mode selection boundary for each transmission efficiency of each gear.Driving generating mode and forced generating mode are designed to make full use of power.The power distribution path of the minimum fuel is searched by dynamic programming algorithm of which variable is SOC,and the minimum fuel value is calculated in NEDC cycle.This calculating value and the value of fuel counterpart model are compared,and the strategy is evaluated with the comparison result.The vehicle model is embedded into SCALAXIO system and the strategy model is embedded into MicroAutoBox system.The variation about vehicle modes and shifting gears,the output power state of power supplies and the following vehicle speed situation in NEDC and WLTC are observed in real time.The strategy is optimized according to the experimental results.Results show that the proposed strategy makes fuel economy of the hybrid model increased by 35.9% at maximum compared with the fuel counterpart model,the frequent engine start-stop is avoided effectively and the SOC is balanced in NEDC,WLTC and other working conditions.