Study On Energy-management Strategy Of SUV Electrohydraulic Hybrid System Based On Comprehensive Efficiency Optimization

With the development of automobile industry,the oil resources consumed by transportation are increasing year by year.The development of new energy vehicles is closely linked to the theme of energy conservation and environmental protection,and has gradually become a research hotspot.Plug-in hybrid electric vehicles can effectively reduce emissions and fuel consumption,and are more pragmatic and low-cost options.The electrohydraulic hybrid electric vehicle is equipped with a high power density hydraulic energy storage system on the basis of the pure electric system,which can quickly recover the braking energy and release the energy under low-speed and low-load conditions with low motor efficiency,and can effectively reduce the power loss of the vehicle.This paper is based on the National Key Research and Development Project "Development of High-Performance Pure Electric Sport Utility Vehicle",and an electrohydraulic hybrid four-wheel drive SUV is designed,For the purpose of improving the economy and the dynamic performance of vehicle,the energy management strategy is focused on.The specific work is as follows:Based on the configuration of the four-wheel drive electric SUV,a parallel electrohydraulic hybrid system with front and rear dual motors and dual hydraulic pumps/motors is designed.The working mode of the new system is analyzed.Based on the dynamic performance indicators of the prototype vehicle,the parameters of motor,battery,hydraulic pump/motor and other system components are matched.In MATLAB,the component models and vehicle dynamic model of four-wheel drive electrohydraulic hybrid system are established,and the dynamic performance simulation is carried out to verify the correctness of parameter matching.Taking the optimal energy consumption of the vehicle as the objective function,the dynamic programming algorithm is adopted to solve the theoretical optimal driving control of the vehicle,and the corresponding driving control rules are summarized.Under the restriction of ECE R13 braking regulations,the braking-force distribution strategy of front and rear axles of the vehicle is formulated.Finding the optimal efficiency curve of the motor,based on the above driving control rules and braking-force distribution strategy,an energy-management strategy based on the optimal efficiency curve of the motor is developed.The simulation results show that the strategy can well follow the results of the dynamic planning energy-management strategy,and solve the problem caused by excessive grid division of the front-axle torque-distribution coefficient in dynamic programming.In order to solve the problem that the energy-management strategy based on the optimal efficiency curve of the motor does not comprehensively consider the optimal efficiency of the two motors,which makes the motor lose high power under certain operating conditions.The comprehensive efficiency of the front and rear dual motors under the driving and braking conditions is defined respectively,the energy-management strategy with the optimal comprehensive efficiency of the dual motor is established.The simulation results under NEDC condition show that the maximum power loss of the strategy under the entire condition is reduced by 15.95% compared with the energymanagement strategy based on the optimal efficiency curve of the motor,and the equivalent energy consumption per 100 km is reduced by 0.52%.In order to solve the problem that the determination of the threshold speed in the energy-management strategy with the optimal comprehensive efficiency of the dual motor does not take into account the change of accumulator state,and it cannot adapt to the actual complex working conditions.A fuzzy-logic controller with the accumulator pressure and its variation as the input and the threshold speed as the output is proposed,which can adaptively control the threshold speed according to the state of the accumulator,feed back to the energy-management controller,and change the working area of the hydraulic energy storage system.The simulation results show that the equivalent energy consumption per 100 km of the improved strategy is further reduced by 0.08%.