Downshift Decision Optimization And Braking Force Distribution Strategy Of Dual Clutch Transmission For Electric Vehicles Under Braking Condition

Due to the shortage of fossil oil sources,along with concerns about environmental issues,electric vehicles(EV)are being more widely investigated and utilized.The EV is favored in automotive applications due to its zero emission,high efficiency and low noise.However,due to the limitation of battery technology,the range of electric vehicle is short,which makes the adoption of EV is slow.Under the braking condition,making full use of motor regenerative braking can not only reduce the workload of a hydraulic braking system,but also recover the braking energy,which can further improve vehicle fuel economy.Therefore,regenerative braking is the most effective way to solve the problem of short range for electric vehicles.Based on the project of "Research on New Electronic Hydraulic Braking System",this paper presents an electronic hydraulic assist brake system,and studies the shift decision and regenerative braking strategy in the braking process of electric vehicles.Thus,this paper has important research significance for improving regenerative braking energy recovery rate and vehicle comfort.Firstly,a hybrid braking system based on dual clutch electric vehicle is proposed,which consists of an electronic hydraulic assist brake system and a regenerative braking system.The working principles of these two subsystems are introduced separately.Then the structure design and parameter matching of the hydraulic braking force generating unit and the gear shifting device of DCT are carried out.This hybrid braking system can provide hardware support for the realization of regenerative braking strategy.Secondly,a multi-objective optimization method is applied to improve the regenerative braking energy recovery and shift comfort of electric vehicles.The influence of shift decision on braking process of electric vehicle is studied.Then an optimal model of shift decision is established,which takes regenerative braking energy recovery and shift jerk as optimization objective,braking conditions and motor performance as constraints.Moreover,based on multi-objective cuckoo algorithm,the shift decision which considering regenerative braking energy recovery and shift comfort is obtained.Thirdly,the regenerative braking strategy without shift and the regenerative braking strategy based on shift are formulated.According to the ideal braking force distribution curve,braking forces are distributed and the regenerative braking strategy without shift is designed.By analyzing the shift process of DCT,it is found that the regenerative braking force will fluctuate when shifting.Therefore,the hydraulic braking force generated by the electronic hydraulic assist brake system is used to compensate for the fluctuation of regenerative braking force.Therefore,the regenerative braking strategy that can ensure the shifting comfort is obtained.Finally,simulation study is completed in Matlab/Simulink.The multi-objective optimization method of shifting decision and regenerative braking strategy based on shifting proposed in this paper are simulated and analyzed under typical braking and European cycle conditions,and the effectiveness of the method is verified.