| Due to the environmental deterioration around the world,in order to reduce environmental pollution caused by the automobile industry,new energy vehicles have become the main research and development direction of global automobile manufacturers.Pure electric vehicles cannot solve the problems of short driving range and high battery cost in the short term.Therefore,hybrid electric vehicles are the most suitable products during the transition period from traditional vehicles to electric vehicles.They have the advantages of strong power of traditional fuel vehicles and energy conservation and emission reduction of electric vehicles.Regenerative braking is an important technology to increase the fuel economy of automobiles.It can convert braking energy into electric energy and increase the driving distance.The performance of electric-hydraulic composite braking system affects the safety and energy recovery directly of braking process.The dynamic response characteristics of the motor braking force and the hydraulic braking force are inconsistent when the brake strength changes,so the correct establishment of the braking system model and control model is the key to achieve coordinated control strategy and dynamic performance optimization.In this paper,a new plug-in hybrid electric vehicle with dual-motor was taken as the research object.On the premise of ensuring the braking safety,the goal is to make the best use of the regenerative braking force of the motor,and to improve the coordination performance of electric-hydraulic composite braking system.Aimed at the difference of the working characteristics between the motor braking system and the hydraulic braking system,the motor loss model and the hydraulic braking system model which can dynamically control the pressure are established to simulate the actual working characteristics of the electric-hydraulic composite braking system.The specific researches are as follows:(1)Through the mathematical modeling of the motor in the synchronous rotating coordinate system,the electrical loss of the motor was studied to find out the key factors affecting the loss of the motor and realize the minimum loss by controlling the motor current.(2)Through the AMESim simulation platform,the hydraulic braking system was modeled,and the working parameters of each component are analyzed.The high-speed switch valve of the hydraulic braking system was adjusted by PID control to achieve the dynamic coordinated control of wheel and cylinder pressure.(3)The CVT ratio was controlled by dynamic programming algorithm to achieve the optimal motor-CVT joint working efficiency.The coupling working point of the electric-hydraulic composite braking system is determined according to the speed and braking strength,so as to realize the maximum regenerative braking power.(4)Based on the analysis of vehicle braking dynamics and ideal braking force distribution curve,and combined with the common electric-hydraulic composite braking force distribution idea,the braking force distribution strategy based on the real-time optimization of the threshold value and the coordinated control strategy based on the brake strength correction were developed.(5)The vehicle dynamics model of electric-hydraulic composite braking system and transmission system were established by MATLAB/Simulink and AMESim simulation platforms.Co-simulation experiments under typical braking conditions and cycle conditions(UDDS,NYCC)were conducted to verify the performance of the control strategy developed in this paper.The results show that the control strategy can play the advantages of the dual-motor braking recovery system,improve the braking energy recovery rate greatly,braking safety and comfort ride of the vehicle braking,reduce braking force fluctuations. |
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