| In order to solve the problem of large consumption of oil resources and environmental pollution caused by traditional fuel vehicles,electric vehicles with the advantages of energy saving and emission reduction have become the focus of the development of the automobile industry,but the disadvantage of its unsatisfactory driving range also limits its large-scale application.Regenerative braking technology has become one of the key technologies of electric vehicles because it can recover braking energy and effectively extend the driving range of vehicles.Considering the influence of regenerative braking on vehicle braking stability,in order to ensure the braking stability and braking energy recovery effect of vehicle during regenerative braking,this paper mainly studies the following aspects:Firstly,based on the analysis of the advantages and disadvantages of two classical electrohydraulic-compound regenerative braking systems,the overall structure of the electrohydraulic-compound regenerative braking system of all wheel drive electric vehicle which can realize the regenerative braking control strategy in this paper is designed.Because it contains two different AC asynchronous motors,the front and rear drive shafts can recover braking energy,and the coordinated distribution of the electro-hydraulic braking force can be realized by combining with the hydraulic braking system,so its braking energy recovery potential has been greatly improved compared with the previous regenerative braking system.Secondly,the adhesion characteristics between the driving wheels and the ground and the braking force are analyzed.Based on this,the distribution range of front and rear drive axle braking force is limited by the relevant theory of the braking force distribution.In order to recognize the current road adhesion conditions during regenerative braking,a road surface recognizer is designed,which is based on the μ-s data of Burckhardt formula under eight kinds of road surface and the fuzzy control strategy is used to identify the similarity of the input slip ratio of each wheel and adhesion utilization with eight kinds of road surface,then the peak road adhesion coefficient between each wheel and the current road surface is calculated.Thirdly,an electro-hydraulic-compound regenerative braking control strategy based on the external characteristics of dual motors and considering the road adhesion conditions is designed.The control strategy uses the external characteristics of the front and rear motor and its charge and discharge efficiency obtained from the bench test,combined with the safe front and rear axle braking force distribution area designed by the braking force distribution theory and the peak road adhesion coefficient.The front axle regenerative braking force and the initial front axle hydraulic braking force are distributed firstly,then the rear axle regenerative braking force and the initial rear axle hydraulic braking force are distributed,and finally the front and rear axle hydraulic braking force are distributed to meet the braking demand.Finally,in order to verify that the designed regenerative braking control strategy can not only ensure the vehicle braking stability but also improve the braking energy recovery rate.The vehicle system model is built in CarSim,and the battery model,dual motors’ model,road surface recognizer and regenerative braking control strategy module are built in Simulink,and then the joint simulation experiment is carried out by CarSim and Simulink.The simulation results of single braking condition verify the effectiveness of the road surface recognizer designed in this paper.At the same time,the energy recovery rate of the designed control strategy can reach to 65.54% when the braking strength is 0.3,and the vehicle slip rate is low when braking which ensures the vehicle braking stability.In the cycle condition,the designed control strategy is simulated and analyzed together with the control strategy of regenerative braking with dual motors in parallel and variable braking intensity.The simulation results show that the braking energy recovery rate of the control strategy designed in this paper is 63.98%,62.63%,and 70.79% respectively under the three simulation cycle conditions of NEDC,UDDS and JP10-15,and compared with the two control strategies,the braking energy recovery rate of JP10-15 is increased by 22.01% and 41.26%. |
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