| The electro-hydraulic composite braking system is widely used in the field of new energy vehicles by virtue of its good performance.In order to further improve the dynamic response capability of the braking system,the design of a reasonable control strategy for the composite braking system has gradually become an important development trend.In the process of designing the control strategy of composite braking also ushered in new challenges: on the basis of ensuring the braking stability of the vehicle,it is necessary to recover as much braking energy as possible;taking into account the different response characteristics of hydraulic braking system and regenerative braking system,it is necessary to reduce the braking shock generated by the vehicle when switching between braking modes as much as possible.Therefore,on the one hand,this paper optimizes the structural parameters of the electromagnetic linear actuator in the linear control actuation system to improve the static/dynamic performance of the electromagnetic linear actuator;on the other hand,based on the fuzzy control for driver braking intention recognition,it proposes a control strategy that considers the dynamic response characteristics of the electro-hydraulic composite braking system to meet the performance requirements of the vehicle in the braking process.The main work of this paper is specified as follows:(1)Design the direct-drive composite braking system scheme and establish the mathematical model of the system.This paper takes a pure electric vehicle as the research object,analyzes the basic structure of the composite braking system;elaborates the composition and working principle of the direct-drive solenoid-based linear control system;builds a mathematical model including linear control system,vehicle dynamics,battery and hub motor,and lays the foundation for the subsequent joint simulation.(2)Multidisciplinary optimization of structural parameters of electromagnetic direct-drive valve drive motor.In this paper,based on the study of linear control actuation based on electromagnetic direct drive valve,the finite element model of electromagnetic direct drive valve drive motor is established,and the optimization variables are determined by fuzzy gray scale theory;the maximum electromagnetic force,electromagnetic force fluctuation rate,dynamic time constant and efficiency of the electromagnetic linear actuator are used as the optimization objectives by using the multidisciplinary algorithm based on second generation non-dominated ordering to optimize the structural parameters.The results show that the maximum electromagnetic force and efficiency are improved by18.1% and 12%,and the maximum electromagnetic force fluctuation rate and time constant are reduced by 38.5% and 1.82 ms,respectively,compared with those before the optimization,which effectively improves the static/dynamic performance of the electromagnetic linear actuator.(3)Design of fuzzy control-based driver braking intention recognition algorithm.According to the specific performance of the braking process,the driver’s braking intention is classified into four categories: light braking,moderate braking,heavy braking and emergency braking;a progressive fuzzy logic controller containing brake pedal state recognition and braking intention recognition is designed,and the brake pedal displacement,change rate and vehicle deceleration rate are selected as recognition parameters.According to the simulation results,the established fuzzy logic controller can identify the brake pedal state and the braking intention of the driver more accurately.(4)Design a coordinated control strategy for the electro-hydraulic composite braking system of pure electric vehicles.By analyzing the dynamics of the vehicle braking process and combining with relevant regulations,the front and rear axle braking forces are divided according to the braking intensity;the dynamic electro-hydraulic braking torque distribution strategy is designed according to the recognition results of the driver’s braking intention;the dynamic response characteristics of the regenerative braking system and the hydraulic braking system are obtained through simulation,and a feedforward-feedback based composite braking coordinated control strategy based on feedforward-feedback.(5)The feasibility verification of control strategy of direct-drive electro-hydraulic composite braking system.A joint simulation model of electro-hydraulic composite braking system is built based on Carsim and Simulink;the distribution strategy and coordinated control strategy of the composite braking system are simulated and analyzed in the simulation model.The simulation results show that: when the vehicle is driven in conventional road conditions,the maximum impact degree and the impact degree difference can be reduced to 95.67% and 91.18% respectively after the coordinated composite braking system compared with the uncoordinated one. |
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