| With the rapid development of China’s auto manufacturing industry,environmental pollution and energy crisis have surfaced,and the auto industry now regards electric vehicles as a key research and development object.The development of electric vehicles is limited by the key problem of short driving range of electric vehicles.The electromechanical braking energy recovery technology can recover the kinetic energy or potential energy consumed by braking the vehicle and convert it into electrical energy to be stored in the energy storage device,thus improving the driving range.Therefore,the recovery of braking energy is one of the key technologies to extend the driving range of electric vehicles.Nowadays,experts and scholars at home and abroad have made certain achievements in braking energy recovery technology for electric vehicles,but there are still problems in the recognition of road conditions,the distribution of braking force between front and rear axles,and the switching of braking modes.To address the problems of electromechanical composite braking technology,the following research is conducted in this paper:Firstly,the history of the development of travel braking is introduced,and the advantages and disadvantages of various braking systems are analyzed.Based on the wire-controlled hydraulic braking system as the research object,the principle of braking energy recovery of electric vehicles and the dynamics of vehicle driving state and braking state are analyzed.The relationship between slip rate and road surface adhesion coefficient is introduced to lay the theoretical foundation for the design of road surface identifier below.Secondly,in order to make fuller use of the ground adhesion conditions,a pavement identifier that can identify the pavement adhesion conditions is designed.Based on the slip rate between the tires and the road surface when the vehicle is braking and using the adhesion coefficient,the fuzzy algorithm calculates the similarity between the current road surface and the eight standard road surfaces to obtain the peak adhesion coefficient of the road surface at this time,so as to ensure the braking safety and stability of the vehicle.Thirdly,the constraints of front and rear axle braking force distribution are determined,several classical braking force distribution control strategies are analyzed,and a braking force distribution control method that can take into account the braking energy recovery and braking stability is designed by combining the advantages of classical braking force distribution,and the optimal braking mode is switched according to the different braking intensity.For braking energy recovery,a particle swarm optimization algorithm is used to determine the objective function to modify the magnitude of the electric force.In order to verify the superiority of the method,the proportion of electric braking force to the total braking force is adjusted based on the fuzzy algorithm considering the braking intensity,vehicle speed,and battery SOC,and the comparison is verified in the following simulation analysis.Finally,the control strategy model is built in Matlab/Simulink and the whole vehicle model is built in Cruise for joint simulation to determine the braking performance evaluation index.Firstly,the designed control strategy is verified under New European Driving Cycle(NEDC)and Federal Test Procedure(FTP75)in terms of feasibility and braking energy recovery.Secondly,the braking is performed under different braking modes to verify the braking efficiency of the control strategy.The control strategy based on particle swarm optimization algorithm has shorter braking distance and braking time,higher braking torque,4.66% and 8.7% higher braking energy recovery efficiency,and slower decrease of battery SOC under different vehicle speeds and braking modes compared with the control strategy provided by Cruise and the electromechanical composite braking control strategy based on fuzzy algorithm. |
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