Research On Driving & Braking Control Strategy And Test Bench Development For Dual Front Motor And Single Rear Motor 4-wheel-drive Electric Vehicle

Due to the increasingly severe energy crisis and environmental crisis,the development of the electric vehicle has become the strategic consensus of the domestic and international automobile industry.Four-wheel drive electric vehicle has become a trend in recent years,because it not only has the advantages of energy saving and environmental protection,but also has the advantages of power and stability performance.In this paper,a Dual Front Motor and Single Rear Motor Four-wheel-drive Electric vehicle(short for: DFSRM 4WEV)was chosen as the research object.Three key problems for control strategies of driving,coasting braking and composite braking are studied by using the theory of automobile dynamics,motor control theory and intelligent control theory.Based on the characteristics of DFSRM 4WEV,the corresponding solutions and control strategies are put forward to each problem,and the performance of the proposed control strategies are verified by simulation and experiment.The main contents are as follows:(1)According to the performance characteristics of the four-wheel drive electric vehicle,by comparing the advantages and disadvantages of the six different types of four-wheel drive electric vehicle with different topologies,a four-wheel drive electric vehicle driven by the dual front motor and single rear motor is selected as the research object.According to the structural characteristics of the vehicle,the type and topology of the motor and the battery are analyzed and determined.The parameters matching of the power system are carried out according to the vehicle performance index.A vehicle simulation model and power system model are established by AVL Cruise and MATLAB/Simulink based on the power system matching results.Which can provide a reliable simulation platform for the control strategies.(2)Driving control strategy for DFSRM 4WEV.For the problem of the energy consumption for the four-wheel-drive electric vehicle,the standard torque allocation strategy of the motor efficiency optimization based on the motor loss model and the Lagrangian multiplier method is established from the economic point of view.For the large dynamic demand conditions of start or rapid acceleration,the fuzzy control strategy of torque compensation based on driving intention is put forward from the power point of view.For the dangerous conditions such as wheel slip under low adhesion coefficient of slippery road surface,the anti-skid control strategy based on the straight-ahead driving condition is developed based on the similarity of the front wheel slip rate and the high speed of the rear wheel slip from the point of view of safety strategy.The driving control strategy is simulated under the condition of variable acceleration starting condition,CCBC and HWYFET cycle conditions and split road conditions by using the vehicle dynamic simulation platform.The simulation results show that the proposed control strategy can achieve good results in dynamic performance,economic performance and safety performance.(3)Coasting braking control strategy for DFSRM 4WEV.For the problem of the contradiction between the coasting distance and coasting energy recovery ratio for the electric vehicle,the coasting state judgement method based on the driving style fuzzy identification is proposed according to the analysis of the characteristics of the driver’s operation during the coasting braking.The fuzzy control strategy of highway condition and suburban/urban road condition is developed respectively according to the characteristics of coasting braking of different road conditions.The coasting braking control strategy is simulated under the highway condition,suburban/urban road condition and coasting-then-driving condition by using the vehicle dynamic simulation platform.The simulation results show that the coasting braking control strategy proposed in this paper can ensure the coasting distance and recover the coasting braking energy well.(4)Composite braking control strategy for DFSRM 4WEV.For the problem of energy recovery efficiency and braking comfort of DFSRM 4WEV composite braking system,a composite braking hierarchical control strategy based on braking intention recognition and comfort optimization is proposed.The hydraulic braking force and the front/rear axle motor braking force are optimized by the identification of the braking intention based on the LVQ neural fuzzy system.According to the differences between the motor braking and the hydraulic braking response characteristics,the braking comfort is ensured by coordinating the braking force in the execution layer.Using the vehicle dynamics simulation,the braking performance under the condition of single brake condition and NEDC cycle condition is simulated.The simulation results show that the proposed composite braking control strategy can improve the braking energy recovery and braking comfort.(5)Development of simulation test bench for DFSRM 4WEV driving brake system and verification of control strategies.As the verification of electric vehicle control strategy needs long development time cycle and high cost,a simulation test bench for driving brake system which can reflect the structural characteristics of DFSRM four-wheel drive electric vehicle is developed.The test bench adopts the full electric inertia simulation model to simulate the load.The motor and hydraulic braking control system is also designed.Taking into account the premise of real-time factors,a driving brake control system for simulation test bench was developed based on the A&D5435.The control strategies of driving,coasting braking and compound braking are verified by the test.