Research On Control Strategy Of Electro-hydraulic Composite Braking For Multi-axle Electric Drive Vehicles

Multi-axle heavy-duty vehicles have powerful transportation capabilities and play an important role in social and economic development and national defense construction.However,with the growing demand for diversification and the context of green and sustainable development,multi-axle heavy-duty vehicles also need to make corresponding changes to adapt to social development.Electric vehicles driven by in-wheel motors have the advantages of independently controllable torque,flexible space layout,and easy modular design.However,due to the heavy load,long wheelbase and large energy supply of multi-axle vehicles,energy supply may become a key factor affecting its development.Considering that the current battery technology cannot effectively improve the energy density,the development of braking energy recovery technology plays an important role in improving the cruising range of multi-axle electric drive vehicles.In this paper,according to the structural characteristics and working requirements of the multi-axle electric drive vehicle studied,the whole vehicle braking system architecture is analyzed,and the regenerative braking system model and the pure hydraulic braking system model are established according to the relevant real vehicle parameters.The dynamic response characteristics of each system are obtained through simulation.Combined with the analysis of the composite braking system,the control objectives of the composite braking system are clarified,and the direction for the establishment of the composite braking control strategy of the multi-axle electric drive vehicle is pointed out in the next step.The model structure of the established multi-axis electric vehicle composite braking control strategy consists of four parts: perception layer,control layer,execution layer and vehicle model.The braking force distribution strategy of the braking system is established.By analyzing the simplified braking dynamics model of the multi-axle vehicle,a braking force distribution strategy based on the real-time axle load is established,and the distribution of the motor and hydraulic braking force is completed according to the braking characteristics of the motor.The second is the coordinated control strategy of the compound braking system.Aiming at the problem of vehicle braking jitter that is easy to occur in the process of compound braking in the process of braking mode switching,the motor braking force correction strategy in the pressure build-up stage and the coordinated control based on feedforward-feedback are established.The third is a composite braking anti-lock control strategy based on coordinated control,which divides the control area of the traditional pure hydraulic anti-lock control strategy into an adjustment control area and a basic stability area,and then obtains the braking torque of the motor under different road adhesion conditions.Based on the safe and stable value,combined with the prediction of the wheel locking trend,the ABS control strategy of the motor braking power pre-retirement to the safe range is established.Finally,considering the fast response of motor braking and the small torque adjustment range of PID anti-lock control algorithm,this paper further builds an ABS control strategy with motor adjustment as the main and hydraulic adjustment as the auxiliary.A co-simulation model is established by comprehensive application of Truck Sim,Matlab/Simulink and AMESim software.Based on this model,the simulation analysis of the corresponding operating conditions is carried out for the control strategy designed in this paper.The simulation results show that: in the conventional braking condition,under the input of different vehicle speeds and different braking strengths,the composite braking force distribution strategy established in this paper can satisfy the driver’s braking demand,and the torque distribution is reasonable,and the vehicle speed and wheel speed are reasonable.The change is stable,and the braking energy recovery can be realized at the same time;under the mode switching condition,the established composite braking coordination control strategy reduces the maximum braking shock to 20.66% during the pressure build-up stage,and at the motor exit stage.When the braking impact is reduced by92.59%,the driving feeling is significantly improved;in the anti-lock braking condition,through the simulation of the vehicle on a single adhering road and a docking road,it is verified that the two composite brakes established All anti-lock control strategies can keep the wheel slip rate near the ideal slip rate,and can realize the function of braking energy recovery,and the energy recovery effect of the ABS control strategy based on motor adjustment and supplemented by hydraulic adjustment is as follows: On low-adhesion roads,it is better than the ABS control strategy in which the motor pre-retracts to a safe range.In order to further verify the feasibility of the established control strategy,the hydraulic brake circuit bench test and the vehicle brake test were carried out respectively.The hydraulic brake circuit test platform built based on the principle of the hydraulic brake system was tested for the response characteristics under emergency braking and step input.The results show that the response time of the actual hydraulic brake system is between0.1-0.2s,which meets the requirements of the brake regulations,and the consistency of the built hydraulic brake system model with the actual system is further verified.Based on the whole vehicle,a small-intensity braking test is carried out,including regenerative braking test and composite braking test.The test results show that the coordinated control strategy can meet the control requirements under small braking intensity,the motor braking torque,hydraulic braking The torque changes are as expected,the motor current changes are stable,and braking energy recovery is achieved.