Research On Torque Distribution Control System Of On-Demand 4WD Vehicle

Vehicles equipped with four-wheel drive system have better traction performance,handling stability and ability to get out of trouble than single axle drive vehicles.On-demand four-wheel drive system is the most widely used four-wheel drive system type in urban SUVs.It is of great significance to analyze its characteristic principle and develop corresponding control strategy.This paper studies on four-wheel drive vehicle equipped with multi-disc electromagnetic clutch as the inter-axle differential.Following the ‘V' model of electronic control system,this paper analyzed the dynamic characteristic of 4WD vehicles,designed a control strategy on inter-axle torque distribution,calibrated and verified it in offline co-simulations.And optimized the calibration and verification in real vehicle tests with rapid ECU tools such as MicroAutoBox.It was prepared to integrate the software with hardware.First of all,this paper introduced the powertrain architecture of on-demand 4WD vehicles and built a basic powertrain model,analyzed the operating principle and characteristic and built a torque transfer model of the key coupling device-the electromagnetic clutch,validated the model in simulations to make it useful for strategy simulating.Secondly,this paper studied the relationship between inter-axle torque distribution and vehicle traction and handling performance,which was the theoretical guidance of developing the control strategy,based on the 2DOF vehicle dynamic model,the 7DOF vehicle dynamic model and the tire dynamic theory.Based on the theoretical analysis,this paper designed strategy of ‘driver input feedforward + wheel slip deviation feedback' control for straight-line driving and ‘yaw rate deviation feedback' control for steering driving,respectively.Designed coordinating strategy and ESC-4WD coordinating logic.Besides,this paper built a thermodynamic model of the clutch based on the analysis of the thermodynamic property,calibrated and validated the thermodynamic model with experiment data.Finally,CarSim and Matlab/Simulink software were used to build an offline simulation environment,and simulations were carried out in typical straight line and steering driving conditions,which preliminarily verified the effectiveness of the control strategy.Rapid prototype ECU tools like MicroAutoBox were used to carry out a real car test under typical working conditions,and the experimental results were analyzed to draw the conclusion: the torque distribution control strategy designed in this paper can improve the wheel adhesion in low-? environment such as ice & snow road,can greatly improve the vehicle's dynamic performance and escape performance,and ensure the stable driving of the vehicle.And in steering driving,the control strategy can minimize the understeering within the operating filed of 4WD system and improve the steering stability,the control goal of the on-demand 4WD control system was realized.