Research On Torque Characteristics Of Clutch And Control Strategy For On-demand 4WD Vehicle Based On Inter-axle Torque Distribution

In recent years,the rapid growth of the domestic SUV model market has driven the rapid development of four-wheel drive technology.In order to meet people's needs for improving the dynamics and stability of 4WD vehicles,it is necessary to develop a set of on-demand 4WD control systems with independent intellectual property rights and complete performance,which is based on a domestic inter-axle clutch.This paper takes an on-demand 4WD vehicle equipped with a domestic electromagnetic multi-plate wet central clutch as the research object,and studies the torque characteristics of the clutch through a bench test.The paper studies the effect of torque distribution between axles on the dynamics and stability of the vehicle by means of dynamics analysis,then put forward four-wheel drive control strategies for different driving conditions.Finally,we verify the control strategy by means of offline simulation and real vehicle calibration.The main content of the paper are as follows:(1)This paper analyzes the transmission configuration of the on-demand 4WD vehicle and builds a basic powertrain model,then studies the working principle and the torque characteristics of a domestic electromagnetic multi-plate wet central clutch.At the same time,several important influencing factors of torque characteristics are proposed,and then a clutch test bench is set up for data collection and analysis.At last,a clutch torque model and temperature model are established based on the experimental results.(2)Based on the tire dynamics of the car,this paper analyzes the effects of the inter-axle torque distribution on the longitudinal traction characteristics and lateral stability performance.At the same time,we study the calculation methods of the key parameters of the 4WD control system based on the two-degree-of-freedom and seven-degree-of-freedom vehicle dynamics models.(3)Aiming at the different performance requirements of 4WD vehicles under straight-line driving conditions and steering conditions,this paper designs two kinds of control strategies,including ‘preload control based on driver's driving intention recognition + feedback control based on the difference between the front and rear axle wheel slip ratios' and ‘active steering intervention control based on driver's driving intention recognition + active steering correction control based on yaw moment deviation rate'.At the same time,based on the needs of industrialization,this paper proposes a clutch temperature overload protection control strategy and a coordinated control strategy for the 4WD control system and the entire vehicle braking system.(4)Based on the established 4WD control Simulink model,this paper uses CarSim software to set up an offline simulation environment,and performs simulation experiments under several typical straight-line driving conditions and steering driving conditions.Then,a domestic SUV model was modified based on a domestic shaft-to-axle clutch.At the same time,this paper uses the self-developed circuit board as the ECU to perform real vehicle calibration experiments under several typical working conditions.At last,the experimental data was collected and analyzed by a software named VehicleSpy.The offline simulation and real vehicle calibration results show that the on-demand 4WD system designed in this paper can suppress undesired wheel slippage and improve the vehicle's dynamic performance under straight-line driving conditions.While under steering conditions,the on-demand 4WD system can widen the lateral stability limit of the vehicle,and properly adjust the vehicle's steadystate steering attitude to meet the needs of different steering characteristics.