Research On Torque Distribution Strategy Of AWD Vehicle Based On Characteristics Of Wet Clutch In Transfer Case

The transfer case is the core part of the AWD vehicle.The key to the research and design of the active transfer case is to analyze its torque characteristics and explore the torque distribution ratio of the front and rear axles under different working conditions.In this thesis,the AWD transfer case is taken as the research object,aiming at improve the torque transmission quality and the dynamic performance of the vehicle,the working characteristics of transfer case and the torque distribution strategy of the front and rear axles of the vehicle are theoretically analyzed and discussed.The main contents of this thesis are as follows:(1)The structure of the wet clutch in the transfer case is simplified as a single friction pair model.Based on the hydrodynamic lubrication theory and the thermodynamic dimension simplification method,the required lubricating oil flow model to maintain the full oil film state of the friction pair is established,and the validity of the mathematical model is verified by FLUENT/VOF.(2)The different engagement stages of friction pair in transfer case are analyzed,and the oil film pressure model is established considering the surface roughness of friction pair and the permeability of friction material.Based on GT contact model,the rough contact pressure model is established considering the influence of physical properties of friction pair.The dynamic performance of the friction pair in the bonding process is analyzed,and the variation law of oil film thickness between friction pairs in different bonding stages under the action of motor pressing force is obtained.(3)The drag torque model of friction pair in separation condition and sliding torque model in combination condition are established.The influence rules of lubricating oil supply flow,transfer case working temperature on drag torque,and the influence rules of speed difference between active and passive end of transfer case,motor control pressure on sliding friction torque are compared and analyzed.The static torque test bench of transfer case friction pair is built,and the torque transfer model under locking condition is tested and verified.(4)Considering the working conditions of real-time AWD vehicle,the torque distribution characteristics of transfer case under small radius turning,straight driving and rear axle wheel slip are analyzed,the torque distribution strategy under corresponding working conditions is proposed.MATLAB is used to solve the target pressure under different torque distribution strategies,and the influence of different pressure establishment schemes on the working characteristics of the transfer case is explored.The simulation results show that different pressure building schemes have great influence on the operating characteristics of the transfer case.When pressure building rate of the control motor decreases,the torque build-up time increases;the amplitude of torque fluctuation decreases.When there is a speed difference between the active and passive ends,the sliding friction work increases with the decrease of the pressure building rate.Which can provide theoretical support for the design of transfer case.