Numerical Analysis And Experimental Research On Friction Characteristics And Dynamic Strength Of High-speed And High-power Wet Clutches

In recent years,military heavy tracked vehicles have been developing towards high speed and high power density.The performance requirements of key transmission components under high speed and high power conditions have been continuously improved,and the linear speed of disengaged wet clutches has reached 60-110 m/s.The combination and completeness of the traditional design method needs to be improved with the high power density and engineering design and application of the power cabin.As the key component of the power transmission system[1],the wet clutch is widely used in heavy-duty military vehicles.The friction characteristics and dynamic strength are directly related to the stability and reliability of the power transmission system.For the high-speed and high-power wet clutch,which is one of the key components of the transmission system of heavy special vehicle,the basic research on the mechanism and its working characteristics of its friction characteristics and dynamic strength is of great national defense significance.In this paper,a large-size wet clutch composed by friction elements used in high-power density power cabin of high-speed military tracked vehicle under complex road conditions is studied.Combined with the early tooth defects and whole fracture damage of wet clutch componernts in the gearbox of tracked vehicle during field test,a numerical and experimental research on friction characteristics and dynamic strength of wet clutches for high-speed and high-power tracked vehicles is presented in this paper,which provides a reference for improving its design method system and its design database.The friction characteristic mainly revolves the drag torque behavior of disengaged wet clutch and the dynamic engangement characteristic of the engaged wet clutch under high-speed condition with grooves.With the introduction of high-speed motor in a new type of hybrid tracked vehicle,the cooling flow rate based on the traditional drag torque loss design is invalidated.The characteristics of drag torque loss and dynamic engagement torque of wet clutch with grooves are studied in this paper.The research on dynamic strength characteristics is mainly aimed at dynamic strength design w:ith the adjustable wide frequency band and large amplitude(0-200Hz,0-1.5°)to simulate the field test.Dynamic stress simulation and experimental research are carried out by using target tracking to obtain moving information of dynamic load.The research on friction characteristic and dynamic strength characteristic of wet clutches provides reference for impro ving its design system and design database.The detailed research contents are as follows.(1)In this paper,the trend of drag torque of wet clutch rising again under high-speed and high-power operating conditions is studied.The first and second critical speeds,which represent the turning points of drag torque,are proposed to divide the drag torque trend into three main stages combined with the oil film state.Based on VOF two-phase flow model,the gas-liquid two-phase distribution of wet clutches with or without grooves at different rotational speeds is simulated.The temperature distribution of wet clutch is simulated and analyzed based on the thermal-fluid-solid coupling simulation method under different relative rotational speeds and flow boundary conditions.The effects of relative speed,temperature of cooling lubricant(ATF),flow rate of automatic transmission fluid(ATF),friction material and grooves on the characteristics of drag loss were investigated by numerical simulatioin and experiments.It provides a reference for the research on the mechanism change of drag loss behavior of wet clutches for high-speed and high-power tracked vehicles and the establishment of the test database for high-speed(linear speed is about 90m/s)design.(2)For the dynamic engagement characteristics of high-speed and high-power wet clutches,a comprehensive dynamic engagement prediction model based on KE rough contact model,parametric groove model and heat-flow coupling model is proposed in this paper.The oil film thickness,temperature change and dynamic torque change during engagement process are simulated and studied for the dynamic torque characteristics and for high-speed and grooved wet clutch engagement characteristics.Based on simulation and experiments,the effects of appllied pressure,ATF temperature,relative rotation speed,permeability and surface grooves on dynamic engagement troque are investigated.(3)In view of the problems of torsional vibration,load impact and changing clearance coaused by power transmission and driving conditions of heavy tracked vehicles under complex road conditions,dynamic load fatigue stresses will occur in friction components of wet clutches.which will lead to fracture and plastic deformation in field tests.Based on the actual application status of military tracked vehicles,the investi"gation of dynamic strength is proposed.Dynamic strength concdition design with the adjustable wide frequency band and large-amplitude is carried out by combining the control model and the system dynamic model.A dynamic strength test method is proposed to capture dynamic motion information by video target tracking test method.Based on this method.,dynamic stress simulation and experiments are carried out.(4)For the friction and dynamic strength characteristics of high-speed and high-power wet clutches,an automatic measurement and control platform based on flexible modular design for large-size friction components in high-power density power cabin of high-speed and high-power tracked vehicle is developed in this paper.Its control system and software are flexable and can be changed according to engineering design methods for friction characteristics and dynamic strength.It is of great significance for the establishment of parametric test database of wet clutches for high-speed and high-power tracked vehicles.Its key technical parameters are as follows:working speed range of 0-10000 r/min,maximum diameter of 550 mm test plates by expanding,adjustable dynamic strength working conditions with wide frequency band and large amplitude:0-200 Hz,0-1.5 degrees.