Research On Basic Features Of Wet Clutch Affecting Service Performance Of DCT

Dual Clutch Transmission(DCT)has the advantages of fast power response,high transmission efficiency,good production inheritance,and strong adaptability with electric vehicle power system,etc.Its market share has been increasing year by year.However,there are still many problems with DCT products in dynamic service,especially the starting and shifting performance of DCT vehicles will deteriorate with the increase of service time.As one of the key components of DCT,the basic characteristics of wet clutch have an important impact on the starting and shifting performance of DCT vehicles.The high temperature rise of wet clutch will not only cause the power interruption of the whole vehicle and the ablation of the clutch,but also affect the change of friction coefficient of wet clutch.The unclear understanding of the variation law of friction coefficient will make the clutch transmission torque control of DCT vehicles unstable in the process of starting and shifting,which is easy to lead to starting impact and shifting setback.In addition,as the service time of the DCT vehicle increases,the friction characteristics of the wet clutch will change,which aggravates the control instability of the clutch transmission torque during the starting and shifting process of the DCT vehicle.In addition,the change of the drag torque of the wet clutch will also cause the change of the driving torque of the whole vehicle,thereby affecting the starting and shifting performance of the DCT vehicle.In response to these problems,there have been numerous studies on the temperature rise characteristics,friction characteristics and drag characteristics of wet clutches.However,the following important scientific issues still need to be addressed in the current research: to propose a coupled temperature field calculation model that integrates the non-uniform distribution of the contact stress field of the friction pair,the time-varying characteristics of the cooling flow field in the groove of the friction plate,and the variation of the friction coefficient;to reveal the variation law and mechanism of the wet clutch friction characteristics and drag characteristics with service time.Therefore,this paper relies on the National Natural Science Foundation of China-the key project of the China Automobile Industry Innovation and Development Joint Fund:intelligent control and evaluation method of DCT considering dynamic service performance,driving behavior and driving environment,the wet clutch temperature rise characteristics,friction characteristics and their change law with service time,drag characteristics and their change law with service time are studied by combining theory with experiment.The main research contents of this paper are as follows.(1)In order to reveal the distribution characteristics and change law of the wet clutch temperature field during the engagement process,a finite element model of the friction pair contact stress was established considering the non-uniform distribution of the friction pair contact stress.Based on the time-varying characteristics of the cooling flow field in the groove of the friction plate,a numerical calculation model of the cooling flow field was established.On the basis of this,a temperature field coupling calculation model of the wet clutch during the engagement process is proposed and experimentally verified,taking into account the non-uniform characteristics of the friction pair contact stress field,the time-varying characteristics of the cooling flow field in the friction disc groove,and the interaction between the friction coefficient and the friction surface temperature.The effects of the friction pair contact stress field,the cooling flow field,and different clutch engagement conditions on the temperature field of the wet clutch are theoretically and experimentally investigated.(2)In order to obtain the variation law and numerical calculation model of the friction coefficient of the wet clutch,the effects of the engagement pressure of the friction pair,the lubricating oil temperature between the friction surfaces,the lubricating oil flow between the friction surfaces,friction surface temperature,clutch driving end speed and driven end speed on the friction coefficient were experimentally studied.Based on the study of the influence law of different factors on the friction coefficient of wet clutch,considering the influence of the engagement pressure of friction pair and the relative speed difference of clutch on the friction surface temperature,the numerical calculation model of the friction coefficient of wet clutch with the friction pair engagement pressure,lubricant temperature,friction surface temperature and the relative speed difference of the clutch as independent variables is proposed,and the correctness of the model is verified by experiments.(3)In order to explore the variation law of friction characteristics of wet clutch with service time,experiments were conducted to study the influence of service mileage of wet clutch and service time of lubricant on friction characteristics,as well as the influence of contact pressure of frictional pair,lubricant temperature,relative speed difference of clutch,and friction surface temperature on the variation law of wet clutch friction characteristics with service time.Based on the study of the variation law of wet clutch friction characteristics with service time and the three-dimensional profile analysis of friction plates with different service mileage,the influence law of wet clutch service mileage on friction characteristics was revealed.on this basis,a theoretical analysis model of the friction characteristics considering the influence of the service mileage of the wet clutch was proposed.(4)In order to obtain the wet clutch drag torque and its variation law with service time,the influence law of lubricant temperature between friction surfaces,lubricant flow between friction surfaces,clutch driving end speed,clutch service mileage,and lubricant service time on drag torque was investigated.Based on the analysis of the three-dimensional profile of the friction plate with different service mileage,the variation law of the drag torque with increasing service mileage of the wet clutch is revealed.On this basis,a theoretical analysis model of the variation of wet clutch drag torque with service mileage is proposed,considering the influence of clutch driving end speed and clutch service mileage on the lubricant coverage area between the friction surfaces.The results of the above research work can provide a basis for the precise control of the transmission torque of DCT wet clutch,so as to lay a foundation for DCT vehicles to maintain good starting and shifting performance for a long time.