Drag Torque Modeling And Analysis Of Wet Clutch

As a basic part of an automobile,AT(Automatic Transmission)is used more and more widely.But still,it is criticized for its efficiency.As one of the basic components of AT,wet clutch plays a key role in improving its efficiency.The relative rotation of the friction and separator disks in wet clutch during the disengaged mode causes viscous shearing of fluid film in the gap between the disks.This results in a drag torque on both the disks that wastes energy and decreases fuel economy.Given the facts above,reduction of drag torque loss in disengaged wet clutches is the focus of today’s automatic transmission design.The objective of the study is to develop an accurate mathematical model for predicting drag torque,and the affected factors were analyzed according to the model,so it can be used to reduce the drag torque.In this study,the mathematical model was established based on Navier-Stokes and continuity equations,considering the non-grooved friction.To solve the equations,we introduce some dimensionless variables,and bring in the concept of equivalent outer radius in order to consider the rupture of the film due to cavitation at high speed region.By taking into the surface tension at the interface between fluid and air,we can get the relationship between equivalent outer radius and the rotation speed,and finally get the mathematical model.According to the mathematical model,we analyzed the parameters such as rotation speed,ATF flow rate,viscosity of ATF,gap between the disks that influence the drag torque.As the results showed,the drag torque increases first and then decrease with the increase of rotation speed.About other parameters,the drag torque grows with the increase of ATF flow rate and viscosity of ATF;besides,when the gap between the disks increase,the drag torque decreases properly.After deduced the drag torque theoretically,we verified the conclusion with a CFD model.In order to gain the effect of the groove,we explored that some parameters such as groove depth,groove width,also has an effect on drag torque.In the end,we validated the model with certain experiments on SAE#2 wet clutch test rig.Through mutual verification between mathematical model,CFD model and experiment,we not only got the mathematical model validated,but also decreased the cost of experiments.From this paper,we provided a new method to build the mathematical model of drag torque.By introducing some dimensionless variables,we can simplify the complex equations and then solve it.Meanwhile,the factor analysis of drag torque is useful to improve the efficiency of wet clutch in theory and practice.