Theoretical and experimental study on drag torque of wet clutch considering surface tension and shrinkage of oil film

The drag torque produced by the viscous shearing action of lubricating oil is an important component of the power loss of wet clutches. Studying the prediction model and its influencing factors will provide important theoretical support for reducing the drag torque. Taking a single friction pair wet clutch as the research object, this research obtained the oil film shrinkage under different working conditions based on the VOF model. On this basis, a drag torque calculation model considering the surface tension and shrinkage of oil film is established, in which the drag torque is composed of the torque transmitted by oil film in the oil film continuous zone and the torque transmitted by oil-liquid and gas-liquid in the oil film rupture area, respectively. Comparing the theoretical drag torque with the simulation and experimental results, the variation law of drag torque with the speed difference under different oil film thicknesses and different supply flow is obtained, and the validity of the theoretical model is also verified. Results show that increasing the oil film thickness and decreasing the supply flow will lead to a decrease in drag torque, which provides a useful reference for reducing the drag torque.