Numerical and Physical Experiments on Drag Torque in a Wet Clutch

Abstract

The effect of flow field on drag torque in a wet clutch was examined through numerical and physical experiments. Three-dimensional hydrodynamic numerical simulations were carried out, and the drag torque was measured experimentally for a single wet clutch pack. Two-phase flow induced by aeration was visualized in the experiment. The wet clutch consists of two parallel circular plates. The plate with one side covered with the frictional material was rotated. The radial or circumferential grooves were made on the rotating disk by dividing the frictional material. The lubrication oil was supplied from the axial center, and ejected into the surrounding open boundary. At low rotation speeds, the oil flow was of single-phase, and the drag torque was linearly proportional to the rotation speed since the wall shear stress increased monotonically. In the single-flow regime, the slope of drag torque curve was controlled with the clearance between the clutch plates. The drag torque reached a peak value at a certain rotation speed, and it decreased gradually after the peak because of aeration. The peak of drag torque was controlled by both the flow rate of supplied oil and the arrangement of grooves on the frictional material. It also was found that the smooth ejection of oil and the enhancement of aeration led to the drag torque reduction.