Coupled Effect of Lubricant Fill Volume on Drag and Friction Torque of Dip-Lubricated Wet Clutches

Multi-disc wet clutches are widely used in automotive and industrial power transmission systems and their performance is strongly influenced by operating conditions and the lubricating oil. In particular, the volume of lubricant in dip lubricated clutches, or equivalently, the oil level with respect to the rotation axis, affects both the drag torque in the open state and the torque response during engagement, yet these coupled effects are not fully quantified. This study investigates how lubricant fill volume influences (i) disengaged clutch drag torque and (ii) friction torque during engagement. A series of experiments were carried out on a scaled SAE No. 2 test rig using SAE 10W-40 and 20W-50 lubricants, and drag and engagement torque were recorded along with high-speed flow visualization. The results show that increasing lubricant volume leads to higher drag torque in the open state. During engagement, higher volumes reduce torque overshoot at the end of the slip phase but also slightly extend the engagement time. These trends can be used by researchers and industry to optimize lubricant quantity for wet clutch systems operating in dip-lubricated conditions.