A comparative study on the effect of disks geometrical features on the drag torque of a wet friction clutch

Abstract

In recent years, the need for highly efficient automatic and semiautomatic powertrains has led to the wide use of wet friction clutches as power transmission systems. While wet friction clutches surpass their counterparts dry-friction clutches in the engagement process as they provide higher efficient torque and smoother torque and speed transmission, yet they fall behind in their disengaged state where the clutch acts as a power loss to the system due to the drag torque developed on the disks from fluid’s viscous shear stresses. Shear stresses are developed due to the relative speed difference of coaxial disks distanced at a prescribed axial clearance and rotating independently, yielding to a torsional Couette shear flow. This matter has been investigated thoroughly in the literature with experimental and numerical approaches for the case of flat disks admitting the complex flow pattern, which is augmented even more from the presence of geometrical features (grooves) on the surface of the disks. It becomes clear that the efficient calculation and understanding of drag torque can lead to its minimization and therefore to further establishing the use of wet clutches. In this work the effect of various disks geometrical features on the drag torque of a wet clutch is examined. The results are obtained via FEA (Finite Element Analysis) using the commercial software ANSYS.