Spin Loss Computation for Open Clutch Using CFD 2011-01-1238

Open clutch spin loss computation is of interest for new clutch designs. It is desirable to minimize open clutch spin loss. Spin loss in automatic transmission clutches is mainly due to the viscous shear of the transmission fluid. Depending on the relative rotational speed of the plates the spin loss varies. At low rotational speeds the gap between the plates is filled with ATF (Automatic Transmission Fluid) and spin loss increases linearly with the rotational speed. At higher speeds the ATF layer, which is held together primarily by surface tension, begins to breakdown due to higher centrifugal forces and air pockets form at outward radial locations of the clutch plates. This results in a decrease in spin loss for the open clutch. CFD (computational fluid dynamics) modeling is an attractive option in calculating the spin loss for an open clutch. Not only can a CFD model give an accurate estimation of the magnitude and trend of spin loss variation but it can also compare various groove designs. This is a significant advantage compared to some existing analytical methods for spin loss estimation of open clutches, as they are limited to either groove-less designs or designs with radial grooves. This work describes a 3D CFD modeling procedure that yields spin loss computations of sufficiently high accuracy by improvements made to some stated procedures in literature. Effect of variation of design parameters such as number of grooves, flow rates, etc, is studied.