DCTF Flow Distribution Design in Clutch Packs of wet DCTs

Abstract

Wet clutch pads require temperature control on contact surface because increased frictional heat abruptly decreases friction coefficient, and eventually, the desired torque transfer becomes difficult to control. Generation of frictional heat is inevitable during clutch engagement, but the frictional heat should be cooled by the convective flow of DCTF for the stable torque transfer capacity in the wet clutch pack. Two-phase DCTF flow behavior was investigated inside the entire cavity space of a wet clutch pack, and detailed flow patterns were computed using CFD analysis. Particularly, outer clutch pack of the DCT, which has severe thermal duty, was studied with respect to DCTF flow rate distribution through the gaps of the clutch pads. Hydrodynamic pressures, velocity fields of DCTF flow, and volume fractions of the DCTF fluid in the wet clutch pack were computed, and evenly distributed flows through the gaps of outer clutch pads to combat unbalanced thermal durability among the clutch pads were achieved by optimizing the design of hub shell outlets. Using computational results, DCTF velocity fields and the volume of fluid (VOF) were compared and they will lead to the well-distributed flow design against the abnormal local frictional temperature rises without unnecessary additional oil pump power.