Effect of a piston hole under the slip control condition of the lock-up clutch in a torque converter

Abstract

A torque converter is a fluid coupling that transfers power from an engine to a transmission. To reduce the energy loss of the fluid coupling in conditions of low speed, the torque converter can be adapted to include a lock-up clutch, which directly connects the engine to the transmission at low speeds. To expand the speed range of these lock-up clutches, slip controls for lock-up clutches have been widely researched. However, slip controls can increase the temperature of friction materials on the piston plate of the lock-up clutch system, potentially reducing their durability. For this reason, the piston hole on the piston plate was developed to promote cooling during slip control. In this study, the effects of various slip conditions and the presence or absence of a piston hole on the temperature of the contact frictional surface were investigated experimentally. We confirmed that the inclusion of a piston hole on the piston plate could promote piston cooling by means of forced convection of cold automatic transmission fluid, and also maintained uniform pressure of the friction material under a greater range of automatic transmission fluid pressures.