Hydraulically actuated piston with an air bleed

摘要

A torque transmitting mechanism has a hydraulically actuated piston that is slidably disposed in a cavity. An apply chamber, formed by the piston and cavity, is filled with hydraulic fluid when the torque transmitting mechanism is to be engaged. One or more gas permeable-liquid impermeable mats are secured in a passage between the chamber and a non-liquid area in a transmission. During initial engagement of the torque transmitting mechanism, any entrapped air is forced out of the chamber through the mat while the leakage of liquid is inhibited. In a rotating torque transmitting mechanism (clutch), the mats are installed near the innermost periphery of the chamber. In a stationary torque transmitting mechanism (brake) the mats are installed near the top outermost periphery of the chamber.