FRICTIONAL ENGAGEMENT DEVICE FOR AUTOMATIC TRANSMISSION

摘要

A factional engagement device for an automatic transmission includes a tubular case (1 1), a friction member (12) on one side that is supported on the case (11), a friction member (14) on the other side that is supported on a rotary element (13), an annular piston (15) having a pressing portion (15b) that presses the friction members (12, 14) toward one axial side with a thrust force from a pressure receiving portion (15a) that defines an annular hydraulic chamber (18) between it and the case (11), and plural return springs (17) for urging the piston (15) toward the other axial side. The piston (15) has a first pressure receiving section (Al) where the pressing portion (15b) is cut out over a predetermined angular range, and a second pressure receiving section (A2) other than the first pressure receiving section (Al). An urging force of the return springs (17F) per unit angular range of the first pressure receiving section (Al) is greater than an urging force of the return springs (17S) per unit angular range of the second pressure receiving section (A2).