| 摘要 |
<P>PROBLEM TO BE SOLVED: To improve durability of a piston member having a pressing portion which moves in an axial direction through oil pressure and presses a frictional engagement element. <P>SOLUTION: A cylindrical member 50 is used as a pressing portion, and a piston presses a multiplate brake along the axial direction through the cylindrical member 50. An interference preventing hole 58 formed on the side of the cylindrical member 50, wherein a portion of a parking cum enters from the outer circumferential side of the cylindrical member 50 to the inner circumferential side, has a stepped shape so that a first opening portion 58a and a second opening portion 58b which is more separated from a step portion 52 that is a pressure receiving portion from the piston than the first opening portion 58a are continued along the axial direction and they make one hole, and the second opening portion 58b is formed so that the width in the circumferential direction is wider than the first opening portion 58a and the opening edge in the circumferential direction side is arch-shaped. <P>COPYRIGHT: (C)2013,JPO&INPIT |
