AUTOMATIC TRANSMISSION

PROBLEM TO BE SOLVED: To allow reduction of an engagement shock without requiring complicated hydraulic control and shorten an engagement control time.SOLUTION: A second brake 22 of an automatic transmission 1 comprises a piston 24 which moves along a cylinder 23 and exerts pressing force to a friction plate unit 5, an engagement hydraulic pressure chamber 26, and a disengagement hydraulic pressure chamber 27. The piston 24 has a first face 24A on the disengagement hydraulic pressure chamber 27 side, and a second face 24B on the engagement hydraulic pressure chamber 26 side. The pressure-receiving area of hydraulic pressure of the second face 24B is set larger than the pressure-receiving area of hydraulic pressure of the first face 24A. The engagement hydraulic pressure chamber 26 and the disengagement hydraulic pressure chamber 27 are supplied with the same hydraulic pressure at the same time through a first oil passage 74 and a second oil passage 75, respectively. With this, the piston 24 receives pressing force of a pressure-receiving area difference between the first face 24A and the second face 24B and moves in a direction of engaging the friction plate unit 5.SELECTED DRAWING: Figure 3 【課題】複雑な油圧制御を要さずに締結ショックの低減が可能であり、締結制御時間を短縮する。【解決手段】自動変速機１の第２ブレーキ２２は、シリンダ２３に沿って移動し、摩擦板ユニット５に押圧力を与えるピストン２４と、締結油圧室２６と、解放油圧室２７とを備える。ピストン２４は、解放油圧室２７側の第１面２４Ａと、締結油圧室２６側の第２面２４Ｂとを有する。第２面２４Ｂの油圧の受圧面積が、第１面２４Ａの油圧の受圧面積よりも大きく設定されている。締結油圧室２６、解放油圧室２７には、各々第１油路７４、第２油路７５を通して、同時に同じ油圧が供給される。これにより、ピストン２４は、第１面２４Ａと第２面２４Ｂとの受圧面積差分の押圧力を受けて、摩擦板ユニット５を締結させる方向に移動する。【選択図】図３