| 摘要 |
PROBLEM TO BE SOLVED: To stably set a changing point of a booster ratio by having an annular groove which is formed on an abutting surface of a reaction disc of a power piston and divides the abutting surface into an outside diameter side abutting surface and an inside diameter side abutting surface. SOLUTION: A reaction disc 22 presents an elastically deformable disc-shape and is arranged between a power piston 131 of a movable wall 13, a plunger 21 and an output rod 4. At the other end of the output rod 4, a cup part 41 is formed. The reaction disc 22 is arranged by constraining an outer peripheral surface 22a within the cup part 41. On an abutting surface 131a of the power piston 131 of the movable wall 13, an annular groove 131b is formed. The annular groove 131b is located at the inner periphery by prescribed quantity from the outer periphery and divides the abutting surface 131a into an outside diameter side abutting surface 131c and an inside diameter side abutting surface 131d. Thus, a changing point of a booster ratio can be stably set and deterioration of operation feeling can be prevented. |
