Patent attributes
To provide a plunger type master cylinder capable of reducing invalid stroke and preventing residual pressure without impairing durability of a seal ling (70). A piston (91) of the master cylinder has a recess (93) at its outer peripheral surface and a relief port (900) in its recess (93). The seal ring (70) has a seal coupling part (70s) on the inner periphery of the distal end part of an inner peripheral lip (701). The seal coupling part (70s) is located at the opening of the relief portion (900) on the piston (91) side when the brake is in a non-operating position. The distance between said seal coupling part (70s) and said relief port (900) is short. The seal ring (70) additionally has first and second projection parts (7006, 7002) on the inner peripheral surface of the inner peripheral lip (701). By this, a flow passage for working fluid can be obtained on the inner periphery side of the inner peripheral lip (701).
