Patent ID: 9663085
Date: 2017-05-30
CPC Classifications: B60T,F16J

Claim:
1. A master cylinder comprising: a cylinder main body with a bottomed cylindrical shape having a discharge passage of a brake liquid and a supply passage in communication with a reservoir; a piston movably disposed in the cylinder main body and forming a pressure chamber configured to supply a hydraulic pressure into the discharge passage between the cylinder main body and the piston; and a seal member installed in a circumferential groove formed in the cylinder main body and capable of sealing between the supply passage and the pressure chamber, wherein the seal member comprises: a base section capable of abutting a circumferential wall of the circumferential groove near an opening section of the cylinder main body; an inner circumferential lip section extending from the base section toward a bottom section of the cylinder main body and configured to come in sliding contact with an outer circumference of the piston; an outer circumferential lip section extending from the base section toward the bottom section of the cylinder main body and configured to abut a bottom section of the circumferential groove; and a center lip section extending from the base section toward the bottom section of the cylinder main body between the outer circumferential lip section and the inner circumferential lip section and having a distal end configured to abut the circumferential wall of the circumferential groove near the bottom section of the cylinder main body, wherein the circumferential wall of the circumferential groove near the bottom section of the cylinder main body has an outer wall section extending from the bottom section of the circumferential groove in a radial direction of the cylinder main body, a stepped surface section extending from the outer wall section in a bottom direction of the cylinder main body, and an inner wall section having a flat surface section parallel to the radial direction of the cylinder main body and formed further inside in the radial direction of the cylinder main body than the stepped surface section, and wherein the inner wall section is formed at a position at which a distal end section of the center lip section overlaps the stepped surface section or the inner wall section in the radial direction of the cylinder main body when the seal member moves toward the bottom section of the cylinder main body.