Master cylinder for vehicle brake system, has the reduced diameter portion of the primary piston slidably fitted into the axial bore in the secondary piston, and a retraction limit member on either the first sleeve or the secondary piston

摘要

The reduced diameter portion of the primary piston (3) is slidably fitted into the axial bore in the secondary piston. A retraction limit member which defines a retraction end of the primary piston is mounted on either the first sleeve or the secondary piston. The retraction limit member restricts the retraction end of the secondary piston is mounted on the housing. The first sleeve and secondary piston are formed integrally. The cross section area with which the secondary piston faces the second liquid pressure chamber is equal to the cross section area with which the secondary piston faces the first liquid pressure chamber. As the primary piston (3) is driven forward, a cup seal (32) moves forwardly of a communication path (17c) in a first sleeve (17) to interrupt a communication between a first reservoir chamber (11) and the first liquid pressure chamber (5), thus generating a liquid pressure in the first liquid pressure chamber (5). As the secondary piston (10) is driven forward, a cup seal (25) moves forwardly of a communication path (18c,) interrupting a communication between a second reservoir chamber (19) and a second liquid pressure chamber (6), thus generating a liquid pressure in the second liquid pressure chamber (6).