| 摘要 |
The invention relates to a master cylinder (10) for a hydraulic vehicle brake system comprising a housing (34) and a boring (36) which is arranged therein. A hollow cylindrical primary piston (38) which acts upon a pressure chamber (40) is guided in said boring in a sealing and axially displaceable manner. An axially displaceable, hollow cylindrical auxiliary piston (42) is accommodated in the primary piston (38). An actuating piston (46) which projects into said auxiliary piston can be actuated by an input element (24), is guided in the auxiliary piston (42) in a sealing and displaceable manner, and, at least during braking, is pretensioned away from the auxiliary piston by a spring. The actuating piston (46) comprises a first hydraulically active diameter (D1), and the auxiliary piston (42) comprises a second hydraulically active diameter (D2). The auxiliary piston (42) couples with the actuating piston (46) in a rigid manner after a determined distance against the spring-loaded pretension thereof is surpassed. In order to realize a brake assistance function, a shift piston (58) arranged in the primary piston (38). Said shift piston is pretensioned by a spring in the direction toward the pressure chamber (40) and can be axially displaced with regard to the auxiliary piston (42). The spring-loaded pretension of the shift piston (58) corresponds to a predetermined pressure level in the pressure chamber (40). After said pressure level is exceeded, the shift piston (58) moves with regard to the auxiliary piston (42) against the spring-loaded pretension, whereby a valve (68) closes the fluid connection between the second hydraulically active diameter (D2) of the auxiliary piston (42) and the pressure chamber (40).
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