Brake slip control apparatus fed with auxiliary energy for use in a vehicular hydraulic brake system

A brake slip control apparatus fed with auxiliary energy for use in a vehicular hydraulic brake system, comprising a master cylinder assembly (12) actuatable by the brake pedal and incorporating a master cylinder piston (23) and an assigned prechamber (36), with a supply bore (34) and with the delivery of auxiliary energy into a working chamber (16) of the master cylinder, wherein at least one positioning tube (39) which is axially slidable between stops and sealed relative to a bore (45) in the master cylinder housing (12) is arranged on a secondary side of the master cylinder piston (23), said positioning tube having a larger external diameter than the master cylinder piston (23) and being guided centrically through the master cylinder piston (23) in a sealed relationship thereto, the master cylinder piston (23) being caused to assume a defined position on actuation of the brake pedal (22) and in the event of the secondary side of the master cylinder piston (23) being applied by auxiliary energy during slip control, wherein an elastic undular washer (59) is arranged between the pedal-side end of the positioning tube (39) and a step (51) of a braking pressure generator (1) isolating the master cylinder assembly (12) from a hydraulic brake power booster (11), wherein said positioning tube (39) is pressed against said undular washer (50) upon initiation of a slip control action to cause said undular washer (50) to cut off fluid communication between an intermediate chamber (54) provided between the master cylinder piston (23) and a booster piston (57) enclosed by the step (51).