HYDRAULIC BOOSTER FOR BRAKE

PROBLEM TO BE SOLVED: To improve a feeling of brake operation while avoiding to cause a feeling of stepped stroke in the brake operation, in a hydraulic booster for a brake equipped with an inlet valve between a booster hydraulic chamber and a hydraulic source, which opens in response to the advancing operation of a control piston, with a return spring means provided between this piston and a master piston. SOLUTION: The return spring means 58 comprises: a spring support member 84 disposed, movably in an axial direction, between the master piston 31 and the control piston 48; a first return spring 86 disposed compressedly between the spring support member 84 and the control piston 48; and a second return spring 87 disposed compressedly between the spring support member 84 and the master piston 31. Until immediately before the inlet valve 60 is opened, the master piston 31 is advanced as the first return spring 86 is compressed, and after the spring support member 84 is advanced to the foremost position relative to the control piston 48, the master piston 31 is advanced as the second return spring 86 is compressed. COPYRIGHT: (C)2003,JPO