Abstract: There is provided a master cylinder in which a large quantity of working fluid can be supplied rapidly, the air bleeding takes less time in the manufacturing process, and satisfactory performance can be provided when traction control is operated. For the master cylinder MC, a first supply passage 19 for supplying a working fluid from a working fluid reservoir to a pressure chamber 9 through a working fluid supply port 20a, supply passages 22, 23 and 24, and a working fluid supply port 5b formed in a piston 5, a second supply passage 50 is formed in parallel with the first supply passage directly between the working fluid supply port 20a and the pressure chamber 9, and a check valve 51 is disposed in the second supply passage 50.

Abstract: An improvement of an output shaft of a booster is disclosed. An output shaft 23 is formed by a push rod 24 and an adjusting screw 25. The push rod 24 is formed with an axial bore 26 in its distal end, the axial bore including a portion 26b of a reduced diameter which is less than an outer diameter of a threaded section 25C of the adjusting screw. The threaded portion is formed as a self-tapping screw. The adjusting screw includes a guide 25D at a location which is initially inserted into the axial bore before the threaded portion is inserted into the threaded portion. The guide comprises a plurality of annular projections 27 having an outer diameter which is substantially equal to the inner diameter of the axial bore. With this construction, when the guide 25D is fitted into the portion 26b of the axial bore 26 which has a reduced diameter, the axis of the adjusting screw 25 may be brought into alignment with the axis of the push rode 24.

Abstract: A brake booster is disclosed. More specifically, an improvement relating to a reinforcing plate which is used to reinforce a shell to which a master cylinder is connected is disclosed. The reinforcing plate comprises a pair of members, i.e. a first reinforcing plate which is disposed along the inner surface of the shell which provides a mounting surface for a master cylinder, and a second reinforcing plate which is disposed along the inner surface of the shell at a location radially outward of the mounting surface for the master cylinder. The rigidity of the shell can be increased without increasing a sheet thickness thereof.

Abstract: A seal unit is provided for a brake booster such as of a tandem type which includes a center plate within its shell. The brake booster includes annular means disposed within the shell for maintaining a hermetic seal between the center plate and a valve body. An axial portion of the center plate is formed with an axially extending cylindrical portion, the end of which is folded radially inward to define a U-shaped fold. The annular seal means is fitted inside the cylindrical portion, with its part disposed between the inner peripheral surface of the cylindrical portion and the outer peripheral surface of the fold. This effectively prevents the annular seal means from being withdrawn from the center plate.

Abstract: A brake booster includes at least two pairs of constant pressure chambers and variable pressure chambers defined within a shell. A clearance is defined between a stepped end face of a valve body which is disposed within the shell and a power piston which is mounted on the valve body at a location rearward of the stepped end face. The clearance is utilized to provide a communication between the constant pressure chambers, thereby allowing a reduction in the axial size of the valve body.