Brake booster with seal housing and key member

摘要

A brake booster is disclosed which reduces an idle stroke of an input shaft, by bringing a key member which is mechanically coupled to a valve plunger into abutment against an inner wall surface of a shell when the brake booster is inoperative. The shell includes a cylindrical projection which extends rearwardly from the center thereof, and the cylindrical projection is formed with a flange which extends radially inward, with its inner periphery cut away to define an opening. A valve body includes a cylindrical portion which extends through the opening to the outside thereof. By disposing the key member for abutment against the inner wall surface of the flange, a reduction in the length of the key member is enabled. A seal member seals the cylindrical portion of the valve body, and is located rearwardly of the flange and is received within a housing which is disposed outside the shell.