Pneumatic braking assistance servomotor for motor vehicle, has piston mounted inside rigid envelope, and valve unit occupying closing position isolating rear and front chambers and open position connecting front chamber with atmosphere

摘要

The servomotor (1) has a front chamber (8) subjected to a pressure varying between a constant pressure in a rear chamber (7) and atmospheric pressure by an assisting valve unit actuated by a plunger (13). The plunger is integrated to a front end of a control rod (16) and moved in a tubular piston (10) slidably mounted inside a rigid envelope (3), based on an axial input effort exerted towards front of a brake pedal. The valve unit selectively occupies a closing position isolating the chamber (7) from the chamber (8) and an open position connecting the front chamber with atmosphere. The assisting valve unit is constituted of annular valve seats (25, 25) and an annular valve (24) mounted in the tubular piston. The valve unit occupies the closing position isolating the rear chamber from the front chamber in which the pressure in the front chamber is equal to the constant pressure, that is higher than the atmospheric pressure, in the rear chamber.