BRAKING ASSISTANCE PNEUMATIC SERVOMOTOR WITH IMPROVED VALVE

摘要

The invention relates to a braking assistance pneumatic servomotor comprising a casing (10) having a symmetry axis (X-X') sealingly divided by at least one mobile wall structure (12) into a front chamber (14) permanently connected to a low pressure source and a back chamber (16) selectively connected to the front chamber (14) or to a high pressure source by means of a three-way valve (36) actuated by a control rod (30) susceptible of bearing, through the front face of a plunger (28), on to the back face of a pushrod (48) integral with a reaction disk (50), the plunger (28) sliding into a bore (26) of the mobile wall (12), the three-way valve (36) comprising a valve element (36) arranged in a back tubular part (22) of the mobile wall (12) and cooperating by means of a front annular face (40), with a first valve seat (28a) formed on the plunger (28) and with a second valve seat (20a, 20b) formed on the mobile wall (12), a space (35) being provided between the two valve seats and communicating with at least a radial passage (44) formed in the mobile wall (12) and opening out into the back chamber (16), at least one axial passage (37) being provided in the mobile wall (12) and opening out into the front chamber (14), the annular front face (40) of the valve element being biased in the direction of the valve seats by means of a valve spring (42). According to the invention, the second valve seat (20a, 20b) formed on the mobile wall (12) is obtained by joining at least two concentric, coplanar arcs of a circle (20a, 20b) having different radii.