PNEUMATIC BRAKE SERVO WITH A FLEXIBLE VALVE

摘要

A pneumatic brake servo comprising a shell (10) with an axis of symmetry (X-X'), sealingly divided by a movable wall structure (12) into a front chamber (14) permanently connected to a low-pressure source, and a rear chamber (16) selectively connected to the front chamber (14) or to a high-pressure source via a three-way valve means (36) operated by a control rod (30) that can engage, via the front surface of a plunger (28), the rear surface of a push rod (48) secured to a reaction disc (49), said plunger (28) being slidable in a bore (26) in the movable wall (12). The three-way valve (36) comprises a valve member (36) arranged in a tubular rear portion (22) of the movable wall (12), wherein a first ring-shaped area (40i) of a ring-shaped front surface (40) thereof engages a first ring-shaped valve seat (28a) on the plunger (28), while a second ring-shaped area (40e) of the ring-shaped front surface (40) engages a second ring-shaped valve seat (20a) on the movable wall (12), said first valve seat (28a) being concentric to and having a smaller diameter than the second valve seat (20a), and the ring-shaped front surface (40) of the valve member being biased towards the ring-shaped valve seats (20a, 28a) by a valve spring (42), and reinforced by a rigid ring-shaped insert (46, 46'; 56, 56'). Said rigid ring-shaped insert (46, 56) is located axially behind one (40e) of said areas (40e; 40i) with which the ring-shaped front surface (40) of the valve member (36) engages one (20a) of the ring-shaped valve seats (20a, 28a).