Importance

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Abstract

A pneumatic brake booster having a casing (10) with an axis of symmetry (X-X') divided in a leaktight fashion by a movable wall structure (12) into a front chamber (14) permanently connected to a source of low pressure, and a rear chamber (16). The rear chamber (16) is connected selectively to the front chamber (14) or a source of high pressure by a three-way valve means (36). The three-way valve means (36) is actuated by a control rod (30) capable of pressing, via a front face of a plunger (28), on a rear face of a push rod (56) secured to a reaction disc (58) when a plunger (28) slides in a bore (26) of the movable wall (12). The three-way valve (36) includes a valve element (36) located in a tubular rear part (22) of the movable wall (12) and interacts via of an annular front face (40) with a first annular valve seat (28a) formed on the plunger (28) and with a second annular valve seat (20a) formed on the movable wall (12). The first valve seat (28a) is concentric with the second valve seat (20a) and a smaller diameter. The annular front face (40) of the valve element (36) is able to move in the tubular rear part (22) of the movable wall (12) and sealed therein by outer and inner edges. The annular front face (40) of the valve (36) has a least one opening (46) causing a chamber (44) to be situated behind the annular front face (40) of valve (36) to communicate with a space (35) situated between the first valve seat (28a) and the second valve seat (20a). The resultant of forces generated by the low pressure and high pressure exerted on the plunger (28) is permanently and essentially negligible.

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First Claim