| 摘要 |
Pneumatic brake servo comprising a body (10) having an axis of symmetry (X-X') sealingly separated by a moveable partition (12, 20) into a front chamber (14) permanently linked to a vacuum source, and a rear chamber (16) selectively linked to the front chamber (14) or the outer atmosphere by a three-way valve (36) operated by a plunger (28) sliding in a bore (26) in the moveable partition (12, 20) and integral with an axial control rod (30). The three-way valve (36), which is located in a rear tubular portion (22) of the moveable partition (12, 20) projects outwardly from said body (10), comprises a flap (36) cooperating by a first annular surface (A) with a first flap seat (28a) formed on the plunger (28) and by a second annular surface (B) with a second flap seat (20a) formed on the moveable partition (20). According to the invention, the second annular surface (B) is located in a transverse plane frontwards of the transverse plane in which is located the first annular surface (A), the first (A) and the second (B) annular surfaces being joined by a surface (C; C1, C2) of the flap (36) located opposite one surface (D) of the plunger (28), the first annular surface (A) and the surface (C; C1, C2) of the flap (36) defining, in conjunction with the flap seat (28a) formed on the plunger (28), a valve passage (28a, 36) whose cross section is a non-linear function of the distance (d) between the first flap seat (28a) and the first annular surface (A).
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