| 摘要 |
<p>A pneumatic brake servo comprising a housing (10) containing a piston which consists of a hub (20) and a skirt (14), and defining, by means of a roll-up membrane (12), a forward chamber (16) which constantly communicates with a vacuum source, and a rear chamber (18) which is selectively communicable with the forward chamber (16) when a first valve passage (56, 58) is open, or with the atmosphere when a second valve passage (76, 78) is open, said valve passages (56, 58; 76, 78) being defined by first valve members (58, 78) cooperating with second valve members (56, 76), and actuated by a control rod (35) which is engageable, via a plunger (32), with one side of a reaction disc (42) that is rigidly fixed to a push rod (44). Said first valve members (58, 78) are provided on the piston hub (20).</p> |
