| 摘要 |
A brake booster (12) having a housing (14, 16) with a control valve (70) located in an axial bore (54) of a hub (50) carried by a movable wall (22, 24). The movable wall (22, 24) separates the interior of the housing into a first chamber (26, 26') and a second chamber (28, 28'). The control valve (70) in a first mode communicates the first chamber (26, 26') with the second chamber (28, 28') to provide for equal pressures therein and in a second mode communicates the second chamber (28, 28') with a surrounding environment to create a pressure differential across the movable wall (22, 24). A reaction member (96) carried by the movable wall (22, 24) communicates an operational force created by the pressure differential into an output push rod (94). After the operational force overcomes a return spring arrangement (129), the output push rod (94) moves pistons (200) in a master cylinder (202) to correspondingly pressurize fluid therein which is supplied to wheel brakes to effect a brake application. The brake booster (12) is characterized by the return spring arrangement (129) having a first spring (130) with a right hand spiral and a second spring (130') having a left hand spiral. The first spring (130) is secured to a base (102) of a retainer (100) and to an end cap (136) to hold the second spring (130') in a concentric relationship between the end cap (136) and base (102). A housing (202) of a master cylinder (200) engages the end cap (136) to compress the return spring arrangement (129) to an installation height such that the movable wall (22, 24) is located in a ready rest position.
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