| 摘要 |
A hydraulic brake booster is disclosed which includes a spool valve slidably mounted within the booster housing to control fluid communication between a source of hydraulic pressure and the booster pressure chamber. A secondary valve mechanism is slidably mounted on the end of the spool valve which closes when the vehicle operator effects a brake application and the spool valve fails to move. Closure of the secondary valve prevents a surge of hydraulic fluid from being communicated into the booster pressure chamber, should the spool valve move after a manual brake application has been initiated. A stop piston, which is slidably mounted in the booster housing, engages the other end of the spool valve and cooperates with the secondary valve mechanism to prevent the latter from closing upon actuation of the spool valve if the fluid pressure level at the inlet of the booster is below a predetermined level. This feature permits hydraulic fluid to be communicated into the booster pressure chamber as soon as the vehicle's engine is started to assist the vehicle operator in applying the brakes of the vehicle.
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