Reserve system activation and modulation for hydraulic feedback brake boosters

摘要

A hydraulic brake booster is disclosed which is normally actuated by a primary pressure source, but which may be actuated by a secondary pressure source during failure of the primary pressure source. The booster includes a spool valve which controls communication between the primary pressure source and the booster pressure chamber. The spool valve is actuated by a control pressure which is generated by the vehicle operator when a brake application is effected. The control pressure shifts the spool valve to cause the latter to communicate fluid pressure from the primary pressure source into the pressure chamber. A pressure differential responsive piston is responsive to a pressure differential between the control pressure and the pressure communicated into the booster pressure chamber. When the control pressure exceeds the pressure communicated to the booster pressure chamber by some predetermined amount, the differential pressure responsive piston shifts to actuate a valve mechanism to communicate fluid from the secondary pressure source to the booster pressure chamber. Simultaneously, shifting of the differential pressure responsive piston to actuate the valving mechanism also terminates communication between the spool valve and the booster pressure chamber, so that fluid from the secondary pressure source communicated into the booster pressure chamber may not leak through the spool valve.