Patent ID: 8366205

Claim:
A brake booster for use in a brake system having a housing with a first axial bore therein for receiving a first piston that is separated from the bottom of the axial bore by a first spring to define a first chamber, a second piston that is separated from the first piston by a second spring to define a second chamber and a third piston that is separated from the second piston by a third spring to define a third chamber, said first chamber being connected to a reservoir through a first inlet port and to a first set of wheel brakes through a first outlet port, said second chamber being connected to a second set of wheel brakes through a second outlet port, said third chamber being connected to the reservoir through a second inlet port and to the second chamber through a first passage in the second piston, said second piston having a second axial bore connected to a source of pressurized fluid through a supply port, the supply port being fluidly connected to the second axial bore, a control valve located in the second axial bore for controlling communication of pressurized fluid from the supply port to the first passage in response to an input force supplied by an actuator rod connected to the third piston in response to a manual brake force applied to a pedal by an operator, and compensation valve means located in the second inlet port for controlling fluid communication between the reservoir and the third chamber as a function of pressurized fluid available from the source and the position of the third piston, said brake booster being characterized by the second piston being held against a stop when pressurized fluid is supplied to the first passage to effect a first brake application and in an absence of pressurized fluid available from the source, the compensation valve closes and fluid in the third chamber acts on and moves the second piston away from the stop as a function of movement of the third piston by the manual brake force to immediately pressurize fluid in the second chamber and effect a second brake application.