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8A-4
Brake Booster
The brake booster is a power assist device for brake
system. It relieves the pedal depressing force by using
the pressure difference between the vacuum pressure gen-
erated by vacuum pump in intake manifold and the atmo-
spheric pressure.
1. Pressure distribution at working
When depressing the brake pedal, the push rod (1) in
booster pushes the poppet (2) and valve plunger (3). The
poppet (2) pushes the power piston seat (5) resulting in
closing the vacuum valve (9). The chamber (A) and (B) in
power cylinder are isolated and the valve plunger (3) is
separated from the poppet (2). And then the air valve (6)
opens and air flows into the chamber (B) through filter.
Then, the power piston (5) pushes the master cylinder
push rod (7) to assist the brake operation.
CHANGED BY
EFFECTIVE DATE
AFFECTED VIN
2. Pressure distribution after working
Vacuum pump
Y220_08A004
When releasing the brake pedal, the valve plunger (3) re-
turns back to the original position by return spring (4) and
the air valve (6) closes. At this time, the vacuum valve (9)
opens and the pressure difference between chamber (A)
and (B) in power cylinder is eliminated. Accordingly, the
power piston (5) returns back to original position by the
reaction of master cylinder (10) and the diaphragm return
spring (8).
Y220_08A005
BRAKE SYSTEM
REXTON SM - 2004.4
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