Escape 4WD L4-2.5L (2010)
Vacuum Brake Booster: Description and Operation
Brake Booster
The power brake actuation system consists of the following components:
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Brake booster
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Brake booster check valve
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Brake booster travel sensor (hybrid vehicles)
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Brake booster vacuum sensor (hybrid vehicles)
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Brake booster vacuum supply hose
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Vacuum pump (hybrid vehicles)
Conventional brake booster
The brake booster uses engine vacuum from the intake manifold to create a partial vacuum inside the vacuum booster on both sides of the diaphragm.
When the brake pedal is pressed, the booster rod opens a valve, allowing air to enter the booster on one side of the diaphragm while sealing off the
opposite side. This increases pressure on that side of the diaphragm so that it helps push the rod, which in turn pushes the piston in the master cylinder.
As the brake pedal is released, the valve seals off the outside air supply while opening the vacuum valve. This restores vacuum to both sides of the
diaphragm, allowing everything to return to its original position.
Active brake booster (hybrid vehicles)
The active brake booster uses vacuum supplied by an engine-mounted electronic vacuum pump and is similar to a conventional vacuum assist brake
booster with the addition of a brake booster (vacuum) solenoid, a brake booster travel sensor and a vacuum sensor. If it is necessary to apply the friction
brakes, the ABS module will send a signal to the brake booster solenoid that is proportional to the amount of brake torque requested. The booster
solenoid will open to allow vacuum to draw the booster diaphragm and push rod towards the master cylinder piston, building hydraulic pressure. The
brake booster vacuum sensor is used by the ABS module to monitor vacuum maintained inside the brake booster. The brake booster travel sensor is used
to monitor the performance of the brake booster.
