Fusion FWD V6-3.5L (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 vacuum supply hose
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Brake booster vacuum sensor
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Brake booster travel sensor (hybrid vehicles)
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Engine-mounted 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. Vehicles with 3.0L All-Wheel Drive (AWD) and 3.5L engines are equipped with a
vacuum sensor. The ABS module uses the signals produced by the vacuum pressure sensor to verify that vacuum maintained in the brake booster.
Active brake booster (hybrid vehicles)
The active brake booster uses vacuum supplied by an electric vacuum pump mounted on the engine when engine vacuum is unavailable. The active brake
booster is similar to a conventional brake booster but 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 Pulse Width Modulated (PWM) 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 toward the master cylinder piston, building hydraulic pressure. The 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.
