An alternator vacuum pump, typically found in diesel vehicles, works by using the rotation of the alternator shaft to power a mechanical pump that evacuates air from the brake booster, creating a vacuum necessary for power-assisted braking.
Here's a breakdown of the process:
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Drive Source: The vacuum pump is directly coupled to and driven by the alternator shaft. This ensures that the pump operates whenever the engine is running and the alternator is spinning.
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Pumping Mechanism: Inside the pump, various designs exist to create the vacuum. Common designs include:
- Vane Pump: A rotor with vanes spins inside a housing. As the rotor spins, the vanes extend and retract, creating chambers that expand and contract. This expansion draws air in from the brake booster (creating the vacuum), and the contraction forces the air out through an exhaust port.
- Diaphragm Pump: A diaphragm is mechanically moved back and forth by the rotating shaft. One direction creates a vacuum, drawing air from the brake booster. The other direction expels the air.
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Vacuum Creation: The pumping action evacuates air from the brake booster. The brake booster is a sealed container connected to the brake pedal. When a vacuum is present in the booster, less force is required to apply the brakes.
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Brake Booster Assist: The vacuum created by the pump assists the driver in applying the brakes. When the brake pedal is pressed, a valve opens within the booster, allowing atmospheric pressure to enter one side of a diaphragm. The pressure difference between the vacuum on one side of the diaphragm and the atmospheric pressure on the other side assists in pushing the master cylinder, applying the brakes.
In essence, the alternator vacuum pump supplements or replaces traditional intake manifold vacuum (which is low or nonexistent in diesel engines) to provide reliable vacuum for the brake booster, ensuring proper brake function. Without it, braking would require significantly more physical effort from the driver.
