Working principle of hydraulic brake booster

Date:28 Feb 2020

The hydraulic brake booster uses the hydraulic pressure […]

The hydraulic brake booster uses the hydraulic pressure generated by the power steering pump instead of the engine vacuum to provide the required power assistance.

Leaks related to accumulator capacity can be checked by pumping the brake multiple times while the engine is running and then shutting the engine off. The vehicle should then be left for about an hour and the brakes should be applied without starting the engine. In an efficient and operable system, it should take more effort to apply 2 to 3 soft brakes.

Although not as common as conventional braking systems equipped with vacuum boosters, many vehicles are now equipped with hydraulic booster brakes. This system uses hydraulic pressure generated by a power steering pump instead of engine vacuum to provide the power assistance required by conventional systems. This application is particularly suitable for vehicles with diesel engines, as it is not necessary to provide a separate vacuum source for system operation.

Because the system uses hydraulic pressure from existing power steering pumps, the supercharger uses the pressure generated by the hydraulic pressure that has been circulated through it as a pressure source applied to the master cylinder actuating piston.
The hydraulic pressure generated by the power steering pump is stored in an accumulator, which is then guided to the master cylinder by the hydraulic booster when the brake pedal is depressed.

When the brake booster is applied, a pressure of 1200 to 2,000 psi or 8273 to 13789 Kpa is applied to the caliper. This system can usually be used with or without a master cylinder. The system containing the master cylinder has a reservoir as part of the assembly.
As a safety measure, part of the system includes components called “accumulators” that help maintain system pressure. Depending on the application, some are pressurized with nitrogen and some are spring loaded. In the event of pressure loss (for example, when the engine stalls or the steering pump drive belt breaks), the system accumulator is designed to store enough pressure to provide three full power applications. If this is not enough, the system will use manual braking.

A simple way to test the system is to pump the brake five to six times with the engine off to drain the accumulator. Press the pedal firmly and start the engine. Just like a vacuum booster, when the engine starts, you should feel the pedal drop slightly and then rise again.