Friday, March 13, 2009


This system can increase brake fluid pressure effectively with lighter pedal pushing force than that of conventional system,when emergency braking. On the braking of unskilled driver,even if pedal pushing speed of both skilled and unskilled drivers are same, unskilled driver cannot apply enough force on the brake pedal until the brake booster functions because the unskilled driver is rather hard to increase the pedal pushing force during braking comparing with that the skilled driver.

In the conventional type of brake booster system has an almost constant boost ratio from small to large pedal pushing force, but brake assist system makes the boost ratio larger when the pedal pushing force exeeds certain level.this is function of brake assist.

On conventional system the valve plunger , which transmits the operating force of operating rod to reaction disc, is one peace part. On brake assist system the valve plunger is divided into two pieces, and there is a rubber damper or a spring for boost ratio control between them.

Primary period
The power piston moves to left direction by booster function introducing atmospheric pressure,and the reaction disc starts to be deformed due to pressure from the power piston. By the pressure the deformed part of reaction disc goes into inside of a plunger plate holder.

Boost ratio increasing period
The deformed part of reaction disc inside of plunger plate holder contacts to plunger plate, and it compresses the control rubber damper of spring .By the compression a reaction force is applied on the reaction disc, and finally the reaction force is applied on output rod as an additional force from input rod.

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Monday, March 2, 2009



The force with which the driver steps on the brake pedal would not be enough to cause the brakes to operate to stop the vehicle quickly.
The brake booster therefore multiples the driver's pedal effort so that a large braking force is created.the brake booster may be an integrsl part of the master cylinder or fitted separately from it.
The brake booster has a diaphragm that is operated by the difference in pressure between atmospheric pressure and the vacum that is generated inside the engine's intake manifold.

The master is activated jointly by the pedal and the diaphragm to create a large braking force from a minimum of pedal effort.

Should the brake booster start to malfunction for one reason or another,it is designed in such a way that only the bossting power applied to the brakes is lost.The brakes will require additional pedal effort in such a case , but the vehicle can be braked normally without the booster.

On vehicle powered by a diesel engine , negative pressure is generated by a vacum pump because the intake manifold vacuum of a diesel is not sufficiently strong for this.The brake booster is installed between the brake pedal and the master cylinder,and consists of the following part;

  • Front/rear shell

  • Power piston ( diaphragm plate and valve body )

  • Input rod

  • Poppet seal

  • Output rod

  • Reaction disc

When the brake pedal is not depressed

The input rod,power piston and output rod are forced to the right by the diaphragm return spring.the air valve , consisting of the valve plunger and the interior of the poppet seal,closes, allowing no air to enter chamber B.Further, since the vacum seal, consisting of a power and exterior of the poppet seal, is open, chamber A is connected to chamber B through a vent hole provided in the power piston. both chambers contain a vacum due to the vacuum in the intake manifold.

When the brake pedal is depressed

When the brake pedal is depressed, the input rod and poppet seal move to the left( front), the vacum valve closes,and the vent hole connecting chambers A and B is blocked.Futher movement of input rod pushes the valve plunger and forces the air valve to open ,and air enters chambers B through a gap between the input rod and poppet seal.this causes a pressure differential between the two sides of power piston.The force resulting from this difference in pressure overcomes the force of the diaphragm return spring,moving the power piston to the letf ( front).The leftward movementof the power piston actuates the output rod,producing the required hydraulic pressure.

When the brake pedal is released

When the brake pedal is released, the master cylinder spring ,diaphragm return spring and pedal return spring cause the output rod,power pistonand input rod return to their original positions ( same as not depressed). The cause the air valve to close , and the vacum valve to open, so that the air in chamber B is drawn into the intake manifold, restoring the brake booster to its non-operating condition.

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