The Working Principle Of The Power Brake Booster

The vacuum booster uses the principle of sucking in air when the engine is working, which creates the vacuum on the first side of the booster. In response to the pressure difference of the normal air pressure on the other side, the pressure difference is used to strengthen the braking thrust.

If there is even a small pressure difference between the two sides of the diaphragm, due to the large area of the diaphragm, a large thrust can still be generated to push the diaphragm to the end with low pressure. When braking, the vacuum booster system also controls the vacuum entering the booster to make the diaphragm move, and uses the push rod on the diaphragm to assist human to step on and push the brake pedal through the combined transport device.

In the non working state, the return spring of the control valve push rod pushes the control valve push rod to the lock position on the right side, and the vacuum valve port is in the open state. The control valve spring makes the control valve cup and the air valve seat closely contact, thus closing the air valve port.

At this time, the vacuum gas chamber and application gas chamber of the booster are communicated with the application gas chamber channel through the vacuum gas chamber channel of the piston body through the control valve cavity, and are isolated from the external atmosphere. After the engine is started, the vacuum (negative pressure of the engine) at the intake manifold of the engine will rise to -0.0667mpa (that is, the air pressure value is 0.0333mpa, and the pressure difference with atmospheric pressure is 0.0667mpa). Subsequently, the booster vacuum and the vacuum of the application chamber increased to -0.0667mpa, and they were ready to work at any time.

When braking, the brake pedal is depressed, and the pedal force is amplified by the lever and acts on the push rod of the control valve. First, the return spring of control valve push rod is compressed, and the control valve push rod and air valve column move forward. When the control valve push rod moves forward to the position where the control valve cup contacts the vacuum valve seat, the vacuum valve port is closed. At this time, the booster vacuum and application chamber are separated.

At this time, the end of the air valve column just contacts the surface of the reaction disk. As the control valve push rod continues to move forward, the air valve port will open. After air filtration, the external air enters the application chamber of the booster through the open air valve port and the channel leading to the application air chamber, and the servo force is generated. Because the material of reaction plate has the physical property requirement of equal unit pressure on the stressed surface, the servo force increases in a fixed proportion (servo force ratio) with the gradual increase of input force of control valve push rod. Due to the limitation of the servo force resources, when the maximum servo force is reached, that is, when the vacuum degree of the application chamber is zero, the servo force will become a constant and will not change any more. At this time, the input force and output force of the booster will increase by the same amount; when the brake is cancelled, the control valve push rod moves backward with the decrease of input force. When the maximum boost point is reached, after the vacuum valve port is opened, the booster vacuum and the application air chamber are connected, the vacuum degree of the application chamber will decrease, the servo force will decrease, and the piston body will move backward. In this way, as the input force gradually decreases, the servo force will decrease in a fixed proportion (servo force ratio) until the brake is completely released.


Post time: 2022-09-22 09:43:42
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