Brake master cylinder, also known as brake master cylinder, is one of the core components of automobile braking system. For example, it is like the heart of the braking system, which is responsible for converting the pressure applied by the driver on the brake pedal and the vacuum force provided by the vacuum booster into hydraulic pressure and pumping it to the sub cylinder of each brake caliper, so as to realize the braking of the vehicle.
Installation position of brake master cylinder
1. Composition, structure and working principle
The composition structure and working principle of the brake master cylinder are not complex. It is mainly composed of cylinder block, piston, return spring, rubber sealing element (leather cup), central valve and other elements. In order to adapt to the development of ABS and ESP systems, the structure of brake master cylinder has also experienced several development stages, such as compensation type, central valve type and plunger type, but its basic working principle has not changed. When braking, the push rod connected with the brake pedal pushes the piston to move, and the pressure in the working chamber composed of the piston, sealing cup and shell increases, which sends the brake oil pressure to the brake wheel cylinder at the wheel.
Tandem double chamber brake master cylinder structure
At present, most countries and regions require passenger cars to adopt dual circuit braking system in the form of regulations, so that when one circuit leaks, the other circuit can still maintain a certain braking force. Therefore, the tandem dual chamber brake master cylinder is widely used in passenger cars. The difference is that in some models, diagonal wheels form a circuit respectively, and in some models, front and rear axle wheels form a circuit respectively.
Diagonal double circuit braking system
Front and rear axle dual circuit braking system
2. Common faults of brake master cylinder
(1) The brake pedal is soft
A common fault of the brake master cylinder is the soft feeling of the foot after pressing the brake pedal. Under normal circumstances, when the brake pedal is pressed, obvious feedback force should be felt, indicating that the braking force has acted on the brake caliper. If you press the brake pedal, it is like stepping on a sponge, which means that the output pressure of the brake master cylinder decreases or even no pressure output at all. If it is reflected on the wheel brake, the braking force decreases or even disappears, which is a very dangerous situation for driving.
The most common cause of this situation is the wear or aging of the sealing elements (leather cups) in the master cylinder, which makes the hydraulic pressure in different chambers unable to be effectively isolated, and the oil flows from the high-pressure chamber to the low-pressure chamber, that is, the so-called "internal leakage" occurs. It should be noted that if there is oil leakage in the pipeline and wheel cylinder in the braking system, or there is gas in the braking pipeline, the brake pedal may also be soft.
Brake master cylinder internal parts
(2) No free travel of brake pedal
The problem of soft brake pedal has been mentioned earlier, but if the brake pedal feels hard, it is also abnormal. In addition to the brake booster, this may also be a problem with the brake master cylinder. It can be seen from the structure of the brake master cylinder that at the initial stage when the brake pedal is pressed, the compensation hole is not blocked by the piston, and the working chamber is not completely closed. At this time, the oil pressure in the working chamber cannot be established, so there should be a free stroke of the pedal. If the brake pedal feels hard and has no free travel, it is often related to the blockage of the compensation hole, which may be caused by too many impurities in the brake oil or the expansion and deformation of the main leather cup. In addition, improper installation of the brake master cylinder or brake booster may cause abnormal forward movement of the piston in the master cylinder.
brake master cylinder
(3) Brake oil leakage
Brake oil leakage is also a common fault of the brake master cylinder. The brake master cylinder is directly connected with the brake oil reservoir. If they are not installed in place, or the seals between them are aging and damaged, brake fluid leakage will be caused. In addition, the brake master cylinder also supplies oil to 2 brake circuits, so there are 2 oil outlets. The two oil outlets are generally connected with the oil pipe through threads. If there is an error during installation or the threads are corroded, it may also cause oil leakage. However, fortunately, most models now have brake oil level sensors installed at the brake oil reservoir. When the level is abnormal, a fault prompt will be given in the instrument cluster. At this time, you need to carefully check whether there is a leakage problem in the brake system.
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Leaking brake master cylinder
Jiashun auto parts brake tips
Although the brake master cylinder looks insignificant, it is a very important component in the brake system. Its normal operation is directly related to driving safety. Maintenance technicians must not ignore its inspection. The machining accuracy of metal parts such as piston and needle valve in the brake master cylinder and the material quality of rubber seals such as leather cups have high requirements. Therefore, we must buy brand products with excellent quality. The operation requirements of the maintenance manual shall also be followed during installation to avoid hidden trouble.
