Brake master cylinder (master cylinder)
1. The role of the brake master cylinder
The role of the brake master cylinder is to convert pedal force into hydraulic pressure.
2. Brake master cylinder structure
Brake master cylinder. The upper part is a storage tank for storing brake fluid (Figure 4-5). In order to prevent oil leakage in one of the two pipelines, the oil in the storage tank will run out.
The liquid storage tank is divided into two chambers by a fence, the two chambers are communicated at the upper part and separated at the lower part. The lid of the liquid storage tank. There are small holes on it to open the atmosphere, and the lid
Indicate what type of brake fluid is used, such as "WARNING: CLEAN FILLER CAP BEFORE REMOVING USE 0NLY
DOT3 FLUID, FROM A SEALED CONTAINER" "Warning: Only use DOT3 brake fluid whose container is sealed, replace DOT3 system
Clean the filling equipment when moving fluid".
Figure 4-5 Liquid storage tank
The structure of the dual-chamber tandem brake master cylinder is shown in Figure 4-6.
3. Working principle
1) When the brake pedal is depressed
As shown in Figure 4-6, when braking, the driver depresses the brake pedal and the vacuum
The booster pushes the brake push rod to move to the left, and the compensation hole is covered by the sealing ring in the rear cavity
(Figure 4-7 shows the position of the compensation hole and the oil inlet hole), the oil pressure in the rear cavity opens
Begin to rise, on the one hand, the oil enters the right front and left rear brake through the oil outlet in the cavity
The pipeline (the premise is the X-type pipeline),--the front cavity piston is pushed again.
Force, under the combined action of this hydraulic thrust and the spring force of the rear cavity piston, the front cavity
The piston also moves to the left, so that pressure is also generated in the front chamber, and the oil enters the left
The front and right rear brake pipelines, so the two brake pipelines brake the car.
2) When the brake pedal is released
Figure 4-7 Compensation hole and oil inlet hole
When the brake is released, the driver releases the brake pedal, the front chamber piston returns to its position under the action of the spring, and the hydraulic oil flows from the brake wheel cylinder (or hydraulic cylinder) and pipeline
The flow returns to the master cylinder of the brake. If the piston returns to the position quickly, the internal volume of the working chamber expands rapidly, causing the oil pressure to drop rapidly. Due to the influence of pipeline resistance, in the pipeline.
The oil cannot flow back to the working chamber in time to fill the space made by the piston movement, so that the working chamber can form a certain degree of vacuum. At this time, the oil in the storage tank
Then through the oil inlet and the small hole behind the piston oil seal, the edge of the sealing ring is pushed open and flows into the working cavity (front cavity and rear cavity). When the piston is fully returned, the compensation hole
Open, the excess oil in the working chamber flows back to the reservoir through the compensation hole. If the hydraulic system is caused by oil leakage and temperature changes, the working chamber, pipeline, wheel of the main cylinder
The expansion or contraction of the oil in the cylinder can be adjusted through the compensation hole.
3) Failure replacement
If the left front and right rear brake pipes are damaged (front cavity) and leak oil, when the brake pedal is stepped on, only the rear cavity can build constant pressure, and the front work
There is no pressure in the cavity. At this time, under the action of the pressure difference between the two chambers, the front chamber piston is quickly pushed to the bottom. After that, the oil pressure in the rear cavity rises rapidly, making the right
The front and left rear wheels produce braking action.
If the right front and left rear brake pipelines are damaged (rear cavity) and leak oil, when the brake pedal is stepped on, only the rear cavity piston will move forward at first, because the rear cavity cannot
The oil pressure is built up, so the front chamber piston cannot be pushed forward. Continue to depress the brake pedal, and when the rod at the front end of the rear cavity piston directly hits the front cavity piston,
Then the front cavity piston can be pushed to build up oil pressure in the front cavity.
It can be seen that in the dual-circuit hydraulic brake system, when one set of pipelines is damaged and leaks oil, the other pipeline can still work, but the pedal stroke required is increased.
It's just big.
4. Troubleshooting of the brake master cylinder
1) Leakage of brake master cylinder
There are two types of brake master cylinder oil leakage: external leakage and internal leakage.
External leakage: The oil leakage can be seen from the outer surface. There are three types:
①Oil leaks at the connection between the brake master cylinder and the booster;
②Oil leakage at the piston limit screw;
③There are pores in the cylinder body causing leakage.
For oil leakage at the limit screw (stop screw), tighten it with a wrench. For the other two types of oil leakage, the brake master cylinder needs to be replaced, but it is not necessary to replace the auxiliary cylinder.
Power device.
Internal leakage: In this case, the pedal can be pedaled to the bottom or gradually sink to the bottom, but the brakes are poor or fail, which may be caused by internal leakage of the master cylinder.
2) The brakes are locked
There are two main reasons for brake lock.
(1) The compensation hole (o.5~0.7mm) of the master cylinder is blocked. This is the most common phenomenon, and there are two reasons: one is the booster installation
When driving, the control push rod with fork is not properly adjusted when connected with the pedal lever, making the control push rod too long, pushing the piston of the master cylinder forward, and blocking the cylinder block.
Oil return hole: The second is that the brake fluid is dirty and debris is blocking the oil return hole, which can be dealt with separately according to different situations.
(2) The booster control push rod does not return, or the return is too slow, causing the pedal to not return or the return is too slow, causing the brakes to lock or severely drag the brakes.
If the wheel is hot, the booster should be replaced instead of the main cylinder. Whether a car brakes well is related to the entire braking system. For example, only There is a bad brake on one side (left or right), basically it can be judged to be a problem with the sub-cylinder, and there is no need to doubt the booster, so there must be many aspects during maintenance analysis.