Working brake mechanism. How it is arranged and how it works

We have already written about in general, what problems may arise with it, and how to identify possible problems with the brakes. Now let's talk a little more about such an important element of the system as the actuator and its key part - the working cylinder.

A little about the brakes in general and the role of the slave cylinder in the implementation of braking

In almost any passenger vehicle, the executive brake mechanism is activated hydraulically. In a simplified form, the braking process is as follows.

The foot presses on the brake pedal (3). The pusher (4) connected to the pedal actuates the main brake cylinder (GTZ) (6). Its piston extends and pushes the brake fluid into the lines (9, 10) of the hydraulic system. Due to the fact that the liquid does not compress at all, the pressure is immediately transferred to the wheel (working) cylinders (2, 8), and their pistons begin to move.

It is the working cylinder with its piston that acts directly on the actuator. As a result, the pads (1, 7) are pressed against the disc or drum, causing the wheel to brake.

Releasing the pedal leads to a drop in pressure in the system, the pistons move into the cylinders, and the pads move away from the disc (drum) due to the return springs.

Significantly reduce the required force of pressing the pedal and improve the efficiency of the system as a whole allows the use of a vacuum booster. Often it is a single module with the GTZ. However, some hydraulic actuators may not have an amplifier.

The hydraulic system provides high efficiency, fast brake response and at the same time has a simple and convenient design.

In freight transport, a pneumatic or combined system is often used instead of hydraulics, although the basic principles of its operation are the same.

Variants of hydraulic drive schemes

On passenger cars, the brake system is usually divided into two hydraulic circuits that operate independently of each other. In most cases, a two-section GTZ is used - in fact, these are two separate cylinders combined into a single module and having a common pusher. Although there are models of machines where two single GTZ are installed with a common pedal drive.

Diagonal is considered the optimal scheme. In it, one of the circuits is responsible for braking the left front and right rear wheels, and the second works with the other two wheels - diagonally. It is this scheme of operation of the brakes that can most often be found on passenger cars. Sometimes, on rear-wheel drive vehicles, a different system construction is used: one circuit for the rear wheels, the second for the front wheels. It is also possible to include all four wheels in the main circuit and separately the two front wheels in the backup.

There are systems where each wheel has two or even three working cylinders.

Be that as it may, the presence of two separate independently operating hydraulic circuits increases the fail-safety of the brakes and makes driving safer, since if one of the circuits fails (for example, due to brake fluid leakage), the second will make it possible to stop the car. Nevertheless, the braking efficiency is somewhat reduced in this case, therefore, in no case should it be delayed in correcting this situation.

Design features of brake mechanisms

On passenger vehicles, friction actuators are used, and braking is carried out due to the friction of the pads against the disc or the inside of the brake drum.

For the front wheels, disk-type mechanisms are used. The caliper, which is mounted on the steering knuckle, houses one or two cylinders, as well as brake pads.

It looks like a working cylinder for a disc brake mechanism.

During braking, fluid pressure pushes the pistons out of the cylinders. Usually the pistons act directly on the pads, although there are designs that have a special transmission mechanism.

The caliper, resembling a bracket in shape, is made of cast iron or aluminum. In some designs it is fixed, in others it is mobile. In the first version, two cylinders are placed in it, and the pads are pressed against the brake disc by pistons on both sides. The movable caliper can move along the guides and has one working cylinder. In this design, the hydraulics actually control not only the piston, but also the caliper.

The movable version provides more even wear of the friction linings and a constant gap between the disc and pad, but the static caliper design gives better braking.

The drum-type actuator, which is often used for the rear wheels, is arranged somewhat differently.

The working cylinders are also different here. They have two pistons with steel pushers. Sealing cuffs and anthers prevent the penetration of air and foreign particles into the cylinder and prevent its premature wear. A special fitting is used to bleed air when pumping hydraulics.

In the middle part of the part there is a cavity, in the process of braking it is filled with liquid. As a result, the pistons are pushed out of opposite ends of the cylinder and put pressure on the brake pads. Those are pressed against the rotating drum from the inside, slowing down the rotation of the wheel.

In some models of machines, to increase the efficiency of drum brakes, two working cylinders are included in their design.

Diagnostics

Too soft pressure or failure of the brake pedal is possible due to depressurization of the hydraulic system or the presence of air bubbles in it. A GTZ defect cannot be ruled out in this situation.

Increased pedal stiffness indicates a vacuum booster failure.

Some indirect signs allow us to conclude that the wheel actuators are not working properly.

If the car skids during braking, then it is likely that the piston of the working cylinder of one of the wheels is jammed. If it is stuck in the extended position, it can press the pad against the disc, causing permanent braking of the wheel. Then the car in motion can lead to the side, the tires will wear out unevenly, and vibrations can be felt on the steering wheel. It should be borne in mind that piston seizure can sometimes be triggered by excessively worn pads.

You can try to restore a faulty working cylinder, for example, using a suitable repair kit. If this is not possible, then you need to purchase a new part that matches your car model. The Chinese online store has a large selection of Chinese cars, as well as parts for European-made cars.