The device of brake systems

Brake systems are designed to reduce the speed of movement, stop and hold the car in place when parking.

Reducing the speed of movement and stopping the car is provided by a working brake system, holding the car in place during parking is a parking brake.

The car is equipped with two brake systems: working and parking. In case of damage to the working system, the car is stopped by a serviceable part (front or rear wheel brake circuit) working brake system. Each brake system consists of brake mechanisms (brakes) and brake drive.

Service brake system

The service brake system acts on all wheels of the vehicle and is driven by pedal 7 (pic. 45) when you press it with your foot. The service brake system includes front 1 and rear 12 brake mechanisms and hydraulic dual-circuit drive: primary 4 (front brakes) and secondary 5 (rear brakes).




Front brakes (pic. 46) disk. They are located in the front wheels of the car. The rotating and rubbing parts of the brake mechanisms are the brake discs.



The cast-iron brake disc 10 is attached with studs 8 to the hub 9 of the front wheel. From the front side in the direction of the car, the brake disc is covered by a caliper 7, which is a U-shaped bracket with guide bevels 13, which are sandwiched between the guide 6 of the brake pads and the pressure levers 3, which also have guide bevels. Such fastening of the caliper ensures its movement along the guide bevels of the levers 3 and guide 6 during braking. The caliper has a protective cover.


In the guide 6, attached to the steering knuckle, there are brake pads 2 with friction linings. With the help of axes 5, two clamping levers 3 of the caliper are hinged to the guide of the brake shoes. The block of brake cylinders 1 is pressed into the brake caliper 7. There are three cylinders in the block, of which the middle and lower ones are interconnected by a channel and connected to the front brake drive circuit, and the upper cylinder is connected to the rear brake drive circuit. A piston 12 is installed in each cylinder and a rubber sealing ring 16 is installed in the cylinder groove. This ring not only seals the piston in the cylinder, but also ensures, due to its elasticity, that the piston is removed from the block after braking. Thus, the rubber sealing rings 16 provide automatic adjustment of the gap between the brake disc and the brake pads. The pistons of all cylinders are in contact with the inner brake shoe and are closed with rubber protective caps 15 on its side. On the inside, the front brake mechanism is closed with a brake shield 4.

When braking under the action of fluid pressure in the hydraulic drive, the pistons move the inner brake shoe relative to the guide 6 and caliper 7 and press it against the brake disc 10. At the same time, under the action of fluid pressure, the cylinder block 1 moves along with the caliper 7 along the bevels of the guide 6 and clamping levers 3. In this case, the caliper moves the outer brake pad relative to the guide 6 and presses it against the brake disc. Both brake pads are pressed against the brake disc with the same force, since the fluid pressure on the pistons and the bottom of the cylinder block is the same.


After braking stops, the fluid pressure on the pistons and the bottom of the cylinder block drops sharply. Due to the elasticity of the rubber rings 16, the pistons are retracted from the inner brake pad, which in this case moves away from the brake disc due to its beating. At the same time, the outer brake pad, together with the caliper 7, also moves away from the brake disc as a result of its beating.

With wear of the friction linings of the brake pads, the gap between the linings and the brake disc increases. When braking under the action of fluid pressure, the pistons will move relative to the sealing rings 16 and take a new position in the cylinders, which will compensate for the wear of the friction linings. After stopping braking, the brake pads will move away from the brake disc by the same amount, determined by the deformation of the rubber rings 16. Thus, a constant gap between the brake pads and the disc is automatically maintained. In this regard, during operation, the gap between the pads and the front brake disc does not require adjustment.

When braking, the brake pads act on a relatively small part of the surface of the brake disc, leaving a large part of it open, which is effectively blown by air. The result is a very rapid cooling of the brake disc, which ensures high braking efficiency even with frequent braking at high speeds.

Rear brakes (pic. 47) drums, drums. They are located in the rear wheels of the car. The rotating parts of the brake mechanisms are the brake drums, the rubbing parts are the brake shoes, which, when braking, self-align relative to the brake drum, which ensures the greatest braking effect and more uniform wear of the friction linings.




The stamped steel brake shield 6 is bolted to the flange of the rear axle beam. In the lower part of the brake shield, a support 12 is installed, against which the brake shoes 4 with friction linings rest with their lower ends. The upper ends of the pads are in contact with the pistons of the wheel brake cylinder 8. The lower and upper ends of the brake pads are pulled together by springs 1 and 9. Lateral displacement of the pads is limited by racks 8 with springs that press the pads to the brake shield. This fastening of the brake pads on the brake shield allows them to freely self-align relative to the brake drum during braking. Brake pads with their ribs abut against eccentrics 11, fixed on the brake shield. With the help of these eccentrics, the gap between the shoes and the brake drum is adjusted. The brake drum is bolted to the axle shaft flange.

When braking under the action of fluid pressure in the brake actuator, the pistons of the wheel brake cylinder press the shoes against the brake drum. In this case, the coupling spring 9 of the pads is stretched. After braking stops, the fluid pressure on the pistons drops sharply, and under the action of the spring 9, the pads move away from the brake drum until they stop against the adjusting eccentrics 11.

The rear brake mechanisms, being elements of the working brake system, simultaneously perform the functions of the brake mechanisms of the parking brake system. For this purpose, they are equipped with additional devices, which include: an expansion lever 5, mounted on an axle on the rear brake shoe, and a spacer bar 10, installed between the expansion lever and the front brake shoe. When using the parking brake system, the lower end of the expansion lever 5 moves under the action of the cable 2 to the front brake shoe. In this case, the expanding lever, turning around the axis, through the spacer bar 10, first presses the front brake shoe against the brake drum, and then the rear one.

Brake drive designed to control brakes. The working brake system of the car has a hydraulic double-circuit drive. In hydraulic drive car (see fig. 45) includes: brake pedal 7, vacuum booster 6, master brake cylinder 3, front brake cylinders 1 and rear 12 brake mechanisms, pipelines of primary 4 and secondary 5 circuits, brake reservoir 2 and pressure regulator 14 rear brakes.

vacuum booster (pic. 48) reduces the force applied to the brake pedal when braking, and facilitates the work of the driver. The reinforcing effect of the vacuum booster is based on the use of vacuum in the intake manifold of a running engine.



The rubber diaphragm 23, installed between the housing 2 and the cover 4, divides the vacuum booster into two cavities: vacuum I and atmospheric II. The vacuum cavity is connected to the engine inlet pipe by a hose, in the tip 29 of which valve 30 is located. When the engine is running and the brake pedal is released, the pressure in the vacuum and atmospheric cavities of the amplifier is the same, since the vacuum from the engine inlet pipe through the hose and tip 29 is transmitted to cavity I and from it into the cavity II through the channel III, the gap between the valve 9, its seat on the body 22 and through the channel IV. When braking, the pusher 14 moves the piston 5 inside the body 2 of the amplifier, and the movable part of the valve 9 is pressed against the seat on the body 22 by the spring 17 and separates the vacuum I and atmospheric II cavities. With further movement of the pusher 14, the piston 5 moves away from the valve 9, and air enters the cavity II through the resulting gap, channel IV and air filter 15. In this case, vacuum is maintained in cavity I, and atmospheric pressure is established in cavity II. The pressure difference in the cavities of the amplifier creates an additional force, which, together with the force the driver presses on the brake pedal, moves the valve body 22 with the diaphragm 23. In this case, the rod 3 moves through the buffer 21, which acts on the pistons of the main brake cylinder. When you stop pressing the brake pedal and stop it in the locked position, the body 22, together with the valve 9 pressed against it, will move under the influence of the pressure difference in the cavities I and II until the valve 9 rests against the end of the stopped piston 5. The air flow into the cavity II in In this case, it will stop, and the body 22 will take a certain position. If the brake pedal is released in this position, then piston 5 will move valve 9 away from body 22, the pressure in cavity II will decrease and under the action of spring 24 body 22 will move until it comes into contact with valve 9.

During emergency braking, when a large force is applied to the brake pedal, a gap is maintained between piston 5 and valve 9, and air continues to flow into cavity II of the amplifier. After stopping braking, when the brake pedal is released, the pusher 14 with the piston 5 will return to its original position under the action of the return spring 24. In this case, the piston 5 presses the valve 9 from the body 22, part of the air from the cavity II will enter the cavity I, and the pressure in amplifier cavities will be aligned. In this case, the housing 22 with the diaphragm 23 and the rod 3 under the action of the spring 24 will move to the cover 4 of the amplifier and will take its original position.

Master brake cylinder (pic. 49) dual-chamber and simultaneously actuates the circuits of the front and rear brakes. It is attached to the vacuum brake booster.



In the cylinder body 3 there are pistons 5 and 7, which actuate different brake circuits and differ slightly from each other in their design. The rod of the vacuum brake booster rests against the piston 7. The pistons form two chambers I and II in the cylinder, which through holes 2 are connected by pipelines to the wheel brake cylinders of the rear and front brake mechanisms. Through holes 4, the main brake cylinder is connected by pipelines to the brake reservoir. When the brake pedal is released, the return spring 13 moves the piston 5 to the far right (original) position. In this case, the piston rests against the limiter 12, and the piston 7, under the action of the spring 10, rests against the limiter 9. Chambers I and II are separated from one another by the cuff 11, put on the piston 5.

Rubber sealing rings 16 and spacer rings 18 are inserted into the annular grooves of the pistons. In the initial position, the spring 15 presses the sealing ring against the spacer ring, as a result of which gaps 17 are formed between the sealing ring, the spacer ring and the piston. Through these gaps and openings 19, chambers I and II communicate with the brake reservoir, as a result of which the brake fluid does not experience excess pressure in the front and rear brake drive circuits.

When braking, the piston 7 moves, the annular gap 17 is eliminated, and the piston shoulder is pressed against the sealing ring 16. After that, the fluid from the master brake cylinder is forced into the wheel brake cylinders, and the fluid pressure necessary for braking is created in the front brake drive circuit. Simultaneously with piston 7, piston 5 moves, increasing the fluid pressure in the rear brake drive circuit. The fluid pressure that occurs in chamber II is transmitted through the piston 5 of the fluid in chamber I. Therefore, if the front rear brake drive circuits are in good condition, the fluid pressure in both circuits is the same.

In case of damage to the front brake drive circuit and fluid leakage from it during braking, piston 7 rests on piston 5. As a result, fluid pressure will be created in chamber I, which will actuate the rear brakes. When fluid leaks from the rear brake drive circuit during braking, piston 5 rests against the brake cylinder plug 1, as a result of which fluid pressure is created in chamber II, which actuates the front brake mechanisms.

Rear wheel brake cylinder mounted on the brake shield of the rear brake mechanism. There are two pistons in the cylinder body, between which an expanding spring with support cups is installed. Stops are pressed into the pistons, into the grooves of which the upper ends of the brake pads enter. In the cylinder, the pistons are sealed with cuffs. The cylinder is protected from contamination by rubber covers. There are two holes in the cylinder body. A fitting of the pipeline supplying brake fluid to the cylinder is screwed into the lower hole, and a bypass valve is screwed into the upper hole, designed to remove air from the brake actuator.

pressure regulator (pic. 50) sets the fluid pressure in the rear brake actuator, depending on the position of the car body relative to the rear axle. The regulator is included in the rear brake drive circuit and acts as a valve that automatically cuts off the fluid supply to the rear brakes. As a result, drift is excluded (yuz) rear wheels and increases vehicle safety.



Housing 1 of the pressure regulator is rigidly fixed to the car body. In the body of the regulator there is a piston 5, the rod of which rests on the torsion bar 11 of the drive connected to the rear axle of the vehicle. There is a bushing 7 in the housing, an annular gap is formed between it and the cylindrical piston head. A rubber seal 6 of the piston head is pressed against the sleeve 7. The spring 4, put on the piston rod, rests at one end on the plate 5, and at the other end on the sealing rubber ring 2. There are two cavities inside the regulator housing. Cavity II is connected by a pipeline to the main brake cylinder, and cavity I is connected to the wheel brake cylinders of the rear brake mechanisms.

The pressure regulator does not work if the vehicle is not braked. In this case, the piston 8 under the action of the torsion bar 11 and the spring 4 abuts against the plug 10 of the regulator. Cavities I and II communicate with each other through the gaps between the piston, sleeve 7 and seal 6.

The force acting on the piston rod from the torsion bar 11 depends on the relative position of the car body and the rear axle. It increases as the body approaches the axle and decreases as it moves away from the rear axle.

When braking, the fluid from the master brake cylinder flows into the wheel brake cylinders of the front and rear brakes. Moreover, it enters the brake cylinders of the rear brakes through the pressure regulator. In the regulator body, the brake fluid passes through cavity II, the gaps between the piston, seal 6, bushing 7 and through cavity I. At the beginning of braking, when the pressure on the fluid is low, the fluid freely passes through the regulator, actuating the rear brakes. With an increase in fluid pressure, when the brakes are applied, the rear of the car body rises, and the force acting on the piston rod from the side of the torsion bar 11 decreases. II will be disconnected from one another, and the flow of brake fluid to the rear brakes will stop. Moreover, each position of the car body relative to the rear axle will correspond to a certain limiting fluid pressure in the rear brake mechanisms.

Consequently, each value of the load on the rear wheels of the car during braking corresponds to a certain braking torque. This is necessary to reduce the likelihood of skidding the rear wheels when braking the car.

At the end of braking, when the rear of the car body is lowered, the force acting on the piston rod from the torsion bar 11 will increase. The pressure regulator piston will take its original position, and through the resulting gaps, cavities I and II will connect to each other, and the wheel brake cylinders of the rear brakes will connect to the main brake cylinder.

Parking brake system

The parking brake system acts on the rear wheels of the car and is driven from the lever by the driver's hand.

The parking brake system includes rear brake mechanisms and a mechanical drive.

mechanical drive (pic. 51) includes: hand lever 3, front cable 2, guide 9, rear cable 14, spreader arms 13 and spacers 12.



The lever 3 is hinged on the bracket 7, which is mounted on the floor of the car body. When the lever is moved upwards, the force from it is transmitted through the lever 8, the front cable 2, the guide 9 and the rear cable 14 to the expansion levers 13 and spacer bars 12 and from them to the brake pads of the rear brake mechanisms. Lever 3 is fixed in a predetermined position by a latch, which is constantly pressed against the toothed sector by spring 5 through rod 6. The latch is released by pressing button 4. Spring 11 ensures that the front and rear cables return to their original position when lever 3 of the parking brake system is released.