Open large image in new tab »
Pic. 28: 1. Brake disc. 2. Brake shoe. 3. Piston O-ring. 4. Wheel cylinder piston. 5. Front brake wheel cylinder. 6. Brake hose of the front brake drive circuit. 7. Finger of fastening of brake pads. 8. Piston stroke limit screw. 9. O-ring. 10. Resistant cup. 11. Rear brake drive piston. 12. O-ring spring. 13. Sleeve. 14. Master cylinder housing. 15. Front brake drive piston. 16. Seal. 17. Stock. 18. Vacuum valve. 19. Valve body return spring. 20. Valve body. 21. Diaphragm. 22. Vacuum valve body. 23. Cover of the vacuum booster housing. 24. Buffer rod. 25. Piston thrust plate. 26. Piston. 27. Vacuum booster valve. 28. Valve spring. 29. Valve return spring. 30. Air filter. 31. Valve lifter. 32. Pedal return spring. 33. Tip of the brake light switch. 34. Stoplight switch. 35. Plug of the pressure regulator housing. 36. Pressure regulator piston. 37. Housing sleeve. 38. Piston head seal. 39. Spring plate. 40. Piston spring. 41. Pressure regulator piston sealing ring. 42. Lever drive pressure regulator. 43. Rear brake pad. 44. Rear brake wheel cylinder piston. 45. Wheel cylinder piston seals. 46. thrust ring. 47. Brake pedal. A - Vacuum cavity. B - Channel connecting the vacuum cavity with the internal cavity of the valve. C - Channel connecting the internal cavity of the valve with the atmospheric cavity. D - Atmospheric cavity. K - A hose connecting the vacuum booster to the engine intake pipe. I - The pedal is not pressed. II - braking. III - Pressing the pedal is suspended. IV - Release.
The entire brake cycle consists of four positions of the brake pedal:
- I - pedal is not pressed (the system is disinhibited);
- II - pedal pressed (braking);
- III - pressing the pedal is suspended (braking with constant braking torque);
- IV - pedal released (disinhibition).
I. When the system is disengaged and the brake pedal under the action of the spring 32 is pulled all the way to the stoplight switch, then the pusher 31 with the piston 26 of the vacuum booster is pulled along with the pedal. The body 20 of the valve and the stem 17 are pressed by the spring 19 to the rearmost position. In this position, a gap is formed between the valve head 27 and the valve seat, as the piston 26 depresses the valve from the seat. The vacuum cavity A through channel B, the gap between the seat and the valve and further through channel C communicates with the atmospheric cavity D. Therefore, when the engine is running, the vacuum from the engine intake pipe through valve 18 is transmitted to cavity A and through channels and gaps to cavity O.
The pistons 11 and 15 of the main cylinder under the action of the return springs are pressed into the rear extreme position until they stop against the locking screws 8. In this position, the spacer sleeves 13, resting against the screws 8, press the sealing rings 9 from the end of the piston groove and through the gaps formed, the working cavities of the cylinder communicate with hydraulic cylinder reservoir and high pressure pipelines. Thus, there is no pressure in the brake actuator. Therefore, the pistons 4 under the action of elastic deformation of the sealing rings 3 are retracted into the cylinders and do not exert pressure on the brake pads of the front brakes, which will be in light contact with the surface of the brake disc.
When the car is moving without braking, that is, when there is no pressure in the hydraulic drive, the piston 36 under the action of the spring 40 and the torsion lever 42 is raised up until it stops in the plug 35. Therefore, the body cavities above and below the piston head are freely communicated.
This opens the free passage of fluid to the rear brake wheel cylinders. But since there is no pressure in the entire brake drive, the brake shoes 43 are pressed out of the drums, and the pistons 44 are pushed inside the wheel cylinder until the crackers stop against the shoulders of the thrust rings 46.
II. When braking, when the driver presses the brake pedal, the pusher 31 moves the piston 26. Following the piston, the valve 27 moves under the action of the spring 28 until it stops against the seat of the valve body. When the saddle overlaps, cavities A and B are separated. With further movement of the piston 26, a gap is formed between it and the shoulder of the valve 27, through which the cavity O communicates with the atmosphere. Outside air enters cavity B through the air filter 30, through the gap between the pusher and the valve, and then through channel C. Atmospheric air creates pressure on diaphragm 21. Due to the pressure difference in cavities A and D, as well as the force on the brake pedal, the body valve moves along with the rod 17, which in turn acts on the piston 15 of the master cylinder. The force acting on the valve body depends on the degree of vacuum in the engine intake pipe and on the force applied to the brake pedal.
When the piston 15 moves, the spacer sleeve 13 moves away from the locking screw 8 and the sealing ring 9 is pressed by the spring 12 against the end face of the piston groove. Thus, the compensation gap is blocked and the cavities of the cylinder and the tank are separated. Therefore, with further movement of the piston 15, fluid pressure is created in the working cavity of the front brake drive, which is transmitted through pipelines and hoses to the wheel cylinders of the front brakes. It also affects the floating piston 11, which, moving, creates pressure in the rear brake drive. Under increasing fluid pressure in the working cavities, the front sealing rings of the pistons expand and begin to fit more closely to the surface of the cylinder and to the end of the grooves, improving the sealing of the pistons in the cylinder.
Under fluid pressure, pistons 4 and 44 of the wheel cylinders of the front and rear brakes are extended, pressing the pads against the brake disc 1 and against the drum. The created braking moments slow down the rotation of the front and rear wheels. In this case, the load is redistributed along the axes of the car: the load on the front axle increases, on the rear axle it decreases. This causes the rear of the body to rise, i.e. the distance between the rear axle beam and the body increases. In this case, the short arm of the lever 42 is lowered, and the piston 36 of the pressure regulator under the pressure of the liquid begins to lower, compressing the spring 40.
At the moment of full braking, the maximum movement of the load from the rear axle to the front axle and the largest body lift occur. The grip of the wheels with the road is deteriorating, the pressure of the torsion lever 42 on the piston 36 is reduced. Due to the larger end area of the piston head, the pressure force P2 fluid lowers the piston down until the head touches the seal 38. Further flow of fluid to the wheel cylinders of the rear brakes stops, that is, the braking torque on the rear wheels does not increase, despite the strong pressure on the brake pedal and a further increase in pressure. Therefore, the rear wheels do not block and do not the car is skidding.
III. If, during braking, the driver stops pressing the pedal, but without removing his foot leaves it pressed in some position, then the vacuum booster body will move forward under atmospheric air pressure by the amount of the gap between the plate 25 and the piston groove, that is, it will move away from the valve. The released valve, moving, will reach the fixed piston and block the air supply to cavity D, and the excess air in cavity D will pass into the vacuum cavity A through the gap formed between the seat and valve 27 and channel B. The pressure in both cavities will equalize and the servo action of the amplifier will stop. At some point, a constant pressure is established in the brake drive circuits, and a constant braking torque is established on the wheels.
IV. When the brake pedal is released, it returns to its original position under the action of the return spring 32, dragging the pusher 31 and the piston 26 with it. and the communication of cavities A and B occurs, that is, the pressure in both cavities is equalized; under the action of the spring 19, the valve body with the stem returns to its original position, stopping the pressure on the piston 15 of the main cylinder.
Pistons 11 and 15, under the force of the return springs, are pressed to the extreme position and abut against the locking screws 8. The spacer sleeves 13 remove the sealing rings 9 from the end of the grooves and, through the formed gap, the working cavities of the master cylinder communicate with the cavities of the hydraulic cylinder reservoir. Pistons 4 of the front brake are retracted from the pads due to the elasticity of the sealing rings 3, and the pistons 44 of the rear brake are reduced by the reduction of the coupling springs to a gap of 1.4-1.6 mm between the crackers. and shoulder of the thrust ring 46.
If the rear brake drive circuit fails, due to its leakage, the piston 11 moves under fluid pressure until it stops in the master cylinder plug, after which the pressure in the front brake drive circuit begins to increase. Due to the free movement of the piston 11, the free travel of the brake pedal increases and only the front brake drive is active.
When the front brake drive circuit fails, piston 15 moves forward until it stops against piston 11, after which the rear brake drive circuit begins to operate. The brake pedal free play is also increased.
It should be remembered that when increasing the free play of the brake pedal, it is not recommended to repeatedly press the pedal, as this will not accelerate braking, but rather lengthen the brake response time. Continue depressing the pedal all the way down and, if necessary, apply the parking brake.
If any brake circuit is damaged, the fluid level control lamp lights up, signaling a drop in the fluid level in the reservoir.
The parking brake system, through a mechanical drive, acts on the brake mechanisms of the rear wheels. When applying the lever 47 (see fig. 27) up, after selecting the free play of the lever, equal to 3-4 clicks, the drive cable is tensioned and the force is transmitted to the levers 21 (see fig. 26) manual drive pads. When the lever 22 is turned on the pin 23, the force is first transmitted through the expansion bar 37 to the front brake shoe until it is completely pressed against the drum. After that, the lever 22 moves relative to the point of contact with the expander bar, and its upper arm presses the other shoe against the drum. At the same time, the control lamp on the instrument cluster lights up with a red flashing light, since the lever stop moves away from the lamp switch rod, and the circuit closes.