If one of the circuits of the working brake system fails, the second circuit is used, which ensures that the car stops with sufficient efficiency.
The hydraulic drive includes a vacuum booster and a dual-circuit rear brake pressure regulator.
The parking brake system is driven by the rear wheel brakes.
Vacuum brake booster (pic. 8.1) diaphragm type works on the principle of pressure difference in the vacuum and atmospheric chambers, as a result of which an additional force is created on the piston of the main brake cylinder when the brake pedal is pressed. The vacuum chamber is connected to the receiver of the engine power system through a hose and a check valve, and the atmospheric chamber is connected to the atmosphere through a filter at the moment the brake pedal is pressed. When the brake pedal is released, the vacuum and atmospheric chambers communicate with each other through a special valve.
Brake pressure regulator regulates the pressure in the hydraulic drive of the brake mechanisms of the rear wheels, depending on the load on the rear axle of the car. The brake pressure regulator is included in both circuits of the brake system, and through it the brake fluid flows to both rear brake mechanisms.
Brake pressure regulator 1 (pic. 8.2) attached to the bracket 9 with two bolts 2 and 16. The front bolt 2 simultaneously fastens the fork bracket 3 of the lever 5 of the brake pressure regulator drive. On the pin of this bracket, a two-arm lever 5 is pivotally fixed with a pin 4. Its upper arm is connected to an elastic lever 10, the other end of which is pivotally connected through an earring 11 to the rear suspension arm bracket.
Bracket 3 together with lever 5 can be moved relative to the brake pressure regulator due to the oval holes for the fastening bolt. Thus, the force with which the lever 5 acts on the piston of the brake pressure regulator is regulated.
The brake pressure regulator has four chambers: A and D (pic. 8.3) connected to the master brake cylinder, IN - with the left WITH - with the right wheel cylinder of back brakes.
In the initial position of the brake pedal, piston 2 is pressed by lever 5 (see fig. 8.2) through the leaf spring 7 to the pusher 20 (see fig. 8.3), which, under the action of this force, is pressed against the seat 14 of the valve 18. In this case, the valve 18 is pressed from the seat and a gap is formed H, as well as the clearance TO between the piston head and seal 21. Through these chamber gaps A and D communicate with cameras IN and WITH.
When you press the brake pedal, the brake fluid through the gaps TO and H, as well as cameras IN and WITH enters the wheel cylinders of the brake mechanisms. With an increase in brake fluid pressure, the force on the piston increases, tending to push it out of the housing. When the force from the pressure of the brake fluid exceeds the force from the elastic lever, the piston begins to move out of the body, and after it, under the action of springs 12 and 17, the pusher 20 moves along with the sleeve 19 and rings 10. Clearance M increases, and gaps H and TO decrease. When the gap H is selected completely and valve 18 isolates the chamber D from the camera WITH, the pusher 20, together with the parts located on it, will stop moving after the piston. Now the chamber pressure WITH will vary depending on the pressure in the chamber IN. With a further increase in the effort on the brake pedal, the pressure in the chambers D, IN and A increases, the piston 2 continues to move out of the body, and the sleeve 19, together with the sealing rings 10 and the plate 11, under increasing pressure in the chamber IN shifts towards plug 16. Gap M starts to decrease. By reducing the volume of the chamber WITH the pressure in it, and hence in the brake drive, increases and will practically be equal to the pressure in the chamber IN. When the gap TO becomes zero, the pressure in the chamber IN, and hence in the chamber WITH will increase to a lesser extent than the pressure in the chamber A, due to the throttling of the brake fluid between the piston head and the seal 21. The relationship between the pressure values in the chambers IN and A is determined by the ratio of the difference between the areas of the head and the piston rod to the area of the head. With an increase in the load of the car, the elastic lever 10 is loaded more and the force from the lever 5 on the piston increases, i.e. the moment of contact between the piston head and the seal 21 is achieved with a higher pressure in the master brake cylinder. Thus, the effectiveness of the rear brakes increases with increasing load.
In the event of a brake circuit failure, the left front - right rear sealing rings 10 and sleeve 19 are under fluid pressure in the chamber IN will move towards plug 16 until plate 11 stops in seat 14. The pressure in the rear brake will be regulated by the part of the brake regulator, which includes piston 2 with seal 21 and bushing 7. The operation of this part of the brake regulator in case of failure of the named circuit is similar to that in a working system. The nature of the change in pressure at the outlet of the regulator is the same as with a working brake system.
In case of failure of the brake circuit, the right front - left rear, under the pressure of the brake fluid, the pusher 20 with the sleeve 19 and the sealing rings 10 moves towards the piston, pushing it out of the housing. Gap M increases, and the gap H decreases. When the valve 18 touches the seat 14, the pressure increase in the chamber WITH stops, i.e. The brake pressure regulator in this case works as a pressure limiter. However, the achieved pressure value is sufficient for reliable operation of the rear brake.
In case 1, a hole is made, closed by a plug 24. Leakage of brake fluid from under the plug when it is squeezed out indicates leakage of the rings 10.
Master brake cylinder (pic. 8.4) two-section, with a sequential arrangement of pistons. A tank is fixed on the body of the main brake cylinder, in the filler neck of which a brake fluid emergency level sensor is installed.
Pic. 8.4. Master brake cylinder: 1 - the body of the main brake cylinder; 2, 3 - pistons for driving the brake circuits; 4 - spacer washer; 5 - pusher
Front wheel brake disk, with automatic adjustment of the gap between the brake pads and the brake disc, with a floating caliper and a brake pad wear sensor. The clip is formed by the brake caliper 3 (pic. 8.5) and wheel cylinder 5, which are tightened with bolts. The movable bracket is bolted to the pins 10 installed in the holes of the guide 2 of the brake shoes. These holes are lubricated, rubber boots 9 are installed between the fingers and the guide of the brake pads. Brake pads 4 are pressed against the grooves of the guide by springs, of which the inner one is equipped with a wear sensor 7 of the brake pads.
Pic. 8.5. Front wheel brake: 1 - brake disc; 2 - brake pad guide; 3 - brake caliper; 4 - brake pads; 5 - cylinder; 6 - piston; 7 - pad wear indicator; 8 - sealing ring; 9 - protective cover of the guide pin; 10 - guide pin; 11 - protective cover
A piston 6 with a sealing ring 8 is installed in the cavity of the brake cylinder 5. Due to the elasticity of this ring, an optimal gap between the brake pads and the brake disc is maintained. Rear wheel brake (pic. 8.6) drum, with automatic adjustment of the gap between the shoes and the drum. The automatic clearance adjustment device is located in the wheel brake cylinder.
Pic. 8.6. Rear wheel brake: 1 - hub fastening nut; 2 - wheel hub; 3 - lower coupling spring of brake pads; 4 - brake shoe; 5 - guide spring; 6 - wheel brake cylinder; 7 - upper coupling spring; 8 - expanding bar; 9 - finger of the parking brake lever; 10 - parking brake drive lever; 11 - shield of the brake mechanism
Its main element is a split thrust ring 9 (pic. 8.7), installed on the piston 4 between the shoulder of the stop screw 10 and two crackers 8 with a gap of 1.25-1.65 mm.
Thrust rings 9 are inserted into the brake cylinder with an interference fit, providing a shear force of the ring along the cylinder mirror of at least 343 N (35 kgf), which exceeds the force on the piston from the coupling springs 3 and 7 (see fig. 8.6) brake pads.
When, due to wear of the brake linings, the gap of 1.25-1.65 mm is completely selected, the shoulder on the stop screw 10 (see fig. 8.7) presses against the shoulder of the ring 9, as a result of which the thrust ring will move after the piston by the amount of wear. With the cessation of braking, the pistons are shifted by the force of the coupling springs until the crackers stop against the collar of the thrust ring. Thus, the optimal clearance between the brake pads and the brake drum is automatically maintained.
Parking brake system with a mechanical drive acts on the brake mechanisms of the rear wheels. The parking brake drive consists of a lever 2 (pic. 8.8), adjusting rod 4, equalizer 5, cable 8, lever 10 (see fig. 8.6) manual drive of brake pads and expansion bar 8.
Emergency brake fluid level sensor mechanical type. Pavilion 2 (pic. 8.9) sensor with a seal 4 and base 3 with a reflector 6 are pressed by a clamping ring 5 to the end face of the tank neck.
A pusher 7 passes through the hole in the base, connected to the float 9 by means of a bushing 8. A movable contact 11 is located on the pusher, and fixed contacts 10 are located on the sensor housing. the contact falls on the fixed contacts and closes the circuit of the alarm lamp in the instrument cluster.
Pic. 8.9. Brake fluid emergency level sensor: 1 - protective cap; 2 - sensor housing; 3 - sensor base; 4 - sealing ring; 5 - clamping ring; 6 - reflector; 7 - pusher; 8 - bushing; 9 - float; 10 - fixed contacts; 11 - moving contact
Pic. 8.1. Vacuum brake booster: 1 - flange for fastening the tip; 2 - stock; 3 - diaphragm return spring; 4 - sealing ring of the flange of the main cylinder; 5 - main cylinder; 6 - amplifier pin; 7 - amplifier housing; 8 - diaphragm; 9 - housing cover of the vacuum booster; 10 - piston; 11 - protective cover of the valve body; 12 - pusher; 13 - pusher return spring; 14 - valve spring; 15 - valve; 16 - stock buffer; 17 - valve body; A - vacuum chamber; B - atmospheric chamber; С, D - channels
Pic. 8.2. Brake pressure regulator drive: 1 - pressure regulator; 2, 16 - bolts for fastening the brake pressure regulator; 3 - arm of the pressure regulator drive lever; 4 - pin; 5 - pressure regulator drive lever; 6 - axis of the pressure regulator drive lever; 7 - lever spring; 8 - body bracket; 9 - pressure regulator mounting bracket; 10 - elastic lever drive pressure regulator; 11 - earring; 12 - earring bracket; 13 - washer; 14 - retaining ring; 15 - bracket pin; A, B, C - holes
Pic. 8.3. Brake pressure regulator: 1 - pressure regulator housing; 2 - piston; 3 - protective cap; 4, 8 - retaining rings; 5 - piston sleeve; 6 - piston spring; 7 - housing sleeve; 9, 22 - support washers; 10 - pusher sealing rings; 11 - support plate; 12 - pusher bushing spring; 13 - valve seat sealing ring; 14 - valve seat; 15 - sealing gasket; 16 - cork; 17 - valve spring; 18 - valve; 19 - pusher bushing; 20 - pusher; 21 - piston head seal; 23 - piston rod seal; 24 - plug; A, D - chambers connected to the main cylinder; B, C - chambers connected to the wheel cylinders of the rear brakes; K, M, H - gaps
Pic. 8.7. Wheel brake cylinder: 1 - pad stop; 2 - protective cap; 3 - cylinder body; 4 - piston; 5 - sealant; 6 - support plate; - 7 - spring; 8 - crackers; 9 - thrust ring; 10 - stop screw; 11 - fitting; A - a slot on the thrust ring
Pic. 8.8. Parking brake drive: 1 - button for fixing the lever; 2 - parking brake drive lever; 3 - protective cover; 4 - thrust; 5 - cable equalizer; 6 - adjusting nut; 7 - locknut; 8 - cable; 9 - cable sheath