Open large image in new tab »
Pic. 24: Shock absorbers: 1. Bottom head (eye) shock absorber. 2. Compression valve body. 3. Compression valve discs. 4. Throttle disc compression valve. 5. Compression valve spring. 6. Clip of the compression valve. 7. Compression valve plate. 8. Recoil valve nut. 9. Recoil valve spring. 10. Shock absorber piston. 11. Recoil valve plate. 12. Recoil valve discs. 13. Piston ring. 14. Recoil valve nut washer. 15. Throttle disk of the recoil valve. 16. Bypass valve plate. 17. Bypass valve spring. 18. Restrictive plate. 19. Reservoir. 20. Stock. 21. Cylinder. 22. Casing. 23. Stem guide bushing. 24. Tank O-ring. 25. Rod gland holder. 26. Stem seal. 27. Gasket of a protective ring of a rod. 28. Stem protection ring. 29. Tank nut. 30. Upper shock absorber head. 31. Nut for fastening the upper shock absorber of the front suspension. 32. Spring washer. 33. Pillow washer. 34. Pillows. 35. Spacer sleeve. 36. Front suspension shock absorber casing. 37. Buffer rod. 38. Rubber-metal hinge. I - Scheme of the shock absorber. II - Compression stroke. III - Recoil course.
To dampen body vibrations, double-acting hydraulic telescopic shock absorbers are installed on the suspensions, which create resistance to body vibrations both during compression and during recoil.
The shock absorbers of the front and rear suspensions differ in size, the method of attaching the upper part, the presence of a buffer 37 at the front shock absorber, which limits the length of the rod during recoil and thereby prevents the front wheels from moving excessively down when driving on very uneven roads. In addition, shock absorbers differ in performance parameters. However, the main parts of the front shock absorber are the same as those of the rear shock absorber, so only the rear shock absorber will be considered in the following.
The shock absorber consists of the following main parts: a reservoir with a head 1, a working cylinder, a compression valve and a rod assembly with a piston and valves, a guide sleeve, a nut, seals and a casing. The volume for the working fluid is the cylinder 21 and the reservoir 19, made of a pipe. In the lower part of the tank, the bottom is rolled, on which the compression valve rests. A thread for a nut 29 is cut in the upper part of the tank. The lower head of the shock absorber is welded to the bottom of the tank from the outside. The compression valve consists of body 2, discs 3 and 4, disc 7, spring 5 and clip 6.
The compression valve body is ceramic-metal. In its upper part, a socket with a chamfer is machined, covered by disks, which are pressed to the socket by spring 5 through plate 7. The upper end of the spring abuts against holder 6, which is put on the cylindrical belt of the valve body. To ensure the passage of fluid from reservoir 19 to cylinder 21 and vice versa, a cylindrical groove and four vertical grooves approximately the same depth as the groove are made in the lower part of the valve body. The same grooves are found in the upper part of the compression valve housing.
Discs 3 of the compression valve are flat, made of steel tape 0.15 mm thick, have holes in the center for the passage of fluid. In the central hole of the disk 4 there is a cutout through which the liquid is throttled at a low speed of the piston 10. The plate 7 has a cylindrical protrusion in the lower central part, which overlaps the central hole of the disks 3 and 4, but does not cover the throttling cutout. When assembled, a gap is formed between the plate 7 and the disk 4 for the passage of liquid. For the same purpose, four through holes are made along the outer diameter of the plate.
The clip 6 has a flare and a cylindrical belt, on which the cylinder 21 is tightly fitted, which provides the necessary tightness between the compression valve and the cylinder. On the stamped surface of the holder, there are six lateral and one central holes for the passage of liquid.
Cylinder 21 has a rod with piston 10, on which a bypass valve and a return valve are mounted. The piston has vertical channels arranged in two circles; between themselves, the channels of each circle are connected by an annular groove. The channels located closer to the center of the piston are blocked from below by disks 15 and 12 of the recoil valve, and from above, farther from the center by the plate 16 of the bypass valve, pressed by the spring 17. The stroke of the plate is limited by the stop of the spring against the plate 18. The piston is sealed in the cylinder by ring 13.
The recoil valve disks are pressed against the lower end part of the piston by the spring 9 through the plate 11. In this case, the spring presses the outer part of the disks, and the inner part of the disks 15 and 12 is tightly pressed against the piston by the nut 8 screwed onto the threaded end of the rod. To protect the recoil valve discs from damage and stable operation of the valve, a washer 14 is installed between the discs and the nut. The throttle disc 15 of the recoil valve has six cutouts along the outer diameter for the passage of fluid with a smooth recoil stroke.
For directional movement of the rod 20 relative to the cylinder is a ceramic-metal guide sleeve 23, mounted in a cylindrical belt in the calibrated bore of the cylinder. The sleeve has an inclined channel for draining the working fluid that has passed through the gap between the stem and the guide sleeve back into the reservoir. An oil seal 26 made of petrol- and oil-resistant rubber is installed on top of the bushing socket. The lips of the stuffing box cover the chromed surface of the rod, preventing fluid from escaping from the shock absorber. The stuffing box, together with the ring 24, which seals the gap between the guide bushing 23 and the tank 19, is pressed by the clip 25. Between the clip and the nut 29, a ceramic-metal protective ring 28 and a rubber gasket 27 are installed. The protective ring removes dirt from the rod during compression. Nut 29 has four holes for wrench pins for disassembly (assembly) shock absorber.
Shock absorber operation
The principle of operation of the shock absorber is based on creating increased resistance to body swaying due to the forced flow of fluid through small flow sections in the valves.
Compression stroke
With this stroke, when the wheels of the car move up, the shock absorber is compressed, i.e. the piston goes down and displaces liquid from the lower part of the cylinder, part of which, overcoming the resistance of the flat spring of the bypass valve, flows from the under-piston space to the over-piston space. All the displaced liquid cannot pass in this way, since the inserted rod occupies part of the volume released by the piston, therefore, part of the liquid, bending the inner edges of the compression valve disks, flows from the cylinder to the reservoir.
With a smooth stroke of the rod, the force from the fluid pressure will not be sufficient to press the inner edges of the discs from the plate, and the fluid will pass into the tank through the cutout of the throttle disc 4.
Recoil stroke
In this course, the wheels of the car, under the action of the elastic elements of the suspension, go down, and the shock absorber is stretched, i.e., the piston moves up. In this case, fluid pressure is created above the piston, and a vacuum is created below the piston. The liquid from the over-piston space, overcoming the resistance of the spring, bends the outer edges of the recoil valve disks and flows into the lower part of the cylinder. In addition, due to rarefaction, part of the liquid from the reservoir, bending the outer edges of the compression valve disks away from the valve body, fills the lower part of the cylinder.
At a low piston speed, when the fluid pressure is insufficient to squeeze the recoil valve discs, the fluid will be throttled through the side cutouts of the throttle disc 15, creating resistance to the recoil stroke.
The condition of the shock absorbers affects not only the smoothness of the car, but also the safety of its movement and the condition of the supporting parts of the car (racks, mudguards, spars). With faulty shock absorbers, "breakdowns" suspensions, which leads to cracks in the body drains and to the breakage of the shock absorber mounting pins, and the rocking of the body tires the driver. Therefore, it is important to keep the shock absorbers in working condition.
The condition of the shock absorbers can be checked in the following way:
- install the car on a flyover or inspection ditch and swing it by the front or rear bumper, applying a force of 400-500 N (40-50 kgf). With serviceable shock absorbers, the number of body vibrations should not exceed three;
- Disconnect the lower mounting point of the shock absorber and pump it by hand. A serviceable shock absorber pumps smoothly, without dips and jamming, with little resistance. In this case, the resistance during the rebound stroke should be greater than during the compression stroke. The maximum force during the compression stroke of the front shock absorbers is approximately the same, and during the recoil stroke, the front shock absorbers are 1.2 times more than the rear shock absorbers.