Shock absorbers come in different designs.
Two-pipe hydraulic - the most common design, when two cylinders are located one inside the other and filled with oil.
The inner cylinder contains a piston and valves through which the cavities outside and inside the cylinder communicate with each other. When a load occurs on the cylinder rod, the piston presses on the oil and forces it to flow into the strained cylinder, dissipating the energy. These shock absorbers have the softest operating characteristics, however, at high temperatures and increased loads, the oil in hydraulic shock absorbers can foam, which will greatly affect its operation.
In single-tube gas-filled shock absorbers, the lower part of the working cylinder is filled with gas (nitrogen) under high pressure.
Oil and gas are separated by a floating spacer (piston) and do not mix, which allows maintaining stable characteristics throughout the entire range of suspension travel and temperature. These shock absorbers work in the same way as twin-tube hydraulic ones, only the role of the outer cylinder is filled with nitrogen, which is compressed under load, compensating for the volume of displaced oil. Gas pressure not only prevents oil foaming and reduces shock absorber response time, but such shock absorbers are also more rigid and durable.
Twin-tube gas-filled shock absorbers - similar in design to hydraulic ones, only here the upper part of the outer cylinder is filled with nitrogen at low pressure (about 5 bar) pressure.
This design combines the strength and reliability of a hydraulic shock absorber with the advantages of a gas-filled one and is well suited for MacPherson front suspension.
Under constant loads, shock absorbers wear out quickly, the seals are damaged, scratches and traces of corrosion appear on the surface of the rod, which also negatively affects the operation of the shock absorber. The cause of shock absorber failure may be incorrect installation, loose mounting nuts, lack of a dust cover protecting the rod, and severe suspension breakdowns.
A faulty shock absorber affects the technical condition of the suspension, handling deteriorates, the density of contact between the wheel and the road decreases and, consequently, the braking distance increases, wear of almost all transmission and suspension components increases, tires wear unevenly, and discomfort and fatigue of the driver and passengers increases. The technical condition of the shock absorbers must be checked in accordance with the maintenance plan.
As for the choice of shock absorber, there is no clear answer. At the manufacturer's plant, shock absorbers are optimally selected for a specific car model based on multiple experiments and tests. Therefore, when replacing shock absorbers with softer or harder ones, be prepared for the car to behave differently on the road.
Stiffer shock absorbers hold the car well on a smooth road, improving handling at the expense of comfort and ride smoothness. However, on a road with potholes and bumps, such shock absorbers will not be able to constantly maintain the wheels' grip on the road, and the car will lose control. Softer hydraulic shock absorbers are suitable here, which will allow the wheel to flow around all the unevenness of the road and maintain good control and comfort.
Twin-tube hydraulic shock absorber
Monotube gas-filled shock absorber
Twin-tube gas-filled shock absorber
- 1 — shock absorber rod;
- 2 - outer cylinder;
- 3 - inner cylinder;
- 4 - oil;
- 5 - airspace;
- 6 - floating piston;
- 7 - high pressure gas (25 atm);
- 8 - gas under low pressure (5 atm).