A Shock Absorber is any of several mechanical devices for absorbing the energy of sudden impacts. Spring-type shock absorbers, which are often made of rubber, generally are used to protect delicate instruments from direct impacts. Hydraulic shock absorbers, which basically consist of a piston and cylinder and a fluid such as oil, are used in airplane landing-gear systems and in automobiles.
An automobile has two front and two rear shock absorbers. The two front ones are mounted between the vehicle frame and the lower control arm, and the two rear ones are mounted between the vehicle frame and the axle housing. A typical hydraulic shock absorber used in an automobile is shown in the accompanying diagram. The shock absorber opposes the compression of a spring in the suspension system when the automobile hits a bump, and it opposes the rebound of the spring after the automobile has passed over the bump. This damping action on the oscillation of the suspension-system spring provides a smooth ride and helps keep the wheel firmly on the road at all speeds.
On a bump stroke, the piston rod and piston travel downward in the cylinder, forcing oil through the foot-valve assembly and into the oil reservoir. The controlled resistance that the oil encounters in passing through the foot-valve assembly produces the bump-damping force of the shock absorber.. On a rebound stroke, the piston rod and piston travel upward in the cylinder, forcing the oil to escape downward through small. passageways in the piston assembly. The controlled resistance that the oil encounters in flowing through these passageways produces the rebounding damping force of the shock absorber.