By David Wu

When a spring is compressed and then released it will oscillate for a period of time before coming to rest. Applied to a vehicle this action will cause a most uncomfortable ride.

 

The purpose of a shock absorber is to absorb the energy stored in the spring and so reduce the time that the vehicle is bouncing.

 

Most modern shock absorbers are hydraulic: they dissipate the energy by pumping oil through small orifices.

 

A shock absorber includes a tubular cylinder filled with fluid and a piston attached to a metal rod. The piston is not solid, but contains two valves through which the shock absorber fluid can travel as the piston moves up or down.

 

When the wheel hits a bump or drops into a hole, the shock absorber piston moves through fluid. The difficulty of forcing the piston to move through the fluid creates the "damping" action that helps to stop the springs from bouncing.

 

Typically, one shock absorber is used for each wheel. Shock absorbers are mounted through the center of a coil spring, beside the spring, or in any number of locations. Shock absorber placement and method of attachment depend on suspension design.

 

In an electronically controlled suspension system, solenoids can position metering needles within shock absorber passages to allow more or less fluid to pass through the plunger and/or other passages. In addition, air pressure can be applied to the fluid within the shock absorber to "pump up", or raise, the height of the vehicle.

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