Lesson 3/Learning Event 1
CONSTRUCTION AND OPERATION OF SHOCK ABSORBERS
When a vehicle is traveling on a level road and the wheels strike a bump, the spring is
compressed quickly. The compressed spring will attempt to return to its normal loaded
length and, in so doing, will rebound past its normal height, causing the body to be lifted.
The weight of the vehicle will then push the spring down below its normal loaded height.
This, in turn, causes the spring to rebound again. This bouncing process is repeated over
and over, a little less each time, until the up-and-down movement finally stops.
If bouncing is allowed to go uncontrolled, it will not only cause an uncomfortable ride
but will make handling of the vehicle very difficult. To overcome bouncing, assemblies
called shock absorbers are used. The main function of a shock absorber is to control
(regulate) the spring rebound.
A shock absorber that checks (resists) only the spring rebound is single-acting.
A shock absorber may also deaden (regulate) the compression of the spring by absorbing
part of the energy as the spring is depressed. A shock absorber that regulates
compression in addition to rebound is double-acting. Most shock absorbers used at the
present time are double-acting, because they permit the use of more flexible springs and
give a more comfortable ride.
Many types of shock absorbers have been used. Some were operated by friction and
spring tension. Those used at present are usually hydraulically operated. These depend
upon the resistance of a liquid flowing through small openings to check the action of the
spring.
A typical cam-operated (also known as indirect-acting) hydraulic shock absorber is
attached to the frame of the vehicle and contains a lever that pivots in the housing. The
lever is pinned to a link that is attached to the spring clamp assembly. Rubber grommets
are used at both ends of the link to prevent metal-to-metal contact and to provide
flexibility. Whenever the spring compresses and rebounds, the shock absorber lever is
activated.
One cam-operated shock absorber is made to check the rebound only (single-acting). The
housing (body) contains an oil-filled reservoir and cylinder. A cam-operated piston is
located in the cylinder. The cam is mounted on a shaft to which the shock absorber
lever is connected. The piston is held against the cam by a coil spring in the cylinder.
An intake/check valve, which permits oil to enter the cylinder from the outer reservoir, is
located in the piston head.
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