Lesson 3/Learning Event 1
TYPES OF SPRINGS
For a number of years, passenger vehicles have used coil-type springs in their suspension
systems. At first, they were used mainly in independent suspension of the front wheels.
At present, coil springs are widely used on both the front and rear of passenger vehicles
and some light trucks.
One military vehicle that uses coil-spring suspension at both front and rear is the 1/4-ton
truck M151.
Coil springs have wide application because they cost less to make, they are compact, and
they are effective. The main disadvantage is that excessive bouncing of the vehicle
results from their frictionless action, making shock absorbers necessary.
Coil springs are made of special steel rods, heated and wound in the shape of a spiral
coil. One end contacts the vehicle frame, and the other end contacts the axle or the
suspension device used. A rubber-like pad or insulator is used at the end of the spring
that contacts the frame. The insulator prevents vibrations from transferring from the
spring to the vehicle frame.
Another type of suspension spring used in tracklaying vehicles is the torsion bar. The
torsion bar is also being successfully used in some passenger cars and trucks. This
suspension spring consists of a long spring-steel bar. One end of the bar is secured to a
nonmovable mounting called an anchor. The other end is fastened to a suspension arm
or lever. When the lever arm is moved up, it twists the long torsion bar. The bar resists
the twisting and gives a spring action, always returning to its original position unless it is
overloaded. Torsion bars are usually made to take stress in one direction only and often
are marked by an arrow stamped into the metal to indicate the direction of stress.
Large wheeled vehicles are built to carry both heavy and light loads. Several methods
have been used to change the load rating of the spring suspension as the vehicle load is
changed. Auxiliary springs, often called secondary springs, are commonly used in
addition to the main springs for this purpose. The secondary spring is often secured to
the frame at its center with its end free. When the vehicle load is increased to a certain
amount, the main spring is compressed, bringing the free ends of the secondary spring
against the axle. Both springs now support the load, and their load ratings are added.
This arrangement permits the vehicle to carry heavy loads without compressing the main
spring too much.
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