Automotive Suspension Systems

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Automotive SuspensionSystems
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The purpose of the suspension is to provide the
vehicle with the following1. A smooth ride2.
Accurate steering3. Responsive handling4.
Support the weight of a vehicle5. Maintain
acceptable tire wear
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FRAME CONSTRUCTIONThe frame of a vehicle
supports all the running gear of the vehicle,
including the engine, transmission, rear axle
assembly (if rear-wheel drive), and all
suspension components.There are many terms used
to label or describe the frame of a vehicle,
including the following.
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Ladder Frame A ladder frame is a common name
for a type of perimeter frame where the
transverse (lateral) connecting members are
straight across.
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Perimeter Frame A perimeter frame consists of
welded or riveted frame members around the entire
perimeter of the body.
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Stub-Type FramesA stub frame is a partial frame
often used on unit-body vehicles to support the
power train and suspension components. It is also
called a cradle on many front-wheel-drive
vehicles.
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Unit-Body ConstructionUnit-body construction
(sometimes called unibody) is a design that
combines the body with the structure of the
frame. The body supports the engine and driveline
components, as well as the suspension and
steering components.
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The area separating the engine compartment from
the passenger compartment is called the bulkhead.
The height and location of this bulkhead panel to
a large degree determines the shape of the rest
of the vehicle.
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The track of a vehicle is the distance between
the wheels, as viewed from the front or rear. A
wide-track vehicle is a vehicle with a wide wheel
stance this increases the stability of the
vehicle, especially when cornering. The
wheelbase of a vehicle is the distance between
the center of the front wheel and the center of
the rear wheel, as viewed from the side.
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UNSPRUNG WEIGHTA suspension system has to be
designed to allow the wheels to move up and down
quickly over bumps and dips without affecting the
entire weight of the car or truck. This weight
is called unsprung weight. For best handling and
ride, the unsprung weight should be kept as low
as possible. Sprung weight is the term used to
identify the weight of the car or truck, which
does not move up and down and is supported or
sprung by the suspension.
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TYPES OF SUSPENSIONSEarly suspension systems on
old horse wagons, buggies, and older vehicles
used a solid axle for front and rear wheels.
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Most vehicles today use a separate control
arm-type of suspension for each front wheel which
allows for movement of one front wheel without
affecting the other front wheel. This type of
suspension is called independent front
suspension.
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SpringsA suspension spring serves two purposes.
First, it acts as a buffer between the
suspension and frame to absorb vertical wheel and
suspension movement without passing it on to the
frame. Second, each spring transfers part of the
vehicle weight to the suspension component it
rests on, which transfers it to the wheels.
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Spring Materials. Most springs are made of a
tempered steel alloy known as spring steel,
usually chrome silicon or chrome-vanadium alloy.
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COIL SPRINGSCoil springs are made of special
round spring steel wrapped in a helix shape. The
strength and handling characteristics of a coil
spring depend on the following.1. Coil
diameter2. Number of coils3. Height of
spring4. Diameter of the steel coil that forms
the spring
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The larger the diameter of the steel, the
stiffer the spring. The shorter the height of
the spring, the stiffer the spring. The fewer
the coils, the stiffer the spring.
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Springs are designed to provide desired ride and
handling and come in a variety of spring ends.
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Spring Rate Spring rate, also called
deflection rate, is a value that reflects how
much weight it takes to compress a spring a
certain amount.
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A constant-rate spring continues to compress at
the same rate throughout its complete range of
deflection.
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A variable-rate spring may compress one inch
under a 100-pound load, but only compress an
additional half an inch under a 200-pound load.
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Before a spring is installed on a vehicle or any
load is placed on it, it is at its uncompressed
length, or free length. Once installed, the
weight of the corner of the vehicle resting on
the spring is called its static load.
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Coil Spring MountingCoil springs are usually
installed in a spring pocket or spring seat. Hard
rubber or plastic cushions or insulators are
usually mounted between the coil spring and the
spring seat.
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Spring CoatingsAll springs are painted or
coated with epoxy to help prevent breakage. A
scratch, nick or pit caused by corrosion can
cause a stress riser that can lead to spring
failure.
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Instead of cutting springs to lower a vehicle,
there are several methods available that are
preferred if the vehicle must be lowered1.
replacement springs2. replacement spindles
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LEAF SPRINGSLeaf springs are constructed of one
or more strips of long, narrow spring steel.
These metal strips, called leaves, are assembled
with plastic or synthetic rubber insulators
between the leaves, allowing freedom of movement
during spring operation.
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The ends of the spring are rolled or looped to
form eyes. Rubber bushings are installed in the
eyes of the spring and act as noise and vibration
insulators.
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The leaves are held together by a center bolt,
also called a centering pin.
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One end of a leaf spring is mounted to a hanger
with a bolt and rubber bushings directly attached
to the frame. The other end of the leaf spring is
attached to the frame with movable mounting
hangers called shackles.
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Rebound or spring alignment clips help prevent
the leaves from separating whenever the leaf
spring is rebounding from hitting a bump or rise
in the roadway.
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Single leaf steel springs, called mono leaf, are
used on some vehicles. A single or mono leaf
spring is usually tapered to produce a variable
spring rate.
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To provide additional load-carrying capacity,
especially on trucks and vans, auxiliary or
helper leaves are commonly used.
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Composite Leaf SpringsFiberglass-reinforced
epoxy plastic leaf springs have been used on
production vehicles. Using 70 fiberglass with
30 epoxy composite.Leaf spring rate increases
when the thickness increases, and decreases as
the length increases.
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TORSION BARSA torsion bar is a spring which is
a long, round, hardened steel bar similar to a
coil spring except for a straight bar.
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One end is attached to the lower control arm of a
front suspension and the other end to the frame.
When the wheels hit a bump, the bar twists and
then untwists.
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SUSPENSION PRINCIPLES1. Transverse (or
side-to-side) wheel support.Transverse links are
also called lateral links.
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2. Longitudinal (front-to-back) wheel
support.Some suspension designs use an
additional member to control forward-back
movement.
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STEERING KNUCKLESA steering knuckle is hard to
classify either as part of the suspension or as
part of the wheel. A knuckle serves two
purposesTo join the suspension to the wheel To
provide pivot points between the suspension and
wheel
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The only knuckle that uses a kingpin is a
steering knuckle on an I-beam or twin I-beam
front suspension. The steering axis is the
vertical center of the kingpin.
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CONTROL ARMSA control arm is a suspension link
that connects a knuckle or wheel flange to the
frame.
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BALL JOINTSBall joints are actually
ball-and-socket joints, similar to the joints in
a person's shoulder. Ball joints allow the front
wheels to move up and down, as well as side to
side (for steering).
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If the coil spring is attached to the top of the
upper control arm, then the upper ball joint is
carrying the weight of the vehicle and is called
the load-carrying ball joint. The lower ball
joint is called the nonload carrying or follower
ball joint.
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If the coil spring is attached to the lower
control arm, then the lower ball joint is the
load-carrying ball joint and the upper joint is
the follower ball joint.
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Ball Joint DesignThere are two basic designs of
ball joints compression loaded and tension
loaded.
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A ball joint that does not support the weight of
the vehicle and acts as a suspension pivot is
often called a follower ball joint or a friction
ball joint.
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STRUT RODSSome vehicles are equipped with round
steel rods which are attached between the lower
control arm at one end and the frame of the
vehicle with rubber bushings, called strut rod
bushings, at the other end.
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Strut rods are also called tension or compression
rods or simply TC rods. Some vehicle
manufacturers call the strut rod a drag rod
because it was attached in front of the wheels,
and therefore acted on the lower control arm as
if to drag the wheels behind their attachment
points.
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If a strut rod has a nut on both sides of the
bushings, then the strut rod is used to adjust
caster.
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STABILIZER BARSMost cars and trucks are
equipped with a stabilizer bar on the front
suspension, which is a round, hardened steel bar
(usually SAE 4560 or 4340 steel) attached to both
lower control arms with bolts and rubber bushing
washers called stabilizer bar bushings.
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A stabilizer bar is also called an anti-sway bar
(sway bar) or anti-roll bar (roll bar). A
stabilizer bar operates by twisting the bar if
one side of the vehicle moves up or down in
relation to the other side, such as during
cornering, hitting bumps, or driving over uneven
road surfaces.
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Stabilizer links connect the ends of the
stabilizer bar to the lower control arm.
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SHOCK ABSORBERSShock absorbers are used on all
conventional suspension systems to dampen and
control the motion of the vehicle's springs.
Without shock absorbers (dampers), the vehicle
would continue to bounce after hitting bumps.
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The major purpose of any shock or strut is to
control ride and handling. Standard shock
absorbers do not support the weight of a vehicle.
The springs support the weight of the vehicle
the shock absorbers control the actions and
reactions of the springs. Shock absorbers are
also called dampers.
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As a wheel rolls over a bump, the wheel moves
toward the body and compresses the spring(s) of
the vehicle. As the spring compresses, it stores
energy. The spring then releases this stored
energy, causing the body of the vehicle to rise
(rebound).
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Shock Absorber OperationThe hydraulic shock
absorber operates on the principle of fluid being
forced through a small opening (orifice).
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Gas-Charged ShocksMost shock absorbers on new
vehicles are gas charged. Pressurizing the oil
inside the shock absorber helps smooth the ride
over rough roads. This pressure helps prevent air
pockets from forming in the shock absorber oil as
it passes through the small passages in the
shock.
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Some gas-charged shock absorbers use a single
tube that contains two pistons that separate the
high-pressure gas from the working fluid. Single
tube shocks are also called monotube or DeCarbon
after the French inventor of the principle and
manufacturer of suspension components.
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Remote Reservoir ShocksRemote reservoir shock
absorbers are units designed for heavy-duty use
that use a separate container for the working
fluid.
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Air Shocks/StrutsAir-inflatable shock absorbers
or struts are used in the rear of vehicles to
provide proper vehicle ride height while carrying
heavy loads.
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Air-inflatable shocks are standard shock
absorbers with an air chamber with a rubber bag
built into the dust cover (top) of the shock.
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Air SpringsSome electronically controlled
suspension systems use air springs. A basic air
spring consists of a rubber air chamber,
generally closed at the bottom by a piston fitted
into a control arm, or by a strut shock absorber.
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Some air springs are in effect auxiliary springs
inside a coil-spring strut. In these designs,
the coil spring supports the weight of the
vehicle, while the air spring raises or lowers
the body to adjust ride height according to load.
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Coil-Over ShocksA coil-over shock absorber uses
the force of an external coil spring to boost the
performance of the basic shock absorber.
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STRUTSA strut is a sturdy shock absorber that
is also a structural component of the suspension.
A strut is a suspension link as well as a shock
absorber.
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MacPherson Struts The MacPherson strut, which
is named after Earle S. MacPherson, who developed
the suspension design in the late 1940s and
patented it in 1953, is the most commonly used
type.
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Modified Struts Unlike a MacPherson unit, a
modified strut does not include a spring as part
of the assembly and is used in the front on some
vehicles and on the rear of others.
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BUMP STOPSAll suspension systems have a limit
of travel. If the vehicle hits a large bump in
the road, the wheels are forced upward toward the
vehicle with tremendous force.
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Instead of allowing the metal components of the
suspension to hit the frame or body of the
vehicle, a rubber or foam bumper is used to
absorb and isolate the suspension from the frame
or body.These bumpers are called bump stops,
suspension bumpers, strike-out bumpers, or jounce
bumpers. Jounce means jolt.
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SUMMARY1. The lighter the wheel/tire
combination, the lower the unsprung weight and
the better the ride and handling of the
vehicle.2. All springs including the coil,
leaf, and torsion bar types share Hooke's Law,
which states that the force exerted by the spring
is directly proportional to the amount the spring
is deflected.3. All springs are similar to
torsion bars. As the torsion bar becomes longer
or smaller in diameter, it becomes easier to
twist. If a coil spring is cut, the remaining
spring is shorter, yet stiffer.4. Ball joints
attach to control arms and allow the front wheels
to move up and down, as well as turn.5.
Suspension designs include a straight or
solid-axle, two-control-arm-type called an SLA or
a MacPherson strut.6. All shock absorbers
dampen the motion of the suspension to control
ride and handling.
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REVIEW QUESTIONS1. List the types of
suspensions and name their component parts.3.
Describe the purpose and function of a stabilizer
bar.3. Explain the difference between a
load-carrying and a friction ball joint.