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Suspension Systems - 1

• Topics covered in this presentation
• Basic Suspension System
• Spring Types
• Suspension System Construction

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Basic Suspension System
The primary purpose of a suspension system is to
support the weight of the vehicle and give a
smooth ride.
It is desirable that it should also

• allow rapid cornering without body roll when the
  car leans to one side.
• keep tires in firm contact with the road at all
  times and conditions.
• prevent body squat (tilting down at rear) when
  accelerating.
• prevent body dive (tilting down at front) when
  braking.
• allow front wheels to turn for steering.
• keep the wheels vertical and in correct alignment
  at all times.

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Elementary Suspension System
In a modern car, the typical suspension
components are
Coil spring
A control arm that pivots on the vehicle frame.
Shock absorber
The steering knuckle is ball-jointed to the
control arm to allow for vertical and horizontal
movements.
Steering knuckle
Control arm
This simple example has a coil spring and
built-in shock absorber.
Frame
All of the components are attached to the frame.
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Independent Suspension
A solid axle tilts with road bumps.
Solid axle
This causes both wheels to be tilted.
Independent suspension allows one wheel to move
up or down without appreciably affecting the
other.
Independent Suspension
The design of the control arm keeps the wheel
upright.
This is the preferred system for most modern cars.
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Coil Spring
There are four main types of springs in common
use

• Coil Spring
• Leaf Spring
• Torsion Bar
• Air Spring

Coil spring
Coil Spring
This consists of a spring-steel rod wound into a
coil.
It is ideally suited to independent suspension.
This is the most common type of spring used by
modern vehicles.
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Leaf Spring
Flat plates of spring steel are bolted together.
The front end of the spring is bolted directly to
the frame.
A swinging shackle at the rear permits the length
of the spring to change when it is flexed.
U-bolts and plates clamp spring to axle housing.
This type used to be common but is now only used
on a few rear suspension systems.
Swinging shackle
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Torsion Bar
One end of the torsion bar is fixed to the
vehicle frame.
The other end of the torsion bar is attached to
the control arm so that it twists as the control
arm moves up or down.
A strut bar prevents front or rear movements of
the control arm.
When the control arm is moved by the suspension,
the twisting motion of the torsion bar resists
the movement.
Vehicle frame
Torsion bar
Control arm
Steering knuckle connects onto control arm
Strut bar
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Air Spring
This is normally a two-ply rubber cylinder filled
with compressed air.
It has similar rebound reaction to a coil spring.
The air spring is much lighter in weight,
compared with its steel sprung equivalent,
resulting in increased economy and an adjustable
controllable ride.
Rebound (expansion) allows the control arm to
move down when there are hollows in the road
surface.
This is especially adaptable to automatic
leveling systems.
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Control Arm
A control arm holds the steering knuckle, bearing
support or axle housing.
Bushings
The control arm is connected to the steering
knuckle by a ball joint.
Ball joint
Control arm bushings act as bearings.
The control arm is free to move up and down with
the suspension.
Control arm
Steering knuckle
Rear suspension control arms may have bushings at
both ends.
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Control Arm and Strut Rod
The picture below shows a typical independent
suspension front wheel unit.
Steering knuckle
Frame
The control arm is attached to a frame or cradle.
The other end of the control arm is attached to
the steering knuckle.
A strut rod prevents forward or backward movement
of the control arm.
Rubber bushes on both the control arm and the
strut rod soften the action and absorb shocks.
Control arm
Strut rod
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Ball Joints
Ball joint is short for ball-and-socket joint.
Upper pivot ball joint
Steering knuckle
Ball joints allow limited movement in all
directions.
Two pivots, one above and one below, keep the
wheel vertical.
Drive axle
A front wheel system is shown, including a
steering knuckle.
Hub
The drive axle must allow universal movement.
Lower pivot ball joint
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Shock Absorber
Top mount
The function of a shock absorber is to reduce
spring oscillations (up and down movements)
following a road shock.
The upper end (top mount) is attached to the
frame and the lower end (bottom mount) to the
suspension unit.
Dust cover
A piston and valve assembly moves in an
oil-filled cylinder. Movement is controlled by
the valve, rate-of-flow, restriction.
Oil cylinder
Piston and valve assembly
A pressurized gas chamber is sometimes added to
prevent air bubbles in the oil causing foaming.
Pressurized gas chamber
Bottom mount
The cylinder is enclosed in a dust cover.
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MacPherson Strut Shock Absorber
This is a combined coil spring and shock absorber
assembly.
The upper pivot is the strut mounting to the
frame.
A ball bearing mounting at the top allows
steering movements.
Bump stops or rebound bumpers prevent
metal-to-metal contact.
The shock absorber is inside the strut.
The lower spring seat is part of the shock
absorber body.
Metal strut tube houses shock absorber reservoir,
valve, pressure tube etc.
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Stabilizer (Sway) Bar
The purpose of the stabilizer bar is to prevent
excessive body leaning when turning.
Links both the lower control arms together.
When one end of the bar is deflected in either
direction (up or down), the bar tries to pull the
other side in the same direction, this has the
effect of stabilizing and controlling the
suspension.
Stabilizer bar
When cornering, the outside of the body tends to
drop, which twists the bar and limits the amount
of the sway.
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Track (Lateral Control) Bar
Support bracket
A track bar prevents side-to-side rear axle
movement when cornering.
Diagonal brace
Track bar
One end of the track bar is fastened to the axle,
the other end to the frame on the opposite side
of car.
Rear (solid) axle