chapter 67 suspension
TRANSCRIPT
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Publisher
The Goodheart-Willcox Co., Inc.Tinley Park, Illinois
by
Russell Krick
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Functions of a suspension system Basic suspension system Independent and nonindependent
suspension systems Understeer and oversteer Suspension system springs Suspension system construction
(14 Topics)
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Long-short arm suspension Torsion bar suspension MacPherson strut suspension Pickup truck suspension systems Rear suspension systems Suspension leveling systems Electronic suspension system Active suspension system
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Supports the weight of the vehicle Allows the wheels to move up and
down Allows rapid cornering without extreme
body roll Keeps the tires in firm contact with the
road
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Prevents excessive body squat when accelerating or heavily loaded
Prevents excessive body dive when braking
Allows the front wheels to turn left or right for steering
Helps keep the wheels in correct alignment
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Suspensions
Independent
Nonindependent
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Independent Suspension
Allows one wheel to move up and down with minimal effect on the other wheels
Each wheel is attached to its own suspension unit
Movement of one wheel does not cause direct movement of the wheel on the other side of the vehicle
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Nonindependent Suspension
Both left and right wheels are attached to the same solid axle
When one tire hits a bump in the road, its upward movement causes a slight upward tilt of the other wheel
Neither wheel is independent of the other
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Understeer
The vehicle is slow to respond to steering changes in a turn the rear tires retain traction the front tires may slip on the road
surface due to lack of downforce or other factors
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Oversteer The rear tires try to skid around
sideways in a sharp or hard turn the front tires retain traction
Suspension systems are designed to balance understeer and oversteer
Neutral steering is the result, where all four wheels have equal traction in turns
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Lateral Acceleration Amount of side force a vehicle can
achieve before its tires lose traction and skid in a high speed turn
Measured in units of gravity (g-force) Passenger cars might achieve 1.0 g Race cars might achieve 3.0 g
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Springs must jounce (compress) and rebound (extend) as a vehicle travels over bumps and holes in the road surface
Springs must support the weight of the vehicle while still allowing suspension travel (movement)
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Types of Springs
A. Coil spring
B. Leaf spring
C. Air spring
D. Torsion bar
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Coil Spring
Length of spring-steel rod wound into a spiral
Most common type of spring Used on front and rear suspension
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Coil Spring
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Leaf Spring Flat strips of spring steel that are bolted
together Limited to the rear of some cars A monoleaf spring is made from a
single, thick leaf of reinforced fiberglass A shackle fastens the rear leaf spring
eye to the frame or body and allows the spring to change length when bent
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Leaf Spring Assembly
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Leaf Spring Windup
Rear leaf springs flex when driving or braking forces are applied
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Air Spring Rubber cylinder filled with air End caps are formed on the ends for
mounting Air pressure in the rubber cylinder
gives the unit a spring action Special synthetic rubber compounds
are used so the air spring can operate properly in cold weather
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Air Springs
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Torsion Bar
Made of a large spring-steel rod One end is attached to the frame The other end is fastened to the control
arm Jounce and rebound twists the torsion
bar
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Torsion Bar
The bar resists twisting action and acts like a conventional spring
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Spring Rate
Stiffness, or tension, of a spring Determined by the weight needed to
bend the spring
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Sprung Weight
Weight of the parts that are supported by the springs
Sprung weight should be kept high in proportion to unsprung weight
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Unsprung Weight The weight of the parts that are not
supported by the springs: tires and wheels wheel bearings and steering knuckles axle housing
Unsprung weight should be kept low to improve ride smoothness
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Control Arms Used to hold the steering knuckle,
bearing support, or axle housing in position as the wheel moves up and down
The inner end contains bushings The outer end contains a ball joint
(independent) or bushing (solid axle)
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Control Arm Assembly
Control arm bushings act as bearings
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Strut Rod Fastens to the outer end of the lower
control arm and to the body or frame Keeps the control arm from swinging
toward the front or rear of the vehicle The rod ends contain rubber bushings
that soften the action of the rod and permit a controlled amount of lower control arm front-to-rear flex
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Connections that allow limited rotation in every direction
Filled with grease for lubrication A grease fitting may be provided A grease seal holds grease in and
prevents water and contaminant entry
Ball Joints
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Ball Joints
Steering knuckle for front-wheel-drive
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A tapered stud provides a force fit into the steering knuckle or bearing support
Ball Joints
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Shock Absorbers Limit spring oscillations to smooth a
vehicle’s ride One end is connected to the body or
frame, the other to the axle or control arm
When compressed or extended, oil inside the shock is forced through small orifices, absorbing energy, damping spring action
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Shock Absorber
This shock uses pressurized gas to reduce foaming in
the oil
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Shock Absorber Action
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Gas-Charged Shock Absorbers
Use a low-pressure gas to help keep the oil in the shock from foaming
Nitrogen gas is enclosed in a chamber separate from the main oil cylinder
Gas pressure acting on the oil prevents air bubbles from forming
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Self-Leveling Shock Absorbers
The special design causes a hydraulic lock action to help maintain normal curb height
A valve system in the shock retains hydraulic pressure when the shock is compressed near its minimum length helps keep the shock rod at the same
length with changes in force or curb weight
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Adjustable Shocks
Provide a means of changing shock stiffness
The shock can be set for different damping stiffness, usually by turning the shock’s outer body
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Strut Assembly
Consists of a shock absorber, a coil spring, and an upper damper unit
Replaces the upper control arm Only the lower control arm and the strut
are needed to support the wheel assembly
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Strut Assembly
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Strut Components
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Sway Bar (Stabilizer Bar) Used to keep the body from leaning
excessively in sharp turns Made of spring steel Fastens to both lower control arms and
to the frame When the body leans, it twists the bar The bar’s resistance to twisting limits
body lean in corners
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Sway Bar (Stabilizer Bar)
Sway bar links connect the barto the control arms
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Track Rod
Used on the rear axle to prevent side-to-side movement during cornering
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Uses control arms of different lengths Minimizes tire tilting (camber change)
with suspension action Reduces tire scuffing and wear The upper control arms are shorter
than the lower control arms
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Long-Short Arm
Suspension
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Contains torsion bar springs instead of coil springs
Most allow curb height adjustment By turning an adjustment bolt, you can
increase or decrease the tension on the torsion bar, raising or lowering the vehicle
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Uses only a lower control arm and a strut to support each wheel assembly
The top of the strut is fastened to the reinforced body structure, which supports the weight of the car
The most common system in use on late model cars
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Front Suspension(MacPherson Strut)
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MacPherson Strut
Suspension
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Front Strut Suspension
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Rear Strut Suspension
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Pickup trucks use numerous designs: long-short arm MacPherson strut solid axle and twin axle (twin I-beam)
A four-wheel-drive truck can have a solid axle and differential housing on the front, or independent front suspension
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Twin I-Beam Suspension
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The rear axle housing may be solid nonindependent suspension
Rear swing axles can also be used independent suspension
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Nonindependent Rear Suspension
Solid axle housing for rear-wheel-drive
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Dead Axle
A solid axle that does not drive wheels
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Semi-Independent Suspension
Uses a flexible axle, allowing the right and left wheels to be partially independent of each other
When one wheel hits a bump, its control arm moves up
Since the axle can flex, the effect on the other tire is minimized
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Trailing arm design
Independent Rear Suspension
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Independent Rear Suspension
This differential is mounted to the frame
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Double wishbone suspension system
Independent Rear Suspension
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Used to maintain the same vehicle attitude (body height) with changes in the amount of weight in the car
Common classifications: manual system automatic system
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Manual System
Uses air shocks and an electric compressor to counteract changes in passenger and luggage weight
A manual switch is used to activate the compressor to alter air shock pressure and body height
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Automatic System Uses air shocks or air springs, height
sensors, and a compressor to maintain curb height
A height sensor is connected to the frame and to the axle housing
If the load changes, the sensor can turn the compressor on to increase pressure to the shocks, or turn a solenoid on to vent pressure from the system
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Automatic System
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This system uses air springs and height sensors on all four wheels
Automatic System
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Electronic Height Control
Uses height sensors and an electronic control module to control the operation of a small electric air compressor, which maintains the correct ride height
Used on the rear of the car to compensate for heavy loads
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Components: height sensor compressor assembly pressure lines air shocks sensor link solenoid valve suspension control module
Electronic Height Control
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Operation If the trunk is heavily loaded, the weight
will compress the rear air shocks When the car is started, the height
sensor will be activated by the action of the sensor link and the sensor switch will close, energizing the compressor rear shock air pressure increases car body rises
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When the weight is removed, the car body will rise
The height sensor will then be moved in the other direction by the link, closing another set of internal contacts, energizing the pressure release solenoid valve air pressure is vented from the rear shocks body drops down to the correct ride height
Operation
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Uses various sensors, a computer, and shock absorber actuators to control ride stiffness
Increases comfort and safety by matching suspension system action to driving conditions
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Electronic Suspension System Components
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Electronic Suspension System Control
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Operation The system can produce a soft, smooth
ride when traveling down a straight highway
Based on the selector switch setting and other inputs, the electronic control module would energize the shock actuators to open the valves more reduces internal fluid restriction softens the ride
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Operation The system can stiffen the ride when
cornering, accelerating, or braking Based on the selector switch setting
and other inputs, the electronic control module would energize the shock actuators to close the valves more increases internal fluid restriction increases damping action prevents body roll and dive
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Shock Actuator
Uses a solenoid and a small dc motor to move the control rod
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Uses computer-controlled hydraulic rams instead of conventional springs and shock absorber actuators to control ride characteristics
Hydraulic rams support the weight of the car and react to the road surface
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Operation Pressure sensors on each ram provide
the main control for the system The sensors react to suspension
system movement and send signals to the computer
The computer extends or retracts each ram to match the road surface
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Operation Pressure control valves are located on
each ram By opening and closing these valves,
the computer can adjust the pressure of the rams and the resulting height of each corner of the vehicle
The computer can theoretically eliminate most body movement as the car travels over small dips and bumps
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Active Suspension System
A hydraulic pump provides pressure to
operate the rams
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Active Suspension Advantages
In turns, body roll is controlled, even banking into a turn is possible
For highway driving, the car can be lowered to improve aerodynamics
During city driving, the car can be raised for added ground clearance