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Automotive Suspension Systems. The purpose of the suspension is to provide the vehicle with the following: 1. A smooth ride 2. Accurate steering 3. Responsive handling 4. Support the weight of a vehicle 5. Maintain acceptable tire wear.
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The purpose of the suspension is to provide the vehicle with the following:1. A smooth ride2. Accurate steering3. Responsive handling4. Support the weight of a vehicle5. Maintain acceptable tire wear
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.
Ladder FrameA ladder frame is a common name for a type of perimeter frame where the transverse (lateral) connecting members are straight across.
Perimeter FrameA perimeter frame consists of welded or riveted frame members around the entire perimeter of the body.
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.
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.
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.
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.
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.
TYPES OF SUSPENSIONSEarly suspension systems on old horse wagons, buggies, and older vehicles used a solid axle for front and rear wheels.
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.
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.
Spring Materials. Most springs are made of a tempered steel alloy known as spring steel, usually chrome silicon or chrome-vanadium alloy.
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
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.
Springs are designed to provide desired ride and handling and come in a variety of spring ends.
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.
A constant-rate spring continues to compress at the same rate throughout its complete range of deflection.
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.
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.
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.
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.
Instead of cutting springs to lower a vehicle, there are several methods available that are preferred if the vehicle must be lowered:1. replacement springs2. replacement spindles
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.
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.
The leaves are held together by a center bolt, also called a centering pin.
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.
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.
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.
To provide additional load-carrying capacity, especially on trucks and vans, auxiliary or helper leaves are commonly used.
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.
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.
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.
SUSPENSION PRINCIPLES1. Transverse (or side-to-side) wheel support.Transverse links are also called lateral links.
2. Longitudinal (front-to-back) wheel support.Some suspension designs use an additional member to control forward-back movement.
STEERING KNUCKLESA steering knuckle is hard to classify either as part of the suspension or as part of the wheel. A knuckle serves two purposes:To join the suspension to the wheel To provide pivot points between the suspension and wheel
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.
CONTROL ARMSA control arm is a suspension link that connects a knuckle or wheel flange to the frame.
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).
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.
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.
Ball Joint DesignThere are two basic designs of ball joints: compression loaded and tension loaded.
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.
