Auto Pro Automotive Engineering Related Site

Home Contact Order Request Links Downloads


Suspension Systems:


The modern automobile has come along way since the days when “just being self propelled” was enough to satisfy the car owner. Improvement in suspension, increased strength & durability of components, and advances in tire design and construction has made large contributions to tiding comfort and driving safety.

Basically, suspension refers to the use of front and rear springs to suspend a vehicles frame, body, engine & power train above the wheels. These relatively heavy assemblies constitute what is known as “Sprung” weight. “Unsprung” weight, on the other hand, includes wheels and tire, break assemblies and other structural members not supported by the springs.

The springs used in today's cars and trucks are engineered in a wide variety of types, shapes, sizes, rates and capacities. Types includes leaf springs, coil springs, air springs and torsion bars. These are used in sets of four per vehicle, or they are paired off in various combinations and are attached to the vehicle by a number of different mounting techniques.

Front suspension types

There are two types of front suspension in general use: the independent system & the solid axle system. Independent suspension usually operates through heavy-duty coil springs or torsion bars and direct, double acting shock absorbers. In solid axle construction, the axle beam and wheel assemblies are connected to the car by leaf springs and direct or in-direct shock absorber.

With the solid axle setup, the steering knuckle and wheel spindle assemblies are

Connected to the axle beam by bronze-bushed kingpins, or spindle bolts, which provide pivot points for each front wheel. Modern independent front wheel suspension systems use ball joints, or spherical joints, accomplish the purpose. In operation, the swiveling action of the ball joints allows the wheel and spindle assemblies to be turned left and right and to move up & down with changed in road service.

Leaf spring

Front leaf, or late, springs are used in conjunction with solid axle beams in most truck applications. Rear leaf springs are used on trucks and some passenger cars. Single leaf or multi-leaf springs are usually mounted longitudinally over the front axle beam or under the rear axle housing.

The spring center bolt fastens the leaves together, and its head locates the spring in the front axle beam or saddle on the rear axle housing. U-bolts clamp the spring firmly in place and keep it from shifting. Eyebolts, brackets and shackles attach it to the frame at each end.

In many cases, leaf springs are used at the rear of the vehicle in combination with another type of spring in front. Chrysler, for example, uses leaf springs at the rear, torsion bars in front.

For many years, Ford used leaf springs at rear, coil springs in front. Now, full-size cars have coil spring suspension, front and rear. Ford’s small cars have coil springs in front; leaf springs at rear. Buick still uses coil spring at all around. In some foreign cars, torsion bars are used front and rear; in others, leaf springs are mounted crosswise for use with independently suspended wheels.

Rear leaf spring in U.S vehicles generally are placed parallel to the frame to absorb the torque of the driving wheels the front half of each leaf spring acts like a radius rod or control arm to transmit the driving force from the rear wheels to the frame. With this suspension setup, the leaf springs also serve as stabilizer side sway of the chassis.

Coil springs

Many independent front suspension systems incorporate compression-type coil springs mounted between the lower control arms and spring housing in the frame. Others have the coil springs mounted above the upper control arms, compressed between a pivoting spring seat bolted to the control arm and a spring tower formed in the front-end sheet metal.

Generally, the upper control arm pivots on a bushing and shaft assembly, which is bolted to the frame. The lower arm pivots on a bushing and shaft assembly or on a bolt cross frame member. When the lower control arm is not the A-frame type, its supported by strut, which runs diagonally from the lower control arm to a bracket attached to the frame. On some models, this strut serves as a support; on others, it provides a means of adjusting caster.

Stabilizers or sway bars are used in conjunction with front suspension on many cars to dampen rod shocks and minimize road sway. These bars are bracketed to the frame front cross member and extend from one lower control arm to the other.

Actually, the S.L.A (short-long arms) system of front suspension has been adopted almost universally for passenger cars. The proportional lengths of the upper and lower control arms (and their engineered placement) are designed to keep the rise and fall of each front wheel in a vertical plane. With this arrangement, changes in wheel angularity, weight balance and tire-scuffing tendencies are negligible when compared with solid axle suspension.
Another coil spring setup that is gaining application in small cars is MacPherson strut suspension. It combines coil spring, shock absorber and strut in a single assembly.
When coil springs are used in both front and rear suspension, three or four control arms are placed between the rear housing axle and the frame to carry driving and braking torque. The lower control arms pivot in the frame members and sometimes support the rear coil spring to provide for up & down movement of the axle & wheel assembly.
In addition, a sway bar (track bar) is usually attached from the upper control arm to the frame side rail to hold the rear axle housing in proper alignment with the frame and to prevent side sway of the body. However, if the rear coil springs are mounted between the frame and the swinging half axle, the independently suspended rear wheels have a sturdy axle housing attached to the deferential housing which, in turns, is bolted to the frame.

Torsion bars

Although torsion bars were and are used extensively on European cars, this type of suspension system received only token attention from the U.S. manufacturers until Chrysler developed their system in the early 1950s. Before that only a few buses, trailers and race cars were equipped with torsion bar suspension.

Basically, torsion bar suspension is a method of utilizing the flexibility of a steel bar or tube twisting lengthwise to provide spring action. Instead of the flexing action of a leaf spring, the torsion bar twists to exert resistance against up and down movement.

For example, an independently suspended front system with torsion bars mounted lengthwise would have one end of the bars anchored to the car frame and the other end attached to the lower control arms. With each rise and fall of a front wheel, the control arm pivots up and down, twisting the torsion bar along its length to absorb road chock and cushion the ride.

Chrysler cars are equipped with left and rights, non-interchangeable, front torsion bars with hex-shaped ends. In position, the bars extend from hex-shaped rear anchors in the frame cross members to hex-shaped holes in the front lower control arm, adjusting bolts are provided at the front mounting to increase or decrease torsion bar twist and thereby control front suspension height. Over the years, Chrysler has made many improvements in the system, including lengthening the torsion to lower the spring rate; adding a removable rear anchor cross member that rubber-isolated from the frame; devising a plastic plug and a balloon seal for the rear anchor. Olds mobile Tornado and Cadillac Eldorado front wheel drive cars also use lengthwise mounted torsion to support the front and to provide for high adjustment.

Torsion bars can also be used laterally to provide spring action for front and/or rear wheel independent suspension system. Older Volkswagen cars offer a unique torsion bar arrangement with all four wheels independently suspended, but with two different torsion bar setup in use. At the front, two laminated square torsion bars hin separate axle tubes are anchored at the center to counteract twisting and lateral movement. Each has a lever or torsion arm attached to its outer end. Ball joints connect the torsion arms to the steering knuckle. The wheel spindle trails behind the axle and tends to swing in an arc when moved up and down by road irregularities.

At the rear, Volkswagen utilized one short, round torsion bar on each side. These bars are splendid at each both ends and anchored in the center of the frame cross member. The outer ends of the torsion bars carry the spring plates to which the wheels are attached. Here, too, the wheels follow behind the torsion bar on “trailing arms”.

Air suspension

Air suspension system are designed to cushion the ride and keep the car, bus or truck level fore and aft and at a constant height regardless of load. Air suspension was introduced on many luxury cars in the late 1950s, but it was dropped after one or two model years. Recently, however, new leveling systems have been researched and developed for passenger car use, including air—adjustable rear shock absorber.

A typical air suspension system consists of an engine-driven air compressor, supply tank, filter or condenser, valves, piping, controls and air springs or operation, the air compressor maintains a constant pressure in the supply tank. Air is piped to the control valves, which feed air to each spring as needed. Pressure is automatically increased on either side or at front or rear as required to keep the car level and to keep any desired height from the road (within limit of system).

Automatic level control

Air springs are not used in Cadillac’s automatic level control system. Rather, the rear shock absorber extends or compresses to bring the rear of the car to the same level as the front. This automatic system utilizes on air compressor, reservoir tank assembly, pressure regulator, hoses, flexible airlines, height control valve and special shock absorbers.

Older Ford cars used one of two leveling systems that utilize air bags in conjunction with rear coil springs. The automatic system consists of air reservoir and pump, leveling valve, air bags, nylon tubing & metal fittings and connectors. The manual system has similar air bags connected to lines leading to the trunk of the car where an air valve connection permits leveling by application of air under pressure from an outside compressed air source.

Late model Ford cars carry an option for a rear suspension automatic load-leveling system that functions only after a load (approximately 400 lbs.) is added to the vehicle.

When the load lowers the vehicle to a specific level, air sleeve rear shock absorber inflate and extend, raising the vehicle to design height. When the load is removed, the air sleeve shock absorbers deflate and lower the vehicle to design height.

Ford’s rear suspension automatic load-leveling system includes a compressor and air bleed valve, pressure reservoir tank height control valve and link, three flexible nylon air lines and a rubber vacuum hose.

The compressor maintains 60 or 125 psi in the system. The air bleed valve permits air to bleed for testing and servicing or for hooking up a trailer. The pressure tank stores high - pressure air. The height control valve and link maintain vehicle design height at rear.

The lever on the height control valves is attached to the rear suspension upper arm by means of the link. The control valves senses riding height and either admits or exhausts height pressure air to or from the air sleeve shock absorber. A time delay mechanism in the height control valve prevents the transfer of air when the lever is moving during normal ride motions.

Shock absorber

A wide variety of shock absorbing device have been used to control spring action. Today, however, direct double – acting, “telescoping” hydraulic shock absorbers have almost universal application.

At the front, each shock absorber often extends through the coil spring from the lower control arm to a bracket attached to the frame. On Chrysler cars with torsion bar suspension, the front shock absorbers attach to the lower control arm and mount to a bracket on the frame.

In the case of high-mounted coil springs, each front shock absorber extends from the upper control arm to a platform mounted in the spring tower or to a bracket on the wheel housing in the engine compartment.

At the rear, the lower end of the shock absorber usually is attached to a bracket welded to the axle housing. The upper end is fastened to the frame or to the coil spring upper seat, which is integral with the frame or body.

On cars with rear leaf springs the rear shock absorbers generally extend from a stud attached to the spring U-bolt mounting bracket to the frame cross member. Quite often the rear shock absorbers are mounted at an angle to assist in restricting lateral movement as well as vertical movement.

Some Olds mobile Tornado and Cadillac Eldorado cars use four rear shock absorbers to give better control. And, for this same reason, some Chevrolet cars have “bias-mounted “ rear shock absorber. The cub – side unit is mounted in front of the axle housing. Some Ford cars feature this arrangement , too .

The operating principle of direct-acting hydraulic shock absorbers consists of forcing fluid through restricting orifices in the valves. The restricted flow serves to slow down and control the rapid movement of the car springs as they react to road irregularities. Generally fluid flow through the piston is controlled by spring loaded valves.

The hydraulic shock absorber automatically adapts itself to severity of the shock. If the axle moves slowly, resistance to the flow of the fluid will be light. If axle movement is rapid or forceful, the resistance is much stronger since more time is required to force the fluid through the orifices.

By these hydraulic actions and reactions, the shock absorbers permit a soft ride over small valves and provide firm control over spring action for cushioning large bumps. The double – acting units operate efficiently in both directions. Spring rebound can be almost as violent as the original action that compressed the shock absorber.

  Automotive Articles  
    Suspension Systems  
    Suspension Modeling  
    Engine Performance  
    Engine Design  
    Torque Converter  
    A B S  
    Car Stability  
    Clutch Design  
    Engine Design  
    Operating Cost  
  Tractive Performance  
  Tractor Semi Trailer  
  Related Links  
  Find site  



Home Contact Order Request Links Downloads

The contents of this web page are copyright © 1998-2000 Auto Pro , Awad. All Rights Reserved