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Automotive Suspension System Overview

The impact of the Vehicle in many aspects, Suspension plays a very important role .

The components of the suspension system perform six basic functions: 1.Maintain correct vehicle ride height. 2.Reduce the effect of shock forces. 3.Maintain correct wheel alignment. 4.Support vehicle weight.

5.Keep the tires in contact with the road. 6.Control the vehicle’s direction of travel.

Most suspension systems have the same basic parts and operate basically in the same way. They differ, however, in the way the parts are arranged. The vehicle wheel is attached to a steering knuckle. The steering knuckle is attached to the vehicle frame by two control arms, which are mounted so they can pivot up and down. A coil spring is mounted between the lower control arm and the frame.

When the wheel rolls over a bump, the control arms move up and compress the spring. When the wheel rolls into a dip, the control arms move down and the springs expand. The spring force brings the control arms and the wheel back into the normal position as soon as the wheel is on flat pavement. The idea is to allow the wheel to move up and down while the frame, body, and passengers stay smooth and level. The unequal length control arm or short, long arm (SLA) suspension system has been common on American vehicles for many years. Because each wheel is independently connected to the frame by a steering knuckle, ball joint assemblies, and upper and lower control arms, the system is often described as an independent suspension. The short, long arm suspension system gets its name from the use of two control arms from the frame to the steering knuckle and wheel assembly. The two control arms are of unequal length with a long control arm on the bottom and a short control arm on the top. The control arms are sometimes called A arms because in the top view they are shaped like the letter A.

In the short, long arm suspension system, the upper control arm is attached to a cross shaft through two combination rubber and metal bushings. The cross shaft, in turn, is bolted to the frame. A ball joint, called the upper ball joint, is attached to the outer end of the upper arm and connects to the steering knuckle through a tapered stud held in position with a nut. The inner ends of the lower control arm have pressed-in

bushings. Bolts, passing through the bushings, attach the arm to the frame. The lower ball joint is usually pressed into the control arm and connects to the steering knuckle through a tapered stud that is held in position with a nut. A ball joint is used on the control arms because it allows movement in more than one direction. It allows the up-and-down motion required as the wheels pass over dips and bumps. This type of joint also allows side-to-side motion as the wheels are turned back and forth for turns.

For the upper and lower ball joint, the ball stud in the ball joint is a tapered stud at one end with a ball-shaped end. The ball end is supported in a similarly shaped housing called a socket. The shape of the housing allows the ball stud to turn around or move side to side. A plastic or sintered iron bearing is positioned between the ball and socket .The bearing allows the ball stud to turn in relation to the housing for steering. The tapered stud and nut hold the ball joint in position in the steering knuckle.

There are four basic types of springs used in suspensions: coil, torsion bar, leaf spring, and air spring. The coil spring is the most popular type of spring in both front and rear suspension systems. It is simply a round bar of spring steel that is wound into the shape of a coil. Usually, the top and bottom coils are closer together than the middle coils.

A coil spring is commonly used on the short, long arm suspension system. Some cars have the spring mounted from the frame to the upper control arm. In either case, the shock absorber is mounted through the center of the spring. Most short, long arm systems use a stabilizer bar between the two sides of the suspension. The sway bar connects both lower control arms to the frame crossmember. Movements affecting one wheel are partially transmitted to the opposite wheel through the frame to stabilize body roll. The sway bar is attached to the frame crossmember and lower control arms through rubber insulator bushings to reduce noise and vibrations. Sway bar end bushings and crossmember bushings are permanently installed on the sway bar.

The advantages of the coil spring are its compactness, lack of moving parts, and excellent weight supporting characteristics.

The disadvantage of a coil spring is its weakness in supporting side-to-side or lateral movement. When coil springs are used at the drive wheels, heavy traction bars or torque tubes are often required to maintain axle housing alignment.

A number of vehicles use a torsion bar spring. It is a long, solid steel shaft that is anchored at one end to the suspensions control arm and at the other end to the vehicle's frame. Torsion is the twisting action that occurs in the bar when one end is twisted and the other end remains fixed. When a vertical impact on a wheel is transmitted through the control arm to the torsion bar, the bar twists to absorb the

impact. The bar's natural resistance to twisting quickly restores it to its original position, returning the wheel to the road.

A torsion bar can store a significantly higher maximum amount of energy than either an equally stressed leaf or coil spring. The torsion offers important weight savings and it is adjustable. In addition, it requires significantly less space than a coil spring.

The leaf spring is made of several layers of spring steel stacked one upon the other, Usually, there is one main leaf that uses spring eyes for locating and fastening the spring toe frame or underbody. Several other progressively shorter leaves are placed on the main leaf, and the assembly or leaf pack is held together in the middle by a center bolt and on the ends by rebound clips. Some spring packs use fiber. or plastic pads between leaves to reduce the internal leaf friction. Some vehicles use a single leaf instead of a buildup of multiple leaves. One manufacturer is using a leaf spring manufactured from a nonmetal composite. Leaf springs are usually arched so that the ends are higher than the center when viewed from the side.

The leaf spring is usually mounted in three places. A bushing is installed in each of the spring eyes. A bolt through the bushing in the rear spring eye attaches the rear of the spring directly to the vehicle frame. A shackle assembly is attached to the front spring eye and bushing and is then mounted through a shackle bushing to the frame. The shackle assembly allows the leaf spring to pivot up and down. A pair of U-bolts and a tie plate are used to clamp the front or rear axle assembly to the leaf spring.

The main advantage of leaf springs is their ability to control vehicle sway and lateral movement. For these reasons, leaf springs are often used on the rear suspension of rear drive vehicles.

Many late-model luxury cars use air springs. The spring is essentially a rubber bag or bladder full of air. A piston is attached to the lower control arm. Movement of the lower control arm causes the piston to move into the air bladder and compress the air in the bladder. Air pressure is used to regulate how easy or hard the bladder can be compressed. The air bladder is usually connected to an air compressor, which regulates the action of the air spring based on road conditions.

All suspension systems use a shock absorber at each wheel. When the coil, torsion bar, leaf spring, or air spring is deflected, it can oscillate (bounce up and down) uncontrollably, possibly causing the tires to lose contact with the road. This could cause the car to bounce up and down without any control. To prevent this from happening, shock absorbers are used, not to absorb shocks, but to control spring rate and dampen spring oscillations.The shock absorber is a hydraulic device. One end of the shock absorber is attached to a wheel assembly and the other end is attached to the vehicle frame. Shock absorber movement is limited by forcing fluid inside the shock