Suspension Systems - 1 Topics covered in this presentation: Basic Suspension System Spring Types Suspension System Construction

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.

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.

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.

Coil Spring There are four main types of springs in common use: 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.

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

Steering knuckle connects onto control arm 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. Torsion bar Vehicle frame Control arm Steering knuckle connects onto control arm Strut bar

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.

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.

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

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

Pressurized gas chamber 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.

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.

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.

Track (Lateral Control) Bar A track bar prevents side-to-side rear axle movement when cornering. Support bracket 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