06-12-2012, 05:04 PM
Independent Suspension System
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INTRODUCTION
Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically (i.e. reacting to a bump in the road) independently of each other. This is contrasted with a beam axle, live axle or de Dion axle system in which the wheels are linked - movement on one side affects the wheel on the other side. It is common for the left and right sides of the suspension to be connected with anti-roll bars. The anti-roll bar ties the left and right suspension spring rates together but does not tie their motion together.
Most modern vehicles have independent front suspension (IFS). Many vehicles also have an independent rear suspension (IRS). IRS, as the name implies, has the rear wheels independently sprung. A fully independent suspension has an independent suspension on all wheels. Some early independent systems used swing axles, but modern systems use Chapman or MacPherson struts, trailing arms, multilink, or wishbones.
Independent suspension typically offers better ride quality and handling characteristics, due to lower unsprung weight and the ability of each wheel to address the road undisturbed by activities of the other wheel on the vehicle. In the case of straight line drag racing though, it can be more of a burden because of the design, IRS may cause the vehicle to experience wheel hop on a hard launch. Independent suspension requires additional engineering effort and expense in development versus a beam or live axle arrangement. A very complex IRS solution can also result in higher manufacturing costs.
SWING AXLE
A swing axle is a simple type of independent suspension first used in early aircraft (1910 or before), such as the Sopwith and Fokker, usually with rubber bungee and no damping. Some later motor-car rear swing axles have universal joints connecting the drive-shafts to the differential, which is attached to the chassis. They do not have universal joints at the wheels: the wheels are always perpendicular to the drive shafts. Swing axle suspensions traditionally used leaf springs and shock absorbers. This type of suspension was considered better than the more typical live axle for two reasons:
It reduced unsprung weight since the differential is mounted to the chassis
It eliminates sympathetic camber changes on opposite wheels
However, there are a number of shortcomings to this arrangement:
A great amount of single-wheel camber change is experienced, since the wheel is always perpendicular to the driveshaft
"Jacking" on suspension unloading (or rebound) causes positive camber changes on both sides, which (In extreme cases) can overturn the car.
Reduction in cornering forces due to change in camber can lead to over steer instability and in extreme cases lift-off over steer
SLIDING PILLAR
Sliding pillar suspension is one in which the stub axle and wheel assembly are attached to a fixed vertical "pillar" or kingpin which slides up and down through a bush or bushes which are attached to the vehicle chassis, usually as part of transverse outrigger assemblies. Sliding pillar independent suspension was the first recorded instance of independent front suspension on a motor vehicle. In this system, the stub axle carrying the wheel was fixed to the bottom of a pillar which slid up and down through a bush in a transverse axle member fixed to the front of the chassis. The top of the pillar was fixed and pivoted on a transverse semi-elliptic spring.
MACPHERSON STRUT
The most widely used front suspension system in cars comprises of a strut-type spring and shock absorber combo, which pivots on a ball joint on the single, lower arm. The steering gear is either connected directly to the lower shock absorber housing, or to an arm from the front or back of the spindle. In this case, when you steer, it physically twists the strut and shock absorber housing and consequently the spring to turn the wheel.
DOUBLE WISHBONE SUSPENSION
The double wishbone suspension can also be referred to as double 'A' arms, and short long arm (SLA) suspension if the upper and lower arms are of unequal length. A single wishbone or A-arm can also be used in various other suspension types, such as MacPherson strut and Chapman strut. The upper arm is usually shorter to induce negative camber as the suspension jounces (rises). When the vehicle is in a turn, body roll results in positive camber gain on the inside wheel. The outside wheel also jounces and gains negative camber due to the shorter upper arm. The suspension designer attempts to balance these two effects to cancel out and keep the tire perpendicular to the ground. This is especially important for the outer tire because of the weight transfer to this tire during a turn.
MUTLI-LINK SUSPENSION SYSTEM
A multi-link suspension is a type of vehicle suspension design typically used in independent suspensions, using three or more lateral arms, and one or more longitudinal arms. These arms do not have to be of equal length, and may be angled away from their 'obvious' direction.
Typically, each arm has a spherical joint (ball joint) or rubber bushing at each end. Consequently, they react on loads along their own length, in tension and compression, but not in bending. Some multi-links do use a trailing arm or wishbone, which has two bushings at one end. On a front suspension one of the lateral arms is replaced by the tie-rod, which connects the rack or steering box to the wheel hub.
TRAILING AND SEMI-TRAILING
A trailing-arm suspension is an automobile suspension design in which one or more arms (or "links") are connected between (and perpendicular to and forward of) the axle and the chassis. It is usually used on rear axles. A 'leading arm' as used on a Citroën 2CV, has an arm connected between (and perpendicular to, and to the rear of) the axle and the chassis. It is used on the front axle.
Trailing-arm designs in live axle setups often use just two or three links and a Panhard rod to locate the wheel laterally. A trailing arm design can also be used in an independent suspension arrangement. Each wheel hub is located only by a large, roughly triangular arm that pivots at one point, ahead of the wheel. Seen from the side, this arm is roughly parallel to the ground, with the angle changing based on road irregularities.
WORKING OF A SUSPENSION:
When people think of automobile performance, they normally think of horsepower, torque and zero-to-60 acceleration. But all of the power generated by a piston engine is useless if the driver can't control the car. That's why automobile engineers turned their attention to the suspension system almost as soon as they had mastered the four-stroke internal combustion engine.
The job of a suspension is to maximize the friction between the tires and the road surface, to provide steering stability with good handling and to ensure the comfort of the passengers. In this article, we'll explore how car suspensions work, how they've evolved over the years and where the design of suspensions is headed in the future.
If a road were perfectly flat, with no irregularities, suspensions wouldn't be necessary. But roads are far from flat. Even freshly paved highways have subtle imperfections that can interact with the wheels¬ of a car. It's these imperfections that apply forces to the wheels. According to Newton's laws of motion, all forces have both magnitude and direction. A bump in the road causes the wheel to move up and down perpendicular to the road surface. The magnitude, of course, depends on whether the wheel is striking a giant bump or a tiny speck. Either way, the car wheel experiences a vertical acceleration as it passes over an imperfection.
Without an intervening structure, all of wheel's vertical energy is transferred to the frame, which moves in the same direction. In such a situation, the wheels can lose contact with the road completely. Then, under the downward force of gravity, the wheels can slam back into the road surface. A system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road is needed.