Suspension Systems

Suspension Systems

The Suspension is one of the main components mounted on the frame part or the
basics structure of the vehicle. Also known as the chassis, the basic structure of the
vehicle is the carrying unit upon which mounts several parts such as Power plant,
Transmission, Suspension, Wheels & Tires, and the braking systems. The
illustration below depicts the basic components of vehicle on which frame or body
gets mounted.

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The structure of car chassis has changed with course of time. Previously the chassis
frame was either an integral or semi-integral frame upon which the car components,
which included suspension system, got mounted. But recently, the manufacturers
attach assembly parts to the body itself, thus eliminating the concept of frame
functionality during its manufacture. By doing so, all the functions of the frame are
carried out by the body. As an integral part of vehicle’s wheel alignment, the
suspension system contributes in reducing the tear & wears of the tires, and also
assists in providing stability in driving of the vehicle.

Components of Suspension System
The Suspension system in the vehicle essentially comprises of shock absorbers, coil
springs, spring shackles, stabilizer and leaf springs. This independent suspension
system of the car acts as an intermediate, connecting the rear wheels to its body so
as to satisfy enjoyable as well as safety driving needs. The following gives a brief
description about prime components in vehicle’s suspension system:

Shock absorbers
These are also referred to as dampers, as they provide driving comfort by
dampening the car’s vertical motion. In other words, they render a smooth drive
without letting the car sway away or wallow alongside the road. Moreover, the
shock absorbers eliminate the car vibrations that would otherwise have had
experienced by its driver in the absence of shock absorbers. As significant unit of
vehicle’s suspension system, its presence provides dual benefit to the vehicle.
Firstly, it makes sure that car chassis is protected from the bumps on the road.
Shock absorbers absorb the shocks resulting from the road bumps by ensuring that
the velocity of the car is not disturbed. In the absence of shock absorbers, every

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bump on the road would have otherwise directly passed on the thrust to the car
chassis, thus causing physical imbalance to car’s frame or body. Indirectly, shock
absorbers aid in prolonging a car’s physical life span. Secondly, they aid in keeping
the tires mobile on the road. Shock absorbers work in conjunction with other
suspension system components, primarily the springs. Technically, the shock
absorbers take the shocks from road bumps onto it through springs, which transfer
the road shocks to the absorbers in form of kinetic energy. Shock absorbers in fact
can allow the road shocks to be dissipated upon them by way of a constriction
valve. It is suggested that the stiffness of any suspension is directly proportional to
the size of the constriction valve.

Springs
Springs transforms the energy in road shocks onto the shock absorbers in form of
kinetic energy. They come either as coil springs or as leaf springs or in form of
torsion bars. Coil springs are essentially coiled torsion bars. All the pre-1985 makes
of cars had leaf springs, and even today a significant number of heavy duty vehicles
contain it. Further, leaf springs can be bifurcated as either full-elliptic or semi-
elliptic or three-quarter elliptic or transverse spring type or in form of helper spring
type. Amongst these, the semi-elliptic, transverse spring and helper spring type of
leaf springs are common in use today. In fact, 75% of the cars today carry semi-
elliptic leaf spring within its suspension system. The torsion bar renders
performance very similar to coiled-spring type. However, its degree of performance
rests on the twisting abilities of its steel bar. The rear suspension of Peugeot 205s,
Porsches (pre- 1989), amongst other cars had torsion bar springs, wherein the axle
gets directly attached to one end of steel shaft. The other end of it gets held by
splines through a slotted tube. As aforementioned, the twisting ability of steel bar
dictates its magnitude of its performance.

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A Coil-over unit
It is typical all-in-one unit which assists the shock absorber as well as the
suspension spring. This unit takes care of the adjustable spring plate and adjustable
dampening valve of the car. Essentially, this small unit is a tension adjuster. In
today’s times of enhanced technology and innovative technicalities, a large number
of cars carry adjustable compression dampening whereas motor bikes are rewarded
with spring tension preload adjustments.

Types of Suspension System
Various technical experts give different meanings to vehicle’s suspension system.
However, they more or less tend to confuse a layman. With advancement in
technology implicating added computer software systems to regulate most of the
car component’s architecture, it is not ideal anymore to relate a car’s suspension
system to given one type. Although for the sake of understanding, suspension
system could be ideally dissected into four main types, namely – Conventional
suspension system, Independent suspension system, Air suspension system
and Hydro elastic suspension system. In fact the later two types can be termed as
Digital suspension systems.

Conventional suspension system
In this traditional type of suspension system, two wheels get mounted on each side
of the axle, so as to disallow its wheels from experiencing gyroscopic effect,
although when the bump is experienced by only one of the wheels. Thus, the
upward velocity to be effected by both the wheels is eliminated. This type of
suspension system is popularly used in rear driving wheels, whereby the wheels get
placed on the live axle, with the aid of shock absorbers and leaf springs or coil
springs suspending it accordingly. This type of suspension system makes use of Coil

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springs. In more recent times, the air spring finds place instead of conventional coil
spring, immaterial whether powered by an engine driven or compressor. In this, the
pressurized air acts as a spring. This type of suspension has simple structure,
therefore can be built on a low cost budget. Asymmetric tandem axle suspension
systems are purely conventional or traditional in form of their getting used on heavy
trucks or trailers. However, tandem axle could be classified into either Air
suspension or spring suspension or a torsion bar suspension. This type of
suspension is better than single axle and resolves the problem of diversification of
load, which single axle suspension suffered from.

The following illustration depicts key suspension types with efficacy.

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Independent suspension system
This suspension type utilizes the front wheels in order to have its design
incorporated. However, both the front and rear wheels get benefited from it.
Independent suspension system comes in 3 forms, namely - McPherson Strut,
double wishbone and trailing arm or multi-link suspension.

McPherson Strut
It consists of a ball joint on the single arm over which is pivoted combo of strut-
strut shock absorber and spring. It is most widely used suspension system in
cars, wherein the steering gear is either connected to the arm of the spindle or to
the lower end of shock absorber. In this, all the three components – the shock
absorber, spring and spindle assist in steering operations. In fact, the strut acts
more than the shock absorbers in providing support to the vehicle, while
simultaneously absorbing the shock.

Double Wishbone
The system in this allows the free upward and downward movement of the spindle.
By this, its wishbone movement around pivot points is described by its slight motion
varying side to side, such a motion or movement also called as scrub. The scrub
motion always exists, except where the motion is too long. This type of suspension
is also articulated by movements of Steer and Camber. Although this type is mostly
articulated by Double A arm, Double wishbone can also be in the form of a single A-
arm combined with a solid arm. Double Wishbone aids in providing a consistent feel
in handling of steering.

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Multi-link Suspension
In this, each arm is separately placed unlike the other forms of independent
suspension system. However, the mechanics or the principle used by multi-link
suspension is identical to other forms of independent suspension system. All four
suspension arms are torque by the spindle, so as to turn according to the steering.
The benefits of this type of front wheel independent suspension system can be
found in experiencing lesser vibrations, enhanced tire grip, and negligible steering
reaction. However, multi-link suspension is expensive, which increases the wear &
tear of tires due to increased torque transmission. Moreover, upon installation of
Multi-link suspension, vehicle would require better performing shock absorbers.

Air Suspension system
This system comprises of an air tank, compressor and air bags for each wheel.
While maintaining pressure to approximately 5.6 to 7 kg/sq.m, air tank gets filled
with air. Further, with application of load the leveling valve gets actuated
compressing the air bag. The level of frame is enhanced when the compressed air
bag gets filled by the air in the tank. As and when the load from chassis is
decreased, the air bag releases more air.

The diagram below could clarify the working of Air Suspension System.

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The prime advantage of Air suspension system lies in the maintenance of
constant frequency of vibration irrespective of whether the vehicle is unladed or not.
This is the system incorporating today’s digital technology, which aids in rendering
of smooth and comfortable ride. Once the vehicle sets in motion, Air suspension
system helps in reducing weight. Moreover, this suspension system favors
maintain constant frame height. However, common problems faced by Air
suspension system may be due to dryer failure, compressor failure and Air strut
or Air bag failure.

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Hydrolastic suspension system
This kind of suspension provides better leveling of the car, by connecting front and
rear system amicably. Hydrolastic displacers are each provided in front and end
suspension units. The rubber valves take care of damping necessities. A small bore
pipe interconnects the front and end suspensions. In this case, if the front wheel
experiences a bump, fluid is transmitted to the rear suspension unit by aid of a
piston giving pressure to such fluid. With changing times, Hydrolastic suspension is
now refined to Hydro pneumatic suspension. The main difference between the two
lies in the architecture of displacer unit, removal of rubber springs in the refined
version and the inclusion of nitrogen gas which acts as a damper as well as the
spring. The fluid however is allowed to freely flow from the front to rear unit, merely
acting as separating diaphragm.

Usage of Auxiliary Devices in modern day usage

It is unanimously agreed that different suspension systems suffer from different
drawbacks. As a solution to correct this situation and also for striving for achieving
‘Driving safety’ as well as ‘Driving comfort’, vehicles are now being incorporated by
auxiliary devices such as Panhard rod, torque arm and sway bar. These devices are
attached to a suspension system in use without disturbing its architecture of
application. While a Panhard rod assists in preventing the axel wheel from swaying
or moving laterally, the Sway bar acts as a stabilizer. A torsion spring function in
the Sway bar aids in enhancing the roll stiffness of the suspension.

In today’s global scenario, the significance of suspension systems in the car is
well-recognized. That the vehicle suspension systems add immense value to the
mobility of the vehicle and also operates as a pertinent part for its life-long

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maintenance is an undisputed recognition. The manufacturers have now gone a step
forward to patent some of its suspension system designs. As to how the
suspension systems can add better value to comfortable driving on the platform
of economies of scale, will be elaborated in the following article. Equally important is
to take notice on how the use of lightweight materials could add to driving
scalability. Use of lightweight materials also accentuates the need for lightweight
suspension systems, in order to provide effective results as well as an adherence
to the government regulations proposing the need for lighter vehicles.

References:

http://www.carbibles.com/suspension_bible.html
www.frost.com
www.benthamscience.com
http://autoshepherd.com/category/Steering-Suspension/1072

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