SUSPENSION SYSTEM: COMPONENTS, TYPES AND WORKING PRINCIPLE

A system of mechanical linkages, springs, dampers that is used to connect the wheels to the chassis is known as a suspension system. It has usually done two works-controlling the vehicle’s handling and braking for safety and keeping the passengers comfortable from bumps, vibrations etc.

It also helps to maintain correct vehicle height and wheel alignment.it also control the direction of the vehicle and has to keep the wheel in a perpendicular direction for their maximum grip. The suspension also protects the vehicle itself and luggage from damage and wear. The design of the front and rear suspension of a car may be different.

COMPONENTS OF THE SUSPENSION SYSTEM

A suspension system irrespective of their type has some main components in common that are:-

1. Knuckle or Upright-

It is the component of the suspension system that is mounted over the wheel’s hub through which the wheels and the suspension of the vehicle connect with each other by the linkages provided.
A knuckle is provided with the king-pin and the caster angles that help the front wheels of the vehicle to steer in right or left direction which in turn steers the vehicle.
A knuckle provides housing for central bearing over which the wheel’s hub rotates along with the rotation of the wheels.

2. Linkages-

linkages are the rigid connections that are used in the suspension system to connect the mainframe of the vehicle with the knuckle of the wheels through mechanical fasteners.

On the basis of the type of suspension used linkages are of 3 types-

i. Wishbones or A-arm – 
It is the type of the mechanical linkage which is in shape of the alphabet A, the pointy end of the A-arm is fastened to the knuckle and the other 2 ends of the A-arm are fastened to the mainframe of the vehicle.
On the basis of the application of the vehicle, either a single A-arm or double A-arm are used.

ii. Solid axle or live axle- 
It is the type of linkage which is used to connect the mainframe of the vehicle with the knuckle on the wheel, this is the solid axle casing that supports the overall weight of the vehicle, this type of linkage can be seen in trucks.

iii. Multiple links- 
Instead of using double wishbone or solid axle linkage various high-end cars are adopting multiple link type of suspension in which multiple solid links are used to connect the mainframe of the vehicle to the knuckle on the wheel.

3. Shock absorbers or springs-

They are the flexible mechanical components that are used to absorb shock provided by the road condition and is placed between the linkages ( wishbone. Solid axle, multi-links) and the mainframe such that the road shock is minimised before transmitting to the mainframe of a vehicle.

On the basis of the application and type of suspension used shock absorbers are of many types that are-

i. Spring and damper type shock absorber- 
It is the type of shock absorber in which a pneumatic or hydraulic piston is known as the damper is used that provides damping by absorbing the road shocks.

This damper is surrounded by a compression coil spring which is an elastic mechanical constraint that compresses when force is applied by the bump and recoil back or regains its original shape and size when the force is removed.

It is used to maintain the surface contact of the tyres with the road by providing stiffness (resistance to compress), also maintain the damper at its original length after absorbing the shock.

ii. Leaf spring- 
It is the type of spring in which a number of ductile metal plates called leaf are arranged in a special pattern i.e. one over one in ascending order of their length, leaves of the leaf spring shock absorber are pre-stressed such that when the shock is transferred by the wheels these pre-stressed leaves being ductile tries to regain their original shape i.e. straighten,. Due to which shock is absorbed by the leaves.

This type of shock absorber can be easily seen in trucks on the road in which leaf spring shock absorber is used in between the solid or live axle and the mainframe of the vehicle.

iii. Air spring- 
It is the latest type of shock absorbers which can be easily seen in Volvo buses, in air spring shock absorbers the damping of shock is a function of air compression, which means air is used as a shock absorber.
The air needed for different load conditions is controlled and monitored by the Electric control unit of the vehicle.

TYPES OF SUSPENSION SYSTEM

1) INDEPENDENT SUSPENSION SYSTEM

This system means that the suspension is set-up in such a way that allows the wheel on the left and right side of the vehicle to move vertically independent up and down while driving on an uneven surface. A force acting on the single wheel does not affect the other as there is no mechanical linkage present between the two hubs of the same vehicle. In most of the vehicle, it is employed in front wheels.
This type of suspension usually offers better ride quality and handling due to less unsprung weight. The main advantage of independent suspension is that they require less space, they provide easier steerability, low weight etc.. Examples of Independent suspension are

i. Double Wishbones

It is an independent suspension system design using two wishbone-shaped arms(called A-ARM in USA and WISHBONE in the UNITED KINGDOM)to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The angle movements of the compressing and rebounding wheels can be managed by using arms of unequal length.
The main advantage of the double-wishbone suspensions is that they allow easy adjustments of camber, toe and other properties. This type of suspension also provides increasing negative camber gain all the way to full jounce travel. On the other hand, it takes more space and is slightly more complex than the other system like Macpherson strut. It also offers less design choice.

ii. MacPherson Strut

This type of independent suspension got its name from Earle S. McPherson who developed this design. The MacPherson strut is a further development of the double-wishbone suspension. The main advantage of the MacPherson is that all the parts providing the suspension and the wheel control can be combined into the one assembly.

It makes it easy to fit in transverse engine. This design is very popular due to its simplicity and low manufacturing cost. The disadvantage is that it is more difficult to insulate against road noise. for this, an upper strut mount is necessary, which should be decoupled as possible. It also requires greater clearance height.

2) DEPENDENT SUSPENSION SYSTEM

IN Dependent Suspension there is a rigid linkage between the two wheels of the same axle. A force acting on one wheel will affect the opposite wheel. For each motion of the wheel caused by road, irregularities affect the coupled wheel as well.
It is mostly employed in heavy vehicles. It can bear shocks with a great capacity than independent suspension. Example of this system is

I. Solid Axle.
A solid axle or beam axle is a dependent type suspension. It is mostly used in rear wheels in which the rear axle is supported and located by two leaf springs. The vertical movement of one wheel influences the other. They are simple and economical to manufacture.
They are so rigid that there is no change in track width, toe-in and camber on a full bump which helps in the low wearing of tyres. The main disadvantage is that the mass of the beam is included in the unsprung weight of the vehicle which results in low ride quality. The cornering ability is also poor due to zero camber angle.

3) SEMI-INDEPENDENT SYSTEM

This type of system has both the characteristics of a dependent as well as independent suspension. In semi-independent suspension, the wheel move relative to one another as in independent suspension but the position of one wheel has some effect on the other wheel. This is done with the help of twisting suspension parts. Example of semi-independent is

i. Twist Beam
The twist-beam suspension also known as the torsion-beam axle. These are mostly based on C or H shaped members. The cross beam of the H-shape holds the two trailing arms together and provides the roll stiffness to the suspension.
It is mostly used in the rear wheel of the cars. It is very favourable due to its low cost and it is very durable. It is simple in design and is very light in weight. But on the other side camber angle is limited and the roll stiffness is also not very easy. Toe characteristics may be unsuitable.