What is Suspension System : Functions, Parts, Type, Working

Suspension System

Suspension system is a mechanical device which absorb uneven vehicle shocks. It is a set of mechanical connections, springs, and dampers that connect the wheels to the chassis.

The conventional system, in which the road springs are attached to a rigid beam axle.

The independent system in which there is no rigid axle beam and which is free to move vertically without any reaction on the other wheel.

Need of Suspension System

1. In order to provide comfortable ride to the passengers and avoid additional stresses in the vehicle frame.
2. The vehicle should neither bounce or role or sway the passengers when Cornering nor pitch when accelerateing, braking or sudden lifting or dropping of the front wheel with respect to real wheels.
3. Although some of the road irregularities and inequalities are absorbed by large tyres.
4. It is necessary to provide a suspension system for reducing the shocks to passengers and for comfortable ride also reduce additional stresses in the automobile frame and body.
5. All the parts which perform the function of isolating the automobile from the road shock are collectively called as a suspension system.
6. A good suspension should have springness and damping.
7. The springness is the elastic resistance to load while damping is ability of absorbing shocks.

Functions of Suspension System

• To act as a safeguard for the occupants against road shocks and provide comfort ride.
• To preserve the stability of the vehicle in rolling, pitching while in motion.
• To minimise the effects of stresses due to road shocks on mechanism of a vehicle and provide cushionong effect.
• To provide the required height to body structure as well as beer the torque and breaking reaction.
• To keep the body perfectly in level while travelling over the uneven road.

Construction and Working of Leaf Spring

• Semi-elliptical leaf spring are widely used for suspension in light and heavy commercial vehicle.
• In car these are used for rear suspension.
• The leaf springs are made of flat semi-elliptical plate.
• The advantages of leaf spring over helical spring is that the ends of the spring maybe guided, along the definite path as it deflect to acts as a structural member in addition to energy absorbing device.
• Thus leaf spring carry lateral load, brake torque, driving thrust and shocks.
• It consist of number of semi-elliptical plates called blade or leaves.
• The leaves are given initially curvature or camber so that they tends to straighten under the load.
• The blades are vary in length and are held together by a bolt passing through the centre acting as a beam of uniform strength.
• The spring is clamped to the axle housing by means of U bolts.
• The longest leave is called as master leaves has its end formed in the shaped of an eye through which the boltsare passed tosecure the spring to its supports.
• The eyes are attached to shackle provided with anti-friction material such as bronze or rubber. The Other leaves are graduated leaves.
• To prevent digging in the adjacent leaves, the end of graduated leaves are trimmed in various forms.
• The master leaf has to withstand vertical bending load, side thrust and twisting movement due to presence of stresses caused by these load so it is usually to provide two full length leaves and rest graduated leaves.
• Reborn clips are located at intermediate position in the length of the spring so that graduated leaves also shear the stresses induced in the full length leaves when the spring rebound.
• Highly cambered spring provide a soft suspension but they also increase tendency to jaw. Flat spring reduces tendency of the vehicle to dip (pitching), when break or accelerate suddenly.
• Use of longer is spring give soft suspension.
• Generally rear spring are kept longer than the front spring. this causes them to vibrate at different frequencies, which prevent excessive bounce.

Rigid Axle suspension

• Greater part of the extra weight of passengers are and luggage has to be carried by rear suspension in most of the vehicles.
• In one rigid unit known as a live action, the driving axle combines the right angle drive, differential, axle shaft, and wheel hub mounting. it is connected to the propeller shaft.
• The unit connected to propeller shaft is attached to the vehicle structure in such a way that it can move up and down on its spring and can cope with the loads as well as the torque or turning forces imposed on it.
• Further rear suspension is designed in such a way as to position the axle for minimising bouncing and associated vibrations to which is liable while moving off, braking and concerning particularly.
• For suppressing the bouncing of the springs the damper which are mostly hydraulic and telescopic type are widely used.

The real axle suspensions are

1. Helical coil spring

• It is circular for best energy storing shape for a given weight, and a coil spring store energy produced by its up and down movement in the most efficient way.
• The energy stored per unit volume is double than leaf Spring.
• Coil spring has an advantages of fitted in compact space.
• It takes the shear as well as bending stress only and for the torque reaction and side thrust an alternative arrangement has to be provided.
• The life of coil is increased by shot paining their surfaces to induce compressive stress in them and to reduce the effect of scratches in initiating fatigue cracks.
• Immediately after shot such spring maybe given an anticorrosion treatment again to increase their fatigue life.
• The ends of the coil spring maybe square and ground for stability, upon the surfaces through which the load is applied to the rest of the spring.
• The tendency of buckling of a spring under compressive load is prevented by mounting it in the cylindrical dampers or shock absorber so that the possibility of buckling is reduced.
• These spring do not have noise problem and static function.
• These springs are mainly with independent suspension through they have also been used in the conversional rigid axle suspension.
• A helper coil spring are provided for progressive stiffness against increase load.

2. Torsion bar

• The tosson bar is used with independent front suspension system.
• Two such units are there on either side of the frame.
• Each suspension housing is pivoted at its front end to the tubular cross member (front axe) and carries at its rear and a wheel carrier arm mounted on needle roller bearings.
• Wheel hub and brake anchor plate are mounted on the forward end of the wheel carrier arm.
• Combined torsion bar and torsion tube splined together at their inner and provide main spring load.
• It is made of heat treated alloy spring steel.
• One end of the torsion bar is connected by splines with the wheel carrier arm.
• While the other end of torsional bar asssembly is rigidly connected to the steering knuckle.
• When the wheel moves, the rod and tube are twisted and the formed and elastic line between the wheel and steering knuckle.
• The length of the combine torsion bar is composed of the length of the tube and the rod to make softer suspension.
• Double acting shock absorber assembly is bolted to the rear face of the suspension unit.
• It is lighter than leaf spring and occupies less space.
• It does not take braking or driving thrust. So additional linkage must be provided.

Air suspension system

• Now a days pneumatic suspension system are employed in some tourist vehicles to improve the riding comfort of the passengers.
• A line diagram of air suspension system with air shown in figure. It consist of four air bags.
• The elastic element consists of housing, diaphragm with suitable air inlate and piston group. The housing is linked with the frame. The housing contains the piston group which is linked with unsprung mass.
• The housing and piston group are connected by a metallic diaphragm for better sealing and to friction between the members of elastic elements.
• Each air bag is filled with compressed air.
• The component of air suspension system are air filter, compressor, air reservoir, relief valve, pressure regulator, solenoid valve, levelling valve and T check valve.
• A air compressor is mounted on the vehicle frame supplies high pressure air into the reservoir. The compressor suck the air from atmosphere through air filter.
• The pressure in the reservoir is maintained at about 20 kg/cm2.
• The compressed air in the air bags support the weight of vehicle whenever vehicle come across the bump of the surface, the air in the air bag compressed and absorb the shocks.
• Air is admitted into the four air bag through two circuits. In one circuit a pressure reduced to 12 kg/cm2 by pressure regulator.
• This pressure is kept in air bag through levelling valve if the pressure in one of the bag is low, the leveling arm moves and air is admitted into low pressure air bag through inlet valve.
• This can be achieved by special regulator, which keeps the same distance between wheel and frame under the various load. This circuit maintain the vehicle level constant in loaded or unloaded condition.
• For this situation, the air at 20 kgf/cm2 pressure is admitted into the levelling valve through solenoid valve.
• Also the air is quickly released by levelling valve whenever load is decreases from corresponding air bag. This lower the air bag and hence the vehicle to the proper level.

FAQ

What is Suspension system?
Suspension is the system of tires, tire air, springs, shock absorbers, and linkages that connects a vehicle to its wheels and allows relative movement between the two. Suspension systems must support both road grip/handling and ride quality, which are at odds with each other.
A suspension system is a set of mechanical links, springs, and shock absorbers that connect the wheels to the chassis.

What are the 4 types of suspension system?
1. leaf springs
2. Coil springs
3. Torsion bars
4. Air springs

What causes suspension damage?
Major suspension system components include springs, shock absorbers, struts, control arms, and more. Being exposed on the underside of your vehicle, these parts are constantly exposed to debris, rocks, speed bumps, potholes, and other driving incidents that can damage components.

What are the main parts of the suspension?
Main Parts of Suspension System is
1. Spring
2. Wheel
3. Shock absorbers
4. rods
5. Joints, Bearings and Bushings
6. Direction system
7. Frame.

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