The modern automobile has come along way since the days when “just being self propelled” was enough to satisfy the car owner. Improvement in suspension, increased strength & durability of components, and advances in tire design and construction has made large contributions to tiding comfort and driving safety.
Basically, suspension refers to the use of front and rear springs to suspend a vehicles frame, body, engine and power train above the wheels. These relatively heavy assemblies constitute what is known as Sprung weight. Unsprung weight, on the other hand, includes wheels and tire, break assemblies and other structural members not supported by the springs.
The springs used in today’s cars and trucks are engineered in a wide variety of types, shapes, sizes, rates and capacities. Types include leaf springs, coil springs, air springs and torsion bars.
Independent Suspension System
These are used in sets of four per vehicle, or they are paired off in various combinations and are attached to the vehicle by a number of different mounting techniques.
The automobile frame and body are mounted on the front and rear axle not directly but through the springs and shock absorbent. The assembly of parts, which perform the isolation of parts from the road shocks, may be in the forms of bounce, pitch and roll is called suspension system. Suspension system of an automobile separates the wheel and axle assembly of the automobile from its body. Main function of the suspension system is to isolate the body of the vehicle from shocks and vibrations generated due to irregularities on the surface of roads. Shock absorbers are provided in the vehicles for this purpose. It is in the form of spring and damper. The suspension system is provided both on front end and rear end of the vehicle.
A suspension system also maintains the stability of the vehicle in pitching or rolling when vehicle is in motion.
Functions of suspension system:
1. It prevents the vehicle body and frame from road shocks. 2. It gives stability of the vehicle. 3. It safeguards the passengers and goods from road shocks. 4. It gives the good road holding while driving, cornering and braking. 5. It gives cushioning effect. 6. It provides comfort.
Requirements of suspension system:
1. There should be minimum deflection. 2. It should be of low initial cost. 3. It should be of minimum weight. 4. It should have low maintenance and low operating cost. 5. It should have minimum tyre wear.
Components of Suspension system:
Coil springs, Leaf springs, shock absorbers, Spring shackles, stabilizer
To construct any automobile, chassis is the basic requirement: Chassis is a French term and it was initially used to denote the frame or main structure of a vehicle. It is extensively used in complex vehicles except for the body. A vehicle without a body is called chassis.
Basic Construction of Chassis
Chassis is the backbone of the vehicle. The components of the vehicle such as power plants, transmission systems, axles, wheels and tires, suspension, controlling systems such as braking, steering, etc., and also electrical system parts are mounted on the chassis frame. It is the main mounting of all components including the body. So, it is also called a carrying unit.
Main Components of Chassis
1. Frame 2. Front suspension 3. Steering mechanism 4. Engine, clutch and gearbox 5. Radiator 6. Propeller shaft 7. Wheels 8. Rear and front springs and shock absorber 9. Differential unit 10. Universal joint 11. Brakes and braking systems 12. Storage battery 13. Fuel tank 14. Electrical systems 15. Silencer 16. Shock absorbers, fuel tank, petrol, and hydraulics pipe cables, and some means of mounting these components.
Classification of Chassis
The chassis can be classified into different types on the following basis.
1. According to the fitting of the engine:
(a) Full-forward (b) Semi-forward (c) Bus chassis (d) Engine at back (e) Engine at the center.
In full-forward chassis, the engine is fitted outside the driver cabin or seat. Example: Cars and Mahindra jeeps. In semi-forward chassis, a half portion of the engine is exactly in the driver’s cabin whereas the remaining half is at the front side but it is outside the driver’s cabin. Example: Tata SE series of vehicles.
chassis according to fitting
In bus chassis, the total engine is fitted in the driver cabin. It provides an increased floor area in the vehicle. The driver seat is just above the front wheel. Example: Busses and trucks. In most of vehicles, the engine is fitted at the front portion of chassis. The drive is only given to the front wheels. Example: Matador vehicles. In some vehicles, the engine is fitted at the back portion of the chassis. Example: Volkswagen cars, Leyland bus of England. In some vehicles, the engine may be fitted at the centre of the chassis. Example: Royal tiger world master buses of Delhi transport.
2. According to the number of wheels fitted in the vehicles and the number of driving wheels:
(a) 4 x 2 drive chassis – It has four wheels out of which 2 are driving wheels (b) 4 x 4 drive chassis – It has four wheels and all of them are driving wheels (c) 6 x 2 drive chassis – It has six wheels out of which 2 are driving wheels (d) 6 x 4 drive chassis – It has six wheels out of which 4 are driving wheels.
Types of automobile chassis
1. Full forward chassis:
This type of chassis consists of an engine fitted in front of the driver seat or driver cabin. It is commonly used in cars and old models of TATA trucks. The driver cannot see the road just in front of the front tires because he sits behind the engine quite far off from the front axle. To help the driver to see as close to the wheels as possible, the slope is provided at the mudguard. Moreover, passengers or goods cannot be carried in a portion of the chassis where the engine is fitted.
2. Semi-forward chassis:
This chassis, the engine is mounted in such a way that half of it is placed in the driver compartment and half out of the driver compartment. These extra passengers or luggage can be placed in the portion of chassis thus saved. Semi forward chassis are used in standard Bedford pick-ups and Tata-Mercedez trucks.
3. Bus Chassis:
To allow the driver to see the road just in front of the front wheels as well as to make driving easier and trouble-free especially in the congested areas, full forward chassis was modified by mounting the engine completely inside the driver cabin. In addition to providing an extra clear view of the road in front of the front wheels, it provided an increased floor area to accommodate three extra seats.
4. Engine at front chassis:
This chassis is used in most of the heavy vehicles is of three common types.
(i)In this type, the engines are fitted at the front but the drive to wheels is provided from the rear wheels (rear-wheel drive). (ii) In the second type, the engine is fitted at the front and the drive is also provided through the front wheels (front-wheel drive) as in the case of Matador vehicles. (iii) In the third type, the engine is fitted in front in a crosswise manner and the drive is also provided to the front wheels as in the case of B.M.C. Minis.
5) The engine fitted at the rear:
In this chassis, the engine is fitted at the rear of the vehicle thus saving a lot of space at the front eliminating long propeller shafts and providing a clear view of the road at the front. This system is used in popular vehicles like Renault, Daulphine, and Volkswagen. The engine is also mounted at the rear end of the chassis in imported Leyland Double Decker Buses. In this chassis fix up of controls like gear shift lever, oil, and fuel gauge, the accelerated linkage is very complicated. Moreover natural draft of air to the radiator due to forward motion of the vehicle is also missing.
6) The engine fitted in center chassis :
In this chassis, the engine is fitted in the centre its centre under the chassis to remove defects of the engine fitted at the rear chassis and to use the complete floor of the space. This chassis was used in Royal Tiger Wordmaster busses previously plied in Delhi by Delhi Transport Undertaking.
7) Long wheelbase chassis :
Standard truck chassis are used for making trucks and to permit the truck to carry the exact weight for which they are designed, the load is piled up. But in case of bus chassis, seats are fixed and distance between each seat is fixed as per Motor Vehicle Rules, therefore the vehicle will be running with less weight as less number of passengers can travel in it. To accommodate more passengers and to carry more weight, bus chassis are provided with a longer wheelbase(i.e. the center distance of front and rear wheels) resulting in longer chassis.
8) Overhang Chassis:
In order to increase the floor space to accommodate more goods and passengers, a certain length of the chassis is extended after the rear axle(rear overhang) and after the front axle (front overhang).
9) Half- integral and Half-frame chassis:
It is an improved form of chassis used in fiat of Padmani cars. In this chassis half-frame bolted to the floor of the vehicle is fixed at the front end, where the engine gearbox and front suspension is fixed. The rear portion of the floor functions as a frame for the vehicle body.
