Automobiles: Definition, Classification, and Components

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Automobile engineering is the one of the best stream of mechanical engineering. It deals with the various types of automobiles engineering, their mechanism of transmission systems and its applications. Automobiles are the used different types of the vehicles for transportation of passengers, goods, etc.

Basically all the types of the vehicles works on the principle of internal combustion processes or sometimes the engines are called as internal combustion engines. Different types of fuels are the burnt inside the cylinder at higher temperature to get the high transmission motion in the vehicles. Most of the automobiles system are the internal combustion engines vehicles only. Therefore, every mechanical engineer and automobile engineers should have the knowledge of automobile engineering its mechanism and its various applications.


  • After studying this unit, you should be able to
  • define automobile engineering,
  • classify the vehicles,
  • list the various components of automobile, and
  • describes the function of components of automobile


Automobile engineering is the branch of engineering which deals with the everything about automobiles and practices to propel them. Automobile is the vehicle driven by the internal combustion engine and it is used for transportation of passengers, goods and riding on the ground. Automobile can also be the defined as a vehicle which can be moved by itself. Examples: Car, jeep, bus, truck, scooter, etc.

Classification of Automobile

Automobiles or vehicles can be classified into different bases as given below:

On the Basis of Load

  • Heavy transport vehicle (HTV) and heavy motor vehicle (HMV), e.g. trucks, buses, car, jeep etc.
  • Light transport vehicle (LTV), e.g. pickup, station wagon, etc.
  • Light motor vehicle (LMV), e.g. cars, jeeps, etc.


  • Two wheeler vehicle types, for example: Scooter, motorcycle, scooty, etc.
  • The three wheel drive vehicle, for example: Auto rickshaw, three wheeler scooter for handicaps and tempo, etc.
  • Four wheeler vehicle, for the example: Car, jeep, trucks, buses, tempo etc.
  • Six wheeler vehicle, for the example: Big trucks with the two gear axles for each having four wheels drive.

Fuel Used

  • Petrol vehicle, e.g. motorcycle, scooter, cars, etc.
  • Diesel vehicle, e.g. trucks, buses, etc.
  • Electric vehicle (EV) which is the use battery to drive.
  • Steam vehicle, e.g. an engine which uses steam engine. These engines are now obsolete.
  • Gas vehicle, e.g. LPG and CNG vehicles, where is the LPG liquefied petroleum gas and CNG is the compressed natural gas.


On the basis of the body vehicles are classified as below :

  • Sedan with two doors
  • Sedan with four doors
  • Station wagon
  • Convertible, e.g. jeep, etc.
  •  Van
  • Special purpose vehicle, e.g. ambulance, milk van, etc.


  • Conventional vehicles with manual transmission, e.g. car with 5 gears.
  • Semi-automatic
  • Automatic: In automatic transmission system, gears are the not required to be changed manually. It is automatically changes as per the speed of the automobile vehicles.

 Position of Engine

Engine in Front

Most of the vehicles have the engine in the front of vehicles. Example: most of the cars, buses, trucks, jeep,tempo in India.

Engine in the Rear Side

 Very few vehicles have the engine located in the rear side. Example: Nano car


The automobile system can be the considered as to consist of the five basic components:

  • Is the Engine or Power Plant: It is the source of power plant.
  • The Frame and Chassis: It is the supports engine, wheels, body, braking system, steering, etc.
  • The transmission which transmits the power from the engine into the car wheels. The consists of the clutch, transmission, shaft, axles and differential.
  • The body.
  • Accessories are including light, air conditioner/hearer, stereo, wiper, etc.


A brake is a mechanical device which inhibits motion, slowing or stopping a moving object and preventing its motion. The rest of this article is dedicated to the various types of vehicle brakes system.

Most of commonly brakes use the friction between the two surfaces and pressed together to convert the kinetic energy of the moving object into heat, though other methods of energy conversion may be employed. For example the regenerative braking converts so much of the energy to the electrical energy, which may be stored for later use. Other methods convert kinetic energy into potential energy in such stored forms as pressurized air or pressurized oil. Eddy current brakes are use magnetic fields to be converted kinetic energy into electric current in the brake disc, fin, or rail, which is converted into heat. The other still braking system even transfer kinetic energy into the different forms, for example by transferring the energy to a rotating flywheel energy.

Brakes are the generally applied to the rotating axles or wheels, but may be also take other forms such

as the surface of the moving liquid fluid (flaps deployed into water or air). Some vehicles are use as the combination of braking mechanisms, such as the drag racing cars with the both wheels brakes and a parachute, or airplanes with both wheel brakes and drag flaps increased into the air during landing.

Since kinetic energy increases quadratic ally with velocity (K=1/2 mv2 ), an object moving at 10 m/s has 100 times as much energy as one of the same mass moving at 1 m/s, and the  consequently the theoretically braking distance, when braking at the frication limit, is 100 times as long. In practice, fast vehicles usually have the significant air drag system, and the energy lost to air drag rises quickly with high speed. Almost all the wheels vehicles have the brake of some sort. Even baggage carts and the shopping carts may have them for the use on as moving ramp. Most fixed-wing aircraft are fitted with the wheel brakes on the under-carriage. Some aircraft also feature the air brakes system designed to reduce their speed in the flight.

When the brake pedal of the modern vehicle braking system with hydraulic brakes is the pushed, ultimately a piston pushes the brake pad against the brake disc which slows the wheel down. On the brake drum system it is similar to the cylinder pushes the brake shoes against the drum which also slows the wheel down. Brakes may be broadly defined as the using friction, pumping, or electromagnetic.

One brake system may be use the several principles of brake system: for example, a pump may pass fluid through an orifice to create the friction: Frictionally brakes are most commonly and can be the divided broadly into the “shoes” or “pads” brakes, using an explicit wear surface, and hydrodynamic brakes, such as parachutes, which is use friction in the working fluid and do not explicitly wear.

Typically the terms “friction brake system” it is the used to mean pads/shoes brakes and excludes hydrodynamic brakes, even though hydrodynamic brakes use friction. Friction (pad/shoe) brakes are often rotating devices with a stationary pad and a rotating wear surface.

Common configurations include shoes that contract to rub on the outside of a rotating drum, such as a band brake; a rotating the drum with shoes that expand to the rub inside of the drum, commonly called as a “drum brake system”, although other drum configurations are possible; and pads that pinch a rotating disc, commonly called a “disc brake”


The disc brake is a device for slowing or stopping the rotation of the wheel while it is in motion. A brake disc is generally use made of cast iron, but may in some cases be made of composites such as reinforced carbon-carbon or ceramic-matrix composites.

This is the connected to the wheel and the axle. To stop the brake wheel, friction material in the form of brake system pads mounted on a device called a brake calliper is forced mechanically, hydraulically, pneumatically or electromagnetically against both sides of the disc. The friction causes the disc and attached wheel to slow or brake. Brakes both the disc and drum convert motion to heat, but if the brakes get too hot, they will become less effective because they cannot dissipate enough heat. This condition of failure is known as the brake fade.


The most of common arrangement of the hydraulic brakes for passenger vehicles, motorcycles, scooters, and mopeds, jeep, consists of the following.

  • Brake pedal or lever
  • A push-rod (also called an actuating rod)
  • The master cylinder assembly containing a piston assembly
  • Reinforced hydraulic lines
Braking system

Brake calliper assembly usually consisting of the one or 2 hollow aluminium and chrome plated steel pistons called as the calliper pistons, a set of thermally conductive brake pads and a rotor also called a the brake disc or drum brake  attached to an axle. The brake system is usually filled with the glycol-ether based brake fluid other fluids may also be used.

At the one time, passenger vehicles commonly employed drum brakes system on all four wheels. Later, disc brakes system were used for the front and drum brakes system for the rear. However disc brakes have shown the better heat dissipation and increase resistance to ‘fading’ and are therefore generally safer than drum brakes. Many 2-wheeler vehicle designs, however, continue to the employ a drum brake for the rear wheel.

In the hydraulic braking system, when the brake pedal is pressed, a push-rod exerts force on the piston(s) in the master cylinder, causing fluid from the brake fluid reservoir to flow into a reassure chamber through a compensating port. This results is increase in the pressure of the entire hydraulic braking system, forcing fluid through the hydraulic lines toward one or more callipers where it acts upon one or 2 calliper pistons sealed by one and more seated O-rings which prevent leakage of the fluid.

 The brake calliper pistons is apply to force to the brake pads, pushing them against the spinning rotor, and the friction between to the pads and the rotor causes the braking torque to be generated, slowing a vehicle. Heat generated by this friction is the either dissipated through vents and channels in the rotor or is conducted through the pads, which are made of specialized heat-tolerant materials such as Kevlar or sintered glass.

Subsequent release the brake pedal/lever allows the spring in my master cylinder assembly to return the master piston back into position. This action is first relieves the hydraulic pressure on the brake caliper, then applies suction to the brake piston in the caliper assembly, moving it back into its housing and allowing to the brake pads to be release the rotor.


An air brake system and more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake paddle needed to the stop the vehicle. Air brakes are used in the large heavy loaded vehicles, particularly those having a multiple trailers which must be the linked into the brake system, such as trucks, buses, trailers, and the semi-trailers in addition to their use in the rail road trains.


Air braking systems are the typically used on heavy trucks and buses. The system consists of the service brakes, parking brakes, control pedal, and an air storage tank. For the parking brake, there is a disc brake or drum brake arrangement which is the designed to be held in the ‘applied’ position by spring pressure. Air braking pressure must be the produced to release these “spring break” parking brakes. For the service brakes is ones of  used while the driving for slow or stop to be applied, the brake pedal is pushed, routing the air under pressure approx. 100–120 PSI and 690–830 Pascal (Kpa) to the brake chamber, causing the brake to be engaged.

Most types of the truck are used air brakes are the drum brakes system, though there is an increasing trend towards the use of disc brakes in this application. Air is compressor draws filtered air from the atmosphere and forces it into the high-pressure reservoirs at around 120 psi 830 kPa. Most the heavy vehicles have a gauge within the driver view, indicating the availability of the air pressure for the safe vehicle operation, often including warning tones or lights. Setting of the parking or emergency brake releases the pressurized air in the lines between the compressed air storage tank and the brakes, thus allowing the spring actuated parking. Brake to engage. The sudden loss of air pressure would be result in full spring breaking pressure immediately.

The air compressed brake system is divided into the supply system and a control system. The supply system of compresses, stores and supplies high-pressure system air to the control system as well as to additional air operated auxiliary truck systems gearbox shift control, clutch pedal air assistance servo, etc.

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