Automobile | Definition, Types, Parts [Fully Explained with Images]

By | October 17, 2018

What is an Automobile?

An automobile can be defined as

“A self-propelled passenger vehicle, used for land transport and generally has four to eight tires, and is powered by an internal combustion engine or an electric motor”

The branch of Engineering which deals with the manufacturing and technology of automotive vehicles is known as Automobile engineering.

Today automobiles play a major role in our lives, without them luxuries of modern world cannot be imagined.

Automobiles are used for both passenger and goods transport, hence performing as a lifeline to humans.

Classification of automobiles

There are several bases of classification of automobiles, hence they can be categorized as follows.

Based on purpose

  1. Passenger vehicle
  2. Goods vehicle

Based on capacity

  1. Heavy motor vehicle (HMV)
  2. Medium motor vehicle (MMV)
  3. Light motor vehicle (LMV)

Based on fuel used

  1. Petrol engine vehicles
  2. Diesel engine vehicle
  3. Gas vehicle
  4. Solar vehicle
  5. Hydrogen engine vehicle
  6. Electric powered vehicle
  7. Steam engine vehicles
  8. Hybrid vehicles
  9. Hybrid electric vehicle (HEV)

Based on transmission

  1. Automatic transmission vehicle
  2. Manual (or conventional) transmission vehicle
  3. Semi-automatic transmission vehicle

Based on number of wheels

  1. Two-wheeler
  2. Three-wheeler
  3. Four-wheeler
  4. Six-wheeler and more

Based on driving side

  1. Left handed drive automobile
  2. Right handed drive automobile

Based on drive availability

  1. Four-wheel drive
  2. All wheel drive

Components of an engine

Engine is one of the most important parts of an automobile. It is the source of power to the vehicle which is used to propel it. It is very important to understand different parts of an engine.

Parts on an engine can be classified into two parts.

  1. Stationary or structure forming components
  2. Moving or mechanism forming components

Mechanism forming components

  • Piston
  • Piston rings
  • Gudgeon pin
  • Connecting rod
  • Crank
  • Crankshaft
  • Camshaft
  • Valves
  • Valve operating mechanism timing gears
  • Chain and sprocket
  • Belt and pulley
  • Flywheel

Structural components

  • Cylinder block
  • Cylinder head
  • Gaskets
  • Cylinder liner
  • Crankcase
  • Inlet and outlet manifold
  • Oil pan
  • Resonator
  • Muffler (or silencer)
  • Vibration damper
  • Bearing
  • Fasteners
  • Turbocharger

Resistance to the motion of an automobile

While moving a vehicle has to overcome several types of resistances offered to it. Broadly the resistance can be classified into following categories.

  1. Aerodynamic drag
  2. Gradient resistance
  3. Rolling resistance
  4. Inertia


Friction clutches

Image source: NPTEL

Clutch is a machine member which connects two rotating shafts, so that driven shaft can be stopped at the will of operator without stopping driving shaft.

A clutch has to provide interruptible connection between two shafts.

Clutches are used in automobiles and often used while changing gears or using brakes. In a modern automobile clutch is situated just between engine and gear box.

Types of clutch

  • Single plate clutch
  • Multi plate clutch
  • Centrifugal clutch
  • Semi centrifugal clutch
  • Cone clutch

Clutch operating mechanisms

  1. Mechanically operated clutch
  2. Hydraulically operated clutch


Overdrive is a mechanical component which provides faster output speed for slower input speed.

Fluid coupling

A fluid coupling is used to transmit motion between two shafts with the help of acceleration and deacceleration of working fluid. It works similar to the clutch.


It is a special type of clutch which disengages driven shaft from the driving shaft when the speed of driven shaft becomes more than driving shaft.


Spur Gear Diagram

Gears are another important part of an automobile. These are used to adjust speed and torque of the wheels. Since high torque is required for starting a vehicle and high speed is required for running it.

For a given power engine speed and torque are always inversely proportional.

Types of transmissions

Manual Transmission

Several kinds of transmissions can be employed in a vehicle. Transmissions can be classified as follows.

Manual transmission

  1. Sliding mesh gearbox
  2. Constant mesh gearbox
  3. Synchronous gearbox
  4. Synchronous gearbox with overdrive

Semi-automatic transmission

  1. Electric controlled with overdrive
  2. Electric controlled without overdrive
  3. Fluid torque drive

Automatic drive

  1. Hydraulic drive
  2. Torque converter drive

Braking system

hydraulic rim brake

Brakes are used to stop or slow down the vehicle. When brakes are applied it creates a force against the motion of tires which ultimately stops the vehicle.

Requirements of an efficient braking system

There are some requirements of a good braking system. It should ensure following things.

  • It must operate on least effort
  • It produces less heat during operation
  • It should not slip
  • It must have strong braking force
  • It must act suddenly during emergency
  • The vehicle must stop at a smallest distance

Types of brakes

Following are the main types of the brakes used.

On the basis of purpose served

  1. Main brake
  2. Parking brake

On the basis of location

  1. Wheel mounted
  2. Transmission mounted

On the basis of driver’s ergonomics

  1. Hand brake
  2. Foot brake

On the basis of actuating

  1. Mechanical brake
  2. Hydraulic brake
  3. Air brake
  4. Electric brake

On the basis of construction

  1. Disc brake
  2. Drum brake

On the basis of application of brake efforts

  1. Manual brake
  2. Power brake
  3. Power assisted

On the basis of action of brake shoes

  1. External expending brake
  2. Internal expending brake

Brake lining

Drum shoes with linings

Drum shoes with linings

Brake lining is a high friction material which is used to stop the moving vehicle by providing friction resistance to the motion of vehicle.

Properties of brake lining

For high performance brake lining should have following properties

  • Low heat swell
  • Low water swell
  • Low wear rate
  • High coefficient of hot and normal friction
  • High strength and physical properties

Brake lining material

Brake linings are generally made from asbestos, rubber, metallic plates, resin, minerals and coefficient of friction modifiers.

Loads on the frame

Frame of an automobile bears several types of loads. These loads are dependent of terrain and driving conditions.

  1. Flexural (or bending) load

Factors responsible for flexural load

  • Dead weight of vehicle
  • Weight of passengers
  • Engine torque
  • Braking torque
  • Road camber
  • Cornering force
  • Side wind
  1. Torsional load (or twisting moment)

Following things are employed to curb torsional load

  • Torque resisting members
  • Cross members
  • A radius rod
  • Benzo frame type torque members
  1. Impact load

Steering system

Rack and pinion steering mechanism

A steering system provides directional stability to a vehicle. It also helps in move the vehicle in a particular direction.

Types of steering systems

There are different types of steering systems. On the basis of gearing arrangement steering systems can be classified into following types.

  1. Worm and nut steering gear
  2. Cam and lever steering gear
  3. Worm and roller steering gear
  4. Worm and sector steering gear
  5. Rack and pinion steering gear

Differential assembly

Automobile differential

A differential assembly is a special kind of gear arrangement which allows outer tire to move with a greater speed than inner tires while turning.

Types of differentials

  1. Double reduction type
  2. Power lock or non-slip
  3. Conventional

Suspension system

Mini Shock Absorbers

A good suspension system is the luxury and necessity of a modern vehicle. It prevents and mitigates sudden jerks to the vehicle from the uneven road surface. A suspension system consists spring and damper elements for its working.

Types of suspension systems

  • Leaf spring
  • Coil spring
  • Torsion bars
  • Air suspension
  • Automatic level control

Image source:

Gear: Attribution: By Inductiveload – Self-madeiThe source code of this SVG is valid.This vector image was created with Inkscape., Public Domain,

Transmission: Attribution: By Tuner tom – Own work, CC BY-SA 3.0,

Brake: Attribution: By AndrewDressel at English Wikipedia, CC BY-SA 3.0,

Brake shoe: Attributions: By Maly LOLek – Own work, CC BY-SA 3.0,

Steering system: Attributions: By LaurensvanLieshout – Own work, CC BY-SA 3.0,

Differential: Attributions: By Aconcagua (talk) – Own work, CC BY-SA 3.0,

Suspension: Attribution: By Avsar Aras – Own work, CC BY-SA 3.0,

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