Automobile Engineering: Chassis, Engines, and Systems
Unit 1: Automobile Engineering Fundamentals
Definition of an Automobile
An automobile is a self-propelled road vehicle designed to transport passengers or goods from one place to another without the need for external power. It operates mainly with the help of an internal combustion engine or an electric motor, which converts fuel or electrical energy into mechanical energy for movement.
An automobile consists of several important systems and components such as the engine, transmission system, steering system, braking system, suspension system, wheels, tyres, and chassis. These components work together to provide motion, control, safety, comfort, and stability of the vehicle.
[Diagram: Fig. 01 – Automobile Chassis Layout]
Major Components of an Automobile Chassis
- Frame or chassis
- Engine
- Clutch
- Gear box
- Propeller shaft
- Differential
- Front axle
- Rear axle
- Suspension system
- Steering system
- Braking system
- Wheels and tyres
- Fuel tank
- Radiator and cooling system
Working of a 4-Stroke CI Engine
A four-stroke compression ignition (CI) engine is an internal combustion engine in which only air is compressed inside the cylinder and fuel is injected at the end of the compression stroke. Due to the high temperature produced by compression, the fuel burns automatically without the use of a spark plug. The cycle of operation is completed in four strokes of the piston and two revolutions of the crankshaft.
[Diagram: Fig. 02 – 4-Stroke CI Engine]
Four Strokes of a CI Engine
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1) Suction Stroke:
- a) The inlet valve remains open and the exhaust valve remains closed.
- b) The piston moves from Top Dead Centre (TDC) to Bottom Dead Centre (BDC).
- c) Only fresh air enters the cylinder during this stroke.
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2) Compression Stroke:
- a) Both inlet and exhaust valves remain closed.
- b) The piston moves from BDC to TDC and compresses the air to a very high pressure and temperature.
- c) Near the end of the compression stroke, diesel fuel is injected into the cylinder by the fuel injector.
- d) The fuel gets ignited automatically due to the high temperature of compressed air.
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3) Power or Expansion Stroke:
- a) The burning fuel produces high-pressure gases.
- b) These gases force the piston to move from TDC to BDC.
- c) Both valves remain closed during this stroke.
- d) This is the only stroke that produces useful power.
-
4) Exhaust Stroke:
- a) The exhaust valve opens and the inlet valve remains closed.
- b) The piston moves from BDC to TDC.
- c) Burnt gases are expelled out of the cylinder through the exhaust valve.
- d) After this stroke, the cycle repeats again.
Main Components of a CI Engine
- Cylinder
- Piston
- Connecting rod
- Crankshaft
- Inlet valve
- Exhaust valve
- Fuel injector
- Combustion chamber
- Flywheel
- Cylinder head
Advantages of a CI Engine
- Higher thermal efficiency
- Better fuel economy
- High torque output
- Longer engine life
- Suitable for heavy vehicles
Applications of CI Engines
- Trucks
- Buses
- Tractors
- Generators
- Construction equipment
Working of a 4-Stroke SI Engine
A four-stroke spark ignition (SI) engine is an internal combustion engine in which the air-fuel mixture is ignited by a spark produced by the spark plug. Petrol is generally used as fuel in this engine. The cycle of operation is completed in four strokes of the piston and two revolutions of the crankshaft.
[Diagram: Fig. 03 – 4-Stroke SI Engine]
Four Strokes of an SI Engine
-
1) Suction Stroke:
- a) The inlet valve remains open and the exhaust valve remains closed.
- b) The piston moves from Top Dead Centre (TDC) to Bottom Dead Centre (BDC).
- c) During this movement, the air-fuel mixture enters the cylinder through the inlet valve.
-
2) Compression Stroke:
- a) Both inlet and exhaust valves remain closed.
- b) The piston moves from BDC to TDC and compresses the air-fuel mixture.
- c) At the end of the compression stroke, the spark plug produces an electric spark to ignite the compressed mixture.
-
3) Power or Expansion Stroke:
- a) The combustion of the air-fuel mixture produces high-pressure gases.
- b) These gases force the piston to move from TDC to BDC.
- c) Both valves remain closed during this stroke.
- d) This is the only stroke which produces useful power.
Main Components of an SI Engine
- Cylinder
- Piston
- Connecting rod
- Crankshaft
- Inlet valve
- Exhaust valve
- Spark plug
- Combustion chamber
- Flywheel
- Carburetor or fuel injector
Advantages of an SI Engine
- Simple construction
- Smooth operation
- Less noise and vibration
- High-speed operation
- Lower initial cost
Applications of SI Engines
- Motorcycles
- Cars
- Scooters
- Small generators
- Light transport vehicles
Need for an Engine Lubrication System
The lubrication system is used in an automobile engine to supply lubricating oil to the moving parts of the engine in order to reduce friction and wear between the contacting surfaces.
Functions of a Lubrication System
- Reduces friction between moving parts.
- Minimizes wear and tear of engine components.
- Removes heat generated due to friction.
- Cleans engine parts by carrying away dirt and carbon particles.
- Prevents rust and corrosion of metal surfaces.
- Provides sealing between piston rings and cylinder walls.
- Reduces noise produced by moving parts.
- Increases efficiency and life of the engine.
Classification of Lubrication Systems
- Splash lubrication system
- Pressure lubrication system
- Wet sump lubrication system
- Dry sump lubrication system
- Semi-pressure lubrication system
1) Splash Lubrication System
Working:
- a) In this system, lubricating oil is stored in the oil sump.
- b) A dipper attached to the connecting rod dips into the oil during engine operation.
- c) The rotating crankshaft splashes oil to different engine parts such as cylinder walls, piston, and bearings.
- d) The oil returns back to the sump after lubrication.
[Diagram: Fig. 04 – Splash Lubrication System]
Advantages:
- a) Simple construction.
- b) Low cost.
- c) Easy maintenance.
Disadvantages:
- a) Inadequate lubrication at high speed.
- b) Not suitable for multi-cylinder engines.
- c) Uneven oil supply.
Applications:
- a) Small stationary engines.
- b) Scooters and mopeds.
- c) Small agricultural engines.
2) Wet Sump Lubrication System
Working:
- a) In this system, lubricating oil is stored in the oil sump located below the crankcase.
- b) An oil pump draws oil from the sump through a strainer.
- c) The oil is supplied under pressure to various engine parts through oil passages.
- d) After lubrication, oil returns to the sump by gravity.
[Diagram: Fig. 05 – Wet Sump Lubrication System]
Advantages:
- a) Simple and compact system.
- b) Less cost.
- c) Easy lubrication arrangement.
Disadvantages:
- a) Oil starvation may occur during sharp turns or slopes.
- b) Cooling of oil is limited.
- c) Not suitable for racing vehicles.
Applications:
- a) Passenger cars.
- b) Motorcycles.
- c) Light commercial vehicles.
3) Dry Sump Lubrication System
Working:
- a) In this system, oil is stored in a separate oil tank outside the engine crankcase.
- b) The pressure pump supplies oil from the tank to engine parts.
- c) After lubrication, the oil collects in the crankcase.
- d) A scavenging pump transfers the oil back to the external oil tank.
- e) The cycle repeats continuously.
[Diagram: Fig. 06 – Dry Sump Lubrication System]
Advantages:
- a) Better lubrication at high speed.
- b) Improved cooling of oil.
- c) Prevents oil starvation during sharp turns and inclinations.
- d) Longer engine life.
Disadvantages:
- a) Complex construction.
- b) Higher cost.
- c) Requires more space.
Applications:
- a) Racing cars.
- b) Sports cars.
- c) Aircraft engines.
- d) Heavy-duty vehicles.
Need for an Engine Cooling System
The cooling system is used in an automobile engine to remove excess heat produced during combustion and maintain the engine temperature within the suitable operating range.
Functions of a Cooling System
- a) Prevents overheating of the engine.
- b) Maintains proper operating temperature.
- c) Improves engine efficiency.
- d) Prevents seizure and distortion of engine parts.
- e) Reduces wear and tear of components.
- f) Increases engine life.
- g) Prevents lubricating oil from burning.
- h) Ensures smooth and efficient engine operation.
Classification of Cooling Systems
Types of Cooling Systems:
- Air cooling system
- Water cooling system
Types of Water Cooling Systems:
- Thermosyphon cooling system
- Pump or forced circulation cooling system
- Pressure cooling system
1) Air Cooling System
Working:
- a) In this system, the heat from the engine cylinder is directly dissipated to the surrounding air.
- b) Fins are provided on the cylinder head and cylinder walls to increase the surface area.
- c) Air flows over the fins either naturally or by a fan.
- d) The heat is carried away by the moving air.
[Diagram: Fig. 07 – Air Cooling System]
Advantages:
- a) Simple construction.
- b) Light in weight.
- c) No leakage problem.
- d) Low maintenance cost.
Disadvantages:
- a) Cooling is not uniform.
- b) Less efficient for large engines.
- c) Engine becomes noisy.
Applications:
- a) Motorcycles.
- b) Scooters.
- c) Small aircraft engines.
- d) Small portable engines.
2) Thermosyphon Cooling System
Working:
- a) This system works on the principle of natural circulation of water due to density difference.
- b) Water heated in the engine jacket becomes lighter and rises upward to the radiator.
- c) In the radiator, water gets cooled by air circulation.
- d) The cooled water becomes heavier and returns to the engine water jacket.
- e) Thus, continuous circulation of water takes place without using a pump.
[Diagram: Fig. 08 – Thermosyphon Cooling System]
Advantages:
- a) Simple construction.
- b) No water pump required.
- c) Low maintenance cost.
Disadvantages:
- a) Slow circulation of water.
- b) Less efficient cooling.
- c) Not suitable for heavy vehicles.
Applications:
- a) Old automobiles.
- b) Small stationary engines.
- c) Small tractors.
3) Pressure Cooling System
Working:
- a) In this system, cooling water circulates under pressure through the engine water jackets and radiator.
- b) A water pump forces the coolant through the engine passages.
- c) The radiator is sealed with a pressure cap to maintain pressure inside the system.
- d) Due to increased pressure, the boiling point of water increases and better cooling is achieved.
- e) The cooled water again circulates to the engine continuously.
Advantages:
- a) Efficient cooling system.
- b) Prevents boiling of coolant.
- c) Suitable for high-speed engines.
- d) Uniform cooling is achieved.
Disadvantages:
- a) Complex construction.
- b) Higher maintenance cost.
- c) Requires pump and pressure fittings.
Applications:
- a) Modern cars.
- b) Trucks and buses.
- c) Heavy-duty diesel engines.
- d) High-performance vehicles.
Classification of Automobile Frames
The frame is the main supporting structure of an automobile on which all the components such as the engine, transmission system, body, and wheels are mounted.
Types of Automobile Frames
- a) Conventional frame
- b) Integral frame
- c) Semi-integral frame
- d) Frameless chassis (Monocoque chassis)
Frameless Chassis (Monocoque Chassis)
- Frameless chassis is also called monocoque chassis or unitary construction.
- In this type, there is no separate frame used in the vehicle.
- The vehicle body itself acts as the load-carrying structure.
- Engine, transmission system, and suspension are mounted directly on the body.
- The body and chassis are manufactured as a single unit.
- The load and stresses are distributed throughout the body shell.
- It reduces the overall weight of the automobile.
- It provides better fuel efficiency due to less weight.
- It gives better stability and riding comfort.
- It provides more passenger and luggage space.
- Repairing is difficult in case of major damage or accident.
- Frameless chassis is commonly used in modern cars, SUVs, and sports vehicles.
[Diagram: Fig. 09 – Frameless Chassis]
Important Components of an Engine
- Cylinder
- Cylinder head
- Piston
- Piston rings
- Connecting rod
- Crankshaft
- Camshaft
- Inlet valve
- Exhaust valve
- Spark plug
- Fuel injector
- Flywheel
- Crankcase
- Gudgeon pin
- Timing gear
Functions of Key Engine Components
-
1) Cylinder:
- a) The cylinder is the main working part of the engine in which the piston moves up and down.
- b) It forms the combustion chamber where fuel burns and power is produced.
- c) It also guides the piston movement and withstands high pressure and temperature.
-
2) Piston:
- a) The piston is a cylindrical component fitted inside the cylinder.
- b) It receives force from the high-pressure gases produced during combustion.
- c) It transmits this force to the connecting rod.
- d) It also helps in compressing the air-fuel mixture inside the cylinder.
-
3) Connecting Rod:
- a) The connecting rod connects the piston to the crankshaft.
- b) It transmits the force developed on the piston to the crankshaft.
- c) It converts the reciprocating motion of the piston into rotary motion of the crankshaft.
-
4) Crankshaft:
- a) The crankshaft is connected to the connecting rod and rotates inside the crankcase.
- b) It converts the reciprocating motion of the piston into rotary motion.
- c) It transmits engine power to the flywheel and transmission system.
- d) It also drives various engine accessories.
-
5) Flywheel:
- a) The flywheel is mounted on the crankshaft.
- b) It stores energy during the power stroke and supplies it during other strokes.
- c) It helps in maintaining uniform engine speed.
- d) It reduces vibration and ensures smooth running of the engine.
Difference Between 2-Stroke and 4-Stroke Engines
| 2-Stroke Engine | 4-Stroke Engine |
|---|---|
| The cycle is completed in two strokes of the piston. | The cycle is completed in four strokes of the piston. |
| Requires one revolution of crankshaft for one power stroke. | Requires two revolutions of crankshaft for one power stroke. |
| Power stroke occurs in every revolution. | Power stroke occurs in every two revolutions. |
| Construction is simple. | Construction is comparatively complex. |
| Has ports instead of valves. | Uses inlet and exhaust valves. |
| Produces more power for same engine size. | Produces less power for same engine size. |
| Fuel consumption is high. | Fuel consumption is less. |
| Lubrication is difficult and less effective. | Lubrication is better and more effective. |
| More smoke and pollution are produced. | Less smoke and pollution are produced. |
| Engine life is shorter due to more wear. | Engine life is longer. |
| Cooling requirement is higher. | Cooling requirement is lower. |
| Used in scooters, motorcycles and small engines. | Used in cars, trucks and heavy vehicles. |