UNIT
1 INTRODUCTION TO AUTOMOBILE ENGINEERING
Structure
1.1 Introduction
Objectives
1.2
Definition
1.3
Classification of Vehicles
1.4
Layout of an Automobile Chassis
1.5
Components of the Automobile
1.6
Functions of Major Components of an Automobile
1.7
Summary
1.8
Key Words
1.9 Answers to SAQs
1.1 INTRODUCTION
Automobile engineering is the
one of the stream of mechanical engineering. It deals with the various types of
automobiles, their mechanism of transmission systems and its applications.
Automobiles are the different types of vehicles used for transportation of
passengers, goods, etc. Basically all the types of vehicles works on the
principle of internal combustion processes or some times the engines are called
as internal combustion engines. Different types of fuels are burnt inside the
cylinder at higher temperature to get the transmission motion in the vehicles.
Most of the automobiles are internal combustion engines vehicles only.
Therefore, every mechanical and automobile engineers should have the knowledge
of automobile engineering its mechanism and its various applications.
Objectives
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.
1.2 DEFINITION
Automobile engineering is a
branch of engineering which deals with everything about automobiles and
practices to propel them.
Automobile is a vehicle driven
by an internal combustion engine and it is used for transportation of
passengers and goods on the ground. Automobile can also be defined as a vehicle
which can move by itself.
Examples : Car, jeep, bus, truck, scooter, etc. 6 Automobile Engineering
1.3 CLASSIFICATION OF VEHICLES
Automobiles or vehicles can be
classified on different bases as given below :
On the Basis of Load
(a)
Heavy transport vehicle (HTV) or heavy motor vehicle (HMV), e.g. trucks, buses,
etc.
(b)
Light transport vehicle (LTV), e.g. pickup, station wagon, etc.
(c) Light motor vehicle (LMV),
e.g. cars, jeeps, etc.
Wheels
(a)
Two wheeler vehicle, for example : Scooter, motorcycle, scooty, etc.
(b)
Three wheeler vehicle, for example : Autorickshaw, three wheeler scooter for
handicaps and tempo, etc.
(c)
Four wheeler vehicle, for example : Car, jeep, trucks, buses, etc.
(d) Six wheeler vehicle, for
example : Big trucks with two gear axles each having four wheels.
Fuel Used
(a)
Petrol vehicle, e.g. motorcycle, scooter, cars, etc.
(b)
Diesel vehicle, e.g. trucks, buses, etc.
(c)
Electric vehicle which use battery to drive.
(d)
Steam vehicle, e.g. an engine which uses steam engine. These engines are now
obsolete.
(e) Gas vehicle, e.g. LPG and
CNG vehicles, where LPG is liquefied petroleum gas and CNG is compressed
natural gas.
Body
On the basis of body, the
vehicles are classified as :
(a)
Sedan with two doors
(b)
Sedan with four doors
(c)
Station wagon
(d)
Convertible, e.g. jeep, etc.
(e)
Van
(f) Special purpose vehicle,
e.g. ambulance, milk van, etc.
Transmission
(a)
Conventional vehicles with manual transmission, e.g. car with 5 gears.
(b)
Semi-automatic
(c) Automatic : In automatic
transmission, gears are not required to be changed manually. It is
automatically changes as per speed of the automobile.
Position of Engine
Engine in Front
Most of the vehicles have
engine in the front. Example : most of the cars, buses, trucks in India.
Engine in the Rear Side
Very few vehicles have engine
located in the rear. Example : Nano car. 7 Introduction to Automobile Engineering
1.4 LAYOUT OF AN AUTOMOBILE CHASIS
Layout of an engine chasis is
shown in the Figure 1.1 given below :
Figure 1.1 : Chasis of a
Passenger Car
It contains the source of
power, i.e. engine, the frame, which supports the engine, wheels, body,
transmission, the braking system and the steering. It also gives support to
suspension system and springs. Besides these parts
1.5 COMPONENTS OF THE
AUTOMOBILE
The automobile can be
considered to consist of five basic components :
(a)
The Engine or Power Plant : It is source of power.
(b)
The Frame and Chasis : It supports the engine, wheels, body, braking
system, steering, etc.
(c)
The transmission which transmits power from the engine to the car wheels. It
consists of clutch, transmission, shaft, axles and differential.
(d)
The body.
(e) Accessories including
light, air conditioner/hearer, stereo, wiper, etc.
1.6 FUNCTIONS OF MAJOR
COMPONENTS OF AN AUTOMOBILE
Chasis and Frame
The chasis is formed by the
frame with the frame side members and cross members. The frame is usually made
of box, tubular and channel members that are welded or riveted together. In
addition to this, it comprises of the springs with the axles and wheels, the
steering system and the brakes, the fuel tank, the exhaust system, the
radiator, the battery and other accessories. Along with this the frame supports
the body. 8 Automobile Engineering
Engine or Power Plant
The engine is the power plant
of the vehicle. In general, internal combustion engine with petrol or diesel
fuel is used to run a vehicle. An engine may be either a two-stroke engine or a
four-stroke engine.
An engine consists of a
cylinder, piston, valves, valve operating mechanism, carburetor (or MPFI in
modern cars), fan, fuel feed pump and oil pump, etc. Besides this, an engine
requires ignition system for burning fuel in the engine cylinder.
Transmission System (Clutch
and Gear Box)
The power developed by the
engine is transferred to the wheels by transmission system. Transmission system
must do three jobs :
(a)
It must provide varying gear ratios. Number of gear ratios are equal to number
of gears in a vehicle.
(b)
It must provide a reverse gear for moving vehicle in reverse direction.
(c) It must provide a neutral
or disconnecting arrangement so that the engine can be uncoupled from the
wheels of the vehicle. In a conventional transmission system, there is a
clutch, a manually operated transmission (gear box), a propeller shaft and a
differential or final drive.
Clutch
The purpose of the clutch is to
allow the driver to couple or decouple the engine and transmission. When clutch
is in engaged position, the engine power flows to the transmission through it
(clutch). When gears are to be changed while vehicle is running, the clutch
permits temporary decoupling of engine and wheels so that gears can be shifted.
In a scooter, the clutch is operated by hand where as in a car the clutch is
operated by foot. It is necessary to interrupt the flow of power before gears
are changed. Without a clutch, it will by very difficult.
Final Drive
Final drive is the last stage
in transferring power from engine to wheels. It reduces the speed of the
propeller shaft (drive shaft) to that of wheels. It also turns the drive of the
propeller shaft by an angle of 90o to drive the wheels.
Figure 1.2 : Final Drive
The propeller shaft has a small
bevel pinion which meshes with crown wheel. The crown wheel gives rotary motion
to rear axles. The size of crown wheel in bigger than that of bevel pinion,
therefore, the speed of rear axles (or crown wheel) in lower than the speed of
pinion. Final drive is of two types, i.e. chain type and gear type.
Braking System
Brakes are used to slow down or
stop the vehicle. Hydraulic brakes are generally used in automobiles, where
brakes are applied by pressure on a fluid. Mechanical brakes are also used in
some vehicles. These brakes are operated by means of 9 Introduction to Automobile Engineering
leavers,
linkages, pedals, cams, etc. Hand brake or parking brake is usually a
mechanical brake. These are used for parking the vehicles on sloppy surfaces
and also in case of emergency.
Gear Box
Gear box contain gearing arrangement
to get different speeds. Gears are used to get more than one speed ratios. When
both mating gears have same number of teeth, both will rotate at same number
speed. But when one gear has less teeth than other, the gear with less number
of teeth will rotate faster than larger gear. In a typical car, there may be
six gears including one reverse gear. First gear gives low speed but high
torque. Higher gears give progressively increasing speeds. Gears are engaged
and disengaged by a shift lever.
Steering System
In front wheels can be turned
to left and right by steering system so that the vehicle can be steered. The
steering wheel is placed in front of driver. It is mechanically linked to the
wheels to provide the steering control. The primary function of the steering
system is to provide angular motion to front wheels so that vehicle can
negotiate a turn. It also provides directional stability to vehicle when the
vehicle moves ahead in straight line.
Figure 1.3 : Simple Driving
of a Steering System
Now-a-days, many vehicles are
equipped with power steering which uses pressure of a fluid to reduce steering
effort. When driver turns the steering wheel, a hydraulic mechanism comes into
play to provide most of the effort needed to turn the wheel.
Front Axle
Front axles are mounted at the
end of front axle. A part of the weight of vehicle is transmitted to the wheels
through this axle. The front axle performs several functions.
It carries the weight of the
front of the vehicle and also takes horizontal and vertical loads when vehicle
moves on bumpy roads. When brakes are provided on front wheels, it endures
bending stresses and torsional stresses. It is generally made from steel drop
forging. It is robust in construction.
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. 10 Automobile Engineering
SAQ 1
(a) Define automobile
engineering.
(b) Classify the vehicles on
the basis of different aspects.
(c) What are the various
components of automobile?
(d) Describe the functions of
various components of automobile.
(e) Describe the working of
steering system mechanism
0 comments:
Post a Comment