09-09-2014, 11:06 AM
AUTOMOBILE ENGINEERING
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INTRODUCTION
Automobile is a self-propelled vehicle used for transportation of goods and
passengers on the ground. Automobiles or Automotive means a vehicle which can move by
itself. It differs from aeronautical vehicle ship, like aeroplanes, helicopters, rockets e.t.c
which fly in air as well as from marine vehicles like motor boat which sail in water.
The automobile is essentially a transportation equipment unit. It is made up of a frame
supporting the body and certain power-developing and transmitting units. These are further
supported by tyres and wheels through the springs and axles. The engine supplies the power.
It is delivered by the transmitting system and the rear axles through the clutch or fluid
coupling to the rear wheels. The automobile is propelled through the friction of the contact
between the road and the wheels. The various units are held together in proper arrangement
on the frame. The protection and comfort is provided by the body of the vehicle.
Germany is the birth place of automobile. It was invented there. It went through its
first phases there and it was developed there to a high level of technical maturity. The list of
German automobile pioneers is a long one starting with Nicholas Cugnot, August, Otto, Carl
Benz, Gottlieb, Daimler, Wilhelm Maybach and Rudolf Diesel and going all the way up to
Ferdinand Posche and Felix Wankel.
GENERAL CLASSIFICATION OF VEHICLES
There are numerous types of automobiles used in the world. In general, there are three
main classifications of the various types of vehicles:
i.) The single unit vehicles or load carriers
ii.) Articulated vehicles
iii.) The heavy tractor vehicles
Articulated Vehicles
A lower powered three-wheeler with a single steering wheel in front and a
conventional rear driving axle is an example of articulated vehicles. It has a greater handling
ability in awkward places. It can be turned about its own tail due to the three-wheel
construction. The coupling mechanism between semi-trailer and tractor in most of these vehicles is arranged for automatic connection and coupling up necessitating only its reversing
into the position. But for uncoupling operation, a lever is provided within the driver’s cabin
to reverse the whole process. A pair of retractable wheels in front is also provided. Along
with the coupling or uncoupling operation, they can be raised or lowered automatically.
TYPES OF CYLINDER ENGINE
By enlarging the size of a single cylinder or having more cylinders of same size
increases the power developed by an engine. Although a single large cylinder has fewer parts
to manufacture and maintain, yet the advantage of are over – weighed by the disadvantages.
This is due to the fact that the power may be increased by increasing the size of the cylinder,
but the engine power varies as the square of the bore with the weight varying as the cube of
the bore for a given speed and cylinder pressure. Therefore, by doubling the bore in size, the
power would become four times as great while the weight would become eight times . hence
the weight increase at a greater rate in comparison to the power providing a lower power to
weight ratio.
The multi – cylinder engines are capable of producing higher powe output due to
increase in revolution per minute in comparison to single cylinder engines. The benefits
derived from multi – cylinder engines all developing the same horse power will be clear from
Table 1.1
The Single Cylinder Engine
This engine is generally employed in auto cycles, motor cycles and on certain small three
wheeled cars. In this engine, there is only one power stroke in two revolutions of the
crankshaft. It may be two or four-stroke cycle engine. 600 to 700c.c. is maximum size of such
an engine. Very heavy flywheels are required for size above this. Due to the lack of balance
of the reciprocating parts, the vibrating effects are very much marked. The crankshaft
consists of one crankpin and the two main journals made either as a one-piece forging of
alloy steel or as bolted together assembly.
BODY AND CHASIS
The shape of the chassis is determined by location of the power unit, the arrangement
of the suspension system and the loads to be carried. The function of the chassis is to act as
the frame or skeleton of the vehicle, providing a mounting for all the other assembles and
keeping them in correct relative positions, inspite of all the varying loads to which they are
subjected. It must be strong and rigid, and is usually made from steel pressings which are
welded and riveted together. Reinforcement is provided, where necessary, to add to its
rigidity
LAYOUT OF A CHASSIS AND ITS MAIN COMPONENTS
Various components of the motor vehicle, i.e. engine car body, wheels e.t.c. are
required to be supported. These are supported on a rigid structure providing a skeleton to hold
the components together. To withstand the shocks, blows, twists and vibrations coming
during operation, chassis are provided cross-bracings to increase rigidity. The whole of the
chassis is now fastened to a frame of channel or U-shaped section. The engine is mounted in
the front portion of frame through rubber cushioned motor mounts or pads or washer placed
between the brackets on the frame and support lugs on the engine.
VEHICLE COMPONENTS
An automobile is a combination of a large number of parts. It can be divided into
chassis and body as the two major constituents. Body is the part where the passengers have
their seat on the luggage and cargo to be carried is placed. Chassis is the main machine
portion, which contain most of the components required for the operation and running of the
automobile. The portion of the automobile without body is called chassis. The body fixed
over the frame of the vehicle is generally detachable. All parts and accessories needed for the
comfort of the human being are contained in the body of the vehicle. These include doors,
windows, lights, fans, seats, air-conditioner and other accessories. The body differing in
shape and size from vehicle to vehicle is generally made of steel and wood or steel alone.
The components of the cars and their proper locations are discussed below:
INTERNAL COMBUSTION ENGINES
In the internal combustion engine, combustion takes place within the engine unlike in
steam engine which works by virtue of the introduction of steam which has been raised
externally in a boiler. All internal combustion (I.C.) engines aspirate air into which is
introduced a measured quantity of fuel. This fuel burns within the engine and in such a way
that it produces a high pressure, high temperature gas.
There are two principal classes of reciprocating internal-combustion engine. They are
distinguished mainly by whether the combustion is initiated by spark, or spontaneously by
virtue of the rise in temperature during compression process. Petrol and gas engines are
referred to as spark-ignition (or SI) engines while diesel and oil engine are referred to as
compression-ignition (or C.I.) engines.
In the theoretical cycles described under power cycles, there is no chemical change in
the working fluid, the working fluid is assumed to be air, and the heat exchanges in the cycle
are made externally to working fluid. In the practical cycle, the heat supply is obtained from
the combustion of a fuel in air and thus the air charge is consumed during combustion and the
combustion products must be exhausted from the cylinder before a fresh charge of air can be
induced for the next cycle
Comparison between Carburettors and Petrol Injection Systems
The carburettor is a simple, cheap device which has served its purpose for many
years, but the trend to higher powered multi cylinder engines has shown the carburetor
system to be inadequate. As a consequence several designs of petrol injection system have
been introduced to meet increasingly sophisticated engine requirements. The petrol injection
system, from the point of view of control, is accurate in fuel metering and has good fuel
consumption characteristics in comparison with the carbureted petrol engine at has poor fuel
consumption.
In recent years the added requirement for engines to meet exhaust gas emission
regulations has increased the demand for accurate fuel metering and engine control. These
factors have increased the interest in petrol injection system.
FUEL INJECTION FOR DIESEL ENGINES
The function of a fuel injection system is to meter the fuel accurately and uniformly to
the engine cylinders under all operating conditions from idling to full load. The timing of the
injection should be accurate enough to give the required combustion characteristics. The fuel
from the tank is filtered before passing to the pump, and the metered fuel is than passed to the
injector which is fitted in the engine cylinder.
WHEEL ALIGNMENT
Alignment of automobile wheels is defined as the correct adjustment of pivot axes
controlling the movement of the wheels. The wheel alignment, therefore, refers to the
positioning of the front wheels and steering mechanism for promoting ease of steering,
reduce tyre wear to minimum as well as to provide directional stability to the vehicle.
Excessive tyre wear, vibration, stability to the vehicle. Excessive tyre wear, vibration, hard
steering, shimmy etc. are caused due to incorrect alignment of wheels. For making wheel
alignment, the following checking, inspection and adjustment should be made
WHEEL BALANCING
In order to maintain good steering, proper balancing of the front wheel is necessary.
Unbalanced front-wheel assembly results in tramp or high-speed shimmy while the
unbalanced rear wheels producing variations in the vehicles also affect the front suspension
system. The unbalanced wheels also result in uneven tyre wear and rough ride. For ensuring
the rotation of wheel free from vibration, balancing of the wheel assembly is necessary. By
adding small weights on the rim of the wheel, an unbalanced wheel assembly gets balanced.
A special machine known as wheel balancing machine is used to balance and determine the
location of balancing weights on the rim