ME- 314 F AUTOMOBILE ENGINEERING LAB
Sessional : 25 Marks
L T P Practical : 25 Marks
- - 2 Total : 50Marks
Duration of Exam : 3 hrs.
List of Experiments:
1. To study and prepare report on the constructional details, working principles and operation of the following Automotive Engine Systems & Sub Systems.
(a) Multi-cylinder : Diesel and Petrol Engines.
(b) Engine cooling & lubricating Systems.
(c) Engine starting Systems.
(d) Contact Point & Electronic Ignition Systems.
2. To study and prepare report on the constructional details, working principles and operation of the following Fuels supply systems:
(a) Carburetors
(b) Diesel Fuel Injection Systems
(c) Gasoline Fuel Injection Systems.
3. To study and prepare report on the constructional details, working principles and operation of the following Automotive Clutches.
(a) Coil-Spring Clutch
(b) Diaphragm – Spring Clutch.
(c) Double Disk Clutch.
4. To study and prepare report on the constructional details, working principles and operation of the following Automotive Transmission systems.
(a) Synchromesh – Four speed Range.
(b) Transaxle with Dual Speed Range.
(c) Four Wheel Drive and Transfer Case.
(d) Steering Column and Floor – Shift levers.
5. To study and prepare report on the constructional details, working principles and operation of the following Automotive Drive Lines & Differentials.
(a) Rear Wheel Drive Line.
(b) Front Wheel Drive Line.
(c) Differentials, Drive Axles and Four Wheel Drive Line.
6. To study and prepare report on the constructional details, working principles and operation of the following Automotive Suspension Systems.
(a) Front Suspension System.
(b) Rear Suspension System.
7. To study and prepare report on the constructional details, working principles and operation of the following Automotive Steering Systems.
(a) Manual Steering Systems, e.g. Pitman –arm steering, Rack & Pinion steering.
(b) Power steering Systems, e.g. Rack and Pinion Power Steering System.
(c) Steering Wheels and Columns e.g. Tilt & Telescopic steering Wheels, Collapsible Steering Columns.
8. To study and prepare report on the constructional details, working principles and operation of the following Automotive Tyres & wheels.
(a) Various Types of Bias & Radial Tyres.
(b) Various Types of wheels.
9. To study and prepare report on the constructional details, working principles and operation of the Automotive Brake systems.
(a) Hydraulic & Pneumatic Brake systems.
(b) Drum Brake System.
(c) Disk Brake System.
(d) Antilock Brake System.
(e) System Packing & Other Brakes.
10. To study and prepare report on the constructional details, working principles and operation of Automotive Emission / Pollution control systems.
11.
Modeling of any two automotive systems on 3D CAD using educational
softwares (eg. 3D modeling package/Pro Engineering/I-Deas/ Solid edge
etc.)
12. Crash worthiness of the designed frame using Hypermesh and LS-Dyna solver or other software.
NOTE :
1. At least ten experiments are to be performed in the Semester.
2.
At least seven experiments should be performed from the above list.
Remaining three experiments may either be performed from the above list
or as designed & set by the concerned institution as per the scope
of the syllabus.
Experiment No:1
Aim: To
study and prepare report on the constructional details, working
principles and operation of the Automotive Engine Systems & Sub
Systems.
Apparatus: Models of
(a) Multi-cylinder : Diesel and Petrol Engines.
(b) Engine cooling & lubricating Systems.
(c) Engine starting Systems.
(d) Contact Point & Electronic Ignition Systems.
Theory:
(a) Multi-cylinder: Diesel and Petrol Engines.
Both
are internal combustion engines. The difference is that Diesel engine
is CI (compression Ignition) and petrol is SI (Spark Ignition). In a
petrol engine spark is used to initiate the ignition of the petrol air
mixture. In a diesel engine the Air is compressed to 21 times its normal
volume (Approx) and then fuel is injected into the Cylinder head/ or
piston, due to the high compression the temperature rises and as fuel is
injected it ignites.
Both
diesel and petrol engines may be 2 stroke or 4 stroke engines. In 2
stroke cycle engine: The engine revolves once (two strokes of the
piston, one down, one up) for a complete cycle of the engine. Whereas in
4-stroke cycle engine: Each complete cycle of the engine involves four
strokes of the piston, a down, an up, a down, and an up stroke for each
complete cycle of the engine (which is two revolutions of the engine).
A
single cylinder four-stroke piston engine spends three quarters of its
running time exhausting burned gas, drawing in fresh mixture and
compressing it. On only one of
the four strokes the power stroke is any energy produced and this makes
the output of a single cylinder four stroke engine very uneven. This can
be smoothed out if more cylinders, with their pistons driving a common
crank shaft, are used. A twin-cylinder four stroke, for instance, will
produce one power stroke for each revolution of the crank shaft, instead
of every other revolution as on a single cylinder engine. If the engine
has four cylinders it produces one power stroke for each half-turn of
the crankshaft and at no time is the crankshaft free wheeling’ on one of
the three passive strokes. Even better results can be obtained using
six cylinders, as the power strokes can be made to overlap, so that the
crankshaft receives a fresh impulse before the previous power stroke has
died away on an in-line six-cylinder engine the crankshaft receives
three power impulses each revolution. In theory, the more cylinders you
can use to drive the crank- shaft, the smoother the power output, and 8
and 12 cylinder engines are used on some of the more expensive cars. A
large number of cylinders can pose practical problems. An engine with
eight cylinders in a straight line for instance would have a very long
crank- shaft which would tend to twist and be more likely to break at
higher engine speeds. The car would also need a long bonnet to enclose
the engine. So in the interests of crank- shaft rigidity and
compactness, 8 and 12 cylinder engines have their cylinders arranged in a
V, with two cylinder heads and a common crankshaft. There are also V-6
and V-4 cylinder engines.
Fig: In line engine or 6 cylinder engine
Fig: V8 Engine
The
construction, working principle and operation of multi cylinder engines
is same as single cylinder diesel and petrol engines so are explained
as follows:
Single-cylinder Petrol Engines:
Working Principle and Operation of 2-Stroke (S.I) Engines: In
a 2-Stroke engine, the filling process is accompanied by the change
compressed in a crank case or by a blower. The induction of compressed
charge moves out the product of combustion through exhaust ports.
Therefore, no piston stroke is required. Out of these 2-strokes, one
stroke is for compression of fresh charge and second for power stroke.
The charge conducted into the crank case through the spring loaded valve
when the pressure in the crank case is reduced due to upward motion of
piston during the compression stroke. After the compression &
ignition expansion takes place in usual way. During the expansion stroke
the charge in crankcase is compressed. Near the end of the expansion
stroke, the piston uncovers the exhaust ports and the cylinder pressure
drops to atmosphere pressure as combustion produced leave the cylinder.
Fig: 2 stroke petrol engine
Working Principle and Operation of Four Stroke (S.I) Engine: In
a four stroke engine, the cycles of operations is completed in 4
strokes of piston or 2 revolution of crank shaft. Each stroke consists
of 180° & hence the fuel cycle consists of 720° of crank rotation.
The 4-Strokes are; Suction or Intake Stroke: It starts at, when the
piston is at top dead centre & about to move downwards. The inlet
valve is open at that time and exhaust valve is closed due to suction
created by the motion of the piston towards the bottom dead centre, the
charge containing air fuel mixture is drawn into the cylinder. When the
piston reaches BDC the suction stroke ends and inlet valve is closed.
Compression Stroke: The charge taken into the cylinder during suction
stroke is compressed by return stroke of piston. During this stroke both
the valves are closed. The mixture which fills the entire cylinder
volume is now compressed into the clearance volume. At the end, the
mixture is ignited with the help of electrode of spark plug. During the
burning process the chemical energy of fuel is converted to heat energy.
The pressure is increased in the end due to heat release. Expansion
Stroke: The burnt gases escape out and the exhaust valve opens but inlet
valve remaining closed the piston moves from BDC to TDC and sweeps the
burnt gases out at almost atmospheric pressure. The exhaust valve gets
closed at the end of this stroke. Thus, for one complete cycle of
engine, there is only one power stroke while crank shaft makes 2
revolutions. Exhaust Stroke: During the upward motion of the piston, the
exhaust valve is open and inlet valve is closed. The piston moves up in
cylinder pushing out the burnt gases through the exhaust valve. As the
piston reaches the TDC, again the inlet valve opens and fresh charge is
taken in during next downward movement of the piston and the cycle is
repeated.
Fig: 4 stroke petrol engine
Construction Details
Cylinder is
a cylindrical vessel or space in which the piston makes a reciprocating
produces. Piston is a cylindrical component fitted into the cylinder
forming the moving boundary of combustion system. It fits in cylinder
perfectly. Combustion Chamber is the space enclosed in the upper part of
cylinder, by the cylinder head & the piston top during combustion
process. Inlet Manifold is the pipe which connects the intake system to
the inlet valve of engine. Exhaust Manifold is the pipe which connects
the exhaust system to the exhaust valve of engine. Inlet / Exhaust
Valves are provided on the cylinder head to head to regulate the charge
coming into or going out of the chamber. Spark Plug is used to initiate
the combustion process in S.I engines. Connected Rod connects piston
& the crank shaft. Crank shaft converts the reciprocating motion of
the piston into useful rotary motion of output shaft. Gudgeon pins form a
link between connection rod and the piston. Cam shaft controls the opening & closing of the valves. Cam
opens the valves at the correct tunes. Carburetor used in S.I engine
for atomizing & vaporizing and mixture it with air in varying
proportion.
Single-cylinder Diesel Engines:
Fig: 2 stroke diesel engine
Construction Details
Cylinder is
in it the piston makes a reciprocating process motion. Piston is a
cylindrical component fitted into the cylinder forming the moving
boundary of the combustion system. It fits into cylinder. Combustion
Chamber the space enclosed in the upper part of the cylinder, by the
head and the piston top during the combustion process. Inlet/ Outlet
ports, they are provided on the side of cylinder to regulate the charge
coming in and out of cylinder. Fuel Injector injects the fuel in
combustion chamber to initiate combustion process for power stroke.
Connecting Rod interconnects crank shaft and the piston. Fly Wheel, the
net torque imparted to the crankshaft during one complete cycle of
operation of the engine fluctuating change in angular velocity of shaft.
In order to achiever uniform torque an internal mass is attached to the
output shaft & this is called as fly wheel.
Working Principle and Operation of Four Stroke (C.I.) Engine: In
four strokes C.I. Engine compression ratio is from 16 to 20. During
suction stroke air is inducted. In C.I. engines high pressure. Fuel pump
and injectors are provided to inject the fuel into combustion chamber
and ignition chamber system is not necessary. During suction stroke, air
is inducted through inlet valve. During Compression stroke the air
inducted is compressed into the clearance volume. During Expansion
stroke the fuel injection starts nearly at the end of the compression
stroke. The rate of injection is such that the combustion maintains the
pressure constant inspired of piston movement on its expansion stroke
increasing the volume. After injection of fuel, the products of
combustion chamber expand. During Exhaust stroke the piston traveling
from BQC to TDC pushes out the products of combustion out of cylinder.
Fig: 4 stroke diesel engine
Construction Details:
Cylinder
is a cylindrical vessel in which a piston makes up and down motion.
Piston is a cylindrical component making up and down movement in the
cylinder. Combustion Chamber is the portion above the cylinder in which
the combustion of the Fuel-air mixture takes place. Inlet and Exhaust
valves, the inlet valves allow the fresh fuel-air mixture to enter the
combustion chamber and the exhaust valve discharges the products of
combustion. Crank Shaft is a shaft which converts the reciprocating
motion of piston into the rotary motion. Connecting Rod connects the
Piston with the crankshaft. Cam shaft
controls the opening and closing of inlet and Exhaust valves. Fuel
Injector is located at the top of head to inject the fuel into the
combustion chamber.
(b) Engine cooling & lubricating Systems.
Engine Cooling Systems: The cooling system removes excess heat to keep the inside of the engine at an efficient temperature, about 200oF (94oC). There are two types of cooling systems found on automotives, they are liquid cooling system and air cooling system.
Construction, Working Principle and Operation of Air Cooling System:
The
air cooling system will have metal FINS on the outer perimeter of the
engine. The heat is transferred from the engine, through these fins,
into the atmosphere.
Fig: Air Cooling System
Construction, Working Principle and Operation of Liquid Cooling System:
The
cooling system is made up of the passages inside the engine block and
heads, a water pump to circulate the coolant, a thermostat to control
the temperature of the coolant, a radiator to cool the coolant, a
radiator cap to control the pressure in the system, and some plumbing
consisting of interconnecting hoses to transfer the coolant from the
engine to radiator and also to the car's heater system where hot coolant
is used to warm up the vehicle's interior on a cold day.
A
cooling system works by sending a liquid coolant through passages in
the engine block and heads. As the coolant flows through these
passages, it picks up heat from the engine. The heated fluid then makes
its way through a rubber hose to the radiator in the front of the car.
As it flows through the thin tubes in the radiator, the hot liquid is
cooled by the air stream entering the engine compartment from the grill
in front of the car. Once the fluid is cooled, it returns to the engine
to absorb more heat. The water pump has the job of keeping the fluid
moving through this system of plumbing and hidden passages. A thermostat
is placed between the engine and the radiator to make sure that the
coolant stays above a certain preset temperature. If the coolant
temperature falls below this temperature, the thermostat blocks the
coolant flow to the radiator, forcing the fluid instead through a bypass
directly back to the engine. The coolant will continue to circulate
like this until it reaches the design temperature, at which point, the
thermostat will open a valve and allow the coolant back through the
radiator. In order to prevent the coolant from boiling, the cooling
system is designed to be pressurized. Under pressure, the boiling point
of the coolant is raised considerably. However, too much pressure will
cause hoses and other parts to burst, so a system is needed to relieve
pressure if it exceeds a certain point. The job of maintaining the
pressure in the cooling system belongs to the radiator cap. The cap is
designed to release pressure if it reaches the specified upper limit
that the system was designed to handle. Prior to the '70s, the cap
would release this extra pressure to the pavement. Since then, a system
was added to capture any released fluid and store it temporarily in a
reserve tank. This fluid would then return to the cooling system after
the engine cooled down. This is what is called a closed cooling system.
Fig: Liquid Cooling System
Engine Lubricating Systems: The
engine lubrication system includes the lubricating oil, oil pump, oil
filter and the oil passages. Oil lubrication provides a barrier between
rotating engine parts to prevent damage by friction. The engine oil
provides a method of cooling engine parts that are not cooled by the
engine cooling system. Engine oil helps to protect engine components
from corrosion by neutralizing harmful chemicals that are the by-product
of combustion.
Construction, Working Principle and Operation of Lubricating System:
To
protect moving parts and reduce friction, automotive engine oil
provides a barrier between the rotating or moving engine components.
Ideally, a film of oil should exist between moving components. This is
called full film lubrication. In order to achieve full film lubrication,
a constant supply of clean oil is required. The engine oil system
constantly filters and circulates engine oil to ensure that all
components are protected. The engine oil is stored in the crankcase.
Most engines hold between 4 to 6 quarts of oil. The engine oil pump
pressurizes and circulates the engine oil. The oil will flow from the
pump to the oil filter, where it is cleaned. The cleaned engine oil then
moves through passages, into the crankshaft where it circulates through
the engine bearings. The crankshaft has passages bored into it that
allows oil to travel to all the bearing surfaces. The cylinder walls and
pistons are lubricated by the oil that is thrown from the crankshaft as
it rotates. This is sometimes referred to as splash lubrication. Engine
oil will leave the crankshaft, usually at a passage in one of the main
bearings and is fed to the camshaft and lifters. On some overhead valve
engines, oil will travel through the pushrods up to the valve train to
lubricate the rocker arms. Other designs use a passage to feed oil
through a rocker arm shaft to achieve the same purpose. The oil then
returns to the crankcase by return holes in the cylinder heads. It is
then picked up by the oil pump to be circulated again.
Fig: Engine Lubrication System
(c) Engine starting Systems: The
"starting system", the heart of the electrical system in the engine.
The starting system converts electrical energy from the batteries into
mechanical energy to turn the engine over.
Construction, Working Principle and Operation of Engine starting System: Engine starting system, begins with the Battery.
The key is inserted into the Ignition Switch and then turned to the
start position. A small amount of current then passes through the
Neutral Safety Switch to a Starter Relay or Starter Solenoid which
allows high current to flow through the Battery Cables to the Starter
Motor. The starter motor then cranks the engine so that the piston,
moving downward, can create a suction that will draw a Fuel/Air mixture
into the cylinder, where a spark created by the Ignition System will
ignite this mixture. If the Compression in the engine is high enough and
all this happens at the right Time, the engine will start.
The
starting system has five main components: the ignition switch or start
button, a neutral safety switch (an option on some vehicles), the
starter solenoid, the starter motor, and the batteries.
When
the key is turned in the ignition switch to the start position, or the
start button is pushed, electricity flows from the batteries to the
starter solenoid. Some vehicles are equipped with a neutral safety
switch. If the vehicle is in gear when the key is turned, the neutral
safety switch blocks the signal to the batteries, so the engine doesn't
start cranking. Otherwise, the vehicle could jump forward or backward
when the key is turned. The starter solenoid is an electromagnetic
switch mounted on the starter motor. When coils inside the solenoid are
energized by electricity, they create a magnetic field which attracts
and pulls a plunger. Attached to one end of this plunger is a shift
lever. The lever is connected to the drive pinion and clutch assembly of
the starter motor. The starter motor is a small but powerful electric
motor that delivers a high degree of power for a short period of time.
When the starter motor is energized it engages the flywheel ring gear
and produces torque, which turns the flywheel and cranks the engine.
When the driver releases the ignition switch from the start position to
the run position, the solenoid is deactivated. Its internal return
springs cause the drive pinion to be pulled out of mesh with the
flywheel, and the starter motor stops.
Fig: Engine Starting System
(d) Contact Point & Electronic Ignition Systems: An
ignition system is a system for igniting a fuel-air mixture. There are
two common ignition types associated with automotive engines, they are
contact points and fully electronic. For many years, the contact point
ignition was the favored system to control the timing of the ignition
spark. However, as electronics in general became more reliable and less
costly to produce, manufacturers turned to full electronic systems
cutting out the mechanical contact points.
Construction, Working Principle and Operation of Contact Point Ignition System:
The contact point ignition system consists of:
- A battery or magneto to supply low voltage current for the spark
- Mechanical contact points to control the point of ignition
- A rotating cam to operate the contact points
- A condenser to reduce arcing across the contact point surfaces
- An ignition coil
- A spark plug
The
job of the ignition system is to supply a spark at the correct time
within the cylinder. The distributor cam is a part of, or is attached
to, the distributor shaft and has one lobe for each cylinder. As the
cam rotates with the shaft at one half of engine speed, the lobes cause
the contact points to open and close the primary circuit. The contact
points, also called breaker points, act like spring-loaded
electrical switches in the distributor. Its function is to cause
intermittent current flow in the primary circuit, thus causing
the magnetic field in the coil to build up and collapse when it
reaches maximum strength. Wires from the condenser and ignition
coil primary circuit connect to the points. The condenser, also known
as a capacitor, is wired in parallel with the contact points and
grounded through the distributor housing. The condenser
prevents arcing or burning at the distributor contact points when
the points are first open. The condenser provides a place where current
can flow until the contact points are fully open. With the engine
running, the distributor shaft and distributor cam rotate. This
action causes the distributor cam to open and close the contact
points. With the contact points wired to the primary windings of
the ignition coil, the contact points make and break the ignition
coil primary circuit. With the contact points closed, the
magnetic field builds up in the coil. As the points
open, the magnetic field collapses and voltage is sent to the
spark plugs. With the distributor operating at one half of engine speed
and with only one cam for each engine cylinder, each spark plug only
fires once during a complete revolution of the distributor cam. To
ensure that the contact points are closed for a set time, point
dwell, also known as cam angle, is set by using a dwell meter.
Point dwell is the amount of time given in degrees of distributor
rotation that the points remain closed between each opening. A
dwell period is required to assure that the coil has enough time
to build up a strong magnetic field. If the point dwell is too
small, the current will have insufficient time to pass through the
primary windings of the ignition coil, resulting in a weak
spark. However, if the point dwell is too great, the contact
points will not open far enough, resulting in arcing or burning of the
points.
The
spark must be sufficiently strong enough to jump a gap at the spark
plug electrodes. To achieve this, the voltage must be increased
considerably from the motorcycle’s electrical system (6 or 12 volts) to
around 25,000 volts at the plug. To achieve this increase in voltage,
the system has two circuits: the primary and the secondary. In the
primary circuit, the 6 or 12 volt power supply charges the ignition
coil. During this phase the contact points are closed. When the contact
points open, the sudden drop in power supply causes the ignition coil to
release stored energy in the form of the increased high voltage. The
high voltage current travels along a lead (HT lead) to a plug cap before
entering the spark plug via the central electrode. A spark is created
as the high voltage jumps from the central electrode to the ground
electrode.
Fig: Contact Point Ignition System
Construction, Working Principle and Operation of Electronic Ignition System:
The
basic difference between the contact point and the electronic ignition
system is in the primary circuit. The primary circuit in a contact
point ignition system is open and closed by contact points.
In the electronic system, the primary circuit is open and
closed by the electronic control unit (ECU).The secondary circuits
are practically the same for the two systems. The difference is that the
distributor, ignition coil, and wiring are altered to handle the high
voltage produced by the electronic ignition system. One advantage
of this higher voltage (up to 60,000volts) is that spark plugs with
wider gaps can be used. This results in a longer spark, which can ignite
leaner air-fuel mixtures. As a result engines can run on leaner
mixtures for better fuel economy and lower emissions.
The
basic components of an electronic ignition system are as
follows: The trigger wheel, also known as a reluctor, pole piece, or
armature, is connected to the upper end of the distributor shaft.
The trigger wheel replaces the distributor cam. Like the distributor
cam lobes, the teeth on the trigger wheel equal the number of
engine cylinders. The pickup coil, also known as a sensor assembly,
sensor coil, or magnetic pickup assembly, produces tiny voltage
surges for the ignition systems electronic control unit. The pickup
coil is a small set of windings forming a coil. The ignition
system electronic control unit amplifier or control module is
an "electronic switch" that turns the ignition coil primary
current ON and OFF. The ECU performs the same function as the
contact points. The ignition ECU is a network of transistors,
capacitors, resistors, and other electronic components sealed in
a metal or plastic housing. The ECU can be located (1) in the
engine compartment, (2) on the side of the distributor,(3) inside the
distributor, or (4) under the vehicle dash. ECU dwell time (number
of degrees the circuit conducts current to the ignition coil)
is designed into the electronic circuit of the ECU and is NOT
adjustable. Electronic Ignition System Operation With the engine
running, the trigger wheel rotates inside the distributor. As a tooth of
the trigger wheel passes the pickup coil, the magnetic field
strengthens around the pickup coil. This action changes the output
voltage or current flow through the coil. As a result, an electrical
surge is sent to the electronic control unit, as the trigger wheel teeth
pass the pickup coil. The electronic control unit increases the
electrical surges into ON/OFF cycles for the ignition coil. When the
ECU is ON, current passes through the primary windings of the
ignition coil, thereby developing a magnetic field. Then,
when the trigger wheel and pickup coil turn OFF the ECU,
the magnetic field inside the ignition coil collapses and fires a
sparkplug. Hall-Effect Sensor Some electronic distributors have a
magnetic sensor using the Hall effect. When a steel shutter
moves between the two poles of a magnet, it cuts off the magnetism
between the two poles. The Hall-effect distributor has a rotor with
curved plates, called shutters. These shutters are curved so
they can pass through the air gap between the two poles of
the magnetic sensor, as the rotor turns. Like the trigger wheel,
there are the same number of shutters as there are engine cylinders.
Each time a shutter moves through the air gap between the two
poles of the magnetic sensor, it cuts off the magnetic field
between the poles. This action provides a signal to the ECU. When a
shutter is not in the way, the magnetic sensor is producing
voltage. This voltage is signaling the ECU to allow current to flow
through the ignition coils primary winding. However, when the
shutter moves to cut off the magnetic field, the signal
voltage drops to zero. The ECU then cuts off the current to
the ignition coils primary winding. The magnetic field
collapses, causing the coil secondary winding to produce a high voltage
surge. This high voltage surge is sent by the rotor to the
proper spark plug.
Fig: Electronic Ignition System
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Engine Systems &
Sub Systems is completed.
Experiment No:2
Aim: To study and prepare report on the constructional details, working principles and operation of the Fuels supply systems.
Apparatus: Models of
(a) Carburetors
(b) Diesel Fuel Injection Systems
(c) Gasoline Fuel Injection Systems.
Theory:
(a) Carburetors: A
carburetor is a mechanical device on an internal combustion engine, for
the purpose of mixing air and gasoline into a combustible fine vapor,
in automatically changing proportions, depending on the operating
conditions of the engine. As an example, an engine that runs continually
at one speed, day in and day out has need only for a carburetor of the
simplest construction. One that has only to mix air and gasoline in one
fixed ratio. However, when the demands of the engine are changed and it
is desirable to run it at variable speeds, the carburetor must mix air
and gasoline in different proportions and therefore, its construction
must be more complex.
Construction, Working Principle and Operation of Carburetors:
In
the part of the carburetor known as the body is located the float bowl
or chamber. This chamber is used for the storage of a certain quantity
of gasoline. It serves two purposes, namely, to keep all the other
circuits of the carburetor supplied with the amount of fuel they need
and to absorb the pulsation of the fuel pump, as it delivers the
gasoline to the carburetor. Though its construction is simple, it plays a
very important part in the proper functioning of the engine. The float
system consists of the following: float chamber or bowl, fuel inlet,
needle valve and seat, float, float pin and on some carburetors a float
pin retainer, and the float chamber or bowl cover which contains the
float chamber vent. The pump system consists of pump cylinder, pump
plunger, plunger operating rod, plunger spring, intake check valve,
outlet check valve and pump jet. It also contains the throttle system
and choke system.
Fig: Carburetor parts
A
carburetor is a tube attached to the intake port of the engine and open
to the atmosphere. On the intake stroke a volume with little to no
pressure develops in the combustion chamber. As a result air flows from
outside to inside the engine. As the air flows through the carburetor,
the fuel is metered, atomized and vaporized. To have available fuel, the
carburetor must have a source of fuel. In the float type carburetor
this source is the fuel bowel. A pressure difference is also needed to
cause the fuel to flow from the fuel bowel into the air stream. This is
accomplished using a venturi, Bernoulli’s principle and a tube
connecting the mouth of the venture to the fuel bowel.
This
is a functioning carburetor and it will operate an engine as long as it
has a constant load and constant speed. Very few engines operate at a
constant load and constant speed. To adjust the rate of fuel flow a
throttle is used. When the throttle is in the closed position there is
minimum air flow through the carburetor. When the throttle is in the
wide open position, there is maximum air flow through the carburetor. To
provide a means to adjust maximum fuel flow, a needle valve was added
to the orifice in the emulsion tube. A carburetor with this design would
function well under varying loads and speeds. Starting is a different
condition; an engine needs a richer fuel-air mixture. This was
accomplished by adding a choke. Closing the choke increases the pressure
difference between the fuel bowel and the venturi. Once engine starts
the choke must be opened to prevent the engine from running too rich.
The addition of a choke/primer improved engine starting, but this
carburetor still has a problem if the engine needs to idle. When the
throttle is in the idle position, almost closed, the area with greatest
restriction, and greatest pressure difference, moves from the venturi to
the area between the throttle plate and the wall of the tube. This
problem was solved with the addition of an idle circuit and idle needle
valve. To have constant fuel flow with constant pressure difference the
lift, distance from the top of the fuel to the top of the main nozzle,
must remain constant. A constant level of fuel is maintained in the fuel
bowel by the float, float needle valve and float needle valve seat.
Fig: Carburetor Operation
(b) Diesel Fuel Injection Systems:
The injection system in diesel engines can be of two types as air
injection and airless injection. In air injection system the diesel
is injected along with the compressed air whereas in airless
injection system only the liquid diesel is injected into the
cylinder.
Construction, Working Principle and Operation of Diesel Fuel Injection Systems:
The construction details of diesel fuel injection system are fuel tank, fuel filter, fuel pump, fuel injector, nozzle.
Fig: Diesel Fuel Injection System
A
fuel tank is used for storage. The feed pump is used to feed the fuel
to filter where fuel can be filtered. A fuel injection pump is used to
supply precisely metered quantity of diesel under high pressure to the
injectors at well timed instants. A fuel injector is used to inject
the fuel in the cylinder in atomized form and in proper
quantity. Main components of fuel injectors are nozzle, valve, body and
spring. The nozzle is its main part which is attached to the nozzle
holder. Entry of fuel in the injector is from the fuel injection pump.
Diesel injector nozzles are spring-loaded closed valves that spray fuel
directly into the combustion chamber. Injector nozzles are threaded into
the cylinder head, one for each cylinder. The top of the injector
nozzle has many holes to deliver an atomized spray of diesel fuel into
the cylinder.
(c) Gasoline Fuel Injection Systems: A
modern gasoline injection system uses pressure from an electric fuel
pump to spray fuel into the engine intake manifold. Like a carburetor,
it must provide the engine with the correct air-fuel mixture for
specific operating conditions. Unlike a carburetor, however, pressure,
not engine vacuum, is used to feed fuel into the engine. This makes the
gasoline injection system very efficient.
A
gasoline injection system has several possible advantages over a
carburetor type of fuel system. Some advantages are as follows:
- Improved atomization: Fuel is forced into the intake manifold under pressure that helps break fuel droplets into a fine mist.
- Better fuel distribution: Equal flow of fuel vapors into each cylinder.
- Smoother idle: Lean fuel mixture can be used without rough idle because of better fuel distribution and low-speed atomization.
- Lower emissions: Lean efficient air-fuel mixture reduces exhaust pollution.
- Better old weather drivability: Injection provides better control of mixture enrichment than a carburetor.
- Increased engine power: Precise metering of fuel to each cylinder and increased air flow can result in more horsepower output.
- Fewer parts: Simpler, late model, electronic fuel injection system has fewer parts than modern computer-controlled carburetors.
There are
many types of gasoline injection systems. Before studying the most
common ones, you should have a basic knowledge of the different
classifications:
1. Single- or Multi-Point Injection
2. Indirect or Direct Injection
1. Single- or Multi-Point Injection
2. Indirect or Direct Injection
The
point or location of fuel injection is one way to classify a gasoline
injection system. A single-point injection system, also call
throttle body injection (TBI), has the injector nozzles in a throttle
body assembly on top of the engine. Fuel is sprayed into the top center
of the intake manifold.
Fig: Single Point Gasoline Fuel Injection System
A
multi-point injection system, also called port injection, has an
injector in the port (air-fuel passage) going to each cylinder. Gasoline
is sprayed into each intake port and toward each intake valve. Thereby,
the term multipoint (more than one location) fuel injection is used.
Fig: Multi-point Gasoline Fuel Injection System
An indirect injection system sprays fuel into the engine intake manifold. Most gasoline injection systems are of this type.
Fig: Indirect Injection Gasoline Fuel System
Direct
injection forces fuel into the engine combustion chambers. Diesel
injection systems are direct type. So, Gasoline electronic Direct
Injection System is classified as multi-point and direct injection
systems.
Fig:Direct Injection Gasoline Fuel System
Construction, Working Principle and Operation of Gasoline Fuel Injection Systems:
Its
construction details consists of parts as fuel tank, electric fuel
pump, fuel filter, electronic control unit, common rail and pressure
sensor, electronic injectors and fuel line.
1.
Fuel tank is safe container for flammable liquids and typically part of
an engine system in which the fuel is stored and propelled (fuel pump)
or released (pressurized gas) into an engine.
2.
An electric fuel pump is used on engines with fuel injection to pump
fuel from the tank to the injectors. The pump must deliver the fuel
under high pressure (typically 30 to 85 psi depending on the
application) so the injectors can spray the fuel into the engine.
Electric fuel pumps are usually mounted inside the fuel tank.
3.
The fuel filter is the fuel system's primary line of defense against
dirt, debris and small particles of rust that flake off the inside of
the fuel tank. Many filters for fuel injected engines trap particles as
small as 10 to 40 microns in size. Fuel filter normally made into
cartridges containing a filter paper.
4.
In automotive electronics, electronic control unit (ECU) is a generic
term for any embedded system that controls one or more of the electrical
systems or subsystems in a motor vehicle.
An
engine control unit (ECU), also known as power-train control module
(PCM), or engine control module (ECM) is a type of electronic control
unit that determines the amount of fuel, ignition timing and other
parameters an internal combustion engine needs to keep running. It does
this by reading values from multidimensional maps which contain values
calculated by sensor devices monitoring the engine. Control of fuel
injection: ECU will determine the quantity of fuel to inject based on a
number of parameters. If the throttle pedal is pressed further down,
this will open the throttle body and allow more air to be pulled into
the engine. The ECU will inject more fuel according to how much air is
passing into the engine. If the engine has not warmed up yet, more fuel
will be injected. Control of ignition timing : A spark ignition engine
requires a spark to initiate combustion in the combustion chamber. An
ECU can adjust the exact timing of the spark (called ignition timing) to
provide better power and economy. Control
of idle speed : Most engine systems have idle speed control built into
the ECU. The engine RPM is monitored by the crankshaft position sensor
which plays a primary role in the engine timing functions for fuel
injection, spark events, and valve timing. Idle speed is controlled by a
programmable throttle stop or an idle air bypass control stepper motor.
5.
The term "common rail" refers to the fact that all of the fuel
injectors are supplied by a common fuel rail which is nothing more than a
pressure accumulator where the fuel is stored at high pressure. This
accumulator supplies multiple fuel injectors with high pressure fuel.
6.
The fuel injectors are typically ECU-controlled. When the fuel
injectors are electrically activated a hydraulic valve (consisting of a
nozzle and plunger) is mechanically or hydraulically opened and fuel is
sprayed into the cylinders at the desired pressure. Since the fuel
pressure energy is stored remotely and the injectors are electrically
actuated the injection pressure at the start and end of injection is
very near the pressure in the accumulator (rail), thus producing a
square injection rate. If the accumulator, pump, and plumbing are sized
properly, the injection pressure and rate will be the same for each of
the multiple injection events. The injectors can survive the excessive
temperature and pressure of combustion by using the fuel that passes
through it as a coolant. The electronic fuel injector is normally
closed, and opens to inject pressurized fuel as long as electricity is
applied to the injector's solenoid coil. When the injector is turned on,
it opens, spraying atomized fuel at the combustion chamber. Depending
on engine operating condition, injection quantity will vary.
7.
Fuel line hoses carry gasoline from the tank to the fuel pump, to the
fuel filter, and to the fuel injection system. While much of the fuel
lines are rigid tube, sections of it are made of rubber hose, which
absorb engine and road vibrations. 
Fig: Electronic Gasoline Fuel Injection System
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Fuels supply systems is
completed.
Experiment No:3
Aim: To study and prepare report on the constructional details, working principles and operation of the Automotive Clutches.
Apparatus: Models of
(a) Coil-Spring Clutch
(b) Diaphragm – Spring Clutch.
(c) Double Disk Clutch.
Theory:
A
Clutch is a machine member used to connect the driving shaft to a
driven shaft, so that the driven shaft may be started or stopped at
will, without stopping the driving shaft. A clutch thus provides an
interruptible connection between two rotating shafts. Clutches allow a
high inertia load to be stated with a small power. A popularly known
application of clutch is in automotive vehicles where it is used to
connect the engine and the gear box. Here the clutch enables to crank
and start the engine disengaging the transmission and change the gear to
alter the torque on the wheels.
(a) Coil-Spring Clutch: The
coil spring clutch shown in figure uses coil springs as pressure
springs (only two pressure spring is shown). The coil-spring clutch has a
series of coil springs set in a circle. At high rotational speeds,
problems can arise with multi coil spring clutches owing to the effects
of centrifugal forces both on the spring themselves and the lever of the
release mechanism.
Fig: Coil Spring Clutch
(b) Diaphragm – Spring Clutch: The
diaphragm spring clutch shown in figure. The diaphragm spring clutch
has consistently eliminated bolt springs which means it very from coil
spring clutch by type of spring used.
Fig: Diaphragm Spring Clutch
(c) Double Disk Clutch: Basically,
the clutch needs three parts. These are the engine flywheel, a friction
disc called the clutch plate and a pressure plate. When the engine is
running and the flywheel is rotating, the pressure plate also rotates as
the pressure plate is attached to the flywheel. The friction disc is
located between the two. When the driver has pushed down the clutch
pedal the clutch is released. This action forces the pressure plate to
move away from the friction disc. There are now air gaps between the
flywheel and the friction disc, and between the friction disc and the
pressure plate. No power can be transmitted through the clutch.
Fig: Double Disk Clutch
Construction, Working Principle and Operation of Automotive Clutches:
A
clutch is that part of engine which engages or disengages power from
the engine crankshaft to transmission. A clutch is mechanism by which
you change the gears. In simple words, it turns on or off power to rear
wheel. A clutch is made of clutch assembly which includes clutch plate,
Clutch basket, Clutch hub, pressure plates, Clutch springs, lever and
clutch cable.
Clutch
Basket: It is bowl shaped basket which holds entire clutch assembly. It
has teethes on the outside surfaces which fix on the primary drive
teethes. It means that it is connected with the transmission. It is
bolted onto the end of clutch shaft.
Clutch
Hub: The clutch hub places between clutch basket and pressure plate.
The clutch plates are mounted on it. It has teethes in the centre hole
which rotate with main shaft. It means it is connected with the engine.
Clutch Plate: There are two types of plates in clutch plate. One is Drive (friction) plate another is Driven (Steel) plate
Drive
(friction) plate: The friction plate is ring shaped and coated with
fiber. It is a wear and tear part of clutch assembly. The friction plate
surfaces interface between the clutch basket tangs (gaps) and pressure
plate. It has teethes on the outside surfaces. These teethes fix on the
cutouts between clutch hub tangs (gaps). It is coated with the same
material as you see in brake pad (shoe).
Driven
(steel) plate: It is ring shaped and made of steel and sometime of
aluminum. The surfaces of steel or aluminum plate interfaces between
pressure plate and clutch hub. It has teethes on inside surfaces. This
teethes are fix on the cutouts of clutch hub. Mostly steel plates are
used in clutch assembly due to their durability. The aluminum plates are
used in Moto GP due to their lighter weight. These plates are worn out
very fast compare to steel plate.
Pressure
Plate: It is the moving part of the clutch assembly which works against
clutch spring tension. It releases the clamping action on the clutch
plates when the clutch lever is engaged.
Clutch
springs: The clutch springs shape is like short coil. These springs
continuously hold the friction and steel or aluminum plates through
spring tension. It also prevents slippage except when the clutch lever
is engaged. Most of motorcycle has five or more springs used per clutch
assembly. For higher engine output stiffer or more springs are used
while softer or few springs used in order to lighter clutch level
pulling effort.
Lever: It is metal rode which pivots on a perch located of the left handlebar. It gives input to clutch assembly.
Clutch Cable: The clutch cable is a cable through which the rider’s input passes to the clutch internals.
Clutch Cover: It covers the entire clutch assembly.
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Clutches is
completed.
Experiment No:4
Aim: To
study and prepare report on the constructional details, working
principles and operation of the Automotive Transmission systems.
Apparatus: Models of
(a) Synchromesh – Four speed Range.
(b) Transaxle with Dual Speed Range.
(c) Four Wheel Drive and Transfer Case.
(d) Steering Column and Floor – Shift levers.
Theory:
The
most common transmission systems that have been used for the automotive
industry are manual transmission, automatic transmission (transaxle),
semi-automatic transmission, and continuously variable transmission
(CVT).
The
first transmission invented was the manual transmission system. The
driver needs to disengage the clutch to disconnect the power from the
engine first, select the target gear, and engage the clutch again to
perform the gear change. An automatic transmission uses a fluid-coupling
torque converter to replace the clutch to avoid engaging/disengaging
clutch during gear change. A completed gear set, called planetary gears,
is used to perform gear ratio change instead of selecting gear
manually.
Automobile
or automotive transmission system consists of various devices that help
in transmitting power from the engine through the drive shaft to the
live axle of an automobile. Gears, brakes, clutch, fluid drive and other
auto transmission parts work together for transforming the speed ratio
between the engine and wheels of a vehicle.
Types of Gearboxes:
} Sliding Mesh Gear box
} Constant Mesh Gear Box
} Synchromesh Gear Box
} Epicyclic Gear Box
An engine may consist of one or more gearbox. There may be gearboxes which are a mixture of these types.
(a) Synchromesh – Four Speed Range: Most
modern manual-transmission vehicles are fitted with a synchronized gear
box or synchromesh. Transmission gears are always in mesh and rotating,
but gears on one shaft can freely rotate or be locked to the shaft. The
locking mechanism for a gear consists of a collar (or dog collar) on
the shaft which is able to slide sideways so that teeth (or dogs) on its
inner surface bridge two circular rings with teeth on their outer
circumference: one attached to the gear, one to the shaft. When the
rings are bridged by the collar, that particular gear is rotationally
locked to the shaft and determines the output speed of the transmission.
The gearshift lever manipulates the collars using a set of linkages, so
arranged so that one collar may be permitted to lock only one gear at
any one time; when "shifting gears", the locking collar from one gear is
disengaged before that of another is engaged. One collar often serves
for two gears; sliding in one direction selects one transmission speed,
in the other direction selects another.
In
a synchromesh gearbox, to correctly match the speed of the gear to that
of the shaft as the gear is engaged the collar initially applies a
force to a cone-shaped brass clutch attached to the gear, which brings
the speeds to match prior to the collar locking into place. The collar
is prevented from bridging the locking rings when the speeds are
mismatched by synchro rings. The synchro ring rotates slightly due to
the frictional torque from the cone clutch. In this position, the dog
clutch is prevented from engaging. The brass clutch ring gradually
causes parts to spin at the same speed. When they do spin the same
speed, there is no more torque from the cone clutch and the dog clutch
is allowed to fall in to engagement. With continuing sophistication of
mechanical development, fully synchromesh transmissions with three
speeds, then four, and then five, became universal.
Fig: 4 speed gearbox
Construction, Working Principle and Operation of Synchromesh – Four Speed Range:
If
the teeth, the so-called dog teeth, make contact with the gear, but the
two parts are spinning at different speeds, the teeth will fail to
engage and a loud grinding sound will be heard as they clatter together.
For this reason, a modern dog clutch in an automobile has a
synchronizer mechanism or synchromesh, which consists of a cone clutch
and blocking ring. Before the teeth can engage, the cone clutch engages
first which brings the selector and gear to the same speed using
friction. Moreover, until synchronization occurs, the teeth are
prevented from making contact, because further motion of the selector is
prevented by a blocker (or baulk) ring. When synchronization occurs,
friction on the blocker ring is relieved and it twists slightly,
bringing into alignment certain grooves and notches that allow further
passage of the selector which brings the teeth together.
Fig: Synchromesh Concept
(b) Transaxle with Dual Speed Range:
I
think it is beyond the scope of the students. The above statement
involves electric speed control system, hybrid transmission technology
and race cars system.
(c) Four Wheel Drive and Transfer Case: A
transfer case is a part of a four-wheel-drive system found in
four-wheel-drive. The transfer case is connected to the transmission and
also to the front and rear axles by means of drive shafts. It is also
referred to as a "transfer gearcase", "transfer gearbox", "transfer box"
or "jockey box".
Construction, Working Principle and Operation of Four Wheel Drive and Transfer Case:
A
manually shifted 2-speed transfercase in the 4-wheel drive controls the
power from the engine and transmission to the front and rear driving
axles (Fig). The transfer case shift lever positions, from front to
rear, are 4L (low gear, all wheels), N (Neutral), 2H (high gear, rear
wheels), and 4H (high gear, all wheels).
POWER
FLOW - NEUTRAL POSITION: When the transfer case gears are in neutral
(Fig), power from the front main transmission drives the transfer case
input shaft and drive gear. The drive gear drives the idler shaft and
the high-speed gear that free-runs on the front output shaft. Therefore,
no power can be delivered to either the front, or rear axle, even when
the front main transmission is in gear.
POWER
FLOW—4L POSITION (LOW GEAR, ALL WHEELS): When the transfer case shift
lever is shifted into the 4-wheel low position, it pushes the two
sliding gears back into engagement with the idler shaft low-speed gear
teeth. The power flows from the main drive gear to the idler drive gear
and shaft, and to the idler low-speed gear. From the low-speed, the
power flows through the two sliding gears to their respective output
shafts to give speed reduction.
POWER
FLOW—2H POSITION (HIGH GEAR, REAR-WHEELS): When the transfer case shift
lever is shifted into the 2-wheel high position, the two sliding gears
are pulled forward out of engagement from the idler shaft low-speed
gear, leaving the front output sliding gear in neutral and pulling the
rear output sliding gear farther forward into engagement with the clutch
teeth of the main drive gear. This locks the main input shaft directly
to the rear wheel output shaft. The power flows directly from the
transmission to the rear axle without any reduction of speed. The front
output sliding gear remains in a neutral position, the idler shaft drive
gear turns the high-speed gear free on the front output shaft, and
there is no power to the front axle.
POWER
FLOW—4H POSITION (HIGH GEAR, ALL WHEELS): When the transfer case shift
lever is shifted into the 4-wheel high position, it pulls the rear
output and front output sliding gears forward into engagement with the
clutch teeth of the main drive gears. This locks the rear output shaft
directly to the main input shaft, and the front output shaft to the
high-speed idler shaft gear. The power from the transmission flows from
the drive gear in two directions. Direct drive to the rear axle flows
through the rear output shaft. Direct drive to the front axle flows
through the idler shaft drive gear, high-speed gear, and front output
shaft.
(d) Steering Column and Floor – Shift levers: It
comes under gear selection concept. In manual transmissions, an
interlock mechanism prevents the engagement of more than one gear at any
one time and a detent mechanism holds the gear, in detention, in the
selected position. A gearshift lever allows the driver to manually
select gears via a gearshift mechanism.
Construction, Working Principle and Operation of Steering Column and Floor – Shift levers: The
lever can be mounted remote from the gearbox, on the floor or on the
steering column, and connected to the gearbox by a rod linkage or
cables. It can also be mounted in the top of the gearbox where it acts
through a ball pivot in the top of the extension housing. In this
design, the lower end of the gear lever fits into a socket in a control
shaft, inside the transmission extension housing. A short lever on the
other end of the shaft is located in a selector gate, formed by slots in
the three selector shift rails. They are supported in the casing and
are moved backwards or forwards by the lever. One rail moves to engage
first or second gear, another serves to engage third or fourth, and the
other operates fifth or reverse. A selector fork is attached to the
first and second shift rail. It sits in a square section groove on the
outside of the first and second engagement sleeve. Similarly for the
selection of third and fourth gears. The reverse selector fork engages
in a groove in the reverse engagement sleeve. Lateral movement of the
gear lever positions the control rod in line with the appropriate
selector rail. Longitudinal movement is transferred through the control
rod and selector rail, to the fork, and the engagement sleeve. Each rail
has a detent mechanism, usually in the form of a spring loaded steel
ball, held in the casing. The ball engages in a groove in the rail when
the gear lever is in neutral and in a similar groove when a gear is
selected. This holds the gear, in detention, in the selected position.
When a gear is changed or selected, an interlock mechanism prevents more
than one gear being engaged at the same time.
Fig: Steering Column Floor Shift Liver
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Transmission systems
is completed.
Experiment No:5
Aim: To
study and prepare report on the constructional details, working
principles and operation of the Automotive Drive Lines &
Differentials.
Apparatus: Models of
(a) Rear Wheel Drive Line.
(b) Front Wheel Drive Line.
(c) Differentials, Drive Axles and Four Wheel Drive Line.
Theory:
(a) Constructional details, Working Principles and Operation of Rear Wheel Drive Line:
Rear-wheel
drive (RWD) typically places the engine in the front of the vehicle and
the driven wheels are located at the rear, a configuration known as
front-engine, rear-wheel drive line. The vast majority of
rear-wheel-drive vehicles use a longitudinally-mounted engine in the
front of the vehicle, driving the rear wheels via a driveshaft linked
via a differential between the rear axles. Some FRL(front engine rear
wheel drive line) vehicles place the gearbox at the rear, though most
attach it to the engine at the front. Some of the advantages of FRL are
even weight distribution, weight transfer during acceleration, steering
radius, better handling in dry conditions, better braking, towing,
serviceability and robustness.
Fig: Rear Wheel Drive Line
(b) Constructional details, Working Principles and Operation of Front Wheel Drive Line.
Front-wheel-drive
lines are those in which the front wheels of the vehicle are driven.
The most popular lines used in cars today is the front-engine,
front-wheel drive, with the engine in front of the front axle, driving
the front wheels. This line is typically chosen for its compact
packaging; since the engine and driven wheels are on the same side of
the vehicle, there is no need for a central tunnel through the passenger
compartment to accommodate a prop-shaft between the engine and the
driven wheels. As the steered wheels are also the driven wheels, FFL
(front-engine, front-wheel-drive line) cars are generally considered
superior to FRL (front-engine, rear-wheel-drive line) cars in conditions
such as snow, mud or wet tarmac. Some of the advantages are interior
space, cost, improved drive train efficiency, placing the mass of the
drive train over the driven wheels moves the centre of gravity farther
forward than a comparable rear-wheel-drive layout, improving traction
and directional stability on wet, snowy, or icy surfaces.
Fig: Front Wheel Drive Line
(c) Constructional details, Working Principles and Operation of Differentials, Drive Axles and Four Wheel Drive Line:
In
four wheel drive line vehicles, differentials are fitted to both front
and rear axle assemblies. When a two-wheel drive range is selected, the
drive is transferred through the rear final drive and the differential
gears to the rear axle shafts and road wheels. The differential gears
allow the rear wheels to rotate at different speeds when the vehicle is
turning, while continuing to transmit an equal turning effort to each
wheel. When four-wheel drive is engaged, the drive is transmitted
through both front and rear axle assemblies, and differential action
occurs in both. However, in a turn, side-swiveling of the front wheels
for steering makes the front wheels travel a greater distance than the
rear wheels. This causes a difference in the rotational speeds of the
front and rear wheels. Since there is also a difference between inner
and outer wheels, each axle shaft now turns at a different speed.
Differences in speed can also arise from differences in tread wear
between front and rear, or in tire inflation pressures. Since front and
rear propeller shafts are locked together at the transfer case, the
difference in speed cannot be absorbed in the transmission, and the
transmission drive line can be subjected to torsional stress.
Fig: 4 Wheel Drive Differential Axle Line
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Drive Lines &
Differentials is completed.
Experiment No:6
Aim: To
study and prepare report on the constructional details, working
principles and operation of the Automotive Suspension Systems.
Apparatus: Models of
(a) Front Suspension System.
(b) Rear Suspension System.
Theory:
Fig: Front Suspension System
Another
Example: This non-driven or 'dead' axle front suspension arrangement
consists of: coil springs; lower wishbone and upper wishbone as shown
below.
Fig: Front Suspension System Layout
(b) Constructional details, working principles and operation of the Rear Suspension System: The
front of the leaf spring is attached to the chassis at the rigid spring
hanger. This spring eye is bushed with either rubber bushes or, in the
case of heavy vehicles, steel bushes. The axle housing is rigid between
each road wheel. This means that any deflection to one side is
transmitted to the other side. The swinging shackle allows for
suspension movement by allowing the spring to extend or reduce in
length, as the vehicle moves over uneven ground. The top of the shock
absorber is attached to the chassis, and to the spring pad at the
bottom. It is a direct-acting shock absorber. The U-bolts attach the
axle housing to the leaf spring. They have a clamping force that helps
to keep the leaf spring together. Leaf springs are usually made of
tempered steel. They hold the axle in position, both laterally and
longitudinally. The leaf spring is usually made up of a number of leaves
of different length. The top, or longest leaf, is normally referred to
as the main leaf.
Fig: Rear Suspension System
Another
example: This driven or 'live' rear axle arrangement consists of: shock
absorbers; u-bolts; fixed shackle; rebound clips and swinging shackles
as shown below.
Fig: Rear Suspension System Layout
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Suspension Systems is
completed.
Experiment No:7
Aim: To study and prepare report on the constructional details, working principles and operation of the Automotive Steering Systems.
Apparatus: Models of
(a) Manual Steering Systems, e.g. Pitman –arm steering, Rack & Pinion steering.
(b) Power steering Systems, e.g. Rack and Pinion Power Steering System.
(c) Steering Wheels and Columns e.g. Tilt & Telescopic steering Wheels, Collapsible Steering Columns.
Theory:
(a)
Constructional details, working principles and operation of the Manual
Steering Systems, e.g. Pitman –arm steering, Rack & Pinion steering:
The Pitman arm
is a steering component in an automobile or truck. The pitman arm shaft
is attached to the steering box by a spline and nut. As the driver
turns the steering wheel, the steering box mechanism moves the steering
linkages via the pitman arm shaft either left or right, depending on the
direction in which the steering wheel is turned. The steering box
provides the change of angle at 90° to the steering linkage. The idler
arm is attached to the chassis and is positioned parallel to the pitman
arm. The track rod connects the pitman arm shaft to the idler arm shaft.
In this way any movement in the pitman arm shaft is directly applied to
the idler arm shaft.
The
tie rods connect the track rod to the steering arms that are located on
the steering knuckles. Thus all movement from the pitman arm shaft is
relayed directly to the front wheels, which steer the vehicle. Tie rod
ends are attached to the tie-rod shaft. These pivot as the rack is
extended or retracted when the vehicle is negotiating turns. Tie-rods
and tie-rod ends are left or right hand threaded. The adjustment sleeve
connects the tie-rod to the tie-rod end.
Fig: Pitman Arm Steering
The primary components of the rack and pinion steering system
are: rubber bellows, pinion, rack, inner ball joint or socket and
tie-rod. This rubber bellows is attached to the Rack and Pinion housing.
It protects the inner joints from dirt and contaminants. In addition,
it retains the grease lubricant inside the rack and pinion housing.
There is an identical bellows on the other end of the rack for the
opposite side connection. The pinion is connected to the steering
column. As the driver turns the steering wheel, the forces are
transferred to the pinion and it then causes the rack to move in either
direction. This is achieved by having the pinion in constant mesh with
the rack.
The
rack slides in the housing and is moved by the action of the meshed
pinion into the teeth of the rack. It normally has an adjustable bush
opposite the pinion to control their meshing, and a nylon bush at the
other end. The inner ball joint is attached to the tie-rod, to allow for
suspension movement and slight changes in steering angles. A tie rod
end is attached to the tie-rod shaft. These pivot as the rack is
extended or retracted when the vehicle is negotiating turns. Some
tie-rods and tie-rod ends are left or right hand threaded.
Fig: Rack & Pinion Steering
(b)
Constructional details, working principles and operation of the Power
steering Systems, e.g. Rack and Pinion Power Steering System:
The
use of electronics into automotive steering systems enables much more
sophisticated control to be achieved. Electric steering is more
economical to run, and easier to package and install than conventional
hydraulic power steering systems. Electrically Powered Hydraulic
Steering, or EPHS, replaces the customary drive belts and pulleys with a
brushless motor that drives a high efficiency hydraulic power steering
pump in a conventional rack and pinion steering system. Pump speed is
regulated by an electric controller to vary pump pressure and flow. This
provides steering efforts tailored for different driving situations.
The pump can be run at low speed or shut off to provide energy savings
during straight ahead driving. An EPHS system is able to deliver an 80
percent improvement in fuel economy when compared to standard hydraulic
steering systems. Electrically assisted steering or EAS, is a
power-assist system that eliminates the connection between the engine
and steering system. EAS or direct electric power steering takes the
technology a step further by completely eliminating hydraulic fluid and
the accompanying hardware from the system, becoming a full “electronic
power steering system” or EPS. An EPS Direct electric steering system
uses an electric motor attached to the steering rack via a gear
mechanism and torque sensor. A microprocessor or electronic control
unit, and diagnostic software controls steering dynamics and driver
effort. Inputs include vehicle speed and steering, wheel torque, angular
position and turning rate.
There are four primary types of electric power assist steering systems:
1. Column-assist type. In this system the power assist unit, controller and torque sensor are attached to the steering column.
2.
Pinion-assist type. In this system the power assist unit is attached to
the steering gear pinion shaft. The unit sits outside the vehicle
passenger compartment, allowing assist torque to be increased greatly
without raising interior compartment noise.
3.
Rack-assist type. In this system the power assist unit is attached to
the steering gear rack. It is located on the rack to allow for greater
flexibility in the layout design.
4.
Direct-drive type. In this system the steering gear rack and power
assist unit form a single unit. The steering system is compact and fits
easily into the engine compartment layout. The direct assistance to the
rack enables low friction and inertia, which in turn gives an ideal
steering feel.
Fig: Power Steering
(c)
Constructional details, working principles and operation of the
Steering Wheels and Columns e.g. Tilt & Telescopic steering Wheels,
Collapsible Steering Columns:
The
original Tilt Wheel was developed by Edward James Lobdell in the early
1900s. Originally a luxury option on cars, the tilt function helps to
adjust the steering wheel by moving the wheel through an arc in an up
and down motion. Tilt Steering Wheels rely upon a ratchet joint located
in the steering column just below the steering wheel. By disengaging the
ratchet lock, the wheel can be adjusted upward or downward while the
steering column remains stationary below the joint. Some designs place
the pivot slightly forward along the column, allowing for a fair amount
of vertical movement of the steering wheel with little actual tilt,
while other designs place the pivot almost inside the steering wheel,
allowing adjustment of the angle of the steering wheel with almost no
change it its height. Telescope Wheel was developed by General Motors
and can be adjusted to an infinite number of positions in a 3-inch
range. The Tilt and Telescope steering wheel was introduced as an
exclusive option on Cadillac automobiles.
Fig: Tilt & Telescope Column
Fig: Tilt & Telescope Wheel
Collapsible steering columns were invented long back but not successful in case of crash applications.
Fig: Collapsible Steering Column
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Steering Systems is
completed.
Experiment No:8
Aim: To
study and prepare report on the constructional details, working
principles and operation of the Automotive Tyres & wheels.
Apparatus: Models of
(a) Various Types of Bias & Radial Tyres.
(b) Various Types of wheels.
Theory:
(a) Constructional details, working principles and operation of the Various Types of Bias & Radial Tyres:
- Bias: Bias tire (or cross ply) construction utilizes body ply cords that extend diagonally from bead to bead, usually at angles in the range of 30 to 40 degrees, with successive plies laid at opposing angles forming a crisscross pattern to which the tread is applied. The design allows the entire tire body to flex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic also causes the major disadvantages of a bias tire: increased rolling resistance and less control and traction at higher speeds.
- Belted bias: A belted bias tire starts with two or more bias-plies to which stabilizer belts are bonded directly beneath the tread. This construction provides smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. The plies and belts are at different angles, which improve performance compared to non-belted bias tires. The belts may be cord or steel.
- Radial tyres: Radial tyre construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to each other, as well as stabilizer belts directly beneath the tread. The belts may be cord or steel. The advantages of this construction include longer tread life, better steering control, and lower rolling resistance. Disadvantages of the radial tire include a harder ride at low speeds on rough roads and in the context of off-roading, decreased "self-cleaning" ability and lower grip ability at low speeds.
- Solid: Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plastic compounds via molding operations. Solid tires include those used for lawn mowers, skateboards, golf carts, scooters, and many types of light industrial vehicles, carts, and trailers. One of the most common applications for solid tires is for material handling equipment (forklifts). Such tires are installed by means of a hydraulic tire press.
- Semi-pneumatic: Semi-pneumatic tires have a hollow center, but they are not pressurized. They are light-weight, low-cost, puncture proof, and provide cushioning. These tires often come as a complete assembly with the wheel and even integral ball bearings. They are used on lawn mowers, wheelchairs, and wheelbarrows. They can also be rugged, typically used in industrial applications, and are designed to not pull off their rim under use.
Fig: Bias Tyre
Fig: Radial Tyre
(b) Constructional details, working principles and operation of the Various Types of wheels:
Wheels
must be strong enough to carry the mass of the vehicle, and withstand
the forces that are generated during use. Some are made from steel. They
are pressed in 2 sections - the wheel center, with a flange or disc
that is drilled for the wheel fasteners, and the rim. They are then
welded together. Others are made from cast aluminum alloy. Alloy wheels
are lighter than similar steel wheels, and since aluminum is a better
heat conductor than steel, alloy wheels dissipate heat from brakes and
tires more quickly than steel wheels. The wheel center must accurately
locate the wheel rim centrally on the axle. It must also provide the
required distance from the centerline of the wheel, to the face of the
mounting flange. This is called offset. Offset is important because it
brings the tire centerline into close alignment with the larger inner
hub bearing, and reduces load on the stub axle. This allows the inside
of the wheel center to be shaped to provide space for the brake
assembly, usually located inside the wheel. Ventilation slots allow air
to circulate around the brakes. In some cases wheels are directional to
assist the airflow. The rim must be accurately shaped, and dimensioned,
and strong enough to support the tire under the load of the vehicle and
the forces generated by the motion of the vehicle. Passenger cars
normally use rims which are of well based, or drop-center design. The
drop-center is used for mounting and demounting the tire onto the rim.
When inflated, the tire is locked to the rim by tapering the bead seat
towards the flange, or by safety ridges or humps, close to the flange.
In the event of sudden deflation, or blowout, safety ridges prevent the
tire moving down into the well. This helps maintain control of the
vehicle while it is being braked. Well-based rims can also be used on
heavy commercial vehicles for tubeless tires. The rims are referred to
as 15-degree drop-center rims, because the bead seats are inclined at 15
degrees towards the flange. The taper gives a good grip, and an
airtight seal between the tire beads, and the rim. The low flanges and
drop-center allow the special size, flexible, tubeless truck tires to be
mounted and demounted in a similar manner to that used on smaller
passenger car tires. The stiff sidewalls of larger cross-ply tires mean
they cannot be mounted and demounted in this way, and many 4-wheel-drive
and commercial vehicles use a flat-base, demountable flange rim. When
all of the air is removed from the tire, one flange can be removed so
the tire can be demounted. Wheels are fastened to the hubs by wheel
studs and nuts.
They
are highly stressed by loads from the weight of the vehicles, and the
forces generated by its motion, and they’re made from heat-treated,
high-grade alloy-steel. The threads between the studs and nuts are close
fitting and accurately-sized. All wheel nuts must be tightened to the
correct torque, otherwise the wheel could break free from the hub.
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Tyres & wheels is
completed.
Experiment No:9
Aim: To study and prepare report on the constructional details, working principles and operation of the Automotive Brake systems.
Apparatus: Models of
(a) Hydraulic & Pneumatic Brake systems.
(b) Drum Brake System.
(c) Disk Brake System.
(d) Antilock Brake System.
(e) System Packing & Other Brakes.
Theory:
(a) Constructional details, working principles and operation of the Hydraulic & Pneumatic Brake systems:
The Hydraulic brake system
is a braking system which uses brake fluid usually includes ethylene
glycol, to transmit pressure from the controlling unit, which is usually
near the driver, to the actual brake mechanism, which is near the wheel
of the vehicle. The most common arrangement of hydraulic brakes for
passenger vehicles, motorcycles, scooters, and mopeds, consists of the
following:
Brake pedal or Brake lever Pushrod, also called an actuating rod Reinforced hydraulic lines Rotor or a brake disc or a drum attached to a wheel Master
cylinder assembly includes: Piston assembly is made up of one or two
pistons, a return spring, a series of gaskets or O-rings and fluid
reservoir. Brake
caliper assembly usually includes: One or two hollow aluminum or
chrome-plated steel pistons called caliper pistons and set of thermally
conductive brake pads.
A
glycol-ether based brake fluid regularly loads the system or some other
fluids are also used to control the transfer of force or power between
the brake lever and the wheel. The automobiles generally use disc brakes
on the front wheels and drum brakes on the rear wheels. The disc brakes
have good stopping performance and are usually safer and more efficient
than drum brakes. Many two wheel automobiles design uses a drum brake
for the rear wheel.
Fig: Hydraylic-Brake
In
Hydraulic brake system when the brake pedal or brake lever is pressed, a
pushrod applies force on the piston in the master cylinder causing
fluid from the brake fluid tank to run into a pressure chamber through a
balancing port which results in increase in the pressure of whole
hydraulic system. This forces fluid through the hydraulic lines to one
or more calipers where it works upon one or two extra caliper pistons
protected by one or more seated O-rings which prevent the escape of any
fluid from around the piston. The brake caliper piston then apply force
to the brake pads. This causes them to be pushed against the rotating
rotor, and the friction between pads and rotor causes a braking torque
to be generated, slowing the vehicle. Heat created from this friction is
dispersed through vents and channels in rotor and through the pads
themselves which are made of particular heat-tolerant materials like
kevlar, sintered glass. The consequent discharge of the brake pedal or
brake lever lets the spring(s) within the master cylinder assembly to
return that assembly piston(s) back into position. This reduces the
hydraulic pressure on the caliper lets the brake piston in the caliper
assembly to slide back into its lodging and the brake pads to discharge
the rotor. If there is any leak in the system, at no point does any of
the brake fluid enter or leave.
In
hydraulic brake the brake pedal is called as brake pedal or brake
lever. One end of the hydraulic brake is connected to the frame of the
vehicle, the other end is connected to the foot pad of the lever and a
pushrod extends from a point along its length. The rod either widens to
the master cylinder brakes or to the power brakes. The master cylinder
is separated as two parts in cars, each of which force a separate
hydraulic circuit. Every part provides force to one circuit. A
front/rear split brake system utilizes one master cylinder part to
pressure the front caliper pistons and the other part to pressure the
rear caliper pistons.
Pneumatic or Air Brake System
is the brake system used in automobiles such as buses, trailers,
trucks, and semi-trailers. The Compressed Air Brake System is a
different air brake used in trucks which contains a standard disc or
drum brake using compressed air instead of hydraulic fluid. The
compressed air brake system works by drawing clean air from the
environment, compressing it, and hold it in high pressure tanks at
around 120 PSI. Whenever the air is needed for braking, this air is
directed to the functioning cylinders on brakes to activate the braking
hardware and slow the vehicle. Air brakes use compressed air to increase
braking forces. Design and Function: The Compressed air brake system is
separated into control system and supply system. The supply system
compresses, stores and provides high pressure air to the control system
and also to other air operated secondary truck systems such as gearbox
shift control, clutch pedal air assistance servo, etc., Control system:
The control system is separated into two service brake circuits. They
are the parking brake circuit and the trailer brake circuit. This two
brake circuits is again separated into front and rear wheel circuits
which gets compressed air from their individual tanks for more
protection in case of air leak. The service brakes are applied by brake
pedal air valve which controls both circuits. The parking brake is the
air controlled spring brake which is applied by spring force in the
spring brake cylinder and released by compressed air through the hand
control valve. The trailer brake consists of a direct two line system
the supply line which is marked red and the separate control or service
line which is marked blue. The supply line gets air from the main mover
park brake air tank through a park brake relay valve and the control
line is regulated through the trailer brake relay valve. The working
signals for the relay are offered by the prime mover brake pedal air
valve, trailer service brake hand control and Prime Mover Park brake
hand control. Supply system: The air compressor is driven off of the
automobile engine by crankshaft pulley through a belt or straightly off
of the engine timing gears. It is lubricated and cooled by the engine
lubrication and cooling systems. The Compressed air is initially
directed through a cooling coil and into an air dryer which eliminates
moisture and oil impurities and also contains a pressure regulator,
safety valve and a little purge reservoir. The supply system is
outfitted with an anti freeze device and oil separator which is an
alternative to the air dryer. The compressed air is then stored in a
tank and then it is issued through a 4 - way protection valve into the
front and rear brake circuit air reservoir, a parking brake reservoir
and an auxiliary air supply distribution point. The Supply system also
contains many check, pressure limiting, drain and safety valves.
Fig: Air Break
(b) Constructional details, working principles and operation of the Drum Brake System:
Drum
brakes consist of a backing plate, brake shoes, brake drum, wheel
cylinder, return springs and an automatic or self-adjusting system. When
you apply the brakes, brake fluid is forced under pressure into the
wheel cylinder, which in turn pushes the brake shoes into contact with
the machined surface on the inside of the drum. When the pressure is
released, return springs pull the shoes back to their rest position.
As the brake linings wear, the shoes must travel a greater distance to
reach the drum. When the distance reaches a certain point, a
self-adjusting mechanism automatically reacts by adjusting the rest
position of the shoes so that they are closer to the drum.
Brake
Shoes: Like the disk pads, brake shoes consist of a steel shoe with the
friction material or lining riveted or bonded to it.
Backing
Plate: The backing plate is what holds everything together. It
attaches to the axle and forms a solid surface for the wheel cylinder,
brake shoes and assorted hardware.
Brake
Drum: Brake drums are made of iron and have a machined surface on the
inside where the shoes make contact. Just as with disk rotors, brake
drums will show signs of wear as the brake linings seat themselves
against the machined surface of the drum.
Wheel
Cylinder: The wheel cylinder consists of a cylinder that has two
pistons, one on each side. Each piston has a rubber seal and a shaft
that connects the piston with a brake shoe. When brake pressure is
applied, the pistons are forced out pushing the shoes into contact with
the drum. Wheel cylinders must be rebuilt or replaced if they show
signs of leaking.
Return
Springs: Return springs pull the brake shoes back to their rest
position after the pressure is released from the wheel cylinder. If the
springs are weak and do not return the shoes all the way, it will cause
premature lining wear because the linings will remain in contact with
the drum.
Self
Adjusting System: The parts of a self adjusting system should be clean
and move freely to insure that the brakes maintain their adjustment over
the life of the linings. If the self adjusters stop working, you will
notice that you will have to step down further and further on the brake
pedal before you feel the brakes begin to engage. Disk brakes are self
adjusting by nature and do not require any type of mechanism.
(c) Constructional details, working principles and operation of the Disk Brake System:
The
disk brake is the best brake we have found so far. Disk brakes are used
to stop everything from cars to locomotives and jumbo jets. Disk
brakes wear longer, are less affected by water, are self adjusting, self
cleaning, less prone to grabbing or pulling and stop better than any
other system around. The main components of a disk brake are the Brake
Pads, Rotor, Caliper and Caliper Support.
Brake
Pads: There are two brake pads on each caliper. They are constructed of
a metal "shoe" with the lining riveted or bonded to it. The pads are
mounted in the caliper, one on each side of the rotor. Brake linings
used to be made primarily of asbestos because of its heat absorbing
properties and quiet operation; however, due to health risks, asbestos
has been outlawed, so new materials are now being used.
Rotor:
The disk rotor is made of iron with highly machined surfaces where the
brake pads contact it. Just as the brake pads wear out over time, the
rotor also undergoes some wear, usually in the form of ridges and groves
where the brake pad rubs against it.
Caliper
& Support: There are two main types of calipers: Floating calipers
and fixed calipers. A floating caliper "floats" or moves in a track in
its support so that it can center itself over the rotor. As you apply
brake pressure, the hydraulic fluid pushes in two directions. It forces
the piston against the inner pad, which in turn pushes against the
rotor. It also pushes the caliper in the opposite direction against the
outer pad, pressing it against the other side of the rotor. Four Piston
Fixed Calipers are mounted rigidly to the support and are not allowed to
move. Instead, there are two pistons on each side that press the pads
against the rotor.
(d) Constructional details, working principles and operation of the Antilock Brake System:
An anti-lock braking system abbreviated as ABS
is a braking system or security system which prevents the wheels on an
automobile from locking up while braking. The wheels revolving on the
road let the driver to maintain steering control under heavy braking by
preventing a skid and allowing the wheel to continue interacting
tractively with the road surface as directed by driver steering inputs.
The ABS offers better vehicle control, and may reduce ending distances
on dry and especially slippery surfaces. It can also boost braking
distance on loose surfaces such as snow and gravel.
The
Anti-lock Brake System is composed of a central electronic control unit
(ECU), four wheel speed sensors one for each wheel and two or more
hydraulic valves inside the brake hydraulics. The ECU continuously
observes the revolving speed of every wheel, and when it senses a wheel
rotating significantly slower than the other wheels a condition
indicative of approaching wheel lock it trigger the valves to decrease
hydraulic pressure to the brake at the affected wheel, thus dropping the
braking power on that wheel. Then the wheel turns quicker when the ECU
senses it is rotating significantly faster than the others, brake
hydraulic pressure to the wheel is improved so the braking force is
reapplied and the wheel slows. This process is repeated always, and it
is perceived by the driver via brake pedal pulsation. A typical
anti-lock system can apply and discharge braking pressure up to 20 times
a second.
Fig: Antilock-Braking-System-(ABS)
(e) Constructional details, working principles and operation of the System Packing & Other Brakes:
Parking
Brakes: The parking brake (a.k.a. emergency brake) system controls the
rear brakes through a series of steel cables that are connected to
either a hand lever or a foot pedal. The idea is that the system is
fully mechanical and completely bypasses the hydraulic system so that
the vehicle can be brought to a stop even if there is a total brake
failure. On drum brakes, the cable pulls on a lever mounted in the rear
brake and is directly connected to the brake shoes. This has the effect
of bypassing the wheel cylinder and controlling the brakes directly.
Disk brakes on the rear wheels add additional complication for parking
brake systems. There are two main designs for adding a mechanical
parking brake to rear disk brakes. The first type uses the existing rear
wheel caliper and adds a lever attached to a mechanical corkscrew
device inside the caliper piston. When the parking brake cable pulls on
the lever, this corkscrew device pushes the piston against the pads,
thereby bypassing the hydraulic system, to stop the vehicle. This type
of system is primarily used with single piston floating calipers, if the
caliper is of the four piston fixed type, then that type of system
can't be used. The other system uses a complete mechanical drum brake
unit mounted inside the rear rotor. The brake shoes on this system are
connected to a lever that is pulled by the parking brake cable to
activate the brakes. The brake "drum" is actually the inside part of the
rear brake rotor.
I think system packing is not the relevant word w.r.t brake system, so it is beyond the scope.
Conclusion: Hence
the study and preparation of report on the constructional details,
working principles and operation of the Automotive Brake systems is
completed.
Experiment No:10
Aim: To
study and prepare report on the constructional details, working
principles and operation of Automotive Emission / Pollution control
systems.
Apparatus: Model of Automotive Emission / Pollution control systems.
Theory: The
need to control the emissions from automobiles gave rise to the
computerization of the automobile. Hydrocarbons, carbon monoxide and
oxides of nitrogen and particulates are created during the combustion
process and are emitted into the atmosphere from the tail pipe. There
are also hydrocarbons emitted as a result of vaporization of gasoline
and from the crankcase of the automobile. Some of the more popular
emission control systems installed on the automobile are: EGR valve,
catalytic converter, EVAP system, air injection system, PCV valve,
charcoal canister.
Sources
of vehicle emissions are Engine Crankcase Blow-by Fumes (20%)– heating
oil and burning of fuel that blows past piston rings and into the
crankcase. Fuel Vapour (20%) – chemicals that enter the air as fuel
evaporates. Engine Exhaust (60%)- blown out the tailpipe when engine
burns a hydrocarbon based fuel.
Constructional details, working principles and operation of Automotive Emission / Pollution control systems:
PCV Valve: The purpose of the positive crankcase ventilation
(PCV) system is to take the vapors produced in the crankcase during the
normal combustion process, and redirecting them into the air/fuel
intake system to be burned during combustion. These vapors dilute the
air/fuel mixture so they have to be carefully controlled and metered in
order to not affect the performance of the engine. This is the job of
the positive crankcase ventilation (PCV) valve. At idle, when the
air/fuel mixture is very critical, just a little of the vapors are
allowed in to the intake system. At high speed when the mixture is less
critical and the pressures in the engine are greater, more of the vapors
are allowed in to the intake system. When the valve or the system is
clogged, vapors will back up into the air filter housing or at worst;
the excess pressure will push past seals and create engine oil leaks. If
the wrong valve is used or the system has air leaks, the engine will
idle rough, or at worst, engine oil will be sucked out of the engine.
Fig: PCV System
Evaporative Emission Control Systems (EVAP): It
prevents toxic fuel system vapours from entering the atmosphere. It
consists of parts non-vented fuel tank cap which prevents fuel vapours
from entering the atmosphere, air dome is hump formed at the top of the
tank for fuel expansion, charcoal canister which stores vapours when the
engine is not running, purge line/valve which controls the flow of
vapours from the canister to the intake manifold that allows flow when
engine reaches operating temperature and is operating above idle speed.
Fig: EVAP System
Exhaust Gas Recirculation (EGR): The
purpose of the exhaust gas recirculation valve (EGR) valve is to meter a
small amount of exhaust gas into the intake system, this dilutes the
air/fuel mixture so as to lower the combustion chamber temperature.
Excessive combustion chamber temperature creates oxides of nitrogen,
which is a major pollutant. While the EGR valve is the most effective
method of controlling oxides of nitrogen, in it's very design it
adversely affects engine performance. The engine was not designed to run
on exhaust gas. For this reason the amount of exhaust entering the
intake system has to be carefully monitored and controlled. This is
accomplished through a series of electrical and vacuum switches and the
vehicle computer. Since EGR action reduces performance by diluting the
air /fuel mixture, the system does not allow EGR action when the engine
is cold or when the engine needs full power.
Fig: EGR System
Air Injection System:
Since no internal combustion engine is 100% efficient, there will
always be some unburned fuel in the exhaust. This increases hydrocarbon
emissions. To eliminate this source of emissions an air injection system
was created. Combustion requires fuel, oxygen and heat. Without any one
of the three, combustion cannot occur. Inside the exhaust manifold
there is sufficient heat to support combustion, if we introduce some
oxygen than any unburned fuel will ignite. This combustion will not
produce any power, but it will reduce excessive hydrocarbon emissions.
Unlike in the combustion chamber, this combustion is uncontrolled, so if
the fuel content of the exhaust is excessive, explosions, that sound
like popping, will occur. There are times when under normal conditions,
such as deceleration, when the fuel content is excessive. Under these
conditions we would want to shut off the air injection system. This is
accomplished through the use of a diverter valve, which instead of
shutting the air pump off, diverts the air away from the exhaust
manifold. Since all of this is done after the combustion process is
complete, this is one emission control that has no effect on engine
performance. The only maintenance that is required is a careful
inspection of the air pump drive belt.
Fig: Air Injection System
Catalytic Converter System: Automotive
emissions are controlled in three ways, one is to promote more complete
combustion so that there are less by products. The second is to
reintroduce excessive hydrocarbons back into the engine for combustion
and the third is to provide an additional area for oxidation or
combustion to occur. This additional area is called a catalytic
converter. The catalytic converter looks like a muffler. It is located
in the exhaust system ahead of the muffler. Inside the converter are
pellets or a honeycomb made of platinum or palladium. The platinum or
palladium are used as a catalyst (a catalyst is a substance used to
speed up a chemical process). As hydrocarbons or carbon monoxide in the
exhaust are passed over the catalyst, it is chemically oxidized or
converted to carbon dioxide and water. As the converter works to clean
the exhaust, it develops heat. The dirtier the exhaust, the harder the
converter works and the more heat that is developed. In some cases the
converter can be seen to glow from excessive heat. If the converter
works this hard to clean a dirty exhaust it will destroy itself. Also
leaded fuel will put a coating on the platinum or palladium and render
the converter ineffective.
Fig: Catalytic Converter System
MY NAME ASHU GUPTA
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