The document discusses the inlet system of internal combustion (IC) engines, including their components and functions. It contrasts spark ignition (SI) and compression ignition (CI) engines, detailing their fuel systems, carburetors, and modern electronic fuel injection systems. The importance of the inlet system in ensuring efficient air-fuel mixture for optimal combustion and engine performance is emphasized.

1. Greetings dear viewers
Topic of Discussion: Inlet System of an IC
Engine
 Group participants:
 Razin Sazzad Molla 13107010
 Sazzad Ibne Rafiq 08207071
 Sohel Mia 12107007
 Arif Ahmed 14107024
 Debabrata Karmakar 14107034

2. Topics covered:
 Overview of IC engines
 Inlet system and its significance
 Inlet system of SI engines
 Carburetor function
 Inlet system of CI engines
 Ignition systems
 Injection pumps and injectors
 Intake manifold and valves
 Camshaft mechanism
 Starting system
 Engine governors

3. Overview of IC Engines
IC engines or Internal Combustion Engines are mechanical devices that produces mechanical power
by rotating shaft using the derived heat energy from burnt fuel in the presence of oxygen of the
atmospheric air and in which the air fuel combustion takes place inside the cylinder of the engine. IC
engines can be of 2 types depending upon the movement of the energy transmitting member. One is
the reciprocating type in which linear motion of the pistons is converted to rotary motion of the
crank shaft and the other type is rotary engines where we have rotors to produce motions.
IC Engines are broadly classified into many groups depending upon a lot of factors. Take for instance
there are spark ignition & compression ignition engines based on the method of igniting the working
fluid. Depending upon working cycles there are basically two major types, engines that work on otto
cycle and engines that work on diesel cycle. There are also 2 stroke & 4 stroke cycle engines.
All IC engines converts the chemical energy
stored in hydrocarbon fossil fuel to
mechanical work. This is the principle of all
engines. About only 20% is used to propel the
vehicle, 80% is lost to friction, aerodynamic
drag, accessory operation or simply heat
dissipated to the environment/cooling system
SI engine: Uses
petrol/gasoline(octane number
87-89), low compression
ratio(8:1 to 12:1) Energy content
34.6 MJ/litre high rpm,less
torque
CI Engines: Uses Diesel(cetane
number between 40&60)
compression ratio 14:1 to 25:1
38.6 MJ/litre low rpm high
torque

4. Inlet system and its significance
The combustion of fuel in internal combustion engine is a fast exothermic reaction in the gaseous
phase where oxygen obtained from air is usually one of the reactants. In actual practice the working
fluid is considered to be a mixture of air fuel and residual gases(fuel-air cycle). For an engine to perform
properly and most efficiently the system has to provide air fuel mixture at an exact time and at an
exact amount in all the cylinders so the combustion takes place as designed. The inlet system of an IC
engine consists of all the interconnected components that perform the task of drawing clean air and
mixing it with fuel vapor at varying proportions and permitting it into all the chambers at proper
time and through the ignition process oxidizing it.
Typical components associated with Inlet system:
Air filter, carburetor, throttle valve, oil tank, oil filter, oil pump, spark plug, glow plug, pressure pump, injector,
distributor, fuel supply unit, common rail system, intake manifold, gaskets, poppet valves, cam shaft
assembly(cam lobes, cam timing belt, rocker arm, camshaft sprocket, tensioner), ignition system (coil ignition,
magneto ignition), alternator, Electronic control unit, starter motor, sensors.
Engine subsystems:
Air & exhaust system, Fuel
system, Ignition system, Cooling
subsystem, Lubrication system,
Electronic system, Mechanical
system, Governing subsystem
In the following slides our discussion will be limited to
the inlet system of the conventional IC engines only.

5. Inlet system of petrol engines
Typical Fuel System
Components that supply clean fuel to the fuel
metering system (fuel pump, fuel pipes, fuel
filters).
1. Fuel Supply System
Components that supply controlled clean air
to the engine (air filter, ducting, valves).
2. Air Supply System
Components that meter the correct amount of
fuel (and air) entering the engine (injectors,
pressure regulator, throttle valve).
3. Fuel Metering System

6. Petrol engine- carburetor fuel system

7. Engine Fuel System (SI Petrol)
• Fuel Tank – normally positioned in the rear
boot area, The fuel tank may be made
from pressed steel and coated inside to
prevent corrosion, or a synthetic rubber
compound or flame resistant plastic.
Inside the fuel tank is normally located the
fuel gauge sender unit and electrically
driven fuel pump with a primary filter in a
combined module. The fuel tank is
pressurised to about 2 psi to prevent fuel
vaporization and pollution. The fuel tank is
vented through its own venting system
and the engine managements emission
control systems again to control pollution.
• Fuel pipes – These can be made from steel
or plastic and are secured by clips at
several points along the underside of the
vehicle. To allow for engine movement
and vibration, rubber hoses connect the
pipes to the engine.

8. Engine Fuel System (SI Petrol)
• Fuel Filters – to prevent dirt and fluff entering the fuel
pump a filter is fitted on the suction side of the pump.
On the pressure side of the pump a secondary filter is
used, this is a much finer filter in that it prevents very
small particles of dirt reaching the carburettor or fuel
injection equipment.
• Air Filters – air cleaners and silencers are fitted to all
modern vehicles. Its most important function is to
prevent dust and abrasive particles from entering the
engine and causing rapid wear. Air filters are designed
to give sufficient filtered air, to obtain maximum
engine power. The air filter/cleaner also acts as a flame
trap and silencer for the air intake system.
• Fuel Pump – this supplies fuel under high pressure to
the fuel injection system, or under low pressure to a
carburettor.
• Carburettor – this is a device which atomizes the fuel
and mixes it which the correct amount of air, this
device has now been superseded by modern electronic
fuel injection.

9. Petrol
Petrol

10. • Float chamber – to set and maintain the fuel level within the carburettor, and to control
the supply fuel to the carburettor venturi.
• Operation – when air passes through the venturi due to the engines induction strokes, it
creates a depression (suction), around the fuel spray outlet. Atmospheric pressure is
acting on the fuel in the float chamber, the difference in theses pressures causes the fuel
to flow from the float chamber, through the jet and into the stream. This causes the petrol
to mix with the air rushing in to form a combustible mixture. The required air fuel ratio can
be obtained by using a jet size which allows the correct amount of fuel to flow for the
amount of air passing through the
Defects of the simple carburettor
• As engine speed increases, air pressure and density decreases i.e. the air gets thinner,
however the quantity of fuel increases i.e. greater pressure exerted on the fuel, this
causes the air/fuel mixture to get progressively richer (to much fuel).
• As the engine speed decreases, the air/fuel mixture becomes progressively weaker. Some
form of compensation is therefore required so that the correct amount of air and fuel is
supplied to the engine under all operating conditions.

11. Petrol
Operation of the Venturi
The Choke Valve is used
to provide a rich air/fuel
ratio for cold starting
Choke
Valve
closed
The Float Chamber
The Throttle Valve controls the
amount of air fuel mixture entering
the engine and therefore engine
power
The Simple
Carburettor

16. Air Fuel Ratio
• Fuel mixture strengths – petrol will not burn unless it is mixed with air, to obtain the best
possible combustion of the fuel, which should result in good engine power and fuel
consumption and low emissions (pollution), the air fuel ratio must be chemically correct i.e.
the right amount of air and fuel must be mixed together to give an air fuel ratio of 14.7 to 1
by mass. This is referred to as the stoichiometric air fuel ratio, this ratio can also be describe
by the term Lambda. Lambda is the Greek word meaning ‘air’. When their is more air
present than fuel in the air fuel mixture, it is said to be ‘weak’ or ‘lean’ i.e. not enough fuel
e.g. a ratio of 25 to 1, this results in a Lambda reading of more than 1.When their is not
enough air present, the mixture is referred to as ‘rich’ e.g. a air fuel ratio of 8 to 1, in this
case Lambda equals less than 1.
• Weak/lean air/fuel mixtures – can result in low fuel consumption, low emissions (pollution),
however, weak air fuel mixtures can also result in poor engine performance (lack of power)
and high engine temperatures ( because the fuel burns more slowly)
• Rich air/ fuel mixtures – can result in greater engine power, however this also results in
poorer fuel consumption and greatly increased emissions (pollution)

17. Engine (S I) Fuel System
• ECU – Electronic control unit- This contains a computer which takes information from
sensors and controls the amount of fuel injected by operating the injectors for just the
right amount of time. The ECU also controls the operation of the ignition and the other
engine rated systems.
• Air flow/mass meter – A sensor used to tell the ECU how much air is being drawn into the
engine.
• MAP sensor – Manifold absolute pressure sensor. This senses the pressure in the engines
inlet manifold, this gives an indication of the load the engine is working under.
• Speed/crankshaft sensor – This tells the ECU has fast the engine is rotating and sometimes
the position of the crankshaft.
• Temperature sensor – Coolant temperature is used determine if more fuel is needed when
the engine is cold or warming up.
• Lambda sensor – A sensor located in the exhaust system which tells the ECU the amount of
oxygen in the exhaust gases, form this the ECU can determine if the air/fuel ratio is correct.
• Fuel pump – A pump, normally located in the fuel tank, which supplies fuel under pressure
to the fuel injectors.

18. Engine S I Fuel System
• Fuel filter – keeps the fuel very
clean to prevent the injectors
becoming damaged or blocked.
• Fuel rail – A common connection to
multi point injectors, acts a
reservoir of fuel (small tank of fuel).
• Injector – A electrical device which
contains a winding or solenoid.
When turned on by the ECU, the
injector opens and fuel is sprayed
into the inlet manifold, or into the
combustion chamber itself.
• Idle actuator – A valve controlled by
the ECU which controls the idle
speed of the engine.
Electronic control unit

19. Introduction to Electronic Petrol
Throttle/Single Point Fuel Injection Systems
The Carburettor has now been replaced with petrol injection systems. These systems supply the
engine with a highly atomized mixture of air and fuel in the correct air/fuel ratio. This has the following
advantages over the carburettor systems
Lower exhaust emissions (pollution)
Better fuel consumption
Smoother engine operation and greater power
Automatic adjustment of the air/fuel ratio to keep the vehicles emissions (pollution) to a
minimum.

20. Air drawn in by the engine
Fuel Supply
Throttle Body
Throttle Valve
Inlet Manifold
Fuel Injector (one off)
The Engine
Throttle Body/Single Point
S.I. Fuel Injection

21. Single Point Electronic Fuel Injection (EFI)
Systems
EFI systems are classified by using the point of injection.
A fuel injector (may be 2) is
located in a throttle body
assembly that sits on top
of the inlet manifold.
Fuel is sprayed into the
inlet manifold from above
the throttle valve, mixing
with incoming air.
Fuel quantity, how much
fuel is injected is
controlled by an ECU.
Single Point (Throttle Body) Fuel Injection
ECU
Fuel in
Inlet manifold
Air in
TB injector

22. Needle valve
Electrical connector
Fuel filter
Fuel in
SpringArmatureNozzle/jet
Solenoid coil
Electronic Fuel Injector Operation
An injector sprays fuel into the inlet manifold by use of a solenoid coil.
When the coil is switch on by the ECU, it pulls the armature/needle valve
away from the nozzle, allowing pressurized fuel into the engine.
When the coil is not switched on, the spring pushes the armature/needle
against the nozzle, no fuel is injected into the inlet manifold
Injectors are more precise and
efficient than carburettors.

23. Protective
cap with gas
intake slots
Wires
to ECU
Protective
cap with gas
intake slots
Wires
to ECU
Reference
voltage
Engine coolant
temperature sensor
+V
V
0V

Reference
voltage
Reference
voltage
Engine coolant
temperature sensor
+V
V
0V

+5V
0V
TPS
+5V
0V
TPSTPS ECU
IAC valve
Throttle valve
Air in
Solenoid coil
ECU
IAC valve
Throttle valve
Air in
Solenoid coil
The ECU (Brain) receives
Information from varies sensors.
From this information it works out
how much fuel the engine needs
Outputs
Single Point Injection
Sensor Inputs

24. Air drawn in by the engine
Fuel Injectors
Throttle Valve
Fuel
Supply
Inlet Manifold
Injectors
Engine
Multi – Point S.I. Fuel Injection

25. Typical S.I. Fuel System Layout (Simplified)
Fuel Tank
Fuel Pump
Fuel
Filters
Carburettor
Or Single
Point Throttle
Body Housing
Fuel Injector or
Carburettor
Venturi
Fuel Not
used is
returned to
the fuel tank
Inlet Manifold
Engine Combustion
Chamber
Fuel Pressure
Regulator
EFI Only

26. Ignition Systems
Ignition process in Petrol Engines requires an electric
spark
produced at the spark plug. This spark is generated by an
electric discharge produced by the ignition system.
Ignition systems in petrol engines are classified as:
1.Battery ignition system.
2.Magneto ignition system
The difference between the two systems is in the source
of
primary voltage.
Basic requirements of an ignition systems
A source of electrical energy
A device for boosting the low voltage to produce
high voltage
A device for timing and distributing the high
voltage to each
spark plug
Battery ignition system
It is also called coil ignition system.
The source of energy to the primary windings is a 6V or
12V battery.
As the number of windings in the secondary is 50 to 100
times more than that of the primary , the output voltage
induced will be of the order of 10000v to 20000V.
Magneto Ignition System
The source of energy is either rotating magnets
with fixed coils or rotating coils with fixed
magnets.
The rapid collapse and reversal of magnetic
field induces a very high voltage in the
secondary winding.
It is generally employed in racing cars, motor
cycles etc.

29. Spark plug
The spark plug ignite the suctioned and compressed fuel-
air
mixture due to arcing between the electrodes.
Function: The ignition voltage travels to the spark plug
from directly connected ignition coils or over the ignition
lines from the Ignition coils causing arcing in the air gap
between the center and ground electrodes.
Spark plug is located in the cylinder head. It ignites the air
and fuel mixture.
Has center and side electrodes, with an air gap between
them. Centre electrode receives coil voltage. Side
electrode is grounded. High voltage jumps the air gap,
creating a spark. Insulator prevents high voltages from
shorting to ground.

30. INLET SYSTEM OF DIESEL ENGINE
Air intake systems vary greatly from vendor to vendor but are usually one of the two types, wet or dry.
In a wet filter intake system as shown in figure the air is sucked or bubbled through a housing that
holds a bath of oil such that the dirt In the air is removed by the oil in filter. The air then flows through a
screen type material to ensure any entrained oil is removed from the air. In a dry filter system paper
cloth or a metal screen material is used to catch and trap dirt before it enters the engine.(similar to the
type used in automobiles)
In addition to cleaning the air the intake system is designed to intake fresh air from as far as practicable,
usually just outside the engines building or enclosure. This provides the engine with a supply of air that
has not been heated by the engine’s own waste heat.
The reason for ensuring that the engines air supply is as cool as possible is that cool air is more dense
than hot air. This means that cool air has more oxygen per unit volume than hot air. Thus cool air
provides more oxygen per cylinder charge than hot less dense air. More oxygen means a more efficient
fuel burn and more power.
After being filtered the air is routed by the intake system into the engines intake manifold or air box.
The manifold or air box is the component that directs the fresh air to each of the engines intake valve
or port. If the engine is turbocharged or supercharged the fresh air will be compressed with a blower
and possibly cooled before entering the intake manifold or air box. The intake system also serves to
reduce the airflow noise.

32. FUEL SYSTEM OF DIESEL ENGINE
During engine operation, the fuel is supplied by gravity from fuel tank to the primary filter where coarse
impurities are removed. From the primary filter, the fuel is drawn by fuel transfer pump and is delivered to fuel
injection pump through second fuel filter. The fuel injection pump supplies fuel under high pressure to the
injectors through high pressure pipes. The injectors atomize the fuel and inject it into the combustion chamber
of the engine. The fuel injection pump is fed with fuel in abundance. The excess fuel is by-passed to the intake
side of the fuel transfer pump through a relief valve.
The main components of the fuel system in diesel engine are: (1) fuel filter (2) fuel lift pump (3) fuel
injection pump (4) atomizers and (5) high pressure pipe. Two conditions are essential for efficient operation of
fuel system: (i) The fuel oil should be clean, free from water, suspended dirt, sand or other foreign matter, (ii)
The fuel injection pump should create proper pressure, so that diesel fuel may be perfectly atomized by
injectors and be injected in proper time and in proper quantity in the engine cylinder.

33. Layout of diesel fuel system

34. FUEL LIFT PUMP (FEED PUMP OR TRANSFER PUMP)
It is a pump, which transfers fuel from the fuel line to the fuel injection pump. It is mounted on the body of fuel
injection pump. It delivers adequate amount of fuel to the injection pump. The pump consists of: (I) body (2)
piston (3) inlet valve and (4) pressure valve. The valves are tightly pressed against their seats by springs. The
piston is free to slide in the bore. The fuel contained in the space below the piston is forced to flow through
secondary fuel filter to the injection pump. At the same time downward movement of the piston creates a
depression in the space above the piston which, causes the fuel to be drawn in the transfer pump from the fuel
tank through the inlet valve and the primary filter.
Bosch-Fuel-Lift-Pump

35. FUEL INJECTING PUMP
It is a pump, which delivers metered quantity of fuel to each cylinder at appropriate time
under high pressure. Tractor engines may use two types of fuel injection pump:
(i) Multi-element pump and (ii) Distributor (Rotary) type pump.
Fuel Injector: It is the component, which delivers finely atomized fuel under high pressure to
the combustion chamber of the engine. Modern diesel engines use fuel injectors, which have
multiple holes. Main parts of injector are: nozzle body and needle valve. The nozzle body and
needle valve are fabricated from alloy steel. The needle valve is pressed against a conical seat
in the nozzle body by a spring. The injection pressure is adjusted by adjusting the screw.
FUEL INJECTION SYSTEM
Diesel fuel is injected in diesel engine through injectors with the help of fuel injection pump.
The system using injectors, fuel injection pump, fuel filter, and fuel lines is called fuel injection
system. The main functions of fuel injection system are:
(i) To measure the correct amount of fuel required by engine speed and load,
(ii) To maintain correct timing for beginning and end of injection,
(iii) To inject the fuel into the combustion space against high compression pressure.
(iv) To atomize the fuel for quick ignition.

36. Based on the methods used to produce the required pressure for atomization of the fuel process of
fuel injection in diesel engine is of two types: (i) Air injection (ii) Solid injection.
Air injection: In this process, the engine uses compressed air to force the fuel into the cylinder. It is
a bulky system and hence it is not considered very suitable for vehicles and tractors. It is mostly
used on heavy-duty stationary engines.
Solid injection: A high-pressure pump is used for forcing the fuel into the combustion chamber.
Depending upon the location of the fuel
pumps, the grouping, the method of actuating
the pumps and the methods used to meter
the fuel the solid injection system can be
classified as follows:
1. Individual pump system or the divided fuel
feed device
2. Unit injector system or the undivided fuel
feed device
3. Distributor system
4. Common rail system
Fuel injection system
components
1. Pumping elements
2. Metering elements
3. Metering control
4. Distributing elements
5. Timing controls
6. Mixing elements

37. Individual pump system or the divided fuel feed device
Each cylinder is provided with one pump and one injector. The injector is located on the cylinder while the
pump is on the side of the engine. Jerk pump is used.

38. Unit injector system or the undivided fuel feed device
The high pressure pipeline connecting the individual pump and the associated injector can be avoided by the
design of a unit injector.in this system the pump and injector nozzle are combined in one housing. Each cylinder
has one of these injector units. Fuel is brought up to the pump by a low pressure pump. This system requires a
pushrod and a rocker arm to actuate the plunger and injects the fuel into the cylinder at the proper time.

39. The distributor system
A single pump for compressing the fuel and a dividing device to distribute the fuel to the
cylinders are used.

40. Common rail system
The fuel from the fuel storage tank is drawn through the
primary fuel filters by a low pressure fuel feed pump. The
discharge from this pump enters the high pressure fuel
injection pump. This pump serves only to deliver fuel under
high pressure to a common rail called the header with the
pressure held constant by a pressure regulating valve.

41. Inline injection pump
Traditional inline injection pump
Have a pump element (plunger, cylinder) for
each engine cylinder
- Pump elements in line disposal
Body
- Crankcase, Camshaft, Feeding pump (or not)
,Pushers (or not), Visit window ,Gear rack, Pump
elements (plungers, cylinder, gear), Feeding
collector, Retention valves, Automatic speed
regulator Camshaft
- It have the same rotation as the engine
camshaft (one turn for two turns of the
crankshaft) Causes an linear movement on the
plungers , Plungers
- Push the fuel in the direction of the injector
- Gear rack
-Causes an rotation movement on the plungers
that is function of the accelerator pedal
- Pump elements
- Control the amount of fuel that goes to the
injector

42. Inline injection pump

43. Basic operation
he eccentric on the camshaft causes
constant linear movement of the pushers
- the plungers, by the action of the
pushers, push the fuel in the direction of
the retention valve
- the pressure is high enough to open the
retention valve and the fuel is conducted
by pipes to the injectors
- the amount of fuel is controlled by the
gear rack. The gear rack causes an rotation
movement to the plunger that is function of the
accelerator pedal
The plunger has cannelures around it self to fuel
flow, and the position of the rack determines the
position of the plunger that determines the
amount of fuel injected. The end of injection
occurs when the cannelure of the plunger
reaches a position that makes connection
between the cylinder and the feeding collector,
balancing the pressure

44. Radial rotary injection pumpUsed on small diesel engines
- Low volume and weight
- High efficiency
An example is VR BOSCH radial
rotary injection pump - One pump element
for all the engine cylinders
- Presence of internal sensors (fuel
temperature, rotation angle)
- Has a pump control unit, independent
from the engine control unit.
There is a high pressure side and a low
pressure side.
Basic operation -Distributor functions
- Send fuel to plungers
- Time duration in close position of electro-valve
determines the injection flow
-Send fuel to injectors
-The plungers are pressed by cam
-Fuel high pressure generated
- Distributor rotates to injector flow position

45. Electronic Diesel Control
The EDC is divided into these main
groups of components:
Electronic sensors for registering
operating conditions and changes. A
wide array of physical inputs is
converted into electrical signal
outputs.
Actuators or solenoids which convert
the control unit's electrical output
signal into mechanical control
movement.
ECM (Electronic Control Module ) or
Engine ECU (Electronic Control Unit)
with microprocessors which process
information from various sensors in
accordance with programmed
software and outputs required
electrical signals into actuators and
solenoids.
EDC distributor injection pump
EDC injection inline pumpEDC control unit
EDC accelerator pedal assembly

46. Fuel injector
Nozzle refers to the part of the nozzle
body/needle assembly which interfaces
with the combustion chamber of the
engine. Terms like P-Type, M-Type, or S-
Type nozzle refer to standardized
dimensions of nozzle parameters, as per
ISO specifications.
Nozzle holder or injector body refers to
the part the nozzle is mounted on. In
conventional injection systems this part
mainly served the nozzle mounting and
nozzle needle spring preloading function.
In common rail systems, it contains the
main functional parts: the servo-hydraulic
circuit and the hydraulic actuator
(electromagnetic or piezoelectric).
Injector commonly refers to the nozzle
holder and nozzle assembly.
Fuel injector
Under high pressure, the temperature
of the diesel fuel increases to a point
where the fuel self-combusts. In cold
weather however, this temperature is
not always achieved and glow plugs
assist by heating the air-fuel mixture
to assist in cold starting.
Glow plug

47. Intake Manifolds
The primary function of the intake manifold is to evenly distribute
the combustion mixture (or just air in a direct injection engine) to
each intake port in the cylinder head(s). Even distribution is
important to optimize the efficiency and performance of the engine.
It may also serve as a mount for the carburetor, throttle body, fuel
injectors and other components of the engine. The design and
orientation of the intake manifold is a major factor in the volumetric
efficiency of an engine. Modern intake manifolds usually employ
runners, individual tubes extending to each intake port on the
cylinder head which emanate from a central volume or "plenum"
beneath the carburetor. The purpose of the runner is to take
advantage of the Helmholtz resonance property of air.

48. Engine Intake Valves(Poppet valve)
A poppet valve (also called mushroom valve) is
a valve typically used to control the timing and
quantity of gas or vapor flow into an engine. It
consists of a hole, usually round or oval, and a
tapered plug, usually a disk shape on the end
of a shaft also called a valve stem. The portion
of the hole where the plug meets with it is
referred to as the 'seat' or 'valve seat'. The
shaft guides the plug portion by sliding through
a valve guide. Poppet valves are used in most
piston engines to open and close the intake
and exhaust ports in the cylinder head.
Three-valve cylinder head: This
has a single large exhaust valve
and two smaller intake valves.
Four-valve cylinder head: This is
the most common type of multi-
valve head, with two exhaust
valves and two similar (or slightly
larger) inlet valves.
A cylinder head of a four valve
engine. ( Nissan VQ engine )

49. Camshafts mechanism
Primary purpose is to operate the valve train. The camshaft may also operate the following:
■ Mechanical fuel pump ■ Oil pump ■ Distributor
The cam is driven by timing gears, chains, or belts located at the front of the engine. The gear or sprocket on the camshaft has
twice as many teeth, or notches, as the one on the crankshaft. This results in two crankshaft revolutions for each revolution of
the camshaft. The camshaft turns at one-half the crankshaft speed in all four-stroke-cycle engines.
Push Rods and Rocker Arms:
Push rods are used only on cam-in-block engines. They transmit the lifter motion to the rocker arm. Rocker arms are pivoting
levers that convert the upward movement of the push rod or lifter into downward movement of the valve. The camshaft is
supported in the block by camshaft bearings and driven by the crankshaft with a gear or sprocket and chain drive.
On overhead cam engines, the camshaft is installed on top of the cylinder head. It opens the valves from above. In some
overhead cam engines, the lifter is placed between the cam lobe and the rocker arm. In many cases, the rocker arm is directly
operated by the camshaft. A hydraulic lash adjuster, similar in operation to a hydraulic lifter, maintains the proper valve
clearance

50. Valve train assembly

51. Starting system
The starter motor drives the engine through a pinion gear that
engages the ring gear on the flywheel.
The starting system:
•Uses a powerful electric motor to drive the engine at about 200
RPM (fast enough to allow the fuel and ignition systems to operate).
•Drives the engine through a pinion gear engaged with a ring gear
on the flywheel.
•Disengages as soon as the engine starts.
Starting System Components:
These components make up a typical Toyota starting system:
•Starter motor
•Magnetic switch
•Over-running clutch
•Ignition switch contacts
•Park/neutral position (A/T) or clutch start (M/T) switch
•Clutch start cancel switch (on some models)
•Starter relay

52. Engine governor
Governor is a mechanical device which is used to
regulate the mean speed of the engine, when there are
variations in the load. When load on the engine varies,
the configuration of the governor changes and it
controls the supply of the fuel to the engine.
When load on the engine increases, its speed
decreases, so it becomes necessary to increase the
supply of the working fluid (ex petrol or diesel) to the
engine. On the other hand when the load on the engine
decreases, the governor’s speed increases, so it requires
to decrease the supply of the fuel.
When the speed of the governors increases, its sleeve
moves in upward direction, which is connected to a
throttle valve through a bell crank lever. This upward
motion of the sleeve operates the valve to decrease the
supply of the fuel. And when the speed of the governor
decreases due to the increase in the load, the sleeve
move downward, this made the valve to open to a
larger extent and increases the fuel supply.

53. The End