watt governor

LNCT GROUP OF COLLEGES
Name of Faculty: Prem Kumar Soni
Designation: Assistant Professor
Department: Mechanical Engineering
Subject: Theory of Machines (403)
Unit: 6
1
Lecture – II
Governor
Topics
 Classification of governor
 Watt governor and its construction
A governor is a system that is used to maintain the mean speed of an engine, within certain
limits, under fluctuating load conditions. It does this by regulating and controlling the amount
of fuel supplied to the engine. The governor hence limits the speed of the engine when it is
running at the no-load condition, i.e., it governs the idle speed, and ensures that the engine
speed does not exceed the maximum value as specified by the manufacturers.
All marine vessels need a speed control system to control and govern the speed of the
propulsion plant being used on board, as there can be a large number of variations that arise
on engine load, which may damage the engine and cause loss of life and equipment. The
variations in the load on the engine may arise due to several factors such as rough seas,
rolling and pitching of the vessel, compromised ship structure, changes in weight of the ship
among others.
Governor Serves The Following Purposes:
It controls fuel delivery at all engine speeds and varying load conditions. The quantity of fuel
for idling and maximum speed is controlled and correct fuel delivery is ensured for all
conditions in between these two extremes.
It ensures that adequate fuel is delivered to the engine when idling, to avoid stalling and also
to limit the maximum amount of fuel that can be supplied to the injectors to prevent excessive
engine speed, but accelerator pedal to piston the control rod for all other speeds.

Unit: 6
2
Based on the source of controlling force, the governors can be classified into two types.
Centrifugal Governors:
In centrifugal governors, multiple masses know as governor balls, are responsible to revolve
about the axis of a shaft, which is driven by suitable gearing from the engine crankshaft. Each
ball is acted upon by a force which acts in the radially inward direction and is provided by
dead weight, a spring or a combination of two. This force is commonly called as the
controlling force and it will increase as the distance of the ball from the axis of rotation
increases. The inward or outward movement of the ball is transmitted by the governor
mechanism to the valve which controls the amount of energy supplied to the engine.
Inertia Governor:
In inertia governors, the balls are arranged in a manner that the inertia forces caused by
angular acceleration or retardation of the governor shaft tend to change their position. The
obvious advantage of inertia governor lies in its rapid response to the effect of a change of
load. This advantage is small, however by the practical difficulty of arranging for the
complete balance of the revolving parts of the governor. For this reason, Centrifugal
governors are preferred over the inertia governors.
********
In a gasoline engine, the governor is usually placed between the carburetor and the intake
manifold. Centrifugal governor is attached to the camshaft by a gear drive.
The movement of the flywheel attached to the pivot arms of centrifugal governors is used to
control the flow of gasoline in the carburetor, thus controlling the engine speed.
Types of Governors
Following are the three different types of governors used in automobile vehicle:
1. Mechanical or centrifugal governor.
2. Pneumatic governor.
3. Hydraulic governor.
Mechanical or Centrifugal Governor
Mechanical governors are fitted to large engines on an extension of the pump camshaft.

Unit: 6
3
Working of Mechanical Governor
When the engine starts, the weights take up a position to maintain a stable idling speed. As
the accelerator pedal is depressed against the spring, the weight moves inwards, and since the
weight are linked to the control rod, the fuel delivery is increased and hence the engine speed
also increases.
The increased engine speed causes the pump camshaft to rotate faster, which moves the
weights outward against the action of control springs, so reducing the fuel delivery until the
correct balance is arrived at for a particular engine operating condition.
Thus, the accelerator does not increase delivery directly but delays the action of the governor.
The relative position of governor-weight and control-rod positions when the engine is at
idling and full-load positions.

Unit: 6
4
Pneumatic Governor
Pneumatic governors are most successfully used in small and medium-sized engines. They
are sensitive to variations in torque loading and ensure stable idling control. As with
pneumatic induction pipe control, the air supply at light loads is throttle by a butterfly valve
placed in a choke.
This valve is directly operated by the accelerator pedal. The throttle unit is placed between
the air cleaner and the entry to the inlet manifold. Which results in the reduced air pressure at
the end of induction?
Injection then takes place into less dense air than with unrestricted induction, and the control
thus becomes quantity rather than quality control. The fuel injection is controlled by the
depression at the choke to a diaphragm chamber mounted on the end of the injection pump.

Unit: 6
5
The diaphragm plate is mounted on the end of the control rack of the pump. It is pushed to
the full load position (to the right) by the main control spring. Again, the increased
depression at the throttle, arising when the accelerator pedal is released. It will pull the
diaphragm and control rod to the left, thus reducing the fuel supply.
An auxiliary spring is also used to balance the height depression at idling speed. It is brought
into action progressively by the action of a cam.
Hydraulic Governor
Hydraulic governors eliminate the high mechanical forces bearing loads and possible
torsional vibrations in the drive. And, hence they are preferred over mechanical governors.

Unit: 6
6
In a mechanical governor, the operative agent is the centrifugal force which governs the
speed. In a hydraulic governor, it is the pressure difference across an orifice required to pass
the oil flow from a positive oil pump driven by an engine.
The pressure difference varies as the square of the engine speed. And it is determined at
equilibrium by the pressure of the driver’s foot on the accelerator pedal.
A hydraulic governor, like a mechanical governor, is an all-speed governor i.e., the governor
is in control throughout the whole rack is operated by the governor and not directly by the
accelerator to the supply to maintain the speed, no matter what the power requirements may
be from moment to moment.
Watt Governor
Watt governor is the simplest form of centrifugal governors. Centrifugal governors are
special type of governors with a feedback system that controls the speed of an engine by
regulating the flow of fuel or working fluid.

Unit: 6
7
Watt governor has two fly balls attached to two arms of negligible masses. Watt governor is
used to supply the required amount of fuel at different speed.
When the speed of engine increases, the supply of fuel needs to increase and as the engine
speed decreases the supply of fuel should be decreased. So the fuel supply should be
regulated according to the speed of the engine. With the help of watt governor we can obtain
a required load on the engine with constant smooth function.
Construction:-
Watt governor consists of two fly balls which are located at the end of the arms. The upper
parts of these two arms are pivoted to the spindle. This spindle is driven by the engine
through the bevel gears. The lower parts of arms are connected to the sleeve which moves
upward or downward as the balls moves upward or downward. The sleeve has stopper which
are placed at up and down of sleeve to limit its movement. The sleeve is connected to throttle
valve through bell crank lever . The movement of sleeve controls opening and closing of
throttle valve.
Working of Watt Governor
Watt governors consist of two balls which are attached to both arms which are of negligible
mass. The upper side of arms is pivoted so that its balls can move upwards and downwards.
These arms are connected to the spindle . The engine drives the spindle through bevel gears.

Unit: 6
8
When the speed of the engine increases, the spindle rotates at high speed. The arms as well as
the balls connected to spindle rotate at high speed. As the balls rotate at high speed and the
upper side of arms are pivoted to the spindle, the balls moves in upward direction.
The lower arms are connected to the sleeves. These sleeves are keyed to the spindle in such a
way that it revolves with the spindle and can slide up and down according to the speed of
rotation of spindle.
As the engine speed increases and the balls move in upward direction, the sleeve connected to
arms also moves upward and similarly moves downward when the speed of engine decreases.
There are stoppers placed above and below the sleeve to limit the upward and downward
motion of the sleeve.
Now, there are two cases:-
i) When engine speed increases.
ii) When engine speed decreases.
Let’s discuss these two cases.
i) When the engine speed increases:-
When the speed of engine increases, the load on the engine decreases and the speed of
rotation of spindle increases. The centrifugal force on balls increases and the balls move
upwards and hence the sleeve moves upward. As the sleeve moves upward. The upward
movement of sleeve causes the throttle valve at the end of the ball crank lever to decrease the
fuel supply. The power output is reduced.
ii) When the engine speed decreases:-
When the engine speed decreases, the load on engine increases and speed of rotation of
spindle decrease. The centrifugal force on balls decreases and the balls moves downwards.
As the balls move downwards, hence the sleeve moves downward which causes the throttle
valve to increase the fuel supply and the power output is increased.

Unit: 6
9

watt governor

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