06-05-2014, 02:20 PM
[size=]GOVERNORS[/size]
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INTRODUCTION
In the last unit, you studied flywheel which minimises fluctuations of speed within the
cycle but it cannot minimise fluctuations due to load variation. This means flywheel does
not exercise any control over mean speed of the engine. To minimise fluctuations in the
mean speed which may occur due to load variation, governor is used. The governor has
no influence over cyclic speed fluctuations but it controls the mean speed over a long
period during which load on the engine may vary.
When there is change in load, variation in speed also takes place then governor operates
a regulatory control and adjusts the fuel supply to maintain the mean speed nearly
constant. Therefore, the governor automatically regulates through linkages, the energy
supply to the engine as demanded by variation of load so that the engine speed is
maintained nearly constant.
Figure 5.1 shows an illustrative sketch of a governor along with linkages which regulates
the supply to the engine. The governor shaft is rotated by the engine. If load on the
engine increases the engine speed tends to reduce, as a result of which governor balls
move inwards. This causes sleeve to move downwards and this movement is transmitted
to the valve through linkages to increase the opening and, thereby, to increase the supply.
CLASSIFICATION OF GOVERNORS
The broad classification of governor can be made depending on their operation.
(a) Centrifugal governors
(b) Inertia and flywheel governors
© Pickering governors.
Centrifugal Governors
In these governors, the change in centrifugal forces of the rotating masses due to
change in the speed of the engine is utilised for movement of the governor sleeve.
One of this type of governors is shown in Figure 5.1. These governors are
commonly used because of simplicity in operation.
Inertia and Flywheel Governors
In these governors, the inertia forces caused by the angular acceleration of the
engine shaft or flywheel by change in speed are utilised for the movement of the
balls. The movement of the balls is due to the rate of change of speed in stead of
change in speed itself as in case of centrifugal governors. Thus, these governors
are more sensitive than centrifugal governors.
Pickering Governors
This type of governor is used for driving a gramophone. As compared to the
centrifugal governors, the sleeve movement is very small. It controls the speed by
dissipating the excess kinetic energy. It is very simple in construction and can be
used for a small machine.
Hartnell Governor
The Hartnell governor is shown in Figure 5.5. The two bell crank levers have been
provided which can have rotating motion about fulcrums O and O. One end of each bell
crank lever carries a ball and a roller at the end of other arm. The rollers make contact
with the sleeve. The frame is connected to the spindle. A helical spring is mounted
around the spindle between frame and sleeve. With the rotation of the spindle, all these
parts rotate.
With the increase of speed, the radius of rotation of the balls increases and the rollers lift
the sleeve against the spring force. With the decrease in speed, the sleeve moves
downwards. The movement of the sleeve are transferred to the throttle of the engine
through linkages.