Introduction To Governors
Flywheel which minimizes fluctuations of speed within the cycle but it cannot minimize fluctuations due to load variation. This means flywheel does not exercise any control over mean speed of the engine. To minimize 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.
The function of governor is to increase the supply of working fluid going to the primemover when the load on the prime-mover increases and to decrease the supply when the load decreases so as to keep the speed of the prime-mover almost constant at different loads.
Example: when the load on an engine increases, its speed decreases, therefore it becomes necessary to increase the supply of working fluid. On the other hand, when the load on the engine decreases, its speed increases and hence less working fluid is required. 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.
CLASSIFICATION OF GOVERNORS
The broad classification of governor can be made depending on their operation.
(a) Centrifugal governors
(b) Inertia and flywheel governors
(c) Pickering governors.
In these governors, the change in centrifugal forces of the rotating masses due to change in the speed of the engine is utilized for movement of the governor sleeve. One of this type of governors is shown in Figure. These governors are commonly used because of simplicity in operation.
|Fig. Centrifugal Governor|
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 utilized 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.
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.
Types of Centrifugal Governors
Depending on the construction these governors are of two types :
(a) Gravity controlled centrifugal governors, and
(b) Spring controlled centrifugal governors.
Gravity Controlled Centrifugal Governors
In this type of governors there is gravity force due to weight on the sleeve or weight of sleeve itself which controls movement of the sleeve. These governors are comparatively larger in size.
Spring Controlled Centrifugal Governors
In these governors, a helical spring or several springs are utilised to control the movement of sleeve or balls. These governors are comparatively smaller in size.