Governors : Types, Working, Performance, Example

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 the mean speed of the engine. To minimize fluctuations in the mean speed which may occur due to load variation, the 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 a 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 the load so that the engine speed is maintained nearly constant.

Function Of Governor : 

  • The function of the governor is to increase the supply of working fluid going to the prime mover 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.
  • The Governor mechanism is used to regulate the mean speed of an engine, when there are variations in the load e.g. 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 thus less working fluid is required.
  • The governor automatically controls the supply of working fluid to the engine with the varying load conditions and keeps the mean speed within certain limits.
Fig. Governor
Fig. Governor
Example of Governor Mechanism : 
  • Figure 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 the load on the engine increases the engine speed tends to reduce, as a result of which governor balls move inwards. This causes the sleeve to move downwards and this movement is transmitted to the valve through linkages to increase the opening and, thereby, to increase the supply.
  • On the other hand, a reduction in the load increases engine speed. As a result of which the governor balls try to fly outwards. This causes an upward movement of the sleeve and it reduces the supply.
  • Thus, the energy input (fuel supply in IC engines, steam in steam turbines, water in hydraulic turbines) is adjusted to the new load on the engine. Thus the governor senses the change in speed and then regulates the supply.
  • Due to this type of action it is a simple example of a mechanical feedback control system which senses the output and regulates input accordingly.

CLASSIFICATION OF GOVERNORS  

The broad classification of the governor can be made depending on their operation.
There are basically two types of governors.
1. Centrifugal governors, and
2. Inertia governor.
In centrifugal governors, the centrifugal force is balanced by the controlling force. These types of governors are used extensively. In the inertia type of governors, the inertia force is balanced by the controlling force. They are not used popularly.
The centrifugal governors can be further classified as follows:
1. Pendulum type—Watt governor
2. Loaded type
(a) Dead weight type
(i) Porter governor
(ii) Proell governor
(b) Spring-loaded type
(i) Hartnell governor
(ii) Hartung governor
(iii) Wilson–Hartnell governor
(iv) Pickering governor
types Of governors
types Of governors

Centrifugal Governors

  • These governors work on the principle of centrifugal action. They have two balls that rotate along with the sleeve. As the centrifugal forcer is directly proportional to the radius of rotation of the mass, therefore, when the speed of a device increases, the balls rotate at a larger radius.
  • As a result of it, the sleeve slides upwards on the spindle and with the help of a lever, the throttle is closed to the required extent.
  • With the decrease in speed, the balls rotate at a smaller radius of rotation, compelling the sleeve to move down on the spindle. The downward movement of the sleeve opens the throttle to the required extent to admit more fuel into the prime movers. By this process, the speed of the prime mover and in turn that of the driven device is maintained constant.
Fig. Centrifugal Governor
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 the 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 instead of the change in speed itself as in the 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. 

 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 the gravity-loaded governors, a central load is attached to the sleeve, which slides on the spindle.
  • There is a force of friction between the loaded sleeve and the spindle. The frictional force acts downwards when the sleeve moves up and acts upwards when the sleeve moves down. Thus, the height of the governor increases or decreases from the normal value.
Spring Controlled Centrifugal Governors
In these governors, a helical spring or several springs are utilized to control the movement of sleeve or balls. These governors are comparatively smaller in size.
 
Watt’s Governor:
Watt governor is the simplest and gravity controlled form of the centrifugal governors. It consists of two fly balls attached to the sleeve of negligible mass. The upper sides of arms are pivoted so that its balls can move upward and downward as they revolve with a vertical spindle. The engine drives the spindle through bevel gears. The lower arms are connected to the sleeves. The sleeve is keyed to the spindle in such a way that it revolves with the spindle. At the same time, it can slide up and down according to the spindle speed. Two stoppers are provided at the bottom and top of the spindle to limit the movement sleeve.
Watts Governor

Watts GovernorWhen the load on the engine decreases, the speed of the engine and then the angular velocity of the governor spindle increase. The centrifugal force on the ball increase; that tends balls move outward and sleeve move upward. The upward movement of the sleeve actuates a mechanism that operates the throttle valve at the end of ―bell crank lever to decrease the fuel supply. The power output is reduced.

When the speed of the engine decreases as the load on the engine increase, the centrifugal force decreases. The result is that the inward movement fly-balls and downward movement of the sleeve. The movement causes a wide opening of the throttle valve. The increase in the fuel supply also increases engine speed.

Terms Used in Governors

The following terms used in governors are important from the subject point of view ;
1. Height of a governor. – It is the vertical distance from the centre of the ball to a point where the axes of the arms (or arms produced) intersect on the spindle axis. It is usually denoted by h.
2. Equilibrium speed.-  It is the speed at which the governor balls, arms etc., are in complete equilibrium and the sleeve does not tend to move upwards or downwards.
3. Mean equilibrium speed.-  It is the speed at the mean position of the balls or the sleeve.
4. Maximum and minimum equilibrium speeds. – The speeds at the maximum and minimum radius of rotation of the balls, without tending to move either way are known as maximum and minimum equilibrium speeds respectively.
Note: There can be many equilibrium speeds between the mean and the maximum and the mean and the minimum equilibrium
speeds
5. Sleeve lift. – It is the vertical distance which the sleeve travels due to change in equilibrium speed.

Performance of Governors : 

1. Sensitiveness:

  • For maintaining a constant speed of rotation, the movement of the sleeve of the governor should be as large as possible and the corresponding change of equilibrium speed as small as possible.
  • The bigger the displacement of the sleeve for a given fractional change of speed, the more sensitive is the governor. Sensitiveness is more correctly defined as the ratio of the difference between the maximum and minimum equilibrium speeds to the mean equilibrium speed.
  • A too sensitive governor changes the fuel supply by a large amount when a small change in the speed of rotation takes place. This causes wide fluctuations in the engine speed, resulting in the hunting of the governor.
If,
Nmax = maximum equilibrium speed
Nmin = minimum equilibrium speed
Nmean = mean equilibrium speed
Nmean = ( Nmax +Nmin ) / 2
Speed Range : Nmax – Nmin
Then, Sensitiveness =  (Nmax – Nmin) / Nmean
Putting Nmean Value in Above Equation we get,
Sensitiveness = 2( Nmax – Nmin)  /  ( Nmax +Nmin ) 
2. Stability:
  • A governor is said to be stable when for each speed within the working range, there is only one radius of the governor balls at which the governor is in equilibrium. For a stable governor, if the equilibrium speed increases, the radius of the governor balls must also increase.
3. Isochronism:
  • A governor is said to be isochronous, when the equilibrium speed is constant for all radii of rotation of the balls, within the working range. An isochronous governor will be infinitely sensitive.

4. Hunting:

  • It is a condition in which the speed of the engine controlled by the governor fluctuates continuously above and below the mean speed. It is caused by a governor which is too sensitive.

5. Governor effort:

The effort of a governor is the force it can exert at the sleeve on the mechanism, which controls the supply of fuel to the engine. The mean force exerted during the given change of speed is termed as effort. Generally efforts are defined for 1% change of speed.

6. Power:

The power of a governor is defined as the work done at the sleeve for a given percentage change of speed.

Power = efforts X displacement of sleeve


More Resources /articles

IC Engine Articles , Notes , Question and Answer
Automobile Engineering Parts and System Notes , Article
Mechanical Subjectwise Basic Concept Notes ,Articles

Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Recent Posts