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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. Governor is a device which used in an engine to maintain the mean speed of the engine by controlling the flow of fuel with respect to load on the engine. It means that, if the load on the engine increases, then it requires more fuel to supply & in another case when the load on the engine decreases, then it requires less amount of fuel to be supplied.
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. 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
- 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
Centrifugal governor
A flyweight mechanism driven by the engine is linked to the throttle and works against a spring in a fashion similar to that of the pneumatic governor, resulting in essentially identical operation. A centrifugal governor is more complex to design and produce than a pneumatic governor. However, the centrifugal design is more sensitive to speed changes and hence is better suited to engines that experience large fluctuations in loading.
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. Constructional Details: Spindle axis is driven by bevelled gears of engine shaft which rotates the flyball and it is connected to the sleeves with the help of links. Sleeves can slides up and down along with flyball along the spindle axis. To limit the motion of sleeves up and down two stops are there. Throttle valve is connected to the sleeves through bell crank lever which can controls opening and closing of the valve. Working: When the load on engine increases, its speed decreases. The flyball’s speed and speed of governor’s spindle which is geared with engine shaft also decreases and consequently throttle valve opens, increases the supply of fluid and hence engine speed increases and vice-versa when load decreases on engine, its speed increases and hence throttle valve closes to decrease the supply of fluid and hence speed decreases. **Performance of Governors :
- 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 )
. 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 Hartnell Governors Mr. Hartnell designed his governor circa 1875 and at the time it was considered to be of a superior design to other governors of the day. It rotated between 500 and 600rpm and by utilizing smaller fly balls and fewer parts, the internal friction was less than that of others. The function of a governor is 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. Construction of Hartnell Governors – It is a Spring-loaded Governor. It has two bell crank levers carrying the fly ball at one end and roller attached to the other end, the function of spring is to provide the counterforce which acts against centrifugal force. The spring and shaft are enclosed inside a casing. The sleeve is pressed against the spring when the centrifugal force on the balls increases. Due to spring return nature this governor can be mounded in a horizontal, inverted, (inclined) position. Parts of Hartnell Governor: The following are the main parts of the Hartnell Governor. Bellcrank lever
The sleeve moves up and down depending on the governor’s speed. When the speed of the governor/ engine increases, the ball tends to fly outward from the axis of the governor, but the ball’s movement is constrained. The bell crank lever moves on a pivot, roller end of lever lifts the sleeve upward against the spring force. This movement transferred to the throttle valve through a suitable mechanism, the result is low fuel supply and decreasing speed. When speed decreases the sleeve moves downward, and throttle open to more fuel supply; which results in increasing speed. Advantages of Hartnell governor It can be operated at very high speed Smaller in size Very close regulation Pre-compression can be adjusted to give the required equilibrium speed. Porter governor 1] Porter governor is a type of centrifugal governor with a dead weight attached onto the sleeve. 2] The porter governor is basically invented to overcome the disadvantage of the watt governor since the watt governor is not suitable for high-speed engines. In watt governor, it becomes difficult to adjust the fuel supply at a higher speed. 3] Because of the dead weight attached to the sleeve, the flyball requires more effort to lift the sleeve. hence after attaining the required speed of the engine sleeve starts to slide onto the spindle. 4] Hence the difference because of dead weight between the watt governor and porter governor which causes watt governor is not able to control fuel supply at high speed but porter governor has dead weight which helps to control fuel flow even at high speed.
The porter governor consists of the following components: - 1] Arms & links: - Upper end of the arm is pivoted to the spindle and the lower end is connected to the flyball. One end of the link is connected to flyball & another end of the link is pivoted to the sleeve. 2] Flyballs: - The flyballs are connected between arms & links. The flyballs are rotates with the spindle. When the spindle starts to rotate, the flyballs are pushed outward because of centrifugal force which results in the movement of the sleeve over the spindle of the governor. 3] Dead weight: - This is the main component of this governor which makes it different from other governors. The deadweight exerts extra force onto the sleeve. Hence sleeve is not easily lifted at lower RPM. Hence when the speed of the engine reaches the desired level the sleeve starts to move onto the spindle.
Proell Governor: Proell Governor: Proell Governor is a little different type of governor and which an updated form of simple centrifugal governor. Proell Governor is a type of governor contains an additionally extended arm which is used to support the rotating balls mounted on it. the extended arm is connected to the arms and makes an equal rotational speed along with balls mounted on the extended arm.and this type of governor use additional dead weights, which helps to increase the speed of rotation. Proell governor helps to function accurately and with high speed and maintain a constant function without any fluctuations. Construction of Proell Governor: In this Governor both the arms are connected at a sing point called pivot and there is an extended arm connected to the arm as shown in the figure and the extended arms used to support the balls on it. And with the help of connecting rod the sleeve and arm gets connected to lift the sleeve when the balls rotate at a fixed center called pivot. Main parts of Proell Governor: Pivot Arms Extended arms Balls Connecting rod: Sleeve Fuel pump Pivot: This is the point at the top end which connects the arms. Arms: This is connected to the balls and makes rotations along with the balls.
Extended arms: This is the straight arms provided at the end of the arm and this is used to support the balls on it. Balls: Balls connected at the top of the extended arm and the balls have some specified weight according to the application and this helps to move the sleeve up and down direction, by connecting the end of the arm to the sleeve with the help of connecting rod. Connecting Rod: This is used to connect between the balls and the sleeve. Sleeve: Sleeve gets connected with the balls with the help of connecting rod to slides on the spindle and which helps to flow the fuel from fuel tank to engine. Fuel pump: This is used to supply the fuel from the fuel tank to the engine when the sleeve moves in an upward direction and stops when the sleeve reaches the bottom endpoint. Working of Proell Governor: The working of proell governor is the same as other types of governors eg: Watt Governor, Hartnell Governor etc. but the construction is little different When the extended arms rotate along with the balls mounted on it, the sleeve gets moved in an upward direction due to the connection between the arm and the sleeve and the moment of sleeve helps to flow the fuel from the fuel tank to engine.
