TERM PAPER
OF
MECHANICS-101
TOPIC-STUDY DIFFERENT TYPES OF GOVERNORS AND ALSO STUDY DIFFERENCE BETWEEN GOVERNOR AND FLYWHEEL.
SUBMITTED TO: SUBMITTED BY:
JASPREET SINGH JASHANDEEP KAUR
ROLL N0- A12
SECTION- B2001
REG NO- 11002566
ACKNOWLEDGEMENT
First and the foremost I would like to thank to my almighty for giving me courage to bring up this term paper.
At the outset, I would like to propose a word of thanks to my teacher, friends and other sources that gave an unending support and helped me in numerous ways from the first stage of my term paper conceived.
I would also like to thank my family members for their whole hearted support and cooperation.
I duly acknowledge the contribution of mr.Jaspreet Singh for invaluable help. Writing about different types of governors was an uphill task and would have not been possible without proper and timely assistance of mr.Jaspreet Singh
I would also thanks to all my friends for forwarding their suggestions to make necessary modifications.
Special thanks to Mr.Jaspreet Singh for his able guidance in my term assignment.
INTRODUCTION
A governor, or speed limiter, is a device used to measure and regulate the speed of a machine, such as an engine. A classic example is the centrifugal governor, also known as the Watt or fly-ball governor, which uses weights mounted on spring-loaded arms to determine how fast a shaft is spinning, and then uses proportional control to regulate the shaft speed.
History
The Gibbs Governor
Centrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. Early steam engines employed a purely reciprocating motion, and were used for pumping water – an application that could tolerate variations in the working speed. It was not until the Scottish engineer James Watt introduced the rotative steam engine, for driving factory machinery, that a constant operating speed became necessary. Between the years 1775 and 1800, Watt, in partnership with industrialist Matthew Boulton, produced some 500 rotative beam engines. At the heart of these engines was Watt’s self-designed "conical pendulum" governor: a set of revolving steel balls attached to a vertical spindle by link arms, where the controlling force consists of the weight of the balls.
Building on Watt’s design was American engineer Willard Gibbs who in 1872 theoretically analyzed Watt’s conical pendulum governor from a mathematical energy balance perspective. During his Graduate school years at Yale University, Gibbs observed that the operation of the device in practice was beset with the disadvantages of sluggishness and a tendency to overcorrect for the changes in speed it was supposed to control.
A flywheel is a mechanical device with a significant moment of inertia used as a storage device for rotational energy. Flywheels resist changes in their rotational speed, which helps steady the rotation of the shaft. Flywheels can be used to produce very high power pulses for experiments, where drawing the power from the public network. Recently, flywheels have become the subject of extensive research as power storage devices for uses in vehicles and power plants.
History
The principle of the flywheel is found in the Neolithic spindle and the potter's wheel. The Andalusian agronomist Ibn Bassal (fl. 1038-1075), in his Kitab al-Filaha, describes the flywheel effect employed in a water wheel machine, the saqiya. The flywheel as a general mechanical device for equalizing the speed of rotation is, according to the American medievalist Lynn White, recorded in the De diversibus artibus (On various arts) of the German artisan Theophilus Presbyter (ca. 1070-1125) who records applying the device in several of his machines. In the Industrial Revolution, James Watt contributed to the development of the flywheel in the steam engine, and his contemporary James Pickard used a flywheel combined with a crank to transform reciprocating into rotary motion.
TABLE OF CONTENTS
- Governor
- Types
- Principle of operation
- Centrifugal governor
1)Gravity loaded controlled governors
a)Watt governor
b)Porter governor
c)Proell governor
2)Spring loaded controlled governors
a)Hartnell governor
b)Hartung governor
- Inertia governor
- Function of a governor
- Requirements of a governor
- Examples
- Flywheel
- Applications
- Difference between governor and flywheel
- References
GOVERNOR
A governor, or speed limiter, is a device used to measure and regulate the speed of a machine, such as an engine.It’s a device that automaticallymaintains the rotary speed of an engine within reasonably close limits regardless of the load. A classic example is the centrifugal governor, also known as the Watt or fly-ball governor, which uses weights mounted on spring-loaded arms to determine how fast a shaft is spinning, and then uses proportional control to regulate the shaft speed.A governor changes its mechanical and/or electrical configuration in response to speed variations. Those changes are used to control the input.
TYPES:
The type of governor used on diesel engines is dependent upon the application required. The six basic types of governors are as follows:
1. Mechanical centrifugal flyweight style that relies on a set of rotating flyweights and a control spring; used since the inception of the diesel engine to control its speed.
2. Power-assisted servo mechanical style thatoperates similar to the mechanical centrifugal flyweight but uses engine oil under pressure to move the operating linkage.
3. Hydraulic governor that relies on the movement of a pilot valve plunger to control pressurized oil flow to a power piston, which, in turn, moves the fuel control mechanism.
4. Pneumatic governor that is responsive to the air flow (vacuum) in the intake manifold of an engine. A diaphragm within the governor housing is connected to the fuel control linkage that changes its setting with increases or decreases in the vacuum.
5. Electromechanical governor uses a magneticspeed pickup sensor on an engine-driven component to monitor the rpm of the engine. The sensor sends a voltage signal to an electronic control unit that controls the current flow to a mechanical actuator connected to the fuel linkage.
6. Electronic governor uses magnetic speed sensor to monitor the rpm of the engine. The sensor continuously feeds information back to the ECM (electronic control module). The ECM then computes all the information sent from all other engine sensors, such as the throttle position sensor, turbocharger-boost sensor, engine oil pressure and temperature sensor, engine coolant sensor, and fuel temperature to limit engine speed
The governors, used on heavy-duty truck applications and construction equipment, fall into one of two basic categories:
1. Limiting-speed governors sometimes referred to as minimum/maximum models since they are intended to control the idle and maximum speed settings of the engine. Normally there is no governor control in the intermediate range, being regulated by the position of the throttle linkage.
2. Variable-speed or all range governors that are designed to control the speed of the engine regardless of the throttle setting.
Other types of governors used on diesel engines are as follows:
1. Constant-speed, intended to maintain the engine at a single speed from no load to full load.
2. Load limiting, to limit the load applied to the engine at any given speed. Prevents overloading the engine at whatever speed it may be running.
3. Load-control, used for adjusting to the amount of load applied at the engine to suit the speed at which it is set to run.
4. Pressure regulating, used on an engine driving a pump to maintain a constant inlet or outlet pressure on the pump.
Mechanical Governors
In most governors installed on diesel engines used by the Navy, the centrifugal force of rotating weights (fly balls) and the tensions of a helical coil spring (or springs) are used in governor operation. On this basis, most of the governors used on diesel engines are generally called mechanical centrifugal flyweight governors.
PRINCIPLE OF OPERATION
When the load on an engine increases or decreases, obviously its speed will respectively decrease or increase to the extent of variation of load. This variation of speed has to be controlled by the governor, within small limits of the mean speed. This necessities that when the load increases and consequently the speed decreases, the supply of fuel to one engine has to be increased accordingly, to compensate for the loss of the speed, so as to bring back the speed close to the mean speed. Conversely when the load decreases, and the speed increase, the supply of fuel has to be reduced. This implies that the governor should have its mechanism working such a way, that the supply of fuel is automatically regulated according to the load requirement for maintaining approximately a constant speed.
Governors are classified based upon two different principles:
- Centrifugal
- Inertia
In the first type two or more masses termed the governor balls are caused to revolve about the axis of the shaft, which is driven through 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 a dead weight, a spring or a combination of the two. This force is termed as the controlling force and it must increase in magnitude as the distance of the ball from the axis of rotation increases. When the governor balls are revolving at a uniform speed, the radius of rotation clearly will be such that the outward inertia or centrifugal force is just balanced by inward controlling force. If the speed of rotation now increases owing to decrease of a load on the engine, the governor balls will move outward until the centrifugal force is again balanced by the controlling force. Conversely, if the speed of rotation decreases owing to the increase of the load on the engine, the governor balls will move inward until the centrifugal force is again balanced by the controlling force. This movement of balls is transmitted by the governor mechanism to the valve, which controls the amount of energy supplied to the engine, so that movement in the outward direction reduces the valve opening and movement in the inward direction increases the valve opening.
Governors of the second type operate on a different principle. The governor balls are so arranged that the inertia force caused by an angular acceleration or retardation of the governor shaft tend to alter their positions. The amount of the displacement of the governor balls caused by inertia forces is controlled by suitable springs and, through governor mechanism, alters the amount of energy supplied to the engine. The obvious advantage of this type of governor lies in its more rapid response to the effect of the change of load, since the displacement of the balls is determined by the rate of change of speed of rotation, as distinct from the actual change of speed of rotation, such as is required in governors of the first type. This advantage is offset, however, by the practical difficulty of arranging for the complete balance of the revolving parts of the governor. For this reason centrifugal governors are much more frequently used than the inertia governors.
CENTRIFUGAL GOVERNOR
Drawing of a centrifugal "flyball" governor
Centrifugal governors may be divided into:
a) Gravity loaded- controlled governors as in fig. 3.1
b) Spring loaded- controlled governors as in fig. 3.2
In the gravity loaded- controlled governors, an equation of equilibrium is obtained by taking moments of forces about instantaneous center, I, of the lower link, thus eliminating the tension in the upper link and the side thrust at the sleeve.
In the spring loaded- controlled governors, moment of forces are taken about the fulcrum of the bell-crank levers, eliminating the reaction at the point, and in the type shown in fig. 3.2© moments are taken about the instantaneous center, I, for the upper bell-crank arm to eliminate the reaction between the roller and the top of the spindle.
GRAVITY LOADED CONTROLLED GOVERNORS
a)WATT GOVERNOR
b)PORTER GOVERNOR
c)PROELL GOVERNOR
a)WATT GOVERNOR
Probably the most widely used governor in the early days, it is named the Watt governor because James Watt applied it to his early beam engines. He did not however invent it as it had been in use on wind and water mills many years before this.
A belt or gearing from the engine crankshaft drives the input shaft 'm' causing the bevel gears 'l' to revolve and in turn rotate the vertical shaft 'a'. The bracket 'b' at the top of 'a' supports two arms 'c' which are pivoted at the top, at the end of the arms are two very heavy metal weights 'B' partway along the arms 'c' are fixed two pivoted link arms’d’ which link to a collar 'c' which rotates with them but is able to slide up and down shaft ‘a’.
The up and down motion of this collar is followed by a pair of pins 'f' which move a bell crank 'g' which is in turn linked to a throttle actuating rod 'i' linked to a throttle or butterfly valve in the supply of steam to the engines cylinder which can allow more or less steam through.
At rest the governor weights are held in the lowest position by gravity, the throttle will be in its most open position. As the engine speed increases these weights rotate faster until centrifugal force exceeds that of gravity and they fly further outwards and as a result of the linkages, upwards, this movement is transmitted to the throttle valve which begins to close. The faster the governor is driven the further out the weights move and the more the throttle is closed, until the amount of steam it lets through balances the demand and the engine speed stabilises.
If the load the engine drives is reduced it will increase speed, the governor restricts steam flow more until the speed stabilises, if load is added to the engine the speed drops, the throttle is opened more and more steam allowed in to compensate for the demand.
The Watt governor is a simple governor but is not terribly accurate where very fine control of speeds in needed and so was superseded in many applications by more specialised and accurate governors, however for many agricultural end pumping engines where absolute speed was not essential it survived and can still be seen on numerous preserved engines.
The height of a watt governor is inversely proportional to the square of speed. At high speeds, the movement of the sleeve becomes very small and thus this type of governor is unsuitable for high speeds.
b)PORTER GOVERNOR
The Porter Governor was the first effective High Speed engine governor, Designed by the American engineer George Porter. The governor is driven via a pulley (k) through a set of bevel gears (not shown) a vertical shaft (d) is rotated, this in turn drives from above the governor balls (a), through linkages (c) the large and heavy governor deadweight (b) is also rotated, this is free to slide up and down the shaft (d) but rotates at the same speed as the balls.
As rotational speed increases centrifugal force acts on the balls and they try to fly outwards, they are restricted by the linkages (c) held by the weight of the dead-weight (b), however, when a speed is reached at which this force exceeds the resistance imposed by the dead-weight they will lift the weight up and be allowed move outwards.
This action lifts the collar at the base of the dead-weight at point (f) this lifts the lever (g) which is pivoted at point (e) the lever has a counterbalance weight (a) and a dashpot or oil damper (i) which prevents rapid movements of the governor mechanism which can lead to the engine 'hunting' which is unwanted speed fluctuations due to the sensitivity of the governor.
Linkage (l) moves up or down and is connected to the engine this controls the steam allowed into the cylinder either by the amount allowed through a valve or the amount of time a valve is open for, if the engine runs too fast either the quantity of steam allowed in will be reduced or it will be let in for a shorter time, if the engine runs slower then either more steam is let in or it is let in for a longer time.
In porter governor, the sleeve is loaded with a heavy mass which improves the action of the governor.
c)PROELL GOVERNOR
It is similar to the porter governor having a heavy central load at the sleeve. But it differs from the porter governor at the arrangement of balls. The balls are carried on the extension of the lower arms instead at the junction of upper and lower arms. The action of this governor is similar to the watt’s governor. An increase in the speed of rotation increases the radius of rotation and raises the sleeve, thus reducing the amount of energy supplied to the engine. Conversely, a decrease in speed results in decrease in radius of rotation, thus lowering the sleeve and increasing the amount of energy supplied to the engine.
Proell governor runs at a lower speed then the porter governor. In order to give the same equilibrium speed a ball of smaller mass maybe used.
SPRING LOADED CONTROLLED GOVERNORS
a)HARTNELL GOVERNOR
A Hartnell governor is a spring loaded governor in which the balls are controlled by a spring. It consists of a casing in which a pre-compressed spring is housed so as to apply the force to the sleeve. Two bell crank levers, each carrying a ball at one end and the roller at anotherend, are fitted on the frame of casing. The casing along with the frame and spring rotates about the axis of governor. When the speed of governor is increased, the balls flyout away from the governor axis, the bell crank lever moves on pivot and its roller end lifts the sleeve against the spring force. This movement of sleeve is transferred to the throttle of an engine through suitable intermediate links. The spring force can be adjusted with the help of a nut.