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governor

 
 

A device used to control the speed of a prime mover. A governor protects the prime mover from overspeed and keeps the prime mover speed at or near the desired revolutions per minute. When a prime mover drives an alternator supplying electrical power at a given frequency, a governor must be used to hold the prime mover at a speed that will yield this frequency. An unloaded diesel engine will fly to pieces unless it is under governor control. See also Prime mover.

A governor regulates the speed of a prime mover by properly varying the flow of energy to or from it. In the case of gas and steam turbines and internal combustion engines, the fuel furnishes the energy to the prime mover. For such applications, the governor usually controls the speed of the unit by regulating the rate at which fuel, and hence energy, is furnished to the prime mover. The governor controls the fuel flow so that the speed of the prime mover remains constant regardless of load and other disturbances, or changes in accordance with such operating conditions as changes in speed setting.

The speed of a prime mover is usually measured by a ball-head that contains flyweights driven at a speed proportional to the speed of the prime mover. The force from the flyweights is balanced, at least in part, by the force of compression of a speeder spring (see illustration). The upper end of this spring is positioned according to the speed setting of the governor.

Ballhead governor.
Ballhead governor.

To increase the power output of a governor, a hydraulic amplifier is often employed. A governor that keeps the speed of a prime mover constant is said to be isochronous. In a simple isochronous governor, the ballhead senses the speed and strokes a pilot valve plunger that regulates the flow of fluid to a servomotor. The performance of the simple isochronous governor is often greatly improved by the introduction of a dashpot in the feedback path from the output to the ballhead. If there is little damping in the prime mover, instability often occurs when the simple isochronous governor is used, whereas this instability is removed when the dashpot is incorporated. Acceleration governors are sometimes used in place of governors with dashpots. In such governors a flywheel is employed instead of a dashpot. The prime mover drives the flywheel through a spring.


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In technology, a device that automatically maintains the rotary speed of an engine within reasonably close limits regardless of the load. A typical governor regulates an engine's speed by varying the rate at which fuel or working fluid is furnished to it. Nearly all governors work by centrifugal force and consist of a pair of masses rotating about a spindle driven by the engine and kept from flying outward, usually by springs. With an increase in speed, the controlling force of the springs is overcome and the masses move outward, opening valves supplying the engine with its working fluid or fuel. James Watt invented a governor for controlling steam engines. Modern governors are used to regulate the flow of gasoline to internal-combustion engines and the flow of steam, water, or gas to various types of turbines. See also flywheel.

For more information on governor, visit Britannica.com.

 
Columbia Encyclopedia: governor
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governor, automatic device used to regulate and control such variables as speed or pressure in the functioning of an engine or other machine. A governor may be an electric, hydraulic, or mechanical device, or it may employ some combination of electric, hydraulic, and mechanical components. The constant-speed governor serves to keep the speed of an engine constant under changes in load and other disturbances. It is very often a mechanical device, employing centrifugal force. Such a governor contains weights, called flyballs, each attached to the end of an arm. The arms are arranged, like the spokes of wheels, around a central spindle and are connected to the inlet valve (commonly called the governor valve). The flyballs are so attached that they move away from the spindle as the speed increases (decreasing the fuel or steam to the inlet) and come closer to the spindle as the speed decreases (increasing the fuel or steam), thereby keeping the speed constant. Varying degrees of closure and the speeds at which they are to occur can be set in advance. Where changes are required while an engine is in operation, a variable-speed governor is employed. A governor-synchronizing device is used to equalize the speed of two or more engines driving electric generators before they engage the generators. In order to control the speed of some engines, a governor's output must be strengthened by connecting the output to a hydraulic amplifier.


 
Wikipedia: Governor (device)
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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.

Contents

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, 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.[1]

Gibbs theorized that, analogous to the equilibrium of the simple Watt governor (which depends on the balancing of two torques: one due to the weight of the “balls” and the other due to their rotation), thermodynamic equilibrium for any work producing thermodynamic system depends on the balance of two entities. The first is the heat energy supplied to the intermediate substance, and the second is the work energy performed by the intermediate substance. In this case, the intermediate substance is steam. These sorts of theoretical investigations culminated in the 1876 publication of the Gibbs' famous work On the Equilibrium of Heterogeneous Substances and in the construction of the Gibbs’ governor, shown adjacent. These formulations are ubiquitous today in the natural sciences in the form of the Gibbs' free energy equation, which is used to determine the equilibrium of chemical reactions; also known as Gibbs equilibrium.[2]

Automobiles

Automobiles are a common application of governors, and modern automobiles may be equipped with such mechanisms for various reasons. There are two types of automobile governors, one limiting the rotational speed of the engine, the other limiting the speed of the vehicle. In small, low power applications, governors are used to protect the engine from damage due to excessive rotational speed, or pushing the engine past its peak abilities. In larger, higher performance engines governors are used to limit the vehicle speed. Many performance cars are limited to a speed of 250 km/h (155 mph)[3] to limit insurance costs of the vehicle and reduce the risk of tires failing. All heavy vehicles in Europe have by law governors that limits their speeds to 90 or 100 km/h (55 or 60 mph). Urban public buses often have speed governors which are typically set to between 65 and 100 km/h (40 and 60 mph).

The German manufacturers initially started the gentlemen's agreement, since high speeds are more likely on the Autobahn. This was done to reduce the political willpower to introduce a speed limit. German Autobahns are often used officially and unofficially to use such cars to their potential. It should however be realised that according to the German road traffic code, vehicle speed must be appropriate for traffic conditions at all times even on unrestricted stretches of the Autobahn, and if traffic conditions make traveling at high speeds unsafe (e.g. due to heavy traffic or poor weather and/or road conditions), a driver can be fined by the Autobahn police for dangerous driving, even if the advisory speed limit of 130 km/h (80 mph) was not exceeded.

Today, BMW, Audi, Volkswagen and Mercedes-Benz limit their production cars to 250 km/h (155 mph). Certain AMG cars and the Mercedes/McLaren SLR are exceptions. The BMW Rolls-Royces are limited to 240 km/h (150 mph). Jaguars, although British, also have a limiter. As do the Swedish Saab and Volvo on cars where it is necessary.

In European markets, GM sometimes choose to discount the agreement, meaning that certain high-powered Opel or Vauxhall cars can exceed the 250 km/h mark, whereas their Cadillacs do not. Ferrari, Lamborghini, Maserati, Porsche, Aston Martin and Bentley also do not limit their cars, at least not to 250 km/h (155 mph). Chryslers in Europe such as the 300C SRT8 have no limiter. High-powered Japanese cars such as the Mitsubishi Evo or Nissan Skyline GT-R have no limiter. The top speed is a strong sales argument, though speeds above about 300 km/h or 200 mph are not likely reachable on public roads.

Aircraft

Aircraft propellers are another application; The governor senses shaft rpm, and adjusts or controls the angle of the blades to vary the torque load on the engine. Thus as the aircraft speeds up (as in a dive) or slows (in climb) the RPM is held constant.

Small engines

Small engines, such as used to power lawn mowers, portable generators, and lawn and garden tractors, are equipped with a governor to limit the engine to a maximum safe speed when unloaded and to maintain a relatively constant speed despite changes in loading. In the case of generator applications, the engine speed must be closely controlled so the output frequency of the generator will remain reasonably constant.

Small engine governors are typically one of three types:

  • Pneumatic: the governor mechanism sense air flow from the flywheel blower used to cool an air-cooled engine. The typical design includes a air vane mounted inside the engine's blower housing and linked to the carburetor's throttle shaft. A spring pulls the throttle open and as the engine gains speed, increased air flow from the blower forces the vane back against the spring, partially closing the throttle. Eventually a point of equilibrium will be reached and the engine will run at a relatively constant speed. Pneumatic governors are simple in design and inexpensive to produce. However, they do not regulate engine speed very accurately and are affected by air density, as well as external conditions that may influence airflow.
  • Centrifugal: 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.
  • Electronic: a servo motor is linked to the throttle and controlled by an electronic module that senses engine speed by counting electrical pulses emitted by the ignition system or a magnetic pickup. The frequency of these pulses varies directly with engine speed, allowing the control module to apply a proportional voltage to the servo to regulate engine speed. Due to their sensitivity and rapid response to speed changes, electronic governors are often fitted to engine-driven generators designed to power computer hardware, as the generator's output frequency must be held within narrow limits to avoid malfunction.

See also

References

  1. ^ Wheeler, Lynder Phelps (1947), "The Gibbs Governor for Steam Engines", in Wheeler, Lynder Phelps; Waters, Everett Oyler; Dudley, Samuel William, The Early Work of Willard Gibbs in Applied Mechanics, New York: Henry Schuman, pp. 63-78 
  2. ^ Wheeler, L. (1951). Josiah Willard Gibbs - the History of a Great Mind. Woodbridge, CT: Ox Bow Press.
  3. ^ The "gentlemen's agreement" top speed of 250 km/h (155 mph)

 
 

 

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Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Governor (device)" Read more

 

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