Governor (device)
From Wikipedia, the free encyclopedia
A governor 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.
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[edit] History
Historically, in 1698 the first engine was built by the English engineer Thomas Savery. In 1769 the French engineer Nicolas Cugnot built the first pseudo-automobile, a steam-powered tricycle. Between the years 1775 and 1800 Scottish engineer James Watt in partnership with industrialist Matthew Boulton produced some 500 engines. At the heart of these engines was Watt’s self-designed “conical pendulum” governor, being a set of revolving steel balls attached to a vertical spindle by link arms, and 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.
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 heat energy supplied to and the work energy performed by the intermediate substance, in this case 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.[1]
[edit] Automobile governors
Automobiles are a common application, and modern automobiles are equipped with such a mechanism 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)[2] to limit insurance costs of the vehicle. Urban public buses often have speed governors which are typically set at 40 to 55 miles per hour.
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.
[edit] See also
[edit] References
- ^ Wheeler, L. (1951). Josiah Willard Gibbs - the History of a Great Mind. Woodbridge, CT: Ox Bow Press.
- ^ The "gentlemen's agreement" top speed of 250 km/h (155 mph)
