A centrifugal governor is a specific type of governor a feedback system that
controls the speed of an engine by regulating the amount of fuel admitted,
so as to maintain a near-constant speed, irrespective of the load or fuel-supply
conditions. It uses the principle of proportional control.
It was invented in 1788 by James Watt to control his steam engine where it
regulates the admission of steam into the cylinder(s). Its widest use was on
steam engines during the Steam Age in the 19th century. It is also found on
internal combustion engines and variously fueled turbines, and in some
modern striking clocks. Operation
The device shown is from a steam engine. Power is supplied to the governor from
the engine's output shaft by a belt or chain connected to the lower belt wheel.
The governor is connected to a throttle valve that regulates the flow of working
fluid supplying the prime mover. As the speed of the prime mover increases, the
central spindle of the governor rotates at a faster rate and the kinetic energy
of the balls increases. This allows the two masses on lever arms to move
outwards and upwards against gravity. If the motion goes far enough, this motion
causes the lever arms to pull down on a thrust bearing, which moves a beam
linkage, which reduces the aperture of a throttle valve. The rate of
working-fluid entering the cylinder is thus reduced and the speed of the prime
mover is controlled, preventing over-speeding.
Mechanical stops may be used to limit the range of throttle motion, as seen
near the masses in the image at right. = Non-gravitational regulation=
A limitation of the two-arm, two-ball governor is its reliance on gravity, and
that the governor must stay upright relative to the surface of the Earth for
gravity to retract the balls when the governor slows down.
Governors can be built that do not use gravitational force, by using a single
straight arm with weights on both ends, a center pivot attached to a spinning
axle, and a spring that tries to force the weights towards the center of the
spinning axle. The two weights on opposite ends of the pivot arm
counterbalance any gravitational effects, but both weights use
centripetal force to work against the spring and attempt to rotate the pivot
arm towards a perpendicular axis relative to the spinning axle.
Spring-retracted non-gravitational governors are commonly used in
single-phase alternating current induction motors to turn off the
starting field coil when the motor's rotational speed is high enough.
They are also commonly used in snowmobile and all-terrain vehicle
continuously variable transmissions, both to engage/disengage vehicle motion
and to vary the transmission's pulley diameter ratio in relation to the engine
revolutions per minute. History
James Watt designed his first governor in 1788 following a suggestion from his
business partner Matthew Boulton. It was a conical pendulum governor and one of
the final series of innovations Watt had employed for steam engines. James Watt
never claimed the centrifugal governor to be an invention of his own.
Centrifugal governors were used to regulate the distance and pressure
between millstones in windmills since the 17th century.
A giant statue of Watt's governor stands at Smethwick in the English West
Midlands. It is known as the flyball governor.
Another kind of centrifugal governor consists of a pair of masses on a
spindle inside a cylinder, the masses or the cylinder being coated with pads,
somewhat like a drum brake. This is used in a spring-loaded record player and a
spring-loaded telephone dial to limit the speed.
Dynamic systems The centrifugal governor is often used
in the cognitive sciences as an example of a dynamic system, in which the
representation of information cannot be clearly separated from the operations
being applied to the representation. And, because the governor is a
servomechanism, its analysis in a dynamic system is not trivial. In 1868,
James Clerk Maxwell wrote a famous paper "On governors" that is widely considered
a classic in feedback control theory. Maxwell distinguishes moderators and
governors which control motive power input. He considers devices by James
Watt, Professor James Thomson, Fleeming Jenkin, William Thomson, Léon Foucault
and Carl Wilhelm Siemens. = As an influence on cybernetics=
In a largely overlooked passage from his famous 1858 paper to the Linnean
Society, Alfred Russel Wallace says of the evolutionary principle:
The action of this principle is exactly like that of the centrifugal governor of
the steam engine, which checks and corrects any irregularities almost
before they become evident; and in like manner no unbalanced deficiency in the
animal kingdom can ever reach any conspicuous magnitude, because it would
make itself felt at the very first step, by rendering existence difficult and
extinction almost sure soon to follow. The cybernetician and anthropologist
Gregory Bateson would observe in the 1970s that though seeing it only as an
illustration, Wallace had "probably said the most powerful thing that’d been said
in the 19th century". Bateson revisited the topic in his 1979 book Mind and
Nature: A Necessary Unity, and other scholars have continued to explore the
connection between natural selection and systems theory.
See also Cataract
Hit and miss engine References