Centrifugal governor

Lore & Background

The centrifugal governor is widely credited to James Watt, who adapted it in 1788 to control his steam engine, where it regulated the admission of steam into the engine's cylinders. Watt designed his first governor following a suggestion from his business partner Matthew Boulton; it was a conical pendulum governor and one of the final series of innovations Watt employed for steam engines. Earlier uses of similar devices for windmills are sometimes attributed to other inventors, such as Thomas Mead in 1787, but these are not reliably linked to Christiaan Huygens, and the specific claim that such a governor regulated the distance and pressure between millstones is not supported by mainstream historical sources.

Over subsequent decades, a series of improvements and modifications were made by a number of different engineers and manufacturers, including Charles Porter, Wilson Hartnell, Richard Tangye, Rudolph Proell, and Buss. As engine speeds increased, the basic Watt-type governor became less reliable, tending to over-compensate and oscillate between opening and closing the steam valve. This led to modifications such as adding a dead weight around the spindle and applying springs. A number of firms patented their own variations, and more modern governors were sometimes retrofitted to engines already in service.

A limitation of the two-arm, two-ball governor is its reliance on gravity to retract the balls when the governor slows down, requiring the governor to stay upright. Non-gravitational governors have been built using a single straight arm with weights on both ends, a center pivot attached to a spinning axle, and a spring that forces the weights toward the center. These spring-retracted governors are commonly used in single-phase AC induction motors to turn off the starting field coil and in snowmobile and ATV continuously variable transmissions.

Reader's Guide

The centrifugal governor is significant as one of the earliest feedback control mechanisms, embodying the principle of proportional control. Its invention by Huygens in the 17th century and Watt's adaptation in 1788 were pivotal for the Industrial Revolution, enabling steam engines to maintain steady speeds under varying loads. The governor's widest use was on 19th-century steam engines, but it also found applications in internal combustion engines, turbines, and striking clocks. Its legacy extends beyond engineering: in 1868, James Clerk Maxwell wrote a famous paper 'On Governors' considered a classic in feedback control theory. In 1858, Alfred Russel Wallace used governors as a metaphor for natural selection, and the cybernetician Gregory Bateson discussed the topic in his work. The governor appears in culture as a statue in Smethwick, England, on the city seal and flag of Manchester, New Hampshire, and as a metaphor in Liu Cixin's science fiction novel 'Death's End'. A stylized centrifugal governor is also part of the coat of arms of the Swedish Work Environment Authority.

Did You Know?

• Earlier windmill governors are sometimes associated with Thomas Mead (1787), but not reliably with Christiaan Huygens.
• A simple governor does not maintain an exact speed but a speed range, as under increasing load it opens the throttle as speed decreases.
• In 1868, James Clerk Maxwell wrote a famous paper 'On Governors' that is widely regarded as a foundational work in control theory.