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Cruise control (sometimes known as speed control or Autocruise) is a system to automatically control the speed of an automobile. The driver sets the speed and the system will take over the throttle of the car to maintain the same speed. more...

History

Speed control with a centrifugal governor was used in automobiles as early as the 1910s, notably by Peerless. Peerless advertised that their system would "maintain speed whether up hill or down". The technology was invented by James Watt and Matthew Boulton in 1788 for use in locomotives. It uses centrifugal force to maintain a constant throttle position.

Modern cruise control was invented in 1945 by the blind inventor and mechanical engineer Ralph Teetor. His idea was born out of the frustration of riding in a car driven by his lawyer, who kept speeding up and slowing down as he talked. The first car with Teetor's system was the Chrysler Corporation Imperial in 1958. This system calculated ground speed based on driveshaft rotations and used a solenoid to vary throttle position as needed.

Theory of operation

In modern designs, the cruise control may or may not need to be turned on before use — in some designs it is always "on" but not always enabled, others have a separate "on/off" switch, while still others just have an "on" switch that must be pressed after the vehicle has been started. Most designs have buttons for "set", "resume", "accelerate", and "coast" functions. Some also have a "cancel" button. The system is operated with controls easily within the driver's reach, usually with two or more buttons on the steering wheel or on the turn signal stalk.

The driver must bring the car up to speed manually and use a button to set the cruise control to the current speed. The cruise control takes its speed signal from a rotating driveshaft, speedometer cable or from the engine's RPM. Most systems do not allow the use of the cruise control below a certain speed (normally 35 mph/55 km/h) to discourage use in city driving. The car will maintain that speed by pulling the throttle cable with a solenoid or a vacuum driven servomechanism. On the latest vehicles fitted with electronic throttle control, cruise control can be easily integrated into the vehicle's engine management system. Most systems can be turned off both explicitly and automatically, when the driver hits the brake or clutch. Cruise control often includes a memory feature to resume the set speed after braking and a coast feature to reset the speed lower without braking. When the cruise control is in effect, the throttle can still be used to accelerate the car, but once it is released the car will then slow down until it reaches the previously set speed.

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