How Cruise Control Works, From Teetor to Adaptive Systems
Cruise control holds a speed you set by adjusting the throttle. Here is how it works, who invented it, and what adaptive cruise adds with radar.
In this article
Cruise control is a system that adjusts the throttle on its own to hold a speed the driver has chosen. The basic version has existed since the late 1950s, and today's adaptive version adds radar or cameras so the car can also keep a gap behind the vehicle ahead. This article covers how each works and where the idea came from.
The basic idea
Wikipedia describes cruise control as a servomechanism, which simply means a system that compares what is happening with what is wanted and corrects the difference. The car measures its own speed, compares it with the speed the driver set, and moves the throttle to close any gap. Going uphill, the throttle opens a little more; going downhill, it closes.
Speed can be read from the driveshaft, a speedometer cable, wheel-speed sensors or electronic pulses. The throttle can be moved by a solenoid, by a vacuum-operated servo, or, in cars with drive-by-wire throttles, simply by a command to the engine computer.
How the driver controls it
- Switching the system on and setting a speed holds that speed.
- Touching the brake switches it off. Many systems remember the last speed, so a resume button brings it back.
- Most systems also offer buttons to raise or lower the set speed in steps.
- Most systems will not engage below roughly 25 to 30 mph, according to Wikipedia.
- In manual-transmission cars, pressing the clutch normally cancels it.
Where it came from
Early attempts at speed control date back to the early 1900s. Wikipedia mentions the Wilson-Pilcher, which had a steering-column lever to set engine speed, and the 1908 Peerless, which added a governor and a throttle lever on the steering wheel. These were closer to engine-speed regulators than the modern idea.
The modern system is credited to Ralph Teetor, a blind engineer from Indiana. The Inventors Hall of Fame says the idea came to him in 1936 while he was a passenger with his friend and patent attorney Harry Lindsey, whose driving speed rose and fell as they talked. Teetor developed a device that held a steady speed. A dashboard selector was linked along the drive shaft to a mechanism under the bonnet, so the driver could set a speed and take the foot off the pedal.
Dates differ slightly between sources. The Hall of Fame says he filed his first speed-control patent in 1948, while Wikipedia also gives 1948 as the year he developed the modern version. Wikipedia adds that a 35 mph wartime speed limit in the United States helped drive interest in the technology.
From Speedostat to cruise control
The Hall of Fame says the device was made by Perfect Circle under the trademark "Speedostat" and first appeared in Chrysler cars, including the 1958 Imperial, New Yorker and Windsor; in 1959 Chrysler offered it as an option on all its models. Chrysler marketed it as "Auto-Pilot." Wikipedia agrees that the 1958 Chrysler Imperial was the first car to use Teetor's system, and says Cadillac later marketed the feature as "cruise control." The Hall of Fame puts Cadillac's use of the name in 1959. Whichever company coined it, "cruise control" is the name that stuck.
Electronics changed the design later. Wikipedia says Daniel Aaron Wisner patented an electronic cruise control design in 1968, and that Motorola commercialised an integrated circuit based on it in the late 1980s.
Adaptive cruise control
Adaptive cruise control keeps a set speed when the road ahead is clear, but slows the car to keep a chosen distance from the vehicle in front, then returns to the set speed when traffic clears. Wikipedia says these systems use radar, often at millimetre-wave frequencies, as well as lasers and cameras, and some also use GPS-linked speed-limit data.
The same page points out limits. Some systems cannot detect stationary cars or pedestrians, so the driver has to stay attentive. SAE International classes a car with adaptive cruise control as Level 1 driving automation, meaning the system helps with one task, speed, while the human does the rest.
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