Few people know that cruise control was invented Ralph Teetor, a blind yet ingenious engineer. And as is often the case, it was the result of intuition: during a car trip as a passenger, Teetor was deeply bothered by the style of the driver, who kept accelerating and braking as he chatted with Teetor. Classic "stop and go" behaviour – when somebody slows down when they look at their passengers, the radio or their phone, then accelerates when their attention turns to the road, causing the heads of their passengers to rock back and forth. Thanks to his studies in mechanical engineering, Teetor was able to develop a system that controlled the speed of the car, and patented it in 1945.
The Speedostat is born
Teetor imagined a mechanism of controlled speed. Upon reaching a set speed, the driver's foot would immediately perceive the resistance to accelerator pressure as a warning. The stationary pedal would enable the motorist to maintain the set speed. The first Speedostat prototype included a speed selector on the dashboard connected to a mechanism that slid off the drive shaft. When the speed set by the driver reached a certain threshold value, the regulating mechanism exceeded the spring tension to activate a vacuum piston capable of pushing the accelerator pedal back. Teetor filed the second patent for his invention on 22 August 1950.
First Chrysler, then Cadillac
In 1958, Chrysler was the first to offer Speedostat as an option in one of its luxury models. One year later, the feature's popularity convinced the car maker to install it across all its car models. In 1960 came the Cadillac division of General Motors arrived, who renamed it Cruise Control and adopted it for its own cars. But the real breakthrough for the feature came in 1973, when OPEC sheikhs imposed an oil embargo on the United States and people realised Teetor's innovation would save them fuel. Contemporary studies showed that the new limits speeds set on American roads – which cruise control perfectly helped you to comply with – led to savings of approximately 167,000 barrels of oil per day. This was a source of huge satisfaction for Teetor (who passed away in 1982, six years after making it to the Automotive Hall of Fame), who ultimately saw his invention as a method of limiting speed.
A question of the throttle
Today, cruise control works by acting on the throttle, a vital part of the engine that regulates the amount of air that can enter the combustion chambers. It is operated by an electric motor controlled by the engine control unit: when the latters sends information on the degree of pressure of the accelerator pedal, the throttle opens or closes – the injector is simultaneously opened to let in the right amount of petrol – and this affects the amount of air introduced into the combustion chambers, and consequently the engine rotation and ultimately the speed of the car. This means that though cruise control works mechanically, the driver manages the system through electronics: when the desired cruising speed is reached, you simply press a button (usually with the word SET) and the car maintains the set pace. To change the speed, the driver has to press the + and – buttons next to the SET button. Cruise control works until you press either the accelerator pedal again, or the brake or clutch pedal, when it is then deactivated.
The transition to ACC
Classic cruise control maintains a set speed, so the driver must deactivate it when the car approaches a slower vehicle, a turn or a roundabout. This limitation has been overcome by adaptive cruise control (ACC), which is able to automatically regulate the speed: if the adaptive cruise control detects a slower previous vehicle, it decreases the speed until it "catches up" to the vehicle in front, while maintaining a safe distance; as soon as the vehicle gains speed, adaptive cruise control brings the car back to the originally set speed. ACC was first introduced in the mid-90s thanks to Mitsubishi, which brought in a system designed to slow down the car by downshifting the automatic gearbox. However, it was Mercedes that made it popular on the market a few years later: the S-Class luxury sedan saw the introduction of adaptive cruise control that was very similar to today's systems – it was equipped with a radar hidden behind the grill that measured the distance from the vehicle in front and was also able to operate the brakes (in addition to the throttle) in order to enable more sudden decelerations. Adaptive cruise control has been refined over the years, leading to the recent versions of adaptive cruise control with a stop and go function, highly useful when you are in traffic jams on the motorway or in crowded urban traffic!
