Around It Goes: 110 Years Of The Speedometer

In October 2012, the speedometer turned 110 years old. It is considered to have been born in 1902, because October 7 of that year was when engineer Otto Schulze registered the eddy-current speedometer at the Imperial Patent Office in Berlin. The ground-breaking invention quickly spread through the global automotive industry.

Speedometers are rev counters, which show the number of revolutions of the wheel or the gear shaft as a distance per unit of time. "Nowadays, at a time when we travel at 100 km/h or faster on a daily basis, the idea behind the speedometer is even more relevant than when it was first invented, when most motorized vehicles had a top speed of just 30 km/h. The speedometer is necessary, because although humans with their vestibular system can perceive positive or negative acceleration, they are not so perceptive at constant speeds," explains Eelco Spoelder, Head of the Instrumentation & Driver HMI Business Unit at Continental.

"In most vehicles, the driving force behind the speedometer and rev counter needle is a stepper motor," says Spoelder. The stepper motor moves the speedometer needle by a minimal angle (step) or by a multiple thereof. The smaller the step length, the more precise the movement of the speedometer needle. Microcontrollers convert the signals from the speed sensor on the wheel into the necessary steps of the stepper motor.

The type of indication does not differ much from the first speedometers 110 years ago, in terms of the main aspects. Even though the first fully digital LCD display appeared in 1986 in the Volkswagen Golf II GTI, drivers in the cockpits of most cars still look at a needle that moves on a round scale and indicates the speed or number of revs. "The fact that speedometers and rev counters are usually round is largely for ergonomic reasons. Round instruments can be read intuitively. The driver doesn't need to concentrate much, can focus their attention on the road and still obtains the most important information," says Spoelder.

That is why instruments such as the speedometer, the rev counter, the tank display and the most important warning lights are all kept together within the driver's direct field of vision (of around 30 degrees), usually in an instrument panel behind the steering wheel.

The instrument panel is supported by a head-up display, which shows driving-relevant information in the driver's direct field of vision, as if floating above the hood. Displays such as the radio, internal temperature, or navigation, which are not of primary relevance to the task of driving, are ultimately part of the infotainment area and are available to the driver in the center console display.

However, there is a trend towards more infotainment in the automotive industry, which is calling for new strategies. "A strict separation between driving-relevant information in the instrument panel and infotainment in the center console is almost no longer possible today, when in addition to radio, navigation, and cell phones we also have the Internet coming into the car," says Spoelder. The more infotainment available to the driver in the center console, the greater the risk of visual distraction.

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