Telling Drivers Their Speed for Over 100 Years
When the first horseless carriages rolled on the earth, their drivers had little idea how fast they were going. There were no meters to measure the speed which wasn’t all that fast then and drivers could still sense how fast they were going and adjust their speed. Nevertheless, it became increasingly important to know the speed because the cars were going faster and faster and the human brain’s ability to reliably gauge and evaluate speed was diminishing.
There were devices for measuring speed as back in the 16th century, Leonardo da Vinci had drawn the outline for such a device. By 1835, they were being used for railroad vehicles but were not suited for the cars that started appearing in the late 19th century.
It was Otto Schulze, an inventor from Strasbourg, who finally succeeded in developing a system for road vehicles with his eddy current speedometer. Schulze used a flexible shaft to transmit the rotational speed of the wheel or transmission to the speedometer, which was equipped with a permanent magnet in constant rotation. Above the speedo magnet – but without direct contact – was a metal disc or metal cup with a pointer. The revolving magnet induced “eddy currents” which the metal disc and pointer tried to follow. However, because the metal disc was attached to a spring, it could only manage a slight turning movement instead of a complete rotation. With the increasing speed of the magnet, the force of the eddy currents rises so that the pointer on the metal disc indicates a higher speed.
Otto Schulze had his invention patented in Berlin on 7 October 1902, thus laying claim to being the inventor of the speedometer which millions of motorists have referred to.
Once this device was available, authorities started to make it a mandatory fitment. In many countries, the authorities were beginning to become concerned about rising speeds and accidents that resulted, and introduced speed limits. In order that motorists did not break the speed limits, they were required to have speedometers in their cars and manufacturers began making them standard. By around 1910, the speedometer was very much a part of the car.
By the mid-1930s, an instrument cluster attached to the steering column grouped all the important gauges and indicators together, including those for engine rpm, fuel, lights and turn signals. Although integration at that time was limited to a common mounting plate for separate scales and dials – a bracket really – it nevertheless was the first step towards combining several different instruments into a single instrument cluster.
It is not until the mid-1950s that automobile speed measurement enjoyed its next major technology leap with the introduction of the electric speedometer originally developed by VDO for city buses. Instead of communicating wheel revolutions by means of a lengthy shaft, the rotational speed of the wheel or transmission was transformed into an electric signal with a dynamo. An electric motor on the speedometer then used this current to move the needle.
Parallel to this development, VDO developed a moving coil instrument in which the voltage of the current generated by the dynamo is displayed as the current speed. Also, a stepper motor was developed to drive the odometer. It all fit into an 80 mm housing that remained the worldwide speedometer standard well into the 1980s.
The age of the electronic speedometer began in the 1980s. Roller counters for mileage were replaced by liquid crystal displays. Sensors in the vehicle network took over the role of shafts, dynamos and rotating magnets. Stepper motors again transformed electric pulses into pointer deflections using electronic control systems. All the components were grouped tightly together in the driver’s line of sight. At a glance, the driver could monitor complex information with a choice of classic round instruments, text-based displays, indicator lights and large monitors, or LCD for navigation and communication. The invention of the LED opened up completely new solutions for the illumination of the instrument panel.
The graphic presentation of information has always been subject to certain fashion trends. Sometimes there’s a roller instead of the round dial. Perhaps only a section of the scale is displayed. There may even be a preference for speed to be displayed in large digital figures behind the steering wheel. Still, during the last 100 years, the round instrument has been dominant.
Nevertheless, electronics are changing the whole concept of presenting information today and just as with aircraft, the speed and other information can be displayed on a single screen, changing to different ‘panels’ as needed. Because of the familiarity with the round instrument shape, the speedometer may still be shown in such a form even though a new generation of motorists may be happy with digits being shown.
The next big thing will be the projection of information onto the windscreen, a concept called the Heads-Up Display (HUD), which has its origins in jet fighters. This is not entirely new in cars and even back in the 1980s, some cars already had it. However, motorists never took to it and it has never become popular. Still, BMW is offering it in the new 5-Series and with this move, the HUD could well become more widely used.
