Induction instead of mechanics

The problem was tackled not only by Daimler-Benz engineers but also at TELDIX GmbH in Heidelberg. The two companies did not make any headway with mechanical sensors, so they had to look for another, new solution.

In 1967, they came up with a solution to the problem in a joint effort – in the form of contactless speed pickups which operate on the principle of induction. Their signals were to be evaluated by an electronic unit which controlled brake pressure via solenoid valves.

At the time, electronics still worked on the basis of analogue technology which was relatively susceptible to failure and consisted of complicated circuitry. Integrated modules did not yet exist. And yet, this proved to be a first, promising approach.

For this reason, Daimler-Benz introduced this first generation of an anti-lock braking system for cars, trucks and buses to the public on the test track in Untertürkheim on December 12, 1970 – with a resounding echo by an enthusiastic expert world and press. The principle had been found to be convincing.

Development of the production ABS

Another eight years passed before Daimler-Benz was able to offer a reliably functioning anti-lock braking system for production cars; this time was required to give the prototype the degree of technical maturity and reliability that is indispensable for large-scale production. In development, the engineers benefited from the revolution in electronics. It was not until the invention of integrated circuits that small, robust computers could be built, capable of recording wheel sensor data in next to no time and reliably actuating the valves for adjusting brake pressure.

It took development partner Bosch five years to supply the first digital control unit to Untertürkheim for test purposes. Digital instead of analogue: this meant fewer components with the advantage of the risk of malfunction being reduced down to virtually zero.

Thanks to digital technology, the electronic components were capable of recording, comparing, evaluating and transforming sensor data into governor pulses for the brakes' solenoid valves within milliseconds. What's more, not only the front wheels but also the rear wheels were included in the control operations.

Despite an emergency braking maneuver on a wet road, the bus equipped with ABS (top) retains its steerability, directional stability and safe tire-to-road contact. It is effectively decelerated whereas the bus without ABS (bottom) skids across the wet road surface without being decelerated as strongly as with ABS intermittent braking.