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ABS is thus an example of the great staying power sometimes required to bring a pioneering new product up to production standard – a responsibility which the Mercedes-Benz brand takes upon itself again and again with its numerous innovations.
An anti-lock braking system had been on the automotive engineers' list of wishes for decades – it was, after all, expected to improve handling safety drastically by retaining steerability during braking. As early as 1928 the German Karl Wessel had been granted a patent on a braking force regulator for automobiles, but this design only existed on paper.
Nevertheless, these first attempts set the course: an anti-lock braking system had to have sensors for measuring the speeds of each front wheel, as well as a control unit for recording and comparing the data measured by the sensors. This control unit was to correct excessive deviations by individually controlling the brake pressure at every wheel up to the point at which the wheel is about to lock.
However, the transfer of the idea into hardware for use on the road proved to be significantly more difficult than expected. The sensors did work satisfactorily as early as 1952 when used in an anti-skid system for aircraft, and in 1954 in a Knorr braking system for railways.
But in the car, the demands on the mechanical friction wheel sensors were much higher: they had to register decelerations and accelerations in wheel speeds, they had to react reliably in corners and on rough ground and work perfectly even when heavily soiled and at high temperatures.
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 contact-less 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.
Another eight years passed before Daimler-Benz was able to offer a reliably functioning anti-lock braking system for production cars; this time the challenge was to give the prototype the degree of technical maturity and reliability that is absolutely necessary 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.
Thus, it had taken a long, long time before Mercedes-Benz became the world's first motor manufacturer in August 1978 to officially launch the second-generation anti-lock braking system and to offer it as an option from December 1978 – initially in the S-Class at a surcharge of DM 2,217.60.
Mercedes-Benz also adopted a pioneering role where ABS for commercial vehicles was concerned. As early as 1981 ABS was offered for compressed-air brakes, a joint development with Wabco. ABS has been standard equipment on all touring coaches of the brand since 1987 and on all trucks of the brand since 1991.
ABS development never stops. The complete control system is becoming ever smaller, ever more effective, and ever more robust. The initial, typical pulsating of the brake pedal, indicating ABS activation, has largely been eliminated today.
However, the system not only optimally decelerates the car and retains its steerability, it also serves as the basis and pulse generator for the acceleration skid control (ASR) system, the Electronic Stability Program ESP®, the Brake Assist and also for the electro-hydraulic brake system, Sensotronic Brake Control (SBCTM).
In Mercedes-Benz passenger cars, the wheel sensor data also serves less conspicuous functions in that it is, for instance, processed by the electronically controlled automatic transmission that adjusts to the driver's wishes, the navigation computer, the DISTRONIC proximity control, the engine and windshield wiper control, the active suspension control (ABC, or Active Body Control), 4MATIC all-wheel drive – in short, by everything in the car that is controlled on the basis of speed. The same naturally applies to trucks and buses.
If the anti-lock braking system is today taken for granted in virtually all cars of the majority of automotive brands throughout the world, we owe this to the commitment of the large number of engineers and technicians at Daimler-Benz and cooperation partners Bosch, TELDIX and Wabco, who searched for the best solution for this system which improves handling safety, avoids accidents and saves lives.
This is what Heinz Leiber, the then head of ABS development at Daimler-Benz and also called the "Father of ABS", has to say: "The anti-lock braking system – and with it Mercedes-Benz – was also a pioneer in automotive digital electronics."
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