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Anti-lock braking system for commercial vehicles

Dec 26, 2005
  • Presentation and introduction by Daimler-Benz in 1981
  • Crucial contribution to traffic safety
  • Forerunner of ASR, EBS and future safety systems
What is matter-of-course standard equipment on commercial vehicles from Mercedes-Benz today was a big step towards greater traffic safety in 1981: the first anti-lock braking system (ABS) for commercial vehicles. With ABS, steering maneuvers became possible during emergency braking, trucks and buses no longer skidded when braking on road surfaces with different tire-to-road adhesion levels on the left- and right-hand sides, articulated trucks no longer jackknifed and trailers no longer broke away during braking. ABS quickly proved to be one of the crucial safety developments in automotive history. Pioneers in the development of this technology were the engineers of the then Daimler-Benz AG.
Start of ABS development as early as the 1960s
The engineers began developing the ABS as early as the 1960s. In 1970 the first operational systems with electronic control for passenger cars, trucks and buses were presented to the press. A precondition for the further development through to production maturity was the advent of digital technology which replaced analogue technology in the electronic control unit. This is because ABS, i.e. the individual, sensitive control of the wheel brakes depending on wheel slip, is inconceivable without reliable electronics. Daimler-Benz had already been doing pioneering work in the development of ABS for passenger cars, available as optional equipment since 1978. Where the extremely complex commercial vehicle series were concerned, the task proved to be clearly more demanding, however, in that different weight and load conditions, solo trucks, truck-and-trailer combinations and articu-lated trucks, different wheelbase lengths, superstructure variants and axle configurations had to be taken into account.
Commercial vehicle brakes controlled by micro-computers for the first time
Development partners Daimler-Benz and brake producer WABCO succeeded in overcoming these hurdles. On a test track in Rovaniemi, Finland, Daimler-Benz demonstrated the advantages of the new ABS at the end of January 1981. In the fall of that year, ABS became available first for heavy-duty trucks and touring coaches and, at a later stage, for other vehicle categories. The aim of ABS is to ensure maximum directional stability, full steerability and the shortest possible stopping distance. The introduction of ABS in 1981 marked a world first, namely the control of a commercial vehicle’s brakes by a micro-computer.
ABS: The first step towards additional safety systems
In addition, the introduction of the anti-lock braking system laid the foundations for the rapid further development of commercial vehicle braking technology. On the basis of ABS, the engineers developed acceleration skid control (ASR) which is basically just the reverse of ABS. In 1991, the Mercedes-Benz O 404 touring coach was presented with disc brakes all round. In 1996, the Mercedes-Benz Actros heavy-duty truck set a new milestone in that it incorporated the first electronic brake control system (EBS) and disc brakes all round for trucks. This marked the course for the next steps: Mercedes-Benz was the world’s first commercial vehicle producer to introduce the Electronic Stability Program (ESP) for trucks at the International Commercial Vehicle Show in 2000.
At the time, two additional systems were introduced: Telligent autonomous intelligent cruise control (ART for short) and the so-called Lane Assistant. With ESP, selective brake and engine management intervention prevents the truck from skidding or toppling over – within the limits of what is physically possible. With ART, three radar sensors scan the area in front of the truck. The results permit the driver to determine a specific distance – within certain limits – from the vehicle driving ahead, i.e. a distance which is then automatically retained by the truck. With the Lane Assistant, a small camera in the center of the instrument panel scans the lane markings on the road while a computer uses this data to determine the position of the vehicle. When the truck crosses the left- or right-hand edge of the lane without the driver having activated the indicator, a rumble-strip noise is sounded. When the truck deviates from the lane to the right side, the rattling comes from the right-hand side speaker. When the truck drifts off to the left, the sound comes from the left-hand speaker.
Expansion into an automatic emergency braking system
From 2006, a new version of the ART system, further developed into an automatic emergency brake, will be available. Trucks will no longer be limited to adjusting braking maneuvers with restricted intensity but trigger an automatic emergency braking maneuver when the worst comes to the worst. The possibility of upgrading the Lane Assistant by automatic intervention in either the steering or the wheel brakes is already being discussed. Additional intervention in the steering would, for instance, have another advantage, namely that the ESP could be designed to react even more subtly and even more precisely.
On a vehicle braked with the ABS developed by Mercedes-Benz/WABCO, steerability and directional stability are fully retained. ABS prevents the dreaded breaking away of the trailer on truck-and-trailer combinations, and the jackknifing of tractor and semitrailer on articulated trucks.
The Mercedes-Benz/WABCO anti-lock braking system of 1981 – the first ABS for commercial vehicles included components such as the electronic control unit with four microcomputers, rotors and sensors on four wheels and four solenoid valves.
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.