Mercedes-Benz taught the car to see in the 1990s: DISTRONIC adaptive cruise control had its world premiere in 1998 as an optional extra in S-Class model series 220. The system used radar to monitor the traffic continuously from three defined angles. The emitted impulses were reflected by the vehicle in front and received by DISTRONIC. Based on these received signals, the control electronics deduced the distance to the vehicle in front and its speed.
On this data basis, the assistance system calculated the driving commands needed to keep a safe distance behind the vehicle in front with the cruise control activated: Providing there was no vehicle driving directly in front of the car, the cruise control maintained the programmed speed. If the distance to another vehicle shortened, however, DISTRONIC decelerated the car by intervening to adjust the engine, brakes and automatic transmission. As soon as the lane was free again – due to the vehicle in front turning off or changing lanes, for example – the assistance system accelerated the car back up to the programmed speed. This process took place fully automatically, initially in a speed range from 40 to 160 km/h. In this way, DISTRONIC made the driver’s job easier all the time, not just in extreme situations as ABS and ESP® had done before it. The car therefore supported the driver with many actions and decisions under normal driving conditions.
Radar as the car’s ‘eyes’
This was followed in 2005 by the enhanced DISTRONIC PLUS, which worked in the speed range of 200 km/h to standstill, making the driver’s job even easier still. After this, it accelerated back up to the speed programmed in the cruise control. This evolution was based on key developments in the tried-and-tested technology employed since 1998: the previous DISTRONIC radar, which operated in the 77-gigahertz range with a very narrow viewing angle, was combined with a newly developed short-range radar operating in the 24-gigahertz range with an exceptionally wide viewing angle. This not only extended the field of view of the vehicle being driven, it also provided data for other assistance systems such as Brake Assist BAS PLUS. Thanks to the combination of both radar systems, the operating range of the adaptive cruise control was extended to 0.2 to 150 metres. DISTRONIC PLUS was unveiled in S-Class model series 221 launched in 2005.
Ever improving sensor systems for more effective assistance systems is a leitmotif in the history of Intelligent Drive. The radar systems of the first DISTRONIC system have therefore been augmented by an increasing number of sensors that the car uses to observe its surroundings in a range of 360 degrees and with an increasingly long range in the direction of travel. Today these include long and short-range radars, stereo cameras, conventional cameras, and ultrasonic sensors.
DISTRONIC has a long history of research and development, too. Group Research began early tests with radar-based distance control back at the end of the 1970s. Daimler-Benz tested its first distance assistance systems at the start of the 1980s in medium-size model series 123. The next step in the mid and late 1980s was an adaptive cruise control prototype whose functions were already similar to those of the later DISTRONIC system. The Stuttgart engineers developed and tested the system, which was already based on radar, in S-Class model series 126. During the development work, it emerged that the main challenge lay in detecting stationary obstacles rather than moving objects.
The company conducted research into technical alternatives to radar whilst work on the later DISTRONIC system was ongoing. In the aforementioned PROMETHEUS project, for example, Daimler-Benz developed Advanced Intelligent Cruise Control, which worked using a five-beam infrared laser and was tested in the W 124. Even though this solution was not initially incorporated into DISTRONIC, the wide range of investigated sensor systems paid off handsomely in terms of the development of assistance systems as a whole. After all, the vehicle did not just locate itself in the traffic area when the adaptive cruise control was working, but also when parking, for example. The application in this instance was Mercedes-Benz PARKTRONIC, which was made available as an option in 1995 and calculated the distance to an obstacle with the help of ultrasonic signals. Transmitter and receiver were combined in sensors integrated in the front and rear bumpers. This means that it was possible to prevent typical damage caused by minor bumps when parking in tight spaces. At the same time, parking was made easier thanks to vehicle support.
Mercedes-Benz collaborated with various partners when developing DISTRONIC. At the start of the project, Dornier, which was then a subsidiary of the Daimler-Benz Group, supplied the sensors, which worked well in the prototypes. To meet the challenge of transferring the technology to series production, the company entered into a partnership with DASA (Deutsche Aerospace AG), which had merged with Dornier in 1989. The DASA sensors were based on military technology. The inadequate detection of stationary obstacles remained a challenge. The sensors were ultimately made by TEMIC in Heilbronn. Launched on the market successfully in 1998, DISTRONIC received the Daimler-Benz Innovation Prize in the same year.