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Mercedes-Benz' new S-class will be equipped with the option of the innovative DISTRONIC distance control system when it becomes available in Australia around March 1999.

Utilising a radar sensor mounted in the radiator grille, plus a high- performance micro-computer, DISTRONIC can constantly maintain a safe distance to the car, truck or motorcycle in front.

Electronics automatically apply the brakes if the distance to the vehicle ahead drops to a critical level and, as soon as traffic conditions permit, will automatically accelerate the car back to the pre-selected speed.

Tests on German autobahns have shown that DISTRONIC provides a considerable comfort gain and reduces stress in dense traffic.
Automotive technology, today more than ever before, is designed to take some of that strain off the driver, reduce the physical and emotional stress and increase his/her ability to concentrate.

A totally new driving feel

With its new S-class, Mercedes-Benz has made a major advance. The new feature is having its world premiere in the new Mercedes flagship.

Hidden away behind the radiator grille is the radar sensor which monitors the traffic situation ahead up to a distance of 150 metres. In conjunction with a micro-computer, it ensures that a safe distance is maintained. If the Mercedes moves too close to the rear of another vehicle, the electronic system automatically reduces the speed and — if necessary — activates the brakes.

Once a safe distance has been re-established, the system will accelerate the S-class back to the driving speed originally selected.

World premiere for super chips

Digital signal processors (which are vastly superior to conventional micro-chips'operating speed and storage capacity) are capable of analysing the massive flow of data. "This is the first time signal processors have been used in a motor car," explains development project manager, Bernd Danner.

The DISTRONIC development team also completed pioneering work on the brakes, as a conventional brake booster cannot be used in conjunction with automatic brake control.

Instead the new S-class features an electronically controlled system which, thanks to a special solenoid valve, will also respond to the very gentle brake commands issued by the DISTRONIC computer which often the driver does not even notice.

Concealed co-pilot

The centrepiece of this new development, however, is the compact radar sensor behind the radiator grille which comprises three transmitting and receiving units. They emit their signals permanently, and can monitor all three lanes of a motorway from a distance of around 80 metres. If the short-wave radar signals detect an obstacle they are reflected back and change their frequency.

Engineers refer to this phenomenon as a Doppler effect. Its purpose is to compute the relative 'speed between the two vehicles while the distance is calculated on the basis of the time it takes for the signals to be reflected.

Operating the distance and cruise control system is basically the same as the SPEEDTRONIC cruise control which Mercedes has been fitting to its passenger car models for a number of months. Once the S-class has reached the speed selected by the driver within a range between 40 and 160 km/h, the driver need only move the lever on the steering column up or down for the DISTRONIC system to be activated.

Once the radar sensor has detected a vehicle in front, the central display will show both vehicles and will continue to display the safe distance to this vehicle via a segmented display. If the distance drops, DISTRONIC automatically reduces the current driving speed.

Normally, DISTRONIC is set to a distance of 1.5 seconds. At a speed of 100 km/h, for example, this corresponds to about 42 metres. Depending on the traffic density and flow, different distances may, however, be more appropriate.

This is why the driver is able to make certain adjustments using a rotary control with "Mm" and "Max" settings. In the "Mm" position, a time gap of one second is pre-selected. In the "Max" position, a two-second distance to the vehicle in front is maintained.

Individually selectable distance

The mid position corresponds to a value of 1.5 seconds which in trials was found to be ideal. because radar signals are emitted and received back in very short intervals, the system can also detect sudden deceleration of the vehicle in front and will trigger heavier braking as appropriate.

Deceleration using DISTRONIC is limited to a maximum of two metres per second, that is about one fifth of the maximum braking available on the S-class. If the situation gets too risky to leave braking up to the computer alone, the driver is given an additional audible warning.

Furthermore, a red warning triangle will light up in the instrument cluster urging him to apply the brakes himself/herself.
Says project manager Danner: "DISTRONIC is no automatic emergency brake; this electronic system has not been designed as a substitute for the driver. He or she is still in charge. It is still the driver's responsibility to observe the traffic and to react in a critical situation."

Nonetheless autonomous speed and distance control makes driving a great deal more comfortable.

This ground-breaking assistance system for the new S-class has already been subjected to several years of development and trials at Daimler-Benz as part of the European "Pometheus" project.

Autobahns

Tests at the Berlin driving simulator contributed to the development of DISTRONIC and provided engineers with information about motorists' acceptance. The positive experience from the driving simulator finally was confirmed by practical tests which Daimler engineers carried out together with experts from TUV Rhineland.