PARIS - Vehicle radar, or adaptive cruise control, made its production debut with the new Mercedes-Benz S class, and it will become increasingly commonplace on top-range cars over the next few months.
The S class uses a system developed with Robert Bosch GmbH. And Jaguar Cars Ltd. is working closely on such technology with Delphi Automotive Systems.
Adaptive cruise control is being marketed as a comfort feature, to help reduce driver stress or as an additional safety feature.
At the Paris auto show, Delphi President J.T. Battenberg described adaptive cruise control as 'a major step toward the collision warning and avoidance systems that will offer additional safety benefits to vehicle drivers and passengers.'
The technology allows a vehicle to keep a safe distance between itself and the vehicle in front of it automatically. Development began in the late 1970s, but only now can it come to market after significant progress in both sensor and signal-processing technologies.
Progress was triggered partly by Prometheus, a European research project involving all European car manufacturers. Similar activities were initiated in the United States and Japan as well.
In 1993, Prometheus started to investigate the feasibility of autonomous systems that could warn drivers when their cars are too close to the vehicles in front of them. The fairly simple prerequisite was the availability of a suitable radar system.
By 1995, the Prometheus project was working on the automatic control of speed and distance in relation to the vehicle ahead.
The prerequisites became more complex. There had to be a new definition of 'safe distance'; traffic regulations would have to be adapted to the new technology; there would need to be a definition of driver responsibility and product liability, as well as regulations to cover the mandatory equipment of vehicles with reflectors and transponders.
Those prerequisites have not yet been satisfied, but the product itself is alive and kicking.
Juergen Gerstenmeier, director of component development and control systems at Bosch, described adaptive cruise control as a comfort rather than a safety system, designed to make highway driving more relaxing. But it has the potential to be expanded. In Europe, where traffic speeds are often irregular, less than 10 percent of cars have cruise control; in the United States, where speeds are more regular, 90 percent of cars have cruise control.
Bosch's adaptive system automatically adjusts the speed of a car up to a predetermined maximum and maintains a constant distance from the car in front. It takes into account other vehicles cutting in and out of the sensing range and operates only at speeds above 18 mph.
'A system for city traffic and stop-go driving, which recognizes all relevant objects and barriers, is still in the preliminary development stage,' Gerstenmeier said.
Additional capabilities of adaptive cruise control include reacting to traffic events by accelerating or decelerating and, if necessary, braking.
'Technically speaking, adaptive cruise control is based less on conventional cruise control than on the function of brake, traction and dynamics control systems,' Gersten-meier said. That's why the development of adaptive cruise control has been possible only since the development of traction control and the electronic stability program.
How it works
Mercedes-Benz has coined the name 'Distronic' for the system on its new S class. If the distance to the vehicle in front becomes too short, the speed of the S class is automatically reduced, first by closing the throttle and then, if necessary, by applying the brakes.
Once a safe gap is re-established, the S class accelerates back to the original speed. All the driver has to do is steer.
The system, which monitors the traffic for up to about 490 feet ahead, reacts instantly. If the vehicle ahead brakes suddenly, it automatically will trigger heavier braking on the S class.
Distronic operates at speeds between 25 mph and 100 mph and is limited to a maximum braking force of about 6.5 feet per second, or about one-fifth the maximum braking available on the S class. If more urgent braking is needed, the driver is warned to apply the brakes manually by an audible warning and a red light on the instrument panel.
Because the system uses radar, it can see through fog or heavy rain.
Hidden behind the radiator grille on the S class is the radar sensor with three transmitting and receiving units. They emit signals constantly, each with an opening angle of 3 degrees, and can monitor all lanes of the road ahead.
If the short-wave radar signals detect an obstacle, they are reflected back and change their frequency. This is known as the Doppler effect. The distances and speeds between the two vehicles then can be calculated. Digital signal processors, which are vastly superior to microchips in terms of operating speed and storage capacity, are used for this, the first time such sensors have been used in cars.
Conventional brake boosters could not cope with the demands of the automatic brake system, so instead the S class uses an electronically controlled system with a special solenoid valve. This also allows for the very gentle brake commands issued by the system to keep the S class at a safe distance from vehicles ahead of it. Most of the correcting forces are so subtle that the driver is not aware that the car is being braked.
Operating the new system is similar to cruise control. Once the S class has reached the desired cruising speed, within the 25-to-100-mph range, the driver merely moves a lever on the steering column up or down to engage Distronic.
The selected speed is stored on a central display in the instrument cluster. One or two segments in the speedometer light up to highlight the selected speed range. The central display indicates both the actual and desired distance to any vehicle ahead.
Once the radar sensor detects a vehicle ahead, the central display shows both vehicles and continues to show the safe distance between them. If the distance shortens, Distronic automatically reduces the speed, and the speedometer segments enlarge to show the actual driving speed and the preselected speed.
Distronic project manager Bernd Danner said: 'This electronic system has not been designed as a substitute for the driver. He or she is still the one in charge. It is still the driver's responsibility to observe the traffic and to react correctly in a critical situation.'
Tests with the new system have shown significant reductions in driver heart rates while the tracking stability of the car is improved greatly.