High-tech cars cruising on radar
By: Drivers.com staff
Date: 1999-09-11
Talk about being paranoid. You look in the rearview mirror and there sits a luxury car for mile after mile keeping a precise-and safe-distance from your car. No, you're being neither tailed nor tailgated. What you're observing is one of the latest technological gizmos in action-adaptive cruise control.
Jaguar has just announced an ACC option on some of its models, hailing it as a significant step toward easier and safer driving. A company spokesman even said the system may lay the foundations for future collision-avoidance systems. "But that's way in the future," he added. "This is an aid for the driver, not a substitute."
Skeptics might argue that drivers may come to rely too heavily on new technology rather than concentrating on basic driving skills, but the radar-based, sensing device could well be instrumental in preventing one running into a vehicle pile-up shrouded by blowing snow or thick fog. Of course, that doesn't prevent a driver from being rammed from behind.
Mercedes-Benz has also announced a smart cruise control for its new line of S-Class cars, unveiled at the Paris Auto Show last fall. The technology, again offered as an option, incorporates an LCD display in the centre of the speedometer showing the relative position of the two vehicles.
Mercedes' Distronic system, which monitors the traffic for up to 150 meters ahead, reacts instantly. If the vehicle in front brakes suddenly the system automatically triggers heavier braking. The system operates at speeds between 25 and 100mph and is limited to a maximum braking force of two-meters-per second, or about one-fifth of the maximum braking available on the S-class.
If more urgent braking is needed, the driver is warned to apply the brakes himself by an audible warning and a red light on the instrument panel.
And because the system uses radar, it can see through fog or heavy rain. Testing on German autobahns has already proved that the system relieves stress and allows drivers to drive in a safe and relaxed way.
How it works
Hidden behind the radiator grille on the S-class is the radar sensor, which has three transmitting and receiving units, and is at the heart of the new system. They emit signals constantly, each with an opening angle of three degrees, and can monitor all lanes of the road ahead.
If the short-wave radar signals (77 gigahertz) 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 can then be calculated. The system uses digital signal processors, which are vastly superior to micro-chips in terms of operating speed and storage capacity.
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 Distronic to keep the S-class at a safe distance from vehicles ahead. Most of the correcting forces are so subtle the driver is not aware of the car being braked.
Operating the new system is similar to using the Merc's conventional cruise control. Once the car has reached the desired cruising speed, within the 25 to 100mph range, the driver merely moves a lever on the steering column up or down to engage the ACC.
The selected speed is then stored on a central display on the instrument cluster. One or two segments in the speedometer light up to highlight the selected speed range. The central display then indicates both the actual and desired distance to any vehicle ahead.
Once the radar sensor detects a vehicle in front, the central display shows both vehicles and continues to show the safe distance between them. If the distance shortens the system automatically reduces the speed and the speedometer segments enlarge to show the actual driving speed and the pre-selected speed.
What do these systems cost? Jaguar-a division of Ford-is making the ACC option available on its XKR coupes and convertibles in Britain and Germany for around $2,000. That's small change when you're shelling out about $100,000 for a car. North Americans may get a chance to purchase the system late this year.
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