26-11-2012, 04:00 PM
TECHNICAL REPORT ON ADAPTIVE CRUISE CONTROL
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INTRODUCTION
Mentally, driving is a highly demanding activity - a driver must maintain a high level of concentration for long periods and be ready to react within a split second to changing situations. In particular, drivers must constantly assess the distance and relative speed of vehicles in front and adjust their own speed accordingly.
Those tasks can now be performed by Adaptive Cruise Control (ACC) system, which is an extension of the conventional cruise control system.
Like a conventional cruise control system, ACC keeps the vehicle at a set constant speed. The significant difference, however, is that if a car with ACC is confronted with a slower moving vehicle ahead, it is automatically slowed down and then follows the slower vehicle at a set distance. Once the road ahead is clear again, the ACC accelerates the car back to the previous set cruising speed. In that way, ACC integrates a vehicle harmoniously into the traffic flow.
WHY ADAPTIVE CRUISE CONTROL?
Comfortable distance to the car ahead increases driving safety and ensures a more relaxed driving experience. Adaptive Cruise Control ensures that there is enough distance to the car ahead, even if it unexpectedly lowers the speed.
With Adaptive Cruise Control we have enhanced the conventional systems for speed control to a driver assistant with an added value. The system makes it possible to adapt the distance to the car ahead without the driver’s intervention, effectively relieving the driver. Highway and rural road drives are more relaxed and traffic flows better altogether, since acceleration and braking maneuvers are automatically adjusted.
ADAPTIVE CRUISE CONTROL
Two companies are developing a more advanced cruise control that can automatically adjust a car's speed to maintain a safe following distance. This new technology, called adaptive cruise control, uses forward-looking radar, installed behind the grill of a vehicle, to detect the speed and distance of the vehicle ahead of it.
Adaptive cruise control is similar to conventional cruise control in that it maintains the vehicle's pre-set speed. However, unlike conventional cruise control, this new system can automatically adjust speed in order to maintain a proper distance between vehicles in the same lane. This is achieved through a radar headway sensor, digital signal processor and longitudinal controller. If the lead vehicle slows down, or if another object is detected, the system sends a signal to the engine or braking system to decelerate. Then, when the road is clear, the system will re-accelerate the vehicle back to the set speed.
The 77-GHz Autocruise radar system made by TRW has a forward-looking range of up to 492 feet (150 meters), and operates at vehicle speeds ranging from 18.6 miles per hour (30 kph) to 111 mph (180 kph). Delphi's 76-GHz system can also detect objects as far away as 492 feet, and operates at speeds as low as 20 mph (32 kph).
Adaptive cruise control is just a preview of the technology being developed by both companies. These systems are being enhanced to include collision warning capabilities that will warn drivers through visual and/or audio signals that a collision is imminent and that braking or evasive steering is needed.
HOW DOES IT WORK?
The radar headway sensor sends information to a digital signal processor, which in turn translates the speed and distance information for a longitudinal controller. The result? If the lead vehicle slows down, or if another object is detected, the system sends a signal to the engine or braking system to decelerate. Then, when the road is clear, the system will re-accelerate the vehicle back to the set speed.
The adaptive cruise control (ACC) system depends on two infrared sensors to detect cars up ahead. Each sensor has an emitter, which sends out a beam of infrared light energy, and a receiver, which captures light reflected back from the vehicle ahead.
The first sensor, called the sweep long-range sensor, uses a narrow infrared beam to detect objects six to 50 yards away. At its widest point, the beam covers no more than the width of one highway lane, so this sensor detects only vehicles directly ahead and doesn't detect cars in other lanes. Even so, it has to deal with some tricky situations, like keeping track of the right target when the car goes around a curve. To deal with that problem, the system has a solid-state gyro that instantaneously transmits curve-radius information to the sweep sensor, which steers its beam accordingly.
Another challenge arises when a car suddenly cuts in front of an ACC-equipped car. Because the sweep sensor's beam is so narrow, it doesn't "see" the other car until it's smack in the middle of the lane. That's where the other sensor, called the cut-in sensor, comes in. It has two wide beams that "look" into adjacent lanes, up to a distance of 30 yards ahead. And because it ignores anything that isn't moving at least 30 percent as fast as the car in which it is mounted, highway signs and parked cars on the side of the road don't confuse it.
CONCLUSIONS
Despite the introduction of the system to the market place, these are still early days. The current system can measure up to 150m ahead of the car and reduce the car's speed if an obstruction appears. What it can't do, at the moment, is bring the car to a halt.
Whatever happens, the ACC market looks set to explode. The projected figures make startling reading. In 2002 there are no more than 100,000 vehicles fitted with ACC, but that figure is set to reach eight million in four years' time, with Europe, South-East Asia and the US accounting for about a third each. Around 17% of all European-built cars are likely to have ACC fitted as standard by then.
Expansion is bound to slow down thereafter, but by 2010 the global market will be 11.5 million units, representing an industry value of around $2.4 billion - and enormously more than that saved in repair bills, hospital bills and, indeed, funeral bills.