Numerous publications deal with an automatic control of the speed of a motor vehicle, taking into consideration the distance to vehicles in front. Such systems are frequently designated as adaptive cruise control (ACC), or in German as adaptive or dynamic traveling-speed controllers. In view of today's traffic conditions, a basic problem in such systems is an automatic decision as to which of several preceding-traveling vehicles is relevant or the most relevant for the cruise or proximity control. This decision is particularly difficult when the road upon which the controlled vehicle is moving is multi-lane and curvy. In this case, a proximity sensor which, inter alia, is used for detecting vehicles in front, generally also detects vehicles that are located on adjacent traffic lanes and therefore have only secondary relevance for a proximity control.
Accordingly, there is a need in an ACC system to determine a future travel-course progression or a future travel-course range of the controlled vehicle in order to ascertain in each case the most relevant vehicle in front or, conversely, the most dangerous obstacle at an instantaneous point of time based on the knowledge of this range. Both variables--the course progression and the course range--are basically oriented to the run of the road, but in the optimum case, also take into account lane-change or turning operations of the controlled vehicle possibly taking place. In this context, the term "future course range" differs in the following from the term "future course progression" to the effect that it includes the entire spatial range in which the controlled vehicle will probably move. This means that it also takes into account the breadth necessary for the motor vehicle in each case.
Presently known solutions to the problem formulation indicated above are described, for example, in the publication "Adaptive Cruise Control--System Aspects and Development Trends" by Winner, Witte et al., published as SAE Technical Paper Series No. 961010 at the SAE of Feb. 26-29, 1996. According to that, the easiest way of predicting a future course of a controlled vehicle is to assume a linear movement. However, it is obvious that this type of predicting will not function in the case of curves or lane changes. A more complex case, which, however, furnishes adequate results for wide ranges, is the assumption of a course having a constant curve. This is determined, for example, from a difference of wheel speeds, from a steering angle or steering-wheel angle, from transverse accelerations and/or from yaw rates. Corresponding methods are known from the field of operating-dynamics control. The disadvantage of this method is that, in each case, the future course or course range is estimated only on the basis of the current course. Thus, errors arise here as well in response to each change of the course, such as when driving into or out of curves. A further possibility for predicting a course progression, which is likewise mentioned in the publication indicated, is the use of navigation systems. However, the limits of this method depend upon how up-to-date and accurate the available maps are, as well as the ability of the system to determine the current position of the vehicle. The prediction is faulty particularly in construction-site areas or in the case of new roads. Another possibility indicated in the aforesaid publication is a prediction of the road progression or of the lane based on radar data. Stationary objects such as reflectors or crash barriers, which are detected by a signal processor, are used to reconstruct the road boundaries. However, according to the publication, little is known at this point about the quality and reliability of this method.
U.S. Pat. No. 4,786,164 describes a system and a method for detecting a distance between two vehicles moving in the same traffic lane. The traffic lane in which each of the two vehicles is moving is determined on the basis of a comparison of angles at which reflectors, which are distributed at both sides of the road, are detected. However, the method described in that case is applicable only if suitable reflectors are actually available on both sides of a road, and thus is dependent upon infrastructure conditions.
German Patent No.196 14061 describes a system for controlling the distance to a vehicle in front on the basis of an adjustable probability distribution. This described system has a curve-determination device, in which the curve of a road is determined on the basis of a steering angle and a vehicular speed. To improve reliability, according to a first modification, the steering angle is ascertained on the basis of the movement of a specified stationary object. To that end, the locations of a stationary object relative to a moving system vehicle are monitored at uniform time intervals. The locations are then defined as circular arcs in order to calculate the curve of the road upon which the system vehicle is traveling. According to a second modification, a sharp curve of the road can likewise be detected with reference to a stationary object. According to a fourth modification, the calculated curve can be increased or reduced when a turn indicator indicates the right or the left direction. According to a tenth modification, with the aid of a navigation system such as a GPS system, it is possible to determine whether or not a curve exists in a forward direction of the system vehicle. However, none of the methods put forward in this patent eliminates the disadvantages already indicated in detail.