Abstract:
In a method and a device for triggering a request for taking control (RTC), a driver of a vehicle having adaptive cruise control is signaled that the adaptive cruise control system may not be capable of controlling a driving situation, and that the driver may have to intervene, the signaling of the driver being generated in accordance with at least two vehicle variables, whereby the probability of a false alarm by the system is reduced, and the triggering of the RTC is adapted to the instantaneous vehicle speed.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method and a device for triggering a request for taking control (RTC) in vehicles having adaptive cruise control. 
   BACKGROUND INFORMATION 
   Methods and devices for regulating speed and/or acceleration are conventional under the term “tempomat”. Supplementing such a device with a sensor, which can recognize preceding vehicles and/or obstacles located in the direction of travel, is also known. These devices may utilize, in the control of vehicle speed, not only their own internal traffic variables, but also traffic variables of the surroundings. Such devices are denoted as adaptive or dynamic vehicle speed controllers or adaptive cruise control (ACC). Such an adaptive travel regulating system may be a convenient assistance to a driver. Therefore, the acceleration and deceleration dynamics, with which the control system activates the forward propulsion and the brakes of the vehicle, may be limited. Furthermore, the adaptive vehicle speed regulator neither should nor can relieve the driver of any responsibility. Instead, the regulator may only relieve the driver of monotonous and tiring activities. Therefore, existing ACC systems may be deliberately made incapable of independently initiating either sharp or full braking, even though the sensory system may be capable of recognizing dangerous situations. In these dangerous situations, existing ACC systems provide a so-called request for taking control,-which is activated when the maximum deceleration provided by the automatic system may be no longer sufficient to avoid a collision. The request for taking control signals the driver acoustically, optically, haptically or kinesthetically that manual intervention using the brake pedal may become necessary. In supplementary fashion, the driver has priority over the vehicle control system at all times, in that he may operate the gas or brake pedal and override or deactivate the system, thereby putting the automatic drive control out of commission. 
   A fundamental description of such a device is referred to in the paper “Adaptive Cruise Control—System Aspects and Development Trends,” given by Winner, Witte et al., at SAE 96, Feb. 26 to 29, 1996 in Detroit (SAE Paper No. 961010). The paper discusses the dynamic restriction of the system for the purpose of riding comfort. 
   The request for taking control is mentioned in this article as possibly being an acoustic signal which is activated when no sufficient deceleration can be made available so as to react fittingly to the instantaneous situation. 
   One method and device for travel regulation are described in German Published Patent Application No. 195 44 923. The system includes a radar system and a vehicle speed sensor, from the measured values of which, an acceleration requirement signal is formed. This signal is then used to activate the throttle and the brakes (EGAS system). A limiter assures that the acceleration requirement signal does not exceed the range between a predefined maximum or minimum value, in order to guarantee a designated travel comfort to vehicle passengers. In this system, the driver is notified by a blinking light, a tone generator, a haptic device or a combination of these possibilities. These signal elements are activated when the current deceleration requirement of the vehicle exceeds or approximately reaches the maximum permissible deceleration for the vehicle, and the vehicle is subject to travel control at the same time. European Published Patent No. 0 348 691 describes concepts for haptic signaling. However, no method is described which points to a reference for triggering a request for taking control. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide criteria with the aid of which the activation of a request for taking control may be triggered, so that the frequency of false alarms may be reduced to a minimum. 
   This object may be achieved by simultaneously satisfying at least two criteria with respect to deceleration values for activating the request for taking control. In one example embodiment, the two criteria include inequalities with regard to the deceleration values aSoll and aWarn, which must be fulfilled simultaneously before the request for taking control is activated. In this connection, the two deceleration-related variables lead to as complete as possible a reduction in false alarms. Furthermore, the decision thresholds “aMaxDecel+Offset 1 ”  221  and “aMaxDecel+Offset 2 ”  231  of these criteria are not provided as constant threshold values. Instead, they are changed dynamically as a function of instantaneous values, such as vehicle speed. 
   The acceleration requirement may be used for the activation of actuators, for the setting of a throttle and/or for brake operation. In the present case, the acceleration requirement is denoted as aWarn. If aWarn undershoots a negative acceleration value which corresponds to the brake energizing hysteresis, the vehicle may be decelerated using a braking force in accordance with the absolute value of aWarn. If short term error measurements appear, the system may trigger a request for taking control, even though the situation would not require it. In this manner, false alarms may be created, which may irritate the driver and make the system appear unsophisticated. 
   To solve this problem, a second acceleration value is introduced, which is subsequently denoted as aSoll. This value aSoll, in addition to aWarn, must undershoot a certain negative acceleration threshold, denoted as “aMaxDecel+Offset 2 ”  231 , before the request for taking control can be triggered. The value aSoll may be passed to the brake control or, in the case of propulsion, to the engine control, where it may be used to recalculate a desired engine torque. In order to impart comfort to the vehicle passengers, the value aSoll, which acts directly on the power train and the deceleration elements, may be restricted in several ways. For instance, the maximum admissible acceleration value may be limited by a positive and/or a negative limiting value, so as to impart a comfortable riding sensation. Furthermore, the change over time of the acceleration value may be bounded by limiter  103 , in order to prevent a “jolt” in response to a load alteration. Or, the two switching thresholds “aMaxDecel+Offset 1 ”  221  and “aMaxDecel+Offset 2 ”  231  for the input values aWarn and aSoll respectively, may be changed during vehicle operation in accordance with the instantaneous driving situation. For example, the value aMaxDecel may be formed as a function of the instantaneous driving speed, and the starting point of the deceleration can be selected differently for different speeds. 
   These innovations, according to an example embodiment of the present invention, may avoid false alarms of the ACC request for taking control. If the system recognizes an object in the travel-path area of the vehicle, even for a very short duration (e.g., through disturbances in the side lane or error measurements), the request for taking control is no longer triggered immediately, but rather braking is begun. If the object disappears before the instantaneous deceleration aSoll corresponds to about the maximum deceleration “aMaxDecel+Offset 2 ”  231  available to the system, braking is discontinued without jolting, and the vehicle continues under normal operation. However, if the detected object does not disappear, and the instantaneous deceleration approaches or reaches the maximum deceleration “aMaxDecel+Offset 2 ” available to the system, the request for taking control  109  may be triggered, if the system predicts that it can no longer decelerate the vehicle in time or in sufficient measure. Further, since braking action may be different at high speeds as compared to low speeds, the system may control the automatic braking action of the ACC system in accordance with the instantaneous speed, in order to generate a braking action which corresponds to that of a responsible driver. This may yield a comfortable and pleasant traveling experience, in view of the time gradient limitation of the value aSoll. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an example embodiment according to the present invention. 
       FIG. 2  illustrates an example functional sequence scenario which may occur during operation of a vehicle under ACC, the sequence scenario being made up of four partial diagrams, each of which plots one variable of the ACC system versus time. 
       FIG. 3  shows a possible functional sequence scenario which can occur during operation of the vehicle under ACC, according to an example embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a block diagram of an ACC system that represents how the decision to trigger the request for taking control is formed. The distance dZO between one&#39;s own and a preceding vehicle, the relative speed of the target object vRelZO in relation to the preceding vehicle, and the acceleration of the target object aZO enter as input variables into function block  101 , in which the value aWarn is formed. The formation of the value aWarn may be accomplished by calculation of a mathematical formula or by storing a characteristics map or table in block  101 . In the case of mathematical formula, aWarn may be calculated from
   a Warn=((sign( vRelZO )( vRelZO ) 2 )/(2 d Warn))+ aZO   (1) 
where, in turn, the warning distance dWarn (the relative deceleration path) is calculated from
   d Warn=( f Warn  dZO )−Offset 3   (2) 
   fWarn is a factor which may be either definitely predefined as a parameter or variably calculated, for example, in accordance with a set time gap. Using this factor fWarn, for example, the time gap set by the driver or a travel program (comfortable, safe, economical, sporty, . . . ) predefined by the driver may be taken into consideration. 
   The value of aWarn thus calculated is then passed on to function block  105 . 
   In function block  102 , in a manner similar to block  101 , using the input variables distance dZO, the relative speed of the target object vRelZO and the acceleration of the target object aZO, the value aSoll is formed. As in block  101 , the formation of aSoll may be accomplished by mathematical formula or by storing characteristics maps or tables. The value aSoll thus formed is then routed to a limiter which limits the value with respect to minimum or maximum values and a time-related acceleration change. The limited value is then routed to decision block  106  as the value aSollStar. At the same time, aSollStar is passed on to the throttle control and the brake control, which are referred to in  FIG. 1  as “EGAS System”, where they are used in propulsion and braking systems. In function block  104  the maximum deceleration controllable by the ACC system, aMaxDecel, is formed and forwarded to decision blocks  105  and  106 . The maximum deceleration controllable by the adaptive driving speed regulating system, “aMaxDecel+Offset 2 ”, is changed in blocks  105  and  106  as a function of the instantaneous driving speed, so that the system provides, at all times, a dynamics region that is as great as possible but nevertheless comfortable. 
   In block  105  an inequality is monitored. Block  105  determines whether the condition
 
 a Warn&lt; a MaxDecel+Offset 1   (3)
 
is fulfilled. If so, a signal is sent to AND element  107  that the condition examined in block  105  is fulfilled. Similarly, decision block  106  determines whether the condition
 
 a SollStar&lt; a MaxDecel+Offset 2   (4)
 
is fulfilled, using input values aSollStar and aMaxDecel. If inequality (4) is fulfilled, decision block  106  signals to AND element  107  that the trigger condition is fulfilled.
 
   The offset values Offset 1  and Offset 2  are parameters that allow the warning thresholds of equations (3) and (4) to be further varied and optimized. 
   The AND element  107  monitors whether all inputs report simultaneously that the conditions of decision blocks  105  and  106  are fulfilled. 
   If so, AND element  107  signals the OR element  108  that the conditions for triggering the request for taking control are fulfilled. The OR element  108  signals the request for taking control block  109  that the latter is to be triggered and that the driver is thereby notified that the comfortable braking of the system is not sufficient for obtaining enough deceleration. 
   Function block  110 , which is connected to one of the inputs of AND element  107 , and function block  111 , which is connected to an input of OR element  108 , allow additional criteria to be considered with regard to activating the request for taking control. 
   The output of function block  110  is connected to the input of AND element  107 . Block  110  may monitor the active operational state. For example, block  110  may monitor the operational state of the ACC control and report it to block  107 . Further, block  110  may include a function of speed as an AND condition, which may permit activation of the request for taking control only when the vehicle fulfills certain speed requirements. This may allow the activation of the taking-control signal only when the ACC control and regulating device may actively control the gas and the brakes. 
   In the same manner, a self-diagnosing function may be used to determine whether the ACC control and regulating device is functioning properly. In case the device does not work without error, an output signal is generated in function block  111 , which OR element  108  receives, thereby causing the activation of the request for taking control. This arrangement guarantees that the driver is requested to take control in the case of operational failure, and that the ACC control and regulating device can switch itself off safely following the activation of the brake pedal. Furthermore, the sensor function may be checked to ensure that it is properly functioning. Further, the system may process a blindness recognition signal, a rain recognition signal, or a signal which brings about a warning of standing objects in one&#39;s own lane, during limited vision conditions, such as fog. 
     FIG. 2  illustrates an example functional sequence scenario which may occur during operation of a vehicle under ACC. The example scenario includes four diagrams, each of which plots one characteristic variable against time. In diagram  210 , the distance to target object dZO is plotted against time. In diagram  220 , the warning acceleration aWarn is plotted against time. The drawn-in borderline  221  denotes a threshold value “aMaxDecel+Offset 1 ”. When this threshold is exceeded, a corresponding signal is passed on to AND element  107  in FIG.  1 . 
   In diagram  230 , the restricted desired acceleration aSollStar is plotted against time. The variable aSollStar is the variable which is also passed to the control for the electronically controlled throttle (EGAS) or the electronically controlled brake. The drawn-in value  231  represents the threshold value “aMaxDecel+Offset 2 ”, at the undershooting of which a corresponding signal is also passed on to AND element  107 . In diagram  240 , the request for taking control is represented as a digital signal. Here the transition from “0” to “1” indicates the activation of a signal for the request for taking control. The pulse duration of the RTC(t) signal is a function of the duration of the taking-control signal. When the signaling is ended, the RTC(t) curve transitions from “1” to “0”. 
   The four diagrams  210 ,  220 ,  230  and  240  are arranged in such a way that their respective time lines run parallel. Thus, the vertical dotted lines of  FIG. 2  each intersect the four time lines at the same point in time, each intersected point in time being labeled with Latin letters (a to f) at the bottom of FIG.  2 . 
   At point in time t=0 in dZO-t diagram  210 , a certain constant distance dZO(t=0) separates the ACC-controlled vehicle and the preceding vehicle. 
   At point in time t=a an additional object of reflection suddenly appears at a very short distance from the ACC-controlled vehicle, is detected for only a very short time, and then disappears suddenly. In this case, the system tries to make available a strong deceleration which is far below warning threshold  221  of the aWarn-t diagram  220 . As a result, block  105  in  FIG. 1  passes a corresponding signal to AND element  107 . Signal aSollStar, which also controls the propulsion and brake elements, is created essentially in the same way as aWarn, the only difference being that aSollStar is limited as to a maximum value as well as a gradient. Thus jumps, steep transitions and values great in amount are excluded from the calculation of aSollStar. Until the desired end values for aSollStar are adjusted, a certain time lapses. Thus, aSollStar may be denoted as being inert or delaying compared to aWarn. In the aSollStar-t diagram  230  the gradient for the curve tangents in each case is a gradient triangle. Thus the gradient of gradient triangles  232  is equal in amount to the maximum possible gradient, since at time point t=a, at least the maximum deceleration controllable by the ACC is required. The deceleration requirement at point t=a lasts only a very short time, so that the curve in aSollStar-t diagram  230  does not reach triggering threshold  231 . Thus, no triggering signal is sent by block  106  to AND element  107  and, thus, the RTC-t curve in  240  remains at “0.” As a result, the request for taking control is not activated. 
   Between the two time points t=b and t=c, the preceding vehicle applies its brakes gently. Point t=b is the starting point in time of this gentle brake maneuver and point t=c is the end point in time of this brake maneuver. The distance dZO in diagram  210  decreases during this time, until the brake maneuver is ended at point in time t=c. The deceleration values aWarn in diagram  220  are so small in amount between t=b and t=c that triggering threshold  221  is not reached, since braking is so slight that the brake dynamics region of the ACC system is sufficient for a corresponding deceleration. In the aSollStar-t diagram  230  this becomes noticeable in that the curve takes a flatter course, and the tangent having gradient triangle  233  is also flatter than in the situation at point t=a. Since the ACC system is able to make available sufficient deceleration from t=b to t=c, in the case of this gentle braking, the curve in the RTC-t diagram  240  remains at “0”, and, therefore, a request for taking control is not activated. 
   Between time points t=c and t=d, the preceding vehicle accelerates, which becomes noticeable by the increase in distance dZO and the decrease of the deceleration. 
   At point t=d, the preceding vehicle decelerates again, but very strongly this time. The value of aWarn immediately darts downwards and crosses the triggering threshold  221  of aWarn. The value of aSollStar drops off at the maximum steepness  232  possible, and reaches triggering threshold “aMaxDecel+Offset 2 ”  231  at point in time t=e. 
   As of point in time t=e, both triggering criteria are simultaneously fulfilled, and triggering the request for taking control takes place as described in  FIG. 1 , by the AND element  107  and the OR element  108 . Activation of the request is represented in the RTC-t diagram  240  by the transition from “0” to “1” at point t=e. At this point in time, the driver is informed that the deceleration of the ACC system is not sufficient to prevent a collision. 
   At time point t=f the driver steps on the brake pedal in order to achieve a greater deceleration than may be made available by the ACC system. As the driver intervenes by braking at point t=f, the ACC system is simultaneously deactivated. 
   Triggering thresholds  221  and  231  are not constant values, but rather are variable thresholds, which may be made functions of parameters such as speed. However, curves “aWarn(t)”  220  and aSoll(t)”  230  are normalized in each case with respect to thresholds  221  and  231 , for the purpose of making  FIG. 2  more understandable. The normalization causes the variable thresholds themselves to appear as constant values on the diagrams of  FIG. 2  (i.e., as horizontals in the diagram). 
   The calculation of aWarn may take into consideration not only the necessity of reducing the present relative speed within the distance available dWarn, but also the absolute deceleration of the target object which has to be additionally produced to avoid a collision. The value dWarn may further be modified by a factor fWarn, to take into account the time gap or a driving program predefined by the driver. 
   If the request for taking control is triggered at time point t=e, the system may either alarm the driver for a fixed, definite time period, or it may alarm the driver until the triggering criteria are no longer fulfilled. Necessarily, the request has to be activated for a minimum time, since even during a very short alarm period, the alarm must be noticeable to the driver and clearly understandable. Further, the system may also require a minimum time period to elapse between two requests for taking control, so as not to overload the driver with ACC alarms. 
   Beside changing the request for taking control by time conditions, one may also do it as a function of distance conditions. For example, a request for taking control that is once activated may remain until a minimum distance from the target object has been achieved or until the distance from the target object increases. 
   In the RTC-t diagram illustrated in  FIG. 2 , the deactivation of the request for taking control in the form of a negative transition from “1” to “0” is not shown, since this would have a different profile depending on time duration and resetting conditions. 
   By the use of the measures described in one of the mentioned example embodiments, the probability of a false activation of the ACC request for taking control may be drastically reduced. The motor vehicle driver may, thereby, have more trust in the request for taking control than in conventional systems, and the request for taking control will be received more meaningfully at the same time. 
     FIG. 3  shows a possible functional sequence scenario which can occur during operation of the vehicle under ACC, according to an example embodiment of the present invention. At a, an additional object of reflection suddenly appears from nowhere, which is at a very short distance from the ACC-controlled vehicle, is detected for only a very short time, and disappears again just as suddenly. Between b and c, the preceding vehicle applies its brakes gently. It follows that b is the starting point in time of this gentle brake maneuver and that c is the end point in time of this brake maneuver. At point d, the preceding vehicle decelerates again, but not very strongly this time. At e, both triggering criteria are simultaneously fulfilled, and triggering the request for taking control takes place as described in  FIG. 1 , by the AND element  107  and the OR element  108 . This is illustrated in  FIG. 2 , in the RTC-T diagram  240  by the curve jumping from “0” to “1” at point t=e. At this point in time e the driver is informed that the deceleration of the ACC system is not sufficient to prevent a collision. At f, the driver decides to step on the brake pedal in order to achieve a greater deceleration than could be made available by the ACC system. As the driver intervenes by braking at f, the ACC system is simultaneously deactivated.