Patent Publication Number: US-2021163000-A1

Title: Method and system for distance control of a subject vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/EP2019/057299, filed on Mar. 22, 2019, and claims benefit to German Patent Application No. DE 10 2018 109 235.0, filed on Apr. 18, 2018. The International Application was published in German on Oct. 24, 2019 as WO 2019/201555 A1 under PCT Article 21(2). 
    
    
     FIELD 
     The invention relates to a method for distance control of a subject vehicle and to an adaptive cruise control. 
     BACKGROUND 
     The fuel consumption of utility vehicles, in particular trucks, is substantially determined by the air resistance, in particular on longer trips at uniform velocity. A zone having turbulence and lower air pressure, which zone is also referred to as a slipstream, forms behind a truck. If a following vehicle travels sufficiently close behind the front vehicle, the fuel consumption of the rear vehicle thus decreases; however, in the case of trucks having a travel velocity of, for example, 80 to 100 km/h, distances of significantly less than the typical safety distance of, for example, 50 m are necessary for this purpose, but a sufficiently large safety distance is necessary so that the rear vehicle can brake sufficiently quickly, for example, in the event of abrupt braking of the front vehicle. 
     Autonomous adaptive cruise controls (ACC) are used as comfort systems and generally have an environmental detection system, for example, a radar device, to consistently control a distance to the front vehicle by autonomous braking interventions and also engine interventions. As comfort systems, the maximum deceleration and the braking ramps, i.e., the change over time of the deceleration, are limited. However, the distances provided for this purpose are too large to enable slipstream driving of a rear vehicle. 
     Furthermore, AEBS (Advanced Emergency Brake Systems) are known, which engage as emergency braking systems if an accident is immediately imminent and probably can no longer be prevented by the driver alone. For an AEBS, an AEBS cascade is provided, according to which firstly a first warning is output, for example, optically, acoustically, or haptically, before the emergency braking, for example, at least 1.4 seconds before. In this way, the driver is given the opportunity to react thereto; the driver can thus, for example, depending on the traffic situation, initiate an evasive maneuver and change the lane, or initiate braking himself. After the first warning, partial braking can be initiated. Shortly before the emergency braking, a second warning is output and then the full braking, i.e. at full brake pressure, is initiated as emergency braking. 
     In platooning systems or systems for initiating automated convoy driving (column driving), two or more vehicles have a data connection to one another (V2V, vehicle-to-vehicle communication). The vehicles of the group or convoy can communicate with one another in this way, so that, for example, the front vehicle at once communicates an immediately imminent or initiated braking to the rear vehicles, and therefore the rear vehicles do not first have to detect the braking process of the front vehicle, but rather can immediately initiate a corresponding braking process, in particular using brake pressures and/or target decelerations adapted to one another. Such platooning systems permit very low distances of, for example, 15 m to the respective front vehicle and thus a significant fuel saving. However, they presume a corresponding V2V data connection between the vehicles having standardized command sets, wherein the technical equipment, for example, the state of the brakes, also has to be sufficiently adapted. 
     SUMMARY 
     In an embodiment, the present invention provides a method for distance control of a subject vehicle in relation to a front vehicle. The method includes setting, by an adaptive cruise control of the subject vehicle, an automatic distance control mode, wherein: a front object in front of the subject vehicle is detected by an environmental detection system of the subject vehicle, the front object is recognized as the front vehicle, and a distance to the front vehicle is regulated to an adaptive cruise control (ACC) target distance. The method further includes establishing that a safe following driving situation is present based on at least one of the following criteria being met: the front vehicle is a moving object, the front vehicle is tracked over at least a minimum following period, the front vehicle is tracked in a minimum following period, the distance to the front vehicle is within a predetermined distance range, or a relative velocity is within a predetermined velocity tolerance range. The method additionally includes outputting, to a driver upon establishing that the safe following driving situation is present, a display signal, and setting, upon input of a confirmation signal by the driver, an automatic distance control platooning mode. The automatic distance control platooning mode has a shorter target distance than the ACC target distance of the automatic distance control mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  shows a side view of a column made up of two vehicles with a front vehicle and a subject vehicle in a top view; 
         FIG. 2  shows the corresponding illustration with a merging vehicle; 
         FIG. 3  shows a block diagram of a control system according to an embodiment; 
         FIG. 4  shows a flow chart of a method according to an embodiment; 
         FIG. 5  shows time diagrams of the velocities and accelerations in the ACC mode and in the ACC-P mode; 
         FIG. 6  shows time diagrams of the velocities and accelerations in the AEBS mode and in the ACC-P mode; and 
         FIG. 7  shows a design modified in relation to  FIG. 3  having additional CC control unit. 
     
    
    
     DETAILED DESCRIPTION 
     Problems occur in the typical environmental detection systems based on radar detectors or radar measuring devices. Radar systems can incorrectly recognize objects which are fundamentally traversable as stationary obstacles (for example, bridges). Foliage or paper on the road can also be incorrectly recognized as a collision-causing stationary object. As a result, limits are placed on expansions of ACC or AEBS systems. 
     The present disclosure therefore provides a method for distance control and an adaptive cruise control for a subject vehicle, which enable a high level of safety and the possibility of economical driving with low fuel consumption. 
     A method according to the disclosure can be carried out in particular using an adaptive cruise control; an adaptive cruise control according to the disclosure can, in particular, use a method according to the disclosure. 
     An adaptive cruise control of the vehicle, upon detecting a front object using its environmental detection system, in particular a radar device, automatically checks whether the conditions are met to initiate a distance control method at reduced distance. Such a distance control method having reduced distance or ACC-P takes place here without data connection to a front vehicle, i.e., it does not represent a platooning system. Accordingly, only a first safety distance is advantageously also set, which is significantly greater than the safety distances possible with platooning systems. 
     However, changes are performed in relation to an ACC system, said changes being provided, on the one hand, upon initiation as selection criteria, in order to select only suitable front vehicles; furthermore, changes in relation to a conventional ACC are advantageously provided in the control interventions. 
     The adaptive cruise control having reduced distance thus represents an ACC-platooning mode or ACC-P mode or ACC-P as an adaptive cruise control having reduced safety distance without a data connection to the front vehicle. 
     The following are provided in particular as suitable criteria or selection criteria: the environmental detection system, in particular the radar device of the vehicle, detects a moving object in front of the subject vehicle. In particular when a radar device is used, significant advantages are thereby afforded, since the radar system limits relate to stationary objects in particular and spurious detections generally do not occur in the case of moving objects. 
     According to a further criterion, the front vehicle is tracked at least for a minimum time or minimum tracking time, for example, having an object lifetime &gt;30 s. It is thus possible in an automated manner to recognize that the front vehicle is carrying out correspondingly uniform, calm driving, which is sufficient for forming a convoy-type system. 
     According to a further criterion, the relative velocity or differential velocity between the front vehicle and the subject vehicle is sufficiently low or close to 0 m/s, as a result of which convoy-type driving is again ensured. 
     According to a further criterion, the distance between the front vehicle and the subject vehicle is sufficiently constant, i.e., for example, a change of the distance is less than a distance limiting value, as a result of which convoy-type driving is again ensured. 
     Furthermore, supplementary criteria or selection criteria can be provided. It is thus possible for the front vehicle to be classified, wherein then a suitable object class can be provided as a criterion, for example, the object class truck, so as not to follow a vehicle which will more likely select a nonmatching driving style. Furthermore, the front vehicle can be detected with respect to its width and/or height. In this case, a criterion which can be set is that the width or height is constant. The vehicle width and/or vehicle height can also be in a suitable range, for example, a vehicle width of 2.5 m. It is also ensured in this way that the slipstream produced by the front vehicle matches with the subject vehicle, since when following another object, for example, a passenger vehicle, no relevant fuel saving can be anticipated and instead again it is rather more possible for the front vehicle to be driven less calmly or unsuitably, which can only raise safety problems. 
     According to a further criterion, it can be provided that the ACC is already switched on in the subject vehicle. However, it can also be provided that the environmental detection system already checks whether ACC-P is possible even when the ACC is not yet switched on. 
     As soon the subject system or the ACC control unit of the adaptive cruise control has established that the designated criteria are met, it preferably first gives a notification to the driver, for example, optically, but also, for example, acoustically or haptically. In this way, the driver is asked whether he wishes to select the ACC-P mode. If the driver gives a confirmation signal in response to said display signal or query signal, for example, by pressing a button in the dashboard, to the ACC control unit, the latter thus subsequently starts the ACC-P mode. 
     Different settings are then set in the ACC-P mode in relation to a conventional ACC. The safety distance or control distance to the front vehicle is thus shortened in particular. 
     The ACC-P also has differences in relation to an AEBS. Thus, the provided AEBS cascade made up of warning-partial braking-full braking is advantageously shortened and can enable solely warning-full braking or also braking directly, for example, as partial braking or also full braking, since the entire autonomous braking process is already initiated from a reduced distance and thus time is not unnecessarily lost by the driver warning and reaction of the driver, which is problematic at the reduced control distance. Therefore, in spite of the short distance in the case of the ACC-P, a high level of safety can be ensured. However, a supplementary driver warning is preferably provided at least upon initiating emergency braking or full braking. 
     It can thus be provided in the ACC that a first target distance or safety distance and a subsequent, lesser safety distance are to be provided, wherein the ACC “plunges” into the first target distance until the second target distance or second safety distance is reached, which then represents an absolute limit. In contrast, in the ACC-P mode, no such division is provided, since the reduced target distance is already sufficiently close to the second safety distance. 
     In particular, the AEBS cascade already mentioned above can be reduced to direct braking, for example, to direct emergency braking. However, a driver warning is advantageously additionally provided in this case to inform the driver about the initiated emergency braking. 
     Furthermore, the cruise control function, i.e. a cruise control mode CC is preferably already set in the ACC mode ACC. A set velocity or target velocity is thus specified by the CC mode. The ACC mode ACC additionally set to the CC mode thus only restricts the engine torque, but does not increase the latter. In contrast, according to one advantageous embodiment, the ACC-P mode—in contrast to the ACC mode—can also actively request a higher engine torque than the CC-mode. In particular, separate control units can be provided for this purpose: the CC control unit gives engine request signals to the engine controller, and the ACC control unit limits only the engine torque in the ACC mode, but said ACC control unit can also request higher engine torques in the ACC-P mode. The advantage of an additional CC control unit in addition to the ACC control unit is that said control units can be installed modularly in the vehicle. A high level of flexibility is thus achieved. 
     This can take place directly according to one design, i.e. the ACC control unit has the option in the ACC-P mode of requesting a higher power via an engine request signal in the engine controller. According to a second embodiment alternative thereto, the ACC control unit sends an engine request signal to the CC control unit, which then optionally sends an engine request signal to the engine controller. According to a third embodiment, the ACC controller in the ACC-P mode, upon recognizing that the limiting of the engine torque is not sufficient to catch up sufficiently close to the front vehicle in the ACC-P mode, gives a display signal to the driver that he should increase the set velocity or target velocity of the CC; the driver thus enables the increase of the engine torque. 
     Furthermore, in the ACC-P mode, the maximum deceleration is advantageously significantly increased in relation to the ACC, for example, from 2.5 m/s 2  to 7.5 m/s 2 . According to a further advantageous design, more severe controls of the ACC-P are provided in comparison to the ACC, for example, steeper braking ramps, i.e. changes over time of the target decelerations, a braking ramp of 2.5 m/s 3  can thus be set to double that or more, for example, so that the exerted acceleration is also increased faster—in relation to the absolute value. 
     Emergency braking is thus also automatically achieved faster, comparably to the sudden pressing of the brake pedal for full emergency braking. 
     Furthermore, in the ACC-P—in contrast to the ACC—a higher deceleration can be requested than that of the front vehicle, to keep the distance constant or also increase it in this way. Thus, for example, it can also be provided that, upon recognition of a deceleration of the front vehicle, a greater deceleration of the subject vehicle is intentionally set. This is based on the consideration that, owing to the measurement principle of the environmental detection system, for example, a radar device, firstly the front vehicle has to decelerate first so that the environmental detection system of the following vehicle measures this deceleration and reacts thereto. During a braking process or deceleration process of the front vehicle, the following vehicle would thus initially react with a time delay in each case, so that even with identical deceleration of both vehicles, a continuous distance reduction can occur. By the following vehicle intentionally requesting a higher target deceleration upon recognition of a deceleration process of the front vehicle, such a continuous distance reduction can be prevented. 
     The ACC control unit can in principle request in the ACC-P mode—as in the conventional ACC mode or also like an AEBS—target values by way of request signals or control signals at the engine control unit and the brake control unit, for example, a target deceleration or a target acceleration torque. A conventional ACC generally attempts to use the sustained-action brakes or retarder of the vehicle to keep the wear of the service brakes (deceleration) low. However, this control strategy is advantageously changed in the ACC-P mode. It can thus be provided that the sustained-action brakes are not used at all, or the sustained-action brake is requested only for lower target decelerations. 
     The ACC-P mode is advantageously immediately ended when one of the criteria is no longer met. It is also immediately ended when a merging process of a vehicle from an adjacent lane is recognized. If the merging driving object is then detected by the environmental detection system, the above-mentioned criteria thus firstly have to be met again so that the ACC-P mode is proposed to the driver. 
     A subject vehicle  1  drives on a roadway (road)  2 , according to the top view of  FIG. 2  on a separate lane  2   a . A front vehicle  3  drives in front of the subject vehicle  1 , which front vehicle does not have a data connection or a data connection with autonomous transmission of driving dynamics data and/or control signals for vehicle interventions, in particular braking processes, to the subject vehicle  1 . 
     The subject vehicle  1  has as the first environmental detection system a radar device  4 , using which a distance d to a front object  3  can be detected. In addition, the subject vehicle  1  can also have yet further environmental detection systems, for example, a camera  5 , which is not required in principle, however. The subject vehicle  1  furthermore has an adaptive cruise control  8 , which has the first environmental detection system  4  and an ACC control unit  10 , wherein the ACC control unit  10  of the adaptive cruise control  8  records first measurement signals Si and outputs engine request signals S 2  to an engine control unit  12  to activate a vehicle engine, and brake request signals S 3  to a brake control unit  14  to activate, on the one hand, service brakes (friction brakes)  15  and furthermore a retarder (non-wearing brake, sustained-action brake)  16 . 
     The ACC control unit  10  can set various modes. Thus, a normal driving mode M 0  can be present, and an autonomous distance control mode ACC can be set, in which the environment is detected in a known manner via at least the first environmental detection system, i.e. the radar device  4 , and possibly also via the camera  5 , so that a constant spatial distance d and/or time interval dt at constant differential velocity Δv=0 can be set between the front vehicle  3  and the subject vehicle  1 , i.e. as an autonomous distance keeping system. 
     In principle, the adaptive cruise control  8  can additionally also have a platooning mode, in which it exchanges signals with further vehicles, for example, the front vehicle  3 . In the method described hereinafter, however, no data transfer takes place with the front vehicle  3 , to set a short distance d by way of such a platooning system. 
     Furthermore, the adaptive cruise control  8  can have an AEBS as an autonomous emergency braking method, so that, upon recognition of an emergency braking situation, the AEBS cascade made up of driver warning, partial braking, and emergency braking is automatically initiated. The AEBS can also be initiated automatically from an ACC mode in particular. 
     A slipstream or drag zone  18  arises behind the front vehicle  3 , in which fundamentally turbulence and a slight negative pressure arise. The subject vehicle  1  experiences either the normal travel wind  21  or additional turbulence in the normal driving mode MO and also in the ACC mode ACC, but does not enter the drag zone  18 , to achieve slipstream driving with reduced fuel consumption in this way. 
     The ACC control unit  10  is furthermore designed to pass from the normal ACC into an automated distance control platooning mode ACC-P. 
     The ACC control unit  10  can thus set a normal driving mode MO, an ACC mode ACC, and the automatic distance control platooning mode, abbreviated ACC-P mode, ACC-P. 
     In this case, the ACC control unit  10  sets the ACC-P if it recognizes according to the flow chart of  FIG. 4  that the criteria (decision criteria) K 1  to at least K 5  are met. In this case, a following driving situation FS with respect to the front vehicle  3  is to be recognized in particular, which ensures sufficient safety. After the start St 0 , measurement signals S 1  are thus recorded via the first environmental detection system in step St 1 . The following criteria are then evaluated in step St 2 :
         First criterion K 1 : the radar device  4  detects as the front object a front vehicle  3 , i.e., a moving object: the effect also achieved by this means, in particular, is that the radar system limits, which are problematic in the case of stationary objects, for example, the incorrect recognition of nonrelevant objects such as bridges and, for example, also dirt, paper, or road edges, can be excluded as distance objects. The knowledge is taken into consideration here that the detection of moving objects by a radar device  4  is very reliable.   Second criterion K 2 : furthermore, the front vehicle  3  is continuously detected over at least one minimum following period t_min,   Third criterion K 3 : the same object is always detected as the front vehicle  3 , i.e. no changing objects.   Fourth criterion K 4 : the ACC control unit  10  furthermore recognizes that the subject vehicle  1  drives at an approximately constant spatial distance d or time interval dt in relation to the front vehicle  3 . In this case, approximately constant is selected, for example, to be a following distance range of Δd_lim of ±1 m, or as a following time interval range Δt_lim of 0.1 seconds, i.e. with high consistency.   Fifth criterion K 5 : furthermore, the ACC control unit  10  recognizes that a relative velocity Δv=v 1 −v 3 , i.e. the difference of the inherent velocity of the subject vehicle to the velocity of the front vehicle  3  is approximately 0, i.e., for example, in a distance range of ±0.1 m/s. Approximately constant driving is thus present.       

     Further criteria can also be used in this case, for example, the following criteria:
         sixth criterion K 6 : the front vehicle  3  can be classified in a classification of vehicle types which does not change at least during the minimum following period (t min ). In this case, a classification in an applicable vehicle class is recognized, in particular as a truck. Other vehicle types such as passenger vehicle, tractors, etc. are not to be used in this case for safety reasons.   Seventh criterion K 7 : an object width b 3  of the front vehicle  3  is within a permissible range,   eighth criterion K 8 : the object width b 3  of the front vehicle  3  is constant within a measurement accuracy,   ninth criterion K 9 : a relative transverse velocity (Δvy) of the front vehicle  3  in relation to the subject vehicle is less than a transverse velocity limiting value (Δvy_tres),   tenth criterion K 10 : an object height h 3  of the detected front vehicle  3  is within a permissible range,   eleventh criterion K 11 : the object height h 3  is constant within a measurement accuracy.   In particular, the twelfth criterion K 12  can be provided: the ACC is already active before an ACC-P is offered. The ACC-P is thus only offered from the safe ACC, in which an ACC target distance d_ACC is therefore already autonomously regulated.   Thirteenth criterion K 13 : the spatial distance d and/or the time interval dt with respect to the front vehicle  3  is sufficiently constant. For this purpose, it can be checked, for example, whether a change over time dd of the spatial distance d and/or a change over time ddt of the time interval dt is less than a distance limiting value d_tres.       

     As soon the ACC control unit  10  thus recognizes that the required criteria K 1  to K 5  and possibly further criteria are met, it suggests, according to branch y in step St 3 , the ACC-P mode ACC-P, by outputting a query signal or display signal S 4  at a display unit  22 , for example, in the dashboard region of the driver. If the driver, in step St 4  according to branch y, confirms this display by a confirmation signal S 5 , for example, by pressing a corresponding actuating unit  23  or a pushbutton, the ACC control unit  10  will subsequently set the ACC-P mode ACC-P upon receiving the confirmation signal S 5  according to step St 5  and for this purpose will correspondingly output request signals S 2 , S 3  to the engine control unit  12  and to the brake control unit  14 . 
     In the ACC-P mode ACC-P, the ACC control unit  10  automatically regulates the ACC target distance d_ACC by outputting engine request signals S 2  and brake request signals S 3 . 
     More abrupt braking actions are permissible in ACC-P. Thus, for example, in the ACC-P mode ACC-P, a maximum ACC deceleration is increased from the ACC value 2.5 m/s 2 , for example, to 7.5 m/s 2 , i.e. significantly more abrupt braking actions are permissible. A severity control also takes place in such a way that the ACC braking ramps are set steeper or faster in the ACC-P mode ACC-P, i.e. as higher changes over time of the deceleration, in m/s 3 . 
     Furthermore, the brake control unit  14  is activated in such a way that the priorities of conventional braking are changed in the ACC mode: 
     In the ACC mode ACC, the sustained-action brake or retarder  16  is given priority over the service brakes  15  to keep the brake wear low. In contrast, this priority is dispensed with in the ACC-P mode ACC-P, and therefore here owing to greater safety and faster effectiveness, the service brakes  15  are preferably activated. 
     The engine control unit  12  is accordingly activated using different parameters. The engine limit can thus be reduced in the ACC-P mode ACC-P, and therefore in the context of the set ACC-P target velocity, the vehicle drives at correspondingly equal velocity as the front vehicle  3 . 
     The ACC-P mode ACC-P is advantageously ended in this case by the ACC control unit  10  if at least the basic criteria K 1  to K 5 , or also all criteria set at the beginning are no longer met. 
     In particular upon merging of the third object  7  from a further lane  2   b  between the front vehicle  3  and the subject vehicle  1 , the ACC-P mode ACC-P can be ended immediately. The subject vehicle  1  subsequently then follows the third object  7  which has merged in between and can switch on the ACC-P mode ACC-P again only after meeting the criteria K 1  to K 5 . 
       FIG. 5  shows a braking process in the ACC mode and in the ACC-P mode in each case as a time diagram of the velocity v and the acceleration a, which is plotted here downward or in the negative range, since decelerations, i.e. negative accelerations, are present.  FIG. 6  accordingly shows such a comparison between the AEBS mode and the ACC-P mode. 
     In  FIG. 5 , the front vehicle  3  decelerates strongly or performs emergency braking at the time t 0 . The radar device  4  also detects this; however, a strong deceleration is not immediately executed in the ACC mode, but rather the ACC control unit  10  firstly limits at a first time t 1  the engine torque MM, then requests the first retarder  16  from the brake control unit  14  at a second time t 2  and—if provided—a second retarder later at a third time t 3 , and the service brakes  15  only in the fourth step at a fourth time t 4 . All of these requests are executed in the form of ramps for reasons of comfort, so that the starting phase b 0  (after detection of the braking process of the front vehicle  3 ) and the four braking phases b 1 , b 2 , b 3 , b 4  of the ACC result after the first to fourth times t 1  to t 4 . 
     The ACC-P or the ACC-P mode can in particular immediately upon recognizing a deceleration of the front vehicle  3 , firstly in a retarder braking phase bbl. request a maximum (i.e. full) braking torque M 16 _max from the retarder  16  or also the multiple retarders/sustained-action brakes, also without ramps, i.e., suddenly at an acceleration value a_bb 1 . In a subsequent service brake phase bb 2 , the ACC-P can suddenly request maximum (i.e. full) deceleration a_bb 2  from the service brakes  15 , if the situation is identified as extremely critical. However, the ACC-P can also immediately request full deceleration a_bb 2  from the service brakes  15 , see the following comparison of  FIG. 6 . 
     According to  FIG. 6 , the radar device  4  again detects at a (start) time t 0  that the front vehicle  3  is strongly decelerating or performing emergency braking. The ACC control unit  10  does not carry out emergency braking immediately in the AEBS mode. Certain criticality criteria KK first have to be met, i.e. it has to be sufficiently critical, then first the first warning comes at the first time t 1 , then the second warning at the second time t 2 , which is accompanied by a partial braking apart and then the full braking a_max. 
     In the ACC-P mode, in contrast, the ACC control unit  10  can immediately carry out emergency braking or full braking at a_max according to the dot-dash line, i.e., from the (start) time to, as soon as a strong deceleration a 3 &gt;a 3 _tres of the front vehicle  3  is recognized. 
       FIG. 7  shows an embodiment modified in relation to  FIG. 3 , in which a CC control unit  13  is installed in the subject vehicle  1 , which CC control unit executes a cruise control function and is activated in each case before the setting of an ACC mode. The CC control unit  13  thus outputs engine request signals S 2   a  and brake request signals S 3   a  to the control units  12 ,  14 . In this case, the ACC control unit  10  and the CC control unit  13  are often supplied by different producers. In the ACC mode, there is no communication from the ACC control unit  10  to the CC control unit  13 . 
     If the ACC control unit  10  recognizes that the present maximum engine torque is not sufficient so that in the ACC-P mode the subject vehicle  1  can catch up to the front vehicle  3 , various embodiments can thus be provided to request a higher maximum engine torque: according to a first embodiment for this purpose, the ACC control unit  10  can request a higher power, i.e. a higher maximum engine torque directly at the engine controller  12  via an engine request signal S 3 . 
     According to a second embodiment, the ACC control unit  10  can output engine torque request signals S 6  in the ACC-P mode to the CC control unit  13 , so that the CC control unit  13  requests a higher engine torque via an engine request signal S 2   a , and therefore the subject vehicle  1  can catch up to the front vehicle  3 . 
     According to a third embodiment, the ACC control unit  10  outputs in the ACC-P mode, upon recognizing that the limiting of the engine torque is not sufficient to catch up close enough to the front vehicle  3  in the ACC-P mode, a display signal S 4  to the driver that he should increase the set velocity or target velocity of the CC; the driver thus enables the increase of the engine torque at the CC control unit  13 , which outputs an engine request signal S 2   a  for a higher maximum engine torque. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 
     LIST OF REFERENCE CHARACTERS 
       1  subject vehicle 
       2  roadway, road 
       2   a  own lane 
       3  front object, in particular front vehicle 
       4  first environmental detection system, radar device 
       7  third object 
       8  adaptive cruise control 
       10  ACC control unit 
       12  engine control unit 
       13  CC control unit 
       14  brake control unit 
       15  service brakes 
       16  retarder, sustained-action brake 
       22  display unit 
       23  actuating unit 
     ACC distance control mode or adaptive cruise control 
     ACC-P distance control platooning mode 
     d spatial distance of the subject vehicle  1  in relation to the front vehicle  3   
     dt time interval of the subject vehicle  1  in relation to the front vehicle  3   
     d_ACC ACC target distance 
     d_P ACC-P target distance 
     Δd_lim spatial distance range 
     Δt_lim time interval range 
     Δd_ACC-P target spatial distance of the ACC-P 
     Δt_ACC-P target time interval of the ACC-P 
     ddt, dd change over time of the time interval dt 
     ddt, dd change over time of the spatial distance d 
     d_tres distance limiting value 
     t 0  (start) time 
     t 1  first time 
     t 2  second time 
     t 3  third time 
     Δvy_tres transverse velocity limiting value 
     Δvy relative transverse velocity 
     Δv relative velocity 
     FS safe following driving situation 
     S 1  measurement signals 
     S 2  engine request signal 
     S 3  brake request signal 
     S 4  query signal to the driver 
     S 5  confirmation signal by the driver 
     S 6  engine torque request signal 
     S 2   a  engine request signal of the CC control unit  13   
     S 3   a  engine request signal of the CC control unit  13   
     K 1  to K 12  decision criteria