Abstract:
An object candidate position detecting apparatus which detects a position of an object candidate includes a unifying mechanism which unifies a plurality of object candidates detected within a predetermined unified range into a single group. Where the relative positions of the object candidates stored in a unified information storage device changes such that the single group splits into a plurality of groups, a tracking mechanism judges whether any object candidate forming the group before the split continuously remains to be detected in a running lane in which a subject vehicle runs and which is estimated by a running lane estimator. Where any object candidate forming the group before the split is determined as continuously remaining to be detected in the running lane, the tracking mechanism determines that there is continuity between a group after the split including the thus-determined object candidate and the group before the split.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Japanese Application No. JP 2009-052283, filed Mar. 5, 2009, the entire specification, claims and drawings of which are incorporated herewith by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an object detecting apparatus for a vehicle for accurately tracking targets by grouping multiple targets detected by a transmitting/receiving mechanism in each predetermined detection cycle; and making a judgment on continuity between a group of targets detected in a previous detection cycle and a group of targets detected in a current detection cycle. 
     2. Description of the Related Art 
     Japanese Patent No. 3959100 (JP &#39;100) discloses a drive control apparatus for a vehicle for controlling a driving condition of a subject vehicle relative to a representative point of a group into which multiple objects are unified by a unifying means when the multiple objects are detected within a predetermined range based on the transmission and reception results of an electromagnetic wave by a radar apparatus. 
     However, the drive control apparatus disclosed by JP &#39;100 suffers from a drawback of when a group into which the multiple objects are unified by the unifying means splits into two groups, tracking the two groups is not adequately performed. Hence, vehicle control is inadequately performed relative to one of the split groups which does not include the vehicle running in front of the subject vehicle. A reason why such a drawback exists in the drive control apparatus disclosed in JP &#39;100 is described in the following section entitled “DETAILED DESCRIPTION OF THE INVENTION” with reference to  FIGS. 5 to 7B . 
     SUMMARY OF THE INVENTION 
     The present invention has been attained with at least the above-described drawback in the related art being taken into consideration. An aspect of the present invention is to perform adequate tracking when a single group into which the object candidates are unified by the unifying means splits into two or more groups. 
     According to a first feature of the present invention, an object detecting apparatus for a vehicle is provided that includes a transmitting/receiving mechanism which transmits an electromagnetic wave in a driving direction of a subject vehicle at predetermined intervals and which receives a reflected wave from an object, the transmitting/receiving mechanism being installed in a vehicle; an object candidate position detecting mechanism which detects a position of an object candidate based on a result of the transmission and reception performed by the transmitting/receiving mechanism; a unifying mechanism which unifies or arranges a plurality of object candidates into a single group in a case where the plurality of object candidates are detected within a predetermined unified range; a group representative point calculating mechanism which calculates a representative point of the group unified by the unifying mechanism; a tracking device which judges whether there is continuity between a group made in a previous detection cycle and a group made in a current detection cycle based on the group representative point calculation; and an object information outputting mechanism which outputs a representative point of a group after a split, based on an output from the group representative point calculating mechanism and an output from the tracking device. The apparatus also includes a unified information storage device which stores the object candidates constituting each group; and a running lane estimating mechanism which estimates a running lane in which the subject vehicle runs. The afore-mentioned components are configured and arranged such that in a case where a change in the relative positions of the plurality of object candidates of the single group splits the single group into a plurality of groups having representative points located in different lanes, the tracking device judges whether any of the object candidates constituting the group before the split continuously remains to be detected in a running lane including the representative point of the group before the split based on an output from the unified information storage device and an output from the running lane estimating mechanism, and in a case where any of the object candidates constituting the single group before the split is determined as continuously remaining to be detected in the running lane, the tracking device determines that there is continuity between a group after the split including the thus-determined object candidate and the group before the split. 
     With the above described structural configuration, when the object candidate position detecting mechanism detects a position of an object candidate based on the result of the transmission and reception of the electromagnetic wave performed by the transmitting/receiving mechanism, the unifying mechanism unifies a plurality of object candidates detected within the predetermined unified range as a single group and then the group representative point calculating mechanism calculates a representative point of the unified group. Thereafter, the tracking device judges whether there is continuity between the group made in the previous detection cycle and the group made in the current detection cycle based on the representative positions of the groups. In this regard, in a case where the relative positions of the object candidates stored in the unified information storage device changes and thus the single group splits into a plurality of groups, the tracking device judges whether any of the object candidates constituting the group before the split continuously remains to be detected in the running lane in which the subject vehicle runs and which is estimated by the running lane estimating mechanism; and in a case where any of the object candidates constituting the group before the split is determined as continuously remaining to be detected in the running lane, the tracking device determines that there is continuity between the group after the split including the thus-determined object candidate and the group before the split. Accordingly, it is possible to prevent performing an inappropriate vehicle control by erroneously associating the group detected in the subject vehicle&#39;s lane with the split group in a lane other than the subject vehicle&#39;s lane. 
     According to a second feature of the present invention, the tracking device sets up an emergence estimation area where an object candidate detected in a previous detection cycle is expected to be detected in a current detection cycle. Thus, in a case where an object candidate is detected in the emergence estimation area, which is situated in the running lane including the representative point of the group before the split, the tracking device determines that any of the object candidates constituting the group before the split is continuously detected in the running lane, including the representative point of the group before the split. 
     With the above described structural configuration, since the tracking device sets up the emergence estimation area, and in a case where the object candidate is detected in the emergence estimation area, the tracking device determines that any of the object candidates constituting the group before the split is continuously detected in the running lane including the representative point of the group before the split, it is possible to prevent erroneously associating the object candidates of the group before the split with the group after the split, including the different object candidates. 
     According to a third feature of the present invention, the tracking device sets up the emergence estimation area as an area extending longitudinally and transversely which is included within a predetermined range from a previous position of the object candidate. 
     With the above described structural configuration, since the tracking device sets up the emergence estimation area as an area extending longitudinally and transversely which is included within a predetermined range from a previous position of the object candidate, it is possible to reliably confirm the corresponding relationship between the previous position and the current position of the object candidate. 
     According to a fourth feature of the present invention, the running lane estimating mechanism estimates the running lane in which the subject vehicle runs based on a vehicle speed of the subject vehicle detected by a vehicle speed sensor and a yaw rate of the subject vehicle detected by a yaw rate sensor. 
     With the above described structural configuration, since the running lane estimating mechanism estimates the running lane in which the subject vehicle runs based on a vehicle speed and a yaw rate of the subject vehicle, it is possible to easily estimate the running lane and to do so with high precision. 
     According to a fifth feature of the present invention, the group representative point calculating mechanism calculates a transverse location of a representative point of a group as a middle position between leftmost and rightmost object candidates among the plurality of object candidates, and also calculates a longitudinal location of the representative point of the group as a position of an object candidate which is the nearest to the subject vehicle among the plurality of object candidates. 
     With the above described structural configuration, since the group representative point calculating mechanism calculates a transverse location of a representative point of a group as a middle position between leftmost and rightmost object candidates among the plurality of object candidates, and calculates a longitudinal location of the representative point of the group as a position of an object candidate which is the nearest to the subject vehicle among the plurality of object candidates, it is possible to make the obtained representative position of the group accurate. 
     The above description, other aspects, characteristics and advantages of the present invention will be clear from detailed descriptions which will be provided for the preferred embodiment referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an object detecting apparatus for a vehicle according to a preferred embodiment of the present invention; 
         FIG. 2  is a schematic diagram of a FMCW (Frequency Modulated Continuous Wave) radar system; 
         FIGS. 3A and 3B  are graphs showing a waveform and a peak frequency of transmitted/received waves when an object approaches a transmitting/receiving mechanism; 
         FIGS. 4A and 4B  are graphs showing a peak signal; 
         FIG. 5  is a schematic diagram used to explain operation of a unifying mechanism and a group representative point calculating mechanism; 
         FIG. 6  is a schematic diagram used to explain a case in which a front-running vehicle and an adjoining vehicle are unified into a single group; 
         FIGS. 7A and 7B  are sketches used to explain a drawback that occurs when operating a conventional tracking mechanism; 
         FIGS. 8A and 8B  are sketches explaining how the tracking device of the present invention operates; 
         FIG. 9  is a flowchart of a main routine; and 
         FIG. 10  is a flowchart of a subroutine of step S 8  of the main routine shown in  FIG. 9 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A detailed description of a preferred embodiment of the present invention is provided below while referring to  FIGS. 1 to 10 . 
     As shown in  FIG. 1 , an FMCW (Frequency Modulated Continuous Wave) radar system R includes a transmitting/receiving means M 1 , an object candidate position detecting means M 2 , a unifying means M 3 , a group representative point calculating means M 4 , a tracking means M 5 , an object information outputting means M 6 , a unified information storage means M 7 , and a running lane estimating means M 8 . A vehicle speed sensor Sa and a yaw rate sensor Sb are connected to the running lane estimating means M 8 . A vehicle controlling means M 9  having an electronic control unit U is connected to the object information outputting means M 6 . A brake actuator Aa and a throttle actuator Ab are connected to the vehicle controlling means M 9 . 
     The configuration of the FMCW radar system R will now be provided while referring to  FIGS. 2 to 4 . 
     As shown in  FIG. 2 , the transmitting/receiving means M 1  is configured to include a timing signal generating circuit  1 , an FM modulation controlling circuit  2 , an oscillator  3 , an amplifier  4 , a circulator  5 , and a transmission/reception antenna  6 . Based on a timing signal inputted from the timing signal generating circuit  1 , the FM modulation controlling circuit  2  modulates and controls oscillation of the oscillator  3 . Thus, as shown by a solid line in  FIG. 3A , the frequency of the signal is modulated into a frequency with triangular waveforms. The thus-modulated transmission signal from the oscillator  3  is inputted into the transmission/reception antenna  6  through the amplifier  4  and the circulator  5 . As such, an FMCW wave is transmitted from the transmission/reception antenna  6 . When an object, such as a front-running vehicle, is ahead of the transmission/reception antenna  6 , a reflected wave resulting from the transmitted wave reflecting off of the object is received by the transmission/reception antenna  6 . The reflected wave appears, for instance, as shown by a broken line in  FIG. 3A , when the object ahead comes closer. On each increase side where the frequency of the transmitted wave linearly increases, the reflected wave appears with a frequency lower than that of the transmitted wave, and appears later than the transmitted wave. On each decrease side where the frequency of the transmitted wave linearly decreases, the reflected wave appears with a frequency higher than that of the transmitted wave, and appears later than the transmitted wave. 
     The radar system R further includes a mixer  7 , additional amplifiers  8  and  9 , an A/D converter  10 , a memory  11 , and a central processing unit C. The central processing unit C defines the object candidate position detecting means M 2 , the unifying means M 3 , the group representative point calculating means M 4 , the tracking means M 5 , the object information outputting means M 6 , the unified information storage means M 7 , and the running lane estimating means M 8 . 
     The received wave received by the transmission/reception antenna  6  is inputted into the mixer  7  through the circulator  5 . In addition to the received wave from the circulator  5 , a transmitted wave, which is distributed from the transmitted wave outputted from the oscillator  3 , is inputted into the mixer  7  through the amplifier  8 . The mixer  7  mixes the transmitted wave and the received wave. Thereby, as shown in  FIG. 3B , the mixer  7  generates a beat signal which has a peak frequency Fup on each increase side where the frequency of the transmitted/received wave linearly increases; and a peak frequency Fdn on each decrease side where the frequency of the transmitted/received wave linearly decreases. 
     The beat signal obtained by the mixer  7  is amplified to a predetermined amplitude level by the amplifier  9 . The resultant beat signal is converted from analog to digital by the A/D converter  10  at each sampling time. Thus, a digitalized data set is stored and retained in chronological order in the memory  11 . The timing signal is inputted into the memory  11  from the timing signal generating circuit  1 . In response to the timing signal, the memory  11  stores and retains the data set on each increase side where the frequency of the transmitted/received signal increases, and on each decrease side where the frequency thereof decreases. 
     Based on the data set stored in the memory  11 , the central processing unit C calculates an angle, distance and relative speed, at which the object is detected, based on the subject vehicle, and sends the calculation results to the electronic control unit U in a manner that is described below. Upon reception of the signal from the central processing unit C, the vehicle controlling means M 9 , which includes the electronic control unit U, controls the operations, respectively, of the brake actuator Aa and the throttle actuator Ab, for the purpose of keeping a constant distance between the subject vehicle and, for example, the front-running vehicle. 
     It should be noted that the search by the radar system R to detect an object is performed at cycles of 100 msec, for instance. 
     The object candidate position detecting means M 2  in the central processing unit C first analyzes the frequency of the beat signal by applying the FFT (Fast Fourier Transform) to the data set on the beat signal stored in the memory  11 , and thus finds a spectral distribution. Based on the spectral data set, the object candidate position detecting means M 2  detects a spectrum (a peak signal), the detection level of which reaches the maximum value that is equal to or more than a predetermined threshold value. The peak signal on the increase side shown in  FIG. 4A  and the peak signal on the decrease side shown in  FIG. 4B  are detected symmetrically with respect to a peak position at a time when the relative speed between the subject vehicle and the object is “zero”. Hence, based on the peak frequency Fup on the increase side and the peak frequency Fdn on the decrease side, the object candidate position detecting means M 2  calculates the distance of the object from the subject vehicle and the relative speed between the object and the subject vehicle. Specifically, the object candidate position detecting means M 2  calculates the distance of the subject vehicle to the object based on the sum of the two peak frequencies Fup, Fdn, and the relative speed between the subject vehicle and the object based on the difference between the two peak frequencies Fup, Fdn. Furthermore, based on the direction in which the transmitted wave is transmitted when the object is detected, the object candidate position detecting means M 2  calculates the angle (direction) of the object. 
     Suppose a case where: as shown in  FIG. 5 , three targets T 1  to T 3  are detected from a front-running vehicle Va, which is running ahead in the same lane as a subject vehicle is running; and the three targets T 1  to T 3  are located within a predetermined unified range. In this case, because the speeds of the respective three targets T 1  to T 3 , relative to the speed of the subject vehicle are equal to one another, the unifying means M 3  unifies the three targets T 1  to T 3  into a single group G. The group representative point calculating means M 4  calculates a transverse location of the representative point P of the group as the middle position between the leftmost target T 1  and the rightmost target T 3 , as well as a longitudinal location of the representative point P as the position of the target T 1  (or T 3 ) which is nearest to the subject vehicle. The calculation of the representative point P of the group makes it possible to accurately define the representative point P of the obtained group. 
     Suppose a case where: as shown in  FIG. 6 , the front-running vehicle Va is running in the same lane as the subject vehicle and an adjacent vehicle Vb running in an adjacent lane are running side-by-side at the same speed; and a target T 1  is detected from the adjacent vehicle Vb whereas two targets T 2 , T 3  are detected from the front-running vehicle Va. In a case where the detection of the three targets T 1  to T 3  is achieved within the predetermined unified range while the speeds of the respective three targets T 1  to T 3  relative to the speed of the subject vehicle are equal to one another, the unifying means M 3  unifies the three targets T 1  to T 3  into a group G, and thus recognizes the group G as a single object as enclosed by the broken line. The group representative point calculating means M 4  sets the transverse location of the representative point P of the group G in the middle position between the leftmost target T 1  and the rightmost target T 3 , as well as sets the longitudinal location of the representative point P at the position of the target T 1 , which is the nearest to the subject vehicle. 
     The unified information storage means M 7  stores the positions of the respective three targets T 1  to T 3 , which are unified by the unifying means M 3 . 
     Next, suppose a case where the three targets T 1  to T 3  move from the positions shown in  FIG. 6 , which have been detected in the previous cycle, to the positions shown in  FIG. 7A , which are detected in the current detection cycle. In the current detection cycle, there may be a case where the three targets T 1  to T 3  do not gather into the same unified range; the target T 1  enters a left unified range to make a group G 1 ; and the targets T 2 ,  13  enter a right unified range to make a group G 2 . In this case, the tracking means M 5  associates the previous group G with either the current first group G 1  or the current second group G 2  (or the previous group G is tracked by either the current first group G 1  or the current second group G 2 ). 
     The conventional art performs the tracking operation as follows. 
     Based on the previous representative point P of the previous group G shown in  FIG. 6 , a currently estimated representative point P′ shown in  FIG. 7A  is estimated from the position and speed of the previous representative point P relative to the subject vehicle. After that, the distance between the representative point P 1  of the current first group G 1  and the currently estimated representative point P′ is compared with the distance between the representative point P 2  of the current second group G 2  and the currently estimated representative point P′. If the latter distance is shorter than the former distance, the previous group G is tracked by the current second group G 2 . 
     In this case, a vehicle-to-vehicle distance control, which has been achieved relative to the group G present in the same lane as is the subject vehicle in the previous detection cycle, continues to be similarly achieved relative to the current second group G 2  present in the same lane as is the subject vehicle in the current detection cycle. Accordingly, the vehicle-to-vehicle distance control relative to the front-running vehicle present in the same lane as the subject vehicle is continuously performed without trouble. 
     On the other hand, as shown in  FIG. 7B , if the distance between the representative point P 1  of the current first group G 1  and the currently estimated representative point P′ is shorter than the distance between the representative point P 2  of the current second group G 2  and the currently estimated representative point P′, as a result of the comparison between the former distance and the latter distance, the previous group G is tracked by the current first group G 1 . In this case, the vehicle-to-vehicle distance control, which has been achieved relative to the group G present in the same lane as the subject vehicle in the previous detection cycle, is taken over by the vehicle-to-vehicle distance control, which is achieved relative to the adjacent vehicle Vb present in the adjacent lane in the current detection cycle. Accordingly, it is more likely that the vehicle-to-vehicle distance between the subject vehicle and the front-running vehicle Va, which is actually present in the same lane as the subject vehicle, may be increased or decreased inadequately. 
     The present invention solves the foregoing drawback as follows. 
     The running lane estimating means M 8  shown in  FIG. 1  estimates a future course of the subject vehicle, namely a lane in which the subject vehicle will run in the future, based on the vehicle speed detected by the vehicle speed sensor Sa and the yaw rate detected by the yaw rate sensor Sb. Accordingly, the running lane in which the subject vehicle will run in the future may easily and accurately be estimated. The tracking means M 5  checks whether the current positions of the targets T 1  to T 3  are situated in currently estimated emerging areas (square areas measuring ±1 m in the longitudinal direction and ±1 m in the transverse direction) which are set around the previous positions of the targets T 1  to T 3 , respectively, as shown in  FIG. 8A . The check by the tracking means M 5  is performed when the three targets T 1  to T 3 , which have existed within the same unified range in the previous detection cycle, as shown in  FIG. 6 , no longer fall within the same unified range in the current detection cycle and the target T 1  constitutes the group G 1  as a result of falling within the left unified range whereas the targets T 2 , T 3  constitute the group G 2  as a result of falling within the right unified range. Thus, it is possible to securely check on the corresponding relationship between the previous positions and current positions of the targets T 1  to T 3 , respectively. 
     Once the current positions of the targets T 1  to T 3  are found to exist in the estimated emerging areas as a result of the check by the tracking means M 5 , the second group G 2 , including the targets  12 , T 3 , which are present in the same lane as the representative point P of the previous group G (in the same lane as is the subject vehicle), is associated with the previous group G, as shown in  FIG. 8B . Thus, the previous group G is tracked by the second group G 2 . For this reason, even if, out of the first and second groups G 1 , G 2  into which the previous group G splits up or is divided, the distance between the representative point P 1  of the first group G 1  and the currently estimated point P 1 , which is estimated from the previous representative point P, is shorter than the distance between the representative point P 2  of the second group G 2  and the currently estimated point P 1  (see  FIG. 7B ), the first group G 1  is regarded as a group which newly emerges. The second group G 2  is continuously treated as the basis of the vehicle-to-vehicle distance control by making the previous group G tracked by the second group G 2 . 
     The tracking operation of the present invention will again be explained based on the flowcharts, respectively, shown in  FIGS. 9 and 10 . 
     First, in step S 1 , it is checked how many groups the targets constituting the previous group have been split up into during the current detection cycle. If the targets are split up into two or more groups in step S 2 , a search is made for targets constituting the previous group and remaining targets present in the same lane as the representative point of the previous group in step S 3 . If, as a result of the search, there are targets in question in step S 4 , it is checked in step S 5  whether any of the targets is detected in the estimated emerging area. If any of the targets in question is detected in the estimated emerging area in step S 5 , of the two or more split groups, a split group including the target remaining present in the same lane as the representative point of the previous group is associated with the previous group prior to the other split groups in step S 6 . 
     In step S 7 , each of the previous groups is checked to determine whether the previous group splits up into two groups or more. Until it is determined in step S 7  that the check on all the previous groups is completed, steps S 1  to S 6  are repeated. Once it is determined in step S 7  that the check on all the previous groups is completed, the other previous groups which are not preferentially associated with the current group are associated with the other current group. The associating process carried out by the present invention is the same process as the process used by the object detecting apparatus for a vehicle according to the conventional art. Descriptions will be hereinbelow provided for a subroutine for the associating process based on a flowchart shown in  FIG. 10 . 
     First, in step S 11 , the currently estimated point of the representative point of the previous group is calculated. Subsequently, in step S 12 , the representative points of the current groups are searched for a representative point which is situated within the predetermined range from the currently estimated point, which is the nearest to the currently estimated point, and which is not associated with the previous group. If, as a result of the search, there are no such representative points in step S 13 , it is judged in step S 14  that none of the current groups are continued from the previous group. If, as a result of the search, such a representative point is found in step S 13 , the current group represented by such a representative point is associated with the previous group in a way that the current group is continued from the previous group. 
     Until it is judged in step S 16  that the search on each of all the previous groups is completed, steps S 11  to S 15  are repeated. It is judged in step S 17  that the remaining current groups which are not associated with the previous group are new groups which have newly emerged. 
     Once the arrangement for the previous groups to be tracked by the current groups is completed in this manner, the object information outputting means M 6  outputs the group representative point, which results from the tracking arrangement to the vehicle controlling means M 9 . Thus, the vehicle controlling means M 9  controls the vehicle-to-vehicle distance relative to the group representative point, which results from the tracking arrangement. 
     The foregoing descriptions have been provided for the preferred embodiment of the present invention. However, the present invention can be carried out by variously modifying the structural configuration of the aforementioned features within the scope of the invention and without departing from the gist of the present invention. 
     For example, the embodiment applies the object detecting apparatus for a vehicle according to the present invention to the vehicle-to-vehicle distance control apparatus, but the object detecting apparatus for a vehicle according to the present invention can be applied to a cruise control apparatus with a vehicle-to-vehicle distance control function, a collision damage reduction brake system, a congestion following running control apparatus, and the like.