Abstract:
A passenger detection device for a vehicle is provided with multiple load sensors, each of which detects a load on a seat of the vehicle within a predetermined detection range of the load sensor, and an ECU that determines passenger information of the seat. The ECU has at least one calculation range, each of which limits the detection range of each corresponding one of the multiple load sensors. The ECU determines the passenger information based on a detection data value of each load sensor, which is outputted from the load sensor and falls within the corresponding calculation range of the load sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on Japanese Patent Applications No. 2004-44541 filed on Feb. 20, 2004, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The invention relates to a passenger detection device for providing information of passengers in a vehicle and sending corresponding signal to a passenger protection device (e.g., airbag device or seatbelt) and an alarm device which gives a seatbelt-wear indication.  
       BACKGROUND OF THE INVENTION  
       [0003]     Generally, a passenger detection device is used for providing information of passengers on seats of a vehicle. Referring to JP-2003-14528-A, for example, the passenger detection device includes multiple load sensors and a passenger detection electronic control unit (ECU), in which at least one passenger detection threshold value is memorized. Based on the passenger detection threshold value, the passenger information can be determined.  
         [0004]     Specifically, by comparing a total of detection data of the multiple load sensors with the two passenger detection threshold values, it is determined whether or not the seat is vacant, or whether or not the passenger on the seat is analdlult. When the total is smaller than the passenger detection threshold value for a child-vacancy judgment, the passenger detection ECU determines that the seat is vacant. On the other hand, when the total is larger than or equal to the passenger detection threshold value for the child-vacancy judgment, and smaller than the passenger detection threshold value for a child-adult judgment, the passenger detection ECU determines that the passenger is a child. When the total is larger than or equal to the passenger detection threshold value for the child-adult judgment, the passenger detection ECU determines that the passenger is an adult. In the case where the seat is vacant or the passenger is a child, an airbag corresponding to this seat will be restricted from deploying. In contrast, when the passenger is an adult, the airbag can be activated. Furthermore, when the passenger having been determined to be an adult does not wear a seatbelt, a seatbelt-wear alarm is given.  
         [0005]     However, a vacancy zero point (detection load for vacant seat) of the load sensor is readily influenced by errors of both an attachment of the load sensor to the seat and an attachment of the seat, at which the load sensors having been mounted, to the vehicle. Therefore, there is a variation in the vacancy zero points of the multiple load sensors mounted at the seat.  
         [0006]      FIG. 8A  shows the variation in the vacancy zero points of the load sensors a 1 -d 1 . The load sensors a 1  and b 1  are mounted at the two front corners of the seat, and the load sensors c 1  and d 1  are mounted at the two rear corners of the seat. Here, a sensor detection range is an inherent dynamic range of the load sensor. A zero-point variation range is a range of the vacancy zero points which is admissible to be input to a passenger detection ECU considering the variation in the vacancy zero points. In  FIG. 8A , (+) indicates a plus direction (downward direction) of the load, and (−) indicates a minus direction of the load (upward direction). Referring to  FIG. 8A , the vacancy zero points of the four load sensors a 1 -b 1  are dispersed at the plus side and the minus side.  
         [0007]     When a passenger sits on the seat, a 1 -d 1  ownward load is additionally exerted on the seat, so that each of the load sensors a 1 -d 1  has a plus-side detection load in addition to the vacancy zero point thereof, as shown in  FIG. 8B .  
         [0008]     When the vehicle is accelerated or decelerated, the load exerted on the seat will be changed.  FIG. 8C  shows the detection loads of the load sensors a 1 -d 1  when the vehicle is accelerated. As compared with  FIG. 8B , the detection loads of the load sensors a 1 , b 1 , c 1 , d 1  indicted in  FIG. 8C  are respectively moved toward the minus side by Δfa, the minus side by Δfb, the plus side by ΔFc and the plus side by ΔFd.  
         [0009]     Because the vacancy zero points of the load sensors a 1  and b 1  are originally near a lower limit of the vacancy zero point variation range, the detection loads of the load sensor a 1  and b 1  exceed a lower limit of the sensor detection range. As shown in  FIG. 8C , the exceeding parts of the detection loads are eliminated, so that the detection loads are limited within the sensor detection range. Therefore, the real load exerted on the seat cannot be detected by the load sensors a 1 -d 1 . Specifically, as compared with  FIG. 8B , the detection load of the load sensor a 1  has a minus-side movement value Δfa, while the real minus-side movement value is (Δfa+Δfa′). Similarly, the detection load of the load sensor b 1  has a minus-side movement value Δfb, while the real minus-side movement value is (Δfb+Δfb′). On the other hand, the detection loads of the load sensors c 1  and d 1  does not exceed the sensor detection range to be the loads exerted on the corresponding portions of the seat. Therefore, an actual total of the detection loads of the load sensors a 1 -d 1  is (Δfc+Δfd−Δfa−Δfb), instead of the real total (Δfc+Δfd−Δfa−Δfb−Δfa′−Δfb′). That is, (−Δfa′−Δfb′) is not added to the actual total, so that the actual total of the detection loads of the load sensors a 1 -d 1  is larger than the load exerted on the seat.  
         [0010]     Therefore, the actual total of the detection loads is changed from the minus side toward the plus side. If the total exceeds the passenger judgment threshold value, a judgment result of the passenger information, which is determined by the passenger detection ECU before the vehicle is accelerated, will be switched from “child” to “adult” even when the passenger is actually a child.  
         [0011]     When the vehicle is turned while being accelerated, a load in the plus side will be centralized at one of the four load sensors.  FIG. 9A  shows loads detected in an ordinary traveling of the vehicle.  FIG. 9B  shows loads detected when the vehicle is turned while being accelerated. Here, the load beyond the upper limit of the sensor detection range is centralized at the load sensor d 1  among the load sensors c 1  and d 1  which are mounted at the vehicle rear portion. In this case, the exceeding part Δfd′ at the plus side is eliminated from the detection load, so that the detection load of the load sensor d 1  is limited within the sensor detection range. Thus, the total of the detection loads of the load sensors a 1 -d 1  will be smaller than the load exerted on the seat.  
         [0012]     Therefore, the total of the detection loads of the load sensors a 1 -d 1  is changed from the plus side toward the minus side. If the total exceeds the passenger judgment threshold value, the judgment result of the passenger information, which is determined by the passenger detection ECU before the vehicle is turned, will be switched from “adult” to “child” or “vacancy” even when the passenger is actually an adult.  
       SUMMARY OF THE INVENTION  
       [0013]     In view of the above disadvantages, it is an object of the present invention to provide a passenger detection device for a vehicle, which determines passenger information with a high and stable detection accuracy regardless of an influence of a vehicle acceleration or the like.  
         [0014]     According to the present invention, a passenger detection device for a vehicle is provided with a plurality of load sensors, each of which detects a load on a seat of the vehicle within a predetermined detection range of the load sensor, and an ECU that determines passenger information of the seat. The ECU has at least one calculation range, each of which limits the detection range of each corresponding one of the plurality of load sensors. The ECU determines the passenger information based on a detection data value of each load sensor, which is outputted from the load sensor and falls within the corresponding calculation range of the load sensor.  
         [0015]     As above described with reference to  FIG. 8C , a total of detection loads of the load sensors is larger than the load exerted on the seat, because vacancy zero points of the load sensors a 1  and b 1  are originally near a lower limit of a vacancy zero point variation range. According to the present invention, the ECU is set to have the calculation range for limiting the detection range of the load sensors, so that only the detection data of the load sensors within the calculation range are used for a calculation of the load exerted on the seat. Accordingly, not only the load sensors a 1  and b 1  but also the load sensors c 1  and d 1  have parts of the detection loads not to be used for the calculation, so that the uncalculated parts at a plus side are offset with and those at a minus side. Accordingly, a judgment accuracy of the passenger information is improved.  
         [0016]     Preferably, the at least one calculation range of the ECU includes at least two kinds of calculation ranges to correspond with a variation in the load applied to the respective load sensors.  
         [0017]     Generally, the shape of the seat is set to make the passenger thereon easy to rest against the back of the seat. Therefore, a load in the minus side is easier to be exerted at the load sensors at the seat front portion than a load in the plus side. In contrast, the load in the plus side is easier to be exerted at the load sensors at the seat rear portion than the load in the minus side. Therefore, if the calculation range for the load sensors at the seat front portion is the same with that for the load sensors at the seat rear portion, the detection loads of the load sensors at the seat front portion are easy to exceed the lower limit of the calculation range, and the detection loads of the load sensors at the seat rear portion are easy to exceed the upper limit of the calculation range.  
         [0018]     In this case, for example, the lower limit of the calculation range for the load sensors at the seat front portion can be lowered toward the minus side, and the upper limit of the calculation range for the load sensors at the seat rear portion can be heightened toward the plus side. Thus, it is difficult for the detection load to exceed both the lower and upper limits of the calculation range. Accordingly, the judgment accuracy of the passenger information can be improved. The calculation range can be also set corresponding to the individual load sensor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which:  
         [0020]      FIG. 1  is a perspective diagram showing a seat at which a passenger detection device is mounted according to a first embodiment of the present invention;  
         [0021]      FIG. 2  is a block diagram of the passenger detection device shown in  FIG. 1 ;  
         [0022]      FIG. 3  is a schematic diagram showing the seat at which the passenger detection device shown in  FIG. 1  is mounted.  
         [0023]      FIG. 4A ,  FIG. 4B  and  FIG. 4C  are graphs showing a calculation method of the passenger detection device shown in  FIG. 1 ;  
         [0024]      FIG. 5  is a schematic diagram showing that a vehicle at which a passenger detection device is mounted is turned while being accelerated according to a second embodiment of the present invention;  
         [0025]      FIG. 6A  and  FIG. 6B  are graphs showing a load variation when the vehicle is turned while being accelerated according to the second embodiment;  
         [0026]      FIG. 7  is a flow diagram showing a passenger judgment procedure by CPU of the passenger detection device according to the second embodiment;  
         [0027]      FIG. 8A ,  FIG. 8B  and  FIG. 8C  are graphs showing a calculation method of a passenger detection device according to a related art; and  
         [0028]      FIG. 9A  and  FIG. 9B  are graphs showing a load variation when a vehicle at which the passenger detection device is mounted is turned while being accelerated according to the related art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0029]     In the first embodiment, a passenger detection device  1  for a vehicle will be described with reference to  FIGS. 1-4 .  
         [0030]      FIG. 1  shows a seat  96  (e.g., assistant seat), at which the passenger detection device  1  including load sensors  20   a - 20   d  and a passenger detection ECU  3  is mounted. Two rails  8  are arranged under the seat  96  to be parallel with each other with respect to a vehicle width (right-left) direction. Each of the rails  8  includes an upper rail  80  and a lower rail  81 . The lower rail  81  is fixed on a floor (not shown) of the vehicle. The upper rail  80  is mounted on the lower rail  81  to be slideable in a vehicle longitudinal (front-rear) direction along the lower rail  81 . Thus, the seat  96  is slideable together with the upper rail  80  in the vehicle front-rear direction.  
         [0031]     The load sensors  20   a - 20   d,  being disposed between the seat frame (not shown) of the seat  96  and the upper rail  80 , are provided at the right front portion, the left front portion, the left rear portion and the right rear portion, respectively, of the seat  96 . Detection directions of the load sensors  20   a - 20   d  are arranged corresponding to an up-down direction shown in  FIG. 1 . In this case, the right-left direction is defined with respect to a traveling direction of the vehicle.  
         [0032]     The load sensors  20   a - 20   d  are respectively communicated with the passenger detection ECU  3  through, for example, a wire harness (not shown). The passenger detection ECU  3  is fixed at the reverse surface of the seat  96  and communicated with an airbag ECU  94 , which is buried under an instrument panel (not shown) of the vehicle through a wire harness (not shown) or the like.  
         [0033]      FIG. 2  shows the composition of the load sensors  20   a - 20   d  and the passenger detection ECU  3 . The load sensor  20   a  is provided with a gauge portion  22 , an amplifier  23  (AMP) and a control portion  24 , which are the same with those construct the load sensor  20   b,    20   c  or  20   d.  The gauge portion  22  includes four strain gauges  220  which construct a bridge circuit. The AMP  23  amplifies a voltage value output from the gauge portion  22 . The control portion  24  adjusts the slope and intercept of the voltage values so that the AMP  23  has an aimed linear output characteristic.  
         [0034]     The passenger detection ECU  3  includes a 5V power supply  30 , a central processing unit  31  (CPU), an electrically erasable programmable read-only memory  32  (EEPROM), and a communication interface  33  (communication I/F). The CPU  31  is provided with an A/D converter  310 , a RAM  311  and a ROM  312  in which a program for a passenger judgment procedure is memorized beforehand. The analog voltage value generated by the AMP  23  is input to the A/D converter  310  to be converted into a digital voltage value. The digital voltage value will be temporarily memorized in the RAM  311 . The EEPROM  32  is provided for memorizing the content of a failure of the load sensors  20   a - 20   d,  for example. Data memorized in the EEPROM  32  can be updated. That is, the previous data memorized in the EEPROM  32  can be replaced by the current data. The communication I/F  33  is provided for sending a judgment result of passenger information having been determined by the CPU  31  to the airbag ECU  94  of an airbag unit  95 .  
         [0035]     The 5V power supply  30  is connected to a vehicle battery  7  through an ignition switch  70 . When the ignition switch  70  is turned on, the vehicle battery  7  supplies a 12V voltage to the 5V power supply  30  through a power cord L 1 . Then, the 5V power supply  30  converts the voltage from 12V into 5V, and thereafter supplying the 5V voltage to the load sensors  20   a - 20   d  and the CPU  31  through power cords L 2  and L 3 , respectively. Thus, a predetermined voltage is supplied to the strain gauges  220  of the gauge portion  22 .  
         [0036]     Next, the signal transmission in the passenger detection device  1  will be described.  
         [0037]     When a load from the right front portion of the seat  96  is applied at the load sensor  20   a,  resistances of the strain gauges  220  thereof will vary, so that the bridge circuit unbalances to generate a little voltage, which is supplied to the gauge portion  22 . The voltage value of the gauge portion  22  is sent to the AMP  23  through signal cords S 1 , S 2  to be amplified. Then, the analog voltage value having been amplified is sent to the A/D converter  310  of the CPU  31  through a signal cord S 3 . The A/D converter  310  converts the analog voltage value into a corresponding digital voltage value. Similarly, analog voltage values from the load sensors  20   b,    20   c  and  20   d  due to loads exerted at corresponding attachment positions of the seat are also input to the A/D converter  310  to be converted into corresponding digital voltage values.  
         [0038]     The digital voltage values of the load sensors  20   a - 20   d  are temporarily memorized in the RAM  311 , and thereafter sent to the CPU  31  to be processed (added) therein. The calculation procedure will be described later. A total of the digital voltage values of the four load sensors  20   a - 20   d  will be compared with a passenger judgment threshold value, so that passenger information is determined by the CPU  31 . Specifically, when the total is smaller than or equal to a vacancy threshold value W th1  (passenger judgment threshold value for vacancy judgment), it is determined that the seat  96  is vacant. When the total is larger than the vacancy threshold value W th1 , and smaller than or equal to an adult-child threshold value W th2  (passenger judgment threshold value for adult-child judgment), it is determined that the passenger is a child. Here, W th2  is larger than W th1 . When the total is larger than the adult-child threshold value W th2 , it is determined that the passenger is an adult.  
         [0039]     Then, the judgment result of the passenger information is input to the airbag ECU  94  through the signal cord S 4 , the communication I/F  33  and the signal cord S 5 . Corresponding to the passenger information, the airbag ECU  94  sends a demand to an airbag  940 . Thus, the airbag  940  will be restricted from deploying when it is determined that the seat  96  is vacant or the passenger is a child. On the other hand, the airbag  940  will be activated when it is determined that the passenger is an adult.  
         [0040]     With reference to  FIG. 3  and  FIGS. 4A-4C , the calculation procedure of the passenger detection ECU  3  will be described.  
         [0041]     A variation in vacancy zero points of the load sensors  20   a - 20   d  mounted at four corners of the seat  96  is shown in  FIG. 4A , in which a sensor detection range is an inherent dynamic range of the load sensor. A zero point variation range is a range of the vacancy zero points which is admissible to be input to the passenger detection ECU  3  considering the variation in the vacancy zero points.  
         [0042]     In  FIG. 4A , (+) indicates a plus side (downward direction) of the load exerted on the seat  96 , and (−) indicates a minus side (upward direction) of the load. The vacancy zero points of the four load sensors  20 A- 20 D are disposed at both the plus side and the minus side. A calculation range of the EEPROM  32  of the passenger detection ECU  3  is set to have a predetermined width from the plus side of the vacancy zero point to the minus side thereof. The calculation ranges of the EEPROM  32  for each of the load sensors  20   a - 20   d  is set to have a same width.  
         [0043]     When a passenger sits on the seat  96 , a downward load is additionally exerted on the seat  96  referring to  FIG. 4B . Thus, loads in the plus side will be detected by the load sensors  20   a - 20   d  in addition to the vacancy zero points thereof.  
         [0044]     When the vehicle is accelerated, the load exerted on the seat  96  will be changed. The case where the vehicle is accelerated is shown in  FIG. 3 , in which (+) and (−) are same set as shown in  FIG. 4A . In this case, a force moment M is applied at the seat  96 . An upward force is additionally exerted on the right front portion of the seat  96 . Therefore, the detection load of the load sensor  20   a  indicted in  FIG. 4C  moves toward the minus side by ΔFa with respect to that indicated in  FIG. 4B . Moreover, an upward force is additionally exerted on the left front portion of the seat  96 , so that the detection load of the load sensor  20   b  indicted in  FIG. 4  moves toward the minus side by ΔFb with respect to that indicated in  FIG. 4B . A downward force is additionally exerted on the left rear portion of the seat  96 , so that the detection load of the load sensor  20   c  indicted in  FIG. 4C  moves toward the plus side by ΔFc with respect to that indicated in  FIG. 4B . Furthermore, a downward force is additionally exerted on the right rear portion of the seat  96 , so that the detection load of the load sensor  20   d  indicted in  FIG. 4C  moves toward the plus side by ΔFd with respect to that indicated in  FIG. 4B .  
         [0045]     In this case, the detection loads of the load sensor  20   a  and  20   b  are a lower limit value of the calculation range. That is, the detection load is limited within the calculation range. Accordingly, for the load sensor  20   a,  ΔFa′ is eliminated from the detection load of the load sensor  20   a,  while (ΔFa+ΔFa′) is a real load exerted at the load sensor  20   a  due to the vehicle acceleration. That is, only ΔFa will be used for the calculation of the load exerted on the seat  96 . Similarly, for the load sensor  20   b,  ΔFb′ is eliminated from the detection load of the load sensor  20   b,  while (ΔFb+ΔFb′) is a real load exerted at the load sensor  20   b  due to the vehicle acceleration. That is, only ΔFb will be used for the calculation of the load exerted on the seat  96 .  
         [0046]     Moreover, the detection loads of the load sensors  20   c  and  20   d  are an upper limit value of the calculation range. That is, the detection loads are limited within the calculation range. Accordingly, ΔFc′ is eliminated from the detected load of the load sensor  20   c,  while (ΔFc+ΔFc′) is a real load exerted at the load sensor  20   c  due to the vehicle acceleration. That is, only ΔFc will be used for the calculation of the load exerted on the seat  96 . Similarly, ΔFd′ is eliminated from the detected load of the load sensor  20   d,  while (ΔFd+ΔFd′) is a real load exerted at the load sensor  20   d  due to the vehicle acceleration. That is, only ΔFd will be used for the calculation of the load exerted on the seat  96 .  
         [0047]     Therefore, the total of the detection loads (detection data values) of the load sensors  20   a - 20   d  to be used in the calculation is (ΔFc+ΔFd−ΔFa−ΔFb), instead of the real total (ΔFc+ΔFd+ΔFc′+ΔFd′−ΔFa−ΔFb−ΔFa′−ΔFb′). That is, (ΔFc′+ΔFd′−ΔFa′−ΔFb′) is uncalculated. Thus, the uncalculated parts of the detection loads at the plus side will offset the uncalculated parts at the minus side.  
         [0048]     According to the passenger detection device  1 , the detection loads (detection data values) of the load sensors  20   a - 20   d  are limited within the calculation range of the passenger detection ECU  3 . Then, the uncalculated parts of the detection loads at the plus side offset the uncalculated parts at the minus side, thus reducing a detection error of the load exerted on the seat  96 . Accordingly, a detection accuracy of the load sensors  20   a - 20   d  is improved.  
         [0049]     As described above, the variation exists in the vacancy zero points of the load sensors  20   a - 20   d.  The variation is generated due to errors of both an attachment of the load sensors  20   a - 20   d  to the seat  96  and an attachment of the seat  96 , at which the load sensors  20   a - 20   d  have been mounted, to the vehicle. That is, the variation is inherent for the seat  96  and different from those of the load sensors mounted at the other seats in the vehicle. Considering that, the ECU  3  of the passenger detection device  1  is set to have the calculation range having the vacancy zero point as a standard point, thus reducing an influence of the variations in the vacancy zero points of the multiple seats on the detection accuracy of the load exerted on the corresponding seat. Then, judgment accuracy of the passenger information of the multiple seats can become more homogeneous.  
         [0050]     In this embodiment, the vacancy zero points and the calculation range of the passenger detection device  1  are memorized in the EEPROM  32 , and can be updated to correspond to various attachment states of the loads sensors  20   a - 20   d.    
       Second Embodiment  
       [0051]     In the second embodiment, a passenger detection threshold value for the digital voltage value (detection load) of the individual load sensor  20   a,    20   b,    20   c  or  20   d  is memorized in the passenger detection ECU  3  besides that for the total of the digital voltage values of the four load sensors  20   a - 20   d,  which is used in the above-described first embodiment. In this embodiment, what is different from the first embodiment will be described referring to  FIGS. 5-7 .  
         [0052]     When the vehicle is turned left while being accelerated, the passenger has accelerations both in the vehicle front-rear direction and the vehicle right-left direction, so that the center of gravity thereof is changed. Thus, the load exerted at the load sensors  20   a - 20   d  (indicated with hatching) is changed with reference to  FIG. 5 . Specifically, the load of the minus side is applied at the load sensors  20   a,    20   b  and  20   c,  and the load of the plus side is applied at the load sensor  20   d.  That is, the load, being downward with respect to the seat  96 , is centralized on the load sensor  20   d.    
         [0053]      FIG. 6A  shows the load detected in an ordinary traveling of the vehicle and  FIG. 6B  shows the load detected when the vehicle is turned while being accelerated. Here, the load is centralized on the load sensor  20   d  among the load sensors  20   c  and  20   d,  which are mounted at the vehicle rear portion.  
         [0054]     In this case, the detection load of the load sensor  20   d  is beyond the upper limit value of the calculation range, and will be limited within the calculation range. Specifically, the exceeding part ΔFd′ at the plus side is eliminated from the detection load of the load sensor  20   d.  Thus, the detection load within the calculation range is used for the calculation of the load exerted on the seat  96 . Thus, after the vehicle is turned while being accelerated, the total of the detection loads of the load sensors  20   a - 20   d  is changed from the plus side toward the minus side, as compared with that before the turn along with the acceleration of the vehicle.  
         [0055]      FIG. 7  shows a procedure which is processed by the passenger detection ECU  3  to determine the passenger information. At first, it is determined whether or not the total of the detection loads of the load sensors  20   a - 20   d  exceeds the passenger detection threshold value W th1  or W th2  at step ST 2 .  
         [0056]     When it is determined that the total does not exceed W th1  or W th2  (ST 2 : NO), the judgment result of the passenger information having been determined before the turn along with the acceleration will be maintained at step ST 4 . Thereafter, the procedure is ended.  
         [0057]     In contrast, when it is determined that the total exceeds W th1  or W th2  (ST 2 : YES), step ST 3  will be performed. At step ST 3 , it is determined whether or not the detection load of the individual load sensor  20   d  exceeds an individual passenger detection threshold value F th .  
         [0058]     When it is determined that the detection load of the individual load sensor  20   d  exceeds F th  (ST 3 : YES), the judgment result of the passenger information having been determined before the turn along the acceleration will be switched at step ST 5 . At step ST 5 , for example, the judgment result is switched from “adult”, which has been determined before the turn along with the acceleration, to “child” or “vacancy”. Thereafter, the procedure is ended.  
         [0059]     On the other hand, when it is determined that the detection load of the individual load sensor  20   d  does not exceed F th  (ST 3 : NO), the judgment result of the passenger information having been determined before the turn along with the acceleration will be maintained at step ST 4 . For example, it is determined that the passenger is an adult. Thereafter, the procedure is ended.  
         [0060]     According to this embodiment, the judgment accuracy of the passenger information can be maintained even when the load is partially centralized on the seat  96 .  
       Third Embodiment  
       [0061]     In the third embodiment, the upper limit of the calculation range is used as the individual passenger detection threshold value. What is different from the above-described second embodiment will be described.  
         [0062]     Referring to  FIG. 5 , when the vehicle is turned while being accelerated, the load of the plus side is centralized at the load sensor  20   d.  Thus, the detection load of the load sensor  20   d  exceeds the upper limit (boundary value) of the calculation range, so that the part of the detection load which exceeds the calculation range is not used for the calculation of the load exerted at the seat  96 . That is, the detection load of the load sensor  20   d  corresponds to the upper limit of the calculation range. Therefore, the detection accuracy can be maintained even when the load is patricianly centralized at the seat  96 .  
         [0063]     Moreover, the lower limit of the calculation range can be also used as the individual passenger detection threshold value.  
       Other Embodiment  
       [0064]     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.  
         [0065]     For example, the judgment result of the passenger information can be also used for determining an activation of a seatbelt pretensioner device or the like.  
         [0066]     Moreover, the calculation range of the passenger detection ECU  3  can be also memorized in the ROM  312  instead of the EEPROM  32 , so that a mistaken elimination of the calculation range can be reduced.  
         [0067]     Furthermore, the number of the load sensors mounted at the one seat is not limited to four.  
         [0068]     Moreover, the calculation range can be also set to have different widths for the multiple load sensors. For example, the lower limit of the calculation range for the load sensors at the seat front portion can be lowered toward the minus side, and the upper limit of the calculation range for the load sensors at the seat rear portion can be heightened toward the plus side.  
         [0069]     Such changes and modifications are to be understood as being in the scope of the present invention as defined by the appended claims.