Abstract:
From a collision load, a one-time integration value and a two-time integration value are computed. The one-time integration value and two-time integration value are then used for obtaining a mass and rigidity of a collision object as two primary parameters. The obtained two primary parameters are used for determining whether or not the collision object is a pedestrian. This achieves accuracy in determining the collision object that is remarkably superior to a conventional method that uses a collision load waveform.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based on and incorporates herein by reference Japanese Patent Applications No. 2003-369477 filed on Oct. 29, 2003, and No. 2004-134451 filed on Apr. 28, 2004.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a vehicular collision object determining system that determines an object that collides with a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0003]     An invention of lifting a hood of a vehicle or a technology of disposing an airbag on the hood is proposed for decreasing an impact that is suffered by a head of a pedestrian when the vehicle collides with the pedestrian. In adopting the invention or technology, various adverse influences result from operating a protecting device on the hood (e.g., active hood) when a collision object is not a pedestrian.  
         [0004]     For instance, when a vehicle collides with a light object that is not discriminated from a pedestrian, such as a triangle corn or a signboard indicating road construction, the protecting device is uselessly operated. This involves a useless repair cost. Further, by contrast, when a vehicle collides with a heavy stationary object that is not discriminated from a pedestrian, such as a concrete wall or another vehicle, a problem occurs that the hood being lifted is backed into an interior of the vehicle.  
         [0005]     Accurately determining whether a collision object is a pedestrian is thereby more required than before, so that several methods for determining the collision object are proposed. For instance, a first method (Patent document 1) uses a collision load (or deformation amount), duration of the collision load, and a vehicle speed. A second method (Patent document 2) uses a deformation amount at a collision timing (corresponding to collision load), a time-series variation of the deformation amount, and a vehicle speed. In the two methods, a pedestrian is discriminated from other collision objects by setting a threshold in the load, variation amount, and time. 
        (Patent document 1: JP-H11-028994 A)     (Patent document 2 JP-H11-310095 A (U.S. Pat. No. 6,561,301 B1))        
 
         [0008]     However, it was known that these methods that simply utilize collision load waveforms involve insufficient determination accuracy, resulting in insufficient reliability, regardless of a lot of workloads for experiments. Here, the experiments are required for specifying the threshold for the time and load (variation amount) with respect to each of various vehicle speeds.  
         [0009]     Collision objects have individual shapes and rigidity. Even when each of the collision objects has an equal speed and an equal mass, a waveform of a collision load F (=ma) is thereby variable. As a result, a characteristic of the collision load waveform such as duration of the collision load, an increasing ratio, or a peak value cannot easily nor accurately discriminate a pedestrian from the other objects.  
       SUMMARY OF THE INVENTION  
       [0010]     It is an object of the present invention to provide a vehicular collision object determining system that has, in determining a pedestrian, accuracy higher than that of a conventional method.  
         [0011]     To achieve the above object, a vehicular collision object determining system mounted on a vehicle is provided with the following. A collision load sensor detects a collision load. A speed sensor detects a vehicle speed of the vehicle. A computing unit computes at least one of a mass and rigidity of a collision object based on at least outputs from the collision load sensor and the speed sensor. A determining unit determines whether the collision object is a pedestrian or not based on the at least one of the mass and the rigidity of the collision object.  
         [0012]     In this structure, a mass or rigidity of a collision object is computed based on at least a collision load (including information correlated with the collision load) and a vehicle speed. The mass or rigidity is an important parameter as a characteristic of the collision object, so that it is used for determining the collision object. Even an object resembling a pedestrian can be thereby discriminated from the pedestrian, which provides a high accurate determining system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and 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 the drawings:  
         [0014]      FIG. 1  is a block diagram showing a vehicular collision object determining system according to a first embodiment of the present invention;  
         [0015]      FIG. 2  is a schematic perspective view of a vehicle having a vehicular collision object determining system of the first embodiment;  
         [0016]     FIGS.  3  to  6  are schematic plan views showing examples of a collision load sensor in the vehicular collision object determining system of the first embodiment;  
         [0017]      FIG. 7  is a flow chart diagram showing a pedestrian determining process according to the first embodiment;  
         [0018]      FIG. 8  is a graph showing a waveform of a collision load detected in the first embodiment;  
         [0019]      FIG. 9  is a flow chart diagram showing a pedestrian determining process according to a second embodiment;  
         [0020]      FIG. 10  is a graph showing a waveform of a collision load detected in the second embodiment;  
         [0021]      FIG. 11  is a flow chart diagram showing a pedestrian determining process according to a third embodiment;  
         [0022]      FIG. 12  is a block diagram showing a vehicular collision object determining system according to a third embodiment of the present invention;  
         [0023]      FIG. 13  is a schematic perspective view of a vehicle having a vehicular collision object determining system according to the third embodiment;  
         [0024]      FIG. 14  is a circuit diagram showing an example of a width sensor according to the third embodiment;  
         [0025]      FIG. 15  is a block diagram showing an output processing circuit of a width sensor according to the third embodiment; and  
         [0026]      FIG. 16  is a diagram explaining a principle of computing a collision width in a width sensor according to the third embodiment.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0027]     A structure of a vehicular collision object determining system mounted on a vehicle according to a first embodiment of the present invention will be explained with reference to  FIGS. 1, 2 . The vehicle includes a collision load sensor  2 , a bumper absorber  3 , a controller  4  for computing and determining, a wheel speed sensor  5  as a vehicle speed sensor, a side member  9 , a bumper cover  8 , and a vehicle body  6 . Here, the bumper cover  8 , the bumper absorber  3 , and the bumper reinforcement  7  mainly constitute a bumper of the vehicle. The controller  4  outputs collision-related information to an occupant protecting device or a pedestrian protecting device  10  based on outputs from the sensors. This collision-related information includes as least whether a collision object is a pedestrian or not.  
         [0028]     The collision load sensor  2  outputs analog signal voltage corresponding to a collision load. The collision load sensor  2  is disposed as being extended, in a vehicle-width direction (in a side to side direction of the vehicle), on a rear surface of a bumper absorber  3  that is also disposed as being extended in a vehicle-width direction in front of a bumper reinforcement  7 . The bumper reinforcement  7  is disposed in a vehicle-width direction in a forward portion of the vehicle body  6 .  
         [0029]     The collision load sensor  2  only needs to generate an output signal corresponding to a collision load, so that various structures shown in FIGS.  3  to  6  can be selectable. For instance, a rubber tube internally accommodating a pressure sensor can be disposed in a vehicle-width direction. When a collision occurs, the rubber tube is compressed to increase internal pressure, which is then detected by a pressure sensor. The collision load can be detected by an acceleration sensor  22  or a load sensor  21 . Namely, the collision load sensor  2  can include as follows: a load sensor  21  that is disposed between a bumper reinforcement  7  and a side member  9  (in  FIG. 3 ); an acceleration sensor  22  that is disposed in a bumper reinforcement  7  or a side member  9  for detecting an acceleration at a collision ( FIG. 4 ); a thin-film-type surface-pressure sensor  23  or a contact-type switch sensor that is disposed on a surface of a reinforcement  7 , side member  9 , or bumper cover  8  for detecting individual surface pressure at a collision; and a deformation sensor  24  that is disposed in an absorber  3  or bumper cover  8  for detecting deformation at a collision ( FIG. 6 ). The thin-film-type surface-pressure sensor  23  can be disposed as being extended in a vehicle-width direction along the front surface of a bumper reinforcement  7  ( FIG. 5 ). For instance, the thin-film-type surface-pressure sensor  23  is constructed of a pair of electrode lines that are disposed as being extended in a vehicle-width direction with a given gap therebetween, and a carbon-containing rubber film that is disposed between the pair of the electrode lines. When a collision load is applied to the rubber film, the rubber film is compressed in a forward-backward direction. An electric resistance of the rubber film is thereby decreased in the forward-backward direction of the vehicle (film&#39;s thickness direction). The collision load is eventually detected by detecting the electric resistance between the two electrode lines. Detecting the collision load (or impact) by the acceleration sensor  22  or collision load sensor  2  is already known, so that explanation is eliminated here. In particular, a load sensor  21  can detect the collision load without loss when the load sensor  21  is disposed in front of a bumper reinforcement  7  or between a bumper reinforcement  7  and side member  9 .  
       PEDESTRIAN DETERMINING EXAMPLE 1  
       [0030]     A pedestrian determining method using the above-described collision load will be explained with reference to a flow chart diagram in  FIG. 7 .  
         [0031]     At Step S 100 , a collision load F(t) is read. At Step S 102 , it is determined whether the collision load F(t) exceeds a certain threshold Tth 0  indicating a collision occurrence. When it is determined to be exceeding, an internal timer T 1  is initialized and individual internal registers (or memory) are reset to zero at Step S 104 . Here, the internal registers store a one-time integration value, a two-time integration value, and a maximum load value, respectively. A count value of the timer T 1  is incremented (or accumulated) every a given short sampling interval T.  
         [0032]     Next, at Steps S 106 , S 108 , a vehicle speed V and a this-time collision load F(T 1 ) are read, respectively. At Step S 110 , a one-time integration value is computed. The this-time collision load F(T 1 ) represents a collision load F(t) when the count time of the timer T 1  is T 1 . The one-time integration value of the collision load is computed by adding up the previous one-time integration value and the product from multiplying the this-time collision load F(T 1 ) that is read at Step S 108  by the given sampling interval T.  
         [0033]     Next, at Step S 112 , a two-time integration value is computed. The two-time integration value of the collision load is computed by adding up the previous two-time integration value and a product from multiplying the one-time integration value F(T 1 ) that is computed at Step S 110  by the given sampling interval T.  
         [0034]     At Step S 114 , a count value T 1  of the timer T 1 , one-time integration value, and two-time integration value are stored in the internal registers, respectively. At Step S 116 , it is determined whether the this-time collision load F(T 1 ) read at Step S 108  exceeds the maximum load Fmax. When it is determined to be exceeding, the collision load F(T 1 ) is stored as the maximum value at Step S 118 . When it is determined to be not exceeding, Step S 118  is skipped; then, it is determined whether the this-time collision load F(T 1 ) decreases to the threshold value Fth 0  at Step S 120 . When the this-time collision load F(T 1 ) is determined to be not decreasing to the threshold value Fth 0 , the timer T 1  is incremented by the sampling interval T when the sampling interval T elapses at Step S 122 . The process then returns to Step S 108 . When the this-time collision load F(T 1 ) is determined to be decreasing to the threshold value Fth 0 , the process advances to Step S 124 .  
         [0035]     A collision load waveform at collision is presumed as a simple single-peaked pattern as shown in  FIG. 8 . When the this-time value F(T 1 ) becomes larger than the previous value, the previous value can be determined as the maximum value Fmax. Here, a high-frequency noise component can be removed from a collision load read from the collision load sensor  2  using a given low-path filter.  
         [0036]     Thus, the above-described process obtains an elapsed time T 1 , the one-time integration value, and the two-time integration value. Here, the elapsed time T 1  is a period from when the this-time value F(T 1 ) of the collision load exceeds the threshold value Fth 0  (at T 1 =0) through when the this-time value F(T 1 ) undergoes the maximum load Fmax to when the this-time value F(T 1 ) decreases to the threshold value Fth 0 . Mathematical formulas for the one-time and two-time integration values are shown at Steps S 110 , S 112  in  FIG. 7 , respectively. Here, the one-time integration value of the this-time value F(T 1 ) of the collision load represents an impulse due to a collision of an object.  
         [0037]     Next, at Step S 124 , a mass of the collision object is computed by dividing the one-time integration value by a function value ((1+e)/V). At Step S 126 , it is determined whether the computed mass corresponds to a pedestrian. When the object is determined to be not corresponding to a pedestrian, the object is determined to be an object other than a pedestrian at Step S 128 , returning the process to a main routine. Namely, since the impulse equals to a variation of kinetic momentum, a mass of a collision object can be computed by a known collision speed V and a known rebound speed e×V (e: constant, rebound coefficient) using a mathematical formula as follows: 
 
∫ F ( t ) dt=M×V+M×e×V   Formula 1 
 
         [0038]     The Inventors found from experiments that a rebound coefficient e is much affected by a property of a bumper, but less affected by a collision object. When a bumper of a vehicle collides with a pedestrian or metal-made object (e.g., fence disposed in a construction site), a rebound coefficient of the bumper can be practically used as the constant e. The rebound coefficient of the bumper is approximately between 0.4 and 0.6 although the coefficient is varied depending on the kind of the bumper. As a result, a mass of the collision object is obtained by modifying Formula 1 to Formula 2 as follows:  
         Formula   ⁢           ⁢   2     :       
       M   =         ∫     t   =   0       t   =   T1       ⁢       F   ⁡     (   t   )       ⁢     ⅆ   t             (     1   +   e     )     ×   V           
 
         [0039]     When the computed mass M falls within a given range corresponding to a pedestrian at Step S 126 , the process advances to Step S 130 .  
         [0040]     At Step S 130 , a collision stroke S(T 1 ) is computed based on a formula shown at S 130  in  FIG. 7  using the two-time integration value, vehicle speed, and mass. The collision stroke S(T 1 ) is a parameter that represents, of the collision object and bumper, a total deformation distance at collision in a collision direction. The stoke S(T 1 ) is obtained by the following: computing the certain product of the vehicle speed V and the timer count T 1 ; computing the certain quotient when the two-time integration value is divided by the mass M; finally, obtaining the stroke as the difference when the certain quotient is subtracted from the certain product. At Step S 132 , rigidity Kc is obtained using a formula shown at S 132  in  FIG. 7 .  
         [0041]     In this embodiment, of the collision object, the rigidity Kc being an important parameter is defined as a value obtained as the quotient when the collision load F(t) is divided by the deformation stroke S(t) of the collision object at collision, as follows:  
               ⁢         Formula   ⁢           ⁢   3     :     
     ⁢   K     =       F   ⁡     (   t   )         S   ⁡     (   t   )               
 
         [0042]     Here, the deformation stroke S(t) is the sum of the deformation stroke So(t) of the collision object and the deformation stroke Sb(t) of the bumper, as follows: 
 
 S ( t )= So ( t )+ Sb ( t )  Formula 4 
 
         [0043]     The deformation stroke S(t) is obtained from the collision load F(t) and the mass M of the collision object. The quotient when F(t) is divided by the mass M represents an acceleration derived from the collision, so that the deformation stroke is obtained by integrating the acceleration in two times. Therefore, the deformation stroke can be represented by the two-time integration value, collision acceleration V, and mass M as follows:  
           Formula   ⁢           ⁢   5     :     
     ⁢     S   ⁡     (   T1   )         =       V   ×   T1     -       1   M     ⁢       ∫     t   =   0       t   =   T1       ⁢     ∫     F   ⁢     ⅆ   t     ⁢     ⅆ   t                   
 
         [0044]     Since the two-time integration value of F(T 1 ), the this-moment time T 1 , the collision speed V, and the mass M are stored at Step S 114  as a set in the internal registers, the deformation stroke S(t) is obtained with respect to time-series. Accordingly, a time-series relationship between the collision load F(t) and deformation stroke S(t) can be obtained. In practice, it is troublesome that the rigidity Kc of the collision object being the quotient when F(t) is divided by the deformation stroke S(t) is computed every time (each stroke value). In this embodiment, the rigidity of the collision object is obtained at Step S 132  by the following: specifying the count time Tk of the timer T 1  when the value S(T 1 ) of the deformation stroke S(t) reaches a given value So; reading out the value F(Tk) of the collision load F(t) at the count time Tk from the internal register; finally, obtaining the rigidity being the quotient when the value F(Tk) is divided by the So of the deformation stroke S(T 1 ). The computed rigidity Kc of the collision object is inherently a combined value of the rigidity of the collision object and the rigidity of the bumper; however, the rigidity of the bumper is peculiar to a kind of the bumper. Therefore, the rigidity Kc obtained at Step S 132  can be recognized as the rigidity of the collision object. Otherwise, when the rigidity Kb of the bumper is assumed to be a known constant, the rigidity Ko of the collision object can be also obtained by the following formula: 
 
 Ko= ( Kb−Kc )/( Kc×Kb )  Formula 6 
 
         [0045]     Next, at Step S 134 , it is determined whether the rigidity Kc (or Ko) of the collision object falls within a region corresponding to that of a pedestrian. When the rigidity Kc is determined to be falling within the region, the collision object is determined to be a pedestrian at Step S 136 . Otherwise, the collision object is determined to be an object other than a pedestrian at Step S 138 , which returns the process to the main routine. Here, it is preferable that the collision object is determined to be a pedestrian, in practice, when the region of Kc is from 30 N/mm to 150 N/mm, while the collision object is determined to be an object other than a pedestrian when Kc is oustside the foregoing region. Namely, at S 134  in  FIG. 8 , Kth — 1 can be equal 30, while Kth_h can be equal 150.  
         [0046]     The rigidity of the collision object is a parameter indicating difficulty in deformation at collision occurrence. A pedestrian or person is much different from other collision objects in the rigidity. Namely, determining the collision object based on the rigidity of the collision object enables proper determination whether the collision object is a pedestrian or not. For instance, when a result from the determination is used for controlling driving of the pedestrian protecting device, mis-operation of the pedestrian protecting device can be prevented.  
         [0047]     In the above-described embodiment, a mass and rigidity of a pedestrian can be computed only from outputs from a collision load sensor and a vehicle speed sensor that are conventionally used for determining a pedestrian, without using other-sensors. Since the pedestrian determining is executed based on the computed mass and rigidity, a simple structure for the pedestrian determining having high accuracy can be achieved.  
         [0048]     Modification  
         [0049]     In the above embodiment, the mass and the rigidity of the collision object are separately determined whether they fall within the regions corresponding to a pedestrian, respectively. However, the pedestrian determining can be also performed by previously preparing a map showing a pedestrian range using the mass and rigidity.  
       Second Embodiment  
       [0050]     Pedestrian determining according to a second embodiment will be explained with reference to  FIG. 9 .  
         [0051]     In the first embodiment, the one-time integration value and the two-time integration value continue to be computed until the this-time value F(T 1 ) decreases to a threshold value Fth 0 , which is used for determining of existence or not existence of the collision at Step S 120 . However, after the collision load exceeds the maximum value Fmax, computing the one-time integration value and the two-time integration value is not continuously necessary. Namely, computing the one-time integration value and the two-time integration value can be finished at a certain timing when the collision load F(t) decreases to a certain level after exceeding the maximum load Fmax. The mass and rigidity can be estimated by using the data obtained up to the certain timing.  
         [0052]     In this case, Step S 220  in  FIG. 9  is adopted instead of Step S 120  in  FIG. 7 . Computing the one-time integration value, two-time integration value, and this-time value F(T 1 ) is finished at a timing when the collision load F(t) decreases to a value of the product of the maximum load Fmax and a given ratio α (preferably 0.3 to 0.9) after exceeding the maximum load Fmax. This shortens the necessary computing period.  
         [0053]     Here, in this case, the one-time integration value of the collision load is a part of the impulse, the computed value of the mass M becomes smaller than the real value of the mass M. However, the inventors found that, when the computed value is corrected by a given correction constant, the corrected value has only few errors, generating no practical problem. For instance, at α=0.9, a correction constant C being 1.5 can correct the value properly. The constants α, C can be obtained by experiments with respect to a bumper.  
       Third Embodiment  
       [0054]     In this embodiment, rigidity Kc of a collision object is accurately computed. For this purpose, as shown in  FIG. 11 , the flow chart in  FIG. 7  adds Steps S 200 , S 202 . At Step S 200 , collision rigidity Kb of a bumper is computed, while, at Step S 202 , collision rigidity Kc of a collision object is computed from the collision rigidity Kb of the bumper and combined collision rigidity K. Step S 132  in  FIG. 11  corresponds to Step S 132  in  FIG. 7 . Since the collision rigidity Kc of the collision object obtained in  FIG. 7  is inherently combined collision rigidity K as explained above, Step S 132  in  FIG. 11  computes the combined collision rigidity K.  
         [0055]     In this structure, a pedestrian can be more accurately determined using the rigidity. Further, a pedestrian region is assigned to a certain region in three dimensional space of the collision rigidity, mass, and collision width of the collision object. The pedestrian determining is performed by whether a data set of the computed collision rigidity, mass, and collision width falls within this certain region.  
         [0056]     Next,  FIG. 12  shows a structure where the system includes a collision width sensor  1 .  FIG. 13  shows a schematic perspective view of an example of a vehicle having the collision width sensor  1 .  FIG. 14  shows a circuit diagram showing an example of a collision width sensor  1 . It is preferable that, to accurately detect a collision width, the collision width sensor  1  is disposed on the front surface of a bumper cover  8  or in the rear surface of a bumper cover  8  (i.e. between the bumper cover  8  and the absorber  3 ).  
         [0057]     The collision width sensor  1  detects a right-left (horizontal-directional) width of a contact portion of a collision object. The contact portion of the collision object means a contact portion between the collision object and the collision width sensor  1 . An example of the collision width sensor I will be explained with reference to  FIGS. 13, 14 . The collision width sensor  1  includes a pair of current-conducting lines  11 ,  12  that are disposed as being extended in a vehicle-width direction with a given gap therebetween. The given gap is formed by fixing the current-conducting line  12  to the current-conducting line  12  via, e.g., an elastic member such as a rubber. The elastic member is formed of multiple elastic portions that are disposed in the vehicle-width direction with given intervals. Therefore, the current-conducting lines  11 ,  12  face directly each other in spaces formed between the adjoining elastic portions. When a collision is generated on the current-conducting line  11 , the current-conducting line  11  is biased to move rearward and compresses the elastic portions. The current-conducting line  11  thereby makes direct contact with the current-conduction line  12 . Further, when the collision is then removed, compression of the rubber is released and the current-conducting line  11  returns to the original position to be reused. The contact between the current-conducting lines  11 ,  12  requires a threshold collision load more than a given level to prevent mis-detection. In  FIG. 14 , a circuit can be exchangeable between the two current-conducting lines  11 ,  12 . In this embodiment, the current-conducting line  11  has a negligible low resistance, while the current-conducting line  12  (or resistance line) has a given level resistance. Here, both can be exchangeable with each other. The current-conducting line  11  is grounded. By contrast, power source voltage Vc is applied to the current-conducting line  12  via resistances R 1 , R 2  that are connected with the both ends of the resistance line  12 , as shown in  FIG. 14 . Here, the power source voltage Vc can be applied to the current-conducting line  11 , while the current-conducting line  12  can be grounded.  
         [0058]     Thus, when a collision is not generated, voltages Vo 1 , Vo 2  at connecting points of the resistances R 1 , R 2  with the resistance line  12 , respectively, remain at the power source voltage Vc. This indicates that no collision occurs. It is supposed that, in the vehicle-width direction of the current-conducting line  11 , a region from a point P 1  to a point P 2  (disposed closer to the resistance R 2  than the resistance P 1 ) makes contact with the resistance line  12  due to occurrence of collision. The output voltage Vo 1  becomes Vc×r 1 /(r 1 +R 1 )) when r 1  is a resistance value from the lower end in  FIG. 14  to the point P 1  in the resistance line  12 . The output voltage Vo 2  becomes Vc×(r 2 /(r 2 +R 1 )) when r 2  is a resistance value from the upper end in  FIG. 14  to the point P 2  in the resistance line  12 . It is preferable that R 1  and R 2  are equal to each other. The output voltages Vo 1 , Vo 2  are varied based on distances from both ends of the resistance line  12  to the corresponding ends of the collision region. These distances W 1 , W 2  are thereby computed from a map that is previously memorized. The right-left width of the collision region can be computed by subtracting these W 1 , W 2  from the entire length Wo of the resistance line  12 . In this embodiment, as shown in  FIG. 15 , the output voltages Vo 1 , Vo 2  are converted to digital signals by A/D converters to be sent to a width computing unit that is formed of a micro-computer that computes the above-described collision width (or contact width). The collision width is thereby computed and outputted as the digital signal.  
         [0059]     A modification example of the collision width sensor  1  will be explained with reference to  FIG. 16 . In this example, current conducting lines  11 ,  12  are resistance lines that have equal resistance values, respectively. One end of the current-conducting line  11  is grounded, while power source voltage Vc is applied to one end of the current-conducting line  12  via a resistance element R, as shown in  FIG. 16 . Electric resistances of the current-conducting lines  11 ,  12  are r in their vehicle-width directions, respectively. When collision is not generated, an output voltage Vo equals Vc. When the current-conducting lines  11 ,  12  are contacted with each other at a very small point, the output voltage Vo becomes Vc×(r/(r+R)). Each of the entire lengths of the current-conducting lines  11 ,  12  is Wo. When a contact region P has a collision width W, the output voltage Vo becomes Vc×(r 1 /(r 1 +R)). Here, r 1  is a resistance value of the current-conducting lines  11 ,  12 , so that r 1  is r×((Wo−W)/W). Namely, as the contact width increases, the output voltage Vo decreases from Vc×(r/(r+R)). Therefore, the collision width W can be computed from the output voltage Vo using a map that is previously memorized.  
         [0060]     (Others)  
         [0061]     In the above embodiments, whether a collision object is a pedestrian is determined based on a mass and rigidity of the collision object; however, it can be determined based on either of the mass and rigidity of the collision object.  
         [0062]     As a collision load, a signal having correlation with the collision load can be also used instead of the collision load itself. As a mass or rigidity of a collision object, a signal having correlation with the mass or rigidity of the collision object can be also used instead of the mass or rigidity of the collision object itself. In addition to an analog signal, a step-wise signal or digital signal can be also used. The computing circuit (or unit) or determining circuit (or unit) can be formed by a hardware circuit including an analog circuit or digital circuit or by a micro-computer including software for computing data corresponding to the mass or rigidity by a given routine.  
         [0063]     A mass of a pedestrian means a mass as a function of collision force that is applied to a collision load sensor in a bumper when the bumper collides with the pedestrian. Since the pedestrian has many joints, the mass does not need to be the quotient when the body weight is simply divided by gravity. The pedestrian mass can be 7 kg with respect to a child (around six years old), or 13 kg with respect to an averaged adult person when a height of a bumper is approximately 500 mm. The rigidity of a person is 50 N/mm to 140 N/mm according to a study result. Accordingly, when a mass and rigidity of a collision object is computed from a collision load and a collision speed, a threshold for determining can be specified based on the foregoing values. Discriminating a person from an object other than a person can be thereby enabled. In this invention, a physical parameter obtained as electricity quantity other than the mass or rigidity can be also used for determining.  
         [0064]     It will be obvious to those skilled in the art that various changes may be made in the above-described embodiments of the present invention. However, the scope of the present invention should be determined by the following claims.