Patent Publication Number: US-2007115104-A1

Title: Collision detection system and protection system using the same

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is based on and incorporates herein by reference Japanese Patent Application No. 2005-336145 filed on Nov. 21, 2005.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a collision detection system for detecting a collision, and to a protection system for protecting by using the detection system a passenger in a vehicle or a pedestrian colliding with the vehicle.  
      2. Description of Related Art  
      JP-H5-116592A discloses a vehicle body collision detection system as a conventional collision detection system for detecting a collision with a vehicle. The vehicle body collision detection system includes an optical fiber, a light emitting device, an optical conversion device, collision sensors, and a collision detection circuit. Each of the collision sensors includes a cylindrical body and protrusions formed at predetermined intervals on the inner surface of the cylindrical body. The optical fiber extends in a loop around the vehicle and through the cylindrical bodies of the collision sensors. When the vehicle is in a collision, so that an external force is exerted on the cylindrical body of at least one of the collision sensors, the protrusions of the sensor bend the optical fiber locally, so that the light transmission characteristic of the fiber changes. As the exerted force increases, the quantity of light transmitted through the optical fiber decreases. The detection of the decrease in the quantity of the light detected by the collision detection circuit makes it possible to detect the collision.  
      Because of the difference in structure between parts of the vehicle, the load created by a collision to the vehicle transfers in the vehicle in different ways depending on the collision positions, at which the vehicle is collided. Accordingly, even when an equal load is exerted on the vehicle by collisions with different positions on the vehicle, the external forces applied to the cylindrical-bodies of the collision sensors differ. In addition, the quantities of light transmitted through the different optical fibers decrease differently from one another. This may make it impossible to accurately detect collisions that occur at certain positions on the vehicle.  
     SUMMARY OF THE INVENTION  
      The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages.  
      To achieve the objective of the present invention, there is provided a collision detection system, which includes a shock detecting device, a collision position detecting device, a correcting device, and a collision determining device.  
      The shock detecting device detects a magnitude of a shock due to a collision. The collision position detecting device detects a collision position of the collision. The correcting device corrects a detection result detected by the shock detecting device based on a detection result detected by the collision position detecting device. The collision determining device determines the collision based on a corrected result corrected by the correcting device.  
      To achieve the objective of the present invention, there is also provided a protection system, which includes the collision detection system and a protecting device. The protecting device protects one of a passenger of a vehicle and a pedestrian based on the detection result of the collision position detecting device and a determining result of the collision determining device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:  
       FIG. 1  is a typical plan view relating to a whole configuration of an air bag system of a first embodiment of the present invention;  
       FIG. 2  is a perspective view of a periphery of a front bumper shown in  FIG. 1 ;  
       FIG. 3  is a rear view of a sensor retaining plate shown in  FIG. 2 ;  
       FIG. 4  is an enlarged sectional view taken along line IV-IV in  FIG. 3 ;  
       FIG. 5  is a top view of the sensor retaining plate;  
       FIG. 6  is a rear view of an optical fiber sensor shown in  FIG. 2 ;  
       FIG. 7  is an enlarged sectional view of a portion of the optical fiber sensor when observed from a rear side thereof;  
       FIG. 8  is an enlarged sectional view of a portion of the optical fiber sensor when observed from a top side thereof;  
       FIG. 9  is a top view of the optical fiber sensor;  
       FIG. 10  is a typical sectional view of a touch sensor of the first embodiment;  
       FIG. 11  is an enlarged sectional view taken along line XI-XI in  FIG. 10 ;  
       FIG. 12  is a typical sectional view of the touch sensor, which is collided by a body;  
       FIG. 13  is an enlarged sectional view taken along line XIII-XIII in  FIG. 12 ;  
       FIG. 14A  is a circuit diagram for detecting a collision of the body using the touch sensor;  
       FIG. 14B  is a circuit diagram for detecting the collision of the body using the touch sensor;  
       FIG. 15  is a rear view of the sensor retaining plate assembled with the optical fiber sensor and the touch sensors of the first embodiment;  
       FIG. 16  is a front view of the sensor retaining plate assembled with the optical fiber sensor and the touch sensors;  
       FIG. 17  is a top view of the sensor retaining plate assembled with the optical fiber sensor and the touch sensors;  
       FIG. 18  is an enlarged sectional view taken along line XVIII-XVIII in  FIG. 17 ;  
       FIG. 19  is a sectional view of the periphery of the front bumper;  
       FIG. 20  is a diagram of a collision detection circuit of the first embodiment;  
       FIG. 21  is an explanatory drawing showing an operation of a pedestrian collision detection system in the first embodiment;  
       FIG. 22  is a front view of a sensor retaining plate assembled with touch sensors in a different arrangement;  
       FIG. 23  is an enlarged sectional view of a portion of the mat sensor of a second embodiment of the present invention;  
       FIG. 24  is a sectional view taken along line XXIV-XXIV in  FIG. 23 ;  
       FIG. 25  is a sectional view of a portion of the mat sensor collided by the body;  
       FIG. 26  is a front view of the sensor retaining plate assembled with the mat sensor; and  
       FIG. 27  is an explanatory drawing showing an operation of a pedestrian collision detection system in the second embodiment. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      A collision detection system according to the present invention is embodied by a pedestrian collision detection system for detecting a pedestrian&#39;s collision with a bumper. A protection system according to the preferred embodiment of the present invention is embodied by an air bag system for protecting a pedestrian colliding with a bumper by using the pedestrian collision detection system.  
     First Embodiment  
      With reference to  FIGS. 1-21 , a structure, an operation and advantages of the first embodiment of the present invention will be described. First, the structure of the first embodiment will be described in detail. With reference to  FIG. 1 , an air bag system  1  (protection system) protects a pedestrian colliding with a front bumper  2  of a vehicle and includes a pedestrian collision detection system  10  (collision detection system), an air bag ECU  11  (protecting device), pillar air bag inflators  12  and  13 , and a pillar air bag  14 .  
      The pedestrian collision detection system  10  is fitted (provided) near the front bumper  2  and detects a pedestrian&#39;s collision with the bumper  2 . Based on a detection result output from the pedestrian collision detection system  10 , the air bag ECU  11  outputs an ignition signal for inflating the pillar air bag  14 . The air bag ECU  11  is fitted at the center of the vehicle. The pillar air bag inflators  12  and  13  are respectively fitted near the right and left front pillars of the vehicle. Based on the ignition signal from the air bag ECU  11 , the pillar air bag inflators  12  and  13  inflate the pillar air bag  14  over a window shield of the vehicle so as to protect a pedestrian colliding with the front bumper  2 . The pillar air bag  14  is fitted near the front pillars. The pedestrian collision detection system  10  and the pillar air bag inflators  12  and  13  are connected electrically to the air bag ECU  11 .  
      As shown in  FIG. 2 , the pedestrian collision detection system  10  includes a sensor retaining plate  100 , an optical fiber sensor  101  (shock detecting device), touch sensors  102 - 106  (collision position detecting device), and a collision detection circuit  107 . The front bumper  2  includes a bumper cover  20  and an energy absorber (bumper absorber)  21 . The front bumper  2  is fitted to a bumper reinforcement  32 , which is fixed to fore end portions of side members  30  and  31  that serve as parts of the vehicle body. End portions of the bumper reinforcement  32  curve backward along the front bumper  2 . The bumper cover  20  is fixed to the energy absorber  21 , which is fixed to the bumper reinforcement  32 . The optical fiber sensor  101  and the touch sensors  102 - 106  are positioned between the energy absorber  21  and the bumper reinforcement  32 , and are retained by the sensor retaining plate  100 . The optical fiber sensor  101  is connected optically to the collision detection circuit  107 . The touch sensors  102 - 106  are connected electrically to the collision detection circuit  107 . The collision detection circuit  107  is connected electrically to the air bag ECU  11 .  
      The pedestrian collision detection system  10  will be described below in detail. The sensor retaining plate  100  is a resinous, generally rectangular plate for retaining the optical fiber sensor  101 . As shown in  FIGS. 3 and 4 , the sensor retaining plate  100  has on a rear side (aft side) thereof ribs  100   a - 100   d , which project in an aft direction, and which extend in a longitudinal direction of the sensor retaining plate  100 . Here, the longitudinal direction of the sensor retaining plate  100  is generally a transverse direction of the vehicle. The ribs  100   a - 100   d  hold the optical fiber sensor  101 . A dimension between the ribs  100   a  and  100   b  and a dimension between the ribs  100   c  and  100   d  are designed such that the ribs can securely hold the optical fiber sensor  101 . As shown in  FIG. 5 , end portions of the sensor retaining plate  100  curve backward along the bumper reinforcement  32 . A dimension between the front and rear sides (fore and aft surfaces) of the rib  100   a  is equal at any position in the longitudinal direction of the sensor retaining plate  100  (i.e., the projecting length of the rib  100   a  is equal at any position in the longitudinal direction of the sensor retaining plate  100 ). A dimension between the front and rear sides of each of the ribs  100   b - 100   d  is equal at any position in the longitudinal direction of the corresponding rib  100   b - 100   d , and is equal to a dimension between the front and rear sides of the rib  100   a.    
      When the load created by the shock of the collision is exerted on the optical fiber sensor  101 , the quantity of light transmitted by this sensor decreases. As shown in  FIG. 6 , the optical fiber sensor  101  includes an optical fiber  101   a , load concentration plates  101   b  and  101   c , and load transfer members  101   d  and  101   e.    
      The light is transmitted through the optical fiber  101   a . When the optical fiber  101   a  is bent under a load, a light transmission characteristic of the fiber  101   a  changes, so that the quantity of light transmitted through the fiber  101   a  decreases. The optical fiber  101   a  is turned back to have a U-shape. The load concentration plate  101   b  and the load transfer member  101   d  are assembled with an upper located portion of the optical fiber  101   a . The load concentration plate  101   c  and the load transfer member  101   e  are assembled with an lower located portion of the optical fiber  101   a.    
      The load concentration plates  101   b  and  101   c  are identical in structure. The load transfer members  101   d  and  101   e  are identical in structure. Thus, only the load concentration plate  101   b  and the load transfer member  101   d  will be described below.  
      The load concentration plate  101   b  is a generally rectangular plate, which may be metallic, and concentrates load locally to the optical fiber  101   a  so that the optical fiber  101   a  can be bent reliably. As shown in  FIGS. 7 and 8 , the load concentration plate  101   b  includes multiple protrusions  101   f  arranged at regular intervals and connectors  101   g ,  101   h , which connect both ends of the protrusions  101   f . The back surfaces of the protrusions  101   f  contact the optical fiber  101   a.    
      The load transfer member  101   d  is a generally rectangular parallelepiped, which may be made of elastic silicon resin, and transfers to the optical fiber  101   a  the load created by the shock of the collision. The load transfer member  101   d surrounds the optical fiber  101   a  and the load concentration plate  101   b . As shown in  FIG. 9 , end portions of the load transfer member  101   d  curve backward along the bumper reinforcement  32 . The dimension between the front and back sides of the load transfer member  101   d  (i.e., a projection length of the load transfer member  101   d ) is equal at any position in the longitudinal direction of the load transfer member  101   d , and is larger than that of the ribs  100   a  and  100   b.    
      Each of the touch sensors  102 - 106  has a contact that can be turned on by the shock of a collision (i.e., each touch sensor  102 - 106  serves as one of a plurality of contacts of the invention, the contacts being turned on by the shock of the collision). Because the touch sensors  102 - 106  are identical in structure, only the touch sensor  104  will be described below. As shown in  FIGS. 10 and 11 , the touch sensor  104  includes an elastic cylindrical electrical insulator  104   a  and wire electrodes  104   b - 104   e , which extend spirally on an inner peripheral surface of the insulator  104   a . The electrodes  104   b ,  104   d are positioned opposite from each other on the inner peripheral surface of the insulator  104   a . The electrodes  104   c ,  104   e  are positioned opposite from each other on the inner peripheral surface of the insulator  104   a . One end of the electrode  104   b  is connected electrically to one end of the electrode  104   c . One end of the electrode  104   d  is connected electrically to one end of the electrode  104   e . As shown in  FIGS. 12 and 13 , the touch sensor  104  is fitted on a rigid base member  4 . When a body  5  collides with the touch sensor  104  at a position that is located between both ends of the touch sensor  104 , the shock of the collision deforms the insulator  104   a . This brings the electrodes  104   b  and  104   e  into contact with each other, which extend spirally on the inner peripheral surface of the insulator  104   a . This also brings the electrodes  104   c  and  104   d  into contact with each other, which extend spirally on the inner peripheral surface of the insulator  104   a.    
      The contact of the electrodes  104   b - 104   e  can be detected by a circuit as shown in  FIGS. 14A and 14B , for example. The other ends of the electrodes  104   c  and  104   e  are connected via a resistor R 0 . The other end of the electrode  104   d  is grounded. The other end of the electrode  104   b  is connected to a power supply V 0  via a resistor R 1 . When the electrodes  104   b - 104   e  are out of contact with one another, as shown in  FIG. 14A , the voltage at the other end of the electrode  104   b  is a voltage calculated using the voltage of the power supply V 0 , the resistors R 0  and R 1 . When a shock is applied to the touch sensor  104  at a position that is located between both ends of this sensor, the electrodes  104   b  and  104   c  are brought into contact with the electrodes  104   e  and  104   d  respectively, as shown in  FIG. 14B . Thus, the other end of the electrode  104   b  is grounded so that the voltage at this end becomes 0 volt. Thus, it is possible to detect the contact of the electrodes  104   b  - 104   e  as a voltage change.  
      As shown in  FIGS. 15-18 , the optical fiber sensor  101  is fitted on the back surface of the sensor retaining plate  100 . The load transfer member  101   d  is fitted (assembled) between the ribs  100   a ,  100   b  and extends along them, in a state, where its curved portions extend along the curved portions of the sensor retaining plate  100 . The load transfer member  101   e  is assembled between the ribs  100   c ,  100   d  and extends along them in a state, where its curved portions extend along the curved portions of the sensor retaining plate  100 . The load transfer members  101   d ,  101   e  project backward from the ribs  100   a - 100   d  at any position in the longitudinal direction of the load transfer members  101   d ,  101   e.    
      The touch sensors  102 - 106  are provided on the front surface of the sensor retaining plate  100  to extend along the plate  100 , and are adjacently arranged relative to one another in the longitudinal direction of the plate  100 . The touch sensors  102 ,  106  are positioned at a right end portion and a left end portion respectively of the sensor retaining plate  100 . The touch sensors  103 ,  105  are positioned at the right and left curved portions respectively of the sensor retaining plate  100 . The touch sensor  104  is positioned at a middle portion of the sensor retaining plate  100 . This makes it possible to detect which of the right and left end portions, the right and left curved portions, and the middle portion of the sensor retaining plate  100  a shock is applied to.  
      As shown in  FIG. 19 , the optical fiber sensor  101  and touch sensors  102 - 106 , which are fitted to the sensor retaining plate  100 , are positioned between the energy absorber  21  and the bumper reinforcement  32 . The optical fiber sensor  101  is positioned between the sensor retaining plate  100  and the bumper reinforcement  32 . The touch sensors  102 - 106  are positioned between the sensor retaining plate  100  and the energy absorber  21 . The curved portions of the optical fiber sensor  101  and the touch sensors  103 ,  105  extend along the curved portions of the bumper reinforcement  32 .  
      The collision detection circuit  107  emits light, which is transmitted to the optical fiber sensor  101 . Based on the quantity of light transmitted by the optical fiber sensor  101 , the collision detection circuit  107  detects a pedestrian&#39;s collision with the front bumper  2 . As shown in  FIG. 20 , the collision detection circuit  107  includes a light emitting block  107   a  (shock detecting device), a light receiving block  107   b  (shock detecting device), a collision position detection block  107   c  (collision position detecting device), a correcting block  107   d  (correcting device), and a collision determining block  107   e  (collision determining device).  
      The light emitting block (portion)  107   a  emits light, which is supplied to the optical fiber  101   a . The light emitting block  107   a  is connected optically to one end of the optical fiber  101   a . The light receiving block (portion)  107   b  detects the quantity of light transmitted through the optical fiber  101   a . The light receiving block  107   b  outputs to the collision determining block (portion)  107   e  a signal having a magnitude equivalent to the transmitted quantity of light. The light receiving block  107   b  is connected optically to the other end of the optical fiber  101   a.    
      Based on voltage changes at the touch sensors  102 - 106 , the collision position detection block (portion)  107   c  detects a collision position. The collision position detection block  107   c  outputs a signal representing the collision position to the correcting block (portion)  107   d  and the air bag ECU  11 . The collision position detection block  107   c  is connected electrically to the touch sensors  102 - 106  and the air bag ECU  11 .  
      Based on an output signal from the collision position detection block  107   c , the correcting block  107   d  corrects an output signal from the light receiving block  107   b . Depending on the collision position, the correcting block  107   d  shifts a signal outputted from the light receiving block  107   b  by a preset (predetermined) amount, and outputs the shifted signal. That is, in one embodiment, depending on the collision position, the correcting block  107   d  corrects (changes) an amount, which is indicated by the signal outputted from the light receiving block  107   b , by the preset amount, and outputs the corrected signal. The correcting block  107   d  is connected electrically to the light receiving block  107   b , the collision position detection block  107   c , and the collision determining block  107   e.    
      Based on the corrected signal from the correcting block  107   d , the collision determining block  107   e  determines a pedestrian&#39;s collision with the front bumper  2  (shown in  FIG. 19 ). For example, when the magnitude of the output signal from the correcting block  107   d  is equal to or larger than a preset (predetermined) value, the collision determining block  107   e  determines that the pedestrian collides with the front bumper  2 . The collision determining block  107   e  is connected electrically to the correcting block  107   d  and the air bag ECU  11 .  
      The optical fiber sensor  101 , the light emitting block  107   a , and the light receiving block  107   b  correspond to the shock detecting device in the present invention. The touch sensors  102 - 106  and the collision position detection block  107   c  correspond to the collision position detecting device in this invention.  
      Next, the operation of the first embodiment will be described in detail. With reference to  FIG. 19 , when a pedestrian collides with the bumper cover  20 , the load created by the collision shock is applied through the energy absorber  21  to the touch sensors  102 - 106 . The load application turns on a corresponding one of the touch sensor  102 ,  103 ,  104 ,  105 , or  106  correspondingly to the collision position. The load is also applied through the sensor retaining plate  100  to the optical fiber sensor  101 . With reference to  FIG. 18 , the load on the optical fiber sensor  101  is transferred through the load transfer members  101   d ,  101   e  and the load concentration plates  101   b ,  101   c  to the optical fiber  101   a . Depending on the magnitude of the transferred load, the optical fiber  101   a  bends locally, so that the quantity of light transmitted through the fiber  101   a  decreases.  
      Even when the same load is applied to the front bumper  2  by the shocks of collisions, the load transferred to the optical fiber  101   a  varies greatly with different positions of the front bumper  2 , to which positions the load is applied. The transferred load is higher away from the middle portion toward the curved portions, and is the highest at the curved portions. Also, the transferred load is lower away from the curved portions toward the end portions, and is the lowest at the end portions. This is caused because the transferred load is reduced at the middle and end portions by deformation of the bumper reinforcement  32  or the like. The quantity of light transmitted through the optical fiber  101   a  varies greatly with the load transferred to it.  
      With reference to  FIG. 20 , based on the voltage change at the touch sensor  102 ,  103 ,  104 ,  105 , or  106  turned on by the shock of the collision, the collision position detection block  107   c  detects the position where the collision has occurred. Then, the collision position detection block  107   c  outputs a signal representing the collision position. The light receiving block  107   b  outputs a signal indicative of a magnitude equivalent to the quantity of light transmitted through the optical fiber  101   a . As shown in  FIG. 21 , the output signal from the light receiving block  107   b  indicates larger away from the middle portion toward the curved portions, and is the largest at the curved portions. Also the output signal indicates smaller away from the curved portions toward the end portions, and is the smallest at the end portions, similarly to the load transmitted to the optical fiber  101   a.    
      With reference to  FIG. 20 , based on the collision position signal outputted from the collision position detection block  107   c , the correcting block  107   d  corrects the output signal from the light receiving block  107   b  and outputs the corrected signal. With reference to  FIG. 21 , when the touch sensor  102  or  106  is turned on, the correcting block  107   d  shifts the output signal from the light receiving block  107   b , for example, by a preset amount S 1 , and outputs the shifted signal. When the touch sensor  104  is turned on, the correcting block  107   d  shifts the output signal from the light receiving block  107   b  by a preset amount S 2  and outputs the shifted signal. That is, in one embodiment, when the touch sensor  104  is turned on due to the collision of an object to a corresponding position of the bumper  2 , the correcting block  107   d  changes an amount indicated by the output signal from the light receiving block  107   b  by a preset amount S 2 , and the correcting block  107   d  outputs the corrected signal. Returning to the description of the present embodiment, when the touch sensor  103  or  105  is turned on, the correcting block  107   d  outputs the output signal from the light receiving block  107   b  without shifting the signal.  
      With reference to  FIG. 20 , when the magnitude of the output signal from the correcting block  107   d  is not lower than (i.e., is equal to or larger than) the preset value, the collision determining block  107   e  determines that a pedestrian is colliding with the front bumper  2 . When the collision determining block  107   e  determines that the pedestrian collides with the front bumper  2 , and when the collision position detection block  107   c  detects the collision position, with reference to  FIG. 1 , the air bag ECU  11  outputs an ignition signal, which causes the pillar air bag inflators  12 ,  13  to inflate the pillar air bag  14 , thereby protecting the colliding pedestrian.  
      Lastly, the advantages of the first embodiment will be described in detail. The pedestrian collision detection system  10  can detect the pedestrian&#39;s collision with the front bumper  2  accurately and precisely, regardless of the collision position. When the pedestrian collides with the vehicle, the shock of the collision causes a load to be transferred to the optical fiber sensor  101 . Even when the same load is applied to the front bumper  2  by the shock of the collision, the transferred load varies greatly with the different collision positions due to deformation of the bumper reinforcement  32  or the like. That is, the collision shock detected by the shock detecting device varies with a route, through which the shock is transmitted. Accordingly, as shown in  FIG. 21 , the output signal from the light receiving block  107   b  varies greatly. It is possible to reduce the signal variation (i.e., the difference of the magnitude among detection result for different collision positions) by correcting the output signal from the light receiving block  107   b  based on the collision position signal from the collision position detection block  107   c . Therefore, the determination based on the corrected signal from the correcting block  107   d  makes it possible to detect the pedestrian&#39;s collision with the front bumper  2  accurately and precisely, regardless of the collision position.  
      By having touch sensors  102 - 106  that can be turned on by the shock of the collision, the pedestrian collision detection system  10  can reliably detect the collision position.  
      The air bag system  1  can accurately and reliably detect and protect the pedestrian colliding with the front bumper  2 . It is possible to improve protection reliability for protecting the pedestrian using the air bag system  1  by determining the collision based not only on the determination result from the collision determining block  107   e  but also on the collision position detection result from the collision position detection block  107   c  to output an ignition signal. Also, because the touch sensors  102 - 106  and the collision position detection block  107   c  also function as a conventional safing sensor, the need for the safing sensor can be limited, thereby reducing the cost.  
      The touch sensors  102 ,  106  are, respectively, adjacent to the right and left end portions of the sensor retaining plate  100 . The touch sensors  103 ,  105  are, respectively, adjacent to the right and left curved portions of the sensor retaining plate  100 . The touch sensor  104  is adjacent to the middle portion of the sensor retaining plate  100 . This is an example of touch sensor arrangement, to which the touch sensor arrangement of the present invention is not limited.  FIG. 22  shows another example of touch sensor arrangement. In  FIG. 22 , a sensor retaining plate  100  retains touch sensors  202 ,  204 , and  206 . The touch sensors  202  extends from the left end portion of the sensor retaining plate  100  to the left curved portion of the plate  100  as shown in  FIG. 27 . Also, the touch sensors  206  extends from the right end portion of the sensor retaining plate  100  to the right curved portion of the plate  100  as shown in  FIG. 27 . The touch sensor  204  extends between the curved portions. The detection regions overlap at the curved portions. That is, at least one of the plurality of contacts  202 ,  204 ,  206  has the detection region, which overlaps with that of anther one of the plurality of contacts  202 ,  204 ,  206 . This makes it possible to detect the collision position more effectively based on combination of state (on and off state) of the touch sensors  202 ,  204 , and  206 . Detection resolution of the detection system, the resolution for detecting the collision position, can be improved without increasing the number of touch sensors  202 ,  204 , and  206 .  
     Second Embodiment  
      An air bag system of the second embodiment is substantially identical with that of the first embodiment, but the pedestrian collision detection system in the second embodiment has a mat sensor in place of the touch sensors in the first embodiment. A description will be provided below only for the mat sensor, which is a component of the pedestrian collision detection system of the second embodiment that differs from the counterpart in the first embodiment. No description will be provided for the common parts that do not need to be described. The elements of the second embodiment that are identical with the counterparts of the first embodiment will be assigned the same reference numerals as the counterparts are assigned.  
      First, the structure of the second embodiment will be described in detail with reference to  FIGS. 23-26 . The mat sensor  108  of the present embodiment has contacts (e.g., seventeen contacts in the present embodiment) that can be turned on by shocks. Thus, collision position detection regions are located at seventeen positions in the present embodiment. As shown in  FIGS. 23 and 24 , the mat sensor  108  includes elastic electrical insulators  108   a - 108   c  in the form of rectangular plates, seventeen electrodes  108   d  in the form of square plates, and seventeen electrodes  108   e  in the form of square plates. The insulators  108   a - 108   c  are laminated together, with the insulator  108   b  interposed between the insulators  108   a  and  108   c . The insulator  108   b  has seventeen square holes  108   f  arranged relative to each other at regular intervals in the longitudinal direction. The electrodes  108   d ,  108   e  are respectively formed on surfaces of the insulators  108   a ,  108   c . Each of the electrodes  108   d  and a corresponding one of the electrodes  108   e  are positioned in a corresponding one of the square holes  108   f  such that each of the electrodes  108   d  faces the corresponding one of the electrodes  108   e . A pattern (not shown) for electrically connecting the electrodes  108   d  and  108   e  to the collision position detection block  107   c  is formed. As shown in  FIG. 25 , the insulator  108   c  is fixed on the rigid base member  4 . When the body  5  collides with and applies the shock to the mat sensor  108  at any position thereof in the longitudinal direction, an area of the insulator  108   a  corresponding to the collision position deforms so that a corresponding electrode  108   d  that is positioned at the surface of the above deformed area contacts a corresponding electrode  108   e . The contact between the two corresponding electrodes  108   d ,  108   e  can be detected similarly to the first embodiment.  
      As shown in  FIG. 26 , the mat sensor  108  extends along the sensor retaining plate  100  on the front side of the sensor retaining plate  100  in a state the insulator  108   a  faces the fore direction and the insulator  108   c  faces the aft direction of the vehicle. This makes it possible to detect which of the seventeen areas in the longitudinal direction of the mat sensor  108  a shock is applied to.  
      The mat sensor  108  and the collision position detection block  107   c  correspond to the collision position detecting device of the present invention.  
      Next, the operation of the second embodiment will be described in detail. The other components other than the correcting block  107   d  of this embodiment operate in the same manner as in the first embodiment, and therefore an operation of the other components will not be described. A description will be provided below of the operation of the correcting block  107   d  for the output signal from the light receiving block  107   b . As shown in  FIG. 27 , when any one pair of electrodes  108   d  and  108   e  in the right or left curved portion of the mat sensor  108  is turned on, the correcting block  107   d  outputs the same output signal, which is the same as the output signal outputted from the light receiving block  107   b , without shifting the signal. When any one pair of electrodes  108   d ,  108   e  in one of the other portions of the mat sensor  108 , other than the above curved portion, is turned on, the correcting block  107   d  shifts the output signal from the light receiving block  107   b  by a corresponding preset amount, and outputs the shifted signal.  
      Lastly, the advantage of the second embodiment will be described in detail. It is possible to correct the output signal from the light receiving block  107   b  more effectively by increasing the number of the collision position detection regions to seventeen in the present embodiment from five in the first embodiment. This makes it possible to further reduce the output signal variation among collision positions, thereby further improving the collision detection accuracy of the detection system.  
      In each of the two embodiments, the optical fiber sensor  101  is used as a sensor for sensing the magnitude of the collision shock. However, the sensor for sensing the magnitude of the collision shock is not limited to the optical fiber sensor  101  but may be a strain gauge, a pressure sensor, or an acceleration sensor, which can sense a collision shock likewise with similar advantage.  
      In each of the two embodiments, the pedestrian collision detection system  10  detects the pedestrian&#39;s collision with the front bumper  2  of the vehicle. However, the collision detection system according to the present invention is not limited to the pedestrian collision detection system  10  but can also be applied to any other collision objects than pedestrians, and to collisions in any other directions than the forward direction, such as a left-right direction collision, a backward collision.  
      Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.