Abstract:
A load detecting sensor includes a first member, a second member, and an optical fiber. The first member has a groove having a bottom portion and a column portion which defines the groove. The second member covers the groove of the first member so that a surrounded space is formed. The optical fiber is arranged in the surrounded space. At least one of the first member and the second member is made of an elastic body. The surrounded space is deformable when load is applied to at least one of the first and the second members. When load is applied to at least one of the first and the second members, the deformation of the optical fiber is caused following the deformation of the surrounded space. Hereby, the load detecting sensor, which can decrease the manufacturing cost and increase the detecting sensitivity by the optical fiber, can be obtained.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2007-186023 filed on Jul. 17, 2007, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a load detecting sensor and a collision detecting sensor using the same. 
     BACKGROUND OF THE INVENTION 
     Conventional collision detecting sensors are disclosed in JP-A-2006-105973 (Reference 1) corresponding to EP 1795878A1 and in JP-A-2005-249680 (Reference 2) corresponding to US 2005/0193830 A1. The collision detecting sensor of Reference 1 includes an optical fiber and a corrugated plate, which are covered by a mold rubber. The collision detecting sensor of Reference 2 includes a concave holding member, a corrugated member arranged at the bottom of the holding member, an optical fiber arranged inside the concave holding member, and a counterpart member arranged so as to space from the holding member and the optical fiber at the initial state. 
     However, the sensor of Reference 1 needs to reshape the mold rubber by the press work after the mold rubber is extruded. If the mold rubber is pressed with the optical fiber is set in advance, the optical fiber may be broken. Therefore, for example, the mold rubber is pressed with a metal rod is set in advance, and after the metal rod is removed, the optical fiber needs to be inserted into a hole in which the metal rod was filled. Therefore, the manufacturing cost becomes high in the constitution that the optical fiber is covered by the mold rubber. 
     On the other hand, the sensor of Reference 2 can resolve the problem of the manufacturing cost since a mold rubber such as Reference 1 is not used. As described in Reference 2, the optical fiber is easily broken. According to Reference 2, when the excessive impact force is generated, since the impact is not transmitted to the optical fiber, the breakage of the optical fiber can be avoided. However, even though the impact force is small, when the optical fiber is pressed by the highly-rigid member directly, the optical fiber may be broken. To solve this problem, an outer surface of the optical fiber is covered by an elastic member such as a rubber. However, by the elastic force of the rubber which is attached to the outer surface of the optical fiber, the pressing force by the corrugated member is likely to be decreased and the sensitivity of the optical fiber is decreased. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems, it is an object of the present disclosure to provide a load detecting sensor and a collision detecting sensor using the same which can decrease the manufacturing cost and increase the detecting sensitivity by the optical fiber. 
     According to the present disclosure, a load detecting sensor includes a first member, a second member, and an optical fiber. The first member has a groove having a bottom portion and a column portion which defines the groove. The second member covers the groove of the first member so that a surrounded space is formed. The optical fiber is arranged in the surrounded space. At least one of the first and the second members is made of an elastic body. The surrounded space is deformable when load is applied to at least one of the first and the second members. 
     In the load detecting sensor, when load is applied to at least one of the first and the second members, the deformation of the optical fiber is caused following the deformation of the surrounded space. Hereby, the load detecting sensor, which can decrease the manufacturing cost and increase the detecting sensitivity by the optical fiber, can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a vertical cross sectional view of a vehicle in a front-back direction showing an anterior portion of a vehicle in a load detecting sensor according to a first embodiment; 
         FIG. 2  is a cross sectional view showing a portion of the load detecting sensor taken along line I-I in  FIG. 1 ; and 
         FIG. 3  is a vertical cross sectional view of a vehicle in a front-back direction showing an anterior portion of the vehicle in a load detecting sensor according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Next, a load detecting sensor will be described by taking a collision detecting apparatus for vehicles as an example, which detects that a vehicle collides with an object in front of the vehicle. The load detecting sensor is used as a collision detecting sensor. A collision detecting apparatus for vehicles of a first embodiment will be described with reference to  FIG. 1  and  FIG. 2 . 
     The collision detecting apparatus is mainly an apparatus which detects that the vehicle collides with a pedestrian (hereinafter referred to as “an outside object”). The collision detecting apparatus includes a bumper reinforcement  1 , a bumper cover  2 , a bumper absorber  3 , a load detecting sensor  4  and an electronic control unit (hereinafter referred to as “ECU”)  5 . 
     The bumper reinforcement  1  is extended in the lateral direction of the vehicle horizontally, and is a structural member constituting a chassis frame of the vehicle. As shown in  FIG. 1 , for example, double-deck beams  1   a  are provided in the center of inside the bumper reinforcement  1 , so that the bumper reinforcement  1 , which has a cross section like a grid, is formed from a metallic hollow member. The bumper reinforcement  1  is fixed to the forward end of the vehicle of a front side member  6 , which is arranged at right and left ends of the vehicle. 
     The bumper cover  2  is arranged at the most anterior surface of the vehicle and covers the front side of the vehicle of the bumper reinforcement  1 . That is, the bumper cover  2  covers the front side of the vehicle of the bumper absorber  3 . Therefore, when the vehicle collides with the outside object which locates in front of the vehicle, the bumper cover  2  collides with the outside object. The bumper cover  2  is supported by the bumper absorber  3  so as to be movable relatively with respect to the bumper reinforcement  1  in the direction of the rear side of the vehicle. 
     As shown in  FIG. 1 , the bumper absorber  3  is formed from a foam resin, for example. The shape of the bumper absorber  3  is rectangular as seen in the vertical cross sectional view of the vehicle in the front-back direction. The bumper absorber  3  is attached to the load detecting sensor  4  so as to be sandwiched between the bumper reinforce  1  and the bumper cover  2  and so as to extend in the lateral direction of the vehicle horizontally. The bumper absorber  3  has a function of absorbing the impact by crashing and deforming itself, when the front side of the vehicle collides with the outside object. For example, when a pedestrian collides with the bumper cover  2 , the bumper absorber  3  has a function to guard the pedestrian&#39;s leg portion. 
     The shape of the load detecting sensor  4  is rectangular as seen in the vertical cross sectional view of the vehicle in the front-back direction. The load detecting sensor  4  is arranged so as to be sandwiched between the bumper reinforcement  1  and the bumper absorber  3  and so as to extend in the lateral direction of the vehicle horizontally. The load detecting sensor  4  includes a first member  41 , a second member  42 , concave-convex members  43  and optical fibers  44 . 
     The first member  41  is formed from a resin. The shape of the first member  41  is a substantially elongated flat plate. Two concave portions, i.e., grooves  41   a  and  41   a  are formed on one surface of the flat plate-shaped first member  41  in the lateral direction. Specifically, the groove  41   a  is formed so as to extend in the direction (the lateral direction of the vehicle) which intersects the front-back direction of the vehicle (the collision detecting direction of the outside object, the front-back direction in  FIG. 1 ), and so as to open toward the rear side of the vehicle. That is, the first member  41  includes a bottom portion  41   b , which forms the bottom surface of the groove  41   a , and at least a pair of column portions  41   c , which form the side surfaces of the groove  41   a  and is formed on the bottom portion  41   b  integrally. The cross-sectional surface of the groove  41   a  is substantially rectangular. The first member  41  is arranged so that the front side of the bottom portion  41   b  is attached to the rear side of the bumper absorber  3 . Therefore, when the outside object collides with the bumper cover  2 , the first member  41  also moves relatively with respect to the bumper reinforcement  1  in the direction of the rear side of the vehicle as the bumper cover  2  moves relatively with respect to the bumper reinforcement  1  in the direction of the rear side of the vehicle. 
     The second member  42  is formed to be substantially elongated flat plate-shaped. The size of the second member  42  is substantially same as that of the first member  41 . The second member  42  is arranged so that one surface of the second member  42  is attached to the end surfaces of the column portions  41   c  of the first member  41 . The second member  42  covers each of the two grooves  41   a  to form two surrounded spaces  4   a  and  4   a . Furthermore, another surface of the second member  42  is arranged so as to attach to the front side of the vehicle of the bumper reinforcement  1 . That is, a part of the second member  42  is arranged to be sandwiched between the column portions  41   c  and the bumper reinforcement  1 . 
     The second member  42  is formed from an elastic member such as a silicone rubber. Thus, the rigidity of the second member  42  is lower than that of the first member  41 . Therefore, when the outside object collides with the bumper cover  2 , the first member  41  moves relatively in the rear side direction of the vehicle with respect to the bumper reinforcement  1  and the second member  42  is deformed. The surrounded spaces  4   a  become narrower by the deformation of the second member  42 . 
     Each concave-convex members  43  is formed from resin and elongated flat plate-shaped. Specifically, the concave-convex member  43  is formed to be corrugated (concave-convex) at a constant pitch on one surface of the elongated flat plate in its longitudinal direction (vehicle lateral direction). The concave-convex member  43  is formed so that another side of the concave-convex member  43  contacts the bottom of the groove  41   a , that is, the bottom portion  41   b  of the first member  41 , in the surrounded space  4   a . That is, the concave-convex member  43  is fixed to the bottom of the corresponding groove  41   a  so that the convex portion of the member  43  faces an aperture side of the groove  41   a . The concave-convex member  43  may be formed with the first member  41  integrally or separately. When the concave-convex member  43  is formed with the first member  41  integrally, the manufacturing cost can be decreased by reducing the number of components. 
     The optical fiber  44  includes a fiber core  44   a , which has high refractive index, and a fiber clad  44   b , which has low refractive index. The fiber clad  44   b  is arranged around the fiber core  44   a . The optical fiber  44  is arranged in each surrounded space  4   a . Specifically, in an initial state (a state that the outside object does not collide), the optical fiber  44  contacts the one surface of the second member  42  and the convex portion of the concave-convex member  43  in the surrounded space  4   a . That is, when the outside object collides with the bumper cover  2 , the flectional deformation of the optical fiber  44  is caused following the deformation of the surrounded space  4   a . Therefore, the amount of transmitted light through the optical fiber  44  is changed before or after the collision with the outside object. In addition, the optical fiber  44  and the column portion  41   c  of the first member  41  may be separated through a space or not. 
     As known well, the ECU  5  receives a signal of light emitted from a light emitting element at one end of the optical fiber  44  and received at another end of the optical fiber  44 . Based on the amount of transmitted light through the optical fiber  44 , whether the outside object collides with the bumper cover  2  is determined. For example, when the amount of transmitted light is changed significantly, it is determined that the outside object collides with the bumper cover  2 . Moreover, the ECU  5  determines whether the collided outside object is a pedestrian based on the change of the amount of transmitted light. 
     When the collided outside object is determined a pedestrian, a pedestrian protection device (not shown) is activated. The pedestrian protection device may be mounted on a hood of the vehicle and protects the pedestrian when the vehicle collides with the pedestrian. For example, a device which flips up the hood and an airbag device arranged on the hood may be used as the pedestrian protection device. 
     Since the optical fiber  44  is not covered by a mold rubber, the manufacturing cost can be decreased. In the initial state, the second member  42  contacts the column portions  41   c  of the first member  41 . Therefore, considering the impact force, which is generated when the outside object collides with the bumper cover  2  and the impact force is received by the second member  42 , the impact force is dispersed into a pressing force to the column portion  41   c  of the first member  41  and a pressing force to the optical fiber  44 . Therefore, when the outside object collides with the bumper cover  2 , the pressing force received from the first member  41  and the second member  42  is decreased. That is, the damage of the optical fiber  44  can be decreased. 
     An elastic member such as a rubber is not arranged between the optical fiber  44  and the concave-convex member  43 . Thus, when the outside object collides with the bumper cover  2 , the optical fiber  44  directly contacts one surface of the concave-convex member  43  and the optical fiber  44  is pressed. That is, the sensitivity of the optical fiber  44  is increased. Furthermore, the optical fiber  44  contacts one surface of the second member  42  and the convex portion of the concave-convex member  43 . Thereby, when the outside object collides with the bumper cover  2 , the collision can be detected by the optical fiber  44  immediately. Therefore, the detecting sensitivity can be increased. 
     It is noted that in the first embodiment, the attachment of the optical fiber  44  can be performed as follows. The first attaching method is that the optical fiber  44  is inserted into the groove  41   a  of the first member  41 , and then the second member  42  is fixed to the first member  41 . The second attaching method is that the optical fiber  44  is attached to one surface of the second member  42  by adhesion, and then the second member  42  is fixed to the first member  41  so that the optical fiber  44  is inserted into the groove  41   a.    
     Second Embodiment 
     Next, a load detecting sensor  14  of a second embodiment will be described with reference to  FIG. 3 . Here, the load detecting sensor  14  of the second embodiment differs from the load detecting sensor  4  of the first embodiment only in a second member  142 . 
     The collision detecting sensor  14  has two second members  142  and  142 . Each second member  142  includes a main body portion  142   a  and a protruding portion  142   b . The main body portion  142   a  is formed to be a generally elongated flat plate shape, and the width of the main body  142   a  is same as the width between the pair of column portions  41   c . The protruding portion  142   b  is formed to project in the longitudinal direction of the vehicle at substantially center portion of one surface of the main body portion  142   a . A concave portion, which receives the optical fiber  44 , is formed at an end surface of the protruding portion  142   b . Furthermore, the protruding width of the protruding portion  142   b  in the vehicle lateral direction is substantially same as the groove width of the groove  41   a  of the first member  41 , and the protruding height of the protruding portion  142   b  from the main body portion  142   a  is smaller than that of the groove depth of the groove  41   a  of the first member  41 . The second member  142  is arranged so that the protruding portion  142   b  is fit in the groove  41   a  and one surface of the main body portion  142   a  is attached to an end surface of the pair of column portions  41   c  of the first member  41 . As shown in  FIG. 3 , the concave-convex member  43  and the protruding portion  142   b  are arranged so as to face each other in a collision detecting direction, i.e., a load detecting direction, and a space is formed between the concave-convex member  43  and the protruding portion  142   b . Thus, in case that the concave-convex member  43  shifts to the optical fiber  44  side due to collision, the shifting of the member  43  stops when the member  43  contacts the protruding portion  142   b . Therefore, a breakage of the optical fiber  44  by a crash which occurs by the shifting can be prevented. 
     The attaching method of the load detecting sensor  14  is as follows. Firstly, the optical fiber  44  is fit in the protruding portion  142   b  of the second member  142 . On the other hand, in case that the concave-convex member  43  is arranged separately from the first member  41 , the concave-convex member  43  is arranged in the bottom of the groove  41   a  of the first member  41 . Subsequently, the second member  142  holding the optical fiber  44  is fixed to the first member  41  so that the optical fiber  44  and the protruding portion  142   b  are inserted to the groove  41   a  of the first member  41 . Thereby, the attachment of the optical fiber  44  can become easy, and the manufacturing processes can be decreased. 
     In the above embodiments, the first member  41  forming the groove  41   a  is arranged at the front portion of the vehicle. However, the arrangement of the first member  41  and the second member  42 ,  142  may be reversed in the front-back direction of the vehicle. Moreover, the rigidity of the first member  41  is higher than that of the second member  42 ,  142 . However, the rigidity of the second member  42 ,  142  may be higher than that of the first member  41 . Furthermore, both the first member  41  and the second member  42 ,  142  may be formed from the elastic body. 
     In the above embodiments, the concave-convex member  43  is arranged in the bottom of the groove  41   a . However, the concave-convex member  43  may be arranged at one surface of the second member  42 ,  142 . In this case, the concave-convex member  43  may be formed with the second member  42 ,  142  integrally or separately. Moreover, the concave-convex member  43  may be arranged at both the bottom of the groove  41   a  and one surface of the second member  42 ,  142 . In this case, the pressing forth to the optical fiber  44  can be increased. Furthermore, the concave-convex member  43  is formed to be corrugated, however, may be formed to be stepwise. 
     While the invention has been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments and constructions. The invention is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, which are preferred, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.