Abstract:
A bumper beam assembly for a vehicle comprises a bumper beam having at least two round pipes, a bracket, first and second support members, first and second side frames, and a bracket formed into a rounded shape to match the external shape of the round pipes. The round pipes are arranged vertically and the sum of the diameters of the round pipes is smaller than the height of the bumper beam. The first and second support members have arc-shaped recesses which conform to the external shape of the round pipes and support the round pipes to connect the side frame to the round pipes, and one of the round pipes is positioned below a central point of the first and second side frames, and one of the round pipes is positioned above the central point.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a mounting structure of a bumper beam on at least one of the front and rear sides of a vehicle. 
   At lower parts on the front side and rear side of a vehicle, bumpers are provided. Bumpers protect functional parts such as the body and lamps of a vehicle when the vehicle collides with other objects. At the back of a bumper, a bumper beam is provided to absorb shock energy when the vehicle body receives a shock in a collision. 
   Bumpers come in various shapes depending on the size of the vehicle. Furthermore, because bumpers also play a role in enhancing design properties, bumpers have a variety of different design shapes used in accordance with the vehicle type. Therefore, many types of bumper beams have been manufactured so as to match the bumper shape. 
   To manufacture a bumper beam, a material such as a steel sheet is used. The steel sheet used for the bumper beam has a thickness larger than a predetermined thickness to ensure the strength of the whole bumper beam. The bumper beam is manufactured by being integrally molded so as to match the length in the vehicle width direction by means of roll molding or press molding. 
   A bumper beam structure is disclosed in, for example, Japanese Patent Provisional Publication No. 2000-85496. In this vehicular bumper device, a recessed part is provided in the front surface of a bumper reinforce member, and one pipe-shaped reinforcing matter is attached to this recessed part so as to be fitted in the recessed part. 
   Further, Japanese Utility Model Publication No. 5-27315 discloses a bumper structure in which a pair of upper and lower reinforce members formed of a steel pipe are arranged at an upper part of a side frame. 
   However, in order to manufacture bumper beams having different shapes and sizes depending on the vehicle type and model, many kinds of press molding dies are needed to fabricate steel sheets. Also, in order to integrally press mold the bumper beam over the total length in the width direction of vehicle, a large molding die is needed, and further the manufacturing equipment is also increased in size. This requires high manufacturing cost and managing expense for the dies, so that it is not easy to reduce the manufacturing cost of vehicle as a whole. 
   Also, in order to decrease the weight of a bumper beam, it is necessary to decrease the material thickness thereof. However, a decrease in material thickness lowers the bending strength of the whole of the bumper beam. Therefore, there is a limit in achieving decreased weight and increased strength of the bumper beam at the same time. 
   On the other hand, in the structure described in Japanese Patent Provisional Publication No. 2000-85496, since the reinforcing matter is formed by only one pipe, shock energy is absorbed insufficiently. 
   Also, in the structure described in Japanese Utility Model Publication No. 5-27315, since the reinforce members are provided at the upper part of the side frame, for example, when a force is applied to the reinforce member from the outside of vehicle, the force is received only by the strength of the reinforcing members. To compensate for that, the steel pipe forming the reinforcing member is increased in size. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above situation, and accordingly an object thereof is to provide a mounting structure of a bumper beam in which the weight is decreased while a sufficient strength is ensured by using two or more pipes. 
   To solve the problems with the related art, the present invention provides a mounting structure of a bumper beam for mounting the bumper beam to at least one of a front part or a rear part of a side frame which is provided on both sides in the vehicle width direction and extends in the longitudinal direction of vehicle, wherein the bumper beam has two or more pipes each having a length at least equal to a distance between the side frames, the pipes being arranged vertically one above another so that the outside surfaces of the pipes are located at the same position in the longitudinal direction of the vehicle, and a central position in the height direction of the bumper beam approximately coincides with a central position in the height direction of the side frame. 
   In a central portion in the vehicle width direction of the bumper beam, a bracket is provided so as to have a length of at least about one-fourth the length of the bumper beam and to connect the pipes to each other. 
   Also, regulating portions for regulating the vertical positions of the pipes are formed in the upper and lower end portions of the bracket. 
   Further, a strength increasing/decreasing portion is provided in an intermediate portion of the bracket in the vertical direction of the pipes. 
   As described above, in the present invention, the bumper beam is formed of pipes. Therefore, no large die for press molding is required, and the manufacturing cost and managing expense of dies can be reduced. Moreover, if an ordinary pipe is used, the cost can further be reduced. 
   Also, since the pipes are arranged vertically one above another so that the outside surfaces thereof are located at the same position in the longitudinal direction of the vehicle, when a force is applied from the outside of the vehicle, the force is distributed to and absorbed by the upper and lower pipes. Thereby, for example, when a force is applied to the bumper beam from the outside of the vehicle, the bumper beam can withstand a stronger force. 
   Further, since the bumper beam is arranged so that the central position in the height direction of the bumper beam approximately coincides with the central position in the height direction of the side frame, the side frame can receive the force applied from the outside of the vehicle. Thereby, the weight of the bumper beam can be reduced because the pipe need not have a larger shape than necessary. 
   In the central portion in the vehicle width direction of the bumper beam, the bracket is provided so as to have a length of at least about one-fourth the length of the bumper beam and to connect the pipes to each other. Therefore, the strength of the central portion of the bumper beam can further be increased, and the outside surfaces of the pipes can easily be arranged in line with each other. Also, since the upper and lower pipes are connected to each other, the deformation of upper and lower pipes becomes almost the same, so that energy is absorbed effectively. 
   Since the bracket has a length of at least about one-fourth the length of the bumper beam, the deformation mode of pipe of the bumper beam can be stabilized at the time of offset collision etc. 
   Since the regulating portions for regulating the vertical positions of the pipes are formed in the upper and lower end portions of the bracket, when a force is applied to the bumper beam from the outside of the vehicle, the pipes can be prevented from deforming vertically. Also, when the bumper beam is assembled, the vertical positioning of the pipes can be performed easily. Therefore, the assembling accuracy can be increased, which eliminates variations in assembly dimensions, so that the energy absorbing performance can be stabilized. 
   Also, the strength of the central portion of the bumper beam is adjusted by providing the strength increasing/decreasing portion in an intermediate portion of the bracket in the vertical direction of the pipes. Therefore, the strength necessary in the central portion of the bumper beam can be increased or decreased according to the type of vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a general perspective view of a mounting structure of a bumper beam in accordance with an embodiment of the present invention; 
       FIG. 2  is an exploded perspective view of a mounting structure of a bumper beam in accordance with an embodiment of the present invention; 
       FIG. 3  is a sectional view of a mounting structure of a bumper beam in accordance with an embodiment of the present invention; 
       FIG. 4  is a schematic view showing a state of a load-displacement test for a mounting structure of a bumper beam in accordance with an embodiment of the present invention; 
       FIG. 5  is a sectional view of a conventional bumper beam; 
       FIG. 6  is a graph showing a result of a load-displacement test, comparing the strength of a mounting structure of a bumper beam in accordance with an embodiment of the present invention with a conventional mounting structure; 
       FIG. 7  is a sectional view of a mounting structure of a bumper beam in accordance with another embodiment of the present invention; and 
       FIG. 8  is a sectional view showing brackets used for a mounting structure of a bumper beam in accordance with another embodiment of the present invention,  FIGS. 8(   a ) to  8 ( c ) showing modifications of the bracket. 
   

   DETAILED DESCRIPTION 
   The best mode for carrying out the present invention will now be described in detail with reference to  FIGS. 1 to 3 .  FIG. 1  is a perspective view showing a state before a bumper beam  1  is mounted to side frames  2 , and  FIG. 2  is an exploded perspective view showing the bumper beam  1  disassembled into parts.  FIG. 3  is a sectional view showing the bumper beam mounted to the side frames  2 , which is cut at a central portion in the vehicle width direction. 
   In this embodiment, explanation is given of a case where the number of pipes forming the bumper beam  1  is two. Also, in this embodiment, explanation is given of a mounting structure of a bumper beam for mounting the bumper beam  1  at a lower part on the front side of a vehicle. 
   In the mounting structure of a bumper beam shown in  FIG. 1 , the bumper beam  1  is mounted to the side frames  2  provided on the vehicle body side. As shown in  FIGS. 1 and 2 , the bumper beam  1  has two pipes  3 , support members  4  for fixing both end portions in the vehicle width direction of the pipes  3 , and a bracket  5  provided on the front side in a central portion in the vehicle width direction of the pipes  3 . As shown in  FIG. 3 , a bumper cover  31  covers the front surface of the bumper beam  1  on the side opposite to the side frames  2  with the bumper beam  1  being held therebetween. The side frame  2  is formed of a steel pipe having a square cross section which is provided on both sides in the vehicle width direction so as to extend in the longitudinal direction of vehicle. 
   The two pipes  3  used for the bumper beam  1  are provided between the side frames  2  provided on both sides. The pipes  3  are arranged so that the lengthwise direction thereof substantially coincides with the vehicle width direction. The two pipes  3  are arranged vertically in parallel with each other, and front surfaces  3   a  (outside surfaces, refer to  FIG. 3 ) of the pipes  3  are located at the same position in the longitudinal direction of the vehicle. Also, the two pipes  3  are bent delicately so as to match the bumper shape and the fixing positions of the support members  4 . For these pipes  3 , a high tensile strength steel such as STAM980 is used. This high tensile strength steel has a tensile strength about 150% of that of a non-tempered steel. 
   As shown in  FIGS. 1 and 2 , the support member  4  is formed by a pipe fixing member  6  and a side frame mounting member  7 , and the pipe fixing member  6  and the side frame mounting member  7  are fixed integrally by welding. 
   The pipe fixing member  6  is manufactured by pressing a steel sheet. As shown in  FIG. 2 , the pipe fixing member  6  has a body portion extending vertically, and two arc-shaped recesses  8  (refer to  FIG. 2 ) are provided in this body portion with a space provided in the vertical direction therebetween. The arc-shaped recess  8  is formed so that the shape thereof coincides with the external shape of the pipe  3 . The end portions of the pipes  3  are arranged in these arc-shaped recesses  8 , and are fixed thereto by welding. Also, as shown in  FIG. 2 , at a lower part of the pipe fixing member  6 , two holes  14  are provided. 
   The positions in the height direction of the arc-shaped recesses  8  are such that as shown in  FIG. 3 , in the state in which the bumper beam  1  is mounted to the side frame  2 , a central position  32  in the height direction of the bumper beam  1  approximately coincides with a central position  33  in the height direction of the side frame  2 . More specifically, when the bumper beam is formed by two pipes  3 , the upper pipe and the lower pipe are arranged so as to be at an approximately equal distance from the central position  33  in the height direction of the side frame  2  with the central position  33  being held between the two pipes. 
   As shown in  FIGS. 1 and 2 , the side frame mounting member  7  is formed so as to extend from an upper part of the pipe fixing member  6  toward the rear of the vehicle. At the rear end of the side frame mounting member  7 , an engagement portion  11  is provided. This engagement portion  11  is formed by bending a rear end portion of the side frame mounting member  7  downward. Also, the side frame mounting member  7  is provided with a hole  12  (refer to  FIG. 2 ) on the front side of the engagement portion  11 . 
   On the other hand, in a top surface  2   a  of the side frame  2  shown in  FIG. 1 , an engagement hole  13  is provided so that the engagement portion  11  of the side frame mounting member  7  engages with the engagement hole  13 . Also, in the top surface  2   a , a mounting screw hole  9  is provided on the front side of the engagement hole  13 . This screw hole  9  is provided so as to align with the hole  12  in the side frame mounting member  7  in the state in which the engagement portion  11  is engaged with the engagement hole  13 . 
   Also, as shown in  FIG. 1 , in the tip end portion on the front side of the side frame  2 , an attachment member  10  is provided so as to cover the opening of the square steel pipe of the side frame  2 . At a lower part of the attachment member  10 , screw holes  15  are provided. Like the screw hole  9 , the screw holes  15  are provided so as to align with the holes  14  in the pipe fixing member  6  in the state in which the engagement portion  11  is engaged with the engagement hole  13 . 
   The bracket  5  is provided on the front side in a central portion in the vehicle width direction of the two pipes  3 , and has a length of at least about one-fourth the length of the bumper beam  1 . As shown in  FIG. 3 , the bracket  5  is put on the front surfaces  3   a  of the two pipes  3  in a state of being in contact with them, and is fixed to the pipes  3  by welding of the periphery thereof. Also, an upper end portion  5   a  and a lower end portion  5   b  of the bracket  5  are bent toward the rear of the vehicle into a round shape such as to match the external shape of the pipe  3 . The upper end portion  5   a  and the lower end portion  5   b  regulate the vertical position of the pipes  3  by being in contact with the upper or lower outer peripheral surface of the pipe  3 . 
   Next, a method for mounting the bumper beam  1  to the side frame  2  is explained. 
   The bumper beam  1  is aligned with the side frame  2  by engaging the engagement portion  11  of the side frame mounting member  7  with the engagement hole  13  in the side frame  2  from the upside. A bolt, not shown, is inserted into the hole  12  from the upside, and the bolt is tightened, by which the side frame mounting member  7  is mounted to the side frame  2 . Likewise, bolts, not shown, are inserted into the holes  14  and  15 , and are tightened. Thereby, the bumper beam is mounted to the side frame  2 . 
   Also, when this bumper beam  1  is used on a vehicle type having a different vehicle width, the lengths of the pipes  3  are changed. In this case, the shapes of the support member  4  and the bracket  5  need not be changed. Further, when this bumper beam  1  is applied to a vehicle type having a different vehicle height, the support member  4  and the bracket  5  are replaced with those that are manufactured so as to match the vehicle height. In this case, dies for the support member  4  and the bracket  5  must be manufactured newly. However, the newly manufactured dies may be smaller in size than the conventional dies. 
   Next, a strength test conducted on the mounting structure of a bumper beam in accordance with the embodiment of the present invention and the test results thereof are explained. 
     FIG. 4  shows a state in which the mounting structure of a bumper beam in accordance with the embodiment of the present invention is subjected to a load test by using a three-point bending test machine. The bumper beam  1 , which has been assembled in the same way as in the case where it is mounted to the vehicle, is set on a test jig  21   a  with the front side thereof being directed to the upside. The bumper beam  1  is set so as to receive a test load (bending load) in the central portion of the bumper beam  1  from a loading machine  21   b  that presses the bumper beam  1  downward. In this test, a setting pitch L of the bumper beam  1  is about 900 mm. Also, a load test was conducted under the same test conditions on a conventional bumper beam  34  having a cross-sectional shape shown in  FIG. 5 . This conventional bumper beam  34  was manufactured of a steel sheet having the same material and thickness as those of the pipe  3 .  FIG. 6  shows the relationship between test load F and displacement, which was obtained by this test. 
   From the test results shown in  FIG. 6 , it can be seen that the mounting structure of a bumper beam explained in the embodiment achieves an about 25 percent increase in strength as compared with the conventional structure. Also, the same test revealed that if the number of pipes  3  is decreased to one, the strength decreases compared with the conventional structure. Therefore, at least two pipes are used. Further, unless the two pipes  3  receive the test load F substantially at the same time, the load resistance decreases. Therefore, the two pipes  3  must be assembled so that the front surfaces  3   a  of the pipes  3  are located approximately the same position in the longitudinal direction of the vehicle. 
   For the mounting structure of a bumper beam in accordance with this embodiment of the present invention, the product cost can be reduced by about 15% and the die cost and the jig cost can be reduced by about 45% as compared with a conventional structure because the pipe  3  formed of an ordinary pipe is used. Also, the product weight can be reduced by about 20%. 
   Also, since the pipes  3  are arranged vertically and the outside surfaces  3   a  thereof are located at the same position in the longitudinal direction of the vehicle, when a force is applied from the outside of the vehicle, the force is distributed to and absorbed by the upper and lower pipes  3 . Thereby, for example, when a force is applied to the bumper beam  1  from the outside of the vehicle, the bumper beam  1  can withstand a stronger force. 
   Further, since the bumper beam  1  is arranged so that the central position  32  in the height direction of the bumper beam  1  approximately coincides with the central position  33  in the height direction of the side frame  2 , the side frame  2  can receive, via the support member  4 , the force applied from the outside of the vehicle. Thereby, the weight of the bumper beam  1  can be reduced because the pipe  3  need not have a larger shape than necessary. 
   In the central portion in the vehicle width direction of the bumper beam  1 , the bracket  5  is provided so as to have a length of at least about one-fourth the length of the bumper beam  1  and to connect the pipes  3  to each other. Therefore, the strength of the central portion of the bumper beam  1  can further be increased, and the outside surfaces  3   a  of the pipes  3  can easily be located at the same position in the longitudinal direction of the vehicle. 
   Since regulating portions for regulating the vertical positions of the pipes  3  are formed in the upper and lower end portions of the bracket  5 , when a force is applied to the bumper beam  1  from the outside of the vehicle, the pipes  3  can be prevented from deforming vertically. Also, when the bumper beam  1  is assembled, the vertical positioning of the pipes  3  can be performed easily. 
   The above is description of one embodiment of the present invention. The present invention is not limited to the above-described embodiment, and various changes and modifications can be made based on the technical concept of the present invention. 
   For example, when this mounting structure of a bumper beam is used for a large vehicle, three or more pipes  3  can be used to increase the load resistance. In this case, provision can be made easily by increasing the number of arc-shaped recesses  8  in the support member  4  and by changing the shape of the bracket  5 . Also, in the embodiment of the present invention, the case where the pipe  3  is formed of a round pipe has been described. However, the use of a square pipe or an irregularly shaped pipe achieves the same effect. 
   As shown in  FIG. 7  and  FIGS. 8(   a ) to  8 ( c ), the bracket  5  having a different cross-sectional shape is selected and installed to the bumper beam  1 , by which the strength of the central portion of bumper beam can be increased or decreased so as to match the kind of vehicle. The cross-sectional shape of a bracket  51  shown in  FIG. 7  is formed by installing the bracket  51  from the back side of the pipes  3  and by bending the central portion in the height direction so that the central portion extend along a plane on which the two pipes  3  are opposed to each other. The cross-sectional shape of a bracket  52  shown in  FIG. 8(   a ) is formed by bending the bracket  52  so that the upper and lower end portions thereof are fitted along the opposed surfaces of the two pipes  3 . The cross-sectional shape of a bracket  52  shown in  FIG. 8(   b ) is formed by bending the central portion in the height direction so that the central portion extend along a plane on which the two pipes  3  are opposed to each other and further by forming a convex portion  55  in the central portion. Thereby, the strength of the central portion of the bumper beam  1  is. increased. The cross-sectional shape of a bracket  52  shown in  FIG. 8(   c ) is formed by providing a hole  56  in the central portion. Thereby, the strength of the central portion of the bumper beam  1  is decreased. 
   In the present invention, explanation has been given of the mounting structure of a bumper beam on the front side of vehicle. However, the present invention can be applied similarly to the mounting structure of a bumper beam on the rear side of vehicle. When the present invention is applied to the mounting structure of a bumper beam on the rear side of a vehicle (rear bumper), the mounting position and shape of the support member  4  can be changed appropriately so as to match the structure on the rear side of vehicle. 
   For the pipe  3 , any materials having various strengths ranging from a lower high tensile strength steel to an ultra high tensile strength can be used as necessary.