Bumper beam and bumper system for vehicle

[0002] 1. Field of the Invention

[0003] The present invention relates to a bumper beam and a bumper system for a vehicle.

[0004] 2. Background Art

[0005] Japanese Patent Applications Laid-open No. Toku-Kai-Hei 5-178144 or No. Toku-Kai-Hei 5-278537 disclose vehicular bumper beams formed by extruded material of aluminum. FIG. 8 is a schematic view showing the construction of an example of these bumper beams. This bumper beam 70 is formed by a plurality of box-like closed cross sections 72 and every wall constituting the bumper beam 70 has a uniform wall thickness T. In an event of collision, the impact load inputted from the front of the vehicle is absorbed by the buckling deformation of wall sections of the bumper beam 70.

[0006] However, in an actual collision, the vehicle does not always take a desirable attitude for impact absorption. Further, the input direction of impact energy differs in every specific event of collision. Therefore, in some case of collision, the buckling deformation is inadequate and rather, for example, the bumper beam is deformed to a rhomboid configuration. This inadequate buckling deformation makes it difficult to absorb the impact energy efficiently.

[0007] It is an object of the present invention to provide a bumper beam having such a structure as always generating a stable buckling deformation.

[0008] A bumper beam having a box-like closed cross section comprises a front wall, a rear wall, a plurality of horizontal walls connecting the front wall and the rear wall and at least one of said horizontal walls having a smaller thickness in the neighborhood of a center thereof than a thickness in the neighborhood of connecting points thereof with the front wall and the rear wall respectively.

[0009] FIG. 1 is a sectional view showing a bumper system according to an embodiment of the present invention;

[0010] FIG. 2 is a partially sectional view showing a bumper beam of the bumper system of FIG. 1;

[0011] FIG. 3 is a sectional view showing a variation of bumper beams;

[0012] FIG. 4 is a partially sectional view showing a variation bumper beams;

[0013] FIG. 5 is a partially sectional view showing a variation bumper beams;

[0014] FIG. 6 is apartially sectional view showing a variation of bumper beams;

[0015] FIG. 7 is a sectional view showing a variation of bumper beams;

[0016] FIG. 8 is a perspective view showing a bumper beam according to a prior art; and

[0017] FIG. 9 is a sectional view showing the bumper system of FIG. 1 wherein the bumper protruding portion is larger than a residual compressed width of the energy absorbing medium.

[0018] Referring now to FIG. 1, a bumper system 1 comprises a bumper beam 2 formed by lightweight aluminum, an urethane foam 3 which is an energy absorbing medium and a fascia 4 which is fitted over the urethane foam 3, and which is made of synthetic resin. The bumper beam 2 extending in a transverse direction of the vehicle is attached to a beam stay 6 fixed to a body frame. The urethane foam 3 is provided at the front of the bumper beam 2 so as to absorb impact energy imparted from the front of the vehicle to some extent. The fascia 4 is secured to the body frame 5 and the bumper beam 2.

[0019] FIG. 2 is a sectional view of the bumper beam 2 as seen in the transverse direction or from the side of the vehicle. The bumper beam 2 is formed by an extruded or drawn aluminum material and has a box-like closed cross section enclosed by four walls, a rear wall 7, a front wall 8, an upper wall 9 and a lower wall 10. The rear wall 7 is secured to the beam stay 6. The front wall 8 disposed opposite to the rear wall 7 supports the urethane foam 3. These front and rear walls 8, 7 are respectively connected by the upper wall 9 and the lower wall 10.

[0020] Further, the closed cross section enclosed by four walls 7, 8, 9 and 10 has two webs 11, 12 for interconnecting the front and rear wall, 8 and 9. Two walls 9, 10 and two webs 11, 12 extending in a longitudinal or horizontal direction of the vehicle in FIG. 2, do not have an uniform thickness along the lengthwise direction of the vehicle. The thickness is largest, for example, 3 millimeters, at the connecting sections of the upper and lower walls 9, 10 with the front and rear walls 8, 7, decreases gradually, linearly towards the center thereof and is smallest, for example, 1.5 to 2.0 millimeters, in the neighborhood of the central sections 9b, 10b, 11band 12b. In other words, the wall sections 9, 10 and the web sections 11, 12 are provided with yieldable portions 9b, 10b, 11b, 12bwhich are apt to be deformed, respectively. These yieldable portions, as shown in

[0021] FIG. 2, are located on an identical line C passing through near the center of the bumper beam 2.

[0022] Further, a protruding portion 13 is integrally formed on the front wall 8. The protruding portion 13 is formed by protruding a part of a central portion of the front wall 8 toward the front of the vehicle.

[0023] In the bumper beam 2 thus constituted, the yieldable portions 9b, 10b, 11b, 12benable a stable generation of buckling in the event of impact. As described before, since the yieldable portions 9b, 10b, 11b, 12bhaving a small thickness are formed in the central part of the bumper beam 2, when the vehicle has a collision, the buckling of the bumper beam 2 starts to generate from these yieldable portions. That is, the yieldable portions operate like buckling starting points. Further, since the yieldable portions 9b, 10b, 11b, 12bare located on the center line C of the bumper beam 2, such a buckling as deforming the bumper beam 2 in the longitudinal direction (from front to rear), like bellows can be generated in a relatively stable manner regardless of vehicle attitudes or load input direction. Thus, since positions where the buckling starts to generate are determined beforehand, an inappropriate generation of buckling, such as a rhomboid deformation, can be prevented and an effective absorption of impact energy in the bumper beam 2 is available.

[0024] The protruding portion 13 formed on the front wall 8 enables an air bag to deploy at an earlier timing in the event of impact. For example, considering a light collision, first impact load is absorbed by the compression of the urethane foam. In case where the impact load is more than the urethane foam can absorb, resistance forces are generated in the bumper beam, the beam stay and the body frame in this order to absorb impact energy. At this moment, in case where the resistance force of the body frame exceeds a specified value, for instance, in case where an acceleration sensor installed in the body frame detects an impact acceleration larger than a specified value, the air bag is operated for deployment.

[0025] However, in case of the prior bumper beam having no protruding portion in the front, since the bumper beam does not generate a resistance force, until the urethane foam is completely compressed or until the energy absorption of the urethane foam is finished, it has been difficult to deploy the air bag at an earlier timing.

[0026] On the other hand, in case of the bumper beam 2 according to the embodiment of the present invention, since the protruding portion 13 is formed at the front of the bumper beam 2, the bumper beam 2 generates resistance force before the urethane foam 3 is completely compressed. That is, resistance force is generated in the bumper beam 2 earlier than the bumper beam of the prior art, consequently an early deployment of the air bag is available. The height of the protruding portion 13 is preferably established to a larger value (for example, 10 millimeters) than a residual width of the urethane foam 3 in a completely compressed state of the urethane foam 3.

[0027] In the aforegoing embodiment, all of the walls or webs extending longitudinally have the yielding portions, however, it is not necessary to form yielding portions in all of walls or webs. From the view point of giving a buckling starting point, yielding portions are preferably formed at least in webs.

[0028] FIG. 3 is a sectional view showing a variation of bumper beams. As seen from the drawing, the yielding portions are formed only in the webs 11, 12 but are not formed in the upper wall 9 and lower wall 10. Further, these upper and lower walls 9, 10 have a uniform thickness and are slightly bent outwardly.

[0029] Thus constituted bumper beam 2 is subjected to such a buckling deformation that the yielding portions 11b, 12bare buckled in the outward direction of the bumper beam 2. Accordingly, the bumper beam 2 can be prevented from the rhomboid deformation and can be expected to have an efficient energy absorption. In the embodiment described before, the yielding portion has been defined as a portion whose thickness is smallest in the upper and lower walls or the webs connecting the front and rear walls. However, considering that the yielding portion has a function as a buckling starting point, namely, a point from which a buckling starts to generate, the yielding portion is not limited to the portion having a smallest thickness. For example, as indicated in FIG. 4, the webs 11, 12 may be formed such that their thickness is largest at both connecting portions with the front and rear walls 8, 7, it becomes gradually small along a curved line as it goes from both connecting portions to the center thereof, and it is smallest in the neighborhood of the center of the webs 11, 12. Further, as indicated in FIG. 5, notches 11b, 12bmay be provided in the neighborhood of the webs 11, 12 on either of the upper or lower sides thereof. Further, as shown in FIG. 6, notches 11b, 12bmay be provided on both of the upper and lower sides thereof.

[0030] Further, it is not always necessary to provide the yieldable portions in the center of the bumper beam 2. That is, the yieldable portions may be provided in an offsetting manner on either of left or right sides of the bumper beam 2. Since the yieldable portion is for giving a starting point of buckling in itself, what extent the yieldable portion is offset from the center of the bumper beam is dependant upon what is a most desirable buckling. Therefore, the yieldable portion defined in the present invention is not limited to that provided in the neighborhood of the center of the bumper beam. It should be noted that the position of the yieldable portion in the present invention includes a wider range.

[0031] FIG. 7 is a sectional view showing a bumper beam according to another embodiment. The bumper beam 2 of this embodiment is formed by aluminum material having a uniform thickness of 3 millimeters or thereabout and it has no such yieldable portions as described above. A front wall 22 is divided into an upper front wall 22aand a lower front wall 22bwhich are provided opposite to a rear wall 21. The upper front wall 22ais connected with the rear wall 21 through an upper wall 23 and a web 25. Further, the lower front wall 22bis connected with the rear wall 21 through a lower wall 24 and a web 26. Further, these upper and lower front walls 22a, 22bare connected with a protruding portion 27 projected forwardly, respectively. That is, the webs 25, 26 are connected with each other through the protruding portion 27.

[0032] The upper wall 23 gradually expands outwardly (upwardly in the drawing) between the upper front wall 22aand the center line C of the bumper beam 2 and extends horizontally between the center line C and the rear wall 21. Further, the lower wall 24 gradually expands outwardly (downwardly in the drawing) between the lower front wall 22band the center line C of the bumper beam 2 and extends horizontally between the center line C and the rear wall 21.That is, the interval between the upper and lower walls 23, 24 becomes large gradually from the front of the vehicle toward the center of the bumper beam 2 and is kept constant between the center line C and the rear wall 21. On the other hand, two webs 25, 26 are disposed slantingly in the longitudinal direction of the vehicle such that the interval therebetween becomes gradually large from the front toward the rear of the vehicle.

[0033] Thus constituted bumper beam 2 can generate an appropriate buckling in a stable manner in the event of collision. Since the upper front wall 22ais connected with the lower front wall 22bthrough the protruding portion 27, when an input load is applied to the protruding portion 27, stress is concentrated on the webs 25, 26 and as a result the webs 25, 26 start to be deformed. At this moment, since stress is concentrated on respective refracting points of the upper and lower walls 23, to start with the refracting points, the buckling of the bumper beam 2 goes on. Hence, an appropriate buckling deformation, i.e., a bellows-like deformation of the bumper beam 2 can be generated in a relatively stable manner without depending on the vehicular attitudes, the way of load input and the like. As a result, the bumper beam 2 can absorb effectively the impact energy imparted from a collision.

[0034] Further, providing the yieldable portions on the webs 25, 26 along the center line C enhances a stability of buckling.

[0035] While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.