Vehicle bumper reinforcement structure

A vehicle bumper reinforcement structure to increase energy absorption capacity is provided. The vehicle bumper reinforcement structure comprises a base member extending in the width direction of the vehicle that is attached to the vehicle at both width ends, and a first reinforcement member and a second reinforcement member attached to the base member at a width center of the vehicle. Widths of the reinforcement members are differentiated in such a manner to cause fracture of the base member at width ends of the reinforcement members by a predetermined collision impact applied to the width center of the base member.

The present invention claims the benefit of Japanese Patent Application No. 2015-033925 filed on Feb. 24, 2015 with the Japanese Patent Office, the disclosures of which are incorporated herein by reference in its entirety.

BACKGROUND

Field of the Invention

Embodiments of the present invention relates to the art of a reinforcement structure for a vehicle bumper that is deformed to absorb collision energy of a vehicle colliding with an obstacle.

Discussion of the Related Art

JP-A-2001-322517 describes a bumper beam comprising a base member attached to the front or rear of an automobile, and a reinforcement member having high compressive stiffness attached to the base member. The bumper beam taught by JP-A-2001-322517 can absorb low-speed impact without permanent deformation, and the base member and the reinforcement member are designed to be deformed by relatively high speed impact to absorb collision energy.

JP-A-2004-203066 describes a vehicle bumper assembly in which an upper wall and a lower wall of a bumper reinforce is prevented from being damaged to reduce displacement of the bumper reinforce. To this end, according to the teachings of JP-A-2004-203066, a reinforcement member having a hollow space is fitted onto a front wall of the bumper reinforce as a rectangular pipe in such a manner to cover the upper and lower walls.

JP-A-H04-143014 describes a reinforcement steel tube for vehicle body. According to the teachings of JP-A-H04-143014 a short cylindrical cover member is fitted onto a width center of the reinforcement steel tube so that the steel tube is bent at both ends of the cylindrical cover to prevent a local deformation toward a vehicle interior.

Bending strength of the bumper at width center can be enhanced by the reinforcement members taught by the above-mentioned prior art documents and hence the kinetic energy generated by an impact applied to the width center of the bumper can be dissipated to supporting members at width ends of the bumper. That is, larger energy can be absorbed by the bumper thus reinforced.

An absorption capacity of the bumper of this kind is governed by a product of a deformation and a reaction of the bumper. In order to enhance the absorption capacity of the bumper, therefore, it is preferable to enhance deformability of the bumper in addition to enhance bending strength. For example, deformability of the bumper may be enhanced by arranging a plurality of reinforcement members on the bumper to increase a number of bend points at both width ends of each reinforcement member where the bumper is fractured by the collision impact. However, once the bumper is fractured at some of the bend point(s), reaction of the bumper is no longer established and hence the bumper may not be fractured at the other bend points as intended. For this reason, absorption capacity of the bumper may not be enhanced as desired.

SUMMARY

Aspects of an embodiment of the present invention have been conceived noting the foregoing technical problems, and it is therefore an object of embodiments of the present invention is to enhance an absorption capacity of a vehicle bumper to absorb collision impact to the width center of a vehicle.

The vehicle bumper reinforcement structure according to the preferred example for a vehicle is attached to a front side of a vehicle while extending in a width direction of the vehicle to be deformed by a collision impact to absorb collision energy. In order to achieve the above-explained objective, according to the preferred example, the vehicle bumper reinforcement structure is provided with a base member extending in the width direction of the vehicle that is attached to the vehicle at both width ends, and a first reinforcement member and a second reinforcement member respectively attached to the base member at a width center of the vehicle. In addition, widths of the first reinforcement member and the second reinforcement member are differentiated in such a manner to cause fracture of the base member at width ends of the first reinforcement member and at width ends of the second reinforcement member by a predetermined collision impact applied to the width center of the base member.

Specifically, the widths of the first reinforcement member and the second reinforcement member may be individually determined based on a bending moment applied to each width end of the reinforcement member by the collision impact to the width center of the base member, and a maximum allowable bending moment of the reinforcement member.

More specifically, the widths of the first reinforcement member and the second reinforcement member may be determined in such a manner to increase the maximum allowable bending moment of the base member stepwise from the width end of the base member to the width end of the second reinforcement member and from the width end of the base member to the width end of the first reinforcement member at a same increasing rate.

According to the preferred example, the first reinforcement member may be attached to any of a front wall and a rear wall of the base member symmetrically across the width center of the vehicle, and the second reinforcement member may be attached to the other front wall or rear wall of the base member symmetrically across the width center of the vehicle.

The vehicle bumper reinforcement structure is further provided with a pair of side members extending from the width ends of the vehicle, and the base member may be connected to the vehicle through the side members at width ends.

Thus, according to the preferred example of the present invention, the first reinforcement member and the second reinforcement member are respectively attached to the base member connected to the vehicle at width ends. In addition, widths of the first reinforcement member and the second reinforcement member are differentiated in such a manner to cause fracture of the base member at width ends of the first reinforcement member and at width ends of the second reinforcement member by a predetermined collision impact applied to the width center of the base member. According to the preferred example, therefore, a number of fracture points of the base member is increased so that energy absorption capacity of the vehicle bumper can be increased.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The bumper reinforcement structure is attached to the front or rear of a vehicle at both width ends, and adapted to be deformed inwardly by a collision impact to absorb kinetic energy. Referring now toFIG. 6, there is shown one example of a bumper assembly1attached to the front side of the vehicle. InFIG. 6, a pole barrier B is erected in front of the width center of the vehicle.

In the example shown inFIG. 6, the bumper assembly1is connected to a front side of a frame of the vehicle at both width ends through a pair of side members2. That is, a collision impact to the bumper assembly1propagates to the frame via the side members2. As known in the conventional art, the frame is comprised of a plurality of members to dissipate the kinetic energy generated by collision impact. The side member2is formed of metal material having high rigidity, and shaped to have a cross-sectional shape possible to enhance buckling strength.

Each width end of the bumper assembly1is attached individually to a leading end of the side member2by a bolt (not shown) so that a width center Ce of the bumper assembly1is deformed inwardly by a collision impact to absorb collision energy. Optionally, a conventional crush box (not shown) may be interposed between the leading end of the sider member2and the bumper assembly1to absorb kinetic energy generated by collision impact. Alternatively, a weakened portion may be formed in the leading end of the side member2instead of the crush box. In addition, a not shown ornamental bumper member is attached to the front side of the bumper assembly1. As illustrated inFIG. 6, an engine room3is formed on the rear side of the bumper assembly1, and an engine and a powertrain including a transmission and so on are arranged in the engine room3.

Here will be explained a structure of the bumper assembly1in more detail with reference toFIG. 1. As illustrated inFIG. 1, the bumper assembly1comprises a base member4connected to the side members2at its width ends, an inner bracket5attached to a back face of the base member4(facing to the engine room3) at the width center Ce, and an outer plate6fitted onto the front face of the bumper assembly1at the width center Ce. Accordingly, the inner bracket5serves as the claimed first reinforcement member and the outer plate6serves as the claimed second reinforcement member to enhance bending strength of the bumper assembly1. Here, the bending strength of the bumper assembly1can be calculated by dividing a maximum bending moment to cause fracture of the bumper assembly1by a cross-sectional coefficient of the bumper assembly1.

The base member4is formed by a roll-forming method using a metal sheet having a constant thickness. Specifically, in order to trim weight of the bumper assembly1, the base member4is shaped into a hollow structure such as an arcuate rectangular pipe. In addition, in order to prevent a deformation of the base member4by a relatively small impact, a height center of a rear wall of the base member4facing to the vehicle body is depressed to form a laterally extending first bead7. According to the preferred example, therefore, bending strength of the base member is constant in widthwise.

Turning toFIG. 2, there is shown a cross-section of the bumper assembly1in which the inner bracket5and the outer plate6are attached to the base member4. As illustrated inFIG. 1, the inner bracket5comprises a base plate8and a plurality of protrusions9at predetermined intervals. The protrusions9of the inner bracket5are inserted into the first bead7of the base member4, and the base plate8of the inner bracket5is fixed to a back face of the base member4by a bolt or welding method. That is, a length of each of the protrusions9of the inner bracket5is substantially identical to a depth of the first bead7of the base member4, and the inner bracket5is inserted into the first bead7symmetrically across the width center Ce.

Thus, the bending strength of the base member4is enhanced at the width center Ce by the inner bracket5. To this end, material, configuration, bending strength etc. of the inner bracket5may be altered arbitrarily according to need. Turning now toFIG. 3, there is shown another example of the inner bracket5. According to the example shown inFIG. 3, the inner bracket5is formed of three rectangular aluminum pipes10individually formed by an extrusion method, the base plate8made of resin by an injection method, and a holder11integrated with the base plate8to bundle the aluminum pipes10. The holder11thus holding the aluminum pipes10is inserted into the first bead7, and the base plate is fixed to the back face of the base member4by a bolt.

Turning back toFIG. 1, the above-explained outer plate6is fitted onto the front face of the base member4in a symmetrical manner across the width center Ce. This means that the bending strength of the outer plate6is homogeneous in both sides of the width center Ce. In addition, a length of the outer plate6in the width direction of the vehicle is longer than that of the inner bracket5. Specifically, the outer plate6comprises a front wall12covering the front wall of the base member4, an upper wall13formed by bending an upper portion of the front wall12toward the vehicle body, and a lower wall14formed by bending a lower portion of the front wall12toward the vehicle body. A leading end of the upper wall13is bent into L-shape to be fixed to the upper wall of the base member4, and a leading of the lower wall14is also bent into L-shape to be fixed to the lower wall of the base member4. In order to enhance bending strength of the outer plate6, a height center of a front wall of the outer plate6is depressed toward the base member4to form a laterally extending second bead15, and a bottom wall of the second bead15is brought into contact to the front wall of the base member4. For example, the outer plate6thus structured may be formed by a press method and a roll method.

The bending moment applied to the bumper assembly1by a maximum collision impact to the width center Ce is indicated inFIG. 4. InFIG. 4, the horizontal axis represents the width of the vehicle, and the vertical axis represents a magnitude of the bending moment. InFIG. 4, in addition, the maximum allowable bending moment at each point of the bumper assembly1is also indicated.

As described, the bending strength of the base member4is homogeneous entirely widthwise. The outer plate6the bending strength thereof is also homogeneous entirely widthwise is attached to the front wall of the base member4in a symmetrical manner across the width center Ce so that the bending strength of the outer plate6is added to the base member4equally on both sides of the width center Ce. In addition, the inner bracket5the bending strength thereof is also homogeneous entirely widthwise is attached to the rear wall of the base member4in a symmetrical manner across the width center Ce so that the bending strength of the inner bracket5is further added to the base member4equally on both sides of the width center Ce. Since each of the base member4, the inner bracket5and the outer plate6is individually formed into the symmetrical shape, a section modulus of the bumper assembly1at the intermediate portion where the inner bracket5and the outer plate6are attached to the base member4is entirely homogeneous widthwise. As indicated inFIG. 4, therefore, the maximum allowable bending moment of the bumper assembly1is increased stepwise toward the intermediate portion at which the bending strength thereof is enhanced by the inner bracket5and the outer plate6. Here it is to be noted that only the left part of the bumper assembly1will be explained for the sake of convenience. InFIG. 4, specifically, “c” represents a width end point of the base member4, “b” represents a width end point of the outer plate6, and “a” represents a width end of the inner bracket5. As can be seen fromFIG. 4, the maximum allowable bending moment is increased stepwise at the points “b” and “a”.

When the collision impact is applied to the bumper assembly1at the width center Ce, the bumper assembly1is subjected to the bending moment between the width end points “c”. The bending moment at each point of the bumper assembly1can be calculated by multiplying a distance from the width end point “c” by a load applied to the width center Ce. That is, the bending moment acting on the bumper assembly1is increased proportionally from the width end point “c” toward the width center Ce.

Specifically, the bumper assembly1is bent at a point where the bending moment acting thereon exceeds the maximum allowable bending moment. As shown inFIG. 4, when the collision impact is applied to the width center Ce of the bumper assembly1, the bumper assembly1will be subjected to the bending moment greater than the maximum allowable bending moment thereof at the point “a” and the point “b”, but the bending moment applied to the point “c” will not exceed the maximum allowable bending moment. That is, when the collision impact is applied to the bumper assembly1at the width center Ce, the bumper assembly is fractured at the point “a” and the point “b”.

That is, the most significant collision impact is applied to the width center Ce of the bumper assembly1and hence the width center Ce is subjected to the bending moment most significantly. Such bending moment is lightened proportionally toward the both width end points “c”. InFIG. 4, specifically, the slopes extending downwardly on both sides of the width center Ce get steeper with an increase in the collision impact applied to the width center Ce. As described, the bumper assembly1is fractured at the width end points “a” of the inner bracket5shown inFIG. 4and at the width end points “b” of the outer plate6shown inFIG. 4by the collision impact to the width center Ce. According to the preferred example, widths of the inner bracket5and the outer plate6are determined to cause fracture at the width end points “a” and “b” by a target maximum collision impact to the width center Ce at a peak of the slope representing the bending moment inFIG. 4. Specifically, as indicated inFIG. 4, the widths of the inner bracket5and the outer plate6are determined in such a manner to increase the maximum allowable bending moment of the bumper assembly1stepwise from the width end point “c” to the width end point and “b” and from the width end point “c” to the width end point and “a” at a same increasing rate. In other words, an inclination of the slope indicating the maximum bending moment of the bumper assembly1is identical between the points “c” and “b” and between the points “c” and “a”.

Thus, according to the preferred example, the bumper assembly1is fractured by the target maximum collision impact to the width center Ce at the width end points “a” and “b”. Energy absorption of the bumper assembly in this situation is schematically indicated inFIG. 5. InFIG. 5, the vertical axis represents deformation of the bumper assembly toward the vehicle body, the horizontal axis represents the width of the vehicle, the solid polygonal line represents a situation in which the bumper assembly1is fractured at both width end points “a” and “b” of the inner bracket5and the outer plate6, the dashed lines represent a situation in which the bumper assembly1is fractured only at the width end points “a” of the inner bracket5, and the dashed-dotted line represents a situation in which the bumper assembly1is fractured at the width center Ce. Specifically, energy absorption of the bumper assembly1can be calculated by multiplying the deformation of the fractured point by the reaction itself. That is, given that the reaction of the bumper assembly1is constant, the energy absorption of the bumper assembly1can be increased by increasing an area inFIG. 5enclosed by any of the above-mentioned lines and the horizontal axis. As indicated inFIG. 5, the energy absorption capacity of the bumper assembly1is increased when fractured at both width end points “a” and “b” of the inner bracket5and the outer plate6in the amount of hatched area, in comparison with that of the case in which the bumper assembly1is fractured only at the width end points “a” of the inner bracket5.

According to the preferred example, the energy absorption capacity of the bumper assembly1can be increased by thus attaching the inner bracket5and the outer plate6to the base member4having the above-explained widths.

Specifically, both of the inner bracket5and the outer plate6are attached to the base member4symmetrically across the width center Ce of the vehicle to increase the energy absorption capacity of the bumper assembly1as well as to prevent fracture of the bumper assembly1at the width center Ce. That is, the bending strength of the bumper assembly1can be increased without increasing the bending strength of the base member4. For this reason, a smaller base member4can be employed to downsize the bumper assembly1.

It is to be understood that various modifications may made in the bumper assembly within the spirit of the present invention. For example, more than three reinforcement members may be attached to the base member4while adjusting widths and bending strength thereof in the above-explained manner. In addition, configurations of the inner bracket5and the outer plate6may be altered according to need. For example, the inner bracket5may also be formed longer than the outer plate6widthwise. Further, the bracket5may be attached to the front wall of the base member4while attaching the plate6to the rear wall of the base member4.