Patent Application
20130181463
The present invention relates to a bumper beam to be mounted on an automotive body.
Many of automotive bumper beams to be mounted on automotive bodies are formed by use of steel plate of 980 MPa·class so that a cross section orthogonal to the longitudinal direction has a B-shape. The “B-shape” referred to in the specification means a shape having a reference wall extending in a specific direction on the cross section and a pair of swelling parts each swelling from the reference wall in a direction orthogonal to the reference part to form a space inside thereof.
The principal roles of such an automotive bumper beam are (i) to absorb, in a collision with a collision object, the impact energy of the collision by itself through its own deformation and (ii) to cause, in the collision, side members on the lateral side of a vehicle body to absorb the energy of collision by transmitting the impact load to the side members to deform the side members. Namely, the bumper beam is configured to suppress the deformation of an automotive cabin as designed to protect the occupant from the impact by causing the side members to absorb the impact energy.
With respect to concrete structures of such a bumper beam, various technologies are conventionally known.
For example, Patent Literature 1 discloses a support for automotive bumper including a B-shaped sectional reinforcement having an upper cylindrical part and a lower cylindrical part, and a foam material filled in each of the cylindrical parts. This support attains reduction in weight thereof and prevention of buckling of the reinforcement by filling the foam material.
Patent Literature 2 discloses a bumper main beam having an upper wall, an upper-side intermediate piece, a lower wall, and a lower-side intermediate piece that constitute the B-shaped cross section, the upper wall and the lower intermediate piece being inclined downwardly, and the lower wall and the upper intermediate piece being inclined upwardly. In this structure, the upper wall and lower wall of the main beam are buckled in a bellows shape in a vehicular crash, whereby the safety to the occupant of the crashing vehicle and the occupant of the crashed vehicle is improved.
Patent Literature 3 discloses a back beam for automotive bumper, including two hollow members, a plurality of brackets mutually connecting the hollow members so that the hollow members constitute a B-shaped cross section, and a reinforcement member locally reinforcing a relatively weak center part that is the connection part between the hollow members.
Patent Literature 4 discloses a reinforcement for automotive bumper, including a web, a compressive flange and a tensile flange which constitute a hollow rectangular section. In this reinforcement, the overall bending strength is enhanced by setting the thickness of the web so as to be larger on the side close to the compressive flange with respect to a neutral axis than that of the web on the side closer to the tensile flange.
Patent Literature 5 discloses a bumper reinforcement having three ribs. The plate thickness of the intermediate rib of the above-mentioned ribs is set larger than those of the other ribs, whereby the deterioration of energy absorbing capability upon buckling of the three ribs is prevented.
Patent Literature 6 discloses a structural member having a pair of flanges disposed in parallel to each other. In this structural member, an FRP material is provided on the surface of the flange on the tensed side upon receipt of bending load (the flange disposed oppositely to the flange on the compressed side) of both the flanges, and the ratio of width to thickness of the flange on the compressed side is set to 12 or less. This enhances the energy absorbing quantity of the structural member.
Patent Literature 7 discloses a composite structural member including a steel pipe and a reinforcement pipe inserted thereto. The reinforcement pipe has an outer shape along the inner wall of the steel pipe, and a rib is formed on the inside of the reinforcement pipe. This ensures a sufficient strength.
Patent Literature 8 discloses a filled structure including a hollow member and a filler inserted thereto. The filler is excellent in energy absorbing performance, and is fixed to the inside of the hollow member. In this filled structure, satisfactory corrosion resistance is ensured.
Patent Literature 9 discloses a vehicle body structural member composed of a plurality of members differed in strength. In this vehicle body structural member, this difference in strength of each member causes a twisting moment in the vehicle body structural member to disperse the bending load to the other members. Therefore, the energy absorbing efficiency of the vehicle body structural member is improved.
Patent Literature 10 discloses a bumper beam provided with a bumper reinforcing material. The bumper reinforcing material has a hollow part, and a crush deformation preventing body is disposed in the hollow part. The crush deformation preventing body suppresses buckling deformation of the bumper reinforcing member to enhance the impact energy absorbing capability.
The conventional structural members described above have the following problems when used as a bumper beam.
An automotive bumper beam requires a high bending strength in a high-speed collision of a pole-like object with the front or rear of a vehicle body. Namely, the automotive bumper beam has to transmit, in the collision with the pole-like object, the load to side members without its serious deformation.
However, a steel automotive bumper beam has limitation in improvement in bending strength because of insufficient exercise of sectional performance. The causes of the insufficient exercise of sectional performance include (i) deflection of a flange (vertically extending wall part), and (ii) compressive buckling of a web (longitudinally extending wall part).
On the other hand, it is desirable to enhance the bending strength of the bumper without increasing the weight of the bumper as much as possible.
With respect to the above-mentioned issue of (ii), since the buckling load of the web is proportional to the Young's modulus and the cube of plate thickness of the material, the buckling of the web can be suppressed more efficiently by increasing the thickness of the material than by improving the strength of the material. However, the increase in thickness is associated with significant increase in overall weight of the bumper beam. Particularly, in a steel automotive bumper beam manufactured by roll forming, an increased thickness of the web results in an increased overall weight of the beam in proportion thereto since the overall thickness of the bumper beam is uniform. Thus, remarkable improvement in the durability performance (to buckling) per unit weight cannot be expected. Further, as the background, reduction in overall weight of a vehicle is recently required for reduction in CO2 emission.
Further, it is very difficult in manufacturing to attach a reinforcing material (addition product) within the automotive bumper beam, and the use of a large reinforcing material involves remarkable increase in weight and cost. On the other hand, the use of FRP (Fiber Reinforced Plastics) as a component of bumper beam for the purpose of reducing the weight offers little hope of preventing the compressive buckling of the beam.
[Patent Literature 1] Japanese Patent Application Laid-Open No. 11-334500
[Patent Literature 2] Japanese Patent Application Laid-Open No. 2006-218904
[Patent Literature 3] Japanese Patent Application Laid-Open No. 2005-8146
[Patent Literature 4] Japanese Patent Application Laid-Open No. 11-059296
[Patent Literature 5] Japanese Patent Application Laid-Open No. 2004-148915
[Patent Literature 6] Japanese Patent Application Laid-Open No. 2003-129611
[Patent Literature 7] Japanese Patent Application Laid-Open No. 2003-312404
[Patent Literature 8] Japanese Patent Application Laid-Open No. 2005-88651
[Patent Literature 9] Japanese Patent Application Laid-Open No. 2006-248336
[Patent Literature 10] Japanese Patent Application Laid-Open No. 2000-52897
The present invention has an object to provide a bumper beam, which can be improved in bending strength with minimum increase in weight.
A bumper beam according to a first aspect of the present invention, which is configured to be mounted on the front or rear of a vehicle body and to extend along a reference line, includes a beam body formed of a metallic plate and extending along the reference line, and a metallic first reinforcing plate extending along the reference line and attached to the beam body. In at least one cross section perpendicular to the reference line, the first reinforcing plate extends linearly, and the beam body includes a pair of swelling parts each swelling from the first reinforcing plate in a direction intersecting it while enclosing an internal space.
Further, the beam body and the first reinforcing plate satisfy the following condition:
(Est/ρst3)<(E2/ρ23)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E2: Young's modulus of the first reinforcing plate
ρ2: Density of the first reinforcing plate
A bumper beam according to a second aspect of the present invention, which is configured to be mounted on the front or rear of a vehicle body and to extend along a reference line, includes a beam body formed of a metallic plate and extending along the reference line, and a metallic second reinforcing plate extending along the reference line and attached to the beam body. In at least one cross section perpendicular to the reference line, the beam body includes a reference wall extending linearly and a pair of swelling parts each swelling from the reference wall in a direction intersecting it while enclosing an internal space, each of the swelling parts has an outer wall part extending in a direction intersecting the reference wall, and an inner wall part extending in a direction intersecting the first reinforcing plate at a position closer to the other swelling part than the position of the outer wall part, and the outer wall parts and the inner wall parts are aligned along the reference wall. The second reinforcing plate is attached to at least either both the outer wall parts or both the inner wall parts in an attitude parallel thereto.
Further, the beam body and the second reinforcing plate satisfy the following condition.
(Est/ρst3)<(E2/ρ23)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E3: Young's modulus of the second reinforcing plate
ρ3: Density of the second reinforcing plate
a) is a cross sectional view of a bumper beam according to a sixth embodiment of the present invention, and (b) is a cross sectional view of a bumper beam according to a first modification example thereof;
a) is a cross sectional view of a bumper beam according to a second modification example of the sixth embodiment, (b) is a cross sectional view of a bumper beam according to a third modification example thereof, and (c) is a cross sectional view of a bumper beam according to a fourth modification example thereof;
a) is a cross sectional view of a bumper beam according to a first modification example of the eighth embodiment, and (b) is an enlarged view of a part surrounded by a circle 20B in (a);
A bumper beam 1 in a first embodiment of the present invention will be described in reference to
Each of cross sections shown in
The bumper beam 1 has a B-shaped cross section, as shown in
The reinforcing plate 3 corresponds to the first reinforcing plate according to the present invention, and is disposed along the beam body 2. The reinforcing plate 3 also has an arch-like shape curved in top view similarly to the beam body 2.
A synthetic resin-made bumper cover (not shown) is attached to the bumper beam 1 so as to cover the bumper beam 1, whereby a bumper assembly is formed.
The bumper beam 1 according to this embodiment is mounted on the front of a vehicle body. Concretely, the beam body 2 is attached by welding to side members S (
In the following description, the front side of the longitudinal direction B of the vehicle body (refer to the direction of arrow B in the drawings) is referred to as B2 side and the rear side to as B1 side. The B2 side corresponds to a side approaching the vehicle body along the longitudinal direction B (vehicle body side), and the B1 side corresponds to a side leaving the vehicle body along the longitudinal direction B. The upper side in the vertical direction A of the vehicle body (refer to the direction of arrow A in the drawings) is referred to as A1 side, and the lower side to as A2 side. The “collision direction” in the following description is a direction shown by arrow D in
The beam body 2 is composed of a plate material, and formed to be B-shaped in cross section perpendicular to the reference line W Concretely, the beam body 2 has each wall part of a first wall (central flange) 2j, a second wall (inner web) 2k, a third wall (rear flange) 2m, a fourth wall (outer web) 2a, a fifth wall (inner web) 2e, a sixth wall (rear flange) 2d, a seventh wall (outer web) 2c, and an eighth wall (front flange; reference wall) 2b, and extends along the reference line W.
The first wall 2j is located at the center in the vertical direction A, and extends along the vertical direction A. The second wall 2k extends from the upper end of the first wall 2j toward the B2 side (to the side approaching the vehicle body) along the longitudinal direction B orthogonal to the first wall 2j. The third wall 2m extends upwardly from an end on the vehicle body side (B2 side) of the second wall 2k along the vertical direction A. The fourth wall 2a extends from the upper end of the third wall 2m toward the B1 side (the side leaving the vehicle body) along the longitudinal direction B.
The fifth wall 2e extends from the lower end of the first wall 2j toward the B2 side along the longitudinal direction B. The sixth wall 2d extends downwardly from an end on the vehicle body side of the fifth wall 2e. The seventh wall 2c extends from the lower end of the sixth wall 2d toward the B1 side along the longitudinal direction B.
The eighth wall 2b extends along the vertical direction A and connects an end on the B1 side of the fourth wall 2a to an end on the B1 side of the seventh wall 2c.
The first wall 2j and the eighth wall 2b are integrated together by welding so that the respective surfaces are closely fitted to each other. Each of the wall parts constituting the beam body 2 extends along the reference line W (refer to
In this embodiment, the first wall 2j, the third wall 2m, the sixth wall 2d, and the eighth wall 2b are orthogonal to the longitudinal direction B, and the second wall 2k, the fourth wall 2a, the fifth wall 2e, and the seventh wall 2c are parallel to the longitudinal direction B (or orthogonal to the vertical direction A). If a wall part orthogonal to the longitudinal direction B is regarded as a flange, and a wall part parallel to the longitudinal direction B as a web, the first wall 2j, the third wall 2m, the sixth wall 2d, and the eighth wall 2b correspond to the flange, and the second wall 2k, the fourth wall 2a, the fifth wall 2e, and the seventh wall 2c correspond to the web.
The fourth wall 2a and the seventh wall 2c are outer webs parallel to the collision direction. The fifth wall 2e and the second wall 2k are inner webs parallel to the collision direction. The first wall 2j connects the fifth wall 2e to the second wall 2k. The eighth wall 2b is located on the upstream side in the collision direction shown by arrow D, and a surface on the B1 side of the eighth wall 2b constitutes a collision surface (a surface orthogonal to the collision direction).
In this embodiment, the plate thickness of each flange and each web in the beam body 2 is 1.4 mm. The Young's modulus of a steel product constituting the beam body 2 is 21,000 MPa, and the density thereof is 7,874 kg/m3.
In an optional cross section perpendicular to the reference line W, the reinforcing plate 3 extends along the vertical direction A. The fourth wall 2a, the third wall 2m and the second wall 2k constitute an upper swelling part 2t located above the first wall 2j and swelling from the reinforcing plate 3 toward the B2 side of the longitudinal direction B, and the fifth wall 2e, the sixth wall 2d and the seventh wall 2c constitute a lower swelling part 2s located below the first wall 2j and swelling from the reinforcing plate 3 toward the B2 side of the longitudinal direction B. Each of the swelling parts 2t and 2s encloses an internal space on the inside thereof.
The fourth wall 2a and the seventh wall 2c constitute, respectively, outer wall parts of the swelling parts 2t and 2s (wall parts extending from the reinforcing plate 3 in the direction orthogonal thereto on both the outer sides of the beam body 2), and the second wall 2k and the fifth wall 2e constitute inner wall parts of the swelling parts 2t and 2s (wall parts extending from the reinforcing plate 3 in the direction orthogonal thereto at a position closer to the other swelling part than the position of the outer wall part). These four wall parts (the fourth wall 2a, the second wall 2k, the fifth wall 2e and the seventh wall 2c) extend in the longitudinal direction B that is a direction intersecting the reinforcing plate 3, and are aligned along the vertical direction A.
In
The second wall 2k extends from one end (the A1-side end) of the first wall 2j along a direction intersecting the first wall 2j (the longitudinal direction B). The third wall 2m extends from the B2-side end (an end opposite to the first wall 2j) of the second wall 2k along a direction intersecting the second wall 2k. The third wall 2m extends from the B2-side end of the second wall 2k to the A1 side (the side opposite to the first wall 2j in relation to the second wall 2k). The fourth wall 2a extends from the A1-side end (an end opposite to the second wall 2k) of the third wall 2m along a direction intersecting the third wall 2m. The fourth wall 2a also extends from the A1-side end of the third wall 2m to the B1 side (the side of the second wall 2k in relation to the third wall 2m).
The fifth wall 2e extends from the other end (the A2-side end) of the first wall 2j in a direction intersecting the first wall 2j. The fifth wall 2e also extends from the A2-side end of the first wall 2j to the B2 side (the same side as the second wall 2k in relation to the first wall 2j). The sixth wall 2d extends from a end on the B2 side (the side opposite to the first wall 2j) of the fifth wall 2e in a direction intersecting the fifth wall 2e. The sixth wall 2d extends also from the B2-side end of the fifth wall 2e to the A2 side (the side opposite to the first wall 2j in relation to the fifth wall 2e). The seventh wall 2c extends from an end on the A2 side (the side opposite to the fifth wall 2e) of the sixth wall 2d in a direction intersecting the sixth wall 2d. The seventh wall 2c extends from the A2-side end of the sixth wall 2d to the B1 side (the side of the fifth wall 2e in relation to the sixth wall 2d).
The eighth wall 2b constitutes a reference wall. Namely, the eighth wall 2b extends along a direction parallel to the reinforcing plate 3 or the vertical direction A, and connects an end part opposite to the third wall 2m of end parts of the fourth wall 2a as the outer wall part to an end part opposite to the sixth wall 2d of end parts of the seventh wall 2c as the similarly outer wall part while closing the internal space inside each of the swelling parts 2t and 2s. The eighth wall 2b extends also in the extending direction of the first wall 2j.
The reinforcing plate 3 is attached to the beam body 2 so as to extend along the reference line W, to extend along the vertical direction A in an optional cross section orthogonal to the reference line W, and to be perpendicular to the longitudinal direction B. The reinforcing plate 3 is attached to the B1-side end part (an end away from the vehicle body) of the beam body 2. Concretely, the reinforcing plate 3 is disposed on the collision surface side (B1 side) of the beam body 2, and attached to the eighth wall 2b of the beam body 2 by welding so that the respective surfaces are closely fitted to each other.
The reinforcing plate 3 according to this embodiment is attached to all over the whole front surface of the eighth wall 2b to thereby reinforce the eighth wall 2b. Namely, the reinforcing plate 3 in this embodiment functions as a reinforcing material of the beam body 2, particularly, as a reinforcing material of the eighth wall 2b. The thickness of the reinforcing plate 3 in this embodiment is 2.0 mm. The Young's modulus of the aluminum-based material constituting the reinforcing plate 3 is 6,900 MPa, and the density thereof is 2,700 kg/m3. The reinforcing plate 3 may be formed of another metallic material without being limited to the aluminum-based material.
In
A bumper beam 21 in a second embodiment of the present invention will be described in reference to
The bumper beam 21 according to this embodiment also includes a beam body 22 and a reinforcing plate 3. The bumper beam 21 is formed to be B-shaped in cross section as shown in
The B1-side surface of the reinforcing plate (first reinforcing plate) 3 constitutes a collision surface. In this bumper beam 21, the reinforcing plate 3 functions as an alternate member of the eighth wall 2b in the beam body 2, and functions as an overall reinforcing material of the beam body 22.
The relation between Young's modulus and density in the first embodiment and the second embodiment will be then described. As a typical example, the structure of the bumper beam 21 is described below.
If the Young's modulus of the beam body 22 is shown as Est, the density of the beam body 22 as ρst, the Young's modulus of the reinforcing plate 3 as E2, and the density of the reinforcing plate 3 as ρ2, Est, E2, ρst and ρ2 in the bumper beam 21 satisfy a condition represented by the following expression (1). In other words, the steel product that is the material of the beam body 22 and the aluminum-based material that is the material of the reinforcing plate 3 are selected so as to satisfy this condition.
(Est/ρst3)<(E2/ρ23) (1)
The reason for selecting each material according to the expression (1) will be described. Assuming that the buckling length of the reinforcing plate 3 is constant, the buckling load Pcr of the reinforcing plate is represented by the following expression 2, wherein t is the thickness of the reinforcing plate 3, and E is the Young's modulus of the reinforcing plate 3.
P
cr
∝E·t
3 (2)
According to the expression (2); the beam body 22 can be effectively reinforced by satisfying the relation of the following expression (3), wherein Est is the Young's modulus of the beam body 22, tst is the thickness of the beam body 22, E2 is the Young's modulus of the reinforcing plate 3, and t2 is the thickness of the reinforcing plate 3.
E
st
·t
st
3
<E
2
·t
2
3 (3)
On the other hand, the weight W of a certain material is represented by the following expression (4), wherein ρ is the density of the material.
W∝ρ·t (4)
When the reinforcing plate 3 is provided so that the weight of a “portion subjected to attachment” of the beam body 22 is equal to the weight of the reinforcing plate 3, the relation of the following expression (5) is satisfied. The area of the portion subjected to attachment is equal to the area of the reinforcing plate.
ρst·tst=ρ2·t2 (5)
The “portion subjected to attachment” means the eighth wall 2b itself (i) when the reinforcing plate 3 is attached to the eighth wall 2b that is the reference wall as the reinforcing material of the eighth wall 2b as in the first embodiment. In contrast, (ii) when the reinforcing plate 3 functions as an alternate member of the eighth wall 2b without the eighth wall 2b as in the second embodiment (refer to the second embodiment), a reference wall corresponding to the eighth wall which has the same thickness as the first to the seventh wall is virtually determined, and this virtual wall corresponds to the portion subjected to attachment.
The above-mentioned relation of the expression (1) is derived from the above-mentioned expressions (5) and (3). Thus, the buckling load per weight (Pcr/W) can be efficiently improved by reinforcing the B1 side of the beam body 22 with a material such that it satisfies the condition of the expression (1).
Further, each of the embodiments will be concretely described.
(i) In the first embodiment in which the reinforcing plate 3 functions as a reinforcing material of the eighth wall 2b, when the reinforcing plate 3 having substantially the same weight as the “eighth wall 2b” is attached to the beam body 2, for example, the total weight of the eighth wall 2b and the reinforcing plate 3 is about twice the weight of the eighth wall 2b, while the buckling load of the eighth wall 2b and the reinforcing plate 3 is larger than twice the buckling load of the eighth wall 2b.
(ii) In the second embodiment in which the reinforcing plate 3 functions as an alternate member of the eighth wall 2b, when the reinforcing plate 3 having substantially the same weight as the “eighth wall 2b” is attached to the beam body 22, for example, the weight of the reinforcing plate 3 corresponding to the front wall of the bumper beam 21 composed of the beam body 22 and the reinforcing plate 3 is substantially equal to that of the eighth wall 2b corresponding to the front wall of the beam body 2, while the buckling load of the reinforcing plate 3 becomes larger than that of the eighth wall 2b of the beam body 2.
In the above-mentioned two embodiments, the condition of the expression (1) is satisfied with Est/ρst3=4.30×10̂(−8) [MPa·m/kg3] and E2/ρ23=3.51×10̂(−7) [MPa·m/kg3], wherein Est=21,000 MPa, E2=6,900 MPa, ρst=7,874 kg/m3, and ρ2=2,700 kg/m3.
The bumper beam has only to satisfy at least the condition shown in the expression (1), and does not always have to satisfy the condition shown in the expression (5).
Results of evaluation for bending moment in bumper beam will be then described. In the evaluation, with respect to five types of bumper beams (bumper beams of single steel differed in plate thickness, a bumper beam of flange steel-reinforcement, a bumper beam of flange aluminum-reinforcement (1), and a bumper beam of flange aluminum-reinforcement (2)), calculation of maximum bending moment was performed by three-point bending analysis.
The “bumper beam of single steel” is a bumper bean free from the reinforcing plate 3, and corresponds to the beam body 2. The “bumper beam of flange steel-reinforcement” is the bumper beam 1 shown in
Each of the bumper beam 1 and the bumper beam 21 can be regarded as a beam in which portions near both ends thereof (both ends related to the width direction C) are supported by side members. Therefore, the reinforcing material resists a load received by the bumper beam at the time of collision by bending action (in a state where the bending action is dominant). Thus, the larger the maximum bending moment bearable (durable) by the bumper beam is, the higher the bending strength of the bumper beam is.
As the plate material constituting the beam body 2 and the beam body 22, steel plate of 1,470 MPa-class with yield strength (YP) of 1,200 MPa was used, and as the material of the reinforcing plate 3, 7,000-series aluminum alloy with yield strength (YP) of 310 MPa was used. The yield strength and thickness of the steel plate constituting each beam body, and the yield strength and thickness of the aluminum-based material constituting the reinforcing plate are shown in Table 1.
It is found from the graph of
It is also found from the graph of
In contrast to the above, the bumper beam 21 of flange aluminum-reinforcement (2) is equal to the bumper beam BS with respect to the maximum bending moment ratio (bending moment ratio: about 1.05), although the weight is reduced (weight ratio: about 0.91), compared with the bumper beam BS, since it is free from the eighth wall 8b.
As described above, the bumper beam is effectively reinforced by fixing a reinforcing plate formed of aluminum or steel to the B1 side of the beam body formed of steel. Further, the Young's moduli and densities of the beam body and the reinforcing plate satisfy the condition shown in the expression (1), whereby the bending strength can be improved while minimizing the increase in weight.
The summary of the bumper beams of the first embodiment and the second embodiment will be described again. As a typical structure; the bumper beam 21 shown in
In an optional cross section perpendicular to the reference line W of the bumper beam 21, (a) the reinforcing plate 3 extends linearly, and (b) the beam body 22 has an upper swelling part 2t and a lower swelling part 2s each swelling from the reinforcing plate 3 in a direction intersecting it while enclosing an internal space. Namely, the cross section has a B-shape. The beam body 22 and the reinforcing plate 3 satisfy the following condition.
(Est/ρst3)<(E2/ρ23)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E2: Young's modulus of the reinforcing plate
ρ2: Density of the reinforcing plate
In this bumper beam 21, the reinforcing plate 3 formed of aluminum-based material is disposed on the front part of the beam body 22, whereby the beam body 22 is reinforced. The Young's moduli and densities of the beam body 22 and the reinforcing plate 3 satisfy the above-mentioned condition, whereby the bending strength of the bumper beam 21 can be increased while minimizing the increase in weight of the bumper beam 21. In other words, the bending strength of the bumper beam 21 can be improved while minimizing the increase in weight of the bumper beam 21 by manufacturing the bumper beam so as to satisfy the above-mentioned condition. This manufacturing method includes an attachment step of attaching the reinforcing plate 3 to the beam body 22.
A bumper beam 31 in a third embodiment of the present invention will be described in reference to
The bumper beam 31 has a beam body 32 formed of a steel plate and an aluminum-made reinforcing plate (first reinforcing plate) 33. The bumper beam 31 is B-shaped in cross section as shown in
The reinforcing plate 33 is formed by extrusion-molding an aluminum-based material, and a surface on the B1 side of the reinforcing plate 33 constitutes a collision surface. In the bumper beam 31, the reinforcing plate 33 functions as an alternate member of the eighth wall 2b in the beam body 2 shown in
The reinforcing plate 33 has a body part 33b, and two projection parts (first projection parts) 33a projecting from the inside surface (a surface opposite to the collision surface) of the body part 33b.
The body part 33b extends along the reference line W and also along the vertical direction A, and has a thickness of about 10 mm.
Both the projection parts 33a are disposed to project along the longitudinal direction B, and to hold the second wall 2k and the fifth wall 2e (the respective inner wall parts of the swelling parts 2t and 2s) from both the outer sides in the vertical direction A of the vehicle body. The projecting direction of both the projection parts 33a is a direction intersecting the reinforcing plate 33, which is orthogonal to the reinforcing plate 33 in the example of the drawing. However, the projecting direction does not have to be always orthogonal to the reinforcing plate 33, and may be inclined relative to the normal to the reinforcing plate 33. Both the projection parts 33a are located at angle parts formed by the body part 33b and two inner webs, or the second wall 2k and the fifth wall 2e, respectively, to reinforce the corresponding inner webs.
If the Young's modulus of the beam body 32 is Est, the density of the beam body 32 is ρst, the Young's modulus of the reinforcing plate 33 is E2, and the density of the reinforcing plate 33 is ρ2, Est, ρst, E2 and ρ2 satisfy the above-mentioned expression (1).
In the above-mentioned bumper beam 31, buckling of the second wall 2k and the fifth wall 2e (buckling in which the middle portion of the second wall 2k and the middle portion of the fifth wall 2e are deformed to separate from each other) is suppressed by holding the second wall 2k and the fifth wall 2e from both the outer sides by the two projection parts (first projection parts) 33a projecting from the reinforcing plate 33 in the direction intersecting it (orthogonal in the drawing), whereby the bending strength of the bumper beam is further improved.
Both the projection parts 33a may be joined to the respective inner webs by welding, adhesion or the like.
A bumper beam 41 in a fourth embodiment of the present invention will be described in reference to
The bumper beam 41 has a beam body 32 and an aluminum-made reinforcing plate (first reinforcing plate) 43. The bumper beam 41 has a B-shaped cross section as shown in
The reinforcing plate 43 (corresponding to the above-mentioned reinforcing plate 33) is formed by extrusion molding, and has a collision surface. In-the bumper beam 41, the reinforcing plate 43 functions as an alternate member of the eighth wall 2b in the beam body 2, and functions as a reinforcing material of the beam body 32.
The reinforcing plate 43 has a body part 33b and two projection parts (second projection parts) 43a projecting from the inside surface (a surface opposite to the collision surface) of the body part 33b. These projection parts 43a are disposed to project along the longitudinal direction B and to hold the fourth wall 2a and the seventh wall 2c (or the outer wall parts of the swelling parts 2t and 2s) from both the outer sides in the vertical direction A of the vehicle body. The projecting direction of both the projection parts 43a is a direction intersecting the reinforcing plate 43, which is orthogonal to the reinforcing plate 43 in the example of the drawing. However, the projecting direction may be inclined relative to the normal to the reinforcing plate 43. Both the projection parts 43a are located at angle parts formed by the body part 33b and two outer webs, or the fourth wall 2a and the seventh wall 2c, respectively, to reinforce the corresponding outer webs.
An inclined surface (a surface inclined relative to the vertical direction A and the longitudinal direction B) 43b having an inclination angle capable of surface-contacting with each of the overhang parts 2g of the beam body 32 is formed inside the root part of each projection part 43a, and integrated to the corresponding overhang part 2b so that the surface of the inclined surface 43b is closely fitted to the surface of this overhang part 2g. The reinforcing plate 43 is attached to both the overhang parts 2g that are the B1-side end parts in the beam body 32.
If the Young's modulus of the beam body 32 is Est, the density of the beam body 32 is ρst, the Young's modulus of the reinforcing plate 43 is E2, and the density of the reinforcing plate 43 is ρ2, Est, E2, ρst and ρ2 satisfy the above-mentioned expression (1).
In the bumper beam 41, buckling of the fourth wall 2a and the seventh wall 2c (buckling in which the middle portion of the fourth wall 2a and the middle portion of the seventh wall 2c are deformed to separate from each other) is suppressed by holding the fourth wall 2a and the seventh wall 2e from both the outer sides by the two projection parts (second projection parts) 43a projecting from the reinforcing plate 43 in the direction intersecting it (orthogonal in the drawing), whereby the bending strength of the bumper beam is further improved.
Both the projection parts 43a may be joined to the respective outer webs by means of welding, adhesion or the like.
A bumper beam 51 in a fifth embodiment of the present invention will be described in reference to
The bumper beam 51 has a beam body 32 and an aluminum-made reinforcing plate (first reinforcing plate) 53, as shown in
The reinforcing plate 53 (corresponding to the above-mentioned reinforcing plate 33) is formed by extrusion molding, and has a collision surface. In the bumper beam 51, the reinforcing plate 53 functions as an alternate member of the eighth wall 2b in the beam body 2, and functions as a reinforcing material of the beam body 32. The reinforcing plate 53 includes a body part 33b, two projection parts 43a projecting from the inside surface (a surface opposite to the collision surface) of the body part 33, and two projection parts 33a projecting from the inside surface within an area sandwiched between the projection parts 43a. Namely, the reinforcing plate 53 according to this embodiment has both the projection parts 33a corresponding to a pair of first projection parts and the projection parts 43a corresponding to a pair of second projection parts.
If the Young's modulus of the beam body 32 is Est, the density of the beam body 32 is ρst, the Young's modulus of the reinforcing plate 53 is E2, and the density of the reinforcing plate 53 is ρ2, Est, E2, ρst and ρ2 satisfy the above-mentioned expression (1).
Results of evaluation for bending moment in bumper beam will be then described. In the evaluation, with respect to five types of bumper beams (two types of bumper beams of single steel differed in plate thickness, a bumper beam of flange aluminum-reinforcement (3), a bumper beam of flange aluminum-reinforcement (4), and a bumper beam of flange aluminum-reinforcement (5)), calculation of bending moment of each bumper beam is performed by three-point bending analysis.
The “bumper beam of single steel” is a bumper bean free from the reinforcing plate 3, and corresponds to the beam body 2. The “bumper beam of flange aluminum-reinforcement (3)” is the bumper beam 31 shown in
As the plate material constituting the beam body 2 and the beam body 32, steel plate of 1,500 MPa-class with yield strength (YP) of 1,200 MPa was used, and as the material of the reinforcing plate 33 (the reinforcing plate 43 and the reinforcing plate 53), 7,000-series aluminum alloy with yield strength (YP) of 310 MPa was used. The yield strength and plate thickness of the steel plate constituting each beam body, and the yield strength and plate thickness of the aluminum-based material constituting the reinforcing plate are shown in Table 2.
It is also found from
As described above, the bumper beam is reinforced by disposing a reinforcing plate formed of aluminum on the B1 side of the beam body 32 formed of steel. Further, the Young's moduli and densities of the beam body and the reinforcing plate satisfy the relation of the expression (1), whereby the bending strength can be improved while minimizing the increase in weight.
The concrete structures of bumper beam may include, for example, those shown in
The bumper beam 61 shown in
In the bumper beam 61, the reinforcing plate 63 is attached to all over the whole front surface of the eighth wall 2b to reinforce the eighth wall 2b. Namely, the reinforcing plate 63 in this embodiment functions as a reinforcing material of the eighth wall 2b. The reinforcing plate 63 is attached to the eighth wall 2b by welding so that the respective surfaces are closely fitted to each other.
The reinforcing plate 63 has a body part 33b and two projection parts (second projection parts) 63a projecting from the inside surface (a surface opposite to the collision surface) of the body part 33b. Both the projection parts 63a (corresponding to the above-mentioned projection parts 43a) are formed to project along the longitudinal direction B and to hold the fourth wall 2a and the seventh wall 2c (or the respective outer wall parts of the swelling parts 2t and 2s) from both the outer sides in the vertical direction A of the vehicle body. Both the projection parts 63a are located at angle parts formed by the body part 33b and two outer webs, or the fourth wall 2a and the seventh wall 2c, respectively to reinforce the corresponding outer webs.
The bumper beam 71 shown in
The bumper beam 81 shown in
The bumper beam 91 shown in
In each of the bumper beams shown in
A bumper beam in a sixth embodiment of the present invention will be described in reference to
The bumper beam of this embodiment includes, as shown in
The reinforcing plate 73 (corresponding to the above-mentioned reinforcing plate 33) is formed by extrusion molding, and has a collision surface. The reinforcing plate 73 functions as an alternate member of the eighth wall 2b.
The reinforcing plate 73 has a body part 33b, and two projection parts 33a and two projection parts 63a projecting from the inside surface (a surface opposite to the collision surface) of the body part 33b. Both the projection parts 33a are located at angle parts formed by the body part 33b and two inner webs (the second wall 2k and the fifth wall 2e) respectively to reinforce the corresponding inner webs. Both the projection parts 63a are located at angle parts formed by the body part 33b and two outer webs (the fourth wall 2a and the seventh wall 2c) respectively to reinforce the corresponding outer webs.
The respective tips (end parts 2h) of the fourth wall 2a and the seventh wall 2c are integrated to the two projection parts 63a respectively by welding to form a weld bead part 73W as shown in
The bumper beam of this embodiment has the following effects by holding the fourth wall 2a and the seventh wall 2c from both the sides by the two projection parts (second projection parts) 63a projecting from the body part 33b of the reinforcing plate 73 in a direction orthogonal thereto, and fixing the two projection parts to the tips of the fourth wall 2a and the seventh wall 2c.
(a) Outwardly swelling buckling (buckling in which the middle portion of the fourth wall 2a and the middle portion of the seventh wall 2c are deformed to separate from each other) is suppressed. The reason is that (i) the deformation of the fourth wall 2a and the seventh wall 2c is suppressed by their contact with the two projection parts 63a, and (ii) the buckling load of the fourth wall 2a and the seventh wall 2c is enhanced by the integration of the fourth wall 2a and the seventh wall 2c to the two projection parts 63a.
(b) Inwardly contracting buckling (buckling in which the middle portion of the fourth wall 2a and the middle portion of the seventh wall 2c are deformed to approach each other) is suppressed. The reason is that the buckling load of the fourth wall 2a and the seventh wall 2c is enhanced by the integration of the fourth wall 2a and the seventh wall 2c to the two projection parts 63a.
The projecting direction of each projection part 63a has only to be a direction intersecting the reinforcing plate 73 in one cross section perpendicular to the reference line W and, for example, may be inclined relative to the normal to the reinforcing plate 73.
The bumper beam of the sixth embodiment may have structures shown in
The points different from the above-mentioned sixth embodiment are mainly described below without the description for the same items as in the sixth embodiment. Since the bumper beam according to each modification example has a symmetric shape relative to the lateral direction in
The bumper beam of
The bumper beam of
The bumper beam of
(Effect of Bumper Beam of Each Modification Example)
The effects of the above-mentioned modification examples will be described typically with respect to the bumper beam of
The bumper beam of
Recessed parts 83c are formed respectively outside the root parts of the two projection parts 83b. The recessed parts 83c for housing the tips of the fourth wall 2a and the seventh wall 2c respectively to restrict the movement of the end parts 2h to the A1 side and to A2 side are formed in positions where the two projection parts 83b are held thereby from both the outer sides in the vertical direction A, and dented to the B1 side beyond the B2-side surface of the body part 33b. The recessed parts 83c are located at angle parts formed by the body part 33b and two outer webs (the fourth wall 2a and the seventh wall 2c) respectively to reinforce the corresponding outer webs from the inside.
The tips of the fourth wall 2a and the seventh wall 2c (the end parts 2h) are integrated to the reinforcing plate 83 by welding to form a weld bead part 83W shown in
If the Young's modulus of each beam body in
The effect of the modification example of
Since the projection parts 83b are fixed and integrated to the tips of the fourth wall 2a and the seventh wall 2c (the end parts 2h) respectively, the outwardly swelling buckling and the inwardly swelling buckling of the fourth wall 2a and the seventh wall 2c are suppressed.
The recessed parts 83c formed respectively outside the root parts of the projection parts 83b of the reinforcing plate 83 house the tips of the fourth wall 2a and the seventh wall 2c respectively, whereby the peeling (disassembling) of the integrated part (the weld bead part 83W) is suppressed to maintain the integrated state of the reinforcing plate 83 to the beam body 92 at least until the beam body 92 is buckling-deformed. Thus, the inward buckling of the beam body (buckling in which the middle portion of the fourth wall 2a and the middle portion of the seventh wall 2c are deformed to approach each other) is suppressed.
The projecting direction of each projection part 83b has only to be a direction intersecting the reinforcing plate 83 in one cross section perpendicular to the reference line W, and may be inclined relative to the normal to the reinforcing plate 83.
A bumper beam 121 according to a seventh embodiment of the present invention will be then described in reference to
The bumper beam 121 includes, as shown in
Each reinforcing plate 4 is produced by extrusion-molding an aluminum-based material, and is attached to each outside surface of the fourth wall 2a and the seventh wall 2c. Concretely, each reinforcing plate 4 is disposed in parallel to the fourth wall 2a and the seventh wall 7c, and also in parallel to the longitudinal direction B. The reinforcing plates 4 are integrated to the beam body 2 by welding, with the surfaces of the reinforcing plates 4 being closely fitted to the surfaces of the fourth wall 2a and the seventh wall 2c respectively. Both the reinforcing plates 4 are disposed to hold the fourth wall 2a and the seventh wall 2c from both the outer side in the vertical direction A. Concretely, one reinforcing plate 4 is fixed to the lower surface of the seventh wall 2c, and the other reinforcing plate 4 to the upper surface of the fourth wall 2a.
Both the reinforcing plates 4 are attached to all over the whole outer surfaces of two outer webs, or the fourth wall 2a and the seventh wall 2c, respectively to reinforce the corresponding outer webs. Namely, both the reinforcing plates 4 function as reinforcing materials of the fourth wall 2a and the seventh wall 2c respectively. The thickness of each reinforcing plate 4 in this embodiment is 2.0 mm, and the aluminum-based material constituting the reinforcing plate 4 has a Young's modulus of 6,900 MPa and a density of 2700 kg/m3.
The relation between Young's modulus and density in the seventh embodiment will be described. If the Young's modulus of the beam body 2 is Est, the density of the beam body 2 is ρst, the Young's modulus of the reinforcing plate 4 is E3, and the density of the reinforcing plate 4 is ρ3, Est, E3, ρst and ρ3 satisfy a condition shown in the following expression (6).
E
st/ρst3<E3/ρ33 (6)
The thickness t3 of the reinforcing plate 4 is set so as to satisfy a condition shown in the following expression (7), wherein tst is the thickness of the beam body 2.
t
3<(ρst/ρ3)×tst (7)
Further, the thickness t3 of the reinforcing plate 4 is set so as to satisfy a condition shown in the following expression (8) so that the reinforcing plate 4 can exhibit a sufficient reinforcing effect.
0.3×tst<t3 (8)
The effectiveness that each material satisfies the conditions shown in the above-mentioned expressions (6) to (8) will be described. If the buckling length of the reinforcing plate 4 is L, the thickness of the reinforcing plate 4 is t, and the Young's modulus of the reinforcing plate 4 is E, the buckling load Pcr of the reinforcing plate 4 can be represented by the following expression (9).
P
cr∝(E·t3)/L2 (9)
Assuming that L is constant, the expression (9) can be represented by the following expression (10).
P
cr
∝E·t
3 (10)
According to the expression (10), if the Young's modulus of the beam body 2 is Est, the thickness of the beam body 2 is tst, the Young's modulus of the reinforcing plate 4 is E3, and the thickness of the reinforcing plate 4 is t3, effective reinforcement of the beam body 2 can be attained by satisfying a condition shown in the following expression (11).
E
st
·t
st
3
<E
3
·t
3
3 (11)
On the other hand, the relation between weight W and density ρ of a certain material is represented by the following expression (12).
W∝ρ·t (12)
Thus, the relation of the following expression (13) is established by providing the reinforcing plate 4 so that the weight of a “portion subjected to attachment (to be described later)” of the beam body 2 is equal to the weight of the reinforcing plate 4.
ρst·tst=ρ3·t3 (13)
The area of the portion subjected to attachment is equal to the area of the reinforcing plate. The “portion subjected to attachment” corresponds to the fourth wall 2a and the seventh wall 2c of this embodiment. When the reinforcing plate 4 is attached to the second wall 2k (or the fifth wall 2e) as described later, the second wall 2k (or the fifth wall 2e) corresponds to the “portion subjected to attachment”.
The above-mentioned relation of the expression (6) is derived from the above-mentioned expressions (13) and (11). Thus, reinforcement of the beam body 2 with a material such that it satisfies the expression (6) enables efficient improvement in buckling load per weight (Pcr/W).
Further concretely, for example, when the reinforcing plate 4 having substantially the same weight as the fourth wall 2a is attached to the beam body 2, the weight of the fourth wall 2a and the reinforcing plate 4 is about twice the weight of the fourth wall 2a, while the buckling load of the fourth wall 2a and the reinforcing plate 3 becomes larger than twice the buckling load of the fourth wall 2a. The same can be said in a case in which the reinforcing plate 4 is attached to the seventh wall 2c.
In this embodiment, the expression (6) is satisfied with Est/ρst3=4.30×10̂(−8) [MPa·m/kg3] and E3/ρ33=3.51×10̂(−7) [MPa·m/kg3], wherein Est=21,000 MPa, E3=6,900 MPa, ρst=7,874 kg/m3, and ρ3=2,700 kg/m3.
In this embodiment, the expression (7) is also satisfied with (ρst/ρ3)×tst=4.08 mm>t3 (=2.0 mm), wherein tst=1.4 mm, and t3=2.0 mm. Further, the expression (8) is also satisfied with 0.3×tst=0.42 mm<t3 (=2.0 mm).
The bumper beam according to this embodiment does not have to always satisfy the expression (13).
Results of evaluation for buckling load will be then described. The buckling load was calculated using a sample 10 shown in
The buckling load of the sample 10 was calculated in a condition where mutually reversed forces along a direction parallel to the aluminum plate 13 and the steel plate 12a (refer to the directions of arrows in the drawing) are worked on the upper end and lower end of the sample 10. The steel plate 12a corresponds to the seventh wall 2c of
The steel plate 12a is of 980 MPa-class, and the aluminum plate 13 is composed of 7000 series aluminum alloy. The thickness of the steel plate 12a, the thickness of the aluminum plate 13, the weight ratio, the plate thickness ratio and the buckling load ratio are shown in Table 3.
(1) The 2.5-mm-thick steel plate 12a which is not reinforced with the aluminum plate 13 has a weight ratio of 1.79 and a buckling load ratio of 5.69, while (2) the 1.4-mm-thick steel plate which is reinforced with the 3.0-mm-thick aluminum plate 13 has a weight ratio of 1.74, which is substantially equal to the weight ratio of the steel plate of (1), and a buckling load ratio of 16.63, which is about three times the buckling load ratio of the steel plate of (1).
As is apparent from the examples of (1) and (2), Table 3 and the graph of
A bumper beam 131 according to an eighth embodiment of the present invention will be then described in reference to
The bumper beam 131 of this embodiment is obtained by adding further two reinforcing plates (second reinforcing plates) 5 to the bumper beam 121 shown in
The two reinforcing plates 5 are attached to all over the whole outer surfaces of inner webs, or the second wall 2k and the fifth wall 2e, respectively, to reinforce respective inner webs.
Results of evaluation for bending strength in bumper beam will be then described. With respect to four types of bumper beams (the bumper beam 121 shown in
It is found from the graph of
The maximum bending moment ratio of the bumper beam 131 is 1.67, in contrast to the maximum bending moment ratio of 1.75 of the bumper beam composed of only the beam body 2 formed of 2.0-mm-thick steel plate. Thus, the maximum bending moment ratio of the bumper beam 131 is comparable to that of the beam body 2 formed of 2.0-mm-thick steel plate. On the other hand, the weight ratio of the bumper beam 131 is kept as low as 1.19 (weight increasing rate: 20%), compared with the weight ratio of 1.41 of the beam body 2 formed of 2.0-mm-thick steel plate (weight increasing rate: 40%).
As described so far, the outer webs and inner webs of the beam body 2 formed of steel are effectively reinforced by fixing reinforcing plates formed of aluminum to the whole surfaces thereof. The Young's moduli and densities of the beam body and the reinforcing plate satisfy the condition shown in the expression (6), whereby the bending strength can be improved while minimizing the increase in weight.
The bumper beam according to the eighth embodiment is never limited to the above-mentioned structure. Modification examples thereof are shown in
The bumper beam 141 shown in
Each reinforcing plate 14 (corresponding to the above-mentioned reinforcing plate 4) has an L shape in an optional cross section orthogonal to the reference line W. Concretely, as shown also in
On the other hand, dents 2b′ shown in
Of the reinforcing plate 14, the reinforcing plate body 14a is fixed to the whole outer surface of the outer web, and the overhang wall 14c is fixed to the eighth wall 2b while being fitted to the dent 2b′ of the eighth wall 2b. This fitting of the overhang wall 14c to the dent 2b′ allows to continue the front surface of the overhang wall 14c to the front surface of the eighth wall 2b on the same plane while matching the front surface position of the overhang wall 14c to the front surface position of the eighth wall 2b.
The above-mentioned reinforcing plate composite body 15, which is attached to a middle part of the beam body 2, includes two reinforcing plates 5 and a center wall 15c connecting one-side ends of the reinforcing plates to each other. The center wall 15c is fixed to the first wall 2j so as to extend in parallel to the vertical direction A, and to be closely fitted to the whole surface of the first wall 2j. Both the reinforcing plates 5 are fixed respectively to the surfaces of the second wall 2k and the fifth wall 2c so as to be closely fitted to the whole surfaces thereof.
As the metallic materials constituting the reinforcing plate 14 and the reinforcing plate composite body 15, any material which satisfies the condition shown in the above-mentioned expression (6) can be adopted without particular limitation.
In the structure shown in
The bumper beam 151 shown in
Similarly to the above-mentioned bumper beam 141, the same dents as the dents 2b′ may be formed respectively at both ends of the eighth wall 2b. Further, dents dented along the longitudinal direction B may be formed also at end parts (end parts relative to the vertical direction A) of the third wall 2m and the sixth wall 2d. A total of four overhang walls 24c are fitted respectively to these four dents, whereby the front surface positions of two overhang walls 14c on the front side can be matched to the front surface position of the eighth wall 2b, and the rear surface positions of two overhang walls 14c on the rear side can be matched to the rear surface positions of the third wall 2m and the sixth wall 2d.
The summary of the bumper beams according to the seventh embodiment and the eighth embodiment will be then described. As a typical structure, the bumper beam 121 shown in
The beam body 2 has, in an optional cross section perpendicular to the reference line W, (a) an eighth wall (reference wall) 2b extending linearly, and (b) an upper swelling part 2t and a lower swelling part 2s each swelling in a direction intersecting the eighth wall 2b while enclosing an internal space, and these constitute a B-shaped cross section. In this cross section, the upper swelling part 2t has a fourth wall 2a as an outer wall part and a second wall 2k as an inner wall part, and the lower swelling part 2s has a fifth wall 2e as an inner wall part and a seventh wall 2c as an outer wall part. These four wall parts extend in a direction intersecting the eighth wall 2b (a direction orthogonal thereto in the drawing) and are aligned along the eighth wall 2b.
The reinforcing plates 4 are attached to the fourth wall 2a and the seventh wall 2c as the outer wall parts respectively in an attitude parallel thereto. Further, the reinforcing plate 4 and the beam body 2 satisfy the following condition.
(Est/ρst3)<(E3/ρ33)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E3: Young's modulus of the second reinforcing plate
ρ3: Density of the second reinforcing plate
The two reinforcing plates 4 each formed of a plate of aluminum-based material (aluminum or aluminum alloy) efficiently reinforce the beam body 2 by being disposed respectively on two outer webs (the fourth wall 2a and the seventh wall 2c) of the beam body. Further, the Young's moduli and densities of the reinforcing plate 4 and the beam body 2 satisfy the above-mentioned condition, whereby the bending strength of the bumper beam can be improved while minimizing the increase in weight of the bumper beam.
Further, the above-mentioned bumper beam 121 satisfies the following condition.
t
3<(ρst/ρ3)×tst
t3: Thickness of the reinforcing plate 4
tst: Thickness of the beam body 2
This enables to suppress the increase in weight of the attachment object part of each reinforcing plate 4 by addition of the reinforcing plate 4 to less than twice the weight of the wall part to which the reinforcing plate 4 is attached (the fourth wall 2a or the seventh wall 2c). For example, the weight of the attachment object part in attachment of the reinforcing plate 4 to the fourth wall 2a (the weight of the reinforcing plate 4 and the fourth wall 2a) is below twice the weight of the fourth wall 2a.
The bumper beam 121 further satisfies the following condition.
0.3×tst<t3
The reinforcing plate 4 which satisfies this condition can surely improve the bending strength of the bumper beam.
In other words, the bending strength of the bumper beam 121 can be improved while minimizing the increase in weight of the bumper beam 121 by manufacturing the bumper beam so as to satisfy each of the above-mentioned conditions. This manufacturing method includes an attachment step of attaching the reinforcing plate 4 to the beam body 2.
The above-mentioned embodiments are only concrete examples and never particularly limit the present invention. The concrete structure of the present invention can be changed in design. The functions and effects described in the embodiments are only the most preferable functions and effects resulting from the above-mentioned embodiments, and the functions and effects by the present invention are never limited to those described in the above-mentioned embodiments.
For example, each of the above-mentioned projection parts 33a, 43a, 63a, 83a, and 83b does not have to be always formed integrally with the body part of the reinforcing plate. These projection parts may be formed of members separate from the plate constituting the body part of the reinforcing plate, and fixed to the plate by welding or the like.
The reinforcing plate does not have to be bonded to all over the whole surface of each web. For example, the surface of the reinforcing plate may be bonded to part of the surface of the web when the surface area of the reinforcing plate is smaller than the surface area of the web, or part of the surface of the reinforcing plate may be bonded to part of the surface of the web.
The method of attaching the reinforcing plate to each web is never limited to the method of joining the surfaces of the both to each other. For example, the reinforcing plate may be embedded in the web surface.
The collision direction with a collision object does not have to be matched to the longitudinal direction, and may be inclined relative to the longitudinal direction. Namely, the collision direction does not have to be orthogonal to the first reinforcing plate or the eighth wall 2b.
The second reinforcing plate may be attached to not the outside of the beam body but the inside thereof. For example, the reinforcing plates 4 shown in
The bumper beam according to the present invention may be configured to be mounted not only on the front of the vehicle body as in each of the above-mentioned embodiments, but also on the rear of the vehicle body.
Although the cross section orthogonal to the reference line W in the bumper beam according to each of the above-mentioned embodiments is uniform with respect to the longitudinal direction of the bumper beam, the bumper beam according to the present invention is never limited to a one having a uniform cross section, and has only to satisfy, with respect to at least one cross section orthogonal to the reference line W, the conditions for the shapes of the beam body and the reinforcing plate described so far.
As described so far, the present invention provides a bumper beam which can be improved in bending strength with minimum increase in weight.
(1) A bumper beam according to the first aspect of the present invention, which is configured to be mounted on the front or rear of a vehicle body and to extend along a reference line, includes a beam body formed of a metallic plate and extending along the reference line, and a metallic first reinforcing plate extending along the reference line and attached to the beam body. In at least one cross section perpendicular to the reference line, the first reinforcing plate extends linearly, and the beam body includes a pair of swelling parts each swelling from the first reinforcing plate in a direction intersecting it while enclosing an internal space.
Further, the beam body and the first reinforcing plate satisfy the following condition:
(Est/ρst3)<(E2/ρ23)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E2: Young's modulus of the first reinforcing plate
ρ2: Density of the first reinforcing plate
This bumper beam is preferably mounted on the vehicle body so that the first reinforcing plate is located outside the beam body (on the front side of the beam body in the case of a front bumper, and on the rear side of the beam body in the case of a rear bumper). According to this, the first reinforcing plate can reinforce the beam body. Further, the Young's moduli and densities of the beam body and the first reinforcing plate satisfy the above-mentioned condition, whereby the bending strength of the bumper beam can be improved while minimizing the increase in weight of the bumper beam.
The materials for the beam body and the first reinforcing plate may be the same or different. Examples of a preferable combination of materials of “beam body-first reinforcing plate” include “steel-aluminum”, “steel-steel”, “steel-copper”, and “copper-copper”.
The formation of a sectional shape as described above, or, the formation that the first reinforcing plate linearly extends, and the beam body includes a pair of swelling parts each swelling from the first reinforcing plate in a direction intersecting it, and each swelling part encloses an internal space with the first reinforcing plate, has only to be established with respect to at least one of cross sections perpendicular to the reference line, and the above-mentioned sectional shape does not have to be always present on all the cross sections of the bumper beam.
The extending direction of the bumper beam (the direction of the reference line) may be paralleled to the width direction of the vehicle body or may be inclined relative to the width direction. The reference line may be straight line or curved line (for example, lines having arch-like shape or other curved shapes). The angle of the above-mentioned “intersecting” is not limited to right angle, and may be smaller than right angle.
(2) Concretely, the bumper beam of (1) may be such that, with respect to at least one cross section perpendicular to the reference line, each of the swelling parts has an outer wall part extending in a direction intersecting the first reinforcing plate and an inner wall part extending in a direction intersecting the first reinforcing plate at a position closer to the other swelling part than the position of the outer wall part, both the outer wall parts and both the inner wall parts being aligned along the first reinforcing plate. Four wall parts composed of the inner wall parts and the outer wall parts may be paralleled or may be inclined relative to the longitudinal direction of the vehicle body. The intersecting angle of the wall parts with the first reinforcing plate may be equal to or smaller than right angle.
(3) In the bumper beam of (2), the first reinforcing plate preferably includes first projection parts projecting from the first reinforcing plate in a direction intersecting the longitudinal direction of the first reinforcing plate to hold both the inner wall parts from the outside. The first projection parts suppress the buckling of each inner wall part (buckling in which the middle portions of the inner wall parts are deformed outwardly or to separate from each other), whereby the bending strength of the bumper beam is further improved.
(4) In the bumper beam of (2), the first reinforcing plate preferably includes also second projection parts projecting from the first reinforcing plate in a direction intersecting the longitudinal direction of the first reinforcing plate to hold both the outer wall parts from the outside. The second projection parts suppress the buckling of each outer wall part (buckling in which the middle portions of the outer wall parts are deformed outwardly or to separate from each other), whereby the bending strength of the bumper beam is further improved.
(5) In the bumper beam of (4), it is further preferred to fix each outer wall part to the corresponding second projection part. This allows further effective suppression of both the inward and outward buckling of each outer wall part. Concretely, the suppression of the outwardly swelling buckling of each outer wall part (buckling in which the middle portion of the outer wall part are deformed outwardly or to separate from each other) can be attained by (i) suppressing the deformation of the outer wall part by contact of each second projection part with the corresponding outer wall part and by (ii) enhancing the buckling load by the integration of each outer wall part to the corresponding second projection part. The suppression of the inwardly denting buckling of each outer wall (buckling in which the middle portion of the outer wall part deforms inwardly or to approach each other) can be attained by enhancing the buckling load by the integration of each outer wall part to the corresponding second projection part.
The means for fixing each outer wall part to the corresponding second projection part includes adhesion, welding, and bolting.
(6) Further, in the bumper beam of (5), it is further preferred to form, in a position inside a root part of each second projection part of the first reinforcing plate, a recessed part for housing a tip of the corresponding outer wall part. By housing the tip of the outer wall part in the recessed part, the peeling of the outer wall part from the second projection part in the joint part between the both is suppressed to maintain the integrated state of the first reinforcing plate and the beam body at least until the beam body is buckling-deformed. Consequently, the inward buckling of each outer wall part (buckling in which the middle portion of each outer wall part is deformed to approach each other) is suppressed.
(7) In the bumper beam of (2), it is also preferred to provide, on the first reinforcing plate, third projections projecting from the first reinforcing plate in a direction intersecting its longitudinal direction to constrain both the outer wall parts from the inside, and to fix the corresponding outer wall part to each third projection part. The third projection parts suppress the inward buckling of each outer wall surface (buckling in which the middle portions of the outer wall parts are deformed inwardly or to approach each other), whereby the bending strength of the bumper beam is further improved. Further, the integration of each outer wall part to the first reinforcing plate also suppresses the outwardly swelling buckling and inwardly contracting buckling of the outer wall part.
(8) With respect to the third projection parts, also, it is further preferred to form a recessed part for housing the tip of the corresponding outer wall part in a position outside the root part of each third projection part of the first reinforcing plate. By housing the tips of the outer wall parts in the recessed parts, the peeling of the outer wall part from the third projection part at the joint part thereof is suppressed to maintain the integrated state of the first reinforcing plate and the beam body at least until the beam body is buckling-deformed. Thus, the inward buckling of each outer wall part (buckling in which the middle portion of each outer wall part deforms to approach each other) is suppressed.
The means for fixing each outer wall part to the corresponding third projection part includes adhesion, welding, and bolting.
(9) In the bumper beam according to the present invention, as the material of the first reinforcing plate, for example, aluminum or aluminum alloy (duralumin, etc.) is preferred. A lightweight first reinforcing plate can be obtained by using such material. The use of aluminum alloy enhances the strength of the first reinforcing plate, compared with the use of pure aluminum.
(10) The bumper beam according to the second aspect of the present invention, which is configured to be mounted on the front or rear of a vehicle body and to extend along a reference line, includes a beam body formed of a metallic plate and extending along the reference line, and a metallic second reinforcing plate extending along the reference line and attached to the beam body. In at least one cross section perpendicular to the reference line, the beam body includes a reference wall extending linearly and a pair of swelling parts each swelling from the reference wall in a direction intersecting it while enclosing an internal space, each of the swelling parts has an outer wall part extending in a direction intersecting the reference wall, and an inner wall part extending in a direction intersecting the first reinforcing plate at a position closer to the other swelling part than the position of the outer wall part, and the outer wall parts and the inner wall parts are aligned . along the reference wall. The second reinforcing plate is attached to at least either both the outer wall parts or both the inner wall parts in an attitude parallel thereto.
Further, the beam body and the second reinforcing plate satisfy the following condition.
(Est/ρst3)<(E2/ρ23)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E3: Young's modulus of the second reinforcing plate
ρ3: Density of the second reinforcing plate
In this bumper beam, the second reinforcing plate formed of metallic material is attached to at least one wall part, whereby the beam body can be reinforced. The Young's moduli and densities of the beam body and the reinforcing plate satisfy the above-mentioned condition, whereby the bending strength of the bumper beam can be improved while minimizing the increase in weight of the bumper beam.
The materials of the beam body and the reinforcing plate may be the same or different. Examples of a preferable combination of the materials of “beam body-second reinforcing plate” includes “steel-aluminum”, “steel-steel”, “steel-copper”, and “copper-copper”.
The formation of a sectional shape as described above, or the formation that the beam body includes a reference wall extending linearly and a pair of swelling part each swelling from the reference wall in a direction intersecting it while enclosing an internal space, each swelling part has an inner wall part and an outer wall part extending in a direction intersecting the reference wall, each inner wall part and each outer wall part being aligned along the reference wall, and the second reinforcing plate is attached to at least either both the inner wall parts or both the outer wall parts in an attitude parallel thereto, has only to be established with respect to at least one of cross sections perpendicular to the reference line, and the above-mentioned sectional shape does not have to be always present in all the cross sections of the bumper beam.
The extending direction of the bumper beam (the direction of the reference line) may be paralleled to the width direction of the vehicle body or may be inclined relative to the width direction. The reference line may be straight line or curved line (for example, lines having arch-like shape or other curved shapes). The angle of “intersecting” described above is never limited to right angle, and may be smaller than right angle.
Each of the wall parts may be paralleled or inclined relative to the longitudinal direction. The intersecting angle of these wall parts to the reference wall is never limited to right angle.
The number of the second reinforcing plates may be one or two or more. For example, a total of two second reinforcing plates may be attached to both the outer wall parts respectively, or a total of four second reinforcing plates may be attached to both the outer wall parts and both the inner wall parts respectively.
An overhang wall overhanging in a direction orthogonal to the other part of the second reinforcing plate may be formed at the front end or rear end of the second reinforcing plate. The second reinforcing plate may be attached to the outer surface of the beam body or the inner surface thereof.
The means for connecting and integrating the beam body to the second reinforcing plate includes welding, screw fastening, and adhesion and the like.
(11) The bumper beam of (10) further preferably satisfies the following condition.
t
3<(ρst/ρ3)×tst
tst: Thickness of the beam body
t3: Thickness of the second reinforcing plate
In a bumper beam which satisfies this condition, the total sum of the weight of the second reinforcing plate and the weight of a wall part to which the second reinforcing plate is attached can be suppressed to below twice the weight of the wall part alone. Namely, the weight of the wall part to which the second reinforcing plate is attached, including the second reinforcing plate, is below twice the weight of the wall part.
(12) The bumper beam of (10) further preferably satisfies the following condition.
0.3×tst<t3
The bumper beam satisfies the above-mentioned condition, whereby the bending strength of the bumper beam is surely improved.
(13) In the bumper beam of (10), also, as the material of the second reinforcing plate, for example, aluminum or aluminum alloy (duralumin, etc.) is suitably used. A lightweight first reinforcing plate can be obtained by using such material. The use of aluminum alloy enhances the strength of the first reinforcing plate, compared with the use of pure aluminum.
(14) The bumper beam for solving the above-mentioned problem, which is configured to be mounted on the front or rear of a vehicle body and to extend along a reference line, may be such that it includes a metallic beam body extending along the reference line, and having a first wall, a second wall, a third wall, a fourth wall, a fifth wall, a sixth wall, and a seventh wall; and a metallic first reinforcing plate extending along the reference line, and satisfies the following conditions A and B.
A. In at least one cross section perpendicular to the reference line, the following conditions (a) to (g) are satisfied.
(a) The second wall extends from one end of the first wall in a direction intersecting the first wall.
(b) The third wall extends from an end part opposite to the first wall of the second wall in a direction intersecting the second wall toward the opposite side to the first wall relative to the second wall.
(c) The fourth wall extends from an end part opposite to the second wall of the third wall in a direction intersecting the third wall toward the second wall relative to the third wall.
(d) The fifth wall extends from the other end part of the first wall in a direction intersecting the first wall toward the same side as the second wall relative to the first wall.
(e) The sixth wall extends from an end part opposite to the first wall of the fifth wall in a direction intersecting the fifth wall toward the opposite side to the first wall relative to the fifth wall.
(f) The seventh wall extends from an end part opposite to the fifth wall of the sixth wall in a direction intersecting the sixth wall toward the fifth wall relative to the sixth wall.
(g) The reinforcing plate extends in the extending direction of the first wall, and is attached to the end part opposite to the third wall and the sixth wall of the beam body relative to the direction perpendicular to the first wall.
B. The beam body and the reinforcing plate satisfy the following condition.
(Est/ρst3)<(E2/ρ23)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E2: Young's modulus of the reinforcing plate
ρ2: Density of the reinforcing plate
In this bumper beam, the second wall, the fourth wall, the fifth wall, and the seventh wall may be paralleled or inclined relative to the longitudinal direction. The first wall, the third wall and the sixth wall may be paralleled or inclined relative to the vertical direction. Each of the first to the seventh walls may extend linearly or extend in a curved shape in at least one cross section perpendicular to the reference line. With respect to each “intersecting” described above, the intersecting angle is never limited to right angle.
The beam body may include an eighth wall (a wall part connecting an end part opposite to the third wall of the fourth wall to an end part opposite to the sixth wall of the seventh wall and extending in the extending direction of the first wall), or does not have to include it.
When the beam body is free from the eighth wall, overhang parts extending in a direction orthogonal to the fourth wall and the seventh wall may be formed at the end parts of the fourth wall and the seventh wall (an end part opposite to the third wall of the fourth wall and an end part opposite to the sixth wall of the seventh wall) respectively. When the beam body has the eighth wall, the eighth wall may be paralleled or inclined relative to the vertical direction. In at least one cross section perpendicular to the reference line, the eighth wall may extend linearly or extend in a curved shape.
When the eighth wall is not provided on the beam body, the reinforcing plate may be attached to the fourth wall and the seventh wall, or may be attached to the surface of the first wall. When the eighth wall is provided on the beam body, the reinforcing plate may be attached to the surface of the eighth wall. The means for connecting and integrating the beam body and the reinforcing plate includes welding, screw fastening, adhesion and the like.
(15) The bumper beam for solving the above-mentioned problem, which is configured to be mounted on the front or rear of a vehicle body and to extend along a reference line, can be such that it includes a metallic beam body extending along the reference line and having a first wall, a second wall, a third wall, a fourth wall, a fifth wall, a sixth wall, a seventh wall and an eighth wall; and a metallic second reinforcing plate extending along the reference line, and satisfies the following conditions C and D.
C. In at least one cross section perpendicular to the reference line, the following conditions (a) to (g) are satisfied.
(a) The second wall extends from one end of the first wall in a direction intersecting the first wall.
(b) The third wall extends from an end part opposite to the first wall of the second wall in a direction intersecting the second wall toward the opposite side to the first wall relative to the second wall.
(c) The fourth wall extends from an end part opposite to the second wall of the third wall in a direction intersecting the third wall toward the second wall relative to the third wall.
(d) The fifth wall extends from the other end part of the first wall in a direction intersecting the first wall toward the same side as the second wall relative to the first wall.
(e) The sixth wall extends from an end part opposite to the first wall of the fifth wall in a direction intersecting the fifth wall toward the opposite side to the first wall relative to the fifth wall.
(f) The seventh wall extends from an end part opposite to the fifth wall of the sixth wall in a direction intersecting the sixth wall toward the fifth wall relative to the sixth wall.
(g) The eighth wall extends in the extending direction of the first wall while connecting an end part opposite to the third wall of the fourth wall to an end part opposite to the sixth wall of the seventh wall, and the second reinforcing plate is attached to at least one of the second wall, the fourth wall, the fifth wall and the seventh wall in parallel thereto.
D. The beam body and the second reinforcing plate satisfy the following condition.
(Est/ρst3)<(E3/ρ33)
Est: Young's modulus of the beam body
ρst: Density of the beam body
E3: Young's modulus of the second reinforcing plate
ρ3: Density of the second reinforcing plate
The second wall, the fourth wall, the fifth wall and the seventh wall may be paralleled or inclined relative to the longitudinal direction. The first wall, the third wall, the sixth wall and the eighth wall may be paralleled or inclined relative to the vertical direction. Each of the first to the eighth walls may extend linearly or extend in a curved shape in at least one cross section perpendicular to the reference line. With respect to each “intersecting” described above, the intersecting angle is not limited to right angle.
The number of the second reinforcing plates may be one or two or more. For example, a total of two second reinforcing plates may be attached to the fourth wall and the seventh wall respectively, or a total of four second reinforcing plates may be attached to the second wall, the fourth wall, the fifth wall and the seventh wall respectively.
For example, the second reinforcing plates attached to the second wall and the fifth wall respectively may be connected to each other by a connecting plate (a plate extending in the extending direction of the first wall). An overhang wall extending perpendicular to the other part of the second reinforcing plate may be formed at the front end or rear end of the second reinforcing plate. The second reinforcing plate may be attached to the outer surface of the beam body, or may be attached to the inner surface thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-045913 | Feb 2008 | JP | national |
| 2008-081061 | Mar 2008 | JP | national |
| 2009-009537 | Jan 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/053423 | 2/25/2009 | WO | 00 | 8/24/2010 |
