JP2005349918A - Shock absorbing member for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an impact absorbing performance whose entire length can be an effective displacement portion for absorbing impact energy.
SOLUTION: In a vehicle impact absorbing member 1 having an upper surface portion 3 and an outer peripheral wall portion 2 and having a hollow cross section, the outer peripheral wall portion 2 has a flat plate shape, and R connecting the upper surface portion 3 and the outer peripheral wall portion 2 is provided. The shape of the portion 4 is such that the radius of curvature of the R portion is R, the breaking strain of the material is ε, and the thickness of the plate is t. It is characterized by being.
[Selection] Figure 6

Description

  The present invention relates to an impact absorbing member for a vehicle that is suitably used for, for example, a bumper of a vehicle.

  Vehicles such as automobiles are provided with various means for effectively absorbing impact energy when colliding with other objects and protecting expensive parts and functional parts together with passengers. One. In Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-79856), as shown in FIG. 8, a cylindrical base 50 that is an extruded material of an aluminum alloy, and an elastic foam 51 disposed in the internal space of the cylindrical base 50. And a light impact absorbing portion 54 that is provided integrally with the cylindrical base portion 50 to form a hollow portion 52 between the cylindrical base portion 50 and a side wall 53 that extends in a wavy shape along the impact input direction. The bumper is described. In this bumper, impact energy is effectively absorbed by the deformation of the side wall 53 extending in a wavy shape and the elastic foam 51.

  In Patent Document 2 (Japanese Patent Laid-Open No. 2000-62551), as shown in FIG. 9a, a hollow cross section made of an aluminum alloy extruded shape is used as a crash box (impact absorber) interposed between a bumper and a vehicle body frame. A cylindrical rectangular crush box 60 having a structure is described, and at the time of collision, as shown in FIG. 9b, the side wall of the crush box 60 is deformed by a regular buckling 61 and is crushed to effectively reduce impact energy. Absorb.

JP 2000-79856 A JP 2000-62551 A

  As described in Patent Documents 1 and 2, in current vehicles and the like, a hollow member made of an aluminum alloy or the like is used as an impact absorbing member, and the impact energy is absorbed by its shape change (displacement due to crushing or the like). Many of these have been adopted. FIG. 10a is a displacement-load diagram for such an impact absorbing member, FIG. 10b is a state before the impact absorbing member is displaced (length Ho), and FIG. 10c is a state after the impact load is displaced (long). H) is schematically shown.

  As shown by the solid line in FIG. 10a, the ideal shock absorbing member has a constant load until the load suddenly rises at an initial stage and then the shock absorbing member is broken or deformed at a certain constant load until the shock absorbing material is completely crushed. Is desired (so that the effective displacement H is approximately equal to the initial length Ho of the shock absorbing material) so-called rectangular waves are desired.

  However, the shock absorbing member currently used is mainly broken or deformed by ductile fracture, and as shown in FIG. 10c, the collapsed outer peripheral wall part finally has a collapsed portion (distance h). For this reason, the effective displacement H of the shock absorbing member is a distance obtained by subtracting the remaining crush h from the initial length Ho. After this effective displacement, a so-called bottoming phenomenon occurs, the load increases rapidly, and the allowable load is increased early. It will exceed.

  That is, the currently used shock absorbing member for vehicles has a disadvantage that the effective displacement H with respect to the total length Ho is short. In an actual machine, the length of the shock absorbing member is set to “ductility” in order to absorb necessary energy. Since it is necessary to design in consideration of “destructive displacement (effective displacement H) + residual crushing amount h”, this leads to an increase in cost and an increase in mass. Further, if the length of the shock absorbing member is longer than necessary, there is a problem that the degree of freedom in design is restricted in a limited vehicle space.

  The present invention has been made in view of the above circumstances, and in a vehicle impact absorbing member, the overall length is substantially shorter than the conventional one by making the entire length an effective displacement region during impact absorption. It is an object of the present invention to provide an improved vehicle shock absorbing member that can achieve the same shock absorbing performance even if it is a member.

  The impact absorbing member for a vehicle according to the present invention is an impact absorbing member for a vehicle having an upper surface portion and an outer peripheral wall portion and having a hollow cross section, the outer peripheral wall portion is a flat plate, and the upper surface portion and the outer peripheral wall portion are The shape of the connected R part satisfies the relationship of R ≦ 5t / ε, where R is the radius of curvature of the R part, ε is the breaking strain of the material, and t is the thickness of the material, and the collision with the object is It is performed.

  In the vehicle impact absorbing member according to the present invention, when a load due to a collision is applied substantially perpendicularly to the upper surface portion, the R portion connecting the upper surface portion and the outer peripheral wall portion bulges outward, and the R portion breaks due to brittle fracture. Thereafter, when further load is applied, the upper surface portion broken at the R portion descends the side wall portion so as to push the side wall surface outward. By this descent, the side wall portion develops in a petal shape outward while brittle fracture, and impact energy is effectively absorbed in the process of brittle fracture, and the deployment reaches the lowest end position.

  Therefore, the full length Ho can be substantially the effective displacement portion H for absorbing shock energy, and the same shock absorbing performance can be achieved even if the total length is shorter than the conventional one. Since the total length is short, the mass is reduced along with the cost, and the degree of freedom of design in the vehicle space is increased.

  In the vehicle impact absorbing member of the present invention, the relationship of R ≦ 5 t / ε is derived as follows. FIG. 1a is an overall view showing an example of a vehicle impact absorbing member, and FIG. 1b is a cross-sectional view taken along line AA of FIG. 1a. In this example, the vehicle impact absorbing member 1 is composed of an outer peripheral wall portion 2 having a rectangular horizontal section and an upper surface portion 3 that closes the upper end side thereof, and the outer peripheral wall portion 2 and the upper surface portion 3 having a flat plate shape. Are connected by the R portion 4. Now, let the end points of the R part be the B point (upper surface part side) and the C point (outer peripheral wall part side). The impact load is received by the upper surface portion 3 and the upper surface portion 3 is pushed downward, but the outer peripheral wall portion 2 is not easily deformed because it is perpendicular to the impact direction. Therefore, as shown in FIG. 2, the point B can be considered as a moving point directly below, and the point C can be considered as a fixed point.

Let r be the radius of curvature of the R portion before deformation, and r be the radius of curvature of the r portion after deformation. Distance from point B to point C = point B ′ to point C ′ after deformation,
1/4 · 2πR = R + r + 3/4 · 2πr
r ≒ 0.1R ・ ・ ・ ・ ・ ・ Formula (1)

An enlarged view of the portion r after deformation is shown in FIG. The center line of the thickness t is defined as point D to point E. The outer side surface is extended to points D ′ to E ′.
Dimension from point D to point E = 1/2 · 2πr = πr
Dimensions from point D ′ to point E ′ = 1/2 · 2π (r + t / 2) = πr + π / 2 · t
The breaking strain ε is
ε = π / 2 · t / πr = t / 2r
Substituting equation (1),
ε = t / 2t × 0.1R = 5t / R
Therefore, since the relational expression of R = 5t / ε is established, it can be seen that when R ≦ 5t / ε, breakage occurs at the R portion.

  More specifically, for example, in the case of a typical magnesium alloy, the fracture strain ε = 0.1, and when substituted for R ≦ 5 t / ε, R ≦ 50 t, that is, a curvature equal to or less than 50 times the plate thickness t. It can be seen that by configuring the shape of the R portion with the radius R, the vehicle impact absorbing member can achieve the initial purpose.

  Further, in the case of a typical aluminum alloy, the breaking strain ε = 0.15, and when substituted for R ≦ 5 t / ε, R ≦ 33 t, that is, the radius R of the curvature radius R is not more than 33 times the plate thickness t. It can be seen that the vehicle impact absorbing member can achieve the initial purpose by configuring the shape.

  Further, in the case of a typical steel, the breaking strain ε = 0.5, and substituting R ≦ 5t / ε, R ≦ 10t, that is, the radius of curvature R less than 10 times the plate thickness t, It can be seen that the vehicle impact absorbing member can achieve the initial purpose by configuring the shape.

On the other hand, the vehicle impact absorbing member usually requires a radius of curvature R of R = 2t or more as the radius of curvature of the R portion so as not to cause creases or the like during molding. FIG. 4 shows these relationships in a graph. As shown in FIG. 4, the smaller the breaking strain, the wider the degree of freedom (effective range) from the limit value (R = 2t straight line) at the time of molding. Becomes narrower. Therefore, in the present invention, it is desirable to use a material having a small breaking strain as the material of the impact absorbing member for a vehicle. For example, a magnesium alloy, an aluminum alloy, or the like is a preferable material. However, those having a value of breaking strain of less than 0.01 are not preferred because cracks may occur during molding. In addition, a material having a fracture strain exceeding 0.5 is not preferable because the degree of freedom of brittle fracture becomes narrow as in the case of the steel.
More specifically, materials as shown in Table 1 can be listed.

  In the present invention, the overall size and thickness t of the vehicle impact absorbing member are in accordance with the use location, required impact absorbing performance, etc., under the same conditions as employed in conventional vehicle impact absorbing members. May be determined as appropriate.

  In the vehicle impact absorbing material according to the present invention, the entire length is an effective displacement portion for absorbing impact energy. Therefore, even if the total length is shorter than that of the conventional one, the same shock absorbing performance can be achieved. Since the total length is short, both cost and mass are reduced, and the degree of freedom of design in the vehicle space is increased.

  Hereinafter, the present invention will be described based on embodiments with reference to the drawings. FIG. 5 shows a bumper portion of an automobile as an example of using the vehicle impact absorbing member 1 according to the present invention. This vehicle impact absorbing member 1 has the same shape as that described above with reference to FIG. 1, and is composed of an outer peripheral wall portion 2 having a horizontal sectional quadrangle and an upper surface portion 3 that closes its upper end side, The outer peripheral wall portion 2 and the upper surface portion 3, which are flat, are connected by the R portion 4 described above.

  In this example, the vehicle impact absorbing member 1 functions as a crash box, and a bumper 10 is fastened to the front end, that is, the upper surface portion 3 by a bolt 5, and a flange 7 provided at the rear end is attached to a front side member 8 of an automobile. It is fastened with a bolt 9 to the tip.

  When the bumper 10 receives an impact due to the collision with the colliding body, the bumper 10 is deformed and partially absorbs the impact. Further, the impact is transmitted to the vehicle impact absorbing member 1 functioning as a crash box, and the impact energy is effectively absorbed when the vehicle impact absorbing member 1 is broken (displaced) as described above. In this way, the crew and the expensive and functional parts can be protected.

  That is, as described above, the impact load is received at the upper end surface 3 as shown in FIG. The upper end surface 3 is pushed downward in FIG. 6, but the outer peripheral wall portion 2 is not easily deformed because it faces the impact direction. Therefore, the R portion 4 bends outward and deforms. At this time, if the ductile material is steel, the outer peripheral wall portion 2 is gradually folded and progresses to ductile fracture. However, when a brittle material such as magnesium alloy or aluminum alloy is used, the fracture strain ε is As shown in FIG. 6b, the bent portion R breaks (ruptures) due to strain exceeding the breaking limit at a certain point. In addition, as a condition for causing such fracture (break), as described above, the shape of the R portion 4 connecting the upper surface portion 3 and the outer peripheral wall portion 2 is such that the radius of curvature of the R portion is R, the fracture strain of the material is ε, When the plate thickness is t, it is necessary that the relationship of R ≦ 5 t / ε is satisfied and the collision with the object (collision body) is performed on the upper surface portion 3.

  Thereafter, as shown in FIG. 6c, the fractured surface progresses while the outer peripheral wall portion 2 is turned outward by pushing the outer peripheral wall portion 2 turned outward by the broken upper surface portion 3. Since the destruction can reach the lowest end of the outer peripheral wall portion 2, the remaining amount of crushing in the impact direction is almost zero. That is, the entire length of the outer peripheral wall portion 2 functions as an effective length for absorbing shock.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
[Examples 1 and 2]
FIG. 1 shows a shock absorber in the shape of a hollow square prism closed at the top, an aluminum alloy having a breaking strain ε of 0.15 (Example 1), and a magnesium alloy having a breaking strain ε of 0.1 (implementation). Prepared according to Example 2) and subjected to an impact test, a displacement-load diagram was obtained. The result is shown in FIG. Each shock absorber had a total length of 70 mm, a distance between the outer sides of the outer peripheral wall portion of 67 mm, and a thickness t of the upper surface portion, the outer peripheral wall portion, and the R portion were all 1 mm. Further, R (curvature radius) of the R portion was 10 mm. In Examples 1 and 2, the condition of R ≦ 5 t / ε is satisfied.

[Comparative Example 1]
A shock absorber having the same shape as that of the example was used except that a steel material having a breaking strain ε of 0.6 was used as a material, and an impact test was performed under the same conditions as in the example to obtain a displacement-load diagram. The result is shown in FIG. This shock absorber does not satisfy the condition of R ≦ 5 t / ε.

[Evaluation]
As shown in the graph of FIG. 7, the example products 1 and 2 have an effective length of about 66 mm, which absorbs the impact load, over almost the entire length. However, in the comparative example product, a sudden increase in load occurs at a distance exceeding 50 mm, and the effective length is shorter than that of the example product. This is because the comparative example product does not satisfy the condition of R ≦ 5 t / ε, so the impact load is absorbed mainly by fracture or deformation due to ductile fracture, and the resulting folded outer peripheral wall portion is It is because it finally remains as a crushing residue (distance of about 10 to 20 mm).

FIG. 1A is an overall view showing an example of a vehicle impact absorbing member according to the present invention, and FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A. The figure for demonstrating the aspect which the impact-absorbing member for vehicles deform | transforms by an impact. The enlarged view explaining R part after a deformation | transformation. The graph which shows the relationship between R part and plate | board thickness in the impact-absorbing member for vehicles by this invention. The exploded view which shows the bumper part which employ | adopted the impact-absorbing member for vehicles by this invention. The schematic diagram for demonstrating the state which the impact-absorbing member for vehicles by this invention receives an impact, and destroys (deforms). The graph which shows the displacement-load diagram in an Example product and a comparative example product. Sectional drawing which shows the principal part of the conventional impact-absorbing member. 9A shows another conventional shock absorbing member, FIG. 9A is a main part perspective view showing a state before deformation, and FIG. 9B is a state after deformation. The figure which shows the displacement-load diagram (FIG. 10a) in the conventional impact-absorbing member (FIG. 10a), the state before the displacement (FIG. 10b), and the state after a displacement (FIG. 10c).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle impact-absorbing member, 2 ... Outer peripheral wall part, 3 ... Upper surface part, 4 ... R part, ε ... Breaking strain, t ... Plate thickness, R ... Curvature radius of R part

Claims (3)

  An impact absorbing member for a vehicle having an upper surface portion and an outer peripheral wall portion and having a hollow cross section, the outer peripheral wall portion is a flat plate shape, and the shape of the R portion connecting the upper surface portion and the outer peripheral wall portion is A vehicle impact characterized in that when R is the curvature radius, ε is the breaking strain of the material, and t is the plate thickness, the relationship R ≦ 5t / ε is satisfied and the collision with the object occurs at the upper surface. Absorbing member.   2. The impact absorbing member for a vehicle according to claim 1, wherein the material is a material having a breaking strain [epsilon] in the range of 0.01 to 0.5.   2. The vehicle impact absorbing member according to claim 1, wherein the material is an aluminum alloy or a magnesium alloy.

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