GB2331492A

GB2331492A - Vehicle bumper assemblies

Info

Publication number: GB2331492A
Application number: GB9725032A
Authority: GB
Inventors: Keith Robert Weedon
Original assignee: Lin Pac Mouldings Ltd
Current assignee: Linpac Mouldings Ltd
Priority date: 1997-11-25
Filing date: 1997-11-25
Publication date: 1999-05-26
Also published as: FR2771355B1; FR2771355A1; DE19830099A1; GB9725032D0; IT1298935B1; ITMI980345A1

Abstract

A vehicle bumper assembly contains an energy absorbing layer 5 formed by a plurality of elements 6 each comprising a first, truncated pyramid section 6A and a second, base section 6B. In an impact the truncated pyramid sections absorb energy by deforming into the base sections.

Description

1 1 VEHICLE BUMPER ASSEMBLIES 2331492

Technical Field and Background Art

The present invention relates to a vehicle bumper assembly and a vehicle which includes such an assembly. The invention primarily concerns motor vehicles of the automobile type where the bumper assembly is, or is intended to be, fitted to the ends of the vehicle.

Bumper assemblies are primarily intended to alleviate damage to a vehicle body as a result of an impact and as such generally provide the leading and trailing parts of the vehicle.

Bumper assemblies alleviate damage to a vehicle body in an impact by absorbing at least a part of the impact energy and so reduce the potentially damaging forces applied to the vehicle body, and ultimately to the vehicle occupants, by an impact.

Further, in the event of a collision between a vehicle and a pedestrian, the likelihood and severity of injury to the pedestrian can be reduced by increasing the amount of the impact energy which is absorbed by the bumper assembly.

One known energy absorbing bumper assembly is a hollow bumper shell of plastics material filled with an expanded foamed plastics material. However bumper assemblies of this type are expensive.

It is an object of the present invention to provide a relatively cheap vehicle bumper assembly having an increased capability to absorb impact energy and a vehicle which includes such an assembly.

Statement of Invention and Advantaqes

According to the present invention, there is provided a vehicle bumper assembly comprising an impact face and a support member located behind the impact face and separated therefrom by a plurality of energy absorbing elements each comprising a first section shaped as a pyramid and a second 1 2 section shaped as a polygonal cross-sectioned tube having faces parallel to the axis of the symmetry of the first section, each face of the second section being joined to a respective face of the first section.

The invention also provides a vehicle which includes a bumper assembly as specified above.

A bumper assembly according to the invention can absorb large amounts of impact energy by deformation of the energy absorbing elements and can be cheaply and easily manufactured, for example by injection moulding.

Preferably, the first section is a truncated pyramid.

Preferably, the first section is a square based pyramid and the second section has a square cross section.

Preferably, the energy absorbing elements are arranged in a two dimensional tessellated array to maximize the amount of impact energy absorbed per unit volume of the assembly.

Preferably, each first section is truncated by an end face having a circular hole therethrough, the hole being coaxial with the axis of symmetry of said first section. This allows the first section to stably and predictably collapse progressively in on itself.

Preferably, reinforcing ribs are provided along the joins between adjacent faces of each first section. The resistance to deformation of the energy absorbing elements can be controlled by varying the width and thickness of the reinforcing ribs.

Preferably, the energy absorbing elements form a unitary structure with adjacent energy absorbing elements having second sections sharing common faces. This stabilises the deformation of the energy absorbing elements becLuse the sharing of faces of the second section helps to keep the loads on the faces balanced and so reduces the tendency of the faces to buckle. Further, such a unitary structure can easily be formed by injection moulding.

Preferably, the first and second sections of each energy absorbing element are arranged so that when the element is crushed the first section deforms until it lies within the second section. As a result, as the element is crushed the second, base, section is progressively filled with the plastics mAterial of the first, pyramid, section as the first section collapses progressively inward and into the second section. This will cause the second section of the energy absorbing element to increase in density and rigidity against impact. f Draw "ns Embodiments of a vehicle bumper assembly will now be described by way of example only with reference to the accompanying illustrative drawings, in which:

Figure 1 is a perspective view showing a part of a vehicle bumper assembly according to the invention; Figure 2 is a cross sectional view through the bumper assembly of Figure 1; Figure 3 is a rear view of an energy absorbing layer used in the bumper assembly of Figure 1; Figure 4 is a cross-section along the line A-A of Figure 3; Figure 5 is a rear view of a single energy absorbing element of the energy absorbing layer of Figure 3; Figure 6 is a cross-section along the line B-B of Figure 5; Figures 7 to 9 are perspective views showing successive stages of the crushing of a group of energy absorbing elements of the energy absorbing layer of Figure 3.

Detailed Description

Referring to Figure 1, a vehicle bumper assembly 1 is shown in part. As can be seen in cross-section in Figure 2, the upper part of the bumper is a composite structure formed by an impact f ace 2 supported by a support member 3. The support member 3 is integrally formed with the rest of the bumper assembly 1 which is attached to an automobile body (not shown).

The impact face 2 is situated at the part of the bumper assembly 1 which is likely to strike another object first in the event of an impact, and, in particular, at a location -1 4 which is likely to be the first part of the bumper assembly 1 to strike a pedestrian with whom the bumper assembly 1 of a moving vehicle may collide.

The impact face 2 has a pair of opposed side members 2A,2B which bear against cooperating parts 3A,3B of the support member 3.

The impact f ace 2 and the support member 3 are both formed of a resilient plastics material and the bearing surfaces of cooperating parts 2A,2B and 3A,3B are arranged so that the impact face 2 is held in position on the support member 3 by frictional forces generated between the support elements 2A,2B and 3A,3B.

The impact f ace 2 and support member 3 are shaped to define a space 4 therebetween and an energy absorbing layer 5 is held within this space 4.

The energy absorbing layer 5 is formed by a plurality of energy absorbing elements 6 arranged in a regular 2-di-mensional grid as shown in Figure 3. All of the energy absorbing elements 6 in the energy absorbing layer 5 are integrally formed from plastics material by moulding.

Referring to Figures 4 to 6, each energy absorbing element is formed by a first square based truncated pyramid section 6A mounted on a respective second base section 6B comprising four skirt walls 6c arranged in a square shape and parallel to the axis of symmetry of the truncated pyramid. Each of the skirt walls 6C is linked to a respective face 6D of the truncated pyramid section 6A along a joint line 6E.

Adjacent energy absorbing elements 6 in the array making up the energy absorbing layer 5 share a common skirt wall 6C so that the respective f aces 6D of the truncated. pyramid section 6A of adjacent energy absorbing elements 6 are linked along the joint line 6E.

The truncated pyramid section 6A of each energy absorbing element 6 ends in a planar end face 6F bearing a central hole 6G coaxial with the axis of symmetry of the truncated pyramid section 6A.

Four ribs 6H run along the insides of respective joints between adjacent faces 6D of each pyramid section 6A. The ribs 6H extend across the planar end face 6F to the hole 6G.

The energy absorbing elements 6 at the edges of the array making up the energy absorbing layer 5 bear projections 7 which contact the support member 3 to stably secure the energy absorbing layer 5 within the space 4.

As explained above, the impact face 2 and support member 3 of the bumper assembly 1 are sized and shaped so that the impact face 2 fits over projecting parts 3A,3B of the support member to provide an interference fit so that the impact face 2 is held in place by friction with the support member 3.

In the event of an impact on the impact face 2 caused by a collision between the vehicle and another object, the frictional resistance to movement of the impact face 2 will be overcome and the impact face 2 will move towards the support member 3, closing up the space 4.

As the impact face 2 moves towards the support member 3, the impact face 2 comes into contact with the end faces 6F of the energy absorbing element 6. The impact f ace 2 then progressively crushes the energy absorbing elements against the support member 3.

The progressive crushing of a group of four energy absorbing elements 6 is shown in Figures 7 to 9, which show the energy absorbing elements at successive times during an impact. As can be seen, the truncated pyramid sections 6A of the energy absorbing elements 6 tend to collapse inwards and downwards towards their base sections 6B. As this collapse takes place the resistance to crushing of the energy absorbing elements 6 progressively increases as the elements 6 are supported by the material forced inwards and downwards by the collapse. The base sections 6B are progressively filled with plastics material of the truncated pyramid section 6A so that the base sections 6B progressively become more dense and solid as the impact continues. This results in a progressive increase in the rigidity of the base sections 6B. Ultimately, if the collision is severe enough, the energy absorbing 6 elements 6 will be crushed sufficiently that the whole of the truncated pyramid section 6A of each energy absorbing element 6 is situat-ed entirely inside its base section 6B. The base sections 6B are then almost completely filled with the crushed truncated pyramid sections 6A. If the impact continues, the resistance to crushing and rigidity of the energy absorbing layer 5 will rise to a maximum level approximately equal to the resistance provided by a solid block of the plastics material from which the energy absorbing layer 5 is formed.

In the illustrated example, the separation between the impact f ace 2 and the support member 3 in the space 4 f or containing the energy absorbing layer 5 is equal to the height of the base portions 6B of the energy absorbing elements 6 so that when the truncated pyramid sections 6A of the energy absorbing elements 6 are entirely contained within their base sections 6B, further movement of the impact face 2 relative to the support member 3 is prevented by the impact face 2 coming into supporting contact with the projections 3A and 3B of the support member 3 so that further crushing of the energy absorbing elements 6 does not occur. The projections 3A and 3B of the support member 3 could be arranged not to so contact the impact face 2 so that further crushing of the energy absorbing elements 6 could occur. However, this would increase the depth of the vehicle bumper assembly 1.

The base element 6B of each energy absorbing element 6 provides a space into which the truncated pyramid section 6A of the energy absorbing element 6 can collapse when the energy absorbing element 6 is crushed. Hence the progressive deformation of the truncated pyramid sections 6A of the energy absorbing elements 6 is more predictable and stable than would otherwise be the case. As a result, the resistance to movement of the impact face 2 produced by the energy absorbing layer 5 and the total amount of impact energy absorbed by the energy absorbing layer 5 can be more accurately and repeatedly predicted.

The provision of holes 6G in the end faces 6F of the truncated pyramid sections 6A allow the truncated pyramid 7 sections 6A to stably and predictably crush inwards and downwards.

The resistance forces to movement of the impact face 2 and the changes in these resistance forces with movement of the impact face 2 and the total amount of energy absorbed by each energy absorbing element 6 can be controlled by selection of appropriate materials and wall thicknesses for the elements 6 and by selection of the appropriate thickness and width profile for the ribs 6H.

In the illustrated example, the ribs 6H are of a continuous thickness and width along their entire length. If desired, the thickness and width of the ribs 6H can be varied along their length to adjust the resistance forces produced by each energy absorbing element 6.

In the illustrated embodiment, the thicknesses of all of the faces of the energy absorbing element 6 are the same and the thickness of each face is constant. This is convenient and simplifies manufacture. However, the thicknesses of different faces of the energy absorbing element 6 could be different or the thickness of individual faces of the energy absorbing element 6 could be varied from point to point in order to modify the resistance forces produced by each element 6 or if this were more convenient for a particular material or method of manufacture.

Preferably, each energy absorbing layer 5 is unitarily formed from a firm plastic material by a single injection moulding operation. However, other materials and manufacturing methods could be used.

It is advantageous to form the entire energy absorbing layer 5 unitarily. This helps to stabilise the deformation of the energy absorbing element 6 because the sharing of individual walls 6E of base sections 6B of adjacent energy absorbing elements 6 helps to keep the loads on the walls 6C balanced, thus reducing the tendency of the walls 6C to buckle and destabilise the energy absorbing elements 6.

In the illustrated example, the energy absorbing elements 6 are situated between the impact face 2 and the support 8 member 3 with the truncated pyramid sections 6A of the energy absorbing elements 6B opposed to the impact face 2. It would of course be equally effective to arrange the energy absorbing elements 6 with the truncated pyramid sections 6A opposed to the support member 3.

9

Claims

1. A vehicle bumper assembly comprising an impact face and a support member located behind the impact face and separated therefrom by a plurality of energy absorbing elements each comprising a first section shaped as a pyramid and a second section shaped as a polygonal crosssectioned tube having faces parallel to the axis of the symmetry of the first section, each face of the second section being joined to a respective face of the first section.

2. A vehicle bumper assembly as claimed in Claim 1, in which the first section is shaped as a truncated pyramid.

3. A vehicle bumper assembly as claimed in Claim 1 or Claim 2 in which the first section is a square based pyramid and the second section has a square cross-section.

4. A vehicle bumper assembly as claimed in any preceding claim in which the plurality of energy absorbing elements are arranged in a two dimensional tessellated array.

5. A vehicle bumper assembly as claimed in any preceding claim in which each first section is truncated by an end face having a circular hole therethrough, the hole being coaxial with the axis of symmetry of said first section.

6. A vehicle bumper assembly as claimed in any preceding claim in which reinforcing ribs are provided along the joins between adjacent faces of each first section.

7. A vehicle bumper assembly as claimed in any preceding claim in which the plurality of energy absorbing elements form a unitary structure.

8. A vehicle bumper assembly as claimed in Claim 7 in which adjacent energy absorbing elements have second sections sharing common faces.

9. A vehicle bumper assembly as claimed in any preceding claim in which the f irst and second sections of each energy absorbing element are arranged such that when the energy absorbing element is crushed between the impact f ace and the support member the first section will deform until it lies within the second section.

10. A vehicle which includes a bumper assembly as claimed in any preceding claim.

11. A bumper assembly substantially as shown in or as described with reference to any one of the accompanying drawings.

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