WO2004083673A1

WO2004083673A1 - Energy absorbing structure

Info

Publication number: WO2004083673A1
Application number: PCT/GB2004/001188
Authority: WO
Inventors: Michael Ashmead
Original assignee: Cellbond Limited
Priority date: 2003-03-21
Filing date: 2004-03-18
Publication date: 2004-09-30
Also published as: GB0306541D0

Abstract

An energy absorbing structure (30) comprises a nonplanar member (31) sandwiched between two peripheral members or skins (41, 43). The non-planar member (31) has alternating front projections (13) and rear projections (15). A plurality of support pillars (45, 47) are provided on both sides of the non-planar member (31), each positioned between adjacent projections (13, 15) on its respective side. The support pillars (45, 47) brace the skins (41,43) in between the projections (13, 15).

Description

TITLE: ENERGY-ABSORBING STRUCTURE

DESCRIPTION

FIELD OF INVENTION

The present invention relates to an energy-absorbing structure for absorbing impact energy.

BACKGROUND ART Energy-absorbing structures are widely used in vehicles such as motor cars to absorb energy should the vehicle be involved in an accident. In particular, energy- absorbing structures are used on the interior of the vehicle, for example behind the headlining of the vehicle, to absorb the energy of an occupant of the vehicle impacting the energy-absorbing structure during a motor vehicle accident. The intention is that the energy- absorbing structure absorbs the energy of impact so that the vehicle occupant is not killed or severely injured. The energy absorption by an energy-absorbing structure may be characterised by a stress-deformation curve that plots the force of stress exerted by the structure as a function of the deformation. The stress-deformation curve may be measured for a variety of impact bodies impacting the energy-absorbing structure, and either statically or dynamically. In a dynamic test, the impact body is moving rapidly; in a static test the body moves slowly.

As taught in International application WO 00/31434, an energy-absorbing structure has an "egg-box" shape in which a sheet is formed to have front and rear projections. Stress-deformation curves for such structures exhibit a plateau "P" and this is achieved by appropriate selection of the angle of the sheet between the front and rear projections. The plateau "P" is intended to be below a predetermined level, in particular it may at a level sufficiently low that such force does not cause severe injury.

Although good results are achieved with such a component having a plateau in the stress-deformation curve, there remains a compelling need for improved energy absorbing structures .

DISCLOSURE OF INVENTION According to a first aspect of the invention, there is provided an energy absorbing structure comprising a non- planar member comprising a sheet having a pattern of integrally formed projections extending from at least one face of the sheet; characterised in that a plurality of support pillars are provided, with each pillar being configured to brace a peripheral member against a portion of the sheet between adjacent projections and to absorb impact energy by deformation. The pillars may make the deformation resistance (and hence energy absorption) of the structure more homogeneous by supporting potential soft "spots" in the structure. The pillars are configured to do this without impeding deformation of the projections which is the primary mechanism for energy absorption during impact.

The peripheral member may be a part of the energy absorbing structure, and may itself be configured to deform during impact. The peripheral member may be sheet-like and may be configured as a skin over one side of the non-planar member. The peripheral member may be bonded to end faces of the projections.

The pillars may be integrally formed in the non-planar member or in the peripheral member. Each pillar may be substantially cylindrical, and opposed ends of each pillar may be substantially parallel. In contrast, each projection may be substantially frusto-conical . Each pillar may have a length equal to the depth of the non-planar member, measured from the portion of the sheet it braces to the ends of adjacent projections. Each pillar may be hollow. The sheet may be provided with projections extending from both faces of the sheet which may be arranged in a pattern of alternating front and rear projections in front of and behind a median plane respectively. The projections may be configured to alternate in two directions (for example, perpendicular directions) in the median plane, and there may be no substantial flat areas between projections, at least not parallel to the median plane. The pillars may be located behind end faces of at least one of the front and rear projections, with the pillars extending through the median plane to brace the peripheral member (e.g. skin) on an opposing side of the median plane. The pillars may be provided behind end faces of the front and rear projections, e.g. to brace skins on opposing sides of the non-planar member. The non-planar member may thus be sandwiched between two skins each supported by both projections and pillars.

The structure may be designed to absorb impact during deformation in such a way as to provide a plateau at a predetermined level in the stress-deformation curve, i.e. the curve of stress normal to the median plane required to deform the sheet against increasing deformation. For the structure taught in WO 00/31434, the time to attain the plateau and rate at which the plateau region is attained may vary depending on whether or not an impact is centred on one of the projections. For example, if the impact is centred squarely on a projection, the projection deforms relatively evenly and a plateau in the resulting stress- deformation curve is reached relatively quickly. In contrast, if the impact is centred to one side of a projection, i.e. in between adjacent peaks in the structure, the plateau may not be reached as uniformly as before, and the energy absorbed at least in the early stages of impact may be less than optimum.

By using the pillars between adjacent peaks, any differences in time and rate taken to attain the plateau due to different impact sites may be reduced. For example, an impact centred to one side of a projection will cause the pillar to deform so that the plateau in the resulting stress-deformation curve may be reached at a time and rate which is similar to that attained if the impact is centred squarely on a projection. The pillars may be considered to increase the homogeneity of the deformation of the structure.

The density of the pillars across the structure may be sufficient to provide a desired increase in homogeneity. For example, pillars may be provided in at least 60%, preferably 80% of the interstices between adjacent projections. Alternatively, a pillar may be provided in each interstice between adjacent projections.

According to a second aspect of the invention, there is provided a method of making an energy-absorbing structure comprising providing a non-planar member comprising a sheet having a pattern of integrally formed projections extending from at least one face of the sheet and providing a plurality of support pillars, with each pillar being configured to brace a peripheral member against a portion of the sheet between adjacent projections and to absorb impact energy by deformation.

The method may further comprise bonding a skin to end faces of the projections. The pillars may be integrally formed with the non-planar member or the skin.

The energy-absorbing structure may be formed in a two stage process, with the projections being formed at a first stage, e.g. by moulding or pressing and the pillars being formed at a second stage, e.g. by deep drawing the non-planar member or skin. Alternatively, individual pillars may be mounted to the non-planar member or skin, by adhesive or other bonding methods . In this way, the pillars and projections may be formed from the same or different materials. For example, the projections and pillars may comprise a material which deforms plastically, including aluminium or plastics.

The method may comprise forming projections which extend from both faces of the sheet with the projections being arranged in a pattern of alternating front and rear projections in front of and behind a median plane. The pillars may be provided behind end faces of at least one of the front and rear projections with the pillars extending through the median plane to brace the peripheral member on an opposing side of the median plane. The end face of each projection may be formed with a sufficient depth so that in the second stage each pillar may be integrally formed by deep drawing. The method may comprise bonding a skin to the end faces of each of the front and rear projections. Pillars may be provided behind the end faces of both the front and rear projections to brace each skin against the non-planar member.

In each embodiment, the energy-absorbing structure is preferably sacrificial, i.e. deforms permanently when absorbing energy from an impact. In other words plastic not elastic deformation occurs. However, since the pillars and projections may be formed from different materials, the pillars may deform plastically or elastically. The energy- absorbing structure may absorb impact by bending in the pitch region and/or by deformation of the pillars. In one embodiment, the properties of the energy- absorbing structure may be determined such that the plateau level is at a level of stress that does not cause serious injury or that avoids death when a living human body part such as a head impacts the energy-absorbing sheet. These properties may include the material and the thickness of the sheet forming the projections, the density of projections over the area of the sheet, the material and shape of the pillars and the density of the pillars over the structure. In particular, the energy absorbing structure may be an energy-absorbing vehicle component for reducing the risk of injuries. Thus, according to another aspect of the invention, there is provide a vehicle comprising an energy absorbing structure as hereinbefore described. The vehicle may have a headlining and the component may be mounted behind the headlining.

In each embodiment, the front and rear projections may be arranged to alternate in two directions in the median plane and to cover at least 80% of the sheet, preferably without substantial flat areas therebetween. Each projection may have an end face, a pitch region spaced from the end face and a transition region therebetween. The pitch region is inclined at an angle from the median plane of the sheet with the pitch angle being determined at the position of maximum steepness in the pitch region. The position of maximum steepness may occur midway between the centres of adjacent front and rear projections. The angle may be 25 to 89 degrees, in particular 25 to 60 degrees. Each projection may be hollow and the end face may be flat and may extend parallel to the median plane. The median plane may be flat or curved. The projections may have the same or differing heights. BRIEF DESCRIPTION OF DRAWINGS

For a better understanding of the invention specific embodiments will now be described, purely by way of example, with reference to the accompanying drawings in which Figure 1 is a perspective view of a structure according to the prior art;

Figure 2 is a graph of stress against strain comparing two impacts on the structure of Figure 1;

Figures 3a and 3b are two different perspective views of a structure according to a first aspect of the invention;

Figure 3c is a side view of the structure of Figure 3a; Figures 4a and 4b are perspective views of the components of the structure of Figure 3a;

Figure 5a is a cross-section of a projection of a the component of Figure 4a, and Figure 5b is a schematic plan view of a section of the component of Figure 4a.

DETAILED DESCRIPTION OF DRAWINGS

Figure 1 shows a prior art structure in the form of a non-planar member having a pattern of alternating front projections 13 and rear projections 15, without substantial flat areas therebetween. The projections are frustoconical and hollow with substantially flat end faces

17, pitch regions 14 spaced from the end faces and transition (edge) regions 16 between the end faces 17 and adjacent pitch regions 14. The pitch region is inclined at an angle A of approximately 45 degrees to a median plane which is a notional plane which locally represents the position of the non-planar member with the projections smoothed out. The flat end faces 17 are parallel to the median plane.

If the structure of Figure 1 is used as an energy absorbing component, e.g. in vehicle headlining, impact by a head may be mimicked using a rounded form, e.g. part of a sphere of diameter between 15cm and 30cm. When such a rounded form impacts a structure, the area of contact will initially be small and will increase as the round form continues to impact and the structure continues to deform. Thus, the force on the round form would increase with deformation if the stress was constant.

Figure 2 shows schematic stress-deformation graphs 21,23 for the structure of Figure 1 (with skins) with impacts centred on a front projection or in between front projections respectively. Both graphs show a plateau region at the same level but the time to attain the plateau is longer if the impact is in between front projections rather than centred on a front projection.

Figures 3a to 3c show a structure 30 embodying the present invention and comprising a non-planar member 31 which is generally similar to that of Figure 1 and thus features in common have the same reference number. The non-planar member 31 is sandwiched between two peripheral members or skins 41,43 each of which comprise an array of pillars 45,47. The pillars 45 extending from the first skin 41 are bonded at one end to the inner side of the end faces 17 of the front projections 13 and the skin 41 is bonded direct to the outer side of the end faces 17 of the rear projections 15. Similarly, the pillars 47 extending from the second skin 43 are bonded to the rear projections 15 and the skin 41 to the front projections 13. Figure 3c shows that each pillar 45,47 has a length which is about equal to the depth of the structure 30.

Figure 4b shows a perspective view of the first skin 41; the second skin corresponds. The pillars 45 are generally cylindrical with flat end faces 51 to provide a good load-bearing and bonding surface with the flat end faces of the corresponding projections. The pillars 45 are equally spaced across the surface of the skin and are of equal height. Figure 4a shows the non-planar member 31 which is bonded to the skins with the pillars aligned with the respective projections. Figures 5a and 5b illustrate a generalised non-planar member 31 which may be used in any preceding embodiment. The non-planar member 31 has a pattern of alternating front projections 33 and rear projections 35 both of which are frustoconical with substantially flat end faces 37. The projections have a wall thickness t, a height H, a top face having a diameter D and a pitch region inclined at an angle A to the median plane. The interpitch P is the distance between two projections extending in the same direction from the median plane and is measured across a projection extending in the opposition direction.

The characteristics of the pattern and the projections may be selected from the following table although geometry 1 is particularly suited to each of the previous embodiments:

Thus, the height of each projection may vary from 7.5mm to 30mm and the diameter of each flat end face may vary from 3.125mm to 22.5mm. The interpitch may vary between 12.5mm and 105mm. The angle may vary between 14 and 51.34 degrees. The angle is measured relative to the median plane 41 which is the notional plane which locally represents the position of the non-planar member with the projections smoothed out. The sheet may have a thickness of 0.5mm to 0.7mm.

Claims

CLAIMS 1. An energy absorbing structure comprising a non-planar member comprising a sheet having a pattern of integrally formed projections extending from at least one face of the sheet; characterised in that a plurality of support pillars are provided, with each pillar being configured to brace a peripheral member against a portion of the sheet between adjacent projections and to absorb impact energy by deformation.

2. An energy-absorbing structure according to claim 1, wherein the peripheral member is configured as a skin over one side of the non-planar member.

3. An energy-absorbing structure according to claim 1 or claim 2, wherein the peripheral member is bonded to end faces of the projections.

4. An energy absorbing structure according to any one of the preceding claims, wherein the pillars are integrally formed in the non-planar member or in the peripheral member.

5. An energy-absorbing structure according to any one of the preceding claims, wherein each pillar is substantially cylindrical .

6. An energy-absorbing structure according to any one of the preceding claims, wherein each pillar is hollow.

7. An energy-absorbing structure according to any one of the preceding claims, wherein the projections extend from both faces of the sheet and are arranged in a pattern of alternating front and rear projections in front of and behind a median plane .

8. An energy-absorbing structure according to claim 7, wherein the pillars are located behind end faces of at least one of the front and rear projections, with the

5 pillars extending through the median plane to brace the peripheral member on an opposing side of the median plane.

9. An energy-absorbing structure according to claim 7 or claim 8, wherein pillars are provided behind end faces of the front and rear projections to brace peripheral members

10 on opposing sides of the non-planar member.

10. An energy-absorbing structure according to any one of the preceding claims, wherein pillars are provided in at least 60% of the interstices between adjacent projections.

11. An energy-absorbing structure according to any one of 15 the preceding claims, wherein the pillars and projections are made from the same material .

12. A method of making an energy-absorbing structure comprising providing a non-planar member comprising a sheet having a pattern of integrally formed projections

20 extending from at least one face of the sheet and providing a plurality of support pillars, with each pillar being configured to brace a peripheral member against a portion of the sheet between adjacent projections and to absorb impact energy by deformation.

25 13. A method according to claim 12, comprising bonding a peripheral member in the form of a skin to end faces of the projections.

14. A method according to claim 12 or claim 13, wherein the pillars are integrally formed with the non-planar member or the peripheral member.

15. A method according to any one of claims 12 to 14, comprising forming the projections and then forming the pillars.

16. A method according to claim 15, wherein the pillars are formed by deep drawing the non-planar member or the skin.

17. A method according to any one of claims 12 to 16 comprising forming projections which extend from both faces of the sheet with the projections being arranged in a pattern of alternating front and rear projections in front of and behind a median plane .

18. A method according to claim 17 comprising providing pillars behind end faces of at least one of the front and rear projections with the pillars extending through the median plane to brace the peripheral member on an opposing side of the median plane.

19. A method according to any one of claims 16 to 18, comprising bonding a skin to the end faces of each of the front and rear projections.

20. A method according to claim 19 comprising providing pillars behind the end faces of both the front and rear projections to brace each skin against the non-planar member.

21. A vehicle comprising an energy absorbing structure according to any one of claims 1 to 11.