GB2434125A

GB2434125A - Sheet member with part-conical elements providing impact protection

Info

Publication number: GB2434125A
Application number: GB0707384A
Authority: GB
Inventors: Alan Robert Carr; Behdad Arian
Original assignee: Novelis Inc Canada
Current assignee: Novelis Inc Canada
Priority date: 2007-04-17
Filing date: 2007-04-17
Publication date: 2007-07-18
Also published as: GB0707384D0

Abstract

The invention relates to a high strength light weight sheet for use as a panel component comprising a shaped sheet formed of a plurality of generally truncated conical spaced elements, a sidewall of each element being formed with a stepped contour to promote sidewall collapse during an impact. The novel stepped design feature acts as a trigger mechanism during impact to absorb additional energy compared to conventional structural sheet inner panel designs. Further, the invention includes additional features to promote increased stiffness and hence additional energy absorption during impact. These additional features encompass an array of stiffening ribs, and hemispherical dome features in the gaps between the distributed conical features (figures 2, 3 and 8). The sheet may be combined with one or more further planar or curved sheets so as to form a vehicle bonnet or hood with improved impact protection for a pedestrian's head. The sheets may be adhered together and formed from materials such as aluminium or steel.

Description

IMPROVEMENTS IN STRUCTURAL SHEETS AND PANELS

Field of the Invention

The present invention relates to a structural sheet and panel for impact protection and more particularly, but not exclusively, for head impact protection.

Background of the Invention

It has been conventional to make panels such as hoods or deck lids for use on automobiles or the like from two components, an inner and outer panel, that must have the requisite strength and rigidity to meet the functional performance characteristics yet be relatively light in weight. However, a relatively new consideration, recently introduced by legislation in the form of Impact Criterion assessment, now needs to be fulfilled. This is specifically related to damage to the human body/anatomy resulting from impact with a moving vehicle. In order to minimise the mass of the component assembly, it is necessary to have high strength in the outer panel for local resistance to denting, a high amount of geometric form in the inner panel to promote the stiffness of the assembly, but local compliance to absorb energy during an impact situation.

Typical hood inner panel designs are shown in Figs. 4 & 5 below. Figure 4 shows a conventional ribs design, and Figure 5 shows a truncated multi-conical design. Both designs have limited energy absorption during impact and can result in serious damage/injury to a human being on impact.

Another design variant has been proposed, as shown in Fig 6, published in Proceedings of IBEC 2003 (International Body Engineering Conference) entitled "Development of aluminium hood structure for pedestrian protection" by co-authors K Ikeda and h Ishitobi. This design increases the secondary mass utilised during impact, such as head impact upon a hood/bonnet, and hence to absorb the required energy in the limited gap between the outer panel and the plane under the hood defining the hard points such as the engine block, Fig 7. Note: with this design, the inner panel will be heavier as a result of a lack of cut outs compared to the other designs above, Figures 4 & 5.

to However, this design was reported to have achieved a 13mm reduction in the necessary distance between the inner panel and the engine block plane to obtain the same HIC value, i.e. a HIC value of 1000.

The Head Impact Criterion target, HIC value, during head impact has been set by European regulations at 1000 or less. The above target value of HIC=1,000 for the design of Fig. 6 was met at a distance between the outer panel and the engine block of approximately 62mm, Fig. 7, and a value of HIC=800 achieved with a gap of approximately 75mm.

In terms of bending and torsion performance, the design of Fig. 6 is very directional, having a high bending resistance front to back of the hood, and a relatively low value side to side. The high bending resistance front to back of the hood is contrary to that required during frontal impact where the hood is required to "tent" to avoid penetration through the windscreen.

Summary of the Invention

The present invention relates to a sheet member as defined in any one of claims 1 to 24, a structural panel as defined in any one of claims 25 to 35, and to a vehicle incorporating the structural panel defined in claim 36, said claims being hereinafter defined at the end of this specification..

The present invention is directed to a structural sheet that can be used in a variety of configurations, and particularly to such a sheet that can be used in a two-component structural panel for use wherever it is desired to have at least one exposed smooth and stiff metallic or plastic surface and a strong and stiff yet light in weight structural inner support panel such as for automobile hoods, roofs, deck lids, etc. The present invention is further directed to applications requiring the ability to absorb a greater amount of energy than conventional designs, whilst reducing the amount of damage/injury to a human being during a vehicle impact. It is important that the novel panel design be light in mass, yet have sufficient strength for intended use. It is important that this be made in a cost efficient manner, the sheet being formed in a single press stroke between a matched die set, this being more economical than forming each individual feature sequentially as per US Patent 5,244,745. However, the innovative features could equally be formed individually if required.

To obtain the required strength and stiffness, the sheet is formed with a series of projections, which construction is known to provide the necessary regular support for stiffness and resistance to local denting to the outer panel, and hence a design striving towards minimum mass. The additional novel feature of the stiffening rib array enhances the stiffness of the inner panel, improving the overall efficiency, whilst the addition of the novel trigger step in the part-conical feature promotes collapse of the part-conical feature during an impact, absorbing an increased amount of energy in a controlled manner. This is directly beneficial to reducing the damage to a human being's anatomy during vehicle impact, as measured by HIC value, and in particular to head impact on vehicle hoods or bonnets. The importance of the design is to enable a high static structural perlormance to be achieved, requiring a strong stiff design, whilst at the same time achieving a compliant dynamic design capable of absorbing energy with minimal damage to a human during impact. It is to these requirements that the present invention is directed. In a typical embodiment the structural panel segment includes spaced flat portions that can be adhesively secured to an outer smooth metallic or plastic panel to which it is connected.

The stiffening array of ribs can form a grid with the part-conical features within the array of ribs, as in Figure 8c, or at the nodal points of the rib array as in Figs. 8b and 2.

While the particular structural panel member can be used in a number of different situations or applications, in a preferred embodiment, it is employed as part of a two-component panel assembly for use in automobiles. In the particular illustrated embodiment, both of the thin gauge members are made of thin gauge aluminium alloy sheet, but this is by way of example, and the invention is not so limited. Generally speaking, the panel assembly consists of an outer sheet panel that can be formed in the aerodynamic shape and an inner structural panel adhesively secured to the outer sheet and providing the majority of the strength and stiffness, and as a result of the current novel invention, a significantly increased amount of energy absorbed in crash impact.

The invention is equally applicable to steel, with steel inner and outer panels, or a combination of aluminium and steel panels in either combination between the inner and outer panels. Also the invention is equally applicable to a plastic or SMC outer panel combined with either an so aluminium or steel inner panel.

The term part-conical is intended to describe and include for any protrusion a feature whereby at least a part of the sidewall of the protrusion is inclined to the lower portion of the protrusion. The invention is equally valid with a regular polygon shaped "part-conical" feature rather than a circular feature s as detailed in the following embodiments. Merely by way of illustration, a regular polygon in the form of a hexagonal protrusion with inclined faces is also considered within the meaning of part-conical and the skilled person will understand that other polygonal shapes are possible.

By way of example, the HIC value graph associated with a design shown in Fig.2, (with trigger mechanism and stiffening ribs), is shown in Fig. 9. A HIC value of 789 was obtained with a gap of 65mm, cone height of 25mm, and a 2.0mm inner panel gauge. However, the assembly is too stiff as designed, with most energy being absorbed in the first peak, largely is associated with the elastic deflection.

Figure 10 highlights a more balanced HIC value graph showing energy absorption in both the initial elastic deflection and the deformation of the conical protrusion, second peak, aided by the trigger mechanism. This is representative of the design shown in Fig.lla and lib below, (trigger mechanism but no stiffening ribs), and gave a HIC value of 776 with an inner panel gauge of 1.25mm, and a cone height 25mm.

Similarly, with a gap of 62.5mm, the corresponding HIC value is in the range of 793 to 858 depending upon the head position. To achieve these figures, the design of Fig. 6 would need a gap between the outer panel and the engine block of somewhere between 70 and 75mm.

The above examples highlight the efficiency of the stepped trigger feature in absorbing the impact energy, whilst indicating that the rib design dimensions can be optimised to produce the required assembly stiffness, whilst achieving the legally required impact protection.

The invention can be best understood when considered in conjunction with the accompanying drawings, in which:

Brief Description of the Drawings

Fig. 1 shows a view of the inner panel with a regular array of truncated conical features, and the stepped trigger invention in the sidewall to aid collapse in crash impact.

Fig. 1 la and 1 lb show a stepped trigger in the cone sidewall in both its Un-deformed and deformed position, before and after impact.

is Fig. 2 shows a view of the regular array of truncated conical features, and the introduced array of stiffening ribs. In this case, the truncated conical features are centre at the nodal points, as illustrated in Fig. 8b.

Fig. 3 shows the introduction of hemispherical domes in the gaps between the distributed part-conical features.

Detailed Description

While the present invention is susceptible of embodiments in various forms, there is shown in the drawings and will hereinafter be described a preferred embodiment, with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated.

Referring to Fig 12a and 12b, there is illustrated a structural panel assembly 10 which is shown in the inverted position. The structural panel assembly consists of a first outer aluminium alloy sheet 12 having substantially smooth inner and outer surfaces, and a second inner rigidifying sheet 14 also made of an aluminium alloy. The outer panel can be formed with a constant or varying curved surface as desired, or could s even be essentially flat. These sheets have a thickness in the range 0. 7mm to 2.0mm.

The inner rigidifying sheet is formed in a single press stroke between a matched die set, to form a plurality of generally truncated conical configurations 16 having generally circular top and bottom cross sections 18, 20 respectively. This production route is the most economical medium to high volume production route, and ensures improved manufacturing tolerances compared to individually formed truncated conical protrusions.

The matched upper and lower die set, (not shown), have essentially the same profile as that shown for the upper and lower surfaces of the inner rigidity panel. The die set is mounted in a conventional mechanical or hydraulic press, and the sheet, placed between the upper and lower dies, is formed into the shape illustrated upon closing of the matched die set during the forming process.

The panel assembly 10 is produced by connecting the structural rigidity sheet 14 to the inner surface of the outer aluminium sheet by local use of adhesive 26 in the region of the conical protrusions, and a mechanical fixing around the periphery of the outer to the inner panel in the form of hemming or mechanical fixings, or a combination of both methods. The application of adhesive in the region of the conical protrusions secures the upper planar portions 18 of the conical protrusions 16 to the inner surface of the outer sheet 12. The adhesive joints have a significant role in transferring the external head impact energy to the conical protrusions, and hence to the trigger mechanism in the sidewall to absorb the impact energy through plastic deformation of the conical protrusion. The size of the flattened top 18 is designed to ensure stiffness compatibility between the mating surfaces of the sheets 12 and 14. The exact dimensions of the projections and their disposition are optimised for the specific strength and stiffness required of the panel assembly, as well as the ability to accommodate and absorb the energy of impact without serious damage to a human's anatomy.

Referring to Fig. 12b, there is illustrated a structural inner panel 14 which is shown in the normal orientation for its intended use. Note the outer panel has been removed from the assembly 10 to allow details of the inner panel to be observed. This Figure shows a general view of the inner panel with the plurality of truncated conical protrusions, and Figure 1 a view in cross section of one half of the profile of a truncated conical protrusion, as is detailed from the centre-line of the axis of rotation.

The dome shaped feature shown above the conical protrusions both in Figure 1, and reproduced in Figure 1 2b, is representative of an object, such as a person's head, angled to the inner panel during impact. Figure 1 shows details of the innovative stepped trigger feature introduced to promote collapse of the sidewall during that impact. The main innovative feature of the trigger mechanism is that the location of the head impact support position of the inner panel 18 and the engine block restraining position after the elastic deflection 22 are offset in their line of action, as shown in Figures 1 and 12b. This allows the upper conical feature to collapse down inside the lower conical features thus taking away a potential hard point, and increasing the energy absorption by the plastic work of deformation as the inner panel conical feature collapses. Note: collapse of the upper cone into the lower cone feature gives a magnification to the distance available -hood outer to engine block. Views of the conical feature before and after impact are shown in Figures 11 a and 11 b, highlighting the effectiveness of the collapse and hence energy absorption.

The angle of the conical protrusion is detailed in Figure 1 as 600, although this is only by example, and the angle may be varied from 25 to 85 to achieve the desired performance for a particular design. The angle is shown inclined to the upper substantially flat surface of the sheet member surrounding the base of the conical protrusion. Equally, the stepped trigger feature is detailed in Figure 1 as being positioned essentially mid way up the conical protrusion sidewall, although again this is only by example, and could be positioned anywhere between 25% and 75% of the vertical conical protrusion height, as measured from the lower generally planar portion. The blend fillet radii detailed in Figure 1 are shown varying from an R5 to Rl5mm, but again these are only by example, and the range can vary from IS an (R/t) ratio of 3 to 20, where t is the gauge of the material used to produce the inner rigidity panel. The diameter of the base of the conical protrusions is again detailed in Figure 1, by way of example, and may be varied significantly to suit individual designs, being influenced by the gap available, the angle of the conical protrusion, the amount of "flat portion" in the trigger feature, and the amount of generally flat top portion of the truncated conical protrusion required for adhesive bonding. Also, the overall height of the conical protrusions is detailed in Figure 1 as 40mm, by way of example, and again may be varied significantly to suit the total gap availability between the inner surface of the outer panel and the plane under the hood defining the hard points such as the engine block. Typically, it would be anticipated that the overall height of the conical protrusions would be in the range 10mm to 60mm. Finally, the yield stress and work hardening rate of the alloy used for the inner panel will be important in determining the amount of energy which may be absorbed during impact without causing serious injury. The actual in-service proof stress used in -10-generating the results shown in Figures 9 and 10 was l2OMpa. However, this value is again by way of example, and the value may need to be varied for certain hood designs/geometries and the total height clearance available. It is envisioned that an in-service proof stress range of 5OMPa to 25OMPa may be required to optimise the performance for a given hood design and total height clearance.

It is envisioned that the optimum distribution of truncated conical features would form an equilateral triangulated or square distribution, but variations io from this optimum would be equally applicable to the current invention.

Similarly, it is envisioned that if ribs are introduced, the optimum distribution of truncated conical features would lie at the nodal points of an equilateral triangle or a square array of ribs, or within central region of a equilateral or square array of stiffening ribs, as in Figure 8, but variations from this optimum would be equally applicable to the current invention.

It is important to note that the distance between the hard point plane, defined largely by the top of the engine block, and the inside of the inner rigidity panel, (as shown in Fig. 7), is controlled to a minimum by styling.

Hence it is necessary to develop a design solution to overcome the head impact issue with the minimum gap possible. The current invention allows head HIC values of 800 to be obtained with a total gap of approximately 64mm. This is significantly better than that quoted for a beam type hood design (80mm), and the new proposed wave type design (75mm).

Due to a reduced gap, it will be necessary to introduce additional stiffening features over and above a conventional design, as shown in Fig. 5, to achieve the overall bending and torsion requirements of the hood assembly. Hence the introduction of the array of stiffening ribs as in Fig. 2.

so The stiffening ribs contribute to the resistance to elastic deflection during -11 -head impact, absorbing some impact energy, followed by the sidewall collapse of the truncated conical protrusions, absorbing the remainder of the impact energy. Depending upon the stiffness of the inner rigidity panel, the array of ribs can be adjusted in height and size, and in the extreme s case the ribs may not be required at all to satisfy the Head Impact requirement, (HIC value).

Additional hemispherical dome features, in the gaps between the distributed conical features, can be added to absorb energy in areas where no truncated cones are present. These domes do not need to contact the inside of the outer panel, nor do they require an adhesive joint to be present to work effectively. However, an adhesive could be present and it would not materially affect the functionality of the feature, energy would still be absorbed during impact. Is

While it is to be noted that there is illustrated a two component panel construction wherein the unique structural sheet portion has a generally uniform configuration, this is by example only. The projections need not be uniformly disposed, or indeed of uniform height, and the rigidity sheet can be used in other configurations, such as a sandwich wherein the structural rigidity component is disposed between two flat or curved sheet members.

The top of the truncated conical feature can either be open as shown in Fig ha and lib, i.e. the top cut out, or remain as a filled feature, i.e. no material cut out. Also, while the panel as made up in aluminium alloy sheets, it, of course, can be made up of other metallic materials if desired, such as steel outer and inner components, and a combination of aluminium and steel in either combination between the inner and outer panels. Also the invention is equally applicable to a plastic or SMC outer panel combined with a metallic inner rigidity panel such as aluminium or steel. -12-

As will be apparent to those skilled in the art although the above description describes a metal sheet formed with numerous part-conical features together with stiffening features, including ribs and domes, which are designed to promote stiffness in the panel itself, the arrangement of these features can be varied. It is the incorporation into the part-conical feature of a triggering feature, like or similar to the stepped feature, to promote collapse of the part-conical feature during an actual impact which is desirable. The novelty of this stepped feature is its ability to absorb an increased amount of energy in a controlled manner. This is directly to beneficial to reducing the damage to a human's anatomy during vehicle impact, as measured by the HIC value, and in particular to head impact on vehicle hoods or bonnets. However, the design concept of a stepped sidewall design with an array of stiffening ribs, promoting material collapse during impact, is equally applicable to other areas of a moving vehicle, t5 such as deck lids, roofs, etc., interior protection for head and hip damage, or indeed the likes of static barrier members designed to absorb energy

during an impact of any description.

However, it is intended to cover by the following claims, all embodiments which fall within the true spirit and scope of the invention. -13-

Claims

CLAIMS

1. A sheet for use as a panel component comprising a shaped sheet formed of a plurality of part-conical spaced elements, a sidewall of each element being formed with one or more stepped contours to promote sidewall collapse during an impact.

2. A sheet member as claimed in claim 1, wherein the part-conical shaped elements are truncated. 1 0

3. A sheet member as claimed in claim 1, wherein the part-conical shaped elements each have a generally flat top portion.

4. A sheet member as claimed in claim 1, wherein the part-conical is shaped elements each have a non-flat top portion.

5. A sheet member as claimed in claims 1 to 4, wherein the part-conical shaped elements each have a lower generally planar portion.

6. A sheet member as claimed in any one of claims I to 5, wherein the stepped feature is located up the conical protrusion sidewall positioned anywhere between 25% and 75% of the vertical conical protrusion height, as measured from the lower portion of the conical shaped element.

7. A sheet member as claimed in claim 6, wherein the stepped feature is located substantially mid way up the part-conical protrusion sidewall 8. A sheet member as claimed in any one of claims 1 to 7, wherein the angle of a non-stepped portion of the sidewall is inclined to the lower portion of the conical element at an angle of between 25 to 85 -14- 9. A sheet member as claimed in claim 8, wherein the non-stepped portion of the sidewall is inclined at an angle of approximately 600 to the lower portion of the conical element.

10. A sheet member as claimed in any one of claims ito 9, including an array of stiffening ribs to increase the stiffness of the sheet to absorb additional elastic energy, and to meet the bending and torsion requirements of the panel component into which it is formed.

11. A sheet member as claimed in claim 10, wherein the part-conical elements are formed at nodal points of the rib array.

12. A sheet member as claimed in claim 10, wherein the part-conical elements are formed within the array of ribs.

13. A sheet member as claimed in any one of claims ito 12, including one or more domed features located in each gap defined between the distributed part-conical elements to absorb energy for impacts in areas other than over the truncated conical elements.

14. A sheet member as claimed in any one of claims ito 13 in which the part-conical elements are substantially uniformly spaced throughout the major portion of the sheet.

15. A sheet member as claimed in any one of claims ito 14 constructed of a thin gauge aluminium alloy.

16. A sheet member as claimed in any one of claims ito 15 in which the part-conical elements include a generally flat circular top and in which the stepped sidewall section is formed between the circular top portion and a -15-generally flat lower portion.

17. A sheet member as claimed in any one of claims I to 16, wherein the height of the part-conical elements lies substantially within the range l0mmto6Omm.

18. A sheet member as claimed in claim 17 wherein the height of the part-conical element is approximately 40mm.

19. A sheet member as claimed in claim 18 wherein the blend fillet radii R of the stepped sidewall section is chosen so that the ratio (RIt) lies substantially within the range 3 to 20, where t is the gauge of the material used to produce the sheet member.

20. A sheet member as claimed in claim 19 wherein the blend fillet radii R lies substantially within the range of 5 to 15mm.

21. A sheet member as claimed in any one of claims I to 20, wherein the proof stress of the material lies substantially within the range 5OMPa to 25OMpa.

22. A sheet member as claimed in claim 21, wherein the proof stress of the material is approximately 12OMPa.

23. A sheet member as claimed in any one of claims 1 to 22, wherein the part-conical features are arranged to form an equilateral triangulated or square distribution.

24. A sheet member as claimed in any one of claims 11 to 23, when dependent on claim 10, wherein the part-conical features lie at nodal points of an equilateral triangle or a square array of stiffening ribs, or within a central region of an equilateral or square array of stiffening ribs.

25. A structural panel assembly comprising a first sheet and a second rigidifying, high strength light weight sheet member as claimed in any one of claims 1 to 24.

26. A structural panel assembly as claimed in claim 25, in which the first sheet is constructed of a thin gauge aluminium alloy.

27. A structural panel assembly as claimed in claim 25 in which the first and second sheets are constructed of a thin gauge aluminium alloy.

28. A structural panel assembly as set forth in claim 25 in which the is second sheet is constructed of a thin gauge aluminium alloy.

29. A structural panel as claimed in claim 25, wherein one or both of the sheets are manufactured from steel 30. A structural panel as claimed in claim 25 wherein one sheet is manufactured from steel and the other sheet is manufactured from aluminium.

31. A structural panel as claimed in claim 25 wherein the first sheet is manufactured from plastic or fibreglass and the second sheet is an aluminium or steel panel.

32. A structural panel as claimed in claim 25 wherein upper planar portions of the conical elements on the second sheet are secured to a surface of the first sheet by adhesive. -17-

33. A structural panel as claimed in any one of claims 25 to 32, wherein a third sheet is provided, the second sheet being sandwiched between said first and second sheet.

34. A structural panel as claimed in claim 33 wherein the sheets are flat or curved.

35. A structural panel as claimed in any one of claims 25 to 34, wherein the panel is designed for use in vehicle construction.

36. A vehicle incorporating a structural panel as claimed in any one of claims 25 to 34.