GB2340798A - An airbag panel - Google Patents

Abstract

An airbag panel (1) includes a rupture path (3) associated with a brace arrangement (4). The brace arrangement (4) comprises a lateral member (5), an opposed member (6) and at least one rib member (7). The rib members (7) between the opposed member (6) and a rear surface (2) of the panel (1) being arranged to resist compressive deformation applied upon a front surface (9) about the rupture path (3) whilst having limited effect upon panel (1) rupture through the rupture path (3) as a result of airbag deployment outwardly against the surface (2) of that panel (1). The ribs (7) may be integral along with the other components of the arrangement (4) with the panel (1) or discrete components secured together in order to provide the necessary brace arrangement (4) to resist compressive deformation about the rupture path (3) of the panel (1).

Description

2340798 - 1 AN AIRBAG PANEL The present invention relates to an airbag

panel and more particularly to an airbag panel through which an airbag is deployed by rupture of that panel.

It will be appreciated that airbags have become relatively commonplace 5 within motor vehicles. Typically, an airbag is deployed through a rupturable panel including an appropriate line of weakness or rupture path which is stressed to rupture under the load presented by an inflating airbag under deployment.

Clearly, lines of weakness within a motor vehicle air bag panel must be sufficiently weak to allow rapid air bag deployment whilst avoiding inadvertent normal knock damage or low impact rupture when the airbag is not deployed. If the panel were to rupture or split as a result of normal use, any jagged edges presented to a vehicle occupant would be dangerous and potentially injurious.

Lines of weakness can be incorporated into an airbag panel through laser etching an appropriate notch groove. Laser etching is preferred in order to ensure an accurate depth of notch groove is achieved and so allow accurate determination of the burst pressure necessary to rupture the airbag panel.

Normally, airbag panels will be made from a plastics material such as polypropylene. Thus, an acceptable panel weight and an aesthetic surface can be provided within the motor vehicle. Unfortunately, such plastics materials have properties which can vary significantly over the expected operational temperature ranges for a motor vehicle. Of particular concern is the crystallinity, and therefore brittleness, of the plastics material at low temperatures, ie. below -300C.

At low temperatures, the plastics materials from which airbag panels are made can become quite brittle. For example, polypropylene has a glass transition temperature of -16"C. In such circumstances, there is a wide differential between the depth of groove necessary for normal ambient temperature operation, i.e. 10 to 20"C and that acceptable at very low temperatures, i.e. circa -30"C, typical in Scandinavian countries, etc. Thus, normally the greater usage at ambient temperature prevails and the -15 potentially unacceptable performance at lower temperature simply accepted.

Unfortunately, when such plastics materials are brittle, they are more susceptible to shock fracture, Thus, as indicated above, at low impacts, i.e. below that necessary to deploy the airbag, the rupture hnes of weakness within the airbag panel may be split or fractured exposing jagged edges to an occupant. Such jagged edges could severely damage, in particular an occupant's head, during such relatively minor impacts.

Previously, these low temperature problems with airbag panels have lead to more expensive and complicated constructions. For example, separate airbag panel segments have been secured together about a line of weakness or relatively sophisticated notch grooves, in terms of depth, patterning and intermittent spacing, have been used for adequate performance during low impact scenarios over a wide temperature range including lower temperatures.

It is an object of the present invention to provide an airbag panel which can substantially relieve the above-mentioned problems.

In accordance with the present invention there is provided an airbag panel through which an airbag can be deployed by panel rupture, the panel including at least one rupture path on one side of the panel and associated with a brace arrangement which presents ribs against and across that rupture path to resist compressive deformation of the rupture path from the other side of that panel.

Preferably, the rupture path is a notched groove. Furthermore, this notched groove may be discontinuous or continuous or regularly spaced or irregularly spaced across the airbag panel. In such circumstances, the rupture path may be tuned to provide the necessary panel rupture for airbag deployment in line with that paneFs curvature and orientation within a motor vehicle.

The brace arrangement may comprise a lateral member from one edge of the rupture path with an opposed member opposing the one side of the panel including the rupture path to retain the ribs in between against and across the rupture path. The opposed member may include a stiffener beam to further augment resistance to compressive deformation of the rupture path from the other side of the panel.

The ribs may be integral with the panel and brace arrangement. Alternatively, the ribs may be formed into a separate rib assembly slotted between the opposed member and the one side of the panel including the rupture path. Further, alternatively individual ribs may be located in opposed pairs of slots or ridges respectively in the opposed member and the one side of the panel including the rupture path.

The space in between the ribs may be filled with an energy absorption means such as a styrene foam.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing, in which:

Figure 1 is a pictorial rear perspective representation of an airbag panel; Figure 2 is a pictorial cross-section of an airbag panel at an intermediate position between rib sections; and, Figure 3 is a pictorial cross-section of an airbag through a rib section.

As indicated previously, an airbag upon deployment must burst through an airbag panel in order to engage an occupant of a motor vehicle during a traffic accident. In order to control this airbag panel burst through, it is necessary to provide a rupture path in the panel which, not only precipitates convenient rupture of the airbag panel at a desired airbag inflation pressure but also, ensures that that rupture occurs in the most acceptable part of the airbag panel and without jagged edges or whole panel projection towards the occupant.

It will be understood that the airbag panel, prior to deployment should provide little, if any, indication of the rupture path and therefore the airbag beneath the air bag panel. Thus, typically, a rupture path will be provided within the airbag panel through a notched groove on one side only of the panel, whilst the other side is relatively smooth. Normally such notched grooves are provided through a laser etching technique rather than moulding in order to avoid the potential problems of mould sink marks on 5 the supposedly smooth, as viewed, surface of the airbag panel. Furthermore, precipitation of rupture paths through weakening, i.e. chemically or through physical treatment, can also precipitate undesirable marking of the viewed surface of the airbag panel.

In Figure 1, a pictorial rear perspective of an airbag panel 1 section is 10 illustrated. Thus, a panel 1 presents a side or surface 9 inward of a vehicle and towards an occupant of the vehicle, whilst a rear side 2 includes a rupture path 3 associated with a brace arrangement 4. In an airbag deployment, an airbag (not shown) will inflate to present a load force in the direction of arrow head F. This load force will propagate rupture along the rupture path 3 and so displacement of panel portions in the direction of arrowheads D. The rupture path 3, in addition to propagating such rupture of the panel 1 also ensures and controls where that rupture will take place.

Normally, the rupture path 3 will be provided by a notched groove cut into the panel 1 using a laser erosion or etching technique. The depth of the notch groove will determine the burst strength of the panel 1. A balance must be struck between sufficient weakness in the rupture path 3 for swift airbag deployment whilst retaining adequate strength for normal operation of the panel 1 within a motor vehicle, i.e. against accidental knocking, etc.

In order to determine this groove depth, consideration of the panel I materials is highly determinate. Thus, with plastics materials where there is a radical change in the brittleness of the material below the glass transition temperature (GTT), determination of groove depth is difficult if not impossible for a full range of operational temperatures required of a motor vehicle. Inadvertent or low impact, i.e. below airbag deployment strength rupture of the panel 1, due to increased brittleness at low temperatures, will present serrated edges between the then split upper and lower portions of the panel 1.

In accordance with the present invention, associated with the rupture path 3 is a brace arrangement 4 comprising a lateral member 5 and an opposed member 6 arranged to present ribs 7 against and across the rupture path 3. Thus, compressive deformation about the rupture path as a result of inadvertent or low strength collision with the panel 1 is resisted by the reinforcement of the spaced ribs 7. However, the ribs 7 do not inhibit outward expulsion of the panel I and so rupture about the rupture path 3 as a result of airbag deployment in the direction of arrowhead F.

Normally, several opposed members 6 will be arranged at appropriate spacing along the length of the panel 1. Thus, each opposed member 6 will engage two or more ribs 7 to reinforce the panel 1 about and across the rupture path 3. Furthermore, and although depicted as a continuous section, it will be appreciated that the lateral member 5 may also be a plurality of separate sections coincident with opposed members 6 spaced along the width of the panel 1. In such circumstances, each combination of lateral member 5, opposed member 6 and ribs 7 would constitute an individual brace arrangement 4 and the spacing of such individual brace arrangements 4 will determine the strength of resistance to compressive deformation. However, it is preferred, provided the rupture path 3 can be formed, that either, or both, the lateral member 5 and the opposed member 6 are a continuous section across the width of the panel 1 in order to provide adequate resistance to compressive deformation about the rupture path 3.

Furthermore, a stiffener beam 8 may be secured to the brace arrangement 4 in order to further reinforce the panel 1 against compressive deformation.

As the panel 1 is made from a plastics material, it will be appreciated that the ease with regard to manufacture through moulding must be considered. Thus, the space between opposed members 6 forms a window through which a laser beam can be applied to the rear surface 2 in order to create a rupture path 3 as a discontinuous series of notched grooves in that rear surface 2 of the panel 1. These discontinuous grooves will be sufficient in order to propagate rupture upon airbag deployment in the direction of arrowhead F.

It will be understood that typically the panel 1 will be curved for aesthetic purposes within a motor vehicle interior. Thus, through appropriate spacing of the opposed members 6 and/or lateral members 5 along with ribs 7 and rupture path 3 in terms of the discontinuities in the notched grooves, the panel 1 can be tuned to achieve the desired rupture propagation response as the airbag is deployed in the direction of arrowhead I F.

As indicated above, it is preferred that the panel 1 is formed in a single moulding manufacture stage. However, it will also be understood that the panel 1 could be assembled from several discrete components. Thus, the lateral member 5 and/or the opposed member 6 and/or the ribs 7 along with stiffener beam 8 could all be assembled together as required using an appropriately strong adhesive or fusion bond. In such circumstances, provision of a continuous rupture path in terms of a single notched groove extending across the width of the panel 1 may be more easily achieved. Alternatively, the lateral member 5 and opposed members 6 can be formed as part of a moulding stage with the panel 1 whilst the ribs 7 are located between the rear surface 2 and the opposed member 6 using a rib assembly insert separately formed. Furthermore, appropriate rib location could be 10- achieved through opposed pairs of slots or ridges into which the ribs may be located and may be secured using an adhesive.

Provision of a separate rib assembly insert or individual ribs located appropriately will clearly allow the compressive resistance response of the 5 panel 1 to be tuned as required through appropriate spacing of the ribs 7. Thus, different rib spacings 7 may be provided dependent upon the expected operational temperature in which the panel 1 will be asked to perform and so the expected brittleness of the material from which the panel 1 is made.

I In order to further augment the compressive resistance of the panel 1, it 10 will be appreciated that the spacing volumes between the ribs 7 may be filled with a suitable energy absorption means such as a polystyrene foam. Such energy absorption means may also facilitate an environmental seal where hairline cracks have been precipitated through the panel in the area of the rupture path 3 as a result of thermal cycling or other factors.

The effects of the ribs 7 upon proper airbag deployment in the direction of arrowhead F should be minimal. Thus, the ribs 7 will generally be of a very thin nature in comparison with the panel 1 thickness. Typically, the ribs 7 will have a width in the order of 0.25 to 0.5 mm. However, it will be understood that where the ribs 7 are secured by an adhesive or merely held 20 between opposed slots or ridges, greater rib thicknesses may be acceptable.

Normally, the ribs 7 will be spaced about 15 to 20 min apart in order to provide the necessary resistance to compressive deformation of the panel 1 against the surface 9 opposite that including the rupture path 3.

It will be appreciated where necessary an airbag panel 1 could include 5 several rupture paths with associated brace arrangement 4.

In Figures 2 and 3, pictorial cross-sections of the airbag panel 1 depicted in Figure 1 are illustrated. In Figure 2 a representation is depicted in the intermediate spacing between neighbouring ribs 7. Thus, a rupture path 3 is etched into the panel 1 through a laser beam in the direction of arrowhead B. The depth of this rupture path 7 in terms of its notched groove being determined by design burst through response under pressure from an inflating airbag.

The brace arrangement 4 comprising the lateral member 5, the opposed member 6, ribs 7 and stiffener beam 8 are all squarely aligned behind the rupture path 3 and so the panel 1. It will be appreciated that the crosssection illustrated in Figure 2 is between neighbouring ribs 7 and so the panel 1 is not directly supported to resist compressive deformation applied to the front surface 9 of the panel 1. However, by the nature and depth of the lateral member 5 along with its alignment to an edge of the rupture path 3, the combined effect is to brace the panel 1 between the ribs 7 over 12- the relatively short distance therebetween. In such circumstances, it will be appreciated that the spacing of ribs 7 along with the streng-th of the lateral and opposed members 6 in addition to stiffener beam 8 must all be considered to achieve an appropriate localised resistance to compressive 5 deformation presented upon surface 9 between ribs 7.

In Figure 3, a cross-section of the airbag panel 1 is shown through a rib 7. It will be noted that as laser beam access was denied, that there is a discontinuity in the rupture path 3 and so no indication of that path 3 in the cross-section depicted in Figure 3. Although indicated as a separate component in Figure 3, it will be appreciated that the rib 7 could be integral with the material forming the panel 1 including the brace arrangement 4. The effect of the rib 7 is to fill the gap between the rear surface 2 and the opposed member 6 in order to provide over the thickness of the rib 7 a solid reinforcement of the panel 1 and so resistance to compressive deformation - 15 applied to the surface 9, typically presented inwardly of a motor vehicle in use.

It will be noted that the rib 7 in the cross-section depicted in Figure 3 essentially crosses the rupture path 3 (shown in broken line). This will also be the case where a continuous groove is provided as the rupture path 3 across the width of the panel 1 with the effect that the brace arrangement 4 comprising the lateral member 5, opposed member 6, rib 7 and where included beam 8 will brace the panel 1 across that rupture path resisting rearward compressive deformation presented through the front surface 9 against the rupture path 3.

The ribs 7 may be made from a different material to that from which the panel 1 is made in order to reduce the effects of glass transition temperature upon the panel 1. Such different material types could be achieved through incorporating the ribs 7 as a separate component, i.e. in a rib assembly insert or individual ribs between opposed pairs of slots or ridges or through a two-part moulding process.

Claims (12)

1. An airbag panel through which an airbag can be deployed by panel rupture, the panel including at least one rupture path on one side of the panel and associated with a brace arrangement which presents ribs against and across that rupture path to resist compressive deformation of the rupture path from the other side of that panel.

2. A panel as claimed in Claim 1, wherein the rupture path is a notched groove.

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3. A panel as claimed in Claim 1 or Claim 2, wherein the rupture path is discontinuous across the width of the panel.

4. A panel as claimed in Claim 1, 2 or 3, wherein the rupture path is tuned to facilitate resistance to compressive deformation of the rupture path in accordance with actual panel curvature or configuration.

5. A panel as claimed in any preceding claim, wherein the brace arrangement comprises a lateral member from one edge of the rupture path with an opposed member opposing the side of the panel including the rupture path to retain the ribs in between against and across the rupture path.

6. A panel as claimed in Claim 5, wherein the opposed member includes a stiffener beam.

7. A panel as claimed in Claim 5 or 6, wherein the ribs are integral with the panel and the brace arrangement.

8. A panel as claimed in Claim 5 or 6, wherein the ribs are formed into a rib assembly insert slotted between the opposed member and the one side of the panel including the rupture path.

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9. A panel as claimed in Claim 5 or 6, wherein individual ribs are located in opposed pairs of slots or ridges respectively in the opposed member and the one side of the panel including the rupture path.

10. A panel as claimed in any preceding claim, wherein the brace arrangement includes energy absorption means such as a styrene foam to augment resistance to compressive deformation of the rupture path from the other side of the panel.

11. An airbag panel substantially as hereinbefore described with reference to the accompanying drawings.

12. A vehicle including an airbag panel as claimed in any preceding claim-