Impact absorbing structures are used for safety to decelerate a body or bodies in a controlled manner. They can be used in sports such as motor sports, and winter sports where persons or objects moving at speed are likely to be injured or damaged due to uncontrolled decelerations. They can also be used in civil applications, in, for example, impact absorbing structures placed on public highways or military applications for protecting persons or inanimate objects dropped from a height.

Examples of such barriers currently in use include netting, walls of motor tyres and metal barriers.

According to a first aspect of the invention, there is provided an impact absorbing structure comprising at least one inflatable member conforming a flexible cover to produce a chamber, the chamber deforming when impacted by a moving body to provide controlled deceleration of the body.

According to a second aspect of the invention, there is provided a crash barrier comprising a plurality of impact absorbing structures according to the first aspect of the invention in which each chamber has an associated front wall forming an impact surface, structures being placed side by side so that the front walls form a continuous impact surface. The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a schematic perspective view of an impact absorbing structure, Figure 2 is a schematic plan view from above of part of a crash barrier formed by a number of impact absorbing structures of the kind shown in Figure 1 placed side by side and with a protective cover, Figure 3 is a schematic cross section through a part of a drop thread fabric for use in the impact absorbing structure of Figure 1, and Figure 4 is a detail on X of Figure 3.

Referring first to Figure 1, the impact absorbing structure comprises a closed outer chamber indicated generally at 10 formed by a cover having a front wall 11, a rear wall 12, an upper surface 13, a lower surface 14 and first and second side walls 15,16.

As seen in Figure 1, the front wall 11 and the rear wall 12 are significantly longer than the first and second side walls 15,16. For example, the front wall 11 and the rear wall 12 maybe 8 metres in length and the first and second side walls 15, 161. 15 metres in length with a height of 1 metre. The chamber 10 has, in plan view from above, the form of a parallelepiped in which the first side wall 15 makes an acute angle with the front wall 11 and the second side wall 16 makes a complimentary obtuse angle with the front wall 11. The front wall 11, the rear wall 12 and the first and second side walls 15,16 are formed from a drop stitch fabric of the kind shown in Figures 3 and 4. Referring to those figures, the fabric comprises a first textile layer 17 interconnected to a second textile layer 18 by a plurality of threads shown schematically at 26. The textile layers may be a woven polyester, polyamide or similar material. The threads maybe made from polyester, polyamide or similar material. Both the first layer 17 and the second layer 18 are provided with an inner coating which may be of any suitable cross-linked polymeric material such as polychloroprene or a non cross-linked thermoplastic material, a textile chaffing layer 19 and an outer coating 20 which may be of any suitable cross-linked polymeric material or such as polychloroprene or a non cross- linked thermoplastic material. An elongate rectangular sheet of such thread material has the side edges of the first textile layer 17 connected to the side edges of the second textile layer 19 to form a rectangular closed panel. The panel is provided with an air inlet (not shown) to allow it to be inflated. Appropriately sized panels are used to form the front and rear walls 11, 12 and the first and second side walls 15,16 with all the walls 11, 12, 15,16 communicating with one another to form a unitary inner chamber.

The upper surface 13 and the lower surface 14 are formed from appropriately sized sheets of flexible air impervious material such as a plastic covered fabric material.

The outer chamber is conformed by a plurality of inflatable struts 21. Each strut 21 is formed by an inflatable tube of an air impermeable material. As seen in Figure 1, the struts 21 extend between an inner surface of the front wall 11 and an inner surface of the rear wall 12, between an inner surface of the front wall 11 and an inner surface of the first side wall 15 and between an inner surface of the rear wall 12 and an inner surface of the second side wall 16. At the connection between each strut 21 and wall 11,12, 15,16, the strut 21 is in communication with the associated wall to form part of the unitary inner chamber with the walls 11,12, 15,16. It will also be seen that none of the struts 21 lies in a horizontal plane ; the struts 21 are angled to the horizontal and are angled relative to vertical planes normal to the front wall 11. The reason for this will be explained below. There are also triangulation struts 22 which are formed identically to the struts 21 but which extend between adjacent pairs of struts 21 to provide an element of rigidity to prevent the front wall 11 and the rear wall 12 becoming mis-aligned. The triangulation struts 22 are also in communication with the associated walls 11,12, 15,16 to form part of the unitary inner chamber. Referring next to Figure 2, in use, a plurality of structures of the kind shown in Figure 1 are placed side by side to form a continuous crash barrier. As seen in Figure 2, in this disposition, each first side wall 15 abuts against the second side wall 16 of the next adjacent structure to provide overlap between the structures in a direction normal to the front walls 11 of the structures. The front walls 11 are covered by a continuous protective sheet or cover indicated generally at 23 formed by an end to end succession of panels 24. Each panel is formed from a drop thread fabric of the kind shown in Figures 3 and 4 with closed edges so that the panel is inflatable to form a third chamber independent of the outer and inner chambers. The protective sheet 23 may be covered by an additional layer or layers of material to provide fire retardency and to provide resistance to puncturing. In addition, such a layer may also provide a means of anchoring the front edge of the barrier to the ground and can provide advertising space.

The barrier described above with reference to the drawings is designed to be used to absorb the impact of vehicles and more particularly motorcycles. The individual structures can be readily transported in a deflated condition and taken to a required location. There, unitary inner chamber formed by the struts 21, the triangulation struts 22, the front wall 11, the rear wall 12 and the first and second side walls 15,16 is inflated. The pressure in this inner chamber may, for example, be 5. 17kPa (0.75psi).

This conforms the outer chamber to the shape shown in Figures 1 and 2. In addition, air under pressure is introduced into the outer chamber 10. The pressure in the outer chamber 10 is lower than the pressure in inner chamber and may be as low as 0. 17kPa (0.025psi). The structures are placed side by side as shown in Figure 2 and the sheet 23 formed by the panels 24 are inflated and located on the front walls 11.

In the barrier, the inflated walls 11, 12, 15,16 and the inflated struts 21,22, the parts making up the inner chamber, are designed simply to provide sufficient rigidity to allow the structure to maintain and retain its shape. The effect of any impact is absorbed principally by the outer chamber 10. When a body such as a motorcycle, impacts the front wall 11, the chamber 10 deforms to absorb the load. The pressure in the struts 21 and the triangulation struts 22 and their diameter are such, that under such impact loads, they simply buckle. This is assisted by the fact that none of the struts 21,22 extends normal to the front wall 11. The same is true of the front wall 11; under impact load it simply bends inwardly.

After impact the buckled struts 21 and triangulation struts 22 and any buckled walls 11,12, 15 and 16 straighten to re-conform the outer chamber but do not product large forces while straightening. This prevents the structure from returning rapidly to its original shape and keeps rebound velocity to a minimum.

The third chamber formed by the sheet 23 has as its principle purpose to reduce if not eliminate the chance of an impacting body from entering the gap between two adjacent structures. Its presence is not essential for the proper functioning of the structure and if, for example, a sharp edge or an impacting body were to burst the panels 24 making up the sheet 23, the structure would still function effectively.

It will be appreciated that the structure and the barrier described above with reference to the drawings are designed specifically to take the impact of a motorcycle. Parts may be differently dimensioned and arranged to take other impacts such as the impact of a car or a person performing a sport such as skiing. In addition, the structure could be designed to absorb vertically downward impact loads. It will also be appreciated that there are many other variations that can be made to the structure described above with reference to the drawings. For example, while the front wall 11, rear wall 12 and first and second side walls 15,16 of the cover have been described as being inflatable; they need not be inflatable. They could be formed by non-inflatable panels of suitable material. In addition, while the chamber 10 is described above as closed; it need not be closed. There could be provided vents which could provide controlled venting and air from the interior of the chamber 10 in the event of an impact and control the return of air after impact. Where the walls 11,12, 15 and 16 are not inflated, the shape of the chamber 10 may be defined by additional inflatable tubes. For example, there could be a framework of tubes in the shape of a parallelepiped supporting the walls 11,12, 15 and 16. Although the front wall 11 is shown as vertical; it need not be vertical. It could subtend an angle to the vertical from example 5° or 10° either forwards or backwards.