Protective helmet

The present invention relates to a protective helmet according to the introductory portion of the independent claim.

Background of the invention

Protective helmets, such as ski helmets, motorcycle helmets and bicycle helmets are typically constituted by a hard outer surface substance having on its interior an elastic substance such as EPS (Expanded Polystyrene) or EPP (Expanded polypropylene) which is intended to attenuate mechanical chocks. The helmet fits the wearers head closely and in a crash the retardation of the head inside the helmet is not only attenuated as intended, but the movement of the head inside the helmet tend to have resonant properties, i.e. the head bounces back and forth inside the helmet. This is due to the elasticity of the EPS or EPP and the result my be disadvantageous or in a worst case counteract the intended protective action of the helmet by causing a larger degree of acceleration of the head than what would had been the case without the helmet.

Both EPS and EPP are highly impenetrable to water and water vapour, which prohibits sweat from vaporising and leaving the helmets. This makes helmets cushioned by these and similar substances have a tendency to collect sweat on the inside which is uncomfortable.

A patent related to helmets with a inner cushioning layer attempting to dimmish the problems arising from the elasticity of EPS or EPP is WO03059102 which discloses a helmet with a cushioning layer of a foamized substances such as Silica Aerogel or Carbon Aerogel. The suggested substances are intended to absorb the impact forces by irreversibly deforming rather than being elastic. The disclosed foamized substances are however, like EPS and EPP, unfortunately highly impenetrable to water and water vapour.

An object of the invention is therefore to provide a helmet with a inner cushioning layer which absorb the impact forces by irreversibly deforming that has a much higher degree of permeability to water vapour than prior art helmets.

These and other objects are attained by a protective helmet according to the characterising portions of the independent claim.

Summary of the invention

The invention relates to a protective helmet with a hard outer surface 2 that has a cushioning substance 3 extending over its interior, where the cushioning substance 3 is aluminum foam. This has the advantage that the aluminum foam is permeable to water vapour and thus keeps the users head dry. The hard outer surface 2 of the helmet may advantageously have ventilation openings (4a-b) to allow water vapour to be emitted through the openings rather than having to permeate a longer distance through the foam and being vented at the edges of the foam.

Brief description of the drawings

Fig. 1 shows a first embodiment of the protective helmet in cross section

Fig. 2 shows an external view of a second embodiment of the protective helmet

Description of preferred embodiments

Fig. 1 shows in cross section a first embodiment of the protective helmet 1 which protects only the neck and top of the head. It has an outer shell 2 of a hard substance such as a polymer, metal or layers of both polymers and metal. The outer shell has on its inside a layer of aluminium foam 3 which upon impact deforms irreversibly and thereby absorbs impact forces, rather than acting as an elastic substance.

Fig. 2 shows an external view of a second embodiment of the protective helmet which is embodied to protect the whole head and is provided with a transparent front portion. This embodiment also has an outer shell of a hard substance which on its inside has a layer of aluminium foam. The aluminium foam which has the advantageous property of being permeable to water vapour and water, keeps the wearers head dry by allowing the water vapour to be emitted though openings 4a, 4b in the hard outer shell. The openings on the top 4a and on the sides 4b of the helmet is particularly useful with this embodiment of the helmet as it encloses the whole of the head, but water vapour can obviously also permeate the aluminium foam an be emitted at the edges of the foam rather than through its surface.

The structure of aluminium foam that allows it to be permeable to water vapour is that it may be described as a contiguous series of interconnected air pockets, defined by a solid structure of

aluminium, whereas such substances as EPS or EPP should rather be described as a near solid polymer with embedded, separate, air pockets. Obviously, the aluminium foam may be produced of different types, having a larger or smaller portion of air per substance volume and also possibly incorporating a larger or smaller percentage of air pockets that are fully enclosed in the aluminium.

Although the invention has been described in conjunction with a number of preferred embodiments, it is to be understood that various modifications may still be made without departing from the scope of the invention as defined by the appended claims. One such obvious modification is varying the thickness of the aluminium foam or altering the area over which the foam extends.