Helmet comprising deformable elements

Abstract

The present invention relates to a helmet (1), comprising: at least one first layer (10) forming an outer surface (10a) of the helmet (1), a second layer (30) comprising an outer surface facing the at least one first layer (10), and a plurality of balls (2) arranged between the first layer (10) and the second layer (30) and connected to the second layer and configured to disconnect from the second layer and to roll over the outer surface (30a) of the second layer (30) upon an oblique impact on the outer surface of the helmet (1), wherein the helmet (1) further comprises a plurality of deformable elements (20) arranged between the at least one first layer (10) and the second layer (30).

Description

[0001] HELMET COMPRISING DEFORMABLE ELEMENTS

[0002] Specification

[0003] The invention relates to an impact mitigation structure, particularly a helmet, particularly a helmet for cycling, as well as to a method for producing such an impact mitigation structure, particularly helmet.

[0004] Injury to a person or damage to an object can occur when the person or object is subjected to an impact of sufficient magnitude. Considerable developmental effort has been expended to produce helmets which provide protection from potentially damaging or injurious impacts.

[0005] Head injuries, which can be incurred as a result of participation in sports such as cycling are a common cause of serious brain injuries.

[0006] A brain trauma may occur as a consequence of either a focal impact upon the head, a sudden acceleration or deceleration within the cranium, or a combination of both impact and movement. Impact protection is therefore important in preventing brain injuries as a result of impacts to the head.

[0007] Head protection, in the form of helmets, is designed to reduce the forces experienced by a user’s head during an impact. Generally, a helmet comprises at least one impact absorbing layer which is designed to absorb a portion of the forces to which the helmet is subjected during an impact.

[0008] However, helmets often do not provide adequate protection during an impact against both linear and tangential forces. As oblique impacts are common, impacts will often include both linear and tangential components. Particularly, an oblique impact means that the force acting on the outer surface of the helmet that is e.g. hitting the tarmac upon a crash comprises a component that extends tangentially with respect to said outer surface at the location of the impact.

[0009] Unfortunately, such tangential forces in particular result in the rotational acceleration of the brain, which has been linked to bridging vein rupture. In turn, this may be responsible for subdural hematomas, and diffuse axonal injuries. Tangential forces during an impact may also result in neck injuries. Based on the above, the problem to be solved by the present invention is to provide an improved helmet that is capable of reducing the above-mentioned injuries related to oblique impacts comprising a tangential force acting on the helmet I head of the person wearing the helmet.

[0010] This problem is solved by an impact mitigation structure, particularly helmet, having the features of claim 1 .

[0011] Preferred embodiments of this first aspect of the present invention are stated in the corresponding dependent claims and are described below.

[0012] According to claim 1 , a helmet is disclosed, particularly a cycling helmet, comprising:

[0013] - at least one first layer, particularly forming an outer surface of the helmet,

[0014] - a second layer comprising an outer surface facing the at least one first layer, and

[0015] - a plurality of preferably rigid balls (that preferably remain rigid during intended use of the helmet), the balls being arranged between the at least one first layer and the second layer and connected to the second layer and configured to disconnect from the second layer and to roll over the outer surface of the second layer upon an oblique impact on the outer surface of the helmet (particularly on the at least one first layer or on a first layer of a plurality of first layers of the helmet), wherein the helmet further comprises a plurality of deformable elements arranged between the at least one first layer and the second layer and preferably connecting the at least one first layer to the second layer for enhancing durability of a connection of the at least one first layer to the second layer in the absence of the oblique impact.

[0016] Particularly, the fact that the balls are preferably rigid, can mean that the balls are more rigid than the surface of the second layer. Particularly, in an embodiment the balls are spheres.

[0017] The oblique impact can e.g. occur when a person wearing the helmet falls down or crashes, so that an object hits the at least one first layer or the latter hits the ground etc.

[0018] Particularly, the helmet can comprise multiple first layers arranged side by side on the second layer. Thus, when an impact occurs, just a single first layer that is hit by the oblique impact may move relative to the second layer and rolling of balls arranged between this single first layer and the second layer is then activated due to the oblique impact. In a preferred embodiment of the invention, the respective deformable element is connected to the second layer by an adhesive bond and is particularly configured to disconnect from the second layer upon said oblique impact, and / or wherein the respective deformable element is connected to the at least one first layer by an adhesive bond and is particularly configured to disconnect from the at least one first layer upon said oblique impact.

[0019] Particularly, according to an embodiment, the balls and / or the deformable elements are configured to hold the at least one first layer such that a tangential force generated by said oblique impact and required to activate rolling of balls is about 0.1 kN, or such that an energy introduced by the tangential force (FT) has to exceed a threshold of 1 Joule to activate rolling of the balls.

[0020] Particularly, in an embodiment, the balls are configured to promote the motion of the second layer relative to the at least one outer layer upon said oblique impact. Particularly, the balls may comprise a circular diameter between 0.1 mm and 4 mm, particularly between 1 mm and 2 mm, wherein the circular diameter refers to a circular cross-section of the balls (i.e. spheres). The balls advantageously contribute to a substantially lower friction force and rolling resistance between the at least one first layer and the balls and the second layer and the balls.

[0021] Particularly, the balls are configured to facilitate relative movement between the at least one first layer and the second layer by the rolling of balls of said plurality of balls between the first and the second layer, wherein said rolling of balls provides a low rolling resistance in the range from 0.0001 to 0.2, particularly 0.03 to 0.05, particularly 0.025 to 0.04, between the balls and an inner surface of the at least one first layer or between the balls and the outer surface of the second layer. Generally, the first and / or the second layer can each comprise or consist of further layer connected to one another to form the first or second layer.

[0022] Furthermore, according to a preferred embodiment of the invention, the respective deformable element is connected to the at least one first layer by an adhesive bond and to the second layer by an adhesive bond.

[0023] Furthermore, according to a preferred embodiment of the invention, the respective deformable element forms a round body or dot-shaped body, particularly having a circular cross-section in a cross-sectional plane running perpendicular to a normal of a surface of the first or second layer at the location of the deformable element.

[0024] Furthermore, according to a preferred embodiment of the invention, the respective deformable element is elastic and / or viscoelastic, which particularly aids in providing some knock stability to the at least one first layer. Furthermore, according to a preferred embodiment of the invention, the respective deformable element is configured to not plastically deform when under load. In certain embodiments the deformation can be plastic in case it is not irreversible.

[0025] Furthermore, according to a preferred embodiment of the invention, the respective deformable element can be deformed by up to 2 mm under load in a typical crash situation where the helmet suffers an impact from a surface (e.g. ground) or another object. Such a force may be in the range of 50 to 150 Gs, G being the acceleration due to gravity.

[0026] Furthermore, according to a preferred embodiment of the invention, the respective ball is connected to the second layer via an adhesive configured to break (e.g. undergo brittle failure) due to said oblique impact on the outer surface of the helmet.

[0027] Further, according to yet another preferred embodiment, the balls are also connected to the at least one first layer (or said multiple first layers) and are configured to disconnect from the at least one first layer upon said impact, wherein the respective ball is connected to the second layer via an adhesive configured to break (e.g. undergo brittle failure) due to said oblique impact on the outer surface of the helmet.

[0028] Furthermore, according to a preferred embodiment of the invention, said oblique impact has a tangential force component with respect to the outer surface at an impact point being larger than 0.1kN.

[0029] Furthermore, according to a preferred embodiment of the invention, the respective deformable element is configured to attenuate energy, e.g. from a non-crash impact on the outer surface of the helmet, particularly from an impact on the outer surface that does not lead to disconnecting of the balls from the second and / or the at least one first layer (e.g. an impact having a tangential component being smaller than the above specified force).

[0030] Furthermore, according to a preferred embodiment of the invention, the deformable elements are configured to act against release, i.e. disconnecting of the balls from the second and / or at least one first layer, and / or against rolling of the balls during the oblique impact.

[0031] Furthermore, according to a preferred embodiment of the invention, the deformable elements are unevenly distributed over the second layer. Typically, in an embodiment, the balls may be placed e.g. on a regular grid with a distance between nearest neighbors of about 5 mm. On the other hand, in an embodiment, the deformable elements may be placed on the second layer between the balls so that they have distance of about 5 cm with respect to the nearest neighbor. Further, in a preferred embodiment of the invention, the deformable elements can differ in material composition with respect to one another. Thus, the deformable elements may form several groups, wherein deformable elements from one group differ in material composition with respect to deformable elements from the other group(s).

[0032] Particularly, in an embodiment, the deformable elements are configured to address different combinations of requirements of the helmet such as manufacturability, safety, durability.

[0033] Furthermore, according to yet another embodiment of the invention, the deformable elements are configured to compromise on some requirements of the helmet to better address other requirement. Particularly, e.g. silicone complicates manufacturability and decreases impact performance, but improves durability of the helmet greatly.

[0034] Further, in an embodiment of the invention, attributes of the helmet remain stable over a range of environmental conditions (-20°C to +50°C), water, dust, UV exposure, etc.

[0035] Furthermore, in preferred embodiment of the present invention, the deformable elements comprise siloxane, wherein particularly the deformable elements are formed out of or comprise a silicone (also denoted as polysiloxane). Polysiloxane is a polymer comprising repeating units of siloxane (-O-R2Si-O-SiR2-, where R is an organic group).

[0036] Particularly, the deformable elements can comprise or can be formed out of a silicone adhesive, as HMPSA (hot melt pressure sensitive adhesive) is often too sensitive to temperature fluctuations resulting in either becoming too hard at low temperatures or too liquid at high temperatures. Particularly, silicone has a very flat temperature response remaining at ideal conditions throughout the typical temperature window during use of the helmet (including time-temperature response). Further, it is difficult to find a less temperature sensitive hot melt adhesive (HMA) with a flat response over an extended temperature range. Furthermore, as a bond failure of the deformable elements regarding their connection to the first and / or second layer preferably lies at a particular level which may further limit selection of appropriate HMAs. Furthermore, creep forces and impulses can expand the temperature window even further to -100 °C.

[0037] Particularly, the silicone adhesive can be an RTV (room temperature vulcanizing) silicone comprising polydimethylsiloxane (PDMS) polymers that can be terminated with hydroxy or acetoxy groups. These adhesives often include cross-linkers (such as tetraethoxysilane for condensation cure systems) and catalysts (like tin compounds for condensation cure or platinum compounds for addition cure systems). Further, the silicone adhesive can be a high-temperature silicone. These can contain silicone polymers with one or several additives or modifiers that allow them to resist high temperatures. They can also include fillers to improve thermal stability.

[0038] Furthermore, the silicone adhesive can be a two-part silicone adhesive that comprises two components that, when mixed, react and cure to form a strong bond. Part A can comprise a vinyl-terminated PDMS, and Part B can comprise a silicone cross-linker that may comprise a platinum catalyst.

[0039] Further, in certain embodiments non-HMA pressure sensitive adhesives (PSA) may be used, like silicone PSA. Particularly, the HMA-component allows for very fast bond formation - to the extent it’s near instant. However, solvent-based silicone PSAs are more difficult to process, not common and often require high temperatures to cure and may thus bear the risk of melting other polymers in the product. Particularly, UV curable PSAs do not comprise viscoelastic bulk properties preferred for a top bond between the respective deformable element and the respective first layer and / or a bottom bond between the respective deformable element and the second layer of the helmet.

[0040] Generally, in certain embodiments, the helmet may use HMPSA, e.g. to bond the rigid balls to the first and / or second layer. Generally, it is preferred not to replace HMPSA in this regard with silicone, as HMPSA has beneficial features such as re-healing, wherein particularly an unlimited open time means if a helmet is dropped, broken bonds can re-form. improved durability, elimination of rattling when the helmet is moved, and instant bonding during assembly so that no jigs are needed for holding bonding partners.

[0041] On the other hand, it is less preferable to use silicon for generating a top bond between the respective ball and the at least one first layer, e.g. by applying a miniscule quantity or droplet onto a top of the balls, as the silicon adhesive may cure too fast for such quantities. Particularly, during assembly, uncured silicone may move / spread too much, making it more difficult to control volume of silicone actually bonding. Furthermore, silicone does not comprise a rehealing property. Furthermore, a deformable element formed from an HMPSA may not hold the at least one first layer down in place homogeneously enough to guarantee all silicone-ball bonds form. Furthermore, according to an embodiment of the helmet according to the present invention, the balls are connected by a pressure sensitive adhesive (PSA) to the at least one first layer (or the respective first layer) forming the outer surface of the helmet.

[0042] Particularly, such a PSA can aid in providing durability to the helmet through basically three mechanisms, namely maintaining contact throughout the stacked first and second layers, particularly from the impacted outer surface of the helmet to an energy absorbing layer (e.g. EPS layer) supporting the second layer changes the stress distribution between said layers, attenuating transmission of an impact force on the outer surface of the helmet to the respective bottom bond (e.g. bond of respective ball to second layer) through viscoelastic deformation by micro-deposition of PSA, and

[0043] Micro-deposition of PSA distributes stress differently

[0044] Furthermore, PSA can inhibit an impact performance of the helmet as energy is spent breaking the bonds of the balls initially and during rolling of the balls.

[0045] Particularly, the PSA can be an acrylic adhesive. Furthermore, the PSA can be a rubber-based adhesive, e.g. an adhesive made from a natural or a synthetic rubber. Furthermore, the PSA can be a silicone-based PSA. Furthermore, the PSA can be a polyurethane adhesive or an ethylene vinyl acetate (EVA) adhesive.

[0046] Particularly, according to yet another embodiment the balls can be connected by an ultraviolet light (UV) curable adhesive, i.e., an adhesive that can be cured by irradiating the adhesive with ultraviolet (UV) light, to the second layer. Particularly, the UV curable adhesive can be an UV curable silicone-based adhesive. Furthermore, the UV curable adhesive can be a UV curable polyurethane-based adhesive. Furthermore, the UV curable adhesive can comprise UV curable acrylated urethanes. Further, the UV curable adhesive can be a UV curable acrylic elastomer.

[0047] According to yet another embodiment of the helmet according to the present invention, the at least one first layer is connected to the second layer via at least one connection. The at least one connection can be formed by an adhesive, wherein particularly the adhesive is a cyanoacrylate-based adhesive, or by a weld seam that may be formed by ultrasonic welding.

[0048] Particularly, the cyanoacrylate-based adhesive can be one of: methyl 2-cyanoacrylate (MCA), ethyl 2-cyanoacrylate (ECA, commonly also denoted as Super Glue), n-butyl cyanoacrylate (n- BCA), octyl cyanoacrylate, 2-octyl cyanoacrylate. According to a further embodiment, said adhesive bond connects a boundary region of the at least one first layer to the second layer.

[0049] In the following, exemplary embodiments as well as further features and advantages of the present invention are described below with reference to the Figures, wherein

[0050] Fig. 1 shows schematic cross-section of an embodiment of the helmet according to the present invention,

[0051] Fig. 2 shows a perspective top view of the balls and deformable elements arranged on the surface of the second layer according to an embodiment of the invention, and

[0052] Fig. 3 shows a perspective view of a front side of a helmet according to an embodiment of the present invention, wherein first layers of the helmet are in addition also connected to the second layer of the helmet via an adhesive bond or a weld seam, respectively, wherein the respective adhesive bond is particularly formed with a cyanoacrylate-based adhesive.

[0053] Fig. 1 shows an embodiment of a helmet 1 according to the present invention. The helmet 1 serves to protect a head H of a user and comprises at least one first layer 10 forming an outer surface of the helmet 1 , a second layer 30 comprising an outer surface 30a facing the at least one first layer 10, and a plurality of balls 2 arranged between the at least one first layer 10 and the second layer 30 and connected to the second layer 30 and configured to disconnect from the second layer 30 and to roll over the outer surface 30a of the second layer 30 upon an oblique impact on the outer surface 1 a of the helmet 1. The helmet 1 further comprises a plurality of deformable elements 20 arranged between the at least one first layer 10 and the second layer 30 and connecting the at least one first layer 10 to the second layer 20.

[0054] An impact threshold corresponds to a pre-defined tangential force FT on a first layer 10 that is generated by an oblique impact (e.g. due to a crash causing an object to hit the at least one first layer 10 of the helmet 1 ), and, if exceeded upon the oblique impact, causes the balls 2 to disconnect from the second layer 30 and particularly from the first layer 10 and to roll over the surface 30a of the second layer 30. Further, due to the oblique impact, the deformable elements 20 are disconnected from the first and / or second layer 10, 30.

[0055] The deformable elements 20 can be connected to the first and / or second layer 10, 30 by adhesive bonds. Upon impacts below the above-states threshold, the deformable elements are configured to attenuate such impacts. In particular, they also serve to act against activation of rolling of the balls 2. In a preferred embodiment, the balls comprise a diameter of e.g. about 2 mm.

[0056] Furthermore, in a preferred embodiment, the deformable elements 20 can comprise a diameter D along the surface 30a of the second layer in the range from 1 mm to 10 mm, particularly in the range from 3 mm to 7 mm. Particularly, the diameter can be about 6 mm.

[0057] Furthermore, the helmet can comprise an energy absorbing layer 40 that may form part of the second layer 30 or can be connected thereto. Generally, in the present invention, the respective first layer 10 can comprise a sub structure, e.g., may itself be comprised of several layers stacked e.g. on top of one another. The same applies to the second layer 30.

[0058] Particularly, as shown in Fig. 2, in a preferred embodiment, the deformable elements 20 can be formed by dispensing a droplet comprising a polysiloxane (e.g. a droplet of a one-part silicone adhesive) onto the surface 30 of the second layer. Particularly, in an embodiment, the deformable elements 20 are distributed on the surface 30a of the second layer 30 between the balls 2 (cf. Fig. 2).

[0059] Fig. 3 shows an embodiment of a helmet according to the invention comprising the afore- described deformable elements 20 that can connect the second layer 30 to the respective first layer 10 (here the helmet comprises multiple first layers 10 arranged side by side on the second layer 30). For the sake of visibility, the first layers 10 are shown transparent in Fig. 3 so that the underlying balls 2 and deformable elements 20 can be seen. However, the first layers 10 may also be non-transparent or may comprise any color.

[0060] Apart from the deformable elements 20, an inner surface of the respective first layer 10 can be connected to the outer surface 30a of the second layer 30 (e.g. in a pointwise fashion) via at least one connection 40 such as an adhesive bond 40 or a weld seam 40 generated e.g. by means of ultrasonic welding. Particularly, the respective adhesive bond 40 can be formed by an adhesive that is preferably a cyanoacrylate-based adhesive (see also above). Particularly, the respective connection 40 can connect a boundary region of an inner surface 10a of the respective first layer 10 to the outer surface 30a of the second layer 30.

[0061] Particularly, the connections 40 can provide a stiffer connection between the first layers 10 and the second layer 30 than the deformable elements 20 to prevent small movement of the outer first layers 10 when rubbing, given e.g. the viscoelastic nature of the silicone bond provided by the deformable elements 20.

Claims

Claims1. A helmet (1 ), comprising:- at least one first layer (10) forming an outer surface of the helmet (1 ),- a second layer (30) comprising an outer surface (30a) facing the at least one first layer (10), and- a plurality of balls (2) arranged between the at least one first layer (10) and the second layer (30) and connected to the second layer (30) and configured to disconnect from the second layer (30) and to roll over the outer surface (30a) of the second layer (30) upon an oblique impact on the outer surface (1 a) of the helmet (1 ), wherein the helmet (1 ) further comprises a plurality of deformable elements (20) arranged between the at least one first layer (10) and the second layer (30) and connecting the at least one first layer (10) to the second layer (20).

2. The helmet (1 ) according to claim 1 , wherein the respective deformable element (20) is connected to the second layer (30) by an adhesive bond and is particularly configured to disconnect from the second layer (30) upon said oblique impact, and / or wherein the respective deformable element (20) is connected to the at least one first layer (10) by an adhesive bond and is particularly configured to disconnect from the at least one first layer (10) upon said oblique impact.

3. The helmet according to claim 1 or 2, wherein the respective deformable element (20) forms a round body, particularly having a diameter along the first and / or second layer (10, 30) in the range from 1 mm to 10 mm.

4. The helmet according to one of the preceding claims, wherein the respective deformable element (20) is elastic and / or viscoelastic.

5. The helmet according to one of the preceding claims, wherein the respective deformable element (20) can be deflected by up to 2 mm under load.

6. The helmet according to one of the preceding claims, wherein the respective ball (2) is connected to the second layer (30) via an adhesive bond configured to break due to said oblique impact on the outer surface (1 a) of the helmet (1 ).

7. The helmet according to one of the preceding claims, wherein said oblique impact generates a tangential force (FT) on the at least one first layer (10) at a location of the impact being larger than 0.1 kN.

8. The helmet according to one of the preceding claims, wherein the respective deformable element (20) is configured to attenuate energy from an impact on the outer surface.

9. The helmet according to one of the preceding claims, wherein the deformable elements (20) are configured to act against disconnection of the balls (2) from the first and / or second layer (10, 30) and / or against rolling of the balls (2) during the oblique impact.

10. The helmet according to one of the preceding claims, wherein the deformable elements (20) are unevenly or evenly distributed over the second layer (30).11 . The helmet according to one of the preceding claims, wherein said plurality of deformable elements (20) comprises deformable elements (20) that differ in material composition from one another.

12. The helmet according one of the preceding claims, wherein the deformable elements (20) comprise siloxane, wherein particularly the deformable elements are formed out of or comprise a silicone.

13. The helmet according to one of the preceding claims, wherein the balls (2) are connected to the at least one first layer (10) by a pressure sensitive adhesive (PSA).

14. The helmet according to one of the preceding claims, wherein the balls (2) are connected to the second layer (30) by a UV curable adhesive.

15. The helmet according to one of the preceding claims, wherein the at least one first layer (10) is connected to the second layer (30) via at least one connection (40), wherein particularly the connection is formed by an adhesive, wherein particularly the adhesive is a cyanoacrylate-based adhesive, or by a weld seam, particularly formed by ultrasonic welding.

16. The helmet according to claim 15, wherein said connection (40) connects a boundary region of an inner surface (10a) of the at least one first layer (10) to the outer surface (30a) of the second layer (30).

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