Abstract:
A compressible liner for a helmet or other apparatus subject to shock loading comprises three substantially co-extensive layers mutually engaged by respective cone-like protuberances and cone-like recesses. The intermediate layer is of a different compressibility and provides for de-coupling of the layers in an oblique impact.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
       [0001]    This application is a national phase application pursuant to 35 U.S.C. §371 of International Application No. PCT/US15/01526, filed Sep. 7, 2015, which claims priority to Great Britain Patent Application No. 1416556.7 filed on Sep. 19, 2014. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a compressible liner for impact protection, and to a method of impact protection using a compressible liner. The invention may be used in a helmet or the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    Compressible liners are used in helmets to provide cushioning upon impact. Such liners may also be used wherever a structure or apparatus may be at risk from shock loading, for example in relation to motor vehicles; baby capsules; protective clothing, such as vests; packing materials and protection of valuable goods in transit. 
         [0004]    WO2010/001230A discloses an example of a compressible liner having dual compressible layers with mutually engageable cone-shaped projections and recesses; the layers comprise foam materials of different compressibility. 
         [0005]    Analysis of impacts, particularly helmet impacts, shows that typical impact forces are both translational and rotational. The translational force is generally orthogonal to the impact surface, and in the case of a helmet causes a rapid deceleration which is required to be cushioned in order to remove impact energy. 
         [0006]    The rotational impact force is more complex, and in an oblique impact causes an acceleration due to frictional contact, for example between a helmet and the contact surface. It is desirable for the liner to minimize both this acceleration and the inevitable deceleration that follows, to the intent that, for example, energy imparted to the head and neck of a helmet wearer is minimized. Similar considerations apply to non-helmet applications undergoing an oblique impact. 
         [0007]    What is required is a compressible liner which better accommodates an oblique impact. 
       SUMMARY OF THE INVENTION 
       [0008]    According to the invention there is provided a compressible liner for impact protection, said liner comprising three substantially co-extensive layers mutually engaged by respective arrays of cone-like protuberances and corresponding cone-like recesses, the outer surface of the liner being substantially smooth and the intermediate layer having a different compressibility to that of an adjacent layer. 
         [0009]    In the invention, an intermediate layer having portions of different compressibility is envisaged. Accordingly a portion of the intermediate layer may have a different compressibility to that of an adjacent layer, or the intermediate layer may be of uniform compressibility. 
         [0010]    The invention is characterized by providing that the intermediate layer (or a portion thereof) is of a different compressibility to that of the inner and outer layers, or that the intermediate layer (or a portion thereof) is of a different compressibility to an adjacent layer. Alternatively the invention may be characterized by the intermediate layer (or a portion thereof) having a different density to that of the inner and outer layers, or by the intermediate layer (or a portion thereof) having a different density to that of an adjacent layer. 
         [0011]    One configuration of the invention comprises an inner layer of low density, an intermediate layer of density greater than the inner layer and the outer layer density greater than the intermediate layer thereby producing an increasing density configuration from the inner layer to the outer layer (i.e. a compression or crushing gradient). 
         [0012]    Another configuration of the invention comprises an inner layer of a certain density, an intermediate layer of density lower than the inner layer and an outer layer of density greater than the inner layer and the intermediate layer. The intermediate ‘softer’ layer would have a decoupling effect on the inner and outer layer and act as a ‘crumple zone’ between the two layers (i.e. the low density ‘softer’ intermediate foam layer would reduce the transfer of impact energy from the outer layer to the inner layer and vice versa). 
         [0013]    Another configuration of the invention comprises an inner layer and an outer layer of low density foam and the intermediate layer made of higher density foam. This configuration is suitable for use in, for example, body vests for footballers exposed to different levels of impact tackling, where the three layered liner could be used to soften the blow to the body of the player wearing the vest (being tackled) and soften the blow to the body of the player (the tackler) coming in contact with the vest. The intermediate layer of the higher density foam will act like a decoupling zone between the two softer layers, allowing a small amount of shear with respect to the inner layer which remains stationary with respect to the head. 
         [0014]    It will be understood that many additional combinations are possible, in addition to variation of the shape, size and spacing of the protuberances and recesses. The protuberances may have a base which is circular, triangular, square or having a greater number of sides. A symmetrical protuberance is preferred. 
         [0015]    It will also be noted that the interlocking structure of the inner cones embedded within the cones of the overlying intermediate layer and the intermediate cones embedded within the thickness of the overlying outer layer produces a stronger shock absorbing liner that would prevent shearing effects of layers during oblique impacts. 
         [0016]    A further feature of the invention is to allow the incorporation of segmentation/zoning of the inner and intermediate layers, and the outer layer constructed of one piece. The use of segmentation/zoning of the inner and intermediate layers allows the combinations of different density foams close to the vulnerable areas of the skull to be of different thicknesses and strengths. Typically such segmentation allows compressibility of four regions to be selected, namely front, back, top and sides. 
         [0017]    The three layered shock absorbing liner of the invention can be used in all kinds of helmets and applications where it is required to absorb different levels of impact forces. The thickness thereof may be in the range 20-50 mm, according to the use for which the liner is intended. 
         [0018]    The combination of lower density foams incorporated within the thickness of the three layers produces a lighter helmet thereby reducing rotational acceleration effects of the head during impacts (thus reducing the potential of focal and diffuse head injuries). 
         [0019]    The combination of three different densities incorporated within the thickness of the three layers provides a liner to:
       I. Absorb different levels of impact forces more efficiently thereby reducing the risk of concussion at low level impacts and more severe head injuries at high level of impacts.   II. Direct impact energy sideways away from the brain (in a helmet liner) thereby lowering g-forces to the head.   III. Reduce slab-cracking.       
 
         [0023]    Other features of the invention will be apparent from the claims appended hereto. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]    Other features of the invention will be apparent from the following description of a preferred embodiment illustrated by way of example only in the accompanying drawings in which: 
           [0025]      FIG. 1  illustrates a transverse vertical section through a prior art helmet having a compressible liner. 
           [0026]      FIG. 2  corresponds to  FIG. 1  and shows an orthogonal section on line  2 - 2  of  FIG. 1 . 
           [0027]      FIG. 3  illustrates in part the inner liner of  FIGS. 1 and 2 , showing a regular array of outwardly directed conical protuberances. 
           [0028]      FIG. 4  illustrates a straight section of a compressible liner according to a first embodiment of the invention. 
           [0029]      FIG. 5  corresponds to  FIG. 4  and illustrates a second embodiment of the invention. 
           [0030]      FIGS. 6 and 7  show alternative conical forms for use in the invention. 
           [0031]      FIG. 8  shows a dual version of the compressible liner of the invention. 
           [0032]      FIGS. 9-15  illustrate the variety of configurations which are possible with the interlocking structure of the present invention, by reference to a curved liner (for example for a helmet). 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]      FIGS. 1-3  illustrate the helmet of WO 2010/001230A. 
         [0034]    A helmet  112  comprises an outer shell  116 , typically of a hard plastics material, within which is provided a double compressible layer  124 ,  128  and an optional soft internal comfort liner  120 . 
         [0035]    As best illustrated in  FIG. 3 , the inner compressible layer  124  comprises an array of integral conical protuberances  130  which fit closely within corresponding conical recesses  132  of the outer compressible layer  128 . The materials of the layers  124 ,  128  are of different compressibility, which gives an advantageous compression characteristic as compared with a conventional unitary liner of single compressibility. 
         [0036]    Particular details of the prior art construction can be obtained by reference to the description of WO 2010/001230A, and will not be further described here. 
         [0037]    The invention will be described with reference to a helmet of the kind illustrated in  FIGS. 1-3 , it being understood that the compressible liner of the invention may be used in apparatus other than helmets, as previously mentioned. 
         [0038]      FIG. 4  illustrates a first embodiment of the invention. A compressible liner  1110  comprises an inner layer  1124 , an outer layer  1128  and an intermediate layer  1160 . The inner layer  1124  has many protuberances  1130  which project into matching recesses  1161  of the intermediate layer  1160 , and the intermediate layer has many protuberances  1162  which project into matching recesses  1132  of the outer layer  1128 . The protuberances  1130 ,  1162  and corresponding recesses  1161 ,  1132  are integrally formed from a respective base region  1134 ,  1163  of relatively uniform thickness, and may have variability in size, shape and spacing, though, as illustrated in this embodiment, the protuberances of the inner and intermediate layers are uniform. In this example the outer layer has a continuous surface layer  1122  of relatively uniform thickness. The inner layer also includes inwardly facing projections or ribs  1164  to engage a comfort liner, but the inner surface may also be smooth. 
         [0039]    Each of the three layers  1124 ,  1128 ,  1160  typically comprises a shock absorbing expanded polystyrene material (or other suitable thick absorbing material as previously described). The layers may be respectively homogeneous. Adjacent layers are of different compressibility so as to permit greater variation in the compression and crushing gradients across the thickness of the liner  1110 . As will be appreciated the invention permits three different densities of material in three different layers (i.e. a factorial three possibility) which provides many more potential combinations than the prior art, but maintaining a comparatively low manufacturing cost. 
         [0040]    An alternative embodiment is illustrated in  FIG. 5 , to show a degree of variation which is possible with the invention. In  FIG. 5 , the inner and outer layers  1224 ,  1228  have the same compressibility, whereas the intermediate layer  1260  is different. Furthermore the underside of the inner layer  1224  is planar, and at the outer side, the peaks of the protuberances  1262  of the intermediate layer  1260  are permitted to appear through the outer layer  1228 , thus permitting a substantial sharing of an orthogonal impact load. 
         [0041]    In both embodiments of  FIGS. 4 and 5 , it will be understood that a straight liner is shown for ease of illustration, but that in practice a three-dimensional form may be required as in the case of the helmet liner illustrated in  FIGS. 1-3 . 
         [0042]      FIGS. 6 and 7  illustrate two examples of different shapes of protuberance  1301 ,  1401  which allow the material of the protuberance to have a changing effect as the degree of compression increases. It will be understood that a corresponding recess is provided in the adjacent layer. 
         [0043]    In  FIG. 6 , a broad protuberance  1301  has a first portion  1302  comprising a regular conical tip  1303  with an included angle in the range 80-120°. A second portion  1304  comprises a regular circular supporting pillar  1305  which constitutes the main body of the protuberance, and has a slight outward taper in the range 5-15° towards the base. The first portion  1302  has an axial height which is about 25% of the total height of the protuberance. In this embodiment the base region  1306  is of substantially constant thickness across the layer. 
         [0044]    The protuberance  1301  exhibits a resistance to compression which increases quickly over the tapering point  1303 . The main body  1305  of the protuberance is of substantially constant section, and exhibits substantially increased stiffness. The shaft taper of the main body ensures a snug fit in the corresponding recess. 
         [0045]    In  FIG. 7 , a slim protuberance  1401  also has a first portion  1402  comprising a regular conical tip  1403  with an included angle in the range 30-60°. A second portion  1404  comprises a tapering shallow frustoconical base  1405  having an included angle in the range 120-160°. The first portion  1402  has a height which is in the range 75-125% of that of the second portion  1404 . As illustrated the height of the first portion  1402  is greater than that of the second portion  1404 . In this embodiment the base region  1406 , as before is a substantially constant thickness across the layer. 
         [0046]    The protuberance  1401  exhibits a resistance to compression at the tapering point  1403  which is slight. The main body  1403  of the protuberance permits only further compression before the entire base thickness  1404  is engaged to resist compression. It will be appreciated that the protuberance  1401  squashes down more readily than the protuberance  1301 . 
         [0047]      FIG. 8  illustrates a double compressible liner, of the kind shown in  FIG. 4 , incorporating the triple layered construction of the present invention whereby a common inner layer  1524  is surmounted by respective intermediate layers  1560  and outer layers  1528  on either side. In the embodiment of  FIG. 8  it will be understood that the inner layer  1524  may be constituted by a single component such as a one-piece moulding, or may comprise two inner layers of single compressible liners placed back to back and secured together, if required, by any suitable means. This embodiment may also be characterised on a common outer layer (placed innermost) surmounted by respective intermediate and inner layers. 
         [0048]      FIGS. 9-15  illustrate the variety of configurations which are possible with the interlocking structure of the present invention, by reference to a curved liner (for example for a helmet). 
         [0049]      FIG. 9  illustrates three layers with relatively small inner cones  1601  aligned with somewhat larger outer cones  1602 , the outer cones being somewhat inward of a smooth outer surface  1603 , and the inner surface  1604  being also smooth. 
         [0050]      FIG. 10  corresponds to  FIG. 9 , but in this case the outer cones  1602  just reach the outer surface  1603 . 
         [0051]      FIG. 11  corresponds to  FIGS. 9 and 10 , but in this case the outer cones  1602  appear in truncated form on the outer surface  1603 . 
         [0052]      FIG. 12  illustrates a reversed cone arrangement, corresponding to  FIG. 10 , with the inner and outer cones  1605 ,  1606  facing inwardly. A reversed arrangement corresponding to  FIGS. 9 and 11  is also possible. 
         [0053]      FIG. 13  corresponds to  FIG. 9 , and illustrates a somewhat narrower intermediate layer  1607  having outer cones  1608  of reduced wall thickness; the inner cones  1609  are of somewhat greater height than those illustrated in  FIG. 9 . 
         [0054]      FIG. 14  illustrates one element  1701  of an inner or intermediate layer, having cones  1702  in a regular pattern. The edges  1703  of the element  1701  have a male or female locking form or key  1704 ,  1705  whereby adjacent elements can be retained together against transverse forces, in the manner of a jigsaw puzzle. It will be appreciated that the arrangement of  FIG. 14  permits adjacent elements to be of different material, different size and/or different compressibility. The element of  FIG. 14  is rectangular, but this aspect of the invention is not limited to edge shape—curved and non-regular shapes are possible, and may be necessary for a helmet liner. The outer layer (not shown) is one piece. 
         [0055]      FIG. 15  illustrates how adjacent elements  1801 ,  1802  of an intermediate layer have a junction  1803  which does not correspond with junctions  1804 ,  1805  between adjacent elements  1806 ,  1807 ,  1808  of an inner layer. Such an arrangement provides a more stable and strong construction. The outer layer  1809  is one piece. 
         [0056]    In the variations disclosed in  FIGS. 9-13 , the cones have substantially the same apex angle, it will however be understood that the inner and outer cones may have a different apex angle, and/or be different between adjacent keyed elements. 
         [0057]    The invention comprises layers whose comparative densities (or portions thereof) may be characterized as follows (‘a’ being the outer layer; ‘b’ being the intermediate layer, and ‘c’ being the inner layer): 
         [0000]    a&gt;b&gt;c, or a&gt;c&gt;b, or b&gt;a&gt;c, or b&gt;c&gt;a, or c&gt;b&gt;a, or c&gt;a&gt;b, or (a=c)&gt;b, or (a=c)&lt;b. 
         [0058]    It follows that the respective compressibilities are: 
         [0000]    c&gt;b&gt;a, or b&gt;c&gt;a, or c&gt;a&gt;b, or a&gt;c&gt;b,
 
or a&gt;b&gt;c, or b&gt;a&gt;c, or (a=c)&lt;b, or (a=c)&gt;b.
 
         [0059]    Densities of the respective layers (or portions thereof) are in the following ranges: 
         [0000]    a 35-110 kgm −3  
 
b 15-100 kgm −3  
 
c 15-90 kgm −3  
 
         [0060]    In an embodiment of the invention, the materials of the respective layers are foam expanded polystyrene and/or a viscoelastic foam material. The material may be isotropic (having a material property that is identical in all directions) or anisotropic (having a material property that preferentially shears in one direction) to give a shearing in the direction substantially parallel to the layer direction. 
         [0061]    Thicknesses of the respective layers in a helmet gives an overall thickness in the range 15-45 mm, but is typically in the range 20-30 mm. The three layers may each have a uniform thickness, which may not be equal between layers, or may have a varying thickness. 
       EXAMPLE 
       [0062]    A comparative impact test using a variety of anvil shapes and ambient conditions has been carried out, with the following characteristics and results. 
         [0063]    A ‘standard’ single layer liner had a thickness of 30 mm and consisted of expanded polystyrene foam with a density of about 60 kg/m 3 . 
         [0064]    A triple layer liner according to the invention had an average thickness of 30 mm (25 mm to 35 mm) and consisted of expanded polystyrene foam having an outer layer density of 60 kg/m 3 . The middle layer had bigger cones than the inner layer. The density of the cones of the middle layer at the front, back and sides was 55 kg/m 3 , whereas on the top the density was 40 kg/m 3 . The density of the cones of the inner layer at the front, back and sides was 45 kg/m 3 , whereas on the top the density was 40 kg/m 3  (the same as the corresponding cones of the middle layer). 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                   
                   
                   
                 Height 
                   
                   
               
               
                   
                   
                   
                   
                 above 
               
               
                   
                   
                   
                   
                 base of 
                 Standard Liner 
                 Triple Liner 
               
               
                 Ref 
                 Anvil 
                 Test 
                 Helmet 
                 Helmet 
                 Compression (mm) 
                 Compression (mm) 
               
             
          
           
               
                 No. 
                 Shape 
                 Conditions 
                 Angle 
                 (mm) 
                 Test 1 
                 Test 2 
                 Test 1 
                 Test 2 
               
               
                   
               
             
          
           
               
                 1 
                 Flat 
                 Ambient 
                  0 
                 300 
                 21.6 
                 21.7 
                 27.3 
                 27.6 
               
               
                 2 
                 Flat 
                 Hot 
                 180 
                 140 
                 15.0 
                 14.3 
                 17.8 
                 18.1 
               
               
                 3 
                 Hemispherical 
                 Cold 
                 Right 
                 160 
                 23.4 
                 23.5 
                 26.0 
                 26.1 
               
               
                   
                   
                   
                 125 
               
               
                 4 
                 Flat 
                 Wet 
                 Right 
                 180 
                 20.2 
                 19.4 
                 23.0 
                 22.5 
               
               
                   
                   
                   
                 120 
               
               
                   
               
             
          
         
       
     
         [0065]    The helmet angle is the rotational position of the impact, with respect to the anvil; front being 0°, rear being 180° and so on. The test helmet in which the comparative liners were tested at a standard impact, and included a dummy head of appropriate size and mass (about 5 kg in total). Impacts were in each case translational. For impacts where the helmet was dropped onto a flat steel anvil, the drop height was 1.92 m and for impacts onto hemispherical anvil, the drop height was 1.43 m. 
         [0066]    It may be seen by comparison that the triple layer liner according to the invention provided a substantial percentage improvement (i.e. increased compression) over a single layer liner of the same thickness. 
         [0067]    The comparative g-forces measured during the tests exemplified in Table 1 are as follows: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Ref  
                 Standard Liner 
                 Triple Liner 
               
             
          
           
               
                 No. 
                 Test 1 
                 Test 2 
                 Test 1 
                 Test 2 
               
               
                   
               
             
          
           
               
                 1 
                 151.6 
                 163.8 
                 126.7 
                 134.4 
               
               
                 2 
                 94.1 
                 98.2 
                 79.6 
                 78.3 
               
               
                 3 
                 100.5 
                 97.7 
                 84.2 
                 86.9 
               
               
                 4 
                 181.5 
                 202.3 
                 140.7 
                 166.1 
               
               
                   
               
             
          
         
       
     
         [0068]    The substantial reduction in measured g-force can be clearly seen, and hence the effectiveness of the triple layer liner of the invention. 
         [0069]    A comparative table of the mass of the respective helmets under test now follows: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Test 
                 Standard Liner 
                 Triple Inner 
               
               
                 Conditions 
                 (g) 
                 (g) 
               
               
                   
               
             
             
               
                 Ambient 
                 275 
                 224 
               
               
                 Hot 
                 277 
                 225 
               
               
                 Cold 
                 277 
                 227 
               
               
                 Wet 
                 280 
                 227 
               
               
                   
               
             
          
         
       
     
         [0070]    This comparison clearly shows that the triple layer liner of the invention results in a lighter helmet, typically around 18% less mass. 
         [0071]    By way of illustration an alternative triple layer liner of expanded polystyrene foam could have the following density characteristics: 
         [0072]    Outer layer: uniform 70 kg/m 3    
         [0073]    Middle layer: top 50 kg/m 3 ; front 55 kg/m 3 ; back 60 kg/m 3 ; side 65 kg/m 3 ; 
         [0074]    Inner layer: top 30 kg/m 3 ; front 35 kg/m 3 ; back 40 kg/m 3 ; side 45 kg/m 3 . 
         [0075]    Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiments, it is recognized that departures can be made within the scope of the invention, which are not to be limited to the details described herein but are to be accorded the full scope of the appended claims so as to embrace any and all equivalent assemblies, devices and apparatus.