Patent Publication Number: US-8966670-B2

Title: Sports safety helmet

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119 of the earlier filing date of United Kingdom application Ser. No. UK 1011598.8, filed Jul. 9, 2010. The aforementioned patent application is expressly incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     This invention relates to improvements in the design of safety helmets for sports such as snowboarding, skiing, motorcycling, cycling, equestrian sports and skating. 
     BACKGROUND OF THE INVENTION 
     It is known for protective head gear to be worn by people undertaking sports where there is a risk of impact to the head. A range of helmets are produced, usually with a specific sport in mind. For snow sports such as skiing and snow boarding there are two main types of protective helmet. The first of these uses an injection moulded acryonitrile butadiene styrene (ABS) shell having a glued-in liner of expanded polystyrene (EPS). Using ABS provides a strong shell, and this kind of helmet is relatively inexpensive. However, ABS is heavy as well as durable. It is known that heavier helmets can increase the risk of injury to the wearer&#39;s head and neck, particularly when it comes to rotational injuries. 
     A lighter form of helmet can be made by using a vacuum formed polycarbonate (PC) shell. It is also known to line a PC shell with injected EPS, forming a bonded lining. Bonding a liner to a helmet shell in this way improves the structure of the helmet and increases strength. However, while PC can be used to form a lighter shell than ABS, it is not as durable and can be more easily damaged on impact. 
     What is required is a helmet with an improved strength to weight ratio; that is one having optimum structural strength and impact resistance while being as light as possible. Such a helmet should also meet appropriate safety standards and be inexpensive to produce. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a safety helmet comprising an outer shell and an inner shell, wherein the outer shell comprises a crown of thermoplastic polymer and a skirt substantially of thermoplastic polymer. Preferably, the crown is of polycarbonate. Preferably, the skirt is of acrylonitrile butadiene styrene. The inner shell may comprise a liner of expanded polystyrene, co-moulded with the outer shell. Preferably, the inner shell is co-moulded with both the crown and the skirt of the outer shell. 
     In a further embodiment, the crown has a return edge, which may be continuous, and which may comprise an in-turned flange. The skirt may also have a return edge, which again may be continuous. The crown and/or the skirt may have air vents, and the helmet may have a brim and/or a chin strap. 
     A return edge improves bonding and location of the crown and/or skirt with the EPS liner, and also provides a neat external appearance. The return edge of one of the crown and skirt may provide form locking with the other. 
     There are numerous advantages to a helmet having an outer shell comprising the above combination of PC and ABS. As previously stated, ABS is stronger and more impact resistant than PC, so is used at structurally weaker areas around the helmet skirt. The structurally stronger crown of the helmet does not need to be made from ABS, so the lighter PC may be used. The strength of the outer shell is improved by co-moulding the EPS liner to both the PC and the ABS. 
     Another advantage to the PC/ABS combination is cost reduction. Injection-moulding is more expensive than vacuum-forming, so keeping the amount of ABS used to a minimum reduces mould cost. Yet another advantage is that of weight—using PC where possible keeps the weight of the helmet low, and thus may decrease damage to the wearer&#39;s head and neck in the event of a rotational injury. Yet a further advantage is that of size reduction. Bulky safety helmets can be seen as unfashionable, leading to low use of helmets, particularly amongst participants in image-conscious snow sports. Co-moulding the inner shell to the outer shell improves the strength of the outer shell such that it may be thinner, improving the appearance of the helmet and thus making it more desirable to potential wearers. Normally, injection moulded shells are more than 3 mm thick. Due to the additional strength provided by the co-moulding process, the thickness of the injection-moulded portion can be reduced to less than 3 mm. 
     There is also provided a method of making a safety helmet comprising the steps of
         a) vacuum forming a crown of thermoplastic polymer;   b) injection moulding a skirt of thermoplastic polymer;   c) placing the crown and skirt in a pre-determined relative position; and   d) in-moulding a lining of expanded polystyrene.       

     This method has the advantage of retaining the crown and the skirt in a fixed relationship. A further advantage can be achieved by fixing the return edges of the crown and skirt, for example by interlocking, prior to in-moulding of the liner, as this would provide location features for positioning in step c). 
     As with the materials, there are advantages to the methods of manufacture used. Injection-moulding is used to create a stronger, more impact resistant area around the skirt, whilst vacuum-forming can be used to create the structurally stronger crown of the helmet. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Other features of the invention will be apparent from the following description of a preferred embodiment of the invention, shown by way of example in the accompanying drawings in which: 
         FIG. 1  shows a perspective view of a helmet according to the present invention; 
         FIG. 2  shows a rear perspective view of the embodiment of  FIG. 1 ; and 
         FIG. 3  shows a cross-sectional view of the embodiment of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, a helmet  10  comprises an outer shell  12  and an inner shell  14 . The outer shell  12  has an upturned-bowl shaped crown  16  and a skirt  18  descending from the edge of the crown  16 . In use, the skirt  18  covers the wearer&#39;s temples, protrudes down the cheeks to the jaw line, and extends around the back of the wearer&#39;s head, covering roughly two thirds of the periphery of the crown. The skirt  18  is preferably slightly concave, following the shape of the wearer&#39;s head. The skirt  18  and the crown  16  fit together to form a substantially continuous convex surface. 
     The outer shell  12  has six air vents  20  positioned in two rows of three on either side of the top of the crown  16 . The air vents  20  are adjustable, and can be opened or closed by a sliding mechanism  22  positioned towards the centre rear of the crown  16 , A goggle strap holder  24  is attached to the rear of the outer shell  12  below the sliding mechanism  22 . In this embodiment, the helmet  10  comprises a brim  26  at the front of the crown  16 . The brim  26  has air vents  28  positioned along the join of the brim  26  and the crown  16 . 
     The skirt  18  comprises two side panels  30  of less than 3 mm thick injection-moulded acrylonitrile butadiene styrene (ABS), one positioned on either side of the helmet  10 . Each side panel  30  has an ear vent  32 . The crown  16  and the remaining parts of the skirt  18  are 2 mm thick vacuum-formed polycarbonate (PC). 
     The inner shell  14  is an expanded polystyrene (EPS) liner  34 , of thickness ranging from 15 mm to 25 mm, co-moulded to the outer shell  12  during manufacture. The liner  34  is thickest at the crown  16  (see  FIG. 3 ). The thickness of the liner  34  is increased at the crown  16  in order to allow impact energy to be absorbed. The liner  34  has air vents (not shown) aligned with the air vents  20  of the outer shell  12 . 
       FIG. 3  shows a cross-sectional view through a part of the helmet  10 . The arrangement of the crown  16 , skirt  18  and liner  34  is clearly shown, The crown  16  comprises a return edge  36  extending into the liner  34  substantially orthogonal to the crown. The return edge  36  has a rim  38  which extends downwardly into the liner  34 , substantially orthogonal to the return edge  36 . The skirt  18  also comprises a return edge  40 , which extends beneath the lower edge of the liner  34  substantially orthogonal to the skirt  18 . The return edge  40  does not extend fully over the bottom of the liner  34 , so that no sharp edge comes into contact with the wearer. 
     The method of manufacture of the helmet  10  involves vacuum forming the PC crown  16  and injection moulding the ABS side panels  30 . The outer shell parts are placed in the required position in a mould (not shown), which is then closed. EPS is injected into the mould to form the liner  34 . Apertures are left for the fitting of any chin straps or other features. 
     This method is advantageous in that the liner is used to retain the parts of the outer shell in a fixed relationship. The edges of the outer shell parts can be designed to interlock to strengthen that relationship. 
     Further advantages of the invention include that the crown return edge  36  provides a seat for the skirt  18 . The skirt return edge  40  prevents damage to the liner  34  when the helmet  10  is not being worn, for example damage caused by placing the helmet  10  on a rough surface. As the ABS side panels  30  are injection moulded, their thickness may be varied, allowing an optimum protection/weight ratio to be achieved. Material can be added at areas where most protection is required, but need not be added over the whole of a panel. Fixings for chin straps can be moulded in to the strong ABS. Contrasting colours of PC and ABS may be used to create a distinctive design. 
     In further embodiments of the invention the skirt may comprise a single panel of injection-moulded ABS extending around the helmet, or the whole of the skirt  18  may be ABS. Alternatively, more than two ABS panels may be included in the skirt. The helmet may have a chinstrap. The return edges  36 ,  40  may provide form-locking of the crown and skirt so that the strength of the outer shell is improved and the parts may be easily located during manufacture.