Patent Publication Number: US-2018049505-A1

Title: Helmet Retention System

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/137,700, filed Mar. 24, 2015, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention, according to some embodiments, relates to a dual chin strap retention system and helmet liner that may be positioned into an interior region of a helmet. 
     BACKGROUND OF THE INVENTION 
     Helmets for head protection are worn in a variety of environments and for various purposes. Helmets are often secured to a wearer&#39;s head by a flexible chin strap. The chin strap may include multiple segments of flexible strap material that are secured at either side of the helmet and pass below the chin, where the segments are releasably joined. In some helmets the strap segments on either side of the helmet are attached to the helmet at two positions, in front of and behind the wearer&#39;s ear. When joined, the two strap segments form a single strap that may be adjusted in length. 
     Conventional helmet straps may be difficult to adjust. If only a single strap is provided on each side of the helmet, for example, the adjustment can be made at the buckle where the straps are joined. If the chin strap has connections at two positions on each side of the helmet, however, the two separate strap segments each need adjustment for length, but generally have no convenient buckle or termination to accommodate such adjustment. A typical approach for adjusting the length of these strap segments is to fix one end of the strap and loop the free end through a buckle or loop, returning it to a ladder-lock adjustment mechanism positioned along the length of strap. By pushing more or less of the free end through the ladder lock, the length of a strap segment is altered. The geometry of this solution dictates that for each inch of length adjustment, the free end must move two inches. The free strap end that extends beyond the ladder lock may be secured with an additional component such as a clasp, or in some designs the wearer can adjust the position of the ladder lock along the strap segment to minimize the length of the exposed strap. In any case, the result is that adjusting the length of helmet straps is neither fast nor convenient and may require removing the helmet and making multiple adjustments, repositioning the ladder lock, and trying the helmet again for proper fit. 
     While adjustment theoretically is needed only when the helmet is first acquired, in practice the wearer may wish to adjust the tightness of the straps according to circumstances. In active situations, for example, especially if additional accessories such as night-vision goggles are attached to the helmet, the wearer may wish the straps to be tighter than normally required. 
     A current liner system for helmets includes a plurality of separate impact-absorbing foam pads that are positioned in the interior of a helmet. An example of such a system is the Zorbium® Action Pad (ZAP™) system available from Team Wendy®. One drawback of such systems is that the foam pads comprise foam blocks that do not generally match the geometry of the wearer&#39;s head, leading to discomfort or instability of the helmet on the wearer&#39;s head. A wearer may remove one or more the foam pads in order to improve fit and comfort, however, removal of the foam pads eliminates the impact protection from that portion of the helmet. Another drawback of these systems is that the materials used in the foam pads (e.g., Zorbium® polyurethane foam) absorb water. This can lead to increased weight on the wearer&#39;s head and greater discomfort. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one embodiment, a retention system for a helmet includes a horizontal chin strap and a vertical chin strap. The horizontal chin strap may include a center horizontal chin strap portion, and at least one mounting strap for affixing the mounting strap to a helmet. The mounting strap may have at least one hole by which the mounting strap is configured to be affixed to the helmet. The center portion of the horizontal chin strap may include a first central horizontal chin strap portion, a second central horizontal chin strap portion, and a first fastener for reversibly coupling the first central horizontal chin strap and the second central horizontal chin strap. The vertical chin strap may include a center portion, a loop through which the center portion of the vertical chin strap passes through; and at least one forward strap for affixing the forward strap to a helmet. The forward strap may have at least one hole by which the mounting strap is configured to be affixed to the helmet. The center portion of the vertical chin strap may include a second fastener for reversibly coupling a first end of the center portion of the vertical chin strap to a body of the center portion of the vertical chin strap. In some embodiments the vertical chin strap is secured to the horizontal chin strap at one or more points (e.g. two points) of intersection. 
     In some embodiments, the vertical chin strap further includes a buckle, for example a double D-ring buckle, configured to adjust the length of the vertical chin strap between the two points of intersection with the horizontal chin strap. 
     In some embodiments the first fastener includes a first fastener pile mounted to a surface of the first central horizontal chin strap and a second fastener pile mounted to a surface of the second central horizontal chin strap, wherein the fastener piles are configured to provide a separable interconnection when pressed together. One of the first fastener pile and the second fastener pile may include a plurality of hooks and the other of the first fastener pile and the second fastener pile may include a plurality of loops. 
     In some embodiments the forward strap and center portion of the vertical chin strap are coupled to the loop such that the vertical strap is substantially linear. In some embodiments, the forward strap is coupled to the loop such that the forward strap and mounting strap are substantially perpendicular. 
     According to another embodiment, a retention system for a helmet includes a horizontal chin strap and a vertical chin strap. In some embodiments the horizontal chin strap is secured to the vertical chin strap at one or more points (e.g. two points) of intersection. The horizontal chin strap may include a center portion, a loop through which the center portion of the horizontal chin strap passes through; and at least one mounting strap having at least one hole for affixing the forward strap to a helmet. The center portion of the horizontal chin strap may include a second fastener for reversibly coupling a first end of the center portion of the horizontal chin strap to a body of the center portion of the horizontal chin strap. The vertical chin strap may include a center vertical chin strap portion, and at least one mounting strap having at least one hole for affixing the mounting strap to a helmet. The center portion of the vertical chin strap may include a first central vertical chin strap portion, a second central vertical chin strap portion, and a first fastener for reversibly coupling the first central vertical chin strap and the second central vertical chin strap. 
     According to another embodiment, a retention system for a helmet includes a horizontal chin strap and a vertical chin strap. In some embodiments the horizontal chin strap is secured to the vertical chin strap at one or more points of intersection. The horizontal chin strap may include a center horizontal chin strap portion, and at least one mounting strap having at least one hole for affixing the mounting strap to a helmet. The center portion of the horizontal chin strap may include a first central horizontal chin strap portion, a second central horizontal chin strap portion, and a first fastener for reversibly coupling the first central horizontal chin strap and the second central horizontal chin strap. The vertical chin strap may include a center vertical chin strap portion, and at least one mounting strap having at least one hole for affixing the mounting strap to a helmet. The center portion of the vertical chin strap may include a first central vertical chin strap portion, a second central vertical chin strap portion, and a first fastener for reversibly coupling the first central vertical chin strap and the second central vertical chin strap. 
     According to an embodiment, a retention system for a helmet includes an adjustable nape assembly, which includes a semi-rigid shell sized and configured to fit within an interior of a helmet and around a portion of a wearer&#39;s head, the liner body comprising a body and two legs and having an outer surface and an inner surface; a pad comprising a body and two legs attached to the interior surface of the semi-rigid shell so that the pad body and pad legs are generally aligned with the semi-rigid shell body and semi-rigid shell legs; an adjustment strap having a first end attached to a semi-rigid shell leg and a second end portion having a mount point for attaching the adjustment strap to an interior of a helmet; and a buckle capable of adjusting the length of the strap between the pad leg and mount point. 
     In some embodiments an upper portion of the semi-rigid shell extends beyond the pad body and has a mount point for mounting the semi-rigid shell to a helmet. In some embodiments the semi-rigid shell comprises expanded polypropylene. In some embodiments the pad comprises a foam material enclosed in fabric. In some embodiments the semi-rigid shell comprises a flexible joint between each of the semi-rigid shell legs and the semi-rigid shell body. 
     According to an embodiment, a retention system for a helmet includes a horizontal chin strap and a vertical chin strap and an adjustable nape assembly including a semi-rigid shell sized and configured to fit within an interior of a helmet and around a portion of a wearer&#39;s head, the liner body comprising a body and two legs and having an outer surface and an inner surface; a pad comprising a body and two legs attached to the interior surface of the semi-rigid shell so that the pad body and pad legs are generally aligned with the semi-rigid shell body and semi-rigid shell legs; an adjustment strap having a first end attached to a semi-rigid shell leg and a second end portion having a mount point for attaching the adjustment strap to an interior of a helmet; and a buckle capable of adjusting the length of the strap between the pad leg and mount point. The horizontal chin strap may include a center horizontal chin strap portion, and at least one mounting strap having at least one hole for affixing the mounting strap to a helmet. The center portion of the horizontal chin strap may include a first central horizontal chin strap portion, a second central horizontal chin strap portion, and a first fastener for reversibly coupling the first central horizontal chin strap and the second central horizontal chin strap. The vertical chin strap may include a center portion, a loop through which the center portion of the vertical chin strap passes through; and at least one forward strap having at least one hole for affixing the forward strap to a helmet. The center portion of the vertical chin strap may include a second fastener for reversibly coupling a first end of the center portion of the vertical chin strap to a body of the center portion of the vertical chin strap. In some embodiments the vertical chin strap is secured to the horizontal chin strap at least one point of intersection. 
     According to an embodiment, a kit includes a retention system for a helmet, an adjustable nape assembly, or both a retention system for a helmet and an adjustable nape assembly and a helmet. The helmet may be an advanced combat helmet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of embodiments of the helmet retention system, will be better understood when read in conjunction with the appended drawings of an exemplary embodiment. It should be understood, however, that the invention can be embodied in different forms and thus should not be construed as being limited to the embodiments set forth herein. 
         FIG. 1  is a front, right side perspective view of a helmet retention system in accordance with an embodiment of the invention shown attached to a helmet and on a mannequin; 
         FIG. 2  is a front, left side perspective view of the helmet retention system of  FIG. 1 ; 
         FIG. 3  is a left side elevational view of the helmet retention system of  FIG. 1 ; 
         FIG. 4  is a left side elevational view of the helmet retention system of  FIG. 1  shown with the helmet shell in phantom; 
         FIG. 5  is a rear, right side perspective view of the helmet retention system of  FIG. 1  shown with the helmet shell in phantom; 
         FIG. 6  is a plan view of an assembled chin strap assembly of the helmet retention system of  FIG. 1 ; 
         FIG. 7  is a partially exploded plan view of the assembled chin strap assembly of  FIG. 6 ; 
         FIG. 8A  is a plan view of a portion of the chin strap assembly of  FIG. 6 ; 
         FIG. 8B  is a side elevational view of the portion of the chin strap assembly shown in  FIG. 8A ; 
         FIG. 9A  a plan view of a portion of the chin strap assembly of  FIG. 6 ; 
         FIG. 9B  is a side elevational view of the portion of the chin strap assembly shown in  FIG. 9A ; 
         FIG. 9C  is a perspective view of the portion of the chin strap assembly shown in  FIG. 9A ; 
         FIG. 10  is a front perspective view of a nape assembly of the helmet retention system of  FIG. 1 ; 
         FIG. 11  is a rear perspective view of the nape assembly of the helmet retention system of  FIG. 1 ; and 
         FIG. 12  is an exploded view of the nape assembly of the helmet retention system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present subject matter will now be described more fully hereinafter with reference to the accompanying Figures, in which representative embodiments are shown. The present subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to describe and enable one of skill in the art. 
     Referring to the drawings in detail, wherein like reference numerals indicate like elements throughout, there is shown in  FIGS. 1-12 , a helmet retention system, generally designated  10 , in accordance with an exemplary embodiment of the present invention. The helmet retention system may include a chin strap assembly  100  and a nape assembly  200  (see  FIG. 5 ). 
     Referring to  FIG. 1 , in certain embodiments of the present invention, chin strap assembly  100  is configured to be mounted to an interior of a head protection device, such as a helmet  103 . More particularly, chin strap assembly  100  in some embodiments is configured to be worn across a wearer&#39;s chin and secure helmet  103  to a wearer&#39;s head during use. In some embodiments chin strap assembly  100  provides helmet lift and pitch constraint to the wearer, for example, by providing adjustable, vertical and horizontal, straight-line paths from the wearer&#39;s chin directly to hard-mount, connection points near the brow area, and near the bottom edges of the helmet shell. Helmet  103  may be any type of head protection helmet known in the art, for example, those used for sporting, police, or military purposes. In certain embodiments, helmet  103  is a standard infantry ballistic helmet. In some embodiments, helmet  103  is an advanced combat helmet (ACH). 
     Referring to  FIGS. 6 and 7 , in some embodiments a chin strap assembly  100  includes a horizontal chin strap  105  and a vertical chin strap  110 , wherein the vertical chin strap  110  is secured to the horizontal chin strap  105  at two points of intersection  140 . In some embodiments the vertical chin strap  110  is oriented approximately perpendicular to the horizontal chin strap at each point of intersection. In other embodiments, the angle α between the vertical chin strap and the horizontal chin strap is about 85°, about 80°, about 75°, about 70°, about 65°, or about 60°. In other embodiments, the angle α between the vertical chin strap and the horizontal chin strap is between about 90° and about 80°, between about 85° and about 75°, between about 80° and about 70°, between about 75° and about 65°, between about 73° and about 67°, or between about 70° and about 60°. In some embodiments, the vertical chin strap  110  and horizontal chin strap  105  are permanently-fixed together where they intersect  140 . When worn by a user, intersection  140  may be aligned with the user&#39;s jaw hinge, allowing a user to move his jaw freely or largely freely. When worn by a user to secure a helmet to the user&#39;s head, horizontal strap  105  may pass between the user&#39;s chin and lower lip, and the vertical strap  110  may pass between the user&#39;s chin and throat, as shown in  FIGS. 3 and 4 . 
     In some embodiments, the chin strap assembly  100  offers more freedom of movement and/or comfort than a conventional chin-cup retention system. In some embodiments, the chin strap assembly  100  allows a user to move his jaw more freely than a conventional chin-cup retention system. In some embodiments horizontal chin strap  105  and/or vertical chin strap  110  may include vinyl webbing. Still referring to  FIGS. 6 and 7 , in some embodiments vertical chin strap  110  includes center portion  114 , forward strap  125  and mount strap  130 . In some embodiments center portion  114  includes a first end  112  and body  113 . In some embodiments the horizontal chin strap  105  and/or the vertical chin strap  110  includes a mount point  151 , which may fasten the chin strap to a helmet  103  at connection point  153 . The horizontal chin strap  105  may comprise a mount strap  130 , wherein the mount strap  130  includes a mount point  151 . In some embodiments the vertical chin strap  110  comprises a forward strap  125 , wherein the forward strap includes a mount point  151 . In some embodiments, helmet mount point  151  may be removeably attached to helmet  103 , for example by button, clamps, straps, buttons, snap fasteners, latches, hook-and-loop, hook-and-pile, or other mechanical fasteners. In other embodiments, adhesives are used, for example, adhesive tapes, pressure-sensitive adhesives, or putty-like adhesives (e.g., Blu Tack). In still other embodiments a chin strap assembly  100  is attached to a helmet  103  via a bolt, screw (e.g. a screw and T-nut), nail, or pin. 
     Referring to  FIGS. 6 and 7 , in some embodiments a vertical chin strap  110  comprises a forward strap  125 , a vertical chin strap center portion  114 , and a second fastener  135 . In some embodiments the second fastener  135  is configured to adjust the length of the vertical chin strap  110  (e.g. the length of the vertical chin strap center portion  114 ) extending between the two points of intersection  140  with the horizontal chin strap  105 . The second fastener  135  may be any reversible coupling mechanism (e.g. snap, button, buckle, clip, double D-ring, hook and loop, etc.). In some embodiments the vertical chin strap  110  comprises a plurality of second fasteners  135 , such that the length of the vertical chin strap  110  extending between the two intersection points  140  is capable of being adjusted by changing which of the plurality of second fasteners  135  is employed. In a preferred embodiment second fastener  135  is a buckle or a double D-ring. In some embodiments a double D-ring may include a first ring having another smaller ring extending from the outer periphery. In one embodiment, each ring has a flat portion forming the ring into a capital D shape, while in other embodiments one or both rings may be O-shaped. In one embodiment, the second smaller ring is at an obtuse angle relative to the larger ring (see  FIG. 9C ). Having the rings bent relative to one another may allow for a user to more easily grasp the second ring. In other embodiments a double D ring may include two equally sized rings, each ring having a flat portion forming the ring into a capital D shape, while in other embodiments, one or both rings may be O-shaped. In other embodiments a double D ring may include a ring having a flat portion forming the ring into a capital D shape with a rectangular loop extending from the flat portion of the capital D shaped ring. Referring to  FIG. 5 , fastener  135  may couple forward strap  125  with vertical chin strap center portion  114  to form a substantially straight line. Referring to  FIGS. 3 and 4 , fastener  137  may couple forward strap  125  with vertical chin strap center portion  114  to form a substantially straight line. 
     A horizontal chin strap  105  and/or a vertical chin  110  strap may have a length between first and second intersection points  140  that may be adjusted. Referring now to  FIG. 7 , in some embodiments, horizontal chin strap  105  includes a first horizontal strap portion  107 , a second horizontal strap portion  108 , and a first fastener  109  for reversibly coupling the first horizontal chin strap portion  107  and the second horizontal chin strap portion  108 . The first fastener may be any reversible coupling mechanism (e.g. snap, button, buckle, clip, double D-ring, hook and loop, etc.) capable of reversibly coupling the first horizontal strap portion  107  to the second horizontal strap portion  108 . The first fastener may comprise a first fastener pile (e.g. one of hooks or loops) mounted to a surface of the first horizontal chin strap portion  107  and a second fastener pile (e.g. the other of hooks or loops) mounted to a surface of the second horizontal chin strap portion  108 , wherein the fastener piles are configured to provide a separable interconnection when pressed together. In some embodiments, the horizontal chin strap  105  is mounted to the bottom edge of the helmet shell, as far aft and horizontal as possible (e.g., see  FIG. 4 ) to maximize helmet stability. The horizontal chin strap  105  may be length-adjustable through a set of overlapping, hook &amp; pile interlocking, attachment straps. 
     Referring to  FIGS. 6 and 7 , in some embodiments a vertical chin strap  110  comprises vertical chin strap center portion  114  having a first end  112  and a body  113 . In some embodiments the vertical chin strap further comprises a third fastener  120  for reversibly coupling first end  112  to body  113  of the vertical chin strap center portion  114 . The third fastener  120  may be any reversible coupling mechanism (e.g. snap, button, buckle, clip, hook and loop, etc.) capable of reversibly coupling the first end  112  to the body  113  of the vertical chin strap center portion  114 . The third fastener  120  may include a quick-disconnect component (e.g. a two point quick-release fastener, or a single-point quick-release fastener) such as a snap. 
     The vertical chin strap  110  may further include a loop  137  through which the vertical chin strap center portion  114  passes through. In some embodiments loop  137  may couple the vertical chin strap center portion  114  with forward strap  125 . Loop  137  may couple the vertical chin strap center portion  114 , with forward strap  125  and mounting strap  130 . When vertical chin strap center portion  114 , forward strap  125 , and mounting strap  130  are coupled by loop  137 , each may be slideably moveable relative to the others. While worn by a user to retain a helmet to the user&#39;s head, the forward straps  125  and vertical chin strap center portion  114  may align to form a generally straight line. While worn by a user to retain a helmet to the user&#39;s head, the mounting strap  130  may be oriented approximately perpendicular to the forward strap  125 . In some embodiments, mounting strap  130  is oriented about 60°, 65°, 70°, 75°, 80°, or 85° from forward strap  125 . In some embodiments, mounting strap is oriented about 95°, 100°, 105°, 110°, 115°, or 120° from forward strap  125 . In some embodiments, mounting strap  130  is oriented in a range of from about 85° to about 95°, about 80° to about 100°, or about 75° to about 105°. 
     In some embodiments one side of the vertical chin strap  110  (e.g. center portion  114 ) is adjustable through a set of double D rings. In some embodiments the other side is constrained by a single D ring (e.g. loop  137 ) and a quick release snap (e.g. fastener  120 ). Such arrangement may allow the wearer to quickly attach and release both the horizontal chin strap  105  and the vertical chin strap  110  in one, single step. 
     Referring now to  FIG. 4 , the horizontal chin strap  105  may include one or more (e.g. 2, 3, 4, 5, 6, 7, or 8) helmet mount points  151 , any one of which can be used to fasten the vertical chin strap to a helmet  103  at connection point  153 . Horizontal chin strap  105  may include 5 helmet mount points  151 . In some embodiments the horizontal chin strap  105  includes a plurality of helmet mount points  151  to enable a wearer to adjust a length of horizontal chin strap between connection point  153  and intersection point  140 . The horizontal chin strap  105  may include a plurality of helmet mount points  151  so a wearer can adjust a length of horizontal chin strap between a connection point  153  to the helmet and intersection point  140 . In some embodiments a horizontal chin strap  105  includes a mounting point  151  that is a slot or elongated hole allowing for a continuously variable connection point position. In embodiments in which mounting point  151  includes a slot or elongated hole, the horizontal strap may be coupled to a helmet  103  by a tension buckle, for example. When being used to secure a helmet to a wearer&#39;s head, the horizontal chin strap  105  may provide a generally straight line path from the wearer&#39;s chin to a connection point  153  located near a bottom edge of the helmet. The vertical chin strap  110  may include one or more (e.g. 2, 3, 4, 5, 6, 7, or 8) helmet mount points  151 , any one of which can be used to fasten the vertical chin strap to a helmet  103  at a connection point  153 . Vertical chin strap  110  may include 3 helmet mount points  151 . In some embodiments the vertical chin strap  110  includes a plurality of helmet mount points  151  to enable a wearer to adjust a length of vertical chin strap  110  between a connection point  153  and intersection point  140 . In some embodiments a vertical chin strap  110  includes a mounting point  151  that is a slot or elongated hole allowing for a continuously variable connection point position. In embodiments in which mounting point  151  includes a slot or elongated hole, the vertical strap  110  may be coupled to a helmet  103  by a tension buckle, for example. When being used to secure a helmet to a wearer&#39;s head, the vertical chin strap  110  may provide a generally straight line path from the wearer&#39;s chin to a connection point  153  near the wearer&#39;s brow. In some embodiments the vertical chin strap  110  is mounted to a connection point  153  near the temple-area of the helmet shell. In some embodiments the vertical chin strap  110  is mounted to a connection point  153  as high-up and vertical as possible to maximize helmet stability. In preferred embodiments, multiple mounting points  151  (e.g. adjustment holes) are provided at the strap-to-helmet-shell connection points to ensure that both the vertical and horizontal chin straps remain in straight-line paths from the individual wearer&#39;s chin to the helmet-shell connection points. 
     It is to be understood that while the figures show loop  137  and third fastener  120  positioned on the left side of the user&#39;s face and second fastener  135  on the right side of the user&#39;s face, other arrangements are within the scope of the invention, for example loop  137  and third connection  120  may be located on the right side of the user&#39;s face and second fastener  135  may be located on the left side of the user&#39;s face. Similarly, while an embodiment having an adjustable horizontal chin strap and vertical chin strap has been described in detail, it is to be understood that alternative embodiments are within the scope of the invention, for example a vertical strap may be designed to be adjustable using a first and second vertical chin strap portions and a fastener (e.g. hook-and-loop or hook-and-pile) as the horizontal strap is described herein, and/or a horizontal chin strap may be designed to be adjustable using a buckle (e.g. a double D ring) and may include a quick release fastener, as the vertical chin strap is described herein. Such alternate embodiments are within the scope of the invention. 
     Retention systems according to some embodiments of the invention provide for increased adjustability over prior art helmet retention systems by allowing the position relative to the wearer&#39;s jaw of the intersection points of the horizontal and vertical straps, the length of the center portion of each of the horizontal and vertical chin straps, and the points of attachment to the helmet of each of the forward straps and mounting straps to be adjusted independently. Retention systems according to some embodiments of the invention further provide for ease of use over prior art helmet retention systems providing for a single release point (e.g. fastener  120 ) which upon release allows the helmet to be removed from the wearer without further adjustment to any components of the retention system. The single release point allows a user to adjust the helmet straps and connection points to best fit the helmet to the user&#39;s head and retain the fit (e.g. the length and position of the vertical and horizontal straps) as the user removes and re-dons the helmet without requiring further adjustment to the fit. Retention systems according to some embodiments of the invention provide for the intersection of the horizontal and vertical chin straps (e.g. intersection point  140 , or center of fastener  135  and/or  137 ) to be aligned with or aligned approximately with the hinge point of the user&#39;s jaw, allowing the user greater ability to articulate his jaw (e.g. to speak). When aligned with or aligned approximately with the hinge point of the user&#39;s jaw, the horizontal strap  105  may form an approximately straight line with the mounting strap from the user&#39;s chin to the mounting point. Similarly, when aligned with or aligned approximately with the hinge point of the user&#39;s jaw, the center portion of the vertical strap  114  may foam an approximately straight line with the mounting strap from the user&#39;s chin to the mounting point. Retention systems according to some embodiments of the invention provide greater stability than prior art retentions systems. For example, retentions systems according to some embodiments of the invention include mounting straps  130  that are mounted directly to the helmet  103  rather than to the nape assembly  200 . In another example, retention systems according to some embodiments of the invention provide intersection points of the vertical  105  and horizontal  110  straps in alignment or in approximate alignment with the user&#39;s jaw, providing increased stability. 
     Referring now to  FIGS. 5, and 10-12 , in some embodiments a liner or nape assembly  200  generally includes an impact liner  210  sized and configured to fit within an interior of a helmet and around a portion of a wearer&#39;s head. The nape assembly  200  may be pivotable with respect to the helmet  103  to allow the nape assembly  200  to move relative to the helmet  103 . In some embodiments, the nape assembly  200  includes a body  225  and two legs  230 . Impact liner  210  may have an interior surface with a generally or slightly concave shape to encourage a good fit against a user&#39;s head. Impact liner  210  may have an exterior surface with a generally or slightly convex shape to nest in a backing shell  205  and/or helmet  103 . In some embodiments liner assembly  200  further comprises a backing shell  205  sized and configured to fit within an interior of a helmet and around an outer surface of impact liner  210 . In some embodiments the backing shell includes a body  215 . In some embodiments the backing shell  205  includes two legs  220 . In some embodiments the impact liner is arranged with respect to the backing shell  205  such that impact liner body  225  is generally aligned with the backing shell body  215  and impact liner legs  230  are generally aligned with backing shell legs  220 . In such embodiments the shell  205  may cover substantially all of an outer surface area of the impact liner  210 . In other embodiments the shell  205  may cover a portion of an exterior surface area of the impact liner  210 . In some embodiments, backing shell  205  is constructed from a material that provides strength and flexibility such as a plastic (e.g. an injection molded plastic), aluminum, an aramid, etc. Backing shell  205  may be constructed from an aramid, e.g. Kevlar. In some embodiments, backing shell  205  is constructed of a material that may help with impact absorption. In some embodiments, backing shell  205  is composed of a material that is substantially rigid. In other embodiments, backing shell  205  may be elastic or flexible. Backing shell  205  may be semi-rigid. In some embodiments, backing shell  205  is of a single-piece construction, having a unitary or monolithic structure. Backing shell  205  may be articulated, having two or more rigid portions joined by one or more flexible joints. In some embodiments the backing shell body  215  has a unitary structure and is joined to backing shell legs  220  by a flexible joint. In other embodiments the backing shell body  215  and/or backing shell legs  220  are articulated. For example, a backing shell  205  that is constructed from a rigid material may have a plurality of joints or articulations to provide the backing shell  205  with flexibility. In some embodiments a backing shell  205  may include one or more living hinges (e.g. a thin, flexible hinge made from the same material as the two rigid pieces it connects). In some embodiments the backing shell  205  is coupled to the impact liner  210  by an adhesive patch  216 . In another embodiment, the nape assembly  200  may be coupled to the chin strap assembly  100 . 
     In some embodiments a modular, articulated backing shell  205  may provide helmet lift constraint. In some embodiments the modular, articulated, hard-shell comfortably provides helmet lift constraint, while the inboard-mounted impact liner material remains the dominant, rear impact attenuation contributor. 
     In some embodiments, the nape assembly  200  is sufficiently sized to extend from about the middle of the back of the head of the wearer (as shown in  FIG. 5 ) to about the nape of the neck of the wearer during use. In some embodiments nape assembly  200  extend from about the top of the user&#39;s head to about the nape of the neck of the user during use. In some embodiments, nape assembly  200  may cover the sides of a user&#39;s head during use. In some embodiments, impact liner body  225  includes an outer surface that is convexly contoured to generally match the interior curvature of helmet  203  and/or backing shell  205 . In one embodiment, impact liner body  225  is shaped such that it retains the same shape whether or not it is coupled to the backing shell  205 , helmet  203  and/or the user&#39;s head. In some embodiments, impact liner  210  is configured to entirely fit within the interior of backing shell  205  and/or helmet  203  and to not extend beyond the periphery of backing shell  205  and/or helmet  203  during use. In some embodiments, impact liner body  225  includes an interior surface  227  that is concavely contoured to fit around the wearer&#39;s head during use. In some embodiments, impact liner  210  and backing shell  205  are generally the same size. Backing shell  205  may be slightly smaller than impact liner  210 . In some embodiments, backing shell  205  covers a larger percentage of area of the impact liner towards the user&#39;s head than away from the user&#39;s head. In some embodiments, impact liner body  225  has a generally uniform thickness between the convex outer surface and the concave interior surface  227 . In some embodiments, the thickness of the impact liner  210  may generally relate to the thickness of a helmet liner. The thickness of the impact liner  210  may allow the liner to be generally flush with the rest of the helmet shell. In some embodiments, impact liner  210  has a thickness in a range from about 10 mm to about 20 mm, from about 12 mm to about 18 mm, or from about 14 mm to about 16 mm. In some embodiments, liner body  102  is at least 10 mm thick, at least 12 mm thick, at least 14 mm thick, at least 16 mm thick, at least 18 mm thick, or at least 20 mm thick. In some embodiments, impact liner  210  has a thickness less than 20 mm. 
     In some embodiments, impact liner  210  is configured to provide different levels of impact attenuation to different locations around the wearer&#39;s head. For example, impact liner body  225  may be configured to provide greater or lesser impact attenuation versus the left and right sides impact liner legs  230 . In some embodiments, different levels of impact attenuation can be achieved by having an impact liner  210  with different densities of the impact-absorbing material at the different locations. In some embodiments, impact liner  210  may include denser material at locations where greater impact attenuation is desired. In other embodiments, impact liner  210  may have a variable thickness, for example, such that impact liner  210  is thicker at portions where greater impact attenuation is desired. 
     In some embodiments, backing shell  205  comprises an upper portion  250  that extends beyond the exterior surface of the impact liner  210 , as shown in  FIGS. 10 and 11 . In some embodiments backing shell  205  comprises a helmet mount point  255  for attaching the backing shell to a helmet. In some embodiments the backing shell  205  is hard-mounted to the helmet. In some embodiments the backing shell  205  is hard mounted to the helmet near the top of an interior surface of the helmet. In some embodiments backing shell  205  may be hard mounted to the helmet by a screw, bolt, pin, or nail. In other embodiments, backing shell  205  may be removeably attached to helmet  203 , for example by button, clamps, straps, buttons, snap fasteners, latches, hook-and-loop, hook-and-pile, or other mechanical fasteners. In other embodiments, adhesives may be used, for example, adhesive tapes, epoxy, pressure-sensitive adhesives, or putty-like adhesives (e.g., Blu Tack). 
     Referring in particular to  FIG. 12 , in some embodiments a contact liner  211  may be affixed to an interior surface and/or bottom surface of impact liner  210 . In some embodiments, the contact liner  211  may provide reinforcement to the impact liner  210  (e.g. help provide cracking of the impact liner  210 ). In some embodiments, the contact liner  211  may be made of a sufficiently durable material that provides comfort to the user&#39;s nape. The contact liner may be made of moleskin. The contact liner  211  may be affixed to the interior and/or bottom surface of the impact liner  210  by an adhesive, for example, adhesive tapes, pressure sensitive adhesives, glues, or putty-like adhesives. In some preferred embodiments contact liner  211  is coupled to impact liner  210  using hook-and-loop or hook-and-pile fasteners. In some embodiments, contact liner  211  includes a contact liner body  212  and two contact liner legs  213 . In some embodiments contact liner body  212  and contact liner legs  213  form a single liner piece, while in other embodiments contact liner body  212  and contact liner legs  213  are separate pieces. In some embodiments the contact liner  211  is arranged with respect to the impact liner  210  such that contact liner body  212  is generally aligned with the impact liner body  225  and contact liner legs  213  are generally aligned with impact liner legs  230 . In such embodiments the contact liner  211  may cover substantially all of an interior surface area of the impact liner  210 . In other embodiments the contact liner  211  may cover a portion of an interior surface area of the impact liner  210 . In some preferred embodiments contact liner  211  is coupled to impact liner legs  230  and a portion of impact liner body  225  (e.g. a bottom portion of impact liner body  225 ). In some embodiments contact liner legs  213  comprise a fabric configured to provide comfort to a wearer, such as moleskin. In other embodiments, contact liner legs  213  each comprise an adhesive backed patch with a hook (e.g. Velcro™) face. The hook face may allow the comfort liner legs  113  to grip a helmet&#39;s cloth comfort liner in order to minimize bunching of the comfort liner when the wearer dons the helmet. 
     Referring to  FIG. 12 , in some embodiments, nape assembly  200  further comprises a double-sided adhesive patch  216 . The adhesive patch  216  may be provided to adhere the backing shell  205  to the impact liner  210 . In some embodiments, adhesive patch  216  is made of a para-aramid synthetic fiber such as Kevlar. 
     Referring now to  FIGS. 10 and 11 , in some embodiments liner assembly  200  further comprises an adjustment strap  235  having a first end  237  attached to a backing shell leg  220  and a second end portion  239  having a liner assembly mount point  240  for attaching the adjustment strap  235  to an interior surface of a helmet. In some embodiments the liner assembly  200  also includes a buckle  245  that is capable of adjusting the length of the adjustment strap  235  between the backing shell leg  220  and liner assembly mount point  240 . In some embodiments adjustment strap  235  may be hard mounted to the helmet by a screw, bolt, pin, or nail. In other embodiments, adjustment strap  235  may be removeably attached to helmet  203 , for example by button, clamps, straps, buttons, snap fasteners, latches, hook-and-loop, hook-and-pile, or other mechanical fasteners. In other embodiments, adhesives may be used, for example, epoxy, adhesive tapes, pressure-sensitive adhesives, or putty-like adhesives (e.g., Blu Tack). In some embodiments the adjustment straps are hard mounted to points on a bottom edge of the helmet shell. The adjustment strap mount point may be low and far forward on the helmet shell. In some embodiments, when the adjustment strap and the horizontal chin strap are both attached to the helmet, the adjustment strap may cross the horizontal chinstrap (e.g. the connection point  253  where the horizontal chinstrap is attached to the helmet may be lower than the point where the adjustment strap is connected to the impact liner leg  230  or backing shell leg  220 , while the adjustment strap attachment point  240  is lower than the point where the horizontal chin strap  205  is attached to loop  237 ). In some embodiments the entire liner assembly is free to hinge and/or flex, allowing it to wrap around the user&#39;s occipital lobe as the adjustment straps are pulled taut. For example, in embodiments where the liner assembly  200  is mounted to the helmet  103  at a single point  255 , the fit of the liner assembly to the back of the user&#39;s head may be adjusted by adjusting the length of straps  235 , for example by adjusting buckle  245 , or by adjusting the point at which the strap  235  is mounted to the helmet  103 . 
     Referring now to  FIG. 5 , in some embodiments a retention system comprises a chin strap assembly  100  as described herein and a liner assembly  200  as described herein. In some embodiments a helmet retention system that includes both a dual chinstrap assembly  100  and an articulated, hard-shell backed impact liner assembly  200  may provide a comfortable, stable, adjustable, impact-tolerant method of constraining a helmet to a user&#39;s head. 
     In some embodiments, chin strap assembly  100  and liner assembly  200  may each be supplied alone, may be supplied together as a retention system, or may be supplied as a kit together with helmet  103 . In some embodiments, chinstrap assembly  100  and liner assembly  200  are supplied together as a kit, with or without helmet  103 . 
     It will be appreciated by those skilled in the art that changes could be made to the exemplary embodiments shown and described above without departing from the broad inventive concepts thereof. It is understood, therefore, that this invention is not limited to the exemplary embodiments shown and described, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the claims. For example, specific features of the exemplary embodiments may or may not be part of the claimed invention and various features of the disclosed embodiments may be combined. Unless specifically set forth herein, the terms “a,” “an,” and “the” are not limited to one element but instead should be read as meaning “at least one.” 
     It is to be understood that at least some of the figures and descriptions of the invention have been simplified to focus on elements that are relevant for a clear understanding of the invention, while eliminating, for purposes of clarity, other elements that those of ordinary skill in the art will appreciate may also comprise a portion of the invention. However, because such elements are well known in the art, and because they do not necessarily facilitate a better understanding of the invention, a description of such elements is not provided herein.