Abstract:
A protective helmet of the type used in football has an external soft elastomer layer to absorb/dissipate some of the energy of an impact. Other features include a quick disconnect face guard, carbon fiber face guard with Kevlar wrap at junction points, a soft foam inner shell inside the intermediate hardened shell, and a head fitting structure including a plurality of pads, visco-elastic cells and at least one inflatable bladder. In addition, the hardened shell may be formed as a lattice frame of strips having a plurality of fibers impregnated with resin. The resin may have a dye added that will indicate if and where an impact exceeding a predetermined value is incurred by the helmet to assist a physician in diagnosing a possible head trauma injury.

Description:
BACKGROUND 
   The present invention is directed to the field of sporting goods. More particularly, the present invention is directed to a helmet, such as a football helmet, with enhanced protection performance characteristics. The present application claims priority of provisional patent application Ser. No. 60/545,676 filed Feb. 17, 2004. 

   Over the course of many years, protective helmets have evolved for use in sporting activities and other pursuits for which there is a risk of head injury, including football, hockey, baseball, softball, lacrosse, roller skating, skate boarding, cycling, motorcycling, automobile racing, snowmobiling, skiing, horseback riding, climbing, construction work, police activities, firefighting, and military activities. Using football as an example, early helmets were made of sewn leather. Helmets evolved to molded plastic outer shells with suspension webbing on their interior. Later, the suspension webbing was replaced with other head fitting structures such as foam fit pads of various types, air filled bladders, and padding molded to fit a particular user&#39;s head. Variations of these concepts are used for protective helmets to the present day. The functions of these helmets is to absorb as much of the energy transmitted to the helmet by impact with another object, whether the object is equipment worn or used by another person, a body part of another person, the ground, or a structural object, as well as to deflect, to the extent possible, impacts which occur at an oblique angle to the helmet. The purpose of these helmets is to diminish the risk of head and brain injury resulting from the activities with respect to which the helmets are used. The most common head injuries that helmets are designed to reduce are brain concussions. 
   Over the past two decades, epidemiological data on concussions have been gathered. Using football as an example once again, in about 1999, an article in the  Journal of the American Medical Association  estimated that approximately 250,000 concussions are suffered annually by those participating in football. Many high profile professional football players in the National Football League (“NFL”) had their careers shortened due to brain concussion injuries. Notable examples are Troy Aikman, Steve Young, and Merle Hodge. Concern has been raised about the prevalence of concussions incurred by those playing football, and this concern has been widely reported. 
   As a result, the NFL has launched a comprehensive study on the occurrence of concussions. Through the analysis of game films showing the impacts which occurred when concussions were suffered by NFL players, the mechanics of impacts resulting in concussions are being understood. The purpose is to continually apply the knowledge which is gained toward the further development of a helmet which reduces the occurrence of concussions. The hard exterior plastic shells of the helmets most commonly used by NFL players and the interior foam fit padding and air filled bladders most commonly used as head fitting structures for these helmets have the ability to absorb a certain amount of the impact energy when a helmet impacts an object. The impact energy that is not absorbed by the helmet is transferred to the skull of the user of the helmet, which can result in injury that can range from a mild concussion to severe brain injury. The most popular helmet currently being used in the NFL is the VSR4 manufactured by Riddell, Inc. Riddell, Inc. has also recently introduced a newer helmet for use by NFL players, as well as those playing football in college and high school, called the Riddell Revolution. Each of these helmets is constructed with hardened plastic exterior shell and commonly includes a form of foam fitting pads and/or air filled bladders as a head fitting structure mounted within each shell. 
   In the course of the study of head and brain injuries resulting from impacts with the head, researchers have developed various indices that attempt to identify and select the part of a measured acceleration pulse resulting from a head impact that would most likely contribute to injury. A mathematical relationship which resulted from this research is known as the Head Injury Criterion (“HIC”). HIC was incorporated into the Federal Motor Vehicle Safety Standards by the National Highway Traffic Administration. Standardized tests measuring the HIC of helmets are widely accepted in evaluating the ability of helmets to diminish the risk of impact head injury. It has been reported that HIC values of 1,000 and above resulting from the test for HIC represent conditions of moderate to severe brain injury, HIC values between 850 and 1,000 are likely to correspond to conditions of mild brain injury, and HIC levels below about 700 are considered not to be severe enough to cause mild brain injury. Thus, the lower the HIC measured by the standardized test the more effective a helmet is likely to be in reducing brain injury due to impact. The development of HIC is discussed in Lawrence M. Ilson, Ph.D. and Carley C. Ward, Ph.D., “Mechanisms and Pathophysiology of Mild Head Injury,” Seminars in Neurology, Volume 14, No. 1, March 1994, pp. 8-18. 
   The Biomechanical Engineering Laboratory of Wayne State University has been in the forefront of research regarding brain injury from impact, in the development of the HIC and the standardized test to measure it, and in testing helmets to determine their HIC levels. The NFL has recommended that helmets developed for potential use in the NFL be tested by the Biomechanical Engineering Laboratory of Wayne State University. 
   In an attempt to further improve existing helmets, the inventor of this invention developed a helmet cover which could be placed over and secured to an existing helmet without modifying the helmet. This helmet cover was an elastomeric cellular, foam material having an integral inner skin and an integral outer skin. The foam material had physical characteristics which caused it to absorb energy from impact with another object, and rapidly and fully recover to absorb energy from the next impact, thereby reducing the potential for injury to the wearer of the helmet on which the helmet cover was mounted. This helmet cover is the subject of U.S. Pat. No. 4,937,888 issued to Albert E. Straus on Jul. 3, 1990. Knowledge gained from the development and use of the helmet cover on existing helmets and gained from a study of the continuing research discussed above had led to the development of a fully integrated helmet system which outperforms alternatives when measured by the latest laboratory standards, as well as the development of helmet subsystems which can be useful in other helmets. 
   SUMMARY 
   In one embodiment, a helmet for protecting the head of a user of the helmet includes a hardened shell having an inside surface and an outside surface. The helmet also includes an outer layer comprising an elastomeric, cellular foam material that has an integral inner skin and an integral outer skin that is abrasion resistant and has a low coefficient of friction. The elastomeric, cellular foam material has physical characteristics that cause it to absorb some of the energy due to an impact with an object and rapidly and fully recover to absorb energy from the next impact. The outer layer is mounted on the hardened shell so that the outer layer&#39;s inner skin is adjacent the outside surface of the hardened shell. The hardened shell can be a solid structure or can be constructed from materials which allow it to be in the form of a frame. 
   A foam inner shell is normally located at a first position within the hardened shell. A plurality of visco-elastic cells is located between the inner shell and the inside surface of the hardened shell so as to form an air space between at least a portion of the inner shell and the inside surface of the hardened shell. A visco-elastic cell is a package of material that is normally in a fluid state, but rapidly solidifies as it deforms in response to the force of an impact. Thus, when the helmet receives an impact the visco-elastic cells deform to allow a limited movement of the inner shell from its first position within the air space, thereby absorbing components of the energy from the impact. A head fitting structure can be located within the inner shell. While the head fitting structure can be of any type desired, normally the head fitting structure is constructed to absorb a portion of the energy of impact. 
   Some helmets that use a hardened shell as an outer layer will benefit from incorporating a foam inner shell within the hardened shell and mounting a plurality of visco-elastic cells between the inside surface of the hardened shell and the foam inner shell to form an air space between the inner shell and the inside surface of the outer shell, as described above. The limited movement of the inner shell due to the deformation of the visco-elastic cells following an impact will dissipate components of the energy from the impact, as explained above, thereby benefiting the user of the helmet. 
   Another embodiment of the helmet includes an outer layer comprising the elastomeric, cellular foam material, described above, which has an integral inner skin and an integral outer skin that is abrasion resistant and has a low coefficient of friction. As previously stated, the elastomeric, cellular foam material has physical characteristics that cause it to absorb some of the energy due to an impact with an object and rapidly and fully recover to absorb energy from the next impact. As a result of using this elastomeric, cellular foam material with the described integral skin as the outer layer, the hardened shell can be constructed out of resin-impregnated fibers so as to reduce the weight of the hardened shell and substantially increase its strength-to-weight ratio. While a solid, hardened shell made of resin impregnated fibers can be advantageously constructed for such a helmet, due to the strength-to-weight ratio of resin impregnated fibers, the helmet can be constructed as a frame which includes elongated frame members, thereby further decreasing the weight of the helmet and thus decreasing the load on the head of someone using it. 
   Various other features, advantages, and characteristics of the present invention will become apparent to one of ordinary skill in the art while reading the following specification. This invention does not reside in any one of the features of the helmet disclosed below. Rather, this invention is distinguished in the prior art by its particular combination of features which are disclosed. Important features of this invention have been described below and shown in the drawings to illustrate the best mode contemplated to date for carrying out this invention. 
   Those skilled in the art will realize that this invention is capable of embodiments which are different from those shown and described below, and that the details of the structure of this helmet can be changed in various manners without departing from the scope of this invention. Accordingly, the drawings and description below are to be regarded as illustrative in nature and are not to restrict the scope of this invention. The claims are to be regarded as including such equivalent helmets as do not depart from the spirit and scope of this invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding and appreciation of this invention and its many advantages, reference will be made to the following, detailed description of this invention taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a perspective view of one embodiment of a particular helmet of this invention illustrated as a football helmet; 
       FIG. 1   a  is a front view of the helmet of  FIG. 1 ; 
       FIG. 1   b  is a side view of the helmet of  FIG. 1 ; 
       FIG. 2  is an exploded view of the football helmet of  FIG. 1 ; 
       FIG. 3  is a side section view along the line  3 - 3  of the helmet shown in  FIG. 1   a;    
       FIG. 3   a  is identical to  FIG. 3 , except that a self inflatable bladder is shown; 
       FIG. 4  is a front elevation section along the line  4 - 4  of the helmet shown in  FIG. 1   b;    
       FIG. 5  is a perspective view of the hardened frame shell; 
       FIG. 6  is a side view of the hardened frame shell; 
       FIG. 7  is an exploded view of a helmet with a solid shell; 
       FIG. 8  is an enlarged view, partially cut away, from the inside of the helmet showing the side plate and side plate mounting area of the helmet of  FIG. 1 ; 
       FIG. 8   a  is a cross section of the mounting area of a face guard within the side plate of  FIG. 8 ; 
       FIG. 9  is a cross section of the side plate and side plate retainer along the line  9 - 9  as shown in  FIG. 3 ; 
       FIG. 9   a  is an enlarged cross section of a portion of  FIG. 9 ; 
       FIG. 10  is a side view of a helmet with a face guard integrated with the side plate; 
       FIG. 11  is a side view of a helmet without side plates and having a recess in the outer layer to receive the end(s) of a face guard; 
       FIG. 12  is a side view of the helmet of  FIG. 11  with a filler of outer layer material to cover distal ends of the face guard; 
       FIG. 13   a  is a cross section of a side of the helmet showing attachment of the outer layer to the shell using a T-nut; 
       FIG. 13   b  is a cross section of a side of the helmet showing attachment of the outer layer to the shell using hook and loop fasteners; 
       FIG. 13   c  is a cross section of a side of the helmet showing attachment of the outer layer to the shell using an adhesive; 
       FIG. 13   d  is a cross section of a side of the helmet showing attachment of the outer layer to the shell through the use of inwardly projecting bosses of portions of the outer shell within open areas of the frame; 
       FIG. 14  is a cross section of the outer layer frame and inner liner showing inwardly projecting bosses on the outer layer extending through the frame shell to the inner layer; 
       FIG. 15   a  is a graph of Head Injury Criterion resulting from impact tests of helmets; 
       FIG. 15   b  is a graph of rotational accelerations resulting from impact tests of helmets; 
       FIG. 15   c  is a graph of side impact neck forces and torque resulting from impact tests of helmets; 
       FIG. 15   d  is a graph of high frontal neck G&#39;s and torque resulting from impact tests of helmets; 
       FIG. 16  is a front view of the face guard made of resin impregnated fibers covered with Kevlar material wraps; 
       FIG. 17  is a section of the face guard of  FIG. 16  along the line  17 - 17 ; 
       FIG. 18  shows two bundles of carbon fibers encased with braided Kevlar which are joined together with braided Kevlar; 
       FIG. 18   a  shows two bundles of carbon fibers encased with braided Kevlar which are joined together with resin impregnated carbon fibers; 
       FIG. 19  is a perspective view of an air filled bladder with a built in pump; 
       FIG. 20  is a perspective view of an air filled bladder with a built in pump. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the drawings, identical reference numerals and letters designate the same or corresponding parts throughout the several figures which are shown. 
     FIGS. 1-4  will be referenced initially to describe one embodiment of this invention.  FIG. 1  shows a protective helmet  30  constructed according to this invention for use as a football helmet. Referring to the exploded view of the helmet shown in  FIG. 2 , the helmet  30  includes a hardened shell  32  which has an inside surface  34  and an outside surface  36 . The helmet  30  also includes an outer layer  38  comprising an elastomeric, cellular foam material that has an integral inner skin  40  and an integral outer skin  42 . The elastomeric, cellular foam material of the outer layer  38  has physical characteristics that cause it to absorb some of the energy exerted on the helmet  30  as a result of an impact on the helmet  30  with an object and to rapidly and fully recover to absorb energy from the next impact. The integral outer skin  42  must be strong and tough so as to resist tears and abrasion due to impacts with objects. It should also have a low coefficient of friction so that it can deflect impacts which occur at an oblique angle to the surface of the helmet  30 . One material that meets these requirements is a urethane polyol produced by a reaction molded process to provide a flexible urethane foam that is self-skinning and meets the following specifications: 
   
     
       
             
             
             
             
           
             
             
             
             
           
         
             
                 
                 
             
             
                 
               Product 
               SES-5304 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Density 
               0.12-0.15 
               g/cc 
             
             
                 
               Tensile (D412) 
               260-300 
               psi 
             
             
                 
               Elongation 
               70-100% 
             
             
                 
               Tear Die C (ASTM D624) 
               27-37 
               lbs/in. 
             
             
                 
               Tear F.F. (ASTM D3574) 
               3.0-3.6 
               lbs/in. 
             
             
                 
               C.F.D. (ASTM D3574C) 
               12-15 
               lbs. 
             
             
                 
               Ball Rebound 
               42-52% 
             
             
                 
               Shore A 
               50-60 
             
             
                 
               Coefficient of Friction 
             
             
                 
               Static (ASTM D1894) 
               0.27-0.35 
             
             
                 
               Kinetic (ASTM D1894) 
               0.20-0.28 
             
             
                 
               Taber Abrasion 
             
             
                 
               CS-17 
               0 mg/1000 
               cycles 
             
             
                 
               H-18 
               320 mg/1000 
               cycles 
             
             
                 
                 
             
             
                 
               These physical properties are exemplary and are subject to changes relative to density of the polyurethane and molding conditions. 
             
           
        
       
     
   
   A product of this type is sold by HEHR International of Conyers, Ga. and is mixed as one part catalyst and four parts polyurethane. The mixture is placed into a secure mold with a humidity free environment to form the outer layer  38  and has a de-mold time of three minutes. To cause the outer skin  42  to grow thicker than the inner skin  40  so as to withstand impacts, the temperature of the core side of the mold is set at 130° F. The temperature of the cavity side of the mold is set at 95° F. since the inner skin  40  can be thinner. 
   Integral outer skin can also be formed on the outer layer  38  when the elastomeric, cellular foam material produced is not self-skinning. First, place an insert, such as a silicone material, into the core side of the tool to replicate the volume of the foam to the outer layer  38 . This insert becomes a new core. Add a tough, high density material, such as urea, to the tool to form an outer skin. Once the skin is formed on the tool, the insert is removed from the mold and the skin is allowed to remain on the cavity side. The material used to form the outer layer  38  is then placed into the mold and is foamed to become integral with the previously formed skin so as to form an outer layer with an integral skin. Normally, any self-skinning of a foaming material is sufficient as the inner skin since the inner skin is not subject to abuse. 
   As seen in  FIG. 3 , the outer layer  38  is configured so that it is thicker in areas where impact is customarily greater, providing a greater absorption of impact energy at those areas. Thus, the outer layer is thickest at about the front of the helmet  30  and tapers in thickness toward the rear. In the embodiment shown in  FIG. 3 , the outer layer  38  increases in thickness to an area  39  near the bottom of the rear of the helmet  30  to absorb potential impacts of the back of a helmeted head with the ground or another object. As shown in the front section view of  FIG. 4 , the outer layer  38  is thickest at about a 120° arc centered at the top of the helmet and tapers in thickness toward each side. The outer layer  38  can be finished in the desired color or colors by adding coloring and ultraviolet ray protection to the mold cavity when the outer skin  42  is formed. 
   The outer layer  38  is mounted on the hardened shell  32  so that the inner skin  40  is adjacent the outside surface  36  of the hardened shell  32 . The outer layer  38  is more resilient than the unforgiving hardened outer shell of most other football helmets, allowing the outer layer  38  to initially absorb energy of impact with an object before it disburses unabsorbed energy through the hardened shell  32 . This is the first component of a selective layering of spring like materials that allows the helmet  30  to accommodate the varying frequencies of impact vibrations. 
   A foam inner shell  44  is constructed of a size and shape that enables it to be mounted within the hardened shell  32 . The inner shell  44  should be chosen to be extremely lightweight and to have the ability to absorb high impact. It must be economically configured to facilitate the location of one or more components of a head fitting structure, such as fit pads, and to facilitate the placement of ventilation paths within it. One material that was found to be satisfactory for this purpose is an expanded polyethylene or polypropylene foam having a density of about 3-3.5 pounds per cubic foot which is manufactured and sold by Shell Chemical Company. 
   As best seen in  FIGS. 3 and 4 , the inner shell  44  is located at a first, normal position within the helmet  30  by a plurality of visco-elastic cells  46 ,  48 , and  50 , which are mounted between the inner shell  44  and the inside surface  34  of the hardened shell  32 . As indicated above, a visco-elastic cell is a flexible plastic package of material that is normally in a fluid state, but rapidly solidifies as it deforms in response to the force of an impact. Visco-elastic material is a polymer that solidifies from its normal fluid state in proportion to the energy applied upon impact and then returns to its original fluid state. It does not return to its normal fluid state as rapidly as the outer layer  38  recovers from an impact. These characteristics of the visco-elastic cells  46 ,  48  and  50  give them a lower vibration frequency response than that of the outer layer  38 . Visco-elastic cells are manufactured and sold under the trademark REASORB by Impact Innovative Products, Inc. of Manor, Pa. 
   The installation of the visco-elastic cells  46 ,  48 , and  50  between the hardened shell  32  and the foam inner shell  44  forms an air space  52  between at least a portion of the inner shell  44  and the inside surface  34  of the hardened shell  32 . As seen in  FIGS. 2 and 3 , the inner shell  44  includes a raised ridge  54  which extends around the front end of the helmet. The ridge  54  holds the inner shell  44  away from the inside surface  34  of the hardened shell  32  at the front of the helmet, thereby helping to form the portion of the air space  52  near the front of the helmet. Similarly, a ridge  56  which runs along the back end of the foam inner shell  44  assists in forming that portion of the air space  52  which exists toward the rear of the helmet. A ledge  57  that extends inwardly at the rear end of the outer layer  38  contacts the bottom of the ridge  56  to help support the inner shell  44 . 
   Referring now to  FIGS. 5 and 6 , the hardened shell  32  comprises a frame which includes a first plurality of lateral frame members  58 ,  60 ,  62 ,  64 , and  66  which extend laterally across the helmet  30 , and a second plurality of longitudinal frame members  68 ,  70 ,  72 ,  74  and  76  which extend in a longitudinal direction with respect to the helmet and cross the lateral frame members  58 ,  60 ,  62 ,  64 , and  66 . 
   The visco-elastic cell  48  is installed beneath the top of the helmet adjacent the inside surface of the lateral frame member  62  and is centered with respect to the longitudinal frame member  72  as shown in  FIGS. 3 and 4 . The visco-elastic cell  46  is installed on the longitudinal frame member  72 , toward the front of the helmet  30  as shown in  FIG. 3 , while the visco-elastic cell  50  is installed on the longitudinal frame member  72 , toward the rear of the helmet  30 . The purpose of this configuration is to install one of the visco-elastic cells  48  at the center of the top of the helmet and the other two visco-elastic cells  46  and  50  centered toward the front and rear of the helmet, respectively, so that helmet structure spreads the reaction of the visco-elastic cells to an impact force and their absorption of impact energy between the front and back of the helmet. The visco-elastic cells  46 ,  48  and  50  could be oriented onto other lateral and longitudinal frame members and/or additional visco-elastic cells could be added between the hardened shell  32  and the inner shell  44  as needed to further absorb energy of impact that has been transferred from the outer layer  38  to the hardened shell  32 . The exact physical characteristics, number, size and orientation of the visco-elastic cells needed to optimize the performance of a particular helmet are determined empirically. 
   Following impact of the helmet  30  with an object, the outer layer  38  absorbs some of the energy of impact, as described above. Unabsorbed impact energy is then dispersed through the hardened shell  32  to the visco-elastic cells  46 ,  48  and  50  which deflect to a limited extent until they solidify in proportion to the level of impact energy. The inner shell  44  moves to a limited extent, or floats, within the air space  52  as the visco-elastic cells deform while the visco-elastic material solidifies. 
   One preferred embodiment of the hardened shell  32  is made from fibers impregnated with a thermal setting resin that can be heated under a vacuum in an autoclave to hold the fibers together. Each of the lateral frame members  58 ,  60 ,  62 ,  64  and  66  and each of the longitudinal frame members  68 ,  70 ,  72 ,  74  and  76  has a pair of ends which terminates at a lateral band  78  that is a strip of material that encircles the equator of the helmet. The lower half  80  of the hardened shell  32  is also made from resin impregnated fibers. 
   The method of construction of an item such as the hardened shell from fibers wetted with thermal setting resin is well known to those skilled in the art. Generally speaking, a tool is constructed that can receive and retain strips of resin impregnated fibers in the shape of the hardened shell itself. One or more layers of the resin impregnated fibers are used to form the lateral frame members, the longitudinal frame members, the lateral band  78  and the lower half  80  of the hardened shell  32 . The hardened shell  32  itself should be constructed with a strength that allows it to receive impact force through the outer layer  38  and disperse that force without losing its shape. One such hardened shell was constructed by Composiflex, Inc. of Erie, Pa. out of carbon fibers wetted with an epoxy resin. Up to eight layers of resin impregnated fibers were used to form each component of the hardened shell. While the fibers of each layer of the lateral frame members  58 ,  60 ,  62 ,  64  and  66 , the longitudinal frame members  68 ,  70 ,  72 ,  74  and  76  and the lateral band  78  extended in the same direction, the lower half  80  of the hardened shell  32  was formed of alternating sheets of epoxy resin impregnated carbon fibers that had the carbon fibers at right angles in each adjacent sheet. 
   The hardened shell  32  can be made from materials other than epoxy resin impregnated carbon fibers. It can also be made from such materials as glass fibers, boron fibers and Kevlar fibers, as well as carbon fibers, any of which can be impregnated with epoxy resin, vinyl ester resin or polyester resin. Once a hardened shell is formed over a tool in which the shape of the desired frame, it can be heated in a vacuum within an autoclave to cure the resin under pressure. 
   Another feature of the present invention has been evaluated through empirical tests. By inserting a dye into the resin used in laying up the frame of the hardened shell, a visual indication that a blow to the helmet of a predetermined amount has been experienced by the hardened shell and, therefore, that a blow of a known lesser force has been experienced by the wearer&#39;s head. The predetermined magnitude of the blow can be adjusted by the amount of dye added to the resin and may range, for example, between 80 and 120 G&#39;s with the desired optimum being 100 G&#39;s. The helmet will register not only the fact that the impact has occurred but the exact location. This can be important in diagnosing the degree and location of head trauma suffered by a player that leaves the field of play in a dazed condition. The assessment may be made by either removing the inner shell  44  or the outer layer  38  to determine whether an impact-indicating discoloration has occurred. 
   Referring now to  FIGS. 2-4 , the helmet  30  further includes a head fitting structure  82  installed within the foam inner shell  44 . While the head fitting structure  82  could take any form that a user desires, it is preferable that it include padding which is capable of absorbing impact energy transmitted through the inner shell  44 . By way of illustration, the embodiment of this invention shown in  FIGS. 2 and 3  includes a series of fit pads  84   a ,  84   b ,  84   c ,  84   d ,  84   e ,  84   f  and  84   g  that are mounted within the foam inner shell  44 . Fit pad  84   a  is installed toward the front of the helmet, fit pad  84   b  is installed at the middle of the helmet, fit pad  84   c  is installed at the rear of the helmet, fit pads  84   d  and  84   f  are installed at the helmet user&#39;s right side and fit pads  84   e  and  84   g  are installed on the user&#39;s left side. All of the fit pads were made from a foam material that was chosen empirically to optimize the performance of the helmet  30  in absorbing the energy of its impact with an object. Preferably, the material of the fit pads  84   a - 84   g  are selected to respond to a different frequency of vibration caused by impact than the other components of the helmet  30 . One foam material which was satisfactorily tested to make fit pads for the helmet  30  is sold under the trademark ENSOLITE® AHC by RBX Industries, Inc. of Roanoke, Va. and has the following physical properties: 
   
     
       
             
           
             
             
           
         
             
                 
             
             
               Foam Fit Pads 
             
           
        
         
             
               Type 
               AHC 
             
             
                 
             
             
               Polymer 
               Polyvinyl Chlor- 
             
             
                 
               ide/Acrylonitrile 
             
             
                 
               Butadiene Rubber 
             
             
               ASTM D1056-00 Classification 
               2B2 
             
             
               Suffix Requirements 
               B3, C1, M 
             
             
               1. 25% Compression Resistance (psi) (ASTM D-1056) 
               7.0-9.0 
             
             
               2. 50% Compression Set (%) (ASTM D-1056) 
               30 
             
             
               3. Density (lb/ft 3 ) (ASTM D-1056) 
               6.5-8.5 
             
             
               4. Water Absorption (lb/ft 3 ) (ASTM D-1667) 
               0.1 max. 
             
             
               5. Tensile (psi) (ASTM D-412) 
               90 min. 
             
             
               6. Elongation (ASTM D-412) 
               100 min. 
             
             
               7. Flammability-MV38302 
               Pass 
             
             
               UL94 
               HF-1 - ⅛″ min. 
             
             
                 
               VO - ½ 
             
             
                 
             
           
        
       
     
   
   The foam fit pads  84   a - 84   g  can be sized and shaped to produce a comfortable fit on the head of a user of the helmet  30 . These pads may be encapsulated in a fabric which wicks moisture generated by the user. In accordance with the normal construction of head fitting structures used in regulation football helmets, the foam fit pads  84   a - 84   g  are separated from one another when they are installed so as to allow space for the installation of an air inflatable bladder  86  made up of a series of relatively narrow inflatable bladder elements  86   a - 86   i  which are nestled between adjacent fit pads. A valve stem  86   j , shown in  FIG. 3 , has a hole  86   k  within it which leads to a rubber flap check valve  86   i  within bladder element  86   i . An air pump can be attached to the stem  86   j  to inflate the bladder  86  through the rubber flap check valve  86   l  to tighten the fit of the helmet on the head of the user. 
   Visco-elastic cells can also be mounted between the foam inner shell  44  and components of the head fitting structure  82  to further absorb impact energy transmitted through a foam inner shell  44 . The use of visco-elastic cells is particularly useful near the lower ends of the inner shell  44  which are remote from the more central areas of the shell that benefit from the impact energy absorption characteristics of the combination of the visco-elastic cells  46 ,  48  and  50  and the air space  52 . Thus, as seen in  FIGS. 2-4 , visco-elastic cells  92  and  94  are placed between the front and rear inside surfaces of the inner shell  44  and the bladder elements  86   a  and  86   i , respectively. In a similar manner, as seen in  FIG. 4 , visco-elastic cells  96  and  98  are placed between the user&#39;s lower left hand and lower right hand portions of the inner shell  44  and the bladder elements  86   c  and  86   b , respectively. 
   Referring once again to  FIGS. 2-4 , the helmet  30  further includes a pair of jaw pads  88  and  90  installed adjacent the user&#39;s lower right and left side extensions, respectively, of the inside surface  34  of the hardened shell  32 . The selection of appropriate jaw pads is well within the skill of those persons who design and fit football helmets. 
   Referring to  FIGS. 2-4 , helmet  30  further includes a face guard  100  that is installed through the use of a pair of side plates  102  and  104  installed on the user&#39;s right and left sides, respectively, of the helmet  30 . Alternatively, the helmet could be used with any type of face guard selected. By way of example,  FIG. 10  shows a helmet made according to this invention used with a face guard that is integral with the helmet&#39;s side plates, and  FIG. 11  shows a helmet made according to this invention used with a conventional face guard. 
   The side plate  102  has a hole  106  in it to receive a tabbed twist lug assembly  108  that is sized to fit into a notched hole  110  in the user&#39;s right side of the hardened shell  32  when the tabs of the twist lug assembly  108  are aligned with the notches in the hole  110 . The twist lug assembly  108  can be turned within the hole  110  so that the tabs of the twist lug assembly  108  engage the hardened shell  34  around the hole  110  to lock the side plate  102  in place. Similarly, the side plate  104  has a hole  112  through it to receive a tabbed twist lug assembly  114  which is sized to fit into the notched hole  116  when the tabs of the twist lug assembly  114  are aligned with the notches in the hole  116  in the left user&#39;s side of the hardened shell  32 . The twist lug assembly  114  can be turned within the hole  116  to cause the tabs on the assembly  114  to lock the side plates  104  in place. 
   The structure of the side plates  102  and  104  and their associated tab twist lug assemblies  108  and  114  can be best understood by referring to  FIG. 8  which shows a partially cut away view of side plate  104  and tabbed twist lug assembly  114  from  FIG. 3  and by referring to  FIGS. 9-9   a . The twist lug assembly  114  includes an outer female lug  118  with internal threads and a centrally located finger bar  120  for use in turning it. The twist lug assembly  114  further includes a notched male member  122  having external threads, which are sized to mesh with the threads of the female lug  118 , and also includes tabs  124  which can lock the tabbed twist lug assembly  114  onto the hardened shell  32 . The female lug  118  has a head  126  that engages a notch  127  surrounding the hole  112  in the side plate  104 . Thus, when the tabs  124  engage the inside surface of the hardened shell  32 , the twist assembly lug  114  holds the side plate  104  onto the helmet. Additionally, as best seen in  FIG. 9   a , a snap ring  128  fits around the outside of the female lug  118  and in contact with the underside of the side plate  104  to hold the female lug  118  onto the side plate  104  when the side plate  104  is removed from the hole  116  in the hardened shell  32 . 
   As will be explained below, one function of the side plates  102  and  104  is to secure the face guard  100  onto the helmet  30 . Another function of the side plates  102  and  104  is to help anchor the outer layer  38  against the hardened shell  32  to help secure the outer layer  38  in place while the helmet is being used. Referring again to  FIGS. 9 and 9   a , as an example of the structure and function of the side plates  102  and  104 , the side plate  104  fits within a notch  130  formed in the periphery of a cut out of the outer layer in the shape of the curved sides of the side place  104 . See  FIGS. 2 and 3  by way of example. As shown in  FIGS. 9 and 9   a , bead  132  surrounds the outside of the notch  130  in the outer layer  38 , and the underside of side plate  104  has a small notch matching the shape of the bead  132  so that the bead  132  can fit into it. As a result, the side plate  104  fits within the notch  130  of the outer layer  38  so that the bead  132  is held within the corresponding notch in the underside of the side plate  104 . Thus, when the twist lug assembly  114  locks the side plate  104  onto the helmet, the side plate  104  squeezes the bead  132  and the notch  130  of the outer layer  38  against the hardened shell  32  so as to help retain the outer layer  38  in place during use of the helmet. 
     FIGS. 8 and 8   a  show the manner in which the face guard  100  is mounted onto the helmet  30  in the illustrated embodiment of this invention. The construction of the face guard  100  will be more fully explained in relation to  FIGS. 16-18   a . Suffice it to say that the face guard  100  includes an upper bar  100   a , a middle bar  100   b , a lower bar  100   c , a right vertical bar  100   d  and left vertical bar  100   e . It further includes left upper terminal member  100   f , a left lower terminal member  100   i , a right upper terminal member  100   g  and a right lower terminal member  100   h . Referring now to  FIG. 8  and the left side of the helmet  30 , by way of example, the left terminal members  100   f  and  100   i  have key hole shaped holes  134  and  136 , respectively, cut into their flat surfaces. The left side of the hardened shell  32  has a pair of holes  138  and  140  cut into it corresponding to key hole shaped holes  134  and  136 , respectively. Each of the holes  138  and  140  has a square backed T-nut  142  and  144 , placed within it, with a round headed screw installed within each T-nut. The large portion of the key holes  138  and  140  can be placed over the heads of the screws of the T-nuts  142  and  144  when the face guard  100  is installed on the hardened shell. 
   The face plate  104  has a number of elements which enable it to both grip three notches in the front of the hardened shell  32  and to align and hold the face guard  100  in a steady position during its use, while allowing the face guard to be cushioned so as to absorb some of the energy of impacts with it. Notches  146  are shown on the left side of the helmet  32  in  FIG. 2 . Similar notches  148  are shown on the right side of the front of that helmet. 
   The side plate  104  has a set of u-shaped fingers  150  which fit within the notches  146  to hold the front end of the side plate against the hardened shell  32 . The side plate  104  further includes a ridge  152  which is approximately the thickness of the terminal members  100   f  and  100   i  and is shaped to engage portions of the terminal members  100   f  and  100   i  so as to allow them to be mounted firmly in place on the helmet. Referring to  FIG. 8 , along with  FIG. 8   a , the side plate  104  also includes a boss  154 . The boss  154  has a u-shaped piece of elastomeric material  156  attached to it with an adhesive  158 . The upper terminal member  100   f  is installed against the end of the elastomeric material  106 , with a tail piece  160  of the material extending between the tip of the terminal member  100   f  and the side plate  104 . Each of the other terminal members of the face guard  100  are mounted in a similar manner within the side plates  104  and  102 . As a result, impact energy from impacts to the face guard  100  is potentially absorbed by elastomeric members such as  156  that are mounted between the ends of the terminal members and the bosses on the side plates that hold them into place. 
   A football helmet construction substantially as described above was tested with a standard face guard at the Biomechanical Engineering Laboratory of Wayne State University using the standard test developed to measure the HIC of the helmet. The standard test involved firing a projectile at a selected lateral site and at a selected high frontal site of the helmet, with the helmet placed on a head form integrated with a hybrid III upper torso. The Riddell Revolution helmet was used as a base line for the high frontal tests conducted by Wayne State University. The Riddell VSR4 was used as the base line for the lateral impact tests because the revolution did not properly fit the narrow jaw of the head form used for these tests, which would have put it at a disadvantage for comparison purposes. Each helmet was struck twice by a projectile for each test, and the resulting average was used for evaluation purposes. Impact velocities of the projectiles were between 9 and 10 meters per second. 
   The results of the tests are set forth in the tables below, and certain of the results are also shown on graphs in  FIGS. 15   a - 15   d . 
   
     
       
             
           
             
             
             
             
             
             
             
             
           
             
           
             
             
             
             
             
             
             
             
           
         
             
                 
             
           
           
             
               Wayne State University Biomechanical Tests 
             
             
               Riddell VSR4 vs. Prototype - Lateral Imnact 
             
           
        
         
             
                 
               VSR4 #1 
               VSR4 #2 
               Ave. 
               PC #1 
               PC #2 
               Ave. 
               % Reduce 
             
             
                 
             
             
               HIC (severity) 
               766.17 
               622.31 
               694.24 
               420.14 
               569.47 
               494.81 
               29 
             
             
               Y axis Gs 
               127.52 
               127.57 
               127.55 
               107.96 
               127.46 
               117.72 
                8 
             
             
               Rotational r/s/s 
               8393.9 
               7318.5 
               7856.2 
               6841.0 
               6950.9 
               6895.9 
               12 
             
             
               Peak Force N 
               2667.1 
               1142.9 
               1905.0 
               1445.6 
               1190.5 
               1318.1 
               31 
             
             
               Peak Torque Nm 
               90.29 
               73.16 
               81.72 
               45.63 
               63.65 
               54.64 
               33 
             
             
               Impact Force N 
               9467.4 
               10850.6 
               10159.0 
               8628.1 
               9014.2 
               8821.1 
               13 
             
             
                 
             
           
        
         
             
               Riddell Revolution vs. Prototype - Hi Front @ 24 degrees 
             
           
        
         
             
                 
               Revo #1 
               Revo #2 
               Ave. 
               PC #1 
               PC #2 
               Ave. 
               % Reduce 
             
             
                 
             
             
               HIC (severity) 
               707.49 
               653.75 
               680.62 
               523.05 
               607.37 
               565.21 
               17 
             
             
               X axis Gs 
               150.70 
               142.83 
               146.76 
               121.65 
               136.94 
               129.28 
               12 
             
             
               Z axis Gs 
               53.62 
               54.63 
               54.12 
               35.75 
               47.61 
               41.68 
               23 
             
             
               Rotational r/s/s 
               1791.99 
               1907.01 
               1849.50 
               1569.73 
               1433.80 
               1501.67 
               19 
             
             
               Peak FxFace N 
               1615.02 
               1584.95 
               1599.98 
               1384.92 
               1399.65 
               1392.29 
               13 
             
             
               Peak FzNeck N 
               7553.73 
               8003.68 
               7778.70 
               6557.72 
               6523.93 
               6690.83 
               14 
             
             
               Peak Torque Nm 
               110.10 
               92.28 
               101.19 
               92.89 
               94.50 
               93.69 
                7 
             
             
               Impact Force N 
               13936.37 
               13565.65 
               13751.01 
               11215.80 
               10256.33 
               10736.07 
               22 
             
             
                 
             
           
        
       
     
   
   In every measurement recorded by Wayne State University, the prototype helmet (PC) made in accordance with this invention showed a reduction in rotational and linear accelerations due to impact and a reduction in forces and moments from impact in comparison with both the Revolution and the VSR4 helmets. Specifically, in lateral or side impact, the helmet of this invention showed a 29% reduction in the HIC as compared with the VSR4. The reduction in rotational accelerations is important since these are also thought to be causal to catastrophic neck injuries, as well as, concussions. In all respects measured, the helmet of this invention was shown to be superior to the VSR4 and the Revolution helmets. 
     FIG. 10  depicts a face guard  100 ′ which is formed integrally with plates  102 ′ and  104 ′.  FIG. 11  shows a modified helmet with the side plate removed, the helmet having an outer layer  38  with a cutout  39  facilitating attachment of a conventional face guard  100  with snaps  41  on the hardened shell of the helmet to allow the chin strap to be fastened to the helmet.  FIG. 12  shows the conventional face guard  100  of  FIG. 11  with a covering of the outer layer material  104 ′ in the area where side plates had been installed for the type of face guard described above. 
     FIGS. 13   a - 13   d  show different methods of attaching the outer layer  38  onto the hardened shell  32 .  FIG. 13   a  shows the attachment of the outer layer to the hardened shell by way of a T-nut  142 ′ having a screw  141 ′ inserted into it from the inside surface of the hardened shell.  FIG. 13   b  shows the attachment of the outer layer  38  to the hardened shell  32  by way of hook and loop fasteners  143   a  and  143   b  such as Velcro® fasteners.  FIG. 13   c  shows the use of an adhesive  145  to attach the outer layer to the hardened shell.  FIG. 13   d  shows the attachment of the outer layer to the hardened shell by means of bosses  146  formed at different locations on the inside surface of the outer layer. Corresponding holes would be formed within the hardened shell so that the bosses could be fitted through the holes to hold the outer layer into place. 
     FIG. 14  shows a structure similar to  FIG. 13   d  wherein the bosses  146 ′ formed within the inner surface of the outer layer extend the distance so that they contact the inner shell  44  of the helmet. The bosses can thus be used to dampen impact forces. 
     FIGS. 16-18   a  show a football face guard  100  constructed of resin impregnated carbon fibers wrapped  152   a  in Kevlar  150   a . Each of the bars of the face guard is a separate bundle of Kevlar wrapped resin impregnated carbon fibers. Bars  100   b  and  100   d ,  100   e  of the face mask which come together can be wrapped either with bands of Kevlar as shown in  FIG. 18  or bands of resin impregnated fibers as shown in  FIG. 18   a.    
     FIGS. 19 and 20  show a portion of two separate embodiments of the bladder  86  which can be used with the helmets described above.  FIG. 20  shows a self-inflating bladder in which an inflating bulb  86   m  on the right side of the bladder has a hole in it  86   n  which allows the user to pump air through a rubber flap check valve  86   p  within the bladder above the bulb. The left side of  FIG. 20  shows a push tab  86   t  attached to a rubber flap check valve  86   p  which can be used to deflate the bladder.  FIG. 19  shows a conventional bladder which is inflated through the use of a pump. 
   Those skilled in the art will recognize that the various features of this invention described above can be used in various combinations with other helmet components without departing from the scope of this invention. Thus, the appended claims are intended to be interpreted to cover such equivalent helmets as do not depart from the spirit and scope of this invention.