Abstract:
A helmet configured to protect a human head against mild traumatic brain injury upon impact includes an outer shell and a liner consisting of fluid fillable flexible fluid chambers fluidly connected to each other by fluid connections. The fluid chambers being spaced around the circumference of the helmet and configured to fill a space between the head and the outer shell when the helmet is positioned on the head. Impact resistant flexible pads are also in the liner and are spaced around an inner circumference of the outer shell adjacent to each of the fluid fillable flexible fluid chambers. A flexible inner shell inside the liner is configured to fit closely on the head. The flexible fluid chambers are configured to compress in response to impacting of the helmet on an impact side and to force liquids through the fluid connections to inflate other fluid chambers inside the helmet thereby cushioning the head against a rebound impact on the inside of the helmet.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 15/227,593 filed Aug. 3, 2016 for “Protective Headwear to Reduce Risk of Injury” by W. H. Tuttle and L. C. Whitaker, which in turn claims the benefit of U.S. Provisional Application No. 62/203,152 filed Aug. 10, 2015, both of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    This invention relates to protective head gear. In particular the invention is a helmet designed to protect against mild traumatic brain injury (MTBI). 
         [0003]    Traumatic brain injuries can occur when the head experiences accelerations or decelerations that cause the brain to move within the skull and generate physical damage to structures within the brain. The accelerations associated with traumatic brain injuries can be linear, rotational, or complex combinations of accelerations. The brain is a soft gelatinous organ housed within the skull surrounded by liquid. During a high speed acceleration event the brain can move within the skull and impact the skull and subsequently rebound and experience additional impact with the skull on the opposite side of the brain (coup-contrecoup). In lower speed acceleration events the brain may not impact the skull, but can still sustain damage as the internal structures of the brain slide past each other and damage neural interconnections. 
         [0004]    These injuries are generally referred to as mild traumatic brain injuries (MTBI). The word mild refers to the manner of impact and not the severity of the injury. The term concussion is often used to describe mild traumatic brain injuries. Symptoms of concussion can include loss of consciousness, headaches, confusion, temporary cognitive impairment, vertigo and balance problems. More severe mild traumatic brain injuries can cause permanent impairment and increased risk of serious long term medical complications. Repeated mild traumatic brain injuries are associated with additional long term health risks including neuro degenerative brain diseases such as chronic traumatic encephalopathy which has been found in former professional athletes who have experienced multiple concussions over their careers. 
         [0005]    Studies of the causes of concussions have demonstrated that a wide range of acceleration forces can cause concussions. For example, studies indicate that American football players regularly sustain accelerations of 20 to 180 Gs with various injury outcomes. In general the higher the G-force, the greater the injury, but some athletes have experienced concussions at impact forces below 60 G while others have been free of concussion injury at impact forces in excess of 100 G. 60 G is often considered a level below which it is unlikely that a concussive injury will occur. 
       SUMMARY 
       [0006]    A helmet configured to protect a human head against mild traumatic brain injury upon impact includes an outer shell and a liner consisting of fluid fillable flexible fluid chambers fluidly connected to each other by fluid connections. The fluid chambers being spaced around the circumference of the helmet and configured to fill a space between the head and the outer shell when the helmet is positioned on the head. Impact resistant flexible pads are also in the liner and are spaced around an inner circumference of the outer shell adjacent to each of the fluid fillable flexible fluid chambers. A flexible inner shell inside the liner is configured to fit closely on the head. The flexible fluid chambers are configured to compress in response to impacting of the helmet on an impact side and to force liquids through the fluid connections to inflate other fluid chambers inside the helmet thereby cushioning the head against a rebound impact on the inside of the helmet. 
         [0007]    In an embodiment, a method of forming a helmet to protect a human head against mild traumatic brain injury upon impact includes forming an outer shell larger than the head and forming a liner consisting of fluid fillable flexible fluid chambers that fit inside the outer shell configured to fill a space between the head and the outer shell when the helmet is positioned on the head. The method further includes connecting the flexible fluid chambers with fluid connections such that at least two fluid chambers are interconnected. The method further includes filling the interconnected flexible fluid chambers with fluid and forming impact resistant flexible pads inside and spaced around the inner circumference of the outer shell adjacent to each of the flexible fluid chambers. The method further includes forming a flexible inner shell inside the liner configured to fit closely on the head and attaching the flexible fluid chambers and flexible pads to the inner and outer shells to form the helmet such that the flexible fluid chambers are configured to compress in response to impacting of the helmet on an impact side and force liquid through the fluid connections to inflate other fluid chambers in the helmet thereby cushioning the head against a rebound impact on the inside of the helmet. The helmet is finished by attaching a chinstrap and fastener to the helmet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic cross-section of a helmet according to an embodiment of the invention on a human head. 
           [0009]      FIG. 2  is a top view of the liner of the helmet with the outer shell removed. 
           [0010]      FIG. 3  is a side view of a helmet with a strap. 
           [0011]      FIG. 4A  is a top view of an embodiment of the liner of the helmet with the head centered in the helmet 
           [0012]      FIG. 4B  is a top view of the embodiment of  FIG. 4A  with the head rotated 25° counterclockwise around the central axis of the brain. 
           [0013]      FIG. 5A  is a side view of an embodiment of the liner of the helmet positioned on a human head facing right. 
           [0014]      FIG. 5B  is a rear view of the embodiment shown in  FIG. 5A . 
           [0015]      FIG. 6A  is a side view of the embodiment of the helmet positioned on a human head facing right. 
           [0016]      FIG. 6B  is a rear view of the embodiment shown in  FIG. 6A . 
           [0017]      FIG. 7  is a side view of an embodiment of the helmet positioned on a human head. 
           [0018]      FIG. 8  is a method of forming a helmet according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The present invention relates to protective headwear typically referred to as a helmet. Such a helmet fulfills the task of protecting a person&#39;s head from injury in the case of impact with other objects. Protective headwear is used in a variety of military, industrial, and sporting activities to prevent, or reduce the severity of, traumatic injury caused by foreseeable impacts associated with those activities. For example, participants in many sports such as American football, baseball, cycling, equestrian, field hockey, ice hockey, lacrosse, skiing, snowboarding, surfing, wakeboarding, and water skiing routinely wear protective helmets to reduce the risk and severity of head injuries in general and traumatic brain injury in particular. Additional activities such as automobile racing, motorcycling, and snowmobiling are sports often associated with the use of specialized protective helmets to protect the users from injuries including traumatic brain injuries. 
         [0020]    Studies have demonstrated that the natural resonant frequency of the brain within the skull is approximately 15 Hz. If an impact generates accelerations that excite brain motions at or near its natural resonant frequency, the motions and impacts of the brain within the skull may be amplified and the damage caused can be greater than would otherwise be expected for the G-force experienced. Thus there is a need for protective helmets that will reduce the accelerations experienced by the users&#39; head and reduce the tendency of an impact event to amplify the brain&#39;s motion at or near its natural resonant frequency. Prior art has been generally good at limiting the peak acceleration forces experienced during impact. One method well known in the prior art is the use of a liner made from non-resilient compressible materials that permanently deform at selected force levels. This deformation absorbs energy and establishes the maximum acceleration level that can be experienced during the time that the material is undergoing compression. One limitation of such helmets is that by only establishing a peak value, the helmets can offer insufficient protection from lower force accelerations that trigger resonant amplifications of brain motions within the skull. An additional limitation of such designs is that after they have functioned, the liner material has lost its protective capacity and must be replaced. The materials may not appear to have been depleted and users may wrongly continue to rely on the helmet for additional impact protection. 
         [0021]    In a typical concussive event, the head is rapidly decelerated, causing the brain to move within the skull. The brain is attached near its bottom-center and can swing about this fulcrum. As the brain moves into contact with the skull, it compresses and rebounds, contacting the opposite side of the skull. This can cause two injury sites in the brain and is referred to as a “coup-contrecoup” injury. Since the brain can be considered as an underdamped mechanical system, a method of protection against coup-contrecoup injury is to supply damping to the system, particularly at the resonant frequency of the brain. 
         [0022]    There is a need for protective helmets that can reduce the impact force transferred to a user&#39;s head in terms of reducing the peak force experienced and to control the effective frequency of the energy transfer to a value that does not tend to excite brain motion amplification at its resonant frequency. 
         [0023]    A non-limiting embodiment of the invention is shown in  FIG. 1 .  FIG. 1  is a schematic cross-section of helmet system  10  on human head  12  containing brain  14 . Helmet system  10  may include outer shell  16 , a middle liner containing fluid filled flexible fluid chambers such as bladders  18  and interconnecting fluid passageways  20 , and inner liner  22 . The energy absorbing mechanism of helmet system  10  is as follows. If the user is travelling forward and experiences a frontal head-on impact with an object, head  12  will continue to move forward generating increased pressure in fluid filled bladder  18 A at the forehead. The higher pressure will force fluid from bladder  18 A to bladder  18 E at the rear of head  12  through fluid passageway  20 . The fluid viscosity and dimensions of fluid passageway  20  may be sized to establish a rate of fluid transfer during acceleration that may absorb impact energy and lengthen the time of the energy absorption process to reduce the effective frequency of the energy transfer. This action may spread the force over time and distance, to reduce the peak force experienced by brain  14 . It may also increase the time over which the brain experiences the force to well above the  33  millisecond half wave period of the approximately  15  Hz resonant frequency of the brain. 
         [0024]    An additional feature of helmet system  10  is shown in  FIG. 2 .  FIG. 2  is a schematic top view of helmet system  10  with outer shell  16  removed. Compressible material  24  may be placed on each side of flexible fluid chambers  18 A- 18 H in the middle liner. Inner liner  22  forms the inside layer of helmet system  10 . The purpose of these compressible devices is to center head  12  within outer shell  16  between impact events. Since the flexible fluid chambers are distributed around the circumference of head  12 , head  12  may be protected against the peak force of torsional accelerations as well as more complicated forms of impact. The compressible strengths of compressible material  24  may be from about 5 G to 10 G in some embodiments. 
         [0025]    Fluid passageways  20  may be sized based on fluid viscosity to establish a rate of fluid transfer during acceleration or deceleration to absorb impact energy and to increase the time of the energy absorption process as mentioned above. In an embodiment, the fluid passageways may be flexible tubing. In another embodiment, the flexible fluid chambers and fluid interconnections may be formed from two or more sheets of a flexible polymeric material by welding patterns in the sheets defining the chambers and associated fluid interconnections. 
         [0026]    A side view of an embodiment of the invention is shown in  FIG. 3 . Outer shell  16  of helmet  10  is shown attached to human head  12  by chinstrap  26  and fastener  28 . Releasing fastener  28  enables the wearer to remove helmet  10  from head  12 . Other forms of securing helmet  10  to head  12  may be used depending on the requirements of the application. 
         [0027]    In another non-limiting embodiment, the fluid passageways may be arranged such that the damping is optimized for impact directions that are not radial to the center of the head, but are instead torsional around the axis of the head.  FIG. 4A  shows a top view of helmet system  130  on human head  112  inside helmet shell  116  with head  112  in a normal symmetrical orientation with respect to helmet shell  116 . Middle liner elements of helmet system  130  comprise flexible fluid chambers  118 , interconnecting fluid passageways  120 , and compressible material  124  placed between the flexible fluid chambers  118  to center head  112  within outer shell  116  (not shown) between impact events. Inner liner  122  forms the inside layer of the helmet system  130 . In contrast to the fluid passageway layout of  FIG. 2 , fluid passageways  120  may be aligned parallel to and perpendicular to the major longitudinal axis of helmet shell  116 . 
         [0028]      FIG. 4B  shows human head  112  rotated 25° counter-clockwise with respect to the normal orientation as a result of a torsional impact to helmet system  130 . Flexible fluid chambers  118 D and  118 H have been compressed forcing fluid through passageways  120  to inflate chambers  118 F and  118 B, thereby cushioning head  112  when it rebounds after impact. A similar result occurs when head  112  is rotated in a clockwise fashion after an appropriate torsional impact in an opposite direction. Such an arrangement is beneficial in certain sports and activities where the wearer is likely to experience off-angle impacts such as often seen in American football. These impacts generate rapid rotations of the head causing torsional distortion of the brain and resulting in MTBI even with lower levels of acceleration in the x, y, z direction. When the helmet is exposed to rotational forces, the hydraulic damping system described herein may reduce the instantaneous force experienced by the wearer to a controlled level and increase the time over which the acceleration is experienced. This reduces the torsional forces coupled to the brain and may reduce the chance of MTBI caused by these forces. 
         [0029]    In another embodiment, the fluid filled damping elements of the invention may be made from at least three interconnected fluid chambers. An example is shown in  FIGS. 5A and 5B . In helmet system  230 , the damping system is optimized for forces applied to the top of the head as indicated by arrow A and interacts with the spine as a downward compression along the Z-axis of the head. In this example, top chamber  218 A communicates with two other chambers,  218 B and  218 C, arranged around the bottom perimeter of helmet shell  216 . An inner liner is not shown in  FIGS. 5A and 5B . Such an arrangement may be beneficial in certain sports activities where the wearer is likely to experience impacts to the top of the head such as American football, bicycling, snow skiing and others. In American football, for example, two players running toward each other with their heads lowered may experience head to head impact. Fluid forced from top chamber  218 A to lower chambers  218 B and  218 C over a time interval dependent on fluid flow rates and fluid interconnections  220  may positively impact the impact dynamics experienced by brain  214 . As mentioned earlier, fluid interconnections between other fluid chambers in the helmet may also effect damping of radial and rotational accelerations induced by off-center impact events. 
         [0030]    In another embodiment, the fluid chambers may have more than a single size of fluid communication connections. Such secondary communication paths may allow different levels of restriction to motion in different directions. This may enable a designer to tailor the directional damping response to anticipated forces experienced by the wearer. An example of this is shown in  FIG. 6A and 6B  which are a side view and a rear view of the embodiment of helmet system  330  positioned on human head  312  respectively. Top fluid chamber  318 A is connected to right and left bottom fluid chambers  318 B and  318 C respectively by fluid interconnections  320  and to rear fluid chamber  318 D by fluid interconnection  321 . In the particular case of helmet system  330 , rear fluid interconnection  321  has a smaller diameter than fluid interconnection  320  which will provide a different dynamic response of chamber  318 D to the other two chambers thereby offering tunable response of the fluid chamber system to an impact. An inner liner is not shown in  FIGS. 6A and 6B . 
         [0031]    In an embodiment, the fluids in some or all of the fluid chambers may be dilatant fluids. Dilatant fluids are non-newtonian in which the viscosity increases with the rate of shear strain. In the helmets of the invention, these fluids provide greater damping when the applied acceleration forces are greater. This enables the helmet to be useful over a greater range of anticipated accelerations. The remaining design elements of other embodiments may remain unchanged when this variable viscosity fluid embodiment is incorporated. 
         [0032]    In other embodiments, some or all of the fluid chamber sets may have a higher or lower viscosity than other sets within the helmet. This may provide the ability to have different damping rates and different acceleration directions while maintaining more constant fluid chamber thicknesses. 
         [0033]    In another embodiment, the helmet may not incorporate a hard shell  16 . Hard shell  16  may be necessary when likely objects of impact necessitate a hard shell to resist transference of energy from a rigid shape with reduced surface contact area. Other uses may not anticipate this type of impact event and therefore may not require a hard shell. A hard shell may reduce protection in certain situations. For example, in wakeboarding and waterskiing a likely collision with water will occur at speeds in excess of 20 mph. At these speeds there is a risk that the hard shell of a helmet may catch its edge on the water surface transferring breaking forces to the head and neck. In this case a risk of whiplash injuries may outweigh the risk of impacts with sharp surfaces that would have required the use of hard shell protection. As impact velocity increases, a requirement for protection from impact with the surface of the water may become important and the hard shell embodiment may be preferred. 
         [0034]    In a soft shell embodiment, the use of interconnected fluid filled chambers, remains the same, but the shell may be a form-fitting compliant cover. This cover may not allow the development of significant hydrodynamic forces at the interface of a helmet and water surface. This may be the preferred embodiment for use in sports including surfing, wakeboarding, wakesurfing, waterskiing and other compliant shell helmet examples. 
         [0035]    Hybrid embodiments combining portions of hard and soft shell embodiments may also be useful for watersports based on anticipated velocities and likely impact surfaces. A typical example of an activity where the merits of soft shell and hard shell designs may be considered is cable towed wakeboarding where there are solid objects such as metal rails in to which the rider may collide. Based on likely impact velocities and impact surfaces the selection of a hard shell or a hybrid embodiment may be preferred. 
         [0036]    An example of a hybrid embodiment is a helmet that contains both the hydraulic system described herein combined with a helmet liner made from non-resilient compressible materials that permanently deforms at force levels from about 60 G to about 150 G. In this embodiment, the hydraulic system may protect the head in lower speed impacts while the non-resilient system may provide additional protection in higher speed impacts by setting a maximum acceleration level for the protecting shell to deform and absorb impact forces. An example of this embodiment is shown in  FIG. 7 . Hybrid helmet system  430  comprises non-resilient crushable inner liner  423  supporting fluid filled flexible fluid chambers  418 A and  418 E connected by fluid passageway  420 . Flexible outer liner  422  closely covers the hydraulic impact resistance system and the _G resistant crushable inner liner  423  providing impact absorbing protection to impacts exceeding _G. In all cases overall helmet performance may be improved because of the reduced initial acceleration and impulse lengthening time associated with the hydraulic helmet liner system. 
         [0037]    Candidate materials for outer shell  16  of the various embodiments described herein may include impact resistant materials such as polycarbonate, fiberglass, or Kevlar. An acceptable hardness for an impact resistant outer shell may be greater than Rockwell N62. Candidate materials for flexible inner or outer shells may be elastomer, elastomeric polymer, polymer impregnated fabric, elastomer impregnated fabric, laminated fabric, polymer fiber composite, leather, synthetic leather or others known in the art. Candidate materials for flexible pads  24  between flexible fluid chambers  18  may include open cell and closed cell foam made from synthetic materials including silicone and polyurethane. Candidate materials for non-resilient crushable inner liner  423  may include expanded polystyrene, expanded polypropylene, or expanded polyurethane. 
         [0038]    In all embodiments described herein, the damping forces may be adjusted by means of fluid flow control. The dynamic interactions of hydraulic systems are well established and understood, therefore only a brief description of how this invention uses hydraulic means to reduce injurious forces is provided herein. 
         [0039]    There is a relationship between applied force and hydraulic pressure that is based on the surface area of the fluid chamber. Simply put, if the chamber has 2 in. 2  of surface and a force of 10 lbs. is applied, a hydraulic pressure of 5 psi. is generated. Increasing the chamber surface area reduces the hydraulic pressure while increasing the volume of fluid being displaced. Reducing the surface area likewise increases the resultant pressure while reducing the volume of fluid being displaced. Using this relationship, a designer can select the quality and sizes of the chambers to control the hydraulic pressure during a protective event. 
         [0040]    There is a relationship between the size of the communication channel (tube) and the flow at any given pressure. Simply put, for any given pressure a larger tube will allow more fluid and a smaller tube will allow less fluid to flow. 
         [0041]    Finally there is a relationship between fluid viscosity and flow. The thicker the fluid the slower the fluid will flow through a given size of tube at a given pressure. 
         [0042]    In practice, the size of individual fluid chambers is based on the strength of the chamber materials to ensure that the parts do not fail. The fluid is selected based on safety, cost and availability, viscosity, as well as compatibility with the materials used and the operating environment of the helmets. The communication tubes are sized based on the desired flow rate. The hydraulic helmet system described herein is designed to reduce the peak force levels and lengthen the period over which the forces are experienced such that stimulation of natural resonant frequency of the brain is reduced. Since there are multiple energy dissipation pathways, the protection can be adjusted to any number of requirements based on the particular impact characteristics expected, which will differ in different sports and applications. The specific arrangement of fluid chambers, communication channels, and fluid composition will be different in helmets optimized for different sports. A helmet designed for use in bicycling may not be suitable for use in American football and vice versa. 
         [0043]    A method of forming helmet  10  according to an embodiment of the invention is shown in  FIG. 8 . Method  530  comprises forming outer shell  16  (step  531 ). Outer shell  16  may be a hard impact resistant shell that is larger than head  12 , or may be a flexible shell that is larger than head  12 . In an embodiment, a preferred hard impact resistant shell material may be a polycarbonate polymer with a Rockwell M hardness greater than 62. In another embodiment, a preferred flexible shell material may be a synthetic leather. The method may also include forming fluidly connected flexible fluid chambers for installation in the space between the outer and inner shells of the helmet (step  532 ). The flexible fluid chambers are designed to contain liquids of different viscosities depending on the application. Each fluidly connected flexible fluid chamber group is connected by tubing of various diameters depending on the anticipated functions of the helmet (step  533 ). Examples of suitable flexible tubing include vinyl, PVC, silicone, and others. In an embodiment, the chambers and interconnected tubes may be made from the same sheets of material with the size and shape of the chambers and fluid passageways established by pattern welding sheets of the material together. The interconnected bladders may then be filled with fluid (step  534 ). Suitable fluids for the invention include water, glycerin, mineral oils, ethylene glycol and others known and not known in the art. Flexible pads may then be formed for installation next to the flexible fluid chambers to fix the location of the flexible fluid chambers in the space between the outer and inner shells of the helmet (step  535 ). In an embodiment, the pads may be designed to deform under impacts exceeding about 5 G to 10 G. Candidate materials include open cell and closed cell foam made from synthetic materials including silicone and polyurethane. In the next step an inner shell may be formed (step  536 ). The inner shell may be a flexible material that conforms closely to the head of the wearer. Materials suitable for an inner shell may include the above materials noted for the flexible outer shell. 
         [0044]    Assembling the helmet may include attaching interconnected flexible fluid chambers and flexible pads to the outer and inner shells in the space between the shells to form the helmet (step  537 ). In the final step, a chinstrap and connector may be attached to the outer and inner shells to form the finished helmet ( 538 ). 
         [0045]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.