Abstract:
A protective helmet includes a plurality of fluid filled bladders, impact sensors, valves, and pumps wherein the helmet absorbs energy from an impact to protect a person wearing the helmet from traumatic brain injury. The bladders expel fluid in response to a triggering event such as energy from an impact detected as a pressure spike event and/or detected as an acceleration event. A selected bladder may expel fluid to other bladders, to a reservoir, to the environment outside of the protective helmet, or combinations thereof. In embodiments where the bladders need additional fluid after an impact, one or more pumps may refill selected deflated bladders. When a bladder is underinflated, an indicator light may emit light on an outer surface of the protective helmet to warn that the bladder is not yet ready to be placed in operation to absorb another impact.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to protective gear including helmets, and more particularly to protective helmets especially adapted for sporting events such as football, lacrosse, hockey and baseball, wherein the protective helmet is designed to reduce traumatic brain injuries. 
       BACKGROUND OF THE INVENTION 
       [0002]    Contact sports, such as football, require the use of helmets to protect players from head injuries caused by impact forces sustained during games or practice. In recent years, a degenerative disease known as chronic traumatic encephalopathy (CTE) has been diagnosed in many retired players of contact sports. While the scientific analysis and characterization of CTE is ongoing, cumulative concussions are believed to cause the physical manifestations of CTE including atrophy of certain regions of the brain. Even numerous sub-concussive events are thought to contribute to CTE. For example, collisions between defensive and offensive linemen in football rarely render players completely unconscious, but numerous sub-concussive impacts may accumulate and contribute to CTE. Spurred by new knowledge of CTE and CTE&#39;s effect on players, the importance and effectiveness of helmet technology has become paramount to the health of sports players and others. 
         [0003]    Several types of helmets have been used in the sport of football ever since players began wearing helmets. Early football helmets were made from hardened leather. Modern helmets are made from plastic and generally include a shock absorbing liner within a plastic shell, a face guard, and a chin strap that fits snugly on the chin of a player to secure the helmet to the player&#39;s head. 
         [0004]    An example of a prior art device may be found in U.S. Patent Publication No. 2014/0000011, which discloses a helmet having cells filled with an attenuating fluid such as CO2, air, or water. An accelerometer on each cell may detect an impact and a microcontroller opens an exhaust valve on the cell, which allows the cell to discharge the attenuating fluid in an effort to absorb some of the impact. The cells must be pre-filled with the attenuating fluid. Therefore, a player must return to the sideline after each impact that triggers a release of attenuating fluid. This interruption can negatively affect the play of the game when players are routinely exiting and entering the field of play. 
         [0005]    Another example of a prior art device may be found in U.S. Patent Publication No. 2012/0304367, which discloses a helmet with a protective bladder and relief valves. If the pressure in the bladder is greater than a threshold pressure, then the relief valve is opened to evacuate the contents of the bladder to help absorb an impact. However, there is no system or protocol for a post-impact inflation of the bladder. During a football game, a player may experience a first impact early in a play and then a second impact later in the play. If the bladder remains deflated for the second impact, then the player is at an increased risk of experiencing a concussive or sub-concussive impact that can contribute to CTE. 
         [0006]    While the prior art may be adequate for its intended purposes, there is still a need for a protective helmet that provides better protection to reduce impact forces sustained by helmet wearers. There is also a need for a protective helmet that provides optimal brain protection for a wearer in which the protective helmet can be re-set or otherwise returned to a ready state by fluid bladders or reservoirs that deflate upon impact but are then automatically re-inflated after an initial impact. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with the invention, a protective helmet is provided that comprises a plurality of fluid bladders or reservoirs that absorb energy from an impact and a system for reinflating the bladders after the impact. Sensors can open and close valves on the bladders to expel fluid. Re-inflation of the bladders can be controlled after a predetermined amount of time elapses after the initial impact or once key pressure readings within the bladders rise or fall below a predetermined threshold pressure. Generally, the systems for reinflating the bladders can be open systems or closed systems. Open systems may expel fluid outside of the helmet to absorb an impact, and then draw in fluid from outside of the helmet to reinflate the bladders. Bladders in a closed system may also expel fluid during an impact, but the expelled fluid is captured by the system and used to reinflate the bladders of the protective helmet after the impact. 
         [0008]    An open system for a protective helmet can incorporate one or more pumps to re-inflate the deflated bladder(s) in the protective helmet. In some embodiments, each bladder in the protective helmet may have its own corresponding pump. When a bladder experiences an impact, a triggering event causes a valve on the bladder to open and expel fluid outside of the bladder system to absorb the impact. This triggering event may be a pressure spike or an acceleration of the helmet and bladder beyond a predetermined threshold. After expulsion of the fluid, the pump re-inflates the deflated bladder to a pre-impact or fill pressure. In other embodiments, the bladders are interconnected to a single pump, which may be positioned in the helmet or remotely such as on the shoulder pads of a football player. The bladders may be arranged in series or in parallel with the pump. 
         [0009]    A closed system for a protective helmet can incorporate a system of valves and reservoirs to store expelled fluid and reinflate a bladder. In some embodiments, the bladders are in fluid communication with a reservoir that defines a volume. During an impact, a bladder may expel fluid into the reservoir such that the pressure of the fluid in the reservoir increases and the pressure of the bladder decreases to absorb the impact. Once the impact has been absorbed, the reservoir may reintroduce the pressurized fluid back to the deflated bladder to return the bladder to its pre-impact or fill pressure. The reservoir may be arranged in many different configurations. For example, the reservoir may be a vessel positioned adjacent to the protective helmet or remotely, for example, in the shoulder pads of a football player. In other embodiments, the reservoir may be incorporated in the interstitial spaces between bladders or a space in a structural support band of the helmet. In yet further embodiments, the reservoir may be a pressure accumulator that has an interior bladder that helps store potential energy by compressing a second fluid. It will be appreciated that some embodiments of the invention can include aspects or components from both an open system and a closed system for a protective helmet. 
         [0010]    Various embodiments of the protective helmet may actively manipulate valves and connections in response to a triggering event to better absorb an impact. For example, the plurality of bladders can be in fluid communication with each other such that a pressure change in one bladder is transmitted to at least one other bladder. Thus, the forces from an impact can be distributed across multiple bladders instead of a single bladder. In some aspects of the invention, a sensor for a given bladder may operably communicate with sensors on more than one bladder. Therefore, when a sensor detects a triggering event, the sensor can open valves on multiple bladders to quickly deflate the bladder absorbing the brunt of the impact. 
         [0011]    In various aspects of the invention, the sensors may employ one of many different types of sensors configured to detect a triggering event or events. For instance, the sensor may be a pressure sensor configured to detect a pressure increase beyond a threshold or a pressure decrease below a threshold. The pressure sensor may also be configured to detect a rate change of pressure beyond a predetermined threshold. In another example, the sensor is an accelerometer that detects an acceleration of the bladder or protective helmet. Embodiments of the instant invention may interpret excessive acceleration of the bladder or helmet as an impact event, and thus, the sensor causes the valve on a bladder to open and release fluid to absorb the impact. The sensor can also detect a follow-up event or second triggering event and cause the valve to close. In various embodiments, the bladders maintain a minimum pressure to prevent a direct impact through a completely deflated bladder and to the head of a person who is wearing the protective helmet. The second triggering event may be, for example, a minimum pressure in the bladder or a delay period after the first triggering event. It will be appreciated that in some embodiments a separate controller may be used to route the logic considerations of the invention. 
         [0012]    Bladders and other components of the invention may be made from a variety of materials and combinations of materials. The bladders can be made from high resistance polyvinyl chloride (“PVC”), polyester with PVC induction, acrylonitrile butadiene rubber, perbunan, butyl rubber, flouro rubber, Viton, ethylene oxide epichlorohydrin rubber, and other various elastomers. Various valves, sensors, and other components may be integrated into a bladder using high frequency soldering techniques. The fluids used in the bladder may include air, water, mineral oil, and/or hydrocarbons. 
         [0013]    While use of the protective helmet described herein reduces the effects of an impact, most helmets currently used in sports do not have a bladder system. Therefore, it is desirable to retrofit existing helmets with a bladder system to incur the benefits associated with embodiments of the protective helmet described herein. Existing helmets often have a foam lining or foam inserts to help absorb an impact. These inserts may be removed, and a bladder system according to embodiments of the invention may be inserted into a shell of the helmet. In more extensive modifications, the helmet may be cut down to a structural support band that allows a facemask to attach to the helmet and allows bladders to absorb impacts without an intermediate shell. Other components such as a reservoir or a pump may also be positioned on the helmet or in another location on a person wearing the helmet. Therefore, a helmet retrofitted with embodiments of the invention may absorb an impact and then reinflate after the impact. 
         [0014]    Considering the above described features and attributes, in one aspect of the invention, it can be considered a protective helmet, comprising (a) a structural support band defining a perimeter edge of the protective helmet; (b) a plurality of bladders interconnected to the structural support band, each bladder in the plurality of bladders having a volume configured to store a fluid; (c) a valve positioned on each bladder in the plurality of bladders, each valve is in fluid communication with the corresponding volume of each bladder in the plurality of bladders; (d) a sensor positioned on each bladder in the plurality bladders, each sensor is in operable communication with the corresponding valve of each bladder in the plurality of bladders, wherein each valve is configured to open and release at least some of the fluid stored in corresponding volume when the corresponding sensor detects a triggering event; and (e) a pump in fluid communication with the volumes of the plurality of bladders, the pump configured to increase the pressure of the fluid stored in the volumes of the plurality of bladders to a fill pressure after deflation of one or more bladders. 
         [0015]    In another aspect of the invention, it can be considered a method for absorbing an impact to a protective helmet, comprising (a) providing a plurality of bladders interconnected to a structural support band that defines a perimeter edge of the protective helmet, each bladder in the plurality of bladders having a volume configured to store a fluid, a valve in fluid communication with the volume, and a sensor in operable communication with the valve; (b) providing a pump in fluid communication with the volumes of the plurality of bladders; (c) detecting, by one of the sensors, a triggering event and then opening the valve on the corresponding bladder to release at least some of the fluid stored in the volume of the corresponding bladder; (d) closing the opened valve when the sensor detects a second triggering event; (e) pumping, by the pump, fluid into the volumes of the plurality of bladders to a fill pressure after deflation of one or more bladders. 
         [0016]    In some aspects, it can be considered a protective helmet, or a method for absorbing an impact to a protective helmet, wherein the plurality of bladders comprises a right front bladder, a right rear bladder, a left rear bladder, a left front bladder, a top left bladder, and a top right bladder. In addition, a pump may be positioned on each bladder in the plurality bladders; each pump is in operable communication with the corresponding sensor of each bladder in the plurality of bladders. 
         [0017]    In various other aspects, it can also be considered a protective helmet, or a method for absorbing an impact to a protective helmet, further comprising a padding layer disposed on an inner surface of the plurality of bladders, the padding layer having an inner surface that is distinct from the inner surface of the plurality of bladders. In addition, it can be considered a protective helmet further comprising an indicator light positioned on an outer surface of the plurality of bladders, the indicator light configured to emit light after deflation of one or more bladders. 
         [0018]    In yet other aspects, it can also be considered a protective helmet, or a method for absorbing an impact to a protective helmet, wherein the sensors are one of (i) pressure sensors configured to detect a triggering event that is a pressure increase beyond a predetermined pressure threshold; and (ii) accelerometers configured to detect a triggering event that is an acceleration beyond a predetermined acceleration threshold. Additionally, each valve may be configured to close when the corresponding sensor detects a second triggering event, wherein the second triggering event may be one of (i) a pressure decrease below a second predetermined pressure threshold; and (ii) a delay period after the first triggering event. The sensors may also be in operable communication with each other, wherein the sensor that detects the triggering event is configured to open more than one valve. 
         [0019]    In some aspects, it can be further considered a protective helmet, or a method for absorbing an impact to a protective helmet, further comprising a plurality of fluid lines that provide fluid communication between bladders in the plurality of bladders such that a pressure change in one bladder is transmitted to at least one other bladder. In addition, a first check valve may be positioned in a first tube of each fluid line in the plurality of fluid lines, the first check valve oriented to allow fluid flow in a first direction; and a second check valve may be positioned in a second tube of each fluid line in the plurality of fluid lines, the second check valve oriented to allow fluid in a second direction. Further, the first check valve may have a first cracking pressure, and the second check valve may have a second cracking pressure, wherein the first cracking pressure is set to the fill pressure of the fluid in the volumes of the plurality of bladders. 
         [0020]    In addition, it can be considered a protective helmet, or a method for absorbing an impact to a protective helmet, further comprising (i) a centralized controller operably interconnected to at least one sensor and at least one valve in the plurality of bladders, the controller configured to receive an input signal from the at least one sensor and transmit an output signal to the at least one valve, depending on a predetermined logic, and/or (ii) a decentralized controller positioned on each bladder in the plurality of bladders, each controller configured to receive an input signal from a corresponding sensor and transmit an output signal to a corresponding valve, depending on a predetermined logic. 
         [0021]    Further advantages and features of the invention will become apparent from a review of the following detailed description, taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Reference is now made to the following detailed description taken in conjunction with the accompanying drawings in order for a more thorough understanding of the invention. 
           [0023]      FIG. 1  is an exploded perspective view of a protective helmet having a system of six deflatable bladders interconnected to a structural support band; 
           [0024]      FIG. 2  is a side view of an open system of bladders where each bladder has a sensor, a valve, and a pump; 
           [0025]      FIG. 3A  is a side view of another open system of bladders where each bladder has a sensor and a valve, and the bladders are each in fluid communication with a remote pump; 
           [0026]      FIG. 3B  is a schematic block diagram illustrating the electronic communication between a sensor, a controller, valves, and a pump in response to multiple triggering events; 
           [0027]      FIG. 4  is a side view of another open system of bladders where each bladder has a sensor and a valve, and the bladders are each in fluid communication with a remote reservoir and a remote pump; 
           [0028]      FIG. 5  is a side view of another open system of bladders where each bladder has a sensor and a valve, and the bladders are connected in series to a remote pump; 
           [0029]      FIG. 6  is a side view of a closed system of bladders where check valves interconnect the bladders to each other; 
           [0030]      FIG. 7  is a side view of a closed system of bladders where check valves interconnect the bladders to each other and to a remote reservoir; and 
           [0031]      FIG. 8  is a cross-sectional view of a protective helmet where check valves interconnect a system of bladders to a reservoir positioned between an inner shell and an outer shell of the protective helmet. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Referring to  FIG. 1 , a protective helmet  10  is shown that incorporates a system of bladders  16  to absorb energy from an impact, such as a collision between players during a football game. The protective helmet  10  has a structural support band  12  which may be made from a plastic material to serve as support for attachment of a facemask  14  and the system of bladders  16 . The structural support band  12  generally follows an edge perimeter of a traditional helmet while the system of bladders  16  supplements the structural support band  12  to cover the rest a person&#39;s head. In some embodiments, the structural support band  12  may include an ear hole, as shown in  FIG. 1 , and the facemask  14  is positioned at the front of the helmet  10  to prevent an object from reaching the face of a person. The facemask  14  may interconnect to a plurality of points on the helmet  10  including grommets (not shown) incorporated in the structural support band  12  of the helmet  10 . 
         [0033]    A system of bladders  16  is joined to the structural support band  12  to deflate and absorb energy from an impact. The system of bladders  16  in this embodiment comprises six bladders. A right front bladder  16   a  and a right rear bladder  16   b  protect the right side of a person&#39;s head, and a left rear bladder  16   c  and a left front bladder  16   d  protect the left side of a person&#39;s head. A left top bladder  16   e  and a right top bladder  16   f  protect the crown of a person&#39;s head. It will be appreciated that embodiments of the system of bladders  16  are not limited to a six-bladder configuration. For example, a protective helmet  10  may be outfitted with more than six bladders or fewer than six bladders, including a single continuous bladder. 
         [0034]    The bladders  16  of the helmet  10  may be used in combination with other types of padding such as stiffened or hardened padding. For example, the helmet  10  may include ear padding  18 , which can be stiffened padding or even deflatable bladders in some embodiments. In addition, the protective helmet  10  in  FIG. 1  comprises an inner padding layer  20  between the system of bladders  16  and the person&#39;s head. The system of bladders  16  may not provide an ergonomic fit with the person&#39;s head since heads come in a wide range of shapes and sizes. A lack of ergonomic fit can cause the helmet  10  to move relative to a person&#39;s head and reduce the effectiveness of the protective helmet  10 . Thus, in some embodiments, the inner padding layer  20  can provide a closer approximation to the shape of a person&#39;s head or in some instances the inner padding layer  20  can be custom fit to the person&#39;s precise head dimensions. The inner padding layer  20  may be made from a viscoelastic or low-resilience polyurethane foam. In other embodiments, a suspension system may be utilized where the system of bladders  16  is set off from the person&#39;s head by a predetermined distance and a series of straps interconnect the person&#39;s head to the system of bladders  16  and the protective helmet  10 . Of course, it will be appreciated that embodiments of the protective helmet  10  may not include an inner padding layer  20  or strap system. 
         [0035]    The outer surface of the protective helmet  10  in  FIG. 1  comprises an outer layer  22 . Team logos and other decals may be difficult to place on the material of the bladders  16 . Therefore, an outer layer  22  can selectively interconnect to the structural support band  12  or the bladders  16  and cover the bladders  16 . The outer layer  22  can be air permeable to allow valves and pumps on the bladders  16  to function and to prevent dirt and other debris from contacting the bladders  16 . The outer layer  22  may also provide a lower coefficient of friction than the material of the bladders  16  to enhance slipping or sliding of the protective helmet, thereby lessening the energy of the impact to be more of a “glancing” blow, such as may be the case when there is contact with other helmets, other players, the ground, etc. This slipping aspect of the outer layer  22  can also reduce the rotation of the protective helmet during an impact, which reduces the likelihood of a concussion and trauma to the brain. 
         [0036]    A series of openings or holes in the protective helmet  10  can aid in the ventilation of heat from a person&#39;s head to the ambient environment. The interconnection or selective interconnection between bladders  16  may set the bladders  16  apart from each other by a predetermined distance. Thus, the gaps in the interstitial spaces between the bladders  16  allow heat to vent away from a person&#39;s head. In various embodiments, the bladders  16  themselves may comprise openings or holes to ventilate heat. For example, a bladder  16  may have a central aperture such that the bladder  16  is substantially shaped like a ring. In some embodiments, the structural support band  12  may comprise an open, lattice-like structure to provide the necessary functionality described above and to provide enhanced heat transfer properties to the protective helmet  10 . Similarly, the outer layer  22  may comprise openings or holes to facilitate heat transfer from a person&#39;s head to the ambient environment. 
         [0037]    Referring to  FIG. 2 , an open system of bladders is provided where each bladder  16  has a sensor  24  and a valve  26  configured to expel fluid during an impact and a pump  28  to reinflate the bladder  16  after the impact. The system of bladders  16  is open to an external source of fluid, which in some embodiments may simply be ambient air. For example, after a bladder  16  expels fluid from a valve  26 , the pump  28  draws in ambient air to reinflate the bladder  16 . 
         [0038]    The valve  26  is configured to open and expel fluid when the sensor  24  detects a triggering event. This event may be a pressure spike or an acceleration of the helmet  10  or bladder  16 , and thus, the sensor  24  may be a pressure sensor or an accelerometer. After opening, the valve  26  may close again to prevent a complete deflation of the bladder  16 . A complete loss of pressure in the system of bladders  16  would allow direct impacts to a person&#39;s head. The valve  26  may close when the sensor  24  detects a second triggering event such as a pressure drop below a predetermined threshold or a delay period. For example, the valve  26  may automatically close 1 second after the first or initial triggering event to prevent further expulsion of fluid. In view of the first and second triggering events, an optimal pressure range may be established. In some embodiments, the pressure range may be between 20 psi and 40 psi. As such, the valve  26  would open when the pressure exceeds 40 psi, and close when the pressure falls below 20 psi. Then, the pump  28  would reinflate the bladder to an intermediate fill pressure, for example, 30 psi. 
         [0039]    Referring to  FIG. 3A , an open system of bladders is provided where each bladder  16  has a sensor  24  and a valve  26  configured to expel fluid during an impact. A series of fluid lines  30  interconnect the bladders  16  to each other to help disperse an impact. An additional fluid line  30  interconnects a remote pump  28  to one of the bladders  16 . When one or more bladders  16  expels fluid to absorb an impact, the pump  28  supplies fluid to the system of bladders  16  to reinflate the one or more bladders  16  after the impact. 
         [0040]    A further aspect of some embodiments is the ability for bladders  16  and components on the bladders  16  to be in electronic communication with each other, which allows a holistic and coordinated response to an impact to improve the effectiveness of the helmet  10 . For instance, a bladder  16  on the right side of a person&#39;s head may experience an impact, but only the valve  26  on this bladder opens and expels fluid. As a result, some fluid in the bladder  16  may compress and exit through a fluid line  30  and then compress fluid in another bladder  16 . This series of compressions takes time and creates backpressure for the bladder  16  absorbing the impact. Thus, the single valve  26  expelling fluid can be a choke point, and the bladder  16  may deflate too slowly to properly absorb the impact. 
         [0041]    The electronic communication between bladders  16 , sensors  24 , and valves  26  allows for valves on multiple bladders  16  to open and expel fluid. Referring to the previous example, when the right bladder  16  is experiencing an impact, the sensor  24  on this bladder  16  communicates a triggering event to valves  26  on other bladders  16 . Therefore, valves  26  may open an expel fluid from bladders  16  that are not experiencing the brunt of an impact, which allows the bladder  16  that is experiencing the brunt of the impact to expel fluid more quickly and without backpressure issues. 
         [0042]    Next, referring to  FIG. 3B , a schematic diagram is provided showing the electronic communication between the sensor  24 , a controller  34 , valves  26 , and the pump  28  in response to multiple triggering events  32   a ,  32   b . The controller  34  serves as an automatic data processor to run algorithms and predetermined logic that control the state of the valves (open/closed) and the pump (on/off). The controller  34  may be connected to an electric power source so that the controller  34  can operate, which includes transmitting output signals to other components. It will be appreciated that the functions of the controller  34  described herein may be integrated into other components, for example, the sensor  24 . 
         [0043]    The sensor  24  on the bladder  16  detects a first triggering event  32   a , and the sensor  24  transmits an input signal to the controller  34 . The controller  34  receives the input signal and orchestrates the proper response to the first triggering event  32   a  with various predetermined logic considerations. A logic consideration with respect to the first triggering event  32   a  may be the pressure reading of the bladder  16  above a threshold, and another logic consideration may be the acceleration of the helmet and bladder  16  above a threshold. If the proper logic consideration is satisfied, the controller  34  transmits an output signal to the first valve  26   a , causing the valve  26   a  to open and expel fluid from the bladder  16 . Further, as described with respect to  FIG. 3A , the controller  34  also may send an output signal to a second valve  26  to open and expel fluid from another bladder. The logic considerations and thresholds may be adjustable and/or pre-programmable. For instance, a “youth setting” may have lower pressure spike or acceleration thresholds for expelling fluid while “high school,” “college,” and “professional” settings can have higher thresholds for expelling fluid. 
         [0044]    Then, the controller  34  dictates how to reinflate the depleted bladder  16  with the pump  28 . One logic consideration is that the controller  34  simply transmits an output signal to the pump  28  to begin pumping after a time delay from the first triggering event  32   a . Another logic consideration is that the controller  34  transmits an output signal to the pump  28  to begin pumping based upon a reading from the sensor  24 . The reading may be a pressure threshold, for example, a minimum pressure to prevent direct impact to the head of the person wearing the protective helmet. Further embodiments of the present invention may combine various logic considerations and even organize logic considerations into a hierarchy. For example, a small pressure spike results in a quick opening of a valve to expel a small amount of fluid, but a large pressure spike will cause the valve to remain open until a minimum pressure is reached, then the valve will close. 
         [0045]    It will be appreciated that a controller  34  can be centralized to control more than one bladder, sensor, and/or valve, but a controller  34  may also be decentralized. For example, each bladder may have a controller  34  such that the bladders are modular and operate independently of each other. Therefore, a controller  34  may receive an input signal from a sensor on a bladder and, depending on the particular logic consideration, transmit an output signal to a valve on the bladder to control the state of the valve. With the modular, decentralized embodiments, a defective bladder system may be replaced without interrupting the operation of other bladders and bladder systems in the protective helmet  10 . 
         [0046]    Referring to  FIG. 4 , an open system of bladders  16  is provided similar to the system of  FIG. 3A , but a remote reservoir  36  is incorporated into the protective helmet  10  to alter the reinflation characteristics of the helmet. The reservoir  36  is positioned on the fluid line  30  that interconnects the pump  28  to the system of bladders  16 . The reservoir  36  may be a vessel defining a volume that can store and release a pressurized fluid. In one example, the pump  28  begins charging the reservoir  36  with pressurized fluid as soon as one of the sensors  24  detects a triggering event such as a pressure spike or an acceleration of the helmet beyond a predetermined threshold. After a charging period, the reservoir  36  dumps the pressurized fluid into the system of bladders  16  to reinflate the bladders  16 . The charging period allows the pump  28  to immediately begin accumulating pressurized fluid in the reservoir  36  during an impact without adding backpressure to the system of bladders  16  and interfering with the ability of the bladders  16  to expel fluid. The charging period, the volume of the reservoir  36 , the number of reservoirs  36 , the configuration of reservoirs  36 , etc. may be altered to adjust the reinflation characteristics of the system of bladders  16  of the protective helmet  10 . It will be further appreciated that instead of a charging period, for example, a pressure reading from one or more bladders can be used to control when the pump  28  begins pressurizing fluid, and when the reservoir  36  subsequently discharges pressurized fluid. 
         [0047]    Referring to  FIG. 5 , an open system of bladders  16  is provided where each bladder  16  is serially interconnected to the pump  28 . Specifically, a fluid line  30  from each bladder  16  extends to a distributor  38 , which is then interconnected to the pump  28  via another fluid line  30 . The distributor  38  can store pressurized fluid like a reservoir and/or selectively control fluid communication from the pump  28  to each of the bladders. The serial interconnection of the bladders in  FIG. 5  is in contrast to the generally parallel interconnection of the bladders in  FIGS. 3A and 4  to the pump  28 . The various types of interconnections can provide different reinflation characteristics for the system of bladders  16  of the protective helmet  10 . 
         [0048]    Referring to  FIG. 6 , a closed system of bladders  16  is provided where fluid lines  30  interconnect the bladders  16  to each other. The system of bladders  16  is closed to external sources of fluid and thus relies on a fixed volume of fluid to absorb an impact. In this embodiment, each fluid line  30  has first and second tubes, and a check valve is positioned in each tube. In a given fluid line  30 , first and second check valves  40   a ,  40   b  are oriented in opposite directions. Thus, when a bladder  16  is absorbing an impact, fluid only flows out of the bladder  16  and into other bladders  16  to help mitigate against backpressure issues. After the impact has been absorbed, the other bladders  16  reinflate the bladder  16  that absorbed the impact. 
         [0049]    Referring to  FIG. 7 , a closed system of bladders  16  is shown that is similar to the embodiment in  FIG. 6 . However, the embodiment in  FIG. 7  comprises an addition fluid line  30  with tubes and check valves  40   a ,  40   b  that leads to a reservoir  36 . This embodiment also operates like the embodiment in  FIG. 6  except that a reservoir  36  is now available to receive pressurized fluid from a bladder  16  absorbing an impact. The bladders  16  are generally interconnected in parallel with the reservoir  36 . Other embodiments may have other configurations such as a serial interconnection with a distributor as discussed elsewhere herein. 
         [0050]    Referring to  FIG. 8 , a cross sectional view of a closed system of bladders  16  is provided where the shell of the helmet  10  comprises an outer shell  42   a  and an inner shell  42   b . The hermetically sealed volume between the shells  42   a ,  42   b  functions as a reservoir  36  in this embodiment. Oppositely oriented check valves  40   a ,  40   b  individually interconnect each bladder  16  to the reservoir  36 . Thus, when a bladder  16  absorbs an impact, the bladder  16  expels fluid into the reservoir  36 . After the impact is absorbed, the now-pressurized reservoir reinflates the bladder  16 . 
         [0051]    It will be appreciated that in other embodiments, the reservoir  36  is positioned in the structural support band defining the perimeter edge of the protective helmet  10 . The structural support band may have an enclosed volume that serves as a reservoir  36  and is interconnected to the bladders with fluid lines and/or check valves. When the bladders absorb an impact, pressurized fluid is stored in the reservoir  36  in the structural support band. 
         [0052]    While the above description and drawings disclose and illustrate embodiments of the invention, it should be understood that the invention is not limited to these embodiments. It will be appreciated that other modifications and changes employing the principles of the invention, particularly considering the foregoing teachings, may be made. Therefore, by the appended claims, the applicant intends to cover such modifications and other embodiments.