Abstract:
A battery pack includes a set of walls made of sturdy material, power interface terminals and battery cells and optionally electronics held within the walls. A spring-loaded check valve installed in a wall of the enclosure fluidly connects an area within the enclosure with an atmosphere outside of the enclosure. The one-way check valve allows pressurized fluids to flow out of the enclosure while preventing pressurized fluids from flowing from the atmosphere into the enclosure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a related to U.S. patent application titled “BATTERY CUSHION AND INSULATOR,” Ser. No. 12/786,473, attorney docket 3037.0, inventor Steven Tartaglia, filed May 25, 2010 and U.S. patent application titled “BATTERY PACK THERMAL PROTECTION FROM HEAT STERILIZATION,” Ser. No. 12/789,597, attorney docket 3044.0, inventor Steven Tartaglia, filed May 28, 2010. The contents of both applications are hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    This invention relates to the field of batteries and more particularly to a system for venting battery packs when external heat is introduced such as during thermal sterilization. 
       BACKGROUND 
       [0003]    Battery cells such as flooded lead-acid, absorbed-glass-matt (AGM), lead-acid, Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMh) and the like perform best at certain temperature ranges and are easily damaged when exposed to very high temperatures. When such battery cells, either standalone or within a battery pack, are exposed to certain high temperatures, various physical changes occur internal to the battery cells such as boiling of the electrolyte, etc. In an extreme case, such as boiling of the electrolyte, high pressure results within the sealed cell, leading to possible deformation of the outer case, deformation of the anode/cathode arrangements and, possible out-gassing or leakage of electrolyte, the later of which resulting in a totally useless cell. 
         [0004]    Many hospital or surgical related devices use battery packs, providing enhanced range of motion to surgeons and reducing the chance of a power cord finding its way into a bad location. There are many examples of such devices for drilling into bone, sawing bone, screwdrivers, making incisions, etc. These devices use battery packs that attach to the devices and provide power during, for example, an operation such as an orthopedic operation. In most systems, the battery pack is removable for charging in a charging station. 
         [0005]    A recent search indicates that many battery packs for such devices contain the heavy metal cadmium, Cd. The labels of these batteries show the chemical symbol, Cd, along with a crossed-out trash can, meaning that these batteries are not to be disposed of in ordinary trash due to land, water table and air pollution from landfills or incinerators. 
         [0006]    Once battery packs for medical devices are depleted and no longer provide ample charge for operating their intended equipment, the entire pack is discarded. This creates a dilemma because the battery packs are often exposed to body fluids, making them a bio-hazard. Bio-hazard material is often incinerated to neutralize the hazard, but most batteries cannot be incinerated due to pollution and/or explosion issued. Therefore, the battery packs should not be placed in bio-hazard disposal containers, yet, since they are now bio-hazardous, the exposed battery packs cannot be disposed in normal recycle locations. 
         [0007]    A majority of such battery packs currently being marketed are rechargeable and reusable, much like a battery pack for a home cordless drill. After use and/or before the next usage, the device and the battery packs must be sterilized to kill any pathogens present on surfaces and in cracks, etc. To sterilize a rechargeable battery pack, per one exemplary manufacturer&#39;s procedure, the battery pack is separated from the device and any debris or accumulation is cleaned. Next, sterilization is performed through an Autoclave Cycle. Autoclave cycles are, for example, 132° C.-137° C. for at least 15 minutes then 5 minutes drying time or 15 minutes of pre-heating, 132° C.-137° C. for at least 10 minutes, then 5 minutes drying time. Another, more typical autoclave cycle is 138° C. for 50 minutes in 28 PSI (pounds per square inch) pressurized steam. 
         [0008]    Such cycles, although hard on mechanical devices such as motors, usually do not severely affect the life of the actual devices. A key feature of most, if not all, battery packs is a vent. The vent is provided to expel gases that are potentially produced by the cells within the battery pack as may occur during charging. The vent is needed to reduce the internal pressure within the battery pack so that it does not reach a point at which the sealed case of the battery pack ruptures or explodes. 
         [0009]    For many non-medical applications, a simple air hole or other opening is sufficient to allow this potential pressure to escape. Such systems work well for applications such as notebook computers, etc., but are not acceptable in medical applications for several reasons, including introduction of biomaterial into the battery pack and introduction of moisture into the battery pack during the autoclave cycles. It is very difficult to sterilize biomaterial that has entered into a cavity such as the internal cavity of the battery pack. Also, moisture entering from the autoclave cycles will increase the weight of the pack, shorten the lifespan of the pack due to corrosion and shorten charge due to internal conduction. 
         [0010]    To reduce the introduction of biomaterial into the battery pack and introduction of moisture into the battery pack during the autoclave cycles, a one-way valve replaces the vent hole or opening, allowing internal pressure to escape while blocking external fluids from entering the battery pack. While several initial attempts at integrating one-way valves into battery packs have met the primary goal of venting gases and reducing the possibility of explosion, these attempts have not succeeded at preventing introduction of fluids into the battery pack. 
         [0011]    What is needed is a battery pack with a one-way vent that prevents introduction of moisture into the battery pack during autoclave and reduces accumulation of biomaterial during use providing for thorough sterilization during autoclave. 
       SUMMARY 
       [0012]    A battery pack is disclosed including a set of walls made of sturdy material, power interface terminals and battery cells and optionally electronics held within the walls. A spring-loaded check valve installed in a wall of the enclosure fluidly connects an area within the enclosure with an atmosphere outside of the enclosure. The one-way check valve allows pressurized fluids to flow out of the enclosure while preventing pressurized fluids from flowing from the atmosphere into the enclosure. 
         [0013]    In one embodiment, a battery pack is disclosed including an enclosure with one or more battery cells held within the enclosure. A one-way check valve, the one way check valve passes through a wall of the enclosure and fluidly connects an area within the enclosure with an atmosphere outside of the enclosure. The one-way check valve allows pressurized fluids to flow out of the enclosure while preventing pressurized fluids from flowing from the atmosphere into the enclosure. 
         [0014]    In another embodiment, a method of reducing battery cell failure during heat sterilization is disclosed including providing one or more battery cells, the battery cells being interconnected (series, parallel or series-parallel) to provide power to a device. The battery cells are enclosed into a battery pack in which the connection terminals are accessible from outside of the battery pack. A one-way check valve is affixed into a hole in a wall of the enclosure. The one way check valve fluidly connects an area within the enclosure with an atmosphere outside of the enclosure, allowing pressurized fluids to flow out of the enclosure and preventing pressurized fluids from flowing from the atmosphere into the enclosure. Thereby, pressurized steam presented during a heat sterilization cycle is prevented from entering the battery pack by the one-way check valve while abnormal pressure from within the enclosure escapes through the one-way check valve and to the atmosphere, reducing the potential for bursting and/or explosion. 
         [0015]    In another embodiment, a battery pack is disclosed including an enclosure that holds two or more battery cells. Conductive paths interconnect battery terminals of the battery cells in series, parallel or series-parallel configurations. A connection terminal that has electrical contacts is on or molded into the enclosure so that the electrical contacts are accessible from outside of the enclosure. A one-way check valve is sealedly installed in a wall of the enclosure. The one-way check valve fluidly connects an area within the enclosure with an atmosphere outside of the enclosure and allows pressurized fluids to flow out of the enclosure while preventing pressurized fluids from flowing from the atmosphere into the enclosure. The one-way check valve comprises of a valve seat, a valve ball, a vented enclosure and a spring. The spring urges the valve ball against the valve seat. The valve seat is fluidly interfaced to the area within the enclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
           [0017]      FIG. 1  illustrates a cut away view of a typical battery pack of the prior art. 
           [0018]      FIG. 2  illustrates a perspective view of a typical battery pack of the prior art. 
           [0019]      FIG. 3  illustrates a perspective view of a battery pack with improved venting. 
           [0020]      FIG. 4  illustrates an exploded view of a battery pack with improved venting. 
           [0021]      FIG. 5  illustrates a cross-sectional view of a battery pack with improved venting. 
           [0022]      FIG. 6  illustrates a cross-sectional view of a typical one-way valve. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Throughout the following detailed description, the same reference numerals refer to the same elements in all figures. 
         [0024]    Referring to  FIGS. 1 and 2 , views of a typical battery pack  10  of the prior art will be described. Typical battery packs  10  have a rigid enclosure  22 , usually made of Acrylonitrile butadiene styrene otherwise known as ABS. Within the plastic enclosure  22  are one or more battery cells  20  connected in series, parallel or series/parallel by interconnecting conductive paths (not shown) which are typically flat metal sheets that are tack-welded to battery terminals as known in the industry. One or more battery terminals are connected to a power connection terminal  15  for the delivery of power to a device and for the charging of the battery cells  20 . In many battery packs  10 , the battery pack  10  engages with a device (e.g. drill, saw, etc.) through a rail  13  and latch  11  system, although other attachment systems are also used to secure the battery pack  10  to the device during use and to conduct electricity to/from the battery pack  10  during use and/or charging. Often, the same rail  15 , contact  15  and latch  11  system is used to hold the battery pack  10  in a charging cradle (not shown). 
         [0025]    Although not shown, for completeness, often such battery packs  10  include other devices such as electronic circuits that prevent over current, over voltage, under voltage, control charging, prevent over-temperature situations during charging, etc. All such devices are known and present in some battery packs  10 , but have been left out for clarity reasons. 
         [0026]    Battery packs for general purpose use often release unexpected internal pressure through a simple pressure relief system such as a vent hole, a vent hole covered by a label, an area of the case that is thinner and breaks under pressure, etc. Such venting is not intended for medical purposes because of the heat and pressure to which the battery pack is subjected during sterilization. These systems are likely to fail under the pressure of a typical autoclave cycle, enabling the introduction of moisture, water and biohazard material into the internal cavities of the battery packs. The exemplary battery pack  10  of the prior art, shown in  FIGS. 1 and 2 , has a simple device  12 / 14 / 16 / 18  that is an attempt to prevent the introduction of moisture, water and biohazard material into the internal cavities of the battery pack  10 . In this, a one-way valve  12  is formed in the shape of a “T” having a planar top  14  that is larger than a hole  21  in the battery pack, a typically cylindrical shaft  18  that extends through the wall  22  of the battery pack  10  and a bulge or dimple  16  that is slightly wider than the hole  21 . The entire valve  12  is made from a rubber material that helps provide a seal between the case wall  22  and the planar top  14 . Since the rubber material is pliable, during manufacture the shaft  18  of the valve  12  is inserted through the hole  21  and the bulge/dimple  16  deforms enough to enable installation, then restores to its original size/shape, thereby holding the valve  12  in place. 
         [0027]    When such a battery pack  10  is placed in a sterilizing chamber such as an Autoclave during a sterilization cycle, external temperatures rise to a temperature between 132° C. and 138° C. and steam pressure is introduced at around 28 PSI. This temperature and pressure is typically maintained for 50 minutes. Under pressure, the valve  12  of the prior art is pushed against the wall  22  of the battery pack  10 , but due to manufacturing and material tolerances, steam under pressure finds its way between the enclosure wall  22  and the valve planar top  14  and into the battery pack  10 . Additionally, during use, since pressure differences between outside and inside of the battery pack  10  vary as the battery cells  20  within the battery pack  10  heat and cool, biohazard material often finds its way beneath the planar top  14  and into the battery pack  10 . 
         [0028]    It has been found that some hospitals are performing short-cycle autoclave procedures on such battery packs  10  to reduce filling of the battery packs  10  with moisture from the high pressure steam. It has also been found that cases of certain infections such as staff infections increase when less-than adequate sterilization processes are used. 
         [0029]    Referring to  FIGS. 3 ,  4  and  5 , views of a battery pack  30  with an improved venting system are described. The improved battery packs  30  have an enclosure  22 , made of any known rigid material such as ABS or a more heat resistant plastic such as Ultem from GE plastics. Within the enclosure  22  are one or more battery cells  20  (not visible) connected in series, parallel or series/parallel by interconnecting conductive paths (not visible), typically flat metal sheets that are tack-welded to battery terminals. Any known or future battery chemistry is anticipated including, but not limited to, alkaline, lead acid, nickel cadmium, nickel metal hydride, lithium, lithium ion, mercury, lithium iron, etc. 
         [0030]    One or more battery terminals are connected to power connection terminals  15  for the delivery of power to a device and for the charging of the battery cells  20 . Although, one specific configuration of connection terminals  15  is shown, any known connection configuration is anticipated. In a preferred embodiment, though not required, rails  13  and a latch  11  provide a secure attachment mechanism to devices such as drills, saws, charging stations, etc. Likewise, although, one specific configuration of rails  13  and latches  11  is shown, any known attachment configuration is anticipated. 
         [0031]    Although not shown, for completeness, often such battery packs  30  include other devices such as electronic circuits that prevent over current, over voltage, under voltage, control charging, prevent over-temperature situations during charging, etc. All such devices are known and present in some battery packs, but have been left out for clarity reasons. 
         [0032]    A one-way valve  50  is mounted in a hole  21  in the wall  22  of the enclosure. Although any industrial one-way valve  50  is anticipated, the exemplary one-way valve  50  as shown in  FIG. 6  is a spring-loaded, seated ball type valve. In such, a spring  52  or other resilient member urges a ball  56  or other shaped object onto a seat  60 . The spring  52  maintains pressure on the ball  56 , holding it tightly against the seat  60 , preventing external materials from entering the battery pack  30  independent upon external pressure, atmospheric conditions and orientation of the battery pack  10 . The spring  52  provides sufficient force to prevent the ball from unseating during internal pressure changes that occur for heating and cooling of the battery cells  20  during use and/or charging. The force of the spring  52  is overcome by extreme pressure from within the battery pack  30  that occurs, for example, when a battery cell  20  failure occurs and gases are vented, thereby the ball  56  lifts from the seat  60  and the gases escape through the vent openings  54 . 
         [0033]    Another, optional, aspect of the improved venting system is a flexible or semi-rigid conduit  36  that surrounds the one-way valve  50 . The flexible or semi-rigid conduit  36  reduces or prevents biohazard material from collecting within and around the one-way valve  50 . In a preferred embodiment, a first end of the flexible or semi-rigid conduit  36  is mounted within the same hole  21  as the one-way valve  50  and a distal end of the flexible or semi-rigid conduit  36  is covered by the latch  11 , thereby covering the flexible or semi-rigid conduit  36  and preventing or reducing material introduction into and around the one-way valve  50 . 
         [0034]    Equivalent elements can be substituted for the ones set forth above such that they perform in substantially the same manner in substantially the same way for achieving substantially the same result. 
         [0035]    It is believed that the system and method as described and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.