Abstract:
A pressure relief valve, according to the invention, is mounted on a vent orifice providing a gas passageway from an interior plenum of a battery or a cell thereof to the ambient atmosphere. The valve fits on the vent orifice and opens to release gas at a high threshold battery gas pressure and reseals the vent orifice when the internal pressure of the battery drops to a low threshold.

Description:
FIELD OF THE INVENTION 
     This invention relates to a recombinant battery and in particular to a pressure relief valve for a recombinant lead acid battery. 
     BACKGROUND OF THE INVENTION 
     Proper operation of a recombinant (valve regulated) sealed lead acid battery, is highly dependent on regulating the proper internal gas pressure within the battery container. A pressure relief valve is an important component to maintain this proper gas pressure. A properly functioning pressure relief valve regulates the gas pressure by releasing gas from the battery container through a vent, coupling the internal battery plenum to the ambient atmosphere, when a high internal threshold pressure is reached, and resealing the vent when the internal pressure drops to a second low threshold pressure. Failure of the pressure relief valve may cause catastrophic failure of the battery due to excessive loss of the battery fluid at an undersirable low pressure or an explosion due to excess gas pressure, depending upon the nature of the performance failure of the pressure relief valve. A properly operating relief valve should accurately release and reseal in its every expected position in which the cell battery operates in response to the high and low pressure thresholds. 
     Pressure relief valves are often constructed of a resilient hard rubber. Venting action by the pressure relief valve depends upon the valve having a pressure responsive movement, such as the flaring of a skirt member of the valve, in response to pressure above some high pressure threshold and an ability to reseal below at another lower pressure threshold. Such a pressure relief valve construction is disclosed in the U.S. Pat. No. 4,780,378. At high pressure the skirt member of the valve flares outwardly to prevent the build up of internal pressure in the battery, but as the pressure drops the skirt member is relaxed and returns to a sealed condition. 
     The movement of the valve can cause the valve to move in a manner which causes it to improperly reseat following pressure reduction after a pressure relief operation. The valve mechanism in such a case ceases to function at the designated release and reseal gas pressures. In some designs resealing may fail to occur altogether. The valve is normally constrained to remain in an operative position by elaborative mechanical structure such as disclosed in U.S. Pat. No. 4,780,378. This structural arrangement is typically expensive. 
     SUMMARY OF THE INVENTION 
     A pressure relief valve, according to the invention, is mounted atop a vent tube orifice providing a gas passageway from an interior plenum of a battery to the ambient atmosphere. The valve fits over the vent orifice and opens to release gas at a high threshold battery gas pressure and properly reseats to reseal vent orifice when the internal pressure of the battery drops to a low threshold. 
     The venting orifice includes a vent tube included in a venting chamber. The venting tube is capped by the relief valve which seals the vent by means of a skirt member of the relief valve which includes an internal annular rib that fits circumferentially about the outer surface of the vent tube. The base portion of the skirt member is dimensioned, relieved and contoured to control the flexing of the skirt member to respond to specific gas pressure thresholds for opening and closing access of the ambient atmosphere to the venting orifice of the vent tube by radially flaring with respect to the outside surface of the vent tube and providing ambient access past the annular rib. The pressure relief valve structure has an internal location controlling shallow flat surfaced convex protrusion which fits into the inside orifice of the valve stem to insure its proper reseating. An annular relief about its periphery insures proper reseating. It is operative to allow a clear gas way passage while also maintaining a positive location restraint for the relief valve. The shallow dimension is selected so that the flat surface of the protrusion clears the end of the vent tube during pressure release. 
     The performance of the pressure relief valve is further enhanced by the annular rib which operates as a pseudo &#34;O&#34; ring molded in place on the interior surface of the skirt member and which enables the maintenance of a precisely located sealing line with respect to the vent stem. The pressure relief valve structure has an internal location controlling shallow flat surfaced convex protrusion which fits into the inside orifice of the valve stem. It is operative to allow a clear gas way passage while also maintaining a positive location restraint for the relief valve. 
     Acid from the gasses during pressure relief collect on the annular rib and advantageously acts as a lubricant for the pressure relief valve enhancing its operation. The annular rib is also located sufficiently above the bottom edge of the skirt member end so as to effectively prevent ambient contaminant particles from adhering to the lubricated rib. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the Drawing: 
     FIG. 1 is a cross section schematic of a venting mechanism for a battery including a pressure relief valve; 
     FIG. 2 is a cross section schematic of the pressure relief valve; and 
     FIG. 3 is a plan view of the pressure relief valve of FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     The outer cover 101 of the battery casing has a cavity member 103 moulded therein for providing support for a tube gas vent 104 and a pressure relief valve 105. The vent 104 is a tube notched at the end with notches 125 occuring at 90° intervals. A flame arrester member 106 is seated atop the pressure relief valve 105 and a vent cap 107 with gas venting holes is positioned above the flame arrester 106. A compressive force is applied by the flame arrester 106 to the top surface 102 of the pressure relief valve 105. This compressive force applied by the flame arrester member 106 to the top surface allows the operation of the pressure relief valve while preventing it from rising up on the vent tube 104. A compressive force is generated by pressure applied to the crown portion 122 and is supplied by the flame arrester member 106. The dimensional distance between the top of the vent tube 104 and the bottom surface of the flame arrester is selected in accord with the dimension 123 (FIG. 2) of the crown 122 to generate this compressive force. While this is described in terms of a flame arrester, it is to be understood that members other than flame arresters may be used to supply this compression. 
     The inner surface of a skirt member 110 of the relief valve 105 includes an annular rib 108 that is physically contiguous to the outer surface 109 of the tube gas vent 104. As the skirt member of the is subjected to a gas pressure from within the battery container equaling and exceeding a high pressure threshold the skirt member distends or flares outwardly so that the annular rib 108 ceases to contact the vent&#39;s outer surface 109 and gas is allowed to vent from the battery plenum to the outside ambient atmosphere. The passageway for this exiting gas is through the orifice of the vent tube orifice 104; along the outer surface 109; past the annular rib 108; into the plenum chamber 111 of the cavity member 103 and through the flame arrester and the openings 112 of the vent cap 107. The annular rib 108 combines the effectiveness of an &#34;O&#34; ring and a rubber memory force in sealing the space between the rib and the outer surface of the vent tube. The rib 108 being affixed to the skirt member 110 maintains a defined continuous tangential sealing line with respect to the vent tube. 
     The pressure relief valve 105 shown in FIGS. 2 and 3 has an outer cylindrical shape with a substantially flat top surface 102 and a cylindrical outer surface 202. The cylindrical portion covered by the linear dimension range 203 forms the skirt member 110 of the valve. This linear dimension is controlled by the size of the battery cell and the expected volume of gas being generated. The internal structure of the pressure relief valve includes the annular rib 108 located on the interior portion of the skirt member 110 having its center at a distance 220 from the bottom of the skirt member. The annular rib 108 has an internal diameter shown by dimension 229. The annular rib 108 contacts the valve stem tangentially and functions much like an &#34;O&#34; ring and is permanently structurally positioned from an end edge of the skirt member by being an integral portion of the skirt member. An annular groove, relief or undercut 222, defining a central location controlling protrusion 226 in the internal base of the pressure relief valve, is asymmetrically proportioned to fit conformably over the notched circumferential end of the vent tube. The flat surface and shallowness of the protrusion 226 advantageously permits free operation of the relief valve in venting gas and prevents mechanical shifting of the valve relative to the vent tube during reseating of the annular rib 108. 
     The annular relief 222 of the pressure relief valve 105 has a dimensioned radius 223 and an inner circumferential tapered slope 227 angled at an angle of θ degrees with the horizontal. The dimensioned radius is connected to the skirt member 110 and the tapered slope 227 is connected to the protrusion 226. The flat surface of protrusion 226, with the diameter shown by dimension 225 forms the inner central base surface of the valve. It has a dimension height 227 above the bottom of the annular relief 222. The internal portion of the valve has a diameter shown by the dimension 228. The material characteristics, shapes and dimensions, such as the annular relief and protrusion dimensions and the thickness and length of the skirt member, are selected to accommodate proper gas gating performance at specific high and low threshold pressures in a predefined operating environment. The chief function of the protrusion 226 is to control the relief valve position during gas venting and further cause to prevent shifting of the valve on the orifice following temination of gas venting action. 
     The valve is preferably constructed from a soft chlorobutyl/EPDM rubber with a durometer range of 25 to 70. In a particular illustrative embodiment constructed of such a material, the durometer is 30 and the following dimensions have been adhered to for a forty-eight volt multi-cell recombinant battery. 
     θ=30 degrees 
     Radius 223=0.030&#34; 
     Length 203=0.177&#34; 
     Length 220=0.051&#34; 
     Length 227=0.024&#34; 
     Diameter 225=0.153&#34; 
     Diameter 229=0.296&#34; 
     Diameter 202=0.464&#34; 
     These dimensions are intended to be illustrative only to assist those skilled in the art in designing a pressure relief valve with the proper response characteristics and are not intended to be limiting.