BATTERY VENT VALVE

Abstract: A relief/check valve (14) for venting an electric storage battery comprising essentially an annular sealing member (26) having an elastomeric skirt (24) engaging a sloping exterior surface (22) of a valve seat (20). The skirt (24) flares outwardly from the valve seat (20) in direct proportion to the pressure in the battery so as to prevent excessive build-up of pressure in the battery when the gassing rate is high. The skirt (24) quickly returns to a sealing condition when the pressure within the battery drops below the opening pressure of the valve (14).

Description: This invention relates to valves for venting electric storage batteries as specified in the preamble of claim 1, for example as disclosed in US-A-4 576 879. Background of the Invention Sealed batteries are well known in the art and typically include a relief/check valve for venting gases generated within the battery when the internal gas pressure exceeds a predetermined superatmospheric level. Nickel-zinc batteries, for example, commonly operate with a positive internal gas pressure of about 3.45 kPa (one half pound per square inch) or more to promote oxygen recombination within the battery and to keep CO₂ in the air from contaminating the electrolyte when the pressure in the cell falls below atmospheric pressure (zero psig). Similarly gas recombination type lead-acid batteries are known to operate at internal gas pressures ranging from about 3.45 kPa to about 345 kPa (1/2 psig to about 50 psig) (i.e., depending on the particular application) to promote the oxygen recombination reaction and to exclude ambient oxygen from the battery. It is necessary for the prolonged life of such batteries that, after the gases have been vented, the relief/check valves close and reseal as near as possible to their opening pressure in order (1) to prevent unnecessary loss of the internal gases otherwise available for recombination and (2) to prevent any influx of ambient atmosphere into the battery as the internal gas pressure within the battery falls. Under uncontrolled recharge, batteries can generate so much gas that the internal pressure can rapidly exceed the design pressure of the container unless the check valves are capable of quickly dumping or venting relatively large volumes (i.e., litres per minute) of the gases at relatively low internal gas pressures. For example, under high rate charge conditions such as can occur with a full field charge from an unregulated automobile generator/alternator or with other faulty charging equipment, some lead-acid batteries can generate more than 10 times the amount of gas otherwise generated under normal charging conditions. Some valves commonly used in batteries do not actually reseal again until pressures as low as 25% or less of their opening pressure are reached. In fact, some such valves tested by General Motors Corporation did not reseal until the pressure in the battery had dropped below atmospheric pressure (zero psig). Moreover, valves designed for rapid resealing at relatively high pressures do not usually have a capability for low pressure dumping of large volumes of gas, and vice versa. No commercially available battery check valve has been found which provides both rapid, effective resealing near the opening pressure thereof as well as a high gas volume venting capability at relatively low internal gas pressures. In this latter regard, all of the commercial valves tested produced pressure build-ups which were significantly more than twice the opening pressure of the valve in order to dump high volumes of gas. Accordingly, it is an object of the present invention to provide a unique, compact, relief/check valve for venting an electric storage battery which valve is capable of resealing at pressures of at least 50% or more of its opening pressure and of dumping relatively large volumes of gases under abnormal operating conditions without excessive build up of gas pressure within the battery container. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows. Brief Description of the Invention A battery vent valve in an electric storage battery according to the present invention is characterised by the features specified in the characterising portion of claim 1. The present invention comprises a check/relief valve for an electric storage battery which is capable of resealing at pressures of at least 50% or more of its opening pressure and of releasing relatively large volumes of internal gases without excessive gas pressure build-up within the battery. The valve of the present invention comprises a housing defining a vent chamber having a gas inlet for receiving gases from within the battery and an outlet for discharging them to the atmosphere. The housing includes a valve seat projecting into the chamber and having a sloping (preferably conical) exterior sealing surface. A sealing member circumscribes the inlet and includes an annular elastomeric skirt having a sealing edge circumferentially sealingly engaging the sealing surface of the seat. The elasticity of the skirt is selected based on the desired relief pressure sought for the battery under normal operating conditions and is such that the skirt will begin to flare radially outwardly when the desired pressure is reached so as to form an annular gap between the sealing edge of the skirt and the sealing surface of the seat through which the gases flow. Elasticity of the skirt, and hence the opening pressure of the valve, may be varied over a wide range by varying the dimensions of the skirt and the hardness (i.e., durometer hardness) of the elastomer used. The gases generated inside the battery act against the relatively large surface area on the inside of the skirt so as to cause outward flaring of the skirt at relatively low pressures. Under conditions where excessive gases are formed (e.g., run-away charging), the skirt will simply flare out further so as to increase the gap (i.e., the area of the flow path), between the skirt and the seat. Hence with only a slight increase in the diameter of the flared out skirt, the area of the gap through which the gas flows increases exponentially (i.e., by the square of the radius - R²) so that much larger volumes of gas than normal can be vented without a significant increase in internal pressure. Vents made in accordance with the present invention have demonstrated the capability of dumping more than 10 times the normal volume of gases generated with a pressure build-up of less than twice the opening pressure of the valve. According to a preferred embodiment of the present invention, the opening pressure of the relief/check valve is adjustable by providing means for moving the sealing member to and fro with respect to the seat such that the skirt of the sealing member engages the sloping surface of the valve seat at different locations so as to pre-stress the skirt to various degrees and thereby vary the amount of pressure required to flare the skirt outwardly away from the seat. Detailed Description of Specific Embodiments The invention may better be understood when considered in conjunction with the following detailed description of certain specific embodiments thereof which is given hereafter in conjunction with the accompanying drawings, in which: Figure 1 is a side elevational view of an electric storage battery having vent valves in accordance with the present invention; Figure 2 is an enlarged section of a check/relief valve taken in the direction 2-2 of Figure 1; Figure 3 is a view similar to Figure 2 of another embodiment of a relief valve in accordance with the present invention; Figure 4 is a view similar to Figure 2 of still another embodiment of a relief valve in accordance with the present invention showing a valve member in the seated, closed condition; Figure 5 is essentially the same as Figure 4 except that the valve member shown in the unseated open condition(s); Figure 6 is a view in the direction 6-6 of Figure 5; Figure 7 is a view in the direction 7-7 of Figure 5; Figure 8 is a view similar to Figure 2 of still another embodiment of the present invention and showing a skirt of a valve member seated more deeply on a valve seat; and Figure 9 is a view like that of Figure 2 but of still another embodiment of the present invention. Figure 1 shows a battery 2 having a container 4 divided into a plurality of individual cell compartments 6. Each compartment contains, as shown in Figure 2, a cell element 8 comprising a plurality of alternately interleaved positive and negative polarity plates for electrochemically generating electrical current upon discharge of the battery and which generate gases (e.g., hydrogen (H₂) and oxygen (O₂) on recharge, which gases are recombined within the cell as is well-known in the gas recombination battery art. A vent 10 is provided in a cover 12 of the container 4, which vent 10 includes a check/relief valve 14 which is described in more detail hereinafter. The relief valve 14 includes a housing 16 defining a venting chamber 18 and having a valve seat 20 at its lower end. The housing 16 may be integral with the cover 12 as shown in the drawings or may be discrete for positioning in an aperture in the cover (not shown). The valve seat 20 has a sloping (preferably conical) external sealing surface 22 for engagement by an annular skirt 24 on the depending elastomeric tubular sealing member 26. The elastomeric tube 26 will comprise a rubber-like material such as a styrene-butadiene material, sold under the trade name Kraton (RTM) by Shell Oil Company, U.S.A.. The tubular sealing member 26 is secured to a bulbous stud 28 depending from a plug 30 which serves to close off the vent chamber 18 from the ambient atmosphere surrounding the battery. Exhaust ports 32 in the plug 30 allow gases to escape from the vent chamber 18 to the ambient atmosphere. An inlet opening 34 passing through the centre of the seat 20 serves to communicate the vent chamber 18 with the battery cell compartment 6. In the particular embodiment shown in Figure 2, the plug 30 is threaded into the housing 16 so as to permit adjustment of the opening and closing pressure of the tubular valve member 26 by advancing the member 26 to and fro with respect to the seat 20 such that the skirt 24 can locate at different sites along the sloping surface 22 of the seat 20 so as to diametrically pre-stress the skirt 24 to different degrees and thereby change its opening and closing (i.e., flaring) characteristics. The ability to adjust the opening pressure of the valve is particularly useful during the design phase of a battery as a means to readily adjust the pressure in the cell to optimize the recombination reaction. The adjustability feature is likewise advantageous during the commercial development phase of the battery as a means to provide a standardized vent assembly which may simply be set to different opening pressures as may be required for different battery models and/or applications. The embodiment shown in Figure 3 is similar to that of Figure 2 except that a tubular sealing member 40 includes a central elastomeric web portion 42 proximate a skirt 44 which serves to ensure that the gas vents at the skirt 44 rather than leaking out around a mounting stud 46. Moreover, the domed shape and location of the web 42 relative to the skirt 44 permits precise tailoring of the opening and closing pressures of the valve member. Figures 4-7 depict another embodiment of the present invention wherein a sealing member 50 is integrally moulded with a plug portion 52 and includes a hemispherical cavity 54 above a sealing edge 56 of a skirt 58. The plug 52 is seated on a shoulder 53 on the inside of a housing 55 and is held in place by a porous flame-arrestor pellet 57 suitably secured in place as is well-known in the art. An annular space 59 between the pellet 57 and the plug 52 forms a plenum for the gases exiting the exhaust ports 51 to spread out for more uniform passage through the flame arrestor 57. The hemispherically domed cavity 54 in the sealing member 50 provides a skirt 58 which is thicker near its top 61 than at the sealing edge 56 (i.e., its thickness decreases in the direction of the sealing edge) which serves to focus the opening action substantially at the sealing edge 56 (see Figure 5) and helps prevent bulging, rather than flaring, of the skirt 58. A similar result is obtained by providing a skirt whose thickness tapers toward the sealing edge as would result, for example, by replacing the hemispherically domed cavity 54 with a frusto-conically shaped cavity. Figure 5 depicts opening/flaring of the skirt 58 under normal gassing conditions in solid lines and opening/flaring of the skirt 58 under high gassing conditions in phantom lines. The opening/flaring of the skirt 58 provides an annular gap 63 between the skirt 58 and seat 65 through which the gases flow. Figure 8 depicts an embodiment of the present invention wherein a plug 70 is integral with a sealing member 72 and is adapted to be screwed into a housing 74 to provide the adjustable feature discussed above. As shown, a sealing edge 76 of a skirt 78 is further down on a seat 80 so as to pre-stress the skirt and thereby increase the pressure at which the skirt will flare outwardly. Figure 9 depicts still another embodiment of the present invention wherein a housing 90 defines a vent chamber 92 having a valve seat 94 at the exhaust end thereof and a sealing member 96 secured to a hollow cylindrical stud 98 on an end piece 100 at the inlet side of the chamber 92. An opening 102 through the stud 98 serves as the inlet for the gases to the venting chamber 92 from the cell compartment. A sealing edge 95 on a skirt 104 of the sealing member 96 engages the seat 94 in close proximity to exhaust ports 106 as shown. The tubular elastomeric sealing member 96 may conveniently be glued or otherwise permanently secured to the cylindrical stud 98 so as to ensure that all the valving action occurs at the seat 94. In accordance with one specific example of the present invention, a valve substantially as shown in Figure 3 and adapted to open at about 18.96 kPa (2.75 psig) and close at about 15.51 kPa (2.25 psig) was made from a valve member comprising a 50-50 mixture of 45 durometer and 28 durometer Kraton (RTM) and having an outside diameter of 9.65 mm (0.38 inches), an inside diameter of 7.11 mm (0.28 inches) and a skirt length of 2.54 mm (0.1 inches) (i.e., as measured from the centre of curvature of the hemispherical portion). The sealing member engaged a conical seat whose walls sloped downwardly at an angle of 30 degrees from the vertical axis. Valves so made are capable of dumping up to 14 litres/minute of gas at internal gas pressures of 34.47 kPa (5 psig) or less.

Claims: A battery vent valve (14) in an electric storage battery (2) comprising a container (4) defining a compartment (6) containing gas-generating electrochemical means (8) for producing an electric current, said battery vent valve (14) being operatively associated with said compartment (6) upon closing to isolate said electrochemical means (8) from the ambient atmosphere and upon opening to vent said compartment (6) when the internal pressure of the gas generated in said compartment (6) exceeds a predetermined superatmospheric pressure, said valve comprisinga housing (16;55;74;90) defining a vent chamber (18;92) and including a valve seat (20;65;80;94) projecting into said chamber (18;92), an inlet (34;102) in one end of said housing (16;55;74;90) for admitting gas into said chamber (18;92) from said compartment (6); means (32;51;106) for exhausting said gas from said chamber (18;92) to the ambient atmosphere; and a sealing member (26;40;50;72;96) in said chamber (18;92) circumscribing said inlet (34;102) for controlling the internal gas pressures at which said opening and closing occurs, characterised in that said valve seat (20;65;80;94) has a sloping exterior sealing surface (22); said sealing member (26;40;50;72;96) comprises an annular elastomeric skirt (24;44;58;78;104) secured at one end and having a tubular portion extending from said one end above said inlet (34;102) so as to provide an internal annular surface exposed to said internal gas pressure and a sealing edge (56;76;95) on the interior of the other end of said tubular portion circumferentially sealingly engaging said sloping exterior sealing surface (22) when said valve (10) is closed; and said skirt (24;44;58;78;104) is adapted to be responsive to said internal gas pressure acting on said internal surface so as to (a) flare substantially uniformly and radially outwards at said predetermined internal gas pressure to open an annular gap (63) between said sealing edge (56;76;95) and said sloping exterior sealing surface (22) for passing relatively low volumes of said gas into said chamber (18;92) and thence to the ambient atmosphere under normal operating conditions, (b) flare further outwards so as to enlarge the cross-sectional area of said gap (63) exponentially so as to pass significantly more of said gas under abnormal operating conditions without a significant build-up of said internal gas pressure above said predetermined pressure, and (c) rapidly return to said closed sealing engagement by the time said internal gas pressure has fallen to about 50% or more of said predetermined pressure. A battery vent valve (14) in an electric storage battery (2) according to claim 1, in which said inlet (34) is surrounded by said valve seat (20) having said sloping exterior sealing surface (22); there is a plug (30;46) for closing off said chamber (18) at the other end of said housing (16); and said sealing member (26;40) depends from said plug (30;46) into said chamber (18). A battery vent valve (14) in an electric storage battery (2) according to claim 2, in which said sloping exterior surface (22) has a substantially conical shape. A battery vent valve (14) in an electric storage battery (2) according to claim 2, in which said plug (30) is separate from said housing (16) and is adapted for axial, to-and-fro movement within said housing (16) with respect to said valve seat (20) to vary the engagement position of said sealing edge of said skirt (24) on said sloping exterior surface (22) and thereby vary said predetermined pressure. A battery vent valve (14) in an electric storage battery (2) according to claim 1, in which the thickness of said skirt (44;58;78) decreases in the direction of said sealing edge (56;76). A battery vent valve (14) in an electric storage battery (2) according to claim 2, in which the thickness of said skirt (44) decreases in the direction of said sealing edge.

Inventors: COLE, BRUCE A., MCCARTNEY, CHARLES P., JR., MEADOWS, C.A., MONTGOMERY, CHARLES C.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1988
Main classification: H01M2
IPC codes: H01M2