Flooded lead acid batteries (batteries with liquid electrolyte) designed for starting, lighting and ignition (SLI) experience a variety of rough handling during manufacture, storage and distribution including an occasional accidental tilting of the battery on its side, a variety of angled inclines once the battery is installed within a vehicle, as well as normal vibrations. During normal operation of a battery, water is electrolyzed into hydrogen and oxygen while temperature excursions produce water vapor, both of which will tend to be lost through the battery venting system. A well designed vent network must prevent this loss by capturing, condensing and draining all fluids back into the cells. The vent system must also prevent or minimize spilling, and safeguard the battery against external ignition sources. Typically, the vent system includes one or more vent recesses or cavities in which flame arresters are seated. These flame arresters are usually in the form of glass or polypropylene frit material (also referred to simply as "frits") which permit the passage of vapor out of the battery casing but prevent flame intrusion into the battery. At the same time, the flow cover or gang vent manifold cover may be designed to create a flow path which minimizes spilling, at least when the battery is tilted 90.degree. to one side or the other. See, for example, commonly owned U.S. Pat. No. 5,565,282.
Tougher criteria are currently being implemented, or will be implemented in the future, regarding spillage of electrolyte from flooded lead acid batteries to the extent of requiring spillage prevention even when the battery is turned over, i.e., inverted. Thus, there is a need to have flooded lead acid batteries designed to prevent the spilling of corrosive acids not only when the batteries are subjected to a high degree of tilt or even turned on one side, but also when the battery is turned completely upside down as may happen in an automobile accident or as a result of accidental mishandling during installation, removal or transit. Presently, this goal is accomplished by an expensive lead acid battery design utilizing gelled electrolytes, or by using AGM oxygen recombinant valve regulated (VRLA) batteries.
In accordance with this invention, a simple and less costly solution is provided by utilizing porous, hydrophobic polytetrafluoroethylene (PTFE) or TEFLON.RTM. discs or frits sealed within the existing battery vent recesses as replacements for the conventional polypropylene flame retardant frits. These porous PTFE discs are sealed within the battery vent cavities and permit the passage of gas but prevent passage of liquid, while also preventing flame intrusion. No modification of current battery component designs is required, since the frit can be shaped and sized to fit existing vent cavities.
In accordance with associated manufacturing techniques, it has been possible to obtain similar dimensional and physical features along with adequate air flow rate so that no changes in the existing battery cover or gang vent configuration is required to permit substitution of the existing frits and thereby achieve the desired anti-spillage goal.
In addition, the porous PTFE frit in accordance with this invention can be used wherever battery vents are currently located in individual threaded or pushin vent caps, in removable gang vent covers, or in manifold covers heat sealed to the battery cover.
A number of manufacturing techniques for sealing the PTFE discs within existing battery vents have proven successful. In a first technique, a slab of silicone grease is applied to the periphery of the PTFE disc. Subsequently, the upper rim of the polypropylene wall which defines the vent opening is crimped over the upper annular edge of the disc, utilizing applied heat.
Another technique is to mold the PTFE disc with a polypropylene skin or ring surrounding at least the side wall of the disc. This allows the disc assembly to be conventionally and easily welded to the polypropylene vent material. In a variation of the above technique, the frit/ring assembly can be sonically welded to the cover. Further in this regard, it may well be possible to mold the polypropylene battery cover manifold around the PTFE disc, but this arrangement would be more costly due to the requirement for new mold designs.
Another sealing technique is to mold the PTFE disc so as to have an outer diameter establishing an interference fit within the vent cavity. While this technique may be viable in many situations, the temperature range of the battery environment must be maintained below 190.degree. F. to avoid relaxation of the polypropylene which would otherwise break the seal.
Finally, it is possible to utilize a high temperature horn for melting an upper annular edge of the PTFE disc so that the heat is transmitted to the outer polypropylene walls to form a "skin" seal.
Accordingly, in its broader aspects, the invention relates to a flooded lead acid battery which includes a casing enclosing a plurality of cells having liquid electrolyte therein and a cover incorporating negative and positive terminals and having a plurality of vent holes, the vent holes covered by at least one closure having a vent cavity therein, the improvement comprising a porous polytetrofluorethylene disc having hydrophobic properties sealed within the vent cavity.
In another aspect, the invention relates to a battery cover having positive and negative terminals, and a manifold covering a plurality of cell openings in the cover; the manifold having a corresponding plurality of closures for engagement with the cell openings, and at least a pair of vent openings, the vent openings each including recesses on an underside of the manifold, with an internal gas passageway leading from each recess to atmosphere, the improvement comprising a relatively rigid porous polyletrofluorethylene disc having hydrophobic properties sealed within each of the vents.
In still another aspect, the invention relates to a lead acid, flooded battery comprising a battery casing including a plurality of cells defined by vertically oriented electrodes, and wherein the cells contain a liquid electrolyte; a battery casing cover having a plurality of cell openings therein; the cover also having one or more vent openings for permitting vapor to escape from inside the battery; wherein each vent opening includes a porous polytetrofluroethylene disc sealed therein.
In still another aspect, the invention relates to a porous polytetrofluorethylene disc for securement within a lead acid battery vent cavity provided in a battery component, the disc surrounded by a ring of material compatible for purposes of welding or heat sealing with material used for forming the vent cavity.
Other objects and advantages of the subject invention will become apparent from the detailed description which follows.