Electric storage battery lid assembly with venting system

Abstract: A lid assembly for an electric storage battery, comprising a lid moulding (11) arranged to close, in use, an open upper face of a battery box (12) so as to define therewith a plurality of parallel cell receiving compartments (13), the lid moulding including a vent passage (15) open at one end at an end face of the moulding and communicating in use with a plurality of said compartments, and, the assembly further including an insert sleeve (16) introduced axially into said vent passage from the open end thereof, the outer surface of said sleeve sealingly engaging the inner surface of the vent passage, and the through bore (17) of the insert sleeve being obstructed by a porous flame arrestor element (18).

Description: This invention relates to a lid assembly for an electric storage battery. The invention is particularly concerned with batteries, for road vehicles, of the kind which are usually referred to as "Starting, Lighting, Ignition" (S.L.I.) batteries. Such batteries are rechargeable, lead-acid, batteries usually employing six adjacent cells electrically connected in series. Hydrogen and oxygen gases are evolved from the electrolyte of the cells during charging of the battery and there are known arrangements for venting the explosive gas mixture to atmosphere through a flame trap to minimise the risk of explosive combustion of the mixture within the casing of the battery. In many applications it is desirable that the casing vent is at an end wall of the casing and European Patent Application 305822 illustrates an arrangement whereby such "end-venting" can take place through the intermediary of a porous flame arrestor. In the arrangement disclosed in European Patent Application 305822 it has been necessary, in order to accommodate the flame arrestor, to provide a chamber in the lid of the battery, the chamber intersecting the venting passage of the battery and being open at the upper surface of the battery to permit insertion of the flame arrestor. It is essential to seal the flame arrestor assembly into the chamber, the seal being needed inter alia at the top face of the battery around the periphery of a relatively thin walled closure element forming part of the flame arrestor. Such a seal is difficult to achieve reliably during mass production of batteries, and of course if leakage occurs at the periphery of the closure member of the arrestor then the arrestor may be rendered ineffective by combustion initiated at the exterior of the battery propagating back through the faulty seal, and around the arrestor to result in explosive combustion within the casing of the battery. DE-U-8812468 describes a lid assembly including a vent passage, and two-piece moulded insert connected to the vent passage, the insert housing a flame arrestor and being disposed mainly outside the lid moulding. EP-A-0123369 describes a relatively complex battery lid assembly in which the lid includes a vent passage, a flame arrestor element being provided through which gas from the battery cells must pass in order to escape. A combustion chamber is provided on the external side of the flame arrestor element. It is an obiect of the present invention to provide a lid assembly for a battery as set out in appended claim 1 wherein reliable venting can be achieved in a simple and convenient manner. In accordance with the present invention there is provided a lid assembly for an electric storage battery, the lid assembly comprising a lid moulding arranged to close, in use, an open upper face of a battery box so as to define therewith a plurality of parallel cell receiving compartments, the lid moulding having external top, side, and end faces, said end faces extending parallel to said compartments in use, the lid moulding including a vent passage open at one end at an end face of the moulding and communicating in use with a plurality of said compartments, and, the assembly further including an insert introduced axially into said vent passage from the open end thereof, the outer surface of said insert sealingly engaging the inner surface of the vent passage, and the through bore of the insert being obstructed by a porous flame arrestor element, the insert defining, at the atmosphere side of the flame arrestor element, a combustion chamber such that gases passing through the porous flame arrestor element and ignited at the atmosphere side thereof can burn readily within the combustion chamber to be consumed at a rate greater than their flow rate through the arrestor element, and thus to be self-extinguishing, wherein the insert including the flame arrestor element is received substantially wholly within the vent passage of the lid moulding. Preferably said insert sleeve is an interference fit in said vent passage such that the large area of surface contact between the insert sleeve and the wall of the passage effects a seal. Desirably the outer end of said insert sleeve is adapted to receive a tube coupling whereby gases venting from the insert can be conducted through the tube to a remote location. Preferably said insert sleeve is received in an enlarged region of the vent passage and the vent passage and its enlarged region are disposed eccentrically of one another such that the passage opens into the lowermost part in use of the region. Desirably said vent passage is also equipped with a pressure relief valve which opens when gas pressure in the passage exceeds a predetermined value to vent pressure from the passage. One example of the invention is illustrated in the accompanying drawings wherein:- Figure 1 is a diagrammatic perspective representation of part of a lid assembly of an electric storage battery, Figure 2 is a diagrammatic sectional view on the line A-A in Figure 1, Figure 3 is a view similar to Figure 2 of a modification, and Figure 4 is a view similar to Figure 3 but of the opposite end of the lid assembly. Referring first to Figures 1 and 2 of the drawings the battery casing which is illustrated is basically of a known construction comprising a one-piece polypropylene lid moulding 11 and a battery box 12 also moulded in polypropylene. As will be well understood the lid and box mouldings are, in use, welded together by a known heat-sealing technique to define a casing divided internally into a plurality (usually six) of parallel cell compartments 13. The lid moulding has external top, side, and end faces 11 a , 11 b , 11 c , the side faces 11 b extending transverse to the compartments 13 and the end faces 11 c extending parallel to the compartments 13. Above each compartment 13 the lid moulding 11 has a filling aperture 14 whereby electrolyte can be introduced into the cells of the battery individually from the top surface of the lid, the apertures 14 being normally closed by plugs (not shown) received as a sealing, screw fit in the lid moulding 11. Internally the lid moulding 11 includes a compartment venting passage 15 terminating at one end in an enlarged cylindrical region 15 a open at an end face 11 c of the lid moulding. The venting passage 15 can communicate with all of the compartments of the battery, but it may, in many applications, be preferred to have a first passage 15 extending from one end face 11 c and communicating with the first, second, and third compartments, and a second, separate venting passage extending from the opposite end face 11 c and communicating with the sixth, fifth, and fourth compartments. In the event that a second vent passage opening at the opposite end face of the lid moulding is utilised, then it is to be understood that the second vent passage will also have an enlarged cylindrical region 15 a housing an insert to be described hereinafter. Within the cylindrical region 15 a of the vent passage 15 is a moulded synthetic resin insert 16 in the form of a hollow sleeve. The insert 16 is introduced axially into the region 15 a from the outer, open end thereof at the end face 11 c of the lid moulding, an internal shoulder at the junction between the region 15 a and the remainder of the vent passage 15 serving to locate the insert axially within the region 15 a . The insert 16 is an interference fit within the region 15 a and thus there is a substantial area of contact between the outer cylindrical surface of the insert 16 and the inner cylindrical surface of the region 15 a providing a gas tight seal between the insert 16 and the lid moulding 11. The through bore 17 of the insert 16 is enlarged adjacent the axially innermost end of the insert 16 and receives therein a porous ceramic, or synthetic resin flame arrestor element 18. The element 18 is of disc like form and is a tight fit within the enlarged part of the bore 17 such that a gas tight seal is produced between the element 18 and the insert 17. It will be recognised therefore that gases evolved in the battery passing along the vent passage 15 can exit to atmosphere through the insert 17 only by passing through the porous element 18. During construction of the insert 16 the element 18 is pressed into the enlarged region of the bore 17 and is trapped in place by deforming the insert (conveniently by localised melting) to form a ring 19, or a series of projections, preventing withdrawal of the element 18 from the insert 16. The enlarged portion of the bore 17 extends beyond the atmosphere side of the element 18 and within the bore 17 there is an integral obstruction 21 which, with the enlarged region of the bore and the atmosphere presented face of the element 18, defines a combustion chamber 22. The chamber 22 communicates with the remainder of the bore 17 by way of one or more small apertures 23, the arrangement being such that should the evolving gases be ignited at the open end of the insert 16 then flame may propagate along the bore 17 and into the chamber 22, but such combustion will be self-extinguishing in the chamber 22 since the burn rate within the chamber 22 will exceed the rate at which combustible gases flow into the chamber 22 through the porous element 18. Thus it will not be possible for flame to be maintained at the atmosphere presented surface of the porous element 18 thereby avoiding the risk of damage to the element 18 by continued combustion at its surface. As mentioned above where a second vent passage 15 opening at the opposite end face 11 c of the lid moulding 11 is provided then the enlarged region 15 a of that passage will contain a similar insert 16. The outermost end of the bore 17 of the or each insert is dimensioned to receive a tube coupling member whereby a tube can be connected to the or each gas vent to receive the evolved gases and to conduct them to a remote location. For example, where the battery is located in a closed battery compartment of a vehicle it will be desirable to equip the or each vent with tubes whereby the evolving gases can be discharged to atmosphere outside the battery compartment. It will be recognised that mechanically it is a relatively simple exercise to mould the lid with an enlarged region 15 a of the vent passage 15 and to equip the enlarged region 15 a with an insert which is received as an interference fit, and thus requires no additional sealing in order to ensure that it is a gas tight fit within the region 15 a . In the modification illustrated in Figure 3 parts corresponding to those illustrated in Figure 2 carry the same reference numerals. It can be seen therefore that the lid moulding 11 includes an internal compartment venting passage 15 terminating at one end in an enlarged cylindrical region 15 a open at the end face 11 c of the lid moulding. The enlarged cylindrical region 15 a is not co-axial with the remainder of the venting passage 15, but instead is eccentrically positioned with respect thereto such that the passage 15 a opens into that part of the region 15 a which will be lowermost in use. The insert 16, which is received as an interference fit in the region 15 a has a through passage 17 divided into inner and outer regions by an internal wall 21. The internal wall 21 is formed with a pair of small circular venting apertures 23 which are disposed above the axial centre line of the insert 16. The sintered polypropylene disc which constitutes the flame arrestor element 18 is disposed within the insert 16 at the inner side of the wall 21 and a combustion chamber 22 is defined between the outwardly presented face of the element 18 and the inwardly presented face of the wall 21. The combustion chamber 22 acts in the manner described above in that flame propagating back along the passage 17, through the apertures 23, will be self-extinguishing within the chamber 22 since combustion, or controlled minor explosion, will occur within the chamber 22 consuming the gases at a burn rate in excess of the rate at which the gases enter the chamber 22 through the element 18. As is apparent from Figure 3 the element 18 can be retained within the insert 16 as an interference fit, although the securing mechanism described with reference to Figure 2 could be used if desired. The outer end region of the passage 17 is adapted to receive a tube coupling as described above. In order that the insert 16 can only be introduced into the region 15 a in an orientation such that the apertures 23 are above the centre line of the insert in use, the insert includes a radially extending protrusion or key 24 which locates in a corresponding recess 25 in the wall of the region 15 a when the correct orientation of the insert 16 relative to the moulding 11 is achieved. It will be recognised that the positioning of the passage 15 at the lowermost point of the region 15 a ensures that any electrolyte collecting or condensing adjacent the insert 16 will not pool, but instead will drain backthrough the passage 15 into the adjacent cell compartment. Moreover, should any electrolyte be carried through the pores of the element 18 then it will not pass beyond the chamber 22 since the apertures 23 form the only outward exit from the chamber 22, and these are disposed above the centre line of the insert 16. Thus any electrolyte carried with gases through the pores of the element 18 will collect in the lower part of the chamber 22 and will drain back through the pores of the element 18 into the passage 15 and thus into the adjacent cell compartment when there is no flow of gas outwardly through the pores of the element 18. As mentioned above the vent passage 15 may serve the first, second and third compartments of a six compartment battery, and a second, similar passage 15 extending in the opposite direction may serve the fourth, fifth and sixth compartments. The passage 15 opening at the opposite end of the moulding 11 will be provided with a similar insert 16. However, in an embodiment where the passage 15 serves all six compartments then the passage may open at both ends of the lid moulding, being equipped at one end with an insert 16 as shown in Figure 3, and being equipped at its opposite end with a pressure relief valve as illustrated in Figure 4. As can be seen in Figure 4, the opposite end of the passage 15 opens into an enlarged region 15 a and as described with reference to Figure 3 the communication between the passage 15 and the region 15 a is at the part of the region 15 a which is lowermost in use. A moulded synetic resin sleeve 26 is received as an interference fit in the region 15 a , the sleeve 26 having a through bore 27 partially closed by an integral internal wall 28. The wall 28 has a centrally disposed aperture within which a retaining portion 31 of a valve element 29 is sealingly received, and around the central aperture the wall 28 is formed with a plurality of spaced smaller apertures 27 a . The valve element 29 is formed from a resilient synthetic resin material and includes a disc-like head 32 which makes an annular contact with a valve seat 33 formed on the insert 26 outwardly from the wall 28. The engagement of the head 32 with the seat 33 closes the through passage 27 of the insert 26 so that gases from the passage 15 cannot vent through the insert 26 and instead will vent through the insert 16 at the opposite end of the passage 15. However, should the gas pressure within the battery casing rise above a predetermined value then the pressure applied to the inwardly presented face of the head 32 will flex the head 32 away from the seat 33 thus allowing excess pressure to vent to atmosphere through the insert 26. If desired the insert 26 and valve element 29 can be redesigned such that the valve element 29 is within the central region of the insert 26, and the insert 26 has a vent tube coupling facility at its outer end such that gases released through the insert 26 can be vented to atmosphere at a remote location.

Claims: A lid assembly, for an electric storage battery, comprising a lid moulding (11) arranged to close, in use, an open upper face of a battery box (12) so as to define therewith a plurality of parallel cell receiving compartments (13), the lid moulding having external top, side, and end faces (11 a , 11 b , 11 c , said end faces (11 c ) extending parallel to said compartments (12) in use, the lid moulding including a vent passage (15) open at one end at an end face (11 c ) of the moulding (11) and communicating in use with a plurality of said compartments (13), an insert (16) introduced axially into said vent passage (15) from the open end thereof, the outer surface of said insert (16) sealingly engaging the inner surface of the vent passage (15), and the through bore (17) of the insert (16) being obstructed by a porous flame arrestor element (18), the insert (16) defining, at the atmosphere side of the flame arrestor element (18), a combustion chamber (22) such that gases passing through the porous flame arrestor element (18) and ignited at the atmosphere side thereof can burn readily within the combustion chamber (22) to be consumed at a rate greater than their flow rate through the arrestor element (18), and thus to be self-extinguishing, and characterized in that said insert (16), including said element (18), is received substantially wholly within said passage (15) in said lid moulding (11). An assembly as claimed in Claim 1, characterized in that said insert sleeve (16) is an interference fit in said vent passage (15 a ) such that the large area of surface contact between the insert sleeve and the wall of the passage effects a seal. An assembly as claimed in Claim 1 or Claim 2, characterized in that the outer end of said insert sleeve (16) is adapted to receive a tube coupling whereby gases venting from the insert sleeve (16) can be conducted through the tube to a remote location. An assembly as claimed in any one of Claims 1 to 3 characterized in that said insert sleeve (16) is received in an enlarged region (15 a ) of the vent passage (15) and the vent passage (15) and its enlarged region (15 a ) are disposed eccentrically of one another such that the passage (15) opens into the lowermost part in use of the region (15 a ). An assembly as claimed in any one of Claims 1 to 4 characterized in that said vent passage (15) is also equipped with a pressure relief valve (29) which opens when gas pressure in the passage (15) exceeds a predetermined value to vent pressure from the passage (15).

Inventors: MCEWAN KEITH JOHN BRUCE, ROSE ALLAN MICHAEL, MCEWAN, KEITH JOHN BRUCE, ROSE, ALLAN MICHAEL
Applicants: LUCAS YUASA BATTERIES LTD, LUCAS-YUASA BATTERIES LIMITED
Application year: 1992
Main classification: H01M2
IPC codes: H01M2