Abstract:
A composite battery container for housing one or more cell elements comprising positive and negative plates alternately interleaved with separator material includes a battery housing defining one or more cell compartments. The cell compartments have resilient, flexible spacer and plate-rest ribs integrally formed in the sides and bottom of the cell compartments, but having different material properties than the battery housing. The battery housing is made of a rigid, low cost plastic material, while the ribs are a flexible thermoplastic elastomer. The flexible ribs elastically deform when a cell element is disposed within the cell compartment and return to a substantially non-deformed, originally molded position when the cell element is removed. The ribs are formed in any suitable orientation and at any suitable acute or obtuse angle from the cell compartment walls.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to storage batteries, and more particularly, to a battery container having flexible ribs for positioning and supporting one or more battery cell elements in one or more cell compartments. 
     2. Description of the Prior Art 
     The cell elements of conventional storage batteries are formed of multiple positive and negative grids or plates coated with an electrochemical paste and interleaved with inert separator material to form plate stacks. The number and thickness of positive and negative plates in the plate stack as well as the number of cell elements determine a battery&#39;s energy capacity. Increasing the number of plates in the cell elements increases its energy capacity, while decreasing the number of the plates decreases its energy capacity. At the same time, increasing or decreasing the number and thickness of the plates also varies the overall thickness of the cell elements. 
     For multi-cell batteries, individual cell elements are disposed in cell compartments of a battery housing and are electrically connected together but remain physically separated. In order to ensure proper electrical connection and battery performance, the cell element must be securely disposed within the cell compartment. Partitions are formed in the battery housing to define the necessary cell compartment size for each cell element without being too big so that the cell element is unsecured or being too small so that the cell element does not fit or is damaged when inserted into the cell compartment. Since the overall battery thickness of the cell element varies according to energy capacity requirements and design parameters, manufacturers often maintain a large inventory of battery housings. 
     A number of methods have been devised to reduce the number of battery housings needed for various cell element sizes. Some manufacturers use a finite set of battery housings molded to define incrementally different-sized cell compartments and change the thickness of the plates and/or separator material as needed. For example, if a cell element has a small number of plates, then thicker separators are used to fill the cell compartments. However, the separation between the plates in the cell element should be consistent so that the resistivity between the plates is maintained constant. Changing the separator thickness, therefore, adversely affects the electrical performance of the battery. 
     Alternatively, a rigid spacer can be inserted around a cell element inserted into a larger cell compartment. This method requires that a number of spacers be molded to accommodate the difference in thickness between the various cell elements and cell compartments. U.S. Pat. No. 5,558,958 discloses an improvement upon a rigid spacer by using a flexible spacer, this spacer has a U-shaped sheet with vertical ribs molded of a flexible material such that the cell element can be inserted into the spacer and the spacer and cell element can then be inserted into the cell compartment as a unit. The ribs flex as needed according to the difference between the cell element and cell compartment thicknesses. The flexibility of the spacer allows it to be used with various sizes of cell elements and cell compartments. The flexible spacer also dampens vibrations, which adversely affect the electrical performance and life of the battery cell element. 
     Other manufacturers have horizontal or vertical ribs molded into the partition and end walls. These ribs are molded from the same polypropylene material forming the battery housing, and consequently, the ribs are stiff. Such ribs must be either molded or machined to precisely the correct dimension for each cell element thickness so that the cell element fits within the cell compartment without being damaged. Or, for such battery housings, the separator thickness must be varied, which degrades the performance of the battery, as mentioned above. 
     Battery containers have been designed with deformable ribs, as described in U.S. Pat. Nos. 3,607,440 and 4,309,818, the disclosures of which are hereby incorporated by reference as though fully set forth herein. These patents disclose battery housings having integrally molded ribs that deform as needed according to the thickness of the cell element. The deformable ribs compensate for variations in thickness of the cell element so that the number of different sized containers needed is reduced. The ribs are typically molded to the partition walls at an angle other than 90 degrees to reduce the amount of rib deformation as well as facilitate the insertion and removal of the cell elements. However, because the ribs are injection-molded of the same battery-grade polypropylene material as the battery housing, the ribs remain sufficiently rigid such that the battery elements could be damaged when inserted. Moreover, these ribs are not adequately resilient to spring back to their original position after prolonged deformation. Instead, the ribs tend to undergo mechanical creep and take on a permanent set in the deformed position, which further limits their flexibility. Additionally, these ribs do not dampen the vibrations commonly associated with use of a battery in automobiles, trucks, farm equipment or other off-road vehicles. 
     Battery containers also include rib-like projections or rests extending upward from the bottom of the container for supporting the cell elements. Rather than resting the cell elements on the bottom of the container, these projections are used so that electrolytic fluid can circulate through the cell element from the bottom. Typically, the plate rests are rigid and the plates of the cell elements are electrically connected at the top of the container to battery straps which are welded to opposing straps through the partition walls, as known in the art. Throughout the life of lead-acid batteries, the plates in the cell elements corrode and expand in size. Since the cell element is fixed in place at the top of the container, the plates tend to expand laterally and downwardly. However, the rigid plate rests limit the downward growth and cause the upper comers of the expanding plates to rotate upwardly about the strap connection points at the top of the container. This causes a number of problems that significantly decrease the operational life of the battery, such as electrical shorting, plate-buckling and contortion of the wires. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the deficiencies of the prior art and provides a composite battery container with one or more cell compartments having integral, flexible spacer ribs capable of securely retaining cell elements within a range of thicknesses. Furthermore, the battery container has flexible plate-rest ribs that deform to compensate for typical corrosive plate expansion. 
     Specifically, the present invention provides an improved battery container including a housing having side walls, end walls and a bottom. The walls and bottom define a single-cell compartment or a plurality of cell compartments. Multiple cell compartments are formed by at least one partition disposed within the space parallel with the end walls. The cell compartments are sized to hold a cell element comprising multiple positive and negative plates alternately interleaved with a plurality of separators. A plurality of resilient flexible spacer ribs are integrally formed with the end walls and/or the partitions to project into the cell compartments and center cell elements of various sizes within the cell compartments. The flexible spacer ribs deform elastically when the cell elements are within the cell compartments and return to an essentially non-deformed position when the cell compartments are empty. The flexible spacer ribs are integrally formed with the end walls, and with the partitions in multi-cell batteries, but their material properties differ. 
     The walls of the battery housing of the present invention can be made of a suitable sturdy material, such as battery grade polypropylene, while the spacer ribs can be made of a highly resilient, flexible material, such as a thermoplastic elastomer. Thus, the spacer ribs can be integral with the rigid housing, yet be highly flexible. 
     One object and advantage of the present invention is that the integral spacer ribs can center and secure cell elements of various sizes. This permits the use of one or few battery housing sizes for a wide range of energy capacities without the need for separate inserts. Also, the spacer ribs can be formed without excessive precision as to their length. 
     Another object and advantage of this invention is that the cell elements can be inserted and removed easily without being damaged. This is especially important for battery containers assembled on automated lines. 
     The spacer ribs can be molded in any orientation, including vertically, horizontally and diagonally, at a range of acute and obtuse angles from the end walls and partitions, including perpendicular. This and the flexibility of the spacer ribs provides the further object and advantage of a battery housing that can be easily molded and removed from the mold. 
     Still another object and advantage of this invention is to increase the battery&#39;s overall performance in use. The flexible spacer ribs significantly dampen the performance-degrading vibrations realized by the battery cell elements. Also, the spacer ribs permit the use of a single separator thickness. This promotes a consistent electrical resistance within the cell element and improves battery performance. In one embodiment where the spacer ribs are essentially parallel with the battery housing bottom, the ribs include interruptions spaced along their length. These interruptions improve the charging performance of the battery by promoting mixing of the electrolytic fluid, which reduces stratification of the sulfate in the electrolytic fluid. 
     The battery container can also include flexible plate-rest ribs, with or without the partition/end wall spacer ribs, integral with the bottom of the housing and projecting into the cell compartments to at least partially support the cell element. The plate-rest ribs are flexible so as to deform when the cell elements extend toward the bottom of the container due to corrosive expansion of one or more of the plates. This provides the additional object and advantage of a battery container that increases the operational life of the battery cell elements by compensating for the corrosive expansion of the plates and mitigating the related adverse effects. Further, although integral to the housing, the plurality of plate-rest ribs are preferably of a different material. This allows the housing to be constructed of sturdy, rigid battery-grade polypropylene and the ribs to be a resilient, flexible thermoplastic elastomer. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In this description reference is made to accompanying drawings which form a part hereof and in which there is provided by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the composite battery container incorporating the flexible spacer and plate-rest ribs of the present invention; 
     FIG. 2 is a perspective view of the composite battery container of FIG. 1 cut away along line A—A of FIG. 1, showing horizontal spacer ribs and flexible plate-rest ribs; 
     FIG. 3 is a top plan view of the composite battery container of FIG. 1 without cell elements and having horizontal spacer ribs and flexible plate-rest ribs; 
     FIG. 4 is a cross-sectional view taken along line B—B of FIG. 3, showing a cell element within a cell compartment having horizontal spacer ribs; 
     FIG. 5 is a perspective view of an alternate embodiment of the composite battery container of FIG. 1 cut away along line A—A of FIG. 1, showing vertical spacer ribs; 
     FIG. 6 is a top plan view of the composite battery container of FIG. 1 having vertical spacer ribs and flexible plate-rest ribs; 
     FIG. 7 is a cross-sectional view taken along line C—C of FIG. 6, showing a cell element within a cell compartment having vertical spacer ribs; 
     FIG. 8 is a top plan view of FIG. 7, showing a cell element within a cell compartment having vertical spacer ribs and flexible plate-rest ribs; 
     FIG. 9 is a top plan view of an alternate embodiment of the vertical spacer ribs of FIG. 5; 
     FIG. 10 is a cross-sectional side view taken along line D—D of FIG. 1, showing a cell compartment with a cell element having expanded plates deforming the plate-rest ribs; and 
     FIG. 11 is a cut-away cross-sectional side view taken along line E—E of FIG. 3, showing the cell element of FIG. 10 having expanded plates deforming the plate-rest ribs. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings in detail, in particular FIGS. 1,  2  and  5 , a battery container  10  includes a housing  12  and a plurality of flexible spacer ribs  14 . The battery housing  12  has exterior side walls  16  and  18 , end walls  20  and  22 , and a bottom  24 . A support ridge  25  extends around the perimeter of the housing  12  proximate an upper edge of the exterior of the side  16 ,  18  and end walls  20 ,  22 , and defines slotted tabs  27  at the end walls. The bottom  24  has integral plate-rest ribs  29  extending between and generally perpendicular to the end walls  20 ,  22 . The battery housing  12  is a generally rigid plastic material, such as battery grade polypropylene resin as is known in the art, and the spacer  14  and plate-rest  29  ribs are a highly resilient and flexible material, such as a thermoplastic elastomer. In particular, the ribs  14 ,  29  can be made of a suitable grade of “SARLINK” (a registered trademark of DSM Thermoplastic Elastomers, Inc. of Leominster, Me.), which is an elastomer based upon dynamically vulcanized rubber/thermoplastic blends containing a polypropylene component. Preferably, the container  10  is formed by simultaneously co-injection molding the two materials, as known in the art, so that the housing  12  and the spacer ribs  14  are integral with each other as are the housing  12  and the plate-rest ribs  29 . The polypropylene component in the thermoplastic elastomer affords the integral union of the housing  12  and the ribs  14 ,  29  in the co-injection molding process. 
     For multi-cell batteries, the battery housing  12  also has partitions  26  evenly spaced along and perpendicular to the side walls  16 ,  18  forming a plurality of cell compartments  28  for holding multiple cell elements  30 . The number and size of the cell compartments are set according to the number of partitions  26 . In the preferred embodiment, as shown in FIG. 1, five partitions  26  define six equally sized cell compartments  28   a - 28   f . The partitions  26  are generally flat, rectangular walls integrally formed with the side  16 ,  18  and end walls  20 ,  22  of the housing  12 . The partitions  26  extend from the bottom  24  to an opening  32  at the top of the walls  16 ,  18 ,  20 ,  22 . For single cell batteries, the walls form a single, non-partitioned cell compartment  28 . 
     The cell elements  30 , known in the art and commonly referred to as plate stacks, comprise a plurality of alternating positive  33  and negative  34  plates. The positive plates  33  are coated with an electrochemical paste and electrically connected together and to positive plates  33  of other cell elements  30  by straps  36 , as is known in the art. Similarly, the negative plates  34  of the cell elements  30  are electrically connected by straps  35 . Two straps  35 ,  36  are disposed in each cell compartment  28  and suitably fixed to the container  10  near the top of the partitions  26 . 
     The plates  33 ,  34  are physically spaced apart from each other by inert separator material as is also known in the art. The cell elements  30  are disposed within the cell compartments  28  and set upon the plate-rest ribs  29 . The cell compartments  28  are then partially flooded with an electrolytic fluid as is known in the art. It has been a common practice to vary the separator thickness, and thereby the overall thickness of the cell element  30 , so that a small number of battery containers could hold cell elements  30  within a range of thicknesses. The present invention permits a single separator thickness to be used within the cell elements  30 . This provides a consistent electrical resistivity among the cell elements  30  and improves the performance of the battery. 
     Integrally formed to the partitions  26  and the interior of the end walls  20 ,  22  are the plurality of spacer ribs  14 . The ribs  14  project inwardly into each cell compartment  28  and can be formed to extend in any direction, including longitudinally, laterally or diagonally and spaced apart at any suitable distance. Two specific orientations are shown in the drawings, lateral or horizontal (FIGS. 2-4) and longitudinal or vertical (FIGS.  5 - 9 ). 
     Referring to FIGS. 2-3, the lateral spacer ribs  14  extend from proximate one end wall  20  to proximate the other  22 , leaving a passage and reservoir for the electrolyte along the side walls  16 ,  18 . The size of the spacer ribs  14  is set according to the core thickness of the cell compartments  28 , approximately ¼ inch for most standard battery energy capacities. The number of spacer ribs  14  is set according to the longitudinal height of the partitions  26 . For example, a typical battery container  10  would have four horizontal spacer ribs  14  evenly spaced from the bottom  24  of the housing  12 . A battery housing  12  having a greater or lesser core depth could have more or less than four horizontal spacer ribs  14 , respectively. The horizontal spacer ribs  14  include lateral interruptions  38  spaced throughout the spacer ribs  14  to allow passage of electrolyte. The interruptions  38  can extend the full height of the spacer ribs  14  or some amount less than full height, as shown in FIG.  2 . The interruptions  38  act to allow gas produced during the charging process to mix the electrolyte and reduce sulfate stratification along the bottom of the cell compartments  28 , which can degrade battery performance. The interruptions  38  can be spaced to stagger (not shown) from one spacer rib  14  to the next so as to further promote turbulence within the electrolyte. 
     Referring to FIG. 5,  6  and  8 , longitudinal or vertical spacer ribs  14  extend from the bottom  24  toward the opening  32  approximately two-thirds of the longitudinal dimension of the partitions  26 . The spacer ribs  14  have chamfered upper ends  40  angling downward toward the center of the cell compartments  28 , which facilitates insertion of the cell elements  30  into their respective compartments  28 . The vertical spacer ribs  14  are approximately ¼″ for most batteries, but can be varied based on the core thickness of the cell compartment  28 . The number of vertical spacer ribs  14  is set according to the lateral dimension between the side walls  16  and  18 . For example, a typical five-inch-wide battery housing would have five vertical ribs  14 , as shown. The vertical spacer ribs  14  are set off from the side walls  16 ,  18  and spaced apart at equal distances from each other. 
     In FIGS. 2-8, the spacer ribs  14  are shown oriented longitudinally or laterally and formed to project at right angles from the partitions  26  and end walls  20 ,  22 . As mentioned, however, the spacer ribs  14  may extend diagonally across the interior lateral surfaces of the cell compartments  28 . Also, the spacer ribs  14  may be formed uniformly or alternately at acute and obtuse angles from the partitions  26  and end walls  20 ,  22  as desired. For example, all of the spacer ribs  14  may project downwardly toward the bottom  24  or to one of the side walls  16 ,  18 . Horizontal spacer ribs  14  angled downward provide a resultant force acting to retain or lock the cell elements  30  within the cell compartments  28 . Or, as shown in FIG. 9, opposing spacer ribs  14  on the partitions  26  may resemble a wishbone configuration. The spacer ribs  14  may also extend perpendicular from the end walls  20 ,  22  and partitions. Perpendicular spacer ribs  14  have a wide angle through which to flex, and therefore, provide significant vibration dampening as well as facilitate removal from the mold (not shown). 
     Referring to FIGS. 4 and 7, when the cell elements  30  are disposed within the cell compartments  28 , the spacer ribs  14  flex as needed according to the size of the cell elements  30  and the cell compartments  28 . Perpendicular horizontal spacer ribs  14  flex longitudinally downward when the cell element  30  is in the compartment  28 , as shown in FIG. 4, while vertical spacer ribs  14  flex laterally in either direction, as shown in FIGS. 7 and 8. The spacer ribs  14  act to take up space between each cell element  30  and the partitions  26  or end walls  20  and  22 . Thus, cell elements  30  within a range of thicknesses can be inserted into cell compartments  28  of a single battery container  10  without removing material or adding separate spacers. 
     The high flexibility of the thermoplastic elastomer material allows the spacer ribs  14  to flex as needed according to size of the cell element so as to receive a wide range of cell element  30  sizes. Since the spacer ribs  14  are flexible, rather than rigid, when the cell elements  30  are in place, the spacer ribs  14  reduce performance-degrading vibrations to the battery. This is particularly important when the battery is used in trucks, farm equipment or other off-road vehicles. Moreover, material properties of the thermoplastic elastomer material allow the spacer ribs  14  to elastically deform when and while the cell elements  30  are inserted in place. Since the spacer ribs  14  do not plastically deform, they do not take on a permanent set in a fully or partially deformed position, allowing the spacer ribs  14  to retain their sizing and vibration-dampening characteristics. 
     Referring to FIGS. 2,  10  and  11 , the plate-rest ribs  29  extend upwardly from the bottom  24  of the housing  12  from one end wall  20  to the other  22 . The plate-rest ribs  29  are approximately ¼″ for most batteries, but can be varied based on the size of the cell element  30  and container  10 . The number of plate-rest ribs  29  is set according to the lateral dimension between the side walls  16  and  18 . For example, a typical five-inch-wide battery housing would have four plate- rest ribs  29 , as shown in the figures. The plate-rest ribs  29  are set off from the side walls  16 , 18  and spaced apart at equal distances from each other. 
     Referring to FIGS. 4,  7 ,  10  and  11 , a cell element  30  is partially supported by the plate-rest ribs  29  and is also attached to straps  35 ,  36  welded at its top. This attachment and the spacer ribs  14  also act to support the cell element  30  so that the entire weight of the cell element  30  is not acting on the plate-rest ribs  29 . As shown by the hidden lines in FIG. 10, when a properly sized unused or uncorroded cell element  30  is in the cell compartment  28  the plate-rest ribs  29  extend upwardly in a generally non-deformed state. Like the spacer ribs  14 , the plate-rest ribs  29  are integral with the housing  12 , and are soft and flexible so that they will deform as the plates  33 ,  34  of the cell elements  30  corrode and expand longitudinally. The spacer ribs  14  also compensate for the change in thickness of the cell element as its plates  33 ,  34  become corroded. Again, like the spacer ribs  14 , the plate-rest ribs  29  are preferably a different material than the housing  12 , such as a thermoplastic elastomer. The invention is not limited in this regard, however, as the plate-rest ribs  29  and housing  12  may be of the same material, with the plate-rest ribs  29  having a different durameter so that they are sufficiently flexible. With reference to FIG. 11, at some point when the plates  33 ,  34  are significantly corroded and expanded, the plate-rest ribs  29  can no longer deform to provide further downward growth. Then, the plates  33 ,  34  may indent the surface of the plate-rest ribs  29  so as to continue extending downward. 
     The plate-rest ribs  29  allow the plates  33 ,  34  to expand downwardly so that the cell element  30  does not push upward and rotate about the fixed straps  35 ,  36  at the top of the container  10 . This dramatically increases the operational life of the battery and reduces buckling of the plates  33 ,  34 . The flexible plate-rest ribs  29  also reduce damage to the separators and battery wires and help retain active material. All of this further reduces the likelihood that the positive  33  and negative  34  plates would cause an electrical short by directly contacting each other. 
     Illustrative embodiments of the invention has been described in detail for the purpose of disclosing a practical, operative structure whereby the invention may be practiced advantageously. The apparatus described is intended to be illustrative only. The novel characteristics of the invention may be incorporated in other structural forms without departing from the scope of the invention as defined in the following claims. For example, ribs  14  may be disposed at the side walls  16 ,  18 , instead of, or in addition to, being at the end walls  20 ,  22  and partitions  26 . 
     Thus, to apprise the public of the full scope of the present invention, the following claims are made: