Abstract:
A leak retardant automotive battery includes a housing containing a plurality of cells that each have a filling plug and a battery cover closing the housing above the cells. The battery cover includes a central blockage that divides the housing into two compartments that each contain a set of cells. The cells in each compartment are connected by vent holes in the battery cover that are respectively connected to associated vent cap assemblies so as to separately vent each compartment through its associated vent cap assembly.

Description:
TECHNICAL FIELD OF THE INVENTION 
   This invention relates to an automotive battery and more particularly relates to a leak retardant automotive battery adapted to retard a leakage of electrolyte out of a battery housing. 
   BACKGROUND OF THE INVENTION 
   For automotive applications, batteries with free electrolyte are still maintaining their pre-eminent position in the industry due primarily to lower cost as well as ease of manufacturing. Furthermore, the flooded battery designs are known to have certain technical advantages in comparison to acid-starved designs; but the major limitation of these (flooded) designs lies in their inherent possibility of acid leakage during handling, transportation and charging, resulting from internal pressure build-up. As a result, a small percentage of automotive batteries are being converted to leak proof, VRLA (Valve Regulated Lead Acid) type assembled with AGM (Absorptive Glass Mat) separators in spite of a substantial cost penalty. 
   It will be noted from the above that there is a strong need to develop low cost, leak retardant/resistant batteries containing free electrolyte, particularly suitable for the use in the automobiles. 
   Hitherto, there have been many attempts to develop leak resistant battery with free electrolyte using special design of battery covers. Of the several patents filed in this connection, a few of them are being cited below for reference in view of their relative importance: 
   Patent No. Publication Date 
   U.S. Pat. No. 5,843,593 filed Dec. 1, 1998; U.S. Pat. No. 5,683,830 filed Nov. 4, 1997; U.S. Pat. No. 5,424,146 filed Jun. 13, 199; U.S. Pat. No. 5,380,604 filed Jan. 10, 1995; EP 0639862 B1 filed Sep. 18, 1996. 
   In most of the patents cited above, leak retardant characteristics are achieved by using a relatively complex design battery cover, which usually is composed of an upper lid and a lower lid. More particularly, there is a second part of the battery cover, which is fixed with the main cover either by heat sealing or ultrasonically. In the event of battery tilting sideways or in the inverted position, some electrolyte flows out from the container into the space provided between the two parts of the battery cover, which is then allowed to flow back when the battery is restored to its upright position. 
   The design based on two-piece battery cover is relatively expensive and more complex at the manufacturing stage. Clearly, there is a need for a simple, one-piece leak retardant cover design without adversely affecting the cost competitiveness. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is a principal object of the invention to provide a leak retardant automotive battery having a one-piece battery cover having a simple construction without complicating the manufacture and therefore being able to manufacture more inexpensively. 
   In accordance with a fundamental feature of the invention, there is provided a leak retardant automotive battery comprising a housing for a plurality of cells housed therein and having a filling plug, respectively; a battery cover fitted to the housing on its top in a liquid tight manner so as to overlie the cells; and a pair of terminals mounted on the battery cover and connected to said cells, the battery cover having a vent cap assembly liquid-tightly provided in an end of a vent line which communicates the cells with each other, characterized in that the battery cover has means to retard transfer of electrolyte between the vent line and an atmosphere. 
   In accordance with one preferred aspect of the present invention, there is provided a leak retardant automotive battery comprising a housing for a plurality of cells housed therein and each having a filling plug, respectively; a battery cover fitted to the housing on its top in a liquid tight manner so as to overlie the cells and a pair of terminals mounted on the battery cover and connected to the cells, the battery cover having a vent cap assembly liquid-tightly provided in an end of a vent line which communicates the cells with each other, characterized in that the battery cover has central blockage to divide the vent line into some cell groups whereby electrolyte is prevented from moving between the cell groups. 
   In accordance with another preferred aspect of the invention, there is provided a leak retardant automotive battery comprising a housing for a plurality of cells housed therein and having a filling plug, respectively; a battery cover fitted to said housing on its top in a liquid tight manner so as to overlie the cells; and a pair of terminals mounted on said battery cover and connected to said cells, said battery cover having a vent cap assembly liquid-tightly provided in an end of a vent line which communicates the cells with each other, characterized in that the vent cap assembly comprising a vent cap having a helical path provided on an outer periphery of the vent cap and communicating with the end of the vent line and the vent cap having a water-repellant gas filter communicating with a downstream end of the helical path and filtering vented gases. 
   In accordance with further preferred aspect of the present invention, there is provided a leak retardant automotive battery comprising a housing for a plurality of cells housed therein, each of the cells having a filling plug, a battery cover fitted to the housing to overlie the cells and a pair of terminals mounted on the battery cover and connected to the cells, characterized in that the battery cover is divided into two compartments by means of a central blockage, each compartment overlying a set of cells; that vent holes in the battery cover overlying each set of cells are connected by means of a vent line so that the cells in each set are in communication with each other; and that the vent lines are connected at their respective one end to the central blockage so as to isolate the two compartments; and that a vent cap assembly is provided at the other end of each of the vent lines for escape of vented gases. 
   The central blockage may preferably comprise an additional separating wall to isolate the two vent lines and a sealing ring may be provided for sealing the body integrated with the partition wall in the battery cover. 
   The vent cap assembly may comprise a vent cap fitted to the other end of the vent line, and a gas filter may be fitted into the vent cap for allowing the vented gas to escape. 
   In one embodiment of the present invention, the vent cap may have a vent hole in communication with the other end of the vent line, a first upwardly extending vertical hole extending from the vent hole to the outer periphery of the vent cap, a helical path on the outer periphery connected at its one end to the first upwardly extending vertical hole and at its other end to a second downwardly extending vertical hole extending to the center of the vent cap so as to be in communication with the gas filter. 
   The gas filter may be preferably a water-repellant microporous gas filter. The microporous filter may preferably have a grain size of about 270 microns. 
   The gas filter may be flush fitted into the vent cap and then covered a filter cover having a hole for escape of vented gas. 
   Each filling plug having an “O” ring seal may be fitted into each cell. 
   The present invention is based on making a battery leak retardant by creating an air-lock, in addition to using a specially designed vent tube tightly enclosing a microporous gas filter to resist free flow of acid when the battery is rotated or tilted in either direction. 
   A multi-cell (12 volt) configuration with side venting arrangement is divided into two isolated chambers by blocking the common, side vent line through the battery cover at a location corresponding to the middle partition of the battery container. This leaves each of the three-cell battery chambers with a single vent opening fitted with a special type of vent tube enclosing a microporous gas filter. 
   In addition to providing an effective air-lock to prevent the free flow of electrolyte when the battery is tilted in either direction, there is an additional advantage in the present invention of minimizing the transfer of electrolyte from the upper to the lower cells when tilted on the shorter side along the vent line. This is due to the fact that the blockage on the vent line in the middle of the battery cover prevents the transfer of electrolyte from the upper three cells to the lower three cells. As a result, after the tilt for a stipulated period, when the battery is reverted to its original upright condition, a negligible cell to cell variation in the electrolyte levels is observed, as compared to the normal, side vented designs having a common vent line, through the cover. 
   In the present invention, the vent cap containing the microporous filter is so designed that the electrolyte is required to traverse vertically up and move along the helical path on the periphery and then allowed to descend to its central position before coming in contact with the microporous gas filter. This arrangement provides a significant resistance to the flow of electrolyte when the battery is tilted in different directions. 
   Another notable feature of the present invention is that the vent cap assembly can be easily pushed fitted and locked-in into the side vent line without the need for any separate heat sealing or ultrasonic sealing. This simplifies the manufacturing operation, thereby resulting in lower cost. 
   Furthermore, in the vent cap used in the battery of the present invention, a fine grain (approx. 270 microns) microporous gas filter can be used, which is made of plastic alloy and then chemically treated to exhibit water-repellant characteristics. This provides a substantial resistance to the leakage of electrolyte through the vent hole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the invention will be apparent from the detailed description of the preferred embodiments of the invention, which are described and illustrated with reference to the accompanying drawings, in which; 
       FIG. 1  is a front elevation view of an automotive battery according to the present invention; 
       FIG. 2  is a plan view of the battery of  FIG. 1 ; 
       FIG. 3  is a rear view of the battery of  FIG. 1 ; 
       FIG. 4  is a side elevational view of the battery of  FIG. 1 ; 
       FIG. 5  is an enlarged sectional view along line V—V in  FIG. 2 ; 
       FIG. 6  is a sectional view along line VI—VI in  FIG. 2 ; 
       FIG. 7  is an enlarged view of a central blockage means of a battery cover as shown at a circled portion X marked in  FIG. 6   
       FIG. 8  is an enlarged view of a vent cap assembly used in the invention and provided in the battery cover as shown at a circled portion Y marked in  FIG. 6 ; 
       FIG. 9  is an enlarged perspective view of a vent cap for the vent cap assembly of  FIG. 8 ; 
       FIG. 10  is an enlarged front view of the vent cap for the vent cap assembly of  FIG. 8 ; 
       FIG. 11  is a cross sectional view of the vent cap along line XI—XI of  FIG. 10 ; 
       FIG. 12  is a horizontal cross sectional view showing a movement of electrolyte when there is tilted at 90° the battery with the vent cap assembly of  FIG. 8  used, but without any central blockage means; 
       FIG. 13  is a horizontal cross sectional view showing a movement of electrolyte when there is tilted at 90° the battery with both of the vent cap assembly and the central blockage means of  FIG. 8  used; 
     and  FIG. 14  shows graphical representation of test analysis of the battery when it is tilted at 90° along the vent line. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The invention will now be described with reference to accompanying drawings, which show a preferred embodiment of the invention. In the accompanying drawings,  FIGS. 1 through 6  illustrate a leak retardant automotive battery according to the present invention. The battery has a housing  12  in which six cells C 1  to C 6  are housed as shown in FIG.  6 . 
   A battery cover  14  is fitted on and heat-sealed to the housing  12  so that the undersurface of the battery cover  14  is flush with the cells C 1  to C 6 . Battery terminals T 1  and T 2  are connected to the cells C 1  to C 6 . 
   The battery cover  14  is divided into two compartments  14 P and  14 ′P as can be seen from  FIG. 6 , so that the compartment  14 P covers the cells Cl to C 3  and the compartment  14 ′P covers the cells C 4  to C 6 . 
   In the compartment  14 P, a side vent line  16  interconnects the spaces above the cells C 1  to C 3 . Similarly, a side vent line  16 ′ in compartment  14 ′P interconnects the spaces above the cells C 4  to C 6 . 
   The cells C 1  to C 6  are provided with filling plugs  18  which extend into and are flush with the top surface of the cover  14 . It can be seen from  FIG. 5  that the filing plug  18  passes through the cover  14  into the cell C 6  and is screwed onto the cover  14  by means of an “ 0 ” ring  20  so that no electrolyte contained in the cell spills out. The filling plugs  18  corresponding to the other cells C 1  to C 5  are similarly screwed onto the cover  14 . All the filling plugs  18  are closed after the electrolyte is filled. 
   In the battery cover  14  are provided side vent line  16  and  16 ′ in parallel with long sides of the battery across the cells so as to vent gases through the filling plugs  18 . The gases from the respective cells are adapted to reach the vent lines  16  and  16 ′ through the respective filling plugs  18 . 
   In the illustrated embodiment, at the middle of the battery  12 , central blockage means  22  to block the side vent lines  16  and  16 ′ from each other is provided in the battery cover  14 . This is marked as X in FIG.  6  and shown in detail in FIG.  7 . The central blockage means  22  comprises a separating wall  28  integrated with a partition wall  24  in the battery cover  14 . The separating wall  28  is isolating the two side vent lines  16  and  16 ′. The gas from the cells C 1  to C 3  as well as from the cells C 4  to C 6  enters the vent lines  16  and  16 ′, respectively through respective holes  26  and  26 ′ in the filling plugs  18 . The filling plugs  18  fitted with “O” rings  20  are screwed onto the cover  14 . Thus, it will be noted that the vent lines  16  and  16 ′ are isolated from each other. 
   Vent cap assemblies  32  and  32 ′ are push-fitted at the other ends of the side vent lines  16  and  16 ′, respectively. One of the vent cap assemblies  32 ′ is marked as Y in FIG.  6  and shown in detail in FIG.  8 . In the other ends of the side vent lines, there are cylindrical holes  34 H and  34 H′ into which the vent cap assemblies are fitted on the sides of the battery cover  14 , respectively. 
     FIGS. 9 through 11  show the vent cap assemblies  32  and  32 ′ in greater detail. The vent cap assemblies  32  and  32 ′ comprise a vent cap  36  fitted to the other ends of the side vent lines  16  and  16 ′. The vent cap  36  has a vent hole  38  provided in the vent cap  36  while extending in an axial direction thereof so that the vent hole  38  is in communication with the side vent lines  16  and  16 ′, an upwardly extending vertical hole  40  provided in the vent cap  36  while extending upwardly in a radial direction of the vent cap  36  from the bottom thereof to communicate the vent hole  38  with the outer periphery of the vent cap  36 , a helical path  42  helically provided in the surface of the vent cap  36  along the outer periphery of the vent cap  36  from the upper end of the first vertical hole  40  toward the outer end of the vent cap  36  remote from the vent hole  38  and a second vertical hole  44  downwardly extending from the downstream end of the helical path  42  to the center of the vent cap  36  in a radial direction reverse to that of the first vertical hole  40 . 
   As noted from  FIGS. 9 and 11 , the vent hole  38 , the first vertical hole  40 , the helical path  42  and the second vertical hole  44  are positioned in an inside half  36 H 1  of the vent cap  36 . In an outside half  36 H 2  of the vent cap  36  is provided a filter filling chamber  46  communicating through an inner opening  48  of the filter filling chamber  46  with the second vertical hole  44  and opening to atmosphere at an outside end of the vent cap  36 . 
   A water-repellant microporous gas filter  50  is filled in the vent cap  36  by being fitted into the filter fitting chamber  46  while a filter cover  52  having a central hole  52   a  closes an outside opening  48 ′ of the filter filling chamber  46 . The water-repellant microporous gas filter  50  may be made of plastic alloy and comprise a fine grain (about 270 microns) chemically treated to exhibit water-repellant characteristics. 
   When any gas is vented by any cell of the battery, due to central blockage, the gas cannot escape from one compartment  14 P to the other compartment  14 ′P. The gas is forced to escape through the other ends of the respective side vent lines  16  and  16 ′ into the vent holes  38  in the respective vent caps  36 . The gas then passes through the first vertical hole  40 , traverses along the helical path  42  and enters through the second vertical hole  44 . The gas is then filtered by the filter  50  and vented to the atmosphere through the center hole  52   a  in the filter cover  52 . By this arrangement direct contact of electrolyte with filter is prevented. 
   In the battery of the invention, the central blockage means  22  shown in  FIG. 7  serves to reduce a movement of the electrolyte between the cells to be able to resist the leakage of the electrolyte while the vent cap  36  having the helical path  42  shown in  FIGS. 9 and 10  also serves to resist the leakage of the electrolyte. As both of the central blockage means  22  and the vent cap assemblies  32  and  32 ′ shown in  FIGS. 9 and 10  are used, the leakage can be more effectively accomplished. It will be noted that an air-lock is provided by the provision of the central blockage means  22  and the vent cap assemblies  32  and  32 ′. 
   The battery according to the present invention is highly resistant to acid leaks when it is turned through 90° on the front face or inverted, i.e., rotated through 180°. No acid leakage was noticed in the above tilted positions during the period of testing up to 12 hours. 
   The conventional side vented batteries are prone to acid leaks, when it is rotated through 90° along the shorter side in the direction of the vent line. It is in this direction that the efficacy of the central blockage means  22  of the vent lines is revealed. If there is used no central blockage means  22 , the air can pass freely through the vent lines, resulting in continuous leakage of acid from the side vent lines  16  and  16 ′ when tilted through 90° in the direction of the vent lines, but with the central blockage means  22  of the vent lines  16  and  16 ′ according to the present invention, an air-lock is effectively formed which greatly reduces the leakage of electrolyte when the battery is tilted through 90° along the vent lines. 
   In addition to providing air lock preventing free flow of electrolyte when the battery is tilted, the central blockage also minimizes cell-to-cell variation of electrolyte when tilted, by preventing transfer of the electrolyte from one set of cells to the other set of cells. 
   The vent cap assemblies  32  and  32 ′ provide significant resistance to flow of the electrolyte when the battery is tilted in different directions. Furthermore, the vent cap assemblies  32  and  32 ′ can be easily push-fitted into the side vent lines  16  and  16 ′ and thus separate heat-sealing and ultrasonic sealing can be avoided. 
   The effect of the central blockage construction of the vent lines can be foreseen from  FIGS. 12 and 13 . As shown in  FIG. 12 , the conventional side vent type battery (the battery having no central blockage construction) continuously transfer the electrolyte from the upper cell to the lower cell while it is tilted along the shorter side of the battery in the direction of the sides vent lines and as a result, the electrolyte remarkably moves from the upper cells to the lower cells. Furthermore, the vent cap assemblies  32  and  32 ′ are subject to the substantial liquid pressure corresponding to all the length of the battery, which causes the more continuous leakage of the battery through the side vent lines. 
   On the other hand, with the central blockage construction of the vent lines  16  and  16 ′ in the battery cover  14  as shown in  FIG. 13 , when the battery is tilted so that the cell C 1  is downwardly faced, the electrolyte is prevented by the isolating wall  28  integral with the partition wall  24  of the central blockage means  22  from being transferred from the upper cells C 4  to C 6  to the lower cells C 1  to C 3 . Furthermore, it is of significance that the liquid pressure applied to the vent cap assemblies  32  and  32 ′ is reduced by half or less. In addition thereto, with the specially designed vent cap  36  containing water-repellent material together with the central blockage means  22 , the microporous gas filter  50  serves to more effectively retard the leakage of the electrolyte from the side vent lines  16  and  16 ′. 
   Furthermore, the central blockage means of the vent line greatly reduces the cell to cell variation of the electrolyte level after a prolonged tilt at 90° along the shorter side, in the direction of the vent line. There are significant variations in the cell to cell electrolyte levels after 2 hours of tilt at 90° on the shorter side with the conventional side vented design, but in the leak retardant battery of the present invention, only a negligible variation of the electrolyte level is seen in a stabilized condition after the tilt test for 2 hours. 
     FIG. 14  shows a comparative analysis of the tilt tests at 90° along the vent line. The comparative analysis shows electrolyte spillage with the battery of the invention with the aforementioned vent cap design vis-à-vis the conventional side vented battery and the effect of the central blockage means of the vent line creating the air-lock and thereby substantially retarding the acid leakage to the negligible degree. In  FIG. 14 , the triangle mark designates the acid leakage characteristics of the conventional side vented battery; the square mark designates the acid leakage characteristics of the side vented battery of the invention with the new designed vent cap; and the lozenge mark designates the acid leakage characteristics of the side vented battery of the invention with both of the new designed vent cap and the central blockage means provided in the common vent lines. 
   It can be seen from  FIG. 14  that the spillage of the electrolyte when the vent cap assembly of  FIGS. 9 through 11  is used is less than the spillage when no special vent cap assembly is used. When the central blockage means is used, the amount of spillage gets greatly reduced. 
   Although one preferred embodiment of the invention has been described and illustrated with reference to the accompanying drawings, it will be understood by those skilled in the art that it is by way of example, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined only to the appended claims.