Abstract:
A filter providing dual paths through a coarse filter medium and a fine filter medium attaches the coarse filter medium to the fine filter medium directly eliminating an intervening supporting structure and simplifying manufacture.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application 61/836,980 filed Jun. 19, 2013 and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to filters such as oil filters used in engines and transmissions and in particular to a filter providing for two different filtration media. 
       BACKGROUND OF THE INVENTION 
       [0003]    Oil filters are used to remove contaminants from engine oil, transmission oil or the like. In such filtration, there is a trade-off between removing fine contaminants using relatively small filter pore size which provides high filter pressure and the need to limit filter back pressure so that the engine or transmission may receive a steady supply of oil especially on start up when oil viscosity can be highest. 
         [0004]    This trade-off may be effectively managed by means of a design in which separate parallel paths are traversed by the oil, both through a coarse filter media with large pore size and through a fine, high-efficiency filter media with small pore size. The coarse filter media provides a low-pressure drop passage through the filter that is relatively resistant to blinding. The fine filter media is arranged to intercept a portion of the oil flow to eliminate fine particles over time with reduced blinding from larger particles handled by the coarse filter media. Separate supporting structures are generally needed to hold the different filter media in the two oil paths through the filter. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides two separate paths through the filter media while substantially eliminating the need for a separate supporting and path-defining structure. Two different filter media types are attached directly to each other in a single filter structure, typically with the fine filter medium being an insert or overlay to the coarse filter material. In this way, the construction costs of the filter are significantly reduced. 
         [0006]    Specifically then, the present invention in one embodiment provides a fluid filter having a housing providing an inlet port and an outlet port and enclosing a volume therebetween. A coarse filter fabric is attached to a fine filter fabric to form an integrated flexible filter sheet interposed in a path between the inlet port and the outlet port so that fluid flowing from the inlet port to the outlet port passes through the filter medium both through the coarse filter fabric and the fine filter fabric. 
         [0007]    It is thus a feature of at least one embodiment of the invention to simplify the construction of a filter providing parallel paths through different filter media by allowing the filter media to be inter-supporting without a rib tray or plastic scaffolding or the like. 
         [0008]    The integrated flexible filter sheet may provide single continuous opposed first and second surfaces. 
         [0009]    It is thus a feature of at least one embodiment of the invention to eliminate branched or bifurcated filter structures requiring additional support or separation. 
         [0010]    An attachment seam between the coarse filter fabric and the fine filter fabric may be substantially unsupported by the housing. 
         [0011]    It is thus a feature of at least one embodiment of the invention to permit the coarse filter fabric and fine filter fabric to be closely adjacent in the flow of fluid. 
         [0012]    The coarse filter fabric and the fine filter fabric maybe attached to each other without intervening rigid structure. 
         [0013]    It is thus a feature of at least one embodiment of the invention to permit pre-manufacture of the flexible filter sheet before installation into the housing as opposed to systems that require each sheet be assembled in the housing structure. 
         [0014]    The flexible filter sheet may be attached to the housing along only a single closed path so that fluid flowing from the inlet port to the outlet port must pass through the filter medium. 
         [0015]    It is thus a feature of at least one embodiment of the invention to eliminate the need for multiple paths of attachment of the filter media to the housing such as may make assembly difficult. 
         [0016]    At least one of the coarse filter fabric and the fine filter fabric may be thermoplastic materials attached to the other by welding. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide a simple method of attaching different types of filter media. 
         [0018]    The flexible filter sheet may be formed into a bag having an opening attached to a rim of the inlet port and wherein only the coarse filter fabric is attached to the inlet port. 
         [0019]    It is thus a feature of at least one embodiment of the invention to provide a filter structure that presents a substantial area of flexible filter sheet in a compact volume and that avoids the need to attach two different material types to the inlet port. 
         [0020]    Alternatively, the flexible filter sheet may be supported at an outer periphery against an inner wall of the housing. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide a filter where the support may be obtained entirely by interengaging rims of the two-part housing clamping about the filter medium. 
         [0022]    The fine filter medium may be attached at only a portion of its edge to the coarse filter medium. 
         [0023]    It is thus a feature of at least one embodiment of the invention to provide a simple method of implementing two paths of fluid flow in any filter having a flexible filter sheet by seaming two different materials to each other. 
         [0024]    Alternatively, the fine filter medium may be attached about an entire edge periphery to the coarse filter medium to lie against the coarse filter medium. 
         [0025]    It is thus a feature of at least one embodiment of the invention to allow the coarse filter media to fully support the fine filter media without additional structure. 
         [0026]    The fine filter medium may be positioned to lie closer to the outlet than the coarse filter medium. 
         [0027]    It is thus a feature of at least one embodiment of the invention to encourage flow through the fine filter medium under low viscosity flow. 
         [0028]    The volume of the housing may have a greatest extent along a plane and the inlet and outlet ports may be offset from each other along the plane on opposite sides of the plane. 
         [0029]    It is thus a feature of at least one embodiment of the invention to provide a method of controlling relative flow rates between the fine filter medium and coarse filter medium without additional diverting structure. 
         [0030]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is an exploded perspective view in partial cutaway of a first embodiment of the invention providing a bag filter element held at the interface between two housing portions, the bag filter element including a coarse filter medium with a section of inserted fine filter medium; 
           [0032]      FIG. 2  is a perspective phantom view of a filter in which the bag filter has been replaced with a single filter layer; 
           [0033]      FIG. 3  is a perspective partial cutaway of an alternative bag filter design in which the fine filter medium is applied over the coarse filter medium; and 
           [0034]      FIG. 4  is a cross-section along lines  4 - 4  of  FIG. 3  showing the attachment of the fine filter medium over the coarse filter medium. 
       
    
    
       [0035]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    Referring now to  FIG. 1 , a filter system  10  may include an upper cover housing  12 , in one example, providing a generally rectangular top panel  14  having downwardly extending walls  16  at its periphery, the walls  16  terminating at a lower lip as radially extending flange  18 . An outlet port  20  for discharging filtered oil  21  may be provided in the top panel  14  to communicate therethrough. 
         [0037]    A similar lower cover housing  22 , being generally a mirror reflection of the upper cover housing  12  (with the exception of the outlet port  20 ), may also provide for a generally rectangular lower filter panel  24  but with upstanding sidewalls  26  terminating at an upper lip as radially extending flange  28 . Each of the upper cover housing  12  and lower cover housing  22  may be thermoplastic materials and the radially extending flange  28  of the lower cover housing  22  may be sized to abut and be attached to flange  18 , for example, by vibration, laser, thermal or other type of welding to create an enclosed volume  33  of the housing assembly  35 . 
         [0038]    An entrance port  30  may be provided through the lower filter panel  24  for the receipt of unfiltered oil  32  into the enclosed volume  33 . The entrance port  30  may be offset with respect to the outlet port  20  along the lateral axis  23 , the latter generally aligned with the longest dimension of the assembled upper cover housing  12  and lower cover housing  22 , for example, so that the entrance port  30  and outlet port  20  are positioned at opposite ends of the housing  35 . 
         [0039]    A filter bag  36  may be placed within the volume  33  having an outer edge  34  with a generally rectangular periphery. Three sides of the edge  34  maybe sandwiched between the flanges  18  and  28 , the remaining edge being spaced from an inner end of the volume  33  closest to the exit port  20 . The filter bag  36  consists of upper and lower filter panels  38   a  and  38   b  folded from a single sheet of dual filter material at folded edge  45 . The adjacent edges of the panel outside of the folded edge  45  are attached and sealed together at the outer edge  34  to provide an enclosed internal volume accessible through an opening  40  in the lower filter panel  38   b.    
         [0040]    The opening  40  may be welded or otherwise attached to the entrance port  30  so that unfiltered oil  32  flows into the volume of the filter bag  36  and must flow out of the upper filter panel  38   a  or lower filter panel  38   b  to pass through the outlet port  20 . The filter bag  36  is positioned so that the folded edge  45  is closer to the outlet port  20  and further from the inlet port  30 . 
         [0041]    As noted above, the length of the filter bag  36  along the axis  23  is somewhat less than the length along that axis  23  of the internal volume  33  of the housing (formed by upper and lower cover housings  12  and  22 ) to allow the flow out of the lower filter panel  38   b  to pass through the outlet port  20  around the folded edge  45  to the outlet port  20 . 
         [0042]    Each of the upper and lower filter panels  38   a  and  38   b  are constructed in part of a coarse filter material  42  and in part of a high-efficiency filter material  44  having a smaller pore size and being less permeable than the coarse filter material  42 . The coarse filter material  42  may be, for example, a filtration media having a relatively coarse structure with large filtration pore sizes such as a metal fabric or plastic fabric such as a needle-punched non-woven fabric such as a felt. The high-efficiency filter material  44  may, for example, be a fiberglass mat or fine woven wire screen. The term fabric used herein is intended to include both woven and nonwoven fabrics. In one example, the coarse filter material  42  may retain particles greater than 20 to 30 microns and the high-efficiency filter may retain particles greater than 5 to 10 microns. 
         [0043]    The high-efficiency filter material  44  mat may be attached to the coarse filter material  42 , for example, by joining the two together at common seam  46  dividing each of the upper and lower filter panels  38   a  and  38   b  within the outer seam  34 . This common seam  46  may be created using ultrasonic, laser, thermal or other type of welding of the two materials or other comparable fastening method. A fold passing through the high-efficiency filter material  44  may form the folded edge  45 . 
         [0044]    Generally the filtration area provided by the high-efficiency filter material  44  will be smaller than the filtration area of the coarse filter material  42  to filter a lesser proportion of the oil flowing through the filter system  10  in each cycle. 
         [0045]    In use, when oil is cold or viscous, it will preferentially flow through the coarse filter material  42  rather than the high-efficiency filter material  44 , as indicated by arrows  49  as a result of the greater flow resistance offered by the high-efficiency filter material  44 . When the oil is warmer and less viscous a greater proportion will flow through the high-efficiency filter material  44  as indicated by arrows  47 . In this way, back pressure is reduced when the oil is cold as released by flow through the coarse filter material  42  and yet as the oil warms small particles (for example, dirt, metal shavings and the like) that may not be captured by the coarse filter material  42  are captured by the high-efficiency filter material  44 . This flow of heated oil is promoted by placing the high-efficiency filter material  44  closest to the outlet port  20  and thus along the natural path of the oil in leaving the volume  33 . 
         [0046]    In an alternative embodiment, the filter bag  36  may have its upper filter panel  38   a  constructed wholly of the coarse of filter material  42  and the lower panel  38   b  constructed wholly of the high-efficiency filter material  44 . In this way the common seam  46  is moved to what was the folded edge  45 . In other respects this embodiment is the same as the filter bag  36  described above with the shared edges of the upper filter panel  38   a  and  38   b  other then the common seam  46  sealed together between flanges  18  and  28 . 
         [0047]    Referring now to  FIG. 2 , in an alternative embodiment, a single planar filter sheet  50  may replace the filter bag  36 , the single planar filter sheet  58  duplicating the upper filter panel  38   a  without the lower filter panel  38   b . The entire periphery  37  of the single planar filter sheet  50  is captured between the flanges  18  and  28  (shown in  FIG. 1 ). This filter sheet  50  also has coarse filter material  42  and high-efficiency filter material  44  with relative areas similar to that described above with respect to  FIG. 1  so that a majority of the filtration area is provided by coarse filter material  42 . The benefits described above with respect to the flows  47  and  49  are also obtained in this design albeit with less total filtration area. 
         [0048]    Referring now to  FIGS. 3 and 4 , in an alternative embodiment, the filter bag  36  may be constructed of an unbroken piece of coarse filter material  42  folded over on itself at a folded edge  45  and seamed at seam  34  to form an enclosed filter bag  36  with opening  40 . This filter bag  36  may be substantially identical to the filter bag  36  described with respect to  FIG. 1  except for being constructed of a single filter material. The high-efficiency filter material  44  may then be placed as a patch or appliqué over a portion of the surface of the coarse filter material  42 . The patch or appliqué is displaced toward the outlet port  20  relative to the inlet port  30  to be in the path of natural flow between the inlet port  30  and outlet port  20 . The relative areas of the patch and the coarse filter material  42  outside of the patch may stand in the same ratio as that discussed above with respect to the high-efficiency filter material  44  and coarse filter material  42  in the unoverlapping configuration of  FIG. 1 . 
         [0049]    Referring to  FIG. 4 , the high-efficiency filter material  44  may be attached to the coarse filter material  42  by welding at a peripheral seam  52  extending around the entire periphery of the high-efficiency filter material  44 . In this case, unfiltered oil  32  flows in series through coarse filter material  42  and then through high-efficiency filter material  44  providing the same high-efficiency filtration desired. The flows  49  and  47  may also be created in this design with flow  47  being through both coarse filter material  42  and high-efficiency filter  44  and flow  49  being only through coarse filter material  42 . 
         [0050]    It will be appreciated that this overlapping configuration shown in  FIG. 4  may alternatively place the high-efficiency material  44  upstream of the coarse filter material  42  (as opposed to downstream as shown in  FIG. 4 ) welded at its periphery to the coarse filter material  44 . In addition, this configuration of overlapping filter materials may be applied not only to the bag embodiment of  FIG. 3  but also to a single sheet of coarse filter material  42  spanning the entire periphery  37  of the filter volume where a patch of high-efficiency material  44  is placed upstream or downstream against the coarse filter material  42  and welded thereto at a seam running around the periphery of the high-efficiency material  44  in general, the edges of the high-efficiency material  44  may lie wholly within the edges of the coarse filter material  42  or may share some common edges with the coarse filter material  44   
         [0051]    Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.