Patent Publication Number: US-2005133421-A1

Title: Ribbed plastic tray insert apparatus and method for supporting filter media in an engine or transmission filter

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to engine or transmission oil filters. More particularly, the present invention relates to tray inserts for supporting filter media in engine or transmission oil filters, preferably metal or composite engine or transmission oil filters.  
     BACKGROUND OF THE INVENTION  
      Engine and transmission oil filters can include a housing encompassing a filter medium. The housing typically has a top half (or upper cover) and a lower half (or lower cover) and can be all metal, all plastic, or can be composite in construction (metal and plastic). In filters having clean fluid both above and below the filter medium (for example, in bag configuration), the filter media is preferably kept off the bottom of the lower cover so that fluid can flow to the filter outlet unobstructed by the filter bag medium.  
      In the case of metal and composite filters, flow ribs stamped into the metal lower tray are used to keep the filter medium from touching the bottom of the lower cover and blocking fluid flow. This design can have drawbacks. First, the ribs themselves block fluid flow space and can create bottleneck regions in the fluid flow path. Second, in order to provide structural support to alleviate the effects of suction on the oil filter housing, pinch points are built into the oil filters, where a depression in the upper cover presses against a rib in the lower cover. These pinch points compress the filter bag medium, obstructing fluid flow.  
      All-plastic oil filters, on the other hand, have the drawback that the top half of the housing and bottom half of the housing cannot be crimped together. Therefore, expensive welding processes are used to seal the covers together. In addition, certain welding processes such as vibration welding cause contamination of the filters. Filter media fibers can dislodge due to the friction of the vibration welding process and contaminate the filter. As well, all-plastic oil filters are inherently weaker than metal filters and consequently many users demand at least composite oil filters.  
      Engine or transmission filters also typically include inlet tubes. These tubes can be made from metal or they can be made from plastic. Metal inlet tubes are typically formed as a separate component because metal cannot be drawn from the lower cover to the depth or shape that is often needed for the inlet tubes. Utilizing a separate component adds cost to the filter. Further, because separate metal tubes are attached by crimping, the cross-sectional geometry of the metal tubes is limited, and angled or shaped tubes are difficult to implement. Specifically, metal inlet tubes are limited to having a round or oval cross-sectional geometry because it is difficult to crimp other metal shapes. Use of angled or shaped inlets can introduce error in the manufacturing process because an operator must insure that the inlet tube is properly oriented prior to crimping. While all-plastic tubes can be integrally formed when used with all-plastic filters thereby alleviating the problem of limited cross-sectional geometry and angle, as mentioned above, all-plastic filters can have the problem of contamination and/or expense.  
      Accordingly, it is desirable to provide an oil filter method and apparatus that alleviates the fluid flow problems caused by use of lower metal covers having stamped flow ribs. It is also desirable to provide an oil filter method that can utilize the thin walls provided by metal covers. It is also desirable to provide an oil filter method and apparatus that alleviates the fluid flow problems caused by pinch points closing the media (as in a bag filter). It is also desirable to provide an oil filter method and apparatus that includes an inlet tube which can be both cost-efficient and has desirable design flexibility.  
     SUMMARY OF THE INVENTION  
      The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments provides a tray insert for an engine or transmission filter for supporting the filter media off the bottom of the lower cover.  
      In accordance with one embodiment a filter for engines or transmissions is provided having a filter housing encompassing a plastic tray insert for supporting a filter media (usually in bag configuration) off the bottom of the filter housing. The tray insert is configured to rest on the filter housing, which includes an upper cover and a lower cover. In some embodiments, the tray insert rests on the bottom of the lower cover of the filter housing. In some embodiments, the tray insert rests on a lip portion of the lower cover of the filter housing and is suspended above the bottom cover of the filter housing. In some embodiments, the suspended tray insert also includes legs extending downward toward the bottom of the lower cover of the filter housing. In some embodiments, the plastic tray insert can include integral pass-through pinch points. In some embodiments, the plastic tray insert can include an integral plastic inlet opening which may be configured with an anti-drainback device.  
      In accordance with another embodiment, a filter for engines or transmissions is provided having a filter housing, including an upper cover and a lower cover and encompassing a metal tray insert for supporting filter media off the bottom of the filter housing. In some embodiments, the tray insert is configured to rest on a lip portion of the lower cover of the filter housing and is suspended above the bottom cover of the filter housing. In some embodiments, the suspended tray insert also includes legs extending downward toward the bottom of the lower cover of the filter housing.  
      In accordance with another embodiment of the present invention, a metal or composite engine or transmission filter is providing which includes filtering means, means for housing said filtering means wherein the means for housing includes a lower cover, means for suspending the filtering means within said means for housing wherein the means for suspending is not integral with the upper or lower cover.  
      In accordance with yet another embodiment of the present invention, a method for alleviating fluid flow problems associated with filters having ribs stamped into the lower cover is provided. The method includes providing a tray insert for use with a metal or composite oil filter. In some embodiments, the method also includes positioning the tray insert in the lower cover of an oil filter, positioning the filter media on the tray insert, and positioning an upper cover above the filter media and lower cover.  
      There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.  
      In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.  
      As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a top perspective view illustrating a tray insert according to a preferred embodiment of the invention resting on the bottom of the lower cover of an engine or transmission filter.  
       FIG. 2  is a top view of a tray insert according to another preferred embodiment of the invention resting on the bottom of the lower cover of an engine or transmission filter.  
       FIG. 3  is a detail cross-sectional view of a plastic pinch point suitable for use with plastic tray inserts according to the present invention.  
       FIG. 4  is a detail cross-sectional view of a pinch point in accordance the prior art.  
       FIG. 5  is a detail cross-sectional view of an inlet opening suitable for use with plastic tray inserts according to the present invention.  
       FIG. 6  is a perspective view of another tray insert in accordance with the present invention.  
       FIG. 7  is an exploded view of an oil filter made with the tray insert of  FIG. 6 .  
       FIG. 8  is a cross-sectional view of a suspended tray insert design in accordance with another embodiment of the present invention.  
       FIG. 9  is a perspective view of the tray insert of  FIG. 8 .  
       FIG. 10  is a perspective view of a suspended tray insert design in accordance with another embodiment of the present invention.  
       FIG. 11  is a cross-sectional view of a suspended tray insert design in accordance with another embodiment of the present invention.  
       FIG. 12  illustrates the profile of a stamped metal rib versus the profile of an exemplary plastic rib in accordance with an embodiment of the present invention.  
       FIG. 13  is a side view of a metal filter configured with a plastic tray insert having an integral plastic inlet tube in accordance with an embodiment of the invention.  
       FIG. 14  is a cutaway perspective view of the filter of  FIG. 13 . 
    
    
     DETAILED DESCRIPTION  
      The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. A metal or composite engine or transmission filter can comprise a two-part housing having a lower cover and an upper cover encompassing a filter bag. The housing covers are either both metal, or in the case of the composite filter illustrated, the top cover can be plastic, while the lower cover is made from metal. According to the prior art, to support the filter bag above the bottom of the lower cover, yet still permitting fluid flow along the bottom portion of the lower cover, the lower metal cover is stamped with a series of spaced-apart ribs protruding into the interior of the filter housing. The ribs support the filter bag above the bottom of the lower cover, and the space between the ribs provides regions for fluid flow.  
      The present invention provides a tray insert which can take the place of stamped metal ribs, and thus can be used with metal covers which do not have stamped metal ribs. The tray insert is adapted to rest within the filter housing such that the filter bag is supported away from the housing by the tray insert.  
      According to some embodiments of the invention, the tray insert is made of plastic, and is typically injection molded as a single integral piece. According to some embodiments of the present invention, the tray insert is a plastic rib-tray insert, which rests on the bottom of the lower housing (which preferably is not itself stamped with ribs).  FIGS. 1 and 6  illustrate exemplary plastic rib-tray inserts in accordance with the present invention.  
      In the embodiment of  FIG. 1 , the rib-tray insert comprises a set of interlinked linear segments supported by ribs. According to this embodiment, the top face of the interlinked linear segments provides a surface for supporting the filter media, this surface is spaced apart from the bottom of the lower cover by the ribs.  
      In the embodiment of  FIG. 6 , the tray comprises a set of interlinked plastic ribs. According to this embodiment, the top face of the ribs provides a surface for supporting the filter above the bottom of the lower cover, whereas the bottom surface of the ribs rests on the bottom of the lower cover.  
      An advantage of a plastic rib-tray insert, as compared to a metal lower cover having stamped metal ribs, is that plastic ribs can be made with a much higher aspect ratio (i.e. the height of the rib versus the width of the rib) than metal ribs. Therefore, as compared to metal ribs, plastic ribs can block less fluid flow.  FIG. 12  compares the profile of a stamped metal rib versus an exemplary plastic rib illustrating that there can be less blocked flow space associated with plastic ribs suitable for use with plastic tray inserts according to the present invention.  
      Another advantage of using a plastic tray insert over stamping ribs into the lower cover can be that the plastic insert can include an integral plastic inlet tube. Use of a plastic inlet tube provides design flexibility as compared to a separate metal inlet tube. For example, a plastic inlet tube can have cross-sectional geometries other than oval or round shapes. In addition, because the plastic inlet tube can be injection molded along with the tray insert, and can thus be an integral component of the tray insert, implementation problems associated with shaped or angled metal inlet tubes, which are crimped to the filter as a separate component, are alleviated. In addition, because the plastic tray insert can be used with metal and composite filters, a convenient alternative is provided for implementing shaped or angled inlet tubes without requiring the use of an all-plastic filter. An example of a filter incorporating a tray insert having an integral exemplary angled plastic inlet tube in accordance with the present invention is illustrated in  FIG. 13 .  
      Another advantage of a plastic tray insert as compared to stamped metal ribs, is that the plastic tray insert can include a plastic inlet opening (including alternatively a plastic inlet tube), which can accommodate an anti-drainback device. Such devices can prevent or alleviate fluid from flowing out of the filter when fluid is not being drawn into the filter. An example of a plastic inlet opening incorporating an anti-drainback device suitable for use with plastic tray inserts according to the present invention is illustrated in  FIG. 5 .  
      A plastic tray insert can also accommodate “pass-through” pinch points. A “pinch point” is a location in the filter, where the upper cover and lower cover are designed to engage one another in the interior (as opposed to edges) of the housing. For example, the top surface of a rib or projection which is stamped or molded in the lower cover engages the bottom surface of a rib or projection which is stamped or molded in the upper cover. The purpose of the pinch point is to provide structural support to the housing to prevent or alleviate deformations in the housing which may be caused when the filter is subjected to a vacuum. However, in prior art designs using at leat one stamped metal cover, the filter bag is compressed at each such pinch point because the top and bottom of the filter bag are sandwiched between the top and bottom rib (i.e. the top of the bag is pushed against the bottom of the bag such that the bag is not held open at the pinch point), resulting in a loss of fluid flow area. A prior-art pinch point is illustrated in  FIG. 4 .  
      According to some embodiments of the present invention, the plastic rib tray insert includes plastic “pass-through” pinch points, which are capable of holding the filter media open at the pinch point while simultaneously providing structural support. For example, the filter bag can be designed to have a hole through which a plastic pinch point can protrude. Accordingly, the filter media is held open rather than compressed because only the top layer of the media is compressed at the pinch point. Specifically, the top layer of the filter media is sandwiched between the top of the plastic pinch point on the rib tray and the bottom of a rib or protrusion on the upper cover, while the bottom layer of the filter media rests the bottom of the plastic pinch point. To alleviate or prevent loss of fluid, the lower layer of the filter media can be sealed to the bottom of the plastic pinch point, by for example ultrasonic welding. An example of a pass-through pinch point suitable for use with plastic tray inserts according to the present invention is illustrated in  FIG. 3 .  
      According to some embodiments of the invention, rather than resting on the bottom of the lower cover, the tray insert is suspended above the bottom of the lower cover and may be formed, for example, from plastic or metal. To suspend the tray insert, for example, the tray insert may have a bottom portion which includes vents to permit fluid flow and a lip portion spaced apart from the bottom portion by sides extending upward from the bottom portion. The lip portion of the tray insert is configured to rest on the lip portion of the lower cover, suspending the bottom portion of the tray insert above the bottom portion of the lower cover. In such embodiments, there is little or no lost flow area because there are no ribs integral with or adjacent the bottom of the lower cover to interfere with fluid flow.  FIGS. 8-10  illustrate exemplary tray inserts in accordance with this embodiment of the present invention.  
      In some embodiments, the suspended tray insert may also include legs which extend downward from the tray insert toward the bottom of the lower cover. Such legs can be made relatively thin as compared to the stamped metal ribs and accordingly, even where the legs may touch the bottom of the housing, they may affect fluid flow to a lesser degree than the stamped metal ribs. For example, the legs may be the same thickness as the bottom of the tray insert, which is considerably thinner than the base of ribs which are stamped in the bottom of metal covers.  FIG. 11  illustrates an exemplary tray insert in accordance with this embodiment of the present invention. Although the legs may rest on the bottom of the filter housing and may provide a support function with regard to the tray insert and lower cover, such embodiments are still referred to as “suspended try inserts.” 
      An embodiment of the present inventive apparatus is illustrated in  FIG. 1 . The tray insert  10  is shown resting on the bottom portion  14  of the filter housing lower cover  12 . In addition to the bottom portion  14 , the lower cover  12  also includes a side portion  16  extending upward from the bottom portion  14 , and a lip portion  18  extending outward from the side portion  16  and which lip portion  18  is substantially parallel with the bottom portion  14 .  
      The tray insert  10  includes a filter media supporting surface  20 , ribs  22  extending below the supporting surface  20  to the bottom portion  14  of the lower cover  12 , pass-through pinch points  28 , and an inlet opening  30 .  
      The supporting surface  20  is formed from first linear segments  24  substantially oriented in the direction of fluid flow interconnected by second linear segments  26  substantially oriented perpendicular to the direction of fluid flow. Attached to the underside of the first linear segments  24  are the ribs  22  which support the supporting surface  20  above the bottom portion  14  of the lower cover  12 . Embodiments including ribs are sometimes referred to herein as “rib-tray inserts.” 
      The tray insert dimensions preferably correspond to the length and width of the filter media (often in bag configuration). (The filter bag can be formed from filter media material having a length and width. The filter media material is folded in half along its length to form the filter bag. Thus the length of the filter bag is approximately half the length of the filter media material from which it is formed, and the width of the filter bag is approximately the same as the width of the filter media material from which it is formed.) Although  FIG. 1  illustrates first linear segments  24  that extend predominately the length of the filter bag (including where interrupted by inlet opening  30  and/or pass-through pinch points  28 ) and second linear segments  26  that extend predominately the width of the filter bag (including where interrupted by inlet opening  30  and/or pass-through pinch points  28 ), the tray insert  10  can be formed from linear segments with smaller dimensions or larger dimensions. For example,  FIG. 2  illustrates an embodiment wherein the overall dimensions of the tray insert  10  are approximately equal to the length and width of the filter bag, but wherein each of the first linear segments  24  are shorter than the length of the filter bag and each of the second linear segments  26  are shorter than the width of the filter bag.  
      Generally, the length, number, distribution, and width of first linear segments  24  is chosen to be sufficient to provide a filter media supporting surface  20  that keeps the filter media spaced apart from the bottom portion  14  of the cover  12 , while minimizing impact on fluid flow. For example, for stiff filter media, fewer first linear segments  24  are needed for support. The orientation of the first linear segments  24  is preferably in the direction of fluid flow, and the width of first linear segments  24  is preferably as narrow as possible, to alleviate any negative impact on fluid flow.  
      Generally, it is preferred to minimize the number of second linear segments  26  because second linear segments  26  can have a greater impact on fluid flow than the first linear segments  24  as they are not oriented in the direction of fluid flow. Preferably, the number, length, and orientation of second linear segments  26  are chosen to be sufficient to connect the first linear segments  24 , providing structural support and integrity to the tray insert  10 , but also minimize impact on fluid flow. As with the first linear segments  24 , the second linear segments  26  are preferably made as narrow as possible.  
      The tray insert additionally includes plastic pinch points  28  and an inlet opening  30 . As shown in  FIGS. 1 and 3 , the plastic pinch points  28  includes a lip portion  32  that is substantially in the same plane as the first linear segments  24  and thereby forms part of the filter media supporting surface  20 . The pinch point  28  also includes a protruding portion  34  which can pass through the filter media into the interior  36  of the filter bag  38 . Preferably the protruding portion  34  has sufficient length to either engage a corresponding pinch point  40  stamped or molded in the upper cover  42 . When the oil filter is assembled, the filter media  38  includes an opening  44  into which the protruding portion  34  protrudes. The filter media  38  material around the opening is preferably sealed to the lip portion  32  to avoid or alleviate fluid within the filter bag from leaking out through the opening rather than passing through the filter media material. This sealing can be accomplished, for example, by ultrasonic welding the filter bag  38  material to the lip portion  32  of the pass-through pinch point.  
      As best shown in  FIG. 3 , this “pass-through” pinch point configuration allows the pinch point  28  to provide structural support to the housing, while at the same time holding the filter bag  38  open, alleviating fluid flow problems of prior art designs using stamped metal ribs. That is, the pinch point  28  compresses only the upper part  46  of the filter bag  38  against the corresponding pinch point  40  in the upper cover  42 , keeping the lower part  48  of the filter bag spaced apart from the upper part  46  off the filter bag  38 . In contrast, in prior art designs, as illustrated in  FIG. 4 , both the lower part of the filter bag and the upper part of the filter bag are compressed between the lower cover metal rib and the corresponding pinch point in the upper cover.  
      The inlet opening  30 , as illustrated in  FIG. 1 , can be simply a lip portion  50  which forms part of the filter bag supporting surface  20  and provides a surface to which the filter bag may be attached. For example, the filter bag may be ultrasonically welded to the tray insert inlet opening  50 . The lower metal cover also includes an inlet opening  52 , which can be used to align the filter tray and attach the filter tray to the lower metal cover. For example, the lower metal cover inlet opening  52  can be crimped to the plastic tray insert inlet opening  50 . Accordingly, the filter bag need not be ultrasonically welded to the plastic tray insert inlet opening  50 , but may be held in place by the crimped metal inlet opening  52 .  
      In some embodiments, the inlet opening  30  is as shown in  FIG. 5 , and incorporates an anti-drainback device  54 . In this example, the anti-drainback device is formed from an O-ring  56  positioned within the inlet opening  30  and a stopper  58 , which can, for example, be a metal or steel ball or plate. When fluid is drawn into the filter, the stopper is pushed upward and allows fluid into the filter. When fluid is no longer drawn into the filter, the stopper drops (possibly aided by a spring) and prevents or reduces fluid flow out of the filter.  
       FIG. 6  illustrates another embodiment of a tray insert  100  in accordance with the present invention. The tray insert  100  includes a filter media supporting surface  102  formed by ribs  104 , cross-bar segments  108 , and an inlet opening  110 . The ribs  104  and linear segments  106  are generally oriented in the direction of fluid flow. The cross-bar segments, which connect parallel lengths of interlinked rib segments  109 , are therefore not oriented in the direction of fluid flow. In the illustrated embodiment, the cross-bar segments  108  are oriented substantially perpendicular to fluid flow.  
      As is shown, the bottom portion  116  of the lower metal cover  112  is preferably stamped with channels  114  which receive the cross-bar segments  108 . The depth of the channels  114  preferably correspond to the height of the cross-bar segments  108  so that when the cross-bar segments  108  are fitted into the channels  114 , the top face of the cross-bar segments  108  lie in a plane substantially the same as the bottom portion  116  of the lower metal cover  112 .  
      The ribs  104  divide the fluid traveling along the lower cover (toward the outlet) into channels. If one channel has a relatively high flow rate, gaps are provided in the ribs and to allow fluid to “spill over” into the adjacent channel. The gaps cut out of the top  124  of the rib  104  also reduce the amount of media contact area at the top surface  124  of the rib  104  allowing a higher percentage of the media to be utilized (for filtration).  
      As with the embodiment illustrated in  FIG. 6 , the length and width of the tray insert  100  substantially matches the length and width of the filter bag (not illustrated in  FIG. 1 ). And, although in the illustrated embodiment, the ribs  104  are each substantially the length of the filter bag (including where interrupted by the inlet opening  110  and/or optional pinch points) and the cross-bar segments  108  are each substantially the width of the filter bag (including where interrupted by the inlet opening  110  and/or optional pinch points), the tray insert  100  can be formed from ribs  104  and cross-bar segments  108  with smaller dimensions or larger dimensions. For example, although the overall dimensions of the tray insert  100  can be approximately equal to the length and width of the filter bag, each rib  104  may be shorter than the length of the filter bag and each of the cross-bar segments  108  may be shorter than the width of the filter bag.  
      Generally, the length, number, distribution, and width of interlinked ribs  104  is chosen to be sufficient to provide a filter media supporting surface  102  that keeps the filter media spaced apart from the bottom portion  116  of the lower cover  114 , while minimizing impact on fluid flow. For example, for stiff filter media, fewer ribs  104  are needed for support. The orientation of the ribs  104  are preferably in the direction of fluid flow, and the width of interlinked ribs  104  are preferably as narrow as possible, to alleviate any negative impact on fluid flow.  
      Generally, it is preferred to minimize the number of cross-bar segments  108  because the cross-bar segments  108 , as in the embodiment of  FIG. 6 , require corresponding depressions on the lower cover that could interfere with fluid flowing into the filter inlet. Preferably, the number, length, and orientation of cross-bar segments  108  is chosen to be sufficient to connect the interlinked rib segments, providing structural support and integrity to the tray insert  100 , but also minimize impact on fluid flow. As with the interlinked rib segments  109 , the cross-bar segments  108  are preferably made as narrow as possible.  
      The inlet opening  110 , as in the embodiment of  FIG. 6 , can be simply a lip portion  50  which forms part of the filter media supporting surface  20  and provides a surface to which the filter media may be attached. Or else, as with any plastic tray insert according to the present invention, the inlet opening can be configured to include an anti-drainback device as shown, for example, in  FIG. 5 .  
       FIG. 7  is an exploded view of an oil filter  200  according to the embodiment of  FIG. 6 . The purpose of the figure is to illustrate one way in which an oil filter according to the present invention may be assembled. The oil filter  200  includes lower metal cover  112 , tray insert  100 , upper plastic cover  202 , and a media in a bag configuration (not shown). The tray insert  100  includes ribs  104 , cross-bars  108 , and inlet opening  110 . The lower metal cover  112  includes channels  114  for receiving the cross-bar segments  108  and an inlet opening  204 .  
      To assemble the oil filter  200 , a filter bag, which includes an opening to coincide with inlet opening  110 , is positioned on the tray insert  100 . The filter bag, tray insert  100  and lower metal tray  112  are arranged so that the inlet openings  110 , 204  align with each other. The filter bag can be bonded to the tray insert at the location of the inlet opening  110 . For example, filter media material surrounding the opening may be ultrasonically welded to the inlet opening  110 . Alternatively, a portion of the lower metal cover inlet opening  204  is crimped over the tray insert inlet opening  110  and the portion of the filter media surrounding the opening to the filter bag, attaching the three components to one another. The crimped metal from the inlet opening  204  is thus found in the interior of the filter bag. The upper cover  202  is then placed over the lower metal cover so that the lip portion  206  of the upper cover  202  rests on the lip portion  208  of the lower metal cover  112  and the two covers  202 ,  112  are then crimped together.  
       FIGS. 8 and 9  illustrate another embodiment in accordance to the present invention. As shown, the tray insert  300  is a substantially flat pan suspended above the bottom portion of the lower metal cover  312 . The tray insert  300  includes a substantially flat pan portion  301 , sides  303  projecting upward from the pan portion  301 , and a lip portion  305 . The lip portion  305  is configured to engage the lip portion  318  of the lower cover, thereby suspending the tray insert  300  above the bottom portion  314  of the lower cover  312 .  
      The pan can be, for example, plastic or metal material stamped with holes  302  (also referred to as “cut-out portions” or “vents”) to permit fluid flow. The number, distribution, size, and shape of the cut-out portions are sized to adequately support the media thereby minimizing deflection toward the lower cover (which would block fluid on its way to the filter outlet) without reducing the fluid flow through the media. The localized flow rate through the media in areas that are supported by a rib  20 ,  301  is greatly reduced. Consequently, supporting the media too much will result in a higher pressure differential across the media and, therefore, through the filter. Preferably the pan is designed so that the surface area occupied by the pan material, such as the metal or plastic from which the pan is formed, is minimized, to reduce areas of lost fluid flow. Accordingly, the amount of material is preferably only so much as is needed to provide structural support and maintain the filter bag off the bottom portion  314  of the lower cover  312 .  FIG. 9 , for example, is a perspective view showing one possible pattern of vents for a suspended tray insert in accordance with the present invention.  FIG. 10  is a top view of another suspended tray insert in according with the present invention and illustrates another exemplary pattern of vents suitable for use with suspended tray inserts according to the present invention.  
       FIG. 11  illustrates another embodiment of a suspended tray insert design  400  according to the present invention. The embodiment of  FIG. 11  is a variation of that shown in  FIGS. 8-10  and thus too can be plastic or metal and includes a lip portion  405  for suspending the pan portion  401  above the bottom portion  414  of the lower metal cover  412 . Specifically, in the embodiment of  FIG. 11 , the tray includes supporting legs  407 . The legs can be formed from the cut-out portions  402  and may rest on the bottom portion  414  of the lower metal cover  412  and thus may also support the pan portion  401  (or filter supporting surface) above the bottom portion  414  of the lower metal cover  412 . For example, whereas in the embodiment shown in  FIGS. 8 and 9 , the cut-out portion is completely removed and thrown away, in the illustrated embodiment, the cut-out portion is a tab which is bent downward forming both a hole (where the cut-out material was removed) and a leg integrally attached to the pan. Of course, the leg need not be integral and may be separately made and attached to the pan. Enough legs  407  are created to sufficiently support the lower cover  414  from bowing upward and the pan portion from deflecting downward during filter operation. Not every cut-out portion  401  must have a supporting leg  401 . Thus, for example, even where the legs are formed as tabs, by leaving a section of the cut-out portion attached to the pan and bending the cut-out portion downward, the tray insert may include a mixture of cut-out portions which are completely cut-away to form only holes and cut-out portions which are tabs forming both holes and legs.  
      As with the illustrated plastic rib-tray insert embodiments, when the embodiments of  FIGS. 8-10  are made of plastic, they can include plastic pinch-points and plastic inlets, for example, as described above.  
      Plastic tray inserts in accordance with the present invention can include plastic inlet tubes  31 , as shown in  FIGS. 13 and 14 , which are preferably integrally formed with the inlet opening  30 . When used in connection with a plastic rib-tray insert  100 , also as shown in  FIG. 13 , the rib tray insert  100  and its integral inlet tube  31  are assembled into the metal lower cover  500  by press fitting the rib tray insert  100  into the metal lower cover inlet form (hole)  52 . The metal lower cover inlet form  52  can also be formed after the press fit to embed the metal into the plastic tube for additional strength. The filter media can be sonically welded to the rib tray insert at the inlet in this implementation. Further, an o-ring (not shown) can optionally be added at the inlet/lower cover interface to help with sealing.  
      The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.