Abstract:
A method and apparatus are provided for constructing a filter element, having enhanced structural capabilities, through use of a molded end cap having first and second foam portions of differing physical properties meeting at a common juncture of the first and second foam portions and simultaneously cured with one another.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to air filters, and more particularly to air filters having one or more end caps formed either wholly or partially from molded foam material.  
       BACKGROUND OF THE INVENTION  
       [0002]     Filter elements, having media packs of pleated paper or other appropriate materials, are commonly used on over-the-road trucks, agricultural, automotive and off-highway equipment for preventing dirt, dust, and moisture from entering machinery, such as an engine or an air compressor, with the incoming air supply. In one popular style of such filters, the filter element includes a tubular-shaped media pack having an open end, configured to tightly engage a pipe or conduit supplying air to an engine, with the opposite end of the tubular-shaped media pack being closed by a closed end cap. Typically such filter elements are mounted in a housing, in such a manner that air flows through the filter element in an outside-in direction. Contaminants in the air stream are removed as the incoming air flows through the media pack. Often, the closed end cap includes one or more compliant ribs for aiding in properly positioning the filter element within the housing, and/or for providing additional structural and sealing functions at the juncture between the filter element and the housing.  
         [0003]     In the design of such filter elements, a number of factors must be considered. Generally such filter elements must be produceable at low cost, so that they can be replaced, without significant expense, at regular intervals. It is also desirable that such filter elements be constructed in such a manner that they are readily incinerable or recyclable.  
         [0004]     In addition to being produceable at low cost, in a manner that is readily disposable or recyclable, it is necessary that the filter element be designed in a manner which is structurally efficient and effective, so that the filter element can withstand the considerable forces to which the elements may be exposed during operation. As the filter element becomes increasingly plugged with contaminants removed from the incoming air, the pressure drop across the tubular-shaped media pack increases. The filter element must be constructed in such a manner that it can withstand inwardly directed forces, caused by the increased pressure drop, to preclude having the media pack be deformed inwardly when the media pack has absorbed its maximum rated capacity of contaminants.  
         [0005]     The radially inwardly directed force of the incoming air, as the filter media pack becomes increasingly dirty, can also cause problems in maintaining the radial seal between the filter element and the pipe or conduit supplying air to the engine. Commonly assigned U.S. Pat. No. 6,447,567 B1, to Ehrenberg, the disclosure of which is incorporated herein in its entirety, discloses an air filter element having an integral radial seal gasket which is particularly well suited to maintaining the radial seal under demanding operating conditions. Specifically, Ehrenberg &#39;567 includes a substantially stiff insert ring, which in combination with an inner liner provides improved resistance of the media pack to inwardly directed forces.  
         [0006]     Ehrenberg &#39;567 also discloses forming both an open and a closed end cap, at opposite ends of a tubular-shaped media pack, from foam materials, in a manner which is highly conducive to low-cost manufacturing of filter elements. Specifically, Ehrenberg &#39;567 discloses a closed end cap formed entirely of a molded polyurethane material extending over the ends of an inner and outer liner and into the end of the media pack, thereby providing a configuration which is highly manufacturable. Although the one-piece, molded end cap of Ehrenberg &#39;567 provides a highly efficient and effective structure under most operating conditions, for applications where the inwardly directed air forces are substantial, and/or applications where the inner diameter of the tubular-shaped media pack is of a large size, a one-piece end cap, as taught by Ehrenberg &#39;567, may not provide sufficient strength.  
         [0007]     One approach to providing additional strength in a closed end cap is illustrated by U.S. Pat. No. 5,484,466 to Brown, et al., which discloses reinforcing the closed end cap of a filter element with a plate, or pedestal of metal or stiff plastic. Although reinforcing a closed end cap of a filter element with a plate or pedestal of metal or stiff plastic, as disclosed in Brown &#39;466, is highly effective in strengthening the end cap, the addition of the reinforcement undesirably increases the complexity and cost of producing a filter element.  
         [0008]     It is desirable, therefore, to provide an improved filter element, and a method for making such an improved filter element, having additional resistance to operational loads on the filter element, without the use of additional reinforcing plates to the closed end of the filter element.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The invention provides an improved filter element, having enhanced structural capabilities, through use of a molded end cap having first and second foam portions of differing physical properties meeting at a common juncture of the first and second foam portions and simultaneously cured with one another. The invention may be practiced in a variety of forms, including a filter element, and a method for constructing a filter element.  
         [0010]     In one form of the invention, a method is provided for constructing a filter element having a tubular-shaped media pack, defining a longitudinal axis about which the tubular-shaped media pack is disposed, and terminating at one end thereof in an end cap, by molding the end cap to have first and second foam portions of differing physical properties meeting at a common juncture thereof and simultaneously cured with one another. The common juncture may define a cured thickness of the end cap adjacent the common juncture, with a method according to the invention further including the steps of: providing a mold having a first cavity and a second cavity thereof, separated from one another by a rib disposed substantially at the common juncture and having a height less than the cured thickness of the end cap adjacent the common juncture; placing uncured material of the first foam portion into the first cavity of the mold to a level less than the height of the rib in the mold; placing uncured material of the second foam portion into the second cavity of the mold to a level less than the height of the rib in the mold; and curing the material in the first and second mold cavities in a manner causing the material in the first and second cavities to foam, rise to the cured thickness, and join integrally along the common juncture.  
         [0011]     In some forms of a method, according to the invention, the tubular-shaped media pack may define an inner boundary thereof, with the common juncture between the first and second foam portions being located substantially at the inner boundary of the media pack. A method, according to the invention, may further include forming the second foam portion from a foam material having a greater rigidity than the first foam portion. A method, according to the invention, may include inserting an axial end of the filter media pack into the uncured material in the mold. The mold may include a media pack locator for engaging the axial end of the medial pack, to thereby position the media pack within the mold, with the method including engaging the media pack locator with the axial end of the media pack.  
         [0012]     In some forms of the invention, the first mold cavity may define at least one secondary cavity therein, for forming a protruding compliant feature on the first foam portion of the end cap, with the method including forming a protruding compliant feature on the first foam portion of the end cap concurrently with curing the foam material of the first portion of the end cap.  
         [0013]     In some forms of the invention, where a filter element includes an additional component, such as an inner and/or outer liner, molded into the end cap, a method, according to the invention, may include inserting at least a portion of the additional component into the uncured material in the mold, prior to curing the material in the mold.  
         [0014]     The invention may be practiced in forming either open or closed end caps of a filter element having a tubular-shaped media pack. Where the tubular-shaped media pack defines an inner boundary thereof, the first portion of a closed end cap, according to the invention, may be disposed radially outward of the second foam portion and the common juncture between the first and the second foam portions of the closed end cap may be located substantially at the inner boundary of the media pack. The second foam portion may be formed from a material having a greater rigidity than the first foam portion.  
         [0015]     The invention may take the form of a filter element, including a media pack and an end cap molded onto the media pack at one axial end thereof. The media pack may define a longitudinal axes about which the media pack is disposed, with the media pack terminating at axial ends thereof. The molded end cap may have first and second foam portions of differing physical properties meeting at a common juncture thereof and simultaneously cured with one another. Where the media pack is tubular-shaped and defines an inner boundary thereof, the common juncture may be located substantially at the inner boundary of the tubular-shaped media pack, and the second foam portion may be formed from a foam material having a greater rigidity than the first foam portion. The first foam portion may include a protruding compliant feature, to perform various functions such as positioning the filter element in a housing, and/or providing a seal between the filter element and the housing or an outlet air tube of a filter apparatus. A filter element, according to the invention, may further include one or more additional components, such as inner and/or outer liners, operatively attached to the media pack by the molded end cap.  
         [0016]     In one form of the invention, a filter element includes a tubular-shaped media pack, an inner liner, and a closed end cap. The tubular-shaped media pack defines an inner boundary thereof, a longitudinal axis about which the medial pack is disposed, and an axial end of the media pack. The inner liner is disposed along and conforms substantially to the inner boundary of the media pack. The closed end cap is molded onto the axial end of the media pack and inner liner. The closed end cap has first and second simultaneously cured foam portions thereof, meeting at a common juncture of the first and second foam portions, with the common juncture being disposed substantially at the inner boundary of the media pack. The first foam portion of the closed end cap may be disposed radially outward of the second foam portion. The second foam portion may have a greater rigidity than the first foam portion. The first foam portion may further include a protruding compliant feature. The media pack may further define a second axial end thereof, with the filter element further including an open end cap attached to the second axial end. The open end cap may include a substantially radially rigid element operatively engaging the inner liner. The open end cap may also include a molded portion thereof securing the substantially rigid element to the second axial end of the media pack. The molded portion of the open end cap may include a foam material portion thereof, forming a radial seal gasket. The tubular-shaped media pack may also define an outer boundary thereof, with the filter element further including an outer liner disposed substantially at the outer boundary and secured to the media pack by the open and closed end caps.  
         [0017]     Other aspects, objects and advantages of the invention will be apparent from the following detailed description and accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:  
         [0019]      FIG. 1  is a perspective illustration of an exemplary embodiment of a filter element, according to the invention;  
         [0020]      FIG. 2  is a cross-sectional illustration of a filter apparatus, showing the exemplary embodiment of the filter element of  FIG. 1  installed in a filter housing; and  
         [0021]      FIGS. 3-6  are enlarged partial cross-sections illustrating a method, according to the invention, for forming an end cap on a media pack of the exemplary embodiment of the filter element shown in  FIG. 1 . 
     
    
       [0022]     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  shows a first exemplary embodiment of the invention, in the form of a filter element  10 , adapted for installation into a filter housing  12  in the manner illustrated in  FIG. 2 , to provide filtration of air flowing into the housing  12  from an inlet  11 , and exiting the housing through an outlet  13 .  
         [0024]     As shown in  FIG. 1 , the exemplary embodiment of the filter element  10  includes a tubular-shaped media pack  14 , formed from a suitable material, such as pleated filter paper, through which the air being filtered flows in an outside-to-inside direction through the media pack  14 . The media pack  14  defines an inner boundary  16  thereof, a longitudinal axis  18 , about which the media pack  14  is disposed, and first and second axial ends  20 ,  22  of the media pack  14 .  
         [0025]     An inner liner  24  is disposed along and conforms substantially to the inner boundary  16  of the media pack  14 . In similar fashion, an outer liner  26  is disposed substantially along and conforms substantially to the outer boundary  17  of the media pack  14 .  
         [0026]     A closed end cap  28  is molded onto the first axial end of  20  of the media pack  14  in a manner encapsulating the first end  20  of the media pack  14  and a portion of the inner and outer liners  24 ,  26  adjacent the first axial end  20  of the media pack  14 . The closed end cap  28  includes a first and second foam portions  30 ,  32  thereof, meeting at a common juncture  34 , of the first and second foam portions  30 ,  32 , disposed substantially at the inner boundary  16  of the media pack  14 . The first foam portion  30  of the closed end cap  28  is disposed radially outward of the second foam portion  32 , in the exemplary embodiment of the filter element  10 , with the common juncture  34  between the first and second foam portions  30 ,  32  being positioned slightly radially outward of the inner boundary  16  of the media pack  14 .  
         [0027]     In various embodiments of the invention, the common juncture  34  may be located at various positions appropriate to the application and design of the end cap of a given filter element embodiment, with the term “substantially at the inner boundary of the media pack,” as used herein, being contemplated to include an arrangement, such as the one shown in the exemplary embodiment of the filter element  10 , and other arrangements wherein the common juncture  34  is reasonably proximate to the inner boundary  16  of the media pack  14 . It will also be appreciated, by those having skill in the art, that, although the common juncture  34  in the exemplary embodiment of the filter element  10  described herein has a substantially cylindrical shape generally matching the cylindrical shape of the media pack  14 , the common juncture  34  may take a virtually unlimited variety of other forms in other embodiments of the invention. For example, in embodiments of the invention where the filter may have another shape, such as the well known race-track tubular shape, the common juncture between foam portions of an end cap, according to the invention, may also have a race-track shape. It will be further appreciated, that the common juncture need not necessarily have a shape matching that of a media pack in a filter element according to the invention. The common juncture may, for example, have a curvilinear shape, a polygonal shape, a serpentine shape, or any other shape or form appropriate and conducive to practicing the invention.  
         [0028]     The first and second foam portions  30 ,  32 , of the closed end cap  28 , are molded onto the first axial end  20  of the media pack  14  by a method, to be described in greater detail below, allowing the first and second foam portions  30 ,  32  to be simultaneously cured with one another, without mixing with one another. In the exemplary embodiment of the filter element  10 , the second foam portion  32  of the end cap  28  is formed in a manner causing it to have a greater rigidity than the first foam portion  30 , when the first and second foam portions  30 ,  32  are fully cured.  
         [0029]     The first foam portion  30 , of the closed end cap  28  of the exemplary embodiment of the filter element  10  also includes a protruding compliant feature, in the form of a positioning rib  36 , to aid in retaining the filter element  10  in a desired axial position, when the filter element  10  is installed into the filter housing  12 , in the manner shown in  FIG. 2 .  
         [0030]     As shown in  FIGS. 1 and 2 , the exemplary embodiment of the filter element  10  also includes an open end cap, substantially of the type taught in Ehrenberg &#39;567, attached to the second axial end  22  of the media pack  14 . The open end cap includes a substantially radially rigid element  40 , operatively engaging the inner liner  24 , in a manner reinforcing the inner liner  24 . The open end cap  38  also includes a molded portion  40  thereof, which performs a dual function of securing the rigid element  40  to the media pack  14 , and forming a radially acting seal with the filter housing  12 , as indicated at  44  in  FIG. 2 .  
         [0031]     In the exemplary embodiment of the filter element  10 , the molded portion  42  of the open end cap  38  is illustrated as being formed from a foam material, which is highly conducive to forming an effective radial seal  44  between the filter element  10  and the housing  12 . In other embodiments of the invention, the molded portion  42  may be formed from non-foamed materials, or a combination of foamed and non-foamed resilient materials.  
         [0032]     Those having skill in the art will recognize that, although the exemplary embodiment of the filter element  10  described herein includes the rigid element  40  in the open end cap  38 , in other embodiments of the invention it may be desirable to form an open end cap, in the same manner described herein with regard to the closed end cap  28  of the exemplary embodiment of the filter element  10 , in which first and second foam portions of the open end cap are formed from materials having different rigidities, in a manner that allows the separate rigid element  40  of the open end cap  38  of the exemplary embodiment of the filter element  10  described herein to be eliminated. It will also be recognized by those having skill in the art, that the term “closed end cap”, as used herein is intended to encompass other forms of end caps which reasonably fall within the definition of a closed end cap, even though they may include small perforations therethrough, or various shaped openings which are operatively closed by another element of a filter apparatus, when the filter element having a closed end cap, according to the invention, is operatively installed into the filter apparatus.  
         [0033]     A method of forming the closed end cap  28  of the exemplary embodiment of the filter element  10  will now be described with reference to the steps illustrated in  FIGS. 3-6 , using a mold  46  having a first cavity  48  and a second cavity  50  thereof, separated from one another by a rib  52  disposed substantially at the common juncture  34  and having a height “h” (see  FIGS. 3 and 6 ) less than a cured thickness “t” (see  FIG. 6 ) of the closed end cap  28  adjacent the common juncture  34 , with the relationship between the height “h” of the rib  52  in the mold  46  and the thickness “t” being best illustrated in  FIGS. 3 and 6 .  
         [0034]     As shown in  FIG. 3 , a measured amount of uncured material  54  of the first foam portion  30  of the closed end cap  28  is placed into the first cavity  48  of the mold  46  to a level less than the height “h” of the rib  52  of the mold  46 . In similar fashion, a measured amount of uncured material  56  of the second foam portion  32  of the closed end cap  28  is placed into the second cavity  50  of the mold  46  to a level less than the height “h” of the rib  52  of the mold  40 . In the exemplary embodiment of the invention, the foam materials used to form the first and second foam portions  30 ,  32  may consist of a two part formulation of a polyurethane material and an activator material which, when mixed together, almost immediately cause the polyurethane material to foam and begin to fill the first and second mold cavities  48 ,  50 , as indicated in  FIG. 4 .  
         [0035]     As shown in  FIG. 4 , once the measured amounts of uncured materials  54 ,  56  are placed into the first and second cavities  48 ,  50  of the mold  46 , the first axial end  20  of the media pack  14 , with the inner and outer liners  24 ,  26  installed thereon, is inserted into the mold  46 , as shown in  FIGS. 4-6 , until the first axial end  20  of the media pack  14  is brought into abutment with a series of media pack locators  58  radially spaced about the outer circumference of the first cavity  48 , to thereby provide convenient and repetitive control of the depth of insertion of the media pack  14  into the mold  46 . As will be understood from an examination of  FIG. 1 , although these media pack locators  58  leave small depressions  60  in the bottom surface, as shown in  FIG. 1 , of the closed end cap  28 , the depressions  60  have no significant detrimental effect on the operation of the completed filter element  10 .  
         [0036]     Once the first axial end  20  of the media pack  14  is brought into abutment with the media pack locators  58  of the mold  46 , the media pack  14  is left in place while the foam materials  54 ,  56  of the first and second foam portions  30 ,  32  of the closed end cap  28  continue to expand upward into the filter media at the end of the media pack  14  and around the ends of the inner and outer liners  24 ,  26 . As the foam materials  54 ,  56  continue to expand and cure, they rise above the height “h” of the rib  52  and come into abutment with one another to form the common juncture  34  between the first and second foam portions  30 ,  32  of the closed end cap  28 , and eventually rise to the cured thickness “t” of the end cap  28  at the common juncture  34 .  
         [0037]     The materials selected for formation of the first and second foam portions  30 ,  32  are of such a nature that they will join together at the common juncture  34 , through cross-linking or other processes, in such a manner that, although the closed end cap  28  has two distinct first and second foam portions  30 ,  32 , the closed end cap  28  essentially becomes a single piece when the materials  54 ,  56  are completely cured.  
         [0038]     Depending upon the particular materials  54 ,  56  selected for formation of the closed end cap  28 , the media pack  14  may need to remain in the mold  46 , until the materials  54 ,  56  are completely expanded and cured. In some embodiments of the invention, however, it is contemplated that the materials  54 ,  56  may allow the media pack  14 , with the closed end cap  28  attached thereto, to be removed from the mold  46  and set aside part way through the curing cycle, to thereby free up the mold  46  for use in constructing another filter element.  
         [0039]     In the exemplary embodiment of the filter element  10 , the material  56  of the second foam portion of the end cap  28  is selected to provide a cured second foam portion  32  having a greater rigidity than the material  54  selected for forming the first foam portion  30  of the end cap  28 . It will be further noted that the materials  54  selected for the first foam portion  30  of the end cap is somewhat compliant in its fully cured state, to thereby provide resilience to the positioning bead  36  of the closed end cap  28 . As shown in  FIGS. 3-6 , the positioning bead  36  is formed concurrently with the first foam portion  30  of the end cap  28  in a secondary cavity  62  of the mold  46 .  
         [0040]     Those having skill in the art will recognize, that by virtue of the arrangement described above, the second foam portion  32  of the closed end cap  28  provides significant additional rigidity of the filter element  10 , in a manner which makes the filter element  10  substantially stronger, without having to resort to the inclusion of stiffening plates or pedestals of the type used in prior filter elements. It will be further appreciated, that the particular arrangement of components described above in relation to the exemplary embodiment of the filter element  10  results in the rigid foam of the second foam portion  32  locking the inner liner  24 , the media pack  14  solidly together in a manner which creates a strong supporting structure extending along the inner boundary  16  of the filter element  10 . It will be yet further appreciated, that, in combination with the construction of the open end cap  38  of the exemplary embodiment, as described above, and in particular the manner in which the rigid element  40  of the open end cap  38  is locked into engagement with the inner liner  24  by the molded portion  42  of the open end cap  38 , a very robust structure is provided which is capable of withstanding considerable radially and axially directed forces acting against the filter element  10 .  
         [0041]     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.  
         [0042]     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0043]     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.