Abstract:
A cylindrical filter element which comprises a folded filter medium, in particular having a pleated configuration, which is annularly secured to a hollow cylinder, two expanded film axial end plates, and a support tube which is integrated into the cylindrical filter element and upon which the folded filter medium may be affixed. The support tube has an annular components adjacent respective axial end plates which has an interlocking fit with the film end plates and which may be connected to a sealing element.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a cylindrical filter element and to a method for producing such a cylindrical filter element. 
   Cylindrical filter elements having film end plates as a closure are known, for example, from Duerrstein et al., U.S. Pat. No. 5,736,040 (=DE 44 28 139). The end plates on the end faces of the filter element have an elastic design and are made of films which are heated for joining to the filter medium. The heating causes the films to expand toward the filter medium and partially penetrate same, thereby forming a seal on the end face of the filter folds. At the same time, the film material is cured by the heating, thus forming a firm connection by adhesion to the filter material. 
   A filter cartridge is known from Coulonvaux, U.S. Pat. No. 5,547,480 (=WO 95/19832) which is arranged in a housing having an inlet for untreated air and an outlet for clean air. Such a filter cleans the intake air in an internal combustion engine. The filter cartridge is braced between two concentric surfaces of the filter housing. The bracing action simultaneously creates a seal, which must be reliably maintained during shock or vibration. 
   German Patent Application No. DE 199 30 614 A1 (=U.S. Ser. No. 10/032,504) describes a filter cartridge, in particular for the air filter of an internal combustion engine. The filter cartridge is made of a filter paper which is folded in a zigzag shape and annularly joined to a cylindrical casing of the filter element. The end faces of the filter medium are cast inside a base plate and a cover plate. In the cylindrical interior of the filter element is situated a support tube having an elastic zone at its outlet end which is formed by axial slits in the end of the tube. The end of the support tube is made expandable in the radial direction by means of the elastic zone. Since the support tube is cast inside the cover plate, it expands along with the cover plate onto the connecting sleeve during installation of the filter element, thereby maintaining a positive-fit connection between the support tube and the cover plate. 
   Finally, a cylindrical filter element is described in German Patent Application No. DE 198 29 989 A1 which has resilient end plates which terminate the end faces of a filter medium. A support tube has elastic zones on its ends, formed by slits, which have a positive fit with the resilient end plates. This connection yields when sealing surfaces are mounted on corresponding connection pieces in the filter housing, so that an additional seal is not necessary. Integration of the support tube into the filter element facilitates installation in the housing. 
   The film end plates of the known filter elements are usually adhered so as to be even with the support tube. This often results in poor adhesion quality due to the production process in which the film is subjected, for example, to elevated temperatures (approximately 220° C.) for an extended period and fails to cure completely. This can lead to swelling of the end plates, and the adhesive bond can partially detach or pull away under certain conditions. This is especially disadvantageous if the filter is used as a fuel filter. 
   SUMMARY OF THE INVENTION 
   It is therefore the object of the present invention to provide an improved filter element which avoids the aforementioned disadvantages of the prior art. 
   A further object of the invention is to provide a filter element which assures an improved connection between the support tube and the end plates. 
   Another object of the invention is to provide a filter element with improved connections between parts which can be manufactured at reasonable cost. 
   These and other objects are achieved in accordance with the present invention by providing a filter element comprising a folded filter medium which is annularly joined to form a hollow cylinder, a pair of film end plates at axial ends thereof, and a support tube which is inserted into the cylindrical filter element and to which the folded filter medium is affixed, wherein the support tube comprises an annular component adjacent each of the axial end plates, each said annular component having an positively engaged fit with the respectively adjacent axial end plate and being connected to a sealing element. 
   Further advantageous preferred embodiments are described hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawings in which: 
       FIG. 1A  shows a cross section through a cylindrical filter element according to the invention; 
       FIG. 1B  shows an enlarged sectional detail view from  FIG. 1A  depicting a first embodiment of the inventive connection between the adhesive film and the support tube; 
       FIG. 2  shows a second embodiment of the inventive connection between the adhesive film and the support tube; 
       FIG. 3  shows a third embodiment of the inventive connection between the adhesive film and the support tube; and 
       FIG. 4  shows a fourth embodiment of the inventive connection between the adhesive film and the support tube. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1A  shows a section through a cylindrical filter element  2 , which is made of a filter medium  6  folded in a zigzag shape or pleated configuration. A base plate  8  and a cover plate  10  into which the filter medium is cast, are provided on the end faces of filter medium  6 . The base and cover plates are constructed as film blanks with which the folded filter medium  6  is brought into contact. The resulting component assembly is then heated. The film material is thus caused to expand toward an end face of filter medium  6 , with the result that the filter medium is enclosed by or embedded within the expanded film material. The end plates  8  and  10  are then formed by curing the film material. 
   Folded filter medium  6  is affixed to a support tube  12  which is integrated into cylindrical filter element  2 . This support tube may comprise one or more parts. In a multi-part arrangement, the individual parts may be interengaged with one another by a snap lock or similar fastening mechanism. 
     FIG. 1B  shows a section from  FIG. 1A  which represents the lower region of support tube  12  along with base plate  8 . In this lower region, support tube  12  carries on its side facing filter medium  6  an annular component or member  14  which with its lower end terminates at the end face of base plate  8 . 
   Component  14  can be made, for example, of a synthetic resin material, such as polyamide. On its side facing filter medium  6 , component  14  has a shoulder  16  which in the region of base plate  8  forms an annular recess  18  in which the side of base plate  8  facing support tube  12  comes to rest. Below shoulder  16  in the region of annular recess  18 , component  14  has at least one circumferential annular ridge or radially outward protrusion  20  which contacts the film material of base plate  8 . In the present example, two such circumferential ridges  20  are provided. 
   When the film material is heated, it expands toward the support tube  12 , as well as toward the filter material, so that after curing a positive-fit or interengaged connection is formed between base plate  8  and component  14 . 
   Component  14  also comprises an internal circumferential channel or groove  22  which, in the outer region of its opening  24  pointing toward the axial end face of base plate  8 , has side edges  26  which taper in the direction of the support tube. The depth of channel  22  preferably corresponds to the height of annular recess  18 . A circumferential sealing element  28  may be inserted into channel  22 . In this way the filter element can be axially sealed in its housing. For this purpose the seal advantageously projects approximately 4 mm beyond side edges  26 . 
   During manufacture of cylindrical filter elements, support tube  12 , which as already indicated may comprise one or more parts, is completely assembled and adhered to filter medium  6 . It is desirable for the adhesion surface to be as large as possible. Care must be taken not to damage the filter paper or filter medium  6  by the adhesion. In this way a reliable seal is achieved between the end plates, the filter medium, and the support tube. A reliable seal which may be used in particular for fuels is thus formed, since in this way the film end plates may be prevented from swelling under the effect of fuel penetration. 
   Although the invention has been described here only with respect to the connection between support tube  12  and base plate  8 , it should be apparent that a corresponding connection also exists between the support tube and cover plate  10  which is situated opposite base plate  8 . 
   With the described improved connection between the support tube and film end plate, sealing points, which have hitherto been necessary in the prior art, may be omitted. This is important, on the one hand, when the filter element is used as a fuel filter (the filter fineness and the demands on the filter are considerably greater for fuels than, for example, for oil), and on the other hand, this permits simpler production of the cylindrical filter elements as a result of considerably lower machine cycle times. 
     FIG. 2  shows a further advantageous embodiment of the connection according to the invention in which like parts are identified by the same reference numerals. In this case, component  14  at the lower end of support tube  12  is constructed in such a way that it does not terminate at the end face of base plate  8  with its side which faces toward filter medium  6 , but instead has a projecting finger or peg-like extension  30  formed on shoulder  16  which is formed on the side of component  14  which faces toward filter medium  6 . Extension  30  ends just underneath the surface of the axial end face of base plate  8 . 
   Shoulder  16  thus has a narrower design than in the embodiment according to  FIG. 1B , with the result that opening  24  is enlarged. In the present embodiment, only the side of component  14  facing toward support tube  12 , in the axially outer region of component  14  facing toward the end face of base plate  8 , has a side edge  26  which tapers in the direction of the support tube. 
   In this way, the film material of base plate  8  can surround the peg-like extension  30  when the film material is applied to the filter medium  6  in that it fills the space below shoulder  16  and also partially fills opening  24  of component  14 . The side of base plate  8  facing toward support tube  12  thus forms a direct connection with the sealing element  28  which is inserted into opening  24 , resulting in a reliable sealing of filter medium  6  after the film material is cured. 
   In addition, the effective adhesion surface is increased, and a positively engaged connection is created between the end plate and filter medium  6 . As already described in conjunction with the embodiment in  FIG. 1B , a corresponding connection also exists between the support tube and cover plate  10  which is situated opposite base plate  8 . 
   A further advantageous embodiment of the invention is shown in  FIG. 3 . As in  FIG. 1B , the lower region of support tube  12  here also carries on its side facing filter medium  6 , an annular component  14  which terminates with its lower end at the axial end face of base plate  8 . Component  14 , on its side facing toward filter medium  6 , also has a shoulder  16 , thus creating an annular recess  18  in the region of base plate  8 . In this embodiment, however, the edge  32  of annular recess groove  18  pointing toward the axial end face of base plate  8  is beveled in the direction of filter medium  6 , so that annular groove  18  tapers in the direction of the end face of base plate  8 . 
     FIG. 4  shows another advantageous embodiment of the invention. As in the embodiment according to  FIG. 2 , annular component  14  has a peg-like extension  30  which is enclosed by the film material of base plate  8 . However, the component has no groove or opening in which a sealing element  28  may be inserted. Instead, component  14  has a straight construction on its side facing toward support tube  12 , and has a contact surface  34  through which it is connected to a corresponding surface  36  of sealing element  28 . 
   On its side facing away from base plate  8 , component  14  has a shoulder  38  in which a correspondingly shaped projecting piece  40  of sealing element  28  can engage, whereby sealing element  28  requires a sufficiently large installation space for proper seating. 
   For production reasons, e.g. to facilitate removal of molded synthetic resin parts from their molds, a plurality of parts may be interconnected to form an easily handled aggregate part, which can be later divided into individual parts. 
   The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations falling within the scope of the appended claims and equivalents thereof.