Abstract:
A filter element for filtering a fluid stream, comprising a cylindrical support body, which is provided with openings and is sealed at one axial end, and a filter medium arranged on the support body. The filter medium is a strip material, which extends over approximately the entire length of the support body, and is wrapped around the circumference of the support body, and the start and the end of the strip material are welded together.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a filter element for filtering a fluid stream, comprising a cylindrical support body, which is provided with openings and is closed at one axial end, and a filter medium, which is arranged on the support body. 
   German Patent Application no. DE 37 23 807 discloses a tubular filter element that is formed by a rigid, radially perforated support tube, a filter medium and end disks. The exterior of the support tube is covered with the filter medium. The end disks are made of plastic and are subsequently injected onto the support tube. The end disks terminate the filter medium to form a seal, whereby the filter medium is simultaneously fixed on the support tube. It is conventional in the art to cover support tubes with a prefabricated tubular filter medium. The filter medium can, for instance, be sewn together by a longitudinal seam to form the tubular filter medium. This prefabricated tubular filter medium is pulled over the support tube in an assembly step. However, separate tubular filter media must be produced for each support tube diameter, which causes not only significant logistical but also assembly and storage costs. Furthermore, many filter media, particularly coated filter media, cannot be pulled over the support tube in their prefabricated state because they cannot slide on the support tube. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide an improved filter element with a support tube and a filter medium. 
   A further object of the invention is to provide a filter elment for filtering a fluid which can be produced in a reliable process and at low cost. 
   Another object is to provide an apparatus for producing the filter element of the invention. 
   These and other objects are achieved in accordance with the present invention by providing a filter element for filtering a fluid stream, comprising a cylindrical support body, which is provided with openings therethrough so as to be fluid permeable and is closed at one axial end, and a filter medium is arranged on the support body, wherein the filter medium is a strip of filter material that extends over substantially the entire length of the cylindrical support body and is wrapped around the entire circumference of the support body, and has a leading end and a trailing end which are welded together. 
   In accordance with a further aspect of the invention, the objects are achieved by providing an apparatus for producing a filter element, comprising a mandrel for receiving a fluid permeable support body and a welding unit for welding a filter medium around the support body, wherein the welding unit comprises an ultrasonic welding device. 
   The filter element according to the invention is intended to filter a fluid, e.g., air. It comprises a support body with an outer surface and two end faces as well as a weldable filter medium. The filter medium can be, for example, a nonwoven polyester material or polyester fleece. The support body is cylindrical and can have any cross section. The support body is furthermore permeable to the fluid to be filtered. The permeability of the support body can be produced, for example, by a plurality of openings in the support body or by use of a fluid-permeable material if the cylinder is not perforated. The openings can have any shape, e.g., circular or rectangular. 
   The filter medium encloses the support body along its outer surface and is welded along its entire length by at least one weld seam. Welding the filter medium causes the filter medium to become denser in the area of the weld seam, so that the weld is not bulkier than the rest of the material. This makes it possible to realize various assembly variants, which cannot be implemented with the bulkier seams created, for example, by sewing. 
   It is also possible to join the support body to the filter medium by the weld seam. In this case the support body is made of a weldable material that melts at its surface as the filter medium is welded together, so that the filter medium and the support body are joined at least at various points. 
   The filter medium preferably overlaps along the weld seam to produce a reliable weld. The filter medium, in a continuous process, can be directly unwound from a coil, wrapped around the support body, welded and cut. The sequence of these steps can also be varied. Processing the filter medium directly from the coil eliminates the steps involved in prefabricating a filter tube that is subsequently pulled over the support body. In addition, coated filter media, that cannot slide on the support tube, can be wrapped around the support tube and then welded. 
   In one embodiment of the invention, the support tube has a seal in the area of an end face. This seal is preferably made of polyurethane resin (PUR) foam, which bonds with both the filter medium and the support body. 
   In another embodiment, a gripping tab or strap is provided on the closed end face of the support body. This simplifies the replacement of the filter element and furthermore prevents the filter medium from being damaged during handling. 
   To facilitate correct positioning of the filter element, another embodiment of the invention provides that at least three positioning cams are disposed on the closed end face, i.e., on the end opposite the seal. These positioning cams, in conjunction with a support ring, ensure the correct positioning of the filter element. 
   In a further aspect of the invention, an apparatus for producing a filter element is proposed. This apparatus comprises a mandrel for holding the support body and a welding unit. The welding unit is preferably an ultrasonic welding system. Such welding units typically have a modular structure. This means that depending on the length of the filter element or filter medium to be welded a corresponding number of welding modules is provided. These modules are arranged along the weld seam and thereby permit longitudinal welding over any filter length. 
   In a further embodiment of the apparatus for producing a filter element, a feeding device for feeding the filter medium is provided, which has a monitoring unit to monitor the flow of material. This monitoring unit generates a signal when a new coil of filter medium must be put on. 
   In a further refinement, the apparatus is equipped with an inkjet printer to print labeling data onto the filter medium. This creates a complete production system capable of producing filter elements of the described type in very short process cycles. 
   These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either alone or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures in which: 
       FIG. 1  is is a sectional view of a filter element according to the invention; 
       FIG. 2  is an exterior side view of a filter element; 
       FIG. 2   a  is an end view of the filter element of  FIG. 2 ; 
       FIG. 3  is a sectional view of an air filter system incorporating a filter element according to the invention, and 
       FIG. 4  is a schematic view of an apparatus for producing a filter element according to the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows filter element  10  in cross section. The filter element  10  comprises a support body  11 , a filter medium  12  and a sealing segment  13 . The support body  11  has the shape of a circular cylinder and is made of synthetic resin material. To enable the fluid to be filtered to pass through the support body  11 , the support body  11  has a plurality of openings  15  in its radially outer surface  14 . In this embodiment the openings  15  are rectangular. However, embodiments with, e.g., circular or triangular openings  15  are also feasible. 
   The support body  11  has a first end face  16  and a second end face  17 . In the area of the end faces  16 ,  17 , the outer surface  14  has no openings  15 , so that no fluid can pass through the support body  11  at these locations. On the first end face  16 , which is open, the sealing segment  13  is disposed. This sealing segment  13  preferably is made of polyurethane resin foam, which encloses the support body  11  and the first end face  16 , so that the filter element  10  can be inserted into a holder (not shown) forming a seal. The second end face  17  is closed, so that the unfiltered fluid is prevented from moving from an unfiltered side to a filtered side, even without a mating seal. 
     FIG. 2  is a side elevational view of a finished filter element  10 . The sealing segment  13  is clearly visible, as well as the filter medium  12  with its longitudinal weld seam, indicated by line  19 . The circumferential weld seam  18  terminates the filter medium. The support body  11  is provided with a gripping tab or strap  38  on its left-hand end. This gripping strap  38  is also visible in the end view of  FIG. 2   a . Positioning cams  39 ,  40 ,  41 ,  42  for guiding the filter element inside the primary support tube depicted in  FIG. 3  are also mounted at the left-hand end. On the surface of the filter medium  12 , a labeling field is arranged in the area  43 . Using an inkjet printer or some other printing device, the filter element can be labeled by applying appropriate identifying information in this field. 
     FIG. 3  is a sectional view of an air filter. Parts corresponding to those in  FIG. 1  are identified by the same reference numerals. The air filter comprises a cylindrical housing  26  made of synthetic resin material, i.e., plastic, which includes a container  27  and a cover  28 . The container  27  is sealingly connected with the cover  28  through a sealing member  29 . Near the base of the container  27  are a tangential inlet  30  and an outlet port  31  arranged in the center. 
   A filter element  10  as described in  FIGS. 1 and 2  is inserted into the housing  26 . The filter element  10  is arranged coaxially to the outlet port  31  and is surrounded by a hollow cylindrical primary support tube  32  which like the support body  11  is made of synthetic resin material and is provided with openings  15 . In the interior of this primary support tube  32 , a recess  33  is formed against which the filter element  10  with the sealing segment  13  is sealingly supported in the area of the first end face  16 . 
   An annularly closed star-shaped folded primary filter element  34  is arranged around the primary support tube  32  and is sealingly inserted into the housing  26 . This primary filter element  34  is comprised of a filter paper  35  and two end disks  36  sealingly joined thereto. The end disks  36  are made of a resilient material such as polyurethane resin foam which has sealing properties. To enable the air that enters through the inlet  30  to flow toward the primary filter element  34  from more than one point, the container  27  has a flow-guiding wall  37  along which the inflowing air must first rise before it can flow through the primary filter element  34 . 
   If the primary filter element  34  is damaged or missing, the filter element  10  is sealingly interposed as a secondary safety filter between the air inlet  30  and the air outlet port  31 , so that the air must flow through filter element  10  and be at least coarsely filtered before it can exit in the direction indicated by the arrow through the outlet port  31 . 
     FIG. 4  is a schematic representation of an apparatus for producing a filter element according to the invention. The apparatus comprises a mandrel  40  for the support body  11 . A band or strip of filter material  12  is supplied from a coil  44  via a feeding device  42  to the support body  11 . A cutter  45  cuts the band of filter material to an appropriate length to wrap all the way around the support body  11  with sufficient overlap to facilitate welding the overlapping ends to form a tubular structure. Welding is effected by a welding device, such as an ultrasonic welder  41 . A printer, such as ink jet printer  46 , may be provided to apply an identifying legend to the completed filter. The feeding device  42  is provided with a monitoring device  43 , which detects when a new coil of filter material is needed. 
   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 within the scope of the appended claims and equivalents thereof.