Abstract:
A filter device includes a pot-shaped filter housing ( 1 ) that defines a longitudinal axis along which a filter element ( 13 ) can be inserted into and removed form the filter housing ( 1 ). A retaining device detachably retains the filter element ( 13 ) in the filter housing ( 1 ) and has first and second retaining elements on the inner side of the filter housing ( 1 ) and on the filter element ( 13 ) and interacting with one another. At least one set of the retaining elements has a shape coaxial to the longitudinal axis of the filter housing ( 1 ) and forms at least a part of a thread. When the filter element ( 13 ) is rotated about its longitudinal axis, it is locked in a form-fit.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a filter device with a cup-shaped filter housing defining a longitudinal axis, along which a filter element can be inserted into the filter housing and can be removed from it. A retaining means is used for detachable fixing of the filter element in the filter housing, has first and second retaining elements which interact with one another and are provided on the inside of the filter housing and on the filter element. 
     BACKGROUND OF THE INVENTION 
     Filter devices with filter housings and replaceable filter elements are known. A not insignificant portion of production costs arise in these filter devices for the construction of the retaining means for detachable fixing of the filter element. In the filter device of this type disclosed in EP 0 819 214 B1, the retaining means has a spring arrangement of two compression springs which work against one another. By the resulting spring force of the two springs, an end piece, located on the filter element and acting as a sealing and retaining element is slipped onto the housing-side retaining element which is formed by the connecting piece. The connecting piece extends into the support tube of the filter element on the head of the filter housing. 
     The comparatively complex construction of the retaining means leads to high production costs. 
     SUMMARY OF THE INVENTION 
     Objects of the present invention are to provide a filter device with a filter housing and a replaceable filter element characterized by simple construction of the retaining means for the filter element and by the corresponding low production costs. 
     In a filter device of this type, these objects are basically achieved in the present invention by at least one of the retaining elements having a shape which forms at least part of a thread and which is concentric to the longitudinal axis of the filter housing. The filter element, after turning around its longitudinal axis, is fixed by an interlocking connection. 
     A retaining means acts in the manner of a screwed connection. The filter element is fixed in the retaining means and is interlocked by turning. This arrangement can be implemented with simple structure so that in the desired manner economical production is possible. Since, by turning the filter element, an interlocked connection between the filter element and the filter housing is produced, the additional advantages of ease of operation and high operating reliability are achieved. 
     Preferably, first retaining elements form a guide for the second retaining elements when the filter element is rotated. The guide has a thread pitch which is referenced to the longitudinal axis on at least part of its length. 
     The second retaining elements can be cams which project transversely to the longitudinal axis of the filter housing and are guided in cam paths. The cam paths form the first retaining elements and have a thread pitch on at least part of their path length. This arrangement permits prompt fixing in a simple manner. The connection can be made self-locking by the thread pitch. While maintaining the advantages of an otherwise conventional screw connection in this area, the indicated connection can be produced and broken again within a short time with little expenditure of force. In addition, the alignment of the connection is largely unambiguous, i.e., the installation situation of the interchangeable filter element relative to the filter housing can be easily reproduced. 
     Preferably, cams are on the inside of the filter housing and cam paths are on the filter element. 
     The filter element can be a filter cartridge having a fluid-permeable support tube surrounded by filter material and an end cap bordering the edge of the filter material. The end cap located on the filter element bottom-side end assigned to the bottom of the cup-shaped filter housing can have the cam paths on its periphery. 
     In these embodiments, the production of the filter device is especially simple and economical if the cams are made on the inside of a ring body mounted in the cup-shaped filter housing in its bottom area. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure: 
         FIG. 1  is a side elevational view in section of one embodiment of the filter device according to the present invention, with a filter cartridge located in the filter housing, which section is shown schematically simplified; 
         FIG. 2  is a perspective view in section of only the cup-shaped part of the filter housing of the embodiment of  FIG. 1 , without the housing cover, only one bottom-side end cap of the filter cartridge, which is not otherwise shown, being fixed by interlocking in the filter housing; 
         FIG. 3  is an enlarged perspective view of the end cap of the filter cartridge of  FIGS. 1 and 2 ; and 
         FIG. 4  is a top plan view of a ring body attached in the bottom-side end area of the filter housing according to an embodiment of the present invention, with cams used as retaining elements and projecting inwardly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1 and 2 , the illustrated and described preferred embodiment of the filter device has a filter housing  1  in the form of a cup which is rotationally-symmetrical in its outline relative to the longitudinal axis  3 . The housing has a closed bottom  5 , and a housing cover  7  which seals the opposing housing top end and as shown only in  FIG. 1 . The housing cover  7  has, on a sleeve-shaped projection  9 , an outside thread which can be screwed to the inside thread  11  on the top end of the cup-shaped part of the filter housing  1 . Sealing elements for sealing between the housing cover  7  and the cup-shaped part of the filter housing  1  are not shown in the schematic from  FIG. 1 . 
     A filter cartridge  13  is concentric to the longitudinal axis  3  and can be held in the filter housing  1 . Conventionally, the filter cartridge has an inner, fluid-permeable support tube  15  surrounded by filter material  17 . On the bottom-side end facing the bottom  5  of the filter housing  1 , the filter cartridge  13  is closed by an end cap  19 . The end cap forms a border for the facing lower end edge area of the filter material  17 . For this purpose, the end cap  19  has a central, circular cylindrical journal  21  extending into the interior of the support tube  15  of the filter cartridge  13 . On its free end edge, journal  21  has a slight bevel  22  ( FIG. 3 ). Between the outside of the journal  21  and the radially outer peripheral jacket  23  of the end cap, an annular groove-like recess  25  receives the lower edge of the filter material  17 . 
     The filter cartridge  13  on the opposing top end has a top head cap  27  which borders the filter material  17  and the edge of the support tube  15  and which forms a connecting sleeve  29 . When the housing cover  7  is screwed onto the cup-shaped part of the filter housing  1 , a connecting piece  31 , which forms an outlet for the filtered fluid, engages the connecting sleeve  29  to produce the fluid connection to the interior of the support tube  15 . An O ring  33  on the connecting sleeve  29  seals the interior of the filter cartridge (the clean side of the filter device) against the space of the filter housing  1  surrounding the filter cartridge  13  (the fouled side of the filter device). The inlet for the fluid to be filtered into the filter housing  1  is not shown in the figures. 
     The configuration of the retaining means for detachably fixing or retaining the filter cartridge  13  in the filter housing  1  is especially shown in  FIGS. 2 to 4 . The retaining means has first retaining elements which are associated with the filter cartridge  13 , and second retaining element which are associated with the filter housing  1 . The retaining elements which are associated with the filter cartridge  13  are located on the end cap  19 . The retaining elements which are associated with the housing  1  are located on a ring body  35  mounted in the filter housing  1  in the vicinity of its bottom  5  and shown separately in  FIG. 4 . As is apparent from  FIG. 4 , the ring body  35  on its inner jacket or peripheral surface has four journal-like cams  37 . Cams  37  project radially to the inside and are arranged offset to one another by 90°. On the end edge facing the bottom  5  of the filter housing  1 , the ring body  35  on the peripheral side has a slight rounding  39  with which the ring body  35  is matched to the slight arch of the inside wall of the filter housing  1  in the bottom area. As already indicated, the ring body  35  in the filter housing  1  is attached by pressing or welding in. 
     The radially projecting cams  37  of the ring body  35  are designed to engage the cam paths  41  (see  FIG. 3 ) formed as the retaining elements of the filter cartridge  13  on its end cap on the outer peripheral side. These cam paths  41  are formed by recesses which are machined into the periphery of the jacket  23 . As the guide for each cam  37 , one cam path  41  is provided for each cam  37  so that there are four cam paths  41 . Each of these cam paths  41  forms a groove which is open on the lower end edge of the jacket  23  of the end cap  19 . These open areas  43  of the grooves are offset by 90° each to one another, so that when the filter cartridge  13  is inserted into the filter housing  1 , the cams  37  mounted on the housing side can move into the open areas  43 . These open areas  43  adjoin areas  45  with a thread-like pitch for each cam path  43 . If the filter cartridge  13  is turned or rotated around the longitudinal axis  3  after the cams  37  move into the open areas  43  of the cam paths  41 , the cams  37  run over pass through the pitch areas  45 , i.e., the cam ramps which are formed thereby. In this manner, a holding force acting in the axial direction is produced on the end cap  19  of the filter cartridge  13 , by interlocking engagement between the cams  37  and the cam paths  41 . The locking of the filter cartridge  13  created in this way by turning around the longitudinal axis  3  in one direction of rotation can be easily released by turning the filter cartridge  13  in the opposite direction of rotation in order to remove the filter element again from the filter housing  1 . As is best illustrated in  FIG. 3 , the cam paths  41 , following their starting area  45 , have pitch transitions extending into a groove which extends along the entire periphery of the jacket  23  of the end cap  19 . The end cap  19  in the illustrated and described embodiment can be advantageously press-formed from a plastic material. The edge of the filter material  17  held in the recess  25  within the jacket  23  of the end cap  19  can be cemented to the end cap  19 . The journal  21  of the end cap projecting into the interior of the support tube  15  of the filter cartridge  13  can likewise be cemented to the support tube  15 . 
     Instead of using four cams  37  and four associated cam paths  41 , a different number of cams and cam paths can be used. Preferably, no fewer than three cams and cam paths are used. Instead of the configuration shown in which for the cam paths  41  the ramp-like area  45  which has the pitch adjoins an area without a pitch, there can be cam paths  41  with a continuous pitch. Instead of the configuration of the retaining elements shown in the illustrated embodiment as individual cams  37 , there could be a threaded connection between the end cap  19  and the filter housing  1  by means of continuous thread elements in the manner of a screw connection with an inside thread and/or outside thread elements which are made peripherally continuous. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.