Abstract:
A filter device, in particular a return line suction filter, has at least one filter housing ( 3 ) receiving a filter element ( 17 ) defining a longitudinal axis. The filter element has an end cap with an enclosure at one filter element end enclosing an end edge of the filter material ( 39 ) and fixed to an element receptacle ( 5 ) connected to the filter housing ( 3 ) for fixing the location of the filter element ( 17 ) in its functional position. The element receptacle ( 5 ) and the associated end cap ( 21 ) of the filter element ( 17 ) have design irregularities ( 63, 65 ) adapted to each other at their parts ( 23, 47 ) engaging each other in the functional position of the filter element ( 17 ). The irregularities enable the engagement in a positional alignment to each other.

Description:
FIELD OF THE INVENTION 
     The invention relates to a filter device, in particular a return line suction filter, having at least one filter housing. At least one filter element defines a longitudinal axis, is in the form of a filter cartridge and is accommodated in the filter housing. The cartridge on at least one end has an end cap forming an enclosure for the pertinent end edge of the filter material and fixable on an element receptacle connected to the filter housing for fixing the filter element in its operating position. Moreover, the invention relates to a filter element for such a filter device. 
     BACKGROUND OF THE INVENTION 
     Filter devices of this type are readily available commercially in different designs. To a large extent, these filter devices are used for filtration of working fluids, such as hydraulic fluids, fuels, lubricants, and the like. Such device in the form of a suction filter is described, for example, in brochure D7.108.2/06.07 of Hydac Filtertechnik GmbH with the product description of RKM return line suction filter, and is commercially available in different pressure stages (up to 10 bar) and for different return volumetric flows (up to 800 l/min). 
     Return line suction filters are used in hydraulic systems in those cases in which there are both an open hydraulic circuit (for example, working hydraulics) and a closed hydrostatic system (for example, traction drive) in the system. In this connection, return line suction filters can perform both the function of the return line filter of the open circuit and the function of the suction filter of the closed circuit (drive), provided that the return flow of the open hydraulic system is not less than the volumetric flow of the feed pump for the hydrostatic system. In fluid systems, specifically hydraulic systems, in which filter devices are used, the operating reliability of the system depends largely on the reliable operation of the filter device located in the system. In other words, failure of the filter device, beyond the failure of the pertinent system, can lead to serious damage to the system and thus can cause significant financial losses. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to an improved filter device characterized by special operating reliability. 
     This object is basically achieved according to the invention by a filter device having design irregularities formed both on the element receptacle of the pertinent filter housing and on parts of the end cap of the filter element assigned to the element receptacle. The design irregularities on the element receptacle and on the end cap are matched to one another such that if they are aligned to one another, they enable mutual engagement. In this way a pertinent filter element can be moved into the operating position only when complementary design features on the element receptacle and end cap are matched to one another. They then allow the engagement with the corresponding mutual alignment. The filter device can be operated only with a filter element intended for a respective special use and satisfying the pertinent applicable specifications, thereby ensuring operating reliability. 
     This arrangement not only precludes that a filter element will be used which has an unsuitable filter fineness or which is not suitable for the respective application, that is to say, is not assigned to a corresponding pressure stage, but that the risk will also be avoided that possibly a “low-end element” available on the market will be used which does not meet the applicable safety standards. 
     To enable mutual engagement, a positional relation is necessary in which the design irregularities have a positional relation aligned to one another. An additional advantage is that the engagement between element receptacle and end cap forms a locking element. Even for a tangential flow occurring in a filter housing, the filter element is then supported against a possible torque around the longitudinal axis. 
     In preferred exemplary embodiments, the filter housing has the shape of a cup. From the cup top the filter element can be inserted and can be fixed on the element receptacle, forming a housing bottom part. In filter housings with this type of design, a housing cover typically forms the upper termination of the housing and a support for the upper end cap of the filter element. Accordingly, the housing cover can be screwed to the top end of the filter housing or bolted to it, only if the filter element is properly engaged with the element receptacle on the bottom part of the housing. An attempt to inadvertently install an “incorrect” filter element is thus immediately conspicuously indicated to the operator. 
     Preferably, the bottom part forming the element receptacle has a pipe socket projecting coaxially from its top and extending into the inner filter cavity of the filter element that is in the operating position to form a fluid connection. The pipe socket on the outer peripheral side has the design irregularities belonging to the element receptacle. 
     To fix the filter element on an element receptacle designed in this way, the end cap can have a coaxial connector extending into the inner filter cavity surrounded by a fluid-permeable support pipe and engaged by the pipe socket of the element receptacle in the operating position of the filter element. The design irregularities belonging to the end cap are located on the inner wall of the connector of the end cap. 
     In especially advantageous exemplary embodiments, the design irregularities on the pipe socket of the element receptacle have at least one radially projecting rib extending in the longitudinal direction and having a depression assigned which extends in the longitudinal direction in the inner wall of the connector of the end cap. 
     Especially effective protection against confusion exists when there are several longitudinal ribs distributed around the periphery of the pipe socket of the element receptacle and several depressions assigned to the ribs in the connector of the end cap. For this reason, depending on the distribution pattern of the arrangement of the ribs and depressions, only specially adapted filter elements can be used. 
     In advantageous exemplary embodiments, the end cap is composed of an inner sleeve body concentric to the longitudinal axis, forming the inner wall of the connector with the depressions located in it, and integral with a peripheral annular member forming the enclosure for the end edge of the filter material. An outer sleeve surrounds the sleeve body and has an outside forming a contact surface for the support pipe of the filter element. This two-part construction of the end cap is advantageous with respect to production with press-molded plastic parts. 
     If, in this connection, the outer sleeve forms a hollow cylinder whose axial length is greater than that of the inner sleeve body, so that the inner end edge of the outer sleeve projects over the end edge of the sleeve body and so that the end edge of the outer sleeve forms an end part drawn radially to the inside, this end part together with the adjacent end edge of the sleeve body can border an annular groove-like space used as a seat for an annular sealing element. This execution of the end cap thus enables perfect sealing of the inner filter cavity on the bottom part of the housing, and thus, sealing of the inner filter cavity forming the clean side in the filter process relative to the dirty side located on the outside of the filter element. 
     Preferably, the bottom part forming the element receptacle on the bottom facing away from the pipe socket forms a valve housing part integrally molded on and having an outlet connectable to the tank side of a hydraulic system. In this way, a bypass valve and valve arrangements as are used, for example, in return line suction filters can be easily integrated mechanically into the bottom part. 
     In this respect, in the bottom part there can be a first fluid passage leading to a bypass valve located in the valve housing from the dirty side of the filter element. In the operating position, the fluid passage bypasses the pipe socket. A second fluid passage can lead from the pipe socket to at least one other valve located in the valve housing, such as an anti-cavitation valve and/or back pressure valve, which valve or valves is or are connected to the outlet. 
     The subject matter of the invention is also a filter element for use in a filter device according to the invention. 
     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 a filter device according to an exemplary embodiment of the invention, with an attempt being made to bring a filter element that is not suitable for use into the operating position in the filter housing; 
         FIG. 2  is a side elevational view in section, drawn on a slightly smaller scale than  FIG. 1 , of the filter device of  FIG. 1  with a filter element in the operating position; 
         FIG. 3  is a partial side elevational view in section of the region designated as III in  FIG. 2 , drawn on a larger scale than  FIG. 2 ; 
         FIG. 4  is a perspective view of only the housing bottom part of the filter device of  FIG. 1  forming an element receptacle; 
         FIG. 5  is a perspective view of a filter element for use in the filter device of  FIG. 1 , viewed looking at its end cap which interacts with the element receptacle; 
         FIG. 6  a partial perspective view of only the region designated as VI in  FIG. 5 , drawn on a larger scale than  FIG. 5 ; and 
         FIGS. 7   a  to  7   c  are side elevational views in sections of only the parts of the end cap of the filter element which interact with the element receptacle of  FIGS. 5 and 6 , with  FIG. 7   c  showing the end cap in the assembled state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A filter housing  1  has a hollow cylindrical main part  3  which on its bottom side end is sealed by a housing bottom part  5 . The upper end of the main part  3  is adjoined by a housing top part  7 . In the manner conventional for these filter housings, top part  7  has fluid guides, of which the drawings show a fluid inlet  9  via which fluid to be cleaned can be supplied to the space in the filter housing  1  forming the dirty side in the filter process. Another fluid guide is provided in the top part  7 , is connected to the space forming the clean side in the filter process, and leads to an outlet for the emergence of cleaned fluid from the housing top part  7 . This outlet is not shown in the drawings since it is turned by 90 degrees relative to the plane of the drawings. On the top end of the housing top part  7 , an internal thread  11  is provided to threadedly engage the external thread  13  of a housing cover  15 .  FIG. 1  shows that the housing cover  15  is in a position raised off the top part  7  and in which the internal thread  11  and external thread  13  do not engage. 
     The filter housing  1  can accommodate a filter element  17  in the form of a filter cartridge. With the housing cover  15  removed, filter element  17  can be inserted into the filter housing  1  from the open end of the housing top part  7  along the longitudinal axis  19 . For fixing of the filter element  17  in its operating position, the bottom part  5  forms an element receptacle which interacts with the bottom side end cap  21  of the filter element  17 . As the main part of the element receptacle, the bottom part  5  has a pipe socket  23  projecting axially away from the bottom part  5  in the direction to the housing top part  7  and being concentric to the axis  19 .  FIG. 1  shows a state in which the filter element  17  with its end cap cannot be slipped far enough onto the pipe socket  23 , but is blocked in the position shown in  FIG. 1  as a result of the shape of the pipe socket  23 . In this position of the filter element  17 , the housing top part  7  cannot be closed by the housing cover  5  because the housing cover  15  adjoining the cover-side end cap  25  of the filter element  17  is held by the housing top part  7  at a distance at which the internal thread  11  and external thread  13  cannot engage. 
       FIG. 4  shows details of the shaping of the bottom part  5 . It is connected by its circular ring-shaped peripheral edge in the form of an annular member  27  to the bottom end of the housing main part  3 . The bottom end  29  of the main part  3  formed by a steel pipe encompasses the annular member  27 . On the top edge of the annular member  27 , a flanged site  31  is formed. In the outer periphery of the annular member  27 , there is an annular groove  33  for a gasket  35  for sealing between the bottom part  5  and housing main part  3 . 
       FIGS. 2 to 7   a - c  illustrate details of the configuration both of the bottom part  5  and also of the assigned end cap  21  of the filter element  17  suitable for use in the filter device. As is apparent from  FIGS. 5 to 7   a - c , the end cap  21  forms an annulus  37  as enclosure for one end edge of the filter material  39  of the filter element  17 . Filter material  39  surrounds a support pipe  41 . The support pipe  41  borders the internal filter cavity forming the clean side in the filter process in the filter element  17 . As  FIGS. 7   a  to  7   c  show, the end cap  21  has a two-part construction, including an inner sleeve body  45 , which is concentric to the axis  19  and which on its inside forms the inner wall of a concentric connector  47 . Connector  47  projects axially away from the bottom  49  of the annulus  37  and into the inner filter cavity  43 . The end cap  21  is completed by an outer sleeve  51  shown separately in  FIG. 7   a , which is slipped over the outside of the connector  47 . As shown in  FIGS. 2 and 3 , outer sleeve  51  is in contact on its outside with the support pipe  41 . As  FIG. 7   c  shows, the axial length of the outer sleeve  51  is larger than that of the connector  47  so that the inner end edge  53  of the outer sleeve  51  in the assembled state of  FIG. 7   c  projects over the end edge  55  of the connector  47 . Therefore, the end edge  53 , with an end part  57 , drawn radially to the inside, forms a seat  59  ( FIG. 7   c ) for a gasket  61 , see  FIGS. 3 and 2 . 
     As  FIG. 4  shows best, on the outer periphery of the pipe socket  23 , which forms the main part of the element receptacle of the bottom part  5 , radially projecting longitudinal ribs  63  are molded. In this example, four ribs at uniform angular distances are provided with only two being shown in  FIG. 4 . To enable the engagement between the connector  47  of the end cap  21  and the pipe socket  23 , the inner wall of the connector  47 , as design irregularities complementary to the longitudinal ribs  63 , has depressions  65  in the inner wall of the connector  47 . These depressions  65  are in complementary arrangement to the longitudinal ribs  63  of the pipe socket  23  and make it possible for the filter element  17  with its end cap  21  to be able to be slipped onto the pipe socket  23  until the bottom  49  of the end cap  21  makes contact with spacers  67  ( FIG. 4 ) of the element receptacle and for the filter element  17  to be in its operating position. Here, as  FIG. 3  shows best, the inner filter cavity  43  (clean side) is sealed by a gasket  61  relative to the element receptacle on the pipe socket  23 . 
     The depressions  63 , see  FIGS. 5 ,  6  as well as  7   b  and  7   c , have a greater width in the peripheral direction than the longitudinal ribs  63  on the pipe socket  23  of the element receptacle, so that the longitudinal ribs  63  and the depressions  65  can easily be moved toward one another when the filter element  17  is moved into the operating position. Also, the filter element  17  can be removed without obstacles when the element is being changed. Thus, the radial travel path produced in this respect can be used to loosen a possibly fixed seal in which the seal is entrained at least some distance of this travel path. This moving together is moreover facilitated by the depressions  65  on the open end, i.e., on the bottom  49  of the end cap  21 , each having an arc-shaped widening  69 . 
     Instead of the complementary design irregularities formed by longitudinal ribs  63  and depressions  65 , differently shaped configurations in any pattern arrangement on the element receptacle (pipe socket  23 ) and end cap  21  can be provided. The assignment of radially projecting and radially recessed elements could also be chosen to be the reverse of this example so that, for example, there could be longitudinal ribs on the end cap  21  and depressions on the pipe socket  23  of the element receptacle. 
       FIGS. 1 to 4  show that the bottom part  5  forming the element receptacle on its bottom facing away from the pipe socket  23  has a housing part  71  molded on in one piece. Together with an outlet part  73 , part  71  forming the housing termination forms a valve housing. 
     The outlet part  73  in turn forms an outlet  75  which can be connected to the tank side of an assigned hydraulic system (not shown). A fluid passage  77  located in the bottom part  5  connects the space  79  of the filter element  17  which space  79  in the operating position forms the dirty side in the filter process, to a bypass valve  81  in the valve housing  71 ,  73  to enable a pressure decrease from the fluid passage  77  to the tank-side outlet  75  with pressure actuation. When using the exemplary embodiment of the filter device described here as a return line suction filter, within the valve housing  71 ,  73  and in the fluid connection to the outlet  75 , another valve arrangement  83  in the form of a combined anti-cavitation valve and back pressure valve is inserted between a second fluid passage  85  in the bottom part  5 . Second fluid passage  85  is connected to the inner filter cavity  43  forming the clean side, and the tank-side outlet  75 . 
     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.