Abstract:
A filter device, especially a line filter forming part of hydraulic installations, includes a filter housing ( 1 ) that can be removed from a filter head and is used to receive a filter element ( 5 ) that separates a non-filtered side ( 13 ) from a filtered side ( 11 ) in a position in the filter housing for the operation of the filter. The filter device is provided with a display device ( 19, 21 ) signaling the absence or presence of the filter element ( 5 ) in the filter housing ( 1 ) in the operating position.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a filter device, especially a line filter forming a component of hydraulic systems, with a filter housing. The housing can be removed from a filter head and is used to hold a filter element separating the unfiltered side from the filtered side when in the operating position for filter operation in the filter housing. 
     BACKGROUND OF THE INVENTION 
     Filter devices of this type are known, cf.  Der Hydrauliktrainer, Band  1, 1991 [ Hydraulics Training Manual, Volume  1, 1991], published by Mannesmann Rexroth GmbH, pp. 279 and 280. These filter devices can be designed for operation with spin-on cartridges. The filter cartridge contains a filter element permanently installed in the housing to be screwed onto the filter head. After expiration of the useful operating time of the filter element, it is replaced such that the entire cartridge with the used filter element contained therein being disposed of. On the other hand, filter devices such as these can also be operated in a design in which a filter housing interchangeably holds a filter element therein and is removably attached to the filter head so that when the filter element is changed, only the filter element is removed from the filter housing and disposed of. The filter housing provided with a new filter element continues to be used. 
     It is apparent that the latter design is comparatively more advantageous with respect to conservation of resources and the resulting operating costs due to the continued use of the filter housing. On the other hand, the design in which spin-on cartridges are used is characterized by especially high operating reliability, because the fixed installation of the filter element in the housing of the spin-on cartridge avoids the danger that in the course of replacement of a used filter element an empty filter housing without the fresh filter element inserted into it will be unintentionally attached to the filter head. On the other hand, in filter devices with a reusable filter housing serious damage or even destruction of the pertinent hydraulic system can occur if a filter housing without the filter element located therein is inadvertently attached to the filter head, for example through the carelessness of the operator only a used filter element being selected and insertion of a fresh element being omitted. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a filter device avoiding the danger that the hydraulic system assigned to the device will be operated without a filter element in the filter housing. 
     According to the present invention, this object is basically achieved by a filter device having a display device indicating the presence or absence of the filter element located in the filter housing in the operating position. The danger of faulty operation of the filter device without an inserted filter element is then avoided. In this respect, a uniform measure of operating reliability is achieved, as is the case in the design in which spin-on cartridges are used, for which the filter element together with the cartridge housing containing it is replaced. In the present invention, the disadvantages of wasting material and the increased operating costs when using spin-on cartridges are avoided. 
     In preferred embodiments, the display device in the wall of the filter housing has an opening and a closing means. Depending on the absence or presence of a filter element in the operating position, that means can be moved into the open state clearing the opening or into a blocked state closing the opening. Closure or clearance of the opening then indicates the presence or absence of a filter element. Since as a result of the cleared opening of the filter housing fluid emerges from the filter housing when the filter device is operated without the filter element inserted, the fault state is immediately indicated and the pertinent hydraulic systems can be prevented from being operated in the fault state. 
     In one preferred embodiment the closing means has at least one closing body with at least one sealing element. In the operating position of the filter element, the sealing element forms a seal between the closing body and the opening. The closing body is formed by a bearing part of the filter element held in a seat of the filter housing in the operating position. Because in this connection the bearing part of the filter element interacts with the seat of the filter housing and acts as a closing body of the closing means, and thus, as a component of the display means, the design is especially simple, compact and economical. 
     The bearing part of the filter element can be advantageously formed by an extension on the end of its support tube bearing the filter material. In the operating position, the support tube is held in the seat of the filter housing, which seat is formed by a pipe socket-like depression in the bottom of the filter housing concentrically surrounding the opening. On the outside of the bearing part, the sealing element of the closing means interacts with the inside wall of the seat of the filter housing surrounding the opening to form a seal. 
     Since in filter operation axial forces acting in the direction of the longitudinal axis of the support tube can occur on the filter element, it is advantageous to safeguard the bearing part formed by the axial extension of the support tube against lifting caused by axial forces out of the seat of the filter housing. For this purpose the bearing part of the support tube can have a hole with an inside thread flush with the opening of the filter housing in the operating position. The bearing part and the filter element can then be axially locked in the filter housing by a retaining screw extending through the opening of the filter housing. 
     This hole of the bearing part can be made continuous into the interior of the support tube, that is, as far as the filtered side. The closing means has another sealing element sealing the edge of the opening on the outside of the filter housing relative to the head of the retaining screw. In this way even when the filter element is in the operating position, if necessary, the filtered side can be emptied by loosening the retaining screw and taking it out of the hole. 
     In one development of such an embodiment, the bearing part can have at least one connecting channel enabling a connection between the continuous hole and the unfiltered side in the filter housing. The channel can be closed by the unthreaded shaft section and can be cleared by unscrewing the retaining screw. This arrangement also enables emptying of both the filtered side and the unfiltered side as needed when the filter element is in the operating position. 
     If in this embodiment a partial segment of the hole passing through the bearing part has a widening forming a fluid passage between the end region facing the opening of the filter housing and the region of the hole closable by the unthreaded shaft section of the retaining screw, for purposes of emptying of both the filtered side and the unfiltered side with the filter element in the operating position the retaining screw need simply be loosened, but not removed entirely from the hole. 
     The retaining screw can have an inner longitudinal channel open on its end facing the interior of the filter housing and opened by a transverse outlet on its opposite end in the shaft region adjoining the sealing element sealing the head of the retaining screw. In this case as well, without having to remove the retaining screw completely from the hole, the filtered side and the unfiltered side can be emptied when the filter element is in the operating position. 
     To ensure that the unscrewed retaining screw remains captively on the filter housing, the head of the retaining screw on the end facing away from the shaft can have a driving part with radially extending driver blades. The driver blades are guided in a rotary cage supported on the filter housing to be rotatable and axially nondisplaceable around the axis of the screw in a guide. The guide has stops for transmission of the torque to the screw. At least one stop limits the axial motion of the screw when it is loosened. 
     The subject matter of the present invention is also a filter element for the device. 
     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 preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure: 
         FIG. 1  is a cutaway perspective view, showing only the lower partial region of a filter device according to a first exemplary embodiment of the present invention, cut with cutting planes in the longitudinal direction of the filter housing and at a right angle to one another; 
         FIG. 2  is a cutaway perspective view showing only the lower partial region of a filter device according to a second exemplary embodiment of the present invention; 
         FIG. 3  is a cutaway perspective view showing only the lower partial region of a filter device according to a third exemplary embodiment of the present invention; and 
         FIG. 4  is a cutaway perspective view showing only the lower partial region of a filter device according to a fourth exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A filter housing  1 , of which in the figures only the region adjacent to the housing bottom  3  is shown, can be connected in the conventional manner for these filter devices with its end (not shown) open to the top to a filter head, for example by screwing it in. The filter head has connections for feed and discharge of the fluid to be filtered and optional accessories, for example a connection for clogging indicators and the like. In the interior of the filter housing  1  shaped to be circularly cylindrical over a large part of its length, a filter element  5  can be held as shown in its operating position. The filter element  5  has a fluid-permeable support tube  7  surrounded by the filter material  9 . The upper end (not shown) of the support tube  7  is tightly connected on the filter head to the outlet for the filtered fluid. The fluid to be filtered travels from the feed of the filter head to the outside of the filter material  9 . The interior of the support tube  7  in filter operation forms the filtered side  11 , while the space surrounding the filter material  9  within the filter housing  1  forms the unfiltered side  13 . 
     As the seat in which the filter element  5  in its operating position is held within the filter housing  1 , the bottom  3  of the filter housing  1  has a centrally located, pipe socket-shaped depression  15  with an inside wall  17  concentric to the opening  19 . Opening  19  is centrally positioned on the base of the depression  15  and is flush with the longitudinal axis of the support tube  7 . 
     A metallic extension of the support tube  7  projecting on the lower end of the support tube  7  concentrically to its longitudinal axis forms a circularly cylindrical bearing part  21 . The bearing part  21  in the operating position of the filter element  5  is held in a depression  15  forming the seat. A sealing element  23  sits on the outside of the bearing part  21  in an annular groove sealing the bearing part  21  relative to the inside wall  17  of the depression  15 , and thus; relative to the opening  19  located on the base of the depression  15 . The bearing part  21  forms a closing means or closure blocking discharge of fluid from the unfiltered side  13  out of the opening  19  when the filter element  5  is in the operating position. Since the bearing part  21  seals the lower end of the support tube  7  fluid-tight, fluid cannot emerge from the filtered side via the opening  19 . On the other hand, the opening  19  is opened when a filter element  5  is not present. With improper start-up with the filter element  5  missing, this impermissible operating state is indicated by escape of fluid through the opening  19 . 
     The embodiment of  FIG. 2  differs from the embodiment of  FIG. 1  simply in that the bearing part  21  of the filter element  5  is not made entirely as a hollow body having only a thin-walled bottom. The bearing part  21  of  FIG. 2  has an internal solid core in which a hole  33  with an inside thread  25  is formed into which a retaining screw  27  can be screwed. Retaining screw  27  has a head  29  adjoining the outside of the housing. The retaining screw  27  safeguards the bearing part  21  and thus the filter element  5  in the operating position against axial forces which could occur in filtering operations on the filter element  5 . An annular shoulder  31  projecting radially on the bearing part  21  in contact with the assigned stop surface formed by a radial widening on the inside wall  17  of the depression  15  is safeguarded or secured. 
     In contrast to the example of  FIG. 2 , the  FIG. 3  bearing part  21  of the filter element  5  has a through hole  33  via which a fluid connection between the filtered side  11  within the support tube  7  and the opening  19  on the base of the depression  15  can be produced when the filter element  5  is in the operating position. Moreover, the connecting channel  35  extending crosswise in the bearing part  21  connects the hole  33  to the unfiltered side  13  within the filter housing  1 . The hole  33  then enables the unfiltered side  13  to be emptied when the filter element  5  is in the operating position. As seen in  FIG. 3 , the retaining screw  27  provided in this embodiment has an end-side, unthreaded shaft section  37  closing the inner end of the connecting channel  35  when the retaining screw  27  is screwed in tight as shown in  FIG. 3 . As likewise seen in  FIG. 3 , the hole  33  on the longitudinal segment proceeding from the free end of the bearing part  21  has a widening  39  in the form of a groove interrupting the inner thread  25  only on a small peripheral segment and enabling a fluid connection via the hole  33  to the housing opening  19  even when the retaining screw  27  has not been completely unscrewed from the hole  33 , that is, when there is still engagement with the end region of the inner thread  25 . With the filter element  5  in the operating position and with the retaining screw  27  partially screwed out, the opening  19  is no longer sealed by another sealing element  41  which, when the retaining screw  27  has been tightened, seals its screw head  29  relative to the outside edge of the opening  19 . The filtered side  11  and the unfiltered side  13  can then be emptied as soon as the retaining screw  27  has been unscrewed so far that its unthreaded shaft section  37  moves into the region of the widening  39  of the hole. In any case, the retaining screw  27  can be completely unscrewed, i.e., removed. As in the examples of  FIGS. 1 and 2 , when no filter element  5  is in the filter housing  1 , the housing opening  19  is not closed so that in turn possible faulty operation is indicated by escape of fluid from the filter housing  1 . 
     The example of  FIG. 4  differs from the example of  FIG. 3  in two respects.  FIG. 4  shows the filter element  5  in its operating position, but with the retaining screw  27  partially unscrewed. The first major difference relative to the example of  FIG. 3  involves the retaining screw  27  having an inner longitudinal channel  43  extending from the free shaft end  45  up to a transverse outlet  47  located at a location of the shaft of the screw  27  adjacent to the sealing element  41 . Sealing element  41  forms a seal between the screw head  29  and the outside of the housing on or about the opening  19 , with the screw  27  tightened. In the operating state shown in  FIG. 4  with the screw  27  partially released, although the filter element  5  is in the operating position, both the filtered side  11  and the unfiltered side  13  can be emptied via the connecting channel  35 , the inner channel  43  of the screw and its transverse outlet  47 . As in the other embodiments, when the filter element  5  is missing in the filter housing  1 , the housing opening  19  cannot be closed so that a faulty operating state is indicated in turn by escape of the fluid. 
     The second fundamental difference of the example of  FIG. 4  relative to the example of  FIG. 3  is that the retaining screw  27  is captively secured. For this purpose, on the lower end of the housing depression  15  a rotary cage  51  is secured by a snap connection in an annular groove  49 , is in the form of a cap-like molded piece, preferably of plastic, and on the end facing away from the snap connection has a bottom  53  with an outlet opening  55 . The head  29  of the retaining screw  27  on the end side has a driving part  57  with radially projecting driver blades  59  engaging the inner guides  61  of the cage  51 . Driver blades  59  are guided to be axially displaceable in guides  61 , but are nonrotatable. The bottom  53  of the cage forms a stop limiting the axial motion of the retaining screw  27  when being screwed out. The screw  27  can then be screwed out only to the extent that engagement of the thread with the inside thread  25  of the hole  33  is cancelled so that the filter element  5  can be removed from the filter housing  1  and a fresh filter element  5  can be inserted into the operating position. As shown in  FIG. 4 , when the filter element  5  is in the operating position, both the filtered side  11  and the unfiltered side  13  can be emptied via the partially unscrewed screw  27 , with the screw  27  being held captively on the housing by the rotary cage  51 . 
     As in the preceding examples, fluid-tight closure of the housing opening  19  is possible only when the filter element  5  is in the operating position so that faulty operation is indicated in turn by the fluid&#39;s running or flowing out. 
     While various embodiments have 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.