Abstract:
A filter element has a filter material defining a raw side and a clean side of the filter element and to be flowed through by a medium to be filtered from the raw side to the clean side. A non-return element is disposed on the filter material. The non-return element allows a return flow of the filtered medium from the clean side back to the raw side and prevents a flow of the unfiltered medium from the raw side to the clean side. A filter and a filter system with such a filter element are disclosed. The filter system has a pump to supply medium to be filtered to the filter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of international application No. PCT/EP2015/071853 having an international filing date of 23 Sep. 2015 and designating the United States, the international application claiming a priority date of 24 Sep. 2014, based on prior filed German patent application No. 10 2014 013 852.6, the entire contents of the aforesaid international application and the aforesaid German patent application being incorporated herein by reference 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention concerns a filter element comprising a filter material, wherein the filter material can be flowed through from a raw side to a clean side by a medium to be filtered. The invention concerns moreover a filter as well as a filter system. 
         [0003]    It is known to employ filters for filtering a medium, in particular for filtration of a liquid. 
         [0004]    For example, EP 1 648 583 B1 discloses an oil filter. The oil filter comprises a filter element with an overflow valve. When the pressure is too high in the inlet, overflow or bypassing of a filter material of the filter element occurs in the known oil filter. In this context, the overflow valve opens in order to enable direct flow of the oil from the raw side to the clean side of the filter. 
         [0005]    When filters are used outdoors, in particular in a motor vehicle, a great change of the outdoor temperature may cause a volume change of the medium, in particular freezing of the medium in the form of a liquid when the outdoor temperature drops. The volume change can lead to the filter becoming damaged. 
         [0006]    In order to avoid such a filter damage, it is disclosed in DE 10 2012 017 140 A1 to employ a compensation element in the filter which compensates the volume change of the medium in the filter. Such a compensation element requires however a relatively large installation space in the filter. 
         [0007]    Therefore, a compensation element is often not employed in filters and the medium after completion of filtration is pumped out of the filter in order to avoid damage to the filter by temperature changes. In particular, as mentioned before, damage to the filter by a medium freezing in the filter is to be avoided. 
         [0008]    Pumping out the medium has however the disadvantage that dirt particles in the filter material become detached and are also pumped out. This can cause damage to the pump or to the throttles, valves, and the like. 
       SUMMARY OF THE INVENTION 
       [0009]    It is the object of the invention to provide a filter element, a filter, and a filter system that enable pumping out the medium without dirt discharge from the filter material. 
         [0010]    The object according to the invention is solved by a filter element comprising a filter material, wherein the filter material can be flowed through from a raw side to a clean side of the filter element, wherein the filter element comprises a non-return element that is embodied such that a return flow of filtered medium from the clean side back to the raw side is possible but no flow of unfiltered medium from the raw side to the clean side. 
         [0011]    The dependent claims provide expedient further embodiments. 
         [0012]    The non-return element enables thus at least a portion of the medium to bypass the filter material. A strong “reverse” flow through the filter material, i.e., a strong flow through the filter material from the clean side to the raw side is prevented thereby. As a consequence, dirt discharge from the filter material can be prevented. 
         [0013]    The filter element comprises preferably the raw side at its exterior side and the clean side at its interior side. In other words, the filter element preferably has an exterior raw side and an interior clean side. The filter element can therefore be constructed particularly simply. 
         [0014]    The filter element is preferably embodied in the form of a filter element for a liquid, in particular in the form of a filter element for aqueous urea solution. 
         [0015]    The filter element is preferably embodied in the form of a round filter element. The filter material in this context is preferably folded in a star shape in order to provide a large surface area. 
         [0016]    Particularly preferred, the inflow of the medium to be filtered is radial to the filter material, i.e., perpendicular to the central filter element longitudinal axis, and the outflow of the filtered medium is axial, i.e., in the direction of or parallel to the central filter element longitudinal axis. 
         [0017]    In a particularly preferred embodiment of the invention, the non-return element and the filter material are matched to each other in such a way that the flow resistance of the non-return element upon return flow of filtered medium from the clean side to the raw side is smaller than the flow resistance of the filter material upon return flow of filtered medium from the clean side back to the raw side. Therefore, upon pumping, the medium will bypass substantially completely the filter material by means of the non-return element so that dirt discharge from the filter material is practically completely avoided. In this context, the flow resistance relates preferably to aqueous urea solution. 
         [0018]    The filter element may comprise a first end disk, wherein the non-return element is arranged or embodied in the area of the first end disk. Particularly preferred, the non-return element is arranged immediately on the first end disk. In this way, a particularly space-saving arrangement of the non-return element is realized. 
         [0019]    Further preferred, the filter material is framed axially by the first end disk and a second end disk of the filter element. The filter material can be fused and/or glued to the end disks in order to be able to withstand high pressures. In this context, the filter material during manufacture of the filter element can be introduced into the melt of the end disks and/or into an adhesive applied to the end disks. 
         [0020]    The non-return element can be configured as a check valve. In particular, the non-return element can comprise a first through opening for flow of the medium from the clean side to the raw side, wherein non-return element can comprise a blocking body for closing off the first through opening. In this context, when the pressure of the medium at the raw side is higher than at the clean side, the blocking body can rest on a stop of the non-return element and thereby close off the first through opening and, on the other hand, can at least partially open the first through opening partially when the pressure of the medium at the clean side is greater than at the raw side. In this context, the blocking body can be in the form of a flap, a ball, a cone or the like. The first through opening is preferably embodied in the first end disk. 
         [0021]    In order to safely ensure the return flow of the medium from the clean side to the raw side, a plurality of non-return elements can be provided. The non-return element or the non-return elements can comprise a plurality of through openings that each are closable and openable by a blocking body. Preferably, a single blocking body closes off and opens all through openings of the non-return element or an individual blocking body, respectively, closes off and opens all through openings of the respective non-return elements. The through openings can be embodied in the first end disk. 
         [0022]    The blocking body is preferably embodied in the form of a diaphragm which covers at the raw side of the filter element the first through opening. A diaphragm, in particular a monolithic diaphragm, is particularly simply and inexpensively producible. 
         [0023]    In a further embodiment of the non-return element, the diaphragm is made of silicone or of synthetic rubber, in particular of ethylene propylene diene rubber (EPDM). These materials enable a simple manufacture of the diaphragm and at the same time provide a long service life. Particularly preferred, the diaphragm is formed of hydrogenated acrylonitrile butadiene rubber (HNBR) because this material is characterized by a particularly high mineral oil resistance and in particular by a particularly high diesel fuel resistance. 
         [0024]    In order to ensure reliably the seal-tightness of the non-return element with regard to flow from the raw side to the clean side, the blocking body is preferably pressed by an elastic element against the first through opening. Particularly preferred, in this context the diaphragm surface is at least partially pressed by an elastic element against the first through opening. 
         [0025]    The elastic element can be in the form of a spring. Particularly preferred, the elastic element is embodied in the form of the diaphragm body. In this way, a separate elastic element is not needed. 
         [0026]    For attachment of the diaphragm, it can be provided with a locking projection wherein the locking projection is fastened in a locking cutout of the non-return element. The locking cutout is preferably embodied as a through cutout so that the locking projection engages from behind the locking cutout. 
         [0027]    A constructively particularly simple embodiment of the non-return element is provided when the diaphragm is formed to have axial symmetry, in particular rotation symmetry, relative to the central longitudinal axis of the locking cutout. 
         [0028]    The non-return element according to the invention can also be provided with a different constructive configuration and, for example, can be formed as a so-called duckbill valve. Such a valve is obtainable ready-made and inexpensively on the market and can be particularly easily mounted on the filter element. 
         [0029]    One or more of the non-return elements may comprise one or more of the afore described features. 
         [0030]    According to a further embodiment of the invention, the filter element comprises, in addition to the afore described non-return element, a check valve by means of which during a backflushing process (=purging) of the filter or of the filter element an undesirable return flow of the filtered medium or of air through the filter material (=filter medium) is prevented. In this way, on the one hand, an undesirable detachment of contaminants adhering to the filter material at the raw side can be counteracted even more reliably. Moreover, in this way, a reliable response behavior of the non-return element in respect to pressure reversal between clean side and raw side even for minimal pressure differentials can be realized. The check valve together with the non-return element can be arranged on the same end disk of the filter element. The check valve can be designed in particular in a way so as to correspond to the non-return element. 
         [0031]    The object of the invention is further solved by a filter comprising a filter housing and a filter element arranged in the filter housing, wherein the filter element comprises a filter material which can be flowed through from a raw side to a clean side of the filter by the medium to be filtered, wherein the filter comprises a non-return element that is embodied such that a return flow of filtered medium from the clean side to the raw side is possible but no flow of unfiltered medium from the raw side to the clean side. 
         [0032]    The filter element comprises preferably the raw side at its exterior side and the clean side at its interior side. The filter element can therefore be constructed particularly simply. 
         [0033]    The non-return element can thus be provided in the filter element and/or in another area of the filter, in particular in the filter housing. Preferably, the filter according to the invention comprises a filter housing and an afore described filter element arranged in the filter housing, wherein the filter element comprises the non-return element. When the filter element comprises the non-return element, a filter can be retrofitted with the “bypass function” of the non-return element in that simply the conventional filter element is replaced with a filter element according to the invention. The conventional filters can be easily retrofitted with such a “bypass function” in this way. 
         [0034]    The non-return element of the filter comprises preferably one or several of the afore described features. Moreover, on the filter a plurality of non-return elements can be provided that comprise one or several of the afore described features. 
         [0035]    The object according to the invention is finally solved by a filter system with an afore described filter and a first pump for supply of medium to be filtered to the filter. The first pump can be designed for pumping the medium out of the filter. Alternatively or additionally, the filter system can comprise a second pump for pumping out medium from the filter. The filter system can furthermore comprise a valve, in particular a shut-off valve and/or a throttle that is connected fluidically between the pump and the filter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    Further features and advantages of the invention result from the following detailed description of embodiments of the invention, from the drawing showing details important to the invention, as well as from the claims. 
           [0037]    The features illustrated in the drawing are illustrated in such a way that the particularities according to the invention are clearly shown. The different features can be realized individually by themselves but also several of them in any combination in variants of the invention. 
           [0038]      FIG. 1  shows in this context a view of a filter system according to the invention with a filter, wherein the filter is shown in section in one half of the view and the other components of the filter system are illustrated schematically. 
           [0039]      FIG. 2  shows a further filter system with a filter in a detail longitudinal section. 
           [0040]      FIG. 3  shows the detail B identified in  FIG. 2  of the filter system in an enlarged illustration. 
           [0041]      FIG. 4  shows a filter element for a filter system, in particular for an aqueous urea solution, in a partial longitudinal section. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0042]      FIG. 1  shows a filter system  10  with a filter  12 . The filter  12  is in the form of a filter for aqueous urea solution. It comprises an inlet  14  and an outlet  16 . The inlet  14  extends radially, the outlet  16  axially to a filter element  18 . The filter element  18  is in the form of a round filter, i.e., substantially is axial symmetrical to its central filter element longitudinal axis  19 . The filter element  18  is arranged in a filter housing  20  of the filter  12 . The filter housing  20  comprises a filter housing body  22  comprising the inlet  14  and the outlet  16 . The filter housing body  22  is preferably connected fixedly with a motor vehicle. In order to enable an exchange of the filter element  18 , the filter housing body  22  is reversibly connected with a cover  24  of the filter housing  20  so as to be detachable. 
         [0043]    By means of a first pump  26 , medium to be filtered, in this case aqueous urea solution that is to be filtered, can be supplied to the filter  12 . The path of the medium to be filtered is shown in  FIG. 1  by single line arrows. In this context, the medium to be filtered passes a first shut-off valve  28  on its way to the filter  12 . 
         [0044]    The filter element  18  comprises a filter material  30  for filtering dirt particles. The filtered dirt particles remain in the filter material  30 . The filter material  30  separates thus a raw side  32  of the filter element of the filter  12  from its clean side  34 . 
         [0045]    Between raw side  32  and clean side  34 , a non-return element  36  is provided. The non-return element  36  is embodied on a first end disk  37  of the filter element  18 . The non-return element  36  comprises a first through opening  38 , a second through opening  40 , and a diaphragm  42 . The non-return element  36  comprises, in addition to the through openings  38 ,  40 , two further through openings which are arranged symmetrical to the through openings  38 ,  40  but are not visible in the present section view. On the raw side  32 , the diaphragm  42  is resting with an umbrella-shaped head part  44  on the through openings  38 ,  40  in order to close them off. The diaphragm  42  is passed through a locking cutout  46  formed as a through cutout. A locking projection  48  of the diaphragm  42  is fastened in the locking cutout  46  in that it engages from behind the locking cutout  46 . The diaphragm  42  is formed of an elastic material, wherein it closes off the through openings  38 ,  40  when the pressure at the raw side  32  is higher than the pressure at the clean side  34  and opens them when the pressure at the clean side  34  is higher than the pressure at the raw side  32 . 
         [0046]    In this way, filtered medium can be guided from the clean side  34  to the raw side  32  by means of the non-return element  36  without the filtered medium passing through the filter material  30 . Medium that is contained in the filter  12  can thus be pumped out by a second pump  50  from the filter  12  without dirt particles separated in the filter medium  30  becoming detached and the first shut-off valve  28  and/or the second pump  50  becoming soiled and damaged. Pumping out the medium is realized in the direction of the illustrated double-line arrows. 
         [0047]    The filter system comprises a second shut-off valve  52  which, in relation to the filter  12 , is fluidically downstream of the outlet  16 . For pumping, the second shut-off valve  52  is closed and the first shut-off valve  28  opened in order to empty the filter  12  completely. Subsequently, the first shut-off valve  28  is closed. By emptying the filter  12 , damage to the filter  12  by freezing of medium in the filter is prevented. It is understood that the second shut-off valve  52  may also stay open when pumping out the medium in order to allow flow of air (or exhaust gases of an internal combustion engine) through the outlet  16  into the filter housing  20 . 
         [0048]    The filter element  18  can be arranged in the filter housing  20  in principle also with the first end disk  37  facing upwardly, as is the case in the embodiment of the filter system  10  illustrated in  FIG. 2 . It is understood that the non-return element  36  which is embodied on the first end disk  37  of the filter element  18  moreover can have a different configuration than the embodiment illustrated in  FIG. 1 . 
         [0049]    Accordingly, the non-return element  36  can be, for example, in accordance with  FIGS. 2 and 3 , a so-called duckbill valve. The non-return element  36  extends in this case preferably through a cutout of the first end disk  37  of the filter element  18 . The non-return element  36  forms in this context a through opening  38  for the medium which, according to the detail illustration of the duckbill valve in  FIG. 3 , can be fluid-tightly closed by means of two valve flaps  54  of the duckbill valve. At a higher pressure at the raw side  32  than at the clean side  34 , the two valve flaps  54  of the non-return element  36  are resting fluid-tightly against each other. The duckbill valve is thus in its closed position in which the through opening  38  of the duckbill valve is fluid-tightly shut. In the closed position of the duckbill valve, a bypass flow of the medium to be filtered around and about the filter medium  30  is prevented. When the pressure at the clean side  34  is higher than the pressure at the raw side  32 , i.e., when blowing out or sucking off the aqueous urea solution from the inlet  14 , the outlet  16  as well as the filter housing  20  ( FIG. 3 ), the two valve flaps  54  of the non-return element  36  are moved apart, as is illustrated in  FIG. 3  by arrows  56 , and the non-return element  36  is thus transferred into its open position. 
         [0050]    According to the embodiment of  FIG. 4 , the filter element  18  can comprise, in addition to the afore explained non-return elements  36 , a check valve  58  by means of which a return flow of the filtered medium or an incoming air flow through the filter element  30  is completely prevented upon discharge of the aqueous urea solution from the filter system (=purging). In this way, unwanted detachment of dirt that has been filtered from the medium by the filter material  30  can be even more reliably counteracted during the aforementioned backflushing process. The check valve  58  can be arranged in particular on the first end disk  37  of the filter element  18  and can be designed in a way corresponding to the non-return element  36 . By means of such a check valve  58  an even more reliable response behavior of the non-return element  36  can be realized during the backflushing process, in particular for only minimal pressure differentials between the clean side  34  and the raw side  32 . It is understood that a complete emptying of the medium from the filter element  18  by backflushing (=purging) is not realized in the embodiment of the filter element  18  shown in  FIG. 4 . 
         [0051]    In summary, the invention concerns a filter for filtering a medium, in particular for filtering aqueous urea solution. The filter comprises a filter element with a filter material. The medium can be pumped out at least partially, in particular completely, from the filter without it having to pass through the filter material so that dirt that has been filtered out from the medium does not become detached from the filter material and is not pumped out. For this purpose, in the filter, in particular in the filter element, a non-return element is provided that blocks a flow of the medium from the raw side to the clean side of the filter but allows a flow of the medium from the clean side to the raw side of the filter. The non-return element is preferably in the form of a duckbill valve or a mushroom-shaped diaphragm. In this context, the diaphragm is anchored, further preferred, by a thicker portion at the base of the mushroom shape in a through cutout of the filter. The head part of the mushroom shape covers preferably at least a through opening of the filter for flow of medium from the clean side to the raw side.