Abstract:
The invention describes a filter element for an oil separator of a crankcase ventilation system in which a filter element is configured to separate oil from fluid and that has a covering surface extending parallel to a direction of flow, together with at least one cover element covering surface in at least some regions. An oil separator is taught having the filter element with at least one pressure control valve controlling crankcase pressure and has a valve closing body that operates in conjunction with a valve seat.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a filter element for an oil separator, an oil separator of a crankcase ventilation system, and a method for controlling the prevailing pressure in a crankcase ventilation system. 
       BACKGROUND 
       [0002]    With reciprocating piston internal combustion engines, an oil-containing leakage gas, so-called blow-by gas, is produced in the crankcase. The return thereof into the combustion process is legally mandated worldwide, and takes place in so-called closed crankcase ventilation systems. The most important tasks of a crankcase ventilation system are oil separation and oil return into the crankcase, as well as the regulation of the crankcase pressure. The requirements for oil separation have been steadily increasing in recent years, as legislation on emissions has grown increasingly stringent, in order to protect emissions-related engine components such as exhaust gas turbochargers, intercoolers, or sensors from performance loss due to oil contamination. Thus, oil separation is important not only in minimizing oil consumption, but also in making what is now an essential contribution to compliance with emissions legislation throughout the lifetime of the vehicle. In addition to oil separation, a crankcase ventilation system contains other important components, such as, for example, a pressure control valve, depending on the ventilation design. 
         [0003]    A pressure control valve for a crankcase ventilation system of an internal combustion engine is disclosed, for example, in documents DE 10 201 3 005 624 A1, WO 2005 088 417 A1 and WO 2007 13 50 82 A2. Generally-known pressure control valves have a valve closing body that operates in conjunction with a valve seat, and a return spring that acts on the valve closing body in the direction facing away from the valve seat (DE 10 2004 02 22 75 A1). 
         [0004]    In order to extend the life of the return spring in a pressure control valve for an internal combustion engine, DE 10 2004 02 22 75 A1 proposes arranging the return spring on the side of the valve closing body facing away from the valve seat, and thus preventing the return spring from contacting aggressive blow-by gases emerging from the crankcase. Documents WO 2007 13 50 82 A2 and JP 2003 33 65 16 A disclose arranging the return spring on the atmosphere side of a pressure control valve. 
         [0005]    WO 2005 08 84 17 A1, WO 2009 15 63 03 A1, DE 10 2004 02 22 75 A1, and EP 1 32 95 98 A1 disclose fastening a membrane configured as a sealing element onto a valve element by means of at least one spraying process, in particular, by injection-molding onto a valve element or overmolding a valve element. 
         [0006]    With known pressure control valves, the valve seat of the pressure control valve is arranged on the outside of a side wall of the crankcase ventilation system (DE 10 2013 005 624 A1) or formed by a side wall of the housing of the crankcase ventilation system (WO 2005/088 417 A1). 
         [0007]    The invention addresses the problem of developing a filter element of the aforementioned type, an oil separator of the aforementioned type, and a method of the aforementioned type, in such a manner that the functions thereof are optimized, in particular, that the crankcase ventilation system takes up the least installation space possible. 
       SUMMARY 
       [0008]    The invention addresses the problem of developing a filter element of the aforementioned type, an oil separator of the aforementioned type, and a method of the aforementioned type, in such a manner that the functions thereof are optimized, in particular, that the crankcase ventilation system takes up the least installation space possible. 
         [0009]    The invention is based on realizing the functions of the crankcase ventilation system with the fewest possible components. 
         [0010]    According to the invention, the cover element of the filter element comprises at least one clean fluid discharge element that: leads out from the interior of the filter element; in particular, extends away from the filter element; in particular, is tube-shaped; and is configured in order to remove the purified fluid, in particular, clean air. The end surface of this clean fluid discharge element that faces away from the filter element is configured as a sealing surface for a valve of the crankcase ventilation system, or comprises a sealing surface for a valve of the crankcase ventilation system. Preferably, the sealing surface is a valve seat for a valve closing body, in particular, for a valve closing body sealing element of a pressure control valve that surrounds the valve closing body. In addition to the function of discharging or removing the purified fluid, the clean fluid discharge element thus assumes another function, namely, a sealing function. 
         [0011]    The sealing surface is substantially flat and free of burrs, wherein the ends, margins, or edges of the sealing surface may be rounded. In addition, the sealing surface is preferably round, in particular, circular. 
         [0012]    The arrangement of the sealing surface on the clean fluid discharge element, as described, causes the sealing surface and the plane defined thereby to be preferably spaced apart from the axial, outer surface of the cover element. This arrangement likewise defines the distance of the valve from the cover element. Within this distance, the clean fluid outlet of the oil separator housing, in which the filter element is to be incorporated, can be advantageously arranged so as to conserve installation space. For a streamlined overall design, it is therefore preferred that the length of the clean fluid discharge element, as measured from the axial, outer surface of the cover element, corresponds approximately to the diameter of the clean fluid outlet of the oil separator housing. 
         [0013]    The cover element is preferably an end plate of the filter element. The cover element is sealingly and non-releasably connected to the filter medium at an end face of the filter element, for example, by gluing or welding. The cover element is preferably produced from thermoplastic polymer, preferably by injection molding. 
         [0014]    The clean fluid discharge element is preferably non-releasably (i.e., so as not to be non-destructively removable) and sealingly connected to the cover element, so that the pre-filtration side is separated from the post-filtration side. The clean fluid discharge element is particularly preferably integral with the cover element. 
         [0015]    The clean fluid discharge element and the cover element are preferably continuously closed. This means that the clean fluid discharge element and the cover element are connected and designed such that other than the clean fluid exit opening surrounded by the sealing surface, no other openings are present in the cover element or clean fluid discharge element. 
         [0016]    The clean fluid discharge element is preferably an oval cylindrical, in particular, circular cylindrical, in particular, straight tube. This tube comprises a closed cylindrical wall and two open ends, wherein the sealing surface is configured on one end that faces away from the cover element, and the other end is connected to the cover element, so that a fluid connection to the interior of the filter medium or filter body is formed. The ends are preferably oriented so as to be perpendicular to the central axis. 
         [0017]    In a particularly preferred embodiment, the cover element is an annular end plate away from which the clean fluid discharge element, configured as a tube, extends on the side facing away from the filter medium. 
         [0018]    The clean fluid element and the cover element preferably form an L-shaped or T-shaped cross-section. 
         [0019]    A preferred embodiment of the filter element of the present invention comprises a clean fluid discharge element having an end surface configured so as to be flat and/or free of burrs in so as to be usable as a sealing surface, in particular, as a valve seat for a valve closing body of a pressure control valve of the crankcase ventilation system. 
         [0020]    A person skilled in the art will appreciate the filter element of the present invention, in particular, in use in a crankcase ventilation system having an integrated pressure control or integrated pressure control valve. Namely, by means of the sealing surface according to the invention, the filter element may assume another function beyond separating oil from aerosol—namely, a partial function of the pressure control. The sealing surface of the filter element may then serve as a valve seat for the valve closing body of the pressure control valve. The sealing surface may also be configured in order to operate in conjunction with the control of the crankcase pressure, in particular, the limitation of the vacuum of the crankcase ventilation system. 
         [0021]    The sealing surface of the filter element of the present invention makes it possible to significantly reduce the installation space for the crankcase ventilation system in comparison to, for example, prior art disclosed in documents DE 10 201 3 005 624 A1 and WO 2005 088 417 A1, in which the valve seat of the pressure control valve is arranged on a housing side wall of the crankcase ventilation system. Thus, due to the sealing surface of the filter element according to the invention, the components of the pressure control valve, which is configured in order to control the crankcase pressure, can be accommodated in the upper housing part of the crankcase ventilation system. 
         [0022]    A further reduction of the installation space can be achieved by designing the filter element so that the flow therethrough goes from the outside to the inside and so as to have a cavity configured in order to remove the purified fluid, in the interior of the filter medium. Thus, as opposed the prior art, in which the flow through is from the inside to the outside, it is not necessary to provide a channel by means of which the fluid can be delivered to the interior of the filter medium. 
         [0023]    The cavity arranged in the interior of the filter medium and configured in order to remove the fluid is advantageously connected directly to the clean fluid discharge element or transitions directly into a cavity of the clean fluid discharge element that is configured in order to remove the fluid. 
         [0024]    In order to form the filter medium so as to be as stable as possible against forces acting on the filter medium from the outside, the filter medium advantageously has an oval, in particular, circular cross-section. In an advantageous embodiment of the crankcase ventilation system, the housing of the crankcase ventilation system that is formed of at least one housing part and configured in order to accommodate the filter medium also has an oval, in particular, circular cross-section. 
         [0025]    As the filter medium, it is possible to use basically any material, in particular, a non-woven fabric, for example, made of metal fiber, glass fiber, and/or plastic fiber, for example, made of polyester. It would also be possible to combine these materials. In addition, as described in DE 10 2011 016 893 A1, the filter medium may be a coalescence medium. Preferably, the filter element is an annular coalescence element. For this purpose, the filter element preferably has a filter medium configured as a non-woven fabric that preferably is wrapped repeatedly and thus in a plurality of layers annularly around a support tube. This means that the filter medium is preferably configured as at least one non-woven wrap. To stabilize and seal off, a cover element that is preferably configured as an end plate is also provided on respective end faces. 
         [0026]    The oil separator is preferably configured, as described, as a coalescing filter. The crankcase ventilation system may be configured as a closed crankcase ventilation system in which the post-filtration leakage gas is returned to the combustion process, or as an open crankcase ventilation system. 
         [0027]    The sealing surface of the filter element is particularly stable and is particularly easy to produce if the sealing surface, the clean fluid discharge element, and the cover element are integral with one another. 
         [0028]    Independently thereof or in connection thereto, in a preferred embodiment of the filter element of the present invention, the sealing surface and/or the end plate is made of a mechanically fixed and/or rigid material, for example, polyamide 66 having 35% glass fibers (PA 66 GF35). 
         [0029]    In order to improve the tightness of the sealing of the pressure control valve, the valve closing body has at least one elastic valve closing body sealing element, at least on the region thereof that can be arranged in contact with the valve seat of the filter element. 
         [0030]    The sealing element of the valve closing body advantageously has substantially at least one elastomer. In particular, the valve closing body sealing element may be formed of at least one elastomer, for example, ethylene acrylate rubber (EAR) and/or from, in particular, hydrogenated nitrile rubber ([H]NBR) and/or acrylate rubber. In comparison to the prior art, in which the sealing off of the valve seat and the valve closing body is performed solely by hard components, the tightness of the seal of the pressure control valve may be considerably improved by the elastic configuration of the valve closing body sealing element. 
         [0031]    In an advantageous embodiment of an oil separator of the present invention, the sealing happens from soft to hard. Thus, for example, the valve closing body and the clean fluid discharge element, in particular, the valve seat are formed essentially out of polyamide 66 with 35% glass fiber (PA 66 GF35) and the valve closing body sealing element is formed essentially out of ethylene acrylate rubber (EAR) and/or acrylate rubber. 
         [0032]    The tightness of the seal of the pressure control valve can also be improved by connecting the sealing element of the valve closing body fixedly or non-releasably to the valve closing body, in particular, application to the valve closing body by means of at least one spray process. The valve closing body sealing element and the valve closing body thus advantageously form a unit. In one advantageous embodiment of the present invention, the valve closing body sealing element is not tied up into the valve body, as is known in the prior art, but rather the valve body is encapsulated by the valve closing body sealing element, and forms a solid unit with the valve closing body sealing element. 
         [0033]    Another limiting criterion of an advantageous embodiment of an oil separator of the present invention relative to the prior art is thus that the valve closing body and the valve closing body sealing element are fixedly connected to one another. The valve closing body sealing element thus forms a solid unit with the valve closing body, which improves the tightness of the seal. 
         [0034]    A particularly high tightness of the seal of the pressure control valve may also be achieved by configuring the valve closing body so as to be flat or level at a region thereof that faces the valve seat, in particular, a region thereof that can be arranged in contact with the valve seat of the filter element. In contrast, in the prior art, the valve closing body is usually curved in the shape of a dish on the region thereof that faces the valve seat. In contrast to the dish shape in the prior art, the valve closing body—in particular, the valve closing body sealing element—of an optimized embodiment of an oil separator of the present invention thus has a flat or level shape, whereby the sealing properties are greatly improved. 
         [0035]    Independently thereof or in connection therewith, a particularly advantageous embodiment of an oil separator of the present invention has an advantage over the prior art, for example, that is illustrated in  FIG. 12 , in that the components of the pressure control valve or the pressure control are located in the upper part of the housing. 
         [0036]    A special feature of the present invention is that the unit filter element constitutes the end position for the valve closing body. 
         [0037]    Another special feature of the present invention is that the filter element assumes two functions: 
         [0000]    1. Separating oil from the gas
 
2. Partial function of the pressure control
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    As already discussed above, there are several approaches to advantageously em-bodying and developing the teaching of the present invention. 
           [0039]      FIG. 1  illustrates a perspective view of an embodiment of a crankcase ventilation system according to the present invention, in which a pressure control valve thereof works according to the method of the present invention; 
           [0040]      FIG. 2  illustrates a longitudinal depiction of a crankcase ventilation system from  FIG. 1 , with an embodiment of an oil separator according to the present invention, in which a pressure control valve thereof works according to the method of the present invention; 
           [0041]      FIG. 3  illustrates a longitudinal view of a detail of the oil separator from  FIG. 2 ; 
           [0042]      FIG. 4  illustrates a plan view of the oil separator from  FIG. 2 ; 
           [0043]      FIG. 5  illustrates a perspective view of the valve closing body and the valve closing body sealing element of the pressure control valve of the oil separator from  FIG. 2 ; 
           [0044]      FIG. 6  illustrates a longitudinal view of the valve closing body and the valve closing body sealing element from  FIG. 2 ; 
           [0045]      FIG. 7  illustrates a perspective view of the valve closing body, a return spring, and a pressure control insert of the oil separator from  FIG. 2 ; 
           [0046]      FIG. 8  illustrates a perspective exploded view of the components of an embodiment of a filter element according to the present invention; 
           [0047]      FIG. 9  illustrates a perspective exploded view of the components arranged in the housing cover of the crankcase ventilation system depicted in  FIG. 1 ; 
           [0048]      FIG. 10  illustrates a detail of the pressure control valve of the crankcase ventilation system from  FIG. 1 , wherein the forces acting on the valve closing body are marked; 
           [0049]      FIG. 11  illustrates an embodiment of a control characteristic of the crankcase pressure as a function of the vacuum on the outlet side of the pressure control valve of the crankcase ventilation system from  FIG. 1 ; 
           [0050]      FIG. 12  illustrates an oil separator according to the prior art; and 
           [0051]      FIG. 13  illustrates a side view of the oil separator from  FIG. 12 , which is configured according to the prior art. 
       
    
    
       [0052]    Identical or similar designs, elements, or features are provided with identical reference signs in  FIGS. 1 to 12 . 
       DETAILED DESCRIPTION 
       [0053]      FIG. 1  illustrates a perspective view of a crankcase  410  (shown only schematically), which comprises an oil separator  200  of a crankcase ventilation system. The crankcase  410  is part of an internal combustion engine. The internal combustion engine may be installed in a motor vehicle. The oil separator  200  is configured as an oil separator for oil-containing air from an interior of the crankcase  410 . In such applications, the oil-containing air is usually mixed with combustion gases exiting from the cylinders as leakage gas into the crankcase. This mixture is frequently also called crankcase gas, the term “air” still also being used for the sake of simplicity. 
         [0054]    The oil separator  200  comprises a substantially oval-cylindrical—in particular, circular-cylindrical—filter housing composed of a first filter housing part  210 —namely, a housing cover—and a second filter housing part  220 —namely, a housing body. The second filter housing part  220  has an inlet  222  for the oil-containing air  500 . Arranged in the filter housing is a filter element  100  comprising at least one filter medium  10  made of a filter material that has been arranged in an annular shape, e.g., a circular ring shape or an oval ring shape (see  FIG. 2 ). The filter element  100  is covered by the filter housing in  FIG. 1 , and therefore is marked with a dashed reference line. Within the filter housing  210 ,  220 , the air  500  (a corresponding air flow  20  is indicated in  FIG. 2  by an arrow) is filtered by means of the filter medium  10 . The resulting clean air  510  is guided out of an interior  12  ( FIG. 2 ) enclosed by the filter medium  10 , through a clean air discharge element  50  of the filter element  100 , to a clean air outlet  212  of the housing cover  210 , and from the clean air outlet  212  back into the intake duct of the internal combustion engine. Separated oil is removed through an oil outlet  230 . 
         [0055]    The oil separator  200  has a pressure control valve, in order to limit the crankcase vacuum to a defined value. The pressure control valve—depicted by way of example in  FIGS. 2 and 3 —has a valve closing body  310  that is surrounded by a valve closing body sealing element  320 , preferably by a membrane, as is illustrated here. 
         [0056]    On the end facing away from the valve closing body  310 , the membrane  320  is connected to the first filter housing part  210 , for example, by being clipped into the first filter housing part  210 . Alternatively, the membrane  320  may also be mounted between the filter housing part  210  and the cover element  214 . Preferably, the membrane is clamped between the first filter housing part  210  and an insert  350  forming even more preferably the lower stop of the spring  330 , as in the presently-described embodiment. The insert  350  has openings, so that the ambient pressure can act on the membrane  320  and on the valve closing body  310 . 
         [0057]    In order to be closed, the pressure control valve has a valve seat  52  arranged on the filter element  100 . In contrast to the prior art illustrated in  FIGS. 12 and 13 , the filter element  100  illustrated in  FIGS. 2, 3, 8, and 10  has a cover element  40  that is configured as an end plate and has a sealing surface  52  at the end thereof that faces away from the filter element  100 , wherein this sealing surface  52  is provided in order to seal off the pressure control valve  52 ,  310 ,  320 ,  330 , by the ability of the valve closing body sealing element  320  or the valve closing body  310  to come into sealing contact with the sealing surface  52 , preferably with a contact surface  312  (see  FIG. 6 ) of the valve closing body  310  or the membrane  320 . 
         [0058]    The membrane  320  is configured to seal the clean air outlet  212  and the interior  12  of the filter medium  10  off from the ambient air pressure, and to keep the valve closing body axially movable. 
         [0059]    The valve closing body  310  can be moved relative to the valve seat  52 , as illustrated in  FIG. 10 . The left side of the illustrated sectional view depicts the closed state of the valve, where the valve closing body  310  abuts, preferably axially (as is shown), against the sealing surface  52  with a circular ring-shaped contact surface  312  (see  FIG. 6 ); on the right side of the view, the valve closing body  310  is spaced apart from the sealing surface  52 , so that the valve is open. The pressure control valve  52 ,  310 ,  320 ,  330  is configured so as to control the flow rate or volume flow of the fluid flowing away through the clean fluid discharge element  50 , by means of the movement of the valve closing body  310  relative to the valve seat  52 , in particular, through the modification of the cross-section of the flow channel  340  formed by the gap between the sealing surface  52  and the valve closing body  310 . 
         [0060]    The pressure control valve is configured such that the membrane  320  is subjected to the pressure  600  prevailing in the clean air outlet  212  on the side thereof facing the filter element  100  or the housing interior, in the region of the circular ring area A M  defined by the diameters Ø M  and Ø M , and the valve closing body  310  is subjected to the pressure  610  prevailing in the interior  12  of the filter medium  10  on the side thereof facing the filter element  100  or the housing interior, in the region of the circular area A D  defined by the inner diameter Ø D  of the sealing surface  52 . On the side facing away from the filter element  100  or the housing interior, the membrane  320  and the valve closing body  310  are also subjected to the ambient pressure. Preferably also provided is a return spring  330  that subjects the membrane  320  and/or the valve closing body  310  to a force that acts in a direction of opening, i.e., is directed away from the filter element  100 . At least one opening in a pressure control valve cover element  214  and/or an insert  350  causes ambient pressure to be applied to the back side of the membrane; this ventilation makes it possible for the pressure control valve to work undamped. 
         [0061]    Preferably, a return spring  330 —as already described—is arranged on the side of the valve closing body  310  that faces away from the filter element  100 . The return spring  330  subjects the valve closing body  310  and/or the membrane  320  arranged thereon to a force  620  (see  FIG. 10 ) oriented away from the valve seat  52 . The compression spring or return spring  330  services to ensure the rest position of the valve closing body  310 . The rest position corresponds to the position of the valve closing body  310  at which the force of the return spring  330  is exactly as great as the sum of the force of the crankcase pressure  610  and the force of the suction pressure  600 . 
         [0062]    On the way from the interior  12  of the filter medium  10  to the clean air outlet  212 , the clean fluid flows through a flow channel  340  (see  FIGS. 3 and 10 ) that is arranged between the valve closing body  310 —in particular, the membrane  320  arranged on the valve closing body  310 —and the valve seat  52 , and that preferably has the shape of an annular gap, as is provided presently. The diameter of this flow channel  340  can be changed or regulated through relative movement of the valve closing body  310  to the valve seat  52 . 
         [0063]    With decreasing pressure in the clean air outlet  212  or on the exit side of the pressure control valve, the membrane  320  makes a stroke movement in the direction of the valve dome or valve seat  52 , thereby reducing the cross-sectional area of the flow channel  340 . This increases the flow resistance of the pressure control valve over the valve seat  52 . 
         [0064]    The control behavior of the pressure control valve can be adjusted via the diameter cross-section ratios Ø M , Ø D  of the membrane  320  and the inner diameter of the sealing surface  52  or the end surface of the clean fluid discharge element  50  that faces away from the filter element  100 .  FIG. 10  illustrates the cross-section diameter Ø M  of the membrane  320  (which, in the present embodiment, is defined by the roll point of the membrane  320 ) and the cross-section inner diameter Ø M  of the sealing surface  52 . 
         [0065]    The valve closing body  310  is in the rest position (closed position) when
       a) the force F of the return spring  330     b) minus the differential pressure Δp from the atmospheric pressure and the crankcase pressure  610 , multiplied by the cross-sectional area A D  (defined by the inner diameter Ø D  of the valve seat  52 )   c) minus the differential pressure Δp from the atmospheric pressure and the suction pressure  600 , multiplied by the cross-sectional area A M  (defined by the ring between the cross-section diameter Ø M  of the membrane  320  and the inner diameter Ø D  of the valve seat  52 ) equals zero.       
 
         [0069]    In summary, this gives: 
         [0000]    
       
         
           
             
               
                 
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                       F 
                       
                         return 
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                           pressure 
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                       * 
                     
                   
                 
               
             
             
               
                 
                     
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         [0070]    The return spring  330  prevents the membrane  320  from being permanently closed at small suction vacuum pressures  600  from the turbocharger or intake duct of the engine. In addition, the location of the pressure control characteristics can be varied by means of the return spring  330 . This means that with a harder return spring  330 , the suction vacuum pressure  600  can act more intensely on the crankcase, and the curve shifts downward. 
         [0071]      FIG. 11  illustrates an exemplary control characteristic line of a pressure control valve. The Y-axis represents the pressure prevailing in the inlet for pre-filtration fluid  222  or on the pre-filtration side  250 —in particular, the crankcase pressure—in hectopascals [hPa]. The X-axis represents the pressure prevailing in the clean air outlet  212 —in particular, the suction vacuum pressure—in hectopascals [hPa]. The first control characteristic line, represented in  FIG. 11  with a solid line, shows the pressure ratios at a volume flow in the pressure control valve of 100 liters per minute. The second control characteristic line, represented in  FIG. 11  with a dashed line, shows pressure ratios at a volume flow in the pressure control valve of 20 liters per minute. The control range of the two control characteristic lines—shown by way of example—lies in the range of −2 to −28 hPa. The slope of the ranges of the two control characteristic lines marked with the reference signs  700 ,  702  depends on the area ratios A D  and A M  of the valve seat  52  and the membrane  320 . The intersection of the two control characteristic lines with the Y-axis, marked with the reference signs  710 ,  712 , shows the pressure drop with the pressure control valve is open. 
         [0072]    As depicted in  FIG. 11 , the pressure drop of the oil separator  200  also affects the situation of the pressure control curve, wherein when the pressure drop or volume flow increases, the situation of the pressure control curve rises. Conversely, the crankcase pressure decreases with a lower volume flow. 
         [0073]    The ratio of the cross-section diameters Ø M  and Ø D  of the membrane  320  and the sealing surface  52  influences the slope  700 ,  702  of the pressure control curve. If a negative pressure prevails in the crankcase relative to the atmosphere, and the pretension of the return spring  330  is overcome, then the membrane  320  moves onto the sealing surface  52 , and the flow resistance increases. 
         [0074]    First, if the suction vacuum pressure  600  is large enough and the return spring  330  is compressed, this results in a curved curve, and finally in a minimum of the crankcase pressure. 
         [0075]    At even higher suction vacuum pressures, a slight increase in the pressure  610  is to be observed in the interior  12  of the filter medium, in particular, the crankcase pressure. In these operational ranges, the membrane  320  closes the suction side of the valve intermittently, and thus throttles or interrupts the volume flow. This intermediate pressure is higher than the minimum pressure, because when the valve seat  52  is closed and there is a strong suction vacuum pressure  600 , the pressure  610  in the crankcase must be correspondingly higher, in order to for the membrane  320  to again be lifted off from the valve seat  52  against the suction vacuum pressure acting on the outside thereof. 
         [0076]    The oil separator  200  may have an overpressure valve  800  ( FIG. 1 ), for safety reasons. This overpressure valve may be configured, for example, as is described in DE 10 2013 005 624 A1. 
         [0077]      FIG. 8  illustrates the components of an embodiment of a filter element  100  according to the present invention. This filter element  100  is configured for the crankcase ventilation system illustrated in  FIG. 1 . The filter element  100  has a cover element, in particular, an end plate  40 . This end plate  40  covers the covering surface  30  (see  FIG. 3 ) of the filter medium  10  facing the clean fluid outlet  212 , and is connected sealingly thereto, so that the fluid flows through the filter medium  10  into the interior  12  of the filter medium  10 . The filter element  100  is an annular coalescence element. For this purpose, the filter element  100  has, as preferred, a filter medium  10  configured as a non-woven fabric that is wrapped repeatedly and thus in a plurality of layers annularly around the central tube  70  (also called a support tube). The central tube  70  allows for flow therethrough and therefore has openings. This can be realized, for example, by a lattice-shaped configuration—as shown in  FIG. 8 —by means of a perforated plate or the like. The filter medium  10  is a non-woven wrap. For stabilization and sealing, it is preferably sealingly connected at each of the end faces—for example, by means of gluing or welding—to cover elements  40 ,  42  configured as end plates. The construction of the coalescence element with the wrapped non-woven fabric is thus fundamentally different from other filter elements, which are intended to separate solid particles from fluids such as air or oil and generally have a pleated filter medium. 
         [0078]    The sealing surface  52  on the clean fluid discharge element  50  is spaced apart from the axial outer surface of the cover element  40 . The axial installation space required for the clean fluid outlet  212  is thereby bridged. The length of the clean fluid discharge element  50 , as measured from the axial, outer surface of the cover element  40 , corresponds to the diameter of the clean fluid outlet  212  of the upper housing part  210 . This makes it possible to achieve a streamlined overall design with which the positioning of the sealing surface  52  on the cover element  40  or on the filter element  100  is not accompanied by disadvantages. 
         [0079]    The cover element  40  is configured as an end plate of the filter element  100 , as is preferred, in the embodiment illustrated in detail in  FIGS. 2, 3, and 8 . The cover element is sealingly and non-releasably connected to the filter medium at an end face of the filter element, for example, by gluing or welding. The cover element  40  is preferably produced from thermoplastic polymer, preferably by injection molding. 
         [0080]    The clean fluid discharge element  50  is integrally, sealingly connected—as is preferred—to the cover element  40  in the embodiment illustrated in detail in  FIGS. 2, 3, and 8 . 
         [0081]    The clean fluid discharge element  50  is preferably a circular-cylindrical, straight tube, as also illustrated in the drawings. This tube comprises a closed cylindrical wall and two open ends, wherein the sealing surface  52  is configured on one end that faces away from the cover element, and the other end is connected to the cover element  40 , so that a fluid connection to the interior  12  of the filter medium  10  or filter body is formed. The ends are preferably oriented so as to be perpendicular to the central axis. 
         [0082]    In the embodiment illustrated in detail in  FIGS. 2, 3, and 8 , as is preferred, the cover element  40  is configured as an annular end plate away from which the clean fluid discharge element  50 , configured as a tube, extends integrally on the side facing away from the filter medium  10 . The clean fluid element and the cover element preferably form a substantially L-shaped or alternatively T-shaped cross-section, as is illustrated. 
         [0083]    The crankcase ventilation system has two spaces that must be separated from one another—namely, the pre-filtration space or pre-filtration side  250 , on which the not-yet-cleaned blow-by gas is located, and the post-filtration space or post-filtration side  240 , on which the cleaned gas is located. In addition, the pre-filtration space  250  and post-filtration space  240  must also be separated from the atmosphere. To solve this problem only with a seal, the filter element  100 —illustrated, for example, in  FIG. 8 —has a sealing element configured as a combination seal, namely, a filter element seal  60  that makes it possible to separate all three regions from one another. 
         [0084]    The filter element seal  60  (see  FIGS. 2, 3, and 8 ) thus serves to seal off
       the pre-filtration side  250  of the filter element  100  from the post-filtration side  240  of the filter element  100 ,   the interior of the housing upper part  210  to the ambient air pressure, and   the interior of the housing lower part  220  to the ambient air pressure.       
 
         [0088]    A special advantage of the filter element seal  60  illustrated in  FIGS. 2, 3, and 8  over filter element seals from the prior art is the functional decoupling of two sealing functions, namely, the sealing off of the interior of the filter housing  210 ,  220  from the environment on one hand, and the sealing off of the pre-filtration side  250  from the post-filtration side  240  on the other hand. The two sealing regions illustrated in  FIGS. 2 and 8 —namely, the radially sealing region  64  and the axially sealing region  66 —are functionally independent, but integrated into one part, namely, the sealing element  60 . 
         [0089]    The filter element seal  60  illustrated in  FIGS. 2, 3, and 8  thus has a region  64  that is radially compressed by means of a defined force, and a region  66  that is axially compressed by means of a defined force, wherein the radially compressed region  64  and the axial compressed region  66  are connected to one another and form a continuous sealing element, which fulfills two independent sealing functions. The sealing forces are defined by a person skilled in the art, by designing the sealing parameters of Young&#39;s modulus, seal dimensions, and sealing gap dimensions. 
         [0090]    A defined radial seal can be provided in the oil separator  200  illustrated in  FIGS. 2, 3, and 8  by radially compressing the filter element seal  60  by means of a defined force between the housing upper part  210  and the end plate  40 . This is advantageously achieved by the extension of the housing upper art  210  to the height of the end plate  40 , the end plate  40  thus being arranged over the housing edge of the housing upper part  210 . 
         [0091]    The radially sealing region  64  may be configured in the manner of an O-ring (see  FIGS. 2 and 3 ). The axially sealing region  66  is, in particular, configured in the form of a bead having a substantially rectangular cross-section, and preferably also has two opposite sealing surfaces that are in sealing contact with the housing upper part  210  and lower housing part  220 , and are compressed axially between the housing parts. In this case, the filter element seal  60  is composed of an O-ring and an axial seal, which are produced in combination. 
         [0092]    In the interior  12  of the filter medium  10 , a central tube  70  configured as a support element for the filter medium  10  may be arranged. The central tube supports the filter medium  10  and protects same against collapse. 
         [0093]    In order to ensure that the fluid flows through the filter medium  10  into the interior  12  of the filter medium  10 , the filter element  100  has another cover element  42 —in particular, another end plate  42 —on the end thereof that faces the oil outlet  230 . 
         [0094]    In order to seal off the post-filtration side of the filter element from the pre-filtration side of the filter element, another filter element seal  62 —configured, for example, as an O-ring—may be associated with the additional cover element  42 , in order to seal off the additional cover element  42  from the housing part  220 . This additional filter element seal  62  is preferably arranged radially outward on the additional cover element  42 . The cover element  42  is also preferably configured as an end plate, in particular, as an open end plate having a central opening for the oil drain. 
         [0095]      FIG. 9  illustrates an exploded view of the components of pressure control arranged in the upper housing part  210 . The sealing surface  52  is also a component of pressure control. Because the sealing surface  52  is arranged on the filter element  100 , the sealing surface is depicted in  FIG. 8 . 
         [0096]    The valve closing body  310  and the membrane  320  perform a vertical stroke movement in the pressure control (see  FIG. 9 ). In this vertical stroke movement, the valve closing body  310  and the membrane  320  are moved to the filter element  100  and away from the filter element. 
         [0097]    The components of pressure control illustrated in  FIG. 9  include:
       the pressure control element cover element  214 , which is configured to cover the first housing part  210  and has an opening to the atmosphere;   the valve closing body  310 ;   the membrane  320 ;   preferably at least one insert  350  that is arranged between the membrane  320  and the valve closing body  310  and is configured for pressure control;   the return spring  330 ; and   the first housing part  210 .       
 
         [0104]    The return spring  330  is arranged on the side of the valve closing body  310  that faces away from the valve seat  52 , and is supported down in the insert  350 , which preferably also has an opening. The return spring  330  is thus located on the atmosphere side. The valve closing body  310  preferably has at least one and particularly preferable—as is presently shown—three or four continuations  311  that protrude through at least one opening of the insert  350 . The return spring may thus preferably be axially mounted between the insert  350  and the continuation or continuations  311 , in particular, the hooks at the end of the continuations. In this manner, the return spring  330  can exert an opening force—in particular, a force oriented away from the sealing surface  52 —on the valve closing body. 
         [0105]      FIGS. 12 and 13  illustrate an embodiment of an oil separator  200 ′ of a crankcase ventilation system according to the prior art. The pressure control of this oil separator  200 ′ is located on the side of the second housing part  220 ′. The valve closing body  310 ′ has the form of a dish. The valve seat  52 ′ is here injection-molded onto the housing outside. The seal between the valve seat  52 ′ and the valve closing body  310 ′ happens hard to hard, in particular, through identical materials of the two components. This combination of identical materials of the valve seat  52 ′ and the region of the valve closing body  310 ′ that can be brought into contact with the valve seat  52 ′ negatively affects the sealing behavior. 
         [0106]    According to an advantageous embodiment, it is provided that the return spring  330  is located on the atmosphere side in the embodiment of the present invention illustrated in  FIGS. 1 to 11 . Preferably, the return spring is protected in a space formed by the membrane  320  and the valve closing body  310  on one side and by the pressure control valve cover element  214  on the other side. Arrangement on the outside of the fluid flow protects the spring against the influence of impurities that are contained in the fluid flow and are deposited on the spring. 
         [0107]    In contrast to the filter medium  100  illustrated in  FIGS. 2 and 3 , the fluid flows through the filter medium according to the prior art that is illustrated in  FIG. 12  from inside to the outside. The direction of flow of the fluid is marked with an arrow. 
         [0108]    Instead of a combination seal, the crankcase ventilation system illustrated in  FIG. 12  has two separated O-rings  60 ″ in order to seal the post-filtration side  240  of the filter element  100  off from the environment and seal the pre-filtration side  250  of the filter element  100  off from the post-filtration side  240  of the filter element  100 . 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           10  Filter medium, in particular, non-woven wrap 
           12  interior or cavity enclosed by the filter medium  10   
           20  direction of flow of the fluid to be filtered; in particular, direction of flow of the pre-filtration fluid  500  flowing through the filter medium  10 , in the present invention (see  FIGS. 2 and 3 ) 
           30  Covering surface of the filter medium  10   
           32  Outer surface of the filter medium  10   
           40  Cover element of the filter medium  10 ; in particular, end plate of the filter medium  10  that faces the clean fluid outlet  212   
           42  Additional cover element of the filter medium  10 ; in particular, end plate of the filter element  100  that faces the oil outlet  230   
           44  Fastening contour of the end plate  40  configured in order to fasten the sealing element  60   
           46  Support contour of the end plate  40  (see  FIG. 8 ) 
           50  Clean fluid discharge element; in particular, dome or nozzle configured in order to remove the clean fluid—for example, a tubular clean fluid discharge element 
           52  Sealing surface, in particular, valve seat of the filter element  100  of the present invention 
           52 ′ Valve seat in the prior art ( FIGS. 12 and 13 ) 
           60  Sealing element according to the present invention (see  FIGS. 2, 3, and 8 ); in particular, a filter element seal, for example, to seal the pre-filtration side of the filter element  100  off from the post-filtration side of the filter element  100 , and to seal the interior of the filter housing off from the environment; 
           60 ″ Second embodiment for a sealing element, in particular, for a filter element seal according to the prior art (see  FIG. 12 ) 
           62  Additional filter element seal; in particular, O-ring 
           64  Radially sealing region of the sealing element  60 ; in particular, a compressed region of the sealing element  60  within the filter housing 
           66  Axially sealing region of the sealing element  60 ; in particular, a compressed region of the sealing element  60  between the first housing part  210  and the additional housing part  220   
           70  Support element, in particular, central tube, of the filter element  100   
           100  Filter element; in particular, annular filter element, for example, replaceable filter element or exchangeable element 
           110  Longitudinal axis of the annular filter element  100  or the housing body  220  (see  FIG. 8 ) 
           120  Radius of the annular filter element  100  or the housing body  220  (see  FIG. 8 ) 
           130  Axis of rotation (see  FIG. 2 ) 
           200  Oil separator of the crankcase ventilation system of the present invention ( FIGS. 1 to 4, 9, and 10 ) 
           200 ′ Oil separator of the prior art ( FIGS. 12 and 13 ) 
           210  First or upper housing part of the oil separator  200 ; in particular, housing cover of the filter housing of the oil separator  200   
           212  Clean fluid outlet of the oil separator  200  of the present invention; in particular, clean fluid outlet of the first or upper housing part  210   
           212 ′ Clean fluid outlet of the oil separator of the prior art ( FIGS. 12 and 13 ) 
           214  Pressure control valve cover element 
           220  Additional, second, or lower housing part of the oil separator  200  of the present invention ( FIGS. 1 to 3 and 10 ); in particular, housing body of the filter housing of the oil separator  200   
           220 ′ Lower housing part of the oil separator  200 ′ of the prior art ( FIGS. 12 and 13 ) 
           222  Inlet for pre-filtration fluid, in particular, for oil-containing gas, for example, for oil-containing air, of the oil separator  200  of the present invention ( FIGS. 1, 2, and 4 ) 
           222 ′ Inlet for pre-filtration fluid, in particular, for oil-containing gas, for example, for oil-containing air, of the oil separator of the prior art ( FIGS. 12 and 13 ) 
           230  Oil outlet 
           240  Post-filtration space or post-filtration side of the filter element  100  of the present invention 
           240 ′ Post-filtration space or post-filtration side of the filter element according to the prior art (see  FIG. 12 ) 
           250  Pre-filtration space or pre-filtration side of the filter element  100  of the present invention 
           250 ′ Pre-filtration space or pre-filtration side of the filter element according to the prior art (see  FIG. 12 ) 
           310  Valve closing body, in particular, control pin, of the oil separator  200  of the present invention 
           310 ′ Valve closing body, in particular, control pin, of the prior art ( FIGS. 12 and 13 ) 
           311  Continuations; in particular, hook-shaped continuations which protrude upward from the valve closing body and with which the return spring  330  can engage, the continuations preferably being integral with the valve closing body 
           312  Contact surface of the valve closing body for contacting with the sealing surface  52  of the filter element  100 , in particular, in order to close the valve 
           320  Valve closing body sealing element; in particular, a membrane surrounding the valve closing body  320 , for example, a membrane extending between the valve closing body  310  and the first housing part  210   
           320 ′ Valve closing body sealing element of the prior art ( FIGS. 12 and 13 ) 
           330  Return spring of the oil separator  200  of the present invention 
           330 ′ Return spring of the prior art ( FIGS. 12 and 13 ) 
           340  Flow channel arranged between the valve closing body  310 , in particular, the valve closing body sealing element  320 , and the sealing surface  52   
           350  Insert configured for pressure control 
           410  Housing of the crankcase ventilation system 
           500  Pre-filtration fluid, in particular, oil-containing gas, for example, oil-containing air 
           510  Clean fluid, in particular, clean gas, for example, clean air 
           600  Force exerted through the pressure prevailing in the clean air outlet  212 , in particular, suction pressure, for example, suction vacuum pressure 
           610  Force exerted through the pressure prevailing in the interior  12  of the filter medium  10 , in particular, the crankcase pressure 
           620  Force exerted through the return spring  330   
           700  Range of the first control characteristic line where the slope thereof is dependent on the dimensions, in particular, on the area ratios A M /A D    
           702  Range of the second control characteristic line where the slope thereof is dependent on the dimensions, in particular, on the area ratios A M /A D    
           710  Point of intersection of the first control characteristic line with the Y-axis, which shows the pressure drop when the pressure control valve is open 
           712  Point of intersection of the second control characteristic line with the Y-axis, which shows the pressure drop when the pressure control valve is open 
           720  Inflection point of the first control characteristic line as a function of the compression spring or spring rate of the return spring  330   
           722  Inflection point of the second control characteristic line as a function of the compression spring of the return spring  330  or the spring rate of the return spring  330   
           800  Overpressure valve 
         A M  Cross-sectional area of the membrane  320   
         A D  Cross-sectional area of the inner diameter Ø D  of the sealing surface  52 , or the cross-sectional area of the inner diameter of the end surface of the clean fluid discharge element  50  facing away from the filter element  100   
         Ø M  Cross-section diameter of the membrane  320   
         Ø D  Cross-sectional inner diameter of the sealing surface  52  or inner diameter of the end surface of the clean fluid discharge element  50  facing away from the filter element  100