Abstract:
A flat filter element ( 34 ), a filter ( 10 ), and a support/positioning body ( 72, 74, 76 ) are disclosed. The flat filter element ( 34 ) includes a filter medium ( 64 ) with an inflow-side raw side ( 62 ) and an outflow-side clean side ( 58 ). An element sealing section ( 77 ) surrounds, circumferentially closed, the filter medium ( 64 ) on the raw side ( 62 ), the clean side ( 58 ), or between the raw side ( 62 ) and the clean side ( 58 ). The element sealing section ( 77 ) serves for supporting a sealing device ( 78 ) for sealing the raw side ( 62 ) relative to the clean side ( 58 ) upon arrangement of the flat filter element ( 34 ) in a filter housing ( 12 ) of the filter ( 10 ). At least one support/positioning body ( 72, 74, 76 ) can be supported, for positioning and holding at least the sealing device ( 76 ) in the filter housing ( 12 ), on the one hand at least on the sealing device ( 78 ) and on the other hand on the filter housing ( 12 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119 of German patent application No. 10 2012 019 320.3 filed Oct. 2, 2012, and which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The invention concerns a flat filter element of a filter for fluids, in particular air, fuel, oil, or water, in particular of an internal combustion engine, in particular of a motor vehicle, comprising a filter medium with an inflow-side raw side and an outflow-side clean side and with an element sealing section that surrounds, circumferentially closed, the filter medium on the raw side, the clean side, or between the raw side and the clean side for supporting a sealing device for sealing the raw side relative to the clean side upon arrangement of the flat filter element in a filter housing of the filter. 
     Moreover, the invention concerns a filter for fluids, in particular air, fuel, oil, or water, in particular of an internal combustion engine, in particular of a motor vehicle, comprising a flat filter element with a filter medium with an inflow-side raw side and an outflow-side clean side and with an element sealing section that surrounds, circumferentially closed, the filter element at the raw side, the clean side, or between the raw side and the clean side for supporting a sealing device for sealing the raw side relative to the clean side upon arrangement of the flat filter element in a filter housing of the filter. 
     Moreover, the invention concerns a support device of the filter for fluids, in particular air, fuel, oil, or water, in particular of an internal combustion engine, in particular of a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     An air filter of an internal combustion engine of a motor vehicle known in the market has a filter housing in which a flat filter element is arranged. The filter housing comprises a filter cup and a filter cover that can be separated from the filter cup. The flat filter element comprises a filter medium which is folded in a zigzag shape to a filter bellows. The filter bellows has approximately the shape of a parallelepiped. In flat filter elements, the filter media are not closed, i.e., end face folds, like end face edges, are not connected to each other. In contrast thereto, in round filter elements the filter media are closed, i.e., their end face folds are connected to each other. The end face folds are the two outermost folds on opposite end faces of the filter bellows. End face rims are the two free rims of the filter medium which extend along the end face folds and delimit them at the end faces of the filter bellows. The end face edges of the filter bellows are the two other free rims of the filter bellows which extend between the end face rims and extend in accordance with the folding of the filter bellows. The fold edges are those edges along which the filter medium is folded. In the zigzag-shaped folded parallelepipedal filter bellows, the end face rims and the fold edges are straight and extend parallel to each other. The end face edges extend in a zigzag shape and perpendicular to the end face rims and the fold edges. On a sealing rim of the filter bellows that surrounds the inflow side, a seal of polyurethane (PUR) is arranged. The seal surrounds, circumferentially closed, the inflow side relative to an imaginary central axis of the sealing rim. The seal projects past the filter bellows relative to the central axis in radial direction outwardly. The flat filter element is axially inserted relative to the central axis into the filter cup. The filter cup has a sealing surface which relative to the central axis extends in radial direction outwardly and on which a side of the seal of the flat filter element in axial direction is resting seal-tightly. The filter cover has also a sealing surface which relative to the central axis extends in radial direction outwardly. When the filter cover is mounted, its sealing surface in axial direction is resting seal-tightly on the side of the seal that is positioned opposite the sealing surface of the filter cup. The seal of the flat filter element is then tightly clamped between the sealing surfaces of the filter cover and the sealing surface of the filter cup. In this way, the seal seals the inflow-side raw side of the flat filter element from the outflow-side clean side. Thus, on the filter head and on the filter cover a sealing surface is required, respectively. The two sealing surfaces must be arranged such that they can interact with each other for compressing the seal. 
     The object of the invention is to configure a flat filter element, a filter, and a support device of the aforementioned kind with which the expenditure for realizing a sealing action of the raw side relative to the clean side can be reduced. In particular, the expenditure with regard to required sealing surfaces is to be reduced. Moreover, penetration of leak air is to be prevented. 
     SUMMARY OF THE INVENTION 
     An This object is solved according to the invention by at least one support/positioning body which, for positioning and securing at least the sealing device within the filter housing, can rest, on the one hand, at least on the sealing device and, on the other hand, on the filter housing. 
     According to the invention, at least one support/positioning body is thus provided which is arranged on the flat filter element and with which the sealing device is positioned and secured in the filter housing. The at least one support/positioning body can be arranged fixedly or detachably on the flat filter element, in particular the filter medium. In this connection, the at least one support/positioning body takes on the support function of one of the housing-associated sealing surface of the prior art filter. In this way, this housing-associated sealing surface can be eliminated. With the at least one support/positioning body the sealing device can be secured in an optimal position in the filter housing. Advantageously, with the at least one support/positioning body the entire flat filter element can be additionally secured in an optimal position in the filter housing. The at least one support/positioning body can serve as a counter bearing in order to be able to press the sealing device against an appropriate housing sealing surface of the filter housing. The at least one support/positioning device with its side that is facing away from the element sealing section can be supported, in turn, on the housing. The element sealing section can advantageously be a rim that surrounds the raw side or the clean side of the filter medium, in particular of a filter bellows. Alternatively, the element sealing section can be located between the raw side and the clean side of the filter medium. An appropriate support location of the housing is located can be separate in this context from the housing sealing device, in particular, can be remote from it. Advantageously, the sealing device can have at least one seal which can be supported on the element sealing section and a corresponding housing sealing surface of the filter housing. The sealing device can also have a combination of several seals of which one can be supported on the element sealing section and can be supported on the housing sealing surface. Advantageously, the at least one seal can be made of PUR. PUR seals are elastic and can be compressed easily. In this way, the sealing action can be increased. Moreover, seals of PUR can be easily realized. In particular, a PUR seal can be integrally attached by injection molding or foaming to the element sealing section of the filter medium. The at least one seal can advantageously have a sealing lip. Advantageously, the sealing device can have at least one seal that is acting axially relative to the central seal axis, a so-called axial seal. The axial seal can be supported with one side seal-tightly on the housing sealing surface of the filter housing. In addition or alternatively, the sealing device can have a seal that is acting radially relative to the central axis, a radial seal. The radial seal can seal accordingly in radial direction against an appropriate housing sealing surface of the filter housing. The at least one seal can also be designed as a seal that acts radially and axially. The central seal axis is an imaginary axis which is extending through the inflow side and the outflow side of the filter medium when the sealing device is mounted. When the seal has a rectangular profile and extends in a plane, the central seal axis corresponds to an imaginary axis through the center point of this rectangular profile. When the element sealing section has a rectangular profile and extends in a plane, the central element axis corresponds to an imaginary axis through the center point of this rectangular profile. The central element axis intersects the inflow side and the outflow side of the filter medium. The central seal axis and/or the central element axis may coincide with a central axis of the filter or can realize it. The central axis of the filter can also be a mounting axis along which the flat filter element is inserted into the filter housing. The sealing device can be connected fixedly with the element sealing section of the flat filter element. Also, a sealing device can be provided that is detachably arranged on the element sealing section. The element sealing section for this purpose can have an appropriate element sealing surface on which the sealing device is resting seal-tightly. In addition or alternatively, the sealing device can be fixedly or detachably connected with the at least one support/positioning body. Advantageously, the at least one support/positioning body can have at least one elongate support leg which can be arranged in a space-saving way in the filter housing. Advantageously, the at least one support/positioning body can directly or indirectly support the sealing device. The at least one support/positioning body can thus transmit a support force from an appropriate stop of the filter housing directly onto the sealing device. Advantageously, several support/positioning bodies can be arranged so as to be circumferentially distributed; they transmit their support forces, respectively, onto the sealing device and/or the element sealing section. 
     In an advantageous embodiment, the at least one support/positioning body can extend at least axially to a central axis of the filter. The at least one support/positioning body can advantageously be supported on an appropriate stop on a side of the housing opposite the sealing device. The at least one support/positioning body can thus press the sealing device against the housing sealing surface of the filter housing. In this way, a force transmission onto the sealing device can be improved. Moreover, in this way a compression of the sealing device between the at least one support/positioning body and the housing sealing surface can be improved. Also, in this way by means of the at least one support/positioning body the sealing device can be positioned and secured precisely and safely in the filter housing. The at least one stop for the at least one support/positioning body in the filter housing can be arranged on a bottom of the filter housing, in particular of a filter cup. Alternatively, or in addition, appropriate stops, in particular in the form of projections, can be arranged also on the sidewalls of the filter housing onto which the at least one support/positioning body can be placed. 
     In a further advantageous embodiment, the at least one support/positioning body can project past the filter medium at least on one side, when viewed axially relative to the center axis of the filter. In this way, an appropriate stop for the at least one support/positioning body in the filter housing can be spaced relative to the filter medium. In this way, advantageously the at least one support/positioning body can be supported on a housing wall that is positioned opposite the filter medium and which delimits with the appropriate side, i.e., the inflow side or outflow side, of the filter medium an outlet space or inlet space for the fluid. 
     Advantageously, at least two support/positioning bodies can be provided that, viewed axially to a central axis of the filter, have different lengths. In this way, the at least two support/positioning bodies can be supported on appropriate stops of the filter housing which can be positioned at different spacings relative to the filter medium. In this way, also different axial lengths of the filter housing relative to the central axis can be compensated. Advantageously, the at least two support/positioning bodies can thus be supported on a stepped wall, in particular a stepped bottom, of the filter housing. 
     In a further advantageous embodiment, a circumferentially extending support frame on which the at least one support body can be supported can be provided at least for the sealing device. Advantageously, the support frame can be integrated into the sealing device, in particular embedded in at least one seal. Preferably, the support frame can be made of plastic material. It can also be of a different type of material. The support frame can advantageously be embedded in sealing material by casting, injection molding, or foaming. Preferably, the at least one support/positioning body and the support frame can be fixedly connected to each other, preferably as a single piece. With the support frame, the sealing device can be stabilized circumferentially. Pressing forces of the at least one support/positioning body can be distributed with the support frame circumferentially uniformly onto the sealing device. Accordingly, the uniform circumferential sealing action can be improved. Advantageously, the support frame can support and/or stabilize additionally the filter medium. 
     In a further advantageous embodiment, the flat filter element can be exchangeably arranged in the filter housing that is of at least a two-part configuration. In this way, the flat filter element, as needed, in particular for servicing purposes or for cleaning, can be removed easily from the filter housing. A filter housing of at least two parts can be easily opened in that the housing parts are at least partially separated from each other. Advantageously, upon separation of the at least two housing parts, a mounting opening can be opened into which the flat filter element along the mounting axis, preferably axial to the central element axis, can be inserted. Advantageously, the filter element can be arranged such within the filter housing of at least two parts that the at least one support/positioning body with a side facing away from the element sealing section is supported on one of the housing parts and the housing sealing surface of the filter housing is arranged on another one of the at least two housing parts. Advantageously, the filter housing can have a housing cup and a housing cover. A housing sealing surface can advantageously project past an inflow-side or outflow-side filter surface of the filter medium radially relative to the central element axis. In this way, the outer dimensions of the filter housing, in particular in areas in which the filter surface, as a result of the seals or adhesive connections arranged thereat, cannot be flowed through anyway, can be tapered. In this way, the mounting space required for the filter can be reduced. 
     The technical object is solved moreover for the filter by at least one support/positioning body that, for positioning and securing at least the sealing device in the filter housing, can be supported on the one hand at least on the sealing device and on the other hand on the filter housing. The features and advantages that have been explained above in connection with the filter element according to the invention apply likewise to the filter according to the invention and its advantageous embodiments. 
     The technical object is moreover solved by the support device that can be arranged for positioning and securing a sealing device in a filter housing on a flat filter element of the filter. The features and advantages that have been explained above in connection with the flat filter element according to the invention and the filter according to the invention apply likewise to the support/positioning body according to the invention and its advantageous embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features, and details of the invention result from the following description in which embodiments of the invention will be explained in more detail with the aid of the drawing. A person of skill in the art will consider the features disclosed in combination in the drawing, the description, and the claims also expediently individually and combine them to meaningful further combinations. It is shown schematically in: 
         FIG. 1  a longitudinal section of an air filter of an internal combustion engine with a flat filter element according to a first embodiment that is arranged exchangeably/replaceably in an air filter housing; 
         FIG. 2  the air filter of  FIG. 1  wherein the open air filter housing is shown without the filter housing cover; 
         FIG. 3  an isometric illustration of a flat filter element according to a second embodiment which is similar to the flat filter element of  FIGS. 1 and 2 ; 
         FIG. 4  an isometric illustration of a support device of the flat filter element of  FIG. 3 ; 
         FIG. 5  a detail section view of the flat filter element of  FIG. 3 ; 
         FIG. 6  a longitudinal section of a flat filter element according to a third embodiment which is similar to the flat filter elements of  FIGS. 1 through 5 ; and 
         FIG. 7  a longitudinal section of a flat filter element according to a fourth embodiment which is similar to the flat filter elements of  FIGS. 1 to 6 . 
     
    
    
     In the Figures same components are identified with same reference characters. 
     DETAILED DESCRIPTION 
     In  FIG. 1  an air filter  10  of an internal combustion engine of a motor vehicle is shown in longitudinal section. The air filter  10  can be arranged in an intake manifold of the internal combustion engine. With the air filter  10  intake air of the internal combustion can be purified. 
     The air filter  10  comprises an air filter housing  12  that is rectangular in profile. The air filter housing  12  is combined of the housing cup  14 , in  FIG. 1  at the bottom, and a housing cover  16 , at the top. The housing cup  14  as well as the housing cover  16  each have an approximately rectangular cross-section. Flows of the air to be purified into the air filter housing  12  and within the air filter housing  12  and of the purified air from the air filter housing  12  are indicated by arrows  17  in  FIG. 1 . 
     A bottom  18  of the housing cup  14  is stepped multiple times. The bottom  18  in the normal mounting position of the air filter  10 , as illustrated in  FIG. 1 , is spatially at the bottom. In a lower section of the bottom  18 , an inlet  20  for the air to be purified is arranged. The inlet  20  is connected outside of the air filter housing  12  to a line section of the intake manifold of the internal combustion engine. 
     On a respective transition of two adjoining oppositely positioned sidewalls  26  of the housing cup  14  and  28 , the bottom  18  has a recess  22  and  24 , respectively. The recesses  22  and  24  each extend along the respective sidewalls  26  and  28 . Between the recesses  22  and  24 , the bottom  18  has a central recess  30  which is adjacent to a step of the bottom  18  and extends parallel to the recesses  22  and  24 . The recesses  22 ,  24 , and  30  each are approximately U-shaped in profile. The width of the central recess  30  is greater than the respective width of the two lateral recesses  22  and  24 . The axial spacing between the upper lateral recess  22  and a rim  36  of the housing cup  14  is smaller than the axial spacing between the lower lateral recess  24  and the rim  36 . When “axial”, “radial”, “coaxial” or “circumferential” is mentioned, this refers to the imaginary filter axis  38 , if nothing else is indicated. The axial spacing between the central recess  30  and the rim  36  is, with respect to its magnitude, between the respective axial spacing of the lateral recess  22  and the rim  36  and the lateral recess  24  and the rim  36 . 
     On the side that is facing the housing cover  16 , the housing cup  14  has a mounting opening  32  for a flat filter element  34  that is arranged exchangeably/replaceably in the filter housing  12 . The rim  36  of the housing cup  14  which surrounds the mounting opening  32  is flat on the side which is facing the housing cover  16  and is circumferentially closed. In the area of the rim  36 , the radial inner circumferential surfaces of the sidewalls  26  and  28  and of the two other sidewalls  39  of the housing cup  14  are designed as a radial sealing surface  40 . In  FIG. 1 , as a result of the longitudinal section, only the rearwardly positioned one of the two other sidewalls  39  is visible. 
     The housing cover  16  is open at the side which is facing the housing cup  14 . On its rim which is facing the housing cup  14  the sidewalls  42  and  44  and the two other sidewalls  45  of the housing cover  16  connecting the sidewalls  42  and  44  are each bent by  90 ° in radial outward direction to a sealing section  46  of a housing sealing device  48 . The sidewalls  42  and  44  each extend parallel to the sidewalls  26  and  28  of the housing cup  14 . The sidewalls  45  each extend parallel to the sidewalls  39  of the housing cup  14 . The sealing section  46  has a radially outwardly extending housing sealing surface  50  which is circumferentially closed. Radially outwardly, the housing sealing surface  50  is surrounded by a receiving section  52  which extends axially away from a closed side of the housing cup  14  and is circumferentially closed. A spacing between the radial outer circumferential sides of the sidewalls  26  and  28  of the housing cup  14  is smaller than a spacing between the radial inner circumferential sides of the receiving section  52  at the oppositely positioned sidewalls  42  and  44  of the housing cover  16 . A spacing between the radial outer circumferential sides of the sidewalls  39  of the housing cup  14  is smaller than a spacing between the radial inner circumferential sides of the receiving section  52  on the respective oppositely positioned sidewalls  45  of the housing cover  16 . In the assembled air filter housing  12 , as shown in  FIG. 1 , the radial inner circumferential side of the receptacle  52  is resting on the radial outer circumferential side of the housing cup  14 . The housing sealing surface  50  is located on the side of the sealing section  46  that is facing the housing cup  14 . 
     In the side wall  42  of the housing cover  16 , an outlet  54  for purified air is also arranged which is connected outside of the air filter housing  12  with a line section of the intake manifold of the internal combustion engine. 
     An interior of the housing cover  16  forms an outlet space  56  for the air to be cleaned. The outlets space  56  adjoins a clean side  58  of the flat filter element  34 . The interior of the housing cup  14  forms an inlet space  60  for the purified air. The inlet space  60  adjoins a raw side  62  of the flat filter element  34 . The flat filter element  34  is arranged in the inlet space  60  such that it separates the outlet  54  from the inlet  20 . 
     The flat filter element  34  has a filter bellows  63  of a zigzag-shaped filter medium  64 . The filter medium  64  is a nonwoven filter material. The filter medium  64  as a whole is of a parallelepipedal shape. The filter medium  64  of the flat filter element  34  is not closed, i.e., neither end face folds nor the end face edges are connected to each other. The end face folds are the two outer folds on opposite end faces of the filter bellows  63 . The end face rims are the two free rims of the filter medium  64  which extend along the end face folds and delimit them at the end faces of the filter bellows  63 . The end face edges of the filter bellows  63  are the two other free rims of the filter bellows  63  which extends between the end face rims and extend in accordance with the folding of the filter bellows  63 . The fold edges are the edges along which the filter medium  64  is folded. In the zigzag-shaped folded parallelepipedal filter bellows  63  the end face rims and the fold edges are straight and extend parallel to each other. The end face edges extend in a zigzag shape and perpendicular to the end face rims and the fold edges. The end face edges of the filter medium  64  are sealed tightly by glue beads. Fold edges of the filter medium  64  at the outflow side are located at the clean side  58 , in  FIG. 1  at the top. Inflow-side fold edges of the filter medium  64  are located at the raw side  62 , in  FIG. 1  at the bottom, in the inlet space  60 . 
     On the flat filter element  34  a support device  66  is arranged. The support device  66  comprises four corner support legs  72  and  74  and two central support legs  76 . The corner support legs  72  and  74  each are arranged radially outwardly on the lateral edges of the filter bellows  63  that extend axially to the filter axis  38 . The corner support legs  72  and  74  each have an approximately L-shaped profile. They engage the edges of the filter bellows  63  which extend in axial direction. The radial inner circumferential sides of the corner support legs  72  and  74  are resting on the radial outer circumferential side of the filter bellows  63 . From the top side of the filter bellows  63  that is facing the housing cover  16 , the corner support legs  72  and  74  extend in axial direction relative to the filter axis  38  away from the filter medium  64  to the bottom  18  of the housing cup  18 . On their free ends facing away from the filter medium  64  the corner support legs  72  and  74  are each bent by approximately 90° in radial outward direction. In this way, the support surface of the corner support legs  72  and  74  is enlarged at their free ends. The corner support legs  72 , axially viewed, are shorter than the corner support legs  74 . When the flat filter element  34  is mounted, the free ends of the short corner support legs  72  are supported in the upper lateral recesses  22 . The free ends of the long corner support legs  74  are supported in the lower lateral recess  34 . 
     On the sides of the flat filter element  34  which are facing the rear lateral wall  49  and the front lateral wall, respectively, one of the central support legs  76  is arranged, respectively. The central support legs  76  are each planar and elongate in axial direction. The radial inner circumferential sides of the central support legs  76  each are resting on the radial outer circumferential side of the filter bellows  63 . They extend in axial direction to the bottom  18  of the housing cup  14 . On their free ends which are facing away from the filter medium  64 , the central support legs  76  are each bent by approximately 90° in radial direction outwardly. In this way, the support surface of the central support legs  76  is enlarged at their free ends. The axial length of the central support legs  76  is greater than that of the short corner support legs  72  and shorter than that of the long corner support legs  74 . The central support legs  76  are flush with the top side of the filter bellows  63  facing the housing cover  16 . The central support legs  76  each are supported with their free ends in the central recesses  30  in the bottom  18 . 
     At the clean side  58 , the sealing section  46  of the housing cover  16  with the housing sealing surface  50  projects past the filter bellows  63  in radial inward direction. An axial extension of the corner support legs  72  and  74  and of the central support legs  76  is located within the housing sealing surface  50 , respectively. 
     On the top side of the filter bellows  63  a seal  68  of polyurethane (PUR) is arranged. The seal  68  surrounds, circumferentially closed, the filter bellows  63  on the clean side  58 . The seal  78  projects past the filter bellows  63  in axial direction and in radial direction. The ends of the corner support legs  72  and  74  and of the central support legs  76  provided thereat are embedded in the seal  68 . The areas of the filter bellows  63  on which the seal  78  is resting form an element sealing section  77 . 
     In the first embodiment and the further embodiments to be explained in the following, a central element axis of the flat filter element  34 , a central axis of the element sealing section  77 , and a central seal axis of the seal  68  coincide with the filter axis  38  when the flat filter element  34  is mounted so that, for reasons of simplification, in the Figures only one axis  38  in dashed line is indicated for showing the central element axis, the filter axis, the central axis of the element sealing axis section  77 , and the central seal axis of the seal  68 . 
     For mounting the air filter  10 , the flat filter element  34  is inserted, with the free ends of the corner support legs  72  and  74  and of the central support legs  76  leading, in axial direction relative to the filter axis  34  into the housing cup  14 . In the present embodiments, a mounting axis along which the flat filter element  34  is installed into the filter housing  12  coincides also with the filter axis  34 . Upon installation, the flat filter element  34  is oriented such that the long corner support legs  74  are located on the side of the lower recess  24  and the short corner support legs  72  are located on the side of the upper recesses  22  of the housing cup  14 . The bases of the recesses  22 ,  24 , and  30  act as stops for the corner support legs  72  and  74  and the central support legs  76 , respectively. The seal  78  projects in this assembly phase, as indicated in  FIG. 2 , past the rim  36  of the housing cup  14  in axial direction. In this assembly phase, the radial outer circumferential side of the seal  78  is still positioned at a spacing relative to the radial sealing surface  40  of the housing cup  14 . The filter bellows  63  and the seal  78  are positioned and secured by means of the corner support legs  72  and  74  and the central support legs  76  in the housing cup  14 . Subsequently, the housing cover  16  is placed axially relative to the filter axis  38  onto the housing cup  14 . In this connection, the receiving section  52  engages the rim  36  of the housing cup  14 . The seal  78  is compressed by means of the sealing section  46  with the housing sealing surface  50  in axial direction. In this context, the corner support legs  72  and  74  and the central support legs  76  act as counter bearings. Because of the axial compression, the seal  78  is deformed in radial outward direction so that it is also resting seal-tightly on the radial sealing surface  40 . In this way, the seal  78  realizes an axial sealing action as well as a radial sealing action. The seal  68  forms a sealing device for sealing the clean side  58  relative to the raw side  62 . The housing cover  16  is secured on the housing cup  14  in a way that is not of interest in this context. 
     In  FIGS. 3 to 5  a second embodiment of the flat filter element  134  is illustrated. Those elements that are similar to those of the first embodiment of  FIGS. 1 and 2  are identified with the same reference characters with  100  being added. The second embodiment differs from the first embodiment in that in the second embodiment the support device  166  is provided additionally with a support frame  168 . The support frame  168  is arranged on the side of the filter bellows  163  which is facing the housing cover  116 . It projects past the filter bellows  163  in radial direction outwardly. The support frame  168  overlaps the filter bellows  163  on its clean side  158  in radial direction. In the support frame  168  a plurality of through openings  170  is distributed circumferentially. On the corners of the support frame  168  one of the support legs  172  and  174  is arranged, respectively. In contrast to the first embodiment of  FIGS. 1 and 2 , the two central support legs  176  have different axial lengths. The short central support leg  176  is located between the two short corner support legs  172 . The long central support leg  176  is located between the two long corner support legs  174 . The corner support legs  172  and  174  and the central support legs  176  terminate flush with the support frame  168  and are connected monolithically therewith. The corner support legs  172  and  174  and the central support legs  176  extend away from the support frame  168  in axial direction. By means of the support frame  168  the force introduction of the corner support legs  172  and  174  and of the central support legs  176  is uniformly distributed circumferentially onto the seal  178 . 
     When producing the flat filter element  134 , the folded filter medium  174  is arranged in the support device  166  such that the clean side  158  of the filter bellows  63  is resting on the support frame  168 . Subsequently, the seal  168  is realized by foaming or injection molding PUR foam onto the support frame  168 . When doing so, the PUR foam flows through the openings  170  and bonds within the element sealing section  177  with the filter medium  164 , as shown in  FIG. 5 . The support frame  168  is thus embedded partially into the seal  168 . 
     In  FIG. 6 , a third embodiment of a flat filter element  234  is illustrated. Those elements that are similar to those of the second embodiment of  FIGS. 3 to 5  are provided with the same reference characters, with  100  being added. The third embodiment differs from the second embodiment in that corner support legs at the axial edges of the filter bellows  263  and the corners of the support frame  268  are eliminated. Instead, on each side of the filter bellows  263  extending in axial direction, two central support legs  276  are arranged. In contrast to the second embodiment of  FIGS. 3 to 5 , the support frame  268  in the third embodiment is not arranged on the ends of the central support leg  276  but in an area between the ends of the central support legs  276 . The central support legs  276  project thus past the support frame  268  on both sides in axial direction. The support frame  268  is located on the raw side  262  of the filter bellows  263 . On the side facing the filter bellows  263  the support frame  268  is of a groove-shaped configuration. In the groove a circumferentially closed medium seal  280  is arranged. The medium seal  280  seals an element sealing section  277  of the filter bellows  263  relative to the support frame  268 . The ends of the central support legs  276  on the clean side  258  are embedded in the seal  278 . The seal  278  is located, viewed axially relative to the filter axis  238 , at the level of a central area of the radial outer circumferential sides of the filter bellows  263 . The seal  278  and the medium seal  280  form together a sealing device for sealing the clean side  258  relative to the raw side  262 . 
     In  FIG. 7 , a fourth embodiment of a flat filter element is illustrated. Those elements that are similar to those of the second embodiment of  FIGS. 3 to 5  are provided with the same character, with  200  being added. The fourth embodiment differs from the second embodiment in that the filter bellows  363  is arranged on the side of the support frame  368  which is opposite the central support legs  376 . In the fourth embodiment of  FIG. 7 , as in the third embodiment of  FIG. 6 , corner support legs are not provided. Instead, on each side of the filter bellows  363  extending in the axial direction, two central support legs  376  are arranged, respectively. The support frame  363  has a groove  382  which is open toward the filter bellows  363 . The seal  378  is located in the groove  382 . The central support legs  376  have different axial lengths and can thereby compensate corresponding steps of the bottom of the housing cup. The support frame  368  overlaps the filter bellows  363  radially inwardly so that the filter bellows  363  with its raw side  362  is resting on the support frame  368  and a radial inner section of the seal  378 . When the flat filter element  334  is mounted, the filter bellows  363  is located within the housing cover. 
     In all of the above described embodiments of an air filter  10  and of a flat filter element  34 ;  134 ;  234 ;  334  inter alia the following modifications are possible. 
     The invention is not limited to air filters  10  of internal combustion engines of motor vehicles. Instead, it can also be used outside of automotive technology, for example, in industrial motors. The invention is also not limited to filters for air. For example, it can be used also for filters for different fluids, for example, oil, fuel, or water. It can also be used independent of internal combustion engines, for example, in an air supply device of a passenger compartment of a motor vehicle, for example, of an air conditioning device. 
     The radial sealing surfaces  40  on the housing cup  14  can also be eliminated. 
     The filter medium  64 ;  164 ;  264 ;  364  instead of being folded in a zigzag shape can also be flat. Instead of a nonwoven, a different kind of filter medium, for example, a type of foam material, can be used also. 
     The filter bellows  63 ;  163 ;  263 ;  363  instead of being flat can also be bent. Instead of being parallelepipedal, it can also be shaped differently. For example, it can have the shape of a different type of polyhedron or a different type of body that is delimited by at least one curved surface. 
     In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.