FILTER ELEMENT

Abstract

A filtering system may include a holder and an exchangeable filter element. The filter element may include a first end plate, a second end plate, and a filtering material arranged between the first end plate and the second end plate that separates a filtered zone from an unfiltered zone. The second end plate may protrude beyond the filtering material. The filtering system may further include at least one filtered opening and at least one unfiltered opening, and the at least one filtered opening may be disposed in the filter element. The filter element may lie detachably on the holder, and the holder together with the second end plate, the filtering material and an outer wall may enclose the unfiltered zone.

Claims

1. A filtering system for a motor vehicle, comprising: a holder and an exchangeable filter element, the filter element including a first end plate, a second end plate and a filtering material arranged between the first end plate and the second end plate that separates a filtered zone from an unfiltered zone; at least one filtered opening and at least one unfiltered opening, the at least one filtered opening disposed in the filter element, wherein the filter element lies detachably on the holder; at least the second end plate protrudes beyond the filtering material; the holder, the second end plate, the filtering material and an outer wall enclose the unfiltered zone; the unfiltered zone defined between the filtering material and the outer wall; the outer wall runs along a course of the filtering material; the outer wall runs transversely to the first end plate and the second end plate; and wherein one of: the outer wall is disposed securely on the second end plate, and the outer wall lies loosely on the holder; and the outer wall is disposed securely on the holder, and the outer wall lies loosely on the second end plate.

2. The filtering system according to claim 1, wherein the unfiltered zone has channel-shaped structure.

3. The filtering system according to claim 1, wherein the outer wall includes one or more recesses covered by a non-woven material.

4. The filtering system according to claim 1, wherein the outer wall has at least one interruption providing a receiving area and at least one receiving element is arranged in the at least one interruption.

5. The filtering system according to claim 1, wherein at least one of: the filter element further includes a front plate and the at least one filtered opening is disposed in the front plate; and the filter element has at least one further filtered opening disposed in the second end plate.

6. The filtering system according to claim 1, wherein at least one of: the filtering element further includes an intermediate wall, the intermediate wall extending between the outer wall and the filtering material in at least one of the unfiltered zone and the filtered zone, wherein the intermediate wall has a plurality of recesses; the filtering element further includes a pre-filter arranged in the unfiltered zone in front of the filtering material with respect to a flow direction, the pre-filter having a wall-shaped structure and one or more recesses covered with a non-woven material; and the filter element further includes an inner frame arranged in the filtered zone that supports the filtering material, the inner frame having a wall-shaped structure and one or more further recesses.

7. The filtering system according claim 1, wherein one of: the filtering material runs in a curved shape and at least partially encloses the filtered zone; and the filtering material runs in a straight line.

8. The filtering system according to claim 1, wherein: the filtering material of the filter element includes two parts; the two parts of the filtering material run adjacent to one another and enclose the filtered zone therebetween; and the unfiltered zone is divided in two and an external part of the unfiltered zone is associated with each of the two parts of the filtering material.

9. A method for the production of a filter element of a filtering system, comprising: providing a first end plate, a second end plate, and a filtering material arranged between the first end plate and the second end plate to separate a filtered zone from an unfiltered zone, wherein at least the second end plate protrudes beyond the filtering material; providing an outer wall extending along the filtering material between the first end plate and the second end plate, the outer wall extending transversely to the first end plate and the second end plate, wherein the unfiltered zone is defined between the filtering material and the outer wall, and wherein the outer wall is secured to one of the second end plate and a holder, and the outer wall lies loosely against the other of the second end plate and the holder; wherein providing the outer wall includes forming the outer wall from a functional strip; and joining the functional strip by plasticizing at least to the second end plate.

10. The method according to claim 9, further comprising at least one of: forming an intermediate wall from a further functional strip, the intermediate wall disposed between the outer wall and the filtering material; forming a pre-filter from a further functional strip, the pre-filter disposed in the unfiltered zone upstream of the filtering material; and forming an inner frame that supports the filtering material from a functional strip.

11. The method according to claim 9, wherein joining the joining the functional strip by plasticizing includes locally heating a first component at a connection site where a second component is to be connected to the first component until the first component is plastic, and then pressing the second component is onto the connection site the first component, and wherein the functional strip is one of the first component and the second component, and the second end plate is the other of the first component and the second component.

12. The method according to claim 9, further comprising at least one of: forming the functional strip with a pointed connection edges before the plasticizing with the second end plate; punching one or more recesses into the functional strip via a punching roller; and shortening a width of the functional strip.

13. The method according to claim 9, further comprising applying a non-woven material onto the functional strip by plasticizing.

14. The method according to claim 9, further comprising structuring the functional strip forming rollers.

15. The method according to claim 14, wherein structuring the functional strip includes impressing at least one of an undulation shape and a wedge shape on the function strip.

16. The filtering system according to claim 1, wherein the filter element is an air filter element for filtering air.

17. The filtering system according to claim 16, wherein the filter element further includes an intermediate wall extending between the outer wall and the filtering material in at least one of the unfiltered zone and the filtered zone, wherein the intermediate wall has a plurality of recesses.

18. The filtering system according to claim 16, wherein the filter element further includes a pre-filter arranged in the unfiltered zone upstream of the filtering material, the pre-filter having a wall-shaped structure and a plurality of recesses covered with a non-woven fabric.

19. The filtering system according to claim 16, wherein the filter element further includes an inner frame that supports the filtering material arranged in the filtered zone, the inner frame having a wall-shaped structure and a plurality of recesses.

20. The filtering system according to claim 2, wherein the channel-shaped structure has a rectangular cross-section and a curved shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] There are shown, respectively diagrammatically:

[0072] FIG. 1 a perspective illustration of a filter element according to the invention,

[0073] FIG. 2 a sectional illustration along the section plane A of FIG. 1 of a second variant of the filter element,

[0074] FIG. 3 a sectional illustration along the plane B through the filter element of FIG. 1,

[0075] FIG. 4 a sectional illustration along the section plane A of FIG. 1 of the second variant of the filter element, wherein additional optional elements are illustrated,

[0076] FIG. 5 a schematic diagram of a filtering system comprising a holder and the filter element,

[0077] FIG. 6 a sectional illustration along the plane A of FIG. 1 of the first variant of the filter element,

[0078] FIG. 7 a sectional illustration along the plane A of FIG. 1 of a third variant of the filter element,

[0079] FIG. 8 a perspective illustration of an unfiltered air connection with a non-woven material,

[0080] FIG. 9 a perspective view of an unfiltered air connection with a guide rib,

[0081] FIG. 10 a sectional illustration along a horizontal plane through the unfiltered air connection of FIG. 9,

[0082] FIG. 11 a perspective view of an outer wall with an unfiltered air connection inserted in the outer wall,

[0083] FIG. 12 a top view onto the outer wall of FIG. 13, to illustrate the connection between the unfiltered air connection and the outer wall,

[0084] FIG. 13 a perspective sectional illustration along a section plane of a second embodiment of a filter element according to the invention, corresponding to plane A of FIG. 1,

[0085] FIG. 14 a schematic diagram of a cut-out of a sectional illustration along a section plane, corresponding to plane B of FIG. 1, through the filter element of FIG. 13,

[0086] FIG. 15 a-e perspective basic illustrations of a functional strip, from which an outer wall, an intermediate wall, a pre-filter or an inner frame is formed,

[0087] FIG. 16 a cross-sectional illustration through a functional strip,

[0088] FIG. 17 a schematic illustration of the introduction of recesses into the functional strip,

[0089] FIG. 18 a schematic illustration of the application of a non-woven material onto the functional strip,

[0090] FIG. 19 a sectional illustration along a section plane of a third embodiment of a filter element according to the invention, corresponding to plane A of FIG. 1,

[0091] FIG. 20 a perspective sectional illustration of the filter element of FIG. 19,

[0092] FIG. 21 a perspective sectional illustration along a section plane of a fourth embodiment of a filter element according to the invention, corresponding to plane A of FIG. 1,

[0093] FIG. 22 a perspective sectional illustration along a section plane of a fifth embodiment of a filter element according to the invention, corresponding to plane A of FIG. 1,

[0094] FIG. 23 a perspective sectional illustration along a section plane of a sixth embodiment of a filter element according to the invention, corresponding to plane A of FIG. 1,

[0095] FIG. 24 a sectional illustration along a section plane of a seventh embodiment of a filter element according to the invention, corresponding to plane B of FIG. 1, and

[0096] FIG. 25 an illustration corresponding to FIG. 14, wherein the filter element has a curved outer wall with a dust discharge valve.

DETAILED DESCRIPTION

[0097] A filter element 10 illustrated in FIG. 1 is formed to be arranged for operation on a holder 44 of a filtering system 34. For this, the filter element 10 has a first end plate 12 and a second end plate 14, which are arranged substantially parallel to one another, a filtering material 16, which separates a filtered air zone 18 from an unfiltered air zone 20, and an outer wall 22, which at least partially surrounds the unfiltered air zone 20 and is held on the second end plate 14. In addition, the filter element 10 has a front plate 24, in which a filtered air opening 26 of the filter element 10 is arranged and which carries the filtered air connection 28. In addition, the filter element 10 has an unfiltered air opening 30, which is formed by an interruption 48 in the outer wall 22.

[0098] The outer wall 22 runs transversely, in particular perpendicularly, to the end plates 12, 14. The outer wall 22 can be formed as a separate component and can be connected with the second end plate 14. Alternatively, provision can be made that the outer wall 22 is formed integrally with the second end plate 14.

[0099] For the operation of the filtering system 34, the filter element 10 is placed against the holder 44 of the filtering system 34. The outer wall 22 then lies with a sealing element 23 against the holder 44, so that the holder 44 closes off here the unfiltered air zone 20. The holder 44 can be formed by a planar component. For example, the holder 44 can be formed by or on a bodywork part, a design cover, a housing cover, a cylinder head cover, an engine bonnet, an engine compartment rear wall or an oil sump.

[0100] In operation, unfiltered air is directed through the unfiltered air opening 30 into the filter element 10. Within the filter element 10, the unfiltered air must flow through the filtering material 16 and is thereby filtered. From the filtering material 16, filtered air enters accordingly into the filtered air zone 18 and can flow out through the filtered air opening 26 and, for example, can flow into a filtered air inlet of a filtering system 34, arranged at the filtered air connection 28.

[0101] The first end plate 12 and the second end plate 14 are constructed so as to be substantially flat and run substantially parallel to one another. The filtering material 16 is arranged between the two end plates and runs in a U-shape between the two end plates 12, 14. In this way, the filtering material 16 at least partially encloses the filtered air zone 18. At the open side of the U, the front plate 24 is arranged, which runs transversely, substantially perpendicularly, to the end plates 12 and 14 and connects the two end plates 12 and 14 with one another in this region, so that the filtered air zone is closed off by the front plate 24 in the region of the open U of the filtering material.

[0102] The front plate 24 has the filtered air opening 26, through which the air, filtered by the filtering material 16, can flow out from the filter element 10. In order to be able to direct the filtered air to the consumers, the front plate 24 has at the filtered air opening 26 a filtered air connection 28, to which the consumers can be connected directly or via a pipe.

[0103] Apart from in the front plate 24, the filter element 10 can have in addition further filtered air openings 26, for example in one of the end plates 12 or 14. The arrangement of the second filtered air opening 26 can take place alternatively or additionally, which means it is possible for example to have only one filtered air opening 26 either in one of the end plates 12, 14 or in the front plate 24, or both in the front plate 24 and also in one of the end plates 12 or 14 or even in both end plates 12 or 14. This can be expedient for example, if more than one consumer for filtered air is present. Otherwise, the flexible arrangement of the filtered air opening 26 offers great adaptation potential of the filter element 10 to given requirements.

[0104] Lying opposite the filtered air zone 18, in relation to the filtering material 16, the unfiltered air zone 20 is arranged, therefore outside the filtering material 16. The unfiltered air zone 20 is delimited by the second end plate 14, which protrudes beyond the filtering material 16, and delimits the holder 44. Toward the interior, the unfiltered air zone 20 is delimited by the filtering material 16 and toward the exterior the unfiltered air zone 20 is delimited by the outer wall 22. The outer wall 22 likewise runs substantially in a U-shape, therefore adapted to the course of the filtering material 16.

[0105] Here, the outer wall 22 has a distance from the filter material 16, in order to form the unfiltered air zone 20. In the region of the unfiltered air opening 30, the distance of the outer wall 22 to the filtering material 16 is greater than in regions which lie remote from the unfiltered air opening 30. As the unfiltered air zone 20 extends along the filtering material 16, through the unfiltered air zone 20 starting from the unfiltered air opening 30 at the beginning more unfiltered air must flow through the unfiltered air zone 20 than at the end of the unfiltered air zone 20. By the reducing distance between the outer wall 22 and the filtering material 16, the cross-section of the unfiltered air zone 20 also reduces according to the quantity of unfiltered air which flows through the unfiltered air zone 20, so that the flow resistance within the unfiltered air zone 20 varies less intensively than it would in the case of a constant cross-section of the unfiltered air zone 20.

[0106] In addition, in the unfiltered air zone 20 or filtered air zone 18 between the two end plates 12, 14 further elements can be arranged, for example a guide vane 36 by which the flow is influenced within the unfiltered air zone 20, in order to influence the loading of the filtering material 16 and/or to adjust this. Furthermore, one or more supporting domes 38 can be arranged between the end plates 12 and 14, in order to increase the stability of the filter element. Furthermore, it is possible to arrange one or more sensors 40, for example air mass or air quality sensors, in the filtered air zone 18 or unfiltered air zone 20. In addition, the possibility exists to provide for example a tension anchor 42, abbreviated to anchor 42, which draws the two end plates 12 and 14 to one another and therefore prevents oscillations of the two end plates 12 and 14. In addition, the anchor 42 can be used in order to hold the filter element 10 against the holder 44 of the filtering system 34.

[0107] Alternatively, the filter element 10 can also be held via the outer wall 22 on the holder 22. For example, detent lugs can be arranged on the outer wall 22, which engage in openings on the holder 44, or vice versa. In addition, the holder 44 can have grooves, into which the outer wall 22 can be inserted. Finally, a screwed connection or a clamping connection, for example with a bracket or a clamp, between the holder 44 and the outer wall 22 is also conceivable.

[0108] At the unfiltered air opening 30, the filter element 10 can have an unfiltered air connection 46, which is arranged for example in a recess, or interruption 48 of the outer wall 22. The unfiltered air connection 46 offers the possibility of the connection of further fluidic elements, for example of a pipe. The unfiltered air connection 46 has a cylindrical connection portion 50, to which for example a pipe can be connected. The connection portion 50 is arranged on a wall portion 51 which replaces the outer wall 22 within the interruption 48 of the outer wall 22.

[0109] In addition, at the unfiltered air connection 46 a guide rib 52 is arranged, which is arranged on a side of the wall portion 51 lying opposite the connection portion 50, and in the mounted state lies within the unfiltered air zone 20. To stabilize the filter element 10, provision can be additionally made that the guide rib 52 is connected to one or both end plates 12, 14. For example, the guide rib 52 can be connected to the end plates 12, 14 by plasticizing.

[0110] A connecting technique is designated as plasticizing in which one of the objects which is to be connected is heated at the connection site until the material becomes plastic, then the other object is pressed onto this connection site, so that the latter partially dips in and partially likewise becomes slightly plastic, so that a form-fitting and partially substance-bonded connection arises between the two objects.

[0111] Unfiltered air, which flows through the unfiltered air opening 30 in the unfiltered air connection 46 into the filter element 10, thereby impinges onto the guide rib 52, whereby the filtering material 16, which is arranged directly at the unfiltered air opening 30, can be protected from too intensive a loading.

[0112] The guide rib 52 can be held for example with telescopic cylinders 54 on the wall portion 51 of the unfiltered air connection 46. By the telescopic cylinders 54, the angle and the distance of the guide ribs 52 with respect to the filtering material 16 can be adapted, so that the unfiltered air connection 46 can be arranged in a variable manner at different locations in the outer wall 22 of the filter element 10. In particular, at locations with a different distance between outer wall 22 and filtering material 16. The telescopic cylinder can have fine ribs, which regulate a withdrawal force of the telescopic cylinders 54.

[0113] The connection from the unfiltered air connection 46, in particular of the wall portion 51 with the outer wall 22 is, for example a detent connection. Thus, for example, the unfiltered air connection 46 illustrated in FIGS. 8 and 9 has two detent lugs 53, which engage behind the outer wall 22, when the unfiltered air connection 46 is pushed from the exterior into the interruption 48 of the outer wall 22.

[0114] Alternatively hereto, for example as illustrated in FIGS. 11 and 12, the unfiltered air connection 46 can have connection elements 56 formed in a C-shape, which have a corrugation 85 on the inner side. Accordingly, the outer wall 22 is likewise corrugated. The corrugations 85 of the connection element 56 and of the outer wall 22 are oblique, so that the outer wall 22 can in fact push itself into the connection element 56, but a withdrawal of the outer wall 22 out from the connection element 56 is not possible, or is only possible with difficulty.

[0115] The guide rib 52 can be formed so as to be rigid or can be formed as a non-woven material, wherein then the guide rib 52 can lay itself against the filtering material 16.

[0116] In an alternative which is not shown, the unfiltered air connection 46 can also be held detachably on the outer wall 22 of the filter element 10. For example, the unfiltered air connection 46 can be held detachably by a screwed connection, a plug-in connection, clamping connection, a bracket or a clip connection on the filter element 10, in particular on the outer wall 22. In this alternative, provision can also be made that the guide rib 52 is held on at least one of the end plates 12, 14, instead of at the unfiltered air connection 46.

[0117] A second embodiment of the filtering system 34, illustrated in FIGS. 13 to 18, differs from the first embodiment of the filtering system 34 illustrated in FIGS. 1 to 12 in that the filter element 10 has further elements for improving or expanding the function of the filter element 10, as illustrated for example in FIG. 14.

[0118] Thus, for example, the filter element 10 can have an intermediate wall 58, which extends from the second end plate 14 to the holder 44 within the unfiltered air zone 20 and thereby subdivides the unfiltered air zone 20. On the intermediate wall 58 a sealing element 23 is arranged, which lies against the holder 44 when the filter element 10 is arranged on the holder 44.

[0119] The intermediate wall 58 has recesses 60, by which a connection is made possible between the two parts of the unfiltered air zone 20. Between the intermediate wall 58 and the outer wall 22, a resonator 62 is thereby formed, which can interact with the inner part of the unfiltered air zone 20 and can thereby reduce the noise development.

[0120] Furthermore, a pre-filter 64 can be arranged in front of the filtering material 16, which pre-filter has a plurality of recesses 66, which in turn are covered by an air-permeable medium, for example a non-woven material 68. The non-woven material 68 has coarser and/or larger pores here than the filtering material 16, so that the non-woven material 68 of the pre-filter removes coarser particles/dirt particles from the unfiltered air, before it flows through the filtering material 16. Thereby, the lifespan of the filter element 10 can be increased. Furthermore, the non-woven material 68 holds back drops of moisture.

[0121] In order to improve the stability of the filtering material 16, an inner frame 70 can be provided, which lies against the filtering material 16 on the side of the filtering material 16 facing the filtered air zone 18, in order to support the filtering material 16. For this, the inner frame 70 runs from the first end plate 12 up to the second end plate 14 and is connected to these two end plates 12, 14, so that the inner frame 70 can support the filtering material 16. So as not to impair the operation of the filter element 10, the inner frame 70 has recesses 72, through which the filtered air can flow through the inner frame 70 into the filtered air zone 18.

[0122] In a variant illustrated in FIG. 25, the outer wall 22 does not have a straight course between the second end plate 14 and the holder 44, but rather is curved outwards. The connection between the outer wall 22 and the second end plate 14 or respectively the holder 44, and to the intermediate wall 58 takes place here via clips 74, which hold together a flange-like projection of the outer wall 22 or of the holder 44 and the intermediate wall 58.

[0123] In the outer wall 22, a dust discharge valve 76 can be provided, by which dust, which was collected for example by the pre-filter 64 and has detached itself from the pre-filter 64, can be removed from the filter element 10. Furthermore, for example in the second end plate 14 a plug 78 can be provided, by which likewise dust or else water can be discharged from the filter element 10. The plug 78 is preferably constructed as a lip valve, which has lips which lie from the exterior on the filter element 10, so that the lip valve can open in the case of an excess pressure in the filter element 10. For example, the plug 78 opens in the case of a pressure pulsation at the pressure peaks, so that thereby dust and water can be automatically discharged from the filter element 10.

[0124] The outer wall 22, the intermediate wall 58, the pre-filter 64 and the inner frame 70 are preferably formed from a functional strip 80. The functional strip 80 is a plastic strip which is formed as an endless strip. Endless in this case means only very long, in particular the functional strip 80 is stored on rolls. The functional strip 80 therefore has a constant wall thickness and a constant width. Thereby, it is suitable both for the outer wall 22, for the intermediate wall 58, for the pre-filter 64 and the inner frame 70, because these elements have approximately the same height, because they run respectively from the first end plate 12 up to the second end plate 14, which run substantially parallel to one another.

[0125] The functional strip 80 can be modified respectively for the formation of the individual elements. For example, the functional strip 80 can be provided with reinforcement ribs 82, which for example give the outer wall 22 a greater stability and therefore give the filter element 10 a greater stability.

[0126] Alternatively or additionally hereto, provision can be made to impress an undulation and/or wedge shape on the functional strip 80. Thereby, also, the stability of the outer wall 22, formed from the functional strip 80, can be increased.

[0127] Furthermore, recesses 60, 66, 72, 83 can be introduced into the functional strip 80, in order to expand or enable the function of the individual elements. Thus, for example recesses 83 can be introduced in the outer wall 22, which in turn are covered by a non-woven material, so that condensation can flow out from the filter element through these recesses 83 in the outer wall 22. Furthermore, non-woven material can be applied onto the functional strip, in order for example to cover the recesses 66 of the pre-filter. This can take place for example by plasticizing or gluing.

[0128] Finally, the functional strip 80 can be provided with a corrugation 85, which increases both the rigidity of the functional strip and also enables a detent connection, for example to the unfiltered air connection 46.

[0129] The elements which are formed from the functional strip 80, therefore the outer wall 22, the intermediate wall 58, the filter 64 and the inner frame 70 are connected for example by plasticizing at least to the second end plate 14. In order to simplify or improve the plasticizing, the functional strip 80 can be pointed at a connection edge 84, by which the elements, which are formed from the functional strip 80, are arranged on the end plates 12, 14 (see FIG. 16).

[0130] The recesses 60, 66, 72, 83 can be introduced into the functional strip 80 by a punching roller 86, preferably by a variable punching roller 86. The non-woven material 68 can be pressed onto the functional strip 80 for example by a pressing roller 88. After the functional strip 80 has been heated, the functional strip 80 is plastic at least on the surface, so that the non-woven material 68 connects with the functional strip 80.

[0131] Otherwise, the second embodiment of the filtering system 34 illustrated in FIGS. 13 to 18 coincides with regard to structure and function with the first embodiment of the filtering system 34 illustrated in FIGS. 1 to 12, to the above description of which reference is to be made in this respect.

[0132] A third embodiment of the filtering system 34 illustrated in FIGS. 19 and 20 differs from the second embodiment of the filtering system 34 illustrated in FIGS. 13 to 18 in that the filtering material 16 is divided in two and runs in a straight line, wherein the filtered air zone 18 lies between the two parts of the filtering material 16, the two end plates 12, 14 of the front plate 24 and a back plate 100, which runs transversely to the two end plates 12, 14 and connects the first end plate 12 with the second end plate 14.

[0133] Thereby, the filter element 10 has two unfiltered air zones 20, separated from one another, which are arranged externally on both sides of the filtering material 16. The front plate 24 has, furthermore, the filtered air opening 26, through which filtered air from the filtered air zone 18 can flow out from the filter element 10. Furthermore, the front plate 24 has two unfiltered air openings 30, which belong respectively to one of the two unfiltered air zones 20 and through which unfiltered air can flow into the filter element 10.

[0134] It shall be understood that the unfiltered air openings 30 can also be arranged in the back plate 100, in the outer walls 22, and/or at an angle in the outer wall 22 and the end plates 12, 14. In addition, it shall be understood that the arrangement of the filtered air opening 26 is not restricted to the front plate 24.

[0135] Alternatively hereto, provision can also be made that unfiltered air zone 20 and filtered air zone 18 are exchanged. The filter element 10 would then have two filtered air zones 18, separately from one another, which can also have a different quality, if the two parts of the filtering material 16 are selected accordingly.

[0136] Otherwise, the third embodiment of the filtering system 34 illustrated in FIGS. 19 and 20 coincides with the second embodiment of the filtering system 34 illustrated in FIGS. 13 to 18 as regards structure and function, the above description of which is to be referred to in this respect.

[0137] A fourth embodiment of the filtering system 34 illustrated in FIG. 21 differs from the third embodiment of the filtering system 34 illustrated in FIGS. 19 and 20 in that the back plate 100 also has a filtered air opening 26, a filtered air connection 28 and two unfiltered air openings 30 with associated unfiltered air connections 46.

[0138] Otherwise, the fourth embodiment of the filtering system 34 illustrated in FIG. 21 coincides with the third embodiment of the filtering system 34 illustrated in FIGS. 19 and 20 as regards structure and function, the above description of which is to be referred to in this respect.

[0139] A fifth embodiment of the filtering system 34 illustrated in FIG. 22 differs from the fourth embodiment of the filtering system 34 illustrated in FIG. 21 in that the filter element 10 has only one unfiltered air zone 20 and one filtering material 16.

[0140] Alternatively or additionally hereto, provision can be made that in the filtered air zone 18 an intermediate wall can be arranged, which forms a resonator 62 between the intermediate wall and the outer wall 22.

[0141] Otherwise, the fifth embodiment of the filtering system 34 illustrated in FIG. 22 coincides with the fourth embodiment of the filtering system 34 illustrated in FIG. 21 with regard to structure and function, to the above description of which reference is to be made in this respect.

[0142] A sixth embodiment of the filtering system 34 illustrated in FIG. 23 differs from the fifth embodiment of the filtering system 34 illustrated in FIG. 22 in that a filtered air opening 26 and an unfiltered air opening 30 are arranged only in the front plate 24, and in that the unfiltered air zone 20 and the filtered air zone 18 taper in a wedge-shaped manner.

[0143] This is achieved in that the outer wall 22 at the unfiltered air zone 20 starting from the unfiltered air opening 30 up to the back plate 100 reduces the distance to the filtering material 16, and that the intermediate wall 58 likewise runs such that a distance from the intermediate wall 58 to the filtering material 16 reduces, starting from the unfiltered air opening 30 up to the back plate 100.