Air filters and the use of filter elements in air filters

Abstract

The present invention relates to an air filter (10) comprising two filter elements (20, 26), each of which is designed as a planar filter element and includes a filter medium body (48) having an inlet face (22, 28) and an outlet face (24, 30), a filter housing (12) in which the two filter elements (20, 26) are arranged, and a filter housing (12) for selectively directing a filtered air flow through the two filter elements (20, 26) in succession or at least partially bypassing the second of the filter elements (26). and a fluid guide device (32) as described above, wherein an outlet surface (24) of a first filter element (20) among the filter elements and an inlet surface (28) of a second filter element (26) among the filter elements are spaced apart from each other to form an expanding bypass passage (36), and a filter medium body (48) of at least one of the filter elements (20, 26) has an inherently varying height, such that the height of the filter medium body (48) of at least one of the filter elements (20, 26) decreases as the width of the bypass passage (36) increases.

Description

[Technical Field]

[0001] The present invention provides an air filter, two filter elements, each designed as a planar filter element and including a filter medium body having an inlet face and an outlet face; a filter housing in which two filter elements are disposed; a fluid guide device for selectively directing the airflow to be filtered through the two filter elements in series or at least partially bypassing the second of the two filter elements; The air filter includes an outlet flow surface of a first one of the filter elements and an inlet flow surface of a second one of the filter elements spaced apart to form an expanding bypass passage. [Background technology]

[0002] Such an air filter is disclosed in U.S. Patent Application Publication No. 2020 / 0376934.

[0003] High-efficiency cabin air filters often use two filter elements. The first filter element can be a pre-filter element for separating larger particles and / or harmful gases. The second filter element can be a fine filter element, such as a HEPA filter element, for separating finer particles. These filter elements are typically arranged in succession.

[0004] However, if the particle concentration in the air passing through the filter is low, the use of a fine filter element is not necessarily required. To reduce pressure loss, energy consumption of the air filter blower, and noise generation, some air filters allow the fine filter element to be bypassed. For this purpose, air passes through the pre-filter element and then exits between the two filter elements. For this purpose, a sufficiently large bypass path is required between the filter elements. To achieve this, the filter elements must be spaced apart appropriately. This increases the installation space requirements for the air filter.

[0005] In the air filter described in the aforementioned U.S. Patent Application Publication No. 2020 / 0376934, two rectangular parallelepiped filter elements are disposed diagonally relative to one another, forming an enlarged bypass passage between them. A bypass flap can selectively open and close the bypass passage to bypass or pass through the second filter element.

[0006] German Patent Application Publication No. 102008058356 discloses a filter element with a folded bellows having a plurality of adjacent upper pleat apexes and a plurality of adjacent lower pleat apexes, the lower pleat apexes being arranged on a base surface and the upper pleat apexes projecting from the base surface by a pleat height. This filter element is characterized in that the upper pleat apexes have at least two different pleat heights. This allows the filter element to be incorporated into a filter housing that deviates from a rectangular parallelepiped shape while maintaining high filter efficiency and optimizing the flow of the fluid to be filtered.

[0007] German Patent Application Publication No. 102019206911 describes an air filter element for an air filter device in a motor vehicle or cabin air filter. The air filter element comprises a plate-shaped filter body made of filter material and a frame surrounding the filter body. The filter material is folded so that the filter body has a plurality of adjacent pleats, which are connected to each other at the pleat ends and extend in the longitudinal direction and transverse direction of the filter. The frame has two longitudinal end walls extending parallel to the transverse direction of the filter and two side walls extending parallel to the longitudinal direction of the filter. The filter body is formed with at least one short pleat group consisting of two or more consecutive pleats in the longitudinal direction of the filter, each of which is shorter in the filter height direction than the adjacent pleats. At least one notch is formed in the frame in each short pleat group. In the region of each notch, a bent tab is formed in the frame, bending from the frame toward the short pleat group. The bent tabs contact at least some of the flutes in the short flute group and are secured by a material bond.

[0008] The object of the present invention is to achieve a compact design in an air filter having a pre-filter element and a fine filter element that is selectively passed through or bypassed, and to minimize flow resistance, especially when bypassing the fine filter element. Summary of the Invention

[0009] This object is solved by an air filter according to claim 1 and by a use according to claim 12. Preferred embodiments or variants are disclosed in the respective dependent claims and in the description.

[0010] According to the present invention, an air filter is provided, which can be used in particular as a cabin air filter for a motor vehicle.

[0011] The air filter includes two filter elements, each of which is designed as a planar filter element and includes a filter medium body having an inlet face and an outlet face, and during operation, air to be filtered flows from the inlet face to the outlet face of each filter medium.

[0012] The air filter further comprises a filter housing in which the two filter elements are disposed.

[0013] The air filter further comprises a fluid guide device for selectively directing the filtered air flow through the two filter elements in series or at least partially bypassing the second of the two filter elements. In a first operating state, the fluid guide device allows the air flow to pass through the first and second filter elements in series. In this case, the air flow first passes through the first filter element and then through the second filter element. In the description of the present invention, the first filter element is also referred to as the first filter element, and the second filter element is also referred to as the second filter element. In a second operating state, the fluid guide device allows the second filter element to be bypassed (in the flow direction). The air flow is directed to completely or partially, particularly by 50% or more, bypass the second filter element.

[0014] The first filter element may be an adsorptive filter element, in particular comprising activated carbon.

[0015] The second filter element is preferably a HEPA filter element, and particularly preferably one having a filter class H13 or higher performance in accordance with EN1822-1:2009.

[0016] The outlet surface of a first filter element and the inlet surface of a second filter element are spaced apart to form an expanding bypass passage. The bypass passage generally expands in a direction intersecting the planar extension direction of at least one of the filter elements. In the second operating state, the bypass passage can divert air filtered by the first filter element before it passes through the second filter element. Because the bypass passage expands in the direction of the bypass flow through the bypass passage, i.e., toward the outlet of the air filter, the air filtered by the first filter element can be easily discharged, reducing the flow resistance of the air filter.

[0017] According to the present invention, the filter medium body of at least one of the filter elements has an inherently varying height, with the height of the filter medium body decreasing as the width of the bypass passage increases. That is, the inlet and outlet faces of the filter medium body are spaced apart from each other at different distances along the bypass passage. This allows the filter elements to be positioned closer to each other without narrowing the bypass passage. This reduces the installation space required to accommodate the two filter elements. The height or thickness of the filter medium body can be measured along the main direction of air flow through the filter medium body. Typically, the height or thickness is measured perpendicular to the inlet or outlet face of the filter medium body. The width of the bypass passage represents the extent of the bypass passage in a direction crossing the main direction of the bypass flow through the bypass passage, particularly in the second operating state.

[0018] The filter media body may be constructed of a filter mat, foam, honeycomb, or porous material.

[0019] Preferably, pleats of different heights are formed in the filter medium bodies. Particularly preferably, pleats are formed in both filter medium bodies. One or both of the filter medium bodies can be made of folded filter paper. The wider the bypass path, the lower the pleats are provided. That is, the pleat ends of one filter element facing the other filter element are arranged at different distances from the pleat ends opposite the other filter element. The lower the pleats (the shorter the pleat end spacing), the wider the bypass path.

[0020] Preferably, the inlet flow surface of the first filter element and the outlet flow surface of the second filter element extend parallel to one another, which allows a particularly compact construction of the air filter to be obtained.

[0021] Preferably, the height of the filter medium body decreases continuously in the direction of the width or flow of the bypass passage, which is advantageous for the flow through the bypass passage.

[0022] Alternatively, the height of the filter media body may decrease in a stepwise manner in the direction of the width or flow of the bypass passage, which can simplify the manufacture of the filter element.

[0023] Furthermore, both filter elements preferably include filter media bodies with an inherently varying height, where the height of each filter media body decreases as the bypass passage width increases, allowing the two filter elements to be positioned particularly close together while minimizing flow resistance in the bypass passage.

[0024] The minimum height of one or both filter medium bodies, in particular the minimum height of the pleats of one or both filter elements, may be 5 mm or more, preferably 8 mm or more, and / or 20 mm or less, preferably 15 mm or less.

[0025] The maximum height of one or both filter medium bodies, and in particular the maximum height of the pleats of one or both filter elements, may be 30 mm or more, preferably 40 mm or more, and / or 70 mm or less, preferably 60 mm or less.

[0026] The variable height filter element may include at least one frame element. The frame element provides a lateral seal for the filter media body. The frame element may be a side band for sealing the pleats. Alternatively or additionally, the frame element may include a plastic frame to which the filter media body is indirectly or directly bonded or injection molded.

[0027] The frame elements protrude more from the filter body in the region of the lower height. In particular, the frame elements or side bands protrude more from the pleat ends in the region of the lower pleats. The frame elements may have a substantially constant height. Advantageously, the frame elements have at least one protrusion reduction, in particular a recess. In other words, the protrusion of the frame elements is locally reduced. Preferably, the filter housing has a protrusion adjacent to the protrusion reduction. The protrusion at least partially fits into the recess. The protrusion may protrude inward from the side wall of the filter housing. This protrusion ensures that the filter element is only installed in an orientation in which the protrusion reduction coincides with the protrusion. This ensures that the bypass path expands in the desired direction. It also prevents incorrect installation of the filter element. Furthermore, the protrusion can prevent the installation of an inappropriate filter element, for example, one that does not meet certain technical requirements (e.g., a predetermined separation efficiency).

[0028] If the heights of both filter elements vary, each filter element may have at least one frame element that protrudes from the filter medium body as its height decreases, and each frame element may have at least one protrusion reduction portion, particularly a recess. The filter housing may have protrusions adjacent to each of these protrusion reduction portions. Preferably, the filter housing is provided with a common protrusion that is adjacent to both protrusion reduction portions, particularly one that at least partially fits into both recesses. Providing only one common protrusion can simplify the manufacture of the filter housing, if necessary.

[0029] One of the filter elements, especially the filter element with varying height and / or the filter element with relatively better separation performance, may be provided with a seal, by means of which the two housing parts of the filter housing can be sealed to each other.

[0030] Preferably, the seal includes a first seal portion and a second seal portion, the first seal portion surrounding the filter medium body and the second seal portion surrounding the flow passage opening. The first seal portion is configured to seal the filter medium body to the filter housing, particularly the first seal portion sealing the inlet untreated side to the outlet clean side. Furthermore, the first seal portion may be configured to seal the housing sections of the filter housing together. The second seal portion having an opening is typically configured to seal the housing sections of the filter housing together. The opening generally does not contain filter material. The second seal portion having an opening is also referred to as the handle of the filter element. The second seal portion having an opening is generally located radially outside the cross section of the filter medium body. The first seal portion and the second seal portion may share a common seal segment.

[0031] The airflow path directed through the two filter elements in series can extend through an opening in the second frame segment, simplifying flow direction and filter housing construction.

[0032] Preferably, the fluid connection between the outlet face of the second filter element and the outlet of the filter housing is established exclusively via the flow opening, through which all of the filtered air flows in the case of continuous flow through both filter elements.

[0033] The seal can be made of polyurethane, particularly polyurethane foam. The seal can be integrally formed with the filter element body. The seal's hardness can be, for example, 13 Shore A or more and / or 25 Shore A or less. In another embodiment, the seal can be injection molded into the plastic frame of the filter element, in which case the seal is particularly made of a thermoplastic elastomer material. The seal can particularly include one or more sealing lips, which allows for particularly good sealing performance with a relatively small seal pretension.

[0034] Preferably, the second seal portion of the seal is reinforced by a reinforcing portion, which ensures that the second frame segment contacts the sealing position of the filter housing. The seal may be integrally formed with the reinforcing portion. In particular, the reinforcing portion may be embedded in the seal. In another embodiment, a plastic frame is formed to surround the flow path opening surrounded by the second seal portion, and in particular, the second seal portion is also injection molded into the plastic frame.

[0035] The second sealing part may be provided with air guide ribs, which allow the flow through the air filter to be optimized, especially in the region of the flow openings.

[0036] Preferably, the air guide rib is integrally molded with the reinforcing portion. This simplifies the manufacture of the filter element. Preferably, the fluid guide device includes a flap that closes the bypass passage in a first position and opens it in a second position. The operating state can be particularly easily switched by rotating the flap. In the second position, the flap can completely or partially block the flow through the flow passage opening of the second sealing portion of the seal. The flap may include one or more sealing lips, particularly for contacting a sealing portion of the filter housing. Typically, a sealing lip is provided between the filter housing and the flap at the outlet side of the bypass passage. The sealing lip can be provided on the filter housing or on the flap.

[0037] The scope of the present invention also includes the use of a filter element in an air filter of the present invention as described above, the filter element being configured as a planar filter element and including a filter medium body having an inflow surface and an outflow surface, the filter medium body having an inherently varying height. The filter element is used in combination with an additional filter element in the air filter, the additional filter element being configured as a planar filter element and including a filter medium body having an additional inflow surface and an outflow surface. The air filter comprises a filter housing in which the two filter elements are disposed during use, and further comprises a fluid guide device for selectively directing the filtered air flow to pass through the two filter elements in succession or to at least partially bypass one of the filter elements. An expanding bypass passage is formed between the filter elements, and the filter element has a reduced height as the bypass passage width increases. The filter element with a varying height may be either the first filter element or the second filter element (in the flow direction). In the use of the present invention, the tapered shape of the filter element is utilized to form a fluidically advantageous bypass passage between the filter element and the additional filter element with minimal installation space.

[0038] The filter media body may be constructed of a filter mat, foam, honeycomb, or porous material.

[0039] Preferably, pleats of different heights are formed in the filter medium body, which may consist of folded filter paper, and in use, the filter element is positioned so that the lower pleats are located in the area where the bypass passage is wider.

[0040] The height of the filter media body preferably decreases continuously, which is advantageous with respect to flow through the bypass passage.

[0041] Alternatively, the height of the filter media body may decrease in steps, which can simplify the manufacture of the filter element.

[0042] The filter element may include at least one frame element. The side bands provide a lateral seal for the filter medium body. The frame element may be a side band for sealing the pleats. The frame element protrudes more beyond the filter medium body as the height of the filter medium body decreases. In particular, the frame element or the side band protrudes more from the pleat ends in areas with lower pleats. The frame element may have a substantially constant height. Advantageously, the frame element has at least one protrusion reduction, particularly a recess. In other words, the protrusion of the frame element is locally reduced. If the filter housing has a protrusion, a frame element designed in this way allows the filter element to be mounted in a defined position. The filter element can be installed in the filter housing only if the protrusion is located adjacent to the protrusion reduction, particularly if it at least partially fits into the recess.

[0043] The filter element can include a seal that forms a first seal and a second seal, where the first seal surrounds the filter medium body and the second seal surrounds the flow path opening. The first seal is configured to seal the filter medium to the filter housing, particularly the first seal seals the inlet untreated side to the outlet clean side. Furthermore, the first seal may be configured to seal the housing sections of the filter housing together. The second seal with an opening is typically configured to seal the housing sections of the filter housing together. The opening generally does not contain filter material. The second seal with an opening is typically located radially outward of the cross section of the filter medium body. The first seal and the second seal may share a common seal segment.

[0044] The filter element with the seal is usually used as the second filter element in the flow direction.

[0045] The flow path for airflow directed through the two filter elements in series may extend through an opening in the second frame segment.

[0046] Preferably, the fluid connection between the outlet face of the second filter element and the outlet of the filter housing is established exclusively via the flow opening, through which all of the filtered air flows in the case of continuous flow through both filter elements.

[0047] The seal may be made of polyurethane, particularly polyurethane foam. The seal may be integrally formed with the filter body. The seal may have a hardness of 13 Shore A or greater and / or 25 Shore A or less.

[0048] Preferably, the second seal portion of the seal is reinforced by a reinforcing portion, which ensures that the second seal portion contacts the predetermined seal position on the filter housing. The seal may be integrally formed with the reinforcing portion. In particular, the reinforcing portion may be embedded in the seal.

[0049] The second sealing part may be provided with air guide ribs, which allow the flow through the air filter to be optimized, especially in the region of the opening.

[0050] Preferably, the air guide ribs are integrally formed with the reinforcement, which simplifies the manufacture of the filter element.

[0051] Further features and advantages of the invention can be obtained from the following detailed description of embodiments of the invention, from the claims and from the drawings showing the details according to the invention. The features mentioned above and below can be realized individually by themselves or can be combined in any suitable combination in a variant of the invention. The features shown in the drawings are illustrated so as to allow a clear visualization of the features of the invention. [Brief explanation of the drawings]

[0052] [Figure 1] 1 is a schematic cross-sectional view of an air filter of the present invention comprising two cone-shaped planar filter elements with an expanding bypass passage formed therebetween. [Figure 2] 2 is a schematic cross-sectional view of a second filter element in the flow direction of the air filter of FIG. 1. FIG. [Figure 3] 2 is a schematic perspective view of a rectangular parallelepiped-shaped filter element used as a second filter element in combination with a first cone-shaped filter element in an air filter similar to that of FIG. 1; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0053] 1 shows an air filter 10. The air filter 10 includes a filter housing 12 having a lower housing portion 14 and an upper housing portion 16. Air to be filtered is directed into the filter housing 12 through an inlet 17. The filtered air is directed out of the filter housing 12 through an outlet 18, for example, into the passenger compartment of an automobile, although this is not shown in detail.

[0054] Two filter elements 20, 26 are arranged in the filter housing 12. The two filter elements 20, 26 are formed as planar filter elements. The first filter element 20 in the flow direction has a first inlet face 22 and a first outlet face 24. The second filter element 26 is arranged behind the first filter element 20 in the flow direction. The second filter element 26 has a second inlet face 28 and a second outlet face 30. Here, the first inlet face 22 of the first filter element 20 and the second outlet face 30 of the second filter element 26 extend parallel to each other.

[0055] The first filter element 20 is a so-called environmental filter or pre-filter element and may contain activated carbon, especially for the adsorption of harmful gases. The second filter element 26 may be a HEPA filter element for filtering particulates.

[0056] The air filter 10 further includes a fluid guide device 32 formed by a flap 34 rotatable about a rotation axis 33 by a rotary drive (not shown in detail). In FIG. 1 , the air filter 10 is in a first operating state in which the air passes through the two filter elements 20, 26 sequentially. For this purpose, the flap 34 closes the bypass passage 36 formed between the two filter elements 20, 26 in a first position. For this purpose, a sealing lip 37 formed on the flap 34 can be in sealing contact with an opening 38 of the bypass passage 36 formed by the filter housing 10. In the first operating state, after passing through the second filter element 26, the filtered air flows out to the outlet 18 through a flow passage opening 40, which in this example is formed in the transition region between the upper housing part 16 and the lower housing part 14. The air flow path 41 in the first operating state is indicated diagrammatically in FIG. 1 by a dashed arrow.

[0057] In a second operating state, the fluid guide device 32 opens the bypass passage 36. For this purpose, the flap 34 is rotated away from the mouth 38 (see the direction of rotation 42 indicated by the arrow). Although not shown in detail, in the second position the flap 34 can close, by means of a further sealing lip 44, a clean air passage 46 arranged in the flow direction between the second filter element 26 and the outlet 18.

[0058] In the second operating state, air filtered by the first filter element 20 flows through the bypass path 36 to the outlet 18. The air flow path 47 in the second operating state is shown schematically by the dotted arrows in Figure 1. The bypass path 36 widens toward its mouth 38, thereby eliminating the flow resistance of the second filter element 26 and reducing the flow resistance of the entire air filter 10.

[0059] Each of the two filter elements 20, 26 includes a filter medium body 48. In the illustrated embodiment, the filter medium body 48 is formed from folded filter paper. An exemplary configuration of the second filter element 26 is shown in FIG. 2. The pleats 50 of the filter medium body 48 are bounded on the inlet and outlet sides by pleat ends 52 and 54, respectively. The height 56 ​​or thickness (measured perpendicular to the outlet or inlet face) of the filter medium body 48 corresponds to the height of the pleats 50 in the illustrated embodiment and decreases along the bypass path 36. The maximum height 56a of the filter medium body 48 or its pleats 50 is, for example, 48 mm. The minimum height 56b of the filter medium body 48 or its pleats 50 is, for example, 11 mm.

[0060] Here, the thickness of the filter elements 20, 26 continuously decreases along the flow direction (from left to right in FIG. 1 ) of the bypass passage 36 in the second operating state. Correspondingly, the bypass passage 36 continuously widens toward the mouth 38. Therefore, air entering the bypass passage 36 from the entire surface of the first filter element 20 can utilize an increasing cross-sectional area toward the mouth 38, thereby reducing the pressure difference between the first inlet surface 22 and the outlet 18 required for flow through the bypass passage 36. This reduces energy consumption and enables the mileage of a vehicle equipped with the air filter 10 to be extended.

[0061] Each of the two filter elements 20, 26 has frame elements 58 in the form of side bands that seal the pleats 50 transversely to the pleat ends 52, 54 and the respective inlet or outlet faces 22-28 (see FIGS. 1 and 2). In some embodiments, the frame elements 58 are part of a plastic frame that directly or indirectly secures the filter media bodies 48. For example, the filter media bodies 48 may be directly bonded to the plastic frame or molded around the plastic frame material. Alternatively, the filter media bodies may include side bands that indirectly connect, particularly bond, the filter media bodies 48 to the plastic frame. As the pleats 50 become lower, the frame elements 58 protrude more from the inlet pleat ends 52 of the second filter element 26 or the outlet pleat ends of the first filter element 20. The frame elements 58 are the same height throughout, except for their respective recesses 60. Each recess 60 defines a reduced protrusion 62 in the frame elements 58.

[0062] The sidewall of the filter housing 12 is formed with a protrusion 64 (see FIG. 1). When the filter elements 20, 26 are installed, the protrusion 64 fits into the recess 60 of each frame element 58. This ensures that the filter elements 20, 26 can be inserted into the filter housing 12 only when they are properly oriented and the reduced projection portions of the frame elements 58 are properly positioned.

[0063] The second filter element 26 is provided with a seal 66, which in this example is made of polyurethane foam. The seal 66 forms two rectangular seal portions 68, 70, which share a common seal segment 71. The first seal portion 68 is located on the outer periphery of the outlet flow surface 30 of the filter media body 48 of the second filter element 26. The second seal portion 70 is shaped like a handle and protrudes from the filter media body 48, but does not contain any filter material. In the illustrated embodiment, the second seal portion 70 surrounds the flow passage opening 40, which is fluidly disposed forward of the clean air passage 46.

[0064] On the one hand, seal 66 is configured to seal lower housing portion 14 and upper housing portion 16 from one another, and on the other hand, first seal portion 68 seals second filter element 26 to filter housing 12 in a first operating state such that all air passes through filter media body 48 of second filter element 26.

[0065] The second sealing portion 70 is reinforced by a reinforcing portion 72. Air guide ribs 74 are integrally molded with the reinforcing portion 72. In the first operating state, the air guide ribs 74 are configured to guide filtered air into the clean air passage 46 in the region of the flow path opening 40. In some embodiments, the reinforcing portion 72 is integrally molded with a plastic frame that forms the frame element 58.

[0066] Sealing between the first filter element 20 and the filter housing 12 is achieved through the frame elements 58 of the first filter element (side bands and a head band, not shown in detail in this example). The second filter element 20 also typically includes two head bands (not shown in detail) in addition to two side bands. The side bands and head bands form a circumferential frame for each filter media body 48.

[0067] FIG. 3 illustrates an alternative second filter element 76 that can be used in place of the second filter element 26 in an air filter similar to that of FIG. 1. The filter element 76 includes a rectangular parallelepiped-shaped filter media body 78. The rectangular parallelepiped-shaped filter element 76 can be used in combination with a tapered filter element in accordance with the present invention. In this case, as shown, the second filter element 76 can be rectangular parallelepiped-shaped, and the first filter element 20 can be configured with a variable height 56, particularly pleats 50 of different heights. Alternatively, the first filter element can be rectangular parallelepiped-shaped, and the second filter element can be configured with a variable height, particularly pleats 50 of different heights (not shown). In either case, as the height (thickness) of one filter element decreases or the pleats become lower, the bypass passage 36 formed between the two filter elements becomes larger. It will be appreciated that when a rectangular parallelepiped filter element is used, the protrusions 64 of the filter housing 12 interact only with the recesses partially provided in the protruding side bands of the tapered filter element to ensure proper installation position. With regard to the configuration of the seals 66, reinforcements 72, and air guide ribs 74, the second filter element 76 shown in Figure 3 is identical to the second filter element 26 described above (see Figures 1 and 2).

[0068] In summary, the present invention relates to an air filter comprising two filter elements through which fluid passes sequentially (consecutively) in a first operating state. A bypass passage is provided between the filter elements for at least partially bypassing one of the filter elements in a second operating state. The bypass passage expands in the direction of the bypass flow generated in the second operating state. At least one of the filter elements comprises a filter medium body whose thickness decreases along the direction of the bypass flow. A filter medium body with a variable height or thickness can be obtained by folding filter paper. To ensure proper installation of the tapered filter element, frame elements for sealing the filter medium body, particularly side bands, have a substantially constant height and are configured to protrude beyond a portion of the filter medium body, particularly the lower pleats, while a recess is provided in a portion of the side band. A protrusion on the filter housing can fit into this reduced protrusion. [Explanation of symbols]

[0069] Air Filter 10 Filter Housing 12 Housing bottom 14 Housing top 16 entrance 17 exit 18 First filter element 20 First inlet surface 22 First outflow surface 24 Second filter element 26 Second inlet surface 28 Second outflow surface 30 Fluid guide device 32 Axis 33 Flap 34 Bypass Route 36 Seal Lip 37 Mouth 38 Flow path opening 40 Flow path for continuous flow 41 Rotation direction 42 Additional sealing lip 44 Clean air passage 46 Flow path for bypass flow 47 Filter media 48 Pleats 50 Pleated ends 52, 54 Pleats 50 height 56 Maximum height 56a Minimum height 56b Side band 58 Recess 60 Protrusion amount reduction part 62 Convex part 64 Seal 66 First seal portion 68 Second seal portion 70 Common Seal Segment 71 Reinforcement 72 Air guide rib 74 Second filter element 76 Filter media 78

Claims

1. An air filter (10), comprising: two filter elements (20, 26), each formed as a planar filter element and including a filter medium body (48) having an inflow surface (22, 28) and an outflow surface (24, 30); a filter housing (12) in which the two filter elements (20, 26) are disposed; a fluid guide device (32) for selectively directing the air flow to be filtered through the two filter elements (20, 26) in series or at least partially bypassing the second one of the filter elements (26); an outlet flow surface (24) of a first one of the filter elements (20) and an inlet flow surface (28) of a second one of the filter elements (26) are spaced apart from one another to form an expanding bypass passage (36); The filter element (48) of at least one of the filter elements (20, 26) has an inherently varying height (56), and the height (56) of the filter element (48) of the at least one of the filter elements (20, 26) decreases as the width of the bypass passage (36) increases.

2. 2. The air filter (10) of claim 1, wherein pleats (50) having different heights (56) are formed in the filter medium body (48) in at least one of the filter elements (29, 26), and the wider the bypass path (36), the lower the pleats (50) are provided.

3. 3. The air filter (10) of claim 1 or 2, wherein the inlet flow surface (22) of the first filter element (20) and the outlet flow surface (30) of the second filter element (26) extend parallel to each other.

4. The air filter (10) of any one of claims 1 to 3, wherein the height (56) of the filter medium body (48) of the at least one filter element (20, 26) decreases continuously or in steps.

5. 5. The air filter (10) of claim 1, wherein both of the two filter elements include a filter medium body (48) having an inherently varying height (56), the height (56) of each filter medium body (48) decreasing as the width of the bypass passage (36) increases.

6. The filter element (20, 26) having a varying height (56) has at least one frame element (58) that protrudes from the filter medium body (48) as the height decreases, and the frame element (58) has at least one protrusion reduction portion (62), particularly a recess (60), and the filter housing (12) has a protrusion (64) adjacent to the protrusion reduction portion (62) and at least partially fitting into the recess (60). An air filter (10) according to any one of claims 1 to 5, comprising:

7. 7. The air filter (10) of claim 1, wherein at least one of the filter elements (26) comprises a seal (66) forming a first seal portion (68) and a second seal portion (70), the first seal portion (68) surrounding the filter medium body (48) and the second seal portion (70) surrounding a flow passage opening (40).

8. 8. The air filter (10) of claim 7, wherein the flow path of air directed through the two filter elements (20, 26) in series extends through the flow opening (40).

9. 9. The air filter (10) of claim 7 or 8, wherein a fluid connection between the outflow surface (30) of the second filter element (26) and the outlet (18) of the filter housing (12) is established only via the flow path opening (40).

10. An air filter (10) according to any one of claims 7 to 9, wherein the seal (66) seals the two housing parts (14, 16) of the filter housing (12) from each other.

11. The air filter (10) according to any one of claims 1 to 10, wherein the fluid guide device (32) comprises a flap (34) that closes the bypass passage (36) in a first position and opens the bypass passage (36) in a second position.

12. Use of a filter element (20, 26) in an air filter (10) according to any one of claims 1 to 11, comprising: The filter elements (20, 26) are configured as planar filter elements and include a filter medium body (48) having an inflow surface (22, 28) and an outflow surface (24, 30), the filter medium body (48) having an inherently varying height (56).

13. 13. The use of a filter element (20, 26) according to claim 12, wherein the filter medium body (48) is formed with pleats (50) having different heights (56).

14. 14. Use of a filter element (20, 26) according to claim 12 or 13, wherein the height (56) of the filter medium body (48) decreases continuously or in steps.

15. 15. The use of a filter element (20, 26) according to any one of claims 12 to 14, wherein the filter element (20, 26) has at least one frame element (58) that protrudes from the filter medium body (48) so that the height (50) decreases, and the frame element (58) has at least one protrusion reduction portion (62), in particular a recess (60).

16. 16. The use of a filter element (20, 26) according to any one of claims 12 to 15, wherein the filter element (26) comprises a seal (66) forming a first seal portion (68) and a second seal portion (70), the first seal portion (68) surrounding the filter medium body (48) and the second seal portion (70) surrounding a flow opening (40).

17. 17. Use of filter elements (20, 26) according to claim 16, wherein the flow path of the airflow directed through the two filter elements (20, 26) in succession extends through the flow opening (40).

18. 18. Use of a filter element (20, 26) according to claim 16 or 17, wherein a fluid connection between the outflow surface (30) of the filter element (26) and the outlet (18) of the filter housing (12) is established only via the flow passage opening (40).

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