AIR FILTER AND THE USE OF A FILTER ELEMENT IN AN AIR FILTER

Description

Technical field

[0001] The invention relates to an air filter comprising two filter elements, each designed as a flat filter element and comprising a filter medium body with an inlet surface and an outlet surface, a filter housing in which the two filter elements are arranged, and a flow guide device to direct an airflow to be filtered either serially through the two filter elements or at least partially past a second of the filter elements, wherein the outflow surface of a first of the filter elements and the inflow surface of the second of the filter elements are spaced apart from each other, forming an expanding bypass channel. State of the art

[0002] Such an air filter is known from US 2020 / 0376934 A1.

[0003] High-efficiency cabin air filters often use two filter elements. The first element can be a pre-filter for removing larger particles and / or harmful gases. The second element can be a fine filter, such as a HEPA filter, for removing finer particles. The filter elements can generally be passed through sequentially.

[0004] However, the use of the fine filter element is not strictly necessary when particle concentrations in the air to be filtered are low. To reduce pressure loss during airflow through the filter, the energy consumption of the air filter's fan, and noise levels, the fine filter element can be bypassed in some air filters. For this purpose, the air is drawn off between the two filter elements after passing through the pre-filter element. This requires a sufficiently large bypass channel between the filter elements. To create this bypass channel, the filter elements must be spaced a considerable distance apart. This increases the overall size of the air filter.

[0005] The air filter known from US 2020 / 0376934 A1, mentioned above, has two cuboid filter elements positioned at an angle to each other, creating an expanding bypass channel between them. A bypass flap allows the bypass channel to be opened or closed, either to allow air to flow around the second filter element or to force air to flow through it.

[0006] From DE 10 2008 058 356 A1, a filter element is known comprising a bellows with adjacent upper folds and adjacent lower folds, wherein the lower folds lie in a base plane and the upper folds project from the base plane with fold heights. The filter element is characterized by at least two different fold heights of the upper folds. This allows the filter element to be used in filter housings that deviate from a cuboid shape, ensuring high filter efficiency and optimized guidance of the fluid to be filtered.

[0007] DE 10 2019 206 911 A1 describes an air filter element for an air filter system of a motor vehicle or a cabin air filter. The air filter element comprises a plate-shaped filter body made of a filter material and a frame surrounding it. The filter material is pleated, so that the filter body has several adjacent pleats connected by folds, which follow one another in a longitudinal direction of the filter and extend in a transverse direction. The frame has two longitudinal end walls extending parallel to the transverse direction of the filter and two side strips extending parallel to the longitudinal direction of the filter. Within the filter body, at least one group of short pleats is formed, consisting of at least two pleats following one another in the longitudinal direction of the filter, which are shorter in a vertical direction than the adjacent pleats. At least one recess is formed in the frame at each group of short pleats.Within the area of ​​each recess, a bending tab is formed on the frame, which is bent from the frame towards the folds of the respective short-pleat group. The bending tab rests on at least some of the folds of the short-pleat group and is thus securely fastened to the material.

[0008] It is an object of the invention to enable a compact design and, in particular, a low flow resistance in an air filter with a pre-filter element and a fine filter element that can be selectively flowed through or bypassed. Disclosure of the invention

[0009] This problem is solved by an air filter according to claim 1 and a use according to claim 10. Preferred embodiments or variants are specified in the respective dependent claims and the description.

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

[0011] The air filter has two filter elements. Each filter element is designed as a flat filter element and comprises a filter medium body with an inlet surface and an outlet surface. During operation, the air to be filtered flows through the respective filter medium from its inlet surface to its outlet surface.

[0012] The air filter also has a filter housing in which the two filter elements are arranged.

[0013] Furthermore, the air filter features a flow guide device to selectively direct the airflow to be filtered either serially through the two filter elements or at least partially around a second filter element. The flow guide device thus makes it possible, in a first operating state, to force a serial flow through the first and second filter elements sequentially. The airflow is first directed through the first and then through the second filter element. For the purposes of describing the present invention, the filter element through which the airflow initially passes is also referred to as the first filter element; the filter element through which the airflow subsequently passes is also referred to as the second filter element. In a second operating state, the flow guide device allows the airflow to bypass the second filter element (in the direction of flow).The airflow can be directed completely or partially, in particular to at least 50%, past the second filter element.

[0014] The first filter element can be an adsorption filter element, in particular containing activated carbon.

[0015] The second filter element can be a HEPA filter element, preferably of filter class H13 according to EN 1822-1:2009 or better.

[0016] The outflow area of ​​the first filter element and the inflow area of ​​the second filter element are spaced apart, forming a widening bypass channel. This bypass channel widens perpendicular to the plane of at least one of the filter elements. In the second operating state, the bypass channel allows the air filtered by the first filter element to be diverted before it flows through the second. By widening in the direction of a bypass flow through the bypass channel, or in other words, towards an outlet of the air filter, the discharge of the air filtered by the first filter element is facilitated; the flow resistance of the air filter is reduced.

[0017] According to the invention, the filter medium body of at least one of the filter elements has a variable height, with the filter medium body having a reduced height in the region of a wider bypass channel. In other words, the inlet and outlet surfaces of the filter medium body are spaced at different distances from each other along the bypass channel. The filter elements can thus be arranged close together without narrowing the bypass channel. This minimizes the space required to accommodate the two filter elements. The height or thickness of the filter medium body can be measured along a main airflow direction through the filter medium body. Typically, the height or thickness is measured perpendicular to the inlet or outlet surface of the filter medium body.The width of the bypass channel describes in particular its extent perpendicular to the main flow direction of the bypass flow through the bypass channel in the second operating state.

[0018] The filter medium body can be formed with a filter mat, foam, a honeycomb structure or porous material.

[0019] Preferably, the filter medium body is formed with pleats of different heights. Particularly preferably, both filter medium bodies are formed with pleats. The filter medium body(s) can consist of pleated filter paper. In the area of ​​the wider bypass channel, lower pleats are provided. In other words, the fold edges of the pleats of one filter element facing the other are spaced at different distances from the fold edges facing away from the other filter element. As the pleats become lower (smaller distance between the fold edges), the bypass channel widens progressively.

[0020] Preferably, the inflow area of ​​the first filter element and the outflow area of ​​the second filter element extend parallel to each other. This allows for a particularly compact design of the air filter.

[0021] The height of the filter medium body preferably decreases continuously in the direction of expansion or flow through the bypass channel. This is advantageous with regard to the flow through the bypass channel.

[0022] Alternatively, the height of the filter medium body can decrease in stages – in the direction of expansion or flow through the bypass channel. This can simplify the manufacturing of the filter element.

[0023] It is also preferred that both filter elements have a filter medium body with a variable height. In this configuration, both filter medium bodies have a reduced height in the area of ​​the wider bypass channel. This allows the two filter elements to be arranged particularly close to each other, while the bypass channel remains permeable with low resistance.

[0024] The minimum height of one or both filter medium bodies, in particular the folds of one or both filter elements, can be at least 5 mm, preferably at least 8 mm, and / or at most 20 mm, preferably at most 15 mm.

[0025] The maximum height of one or both filter medium bodies, in particular the folds of one or both filter elements, can be at least 30 mm, preferably at least 40 mm, and / or at most 70 mm, preferably at most 60 mm.

[0026] The variable-height filter element can have at least one frame element. The frame element provides a lateral seal for the filter medium body. The frame element can be a side band for sealing folds. Alternatively or additionally, the frame element can comprise a plastic frame into which the filter medium body is directly or indirectly glued or injected.

[0027] The frame element projects beyond the filter medium body in the area of ​​its lower height. In particular, the frame element or side band can project beyond the fold edges of the folds in the area of ​​the lower pleats. The frame element can have a substantially constant height. Advantageously, the frame element has at least one section of reduced projection, in particular a recess. In other words, the projection of the frame element is locally reduced. Preferably, the filter housing has a projection adjacent to the section of reduced projection. The projection engages at least partially with the recess. The projection can extend inwards from a side wall of the filter housing. Due to the projection, the filter element can only be installed in the orientation in which the position of the section of reduced projection coincides with the position of the projection.This ensures that the bypass channel widens in the desired direction. Incorrect installation of the filter element is prevented. Furthermore, the projection prevents the installation of unsuitable filter elements, such as those that do not meet certain technical requirements, like a specified separation efficiency.

[0028] If both filter elements have a variable height, each filter element can have at least one frame element that projects beyond the filter medium body in the area of ​​the lower height, wherein each frame element has at least one section of smaller projection, in particular a recess. The filter housing can have a projection adjacent to each of the sections of smaller projection. Preferably, a common projection is provided on the filter housing that adjoins both sections of smaller projection, in particular engaging at least partially in both recesses. The manufacture of the filter housing can be simplified if only one common projection is provided.

[0029] One of the filter elements, in particular the variable-height filter element and / or a filter element with a relatively higher separation efficiency, may have a seal. The seal may seal two housing parts of the filter housing against each other.

[0030] Preferably, the seal forms a first and a second sealing section, with the first sealing section surrounding the filter medium body and the second sealing section enclosing a flow-through opening. The first sealing section serves to seal the filter medium body against the filter housing; in particular, the first sealing section seals an upstream raw side against an downstream clean side. Additionally, the first sealing section can serve to seal housing components of the filter housing. The second sealing section with the opening typically serves to seal housing components of the filter housing. The opening is generally free of filter material. The second sealing section with the opening can also be described as a handle on the filter element. The second sealing section with the opening is generally located (radially) outside the cross-section of the filter medium body.The first and second sealing sections can comprise a common segment of the seal.

[0031] The airflow path of an air stream passed serially through the two filter elements can run through the opening in the second frame segment. This can simplify the flow guidance and the design of the filter housing.

[0032] Preferably, a fluidic connection between the outflow side of the second filter element and an outlet of the filter housing is established only through the flow-through opening. When both filter elements are flowing through in series, the entire filtered airflow then flows through this opening.

[0033] The seal can be made of polyurethane, in particular polyurethane foam. The seal can be molded onto the filter medium body. The hardness of the seal can be at least 13 Shore A and / or at most 25 Shore A. In another embodiment, the seal can be injection-molded onto the plastic frame of a filter element, and the seal can in particular be made of a thermoplastic elastomer material. The seal can in particular comprise one or more sealing lips, which is advantageous for achieving particularly good sealing performance with comparatively low sealing preload forces.

[0034] Preferably, the second sealing section of the seal is stiffened by a reinforcing element. This ensures that the second frame segment comes into contact with the intended sealing points of the filter housing. The seal can be integrally formed with the reinforcing element. In particular, the reinforcing element can be embedded in the seal. In another embodiment, the plastic frame can surround the flow-through opening enclosed by the second sealing section, with the second sealing section also being integrally molded onto the plastic frame.

[0035] An air guide rib can be provided on the second sealing section. This optimizes the airflow through the air filter, particularly in the area of ​​the opening.

[0036] Preferably, the air guide rib is formed integrally with the stiffening element. This simplifies the manufacture of the filter element.

[0037] Preferably, the flow guide device is formed with a flap which, in a first position, closes the bypass channel and, in a second position, opens it. Switching between the operating states is particularly easy by pivoting the flap. In the second position, the flap can completely or partially prevent flow through the opening of the second sealing section of the seal. The flap can have one or more sealing lips, particularly for contact with sealing points of the filter housing. Typically, a sealing lip is provided on the outlet side of the bypass channel between the filter housing and the flap, and this sealing lip can be formed on the filter housing or on the flap itself.

[0038] The present invention also includes the use of a filter element designed as a flat filter element and comprising a filter medium body with an inflow surface and an outflow surface, wherein the filter medium body has a variable height, in an air filter according to the invention as described above.The filter element is thus used in an air filter with another filter element, which is designed as a flat filter element and has a further filter medium body with a further inlet surface and an outlet surface, wherein the air filter has a filter housing in which the two filter elements are arranged during use, and wherein the air filter further has a flow guide device to direct an airflow to be filtered either serially through the two filter elements or at least partially past one of the filter elements, and wherein an expanding bypass channel is formed between the filter elements, the filter element having a lower height in the region of the wider bypass channel. The filter element with variable height can be the first or second filter element (in the direction of flow).The tapered geometry of the filter element is used in the invention to create a flow-efficient bypass channel between the filter element and the further filter element, while requiring little installation space.

[0039] The filter medium body can be formed with a filter mat, foam, a honeycomb structure or porous material.

[0040] Preferably, the filter medium body is designed with pleats of varying heights. The filter medium body can consist of pleated filter paper. During use, the filter element is arranged so that the lower pleats are located in the area of ​​the wider bypass channel.

[0041] The height of the filter medium body preferably decreases continuously. This is advantageous with regard to the flow through the bypass channel.

[0042] Alternatively, the height of the filter medium body can decrease in stages. This can simplify the manufacturing of the filter element.

[0043] The filter element can have at least one frame element. The side band enables lateral sealing of the filter medium body. The frame element can be a side band for sealing folds. The frame element projects beyond the filter medium body in the area of ​​the lower height. In particular, the frame element or side band can project beyond the fold edges of the folds in the area of ​​the lower folds. The frame element can have a substantially constant height. Advantageously, the frame element has at least one section of reduced projection, in particular a recess. In other words, the projection of the frame element is locally reduced. If the filter housing has a protrusion, a defined installation position of the filter element can be enforced by a frame element designed in this way.The filter element can only be installed in the filter housing by arranging the projection adjacent to the section with less overhang, in particular by intervening in the retraction at least section by section.

[0044] The filter element can have a seal forming a first and a second sealing section. The first sealing section surrounds the filter medium body, and the second sealing section forms a flow-through opening. The first sealing section serves to seal the filter medium against the filter housing; in particular, the first sealing section can seal an upstream raw side against an downstream clean side. Additionally, the first sealing section can serve to seal housing components of the filter housing. The second sealing section with the opening typically serves to seal housing components of the filter housing. The opening is generally free of filter material. The second sealing section with the opening is generally located (radially) outside a cross-section of the filter medium body. The first and second sealing sections can comprise a common segment of the seal.

[0045] The filter element containing the seal is typically used as the second filter element in the direction of flow.

[0046] A flow path of an airflow passed serially through the two filter elements can pass through the opening in the second frame segment.

[0047] Preferably, a fluidic connection between the outflow side of the (second) filter element and an outlet of the filter housing is only established through the flow-through opening. When both filter elements are flowing through in series, the entire filtered airflow then flows through this opening.

[0048] The seal can be made of polyurethane, in particular polyurethane foam. The seal can be molded onto the filter medium body. The hardness of the seal can be at least 13 Shore A and / or at most 25 Shore A.

[0049] Preferably, the second sealing section of the gasket is stiffened by a reinforcing element. This ensures that the second sealing section comes into contact with the intended sealing points of the filter housing. The gasket can be integrally formed with the reinforcing element. In particular, the reinforcing element can be embedded in the gasket.

[0050] An air guide rib can be provided on the second sealing section. This can optimize the airflow through the air filter, particularly in the area of ​​the opening.

[0051] Preferably, the air guide rib is formed integrally with the stiffening element. This simplifies the manufacture of the filter element. Brief description of the drawings

[0052] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, from the claims, and from the figures in the drawing, which illustrate details of the invention. The aforementioned and further described features can be implemented individually or in any suitable combination in variants of the invention. The features shown in the drawing are presented in such a way that the special features of the invention are clearly visible. The drawing shows: Fig. 1 shows a schematic sectional view of an air filter according to the invention with two conical flat filter elements, between which an expanding bypass channel is formed; Fig. 2 shows the second filter element of the air filter in the direction of flow. Figure 1, in a schematic sectional view; Fig. 3 a cuboid filter element for use as a second filter element with a first conical filter element in an air filter similar to that in Figure 1 , in a schematic perspective view. Embodiments of the invention

[0053] Figure 1 shows an air filter 10. The air filter 10 has a filter housing 12 with a housing base 14 and a housing top 16 The air to be filtered is drawn in through an inlet. 17 The filtered air is directed into filter housing 12. Filtered air is then discharged through an outlet. 18 the filter housing 12 can, for example, be discharged into a passenger cabin of a motor vehicle not shown in detail.

[0054] The filter housing 12 contains two filter elements. 20, 26The two filter elements 20, 26 are arranged as flat filter elements. The first filter element 20 in the flow direction has a first inlet surface. 22 and a first outflow area 24 The second filter element 26 is provided downstream of the first filter element 20 in the direction of flow. The second filter element 26 has a second inlet surface. 28 and a second outflow area 30 In this case, the first inflow surface 22 of the first filter element 20 and the second outflow surface 30 of the second filter element 26 extend parallel to each other.

[0055] The first filter element 20 can be a so-called ambient or pre-filter element and may contain, in particular, activated carbon for the adsorption of harmful gases. The second filter element 26 can be a HEPA filter element for filtering out fine particles.

[0056] The air filter 10 also features a flow guide device.32 on, which here is equipped with a swivel drive around an axis by means of an unspecified rotary drive 33 swiveling flap 34 is educated. In Figure 1 The air filter 10 is in a first operating state in which the two filter elements 20, 26 are sequentially (serially) filtered through. For this purpose, the flap 34 closes a bypass channel formed between the two filter elements 20, 26 in a first position. 36. A sealing lip formed on flap 34 37 This can be done at an opening formed by the filter housing 10. 38 The bypass channel 36 is sealed against it. In the first operating state, the filtered air flows through a flow-through opening after passing through the second filter element 26. 40, which is formed here in the transition area between the upper housing part 16 and the lower housing part 14, to the outlet 18. A flow path 41 the air in the first operating state is in Figure 1 schematically drawn with dashed arrows.

[0057] In a second operating state, the flow guide device 32 opens the bypass channel 36. For this purpose, the flap 34 is pivoted away from the opening 38; compare the pivot direction indicated by an arrow. 42. In a second position not shown in detail, the flap 34 can be fitted with an additional sealing lip. 44 a clean air passage 46 close off the opening that is arranged in the direction of flow between the second filter element 26 and the outlet 18.

[0058] In the second operating state, the air filtered by the first filter element 20 flows through the bypass channel 36 to the outlet 18. Figure 1 is a flow path 47The airflow in the second operating state is schematically depicted with dotted arrows. The bypass channel 36 widens towards its opening 38. This reduces the flow resistance in the air filter 10 in addition to the elimination of the flow resistance of the second filter element 26.

[0059] The two filter elements 20, 26 each have a filter medium body. 48 In the illustrated embodiment, the filter medium body 48 is formed from folded filter paper. This is shown in Figure 2 The second filter element, 26, is shown as an example. Folds 50 The filter medium body 48 is formed on the upstream and downstream sides by folded edges. 52 or 54 limited. A height (measurable perpendicular to the outflow or inflow surface). 56The thickness of the filter medium body 48, which in the illustrated embodiment corresponds to the height of the pleats 50, decreases along the bypass channel 36. A maximum height 56a The diameter of the filter medium body 48 or its pleats 50 can, for example, be 48 mm. A minimum height 56b The diameter of the filter medium body 48 or its folds 50 can, for example, be 11 mm.

[0060] Here, the thickness of the filter elements 20, 26 decreases in the flow direction of the bypass channel 36 in the second operating state (in Figure 1(from left to right) continuously. Accordingly, the bypass channel 36 widens continuously towards the opening 38. The air flowing into the bypass channel 36 across the entire surface of the first filter element 20 thus has a cross-section that increases towards the opening 38, so that the differential pressure required for the flow through the bypass channel 36 between the first inlet surface 22 and the outlet 18 remains low. This reduces the energy consumption and can increase the range of a motor vehicle with the air filter 10.

[0061] The two filter elements 20, 26 each have frame elements here. 58 in the form of side bands which seal the folds 50 transversely to the fold edges 52, 54 and transversely to the respective inflow and outflow surfaces 22-30, compare Figure 1 and 2The frame elements 58 can be part of a plastic frame in which the filter medium body 48 is attached directly or indirectly. For example, the filter medium body 48 can be glued directly into the plastic frame or overmolded with a material of the plastic frame. Alternatively, the filter medium body can have side bands by which the filter medium body 48 is indirectly connected to the plastic frame, in particular by bonding. As the folds 50 decrease in height, the frame elements 58 increasingly protrude beyond the upstream folded edges 52 of the second filter element 26 or the downstream folded edges of the first filter element 20. A respective retraction 60 Apart from that, the frame elements 58 are all the same height. The recesses 60 each form a section. 62 smaller overhang in frame element 58.

[0062] There is a projection on one side wall of the filter housing 12.64 trained, compare Figure 1 . In the assembled state of the filter elements 20, 26, the projection 64 engages in the recess 60 of the respective frame element 58. A filter element 20, 26 can therefore only be inserted into the filter housing 12 if it is correctly aligned and if its frame element 58 has a smaller protrusion at the appropriate point.

[0063] The second filter element 26 has a seal. 66, Here, it is made of polyurethane foam. The seal 66 forms two, here rectangular, sealing sections. 68, 70 from, which have a common sealing segment 71The assembly comprises a first sealing section 68 arranged circumferentially around the outside of the outflow surface 30 of the filter medium body 48 of the second filter element 26. A second sealing section 70 extends from the filter medium body 48 – in the manner of a handle – and is free of filter material. The second sealing section 70 surrounds the flow-through opening 40, which, in the illustrated embodiment, is located fluidically in front of the clean air passage 46.

[0064] The seal 66 serves, on the one hand, to seal the lower housing part 14 and the upper housing part 16 against each other. On the other hand, the first sealing section 68 serves to seal the second filter element 26 against the filter housing 12, so that in the first operating state all the air must pass through the filter medium body 48 of the second filter element 26.

[0065] The second sealing section 70 is reinforced by a stiffening part. 72reinforced. An air guide rib is integrally formed with the stiffening part 72. 74 designed. In the first operating state, the air guide rib 74 serves to guide the filtered air in the area of ​​the flowable opening 40 to the clean air passage 46. In some versions, the stiffening part 72 can be a single piece with a plastic frame that has the frame elements 58.

[0066] The first filter element 20 is sealed against the filter housing 12 by its frame elements 58, specifically the side bands and the head bands (not shown) of the first filter element. The second filter element 20 also typically has two side bands and two head bands (not shown). The side bands and head bands form a circumferential frame around the respective filter medium bodies 48.

[0067] Figure 3 shows another second filter element 76,which replaces the second filter element 26 in an air filter similar to the one in Figure 1 The illustrated filter element 76 could be used. It has a cuboid filter medium body. 78According to the invention, a cuboid filter element 76 is to be used together with a tapered filter element. Either, as shown here, the second filter element 76 can be cuboid and the first filter element 20 can have a variable height 56, in particular folds 50 of different heights; alternatively, the first filter element could be cuboid and the second filter element could have a variable height, in particular folds of different heights (not shown in detail). In both cases, the decreasing height (thickness) or the decreasing folds of one filter element cause an enlargement of the bypass channel 36 formed between the two filter elements.It is understood that when using a cuboid filter element, a projection 64 on the filter housing 12, which ensures the correct installation position, interacts only with a partially recessed, protruding side band of the tapered filter element. With regard to the design of the seal 66, the stiffening element 72, and the air guide rib 74, the second filter element 76 of Figure 3 corresponds to the second filter element 26 described above (see Figure 3). Figure 1 and 2 .

[0068] In summary, the invention relates to an air filter with two filter elements through which the air flows sequentially (serially) in a first operating state. A bypass channel is formed between the filter elements to at least partially bypass one of the filter elements in a second operating state. The bypass channel widens in the direction of the bypass flow, which occurs in the second operating state. At least one of the filter elements has a filter medium body whose thickness decreases along the bypass channel – in the direction of the bypass flow. The filter medium body of variable height or thickness can be obtained by folding filter paper.The correct installation position of the tapered filter element can be ensured by using a frame element, in particular a side band, to seal the filter medium body. This frame element has a substantially constant height, projecting beyond the filter medium body in certain areas, particularly over the lower folds, while the side band is recessed in certain sections. A projection of the filter housing can engage in this section of reduced projection. Reference symbol list

[0069] Air filter 10 Filter housing 12 Lower housing part 14 upper housing 16 inlet 17 Outlet 18 first filter element 20 first flow surface 22 first outflow surface 24 second filter element 26 second flow surface 28 second outflow surface 30 Flow guide device 32 axis 33 flap 34Bypass channel 36 Sealing lip 37 mouth 38 flow-through opening 40 Flow path 41 Swivel direction in serial flow 42 additional sealing lip 44 Clean air passage 46 Flow path 47 filter medium in bypass flow 48 Fold 50 Folded edges 52, 54 Height 56 the folds 50 greatest height 56a lowest height 56b lateral band 58 Withdrawal 60 Section 62 smaller overhang advantage 64 seal 66 first sealing section 68 second sealing section 70 common sealing segment 71 stiffening part 72 Air guide rib 74 second filter element 76 Filter medium 78

Claims

1. An air filter (10) featuring, - two filter elements (20, 26), each of which is designed as a flat filter element and features a filter medium body (48) with 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, - and a flow-guiding device (32) for selectively guiding an air flow to be filtered either in series through the two filter elements (20, 26) or at least partially past a second of the filter elements (26), wherein the outflow surface (24) of a first of the filter elements (20) and the inflow surface (28) of the second of the filter elements (26) are spaced apart from each other to form an expanding bypass channel (36), wherein the filter medium body (48) of at least one of the filter elements (20, 26) features a variable height (56) within it, wherein the filter medium body (48) of the at least one filter element (20, 26) features a lower height (56) in an area of greater width of the bypass channel (36).

2. The air filter (10) according to claim 1, characterized in that, in at least one of the filter elements (20, 26), the filter medium body (48) is formed with folds (50) of varying height (56), wherein lower folds (50) are provided in the area of the greater width of the bypass channel (36), and / or the inflow surface (22) of the first filter element (20) and the outflow surface (30) of the second filter element (26) extend parallel to each other.

3. The air filter (10) according to one of the preceding claims, characterized in that the height (56) of the filter medium body (48) of the at least one filter element (20, 26) decreases continuously or gradually, and / or both filter elements feature a filter medium body (48) with a height (56) that varies within it, wherein the two filter medium bodies (48) each feature a lower height (56) in an area of greater width of the bypass channel (36).

4. The air filter (10) according to one of the preceding claims, characterized in that the filter element (20, 26) with variable height (56) features at least one frame element (58) which, in the area of the lower height, projects beyond the filter medium body (48), wherein the frame element (58) features at least one section (62) of reduced overhang, in particular a recess (60), and wherein the filter housing (12) features a projection (64) adjacent to the section (62) of reduced overhang, which engages at least section-wise with the recess (60).

5. The air filter (10) according to one of the preceding claims, characterized in that at least one of the filter elements (26) features a seal (66) that forms a first and a second seal section (68, 70), wherein the first seal section (68) surrounds the filter medium body (48) and the second seal section (70) encloses a through-flowable orifice (40).

6. The air filter (10) according to claim 5, characterized in that a flow path of an air flow passing in series through the two filter elements (20, 26) extends through the through-flowable orifice (40).

7. The air filter (10) according to claim 5 or 6, characterized in that a fluid connection between the outflow surface (30) of the second filter element (26) and an outlet (18) of the filter housing (12) is established only through the through-flowable orifice (40).

8. The air filter (10) according to any one of claims 5 to 7, characterized in that the seal (66) seals two housing components (14, 16) of the filter housing (12) against one another.

9. The air filter (10) according to one of the preceding claims, characterized in that the flow-guiding device (32) is formed by a flap (34) which, in a first position, closes the bypass channel (36) and, in a second position, opens the bypass channel (36).

10. A use of a filter element (20, 26) that is designed as a flat filter element and features a filter medium body (48) with an inflow surface (22, 28) and an outflow surface (24, 30), wherein the filter medium body (48) features a variable height (56), in an air filter (10) according to one of the preceding claims.

11. The use of a filter element (20, 26) according to claim 10, characterized in that the filter medium body (48) is designed with folds (50) of varying height (56).

12. The use of a filter element (20, 26) according to claim 10 or 11, characterized in that the height (56) of the filter medium body (48) decreases continuously or gradually.

13. The use of a filter element (20, 26) according to any one of claims 10 to 12, characterized in that the filter element (20, 26) features at least one frame element (58) which projects beyond the filter medium body (48) in the area of the lower height (56), wherein the frame element (58) features at least one section (62) of reduced overhang, in particular a recess (60).

14. The use of a filter element (20, 26) according to any one of claims 10 to 13, characterized in that the filter element (26) features a seal (66) that forms a first and a second seal section (68, 70), wherein the first seal section (68) surrounds the filter medium body (48) and the second seal section (70) encloses a through-flowable orifice (40), and / or a flow path of an air stream passing serially through the two filter elements (20, 26) passes through the through-flowable orifice (40).

15. The use of a filter element (20, 26) according to claim 14, characterized in that a fluid connection between the outflow surface (30) of the filter element (26) and an outlet (18) of the filter housing (12) is established only through the through-flowable orifice (40).