AIR FILTER ELEMENT AND METHOD OF PRODUCTION THEREOF

Abstract

The invention relates to an air filter element (100) comprising: a filter material pack (110) comprising a filter material, the filter material pack having an optionally nearly flat first side (111) and an optionally nearly flat second side (112), the first side (111) and the second side being parallel, optionally (112); and a guide ring (120) comprising a sealing surface having at least one radially oriented component positioned on at least one of the first side (111) and the second side (112); wherein a circumference of the guide ring comprises at least a convex portion and at least one concave portion; and wherein a contour of the filter material pack (110) corresponds to the convex portion of the guide ring and at least part of the concave portion. The invention also relates to a method of producing an air filter element.

Description

AIR FILTER ELEMENT AND METHOD OF PRODUCTION OF THE SAME FIELD OF INVENTION The present invention relates to air filter elements and methods of producing air filter elements. BACKGROUND OF THE INVENTION U.S. Patent No. 9,162,172 B2 describes an air filter that includes a housing and an access cover. The internal volume of the housing can be accessed through an opening in a side wall of the housing. A filter element having grooved filter media can be removed and replaced from the air filter. The housing is constructed and positioned to engage the element in a sealed clutch with the housing. One method of installing the filter element in the air filter includes sliding a portion of the filter element against a sliding surface in the housing. One method of servicing an air filter includes tilting the filter element against an inclined surface in the housing to release a seal between the filter element and the housing. The filter element may have a handle to assist in servicing the air filter.The housing may have an inspection window that allows visual inspection of the internal component. Ref. 341275 accommodation and to determine, visually, whether a filter element is installed in it. The sealing of filter elements of the type described in U.S. Patent No. 9,162,172 B2 has been found to be unsatisfactory in some cases. It has also been found that the generic housing shape described in U.S. Patent No. 9,162,172 B2 could, in some cases, allow for the incorrect insertion of filter elements and the deliberate or unintentional replacement of suitable filter elements with unsuitable ones, which could lead to malfunctions of the air filter system and even damage to systems downstream of the air filter system. U.S. Patent No. 9,205,361 B2 describes an air filter element for an air filter having a tubular filter material, the annular cross-section of which encloses the interior of the filter element and having an inner wall joining the interior of the filter element and extending in the form of at least one convex arc and at least two concave arcs, the concave arc being located between two convex arcs such that the interior of the filter element has a restriction in the area of ​​the concave arc, the restriction being joined by two wide zones of the interior of the filter element. This description QfrZQ ίη / ZZΖΠZΖ / Β / YΙΛΙ is not related to grooved filter materials, nor to the problems described above in the context of United States Patent No. 9,162,172 B2. In the publication of German Patent application no. DE 10 2015 016236 Al describes a filter element comprising a plurality of overlapping vanes, implemented in an irregular manner and having at least one curvature, and interconnected in their curved state, wherein the axes of curvature are parallel to the flow channels. The filter element of DE 10 2015 016236 Al does not have a guide ring with a sealing surface configured to provide radial sealing when installed in the target housing. The filter material of the filter element of DE 10 2015 016236 Al is not tubular in shape. In the publication of European Patent application no. EP 1 656 982 A1 describes a composite filter construction comprising a first layer of open-cell polyurethane foam, an intermediate layer comprising polyester fibers and polypropylene microfibers, a second layer, bonded to the intermediate layer, comprising a polypropylene nonwoven fabric material, and a polypropylene packing material molded together with the layers. The filter construction of EP 1 656 982 A1 does not have a guide ring with a sealing surface configured to QfrZQ ίΠ / ZZΖ / E / YΙΛΙ provides radial sealing when installed in the target housing. The filter material of the filter construction of document EP 1 656 982 Al does not have a tubular shape. In the publication of German Patent application no. DE 10 2014 016908 A filter element for fluids, in particular, of an internal combustion engine, in particular of a motor vehicle, is described in Figures 8 and 9, comprising a filter bellows made of a filter material, this filter material being placed in the filter bellows along folded edges, in particular, in a zigzag shape, in folds, which extend between opposite face edges of the filter bellows, wherein a face fold has a folded edge and an opposite free face boundary is placed on each opposite end face of the filter bellows and at least two folded edges are consecutive along a face edge of a folded end on opposite surfaces of the filter bellows, wherein at least one segment of one of the face edges extends at least at an angle towards one of the folded edges such that, in the segment,The folded edges on one surface have a different length than the folded edges on the other surface, and the folds are sealed laterally by the face or surface edges. The cited modalities do not have a guide ring. QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ with a sealing surface configured to provide radial sealing when installed in the target housing. The filter material of these forms is not tubular in shape. European Patent Application No. EP 2 675 547 A1 describes an air filter system that includes a filter housing with a filter element received within the housing. The filter element comprises a pleated filter material. A secondary housing secures and closes the filter housing. The secondary housing includes a locking element that can be operated to engage the filter housing and the filter element. The filter element includes at least one retaining element wherein the locking element of the secondary housing engages with the retaining element such that, when the filter element is accommodated in the filter housing and positioned between the filter housing and the secondary housing, the secondary housing is detachably secured to the filter housing.This document does not describe a guide ring comprising a sealing surface having at least one component oriented in a radial direction. SUMMARY OF THE INVENTION One objective of the embodiments of the present invention is to provide a filter element with QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ improved sealing characteristics. An additional objective of the embodiments of the present invention is to reduce the risk of incorrect installation of filter elements in filter systems. According to one aspect of the present invention, an air filter element is provided comprising: a filter material pack comprising a filter material, the filter material pack having a first and a second side, which can optionally be arranged as a nearly flat first side and a nearly flat second side, the first side and the second side being optionally parallel; and a guide ring comprising a sealing surface having at least one radially oriented component, positioned on at least one of the first and second sides; wherein a circumference of the guide ring comprises at least a convex portion and at least one concave portion; and wherein a contour of the filter material pack corresponds to the convex portion of the guide ring and at least part of the concave portion. The present invention is based, inter alia, on the inventors' insight that by supplying the filter element with a guide ring having a sufficiently curved circumference, in particular a circumference with at least one convex portion and at least one concave portion, a more reliable seal can be obtained than when the seal Q1?7Q ίη / 77Π7 / E / YΙΛΙ is formed along nearly straight lines. The guide ring comprises a sealing surface having at least one component oriented in a radial direction; in particular, the guide ring could comprise a radially oriented seal (also referred to as a radial seal). The present invention is also based on the inventors' additional insight that by providing the filter element with a guide ring whose circumference has at least one convex portion and at least one concave portion, the overall symmetry of the filter element could be reduced, thereby reducing the chances of incorrect installation of the filter element in the housing. The present invention is also based on the inventors' further insight that, by having a filter material pack whose contour corresponds to the circumference of the guide ring, at least in the convex portions, the space defined by the guide rings is optionally used to provide the filtering capacity. The term "corresponds to" is used herein to indicate that the shape of the filter material pack closely follows the shape of the guide ring; the distance between the contour of the filter material pack and the guide ring is relatively small and does not vary considerably along the contour. Along the convex portion of the periphery, preferably, the guide ring The guide ring remains within a distance of 2 cm, more preferably within 1 cm, and most preferably within 0.5 cm, from the outline of the filter media pack. Along the convex portion of the periphery, the distance between the guide ring and the outline of the filter media pack preferably does not vary by more than 2 cm, more preferably by more than 1 cm, and most preferably by more than 0.5 cm. Optionally, the periphery of the guide ring could correspond with the outline of the filter media pack along its entire length, i.e., not only along the convex portion. An additional advantage of a filter media pack with a contour is that it has a concave portion, the hollow space created in this way being very suitable for the placement of a handle to facilitate the installation or removal of the filter element. Preferably, the sealing surface having at least one directionally oriented component is configured to provide radial sealing when installed in a suitably shaped cavity. Ideally, the filter media pack has a tubular shape. The term quasi-tubular is used to cover shapes obtained by rolling a length of filter media (with or without a core or hollow space in the center). QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ refers to the shapes obtained by arranging folded filter materials as a tube and the shapes obtained by combining multiple units that are almost tubular in the sense mentioned above. The almost tubular shape could include one or more folds and / or creases. In one embodiment of the air filter element according to the present invention, the filter material pack comprises a coiled length of filter material having a tubular shape and a core that is almost geometrically similar to the outline. One advantage of this method is that relatively complex contours can be obtained by winding the filter materials around a sensibly designed core. The filter materials could be wound around a winding core, removed from the cooling core, and then fitted with a final core. Alternatively, the filter materials could be wound around a core that remains in place in the final product. Another advantage of this method is that it provides increased rigidity. The term "geometrically similar" is used herein to designate an object of the same general shape, albeit on a different scale. The term "geometrically almost similar" is used to indicate that the similarity of the shapes of the core and guide ring need not be exact, although it is strong enough for the core to determine QfrZQ ίΠ / ZZΖηZ / Ε / YΙΛΙ the shape and the resulting rolled-up package. In one embodiment of the air filter element according to the present invention, the filter material pack comprises z-type filter materials. In arrangements of this type, the inlet surface and outlet surface of the filter materials are the nearly flat parallel sides where the ends of the grooves of the filter media or materials are aligned. In one embodiment of the air filter element according to the present invention, the filter material pack comprises pleated filter materials arranged in a tubular shape. In arrangements of this type, the inlet and outlet surfaces of the filter media are usually the inner layer or mantle of the tubular hole and the outer mantle of the tubular shape, or vice versa. While the filter media pack has a nearly flat first side and a nearly flat second side, and the first and second sides are parallel, as previously described, pleated filter media could be placed within this filter media pack in a different shape, such as a W-shape. In one embodiment of the air filter element according to the present invention, the outline is elongated and QfrZQ Ln / Zznz / E / YIAI at least one concave portion is present along one longitudinal side of the contour. More specifically, the contour could be essentially bean-shaped or kidney-shaped. The filter element is then of the bean-shaped or kidney-shaped type. One advantage of this approach is that the degree of symmetry can be introduced into the design with minimal added complexity. In one embodiment of the air filter element according to the present invention, the filter material pack comprises at least two separately wound lengths of filter material, which are held together by the guide ring. More particularly, the outline could be essentially 8d-shaped. The filter element is then of the 8-shape or lemniscate type. This design is based, among other things, on the inventors' insight that the filter material pack could advantageously be figure-eight or similar. An advantage of this design is that the individual rollers can be cylindrical and can be obtained simply by winding a sheet of the medium around a cylindrical core or upon itself, while the combination of several rollers still results in the desired contour having a concave part and a curved part. QfrZQ ίΠ / ZZΖηZ / E / YΙΛΙ convex. Each of at least the two separately wound lengths of filter material could comprise a cylindrical core (the winding core on which it was wound, or a different core inserted after removal of the winding core roller), or it may be coreless. In one embodiment of the air filter element according to the present invention, the filter material pack is rolled up so as not to leave a hollow space in its center. In one embodiment, the filter material pack is wound or coiled so that the filter material pack has no hollow space in its center. Since filter media packs consisting of certain types of filter media, such as grooved or Z-type filter media, do not require a tubular shape for the purpose of supplying or extracting air from the hollow center (as is the case in the pleated media examples described in U.S. Patent No. 9,205,361 B2, cited above), the filter media pack could advantageously be completely filled with the filter media, thereby increasing the filtration capacity for a given housing volume. This complete filter media pack could be obtained by winding the filter media around QfrZQ Ln / Zznz / E / YIAI of a removable core of winding and by flattening it after it is taken off the roll. Alternatively, this complete filter media package could be obtained by rolling a sheet of the filter media sheet upon itself. According to one aspect of the present invention, an air filter system is provided comprising a housing and an air filter element with an essentially bean-shaped contour, or a shape as described above; the housing defines a cavity shaped to be able to retain the air filter element; wherein the housing comprises an access window for inserting the air filter element into the cavity and for removing the air filter element from the cavity; and wherein the access window is shaped and positioned such that the air filter element can be inserted and removed by a movement comprising a rotation. A particular advantage of filter elements with bean-shaped or kidney-shaped contours is that the filter system can occupy available space in a system that would otherwise be unable to accommodate a traditionally shaped filter system (particularly a cavity with a bend or corner). Furthermore, air filter elements can be inserted and removed in a non-axial direction. Q1?7Q ίη / ZZΖΠZ / E / YΙΛΙ could be moved into or out of the housing along a path between obstacles, such as previously positioned components of an engine or machine, which would not have been possible with a standard straight-shaped filter element. In these cases, the housing could be adapted to allow the filter element to be inserted and removed from the side (i.e., transversely rather than axially in the direction of the airflow to be filtered). In this case, a relatively small side hole might be sufficient to allow the filter element to slide, in a rotational manner, into or out of the housing. This rotational movement allows the bean- or kidney-shaped air filter element to rotate around the corner during installation or removal. This corner might be necessary because the housing may have to be placed in a part of a machine or engine system where the presence of other essential components does not leave room for a large, straight filter cavity.The bean-shaped or kidney-shaped air filter element can be bent around an obstacle and still be inserted or removed with relative ease. Consequently, obstacles such as components of a predetermined engine arrangement (e.g., the arrangement of engine components under the hood of a car or truck) could be present in the space defined by the filter element. QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ the concave portion of the filter media contour pack during the insertion or removal path of the latter. In some embodiments, the access window is shaped and positioned such that, taking into account the shape of the air filter element, the air filter element can only be inserted and removed by a movement comprising a rotation, for example, following the curvature of the contour. More complex shapes, having two or more concave portions along the contour of the filter media pack, could be used to allow the filter element to travel through more complex combinations of obstacles. Preferably, the sealing surface of the air filter element provides a radial seal against the housing. In some examples, the sealing surface is oriented away from a longitudinal axis of the filter element and can thus be characterized as an outward-facing seal or an outward-facing radial seal. According to one aspect of the present invention, a method for producing an air filter element is provided. The method comprises: winding at least one length of filter material having a constant width to produce a filter material package with a nearly flat first side and a nearly flat second side, the first side and the QfrZQ ίΠ / ZZΖηZ / E / YΙΛΙ second side are parallel; and placing a guide ring comprising a sealing surface having at least one radial component on at least one of the first side and the second side; wherein a circumference of the or each guide ring comprises at least one convex portion and at least one concave portion; and wherein a contour of the filter material pack corresponds to the convex portion of the guide ring and at least part of the concave portion. Ideally, the filter material has a nearly tubular shape. Ideally, the sealing surface is configured to provide a radial seal when installed in a properly shaped cavity. In one embodiment of the method according to the present invention, the winding comprises winding the length of the filter material around a core that has a shape that is almost geometrically similar to a circumference. In one particular form, the outline is elongated, and at least one concave portion is present along one longitudinal side of the outline. More specifically, the outline could be essentially bean-shaped or kidney-shaped. In one embodiment of the method according to the present invention, the winding comprises separately winding at least two lengths of filter material around the respective cylindrical cores and joining the two separately wound lengths of filter material together by placing the guide ring. More particularly, the contour could be essentially 8d-shaped. In one embodiment of the method according to the present invention, the winding comprises winding the length of the filter material around a core; the method further comprises removing the core from the filter material bundle and deforming the filter material bundle to obtain the contour. In one embodiment, an air filter element is provided with a filter media pack, a first guide ring, and a sealing portion. The filter media pack may be formed from wound, grooved filter media and may have an outer circumference defining a convex portion and a concave portion. The first guide ring can be mounted on a first end of the filter media pack. The first guide ring may also define a convex portion corresponding to the convex portion of the filter media pack and a concave portion corresponding to the concave portion of the filter media pack. The sealing portion may be supported by the first guide ring and may define an outward-facing radial sealing surface. The first guide ring may also define the concave and convex portions. In one configuration, a second guide ring mounted on QfrZQ Ln / Zznz / E / YIAI a second end of the filter material package. In one modality, each of the first channel ring and the filter material pack has two convex portions and two concave portions. In one version, the filter material package also includes a central core. In one embodiment, the filter material pack has a cross-sectional shape characterized as a kidney shape, a bean shape, a lemniscate or 8-shape, an S-shape, and a W-shape. The effects and technical advantages of the modalities of the method according to the present invention correspond, mutatis mutandis, to those of the corresponding modalities of the filter element according to the present invention. BRIEF DESCRIPTION OF THE FIGURES These and other features and advantages of the embodiments of the present invention will be described in greater detail with reference to the accompanying figures, in which: - Figure 1 shows a perspective view of a filter element according to a first embodiment of the present invention; - Figure Ib shows an end view of the filter element shown in Figure 1a; - Figure 1c shows a cross-sectional view QfrZQ ίΠ / ΖΖηΖ / Ε / ΥΙΛΙ cross section of the filter element shown in Figure la, taken along line AA in Figure Ib. - Figure 2 shows an exploded view of the filter element according to the configuration shown in Figure 1; - Figure 3 illustrates, schematically, a first method of producing the filter element according to the modality of Figure 1a; Figures 4a-4c illustrate schematically a second method of producing the filter element according to the modality of Figure 1a; - Figure 5a shows a perspective view of a filter element according to a second embodiment of the present invention; - Figure 5b shows an end view of the filter element shown in Figure 5a; - Figure 5c shows a cross-sectional view of the filter element shown in Figure 5a, taken along line AA in Figure 5b; - Figure 6 shows an exploded view of the filter element according to the configuration shown in Figure 5a; - Figure 7a shows a perspective view of a filter element according to a third embodiment of the present invention; QfrZQ ίη / ΖΖΠΖ / Ε / ΥΙΛΙ - Figure 7b shows an end view of the filter element shown in Figure 7a; - Figure 7c shows a cross-sectional view of the filter element shown in Figure 7a, taken along line AA in Figure 7b; - Figure 8 shows an exploded view of the filter element according to the configuration shown in Figure 7a; - Figure 9a shows a perspective view of a filter element according to a fourth embodiment of the present invention; - Figure 9b shows an end view of the filter element shown in Figure 9; - Figure 9c shows a cross-sectional view of the filter element shown in Figure 9a, taken along line AA in Figure 9b; - Figure 10 shows an exploded view of the filter element according to the modality of Figure 9a; Figures 11-11b illustrate, schematically, a method of producing the filter element according to the modality of Figure 10; - Figure 12a presents a first perspective view of an air filter system comprising a QfrZQ ίη / ZZΖΠZΖ / Β / YΥΙΛΙ air filter element according to an embodiment of the present invention; - Figure 12b presents a second perspective view of the air filter system shown in Figure 12a; - Figure 13a shows a first perspective view of the air filter element depicted in Figure 12a; - Figure 13b shows a second perspective view of the air filter element shown in Figure 13a; - Figure 14 shows a sketch of an example of a shape of the filter material package as it could be comprised in an embodiment of the present invention; - Figure 15 shows a sketch of another example of a form of the filter material package as it could be comprised in an embodiment of the present invention; - Figure 16 shows a sketch of another example of a form of filter material package as it might be comprised in an embodiment of the present invention; and - Figure 17 shows a sketch of another example of a shape of the filter material package as it might be comprised in a modality of the present QfrZQ ίΠ / ΖΖηΖ / Ε / ΥΙΛΙ invention. DETAILED DESCRIPTION OF THE INVENTION A first embodiment of the filter element according to the present invention will be described below with reference to Figures 1a-4c. Figures la-lc present, respectively, a plan view (top left), a cross-section view (bottom left), and a perspective view (right) of this type. The illustrated air filter element 100 comprises a filter media pack 110 comprising a rolled length of filter media. The filter media pack 110 has a nearly flat first side 111 and a nearly flat second side 112, which are parallel to each other. The air filter element 100 is intended to be removably installed in a housing (not shown). To allow insertion or removal of the air filter element 100, the housing has one or more openings or windows. Various housing and window arrangements are possible, including systems where the opening is accessed by removing the end of the housing where the inlet or outlet is provided, and systems where access is gained through a window in the side of the housing. For filter media pack designs having an elongated outline, the side loaders could have their window on the narrow side or the wide side. QfrZQ ίη / ΖΖΠΖ / Ε / ΥΙΛΙ The present invention could be implemented with different types of filter materials, including pleated filter materials and grooved filter materials. Several types of pleated filter materials are commercially available and known to the skilled worker. Grooved filter materials include filter material having a plurality of grooves formed therein with alternating ends of adjacent grooves closed to force the fluid to pass through the filter material. Several types of grooved filter materials are commercially available and known to the skilled worker. A filter media package of the grooved filter media or z-type filter media type is known to a person skilled in the art. For example, some types of grooved filter media are known from U.S. Patent No. 3,025,963 to Jordan V. Bauer, U.S. Patent No. 5,895,574 to Francis Friedmann et al., U.S. Patent No. 6,416,605 to Patrick Golden, and from U.S. Patent Application Publication No. US 2014 / 0102057. The entirety of each of U.S. Patent 574, U.S. Patent 605, and U.S. Patent Application Publication No. 057 is incorporated herein by reference in its entirety. A filter media package 110 of the filter media type The grooved QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ could be obtained, for example, by rolling a base sheet comprising generally parallel hollow tubes (grooves, original tubes) and by applying a sealing adhesive between successive layers of the rolled filter material, for example, on the side of the open ends. The base sheet may be composed, for example, of a flat sheet of material and a corrugated sheet of material, which are coupled together. The first axial ends of the hollow tubes are supporting a first almost flat side 111 of the filter material pack 110 and the second axial ends of the hollow tubes are supporting a second almost flat side 112 of the filter material pack 110. Complementary spaces / tubes can be created between the hollow tubes when the base sheets are wound and are defined between the wavy sheet of a certain winding and the flat sheet of its subsequent winding. Hollow tubes and complementary spaces / tubes can be interrupted at suitable locations to force air into a first tube (e.g., an original tube) at its first axial end (on the first flat side 111) to pass through the side wall of the first tube into one or more adjacent second tubes (e.g., complementary tubes). Subsequently, the air is forced out of the second tubes at the second axial end of the second tubes (on the second flat side 112). Some of Q1?7Q ίη / 77Π7 / E / YΙΛΙ These interruptions could be provided initially with the original tubes (e.g., enclosed at their second axial end), others could be provided, for example, when applying the sealing adhesive (e.g., for supplementary tubes, preferably near their first axial ends). Ends 111, 112 then serve as the filter inlet and outlet surfaces. When the filter element 100 is installed in the filter housing system of which it forms part, air is supplied to the inlet surface, preferably, though not necessarily, by means of a pre-cleaning filter which could comprise a number of cyclones and can be removed from the outlet surface. Similarly, another type of filter material package 110 could be obtained which includes a winding stage of a medium that is provided in the form of a sheet. The air filter element 100 further comprises a guide ring 120 positioned on at least one of the first side 111 and the second side 112. Preferably, the guide rings 120 are present on both sides 111 and 112, as illustrated. At least one guide ring 120 comprises an axially oriented sealing surface or a sealing surface having at least one radially oriented component, for example, a radially oriented component. QfrZQ ίΠ / ZZΖηZ / E / YΙΛΙ directed outwards. In addition, this could have an axial component. This could be provided with a packing, which acts as a radial seal or an axial seal with at least one radial component. The guide rings 120 provide the sealing surface that allows the filter element 100 to engage, in a sealed manner, with the filter inlet and / or outlet port system. Furthermore, these rings may contribute to the structural rigidity of the filter element 100 and can assist the operator in correctly positioning the filter element 100 within the filter system (by virtue of their shape and, optionally, by means of additional guide elements such as protrusions, grooves, tabs, and the like). The guide rings 120 could comprise a rigid plastic material 120a (which could be, for example, a support structure) such as, but not only, polyethylene or polypropylene, with a separate gasket or seal 120b made, for example, of a suitable elastomer or polyurethane placed on its sealing surface. Alternatively, the guide rings 120 could be made of a material that can serve as a seal, in particular, a suitable elastomer such as polyurethane. The 120 guide rings could be manufactured separately and could be coupled with the 110 filter media pack, or they could be molded in place (i.e., QfrZQ Ln / Zznz / E / YIAI on molded in the filter material package 110) if the melting and curing properties of the chosen material allow it. In the illustrated case, the air filter, as seen in the plan view, has an elongated shape. The circumference of each guide ring 120 comprises at least one convex portion and at least one concave portion. With reference to the orientation of the plan view for the present purpose, it can be clearly observed in the illustrated case that the left-hand side 120c and the right-hand side 120d of the outline are convex (viewed from outside the filter element), while the upper side 120e and the lower side 120f of the outline (the longitudinal sides) comprise a concave central portion 120e, 120f. In the illustrated case, the outline of the filter media pack 110 (as seen in cross-section in any plane parallel to the flat sides 111, 112) corresponds to (i.e., closely matches) the entire circumference of the guide ring 120. Figure 2 shows an exploded view of the filter element according to the first embodiment. The filter material pack 110 has a tubular shape, meaning its shape closes upon itself around a hollow center and comprises a web 130 that is almost geometrically similar to the outer contour of the material pack. QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ filter material 110. Figure 2 shows the guide rings 120 on each side of the filter material 110 and the core 130 that will be placed in the center of the filter material 110. The guide ring could be contained in an element 125 that covers part of the relevant side 111 or 112, for example, to prevent telescopic deformation of the rolled bundle of filter material 110; to increase structural rigidity, the element 125 could also help to hold the core 130 in place. Figure 3 schematically illustrates a first method for producing the filter element 100 according to the first embodiment. The method comprises winding a length of filter material of constant width to produce a filter material bundle 110 with a nearly flat first side 111 and a nearly flat second side 112, the first side 111 and the second side 112 being parallel. The winding comprises winding the length of filter material around a core 130 having a shape that is geometrically almost the same as the desired circumference. To achieve a sufficiently strong winding, the sheet is held under suitable tension and pressed onto the core 130 and then onto the bundle by suitably positioned alternating rollers 151-154. Adhesive (not shown) is applied to the sheet to bond the successive layers together. Q1?7Q ίη / ΖΖΠΖ / Ε / ΥΙΛΙ Once a filter material package 110 of the desired shape and size has been obtained, the guide ring 120 described above is placed on at least one of the first side 111 and the second side 112 (not illustrated in Figure 3). Figures 4a-4c illustrate, schematically, a second method of producing the filter element according to the first modality. In a preliminary stage (not illustrated), a length of filter material of constant width is wound around an oval or oblong winding core to produce a filter material bundle 110 with a nearly flat first side 111 and a nearly flat second side 112, the first side 111 and the second side 112 being parallel. Because the winding core is oval or oblong, the tension and pressure on the filter material sheet are less complex than in the case illustrated in Figure 3. During the winding operation, adhesive is applied to the sheet to hold the consecutive layers together. After removal of the winding core, the resulting filter material bundle 110 has an elongated shape without the concave portions and hollow center. In a first stage 1010, a 130 core that represents the desired contour shape by being almost geometrically similar to it is inserted in the hollow center of the package QfrZQ Ln / Zznz / E / YIAI of filter material 110. In a second step 1020, the filter material pack 110 with the core 130 is placed in a suitably configured press mold 160, which has protrusions corresponding to the desired concave portions of the contour. In a third step 1030, the press mold 160 is closed to force the filter material pack 110 into the desired shape. Since this deformation inevitably causes some slippage of the filter material layers in the filter material pack 110, this step should preferably be completed before the applied adhesive has fully cured. At a later stage (not illustrated), the guide ring 120, described above, is placed on at least one of the first side 111 and the second side 112. A second embodiment of the filter element according to the present invention will be described below with reference to Figures 5a and 6. This embodiment will be described with emphasis on the elements that differ from those of the first embodiment. Figures 5a-5c present a plan view (top left), a cross-sectional view (bottom left), and a perspective view (right) of this type. The illustrated air filter element 100 comprises a filter material pack 110 comprising two QfrZQ ίΠ / ZZΖηZ / E / YΙΛΙ lengths wound separately from the filter material. The resulting filter material bundle 110 has a nearly flat first side 111 and a nearly flat second side 112, which are parallel to each other. As before, preferably, the filter material is of the grooved filter material type. The air filter element 100 further comprises a guide ring 120 positioned on at least one of the first side 111 and the second side 112. Preferably, the guide rings 120 are present on both sides 111, 112, as illustrated. Since the illustrated filter media pack 110 consists of two separately wound lengths of filter media, the guide ring 120 has the additional function of holding these two rolls together to form a pack. In the illustrated case, the air filter element 100 has an elongated shape. The circumference of each guide ring 120 comprises at least one convex portion and at least one concave portion. With reference to the plan view orientation for the present purpose, it can be clearly observed in the illustrated case that the left-hand side 120c and the right-hand side 120d of the contour are convex (viewed from the outside of the filter element), while the upper side 120e and the lower side 120f of the contour (the longitudinal sides) comprise a concave central portion 120e, 120f. In the illustrated case, the contour of the pack of QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ filter material 110 corresponds to (i.e., closely matches) the convex portion of the circumference of the guide ring 120. However, as the concave portions 120e, 120f are located where the two media rolls coincide with each other, the outline of the filter material pack 110 does not strictly follow the circumference of the guide ring 120 in these portions. Figure 6 shows an exploded view of the filter element according to the second embodiment. The filter media pack 110 consists of two tubular cylinders, i.e., cylinders with a hollow center, and comprises the corresponding cylindrical cores 130. Figure 6 also shows the guide rings 120 on each side of the filter media 110 that hold together the rolls of filter media 110 and the cores 130 that will be placed in the center of the rolls of filter media 110. A third embodiment of the filter element according to the present invention will be described below with reference to Figures 7a-8. This embodiment will be described with emphasis on the elements that differ from those of the first embodiment. Figures 7a-7c respectively depict a plan view (top left), a cross-section view (bottom left), and a perspective view (right) of this type. Q1?7Q ίΠ / ΖΖηΖ / Ε / ΥΙΛΙ The illustrated air filter element 100 comprises a filter material pack 110 comprising a rolled length of filter material. The filter material pack 110 has a first nearly flat side 111 and a second nearly flat side 112, which are parallel to each other. Preferably, the filter material is again of the grooved filter material type. The air filter element 100 further comprises a guide ring 120 positioned on at least one of the first side 111 and the second side 112. Preferably, the guide rings 120 are present on both sides 111, 112, as in the illustrated case. In the illustrated case, the air filter element 100 has an elongated shape. The circumference of each guide ring 120 comprises at least one convex portion and at least one concave portion. With reference to the plan view orientation for the present purpose, it can be clearly observed in the illustrated case that the left-hand side 120c and the right-hand side 120d of the contour are convex (viewed from outside the filter element), while the upper side 120e of the contour is straight and the lower side 120f of the contour comprises a concave central portion 120f. In the illustrated case, the contour of the filter media pack 110 corresponds to (i.e., closely matches) the entire circumference of the guide ring 120. Figure 8 shows an exploded view of the QfrZQ ίΠ / ZZΖηZ / E / YILI filter element according to the first modality. The filter material pack 110 has a tubular shape, i.e., its shape closes upon itself around a hollow center and comprises a core 130 that is almost geometrically similar to the outer contour of the filter material pack 110. Figure 8 shows the guide rings 120 on each side of the filter material 110 and the core 130 that will be placed in the center of the filter material 110. A fourth embodiment of the filter element according to the present invention will be described below with reference to Figures 9a-11b. This embodiment will be described with emphasis on the elements that differ from those of the first embodiment. Figures 9a-9c respectively depict a plan view (top left), a cross-section view (bottom left), and a perspective view (right) of this type. The illustrated air filter element 100 comprises a filter material pack 110 comprising a rolled length of filter material. The filter material pack 110 has a first nearly flat side 111 and a second nearly flat side 112, which are parallel to each other. Preferably, the filter material is again of the grooved filter material type. The air filter element 100 further comprises a guide ring 120 positioned on at least one of the first side 111 and the second side 112. Preferably, the guide rings 120 are present on both sides 111, 112, as in the illustrated case. In the illustrated case, the air filter element 100 has an elongated shape. The circumference of each guide ring 120 comprises at least one convex portion and at least one concave portion. With reference to the plan view orientation for the present purpose, it can be clearly observed in the illustrated case that the upper side 120e, the left-hand side 120c, and the right-hand side 120d of the contour are convex (viewed from outside the filter element), while the lower side 120f of the contour comprises a concave central portion 120f. In the illustrated case, the contour of the filter media pack 110 corresponds to (i.e., closely matches) the entire circumference of the guide ring 120. Figure 10 shows an exploded view of the filter element according to the first configuration. The filter media pack 110 is completely filled, meaning it has no hollow center and no core in this case. Figure 10 also shows the guide rings 120 on each side of the filter media 110. Figures 11-11b illustrate, schematically, a method for producing the filter element of QfrZQ ίΠ / ZZΖηZΖ / Ε / YΙΛΙ in accordance with the fourth modality. In a preliminary stage (not illustrated), a length of filter material of constant width is wound around a cylindrical winding core to produce a filter material pack 110 with a nearly flat first side 111 and a nearly flat second side 112, the first side 111 and the second side 112 being parallel. Since the winding core is cylindrical, the tensioning of the filter material sheet is less complex than in the case illustrated in Figure 3. During the winding operation, adhesive is applied to the sheet to hold the successive layers together. After removal of the winding core, the resulting filter material pack 110 has a cylindrical shape without the concave portions and a hollow center. In a first stage (2010), the filter media pack 110 with a hollow center is placed in a suitably configured press mold 160, which has protrusions and cavities corresponding to the desired contour shape. In a second stage (2020), the press mold 160 is closed to force the filter media pack 110 into the desired shape. Since this deformation inevitably causes some slippage of the filter media layers within the filter media pack 110, this stage should preferably be completed before the applied adhesive has fully cured. QfrZQ ίη / ΖΖΠΖ / Ε / ΥΙΛΙ At a later stage (not illustrated), the guide ring 120, as described above, is placed on at least one of the first side 111 and the second side 112. Figures 12a and 12b show two perspective views of an air filter system comprising an air filter element according to an embodiment of the present invention. Figures 13a and 13b show two perspective views of the air filter element of the air filter system depicted in Figures 12a and 12b. Without loss of generality, the air filter element illustrated in Figures 12a-13b has a coreless, kidney-shaped or bean-shaped filter material pack 110. At one end, a guide ring 120 with a sealing surface is provided. At the other end, a handle 170 is provided through a concave portion of the contour.A handle could be easily obtained by providing a bar or strip of material that connects a concave portion of the contour, so that it can be easily held by a human operator by sliding a finger into the cavity behind the handle. The handle could be flexible and attached after the filter element has been manufactured. For example, it could be glued to the outside of the filter media pack or to an outer protective layer of the pack, specifically to the concave portion. Of course, in certain forms of the present QfrZQ ίη / ZZΖΠZ / E / YΙΛΙ description: An additional protective layer or envelope, also called a curved layer, may be provided around the radial outer surface of the filter media pack. This protective layer or envelope may extend over a limited distance or the entire length of the filter media pack, providing a rigid or more rigid housing for the filter media pack. This protective layer may be made of a hard material such as plastic, or, for example, protective cardboard. Depending on the production process, the handle may also be integrally formed with the protective envelope. Furthermore, the curved envelope or plate may be integrally formed with the guide ring or a support structure contained within the guide ring. As previously stated, the filter media pack is preferably tubular in shape. The term "near-tubular" is used to describe shapes obtained by rolling a length of filter media (with or without a core or hollow space in the center), shapes obtained by arranging folded filter media into a tube, and shapes obtained by combining multiple units that are nearly tubular in the sense described above. The near-tubular shape may include one or more longitudinal folds and / or creases. Sketches of various near-tubular shapes are provided in Figures 14-17. QfrZQ ίη / ZZΖΠZ / B / YΙΛΙ this filter material package which could be placed in embodiments of the present invention. Since the purpose of the sketches is to illustrate different contours of the filter material package and / or the associated guide ring, the sketches only show the solid filter material packages without a core, without loss of generality. The person skilled will appreciate that the illustrated shapes could also be obtained by combining one or more units (e.g., rolls) of the filter material with or without arms. Figure 14 shows an example sketch of an air filter element 100 comprising a nearly tubular filter media pack 110 and a guide ring 120, the shape of which could be described as an oval that has been pressed bilaterally in a direction transverse to its long axis, resulting in an approximately lemniscate, figure-eight, or nut-like shape. As shown, the circumference of the filter media pack 110 and the circumference of the guide ring 120 have concave sections or segments interconnected by two convex segments or portions. Figure 15 shows an example sketch of an air filter element 100, which includes a nearly tubular filter media pack 110 and a guide ring 120, the shape of which could be described as an oval with a single fold. As shown, the circumference of the Q1?7Q ίη / 77Π7 / E / YΙΛΙ filter material pack 110 and guide ring circumference 120 have a concave segment or portion interconnected by one or more convex segments or portions. Figure 16 shows a sketch of an example of an air filter element 100 that includes a nearly tubular filter media pack 110 and a guide ring 120, the shape of which could be described as an oval with two folds, resulting in approximately an S-shape (as illustrated) or a Z-shape (not illustrated). As shown, the circumference of the filter media pack 110 and the circumference of the guide ring 120 are asymmetrical, with two offset concave segments or portions interconnected by two offset convex segments or portions. Figure 17 shows an example sketch of an air filter element 100 that includes a nearly tubular filter material pack 110 and a guide ring 120, the shape of which could be described as an oval with three folds, resulting in approximately a W shape. As shown, the circumference of the filter material pack 110 and the circumference of the guide ring 120 have three concave segments or portions interconnected by three convex segments or portions. The skilled person will appreciate that other suitable shapes can be obtained by combining any number of longitudinal folds and creases, as described above, with a basic tubular form. The longitudinal folds and creases can be arranged to create symmetrical or asymmetrical shapes. While the invention has been previously described with reference to particular embodiments, this was done to clarify and not to limit the invention, the scope of which will be determined with reference to the appended claims. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. An air filter element, characterized in that it comprises: a filter material pack formed from grooved and wound filter materials, the filter material pack having an outer circumference defining a convex portion and a concave portion; a first guide ring mounted on a first end of the filter material pack, the first guide ring defining a convex portion corresponding to the convex portion of the filter material pack and a concave portion corresponding to the concave portion of the filter material pack; and a sealing portion supported by the first guide ring, the sealing portion defining an outward-facing radial sealing surface.

2. The air filter element according to claim 1, characterized in that it further includes a second guide ring mounted on a second end of the filter material pack.

3. The air filter element according to claim 1 or 2, characterized in that it further comprises a curved layer surrounding a radial outer surface of the filter material pack.

4. The air filter element according to any of the preceding claims, characterized in that it further comprises a handle through the concave portion of the filter material pack.

5. The air filter element according to claim 4, characterized in that the handle is adapted so that it can be easily held by a human operator by sliding the fingers into a cavity behind the handle.

6. The air filter element according to any of the preceding claims, characterized in that the handle is flexible.

7. The air filter element according to any of the preceding claims, characterized in that each of the first guide ring and filter material pack has two convex portions and two concave portions.

8. The air filter element according to any of the preceding claims, characterized in that the filter material pack further includes a central core.

9. The air filter element according to any of the preceding claims, characterized in that the filter material pack has a cross-sectional shape characterized as a kidney shape, a bean shape, an 8-shape, an S-shape, and a W-shape.

10. The air filter element according to any of the preceding claims, characterized in that the sealing portion comprises an elastomer or polyurethane.

11. The air filter element according to any of the preceding claims, characterized in that the distance between the first guide ring and the outer circumference of the filter material pack along the convex portion remains below 2 cm.

12. The air filter element according to claim 11, characterized in that the distance between the first guide ring and the outer circumference of the filter material pack along the convex portion remains below 0.5 cm.

13. The air filter element according to any of the preceding claims, characterized in that the outer circumference of the filter material pack corresponds to the entire circumference of the guide ring.

14. The air filter element according to any of the preceding claims, characterized in that the sealing portion is formed along 5 of at least one convex portion and at least one concave portion of the first guide ring.

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