Air filter element and method for producing same

Abstract

The invention pertains to an air filter element comprising: a filter medium pack comprising a filter medium, said filter medium pack having an optionally substantially planar first side and an optionally substantially planar second side, said first side and second side optionally being parallel; and a guiding rim comprising a sealing surface having at least a radially oriented component, arranged on at least one of said first side and said second side, wherein a circumference of the or each guiding rim comprises at least one convex portion and at least one concave portion; and wherein a contour of said filter medium pack corresponds to said convex portion of said guiding rim and at least part of said concave portion. The invention also pertains to a method for producing an air filter element.

Claims

1. An air filter element comprising: a) a filter medium pack comprising a rolled-up length of a fluted filter medium arranged in a tubular shape, said filter medium pack having a substantially planar first flow side and a substantially planar second flow side, the first and second flow sides being parallel, the filter medium pack defining an outer perimeter having a convex portion and an adjacent concave portion; b) a guiding rim formed from a first material and circumscribing a portion of the filter medium pack outer perimeter; c) a sealing surface having at least a radially oriented component arranged on at least one of said first flow side and said second flow side, said sealing surface being configured to provide radial sealing when installed in a suitably shaped cavity; and d) a core disposed within the filter medium such that the filter medium pack is without a hollow space at the center of the filter medium pack, the core being substantially geometrically similar to the filter medium pack outer perimeter; and e) wherein a circumference of the guiding rim or sealing surface comprises at least one convex portion, corresponding to the filter medium pack outer perimeter convex portion, and at least one adjacent concave portion, corresponding to the filter medium pack outer perimeter concave portion.

2. The air filter element of claim 1, wherein said outer perimeter is elongate and wherein at least one concave portion is present along a longitudinal side of said outer perimeter.

3. The air filter element of claim 2, wherein said outer perimeter is essentially bean-shaped or kidney-shaped.

4. The air filter element of claim 1, wherein said outer perimeter is generally 8-shaped.

5. An air filter system comprising: a) a housing; and b) the air filter element of claim 1, c) wherein the housing defines a cavity shaped so as to be able to hold said air filter element; d) whereby said sealing surface provides radial sealing against said housing; e) wherein said housing comprises an access window for inserting said air filter element into said cavity and removing said air filter element from said cavity; and f) wherein said access window is shaped and positioned in such a way that said air filter element can be inserted and removed by a movement that comprises a rotation.

6. The air filter element of claim 1, wherein the sealing surface is provided on a seal member supported by the guiding rim.

7. The air filter element of claim 6, further including a second guiding rim mounted to the second flow side of the filter medium pack.

8. The air filter element of claim 6, wherein the first guiding rim and the filter medium pack each have two convex portions and two concave portions.

9. The air filter element of claim 6, wherein the filter medium pack has a cross-sectional shape characterized as one of a kidney-shape, a bean-shape, an 8-shape, an S-shape, and a W-shape.

10. The air filter element of claim 1, wherein the sealing surface is provided on a sealing member supported by the guiding rim, wherein the sealing member and the guiding rim are separately formed components, wherein both the sealing member and the guiding rim are substantially geometrically similar to the filter medium pack outer perimeter.

11. The air filter element of claim 10, wherein the guiding rim is formed from a first material and the sealing member is formed from a second material different from the first material.

12. The air filter element of claim 11, wherein the guiding rim is a rigid plastic material and the second material is an elastomer or polyurethane material.

13. The air filter element of claim 10, wherein the guiding rim includes a first extension circumscribing the filter medium pack outer perimeter.

14. The air filter element of claim 10, wherein a central grid portion of the guiding rim is substantially geometrically similar to the filter medium pack outer perimeter convex and concave portions.

15. An air filter element comprising: a) a filter medium pack comprising a rolled-up length of a fluted filter medium arranged in a tubular shape, said filter medium pack having a substantially planar first flow side and a substantially planar second flow side parallel to the first flow side, the filter medium pack defining an outer perimeter having a convex portion and an adjacent concave portion; b) a core disposed within the filter medium pack such that the air filter element is without a hollow space at the center of the filter medium pack, the core being substantially geometrically similar to the filter medium pack outer perimeter convex and concave portions; c) a guiding rim formed from a first material, the guiding rim having a grid structure supporting the filter medium pack first flow side and a first end of the core, the guiding rim having oppositely extending first and second axial extensions, wherein each of the guiding rim first axial extension, the guiding rim second axial extension, and a central portion of the grid structure are substantially geometrically similar to the filter medium pack outer perimeter convex and concave portions, the first axial extension circumscribing the filter medium pack outer perimeter convex and concave portions, the second axial extension extending beyond the filter medium pack first flow side and being radially inset from the filter medium pack outer perimeter; and d) a seal member formed from a second material different from the first material, the seal member being secured to the guiding rim second axial extension, the seal member being substantially geometrically similar to the filter medium pack outer perimeter convex and concave portions.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) These and other features and advantages of embodiments of the present invention will be described in more detail with reference to the attached drawings, in which:

(2) FIG. 1 presents a perspective view of a filter element according to a first embodiment of the present invention;

(3) FIG. 1a presents an end view of the filter element shown in FIG. 1;

(4) FIG. 1b presents a cross-sectional view of the filter element shown in FIG. 1, taken along the line A-A in FIG. 1a.

(5) FIG. 2 presents an exploded view of the filter element according to the embodiment of FIG. 1;

(6) FIG. 3 schematically illustrates a first method of producing the filter element according to the embodiment of FIG. 1;

(7) FIGS. 4-4b schematically illustrates a second method of producing the filter element according to the embodiment of FIG. 1;

(8) FIG. 5 presents a perspective view of a filter element according to a second embodiment of the present invention;

(9) FIG. 5a presents an end view of the filter element shown in FIG. 5;

(10) FIG. 5b presents a cross-sectional view of the filter element shown in FIG. 5, taken along the line A-A in FIG. 5a;

(11) FIG. 6 presents an exploded view of the filter element according to the embodiment of FIG. 5;

(12) FIG. 7 presents a perspective view of a filter element according to a third embodiment of the present invention;

(13) FIG. 7a presents an end view of the filter element shown in FIG. 7;

(14) FIG. 7b presents a cross-sectional view of the filter element shown in FIG. 7, taken along the line A-A in FIG. 7a;

(15) FIG. 8 presents an exploded view of the filter element according to the embodiment of FIG. 7;

(16) FIG. 9 presents a perspective view of a filter element according to a fourth embodiment of the present invention;

(17) FIG. 9a presents an end view of the filter element shown in FIG. 9;

(18) FIG. 9b presents a cross-sectional view of the filter element shown in FIG. 9, taken along the line A-A in FIG. 9a;

(19) FIG. 10 presents an exploded view of the filter element according to the embodiment of FIG. 9;

(20) FIGS. 11-11a schematically illustrates a method of producing the filter element according to the embodiment of FIG. 10;

(21) FIG. 12 presents a first perspective view of an air filter system comprising an air filter element according to an embodiment of the present invention;

(22) FIG. 12a presents a second perspective view of the air filter system shown in FIG. 12;

(23) FIG. 13 presents a first perspective view of the air filter element depicted in FIG. 12;

(24) FIG. 13a presents a second perspective view of the air filter element depicted in FIG. 13;

(25) FIG. 14 is a sketch of an example of a shape of the filter medium pack as may be comprised in an embodiment of the present invention;

(26) FIG. 15 is a sketch of another example of a shape of the filter medium pack as may be comprised in an embodiment of the present invention;

(27) FIG. 16 is a sketch of another example of a shape of the filter medium pack as may be comprised in an embodiment of the present invention; and

(28) FIG. 17 is a sketch of another example of a shape of the filter medium pack as may be comprised in an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

(29) A first embodiment of the filter element according to the present invention will now be described with reference to FIGS. 1-4.

(30) FIGS. 1-1b respectively present a plan view (top left), a cross section (bottom left), and a perspective view (right) of this embodiment.

(31) The illustrated air filter element 100 comprises a filter medium pack 110 comprising a rolled-up length of filter medium. The filter medium pack 110 has a substantially planar first side 111 and a substantially planar 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 the outlet is provided, and systems where a window on the side of the housing can be accessed. For filter medium pack designs that have an elongate contour, the “side loaders” may have their window on the narrow side or on the broad side.

(32) The present invention may be implemented with different kinds of filter media, including pleated filter media and fluted filter media. Various types of pleated filter media are commercially available and known to the skilled person. Fluted filter media includes filter material having a plurality of flutes formed therein having alternating ends of adjacent flutes closed to force fluid through filter material. Various types of fluted filter media are commercially available and known to the skilled person.

(33) A filter medium pack of the fluted filter media type or z-type media is known to the skilled person. For example, some types of fluted filter media are known from U.S. Pat. No. 3,025,963 to Jordan V. Bauer, U.S. Pat. No. 5,895,574 to Francis Friedmann et al., U.S. Pat. No. 6,416,605 to Patrick Golden, and from US patent application publication no. US 2014/0102057 A1. The entireties of each of the US '574 patent, the US '605 patent, and the US '057 publication are incorporated by reference herein in their entireties. A filter medium pack 110 of the fluted filter media type may for instance be obtained by rolling up a base sheet comprising generally parallel hollow tubes (flutes, original tubes) and applying a sealing adhesive between the consecutive layers of rolled-up filter medium, for instance at the side of the open ends. The base sheet can for instance be composed of a flat sheet of media and an undulated sheet of media, which are attached to each other. First axial ends of the hollow tubes are abutting a first substantially planar side 111 of the filter medium pack 110 and second axial ends of the hollow tubes are abutting a second substantially planar side 112 of the filter medium pack 110. Complementary spaces/tubes can be created in between the hollow tubes when rolling up the base sheets, and are being defined in between the undulated sheet of a certain winding and the flat sheet of its subsequent winding.

(34) The hollow tubes and the complementary spaces/tubes can be interrupted at appropriate locations such as to force air coming in in a first tube (e.g. an original tube) at its first axial end (at the first planar side 111) to pass through the sidewall of the first tube into one or more adjacent second tubes (e.g. complementary tube(s)), the air thereafter forcing to leave the second tube(s) at the second axial end of the second tube(s) (at the second planar side 112). Some of these interruptions may be provided initially with the original tubes (e.g. closed at their second axial end), others may be provided for instance by applying the sealing adhesive (e.g. for complementary tubes, preferably near their first axial ends). The ends 111, 112 then serve as outlet and inlet surfaces of the filter. When the filter element 100 is installed in the housing of the filter system of which it forms a part, air is supplied to the inlet surface, preferably but not necessarily, via a precleaning filter which may comprise a number of cyclones, and withdrawn from the outlet surface.

(35) Likewise, other types of filter medium pack 110 may be obtained by including a step of rolling up a medium that is provided in the form of a sheet.

(36) The air filter element 100 further comprises a guiding rim 120 arranged on at least one of said first side 111 and said second side 112. Preferably, guiding rims 120 are present on both sides 111, 112, as in the illustrated case. At least one such guiding rim 120 comprises a radially oriented sealing surface or a sealing surface having at least a radially oriented component, for example an outwardly directed radially oriented component. In addition, it may have an axial component. It may be provided with a gasket, acting as a radial seal or an axial seal with at least a radial component.

(37) Guiding rims 120 provide the sealing surface which allows the filter element 100 to sealingly engage with the inlet and/or outlet orifices of the filter system. In addition, they may contribute to the structural rigidity of the filter element 100, and they can assist the operator in correctly positioning the filter element 100 in the filter system (by virtue of their shape, and optionally by means of added guiding elements such as protrusions, grooves, tabs, and the like).

(38) The guiding rims 120 may comprise a rigid plastic material 120a (which may for instance be a supporting structure) such as but not only polyethylene or polypropylene, with a separate seal or gasket 120b made of for instance a suitable elastomer, or polyurethane arranged on their sealing surface. Alternatively, the guiding rims 120 may be made of a material that can serve as a seal, in particular a suitable elastomer such as polyurethane.

(39) Guiding rims 120 may be separately manufactured and attached to the filter medium pack 110, or they may be molded in place (i.e. overmolded onto the filter medium pack 110) if the melting and curing properties of the chosen material allow this.

(40) In the illustrated case, the air filter as seen in the plan view has an elongate shape. The circumference of each guiding rim 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 clearly be seen 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 top side 120e and the bottom side 120f of the contour (the longitudinal sides) comprise a concave central portion 120e, 120f. In the illustrated case, the contour of the filter medium pack 110 (as seen in cross-section in any plane parallel to the planar sides 111, 112) corresponds to (i.e., it closely matches) the entire circumference of the guiding rim 120.

(41) FIG. 2 presents an exploded view of the filter element according to the first embodiment. The filter medium pack 110 has a tubular shape, i.e. its shape closes onto itself around a hollow center, and comprises a core 130 that is substantially geometrically similar to the outer contour of the filter medium pack 110. FIG. 2 shows the guiding rims 120 on each side of the filter medium 110 and the core 130 to be placed at the center of the filter medium 110. The guiding rims may be comprised in an element 125 that covers part of the relevant side 111 or 112, for example to avoid telescopic deformation of the rolled up filter medium pack 110; to increase structural rigidity, the element 125 may also help to keep the core 130 in place.

(42) FIG. 3 schematically illustrates a first method of producing the filter element 100 according to the first embodiment. The method comprises rolling up a length of filter medium having a constant width, to produce a filter medium pack 110 with a substantially planar first side 111 and a substantially planar second side 112, the first side 111 and second side 112 being parallel. The rolling up comprises rolling the length of filter medium around a core 130 having a shape that is substantially geometrically similar to the desired circumference. In order to achieve a sufficiently tight winding, the sheet is kept under appropriate tension and pressed onto the core 130 and subsequently onto the increasing pack by suitably arranged reciprocating rollers 151-154. Adhesive (not shown) is applied to the sheet to keep the consecutive layers together.

(43) Once a filter medium pack 110 of the desired shape and size has been obtained, a guiding rim 120 as described above is arranged on at least one of the first side 111 and the second side 112 (not illustrated in FIG. 3).

(44) FIGS. 4-4b schematically illustrate a second method of producing the filter element according to the first embodiment.

(45) In a preliminary step (not illustrated), a length of filter medium having a constant width is rolled up around an oval or obround winding core, to produce a filter medium pack 110 with a substantially planar first side 111 and a substantially planar second side 112, the first side 111 and second side 112 being parallel. As the winding core is oval or obround the tensioning and pressing of the filter medium sheet is less complex than in the case illustrated in FIG. 3. During the winding operation, adhesive is applied to the sheet to keep the consecutive layers together. After removal from the winding core, the resulting filter medium pack 110 has an elongate shape without concave portions, and a hollow center.

(46) In a first step 1010, a core 130 that represents the desired contour shape by being substantially geometrically similar to it is inserted into the said hollow center of the filter medium pack 110. In a second step 1020 the filter medium pack 110 with the core 130 is placed into an appropriately shaped 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 medium pack 110 into the desired shape. As this deformation inevitably causes some sliding of the layers of filter medium in the filter medium pack 110, this step preferably should be completed before the applied adhesive has completely cured.

(47) In a subsequent step (not illustrated), a guiding rim 120 as described above is arranged on at least one of the first side 111 and the second side 112.

(48) A second embodiment of the filter element according to the present invention will now be described with reference to FIGS. 5 and 6. This embodiment will be described with emphasis on the elements that differ from those of the first embodiment.

(49) FIGS. 5-5b present a plan view (top left), a cross section (bottom left), and a perspective view (right) of this embodiment.

(50) The illustrated air filter element 100 comprises a filter medium pack 110 comprising two separately rolled-up lengths of filter medium. The resulting filter medium pack 110 has a substantially planar first side 111 and a substantially planar second side 112, which are parallel to each other. As before, the filter medium is preferably of the “fluted filter media” type.

(51) The air filter element 100 further comprises a guiding rim 120 arranged on at least one of said first side 111 and said second side 112. Preferably, guiding rims 120 are present on both sides 111, 112, as in the illustrated case. As the illustrated filter medium pack 110 consists of two separately rolled-up lengths of filter medium, the guiding rim 120 has the additional function of keeping these two rolls together to form one pack.

(52) In the illustrated case, the air filter element 100 has an elongate shape. The circumference of each guiding rim 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 clearly be seen 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 top side 120e and the bottom side 120f of the contour (the longitudinal sides) comprise a concave central portion 120e, 120f. In the illustrated case, the contour of the filter medium pack 110 corresponds to (i.e., it closely matches) the convex portion of the circumference of the guiding rim 120. However, as the concave portions 120e, 120f are situated where the two rolls of media meet each other, the contour of the filter medium pack 110 does not strictly follow the circumference of the guiding rim 120 in these portions.

(53) FIG. 6 presents an exploded view of the filter element according to the second embodiment. The filter medium pack 110 consists of two tubular cylinders, i.e. cylinders with a hollow center, and comprises corresponding cylindrical cores 130. FIG. 6 also shows the guiding rims 120 on each side of the filter medium 110 that keeps the rolls of filter medium 110 together and the cores 130 to be placed at the center of the rolls of filter medium 110.

(54) A third embodiment of the filter element according to the present invention will now be described with reference to FIGS. 7 to 8. This embodiment will be described with emphasis on the elements that differ from those of the first embodiment.

(55) FIGS. 7-7b respectively present a plan view (top left), a cross section (bottom left), and a perspective view (right) of this embodiment.

(56) The illustrated air filter element 100 comprises a filter medium pack 110 comprising a rolled-up length of filter medium. The filter medium pack 110 has a substantially planar first side 111 and a substantially planar second side 112, which are parallel to each other. The filter medium is again preferably of the “fluted filter media” type.

(57) The air filter element 100 further comprises a guiding rim 120 arranged on at least one of said first side 111 and said second side 112. Preferably, guiding rims 120 are present on both sides 111, 112, as in the illustrated case.

(58) In the illustrated case, the air filter element 100 has an elongate shape. The circumference of each guiding rim 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 clearly be seen 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 top side 120e of the contour is straight and the bottom side 120f of the contour comprises a concave central portion 120f. In the illustrated case, the contour of the filter medium pack 110 corresponds to (i.e., it closely matches) the entire circumference of the guiding rim 120.

(59) FIG. 8 presents an exploded view of the filter element according to the first embodiment. The filter medium pack 110 has a tubular shape, i.e. its shape closes onto itself around a hollow center, and comprises a core 130 that is substantially geometrically similar to the outer contour of the filter medium pack 110. FIG. 8 shows the guiding rims 120 on each side of the filter medium 110 and the core 130 to be placed at the center of the filter medium 110.

(60) A fourth embodiment of the filter element according to the present invention will now be described with reference to FIGS. 9-11. This embodiment will be described with emphasis on the elements that differ from those of the first embodiment.

(61) FIGS. 9-9b respectively present a plan view (top left), a cross section (bottom left), and a perspective view (right) of this embodiment.

(62) The illustrated air filter element 100 comprises a filter medium pack 110 comprising a rolled-up length of filter medium. The filter medium pack 110 has a substantially planar first side 111 and a substantially planar second side 112, which are parallel to each other. The filter medium is again preferably of the “fluted filter media” type.

(63) The air filter element 100 further comprises a guiding rim 120 arranged on at least one of said first side 111 and said second side 112. Preferably, guiding rims 120 are present on both sides 111, 112, as in the illustrated case.

(64) In the illustrated case, the air filter element 100 has an elongate shape. The circumference of each guiding rim 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 clearly be seen in the illustrated case that the top side 120e, 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 bottom side 120f of the contour comprises a concave central portion 120f. In the illustrated case, the contour of the filter medium pack 110 corresponds to (i.e., it closely matches) the entire circumference of the guiding rim 120.

(65) FIG. 10 presents an exploded view of the filter element according to the first embodiment. The filter medium pack 110 is completely filled, i.e. it does not have a hollow center, and there is no core in this case. FIG. 10 also shows the guiding rims 120 on each side of the filter medium 110.

(66) FIGS. 11-11a schematically illustrate a method of producing the filter element according to the fourth embodiment.

(67) In a preliminary step (not illustrated), a length of filter medium having a constant width is rolled up around a cylindrical winding core, to produce a filter medium pack 110 with a substantially planar first side 111 and a substantially planar second side 112, the first side 111 and second side 112 being parallel. As the winding core is cylindrical, the tensioning of the filter medium sheet is less complex than in the case illustrated in FIG. 3. During the winding operation, adhesive is applied to the sheet to keep the consecutive layers together. After removal from the winding core, the resulting filter medium pack 110 has a cylindrical shape without concave portions, and a hollow center.

(68) In a first step 2010, the filter medium pack 110 with the hollow center is placed into an appropriately shaped press-mold 160, which has protrusions and cavities corresponding to the desired shape of the contour. In a second step 2020, the press-mold 160, is closed to force the filter medium pack 110 into the desired shape. As this deformation inevitably causes some sliding of the layers of filter medium in the filter medium pack 110, this step preferably should be completed before the applied adhesive has completely cured.

(69) In a subsequent step (not illustrated), a guiding rim 120 as described above is arranged on at least one of the first side 111 and the second side 112.

(70) FIGS. 12 and 12a present two perspective views of an air filter system comprising an air filter element according to an embodiment of the present invention. FIGS. 13 and 13a presents two perspective views of the air filter element of the air filter system depicted in FIGS. 12 and 12a. Without loss of generality, the air filter element illustrated in FIGS. 12, 12a and 13, 13a has a coreless kidney-shaped or bean-shaped filter media pack 110. At one end, a guiding rim 120 with a sealing surface is provided. At the other end, a handle 170 is provided across a concave portion of the contour. A handle may be obtained very simply by providing a bar or strip of material that bridges a concave portion of the contour, such that it can easily be grasped by a human operator by slipping one's fingers in the cavity behind the handle. The handle may be flexible and attached after production of the filter element. It may for instance be glued on the outer side of the media pack or on an outer protection layer thereof in a/the concave portion. Indeed, in certain embodiments of the present disclosure, a further protection layer or envelope, also called shell, of the filter medium pack can be provided surrounding its radial outer surface. The protection layer or envelope can extend over a limited distance or over the whole length of the media pack, providing a rigid or more rigid housing of the media pack. This protection layer can be made of hard material such as plastic, or for instance out of a protective cardboard. Depending on the production process, the handle can also be formed integrally with the protection envelope. The protection envelope or shell can moreover be integrally formed with the guiding rim or a support structure comprised in the guiding rim.

(71) As indicated above, the filter medium pack preferably has a tubular shape. The term “substantially tubular” is used to cover shapes obtained by rolling a length of filter medium (with or without a core or a hollow space at the center), shapes obtained by arranging pleated filter media as a tube, and shapes obtained by combining multiple units that are substantially tubular in the aforementioned sense. The substantially tubular shape may include one or more pinches and/or bends. FIGS. 14-17 provide sketches of various substantially tubular shapes in which the filter medium pack may be arranged in embodiments of the present invention. As the purpose of the sketches is to illustrate different contours of the filter medium pack and/or the associated guiding rim, the sketches only show solid filter medium packs without a core, without loss of generality. The skilled person will appreciate that the illustrated shapes may also be obtained by combining one or more units (e.g. rolls) of filter medium with or without cores.

(72) FIG. 14 is a sketch of an example of an air filter element 100 including a substantially tubular filter medium pack 110 and including a guiding rim 120, the shape of which may be described as an oval which has been bilaterally pinched in a direction transverse to its long axis, approximately resulting in an lemniscate, 8-shape, or “peanut” shape. As shown, the circumference of the filter medium pack 110 and the circumference of the guiding rim 120 has two concave segments or portions interconnected by two convex segments or portions.

(73) FIG. 15 is a sketch of an example of an air filter element 100 including a substantially tubular filter medium pack 110 and including a guiding rim 120, the shape of which may be described as an oval with a single bend. As shown, the circumference of the filter medium pack 110 and the circumference of the guiding rim 120 has one concave segment or portion interconnected by one or more convex segments or portions.

(74) FIG. 16 is a sketch of an example of an air filter element 100 including a substantially tubular filter medium pack 110 and including a guiding rim 120, the shape of which may be described as an oval with two bends, approximately resulting in an S-shape (as illustrated) or Z-shape (not illustrated). As shown, the circumference of the filter medium pack 110 and the circumference of the guiding rim 120 are asymmetrically shaped with two offset concave segments or portions interconnected by two offset convex segments or portions.

(75) FIG. 17 is a sketch of an example of an air filter element 100 including a substantially tubular filter medium pack 110 and including a guiding rim 120, the shape of which may be described as an oval with three bends, approximately resulting in a W-shape. As shown, the circumference of the filter medium pack 110 and the circumference of the guiding rim 120 have three concave segments or portions interconnected by three convex segments or portions.

(76) The skilled person will appreciate that other suitable shapes may be obtained by combining any number of “pinches” and “bends” as described above to a tubular basic shape. The pinches and bends may be arranged so as to result in symmetric or asymmetric shapes.

(77) While the invention has been described hereinabove with reference to particular embodiments, this was done to clarify and not to limit the invention, the scope of which is to be determined by reference to the accompanying claims.