Abstract:
A filter element of an air filter, including: a filter medium for filtering air, partially surrounding an element interior of the filter element with respect to an element axis; wherein the filter element replaceably arranged within an openable filter housing having at least one inlet for air to be purified and at least one outlet for purified air so that said filter element separates said inlet from said outlet; wherein the filter element has at least one element-side support element on an outer side facing away from the element interior on at least one end face which is axial with respect to the element axis; wherein the support element includes at least one element supporting portion, which, at least in the installed state of the filter element in the filter housing, has a surface contour deviating from a flat surface on its end face facing away from the element interior.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a filter element of an air filter, in particular of an internal combustion engine, in particular of a motor vehicle, in particular of a commercial vehicle, with at least one filter medium for filtering air, which at least partially surrounds an element interior with respect to an element axis, and which filter element can be replaceably arranged in an openable filter housing having at least one inlet for air to be purified and at least one outlet for purified air in such a way that said filter element separates the at least one inlet from the at least one outlet. 
         [0002]    The invention further relates to a filter housing of an air filter, in particular of an internal combustion engine, in particular of a motor vehicle, in particular of a commercial vehicle, which is openable, which has at least one inlet for air to be purified and at least one outlet for purified air and in which at least one filter element, in particular a filter element according to the invention with at least one filter medium for filtering air which at least partially surrounds an element interior with respect to an element axis, can be replaceably arranged in such a way that said filter element separates the at least one inlet from the at least one outlet. 
         [0003]    Moreover, the invention relates to an air filter, in particular of an internal combustion engine, in particular of a motor vehicle, in particular of a commercial vehicle, with an openable filter housing which has at least one inlet for air to be purified and at least one outlet for purified air and in which at least one filter element with at least one filter medium for filtering air which at least partially surrounds an element interior with respect to an element axis can be replaceably arranged in such a way that said filter element separates the at least one inlet from the at least one outlet. 
       BACKGROUND OF THE INVENTION 
       [0004]    An air filter of an air intake tract of an internal combustion engine of a motor vehicle known from the market has a filter housing comprised of a housing container and a housing cover. The housing cover is removable from the housing container for opening the filter housing. The filter housing has an inlet for air to be purified and an outlet for purified air. A round filter element is arranged in the filter housing such that it separates the inlet from the outlet. The round filter element has a filter medium for filtering the air, which surrounds the element interior with respect to an element axis in a circumferentially closed manner. The filter element is replaceably arranged in the filter housing. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the invention is to design a filter element, a filter housing of an air filter and an air filter of the aforementioned type, in which a positioning and/or a holding of the filter element in the filter housing can be improved, in particular simplified. 
         [0006]    This object is achieved by the filter element according to the invention in that the filter element has at least one element-side support element on an outer side facing away from the element interior on at least one end face which is axial with respect to the element axis, which support element comprises at least one element supporting portion, which, at least in the installed state of the filter element in the filter housing, has a surface contour deviating from a flat surface on its end face facing away from the element interior. 
         [0007]    According to the invention, the end face of the at least one element supporting portion has an uneven surface contour. With an uneven end face, the at least one element supporting portion can be at least partially supported at least axially with respect to the element axis against a corresponding surface of an axial end face of at least one corresponding housing supporting portion of the filter housing. The uneven surface contour enables a more versatile support than a flat surface contour. 
         [0008]    Due to the arrangement of the at least one support element, the filter element can be constructed completely axially on the outer side of the end face. It can thus be arranged in the filter housing in a space-saving manner. 
         [0009]    The filter element can advantageously be clamped and held in the axial direction between two opposing housing supporting portions of the filter housing. 
         [0010]    Advantageously, the axial end face of the at least one housing supporting portion may have a surface contour which deviates from a flat surface. 
         [0011]    Advantageously, the particular surface contours of the end faces of the at least one housing supporting portion and the at least one element supporting portion can be adapted to one another. 
         [0012]    The corresponding end face of the at least one housing supporting portion can advantageously have a surface contour fitting the end face of the at least one element supporting portion, in particular complementarily. In this way, the at least one element supporting portion and the at least one housing supporting portion may engage with one another in a form locking manner. They may thus interact with an improved force transmission in the axial direction and/or the radial direction and/or circumferential direction with respect to the element axis. 
         [0013]    The at least one element supporting portion and the at least one housing supporting portion may advantageously interlock. Force locking can thus be improved. 
         [0014]    The surfaces of the end faces of the at least one element supporting portion and the at least one housing supporting portion may lie at least partially against one another with as little play as possible. Support with respect to different spatial directions can thus be further improved. An additional support on the circumferential side of the filter element radial and/or circumferential with respect to the element axis/housing axis can thus optionally be dispensed with. If an additional radial support of the filter element is present, a radial support by means of the at least one housing supporting portion and the at least one element supporting portion is not necessary. An axial support is sufficient there, in particular at a tip of the housing supporting portion/element supporting portion. 
         [0015]    Advantageously, the at least one housing supporting portion may extend axially with respect to a housing axis of the filter housing. 
         [0016]    When a filter element is correctly installed, the housing axis may advantageously extend parallel, axially or coaxially with the element axis. In this way, the air filter as a whole can be coaxially constructed. The space requirement of the air filter can thus be further reduced. 
         [0017]    The element axis and/or the housing axis may advantageously extend axially to an assembly direction of the filter element relative to the filter housing, in particular relative to a housing part with the at least one housing supporting portion. The filter element can thus easily be inserted into the filter housing in the axial direction. In particular, the filter element can be inserted in the axial direction into a corresponding housing part, in particular a housing container. One of the housing parts, in particular the housing cover, may advantageously placed on the filter element and the other housing part in the axial direction. 
         [0018]    Advantageously, the at least one support element may additionally be supported in the filter housing in the radial direction and/or circumferential direction with respect to the element axis. In this way, the filter element can be better positioned and/or held with respect to further spatial directions. 
         [0019]    Advantageously, the at least one support element and the at least one housing supporting portion may not have a sealing function. In this way, the support function and the possible sealing function can be separated from one another and respectively optimized. A corresponding sealing function may be associated with a component pair separated from the at least one support element and the at least one housing supporting portion and individually optimized. 
         [0020]    Advantageously, the at least one support element may be at least partially elastic. In this way, any installation tolerances of the filter element in the filter housing can easily be equalized with the at least one support element. Further, the at least one support element may additionally serve as a vibration damper, in particular during operation of the air filter. 
         [0021]    In particular, the at least one support element may be made of elastic material, in particular plastic, in particular polyurethane (PUR), or may comprise such a material. Polyurethane may be simply connected directly or indirectly with the at least one filter medium by means of a corresponding connecting body, in particular an end body or end plate. The at least one support element may advantageously be foamed on or onto the filter medium or the connecting body. 
         [0022]    Additionally or alternatively, the at least one support element at least comprises a rigid material, in particular plastic, or consists thereof. 
         [0023]    Advantageously, a plurality of identical or different support elements may be arranged on one of the end faces of the filter element. In this way, the support can be further improved. A tilting of the filter element with respect to the element axis can thus be prevented. 
         [0024]    Advantageously, the element interior can be closed at the end face of the filter element on which the at least one support element is located. In this way, a flow of air out of the element interior or into the element interior can be prevented there. It may thus be achieved that the air must flow through the filter medium. The air may flow through the filter medium from radially outside to radially inside into the element interior, or in the opposite direction out of the element interior. The air may flow through a corresponding throughflow opening on the end face of the filter element axially opposite the at least one support element into the element interior or out of the element interior. 
         [0025]    The filter element may advantageously be a hollow filter element, in particular a round filter element with a round cross-section, an oval round filter with an oval cross-section, a flat-oval round filter element with a flattened oval cross-section, a conical round filter element, in which the round cross-section tapers in the axial direction of the major axis, a conical oval round filter element, in which the oval cross-section tapers in the axial direction at least in the direction of a transverse axis, a conical flat-oval round filter element, in which the flat-oval cross section tapers in the axial direction at least in the direction of a transverse axis, or a hollow filter element with another type of, especially square, cross-section and/or another type of axial cross-sectional extent in the direction of the major axis. 
         [0026]    With respect to the element axis, the filter medium may advantageously be circumferentially closed or open. The filter medium may in particular be star-shaped, preferably zigzag-shaped or wave-shaped, folded or bent. The filter medium may also be unfolded or unbent. 
         [0027]    The filter medium may be a filter paper, nonwoven filter fabric or another type of filter medium suitable for the filtration of air. The filter medium may be one or more layers. 
         [0028]    The filter element can advantageously have a support body, in particular a support tube. The stability of the filter element, in particular of the filter medium, can be increased with the support body. The support body may advantageously be located in the element interior. A support body may also be provided which surrounds the filter medium radially outwardly. A circumferential wall of the support body may advantageously be permeable to air. The circumferential wall may advantageously be skeleton- or grid-like. The support body may advantageously be made of plastic. The filter medium may advantageously be supported on the support body. 
         [0029]    The air filter may advantageously be part of the air intake tract of an internal combustion engine. It may be used for the purifying of combustion air which is supplied to the internal combustion engine. However, the invention is not limited to an air filter of an air intake tract of an internal combustion engine of a motor vehicle, in particular a commercial vehicle. Rather, it may also be used in other types of air systems of motor vehicles. The air filter may also be a cabin air filter. The air filter can also be used outside of the automotive field, in particular in industrial motors. 
         [0030]    Advantageously, the air filter may be a part of an air intake system of a commercial motor vehicle, in particular a commercial vehicle, in particular a bus, construction machine or agricultural machine. 
         [0031]    The air intake system may advantageously be located on a vertical wall, in particular a back side, of a cab of a commercial vehicle. 
         [0032]    In an advantageous embodiment, the at least one element supporting portion may comprise or at least contribute to at least one element-side form locking portion for form locking connection with at least one corresponding housing-side form locking portion. 
         [0033]    Advantageously, the at least one element side form locking portion can comprise at least one surface portion, in particular prongs, waves and/or steps, which can act to effect an axial force transmission with at least one directional component and/or a parallel force transmission with at least one directional component and/or a circumferential force transmission with at least one directional component with respect to the element axis. 
         [0034]    The at least one element side form locking portion and the at least one housing side form locking portion may advantageously engage in one another in a form-locking manner, in particular interlink with one another. 
         [0035]    The interacting form locking portions may have corresponding elevations and depressions which can engage with one another in a form locking manner. 
         [0036]    In a further advantageous embodiment, the at least one element side support element may have at least one element supporting portion, which extends circumferentially with respect to the element axis. 
         [0037]    The at least one element supporting portion may advantageously have a cylindrical or conical shape. Such a shape can enable an optimal force transmission from the at least one element supporting portion to the at least one housing supporting portion radially to a major axis of the at least one element supporting portion. 
         [0038]    The at least one element supporting portion may advantageously have an oval, flat oval, round or polygonal cross-section. 
         [0039]    The at least one element supporting portion may be circumferentially closed with respect to the element axis. It may also have interruptions. 
         [0040]    In a further advantageous embodiment, the end face of the at least one, in particular circumferentially extending, element supporting portion facing away from the element interior may have an alternating, in particular wave-like and/or step-like and/or spike-like surface contour. 
         [0041]    In this way, a stable and precise form locking connection between the at least one element supporting portion and the at least one housing supporting portion can be realized. The flanks, waves and/or steps of the at least one element supporting portion and the at least one housing supporting portion may engage in one another, in particular interlink with one another. A support in the axial, radial and circumferential direction can thus be improved. 
         [0042]    In a further advantageous embodiment, the at least one element side support element may have at least one element supporting portion which is central with respect to the element axis, in particular coaxial or eccentric with respect to the element axis, which element supporting portion has in particular at least one depression and/or at least one elevation. 
         [0043]    On the end face, the at least one element supporting portion may advantageously be designed at least partially pyramidal, cross-shaped, conical, cylindrical, barrel-shaped and/or (semi)spherical and/or uneven in a different manner. 
         [0044]    Advantageously, the at least one element supporting portion may taper in the form of an elevation axial to the element axis when viewed from the element interior out. Alternatively, the at least one element supporting portion may taper in the form of a depression when viewed inward toward the element interior. In both cases, bringing together with at least one corresponding housing supporting portion can thus be simplified. Advantageously, the tip may show a pyramidal, conical or similar depression toward the element interior. Alternatively, the tip may show a pyramidal, conical or similar elevation away from the element interior. 
         [0045]    In a further advantageous embodiment, the at least one element supporting portion, in particular the surface contour of the end face, may be realized separately from the filter housing, in particular prefabricated. 
         [0046]    Alternatively or in addition, the at least one housing supporting portion, in particular the surface contour of the end face, may advantageously be realized separately from the filter element, in particular prefabricated. In this way, the at least one element supporting portion and/or the at least one housing supporting portion, in particular the respective surface contour of the end face, exists even in an uninstalled state of the filter element, as well as when the filter element and filter housing are separated before installation or after removal. 
         [0047]    The shape of at least one element supporting portion and/or the at least one housing supporting portion may be predetermined. The shape of the at least one element supporting portion and/or the at least one housing supporting portion may not thus arise only during or by means of the bringing together of the at least one element supporting portion with the at least one corresponding housing supporting portion. In this way, a force required during bringing together of the at least one element supporting portion and the at least one housing supporting portion may be reduced. Further, the at least one element supporting portion and the at least one housing supporting portion may thus serve as a positioning aid for positioning the filter element in the filter housing. 
         [0048]    The at least one element supporting portion can be realized during the production of the at least one support element. Accordingly, the at least one housing supporting portion can be realized during the production of the housing or housing part, in particular the housing cover. Advantageously the at least one support element and/or the housing can respectively be formed from plastic, in particular injected or cast. 
         [0049]    Alternatively or in addition, at least one element supporting portion may be formed by means of at least one corresponding housing supporting portion or vice versa. The at least one element supporting portion and/or the at least one housing supporting portion may be made from a formable and/or soft, in particular elastic, material. During installation of the filter element into the filter housing, the surface contour of the corresponding end face of the housing supporting portion can be pressed or embedded into the formable material of the at least one element supporting portion and thus form the element side surface contour. Correspondingly, the surface contour of the end face of the element supporting portion can be pressed or embedded into the optionally formable material of the at least one housing supporting portion and thus form the housing side surface contour. 
         [0050]    In a further advantageous embodiment, an element side support element may be arranged centrally, in particular coaxially, on the end face of the filter element with respect to the element axis. The filter element can thus be supported centrally. In this way, a uniform support of the filter element on/in the filter housing may occur with only one support element and only one corresponding housing supporting portion. Support can thus be realized with a small footprint of the required components in the filter housing. 
         [0051]    Advantageously, the at least one element side support element may be coaxial with the element axis. Alternatively, the at least one element side support element may be arranged so as to be displaced to the element axis, in particular eccentrically, in the region of the center of the end face of the filter element. 
         [0052]    Alternatively or in addition, at least one identical or different type of support element can advantageously be provided on the filter element with at least one corresponding housing supporting portion on the housing. 
         [0053]    Advantageously, the at least one alternative or additional support element may be arranged circumferentially with respect to the element axis on the end face on which the at least one central support element is located. 
         [0054]    The at least one additional or alternative support element may advantageously be arranged in an edge region of the end face. Advantageously, the at least one additional or alternative support element can support the filter element with respect to the element axis in the axial, radial and/or circumferential direction against the corresponding additional housing supporting portion. 
         [0055]    The at least one additional or alternative support element may advantageously be at least one web. The at least one additional or alternative support element may advantageously be elastic. It may thus also contribute to a tolerance compensation and/or vibration damping. The at least one additional or alternative support element may also be rigid. 
         [0056]    In a further advantageous embodiment, at least one element side support element may be arranged on an end body, in particular an end plate, of the filter element. 
         [0057]    Advantageously, the end body, in particular the end plate, may face the at least one support element of an inlet portion of space of the filter housing for air to be purified. The inlet portion of space may advantageously be connected with the at least one inlet. The at least one support element may be located on the raw air side of the filter medium. 
         [0058]    The filter medium can be stabilized with the at least one end body. Further, the filter medium can be sealed at the end face with the at least one end body. 
         [0059]    Advantageously, the at least one end body may be made of plastic or comprise plastic. It may advantageously be connected, in particular sealingly, with the end face of the filter medium by adhesion, welding or in another manner. The material of which the end body is comprised may advantageously also be foamed onto or foamed into the end face of the filter medium. 
         [0060]    The at least one support element may advantageously be fixedly connected with the at least one end body. The at least one support element may be integrally connected with the at least one end body. 
         [0061]    The at least one support element and the at least one end body may advantageously be realized integrally, in particular from plastic, or as a two-component unit. 
         [0062]    Alternatively, the at least one support element may in particular be adhered, welded, foamed onto or connected in another fixed manner with the end body as a separate unit. The at least one support element may additionally or alternatively connected with the end body by means of an in particular mechanical connection, in particular a locking connection, a snap connection or in another manner. The at least one support element may be releasably or permanently connected with the end body. 
         [0063]    Advantageously, a seal may be arranged between the filter element and the filter housing on the end face of the filter medium opposite the at least one support element. With the seal, the filter element can be sealed against the filter housing in the axial and/or radial direction. 
         [0064]    The seal may further have a support function. Advantageously, the filter medium may be supported against the filter housing in the axial and/or radial direction by means of the seal. The seal may serve as a counter-bearing for the at least one support element in the axial direction. The filter element may thus be clamped between the seal and the at least one support element. 
         [0065]    Advantageously, the seal may be made from or comprise an elastic material, in particular polyurethane, in particular a polyurethane foam, or another such material. 
         [0066]    Advantageously, the seal may be connected with the filter element, in particular belong thereto. Advantageously, the seal may be connected with an end body, in particular an end plate, of the filter element. The seal may advantageously be integrally realized with the end body. 
         [0067]    The seal may advantageously interact with the corresponding housing side sealing surface. The housing side sealing surface may advantageously be arranged in a housing container of the filter housing. 
         [0068]    The technical object is further achieved by the filter housing in that at least one housing supporting portion is arranged on the side of the filter housing, which housing supporting portion, at least in the installed state of the at least one filter element in the filter housing, has a surface contour deviating from a flat surface on at least one end face which faces the filter element axially with respect to a housing axis, which housing axis extends parallel or axially to the element axis when the air filter is installed. 
         [0069]    The features and advantages shown above in connection with the filter element according to the invention and its advantageous embodiments apply accordingly to the filter housing according to the invention and advantageous embodiments thereof. 
         [0070]    Advantageously, the at least one housing supporting portion may extend in the axial direction with respect to the housing axis. 
         [0071]    Advantageously, the at least one housing supporting portion may be cylindrical or conical. It may be coaxial with the housing axis. 
         [0072]    The at least one housing supporting portion may have at least one groove on its end face which faces the filter element. An outer edge surrounding the groove may have the particular surface contour which deviates from a flat surface. An inner edge surrounded by the groove may have the same or a similar surface contour. Alternatively or in addition, the at least one element supporting portion may correspondingly have at least one groove. 
         [0073]    Advantageously, the at least one housing supporting portion/element supporting portion may have an inner surface in its center, optionally surrounded by the inner edge. The inner surface may be axially set back or protrude forward from the particular surface contour of the possible outer edge and/or possible inner edge with respect to the housing axis/element axis. 
         [0074]    On its axial end face, the filter element may have at least one element supporting portion, which has a negative contour of the at least one housing supporting portion. The two contours may engage in one another. They may realize an at least axial support. 
         [0075]    Alternatively or in addition, the at least one housing supporting portion may advantageously have an end face which tapers axially to the housing axis and which may form the particular surface contour. 
         [0076]    Alternatively or in addition, the particular surface contour can be negatively realized, i.e. as a depression, on the at least one housing supporting portion. 
         [0077]    Advantageously, the at least one housing supporting portion may have a cone-shaped or pyramid-shaped projection. The cone-shaped or pyramid-shaped housing supporting portion may advantageously engage in a corresponding cone-shaped or pyramid-shaped recess or depression of the corresponding element supporting portion of the filter element. Conversely, the element supporting portion may have the cone-shaped or pyramid-shaped projection and the housing supporting portion may have the corresponding recess or depression. 
         [0078]    Instead of a cone-shaped or pyramid-shaped depression and/or recess, the element supporting portion/housing supporting portion may also be realized with cross-like portions similar to Philips screws or Pozidriv screws. 
         [0079]    Advantageously, different, in particular the above-mentioned, surface contours of the end faces of the at least one housing supporting portion and/or the at least one element supporting portion can be combined with one another. In particular, the inner edge of the groove of the at least one housing supporting portion/element supporting portion may pass into the inner surface. A supporting can occur both on the support contour of the groove as well as the inner surface. 
         [0080]    Advantageously, the filter housing may be composed of at least two housing parts. The two housing parts may advantageously be completely or partially separated from one another for opening the filter housing. One of the housing parts may in particular be a housing container. The at least one filter element can in particular be accommodated for the most part in the housing container. The housing container may advantageously be coaxial to the housing axis. It may advantageously have an installation opening, which is coaxial with the housing axis, for the at least one filter element. The at least one filter element can thus be installed easily into the housing container through the installation opening in the axial direction with respect to the housing axis. Another housing part may advantageously be a housing cover. The installation opening of the housing container, and thus the filter housing, may be closed with the housing cover. The at least one inlet and the at least one outlet may be located in the same or in different housing parts. Advantageously, an in particular smaller portion of the at least one filter element may protrude into the housing cover. 
         [0081]    The at least one housing supporting portion may advantageously be located on one of the housing parts. Advantageously, the at least one housing supporting portion may be located on the housing cover. The positioning of the at least one filter element and/or the assembly of the at least one element side support element can thus be simplified by means of the at least one housing supporting portion. 
         [0082]    Advantageously, at least one housing supporting portion may be arranged centrally to the housing axis, in particular axial or coaxial with the housing axis. This housing supporting portion may optionally easily interact with a corresponding centrally arranged element side support element. 
         [0083]    Advantageously, the filter element may be supported on the other housing part, in particular the housing container, on the end face opposite the at least one support element. 
         [0084]    Advantageously, the at least one housing supporting portion may be a sort of pillar or dome, or may comprise these or be a part thereof. The at least one housing supporting portion may be located on the free end of the pillar. With the other end, the pillar or dome can be connected with the filter housing, in particular the housing cover. It may in particular be integrally connected to the filter housing. The pillar or dome may advantageously be hollow. In this way, material and weight can be saved. Further, a hollow pillar or dome can be simply realized and/or unmolded after a molding process, in particular from plastic. 
         [0085]    The pillar or dome may advantageously extend through a portion of space of the filter housing. In this way, the at least one filter element may be supported at a distance from a corresponding housing wall of the filter housing, in particular the housing cover, spanned by the pillar or dome. Advantageously, the portion of space may be flowed through by air during operation of the air filter. Depending on the direction of flow of the air in the filter housing, the portion of space may be an inlet portion of space or an outlet portion of space. 
         [0086]    Advantageously, a plurality of counter-support portions may be arranged on the side of the filter housing. The counter-support portions may advantageously be associated with corresponding support elements on the side of the at least one filter element. 
         [0087]    The technical object is additionally achieved by the air filter according to the invention in that it has at least one filter element according to the invention and/or one filter housing according to the invention. 
         [0088]    The features and advantages shown above in connection with the filter element according to the invention and the filter housing according to the invention and its respective advantageous embodiments apply accordingly to the air filter according to the invention and advantageous embodiments thereof. 
         [0089]    Advantageously, the at least one support element and the at least one counter-support portion may be arranged on a raw air side of the at least one filter element. 
         [0090]    A gap may advantageously be realized between the at least one filter element in the region of the end face with the at least one support element and an inner wall of the filter housing which radially outwardly surrounds the at least one filter element. By means of the gap, air may flow into or out of the space which radially outwardly surrounds the filter element. A stream of air may thus flow, in particular axially to the element axis, from an inlet portion of space of the filter housing to the inflow side of the filter medium. Depending on the direction of flow, the upstream side of the filter medium may be located in the element interior or on the radially outer circumferential side of the at least one filter element. Accordingly, the air stream may flow axially to the element axis from the upstream side of the filter medium into a corresponding outlet portion of space of the filter housing. By means of the axial flow of air, an improved packing size of the filter housing, and thus a smaller footprint, can be realized. Further, in an axial flow of air to the upstream side and/or away from the downstream side, a pressure difference between the upstream side and downstream side can be reduced. Thus, in particular a lower pressure difference can be realized than in a comparable air filter in which the flow of air is led tangentially to the upstream side of the at least one filter element or away from the downstream side. 
         [0091]    Advantageously, an inlet-side inlet portion of space, and element portion of space, in which the at least one filter element is arranged, and an outlet-side outlet portion of space of the filter housing can be arranged one after the other, linearly and along the direction of flow of the air through the air filter. In this way, an axial flow of the air to the upstream side of the filter medium can easily be realized. Further, an axial discharge of the filtered air from the clean air side of the at least one filter element can thus be achieved. Any differences in pressure between the clean air side and the raw air side can thus be reduced. 
         [0092]    Advantageously, a main flow direction of the air from the inlet portion of space through the element portion of space into the outlet portion of space may be substantially axial to the element axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0093]    Further advantages, features and details of the invention will become apparent from the following description in which embodiments of the invention are explained in more detail with reference to the drawings. A person skilled in the art will also appropriately consider the features disclosed in the drawings, the description and the claims individually and combine them into further sensible combinations. 
           [0094]      FIG. 1  shows a first longitudinal section of an air filter of an internal combustion engine of a commercial vehicle with a replaceable flat oval round filter element according to a first embodiment; 
           [0095]      FIG. 2  shows a second longitudinal section of the air filter of  FIG. 1  along a sectional plane perpendicular to the sectional plane of  FIG. 1 ; 
           [0096]      FIG. 3  shows the round filter element in the longitudinal section of  FIG. 1 ; 
           [0097]      FIG. 4  shows the round filter element in the longitudinal section of  FIG. 2 ; 
           [0098]      FIG. 5  shows an isometric representation of the round filter element of  FIGS. 1 to 4 ; 
           [0099]      FIG. 6  shows an isometric representation of the open housing container of the air filter of  FIGS. 1 and 2  with the round filter element; 
           [0100]      FIG. 7  shows an isometric representation of a housing cover of the air filter of  FIGS. 1 and 2 ; 
           [0101]      FIGS. 8 to 14  show isometric representations of alternative embodiments of round filter elements which are similar to the round filter element according to the first embodiment of  FIGS. 1 to 6 . 
       
    
    
       [0102]    In the figures, identical components are provided with the same reference characters. 
       DESCRIPTION OF THE INVENTION 
       [0103]    In  FIG. 1  is shown an air filter  10  of an internal combustion engine of a commercial vehicle according to a first embodiment in a first longitudinal section. The air filter  10  is arranged in an air intake tract, not otherwise shown, of the internal combustion engine. It is used for the purifying of combustion air which is supplied to the internal combustion engine for combustion. 
         [0104]    The air filter  10  includes an openable filter housing  12 . The filter housing  12  is flat-oval. With respect to an oval filter housing with an approximately elliptical cross-section, the filter housing  12  is flattened in the direction of its short transverse axis.  FIG. 1  shows the section along a long transverse axis of the filter housing  12 .  FIG. 2  shows the air filter  10  in a second longitudinal section along a short transverse axis of the filter housing  12 . 
         [0105]    The filter housing  12  has a housing container  14 , to the left in  FIGS. 1 and 2 . The housing container  14  has an installation opening  16 , to the right in  FIGS. 1 and 2 , for installation of a filter element  18 . The open housing container  14  with the filter element  18  is shown in  FIG. 6 . When the air filter  10  is ready to operate, the installation opening  16  is closed with the housing cover  20 , to the right in  FIGS. 1 and 2 . The housing cover  20  alone is shown in  FIG. 7 . 
         [0106]    The housing container  14  has an outlet  22  for filtered air, which leads out of an outlet portion of space  24  of the housing container  14 . The outlet  22  is connected outside the filter housing  12  with the internal combustion engine via air lines, not shown. 
         [0107]    The housing cover  20  has an inlet  26  for air to be filtered, which opens into an inlet portion of space  28  of the housing cover  20  and which is connected with the environment outside the filter housing  12 . 
         [0108]    The filter element  18  is arranged in an element portion of space  30  of the housing container  14  such that it separates the inlet  26  from the outlet  22 . The element portion of space  30  is located in a linear arrangement between the inlet portion of space  28  and the outlet portion of space  24 . 
         [0109]    The inlet portion of space  28 , the element portion of space  30  and the outlet portion of space  24  are arranged one after the other axially to an axis  32 . In the embodiment, the axis  32  coincides with a housing axis of the filter housing  12  and with an element axis of the installed filter element  18 . In the embodiment, the axis  32  further coincides with an installation direction, in which the filter element  18  is inserted into and can be removed from the housing container  14 . In addition, the axis  32  coincides in the embodiment with an assembly direction, in which the housing cover  20  is assembled on the housing cover  14 . The installation opening  16  circumferentially surrounds the axis  32 . 
         [0110]    When further reference is made to “axial,” “radial,” “circumferential” or “coaxial”, this refers unless otherwise written to the axis  32 . 
         [0111]    The housing container  14  has a circumferentially closed sealing surface  34  axially between the element portion of space  30  and the outlet portion of space  24 . The sealing surface  34  extends in the radial direction. The sealing surface  34  faces the housing cover  20 . A seal  36  of the filter element  18  is sealingly applied to the sealing surface  34  in a circumferentially closed manner. 
         [0112]    The radially inner cross-section of the element portion of space  30  is larger than a radially outer cross-section of the sealing surface  34 . 
         [0113]    An upstream annular space  38  is realized between a radially outer circumferential side of the filter element  18  and the radially inner circumferential side of the element portion of space  30 . The upstream annular space  38  is separated by means of the seal  36  from the outlet portion of space  24 . 
         [0114]    The upstream annular space  38  is connected with the inlet portion of space  28  on the side facing the housing cover  20  by means of a circumferential gap  40 . The inlet portion of space  28  and the upstream annular space  38  are located on the raw air side of the filter element  18 . 
         [0115]    A support pillar  42  is arranged in the housing cover  20 . The support pillar  42  is integrally connected with the housing cover  20 . The support pillar  42  is coaxial with the axis  32 , i.e. coaxial with the housing axis. It is arranged centrally with respect to the housing axis. The support pillar  42  extends through the inlet portion of space  28  from an inner side of the housing cover  20  facing the filter element  18  up to the outlet-side end face of the filter element  18 . The support pillar  42  is located on the raw air side of the filter medium  46 . 
         [0116]    At the free end of the support pillar  42  which faces the filter element  18  is arranged a housing supporting portion  44  which extends circumferentially and is radially outward from a major axis of the support pillar  42 , thus to the axis  32  and to the housing axis. In an axial plan view, the radially outer housing supporting portion  44  has the shape of an oval, circumferentially closed path. The long transverse axis of the oval is located in the drawing plane of  FIG. 1 , the short transverse axis is perpendicular to the drawing plane thereof. An end face of the radially outer housing supporting portion  44  which faces the filter element  18  has a surface contour which deviates from a flat surface and which is wave-like when viewed from the side. 
         [0117]    Radially inside the radially outer housing supporting portion  44 , the free end of the support pillar  42  has a central, pyramid-shaped, radially inner housing supporting portion  45  on its end face. The tip of the right pyramid is located on the axis  32  and faces the filter element  18 . The height axis of the pyramid extends coaxially with the axis  32 . The pyramid has a rectangular base surface. The long side of the base surface extends parallel to the long transverse axis of the radially outer housing supporting portion  44 . The four side surfaces of the pyramid form the end face of the radially inner housing supporting portion  45  which faces the filter element  18 . The end face of the radially inner housing supporting portion  45  thus has a surface contour which deviates from a flat surface. 
         [0118]    The filter element  18  is shown in  FIGS. 3 to 5  in various detail views. The filter element  18  is a conical flat oval round filter element. The filter element  18  is coaxial with the element axis, thus coaxial in the installed state with the housing axis, thus with axis  32 . The filter element  18  has a flat oval cross-section. The long transverse axis of the oval is located in the drawing plane of  FIG. 1 , the short transverse axis is perpendicular to the drawing plane. The filter element  18  is additionally flattened in the direction of the short transverse axis, thus the designation “flat oval.” In contrast, “oval” designates an approximately elliptical cross-section. A radially outer circumferential side and a radially inner circumferential side of the filter element  18  respectively have a conical extent. The outer cross-section and the inner cross-section of the filter element  18  are tapered from the outlet-side end face, which faces the outlet portion of space  24 , to the inlet-side end face. 
         [0119]    The filter element  18  comprises a zigzag-shaped, folded filter medium  46  which is circumferentially closed with respect to the element axis. The radially inner folded edges and the radially outer folded edges respectively form the corresponding circumferential sides of the filter element  18 . The filter medium  46  is a non-woven filter which is suitable for the filtration of air. Additionally or alternatively, a different type of filter medium suitable for filtration, for example filter paper, can be provided. The filter medium  46  may be one or more layers. 
         [0120]    The filter medium  46  is connected on its outlet-side end face with a coaxial outlet-side end plate  48 . The outlet-side end plate  48  is made of plastic. It is tightly bonded to the end face of the filter medium  46 . It may also be connected in a different manner with the filter medium  46 . For example, it may also be welded or foamed thereon or therein. The radially outer circumferential side of the outlet-side end plate  48  abuts the radially inner circumferential side of the housing container  14  with minimal play. 
         [0121]    The outlet-side end plate  48  has a central outflow opening  50 . The outflow opening  50  extends over the entire radially inner cross-section of the filter medium  46 . An element interior  52  of the filter element  18 , which is surrounded by the filter medium  46 , is connected with the outlet portion of space  24  via the outflow opening  50 . 
         [0122]    The seal  36  is arranged on the outer side of the outlet-side end plate  48  axially opposite the filter medium  46 . The seal  36  is made of elastic polyurethane foam. It is, for example, integrally foamed onto the outlet-side end plate  48 . Instead of polyurethane foam, the seal  36  can be made of another, preferably elastic, material, such as a plastic. Instead of being foamed on, it may be connected in a different manner to the outlet-side end plate  48 . The outlet-side end plate and the seal can also be realized as a two-component unit. 
         [0123]    The seal  36  is coaxial with the element axis and circumferentially surrounds the outflow opening  50 . It extends in the axial direction. It is supported in the axial direction on the sealing surface  34  of the housing container  14 . 
         [0124]    The filter medium  46  is sealingly connected on its inlet-side end face with an inlet-side end plate  54 . The inlet-side end plate  54  closes the element interior  52  from the inlet portion of space  28 . In a similar manner to the outlet-side end plate  48 , the inlet-side end plate  54  is sealingly connected with the filter medium  46 . It may also be connected in a different manner with the filter medium  46 . 
         [0125]    A coaxial support tube  56  extends in the element interior  52  between the inlet-side end plate  54  and the outlet-side end plate  48 . The support tube  56  is made of plastic. It is structured as a grid. Its circumferential side is permeable to air. The support tube  56  has a conical flat oval shape corresponding to the filter medium  46 . The radially inner circumferential side of the filter medium  46  may be supported on the radially outer circumferential side of the support tube  56 . 
         [0126]    An element-side support element  58  is arranged on the axially outer side of the inlet-side end plate  54  facing the element interior  52 . The support element  58  is located on the raw air side of the filter medium  46 . The support element  58  is fixedly connected to the inlet-side end plate  54 . The support element  58  is made of an elastic material. In the embodiment shown, the support element  58  is integrally foamed from polyurethane with the inlet-side end plate  54 . 
         [0127]    Radially outwardly, the support element  58  has the form of a cylinder, the major axis of which extends coaxial with the element axis in the embodiment shown. The support element  58  has an approximately oval cross-section. In  FIG. 1 , its short transverse axis is in the drawing plane, its long transverse axis is perpendicular to the drawing plane. When an air filter  10  is installed, the orientation of the support element  58  with respect to the axis  32 , thus the housing axis, thus corresponds to the orientation of the housing supporting portions  44  and  45 . 
         [0128]    Radially outwardly, the support element  58  has a radially outer coaxial element supporting portion  60 . An end face of the radially outer element supporting portion  60  which faces away from the element interior  52  has the shape of an oval path in an axial plan view. The end face of the radially outer element supporting portion  60  has a wave-shaped surface contour which deviates from a flat surface when regarded from the side. 
         [0129]    The end face of the radially outer element supporting portion  60  is complementary to the end face of the radially outer housing supporting portion  44 . The dimensions of the radially outer element supporting portion  60  correspond approximately to the dimensions of the radially outer housing supporting portion  44 . 
         [0130]    Radially within the radially outer element supporting portion  60 , the support element  58  has a central, radially inner element supporting portion  62 . The radially inner element supporting portion  62  is circumferentially closed and surrounded by the radially outer element supporting portion  60 . The radially inner element supporting portion has the shape of a pyramid-shaped depression. The tip of the right pyramid is located on the axis  32  and faces the element interior  52 . The height axis of the pyramid extends coaxially with the axis  32 . The pyramid has a rectangular base surface. The long side of the base surface extends parallel to the long transverse axis of the radially outer element supporting portion  60 . The four side surfaces of the pyramid form the end face of the radially inner element supporting portion  62  which faces away from the element interior  52 . The end face of the radially inner element supporting portion  62  thereby has a surface contour which deviates from a flat surface. It is complementary to the end face of the radially inner housing supporting portion  45 . 
         [0131]    As is shown in  FIGS. 1 and 2 , when the filter element  18  is correctly installed, the end face of the radially inner housing supporting portion  45  lies flat and without play against the end face of the radially inner element supporting portion  62 . The end face of the radially outer housing supporting portion  44  lies flat and without play against the end face of the radially outer element supporting portion  60 . Here, the housing supporting portions  44  and  45  engage in a form locking manner in the respective element supporting portions  60  and  62 , and vice versa. The element supporting portions  60  and  62  and the housing supporting portions  44  and  45  respectively form element-side and housing-side form locking portions for form locking connection of the support element  58 , thus the filter element  18 , with the support pillar  42 , thus the filter housing  12 . 
         [0132]    The filter element  18  is supported via the support pillar  42  against the housing cover  20  by means of the support element  48 . The support occurs axially, radially, thus transverse to the element axis and to the housing axis, and circumferentially. Through the interaction of the support element  48  with the support pillar  42 , the filter element  18  is held and positioned axially, radially and circumferentially on the inlet side, i.e. the raw air side. The filter element  18  can thus be held in the filter housing  12  on the side facing the inlet portion of space  28 , without covering the gap  40  by the necessary holding components. 
         [0133]    Further, two support webs  68  are respectively arranged on the radially outer edges of the inlet-side end plate  54  in the region of the short transverse sides. The support webs  68  respectively project beyond the outlet-side end plate  54  both in the radial direction and in the axial direction. The support webs  68  are respectively supported in the radial direction at support points on the inner side of the housing container  20 . 
         [0134]    On the radially outer edges of the inlet-side end plate  54 , a respective guide element  70  is arranged centrally on the long transverse sides, with which the filter element  18  can be guided and positioned on the housing cover  20  during assembly of the air filter  10  in a manner of no further interest here. 
         [0135]    During operation of the air filter  10 , the air to be filtered flows through the inlet  26 , indicated in  FIG. 2  by an arrow  64 , into the inlet portion of space  28 . From there, the air passes substantially axially through the gap  40  into the upstream annular space  38  to the upstream side of the filter medium  46 . The air flows through the filter medium  46  from radially outside to radially inside and is purified. The purified air flows through the circumferential side of the support tube  56  and passes into the element interior  52 . The purified air leaves the element interior  52  with an axial primary flow direction and enters the outlet portion of space  24 . From there, the filtered air exits the filter housing  12  through the outlet  22 , indicated in  FIG. 1  by an arrow  66 . 
         [0136]    For maintenance purposes, for example for maintenance or replacement of the filter element  18 , the filter housing  12  can be opened. For this purpose, the housing cover  20  is removed in the axial direction from the housing cover  14 . Here, the support element  58  is automatically separated from the support pillar  42 . The filter element  18  is pulled out of the element portion of space  30  of the housing container  14  in the axial direction. It may be replaced by a new filter element  18  or may be reinstalled after cleaning. 
         [0137]    For installation, the filter element  18  is advanced in the axial direction in the housing container  14  with the outlet-side end plate  48  forward, until the seal  36  abuts the sealing surface  34 . Subsequently, the housing cover  20  is placed with its open side forward in the axial direction onto the installation opening  16  of the housing container  14 . Here, the support element  58  is brought into relationship with the support pillar  42 . 
         [0138]    Alternative embodiments of the filter element  18  are shown in  FIGS. 8 to 14 . Those elements which are similar to those of the first embodiment of  FIGS. 1 to 7  are denoted by the same reference characters. The alternative embodiments differ from the first embodiment by the configuration of the element-side support element  58 . 
         [0139]    In the second embodiment of  FIG. 8 , the end face of the radially outer element supporting portion  60  has a zigzag-shaped surface contour. The radially inner element supporting portion  62  is configured as a flat surface. 
         [0140]    In the third embodiment of  FIG. 9 , the end face of the radially outer element supporting portion  60  has a step-shaped surface contour. The radially inner element supporting portion  62  is configured as a flat surface. 
         [0141]    In the fourth embodiment of  FIG. 10 , the end face of the radially outer element supporting portion  60  has a bulge-like surface contour. As in the first embodiment, the radially inner element supporting portion  62  is formed as a pyramid-shaped depression. 
         [0142]    In the fifth embodiment of  FIG. 11 , the end face of the radially outer element supporting portion  60  has a bulge-like surface contour. The radially inner element supporting portion  62  is configured as a depression similar to the profile of the lateral surface of a half circular-cylinder with rounded end edges. 
         [0143]    In the sixth embodiment of  FIG. 12 , the end face of the radially outer element supporting portion  60  extends as a flank which is inclined with respect to the element axis and gradually transitions into the radially inner element supporting portion  62 . The radially inner element supporting portion  62  is configured as an elevation. The end face of the radially inner element supporting portion  62  has a surface contour similar to the profile of a half circular-cylinder with rounded edges. 
         [0144]    In the seventh embodiment of  FIG. 13 , the support element  58  has a round cross-section. The end face of the radially outer element supporting portion  60  has a bulge-like contour. The radially inner element supporting portion  62  is configured as a depression. The end face of the radially inner element supporting portion  62  has a surface contour similar to the profile of a spherical segment. 
         [0145]    In the eighth embodiment of  FIG. 14 , the support element  58  has a round cross-section. The end face of the radially outer element supporting portion  60  extends as a flank which is inclined with respect to the element axis and gradually transitions into the end face of the radially inner element supporting portion  62 . The radially inner element supporting portion  62  is configured as an elevation. The end face of the radially inner element supporting portion  62  has a surface contour similar to the profile of a spherical segment.