Abstract:
A filter housing of a filter for air, water, fuel, oil or urea-water solution of an internal combustion engine, including: an inlet for fluid to be purified; and 
     an outlet for purified fluid; a hollow filter element including a filter medium for filtering fluid, which surrounds an element interior space with respect to a filter axis, is exchangeably arranged so as to separate the inlet from outlet; wherein the filter housing has at least two housing parts, which can be partly be separated from one another in order to open up an installation opening of the filter housing for the hollow filter element; wherein at least one of the housing parts has connecting tab(s) and at least one other of the housing parts has a tab receptacle(s) adapted to a connecting tab(s) for the insertion of the at least one connecting tab for connecting the housing parts.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a filter housing of a filter for fluid, in particular air, water, fuel, oil or urea-water solution, in particular of an air filter, in particular of an internal combustion engine, in particular of a motor vehicle, in particular of a commercial vehicle, having at least one inlet for fluid to be purified and at least one outlet for purified fluid, and in which a hollow filter element including a filter medium for filtering a fluid, which surrounds an element interior space with respect to a filter axis, is exchangeably arranged so as to separate the at least one inlet from the at least one outlet, wherein the filter housing has at least two housing parts, which can at least partly be separated from one another in order to open up at least one installation opening of the filter housing for the hollow filter element. 
         [0002]    The invention further relates to a hollow filter element, in particular a conical oval round filter element, of a filter for fluid, in particular air, water, fuel, oil or urea-water solution, in particular of an air filter, in particular of an internal combustion engine, in particular of a motor vehicle, in particular of a commercial vehicle, which can be arranged in a filter housing, in particular according to one of the preceding claims, such that it separates at least one inlet of the filter housing for fluid to be purified from at least one outlet for purified fluid, with a filter medium for filtering the fluid which circumferentially surrounds an element interior space with respect to an element axis. 
         [0003]    Moreover, the invention relates to a filter for fluid, in particular air, water, fuel, oil or urea-water solution, in particular of an air filter, in particular of an internal combustion engine, in particular of a motor vehicle, in particular of a commercial vehicle, having a filter housing composed of at least two housing parts, which can at least partly be separated from one another in order to open up at least one installation opening of the filter housing, and in which a hollow filter element is exchangeably arranged. 
       BACKGROUND OF THE INVENTION 
       [0004]    An air filter is known from the market which has a housing with a raw air inlet and a clean air outlet. A round filter element is arranged between the raw air inlet and the clean air outlet. The round filter element comprises a filter medium for purifying raw air. The housing has a housing container with an installation opening for the round filter element. The installation opening can be closed by a housing cover. In particular, the housing container can be separated from the housing cover for replacement of the round filter element. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the invention is to design a filter housing, a hollow filter element and a filter of the aforementioned type in which assembly of the filter is simplified and/or an in particular mechanical stability of the filter can be improved. In particular, a connection of the housing parts can be simplified. Additionally or alternatively, a positioning and/or holding the filter element in the filter housing can be improved, in particular simplified. 
         [0006]    This object is achieved in that at least one of the housing parts has at least one connecting tab and at least one other of the housing parts has at least one tab receptacle adapted to the at least one connecting tab for the insertion of the at least one connecting tab for connecting the housing parts. 
         [0007]    For connecting the housing parts, in particular a housing cover with a housing container, the at least one connecting tab may be inserted into the at least one tab receptacle. 
         [0008]    According to the invention, at least one connecting tab and at least one tab receptacle are provided which act as adjustment aids, connecting means and/or mechanical stabilization. Through the interaction of the at least one connecting tab with the at least one tab receptacle, the housing parts can be pre-adjusted during assembly. In this way, assembly can be made easier. The at least one connecting tab and the at least one tab receptacle may interact as a guiding aid during assembly of the housing parts. Further, tolerances, in particular component-related and/or assembly-related and/or operational-related tolerances, can be compensated by the at least one connecting tab and the at least one tab receptacle. This is in particular of advantage in the use of relatively large, in particular shallow conical oval, housing parts. During assembly of the filter housing, the at least one connecting tab can improve a mechanical stabilization of at least one corresponding circumferential wall portion of at least one of the housing parts. Here, the at least one connecting tab can support the at least one circumferential wall portion at least radially to the element axis and/or to a housing axis. Through the interaction of the at least one connecting tab with the at least one tab receptacle, a tightness at the transitions between the connected housing parts can be improved. A guiding of the hollow filter element into at least one of the housing parts during assembly of the housing parts can be more precise. 
         [0009]    At least one of the housing parts, preferably all housing parts which are to be connected with one another by means of the at least one connecting tab, may be advantageously made from plastic. Advantageously, at least one of the housing parts may be realized by an injection molding process or blow molding process. 
         [0010]    At least one of the housing parts may have an extension axial to the housing axis of 30 cm to 40 cm and more. 
         [0011]    The at least one tab receptacle may advantageously be an indentation which is circumferentially closed with respect to its axis. In this way, the at least one connecting tab can be guided into and held in the at least one tab receptacle on all circumferential sides. 
         [0012]    The at least one tab receptacle may advantageously have a corresponding insertion opening for the at least one connecting tab on the side facing the respective other housing part. 
         [0013]    The at least one tab receptacle may advantageously be integrated into a circumferential wall of the corresponding housing part. 
         [0014]    Advantageously, the at least one connecting tab and/or the at least one tab receptacle may extend parallel or axially to an assembly axis of the housing parts. In this way, the at least one connecting tab can be easily inserted into the at least one tab receptacle and guided there during assembly of the housing parts. The housing parts can be at least partially inserted into one another and/or connected at the edges. 
         [0015]    Advantageously, the housing parts may be completely or partially separated from one another for opening the filter housing. At least the largest part of the hollow filter element, in particular the largest part of the filter medium, preferably the entire filter medium, can be housed in one of the housing parts, in particular the housing container. This housing part may advantageously be coaxial to the housing axis. 
         [0016]    Advantageously, at least one of the housing parts of the filter housing may have an installation opening for the hollow filter element. The installation opening may be crossed by the filter axis in the installed state of the hollow filter element, and may in particular be coaxial to the filter axis. The installation opening can be at least as large as the largest outer dimension of the hollow filter element radial to the filter axis. The hollow filter element may be inserted into one housing part through the installation opening in the direction of the installation axis. Advantageously, the installation axis and/or the element axis and/or a housing axis and/or the assembly axis, in which the at least two housing parts are assembled or separated, may extend parallel or coaxially to one another. In this way, installation of the filter can be made easier. 
         [0017]    The installation opening for the hollow filter element may advantageously be coaxial to the housing axis. The filter element may thus be installed simply into one housing part in the axial direction with respect to the housing axis. 
         [0018]    The installation opening of the first housing part, and thus the filter housing, may be closed with other housing part, in particular the housing cover. A part of the hollow filter element, in particular a part of a respective end body, can also be accommodated here in the other housing part. 
         [0019]    At least one housing seal may advantageously be provided between the housing parts. An interior space of the filter housing can be sealed at the junction between the two housing parts against the environment by means of the housing seal. The at least one housing seal may circumferentially surround the at least one installation opening. The housing seal may advantageously be arranged in a corresponding seal groove in one of the housing parts. 
         [0020]    The at least one inlet and the at least one outlet may be located on the same or on different housing parts. 
         [0021]    Advantageously, the hollow filter element may have radial extensions at its two end faces which are different with respect to the filter axis, in particular the element axis. Advantageously, the hollow filter element may be inserted into one of the housing parts with the larger end face forward. A size difference between the installation opening and the smaller end face of the hollow filter element can be compensated in the installation position of the hollow filter element by at least one leveling element. 
         [0022]    The filter may advantageously be an air filter. 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. 
         [0023]    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. Advantageously, the air filter may also be a cabin filter. The filter, in particular air filter, can also be used outside of the automotive field, in particular in industrial motors. Advantageously, the filter may be a part of a commercial engine, in particular of a construction machine or a commercial motor vehicle, in particular a commercial vehicle, in particular a bus, construction machine or agricultural machine. 
         [0024]    The invention may also be used for exhaust gas purification in internal combustion engines or other combustion systems. 
         [0025]    In an advantageous embodiment, the at least one connecting tab may taper toward its free edge at least in a direction transverse to its axis of extension. The insertion of the connecting tab into the corresponding tab receptacle can thus be simplified. 
         [0026]    In an advantageous embodiment, the filter housing can have at least one guide track for guiding and/or supporting at least one leveling element of the hollow filter element. A possible height difference at the end faces of the hollow filter element may be compensated by means of the at least one leveling element. 
         [0027]    The at least one guide track, in particular at least one main guide line of the at least one guide track, may define a path of a contact point or contact region of the leveling element as it slides along the guide track during insertion of the hollow filter element into one of the housing parts or while placing one of the housing parts onto the hollow filter element. 
         [0028]    Advantageously, the at least one connecting tab may be arranged in the assembled filter housing on the same circumferential side of the filter housing as the at least one leveling element. In this way, the at least one leveling element may push from the inside against the at least one circumferential wall portion of at least one of the housing parts, and the at least one connecting tab and/or the corresponding tab receptacle may provide resistance from the outside. 
         [0029]    Advantageously, the at least one connecting tab may be arranged in the assembled housing on the same circumferential side of the filter housing as optionally the at least one guide track for the at least one leveling element. The connecting tab/tab receptacle and the corresponding leveling element/guide track may advantageously be arranged circumferentially offset from one another. 
         [0030]    Advantageously, the at least one guide track may be arranged radially with respect to the element axis/housing axis between the at least one leveling element and the at least one connecting tab/tab receptacle. In this way, the at least one guide track can be supported against a pressure from the at least one leveling element by means of the at least one connecting tab/tab receptacle. 
         [0031]    Advantageously, at least one housing part, in particular a housing cover, may comprise the at least one guide track. The at least one guide track may advantageously extend exclusively in one of the housing parts. 
         [0032]    The at least one guide track may extend with an at least imaginary main guide line at least in a plane with the installation axis of the hollow filter element in the housing part, in particular the housing cover, and/or the assembly axis between the housing parts. 
         [0033]    Advantageously, a base area of the installation opening may be oblong, in particular oval. The main guide line of the at least one guide track may be located in a minor plane with a minor axis of the base area of the installation opening and the installation axis. Further features and advantages of the at least one leveling element are described in more detail below in connection with the hollow filter element according to the invention. 
         [0034]    In a further advantageous embodiment, a base area of the installation opening may be oblong, in particular oval, and the at least one connecting tab and the at least one tab receptacle may be located at least partially on or next to a minor plane with a minor axis of the base area of the installation opening and an installation axis of the hollow filter element in the filter housing; the opposing connecting tabs/tab receptacles may optionally be respectively located at least partially on/next to the minor plane. 
         [0035]    Advantageously, the at least one connecting tab and the at least one tab receptacle may be located on a long side of the filter housing, which is oblong in cross-section. When viewed circumferentially with respect to the housing axis, the at least one connecting tab and the at least one tab receptacle may advantageously be centrally located, in particular in or near the center, on the long side. 
         [0036]    Advantageously, the main guide line of the at least one guide track may optionally be located in a minor plane with a minor axis of the base area of the installation opening and the installation axis. Advantageously, the main guide line of any opposing guide tracks may each be located in the minor plane. In this way, the support and guiding by means of the at least one leveling element on the at least one guide track may occur on a long side of the filter housing. The guiding and/or positioning can thus be further improved. 
         [0037]    In an advantageous embodiment, the at least one guide track may extend in a region outside an interior space of the corresponding housing part, in particular the housing cover. 
         [0038]    In this way, a guiding of the at least one leveling element can take place at an early stage in the assembly of the housing parts. 
         [0039]    Advantageously, at least one guide arm may be provided, on which the at least one guide track can be realized. 
         [0040]    The at least one guide arm can advantageously extend beyond the interior space of the corresponding housing part, in particular the housing cover. In this way, the corresponding at least one leveling element can be guided on the at least one guide arm, before the filter element enters into the housing part. 
         [0041]    The interior space of the housing part with the at least one guide track may at least contribute to the formation of an inlet space portion for inletting the fluid. 
         [0042]    Advantageously, the at least one guide arm may be chamfered outside the housing part on a circumferential side facing the housing axis. The chamfered circumferential side contributes to the formation of the at least one guide track. The at least one guide track may thus extend toward the housing axis when regarded in the direction of the housing axis toward the interior space of the housing part. In this way, the insertion or placement of the at least one leveling element can be simplified. 
         [0043]    In a further advantageous embodiment, at least two guide tracks may be located with respect to the filter axis on diagonally opposite radially inner circumferential sides of one of the housing parts, in particular the housing cover. 
         [0044]    In this way, the hollow filter element may be guided evenly into the filter housing, centered and/or held by means of the correspondingly opposite leveling elements. 
         [0045]    The main guide lines of the opposing guide tracks may be respectively located in a minor plane with the minor axis of the base area of the installation opening and the installation axis. 
         [0046]    In a further advantageous embodiment, at least one support portion for supporting at least one support element of the hollow filter element with respect to the housing axis, which may coincide with the element axis in an installed hollow filter element, may be centrally arranged in/on the filter housing. 
         [0047]    Advantageously, the at least one support portion can interact with at least one support element of the hollow filter element in the assembled filter. The positioning of the hollow filter element and/or the assembly of the at least one support element can thus be simplified by means of the at least one support portion. 
         [0048]    Advantageously, the at least one support portion may be located on or in one of the housing parts. In this way, the at least one support portion and the at least one support element can be brought together during installation of the hollow filter element in one of the housing parts and/or during assembly of the housing parts. An assembly of the filter can thus be simplified. 
         [0049]    Advantageously, the at least one support portion may be arranged on a raw fluid side of the hollow filter element. Alternatively or additionally, at least one support portion may be arranged on a clean fluid side. 
         [0050]    Advantageously, the hollow filter element can be supported on the other housing part with its end face which lies opposite the at least one support element. 
         [0051]    Advantageously, the at least one support element and the at least one support portion may not have a sealing function. In this way, the support function and the sealing function can be separated from one another and respectively optimized. The sealing function may be associated with at least one other component pair and optimized, which component pair is separate from the at least one support element and the at least one support portion. 
         [0052]    Advantageously, the at least one support portion may have at least one cylindrical and/or at least one conical portion. A major axis of the at least one support portion, in particular of the cylindrical/conical portion, may advantageously extend axially or parallel to the housing axis. In this way, the at least one support portion and the at least one support element may have the same orientation with an installed hollow filter element. 
         [0053]    With an assembled hollow filter element, the major axes of the at least one support element and the at least one support portion may advantageously extend coaxially. In this way, the at least support element can be easily inserted onto and/or into the at least one support portion. With an assembled hollow filter element, the major axes of the at least support element and the at least one support portion may advantageously extend parallel or axially to the installation axis of the hollow filter element relative to the filter housing and/or to the assembly axis of the housing parts, in particular to the housing part with the at least one support portion. The at least one support element and the at least one support portion may thus be brought easily and automatically into contact during installation of the hollow filter element in the filter housing and/or during assembly of the housing parts. 
         [0054]    Advantageously, the at least one support element may be at least partially complementary to the at least one support portion. The at least one support element can thus lie flat against the at least one support portion. In this way, a reliable and stable support may result which is transverse, in particular radial and/or tangential, to the element axis and/or to the housing axis. 
         [0055]    The at least one support portion may advantageously have an oval, flat-oval or round base area. The at least one support portion may also have another type of base area, in particular a square base area. 
         [0056]    Advantageously, the at least one support portion may have a receptacle on its end face, in particular a groove, at least for a portion of the at least one support element. Advantageously, the groove may extend circumferentially with respect to the major axis of the at least one support portion. The groove may advantageously be located on an end face of the at least one support portion facing the hollow filter element. Alternatively or additionally, the at least one support portion may advantageously have a hollow cylindrical or sleeve-like portion. 
         [0057]    Advantageously, the at least one support portion may be a sort of pillar or dome, or may comprise these or be a part thereof. The at least one support element of the hollow filter element may be supported on the free end of the pillar or dome. With the other end, the pillar or dome may be connected with the filter housing, in particular with the housing part which has the at least one guide track for the at least one leveling element. It may in particular be integrally connected to the filter housing. 
         [0058]    The pillar or dome may advantageously extend through a portion of space of the filter housing. In this way, the hollow filter element may be supported at a distance from a corresponding housing wall of the filter housing spanned by the pillar or dome. Advantageously, the portion of space may be flowed through by fluid during operation of the filter. Depending on the direction of flow of the fluid in the filter housing, the portion of space may be an inlet portion of space or an outlet portion of space. 
         [0059]    The object is further achieved by the hollow filter element in that, radially outward with respect to the element axis, the hollow filter element has at least one leveling element in a region which, in the installed state of the hollow filter element, overlaps or is adjacent to a portion of the filter housing, in/on which at least one connecting tab and/or at least one tab receptacle is arranged for connecting the housing parts. 
         [0060]    The features and advantages shown above in connection with the filter housing according to the invention and its advantageous embodiments apply accordingly to the hollow filter element according to the invention and advantageous embodiments thereof, and vice versa. 
         [0061]    Advantageously, the extension of the filter element may be smaller on a first of its end faces in a direction radial to the element axis than on a second of its end faces. Advantageously, the filter medium may have a first end body at least on the smaller end face. 
         [0062]    The at least one leveling element may be arranged radially outward on a first end body of the hollow filter element with respect to the element axis, in particular the filter axis. 
         [0063]    Advantageously, the first end body may have at least one leveling element in a radially outward portion with respect to the element axis in the at least one direction of the smaller extension with respect to the element axis. 
         [0064]    Advantageously, different distances from the edges of the hollow filter element radial to the element axis can be equalized to the differently-sized end faces of the hollow filter element with the at least one leveling element. A height equalization can be achieved with the at least one leveling element. The hollow filter element can thus be aligned in the filter housing. Advantageously, the element axis may be aligned parallel or coaxially to the filter axis and/or to the housing axis. In particular with a horizontal arrangement of the hollow filter element, in which the element axis extends horizontally, different heights at the differently-sized end faces can be equalized in this way. 
         [0065]    Advantageously, the at least one leveling element may be at least partially elastic. In this way, the hollow filter element can be more easily fixed in the filter housing. The at least one leveling element may give way and be compressed during installation of the filter. Any tolerances, in particular production-related and/or component-related and/or assembly-related tolerances, of the hollow filter element can be easily equalized in the filter housing with the at least one leveling element. Further, the at least one leveling element may additionally serve as a vibration damper, in particular during operation of the air filter. 
         [0066]    Alternatively or additionally, the at least one leveling element may advantageously be at least partially rigid. Advantages may thus result during assembly of the filter. With a rigid leveling element, a more accurate and simpler guiding on the corresponding housing-side guide portion may occur. 
         [0067]    The leveling element may advantageously serve as a spacer. Advantageously, a radial distance with respect to the element axis between the radially outer circumferential side of the first end body and a correspondingly opposite portion of the filter housing can be realized by means of the at least one leveling element. A gap may thus be realized between the filter element in the region of the smaller end face and an inner wall of the filter housing which radially outwardly surrounds the filter element. By means of the gap, fluid may flow into or out of a space which radially outwardly surrounds the filter element. Fluid 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. In the direction of flow through the filter medium from radially outside to radially inside, the upstream side of the filter medium is located on the radially outer circumferential side of the filter element. The downstream side of the filter element is thus located in the element interior space. The fluid 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 fluid, an improved packing size of the filter housing, and thus a smaller footprint, can be realized. Further, in an axial flow of fluid 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 filter in which the flow of fluid is led tangentially to the upstream side of the filter element or away from the downstream side. 
         [0068]    The first end body may advantageously be an end plate or at least comprise an end plate. 
         [0069]    The filter medium can be stabilized with the first end body. Further, the filter medium can be sealed at the smaller end face with the first end body. 
         [0070]    Advantageously, the element interior space may be closed with the first end body at the smaller end face of the filter element. In this way, a flow of fluid out of the element interior space or into the element interior space can be prevented there. It may thus be achieved that the fluid must flow through the filter medium. The fluid may flow through the filter medium from radially outside to radially inside into the element interior space, or in the opposite direction out of the element interior space. The fluid may flow through a corresponding throughflow opening on the other end face of the filter element into the element interior space or out of the element interior space. 
         [0071]    The hollow filter element may advantageously be 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 element axis, a conical oval round filter element, in which the oval cross-section tapers in the axial direction of the element axis 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 of the element axis 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 cross-sectional variation in the direction of the element axis. 
         [0072]    The at least one leveling element may advantageously be arranged on a long, in particular flat, side of an oval, in particular a flat-oval, round filter element. 
         [0073]    The at least one leveling element may advantageously be arranged on the tapered end face of a conical, in particular conical oval or shallow conical oval, round filter element. 
         [0074]    Advantageously, the first end body may have a respective leveling element on the diagonally opposite circumferential sides in the at least one direction of the smaller extension with respect to the element axis. In this way, the first end body may be supported on opposite sides against the filter housing. A more even and/or more precise guiding/positioning/holding in the filter housing can thus occur. 
         [0075]    Advantageously, a base area of the hollow filter element may be oblong, in particular oval, at least in the area of the smaller end face, and an imaginary midpoint of the at least one leveling element may be located on a minor axis of an imaginary plane which extends parallel to the base area of the hollow filter element. Optionally, the midpoints of opposite leveling elements can be respectively located on the minor axis. In this way, the first end plate may be supported approximately centrally on its respective long sides. Support and/or guiding can thus be improved. 
         [0076]    The minor axis is the short axis of the elongated surface through the center thereof. In contrast, the major axis is the long axis of the elongated surface through the center thereof. 
         [0077]    Advantageously, the at least one leveling element may extend radially, in particular radially and axially, outward over the radially outer circumferential side of the filter medium. The at least one leveling element may thus enable a radial support. A distance between a radially outer circumferential side of the filter medium and a corresponding circumferential side of the filter housing can be achieved by means of the at least one leveling element. 
         [0078]    If the at least one leveling element additionally extends beyond the filter medium in the axial direction, an additional axial support may thus result. In this way, a tilting or canting of the at least one end body relative to the element axis can be countered. 
         [0079]    Advantageously, a distance of a radially outer circumferential side of the at least one leveling element from the element axis may advantageously correspond to a distance of the corresponding radially outer circumferential side of the hollow filter element from the element axis at the larger end face. 
         [0080]    In this way, the hollow filter element can be oriented with its element axis uniformly parallel or coaxial to the housing axis. 
         [0081]    Alternatively or additionally, a distance of the radially outer circumferential side of the at least one leveling element from the element axis may advantageously be larger than the corresponding distance of the radially outer circumferential side of the hollow filter element, in particular an end body there, at the larger end face. In this way, different diameters of the filter housing can be equalized at the respective end faces of the hollow filter element. 
         [0082]    In the final installation position of the hollow filter element in a filter housing of the filter in its usual position, the at least one leveling element can advantageously be arranged spatially below. The at least one leveling element can thus support the hollow filter element with respect to gravity against the filter housing. 
         [0083]    In the final installation position in the typical operating position, the at least one direction of the smaller extension can advantageously extend spatially vertically. In the installation location in the typical operating position, the element axis can advantageously extend horizontally. 
         [0084]    In an advantageous embodiment, the hollow filter element may have at least one support element on an end face on an outer side facing away from the element interior space. 
         [0085]    The at least one support element and thus the hollow filter element may be supported at least transverse to the element axis, in particular radially or tangentially to the element axis or radial to another axis which is parallel to the element axis. In this way, the hollow filter element can additionally be positioned and held in the radial direction with respect to the element axis. 
         [0086]    Advantageously, the at least one support element may additionally be supported in the axial direction with respect to the element axis in the filter housing. In this way, the axial position of the hollow filter element can be improved. The hollow filter element can advantageously be clamped and held in the axial direction between two opposing support portions of the filter housing. 
         [0087]    Advantageously, the at least one support element may be arranged centrally with respect to the element axis on the smaller end face of the hollow filter element. The hollow filter element can thus be supported centrally. In this way, an improved support of the hollow filter element on the filter housing may occur with only one support element and only one corresponding support portion. Support can thus be realized with a small footprint of the required components in the filter housing. 
         [0088]    Advantageously, the at least one support element may be at least partially elastic. In this way, any installation tolerances of the hollow 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 filter. 
         [0089]    The at least one support element may have at least one cylindrical and/or at least one conical portion. A major axis of the at least one support element may extend axially or parallel to the element axis. The support element can be supported transversely or axially to the element axis against at least one corresponding support portion on the side of the filter housing. 
         [0090]    The at least one support element may advantageously have an oval, flat-oval or round base area. It may also have another type of base area, in particular a square base area. 
         [0091]    Advantageously, the at least one support element may have a hollow cylindrical or sleeve-like portion. 
         [0092]    The at least one support element may have a cavity which is open to the at least one support portion of the filter housing. A corresponding projection of the at least one support portion may dip into the cavity. In this way, support can be further improved. 
         [0093]    When the hollow filter element is correctly assembled, the hollow cylindrical or sleeve-like portion of the at least one support element may advantageously be inserted into a corresponding end face-side receptacle, in particular a groove, of the at least one support portion. The groove may be regarded as the cavity of the support portion, which is open towards the free end face of the support portion. 
         [0094]    Advantageously, the at least one support element can be arranged on the first end body of the hollow filter element. 
         [0095]    The technical object is achieved by the filter according to the invention, in that at least one of the housing parts has at least one connecting tab and at least one other of the housing parts has at least one tab receptacle adapted to the at least one connecting tab for the insertion of the at least one connecting tab for connecting the housing parts. 
         [0096]    The features and advantages shown above in connection with the filter housing according to the invention and the hollow filter element according to the invention and its advantageous embodiments apply accordingly to the filter according to the invention and advantageous embodiments thereof. 
         [0097]    The filter housing can advantageously be a filter housing according to the invention. 
         [0098]    Advantageously, an inlet-side inlet portion of space, and element portion of space, in which the hollow filter element can be 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 fluid through the filter. In this way, an axial flow of the fluid to the upstream side of the filter medium can easily be realized. Further, an axial discharge of the filtered fluid from the clean fluid side of the hollow filter element can thus be achieved. Any differences in pressure between the clean fluid side and the raw fluid side can thus be reduced. Advantageously, a main flow direction of the fluid 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 and/or to the housing axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0099]    Further advantages, features and details of the invention will become apparent from the following description in which an embodiment of the invention with reference to the drawings is explained in more detail. 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. 
           [0100]      FIG. 1  shows a plan view of an air filter of an internal combustion engine with a filter housing including a housing container and a housing cover, in which an exchangeable conical oval round filter element is arranged; 
           [0101]      FIG. 2  shows a transverse-side cross-section of the air filter of  FIG. 1  along the section line II-II; 
           [0102]      FIG. 3  shows a longitudinal-side cross-section of the air filter of  FIG. 1  along the section line III-Ill; 
           [0103]      FIG. 4  shows a first isometric oblique view of the air filter of  FIGS. 1 to 3 ; 
           [0104]      FIG. 5  shows a second isometric oblique view of the air filter of  FIGS. 1 to 4 ; 
           [0105]      FIG. 6  shows an isometric representation of the open housing container of the air filter of  FIGS. 1 to 5  with the round filter element; 
           [0106]      FIG. 7  shows an isometric representation of the open housing container of the air filter of  FIGS. 1 to 6 , here without the round filter element; 
           [0107]      FIG. 8  shows an isometric representation of the open housing container of the air filter of  FIGS. 1 to 7 , without the round filter element from a different perspective; 
           [0108]      FIG. 9  shows an isometric representation of the housing cover of the air filter of  FIGS. 1 to 5  with the round filter element, without the housing container; 
           [0109]      FIG. 10  shows an isometric representation of the housing cover of the air filter of  FIGS. 1 to 5 , without the round filter element; 
           [0110]      FIG. 11  shows the isometric representation of the housing cover of  FIG. 10  from another perspective; 
           [0111]      FIG. 12  shows a side view of the air filter of  FIGS. 1 to 5  in an early stage of assembly of the housing cover on the housing container; 
           [0112]      FIG. 13  shows a plan view of the air filter in the stage of assembly of  FIG. 12 ; 
           [0113]      FIG. 14  shows a plan view of the air filter in a stage of assembly following the stage of assembly shown in  FIG. 13 ; 
           [0114]      FIG. 15  shows an isometric representation of the round filter element of the air filter of  FIGS. 1 to 5 ; 
           [0115]      FIG. 16  shows a transverse-side longitudinal section of the round filter element of the air filter of  FIGS. 1 to 5 ; 
           [0116]      FIG. 17  shows a longitudinal-side side view of the round filter element of the air filter of  FIGS. 1 to 5 ; 
           [0117]      FIG. 18  shows a transverse-side side view of the round filter element of the air filter of  FIGS. 1 to 5 ; 
           [0118]      FIG. 19  shows a plan view of an inlet-side end plate of the round filter element of the air filter of  FIGS. 1 to 5 ; 
       
    
    
       [0119]    In the figures, identical components are provided with the same reference characters. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0120]      FIGS. 1 to 14  show an air filter  10  of an internal combustion engine of a commercial vehicle in various views and stages of assembly. The air filter  10  is arranged in an air intake tract of the internal combustion engine. It is used for the purifying of combustion air which is supplied to the internal combustion engine for combustion. 
         [0121]    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. 3  shows a section along a short transverse axis of the filter housing  12 . The filter housing  12  has a housing container  14 , to the left in  FIGS. 1 and 3 . The housing container  14  has an installation opening  16 , which is shown for example in the foreground in  FIGS. 6 to 8 , for installation of a filter element  18 . The installation opening  16  is closed with the housing cover  20 , to the right in  FIG. 1 . 
         [0122]    The housing container  14  has an outlet  22  for the filtered air, which opens into 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. 
         [0123]    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 . 
         [0124]    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 . 
         [0125]    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 a filter axis  32 . For the sake of clarity, the filter axis  32  in  FIG. 3  is shown in front of the drawing plane, although it is located outside the sectional plane III-III of  FIG. 1 . 
         [0126]    In the embodiment shown, the filter axis  32  coincides with a housing axis of the filter housing  12  and, with an installed filter element  18 , with an element axis of the filter element  18 . The filter axis  32  also presently coincides with an installation axis, along which the filter element  18  is inserted into and can be removed from the housing container  14 . In addition, the filter axis  32  coincides with an assembly axis, along which the housing cover  20  is assembled on the housing container  14 . For the sake of clarity and comprehensibility, in the embodiment illustrated in the description the enumerated axes are briefly designated as the “filter axis  32 .” When further reference is made to “axial,” “radial,” “circumferential” or “coaxial”, this refers unless otherwise stated to the filter axis  32 . 
         [0127]    The installation opening  16  circumferentially surrounds the filter axis  32 . In the installed state of the filter element  18 , the filter axis  32  crosses the installation opening  16 . The inner dimension of the installation opening  16  is larger than the largest outer dimension of the filter element  18  radial to the filter axis  32 . A base area of the installation opening  16  is an elongated flat-oval. 
         [0128]    A seal groove  33 , shown in particular in the  FIGS. 3 and 9 to 11 , is arranged with a housing seal in the end face of the free edge of the housing cover  20 . The housing seal is sealingly applied against the corresponding end face of the free edge of the housing container  14  and surrounds the installation opening  16  in a circumferentially closed manner. 
         [0129]    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. 
         [0130]    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 . 
         [0131]    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 . 
         [0132]    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 inlet portion of space  38  are located on the raw air side of the filter element  18 . 
         [0133]    A support pillar  42  is arranged on the housing cover  20 . The support pillar  42  is integrally connected with the housing cover  20 . It is approximately coaxial with the filter axis  32 . It is arranged centrally with respect to the filter axis  32 . The support pillar  42  extends into the inlet portion of space  28  from an inner side of the housing cover  20  facing the filter element  18  up to an outlet-side end face  66  of the filter element  18 . The support pillar  42  is located on the raw air side of the filter medium  64 . 
         [0134]    A circumferential counter support groove  44 , shown for example in  FIGS. 10 and 11 , is arranged so as to extend coaxially to a major axis of the support pillar  42 , thus to the filter axis  32 , on the free end face of the support pillar  42  facing the filter element  18 . The counter support groove  44  is an annular cavity in the support pillar  42  which is open towards the free end face of the support pillar  42 . 
         [0135]    The housing container  14  further has two connecting tabs  46  for connection to the housing cover  20 . The connecting tabs  46  are located with respect to the filter axis  32  on opposite flattened circumferential sides of the housing container  14 . They are each integrally mounted with one end on the free circumferential edge of the housing container  14  which surrounds the installation opening  16 . The connecting tabs  46  extend parallel to the assembly axis of the housing cover  20  with the housing container  14 , i.e. parallel to the filter axis  32 . Imaginary central axes of the connecting tabs  46  lie in an imaginary plane with the filter axis  32 . Regarded in the direction of the filter axis  32 , this imaginary plane is inclined with respect to another imaginary plane with a minor axis of the oval installation opening  16 . The imaginary central axes of the connecting tabs  46  are thus, as can be seen for example in  FIG. 2 , respectively laterally offset on opposite sides with respect to the minor axis. 
         [0136]    The mutually facing inner sides of the connecting tabs  46  are smooth. The inner sides of the connecting tabs  46  each form an initial portion of a corresponding guide ramp  48 . The guide ramps  48  are continued on the inside of the housing container  14 . During installation of the filter element  18  in the housing container  14 , respectively radially outer circumferential sides of an outlet-side end plate  50  of the filter element  18  are guided on the guide ramps  48 . 
         [0137]    These mutually-opposite outer sides of the connecting tabs are equipped with stabilization profiles. 
         [0138]    The connecting tabs  46  taper in a wedge-like manner at their free edges facing away from the free circumferential edges of the housing container  14 . This simplifies the insertion of the connecting tabs  46  into the corresponding tab receptacles  52  of the housing cover  20  for connecting the housing container  14  with the housing cover  20 . 
         [0139]    The housing cover  20  has two tab receptacles  52 . The tab receptacles  52  respectively fit one of the connecting tabs  46  of the housing container  14 . 
         [0140]    The tab receptacles  52  are located with respect to the filter axis  32  on opposite flattened circumferential sides of the housing cover  20 . They are respectively integrally arranged in a region of the free circumferential edge of the housing cover  20 . The tab receptacles  52  are integrated in the circumferential wall of the housing cover  20 . 
         [0141]    The tab receptacles  52  extend respectively parallel to the assembly axis of the housing cover  20  with the housing container  14 , i.e. parallel to the filter axis  32 . Imaginary central axes of the tab receptacles  52  lie in a plane with the filter axis  32 . Regarded in the direction of the filter axis  32 , this plane is inclined with respect to an imaginary plane with a minor axis of the oval installation opening  16 . The central axes of the tab receptacles  52  are thus, analogously to the central axes of the connecting tabs  46 , laterally offset on opposite sides with respect to the minor axis. 
         [0142]    With respect to their respective central axes, which extend parallel to the filter axis  32 , the tab receptacles  52  are circumferentially closed depressions. The connecting tabs  46  are respectively held on all circumferential sides in the corresponding tab receptacle  52 . On the side opposite the housing container  14 , the tab receptacles  52  have a corresponding insertion opening  54  for the corresponding connecting tab  46 . The seal groove  33  extends radially outward around the tab receptacles  52 . The interior spaces of the tab receptacles  52  are thus sealed to the environment. 
         [0143]    When the housing cover  20  is assembled, the connecting tabs  46  mechanically stabilize the circumferential wall portions of the housing cover  20 . Here, the connecting tabs  46  support the circumferential wall portions radially to the filter axis  32 , i.e. radially relative to the element axis and to the housing axis. 
         [0144]    The housing cover  20  further has two guide tracks  56  for guiding and supporting the corresponding leveling elements  58  of the filter element  18 . The guide tracks  56  can be seen, for example, in  FIGS. 9 to 11 . With respect to the filter axis  32 , the guide tracks  56  are located on diagonally opposite, radially inner circumferential sides of the housing cover  20 . 
         [0145]    The guide tracks  56  are respectively realized on a guide arm  60 . Within an interior space of the housing cover  20 , which contributes to the formation of the inlet portion of space  28 , the guide arms  60  are integrally connected on a longitudinal side with the respective radially inner circumferential side of the circumferential wall of the housing cover  20 . The respectively opposite longitudinal sides of the guide arms  60  form the corresponding guide tracks  56 . 
         [0146]    The guide tracks  60  respectively extend beyond the interior space of the housing cover  20 . Outside the housing cover  20 , the guide arms  60  are respectively chamfered on the radially inner longitudinal side with the guide tracks  56 . The corresponding guide tracks  56  thus extend in the direction of the filter axis  32  toward the interior space of the housing cover  20  when regarded in the direction of the filter axis  32 . 
         [0147]    The guide tracks  56  respectively extend with an imaginary main guide line  62  in a plane with the installation axis, thus of the filter axis  32 , the housing cover  20  with the housing container  14  and the filter element  18 . During fitting of the housing cover  20  on the filter element  18 , the main guide lines  62  predefines a path of a contact area of the corresponding leveling element  58  as it slides along the corresponding guide track  56 . The main guide lines  62  are located in an imaginary minor plane, which is spanned by the minor axis of the flat-oval base area of the installation opening  16  and the filter axis  32 . 
         [0148]    The filter element  18  which is described in more detail below is shown in  FIGS. 15 to 19  in various perspectives and sections. The filter element  18  is a flat conical oval round filter element. The filter element  18  is coaxial to the element axis, thus to the filter axis  32 . The filter element  18  has a flat-oval cross-section. The short transverse axis, i.e. the minor axis, of the oval is located in the drawing plane of  FIG. 15 , the long transverse axis, i.e. the major 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 conical 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 in the direction of the filter axis  32 . The outer cross-section and the inner cross-section of the filter element  18  are tapered from their outlet-side end faces  68 , which face the outlet portion of space  24 , to the inlet-side end face  66 . 
         [0149]    The direction of the minor axis of the flat-oval filter element  18  extends vertically in the final installation location and normal operating position. In the installation location in the typical operating position, the filter axis  32  extends horizontally. 
         [0150]    The filter element  18  comprises a filter medium  64  which is zigzag pleated to a filter bellows, and which is circumferentially closed with respect to the element axis, thus the filter axis  32 . The filter medium  64  is a non-woven filter which is suitable for the filtration of air. 
         [0151]    The extension of the filter bellows from the filter medium  64  in the direction radial to the element axis, thus to the filter axis  32 , is smaller at its inlet-side end face  66  than at its outlet-side end face  68 . 
         [0152]    The filter medium is connected on its outlet-side end face  68  with the outlet-side end plate  50 . The outlet-side end plate  50  is coaxial with the filter axis  20 . The outlet-side end plate  50  is made of plastic. It is tightly bonded to the end face  68  of the filter medium  64 . The radially outer circumferential side of the outlet-side end plate  50  abuts the radially inner circumferential side of the housing container  14  with minimal play. 
         [0153]    The outlet-side end plate  50  has a central, coaxial outflow opening  70 . The outflow opening  70  extends over the entire radially inner cross-section of the filter medium  64 . An element interior space  72  of the filter element  18 , which is surrounded by the filter medium  64 , is connected with the outlet portion of space  24  via the outflow opening  70 . 
         [0154]    The seal  36  is arranged on the outer side of the outlet-side end plate  50  axially opposite the filter medium  64 . The seal  36  is made of elastic polyurethane foam. It is foamed onto the outlet-side end plate  50 . The seal  36  is coaxial with the element axis, thus with the filter axis  32 , and circumferentially surrounds the outflow opening  70 . It extends in the axial direction. It is supported in the axial direction on the sealing surface  34  of the housing container  14 . 
         [0155]    The filter medium is sealingly connected on its inlet-side end face  66  with an inlet-side end plate  74 . The inlet-side end plate  74  is made of polyurethane. The inlet-side end plate  74  closes the element interior space  72  from the inlet portion of space  28 . In a similar manner to the outlet-side end plate  50 , the inlet-side end plate  74  is sealingly connected with the filter medium  64 . 
         [0156]    A coaxial support tube  76  extends in the element interior space  72  between the inlet-side end plate  74  and the outlet-side end plate  50 . The support tube  76  is made of plastic. It is structured as a grid. Its circumferential side is permeable to air. The support tube  76  has a flat conical oval shape corresponding to the filter medium  64 . The radially inner circumferential side of the filter medium  64  may be supported on the radially outer circumferential side of the support tube  76 . 
         [0157]    A support element  78  is arranged on the axially outer side of the inlet-side end plate  74  facing the element interior space  72 . The support element  78  is located on the raw air side of the filter medium  64 . The support element  78  is fixedly connected to the inlet-side end plate  74 . The support element  78  is made of an elastic polyurethane foam. The support element  78  is foamed onto the outlet-side end plate  74 . 
         [0158]    The support element  78  is sleeve-like. It has the shape of a hollow cylinder, the major axis of which extends coaxially to the filter element  32 , thus to the element axis, in the embodiment shown. A cavity  80  of the support element  78  is open on its end face facing the inlet-side end plate  74 . The support element  78  has an approximately oval cross-section. In  FIG. 16 , its short transverse axis is in the drawing plane, its long transverse axis is perpendicular to the drawing plane. With an installed filter element  18 , the orientation of the support element  78  with respect to the filter axis  32  corresponds to the orientation of the support pillar  42  of the housing cover  20 . 
         [0159]    When the filter element  18  is correctly installed, the portion of the support pillar  42  surrounded by the counter support groove  44  is inserted into the cavity  80  of the support element  78 . Here, the circumferential wall of the support element  78  is inserted into the counter support groove  44  of the support pillar  42 . 
         [0160]    On its free side facing away from the end plate  74 , the wall thickness of the support element  78  reduces in a conical portion toward the free edge. The insertion of the support element  78  into the counter support groove  44  of the support pillar  42  can thus be simplified. 
         [0161]    The filter element  18  is supported via the support pillar  42  against the filter housing  12  by means of the support element  48 . The support occurs radially, i.e. transverse to the filter axis  32 , thus transverse to the element axis and to the housing axis, as well as axially. Through the interaction of the support element  48  with the support pillar  42 , the filter element  18  is held and positioned radially and axially 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 . 
         [0162]    Further, two support webs  82  are respectively arranged on the radially outer edges of the inlet-side end plate  74  in the region of the short transverse sides. The support webs  82  respectively project beyond the outlet-side end plate  74  both in the radial direction and in the axial direction. The support webs  82  are respectively supported in the radial direction at support points  83 , shown inter alia in  FIGS. 3, 10 and 11 , on the inner side of the housing container  20 . 
         [0163]    The aforementioned leveling elements  58  are located radially outward with respect to the element axis, thus the filter axis  32 , on the inlet-side end plate  74 . The leveling elements  58  are made of polyurethane. They are integrally connected to the inlet-side end plate  74 . The leveling elements  58  are arranged on a raw air side of the filter element  18 . 
         [0164]    The leveling elements  58  are arranged on circumferential sides of the inlet-side end plate  74  which are diagonally opposite with respect to the filter axis  32 . The imaginary center point of the leveling elements  58  is located here on a minor axis of a flat-oval cross-section of the filter element  18 . In the direction of the minor axis, the filter bellows of the filter element  18  has a smaller radial extension at the inlet-side end face  66  than at the outlet-side end face  68 . The minor axis lies in an imaginary plane which extends parallel to the flat-oval base area of the filter element  18 . The minor axis is the short axis of the imaginary plane through the midpoint thereof. In contrast, the major axis is the long axis of the imaginary plane through the midpoint thereof. 
         [0165]    The leveling elements  58  respectively extend radially and axially outward over the radially outer circumferential side of the filter bellows of the filter medium  64  and the inlet-side end plate  74 . 
         [0166]    The distances of the radially outer circumferential sides of the leveling elements  58  from the filter axis  32  correspond respectively to the distances of the corresponding radially outer circumferential sides of the outlet-side end plate  50  from the filter axis  32 . 
         [0167]    In the final installation location of the filter element  18  in the filter housing  12  in the usual operating position thereof, one of the leveling elements  58  is arranged spatially below. The other leveling element  58  is arranged spatially above, vertically, above the former leveling element  58 . 
         [0168]    By means of the leveling elements  58 , a uniform radial distance is realized with respect to the filter axis  32  between the radially outer circumference of the inlet-side end plate  74  and an opposite radially inner circumference of the housing cover  20  for the formation of a gap  40 . 
         [0169]    When the filter housing  12  is assembled, the tab receptacles  52  with the connecting tabs  46  are respectively approximately arranged on the same circumferential side of the filter housing  12  as one of the guide tracks  56  for one of the leveling elements  58 . Here, the tab receptacles  52 /connecting tabs  46  and the corresponding leveling elements  58 /guide tracks  56  are arranged circumferentially offset from one another, wherein the tab receptacles  52 /connecting tabs  46  overlap the corresponding leveling elements  58 /guide tracks  56  in the radial direction. 
         [0170]    The guide tracks  56  are respectively arranged between one of the leveling elements  58  and one of the tab receptacles  52 /connecting tabs  46 . By means of the connecting tabs  46 /tab receptacles  52 , the guide tracks  56  are supported against pressure from the leveling elements  58 . The leveling elements  58  press from the inside against the corresponding circumferential wall portion of the housing cover  20 . The connecting tabs  46  and the corresponding tab receptacles  52  respectively act against this from the outside. 
         [0171]    During operation of the air filter  10 , the air to be filtered flows through the inlet  26 , indicated in  FIG. 1  by an arrow  84 , 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  64 . The air flows through the filter medium  64  from radially outside to radially inside and is purified. The purified air flows through the circumferential side of the support tube  76  and passes into the element interior space  72 . The purified air leaves the element interior space  72  substantially in the axial 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 arrow  86 . 
         [0172]    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 container  14 . Here, the support element  78  is automatically pulled out of the counter support groove  44  at the end of the support pillar  42 . The connecting tabs  46  are pulled out of the tab receptacles  52 . The leveling elements  58  glide along the guide tracks  56 . 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 reinstalled after cleaning. 
         [0173]    For installation, the filter element  18  is advanced in the axial direction in the housing container  14  with the outlet-side end plate  50  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 . The connecting tabs  46  are inserted here into the respective tab receptacles  52 . The housing cover  20  is thus pre-adjusted to the housing container  14 . 
         [0174]    During advancing of the housing cover  20  onto the housing container  14  in the axial direction, the connecting tabs  46  and the tab receptacles  52  interact as guiding aids. Once the free ends of the guide arms  60  of the housing cover  20  reach the leveling elements  58 , the guide arms  60  encompass the radially opposite sides of the leveling elements  58  from the outside. Upon further advancement of the housing cover  20 , the leveling elements  58  are then guided along the main guide line  62  of the guide tracks  56  of the guide arms  60 . Upon further pressing of the housing cover  20 , the side of the filter element  18  with the inlet-side end plate  74  is continuously lifted into its final position by means of the lower guide tracks  56 . The filter element  18  is positioned and centered in the housing cover  20 . Finally, upon further pressing, the support element  78  of the housing cover  20  is automatically inserted into the counter support groove  44  of the support pillar  42 . The radially inner portion at the end of the support pillar  42  engages here in the cavity  80  of the support element  78 . In the correct state of installation, the element axis extends coaxially with the housing axis. Finally, the housing cover is fixed to the housing container  14  in a manner of no further interest here.