Patent Publication Number: US-2023158432-A1

Title: Air Filter Device and Filter Element for an Air Filter Device of a Motor Vehicle

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to an air filter device with a filter housing for receiving a replaceable filter element for an air filter device of a motor vehicle, wherein the filter housing has links for guiding and supporting projections on two opposite side walls of the flat filter element, which consists of a filter fleece, which is held in a frame that forms the side walls. The invention further relates to a filter element with projections on the side walls for the air filter device of a motor vehicle. 
     So that a filter element in a housing of an air filter device for a motor vehicle can fulfil its function reliably, it is necessary to ensure that the filter element is fixed in the housing in such a way that it is sealed and positionally stable. 
     DE 10 2014 004 738 A1 describes a filter element with a box-shaped body, wherein, in a frame wall of the body formed from flexible material, in contrast stiffened guide elements are formed, which serve for securing the filter element on guide bars on the housing side. 
     DE 10 2007 048 396 A1 and DE 10 2007 048 395 A1 each describe a filter element for an air conditioning system of a motor vehicle. The filter element has end faces opposite one another, which are made of paper material or plastic material. Two peg-shaped guide elements project perpendicularly from each end face. In order to bring the filter element into its working position, the guide elements are moved along guide grooves, which are formed in a housing of the air conditioning system. In this air conditioning system, two such filter elements are to be arranged next to one another in the flow cross-section of the housing. The entire movement of the filter elements during assembly and dismantling takes place entirely in a plane defined by the guide grooves, perpendicular to the direction of flow. After inserting the second filter element in the housing, the opening in the housing surrounding the flow cross-section, which is provided for inserting the filter elements, is closed by means of a cover. In the cover, a further guide groove is formed, into which the guide elements of the second internal filter are inserted when fitting the edge cover on the housing. Thus, in this configuration, the cover interacts with and supports correct positioning and holding of the filter elements. 
     If, however, the filter element is inserted in a frame cross-section of the air filter device closed all round on the housing side, relative to the flow cross-section, for example in a hinged air scoop or an end of an air duct, the assembly/dismantling of the filter element cannot take place in the same plane in which the filter element assumes its operating position. Rather, the filter element must be displaced in—or against—the direction of flow into the plane of its final operating position. 
     In an air filter device in which the filter element is inserted in a closed housing cross-section like this, a holder of the filter element may be provided, in which case the filter element, in the operating position, is to rest on projections on the housing side. These projections are configured for example in the receiving housing frame as small, inward-projecting projections or brackets on opposite housing walls of the housing. 
     To insert the filter element, the frame of the filter element must first be compressed inwards a little, in order to be able to place the filter element past the projections, which make the housing cross-section narrower, on the projections carrying them, as soon as it springs back to the original shape. It may happen that a wall of the filter frame does not come to rest correctly on the carrying projections, but is merely pressed against the projections. In particular, in the region of the housing of the air filter device, in which the projections are not easy to see, this may remain unnoticed. In this way, undesirable and moreover not easily discernible leakage of the air filter device may occur. 
     DE 10 2013 020 382 A1 describes a filter element with frame for securing in a filter air scoop or in an all-round closed cross-section of an air filter housing. At one end—pointing in the insertion direction of the frame—of two opposite side walls, sideways-projecting contact elements are arranged—transversely to the insertion direction. The contact elements are introduced into sliding block guides on the housing side. In the final position of the contact elements in the sliding block guides, the filter element can be swivelled about the resultant swivel axis, in order to insert it fully in the surrounding housing. On the end face of the frame of the filter element, which is opposite the rear wall near the swivel axis, two elastic snap-in hooks are mounted. The snap-in hooks lock, by swivelling-in the filter element, with respective locking elements, which are formed on the filter housing. 
     The object of the present invention is to provide an improved air filter device of the kind stated at the beginning, with which the filter element can be mounted particularly easily in its predetermined installation position in the filter housing, and an improved filter element for mounting in the corresponding air filter device. 
     The air filter device according to the invention—also called “air filter housing” or “housing” hereinafter—for a motor vehicle comprises a housing with a receiving space for a filter element according to the invention. The filter element has a frame, which surrounds a filter material at least partially, wherein the frame comprises two opposite side walls as well as opposite transverse walls, which join the side walls together. In each case a first projection projects from each side wall near the same transverse wall. 
     The housing has—corresponding to the frame of the filter element—two opposite housing side walls. The two housing side walls each have at least one link, in which the respective first projection of the relevant or corresponding side wall of the filter element can be inserted in each case in a first link end region intended for it, which is attainable along a first direction of the link. 
     According to the invention, it is provided that in each case a second projection projects from the side walls of the filter element near the other one of the two transverse walls, and the housing side walls in each case have a second link end region—directed against the first direction—in which in each case the second projections can be inserted, so that the filter element is then located in its operating position in the receiving space of the housing, wherein the side walls are elastically deformable, so that a distance of the two projections arranged on the same side wall from one another can be reduced, in order to bring the second projections during insertion past inwards-directed link guide flanks into the second end region assigned or intended for them in each case. 
     If the first projections have reached their respective link end region in the housing side walls opposite one another, in this position the filter element can be swivelled about the rotation axis formed by these projections. 
     Next, the two still free—or second—projections of the housing walls opposite one another can be brought into the second link end regions assigned to them, by compressing the side walls of the filter element towards the first projections, for example by pressing on the transverse wall of the filter element nearer the second projections—and still freely accessible. This in each case reduces the distance of the first and second projections from one another, wherein the projections are led along the link guide flanks on the housing side, and at the end of the movement the filter element is raised to the level of the receiving space, where the second projections occupy the link end regions assigned to them as the side walls spring back into their undeformed initial state. The filter element is then held positionally secured in its installation position. The air filter device described and the associated filter element allow assembly of the filter element in a very simply executed, reliable process, with quick and reliable assembly of the filter element being ensured by the controllable and logical movements during installation. With the proposed design of air filter device and filter element, front locking mechanisms are no longer required on the filter element, so there may also be a saving of space. 
     In the link end regions, the projections on the side walls of the filter element are secured in a final position against unintentional moving out or falling out from the link, because for removal or dismantling of the filter element, the filter element must be deformed again. In order to be able to remove the filter element from the housing, the respective projection is for example moved out of its final position by a manual operation on the filter material connected to the walls of the filter element either along the link or orthogonally thereto—towards the centre axis of the filter element—, while deforming at least the corresponding side wall. Without deformation of the side wall, the projections cannot in any case be moved out of the link. Therefore the filter element is also securely fitted in the receiving space if the projections are located in the respective final position or in the link end regions. 
     The air filter device may in particular be configured as an air filter device of an air conditioning system or a ventilation device of the motor vehicle. Moreover, the air filter device may be intended for an intake tract of a combustion engine of the motor vehicle, i.e., as a filter for the air drawn in by a combustion engine. 
     Preferably the at least one link of the respective housing side wall has a guide spacer, along which the first projection of the in each case corresponding side wall of the filter element can be led into the first end region of the link when inserting the filter element in the receiving space, wherein the guide spacer extends along a bottom edge of the respective housing side wall. 
     The bilateral links provided with a guide spacer at the bottom provide convenient and secure assembly of the filter element in the housing of the air filter device. With these splinted link segments, with which a guide for the projections is present both upwards and downwards, the first projections can be led reliably into their respective link end regions even when the view is poor or obstructed. 
     Alternatively it may be provided that both the first housing wall and the second housing wall each have two links, which have guide flanks opposite one another, in the direction of the distance of the projections arranged on the associated side wall of the filter element, and extending obliquely to one another. 
     In this embodiment, for assembling the filter element firstly—optionally—two opposite projections of the filter element may first be inserted in the links or link end regions intended for them, so that again a swivel axis is provided parallel to the corresponding transverse side, so that the filter element can be held on the other, free transverse side, and then the two lateral projections that are still free reach the associated link end regions along the associated link guide flanks—once again by pressing in the direction of the projections inserted first, by reducing the distance from them and by lifting; and therefore the filter element also reaches the operating position. However, the filter element may also simply be pushed into the receiving space of the housing vertically from below. In this way, a very simple and reliable assembly process is attainable in the form of introducing the filter element into the receiving space. 
     Preferably the link end regions of both links of the respective housing wall connect directly to the respective link guide flanks, wherein the link end regions extend in different directions. 
     Owing to the direct vicinity of the end regions to the guide flanks, particularly easy assembly—as well as dismantling—of the filter element is achievable, as this only requires a comparatively slight compression of the side walls to reduce the distance between the projections that are to be supported in the end regions of the links. Owing to the divergent directions of the link end regions, the projections—again diverging after compression of the side walls—are advantageously located spontaneously in the position intended for them for holding the filter element in the operating position. 
     The filter element according to the invention for the air filter device according to the invention of a motor vehicle described above comprises a frame, which surrounds a filter material of the filter element at least partially, wherein the frame has a first side wall and an opposite second side wall, and a first and an opposite second, transverse wall connecting the side walls. Both on the first side wall and on the second side wall, in each case two projections are arranged for holding the filter element to be inserted in the receiving space of the housing of the air filter device in link end regions of corresponding or assigned housing side walls—thus in each case those that are adjacent to the installed filter element of the filter side wall. The two projections project from the respective side wall. 
     According to the invention, it is provided that a distance of the two projections, each arranged on a side wall, corresponds in an undeformed state of the side walls to a distance of the link end regions intended for or assigned to them on the housing side in the corresponding housing side wall, wherein the side walls are configured to be elastically deformable, so that on the basis of elastic deformation of the respective side wall, a distance between the two projections, each arranged on a side wall, can be reduced. 
     A filter element of this kind can be brought easily and reliably into a predetermined installation position, in that firstly two projections of opposite side walls are inserted in the link end regions assigned to them on the housing side, which are formed in opposite housing side walls of the housing of the air filter device, so that a swivel axis is provided parallel to the nearest transverse wall of the filter element. Then the two projections that are still free on the housing walls opposite one another along the link guide flanks on the housing side are brought into the second link end regions intended for or assigned to them, by compressing the side walls of the filter element by pressing on the transverse wall of the filter nearer the second projections towards the first projections, so that in each case the distance between the first and second projections is reduced. When the side walls spring back to their undeformed initial state, so that the second projections occupy the link end regions assigned to or intended for them, the filter element can be held positionally secured in its installation position. 
     Owing to its simple design, the filter element can be produced economically and simply. It is only necessary to provide four similar projections on two side walls of the filter element, which can be placed for example by ultrasonic welding on for example a fleece-like material for the side walls. 
     Preferably, the two projections arranged on the respective side wall, in an undeformed initial state of the respective side wall, are at a distance from one another that is many times greater than a distance of each one of the two projections from an edge of the side wall that is near this projection. 
     The two projections arranged on the same side wall are thus preferably arranged in end regions of the respective side wall. A first one of the two projections is accordingly near a first edge of the side wall, and a second one of the two projections is near a second edge of the side wall, wherein the edges of the side wall are opposite one another in the direction of the distance between the projections. Owing to this edge positioning—or in other words, owing to a distance that is as large as possible—of the projections on the respective side wall, the distance between the two projections arranged on the same side wall can be reduced particularly easily by deforming the side wall. 
     Preferably, a first one of the two projections arranged on the same side wall has a larger overall dimension than a second one of the two projections arranged on this side wall. With these differently configured projections in respect of their overall dimension, with a corresponding configuration of the link end regions on the housing side, it is possible to ensure that the filter element is assembled or installed in the correct position. Thus, it may be provided that only the projection with the appropriate overall dimension can be inserted in the respective link. In this way, correct and positionally accurate mounting of the filter element in the air filter housing can easily be achieved. 
     In particular, the projections may be configured as respective pins. Projections of this kind, for example configured as circular cylinders, can be moved with particularly low friction along the respective link on the housing side. 
     Moreover, pins with different sizes of diameter can be produced very easily in production engineering terms. 
     It may be provided that a first one of the two projections arranged on the same side wall is closer to a bottom edge of the side wall than a second one of the two projections arranged on this side wall. The two projections arranged on the same side wall may be distanced, in the direction of a height of the side wall, by a different amount from the bottom edge of the side wall. The height of the side wall is preferably parallel to a direction in which air passes through the filter material during operation of the filter element. This arrangement of the projections, at different distances from the bottom edge, may ensure that the filter element can only be inserted in a predetermined orientation to the air filter housing, into a receiving space that is formed in the housing. An additional benefit is a more reliable assembly process of the filter element. 
     It may in addition be provided that the side walls, which have the projections, have a lower stiffness than the transverse walls that join the side walls of the frame together. When the side walls provided with the projections have lower stiffness than the other walls, the side walls provided with the projections can be deformed elastically particularly easily. However, the other walls with the comparatively greater stiffness on the whole ensure good stability of the frame. The different stiffness of the walls can be provided particularly easily if the side walls provided with the projections have a smaller thickness than the other walls. 
     The advantages and preferred embodiments described for the filter element according to the invention also apply to the air filter device according to the invention, and vice versa. 
     Further advantages, features and details of the invention will become clear from the following description of preferred embodiment examples, in conjunction with the drawings. The features and combinations of features presented above in the description and the features and combinations of features presented hereunder in the description of the figures and/or only shown in the figures are applicable not only in the combination stated in each case, but also in other combinations or alone, while remaining within the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a filter element for an air filter device of a motor vehicle; 
         FIG.  2    is a perspective view of a housing of the air filter device, in which the filter element according to  FIG.  1    can be inserted or installed; 
         FIG.  3    shows a first step in mounting the filter element according to  FIG.  1    in the housing according to  FIG.  2   ; 
         FIG.  4    shows a second step in mounting the filter element according to  FIG.  1    in the housing according to  FIG.  2   ; 
         FIG.  5    shows a third step in mounting the filter element according to  FIG.  1    in the housing according to  FIG.  2   ; 
         FIG.  6    is a detail of the housing according to  FIG.  2    with the filter element according to  FIG.  1    placed in its installation position; 
         FIG.  7    is a variant of the filter element according to  FIG.  1   ; 
         FIG.  8    is a variant of the housing according to  FIG.  2   ; 
         FIG.  9    shows a first step in insertion of the filter element according to  FIG.  7    in the housing according to  FIG.  8   ; 
         FIG.  10    shows a second step in insertion of the filter element according to  FIG.  7    in the housing according to  FIG.  8   ; and 
         FIG.  11    shows attainment of an installation position of the filter element according to  FIG.  7    in the housing according to  FIG.  8   . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In the figures, identical or functionally equivalent elements have been given the same reference symbol. 
       FIG.  1    shows a schematic perspective view of a filter element  10  for an air filter device of a motor vehicle. The air filter device comprises a housing  12 , which is shown schematically and in perspective in  FIG.  2   . Accordingly, the housing  12  has a receiving space  14 , in which the filter element  10  can be inserted. 
     In the variant of the filter element  10  shown in  FIG.  1   , the filter element  10  has a frame  16 , which surrounds or encloses a filter material  18  completely. In other words, the filter material  18 , configured in particular as filter cloth, through which the air to be filtered flows during operation of the air filter device, is held within the frame  16 . If, as shown here as an example, the filter element  10  is configured as a pleated filter, the filter material  18  may have corresponding pleating with a plurality of pleats. 
     In this case the frame  16  comprises a first side wall  20  and a second side wall  22 , which is opposite the first side wall  20  in the transverse direction of the filter element  10 . The transverse direction is indicated in  FIG.  1    with a double-headed arrow  24 . On the respective side wall  20 ,  22 , in each case two projections are arranged, which in the variant of the filter element  10  shown in  FIG.  1    are configured as retaining pins  26 ,  28 ,  30 . 
       FIG.  1    clearly shows a first retaining pin  26 , which is arranged on the first side wall  20 , and a second retaining pin  28 , which is also arranged on the first side wall  20 . The two retaining pins  26 ,  28  project outwards from the first side wall  20  parallel to the transverse direction, which is indicated by the double-headed arrow  24  in  FIG.  1   . Of the two similarly configured and similarly arranged retaining pins, which are arranged on the opposite second side wall  22  in the transverse direction, only a first retaining pin  30  can be seen partially in  FIG.  1   . 
     The retaining pins  26 ,  28 ,  30  may be glued to the respective side wall  20 ,  22  or connected integrally in some other way, for instance by welding, in particular by ultrasonic welding. Moreover, it is possible to configure the retaining pins  26 ,  28 ,  30  to be integral with the respective side wall  20 ,  22 . 
     In the variant of the filter element  10  shown in  FIG.  1   , the first retaining pin  26  has a larger diameter than the second retaining pin  28 . The same applies to the two retaining pins arranged on the second side wall  22 , of which only the first retaining pin  30 , with the larger diameter, can be seen in  FIG.  1   . 
     Here, the frame  16  also comprises two further walls  32 ,  34 , which extend in the transverse direction, and which join the first side wall  20  and the second side wall  22  together. 
     As can be seen from  FIG.  1   , the retaining pins  26 ,  28  formed on the respective side wall  20 ,  22  are arranged in respective end regions of the side wall  20 ,  22 . In other words the first projection or first retaining pin  26  is near a first edge  36  of the first side wall  20 , and the second projection or second retaining pin  28  is near a second edge  38  of the side wall  20 , wherein these edges  36 ,  38  are formed here by opposite corner regions of the frame  16 . The corner regions or edges  36 ,  38  are defined by the meeting point of each side wall  20 ,  22  with a respective transverse wall  32 ,  34 . 
     A distance of the respective retaining pin  26 ,  28  from the edge  36 ,  38  near this retaining pin  26 ,  28 —or from the corresponding transverse wall  32 ,  34 —is accordingly many times smaller than a distance  40  separating the two retaining pins  26 ,  28 . In other words the distance  40  is many times greater than the distance of the respective retaining pin  26 ,  28  from the edge  36 ,  38  near this retaining pin  26 ,  28 . 
     In the variant of the filter element  10  shown in  FIG.  1   , the first retaining pin  26  is moreover closer to a bottom edge  41  of the first side wall  20  than the second retaining pin  28 . This applies analogously to the retaining pins arranged on the second side wall  22 . In the installed state of the filter element  10  in the housing  12  of the air filter device, the bottom edge  41  of the first side wall  20  faces the surroundings  42  of the housing  12 , towards which the receiving space  14  is open (cf.  FIG.  2   ). 
     According to  FIG.  2   , the housing  12  has a first housing wall—or more precisely housing side wall— 44 , which is associated with or adjacent to the first side wall  20 , when the filter element  10  occupies the receiving space  14  of the housing  12 . In particular, the first side wall  20  or optionally a sealing element arranged on the first side wall  20  rests on an inner side of the first housing side wall  44 , when the filter element  10  is installed in the housing  12 . 
     Furthermore, the housing  12  has a second housing wall—or more precisely housing side wall— 46 , which lies opposite the first housing wall  44  in the transverse direction of the housing  12 . In  FIG.  2   , this transverse direction is indicated by a double-headed arrow  48 , which is parallel to the double-headed arrow  24  in  FIG.  1   . 
     In the first housing wall  44 , a first link  50  is formed, only an upper contour of which can be seen in  FIG.  2   . However, with respect to form, this link  50  is configured exactly like a second link  52 , which is formed in the opposite second housing wall  46  of the housing  12 . It can be seen in the top view of the inner side of the housing wall  46  that the link  52  is formed as a relief in the otherwise closed wall, the bottom edge  60  of which can be seen. 
       FIG.  3    shows the contours more clearly, because here the—outwardly closed—housing wall  44  is sectioned so far that the contours of the link  50  made as a relief in the housing wall  44  are clearly discernible in the form of the guide spacer  58  and an end region—or link end region— 54 . 
     The first link  50  extends almost over the entire length of the housing side wall  44  and is configured in its opposite link end regions  54 ,  72  (cf.  FIG.  2   ) for receiving the two retaining pins  26 ,  28 , which are arranged on the first side wall  20  of the filter element  10 . Similarly, the second link  52  is configured for receiving the retaining pins arranged on the second side wall  22  in the end regions  56 ,  74 , wherein only the larger retaining pin  30  can be seen in  FIG.  1   . 
     It can be seen from  FIG.  3    that during insertion of the filter element  10  in the housing  12 , first the larger projections or retaining pins  26 ,  30  are threaded or pushed into a respective end region  54 ,  56  of the respective link  50 ,  52 . During this insertion, the first retaining pin  26 ,  30 —in the present case, but not necessarily, with a larger diameter than the second retaining pin  28 —is in each case guided on a guide spacer  58 ,  62  of the respective link  50 ,  52 . The upper edge of the guide link  50 ,  52  extending parallel to the guide spacer  58 ,  62  forms, over a region of the link  50 ,  52 , a rail on which the projections or retaining pins  26 ,  30  can be led in a controlled manner. 
     In this connection, it can be seen from  FIG.  2    that this guide spacer  58  extends along a bottom edge  60  of the first housing wall  44  shown in section in  FIG.  3   . Similarly, the larger-diameter retaining pin  30  of the second side wall  22  rests on a guide spacer  62 , which is associated with the second link  52  (cf.  FIG.  3   ). In  FIG.  3   , an arrow  64  indicates the direction in which the two retaining pins  26 ,  30  are pushed into the respective end regions  54 ,  56  of the associated links  50 ,  52 . 
     The threading of the retaining pins  26 ,  30  into the rail-like regions of the links  50 ,  52 , required at the start of assembly of the filter element, as well as the further pushing in of the retaining pins  26 ,  30  along the guide spacers  58 ,  62  in the link end regions  54 ,  56  may in the present case advantageously be carried out very well even when the underside of the housing  12 , on which the receiving space  14  is formed, cannot be seen or cannot be seen well. 
     As illustrated in  FIG.  4   , the respective retaining pins  26 ,  30 , which are larger here, have reached their final position in the respective link end region or end region  54 ,  56  of the link  50 ,  52 . In other words the guide pins or retaining pins  26 ,  30  cannot be pushed farther into the respective end regions  54 ,  56 . As soon as a person carrying out the assembly of the filter element  10  establishes that the final position has been reached, the filter element  10 —shown upwards in the figure—is swivelled into the housing  12  or into the receiving space  14 . Then the filter element  10 , for example on the front transverse wall  34  that is still freely accessible (cf.  FIG.  1   ), is swivelled about a swivel axis, extending parallel to the rear transverse wall  32 , which extends through the retaining pins  26 ,  30  with the larger diameter or is formed by the retaining pins  26 ,  30 . 
     The corresponding swivelling movement is indicated in  FIG.  5    with a further arrow  66 . As can also be seen from  FIG.  5   , through this swivelling of the filter element  10  into the housing  12 , the second retaining pin  28  comes up against an obliquely oriented link guide flank—or guide flank for short— 68  of the first link  50 , which is formed in the first housing wall  44  (cf.  FIG.  2   ). 
     Similarly, the second link  52 , which is formed in the opposite, second housing wall  46 , also has an obliquely oriented guide flank  70  (cf.  FIG.  2   ). In this case the small retaining pin (not shown), which is formed on the second side wall  22 , comes into contact with this guide flank  70 , and projects outwards from this second side wall  22  of the frame  16  parallel to the transverse direction. 
     If the second retaining pin  28  is pushed along the guide flank  68  formed in the manner of an entering slope—for example by pressing on the front transverse wall  34 —towards the housing interior and upwards, this causes compression or elastic deformation of the side wall  20  of the frame  16 . The distance  40  between the retaining pins  26 ,  28  then decreases. Similarly, the opposite second side wall  22  can be compressed or elastically deformed. Accordingly, the distance between the two retaining pins that are arranged on the second housing wall  22  also decreases. 
     The frame  16  compressed in this way, which holds the filter material  18 , springs apart again after reaching an excess pressure point, namely after reaching the point of the respective guide flank  68 ,  70  projecting farthest inwards—i.e., towards the middle of the corresponding side wall—, on reaching the height of the link end regions  72 ,  74 . In other words the filter element  10  again assumes its initial state shown in  FIG.  1   , in which the side walls  20 ,  22  are not elastically deformed. Therefore—as can be seen in  FIG.  6   —the second retaining pin  28  enters the second end region  72  of the first link  50 , which is formed in the first housing wall  44 . 
     This second end region  72  of the first link  50  can only be discerned in  FIG.  2    from its contour. However, the second link  52 , which is formed in the second housing wall  46 , has a corresponding second end region  74 . In the respective link end region  72 ,  74 , the respective retaining pin  28 , intended for or assigned to it, is thus secured against moving out of the link  50 ,  52  when the filter element has reached its operating position. 
     This can also be clearly seen from the schematic diagram of a detail of the filter element  10  installed in the air filter device, shown in  FIG.  6   , which shows the retaining pin  28  arranged on the first side wall  20 . 
     From the installation position or operating position of the filter element  10  in the receiving space  14  of the housing  12 , in which the four retaining pins  26 ,  28 ,  30  are fixed in the respective link end regions assigned to them—or final positions— 54 ,  56 ,  72 ,  74  of the two housing side walls  44 ,  46  (not shown in  FIG.  6   ), the filter element  10  can only be removed again from the housing  12  by elastic deformation of the respective side walls  20 ,  22 . By manually acting upon the filter material  18 , which is connected to the walls  20 ,  22 ,  32 ,  34  of the filter element  10 , and by corresponding compression of the filter element  10 , the respective retaining pins may be moved out of the end region  72 ,  74  of the respective link  50 ,  52  either along the guide slope  68 ,  70 , as is shown in  FIG.  5    for the retaining pin  28 , or the retaining pins can be pulled out of the end regions  54 ,  56 ,  72 ,  74  by pulling on the filter material  18  orthogonally to the travel of the links  50 ,  52 . 
     Accordingly, the filter element  10  can be dismantled easily, firstly by moving the respective retaining pin  28  out of the respective end region  72 ,  74  and then swivelling the filter element  10  downwards. With this swivelling movement of the filter element  10 , the respective retaining pin  28  is firstly pressed against the corresponding guide flank  68 ,  70 , until the position of the filter element  10  shown in  FIG.  5    is reached. Then the two—here larger—retaining pins  26 ,  28  can be withdrawn from the other end regions  54 ,  56  of the associated links  50 ,  52 , against the direction indicated by the arrow  64  in  FIG.  3   . 
       FIG.  7    is a perspective view of a variant of the filter element  10 , which can be installed in a variant of the housing  12 , shown in perspective in  FIG.  8   . Once again, the receiving space  14  for the filter element  10  is formed in the housing  12 . Again for the filter element  10  shown in  FIG.  7   , two projections in the form of a first retaining pin  76  and a second retaining pin  78 , projecting outwards parallel to the transverse direction, are arranged on the first side wall  20 . The transverse direction is indicated by the double-headed arrow  24 . 
     Like the first side wall  20 , the opposite second side wall  22  of the frame  16  in the transverse direction of the first side wall  20  also has two retaining pins (not shown), which also project outwards parallel to the transverse direction of the second side wall  22 . 
     In the variant of the filter element  10  shown in  FIG.  7   , a distance  40  between the retaining pins  76 ,  78  can also be reduced by deforming the side wall  20 . This applies analogously to the distance between the retaining pins arranged on the second side wall  22 . Once again, in this variant the retaining pins  76 ,  78  may be glued or welded to the respective side wall  20 ,  22 , in particular joined by ultrasonic welding, or formed integrally with the respective side wall  20 ,  22 . 
     In the variant of the filter element  10  shown in  FIG.  7   , the retaining pins  76 ,  78  have the same overall dimensions or equally large diameters, wherein—with corresponding configuration of the link end regions  98 ,  100  associated with the retaining pins  76 ,  78 —also different dimensions of the retaining pins  76 ,  78  may be provided, and conversely the embodiments shown in  FIGS.  1  to  6    may be configured with equal sizes of retaining pins  26 ,  28 ,  30  with suitable link end regions  52 ,  54 ,  72 ,  74 . 
     In the variant of the housing  12  shown in  FIG.  8   , the opposite housing side walls  44 ,  46  in each case have two short links  80 ,  82 ,  84 ,  86 , which are formed separately in the respective housing wall  44 ,  46 —once again in the manner of a relief. The perspective view in  FIG.  8    only shows the external contours of the two links  80 ,  82 , which are provided by the first housing wall  44  or are formed in the first housing wall  44 . In shape, however, these links  80 ,  82  are configured exactly like the two links  84 ,  86  provided or formed in the second housing wall  46 . 
     According to  FIG.  9   , installation of the filter element  10  in the receiving space  14  of the housing  12  may also take place substantially as for the embodiment in  FIGS.  1  to  6   , in that firstly two retaining pins  76  or  78  projecting on opposite side walls  20 ,  22  are inserted to form a swivel axis in the link end regions  98 ,  106  or  100 ,  108  assigned to them, and then the other two retaining pins  78  or  76 —as described above—are inserted in the link end regions  100 ,  108  or  98 ,  106  assigned to them. 
     On the other hand, the embodiment shown in  FIGS.  9  to  11    also allows insertion of the filter element  10  vertically from below into the receiving space  14 , wherein the four retaining pins  76 ,  78  on the filter element  10  are pushed simultaneously into the link end regions  98 ,  100 ,  106 ,  108  assigned to them. The pushing-in movement is in this case perpendicular to a plane that is spanned by the distance  40  of the retaining pins  76 ,  78  and the transverse direction indicated by the double-headed arrow  24  in  FIG.  7   . A corresponding insertion direction is indicated in  FIG.  9    by an arrow  88 . This inserting of the filter element  10  into the housing  12  can also be carried out easily by one operator, without the underside of the housing  12 , thus the side of the receiving space  14  facing the surroundings  42 , definitely having to be visible, because owing to the supporting guiding of the retaining pins  76 ,  78  in the links  80 ,  82 ,  84 ,  86 , an intuitive operation is possible, in which all four links  80 ,  82 ,  84 ,  86  are open at the bottom—in a corresponding region of the link relief in the housing side wall  44 ,  46 —for receiving the retaining pins  76 ,  78 , so that haptic feedback is also made possible, as soon as the filter element  10  is correctly oriented for installation. 
     According to  FIG.  10   , as a result of this threading or pushing of the filter element  10  into the housing  12 , the two retaining pins  76 ,  78  come into contact with respective guide flanks  90 ,  92  configured as guide slopes of the links  80 ,  82  provided for the retaining pins  76 ,  78 . In  FIG.  8   , the guide flank  90  for the first link  80  is only discernible from its contour, as the uncut housing wall  44  is shown here, which is closed outwardly, as well as the guide flank  92  of the second link  82 , which is provided by the first housing side wall  44 . 
     It can be seen particularly well from the partially sectional representation of the links  80 ,  82  in  FIG.  10    that the two guide flanks  90 ,  92  are oriented obliquely to one another. Accordingly, a distance of these two link guide flanks  90 ,  92  from one another in the region of the bottom edge  60  of the first housing wall  44  (cf.  FIG.  8   ) is greater than at a greater distance from this bottom edge  60 . This oblique orientation of the two guide flanks  90 ,  92  to one another has the effect that during insertion of the filter element  10  in the receiving space  14  by pushing upwards, the side wall  20  is deformed elastically. The distance  40  between the two retaining pins  76 ,  78  is thus reduced. 
     Similarly, the two links  84 ,  86  formed in the second housing wall  46  have guide flanks  94 ,  96  of this kind, configured as entering slopes (cf.  FIG.  8   ). Once again, the guide flank  94  of the first link  84  is oriented obliquely, and so too is the guide flank  96  of the second link  86 . The oblique orientation of these two guide flanks  94 ,  96  to one another has the effect that the projections or retaining pins arranged on the second side wall  22  of the frame  16  (not shown) are moved towards one another during pushing-in of the filter element  10  into the receiving space  14 , through elastic deformation of the second side wall  22 . 
     It can be seen from  FIG.  11    that after compression of the two opposite side walls  20 ,  22 , the frame  16  returns to its shape shown in  FIG.  7    or the initial state shown in  FIG.  7   . In this case, after the elastic deformation of the respective side wall  20 ,  22 , the first retaining pin  76  enters an end region  98  of the first link  80  (cf.  FIG.  9   ), which is formed in the first housing wall  44 . 
     Similarly, the second retaining pin  78  enters an end region  100  of the second link  82 , which is also formed in the first housing wall  44  (cf.  FIG.  9   ). It can be seen that these link end regions  98 ,  100  extend in opposite directions. The movement of the retaining pins  76 ,  78  arranged on the same side wall  20  into the end regions  98 ,  100  is indicated in  FIG.  11    by corresponding arrows  102 ,  104 . 
     Similarly, an end region  106  of the first link  84  formed in the second housing wall  46  extends in a direction that is opposite to the direction in which an end region  100  of the second link  86  formed in the second housing wall  46  extends (cf.  FIG.  8   ). Because the retaining pins arranged on the second side wall  22  (not shown) also enter these end regions  106 ,  108 , the filter element  10  is accommodated reliably in the predetermined installation position in the receiving space  14  of the housing  12 . 
     Both in the variant of the air filter device described with reference to  FIG.  1    to  FIG.  6    and in the variant presented with reference to  FIG.  7    to  FIG.  11   , the intrinsic elasticity of the filter frame  16 , in particular of the opposite side walls  20 ,  22 , is utilized in order to move the projections in particular in the form of the retaining pins  26 ,  28 ,  30 ,  76 ,  78  into their respective final position in the link end regions  72 ,  74 ,  98 ,  100 ,  106 ,  108 . 
     In the variant explained on the basis of  FIG.  1    to  FIG.  6   , the filter element  10  is first pushed obliquely backwards along the links  50 ,  52  into the final position and then folded into the housing  12  and is then secured in the receiving space  14 . 
     In the variant described with reference to  FIG.  7    to  FIG.  11   , in contrast it is also possible to proceed by inserting the retaining pins  76 ,  78  of the filter element  10  from below into the respective links  80 ,  82 ,  84 ,  86 . After the side walls  20 ,  22  of the filter element  10  expand again, the retaining pins  76 ,  78  reach their respective final position in the respective end regions  98 ,  100 ,  106 ,  108 . Then the filter element  10  is in its fully functional operating position in the receiving space  14  of the housing  12 .