WO2018050233A1

WO2018050233A1 - Air filter

Info

Publication number: WO2018050233A1
Application number: PCT/EP2016/071880
Authority: WO
Inventors: Alexandre LUCHESI DE ALMEIDA; Edson VALDOMIRO DE AZEVEDO JUNIOR; Pedro BASSO; Marcos José DANTAS DE OLIVEIRA
Original assignee: Mahle International Gmbh; Mahle Metal Leve S/A
Priority date: 2016-09-15
Filing date: 2016-09-15
Publication date: 2018-03-22

Abstract

The present invention relates to an air filter (1) for a fresh-air system of an internal combustion engine,comprising a filter housing (2) and a filter element (10) arranged in the filter housing (2), wherein the filter housing (2) has a discharge connector (16) for the discharge of contaminants from the interior (9) of the filter housing (2). Simplified assembly is realized if a functional attachment (17) is fastened by way of a bayonet fastener (18) to the discharge connector (16).

Description

Air filter

The present invention relates to an air filter or an air filter device for a fresh-air system of an internal combustion engine, having the features of the preamble of claim 1 .

A generic air filter is known for example from DE 195 19 438 A1 . Said air filter comprises a filter housing and a filter element arranged in the filter housing. In the filter housing, the filter element separates an untreated side from a clean side. In the case of the known air filter, there is also formed in the filter housing a cyclone separator which, on the untreated side, separates out contaminants entrained in the fresh air by way of inertial separation and thus serves, in effect, as a pre- separator with respect to the filter element. The separated-out contaminants collect, outside the filter element, on the untreated side in the filter housing. For the discharging of such contaminants from the interior of the filter housing, the filter housing is equipped with a discharge connector. A discharge valve may be fastened to said discharge connector. With the aid of a discharge valve of said type, the contaminants can be discharged out of the interior of the filter housing through the discharge connector in pressure-controlled fashion.

Here, it is basically possible for a discharge valve of said type to be fixed to the discharge connector by way of an interference fit. An interference fit of said type is easy to realize in an installation context. However, owing to contaminants, an interference fit of said type will, after some time, become impossible or very difficult to release. A removal of the discharge valve may however be necessary for maintenance purposes and the like. It is also conceivable for the interference fit to be protected against contaminants by way of an adhesive tape. This makes the removal of the discharge valve particularly cumbersome. By contrast, if the interference fit is selected to be too weak, vibrations that arise during the operation of the internal combustion engine may have the effect that the discharge valve departs from the discharge connector and falls out.

The present invention is concerned with the problem of specifying, for an air filter of the type mentioned in the introduction, an improved embodiment which is characterized in particular by simplified handling, for example for maintenance purposes. Furthermore, increased reliability is sought.

Said problem is solved according to the invention by way of the subject matter of the independent claim. The dependent claims relate to advantageous

embodiments.

The invention is based on the general concept of fastening a functional attachment to the discharge connector by way of a bayonet fastener. A bayonet fastener of said type is distinguished by simple handling and by high reliability. Furthermore, a bayonet fastener of said type exhibits relatively low susceptibility to contamination.

A bayonet fastener is characterized generally by the fact that, for the mounting of the functional attachment on the discharge connector and for the removal of the functional attachment from the discharge connector, an at least two-stage movement is necessary. In general, for the mounting, an axial movement is coupled to a subsequent rotational movement. During the dismounting, it is then the case that the rotational movement takes place first, followed by the axial movement.

A bayonet fastener is particularly advantageous in which the rotational movement is positively coupled to a further axial movement, so as to result in a screw-action movement. Furthermore, an altogether three-stage movement is particularly advantageous. In the mounting process, during a first movement stage, exclusively an axial adjustment is performed. During a second movement stage, a screw-action movement is then performed, that is to say a rotational movement with positively coupled axial movement. Finally, in a third movement stage, a purely rotational movement without axial adjustment is performed in order to reach a predetermined rotational end position.

In an advantageous embodiment, the functional attachment may be in the form of a discharge valve for the pressure-controlled discharge of the contaminants through the discharge connector. Such a discharge valve can for example be formed as a flap valve, as a mushroom-type valve or as a lip valve, respectively. During the operation of the internal combustion engine, it is inherently the case that fresh air is drawn through the air filter such that a negative pressure generally prevails in the interior of the filter housing. However, the gas exchange processes of the internal combustion engine, which is in the form of a piston engine, lead to pressure pulsations in the fresh-air system, which pressure pulsations may also exhibit positive-pressure pulses depending on the operating state of the internal combustion engine. It is thus possible for a positive pressure to be generated briefly in the filter housing, too, which positive pressure is utilized by the discharge valve for opening up the discharge connector in order to discharge contaminants from the interior through the discharge connector.

Normally, the discharge connector or the functional attachment and thus the discharge valve open into surroundings of the air filter. It is thus possible for the contaminants to be returned again to the surroundings from which they

originated. Furthermore, it is also possible in particular for transient operating states of the internal combustion engine to lead to a positive pressure in the filter housing. For example, upon a change from full load to part load, intense throttling of the fresh-air supply in the fresh-air system may occur, which throttling at least temporarily generates a positive pressure in the filter housing. With the aid of a discharge valve of said type, it is furthermore the case that, for other operating states in which a negative pressure prevails in the filter housing, an induction of unmetered air through the discharge connector is prevented. This is because it is the intention for the fresh air to enter the filter housing in targeted fashion through an untreated-air inlet, and not through the discharge connector, which is provided in addition to the untreated-air inlet. It is expediently possible for the untreated-air inlet to be connected tangentially to the filter housing, such that, during the operation of the air filter, a rotational flow is generated in the filter housing, which rotational flow effects inertial separation. In this respect, the filter housing with the untreated-air inlet acts as a cyclone separator.

In another embodiment, the functional attachment may have a pot-shaped attachment body which is fitted onto the discharge connector and which, in its pot base, has a passage opening for the contaminants. The pot interior space serves to provide a collecting space or collecting volume in which contaminants can collect. In this respect, here, the functional attachment has at least the function of a collecting volume for contaminants.

In an advantageous refinement, a pivotable control flap for controlling the passage opening may be arranged on the attachment body. In this way, it is thus possible for a discharge valve to be realized in a particularly inexpensive manner.

The control flap may expediently be arranged at the outside on the pot base. In this way, the control flap can be opened particularly easily in the presence of a positive pressure in the housing interior. The control flap may be preloaded, by way of at least one closing pressure spring, into its closed position in which it closes the passage opening. In another embodiment, on the attachment body, there may be integrally formed bearing journals on which the control flap is pivotably mounted. The production of the attachment body is simplified by way of the integration of the bearing journals into the attachment body. It is then also possible for the respective closing pressure spring to be arranged, for example in the form of a leg spring, in the region of said bearing journals.

It is particularly advantageously possible for the control flap to be designed such that it can be clipped onto the bearing journals. For example, the control flap has, for this purpose, C-shaped bearing eyelets which can be clipped onto the respective bearing journal transversely with respect to the pivot axis of the control flap, wherein said bearing eyelets subsequently engage around the respective bearing journal over more than 180°, but less than 360°.

Another embodiment provides for the bayonet fastener to have at least one locking element which projects from the outside of the discharge connector.

Furthermore, the bayonet fastener has, for each locking element, a guide slot which is formed in a pot wall of the attachment body. The bayonet fastener basically has multiple such pairings of locking element and guide slot, which are arranged in distributed fashion in the circumferential direction. It is preferable for precisely two such pairings to be arranged so as to be offset by 180° relative to one another.

The guide slot defines the multi-phase adjustment movement of the bayonet fastener when the locking element is inserted into and adjusted in the guide slot.

It is preferable for a detent means to be integrated into the bayonet fastener, which detent means secures a predetermined rotational end position between discharge connector and functional attachment. While the bayonet fastener ensures that the respectively desired rotational end position is reliably reached, the detent means effects a securing action in said rotational end position.

A refinement is particularly advantageous in which the detent means has, in the guide slot, a detent contour which, in the rotational end position, interacts with a counterpart detent contour, which is formed on the locking element, in order to realize a securing action for preventing rotation of the functional attachment relative to the discharge connector. In this way, the detent means can be integrated particularly easily into the bayonet fastener.

Another refinement provides for the guide slot to have an entrance for the axial introduction of the locking element into the guide slot, a ramp which, in the guide slot, couples a rotational adjustment of the locking element to an axial adjustment of the locking element, and an end stop into which the locking element can be inserted in a circumferential direction and in which the locking element is axially secured. In other words, here, the guide slot is designed for realizing a three- stage movement process. During the mounting of the attachment body, it is firstly the case that a purely axial adjustment is performed for the purposes of inserting the locking element through the inlet into the guide slot. Subsequently, a screw- action movement is performed along the ramp, that is to say the positively coupled movement of the locking element in an axial direction and in a

circumferential direction. Finally, a purely rotational movement is then performed, during which the locking element is introduced in the circumferential direction into the end stop.

The abovementioned detent means may, in an advantageous embodiment, be formed in the region of the end stop. For example, the detent contour may be formed by a projection, whereas the counterpart detent contour is formed by a depression complementary thereto. Likewise, a reversed embodiment is conceivable in which the detent contour is fornned by a depression, whereas the counterpart detent contour is fornned by a projection complementary thereto. For example, the detent contour may be formed on a slot edge which delimits the guide slot axially in the region of the end stop.

In another embodiment, the functional attachment may be equipped with a pot- shaped protective cap which is fitted onto the attachment body and which has a perforated cap base which is permeable to the contaminants. The protective cap prevents interaction with an air flow in the surroundings of the air filter. Likewise, the protective cap may serve as a pivoting delimitation means for the control flap in order to define a maximum open position for the control flap. Furthermore, by way of the protective cap, the control flap arranged on the outside of the attachment body can be protected against external action.

A refinement is particularly advantageous in which the protective cap is fastened to the attachment body by way of a clip-type connection or detent connection. The detent connection may for example have multiple axially projecting detent hooks which are arranged so as to be distributed in a circumferential direction and which are of radially resiliently elastic form and which, during the axial mounting of the protective cap onto the attachment body, engage into tabs complementary thereto. The detent hooks may be equipped, radially on the outside, with detent lugs which are inserted axially through the tabs and which engage radially over the tabs and thus impart a positively locking axial securing action.

Another embodiment provides that an axially open connector-side ring-shaped groove is formed on an axial face side of the discharge connector and is engaged into axially by a ring-shaped web which is formed on the axial face side of the attachment body. In addition or alternatively, an axially open attachment-side ring-shaped groove may be formed on an axial face side of the attachment body and engaged into axially by a ring-shaped web formed on an axial face side of the discharge connector. The ring-shaped groove and ring-shaped web form a tongue-and-groove coupling which, firstly, realizes axial guidance of attachment body and discharge connector. At the same time, it is thus secondly possible to realize a certain sealing action. A refinement is particularly advantageous in which a ring-shaped axial seal is inserted into a ring-shaped groove of said type in order to seal off the respective ring-shaped web with respect to the ring-shaped groove or with respect to a wall of the ring-shaped groove. Here, the axial seal may be inserted either into the connector-side ring-shaped groove or into the attachment-side ring-shaped groove. An embodiment with two ring-shaped axial seals is likewise basically conceivable.

In another embodiment, it may be provided that the filter housing has a housing pot for receiving the ring-shaped filter element and has a housing cover. The housing cover may directly delimit a dirt collecting space in the interior of the filter housing. It is expediently now possible for the discharge connector to be formed on the housing cover and to be fluidically connected to the dirt collecting space. The discharge of contaminants is simplified in this way. As discussed above, the filter housing and the untreated-air inlet may be designed as a cyclone separator. It is expediently possible, for this purpose, for the untreated-air inlet to

tangentially adjoin the housing pot and to be arranged distally with respect to the housing cover. In this way, during the operation of the air filter, in a ring-shaped space which surrounds the ring-shaped filter element in a circumferential direction in the filter housing, a rotational flow can be generated in order to separate out contaminants by inertial action, which contaminants are supplied by way of the rotational flow and by way of gravitational force to the dirt collecting space. Further important features and advantages of the invention will emerge from the subclaims, from the drawings and from the associated description of the figures on the basis of the drawings.

It is self-evident that the features mentioned above and the features yet to be discussed below may be used not only in the respectively specified combination but also in other combinations or individually without departing from the scope of the present invention.

Preferred exemplary embodiments of the invention are illustrated in the drawings and will be discussed in more detail in the following description, wherein the same reference designations are used to denote identical or similar or functionally identical components.

In the drawings, in each case schematically: figure 1 shows an isometric view of an air filter, figure 2 shows a longitudinal section through the air filter in the region of a housing cover, figure 3 shows an isometric view of the air filter in the region of a discharge connector, figure 4 shows an isometric exploded view of the housing cover, figure 5 shows a longitudinal section through the air filter in the region of the discharge connector, figure 6 shows a sectional view as in figure 5, but in the case of another embodiment.

Correspondingly to figure 1 , an air filter device 1 or an air filter 1 , which serves for filtering the fresh air in a fresh-air system of an internal combustion engine, comprises a filter housing 2. In the preferred example shown, the filter housing 2 has a housing pot 3 and a housing cover 4. Furthermore, an untreated-air inlet 5 is provided through which, during the operation of the air filter 1 , uncleaned fresh air is drawn from the surroundings 6 into the filter housing 2. Furthermore, a clean-air outlet 7 is provided which is situated on a pot base 8, situated opposite the housing cover 4, of the housing pot 3 and which, in figure 1 , is averted from the viewer. During the operation of the air filter 1 , purified fresh air is discharged through the clean-air outlet 7.

As per figure 2, there is arranged in an interior 9 of the filter housing 2 a filter element 10 which, in the filter housing 2, separates an untreated side 1 1 from a clean side 12. Normally, the untreated-air inlet 5 is fluidically connected to the untreated side 1 1 , whereas the clean-air outlet 7 is fluidically connected to the clean side 12. The filter element 10 is of ring-shaped design such that it has a ring-shaped filter body 13 (indicated by a dashed line in figure 2) which is composed of a filter material which may for example be of web-like and folded form. Furthermore, the ring-shaped filter element 10 has an end disk 14 at least on one axial face side of the filter body 13. It is expedient for in each case one such end disk 14 to be provided on both axial face sides of the filter body 13. The first end disk 14, which can be seen in figure 2, is in the form of a closed end disk. The opposite, second end disk 14, which is not shown here, is then expediently in the form of an open end disk which has a central passage opening which is open toward an interior space 15 of the filter element 10. It is expediently then the case that the clean-air outlet 7 is fluidically connected by way of said passage opening of the open end disk to the interior space 15 of the filter element 10. In this respect, the interior space 15 of the filter element 10 then corresponds to the clean side 12 in the interior 9 of the filter housing 2.

Corresponding to figures 1 to 6, the filter housing 2 is furthermore equipped with a discharge connector 16 which serves for the discharge of contaminants from the interior 9 of the filter housing 2 into the surroundings 6. A functional attachment 17 is fastened to the discharge connector 16, wherein, for the fastening of the functional attachment 17 to the discharge connector 16, use is preferably made of a bayonet fastener 18, which will be discussed in more detail in particular with reference to figures 3 and 4.

In the embodiments shown here, the functional attachment 17 is in the form of a discharge valve 19 which serves for the pressure-controlled discharge of the contaminants through the discharge connector 16. For this purpose, the functional attachment 17 has a pot-shaped attachment body 20 which, in its pot base 21 , has a passage opening 22 for the contaminants. With its end averted from the pot base 21 , the attachment body 20 is fitted onto the cylindrical discharge connector 16. A pot interior space 23 of the attachment body 20 forms a collecting space for contaminants which accumulate in the interior 9 of the filter housing 2 and which are transported in the direction of the discharge connector 16, for example as a result of vibrations during the operation of the internal combustion engine and as a result of the action of gravitational force. On the attachment body 20 there is pivotably mounted a control flap 24 which serves for controlling the passage opening 22. The control flap 24 is in this case expediently arranged on the outside of the pot base 21 , that is to say on an outer side averted from the discharge connector 16. The control flap 24 is preferably preloaded into its closed position, in which it closes the passage opening 22, by way of at least one restoring spring or closing pressure spring (not shown here). As per figure 3, bearing journals 25 may be formed integrally on the attachment body 20. Here, it is expedient for precisely two such bearing journals 25 to be provided, of which however only one is visible in figure 3. The two bearing journals 25 define a pivot axis 26 about which the control flap 24 is pivotable. For the mounting on the bearing journals 25, the control flap 24 has bearing eyelets

27 which engage around the respective bearing journal 25 over more than 180° but less than 360°. In this respect, the bearing eyelets 27 are of C-shaped design. Furthermore, the bearing eyelets 27 are designed such that they can be fitted or clipped onto the respective bearing journal 25 transversely with respect to the pivot axis 26.

As per figures 3 and 4, the bayonet fastener 18 has at least one locking element

28 which projects from the outside of the discharge connector 16 and which is expediently formed integrally thereon. It is preferable for precisely two such locking elements 28 to be provided which are situated diametrically opposite one another. Furthermore, the bayonet fastener 18 has, for each locking element 28, a guide slot 29 which is formed in a pot wall 30 of the attachment body 20. Here, the guide slot 29 extends radially through the pot wall 30. The guide slot 29 has an entrance 31 , a ramp 32 and an end stop 33. The entrance 31 serves for the axial introduction of the locking element 28 into the guide slot 29. The ramp 32 serves for the positive coupling of a rotational adjustment of the locking element 28 within the guide slot 29 to an axial adjustment of the locking element 28. In other words, the ramp 32 forcibly effects a screw-action movement during the rotation of the attachment body 20 relative to the discharge connector 16. The end stop 33 serves for axially securing the locking element 28 when it has been introduced in the circumferential direction into the end stop 33. The

circumferential direction relates, in the region of the discharge connector 16, to the longitudinal central axis 34 of said discharge connector. Here, the circumferential direction rotates around the longitudinal central axis 34. The longitudinal central axis 34 furthermore defines an axial direction in the region of the discharge connector 16. The axial direction runs parallel to the longitudinal central axis 34. A radial direction in the region of the discharge connector 16 extends transversely with respect to the axial direction. As can be seen in particular from figure 1 , the longitudinal central axis 34 of the discharge connector 16 extends in an inclined manner relative to a longitudinal central axis 35 of the filter housing 2. The longitudinal central axis 35 of the filter housing 2 defines the axial direction, the radial direction and the circumferential direction

correspondingly for the filter housing 2.

In an advantageous embodiment, it is furthermore possible for a detent means 36 to be integrated into the bayonet fastener 18. Said detent means 36 secures a predetermined rotational end position between discharge connector 16 and functional attachment 17. Said rotational end position is in this case defined by the end stop 33. As soon as the locking element 28 has moved fully into the end stop 33 in the circumferential direction, that is to say in the direction of rotation, the predetermined rotational end position between discharge connector 16 and functional attachment 17 has been assumed. The detent means 36 now prevents the functional attachment 17 from rotating of its own accord relative to the discharge connector 16 out of said rotational end position. For this purpose, the detent means 36 may have, in the guide slot 29, a detent contour 37 which, in the rotational end position, interacts with a counterpart detent contour 38 which is complementary to said detent contour and which is formed on the locking element 28. As soon as the detent contour 37 is in engagement, in the rotational end position, with the counterpart detent contour 38, the locking element 28 is secured against rotation of the functional attachment 17 relative to the discharge connector 16. It is expediently possible for the detent means 36 to be formed in the region of the end stop 33. The detent contour 37 is preferably formed by a projection which protrudes into the guide slot 29 from a slot edge which axially delimits the guide slot 29. The counterpart detent contour 28 may in this case be formed directly by an outer contour of the locking element 28. It may likewise conceivably be provided that, a corresponding depression complementary to the abovementioned projection is provided on the locking element 28, into which depression the projection can engage.

As per figures 2 and 6, the functional attachment 17 may furthermore have a pot- shaped protective cap 39 which is fitted onto the attachment body 20. The protective cap 39 has a perforated cap base 40 which is permeable to the contaminants. The protective cap 39 is preferably fastened to the attachment body 20 by way of a detent connection 41 . In this case, purely by way of example, the detent connection 41 has, at two diametrically oppositely situated sides of the protective cap 39, in each case one detent hook 42 which is radially resiliently elastic and which has a radially outwardly protruding detent lug.

Furthermore, the detent connection 41 on the attachment body 20 has a tab 43 through which the detent hook 42 is passed axially and on which the detent hook 42 engages with detent action by way of its detent lug.

Correspondingly to figure 5, an axially open connector-side ring-shaped groove 45, which runs in fully encircling ring-shaped form, may be formed on an axial face side 44 of the discharge connector 16. Complementarily to this, an axially projecting attachment-side ring-shaped web 47, which runs in fully encircling ring- shaped form, is formed on an axial face side 46 of the attachment body 20, which ring-shaped web engages axially into the connector-side ring-shaped groove 45. Furthermore, it is additionally provided here that an axially open attachment-side ring-shaped groove 48, which runs in fully encircling ring-shaped form, is formed on the face side 46 of the attachment body 20, which ring-shaped groove is engaged into axially by a connector-side ring-shaped web 49 which runs in fully encircling ring-shaped form and which is formed on the face side 44 of the discharge connector 16. In the example of figure 5, it is furthermore the case that a ring-shaped axial seal 50 is inserted into the connector-side ring-shaped groove 45.

The above-described bayonet fastener 18 is expediently designed such that the axial seal 50 is axially compressed to a predetermined extent when the locking element 28 reaches the end stop 33, that is to say when the predetermined rotational end position between attachment body 20 and discharge connector 16 is reached.

As per figure 6, a dirt collecting space 51 may be formed in the filter housing 2 on the untreated side 1 1 outside the filter element 10. Said dirt collecting space 51 is, in the example shown here in figure 6, directly delimited axially at one side by the housing cover 4. In the example, said dirt collecting space 51 is furthermore directly delimited, axially at the other side, by that end disk 14 of the filter element 10 which faces toward the housing cover 4. The discharge connector 16 is fluidically connected to the dirt collecting space 51 , specifically by way of a connecting opening 52. In parallel with this, that is to say in addition, the discharge connector 16 is connected by way of a further connecting opening 53 to an untreated-side ring-shaped space 54 which, in the filter housing 2, surrounds the ring-shaped filter element 10 in ring-shaped fashion. It is thus firstly possible for contaminants to pass directly from the ring-shaped space 54 into the discharge connector 16. Secondly, the contaminants can also pass from the dirt collecting space 51 into the discharge connector 16.

Claims

1 . An air filter for a fresh-air system of an internal combustion engine,

- having a filter housing (2),

- having a filter element (10) arranged in the filter housing (2),

- wherein the filter housing (2) has a discharge connector (16) for the discharge of contaminants from the interior (9) of the filter housing (2),

characterized

in that a functional attachment (17) is fastened by way of a bayonet fastener (18) to the discharge connector (16).

2. The air filter as claimed in claim 1 ,

characterized

in that the functional attachment (17) is in the form of a discharge valve (19) for the pressure-controlled discharge of the contaminants through the discharge connector (16).

3. The air filter as claimed in claim 1 or 2,

characterized

in that the functional attachment (17) has a pot-shaped attachment body (20) which is fitted onto the discharge connector (16) and which, in its pot base (21 ), has a passage opening (22) for the contaminants.

4. The air filter as claimed in claim 3,

characterized in that a pivotable control flap (24) for controlling the passage opening (22) is arranged on the attachment body (20).

5. The air filter as claimed in claim 4,

characterized

in that the control flap (24) is arranged at the outside on the pot base (21 ).

6. The air filter as claimed in claim 4 or 5,

characterized

in that, on the attachment body (20), there are integrally formed bearing journals (25) onto which the control flap (24) is clipped, with the control flap (24) being fitted on the attachment body (20) so as to be pivotable about said bearing journals (25).

7. The air filter as claimed in one of claims 3 to 6,

characterized

in that the bayonet fastener (18) has at least one locking element (28) which projects from the outside of the discharge connector (16), and has, for each locking element (28), a guide slot (29) which is formed in a pot wall (30) of the attachment body (20).

8. The air filter as claimed in one of claims 3 to 7,

characterized

in that a detent means (36) is integrated into the bayonet fastener (18), which detent means secures a predetermined rotational end position between discharge connector (16) and functional attachment (17).

9. The air filter as claimed in claims 7 and 8,

characterized in that the detent means (36) has, in the guide slot (29), a detent contour (37) which, in the rotational end position, interacts with a counterpart detent contour (38), which is formed on the locking element (28), in order to realize a securing action for preventing rotation of the functional attachment (17) relative to the discharge connector (16).

10. The air filter as claimed in one of claims 7 to 9,

characterized

in that the guide slot (29) has an entrance (31 ) for the axial introduction of the locking element (28) into the guide slot (29), a ramp (32) which, in the guide slot (29), couples a rotational adjustment of the locking element (28) to an axial adjustment of the locking element (28), and an end stop (33) into which the locking element (28) can be inserted in a circumferential direction and in which the locking element (28) is axially secured.

1 1 . The air filter as claimed in claim 10 and as claimed in claim 8 or 9, characterized

in that the detent means (36) is formed in the region of the end stop (33).

12. The air filter as claimed in one of claims 3 to 1 1 ,

characterized

in that the functional attachment (17) has a pot-shaped protective cap (39) which is fitted onto the attachment body (20) and which has a perforated cap base (40) which is permeable to the contaminants.

13. The air filter as claimed in one of claims 3 to 12,

characterized

- in that an axially open connector-side ring-shaped groove (45) is formed on an axial face side (44) of the discharge connector (16) and is engaged into axially by a ring-shaped web (47) which is formed on an axial face side (46) of the attachment body (20), and/or

- in that an axially open attachment-side ring-shaped groove (48) is formed on an axial face side (46) of the attachment body (20) and is engaged into axially by a ring-shaped web (49) formed on an axial face side (44) of the discharge connector (16).

14. The air filter as claimed in claim 13,

characterized

in that a ring-shaped axial seal (50) is inserted into a ring-shaped groove (45, 48) of said type.

15. The air filter as claimed in one of claims 1 to 14,

characterized

- in that the filter housing (2) has a housing pot (3) for receiving the ring-shaped filter element (10) and has a housing cover (4),

- in that the housing cover (4) directly delimits a dirt collecting space (51 ) in the interior (9) of the filter housing (2),

- in that the discharge connector (16) is formed on the housing cover (4) and is fluidically connected to the dirt collecting space (51 ).