Filtering system, in particular for filtering liquids in internal combustion engines

A filtering device for filtering liquids in internal combustion engines has a filter housing and a filter element inserted into the filter housing. A cover disk closes off the filter housing. The cover disk consists of two individual disks and a central flow connection connects the two individual disks. The two individual disks and the flow connection form a common plastic component.

BACKGROUND OF THE INVENTION

The invention relates to a filtering system, in particular for filtering liquids in internal combustion engines with a filter element insertable into a filter housing, the filter housing being closed by a cover disk.

These filtering devices are used in internal combustion engines for filtering oil or fuel and comprise a hollow cylindrical filter element to be flown through radially from outside to inside and which is inserted into a filter housing of the filtering device. The liquid to be filtered is introduced via an inlet into the filter housing in the area of the outside of the filter element forming the entry side and axially discharged via the central hollow space after being filtered. The filter housing has an approximate cup-shaped design for the reception of the filter element and is closed by a cover disk after the insertion of the filter element. This cover disk is typically made of metal in order to ensure the required stability.

The problem addressed by the invention is to develop a filtering device of the generic kind in a stable design and at the same time of low weight. The filtering device should be able to be disposed of conveniently with little effort.

SUMMARY OF THE INVENTION

This problem is solved according to the invention in that the cover disk consists of two individual disks which are connected via a central flow connection, the two individual disks and the flow connection forming a common plastic component.

The filtering device according to the invention which in particular is used for filtering for example oil or fuel in internal combustion engines has a cover disk that is to be placed onto the filter housing and which consists of two parallel individual disks connected via a central flow connection, both individual disks and the flow connection forming a common plastic component. The double-disk design of the cover disk made of plastic has the advantage that compared with the embodiments of prior art at least an equal high stability with low weight is ensured, at the same time the capability for recycling is considerably improved as the cover disk is now also made completely of plastic making it possible to incinerate it after use together with the filter housing made typically also of plastic without any significant environmental impact.

The bipartite cover disk can for example be produced easily as injection molded part, however, other manufacturing processes for plastic parts such as deep drawing can be considered. If required, the cover disk made of plastic can also be used in combination with a metal pot.

The hollow cylindrical flow connection in the cover disk has two functions: on the one hand, the flow connection connects the two individual disks with each other, on the other hand, the liquid can be introduced into or discharged from the filter housing via the interior area of the flow connection. Furthermore and according to an advantageous embodiment, the flow connection can be provided with a female thread by means of which the cover disk or the complete filtering device can be connected to a subassembly of the internal combustion engine. If required, an external thread can also be considered by means of which the connection between the filter and for example a motor flange can be realized. Such an external thread can also consist of a separate insert in the cover that can preferably be injected or clipped as flow connection.

The flow connection between the individual disks may feature a relatively large diameter, making on the one hand the flow through the flow connection easier and increasing on the other hand the stability of the cover disk. In addition to the flow connection it is possible to provide connecting bars which connect both individual disks and are located radially further outside, by means of which the rigidity of the cover disk is considerably increased.

According to a preferred embodiment one of the individual disks forms a front disk directly placed onto the front end of the filter element that can be firmly connected with the front end, for example by means of welding or gluing. The individual disk forming the front disk ensures a flow separation of entry side and clean side of the filter element and enhances the stability of the filter element.

Typically, the central flow connection which connects the two individual disks of the cover disk forms the flow-off connection via which the filtered liquid is axially discharged from the interior area of the filter element that forms the clean side. The supply of the unfiltered liquid is also conveniently realized via the cover disk which for this purpose features in the outside located individual disk facing away from the filter element at least one towards the filter element opening anti-drain valve via which the liquid to be filtered is introduced into the filtering device. This anti-drain valve is in opening position as long as the pressure of the liquid at the entry side in the filtering device is lower than the pressure under which the liquid is introduced into the filtering device. When dismounting the filter element overhead the anti-drain valve prevents the liquid from flowing out or the filter from idling when the motor is stopped.

In a simple embodiment, this anti-drain valve can be designed as duck bill valve that reacts to pressure differences at the inflow and outflow side of the valve and which is automatically switched into locked position if the pressure exceeds a threshold value at the outflow side.

The individual disk of the cover disk adjacent to the filter element conveniently features slotted holes extending in circumferential direction through which the liquid introduced via the anti-drain valve in the exterior individual disk can flow from the space between the two individual disks to the entry side of the filter element. The exterior edge of the individual disk limiting the slotted holes rests on the inner lateral surface of the filter housing which enhances also the stability. If required, the exterior edge is also welded, glued or otherwise connected with the lateral surface.

As an alternative to the slotted holes extending in circumferential direction the peripheral zone of the individual disk directly adjacent to the filter element can feature radially projecting ribs with radially set back recesses through which a through-flow of the introduced liquid to the entry side of the filter element is possible. The projecting ribs rest on the inner lateral surface of the filter housing.

An overflow opening via which the entry side communicates directly with the clean side of the filter element can be realized in the front disk—which is preferably one of the individual disks of the cover disk—located on the axial front end of the filter element. The overflow opening is closed by an overflow valve which under normal conditions is in closed position in order to separate the entry side from the clean side. If the pressure at the entry side exceeds a threshold value, for example as a consequence of a clogged filter element, the overflow valve opens and the overpressure at the entry side is reduced by a direct overflow of the liquid from the entry side to the clean side. Once the overpressure has been reduced, the overflow valve automatically moves into the closing position.

The connecting female thread in the central flow connection via which the filtering device is connected to a subassembly of the internal combustion engine does conveniently not have a sawtooth geometry but an elliptic geometry which considerably reduces the stress load in the thread. This makes it possible—despite using plastic for the cover disk—to introduce relatively strong forces via he thread in the flow connection so that especially the deadweight of the filtering device can be supported by the female thread.

The figures show the identical components with the same reference signs.

DESCRIPTION OF THE DRAWINGS

The filtering device1represented inFIGS. 1 and 2is mainly used in internal combustion engines for filtering liquids such as oil or fuel. The filtering device1comprises a plastic filter housing2which is approximately cup-shaped and closed by a cover disk3. A filter element4is inserted into the receptacle in the filter housing2which has a hollow cylindrical design and is supported by a central supporting element5made of plastic and arranged in the interior area of the filter element4. Liquid flows radially through the filter element4from outside to inside so that the outside of the filter element4forms the entry side12and the interior area in the filter element the clean side13.

The cover disk3is made completely of plastic and comprises two individual disks6and7which are located parallel to each other and feature approximately the same radius and are connected via a central hollow cylindrical flow connection8. The two individual disks6and7as well as the flow connection8form a common one-piece plastic subassembly which is manufactured for example in injection molding or in other method such as deep drawing. If necessary, additional connecting bars are located in the space between the two parallel individual disks6and7via which both individual disks are supported against each other and which increase the stability of the cover disk3considerably.

The central connecting piece which—as part of the cover disk3—connects the two individual disks6and7features a connecting female thread9via which the cover disk3and therefore the whole filtering device I can be connected to a subassembly of the internal combustion engine. At the same time, the flow connection8serves as off-flow opening which communicates with the clean side13of the filter element4and through which the filtered liquid is axially discharged from the filtering device1. The flow connection8projects axially above the bottom side of the lower disk7facing directly the filter element4and into the cylindrical interior area of the filter element4which is the clean side13.

The lower individual disk7is conveniently connected directly with the front end of the filter element4which can for example be obtained by welding or gluing it with the front end of the filter element. In doing so, the lower individual disk7forms the front end of the filter element and ensures on the one hand the stability of the filter element and on the other hand a separation of clean and entry side.

Inflow openings are realized in the upper individual disk6facing away from the filter element4into which the anti-drain valves10are inserted. These anti-drain valves10are for example designed as duck bill valves which are represented in detail in theFIGS. 8 and 9. At first, the liquid to be filtered is introduced via the anti-drain valves10into the space between the two individual disks6and7, the anti-drain valves10preventing the liquid from flowing out or the filter from running idle when the motor is stopped during overhead dismounting of the filter element. From the space between the individual disks6and7liquid flows through flow-through openings11in the lower individual disk7directly facing the filter element4into the entry side12which is designed as annular gap between the internal wall of the filter housing2and the outside of the filter element4. After flowing through the filter element4in radial direction from outside to inside the filtered liquid is collected in the central cylindrical interior area (clean side13) and discharged axially through the flow connection8of the cover disk3.

On the upper side of the upper individual disk6of the cover disk3a gasket14is inserted into a location groove intended for this in the individual disk6. The gasket14ensures a flow-tight connection of the filtering device1to a subassembly of the internal combustion engine to which the filtering device is connected.

In the lower area of the filtering device facing the bottom of the filter housing2the filter element4is sealed by a frontal end plate15. This end plate15which is located at the front end of the filter element opposite to the cover disk3has a convex cup-shaped fixing connection16which projects from below into the clean room13of the filter element4. The outside of the fixing connection16projecting above the plane of the end plate15is surrounded by a sealing hose17which serves as an overflow valve. Into the axially extending walls of the fixing connection16are made recesses18which are covered by the sealing hose17and normally close the recesses18flow-tight. However, if the pressure at the entry side12exceeds a threshold value and is in particular higher than the pressure at the clean side13the filtered liquid flows via the bottom of the filter housing2from below into the recess in the fixing connection16and has an impact via the recesses18onto the inside of the sealing hose17by which the sealing hose is radially enlarged and the unfiltered liquid can directly flow from the entry side12to the clean side13via the recesses18. If the pressure decreases, the recesses18are again closed flow-tight by the internal stress in the sealing hose17. The sealing hose17combines in one subassembly the functions of a valve body and a valve spring that has an impact on the valve body in closing position.

FIG. 3shows the cover disk3in an individual representation. It can be seen that the flow-through openings11are designed as slotted holes in the lower individual disk7which extend in circumferential direction of the cover disk. The flow-through openings11are located in the radially outside laying area of the individual disk7and communicate when the cover disk3is mounted directly with the entry side12of the filter element.

On the upper side of the upper individual disk6is the location groove19designed as one-piece with the cover disk for the gasket to be inserted.

FIG. 4represents a section in enlarged representation through the connecting female thread9in the flow connection8. The cross-section geometry between two adjacent teeth20of the thread is elliptically designed and follows the continuous line21. For comparison, a conventional sawtooth geometry of prior art is represented in dotted line21′. The advantages of the elliptic geometry according to the continuous line21are the lower tensions which allows the use of relatively soft material such as plastic.

FIGS. 5 to 7show another example of an embodiment for a filtering device1for filtering liquids. The filtering device features an overflow valve22in the upper area of the filter element4facing the cover disk3which—under regular conditions—closes an overflow opening23between the entry side12and the clean side13of the filter element. This overflow opening23is realized in a front disk26which is firmly connected with the upper front end of the filter element4. The front disk26is designed as separate subassembly independent of the cover disk3, however, connected with the cover disk. Within the scope of the invention it can also be appropriate to connect the lower individual disk7of the cover disk3directly with the front end of the filter element4, in this case the overflow opening23would be realized in the individual disk7. Furthermore, it is possible to design the front disk26as a one-piece plastic subassembly with the cover disk3.

The overflow valve22comprises a sealing washer24which ensures the function of the valve body and is axially slidably arranged at the clean side13of the filter element and receives an impact from a valve spring25in its closing position in which the sealing washer24sealingly contacts the overflow opening23in the front disk26. The valve spring25is supported by the supporting element5of the filter element4.

The liquid to be filtered is introduced via the anti-drain valves10into the interior of the filtering device; altogether there are four anti-drain valves10arranged in the cover disk3. If the pressure of the introduced liquid exceeds a threshold value the sealing washer24is then shifted axially downwards against the force of the valve spring25from its closing position, giving way to a flow path via the overflow opening23directly from the entry side12to the clean side13. If the pressure has decreased, the force of the valve spring25is again sufficient to shift the sealing washer24against the pressure at the entry side12upwards into the closing position in which the overflow opening23is closed flow-tight. Conveniently, all components of the overflow valve22are made of plastic, and in particular the sealing washer24and also the valve spring25.

TheFIGS. 8 and 9show an example of an embodiment for an anti-drain valve10designed as duck bill valve which is inserted into openings of the cover disk3and via which the liquid to be filtered is introduced to the filtering device1. The duck bill valve10is also made completely of plastic. At the off-flow side the duck bill valve10features two crosswise arranged flow slits27which are opened under normal conditions so that the liquid to be filtered can flow through the duck bill valve10. Due to the flexibility of the plastic material of the duck bill valve10the wall sections28of the anti-drain valve which limit the flow slits27can be compressed by an externally applied pressure against the wall sections28which exceeds a threshold value, thus closing the flow slits27and making a through-flow of the liquid via the anti-drain valve10impossible. If the external pressure decreases, the internal elasticity of the material of the anti-drain valve10opens the flow slits27again thus allowing a through-flow through the anti-drain valve.

FIGS. 10 to 12show an example of an embodiment for an overflow valve between entry side and clean side in the lower section near the bottom of the filter element. From the end plate15arranged near the bottom of the receptacle of the filter housing2arises the central fixing connection16around which a cylindrical sealing hose17as valve body is placed. The central fixing connection16comprises vertically arising wall sections30separated from each other which are circularly arranged around a central projection31. Each of the wall sections30is designed as one-piece with the end plate15made of plastic and can elastically bounce. This makes it possible to insert a gasket29into the circumferential groove32which is formed at the outside of the wall sections30.

The sealing hose17forming the valve body is inserted into the space between the central cup-shaped projection31and the wall sections30enclosing the projection. In doing so, the sealing hose closes the recesses18which are realized in the walls of the central projection31.

The unfiltered liquid at the entry side of the filter element enters from below axially into the interior area of the central projection31and exerts a pressure on the sealing hose17from inside radially to outside. When exceeding a pressure threshold value at the entry side the sealing hose17expands to such an extend that a flow-through connection is realized via the recesses18between entry side and clean side so that the unfiltered liquid can immediately flow to the clean side. When the pressure at the entry side decreases the overflow valve closes automatically by compressing the sealing hose.

All components of the overflow valve (with the exception of the sealing hose) are made of plastic which enhances considerably the capability for recycling.

FIG. 13ashows an overflow valve22in the bottom area of the filter element in another embodiment. In this embodiment, too, all components of the filter element are made of plastic. The valve body of the overflow valve22is formed by a sealing washer24which is designed as one-piece with snap-in hooks33which are fixed loss-proof, however axially displaceable, in the interior area of the supporting element5at a locking opening of the supporting element. Thus the sealing washer24can be axially shifted between a closing position in which an overflow opening23in the end plate15at the bottom is closed flow-tight, and an opening position. The sealing washer24is subjected to strength by a valve spring25in its closing position.

Under regular conditions, the overflow opening23which is surrounded by the wall sections30of the fixing connection16, is closed flow-tight by the sealing washer24.

If the pressure at the entry side exceeds a threshold value, the unfiltered liquid comes from below via the overflow opening23in contact with the sealing washer24and has an impact on it with an opening pressure against the force of the valve spring25, by which the sealing washer24is lifted up and a flow-through connection between entry side and clean side is realized. When the pressure decreases, the sealing washer24can under the impact of the valve spring25return to the closing position in which the overflow opening23is closed.

The overflow valve22shown inFIG. 13bcorresponds in its basic structure to that inFIG. 13a,however with the difference that the valve spring25and the snap-in hooks33at the valve body support themselves directly at the fixing connection16and not at the supporting element5of the filter element. The supporting element5is placed on the fixing connection16which is conveniently connected in one piece with the end plate15, it can, however, also form a subassembly that is independent of the end plate15.

FIG. 14ato16bshow different examples of embodiments for overflow valves22in a simple construction which in closed position separate the entry side from the clean side in the filter element and in open position allow a direct introduction of the unfiltered liquid. In a valve housing34is arranged the axially displaceable valve body designed as sealing washer24and held in closing position at a valve spring25. If a force is exerted from outside to the sealing washer24against the spring force of the valve spring25, then the sealing washer24is displaced towards the interior area of the valve housing34by which overflow openings23in the wall of the valve housing34are released and a direct flow-through connection is created between entry side and clean side of the filter element. In the three examples of embodiments displayed the valve spring25is designed as an elastically bouncing block, wherein in the example according toFIGS. 14aand14bthe valve spring25is designed as an elastomer block, inFIGS. 15aand15bas an elastomer bellows and in the example according toFIGS. 16aand16bas a foam spring block, consisting of PUR foam or of silicone foam.

FIGS. 17 to 21show another example of an embodiment for a filtering device for filtering liquids. The filtering device1features a cylindrical filter housing2in which the ring-shaped filter element4is inserted which is radially flown through by the liquid to be filtered. For this purpose, the liquid to be filtered is introduced frontally into the filter housing2as shown inFIG. 18. To perform the filtration, the liquid flows through the filter element4radially from outside to inside and is then axially discharged via the interior area which represents the clean side out of the filter housing. The filter element4features a supporting structure5for supporting it. At the axial front end via which the liquid is introduced and/or discharged there are concentrically arranged connecting rings40and41which separate the clean room from the entry side. The space between the connecting rings40and41designates the entry side, the interior area within the smaller connecting ring41the clean side.

As it can be taken from the detailed drawing inFIGS. 20 and 21, at the axial front end via which the liquid is introduced and/or discharged a radially outer supporting ring43is provided for at the filter element4into which radial outflow openings27are realized which are uniformly arranged over the circumference of the supporting ring. At the radial outside these flow openings27are covered by a sealing hose42which consists of a flexible elastic material and which is placed under internal stress on the radial outside of the supporting ring43in order to cover the flow openings27. Together with the sealing hose42the supporting ring43forms an anti-drain valve10designed as hose valve which with a corresponding difference in pressure between inside and outside at the sealing hose42is transferred into the opening position shown inFIG. 21where at least sections of the sealing hose42are lifted up from the locking position that sealingly abuts the outflow openings27so that a flow can radially pass through the outflow openings27. The pressure applied to the inside of the axially introduced liquid to be filtered lifts the sealing hose42radially from the sealing position so that the outflow openings27are released. As soon as the differential pressure between inside and outside at the sealing hose falls below a threshold value which is decisively determined by the inner elasticity of the sealing hose, the sealing hose returns to its sealing position by closing the outflow openings.

FIG. 22shows another example of an embodiment of a filtering device1for filtering liquids. The cup-shaped filter housing2in which the filter element is inserted, is closed frontally by an external cover6in which a centric flow connection8with female thread9is integrated. Between the flow connection8and a radial external edge of the individual disk6extend radial spokes50. Intended is a plurality of such spokes which are arranged in regular distance over the circumference of the individual disk6. The spokes50have a straight-line shape and extend conveniently exclusively in radial direction. As shown in the dotted embodiment it may be appropriate to use bent spokes50′ which in addition to the radial component feature also a component in circumferential direction. Furthermore, spokes having a straight-line shape can also run angularly in radial direction.

FIGS. 23 to 25still show another example of an embodiment for a filtering device for filtering liquids. The filter element4has a ring-shaped design, the inside representing the clean side and the radial outside the entry side of the filter. In the area of an axial front end of the filter element4is arranged an overflow or bypass valve22which is conveniently made completely of plastic and features a valve housing34which is insertable into the axial interior area of the filter element4in the area of the front end. The valve housing34contains a valve spring25which is designed as spiral spring and exerts especially a compressive force. This valve spring25forces a sealing washer24serving as valve body into the closing position. If the liquid pressure at the entry side exceeds a threshold value the sealing washer24is opened against the force of the valve spring25so that a direct through-flow is created between entry side and clean side.

In the area of the axial front end several supporting feet60which project above the axial front end of the filter element are arranged which are conveniently designed as one-piece with the valve housing34. These supporting feet60have the function of an elastically bouncing supporting means, allowing an axial tolerance compensation when inserting the filter element4into the filter housing2and placing it on the bottom of the filter housing. Furthermore, the filter element is centered and guided by means of the supporting feet60. In addition, it is ensured that the filter element can not be inserted inadvertently wrong.

Conveniently, there are three or four of these supporting feet60arranged uniformly over the circumference at the front end of the valve housing34. As it can be taken fromFIG. 25, it may also be appropriate to fix a supporting ring61at the axial front end of the valve housing34instead of the supporting feet, the supporting ring61featuring, however axially displaceable, supporting elements62designed as distant and thorn-shaped supporting springs which are radially inwards and axially opposed to the plane of the supporting ring61.

FIG. 26shows another example of an embodiment in which a bypass valve22cooperates with a mandril70at the bottom of the cup-shaped filter housing2. The bypass valve22between the entry side and the clean side of the filter element that is to be inserted into the filter housing features a sealing washer24forming a valve body which is subjected to strength by a valve spring25in its sealing position at the valve housing34. The valve housing34is approximately designed cup-shaped, the open cup side facing the bottom of the filter housing. The sealing washer24is distant from the bottom of the filter housing, the lateral walls of the valve housing as well as the sealing washer24define a receptacle into which the pin or mandril70projects which is firmly fixed to the bottom of the filter housing.

The task of this mandril70is to place the valve body of the bypass valve in the opening position in case a wrong filter element including a bypass valve is inserted into the filter housing, so that despite the wrong filter element a direct flow-through connection between entry side and clean side is created, thus ensuring a through-flow of the liquid through the filtering device. In particular, when using it as a fuel filter an emergency supply of the internal combustion engine with fuel is thus guaranteed, even if a wrong filter element is inserted inadvertently.

However, if the filter element and the bypass valve are correctly used the mandril has only a centering function for centering the filter element in the filter cup and not an opening function for the bypass valve. In this case, the mandril projects into the recess in the valve housing34, however, without having an impact on the sealing washer24and without placing it into the opening position. If correctly inserted or if the correct filter element is inserted the sealing washer24is placed also in its closing position with sufficient distance to the tip of the mandril.

A further advantage of this mandril is that even if using a filter element intended for this purpose an inadvertent insertion of this filter element in wrong position is prevented. If the filter element is inserted inadvertently wrong into the filter cup, the frontal cover disk at the filter element comes into contact with the mandril70so that the filter element is not completely insertable into the filter cup which is immediately perceived during assembly.

FIG. 27shows a top view of a filter element4′. The filter element4′ has an upper end plate15′ which is formed of a thermoplastic material. The end plate15′ is basically designed as circular ring disk. Here a centrally arranged opening81is provided for through which the liquid can flow. With other embodiments, the end plate15′ can also be designed only as circular disk. The opening81for the liquid is then arranged at the opposing side. Besides the circular form or circular ring form it is clear that the end plate15′ can have any other geometric basic shape such as, for example, square, rectangular or polygonal, and in particular hexagonal. The end plate15′ has at its circumference three key structures80arranged at the circumference. Here the number and distribution of the key structures80at the circumference is arbitrary. That is why only one or more than one key structure80can be arranged at the circumference. The key structure80projects with its geometry above the external circumference of the end plate15′, the key structure80having material bars82of different widths or gaps83.

In this example of an embodiment the key structure80has the form of the letters “M+H”. It is, of course, possible to combine all letters in any sequence and number to form the key structure80. Advantageously, the letters are chosen in such a way that they represent, for example, a company logo or an abbreviation of a company or product name. The key structure may, however, also be formed by other characters such as, for example, Japanese or Chinese characters or Arabic or Roman numerals.

FIG. 28shows a lateral view of the filter element4′. Components identical with those ofFIG. 27have the same reference signs. The filter element4has besides the upper end plate15′ and the lower end plate15another zigzag-pleated and ring-shaped closed filter medium84. The filter medium84is sealingly connected with the end plates15,15′. In this example of an embodiment, the key structure80is inclined towards the surface of the end plate15′ with its area projecting radially above the circular shape of the end plate15′. Here, the angle of inclination a of the key structure is approx. 45°. However, the angle of inclination a may have any value between 0° and 90°, preferably between 30° and 60°. The key structure80engages a lock structure85as it is shown in the perspective detail of the filter housing2′ inFIG. 29.

The lock structure85is arranged at the cup-shaped filter housing2which is appropriate for receiving the filter element4. In this case, the lock structure85has a negative geometry in relation to the key structure80so that the material bars82of the key structure80engage in gaps83of the lock structure85. The material bars82of the lock structure85engage in gaps83of the key structure80. In this embodiment, the lock structure85of the filter housing2′ is designed as notch in the filter housing wall86. The notches may take the whole material thickness of the filter housing wall86or only be a partial recess. In case of a partial recess, part of the filter housing wall86remains to which the key geometry80is attached. With other embodiments, the lock structure85can be arranged at an angle in relation to the filter housing wall86and engage the notches in the end plate15′. Thanks to the interaction of the key-lock structures80,85the structures80,85form one unit. Consequently, the filter element4′ can only be inserted into the filter housing in the correct installation position. The insertion of incorrect filter elements can thus be recognized immediately and avoided if the filter element4′ is not assembled correctly. It is, of course, possible to arrange the key structure80at the filter housing2′ if the appropriate lock structure85is arranged at the filter element4′.

FIG. 30shows a filter element4′ according toFIG. 28in assembled state in a filter housing2′ according toFIG. 29. The structures80,85of the filter element4′ and the filter housing2′ complement each other in such a way that the filter element4′ is positioned distort-proof and precisely in the filter housing2′. This pre-assembled unit consisting of filter element4′ and filter housing2′ can then be screwed into the respective fixing for example at a filter head (not represented) or a cover (not represented). The described key-lock structures80,85can be combined in any way with the above described examples to form embodiments that make sense.