Field of the invention

The invention relates to a filter cartridge for being inserted into a filter housing. The invention further relates to the filter housing, being configured to receive the filter cartridge. Further, the invention relates to a kit comprising the filter housing and the filter cartridge.

Description of the related art

Fluid filters are used in numerous applications, e.g., to filter oil being required as a lubricant and/or coolant of a (e.g., combustion) machine. Oil filters for these kinds of machines shall be as small as possible to keep manufacturing costs low, to use the space provided by the hull of automobiles, planes or ships as effi- ciently and to keep reduce their weight. At the same time the oil filters shall be easy to service, and the pressure drop for a given fluid flow through the filter shall be minimized.

EP 1870 152 A1 suggests a filter having a top part with at least one inlet and at least one outlet channel and a bottom part with a filter element. The upper part has a housing and an insert. The inlet and outlet channel extend into the insert. The insert is interchangeably and rotatably mounted within the housing. WO 01/17654 A1 relates to a filter canister. The filter canister has a main body with a top. An inlet port is positioned on the top of the main body and an outlet port is also positioned on the top of the main body with an offset from the inlet port. A filter cartridge is positioned within the main body. The filter cartridge has an outlet end sealingly engaging the outlet port and an inlet port identifier asso- ciated with the inlet port; and an outlet port identifier associated with the outlet port. The inlet port identifier comprises a first flange positioned on the inlet port and having a first diameter. The outlet port identifier comprises a second flange positioned on the outlet port having a second diameter.

EP 2373398 A1 relates to an air filter with a housing comprising a socket and a cover enclosing a volume in which a replaceable filter cartridge is positioned. The filter cartridge comprises an essentially cylindrical filter element with a fluid channel. On top of the filter element is a connector for connecting the filter ele- ment with the socket. The connector has a first port being in fluid communica- tion with an air outlet of the socket. The air enters the filter cartridge via a first port and passes through a conduit of the connector to a slot in the peripheral surface of the filter cartridge. The air next passes the filter element, enters the fluid channel and from there flows via a second conduit of the connector to an air inlet of the socket. The connector and the upper end of the housing cover jointly engage into a recess of the socket, wherein a collar of the connector is lo- cated in between of the socket facing surface of the tubular housing cover and the bottom of the complementary recess. The housing cover facing surface of the collar is inclined and supports a gasket. When closing the cover, the gasket is compressed in a corner being delimited by the inclined surface of the collar, the radially inward facing surface of the socket's recess the socket facing end of the housing cover. WO 2010/117799 A2 suggest a fluid filter cartridge and a fluid filter housing for the cartridge. The filter cartridge has a filter element defining a longitudinal axis.

A front-end cap is attached to the socket facing end face of the filter element.

The front-end cap has a fluid-outlet port being centered with the longitudinal axis and being delimited by a circular wall. The circular wall has a forward-facing side being inclined to the longitudinal axis. Further, the front-end cap has a pro- trusion configure to engage in a recess with inclined side surfaces, being config- ured to azimuthally orient the filter cartridge relative to the housing while ad- vancing the filter cartridge to the socket. Summary of the invention

The problem to be solved by the invention is to simplify mounting of a fluid filter cartridge in a filter housing.

Solutions of the problem are described in the independent claims. The depend- ent claims relate to further improvements of the invention.

For example, a solution is provided by a fluid filter cartridge, as well referred to as "filter cartridge" or "cartridge". The fluid cartridge comprises at least a filter element with a front end, a rear end and a fluid channel. These filter elements are known in the art and can be made of plied filter paper, cloth, filter foam or the like and may optionally comprise end caps at their front and/or rear ends. The filter cartridge further defines a longitudinal axis. For example, the longitudi- nal axis may be identical to a symmetry axis of the filter element and/or to the symmetry axis of the contour of the front-end cap and/or of the contour of the rear-end cap. Generalizing, the longitudinal axis may extend for example through the front end of the filter element and the through the rear end of the filter ele- ment.

Further, the filter cartridge may preferably comprise a connector element, being referred herein as "connector". The connector may be attached to the front end of the filter element and may hence in operation provide a fluid connection be- tween the filter cartridge and a housing socket ("socket" for short) of a filter housing. The connector may thus comprise a front side facing away from the front end of the filter element in a forward direction and a rear side facing to- wards the front end of the filter element in a rearward direction. Herein we as- sume that the filter cartridge it is shifted during installation in the forward direc- tion to thereby connect it to the socket, while the cartridge may be retracted when separating it from the socket. The connector further may comprise a bottom, fluid-inlet port and a fluid-outlet port. The fluid-inlet port may comprise a fluid inlet wall surrounding an inlet through hole in the bottom. The fluid inlet wall preferably extends from the bot- tom in the forward direction. Similarly, the filter cartridge may comprise a fluid- outlet port with a fluid outlet wall. The fluid outlet wall preferably surrounds an outlet through hole in the bottom and extends from the bottom in the forward direction.

The fluid inlet wall and/or the fluid outlet wall may support at least one gasket on their outward and/or inward facing side, wherein inward and outward in this context reference to center of the fluid-inlet port or fluid-outlet port, respec- tively. Alternatively, at least one gasket may be supported by a gasket support wall extending as well from the bottom e.g., on the inward or outward facing side of the gasket support wall. In all these examples is the at least one gasket preferably be located in between of the bottom and the first plain bearing sur- face.

For example, the fluid-inlet port may be in fluid communication with a first open- ing in the peripheral surface of the fluid filter cartridge and hence may enable a fluid flow through the connector to the peripheral surface of the filter element.

The fluid-outlet port may be in fluid communication with fluid channel of the fil- ter element and hence may enable to withdraw the filtered fluid from the filter cartridge.

In operation, the fluid-inlet port may be connected to a first fluid port of a hous- ing socket and the fluid-outlet port may be connected to a second fluid port of the housing socket. Hence herein we assume that the first fluid port is a fluid- outlet port of the housing socket and the second fluid port is a fluid-inlet port of the housing socket, only to be able to clearly distinguish between ports of the cartridge and ports of the housing socket. Preferably, a peripheral wall with a peripheral surface may be attached to the bottom. The peripheral wall may for example provide for a radial abutment, e.g., to center the connector in a housing cover, preferably already prior to closing the housing cover.

Preferably, a first plain bearing surface of the connector faces in the forward di- rection, wherein the first plain bearing surface is configured to limit an axial movement of the filter cartridge in the forward direction. The first plain bearing surface thus provides for an axial abutment. Particularly preferred is the first plain bearing surface provided by a set of first forward facing sides of walls or sections thereof, wherein the walls extend from the bottom in the forward direc- tion. These walls may comprise the fluid-inlet wall and/or the fluid-outlet wall, but as well other walls extending from the bottom into the forward direction. This first plain bearing surface hence enables to rotate the filter cartridge relative to the socket, while already pushing the filter cartridge against a second plain bearing surface of the socket until the contours of the fluid-inlet port and the fluid-outlet port match with corresponding first and second ports of the socket. Servicing a filter cartridge is thus enhanced by the first plain bearing surface.

In a particularly preferred example is the contour of a first projection of the for- ward-facing sides of the fluid-inlet wall and of the fluid-outlet wall on a reference plane not point symmetric with respect to the longitudinal axis, wherein the ref- erence plane is orthogonal to the longitudinal axis. This measure makes it impos- sible to accidentally invert the fluid flow through the filter cartridge by mis- matching the fluid ports. For example, a fluid port mismatch would be to connect the fluid-inlet port of the cartridge to the second fluid port (i.e., to the fluid-inlet port) of a corresponding socket and/or connecting the fluid-outlet port of the cartridge to the first fluid port of the corresponding socket. Avoiding these mis- matches by the suggested measures hence simplifies servicing the filter cartridge increases safety of operation. If the contour of the first projection is not rotationally invariant relative to a rota- tion around the longitudinal axis (2) the same effect is obtained. Not rotationally invariant means that only rotation of the contour of the first projection by 360° maps the contour of the first projection on itself. Rotationally invariant thus means that a rotation of the corresponding object (in this case around the longi- tudinal axis) maps the object onto itself. In some cases, the object may be rota- tionally invariant only under certain angles; this is generally considered as a dis- continuousl ly rotationally invariant object. A continuously rotationally invariant object is mapped onto itself by any rotation around the corresponding axis or point.

The first plain bearing surface is preferably but not necessarily, a rotationally in- variant surface. In another even preferred example, the first plain bearing sur- face is only a portion of a rotationally symmetric ring surface, wherein the por- tion itself is not rotationally invariant, at least not continuously rotationally invar- iant with reference to the longitudinal axis. In other words, a rotation of the first plain bearing surface by around the longitudinal axis generates at least one continuously rotationally invariant ring surface The continuously rota- tionally invariant ring surface is a set of points , wherein as usual r de - notes the radius, i.e., the distance of the point R from the longitudinal axis and f denotes the azimuth. The radius r may span from a maximum radius r _max to a minimum radius hence S ₁ . Each point has a distance to a plane A, wherein the plane A extends through the bottom and is orthogonal to the longi- tudinal axis. In other words, assuming cylinder coordinates, each point R is de- fined by the triple Preferably, the distance monotonically in- creases or decreases with increasing radius r, while being constant at any given radius for all azimuth angles The ring surface S ₁ and hence as well the first plain bearing surface is this preferably concave or convex. The concave or convex shape centers the first plain bearing surface and hence the connector relative to a socket, while providing a rotational degree of freedom. The filter cartridge can thus be pushed against a another (i.e., convex or concave, respectively) (second) plain bearing surface and automatically centers on the another (second) plain bearing surface. An azimuthal alignment can be obtained by simply rotating the filter cartridge while pushing it against the another (second) surface. Once the azimuthal alignment has been reached, the fluid-inlet port and the first port as well as the fluid-outlet port and the second port may be connected to each other, e.g., by shifting the filter cartridge forward as will be explained below in more detail. Thus, preferably, the first plain bearing surface may have a recess configured to receive the second plain bearing surface and/or the second plain bearing surface may have a recess configured to receive the first plain bearing surface. In the example above, a second plain bearing surface may for example fit in between of the space or void being delimited by the walls extending from the bottom.

Particularly preferred, it exists a point P ₁ which has the same distance to all points on the first plain bearing surface. Thus, the first plain bearing surface may be spherical, i.e. the rotational degree of freedom is enhanced. The filter cartridge can be rotated relative to the longitudinal axis and in addition pivoted relative to the point P ₁ . The location of the point P ₁ is preferably on the longitu- dinal axis. The point P ₁ can be in front of the first plain bearing surface or behind the first plain bearing surface, wherein "in front of" and "behind" reference to the forward direction. In case the point P ₁ is in front of the bearing surface, i.e., spaced in the forward direction from the bearing surface the first plain bearing surface is a concave spherical surface. If the point P ₁ is behind bearing surface, i.e., spaced in the rearward direction from the first plain bearing surface, the first plain bearing surface is a convex spherical surface. Both measures work equally well. Preferably, the filter cartridge has at least a first protrusion which is delimited in a radial direction by an inner radius and by an outer radius wherein the radii are measured relative to the longitudinal axis. The first protrusion may ex- tend in the forward direction over any feature of the connector withing a first ring being delimited by the inner radius and the outer radius of said first protrusion. This measure is another option which may provide for an azimuthal alignment of the filter cartridge relative to a filter socket. In an example, the fil- ter cartridge's first plain bearing surface may be pushed against a corresponding second plain bearing surface while being rotated until the first protrusion abuts a protuberance protruding from the counterpart (e.g., a housing socket) in the rearward direction. Then the corresponding ports are aligned, the cartridge can be advanced in a forward direction, thereby connecting the mutually corre- sponding ports.

If the filter cartridge has at least a second protrusion being delimited in the radial direction by an inner radius and by an outer radius relative to the longi- tudinal axis and if the second protrusion extends in the forward direction over any other feature of the connector within a second ring being delimited by the inner radius and the outer radius of the second protrusion, the azi- muthal alignment is even more reliable. This holds in particular if the first ring and the second ring do not overlap, i.e. if . Particularly preferred are the first and the second protrusion azimuthally spaced by at least essentially 180°. This preferred measure further contributes to safely limit a rota- tion of the filter cartridge. As usual, at least essentially 180° means that 180° is preferred, but deviations α _p can be accepted. Hence the angle a between the first and the second protrusion may be e.g., wherein

{45°, 30°, 15°, 10°, 5°, 2.5°, 1°, 0°}. As usual means that the angle a can be in between of and For example, the ring surface S ₁ ay comprise at least two concentrical ring sur- face sections with a gap in between. The first protrusion and/or the second pro- trusion may extend through the gap, thereby the filter cartridge can be pivoted and rotated particularly reliably. Thus, in between of the walls and/or the wall sections which define the first plain bearing surface may be circular groove, into or through the first and/or second protrusion may extend. This groove enables a protuberance of the socket to rotate relative to the filter cartridge until it abuts the first or second protrusion.

In another embodiment the invention relates to a filter housing. In particular the invention relates to a filter housing for accommodating the filter cartridge being described above. As usual, the filter housing comprises a filter housing volume, being enclosed by a housing socket and a housing cover. Often, the filter housing socket and the filter housing cover each have a screw thread enabling to screw the housing cover to the socket, thereby enclosing a filter cartridge in the hous- ing volume. But other means known in the art for releasably connecting the filter cover to the housing socket may be used as well. Generalizing, the housing cover may be releasably attached to the housing socket. Further, the filter hous- ing has a housing axis. The housing axis is a longitudinal axis, and may e.g., be de- fined as the screw axis of the optional screw threads. In any case, the housing axis extends through the housing cover and through the housing socket and can be considered as a middle axis of the housing volume.

The housing socket, as well briefly "socket" has a first fluid port configured to be connected to the fluid-inlet port. It may further comprise a second fluid port con- figured to be connected to the fluid-outlet port. Assuming no cartridge to be in- serted, the fluid to be filtered would enter the housing volume through the first port and leave it through the second port. The terms first and second port thus are "aligned" with the intended fluid flow and have been selected only to verbally distinguish from the fluid-inlet port and the from the fluid-outlet port of the filter cartridge.

In operation, the first port is intended to be connected to the fluid-inlet port and the second port is connected to the fluid-outlet port. The corresponding align- ment of the port is herein expressed by the verb "to match", i.e., if the ports match, the fluid-inlet port is aligned with the first port and the fluid-outlet port is aligned with the second port.

Further, the socket comprises a second plain bearing surface. It may be the only plain bearing surface of the socket. The term "second" plain bearing surface has been selected only to verbally distinguish it from the first plain bearing surface of the filter cartridge. The second plain bearing surface faces in the rearward direc- tion, i.e., it faces from the socket towards the distal end to the housing cover (as well herein, briefly "cover").

In a preferred example is the second plain bearing surface configured to limit an axial movement of the filter cartridge in the forward direction. Preferably this limitation occurs only in case the respective ports do not match.

Further preferably, is the contour of a second projection of the rear facing sides of the first fluid port and of the second fluid port on a reference plane being or- thogonal to the housing axis not point symmetric with respect to the housing axis. Thus, a port mismatch can be reliably avoided. If the ports of the filter car- tridge are rotated by e.g., 180° around the longitudinal axis relative to their matching orientation, they simply cannot connect to the first port and to the sec- ond port. This can be obtained even if the ports have an identical shape or con- tour by offsetting at least one of the ports radially and/or azimuthally. In addition or alternatively, the contours of the first port and the second port may be differ- ent in shape and/or size. As already apparent, the first fluid port may be defined by a first open end of a first conduit in the second plain bearing surface. Similarly, the second fluid port may be defined by a second open end of a second conduit in the second plain bearing surface. Thus, the front surfaces of the walls forming the first plain bear- ing surface may slide over the second plain bearing surface until the ports match. Once this matching is obtained, the first plain bearing surface may be inserted into a recess in the second plain bearing surface thereby connecting the first fluid port to the fluid-inlet port and the second fluid port to the fluid-outlet port.

Particularly preferred is the contour of the second projection rotationally invari- ant relative to a rotation around the housing axis. This measure as well contrib- utes to avoid connecting mismatching ports.

For example, a rotation of the second plain bearing surface by around the housing axis may generate at least one continuously rotationally invariant ring surface S ₂ , being a set of points , and in that each point has a distance to a plane A ₂ , wherein the plane A ₂ ex- tends through housing and is orthogonal to the housing axis. The dis- tance may preferably monotonically increases or decreases with in- creasing radius r, while being constant at any given radius r for all azimuth an- gles Thus, the surface S ₂ being generated by a rotation of the second plain bearing surface is preferably convex or concave, this holds in particular if the first plain bearing surface of the corresponding filter cartridge is concave or convex, respectively. Each of these measures contributes to align the longitudinal axis to the housing axis, thereby simplifying installation of a filter cartridge.

Particularly preferred, exists a point P ₂ which has the same distance to all points R ₂ or\ the second plain bearing surface. Thus, the second plain bearing sur- face may be a section of a sphere, it may be convex of concave, depending on the location of the point P ₂ . In a preferred example the point P ₂ is on the housing axis. And in case the first and the second plain bearing surfaces contact each other, the point P ₂ is preferably at least essentially at the same location than the point P ₁ of the first plain bearing surface. At least essentially at the same location as usual means that the same location is preferred but deviations may be accepted. For example, if the first surface is convex and the point P ₂ is lo- cated in front of the point P ₁ then the contact surface between the two bearing surfaces is reduced to a line or sections thereof. The same happens if P ₂ is lo- cated behind the point P ₁ and/or if first surface is concave. This is acceptable but less preferred.

Further, the filter housing may further optionally comprise a first protuberance being delimited in a radial direction by an inner radius r _148i and by an outer ra- dius r _148i relative to the housing axis, wherein first protuberance preferably ex- tends in a rearward direction e.g., over the second plain bearing surface. Option- ally, the filter housing may comprise a second protuberance being delimited in a radial direction by an inner radius r _149i and by an outer radius r _149o relative to the housing axis. Similarly, the second protuberance may preferably extend in a rearward direction, for example over the second plain bearing surface. The pro- tuberances may provide an azimuthal abutment limiting a rotation of a filter car- tridge on the second plain bearing surfaces. The inner and outer radii of the first and second protuberances preferably do not overlap, i.e., preferably Similar to the optional first and second protrusions of the connector, the first and second protuberances are preferably azimuthally spaced, e.g., by at least essentially 180°, i.e. by

A preferred filter system may comprise at least one of the filter housing and/or the filter cartridge as described above. The filter cartridge may thus be config- ured to be inserted into the filter housing and the filter housing may be config- ured to receive and/or accommodate the filter cartridge. Description of Drawings

In the following the invention will be described by way of example, without limi- tation of the general inventive concept, on examples of embodiment with refer- ence to the drawings. Figure 1 shows a filter cartridge in a filter housing.

Figure 2 shows a cross sectional view of a connector of the filter cartridge in Fig. 1 to 3.

Figure 3 shows the forward -facing side of the connector.

Figure 4 shows a perspective view of the connector. Figure 5 shows a side view of the housing socket of Fig. 1.

Figure 6 shows a rear view of the housing socket of Fig. 1.

Figure 7 shows a perspective view of the rear side of the housing socket of Fig. 1.

Figure 8 shows a sectional view of the connector being oriented in a first azi- muthal position on a plain bearing surface of the housing socket. Figure 9 shows a sectional view of the connector being oriented in a second azi- muthal position on the plain bearing surface of the housing socket.

Figure 10 shows a sectional view of the connector being oriented in a third azi- muthal position on the plain bearing surface of the housing socket.

Figure 11 shows a first sectional view of the connector being oriented in a fourth azimuthal position on the plain bearing surface of the housing socket.

Figure 12 shows a first sectional view of the connector being oriented in a fifth azimuthal position on the plain bearing surface of the housing socket. Figure 13 shows a detail of the filter cartridge prior to closing the filter housing.

Figure 14 shows the detail of the filter cartridge prior to closing the filter housing after aligning the filter cartridge with the filter housing.

In Fig. 1 a first embodiment of a filter cartridge 1 is shown. The filter cartridge 1 is located inside a filter housing with a socket 10 and a housing cover 20. As can be seen, the housing cover 20 is connected by an optionally threaded connection to the housing socket 10. The filter housing may optionally have a sealing sur- face 25 facing inwards, preferably radially inwards towards a longitudinal axis 2 of the filter cartridge 1. In this figure, the longitudinal axis 2 of the filter car- tridge 1 is aligned with a housing axis 102.

The filter cartridge 1 has a connector element 50, as well briefly "connector 50", for fluidly connecting a filter element 30 of the filter cartridge 1 into a fluid flow. The filter element 30 may define a fluid channel 37 sharing the longitudinal axis 2. The socket may have a first fluid port 151 and a second fluid port 152. As depicted, the first fluid port 151 may be fluidly connected to a fluid-inlet port 51 of the connector 50 and hence of the filter cartridge 1. Similarly, the second fluid port 152 may be fluidly connected to a fluid-outlet port 52 of the connector 50 and hence of the cartridge 50. In operation, a fluid, (e.g., an oil, water, a gas or a fuel), may flow from through the first fluid port 151 and the fluid-inlet port 51 into the connector 50 and from the fluid-inlet port 51 through an optional first conduit 56 to a first fluid opening 58 which may be in the in the peripheral sur- face of the filter cartridge 1. In the depicted example, the first fluid opening 58 is a slot being formed in between of a rearward-facing side 54 of the connector 50 and a front-end cap 33 of the filter element 30. But this location is only a pre- ferred example. In other examples the boundary of the first fluid opening 58 may be entirely defined by the connector 50 or alternatively by the front-end cap 33 or even by some other part of the cartridge 1. In any case, the fluid may leave the filter cartridge 1 via the first fluid opening 58 and may enter a gap 85 being provided between the housing cover 20 and the filter element 30. From there, the fluid may pass the filter element 30 and may enter into the fluid channel 37. The fluid may be removed from the fluid channel 37 via a second fluid port 52, which may e.g., be formed by the optional front-end cap 33. Alternatively, as shown in the depicted example, filtered fluid may be removed through a second fluid opening 59 in the connector 50. The optional second fluid opening 59 may be in fluid communication with an optional fluid-outlet port 52 via an optional second conduit 57. The optional fluid-outlet port 52 may preferably be coupled to a second fluid port 152 of the socket 10.

An optional gasket 80 may be located between a peripheral surface 60 of the connector 50 and the optional sealing surface 25 of the housing, to thereby sepa- rate the gap 85 in a forward portion and a rearward portion. This separation dis- ables a fluid flow from the rearward portion into the forward portion of the gap 85 which fluid flow would lead to leakage of the (e.g., oil or gas or fuel, etc.) filter housing. The optional gasket 80 thus seals the forward portion from the rearward portion of the gap 85.

As can be see in Fig. 2, 3 and 4, the connector 50 has a bottom 40. An optional peripheral wall 60 may extend from the bottom 40 at least essentially parallel to the longitudinal axis 2 for example it may extend at least essentially in the for- ward direction 3. The peripheral wall 60 has a peripheral surface which may sup- port e.g., the optional gasket 80 as shown in Fig. 1. A number of walls 41, 42, 43 may extend from the bottom 40 in the forward direction 3. The walls 41, 42, 43 each have a forward-facing side 413, 423, 433. These forward-facing sides 413, 423, 433 form a first plain bearing surface. This first plain bearing sur- face 413, 423, 433 is preferably discontinuous, namely intersected by the spaces between the walls 41, 42, 43, but as can be seen in Fig. 2, the first plain bearing surface is spherical, i.e., there exists a point P ₁ which has the same distance to all points on the first plain bearing surface413, 423, 433. Preferably, like in the de- picted example the point P ₁ is on the longitudinal axis. In the Figures, the point P ₁ is not shown. Summarizing, the first plain bearing surface 413, 423, 433 is preferably a section of a sphere being formed by forward facing sides 413, 423, 433 of walls 41, 42, 43 extending in the forward direction 3 from the bottom.

The first wall 41 may surround an inlet through hole 414 in the bottom 40 and may hence provide the fluid-inlet port 51, thus when referencing to the fluid-in- let port 51 one may as well use the reference numeral 41 indicating its boundary. In other words, the fluid-inlet port 51 may comprises the first wall 41, which thus is a fluid inlet wall 41 surrounding the inlet through hole 414 in the bottom 40. Similarly, the second wall 42 may surround an outlet-through hole 424 in the bottom 40 and hence may provide the fluid-outlet port 52. Thus, the reference numeral 42 indicating the boundary of the fluid-outlet port 52 may be used as well to indicate the fluid-outlet port 52. To rephrase it slightly differently, the fluid-outlet port 52 may comprise the second wall 42, which thus may thus be considered as fluid-outlet wall 42 surrounding the outlet-through hole 424 in the bottom 40.

As a consequence of the spherical shape of the first plain bearing sur- face 413, 423, 433, the connector 50 may be rotated around the longitudinal axis 2 and may pivot relative to the point P ₁ . As can be seen in Figs. 2, 3 and 4 the fluid-inlet port 51 and the fluid-outlet port 52 are not symmetric to the longitudi- nal axis 2, the effect of which is explained in more detail below.

In between of the walls 41, 42 and 43 is a groove or void, being delimited in the rearward direction 4 by the bottom 40 and being open in the forward direc- tion 3. As will be apparent below, the contour of this groove or void is preferably not rotationally invariant under a rotation around the longitudinal axis 2. A first protrusion 48 and a second protrusion 49 may extend between the walls 41, 42, 43 from the bottom in the forward direction 3. The first protru- sion 48 may extend in the radial direction from a first inner radius r _48i to a first outer radius r _48o and the second protrusion may extend radially between a sec- ond inner radius r _49. and a second outer radius r _49o . As can be seen in Fig. 3, the radii of the first and the second protrusions 48, 49 preferably do not overlap. Further, as can be seen best in Fig. 4, the first and second protrusions 49, 49 may have an azimuthal abutment surface 48a and 49a, respectively. Preferably, the azimuthal abutments 48a and 49a have an azimuthal spacing of at least essen- tially 180°, of 180° ± α _p .

The walls 41, 42 may have recesses 415, 425 in their respective forward -facing sides 413, 423. The recesses may provide a corridor between an inner recess ra- dius r _ri and an outer recess radius r _rQ . Preferably, the outer recess radius r _To is greater (or equal) the maximum of the first and second outer radii, i.e., prefera- bly . Further preferably, is the inner recess radius r _ri smaller (or equal) than the minimum of the first and second inner radii r _48i and r _49i , hence preferably Thus, an optional protuber- ance 148, 149 (see Fig. 5 to Fig. 7) of the socket 10 may rotate relative to the first bearing surface 413, 423, 433 around the longitudinal axis 2, until it abuts the first protrusion 48 or the second protrusion 49. To rephrase this in the corre- sponding other reference system, the first bearing surface 413, 423, 433 may ro- tate on the second bearing surface 146 of the socket 10 until the protrusions 48,

49 abut the corresponding protuberances 148, 149 and thereby align the inlet- fluid port 51 with the first fluid port 151 and the outlet-fluid port 52 with the sec- ond fluid port 152.

A socket 10 configured to receive the filter cartridge is shown in Fig. 5 to Fig. 7.

The socket 10 may have a base 140 with an optional screw thread for engagement with an optional screw thread to the housing cover 20 (see Fig. 1).

As shown in Fig. 5 to Fig. 7, the socket preferably has a second plain bearing sur- face 146. The second plain bearing surface 146 may be provided by the rearward facing side of a wall like structure 147 of the housing socket 10 being supported by the base 140. The denominator "second" is used only to verbally distinguish it from the "first" plain bearing surface 413, 423, 433 which is provided by the filter cartridge 1 (see above).

As can be seen in Fig.5, the second plain bearing surface 146 may as well be spherical, i.e., all points of the second plain bearing surface 146 may have a sin- gle distance to point P ₂ . The point P ₂ is preferably on the housing axis 102 and is not depicted in the figures. Optional first and second protuberances 148, 149 may extend in the rearward direction 4 over the second plain bearing sur- face 146. These first and second protuberances 148, 149 are preferably config- ured as azimuthal abutments for the first and second protrusions 48, 49, respec- tively. Hence, the first protuberance 148 may, e.g. have a radial extension be- tween to that overlaps with the radial extension of the first protru- sion 48 being defined by and Thus, particularly preferred Similarly the sec- ond protuberance 149 may, e.g. have a radial extension between to that overlaps with the radial extension of the second protrusion 49 being defined by and Again, particularly preferred and/or

When mounting a filter cartridge 1 to the housing, the filter cartridge 1 needs to be correctly oriented in azimuthal direction relative to housing socket 10 and in addition, the longitudinal axis 2 of the filter cartridge 1 needs to be aligned with the housing axis 102. Both can easily be accomplished due to the first plain bear- ing surface 413, 423, 433. The azimuthal alignment of the ports 51, 52, 151, 152 will be explained with reference to Fig. 8 to 12 and with the reference to Fig. 13 and 14 we will explain the alignment of the longitudinal axis 2 with the housing axis 102.

When mounting the filter cartridge 1, it may be inserted into a housing cover 20. Next the person servicing the filter may want to attach the housing cover 20 to the housing socket 10. The person may thus advance the first plain bearing sur- face 413, 423, 433 against the second plain bearing surface 146, when trying to close the housing cover 20. As shown in Fig. 8, the ports 51, 52, 151, 152 are not necessarily aligned to each other and often are not even visible to the person try- ing to close the housing cover 20. As the first plain bearing surface 413, 423, 433 is a section of a rotationally invariant surface it may slide on the second plain bearing surface 146. In Fig. 8 the first plain bearing surface 413, 423, 433 is hid- den by the corresponding walls 41, 42, 43, but their projections onto the drawing plane is identical with the contour of the first plain bearing surface 413, 423, 433.

In the next step, the person will rotate the housing cover 20 clockwise (assuming a right-hand thread, and counterclockwise in case of a left-hand thread) trying to engage the threads which have not yet become in contact, because the first plain bearing surface 413, 423, 433 blocks the filter cartridge 1 from being moved fur- ther in the forward direction 3. This rotation entrains the filter cartridge 1 and hence the connector 50 as shown in Fig. 9 to 11. Comparing Fig. 8 and Fig. 9, it becomes clear that the protuberances 148, 149 may pass through the re- cesses 415, 425 in the walls 41 and 42. In Fig. 8 to Fig. 12, the recesses 415, 425 are visible as openings in the walls 41 and 42 and each indicated by an arrow pointing into the openings.

As can be seen in Fig. 9, the fluid-inlet port 41 may be positioned above the sec- ond port 152 and the fluid-outlet port 42 may be positioned above the first port 151, but as the first and second walls 41, 42 are not point symmetric to the longitudinal axis 2, these ports 41(=51), 42(=52), 151, 152 do not fit into each other. The filter cartridge 1 remains supported in the forward direction 3 by the first plain bearing surface 413, 423, 433. The rotation may continue as shown in Fig. 10 and Fig. 11 and the protuberances 148, 149 may each pass through the corresponding other recess 415, 425 in the walls 41, 42 delimiting the fluid-inlet port 51 and the fluid outlet port 52, respectively. The rotation may hence con- tinue until the optional protrusions 48 and 49 abut the optional protuber- ances 148, 149 which is shown in Fig 12. At this point it is noted that a single of the optional protrusions 48, 49 would be sufficient to limit the rotation, but two or more are preferred. The fluid-inlet port 41(=51) now matches with the first port 151 and the fluid-outlet port 42(=52) matches with the second port 152. As can be seen in Fig. 12, in this orientation, the contour of the second plain bearing surface 146 does no longer overlap with the contour of the walls 41, 42 and 43 and as well not with the contour of the protrusions 48, 49. Accordingly the filter cartridge 1 and hence the filter housing 20 can be advanced in the forward direc- tion 3 thereby connecting the corresponding ports 51, 52,151, 152. Further, after advancing the housing cover 20 the screw threads (and/or any other fastening means) can engage and the housing cover 20 may be firmly closed.

The alignment of the longitudinal axis 2 with the housing axis 102 is shown in Fig. 13 and Fig. 14. Initially, when the first bearing surface 413, 423, 433 abuts the second bearing surface 146, the two axes 2, 102 are not aligned. Due to the spherical shape of the first plain bearing surface 413, 423, 433 the filter car- tridge 1 can be pivoted easily until the axes 2, 102 are aligned as shown in Fig. 14. Once the alignment is obtained, the contours of the first and the second plain bearing surfaces 413, 423, 433, 146 no longer overlap and the filter car- tridge 1 can be advanced, thereby connecting the ports 51,52, 151, 152 as ex- plained above. List of reference numerals

1 filter cartridge

2 longitudinal axis

3 forward direction

4 rearward direction

10 socket

102 housing axis

140 base

146 second plain bearing surface

147 wall like structure / structure

148 first protuberance

149 second protuberance

151 first fluid port

152 second fluid port

20 housing cover

25 sealing surface

30 filter element

33 front-end cap

34 rear-end cap

37 fluid channel

40 bottom

41 wall / fluid-inlet wall / fluid-inlet port

413 forward facing side inlet through hole 5 recess in forward facing side wall / fluid-outlet wall / fluid-outlet port4 outlet through hole 3 forward facing side 5 recess in forward facing side wall 3 forward facing side first protrusion a abutment surface of first protrusion second protrusion a abutment surface of second protrusion connector element / connector fluid- inlet port fluid-outlet port forward-facing side rearward-facing side first conduit second conduit first fluid opening second fluid opening peripheral wall gasket gap inner radius of recess outer radius of recess inner radius of first protrusion outer radius of first protrusion inner radius of second protrusion outer radius of second protrusion inner radius of first protuberance outer radius of first protuberance inner radius of second protuberance outer radius of second protuberance