Field of the invention

The invention relates to filter holder, in particular to a bypass valve holder for a fluid filter system, to a corresponding filter cartridge, a filter housing cover, the filter housing and to systems comprising at least two of the identified compo nents.

Description of the related art

Oil filters are crucial elements in operating combustion engines and must be re placed regularly to ensure reliable operation of the combustion engine. The oil filter systems typically comprise a replaceable oil filter cartridge (herein briefly 'filter cartridge' or simply 'cartridge') and a housing for the cartridge. The hous ing positions the cartridge in between of an oil inlet and an oil outlet, to enable an oil flow through the filter element of the cartridge. The cartridge typically comprises a filter element with a tubular shape. The tubular filter element is dis- posed between two end caps. In operation, the oil flows from the oil inlet into the housing accommodating the cartridge and then radially inwards through the filter element, whereby suspended contaminants are separated (to a large ex tend) from the oil and remain in the filter element. The oil pouring through the filter element is withdrawn from the hollow space being enclosed by the tubular filter element through an oil conduit being provided by at least one of the end caps, said end cap being referred to as front-end cap. The oil conduit is in fluid communication with the outlet. Different embodiments of this kind of filter car tridges are disclosed, e.g. in WO 2015112458 and US 2016038859 Al.

US 2016/0001206 discloses a similar filter cartridge. The filter cartridge is directly mounted with its front-end cap to a housing cap. Accordingly, the front-end cap has mounting means for connecting the filter cartridge with the housing top. DE10248907 describes a disk-shaped adapter for connecting the filter element to the cap, the adapter comprising a bypass valve. The disadvantage of this and sim ilar solutions is that the adapter has too much freedom of movement which makes it difficult in some circumstances to remove the snap-fitted filter element due to a lack of leverage.

WO 2016/169754 A1 addresses removing a filter cartridge from a filter housing using a filter removal tool. The filter removal tool is inserted from the rear side into the filter cartridge and engaged behind a front-end cap by a rotation of the tool, thereby enabling to remove the filter by simply pulling the removal tool out of the filter housing.

DE19848978A1 discloses an oil filter cartridge being attached to a filter housing cover by a filter holder. The filter holder has tongues with radial protrusions en gaging behind a rim of a front-end cap of the oil filter cartridge. The front-end cap's face facing the filter holder is essentially plane. Summary of the invention

The problem to be solved by the invention is to provide an enhanced oil filter system providing reduced manufacturing costs and that provides less waist ma terial when disposed after use.

The problem to be solved is as well the provision of means that allow easier re- moval of the spent filter cartridge from the filter, in particular the filter cap.

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

The invention enables to removably attach a filter cartridge, e.g. an oil filter car tridge, to a filter holder of a filter system. The filter holder may be attached to or be integrally formed with a housing cover. The invention enables a safe filter cartridge handling, even when replacing still hot used cartridges. In addition, the material being disposed when replacing a filter cartridge is reduced, thereby low ering production costs and as well reducing waste. As will be described in more detail below, the filter holder may e.g. be a bypass valve holder configured to support a filter cartridge.

The filter holder according to an aspect of the invention enables to safely mount and unmount a corresponding filter cartridge. The filter holder may be part of a bypass valve for the corresponding fluid filter system. In his case the filter holder may as well be a valve holder. The valve holder explained below is an example of a filter holder. Thus, the term "valve holder" may be replaced by "filter holder" (and vice versa).

The filter holder may have a (e.g. bypass) fluid inlet defining a longitudinal axis of the filter holder and a front side of the filter holder (and thus as well of the by pass valve). If the filter holder is a valve holder, it may have as valve set at its rear side. As usual the rear side is the side of the filter holder, facing away from the front side. Of course the terms front and rear could be swapped without chang ing the technical teaching of this application.

The filter holder may comprise a disc having the front side with the fluid inlet and the rear side with the valve seat. If the bypass valve is omitted, we refer to the front side of the filter holder and thus as well of the disc as the side which is configured to face away from the filter cartridge (when the filter is assembled); accordingly, the rear side faces towards the filter cartridge, after assembly. The longitudinal axis is accordingly defined, i.e. to essentially match the filter car tridge's axis. Support means may be attached to the filter holder. The support means may provide a spring abutment for a valve spring. The valve spring preloads the valve member against the valve seat. Thus, as usual, the valve member is movably supported, enabling to move it from a first position, in which it blocks, i.e. closes the valve seat (i.e. the opening being defined by the valve seat), to a second posi tion and back to the first position. In the second position the valve seat is at least partially opened, enabling a fluid to pass the bypass valve. Preferably, at least one tongue extends from the rear side of the filter holder.

The at least one tongue has at least one protrusion, being configured to engage into a space behind a rim. In a preferred example, said protrusion faces radially outwards (radially, as usual is relative to the longitudinal axis) and is thus config ured to engage into a space that is radially outwards from the tongue. This at least one tongue enables to removably fasten the filter holder to a rim, e.g. to a rim being defined by a through hole in an end cap of a filter cartridge. As will be explained in more detail below, the rim preferably faces radially inwards. As ap parent, the valve holder may comprise more than a single one of said tongues, preferably at least two or at least three tongues. The tongues and/or the rim are preferably elastic, enabling to mechanically connect the valve holder to the filter cartridge by simply snapping the protrusions over the rim (snap-in connection). Disconnecting can be obtained by slightly bending the tongues radially inwardly, thereby enabling the corresponding protrusions to slide over the rim (snap-out disconnection). The filter holder may preferably comprise at least one bearing surface facing away from the rear side of the valve holder, i.e. towards the filter cartridge (if mounted). The bearing surface is configured to enable moving, e.g. pivoting the filter holder relative to the filter cartridge (and vice versa). The bearing surface is thus a plain bearing surface of a plain bearing. When the filter holder is attached to a front end-end cap of a filter cartridge, the bearing surface forms together with a complementary bearing surface of the front-end cap a plain bearing that enables the filter holder and the filter cartridge to pivot relative to another. Thus, the plain surface enables to handle misalignments, which can be due to manufacturing tolerances or by design to ease inserting a filter cartridge into a tiny space of an engine compartment.

Preferably, the bearing surface is spherical, i.e. a section of a sphere, particularly preferred a ring section of a sphere, wherein the ring is preferably centered around the longitudinal axis.

In a preferred example the bearing surface may provide a sealing surface, to re duce bypass oil flow through a gap between the two bearing surfaces.

The bearing surface faces away from the rear side of the valve holder, wherein the bearing surface preferably surrounds the optional valve seat at a first radial distance Ri from the axis. The bearing surface may provide or comprise the op tional sealing surface. In this case the filter holder can be attached sealingly to an end cap of a filter cartridge, i.e. there is essentially no fluid bypassing the op tional bypass valve in case it is closed. Thus, the fluid is reliably filtered under normal operating conditions. In a preferred embodiment, the bearing surface/sealing surface is integrally formed by the filter holder, thereby reducing the risk of mistakes when installing a filter cartridge. In addition, manufacturing costs can be reduced. Alternatively, the sealing surface could be provided by a gasket, being positioned between the filter holder and the filter cartridge. But even if the sealing if provided by a sepa- rate gasket, the surface of the filter holder contacting the gasket forms a sealing surface.

An abutment may be being positioned on the rear surface at a second radial dis tance R ₂ from said axis and is configured to limit the (e.g. pivotal) movement of the filter holder relative to a front-end cap of a filter cartridge, when attached. Thereby, the abutment enables to release the tongues and thus a filter cartridge by simply pivoting the rear end of the filter cartridge relative to the axis until the abutment blocks further pivotal movement. For example, if a filter cartridge is connected to the filter holder, which itself may be mounted to a housing cover, one may release the filter cartridge after removing the housing cover from its corresponding socket by providing a radial load on the free end of the cartridge. In a first step, the filter cartridge may pivot, preferably around a point of the fil ter holder's axis until the abutment contacts the filter cartridge. Now the abut ment defines the pivoting point and the lever arm, thus, the tongues can be re tracted from the rim by slightly enhancing the radial load. Thus, the (clean) hous ing cover can be used to grip a hot oil soaked filter cartridge without touching it. The filter cartridge can be moved to a dust bin and is released into the dust bin by slightly pressing the free end of the filter cartridge against the dust bin's wall using the housing cover or the filter holder as griping tool.

Preferably, the second radial distance R ₂ is greater or equal the first radial dis tance Ri, i.e. R ₂ ³R _I . By selecting the distances as indicated, the lever arm for re- leasing the rim is adjusted to provide a particular simple a handling of the filter cartridge when using the filter holder as a gripping tool.

If the sealing surface is inclined to face away from the axis and the rear side, the filter holder may flex and still provide a tight connection. Thus the sealing surface may be preloaded by flexing (i.e. elastically deforming) the filter holder when connecting it to the rim, thereby enabling a particularly tight connection be tween the corresponding end cap and the filter holder.

Particularly preferable, the sealing surface has the shape of a section of a sphere having its center on the axis. This enables an attached filter cartridge to pivot rel ative to the filter holder without damaging the sealing surface. Longevity of the filter holder is thereby enhanced. Preferably, the abutment limits the pivoting angle to an angle b, to thereby en sure that filter cartridge abuts the abutment and not a side wall of a filter hous ing cover, when pivoted.

Preferably, the bearing surface and the abutment are each provided by a ring be ing attached to the rear surface of the filter holder or are provided by a single ring being attached to said rear surface, to thereby enhance the possibility of flexing the filter holder against the end cap to enhance the force pressing the bearing surface against the end cap.

A filter cartridge for filtering a fluid, e.g. engine oil, may be configured to mate with a filter holder, preferably with the filter holder described above, and may comprises preferably at least a filter element with a fluid channel defining a lon gitudinal axis. Herein we assume, that when properly attached to each other, the filter cartridge's longitudinal axis and the filter holder's longitudinal axis match, but this is not necessary, however a preferred embodiment, as it eases rotation of the filter holder relative to the filter cartridge (where to two axes remain aligned). When pivoting the filter cartridge, as suggested above, the axes are as a matter of fact misaligned.

The invention is as well realized by the corresponding filter cartridge or more precisely by its front-end cap. The front-end cap has a front side and a rear side. The rear side is preferably sealingly attached to the front side of the filter ele ment. The front-end cap is configured to be releasably attached to a cover of a filter housing, e.g. via said filter holder. The front-end cap may have a bypass opening for enabling a bypass fluid flow. The bypass opening protects the filter from collapsing in case the pressure drop through the filter element is too high (e.g. due to an enhanced viscosity of the fluid or clogging of the filter medium).

In this case a pressure relief valve may open said optional bypass opening (e.g. at least a portion of the opening) enabling at least a portion of the fluid flow to by pass the filter element without damaging the filter element.

If the filter cartridge provides a space for receiving at least one protrusion of a tongue being inserted from the front side through the bypass opening, the filter holder may be attached to the front-end cap, by simply inserting its tongues with their protrusions into the opening until the tongues flex back outwards and the protrusions engage behind the rim.

The front-end cap's front side may have at least one bearing surface configured to mate with a corresponding bearing surface of a filter holder to form a plain bearing as explained above. In a preferred example, the bearing surface is a seal ing surface. The bearing surface, in particular if it is a sealing surface may sur round the rim and define a first radial distance ri between the sealing surface and the axis. Preferably, the bearing/sealing surface of the front-end cap is con figured to mate with a corresponding sealing surface of a filter holder, as ex- plained above. For example, the diameters of the two sealing surfaces could es sentially match, e.g. at least overlap.

Similarly, the front surface of the front-end cap preferably supports (and/or com prises) an abutment being positioned on the front surface at a second radial dis tance r ₂ from said axis, enabling to release the front-end cap and thus the filter cartridge by simply pivoting the front-end cap relative to the filter holder. The abutment is as well preferably configured to abut its corresponding counterpart of the filter holder, i.e. the filter holder's abutment.

If the rim is provided by a protrusion protruding obliquely out of the front sur face thereby defining a recess providing said space for receiving the tongue's protrusion, a safe and releasable snap in connection between is provided. In par ticular, the rim section of the front-end cap is reinforced without requiring addi tional material. A explained above, the second radial distance r ₂ is preferably greater or equal to the corresponding first radial distance ri, i.e. r ₂ ³ri, to thereby define reasonable lever arms and to protect the bearing surfaces from being potentially damaged.

If the bearing surface is inclined towards the longitudinal axis, the inclination eases connecting the filter cartridge to a filter holder. If the bearing surfaces are configured as sealing surfaces, sealing is enhanced as well, in particular if the fil ter holder and/or the front-end cap are bent e.g. to enhance a sealing force, i.e. the force with which sealing surfaces are pressed together.

Preferably, the bearing and/or sealing surface of the front-end cap is a section of a sphere having its center on the filter element's axis, to thereby provide a spherical bearing surface enabling to pivot the front-end cap relative to the filter holder until at least one of the abutments abuts its respective opposite part without damaging the sealing surface. In addition, one can better sense the pivot angle at which the tongues start to deflect to thereby release the front-end cap and thus the filter cartridge, i.e. the risk of potentially overstressing the tongues is reduced.

As well, the bearing surface and the abutment of the front-end cap may each be provided by at least one ring or preferably by a single ring. But different to the filter holder, the ring(s) of the front-end cap is(are) preferably attached to the front surface of the front-end cap, i.e. the ring(s) extend towards the filter holder(, if the filter holder is mounted to the front-end cap).

At least the filter holder can be attached to or be integrated in a filter housing cover for a filter system. If the filter holder is configured as a valve holder, the bypass valve is preferably attached to or integrated in a filter housing cover. The filter housing cover as well defines a longitudinal axis, which is preferably at least essentially identical (±10°, preferably less) to the filter holder's longitudinal axis. The filter housing cover has a tubular sidewall section for receiving at least a portion of filter cartridge, e.g. said front-end cap. The sidewall section has an open bottom end. The bottom end is preferably configured for being connected to a housing bottom, e.g. by providing a corresponding thread at its open end.

The filter housing cover further comprises a cap section closing the upper end of the tubular sidewall section and thus the top of the housing. Herein it is assumed that the filter housing cover's cap section faces upwards, but of course the filter housing could be rotated without changing the technical teaching of the applica tion. In this sense, the term "upwards" could be replaced by "a direction in space". In a preferred example of the invention, the cap section and the filter holder form a linear bearing enabling a longitudinal displacement of the filter holder and thus of the optional bypass valve as well as of a filter cartridge being con nected to the filter holder. The linear bearing prevents the filter holder to pivot relative to the housing cover's axis. At least said pivoting is limited to an angle a, wherein a is preferably small, e.g. a<2°, preferably a<1° or even smaller.

This longitudinal displacement enables to control an optional drain valve, which can e.g. be positioned in a bottom section of a filter housing. In other words, the valve holder is movably supported by (or relative to) the cap section enabling a movement parallel to the longitudinal axis between a retracted and an extended end position. In a preferred embodiment the valve holder is preloaded towards its extended end position to safely close the drain valve if the housing cover is closed.

If the cap section has a recess with a radially inwardly facing surface and the fil ter holder has a protrusion with a radially outwardly facing surface being in slid- ing contact with the radially inwardly facing surface of said cap section's recess, wherein the radially inwardly and radially outwardly facing surfaces each have at least one axially symmetric section, a linear bearing is provided that can be man ufactured and assembled with ease, i.e. with reduced costs.

Preferably, the radially inwardly surface being in sliding contact with the out wardly facing surface and the radially outwardly facing surface are radially sym- metric, thus enabling a filter cartridge being attached to the filter holder to ro tate relative to the housing cover. This simplifies mounting of the filter cartridge and of the housing cover to the housing bottom.

Of course, the filter housing cover can be completed to a filter system by a corre sponding filter housing bottom with a socket for receiving a conduit of the filter cartridge, as summarized in the introductory portion.

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 fluid filtering system with a filter cartridge being attached to a bypass filter holder.

Figure 2 shows a detail of Fig. 1.

Figure 3 shows a detail of the filtering system of Fig. 1 similar to Fig. 2, wherein the filter cartridge is pivoted relative to the filter holder. Figure 4 shows a further detail similar to Fig. 3.

Figure 5 shows a detail of a filter system being similar to the filter system as de picted in FIG. 1.

In figure 1 a filter holder 71 and a front-end cap 51 according to a preferred em bodiment of the invention are shown in their respective positions in an assembled filter system 1. The filter system 1 has a filter housing 10 comprising a housing bottom 12 and a removable housing cover 11. The housing bottom 12 has a socket for receiving a rear end cap 52 of a filter cartridge 50 with a filter el ement 56 in between of the front-end cap 51 and the rear end cap 52. The filter element 56 forms a fluid channel 561 with a longitudinal axis 2' (cf. FIG. 4, in FIG. 1 to FIG.2 axes 2 and 2' are identical) for collecting filtered fluid after having poured radially inward through the filter element 56. On the top of the filter ele ment 56, herein as well referred to as front-end of the filter element 56 is the front-end cap 51, to inhibit unfiltered fluid to ender the fluid channel 561. How ever, to protect the filter element 56 from collapsing, e.g. if the filter element 56 is partially blocked or if the viscosity is temporarily to high (as it is often the case for still cold engine oil just after startup of a combustion engine), the filter sys tem has a bypass valve 70, being a pressure relief valve for selectively enabling a fluid flow through a bypass opening of the front-end cap 51.

As can be seen best in FIG. 2, the bypass valve 70 is integrated in the filter holder 71, thus being a valve holder 71. In this example the filter holder 71 has a disc portion 719 covering the front-end cap 51, to avoid an uncontrolled bypass flow through the bypass opening. The bypass flow is controlled by the bypass valve 70 having a fluid inlet 73 which is simply an open end of a conduit 77 providing a valve seat 74 at its rear side. To ease terminology, herein, we refer to the side or face of the filter holder 71 having the fluid inlet as front side 711 and to its side having the valve seat 74 as rear side 712, but this in an arbitrary definition, being made only to simplify terminology by introducing a reference direction.

A valve member 79 may be spring loaded against the valve seat 74 by a valve spring 76. Once the pressure gradient between the valve inlet 73 and the fluid channel 561, which accommodates the rear portion of the valve member 79 ex ceeds a threshold being defined by the spring load, the valve member 79 is pushed rearwards and clears the outlet being defined by the valve seat 74, thereby enabling the fluid to bypass the filter element 56.

The valve member 79 may be supported by a valve member support 75 as de picted in Fig. 2. The valve member support 75 is attached to the filter holder 71. To this end, the filter holder 71 may provide an annular cavity being formed in between of the outer wall 771 of the valve conduit 77 and a support ring 78 en closing the valve conduit 77, as depicted. The support ring 78 provides a radial recess into which a corresponding protrusion of the valve member support 75 engages to thereby provide a form fitting connection absorbing the axial load provided by the valve spring 76.

The valve member support 75 has an abutment plate 751 extending essentially orthogonal (±10°or less) to the axis 2 and supporting the valve spring 76, being held in its axial position by an axially extending pin 752 on the valve seat facing surface of the abutment plate 751. A number of fingers 753 (at least two, prefer ably three or more) are connected to the abutment plate 751. The valve fingers 753 each have free distal ends that engage into said annular cavity being in be tween of the outer wall 771 of the valve conduit 77 and a support ring 78. At least a number of these fingers 753 has a recess extending radially outward to engage into the radial recess of the support ring 78. The inwardly facing surfaces essentially provide a linear bearing of the valve member 79 enabling the valve member to be retracted toward the abutment plate 751 in response to the pres sure gradient. If the bypass valve opens, the fluid may flow through slits being formed in between adjacent fingers 753.

To ensure the function of the bypass valve 70 a flow of bypass fluid entering the fluid channel 561 of the filter holder 71 has a disc portion being preferably seal- ingly coupled to the front-end cap 51. The coupling is removable, thereby enabling a simple replacement of used (and e.g. partially clogged) filter car tridges 50.

For coupling of the filter holder 71 to the front-end cap 51, the front-end cap 50 provides a rim 514 (see Fig. 3) enclosing and thus defining the bypass opening (into which the bypass valve 70 is partially inserted). As can be seen in Fig. 3, the rim 514 is provided by a protrusion protruding obliquely out of the front surface 511 of the filter holder's disc portion 719. Thus, the front-end cap 51 has a recess 515 extending essentially radially outward for receiving radial protrusions 251 of essentially axially (±30°, preferably ±20° or less, e.g. ±10°) extending tongues 25 thereby defining a recess 515 providing said space for receiving the tongues' pro trusions 251. When pushing the valve member 79 against the front-end cap 51, the tongues 25 flex inwards until the protrusions 251 engage behind the rim 514 and thereby secure the filter cartridge 50 to the filter holder 71, as depicted in Fig. l and FIG. 2.

The filter holder 71 provides a bearing surface 716 surrounding a disk por tion 719. The bearing surface 716 is advantageously and in this particular exam ple configured to seal the connection between the filter holder 71 and the front- end cap 51. In this example, the sealing surface 716 is positioned radially out wards, surrounding the bypass opening. A corresponding bearing and sealing sur face 516 is provided on the front side 511 of the front-end cap 51, i.e. the radii of the two sealing surfaces 516, 517 are at least essentially identical, i.e. the sealing surfaces 516, 517 contact each other as depicted e.g. in FIG. 2. The bearing sur face 716 of the filter holder 71 and bearing surface 516 of the front-end cap 51 form a plain bearing enabling a movement of the filter holder 71 relative to the front end cap 51 and thus relative to the filter cartridge 50.

In a preferred embodiment, a disk portion 719 of the filter holder 71 is elastically deformed to preload the bearing surfaces 516, 716 against each other, when the tongues 25 engage behind the rim 514. As can be seen in FIG. 3, the bearing sur faces 516, 716 preferably have a spherical shape, i.e. they are ring segments of a sphere. Thereby, the bearing surfaces 516, 716 can slightly slide relative to each other and aligning the filter cartridge 50 relative to the filter holder 71 is not cru cial. In other words, the bearing surface 716 of the filter holder 71 is preferably a section of a sphere having its center on the axis 2. Accordingly, the front-end cap's 51 bearing surface 516 is preferably a section of a sphere having its center on the axis 2 (more precisely axis 2', see FIG. 4), as well. In practice the two cen ters of the spheres should preferably at least essentially match.

As apparent in particular from FIG. 2 and FIG. 3 the bearing surfaces 516, 716 are surfaces of opposed rings 518, 718, i.e. the ring 518 is on the front side 511 of the front-end cap 51 and the ring 718 is on the rear side 712 of the filter holder 71 or more precisely on the rear side 712 of the filter holder's 71 disc portion 719.

To release the engagement of the filter holder 71 with the front-end cap 51, the housing cover 11 is removed from the housing bottom 12, thereby enabling ac cess to the free rear end cap 52 of the filter cartridge 50. By applying a radial force against the free rear end of the filter cartridge 50, the front-end cap 51 piv ots relative to the filter holder 71, until an abutment 717 or/of the filter holder 71 abuts its counterpart, i.e. the abutment 517 on the front side 511 of the front- end cap 51. In the preferred example, as shown in FIG. 2 and FIG. 3, the abut ments 517, 717 are surfaces of the respective rings 518, 718. When the two abutments 517, 717 contact each other the center of the pivotal movement is shifted from the center of the spheres to the point of contact of the two abut ments 517, 717 and it is sufficient to slightly increase the radial force the retract the tongues 25 out of the bypass opening, thereby releasing the filter car tridge 50 as depicted in Fig. 4. As apparent from FIG. 1 and FIG. 4, the filter housing cover 11 supports the filter holder 71. The filter housing cover 11 comprises a cap section 112 having a re ceptacle 111 for a bearing pin 713 of the filter holder 71. The receptacle 111 and the bearing pin 713, as well referred to as protrusion 713, provide a linear bear ing having essentially no play (preferably smaller 2°, even more preferred to less than 1°) with respect to tilting the angle of the filter holder's axis 2 relative to the housing cover's longitudinal axis 2 (in the figures the ideal situation of no tilt at all is depicted). The linear bearing enables a translation of the filter holder 71 rel ative to the cap section 112 parallel to the longitudinal axis 2 between a re tracted and an extended end position. A spring preloads the filter holder 71 to wards the open end of the housing cover 11 and thus towards the housing bot tom (when mounted as depicted in Fig. 1).

The cap section 112 has a recess 113, as well referred to as receptacle, with a ra dially inwardly facing surface 114. Accordingly the protrusion 713 -the bearing pin 713 - with its radially outwardly facing surface714 is in sliding contact with the radially inwardly facing surface 114 of said cap section's recess 113. The radi ally inwardly and radially outwardly facing surfaces 114, 714 each have at least one axially symmetric section, thereby forming the linear bearing.

Figure 5 shows a detail of another example filter system. The housing of the filter system can be the same as the housing as depicted in FIG. 1. The main difference between the filter system as depicted in FIG. 1 to FIG. 4 and the system of FIG. 5 is that the bypass valve 70 is not integrated in the filter holder 71. Instead, a by pass valve can be integrated elsewhere, e.g. in the housing, or it can even be omitted, depending on the application. The filter holder 71 of the example in FIG. 5 has a disc portion 719 covering the front-end cap 51 of the filter cartridge 50, to avoid an uncontrolled bypass flow through an opening in the front-end cap 51. Again the opening is defined by a rim 514. Thus, the filter cartridge 50 can be the same as in FIG. 1 and accordingly the same reference numerals are used. The filter cartridge 50 can be attached to the filter holder 71 essentially like depicted in Fig. 3, i.e. the rim 514, like in Fig. 3, may be provided by a protrusion protrud ing obliquely out of the front surface 511 of the filter holder's disc portion 719. Thus, the front-end cap 50 has a recess 515 extending essentially radially out ward for receiving a radial protrusion 251 of essentially axially (±30°, preferably ±20° or less, e.g. ±10°) extending tongues 25 thereby defining a recess 515 providing a space for receiving the tongues' protrusions 251. When pushing the filter holder 71 against the front-end cap 51, the tongues 25 flex inwards until the protrusions 251 engage behind the rim 514 and thereby secure the filter car tridge 50 to the filter holder 71.

Further, like in Fig. 3, the filter holder 71 provides a bearing surface 516, which is configured to seal the connection between the filter holder 71 and the front-end cap 51. In this example, the sealing surface 716 is as well positioned radially out wards, surrounding the central opening in the front-end cap 51. A corresponding bearing and sealing surface 516 is provided on the front side 511 of the front-end cap 51 and again the radii of the two sealing surfaces are at least essentially identical, i.e. the sealing surfaces contact each other as depicted.

The disk portion 719 may be elastically deformed thereby preloading the bearing surfaces 516, 716 against each other, when the tongues 25 engage behind the rim 514. Like in FIG. 3, the bearing surfaces 516, 716 preferably have a spherical shape, i.e. they are ring segments of a sphere. Thus, the bearing surface 716 of the filter holder 71 is preferably a section of a sphere having its center on the axis 2. Accordingly, the front-end cap's 51 bearing surface 516 is preferably a sec tion of a sphere having its center on the axis 2 (more precisely axis 2', see FIG. 4), as well. In practice the two centers of the spheres should preferably at least es sentially match. Mounting the filter cartridge 50 to the filter holder 71 and sub sequent unmounting can thus take place as already explained with respect to the example being depicted in FIG. 1 to FIG. 4. The filter holder 71 of Fig. 5 is attached to the housing in the same way as the fil ter holder 71 of FIG. 1 to FIG. 4, in this regard the corresponding description can thus as well be read on FIG. 5.

List of reference numerals

1 filter system

2 axis

2' axis of filter cartridge (see FIG. 4)

10 filter housing

11 cover

111 tubular sidewall section

112 cap section

113 receptacle/recess

114 radially inwardly facing surface,

12 bottom

25 tongue

251 protrusion of tongue

50 filter cartridge

51 front-end cap (upper end cap)

511 front surface

512 rear surface

514 rim

515 recess defining a space for a protrusion

516 bearing surface being optionally configured as sealing surface

517 abutment

518 ring on front surface 511

52 rear end cap (lower end cap)

56 filter element

561 fluid channel bypass valve

filter holder, in the FIGs optionally configured as valve holder front side of filter holder

rear side of filter holder

bearing pin / protrusion

radially outwardly facing surface of bearing pin 114

bearing surface of filter holder, being optionally configured as seal ing surface

abutment of filter holder

ring of filter holder

disc portion

fluid inlet / valve inlet

valve seat

valve member support

abutment plate

centering pin

finger

valve spring

valve conduit connecting the fluid inlet and the valve seat wall defining the valve conduit

support ring

valve member