Filter cartridge with improved filtration efficiency under conditions of use

Abstract

The invention relates to a filter cartridge (10) for a fluid filter device, comprising: a) a circumferential first filter element (12), which comprises a folded first filter medium (14), b) a circumferential second filter element (16), which comprises a folded second filter medium (18), c) a first bottom element (20) and a second bottom element (22), which are arranged in a manner so as to be able to be inserted into the first filter element (12), and d) a cover element (24) with a fluid outlet (26), the first filter element (12), the first base element (20) and the cover element (24) forming a first interior space (28), the second filter element (16) being arranged in the first interior space (28), and the second filter element (16) being arranged in the second interior space (28). The second filter element (16), the second base element (22) and the cover element (24) form a second interior (30), and wherein the filter insert (10) is designed to allow a fluid to be filtered to flow from the outside through the first filter element (12) into the first interior (28), and wherein the second filter element (16), the second base element (22) and the cover element (24) form a second interior (30). The fluid flows out of the first interior space (28) through the second filter element (16) into the second interior space (30) and out of the second interior space (30) through the fluid outlet (26), the quotient of the filter area of the first filter element (12) divided by the filter area of the second filter element (16) being greater than 1, the quotient of the filtration level of the first filter medium (14) divided by the filtration level of the second filter medium (18) is 1 or greater, and wherein the first filter medium (14) and the second filter medium (18) have a flexural stiffness of 2.5 N * mm2 or greater according to DIN 53864: 1978-08.

Description

Technical Field

[0001] The present invention relates to a filter element for a fluid filter device and a fluid filter device comprising a corresponding filter element. In addition, the invention discloses the use of the corresponding filter element or the fluid filter device in filtering fluid and an alternative filter unit. Background Art

[0002] In principle, there is a constant demand for high-performance fluid filters with favorable operating characteristics and high filtration efficiency in many branches of industry. Many of the improvements known from the prior art to these characteristics are achieved by selecting suitable materials and / or by improving the construction of the filter.

[0003] A technical field in which there is a particularly large demand for high-performance filters is the field of vehicle technology, in which corresponding fluid filter devices are used, in particular for filtering fuels, such as gasoline or diesel. In addition to separating particulate impurities, the fluid filter devices used here also have to perform other tasks in many cases, such as separating liquid impurities. Corresponding fluid filter devices for filtering fuels are known to those skilled in the art and are disclosed, for example, in US Pat. No. 6,328,883 B1, US Pat. No. 8,034,240 B2 or US Pat. No. 5,643,446 A.

[0004] The performance of modern fluid filters or their filter elements in terms of separation and other properties is currently often determined under controlled test conditions using mostly standardized test methods with relatively static environmental conditions. Many fluid filters known from the prior art for fuels show favorable properties under these "laboratory conditions".

[0005] However, in practice, that is to say, especially during subsequent use in a vehicle, it has been found in many cases that the filter characteristics during driving operation are not sufficient to meet the requirements for reliable operation set by the vehicle manufacturers. In the past, in order to compensate for this observed problem, the focus of development was usually on further improving the initial filter characteristics under laboratory conditions, but nowadays the focus of development is increasingly directed to increasing the stability of the fluid filter device with respect to the loads occurring during use instead, so that the initial filter characteristics should be reduced as little as possible due to the loads occurring during operation.

[0006] According to the inventor's estimation, the main loads to which the fuel filter is subjected under conditions of use in a vehicle, in particular a commercial vehicle, include in particular mechanical vibrations of the fluid filter device, which are caused, for example, by driving on a roadway or by the operation of a motor, and fluctuations in the fluid flow flowing through the fluid filter device, which are caused, for example, by starting and shutting down the motor or by changes in the supply of driving fuel to the motor. According to the inventor's estimation, most of the fluid filter devices known from the prior art are not sufficiently robust with respect to these loads occurring under conditions of use in a vehicle, so that the filtration efficiency under the conditions of use is assessed as insufficient. Summary of the invention

[0007] The main task of the present invention is to eliminate or at least alleviate the above-mentioned disadvantages of the prior art.

[0008] The object of the present invention is, in particular, to provide a filter element and an associated fluid filter device, in particular for fuel filtering, which under typical conditions of use in a vehicle exhibit an improved filtration efficiency compared to the prior art, wherein in particular the stability of the fluid filter device with respect to mechanical vibrations and fluctuations in the fluid flow should be increased.

[0009] Another object of the present invention is to provide a fluid filter device which also has excellent initial filtering properties.

[0010] Furthermore, a supplementary object of the present invention is to provide a fluid filter device which can be designed in such a way that water can be reliably separated even under typical conditions of use in vehicles.

[0011] The inventors of the present invention have now realized that the above-mentioned task can be surprisingly achieved if a first filter element is combined with a (preferably shorter) second filter element arranged in the interior in a fluid filter device, as long as the folded filter medium used accordingly has a certain minimum bending stiffness and is implemented in terms of the filtration grade so that the filter medium of the inner filter has at least the same filtration grade as the filter medium of the outer filter, as defined in the claims.

[0012] This surprisingly results in an advantageous filter element and a corresponding fluid filter device which, under typical conditions of use in a vehicle, exhibit an improved filtration efficiency compared to the prior art, wherein the filtration efficiency under typical conditions of use surprisingly differs only slightly from the filtration efficiency in a standard test on a laboratory test bench according to the current standard specification ISO 19438. Without wishing to be bound by this theory, the inventors assume that the sequential arrangement of the two filter elements in combination with the higher bending stiffness of the multiply folded filter medium contributes to particularly advantageous properties under typical conditions of use, in particular under mechanical vibrations and fluctuating fluid flows, and in this respect complements in a particularly advantageous manner the flow characteristics of the fluid which are determined by the reduced filter area of ​​the second inner filter element which has an at least equally good filtration rating. Without wishing to be bound by this theory, the inventors assume that the folded filter medium provides better damping of mechanical vibrations and fluctuating fluid flows due to the increased bending stiffness, wherein in a preferred embodiment, the fluid chambers created by the shortened inner filter element contribute in an advantageous manner to compensating for load peaks which otherwise could adversely affect the filtration efficiency under typical conditions of use.

[0013] Therefore, the above-mentioned object is achieved by the technical solution of the present invention, as defined in the claims. Preferred embodiments of the present invention are derived from the dependent claims and the following embodiments.

[0014] These embodiments, which are referred to below as preferred, are combined in particularly preferred embodiments with features of other embodiments, which are referred to below as preferred. Therefore, very particularly preferred is a combination of two or more embodiments, which are referred to below as particularly preferred. Also preferred are embodiments in which features of one embodiment, which are referred to as preferred to any extent, are combined with one or more other features, which are referred to as preferred to any extent, of other embodiments. The features of preferred fluid filter devices, applications and filter units are derived from the features of preferred filter elements.

[0015] The present invention particularly relates to a filter element for a fluid filter device, preferably a fuel filter, the filter element comprising:

[0016] a) a surrounding first filter element comprising a pleated first filter medium,

[0017] b) a surrounding second filter element comprising a pleated second filter medium,

[0018] c) a first bottom element and a second bottom element, and

[0019] d) a cover element with a fluid outlet,

[0020] wherein the first filter element, the first bottom element and the cover element form a first interior space, wherein the second filter element is arranged in the first interior space and the second filter element, the second bottom element and the cover element form a second interior space,

[0021] The filter element is designed to allow the fluid to be filtered to flow from the outside through the first filter element into the first internal space, from the first internal space through the second filter element into the second internal space, and from the second internal space to flow outward through the fluid outlet.

[0022] wherein the quotient of the available filter area of ​​the first filter element divided by the available filter area of ​​the second filter element is greater than 1, wherein the quotient of the filter grade of the first filter medium divided by the filter grade of the second filter medium is 1 or greater, wherein the filter grade is a filter grade determined for total separation according to ISO 19438:2003-11, and

[0023] The first filter medium and the second filter medium have a filter capacity of 2.5 N*mm according to DIN 53864:1978-08. 2 or greater bending stiffness.

[0024] The filter element according to the invention is provided for use in a fluid filter device, in particular in a fuel filter. The filter element can be fixedly connected to the housing within the scope of a so-called spin-on filter. However, the filter element according to the invention is preferred, wherein the filter element is a replaceable filter element, which can be arranged in a filter housing of the fluid filter device according to the invention, for example, in a reversible and non-destructively replaceable manner. The filter element according to the invention can be a pre-filter element or a main filter element, wherein the absolute value of the filter grade varies between these designs, since higher values ​​of the filter grade are usually used for pre-filters as well.

[0025] According to the understanding of the person skilled in the art, the filter element according to the invention is described based on a structure that is usually at least largely rotationally symmetrical about an axial direction, which in the context of the invention usually extends between the cover element and the first bottom element and preferably usually coincides with the longitudinal direction of the filter element, so that the filter element is constructed circumferentially around the axial direction. In addition, for the description of the filter element according to the invention, radial directions orthogonal to the axial direction are also used, despite possible deviations from the ideal rotationally symmetrical structure.

[0026] Whenever the volume of the first interior space or the volume of the second interior space is involved within the scope of the present invention, the entire volume of the respective interior space is thus respectively referred to, each of which is formed by the respective filter element, the cover element and the associated bottom element, wherein possible openings in the elements, for example outlet openings in the cover element or openings for conducting water out of the first interior area are ignored, so that when determining the volume of the interior space, the surface surrounding the opening is virtually extended beyond the opening. This means that the volume of the interior space is not a volume difference and correspondingly the volume of possible components arranged in the respective interior space is not subtracted. This means in particular that the volume of the first interior space is not reduced by the second filter element arranged in the first interior space or by the second interior space surrounded by the second filter element.

[0027] Similar to the filter elements known from the prior art, the filter element according to the invention first comprises a surrounding first filter element, which is bounded at the upper end by a cover element with a fluid outlet and at the opposite end by a first bottom element. The surrounding first filter element, the cover element and the bottom element form a first interior space. This filter element from the prior art is designed to allow the fluid to be filtered to flow from the outside through the first filter element into the first interior space and to flow out of the first interior space through the fluid outlet to the outside.

[0028] According to the understanding of a person skilled in the art, the first interior space does not have to be absolutely completely surrounded by these components, so that a fluid outlet can be present in the cover element or a possible opening can be present in the bottom element, which is used, for example, to discharge water from the first interior space. At least in theory, it is conceivable, for example, that the opening in the bottom element is formed so that it substantially corresponds to the cross section of the first interior space, so that the first bottom element substantially only serves to surround the first filter element and the first interior space is substantially not delimited by the first bottom element.

[0029] Unlike most conventional structures of the prior art, a second filter stage is provided in the filter element according to the invention. For this purpose, a surrounding second filter element is provided, which is arranged inside the first interior space. The second filter element, together with a cover element arranged at one end and a second bottom element arranged at the opposite end, forms a second interior space, which is also located inside the first interior space accordingly.

[0030] It is understood by those skilled in the art that in practice, the filter area available for filtering of the second filter element is reduced due to the smaller radius of the second filter element located inside, so that the above-mentioned limitation on the filter area is usually already met for structural reasons. However, the inventors believe that a corresponding gradient between the filter elements is very particularly advantageous, so it is preferred to set a larger gradient in this regard. Due to the importance of the inflow area available for fluid penetration, the filter element according to the invention is particularly preferred as follows, wherein the quotient of the available filter area of ​​the first filter element divided by the available filter area of ​​the second filter element is 1.5 or more, preferably 3.0 or more, and particularly preferably 4.5 or more.

[0031] It is understood by those skilled in the art that the above-defined arrangement of the filter element (i.e., the fluid to be filtered can flow from the outside through the first filter element into the first interior space, from the first interior space through the second filter element into the second interior space, and from the second interior space outwardly through the fluid outlet) means in the design of those skilled in the art that the fluid to be filtered cannot flow into the second interior space in a manner passing by the second filter element (i.e., cannot bypass the second filter stage) and / or flow outwardly through the fluid outlet. This is achieved structurally, for example, by the second bottom element being configured without a through-hole and the resulting composite structure consisting of the second filter element and the second bottom element being arranged on the fluid outlet so that the fluid outlet is completely covered.

[0032] In the filter element according to the invention, the first filter element and the second filter element are each a surrounding filter element, which can be achieved in particular by a hollow cylindrical basic shape, wherein, however, a polygonal base is also conceivable, wherein, in view of the configuration of the surrounding filter element formed by the folded filter medium, the boundaries are smooth in any case. With regard to the volume of the interior space, in addition or alternatively, a filter element according to the invention is also preferred, wherein the volume of the second interior space is 0.6*V 1 or less, preferably 0.5*V 1 or less, particularly preferably 0.4*V 1 or less, where V 1 is the volume of the first interior space.

[0033] The filter elements each comprise a filter medium which is used in a folded manner. Filter media and their use in the form of a folded structure (which is also partly referred to as a so-called bellows by a person skilled in the art) are widely familiar to a person skilled in the art in the field of filtering technology. Synthetic media are of particular interest for the filter media used according to the invention, wherein these synthetic media can also be at least partially combined with natural materials (e.g. cellulose fibers). According to the inventor's estimation, a filter element according to the invention is preferred, wherein the first filter medium and / or the second filter medium, preferably both filter media, are at least partially, preferably predominantly, particularly preferably substantially completely made of a thermoplastic selected from the group consisting of polyolefins, polyamides, polyurethanes, polycarbonates and polyesters, preferably selected from the group consisting of polyolefins and polyesters, particularly preferably selected from the group consisting of polyesters.

[0034] The first surrounding filter element can be obtained from such a filter medium, for example, by folding a flat filter medium into a sawtooth shape, when the ends of the resulting sawtooth structure are placed on top of each other and connected to each other so as to obtain a cylindrical surrounding filter element, the wall of which is formed by the folded filter medium. With regard to simple production and favorable filtration efficiency, a filter element according to the invention is preferred, wherein the first filter medium is a folding group arranged in a surrounding manner, wherein the first filter medium includes a plurality of folds of essentially the same shape, and / or the second filter medium is a folding group arranged in a surrounding manner, wherein the second filter medium includes a plurality of folds of essentially the same shape, wherein the number of folds is preferably different between the first filter medium and the second filter medium.

[0035] The person skilled in the art will appreciate that the filter element according to the invention is very flexible in terms of the design of the individual components, as long as the design does not conflict with the above-mentioned interrelationships. Thus, for example, the cover element or the bottom element can be designed in multiple parts or the outlet opening can be composed of multiple holes instead of providing only one outlet opening.

[0036] As described above, the filter element according to the present invention is a filter element having two filter stages arranged in sequence, which are composed of a first filter element and a second filter element. Within the scope of the present invention, the names of the components, such as the fluid outlet, and the functional connection of the components due to the limitation of the flowability follow the common running direction that is meaningfully expected in practice. In the common running direction, the fluid to be filtered, such as fuel, flows from the outside through the first filter element into the first inner space, flows from the first inner space through the second filter element into the second inner space, and then flows outward from the second inner space through the fluid outlet. However, it is understood by those skilled in the art that the corresponding filter element according to the present invention can also be operated in a reverse flow direction at least in theory, so that the fluid to be filtered can be guided into the second inner space through the fluid outlet, guided into the first inner space through the second filter element, and guided outward from the first inner space through the first filter element. However, since the corresponding use would hardly have practical relevance, this possibility is not further elaborated below. In this regard, the inventors have not checked whether the advantageous technical effects of the filter element according to the invention would also be manifested in such a technically less meaningful use. In fact, the inventors rather believe that for this purpose at least the relationship between the filter grade and the filter area defined above or other relationships between the filter elements must be inverted accordingly, so that in the resulting, alternative and not inventive design, for example, the inner filter element would have to be designed longer in order to achieve a larger filter area despite the internal arrangement.

[0037] In practice, filter element is just in relatively simple structural design scheme in many cases completely made of filter medium.But also can be imagined that, in addition to filter medium, also be provided with other elements for example for water separation in filter element, as disclosed below.In addition, filter element can also be implemented in multi-piece mode including frame element or similar element and at least in theory, for example, be implemented as the half shell of connection, even if one-piece embodiment is particularly preferred.Those skilled in the art understand without restriction in this regard, in the described design scheme, for the described filter element, the filter medium in the center is suitable for correspondingly extending on the whole length and the whole periphery of filter element.For basically all embodiments, filter core according to the present invention is correspondingly preferred, wherein, the first filter medium extends on the whole length of the first filter element in the axial direction, and / or the second filter medium extends on the whole length of the second filter element in the axial direction.For basically all embodiments, additionally or alternatively, filter core according to the present invention is also correspondingly preferred as follows, wherein, the first filter medium extends on the whole periphery of the first filter element, and / or the second filter medium extends on the whole periphery of the second filter element. Particularly preferred are filter inserts according to the invention in which the first filter element is formed from a first filter medium and / or the second filter element is formed from a second filter medium.

[0038] From the point of view of manufacturing technology, it is preferred that the filter elements have a certain distance from each other in the radial direction. However, the inventors have found in this regard that the adjustment of the corresponding intermediate area, that is to say the adjustment of the part of the first inner space between the first filter element and the second filter element, is also advantageous with regard to the stability of the filter characteristics under the conditions of use. The filter element according to the invention is preferred as follows, wherein the first filter element and the second filter element are spaced apart from each other in the radial direction so that the first inner space includes an intermediate area arranged between the first filter element and the second filter element, wherein the intermediate distance is in the range of 3 mm to 20 mm, preferably in the range of 5 mm to 10 mm.

[0039] The bottom element can advantageously be designed very flexibly, wherein, according to the inventor's estimation, a flat, plate-shaped bottom element is preferred. A filter element according to the invention is preferred in which the first bottom element and / or the second bottom element, preferably the first bottom element and the second bottom element, are flat end disks, preferably round end disks, which are connected to the first filter element or the second filter element. In particular, in the case of filter elements of substantially the same length, the first bottom element and the second bottom element can be formed from the same components, so that the first bottom element and the second bottom element are formed from the overall bottom element.

[0040] The filter element according to the present invention is preferred as follows, wherein the cover element is directly connected to the first filter element and the second filter element, i.e., for example, without other frame structures or support structures. The cover element can be implemented in a multi-piece manner, for example, by two cover parts to be screwed to each other, but preferably in a one-piece manner. In particular, due to the simple design, the filter element according to the present invention is preferred as follows, wherein the cover element is a circular end plate, in which the fluid outlet is basically arranged in the center. The cover element can have a macroscopic structure on the side pointing in the direction of the filter element, so that the cover element can, for example, partially extend into the first inner space, whereby, for example, the second filter element is placed in the first inner space more downwardly relative to the first filter element and can be said to be slightly more deeply immersed in the first inner space. However, it is particularly preferred according to the inventor's estimate that the cover element is configured to be flat or flat to a large extent on the side pointing in the direction of the filter element, so that each filter element connected to the cover element is basically located at the same height. In particular, when shortened inner filter elements are used, due to this arrangement, a chamber area is generated by the difference in length of the filter elements, which is described further below and, according to the inventor's estimation, achieves a particularly advantageous filtration efficiency under typical conditions of use. The filter element according to the invention is accordingly preferred as follows, wherein the end of the first filter element pointing in the direction of the cover element and the end of the second filter element pointing in the direction of the cover element are spaced apart by 0.05*L in the axial direction. 1 or smaller, preferably 0.02*L apart 1 or smaller, particularly preferably 0.01*L apart 1 or smaller, where L 1 is the length of the first filter element along the axial direction.

[0041] In particular, when the ends of filter elements of different lengths pointing in the direction of the cover element are arranged substantially at the same height, a free space is obtained in the first interior space between the two bottom elements in the preferred filter element according to the invention, which free space is referred to as a chamber area within the scope of the invention, wherein such a chamber area can also be obtained by an offset arrangement structure when the filter elements are of the same length. According to the inventor's estimation, the design of the filter element according to the invention with such a chamber area is particularly advantageous for achieving particularly advantageous filtration efficiencies under typical conditions of use, especially when using shorter filter elements located in the interior. Therefore, a filter element according to the invention is preferred, in which the first bottom element and the second bottom element are spaced apart from each other in the axial direction, so that the first interior space includes the chamber area arranged between the first bottom element and the second bottom element. In this regard, a filter element according to the invention is preferred, in which the volume share of the chamber area at the first interior space is 10% or more, preferably 12.5% ​​or more, particularly preferably 15% or more.

[0042] In order to achieve a favorable stability with respect to loads under typical conditions of use, the filter element according to the invention combines the concept of two-stage filtration (or the resulting difference in available filter area between the filter elements) with requirements regarding the absolute flexural rigidity of the filter material used and regulations regarding its filtration grade.

[0043] The inventors have recognized that, in particular for both filter media, a certain minimum bending stiffness must be set in order to achieve an excellent filter efficiency even under loads typical of use conditions in vehicles. The bending stiffness of the filter media is determined in accordance with DIN 53864:1978-08, wherein the bending stiffness is determined within the scope of the invention at a bending angle of 5°. If the bending stiffness of the folded filter medium is determined, it is determined by bending parallel to the folding direction (that is to say usually the axial direction in the filter element) in order to neglect any influence of the folding on the bending stiffness.

[0044] According to the inventors' estimates, the minimum bending stiffness required here exceeds the typical bending stiffness known for filter media typically used in the prior art. The inventors have found that particularly flexurally rigid filter media generally achieve particularly advantageous filter properties under typical conditions of use. Therefore, a filter element according to the invention is first preferred, wherein the first filter medium has a bending stiffness of 4.0 N*mm 2 or greater, preferably 5.5N*mm 2 or greater, particularly preferably 7.0 N*mm 2 or greater, very particularly preferably 10.0 N*mm 2 or greater, most preferably 13.0N*mm2 or greater, particularly preferably 16.0 N*mm 2 In addition or alternatively, the filter element according to the invention is also similarly preferred, wherein the second filter medium has a bending stiffness of 4.0 N*mm 2 or greater, preferably 5.5N*mm 2 or greater, particularly preferably 7.0 N*mm 2 or greater, very particularly preferably 10.0 N*mm 2 or greater, most preferably 13.0N*mm 2 or greater, particularly preferably 16.0 N*mm 2 or greater bending stiffness.

[0045] In their own tests, the inventors have determined that in some filter designs very high bending stiffness can lead to less favorable filter properties. Against this background, a filter element according to the invention is preferred in which the first filter medium has a bending stiffness of 2.5 N*mm 2 Up to 34.0N*mm 2 In the range of 3.0N*mm 2 Up to 32.0N*mm 2 In the range of 3.5 N*mm 2 Up to 28.0N*mm 2 In the range of 4.0 N*mm 2 Up to 24.0N*mm 2 The following filter element according to the invention is also preferred, wherein the second filter medium has a bending stiffness in the range of 2.5 N*mm 2 Up to 34.0N*mm 2 In the range of 3.0N*mm 2 Up to 32.0N*mm 2 In the range of 3.5 N*mm 2 Up to 28.0N*mm 2 In the range of 4.0 N*mm 2 Up to 24.0N*mm 2 flexural stiffness within the range of.

[0046] It is understood by those skilled in the art that the bending stiffness of the filter medium relates to the effective bending stiffness of the entire filter medium. In the case of using a composite material made of two or more different materials, the effective composite bending stiffness of the actual filter medium should be determined accordingly and should not be based on the bending stiffness of the pure material. For specific applications, for example, the filter element according to the present invention is preferred, wherein the first filter medium and / or the second filter medium is a composite material, preferably a composite material made of plastic and inorganic fiber material (such as carbon fiber or glass fiber, preferably glass fiber). For example, it is also conceivable that the filter element according to the present invention is a composite material made of plastic and metal, such as a composite material made of a fabric-type planar structure and a metal grid structure. In addition or alternatively, the minimum bending stiffness of the filter medium can also be obtained by a macroscopic structured portion, which is not a folded portion, for example, by providing a so-called groove portion, wherein the groove preferably extends substantially transversely to the folding direction of the filter element.

[0047] The inventors consider it particularly advantageous to also set a gradient between the bending stiffnesses of the filter media used. In this regard, according to the inventors' estimation, particularly advantageous efficiency characteristics result with a filter element according to the invention in which the bending stiffness of the first filter medium is at least equal to the bending stiffness of the second filter medium, wherein the bending stiffness of the first filter medium should preferably be selected to be greater, thereby enabling not only excellent filter characteristics under mechanical loads but also greater flexibility in the design of the second filter medium. A filter element according to the invention is preferred, in which the quotient of the bending stiffness of the first filter medium divided by the bending stiffness of the second filter medium is 1 or greater, wherein the quotient of the bending stiffness of the first filter medium divided by the bending stiffness of the second filter medium is preferably greater than 1. A filter element according to the invention is preferred, in which the quotient of the bending stiffness of the first filter medium divided by the bending stiffness of the second filter medium is 1.1 or greater, preferably 1.2 or greater, particularly preferably 1.5 or greater. Additionally or alternatively, the filter element according to the invention is preferred, wherein the quotient of the bending stiffness of the first filter medium divided by the bending stiffness of the second filter medium is 10 or less, preferably 5 or less, particularly preferably 2.5 or less. Additionally or alternatively, the filter element according to the invention is particularly preferred, wherein the quotient of the bending stiffness of the first filter medium divided by the bending stiffness of the second filter medium is in the range of 1.05 to 10, preferably in the range of 1.15 to 5, particularly preferably in the range of 1.25 to 2.5.

[0048] Another feature that the inventors have identified as being important for achieving a high filtration efficiency under the conditions of use is the filter grade of the filter media used or their ratio relative to one another. According to the understanding of a person skilled in the art, the expression "filter grade" within the scope of the present invention refers to a filter grade according to ISO 19438:2003-11, corresponding to the "filter rating" (see point 3.5 of ISO 19438:2003-11), which specifies the "filter grade" at different degrees of segregation (e.g. 90%, 95% or 99%), and which is determined according to the provisions of ISO 19438:2003-11 according to the total degree of segregation (corresponding to the "cumulative overall efficiency") and specifies for which particle size the corresponding total degree of segregation is achieved. In order to assess the requirement of whether the quotient of the filtration grade of the first filter medium divided by the filtration grade of the second filter medium is 1 or more, the person skilled in the art can in practice select as a reference point a degree of segregation which enables a favorable resolution and correspondingly produces clearly distinguishable filtration grades, since filter media with better filtration grades are generally better at all degrees of segregation. However, in cases of doubt, in particular in the case of assessing whether a specific quotient of filtration grades is achieved, according to the manner of the person skilled in the art, a reference filtration grade according to ISO 19438:2003-11, corresponding to a "reference filtration grade (filter reference rating)" (see point 3.6 of ISO 19438:2003-11), is considered, which specifies a "filtration grade" at a degree of segregation of 99%.

[0049] The inventors have realized that the filtration grade of the second filter medium should be selected to be at least not higher than the filtration grade of the first filter medium, that is, worse, and relatively, it is preferred that the filtration grade of the second filter medium is selected to be lower. Accordingly, the filter element according to the present invention is preferred as follows, wherein the quotient of the filtration grade of the first filter medium divided by the filtration grade of the second filter medium is 1.01 or greater, preferably 1.02 or greater, and particularly preferably 1.05 or greater.

[0050] Therefore, a filter element according to the invention, in particular a main filter element, is firstly preferred in which the first filter medium has a filtration grade of 5.0 μm (c) or less, preferably 4.0 μm (c) or less, particularly preferably 3.0 μm (c) or less, and / or in which the second filter medium has a filtration grade of 5.0 μm (c) or less, preferably 4.0 μm (c) or less, particularly preferably 3.0 μm (c) or less. For the prefilter element, a value for the filtration grade is expediently set which is higher by a factor of 10.

[0051] According to the inventor's estimation, additional improvement of the filtration efficiency can be achieved under typical use conditions by the length difference between the filter elements. Without wishing to be bound by the theory, the inventor believes that the difference in the enhancement of the area available for penetration of the filter medium in each filter stage and the additional reduction of the penetration area in the second filter stage resulting therefrom are advantageous in order to compensate for the loads occurring in the case of fluid flow fluctuations. Here, according to the inventor's estimation, a larger length difference works in principle advantageously. Therefore, according to the inventor's estimation, preferably, the length difference between the filter elements can also be set, because this (in addition to the effect of different radii and, if necessary, different folds) not only reflects a larger minimum difference in the available penetration area of ​​the filter medium, but also reflects the structural dimensions, i.e., the fluid flow is at least partially deflected on the path from the first filter element to the second filter element, wherein, in particular, the configuration of the chamber area is considered to be particularly advantageous. Therefore, the filter element according to the invention is firstly preferred as follows, wherein the first filter element is 10% or more, preferably 15% or more, particularly preferably 20% or more longer than the second filter element in the axial direction. However, since the throughput may be adversely affected, especially in the case of very small second filter elements, the inventors propose to select the length difference within a specific range. In this regard, additionally or alternatively, the filter element according to the invention is preferred, wherein the first filter element L 1 The length along the axial direction is 1.1*L 2 Up to 2.5*L 2 In the range of 1.2*L 2 Up to 2.0*L 2 In the range of 1.3*L 2 Up to 1.7*L 2 In the range of 2 is the length of the second filter element along the axial direction.

[0052] In the embodiment of the filter element with shortened interior, with regard to the distance between the bottom elements delimiting the respective filter element, the filter element according to the invention is preferably as follows, wherein the distance between the first bottom element and the second bottom element in the axial direction is 0.1*L 1 Up to 0.6*L 1 In the range of 0.2*L 1 Up to 0.5*L 1 In the range of 0.25*L 1 Up to 0.45*L 1 In the range of 1 is the length of the first filter element along the axial direction.

[0053] In a particularly preferred embodiment, the filter element according to the invention can be combined with a multi-stage water separation in an efficient manner. The corresponding concepts for multi-stage water separation in fuel filters and the materials used therein are known to the person skilled in the art based on their professional knowledge and can be advantageously integrated into the filter element according to the invention without any loss in separation efficiency.

[0054] Regarding the first stage of water separation, the following filter element according to the present invention is preferred, wherein the first filter element includes a surrounding coalescing agent layer for making liquid impurities dispersed in the fluid, in particular water droplets condensed (this is sometimes also referred to as condensation by those skilled in the art), permeable to the fluid, wherein, preferably, the coalescing agent layer is arranged on the side of the first filter element facing the first internal space, wherein the coalescing agent layer particularly preferably extends in an axial direction over the entire length of the first filter element, and the first bottom element includes a water outlet opening for conducting the coalesced liquid impurities out of the first internal space, wherein the water outlet opening is preferably arranged in the center of the first bottom element.

[0055] In this context, a filter element according to the invention is particularly preferred in which the coalescing agent layer is arranged on the surface of the first filter medium, wherein the coalescing agent layer is preferably folded or wound, particularly preferably folded complementary to the first filter medium. Additionally or alternatively, a filter element according to the invention is particularly preferred in which the coalescing agent layer comprises one or more materials selected from the group consisting of open-pored nonwoven materials, in particular open-pored nonwoven materials made of synthetic fibers.

[0056] When using such a circumferential coalescing agent layer, a filter insert according to the invention is very particularly preferred in which the first filter element is formed from the coalescing agent layer and the folded first filter medium.

[0057] With regard to the first stage of water separation, a filter element according to the invention is preferred in which the second filter element comprises a fluid-permeable, circumferential separation layer for separating liquid impurities, in particular water droplets, present in the fluid, wherein the separation layer is preferably arranged on a side of the second filter element facing the first interior space, wherein the separation layer particularly preferably extends in an axial direction over the entire length of the second filter element.

[0058] In this context, a filter element according to the invention is particularly preferred in that the separation layer is designed as a sieve-shaped layer, which preferably has an average opening diameter in the range of 10 μm to 200 μm, preferably in the range of 12 μm to 150 μm, particularly preferably in the range of 15 μm to 110 μm. Additionally or alternatively, a filter element according to the invention is particularly preferred in that the separation layer comprises one or more hydrophobic materials, wherein the separation layer is preferably made of a hydrophobic material or coated with a hydrophobic material, for example with polytetrafluoroethylene or the like. Additionally or alternatively, a filter element according to the invention is also particularly preferred in that the separation layer is arranged on the surface of a second filter medium, wherein the separation layer is preferably folded, particularly preferably folded complementary to the second filter medium.

[0059] When using such a circumferential separating layer, a filter insert according to the invention is very particularly preferred in which the first filter element is formed from the separating layer and the folded second filter medium.

[0060] The inventors propose that the filter elements as main filter elements should be designed to achieve an overall favorable filtration efficiency, so that they achieve a certain minimum degree of segregation in undisturbed operation. In this regard, filter elements according to the invention are preferred, wherein the filter elements have a degree of segregation of 99.3% or more, preferably 99.5% or more, particularly preferably 99.7% or more, very particularly preferably 99.9% or more for particles with a particle size of ≥4 μm in a standard test according to ISO 19438:2003-11, i.e. in vibration-free operation with a continuous fluid flow, i.e. without vibrations and fluctuations and with virtually no external mechanical load, wherein the degree of segregation is preferably the total degree of segregation determined according to ISO 19438:2003-11 for a particle size of ≥4 μm (corresponding to the "cumulative total efficiency"). For pre-filter elements, the above statements apply accordingly to the total degree of segregation for a particle size of ≥10 μm.

[0061] Furthermore, for the main filter element, the inventors have succeeded in defining the following criteria, by means of which high performance can be ensured under typical conditions of use, in particular in trucks, wherein the filter element according to the invention can advantageously be designed in a targeted manner so as to meet these criteria. Taking into account the mechanical loads occurring under typical conditions of use, the following filter element according to the invention is preferred, wherein the filter element, when filtering under vibration, preferably when vibrating at a frequency in the range of 20 Hz to 2000 Hz and at an acceleration in the range of 2 G to 7 G, has a segregation of 98% or more, preferably 99% or more, particularly preferably 99.5% or more, very particularly preferably 99.9% or more for particles with a particle size of 4 μm, wherein the segregation is the total segregation determined in accordance with ISO 19438:2003-11 for particles with a particle size ≥ 4 μm, the total segregation being calculated with diesel fuel under vibration. As the test fluid, the filter element has a separation degree of 98% or more, preferably 99% or more, particularly preferably 99.5% or more, very particularly preferably 99.9% for particles with a particle size of 4 μm when filtering a fluctuating volume flow, preferably when filtering a volume flow that fluctuates with an intensity of ±10% or more (particularly preferably ±20% or more), very particularly preferably a volume flow that fluctuates by 95% or more, wherein the separation degree is the total separation degree for particles with a particle size of ≥4 μm determined in accordance with ISO 19438:2003-11, the total segregation degree being determined taking into account the fluctuations with diesel as the test fluid. For the prefilter element, the above statements apply accordingly to the total separation degree for particles with a particle size of ≥10 μm.

[0062] The present invention also relates to a fluid filtering device for filtering a fluid, in particular a pre-filter or a main filter, comprising:

[0063] i) a filter housing, and

[0064] ii) A filter element according to the invention arranged in a filter housing.

[0065] Also disclosed is the use of a filter element according to the invention or a fluid filtering device according to the invention in filtering fluids, in particular in the operation of a vehicle, in order to improve the constancy of the filtering efficiency under the influence of conditions common to vehicles, in particular under the influence of vibrating and / or fluctuating volume flow rates of the fluid, in particular dynamically fluctuating volume flow rates.

[0066] The corresponding application is preferred, in which the fluid is a propulsion fuel, in particular diesel. The corresponding application is preferred, in which the vehicle is a commercial vehicle, in particular a truck.

[0067] The inventors consider that the filter elements according to the invention with folded filter media as disclosed above are particularly important in view of practical relevance, especially because the effect of the invention is particularly clearly demonstrated in these cases. However, the inventors propose that by setting the above-mentioned filter area difference, bending stiffness and filtration grade, an advantageous insert for a fuel filter can still be obtained even without or only partially with a folded filter medium. Accordingly, in connection with the present invention, the following insert for a fuel filter is also disclosed, which, in order to distinguish it from the filter element according to the present invention, is referred to as a filter unit. The preferred features disclosed above for the filter element according to the present invention apply accordingly to these disclosed filter units. Therefore, a filter unit for a fluid filtering device is disclosed, which comprises:

[0068] a) a surrounding first filter element comprising a first filter medium,

[0069] b) a surrounding second filter element comprising a second filter medium,

[0070] c) a first bottom element and a second bottom element, and

[0071] d) a cover element with a fluid outlet,

[0072] wherein the first filter element, the first bottom element and the cover element form a first interior space, wherein the second filter element is arranged in the first interior space, and the second filter element, the second bottom element and the cover element form a second interior space,

[0073] The filter element is designed to allow the fluid to be filtered to flow from the outside through the first filter element into the first internal space, from the first internal space through the second filter element into the second internal space, and from the second internal space to flow outward through the fluid outlet.

[0074] wherein the quotient of the available filter area of ​​the first filter element divided by the available filter area of ​​the second filter element is greater than 1, wherein the quotient of the filter grade of the first filter medium divided by the filter grade of the second filter medium is 1 or greater, wherein the filter grade is a filter grade determined for total separation according to ISO 19438:2003-11, and

[0075] The first filter medium and the second filter medium have a filter capacity of 2.5 N*mm according to DIN 53864:1978-08. 2 or greater bending stiffness. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The present invention and preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0077] Figure 1 a shows a schematic diagram of a filter element for a fluid filtering device that is not according to the present invention;

[0078] Figure 1 b shows a schematic diagram of a folded filter element and its deformation under use conditions;

[0079] Figure 2 A schematic diagram showing a filter element for a fluid filter device according to the present invention in a preferred embodiment;

[0080] Figure 3 A schematic diagram showing a filter element for a fluid filter device according to the present invention in an alternative preferred embodiment;

[0081] Figure 4 A graphical plot showing the total segregation in % (Y) measured over time (X) for different filter elements at ≥ 4 μm under different loading scenarios;

[0082] Figure 5 Show Figure 4 an enlarged representation of a portion of a graphical drawing of; and

[0083] Figure 6 Shown for Figure 4 Graphical plot of total segregation for different filter elements at ≥4μm.

[0084] Specific implementation form

[0085] Figure 1 ) shows a cross-sectional view of a filter element 10 for a fluid filter device that is not according to the invention. The rotationally symmetrical filter element 10 has a surrounding first filter element 12, which is formed by a folded first filter medium 14 and is delimited above and below in the axial direction A by a cover element 24 and a first bottom element 20 (both of which are connected to the filter element 12), so that the components together form a first interior space 28.

[0086] When filtering a fluid, a fluid, such as diesel fuel, flows into the filter element 10 from the outside in a radial direction R and passes through the first filter medium 14. The fluid filtered in a single stage in this way flows out of the filter element 10 again through the fluid outlet 26 in the cover element 24. The flow direction of the fluid is Figure 1 a) and Figure 1 b) is indicated by an unfilled directional arrow.

[0087] Figure 1b) schematically visualizes the cross-sectional view in a plane perpendicular to the axial direction A under vehicle use conditions, in particular in the case of dynamically fluctuating volume flows. Figure 1 The first filter medium 14 shown in a) is not a characteristic of the filter element 10 according to the present invention. The folded first filter medium 14 has approximately uniform folds in the initial state. Figure 1 b) is shown by a dashed sawtooth line. Under mechanical loads during use, the sawtooth shape changes, so that the first filter medium 14 is partially deformed, in particular locally compressed or stretched, and its filter properties change accordingly. Without wishing to be bound by this theory, the inventors believe that this can lead in particular to a change in the pore diameter of the first filter medium 14 during operation, so that in particular in the case of flow fluctuations, i.e. when the filter pleats are in a Figure 1 In the case of cyclic loading and unloading between the extreme conditions plotted in b), an opening of the pores occurs at least partially, due to which the filtration efficiency is reduced.

[0088] In contrast, Figure 2 A schematic cross-sectional view of a filter element 10 according to the invention for a fluid filter device according to the invention is shown, in which a corresponding filter element 10 is inserted into a suitable housing, wherein Figure 2 The flow direction of the fluid in the filter element 10 is also indicated by an unfilled direction arrow. The filter element 10 shown is also designed to be essentially rotationally symmetrical, so that the filter element with a folded filter medium, which the filter element 10 comprises, has the basic shape of a hollow cylinder with respect to its envelope, and which, due to its properties, is sometimes also referred to as a bellows by those skilled in the art. As is known from the prior art, the first interior space 28 of the filter element 10 is formed by a surrounding first filter element 12, which is connected to a first bottom element 20 and a cover element 24. However, in accordance with Figure 1 Compared with the prior art, in the filter element 10 according to the present invention, the second internal space 30 is located internally in the first internal space 28 along the radial direction R and is composed of a surrounding second filter element 16, and the second filter element is connected to the second bottom element 22 and the cover element 24, so that an intermediate space is constructed between the first filter element 12 and the second filter element 16, and the intermediate space along the radial direction R can have a width of 8 mm, for example.

[0089] exist Figure 2 In the example shown, the first filter element 12 is formed by a folded first filter medium 14, and the second filter element 16 is formed by a folded second filter medium 18. In the axial direction A, the first filter element 12 is about 40% longer than the second filter element 16 in the preferred embodiment shown, so that the length L of the first filter element 12 is 1is approximately equal to the length L of the second filter element 16 2 Due to the different lengths of the filter elements and the common termination in the axial direction A by the identical, in this case one-piece, cover element 24, a distance is obtained between the first bottom element 20 and the second bottom element 22, each of which is designed as a circular end disk, which is approximately equal to 30% of the length of the first filter element 12, whereby a chamber area is formed between the end disks, the volume share of which in the first interior space 28 is approximately 30%.

[0090] Furthermore, the selected embodiment of the filter element results in a volume difference between the first interior space 28 and the second interior space 30, wherein the proportion of the second interior space 30 in the first interior space 28 is approximately 8%. Due to the different radii and different lengths of the filter elements, the inflow area available for fluid flow, i.e., the filter area available for flow through, is significantly larger for the first filter element 12 than for the second filter element 16.

[0091] The first filter medium 14 and the second filter medium 18 are each a circumferentially arranged fold group consisting of a polyester-based filter material, which has a plurality of folds of substantially identical shape, which extend in the axial direction A over the entire length and the entire circumference of the respective filter element. In the preferred example shown, the first filter medium 14 has a resistance of approximately 18.4 N*mm 2 The bending stiffness of the second filter medium 18 is about 9.12 N*mm 2 , wherein the flexural stiffness is measured at a bending angle of 5° in accordance with DIN 538664:1978-08 and is correspondingly correlated with the effective flexural stiffness of the entire filter medium.

[0092] In the example shown, the quotient of the reference filtration rating of the first filter medium 14 (ie, 2.4 μm(c)) divided by the reference filtration rating of the second filter medium 18 (ie, 2.2 μm(c)) is 1.09.

[0093] The cover element 24, which is also designed as a circular end disk, has a fluid outlet 26 in the center for discharging the fluid introduced into the filter insert 10. The first bottom element 20 has an optional water outlet opening 36 in the example shown in order to enable the discharge of separated water for a two-stage water separation integrated in the filter insert 10.

[0094] When used in a fluid filter device, such as a fuel filter in a truck, Figure 2 The filter element 10 shown in the figure is arranged in the filter housing of the fluid filtering device, in particular as a main filter or a high efficiency filter. The fluid to be filtered, for example, a driving fuel (such as diesel) can be filtered according to the filter housing of the fluid filtering device. Figure 2The flow direction indicated as a direction arrow in FIG. 1 flows from the outside through the first filter element 12 into the first interior space 28 in the opposite direction to the radial direction R, flows from the first interior space 28 through the second filter element 16 into the second interior space 30 and flows out of the second interior space 30 through the fluid outlet 26. Due to the arrangement of the filter stages realized by the first filter element 12 and the second filter element 16 in succession, a two-stage filtration in a common running direction can be realized accordingly, wherein, according to the inventors' estimation, the improved damping resistance of the filter element 10 is realized not only by the selection of the flexural rigidity and the filter grade of the filter medium according to the invention, but also, in the preferred embodiment shown, in particular by the fluid flow at least partially deflected in the first interior space 28 (which fluid flow is generated by the shortened second filter stage).

[0095] In vibration-free operation, the filter element 10 shown can achieve, for example, a total separation of 99.7% for particles with an average diameter of 4 μm with a continuous fluid flow. This filter efficiency is also advantageously achieved for filtration under mechanical loads, such as occur in typical vehicle operation, in particular under vibrations and with fluctuating fluid flows. The filter performance under the influence of vibrations and dynamically fluctuating volume flows of the fluid can be kept correspondingly high with the filter element 10 shown.

[0096] Figure 3 A schematic cross-sectional view in a plane perpendicular to the axial direction A through the filter element 10 according to the invention is shown in an alternative preferred embodiment. In this embodiment, the first filter element 12 is composed of a first filter medium 14 and of a fluid-permeable surrounding coalescing agent layer 32. In the example shown, the coalescing agent layer 32 is folded complementary to the first filter medium 14 and is arranged in the first filter element 12 in the radial direction R. The coalescing agent layer extends over the entire length of the first filter element 12 in the axial direction A. The coalescing agent layer 32 is made of an open-pored nonwoven material in order to condense liquid impurities dispersed in the fluid, in particular water.

[0097] In the example shown, the second filter element 16 is formed by a second filter medium 18 and by a fluid-permeable, circumferential separating layer 34 for separating liquid impurities present in the fluid. The separating layer 34 is folded complementary to the second filter medium 18 and is arranged externally in the second filter element 16 in the radial direction R. The separating layer extends over the entire length of the second filter element 16 in the axial direction A. The separating layer 34 is designed as a sieve-shaped layer and is composed of a hydrophobically treated polyester.

[0098] exist Figure 3 In the embodiment shown, the first bottom element 20 is in any case comprised in Figure 2 A central water outlet opening 36 , mentioned as an option, is provided in order to discharge liquid impurities separated on the coalescing agent layer 32 and the separating layer 34 , in most practically relevant cases in particular water, out of the filter element 10 .

[0099] In addition, the following reference experiment and Figures 4 to 6 The results presented in the accompanying drawings further illustrate and describe the present invention and preferred embodiments of the present invention.

[0100] experiment:

[0101] The inventors studied the total segregation degree of three selected filter elements (hereinafter referred to as A, B and C) under different load conditions in order to evaluate the performance of the filter elements for separating particles with an average diameter of 4 μm or larger under the loads occurring in actual use conditions.

[0102] Filter elements studied:

[0103] Filter elements A and B represent two different commercially available Figure 1 a) of the structure of the filter element, but using a different first filter medium. The first filter medium of the filter element A has a 2 The first filter medium of filter element B has a flexural stiffness of 18.4 N*mm. 2 The reference filter grade for 2.4μm (c) is given by the bending stiffness.

[0104] Filter element C is according to the present invention Figure 2 The bending stiffness of the first filter medium and the second filter medium are 18.4N*mm respectively. 2 and 18.4N*mm 2 The quotient of the reference filtration grade of the filter medium is 1. The length of the first filter element is substantially equal to 1.4 times the length of the second filter element.

[0105] Experimental implementation:

[0106] The total segregation was measured for particles with a size of ≥ 4 μm according to ISO 19438:2003-11, however diesel was used as the test fluid and the load scenarios described below were applied. The filters under investigation were dusted in a conventional manner before use in the measurement method. For the measurements, filter elements A, B and C were each subjected to different load conditions in a total of 7 stages within a defined test period. In load scenario 1, the segregation efficiency of the filter element was measured in a vibration-free and non-fluctuating state, that is to say in a constant volume flow of the fluid flowing through the filter element without mechanical vibrations, which is also referred to as the "steady state".

[0107] In load scenario 2 , the filter elements are each loaded with a mechanical vibration frequency in order to simulate vibrations occurring during vehicle use.

[0108] In load scenario 3 , the filter element is respectively loaded with a fluctuating flow of the fluid to be filtered, the flow rate of which accordingly cyclically alternates between 100% and 25% of the nominal flow rate within one minute.

[0109] In load scenario 2&3, the above-mentioned load scenario 2 and load scenario 3 are applied at the same time.

[0110] result:

[0111] The measurement results are Figure 4 , wherein the total segregation for particles with a size of ≥4 μm is plotted in % on the Y axis and the test time in seconds is plotted on the X axis. Over the entire test period of 10,000 s, filter elements A, B and C were successively subjected to the load scenarios described above and also shown in the diagram, wherein the respective phases with mechanical loading were each separated by time intervals in the "steady state", so that the measurement included a total of 7 phases.

[0112] Depend on Figure 4 It can be clearly seen that in load scenario 2, filter element A has a total segregation of less than 50% and therefore suffers a high loss in segregation efficiency compared to filter element C according to the invention. The reduced segregation efficiency of filter element A can also be seen in load scenario 3, which would make the filter element unusable for many applications. However, for the combination of load scenarios in load scenarios 2 & 3, the total segregation of filter element A drops sharply to such an extent that it can no longer be meaningfully determined in many cases and is below 40% in all cases. Filter element B still shows an acceptable filtration efficiency in isolated load scenarios 2 and 3. However, in the combined load scenarios 2 & 3, a strong fluctuation in the total segregation is shown, wherein the average total segregation is significantly below 90%.

[0113] In order to illustrate the significant improvement in the robustness of the filter element C according to the invention compared to the filter elements A and B, Figure 5 Shown in Figure 4 Detail of the embodiment of the invention, which shows the separation efficiency in the time interval of load scenarios 2 & 3 in an enlarged manner. It can be clearly seen that the filter element C according to the invention has an excellent overall separation of more than 99.7% at any time, and only a relatively small dispersion of the measured values ​​can be observed here.

[0114] Correspondingly, in load scenarios 2 & 3, the average total segregation obtained for filter element C according to the present invention is also 99.90%, while filter element B can only achieve an average of 82.95%, and filter element A can even only achieve less than 10%. Figure 6 The experiments accordingly not only demonstrate a significant improvement in the constancy of the filtration efficiency that can be achieved with the filter element C according to the invention under vehicle use conditions, ie, in particular under mechanical vibrations and dynamically fluctuating volume flows, but also document the consistently high separation values ​​that can be achieved with the filter element according to the invention.

[0115] Reference numerals list

[0116] 10 Filter element

[0117] 12. First filter element

[0118] 14. First filter medium

[0119] 16 Second filter element

[0120] 18 Second filter medium

[0121] 20 First bottom element

[0122] 22 Second bottom element

[0123] 24 Cover element

[0124] 26 Fluid outlet

[0125] 28 First Interior Space

[0126] 30 Second Internal Space

[0127] 32 Coalescence agent layer

[0128] 34 Separation layer

[0129] 36 Water outlet opening

[0130] A Axial direction

[0131] R Radial direction

Claims

1. A filter element (10) for a fluid filtering device, the filter element include: a) a surrounding first filter element (12), said first filter element comprising a pleated first filter medium (14), b) a surrounding second filter element (16) comprising a pleated second filter medium (18), c) a first bottom element (20) and a second bottom element (22), and d) a cover element (24) with a fluid outlet (26), wherein the first filter element (12), the first bottom element (20) and the cover element (24) form a first inner space (28), the second filter element (16) is arranged in the first inner space (28), and the second filter element (16), the second bottom element (22) and the cover element (24) form a second inner space (30), The filter element (10) is designed to enable the fluid to be filtered to flow from the outside through the first filter element (12) into the first inner space (28), to flow from the first inner space (28) through the second filter element (16) into the second inner space (30), and to flow from the second inner space (30) to the outside through the fluid outlet (26). The quotient of the available filter area of ​​the first filter element (12) divided by the available filter area of ​​the second filter element (16) is greater than 1, The quotient of the filtration grade of the first filter medium (14) divided by the filtration grade of the second filter medium (18) is 1 or greater, the filtration grade being a filtration grade determined for total separation according to ISO 19438:2003-11, and The first filter medium (14) and the second filter medium (18) have a resistance of 2.5 N*mm according to DIN 53864:1978-08. 2 or greater bending stiffness.

2. The filter element (10) according to claim 1, in, A quotient of the filtration rating of the first filter medium (14) divided by the filtration rating of the second filter medium (14) is 1.01 or greater.

3. The filter element (10) according to any one of claims 1 or 2, in, A quotient of the bending rigidity of the first filter medium (14) divided by the bending rigidity of the second filter medium (18) is 1 or greater.

4. The filter element (10) according to claim 3, in, A quotient of the bending rigidity of the first filter medium (14) divided by the bending rigidity of the second filter medium (18) is 1.1 or greater.

5. The filter element (10) according to any one of claims 1 to 4, in, The first filter element (12) is longer than the second filter element (16) by 10% or more in the axial direction.

6. The filter element (10) according to any one of claims 1 to 5, in, The first filter element (12) and the second filter element (16) are spaced apart from each other in a radial direction so that the first inner space (28) includes an intermediate area arranged between the first filter element (12) and the second filter element (16), and the intermediate distance is in the range of 3 mm to 20 mm.

7. The filter element (10) according to any one of claims 1 to 6, in, The volume of the second internal space (30) is 0.6*V 1 or less, V 1 is the volume of the first internal space (28).

8. The filter element (10) according to any one of claims 1 to 7, in, The first filter element (12) comprises a fluid permeable surrounding coalescing agent layer (32) for agglomerating liquid impurities dispersed in the fluid, and the first bottom element (20) comprises a water outlet opening (36).

9. The filter element (10) according to any one of claims 1 to 8, in, The second filter element (16) comprises a fluid-permeable surrounding separation layer (34) for separating liquid impurities present in the fluid.

10. A fluid filtering device for filtering a fluid, the fluid filtering device include: i) a filter housing, and ii) A filter element (10) according to any one of claims 1 to 9 arranged in the filter housing.

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