FILTER INSERT WITH IMPROVED FILTER PERFORMANCE UNDER OPERATING CONDITIONS

Abstract

The invention relates to a filter insert for a fluid filter device, comprising: a) a first circumferential filter element comprising a first folded filter medium, b) a second circumferential filter element comprising a second folded filter medium, c) a first base element and a second base element, and d) a cover element with a fluid outlet, wherein the first filter element, the first base element, and the cover element form a first inner chamber, said second filter element being arranged in the first inner chamber, and the second filter element, the second base element, and the cover element form a second inner chamber, wherein the filter insert is designed so that a fluid to be filtered can flow from the outside through the first filter element into the first inner chamber, from the first inner chamber through the second filter element into the second inner chamber and out of the second inner chamber through the fluid outlet, The quotient of the filter surface area of the first filter element divided by that of the second filter element is greater than one, the quotient of the filter rating of the first filter medium divided by the filter rating of the second filter medium equals one or more, and the first filter medium and the second filter medium have a bending strength of 2.5 N*mm.sup.2 or more according to DIN 53864:1978-08.

Claims

1. A filter insert for a fluid filter device, comprising: a) a circumferential first filter element comprising a folded first filter medium, b) a circumferential second filter element comprising a folded second filter medium, c) a first base element and a second base element, and d) a cover element with a fluid outlet, wherein the first filter element, the first base element, and the cover element form a first inner chamber, said second filter element being arranged in the first inner chamber, and the second filter element, the second base element, and the cover element form a second inner chamber, wherein the distance between the first base element and the second base element in the axial direction is in the range of 0.1*L.sub.1 to 0.6*L.sub.1, wherein L.sub.1 is the length of the first filter element in the axial direction, wherein the filter insert is designed so that a fluid to be filtered can flow from the outside through the first filter element into the first inner chamber, from the first inner chamber through the second filter element into the second inner chamber and out of the second inner chamber through the fluid outlet, wherein the quotient of the accessible filter surface area of the first filter element divided by the accessible filter surface area of the second filter element is greater than one, wherein the quotient of the filter rating of the first filter medium divided by the filter rating of the second filter medium equals one or more, wherein the filter rating is the filter rating determined according to ISO 19438:2003-11 for the overall separation efficiency, wherein the first filter medium has a bending strength according to DIN 53864:1978-08 of 10 N*mm.sup.2 or more, wherein the bending strength is determined with a bending angle of 5, wherein the second filter medium has a bending strength of 2.5 N*mm.sup.2 or more according to DIN 53864:1978-08, wherein the bending strength is determined with a bending angle of 5, and wherein the quotient of the bending strength of the first filter medium divided by the bending strength of the second filter medium equals one or more.

2. The filter insert according to claim 1, wherein the quotient of the filter rating of the first filter medium divided by the filter rating of the second filter medium is 1.01 or more.

3. The filter insert according to claim 1, wherein the distance between the first base element and the second base element in the axial direction is in the range of 0.2*L.sub.1 to 0.5*L.sub.1, wherein L.sub.1 is the length of the first filter element in the axial direction.

4. The filter insert according to claim 3, wherein the quotient of the bending strength of the first filter medium divided by the bending strength of the second filter medium is 1.1 or more.

5. The filter insert according to claim 1 wherein the first filter element is 10% or more longer in the axial direction than the second filter element.

6. The filter insert according to claim 1, wherein the first filter element and the second filter element are spaced apart from one another in the radial direction, so that the first inner chamber comprises an intermediate region arranged between the first filter element and the second filter element, wherein the average distance is in the range of 3 to 20 mm.

7. The filter insert according to claim 1 wherein the volume of the second inner chamber is 0.6*V.sub.1 or less, wherein Vi is the volume of the first inner chamber.

8. The filter insert according to claim 1, wherein the first filter element comprises a fluid-permeable circumferential coalescer layer for agglomerating liquid contaminants dispersed in the fluid, and wherein the first base element comprises a water outlet opening.

9. The filter insert according to claim 1, wherein the second filter element comprises a fluid-permeable circumferential separation layer for separating liquid contaminants present in the fluid.

10. A fluid filter device for filtering a fluid, comprising: i) a filter housing, and ii) a filter insert arranged in the filter housing according to claim 1.

11. The fluid filter device according to claim 10, wherein the quotient of the filter rating of the first filter medium divided by the filter rating of the second filter medium is 1.01 or more.

12. The fluid filter device according to claim 10, wherein the distance between the first base element and the second base element in the axial direction is in the range of 0.2*L.sub.1 to 0.5*L.sub.1, wherein L.sub.1 is the length of the first filter element in the axial direction.

13. The fluid filter device according to claim 12, wherein the quotient of the bending strength of the first filter medium divided by the bending strength of the second filter medium is 1.1 or more.

14. The fluid filter device according to claim 10, wherein the first filter element is 10% or more longer in the axial direction than the second filter element.

15. The fluid filter device according to claim 10, wherein the first filter element and the second filter element are spaced apart from one another in the radial direction, so that the first inner chamber comprises an intermediate region arranged between the first filter element and the second filter element, wherein the average distance is in the range of 3 to 20 mm.

16. The fluid filter device according to claim 10, wherein the volume of the second inner chamber is 0.6*V.sub.1 or less, wherein V.sub.1 is the volume of the first inner chamber.

17. The fluid filter device according to claim 10, wherein the first filter element comprises a fluid-permeable circumferential coalescer layer for agglomerating liquid contaminants dispersed in the fluid, and wherein the first base element comprises a water outlet opening.

18. The fluid filter device according to claim 10, wherein the second filter element comprises a fluid-permeable circumferential separation layer for separating liquid contaminants present in the fluid.

Description

[0078] The invention and preferred embodiments of the invention are explained and described in more detail below with reference to accompanying figures, in which:

[0079] FIG. 1a is a schematic representation of a filter insert not according to the invention for a fluid filter device;

[0080] FIG. 1b is a schematic representation of a folded filter element and its deformation under operating conditions;

[0081] FIG. 2 is a schematic representation of a filter insert according to the invention for a fluid filter device in a preferred embodiment;

[0082] FIG. 3 is a schematic representation of a filter insert according to the invention for a fluid filter device in an alternative preferred embodiment;

[0083] FIG. 4 is a graphical representation of measured overall separation efficiencies at 4 m in % (Y) versus time (X) for different filter inserts under different load scenarios;

[0084] FIG. 5 is an enlarged view of a detail of the graphical representation of FIG. 4; and

[0085] FIG. 6 is a graphical representation of the overall separation efficiency at 4 m for the different filter inserts of FIG. 4.

[0086] FIG. 1a) shows a cross-sectional representation of a filter insert 10 not according to the invention for a fluid filter device. The rotationally symmetrical filter insert 10 has a circumferential first filter element 12, which consists of a folded first filter medium 14 and is delimited at the top and bottom in the axial direction A by a cover element 24 and a first base element 20, both of which are connected to the filter element 12, so that the components together form a first inner chamber 28.

[0087] When filtering fluids, a fluid, for example diesel fuel, flows into the filter insert 10 from the outside in relation to the radial direction R and passes through the first filter medium 14. The fluid filtered in this single stage then flows out of the filter insert 10 again through a fluid outlet 26 in the cover element 24. The flow direction of the fluid is indicated in FIGS. 1a) and 1b) by unfilled direction arrows.

[0088] FIG. 1b) schematically visualizes the behavior of the first filter medium 14 of the filter insert 10 not according to the invention shown in FIG. 1a) using a cross-sectional representation in the plane perpendicular to the axial direction A under operating conditions on the vehicle, in particular with dynamically fluctuating volume flows. In the initial state, the folded first filter medium 14 is present in substantially uniform folds. This is indicated in FIG. 1b) by the dashed zigzag line. Under mechanical stress during use, this zigzag shape changes in such a way that the first filter medium 14 is partially deformed, in particular locally compressed or stretched, and accordingly changes its filter properties. Without wishing to be bound to this theory, the inventors assume that this can lead, among other things, to a change in the pore diameter of the first filter medium 14 during operation, so that, particularly in the case of fluctuating flows, i.e., the cyclic loading and unloading of the filter folds between the extreme states shown in FIG. 1b), the pores can at least partially open, thereby reducing the filter efficiency.

[0089] In contrast, FIG. 2 shows a schematic cross-sectional representation of a filter insert 10 according to the invention for fluid filter devices according to the invention, in which a corresponding filter insert 10 is inserted into a suitable housing, wherein the flow direction of the fluid is also indicated in FIG. 2 by unfilled direction arrows. The filter insert 10 shown is also substantially rotationally symmetrical, so that the filter elements encompassed by the filter insert 10 with folded filter media, which are sometimes also referred to by a person skilled in the art as bellows due to their nature, have a hollow cylindrical basic shape with respect to their envelope. As known from the prior art, a first inner chamber 28 of the filter insert 10 is formed by the first circumferential filter element 12, which is connected to a first base element 20 and a cover element 24. In the filter insert 10 according to the invention, in contrast to the prior art according to FIG. 1, however, a second inner chamber 30 is formed in the first inner chamber 28 in the radial direction R inside by a second circumferential filter element 16, which is connected to a second base element 22 and the cover element 24, so that an intermediate space is formed between the first filter element 12 and the second filter element 16, which can have a width of 8 mm in the radial direction R, for example.

[0090] In the example shown in FIG. 2, the first filter element 12 consists of a folded first filter medium 14 and the second filter element 16 consists of a folded second filter medium 18. In the axial direction A, the first filter element 12 in the preferred embodiment shown is approximately 40% longer than the second filter element 16, so that the length of the first filter element 12 L.sub.1 corresponds to approximately 1.4 times the length of the second filter element 16 L.sub.2. According to the different lengths of the filter elements, as well as the common closure in the axial direction A by the same, in this case integrally formed cover element 24, a distance is obtained between the first base element 20 and the second base element 22, which are each designed as circular end disks, which corresponds to approximately 30% of the length of the first filter element 12, whereby a chamber region is formed between the end disks, which has a volume share of the first inner chamber 28 of approximately 30%.

[0091] In addition, the selected design of the filter elements causes a volume difference between the first inner chamber 28 and the second inner chamber 30, wherein the proportion of the second inner chamber 30 to the first inner chamber 28 is approximately 8%. The flow area available for the fluid passage, i.e., the filter surface area available for a flow, is significantly larger for the first filter element 12 than for the second filter element 16 due to the different radii and the different lengths of the filter elements.

[0092] The first filter medium 14 and the second filter medium 18 are each circumferentially arranged fold packages made of a polyester-based filter material with a plurality of substantially uniform folds, which each extend in the axial direction A over the entire length and the entire circumference of the particular filter elements. In the preferred example shown, the first filter medium 14 has a bending strength of approximately 18.4 N*mm.sup.2 and the second filter medium 18 has a bending strength of about 9.12 N*mm.sup.2, wherein the bending strength is measured according to DIN 53864:1978-08 with a bending angle of 5 and is related to the effective bending strength of the entire filter medium.

[0093] The quotient of the filter reference rating of the first filter medium 14, namely 2.4 m(c), divided by the filter reference rating of the second filter medium 18, namely 2.2 m(c), is 1.09 in the example shown.

[0094] The cover element 24, which is also designed as a circular end disk, has a central fluid outlet 26 for discharging a fluid introduced into the filter insert 10. The first base element 20 has an optional water outlet opening 36 in the example shown in order to enable the removal of separated water for a two-stage water separation integrated in the filter insert 10.

[0095] When used in a fluid filter device, for example a fuel filter in a truck, the filter insert 10 shown in FIG. 2 is arranged in a filter housing of the fluid filter device, in particular as a main filter or high-efficiency filter. A fluid to be filtered, for example a fuel such as diesel, can flow according to a flow direction shown in FIG. 2 as direction arrows against the radial direction R from the outside through the first filter element 12 into the first inner chamber 28, from the first inner chamber 28 through the second filter element 16 into the second inner chamber 30 and from the second inner chamber 30 through the fluid outlet 26. Because the filter stages, represented by the first filter element 12 and the second filter element 16, are arranged one behind the other, a two-stage filtering along the usual operating direction is made possible, wherein an improved damping resistance of the filter insert 10 is achieved, in the opinion of the inventors, not only by the inventive choice of the bending strengths and filter ratings of the filter media, but in the preferred embodiment shown in particular also by the fluid flow which is at least partially deflected in the first inner chamber 28 and which results from the shortened second filter stage.

[0096] In vibration-free operation, the filter insert 10 shown can, for example, achieve an overall separation efficiency of 99.7% for particles with an average diameter of 4 m with a continuous fluid flow. This filter performance is also advantageously achieved when filtering under mechanical stress, such as occurs in typical vehicle operation, in particular under vibrations and fluctuating fluid flows. The filter performance under the influence of vibrations and dynamically fluctuating volume flows of the fluid can be kept high in an advantageous manner with the filter insert 10 shown.

[0097] FIG. 3 shows a schematic cross-sectional representation in the plane orthogonal to the axial direction A through a filter insert 10 according to the invention in an alternative preferred embodiment. In this embodiment, the first filter element 12 is formed by the first filter medium 14 and by a fluid-permeable circumferential coalescer layer 32. In the example shown, the coalescer layer 32 is folded complementarily to the first filter medium 14 and is arranged in the radial direction R inside the first filter element 12. It extends in the axial direction A over the entire length of the first filter element 12. The coalescer layer 32 consists of open-pored nonwoven materials in order to coagulate liquid contaminants, in particular water, dispersed in the fluid.

[0098] In the example shown, the second filter element 16 is formed by the second filter medium 18 and by a fluid-permeable circumferential separation layer 34 for separating liquid contaminants present in the fluid. The separation layer 34 is folded complementarily to the second filter medium 18 and is arranged on the outside in the radial direction R in the second filter element 16. It extends in axial direction A over the entire length of the second filter element 16. The separation layer 34 is designed as a sieve-like layer and consists of a hydrophobically treated polyester.

[0099] In the embodiment shown in FIG. 3, the first base element 20 in any case comprises the central water outlet opening 36, which is designated as optional in FIG. 2, in order to drain the liquid contaminants separated on the coalescer layer 32 and the separation layer 34, in most practical cases in particular water, from the filter insert 10.

[0100] In the following, the invention and preferred embodiments of the invention are further explained and described with reference to an experiment and the results shown in FIG. 4 to 6.

Experiment

[0101] The inventors investigated the overall removal efficiency of three selected filter cartridges, hereinafter referred to as A, B and C, under different loading conditions in order to evaluate the performance of the filter cartridges for the removal of particles with an average diameter of 4 m or more under operating conditions encountered in practice under service conditions.

Filter Inserts Examined:

[0102] The filter inserts A and B represent two different commercially available filter inserts with a structure according to FIG. 1a), although different first filter media were used. The first filter medium of filter insert A has a filter reference rating of 4.3 m(c) with a bending strength of 22.8 N*mm.sup.2. The first filter medium of filter insert B, on the other hand, has a filter reference rating of 2.4 m(c) with a bending strength of 18.4 N*mm.sup.2.

[0103] The filter insert C is a filter insert according to the invention, which is designed according to FIG. 2. The bending strength of the first and second filter medium is 18.4 N*mm.sup.2 or 18.4 N*mm.sup.2. The quotient of the filter reference ratings of the filter media is 1. The length of the first filter element is approximately 1.4 times the length of the second filter element.

Experimental Procedure:

[0104] The measurement of the overall separation efficiency was carried out in accordance with ISO 19438:2003-11 for particles with a particle size of 4 m, but diesel was used as the test fluid and the load scenarios described below were applied. The filters examined were dusted in the usual way before use in the measuring procedure. For the measurements, filter inserts A, B and C were exposed to different loading conditions in an overall of seven phases for a defined test period. In a load scenario 1, the separation efficiencies of the filter inserts were measured in a vibration-free and fluctuation-free state, i.e., at a constant volume flow of a fluid flowing through the filter insert without mechanical vibrations, which is also referred to as steady state.

[0105] In a load scenario 2, the filter inserts were each loaded with a mechanical vibration frequency to simulate the vibrations occurring during vehicle use.

[0106] In a load scenario 3, the filter inserts were each loaded with a fluctuating flow of the fluid to be filtered, the flow rate of which was cyclically alternated between 100% and 25% of the nominal flow rate for one minute each.

[0107] In a load scenario 2&3, the load scenarios 2 and 3 described above were created simultaneously.

Results:

[0108] The results of the measurements are represented graphically in FIG. 4, wherein the Y-axis represents the overall separation efficiency for particles with a particle size 4 m in % and the X-axis represents the test time in seconds. Over the entire test period of 10,000 s, the filter inserts A, B and C were successively exposed to the load scenarios described above and also shown graphically, wherein the corresponding phases with mechanical stress were each separated by time intervals in the steady state, so that the measurement comprises an overall of 7 phases.

[0109] From FIG. 4, it is clearly visible that the filter insert A in load scenario 2 has an overall separation efficiency of less than 50% and thus experiences high losses in separation efficiency compared to the filter insert C according to the invention. In load scenario 3, a reduced separation efficiency of filter insert A is also evident, which would make it unusable for many applications. However, for a combination of the load scenarios in load scenario 2&3, the overall separation efficiency of filter insert A drops so much that in many cases it can no longer be meaningfully determined and is below 40% in all cases. The filter insert B still shows acceptable filter performance in the isolated load scenarios 2 and 3.

[0110] However, in the combined load scenario 2&3, a strong oscillation of the overall separation efficiency is observed, wherein the average overall separation efficiency is significantly below 90%.

[0111] To illustrate the significant improvement in the robustness of the filter insert C according to the invention compared to the filter inserts A and B, FIG. 5 shows a detail of FIG. 4, which shows the separation efficiency in the time interval of the load scenario 2&3 in an enlarged manner. It can be clearly seen that the filter insert C according to the invention has an excellent overall separation efficiency of over 99.7% at all times and only a relatively small scatter of the measured values can be observed.

[0112] Accordingly, the average overall separation efficiency resulting in load scenario 2&3 for the filter insert C according to the invention is 99.90%, while the filter insert B can only achieve an average of 82.95% and the filter insert A even less than 10%, as shown in FIG. 6. Accordingly, this experiment not only demonstrates the significant improvement in the consistency of the achievable filter performance with filter inserts C according to the invention under operating conditions on the vehicle, i.e., in particular under mechanical vibrations and dynamically fluctuating volume flows, but also documents the consistently high separation values that can be achieved with filter inserts according to the invention.

LIST OF REFERENCE SIGNS

[0113] 10 filter insert [0114] 12 first filter element [0115] 14 first filter medium [0116] 16 second filter element [0117] 18 second filter medium [0118] 20 first base element [0119] 22 second base element [0120] 24 cover element [0121] 26 fluid outlet [0122] 28 first inner chamber [0123] 30 second inner chamber [0124] 32 coalescer layer [0125] 34 separation layer [0126] 36 water outlet opening [0127] A axial direction [0128] R radial direction