Method for operating a filter, and self-cleaning filter system

Abstract

The invention relates to a method for operating a filter (10), wherein the filter comprises: i) a first polarisation element (12), ii) a second polarisation element (14), iii) a filter medium (16) which can be polarised, and iv) an electrical contacting system (18), wherein the method comprises operating the filter (10) in at least two different operating modes, wherein the filter (10) is operated in a polarisation mode for 80% or more of the operating time, wherein, in the polarisation mode, a continuous direct voltage is applied between the first polarisation element (12) and the second polarisation element (14), which direct voltage varies by 20% or less based on the mean value of the direct voltage in the polarisation mode, wherein the filter (10) is partly operated in a DC cleaning mode, wherein, in the DC cleaning mode, a pulsed direct voltage is applied between the first polarisation element (12) and the second polarisation element (14) with a number of pulses, wherein the average electrical field strength of the electrical field during the pulses is 0.5 kV / cm or more, and / or wherein the filter (10) is partly operated in an AC cleaning mode, wherein, in the AC cleaning mode, a pulsed alternating voltage is applied between the first polarisation element (12) and the second polarisation element (14) with a number of pulses, wherein the high points of the absolute value function of the electrical field strength during the pulses are at least partly 0.5 kV / cm or more.

Description

[0001] Method for operating a filter and self-cleaning filter system

[0002] Description

[0003] The invention relates to a filter and a filter system for use in a corresponding process. Also disclosed are a filter insert for corresponding filter systems and the use of pulsed electric fields for cleaning polarizable filter media in electrostatic precipitators with filter functionality.

[0004] Modern filtration technology now offers numerous efficient alternatives and further developments to the well-known processes for the separation of undesirable components from fluid flows, which are mostly based on essentially mechanical separation, usually on a partially permeable filter medium, which can, for example, consist of a porous material.

[0005] One of these developments, which is used particularly for gas purification, is so-called electrostatic precipitation, whereby the devices used are also referred to as electrostatic precipitators. In these electrostatic precipitators, the particles to be removed are first ionized by an electrode and then deposited on an oppositely charged collecting electrode. Such electrostatic precipitators are used primarily in industrial plants. However, the performance characteristics of cabin air filters, especially for use in vehicles, are subject to different requirements, for example, the reliable separation of pollen and / or particulate matter and / or odors and / or exhaust gases.

[0006] To meet these requirements for cabin air filters, the concept of electrostatic separation, which in many cases is not strictly speaking filtration, was combined with mechanical separation processes to obtain high-performance filter media. By combining conventional filter materials with an ionization device, the separation efficiency of filters can be significantly increased in many cases. For the purpose of clear identification, the corresponding filter media are referred to as electrostatic precipitators with filter functionality within the scope of the present invention. However, it has been observed that the separation efficiency of such filter media can decrease over the service life of the filter medium, which is often attributed to a reduction in the electrostatic charge in the filter material over time.

[0007] To solve this problem, it has been proposed to design electrostatic precipitators with filter functionality in such a way that polarization of the filter material can be induced in the filter insert by applying a voltage to two polarization elements through the creation of an electric field. In combination with an ionization device, this polarization of the filter material can enable efficient separation, which can advantageously usually be maintained over the entire service life of the filter medium. Background information on the basic technology is disclosed, for example, in WO 2007 / 135232 A1 or EP 3 448 540 B1.

[0008] Despite the fundamental advantages of corresponding electrostatic precipitators with filter functionality, the systems known from the prior art still have problems which, in the inventors' opinion, have not yet been satisfactorily resolved. One of these problems, which corresponding electrostatic precipitators with filter functionality share with many other filter media, is that over time, the filter media used usually absorb a large number of contaminants, which can include viruses or microorganisms, especially bacteria. Particularly in the case of bacteria, the filter media used often offer a large potential colonization area due to their large surface area, so that over time, the filter media can become heavily contaminated with bacteria.Such contamination is fundamentally undesirable, as there is always the risk that the flow of the fluid to be filtered could carry away bacteria from the filter medium, for example, and that these could enter the interior of a vehicle.

[0009] The current state of the art, to solve this problem in conventional filter media, usually relies on the use of additional components, such as biocides, which exert an antimicrobial, particularly antibacterial, effect. Due to the lack of effective alternatives to this approach, this solution has also been used in electrostatic precipitators with filter functionality.

[0010] However, the use of such additional components with antimicrobial effects is considered disadvantageous from numerous perspectives. In particular, the required treatment of the filter media used with the corresponding antimicrobial substances is technically complex and significantly increases the overall costs associated with the production of the corresponding filter media. Furthermore, some of the components known from the prior art for this purpose, as biocides, are not without their risks and are therefore not without their handling. Furthermore, in the inventors' opinion, the substances used are not suitable for meeting all requirements in terms of their absolute effectiveness and / or duration of action, especially not over the entire expected service life of a corresponding filter intended for use in a vehicle, for example.

[0011] The primary objective of the present invention was to eliminate or at least mitigate the disadvantages of the prior art. In particular, the objective of the present invention was to provide a solution for electrostatic precipitators with filter functionality that allows for the advantageous removal of microorganisms in the filter, particularly in the filter medium.

[0012] One object of the present invention was to ensure that the advantageous antimicrobial effect can be flexibly adapted to the specific application requirements of the contaminations encountered. Furthermore, one object of the present invention was to provide a solution that exhibits a very long-lasting cleaning effect in the filter media used, desirably a substantially unlimited cleaning effect.

[0013] It was a further object of the present invention that the solution to the problem to be provided should, if possible, do without the use of substances that are potentially harmful to health and / or the environment, whereby it was particularly desirable that, ideally, the use of antibacterial substances or other biocides could be completely dispensed with.

[0014] It was a further object of the present invention that the solution to be specified for preventing colonization of the filter media with microorganisms should ideally have no negative impact on the time and cost efficiency of the production of corresponding filters, wherein it was a desirable requirement that the solution to be specified should ideally be easy to combine with existing structures of typical filter media.

[0015] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if a method for operating a filter, in particular an electrostatic precipitator with filter functionality, is used, in which, in addition to the polarization mode required for the polarization of the filter medium, a cleaning mode is also provided, which can be operated with direct or alternating current and which relies on the concept of electroporation by means of pulsed electric fields, known in particular from the food industry, in order to render microorganisms present in the filter medium harmless, as defined in the claims.

[0016] The present invention is therefore based on the surprising finding that the basic structure of an electrostatic precipitator with filter functionality, in which the polarizable filter medium is arranged between two polarization elements which are designed to create an electric field used for polarization, can be advantageously converted with only minor modifications to provide, in addition to those phases in which polarization is ensured, relatively short phases of pulsed operation with which electroporation can be carried out with little additional effort, which can advantageously render harmless the microorganisms present in the filter medium.In addition to the advantageous circumstance that the basic structure required for carrying out electroporation is already present in the electrostatic precipitators with filter functionality and can be easily achieved in corresponding filter systems in view of the invention by appropriate programming of the electronic control units, the inventive method based on this finding and the filter system suitable for carrying it out are particularly advantageous because the use of biocides can be essentially completely dispensed with. Furthermore, the desired antimicrobial effect is advantageously based on the use of the electrical or electronic devices, which—at least with respect to the service life typically expected for filters—are essentially not subject to any relevant aging that would reduce the effectiveness of the cleaning performance.Furthermore, it can be seen as a major advantage of the invention that in the method according to the invention and the associated filter systems, the level of cleaning performance can be relatively easily adapted to the respective existing application requirements by merely adjusting the operating parameters during the cleaning phases in order to modify the stress experienced by the microorganisms, for example, by changing the field strength and / or the pulse pattern. The above-mentioned objects are accordingly achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following explanations.

[0017] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of one embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred filter systems and uses emerge from the features of preferred filter systems.

[0018] The invention particularly relates to methods for operating a filter, the filter comprising: i) a first polarization element, ii) a second polarization element, iii) a polarizable filter medium arranged between the first polarization element and the second polarization element, and iv) an electrical contacting system, the electrical contacting system being configured to allow a voltage provided by a voltage source to be applied between the first polarization element and the second polarization element, the method comprising operating the filter in at least two mutually different operating modes, the filter being operated in a polarization mode for 80% or more of the operating time, a continuous DC voltage being applied between the first polarization element and the second polarization element in the polarization mode, the DC voltage varying by 20% or less.based on the mean value of the DC voltage in the polarization mode, wherein the filter is partially operated in a DC cleaning mode, wherein in the DC cleaning mode, a pulsed DC voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the mean electric field strength of the electric field during the pulses is 0.5 kV / cm or more, and / or wherein the filter is partially operated in an AC cleaning mode, wherein in the AC cleaning mode, a pulsed AC voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.

[0019] The method according to the invention is a method for operating a filter, which, however, can naturally also be regarded as a method for filtering a fluid to be filtered, in particular air, and which, in the opinion of the inventors, is particularly advantageous for use in the field of automotive technology. Accordingly, a method according to the invention is preferred, wherein the filter is an air filter, preferably an interior air filter, particularly preferably an interior air filter for vehicles, in particular for land vehicles.

[0020] The method according to the invention serves to kill microorganisms, in particular bacteria, present in the filter medium through suitable process control. In the context of the present invention, this is sometimes referred to as cleaning for the purpose of better understanding. In accordance with the expert understanding, this cleaning, which can, for example, be at least partial sterilization, does not, however, require the removal of particles or killed microorganisms from the filter medium. In order to be able to operate with the method according to the invention, the filter used must comprise at least four basic components. In order to enable both the desired polarization of the polarizable filter medium and to achieve the cleaning effect desired for the method according to the invention, it is necessary to have two elements between which an electric field can be built up.In the context of the present invention, these elements are referred to as first and second polarization elements with regard to their main functionality, with the voltage being applied via the electrical contact system.

[0021] One advantage of the method according to the invention is that the polarization elements can, in principle, be designed relatively freely by a person skilled in the art, provided they are configured in such a way that the electric field strengths required in the method according to the invention can be realized. In particularly simple structures, the polarization elements can be designed, for example, as flat elements between which the filter medium is arranged. This is particularly suitable for configurations in which only the filter medium is to be replaced more frequently and in which the polarization elements are intended for recycling, for example because they are designed as part of a module installed on the vehicle.In this case, it is a method according to the invention, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, are separate elements from the filter medium. An example is additionally or alternatively a method according to the invention, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, comprise an electrically conductive grid or an electrically conductive plate, wherein the electrically conductive grid and the electrically conductive plate are preferably coated with a metal or consist of a metal.Additionally or alternatively, a method according to the invention is exemplary, wherein the first polarization element and the second polarization element have an average distance from one another in the range of 0.03 to 30 cm, preferably in the range of 0.05 to 10 cm, particularly preferably in the range of 0.08 to 0.6 cm.

[0022] The electrical contacting system to be provided according to the invention can be designed by a person skilled in the art according to the respective application requirements and the design specifications of the filter system, in particular of the vehicle filter module. Regardless of the specific configuration of the electrical contacting system, it will usually comprise a first contacting element and a second contacting element, which are each intended to establish an electrically conductive contact with the first polarization element and the second polarization element, respectively. For essentially all embodiments, a method according to the invention is preferred, wherein the electrical contacting system comprises a first contact point and a second contact point for contacting the voltage source. A method according to the invention is preferred, wherein the voltage source is a high-voltage source, preferably a high-voltage source of a vehicle.An example in this respect is a method according to the invention, wherein the maximum applied voltage during operation is 0.3 kV or more, preferably 0.5 kV or more.

[0023] The polarizable filter medium provided according to the invention serves in particular for mechanical filtration, i.e., the mechanical separation of particles from the fluid to be filtered, which is promoted during operation of the filter during the filtration of a fluid by the filter medium being polarized as a result of the applied electric field. The corresponding polarizability of the filter medium results, in accordance with expert understanding, from the presence of a dielectric layer. In other words, this is a method according to the invention, wherein the filter medium comprises at least one dielectric layer.

[0024] Particularly advantageous embodiments of these electrostatic precipitators with filter functionality can be achieved if the polarization elements are at least partially, preferably completely, integrated into the filter medium installed in the filter insert. For this purpose, individual layers of a multi-layer filter medium can be designed as electrically conductive layers. Such an electrically conductive conductor layer of the filter medium can, for example, together with a second polarization element arranged on the vehicle or together with a second electrically conductive conductor layer, cause the polarization of a dielectric filter material.By at least partially integrating the polarization elements into the filter medium and thus preferably using a replaceable filter insert, high-performance filters are obtained which, in particular, have an advantageous weight and make it possible to reduce or even completely eliminate the requirements for the equipment required on the vehicle if no vehicle-side polarization elements need to be provided to achieve the polarization of the dielectric layer. Furthermore, a corresponding design as a multi-layer filter medium often leads to a beneficial polarization effect on the particulate filter layer arranged directly between the conductor layers. Furthermore, this makes it possible to integrate all the components required for the polarization effect into a filter insert without incurring high additional costs and requiring additional installation space, which can be designed particularly easily as a replaceable filter insert.Accordingly, a method according to the invention is particularly preferred, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, are elements connected to the filter medium, preferably bonded together.

[0025] Additionally or alternatively, a method according to the invention is preferred, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, form a multi-layer filter medium with the filter medium. A method according to the invention is particularly preferred, wherein the filter comprises a multi-layer filter medium, wherein the multi-layer filter medium comprises:

[0026] I) an electrically conductive first conductor layer as the first polarization element, and III) an intermediate layer connected to the first conductor layer as a filter medium, wherein the intermediate layer comprises at least one dielectric layer

[0027] Particularly preferred is a method according to the invention, wherein the filter comprises a multi-layer filter medium, wherein the multi-layer filter medium comprises:

[0028] I) an electrically conductive first conductor layer as the first polarization element,

[0029] II) an electrically conductive second conductor layer as a second polarization element, and

[0030] III) an intermediate layer arranged between the first conductor layer and the second conductor layer as a filter medium, wherein the intermediate layer comprises at least one dielectric layer.

[0031] Additionally or alternatively, a method according to the invention is preferred, wherein the first conductor layer and the second conductor layer have an average distance from one another in the range of 0.03 to 30 cm, preferably in the range of 0.05 to 10 cm, particularly preferably in the range of 0.08 to 0.6 cm, and / or wherein the multi-layer filter medium at 1 kPa has an average thickness in the range of 0.04 to 35 cm, preferably in the range of 0.06 to 12 cm, particularly preferably in the range of 0.09 to 0.7 cm.

[0032] Particularly when using a multi-layer filter medium which comprises at least one conductor layer as a polarization element, it is preferable, with a view to ensuring the simplest possible maintenance and repair of the filters to be used in the method according to the invention, to design parts of the filter in the form of a filter insert as reversibly and non-destructively replaceable units. In the opinion of the inventors, in addition to the filter medium, at least one polarization element and the corresponding contact should also be designed to be replaceable. Accordingly, a method according to the invention is preferred, wherein the filter comprises at least one polarization element, preferably the first polarization element and the second polarization element, the polarizable filter medium and the electrical contact system as a filter insert arranged in the filter in a reversibly and non-destructively replaceable manner.Preferred embodiments of the multi-layer filter medium, in which one or two electrically conductive conductor layers are used, as well as a particularly preferred electrical contacting system for contacting the conductor layers, are disclosed in more detail below. Regardless of whether a multi-layer filter medium or merely a polarizable filter layer is used, these can advantageously be produced using conventional methods, wherein pleating to increase the available filter area and lamination are particularly useful, especially when the filter is designed with a replaceable filter insert. Accordingly, a method according to the invention is preferred, wherein the filter comprises the filter medium, preferably the multi-layer filter medium, as a pleated filter medium.Particularly preferred is a method according to the invention wherein at least one of the sides of the pleated filter medium, preferably of the multi-layer filter medium, preferably at least two sides, particularly preferably at least the long sides, very particularly preferably all sides, are laminated with a lamination material, wherein the lamination material is preferably selected from the group consisting of textile fabrics, in particular nonwovens and felts. Very particularly preferred is a method according to the invention wherein the electrical contacting system is connected to the lamination of the pleated filter medium, preferably by means of a material bond.

[0033] In the inventors' opinion, the method according to the invention is already advantageous for the purpose of achieving a beneficial effect in a filter that only comprises the components described above. The polarization provided according to the invention improves the separation performance of the filter medium even in the absence of dedicated ionization devices. Furthermore, advantageous cleaning of the filter medium is possible even in the absence of an ionization device. However, those skilled in the art will understand that particularly significant synergistic advantages arise if the filter is an electrostatic precipitator with filter functionality, for which purpose an ionization device is expediently provided which can ionize dirt particles present in the fluid to be filtered, so that they can be separated particularly efficiently in the polarized filter medium.In accordance with the understanding of those skilled in the art, this ionization device interacts with the filter medium polarized between the first and second polarization elements, which can function, in particular, as a collecting electrode. Accordingly, a method according to the invention is preferred, wherein the filter additionally comprises: v) an ionization device for ionizing components of the fluid to be filtered.

[0034] Suitable ionization devices are known to those skilled in the art and are disclosed, for example, in WO 2023 / 012166 A1. For essentially all embodiments, electrical ionization devices are relevant, which are also known from other technological fields and can effect ionization, in particular, by means of a corona discharge. Such electrical ionization devices are far superior to other ionization methods, in particular those using ionizing radiation, in terms of safety aspects as well as their handling and performance. Consequently, a method according to the invention is preferred, wherein the ionization device is an electrical ionization device, wherein the ionization device is preferably configured to effect the ionization of components of the fluid to be filtered at least partially, preferably substantially completely, by means of a corona discharge.Additionally or alternatively, a method according to the invention is preferred, wherein the ionization device does not comprise a radiation source for ionizing radiation. Those skilled in the art will understand that the desired interaction between the ionization device and the filter medium requires that the filter, with the filter medium acting as a collecting electrode, should be placed downstream of the ionization device in the flow direction during subsequent use.

[0035] The method according to the invention is based on the filter, which with regard to its basic structure is designed as described above, being operated in at least two different operating modes, which in the context of the present invention are referred to as polarization mode on the one hand and DC or AC cleaning mode on the other. These different operating modes are disclosed in more detail below. In principle, it is conceivable for the filter to be operated in additional modes which differ from the previously mentioned operating modes with regard to the design of the electric field. However, in accordance with the understanding of those skilled in the art, it is preferred if the filter is operated as largely as possible in the operating modes to be provided according to the invention. Accordingly, a method according to the invention is conceivable in which the filter is partially operated in one or more additional operating modes.Additionally or alternatively, however, a method according to the invention is preferred, wherein the filter is operated for 98% or more, preferably for 99% or more, particularly preferably for 99.5% or more, very particularly preferably for substantially 100% of the operating time in polarization mode or in DC cleaning mode or in AC cleaning mode, preferably in polarization mode or in DC cleaning mode.

[0036] The first central operating mode is referred to in the context of the present invention as the polarization mode. In polarization mode, a DC voltage that is as constant as possible is applied to the polarization elements in order to create a rectified electric field by polarizing the polarizable filter medium to promote its separation effect, particularly in an electrostatic precipitator with filter functionality. In other words, this is a method according to the invention, wherein the filter is configured to cause or promote the separation of electrically charged particles, in particular ionized particles, particularly preferably particles ionized by the ionization device, as a result of polarization of the multilayer filter medium.

[0037] Particularly when used in combination with an ionization device, the polarization mode, according to the inventors' assessment, will be the operating mode in which the filter is operated for the vast majority of the time, while the cleaning modes described below are used only for short periods of time sufficient to achieve the desired cleaning performance in order to impair the otherwise desired polarization of the filter medium as little as possible. Accordingly, a method according to the invention is preferred, wherein the filter is operated in polarization mode for 90% or more, preferably for 95% or more, particularly preferably for 99% or more, and most particularly preferably for 99.5% or more, of the operating time.Additionally or alternatively, a method according to the invention is preferred, wherein the filter is operated in DC cleaning mode or in AC cleaning mode for 10% or less, preferably for 5% or less, particularly preferably for 2% or less, very particularly preferably for 1% or less, particularly preferably for 0.5% or less, of the operating time.

[0038] As explained above, in the inventors' estimation, it is preferable to vary the DC voltage used for polarization as little as possible for the most stable operation. Furthermore, the inventors have succeeded in identifying electric field strengths with which particularly advantageous polarization effects and thus particularly favorable separation performance can be achieved. Accordingly, a method according to the invention is preferred, wherein a DC voltage is applied in the polarization mode that varies by 10% or less, preferably 5% or less, particularly preferably 1% or less, and particularly preferably essentially not at all, relative to the mean value of the DC voltage in the polarization mode.Additionally or alternatively, a method according to the invention is preferred, wherein the average electric field strength of the electric field in the polarization mode is 0.5 kV / cm or more, preferably 1 kV / cm or more, particularly preferably 2 kV / cm or more, and / or wherein the average electric field strength of the electric field in the polarization mode is in the range from 0.5 kV / cm to 30 kV / cm, preferably in the range from 1 kV / cm to 15 kV / cm, particularly preferably in the range from 2 kV / cm to 10 kV / cm.

[0039] In addition to the polarization mode, the filter operates in one of two cleaning modes. These cleaning modes are based on the same concept, but differ in whether a direct current or an alternating current is applied. For ease of differentiation, the corresponding cleaning modes would be referred to as DC and AC cleaning modes, respectively, in the context of the present invention.

[0040] In both cleaning modes, a pulsed electric field is generated by applying pulsed current to the polarization elements. Microorganisms present in the polarizable filter medium are exposed to this pulsed electric field. During this process, also known as electroporation, the cell membranes of the microorganisms become temporarily permeable, allowing molecular transport through the cell membranes. By creating this temporary permeability, components essential to the microorganisms can migrate from the interior to the exterior due to hydrostatic pressure differences and osmotic effects. If the electric field strength exceeds the critical electric field strength, this process is at least partially irreversible, leading to the death of the microorganisms.Those skilled in the art will understand that the pulsed direct current in DC cleaning mode and AC cleaning mode generates a pulsed electric field. In other words, this is a method according to the invention, wherein the filter is operated in DC cleaning mode such that microorganisms, in particular bacteria, located in the filter medium are damaged, preferably irreversibly damaged, by the pulsed electric field, in particular in their cell membrane, or a method according to the invention, wherein the filter is operated in AC cleaning mode such that microorganisms, in particular bacteria, located in the filter medium are damaged, preferably irreversibly damaged, by the pulsed electric field, in particular in their cell membrane.

[0041] The concept of electroporation and the use of pulsed electric fields to kill microorganisms is known from the food industry and is widely used in the food industry to kill harmful microorganisms during food processing. The electric field strengths required for killing depend on the type of microorganisms and the pulse pattern used and can be tailored by a person skilled in the art to the type of microorganisms to be killed. It is conceivable to provide different cleaning modes for the operation of the filters in the method according to the invention, which are tailored to different microorganisms in terms of field strength and / or pulse sequence.When implementing the present invention, the person skilled in the art can advantageously draw on the extensive preparatory work from the food industry, from which a multitude of processes and associated process parameters for killing a wide range of different microorganisms are known and established. Further information on the fundamental technological background of electroporation, the underlying physicochemical relationships, and its general use in the food industry can be found, for example, in the "Handbook of Electroporation," Damijan Miklavcic, ISBN 9783319328850, 2017, or the publication "DLG Expert Knowledge 5 / 2018 - Application of Pulsed Electric Fields (PEF) in the Food Industry."

[0042] The DC cleaning mode and the AC cleaning mode differ in particular in how the nature of the electric field during the pulse can be described. The direct voltage used in the DC cleaning mode means that the pulses can expediently be described via the average electric field strength. A method according to the invention is preferred, wherein in the DC cleaning mode the average electric field strength of the electric field during the pulses is 0.75 kV / cm or more, preferably 1 kV / cm or more, very particularly preferably 2.5 kV / cm or more, and / or wherein in the DC cleaning mode the average electric field strength of the electric field during the pulses is in the range from 0.5 kV / cm to 40 kV / cm, preferably in the range from 1 kV / cm to 25 kV / cm, very preferably in the range from 2 kV / cm to 10 kV / cm.

[0043] In contrast to direct current, an alternating field is maintained during the pulses in AC cleaning mode. Therefore, the inventors consider it appropriate to characterize the pulses by the electric field strength present at the extreme points, whereby the absolute value can be conveniently used. A method according to the invention is preferred, wherein in the AC cleaning mode the peaks of the magnitude function of the electric field strength during the pulses are at least partially, preferably predominantly, particularly preferably all, at 0.75 kV / cm or more, preferably 1 kV / cm or more, very particularly preferably 2.5 kV / cm or more, and / or wherein in the AC cleaning mode the peaks of the magnitude function of the electric field strength during the pulses are at least partially, preferably predominantly, particularly preferably all, in the range from 0.5 kV / cm to 40 kV / cm, preferably in the range from 1 kV / cm to 25 kV / cm, particularly preferably in the range from 2 kV / cm to 10 kV / cm.

[0044] The inventors have identified it as advisable that the voltage selected for the cleaning modes be based on the value also used for polarization, although higher voltages can also be used for particularly pronounced cleaning effects in the cleaning modes.A method according to the invention is preferred, wherein the maximum applied DC voltage in the polarization mode differs from the maximum applied DC voltage in the DC cleaning mode by 50% or less, preferably 25% or less, particularly preferably 10% or less, very particularly preferably 5% or less, particularly preferably by 2% or less, extremely preferably essentially not at all, and / or wherein the maximum applied DC voltage in the polarization mode differs from the maximum amount of the applied AC voltage in the AC cleaning mode by 50% or less, preferably 25% or less, particularly preferably 10% or less, very particularly preferably 5% or less, particularly preferably by 2% or less, extremely preferably essentially not at all.

[0045] The inventors have found that when implementing the present invention, the person skilled in the art can advantageously orient himself on the process procedures known from the food industry with regard to the pulse scheme to be used.

[0046] A method according to the invention is preferred, wherein the pulse sequence of the DC cleaning mode or the AC cleaning mode comprises 5 or more, preferably 10 or more, particularly preferably 20 or more, very particularly preferably 40 or more, pulses. Additionally or alternatively, a method according to the invention is preferred, wherein the pulses in the cleaning mode at least partially, preferably predominantly, particularly preferably substantially all, have a length in the range from 40 to 40,000 ns, preferably in the range from 100 to 10,000 ns, particularly preferably in the range from 300 to 6,000, very particularly preferably in the range from 400 to 5,000 ns, especially preferably in the range from 500 to 4,000 ns, based on the half-width of the pulses or the half-width of the envelope.Additionally or alternatively, a method according to the invention is also preferred, wherein the pulses in the DC cleaning mode are at least partially, preferably predominantly, particularly preferably substantially all, rectangular pulses, triangular pulses, or sine pulses, preferably rectangular pulses. Additionally or alternatively, a method according to the invention is also preferred, wherein the alternating voltage has a constant frequency, preferably a constant frequency and amplitude, during the pulses in the AC cleaning mode.

[0047] Even if the desired cleaning effect can also be achieved using alternating voltage, in the opinion of the inventors it is particularly preferred for essentially all embodiments to rely largely on direct voltage in the method according to the invention and accordingly to forgo the AC cleaning mode as far as possible, preferably essentially completely, in favor of the DC cleaning mode. The fact that the desired polarization always requires a direct voltage means that the devices used can be designed to be significantly simpler and more robust if the possibility of generating an alternating field does not have to be additionally provided. Accordingly, a method according to the invention is particularly preferred in which the filter is partially operated in DC cleaning mode. Accordingly, a method according to the invention is also preferred in which the voltage source is a direct voltage source.

[0048] Even if it would be at least theoretically conceivable not to set the DC voltage completely to zero between the pulses when alternating between the polarization mode and the DC cleaning mode, this is less preferred both with regard to the achievable cleaning effect and the complexity of the control. Accordingly, a method according to the invention is preferred, wherein the DC voltage in the DC cleaning mode between two adjacent pulses drops at least partially, preferably predominantly, particularly preferably essentially completely, to 10% or less, preferably 5% or less, particularly preferably 1% or less, very particularly preferably 0.5% or less, of the average DC voltage value of the pulses, wherein the DC voltage in the DC cleaning mode particularly preferably drops at least partially, preferably predominantly, particularly preferably essentially completely, essentially to 0 V between two adjacent pulses.

[0049] In accordance with the expert's understanding, the method according to the invention will switch between the operating modes. A particularly simple embodiment for designing the switch is to switch between the operating modes at regular intervals, which in preferred embodiments is coordinated with the operating time of the filter. In this respect, a method according to the invention is preferred, wherein the operation of the filter is switched at regular time intervals, in particular operating time intervals, for example after 8 hours or more, 12 hours or more, 24 hours or more, 48 hours or more, or 168 hours or more.

[0050] For particularly advantageous embodiments, however, the inventors propose that the cleaning modes can be used in a demand-optimized manner, with the demand being determined on the basis of a predetermined criterion, although several criteria are also conceivable, which can be met alternatively or cumulatively. In addition to a time-based criterion, the cleaning mode can be tailored in particular to specific situations, for example starting or shutting down the filter system. Particularly when used in a vehicle, refueling or charging processes can also be suitable phases for cleaning the filter. In addition, manual request processes can also be considered, which can be triggered, for example, via a vehicle computer. A method according to the invention is therefore preferred, wherein the operation of the filter is switched to the DC cleaning mode or AC cleaning mode once a predetermined criterion is reached.Particularly preferred is a method according to the invention, wherein the predetermined criterion is selected from the group consisting of the expiration of a predetermined period of time, in particular the expiration of a predetermined operating period, the starting of the vehicle engine, the shutting down of the vehicle engine, the starting of the filter system, the shutting down of the filter system, the recording of a refueling process, the recording of a charging process, the recording of a sensor value with a sensor unit, and manual user requests. An example of a method according to the invention is one in which the predetermined period of time is 60 minutes or more, preferably 360 minutes or more, very particularly preferably 480 minutes or more.

[0051] The inventors consider it particularly preferred if the cleaning modes are controlled using sensors. A wide range of sensors and the sensor values ​​obtained from them can be used to identify suitable times for carrying out a cleaning step. In particular, the determination of temperature and humidity or the detection of precipitation can be used to determine the reproduction conditions for microorganisms, thereby controlling the frequency of the cleaning processes. Furthermore, it is also possible to use a position sensor, for example a GPS sensor, as a sensor to determine the climatic conditions and / or the general microorganism load of the fluid to be filtered from the position of the filter or the vehicle, for example by comparing it with suitable map material, and to control the cleaning activity accordingly.Accordingly, a method according to the invention is particularly preferred, wherein the filter comprises one or more sensor units for detecting the one or more sensor values. A method according to the invention is preferred, wherein the operation of the filter is switched to the AC cleaning mode or DC cleaning mode depending on one or more sensor values, preferably when the one or more sensor values ​​meet a predetermined criterion. Additionally or alternatively, a method according to the invention is preferred, wherein the proportion of the AC cleaning mode or DC cleaning mode in the operating time of the filter is controlled depending on one or more sensor values, preferably when the one or more sensor values ​​meet a predetermined criterion.Particularly preferred in this respect is a method according to the invention, wherein the pulse sequence and / or the level of the applied voltage in the AC cleaning mode or DC cleaning mode is changed depending on one or more sensor values, preferably when the one or more sensor values ​​meet a predetermined criterion. Additionally or alternatively, particularly preferred is a method according to the invention, wherein the one or more sensor values ​​are selected from the group consisting of temperature, air humidity, precipitation data, and position data, preferably selected from the group consisting of temperature and air humidity.

[0052] In the embodiments described above, a method according to the invention is preferably used, wherein the filter comprises one or more sensor units for detecting the one or more sensor values. A method according to the invention is preferred, wherein the sensor units are selected from the group consisting of temperature sensors, humidity sensors, precipitation sensors, and GPS sensors, preferably selected from the group consisting of temperature sensors and humidity sensors.

[0053] In principle, the inventors propose that, with a view to the main effect of advantageous particle separation sought in electrostatic precipitators with filter functionality, it is expedient to provide sufficiently long polarization phases between individual cleaning phases. Conversely, the inventors believe it is expedient to design the cleaning phases sufficiently long to achieve a good cleaning effect during the cleaning phases. In this respect, a method according to the invention is preferred, wherein the filter is operated in polarization mode for 1 minute or more, preferably for 30 minutes or more, particularly preferably for 60 minutes or more, between two operating times in AC cleaning mode or DC cleaning mode.Additionally or alternatively, a method according to the invention is preferred, wherein the filter is operated in AC cleaning mode or DC cleaning mode for a time in the range of 5 ps to 60 s, preferably in the range of 10 ps to 10 s, particularly preferably in the range of 100 ps to 5 s, between two operating times in the polarization mode.

[0054] The inventors propose that, to avoid interference with the surrounding electronics, especially when used in vehicles, it is particularly advantageous to provide electromagnetic shielding for the filter. Accordingly, a method according to the invention is preferred, wherein the filter comprises one or more shielding elements for electromagnetic shielding of the filter.

[0055] A major advantage of the present invention is that it enables the reliable destruction of microorganisms without relying on the use of biocides. In this respect, the inventors propose that it is particularly advantageous to exploit this advantage by omitting the use of such biocides in the filter or filter medium. Accordingly, a method according to the invention is preferred in which the filter does not comprise any antimicrobial additives and / or antimicrobial layers.

[0056] The inventors have succeeded in identifying preferred embodiments for the preferably used multi-layer filter medium and its individual layers, in particular the conductor layers, whereby advantageous cleaning performances have been achieved when using pulsed electric fields, in particular with the particle filter layers disclosed below.

[0057] Firstly, a method according to the invention is preferred, wherein the first conductor layer comprises a first textile fabric, preferably a first textile fabric coated or impregnated at least in sections with an electrically conductive first material, and / or wherein the second conductor layer comprises a second textile fabric, preferably a second textile fabric coated or impregnated at least in sections with an electrically conductive second material.

[0058] The term "textile fabric" is clear to the skilled person and refers to two-dimensional textile products, which can be woven, warp-knitted, needle-punched, or knitted, for example. In accordance with the expert's understanding, non-textile, fiber-containing fabrics, such as paper and cardboard, in which the fibers are primarily held together by binding agents, are not considered textile fabrics. Even though a wide range of textile fabrics could in principle be considered for the textile fabrics of the conductor layers, the inventors have been able to achieve the best performance characteristics with so-called "non-wovens," and in particular with spunbonded nonwovens.A corresponding textile fabric made of a non-conductive material can advantageously be achieved by equipping the textile fabric with a conductive material. According to the inventors' assessment, a variety of possible methods are suitable in principle. Thus, a method according to the invention is preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, are a nonwoven fabric, preferably a spunbonded fabric.

[0059] In practice, the person skilled in the art readily distinguishes between an electrically conductive material and an electrically insulating material based on his or her expert and clear technical understanding of these terms. In this respect, a material is considered to be electrically conductive within the scope of the present invention in particular if its specific electrical resistance at 20 °C is 10 6 Q*m or less, preferably at 10 5 Q*m or less, particularly preferably 10 4 Q*m or less. Conversely, a material is considered to be an electrically insulating material within the scope of the present invention if its specific electrical resistance at 20 °C is 10 7 Q*m or more, preferably at 10 9 Q*m or more, particularly preferably at 10 11Q*m or more. Accordingly, metals and alloys, as well as carbon blacks, in particular conductive carbon black, and plastics made conductive by additives, are electrically conductive materials, whereas typical, unmodified plastics such as PET or PE are also electrically insulating materials, as are most glasses and ceramics. The specific electrical resistance of materials is a value that is well known to those skilled in the art and can be found in relevant tables for most materials. The measurement of the specific electrical resistance of other components is carried out in accordance with common practice, either according to DIN EN ISO 3915 from 1999, which is used in particular for particularly conductive materials, or according to IEC 60093 from 1993, which is used for high specific electrical resistances.The question of which of the two standards should be used depends on the requirements of the two regulations as well as the properties of the respective material being examined.

[0060] Those skilled in the art will understand that the electrical conductivity of conductor layers, for example, the first conductor layer, can in many cases, for example, when using composite materials, result from the presence of conductive material paths running through an otherwise largely insulating material. For example, a dielectric fleece whose fibers are coated with a thin layer of conductive carbon black can be an electrically conductive layer, even though the macroscopic resistivity of the composite material is relatively high due to the dielectric carrier material.

[0061] Furthermore, additionally or alternatively, a method according to the invention is preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, consist of a plastic to a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably substantially 100%, based on the mass of the textile fabric, wherein the plastic is preferably selected from the group consisting of polyacrylonitriles, polyolefins, polyesters and mixtures of these plastics, particularly preferably polyacrylonitriles, polypropylene, polyethylene terephthalate and mixtures of these plastics, especially preferably polyethylene terephthalate.

[0062] Additionally or alternatively, a method according to the invention is also preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, are produced or can be produced by equipping the respective textile fabric, in particular the nonwoven fabric, with the respective electrically conductive material using a method which is selected from the group consisting of impregnation, dip coating, in particular using a padding system, spray coating, application coating, in particular by means of a dispersion in the kiss-coat process, and print coating.

[0063] Additionally or alternatively, a method according to the invention is also preferred, wherein the electrically conductive first material and / or the electrically conductive second material, preferably the electrically conductive first material and the electrically conductive second material, are selected from the group consisting of metals, conductive plastics and carbon, preferably carbon, in particular carbon black or graphene, wherein the electrically conductive material is particularly preferably identical for the first conductor layer and the second conductor layer.

[0064] Additionally or alternatively, a method according to the invention is also preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, as a result of the coating of the respective textile fabric, are electrically conductive over at least 80% or more of the area, preferably over 90% or more, particularly preferably over 95% or more, very particularly preferably over 98% or more, particularly preferably substantially over the entire area.

[0065] Even though the conductor layers can contribute to the filtration performance of the filter media, particularly when designed as textile fabrics, the inventors consider it advantageous if the conductor layers are designed with sufficient open pores so that they primarily restrict the air flow through the filter medium as little as possible. With regard to the weight of the conductor layers, at least when using textile fabrics, there is a trade-off between the influence on the overall weight of the filter medium and a beneficial stabilizing effect of the conductor layers on the filter medium, thus improving the mechanical properties. In this respect, the inventors have succeeded in identifying suitable basis weights for the textile fabrics that advantageously resolve this trade-off.Against this background, a method according to the invention is preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, have an air passage in the range of 500 to 30,000 L / (m) at 200 Pa. 2 s), preferably in the range of 2000 to 20000 L / (m 2 s). Additionally or alternatively, a method according to the invention is also preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, have a basis weight in the range from 5 to 200 g / m 2 , preferably in the range of 10 to 150 g / m 2 , particularly preferably in the range of 15 to 50 g / m 2 , have.

[0066] With regard to the general structure of the multi-layer filter medium, a method according to the invention is preferred, wherein the filter layer comprises one or more further layers, preferably further layers arranged between the first conductor layer and the second conductor layer, wherein the filter layer preferably comprises two or more dielectric layers, particularly preferably three or more dielectric layers.

[0067] Additionally or alternatively, a method according to the invention is also preferred, wherein at least one of the dielectric layers, preferably all of the dielectric layers, consists of a dielectric plastic material to a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably essentially 100%, based on the mass of the dielectric layer. A method according to the invention is particularly preferred, wherein the dielectric plastic material is selected from the group consisting of polyolefins, in particular polytetrafluoroethylene, polytetrafluoroethylene-propylene, polypropylene, and polyethylene, polyesters, in particular polyethylene terephthalate, polycarbonates, polyamides, polyvinylidene fluoride, polyacrylonitrile, and polylactides.Additionally or alternatively, a method according to the invention is particularly preferred, wherein the dielectric plastic material has a specific electrical resistance at 20 °C of 10. 7 Q*m or more, preferably at 10 9 Q*m or more, particularly preferably at 10 11 Q*m or more. For the majority of embodiments, a method according to the invention is preferred, wherein at least one of the dielectric layers is a particle filter layer comprising a third textile fabric. A method according to the invention is particularly preferred, wherein the third textile fabric is a nonwoven fabric, wherein the third textile fabric is preferably selected from the group consisting of needle-punched nonwovens and meltblown nonwovens. Additionally or alternatively, a method according to the invention is particularly preferred, wherein the particle filter layer has a basis weight in the range of 10 to 200 g / m 2, preferably in the range of 15 to 150 g / m 2 , particularly preferably in the range of 20 to 110 g / m 2 , has.

[0068] A method according to the invention is preferred, in particular for multi-layer filter media containing activated carbon, wherein at least one of the dielectric layers is a protective layer which comprises a fourth textile fabric. A multi-layer filter medium according to the invention is particularly preferred, wherein the fourth textile fabric is a nonwoven fabric, preferably a spunbonded fabric.

[0069] Additionally or alternatively, a method according to the invention is preferred, wherein the protective layer at 200 Pa has an air passage in the range of 500 to 30,000 L / (m 2 s), preferably in the range of 2000 to 20000 L / (m 2 s). Additionally or alternatively, a method according to the invention is also preferred, wherein the protective layer has a basis weight in the range of 15 to 400 g / m 2, preferably in the range of 50 to 200 g / m 2 , is particularly preferred. Additionally or alternatively, a method according to the invention is also particularly preferred, wherein the protective layer has a Gurley flexural rigidity, determined according to ASTM D6125-97, in the range from 0.4 to 40 mN, preferably in the range from 0.5 to 20 mN, particularly preferably in the range from 0.6 to 10 mN.

[0070] In the opinion of the inventors, for the majority of embodiments, additionally or alternatively, a method according to the invention is preferred, wherein the filter layer comprises an activated carbon layer, wherein the activated carbon layer comprises activated carbon in a mass fraction of 70% or more, based on the mass of the activated carbon layer. Activated carbon is known to those skilled in the art in the field of filtration technology as an important material and is commercially available from numerous manufacturers. It is preferred that the activated carbon layer is formed from a high mass fraction of activated carbon, so that, for example, the proportion of fibers or other carrier materials in the activated carbon layer should be kept as low as possible. Based on the inventors' experiments, this achieves a particularly good separation effect or cleaning performance while simultaneously minimizing the thickness or weight.The inventors have found that particularly high-performance filter inserts can be obtained using activated carbon layers that are as pure as possible and which, apart from the binder, preferably consist essentially exclusively of activated carbon. Accordingly, a process according to the invention is preferred, wherein the activated carbon layer comprises activated carbon in a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, based on the mass of the activated carbon layer. Additionally or alternatively, a process according to the invention is preferred, wherein the activated carbon is fixed in the activated carbon layer by a binder. The inventors have succeeded in identifying particularly preferred ranges for the selection of the activated carbon and for the dimensioning of the activated carbon layer, with which excellent filter performances have been achieved in their own experiments.A process according to the invention is preferred, wherein the activated carbon is particulate activated carbon, wherein the activated carbon preferably has an average diameter d50 in the range from 0.1 to 4 mm, preferably in the range from 0.2 to 2 mm. Additionally or alternatively, a process according to the invention is also preferred, wherein the activated carbon has a specific surface area of ​​500 m². 2 / g or more, preferably 1000 m 2 / g or more, particularly preferably 2000 m 2 / g or more. In addition or alternatively, a process according to the invention is preferred, wherein the activated carbon layer has a basis weight in the range of 50 to 1000 g / m 2 , preferably in the range of 100 to 600 g / m 2 , has.

[0071] The inventors have developed a particularly preferred electrical contacting system for the preferred use of a multi-layer filter medium that integrates at least one conductor layer. Although very simple configurations of the electrical contacting system, for example, relying on cables, are theoretically conceivable for contacting these preferred multi-layer filter media, the inventors have designed a particularly advantageous electrical contacting system with a view to time- and cost-efficient production, which can be combined particularly efficiently with the conductor layer(s), particularly by bonding it using an electrically conductive plastic material.In the inventors' opinion, it is particularly advantageous if traditional electrical cabling is not used or is used only to a limited extent, but rather the contacting system is designed as largely as possible from components made of an electrically conductive plastic. Accordingly, a method according to the invention is preferred, wherein the electrically conductive components of the electrical contacting system are formed at least partially, preferably predominantly, particularly preferably substantially completely, from an electrically conductive plastic. A method according to the invention is particularly preferred, wherein the electrically conductive plastic of the electrical contacting system has a specific electrical resistance of 10 at 20°C. 6 Q*m or less, preferably 10 5 Q*m or less, more preferably 10 4 Q*m or less.

[0072] According to the inventors' assessment, these electrically conductive components, which preferably consist of an electrically conductive plastic, should be arranged on a preferably thin substrate, which acts as a carrier and advantageously enables the electrically conductive components of the electrical contacting system to be assembled before attachment to the filter to be used according to the invention and to be applied in a single step during the manufacturing process, for example, to the side lamination of the filter. Accordingly, a method according to the invention is preferred, wherein the electrically conductive components of the electrical contacting system are conductive components arranged on a substrate and / or in a substrate.Additionally or alternatively, a method according to the invention is preferred, wherein the substrate is selected from the group consisting of electrically insulating films, preferably plastic films, wherein the average thickness of the substrate is preferably in the range from 20 to 500 pm, particularly preferably in the range from 80 to 150 pm.

[0073] The use of a thin substrate, in particular a film, in combination with conductive components made of plastic, advantageously allows the electrical contacting system to be designed not only in a particularly space-saving and lightweight manner, but also results in an electrical contacting system with a high degree of flexibility in which the substrate and the conductive components lying thereon can be particularly easily adapted to the structural requirements of the filter to be used according to the invention.

[0074] The inventors' experiments have shown, in particular, that a corresponding electrical contacting system can be advantageously printed onto the substrate, although, at least theoretically, other additive manufacturing processes could also be considered. Thus, a method according to the invention is preferred, wherein the electrical contacting system can be produced by printing the substrate with an electrically conductive material, preferably an electrically conductive plastic, wherein the printing is preferably a screen printing process.

[0075] In particular, additive manufacturing processes advantageously make it possible to obtain an electrical contacting system that is provided with the electrically conductive components only on one side and consequently has a bottom side whose properties are largely influenced by those of the substrate, which can advantageously be designed as an electrically insulating substrate. With regard to attachment, a method according to the invention is thus preferred, wherein the electrical contacting system comprises the electrically conductive components of the electrical contacting system at least partially, preferably predominantly, particularly preferably substantially completely, preferably at least the contact points and the contacting elements, on the same side of the substrate.

[0076] In a particularly preferred embodiment, the substrate is designed as a comparatively thin film, in whose central region essential elements of the electrical contacting system are arranged, for example, the contact points for the external voltage source or a potential voltage divider. The inventors propose that wing-like or tab-like projections can be formed on the sides, onto which the contacting elements intended for contacting the conductor layers are applied.When such a contacting system is applied to the lateral lamination of a filter according to the invention, the wing-like tabs can be folded over particularly easily so that they each contact the conductor layer and can then be glued, for example, with an electrically conductive adhesive in such a way that a material-to-material connection is created through the plastic material without this connection being made more difficult by excessive mechanical stresses.Accordingly, a method according to the invention is preferred, wherein the first contacting element and / or the second contacting element, preferably the first contacting element and the second contacting element, are arranged on laterally projecting projections of the substrate, wherein the laterally projecting projections preferably have a deformation region and a contact region, wherein the contact region is preferably wider than the deformation region transversely to the longitudinal direction of the filter. A method according to the invention is particularly preferred, wherein the laterally projecting projections are L-shaped. Additionally or alternatively, a method according to the invention is particularly preferred, wherein the laterally projecting projections are designed to be reversibly and non-destructively deformable, in particular bendable, in the deformation region.

[0077] The preferred multilayer filter media with integrated conductor layers are particularly suitable for combination with an ionization device in an electrostatic precipitator with filter functionality. The voltage required for ionization will usually be significantly higher than the polarization voltage necessary for polarization or the maximum applicable polarization voltage, which is limited, particularly when both polarization elements are integrated into the multilayer filter medium, by the voltage at which undesirable breakdown occurs. One conceivable solution would be to provide different voltage sources for the ionization device and the filter insert. However, the inventors have recognized that such a provision of separate high-voltage sources is often not possible or involves considerable equipment complexity, so this design is less preferred.For this purpose, it is proposed to design the electrical contacting system as a voltage divider, with which a voltage taken over from the ionization device can be adapted to the requirements of the multi-layer filter medium. A method according to the invention is therefore preferred, wherein the electrical contacting system is a voltage divider. For this purpose, the electrical contacting system can have contact points which are intended to be contacted directly or indirectly via the ionization device with an electrical potential difference which is designed for the ionization device. Between these contact points, a resistance path is provided which preferably has a meandering contour. The resistance path applied to the first contacting element orThe voltage possibly omitted from the second contacting element can advantageously be adjusted by positioning the contacting element along this resistance path, so that, for example, only a reduced voltage is present between the two contacted conductor layers compared to the ionization device. Against this background, a method according to the invention is preferred, wherein in the electrical contacting system the first contact point is electrically conductively connected to the second contact point via a resistance path, wherein the first contacting element is electrically conductively connected to the resistance path between the first contact point and the second contact point, and wherein the second contacting element is electrically conductively connected to the second contact point. Additionally or alternatively, a method according to the invention is also preferred, wherein the resistance path is designed in a meandering shape.Additionally or alternatively, a method according to the invention is also preferred, wherein the first contacting element and / or the second contacting element, preferably the first contacting element and the second contacting element, are connected to the resistance path such that the contact area between the resistance path and the contacting element is larger than the cross section of the resistance path orthogonal to the longitudinal direction of the resistance path. Additionally or alternatively, a method according to the invention is also preferred, wherein the second contacting element is not electrically conductively connected to the resistance path between the first contact point and the second contact point.

[0078] In particularly preferred embodiments, in addition to the electrically conductive components of the contact system, machine-readable information, for example in the form of a QR code, can also be provided on the substrate. Especially when the electrical contact system is applied to the side lamination of the multi-layer filter medium, it is particularly easy to read from the outside. This makes it possible to provide the customer or the workshop with important information about the handling and / or installation of corresponding filters.

[0079] The invention also relates to a filter system for use in a method according to the invention, comprising: a) a filter comprising: i) a first polarization element, ii) a second polarization element, iii) a polarizable filter medium arranged between the first polarization element and the second polarization element, and iv) an electrical contacting system, wherein the electrical contacting system is configured such that a voltage can be applied between the first polarization element and the second polarization element, b) a voltage source, and c) an electronic control device for controlling the filter system, wherein the electronic control device is configured to operate the filter in at least two different operating modes, wherein the electronic control device is configured to operate the filter in one polarization mode for 80% or more of the operating time,wherein in the polarization mode, a continuous DC voltage is applied between the first polarization element and the second polarization element, which varies by 20% or less, based on the mean value of the DC voltage in the polarization mode, wherein the electronic control device is configured to operate the filter partially in a DC cleaning mode, wherein in the DC cleaning mode, a pulsed DC voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the mean electric field strength of the electric field during the pulses is 0.5 kV / cm or more, or wherein the electronic control device is configured to operate the filter partially in an AC cleaning mode,wherein in the AC cleaning mode, a pulsed alternating voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, the peaks of the magnitude function of the electric field strength during the pulses being at least partially at 0.5 kV / cm or more.

[0080] A filter system according to the invention is preferred, wherein the filter system is installed in a vehicle, preferably in a land vehicle.

[0081] Also disclosed within the scope of the invention is a filter insert for use as a reversibly and non-destructively replaceable component in a filter system according to the invention, comprising at least one of the polarization elements, preferably the first polarization element and the second polarization element, the polarizable filter medium and the electrical contacting system.

[0082] The use of pulsed electric fields for cleaning polarizable filter media in electrostatic precipitators with filter functionality is also disclosed. The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figures. The figures show:

[0083] Fig. 1 is a schematic representation of a filter system according to the invention in a preferred embodiment;

[0084] Fig. 2 shows an exemplary visualization of an exemplary voltage curve of a filter over the operating time in the method according to the invention; and

[0085] Fig. 3 is a perspective view of a filter to be used according to the invention in a preferred embodiment.

[0086] Fig. 1 shows a schematic representation of a filter system 28 according to the invention in a preferred embodiment during the implementation of the method according to the invention, which is used in the course of fluid filtration. In Fig. 1, the large arrows indicate the flow direction of the fluid to be filtered through the filter 10 or the filter system 28. The fluid to be filtered first passes through an ionization device 32, where dirt particles contained in the fluid are ionized by a corona discharge. After the ionization device 32, the fluid to be filtered encounters a multilayer filter medium 22.The multi-layer filter medium 22 comprises a first conductor layer 24 as the first polarization element 12 and a second conductor layer 26 as the second polarization element 14, wherein the first conductor layer 24 and the second conductor layer 26 are connected to one another by an electrical contacting system 18 such that an electrical voltage can be applied between the conductor layers.

[0087] In the example shown in Fig. 1, the electrical contacting system 18 is supplied from the same voltage source 20 as the ionization device 32, which is a DC voltage source located in the vehicle. A polarizable filter medium 16 is arranged between the first conductor layer 24 and the second conductor layer 26. This filter medium comprises, in addition to a dielectric particle filter layer, an activated carbon layer for absorbing pollutants. The filter system 28 according to the invention is configured to operate the method according to the invention via the electronic control unit 30.

[0088] For this purpose, the filter 10 is operated in polarization mode for the vast majority of the time, in which the DC voltage applied via the electrical contact system 18, which is essentially constant, forms an electric field between the first polarization element 12 and the second polarization element 14, which polarizes the polarizable filter medium 16 and thus promotes the separation of the previously ionized dirt particles. The filter system 28 according to the invention in FIG. 1 is configured, via appropriate software programming of the electronic control device 30, to switch from the polarization mode to the DC cleaning mode at regular intervals based on the operating time of the filter, wherein the DC voltage provided by the voltage source 20 is now no longer passed on to the conductor layers continuously, but in a plurality of short pulses in order to generate a corresponding pulsed electric field.Furthermore, the filter 10 is equipped with sensor units (not shown) by means of which the temperature and humidity can be monitored. After phases of very high humidity combined with high temperature, the filter system according to the invention is designed to additionally switch to DC cleaning mode out of sequence, preferably during stationary phases of the vehicle, in particular during refueling or charging processes.

[0089] In the example shown in Fig. 1, the electronic control device 30 is an on-board computer on board the vehicle, which can assume the necessary control of the filter system 28. To prevent interference with the on-board electronics due to the pulsed operation of the filter 10 in DC cleaning mode, the filter 10 is equipped with suitable electromagnetic shielding.

[0090] Fig. 2 shows a schematic representation of an exemplary curve of the DC voltage over time, in which a first and a second operation in the polarization mode M1 is interrupted by an operation in the DC cleaning mode M2.

[0091] Fig. 3 shows a perspective view of a filter insert 34 usable according to the invention, which has a pleated, multi-layer filter medium 22 with integrated conductor layers, which is fixed by a double-sided lamination 36 with a felt fabric. A preferred electrical contact system 18 is arranged on the side wall formed by the lateral lamination 36. This system is designed as a voltage divider made of an electrically conductive plastic on an insulating substrate and comprises two contact points via which the voltage provided by the voltage source 20 can be tapped indirectly via the ionization device 32. The voltage applied to the multi-layer filter medium 22 can be adjusted via the voltage divider.

[0092] Reference symbol

[0093] 10 filters

[0094] 12 first polarization element

[0095] 14 second polarization element 16 polarizable filter medium

[0096] 18 electrical contact system

[0097] 20 Voltage source

[0098] 22 multi-layer filter medium

[0099] 24 first conductor layer 26 second conductor layer

[0100] 28 filter system

[0101] 30 electronic control device

[0102] 32 ionization device

[0103] 34 Filter insert 36 Lamination

Claims

Claims 1. A method for operating a filter (10), the filter comprising: i) a first polarization element (12), ii) a second polarization element (14), iii) a polarizable filter medium (16) arranged between the first polarization element (12) and the second polarization element (14), and iv) an electrical contacting system (18), the electrical contacting system (18) being configured to allow a voltage provided by a voltage source (20) to be applied between the first polarization element (12) and the second polarization element (14), the method comprising operating the filter (10) in at least two mutually different operating modes, the filter (10) being operated in a polarization mode for 80% or more of the operating time, a continuous DC voltage being applied between the first polarization element (12) and the second polarization element (14) in the polarization mode.which varies by 20% or less, based on the mean value of the DC voltage in the polarization mode, wherein the filter (10) is partially operated in a DC cleaning mode, wherein in the DC cleaning mode a pulsed DC voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the mean electric field strength of the electric field during the pulses is 0.5 kV / cm or more, and / or wherein the filter (10) is partially operated in an AC cleaning mode, wherein in the AC cleaning mode a pulsed AC voltage is applied between the, first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.

2. The method according to claim 1, wherein the filter (10) is partially operated in DC cleaning mode.

3. The method according to claim 1 or 2, wherein the average electric field strength of the electric field in the polarization mode is 0.5 kV / cm or more.

4. Method according to one of claims 1 to 3, wherein in the DC cleaning mode the average electric field strength of the electric field during the pulses is 0.75 kV / cm or more, and / or wherein in the AC cleaning mode the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.75 kV / cm or more.

5. Method according to one of claims 1 to 4, wherein the first polarization element (12) and / or the second polarization element (14) are elements connected to the filter medium.

6. The method according to claim 5, wherein the filter (10) comprises a multi-layer filter medium (22), wherein the multi-layer filter medium (22) comprises: I) an electrically conductive first conductor layer (24) as the first polarization element (12), II) an electrically conductive second conductor layer (26) as a second polarization element (14), and III) an intermediate layer arranged between the first conductor layer (24) and the second conductor layer (26) as a filter medium, wherein the intermediate layer comprises at least one dielectric layer.

7. Method according to one of claims 1 to 6, wherein the operation of the filter (10) is switched to the DC cleaning mode or AC cleaning mode after a predetermined criterion is reached.

8. The method according to claim 7, wherein the predetermined criterion is selected from the group consisting of the expiration of a predetermined period of time, the starting of the vehicle engine, the stopping of the vehicle engine, the starting of the filter system, the stopping of the filter system, the registration of a refueling process, the registration of a charging process, the registration of a sensor value with a sensor unit and a manual user request.

9. Method according to one of claims 7 or 8, wherein the filter comprises at least one polarization element, the polarizable filter medium and the electrical contacting system as a reversibly and non-destructively replaceable filter insert (34) arranged in the filter.

10. Filter system (28) for use in a method according to any one of claims 1 to 9, comprising: a) a filter (10) comprising: i) a first polarization element (12), ii) a second polarization element (14), iii) a polarizable filter medium (16) arranged between the first polarization element (12) and the second polarization element (14), and iv) an electrical contacting system (18), wherein the electrical contacting system (18) is configured to allow a voltage to be applied between the first polarization element (12) and the second polarization element (14), b) a voltage source (20), and c) an electronic control device (30) for controlling the filter system, wherein the electronic control device (30) is configured to operate the filter (10) in at least two different operating modes, wherein the electronic control device (30) is configured to operate the filter (10) in one polarization mode for 80% or more of the operating time,wherein in the polarization mode, a continuous DC voltage is applied between the first polarization element (12) and the second polarization element (14), which varies by 20% or less, based on the mean value of the DC voltage in the polarization mode, wherein the electronic control device (30) is configured to operate the filter (10) partially in a DC cleaning mode, wherein in the DC cleaning mode, a pulsed DC voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the mean electric field strength of the electric field during the pulses is 0.5 kV / cm or more, or, wherein the electronic control device (30) is configured to operate the filter (10) partially in an AC cleaning mode, wherein in the AC cleaning mode a pulsed alternating voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.

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