Lubricant filter with improved soiling detection

Abstract

The invention relates to a lubricant filter (1, 1a..1c) for a lubricant circuit (16) of a transmission (11), which lubricant filter has a housing (2) with an inlet opening (3) and an outlet opening (4) and a filter insert (5, 5a..5c) having a filter medium (9) arranged in the housing (2). A pre-chamber (A) is arranged in the housing (2) between the inlet opening (3) and the filter insert (5, 5a..5c). The lubricant filter (1, 1a..1c) also comprises a plurality of electrodes (6a..6b'') for measuring the electrical conductivity of a lubricant accommodated in the pre-chamber (A), wherein the pre-chamber (A) is arranged between at least one pair of the electrodes (6a..6b''). The invention also relates to a transmission (11) having such a lubricant filter (1, 1a..1c), a vehicle (19) having such a transmission (11), and a method for operating such a transmission (11).

Description

[0001] Lubricant filter with improved contamination detection

[0002] TECHNICAL AREA

[0003] The invention relates to a lubricant filter for a transmission's lubrication circuit, comprising a housing with an inlet opening and an outlet opening, and a filter element containing a filter medium arranged in the housing. A pre-chamber is arranged in the housing between the inlet opening and the filter element. The invention further relates to a transmission with a lubrication circuit configured for lubricating the transmission with a lubricant and including such a lubricant filter. In addition, the invention relates to a vehicle with an electric motor configured for propelling the vehicle and a transmission of the aforementioned type configured for transmitting torque provided by the electric motor to a wheel of the vehicle.

[0004] Finally, the invention relates to a method for operating a gearbox of the aforementioned type.

[0005] STATE OF THE ART

[0006] Such a lubricant filter, such a transmission, such a vehicle, and such a process are generally known from the prior art. Lubricant filters are used in lubrication circuits to filter dirt and foreign particles from the lubricant and to ensure the proper operation of the lubrication circuit. If a contaminated filter element is not cleaned or replaced in a timely manner, damage to the components in the lubrication circuit can result. For example, a transmission can be severely damaged if the lubricant flow is significantly restricted or even stops completely. If the lubrication circuit runs through an electric motor (which is particularly likely to be coupled to the aforementioned transmission), then a contaminated lubricant filter can lead to overheating of the electric motor if the lubricant is also used for cooling in the electric motor.

[0007] To detect a clogged lubricant filter, it is known to measure a pressure difference between the inlet and outlet of the lubricant filter. However, the use of a pressure sensor is comparatively expensive, and moreover, such a pressure sensor, due to its upstream connection from the filter medium, can easily become contaminated and thus rendered ineffective. False readings can result.

[0008] It is also known to measure the pressure difference between an inlet and an outlet of a pump in the lubrication circuit, which serves to generate a lubricant flow. Besides the already mentioned, relatively high cost of a pressure sensor, a further disadvantage is that a measured pressure increase is not necessarily due to contamination of the lubricant filter, but can also have other causes.

[0009] In summary, the use of a pressure sensor is not only expensive, but it also cannot reliably detect contamination of the lubricant filter.

[0010] REVELATION OF THE INVENTION

[0011] One object of the invention is therefore to provide an improved lubricant filter, an improved transmission, an improved vehicle, and an improved method for operating a transmission. In particular, it aims to enable a more cost-effective and reliable detection of lubricant filter contamination compared to the prior art.

[0012] The object of the invention is solved with a lubricant filter of the type mentioned at the outset, which comprises several electrodes for measuring the electrical conductivity of a lubricant received in the pre-chamber, wherein the pre-chamber is arranged between at least one pair of electrodes.

[0013] Furthermore, the object of the invention is solved with a gearbox of the type mentioned above, in which the lubricant filter is designed as described above.

[0014] Furthermore, the problem of the invention is solved with a vehicle of the type mentioned at the outset, which has such a transmission.

[0015] Finally, the object of the invention is solved by a method for operating a gearbox of the type mentioned, wherein the electrical conductivity of a lubricant received in the pre-chamber is measured with the measuring unit using the electrodes.

[0016] The proposed measures allow for the determination of the degree of contamination of the lubricant filter and the lubricant flowing through it. Metallic foreign matter, which may be formed, for example, by abrasion from the aforementioned gearbox, accumulates upstream of the filter medium between the electrodes in the pre-chamber. As mentioned, the pre-chamber is located between the electrodes. In other words, an (imaginary) connecting line between the electrodes runs through the pre-chamber.

[0017] If an electrical voltage is applied to the electrodes by the measuring unit, the electrical conductivity or the specific resistance of the lubricant located between the electrodes can be measured.

[0018] If metallic foreign particles accumulate between the electrodes due to progressive contamination or soiling of the lubricant, the electrical conductivity measured by the measuring unit increases compared to a clean state. Based on the electrical conductivity, the measuring unit can determine the degree of contamination of the lubricant filter or the lubricant itself.

[0019] In particular, significant abrasion, which could contaminate the lubricant filter, is to be expected in a gearbox, making the application of the proposed measures especially advantageous there. If the lubricant circuit also runs through the electric motor, then measuring the degree of contamination of the lubricant filter can, in particular, prevent overheating of the electric motor, since abrasion from the

[0020] If the lubricant originates from gearbox components (e.g., gears), it can clog the lubricant filter and reduce the lubricant flow required for cooling the electric motor.

[0021] In a cost-effective version, the measuring unit can trigger the output of information to a user when the electrical conductivity exceeds a threshold. For example, the measuring unit can send a signal to the vehicle control unit of the aforementioned vehicle, which then prompts the display of a message on a screen in the vehicle's cockpit. Specifically, the measuring unit can trigger the output of a warning or a prompt to replace or clean the filter element when the electrical conductivity exceeds 10 4 S / m, which corresponds to a soiling level of approximately 12%. Other advantageous values ​​are 4.3–10 4 S / m (pollution level 50%) and 6.9-10 4S / m (pollution level 80%). Alternatively, the warning or request can also be issued at a different electrical conductivity, which may depend in particular on the specific application.

[0022] It is advantageous if the electrodes are positioned opposite each other with respect to the pre-chamber (especially in pairs). This allows for a comparatively strong measurement signal. Generally, two electrodes are sufficient in the lubricant filter, but a larger number of electrodes could also be present, with the pre-chamber located between at least one pair of electrodes. In other words, an (imaginary) connecting line between at least two electrodes runs through the pre-chamber. However, not all connecting lines need to pass through the pre-chamber. That is, the electrodes can also be partially arranged side by side.

[0023] It is noted that instead of electrical conductivity, specific electrical resistance or another quantity derived from it can also be measured and used to determine the degree of contamination of the lubricant filter or the lubricant itself.

[0024] Lubricants include, in particular, oils and oily coolants and lubricants, to which additives may also be added. In this context, the term "lubricant" refers specifically to lubricants in both new and used conditions and also includes contaminated lubricants, especially those containing metallic foreign particles.

[0025] The lubricant filter can be designed for easy replacement of the filter element, allowing a contaminated filter element to be easily cleaned or replaced with a new one. The filter element can be cup-shaped or tubular, and in particular rotationally symmetrical about a filter axis. The inlet and outlet openings can be located on opposite end faces of the lubricant filter. Alternatively, the inlet and outlet openings can be located on the same end face of the lubricant filter, and in particular, concentrically. One of the two openings can therefore be essentially ring-shaped. It is also conceivable that the inlet and outlet openings are located around the circumference of the lubricant filter. If the electrodes are located on the filter housing, the filter element can advantageously have a particularly simple design.

[0026] To avoid or minimize distortion of the measurement result, it is advantageous for the filter element and, if applicable, the housing to be made of a non-conductive or poorly conductive material. For example, the filter element and / or the housing could be made of plastic. The proposed measures specifically concern the filter medium and, if applicable, a frame that supports the filter medium. Therefore, it is advantageous for the filter medium and, if applicable, the frame to be made of a non-conductive or poorly conductive material. For example, the filter medium and the frame could again be made of plastic. However, it should be noted that the use of a frame is not necessary and the filter medium can also be self-supporting.

[0027] The measuring unit could be located inside the lubricant filter housing and, for example, cast into it. Alternatively, the measuring unit could be located on the filter element and, for example, cast into a frame of the element. The measurement data can be transmitted via cable or wirelessly. If the measuring unit is located outside the housing, wiring between the electrodes and the measuring unit can be routed through the housing, particularly using a suitable seal.

[0028] The electrical voltage applied to the electrodes by the measuring unit is preferably at least 12 V. This allows the conductivity values ​​to be accurately measured using the current induced by the voltage, without posing any risk to humans. In this context, it is particularly advantageous if the voltage is a maximum of 48 V. It is beneficial if the electrical voltage is applied only intermittently with pauses in between. This saves energy. For example, the electrical voltage can be applied to the electrodes in the form of rectangular pulses. The pulse-pause ratio can also be very small, allowing for long intervals between measurements, potentially lasting hours or even days.

[0029] The electrical voltage used during the measurement can be either direct current (DC) or alternating current (AC). Direct current makes the measurement particularly simple, whereas AC is especially advantageous when multiple conductivity measurements are to be performed simultaneously, as these could interfere with each other using DC. By using different frequencies for the measurements and subsequent frequency filtering, mutual interference between simultaneous conductivity measurements can be prevented or at least minimized.

[0030] On an imaginary line connecting two electrodes to which a voltage is applied, one or more free sections may exist along which no significant change in electrical conductivity occurs, even with substantial contamination of the lubricant filter. Such free sections arise, for example, when the aforementioned line runs not only through the pre-chamber but also through areas outside the pre-chamber where, due to system design, the lubricant filter cannot become contaminated or can only become contaminated to a minimal extent. These areas are generally located downstream of the filter medium. In particular, such free sections occur when the electrodes are located on the lubricant filter housing and the filter element is (significantly) smaller.If the flow passes through the filter element from the inside out, the free channels are located outside the filter element, between the electrodes and the element, since metal particles can only accumulate inside the element. If the flow passes through the filter element from the outside in, the free channels are located inside the element, since metal particles can only accumulate outside the element. Free channels can be advantageously considered when determining the degree of contamination of the lubricant filter. Compared to a lubricant filter without free channels, the electrical conductivity of a lubricant filter with free channels increases less at the same degree of contamination.

[0031] Further advantageous embodiments and developments of the invention will become apparent from the dependent claims and from the description in conjunction with the figures.

[0032] It is advantageous if at least one of the electrodes is directly attached to the filter medium or printed onto it. For example, the electrodes can be printed onto the filter medium using a screen printing or jet printing process. Furthermore, wiring between the measuring unit and the electrodes can also be printed onto the filter medium and / or onto a frame supporting the filter medium. The electrodes can be arranged radially inside or outside the filter medium. Advantageously, when arranged upstream of the filter medium, the electrodes are supported by the filter medium, making them less likely to be pulled away by the lubricant flow.When the electrodes are arranged downstream of the filter medium, the filter medium itself is also advantageously detected, and thus metallic foreign bodies trapped in the filter medium are also detected by the electrodes.

[0033] Furthermore, it is advantageous if the filter element has a frame supporting the filter medium and an electrode is either directly attached to the frame or printed onto it. A particular advantage of this design is that the flow of water through the filter medium via the electrodes is not impeded. For example, the electrodes can be printed onto the frame using a screen printing or jet printing process. Additionally, wiring between the measuring unit and the electrodes can also be printed onto the filter medium and / or the frame.

[0034] It is particularly advantageous if the lubricant filter has another pair of electrodes, or several additional pairs of electrodes, corresponding to the first pair. In the presented method, it is beneficial to measure a first electrical conductivity with the first pair of electrodes and a second electrical conductivity with a second pair of electrodes, and to determine the degree of contamination based on the first and / or the second electrical conductivity. In this way, the degree of contamination can be determined in different areas of the lubricant filter (more precisely, along different imaginary lines connecting the electrodes).

[0035] In particular, a first pair of electrodes can be arranged at a first position along the central axis of the pre-chamber, and a second pair of electrodes at a second position along the central axis. The first pair of electrodes can then be used to measure the electrical conductivity at the first position, or in a first measurement plane, and the second pair of electrodes can be used to measure the electrical conductivity at the second position, or in a second measurement plane. Accordingly, the degree of contamination of the lubricant filter or the filter element can also be determined in different measurement planes. This allows for a particularly differentiated determination of the contamination level of the filter element.The proposed measures can be used in particular to measure whether and to what extent the filter element is clogged with dirt, or how much of the filter surface is actually still available for filtration.

[0036] It is possible to perform the first electrical conductivity measurement at a different time than the second electrical conductivity measurement. Furthermore, it is possible to calculate an average of the results of both measurements, and to determine the degree of pollution using this average.

[0037] It is particularly advantageous if the lubrication circuit includes a pump for generating a lubricant flow that can be controlled based on the measured electrical conductivity or on a derived degree of contamination of the filter element. Specifically, the pump's output is increased as the electrical conductivity rises, and especially when the electrical conductivity exceeds a threshold value. With the proposed measures, a constant flow rate through the lubricant filter can be maintained despite progressive contamination. For example, the pump can be controlled using a lookup table in which a required pump output is assigned to a given electrical conductivity (and thus a corresponding degree of filter contamination).For example, the control of the pump can be taken over by the measuring unit, but the use of a separate pump control is also conceivable.

[0038] BRIEF DESCRIPTION OF THE FIGURES

[0039] Exemplary embodiments of the invention are shown in the accompanying schematic figures. These show:

[0040] Fig. 1 shows a half section through a schematically represented lubricant filter;

[0041] Fig. 2 shows an example of a filter insert in oblique view, where the electrodes are attached to the filter medium;

[0042] Fig. 3 shows a filter insert in which the electrodes are attached to a frame for the filter medium; Fig. 4 shows a similar design to Fig. 2, but with several pairs of electrodes;

[0043] Fig. 5 shows a schematically represented lubricant filter with a filter element through which fluid flows from the inside to the outside and electrodes arranged on the outside of the housing;

[0044] Fig. 6 is the same as Fig. 5, but with the lubricant flowing in the opposite direction;

[0045] Fig. 7 shows an exemplary and schematically illustrated arrangement with a gearbox with a lubrication circuit and a lubricant filter and

[0046] Fig. 8 shows an exemplary vehicle with a transmission of the proposed type.

[0047] DETAILED DESCRIPTION OF THE INVENTION

[0048] It is stated in the introduction that identical parts in the different embodiments are provided with the same reference numerals or component designations, possibly with different indices. The disclosure of a component contained in the description can be applied analogously to another component with the same reference numeral or component designation. Furthermore, the positional indications chosen in the description, such as "top," "bottom," "back," "front," "side," and so on, refer to the figure directly described and illustrated and, in the event of a change in position, must be applied analogously to the new position.

[0049] Fig. 1 shows a half-section through a schematically represented

[0050] Lubricant filter 1a for a lubrication circuit of a gearbox. The lubricant filter 1a comprises a (filter) housing 2 with an inlet opening 3 and an outlet opening 4, and a filter element 5 containing a filter medium arranged in the housing 2. A pre-chamber A is arranged in the housing 2 between the inlet opening 3 and the filter element 5. Finally, the lubricant filter 1a includes several electrodes 6a, 6b for measuring the electrical conductivity of a lubricant contained in the pre-chamber A. The pre-chamber A is arranged between the electrodes 6a, 6b for this purpose. Furthermore, Fig. 1 shows a measuring unit 7a, which is connected to the electrodes 6a, 6b and configured to measure the electrical conductivity using the electrodes 6a, 6b.The filter element 5 is subjected to flow from the inside to the outside in a flow direction B, so that foreign particles in the lubricant, in particular metallic foreign particles 8, collect upstream of the filter medium in the pre-chamber A. The metallic foreign particles 8 can originate, for example, from abrasion of a gearbox in whose lubrication circuit the lubricant filter 1a is arranged (see also Fig. 7). Suitable lubricants include, in particular, oils and oily coolants and lubricants, to which additives can also be added.

[0051] The filter element 5 can, for example, be pot-shaped, as is the case in the example shown in Fig. 1. In particular, the filter element 5 can be rotationally symmetrical about a filter axis C. It would also be conceivable, for example, that the filter element 5 is tubular. Furthermore, the inlet opening 3 and the outlet opening 4 can also be arranged on the same end face of the lubricant filter 1a and, in particular, concentrically. One of the two openings 3, 4 can therefore be essentially ring-shaped. However, it would also be conceivable that the inlet opening 3 and the outlet opening 4 are arranged circumferentially on the lubricant filter 1a.

[0052] As mentioned, the pre-chamber A is located between the electrodes 6a and 6b. In other words, an (imaginary) connecting line between the electrodes 6a and 6b runs through the pre-chamber A. If an electrical voltage is applied to the electrodes 6a and 6b by the measuring unit 7, the electrical conductivity or the specific resistance of the lubricant located between the electrodes 6a and 6b can be measured. That is, the electrical conductivity of the lubricant contained in the pre-chamber A can be measured with the measuring unit 7 using the electrodes 6a and 6b, specifically in the area shown as dashed lines in Fig. 1.

[0053] If metallic foreign bodies 8 accumulate between the electrodes 6a, 6b due to progressive soiling or contamination of the lubricant, the electrical conductivity determined by the measuring unit 7 increases compared to an uncontaminated state. Based on the electrical conductivity, the measuring unit 7a can determine the degree of contamination of the lubricant filter 1a or the lubricant itself. It is also conceivable that the measuring unit 7a could trigger an output of information to a user if the electrical conductivity exceeds a threshold value.

[0054] For example, the arrangement shown in Fig. 1 can be part of a vehicle. In such a case, the measuring unit 7a can send a signal to the vehicle's control unit to output information, which in turn causes a message to be displayed on a screen in the vehicle's cockpit (see also Fig. 8). In particular, the measuring unit 7a can trigger the output of a warning or a request to replace or clean the filter element 5 if the electrical conductivity exceeds 10 4 S / m, which corresponds to a soiling level of approximately 12%. Other advantageous values ​​are 4.3–10 4 S / m (pollution level 50%) and 6.9-10 4S / m (contamination level 80%). Alternatively, the warning can also be issued for a different electrical conductivity, which may depend on the specific application. In particular, the lubricant filter 1a may be designed for replacement of the filter element 5, so that a contaminated filter element 5 can be easily cleaned or replaced with a new one. It should be noted that instead of electrical conductivity, the specific electrical resistance or another derived quantity can also be measured and used to determine the contamination level of the lubricant filter 1a or the lubricant.

[0055] In the example shown in Fig. 1, two electrodes 6a, 6b are provided, but a larger number of electrodes 6a, 6b could also be present, with the antechamber A arranged between at least one pair of electrodes 6a, 6b. In other words, a connecting line between at least two electrodes 6a, 6b runs through the antechamber A. The electrodes 6a, 6b are thus arranged in pairs opposite each other with respect to the antechamber A. However, not all connecting lines need to pass through the antechamber A. That is, the electrodes 6a, 6b can also be arranged partially side by side.

[0056] To avoid or minimize distortion of the measurement result, it is advantageous if the filter element 5 and, if applicable, the housing 2 are made of a non-conductive or poorly conductive material. For example, the filter element 5 and / or the housing 2 can be made of plastic.

[0057] The measuring unit 7a could also be arranged inside the housing 2 and, for example, cast into it. The measurement data can be transmitted via wired or wireless connection. If the measuring unit 7a is located outside the housing 2, wiring between the electrodes 6a, 6b and the measuring unit 7a can be routed through the housing 2, particularly using a suitable seal.

[0058] The electrical voltage applied by the measuring unit 7a to the electrodes 6a, 6b can, in particular, be at least 12 V. In this way, the conductivity values ​​can be accurately measured using the current induced by the voltage, without posing any risk to humans. In particular, in the given

[0059] This connection is advantageous if the voltage is a maximum of 48 V.

[0060] It is also conceivable that the electrical voltage is applied only intermittently, with pauses in between. For example, the electrical voltage can be applied to electrodes 6a and 6b in the form of rectangular pulses. The pulse-pause ratio can also be very small, resulting in long pauses between measurements, potentially lasting hours or even days.

[0061] Generally, the electrical voltage used during measurement can be either direct current (DC) or alternating current (AC). Direct current makes measurement particularly simple, whereas AC is especially advantageous when multiple conductivity measurements are to be performed simultaneously, as these could interfere with each other using DC. By using different frequencies for the measurements and subsequent frequency filtering, mutual interference between simultaneous conductivity measurements can be prevented or at least minimized.

[0062] Fig. 2 shows an example of a filter element 5a in an oblique view. The filter element 5a is again cup-shaped and comprises a filter medium 9 which is attached to and supported by a frame 10. In this embodiment, the electrodes 6a, 6b are directly attached to the filter medium 9. In particular, the electrodes 6a, 6b can be printed onto the filter medium 9. For example, the electrodes 6a, 6b can be printed onto the filter medium 9 using a screen printing process or an abrasive printing process. In addition, wiring between the measuring unit 7a and the electrodes 6a, 6b can also be printed onto the filter medium 9 and / or onto the frame 10. The measurement of the degree of contamination of the filter element 5a or the lubricant is carried out in the manner already described for the lubricant filter 1a in Fig. 1. What has been said about the lubricant filter 1a is therefore also applicable, mutatis mutandis, to the filter element 5a.To avoid or minimize distortion of the measurement result, it is advantageous if the filter medium 9 and the frame 10 are made of a non-conductive or poorly conductive material. For example, the filter medium 9 and the frame 10 can be made of plastic. However, it should be noted that the use of a frame 10 is not necessary and the filter medium 9 can also be self-supporting.

[0063] The electrodes 6a, 6b can be arranged radially inside or outside the filter medium 9. When the electrodes 6a, 6b are arranged radially inside the filter medium 9, they are positioned upstream of the filter medium 9 in the specified flow direction B and downstream of the filter medium 9 in the opposite flow direction B. Advantageously, when arranged upstream, the electrodes 6a, 6b are supported by the filter medium 9, preventing them from being easily pulled away by the lubricant flow. When arranged downstream, the filter medium 9 itself is also advantageously detected, and thus any metallic foreign bodies 8 trapped in the filter medium 9 are also detected by the electrodes 6a, 6b.

[0064] The measuring unit 7a can be positioned directly on the filter insert 5a and, for example, cast into the frame 10. The measurement data can then be transmitted via wired or wireless connection.

[0065] Fig. 3 shows a filter element 5b, which is very similar to the filter element 5a, and to which the statements made regarding the filter element 5a and the lubricant filter 1a therefore also apply. In contrast to the filter element 5a, the electrodes 6a, 6b in the filter element 5b are directly attached to the frame 10. In particular, the electrodes 6a, 6b can be printed onto the frame 10. For example, the electrodes 6a, 6b can be printed onto the frame 10 using a screen printing process or an abrasive printing process. Furthermore, wiring between the measuring unit 7a and the electrodes 6a, 6b can also be printed onto the filter medium 9 and / or onto the frame 10. A particular advantage of this embodiment is that the flow through the filter medium 9 via the electrodes 6a, 6b is not impaired.

[0066] Fig. 4 shows a filter element 5c, which is also very similar to the filter element 5a, and to which what has been said about the filter element 5a and the lubricant filter 1a therefore also applies. In contrast to the filter element 5a, the filter element 5c comprises several (here two) additional pairs of electrodes 6a', 6b' and 6a", 6b", which correspond to the pair of electrodes 6a, 6b. The pairs of electrodes 6a..6b" are each arranged at different positions on the central axis C of the pre-chamber A and are connected in pairs to the measuring unit 7b.

[0067] The measuring unit 7b is designed to measure different electrical conductivities using the different pairs of electrodes 6a and 6b. That is, with the first pair of electrodes 6a and 6b, a first electrical conductivity can be measured at a first position on the central axis C, or in a first measurement plane D1; with the second pair of electrodes 6a and 6b, a second electrical conductivity can be measured at a second position on the central axis C, or in a second measurement plane D2; and with the third pair of electrodes 6a and 6b, a third electrical conductivity can be measured at a third position on the central axis C, or in a third measurement plane D3.

[0068] Accordingly, the degree of contamination of the filter element 5c and the lubricant can also be determined in the first to third measurement levels D1..D3. Therefore, the area shown with dashed lines in the pre-chamber A, for which the degree of contamination can be determined, is subdivided or segmented. This allows the degree of contamination of the filter element 5c to be specified in a particularly differentiated manner. Using the proposed measures, it is possible, in particular, to measure whether and to what extent the filter element 5c is clogged with dirt, and how much of the filter surface is actually still available for filtration.

[0069] Fig. 5 shows a half-section through a schematically represented lubricant filter 1b, which is very similar to the lubricant filter 1a from Fig. 1. In contrast, the lubricant filter 1b, like the filter element 5c of Fig. 4, has several pairs of electrodes 6a...6b, which are arranged at different positions on the central axis C of the pre-chamber A and are connected in pairs to the measuring unit 7b. Accordingly, the electrical conductivities and thus the degree of contamination of the lubricant filter 1b and the lubricant, respectively, can again be determined in the first to third measuring planes D1...D3.

[0070] In Fig. 5, the electrodes 6a..6b" are attached to the outside of the housing 2. Due to the system design, the lubricant filter 1b cannot become contaminated, or only minimally contaminated, in the area outside the filter element 5 between the electrodes 6a..6b" and the filter element 5. This is because, with the specified flow direction B from the inside to the outside, metallic foreign particles 8 in the lubricant can only be deposited upstream inside the filter element 5. This results in free sections a, a', which lie outside the filter element 5 between the electrodes 6a..6b" and the filter element 5. Even with substantial contamination of the lubricant filter 1b, no significant change in electrical conductivity occurs in these free sections. Advantageously, these free sections a, a' can be taken into account when determining the degree of contamination of the lubricant filter 1b.Compared to a lubricant filter 1a without free sections a, a', the electrical conductivity of the lubricant filter 1b increases less at the same degree of contamination. Due to the arrangement of the electrodes 6a..6b" on the outside of the housing 2, the (optionally replaceable) filter element 5 can be advantageously designed to be particularly simple.

[0071] Fig. 6 shows a lubricant filter 1c, which is very similar to the lubricant filter 1b from Fig. 5. In contrast, the filter element 5 is subjected to flow from the outside to the inside. Accordingly, the pre-chamber A is located outside the filter element 5, and metallic foreign matter 8 is deposited only upstream outside the filter element 5 in the specified flow direction B. This results in a free section b, which lies within the filter element 5 and where, even with substantial contamination of the lubricant filter 2, no significant change in electrical conductivity occurs. Advantageously, this free section b can be taken into account when determining the degree of contamination of the lubricant filter 2.

[0072] Fig. 7 shows an exemplary and schematically represented arrangement with a gearbox 11, which comprises a gearbox housing 12 and gearbox components 13 arranged therein, and to which an electric motor 14 is coupled by means of a shaft 15. The electric motor 14 and the gearbox 11 thus form, in particular, a drive unit or a geared motor. The gearbox 11 includes a lubrication circuit 16, which is designed to lubricate the gearbox 11 (in particular the gearbox components 13) with a lubricant and has a lubricant filter 2 and a measuring unit 3 of the type already described. In addition, the lubrication circuit 16 includes a pump 17 for pumping the lubricant.

[0073] In particular, significant abrasion, which could contaminate the lubricant filter 2, is to be expected in a gearbox 11, making the application of the proposed measures especially advantageous there. If the lubricant circuit 16 also runs through the electric motor 14, as is the case in the example shown in Fig. 7, then measuring the degree of contamination of the lubricant filter 2 can, in particular, prevent overheating of the electric motor 14, because abrasion originating from the gearbox components 13 (e.g., from gears) can clog the lubricant filter 2 and reduce the lubricant flow required for cooling the electric motor 14.

[0074] Advantageously, pump 17 is controlled based on the electrical conductivity determined by measuring unit 3. Specifically, the pumping capacity of pump 17 is increased as the electrical conductivity rises, for example, when the electrical conductivity exceeds a threshold value. Consequently, the pumping capacity is increased in the case of greater contamination so that the flow rate of pump 17 remains approximately constant.

[0075] For example, the control of pump 17 can be taken over by measuring unit 3. However, the use of a separate pump controller (not shown) is also conceivable. With the help of the proposed measures, a constant flow rate through the lubricant filter 2 can be maintained despite progressive contamination. For example, pump 17 can be controlled using a table (lookup table) in which a required pumping power is assigned to a given electrical conductivity (and thus filter contamination).

[0076] Figure 8 shows the transmission 11 installed in a vehicle 18, with an electric motor 14 coupled to it. The vehicle 18 has two axles, one of which is driven. Specifically, the electric motor 14 is connected to the half-shafts 19 of the rear axle via the transmission 11. The driven wheels 20 are mounted on the half-shafts 19. The electric motor 14 is configured to drive the vehicle 18, and the transmission 11 is configured to transmit torque provided by the electric motor 14 to a wheel 20 of the vehicle 18. The vehicle 18 is driven at least partially or temporarily by the electric motor 14. That is, the electric motor 14 can serve as the sole drive for the vehicle 18 or, for example, be used in conjunction with an internal combustion engine (hybrid drive). Finally, it should be noted that the scope of protection is defined by the claims.The description and drawings must be used to interpret the claims. The features shown in the figures can be freely exchanged and combined. It is also specifically noted that the devices depicted may, in reality, comprise more or fewer components than shown. In some cases, the devices or their components may also be shown not to scale and / or enlarged and / or reduced in size.

[0077] Reference symbol list

[0078] 1, 1a..1c Lubricant filter

[0079] 2 (filter) housings

[0080] 3 Inlet opening

[0081] 4 Outlet opening

[0082] 5, 5a..5c Filter insert

[0083] 6a..6b“ Electrode

[0084] 7, 7a, 7b Unit of measurement

[0085] 8 metallic foreign bodies

[0086] 9 Filter medium

[0087] 10 Supporting structure

[0088] 11 gearboxes

[0089] 12 Gearbox housings

[0090] 13 Gearbox component

[0091] 14 Electric motor

[0092] 15 wave

[0093] 16 Lubrication circuit

[0094] 17 Pump

[0095] 18 vehicles

[0096] 19 Semi-axis

[0097] 20 wheel a, a', b free distance

[0098] A Prechamber

[0099] B Flow direction

[0100] C Central axis

[0101] D1..D3 Cross plane

Claims

Patent claims 1. Lubricant filter (1 , 1 a..1 c) for a lubricant circuit (16) of a gearbox (11 ), comprising a housing (2) with an inlet opening (3) and an outlet opening (4), a filter element (5, 5a..5c) arranged in the housing (2) with a filter medium (9), a pre-chamber (A) arranged in the housing (2) between the inlet opening (3) and the filter element (5, 5a..5c), and several electrodes (6a..6b”) for measuring the electrical conductivity of a lubricant received in the pre-chamber (A), wherein the pre-chamber (A) is arranged between at least one pair of the electrodes (6a..6b”).

2. Lubricant filter (1 , 1 a..1 c) according to claim 1 , wherein the electrodes (6a..6b”) are opposite each other with respect to the prechamber (A).

3. Lubricant filter (1 , 1a..1 c) according to claim 1 or 2, wherein the filter element (5, 5a..5c) is pot-shaped or tubular.

4. Lubricant filter (1 , 1 a..1 c) according to one of the preceding claims, wherein at least one of the electrodes (6a..6b”) is directly attached to the filter medium (9) or printed on the filter medium (9).

5. Lubricant filter (1 , 1 a..1 c) according to one of the preceding claims, wherein the filter element (5, 5a..5c) has a frame (10) supporting the filter medium (9) and an electrode (6a..6b”) is directly attached to the frame (10) or printed on the frame (10).

6. Lubricant filter (1 , 1 a..1 c) according to one of the preceding claims, comprising a further pair of electrodes (6a..6b”) or several further pairs of electrodes (6a..6b”) corresponding to the pair of electrodes (6a..6b”).

7. Lubricant filter (1 , 1 a..1 c) according to claim 6, wherein a first pair of electrodes (6a..6b”) is located at a first position of a central axis (C) of the a pre-chamber (A) is arranged and a second pair of electrodes (6a..6b”) is arranged at a second position of the central axis (C).

8. Gearbox (1 1 ) with a lubrication circuit (16) which is configured to lubricate the gearbox (1 1 ) with a lubricant and has a lubricant filter (1 , 1 a..1 c) according to one of the preceding claims, and a measuring unit (7, 7a, 7b) which is configured to measure the electrical conductivity using the electrodes (6a..6b”).

9. Gearbox (1 1 ) according to claim 8, wherein the measuring unit (7, 7a, 7b) is configured to trigger an output of information to a user when the electrical conductivity exceeds a threshold value.

10. Gearbox (1 1 ) according to claim 8 or 9, wherein the lubrication circuit (16) has a pump (17) which is controllable by means of the electrical conductivity. 1 1. Vehicle (18) with an electric motor (14) designed to drive the vehicle (19) and a transmission (1 1 ) according to one of claims 8 to 10, designed to transmit a torque provided by the electric motor (14) to a wheel (20) of the vehicle (18).

12. Method for operating a gearbox (1 1 ) according to one of claims 8 to 10, wherein the electrical conductivity of a component in the pre-chamber (A) The amount of absorbed lubricant is measured with the measuring unit (7, 7a, 7b) using the electrodes (6a..6b”).

13. Method according to claim 12 for operating a gearbox (11) according to claim 10, wherein a pumping power of the pump (17) is increased when the electrical conductivity exceeds a threshold value.

14. Method according to claim 12 or 13, wherein a degree of contamination of the lubricant filter (1 , 1 a..1 c) is determined based on the electrical conductivity.

15. Method according to claim 14, wherein the transmission (11) has a lubricant filter (1, 1a..1c) according to claim 7, a first electrical conductivity is measured with the first pair of electrodes (6a..6b”), a second electrical conductivity is measured with a second pair of electrodes (6a..6b”) and the degree of contamination is determined based on the first electrical conductivity and / or the second electrical conductivity.

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