Apparatus and method for determining properties of a fluid

Abstract

A device for determining a property of a fluid, having an electrical conductor assembly (2, 200, 300) which is designed such that it can be at least partially brought into contact with the fluid and is configured as a voltage divider with two elements (21, 221, 321, 521, 22, 222, 322), wherein the first element is a first conductor (21, 221, 321, 521) which has a different electrical resistance value than the second element (22, 222, 322) at least in an energized state, a measurement bridge (4, 240, 340) having two parallel voltage dividers, wherein one of the voltage dividers is formed by the electrical conductor assembly (2, 200, 300), a control unit (6) for applying an alternating voltage (U0) to the measurement bridge (4, 240, 340), a voltage detection unit (8) for detecting a bridge voltage (Ub), and an evaluation unit (10) which is configured such that it determines a thermal conductivity as a property of the fluid by evaluating the bridge voltage (Ub) using a 3ω method.

Description

Technical Field

[0001] The present invention relates to apparatus and methods for determining the properties, particularly the thermal conductivity, of fluids, especially fluid mixtures formed of multiple fluids, particularly washing liquids or urea aqueous solutions used for exhaust aftertreatment of vehicles. The invention also relates to fluid containers and vehicles. Background Technology

[0002] Optical sensors, such as cameras, lidar, and radar, are increasingly being incorporated into vehicles for driver assistance systems and / or systems used for autonomous driving. When using optical sensors for these purposes, it is essential to ensure detection accuracy in every weather condition. Therefore, reliably cleaning optical sensors using washing equipment is crucial.

[0003] Traditional vehicle washing systems, primarily used for cleaning windows and / or lights, lack the ability to monitor the washer fluid. Consequently, problems frequently arise at low temperatures where the fluid mixture—consisting of water and at least one antifreeze used as the washer fluid—freezes in the container, in the piping leading to the nozzles, or on the windows due to insufficient antifreeze. This prevents cleaning or even worsens visibility.

[0004] Furthermore, in modern diesel vehicles, urea aqueous solution (also known as AdBlue (registered trademark)) is used for exhaust aftertreatment (selective catalytic reduction (SCR)) to reduce emitted nitrogen oxides (NOx). The proportion of urea in the urea aqueous solution is, for example, 32.5% in the delivered state, according to standard, with a permissible range between 31.8% and 33.3% for vehicle applications. Because urea is gradually decomposed by ultraviolet light, the urea concentration will change over time in containers used for refilling and exposed to sunlight. Additionally, water can evaporate from containers or fluid containers in the vehicle, causing the urea concentration to also change over time. While the desired urea concentration can be checked using a refractometer, this is costly and therefore impractical during diesel vehicle operation. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide an apparatus, a method, a fluid container, and a vehicle that overcome the aforementioned disadvantages. This reliably prevents the freezing of the fluid mixture used as a washing liquid and / or ensures the necessary concentration of the urea aqueous solution for exhaust gas aftertreatment.

[0006] According to the invention, the properties, particularly the thermal conductivity, of a fluid, especially a fluid mixture, used for example as a washing liquid or for waste gas aftertreatment, are determined in order to infer its composition or degree of contamination. The apparatus for determining the properties of a fluid or fluid mixture thus includes an electrical conductor assembly designed such that it is at least partially, substantially completely, or fully contactible with the fluid. The conductor assembly is configured as a voltage divider and has two elements. A voltage divider should be understood, for example, as a series circuit consisting of, in particular, passive dipoles, through which voltage is distributed.

[0007] The device according to the invention has a measuring bridge with two voltage dividers connected in parallel, each voltage divider having two elements. One of the voltage dividers is formed by the aforementioned conductor assembly. Furthermore, the device has a control unit for applying an AC voltage to the measuring bridge and a voltage detection unit for detecting the bridge voltage.

[0008] Furthermore, the device includes an evaluation unit configured to determine the fluid's properties, particularly its thermal conductivity, by evaluating the bridge voltage using the 3ω method. Using this device, it can be determined whether the fluid possesses preset properties, such as a preset thermal conductivity, thereby reliably preventing freezing, for example, at a temperature corresponding to the preset thermal conductivity. Additionally, it can be determined, for example, whether the fluid used for exhaust gas aftertreatment has the required urea content. Therefore, signals can be output via appropriate devices, such as a display and / or a speaker, in cases of freezing hazards or when the concentration of the fluid used for exhaust gas aftertreatment is too low / high.

[0009] The first element of the conductor assembly is preferably a first conductor, which has a resistance value different from that of the second element, at least in the energized state. Therefore, when an AC voltage is applied to the measuring bridge, the measuring bridge becomes misaligned, allowing the bridge voltage to be detected by the voltage detection unit.

[0010] The second element of the conductor assembly can be a second conductor that has the same resistance as the first conductor in the absence of current. Here, the two conductors are preferably configured such that the first conductor heats more intensely than the second conductor when energized. Therefore, the resistance of the first conductor can differ from that of the second conductor, and the measuring bridge can be misaligned, enabling the detection of the bridge voltage.

[0011] According to another aspect, the second element can be a fixed resistor used in place of the second conductor. A fixed resistor can be understood, for example, as a resistor whose resistance value remains substantially unchanged even when current flows through it and therefore can be considered substantially constant under any conditions. When using a fixed resistor, the two resistors of the other voltage divider are preferably configured such that their resistance values ​​are settable or changeable. Preferably, the two settable resistors are configured as digital potentiometers. When current flows through it, the first conductor heats up and therefore its resistance value changes, such that the first conductor and the fixed resistor have different resistance values ​​when current flows through it. Here, the resistance value of the first conductor is preferably greater than the resistance value of the fixed resistor. However, the resistance value of the first conductor can also be less than the resistance value of the fixed resistor. When using a fixed resistor, the evaluation unit is preferably configured such that it adjusts the two settable resistors before applying an AC voltage to the measuring bridge. This configuration offers the advantage of reducing the requirements for manufacturing precision, which is necessary, for example, to ensure that the first and second conductors have the same resistance value in the absence of current. Furthermore, the detection accuracy is improved because the measurement bridge is reliably calibrated by the evaluation unit before the thermal conductivity is calculated.

[0012] According to one aspect of the invention, the fluid can be a fluid mixture formed from two fluids, preferably, the thermal conductivity of each of the two fluids is known. The evaluation unit can be configured to determine the concentration or mixing ratio as a characteristic of the fluid mixture by comparing the thermal conductivity of the fluid mixture with the thermal conductivity of the two fluids (the fluid mixture is formed by mixing these two fluids). Therefore, the mixing ratio of the fluid mixture can be determined accurately. It should be noted that at least one of the two fluids can also be a fluid mixture, provided that its thermal conductivity is known. Here, the advantage of determining the mixing ratio is that the composition of the fluid mixture can be easily explained to the user.

[0013] According to another aspect of the invention, the freezing points of the two fluids forming the fluid mixture can be additionally known separately. For example, the evaluation unit is configured to use the concentration of the fluid mixture to determine the freezing point as a characteristic of the fluid mixture. Therefore, the freezing point of the fluid mixture can be accurately determined, allowing the user to better determine whether the fluid mixture is suitable for a specific temperature.

[0014] According to another aspect of the invention, the fluid can be a fluid mixture, preferably composed of two fluids, each of which has a known thermal conductivity and freezing point. The evaluation unit can be configured to determine the freezing point as a characteristic of the fluid mixture by comparing the thermal conductivity with a characteristic curve, particularly a linear one. This linear curve is obtained through linear interpolation, where the thermal conductivity and freezing point of the fluids are used as reference points. To obtain the linear curve, the values ​​of the thermal conductivity of the two fluids are plotted on the x-axis of a Cartesian coordinate system, and the values ​​of the freezing points of the two fluids are plotted on the y-axis of the Cartesian coordinate system. The determined value of the thermal conductivity of the fluid mixture formed by the two fluids is then plotted on the x-axis, and thus the value of the freezing point of the thermal conductivity can be used as the y-axis value of the linear curve at that location. Through this linear interpolation, the freezing point can be determined in a simple manner, and the user can accurately determine whether the fluid mixture is suitable for a given temperature.

[0015] According to another aspect of the invention, preferably, the cross-section of the first conductor is smaller than that of the second conductor. This design of the two conductors ensures, in a simple way, that the first conductor heats more intensely than the second conductor when energized.

[0016] According to an additional aspect of the invention, the ratio between the cross-sections of the first conductor and the second conductor can be in the range of 3 to 5, and preferably 4. However, the ratio of the cross-sections of the first conductor and the second conductor can also be in the range of 2 to 6. This design of the first conductor and the second conductor ensures sufficient heating of the first conductor, thereby enabling good detection accuracy of resistance changes.

[0017] According to one aspect of the invention, preferably, the AC voltage is sinusoidal. Therefore, the applied AC voltage can be generated in a simple manner and is suitable for processing in the 3ω method.

[0018] According to another aspect of the invention, advantageously, the current intensity flowing through the conductor assembly is in the range of 150 mA to 250 mA, and preferably 200 mA. However, the current intensity can also be in the range of 100 mA to 300 mA. By determining the current intensity within this range, good adaptation to the device for vehicle electrical systems and good detection accuracy of resistance changes are achieved.

[0019] According to a preferred aspect of the invention, the first conductor and the second conductor can be arranged adjacent to each other. For example, they can act on each other from behind and / or overlap. Preferably, the two conductors are arranged on a common retaining assembly.

[0020] According to one aspect of the invention, preferably, the first conductor and the second conductor are arranged on a common plate or retaining assembly. Here, the first and second conductors can be constructed in a zigzag shape. By arranging one or both conductors in a zigzag shape on the plate, a space-saving conductor assembly is achieved. Furthermore, a cost-effective and easily manufactured conductor assembly can be achieved by using a standard plate (e.g., an FR4 plate).

[0021] If the conductor is constructed in a zigzag shape, it has, for example, at least two legs that are parallel to each other and / or adjacent to each other, connected by a connecting section. Preferably, a plurality of such legs are provided, arranged side by side and connected by connecting sections. Between the legs of the second conductor, for example, the first conductor may be arranged on a retaining assembly. The two legs of the second conductor (with the first conductor arranged between them) can here be spaced apart from each other by a greater distance than the remaining legs. The first conductor is then preferably also constructed with two or more legs, connected by one or more connecting sections. These legs can be arranged side by side, preferably at a parallel distance. At least one or two conductors are advantageously arranged as compactly as possible.

[0022] According to another aspect of the invention, the first and / or second conductors can be configured as wires. For example, a metallic conductor having a circular or angular or flat or quadrilateral or contoured cross-section should be understood as a wire, which, except for one or more of its fastening sections or if the metallic conductor is not arranged or fastened to a substrate or holder, is completely surrounded by the fluid mixture. Conductors configured as wires can be shaped or arranged in a fixed form, as a helix, as a loop, zigzag, or otherwise wound or bent in various ways and methods. Experiments have shown that using wires as the first and / or second conductors, especially compared to designs in the form of circuit traces, significantly improves detection accuracy. Even when the wires are fastened to circuit traces or a substrate such as circuit traces, detection accuracy is improved because the wires can still make fluid contact with a large circumferential surface area. Furthermore, a compact structural form of the device can be achieved through helical or loop arrangements.

[0023] One or more conductors configured as wires can be preloaded by at least one elastic element to compensate for changes in the length of the retaining assembly due to heating under current flow or due to temperature variations. Here, the elastic element can preferably be configured as a spring element. In this way, it prevents one or more conductors configured as wires from contacting other conductive sections of the device or themselves when the length of the retaining assembly changes or when its shape or length changes. This reliably prevents short circuits in the wires. Furthermore, it reliably prevents damage to often thin and sensitive wires due to excessive tension, thus the device with wires according to the invention can also be used in environments subject to large temperature fluctuations, such as in vehicles.

[0024] According to an advantageous aspect, protrusions can be constructed on the circuit board or retaining assembly between two conductors / wires or between conductors / wires. These protrusions can be cylindrical or square. Preferably, the protrusions extend beyond the height of the plane in which the conductors / wires are arranged. Protrusions can also be formed by arranging the conductors / wires in grooves or groove sections, such that the area outside the groove section extends beyond the plane in which the conductors / wires are arranged. Since the freezing point of the urea aqueous solution is approximately -11°C, the urea aqueous solution may freeze in cold winters. Therefore, a heating element can be arranged in the fluid container to heat the urea aqueous solution. Furthermore, the washing liquid may also freeze if the antifreeze content is too low. The protrusions, in the frozen state, restrict or interrupt the frozen portion or portion of the urea aqueous solution or washing liquid in the area of ​​the circuit board or retaining assembly. Therefore, this portion or portion is easier to thaw and thermal conductivity can be determined more quickly. Furthermore, the protrusions prevent contact between the wires / conductors and the frozen portion / body to prevent damage to the wires / conductors. Therefore, the device with wires according to the invention can also be used in environments exposed to low temperatures, such as vehicles. Furthermore, the protrusions can be arranged such that they prevent contact between the first and second conductors or between the various bends or sections of the conductors, thereby reliably preventing short circuits.

[0025] In other words, at least one or more conductor segments of the conductor / wire may be in contact with a fluid. One or more conductors and / or one or more conductor segments extend on the housing side open to the fluid or the component side retaining the assembly. One or more ridges or protrusions extend sequentially from the housing side / component side, covering one or more conductors and / or one or more conductor segments to protect them from mechanical forces, such as ice contact.

[0026] According to another advantageous aspect, the circuit board or retaining assembly can be protected by a cover or cap, which can be configured to allow the fluid whose thermal conductivity is to be determined to pass through in order to contact the first and / or second conductor. For this purpose, the cover or cap can be constructed with slits or holes. This design further reduces frozen sections or portions in the area of ​​the conductor or conductor assembly, enabling rapid thawing in the area of ​​the device used to determine the thermal conductivity of the fluid. Additionally, the cover prevents movable frozen components from colliding with multiple conductors or a single conductor, thereby reliably preventing damage.

[0027] According to another aspect of the invention, the first conductor and the second conductor can be made of the same material. This allows for simple manufacturing of both the first and second conductors without having to consider the different material properties of the two conductors.

[0028] According to an additional aspect of the invention, the first and second conductors may be covered with or include an insulating layer. Paint or solder resist can be used as the insulating layer at low cost. This achieves an extremely compact arrangement of the conductors because it reliably prevents short circuits between bends or turns of the conductor assemblies that are side-by-side.

[0029] According to one aspect of the invention, one of the fluids is water and the other fluid is antifreeze or ethanol. Due to the wide freezing point range of this fluid mixture, its composition is particularly suitable for use as a washing liquid in vehicles.

[0030] According to another aspect of the invention, one of the fluids is urea and the other fluid is water. This composition is particularly suitable for exhaust aftertreatment in diesel vehicles.

[0031] According to an additional aspect of the invention, preferably, the control circuit is cost-effectively and simply formed by two transistor boost stages. In this way, the DC voltage used in the vehicle's onboard electrical system can be converted into AC voltage, preferably into a sinusoidal AC voltage.

[0032] According to another aspect of the invention, the evaluation unit can be configured to filter the signal component of the bridge voltage by means of a software-implemented synchronous rectifier (also known as a software-implemented lock-in amplifier), the signal component having a single or multiple multiple frequency, preferably three times the frequency, of the AC voltage. In the software-implemented synchronous rectifier, the input signal, i.e., the bridge voltage, can be digitized by an A / D converter, preferably by the A / D converter of the evaluation unit. A table is preferably stored in the evaluation unit, storing standardized amplitude values ​​of the signal component to be filtered, that is, storing amplitude values ​​of a sinusoidal voltage having a single or multiple multiple frequency of the voltage applied to the measurement bridge. The digitized value of the input signal can then be multiplied, and in particular correlated, with the value from the table. A sliding sum is then preferably formed over a multiple of the table length, that is, over a multiple of the period duration of the signal component. This sliding sum can then be taken as a measure of the amplitude of the signal component to be filtered in the input signal, that is, in the bridge voltage. In this way, there is no need for costly hardware-intensive synchronous rectifiers or other filter structures, thus achieving significant cost savings in the device according to the invention. Furthermore, since an analog reference signal is not required, filtering of multiple signal components with different frequencies can be achieved simply by storing different tables, without needing to provide a separate reference signal for each signal component. This also reduces the complexity of the circuitry.

[0033] The fluid container or liquid container according to the invention has a means for determining the thermal conductivity of a fluid or fluid mixture. Therefore, the thermal conductivity of a fluid or fluid mixture stored in the fluid container, such as a scrubbing liquid or liquid used for waste gas aftertreatment, can be determined. In this way, it can be reliably determined whether the fluid mixture can be used for the intended application.

[0034] According to one aspect of the invention, an apparatus for determining thermal conductivity can be arranged in a portion of a fluid container, spatially separated from the main region of the fluid container but in fluid communication with it. Here, the apparatus can be partially or completely surrounded by a protruding bottom or wall section of the fluid container, and the bottom or wall section can have slits or holes, thereby allowing the fluid contained in the fluid container to reliably contact the apparatus for determining the fluid properties. In this way, frozen sections in the region of the apparatus for determining thermal conductivity can be limited, and the duration of thawing, for example, by means of a heating element arranged in the fluid container, can be reduced. Furthermore, the risk of mechanical damage to the apparatus for determining thermal conductivity is reduced.

[0035] According to one aspect of the invention, a fluid container may have a sensor for detecting the liquid level. This sensor may, in particular, be an ultrasonic sensor or a sensor for detecting hydrostatic pressure within the fluid container. Thus, the liquid level in the fluid container can be additionally determined. Furthermore, a device can be provided such that when the determined liquid level is insufficient for the intended application, an acoustic and / or optical warning is output, for example, via a speaker and / or display. Therefore, in addition to the characteristics of the fluid, the liquid level in the fluid container can be determined, and a warning is issued if the liquid level is too low for the intended application.

[0036] According to a particularly preferred aspect of the invention, the apparatus for determining the thermal conductivity of the fluid and the sensor for measuring the liquid level can be constructed as a common module. This allows for a cost-effective and space-saving arrangement.

[0037] According to an additional aspect of the invention, the fluid container may have a detection device that detects the liquid filling and / or liquid emptying of the fluid container. During the liquid filling and / or liquid emptying of the fluid container, it can be assumed that filling with water and / or antifreeze liquid or liquid used for exhaust gas aftertreatment at different urea concentrations, or removing a portion of the fluid or fluid mixture, alters its thermal conductivity. Therefore, the advantage provided by using the detection device is that the thermal conductivity can be re-determined to check whether the fluid continues to have a preset thermal conductivity.

[0038] The washing apparatus according to the invention has a fluid container according to the foregoing aspects. Therefore, by using the washing apparatus, the properties of the fluid or fluid mixture, especially the thermal conductivity, can be determined, making it possible to reliably prevent the washing liquid from freezing.

[0039] The apparatus for exhaust gas aftertreatment according to the invention has a fluid container according to the foregoing aspects. Therefore, by using the apparatus for exhaust gas aftertreatment, the characteristics of the fluid or fluid mixture used for exhaust gas aftertreatment, especially the thermal conductivity, can be determined, thereby reliably cleaning the exhaust gas emitted from the vehicle.

[0040] The vehicle according to the invention has a washing device with a fluid container according to any one of the foregoing aspects, which is used to clean vehicle components and / or optical sensors and / or light sources and / or window panels. Therefore, the properties of the fluid or fluid mixture used as the vehicle's washing liquid, especially its thermal conductivity, can be determined to reliably prevent it from freezing.

[0041] According to one aspect of the invention, the vehicle has vehicle components, particularly optical sensors and / or light sources and / or window panels that are cleaned by a washing device. Therefore, cleaning is ensured even at low temperatures because freezing of the washing liquid in the washing device can be reliably prevented by using the device for determining the properties of the fluid according to the invention.

[0042] According to another or additional aspect of the invention, a vehicle according to the invention includes an apparatus for exhaust gas aftertreatment having a fluid container according to any of the foregoing aspects. Therefore, the characteristics of the fluid or fluid mixture used for exhaust gas aftertreatment can be determined, thereby determining the urea concentration in the fluid mixture. Reliable exhaust gas cleaning can be performed in this way.

[0043] The method according to the invention for determining the properties of a fluid, particularly its thermal conductivity, comprises the following steps: applying an alternating voltage to a measuring bridge; detecting the bridge voltage; and, in the case of using the 3ω method, determining the thermal conductivity as a property of the fluid mixture by evaluating the bridge voltage.

[0044] According to one aspect of the invention, the method can be implemented when filling and / or evacuation of the fluid container according to any one of the foregoing aspects is detected. Therefore, the frequency of implementing the method can be reduced, thereby reducing the processing load on the evaluation unit.

[0045] According to another aspect of the invention, the method can be implemented when the vehicle's ignition is turned on and / or off. Therefore, the frequency of implementing the method can be reduced, thereby reducing the processing load on the evaluation unit.

[0046] In the case where the second element of one voltage divider of the measuring bridge is configured as a fixed resistor and the two resistors of the other voltage divider of the measuring bridge are configured as settable resistors, an initial step for calibrating the measuring bridge can be implemented according to one aspect of the invention. An evaluation unit is then configured to cause at least one of the two transistor boost stages to apply a DC voltage to the measuring bridge. Here, the DC voltage has a value of 200 mV. However, the DC voltage value can also be between 100 mV and 500 mV, including 100 mV and 500 mV. The bridge voltage is then detected and the evaluation unit changes the resistance of the two settable resistors. The DC voltage is then reapplied to the measuring bridge and the bridge voltage is detected again. This process is repeated until the bridge voltage detected in response to the applied DC voltage is substantially equal to 0 V. Therefore, the measuring bridge can be reliably calibrated. This process is advantageously implemented at startup or when the detection characteristics are first initiated for initial calibration of the measuring bridge.

[0047] Alternatively or additionally, the evaluation unit can be configured to filter out the signal component of the bridge voltage, which corresponds to a simple frequency of the AC voltage applied to the measuring bridge. The amplitude of this signal component of the bridge voltage can be used as a measure of the bridge detuning, and the evaluation unit can be configured to change the resistance value of a settable resistor such that the signal component of the bridge voltage corresponding to a single frequency of the applied AC voltage is essentially 0 V. This approach offers the advantage of being able to detect bridge detuning during measurement operation. Therefore, bridge detuning (e.g., as a result of heating during operation) can be detected, and the bridge can then be recalibrated.

[0048] In another embodiment of the invention, in one or more of the above aspects, a storage container containing antifreeze or urea may be provided. This storage container may be fluidly connected to a fluid container. It is then conceivable that antifreeze can be introduced into the fluid container when needed, for example, via a controllable valve. This is done, for example, when it is determined that too little antifreeze or urea is present in the fluid container. Attached Figure Description

[0049] The invention will now be described with reference to the accompanying drawings. It is shown that:

[0050] Figure 1 A schematic diagram of an apparatus for determining the properties of a fluid mixture used in a fluid container of a vehicle washing device is shown.

[0051] Figure 2 A conductor assembly having a first conductor and a second conductor mounted on an electrode plate is shown according to an embodiment of the present invention;

[0052] Figure 3 A flowchart is shown for a method of determining the thermal conductivity of a fluid when using a first conductor and a second conductor.

[0053] Figure 4 It is a graph schematically showing a straight line used to determine the freezing point of a fluid mixture;

[0054] Figure 5 A schematic diagram of a device for determining thermal conductivity used in the fluid container of a vehicle's exhaust aftertreatment system is shown.

[0055] Figure 6 and Figure 7 A measuring bridge with conductor assemblies is shown, wherein the first and second conductors are constructed as wires;

[0056] Figure 8 and Figure 9 A measuring bridge with a conductor assembly is shown, wherein a first conductor, configured as a wire, and a fixed resistor are connected in series;

[0057] Figure 10 A flowchart is shown for a method of determining the thermal conductivity of a fluid when using a fixed resistor.

[0058] Figure 11 Embodiments of a holding assembly for holding a conductor configured as a wire are shown; and

[0059] Figure 12 A schematic block diagram of a software-implemented synchronous rectifier is shown. Detailed Implementation

[0060] The embodiments of the present invention are described below. Figure 1 A schematic diagram of the circuit of apparatus 1 for determining the properties of a fluid, particularly its thermal conductivity, is shown. In this embodiment, the fluid is, in particular, a fluid mixture consisting of water and ethanol, which are the base of most commercially available antifreeze, and is used as a washing liquid in a washing device 50 for cleaning optical sensors, window panels, and / or light sources in a vehicle 70. For this purpose, the washing liquid is stored in a fluid container 30. For this reason, the washing liquid will be understood as a fluid mixture in the following description. Furthermore, apparatus 1 according to this embodiment is designed for use in a vehicle 70.

[0061] In this embodiment, the thermal conductivity of the washing liquid is used as a measure of the mixing ratio of water and ethanol. Water has a thermal conductivity of 0.556 [W / (m*K)] and ethanol has a thermal conductivity of 0.173 [W / (m*K)]. Therefore, the washing liquid, a mixture of water and ethanol, has a thermal conductivity between these two values, and the mixing ratio of the washing liquid can be deduced by comparing the obtained thermal conductivity with a preset thermal conductivity. If, for example, a minimum proportion of ethanol is required in the washing liquid to reliably prevent freezing, the obtained thermal conductivity value must be less than or equal to the preset thermal conductivity. The preset thermal conductivity is preset in advance by the manufacturer of device 1, washing equipment 50, or vehicle 70. The preset thermal conductivity can also be adapted accordingly based on different factors, such as date, location, weather forecast, etc.

[0062] The apparatus 1 for determining the thermal conductivity of a fluid mixture formed from multiple fluids has an electrical conductor assembly 2, a measuring bridge 4, a control unit 6, a voltage detection unit 8, and an evaluation unit 10.

[0063] The electrical conductor assembly 2 is designed to allow it to at least partially come into contact with the washing liquid. Figure 1 and Figure 2 The electrical conductor assembly 2 shown in the diagram comes into contact with the fluid mixture by completely immersing the electrical conductor assembly in the washing liquid stored in the fluid container 30 of the washing device 50, so that the electrical conductor assembly is completely surrounded by the fluid mixture.

[0064] The electrical conductor assembly 2 has a first conductor 21 and a second conductor 22 connected in series. The first conductor 21 and the second conductor 22 have the same resistance value when there is no current. In addition, the two conductors 21 and 22 are designed such that the first conductor 21 is heated more intensely than the second conductor 22 when energized.

[0065] In this embodiment, it is used in Figure 2 The conductor assembly 2 shown in the figure has two conductors 21 and 22 arranged in a zigzag pattern on the circuit board 26 in the form of circuit traces. To achieve this zigzag arrangement, the two conductors 21 and 22 are arranged as shown in… Figure 2 The diagram shows multiple legs 23 and connecting sections 24 between these legs 23. Figure 2 In the example, the first conductor 21 is also arranged in a zigzag pattern between the two legs 23 of the second conductor 22. However, the arrangement of the two conductors 21 and 22 is not limited to the arrangement shown, and the two conductors 21 and 22 can also be arranged in a zigzag pattern, for example, only in segments. Furthermore, only one of the two conductors 21 and 22, preferably the second conductor 22, can be arranged in a zigzag pattern. By mounting the two conductors 21 and 22 in the form of circuit traces on the circuit board 26, such as an FR4 circuit board, a cost-effective and robust conductor assembly 2 can be obtained. In addition, the zigzag arrangement of the two conductors 21 and 22 provides the advantage of a space-saving arrangement of the conductor assembly 2 in the fluid container 30.

[0066] As in Figure 2 As seen, the cross-section of the first conductor 21 is smaller than the cross-section of the second conductor 22. Therefore, the second conductor 22 must be longer than the first conductor 21 by a multiple of the cross-section of the first conductor 21, so that the first conductor 21 and the second conductor 22 have the same resistance value when there is no current. Figure 2 In the electrical conductor assembly 2 shown, the cross-section of the second conductor 22 is four times larger, necessitating that the first conductor 21 have four times the length to achieve the same resistance value. However, the multiple is not limited to four and can be in the range of three to five. This design of the two cross-sections ensures sufficient detection accuracy in the resistance change under energized conditions, as described below.

[0067] In this embodiment, the two conductors 21, 22 are implemented via circuit traces made of copper. However, other materials such as nickel can also be used. Preferably, the two conductors 21, 22 are made of the same material, so that the effects of different materials are not taken into account when determining the size and resistance changes described later under energized conditions. Furthermore, using the same material simplifies the manufacture of the electrical conductor assembly 2.

[0068] Furthermore, the first conductor and the second conductors 22, 222, 322 are preferably covered with solder resist to avoid short circuits between the various bends of the first conductor and the second conductor 22, 222, 322 due to the presence of detergent in the first conductor and the second conductor.

[0069] If current flows through two conductors 21 and 22 connected in series, the first conductor 21 is heated more intensely than the second conductor 22 due to its smaller cross-section. Therefore, the resistance of the first conductor 21 increases more than that of the second conductor 22. Because the conductor assembly 2 is completely immersed in the fluid mixture, the heating intensity of the first conductor 21 also depends on the thermal conductivity of the washing liquid. If the washing liquid has high thermal conductivity, the first conductor 21 is heated less than if the washing liquid has low thermal conductivity. Therefore, the washing liquid with high thermal conductivity cools the first conductor 21 better than the washing liquid with low thermal conductivity. Thus, the magnitude of the resistance change of the first conductor 21 can be used as a measure of the thermal conductivity of the washing liquid.

[0070] In order to detect the resistance change of the first conductor 21, such as in Figure 1 As shown, a measuring bridge 4, for example constructed as a Wheatstone measuring bridge, is used. This measuring bridge has two voltage dividers connected in parallel, one of which is formed by an electrical conductor assembly 2, i.e., thus formed by a series circuit of the first conductor 21 and the second conductor 22. The other voltage divider consists of two resistors R1 and R2, each having the same resistance value. The advantage of using measuring bridge 4 is that it completely compensates for changes in the resistance values ​​of the first conductor 21 and the second conductor 22 caused by variations in ambient temperature.

[0071] To generate current in the two conductors 21 and 22, an AC voltage is applied to the measuring bridge 4 via the control unit 6. In this embodiment, the control unit 6 consists of two transistor boost stages, enabling the conversion of the DC voltage of the vehicle's onboard electrical network 70 into an AC voltage. For this purpose, the first transistor boost stage 61 alternately applies a positive voltage to the measuring bridge 4, and the second transistor boost stage 62 alternately applies a negative voltage. Here, the AC voltage is particularly sinusoidal, thus enabling the execution of the 3ω method described below. The control unit 6 applies the AC voltage to the measuring bridge 4, causing a current in the range of approximately 200 mA to flow in the series circuit formed by the first conductor 21 and the second conductor 22. However, the current intensity is not limited to this value and can be in the range of 150 mA to 250 mA. The first conductor 21 is heated by several Kelvin while energized, thereby increasing its resistance, which in turn causes the measuring bridge 4 to detune. Therefore, the bridge voltage Ub detected by the voltage detection unit 8 exists between the two voltage dividers.

[0072] In this embodiment, the voltage detection unit 8 is as follows: Figure 1The configuration shown is an amplifier unit, particularly a differential amplifier, used to amplify the detected bridge voltage Ub by a preset factor, thereby obtaining the amplified voltage Uv intercepted from the evaluation unit 10 across resistor 81. Therefore, the amplified voltage Uv corresponds to the bridge voltage Ub, and the processing of the amplified voltage Uv can be understood as the processing of the bridge voltage Ub.

[0073] In this embodiment, the evaluation unit 10 is composed of a known microcontroller having RAM, ROM, CPU, I / O terminals, A / D converter, etc. The evaluation unit 10 is configured such that, when using the 3ω method, the evaluation unit determines the thermal conductivity of the fluid mixture as a characteristic of the fluid or fluid mixture by evaluating the bridge voltage Ub or the amplified voltage Uv corresponding to the bridge voltage Ub.

[0074] First, in 1999, Jason Randall Foley described the 3ω method in "The 3ω Method as a Nondestructive Testing Technique for Characterizing Composite Materials," the contents of which are incorporated herein by reference.

[0075] In the 3ω method, the metal wire in contact with the sample, i.e., the first conductor 21, serves not only as a heater but also as a thermometer. As described above, an AC voltage U0 is applied to the measuring bridge 4 via the control unit 6, causing a current I with the same frequency to flow through the first conductor 21. Therefore, in the first conductor 21, power oscillating at twice the frequency is converted into heat, causing the temperature of the first conductor 21 and thus its resistance value to change at twice the frequency of the applied AC voltage U0.

[0076] Therefore, the measuring bridge 4 is misaligned and a bridge voltage Ub is generated, which also oscillates at twice the frequency of the resistance change. In this embodiment, the resistance values ​​of the two resistors 41 and 42 constituting the second voltage divider of the measuring bridge 4, as well as the resistance values ​​of the first conductor 21 and the second conductor 22, are designed to have the same resistance value R in the absence of current. Furthermore, the second conductor 22 is designed such that its resistance value remains substantially unchanged in the energized state. The advantage of this is that the bridge voltage is related to the resistance change ΔR of the first conductor 21. 21 It is proportional and can be expressed by the following equation:

[0077]

[0078] Therefore, the bridge voltage Ub has a signal component with a frequency three times that of the AC voltage applied at the measuring bridge 4. This so-called 3ω signal component filtering is performed in software. The evaluation unit 10 is therefore configured such that the evaluation unit utilizes... Figure 12The software-implemented synchronous rectifier or software-implemented lock-in amplifier shown in the diagram filters the signal components of the bridge voltage Ub, which has a frequency multiple, preferably three times, that of the AC voltage. Instead of a reference signal, the software-implemented synchronous rectifier uses table 602, in which the amplitude values ​​of the signal components having a frequency multiple, preferably three times, are stored in a standardized manner as a reference. The evaluation unit 10 then correlates the value of the bridge voltage Ub digitized by the A / D converter 604 of the evaluation unit 10 with the standardized amplitude values ​​stored in table 602 and forms a sliding sum over a multiple of the table length, i.e., a multiple of the period duration of the signal components. The sum ∑ can then be considered as a measure of the share or amplitude of the signal component in the bridge voltage Ub. Thus, the 3ω signal component can be obtained in a simple and cost-effective manner.

[0079] According to the 3ω method, the amplitude of a signal with a frequency three times that of the bridge voltage is a direct measure of the thermal conductivity of the fluid. As already mentioned, the calculated thermal conductivity lies between the two values ​​of the thermal conductivity of water and ethanol, thus it can be used as a measure of the mixing ratio. The calculated thermal conductivity can then be compared with a preset thermal conductivity to determine whether the mixing ratio of the washing liquid stored in the fluid container 30 is suitable for the application set in the washing equipment 50 of the vehicle 70, thereby reliably preventing freezing. If, for example, a minimum proportion of ethanol is required in the washing liquid to reliably prevent freezing, the value of the calculated thermal conductivity must be less than or equal to the preset thermal conductivity. However, if the calculated thermal conductivity is greater than the preset thermal conductivity, an appropriate alarm signal can be displayed to the driver of the vehicle 70 via the vehicle's display and / or speaker, thereby prompting the driver to change the mixing ratio of the washing liquid.

[0080] According to another embodiment, the fluid container 30 has a sensor for measuring the liquid level. Here, the sensor is either an ultrasonic sensor for measuring the liquid level or a sensor for measuring hydrostatic pressure. This ensures not only that the washing fluid is prevented from freezing, but also that a sufficient amount of washing fluid is present within the fluid container 30. This is particularly important when using optical sensors for autonomous driving or driver assistance systems in inclement weather. The planned route is input, and the amount of washing fluid required for driving is estimated, taking into account the weather forecast. If the amount of washing fluid determined by the sensor for measuring the liquid level is lower than the amount required for driving, an optical and / or acoustic warning is issued in the vehicle via the aforementioned device, i.e., a speaker or display. This avoids situations where autonomous driving or driver assistance systems become unusable during driving, as it is impossible to clean the optical sensor.

[0081] An apparatus 1 for determining the properties of a fluid mixture composed of multiple fluids is used in a washing device 50 of a vehicle 70, and its thermal conductivity is determined as a property. The washing device 50 has a fluid container 30 for storing washing liquid and may be equipped with a detection device that detects the filling and / or emptying of the washing fluid container 30. For example, if one of the fluids, ethanol, or water, is filled into the washing fluid container 30, the mixing ratio of the washing liquid and therefore the change in thermal conductivity can be considered. Therefore, for example, since fluid container 30 is detected to be filled with fluid, the determination of thermal conductivity can begin to determine whether the washing liquid continues to have a preset thermal conductivity. Thus, the frequency of thermal conductivity determination can be reduced.

[0082] As described above, the washing liquid is formed from two fluids, water and ethanol, each with a known thermal conductivity. According to another embodiment, the evaluation unit 10 can also be configured to determine the concentration of a characteristic of the fluid mixture by comparing the thermal conductivity of the fluid mixture with that of the two individual fluids. This embodiment offers the advantage that the mixing ratio can be easily and understandably displayed to the vehicle's driver.

[0083] If the freezing points of the two fluids are known, the evaluation unit 10 can be additionally configured, according to another embodiment, to determine the freezing point as a characteristic of the fluid mixture when using the concentration of the fluid mixture. The freezing point of the detergent can then be displayed to the driver, allowing the driver to accurately determine whether to change the mixing ratio of the detergent to reliably prevent freezing.

[0084] If the thermal conductivity and freezing point of the fluid mixture are known, the evaluation unit 10, according to another embodiment, can be configured to determine the freezing point as a characteristic of the fluid mixture by comparing the thermal conductivity with a straight line. This straight line is described here as follows: Figure 4 The values ​​shown are obtained through linear interpolation, where the thermal conductivity and freezing point of the fluids are used as reference points. For this purpose, the thermal conductivity values ​​of the two fluids are plotted on the x-axis of a Cartesian coordinate system, and the freezing point values ​​of the two fluids are plotted on the y-axis of a Cartesian coordinate system. Figure 4 As indicated by the arrow, the freezing point of the fluid mixture can then be determined by comparing the calculated thermal conductivity of the fluid mixture with the corresponding value on the y-axis. The freezing point of the detergent solution can then be communicated to the driver, allowing the driver to accurately determine whether the detergent solution mixing ratio is suitable for the given temperature.

[0085] As already mentioned, the washing device 50 is installed in the vehicle 70 and is particularly used for cleaning optical sensors used in driver assistance systems and / or systems for autonomous driving. However, the washing device 50 can also be used to clean the light sources and / or window panels of the vehicle 70. In addition to the fluid container 30, the washing device 50 has other components, such as piping, pumps, nozzles, wipers, etc., which are necessary for cleaning optical sensors, light sources, or window panels.

[0086] The following reference Figure 3 Steps S1 to S6 of a method 100 for determining the thermal conductivity of a fluid or fluid mixture are described. An evaluation unit 10 is configured to control other components of the apparatus 1 for determining thermal conductivity, thereby implementing each step S1 to S6 of the method 100. The evaluation unit 10 is capable of obtaining additional information besides communicating with other units and devices (e.g., detection devices for detecting filling / emptying) installed in the vehicle 70 and communicatively connected to each other via, for example, a vehicle bus. The method 100 is stored in RAM or ROM as software and is implemented by instructions executed by a CPU and by outputting and receiving signals at I / O terminals.

[0087] In step S1, it is checked whether the ignition of vehicle 70 is turned on and / or off. If no ignition is detected to be turned on and / or off (No in S1), wait until a corresponding signal is received. When the ignition is turned on and / or off (Yes in S1), proceed to S2.

[0088] In S2, it is determined, based on the signal obtained by the detection device, whether liquid filling and / or liquid emptying of the fluid container 30 has been detected. If it is not determined that filling and / or emptying has occurred (No in S2), the process returns to the beginning of the method. When it is determined that filling and / or emptying has occurred, the process proceeds to step S3.

[0089] It should be noted that method 100 can also be implemented without steps S1 and S2, thus method 100 begins directly with step S3. Here, method 100 is repeated at preset intervals. Method 100 can also have only one of the two steps S1 or S2. The order of the two steps S1 and S2 can also be changed.

[0090] In S3, the evaluation unit 10 controls the manipulation unit 6 to apply an AC voltage to the measurement bridge 4 and the method 100 proceeds to step S4.

[0091] In S4, the voltage detection unit 8 detects the bridge voltage Ub or the amplified voltage Uv corresponding to the bridge voltage Ub, and the method 100 proceeds to S5.

[0092] In S5, the evaluation unit 10 filters the signal component of the voltage Uv, which corresponds to three times the frequency of the voltage applied to the measuring bridge 4, and thereby determines the thermal conductivity of the washing liquid.

[0093] In step S6, which can be optionally implemented, the concentration and / or freezing point of the washing solution are determined in the manner and method described above. However, it is not necessary to determine these parameters, so the method 100 can be implemented even without step S6.

[0094] For use in a washing device 50 for a vehicle 70, an apparatus 1, a method 100, and a fluid container 30 for determining the thermal conductivity of a fluid or fluid mixture have been described. It should be noted that apparatus 1 and method 100 are not limited thereto and can be used in any area where the thermal conductivity of the fluid is to be determined. Furthermore, the washing device 50 according to the invention is not limited to application in a vehicle 70 and can be used in monitoring cameras, weather sensors, or other units, wherein freezing of the washing liquid should be reliably prevented to ensure cleanliness even at low temperatures.

[0095] Other embodiments of the present invention will be described below. Figure 5 A schematic diagram of a circuit for a device 1 used to determine the thermal conductivity of a fluid or fluid mixture is shown. In this embodiment, the fluid mixture is, in particular, an aqueous urea solution, which is a mixture of water and urea and is used as a liquid for exhaust gas aftertreatment in an exhaust gas aftertreatment device 60 for a vehicle 70. Therefore, the device 1 for determining the thermal conductivity of the fluid mixture is installed in or on the fluid container 40 of the exhaust gas aftertreatment device 60.

[0096] In this embodiment, the thermal conductivity of the urea aqueous solution is used as a measure of the mixing ratio of urea and water. A suitable urea aqueous solution for waste gas aftertreatment has a concentration of 32.5%, resulting in a thermal conductivity of 0.57 W / (m·K). If the calculated thermal conductivity differs from the preset thermal conductivity, the urea aqueous solution does not have the required urea concentration. Therefore, it may be necessary to replace the urea aqueous solution stored in the fluid container 40 or to replenish it with water or urea.

[0097] Figure 6 and Figure 7 A measuring bridge 240 with conductor assembly 200 is shown, wherein a first conductor 221 and a second conductor 222 are configured as wires. A metallic conductor with a circular or angular cross-section is understood as a wire, which is attached to the retaining assembly only at its two ends. The section therebetween is completely surrounded by a fluid mixture.

[0098] The first conductor 221 here has a length that is several times, preferably four times, that of the second conductor 222, and for this reason has a cross-section that is smaller than the cross-section of the second conductor 222 in proportion to the length of the first conductor 221. Therefore, the first conductor 221 and the second conductor 222 have the same resistance value when there is no current. To reduce the spatial extension of the conductor assembly 200, the first conductor 221 is mounted on the conductor assembly 200 in a zigzag or annular shape. It should be noted that the cross-sections of the two conductors 221 and 222 are... Figure 6 and Figure 7 The same applies for illustrative purposes. The cross-sections of the two conductors 221 and 222 are actually different from each other.

[0099] Two conductors 221 and 222 are tensioned on the recessed surface 202 of the retaining assembly 201 in a plane parallel to the recessed surface 202, such that they are completely surrounded and encircled by the fluid or fluid mixture. In this way, the two conductors 221 and 222 can be in complete contact with the fluid. In this way, the accuracy of thermal conductivity detection can be further improved by the device according to the invention.

[0100] In the edge region of conductor assembly 200, two conductors 221 and 222 are guided through opening 204 to form respective bends. An elastic element, such as a spring (not shown), can be arranged in conductor assembly 200 to preload the two conductors 221 and 222, thereby compensating for length changes caused by heating under current flow conditions. This compensation applies not only to length changes in conductor assembly 200 but also to length changes in the two conductors 221 and 222. In this way, contact between the bends or loops of the two conductors 221 and 222, or the first conductor 221, can be prevented, and short circuits can be reliably prevented. Furthermore, length or shape changes in holding assembly 201 due to temperature variations can also be compensated.

[0101] A square protrusion 206 is arranged between the two conductors 221 and 222 and the bend in the first conductor 221. The protrusion 206 extends from the recessed surface 202 to a plane that is also parallel to the recessed surface and is further away from the recessed surface 202 than the plane where the first conductor 221 and the second conductor 222 are arranged. Therefore, the protrusion 206 also prevents the first conductor 221 and the second conductor 222, as well as the bend in the first conductor 221, from contacting each other. In addition, the protrusion 206 prevents freezing in large sections of the conductor assembly 200. This is necessary because the urea aqueous solution used for exhaust gas aftertreatment has a freezing point of -11°C and therefore may freeze in cold winters. Furthermore, the antifreeze fraction of the washing liquid may be too small, so the washing liquid may also freeze in cold winters. This limitation allows the frozen section of the fluid mixture in the area of ​​the conductor assembly 200 to be melted more quickly by a heater arranged in the fluid container 40 for the urea aqueous solution, thereby enabling the thermal conductivity of the washing liquid or urea aqueous solution to be determined more quickly and reliably after the vehicle 70 is started.

[0102] The two resistors 41 and 42 in the other branch of the measuring bridge 240 are constructed as resistors with fixed resistance values. Here, the resistance values ​​of the two resistors 41 and 42 are selected such that the measuring bridge 240 is calibrated in a no-current state. The two resistors 41 and 42, along with the conductor assembly 200 having the first conductor 221 and the second conductor 222, can be arranged on a common assembly, for example, on a common circuit board, or they can be spatially separated and interconnected by cables or lines.

[0103] Holes 208 are formed in the edge region of the retaining assembly 201 into which pins for a cap or cover (not shown) of the conductor assembly 200 can be inserted. Alternatively, screws with threads can be screwed into the holes to connect the cap to the retaining assembly 201. The cap further prevents the urea aqueous solution from freezing in larger areas of the regions of the two conductors 221 and 222. To allow the fluid mixture to remain in contact with the first conductor 221 and the second conductor 222, the cap has slits or holes through which the fluid mixture can flow into the first conductor 221 and the second conductor 222. Furthermore, the cap reduces the risk of mechanical damage to the first conductor 221 and the second conductor 222.

[0104] exist Figure 8 and Figure 9The diagram illustrates a measuring bridge 340 according to another embodiment of the invention. In the measuring bridge 340, one of the voltage dividers is constituted by a conductor assembly 300 according to another embodiment. In the conductor assembly 300, a first conductor 321 configured as a wire and mounted on a holding assembly 301 is connected in series with a fixed resistor 322. When using this conductor assembly 300, it is not necessary to contact the fixed resistor 322 with the fluid; it is sufficient to contact only the first conductor 321 with the fluid.

[0105] Another voltage divider in the voltage divider is formed by two settable resistors 341 and 342. Resistors 341 and 342 are resistors with variable resistance values ​​and are preferably constructed as digital potentiometers. In this embodiment, the evaluation unit 10 is configured to set or change the resistance values ​​of resistors 341 and 342 to calibrate the measuring bridge 340 when an AC voltage U0 is initially applied.

[0106] In this embodiment, the conductor assembly 300 has only a first conductor 321, which is constructed as a wire. The first conductor 321 is connected to the wiring of the measuring bridge 340 at the terminal 302. Figure 8 and Figure 9 In the illustrated embodiment, terminal 302 is a threaded terminal, but the terminal can also be configured as a clamping terminal or a plug-in terminal. Therefore, the retaining assembly 301 can be easily installed and removed.

[0107] exist Figure 8 and Figure 9 In the example shown, the first conductor 321 is configured as a loop and arranged in a plane parallel to the bottom surface 304 of the retaining assembly 301. A frame 306 is formed around the bottom surface 304, such that the retaining assembly 301 is constructed as a recessed housing containing a small amount of fluid. This configuration of the retaining assembly 301 ensures that the first conductor 321, configured as a wire, is substantially completely surrounded by fluid along its entire length. This further improves detection accuracy.

[0108] The first conductor 321 is guided past the turning position 308 and preloaded by means of an elastic element to compensate for length changes caused by heating under current flow and shape or length changes of the retaining assembly 301 due to temperature variations. In this embodiment, the elastic element is configured as spring elements 310 and 312. The first spring element 310 preloads the first conductor 321 towards the outside of the loop. The second spring element 312 preloads the first conductor 321 towards the inside of the loop by contracting two opposing sections of the first conductor 321. In this way, contact between the first conductor 321 and itself or with other elements of the conductor assembly 300 is reliably prevented. Therefore, short circuits of the first conductor 321 can be reliably prevented. Furthermore, shape or length changes of the retaining assembly 301 due to temperature variations can be compensated.

[0109] Protrusions 314 or projections are arranged inside and outside the loop of the first conductor 321, which further reliably prevent the first conductor 321 from contacting itself or surrounding components. Furthermore, in Figure 8 and Figure 9 In the example shown, the cylindrical protrusion 314 restricts the spatial expansion of the frozen section in the region of the first conductor 321, so that the frozen section of the urea aqueous solution can be rapidly thawed after heating begins.

[0110] The retaining assembly 301 has two hollow pillars 316 in the central region on its outer side. A pin for a cap or cover (not shown) can be inserted into these hollow pillars, or a screw can be screwed into them to connect the cap to the retaining assembly 301. Here, the cap rests on the frame 306 of the conductor assembly 300 and is also configured with slits or holes to allow fluid to enter the interior of the conductor assembly 300. The cap further prevents the urea solution or washing liquid from freezing in the area of ​​the retaining assembly 301 and reduces the risk of mechanical damage to the retaining assembly 301 or the first conductor 321.

[0111] The retaining component 301 is not limited to the first conductor 321, and the second conductor can also be arranged on a similar conductor assembly. Furthermore, the conductor assembly 300 can also be configured such that not only the first conductor but also the second conductor can be mounted on the conductor assembly 300. For this purpose, the two conductors can be guided overlapping each other in two parallel planes, or the second conductor, having a shorter length than the first conductor, can also be configured as a loop inside the loop of the first conductor, which, if necessary, can also be pre-tensioned by an elastic element.

[0112] exist Figure 10 The text shows when using Figure 8 and Figure 9 The flowchart of method 400 implemented when measuring bridge 340 is shown. Method 400 and Figure 3 The difference in the method 100 shown is that step S10 is performed before step S1, in which the evaluation unit 10 adjusts the measurement bridge 340 by setting the resistance values ​​of the two resistors 341 and 342.

[0113] The calibration of the measuring bridge 340 is performed as follows. The evaluation unit 10 is configured to cause at least one of the two transistor boost stages to apply a DC voltage to the measuring bridge 340. Here, the DC voltage has a value of 200 mV. However, the value of the DC voltage can also be between 100 mV and 500 mV, including 100 mV and 500 mV. The bridge voltage Ub is then detected and the evaluation unit 10 changes the two settable resistors 341 and 342. The DC voltage is then reapplied to the measuring bridge 340 and the bridge voltage Ub is detected again. This process is repeated until the bridge voltage Ub detected in response to the applied DC voltage is substantially equal to 0 V. Thus, the measuring bridge 340 can be reliably calibrated. It is advantageous to perform this process at startup or when thermal conductivity is first detected for initial calibration of the measuring bridge 340.

[0114] Alternatively or additionally, the evaluation unit 10 can be configured to filter out the signal component of the bridge voltage Ub, which corresponds to the simple frequency of the AC voltage U0 applied to the measuring bridge 340. The amplitude of this signal component of the bridge voltage Ub can be used as a measure of the detuning of the measuring bridge 340, and the evaluation unit 10 is configured to change the resistance values ​​of the settable resistors 341 and 342 in step S10 such that the signal component of the bridge voltage corresponding to a single frequency of the applied AC voltage Ub is substantially 0 V. This approach provides the advantage that detuning of the measuring bridge 340 can be detected during measurement operation. Therefore, detuning of the measuring bridge 340 (which occurs, for example, as a result of heating during operation) can be detected, and the measuring bridge 340 can then be retuned.

[0115] exist Figure 11 The diagram shows a retaining assembly 501 covered by a cover 502 according to an embodiment. For connection of the cover 502 to the retaining assembly 501, both the retaining assembly 501 and the cover 502 have corresponding holes 504 or 506 into which pins 508 can be inserted. Alternatively, the retaining assembly 501 and the cover 502 can also be connected to each other by screws or rivets. In this case, the holes, for example, have threads for screws or are configured such that rivets can be supported in the holes. Figure 11 As shown, the cover 502 has two slits 510 through which the fluid whose properties are to be determined can communicate with the conductor 521, which is configured as a wire.

[0116] exist Figure 11 The difference between the retaining assembly 501 shown and the previous embodiment is that the conductor 521 is arranged in the recessed section 512. Therefore, the section outside the recessed section 512 corresponds to the protrusion according to the aforementioned embodiment. The conductor 521 can be connected to a measuring bridge, such as the measuring bridge 340 according to the aforementioned embodiment, via two contact pins 514. Furthermore, the conductor 521 is preloaded by an elastic element, particularly a spring element 516, thereby compensating for changes in the length of the conductor 312 and / or the length or shape of the retaining assembly 501 due to temperature variations. This reliably prevents damage to the conductor 521, which is constructed as a wire.

Claims

1. An apparatus for determining the properties of a fluid, comprising: Electrical conductor assemblies (2, 200, 300), said electrical conductor assemblies being designed such that they are at least partially in contact with a fluid and configured as voltage dividers having two elements (21, 221, 321, 521, 22, 222, 322), wherein, The first element is a first conductor (21, 221, 321, 521), and the second element is a second conductor (22, 222, 322). The first conductor, at least when energized, has a resistance value different from that of the second conductor (22, 222, 322). A measuring bridge (4, 240, 340) has two voltage dividers connected in parallel, wherein one of the voltage dividers is formed through the electrical conductor assembly (2, 200, 300). The control unit (6) is used to apply an AC voltage (U0) to the measuring bridges (4, 240, 340). A voltage detection unit (8) for detecting bridge voltage (Ub), and Evaluation unit (10) is configured such that the evaluation unit determines the thermal conductivity as a characteristic of the fluid by evaluating the bridge voltage (Ub) using the 3ω method.

2. The apparatus according to claim 1, wherein, The first conductor (21, 221) and the second conductor (22, 222) have the same resistance value when there is no current, and the first conductor (21, 221) heats up more intensely than the second conductor (22, 222) when energized.

3. The apparatus according to claim 2, wherein, The cross-section of the first conductor (21, 221) is smaller than the cross-section of the second conductor (22, 222).

4. The apparatus according to claim 1, wherein, The second element is a fixed resistor (322), and the first conductor (321, 521) has a resistance value different from that of the fixed resistor (322), at least when current flows through it. Another voltage divider in the voltage divider of the measuring bridge (340) is formed by two settable resistors (341, 342), and The evaluation unit is configured such that it sets the two settable resistors (341, 342) before applying the AC voltage (U0), thereby adjusting the measurement bridge (340).

5. The apparatus according to claim 1, wherein, The first conductor (21, 221, 321, 521) and / or the second conductor (22, 222) are arranged at least in a segmented, tortuous or looped manner on the circuit board (26) or the retaining assembly (201, 301, 501).

6. The apparatus according to claim 1, wherein, The first conductor (221, 321, 521) and / or the second conductor (222) are configured as wires.

7. The apparatus according to claim 1, wherein, The fluid is a mixture of two fluids, each of which has a known thermal conductivity, and The evaluation unit (10) is configured such that the evaluation unit determines the concentration of the fluid mixture as a characteristic of the fluid mixture by comparing the thermal conductivity of the fluid mixture with the thermal conductivity of the two fluids.

8. The apparatus according to claim 7, wherein, The freezing points of the two fluids are known, and The evaluation unit (10) is configured such that it uses the concentration of the fluid mixture to determine the freezing point as a characteristic of the fluid mixture.

9. The apparatus according to claim 1, wherein, The fluid is a mixture of two fluids, each of which has a known thermal conductivity and freezing point. The evaluation unit (10) is configured such that it determines the freezing point as a characteristic of the fluid mixture by comparing the thermal conductivity with a straight line obtained by linear interpolation, wherein the thermal conductivity and freezing point of the two fluids are used as reference points respectively.

10. The apparatus according to claim 1, wherein, The evaluation unit (10) is configured to filter the signal component of the bridge voltage (Ub) by means of a software-implemented synchronous rectifier, the signal component having a single or multiple times the frequency of the AC voltage (U0).

11. The apparatus according to claim 10, wherein, The signal component has a frequency three times that of the AC voltage (U0).

12. A fluid container having the means according to any one of claims 1 to 11.

13. The fluid container of claim 12, wherein the fluid container has a sensor for measuring the liquid level.

14. The fluid container according to claim 13, in, The device according to any one of claims 1 to 11 and the sensor for liquid level measurement are configured as a common module.

15. A vehicle having a washing device (50) for cleaning vehicle components and / or optical sensors and / or light sources and / or window panels and / or having a device (60) for exhaust gas aftertreatment, the device having a fluid container (30, 40) according to any one of claims 12 to 14.

16. A method for determining the properties of a fluid based on the apparatus of any one of claims 1-11, comprising the following steps: An AC voltage (S3) is applied to the measuring bridges (4, 240, 340). Detect (S4) bridge voltage (Ub). Using the 3ω method, the thermal conductivity (S5) is determined as a characteristic of the fluid by evaluating the bridge voltage (Ub).

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