Sensor unit, fluid assembly with sensor unit and method for measuring parameters of a fluid

Abstract

Sensor unit (S) for measuring parameters of a fluid, in particular a hydraulic fluid (H), in a fluid power unit, in particular a hydraulic power unit (A), wherein the sensor unit (S) comprises a contact module (1) and two electrode pairs, each with two electrodes (2), wherein the electrode pairs are connected to the contact module (1) and the longitudinal axes of the electrode pairs are arranged substantially perpendicular to each other.wherein, depending on the orientation of the sensor unit (S), one electrode pair is a measuring electrode pair (M) and the other electrode pair is a reference electrode pair (R), characterized in that the assignment of measuring electrode pair (M) and reference electrode pair (R) to the electrode pairs is automated, in that the sensor unit (S) independently recognizes the orientation of the hydraulic unit (A) on the basis of the measured values ​​of the electrode pairs and performs the assignment of measuring electrode pair (M) and reference electrode pair (R) to the electrode pairs.

Description

The present invention relates to a sensor unit for measuring parameters of a fluid, in particular of a hydraulic fluid, in a fluid assembly, in particular a hydraulic assembly, a fluid assembly having a sensor unit according to the invention, and to a method for measuring parameters of a fluid in a fluid assembly having a sensor unit according to the invention.In the field of capacitive fill level measurement in fluid aggregates, sensor units are known which can measure parameters of the fluid, such as the fill level of the fluid in the tank of the fluid aggregate with respect to a defined direction. In other words: Only when the fluid unit is set up "correctly" can the sensor unit also measure the fill level. It is namely conceivable that the fluid unit is used standing or lying.For measurement, a rod probe, for example, is introduced into the tank from above, which forms an electrode of a capacitor. The metallic wall of the tank can in turn then be used as a second electrode of the capacitor, so that the capacitance measurable between the two electrodes is dependent on the fill level of the fluid and thus allows a statement about the fill level of the tank. Furthermore, solutions are known in which the distal end of the rod probe can be used as a reference electrode to increase the measurement accuracy by compensating parameter drift. If, however, a unit with such sensors is operated horizontally, so that the attached rod probe protrudes from the side into the tank, at most the exceeding or falling below a threshold value could still be checked.In order to be able to make statements about the state of the fluid, further parameters must be detected. For example, the change in conductivity of the fluid in combination with the change in permittivity detected during capacitive fill level measurement represents an important parameter. Thus, for example, U.S. Pat. No. 9,810,567 B2 and U.S. Pat. No. 2018 / 0202989 A1 disclose sensor units for measuring parameters of a fluid, in which two electrode pairs are used. A pair of electrodes is a pair of measuring electrodes and a pair of electrodes is a pair of reference electrodes.Against this background, it is the object of the present invention to show a sensor unit for measuring different parameters of a fluid in a fluid assembly, which sensor unit can reliably measure the fill level in the tank and various other parameters of the fluid depending on the orientation of the fluid assembly.This object is achieved by a sensor unit according to claim 1. Advantageous further developments are described in the dependent claims.The sensor unit according to the invention for measuring parameters of a fluid, in particular of a hydraulic fluid, in a fluid assembly, in particular a hydraulic assembly, comprises a contact module and two electrode pairs each having two electrodes. The electrode pairs are connected to the contact module and the longitudinal axes of the electrode pairs are arranged substantially perpendicular to one another.The sensor unit according to the invention has the advantage that, due to the essentially perpendicular alignment of the longitudinal axes of the electrode pairs with respect to one another, the sensor unit can be mounted in the fluid assembly in such a way that, depending on the alignment of the fluid assembly, it can be used at least in two spatial directions for measuring parameters of a fluid in the fluid assembly without the need for an adaptation of the sensor system. This increases the variability of the use of both the sensor unit and a fluid assembly in which such a sensor unit is used. By providing two electrode pairs, one can be used as a measuring electrode pair and the other as a reference electrode pair. Thus, a drift of the parameters of the fluid-for example over time or as a function of the temperature-can be compensated for with the aid of the reference electrode pair. Furthermore, the reference electrode pair can be used for measuring further parameters of the fluid.According to the invention, depending on the alignment of the sensor unit, one pair of electrodes is used as the measuring electrode pair and the other pair of electrodes is used as the reference electrode pair. The assignment of the measuring electrode pair and reference electrode pair to the electrode pairs is automated. The sensor unit can thus be operated efficiently in different spatial alignments. For the automated assignment, the effect is used that the capacitance changes in proportion to the portion of the electrode that is under fluid. Thus, a pair of electrodes which lies completely in the fluid can be distinguished from a pair of electrodes which lies only partially in the fluid. In particular, it is advantageous for this purpose if a one-time calibration without fluid is performed in advance for both electrode pairs, so that an initial reference capacitance is available. It is conceivable that this calibration already takes place at the factory, so that no further effort arises for the end user.According to the invention, the sensor unit independently recognizes the alignment of the fluid assembly on the basis of the measured values of the electrode pairs and carries out the assignment of the measuring electrode pair and reference electrode pair to the electrode pairs. As a result, the fluid assembly can be operated selectively in different orientations without the sensor system having to be adapted. This increases the flexibility when using the fluid assembly according to the invention.The electrodes of a pair of electrodes are expediently designed as twisted individual conductors or as twin stranded wires. This further increases the structural flexibility when using the sensor unit and facilitates the attachment of the sensor unit in the fluid unit. In particular, the electrodes are individual conductors insulated with Teflon.It is advantageous if the electrodes are each provided at at least one end with crimp contacts for connection to the contact module. This ensures simple mounting of the electrode pairs on the contact module.Preferably, the lengths of the electrode pairs can be adapted to the geometry of the fluid assembly. This creates a particularly variable usability of the sensor unit in different fluid aggregates, since this is thus independent of the different internal geometry of different fluid aggregates and can be individually adapted to the respectively present geometry during assembly.Expediently, the contact module is injection-molded. As a result, the contact module can be mounted in the fluid assembly at a location which is under fluid without the electronics located in the contact module being influenced thereby. This simplifies the assembly of the sensor unit within the fluid assembly. Alternatively, further sensors can also be accommodated in a space-saving manner in the contact module in order to detect additional parameters of the fluid assembly that cannot be detected by the electrode pairs. For example, a Hall sensor may be used which detects the motor speed by means of a magnet mounted on the shaft of a motor.Based on this automated assignment, it is determined that the completely-under-fluid pair of electrodes is the reference pair of electrodes. Thus, the other pair of electrodes is the measuring electrode pair.It is advantageous if the sensor unit has an oscillator, a multiplexer and a reference capacitor, wherein the oscillator can be switched to the measuring electrode pair, the reference electrode pair or to the reference capacitor via a multiplexer. This allows compensation of the drift of the parameters of the oscillator over temperature and time and thus a more accurate measurement of the changes of the parameters of the fluid. It is conceivable that an asymmetric relaxation oscillator is used.The object is further achieved with a fluid assembly, in particular a hydraulic assembly, according to claim 7. The sensor unit is arranged in the tank and the first and the second support surface are arranged substantially perpendicular to one another. During operation, the fluid assembly rests on the first or on the second bearing surface. Furthermore, the longitudinal axis of an electrode pair is oriented in a first direction, which extends substantially parallel to the first and substantially perpendicular to the second bearing surface. The longitudinal axis of the other electrode pair is oriented in a second direction, which extends substantially perpendicular to the first and substantially parallel to the second bearing surface.The advantage of the fluid assembly according to the invention is that during operation in two alternative orientations-resting on the first or on the second bearing surface-the fill level and other parameters of the fluid located in the tank can be measured by the described attachment of the sensor unit according to the invention in the tank without any need to adapt the sensor system.Advantageously, the pair of electrodes oriented in the first direction extends substantially entirely from the contact module to an opposing wall of the tank. Further, the pair of electrodes oriented in the second direction extends substantially entirely from the contact module to an opposing wall of the tank. This ensures that in both possible alignments of the fluid assembly, the fill level of the fluid located in the tank can be detected by the sensor unit without gaps from the contact module by means of capacitive fill level measurement. Depending on the attachment of the contact module, regions may arise for which no fill level measurement is possible. However, these can be compensated for without problems by software.Furthermore, the object is achieved with a method for measuring parameters of a fluid, in particular of a hydraulic fluid, according to claim 9 in a fluid assembly described above. In this case, depending on the orientation of the fluid unit, one pair of electrodes is used as a measuring electrode pair and the other pair of electrodes is used as a reference electrode pair. Furthermore, a first electrode of the reference electrode pair is charged at a first frequency via a first, higher resistor and, when a target voltage is reached, the first electrode is discharged via a second, lower resistor. In this case, a second electrode of the reference electrode pair is connected at a second frequency to the potential of a supply voltage or to ground. The terms "higher resistance" and "lower resistance" are to be understood here with reference to the relative ratio of these two resistances. Furthermore, the fill level of the fluid is determined at the measuring electrode pair by means of capacitive fill level measurement. According to the invention, the pair of electrodes entirely under fluid is the reference electrode pair and the other pair of electrodes is the measuring electrode pair.The method according to the invention has the advantage that not only capacitive fill level measurements can be carried out with the sensor unit according to the invention, but also changes in the conductivity of the fluid can be measured. In addition, it is possible, for example, to draw a conclusion about impurities. An impurity such as metallic abrasion causes the conductivity to increase. This increase is in turn detected with the method according to the invention and a warning can be issued, for example, to protect the system that a change of the fluid is necessary. Changes in the conductivity of the fluid cause changes in the first frequency that can be detected. For example, the first frequency increases when the supply voltage is applied to the second electrode of the reference electrode pair and the conductivity of the fluid increases. In contrast, the first frequency decreases when the second electrode of the reference electrode pair is grounded and the conductivity of the fluid increases.Expediently, the second frequency is less than or equal to the first frequency. If the second frequency is selected to be smaller than the first frequency, the measurement accuracy can be increased by averaging a plurality of measurement values of the first frequency.The first frequency corresponds to that of an oscillator which charges the first electrode of the reference electrode pair via the first resistor and discharges it via the second resistor. The oscillator can be connected via a multiplexer to the measuring electrode pair, the reference electrode pair or to a reference capacitor. The reference capacitor advantageously has a low temperature dependence. This allows compensation of the drift of the parameters of the oscillator over temperature and time and thus a more accurate measurement of the changes of the parameters of the fluid. In particular, an asymmetric relaxation oscillator can be used as the oscillator.The temperature compensation during the measurement of the conductivity can also be effected by means of a built-in temperature sensor.The invention is explained in more detail below with reference to an exemplary embodiment shown in the figures. The following are shown schematically: FIG. 1 shows a fluid unit in the form of a hydraulic unit in a first exemplary orientation with a sensor unit according to the invention; FIG. 2 shows the hydraulic unit shown in FIG. 1 in a second exemplary orientation with a sensor unit according to the invention; FIG. 3 shows an exemplary voltage profile at the first reference electrode at a high potential at the second reference electrode and increasing conductivity of the hydraulic fluid; and FIG. 4 shows an exemplary voltage profile at the first reference electrode with a low potential at the second reference electrode and an increasing conductivity of the hydraulic fluid.The hydraulic unit A depicted in FIGS. 1 and 2 has a first bearing surface F 1 and a second bearing surface F 2 and a tank T. Furthermore, the hydraulic unit has a sensor unit S which comprises a contact module 1 and two electrode pairs each having two electrodes 2. The electrode pairs are connected to the contact module 1 and the longitudinal axes of the electrode pairs are arranged substantially perpendicular to one another.The representation of the electrode pairs in FIGS. 1 and 2 are schematic representations. The electrode pairs are preferably designed as twisted individual conductors or as twin strands, the electrodes 2 preferably being insulated with Teflon. Furthermore, the electrodes are preferably provided with crimp contacts (not shown) for connection to the contact module 1.The longitudinal axis of a pair of electrodes is oriented in a first direction R 1, which extends substantially parallel to the first support surface F 1 and perpendicular to the second support surface F 2. The longitudinal axis of the other pair of electrodes is oriented in a second direction R 2 which extends substantially perpendicular to the first support surface F 1 and parallel to the second support surface F 2.In the exemplary embodiment shown, the contact module 1 is arranged in the region of an inner edge of the tank T, which lies closest to a common edge K of the first bearing surface F 1 and the second bearing surface F 2. Of course, the contact module 1 can also be arranged at another suitable location in the tank T, as will be explained in more detail below. The electrode pairs extend from the contact module 1 substantially completely as far as the wall of the tank T opposite in the respective direction R 1 or R 2. It is thus ensured that in both possible alignments of the hydraulic unit A, the fill level of a fluid located in the tank T, namely a hydraulic fluid H, can be detected by the sensor unit S without gaps over the entire respective height of the tank T by means of capacitive fill level measurement. In the event that the contact module is not arranged, as here, on an inner edge of the tank T which is closest to a common edge K of the first contact surface F 1 and the second contact surface F 2, any dead zones which may occur can be compensated for by software without any problems with regard to the fill level measurement counter to the measurement direction. The measurement direction here refers to the direction in which a pair of measurement electrodes M extends.Furthermore, the tank T is filled with hydraulic fluid H up to a fill level which is marked with a dashed line in FIGS. 1 and 2.In the orientation of the hydraulic unit A shown in FIG. 1, which in this case rests on the first bearing surface F 1, the electrode pair oriented in the second direction R 2 is a measuring electrode pair M and the electrode pair oriented in the first direction R 1 is a reference electrode pair R.In the orientation of the hydraulic unit A shown in FIG. 2, which in this case rests on the second bearing surface F 2, the electrode pair oriented in the first direction R 1 is the measuring electrode pair M and the electrode pair oriented in the second direction R 2 is the reference electrode pair R.The sensor unit S measures the fill level of the hydraulic fluid H in the tank T of the hydraulic unit A by means of the measuring electrode pair M by means of capacitive fill level measurement. This makes it possible to make statements about the quality of the hydraulic fluid H and, for example, to determine whether the hydraulic fluid is contaminated to a degree that it should be exchanged.When using the measuring method according to the invention, a first electrode of the reference electrode pair R is charged at a first frequency via a first, higher resistor and discharged via a second, lower resistor. This produces the schematic voltage profile represented as a solid line in FIGS. 3 and 4.The second electrode of the reference electrode pair R is in turn connected at a second frequency, which is lower than the first frequency, either to a supply voltage or to ground. A direct current component between the electrodes can thus be avoided. If the conductivity of the hydraulic fluid H now changes, this has an influence on the frequency of the voltage profile present at the first electrode.As shown in FIG. 3 as a dotted voltage curve, the first frequency increases for a case in which the supply voltage is applied to the second electrode of the reference electrode pair R and the conductivity of the hydraulic fluid increases.The voltage curve shown in dotted lines in FIG. 4 shows a case in which the second electrode of the reference electrode pair R is at ground and the conductivity of the hydraulic fluid H increases. This results in a reduction of the first frequency.On the basis of the shift of the first frequency, it can thus be established whether, for example, impurities have entered the hydraulic fluid, for example metallic abrasion. It is then conceivable that either a warning signal is output or the power supply of the pump is also interrupted in order to avoid damage to the different components.Because the changes in the conductivity of the hydraulic fluid H and not the absolute conductivity are of interest in the method according to the invention, a complicated calibration of the sensor unit is also superfluous.Furthermore, the sensor unit S has a multiplexer (not shown), an oscillator (not shown) and a reference capacitor (not shown). The oscillator is connected via the multiplexer to the measuring electrode pair M, the reference electrode pair R or to the reference capacitor, so that the compensation of the drift of the parameters of the oscillator over temperature and time and thus a more accurate measurement of the changes of the parameters of the hydraulic fluid H is possible.REFERENCE NUMERALS1 Contact module 2 Electrode A Hydraulic assembly F 1 First contact surface F 2 Second contact surface H Fill level of the hydraulic fluid K Edge M Measuring electrode pair R Reference electrode pair R 1 First direction R 2 Second direction S Sensor unit T Tank

Claims

Sensor unit (S) for measuring parameters of a fluid, in particular of a hydraulic fluid (H), in a fluid assembly, in particular a hydraulic assembly (A), wherein the sensor unit (S) comprises a contact module (1) and two electrode pairs each having two electrodes (2), wherein the electrode pairs are connected to the contact module (1) and the longitudinal axes of the electrode pairs are arranged substantially perpendicular to one another, wherein one electrode pair is a measurement electrode pair (M) and the other electrode pair is a reference electrode pair (R) depending on the orientation of the sensor unit (S), characterized in that the assignment of measurement electrode pair (M) and reference electrode pair (R) to the electrode pairs takes place in an automated manner, in that the sensor unit (S) independently recognizes the alignment of the hydraulic unit (A) on the basis of the measured values of the electrode pairs and carries out the assignment of the measuring electrode pair (M) and the reference electrode pair (R) to the electrode pairs.Sensor unit (S) according to Claim 1, characterized in that the electrodes (2) of at least one electrode pair are designed as twisted individual conductors or as twin stranded wires.Sensor unit (S) according to one of the preceding claims, characterized in that the electrodes (2) are each provided at at least one end with crimp contacts for connection to the contact module (1).Sensor unit (S) according to one of the preceding claims, characterized in that the lengths of the electrode pairs can be adapted to the geometry of the hydraulic unit (A).Sensor unit (S) according to one of the preceding claims, characterized in that the contact module (1) is injection-moulded.Sensor unit (S) according to one of the preceding claims, characterized in that the sensor unit (S) has an oscillator, a multiplexer and a reference capacitor, wherein the oscillator can be connected via the multiplexer to the measuring electrode pair (M), the reference electrode pair (R) or to the reference capacitor.Fluid assembly, in particular hydraulic assembly (A), having a sensor unit (S) according to one of the preceding claims, a tank (T), a first bearing surface (F1) and a second bearing surface (F2), wherein the sensor unit (S) is arranged in the tank (T), wherein the first and the second bearing surface (F1, F2) are arranged substantially perpendicular to one another, wherein the fluid assembly bears on the first or on the second bearing surface (F1, F2), wherein the longitudinal axis of one pair of electrodes is aligned in a first direction (R1), which extends substantially parallel to the first (F1) and substantially perpendicular to the second bearing surface (F2), and the longitudinal axis of the other pair of electrodes is aligned in a second direction (R2), which extends substantially perpendicular to the first (F1) and substantially parallel to the second support surface (F2).Fluid unit according to claim 7, characterised in that the pair of electrodes oriented in the first direction (R1) extends substantially from the contact module (1) as far as an opposite wall of the tank (T), and the pair of electrodes oriented in the second direction (R2) extends substantially from the contact module (1) as far as an opposite wall of the tank (T).Method for measuring parameters of a fluid, in particular of a hydraulic fluid (H), in a fluid assembly according to one of Claims 7 or 8, wherein, depending on the orientation of the hydraulic assembly (A), one pair of electrodes is used as a measuring electrode pair (M) and the other pair of electrodes is used as a reference electrode pair (R), wherein a first electrode (2) of the reference electrode pair (R) is charged at a first frequency via a first, higher resistor and, when a target voltage is reached, the first electrode (2) is discharged via a second, lower resistor, and wherein a second electrode (2) of the reference electrode pair (R) is placed at the potential of a supply voltage or at ground at a second frequency.Method according to claim 9, characterised in that the second frequency is less than or equal to the first frequency.Method according to one of the preceding claims 9 or 10, characterized in that the first frequency corresponds to that of an oscillator which charges the first electrode of the reference electrode pair (R) via the first resistor and discharges it via the second resistor, the oscillator being switched via a multiplexer to the measuring electrode pair (M), the reference electrode pair (R) or to a reference capacitor.

Images