Sensor device for detecting electrically conductive media, and method for operating the sensor device

Abstract

A sensor device for detecting liquid, in particular in a controller of a steering system of a vehicle, includes at least one sensor element and a testing unit. The sensor element is electrically connected to the testing unit. The testing unit has a signal transmitter, connected to the sensor element, that is configured to generate an electrical test signal, and a signal receiver, connected to the sensor element, that is configured to detect a reaction signal for the electrical test signal. The signal transmitter and the signal receiver are each connected at high impedance to the at least one sensor element. The testing unit is configured to detect the reaction signal at least at a time as a first reaction signal for which the electrical test signal has been generated in order to infer a presence of the medium.

Claims

1. A sensor device for detecting at least one electrically conductive medium in a control unit, comprising: a plurality of sensor elements; a plurality of capacitors; a testing unit; and a shared signal line configured to electrically connect the plurality of sensor elements and the plurality of capacitors to the testing unit, wherein the testing unit comprises (i) a signal generator connected to the plurality of sensor elements by the shared signal line and configured to generate an electrical test signal on the shared signal line, and (ii) a signal receiver connected to the plurality of sensor elements by the shared signal line and configured to detect a first reaction signal to the electrical test signal on the shared signal line, wherein the testing unit is configured to analyze the first reaction signal at a first point in time to conclude a presence or absence of the medium, wherein the first point in time is when the electrical test signal is generated and when the electrical test signal has reached a predetermined value, wherein the shared signal line is connected directly (i) to each sensor element of the plurality of sensor elements, and (ii) to each capacitor of the plurality of capacitors, and wherein each capacitor of the plurality of capacitors is connected directly to ground.

2. The sensor device as claimed in claim 1, wherein each sensor element of the plurality of sensor elements is connected to a positive or to a negative electrical voltage potential.

3. The sensor device as claimed in claim 1, wherein the sensor device is connected to a floating ground.

4. The sensor device as claimed in claim 1, wherein the capacitors of the plurality of capacitors each have different capacitances.

5. The sensor device as claimed in claim 1, further comprising: a further capacitor, the further capacitor connected to ground between a second resistor and the signal receiver.

6. The sensor device as claimed in claim 5, wherein a third resistor is connected to ground between a first resistor and the signal generator.

7. The sensor device as claimed in claim 6, wherein the first resistor and the second resistor are connected directly to the at least one sensor element by the shared signal line.

8. The sensor device as claimed in claim 1, wherein: the testing unit is configured to analyze a second reaction signal at a second point in time, the second point in time is before the electrical test signal is generated and before the first point in time, the testing unit is configured to analyze a third reaction signal at a third point in time, and the third point in time is after the electrical test signal is completed and after the second point in time.

9. The sensor device as claimed in claim 6, further comprising: a further capacitor arranged serially in the shared signal line, and wherein first resistor and the second resistor are connected directly to the further capacitor.

10. The sensor device as claimed in claim 1, wherein the sensor device is included in a control unit.

11. A steering system comprising: at least one control unit including at least one sensor device configured to detect at least one electrically conductive medium in the at least one control unit, the at least one sensor device including a plurality of sensor elements, a testing unit, and a plurality of capacitors, wherein a shared signal line is configured to electrically connect the plurality of sensor elements and the plurality of capacitors to the testing unit, wherein the testing unit comprises (i) a signal generator connected to the plurality of sensor elements by the shared signal line and configured to generate an electrical test signal on the shared signal line, and (ii) a signal receiver connected to the plurality of sensor elements by the shared signal line and configured to detect a first reaction signal to the electrical test signal on the shared signal line, wherein the testing unit is configured to analyze the first reaction signal at a first point in time to conclude a presence or absence of the medium, wherein the first point in time is when the electrical test signal is generated and when the electrical test signal has reached a predetermined value, wherein the shared signal line is connected directly (i) to each sensor element of the plurality of sensor elements, and (ii) to each capacitor of the plurality of capacitors, and wherein each capacitor of the plurality of capacitors is connected directly to ground.

12. The sensor device as claimed in claim 1, wherein: the medium is a liquid, and the sensor device and the control unit are included in a steering system of a vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will be explained in greater detail hereafter on the basis of the drawing. In the figures:

(2) FIG. 1 shows an advantageous sensor device for detecting an electrically conductive medium according to a first exemplary embodiment,

(3) FIG. 2 shows the advantageous sensor device according to a second exemplary embodiment,

(4) FIG. 3 shows the sensor device according to a third exemplary embodiment,

(5) FIGS. 4A to 4F show exemplary characteristic curves of the sensor device in dependence on different applications, and

(6) FIG. 5 shows a level measuring device which comprises a plurality of the advantageous sensor devices.

DETAILED DESCRIPTION

(7) FIG. 1 shows a simplified illustration of a sensor device 1 for detecting electrically conductive media, in particular an electrically conductive liquid, in a control unit 6 (not shown in greater detail here) of a steering system of a motor vehicle.

(8) The sensor device 1 comprises multiple sensor elements WS1, WS2, WS3 to WSn, which are electrically connected to a testing unit 2. The sensor elements WS1 to WSn are, for example, electrically conductive testing contacts. The testing unit 2 preferably comprises a microcontroller or an ASIC circuit (application-specific integrated circuit) or is formed thereby. The testing unit 2 comprises a signal generator 3, which is designed to generate an electrical test signal and optionally vary it. In addition, the testing unit 2 comprises a signal receiver 4, which is designed to detect at least one electrical reaction signal in the sensor device 1, which results from the test signal generated by the signal generator 3. The testing unit 2 is designed to determine in dependence on the detected reaction signal whether the sensor device 1 is functional and/or whether electrically conductive medium is detected by one or more of the sensor elements WS1 to WSn. For this purpose, the signal generator 3 and the signal receiver 4 are connected by a shared signal line 5 to the sensor elements WS1 to WSn. Before the signal lines 5 are unified, a first resistor R1 is connected downstream from the signal generator 3 and a second electrical resistor R2 is connected upstream from the signal receiver 4. The resistors R1 and R2 are formed to be high-resistance, so that the respective test signal is output by the signal generator 3 at high resistance to the sensor elements WS1 to WSn and is read back at high resistance by the signal receiver 4.

(9) Each of the sensor elements WS1 to WSn is connected, on the one hand, to the shared signal line 5 and, on the other hand, is connected by a capacitor C1 to Cn to ground of the sensor device 1 or to an external ground, so that interferences and/or interference sources which originate from electrostatic discharges are decoupled to ground.

(10) The signal receiver 4 is additionally connected via a further capacitor Cp to ground, so that high-frequency interference sources are short-circuited at the sensor input and thus decoupled. The capacitor Cp can be formed as an additional component or, however, by the parasitic capacitor present due to the logic input of the signal receiver 4.

(11) Furthermore, a high-resistance resistor R3 for dissipating possible cross currents is connected to ground directly at the logic output and/or at the output of the signal generator 3. If a logical zero is written out by the signal generator 3, the cross currents thus resulting are dissipated thereby to ground. Signal generator 3 and signal receiver 4 are formed in particular as digital components to enable a simple testing method.

(12) FIG. 4A shows characteristic curves of the sensor device 1 in the test mode in a simplified diagram. A first solid characteristic curve K.sub.3 shows the test signal generated by the signal generator 3 over the time t. A dashed line K.sub.4 shows the reaction signal received by the signal receiver 4 from the circuit or the signal line 5. A line Lp indicates the logic level to be reached for the test signal K.sub.3. A shaded region B marks an undefined level or a hysteresis level, within which the reading back of the reaction signal K.sub.4 would not result in an unambiguous result.

(13) At a point in time t1, a water query is started in that the signal generator 3 generates the test signal K.sub.3 in the form of a test pulse. The reaction signal K.sub.4 results in reaction thereto if none of the sensors WS1 to WSn is in contact with electrically conductive medium. The reaction signal K.sub.4 nearly reaches the level of the test signal K.sub.3 at a point in time t2, at which the test signal K.sub.3 is reliably generated, in particular shortly before the test signal or the test pulse is ended at a point in time t3 and thus terminated.

(14) The moisture query is thus performed by emitting and querying the test signal. The signal generator is initially permanently set to “low”. Even before it generates the test signal, it or the test signal is read out at high resistance by the signal receiver 4. If a low level is detected, water can thus be present. However, since a “low” is expected at this point in time, this is evaluated as the absence of water. However, if the input level is at “high”, an external potential W+, for example, the electrically conductive water which is connected to a positive potential, is thus present. This state is then detected or evaluated at this point in time t1 as “water present”.

(15) At a second point in time t2, the reaction signal is also read out by the signal receiver 4, even before the test signal is switched off again or the high level of the test signal is switched to the low level. If a high level is read at this point in time t2, this is thus evaluated as “no water”. However, if the reaction signal is at “low”, this is thus evaluated at this point in time t2 as “water present”, wherein the external potential of the water is a negative here.

(16) Subsequently, at the point in time t3, a low level is again written or output with high resistance by the signal generator by terminating the test signal. A readout by means of the signal receiver 4 is again performed at the point in time t3. If a low level (water could be present) is now read, this is thus evaluated as an “absence of water”. However, if the reaction signal is “high”, “water present” is thus detected. A positive external potential of the water (W+) is then applied. This last writing and reading procedure forces the logic to also perform a hysteresis jump, wherein both a positive external potential and also negative external potential are present. Without this jump, a discovery gap could result. However, this case occurs very rarely. The hysteresis jump can be defined by lengthening and shortening the test signal.

(17) The presence of liquid is thus ascertainable reliably independently of potential by the measurement and/or readout of the three reaction signals or the reaction signal at the three predetermined points in time t1 (before the test signal is generated), t2 (when the test signal is generated), and t3 (when the test signal is completed).

(18) FIG. 2 shows a second exemplary embodiment of the sensor device 1, wherein elements already known from FIG. 1 are provided with the same reference signs and reference is thus made to the above description. Essentially the differences will be discussed hereafter.

(19) In contrast to the first exemplary embodiment, the sensor device according to the second exemplary embodiment provides that, in the shared signal line 5, a capacitor Cr is connected in series with the sensor elements WS1 to WSn and the signal generator 3 and/or the signal receiver 4 in a DC voltage manner. An RC element is thus formed, with the advantage that a decoupled system results, in which the measurement points in time t1 and t3 are no longer relevant, only the point in time t2 is still important. It is presumed that each voltage source acts like a capacitor, so that at the measurement pulse moment, it goes toward 0 ohm. It is therefore unimportant whether the measurement is performed toward a negative or a positive potential (for example, ground or positive potential), because the measurement pulse moment at the point in time t2, when the test signal is generated, is only considered to be the short circuit to ground or to the negative potential, respectively. By adding the capacitor Cr, an even simpler and nonetheless unambiguous determination of the moisture or an electrically conductive medium at one of the sensor elements WS1 to WSn is thus enabled.

(20) While the resistors R1, R2, R3 and the capacitor Cp are located outside the testing unit 2 in FIGS. 1 and 2, it is provided according to a further exemplary embodiment that they are also formed by the testing unit 2 or located therein. This is shown in FIGS. 1 and 2 by a dashed frame.

(21) FIG. 3 shows a further exemplary embodiment of the sensor device 1, which differs from the preceding exemplary embodiments in that the capacitor Cr is connected downstream from the resistor R1 or the high-resistance output of the signal generator 3 even before the shared signal line 5. This is thus a combination of the first two exemplary embodiments. An advantageous measurement is also reliably ensured here.

(22) FIGS. 4A to 4F show different measurement cycles, which can be carried out using the advantageous sensor device 1. FIG. 4A was already explained above, wherein the same reference signs are used in FIGS. 4B to 4F and reference is thus made to the above description.

(23) A measurement cycle is carried out without potential in the exemplary embodiment of FIG. 4A, wherein water is not detected at any of the sensor elements WS1 to WSn.

(24) The exemplary embodiment of FIG. 4B involves a state in which at least one of the sensor elements WS1 to WSn is in contact with water or electrically conductive liquid. The reaction signal K.sub.4 unambiguously differs from the test signal K.sub.3 and does not reach the high level.

(25) FIG. 4C shows a measurement cycle with water present and with a mixed potential of supply voltage and ground. An elevated high reaction signal results at the point in time t2, however, outside this region, the reaction signal K.sub.4 is in the undefined level range B.

(26) In the case of a measurement with water present in relation to a supply voltage, a measurement cycle results as shown in FIG. 4D.

(27) FIG. 4E shows a measurement cycle with water present in relation to an elevated positive potential and FIG. 4F shows a measurement cycle with water present in relation to an elevated negative potential.

(28) It has been shown that the sensor device 1 in its different designs is always capable of unambiguously recognizing the presence of water or another electrically conductive liquid independently of potential.

(29) FIG. 5 shows a further exemplary embodiment, in which a plurality of the sensor devices 1 are combined to form a level measuring device, wherein known elements are provided with the same reference signs and reference is thus made to the above description. It has been shown that the interconnection of multiple such sensor devices 1 results in an advantageous level measuring device, by means of which a fill level, for example, in a water tank or fuel tank, is ascertainable unambiguously.

(30) The resistance measuring range of the measurement voltage can be changed by a variation of the test signal or its pulse width, so that, for example, it is possible to differentiate between condensation (ion-poor), penetrating water (ion-rich), and saltwater (salt ions). The wider the test pulse is, the higher is the measurement pulse voltage and thus the more insensitive the measuring system, and vice versa. In addition, by determining the charging time of the connected sensor elements WS1 to WSn, an absence of one of the sensor elements WS1 to WSn is recognizable, because each sensor element WS1 to WSn receives a separate ESD capacitor C1 to Cn. The capacitors C1 to Cn advantageously have different capacitances to enable an unambiguous assignment. In addition, the sensor device 1 itself can be diagnosed by an overlong test pulse, for example, by recognizing whether the resistors R1, R2, and possibly R3 are present. In contrast, it is recognizable by a very short test pulse whether the decoupling capacitor Cr is present in the sensor device 1 according to the second or the third exemplary embodiment.

(31) The circuit can monitor itself for its functionality by way of the above-mentioned variation of the test pulses. In addition, it is possible by way of the variation of the test pulses and/or the test signal, by repeated query and evaluation, to check for plausibility incorrect measurements caused by interference pulses (periodic or random).

(32) The respective sensor device 1 additionally preferably operates using so-called floating grounds (GND.sub.GP), as shown by way of example in FIGS. 1 to 3, which expands the potential independence thereof by an additional function. The floating ground GND.sub.GP is formed in particular with the aid of a resistor R.sub.SP and/or a capacitor C.sub.GP.

(33) An interference-insensitive water detection of ionized or contaminated water at a processor/ASIC/logic input (signal receiver 4) is possible by way of the sensor device 1. This insensitivity to interference relates both to electrostatic discharges and also to electromagnetic interference fields or external voltage potentials. Positive, negative, and also mixed potentials can be used for water detection. The applied resistance is ascertained independent of potential. This is achieved by the triple signal analysis in the case of the first exemplary embodiment, which is evaluated differently at each signal point in time.

(34) The detection of the water or the medium is performed in this case with low energy by the sensor device 1, since energy in the microwatt range is only required at the measurement point in time. In the case of an external solution, i.e., not integrated in an ASIC or microcontroller, only two contact terminals are necessary, one for outputting the test signal and one for inputting the reaction signal, two high-resistance resistors R1, R2 and also the ESD capacitors C1 to Cn and optionally the decoupling capacitor Cr.

(35) Since the circuit of the sensor device 1 essentially consists of the resistors R1, R2, and R3, it can also be integrated into the microcontroller or into the ASIC, as already explained above. A specialized water sensor input thus results, which is both a high-resistance read input and also a high-resistance write output.

(36) The sensor device 1 additionally has the advantage that the electrodes or the sensor elements WS1 to WSn are substantially freed of corrosion or migration due to the pulse method by the test pulses, so that the long-term durability of the sensor device 1 is ensured.