Method for diagnosing an exhaust gas sensor

Abstract

The invention relates to a method for diagnosing an exhaust gas sensor (20), in particular a wideband lambda sensor, by means of an evaluation and control unit (10), wherein according to the method: - the sum (Us) of the first voltage variable (U1G) and the second voltage variable (U2G) is formed and it is inferred that the first supply line (41) is interrupted if the sum (Us) of a first voltage variable (U1G) and a second voltage variable (U2G) is greater than a threshold value, and / or - the difference (UD) between the first voltage variable (U1G) and the second voltage variable (U2G) is formed and a resistance value (R1) of the first electrical resistance element (21) and / or a temperature of the exhaust gas sensor (20) is inferred from the difference (UD) between the first voltage variable (U1G) and the second voltage variable (U2G).

Description

[0001] Description

[0002] title

[0003] Procedure for diagnosing an exhaust gas sensor

[0004] State of the art

[0005] From DE 10 2017 207 802 A1 a method for determining a temperature or an internal resistance of an exhaust gas sensor is already known. The sensor comprises a sensor element with a first electrode, a second electrode and a solid electrolyte connecting the first electrode and the second electrode.

[0006] Further methods for determining or controlling the temperature of an exhaust gas sensor are known from DE 10 2012 204 808 A1 and from the subsequently published DE 10 2022 211 060 A1 of the applicant.

[0007] Advantages of the invention

[0008] The present invention is based on the inventors' fundamental insight that known methods in connection with exhaust gas sensors, which have a first electrical resistance element (hereinafter also referred to as resistance element) and at least one further resistance element which is electrically connected to the first resistance element via a connecting element, wherein the exhaust gas sensor has a first supply line which is connected to the connecting element, and a second supply line which is electrically connected to the side of the first resistance element facing away from the connecting element, and a third supply line which is electrically connected to the side of the further resistance element facing away from the connecting element, and in connection with evaluation and control units which have a first electrical connection which is connected to the first supply line, and which have a second electrical connection,If the resistor is connected to the second supply line and has a third electrical connection connected to the third supply line, significant errors can occur in determining the resistance value of the first resistive element as soon as the first supply line is interrupted, which represents a load drop from the perspective of the evaluation and control unit. Furthermore, it can also be difficult to reliably detect such interruptions.

[0009] The aim of the present invention is therefore, on the one hand, to detect such line interruptions and / or, on the other hand, to enable the more precise determination of the resistance value of the first resistance element, at least if such line interruptions are present or have already been detected.

[0010] For this purpose, it is initially provided that the evaluation and control unit within the method according to the invention has a virtual ground which is connected to the first electrical connection, and a current source which is connected to the second connection. For example, a corresponding multiplexer can be provided within the evaluation and control unit which is capable of establishing electrically conductive connections between the two connections mentioned.

[0011] In this context, a virtual ground is understood to be an arrangement that keeps the electrical potential of the first terminal constant even when currents of different magnitudes flow into it.

[0012] In this context, a current source is understood to be an arrangement that impresses a constant current into the second terminal, particularly regardless of the load connected to the second terminal; thus, in particular, a constant current source. The current source is capable, for example, of generating current pulses of a specific duration and amplitude.

[0013] Furthermore, it is provided that the evaluation and control unit has a voltage measuring device which determines a first voltage quantity between the first terminal and the second terminal and a second voltage quantity between the first terminal and the third terminal within the framework of the method according to the invention.

[0014] Determining the first voltage value between the first and second terminals, or determining the second voltage value between the first and third terminals, may involve a corresponding voltage measurement. However, these voltage values ​​may also be calculated values ​​with the dimension of voltage, each determined from multiple voltage measurements, particularly by adding or subtracting the measured voltages.

[0015] The method according to the invention provides that the sum of the first voltage quantity and the second voltage quantity is calculated and it is concluded that the first supply line is interrupted if the sum of the first voltage quantity and the second voltage quantity is greater than a predetermined threshold value.

[0016] The underlying physical principle is that, in the event of an interruption in the first supply line, a current impressed from the power source via the second connection into the second lead or the first resistive element of the exhaust gas sensor cannot flow to the virtual ground through the first supply line – unlike in the case of an intact first supply line. Thus, "in theory," a significant potential shift should occur between the first and second connections (first voltage value), corresponding to the relevant capacitances, currents, and times. However, in the case according to the invention, this is contradicted by the fact that, due to the internal structure of the exhaust gas sensor, the impressed current continues to flow via the connecting element into the further resistive element and the third supply line into the third electrical connection of the evaluation and control unit.The potential difference between the first and second terminals (first voltage value) mentioned above is reduced for this reason, thus jeopardizing the reliable detection of an interruption in the first supply line. The invention relies on the fact that the aforementioned flow leads to a further potential difference between the first and third terminals (second voltage value), approximately to the same extent that the potential difference between the first and second terminals (first voltage value) falls short of the "actually" expected value for the reasons explained above. Therefore, the sum of the first and second voltage values ​​provides a criterion for determining whether the first supply line is interrupted: if it exceeds a predetermined threshold, it can be concluded that this is the case.

[0017] The method according to the invention provides, in addition to or as an alternative to the diagnosis described above, for an interruption of the first supply line, or only provides, in the case where such an interruption has actually been detected, for the difference between the first voltage value and the second voltage value to be calculated and for the resistance value of the first resistive element to be deduced from the difference between the first voltage value and the second voltage value. Instead of the resistance value of the first resistive element, a temperature of the exhaust gas sensor can also be directly inferred, or a temperature of the exhaust gas sensor can be inferred from the resistance value of the first resistive element thus determined.

[0018] The underlying physical principle is that the two capacitive charges explained above cancel each other out in the difference, so that only the voltages dropping across the resistance elements as a result of the impressed current remain in the difference and do not cancel each other out due to their opposite signs.

[0019] The capacitances mentioned above to explain the physical relationships can actually be discrete or integrated electronic elements ("capacitors") within the evaluation and control unit, such that a first capacitance with the value Ci is connected between the first and second terminals, and a further capacitance with the value C2 is connected between the first and third terminals. Ci and C2 can preferably be in the range of 100 pF to 100 nF. Ci and C2 can preferably be the same or essentially the same, for example, differing from each other by no more than 5% of their value.

[0020] The current source provided according to the invention can, within the scope of the present invention, provide at least one approximately rectangular current pulse, for example with a pulse length tp = 140ps and a pulse height Ip = 0.1 mA.

[0021] For example, it may be intended that the relations

[0022] 10 mV < Ip * tp / Ci < 2 V and / or 10 mV < Ip * tp / C2 < 2 V must be maintained.

[0023] It is possible that the pulse height Ip of the impressed current is partly determined by a resistor connected in parallel between the first and second terminals in the measuring system. This acts as a current divider and can, among other things, contribute to adjusting the measuring range.

[0024] When determining the first voltage value between the first terminal and the second terminal, or when determining the second voltage value between the first terminal and the third terminal, the procedure disclosed in the applicant's DE 10 2017 207 802 A1 may still be followed; that is, in particular, it may be provided that the first voltage value is determined on the basis of a first voltage measurement between the first terminal and the second terminal, which is carried out before the current pulse, and a second voltage measurement between the first terminal and the second terminal, which is carried out during the current pulse, and a third voltage measurement between the first terminal and the second terminal, which is carried out after the current pulse, in accordance with the context

[0025] UiG = U3 + u2 - 2 Ui, where UiG is the first voltage measurement, U3 is the result of the third voltage measurement, U2 is the result of the second voltage measurement, and Ui is the result of the first voltage measurement; and / or that the second voltage measurement is determined on the basis of a first voltage measurement between the first terminal and the third terminal, which is carried out before the current pulse or before a further current pulse, and a second voltage measurement between the first terminal and the third terminal, which is carried out during the current pulse in question, and a third voltage measurement between the first terminal and the third terminal, which is carried out after the current pulse in question, according to the relationship.

[0026] U 2G= U3 + U2 - 2 Ui where U2G is the second voltage quantity, U3 is the result of the third voltage measurement, U2 is the result of the second voltage measurement, and Ui is the result of the first voltage measurement.

[0027] The first resistance element can be an ohmic resistor, which is located, for example, in a connector belonging to the exhaust gas sensor, such as the lambda probe, between the connecting element and the second supply line.

[0028] Such ohmic resistors serve, for example, to encode a unique characteristic of an exhaust gas sensor, such as the limiting current of a broadband lambda probe at a specific oxygen partial pressure in the exhaust gas under certain other conditions. For this purpose, the resistance value of the ohmic resistor is individually set during the manufacturing process based on a measurement performed on the exhaust gas sensor, for example, by laser ablation; in other words, the ohmic resistor is laser-trimmed. During operation of the exhaust gas sensor, this resistance value can then be read out and taken into account when interpreting the measurements taken with the exhaust gas sensor using digital or analog methods. Clearly, for the reliable operation of the exhaust gas sensor, the most accurate possible knowledge or measurement of the resistance value of the first resistive element is essential.The ohmic resistance is also desirable in the event of an interruption of the first supply line.

[0029] If the second resistive element is an electrochemical cell with a first electrode and a second electrode, which, for example, consist predominantly of platinum, and a solid electrolyte arranged between the first and second electrodes, which, for example, consists predominantly of YSZ, then the internal resistance of the second resistive element or the electrochemical cell can be low, especially if the temperature of the exhaust gas sensor, i.e., the second resistive element or the electrochemical cell, corresponds to an operating temperature (e.g., 780°C). For example, this internal resistance is significantly lower than the resistance value of the ohmic resistance (e.g., at most 10% of its value). With the method according to the invention, it is then possible to determine the value of the ohmic resistance almost completely accurately, even in the event of an interruption of the first supply line.Additionally or alternatively, a suitable correction can be made to the resistance value of the ohmic resistance determined in this way, for example by subtracting an estimated value of the resistance value of the ohmic resistance.

[0030] On the other hand, the invention can also be applied in that the exhaust gas sensor is a ceramic exhaust gas sensor (e.g. a wideband lambda probe) and that the first resistance element is an electrochemical cell with a first electrode, a second electrode and a solid electrolyte arranged between the first and the second electrode.

[0031] In this case, too, the value of the ohmic resistance of the first resistive element, i.e., the internal resistance of the electrochemical cell, is of interest during operation, as it correlates with its temperature. Therefore, in one embodiment of the invention, the temperature of the exhaust gas sensor can be directly inferred from the difference between the first and second voltage values. Since the temperature of the electrochemical cell is highly relevant for the measurements that can be performed with the exhaust gas sensor, for the interpretation of the measurement results, and for the operational reliability of the exhaust gas sensor, there is a desire to be able to determine this temperature as accurately as possible even when the first supply line is interrupted.

[0032] For example, knowledge of the internal resistance of the electrochemical cell (and thus its temperature) can be used to further conclude, based on a comparison of this internal resistance with a lower threshold value, whether the temperature of the exhaust gas sensor is above a minimum temperature required for permissible measurements with the exhaust gas sensor.

[0033] For example, knowing the internal resistance of the electrochemical cell (and thus its temperature) can be used to determine, based on a comparison of this internal resistance with an upper threshold value, whether the temperature of the ceramic exhaust gas sensor is below a maximum temperature that must not be exceeded for permissible measurements with the exhaust gas sensor. Conversely, a lack of knowledge, or inaccurate or faulty knowledge of the internal resistance of the electrochemical cell (and thus its temperature), poses the risk of overheating the exhaust gas sensor and thus potentially damaging it.

[0034] For example, the internal resistance of the electrochemical cell (and thus its temperature) can be used as the actual value of a control loop whose setpoint is specified and whose manipulated variable concerns the electrical control of a heating element of the exhaust gas sensor.

[0035] It can be provided that the second resistance element is also an electrochemical cell with a first electrode, a second electrode, and a solid electrolyte arranged between the first and second electrodes. For example, the first resistance element can be the Nernst cell of a broadband lambda sensor, and the second resistance element can be the pump cell of a broadband lambda sensor. In this configuration, the internal resistance of the Nernst cell (at the same temperature) can be greater than the internal resistance of the pump cell. The internal resistance of the Nernst cell, or the temperature of the broadband lambda sensor, can then be reliably and almost completely accurately determined using the method according to the invention, even in the event of an interruption of the first supply line.

[0036] Additionally or alternatively, a suitable correction can be made to the internal resistance of the Nernst cell determined in this way, for example by multiplying an estimated value of the ratio of the internal resistance of the Nernst cell and the sum of the internal resistance of the Nernst cell and the internal resistance of the pump cell.

[0037] In principle, it is possible to design the voltage measuring device in such a way that it is able to determine the first voltage quantity between the first terminal and the second terminal and the second voltage quantity between the first terminal and the third terminal simultaneously, or it is possible that, within the framework of the proposed method, the voltage measuring device determines the first voltage quantity between the first terminal and the second terminal and the second voltage quantity between the first terminal and the third terminal simultaneously.

[0038] Alternatively, the voltage measuring device can also be designed to determine the first voltage value and the second voltage value sequentially. For example, a suitable multiplexer can be provided within the evaluation and control unit, which is capable of establishing the corresponding electrically conductive connections between the voltage measuring device and the terminals one after the other.

[0039] drawing

[0040] Figure 1 schematically and exemplarily shows an arrangement with which the method according to the invention can be carried out, consisting of a broadband lambda sensor which is connected to an evaluation and control unit via leads and a connector. Figures 2a and 2b schematically illustrate a first embodiment of the method according to the invention.

[0041] Figures 3a and 3b schematically illustrate a second embodiment of the method according to the invention.

[0042] Description of the exemplary implementations

[0043] Figure 1 schematically shows an arrangement with which the method according to the invention can be carried out. It consists of an exhaust gas sensor 20 in the form of a wideband lambda probe, which is connected via leads and a connector 30 to the terminals MES, APE, IPE and RE of an evaluation and control unit 10.

[0044] The broadband lambda sensor in this example has two electrochemical cells, namely a Nernst cell and a pump cell, which are electrically connected to each other. It also has a measuring resistor RCMP, which is connected to the pump cell via the connecting element 25 and is located inside the connector 30.

[0045] The leads to the RE, IPE and APE terminals of the evaluation and control unit 10 pass directly through connector 30.

[0046] The measuring resistor RCMP is located inside the connector 30 and is connected via a supply line to the MES connection of the evaluation and control unit 10.

[0047] Within the evaluation and control unit 10, the terminals APE, IPE, RE, and MES are interconnected via capacitors CEMC. These terminals can also be connected via a multiplexer (not shown) to a virtual ground, a constant current source, and a voltage measuring device (see also Figures 2 and 3).

[0048] In the event of a fault, interruptions in the lines within the arrangement can occur, with such an interruption also being referred to as a load drop or open load. Figure 1 symbolically represents potential interruptions, namely an interruption OL@APE or OL@APEs, an interruption OL@MES, an interruption OL@IPE, or an interruption OL@RE. Furthermore, interruptions of the connecting element 25 are possible: OLE@C or OL@P. Additionally, an interruption between the Nernst cell and the pump cell can occur: OL@N.

[0049] Figures 2a and 2b schematically illustrate a first embodiment of the method according to the invention. The arrangement with which the method according to the invention is carried out corresponds to the device shown in Figure 1, initially and with regard to Figure 2a, with the proviso that all lines of the arrangement are intact.

[0050] Assuming that all lines of the arrangement are intact, it is possible to determine the resistance value R1 of the measuring resistor RCMP (first resistance element 21) by connecting the terminal MES of the evaluation and control unit 10 (second terminal A2) to a constant current source SR of the evaluation and control unit 10, which induces a current pulse of length tp and height Ip into the second supply line 42, and by connecting the terminal APE of the evaluation and control unit 10 (first terminal A1) to a virtual ground VG of the evaluation and control unit 10 or by otherwise keeping it at an at least nearly constant potential.A first voltage value between the first terminal A1 and the second terminal A2 UMA,M (UI G) can be determined and subsequently the resistance value R1 of the measuring resistor RCMP (first resistance element 21) can be determined from it, for example as disclosed in DE 10 2017 207 802 A1 and symbolized by the solid line in Figure 2a.

[0051] In particular, the resistance value R1 of the measuring resistor RCMP (first resistive element 21) can be determined by first determining the first voltage quantity UMA,M (UI G), for example on the basis of a first voltage measurement Ui between the first terminal A1 and the second terminal A2, which is carried out before the current pulse, and a second voltage measurement U2 between the first terminal A1 and the second terminal A2, which is carried out during the current pulse, and a third voltage measurement U3 between the first terminal A1 and the second terminal A2, which is carried out after the current pulse, according to the relationship:

[0052] Ouch G = U3+ U2- 2 Ui.

[0053] The resistance value R1 of the measuring resistor RCMP is then:

[0054] R1 = Ui G / IP.

[0055] On the other hand, if the aim of the measurement is to determine that the first supply line 41 is interrupted, corresponding to a (supposedly) very large measuring resistance RCMP (Figure 2b), then (if the supply line is indeed interrupted; OL@APE) the resistance value R1 of the measuring resistor RCMP (first resistive element 21) cannot be correctly determined as before, because the first voltage value UI G between the first terminal A1 and the second terminal A2 UMA,M no longer represents a quantity from which the resistance value R1 of the measuring resistor RCMP (first resistive element 21) can be determined on its own (possibly in combination with the value of the impressed current Ip). Figuratively speaking, the measurement of UMA,M in this case only "sees" a part of the impressed current Ip and consequently only a part of the voltage swing resulting from intact supply lines (Figure 2a).With this (conventional, non-inventive) strategy, the resistance value R1 of the measuring resistor RCMP corresponding to the line break would consequently be determined too small, and the line break might therefore not be detected.

[0056] In this situation, the application of the method according to the invention provides a remedy. In addition to the first voltage measurement UMA, M (UI G) between the first terminal A1 and the second terminal A2, a second voltage measurement UIA, M (U2G) is determined between the first terminal A1 and the third terminal A3. The determination of the second voltage measurement UIA, M can be carried out analogously using the same method as described above for the first voltage measurement UMA, M. Both measurements can be performed using the same current pulse. Alternatively, the two measurements can be performed sequentially using similar but not identical current pulses.

[0057] In figurative terms, this measurement UIA,M “sees” the part of the impressed current Ip that, due to the line interruption OL@APE, did not flow into the virtual ground VG but via the further resistive element 22 into the third supply line 43 (along the dashed line in figure 2b).

[0058] Therefore, if one forms the sum signal Us = UMA,M + UIA,M, SO, one obtains with Us a quantity from which (if necessary by division with Ip) in the case of the interruption of the first supply line 41 the interruption of the first supply line 41 can be correctly recognized by the fact that it exceeds a predetermined limit value.

[0059] Conversely, if the differential signal UD = UMA, M - UIA, M, SO is calculated, UD represents a quantity that essentially corresponds to the (ohmic) voltage drop across the resistive elements 21 and 22 due to the impressed current Ip. If necessary, after division by Ip, it can be used as an approximate measure of the value R1 of the measuring resistor RCMP, particularly if the resistance RPMP of the second resistive element 22 can be assumed to be small. Corrections can be made if necessary.

[0060] Figures 3a and 3b schematically illustrate a second embodiment of the method according to the invention. This embodiment uses a broadband lambda sensor, which differs from the broadband lambda sensor shown in Figures 1, 2a and 2b in that it, or rather the associated sensor connector 30, does not have a measuring resistor Rc. mpThe broadband lambda probe therefore also lacks a fourth input lead. The evaluation and control unit 10 could be simplified accordingly (unlike the design shown in Figures 3a and 3b).

[0061] The feed line 41 of the broadband lambda probe, referred to below as the first feed line 41, is connected in this example to the IPE port of the evaluation and control unit 10, the feed line 42 of the broadband lambda probe, referred to below as the second feed line 42, is connected in this example to the RE port of the evaluation and control unit 10, and the feed line 43 of the broadband lambda probe, referred to below as the third feed line 43, is connected in this example to the APE port of the evaluation and control unit 10.

[0062] With reference to Figure 3a, it is initially assumed that all leads of the arrangement are intact. In this case, it is possible to determine the resistance value RNemst of the Nernst cell (first resistive element 21) by connecting the terminal RE of the evaluation and control unit 10 (second terminal, A2) to a constant current source SR of the evaluation and control unit 10, which injects a current pulse of length tp and amplitude Ip into the second lead, and by connecting the terminal IPE of the evaluation and control unit 10 (first terminal A1) to a virtual ground VG of the evaluation and control unit 10. A first voltage quantity U RI.R (UI G) between the first terminal A1 and the second terminal A2 can be determined and subsequently the resistance value RNemst of the Nernst cell (first resistance element 21) can be determined from it, for example as disclosed in DE 10 2017 207 802 A1 and symbolized by the solid line in Figure 3a.

[0063] In particular, the resistance value RNemst of the Nernst cell (first resistive element 21) can be determined by first determining the first voltage quantity UI G based on a first voltage measurement Ui between the terminals RE and IPE, which is carried out before the current pulse, and a second voltage measurement U2 between the terminals RE and IPE, which is carried out during the current pulse, and a third voltage measurement U3 between the terminals RE and IPE, which is carried out after the current pulse, according to the following relationship:

[0064] UI G = U3+ U2- 2 Ui.

[0065] The internal resistance value RNemst of the Nernst cell is then:

[0066] RNemst = UI G / Ip.

[0067] On the other hand, if the aim of the measurement is to determine that the first supply line 41 is interrupted, corresponding to a (supposedly) very high internal resistance Ruemst of the Nernst cell (Figure 3b), then (if the supply line 41 is indeed interrupted, OL@IPE) the internal resistance of the Nernst cell (first resistive element 21) cannot be correctly determined as before, because the first voltage quantity U RI.R (UI G) between the first terminal A1 and the second terminal A2 no longer represents a quantity from which the internal resistance of the Nernst cell (first resistive element 21) can be determined on its own (possibly in combination with the value of the impressed current). Figuratively speaking, the measurement of U RI, R in this case only "sees" a part of the impressed current and consequently only a part of the voltage swing resulting from intact supply lines (Figure 3a).With this (conventional, non-inventive) strategy, the resistance value of the internal resistance of the Nernst cell corresponding to the line break would consequently be determined too low, and the line break might therefore not be detected.

[0068] In this situation, the application of the method according to the invention provides a remedy. In addition to the first voltage measurement URI,R (UG) between the first terminal A1 and the second terminal A2, a second voltage measurement UAI,R (U2G) is determined between the first terminal A1 and the third terminal A3. The determination of the second voltage measurement UAI,R can be carried out analogously using the same method as described above for the first voltage measurement URI,R. Both measurements can be performed using the same current pulse. Alternatively, the two measurements can be performed sequentially using similar but not identical current pulses.

[0069] In figurative terms, this measurement UAI, R “sees” the part of the impressed current which, due to the interruption of the line, did not flow into the virtual ground but via the pump cell (the further resistance element 22) into the third supply line 43.

[0070] Therefore, if the sum signal Us = U RI, R + UAI, R, SO is calculated, Us is a quantity from which (by division with Ip) an interruption of the first supply line 41 can be correctly identified by the fact that Us or Us / Ip exceeds a predefined limit. Conversely, if the difference signal UD = URI, R - UAI, R, SO is calculated, UD is a quantity that essentially represents the voltage drop across the internal resistances Ruemst and Rpmp of the electrochemical cells 21, 22 due to the impressed current Ip. If necessary, after division with Ip and possibly after applying further corrections, a measure of the temperature of the broadband lambda probe is thus obtained.

[0071] The described evaluation and control unit 10 can, for example, be integrated on an ASIC.

Claims

Claims 1. Method for diagnosing an exhaust gas sensor (20), in particular in a wideband lambda sensor, wherein the exhaust gas sensor (20) comprises a first electrical resistance element (21) and at least one further electrical resistance element (22) which is electrically connected to the electrical resistance element (21) via a connecting element (25), wherein the exhaust gas sensor (20) comprises a first supply line (41) which is connected to the connecting element (25), and a second supply line (42) which is electrically connected to the side of the first electrical resistance element (21) facing away from the connecting element (25), and a third supply line (43) which is electrically connected to the side of the further electrical resistance element (22) facing away from the connecting element (25), by means of an evaluation and control unit (10) which has a first electrical connection (A1) which is connected to the first supply line (41),and which has a second electrical connection (A2) connected to the second supply line (42), and which has a third electrical connection (A3) connected to the third supply line (43), and which has an arrangement that keeps the electrical potential of the first connection (A1) constant, e.g., a virtual ground (VG) connected to the first electrical connection (A1), and which has a current source (SR) connected to the second connection (A2), and which has a voltage measuring device that determines a first voltage quantity (UIG) between the first connection (A1) and the second connection (A2) and a second voltage quantity (Lhc) between the first connection (A1) and the third connection (A3), wherein the method provides that - that the sum (Us) of the first voltage quantity (UIG) and the second voltage quantity (U2G) is formed and it is concluded that the first The supply line (41) is interrupted if the sum (Us) of the first voltage quantity (UIG) and the second voltage quantity (U2G) is greater than a threshold value, and / or - that the difference (UD) of the first voltage quantity (UIG) and the second voltage quantity (U2G) is formed and from the difference (UD) of the first voltage quantity (UIG) and the second voltage quantity (U2G) a resistance value (Ri) of the first electrical resistance element (21) is determined and / or a temperature of the exhaust gas sensor (20) is determined.

2. Method according to claim 1, characterized in that in the evaluation and control unit (10) a first capacitor (CEMC) having the value Ci is connected between the first terminal (A1) and the second terminal (A2), and a further capacitor (CEMC) having the value C2 is connected between the first terminal and the third terminal, wherein in particular Ci is equal to C2.

3. Method according to claim 1 or 2, characterized in that the current source (SR) generates current pulses of pulse length tp and pulse height Ip.

4. Method according to claims 1, 2 and 3, characterized in that 0.1 V < lp*tp / C1 < 2V and / or 0.1 V < lp*tp / C2 < 2V.

5. Method according to one of claims 3 or 4, characterized in that the first voltage quantity (UIG) is determined on the basis of a first voltage measurement (Ui) between the first terminal (A1) and the second terminal (A2), which is carried out before a current pulse, and a second voltage measurement (U2) between the first terminal (A1) and the second terminal (A2), which is carried out during the current pulse, and a third voltage measurement (Ui) between the first terminal (A1) and the second terminal (A2), which is carried out after the current pulse, according to the context UiG = U3+ u2- 2 Ui, and / or that the second voltage quantity (U)2G ) is determined on the basis of a first voltage measurement (Ui) between the first terminal (A1) and the third terminal (A3), which is carried out before a current pulse, and a second voltage measurement (U2) between the first terminal (A1) and the third terminal (A3), which is carried out during the current pulse, and a third voltage measurement U3 between the first terminal (A1) and the third terminal (A3), which is carried out after the current pulse, according to the relationship U 2G = U3 + U2 - 2 Ui; where in both cases: Ui is the result of the first voltage measurement (Ui); U2 is the result of the second voltage measurement (U2); U3 is the result of the third voltage measurement (U3).

6. Method according to one of the preceding claims, characterized in that the method provides that the sum (Us) of the first voltage quantity (UIG) and the second voltage quantity (U2G) is formed and it is concluded that the first supply line (41) is interrupted when the sum (Us) of the first voltage quantity (UIG) and the second voltage quantity (U2G) 2G ) is greater than a threshold value, and in this case the difference (UD) between the first stress quantity (UIG) and the second stress quantity (U) 2G ) is formed and is from the difference (UD) of the first stress quantity (UIG) and the second stress quantity (U 2G ) is inferred to a resistance value (Ri) of the first electrical resistance element (21); and at most otherwise, if the sum (Us) of the first voltage quantity (UIG) and the second voltage quantity (U) 2G) is not greater than the threshold value and it is not concluded that the first supply line (41) is interrupted, from the first voltage quantity (UIG) independently of the second voltage quantity (U 2G ) is determined to be a resistance value (R1) of the first electrical resistance element (21).

7. Method according to one of the preceding claims, characterized in that the first electrical resistance element (21) is an ohmic resistor arranged in a connector (30) belonging to the exhaust gas sensor (20) between the connecting element (25) and the second supply line (42).

8. Method according to claim 7, characterized in that the exhaust gas sensor (20) is a ceramic exhaust gas sensor (20) and that the second electrical resistance element (22) is an electrochemical cell with a first electrode, a second electrode and a solid electrolyte arranged between the first and the second electrode.

9. Method according to one of claims 1 to 6, characterized in that the exhaust gas sensor (20) is a ceramic exhaust gas sensor (20) and that the first electrical resistance element (21) is an electrochemical cell with a first electrode, a second electrode and a solid electrolyte arranged between the first and the second electrode.

10. Method according to claim 9, characterized in that the exhaust gas sensor (20) is a ceramic exhaust gas sensor (20) and that the second electrical resistance element (22) is an electrochemical cell with a first electrode, a second electrode and a solid electrolyte arranged between the first and the second electrode.

11. Method according to claim 9 or 10, characterized in that the temperature of the ceramic exhaust gas sensor (20) is inferred from the resistance value (R1) of the first electrical resistance element (21) or directly from the difference (UD) between the first voltage quantity (UIG) and the second voltage quantity (Lhc), and / or that a comparison of the resistance value (R1) of the first electrical resistance element (21) with a lower threshold value is used to infer whether the temperature of the ceramic exhaust gas sensor (20) is above a minimum temperature, and / or that a comparison of the resistance value (R1) of the first electrical resistance element (21) with an upper threshold value is used to infer whether the temperature of the ceramic exhaust gas sensor (21) is below a maximum temperature, and / or that the resistance value (R1) of the first electrical resistance element (21) is used as the actual value of a control loop whose setpoint is specified and whose manipulated variable relates to an electrical control of a heating element of the exhaust gas sensor (20).

12. Method according to one of the preceding claims, characterized in that the voltage measuring device simultaneously determines the first voltage quantity (UIG) between the first terminal (A1) and the second terminal (A2) and the second voltage quantity (Lhc) between the first terminal (A1) and the third terminal (A3).

13. Method according to any one of claims 1 to 11, characterized in that the voltage measuring device first determines a voltage quantity of the first voltage quantity (UIG) between the first terminal (A1) and the second terminal (A2) and of the further voltage quantity (U2G) between the first terminal (A1) and the third terminal (A3); and subsequently determines the other voltage quantity of the first voltage quantity (UIG) between the first terminal (A1) and the second terminal (A2) and of the further voltage quantity (U2G) between the first terminal (A1) and the third terminal (A3).

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