Control device for a lambda probe and method for compensating leakage currents

Abstract

The invention relates to a method for compensating leakage currents (48, 50) from at least two connecting lines (18, 22, 100, 102) that connect a lambda probe (2, 78) to a control device (4, 98), wherein the method comprises the following steps: - Determining, for at least one of the connecting lines (18, 22, 100, 102), an associated leakage current (48, 50), - Determining, for each determined leakage current (48, 50), whether the respective leakage current (48, 50) is a result-relevant leakage current (48) that affects the result of a lambda measurement performed by the lambda probe (2, 78), or not, - Determining a compensation current, wherein only the result-relevant leakage currents (48) are taken into account in its determination, - Applying the compensation current to at least one of the connecting leads (18, 22, 100, 102) of the lambda sensor (2, 78).

Description

Technical field The invention relates to a method for compensating leakage currents. The invention also relates to a control device for a lambda sensor and a device for detecting a lambda value. Furthermore, the invention relates to an exhaust system of a motor vehicle and a motor vehicle itself. Technical background Lambda sensors are operated using either application-specific integrated circuits (ASICs) or specific hardware modules with corresponding microcontrollers. The state of the art for lambda sensor evaluation circuits primarily comprises evaluation circuits specific to a particular sensor type, as well as hardware modules with microcontrollers. For newer generations of evaluation circuits, both specific and generic ASICs are being developed. With previous control circuits, particularly for switching sensors, a particularly high level of measurement accuracy was not required. However, with the introduction of newer exhaust emission regulations, such as EU7, the importance of measurement accuracy for such sensors is becoming increasingly crucial in order to improve exhaust emissions and thus comply with the new regulations. It is therefore an object of the invention to provide a method and a control device for a lambda probe that enable improved measurement accuracy in the detection of the lambda value. Disclosure of the invention This problem is solved by the method for compensating leakage currents from at least two connecting lines according to claim 1 and a control device for a lambda probe according to the dependent claim. Further details are specified in the dependent claims. The invention relates to a method for compensating leakage currents from at least two connecting leads that connect a lambda probe to a control device, wherein the method comprises the following steps: - Determining, for at least one of the connecting leads, an associated leakage current, - Determining, for each determined leakage current, whether the respective leakage current is a result-relevant leakage current that affects the result of a lambda measurement carried out by the lambda probe, or not, - Determining a compensation current, wherein only the result-relevant leakage currents are taken into account in its determination, - Applying the compensation current to at least one of the connecting leads of the lambda probe. The starting point of the method is the fact that different leakage currents have different effects on the lambda measurement result. With leakage currents occurring in the supply lines, a distinction can be made between result-relevant leakage currents, which affect the lambda measurement result, and result-irrelevant leakage currents, which have no effect or only a minor effect. According to the embodiments of the invention, it is determined for each leakage current whether it is result-relevant or result-irrelevant. Only the result-relevant leakage currents are then used to determine the compensation current. This yields a compensation current that is able to very precisely correct the change in the lambda sensor measurement result caused by leakage currents. The lambda sensor can therefore determine correct lambda values ​​even if leakage currents are present in the supply lines. Measurement errors caused by leakage currents can be eliminated or at least significantly reduced. This allows for the use of cost-effective insulation for the supply lines. By compensating for the effects of leakage currents, the lambda sensor's measurement accuracy is significantly improved. This is particularly important for meeting the comparatively stringent emissions standards. Furthermore, the invention relates to a control device for a lambda sensor, which can be connected to the control device via at least two connecting lines, wherein the control device is designed to generate control signals for the lambda sensor and to evaluate signals received from the lambda sensor, wherein the control device comprises: - a compensation device designed to determine an associated leakage current for at least one of the connecting lines, to determine for each determined leakage current whether the respective leakage current is a result-relevant leakage current that affects the result of a lambda measurement performed by the lambda sensor, or not, to determine a compensation current, whereby only the result-relevant leakage currents are taken into account in its determination, - an adjustable current source designed toto additionally impose the compensation current on at least one of the connecting leads of the lambda sensor. The adjustable current source allows for precise setting of the compensation current. This compensation current is supplied to at least one connecting wire of the lambda sensor to eliminate or at least reduce measurement errors caused by leakage currents. This increases the measurement accuracy. Furthermore, the invention relates to a device for detecting a lambda value, which comprises: - a control device as described above, - a lambda probe which is connected to the control device via at least two connecting lines. Furthermore, the invention relates to an exhaust system of a motor vehicle, which includes a device for detecting a lambda value as described above. The invention also relates to a motor vehicle comprising an exhaust system with a device for detecting a lambda value as described above. Preferably, those leakage currents that flow through the lambda probe are identified as result-relevant leakage currents. According to a preferred embodiment of the invention, all leakage currents of the connecting lines that are relevant to the result are taken into account when determining the compensation current. Preferably, the method includes the following further steps: - Determining all result-relevant leakage currents, - Determining the compensation current as the sum of all result-relevant leakage currents. According to a preferred embodiment, the lambda probe is a switching probe comprising an inner pump electrode connection (IPE) and an outer pump electrode connection (APE), wherein an associated APE leakage current is determined for the outer pump electrode connection, and wherein the compensation current is set equal to the APE leakage current. The procedure preferably further comprises the following additional steps: - Determining a total leakage current as the current difference between currents flowing from the control device to the lambda probe and currents flowing back from the lambda probe to the control device, - Determining the non-responsible leakage currents of the connecting lines, - Determining the compensation current by subtracting the non-responsible leakage currents from the total leakage current. It is advantageous if the lambda sensor comprises an inner pump electrode connection and an outer pump electrode connection, wherein an associated IPE leakage current is determined for the inner pump electrode connection, and wherein the compensation current is determined by calculating a total leakage current as the current difference between the currents flowing from the control device to the lambda sensor and the currents flowing back from the lambda sensor to the control device, and subtracting the IPE leakage current from this total leakage current. In this example, the IPE leakage current is the non-responsible current contribution. Preferably, the compensation current is based on all result-relevant leakage currents of the connecting lines. According to a preferred embodiment, the lambda probe is a switching probe or a single-cell broadband probe comprising a Nernst cell, wherein the leakage currents relevant to the result are those leakage currents flowing through the Nernst cell. Preferably, the lambda probe is a two-cell broadband probe comprising a Nernst cell and a pump cell, wherein the leakage currents relevant to the result are those leakage currents flowing through the Nernst cell and / or the pump cell. Preferably, the lambda probe comprises an inner pump electrode connection and an outer pump electrode connection, wherein an APE leakage current belonging to the outer pump electrode connection is relevant to the result and an IPE leakage current belonging to the inner pump electrode connection is not relevant to the result. Brief description of the drawings The embodiments are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a lambda sensor configured as a switching probe together with a control unit; Fig. 2 an example of a leakage current relevant to the result; Fig. 3 an example of a leakage current not relevant to the result; Fig. 4 a compensation device implemented on the control unit, configured to determine and compensate for a compensation current; Fig. 5 an example of the implementation of a control unit using an ASIC; Fig. 6 the course of the total leakage current iDeltaAllPin and the Nernst voltage uNernst as a function of time; and Fig. 7 a lambda sensor configured as a broadband probe together with the associated control unit. Description of embodiments Figure 1 shows a lambda sensor 2 together with an associated control unit 4, the control unit 4 preferably being part of an engine control unit (ECU). In the example shown in Figure 1, the lambda sensor 2 is designed as a simple switching sensor comprising a Nernst cell 6. To heat the Nernst cell 6 to the intended operating temperature, the lambda sensor 2 includes a heating element 8 connected between a first operating voltage terminal 10 and a second operating voltage terminal 12. The Nernst voltage provided by the Nernst cell 6 can be tapped between an IPE terminal 14 and an APE terminal 16 of the lambda sensor 2, where IPE denotes the inner pump electrode and APE the outer pump electrode of the lambda sensor 2. The IPE terminal 14 of the lambda sensor 2 is electrically connected to an IPE control terminal 20 of the control unit 4 via an IPE line 18. Likewise, the APE terminal 16 of the lambda sensor 2 is electrically connected to the APE control terminal 24 of the control unit 4 via an APE line 22. The IPE line 18 and the APE line 22 can preferably be configured as part of a single cable or wiring harness. In the control unit 4, the IPE control terminal 20 is connected to a reference potential 28 via a current measuring device 26. The reference potential 28 can be, for example, the ground of the engine control unit or a virtual ground. The abbreviation VG, which stands for Virtual Ground, is used below for the virtual ground. The current measuring device 26 is designed to measure the electric current flowing back to the reference potential 28. For this purpose, the current measuring device 26 includes a measuring resistor 30. The voltage drop across the measuring resistor 30 is converted into a digital value by means of an analog-to-digital converter 32, which indicates the current flowing back to the reference potential 28. The APE control terminal 24 of the control unit 4 is connected on one side to a pulsed current source 34 and on the other side, via a switch 36, to a continuous current source 38. An adjustable current can be supplied to the APE terminal 16 of the lambda sensor 2 via the APE line 22 from the two current sources 34 and 38. Preferably, the continuous current source 38 includes a digital-to-analog converter that adjusts the current supplied to the APE terminal 16 of the lambda sensor 2 based on a digitally preset value. The lambda sensor 2 is typically connected to four, five, or six individual wires, which may be bundled together, for example, to form a cable or wiring harness. In the example shown in Fig. 1, the IPE wire 18 and the APE wire 22 are bundled with the heating wires, which are connected to the operating voltage terminals 10 and 12 of the heating element 8. One of these heating wires is typically connected to the vehicle battery to provide the supply voltage for the heating element 8. Like all bundled electrical cables, probe leads also possess a certain degree of electrical insulation. Depending on the manufacturer, the insulation parameters of the probe leads can vary. Better insulation of the leads is generally associated with higher production costs, which is why manufacturers consider cost optimizations that can lead to poorer insulation of the probe leads. Poor insulation of the individual leads can be caused particularly by such cost savings, but also by manufacturing tolerances, wear and tear on the probe leads, and moisture in the lambda probe 2 and / or the cable connections. The ohmic coupling between the probe leads affects the output signals of the lambda probe because the leakage currents through the insulation resistance of the probe leads degrade the measurement accuracy of lambda probe 2.Under certain worst-case conditions, such as moisture or dew at the probe connections and inside the lambda probe, the insulation between the probe leads can decrease further, leading to a further deterioration in the measurement accuracy of the lambda probe. The insulation resistances of the IPE line 18 and the APE line 22 are shown in Fig. 1. A first insulation resistance 40, labeled RIB, represents the resistance between the IPE line 18 and the battery voltage Ubattan. A second insulation resistance 42, labeled RIG in Fig. 1, represents the resistance between the IPE line 18 and ground. A third insulation resistance 44, labeled RAB, represents the resistance between the APE line 22 and the battery voltage Ubattan. A fourth insulation resistance 46, labeled RAG in Fig. 1, represents the resistance between the APE line 22 and ground. The ohmic coupling between the probe leads caused by the insulation resistances 40 to 46 leads to leakage currents, which impair the measurement accuracy of the lambda probe 2. To comply with stricter emissions regulations, the measurement accuracy of existing lambda sensors can be improved either by using higher-quality cable insulation, which is associated with higher costs, or by measuring and compensating for the leakage currents resulting from the ohmic coupling between the cables, preferably using a software solution in combination with suitable hardware. This second approach, in which the leakage currents resulting from poor cable insulation are compensated for by at least one compensating current, is described in more detail below. First, the leakage current associated with each pin must be determined. Leakage currents can be measured, for example, at the beginning of a journey while the lambda sensor is still cold, or alternatively after a journey has ended, once the lambda sensor has cooled down to a specific temperature. The measured values ​​are stored in non-volatile memory and can then be used for the next journey. The following describes how to differentiate the leakage currents that occur during the operation of the lambda sensor (e.g., at APE or IPE). The simplest method involves measuring the leakage currents on a cold lambda sensor, which is non-conductive and has a very high resistance. First, the virtual ground VG on the control unit 4 is adjusted using an internal VG control circuit. Then, all pins are connected together to obtain a stable voltage. In the next step, all circuit connections to the terminals are opened again, and only the APE control terminal 24 is connected to the virtual ground VG. As a result of this wiring configuration, a leakage current occurs in the event of an insulation problem with the APE conductor 22. However, in the event of an insulation problem with the IPE conductor 18, no leakage current occurs after a short settling time. The measured leakage current in this state is subsequently referred to as iLeakAPE. Now all pins are connected together to obtain a stable voltage. In the next step, all switching connections to the terminals are opened again, and only the IPE control terminal 20 is connected to the virtual ground VG. As a result of this circuit configuration, a leakage current develops in the event of an insulation problem in the IPE conductor 18. In contrast, no leakage current develops after a short settling time if an insulation problem occurs in the APE conductor 22. The measured leakage current in this state is subsequently referred to as iLeakIPE. The magnitude of this APE leakage current or IPE leakage current is measured by the current measuring device 26 and then stored. More complex measurement methods and algorithms exist that do not necessarily require a cold sensor, for example by measuring with and without a parallel resistor and corresponding current measurements. For each detected leakage current, it is determined whether the respective leakage current is relevant to the result, affecting the result of a lambda measurement performed by the lambda probe 2, or not. First, the APE leakage current 48 shown in Fig. 2 is considered. The APE leakage current 48 flows through the Nernst cell 6 and will therefore influence the measurement of the Nernst voltage either positively or negatively, resulting in a deviation of the measured lambda value from the actual lambda value. In the case of poor cable insulation, the APE leakage current 48 shown in Fig. 2 can have a significant effect on the measured values ​​acquired by the lambda sensor 2, as the following example shows. Assuming that the battery voltage Ubatt = 12 V, the virtual ground VG = 2 V, the resistance of the Nernst cell 300 Ω, and the third resistance 44 in the case of poor cable insulation RAB = 1 MΩ, then the APE leakage current 48 is given by This would change the Nernst voltage provided by Nernst cell 6 by 3 mV. In the case of even worse cable insulation with RAB = 100 kΩ, an APE leakage current of 100 µA would result, which would lead to a deviation of 30 mV in relation to the Nernst voltage. Thus, the APE leakage current is a result-relevant leakage current. By compensating for this result-relevant leakage current, the measurement accuracy of lambda sensor 2 could therefore be significantly improved. The situation is different with the IPE leakage current 50 shown in Fig. 3. The IPE leakage current 50 is not relevant to the result because it flows directly to the reference potential 28 via the IPE control terminal 20 without first passing through the Nernst cell 6. Therefore, the IPE leakage current 50 has no influence on the Nernst voltage provided by the Nernst cell 6 and thus does not affect the lambda value measured by the lambda probe 2. The IPE leakage current 50 is therefore not relevant to the result. Consequently, it is not necessary to compensate for the IPE leakage current 50 to improve measurement accuracy. The following describes a method for determining the compensation current, whereby the compensation current is intended to compensate only for the leakage currents relevant to the result, in this case the APE leakage current 48, while the non-responsible leakage currents, in this case the IPE leakage current 50, are disregarded and not compensated when determining the compensation current. The procedure for determining the compensation current will be described in more detail below using the example of a simple jump probe. First, the total leakage current is determined, which is referred to below as iDeltaAllPin. The total leakage current iDeltaAllPin is the current difference between the current flowing from the control unit 4 to the lambda sensor 2, which is referred to as iSet, and the current flowing back from the lambda sensor 2 to the control unit 4, which is referred to below as iRefR. Thus, the total leakage current is given by... Since no continuous current is applied to the continuous current source 38, iSet = 0. If the value iDeltaAllPin > 0 or iDeltaAllPin < 0 is obtained, this indicates that leakage currents are present. In this case, the compensation procedure is activated. In this configuration of the control unit 4, a value of iDeltaAllPin < 0 indicates a weak leakage current towards the battery, whereas a value of iDeltaAllPin > 0 indicates a leakage current to ground. Starting with the total leakage current iDeltaAllPin, the compensation current, referred to below as iShuntCorr, is determined next. It is important to note that the total leakage current iDeltaAllPin includes both the leakage currents relevant to the result and those not relevant to the result. The leakage currents not relevant to the result do not contribute to the measurement error of the lambda value, but are nevertheless included in the total leakage current iDeltaAllPin. Therefore, the leakage currents not relevant to the result must be subtracted from the total leakage current iDeltaAllPin. To determine the compensation current iShuntCorr, all leakage currents not relevant to the result are subtracted from the total leakage current iDeltaAllPin. In this case, the leakage current iLeakIPE, which is not relevant to the result, is subtracted from the total leakage current iDeltaAllPin. The compensation current iShuntCorr is therefore calculated as follows: The calculated value of the compensation current iShuntCorr is fed to the digital-to-analog converter of the continuous current source 38. This adjusts the continuous current source 38 so that it supplies the lambda sensor 2 with the required compensation current iShuntCorr via the APE control terminal 24, the APE line 22, and the APE terminal 16. By applying this compensation current, the measurement error caused by the leakage currents relevant to the results can be prevented or at least reduced. Figure 4 shows the lambda sensor 2 and the control unit 4 again, the control unit 4 comprising a compensation unit 52 designed to perform the compensation procedure described above. The compensation unit 52 can preferably be implemented as a software-implemented compensation unit. The input variables 54 supplied to the compensation unit 52 can be, for example, the value of the backflowing current iRefR and the previously measured amplitudes of the leakage currents. Based on these input variables 54, the compensation unit 52 determines the value of the required compensation current iShuntCorr. The determined value iShuntCorr is supplied to the digital-to-analog converter of the adjustable current source 38, as indicated by arrow 56. The advantage of the solution described here is that the effects of weak leakage currents caused by insulation resistances can be prevented or reduced. This is achieved by a highly precise current measuring device 26 for the return current, capable of determining the current amplitudes with high accuracy. This is further achieved by a flexible switching arrangement for determining the various leakage currents, enabling the identification of both relevant and irrelevant leakage currents, and by a preferably software-based method for determining the deviation between the currents flowing to and from the lambda probe and deriving the relevant leakage currents from this deviation.This is further achieved by a precise current source that supplies the lambda probe with an additional current (positive or negative) and compensates for the leakage currents relevant to the result, in order to eliminate or at least reduce the effects of the leakage currents. It is particularly advantageous to implement some or all components of the control unit 4 on an application-specific integrated circuit (ASIC). Figure 5 shows such an embodiment, in which the components of the control unit 4 described so far are housed on an ASIC 58. The ASIC 58 has an IPE control connection 60 and an APE control connection 62. Furthermore, the ASIC 58 has an RE connection 64 and an MES connection 66. The RE connection 64 (reference electrode connection) and the MES connection 66 are additional ASIC connections specifically for operating broadband probes. The IPE control port 60 is connected to the IPE port 14 of the lambda probe 2 via the IPE line 18 and the APE control port 62 is connected to the APE port 16 of the lambda probe 2 via the APE line 22.The ASIC 58 can be used to provide, in particular, precise power sources and power measuring devices. Fig. 6 shows an example measurement performed on a lambda sensor 2, where the APE terminal 16 of the lambda sensor 2 is connected to the battery voltage Ubatt at a specific time via a high-resistance resistor of 1 MΩ. In Fig. 6, both the total leakage current iDeltaAllPin and the Nernst voltage uNernst are plotted as a function of time. The first dashed line 68 marks a time before the shunt connection, while the second dashed line 70 marks a time after the shunt connection. Based on the time course of the total leakage current iDeltaAllPin, which is plotted in the lower part of Fig. 6 as a fluctuating current waveform 72 and as a smoothed current waveform 74, it can be seen that the total leakage current is approximately 1 µA before the shunt connection and approximately -11 µA after the shunt connection, so that the total leakage current changes by approximately 12 µA. A rough estimate of the leakage current confirms this order of magnitude: The effect of the shunt connection is also directly visible in the time course 76 of the Nernst voltage plotted in the upper part of Fig. 6. As a result of the shunt connection, the Nernst voltage increases from the initial value of 0.772 V to 0.797 V, which corresponds to a voltage change of approximately 25 mV. This increase in the Nernst voltage is therefore attributable to the additional leakage current in the direction of the battery voltage Ubatt. According to the procedure described above, by applying a suitable compensation current, this increase in the Nernst voltage uNernst shown in Fig. 6, which is caused by the additional leakage current in the direction of the battery voltage Ubatther, can be avoided, so that a constant Nernst voltage is obtained regardless of the leakage currents. The procedure described above for compensating leakage currents can also be applied to broadband lambda sensors. Figure 7 shows a broadband lambda sensor 78 comprising a Nernst cell 80 and a pump cell 82. Furthermore, the broadband lambda sensor 78 has a heating element 84 connected between a first operating voltage terminal 86 and a second operating voltage terminal 88. The broadband lambda sensor 78 has an IPE terminal 90, an APE terminal 92, an RE terminal 94, and an MES terminal 96. The broadband lambda sensor 78 is controlled by a control unit 98. For this purpose, the IPE connection 90 and the APE connection 92 are connected via an IPE line 100 and an APE line 102 to the IPE control connection 104 and the APE control connection 106 of the control device 98.The RE terminal 94 is connected via an RE line 108 to the RE control terminal 110 of the control unit 98, and the MES terminal 96 is connected via an MES line 112 to the MES control terminal 114 of the control unit 98. Each of the lines 100, 102, 108, 112 is connected to Ubatt via one of the insulation resistors 116-1 to 116-4 and to ground via one of the insulation resistors 118-1 to 118-4. The control unit 98 has a switching arrangement 120. Each of the lines 100, 102, 108, 112 can be connected to the current measuring device 122 and the reference potential 124 via this switching arrangement 120. Furthermore, it is possible to connect each of the lines 100, 102, 108, 112 to a pulsed current source 126 and / or to a continuous current source 130 via a switch 128 using the switching arrangement 120. Thanks to these switching options, the different leakage currents can be measured individually in succession or subsequently determined based on a multitude of measurements. Determining the compensation current for a broadband lambda sensor is essentially analogous to the procedure described above for a switching probe. Given the larger number of pins, additional measurements are required for the extra pins to determine the leakage currents; however, the basic principle is the same as with the switching probe: First, the leakage currents are measured, then the leakage currents relevant to the result are determined, and then these relevant leakage currents are compensated by appropriately controlling a current source. The following describes the procedure for the wideband lambda sensor in more detail. First, the total leakage current iDeltaAllPin is determined using the equation where iSet denotes the current flowing to the lambda sensor and iRefR the return current. Unlike a switching sensor, iSet can take on any value for a wideband lambda sensor. An iDeltaAllPin < 0 indicates a weak leakage current to the battery, while iDeltaAllPin > 0 indicates a weak leakage current to ground. The total leakage current iDeltaAllPin includes both leakage currents relevant to the result and leakage currents that are not. Therefore, to determine the compensation current iShuntCorr, it is necessary to subtract the non-relevant leakage currents from the total leakage current, resulting in the following compensation current iShuntCorr: The compensation current iShuntCorr is then added to the input value of the digital-to-analog converter of the continuous current source 130 in order to compensate for the leakage current by the value iShuntCorr. The features disclosed in the foregoing description, the claims and the drawings may be important for the realization of the invention in its various embodiments, both individually and in any combination.

Claims

Method for compensating leakage currents (48, 50) from at least two connecting lines (18, 22, 100, 102) connecting a lambda probe (2, 78) to a control device (4, 98), the method comprising the following steps: - Determining, for at least one of the connecting lines (18, 22, 100, 102), an associated leakage current (48, 50), - Determining, for each determined leakage current (48, 50), whether the respective leakage current (48, 50) is a result-relevant leakage current (48) that affects the result of a lambda measurement performed by the lambda probe (2, 78), or not, - Determining a compensation current, whereby only the result-relevant leakage currents (48) are taken into account in its determination, - Applying the compensation current to at least one of the Connection leads (18, 22, 100, 102) of the lambda sensor (2, 78). Method according to claim 1, characterized in that those leakage currents are identified as result-relevant leakage currents (48) which flow through the lambda probe (2, 78). Method according to claim 1 or claim 2, characterized in that when determining the compensation current, all result-relevant leakage currents (48) of the connecting lines (18, 22, 100, 102) are taken into account. Method according to one of claims 1 to 3, characterized by the following further steps: - Determining all result-relevant leakage currents (48), - Determining the compensation current as the sum of all result-relevant leakage currents (48). Method according to one of claims 1 to 4, characterized in that the lambda probe is a switching probe (2) which comprises an inner pump electrode connection (14) and an outer pump electrode connection (16), wherein an associated APE leakage current (48) is determined for the outer pump electrode connection (16), and wherein the compensation current is set equal to the APE leakage current (48). Method according to one of claims 1 to 3, characterized by the following further steps: - Determining a total leakage current as the current difference between currents flowing from the control device (4, 98) to the lambda probe (2, 78) and currents flowing back from the lambda probe (2, 78) to the control device (4, 98), - Determining the non-responsible leakage currents (50) of the connecting lines (18, 22, 100, 102), - Determining the compensation current by subtracting the non-responsible leakage currents (50) from the total leakage current. Method according to one of claims 1 to 6, characterized in that the lambda probe (2, 78) comprises an inner pump electrode connection (14, 90) and an outer pump electrode connection (16, 92), wherein an associated IPE leakage current (50) is determined for the inner pump electrode connection (14, 90), and wherein the compensation current is determined by determining a total leakage current as the current difference between currents flowing from the control device (4, 98) to the lambda probe (2, 78) and currents flowing back from the lambda probe (2, 78) to the control device (4, 98) and subtracting the IPE leakage current (50) from this total leakage current. Control device (4, 98) for a lambda sensor (2, 78), which can be connected to the control device (4, 98) via at least two connecting lines (18, 22, 100, 102), wherein the control device (4, 98) is designed to generate control signals for the lambda sensor (2, 78) and to evaluate signals received from the lambda sensor (2, 78), wherein the control device (4, 98) comprises: - a compensation device (52) designed to determine an associated leakage current (48, 50) for at least one of the connecting lines (18, 22, 100, 102), and to determine for each determined leakage current (48, 50) whether the respective leakage current (48, 50) is a result-relevant leakage current (48) that relates to the result of a to determine whether the lambda measurement performed by the lambda probe (2, 78) has an effect, or not, a compensation current, whereby only the leakage currents relevant to the result (48) are taken into account in its determination,- a controllable current source (38, 130) designed to additionally impose the compensation current on at least one of the connecting lines (18, 22, 100, 102) of the lambda sensor (2, 78). Control device (4, 98) according to claim 8, characterized in that the compensation current is based on all result-relevant leakage currents (48) of the connecting lines (18, 22, 100, 102). Device for detecting a lambda value, comprising: - a control device (4, 98) according to claim 8 or claim 9, - a lambda probe (2, 78) which is connected to the control device (4, 98) via at least two connecting lines (18, 22, 100, 102). Device according to claim 10, characterized in that the lambda probe is a switching probe (2) or a single-cell broadband probe comprising a Nernst cell (6), and that the result-relevant leakage currents (48) are those leakage currents flowing through the Nernst cell (6). Device according to claim 10, characterized in that the lambda probe is a two-cell broadband probe (78) comprising a Nernst cell (80) and a pump cell (82), and that the leakage currents relevant to the result are those leakage currents flowing through the Nernst cell (80) and / or the pump cell (82). Device according to one of claims 10 to 12, characterized in that the lambda probe (2, 78) comprises an inner pump electrode connection (14, 90) and an outer pump electrode connection (16, 92), wherein an APE leakage current (48) belonging to the outer pump electrode connection (16, 92) is relevant to the result and an IPE leakage current (50) belonging to the inner pump electrode connection (14, 90) is not relevant to the result. Exhaust system of a motor vehicle comprising a device for detecting a lambda value according to one of claims 10 to 13. Motor vehicle comprising an exhaust system with a device for detecting a lambda value according to one of claims 10 to 13.

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