METHOD FOR DIAGNOSING EXHAUST GAS SENSORS

Abstract

An evaluation and control unit for operating a wideband lambda sensor that has at least two electrical lines, the evaluation and control unit having at least two electrical terminals for electrical connection to the electrical lines of the wideband lambda sensor. Each of the electrical terminals has assigned to it a respective electrical switch via which each terminal is capable of being individually connected to at least one defined electrical potential. Each switch is voltage-resistant against the maximum short-circuit voltage that is to be expected at the respective terminal in case of fault. In addition, a method is described for the line-specific short-circuit diagnosis of the wideband lambda sensor (pinpointing).

Claims

1-15. (canceled)

16. An evaluation and control unit configured to operate a wideband lambda sensor that has at least two electrical lines, the evaluation and control unit having at least two electrical terminals for electrical connection to the electrical lines of the wideband lambda sensor, each respective terminal of the electrical terminals having assigned to it a respective electrical switch via which each of the terminals is capable of being individually connected to at least one defined electrical potential, wherein each of the switches is voltage-resistant against a maximum short-circuit voltage that is to be expected at the respective terminal in case of fault.

17. The evaluation and control unit as recited in claim 16, wherein the evaluation and control unit is an ASIC.

18. The evaluation and control unit as recited in claim 16, wherein between each of the switches and the defined electrical potential, a voltage divider is provided by which, in case of fault, a partial voltage of the maximum short-circuit voltage to be expected can be picked off, the partial voltage being within a measurement range of a measurement system of the evaluation and control unit.

19. The evaluation and control unit as recited in claim 18, wherein the measurement system is an ADC of the evaluation and control unit.

20. The evaluation and control unit as recited in claim 18, wherein, the voltage devider is only a single voltage divider provided between the defined electrical potential and the switches.

21. The evaluation and control unit as recited in claim 18, wherein the voltage divider is made up of two ohmic resistances.

22. The evaluation and control unit as recited in claim 21, wherein an ohmic resistance of the ohmic resistances, oriented toward the switches, of the voltage divider is voltage-resistant against the maximum short-circuit voltage that is to be expected at the terminals in case of fault.

23. The evaluation and control unit as recited in claim 16, wherein the terminals can be short-circuited with one another via the switches in order to protect the wideband lambda sensor in case of fault, and in addition a further switch is situated between the switches and the defined electrical potential, so that a flow of current through the wideband lambda sensor to the defined electrical potential can be prevented in case of fault.

24. The evaluation and control unit as recited in claim 16, wherein the defined electrical potential can assume two different defined values.

25. A method for diagnosing electrical lines of a wideband lambda sensor, each respective electrical line of the electrical lines of the wideband lambda sensor being connected to a respective terminal of an evaluation and control unit, the evaluation and control unit being configured to operate the wideband lambda sensor, each respective terminal of the electrical terminals having assigned to it a respective electrical switch via which each of the terminals is capable of being individually connected to at least one defined electrical potential, wherein each of the switches is voltage-resistant against a maximum short-circuit voltage that is to be expected at the respective terminal in case of fault, the method comprising: respectively closing exactly one of the electrical switches at a time, one after the other, and ascertaining a current assigned to the respective electrical terminal, or a variable representing the current; and (i) subsequently, in a case in which it is already known that there is a short circuit in one of the electrical lines, the short circuit being assigned to a line of the electrical lines that is connected to a terminal of the respective terminals at which the current having a highest magnitude was ascertained, and/or (ii) comparing a magnitude of a largest current of the ascertained currents to a specified or temperature-dependent threshold value and, when the magnitude exceeds the threshold value, inferring that there is a short circuit, and the short circuit is assigned to a line of the electrical lines that is connected to a terminal of the respective terminals at which the current having the largest magnitude was ascertained.

26. The method as recited in claim 25, wherein the short circuit is assigned to a line of the electrical lines only under the further condition that the current having the largest magnitude differs from a current of the ascertained currents having a second-largest magnitude by a specified minimum difference or by a specified minimum factor.

27. The method as recited in claim 26, wherein when it is known that there is a short circuit at one of the electrical lines, or if it is inferred that there is a short circuit and in addition it is not possible to assign the short circuit to a line because the current having the largest magnitude does not differ from the current having the second-largest magnitude by the specified minimum difference or specified minimum factor, the method is repeated after a waiting time that allows the wideband lambda sensor to cool.

28. A method for diagnosing electrical lines of a wideband lambda sensor, each respective electrical line of the electrical lines of the wideband lambda sensor being connected to a respective terminal of an evaluation and control unit, the evaluation and control unit being configured to operate the wideband lambda sensor, each respective terminal of the electrical terminals having assigned to it a respective electrical switch via which each of the terminals is capable of being individually connected to at least one defined electrical potential, wherein each of the switches is voltage-resistant against a maximum short-circuit voltage that is to be expected at the respective terminal in case of fault, wherein the defined electrical potential can assume two different defined values, the method comprising: respectively closing exactly one of the electrical switches at a time, one after the other, and ascertaining a current assigned to the respective electrical terminal, or a variable representing the current; and (i) subsequently, in a case in which it is already known that there is a short circuit in one of the electrical lines, the short circuit being assigned to a line of the electrical lines that is connected to a terminal of the respective terminals at which the current having a highest magnitude was ascertained, and/or (ii) comparing a magnitude of a largest current of the ascertained currents to a specified or temperature-dependent threshold value and, when the magnitude exceeds the threshold value, inferring that there is a short circuit, and the short circuit is assigned to a line of the electrical lines that is connected to a terminal of the respective terminals at which the current having the largest magnitude was ascertained; wherein for each respective line of the electrical lines, a first current is measured while the defined potential has a first value, and a second current is measured while the defined potential has a second value different from the first value.

29. The method as recited in claim 28, wherein for each line of the electrical lines, a short-circuit resistance is determined from the first value and the second value and a value of the first current and a value of the second current, based on the assumption that the electrical lines of the lambda sensor are high-ohmic to one another.

30. The method as recited in claim 29, wherein for each line of the electrical lines, a short-circuit potential is determined from the first value and the second value and the value of the first current and the value of the second current, based on the assumption that the electrical lines of the lambda sensor are high-ohmic to one another.

31. The method as recited in claim 30, wherein a short circuit is inferred when at least one ascertained short-circuit resistance of the short-circuit resistances is below a specified threshold value and the short circuit is assigned to a line of the electrical lines that is connected to the respective terminal at which a smallest short-circuit resistance occurred.

32. The method as recited in claim 31, wherein information about presence of a short circuit, including about a fact of a short circuit, about a line at which the short circuit was determined, about the short circuit potential, and/or about the short-circuit resistance are stored in a nonvolatile data memory.

33. The method as recited in claim 32, wherein the information is stored an entry in a fault memory of the evaluation and control unit and/or in a fault memory of a control device connected to the evaluation and control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIGS. 1a-1d show a first exemplary embodiment of an evaluation and control unit for operating a wideband lambda sensor, in accordance with the present invention.

[0039] FIG. 2 shows a flow diagram of a diagnostic method with the evaluation and control unit according to FIG. 1, in accordance with the present invention.

[0040] FIGS. 3a-3c show a second exemplary embodiment of an evaluation and control unit for operating a wideband lambda sensor, in accordance with the present invention.

[0041] FIG. 4 shows a flow diagram of a diagnostic method with the evaluation and control unit according to FIG. 3, in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0042] FIG. 1a shows a first exemplary embodiment of an evaluation and control unit 100 for operating a wideband lambda sensor 200. Evaluation and control unit 100 is connected to electrical lines 201, 202, 203, 204 of a wideband lambda sensor 200 via four terminals RE, IPE, APE, MES. These lines lead to electrochemical cells 210, 211 of wideband lambda sensor 200. Possible details of wideband lambda sensor 200 are provided, for example, in German Patent Application No. DE 10 2011 007 068 A1.

[0043] Evaluation and control unit 100 is shown only to the extent necessary for the understanding of the present invention. Possible details of evaluation and control unit 100 are provided, for example, in European Patent No. EP 2 277 035 B1.

[0044] Evaluation and control unit 100 has, in the example, a terminal to ground GND to which each of the terminals RE, IPE, APE, MES is individually connected via a respective voltage-resistant switch Swt.sub.RE, Swt.sub.IPE, Swt.sub.APE, Swt.sub.MES, and via a common voltage divider 140.

[0045] In the example, common voltage divider 140 is made up of two ohmic resistances R_Protn and R_Meas, connected in series. In this example, their resistance values are R_Protn=3.24 kOhm and R_Meas=360 Ohm.

[0046] The voltage U across resistance R_Meas can be measured by an ADC 150 of evaluation and control unit 100. Division by R_Meas yields current I flowing through voltage divider 140.

[0047] For example, a further switch (not shown in FIG. 1a) can be provided between resistance R_Meas and GND. If this switch is opened in case of fault, this has the effect that a flow of current through wideband lambda sensor 200 to GND does not take place.

[0048] FIG. 1b shows the case of fault of a low-ohmic short circuit of line 201 to a supply voltage of 36V, showing, via line 201 of wideband lambda sensor 200 at terminal RE of evaluation and control unit 100, short-circuit voltage U_SC=36V over short-circuit resistance R_SC=0 Ohm.

[0049] In FIG. 1c, the low-ohmic switch Swt.sub.RE assigned to terminal RE (internal resistance R.sub.SwtRE=100 Ohm) has been closed, so that a current I of 9.7 mA flows from line 201 to GND via terminal RE and voltage divider 140. Consequently, there is a voltage of 3.502 V across measurement resistance R_Meas, which voltage is digitized by ADC 150.

[0050] In FIG. 1d, the low-ohmic switch Swt.sub.RE assigned to terminal RE has been opened, and instead the low-ohmic switch Swt.sub.IPE (internal resistance R.sub.SwtIPE=100 Ohm) assigned to terminal IPE has been closed. Because the internal resistance of the wideband lambda sensor between lines 201 and 202 is Ri=300 Ohm in the hot state, a current I of 9 mA now flows to ground GND via voltage divider 140. Correspondingly, across measurement resistor R_Meas there is a voltage of 3.240 V, which is digitized by ADC 150.

[0051] Similar currents and voltages result if, instead of switch Swt.sub.IPE, the switch Swt.sub.APE is closed, or if the switch Swt.sub.MES is closed.

[0052] For terminal RE, the highest current I was unambiguously ascertained. Because it was known ahead of time that, at 36V, there was an impermissibly high potential at this terminal, i.e. it was known that in principle a short circuit was present, it is inferred that the short circuit is at line 201, connected to terminal RE, of wideband lambda sensor 200.

[0053] The exemplary method according to the device shown with reference to FIG. 1 is shown in FIG. 2 as a flow diagram: [0054] method step S1: closing switch Swt.sub.RE [0055] method step S2: measuring current I.sub.RE that subsequently flows to ground GND through voltage divider 140 [0056] method step S3: opening switch Swt.sub.RE and closing switch Swt.sub.IPE [0057] method step S4: measuring current I.sub.IPE that subsequently flows to ground GND through voltage divider 140 [0058] method step S5: determining which of the currents I.sub.RE, I.sub.PE is greater [0059] method step S6: assigning the short circuit to the line 201 that is connected to the terminal RE through which the greater current flowed [0060] method step S7: storing the obtained information that a short circuit is present at line 201 in a fault memory of a control device connected to evaluation and control unit 100.

[0061] FIG. 3a shows a second exemplary embodiment of an evaluation and control unit 100 for operating a wideband lambda sensor 200. Evaluation and control unit 100 is connected, via four terminals RE, IPE, APE, MES, to electrical lines 201, 202, 203, 204 of a wideband lambda sensor 200 that is cold enough that there is a very high internal resistance R.sub.i, for example 1 MOhm, between each two of the lines 201, 202, 203, 204. These lines lead to electric chemical cells 210, 211 of wideband lambda sensor 200. Possible details of wideband lambda sensor 200 are provided, for example, in German Patent Application No. DE 10 2011 007 068 A1.

[0062] Evaluation and control unit 100 is shown only to the extent necessary for the understanding of the present invention. Possible details of evaluation and control unit 100 are provided, for example, in European Patent No. EP 2 277 035 B1.

[0063] In the example, evaluation and control unit 100 has a terminal at a defined potential that can assume the values V.sub.SET1=2V and V.sub.SET2=10V. Each of the terminals RE, IPE, APE, MES can be connected individually to this defined potential, via a respective voltage-resistant switch Swt.sub.RE, Swt.sub.IPE, Swt.sub.APE, Swt.sub.MES, and via a common reference resistance R.sub.Ref=100 Ohm. In addition, a current source SR can be connected at the side of switches Swt.sub.RE, Swt.sub.IPE, Swt.sub.APE, Swt.sub.MES oriented away from terminals RE, IPE, APE, MES. However, in the example this current source is separated by an open switch.

[0064] FIG. 3b shows the fault case of a low-ohmic short circuit of line 201 to a supply voltage, showing, via line 201 of wideband lambda sensor 200 at terminal RE of evaluation and control unit 100, short-circuit voltage Usc over short-circuit resistance Rsc.

[0065] At the defined potential V.sub.SET1=2V, before the closing of switch Swt.sub.RE a current I.sub.0,1 through R.sub.Ref of 0 mA is determined, and after the closing of switch Swt.sub.RE a current I.sub.1 through R.sub.Ref of 100 mA is determined.

[0066] At the defined potential V.sub.SET2=10V, before the closing of switch Swt.sub.RE a current I.sub.0,2 through R.sub.Ref of 0 mA is determined, and after the closing of switch Swt.sub.RE a current I.sub.2 through R.sub.Ref of 20 mA is determined.

[0067] Applying the equations:

R.sub.SC=[R.sub.ref*(I.sub.1−I.sub.2−I.sub.0,1+I.sub.0,2)+V.sub.SET,1−V.sub.SET,2]/(I.sub.2−I.sub.1−I.sub.0.2+I.sub.0,1),

Vsc=1/2*[R.sub.SC*(I.sub.1+I.sub.2+I.sub.0,1+I.sub.0,2)+R.sub.ref*(I.sub.1+I.sub.2)+V.sub.SET,1+V.sub.SET,2]

[0068] yields the result: R.sub.SC=0 Ohm, V.sub.SC=12 V.

[0069] In FIG. 3c, low-ohmic switch Swt.sub.RE assigned to terminal RE is opened, and instead the low-ohmic switch Swt.sub.IPE assigned to terminal IPE is closed. A current of 0 mA flows through resistance R.sub.Ref, independently of whether switch Swt.sub.IPE is opened or closed, and independent of the value of the defined potential V.sub.SET1, V.sub.SET2.

[0070] By applying the equations named above, the information is obtained that, with regard to line 202, a “short-circuit resistance” Rsc is very small.

[0071] Overall, it can be inferred that in this example there is a very low-ohmic short circuit of line 201 against a short-circuit voltage of 12V.

[0072] The exemplary method according to the device shown with reference to FIG. 3 is shown in FIG. 4 as a flow diagram.

[0073] For V.sub.SET 1: [0074] method step S10: opening switches Swt.sub.RE, Swt.sub.IPE, Swt.sub.APE, Swt.sub.MES [0075] method step S11: measuring the current I.sub.01 that flows through reference resistance R.sub.Ref to the defined potential [0076] method step S12: closing the switch Swt.sub.RE [0077] method step S14: measuring the current I.sub.1 that flows through reference resistance R.sub.Ref to the defined potential

[0078] For V.sub.SET 2: [0079] method step S10′: opening switches Swt.sub.RE, Swt.sub.IPE, Swt.sub.APE, Swt.sub.MES [0080] method step S11′: measuring the current I.sub.01 that flows through reference resistance R.sub.Ref to the defined potential [0081] method step S12′: closing the switch Swt.sub.RE [0082] method step S14′: measuring the current I.sub.1 that flows through reference resistance R.sub.Ref to the defined potential [0083] method step 15: calculating the short-circuit resistance Rsc and the short-circuit voltage Usc for the at terminal RE line of the wideband lambda sensor.

[0084] Repetition of steps S10 to S14 and S10′ to S14 and S15 for the other terminals IPN, APN and MES. (Method step S10.sub.IPN to S14.sub.IPN and S10′.sub.IPN to S14′.sub.IPN and S15.sub.IPN; S10.sub.APN to S14.sub.APN and S10′.sub.APN to S14′.sub.APN and S15.sub.APN; S10.sub.MES to S14.sub.MES and S10′.sub.MES to S14′.sub.ME and S15.sub.MES). [0085] Method step S16: assigning the short circuit to line 201, which is connected to the terminal RE for which the smallest short-circuit resistance RSC was determined. [0086] Method step S17: storing the obtained information that there is a short circuit at line 201 in a fault memory of a control device connected to evaluation and control unit 100.