METHOD FOR OPERATING A SENSOR FOR DETECTING AT LEAST A PORTION OF A MEASUREMENT GAS COMPONENT HAVING BOUND OXYGEN IN A MEASUREMENT GAS

Abstract

A method for operating a sensor for detecting at least a portion of a measured-gas component having bound oxygen in a measured gas in an exhaust gas of an internal combustion engine. The sensor encompasses a sensor element including: a first pump cell; a reference cell; and a second pump cell. An electronic control device is connected to the sensor element; the first pump cell is connected using an electrically conductive connection to a first separate terminal of the device; the second pump cell is connected by an electrically conductive connection to a second separate terminal of the device; a measuring resistor is provided in the connection that connects the second pump cell to the second separate terminal; a current excitation and/or voltage excitation of the second pump cell is carried out using the control device to generate a measured signal at the measuring resistor.

Claims

1-16. (canceled)

17. A method for operating a sensor for detecting at least a portion of a measured-gas component having bound oxygen in a measured gas, in an exhaust gas of an internal combustion engine, the sensor including a sensor element having: (i) a first pump cell that has an external pump electrode and an internal pump electrode and adjoins a first cavity that is in communication with the measured gas, (ii) a reference cell that has a Nernst electrode and a reference electrode and adjoins a reference gas space, and (iii) a second pump cell that has a pump electrode and a counter-electrode and adjoins a second cavity, the sensor further including an electronic control device connected to the sensor element, the electronic control device having at least a first separate terminal for the first pump cell and a second separate terminal for the second pump cell, the first pump cell being connected to the electronic control device using an electrically conductive connection to the first separate terminal, the second pump cell being connected to the electronic control device using an electrically conductive connection to the second separate terminal, a measuring resistor being provided in the electrically conductive connection that connects the second pump cell to the second separate terminal, the method comprising: carrying out a current excitation and/or voltage excitation of the second pump cell using the control device to generate a measured signal at the measuring resistor.

18. The method as recited in claim 17, wherein for the carrying out, a predetermined electrical voltage is applied to the second pump cell, the voltage excitation of the second pump cell being carried out, the voltage excitation encompassing a modification of the predetermined electrical voltage for a predetermined time.

19. The method as recited in claim 18, wherein the predetermined electrical voltage is raised for the predetermined time.

20. The method as recited in claim 18, wherein the electrically conductive connection that connects the second pump cell to the second separate terminal is identified as intact when the measured signal has a value not equal to zero for the predetermined time, and is identified as defective when the measured signal has a value of zero for the predetermined time.

21. The method as recited in claim 17, wherein, for the carrying out, a predetermined electrical voltage is applied to the second pump cell, the voltage excitation of the second pump cell being carried out, the predetermined electrical voltage being raised for a first predetermined time, and the predetermined electrical voltage being lowered for a second predetermined time, an integral of the applied electrical voltage having a value of zero for the first predetermined time and the second predetermined time.

22. The method as recited in claim 21, wherein the electrically conductive connection that connects the second pump cell to the second separate terminal is identified as intact when the measured signal has a value not equal to zero for the first predetermined time and the second predetermined time, and is identified as defective when the measured signal has a value of zero for the first predetermined time and the second predetermined time.

23. The method as recited in claim 17, wherein, for the carrying out, a predetermined electrical current is impressed into the second pump cell, the current excitation of the second pump cell being carried out, the predetermined electrical current being raised for a first predetermined time, and the predetermined electrical current being lowered for a second predetermined time, the first predetermined time and the second predetermined time being identical in length.

24. The method as recited in claim 23, wherein the electrically conductive connection that connects the second pump cell to the second separate terminal is identified as intact when an electrical voltage applied to the second pump cell falls below a threshold value for the first predetermined time and for the second predetermined time, and being identified as defective when an electrical voltage applied to the second pump cell exceeds a threshold value for the first predetermined time and for the second predetermined time.

25. The method as recited in claim 17, wherein, for the carrying out, a predetermined electrical voltage is applied to the second pump cell, and the voltage excitation of the second pump cell is carried out, the voltage excitation encompassing a periodic modification of the predetermined electrical voltage.

26. The method as recited in claim 25, wherein a period length is less than an electrochemical time constant of the second pump cell.

27. The method as recited in claim 25, wherein the measured signal is filtered using a low-pass filter, the predetermined electrical voltage being modified at a frequency that is greater than a bandwidth of the low-pass filter.

28. The method as recited in claim 25, wherein the electrically conductive connection that connects the second pump cell to the second separate terminal is identified as intact when the measured signal exhibits a periodic change, and being identified as defective when the measured signal exhibits no periodic change.

29. A non-transitory electronic storage medium on which is stored a computer program for operating a sensor for detecting at least a portion of a measured-gas component having bound oxygen in a measured gas, in an exhaust gas of an internal combustion engine, the sensor including a sensor element having: (i) a first pump cell that has an external pump electrode and an internal pump electrode and adjoins a first cavity that is in communication with the measured gas, (ii) a reference cell that has a Nernst electrode and a reference electrode and adjoins a reference gas space, and (iii) a second pump cell that has a pump electrode and a counter-electrode and adjoins a second cavity, the sensor further including an electronic control device connected to the sensor element, the electronic control device having at least a first separate terminal for the first pump cell and a second separate terminal for the second pump cell, the first pump cell being connected to the electronic control device using an electrically conductive connection to the first separate terminal, the second pump cell being connected to the electronic control device using an electrically conductive connection to the second separate terminal, a measuring resistor being provided in the electrically conductive connection that connects the second pump cell to the second separate terminal, the computer program, when executed by a computer, causing the computer to perform: carrying out a current excitation and/or voltage excitation of the second pump cell using the control device to generate a measured signal at the measuring resistor.

30. An electronic control device configured to operate a sensor for detecting at least a portion of a measured-gas component having bound oxygen in a measured gas, in an exhaust gas of an internal combustion engine, the sensor including a sensor element having: (i) a first pump cell that has an external pump electrode and an internal pump electrode and adjoins a first cavity that is in communication with the measured gas, (ii) a reference cell that has a Nernst electrode and a reference electrode and adjoins a reference gas space, and (iii) a second pump cell that has a pump electrode and a counter-electrode and adjoins a second cavity, the electronic control device comprising: at least a first separate terminal for the first pump cell and a second separate terminal for the second pump cell, the first pump cell being connected to the electronic control device using an electrically conductive connection to the first separate terminal, the second pump cell being connected to the electronic control device using an electrically conductive connection to the second separate terminal, a measuring resistor being provided in the electrically conductive connection that connects the second pump cell to the second separate terminal; wherein the electronic control device is configured to carry out a current excitation and/or voltage excitation of the second pump cell to generate a measured signal at the measuring resistor.

31. A sensor for detecting at least a portion of a measured-gas component having bound oxygen in a measured gas, in an exhaust gas of an internal combustion engine, comprising: a sensor element including a first pump cell that has an external pump electrode and an internal pump electrode and adjoins a first cavity that is communication with the measured gas, a reference cell that has a Nernst electrode and a reference electrode and adjoins a reference gas space, and a second pump cell that has a pump electrode and a counter-electrode and adjoins a second cavity; and an electronic control device connected to the sensor element, the electronic device having at least a first separate terminal for the first pump cell and a second separate terminal for the second pump cell, the first pump cell being connected to the electronic control device using an electrically conductive connection to the first separate terminal, the second pump cell being connected to the electronic control device using an electrically conductive connection to the second separate terminal, a measuring resistor being provided in the electrically conductive connection that connects the second pump cell to the second separate terminal, electronic control device configured to carry out a current excitation and/or voltage excitation of the second pump cell to generate a measured signal at the measuring resistor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further optional details and features of the present invention are described below in the context of preferred exemplifying embodiments that are depicted in the Figures.

[0034] FIG. 1 shows schematically shows the construction of a sensor according to an example embodiment of the present invention.

[0035] FIG. 2 shows part of a sensor with part of a control device connected thereto, in accordance with an example embodiment of the present invention.

[0036] FIG. 3 shows a first example of a time course of electrical voltages and a measured signal in the context of the sensor, in accordance with the present invention.

[0037] FIG. 4 shows a second example of a time course of electrical voltages and a measured signal in the context of the sensor, in accordance with the present invention.

[0038] FIG. 5 shows a third example of a time course of electrical voltages, electrical currents, and a measured signal in the context of the sensor, in accordance with the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0039] FIG. 1 schematically shows a construction of a sensor 100 according to the present invention which is particularly suitable for carrying out the method according to the present invention.

[0040] Sensor 100, which is configured to detect at least a portion of a measured-gas component having bound oxygen, hereinafter referred to by way of example as nitrogen oxide (NO.sub.x), in a gas mixture, by way of example an exhaust gas of an internal combustion engine, encompasses for that purpose a sensor element 110 and a first pump cell 112 that is embodied between an external pump electrode 114 and an internal pump electrode 116. External pump electrode 114, which is separated by way of a porous aluminum oxide layer 118 from the environment of sensor 100, possesses a first electrically conductive connection 120 by way of which a first pump current I.sub.P1 can be generated in first pump cell 112. First electrically conductive connection 120 is connected for that purpose to a first terminal P1 of an external electronic control device 122. In order to obtain a complete circuit, internal pump electrode 116 likewise possesses a second electrically conductive connection 124 that leads to a common terminal COM of external electronic device 122. First pump cell 112 adjoins a first cavity 126 that is located in the interior of sensor element 110 and is in communication with the measured gas. By generation of the first pump current I.sub.P1 in first pump cell 112, a first portion of oxygen ions which are formed from molecular oxygen from the gas mixture can be transported between first cavity 126 and the environment of sensor 100. Two diffusion barriers 128 are present in the entry passage from the environment into first cavity 126.

[0041] Sensor element 110 furthermore has an electrical reference cell 130 that has a Nernst electrode 132 and a reference electrode 134. While Nernst electrode 132 connects via second electrically conductive connection 124, together with internal pump electrode 116, to common terminal COM, reference electrode 134 has a separate third electrically conductive connection 136 to a supply voltage Vs that furnishes the required supply voltage Vs via a terminal Vs of external electronic control device 122. Reference cell 130 adjoins a reference gas space 138. A second portion of the oxygen ions from first cavity 126 and/or from the environment of sensor 100 is transported into reference gas space 138 by application of a reference pump current between terminal Vs and common terminal COM. The value for the reference pump current is adjusted in this context in such a way that a specified portion of the oxygen ions becomes established in reference gas space 138. Preferably, the value for the first pump current I.sub.P1 is also adjusted in this context in such a way that a specified ratio is produced between the first portion of the oxygen ions in first cavity 126 and the second portion of the oxygen atoms in reference gas space 138.

[0042] The measured-gas component, nitrogen oxide (NO.sub.x), which has the bound oxygen and is further contained in the gas mixture, travels, in particular by diffusion and in largely uninfluenced fashion, into a second pump cell 140 of sensor 110 which can also be referred to as an “NO.sub.x pump cell.” Second pump cell 140 has an NO.sub.x pump electrode 142 and an NO.sub.x counter-electrode 144, and adjoins a second cavity 145 in the interior of sensor element 110. Second cavity 145 is separated from first cavity 126 by one of diffusion barriers 128. At least one of the two electrodes (NO.sub.x pump electrode 142 and/or NO.sub.x counter-electrode 144) is configured in such a way that upon application of a voltage, further molecular oxygen can be generated by catalysis from the NO.sub.x measured-gas component and is formed in second pump cell 140.

[0043] Whereas NO.sub.x pump electrode 142 has an electrically conductive connection that leads to common terminal COM, NO.sub.x counter-electrode 144 has a fourth electrically conductive connection 146 by way of which a second pump current I.sub.p2 can be applied to second pump cell 140. Fourth electrically conductive connection 146 is connected for that purpose to a second terminal P2 of external electronic control device 122. Upon application of a second pump current I.sub.P2 to second pump cell 140, a portion of further oxygen ions that have been formed from the further molecular oxygen is transported into reference gas space 138.

[0044] Sensor element 110 furthermore possesses a heating element 148 that has a heating lead 150 having leads HTR+ and HTR− by way of which a heating current can be introduced into heating element 148 which, by generating a heat output, can bring sensor element 110 to the desired temperature.

[0045] Control device 122 has an analog-digital converter 152 that is connected to terminal Vs for the supply voltage. Control device 122 furthermore has a COM voltage source 154 that is connected to common terminal COM. Control device 122 furthermore has an excitation signal source 156 that is connected to the positive pole of an operational amplifier 158. In the exemplifying embodiment shown, operational amplifier 158 is a voltage follower. COM voltage source 154 is also connected to the positive pole of operational amplifier 158. Operational amplifier 158 is in turn connected to second terminal P2. A measuring resistor 160 is disposed in fourth electrical lead 146 between second terminal P2 and counter-electrode 144.

[0046] FIG. 3 shows a first example of a time course of electrical voltages and a measured signal in sensor 100. Time is plotted on X axis 162. Listed from top to bottom, the heating voltage of heating element 148, the electrical voltage U.sub.P2 applied to second pump cell 140, and the voltage drop U.sub.IP2 at measuring resistor 160 are plotted on Y axis 164. The voltage drop U.sub.IP2 at measuring resistor 160 represents the measured signal. The temperature of sensor element 110 is controlled by pulse width modulation (PWM) of the heater power supply (voltage or current). A curve 166 that represents the heating voltage of heating element 148 correspondingly shows at least a first phase or a first time span 168 in which an electrical voltage is applied to heating element 148 and heating element 148 is thus switched on, and a second phase or a second time span 170 in which no electrical voltage is applied to heating element 148 and heating element 148 is thus switched off. Second time span 170 follows first time span 168. A sum of first time span 168 and second time span 170 is, for example, 500 ms. In the exemplifying embodiment shown, curve 166 furthermore exhibits a third phase or a third time span 172 in which an electrical voltage is applied to heating element 148 and heating element 148 is thus switched on, and a fourth phase or a fourth time span 174 in which no electrical voltage is applied to heating element 148 and heating element 148 is thus switched off. Fourth time span 174 follows third time span 172. A sum of third time span 172 and fourth time span 174 is, for example, 500 ms.

[0047] In order to carry out a diagnosis of fourth electrical lead 146 that connects second separate terminal P2 to pump cell 140 or to counter-electrode 144, a voltage excitation of second pump cell 140 is carried out by way of control device 122 in order to generate a measured signal at measuring resistor 160. A predetermined electrical voltage 176 is thus applied to second pump cell 140 via common terminal COM. A voltage excitation of second pump cell 140 is carried out by way of excitation signal source 156. The predetermined electrical voltage is raised for a first predetermined time 178, and the predetermined electrical voltage 176 is lowered for a second predetermined time 180. The exact sequence of the modification of the voltage is not relevant. Alternatively, for example, the predetermined electrical voltage can first be lowered or decreased, and then raised. The voltage excitation is carried out in such a way that an integral of the applied electrical voltage for the first predetermined time 178 and second predetermined time 180 has a value of zero. This can be achieved by way of identical voltage amplitudes over time spans of identical length. In the exemplifying embodiment shown, first predetermined time 178 and second predetermined time 180 are of identical length. For example, proceeding from an electrical voltage of 425 mV applied to second pump cell 140, the electrical voltage is raised to 700 mV for a first predetermined time 178 and then lowered to 150 mV for second predetermined time 180. This occurs in a time span in which heating element 148 is switched on, for example in first time span 168 and in third time span 172. This generates a measured signal 182 at measuring resistor 160. Fourth electrically conductive connection 146 is identified as intact if measured signal 182 has a value not equal to zero for first predetermined time 178 and second predetermined time 180, and is identified as defective if measured signal 182 has a value of zero for first predetermined time 178 and second predetermined time 180. In the exemplifying embodiment shown, upon voltage excitation measured signal 182 has an approximately sinusoidal profile 184 (indicated by an arrow) in first time span 168, and has a value of zero in third time span 172, so that the signal at point 186 (indicated by an arrow) does not change. This means that no current is flowing at point 186, which indicates an interruption of fourth electrical lead 146.

[0048] In the context of a modification, the voltage excitation encompasses a single modification of the predetermined electrical voltage for a predetermined time. For example, the predetermined electrical voltage is raised for the predetermined time. Fourth electrically conductive lead 146 is identified in this context as intact if measured signal 182 exhibits a value not equal to zero for the predetermined time, and is identified as defective if measured signal 182 exhibits a value of zero for the predetermined time. With sensor 100 in the measurement state, the predetermined electrical voltage is thus briefly raised by the hardware by an amount equal to a specific potential, in the form of a one-time pulse in one direction. What is important here is not the duration of the pulse but the change in voltage. The advantage here is that the time during which measured signal 182 is distorted by the voltage excursion is shorter than in the context of an additional counter-pulse in the form of an offset-free pulse.

[0049] FIG. 4 shows a second example of a time course of electrical voltages and a measured signal in sensor 100. Only the differences with respect to the exemplifying embodiment shown in FIG. 3 are described. Identical components or features are labeled with identical reference characters. Time is plotted on X axis 162. Listed from top to bottom, the heating voltage of heating element 148, the electrical voltage U.sub.P2 applied to second pump cell 140, and the voltage drop U.sub.P2 at measuring resistor 160 are plotted on Y axis 164. The voltage drop U.sub.P2 at measuring resistor 160 represents the measured signal. The temperature of sensor element 110 is controlled by pulse width modulation (PWM) of the heating power supply (voltage or current). A curve 166 that represents the heating voltage of heating element 148 correspondingly shows at least a first phase or a first time span 168 in which an electrical voltage is applied to heating element 148 and heating element 148 is thus switched on, and a second phase or a second time span 170 in which no electrical voltage is applied to heating element 148 and heating element 148 is thus switched off. Second time span 170 follows first time span 168. A sum of first time span 168 and second time span 170 is, for example, 500 ms. In the exemplifying embodiment shown, curve 166 furthermore exhibits a third phase or a third time span 172 in which an electrical voltage is applied to heating element 148 and heating element 148 is thus switched on, and a fourth phase or a fourth time span 174 in which no electrical voltage is applied to heating element 148 and heating element 148 is thus switched off. Fourth time span 174 follows third time span 172. A sum of third time span 172 and fourth time span 174 is, for example, 500 ms.

[0050] In order to carry out a diagnosis of fourth electrical lead 146 that connects second separate terminal P2 to pump cell 140 or to counter-electrode 144, a current excitation of second pump cell 140 is carried out by way of control device 122 in order to generate a measured signal at measuring resistor 160. For example, a predetermined electrical current is applied to pump cell 140 via common terminal COM. A current excitation of second pump cell 140 is carried out by way of excitation signal source 156. The predetermined electrical current is raised for a first predetermined time 178, and the predetermined electrical current is lowered for a second predetermined time 180. The exact sequence of the modification of the current is not relevant.

[0051] Alternatively, for example, the predetermined electrical current can first be lowered or decreased, and then raised. The current excitation is carried out in such a way that an integral of the impressed electrical current has a value of zero for first predetermined time 178 and second predetermined time 180. This can be achieved by way of identical current amplitudes over time spans of identical length. In the exemplifying embodiment shown, first predetermined time 178 and second predetermined time 180 are of identical length. For example, proceeding from an electrical current impressed into second pump cell 140, the electrical current is raised for a first predetermined time 178 and then lowered for second predetermined time 180. This occurs in a time span in which heating element 148 is switched on, for example in first time span 168 and in third time span 172. The current excitation is recognizable from a positive peak 188 and a subsequent negative peak 190 of measured signal 182 at measuring resistor 160. The current excitation generates a voltage excursion in the voltage U.sub.P2 applied to the second pump cell. Fourth electrically conductive connection 146 is identified as intact if the voltage U.sub.P2 applied to the second pump cell falls below a threshold value 192 in first predetermined time 178 and second predetermined time 180, and is identified as defective if the voltage U.sub.P2 applied to the second pump cell exceeds a threshold value 192 in first predetermined time 178 and second predetermined time 180. Threshold value 192 is defined here as a magnitude of the amplitude or absolute value of the change in voltage. In the exemplifying embodiment shown, upon current excitation in first time span 168 the voltage U.sub.P2 applied to the second pump cell has an approximately sinusoidal profile 194, indicated by an arrow, which falls below threshold value 192, and in third time span 172 has an approximately sinusoidal voltage excursion 196, indicated by an arrow, which exceeds threshold value 192.

[0052] FIG. 5 shows a third example of a time course of electrical voltages and a measured signal in sensor 100. Only the differences with respect to the exemplifying embodiment shown in FIG. 3 are described. Identical components or features are labeled with identical reference characters. Time is plotted on X axis 162. Listed from top to bottom, the heating voltage of heating element 148, the electrical voltage U.sub.P2 applied to second pump cell 140 without voltage excitation, the electrical voltage U.sub.P2 applied to second pump cell 140 with voltage excitation, the voltage drop U.sub.P2 at measuring resistor 160, and the voltage drop U.sub.P2 at measuring resistor 160 after low-pass filtering, are plotted on Y axis 164. The voltage drop U.sub.P2 at measuring resistor 160 represents the measured signal. The temperature of sensor element 110 is controlled by pulse width modulation (PWM) of the heating power supply (voltage or current). A curve 166 that represents the heating voltage of heating element 148 correspondingly shows at least a first phase or a first time span 168 in which an electrical voltage is applied to heating element 148 and heating element 148 is thus switched on, and a second phase or a second time span 170 in which no electrical voltage is applied to heating element 148 and heating element 148 is thus switched off. Second time span 170 follows first time span 168. A sum of first time span 168 and second time span 170 is, for example, 500 ms. In the exemplifying embodiment shown, curve 166 furthermore exhibits a third phase or a third time span 172 in which an electrical voltage is applied to heating element 148 and heating element 148 is thus switched on, and a fourth phase or a fourth time span 174 in which no electrical voltage is applied to heating element 148 and heating element 148 is thus switched off. Fourth time span 174 follows third time span 172. A sum of third time span 172 and fourth time span 174 is, for example, 500 ms.

[0053] In order to carry out a diagnosis of fourth electrical lead 146 that connects second separate terminal P2 to pump cell 140 or to counter-electrode 144, a voltage excitation of second pump cell 140 is carried out by way of control device 122 in order to generate a measured signal at measuring resistor 160. For example, a predetermined electrical voltage 176 is applied to pump cell 140 via common terminal COM. A voltage excitation of second pump cell 140 is carried out by way of excitation signal source 156. The voltage excitation encompasses a periodic modification of the predetermined electrical voltage. This generates a measured signal 182 at measuring resistor 160, the period length being less than an electrochemical time constant of second pump cell 140. Measured signal 182 at measuring resistor 160 therefore exhibits a superposition of the actual measured signal with the periodic voltage excitation. Measured signal 182 is filtered by way of a low-pass filter (not shown in further detail) of control device 122, and transferred via an interface of the control device to an engine control device. The predetermined electrical voltage is modified at a frequency that is greater than the bandwidth of the low-pass filter. Low-pass filtering of measured signal 182 yields signal 198 from which the periodic voltage excitation has been removed. The measured signal for NO.sub.x is therefore not distorted. Fourth electrically conductive connection 146 is identified as intact if measured signal 182 before low-pass filtering (i.e., the raw signal) exhibits a periodic change 200, and is identified as defective if measured signal 182 before low-pass filtering exhibits no periodic change 200. A periodic change of this kind is caused by the frequency of the voltage change in the context of an intact electrical connection. In the exemplifying embodiment shown, a periodic change 200 exists in first time span 168, whereas no periodic change 200 exists in third time span 172. This indicates that an interruption of fourth electrical lead 146 exists in third time span 172. The frequency on fourth electrical lead 146 does not obligatorily need to be excited over the entire time span. Application of the higher-frequency voltage change in the region around almost 0 ppm NO.sub.x is sufficient for electrical diagnosis.