A method for detecting deviations in the reference potential of a gas sensor and a gas sensor.

Abstract

To detect deviation in reference potential.SOLUTION: A gas sensor 100 comprises a sensor element 101 and a control apparatus 95, and detects specific gas concentration, the concentration of the specific gas in a measured gas. The sensor element 101 comprises: element body (layers 1-6) including an oxygen-ion conductive solid electrolyte layer, which is provided inside thereof with a measured gas circulation part for introducing and circulating the measured gas; a measuring electrode 44 arranged in a third internal vacancy 61 of the measured gas circulation part; and a reference electrode 42 arranged in the element body so as to contact reference gas which serves as reference for detecting specific gas concentration. The control apparatus 95 measures voltage Vrg between ground and the reference electrode 42, and based on the voltage Vrg detects deviation of reference potential which is potential of the reference electrode 42.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a gas sensor and a method for grasping the deviation of the reference potential of the gas sensor.

Background Art

[0002] Conventionally, gas sensors for detecting the concentration of specific gases such as NOx in a measured gas such as automotive exhaust gas are known. For example, the sensor element of the gas sensor described in Patent Document 1 includes a laminate having a plurality of oxygen ion conductive solid electrolyte layers and provided therein with a measured gas flow portion for introducing and flowing the measured gas, a measurement electrode disposed in the measured gas flow portion, a measured gas side electrode disposed on a portion of the laminate exposed to the measured gas, a reference electrode disposed inside the laminate, and a porous reference gas introduction layer for introducing a reference gas (e.g., air) serving as a reference for detecting the concentration of a specific gas in the measured gas and flowing it through the reference electrode. In this gas sensor, the concentration of a specific gas in the measured gas is detected based on the electromotive force generated between the reference electrode and the measurement electrode. Further, this gas sensor includes a reference gas adjustment means for flowing a control current between the reference electrode and the measured gas side electrode to draw in oxygen around the reference electrode. In Patent Document 1, it is described that by this reference gas adjustment means drawing in oxygen around the reference electrode, when the oxygen concentration of the reference gas around the reference electrode temporarily decreases, the decrease in the oxygen concentration can be compensated, and a decrease in the detection accuracy of the specific gas concentration can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, even when oxygen is drawn in around the reference electrode using a reference gas adjustment means, as in the gas sensor described in Patent Document 1, it was difficult to maintain a perfectly constant oxygen concentration around the reference electrode. When the oxygen concentration around the reference electrode changes, the potential of the reference electrode changes, and the detection accuracy of a specific gas concentration decreases. Therefore, there was a need to understand the deviation in the potential of the reference electrode.

[0005] This invention was made to solve these problems, and its main purpose is to detect deviations in the reference potential. [Means for solving the problem]

[0006] To achieve the main objectives described above, the present invention employs the following means.

[0007] [1] The gas sensor of the present invention is A gas sensor comprising a sensor element and a control device, which detects a specific gas concentration, which is the concentration of a specific gas in a gas to be measured, The aforementioned sensor element is The element body has an oxygen ion conductive solid electrolyte layer and is provided with a gas flow section inside through which the gas to be measured is introduced and circulated, A measuring electrode is provided in the measuring chamber of the gas flow section to be measured, Inside the element body, a reference electrode is provided, which is arranged in contact with a reference gas that serves as a reference for detecting the specific gas concentration. Equipped with, The control device measures the voltage between ground and the reference electrode, and based on the measured voltage, determines the deviation of the reference potential, which is the potential of the reference electrode. It is.

[0008] In this gas sensor, the control unit measures the voltage between ground and the reference electrode. This voltage changes in response to changes in the oxygen concentration around the reference electrode, i.e., changes in the reference potential, which is the potential of the reference electrode. Therefore, the deviation of the reference potential can be determined based on this voltage.

[0009] In this case, the control device may determine the deviation of the reference potential by comparing the measured voltage between ground and the reference electrode with a normal value or an acceptable range. Specific examples of determining the reference potential include comparing the measured value with a normal value or an acceptable range, and calculating a value representing the deviation of the reference potential based on the measured value. More specifically, examples include comparing the magnitude relationship between the measured value and the normal value, calculating the difference or ratio between the measured value and the normal value, and determining whether the measured value is within an acceptable range. The control device may determine the deviation of the reference potential by performing one or more of these actions.

[0010] [2] In the gas sensor described above (the gas sensor described in [1] above), the sensor element comprises a reference gas adjustment pump cell comprising a gas-side electrode provided on the element body so as to be in contact with the gas to be measured, and a reference electrode. The control device may control the reference gas adjustment pump cell to pump oxygen from around the reference electrode to around the gas-side electrode if the measured voltage is greater than an allowable range, and control the reference gas adjustment pump cell to pump oxygen from around the gas-side electrode to around the reference electrode if the measured voltage is less than an allowable range. In this way, the oxygen concentration around the reference electrode can be adjusted according to the deviation of the reference potential, thereby reducing the deviation of the reference potential and suppressing a decrease in the detection accuracy of a specific gas concentration. The control device may determine whether the measured voltage is greater than or less than an allowable range by, for example, comparing the measured voltage with the allowable range, or by comparing the amount of deviation of the reference potential based on the measured voltage with the allowable range.

[0011] [3] In the gas sensor described above (the gas sensor described in [1] or [2] above), the sensor element comprises a measuring pump cell comprising an external measuring electrode provided on the outside of the element body so as to be in contact with the gas to be measured, and the measuring electrode, the control device performs a measuring pump control process to control the measuring pump cell so that the measuring voltage, which is the voltage between the measuring electrode and the reference electrode, becomes a target measuring voltage, the control device detects the concentration of the specific gas in the gas to be measured based on the pump current flowing through the measuring pump cell by the measuring pump control process, and the control device may correct the control of the measuring pump cell in the measuring pump control process based on the deviation of the reference potential that has been identified. In this way, even if a deviation occurs in the reference potential, a decrease in the detection accuracy of the specific gas concentration can be suppressed by correcting the control of the measuring pump cell.

[0012] [4] In the gas sensor described above (the gas sensor described in [3] above), the sensor element is configured to include an internal adjustment electrode disposed in an oxygen concentration adjustment chamber located upstream of the measurement chamber in the gas flow section to be measured, and includes an adjustment pump cell for adjusting the oxygen concentration in the oxygen concentration adjustment chamber, and the control device performs an adjustment pump control process to adjust the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump cell so that the adjustment voltage, which is the voltage between the internal adjustment electrode and the reference electrode, becomes the adjustment voltage target value, and the control device may correct the control of the adjustment pump cell in the adjustment pump control process based on the deviation of the reference potential that has been determined. In this way, when a deviation occurs in the reference potential, not only is the control of the measurement pump cell corrected, but the control of the adjustment pump cell is also corrected, so the decrease in the detection accuracy of a specific gas concentration can be further suppressed.

[0013] [5] In the gas sensor described above (the gas sensor described in any of [1] to [4] above), the sensor element is provided with a ground terminal connected to the ground, and the control device may measure the voltage between the ground terminal and the reference electrode as the voltage between the ground and the reference electrode.

[0014] [6] In the gas sensor (the gas sensor described in [5] above), the sensor element includes a heater for heating the element body, and the ground terminal may be a terminal of the heater.

[0015] [7] The method for grasping the deviation of the reference potential of the gas sensor of the present invention is a method for grasping the deviation of the reference potential of a gas sensor that detects a specific gas concentration, which is the concentration of a specific gas in the gas to be measured, where the gas sensor has a solid electrolyte layer with oxygen ion conductivity, and an element body provided therein with a gas to be measured flow section for introducing and flowing the gas to be measured, a measurement electrode disposed in the gas to be measured flow section, and a reference electrode disposed inside the element body so as to contact a reference gas that serves as a reference for detecting the specific gas concentration, and includes a sensor element having the above, measuring the voltage between the ground and the reference electrode, and grasping the deviation of the reference potential, which is the potential of the reference electrode, based on the measured voltage, and includes the above.

[0016] In this grasping method, similar to the gas sensor described above, the deviation of the reference potential can be grasped. In addition, in this grasping method, various aspects of any of the above gas sensors (any of the gas sensors in [1] to [6]) may be adopted, or steps for realizing each function of any of the above gas sensors (any of the gas sensors in [1] to [6]) may be added.

Brief Description of the Drawings

[0017] [Figure 1] Schematic cross-sectional view of the gas sensor 100. [Figure 2] Schematic diagram showing the inside of the sensor element 101, the inside of the control device 95, and the wiring between the sensor element 101 and the control device 95. [Figure 3]Block diagram showing the electrical connection relationship between the control device 95, each cell, and the heater unit 70. [Figure 4] Flowchart showing an example of the reference potential adjustment process. [Figure 5] Flowchart showing an example of the control correction process. [Figure 6] Schematic cross-sectional view of the sensor element 201 of the modification.

Embodiment for Carrying Out the Invention

[0018] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically showing an example of the configuration of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a schematic view showing the inside of the sensor element 101, the inside of the control device 95, and the wiring between the sensor element 101 and the control device 95. FIG. 3 is a block diagram showing the electrical connection relationship between the control device 95, each cell, and the heater 72. This gas sensor 100 is attached to a pipe such as an exhaust gas pipe of an internal combustion engine such as a gasoline engine or a diesel engine. The gas sensor 100 detects the concentration of a specific gas such as NOx or ammonia in the measured gas, taking the exhaust gas of the internal combustion engine as the measured gas. In the present embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The gas sensor 100 includes a sensor element 101 having a long rectangular parallelepiped shape, each cell 15, 21, 41, 50, 80 to 83 configured to include a part of the sensor element 101, a heater unit 70 provided inside the sensor element 101, and a control device 95 that controls the entire gas sensor 100.

[0019] The sensor element 101 is a laminated element having six layers stacked in this order from the bottom as seen in the drawing: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, each consisting of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO2). Furthermore, the solid electrolytes forming these six layers are dense and airtight. Such a sensor element 101 is manufactured, for example, by performing predetermined processing and printing circuit patterns on ceramic green sheets corresponding to each layer, stacking them, and then firing them to integrate them.

[0020] On the tip side of the sensor element 101 (the left end side in Figure 1), a gas inlet 10, a first diffusion rate-limiting section 11, a buffer space 12, a second diffusion rate-limiting section 13, a first internal cavity 20, a third diffusion rate-limiting section 30, a second internal cavity 40, a fourth diffusion rate-limiting section 60, and a third internal cavity 61 are formed adjacent to each other in this order, communicating with each other.

[0021] The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are spaces inside the sensor element 101, provided in a manner in which the spacer layer 5 has been hollowed out, with the upper part partitioned by the lower surface of the second solid electrolyte layer 6, the lower part partitioned by the upper surface of the first solid electrolyte layer 4, and the sides partitioned by the side surface of the spacer layer 5.

[0022] The first diffusion rate-limiting section 11, the second diffusion rate-limiting section 13, and the third diffusion rate-limiting section 30 are all provided as two horizontally elongated slits (with their longitudinal openings perpendicular to the drawing). The fourth diffusion rate-limiting section 60 is provided as a single horizontally elongated slit (with its longitudinal openings perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. The section from the gas inlet 10 to the third internal cavity 61 is also referred to as the gas flow section under measurement.

[0023] The sensor element 101 is equipped with a reference gas introduction section 49 that flows a reference gas to the reference electrode 42 from outside the sensor element 101 when measuring the NOx concentration. The reference gas introduction section 49 has a reference gas introduction space 43 and a reference gas introduction layer 48. The reference gas introduction space 43 is a space provided inward from the rear end surface of the sensor element 101. The reference gas introduction space 43 is located between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, and is provided at a position where its sides are partitioned by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 opens to the rear end surface of the sensor element 101, and this opening functions as an inlet 49a of the reference gas introduction section 49. The reference gas is introduced into the reference gas introduction space 43 from this inlet 49a. The reference gas introduction section 49 introduces the reference gas introduced from the inlet 49a to the reference electrode 42 while imparting a predetermined diffusion resistance to it. In this embodiment, the reference gas is the atmosphere.

[0024] The reference gas introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is a porous material made of ceramics such as alumina. A portion of the upper surface of the reference gas introduction layer 48 is exposed within the reference gas introduction space 43. The reference gas introduction layer 48 is formed to cover the reference electrode 42. The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

[0025] The reference electrode 42 is formed in such a manner that it is sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. Furthermore, as will be described later, it is possible to measure the oxygen concentration (partial pressure of oxygen) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 using the reference electrode 42. The reference electrode 42 is formed as a porous cermet electrode (for example, a cermet electrode made of Pt and ZrO2).

[0026] In the gas flow section, the gas inlet 10 is a part that opens to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion rate-limiting section 11 is a part that imparts a predetermined diffusion resistance to the gas to be measured taken in from the gas inlet 10. The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate-limiting section 11 to the second diffusion rate-limiting section 13. The second diffusion rate-limiting section 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas to be measured, which is rapidly drawn into the sensor element 101 from the gas inlet 10 due to pressure fluctuations of the gas to be measured in the external space (pulsations of exhaust pressure if the gas to be measured is automobile exhaust gas), is not directly introduced into the first internal cavity 20. Instead, the pressure fluctuations of the gas to be measured are canceled out through the first diffusion rate-limiting unit 11, the buffer space 12, and the second diffusion rate-limiting unit 13 before being introduced into the first internal cavity 20. As a result, the pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 become almost negligible. The first internal cavity 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate-limiting unit 13. This partial pressure of oxygen is adjusted by the operation of the main pump cell 21.

[0027] The main pump cell 21 is an electrochemical pump cell comprising an inner pump electrode 22 having a ceiling electrode portion 22a provided over almost the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, an outer pump electrode 23 provided in a manner exposed to the external space in a region corresponding to the ceiling electrode portion 22a on the upper surface of the second solid electrolyte layer 6, and the second solid electrolyte layer 6 sandwiched between these electrodes.

[0028] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that partition the first internal cavity 20, and the spacer layer 5 that provides the side walls. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. A side electrode portion (not shown) is formed on the side wall surface (inner surface) of the spacer layer 5 that constitutes both side walls of the first internal cavity 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and is arranged in a tunnel-shaped structure at the location where the side electrode portion is installed.

[0029] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, cermet electrodes made of Pt containing 1% Au and ZrO2). The inner pump electrode 22, which comes into contact with the gas to be measured, is formed using a material with reduced reducing ability to NOx components in the gas to be measured.

[0030] In the main pump cell 21, by applying a desired pump voltage Vp0 between the inner pump electrode 22 and the outer pump electrode 23, and flowing a pump current Ip0 in the positive or negative direction between the inner pump electrode 22 and the outer pump electrode 23, it is possible to pump oxygen from the first internal cavity 20 to the external space, or pump oxygen from the external space into the first internal cavity 20.

[0031] Furthermore, in order to detect the oxygen concentration (partial pressure of oxygen) in the atmosphere in the first internal cavity 20, an electrochemical sensor cell, i.e., a main pump control oxygen partial pressure detection sensor cell 80, is constructed using an inner pump electrode 22, a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, a third substrate layer 3, and a reference electrode 42.

[0032] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be determined by measuring the electromotive force (voltage V0) in the oxygen partial pressure detection sensor cell 80 for main pump control. Furthermore, the pump current Ip0 is controlled by feedback control of the pump voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes a target value. As a result, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0033] The third diffusion rate-limiting section 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (partial pressure of oxygen) is controlled by the operation of the main pump cell 21 in the first internal cavity 20, and guides the gas to be measured to the second internal cavity 40.

[0034] The second internal cavity 40 is provided as a space for further adjustment of the oxygen partial pressure by the auxiliary pump cell 50 for the gas to be measured, which is introduced through the third diffusion rate-limiting unit 30 after the oxygen concentration (oxygen partial pressure) has been adjusted in the first internal cavity 20. As a result, the oxygen concentration in the second internal cavity 40 can be kept constant with high precision, enabling highly accurate NOx concentration measurement in the gas sensor 100.

[0035] The auxiliary pump cell 50 is an auxiliary electrochemical pump cell composed of an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided over substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40, an outer pump electrode 23 (not limited to the outer pump electrode 23, any suitable electrode on the outside of the sensor element 101 is sufficient), and the second solid electrolyte layer 6.

[0036] The auxiliary pump electrode 51 is disposed within the second internal cavity 40 in a tunnel-shaped structure similar to that of the inner pump electrode 22 provided within the first internal cavity 20. Specifically, a ceiling electrode portion 51a is formed on the second solid electrolyte layer 6 which forms the ceiling surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 which forms the bottom surface of the second internal cavity 40. Side electrode portions (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b are formed on both walls of the spacer layer 5 which forms the side walls of the second internal cavity 40, creating a tunnel-shaped structure. The auxiliary pump electrode 51 is also formed using a material with weakened reduction ability for NOx components in the gas being measured, similar to the inner pump electrode 22.

[0037] In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, it is possible to pump oxygen from the atmosphere in the second internal cavity 40 to the outside space, or pump oxygen from the outside space into the second internal cavity 40.

[0038] Furthermore, in order to control the partial pressure of oxygen in the atmosphere within the second internal cavity 40, an electrochemical sensor cell, namely an oxygen partial pressure detection sensor cell 81 for auxiliary pump control, is constructed using an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, and a third substrate layer 3.

[0039] Furthermore, the auxiliary pump cell 50 is pumped by a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor cell 81 for auxiliary pump control. As a result, the oxygen partial pressure in the atmosphere inside the second internal cavity 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

[0040] Furthermore, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input to the oxygen partial pressure detection sensor cell 80 for main pump control as a control signal, and the aforementioned target value of its voltage V0 is controlled so that the gradient of the oxygen partial pressure in the gas to be measured, introduced from the third diffusion rate-limiting unit 30 into the second internal cavity 40, remains constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm through the action of the main pump cell 21 and the auxiliary pump cell 50.

[0041] The fourth diffusion rate-limiting section 60 is the part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (partial pressure of oxygen) is controlled by the operation of the auxiliary pump cell 50 in the second internal cavity 40, and guides the gas to be measured to the third internal cavity 61. The fourth diffusion rate-limiting section 60 plays a role in limiting the amount of NOx flowing into the third internal cavity 61.

[0042] The third internal cavity 61 is provided as a space for performing processing related to the measurement of nitrogen oxide (NOx) concentration in the gas to be measured, which is introduced through the fourth diffusion rate-limiting unit 60 after the oxygen concentration (partial pressure of oxygen) has been adjusted in advance in the second internal cavity 40. The NOx concentration is measured mainly in the third internal cavity 61 by the operation of the measuring pump cell 41.

[0043] The measuring pump cell 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61. The measuring pump cell 41 is an electrochemical pump cell composed of a measuring electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61, an outer pump electrode 23, a second solid electrolyte layer 6, a spacer layer 5, and the first solid electrolyte layer 4. The measuring electrode 44 is a porous cermet electrode made of a material that has a higher reduction capacity for NOx components in the gas to be measured than the inner pump electrode 22. The measuring electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere within the third internal cavity 61.

[0044] In the measuring pump cell 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 can be pumped out, and its amount can be detected as the pump current Ip2.

[0045] Furthermore, in order to detect the partial oxygen pressure around the measuring electrode 44, an electrochemical sensor cell, namely an oxygen partial pressure detection sensor cell 82 for controlling the measuring pump, is formed by the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor cell 82 for controlling the measuring pump.

[0046] The gas to be measured, introduced into the second internal cavity 40, reaches the measuring electrode 44 in the third internal cavity 61 via the fourth diffusion rate-limiting section 60 under controlled conditions of oxygen partial pressure. Nitrogen oxides in the gas to be measured surrounding the measuring electrode 44 are reduced (2NO → N2 + O2) to generate oxygen. This generated oxygen is then pumped by the measuring pump cell 41, and at this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for measuring pump control remains constant (target value). Since the amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the nitrogen oxide concentration in the gas to be measured is calculated using the pump current Ip2 in the measuring pump cell 41.

[0047] Furthermore, an electrochemical sensor cell 83 is constructed from a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, a third substrate layer 3, an outer pump electrode 23, and a reference electrode 42. The electromotive force (voltage Vref) obtained by this sensor cell 83 makes it possible to detect the partial pressure of oxygen in the gas being measured outside the sensor.

[0048] Furthermore, an electrochemical reference gas adjustment pump cell 90 is composed of a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, a third substrate layer 3, an outer pump electrode 23, and a reference electrode 42. This reference gas adjustment pump cell 90 pumps oxygen when a control current (pump current Ip3) flows due to a control voltage (voltage Vp3) applied by a power supply circuit 92 connected between the outer pump electrode 23 and the reference electrode 42. As a result, the reference gas adjustment pump cell 90 can pump oxygen from around the outer pump electrode 23 to around the reference electrode 42, and pump oxygen from around the reference electrode 42 to around the outer pump electrode 23.

[0049] In a gas sensor 100 having such a configuration, the gas to be measured, whose oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx) by operating the main pump cell 21 and the auxiliary pump cell 50, is supplied to the measuring pump cell 41. Therefore, the NOx concentration in the gas to be measured can be determined based on the pump current Ip2 that flows as oxygen generated by the reduction of NOx is pumped out from the measuring pump cell 41, which is approximately proportional to the NOx concentration in the gas to be measured.

[0050] Furthermore, the sensor element 101 is equipped with a heater section 70 that plays a role in temperature control by heating and maintaining the sensor element 101 to enhance the oxygen ion conductivity of the solid electrolyte. The heater section 70 comprises a heater 72, a heater insulating layer 74, and pressure relief holes 75.

[0051] The heater 72 is an electrical resistor formed sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 generates heat when powered by the heater power supply 76 (see Figures 2 and 3), and heats and maintains the temperature of the solid electrolyte forming the sensor element 101.

[0052] Furthermore, the heater 72 is embedded throughout the entire area from the first internal cavity 20 to the third internal cavity 61, making it possible to adjust the entire sensor element 101 to a temperature at which the solid electrolyte is activated.

[0053] The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 using an insulator such as alumina. The heater insulating layer 74 is formed to provide electrical insulation between the second substrate layer 2 and the heater 72, and between the third substrate layer 3 and the heater 72.

[0054] The pressure relief hole 75 is a portion that penetrates the third substrate layer 3 and the reference gas introduction layer 48 and communicates with the reference gas introduction space 43, and is formed for the purpose of mitigating the rise in internal pressure due to the rise in temperature within the heater insulating layer 74.

[0055] A connector electrode 71 is provided on the rear end of the sensor element 101. The connector electrode 71 comprises connector electrodes 71a to 71d provided on the rear end of the upper surface of the sensor element 101, and connector electrodes 71e to 71h provided on the rear end of the lower surface of the sensor element 101. The connector electrode 71 functions as a terminal for electrically connecting the sensor element 101 to the outside. The connector electrodes 71a to 71e are electrically connected one-to-one with the outer pump electrode 23, the inner pump electrode 22, the auxiliary pump electrode 51, the measuring electrode 44, and the reference electrode 42 via leads provided inside the sensor element 101 (see Figure 2). One end of the heater 72 is connected to the connector electrode 71f via a current-carrying lead 77f provided inside the sensor element 101. The other end of the heater 72 is connected to the connector electrode 71g via a current-carrying lead 77g provided inside the sensor element 101. In Figure 2, the current-carrying lead 77f is schematically shown and therefore omitted from the illustration, but the current-carrying lead 77f also includes the conductor in the through-hole 73 in Figure 1. In addition, a voltage-measuring lead 77h is connected in parallel with the current-carrying lead 77f to one end of the heater 72, and the other end of the heater 72 is connected to the connector electrode 71h via this voltage-measuring lead 77h. Also, as shown in Figure 2, the connector electrode 71f is connected to ground (GND). The connector electrode 71f is an example of a ground terminal. The potential of ground (GND) is used as the reference for the potential of the control device 95 circuit. It is preferable that ground (GND) is earthed.

[0056] As shown in Figure 3, the control device 95 includes the variable power supplies 24, 46, and 52 described above, a power supply circuit 92, a heater power supply 76, a main pump voltage acquisition unit 85, an auxiliary pump voltage acquisition unit 86, a measuring voltage acquisition unit 87, a voltage acquisition unit 88, a reference electrode voltage acquisition unit 89, and a control unit 96.

[0057] As shown in Figure 2, the main pump voltage acquisition unit 85 is connected to the connector electrodes 71b and 71e by leads. This allows the main pump voltage acquisition unit 85 to acquire the voltage between the inner pump electrode 22 and the reference electrode 42, i.e., the voltage V0 of the main pump control oxygen partial pressure detection sensor cell 80 described above. Similarly, the auxiliary pump voltage acquisition unit 86 is connected to the connector electrodes 71c and 71e, respectively, to acquire the voltage V1 between the auxiliary pump electrode 51 and the reference electrode 42 of the auxiliary pump control oxygen partial pressure detection sensor cell 81. The measurement voltage acquisition unit 87 is connected to the connector electrodes 71d and 71e, respectively, to acquire the voltage V2 between the measurement electrode 44 and the reference electrode 42 of the measurement pump control oxygen partial pressure detection sensor cell 82. The voltage acquisition unit 88 is connected to the connector electrodes 71a and 71e, respectively, to acquire the voltage Vref between the outer pump electrode 23 and the reference electrode 42 of the sensor cell 83.

[0058] The reference electrode voltage acquisition unit 89 is connected to the connector electrode 71f and the connector electrode 71e by leads. As a result, the reference electrode voltage acquisition unit 89 acquires the voltage Vrg between the connector electrode 71f and the reference electrode 42. Since the connector electrode 71f is connected to ground as described above, the voltage Vrg acquired by the reference electrode voltage acquisition unit 89 is the voltage between ground and the reference electrode 42.

[0059] As shown in Figure 2, the heater power supply 76 is connected to the connector electrodes 71f and 71g via leads, and supplies power to the heater 72 by applying a voltage between the connector electrodes 71f and 71g. Since the connector electrode 71f is connected to ground, the connector electrode 71f is the low-potential electrode, and the connector electrode 71g is the high-potential electrode. Although both the reference electrode voltage acquisition unit 89 and the heater power supply 76 are connected to the connector electrode 71f, as shown in Figure 2, the connection point between the reference electrode voltage acquisition unit 89 and the connector electrode 71f is closer to ground than the connection point between the heater power supply 76 and the connector electrode 71f. Therefore, the heater current flowing between the heater power supply 76 and the heater 72 does not flow in the circuit for the reference electrode voltage acquisition unit 89 to acquire the voltage Vrg, i.e., the circuit from the connector electrode 71e to ground.

[0060] Although the wiring is not shown in Figure 2, the variable power supplies 24, 52, 46 and the power supply circuit 92 shown in Figures 1 and 3 are actually connected to the electrodes inside the sensor element 101 via the connector electrode 71. The pump currents Ip0, Ip1, Ip2, and Ip3 mentioned above are also acquired (measured) by current acquisition units (not shown) that are actually connected to the electrodes inside the sensor element 101 via the connector electrode 71, similar to the voltage acquisition units 85 to 89.

[0061] The control unit 96 is a microprocessor equipped with a CPU 97 and a memory unit 98. The memory unit 98 is a non-volatile memory that can be rewritten and can store various programs and data, for example. The control unit 96 receives the voltages V0, V1, V2, Vref, and Vrg acquired by the voltage acquisition units 85 to 89 described above. The control unit 96 also receives the pump currents Ip0, Ip1, Ip2, and Ip3 acquired by a current acquisition unit (not shown). Furthermore, the control unit 96 controls the voltages Vp0, Vp1, Vp2, and Vp3 output by the variable power supplies 24, 46, 52 and the power supply circuit 92 by outputting control signals to them, thereby controlling the main pump cell 21, the measuring pump cell 41, the auxiliary pump cell 50, and the reference gas adjustment pump cell 90. The control unit 96 controls the power supplied by the heater power supply 76 to the heater 72 by outputting control signals to the heater power supply 76, thereby adjusting the temperature of the sensor element 101. The memory unit 98 also stores target values ​​V0*, V1*, V2*, which will be described later. The CPU 97 of the control unit 96 controls cells 21, 41, and 50 by referring to these target values ​​V0*, V1*, V2*.

[0062] The control unit 96 performs auxiliary pump control processing to control the auxiliary pump cell 50 so that the oxygen concentration in the second internal cavity 40 reaches a target concentration. Specifically, the control unit 96 controls the auxiliary pump cell 50 by feedback control of the voltage Vp1 of the variable power supply 52 so that the voltage V1 becomes a constant value (referred to as the target value V1*). The target value V1* is defined as a value such that the oxygen concentration in the second internal cavity 40 becomes a predetermined low concentration that does not substantially affect the measurement of NOx.

[0063] The control unit 96 performs a main pump control process to control the main pump cell 21 so that the pump current Ip1 flowing when the auxiliary pump cell 50 adjusts the oxygen concentration in the second internal cavity 40 by the auxiliary pump control process becomes a target current (referred to as target current Ip1*). Specifically, the control unit 96 sets a target value of voltage V0 (referred to as target value V0*) based on the pump current Ip1 so that the pump current Ip1 flowing due to voltage Vp1 becomes a constant target current Ip1* (feedback control). Then, the control unit 96 feedback controls the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (i.e., so that the oxygen concentration in the first internal cavity 20 becomes the target concentration). This main pump control process ensures that the gradient of the oxygen partial pressure in the gas to be measured introduced into the second internal cavity 40 from the third diffusion rate-limiting unit 30 remains constant. The target value V0* is set to a value such that the oxygen concentration in the first internal cavity 20 is higher than 0% but lower than 0%. Furthermore, the pump current Ip0 that flows during this main pump control process changes according to the oxygen concentration of the gas to be measured (i.e., the gas to be measured around the sensor element 101) flowing into the gas flow section from the gas inlet 10. Therefore, the control unit 96 can also detect the oxygen concentration in the gas to be measured based on the pump current Ip0.

[0064] The main pump control process and auxiliary pump control process described above are collectively referred to as the adjustment pump control process. The first internal cavity 20 and the second internal cavity 40 are collectively referred to as the oxygen concentration adjustment chamber. The main pump cell 21 and the auxiliary pump cell 50 are collectively referred to as the adjustment pump cell. The control unit 96 performs the adjustment pump control process, causing the adjustment pump cell to adjust the oxygen concentration in the oxygen concentration adjustment chamber.

[0065] Furthermore, the control unit 96 performs a measurement pump control process to control the measurement pump cell 41 so that the voltage V2 becomes a constant value (referred to as the target value V2*) (i.e., so that the oxygen concentration in the third internal cavity 61 becomes a predetermined low concentration). Specifically, the control unit 96 controls the measurement pump cell 41 by feedback control of the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*. Through this measurement pump control process, oxygen is pumped out from the third internal cavity 61.

[0066] The measurement pump control process is performed so that oxygen is pumped out of the third internal cavity 61 so that the oxygen generated by the reduction of NOx in the gas being measured in the third internal cavity 61 becomes virtually zero. The control unit 96 then acquires the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 originating from the specific gas (in this case, NOx), and calculates the NOx concentration in the gas being measured based on this pump current Ip2.

[0067] The memory unit 98 stores relationships between the pump current Ip2 and NOx concentration, such as relational equations (e.g., linear or quadratic functions) or maps. Such relational equations or maps can be determined in advance through experiments.

[0068] The control unit 96 performs a reference gas adjustment process to control the reference gas adjustment pump cell 90 so that it pumps oxygen from around the outer pump electrode 23 to around the reference electrode 42, or pumps oxygen from around the reference electrode 42 to around the outer pump electrode 23. This reference gas adjustment process adjusts the oxygen concentration around the reference electrode 42. In the reference gas adjustment process, the control unit 96 controls the power supply circuit 92 so that a voltage Vp3 is applied to the reference gas adjustment pump cell 90, thereby supplying a pump current Ip3 to the reference gas adjustment pump cell 90. The voltage Vp3 may be a DC voltage such that the pump current Ip3 becomes a predetermined value (a constant DC current), or it may be a voltage that is repeatedly switched on and off (for example, a pulse voltage). The control unit 96 controls the magnitude of the pump current Ip3 (i.e., the amount of oxygen moved) and the direction of the pump current Ip3 (i.e., the direction of oxygen movement between the outer pump electrode 23 and the reference electrode 42) by changing the magnitude and sign of the voltage Vp3. If the voltage Vp3 is a voltage that is repeatedly switched on and off, the amount of oxygen moved can also be adjusted by the duty cycle (Ton / T), which is the ratio of the repetition period T to the on-time Ton. In this embodiment, the voltage Vp3 is a pulsed voltage, and the control unit 96 controls the amount and direction of oxygen movement by changing the duty cycle and sign of the voltage Vp3. The control unit 96 adjusts the oxygen concentration around the reference electrode 42 by performing a reference gas adjustment process.

[0069] The control unit 96 performs heater control processing to control the heater power supply 76 so that the temperature of the heater 72 reaches the target temperature. Since the temperature of the heater 72 can be expressed as a linear function of the resistance value of the heater 72, in the heater control processing, the control unit 96 controls the heater power supply 76 so that the resistance value of the heater 72 reaches the target resistance value. When the heater control processing starts, first the CPU 97 of the control unit 96 controls the heater power supply 76 to start supplying power to the heater 72 and heat up the heater 72. Then the CPU 97 derives the resistance value of the heater 72 using the three-terminal method. Specifically, the CPU 97 first obtains the first heater voltage Vh1 between the connector electrode 71h and the connector electrode 71g, the second heater voltage Vh2 between the connector electrode 71h and the connector electrode 71f, and the heater current Ih that flows to the heater 72 due to the power supplied from the heater power supply 76, via the voltage acquisition unit and current acquisition unit (not shown) of the control device 95. Next, the CPU 97 derives the heater voltage Vh, which is the voltage across the heater 72 excluding the voltage drop across the power supply leads 77f and 77g, using the relationship Vh = Vh1 - Vh2. Then, the CPU 97 derives the resistance value of the heater 72 by dividing this heater voltage Vh by the heater current Ih. The control unit 96 then outputs a control signal to the heater power supply 76 so that the derived resistance value of the heater 72 becomes the target resistance value, thereby feedback-controlling the power supplied by the heater power supply 76. The heater power supply 76 adjusts the power supplied to the heater 72, for example, by changing the value of the voltage applied to the heater 72.

[0070] An example of the NOx concentration detection process performed by the control unit 96 of the gas sensor 100 configured in this way, which detects the NOx concentration in the gas to be measured, is described below. Before starting the NOx concentration detection process, the CPU 97 of the control unit 96 first starts the heater control process described above to control the temperature of the heater 72 so that it reaches the target temperature (for example, 800°C). Since the temperature of the heater 72 is also affected by the temperature of the gas to be measured, the CPU 97 continues to perform the heater control process even after the NOx concentration detection process has started. When the temperature of the heater 72 reaches near the target temperature, the CPU 97 starts the NOx concentration detection process. In the NOx concentration detection process, the CPU 97 first acquires the voltages V0, V1, V2, and Vref from each of the sensor cells 80 to 83 described above, and starts the control of each of the pump cells 21, 41, and 50 described above, i.e., the adjustment pump control process and the measurement pump control process. In this state, when the gas to be measured is introduced from the gas inlet 10, the gas to be measured passes through the first diffusion rate-limiting section 11, the buffer space 12, and the second diffusion rate-limiting section 13 in that order and reaches the first internal cavity 20. Next, the oxygen concentration of the gas to be measured is adjusted by the main pump cell 21 and the auxiliary pump cell 50 in the first internal cavity 20 and the second internal cavity 40, and the adjusted gas to be measured reaches the third internal cavity 61. Then, the CPU 97 detects the NOx concentration in the gas to be measured based on the acquired pump current Ip2 and the correspondence stored in the memory unit 98. The CPU 97 transmits the detected NOx concentration value to the engine ECU (not shown) and terminates the NOx concentration detection process. The CPU 97 may perform the NOx concentration detection process, for example, at predetermined time intervals, or at the timing instructed by the engine ECU to detect the NOx concentration.

[0071] As can be seen in Figure 2, the voltages V0 to V2 and Vref detected by the voltage acquisition units 85 to 88 of the control device 95 are the voltages between the reference electrode 42 and the electrodes 22, 51, 44, and 23. The potential of the reference electrode 42, i.e., the reference potential, is a value corresponding to the oxygen concentration around the reference electrode 42. Since the reference gas is introduced into the reference electrode 42 via the reference gas introduction unit 49, if the oxygen concentration of the reference gas is constant, the oxygen concentration around the reference electrode 42 will basically be constant. However, in reality, the oxygen concentration around the reference electrode 42 may change during the use of the sensor element 101. For example, in the gas sensor 100, the front and rear ends of the sensor element 101 are sealed by a sensor assembly (not shown) to prevent the gas to be measured and the reference gas to be measured from flowing to each other. However, in cases where the pressure of the gas to be measured is high, a small amount of the gas to be measured may enter the reference gas, causing the oxygen concentration around the reference electrode 42 to decrease. Furthermore, the reference gas introduction section 49 may adsorb external water during periods when the sensor element 101 is not being driven. When the sensor element 101 is started, it heats up and the water in the reference gas introduction section 49 turns into gas and escapes to the outside of the sensor element 101. However, until the water escapes, the presence of gaseous water may cause the oxygen concentration around the reference electrode 42 to decrease. When the oxygen concentration around the reference electrode 42 changes in this way, the reference potential of the reference electrode 42 shifts, and the values ​​of each voltage V0~V2 and Vref also change, thus reducing the accuracy of NOx concentration detection.

[0072] Therefore, in the gas sensor 100 of this embodiment, the control unit 96 performs a reference potential adjustment process to adjust the reference potential by detecting the deviation of the reference potential of the reference electrode 42. Figure 4 is a flowchart showing an example of a reference potential adjustment process routine executed by the control unit 96. The control unit 96 stores this routine in, for example, the storage unit 98. The control unit 96 repeatedly executes this routine, for example, at predetermined intervals.

[0073] When the reference potential adjustment processing routine is started, the CPU 97 of the control unit 96 first inputs the voltage Vrg acquired by the reference electrode voltage acquisition unit 89 (step S100). That is, the CPU 97 measures the voltage Vrg between the ground and the reference electrode 42. Since the potential of the ground is basically constant, the voltage Vrg is a value corresponding to the oxygen concentration around the reference electrode 42. Next, the CPU 97 compares the input voltage Vrg value with a predetermined allowable range of voltage Vrg to determine whether the voltage Vrg is within the allowable range (step S110). The predetermined allowable range is a range that includes the normal value of voltage Vrg and values ​​close to the normal value and is stored in the storage unit 98. The normal value of voltage Vrg is, for example, the value of voltage Vrg when the oxygen concentration around the reference electrode 42 matches the normal oxygen concentration of the reference gas (in this case, the oxygen concentration of the atmosphere). The upper and lower limits of the tolerance range can be predetermined based on, for example, the upper and lower limits of the voltage Vrg range in which a deviation in the reference potential is acceptable because it has little effect on the measurement accuracy of NOx concentration, or in other words, the upper and lower limits of the tolerance range of oxygen concentration around the reference electrode 42. The process of determining whether the voltage Vrg is within the tolerance range corresponds to the process of determining the deviation in the reference potential. The difference between the normal value and the upper and lower limits of the tolerance range of the voltage Vrg corresponds to the upper and lower limits of the tolerance range of the deviation in the reference potential. Since the difference or ratio between the measured voltage Vrg and the normal value is a value that represents the deviation in the reference potential, the CPU 97 may perform the determination in step S110 by comparing this difference or ratio with the tolerance range of the difference or ratio. In this embodiment, the voltage Vrg is defined as the potential of the reference electrode 42 with respect to ground, and the voltage Vrg is a positive value regardless of the magnitude of the oxygen concentration around the reference electrode 42. However, for example, the voltage Vrg may be defined to be a negative value, in which case the absolute value of the voltage Vrg may be compared with the tolerance range of the voltage Vrg.

[0074] On the other hand, if the voltage Vrg in step S110 is greater than the allowable range, that is, if a deviation in the reference potential occurs such that the oxygen concentration around the reference electrode 42 is higher than the upper limit of the allowable range, the CPU 97 controls the reference gas adjustment pump cell 90 to pump oxygen from around the reference electrode 42 to around the outer pump electrode 23 (step S120). As a result, the oxygen concentration around the reference electrode 42 decreases, and the voltage Vrg can be brought within the allowable range. In other words, if the reference potential of the reference electrode 42 has deviated to a value higher than the upper limit of the allowable range, the CPU 97 controls the reference gas adjustment pump cell 90 to lower the reference potential to bring it within the allowable range.

[0075] Furthermore, if the voltage Vrg in step S110 is smaller than the allowable range, that is, if a deviation in the reference potential occurs such that the oxygen concentration around the reference electrode 42 falls below the lower limit of the allowable range, the CPU 97 controls the reference gas adjustment pump cell 90 to draw oxygen from around the outer pump electrode 23 to around the reference electrode 42 (step S130). As a result, the oxygen concentration around the reference electrode 42 increases, and the voltage Vrg can be brought within the allowable range. In other words, if the reference potential of the reference electrode 42 has deviated to a value lower than the lower limit of the allowable range, the CPU 97 controls the reference gas adjustment pump cell 90 to raise the reference potential to bring it within the allowable range.

[0076] CPU97 terminates this routine if, in step S110, the voltage Vrg is within the acceptable range, i.e., the deviation of the reference potential is within the acceptable range. CPU97 also terminates this routine after the execution of step S120 or after the execution of step S130.

[0077] When this reference potential adjustment processing routine is executed, the oxygen concentration around the reference electrode 42 is adjusted based on the determination result of step S110 (i.e., the result of determining the deviation of the reference potential), and the deviation of the reference potential from the normal value is reduced, thereby suppressing the decrease in the detection accuracy of NOx concentration caused by the deviation of the reference potential. In this embodiment, the amount of oxygen pumped out in step S120 and the amount of oxygen pumped in in step S130 are adjusted by the CPU 97 by changing the duty cycle of the pulse voltage Vp3, as described above. The CPU 97 may determine these pumping and pumping amounts to be values ​​that increase as the difference or ratio (i.e., the amount of deviation of the reference potential) between the voltage Vrg value input in step S100 and the normal value of voltage Vrg increases. In other words, the CPU 97 may determine the control amount of the reference gas adjustment pump cell 90 in steps S120 and S130 (here, the duty cycle of the voltage Vp3) as a value corresponding to the amount of oxygen to be moved in order to change the voltage Vrg input in step S100 to a normal value or a value close to the normal value. The correspondence between the voltage Vrg input in step S100 and the control amount of the reference gas adjustment pump cell 90, or the correspondence between the difference or ratio between voltage Vrg and the normal value and the control amount of the reference gas adjustment pump cell 90, may be predetermined and stored in the storage unit 98, and the CPU 97 may determine the control amount of the reference gas adjustment pump cell 90 based on this correspondence. Alternatively, instead of using the duty cycle of the voltage Vp3 as the control amount of the reference gas adjustment pump cell 90, or in addition, the magnitude of the voltage Vp3 may be used, or the operating time of the reference gas adjustment pump cell 90 may be used. In other words, the CPU 97 may adjust the amount of oxygen transferred depending on the magnitude of the voltage Vp3, or it may adjust the amount of oxygen transferred depending on the length of the operating time of the reference gas adjustment pump cell 90.

[0078] The amount of oxygen pumped out in step S120 and the amount of oxygen pumped in in step S130 may be constant values. In this case as well, the voltage Vrg can be brought within an acceptable range by repeatedly executing the reference potential adjustment processing routine, thereby reducing the deviation of the reference potential. In this case, the CPU 97 repeatedly executes the reference potential adjustment processing routine, thereby repeatedly measuring the voltage Vrg and controlling the reference gas adjustment pump cell 90 until the voltage Vrg is within an acceptable range.

[0079] In step S100, it is preferable to measure the voltage Vrg when no pump current Ip3 is flowing through the reference electrode 42. This suppresses the inclusion of the voltage drop due to the pump current Ip3 in the voltage Vrg, resulting in a more accurate value of voltage Vrg corresponding to the oxygen concentration around the reference electrode 42. For example, if the voltage Vp3 is a pulsed voltage, it is preferable for the CPU 97 to measure the voltage Vrg during the period when the voltage Vp3 is off. Alternatively, the CPU 97 may control the power supply circuit 92 so as not to apply the voltage Vp3 when measuring the voltage Vrg. The same applies when measuring voltages V0~V2 and Vref.

[0080] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. The sensor element 101 of this embodiment corresponds to the sensor element of the present invention, the laminate formed by stacking six layers in the order of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 corresponds to the element body, the third internal cavity 61 corresponds to the measurement chamber, the measurement electrode 44 corresponds to the measurement electrode, the reference electrode 42 corresponds to the reference electrode, and the control device 95 corresponds to the control device. Furthermore, the outer pump electrode 23 corresponds to the electrode on the side of the gas to be measured and the outer measurement electrode, the voltage V2 corresponds to the measurement voltage, and the target value V2* corresponds to the measurement voltage target value. The first internal cavity 20 and the second internal cavity 40 correspond to oxygen concentration adjustment chambers, the auxiliary pump electrode 51 corresponds to an internal adjustment electrode, the main pump cell 21 and the auxiliary pump cell 50 correspond to adjustment pump cells, the voltage V1 corresponds to the adjustment voltage, the target value V1* corresponds to the adjustment voltage target value, the connector electrode 71f corresponds to the ground terminal, and the heater 72 corresponds to a heater. In this embodiment, by explaining the operation of the gas sensor 100, an example of a method for determining the deviation of the reference potential of the gas sensor of the present invention is also revealed.

[0081] According to the gas sensor 100 of this embodiment described above, the control device 95 measures the voltage Vrg between the ground and the reference electrode 42 and determines the deviation of the reference potential, which is the potential of the reference electrode 42, based on the voltage Vrg. Since the voltage Vrg changes in accordance with the change in oxygen concentration around the reference electrode 42, i.e., the change in the reference potential, the deviation of the reference potential can be determined based on the voltage Vrg.

[0082] Furthermore, the sensor element 101 includes a reference gas adjustment pump cell 90 comprising an outer pump electrode 23 provided on the element body so as to be in contact with the gas to be measured, and a reference electrode 42. The control device 95 controls the reference gas adjustment pump cell 90 to pump oxygen from around the reference electrode 42 to around the outer pump electrode 23 if the measured voltage Vrg is greater than the allowable range. Conversely, if the measured voltage Vrg is smaller than the allowable range, the control device 95 controls the reference gas adjustment pump cell 90 to pump oxygen from around the outer pump electrode 23 to around the reference electrode 42. This allows the oxygen concentration around the reference electrode 42 to be adjusted according to the deviation of the reference potential, thereby reducing the deviation of the reference potential and suppressing the decrease in detection accuracy of NOx concentration caused by the deviation of the reference potential. While the oxygen concentration around the reference electrode 42 has been adjusted using the reference gas adjustment pump cell 90 in the past, the deviation of the reference potential using the voltage Vrg between ground and the reference electrode 42 has not been determined. Therefore, conventionally, there were cases where the amount of oxygen transferred by the reference gas adjustment pump cell 90 was too much or too little, making it impossible to maintain the oxygen concentration around the reference electrode 42 at an appropriate level (normal oxygen concentration of the reference gas). In the gas sensor 100 of this embodiment, the CPU 97 controls the reference gas adjustment pump cell 90 based on the deviation of the reference potential determined using the voltage Vrg, so the reference gas adjustment pump cell 90 can be controlled more appropriately, making it easier to maintain the oxygen concentration around the reference electrode 42 at an appropriate level.

[0083] It goes without saying that the present invention is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

[0084] In the embodiment described above, the control device 95 adjusted the oxygen concentration around the reference electrode 42 based on a comparison of the measured voltage Vrg with the allowable range, that is, based on the result of grasping the deviation of the reference potential, but is not limited to this. For example, the control device 95 may correct the control of each pump cell 21, 50, 41 based on the grasped deviation of the reference potential. Figure 5 is a flowchart of an example of the control correction process. The control unit 96 stores this routine in, for example, the memory unit 98. The control unit 96 repeatedly executes this routine, for example, at predetermined time intervals. When the control correction processing routine is started, the CPU 97 of the control unit 96 measures the voltage Vrg by performing the same process as step S100 of the reference potential adjustment process described above. Subsequently, the CPU 97 calculates the difference value ΔVrg (= measured value - normal value) between the measured voltage Vrg and the normal value (step S210). Then, the CPU 97 corrects the control of each pump cell 21, 50, 41 based on this difference value ΔVrg (step S220) and terminates this routine. The control correction for each pump cell 21, 50, 41 may be, for example, a correction of the measured value of the voltage involved in the control, or a correction of the target value of the voltage involved in the control. Since the difference value ΔVrg corresponds to the amount of deviation of the reference potential, by correcting the measured value or target value of the voltage involved in the control of each pump cell 21, 50, 41 based on the difference value ΔVrg, the effect of the deviation of the reference potential can be canceled out, and control can be performed in substantially the same way as if there were no deviation of the reference potential. For example, in the embodiment described above, since the oxygen concentration around each electrode 22, 51, 44 is lower than the oxygen concentration around the reference electrode 42, if the reference potential of the reference electrode 42 is shifted in the direction of being higher than the normal value (the difference value ΔVrg is positive), the voltages V0 to V2 measured by each voltage acquisition unit 85 to 87 will be measured as values ​​that are shifted in the direction of being larger in absolute value. If the reference potential of the reference electrode 42 is shifted to a lower value than the normal value (the difference value ΔVrg is negative), the voltages V0 to V2 measured by each voltage acquisition unit 85 to 87 will be measured as values ​​that are shifted in the direction of decreasing absolute value. Therefore, the CPU 97 calculates the corrected voltages V0 to V2 by subtracting the difference value ΔVrg from the absolute value of each of the measured voltages V0 to V2 acquired by each voltage acquisition unit 85 to 87.The CPU 97 then compares the corrected voltages V0 to V2 with the target values ​​V0* to V2* described above and performs the adjustment pump control process and the measurement pump control process. Alternatively, the CPU 97 may calculate the corrected target values ​​V0* to V2* by adding the difference value ΔVrg to the absolute value of the target values ​​V0* to V2*. In this case, the CPU 97 compares the measured values ​​of voltages V0 to V2 with the corrected target values ​​V0* to V2* and performs the adjustment pump control process and the measurement pump control process. Each time the CPU 97 executes step S220 of the control correction process, it updates the correction amount (i.e., the difference value ΔVrg) for the adjustment pump control process and the measurement pump control process. The correction based on the deviation of the reference potential described above may be performed on at least one of the adjustment pump control process and the measurement pump control process, or on at least one of the main pump control process, auxiliary pump control process, and measurement pump control process. However, since the measurement pump control process has the greatest impact on the accuracy of NOx concentration measurement, when performing the control correction process shown in Figure 5, it is preferable that the CPU 97 performs a correction based on the deviation of the reference potential described above, at least for the measurement pump control process. Furthermore, when detecting the oxygen concentration in the gas to be measured based on the voltage Vref acquired by the voltage acquisition unit 88, the CPU 97 may perform the same correction on the voltage Vref in step S220 as the correction on the voltages V0 to V2 described above.

[0085] In the embodiment described above, the gas sensor 100 does not necessarily have to include a reference gas adjustment pump cell 90 and a power supply circuit 92. In this case as well, the control unit 96 can still perform the control correction processing shown in Figure 5.

[0086] In the embodiment described above, the voltage Vrg was defined as the voltage between the connector electrode 71f, which is a terminal of the heater 72, and the reference electrode 42, but it is not limited to this. For example, the voltage Vrg may be the voltage between the reference electrode 42 and a terminal provided by the sensor element 101 and connected to ground, not limited to the terminal of the heater 72. Alternatively, the voltage between ground and the reference electrode 42 may be measured, not limited to the terminal provided by the sensor element 101. For example, the voltage between the reference electrode 42 and another ground that is not connected to any of the connector electrodes 71 of the sensor element 101 may be measured, and the deviation of the reference potential may be determined based on that voltage. The inventors have experimentally confirmed that, not limited to the voltage Vrg in the embodiment described above, the voltage between the reference electrode 42 and another ground that is not connected to any of the connector electrodes 71 of the sensor element 101 also changes in accordance with the change in oxygen concentration around the reference electrode 42, and that the deviation of the reference potential can be determined based on that voltage.

[0087] In the reference potential adjustment process shown in Figure 5 above, the CPU 97 controls the reference gas adjustment pump cell 90 based on the detection of the deviation of the reference potential based on the voltage Vrg (step S110) (steps S120, S130), and in the control correction process shown in Figure 6 above, it corrects the control of each pump cell 21, 50, and 41 based on the detection of the deviation of the reference potential based on the voltage Vrg (step S210) (step S220), but is not limited to this. For example, if the CPU 97 makes a negative determination in step S110, or if the difference value ΔVrg calculated in step S210 is not within the allowable range, or if the detected deviation of the reference potential exceeds the allowable range, the CPU 97 may notify the engine ECU of the abnormality of the reference potential. For example, the CPU 97 may output a signal to the engine ECU to notify it of the abnormality of the reference potential. Thus, the CPU 97 may only diagnose the deviation of the reference potential.

[0088] In the embodiment described above, the reference gas introduction unit 49 included a reference gas introduction space 43 and a reference gas introduction layer 48. However, the reference gas introduction unit 49 only needs to be able to introduce the reference gas from outside the sensor element 101 to the reference electrode 42. For example, the reference gas introduction unit 49 may include at least one of the reference gas introduction space 43 and the reference gas introduction layer 48.

[0089] In the embodiment described above, the gas sensor 100 detected the NOx concentration as the specific gas concentration, but it is not limited to this, and other oxide concentrations may also be used as the specific gas concentration. If the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61, as in the embodiment described above, so the CPU 97 can obtain a detection value corresponding to this oxygen and detect the specific gas concentration. Alternatively, the specific gas may be a non-oxide such as ammonia. If the specific gas is a non-oxide, oxygen is generated when the converted gas is reduced in the third internal cavity 61 by converting the specific gas to an oxide (for example, converting ammonia to NO), so the CPU 97 can obtain a detection value corresponding to this oxygen and detect the specific gas concentration. In this way, whether the specific gas is an oxide or a non-oxide, the gas sensor 100 can detect the specific gas concentration based on the oxygen generated in the third internal cavity 61 originating from the specific gas.

[0090] In the embodiment described above, the sensor element 101 of the gas sensor 100 is provided with a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited to this. For example, as shown in the sensor element 201 of Figure 6, it may not have a third internal cavity 61. In the modified sensor element 201 shown in Figure 6, a gas inlet 10, a first diffusion rate-limiting section 11, a buffer space 12, a second diffusion rate-limiting section 13, a first internal cavity 20, a third diffusion rate-limiting section 30, and a second internal cavity 40 are formed adjacent to each other in this order, communicating between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The measuring electrode 44 is covered by a fourth diffusion rate-limiting section 45. The fourth diffusion rate-limiting section 45 is a film made of a porous ceramic material such as alumina (Al2O3). Similar to the fourth diffusion rate-limiting section 60 in the embodiment described above, the fourth diffusion rate-limiting section 45 plays a role in limiting the amount of NOx flowing into the measuring electrode 44. The fourth diffusion rate-limiting section 45 also functions as a protective film for the measuring electrode 44. The ceiling electrode portion 51a of the auxiliary pump electrode 51 is formed up to directly above the measuring electrode 44. Even with a sensor element 201 configured in this way, the NOx concentration can be detected, for example, based on the pump current Ip2, similar to the embodiment described above. In this case, the area around the measuring electrode 44 functions as a measurement chamber.

[0091] In the embodiment described above, the element body of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6), but it is not limited to this. The element body of the sensor element 101 only needs to have at least one oxygen ion conductive solid electrolyte layer and have a gas flow section for measurement provided inside. For example, in Figure 1, layers 1 to 5 other than the second solid electrolyte layer 6 may be structural layers made of a material other than a solid electrolyte (for example, a layer made of alumina). In this case, each electrode of the sensor element 101 should be arranged in the second solid electrolyte layer 6. For example, the measuring electrode 44 in Figure 1 should be arranged on the lower surface of the second solid electrolyte layer 6. Alternatively, the reference gas introduction space 43 may be provided in the spacer layer 5 instead of the first solid electrolyte layer 4, the reference gas introduction layer 48 may be provided between the second solid electrolyte layer 6 and the spacer layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 may be provided behind the third internal space 61 and on the lower surface of the second solid electrolyte layer 6.

[0092] In the embodiment described above, the control unit 96 sets a target value V0* for the voltage V0 based on the pump current Ip1 so that the pump current Ip1 becomes the target current Ip1* (feedback control), and then feedback controls the pump voltage Vp0 so that the voltage V0 becomes the target value V0*. However, other control methods may be used. For example, the control unit 96 may feedback control the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 becomes the target current Ip1*. That is, the control unit 96 may omit the acquisition of the voltage V0 from the oxygen partial pressure detection sensor cell 80 for main pump control and the setting of the target value V0*, and instead directly control the pump voltage Vp0 (and consequently the pump current Ip0) based on the pump current Ip1.

[0093] In the embodiment described above, the oxygen concentration adjustment chamber had a first internal cavity 20 and a second internal cavity 40, but it is not limited to this, for example, the oxygen concentration adjustment chamber may have another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the embodiment described above, the adjustment pump cell had a main pump cell 21 and an auxiliary pump cell 50, but it is not limited to this, for example, the adjustment pump cell may have another pump cell, or one of the main pump cell 21 and the auxiliary pump cell 50 may be omitted. For example, if the oxygen concentration of the gas to be measured can be sufficiently lowered with only the main pump cell 21, the auxiliary pump cell 50 may be omitted. If the auxiliary pump cell 50 is omitted, the control unit 96 only needs to perform the main pump control process as the adjustment pump control process. Also, in the main pump control process, the setting of the target value V0* based on the pump current Ip1 described above may be omitted. Specifically, a predetermined target value V0* is stored in the memory unit 98 beforehand, and the control unit 96 controls the main pump cell 21 by feedback-controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0*. If the auxiliary pump cell 50 is omitted, the inner pump electrode 22 corresponds to the inner adjustment electrode, the voltage V0 corresponds to the adjustment voltage, and the target value V0* corresponds to the adjustment voltage target value.

[0094] In the embodiment described above, the outer pump electrode 23 served as an outer main pump electrode located on the part of the main pump cell 21 that is exposed to the gas to be measured outside the sensor element 101, an outer auxiliary pump electrode located on the part of the auxiliary pump cell 50 that is exposed to the gas to be measured outside the sensor element 101, an outer measuring electrode located on the part of the measuring pump cell 41 that is exposed to the gas to be measured outside the sensor element 101, and a measured gas side electrode located on the part of the reference gas adjustment pump cell 90 that is exposed to the gas to be measured outside the sensor element 101, but is not limited to this. One or more of the outer main pump electrode, outer auxiliary pump electrode, outer measuring electrode, and measured gas side electrode may be provided outside the sensor element 101 separately from the outer pump electrode 23. Furthermore, the electrode on the side of the gas to be measured in the reference gas adjustment pump cell 90 only needs to be provided on the sensor element 101 so as to be in contact with the gas to be measured. For example, it may be located on the inside of the sensor element 101, not just the outside, and more specifically, it may be located in the gas flow section of the sensor element 101. For example, the inner pump electrode 22 may serve as both the electrode of the main pump cell 21 (inner main pump electrode) and the electrode on the side of the gas to be measured in the reference gas adjustment pump cell 90, and the reference gas adjustment pump cell 90 may pump in or out oxygen between the area around the inner pump electrode 22 and the area around the reference electrode 42. [Industrial applicability]

[0095] This invention can be used in gas sensors that detect the concentration of specific gases, such as NOx, in a gas to be measured, such as automobile exhaust gas. [Explanation of symbols]

[0096] 1 First substrate layer, 2 Second substrate layer, 3 Third substrate layer, 4 First solid electrolyte layer, 5 Spacer layer, 6 Second solid electrolyte layer, 10 Gas inlet, 11 First diffusion-controlled section, 12 Buffer space, 13 Second diffusion-controlled section, 20 First internal cavity, 21 Main pump cell, 22 Inner pump electrode, 22a Ceiling electrode section, 22b Bottom electrode section, 23 Outer pump electrode, 24 Variable power supply, 30 Third diffusion-controlled section, 40 Second internal cavity, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 Fourth diffusion-controlled section, 46 Variable power supply, 48 Reference gas introduction layer, 49 Reference gas introduction section, 49a Inlet section, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode section, 51b Bottom electrode section, 52 Variable power supply, 60 61 Third internal cavity, 70 Heater section, 71, 71a~71f Connector electrodes, 72 Heater, 73 Through hole, 74 Heater insulating layer, 75 Pressure relief hole, 76 Heater power supply, 77f, 77g Leads for energizing, 77h Leads for voltage measurement, 80 Oxygen partial pressure detection sensor cell for main pump control, 81 Oxygen partial pressure detection sensor cell for auxiliary pump control, 82 Oxygen partial pressure detection sensor cell for measurement pump control, 83 Sensor cell, 85 Voltage acquisition section for main pump, 86 Voltage acquisition section for auxiliary pump, 87 Voltage acquisition section for measurement, 88 Voltage acquisition section, 89 Voltage acquisition section for reference electrode, 90 Reference gas adjustment pump cell, 92 Power supply circuit, 95 Control device, 96 Control unit, 97 CPU, 98 Memory unit, 100 Gas sensor, 101, 201 Sensor element.

Claims

1. A gas sensor comprising a sensor element and a device for detecting deviations in a reference potential, for detecting a specific gas concentration, which is the concentration of a specific gas in the gas to be measured, The aforementioned sensor element is The element body has an oxygen ion conductive solid electrolyte layer and is provided with a gas flow section inside through which the gas to be measured is introduced and circulated, A measuring electrode is provided in the measuring chamber of the gas flow section to be measured, Inside the element body, a reference electrode is provided, which is arranged in contact with a reference gas that serves as a reference for detecting the specific gas concentration. The ground terminal connected to ground, Equipped with, The device for determining the deviation of the reference potential measures the voltage between the ground terminal and the reference electrode, and based on the measured voltage, determines the deviation of the reference potential, which is the potential of the reference electrode. Gas sensor.

2. A gas sensor comprising a sensor element and a control device, which detects a specific gas concentration, which is the concentration of a specific gas in a gas to be measured, The aforementioned sensor element is The element body has an oxygen ion conductive solid electrolyte layer and is provided with a gas flow section inside through which the gas to be measured is introduced and circulated, A measuring electrode is provided in the measuring chamber of the gas flow section to be measured, Inside the element body, a reference electrode is provided, which is arranged in contact with a reference gas that serves as a reference for detecting the specific gas concentration. A reference gas adjustment pump cell comprising a gas-side electrode provided on the element body so as to be in contact with the gas to be measured, and a reference electrode, Equipped with, The control device measures the voltage between the ground and the reference electrode, and if the measured voltage is greater than the allowable range, it controls the reference gas adjustment pump cell to pump oxygen from around the reference electrode to around the measured gas side electrode, and if the measured voltage is less than the allowable range, it controls the reference gas adjustment pump cell to pump oxygen from around the measured gas side electrode to around the reference electrode. Gas sensor.

3. The aforementioned sensor element is A measuring pump cell comprising an external measuring electrode provided on the outside of the element body so as to be in contact with the gas to be measured, and the measuring electrode, Equipped with, The control device, based on the measured voltage between the ground and the reference electrode, determines the deviation of the reference potential, which is the potential of the reference electrode. The control device performs a measuring pump control process to control the measuring pump cell so that the measuring voltage, which is the voltage between the measuring electrode and the reference electrode, becomes the target measuring voltage, and detects the concentration of the specific gas in the gas to be measured based on the pump current flowing through the measuring pump cell as a result of the measuring pump control process. The control device corrects the control of the measuring pump cell in the measuring pump control process based on the deviation of the reference potential that has been determined. The gas sensor according to claim 2.

4. A gas sensor comprising a sensor element and a control device, which detects a specific gas concentration, which is the concentration of a specific gas in a gas to be measured, The aforementioned sensor element is The element body has an oxygen ion conductive solid electrolyte layer and is provided with a gas flow section inside through which the gas to be measured is introduced and circulated, A measuring electrode is provided in the measuring chamber of the gas flow section to be measured, Inside the element body, a reference electrode is provided, which is arranged in contact with a reference gas that serves as a reference for detecting the specific gas concentration. A measuring pump cell comprising an external measuring electrode provided on the outside of the element body so as to be in contact with the gas to be measured, and the measuring electrode, Equipped with, The control device measures the voltage between ground and the reference electrode, and based on the measured voltage, determines the deviation of the reference potential, which is the potential of the reference electrode. The control device performs a measuring pump control process to control the measuring pump cell so that the measuring voltage, which is the voltage between the measuring electrode and the reference electrode, becomes the target measuring voltage, and detects the concentration of the specific gas in the gas to be measured based on the pump current flowing through the measuring pump cell as a result of the measuring pump control process. The control device corrects the control of the measuring pump cell in the measuring pump control process based on the deviation of the reference potential that has been determined. Gas sensor.

5. The aforementioned sensor element is The system includes an internal adjustment electrode located in an oxygen concentration adjustment chamber situated upstream of the measurement chamber within the gas flow section to be measured, and comprises an adjustment pump cell for adjusting the oxygen concentration in the oxygen concentration adjustment chamber. Equipped with, The control device performs an adjustment pump control process to adjust the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump cell so that the adjustment voltage, which is the voltage between the inner adjustment electrode and the reference electrode, becomes the adjustment voltage target value. The control device corrects the control of the adjustment pump cell in the adjustment pump control process based on the deviation of the reference potential that has been determined. The gas sensor according to claim 3 or 4.

6. The sensor element is provided with a ground terminal connected to the ground, The control device measures the voltage between the ground terminal and the reference electrode as the voltage between the ground and the reference electrode. The gas sensor according to any one of claims 2 to 4.

7. The sensor element is equipped with a heater for heating the element body, The aforementioned ground terminal is the terminal of the heater. The gas sensor according to claim 6.

8. The sensor element is equipped with a heater for heating the element body, The aforementioned ground terminal is the terminal of the heater. The gas sensor according to claim 1.

9. A method for determining the deviation of the reference potential of a gas sensor that detects the concentration of a specific gas, which is the concentration of a specific gas in the gas being measured, The aforementioned gas sensor is The element body has an oxygen ion conductive solid electrolyte layer and is provided with a gas flow section inside through which the gas to be measured is introduced and circulated, The measuring electrode is disposed in the gas flow section to be measured, Inside the element body, a reference electrode is provided, which is arranged in contact with a reference gas that serves as a reference for detecting the specific gas concentration. A sensor element having, A step of measuring the voltage between ground and the reference electrode, and determining the deviation of the reference potential, which is the potential of the reference electrode, based on the measured voltage. including, A method for determining deviations in the reference potential of a gas sensor.

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