Gas sensor

Abstract

A gas sensor (100) is provided with a sensor element (101) and a control device. A sensor element (101) is provided with an element main body, a first measurement pump unit (41), a second measurement pump unit (66), an auxiliary pump unit (50), and a reference electrode (42). The control device controls the auxiliary pump unit (50) such that the voltage (V1) between the reference electrode (42) and the auxiliary pump electrode (51) reaches a target value (V1 *), and controls the first measurement pump unit (41) such that the voltage (V2) between the reference electrode (42) and the first measurement electrode (44) reaches a target value (V2 *). The second measurement pump unit (66) is controlled so that the voltage (V3) between the reference electrode (42) and the second measurement electrode (67) reaches a target value (V3 *), the specific gas concentration is detected on the basis of the pump current (Ip2), and the specific gas concentration is measured on the basis of the pump current (Ip3) and the change in the pump current (Ip2) when the target value (V1 *) and / or the target value (V2 *) is changed. The concentration of carbon dioxide in the gas to be measured is detected.

Description

Technical Field

[0001] The present invention relates to a gas sensor. Background Art

[0002] In the past, there are known gas sensors for detecting the concentration of specific gases such as NOx in the measured gas such as automobile exhaust gas. For example, Patent Document 1 describes a gas sensor, which includes: an element body, which includes an oxygen ion conductive solid electrolyte layer and a measured gas circulation part for introducing and circulating the measured gas; and a plurality of electrodes, which are arranged on the element body. When the concentration of NOx is detected by using this gas sensor, first, oxygen is sucked out or sucked in between the oxygen concentration adjustment chamber in the measured gas circulation part and the outside of the sensor element, thereby adjusting the oxygen concentration in the oxygen concentration adjustment chamber. The measured gas with the adjusted oxygen concentration reaches the measurement chamber arranged on the downstream side of the oxygen concentration adjustment chamber in the measured gas circulation part. In the measurement chamber, NOx in the measured gas is reduced around the measurement electrode arranged in the measurement chamber. In addition, the measurement pump unit is feedback-controlled in such a way that the voltage V2 generated between the measurement electrode and the reference electrode reaches a predetermined target value, and the oxygen around the measurement electrode is sucked out. Based on the pump current Ip2 flowing at this time, the concentration of NOx in the measured gas is detected.

[0003] In addition, there are also known gas sensors that detect the concentration of carbon dioxide in the measured gas. For example, the gas sensor described in Patent Document 2 adjusts the oxygen partial pressure of the first internal cavity in such a way that the water vapor component and the carbon dioxide component in the measured gas are substantially completely decomposed in the first internal cavity of the sensor element. In addition, oxygen is supplied to the second internal cavity through the first measuring electrochemical pump unit in such a way that the hydrogen generated by the decomposition of the water vapor component is selectively burned in the second internal cavity, and the concentration of the water vapor component in the measured gas is determined based on the magnitude of the current flowing at this time. In addition, the gas sensor supplies oxygen to the surface of the second measuring inner electrode through the second measuring electrochemical pump unit in such a way that the carbon monoxide generated by the decomposition of the carbon dioxide component is selectively burned, and the concentration of the carbon dioxide component in the measured gas is determined based on the magnitude of the current flowing at this time.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-091669

[0007] Patent Document 2: Japanese Patent No. 5918177 Summary of the invention

[0008] However, there is no known gas sensor that detects both the NOx concentration and the carbon dioxide concentration in a gas to be measured.

[0009] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to detect the NOx concentration and the carbon dioxide concentration in a gas to be measured.

[0010] The present invention adopts the following means to achieve the above-mentioned main object.

[0011] [1] The gas sensor of the present invention comprises a sensor element and a control device.

[0012] The sensor element has:

[0013] an element body having an oxygen ion conductive solid electrolyte layer and provided with a gas flow portion for introducing and flowing the gas to be measured;

[0014] a first measurement pump unit, the first measurement pump unit comprising a first inner measurement electrode provided in a first measurement chamber in the measured gas flow portion, and sucking oxygen in the first measurement chamber to the outside of the element body;

[0015] A second measuring pump unit, the second measuring pump unit comprising a second inner measuring electrode provided in a second measuring chamber located downstream of the first measuring chamber in the measured gas flow section, and sucking oxygen in the second measuring chamber to the outside of the element body;

[0016] an adjusting pump unit, the adjusting pump unit including an inner adjusting electrode provided in an oxygen concentration adjusting chamber located upstream of the first measuring chamber in the measured gas flow section, and adjusting the oxygen concentration in the oxygen concentration adjusting chamber; and

[0017] a reference electrode disposed inside the element body in such a manner as to be in contact with a reference gas,

[0018] The control device performs: an adjustment pump control process, in which the adjustment pump unit is controlled so as to adjust the oxygen concentration of the oxygen concentration adjustment chamber in such a manner that the voltage between the reference electrode and the inner adjustment electrode, that is, the adjustment voltage, reaches a target adjustment voltage value; a first measurement pump control process, in which the first measurement pump unit is controlled so as to suck out the oxygen of the first measurement chamber in such a manner that the voltage between the reference electrode and the first inner measurement electrode, that is, the first measurement voltage, reaches a target first measurement voltage value; and a second measurement pump control process, in which the second measurement pump unit is controlled so as to suck out the oxygen of the second measurement chamber in such a manner that the voltage between the reference electrode and the second inner measurement electrode, that is, the second measurement voltage, reaches a target second measurement voltage value.

[0019] The control device detects the NOx concentration in the gas to be measured based on the first measurement pump current flowing when oxygen generated when NOx is reduced in the first measurement chamber is sucked out by the first measurement pump control process.

[0020] The control device detects the carbon dioxide concentration in the measured gas based on the second measuring pump current flowing when the oxygen generated when the carbon dioxide is reduced in the second measuring chamber is sucked out through the second measuring pump control process, and the change in the first measuring pump current flowing during the execution of the adjustment pump control process and the first measuring pump control process when at least one of the adjustment voltage target value and the first measuring voltage target value is changed.

[0021] In the gas sensor, the control device performs the following adjustment pump control processing: the adjustment pump unit is controlled so that the voltage between the reference electrode and the inner adjustment electrode, that is, the adjustment voltage, reaches the adjustment voltage target value to adjust the oxygen concentration of the oxygen concentration adjustment chamber. In addition, the control device performs the following first measurement pump control processing: the first measurement pump unit is controlled so that the voltage between the reference electrode and the first inner measurement electrode, that is, the first measurement voltage, reaches the first measurement voltage target value to suck out the oxygen in the first measurement chamber. The control device performs the following second measurement pump control processing: the second measurement pump unit is controlled so that the voltage between the reference electrode and the second inner measurement electrode, that is, the second measurement voltage, reaches the second measurement voltage target value to suck out the oxygen in the second measurement chamber. Furthermore, the control device detects the NOx concentration in the measured gas based on the first measurement pump current that flows when the oxygen generated when NOx is reduced in the first measurement chamber is sucked out by the first measurement pump control processing. In addition, the control device detects the carbon dioxide concentration in the measured gas based on the second measuring pump current that flows when the oxygen generated when the carbon dioxide is reduced in the second measuring chamber is sucked out by the second measuring pump control process, and the change of the first measuring pump current that flows during the execution of the adjustment pump control process and the first measuring pump control process when at least one of the adjustment voltage target value and the first measuring voltage target value is changed. In this way, the gas sensor of the present invention detects the NOx concentration based on the first measuring pump current and detects the carbon dioxide concentration based on the second measuring pump current. In the case where the measured gas contains water, not only carbon dioxide but also water is reduced in the second measuring chamber, so the second measuring pump current that flows through the second measuring pump control process becomes a value obtained based on the carbon dioxide concentration and the water concentration. However, the inventor of the present invention found that the change of the first measuring pump current when at least one of the adjustment voltage target value and the first measuring voltage target value is changed is correlated with the water concentration in the measured gas. Therefore, the carbon dioxide concentration in the measured gas can be detected based on the change of the second measuring pump current and the first measuring pump current. As described above, the gas sensor of the present invention can detect the NOx concentration and the carbon dioxide concentration in the measured gas.

[0022] [2] In the above-mentioned gas sensor (the gas sensor described in [1] above), the control device can detect the water concentration in the measured gas based on the change in the first measuring pump current. As described above, the change in the first measuring pump current when at least one of the adjustment voltage target value and the first measuring voltage target value is changed is correlated with the water concentration in the measured gas, and therefore, the water concentration in the measured gas can also be detected based on the change. In this case, the control device can detect the carbon dioxide concentration in the measured gas based on the second measuring pump current and the detected water concentration.

[0023] [3] In the above-mentioned gas sensor (the gas sensor described in [2] above), the control device may derive a total value of the carbon dioxide concentration and the water concentration in the measured gas based on the second measurement pump current, and subtract the detected water concentration from the total value to thereby detect the carbon dioxide concentration in the measured gas. In this way, the carbon dioxide concentration can be detected using a relatively simple method.

[0024] [4] In the above-mentioned gas sensor (the gas sensor described in any one of [1] to [3] above), the control device can detect the oxygen concentration in the measured gas based on the adjustment pump current flowing through the adjustment pump control process. Accordingly, the gas sensor can also detect the oxygen concentration in the measured gas.

[0025] [5] In the above-mentioned gas sensor (the gas sensor described in any one of [1] to [4] above), it can be that: the oxygen concentration adjustment chamber has: a first internal cavity; and a second internal cavity, the second internal cavity is arranged downstream of the first internal cavity and upstream of the measurement chamber, the adjustment pump unit has: a main pump unit, the main pump unit adjusts the oxygen concentration of the first internal cavity; and an auxiliary pump unit, the auxiliary pump unit adjusts the oxygen concentration of the second internal cavity, the inner adjustment electrode has: an inner main pump electrode, the inner main pump electrode is arranged in the first internal cavity and constitutes a part of the main pump unit; and an inner auxiliary pump electrode, the inner auxiliary pump electrode is arranged in the second internal cavity and constitutes a part of the auxiliary pump unit, and the adjustment pump control processing includes: a main pump control processing, controlling the main pump unit to adjust the oxygen concentration of the first internal cavity; and an auxiliary pump control processing, controlling the auxiliary pump unit in a manner such that the adjustment voltage reaches the adjustment voltage target value.

[0026] [6] In the above-mentioned gas sensor (the gas sensor described in any one of [1] to [5]), the inner adjustment electrode may include: a noble metal having catalytic activity and Au. Accordingly, the inner adjustment electrode includes Au, so that the catalytic activity against NOx and carbon dioxide is suppressed, thereby suppressing the reduction of NOx and carbon dioxide in the oxygen concentration adjustment chamber.

[0027] [7] In the above-mentioned gas sensor (the gas sensor described in any one of [1] to [6]), the first inner measuring electrode may contain Rh and a noble metal other than Rh having catalytic activity. Thus, the first inner measuring electrode containing Rh can promote the reduction of NOx in the first measuring chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic cross-sectional view schematically showing an example of the structure of the gas sensor 100 .

[0029] Figure 2 It is a block diagram showing the electrical connection relationship between the control device 95 and each unit and the heater 72.

[0030] Figure 3 : is a graph showing the relationship among the target value V1*, the water concentration, and the pump current Ip2.

[0031] Figure 4 : is a graph showing the relationship between the water concentration and the slope of the change in the bias current Ip2offset with respect to the change in the target value V1*.

[0032] Figure 5 : is a graph showing the relationship among the target value V2*, the water concentration, and the pump current Ip2.

[0033] Figure 6 : is a graph showing the relationship between the water concentration and the slope of the change in the bias current Ip2offset with respect to the change in the target value V2*.

[0034] Figure 7 It is a flowchart showing an example of a control routine.

[0035] Figure 8 : is a graph showing the relationship between the total value Cs of the water concentration and the carbon dioxide concentration and the pump current Ip3.

[0036] Fig. 9 : is a graph showing the correspondence relationship among the slope G, the pump current Ip3 and the carbon dioxide concentration.

[0037] Fig.10 is a schematic cross-sectional view of the sensor element 201 . DETAILED DESCRIPTION

[0038] Next, embodiments of the present invention will be described with reference to the drawings. Figure 1 1 is a schematic cross-sectional view schematically showing an example of the structure of a gas sensor 100 as one embodiment of the present invention. Figure 2 : is a block diagram showing the electrical connection relationship between the control device 95 and each unit and the heater 72. The gas sensor 100 is installed in a pipe such as an exhaust pipe of an internal combustion engine. The gas sensor 100 uses the exhaust gas of the internal combustion engine as the measured gas and detects the concentration of a specific gas in the measured gas. In this embodiment, the gas sensor 100 measures the NOx concentration, carbon dioxide concentration, water concentration and oxygen concentration as specific gas concentrations. The gas sensor 100 includes: a sensor element 101, which is in the shape of a long rectangular parallelepiped; each unit 21, 41, 50, 80 to 84 of the sensor element 101; a heater unit 70, which is arranged inside the sensor element 101; and a control device 95, which controls the entire gas sensor 100 having variable power supplies 24, 46, 52, 68 and a heater power supply 76.

[0039] The sensor element 101 is an element having a laminated body, which is obtained by laminating six layers, namely, a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a separator layer 5, and a second solid electrolyte layer 6, which are respectively composed of oxygen ion conductive solid electrolyte layers such as zirconium dioxide (ZrO2) in order from the bottom in the figure. In addition, the solid electrolyte forming these six layers is a dense gas-tight solid electrolyte. The sensor element 101 is manufactured as follows: for example, the ceramic green sheets corresponding to each layer are subjected to prescribed processing and circuit pattern printing, and then they are laminated and fired to achieve integration.

[0040] On the front end side of the sensor element 101 ( Figure 1 The left end side in the figure) and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet port 10, a first diffusion rate control part 11, a buffer space 12, a second diffusion rate control part 13, a first internal cavity 20, a third diffusion rate control part 30, a second internal cavity 40, a fourth diffusion rate control part 60, a third internal cavity 61, a fifth diffusion rate control part 62, and a fourth internal cavity 63 are adjacently formed in a sequentially connected manner.

[0041] The gas inlet port 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, the third internal cavity 61, and the fourth internal cavity 63 are spaces inside the sensor element 101 that are arranged by hollowing out the isolation layer 5, wherein their upper portions are divided by the lower surface of the second solid electrolyte layer 6, their lower portions are divided by the upper surface of the first solid electrolyte layer 4, and their side portions are divided by the side surfaces of the isolation layer 5.

[0042] The first diffusion rate control section 11, the second diffusion rate control section 13, and the third diffusion rate control section 30 are all provided as two horizontally long slits (the length direction of the opening is in the direction perpendicular to the drawing). In addition, the fourth diffusion rate control section 60 and the fifth diffusion rate control section 62 are provided as a horizontally long slit (the length direction of the opening is in the direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. In addition, the portion from the gas inlet 10 to the fourth internal cavity 63 is also referred to as the measured gas flow portion.

[0043] In addition, a reference gas introduction space 43 is provided at a position farther from the front end side than the measured gas flow portion, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position defined by the side surface of the first solid electrolyte layer 4. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

[0044] The reference gas introduction layer 48 is a layer formed of porous ceramics, and the reference gas is introduced into the reference gas introduction layer 48 through the reference gas introduction space 43. The reference gas introduction layer 48 is formed so as to cover the reference electrode 42.

[0045] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, the third internal cavity 61, and the fourth internal cavity 63. The reference electrode 42 is formed as a porous metal ceramic electrode (for example, a metal ceramic electrode of Pt and ZrO2).

[0046] In the measured gas flow section, the gas inlet 10 is a portion open to the external space, and the measured gas enters the sensor element 101 from the external space through the gas inlet 10. The first diffusion rate control section 11 is a portion that applies a predetermined diffusion resistance to the measured gas entering from the gas inlet 10. The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion rate control section 11 to the second diffusion rate control section 13. The second diffusion rate control section 13 is a portion that applies a predetermined diffusion resistance to the measured gas introduced from the buffer space 12 to the first internal cavity 20. When the measured gas is introduced from the outside of the sensor element 101 into the first internal cavity 20, the measured gas that rapidly enters the sensor element 101 from the gas inlet port 10 due to the pressure fluctuation of the measured gas in the external space (when the measured gas is the exhaust gas of an automobile, it is the pulsation of the exhaust pressure) is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure fluctuation of the measured gas is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure fluctuation of the measured gas introduced into the first internal cavity 20 is almost negligible. The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the measured gas introduced through the second diffusion rate control unit 13. Such oxygen partial pressure is adjusted by operating the main pump unit 21.

[0047] The main pump unit 21 is an electrochemical pump unit composed of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 clamped by these electrodes, the inner pump electrode 22 having a top electrode portion 22a arranged on substantially the entire surface of the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is arranged on the upper surface of the second solid electrolyte layer 6 in an area corresponding to the top electrode portion 22a in a manner exposed in the external space.

[0048] The inner pump electrode 22 is arranged across the solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) formed on the upper and lower sides that define the first inner cavity 20, and the isolation layer 5 constituting the side wall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 constituting the top surface of the first inner cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 constituting the bottom surface, and a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the isolation layer 5 constituting the two side wall portions of the first inner cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b, so that the side electrode portion is arranged in a tunnel-shaped structure.

[0049] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, cermet electrodes containing 1% Au, Pt and ZrO2). In addition, the inner pump electrode 22 in contact with the measured gas is formed using a material with a weakened ability to reduce NOx components in the measured gas.

[0050] In the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in a positive direction or a negative direction. Thus, the oxygen in the first internal cavity 20 can be absorbed into the external space, or the oxygen in the external space can be absorbed into the first internal cavity 20.

[0051] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, i.e., an oxygen partial pressure detection sensor unit 80 for main pump control, is formed by the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0052] By measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be known. In addition, the voltage Vp0 of the variable power supply 24 is feedback-controlled so that the voltage V0 reaches a target value, thereby controlling the pump current Ip0. As a result, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0053] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20 , and guides the gas to be measured to the second internal cavity 40 .

[0054] The second internal cavity 40 is provided as a space for performing the following processing: the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal cavity 20, and then the oxygen partial pressure of the measured gas introduced through the third diffusion rate control unit 30 is further adjusted by the auxiliary pump unit 50. As a result, the oxygen concentration in the second internal cavity 40 can be kept constant with high accuracy, so that the NOx concentration can be measured with high accuracy in the gas sensor 100.

[0055] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit composed of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is a suitable electrode on the outside of the sensor element 101), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a that is roughly entirely arranged on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0056] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 in the same tunnel-shaped structure as the inner pump electrode 22 previously disposed in the first internal cavity 20. That is, a top electrode portion 51a is formed on the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40, and a side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed in a tunnel-shaped structure formed on both wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40. In addition, the auxiliary pump electrode 51 is formed of a material having a weakened reducing ability for the NOx component in the measured gas, similarly to the inner pump electrode 22.

[0057] In the auxiliary pump cell 50 , a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23 , thereby allowing oxygen in the atmosphere in the second internal cavity 40 to be absorbed into the external space or oxygen to be absorbed into the second internal cavity 40 from the external space.

[0058] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely, an auxiliary pump control oxygen partial pressure detection sensor unit 81, is formed by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, and the third substrate layer 3.

[0059] The auxiliary pump unit 50 performs pumping using a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81. Thus, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is controlled to a relatively low partial pressure that has substantially no effect on the measurement of NOx.

[0060] At the same time, the pump current Ip1 is used to control the electromotive force of the main pump control oxygen partial pressure detection sensor unit 80. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor unit 80, and the above-mentioned target value of the voltage V0 is controlled to control the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

[0061] The fourth diffusion rate control unit 60 is a portion that applies a predetermined diffusion resistance to the measured gas whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and introduces the measured gas into the third internal cavity 61. The fourth diffusion rate control unit 60 has a function of limiting the amount of NOx flowing into the third internal cavity 61.

[0062] The third internal cavity 61 is provided as a space in which the oxygen concentration (oxygen partial pressure) is adjusted in advance in the second internal cavity 40, and then the gas to be measured introduced through the fourth diffusion rate control unit 60 is processed in relation to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured. The NOx concentration is mainly measured in the third internal cavity 61 by the operation of the first measurement pump unit 41.

[0063] The first measurement pump cell 41 measures the NOx concentration in the measured gas in the third internal cavity 61. The first measurement pump cell 41 is an electrochemical pump cell composed of a first measurement electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, a separator 5, and a first solid electrolyte layer 4, and the first measurement electrode 44 is provided at a position facing the third internal cavity 61 on the upper surface of the first solid electrolyte layer 4. The first measurement electrode 44 is a porous metal ceramic electrode made of a material having a higher reduction ability for the NOx component in the measured gas than the inner pump electrode 22. The first measurement electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere in the third internal cavity 61.

[0064] The first measuring pump cell 41 can absorb oxygen generated by decomposition of nitrogen oxides in the atmosphere around the first measuring electrode 44 , and the generated amount can be detected as the pump current Ip2 .

[0065] In addition, in order to detect the oxygen partial pressure around the first measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the first measuring electrode 44, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a first measuring pump control oxygen partial pressure detection sensor unit 82. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the first measuring pump control oxygen partial pressure detection sensor unit 82.

[0066] The gas to be measured introduced into the second internal cavity 40 passes through the fourth diffusion rate control unit 60 under the condition that the oxygen partial pressure is controlled and reaches the first measuring electrode 44 in the third internal cavity 61. The nitrogen oxides in the gas to be measured around the first measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. And the generated oxygen is pumped by the first measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled in such a way that the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for the first measuring pump control is constant (target value). The amount of oxygen generated around the first measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, so the concentration of nitrogen oxides in the gas to be measured is calculated using the pump current Ip2 in the first measuring pump unit 41.

[0067] In addition, if the first measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42 are combined to form an oxygen partial pressure detection mechanism as an electrochemical sensor unit, the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the first measuring electrode 44 and the amount of oxygen contained in the reference atmosphere can be detected, thereby also being able to determine the concentration of the NOx component in the measured gas.

[0068] The fifth diffusion rate control unit 62 applies a predetermined diffusion resistance to the gas to be measured in the third internal cavity 61 and guides the gas to be measured to the fourth internal cavity 63. The fifth diffusion rate control unit 62 has a role of limiting the amount of carbon dioxide flowing into the fourth internal cavity 63.

[0069] The fourth internal cavity 63 is provided as a space for performing processing related to the measurement of the carbon dioxide (CO2) concentration in the measured gas introduced through the fifth diffusion rate control unit 62 after the nitrogen oxides are reduced in the third internal cavity 61. The measurement of the carbon dioxide concentration is mainly performed in the fourth internal cavity 63 by the operation of the second measurement pump unit 66.

[0070] The second measuring pump cell 66 is an electrochemical pump cell composed of a second measuring electrode 67, an outer pump electrode 23, a second solid electrolyte layer 6, a separator 5, and a first solid electrolyte layer 4, and the second measuring electrode 67 is provided at a position facing the fourth internal cavity 63 on the upper surface of the first solid electrolyte layer 4. The second measuring electrode 67 is a porous metal ceramic electrode made of a material having a higher reducing ability for the carbon dioxide component in the measured gas than the inner pump electrode 22. The second measuring electrode 67 also functions as a carbon dioxide reduction catalyst for reducing carbon dioxide present in the atmosphere in the fourth internal cavity 63.

[0071] The second measuring pump cell 66 can absorb oxygen generated by decomposition of carbon dioxide in the atmosphere around the second measuring electrode 67 , and the generated amount can be detected as the pump current Ip3 .

[0072] In addition, in order to detect the oxygen partial pressure around the second measuring electrode 67, the first solid electrolyte layer 4, the third substrate layer 3, the second measuring electrode 67, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a second measuring pump control oxygen partial pressure detection sensor unit 84. The variable power supply 68 is controlled based on the electromotive force (voltage V3) detected by the second measuring pump control oxygen partial pressure detection sensor unit 84.

[0073] Regarding the gas to be measured in the third internal cavity 61, the NOx component is reduced, and the oxygen generated by the reduction is pumped by the first measurement pump unit 41, and then reaches the second measurement electrode 67 in the fourth internal cavity 63 through the fifth diffusion rate control unit 62. The carbon dioxide in the gas to be measured around the second measurement electrode 67 is reduced (2CO2→2CO+O2) to generate oxygen. And the generated oxygen is pumped by the second measurement pump unit 66. At this time, the voltage Vp3 of the variable power supply 68 is controlled in such a way that the voltage V3 detected by the second measurement pump control oxygen partial pressure detection sensor unit 84 is constant (target value). The amount of oxygen generated around the second measurement electrode 67 is proportional to the concentration of carbon dioxide in the gas to be measured, so the concentration of carbon dioxide in the gas to be measured is calculated using the pump current Ip3 in the second measurement pump unit 66.

[0074] In addition, the electrochemical sensor unit 83 composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42 can detect the oxygen partial pressure in the measured gas outside the sensor by using the electromotive force (voltage Vref) obtained by the sensor unit 83.

[0075] In the gas sensor 100 having such a structure, the main pump unit 21 and the auxiliary pump unit 50 are operated to supply the measured gas whose oxygen partial pressure is always kept at a constant low value (a value that has substantially no effect on the measurement of NOx) to the first measurement pump unit 41. Therefore, the NOx concentration in the measured gas can be known based on the pump current Ip2 that is approximately proportional to the NOx concentration in the measured gas and flows by the oxygen generated by the reduction of NOx being sucked out from the first measurement pump unit 41. In addition, the carbon dioxide concentration in the measured gas can be known based on the pump current Ip3 that flows by the oxygen generated by the reduction of carbon dioxide being sucked out from the second measurement pump unit 66.

[0076] In addition, the sensor element 101 includes a heater unit 70, which has a temperature adjustment function of heating and keeping the sensor element 101 warm so as to improve the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure release hole 75.

[0077] The heater connector electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to an external power source, power can be supplied to the heater unit 70 from the outside.

[0078] The heater 72 is a resistor formed by being sandwiched from the upper and lower sides by the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater connector electrode 71 via the through hole 73, and is supplied from the heater power source 76 (see Figure 2 ) supplies power, thereby generating heat to heat and keep the solid electrolyte forming the sensor element 101 warm.

[0079] Furthermore, the heater 72 is buried in the entire region from the first internal cavity 20 to the fourth internal cavity 63 , and the entire sensor element 101 can be adjusted to a temperature at which the solid electrolyte is activated.

[0080] Heater insulating layer 74 is an insulating layer formed of an insulator such as alumina on the upper and lower surfaces of heater 72. Heater insulating layer 74 is formed to obtain electrical insulation between second substrate layer 2 and heater 72 and between third substrate layer 3 and heater 72.

[0081] The pressure release hole 75 is a portion that penetrates the third substrate layer 3 and the reference gas introduction layer 48 and is connected to the reference gas introduction space 43 . The purpose of forming the pressure release hole 75 is to alleviate the internal pressure increase associated with the temperature increase in the heater insulation layer 74 .

[0082] like Figure 2As shown, the control device 95 includes the above-mentioned variable power supplies 24, 46, 52, 68, the above-mentioned heater power supply 76, and a control unit 96. The control unit 96 is a microprocessor including a CPU 97 and a storage unit 98. The storage unit 98 is a non-volatile storage unit capable of rewriting information, and can store various programs and various data, for example. The control unit 96 receives inputs of the voltage V0 detected by the main pump control oxygen partial pressure detection sensor unit 80, the voltage V1 detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81, the voltage V2 detected by the first measurement pump control oxygen partial pressure detection sensor unit 82, the voltage V3 detected by the second measurement pump control oxygen partial pressure detection sensor unit 84, the voltage Vref detected by the sensor unit 83, the pump current Ip0 detected by the main pump unit 21, the pump current Ip1 detected by the auxiliary pump unit 50, the pump current Ip2 detected by the first measurement pump unit 41, and the pump current Ip3 detected by the second measurement pump unit 66. In addition, the control unit 96 controls the voltages Vp0, Vp1, Vp2, and Vp3 outputted from the variable power supplies 24, 46, 52, and 68 by outputting control signals to the variable power supplies 24, 46, 52, and 68, thereby controlling the main pump unit 21, the auxiliary pump unit 50, the first measurement pump unit 41, and the second measurement pump unit 66. The control unit 96 controls the power supplied from the heater power supply 76 to the heater 72 by outputting control signals to the heater power supply 76. The storage unit 98 also stores target values ​​V0*, V1*, V2*, and V3*, which will be described later. The CPU 97 of the control unit 96 controls each unit 21, 41, 50, and 66 with reference to the target values ​​V0*, V1*, V2*, and V3*.

[0083] The control unit 96 performs the following auxiliary pump control processing: the auxiliary pump unit 50 is controlled so that the oxygen concentration in the second internal cavity 40 reaches the target concentration. Specifically, the control unit 96 controls the auxiliary pump unit 50 by performing feedback control on the voltage Vp1 of the variable power supply 52 so that the voltage V1 reaches a constant value (referred to as the target value V1*). The target value V1* is defined as a value that makes the oxygen concentration in the second internal cavity 40 reach a predetermined low concentration that has substantially no effect on the measurement of NOx.

[0084] The control unit 96 performs the following main pump control processing to control the main pump unit 21 so that the pump current Ip1 flowing when the auxiliary pump unit 50 adjusts the oxygen concentration of the second internal cavity 40 by the auxiliary pump control processing reaches the target current (referred to as the target value Ip1*). Specifically, the control unit 96 sets the target value of the voltage V0 (referred to as the target value V0*) based on the pump current Ip1 so that the pump current Ip1 flowing through the voltage Vp1 reaches a certain target value Ip1* (feedback control). In addition, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0* (that is, so that the oxygen concentration of the first internal cavity 20 reaches the target concentration). Through this main pump control processing, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is always constant. The target value V0* is set to a value such that the oxygen concentration of the first internal cavity 20 is higher than 0% and is low. In addition, the pump current Ip0 flowing in the main pump control process changes in accordance with the oxygen concentration of the measured gas (i.e., the measured gas around the sensor element 101) flowing into the measured gas flow portion from the gas inlet 10. Therefore, the control unit 96 can also detect the oxygen concentration in the measured gas based on the pump current Ip0.

[0085] The main pump control process and the auxiliary pump control process are also collectively referred to as the adjustment pump control process. In addition, the first internal cavity 20 and the second internal cavity 40 are also collectively referred to as the oxygen concentration adjustment chamber. The main pump unit 21 and the auxiliary pump unit 50 are also collectively referred to as the adjustment pump unit. The adjustment pump control process is performed by the control unit 96 so that the adjustment pump unit adjusts the oxygen concentration of the oxygen concentration adjustment chamber.

[0086] Furthermore, the control unit 96 performs the first measurement pump control process as follows: the first measurement pump cell 41 is controlled so that the voltage V2 reaches a constant value (referred to as a target value V2*) (that is, so that the oxygen concentration in the third internal cavity 61 reaches a predetermined low concentration). Specifically, the control unit 96 controls the first measurement pump cell 41 by performing feedback control on the voltage Vp2 of the variable power supply 46 so that the voltage V2 reaches the target value V2*. Oxygen is sucked out from the third internal cavity 61 by the first measurement pump control process.

[0087] By performing the first measurement pump control process, oxygen is sucked out from the third internal cavity 61 so that the oxygen generated by the reduction of NOx in the measured gas in the third internal cavity 61 is substantially zero. In addition, the control unit 96 obtains the pump current Ip2 as a detection value corresponding to the oxygen generated from NOx in the third internal cavity 61, and calculates the NOx concentration in the measured gas based on the pump current Ip2.

[0088] The storage unit 98 stores a relational expression (for example, a linear function or a quadratic function), a map, etc. as the correspondence between the pump current Ip2 and the NOx concentration. Such a relational expression or a map can be solved in advance by experiments.

[0089] Furthermore, the control unit 96 performs the second measurement pump control process as follows: the second measurement pump unit 66 is controlled so that the voltage V3 reaches a constant value (referred to as a target value V3*) (that is, so that the oxygen concentration in the fourth internal cavity 63 reaches a predetermined low concentration). Specifically, the control unit 96 controls the second measurement pump unit 66 by performing feedback control on the voltage Vp3 of the variable power supply 68 so that the voltage V3 reaches the target value V3*. Oxygen is sucked out from the fourth internal cavity 63 by the second measurement pump control process.

[0090] By performing the second measurement pump control process, oxygen is sucked out from the fourth internal cavity 63 so that the oxygen generated by the reduction of carbon dioxide in the measured gas in the fourth internal cavity 63 is substantially zero. In addition, the control unit 96 obtains the pump current Ip3 as a detection value corresponding to the oxygen derived from carbon dioxide and generated in the fourth internal cavity 63, and calculates the carbon dioxide concentration in the measured gas based on the pump current Ip3.

[0091] The control unit 96 performs the following heater control processing: outputs a control signal to the heater power supply 76 to control the temperature of the heater 72 to reach the target temperature (e.g., 800° C.). Here, the temperature of the heater 72 can be expressed by a linear function of the resistance value of the heater 72. Therefore, in the heater control processing, the control unit 96 calculates the resistance value of the heater 72 as a value that can be regarded as the temperature of the heater 72 (a value that can be converted into temperature), and performs feedback control on the heater power supply 76 so that the calculated resistance value reaches the target resistance value (a resistance value corresponding to the target temperature). The control unit 96 can obtain, for example, the voltage of the heater 72 and the current flowing through the heater 72, and calculate the resistance value of the heater 72 based on the obtained voltage and current. The control unit 96 can also calculate the resistance value of the heater 72 using, for example, a three-terminal method or a four-terminal method. When the heater 72 is energized, the heater power supply 76 changes the value of the voltage applied to the heater 72 based on, for example, a control signal from the control unit 96, thereby adjusting the power supplied to the heater 72.

[0092] The inventors of the present invention investigated the relationship between the target value V1* of the gas sensor 100, the water concentration in the measured gas, and the pump current Ip2. First, as the measured gas, three gases were prepared: a first gas with nitrogen as the base gas, 0% oxygen concentration, 3% water concentration, 0 ppm NO concentration, and 0% carbon dioxide concentration; a second gas with the same composition as the first gas except that the water concentration was set to 9%; and a third gas with the same composition as the first gas except that the water concentration was set to 15%. Next, the target value V2* was set to 400mV, the target value V1* was set to 300mV, and the control unit 96 performed the above-mentioned adjustment pump control process and the first measurement pump control process on the first gas, and measured the pump current Ip2 at this time. It should be noted that the control unit 96 starts the above-mentioned heater control process, and after the temperature of the heater 72 reaches the vicinity of the target temperature, the adjustment pump control process and the first measurement pump control process are started, and then the value of the pump current Ip2 is measured in a state where the pump current Ip2 has stabilized. Furthermore, the target value V1* was changed to 350mV, 400mV, and 450mV, and the pump current Ip2 corresponding to the respective target value V1* was measured in the same manner as above. The pump current Ip2 corresponding to the respective target value V1* was measured in the same manner as above for the second gas and the third gas. The results are shown in Figure 3 . Figure 3 : is a graph showing the relationship between the target value V1*, the water concentration in the measured gas, and the pump current Ip2. Figure 3 The pump current Ip2 on the vertical axis in is represented by: the pump current Ip2 is converted into a value of NO concentration (unit: ppm) using the correspondence between the pump current Ip2 and the NOx concentration stored in the storage unit 98. The NO concentration in the first to third gases is 0 ppm, so in any case, theoretically, the pump current Ip2 is 0 μA, but in reality, a small amount of pump current Ip2 flows. The pump current Ip2 that flows due to reasons other than NOx is called the bias current Ip2offset. Therefore, Figure 3 The relationship between the target value V1*, the water concentration in the measured gas, and the bias current Ip2offset is shown. The bias current is also included in the pump current Ip2 when the NOx concentration is not 0 ppm.

[0093] like Figure 3 As shown, there is a linear correlation between the target value V1* and the bias current Ip2offset, and it is confirmed that the higher the target value V1*, the smaller the bias current Ip2offset. In addition, regarding the slope of the change in the bias current Ip2offset relative to the change in the target value V1*, it is confirmed that the higher the water concentration in the measured gas, the larger the absolute value of the slope. Figure 4It shows that according to Figure 3 The graph is a graph showing the relationship between the water concentration in the measured gas calculated from the data shown and the slope of the change in the bias current Ip2offset relative to the change in the target value V1*. Figure 4 As shown in the figure, there is a linear correlation between the water concentration and the slope of the bias current Ip2offset, and it is confirmed that the higher the water concentration, the smaller the slope of the bias current Ip2offset (the larger the negative absolute value). From these results, it can be seen that the water concentration in the measured gas can be detected based on the change in the pump current Ip2 when the target value V1* is changed (for example, the slope of the change in the bias current Ip2offset when the target value V1* is changed). This is a new insight discovered by the inventors of the present invention.

[0094] The inventors of the present invention and Figure 3 Similarly, the relationship between the target value V2* of the gas sensor 100, the water concentration in the measured gas, and the pump current Ip2 was investigated. Specifically, the same first to third gases as above were used, the target value V1* was set to 385mV, the target value V2* was changed to 4 values ​​of 300mV, 350mV, 400mV, and 450mV, and the relationship between the target value V2* and the pump current Ip2 was investigated. Figure 3 The pump current Ip2 corresponding to the respective target value V2* is measured in the same manner as in the data in FIG. Figure 5 . Figure 5 : is a graph showing the relationship between the target value V2*, the water concentration in the measured gas, and the pump current Ip2. Figure 6 It shows that according to Figure 5 The graph shown is a graph of the relationship between the water concentration in the measured gas calculated from the data and the slope of the change in the bias current Ip2offset with respect to the change in the target value V2*.

[0095] like Figure 5 As shown in FIG. 1 , there is a linear correlation between the target value V2* and the bias current Ip2offset, and it is confirmed that the higher the target value V2*, the larger the bias current Ip2offset. In addition, regarding the slope of the change in the bias current Ip2offset relative to the change in the target value V2*, it is confirmed that the higher the water concentration in the measured gas, the larger the absolute value of the slope. Figure 6As shown in the figure, there is a linear correlation between the water concentration and the slope of the bias current Ip2offset, and it is confirmed that the higher the water concentration, the larger the slope of the bias current Ip2offset (the larger the positive absolute value). From these results, it can be seen that the water concentration in the measured gas can be detected based on the change in the pump current Ip2 when the target value V2* is changed (for example, the slope of the change in the bias current Ip2offset when the target value V2* is changed). This is a new insight discovered by the inventors of the present invention.

[0096] From the above, it can be seen that the change in the pump current Ip2 flowing during the execution of the adjustment pump control process and the first measurement pump control process when at least one of the target value V1* and the target value V2* is changed is correlated with the water concentration in the measured gas, so the water concentration can be detected based on the change in the pump current Ip2. In this embodiment, as the relationship between the slope of the change in the pump current Ip2 when the target value V1* is changed and the water concentration in the measured gas, Figure 4 The linear function equation or map showing the linear relationship is stored in the storage unit 98 .

[0097] It should be noted that there is a relationship between the target value V1* and the target value V2*, the water concentration in the measured gas, and the pump current Ip2 (particularly the bias current Ip2offset). Figure 3 to Figure 6 The reason for the shown relationship is as follows.

[0098] First, the relationship between water in the measured gas and the bias current Ip2offset is described. When water exists in the measured gas, when the adjustment pump control process (here, the main pump control process and the auxiliary pump control process) is performed, the voltage Vp1 of the variable power supply 52 causes at least a portion of the water to be decomposed around the auxiliary pump electrode 51 to generate hydrogen (H2) and oxygen (O2). The generated oxygen is sucked out from the periphery of the auxiliary pump electrode 51, that is, the second internal cavity 40, through the auxiliary pump unit 50, but at least a portion of the generated hydrogen reaches the third internal cavity 61. In addition, the hydrogen that reaches the third internal cavity 61 reacts with the oxygen in the third internal cavity 61 to become water, so the amount of oxygen sucked out from the third internal cavity 61 by the first measurement pump control process decreases, that is, the pump current Ip2 decreases. On the other hand, when water is present in the gas to be measured, when the first measurement pump control process is performed, the voltage Vp2 of the variable power supply 46 causes at least a portion of the water to be decomposed around the first measurement electrode 44 in the third internal cavity 61 to generate hydrogen (H2) and oxygen (O2). Therefore, the amount of oxygen sucked out from the third internal cavity 61 by the first measurement pump control process increases, that is, the pump current Ip2 increases. In this way, the pump current Ip2 decreases due to hydrogen generated by water around the auxiliary pump electrode 51, and the pump current Ip2 increases due to oxygen generated by water around the first measurement electrode 44. Therefore, the sum of the decrease and increase of these pump currents Ip2 that have nothing to do with NOx in the gas to be measured is expressed as the offset current Ip2offset.

[0099] Furthermore, the higher the target value V1* is, that is, the lower the target value of the oxygen concentration in the second internal cavity 40 is, the higher the voltage Vp1 becomes through the auxiliary pump control process. Therefore, the more hydrogen is produced by water being decomposed around the auxiliary pump electrode 51 due to the voltage Vp1, and the reduction in the pump current Ip2 also increases. In addition, the higher the water concentration in the measured gas is, the more hydrogen is produced by water being decomposed around the auxiliary pump electrode 51. Therefore, the reduction in the pump current Ip2 corresponding to the change in the target value V1*, that is, the slope of the change in the pump current Ip2 relative to the change in the target value V1* becomes steeper. That is, the absolute value of the slope becomes larger. It is considered that: Based on these reasons, it is shown that Figure 3 and Figure 4 The relationship shown.

[0100] Similarly, the higher the target value V2* is, that is, the lower the target value of the oxygen concentration in the third internal cavity 61 is, the easier it is for the voltage Vp2 to become a higher value through the first measurement pump control process. Therefore, the water produced by the decomposition of the voltage Vp2 in the vicinity of the first measurement electrode 44 increases, and the increase in the pump current Ip2 also increases. In addition, the higher the water concentration in the measured gas, the more oxygen produced by the decomposition of the water in the vicinity of the first measurement electrode 44. Therefore, the increase in the pump current Ip2 corresponding to the change in the target value V2*, that is, the slope of the change in the pump current Ip2 relative to the change in the target value V2* becomes steeper. That is, the absolute value of the slope increases. It is believed that: Based on these reasons, the expression Figure 5 and Figure 6 The relationship shown.

[0101] Next, an example of a process in which the control unit 96 of the gas sensor 100 measures the concentration of a specific gas (here, the NOx concentration, the carbon dioxide concentration, the water concentration, and the oxygen concentration) in the measured gas will be described. Figure 7 2 is a flowchart showing an example of a control routine executed by the control unit 96. The control unit 96 stores the routine in, for example, the storage unit 98. The control unit 96 starts the control routine when a start command is input from, for example, an engine ECU (not shown).

[0102] When the CPU 97 of the control unit 96 starts the control routine, first, the above-mentioned heater control process is started (step S100). Next, the CPU 97 starts the above-mentioned adjustment pump control process, the first measurement pump control process and the second measurement pump control process (step S110). At this time, the values ​​of the target value V1* and the target value V2* are the values ​​pre-stored in the storage unit 98 as the values ​​used when measuring the NOx concentration. Next, the CPU 97 determines whether it is the concentration derivation timing to derive the specific gas concentration in the measured gas (step S120). The CPU 97 determines that it is the concentration derivation timing, for example, every time a specified time has passed or when a concentration derivation instruction is input from the engine ECU.

[0103] When it is determined in step S120 that it is the time to derive the concentration, the CPU 97 first performs an oxygen concentration detection process to derive the oxygen concentration based on the pump current Ip0 (step S125). In the adjustment pump control process (here, especially the main pump control process), the CPU 97 controls the main pump unit 21 in a manner that causes the voltage V0 to reach the target value V0* (that is, in a manner that causes the oxygen concentration in the first internal cavity 20 to reach the target concentration). Therefore, as described above, the oxygen concentration in the measured gas can be derived based on the pump current Ip0. In this embodiment, a relationship expression or mapping that represents the corresponding relationship between the pump current Ip0 and the oxygen concentration is obtained by experiment and is pre-stored in the storage unit 98. In step S125, the CPU 97 calculates the oxygen concentration in the measured gas based on the current pump current Ip0 and the corresponding relationship stored in the storage unit 98.

[0104] Next, the CPU 97 performs the following water concentration detection processing: based on the change of the pump current Ip2 flowing during the execution of the adjustment pump control processing and the first measurement pump control processing when at least one of the target value V1* and the target value V2* is changed, the water concentration in the measured gas is detected (steps S130, S140). In the present embodiment, the CPU 97 changes the target value V1* in the water concentration detection processing, but does not change the target value V2*. In the water concentration detection processing, the CPU 97 first calculates the slope G of the change of the pump current Ip2 when the target value V1* is changed (step S130). Specifically, the CPU 97 first measures the current pump current Ip2 and obtains the value of the pump current Ip2 as the state before the target value V1* is changed. Next, the CPU 97 changes the target value V1*, waits until the value of the pump current Ip2 is stable, measures the stabilized pump current Ip2, and obtains the value of the pump current Ip2 as the state after the change. Then, the slope G is derived by dividing the difference in the pump current Ip2 values ​​before and after the change by the difference in the target value V1* before and after the change. It should be noted that the length of time from the change in the target value V1* to the stabilization of the pump current Ip2 is extremely short (several msec to more than ten msec, etc.), and generally, during this period, there is almost no change in the NOx concentration in the exhaust gas of the internal combustion engine. Therefore, the difference in the pump current Ip2 values ​​before and after the change in the target value V1* can be regarded as the change in the offset current Ip2offset before and after the change in the target value V1*. Therefore, the slope G derived in step S130 is equivalent to Figure 3 The slope of the straight line shown and Figure 4The value of the vertical axis in . Then, the CPU 97 calculates the water concentration in the measured gas based on the derived slope G and the correspondence relationship stored in the storage unit 98 (the correspondence relationship between the slope of the change in the pump current Ip2 when the target value V1* is changed and the water concentration in the measured gas) (step S140). In step S130, the target value V1* may be changed in a direction that increases the absolute value, or may be changed in a direction that decreases the absolute value. However, it is preferred that the values ​​before and after the change are both less than the absolute value of the target value V1* determined for measuring the NOx concentration. For example, when the target value V1* before the change is the same value as the target value V1* determined for measuring the NOx concentration, it is preferred that the target value V1* be changed in a direction that decreases the absolute value. According to this, it is possible to suppress the voltage Vp1 from being too high and causing the decomposition of NOx to occur around the auxiliary pump electrode 51, thereby suppressing the reduction in the accuracy of measuring the NOx concentration.

[0105] When the water concentration is derived in step S140, CPU97 returns the target value V1* to the value before the change. That is, the target value V1* is returned to the value determined for measuring the NOx concentration (step S150). Next, CPU97 obtains the pump current Ip2 that flows through the first measuring pump control process (step S160), and derives the NOx concentration in the measured gas based on the obtained pump current Ip2 and the correspondence relationship stored in the storage unit 98 (the above-mentioned correspondence relationship between the pump current Ip2 and the NOx concentration) (step S170). Then, CPU97 corrects the NOx concentration derived in step S170 based on the water concentration derived in step S140, and derives the corrected NOx concentration (step S180). Figure 3 As shown in FIG. 1 , the bias current Ip2offset of the pump current Ip2 changes according to the water concentration in the measured gas. Therefore, even if the NOx concentration in the measured gas is the same, the pump current Ip2 sometimes changes according to the water concentration in the measured gas, and sometimes an error occurs in the derived NOx concentration. Therefore, in this embodiment, the CPU 97 corrects the NOx concentration obtained based on the pump current Ip2 based on the detected water concentration. For example, Figure 3When the target value V1* is 350mV, the bias current Ip2offset when the water concentration is 15% reaches a value that is 3ppm greater than the bias current Ip2offset when the water concentration is 3% in terms of NOx concentration. Therefore, for example, when the correspondence relationship between the pump current Ip2 and the NOx concentration pre-stored in the storage unit 98 is a relationship calculated using the measured gas with a water concentration of 3%, when the actual water concentration of the measured gas is 15%, the derived NOx concentration is calculated as a value that is 3ppm greater than the actual concentration. Therefore, when the water concentration derived in step S140 is 15%, the CPU 97 derives a value obtained by subtracting 3ppm as a correction amount from the NOx concentration [ppm] derived in step S170 as the corrected NOx concentration. In this way, the change in the bias current Ip2offset caused by the difference in water concentration can be offset, and the corrected NOx concentration becomes a value closer to the actual concentration. Such a correspondence relationship between the water concentration and the correction amount of the NOx concentration can be obtained in advance by experiments or the like and stored in the storage unit 98. In step S180, the CPU 97 derives the correction amount based on the water concentration and the corresponding relationship, and calculates the corrected NOx concentration. It should be noted that, instead of deriving the correction amount, the corresponding relationship between the water concentration, the NOx concentration obtained based on the pump current Ip2, and the corrected NOx concentration may be stored in advance in the storage unit 98, and the corrected NOx concentration may be derived based on the corresponding relationship. In addition, the CPU 97 may correct the pump current Ip2 derived in step S170 based on the water concentration, and derive the NOx concentration based on the corrected pump current Ip2. These methods all belong to the correction of the NOx concentration based on the water concentration.

[0106] When the NOx concentration is derived in step S180, the CPU 97 performs a carbon dioxide concentration detection process for detecting the carbon dioxide concentration in the measured gas (steps S190 and S200). Specifically, first, the CPU 97 obtains the pump current Ip3 flowing through the second measurement pump control process (step S190), and derives the carbon dioxide concentration in the measured gas based on the obtained pump current Ip3 and the water concentration derived in step S140 (step S200). Here, the CPU 97 controls the second measurement pump unit 66 in such a manner that the voltage V3 reaches the target value V3* (that is, such a manner that the oxygen concentration in the fourth internal cavity 63 reaches the target concentration) in the second measurement pump control process as described above. Therefore, the pump current Ip3 flowing through the second measurement pump unit 66 is correlated with the amount of oxygen generated in the fourth internal cavity 63 from carbon dioxide. In particular, when the measured gas contains water, in the fourth internal cavity 63, not only carbon dioxide is reduced but also water is reduced. Therefore, the pump current Ip3 flowing through the second measurement pump control process becomes a value obtained based on the carbon dioxide concentration and the water concentration. Therefore, in this embodiment, the CPU 97 derives the carbon dioxide concentration based on the pump current Ip3 and the water concentration. For example, between the total value Cs[%] of the water concentration and the carbon dioxide concentration in the measured gas and the pump current Ip3, as shown in FIG. Figure 8 As shown, there is a linear correlation. In this embodiment, a relational expression or a map representing the correspondence between such pump current Ip3 and total value Cs is obtained by experiment and stored in the storage unit 98 in advance. In step S200, the CPU 97 calculates the total value Cs based on the current pump current Ip3 and the correspondence stored in the storage unit 98, and derives the value obtained by subtracting the water concentration derived in step S140 from the calculated total value Cs as the carbon dioxide concentration in the measured gas. In this way, the pump current Ip3 is affected by both the water concentration and the carbon dioxide concentration. However, the inventors of the present invention have found that the change in the pump current Ip2 when at least one of the target value V1* and the target value V2* is changed is correlated with the water concentration in the measured gas. Therefore, it has been newly found that the carbon dioxide concentration can be accurately derived from the pump current Ip3 by using this correlation. It should be noted that the NOx in the measured gas is almost completely reduced in the third internal cavity 61 upstream of the fourth internal cavity 63, and the oxygen generated by the reduction is almost completely sucked out through the first measuring pump unit 41. Therefore, the NOx concentration in the measured gas has almost no effect on the pump current Ip3.

[0107] It should be noted that the total value Cs can also be referred to as "the carbon dioxide concentration based on the pump current Ip3 when the water concentration is assumed to be 0%". Therefore, the process of step S200 of subtracting the water concentration from the total value Cs derived based on the pump current Ip3 can also be referred to as the process of correcting the carbon dioxide concentration derived based on the pump current Ip3 using the water concentration derived in step S140.

[0108] After step S200, or when it is not the concentration derivation timing in step S120, the CPU 97 executes the processing after S120. The CPU 97 executes the control routine as described above to repeatedly measure the NOx concentration, carbon dioxide concentration, water concentration, and oxygen concentration in the measured gas. The CPU 97 outputs the values ​​of these concentrations obtained by measurement to the engine ECU or stores them in the storage unit 98.

[0109] Here, the correspondence between the components of the present embodiment and the components of the present invention is clarified. The stacked body obtained by stacking the six layers of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5 and the second solid electrolyte layer 6 in this embodiment in this order corresponds to the element body of the present invention, the third internal cavity 61 corresponds to the first measurement chamber, the first measurement electrode 44 corresponds to the first inner measurement electrode, the fourth internal cavity 63 corresponds to the second measurement chamber, the second measurement electrode 67 corresponds to the second inner measurement electrode, the inner pump electrode 22 and the auxiliary pump electrode 51 correspond to the inner adjustment electrode, the voltage V1 corresponds to the adjustment voltage, the target value V1* corresponds to the adjustment voltage target value, the voltage V2 corresponds to the first measurement voltage, the target value V2* corresponds to the first measurement voltage target value, the pump current Ip2 corresponds to the first measurement pump current, the voltage V3 corresponds to the second measurement voltage, the target value V3* corresponds to the second measurement voltage target value, and the pump current Ip3 corresponds to the second measurement pump current. The pump current Ip0 corresponds to the adjustment pump current, the inner pump electrode 22 corresponds to the inner main pump electrode, and the auxiliary pump electrode 51 corresponds to the inner auxiliary pump electrode.

[0110] According to the gas sensor 100 of the present embodiment described in detail above, the control device 95 detects the NOx concentration in the measured gas based on the pump current Ip2 flowing through the first measuring pump unit 41 by the first measuring pump control process. In addition, the control device 95 detects the carbon dioxide concentration in the measured gas based on the pump current Ip3 flowing through the second measuring pump unit 66 by the second measuring pump control process and the water concentration in the measured gas (a value based on the change in the pump current Ip2 flowing during the execution of the adjustment pump control process and the first measuring pump control process when at least one of the target value V1* and the target value V2* is changed). Therefore, the gas sensor 100 of the present embodiment can detect the NOx concentration and the carbon dioxide concentration in the measured gas.

[0111] In addition, the control device 95 detects the water concentration in the measured gas based on the change in the pump current Ip2 flowing during the execution of the adjustment pump control process and the first measurement pump control process when at least one of the target value V1* and the target value V2* is changed. Therefore, the gas sensor 100 can detect the water concentration in addition to the NOx concentration and the carbon dioxide concentration in the measured gas. In addition, the control device 95 derives the total value of the carbon dioxide concentration and the water concentration in the measured gas based on the pump current Ip3, and subtracts the water concentration detected in step S140 from the derived total value, thereby detecting the carbon dioxide concentration in the measured gas. Accordingly, the control device 95 can detect the carbon dioxide concentration using a relatively simple method.

[0112] Furthermore, the control device 95 detects the oxygen concentration in the measured gas based on the pump current Ip0 flowing through the main pump control process as a part of the adjustment pump control process. Therefore, the gas sensor 100 can detect the oxygen concentration in addition to the NOx concentration and the carbon dioxide concentration in the measured gas.

[0113] It should be noted that the present invention is not limited to the above-described embodiment, and can be implemented in various forms as long as it falls within the technical scope of the present invention.

[0114] For example, in the above embodiment, Figure 7In step S130 of the control routine in , the CPU 97 derives the water concentration based on the slope G of the change of the pump current Ip2 when the target value V1* is changed. However, the water concentration may be derived based on the change of the pump current Ip2 when the target value V1* is changed, without being limited to the slope G. For example, the water concentration may be derived based on the change amount or change rate of the pump current Ip2 before and after the change of the target value V1*. In this case, the correspondence between the change amount or change rate of the pump current Ip2 and the water concentration may be stored in the storage unit 98 in advance.

[0115] In the above embodiment, Figure 7 In step S130 of the control routine in FIG. 1 , the CPU 97 derives the water concentration based on the slope G of the change in the pump current Ip2 when the target value V1* is changed. However, the water concentration may be derived based on the change in the pump current Ip2 when the target value V2* is changed. For example, the CPU 97 may derive the slope of the change in the pump current Ip2 when the target value V2* is changed without changing the target value V1* (equivalent to Figure 5 The slope of the straight line shown and Figure 6 In this case, the correspondence between the slope of the change in the pump current Ip2 when the target value V2* is changed and the water concentration (equivalent to Figure 6 The target value V2* may be changed in a direction that increases the absolute value of the target value V2*, or may be changed in a direction that decreases the absolute value. However, it is preferred that the values ​​before and after the change are both greater than the target value V2* determined for measuring the NOx concentration. For example, when the target value V2* before the change is the same as the target value V2* determined for measuring the NOx concentration, it is preferred that the target value V2* be changed in a direction that increases the absolute value of the target value V2*. In this way, it is possible to prevent the voltage Vp2 from being too low and causing the pump current Ip2 to fail to reach the limiting current, thereby preventing the accuracy of measuring the NOx concentration from being reduced.

[0116] CPU97 can also derive the water concentration based on the pump current Ip2 when both the target value V1* and the target value V2* are changed in the water concentration detection process. In this case, it is preferred that the direction of the change in the pump current Ip2 caused by the change in the target value V1* and the direction of the change in the pump current Ip2 caused by the change in the target value V2* are the same direction. For example, if the absolute value of the target value V1* is changed to a smaller value and the absolute value of the target value V2* is changed to a larger value, these changes all work in the direction of increasing the pump current Ip2. Alternatively, if the absolute value of the target value V1* is changed to a larger value and the absolute value of the target value V2* is changed to a smaller value, these changes all work in the direction of reducing the pump current Ip2. If the target value V1* and the target value V2* are changed by any of the above methods, even if the change amounts of the target value V1* and the target value V2* are small, the change in the pump current Ip2 caused by the water in the measured gas becomes relatively large. Therefore, it is easy to detect the water concentration based on the change in the pump current Ip2. When changing both target value V1* and target value V2*, not only the slope of pump current Ip2 but also the change amount or change rate of pump current Ip2 may be calculated, and the water concentration may be derived based on the change amount or change rate.

[0117] For example, in the above-mentioned embodiment, the CPU 97 derives the carbon dioxide concentration based on the water concentration and the pump current Ip3 derived in S140, but the present invention is not limited thereto. The CPU 97 can derive the carbon dioxide concentration based on the change in the pump current Ip2 flowing during the execution of the adjustment pump control process and the first measurement pump control process when at least one of the target value V1* and the target value V2* is changed, and the pump current Ip3 without deriving the water concentration itself. For example, as a value indicating the change in the pump current Ip2, the slope G derived in step S130 may be used, or the change amount or change rate of the pump current Ip2 may be used. For example, when the slope G is used, the corresponding relationship between the slope G, the pump current Ip3, and the carbon dioxide concentration may be obtained in advance by experiment and stored in the storage unit 98. Fig. 9 is a graph showing an example of this correspondence. Fig. 9 As shown, the correspondence relationship has a tendency that the carbon dioxide concentration decreases as the absolute value of the slope G increases (= the water concentration increases), and has a tendency that the carbon dioxide concentration increases as the pump current Ip3 increases. Fig. 9 For example, when the pump current Ip3 is value A and the absolute value of the slope G is value G1, the derived carbon dioxide concentration is value B. In addition, even if the pump current Ip3 is the same value A, when the absolute value of the slope G is G2 or G3 which is larger than G1 (G1<G2<G3), the greater the absolute value of the slope G, the smaller the derived carbon dioxide concentration value. Fig. 9In FIG. 1 , only three straight lines are shown, but the corresponding relationship stored in the storage unit 98 may include a plurality of straight line relationships with slightly different absolute values ​​of the slope G. Alternatively, Fig. 9 The CPU 97 derives the carbon dioxide concentration while appropriately performing linear interpolation or other interpolation. Fig. 9 The corresponding relationship shown in the figure is used to store the corresponding relationship between the pump current Ip3 and the carbon dioxide concentration when the water concentration is assumed to be a specified value (for example, 0%), that is, the first corresponding relationship, and the corresponding relationship between the slope G and the correction amount of the carbon dioxide concentration, that is, the second corresponding relationship, in the storage unit 98. In this case, the CPU 97 can correct the carbon dioxide concentration derived based on the pump current Ip3 and the first corresponding relationship using the correction amount derived based on the slope G and the second corresponding relationship (for example, the carbon dioxide concentration minus the correction amount), thereby deriving the corrected carbon dioxide concentration. The second corresponding relationship can also be set as the corresponding relationship between the slope G and the correction amount of the pump current Ip3. In this case, the CPU 97 only needs to correct the pump current Ip3 using the correction amount based on the slope G and the second corresponding relationship, and derive the carbon dioxide concentration based on the corrected pump current Ip3 and the first corresponding relationship.

[0118] In the above embodiment, the CPU 97 detects the NOx concentration, the carbon dioxide concentration, the water concentration and the oxygen concentration, but it is sufficient to detect at least the NOx concentration and the carbon dioxide concentration. Figure 7 At least one of steps S125 and S140 of the control routine in . In addition, Figure 7 In the control routine, the order in which the CPU 97 detects the NOx concentration, carbon dioxide concentration, water concentration and oxygen concentration can be reversed, or two or more concentrations can be detected simultaneously.

[0119] In the above embodiment, the CPU 97 uses the water concentration to correct the NOx concentration, but it is not necessary to perform the correction. In addition, the CPU 97 may determine whether the derived water concentration is within a predetermined permissible range that can be regarded as having no influence on the measurement accuracy of the NOx concentration, and correct the NOx concentration if it is not within the permissible range.

[0120] In the above embodiment, the adjustment pump control process, the first measurement pump control process, and the second measurement pump control process are continuously executed after step S110, but the present invention is not particularly limited to this, and at least any one of these control processes may be temporarily stopped. For example, in step S130, the adjustment pump control process and the first measurement pump control process may be temporarily stopped, and then the target value V1* is set to the changed value, and the adjustment pump control process and the first measurement pump control process are restarted.

[0121] In the above embodiment, the oxygen concentration adjustment chamber has the first internal cavity 20 and the second internal cavity 40, but the present invention is not limited thereto. For example, the oxygen concentration adjustment chamber may further include another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above embodiment, the adjustment pump unit has the main pump unit 21 and the auxiliary pump unit 50, but the present invention is not limited thereto. For example, the adjustment pump unit may further include another pump unit, or one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, when the oxygen concentration of the measured gas can be sufficiently low using only the main pump unit 21, the auxiliary pump unit 50 may be omitted. Fig.10 It is a schematic cross-sectional view of a sensor element 201 as an example of a sensor element that does not include the auxiliary pump unit 50 . Fig.10 In, with Figure 1 The same components are marked with the same reference numerals, and detailed descriptions are omitted. The sensor element 201 does not include the auxiliary pump unit 50, the third diffusion rate control unit 30, and the second internal cavity 40. Therefore, the first internal cavity 20 and the fourth diffusion rate control unit 60 are adjacent. In addition, the sensor element 201 does not include the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. When controlling the sensor element 201 in which the auxiliary pump unit 50 is omitted, the control unit 96 only needs to perform the main pump control process as the adjustment pump control process. In addition, in the main pump control process, the setting of the target value V0* based on the pump current Ip1 mentioned above can be omitted. Specifically, as long as the specified target value V0* is pre-stored in the storage unit 98, the control unit 96 can feedback control the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0*, thereby controlling the main pump unit 21. When the auxiliary pump unit 50 is omitted, the voltage V0 is equivalent to the adjustment voltage (the voltage V1 of the above embodiment), and the target value V0* is equivalent to the adjustment voltage target value (the target value V1* of the above embodiment). Therefore, the CPU 97 can detect the water concentration or the carbon dioxide concentration in the same manner as in the above embodiment based on the change of the pump current Ip2 flowing during the execution of the adjustment pump control process and the first measurement pump control process when at least one of the target value V0* and the target value V2* is changed. When the oxygen concentration adjustment chamber has the first internal cavity 20, the second internal cavity 40, and another internal cavity, and the adjustment pump unit has three or more pump units, the target value of the voltage in the control process of the pump unit on the most downstream side among the three or more pump units, that is, the pump unit arranged near the first measurement chamber to the maximum extent, is equivalent to the adjustment voltage target value. In addition, the current flowing through the control process of the pump unit on the most upstream side among the three or more pump units, that is, the pump unit arranged near the gas inlet 10 to the maximum extent, is equivalent to the adjustment pump current.

[0122] In the above embodiment, the inner pump electrode 22 is a metal ceramic electrode of Pt and ZrO2 containing 1% Au, but it is not limited to this. The inner pump electrode 22 only needs to contain a noble metal with catalytic activity. As a noble metal with catalytic activity, for example, at least any one of Pt, Rh, Ir, Ru, and Pd can be cited. However, it is preferred that the inner pump electrode 22 contains Pt as a noble metal with catalytic activity as in the above embodiment. The inner pump electrode 22 preferably contains a noble metal with catalytic activity and Au. As for the auxiliary pump electrode 51, it is also sufficient to contain a noble metal with catalytic activity, similarly to the inner pump electrode 22, and preferably further contains Au. By containing Au in the inner pump electrode 22 and the auxiliary pump electrode 51, the catalytic activity for NOx and carbon dioxide can be suppressed, and therefore, NOx and carbon dioxide can be suppressed from being reduced in the first internal cavity 20 and the second internal cavity 40. The first measuring electrode 44 only needs to contain a noble metal with catalytic activity. The first measuring electrode 44 preferably contains Rh and a noble metal other than Rh having catalytic activity (for example, at least any one of Pt, Ir, Ru, and Pd). The first measuring electrode 44 more preferably contains Rh and Pt. By including Rh in the first measuring electrode 44, the reduction of NOx in the third internal cavity 61 can be promoted. The outer pump electrode 23, the reference electrode 42, and the second measuring electrode 67 only need to contain the above-mentioned noble metal having catalytic activity. Each of the electrodes 22, 23, 42, 44, 51, and 67 is preferably a metal ceramic containing a noble metal and an oxide having oxygen ion conductivity (for example, ZrO2), but at least one of these electrodes may not be a metal ceramic. Each of the electrodes 22, 23, 42, 44, 51, and 67 is preferably a porous body, but at least one of these electrodes may not be a porous body.

[0123] In the above embodiment, although not described, the target value V0* and the target value V1* are preferably values ​​of 300mV or more and less than 400mV, respectively. If the target value V0* and the target value V1* are 300mV or more, respectively, the main pump unit 21 and the auxiliary pump unit 50 can fully absorb the oxygen in the oxygen concentration adjustment chamber. If the target value V0* and the target value V1* are less than 400mV, respectively, NOx and carbon dioxide can be suppressed from being reduced in the oxygen concentration adjustment chamber. The target value V2* is preferably a value of 400mV or more and 500mV or less. If the target value V2* is 400mV or more, NOx around the first measuring electrode 44 can be fully reduced. If the target value V2* is 500mV or less, carbon dioxide can be suppressed from being reduced in the third internal cavity 61. The target value V3* is preferably a value of 1000mV or more and 1500mV or less. If the target value V3* is 1000mV or more, the carbon dioxide around the second measuring electrode 67 can be fully reduced. If the target value V3* is 1500mV or less, the voltage Vp3 will not be too high, so it is possible to prevent the sensor element 101 from blackening and becoming unusable. The blackening of the sensor element 101 occurs as follows: due to the lack of oxygen ions in the solid electrolyte caused by the application of a high voltage, the electronic conduction of the solid electrolyte is exhibited, thereby causing blackening.

[0124] Although not described in the above embodiment, the gas sensor 100 is preferably configured such that when the temperatures of the inner pump electrode 22, the auxiliary pump electrode 51, the first measuring electrode 44, and the second measuring electrode 67 when the heater 72 is heated to at least any temperature in the temperature range of 700°C to 900°C are Tp, Tq, Tm1, and Tm2, ​​respectively, the temperature Tp>Tq>Tm1 and the temperature Tp>Tq>Tm2. The amount of oxygen to be sucked out from the measured gas flow portion is the largest in the main pump unit 21, followed by the auxiliary pump unit 50, and the first measuring pump unit 41 and the second measuring pump unit 66 are relatively small. Therefore, by satisfying the above temperature magnitude relationship, the pumping capacity of the main pump unit 21 and the auxiliary pump unit 50 can be sufficiently improved. The temperatures Tp, Tq, Tm1, and Tm2 are preferably all 1000°C or less so that the sensor element 101 can be prevented from cracking. The temperature Tp is preferably 600°C or higher so that the main pump unit 21 can fully absorb oxygen. The temperature Tp is preferably 900°C or lower so that NOx can be suppressed from being reduced in the first internal cavity 20. The temperature Tq is preferably 600°C or higher so that the auxiliary pump unit 50 can fully absorb oxygen. The temperature Tq is preferably 900°C or lower so that NOx can be suppressed from being reduced in the second internal cavity 40. The temperature Tm1 is preferably 500°C or higher so that the first measuring pump unit 41 can fully absorb oxygen generated by NOx. The temperature Tm2 is preferably 600°C or higher so that the second measuring pump unit 66 can fully absorb oxygen generated by carbon dioxide. For example, by adjusting the shape and configuration of the heater 72, the temperature Tp, the temperature Tq, the temperature Tm1, and the temperature Tm2 can be adjusted.

[0125] In the above-mentioned embodiment, the outer pump electrode 23 has the functions of an electrode paired with the inner pump electrode 22 in the main pump cell 21 (also referred to as an outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 in the auxiliary pump cell 50 (also referred to as an outer auxiliary pump electrode), an electrode paired with the first measurement electrode 44 in the first measurement pump cell 41 (also referred to as a first outer measurement electrode), and an electrode paired with the second measurement electrode 67 in the second measurement pump cell 66 (also referred to as a second outer measurement electrode), but the present invention is not limited thereto. It is also possible that one or more of the outer main pump electrode, the outer auxiliary pump electrode, the first outer measurement electrode, and the second outer measurement electrode are different from the outer pump electrode 23 and are provided outside the element body in a manner in contact with the gas to be measured.

[0126] In the above embodiment, the element body of the sensor element 101 is set as a stacked body having a plurality of solid electrolyte layers (layers 1 to 6), but it is not limited thereto. The element body of the sensor element 101 only needs to include at least one oxygen ion conductive solid electrolyte layer. For example, Figure 1 In the embodiment, the layers 1 to 5 other than the second solid electrolyte layer 6 may be formed of a material other than the solid electrolyte layer (for example, a layer formed of aluminum oxide). In this case, the electrodes of the sensor element 101 only need to be arranged on the second solid electrolyte layer 6. For example, Figure 1 The first measuring electrode 44 and the second measuring electrode 67 in the embodiment can be arranged on the lower surface of the second solid electrolyte layer 6. In addition, the reference gas introduction space 43 can be arranged in the isolation layer 5 instead of being arranged in the first solid electrolyte layer 4, the reference gas introduction layer 48 can be arranged between the second solid electrolyte layer 6 and the isolation layer 5 instead of being arranged between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 can be arranged at the rear of the third internal cavity 61 and at the lower surface of the second solid electrolyte layer 6.

[0127] In the above embodiment, the control unit 96 sets the target value V0* of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 reaches the target value Ip1* (feedback control), and performs feedback control on the pump voltage Vp0 so that the voltage V0 reaches the target value V0*, but other controls may be performed. For example, the control unit 96 may also perform feedback control on the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 reaches the target value Ip1*. That is, the control unit 96 may omit obtaining the voltage V0 from the main pump control oxygen partial pressure detection sensor unit 80 and setting the target value V0*, and directly control the pump voltage Vp0 based on the pump current Ip1 (or even control the pump current Ip0).

[0128] This application claims priority based on Japanese Patent Application No. 2022-169087 filed on October 21, 2022, the contents of which are incorporated herein by reference in their entirety.

[0129] Industrial Applicability

[0130] The present invention can be used in a gas sensor for detecting the NOx concentration and the carbon dioxide concentration in a measured gas such as automobile exhaust gas.

[0131] Explanation of symbols

[0132] 1 first substrate layer, 2 second substrate layer, 3 third substrate layer, 4 first solid electrolyte layer, 5 isolation layer, 6 second solid electrolyte layer, 10 gas introduction port, 11 first diffusion rate control unit, 12 buffer space, 13 second diffusion rate control unit, 20 first internal cavity, 21 main pump unit, 22 inner pump electrode, 22a top electrode portion, 22b bottom electrode portion, 23 outer pump electrode, 24 variable power supply, 30 third diffusion rate control unit, 40 second internal cavity, 41 first measurement pump unit, 42 reference electrode, 43 reference gas introduction space, 44 first measurement electrode, 46 variable power supply, 48 reference gas introduction layer, 50 auxiliary pump unit, 51 auxiliary pump electrode, 51a top electrode portion, 51b bottom electrode portion, 52 variable power supply, 60 fourth diffusion rate control unit, 61 third internal cavity, 62 fifth diffusion rate control unit, 63 fourth internal cavity, 66 second measuring pump unit, 67 second measuring electrode, 68 variable power supply, 70 heater unit, 71 heater connector electrode, 72 heater, 73 through hole, 74 heater insulating layer, 75 pressure release hole, 76 heater power supply, 80 main pump control oxygen partial pressure detection sensor unit, 81 auxiliary pump control oxygen partial pressure detection sensor unit, 82 first measuring pump control oxygen partial pressure detection sensor unit, 83 sensor unit, 84 second measuring pump control oxygen partial pressure detection sensor unit, 95 control device, 96 control unit, 97 CPU, 98 storage unit, 100 gas sensor, 101, 201 sensor element.

Claims

1. A gas sensor comprising a sensor element and a control device, The sensor element has: an element body having an oxygen ion conductive solid electrolyte layer and provided with a gas flow portion for introducing and flowing the gas to be measured; a first measurement pump unit, the first measurement pump unit comprising a first inner measurement electrode provided in a first measurement chamber in the measured gas flow portion, and sucking oxygen in the first measurement chamber to the outside of the element body; A second measuring pump unit, the second measuring pump unit comprising a second inner measuring electrode provided in a second measuring chamber located downstream of the first measuring chamber in the measured gas flow section, and sucking oxygen in the second measuring chamber to the outside of the element body; an adjusting pump unit, the adjusting pump unit comprising an inner adjusting electrode provided in an oxygen concentration adjusting chamber located upstream of the first measuring chamber in the measured gas flow section, and adjusting the oxygen concentration in the oxygen concentration adjusting chamber; as well as a reference electrode disposed inside the element body in such a manner as to be in contact with a reference gas, The control device performs: an adjustment pump control process, in which the adjustment pump unit is controlled so as to adjust the oxygen concentration of the oxygen concentration adjustment chamber in such a manner that the voltage between the reference electrode and the inner adjustment electrode, that is, the adjustment voltage, reaches a target adjustment voltage value; a first measurement pump control process, in which the first measurement pump unit is controlled so as to suck out the oxygen of the first measurement chamber in such a manner that the voltage between the reference electrode and the first inner measurement electrode, that is, the first measurement voltage, reaches a target first measurement voltage value; and a second measurement pump control process, in which the second measurement pump unit is controlled so as to suck out the oxygen of the second measurement chamber in such a manner that the voltage between the reference electrode and the second inner measurement electrode, that is, the second measurement voltage, reaches a target second measurement voltage value. The control device detects the NOx concentration in the gas to be measured based on the first measurement pump current flowing when oxygen generated when NOx is reduced in the first measurement chamber is sucked out by the first measurement pump control process. The control device detects the carbon dioxide concentration in the measured gas based on the second measuring pump current flowing when the oxygen generated when the carbon dioxide is reduced in the second measuring chamber is sucked out through the second measuring pump control process, and the change in the first measuring pump current flowing during the execution of the adjustment pump control process and the first measuring pump control process when at least one of the adjustment voltage target value and the first measuring voltage target value is changed.

2. The gas sensor according to claim 1, wherein: The control device detects the water concentration in the gas to be measured based on the change in the first measurement pump current.

3. The gas sensor according to claim 2, wherein: The control device derives a total value of the carbon dioxide concentration and the water concentration in the gas to be measured based on the second measurement pump current, and detects the carbon dioxide concentration in the gas to be measured by subtracting the detected water concentration from the total value.

4. The gas sensor according to any one of claims 1 to 3, wherein: The control device detects the oxygen concentration in the measured gas based on the adjustment pump current flowing through the adjustment pump control process.

5. The gas sensor according to any one of claims 1 to 3, wherein: The oxygen concentration adjustment chamber comprises: a first internal cavity; and a second internal cavity, the second internal cavity being arranged downstream of the first internal cavity and upstream of the measurement chamber. The adjustment pump unit includes: a main pump unit that adjusts the oxygen concentration of the first internal cavity; and an auxiliary pump unit that adjusts the oxygen concentration of the second internal cavity. The inner adjustment electrode includes: an inner main pump electrode, which is arranged in the first inner cavity and constitutes a part of the main pump unit; and an inner auxiliary pump electrode, which is arranged in the second inner cavity and constitutes a part of the auxiliary pump unit. The adjustment pump control process includes: a main pump control process for controlling the main pump unit to adjust the oxygen concentration of the first internal cavity; and an auxiliary pump control process for controlling the auxiliary pump unit so that the adjustment voltage reaches the adjustment voltage target value.

6. The gas sensor according to any one of claims 1 to 3, wherein: The inner adjustment electrode includes: a noble metal having catalytic activity and Au.

7. The gas sensor according to any one of claims 1 to 3, wherein: The first inner measurement electrode includes Rh and a noble metal other than Rh having catalytic activity.

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