Gas sensor and control method for a gas sensor

Abstract

The objective of this invention is to accurately measure even low concentrations of the target gas. This invention relates to a gas sensor (100) and a control method for the gas sensor (100). The gas sensor (100) detects the target gas in the gas being measured and includes a sensor element (101) and a control device (90). The sensor element (101) includes a main pump unit (21), an auxiliary pump unit (50), a measuring pump unit (41), and a reference electrode (42). The main pump unit (21) allows a main pump current Ip0 to flow through it, which is repeatedly switched on and off, so that the auxiliary pump current flowing in the auxiliary pump unit (50) is... When the current Ip1 reaches the specified target current value, the auxiliary pump unit (50) allows the auxiliary pump current Ip1 to flow, so that the electromotive force V1 between the inner auxiliary pump electrode (51) and the reference electrode (42) reaches the specified target voltage value. The control device (90) includes: a control power supply (24) for allowing the main pump current Ip0 to flow through the repeatedly turned-on and off state; and a setting unit (94) for setting the target voltage value of the auxiliary pump unit (50) based on the potential difference V0 generated between the inner main pump electrode (22) and the reference electrode (42).

Description

Technical Field

[0001] This invention relates to gas sensors and control methods for gas sensors. Background Technology

[0002] Gas sensors are used to detect and determine the concentration of target gas components (oxygen O2, nitrogen oxides NOx, ammonia NH3, hydrocarbons HC, carbon dioxide CO2, etc.) in gases such as automobile exhaust. For example, the concentration of the target gas component in automobile exhaust can be measured, and the exhaust gas purification system installed in the vehicle can be optimized based on the measured value.

[0003] As such gas sensors, those utilizing solid electrolytes with oxygen ion conductivity, such as zirconium dioxide (ZrO2), are known. For example, international publication WO2020 / 196653 discloses a gas sensor comprising a main pump unit and an auxiliary pump unit for oxygen extraction, and a measuring pump unit for extracting oxygen generated from a specific gas. When NOx is detected as a specific gas using this gas sensor, firstly, the oxygen partial pressure in the gas to be measured is controlled to a low partial pressure that substantially has no effect on the NOx measurement using the main pump unit and the auxiliary pump unit. The NOx in the gas to be measured, with its oxygen partial pressure controlled, is reduced at the measuring electrode, resulting in oxygen production. This oxygen is then extracted using the measuring pump unit and detected as a current value.

[0004] Furthermore, international publication WO2020 / 196653 discloses that at least one of the more than one pump units in a gas sensor allows for the absorption of oxygen by circulating a pump current (pulse current) that is repeatedly switched on and off. This suppresses changes in the catalytic activity of the electrodes that occur with the use of the gas sensor.

[0005] Patent Document 1: International Publication WO2020 / 196653 Summary of the Invention

[0006] With stricter regulations on automobile exhaust emissions, there is a growing demand for gas sensors capable of accurately measuring even low concentrations of the target gas. Here, "low concentration" refers to concentrations such as less than 500 ppm, less than 400 ppm, less than 300 ppm, less than 200 ppm, or less than 100 ppm.

[0007] Regarding existing gas sensors, such as those described in international publication WO2020 / 196653, the partial pressure of oxygen in the gas to be measured is controlled to a low partial pressure that substantially has no effect on the measurement of the target gas (e.g., NOx) using a main pump unit and an auxiliary pump unit, ensuring that the gas to be measured, containing a specified low concentration of oxygen and the target gas, reaches the measuring electrode. Furthermore, the measuring pump unit pumps oxygen generated at the measuring electrode due to the target gas in the gas to be measured, thereby detecting the current value corresponding to the concentration of the target gas.

[0008] However, when measuring low concentrations of the target gas (around 10-500 ppm), the detection values ​​sometimes deviate. The inventors of this invention have determined that during the operation of the gas sensor, the amount of oxygen in the target gas reaching the measuring electrode can vary due to certain factors, causing fluctuations in the current value detected by the measuring pump unit. If the amount of oxygen in the target gas reaching the measuring electrode varies, the current value detected by the measuring pump unit will not change according to the concentration of the target gas. Therefore, it is evident that, especially when the concentration of the target gas in the measured gas is low, this can sometimes affect the measurement accuracy.

[0009] Therefore, the object of the present invention is to enable high-precision measurement of target gases even at low concentrations. That is, the object is to accurately measure target gases over a wide concentration range, including low-concentration target gases.

[0010] The inventors of this invention conducted in-depth research and discovered that, according to the following invention, by controlling the oxygen concentration in the gas to be measured to a specified concentration with high precision, even low-concentration target gases can be measured with high precision.

[0011] This invention includes the following inventions.

[0012] (1) A gas sensor for detecting a target gas in a gas to be measured, comprising: a sensor element and a control device for controlling the sensor element.

[0013] The sensor element includes:

[0014] The elongated, plate-shaped base portion includes a solid electrolyte layer that is oxygen ion conductive;

[0015] The gas flow section to be measured is formed from one end of the base portion along its length.

[0016] The main pump unit includes an inner main pump electrode and an outer main pump electrode. The inner main pump electrode is disposed on the inner surface of the gas flow section to be measured, and the outer main pump electrode is disposed at a different position on the base from the gas flow section to be measured, and corresponds to the inner main pump electrode.

[0017] An auxiliary pump unit includes an inner auxiliary pump electrode and an outer auxiliary pump electrode. The inner auxiliary pump electrode is disposed at one end of the inner surface of the gas flow section being measured, which is further away from the base section in the length direction than the inner main pump electrode. The outer auxiliary pump electrode is disposed at a different position on the base section from the gas flow section being measured, and corresponds to the inner auxiliary pump electrode.

[0018] A measuring pump unit includes an inner measuring electrode and an outer measuring electrode. The inner measuring electrode is disposed at one end of the inner surface of the gas flow section being measured, further away from the base portion in the longitudinal direction than the inner auxiliary pump electrode. The outer measuring electrode is disposed at a different position on the base portion from the gas flow section being measured, and corresponds to the inner measuring electrode.

[0019] A reference electrode, which is arranged inside the substrate to contact the reference gas.

[0020] The main pump unit allows the main pump current to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current flowing in the auxiliary pump unit reaches a specified target current value.

[0021] The auxiliary pump unit allows current to flow through it, so that the electromotive force between the inner auxiliary pump electrode and the reference electrode reaches a predetermined target voltage value.

[0022] The control device includes:

[0023] A control power supply, used to allow the main pump current, which is repeatedly switched on and off, to flow in the main pump unit; and

[0024] The setting unit sets the target voltage value of the auxiliary pump unit.

[0025] The setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode, and sets the target voltage value of the auxiliary pump unit based on the potential difference.

[0026] (2) Based on the gas sensor described in (1) above, the setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode during the cutoff period when the main pump current is not flowing using the control power supply in the main pump unit.

[0027] (3) Based on the gas sensor described in (1) or (2) above, the setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode during a stable period in the main pump unit when the main pump current is not circulated using the control power supply and there is no change due to the main pump current circulated due to the potential difference.

[0028] (4) Based on the gas sensor described in any of (1) to (3) above, the control power supply includes: a pulse power supply that causes the main pump current to periodically turn on and off.

[0029] The setting unit obtains, for each period T, the potential difference generated between the inner main pump electrode and the reference electrode during a predetermined time period in the period T of the pulse power supply during which the main pump current is not flowing due to the absence of the pulse power supply.

[0030] (5) A control method for a gas sensor, used to detect the target gas in the gas to be measured.

[0031] The gas sensor includes: a sensor element, and a control device for controlling the sensor element.

[0032] The sensor element includes:

[0033] The elongated, plate-shaped base portion includes a solid electrolyte layer that is oxygen ion conductive;

[0034] The gas flow section to be measured is formed from one end of the base portion along its length.

[0035] The main pump unit includes an inner main pump electrode and an outer main pump electrode. The inner main pump electrode is disposed on the inner surface of the gas flow section to be measured, and the outer main pump electrode is disposed at a different position on the base from the gas flow section to be measured, and corresponds to the inner main pump electrode.

[0036] An auxiliary pump unit includes an inner auxiliary pump electrode and an outer auxiliary pump electrode. The inner auxiliary pump electrode is disposed at one end of the inner surface of the gas flow section being measured, which is further away from the base section in the length direction than the inner main pump electrode. The outer auxiliary pump electrode is disposed at a different position on the base section from the gas flow section being measured, and corresponds to the inner auxiliary pump electrode.

[0037] A measuring pump unit includes an inner measuring electrode and an outer measuring electrode. The inner measuring electrode is disposed at one end of the inner surface of the gas flow section being measured, further away from the base portion in the longitudinal direction than the inner auxiliary pump electrode. The outer measuring electrode is disposed at a different position on the base portion from the gas flow section being measured, and corresponds to the inner measuring electrode.

[0038] A reference electrode, which is arranged inside the substrate to contact the reference gas.

[0039] The control device includes a control power supply for allowing the main pump current, which is repeatedly switched on and off, to flow through the main pump unit.

[0040] The control method includes the following steps:

[0041] The setting step involves acquiring the potential difference between the inner main pump electrode and the reference electrode, and setting a target voltage value for the electromotive force between the inner auxiliary pump electrode and the reference electrode of the auxiliary pump unit based on the potential difference; and

[0042] In the oxygen concentration adjustment step, the control power supply in the main pump unit is controlled to allow the main pump current to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current flowing in the auxiliary pump unit reaches a specified target current value. Furthermore, the auxiliary pump current is allowed to flow in the auxiliary pump unit so that the electromotive force between the inner auxiliary pump electrode and the reference electrode reaches the target voltage value.

[0043] (6) Based on the control method described in (5) above, in the setting step, during the cutoff period when the main pump current is not flowing in the main pump unit using the control power supply, the potential difference generated between the inner main pump electrode and the reference electrode is obtained.

[0044] (7) Based on the control method described in (5) or (6) above, in the setting step, during a stable period in the main pump unit where the main pump current is not circulated using the control power supply and there is no change due to the main pump current circulated due to the potential difference, the potential difference generated between the inner main pump electrode and the reference electrode is obtained.

[0045] (8) Based on the control method described in any one of (5) to (7) above, the control power supply includes: a pulse power supply that causes the main pump current to periodically turn on and off.

[0046] In the setting step, for each period T, the potential difference generated between the inner main pump electrode and the reference electrode is obtained at a predetermined time during the cutoff period in which the pulse power supply is not used to allow the main pump current to flow.

[0047] Invention Effects

[0048] According to the present invention, even low concentrations of the target gas can be measured with high precision. That is, according to the present invention, a wide range of concentrations of the target gas, including low concentrations, can be measured with high precision. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a longitudinal vertical cross-section showing an example of the general structure of a gas sensor 100.

[0050] Figure 2 This is a block diagram showing the electrical connections between the control device 90 and the pump units 21, 50, 41, the sensor units 80, 81, 82, 83, and the heater section 70 of the sensor element 101.

[0051] Figure 3 This is a flowchart illustrating an example of the NOx concentration detection process of the gas sensor 100.

[0052] Figure 4 This is a schematic diagram showing the changes of the main pump current Ip0 and potential difference V0 over time when the main pump current Ip0 flows in the forward direction. Figure 4 (1) is a schematic diagram showing the change of the main pump current Ip0 over time. The horizontal axis represents time t, and the vertical axis represents the main pump current Ip0. Figure 4 (2) is a schematic diagram showing the change of potential difference V0 over time. The horizontal axis represents time t, and the vertical axis represents potential difference V0.

[0053] Figure 5 This is a schematic diagram showing the changes of the main pump current Ip0 and potential difference V0 over time when the main pump current Ip0 flows in the negative direction. Figure 5 (1) is a schematic diagram showing the change of the main pump current Ip0 over time. The horizontal axis represents time t, and the vertical axis represents the main pump current Ip0. Figure 5 (2) is a schematic diagram showing the change of potential difference V0 over time. The horizontal axis represents time t, and the vertical axis represents potential difference V0.

[0054] Figure 6 This is a schematic diagram illustrating an example of the main pump current Ip0 being an instantaneous pulse current. The horizontal axis represents time t, and the vertical axis represents the main pump current Ip0.

[0055] Explanation of reference numerals in the attached figures

[0056] 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 inlet; 11…First diffusion rate control unit; 12…Buffer space; 13…Second diffusion rate control unit; 15…Measured gas flow section; 20…First internal cavity; 21…Main pump unit; 22…Inner main pump electrode; 22a…Top electrode portion (of the inner main pump electrode); 22b…Bottom electrode portion (of the inner main pump electrode); 23…Outer pump electrode; 24…Pulse power supply; 30…Third diffusion rate control unit; 40…Second internal cavity; 41…Measurement pump unit; 42…Reference electrode; 43…Reference gas inlet space; 44…Measurement electrode; 46…Variable power supply (of the measurement pump unit); 48…Atmosphere inlet layer; 50…Auxiliary pump unit; 5 1…Auxiliary pump electrode; 51a…(Top electrode part of auxiliary pump electrode); 51b…(Bottom electrode part of auxiliary pump electrode); 52…(Variable power supply of auxiliary pump unit); 60…Fourth diffusion rate control unit; 61…Third internal cavity; 70…Heater part; 71…Heater electrode; 72…Heater; 73…Through hole; 74…Heater insulation layer; 75…Pressure relief hole; 76…Heater conductor; 77…Heater power supply; 80…Oxygen partial pressure detection sensor unit for main pump control; 81…Oxygen partial pressure detection sensor unit for auxiliary pump control; 82…Oxygen partial pressure detection sensor unit for measuring pump control; 83…Sensor unit; 90…Control device; 91…Control unit; 92…Drive control unit; 93…Concentration calculation unit; 94…Setting unit; 100…Gas sensor; 101…Sensor element; 102…Base part. Detailed Implementation

[0057] The gas sensor of the present invention includes: a sensor element and a control device for controlling the sensor element.

[0058] The gas sensor of the present invention includes the following sensor elements:

[0059] The elongated, plate-shaped base portion includes a solid electrolyte layer that is oxygen ion conductive;

[0060] The gas flow section to be measured is formed from one end of the base portion along its length.

[0061] The main pump unit includes an inner main pump electrode and an outer main pump electrode. The inner main pump electrode is disposed on the inner surface of the gas flow section to be measured, and the outer main pump electrode is disposed at a different position on the base from the gas flow section to be measured, and corresponds to the inner main pump electrode.

[0062] An auxiliary pump unit includes an inner auxiliary pump electrode and an outer auxiliary pump electrode. The inner auxiliary pump electrode is disposed at one end of the inner surface of the gas flow section being measured, which is further away from the base section in the length direction than the inner main pump electrode. The outer auxiliary pump electrode is disposed at a different position on the base section from the gas flow section being measured, and corresponds to the inner auxiliary pump electrode.

[0063] A measuring pump unit includes an inner measuring electrode and an outer measuring electrode. The inner measuring electrode is disposed at one end of the inner surface of the gas flow section being measured, further away from the base portion in the longitudinal direction than the inner auxiliary pump electrode. The outer measuring electrode is disposed at a different position on the base portion from the gas flow section being measured, and corresponds to the inner measuring electrode.

[0064] A reference electrode, which is arranged inside the substrate to contact the reference gas.

[0065] The main pump unit allows the main pump current to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current flowing through the auxiliary pump unit reaches a specified target current value.

[0066] The auxiliary pump unit allows current to flow through the auxiliary pump so that the electromotive force between the inner auxiliary pump electrode and the reference electrode reaches a specified target voltage value.

[0067] The control device included in the gas sensor of the present invention includes:

[0068] A control power supply, used to allow the main pump current, which is repeatedly switched on and off, to flow in the main pump unit; and

[0069] The setting unit sets the target voltage value of the auxiliary pump unit.

[0070] The setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode, and sets the target voltage value of the auxiliary pump unit based on the potential difference.

[0071] Examples of power supplies for control include pulse power supplies.

[0072] Hereinafter, an example of an embodiment of the gas sensor of the present invention will be described in detail.

[0073] [Overall Structure of a Gas Sensor]

[0074] The gas sensor of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a schematic vertical cross-sectional view along the length of an example of the general structure of a gas sensor 100 including sensor element 101. Hereinafter, [the following will be described using...] Figure 1 Based on the benchmark, regarding the upper and lower, Figure 1 The top side is designated as "top", and the bottom side is designated as "bottom". Figure 1 The left side is designated as the front-end side, and the right side is designated as the back-end side.

[0075] exist Figure 1 In the section on gas sensor 100, an example of a NOx sensor is shown, which uses sensor element 101 to detect NOx in a gas to be measured and to measure its concentration.

[0076] Additionally, the gas sensor 100 includes a control device 90 for controlling the sensor element 101. As an example of a control power supply for circulating the main pump current Ip0, which is repeatedly switched on and off, in the main pump unit 21 (described later), the control device 90 includes a pulse power supply 24. Figure 2 This is a block diagram illustrating the electrical connection between the control device 90 and the sensor element 101.

[0077] (Sensor element)

[0078] The sensor element 101 is a strip-shaped element, comprising a substrate 102 having a structure formed by stacking multiple oxygen ion-conducting solid electrolyte layers. "Strip-shaped" refers to a long plate or strip. The substrate 102 has a structure in which six layers—a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an insulating layer 5, and a second solid electrolyte layer 6—are stacked sequentially from the bottom side in the figures, each composed of an oxygen ion-conducting solid electrolyte layer such as zirconium dioxide (ZrO2). The solid electrolyte forming these six layers is a dense and gas-tight solid electrolyte. The six layers can be all of the same thickness or have different thicknesses. The layers are bonded together by an adhesive layer made of solid electrolyte, which is included in the substrate 102. Figure 1 The example shown is a multi-layer structure consisting of the six layers, but the multi-layer structure of the present invention is not limited to this and can be set to any number of layers and multi-layer structure.

[0079] For example, after performing prescribed processing on the ceramic green sheets corresponding to each layer and printing circuit patterns, they are stacked and then fired to integrate them, thereby manufacturing the aforementioned sensor element 101.

[0080] A gas inlet 10 is formed at one end (hereinafter referred to as the front end) along the length of the sensor element 101, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The gas flow section 15 is configured such that: a first diffusion rate control section 11, a buffer space 12, a second diffusion rate control section 13, a first internal cavity 20, a third diffusion rate control section 30, a second internal cavity 40, a fourth diffusion rate control section 60, and a third internal cavity 61 are formed adjacent to each other in the length direction starting from the gas inlet 10.

[0081] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are: the internal space of the sensor element 101 provided by hollowing out the isolation layer 5, wherein the upper part of the internal space is divided by the lower surface of the second solid electrolyte layer 6, the lower part is divided by the upper surface of the first solid electrolyte layer 4, and the side part is divided by the side of the isolation layer 5.

[0082] The first diffusion velocity control unit 11, the second diffusion velocity control unit 13, and the third diffusion velocity control unit 30 are all configured with two horizontally long ( Figure 1 The slit (the length direction of the opening) is perpendicular to the direction shown in the attached figure. Both the first diffusion velocity control unit 11 and the second diffusion velocity control unit 13 can be configured to apply the desired diffusion resistance, and the configuration is not limited to the slit.

[0083] The fourth diffusion velocity control unit 60 is a horizontally long ( Figure 1 A slit (forming an opening along its length, perpendicular to the direction shown in the attached figure) is disposed between the isolation layer 5 and the second solid electrolyte layer 6. The fourth diffusion rate control unit 60 can be configured to apply the desired diffusion resistance, and is not limited to the slit.

[0084] Furthermore, a reference gas introduction space 43 is provided at a location further away from the front end than the gas flow section 15, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and further defined by the side of the first solid electrolyte layer 4. The reference gas introduction space 43 has an opening at the other end of the sensor element 101 (hereinafter referred to as the rear end). As a reference gas for measuring NOx concentration, for example, atmospheric air is introduced into the reference gas introduction space 43.

[0085] The atmosphere introduction layer 48 is a layer composed of porous alumina, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43. In addition, the atmosphere introduction layer 48 is formed to cover the reference electrode 42.

[0086] 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. As described above, an atmospheric inlet layer 48 communicating with the reference gas inlet space 43 is provided around it. That is, the reference electrode 42 is configured to be in contact with the reference gas by means of the porous atmospheric inlet layer 48 and the reference gas inlet space 43. In addition, as described later, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 can be measured using the reference electrode 42. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a metal-ceramic electrode of Pt and ZrO2).

[0087] In the gas flow section 15, the gas inlet 10 is open relative to the external space, and the gas to be measured is taken from the external space into the sensor element 101 through the gas inlet 10.

[0088] In this embodiment, although the measured gas flow section 15 is configured such that the measured gas is introduced through a gas inlet 10 that is open at the front end face of the sensor element 101, the present invention is not limited to this configuration. For example, the measured gas flow section 15 may not have a recess with a gas inlet 10. In this case, the first diffusion rate control section 11 substantially constitutes a gas inlet.

[0089] Alternatively, for example, the gas flow section 15 can be configured such that it has an opening communicating with the buffer space 12 on a side along the length of the base portion 102, or an opening communicating with the buffer space 12 near the first internal cavity 20. In this case, the gas to be measured is introduced from the side along the length of the base portion 102 through the opening.

[0090] Alternatively, for example, the gas flow section 15 to be measured can be formed as a structure in which the gas to be measured is introduced through a porous body.

[0091] The first diffusion rate control unit 11 is a part that applies a predetermined diffusion resistance to the gas to be measured taken from the gas inlet 10.

[0092] The buffer space 12 is a space provided for guiding the gas to be measured, which is introduced by the first diffusion rate control unit 11, to the second diffusion rate control unit 13.

[0093] The second diffusion rate control unit 13 is a part that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20.

[0094] The amount of gas to be measured introduced into the first internal cavity 20 is sufficient as long as it is within a specified range. That is, a specified diffusion resistance is applied to the entire area from the front end of the sensor element 101 to the second diffusion rate control unit 13. For example, it can be configured such that the first diffusion rate control unit 11 is directly connected to the first internal cavity 20, i.e., there is no buffer space 12 and no second diffusion rate control unit 13.

[0095] The buffer space 12 is a space provided to mitigate the impact of pressure fluctuations on the measured value in the event of pressure changes in the gas being measured.

[0096] When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas being measured, which is rapidly drawn into the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (pulsations of exhaust pressure in the case of automobile exhaust), is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 only after the pressure fluctuations of the gas being measured are 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 fluctuations of the gas being measured introduced into the first internal space are almost negligible.

[0097] The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust the oxygen partial pressure.

[0098] The main pump unit 21 is an electrochemical pump unit comprising: an inner main pump electrode 22 disposed on the inner surface of the gas flow section 15; and an outer main pump electrode (in this embodiment, an outer pump electrode 23) disposed on the base portion 102 at a position different from that of the gas flow section 15. Figure 1 The outer pump electrode 23 is located on the outer surface of the substrate 102 and corresponds to the inner main pump electrode 22. "Corresponds to the inner main pump electrode 22" means that the outer pump electrode 23 is configured to be separated from the inner main pump electrode 22 by a second solid electrolyte layer 6.

[0099] That is, the main pump unit 21 is an electrochemical pump unit configured to include an inner main pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between the inner main pump electrode 22 and the outer pump electrode 23. The inner main pump electrode 22 has a top electrode portion 22a disposed on the lower surface of the second solid electrolyte layer 6, facing the entire area of ​​the first internal cavity 20. The outer pump electrode 23 is disposed on the upper surface of the second solid electrolyte layer 6 in a region corresponding to the top electrode portion 22a, in a manner that exposes it to the external space.

[0100] The inner main pump electrode 22 is formed by spanning the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that divide the first internal cavity 20, and the isolation layer 5 that forms the sidewall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that forms the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that forms the bottom surface. Furthermore, side electrode portions (not shown) are formed on the sidewall surfaces (inner surfaces) of the isolation layer 5 that forms the two side walls of the first internal cavity 20 in such a way that the top electrode portion 22a and the bottom electrode portion 22b are connected. The side electrode portions are arranged in a tunnel-shaped structure.

[0101] The inner main pump electrode 22 and the outer pump electrode 23 are porous metal-ceramic electrodes (electrodes in which metal and ceramic components are mixed together). The ceramic component is not particularly limited, but it is preferable to use a solid electrolyte with oxygen ion conductivity, similar to the substrate 102. For example, ZrO2 can be used as the ceramic component.

[0102] The inner main pump electrode 22, which is in contact with the gas being measured, is formed using a material that can reduce the reducing power of NOx components in the gas being measured. The inner main pump electrode 22 may contain: a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd), and a noble metal that is catalytically active and reduces the catalytic activity of the target gas (NOx in this embodiment) (e.g., Au, Ag, etc.). In this embodiment, the inner main pump electrode 22 is a porous metal-ceramic electrode containing 1% Au, Pt, and ZrO2.

[0103] The outer pump electrode 23 only needs to contain the aforementioned catalytically active noble metal. The same applies to the reference electrode 42; it only needs to contain the aforementioned catalytically active noble metal. In this embodiment, the outer pump electrode 23 is a porous metal-ceramic electrode made of Pt and ZrO2.

[0104] In the main pump unit 21, a pulse power supply 24, used as an example of a control power supply, causes the main pump current Ip0 to flow in either a positive or negative direction between the inner main pump electrode 22 and the outer pump electrode 23. This allows oxygen to be drawn from the first internal cavity 20 to the external space, or oxygen to be drawn from the external space into the first internal cavity 20. Here, [the text continues with further details about the process]. Figure 1 The arrow direction of the main pump current Ip0 is set to positive.

[0105] In this embodiment, the pulse power supply 24, serving as the control power supply, is configured as a current source. The pulse power supply 24 allows the intermittent main pump current Ip0, which is repeatedly switched on and off, to flow between the inner main pump electrode 22 and the outer pump electrode 23. The pulse power supply 24 is configured to allow the intermittent main pump current Ip0 to flow in either the positive or negative direction. Those skilled in the art can appropriately design the structure of the pulse power supply 24. For example, the pulse power supply 24 can be a pulse power supply capable of generating bidirectional pulse current, or it can be a structure combining multiple pulse power supplies that generate unidirectional pulse current.

[0106] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, the electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 80 for main pump control, is configured to include an inner main pump electrode 22, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, a third substrate layer 3, and a reference electrode 42.

[0107] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is determined by measuring the potential difference V0 of the oxygen partial pressure detection sensor unit 80 for main pump control.

[0108] 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 (described later) in the first internal cavity 20, thereby guiding the gas to be measured into the second internal cavity 40.

[0109] The second internal cavity 40 is configured to adjust the oxygen partial pressure in the gas to be measured, which is introduced through the third diffusion rate control unit 30, with high precision. The auxiliary pump unit 50 operates to adjust the oxygen partial pressure.

[0110] The oxygen concentration (oxygen partial pressure) is pre-adjusted in the first internal cavity 20, and then the oxygen partial pressure of the gas to be measured, which is introduced through the third diffusion rate control unit 30, is further adjusted in the second internal cavity 40 using the auxiliary pump unit 50. This allows the oxygen concentration in the second internal cavity 40 to be maintained at a constant level with high precision, thus enabling high-precision NOx concentration measurement in the gas sensor 100.

[0111] The auxiliary pump unit 50 is an electrochemical pump unit comprising: an inner auxiliary pump electrode (auxiliary pump electrode 51 in this embodiment), disposed on the inner surface of the gas to be measured flow section 15 at a position further away from the substrate 102 in the longitudinal direction than the inner main pump electrode 22; and an outer auxiliary pump electrode, disposed on the substrate 102 at a position different from the gas to be measured flow section 15, and corresponding to the inner auxiliary pump electrode. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the substrate 102 also functions as an outer auxiliary pump electrode. "Corresponding to the inner auxiliary pump electrode" means that the outer pump electrode 23 is positioned with a second solid electrolyte layer 6 spaced between it and the auxiliary pump electrode 51.

[0112] That is, the auxiliary pump unit 50 is an auxiliary electrochemical pump unit comprising 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, wherein the auxiliary pump electrode 51 has a top electrode portion 51a disposed on the lower surface of the second solid electrolyte layer 6 facing the entire area of ​​the second internal cavity 40.

[0113] The aforementioned auxiliary pump electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner main pump electrode 22 previously disposed in the first internal cavity 20. That is, it is constructed with the following tunnel shape: a top electrode portion 51a is formed relative to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40; 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 side electrode portions (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b are formed on the two walls of the isolation layer 5 constituting the side wall of the second internal cavity 40.

[0114] Furthermore, the auxiliary pump electrode 51, like the inner main pump electrode 22, is formed using a material that weakens the reducing ability against NOx in the gas being measured. Similar to the inner main pump electrode 22, the auxiliary pump electrode 51 may contain: a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd), and a noble metal that has catalytic activity but reduces the catalytic activity against the target gas (NOx in this embodiment) (e.g., Au, Ag, etc.). In this embodiment, like the inner main pump electrode 22, the auxiliary pump electrode 51 is a porous metal-ceramic electrode containing 1% Au, Pt, and ZrO2.

[0115] In the auxiliary pump unit 50, a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23 using a variable power supply 52, thereby enabling oxygen in the atmosphere inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn in from the external space into the second internal cavity 40.

[0116] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, the electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 81 for auxiliary pump control, is configured to include an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, and a third substrate layer 3.

[0117] The main pump unit 21 allows the main pump current Ip0 to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current Ip1 flowing in the auxiliary pump unit 50 reaches a specified target current value. This adjusts the oxygen in the gas to be measured to the concentration that should be introduced into the auxiliary pump unit 50, i.e., the concentration that should be introduced into the second internal cavity 40. The auxiliary pump unit 50 allows the auxiliary pump current Ip1 to flow, so that the electromotive force V1 between the auxiliary pump electrode 51 and the reference electrode 42 reaches a specified target voltage value. This adjusts the oxygen in the gas to the concentration that should be introduced into the measuring pump unit 41 (described later), i.e., the concentration that should be introduced into the third internal cavity 61.

[0118] The auxiliary pump unit 50 pumps using a variable power supply 52 whose voltage is controlled based on the electromotive force V1 detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. This controls the oxygen partial pressure in the atmosphere within the second internal cavity 40 to a low partial pressure that substantially has no effect on NOx measurement.

[0119] Additionally, the auxiliary pump current Ip1 is used to control the pulse power supply 24 of the main pump unit 21. Specifically, the auxiliary pump current Ip1 or a control signal based on the auxiliary pump current Ip1 is input to the pulse power supply 24, and the main pump current Ip0 is made to flow by controlling the pulse power supply 24, thereby drawing oxygen from the first internal cavity 20 to the external space or drawing oxygen from the external space into the first internal cavity 20 in the main pump unit 21.

[0120] This activates the main pump unit 21 and the auxiliary pump unit 50, thereby maintaining a constant gradient of the oxygen partial pressure in the gas to be measured, which is introduced from the third diffusion rate control unit 30 into the second internal cavity 40. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a predetermined concentration by the action of the main pump unit 21 and the auxiliary pump unit 50. The oxygen concentration in the second internal cavity 40 can be maintained at, for example, below 0.1 ppm, below 0.01 ppm, below 0.001 ppm, or below 0.0001 ppm. In this embodiment, it is maintained at a constant concentration of approximately 0.001 ppm.

[0121] The fourth diffusion rate control unit 60 is a part that applies a predetermined diffusion resistance to the gas to be measured in the second internal cavity 40, whose oxygen concentration (oxygen partial pressure) is controlled to be lower by the operation of the auxiliary pump unit 50, thereby guiding the gas to be measured into the third internal cavity 61.

[0122] The third internal cavity 61 is configured as a space for measuring the concentration of nitrogen oxides (NOx) in the gas to be measured, which is introduced through the fourth diffusion rate control unit 60. The measurement of NOx concentration is performed by operating the measuring pump unit 41.

[0123] The measuring pump unit 41 is an electrochemical pump unit comprising: an inner measuring electrode (measuring electrode 44 in this embodiment), disposed on the inner surface of the gas flow section 15, at a position further away from the substrate 102 in the longitudinal direction than the inner auxiliary pump electrode (auxiliary pump electrode 51 in this embodiment); and an outer measuring electrode, disposed on the substrate 102 at a position different from the gas flow section 15, and corresponding to the inner measuring electrode. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the substrate 102 also functions as an outer measuring electrode. "Corresponding to the inner measuring electrode" means that the outer pump electrode 23 is positioned with the second solid electrolyte layer 6, the isolation layer 5, and the first solid electrolyte layer 4 spaced apart from the measuring electrode 44.

[0124] That is, the measuring pump unit 41 is an electrochemical pump unit configured to include the following components: a measuring electrode 44 disposed on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61; an outer pump electrode 23 (not limited to an outer pump electrode 23, as long as it is a suitable electrode on the outside of the sensor element 101); a second solid electrolyte layer 6; an isolation layer 5; and the first solid electrolyte layer 4. The measuring pump unit 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61.

[0125] The measuring electrode 44 is a porous metal-ceramic electrode. The measuring electrode 44 also functions as a NOx reduction catalyst, reducing NOx present in the atmosphere within the third internal cavity 61. The measuring electrode 44 is an electrode containing at least one catalytically active noble metal (e.g., Pt, Rh, Ir, Ru, Pd). Preferably, it contains no catalytically active noble metal and a noble metal (e.g., Au, Ag, etc.) that reduces the catalytic activity towards the target gas (NOx in this embodiment). In this embodiment, the measuring electrode 44 is a porous metal-ceramic electrode of Pt, Rh, and ZrO2.

[0126] Furthermore, in order to detect the oxygen partial pressure around the measuring electrode 44, the electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 82 for measuring pump control, is configured to include a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, a third substrate layer 3, the measuring electrode 44, and a reference electrode 42. The variable power supply 46 is controlled based on the electromotive force V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control.

[0127] Regarding the gas to be measured introduced into the second internal cavity 40, under controlled oxygen partial pressure, it reaches the measuring electrode 44 in the third internal cavity 61 via the fourth diffusion rate control unit 60. Nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to produce oxygen. Furthermore, this generated oxygen is pumped using the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the control voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control remains constant. The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured; therefore, the concentration of nitrogen oxides in the gas to be measured is calculated using the measuring pump current Ip2 of the measuring pump unit 41.

[0128] In addition, the electrochemical sensor unit 83 is configured to include a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, a third substrate layer 3, an outer pump electrode 23, and a reference electrode 42. The partial pressure of oxygen in the gas to be measured outside the sensor can be detected based on the electromotive force Vref obtained by the sensor unit 83.

[0129] Furthermore, the sensor element 101 includes a heater section 70, which serves to adjust the temperature of the sensor element 101 by heating and maintaining its temperature in order to improve the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes: a heater electrode 71, a heater 72, a heater conductor 76, a through hole 73, a heater insulation layer 74, and a pressure relief hole 75.

[0130] The heater electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to a heater power supply 77, which serves as an external power source, power can be supplied to the heater section 70 from the outside.

[0131] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from the top and bottom. The heater 72 is connected to the heater electrode 71 via the heater conductor 76 and the through hole 73, and is heated by external power supplied through the heater electrode 71, thereby heating and keeping the solid electrolyte forming the sensor element 101 warm. The heater conductor 76 is connected to the heater 72 and extends toward the rear end of the sensor element 101 in the longitudinal direction.

[0132] Furthermore, the heater 72 is embedded throughout the entire area from the first internal cavity 20 to the third internal cavity 61, thereby enabling the entire sensor element 101 to be adjusted to the temperature at which the solid electrolyte is activated. It is sufficient to adjust the temperature to allow the main pump unit 21, auxiliary pump unit 50, and measuring pump unit 41 to operate. It is not necessary to adjust the entire area to the same temperature; a temperature distribution can exist within the sensor element 101.

[0133] Regarding the sensor element 101 in this embodiment, although it is formed such that the heater 72 is embedded in the substrate 102, it is not limited to this method. The heater 72 only needs to be configured to heat the substrate 102. That is, the heater 72 only needs to be able to heat the sensor element 101 to a degree that exhibits oxygen ion conductivity sufficient to enable the main pump unit 21, the auxiliary pump unit 50, and the measurement pump unit 41 to operate. For example, as in this embodiment, it can be embedded in the substrate 102. Alternatively, for example, the heater portion 70 can be formed as a heater substrate different from the substrate 102 and disposed adjacent to the substrate 102.

[0134] The heater insulation layer 74 is an insulation layer formed of an insulator such as aluminum oxide on the upper and lower surfaces of the heater 72 and the heater conductor 76. The heater insulation layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and the heater conductor 76, and electrical insulation between the third substrate layer 3 and the heater 72 and the heater conductor 76.

[0135] The pressure relief hole 75 is formed such that it penetrates the third substrate layer 3 and connects the heater insulation layer 74 to the reference gas introduction space 43. The pressure relief hole 75 can mitigate the increase in internal pressure that accompanies the temperature rise within the heater insulation layer 74. Alternatively, a structure without the pressure relief hole 75 may also be used.

[0136] The aforementioned sensor element 101 is assembled in the gas sensor 100 such that the front end of the sensor element 101 is in contact with the gas to be measured and the rear end of the sensor element 101 is in contact with the reference gas.

[0137] (Control device)

[0138] The gas sensor 100 of this embodiment includes: the sensor element 101 described above, and a control device 90 for controlling the sensor element 101. In the gas sensor 100, each electrode 22, 23, 51, 44, 42 of the sensor element 101 is electrically connected to the control device 90 via wires (not shown). Figure 2 This is a block diagram showing the electrical connections between the control device 90 and the pump units 21, 50, 41, sensor units 80, 81, 82, 83, and heater unit 70 of the sensor element 101. The control device 90 includes a pulse power supply 24 (an example of a control power supply), variable power supplies 46 and 52, a heater power supply 77, and a control unit 91. The control unit 91 includes a drive control unit 92, a concentration calculation unit 93, and a setting unit 94.

[0139] The control unit 91 is implemented by a general-purpose or special-purpose computer, utilizing the CPU, memory, etc., mounted on the computer to perform the functions of the drive control unit 92, the concentration calculation unit 93, and the setting unit 94. Furthermore, the gas sensor 100 measures NOx contained in the exhaust gas from the automobile engine. When the sensor element 101 is installed in the exhaust path, some or all of the functions of the control device 90 (especially the control unit 91) can be implemented using the ECU (Electronic Control Unit) mounted on the automobile.

[0140] The control unit 91 is configured to acquire the electromotive forces (V0, V1, V2, Vref) of each sensor unit 80, 81, 82, 83 of the sensor element 101, the pump currents (Ip0, Ip1, Ip2) of each pump unit 21, 50, 41, and the heater voltage Vh and heater current Ih of the heater unit 70. Furthermore, the control unit 91 is configured to output control signals to a pulse power supply 24, variable power supplies 52 and 46 (examples of control power supplies), and a heater power supply 77.

[0141] The drive control unit 92 is configured to control the heater unit 70, the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41 so that the gas sensor 100 can measure the concentration of the target gas (NOx in this embodiment).

[0142] The drive control unit 92 heats the heater 72 and maintains the temperature of the heater 72 at the desired temperature.

[0143] Various known control methods can be used to heat the heater 72. For example, the heater 72 can be heated by applying a constant voltage. The output of the heater power supply 77 can also be controlled based on the resistance value of the heater 72. Alternatively, the output of the heater power supply 77 can be controlled based on at least one of the resistance values ​​of the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41.

[0144] For example, the drive control unit 92 performs feedback control on the control signal output to the heater power supply 77 based on the heater resistance value Rh (=Vh / Ih) calculated according to the heater voltage Vh and heater current Ih of the heater 72, so that the heater 72 reaches the target temperature.

[0145] The drive control unit 92 enables the main pump unit 21 and the auxiliary pump unit 50 to operate in conjunction. Specifically, the drive control unit 92 controls the main pump unit 21 to allow the repeatedly switched-on and switched-off main pump current Ip0 to flow in the main pump unit 21, so that the auxiliary pump current Ip1 flowing in the auxiliary pump unit 50 reaches a predetermined target current value (referred to as the target current value Ip1). SET Furthermore, the auxiliary pump current Ip1 flows through the auxiliary pump unit 50 so that the electromotive force V1 between the auxiliary pump electrode 51 and the reference electrode 42 reaches a predetermined target voltage value (referred to as the target voltage value V1). SET ).

[0146] Specifically, the drive control unit 92 performs feedback control on the pump voltage Vp1 of the variable power supply 52 of the auxiliary pump unit 50, so that the electromotive force V1 of the oxygen partial pressure detection sensor unit 81 for auxiliary pump control reaches the target voltage value V1. SET Therefore, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that has virtually no effect on the determination of NOx.

[0147] In addition, at the same time, the drive control unit 92 performs feedback control on the main pump current Ip0 of the pulse power supply 24 of the main pump unit 21 based on the auxiliary pump current Ip1, so that the auxiliary pump current Ip1 of the auxiliary pump unit 50 reaches a constant value (target current value Ip1). SET Those skilled in the art can appropriately determine the target current value Ip1. SET This can be set to approximately the range of 1 to 20 μA. That is, regarding the auxiliary pump unit 50, as a result of ensuring the constant auxiliary pump current Ip1 flows, the main pump unit 21 is controlled to ensure that the electromotive force V1 reaches the target voltage value V1. SETTherefore, in the main pump unit 21, the oxygen partial pressure (oxygen concentration) near the inner main pump electrode 22 is controlled to a predetermined value. Furthermore, as a result, the main pump current Ip0 of the main pump unit 21 varies according to the oxygen concentration in the gas being measured.

[0148] The drive control unit 92 performs feedback control on the pump voltage Vp2 of the variable power supply 46 of the measuring pump unit 41, so that the electromotive force V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control reaches a constant value (called the target value V2). SET Regarding the measuring electrode 44, nitrogen oxides in the measured gas are reduced (2NO→N2+O2) to produce oxygen. The drive control unit 92 uses the measuring pump unit 41 to pump the generated oxygen out, so that the electromotive force V2 reaches the set value V2. SET Setting value V2 SET It can be set to a value that substantially decomposes all NOx in the measuring electrode 44. The setpoint V2 is set in this way. SET This allows for the detection of virtually all NOx in the gas being measured within the measuring pump unit 41, using the measuring pump current Ip2 as the measurement pump current. More precisely, the measuring pump current Ip2 includes: the current caused by the low concentration of oxygen controlled by the main pump unit 21 and the auxiliary pump unit 50, and the current caused by oxygen originating from NOx in the gas being measured. As described above, by maintaining a constant level of oxygen in the gas being measured reaching the measuring electrode 44, the oxygen originating from NOx in the gas being measured can be accurately measured based on the measuring pump current Ip2. Consequently, the measuring pump current Ip2 can be detected as a current value corresponding to the NOx concentration.

[0149] In addition, the target current value Ip1S ET The set current value (control current value) is stored in the memory of the control unit 91, which functions as the drive control unit 92. Target voltage value V1 SET and target value V2 SET The set voltage value (control voltage value) is stored in the memory of the control unit 91, which functions as the drive control unit 92. The CPU of the control unit 91, which functions as the drive control unit 92, performs drive control of the gas sensor 100 based on the above control value.

[0150] The concentration calculation unit 93 is configured to calculate the NOx concentration in the gas being measured and output it.

[0151] The concentration calculation unit 93 acquires the measuring pump current Ip2 of the measuring pump unit 41, calculates the NOx concentration in the measured gas based on a pre-stored conversion parameter (current-concentration conversion parameter) between the measuring pump current Ip2 and the NOx concentration in the measured gas, and outputs it as the measured value of the gas sensor 100. The current-concentration conversion parameter is pre-stored in the memory of the control unit 91, which functions as the concentration calculation unit 93. Those skilled in the art can appropriately define the current-concentration conversion parameter for the gas sensor 100 in advance through experiments, etc. The current-concentration conversion parameter can be, for example, the coefficient of an approximate formula (linear function, etc.) obtained through experiments, or a mapping table representing the correspondence between the measuring pump current Ip2 and the NOx concentration in the measured gas. The current-concentration conversion parameter can be an inherent parameter of each gas sensor 100, or a parameter common to multiple gas sensors.

[0152] The setting unit 94 acquires the potential difference V0 generated between the inner main pump electrode 22 and the reference electrode 42, and sets the target voltage value V1 of the auxiliary pump unit 50 based on the potential difference V0. SET The setting unit 94 acquires the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 of the main pump control oxygen partial pressure detection sensor unit 80, and sets the target voltage value V1 of the electromotive force V1 of the auxiliary pump control oxygen partial pressure detection sensor unit 81 used in the drive control unit 92 based on the acquired potential difference V0. SET The setting unit 94 performs calculations. The calculated target voltage value V1 is then processed. SET The set voltage value (control voltage value) is set for the drive control unit 92. The drive control unit 92 is based on the target voltage value V1 set by the setting unit 94. SET And to carry out the above controls.

[0153] Target voltage value V1 SET The oxygen concentration near the auxiliary pump electrode 51 is set to a value that ensures the residual oxygen in the gas being measured reaches a predetermined concentration at the measuring electrode 44. As described above, the drive control unit 92 controls the main pump unit 21 and the auxiliary pump unit 50 in a coordinated manner. As a result, the drive control unit 92 maintains a constant oxygen concentration near the inner main pump electrode 22. That is, if the target voltage value V1 is set... SET The design aims to ensure that the residual oxygen in the gas being measured reaches a predetermined concentration at the measuring electrode 44, thereby maintaining a constant oxygen concentration near the inner main pump electrode 22. Therefore, the target voltage value V1 can be determined based on the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42, which corresponds to the oxygen concentration near the inner main pump electrode 22. SET Perform the calculation.

[0154] Specifically, based on the acquired potential difference V0 and the target value calculation parameters stored in the memory of the control unit 91, which functions as the setting unit 94, the target voltage value V1 is... SET Calculations are performed. Target value calculation parameters include, for example: the potential difference V0, the time variation of the potential difference V0, or the deviation of the potential difference V0 from the target value (i.e., the deviation of the oxygen concentration near the inner main pump electrode 22 from the target value), and the target voltage value V1. SET The parameters relating the values ​​or changes in the parameters. Those skilled in the art can pre-determine the target value calculation parameters for the gas sensor 100 through experiments, etc. The target value calculation parameters may be, for example, formulas or mapping tables obtained from experimentally determined relationships between the oxygen concentration near the inner main pump electrode 22 and the potential difference V0, and between the oxygen concentration of the auxiliary pump electrode 51 and the electromotive force V1.

[0155] [Concentration detection of the target gas]

[0156] Next, the method of using the gas sensor 100 configured in this way will be explained. A detection method for controlling the gas sensor 100 to measure the concentration of the target gas in the gas being measured will be described.

[0157] The control method for the gas sensor in this embodiment includes the following steps:

[0158] The setting step involves acquiring the potential difference between the inner main pump electrode and the reference electrode, and setting a target voltage value for the electromotive force between the inner auxiliary pump electrode and the reference electrode of the auxiliary pump unit based on the potential difference; and

[0159] In the oxygen concentration adjustment step, the control power supply in the main pump unit is controlled to allow the main pump current to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current flowing in the auxiliary pump unit reaches a specified target current value. Furthermore, the auxiliary pump current is allowed to flow in the auxiliary pump unit so that the electromotive force between the inner auxiliary pump electrode and the reference electrode reaches the target voltage value.

[0160] Figure 3 This is a flowchart illustrating an example of the NOx concentration detection process of the gas sensor 100.

[0161] For example, if the gas sensor 100 receives a start signal (Dew point), it begins NOx concentration detection processing. When the gas sensor 100 is mounted in a vehicle or similar device, the start signal (Dew point) is, for example, a signal sent to the gas sensor 100 from the vehicle's ECU, exhaust gas treatment system, or similar source. For example, processing can be initiated by manually turning on the power to the control device 90.

[0162] If the NOx concentration detection process is started, the drive control unit 92 of the control unit 91 first powers on the heater 72 to start heating the heater 72 (step S10), and maintains the sensor element 101 at a drive temperature (e.g., about 800°C) that enables the solid electrolyte to be activated and allows for high-precision measurement of NOx concentration.

[0163] Next, the drive control unit 92 begins pump control of the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41 (step S11). Specifically, the drive control unit 92 executes the following oxygen concentration adjustment step: In the main pump unit 21, feedback control is applied to the pulse power supply 24 of the control power supply to allow the repeatedly on / off main pump current Ip0 to flow, so that the auxiliary pump current Ip1 flowing in the auxiliary pump unit 50 reaches the specified target current value Ip1. SET Furthermore, in the auxiliary pump unit 50, the variable power supply 52 is feedback controlled to allow the auxiliary pump current Ip1 to flow, so that the electromotive force V1 between the auxiliary pump electrode 51 and the reference electrode 42 reaches the target voltage value V1. SET In addition, the following control is executed on the measuring pump unit 41: feedback control is performed on the variable power supply 46 to allow the measuring pump current Ip2 to flow, so that the electromotive force V2 between the measuring electrode 44 and the reference electrode 42 reaches the target value V2. SET .

[0164] Regarding the pump control of the main pump unit 21, auxiliary pump unit 50, and measuring pump unit 41, all pumps can start simultaneously, or at least one pump unit's pump control can start at a different time than the pump control of other pump units. Pump control of all pump units can start at different times. Furthermore, step S11 can be executed after the sensor element 101 reaches its driving temperature, or it can be executed at a temperature below the driving temperature.

[0165] Next, the setting unit 94 sets the target voltage value V1. SET The target voltage value V1 is set for the drive control unit 92. SET (Step S12). When the gas sensor 100 is started, a pre-defined target voltage value V1 can be set. SET The target voltage value V1 is set as the initial value in the drive control unit 92.SET In this case, step S12 can be skipped and the process can proceed to the next step without executing it at the start of driving the gas sensor 100. Those skilled in the art can appropriately set the target voltage value V1. SET The decision is to make the oxygen concentration in the gas to be measured at the measuring electrode 44 such that it will not affect the measurement of NOx.

[0166] While executing steps S11 and S12 and continuously controlling the pump, the gas to be measured sequentially passes through the gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13 to reach the first internal cavity 20. The main pump unit 21 adjusts the oxygen concentration to the level required for the auxiliary pump unit 50, i.e., the level required for the second internal cavity 40. Then, the gas to be measured passes through the third diffusion rate control unit 30 to reach the second internal cavity 40. The auxiliary pump unit 50 further adjusts the oxygen concentration to the level required for the measuring pump unit 41, i.e., the level required for the third internal cavity 61. The gas to be measured, with its oxygen concentration adjusted to a constant low concentration using the main pump unit 21 and the auxiliary pump unit 50, passes through the fourth diffusion rate control unit 60 to reach the third internal cavity 61. NOx in the gas to be measured that reaches the third internal cavity 61 is decomposed at the measuring electrode 44, and the measuring pump current Ip2 flows through the measuring pump unit 41 in a manner corresponding to the amount of oxygen produced by the decomposition of NOx.

[0167] Next, the concentration calculation unit 93 acquires the measuring pump current Ip2 of the measuring pump unit 41, calculates the NOx concentration in the measured gas based on the acquired measuring pump current Ip2 and the pre-stored conversion parameter (current-concentration conversion parameter) between the measuring pump current Ip2 and the NOx concentration in the measured gas, and outputs the NOx concentration detection value in the measured gas as the measurement value of the gas sensor 100 (step S13). The NOx concentration detection value is output as the measurement result of the gas sensor 100. During the measurement performed by the gas sensor 100, step S13 is executed continuously or periodically according to the output of the gas sensor.

[0168] Additionally, in parallel with step S13, i.e., in parallel with the detection of NOx concentration by the gas sensor 100, the following setting step is performed: the setting unit 94 acquires the potential difference V0 generated between the inner main pump electrode 22 and the reference electrode 42, and sets the target voltage value V1 of the electromotive force V1 between the auxiliary pump electrode 51 of the auxiliary pump unit 50 and the reference electrode 42 based on the potential difference V0. SET (Steps S13, S23 to S25).

[0169] In this embodiment, the setting unit 94 acquires the potential difference V0 of the oxygen partial pressure detection sensor unit 80 for main pump control (step S23). The setting unit 94 determines whether the acquired potential difference V0 reaches a predetermined target value (step S24). If the potential difference V0 reaches the predetermined target value, the setting unit 94 continuously sets the target voltage value V1 at the time of acquiring the potential difference V0. SET The control voltage value is set to the drive control unit 92. The target voltage value V1 is maintained at the time the potential difference V0 is acquired. SET In this state, the drive control unit 92 continues to perform pump control. In this case, the process returns to step S23, and the setting unit 94 acquires the potential difference V0 of the oxygen partial pressure detection sensor unit 80 for main pump control.

[0170] When the potential difference V0 deviates from the predetermined target value, the setting unit 94 calculates parameters based on the deviation value relative to the value of the potential difference V0 or the target value of the potential difference V0, and the target value stored in the memory of the control unit 91, which functions as the setting unit 94, and sets a new target voltage value V1. SET Calculation is performed (step S25). The setting unit 94 sets the calculated new target voltage value V1. SET The control voltage value for the drive control unit 92 is set (step S12), and steps S13 and S23 onwards are executed. A new target voltage value V1 is set. SET The main pump unit 21 and the auxiliary pump unit 50 are controlled to ensure that the potential difference V0 reaches the target value.

[0171] Setting unit 94 sets target voltage value V1 based on potential difference V0. SET The above-described setting steps enable high-precision control of the oxygen concentration near the auxiliary pump electrode 51. As a result, even when the NOx concentration in the gas being measured is low, the NOx concentration can be measured with high precision.

[0172] The drive control unit 92 of the setting unit 94 performs pump control, and the setting steps are executed in parallel while the concentration calculation unit 93 outputs the NOx concentration detection value in the gas to be measured. Therefore, while continuously measuring the target gas (NOx in this embodiment) in the gas to be measured using the gas sensor 100, the oxygen concentration near the auxiliary pump electrode 51, that is, the oxygen concentration in the gas to be measured reaching the measuring electrode 44, can be controlled with high accuracy. As a result, even when the NOx concentration in the gas to be measured is low, the NOx concentration can be measured continuously and with high accuracy.

[0173] Here, for the target voltage value V1 SET And the potential difference V0 will be described in detail.

[0174] An electromotive force (EMF) is generated between the auxiliary pump electrode 51 and the reference electrode 42, based on the oxygen concentration difference between them. The reference electrode 42 is in contact with a reference gas (atmosphere in this embodiment), therefore, the oxygen concentration near the reference electrode 42 can be considered constant. Therefore, the EMF generated due to the oxygen concentration difference between the auxiliary pump electrode 51 and the reference electrode 42 can be considered as representing the oxygen partial pressure near the auxiliary pump electrode 51.

[0175] Existing gas sensors, such as the aforementioned international publication WO2020 / 196653, disclose the following: The electromotive force between the auxiliary pump electrode and the reference electrode is set to a constant value, thereby controlling the oxygen partial pressure near the auxiliary pump electrode to a low partial pressure that substantially has no effect on the NOx measurement. In this way, the gas to be measured, controlled at a low oxygen concentration, reaches the measuring electrode, and the measuring pump current corresponding to the NOx concentration is detected in the measuring pump unit.

[0176] However, when measuring the target gas in a low concentration range of approximately 10 to 500 ppm, the measured value (i.e., the detected measuring pump current Ip2) sometimes deviates. The inventors of this invention have determined through research that during the operation of the gas sensor, the amount of oxygen (residual oxygen) in the target gas reaching the measuring electrode 44 sometimes varies due to certain factors, causing a change in the value of the measuring pump current Ip2 detected by the measuring pump unit 41. If the amount of residual oxygen in the target gas reaching the measuring electrode 44 varies, the value of the measuring pump current Ip2 detected by the measuring pump unit 41 does not change (varie) according to the NOx concentration in the target gas. Therefore, it is evident that, especially when the concentration of the target gas (NOx in this embodiment) in the target gas is low, it can sometimes affect the measurement accuracy.

[0177] If the residual oxygen concentration in the gas to be measured, after being controlled to a low oxygen concentration using the main pump unit 21 and the auxiliary pump unit 50, remains constant before reaching the measuring electrode 44, then the current in the measuring pump current Ip2 caused by the residual oxygen will also remain constant. Therefore, the measuring pump current Ip2 becomes a value that varies correspondingly to the amount of oxygen generated by the reduction of NOx at the measuring electrode 44. That is, an approximately linear correlation can be obtained between the measuring pump current Ip2 and the NOx concentration in the gas to be measured. As a result, the measuring pump current Ip2 corresponding to the NOx concentration can be detected in the measuring pump unit 41, thereby enabling high-precision measurement of the NOx concentration.

[0178] When the residual oxygen concentration in the gas to be measured changes upon reaching the measuring electrode 44, this change in residual oxygen concentration ΔO2 is manifested as a change in the value of the measuring pump current Ip2 flowing through the measuring pump unit 41, rather than based on the NOx concentration.

[0179] When measuring a gas containing a high concentration of NOx, the measuring pump current Ip2 detected by the measuring pump unit 41 is relatively large. Therefore, the change in measuring pump current Ip2 caused by the change in residual oxygen concentration ΔO2 is relatively small. Thus, it can be considered that high measurement accuracy can be maintained. On the other hand, when measuring a gas containing a low concentration of NOx, the measuring pump current Ip2 detected by the measuring pump unit 41 is relatively small. Therefore, the change in measuring pump current Ip2 caused by the change in residual oxygen concentration ΔO2 is relatively large, showing a trend of increasing impact on measurement accuracy.

[0180] The measuring pump current Ip2 includes the current caused by residual oxygen in the gas being measured reaching the measuring electrode 44, and the current caused by oxygen generated at the measuring electrode 44 from NOx in the gas being measured. However, it is impossible to separately measure the current caused by residual oxygen and the current caused by oxygen from NOx. Therefore, especially when measuring a gas containing a low concentration of NOx, it is important to sufficiently minimize the change in residual oxygen concentration ΔO2, that is, to keep the residual oxygen concentration constant. By keeping the residual oxygen concentration constant, it is possible to accurately detect oxygen from NOx in the gas being measured using the measuring pump unit 41.

[0181] The inventors of this invention further investigated the cause of the change ΔO2 in the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44, and determined that: when the gas sensor 100 is driven, the electromotive force V1 between the auxiliary pump electrode 51 and the reference electrode 42 includes not only the electromotive force generated by the oxygen concentration difference between the auxiliary pump electrode 51 and the reference electrode 42, but also other factors.

[0182] According to the inventor's research based on the present invention, the electromotive force V1 includes:

[0183] (1) The concentration difference electromotive force V (oxygen) generated due to the oxygen concentration difference between the auxiliary pump electrode 51 and the reference electrode 42;

[0184] (2) The thermoelectric potential V(thermal) generated due to the temperature difference between the auxiliary pump electrode 51 and the reference electrode 42; and

[0185] (3) The potential difference generated by the auxiliary pump current Ip1 flowing through the auxiliary pump electrode 51, that is, the potential difference V(IR) generated by the resistance value of the auxiliary pump current Ip1 and the auxiliary pump electrode 51.

[0186] Furthermore, for example, when oxygen is drawn into the reference electrode 42 and the reference gas atmosphere near the reference electrode 42 is controlled, current still flows through the reference electrode 42. In this case, it can be considered that, in addition to the electromotive force described above, the electromotive force V1 also includes the potential difference V(IR)' generated by the current flowing through the reference electrode 42 and the resistance value of the reference electrode 42.

[0187] In order to set the oxygen partial pressure near the auxiliary pump electrode 51 to a constant, it is only necessary to set (1) the concentration difference electromotive force V(oxygen) to a constant. If (2) the thermoelectric potential V(thermal) and (3) the potential difference V(IR) are constant, then the electromotive force V1 is set to a constant, that is, the (1) concentration difference electromotive force V(oxygen) is set to a constant.

[0188] However, if at least one of (2) the thermoelectric potential V(thermal) and (3) the potential difference V(IR) changes for some reason, even if the electromotive force V1 is kept constant, (1) the concentration difference electromotive force V(oxygen) may also change. As a result, the partial pressure of oxygen near the auxiliary pump electrode 51 may change. (2) The thermoelectric potential V(thermal) and (3) the potential difference V(IR) may change, for example, depending on the temperature of the gas being measured or the flow rate / velocity. In addition, for example, the auxiliary pump electrode 51 and the reference electrode 42 may change over time due to the use of a gas sensor, resulting in changes in their resistance values ​​(usually an increase). When the electrode resistance values ​​change over time in this way, (2) the thermoelectric potential V(thermal) and (3) the potential difference V(IR) may also change.

[0189] For example, when the proportions of (2) thermoelectric potential V (thermal) and (3) potential difference V (IR) in the electromotive force V1 increase, the (1) concentration difference electromotive force V (oxygen), which should have been kept constant, decreases relatively. If the electromotive force V1 is kept constant under these conditions, the oxygen concentration near the auxiliary pump electrode 51 is controlled to tend towards a higher oxygen concentration than the target concentration. That is, the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 is controlled to tend towards an increasing direction.

[0190] Conversely, when the proportions of (2) thermoelectric potential V(thermal) and (3) potential difference V(IR) in the electromotive force V1 decrease, the (1) concentration difference electromotive force V(oxygen), which should have been kept constant, relatively increases. If the electromotive force V1 is kept constant under these conditions, the oxygen concentration near the auxiliary pump electrode 51 will be controlled to tend towards a lower oxygen concentration than the target concentration. That is, the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 will be controlled to tend towards a decreasing direction.

[0191] As mentioned above, it can be assumed that the changes in the proportions of (2) thermoelectric potential V (thermal) and (3) potential difference V (IR) in the electromotive force V1 affect the change in residual oxygen concentration ΔO2.

[0192] For example, when the gas sensor 100 is driven in an atmospheric environment, and the pump control of the main pump unit 21, the auxiliary pump unit 50 and the measuring pump unit 41 is all stopped, the electromotive force V1 generated between the auxiliary pump electrode 51 and the reference electrode 42 is measured, and (2) the thermoelectric potential V (thermal) can be obtained.

[0193] As described above, a potential difference V(IR) is generated based on the auxiliary pump current Ip1 and the resistance value of the auxiliary pump electrode 51. For example, when the gas sensor 100 is driven in an atmospheric atmosphere, and the pump control of the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41 is all stopped, the resistance value of the auxiliary pump electrode 51 can be calculated based on the electromotive force V1 generated by the constant auxiliary pump current Ip1 flowing through the auxiliary pump unit 50.

[0194] Thus, (2) thermoelectric potential V(thermal) and (3) potential difference V(IR) are values ​​obtained without pump control. Therefore, it is difficult to determine (2) thermoelectric potential V(thermal) and (3) potential difference V(IR) when the gas sensor 100 is driven to detect NOx concentration.

[0195] As described above, the main pump unit 21 and the auxiliary pump unit 50 are controlled in a coordinated manner. That is, the drive control unit 92 causes the auxiliary pump current Ip1 to flow in the auxiliary pump unit 50, so that the electromotive force V1 between the auxiliary pump electrode 51 and the reference electrode 42 reaches the target voltage value V1. SET Additionally, simultaneously, feedback control is performed on the main pump current Ip0 of the pulse power supply 24 of the main pump unit 21 based on the auxiliary pump current Ip1, so that the auxiliary pump current Ip1 of the auxiliary pump unit 50 reaches the target current value Ip1. SETThat is, by allowing a constant auxiliary pump current Ip1 to flow in the auxiliary pump unit 50, the main pump unit 21 can be controlled to make the electromotive force V1 reach the target voltage value V1. SET The results show that the oxygen concentration near the inner main pump electrode 22 reaches a concentration corresponding to the oxygen concentration near the auxiliary pump electrode 51.

[0196] Therefore, when a change ΔO2 occurs in the oxygen concentration near the auxiliary pump electrode 51, i.e., the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44, it also causes a change in the oxygen concentration near the inner main pump electrode 22. As described above, the oxygen concentration near the inner main pump electrode 22 can be detected based on the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 of the main pump control oxygen partial pressure detection sensor unit 80. Therefore, the inventors of this invention have discovered that a change ΔO2 in the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 can be detected based on a change in the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42.

[0197] Based on the above insights, the inventors of this invention have discovered that by performing the following setting steps, namely, the setting unit 94 acquires the potential difference V0 generated between the inner main pump electrode 22 and the reference electrode 42, and sets the target voltage value V1 of the electromotive force V1 between the auxiliary pump electrode 51 of the auxiliary pump unit 50 and the reference electrode 42 based on the potential difference V0. SET This allows the change in residual oxygen concentration ΔO2 in the gas to be measured reaching the measuring electrode 44 to be corrected to zero or substantially zero. A substantially zero change in residual oxygen concentration ΔO2 indicates that the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 is substantially constant; that is, it is constant to a degree that it does not affect the accuracy of NOx concentration measurement even in low-concentration regions where the current value of the measuring pump current Ip2 is relatively small. Thus, the inventors of this invention have discovered that by performing the above-described measurement steps, the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 can be controlled with high accuracy. By maintaining a constant residual oxygen concentration with high accuracy, oxygen originating from NOx in the gas to be measured can be accurately detected in the measuring pump unit 41. As a result, NOx concentration can be measured with high accuracy even in low-concentration regions.

[0198] As described above, the drive control unit 92 uses the pulse power supply 24 to cause the main pump current Ip0, which is repeatedly switched on and off, to flow in the main pump unit 21. The direction of the main pump current Ip0 that draws oxygen out of the first internal cavity 20 is defined as positive, and the direction of the main pump current Ip0 that draws oxygen into the first internal cavity 20 is defined as negative. The positive direction of the main pump current Ip0 means: Figure 1The arrow pointing to the main pump current Ip0 indicates the direction of the current flow from the inner main pump electrode 22 to the outer pump electrode 23 on the outside of the sensor element 101.

[0199] Figure 4 Yes: This shows a schematic diagram of the changes in the main pump current Ip0 and potential difference V0 over time when oxygen is drawn out from the first internal cavity 20, i.e., when the main pump current Ip0 flows in the forward direction. Figure 4 (1) is: A schematic diagram showing the change of the main pump current Ip0 over time. The horizontal axis represents time t, and the vertical axis represents the main pump current Ip0. The upward direction of the vertical axis is the positive direction of the main pump current Ip0. Figure 4 (2) This diagram illustrates the change of potential difference V0 over time. The horizontal axis represents time t, and the vertical axis represents potential difference V0. Regarding potential difference V0, the state where the potential of the reference electrode 42 is higher than that of the inner main pump electrode 22 is defined as positive. Figure 4 In (2), the upward direction of the vertical axis is set as positive. Regarding the value of potential difference V0, the higher the oxygen concentration near the inner main pump electrode 22, the smaller the value is displayed, and the lower the oxygen concentration near the inner main pump electrode 22, the larger the value is displayed.

[0200] In this embodiment, such as Figure 4 As shown in (1), in the main pump unit 21, the main pump current Ip0 flowing through the pulse power supply 24 is a pulse-shaped waveform current that repeatedly turns on and off with a period T. For example, if the main pump current Ip0 turns on at time t1 at the beginning of a certain period T, the main pump current Ip0 increases from 0A to reach the maximum current Ip0max, and this state continues until the conduction period T has elapsed. ON The main pump current Ip0 is cut off at time t2. If the main pump current Ip0 is cut off at time t2, the main pump current Ip0 will decrease from the maximum current Ip0max to 0A until the cutoff period T has elapsed. OFF Up to time t4, the main pump current Ip0 is 0A. Thus, the period T is calculated from the conduction period T... ON And the subsequent deadline T OFF Composition. Furthermore, regarding the actual main pump current Ip0, both its increase from time t1 and its decrease from time t2 require a small amount of time. Figure 4 (1) is schematically represented by a rectangular wave. Furthermore, the main pump current Ip0 output by pulse power supply 24 is even during the off-state period T. OFF Sometimes, due to noise or other factors, a weak main pump current Ip0 may flow, but... Figure 4 (1) The illustration is omitted.

[0201] As described above, the drive control unit 92 performs feedback control on the main pump current Ip0 of the pulse power supply 24 of the main pump unit 21 based on the auxiliary pump current Ip1, so that the auxiliary pump current Ip1 of the auxiliary pump unit 50 reaches a predetermined value (target current value Ip1). SET In the main pump unit 21, the amount of oxygen drawn from the first internal cavity 20 by the main pump current Ip0 during one cycle (cycle T) is compared with the average value Ip0ave of the main pump current Ip0 during one cycle (refer to...). Figure 4 (1) is proportional to the single-dot dashed line. Therefore, the drive control unit 92 outputs a control signal to the pulse power supply 24 based on the auxiliary pump current Ip1, that is, for example, the conduction period T occupied in the period T. ON The pulse power supply 24 changes at least one of the parameters, such as the duty cycle, period T, and maximum current Ip0max, causing the average value Ip0ave to change. The drive control unit 92 can output the average value Ip0ave as a control signal to the pulse power supply 24, and the pulse power supply 24 changes at least one of the aforementioned parameters based on the control signal. Alternatively, the drive control unit 92 can output the auxiliary pump current Ip1 as a control signal to the pulse power supply 24, and the pulse power supply 24 changes at least one of the aforementioned parameters based on the control signal. In this embodiment, the drive control unit 92 outputs the duty cycle (or the amount of change in the duty cycle) as a control signal to the pulse power supply 24, and the pulse power supply 24 changes the duty cycle of the main pump current Ip0 based on the control signal. The duty cycle changes based on the control signal, and the maximum value of the duty cycle can be, for example, 90% or less. In this case, the cutoff period T OFF The minimum value of the proportion relative to the period T is 10% or more. Furthermore, preferably, the maximum value of the duty cycle can be 80% or less. In this case, the cutoff period T... OFF The minimum proportion relative to period T is 20% or more.

[0202] Figure 4 (1) The period T of the intermittent main pump current Ip0 can be: a shorter period of time during which the actual oxygen concentration in the first internal cavity 20 is maintained to the extent that it has been kept under average control. In other words, the conduction period T ON With the deadline T OFFThe change in actual oxygen concentration within the first internal cavity 20 can be a short period of time during which adjusting the oxygen concentration of the auxiliary pump unit 50 will not have an impact. If such a period T is set, the actual oxygen concentration within the first internal cavity 20, i.e., the oxygen concentration in the gas being measured introduced into the second internal cavity 40, can be controlled to a predetermined concentration. The period T can be set to, for example, 0.1 s or less (frequency 10 Hz or more), 0.02 s or less (frequency 50 Hz or more), or 0.001 s or less (frequency 100 Hz or more). In this embodiment, the period T is set to 0.0005 s (5 ms; frequency 200 Hz).

[0203] Furthermore, for example, when the control device 90 outputs the derived NOx concentration to other devices such as the vehicle's engine ECU in each predetermined cycle Tout, it is preferable that the cycle T is less than one-tenth of the cycle Tout. If the cycle T is set to such a value, the oxygen concentration in the gas being measured can be controlled with a cycle T that is sufficiently short compared to the cycle Tout, thereby enabling a more stable output of the concentration of the gas being measured.

[0204] For example, the auxiliary pump current Ip1 in the auxiliary pump unit 50 is greater than the target current value Ip1. SET In this case, the drive control unit 92 increases the duty cycle of the main pump current Ip0 (extending the conduction period T without changing the period T). ON The pulse power supply 24 is controlled in a manner that increases the average value of the main pump current Ip0 (Ip0ave) and further reduces the oxygen concentration in the first internal cavity 20. Figure 4 In (1), as an example, the conduction period T relative to the first cycle T is shown. ON (Time t1~t2) and the conduction period T of the second cycle T. ON The control is set to a length of twice the normal operating time (t4-t5) (duty cycle is set to twice the normal operating time). In this case, the average value Ip0ave of the second period T becomes twice the average value Ip0ave of the first period T. Since the average value Ip0ave is twice the normal value in the second period T, more oxygen is drawn out of the first internal cavity 20 compared to the period of the first period T. As a result, the oxygen concentration near the inner main pump electrode 22 decreases in the second period T, such as... Figure 4 As shown in (2), the potential difference V0b' at the end of the second period T (time t6) is greater than the potential difference V0b at the end of the first period T (time t4).

[0205] Next, the potential difference V0 of the oxygen partial pressure detection sensor unit 80 for main pump control will be described in detail. The potential difference V0 of the oxygen partial pressure detection sensor unit 80 for main pump control is the potential difference between the inner main pump electrode 22 and the reference electrode 42. The potential difference V0 is mainly due to the oxygen concentration difference between the inner main pump electrode 22 and the reference electrode 42, and therefore, it corresponds to the oxygen concentration within the first internal cavity 20 (near the inner main pump electrode 22). However, during the conduction period T when the maximum current Ip0max flows through the pulse power supply 24... ON During conduction, the potential of the inner main pump electrode 22 changes due to the flow of the maximum current Ip0max. The magnitude of this potential change is approximately the product of the maximum current Ip0max and the resistance of the inner main pump electrode 22. This change is related to the conduction period T. ON Compared to the potential difference V0, the main pump current Ip0 during the cutoff period T when the pulse power supply 24 is not flowing. OFF The potential difference V0 becomes: the value corresponding to the oxygen concentration near the inner main pump electrode 22.

[0206] A more detailed observation of the potential difference V0 reveals that the intermittent main pump current Ip0 flowing through the pulse power supply 24 causes the potential of the inner main pump electrode 22 to also change intermittently. As a result, the potential difference V0 also changes periodically in correspondence with the change in the potential of the inner main pump electrode 22. Figure 4 As shown in (2), the potential difference V0 is also related to Figure 4 (1) The main pump current Ip0 is switched on and off in a pulsating manner and changes periodically.

[0207] For example, in Figure 4 In (2), the potential difference V0 begins to change (increases) due to the potential caused by the maximum pump current Ip0max flowing from time t1. Then, the potential difference V0 changes to its maximum value V0a (maximum value) due to the potential caused by the maximum pump current Ip0max flowing at time t2, since the main pump current Ip0 has a cutoff period T starting from time t2. OFF No current flows through the middle, thus the maximum pump current Ip0max is during the immediately preceding conduction period T. ON The effect of the potential caused by the current flow disappears, and the change begins to converge (begins to decrease). Furthermore, at time t4, it becomes the value V0b (minimum), which shows the least change. It can be considered that the rate of increase or decrease of the potential difference V0 depends on the capacitance (also called capacitance value) of the inner main pump electrode 22 and the resistance value of the inner main pump electrode 22 (e.g., the product of capacitance and resistance). Considering the rate of increase or decrease of the potential difference V0, the cutoff period T can be... OFFThe proportion relative to the period T is set to 10% or more (i.e., the duty cycle is 90% or less). Preferably, the cutoff period T is... OFF The ratio relative to period T can be set to more than 20% (i.e., the duty cycle is less than 80%).

[0208] The cutoff period T of the main pump current Ip0 OFF It consists of a non-stable period Tnon-stable and a stable period Tstable, wherein the non-stable period Tnon-stable is defined as: from the cutoff period T OFF The starting point, due to the main pump current Ip0 at the immediately preceding conduction time T ON The steady-state period Tstable is the time during which the change in potential difference V0 caused by the current in the main pump converges to the value of potential difference V0. This steady-state period is defined as: (excluding the time immediately preceding the on-time T of the main pump current Ip0). ON The period during which the potential difference V0 changes due to the flow of the main pump current Ip0. Here, "no change in potential difference V0 due to the flow of the main pump current Ip0" also implies that the change in potential difference V0 is very small.

[0209] For the main pump current Ip0 not due to the previous adjacent conduction time T ON The stable period Tstable, which is the time period during which the change in potential difference V0 caused by the flow of the main pump current Ip0 is defined as follows: The range of the potential difference V0 values ​​V0b to V0a during one cycle T of the main pump current Ip0 is set to 0% to 100%, and this is used as a reference to define the stable period Tstable of the potential difference V0. Specifically, the stable period Tstable is defined as the time from the moment when the main pump current Ip0 is turned off, causing the potential difference V0 to decrease to a predetermined percentage, to the beginning of the next cycle, i.e., the moment when the potential difference V0 begins to increase due to the conduction of the main pump current Ip0. Those skilled in the art can appropriately set the predetermined percentage. For example, the predetermined percentage can be 1% to 50%. For example, it can be less than 50%, less than 40%, less than 30%, less than 20%, less than 15%, less than 10%, less than 5%, or less than 1%. In this embodiment, the period from when the main pump current Ip0 is cut off, causing the potential difference V0 to fall below 10%, until the potential difference V0 begins to rise due to the conduction of the main pump current Ip0 in the next cycle (time t3~t4) is defined as the stable period Tstable.

[0210] Alternatively, the steady-state period Tstable can be defined as: the potential difference V0 is the cutoff period T OFF The period during which the average potential difference V0 is below the value.

[0211] The non-stable period T is: from the cutoff period TOFF The starting point, due to the main pump current Ip0 at the immediately preceding conduction time T ON The period from which the change in potential difference V0 caused by the current converges to the value of potential difference V0. That is, in one period T, it is: from the cutoff period T OFF The period from the start point to the start point of the stable period Tstable ( Figure 4 (2) The time intervals t2 to t3.

[0212] The length of Tstable during the steady-state period may vary depending on the on-time T within the period T. ON The length (duty cycle) and other parameters change.

[0213] exist Figure 4 In (2), the potential difference V0 begins to change to its maximum value V0a at the moment t2 when the main pump current Ip0 is cut off, and during the conduction period T ON In longer cases, the value V2a is sometimes reached before time t2 and this state continues until time t2. In addition, the potential difference V0 begins to change to the value V0b, which is not at its maximum change, at the time t4 when the main pump current Ip0 turns on in the next cycle. Sometimes, the value V0b is reached before time t4 and this state continues until time t4.

[0214] During the steady-state period Tstable, the main pump current Ip0 is not affected by the preceding adjacent conduction time T. ON The change in potential difference V0 caused by the flow in the middle is very small. Therefore, the potential difference V0 of Tstable during the steady period is: more accurately representing the value of oxygen concentration near the inner main pump electrode 22.

[0215] Thus, the potential difference V0 varies under the influence of the main pump current Ip0. During the cutoff period when there is no main pump current Ip0 flowing through the pulse power supply 24, T... OFF Because the change in potential difference V0 caused by the main pump current Ip0 will decrease, the potential difference V0 represents the oxygen concentration near the inner main pump electrode 22. Furthermore, during the steady-state period Tstable, the change in potential difference V0 is not affected by the main pump current Ip0 during the preceding adjacent conduction time T. ON The change in potential difference V0 caused by the flow in the middle is very small. Therefore, the potential difference V0 is: a more accurate representation of the oxygen concentration near the inner main pump electrode 22.

[0216] As described above, in step S23, the setting unit 94 acquires the potential difference V0 of the oxygen partial pressure detection sensor unit 80 for main pump control. The timing for acquiring the potential difference V0 can be appropriately specified; the setting unit 94 can do so during the cutoff period T when no main pump current Ip0 flows through the main pump unit 21. OFFIn this process, the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 is obtained. Thus, a potential difference V0 with minimal influence from the main pump current Ip0 can be obtained. That is, a potential difference V0 representing the oxygen concentration near the inner main pump electrode 22 can be obtained.

[0217] More preferably, the setting unit 94 can acquire the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 during a stable period Tstable when no main pump current Ip0 flows in the main pump unit 21 and the potential difference V0 is not affected by the flow of the main pump current Ip0. This allows the acquisition of a potential difference V0 with less influence from the main pump current Ip0. In other words, it allows the acquisition of a potential difference V0 that more accurately represents the oxygen concentration near the inner main pump electrode 22.

[0218] In addition, such as Figure 4 As shown in (2), the potential difference V0 exhibits the following trend: the closer to the end of the stable period Tstable (time t4), the smaller the change in potential difference V0 caused by the flow of the main pump current Ip0. Therefore, the setting unit 94 can, for example, obtain the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 at any time during the latter half of the stable period Tstable.

[0219] Additionally, for example, the setting unit 94 can be set during the cutoff period T when no main pump current Ip0 flows in the main pump unit 21. OFF The specified time is used to obtain the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42. For example, the specified time can be defined as: the cutoff period T OFF The time before the specified end time. The closer to the deadline T is. OFF The earlier the end time, the better. The specified time can be set as a stable period Tstable that does not involve changes in the potential difference V0 due to the flow of the main pump current Ip0. For example, the change in the potential difference V0 over time at a pre-defined or pre-set maximum duty cycle can be experimentally determined, and any time within the stable period Tstable at the maximum duty cycle can be set as the specified time. Without monitoring the change in the potential difference V0 over time, a more accurate representation of the oxygen concentration near the inner main pump electrode 22 can be obtained.

[0220] So far, the explanation has taken the case of oxygen being drawn out from the first internal cavity 20, i.e., the case where the main pump current Ip0 flows in the positive direction, as an example. However, when the oxygen concentration in the gas being measured is very low, or when it contains a large amount of hydrocarbons such as HC, oxygen may sometimes be drawn into the first internal cavity 20 depending on the composition of the gas being measured, i.e., the main pump current Ip0 may sometimes flow in the negative direction. Figure 5Yes: This shows a schematic diagram illustrating the changes in the main pump current Ip0 and the potential difference V0 over time when the main pump current Ip0 flows in the negative direction. Figure 5 (1) This diagram illustrates the change of the main pump current Ip0 over time. The horizontal axis represents time t, and the vertical axis represents the main pump current Ip0. Figure 4 (1) Same, the upward direction of the vertical axis is the positive direction of the main pump current Ip0. Figure 5 (2) This diagram illustrates the change of potential difference V0 over time. The horizontal axis represents time t, and the vertical axis represents potential difference V0. Regarding potential difference V0, the state where the potential of the reference electrode 42 is higher than that of the inner main pump electrode 22 is defined as positive. Figure 5 (2) with Figure 4 (2) Same, set the upward direction of the vertical axis as positive.

[0221] When the main pump current Ip0 flows in the negative direction, for example, if the main pump current Ip0 is turned on at time t1 at the beginning of a certain period T, then the main pump current Ip0 changes from 0A to the maximum current Ip0max (-maximum current Ip0max) in the negative direction, and this state continues until: the conduction period T has elapsed. ON At time t2. If the main pump current Ip0 is cut off at time t2, the main pump current Ip0 changes from -maximum current Ip0max to 0A until the cutoff period T has elapsed. OFF Up to time t4, the main pump current Ip0 remains at 0A. In this embodiment, the absolute values ​​of the maximum current Ip0max flowing in the positive direction and the maximum current (-maximum current Ip0max) flowing in the negative direction are set to be the same, but the absolute values ​​for the positive and negative directions can also be different.

[0222] The potential difference V0 also fluctuates intermittently due to the intermittent negative flow of the main pump current Ip0. For example, in Figure 5 In (2), the potential difference V0 begins to change (decline) from time t1 due to the potential caused by the flow of the negative maximum current Ip0max (-maximum current Ip0max). Then, at time t2, the potential difference V0 changes to its maximum value V0c (minimum value) due to the potential caused by the flow of the negative maximum current Ip0max (-maximum current Ip0max). During the cutoff period T starting from time t2... OFF No main pump current Ip0 flows, therefore the negative maximum current Ip0max (-maximum current Ip0max) is during the immediately preceding conduction period T. ON The effect of the flow on the potential disappears and the change begins to converge (begins to increase). Moreover, at time t4, it becomes the value that has not changed at all, V0d (maximum value).

[0223] For example, the auxiliary pump current Ip1 in the auxiliary pump unit 50 is greater than the target current value Ip1. SET In this case, the drive control unit 92 controls the pulse power supply 24 by reducing the duty cycle of the negative main pump current Ip0 or by allowing the positive main pump current Ip0 to flow, thereby further reducing the oxygen concentration in the first internal cavity 20.

[0224] Additionally, for example, the auxiliary pump current Ip1 in the auxiliary pump unit 50 is less than the target current value Ip1. SET In this case, the drive control unit 92 controls the pulse power supply 24 by increasing the duty cycle of the negative main pump current Ip0, thereby further increasing the oxygen concentration in the first internal cavity 20. Figure 5 In (1), as an example, the conduction period T relative to the first cycle T is shown. ON (Time t1~t2) and the conduction period T of the second cycle T. ON The control is set to a length of twice the normal operating time (t4-t5) (duty cycle is set to twice the normal operating time). In this case, the negative average value Ip0ave of the second period T is twice the normal value Ip0ave of the first period T. Because the negative average value Ip0ave is twice the normal value in the second period T, more oxygen is drawn into the first internal cavity 20 compared to the period of the first period T. As a result, the oxygen concentration near the inner main pump electrode 22 increases in the second period T. Figure 5 As shown in (2), the potential difference V0d' at the end of the second period T is smaller than the potential difference V0d at the end of the first period T.

[0225] Even when the main pump current Ip0 flows in the negative direction, the range of the potential difference V0 from V0c to V0d during one cycle T of the main pump current Ip0 is set to 0% to 100%, and the cutoff period T is specified based on this. OFFThe non-stable period Tnon-stable and the stable period Tstable of the potential difference V0 are defined. Specifically, the stable period Tstable is defined as the time from when the main pump current Ip0 is turned off and the potential difference V0 increases to a predetermined percentage to the start of the next cycle, that is, the time from when the main pump current Ip0 is turned on and the potential difference V0 begins to decrease (begins to decrease). Similar to the case of the main pump current Ip0 flowing in the forward direction, those skilled in the art can appropriately set the predetermined percentage. As a predetermined percentage, it can be, for example, 50% to 99%. For example, it can be 50% or more, 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 99% or more. In this embodiment, the stable period Tstable is defined as the period from when the main pump current Ip0 is turned off and the potential difference V0 reaches 90% or more, to when the main pump current Ip0 is turned on in the next cycle and the potential difference V0 begins to decrease (times t3 to t4).

[0226] Alternatively, the steady-state period Tstable can be defined as: the period when the potential difference V0 reaches the cutoff period T. OFF The period above the average value of the potential difference V0.

[0227] The non-stable period T is defined as: from the cutoff period T OFF The starting point, due to the main pump current Ip0 at the immediately preceding conduction time T ON The period from which the change in potential difference V0 caused by the flow converges to the value of potential difference V0. That is, in one period T, it is: from the cutoff period T OFF The starting point, the period up to the starting point of the stable period Tstable ( Figure 5 (2) The time intervals t2 to t3.

[0228] The setting unit 94 determines whether the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 reaches a predetermined target value. If the potential difference V0 reaches the target value, no change in the residual oxygen concentration ΔO2 occurs. Therefore, the target voltage value V1 is continuously obtained using the potential difference V0. SET The potential difference V0 reaching the target value implies that the deviation from the target value is still within a specified range. This means that the deviation from the target value is still within a specified range and does not cause a substantial change in the residual oxygen concentration ΔO2. When the potential difference V0 deviates from the target value, it will cause a change in the residual oxygen concentration ΔO2. Therefore, the setting unit 94 sets a new target voltage value V1 based on the value of the potential difference V0 or the deviation from the target value of the potential difference V0. SET Perform the calculation. A deviation of the potential difference V0 from the target value includes: a deviation from the target value that exceeds the specified range.

[0229] Those skilled in the art can appropriately determine the target value of the potential difference V0. In the auxiliary pump unit 50, the target value can be set as follows: as a result of the constant auxiliary pump current Ip1 flowing, the oxygen concentration near the auxiliary pump electrode 51, i.e., the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44, reaches a predetermined value. The target value can be set as follows: the value that causes the change ΔO2 in the residual oxygen concentration of the gas to be measured reaching the measuring electrode 44 to converge within a range permissible relative to the desired measurement accuracy of the NOx concentration. For example, considering the variation in the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 (described later), the target value of the potential difference V0 can be 150mV to 300mV.

[0230] Those skilled in the art can appropriately determine the specified range of deviation relative to the target value. This range can be determined based on the permissible variation ΔO2 in the residual oxygen concentration in the gas being measured reaching the measuring electrode 44, relative to the desired measurement accuracy of the NOx concentration. Alternatively, it can be determined based on the degree of slight variation in the pump control. For example, considering the magnitude of the variation in the residual oxygen concentration in the gas being measured reaching the measuring electrode 44 (described later), the deviation relative to the target value of the potential difference V0 can be within 5 mV to 30 mV.

[0231] Alternatively, a target range for the potential difference V0 can be preset. When the potential difference V0 between the inner main pump electrode 22 and the reference electrode 42 is within the target range, there is no substantial change in the residual oxygen concentration ΔO2. Therefore, the target voltage value V1 is continuously obtained using the potential difference V0. SET When the potential difference V0 deviates from the target range, it substantially causes a change in the residual oxygen concentration ΔO2. Therefore, the setting unit 94 sets a new target voltage value V1 based on the value of the potential difference V0. SET Perform the calculation.

[0232] Thus, the target voltage value V1 is set based on the potential difference V0. SET The above-described setting steps can substantially prevent changes in the oxygen concentration near the auxiliary pump electrode 51, i.e., the residual oxygen concentration ΔO2 in the gas to be measured reaching the measuring electrode 44. In other words, the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 can be controlled to be constant. Regarding the target voltage value V1... SETAs a result of the setting steps, a value of approximately 300mV to 450mV can be obtained. For example, the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 can be kept constant at a concentration of approximately 0.1ppm or less, 0.01ppm or less, 0.001ppm or less, or approximately 0.0001ppm. The residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 should be kept within a constant range (within a specified range of variation) to achieve the objective of the present invention: to accurately measure low concentrations of the target gas (NOx in this embodiment) of approximately 10 to 500ppm. It is preferable to control the residual oxygen concentration within the smallest possible range (range of variation). If the residual oxygen concentration in the gas to be measured reaching the measuring electrode 44 is controlled to be 0.001ppm, then for example, it is sufficient to set the range of variation of the residual oxygen concentration to be 0.0001ppm or less (1 / 10 or less) or 0.00005ppm or less (1 / 20 or less). Those skilled in the art can appropriately determine the range of variation in residual oxygen concentration based on the intended use of the gas sensor 100.

[0233] If the potential difference V0 deviates from the predetermined target value, the setting unit 94 sets a new target voltage value V1 based on the deviation value relative to the value of the potential difference V0 or relative to the target value of the potential difference V0. SET The calculation is performed. The setting unit 94 can set a new target voltage value V1 based on the value of the potential difference V0 obtained in each period T (e.g., the value in the stable period Tstable). SET Calculations can be performed. Alternatively, the new target voltage value V1 can be determined based on the values ​​of the potential differences V0 obtained in each of the multiple periods T (e.g., based on the average of multiple potential differences V0 obtained in different periods). SET Calculations are performed. For example, the setting unit 94 calculates the new target voltage value V1 based solely on the potential difference V0 acquired in one cycle. SET During calculations, the obtained potential difference V0 may sometimes change due to instantaneous fluctuations in the potential difference V0, electrical noise, etc., and become a value different from the value representing the oxygen concentration near the inner main pump electrode 22. In this case, the setting unit 94 may set the target voltage value V1. SET Excessive variation. If the target voltage value V1 SET Excessive variation will cause excessive changes in the auxiliary pump current Ip1 flowing in the auxiliary pump unit 50 and the main pump current Ip0 (average value Ip0ave) flowing in the main pump unit 21 due to the pulse power supply 24, which may lead to unstable control conditions such as vibration or oscillation. Conversely, for example, if the setting unit 94 sets the target voltage value V1 based on the average value of the potential difference V0 in the stable period Tstable acquired over multiple cycles... SETCalculations are performed, and the target voltage value V1 is adjusted based on the actual oxygen concentration near the inner main pump electrode 22. SET Calculations are performed, thus making control easier and more stable. In this embodiment, the setting unit 94 stores the potential difference V0 at a predetermined timing during the stable period Tstable of each cycle T in the memory of the control unit 91, which functions as the setting unit 94. The target voltage value V1 is set based on the average of the most recently stored multiple (e.g., 3) potential differences V0. SET Perform the calculation.

[0234] As described above, a gas sensor 100 for detecting the NOx concentration in a gas to be measured is shown as an example of an embodiment of the present invention, but the present invention is not limited to this method. As long as it falls within the scope of the present invention's objective of achieving high-precision measurement of a target gas containing a large concentration range of low concentrations of the target gas, the present invention can include gas sensors with structures having various types of sensor elements and control devices.

[0235] In the above embodiments, such as Figure 4 As shown in (1), the discontinuous main pump current Ip0 is formed as a current with one rectangular wave per cycle (rectangular single-pulse current), but it is not limited to this. For example, the pulse power supply 24 can also be used as the discontinuous main pump current Ip0. Figure 6 The instantaneous pulse current is shown. In this case, the drive control unit 92 can change the oscillation period T. A The proportion occupied in period T (instantaneous period) (duty cycle), period T, number of pulses in one period ( Figure 6 The control signal is output to the pulse power supply 24 in a manner that takes at least one of the following parameters: the time Ta of the oscillation (pulse) of 4 times (or 1 time), the period of the pulse (Ta+Tb), and the maximum current Ip0max, and causes the average value Ip0ave of the main pump current Ip0 during one cycle to change.

[0236] In such Figure 6 When the main pump current Ip0 is set as an instantaneous pulse current, the change period Tchange of the potential difference V0 is included in the oscillation period T. A In this context, the stable period Tstable is contained within the non-oscillating period T. B More specifically, when the main pump current Ip0 is a transient pulse current, the oscillation period T... A The period during which the main pump current Ip0 is considered to be conducting ( Figure 4 The time intervals t1 to t2, and the non-oscillating period T B The period during which the main pump current Ip0 is considered to be cut off ( Figure 4The stable period Tstable is defined using the same method as described in the above implementation (times t2 to t4).

[0237] In the above-described embodiments and in the above-described instantaneous pulse current, such as Figure 4 As shown in (1), the pulse power supply 24 allows the pulse current of the rectangular wave to flow as the main pump current Ip0, but it is not limited to the rectangular wave (square wave). It can allow the pulse current of the half wave of the sine wave, the triangular wave, the sawtooth wave, the waveform shape during discharge, etc., to flow, and it can also allow the pulse current of the waveform composed of one or more of the above waves to flow.

[0238] exist Figure 4 (1) Figure 5 (1) and Figure 6 In the diagram, the pulse current of the main pump current Ip0 is shown as a rectangle. However, as mentioned above, the actual rise and fall of the main pump current Ip0 require a small amount of time. That is, there is actually a rise time and a fall time in the pulse current, and the pulse current does not form a complete rectangle. Therefore, for example, if the pulse amplitude of the pulse current is too small [for example, if the time Ta of one oscillation (pulse) in the instantaneous pulse current is too small], sometimes the actual wave height value of the pulse current does not reach the ideal wave height value of the rectangular waveform due to the influence of the rise time. In this case, the drive control unit 92 sets the auxiliary pump current Ip1 to a constant value (target current value Ip1) in the main pump unit 21. SET Even with feedback control, where the control signal is output to a pulse power supply 24 that should set the average value Ip0ave to a target value, the actual average value Ip0ave is still lower than the theoretical average value Ip0ave. As a result, sometimes the actual average value Ip0ave deviates from the target value, making it impossible to control the oxygen concentration in the measured gas with high precision. On the other hand, if the pulse amplitude of the pulse current is large, even with a rise time, the actual wave height of the pulse current will reach the ideal rectangular waveform wave height. In this case, it is difficult to cause a deviation between the actual average value Ip0ave and the target value.

[0239] Therefore, preferably, the drive control unit 92 controls the main pump unit 21 such that the pulse amplitude of the main pump current Ip0 is such that the actual wave height value reaches the wave height value of the ideal rectangular waveform. That is, preferably, the drive control unit 92 controls the main pump current Ip0 such that the pulse amplitude of the main pump current Ip0 is at least a predetermined lower limit value.

[0240] In the above embodiment, the pulse power supply 24 is configured as a current source, but a voltage source can also be used. The pulse power supply 24 can be used to apply an intermittent voltage Vp0 between the inner main pump electrode 22 and the outer pump electrode 23, thereby allowing the intermittent main pump current Ip0 to flow.

[0241] In the above embodiment, the setting unit 94 is configured to appropriately change the target voltage value V1 of the auxiliary pump unit 50 based on the deviation value relative to the value of the potential difference V0 or relative to the target value of the potential difference V0. SET However, the target voltage value V1 of the auxiliary pump unit 50 can also be used. SET Based on this, the target current value Ip1 was also... SET Make changes. For example, if the deviation from the target value of potential difference V0 is large, change the target voltage value V1. SET and the target current value Ip1 SET Both sides, and can be controlled to make the potential difference V0 reach the target value faster.

[0242] In the above embodiment, the gas sensor 100 detects the NOx concentration in the gas to be measured, but the gas to be measured is not limited to NOx. For example, the gas to be measured can be other oxide gases besides NOx (e.g., carbon dioxide CO2, water H2O, etc.). When the gas to be measured is an oxide gas, the gas to be measured, which contains oxide gases itself, is introduced into the third internal cavity 61 in the same way as in the embodiment for detecting NOx concentration described above. The oxide gases in the gas to be measured are reduced at the measuring electrode 44 to generate oxygen. The generated oxygen can be obtained by the measuring pump current Ip2 of the measuring pump unit 41 and the gas to be measured can be detected.

[0243] Alternatively, the target gas can be a non-oxide gas such as ammonia (NH3). When the target gas is a non-oxide gas, it is converted into an oxide gas (e.g., NO in the case of ammonia (NH3)). The target gas containing the converted oxide gas is then introduced into the third internal cavity 61. At the measuring electrode 44, the converted oxide gas in the target gas is reduced to produce oxygen. The generated oxygen can be acquired as the measuring pump current Ip2 of the measuring pump unit 41, thereby detecting the target gas. At least one of the inner main pump electrode 22 and the auxiliary pump electrode 51 can function as a catalyst to convert the non-oxide gas into an oxide gas.

[0244] In the above embodiment, the auxiliary pump unit 50 and the measuring pump unit 41 are controlled to allow continuous current flow using variable power supplies 52 and 46, but this is not a limitation. In addition to the main pump unit 21, control can be performed to allow intermittent pump current flow in at least one or more components of the auxiliary pump unit 50 and the measuring pump unit 41. For example, control can be performed to allow intermittent pump current flow for all components of the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41. That is, a pulsed power supply can be used instead of the variable power supply 52 of the auxiliary pump unit 50 as a current source, and a pulsed power supply can be used instead of the variable power supply 46 of the measuring pump unit 41 as a current source. In this case, in the auxiliary pump unit 50, the auxiliary pump current Ip1 of the pulsed power supply of the auxiliary pump unit 50 is feedback controlled so that the electromotive force V1 of the oxygen partial pressure detection sensor unit 81 for auxiliary pump control reaches the target voltage value V1. SET In the main pump unit 21, the main pump current Ip0 of the pulse power supply 24 is controlled by feedback so that the auxiliary pump current Ip1 reaches the target current value Ip1. SET Therefore, the pump current Ip2 can be detected as a current value corresponding to the NOx concentration in the gas being measured, just as in the above-described embodiment.

[0245] Regarding the gas sensor 100 of the above-described embodiment, as follows: Figure 1 As shown, the sensor element 101 is configured to have three internal cavities: a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61. An inner main pump electrode 22, an auxiliary pump electrode 51, and a measuring electrode 44 are respectively disposed in each internal cavity, but this configuration is not limited to this. For example, it can also be configured to have two internal cavities: a first internal cavity 20 and a second internal cavity 40. The inner main pump electrode 22 is disposed in the first internal cavity 20, and the auxiliary pump electrode 51 and the measuring electrode 44 are disposed in the second internal cavity 40. In this case, for example, a porous protective layer covering the measuring electrode 44 can be formed as a diffusion rate control unit between the auxiliary pump electrode 51 and the measuring electrode 44.

[0246] Regarding the gas sensor 100 of the above embodiment, the outer pump electrode 23 serves as three electrodes: the outer main pump electrode of the main pump unit 21, the outer auxiliary pump electrode of the auxiliary pump unit 50, and the outer measuring electrode of the measuring pump unit 41, but is not limited thereto. For example, the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode can be formed as different electrodes. For example, any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode can be configured to contact the gas to be measured on the outer surface of the base portion 102, different from the outer pump electrode 23. Alternatively, the reference electrode 42 can serve as any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode.

[0247] As described above, according to the present invention, the residual oxygen concentration in the gas to be measured reaching the measuring electrode can be controlled with high precision. Therefore, even in a low concentration range of about 10 to 500 ppm, the target gas can be measured with high precision. As a result, a large concentration range (e.g., 10 to 5000 ppm) of target gas, including low concentrations, can be measured with high precision.

[0248] Furthermore, according to the present invention, the gas sensor 100 is configured to measure NOx concentration while setting a target voltage value V1 based on a potential difference V0. SET Therefore, according to the present invention, while continuously measuring the target gas (NOx in this embodiment) in the gas being measured using the gas sensor 100, the residual oxygen concentration in the gas being measured reaching the measuring electrode can be controlled with high accuracy. As a result, even when the NOx concentration in the gas being measured is low, the NOx concentration can be measured continuously and with high accuracy.

Claims

1. A gas sensor for detecting a target gas in a measured gas, comprising: A sensor element and a control device for controlling the sensor element, wherein, The sensor element includes: The elongated, plate-shaped base portion includes a solid electrolyte layer that is oxygen ion conductive; The gas flow section to be measured is formed from one end of the base portion along its length. The main pump unit includes an inner main pump electrode and an outer main pump electrode. The inner main pump electrode is disposed on the inner surface of the gas flow section to be measured, and the outer main pump electrode is disposed at a different position on the base from the gas flow section to be measured, and corresponds to the inner main pump electrode. An auxiliary pump unit includes an inner auxiliary pump electrode and an outer auxiliary pump electrode. The inner auxiliary pump electrode is disposed at one end of the inner surface of the gas flow section being measured, which is further away from the base section in the length direction than the inner main pump electrode. The outer auxiliary pump electrode is disposed at a different position on the base section from the gas flow section being measured, and corresponds to the inner auxiliary pump electrode. A measuring pump unit includes an inner measuring electrode and an outer measuring electrode. The inner measuring electrode is disposed at one end of the inner surface of the gas flow section being measured, further away from the base portion in the longitudinal direction than the inner auxiliary pump electrode. The outer measuring electrode is disposed at a different position on the base portion from the gas flow section being measured, and corresponds to the inner measuring electrode. A reference electrode, which is arranged inside the substrate to contact the reference gas. The main pump unit allows the main pump current to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current flowing in the auxiliary pump unit reaches a specified target current value. The auxiliary pump unit allows current to flow through it, so that the electromotive force between the inner auxiliary pump electrode and the reference electrode reaches a predetermined target voltage value. The control device includes: A control power supply, used to allow the main pump current, which is repeatedly switched on and off, to flow in the main pump unit; and The setting unit sets the target voltage value of the auxiliary pump unit. The setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode, and sets the target voltage value of the auxiliary pump unit based on the potential difference.

2. The gas sensor according to claim 1, wherein, During the cutoff period when the main pump current is not flowing through the main pump unit using the control power supply, the setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode.

3. The gas sensor according to claim 1 or 2, wherein, The setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode during a stable period in the main pump unit when the main pump current is not flowing using the control power supply and the potential difference does not change due to the flow of the main pump current.

4. The gas sensor according to claim 1, wherein, The control power supply includes a pulse power supply that periodically turns the main pump current on and off. The setting unit acquires the potential difference generated between the inner main pump electrode and the reference electrode for each cycle T during a predetermined time period in the cycle T of the pulse power supply during which the main pump current is not flowing due to the unused pulse power supply.

5. A control method for a gas sensor, used to detect the target gas in a measured gas, wherein, The gas sensor includes: a sensor element, and a control device for controlling the sensor element. The sensor element includes: The elongated, plate-shaped base portion includes a solid electrolyte layer that is oxygen ion conductive; The gas flow section to be measured is formed from one end of the base portion along its length. The main pump unit includes an inner main pump electrode and an outer main pump electrode. The inner main pump electrode is disposed on the inner surface of the gas flow section to be measured, and the outer main pump electrode is disposed at a different position on the base from the gas flow section to be measured, and corresponds to the inner main pump electrode. An auxiliary pump unit includes an inner auxiliary pump electrode and an outer auxiliary pump electrode. The inner auxiliary pump electrode is disposed at one end of the inner surface of the gas flow section being measured, which is further away from the base section in the length direction than the inner main pump electrode. The outer auxiliary pump electrode is disposed at a different position on the base section from the gas flow section being measured, and corresponds to the inner auxiliary pump electrode. A measuring pump unit includes an inner measuring electrode and an outer measuring electrode. The inner measuring electrode is disposed at one end of the inner surface of the gas flow section being measured, further away from the base portion in the longitudinal direction than the inner auxiliary pump electrode. The outer measuring electrode is disposed at a different position on the base portion from the gas flow section being measured, and corresponds to the inner measuring electrode. A reference electrode, which is arranged inside the substrate to contact the reference gas. The control device includes a control power supply for allowing the main pump current, which is repeatedly switched on and off, to flow through the main pump unit. The control method includes the following steps: The setting step involves acquiring the potential difference between the inner main pump electrode and the reference electrode, and setting a target voltage value for the electromotive force between the inner auxiliary pump electrode and the reference electrode of the auxiliary pump unit based on the potential difference; and In the oxygen concentration adjustment step, the control power supply in the main pump unit is controlled to allow the main pump current to flow through the repeatedly switched-on and switched-off state, so that the auxiliary pump current flowing in the auxiliary pump unit reaches a specified target current value. Furthermore, the auxiliary pump current is allowed to flow in the auxiliary pump unit so that the electromotive force between the inner auxiliary pump electrode and the reference electrode reaches the target voltage value.

6. The control method according to claim 5, wherein, In the setting step, during the cutoff period when the main pump current is not flowing in the main pump unit using the control power supply, the potential difference generated between the inner main pump electrode and the reference electrode is acquired.

7. The control method according to claim 5 or 6, wherein, In the setting step, during a stable period in the main pump unit where the main pump current is not flowing using the control power supply and the potential difference does not change due to the main pump current flow, the potential difference generated between the inner main pump electrode and the reference electrode is acquired.

8. The control method according to claim 5, wherein, The control power supply includes a pulse power supply that periodically turns the main pump current on and off. In the setting step, at a predetermined time within the cutoff period during which the main pump current flows without utilizing the pulse power supply in the period T of the pulse power supply, the potential difference generated between the inner main pump electrode and the reference electrode is obtained for each period T.

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