Gas sensor

Abstract

A gas sensor (100) is provided with a sensor element (101) and a control device. The control device performs a heater control process that energizes a heater (72) to heat the heater (72). The control device also performs a normal-time control process after starting the heater control process, the normal-time control process including a main pump control process that controls a main pump unit (21), an auxiliary pump control process that controls an auxiliary pump unit (50) so that a voltage (V1) reaches a target value, and a normal-time measurement pump control process that controls a measurement pump unit (41) so that oxygen is drawn out of a third internal cavity (61) with a voltage (V2) reaching a normal-time target value. The control device detects a specific gas concentration in a measured gas based on a pump current (Ip2) that flows in the measurement pump unit (41) through the normal-time measurement pump control process. The control device performs a correction process that corrects the target value of the voltage (V1) to a higher value than a period after an initial period at the beginning of the normal-time control process.

Description

Technical Field

[0001] This invention relates to a gas sensor. Background Technology

[0002] Previously, gas sensors were known for detecting the concentration of specific gases such as NOx in measured gases, such as automobile exhaust. For example, Patent Document 1 describes a gas sensor comprising: a sensor element having multiple layers of a solid electrolyte with oxygen ion conductivity; an outer pump electrode disposed on the outside of the sensor element; an inner main pump electrode, an inner auxiliary pump electrode, and a measuring electrode disposed inside the sensor element for a gas flow section; and a reference electrode and a heater disposed inside the sensor element. In this gas sensor, the sensor element as a whole is adjusted to a temperature that activates the solid electrolyte by the heater, and the specific gas concentration is detected as follows. First, the oxygen concentration in the measured gas around the inner main pump electrode is adjusted using a control voltage applied between the outer pump electrode and the inner main pump electrode. Next, the oxygen concentration in the measured gas around the inner auxiliary pump electrode is adjusted using a control voltage applied between the outer pump electrode and the inner auxiliary pump electrode. Thus, the measured gas with adjusted oxygen concentration reaches the periphery of the measuring electrode. Furthermore, a specific gas in the measured gas, after oxygen concentration adjustment, is reduced around the measuring electrode. The concentration of the specific gas in the measured gas is detected based on the pump current flowing when oxygen generated around the measuring electrode due to reduction is drawn out. The control voltage applied between the outer pump electrode and the inner auxiliary pump electrode is controlled in such a way that the electromotive force (voltage V1) between the inner auxiliary pump electrode and the reference electrode reaches a target value.

[0003] Patent documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2016-166871 Summary of the Invention

[0005] In this type of gas sensor, during the period from the start of heating the sensor element using a heater until the temperature of each electrode stabilizes, the temperature difference between the inner auxiliary pump electrode and the reference electrode may temporarily increase due to the difference in heating rates. When the temperature difference between the two electrodes is temporarily large, the thermoelectric potential contained in the voltage between the two electrodes (called the auxiliary pump voltage) also temporarily increases. Therefore, the deviation between the auxiliary pump voltage and the electromotive force based on the oxygen concentration around the inner auxiliary pump electrode will temporarily increase. Thus, even if control is implemented to achieve the target value for the auxiliary pump voltage, it is sometimes impossible to achieve high-precision control of the oxygen concentration around the inner auxiliary pump electrode. Consequently, the detection accuracy for a specific gas concentration may decrease.

[0006] This invention was made to solve such a problem, and its main objective is to enable high-precision control of the oxygen concentration around the inner auxiliary pump electrode when the thermoelectric potential contained in the voltage of the auxiliary pump is temporarily large.

[0007] The present invention employs the following method to achieve the aforementioned main objective.

[0008] The gas sensor of the present invention includes: a sensor element, a heater control unit, a pump unit control unit, and a specific gas concentration detection unit.

[0009] The sensor element has the following characteristics:

[0010] The main body of the element includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside to introduce and circulate the gas to be measured.

[0011] The measuring pump unit has an outer measuring electrode disposed on the outside of the main body of the component in a manner that contacts the gas to be measured, and an inner measuring electrode disposed in the measuring chamber of the gas to be measured, and draws oxygen from the periphery of the inner measuring electrode to the periphery of the outer measuring electrode.

[0012] A reference electrode is disposed inside the main body of the element in such a way that it is in contact with a reference gas, which serves as a detection reference for a specific gas concentration in the gas being measured.

[0013] The voltage detection sensor unit for measurement detects the voltage for measurement between the reference electrode and the inner measuring electrode.

[0014] The main pump unit adjusts the oxygen concentration in the first internal cavity located upstream of the measuring chamber within the gas flow section being measured.

[0015] An auxiliary pump unit has an inner auxiliary pump electrode disposed in the second internal cavity, and adjusts the oxygen concentration of the second internal cavity. The second internal cavity is located in the gas flow section being measured at a position that is further downstream than the first internal cavity and further upstream than the measuring chamber.

[0016] An auxiliary pump voltage detection sensor unit detects the auxiliary pump voltage between the reference electrode and the inner auxiliary pump electrode; and

[0017] A heater that heats the main body of the aforementioned components;

[0018] The heater control unit performs heater control processing to energize the heater and cause it to heat up.

[0019] After initiating the heater control process, the pump unit control unit performs a normal operation control process, which includes: a main pump control process for controlling the main pump unit; an auxiliary pump control process for controlling the auxiliary pump unit to achieve a target voltage; and a normal operation measurement pump control process for controlling the measurement pump unit to achieve a target voltage and drawing oxygen from the measurement chamber.

[0020] The aforementioned specific gas concentration detection unit detects the concentration of a specific gas in the gas being measured based on the measuring pump current flowing through the measuring pump unit, which is controlled by the measuring pump as described above under normal operating conditions.

[0021] In the initial stage of the above-mentioned normal control process, the pump unit control unit performs a correction process to adjust the target value of the auxiliary pump voltage to a higher value compared to the period after the initial stage.

[0022] In this gas sensor, during the normal control process following the start of heater control processing, the following steps are performed: main pump control processing to control the main pump unit; auxiliary pump control processing to control the auxiliary pump unit to achieve a target value for the auxiliary pump voltage; and normal measurement pump control processing to control the measurement pump unit to achieve a normal target value for the measurement voltage and draw oxygen from the measurement chamber. Furthermore, the concentration of a specific gas in the gas being measured is detected based on the measurement pump current flowing through the measurement pump unit during the normal measurement pump control process. Additionally, at the beginning of the normal control process, a correction process is performed to adjust the target value of the auxiliary pump voltage in the auxiliary pump control process to a higher value compared to subsequent periods. By increasing the target value of the auxiliary pump voltage at the beginning of the normal control process, the effects of a temporarily large thermoelectric potential (i.e., the thermoelectric potential contained in the auxiliary pump voltage) between the inner auxiliary pump electrode and the reference electrode are reduced. Therefore, compared to the case without correction processing, high-precision control of the oxygen concentration around the inner auxiliary pump electrode is possible when the thermoelectric potential contained in the auxiliary pump voltage is temporarily large.

[0023] In the gas sensor of the present invention, the pump unit control unit can, during the aforementioned calibration process, calibrate the target value of the auxiliary pump voltage based on a calibration mode predetermined in advance, which tends to decrease in calibration amount over time. Here, when the sensor element is heated using a heater, the temperature difference between the inner auxiliary pump electrode and the reference electrode tends to decrease over time. Therefore, the thermoelectric potential included in the auxiliary pump voltage also tends to decrease over time. Therefore, by calibrating the target value of the auxiliary pump voltage based on a calibration mode predetermined in advance, which tends to decrease in calibration amount over time, the influence caused by a temporarily large thermoelectric potential included in the auxiliary pump voltage can be reduced. Therefore, more precise control of the oxygen concentration around the inner auxiliary pump electrode is possible.

[0024] Here, "there is a tendency for the correction amount to decrease over time" includes, for example, the correction amount decreasing linearly, the correction amount decreasing curvilinearly, and the correction amount decreasing as a step function, etc.

[0025] The gas sensor of the present invention includes a reference voltage detection sensor unit that detects a reference voltage between a gas-to-be-measured side electrode disposed on the outside of the main body of the element in contact with the gas to be measured and a reference electrode. The main pump control process involves controlling the main pump unit such that the auxiliary pump current flowing through the auxiliary pump unit, as determined by the auxiliary pump control process, reaches a target current. In the calibration process, the pump unit control unit can, assuming that the main pump current flowing through the main pump unit is stable during the main pump control process, correct the target value of the auxiliary pump voltage in the calibration process according to a trend where a reference voltage calculated based on the main pump current and corresponding to the oxygen concentration in the gas to be measured around the sensor element increases with the larger the deviation from the measured reference voltage detected by the reference voltage detection sensor unit. Here, when adjusting the oxygen concentration in the first internal cavity through the main pump control process, the flowing main pump current is correlated with the oxygen concentration in the gas to be measured around the sensor element. Furthermore, the reference voltage is the voltage between the measured gas-side electrode on the outer side of the sensor body and the reference electrode. Therefore, it is correlated with the oxygen concentration in the measured gas surrounding the sensor element. Thus, assuming the main pump current is stable, the reference voltage corresponding to the oxygen concentration in the measured gas surrounding the sensor element can be derived from the main pump current, i.e., the reference voltage can be calculated. On the other hand, since the reference voltage actually detected by the reference voltage detection sensor unit, i.e., the measured reference voltage, also includes the thermoelectric potential between the measured gas-side electrode and the reference electrode, when the temperature difference between the two electrodes is temporarily large, the thermoelectric potential included in the measured reference voltage also temporarily increases. Therefore, the larger the thermoelectric potential included in the measured reference voltage, the greater the deviation between the calculated reference voltage derived from the main pump current and the measured reference voltage actually detected by the reference voltage detection sensor unit. Additionally, when the thermoelectric potential between the measured gas-side electrode and the reference electrode is large, the thermoelectric potential between the inner auxiliary pump electrode and the reference electrode is often also large. Therefore, by taking into account the trend that the larger the deviation between the calculated reference voltage and the measured reference voltage, the larger the correction amount will be, the target value of the auxiliary pump voltage in the correction process is corrected. In this way, the influence caused by the temporarily large thermoelectric potential contained in the auxiliary pump voltage can be reduced.

[0026] In this case, the pump unit control unit may include a storage unit that stores the correspondence between the main pump current and the calculated reference voltage, that is, the calculated reference voltage corresponds to the oxygen concentration in the gas being measured around the sensor element, and the calculated reference voltage is derived based on the correspondence and the main pump current.

[0027] In the gas sensor of the present invention, the main body of the element can be shaped as an elongated strip with two ends along its long side, namely a front end and a rear end. The inner auxiliary pump electrode and the reference electrode can be disposed on the front end side of the main body, and the reference electrode is disposed at a position away from the front end compared to the inner auxiliary pump electrode. When the inner auxiliary pump electrode and the reference electrode are disposed in such a positional relationship, a difference in the heating rate between the inner auxiliary pump electrode and the reference electrode is likely to occur after the sensor element is heated by the heater until the temperature of the two electrodes stabilizes, thereby temporarily increasing the temperature difference between the two electrodes. Therefore, the calibration process of the present invention is of great significance.

[0028] In the gas sensor that corrects for the discrepancy between the calculated and measured reference voltages as described above, the gas-to-be-measured electrode can be disposed on the front end of the main body of the element, and the reference electrode is disposed at a position away from the front end compared to the gas-to-be-measured electrode. When the gas-to-be-measured electrode and the reference electrode are disposed in this positional relationship, if the temperature difference between the inner auxiliary pump electrode and the reference electrode temporarily increases, the temperature difference between the gas-to-be-measured electrode and the reference electrode is also likely to temporarily increase. Therefore, with this electrode positional relationship, the greater the discrepancy between the calculated and measured reference voltages, the greater the thermoelectric potential contained in the auxiliary pump voltage is likely to become; thus, correction based on the aforementioned discrepancy is suitable.

[0029] However, a gas sensor requires time from the moment the heater is energized until it can accurately detect the concentration of a specific gas; this time is called the light-off time. There is a trend towards longer light-off times: the longer it takes to remove oxygen (not from the specific gas) that was already present in the measuring chamber containing the measuring electrodes before the sensor element is used, to a level that does not affect the measurement accuracy, the longer the light-off time. Furthermore, in recent years, due to stricter exhaust gas regulations, the need to shorten the light-off time in such gas sensors has been increasing.

[0030] Therefore, in the gas sensor of the present invention, the pump unit control unit can perform the normal operation control process during the normal operation of the sensor element, and can also perform a start-up pump control process when the sensor element is started up before the normal operation: controlling the measuring pump unit to draw oxygen from the measuring chamber in a manner that the measuring voltage reaches a higher start-up target value than the normal operation target value. If such a start-up pump control process is performed when the sensor element is started up before the normal operation, the target value of the oxygen concentration in the measuring chamber is lower than that during the normal operation, and oxygen is drawn from the measuring chamber. Thus, compared to the case where the normal operation pump control process is performed from the start-up of the sensor element, oxygen that is already present in the measuring chamber before the sensor element is started can be quickly removed from the measuring chamber. Therefore, the ignition time of the sensor element is shortened. Here, oxygen that is already present in the measurement chamber before the sensor element is activated can be exemplified by, for example, oxygen molecules (O2) present in the space inside the measurement chamber, oxygen molecules (O2) attached to the surface of the inner measurement electrode, and oxygen bonded to the constituent material of the inner measurement electrode (causing oxidation of the constituent material).

[0031] In the gas sensor of the present invention, the heater control process is a process of energizing the heater to heat it up so that the temperature of the heater or the main body of the element, i.e., the temperature of the sensor element, reaches a predetermined target temperature. The pump unit control unit can start the start-up measurement pump control process when the temperature of the sensor element reaches a predetermined threshold below the target temperature at the start of the heater control process. In this way, the start time of the start-up measurement pump control process can be appropriately determined based on the temperature of the sensor element. The predetermined threshold can be a value lower than the target temperature. Here, "energizing the heater to heat it up so that the temperature of the sensor element reaches a predetermined target temperature" includes: controlling the heater based on the temperature of the sensor element itself, and controlling the heater based on a value that can be converted into the temperature of the sensor element (e.g., the resistance value of the heater, the resistance value of the circuit containing the solid electrolyte, etc.). Examples of the resistance value of the circuit containing the solid electrolyte include, for example, the resistance value of the measuring pump unit, the resistance value of the measuring voltage detection sensor unit, etc.

[0032] In the gas sensor of the present invention, the pump unit control unit performs the auxiliary pump control processing and the main pump control processing when the sensor element is started. The main pump control processing involves controlling the main pump unit so that the auxiliary pump current flowing through the auxiliary pump unit, as determined by the auxiliary pump control processing, reaches a target current. When the pump unit control unit determines that the auxiliary pump current has stabilized near the target current, it can switch from the start-up measurement pump control processing to the normal-time measurement pump control processing and begin the normal-time control processing. Here, before the sensor element is started, not only the measurement chamber but also the first and second internal cavities upstream of it are in a state containing a large amount of oxygen (not from a specific gas) (e.g., atmospheric atmosphere). When the sensor element is started, the pump unit control unit performs the main pump control processing and the auxiliary pump control processing, thereby removing the oxygen already present in the first and second internal cavities before the sensor element is started. Furthermore, since the first and second internal cavities are connected to the measuring chamber, oxygen in the measuring chamber can be removed by the operation of the main pump unit and the auxiliary pump unit. Also, as described above, since the first and second internal cavities are connected to the measuring chamber, oxygen in the measuring chamber can be sufficiently drawn out even when the oxygen concentration in the first and second internal cavities has stabilized. Moreover, when the auxiliary pump current has stabilized near the target current, the oxygen concentration in the first and second internal cavities is more likely to stabilize. Therefore, when it is determined that the auxiliary pump current has stabilized near the target current, the switch from start-up measuring pump control processing to normal measuring pump control processing can be performed appropriately. Here, "switching from the pump control process for startup measurement to the pump control process for normal operation when it is determined that the auxiliary pump current has stabilized near the target current" includes: switching immediately when it is determined that the auxiliary pump current has stabilized near the target current, and switching after the time when it is determined that the auxiliary pump current has stabilized near the target current. Examples of the latter include switching after a predetermined time has elapsed following the determination that the auxiliary pump current has stabilized near the target current, and other situations where switching occurs when other conditions besides the determination that the auxiliary pump current has stabilized near the target current are met.

[0033] In the gas sensor of the present invention, when the measuring voltage (i.e., the release measuring voltage) reaches or exceeds a predetermined threshold in a state where the pump unit control unit is not controlling the flow of current through the inner measuring electrode and the reference electrode, it can switch from the start-up measuring pump control process to the normal operating measuring pump control process and begin the normal operating control process. The release measuring voltage is a value corresponding to the oxygen concentration in the measuring chamber; therefore, by comparing this release measuring voltage with the threshold, it is possible to appropriately determine whether sufficient oxygen has been drawn out of the measuring chamber. Thus, it is possible to appropriately switch from the start-up measuring pump control process to the normal operating measuring pump control process.

[0034] In the gas sensor of the present invention, the inner measuring electrode may contain at least one of Pt and Rh. Noble metals such as Pt and Rh sometimes bond with oxygen in the measuring chamber and are oxidized. This oxygen reduces the detection accuracy of a specific gas concentration. Therefore, when the sensor element is started, the oxide of the noble metal contained in the inner measuring electrode needs to be reduced before the oxygen is drawn out of the measuring chamber. Moreover, reducing the oxide of the noble metal to draw out oxygen is more time-consuming than drawing out oxygen molecules from the measuring chamber. Therefore, if oxidized noble metal is present in the measuring chamber, the ignition time is likely to be prolonged. In the gas sensor of the present invention, by performing a start-up measuring pump control process instead of the usual start-up measuring pump control process when the sensor element is started, the oxidized noble metal oxide can be reduced as early as possible, thereby shortening the ignition time. Therefore, performing a start-up measuring pump control process is of great significance when the inner measuring electrode contains at least one of Pt and Rh.

[0035] In the gas sensor of the present invention, the volume C of the inner measuring electrode is 8 × 10⁻⁶. -3 mm 3 ~32×10 -3 mm 3 The difference ΔV between the target value at startup and the target value under normal conditions can be 120mV to 200mV. Here, the volume C is 8×10⁻⁶. -3 mm 3 At the above times, the oxygen extraction capacity around the measuring electrode of the measuring pump unit becomes sufficiently high. Furthermore, when the difference ΔV is below 200mV, the voltage applied to the inner measuring electrode during start-up pump control processing does not become excessively high. Additionally, there is a trend that the larger the volume C, the larger the difference ΔV required to sufficiently increase the ignition time reduction effect, but if the volume C is 8×10... -3 mm 3 ~32×10 -3 mm 3If the difference ΔV is 120mV to 200mV, it can satisfy the lower limit of the volume C and the upper limit of the difference ΔV, and can fully improve the effect of shortening the ignition time.

[0036] In the gas sensor of the present invention, the pump unit control unit can, when determining that the oxygen concentration in the measuring chamber has stabilized based on the operation of the measuring pump unit, switch from the start-up measuring pump control process to the normal operating measuring pump control process and begin the normal operating control process. When the oxygen concentration in the measuring chamber has stabilized, the likelihood of sufficiently drawing oxygen out of the measuring chamber through the start-up measuring pump control process is higher. Therefore, by switching from the start-up measuring pump control process to the normal operating measuring pump control process in this situation, the switch can be appropriately performed.

[0037] In the gas sensor of the present invention, the pump unit control unit can determine that the oxygen concentration in the measuring chamber has stabilized when the measuring pump current flowing through the measuring pump unit during the startup measuring pump control process has stabilized. In this way, it is possible to determine whether the oxygen concentration in the measuring chamber has stabilized based on the measuring pump current during the startup measuring pump control process.

[0038] In the gas sensor of the present invention, the pump unit control unit can determine whether the measuring pump current has stabilized based on the first derivative of the measuring pump current flowing through the measuring pump unit after the startup measuring pump control process. Alternatively, the pump unit control unit can also determine whether the measuring pump current has stabilized based on the second derivative of the measuring pump current flowing through the measuring pump unit after the startup measuring pump control process. In these cases, the pump unit control unit can determine whether the measuring pump current has stabilized based on the measuring pump current flowing through the measuring pump unit after it rises once and then begins to decline after the startup measuring pump control process. Attached Figure Description

[0039] Figure 1 yes Figure 1 This is a cross-sectional schematic diagram of the gas sensor 100.

[0040] Figure 2 This is a block diagram showing the electrical connections between the control device 90 and each unit and the heater 72.

[0041] Figure 3 This is a flowchart illustrating an example of the control processing at startup.

[0042] Figure 4 This is a graph illustrating an example of the control processing during startup and the control processing during normal operation.

[0043] Figure 5 This is a flowchart illustrating an example of the startup control process of a variant.

[0044] Figure 6 This is a graph illustrating an example of the control processing during startup and the control processing during normal operation of the modified example.

[0045] Figure 7 This is a state diagram of Rh2O3.

[0046] Figure 8 This is a cross-sectional schematic diagram of the sensor element 201 in a modified example.

[0047] Figure 9 It is a graph showing the relationship between the volume C of measuring electrode 44, the difference ΔV between the target value and the ignition time.

[0048] Figure 10 This is a graph showing an example of the undershoot of the pump current Ip2.

[0049] Figure 11 This is an explanatory diagram showing the stable region of the pump current Ip2, the first-order differential value of the pump current Ip2, and the second-order differential value.

[0050] Figure 12 This is a flowchart illustrating an example of the startup control process of a variant.

[0051] Figure 13 This is a graph showing an example of the time-varying voltage V1 caused by thermoelectric potential.

[0052] Figure 14 This is a graph showing an example of the time variation of the pump current Ip2 caused by the thermoelectric potential contained in the voltage V1.

[0053] Figure 15 This is a flowchart illustrating an example of the correction process.

[0054] Figure 16 This is a flowchart illustrating an example of another correction process. Detailed Implementation

[0055] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a schematic cross-sectional view showing an example of the configuration of a gas sensor 100 as one embodiment of the present invention. Figure 2This is a block diagram showing the control device 90 and the electrical connections between it, each unit, and the heater 72. The gas sensor 100 is installed in piping such as the exhaust pipe of an internal combustion engine, such as a diesel engine. The gas sensor 100 uses the exhaust gas from the internal combustion engine as the measured gas to detect the concentration of specific gases such as NOx in the measured gas. The gas sensor 100 includes: a rectangular cubic sensor element 101; units 15, 21, 41, 50, 80-83 comprising a portion of the sensor element 101; a heater section 70 disposed inside the sensor element 101; and a control device 90 that controls the entire gas sensor 100.

[0056] The sensor element 101 is a laminated element, which is obtained by sequentially stacking six layers from bottom to top in the attached figure: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an isolation layer 5, and a second solid electrolyte layer 6, each composed of an oxygen ion conductive solid electrolyte layer such as zirconium oxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense, gas-tight solid electrolyte. The sensor element 101 is manufactured, for example, by performing prescribed processing and circuit pattern printing on ceramic green sheets corresponding to each layer, then stacking them, and finally firing them to integrate them into a single unit.

[0057] At the front end side of sensor element 101 ( Figure 1 The gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, the second diffusion rate control unit 13, the first internal cavity 20, the third diffusion rate control unit 30, the second internal cavity 40, the fourth diffusion rate control unit 60, and the third internal cavity 61 are connected in sequence between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4.

[0058] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are: spaces inside the sensor element 101 formed by cutting through the isolation layer 5. The space is divided by the lower surface of the second solid electrolyte layer 6 at the top, the upper surface of the first solid electrolyte layer 4 at the bottom, and the side of the isolation layer 5 at the sides.

[0059] The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are all configured as two horizontally elongated slits (with the opening having its long side in a direction perpendicular to the drawing). Furthermore, the fourth diffusion rate control unit 60 is configured as a single horizontally elongated slit (with the opening having its long side in a direction perpendicular to the drawing) formed as a gap between itself and the lower surface of the second solid electrolyte layer 6. Additionally, the portion from the gas inlet 10 to the third internal cavity 61 is also referred to as the measured gas flow section.

[0060] Furthermore, a reference gas introduction space 43 is provided at a location further away from the front end than the gas flow section being measured, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position demarcated by the side of the first solid electrolyte layer 4. For example, atmospheric air is introduced into the reference gas introduction space 43 to serve as the reference gas for measuring NOx concentration.

[0061] The atmosphere introduction layer 48 is a layer made of porous ceramic, and 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 in such a way that the reference electrode 42 is covered.

[0062] 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, and is surrounded by an atmospheric inlet layer 48 that communicates with the reference gas inlet space 43. Furthermore, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) within the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous cermet electrode (e.g., a cermet electrode of Pt and ZrO2).

[0063] In the gas flow section, the gas inlet 10 is an open portion relative to the external space through which the gas to be measured is introduced from the external space into the sensor element 101. The first diffusion rate control unit 11 is a portion that imparts a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10. The buffer space 12 is a space provided for introducing the gas to be measured from the first diffusion rate control unit 11 into the second diffusion rate control unit 13. The second diffusion rate control unit 13 is a portion that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas, which is rapidly introduced into the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (or, in the case of automobile exhaust, pulsations of exhaust pressure), 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 are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the pressure fluctuations of the gas introduced into the first internal cavity 20 are negligible. The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate control unit 13. The oxygen partial pressure is adjusted by operating the main pump unit 21.

[0064] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between these electrodes. The inner pump electrode 22 has a top electrode portion 22a disposed on almost the entire lower surface of the second solid electrolyte layer 6 facing 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 to the external space.

[0065] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that divide the first internal cavity 20, and the isolation layer 5 that provides the sidewalls. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides 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 provides the bottom surface. Furthermore, with the top electrode portion 22a and the bottom electrode portion 22b connected, a side electrode portion (not shown) is formed on the sidewall surface (inner surface) of the isolation layer 5 that constitutes the two side walls of the first internal cavity 20. The side electrode portions are arranged in a tunnel-shaped structure.

[0066] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous metal-ceramic electrodes (e.g., metal-ceramic electrodes of Pt and ZrO2 containing 1% Au). In addition, the inner pump electrode 22, which is in contact with the gas being measured, is formed using a material that can reduce the reducing power for NOx components in the gas being measured.

[0067] In the main pump unit 21, by applying the desired pump voltage Vp0 between the inner pump electrode 22 and the outer pump electrode 23, a pump current Ip0 flows in the positive or negative direction between the inner pump electrode 22 and the outer pump electrode 23, which can draw oxygen out of the first internal cavity 20 to the external space or draw oxygen from the external space into the first internal cavity 20.

[0068] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal cavity 20, an electrochemical sensor unit, namely the main pump control oxygen partial pressure detection sensor unit 80, is composed of the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0069] The oxygen concentration (oxygen partial pressure) within the first internal cavity 20 is determined by measuring the electromotive force (voltage V0) in the oxygen partial pressure detection sensor unit 80 for main pump control. Furthermore, the pump current Ip0 is controlled by feedback control of the pump voltage Vp0 of the variable power supply 24 in a manner that ensures V0 reaches a target value. Thus, the oxygen concentration within the first internal cavity 20 can be maintained at a predetermined constant value.

[0070] The third diffusion rate control unit 30 is a part that, in the first internal cavity 20, imparts a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) has been controlled by the operation of the main pump unit 21, thereby introducing the gas to be measured into the second internal cavity 40.

[0071] The second internal cavity 40 is configured as a space for further adjusting the oxygen partial pressure of the gas to be measured introduced through the third diffusion rate control unit 30 using the auxiliary pump unit 50 after the oxygen concentration (oxygen partial pressure) has been pre-adjusted in the first internal cavity 20. Therefore, the oxygen concentration within the second internal cavity 40 can be maintained at a constant level with high precision, enabling high-precision NOx concentration measurement in the gas sensor 100 described above.

[0072] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit consisting of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode on the outside of the sensor element 101) and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a disposed on the substantially entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0073] In a tunnel-shaped structure similar to the inner pump electrode 22 disposed in the first internal cavity 20 at the front, the aforementioned auxiliary pump electrode 51 is disposed in the second internal cavity 40. Specifically, a top electrode portion 51a is formed on the second solid electrolyte layer 6 providing the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 providing the bottom surface of the second internal cavity 40. Furthermore, 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 insulating layer 5 providing the side walls of the second internal cavity 40, thus creating a tunnel-shaped structure. Additionally, the auxiliary pump electrode 51, like the inner pump electrode 22, is formed using a material capable of reducing the reducing power of NOx components in the measured gas.

[0074] In the auxiliary pump unit 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere inside the second internal cavity 40 can be drawn out to the external space, or drawn in from the external space into the second internal cavity 40.

[0075] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely an oxygen partial pressure detection sensor unit 81 for auxiliary pump control, is constructed from 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.

[0076] Additionally, the auxiliary pump unit 50 utilizes a variable power supply 52 for pumping, wherein the variable power supply 52 is voltage-controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. Thus, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that has no substantial impact on NOx measurement.

[0077] In addition, the pump current Ip1 is simultaneously used to control the electromotive force of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, by inputting the pump current Ip1 as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and controlling the aforementioned target value of its voltage V0, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is controlled to remain constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

[0078] The fourth diffusion rate control unit 60 is a location in the second internal cavity 40 that imparts a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50, thereby introducing the gas to be measured into the third internal cavity 61. The fourth diffusion rate control unit 60 is responsible for limiting the amount of NOx flowing into the third internal cavity 61.

[0079] 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, after the oxygen concentration (oxygen partial pressure) has been adjusted in the second internal cavity 40. The NOx concentration is primarily measured in the third internal cavity 61 by the operation of the measuring pump unit 41.

[0080] The measuring pump unit 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61. The measuring pump unit 41 is an electrochemical pump unit consisting of 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, a second solid electrolyte layer 6, an isolation layer 5, and the first solid electrolyte layer 4. The measuring electrode 44 is a porous metal-ceramic electrode made of a material with a higher reducing capacity for NOx in the gas to be measured than that of the inner pump electrode 22. The measuring electrode 44 also functions as a NOx reduction catalyst to reduce NOx present in the atmosphere within the third internal cavity 61.

[0081] Specifically, the measuring electrode 44 is an electrode containing at least one of a noble metal with catalytic activity, namely Pt and Rh. The measuring electrode 44 is preferably an electrode made of a cermet containing at least one of Pt and Rh, and an oxide (here, ZrO2) with oxygen ion conductivity. Furthermore, the measuring electrode 44 is preferably a porous material. In this embodiment, the measuring electrode 44 is a porous cermet electrode of Pt, Rh, and ZrO2.

[0082] In the measuring pump unit 41, oxygen generated from the decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 can be drawn out, and the amount generated is used as the pump current Ip2 for detection.

[0083] In addition, to detect the oxygen partial pressure around the measuring electrode 44, an electrochemical sensor unit, namely an oxygen partial pressure detection sensor unit 82 for measuring pump control, is constructed from the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control.

[0084] The gas to be measured, introduced into the second internal cavity 40, reaches the measuring electrode 44 in the third internal cavity 61 through the fourth diffusion rate control unit 60 under controlled oxygen partial pressure. Nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. This generated oxygen is then pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled in a manner that keeps the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 of the measuring pump constant (target value). 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 pump current Ip2 in the measuring pump unit 41.

[0085] In addition, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23 and the reference electrode 42. The electromotive force (voltage Vref) obtained by the sensor unit 83 can be used to detect the oxygen partial pressure in the gas to be measured outside the sensor.

[0086] In the gas sensor 100 configured in this way, the main pump unit 21 and the auxiliary pump unit 50 are operated to supply the measuring pump unit 41 with a gas whose oxygen partial pressure is always kept at a constant low value (a value that has no substantial impact on the determination of NOx). Therefore, oxygen generated from the reduction of NOx in the measuring gas is drawn out by the measuring pump unit 41 in approximately proportional proportion to the concentration of NOx in the measuring gas, thereby flowing the pump current Ip2. Based on this pump current Ip2, the concentration of NOx in the measuring gas can be determined.

[0087] Furthermore, the sensor element 101 includes a heater section 70 that heats and maintains the sensor element 101 to improve the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes a heater connecting electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure diffusion hole 75.

[0088] The heater connection electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. By connecting the heater connection electrode 71 to an external power source, power can be supplied to the heater section 70 from the outside.

[0089] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connection electrode 71 via a through-hole 73, and through this heater connection electrode 71, a heater power supply 76 (see reference) is used. Figure 2 The solid electrolyte forming the sensor element 101 is heated and kept warm by supplying power to the sensor.

[0090] In addition, the heater 72 is embedded in the entire area from the first internal cavity 20 to the third internal cavity 61, which can adjust the entire sensor element 101 to the temperature at which the solid electrolyte is activated.

[0091] The heater insulation layer 74 is an insulation layer formed on the upper and lower surfaces of the heater 72 by an insulator such as aluminum oxide. The purpose of forming the heater insulation layer 74 is to obtain electrical insulation between the second substrate layer 2 and the heater 72, and electrical insulation between the third substrate layer 3 and the heater 72.

[0092] The pressure diffusion hole 75 is a portion provided in a manner that penetrates the third substrate layer 3 and the atmospheric inlet layer 48 and communicates with the reference gas inlet space 43. Its purpose is to mitigate the increase in internal pressure that accompanies the temperature rise within the heater insulation layer 74.

[0093] like Figure 2As shown, the control device 90 includes: the aforementioned variable power supplies 24, 46, and 52, the heater power supply 76, and a control unit 91. The control unit 91 is a microprocessor equipped with a CPU 92 and a storage unit 94. The storage unit 94 is a device for storing, for example, various programs and various data. The control unit 91 receives: voltage V0 detected by the oxygen partial pressure detection sensor unit 80 for main pump control, voltage V1 detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control, voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control, voltage Vref detected by the sensor unit 83, pump current Ip0 detected by the main pump unit 21, pump current Ip1 detected by the auxiliary pump unit 50, and pump current Ip2 detected by the measuring pump unit 41. Furthermore, the control unit 91 controls the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 46, and 52 by inputting control signals to them, thereby controlling the main pump unit 21, the measuring pump unit 41, and the auxiliary pump unit 50. The control unit 91 also controls the power supplied by the heater power supply 76 to the heater 72 by outputting control signals to it. The storage unit 94 stores target values ​​V0*, V1*, V2a*, V2b*, etc., which will be described later. The CPU 92 of the control unit 91 controls each unit 21, 41, and 50 with reference to these target values ​​V0*, V1*, V2a*, and V2b*.

[0094] The control unit 91 controls the auxiliary pump of the auxiliary pump unit 50 to achieve a target oxygen concentration in the second internal cavity 40. Specifically, the control unit 91 controls the auxiliary pump unit 50 by feedback control of the voltage Vp1 of the variable power supply 52 to achieve a constant voltage V1 (referred to as the target value V1*). The target value V1* is defined as a predetermined low concentration in the second internal cavity 40 that has no substantial impact on the determination of NOx.

[0095] The control unit 91 controls the main pump control process of the main pump unit 21 by adjusting the pump current Ip1 flowing through the auxiliary pump unit 50 to reach a target current (referred to as target current Ip1*) when the oxygen concentration in the second internal cavity 40 is adjusted by the auxiliary pump control process. Specifically, the control unit 91 sets a target value (referred to as target value V0*) of the voltage V0 based on the pump current Ip1, such that the pump current Ip1 flowing through the voltage Vp1 reaches a constant target current Ip1*. Moreover, the control unit 91 performs feedback control on the pump voltage Vp0 of the variable power supply 24 in such a way that the voltage V0 reaches the target value V0* (i.e., in such a way that the oxygen concentration in the first internal cavity 20 reaches the target concentration). Through this main pump control process, the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is always constant. The target value V0* is set to a value where the oxygen concentration in the first internal cavity 20 is higher than 0% and is a low oxygen concentration. Furthermore, the pump current Ip0 flowing in the main pump control process varies according to the oxygen concentration of the gas to be measured (i.e., the gas around the sensor element 101) flowing into the gas to be measured passage from the gas inlet 10. Therefore, the control unit 91 can also detect the oxygen concentration in the gas to be measured based on the pump current Ip0.

[0096] The aforementioned main pump control processing and auxiliary pump control processing are collectively referred to as adjustment pump control processing. Furthermore, the first internal cavity 20 and the second internal cavity 40 are collectively referred to as oxygen concentration adjustment chambers. The main pump unit 21 and the auxiliary pump unit 50 are collectively referred to as adjustment pump units. The adjustment pump control processing, performed by the control unit 91, causes the adjustment pump units to adjust the oxygen concentration in the oxygen concentration adjustment chambers.

[0097] Furthermore, the control unit 91 performs measurement pump control processing on the measurement pump unit 41 in a manner that the voltage V2 reaches a constant value (target value) (i.e., the oxygen concentration in the third internal cavity 61 reaches a predetermined low concentration). Specifically, the control unit 91 controls the measurement pump unit 41 by feedback control of the voltage Vp2 of the variable power supply 46 in a manner that the voltage V2 reaches the target value. Oxygen is drawn out from the third internal cavity 61 through this measurement pump control processing. In addition, the control unit 91 performs two measurement pump control processes: a normal operation measurement pump control process and a startup measurement pump control process. The normal operation measurement pump control process is performed during the normal operation of the sensor element 101, and the startup measurement pump control process is performed during the startup of the sensor element 101 before the normal operation. The target value of the voltage V2 is different in the normal operation measurement pump control process and the startup measurement pump control process. The target value of the voltage V2 in the startup measurement pump control process is referred to as the startup target value V2a*. The target value of voltage V2 in the normal measurement pump control process is referred to as the normal target value V2b*. The startup target value V2a* is set to a value higher than the normal target value V2b*. That is, V2a* and V2b* are set in the manner that V2a* > V2b*. Here, voltage V2 is a value related to the oxygen concentration difference between the area around the reference electrode 42 and the third internal cavity 61. The lower the oxygen concentration in the third internal cavity 61, the larger the oxygen concentration difference, and the larger the voltage V2 will be. Therefore, the startup target value V2a* being a higher value than the normal target value V2b* means that during the execution of the startup measurement pump control process, the target value of the oxygen concentration in the third internal cavity 61 is set to a lower value compared to the execution of the normal measurement pump control process. In this embodiment, the normal target value V2b* is set to 400mV, and the startup target value V2a* is set to 600mV.

[0098] By performing a pump control process for normal measurement, oxygen is drawn out from the third internal cavity 61 in such a way that the oxygen generated by the reduction of NOx in the measured gas in the third internal cavity 61 is substantially zero. Then, the control unit 91 obtains the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 from a specific gas (here, NOx), and calculates the NOx concentration in the measured gas based on the pump current Ip2.

[0099] The storage unit 94 stores formulas (such as linear function formulas) and mappings to represent the correspondence between pump current Ip2 and NOx concentration. Such formulas or mappings can be obtained in advance through experiments.

[0100] An example of the startup control processing performed by the control unit 91 of the gas sensor 100 configured in this way on the sensor element 101 will be described. Figure 3 This is a flowchart illustrating an example of the control processing at startup. Figure 4 This is a graph illustrating an example of the control processing during startup and the control processing during normal operation.

[0101] When the CPU 92 of the control unit 91 starts the control process, it first begins the heater control process (step S100) by energizing the heater 72 to generate heat, ensuring that the heater temperature Th, which is the temperature of the heater 72, reaches the target temperature Th*. The heater temperature Th can be expressed by a linear function formula of the resistance value of the heater 72. Therefore, in the heater control process of this embodiment, the CPU 92 calculates the resistance value of the heater 72 and performs feedback control on the heater power supply 76 in a manner that the calculated resistance value reaches the target resistance value (the resistance value corresponding to the target temperature Th*). For example, the CPU 92 can obtain the voltage of the heater 72 and the current flowing through the heater 72, and calculate the resistance value of the heater 72 based on the obtained voltage and current. The CPU 92 can calculate the resistance value of the heater 72, for example, using a three-terminal method or a four-terminal method. The CPU 92 outputs a control signal to the heater power supply 76 in a manner that the calculated resistance value of the heater 72 reaches the target resistance value, and performs feedback control on the power supplied by the heater power supply 76. The heater power supply 76 adjusts the power supplied to the heater 72, for example, by changing the value of the voltage applied to the heater 72. Figure 4 As shown, for example, when the heater control process begins at time t0, the heater temperature Th rises to a target temperature Th* over time. After time t2 when the heater temperature Th reaches the target temperature Th*, the heater temperature Th remains near the target temperature Th*. The target temperature Th* is predetermined as a temperature (e.g., 800°C) that allows the solid electrolyte of the sensor element 101 to be sufficiently activated. Furthermore, Figure 4 For the sake of simplicity, the change of heater temperature Th over time is shown as a straight line. However, in reality, the heater temperature Th sometimes increases in a curve, or the heater temperature Th may overshoot before it stabilizes near the target temperature Th*.

[0102] After the heater control process begins in step S100, the CPU92 determines whether the start condition for the start-up measurement pump control process has been met. In this embodiment, the CPU92 determines whether the heater temperature Th has reached or exceeded a predetermined threshold Thref (step S110). If the determination result is positive, the start condition for the start-up measurement pump control process is considered to have been met. The threshold Thref is a value below the target temperature Th*, or it can be a value less than the target temperature Th*. The threshold Thref is predetermined as the lower limit of the heater temperature Th required to activate (exhibit the ionic conductivity of the solid electrolyte) contained in the measurement pump unit 41 controlled in the start-up measurement pump control process. For example, the threshold Thref can be predetermined experimentally as the lower limit of the heater temperature Th required to heat the second solid electrolyte layer 6, the isolation layer 5, and the first solid electrolyte layer 4 to 600°C or higher. Furthermore, the threshold Thrref can be determined as the value obtained by multiplying the target temperature Th* by a predetermined ratio (a value less than 1). In this embodiment, the threshold Thrref = 0.8 × Th*. That is, the CPU92 determines that the start condition for the pump control process for startup has been met when the heater temperature Th reaches 80% or more of the target temperature Th*.

[0103] If the CPU 92 determines a negative outcome in step S110, it repeats step S110 until the outcome becomes positive. If the outcome in step S110 is positive, the CPU 92 begins the aforementioned pump control process for startup measurement (step S120). Figure 4 In the example, since the heater temperature Th reaches the threshold Thref at time t1 before time t2, the CPU 92 starts the start-up measurement pump control process at time t1. When the start-up measurement pump control process begins, the CPU 92 performs feedback control on the voltage Vp2 of the variable power supply 46 so that the voltage V2 reaches the start-up target value V2a*, thereby controlling the measurement pump unit 41. The measurement pump unit 41 draws oxygen present in the third internal cavity 61 to the vicinity of the outer pump electrode 23 by applying voltage Vp2. At this time, a pump current Ip2 corresponding to the amount of oxygen drawn out flows in the measurement pump unit 41. Here, before the sensor element 101 is started, the gas flow section including the third internal cavity 61 is in a state where there is a lot of oxygen (not oxygen from a specific gas) (e.g., atmospheric atmosphere). This oxygen is drawn to the vicinity of the outer pump electrode 23 by performing the start-up measurement pump control process. Therefore, as... Figure 4As shown in the graph (solid line) of the pump current Ip2 in the illustrated embodiment, the pump current Ip2 increases sharply from time t1, indicating a relatively large pump current Ip2 flow. Specifically, the oxygen present in the third internal cavity 61 before the sensor element 101 is activated includes: oxygen molecules (O2) present in the space within the third internal cavity 61, oxygen molecules (O2) attached to the surface of the measuring electrode 44, and oxygen bonded to the constituent material of the measuring electrode 44. Since the measuring electrode 44 in this embodiment contains Rh and Pt, at least one of Rh2O3 and PtO2 may sometimes be present in the measuring electrode 44. The oxygen (O) in this Rh2O3 and PtO2 is oxygen bonded to the constituent material of the measuring electrode 44. Through the pump control process during startup, not only oxygen molecules can be precipitated, but also oxygen bonded to the constituent material of the measuring electrode 44 can be precipitated, thereby reducing Rh2O3 and PtO2. Furthermore, in this embodiment, the measuring electrode 44 is a porous material; therefore, oxygen molecules (O2) may sometimes be present in the open and closed pores of the measuring electrode 44. These oxygen molecules can also be drawn out by the start-up measuring pump control process. In this embodiment, the CPU 92 starts the aforementioned adjustment pump control process (main pump control process and auxiliary pump control process) simultaneously with the start-up measuring pump control process. As a result, oxygen already present in the oxygen concentration adjustment chambers (first internal cavity 20 and second internal cavity 40) before the sensor element 101 is started is also drawn out to the vicinity of the outer pump electrode 23. Therefore, from time t1, the pump current Ip0 and pump current Ip1 increase sharply, with relatively large pump currents Ip0 and Ip1 flowing. Furthermore, Figure 4 The pump current Ip0 is omitted from the diagram. Furthermore, in the illustrated case, although... Figure 4 The pump current Ip1 is shown as being less than the pump current Ip2, but the actual relationship between the pump currents is basically Ip0 > Ip1 > Ip2.

[0104] After the start-up measurement pump control process begins in step S120, the CPU92 determines whether the end condition of the start-up measurement pump control process has been met. In this embodiment, the CPU92 determines whether the oxygen concentration in the oxygen concentration adjustment chamber has stabilized based on the operation of the adjustment pump unit (step S130). If the determination result is positive, it is considered that the end condition of the start-up measurement pump control process has been met. More specifically, if the CPU92 determines that the pump current Ip1 is stable near the target current Ip1*, it determines that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized.

[0105] For example, such as Figure 4As shown, at time t1, when the start-up measurement pump control processing, main pump control processing, and auxiliary pump control processing begin, as described above, the pump currents Ip1, Ip2 (and Ip0) rise sharply and become relatively large values. Therefore, when oxygen is drawn out from the gas flow section being measured, voltage V2 approaches the start-up target value V2a*, voltage V1 approaches the target value V1*, and pump current Ip1 approaches the target current Ip1*. Thus, after a single rise, pump currents Ip1, Ip2 (and Ip0) slowly decrease. Furthermore, when the oxygen already present in the gas flow section being measured before the sensor element 101 is activated is fully drawn out (time t3), thereafter, voltage V1 stabilizes at a value almost identical to the target value V1*, and pump current Ip1 stabilizes at a value almost identical to the target current Ip1*. Figure 4(The voltage V1 is omitted in the diagram). Here, since the second internal cavity 40 is connected to the third internal cavity 61, the operation of the auxiliary pump unit 50 can remove oxygen not only from the second internal cavity 40 but also from the third internal cavity 61. For example, if the oxygen concentration in the second internal cavity 40 decreases to near the target concentration (the oxygen concentration corresponding to the target value V1* of voltage V1) while the oxygen concentration in the third internal cavity 61 is higher than the target concentration (the oxygen concentration corresponding to the target value V2a* of voltage V2 at startup), oxygen in the third internal cavity 61 may sometimes diffuse back (reverse flow) to the second internal cavity 40, and this oxygen can be drawn out using the auxiliary pump unit 50. Therefore, when the oxygen concentration in the oxygen concentration adjustment chambers (the first internal cavity 20 and the second internal cavity 40) has stabilized, that is, when the pump current Ip1 has stabilized near the target current Ip1*, the oxygen that existed in the third internal cavity 61 before the sensor element 101 was started is also sufficiently drawn out. Therefore, it can be determined whether the oxygen present in the third internal cavity 61 before the sensor element 101 was activated has been sufficiently drawn out based on whether the pump current Ip1 has stabilized near the target current Ip1*. In the determination in step S130, the CPU 92 can determine that the pump current Ip1 has stabilized near the target current Ip1* when the pump current Ip1 rises once and then falls below a predetermined threshold. The predetermined threshold in this case is a value that can be considered as the pump current Ip1 stabilizing near the target current Ip1*, for example, it can be predetermined as: a value the same as the target current Ip1*, or a value 5% greater than the target current Ip1*, or a value above the target current Ip1*. Alternatively, if the CPU 92 continues in a state where the pump current Ip1 is within a predetermined range for a predetermined time or more, it can determine that the pump current Ip1 has stabilized near the target current Ip1*. The specified range in this case is a range that can be considered as the pump current Ip1 being near the target current Ip1*. For example, it can be predetermined as a range within ±5% of the target current Ip1*. In this embodiment, when the CPU92 reaches below the target current Ip1* after the pump current Ip1 rises once and then falls again ( Figure 4 At time t3, it is determined that the pump current Ip1 has stabilized near the target current Ip1*.

[0106] If the CPU 92 determines a negative outcome in step S130, it repeats step S130 until the outcome becomes positive. If the outcome in step S130 is positive, the CPU 92 terminates the startup-time measurement pump control process and begins the normal-time measurement pump control process (step S140), terminating the startup-time control process. Thus, the processing performed by the CPU 92 shifts from startup-time control to normal-time control. In the normal-time control process, the CPU 92 performs the normal-time measurement pump control process while simultaneously continuing the adjustment pump control processes (main pump control and auxiliary pump control) from after the startup-time control process. Then, the CPU 92 calculates the NOx concentration in the measured gas based on the pump current Ip2 flowing due to the normal-time measurement pump control process. Figure 4 In the example, since the pump current Ip1 was not stable before time t3, CPU92 made a negative decision in step S130. When time t3 was reached, it determined that the pump current Ip1 had stabilized, and made a positive decision in step S130. Therefore, CPU92 started normal time control processing from time t3.

[0107] like Figure 4 As shown, during the pump control process for startup measurement (times t1 to t3), since the oxygen already present in the third internal cavity 61 before the sensor element 101 is started is drawn out, the pump current Ip2 becomes a high value, and the value of the pump current Ip2 cannot correspond to the NOx concentration in the measured gas. After time t3, when the oxygen is sufficiently drawn out by the pump control process for startup measurement, almost all the oxygen present in the third internal cavity 61 is from the NOx in the measured gas, and therefore, the value of the pump current Ip2 becomes a value corresponding to the NOx concentration in the measured gas. Therefore, after time t3, the NOx concentration in the measured gas can be detected based on the pump current Ip2. Thus, the time from the start of the sensor element 101 until the value of the pump current Ip2 becomes a value corresponding to the NOx concentration in the measured gas (t0 to t3) is the ignition time. Furthermore, Figure 4 In this example, to facilitate understanding of the behavior of the pump current Ip2, the condition where the NOx concentration in the measured gas is constant is shown; the pump current Ip2 becomes constant after time t3. However, in actual use of the sensor element 101, the NOx concentration in the measured gas changes constantly; therefore, the value of the pump current Ip2 after time t3 varies depending on the NOx concentration. Consequently, it is difficult to determine whether the sensor element 101 has ignited based solely on the value of the pump current Ip2. Therefore, in this embodiment, as described above, the CPU 92 determines whether the termination condition of the pump control process for startup has been met based on the value of the pump current Ip1, not Ip2.

[0108] Here, in this embodiment, when the sensor element 101 is started, as described above, a start-up measurement pump control process is performed: the measurement pump unit 41 is controlled to draw oxygen from the third internal cavity 61 by making the voltage V2 reach a start-up target value V2a* higher than the normal target value V2b*. That is, in the start-up measurement pump control process, the target value of the oxygen concentration in the third internal cavity 61 is lower than the value during normal operation to draw oxygen from the third internal cavity 61. Therefore, compared with the case where the normal measurement pump control process is performed from the start-up of the sensor element 101, oxygen that was already present in the third internal cavity 61 before start-up can be quickly removed from the third internal cavity 61. For example, Figure 4 The comparative example's pump current Ip2 curve (dashed line) shows the time change of pump current Ip2 when adjustment pump control processing (main pump control processing and auxiliary pump control processing) is performed from time t1, and simultaneously, normal time measurement pump control processing is performed instead of startup measurement pump control processing from time t1. In this case, since the measurement pump unit 41 is controlled in a manner where the voltage V2 reaches a normal time target value V2b* that is lower than the startup target value V2a*, the pump current Ip2 does not become a larger value compared to the embodiment's pump current Ip2 curve (solid line), and the amount of oxygen drawn out of the third internal cavity 61 is less. Therefore, the time when sufficient oxygen draw out of the third internal cavity 61 is achieved is time t4, which is later than time t3. That is, the ignition time of the comparative example is longer than that of the embodiment. Thus, in this embodiment, by performing startup measurement pump control processing instead of normal time measurement pump control processing when the sensor element 101 is started, the ignition time of the sensor element 101 can be shortened. In addition, although the diagram is omitted, when the adjustment pump control process (main pump control process and auxiliary pump control process) is performed together with the normal time measurement pump control process from time t1, the time until the pump current Ip1 stabilizes near the target current Ip1* is also time t4, which is later than time t3.

[0109] in addition, Figure 4Although the time when the pump current Ip2 reaches a constant value (the time when the sensor element 101 ignites) and the time when the pump current Ip1 stabilizes near the target current Ip1* are both time t3, in reality, the time when the pump current Ip1 stabilizes near the target current Ip1* is sometimes slightly earlier than time t3. As mentioned above, the auxiliary pump unit 50 can also draw out oxygen flowing back from the third internal cavity 61 to the second internal cavity 40, but since oxygen bonded to the constituent material of the measuring electrode 44 and oxygen molecules present in the closed pores of the measuring electrode 44 do not flow back to the second internal cavity 40, the auxiliary pump unit 50 cannot draw them out. Therefore, sometimes after the pump current Ip1 has stabilized near the target current Ip1*, this oxygen that the auxiliary pump unit 50 cannot draw out is drawn out by the measuring pump unit 41, and the sensor element 101 begins to ignite. In this case, during the period from when the pump current Ip1 stabilizes near the target current Ip1* until the sensor element 101 ignites, it is preferable that the CPU 92 does not perform step S140 but continues the pump control processing for startup measurement. For example, the CPU 92 may perform step S140 after a predetermined time has elapsed after a positive determination in step S130. Alternatively, if the state of the pump current Ip1 being within a predetermined range has lasted for a predetermined time or longer, the CPU 92 may, in the case of a positive determination in step S130, make the predetermined time approximately the same as the time from when the pump current Ip1 stabilizes near the target current Ip1* until the sensor element 101 ignites.

[0110] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is explained. The stacked body formed by the six layers of this embodiment—first substrate layer 1, second substrate layer 2, third substrate layer 3, first solid electrolyte layer 4, isolation layer 5, and second solid electrolyte layer 6—corresponds to the main body of the present invention. The outer pump electrode 23 corresponds to the outer measuring electrode, the third internal cavity 61 corresponds to the measuring chamber, the measuring electrode 44 corresponds to the inner measuring electrode, the measuring pump unit 41 corresponds to the measuring pump unit, the reference electrode 42 corresponds to the reference electrode, the oxygen partial pressure detection sensor unit 82 for measuring pump control corresponds to the measuring voltage detection sensor unit, the sensor element 101 corresponds to the sensor element, the pump current Ip2 corresponds to the measuring pump current, and the control device 90 corresponds to the pump unit control unit and the specific gas concentration detection unit. Furthermore, the control device 90 corresponds to the heater control unit, the first internal cavity 20 and the second internal cavity 40 correspond to the oxygen concentration adjustment chamber, the inner pump electrode 22 and the auxiliary pump electrode 51 correspond to the inner adjustment pump electrode, the outer pump electrode 23 corresponds to the outer adjustment pump electrode, the main pump unit 21 and the auxiliary pump unit 50 correspond to the adjustment pump unit, and the main pump control processing and the auxiliary pump control processing correspond to the adjustment pump control processing. Additionally, the inner pump electrode 22 corresponds to the inner main pump electrode, the outer pump electrode 23 corresponds to the outer main pump electrode, the auxiliary pump electrode 51 corresponds to the inner auxiliary pump electrode, the outer pump electrode 23 corresponds to the outer auxiliary pump electrode, and the pump current Ip1 corresponds to the auxiliary pump current.

[0111] According to the gas sensor 100 of this embodiment described in detail above, when the sensor element 101 is started, a start-up measurement pump control process is performed: the measurement pump unit 41 is controlled to draw out oxygen from the third internal cavity 61 in such a way that the voltage V2 reaches a start-up target value V2a* higher than the normal target value V2b*. Therefore, compared with the case where the normal measurement pump control process is performed from the start-up of the sensor element 101, the oxygen that was already present in the third internal cavity 61 before start-up can be removed quickly. As a result, the ignition time of the sensor element 101 is shortened.

[0112] Furthermore, when the heater temperature Th reaches or exceeds a predetermined threshold Thref below the target temperature Th*, the CPU92 begins the start-up measurement pump control process. Therefore, the CPU92 can appropriately determine the start time of the start-up measurement pump control process based on the heater temperature Th.

[0113] Furthermore, the sensor element 101 includes an adjustment pump unit for adjusting the oxygen concentration in an oxygen concentration adjustment chamber located upstream of the third internal cavity 61 within the gas flow section being measured. Moreover, when the sensor element 101 is started, the CPU 92 performs adjustment pump control processing to operate the adjustment pump unit. If, based on the operation of the adjustment pump unit, it is determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, the CPU 92 switches from the start-up measurement pump control processing to the normal operation measurement pump control processing. Here, before the sensor element 101 is started, not only the third internal cavity 61 but also the oxygen concentration adjustment chamber upstream of it is in a state containing a large amount of oxygen (not from a specific gas) (e.g., atmospheric atmosphere). By performing adjustment pump unit control processing when the sensor element 101 is started, the oxygen already present in the oxygen concentration adjustment chamber before the sensor element 101 is started can be removed. Furthermore, since the oxygen concentration adjustment chamber is connected to the third internal cavity 61, the oxygen in the third internal cavity 61 can also be removed by operating the adjustment pump unit. Furthermore, as described above, since the oxygen concentration adjustment chamber is connected to the third internal cavity 61, when the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, the oxygen in the third internal cavity 61 is also sufficiently drawn out. Therefore, when it is determined that the oxygen concentration in the oxygen concentration adjustment chamber is stable based on the operation of the adjustment pump unit, a switch is made between the start-up measurement pump control process and the normal operation measurement pump control process, thereby allowing for an appropriate switch between the start-up measurement pump control process and the normal operation measurement pump control process.

[0114] Furthermore, the oxygen concentration adjustment chamber includes a first internal cavity 20 and a second internal cavity 40 located further downstream than the first internal cavity 20 and further upstream than the third internal cavity 61. The adjustment pump unit includes a main pump unit 21 for adjusting the oxygen concentration of the first internal cavity 20 and an auxiliary pump unit 50 for adjusting the oxygen concentration of the second internal cavity 40. The adjustment pump control process includes auxiliary pump control process for controlling the auxiliary pump unit 50 to achieve a target oxygen concentration in the second internal cavity 40, and main pump control process for controlling the pump current Ip1 flowing through the auxiliary pump unit 50 to achieve a target current Ip1*. Moreover, when the CPU 92 determines that the pump current Ip1 is stable near the target current Ip1*, it switches from the startup measurement pump control process to the normal operation measurement pump control process. Therefore, based on the pump current Ip1, a switch can be made appropriately: from pump control processing for measurement during startup to pump control processing for measurement during normal operation.

[0115] Furthermore, the measuring electrode 44 contains at least one of Pt and Rh. Noble metals such as Pt and Rh sometimes bond with oxygen within the third internal cavity 61 and are oxidized. Since this oxygen reduces the detection accuracy of a specific gas concentration, it is necessary to reduce the oxide of the noble metal contained in the measuring electrode 44 before drawing the oxygen out of the third internal cavity 61 when the sensor element 101 is started. Moreover, reducing the oxide of the noble metal to draw out oxygen is more time-consuming than drawing out oxygen molecules from the third internal cavity 61. Therefore, the ignition time tends to be longer when oxidized noble metal is present in the third internal cavity 61. In the gas sensor 100 of this embodiment, not only is a pump control process for normal measurement performed when the sensor element 101 is started, but also a pump control process for start-up measurement is performed. This allows for the early reduction of oxidized noble metal and shortens the ignition time. Therefore, in this embodiment where the measuring electrode 44 contains Pt and Rh, the pump control process for start-up measurement is of great significance.

[0116] Furthermore, the present invention is not limited to any of the above embodiments. As long as it falls within the technical scope of the present invention, it can be implemented in various ways.

[0117] For example, in the above embodiment, when the CPU92 determines that the pump current Ip1 has stabilized near the target current Ip1*, it considers the termination condition of the start-up measurement pump control process to be met, and performs a switch from the start-up measurement pump control process to the normal measurement pump control process, but is not limited to this. When the sensor element 101 ignites, in other words, as long as the oxygen in the third internal cavity 61 is sufficiently drawn out, the termination condition of the start-up measurement pump control process can be determined in a way that allows the start-up measurement pump control process to be terminated. For example, the start-up measurement pump control process can be terminated when a predetermined time has elapsed after the heater 72 is energized, or when a predetermined time has elapsed after the start-up measurement pump control process has begun.

[0118] CPU92 can determine whether the termination condition of the start-up measurement pump control process has been met based on the voltage V2 in the state where the control of current flow to the measurement electrode 44 and the reference electrode 42 is not performed, that is, the release measurement voltage V2open. Figure 5 A flowchart illustrating an example of the startup control process of a variant example is provided. Figure 6 A graph illustrating an example of the control processing during startup and normal operation of the modified example is provided. Figure 5 In the middle, to and Figure 3 Same processing tag and Figure 3 The same step numbers are used, and their descriptions are omitted. Figure 6 Is Figure 4A graph showing the time-varying change of the voltage V2open during marker release has been added. Figure 5 In the startup control process of the modified example shown, after the startup measurement pump control process begins in step S120, the CPU 92 determines whether the termination condition of the startup measurement pump control process has been met by determining whether the voltage V2, i.e., the release measurement voltage V2open, in the state where the control of current flow through the measurement electrode 44 and the reference electrode 42 is not performed (step S230). For example, in the above embodiment, instead of controlling the current flow through the reference electrode 42, after the startup measurement pump control process begins in step S120, the pump current Ip2 flows through the measurement electrode 44 through the startup measurement pump control process. Therefore, in step S230, the CPU 92 measures the voltage V2 in the state where the startup measurement pump control process is temporarily stopped, specifically, the state where the voltage Vp2 applied from the variable power supply 46 is stopped, and uses the measured value as the release measurement voltage V2open. The release-time measuring voltage V2open is a value corresponding to the oxygen concentration within the third internal cavity 61; the lower the oxygen concentration, the larger the value. Furthermore, since the release-time measuring voltage V2open is measured without controlling the flow of current through the measuring electrode 44 and the reference electrode 42, it is less susceptible to voltage drops caused by current. Therefore, compared to the voltage V2 measured with current flowing through the measuring electrode 44 (the voltage V2 during the pump control process at startup), the release-time measuring voltage V2open corresponds to the oxygen concentration within the third internal cavity 61 with higher accuracy. The threshold V2opref is predetermined as the value of the release-time measuring voltage V2open under the condition that the oxygen within the third internal cavity 61 is sufficiently drawn out. For example, as... Figure 6As shown, when the pump control process for startup measurement begins, the value of the release measurement voltage V2open increases. After the end of the oxygen absorption in the third internal cavity 61 that existed before startup, i.e., after the ignition of the sensor element 101, it becomes almost constant (stationary value). In this embodiment, this stationary value, which has been experimentally determined beforehand, is defined as the threshold V2opref. In this embodiment, the threshold V2opref is 200mV. The threshold V2opref can be a value slightly lower than the stationary value of the release measurement voltage V2open. If step S230 is a negative determination, the CPU92 repeats step S230 until it becomes a positive determination. If step S230 is a positive determination, the CPU92 executes the above-described step S140 and ends the startup control process. As described above, the release-time measuring voltage V2open is a value corresponding to the oxygen concentration within the third internal cavity 61. Therefore, by comparing this release-time measuring voltage V2open with the threshold V2opref, it can be appropriately determined whether the oxygen within the third internal cavity 61 has been sufficiently extracted. Therefore, the CPU92, during the process... Figure 5 Step S230 is replaced Figure 3 In step S130, it is also possible to appropriately switch from pump control processing for startup measurement to pump control processing for normal operation measurement. Furthermore, as mentioned above, the moment when the pump current Ip1 stabilizes near the target current Ip1* is sometimes slightly earlier than the moment t3 when the sensor element 101 ignites. In contrast, the release-time measurement voltage V2open is different from the pump current Ip1; it is a value corresponding to the oxygen itself present in the third internal cavity 61. Therefore, there is almost no time difference between the moment when the release-time measurement voltage V2open is constant and the moment when the sensor element 101 ignites.

[0119] In the above embodiment, although oxygen in the third internal cavity 61 is drawn out to the vicinity of the outer pump electrode 23 during the start-up measurement pump control process, it is not limited to the outer pump electrode 23; oxygen can be drawn out to the vicinity of any electrode disposed outside the gas flow section to be measured. For example, during the start-up measurement pump control process, a voltage is applied between the measuring electrode 44 and the reference electrode 42 to flow a pump current, thereby drawing oxygen in the third internal cavity 61 to the vicinity of the reference electrode 42. That is, although oxygen in the third internal cavity 61 is drawn out to the vicinity of the outer pump electrode 23, i.e., the outside of the element body, during the start-up measurement pump control process of the above embodiment, it can also be drawn out to the vicinity of the reference electrode 42 or other parts inside the element body. When drawing oxygen to the inside of the element body, it is preferable to draw it out to the vicinity of an electrode disposed outside the gas flow section to be measured, such as the reference electrode 42. In other words, when drawing oxygen to the inside of the element body, it is preferable to draw oxygen to a region in the element body that is not connected to the third internal cavity 61.

[0120] Although not specifically stated in the above embodiments, the voltage Vp2 applied to the measuring pump unit 41 is preferably less than 1500mV. When the voltage Vp2 is 1500mV or higher, oxygen ions in the solid electrolyte may be deficient, resulting in electron conduction of the solid electrolyte and causing the sensor element 101 to blacken and become unusable. However, this adverse condition can be suppressed by keeping the voltage Vp2 less than 1500mV. The higher the target value V2a* at startup, the higher the voltage Vp2 will become during the startup measuring pump control process. Therefore, it is preferable to predetermine the target value V2a* at startup such that the voltage Vp2 will not reach a value greater than 1500mV. In addition, when the startup measuring pump control process is performed in a state where the solid electrolyte is not sufficiently activated, oxygen in the third internal cavity 61 is not drawn out, and the voltage V2 cannot approach the target value V2a* at startup. Therefore, the voltage Vp2 can easily become a higher value through feedback control. Therefore, when the start-up measurement pump control process is performed with the solid electrolyte in an insufficiently activated state, the voltage Vp2 easily becomes 1500mV or higher during the start-up measurement pump control process. Considering this, it is preferable to appropriately determine the start condition of the start-up measurement pump control process (the value of the threshold Thref in the above embodiment) to avoid the voltage Vp2 from reaching 1500mV or higher.

[0121] In the heater control process of the above embodiment, although the CPU 92 controls the heater 72 in such a way that the heater temperature Th reaches the target temperature Th*, it is not limited to the heater temperature Th. It can control the heater 72 as long as the temperature of the heater 72 or the component body, i.e., the sensor element temperature, reaches the target temperature. For example, the resistance value of the circuit of the pump unit 41 or the resistance value of the circuit of the oxygen partial pressure detection sensor unit 82 for pump control can be measured as a value representing the temperature of the component body (which can be converted into a temperature value), and the heater 72 can be controlled so that this resistance value reaches the target resistance value. Similarly, in the above embodiment, the start-up measurement pump control process begins when the heater temperature Th reaches or exceeds a predetermined threshold Thref, but it is not limited to this. Not limited to the heater temperature Th, the start-up measurement pump control process can also begin when the sensor element temperature reaches or exceeds a predetermined threshold (for example, when the resistance value of the circuit of the pump unit 41 reaches or falls below a predetermined threshold). Alternatively, the gas sensor 100 may include a temperature detection unit such as a thermocouple, and use this temperature sensor to directly measure the temperature of the sensor element (the temperature of the heater 72 or the temperature of the element body). In this case, the CPU 92 can control the heater 72 based on the measured sensor element temperature, in a way that the sensor element temperature reaches the target temperature.

[0122] In the above embodiment, although the CPU92 determines that the start-up condition for the pump control process for startup measurement has been met when the heater temperature Th reaches or exceeds the predetermined threshold Thref, it is not limited to this. The start-up condition for the pump control process for startup measurement can be determined in such a way that the pump control process for startup measurement can begin when the solid electrolyte contained in the pump unit 41 controlled in the pump control process for startup measurement is activated. For example, the pump control process for startup measurement can begin after a predetermined time has elapsed after the heater 72 has been energized.

[0123] Alternatively, the start conditions for the start-up pump control process can be determined based on the constituent material of the measuring electrode 44, in a manner that allows the start-up measurement pump control process to begin when a state suitable for adsorbing oxygen bonded to its constituent material is reached. For example, the start conditions for the start-up pump control process can be determined based on a state diagram of the constituent material of the measuring electrode 44. An example of the start conditions when the measuring electrode 44 contains Rh as a constituent material will be explained. Figure 7The state diagram of Rh2O3 (Source: VK Tagirov, DM Chizhikov, EK Kazenas, and L.K. Shubochkin, Zh. Neorg. Khim., The t le: Study of thermal dissociation of ruthenium dioxide and rhodium sesquioxide, Journal: Zhurnnal Neorganicheskoj Khimi i; v.20(8); p.2035-2037(1975)). Figure 7 The vertical axis represents oxygen partial pressure, and the horizontal axis represents temperature. Figure 7 The thick straight line in the figure represents the relationship between the oxygen partial pressure and temperature when Rh₂O₃ and Rh reach equilibrium (the equilibrium line). Based on this equilibrium line, under conditions suitable for the reduction of the oxide (Rh₂O₃) of the constituent material (Rh) of electrode 44 (i.e.,...),... Figure 7 The starting conditions for the start-up measurement pump control process are determined by measuring the point corresponding to the intermediate temperature and oxygen partial pressure within the region to the lower left of the equilibrium line. For example, the logarithm (logP) of the oxygen partial pressure in the third internal cavity 61 corresponding to the target value V2a* at the start-up of the start-up measurement pump control process is used. O2 When the oxygen partial pressure is -2 (i.e., when the oxygen partial pressure is 0.01 Torr), if in Figure 7 As shown by the dashed line added to the state diagram, the temperature of the measuring electrode 44 corresponding to the oxygen partial pressure on the equilibrium line is Ta℃ (approximately 630℃). Therefore, if the voltage V2 reaches near the target value V2a* at startup and the temperature of the measuring electrode 44 reaches or exceeds Ta℃ through the startup pump control process, Rh2O3 is easily reduced to Rh. Therefore, the start condition for the startup pump control process can be determined such that the startup pump control process can be started when the temperature of the measuring electrode 44 reaches or exceeds Ta℃. For example, the threshold Thref can be determined as the lower limit of the heater temperature Th required to bring the temperature of the measuring electrode 44 to or exceed Ta℃. Alternatively, the startup pump control process can be started after a predetermined time has elapsed after the heater 72 is energized, and this predetermined time can be determined based on the time required from the start of the heater control process until the temperature of the measuring electrode 44 reaches or exceeds Ta℃. In addition, according to Figure 7It is also known that the higher the temperature of the measuring electrode 44 and the lower the oxygen partial pressure in the third internal cavity 61, the easier it is for Rh2O3 to be reduced. In other words, the lower the oxygen partial pressure in the third internal cavity 61, the lower the temperature of the measuring electrode 44 will be at the start of the pump control process suitable for startup measurement. Therefore, if the startup target value V2a* is set to a large value, the startup measurement pump control process can be started in a short time from the start of the heater control process corresponding to this large value. However, it is preferable that the startup target value V2a* is set to a value such that the voltage Vp2 does not reach 1500mV or more, as described above. Therefore, considering this point, it is preferable to set the value of the startup target value V2a* in a way that avoids the startup target value V2a* becoming too large. Furthermore, as described above, the pump control process for startup measurement is preferably performed after the solid electrolyte is activated. Therefore, it is preferable to determine the start-up conditions for the pump control process based on the higher of the temperature required for activation of the solid electrolyte and the temperature suitable for the reduction of the oxide of the constituent material of the measuring electrode 44. When the measuring electrode 44 contains Pt as a constituent material, the start-up conditions for the pump control process for startup measurement, suitable for the reduction of the oxide of Pt, can also be determined based on the state diagram of Pt, as in the example above. Furthermore, when the measuring electrode 44 contains both Pt and Rh as constituent materials, it is preferable to determine the start-up conditions for the pump control process based on the higher of the temperature suitable for the reduction of the oxide of Pt and the temperature suitable for the reduction of the oxide of Rh.

[0124] In the above embodiment, although the CPU92 starts the adjustment pump control process (main pump control process and auxiliary pump control process) at the same time as the start-up measurement pump control process, it is not limited to this. There may be a time difference between the start time of the adjustment pump control process and the start time of the start-up measurement pump control process. If the adjustment pump unit (main pump unit 21 and auxiliary pump unit 50) has a higher oxygen extraction capacity than the measurement pump unit 41, it is preferable to start the adjustment pump control process (main pump control process and auxiliary pump control process) simultaneously with or before the start of the start-up measurement pump control process. Furthermore, it is preferable to also perform the adjustment pump control process (main pump control process and auxiliary pump control process) during the start-up measurement pump control process.

[0125] In the above embodiment, although the oxygen concentration adjustment chamber has a first internal cavity 20 and a second internal cavity 40, it is not limited to this. For example, the oxygen concentration adjustment chamber may further have other internal cavities, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above embodiment, although the adjustment pump unit has a main pump unit 21 and an auxiliary pump unit 50, it is not limited to this. For example, the adjustment pump unit may further have other pump units, or one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, the auxiliary pump unit 50 may be omitted when the oxygen concentration of the gas to be measured can be sufficiently reduced by the main pump unit 21 alone. In this case, the CPU 92 may, for example, perform a process to control the main pump unit 21 in such a way that the oxygen concentration of the oxygen concentration adjustment chamber (first internal cavity 20) reaches the target concentration, as an adjustment pump control process. More specifically, by pre-determining a target value V0*, the CPU92 can control the main pump unit 21 by feedback control of the pump voltage Vp0 of the variable power supply 24 in a manner that the voltage V0 reaches the target value V0* (i.e., in a manner that the oxygen concentration in the first internal cavity 20 reaches the target concentration). In this case, the CPU92 can switch from pump control processing for measurement during startup to pump control processing for measurement during normal operation if it determines that the oxygen concentration in the first internal cavity 20 is stable based on the operation of the main pump unit 21. For example, the CPU92 can determine whether the oxygen concentration in the first internal cavity 20 has stabilized based on the value of the voltage V0 or the value of the pump current Ip0. More specifically, the CPU92 can determine that the oxygen concentration in the first internal cavity 20 has stabilized either when the voltage V0 reaches or exceeds a predetermined threshold, or when the pump current Ip0 rises once and then falls below a predetermined threshold.

[0126] In the above embodiment, the outer pump electrode 23 serves as: an outer main pump electrode, an outer auxiliary pump electrode, and an outer measuring electrode. The outer main pump electrode is a part of the main pump unit 21, disposed on the outside of the sensor element 101 and exposed to the gas to be measured. The outer auxiliary pump electrode is a part of the auxiliary pump unit 50, disposed on the outside of the sensor element 101 and exposed to the gas to be measured. The outer measuring electrode is a part of the measuring pump unit 41, disposed on the outside of the sensor element 101 and exposed to the gas to be measured, but is not limited thereto. Alternatively, any one or more of the outer main pump electrode, outer auxiliary pump electrode, and outer measuring electrode may be disposed separately from the outer pump electrode 23 on the outside of the sensor element 101.

[0127] In the above embodiment, although the outer pump electrode 23 is exposed to the outside of the sensor element 101, it is not limited to this. As long as the outer pump electrode 23 is disposed on the outside of the element body (layers 1 to 6) in a manner that allows it to contact the gas being measured. For example, the sensor element 101 has a porous protective layer covering the element body (layers 1 to 6), and the outer pump electrode 23 may also be covered by the porous protective layer.

[0128] In the above embodiment, the sensor element 101 of the gas sensor 100 includes: a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited thereto. For example, such as Figure 8 Like sensor element 201, it may not have a third internal cavity 61. Figure 8 In the modified sensor element 201 shown, the following components are sequentially connected and adjacent to each other between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4: a gas inlet 10, a first diffusion rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, and a second internal cavity 40. Furthermore, a measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The measuring electrode 44 is covered by a fourth diffusion rate control unit 45. The fourth diffusion rate control unit 45 is a membrane composed of a porous ceramic material such as alumina (Al2O3). Similar to the fourth diffusion rate control unit 60 in the above embodiment, the fourth diffusion rate control unit 45 serves to limit the amount of NOx flowing into the measuring electrode 44. Additionally, the fourth diffusion rate control unit 45 also functions as a protective film for the measuring electrode 44. The top electrode portion 51a of the auxiliary pump electrode 51 is formed directly above the measuring electrode 44. Even with this configuration, the sensor element 201 can detect NOx concentration based on, for example, the pump current Ip2, just as in the embodiment described above. In this case, the area around the measuring electrode 44 functions as a measuring chamber.

[0129] In the above embodiments, the main body of the sensor element 101 is a laminate having multiple solid electrolyte layers (layers 1 to 6), but it is not limited to this. It is acceptable as long as the main body of the sensor element 101 includes at least one oxygen ion-conducting solid electrolyte layer, and the gas to be measured flows through it. For example, in... Figure 1 Layers 1 to 5, other than the second solid electrolyte layer 6, can be structural layers made of a material other than a solid electrolyte (e.g., layers made of aluminum oxide). In this case, it is sufficient that each electrode of the sensor element 101 is disposed on the second solid electrolyte layer 6. For example, as long as Figure 1The measuring electrode 44 can be disposed on the lower surface of the second solid electrolyte layer 6. Alternatively, the reference gas introduction space 43 can be disposed in the isolation layer 5 instead of the first solid electrolyte layer 4, and the atmospheric introduction layer 48 can be disposed between the second solid electrolyte layer 6 and the isolation layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3. The reference electrode 42 can be disposed further rearward than the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0130] In the above embodiment, the control device 90 can, in the main pump control processing, set (feedback control) the target value V0* of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 reaches the target current Ip1*, and perform feedback control on the pump voltage Vp0 so that the voltage V0 reaches the target value V0*. However, it can also perform other controls. For example, in the main pump control processing, the control device 90 can perform feedback control on the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 reaches the target current Ip1*. That is, the control device 90 can omit the setting of obtaining the voltage V0 and the target value V0* from the oxygen partial pressure detection sensor unit 80 for main pump control, and directly control the pump voltage Vp0 (and thus control the pump current Ip0) based on the pump current Ip1. In this case, the CPU 92 can use, for example, the above-described... Figure 3 Step S130 or Figure 5 The process in step S230 is used to determine whether the termination condition of the pump control process has been met during startup.

[0131] In the above embodiment, the gas sensor 100 detects NOx concentration as the specific gas concentration, but it is not limited to this; other oxide concentrations can also be used as the specific gas concentration. When the specific gas is an oxide, since oxygen is generated when the specific gas itself is reduced in the third internal cavity 61, similar to the above embodiment, the CPU 92 can detect the specific gas concentration based on the detection value corresponding to this oxygen. Alternatively, the specific gas can also be a non-oxide such as ammonia. When the specific gas is a non-oxide, by converting the specific gas, for example, into an oxide in the first internal cavity 20 (e.g., ammonia being oxidized to NO), and then reducing the converted oxide in the third internal cavity 61 to generate oxygen, the CPU 92 can obtain a detection value corresponding to this oxygen to detect the specific gas concentration. Thus, regardless of whether the specific gas is an oxide or a non-oxide, the gas sensor 100 can detect the specific gas concentration based on the oxygen generated in the third internal cavity 61 from the specific gas.

[0132] In the above embodiments, the target value V2a* at startup can be set according to the volume of the measuring electrode 44. The inventors have discovered that even when the target value V2a* at startup is the same, the ignition time can sometimes differ due to the volume of the measuring electrode 44; whether the target value V2a* at startup is too high or too low, the effect of shortening the ignition time may sometimes be smaller, resulting in an optimal target value V2a* at startup; and the optimal target value V2a* at startup also changes when the volume of the measuring electrode 44 changes. These findings will be described in detail below.

[0133] The inventors measured the volume C [mm] of the measuring electrode 44. 3 The following investigation will examine the relationship between the target value V2a* at startup and the target value V2b* under normal conditions, ΔV (=V2a*-V2b*) [mV], and the ignition time [sec]. First, the use of… Figures 1-2 The sensor element 101 and gas sensor 100 described in the above-described embodiments are used as Experimental Example 1. The volume C of the measuring electrode 44 in Experimental Example 1 is 4 × 10⁻⁶. -3 mm 3 The measuring electrode 44, as described above, is a porous metal-ceramic electrode made of Pt, Rh, and ZrO2. In addition to various modifications to the volume C as shown in Table 1 by changing the thickness and length in the front-to-back direction of the measuring electrode 44, the gas sensor 100, identical to that in Experimental Example 1, was used as Experimental Examples 2 through 5. Specifically, in Experimental Example 2, the thickness of the measuring electrode 44 was doubled compared to Experimental Example 1. In Experimental Example 3, the thickness of the measuring electrode 44 was doubled compared to Experimental Example 2. In Experimental Example 4, the thickness of the measuring electrode 44 was 1.5 times that of Experimental Example 2, and the length in the front-to-back direction was doubled compared to Experimental Example 2. In Experimental Example 5, the thickness of the measuring electrode 44 was doubled compared to Experimental Example 2, and the length in the front-to-back direction was doubled. For the gas sensor 100 of Experimental Example 1, the target value V2a* at startup was set to 500 mV, and the target value V2b* at normal operation was set to 400 mV (therefore, the difference ΔV is 100 mV), and the following investigation was conducted: Figure 3 The table shows the ignition time under the control processing conditions at startup. Similarly, in the gas sensor 100 of Experimental Example 1, the ignition time under each condition was investigated by changing the target value V2a* at startup and varying the difference ΔV by 10mV each time between 110mV and 200mV, as shown in Table 1. In the gas sensors 100 of Experiments 2 to 5, the difference ΔV was also varied between 100mV and 200mV to investigate the ignition time under each condition. Table 1 shows the volume C of the measuring electrode 44 for each of Experiments 1 to 5, and the ignition time corresponding to the difference ΔV (=V2a*-V2b*) between the target value V2a* at startup and the target value V2b* at normal time. Figure 9 The graph in Table 1 shows the relationship between the volume C of the measuring electrode 44, the difference ΔV, and the ignition time. Furthermore, in Experiments 1-5, the ignition time was shorter when the difference ΔV was in the range of 100mV to 200mV compared to the case without pump control during startup (in other words, when the difference ΔV was 0mV). Therefore, Experiments 1-5 are equivalent to embodiments of the present invention.

[0134] [Table 1]

[0135]

[0136] According to Table 1 and Figure 9 It is evident that a larger difference ΔV does not necessarily mean a shorter ignition time; in other words, a higher target value V2a* at startup does not necessarily mean a shorter ignition time. For example, in Experiment 3, the shortest ignition time was observed when the difference ΔV was 160mV, confirming a trend where the ignition time is longer the difference ΔV is lower or higher than 160mV. Experiments 2 and 4 also confirmed the same trend. Experiment 1 confirmed that within the range of 100mV to 200mV, a larger difference ΔV results in a longer ignition time. Therefore, based on Experiment 1, it can be inferred that the difference ΔV value that best shortens the ignition time is less than 100mV. Experiment 5 confirmed that within the range of 100mV to 200mV, a larger difference ΔV results in a shorter ignition time. Therefore, it can be inferred from Experiment 5 that the difference ΔV value that best shortens the ignition time is greater than 200mV.

[0137] The reasons for the aforementioned trend in the relationship between the volume C, difference ΔV, and ignition time of the measuring electrode 44 will be explained. First, the inventors discovered that when switching from the pump control process for measurement during startup to the pump control process for measurement during normal operation, a downsurge in the pump current Ip2 sometimes occurs. Figure 10 This is a graph showing an example of the undershoot of the pump current Ip2. Figure 10 The times t0, t1, t3 and Figure 4 The times shown are the same. For example... Figure 10 As shown, during the switch from the pump control process for startup to the pump control process for normal operation at time t3, the pump current Ip2 does not immediately become a value corresponding to the NOx concentration in the measured gas. Sometimes, a downsurge occurs in the pump current Ip2, and only after time t3' does the value of the pump current Ip2 become a value corresponding to the NOx concentration in the measured gas. In this case, the ignition time is the time from time t0 to t3'. Therefore, the ignition time is extended by the amount of time during the downsurge (time t3 to t3').

[0138] The reason for this downsampling is as follows. When switching from the start-up measurement pump control process to the normal operation measurement pump control process, the target value of voltage V2 changes from the start-up target value V2a* to the normal operation target value V2b* (<V2a*). Therefore, the oxygen concentration in the third internal cavity 61 immediately after the switch is sometimes lower than the oxygen concentration corresponding to the normal operation target value V2b*. Consequently, immediately after switching to the normal operation measurement pump control process, the control unit 91 sometimes controls the measurement pump unit 41 to draw oxygen into the third internal cavity 61 instead of drawing oxygen out of it in order to raise the oxygen concentration in the third internal cavity 61 to the oxygen concentration corresponding to the normal operation target value V2b*. In this case, the pump current Ip2 becomes negative (opposite to the pump current Ip2 in the start-up measurement pump control process). Furthermore, in the start-up measurement pump control process, sometimes the voltage Vp2 applied to the measurement electrode 44 causes water in the measured gas to decompose and generate hydrogen. Furthermore, the oxygen concentration in the third internal cavity 61 decreases due to the reaction of hydrogen and oxygen after switching to the normal measurement pump control process. Even so, the pump current Ip2 sometimes decreases or becomes negative. Additionally, the larger the volume C of the measuring electrode 44, the larger its surface area (not limited to the outer surface of the measuring electrode 44, but also including the surface area of ​​the pores inside the measuring electrode 44). Therefore, there is a tendency for a larger volume C to result in a greater amount of hydrogen generated during the start-up measurement pump control process. As described above, the larger the difference ΔV (=V2a*-V2b*) and the larger the volume C, the longer the downsurge period occurs during the switch from the start-up measurement pump control process to the normal measurement pump control process, resulting in a longer ignition time.

[0139] On the other hand, the larger the difference ΔV (=V2a*-V2b*), the faster the oxygen that was already present in the third internal cavity 61 before the start-up of the sensor element 101 can be removed during the pump control process for start-up measurement. Therefore, the larger the difference ΔV (=V2a*-V2b*), the shorter the time required for the pump control process for start-up measurement (e.g., Figure 10 The shorter the time interval (t1~t3), the shorter the ignition time tends to be. Furthermore, the time for pump-controlled processing during startup (e.g., ...) is measured. Figure 10 The time intervals t1 to t3 and the time of the downstroke (e.g.) Figure 10 The smaller the total time (t3~t3'), the shorter the ignition time (e.g., time between t3 and t3'). Figure 10 The time interval t0~t3' becomes shorter.

[0140] Based on the above, it can be considered that if the target value V2a* at startup, or more precisely, the difference ΔV, is too small, the time required for pump control processing during startup measurement becomes longer (the time required to extract oxygen already present in the third internal cavity 61 before startup becomes longer), thus reducing the effect of shortening the ignition time. Conversely, it can be considered that if the difference ΔV is too large, the time for the downstroke becomes longer, thus reducing the effect of shortening the ignition time. Therefore, it can be considered that a certain sensor element 101 has an optimal difference ΔV at which the ignition time shortening effect is maximized. Furthermore, it can be considered that since the downstroke time also varies with the volume C of the measuring electrode 44 as described above, the optimal difference ΔV at which the ignition time shortening effect is maximized also changes when the volume C changes; specifically, there is a trend that the larger the volume C, the larger the optimal difference ΔV. It can be considered that, for the above reasons, the relationship between the volume C of the measuring electrode 44, the difference ΔV, and the ignition time is shown in Table 1 and... Figure 9 The relationship is shown in the figure.

[0141] Here, the volume C of the measuring electrode 44 is preferably 8 × 10⁻⁶. -3 mm 3 That's all. The volume C is 8 × 10⁻⁶. -3 mm 3 At this point, the oxygen extraction capacity around the measuring electrode 44 based on the measuring pump unit 41 becomes sufficiently high. Therefore, compared to Experimental Example 1, it is preferable that the volume C is 8 × 10⁻⁶. -3 mm 3 The above are experimental examples 2 to 5. Furthermore, when the difference ΔV is too large, the voltage Vp2 during the pump control process at startup becomes a high value, which, as mentioned above, may cause the sensor element 101 to blacken and become unusable. Additionally, when the voltage Vp2 during the pump control process at startup is too high, applying an excessive voltage Vp2 to the measuring electrode 44 promotes the deterioration of the measuring electrode 44, potentially increasing the resistance of the measuring electrode 44 or consequently reducing the sensitivity of NOx concentration detection. Therefore, the difference ΔV is preferably 200 mV or less. Moreover, according to... Figure 9 The results suggest that, compared to Experimental Example 5, as the volume C increases, the effect of shortening the ignition time decreases within the range where the difference ΔV is below 200mV. Therefore, it can be considered that the volume C is preferably below the value of Experimental Example 5, i.e., 32 × 10⁻⁶ mV. -3 mm 3 Below. Furthermore, in Experimental Examples 2-5, the difference ΔV is preferably 120mV to 200mV, which is the range that minimizes the ignition time and is close to it, and where the difference ΔV does not exceed 200mV. Based on the above, the volume C is preferably 8 × 10⁻⁶. -3 mm 3 ~32×10-3 mm 3 The preferred difference ΔV is 120mV to 200mV. Although there is a trend that the larger the volume C, the larger the difference ΔV required to fully improve the ignition time reduction effect, if the volume C is 8 × 10⁻⁶ mV... -3 mm 3 ~32×10 -3 mm 3 If the difference ΔV is 120mV to 200mV, it can satisfy the lower limit of the volume C and the upper limit of the difference ΔV, and can fully improve the effect of shortening the ignition time.

[0142] Furthermore, when adjusting the volume C of the measuring electrode 44, the thickness of the measuring electrode 44 can be, for example, 10 μm to 40 μm. The area of ​​the upper surface of the measuring electrode 44, that is, the product of the left-right width and the front-back length of the measuring electrode 44, can be 0.2 mm. 2 ~1.2mm 2 The width of the measuring electrode 44 in the left-right direction can be 0.5 mm to 2.5 mm. Furthermore, when adjusting the difference ΔV, the target value V2a* at startup is preferably 600 mV or less.

[0143] In the above embodiment, when the CPU 92 determines that the oxygen concentration in the third internal cavity 61 has stabilized based on the operation of the measuring pump unit 41, it can determine that the end condition of the start-up measuring pump control process has been met. For example, when the pump current Ip2 flowing through the measuring pump unit 41 has stabilized through the start-up measuring pump control process, the CPU 92 can determine that the oxygen concentration in the third internal cavity 61 has stabilized, and thus determine that the end condition of the start-up measuring pump control process has been met. The inventors have discovered that a stable region in which the pump current Ip2 stabilizes is exhibited by the stable oxygen concentration in the third internal cavity 61 during the start-up measuring pump control process. Figure 11 The diagram illustrates the stable region of the pump current Ip2, as well as the first and second derivative values ​​of the pump current Ip2. Figure 11 The times t0, t1, t3 and Figure 4 The times shown are the same: pump control processing for startup begins at time t1, and normal time control processing begins from time t3. Additionally, Figure 11 The time t3' in Figure 10 The time t3' shown is the same. For example... Figure 11 As shown in A, sometimes from the start of the pump control process at time t1, until time t3 when it can be determined that the pump current Ip1 has stabilized near the target current Ip1*, the pump control process is measured. Figure 11Between the pump current Ip1 (not shown in the diagram), it is evident that the pump current Ip2 exhibits a stable region. During the pump control processing for startup measurement, the CPU 92 performs feedback control on the voltage Vp2 of the variable power supply 46 so that the voltage V2 reaches the startup target value V2a*. Therefore, it can be considered that the stable pump current Ip2 at this point indicates a stable oxygen concentration in the third internal cavity 61, meaning that the oxygen present in the third internal cavity 61 before startup is sufficiently drawn out through the startup measurement pump control processing. Therefore, by switching from startup measurement pump control processing to normal measurement pump control processing when the pump current Ip2 has stabilized, the switching from startup measurement pump control processing to normal measurement pump control processing can be appropriately performed. Furthermore, as... Figure 11 As shown, the stable region of pump current Ip2 sometimes appears earlier than time t3. For example, when the oxygen concentration in the gas being measured is low, pump current Ip2 stabilizes earlier than pump current Ip1, which stabilizes near the target current Ip1*. Figure 11 Thus, sometimes the stable region of pump current Ip2 appears earlier than time t3. This can be attributed to the smaller volume of the third internal cavity 61 compared to the second internal cavity 40, or the smaller target oxygen concentration in the third internal cavity 61 compared to the target oxygen concentration in the second internal cavity 40. In this case, by switching from pump control processing for startup measurement to pump control processing for normal operation when pump current Ip2 is stable, the switching can be performed at an earlier time compared to the switching performed as described in the above embodiment when pump current Ip1 has stabilized near the target current Ip1*. As a result, the ignition time of sensor element 101 can also be shortened. Conversely, sometimes the time when pump current Ip1 stabilizes near the target current Ip1* is earlier than the time when pump current Ip2 stabilizes. This is because, as described above, the auxiliary pump unit 50 cannot draw out oxygen (oxygen bonded to the constituent material of the measuring electrode 44, or oxygen molecules present in the closed pores of the measuring electrode 44) that will not flow back from the third internal cavity 61 to the second internal cavity 40. In this case, if the switch from the start-up measuring pump control process to the normal measuring pump control process is performed when the pump current Ip1 has stabilized near the target current Ip1*, the oxygen in the third internal cavity 61 may not be sufficiently drawn out, and the switch may occur prematurely. In contrast, by performing the switch from the start-up measuring pump control process to the normal measuring pump control process when the pump current Ip2 has stabilized, premature switching can be suppressed.

[0144] Whether the pump current Ip2 has stabilized can be determined based on the first derivative of the pump current Ip2 flowing through the measuring pump unit 41 during startup, as determined by the pump control processing. For example, Figure 11 A and Figure 11 As shown in Figure B, when the pump current Ip2 reaches the stable region, the first derivative of the pump current Ip2 (dIp2 / dt) becomes 0 or near 0. Therefore, when this first derivative is considered to be 0 (i.e., when the slope of the pump current Ip2 is considered to be 0), it can be determined that the pump current Ip2 is stable. For example, as... Figure 11 In the time-varying curve of the first derivative of the pump current Ip2 shown in Figure B, the pump current Ip2 is considered stable at the moment tb when the first derivative becomes 0. The CPU92 can determine that the pump current Ip2 is stable when the first derivative is considered to be 0 within a defined region. This defined region can be, for example, a region near 0, or a region exceeding a defined threshold slightly less than 0. For example, the defined threshold can be -0.3 [μA / s], and (dIp2 / dt) > -0.3 [μA / s], indicating that the pump current Ip2 is stable. The first derivative of the pump current Ip2 (dIp2 / dt) can be calculated by repeatedly measuring the pump current Ip2 at defined time intervals, dividing the difference between the current measurement and the previous measurement by the defined time interval. Furthermore, according to... Figure 11 B also reveals that after the pump control processing for startup measurement begins at time t1, the first derivative of the pump current Ip2 sometimes reaches or is near zero before reaching a stable region. Therefore, it is preferable that the CPU 92 begins to decrease the pump current Ip2 after it rises once during the startup measurement pump control processing (the moment when the pump current Ip2 crosses its peak value, for example, at...). Figure 11 B represents the first derivative of the pump current Ip2 after time ta, used to determine whether the pump current Ip2 has stabilized. For example, the CPU92 can determine that the pump current Ip2 has started to decrease after one rise when it exceeds a predetermined threshold once and then falls below the predetermined threshold. Alternatively, the CPU92 can determine that the pump current Ip2 has started to decrease after one rise when the first derivative of the pump current Ip2 is lower than a predetermined threshold (negative value).

[0145] Whether the pump current Ip2 has stabilized can be determined based on the second derivative of the pump current Ip2 flowing through the measuring pump unit 41 during startup control processing. For example, Figure 11 A and Figure 11 As shown in Figure C, when the pump current Ip2 reaches the steady region, the second derivative of the pump current Ip2 (d) 2 Ip2 / dt 2The value is 0 or near 0. Therefore, when the second derivative of the pump current Ip2 is considered to be 0 (i.e., considered as the inflection point of the pump current Ip2), it can be determined that the pump current Ip2 has stabilized. For example, in Figure 11 In the time-varying curve of the second derivative of the pump current Ip2 shown in Figure C, the pump current Ip2 can be considered stable at the moment tc when the second derivative becomes 0. CPU92 can determine that the pump current Ip2 has stabilized when the second derivative is within a defined region where the second derivative is considered to be 0. This defined region can be, for example, the region near 0, or a region smaller than a defined threshold slightly greater than 0. The second derivative of the pump current Ip2 (d...) 2 Ip2 / dt 2 For example, the pump current Ip2 can be repeatedly measured at predetermined time intervals to repeatedly derive the first-order derivative value. The difference between the derived first-order derivative value and the previously derived first-order derivative value is divided by the predetermined time interval to calculate the obtained value. When making a judgment based on the second-order derivative value, it is preferable that, similarly to when making a judgment based on the first-order derivative value, the CPU92 determines whether the pump current Ip2 has stabilized based on the second-order derivative value of the pump current Ip2 after the moment when the pump control processing starts and the pump current Ip2 rises once and then begins to decrease. In addition, after the moment when the pump current Ip2 rises once and then begins to decrease, and before the pump current Ip2 stabilizes, sometimes the second-order derivative value of the pump current Ip2 is near 0 (e.g., Figure 11 (between time ta and time tb of C). In order to distinguish this situation from the case where the pump current Ip2 has stabilized, the CPU92 can determine that the pump current Ip2 has stabilized after the pump current Ip2 has increased once and then started to decrease, and when the second derivative value of the pump current Ip2 changes from a state higher than the specified region when it is considered to be 0 to being included in the region considered to be 0 (when the second derivative value decreases and enters the specified region considered to be 0),

[0146] Furthermore, as described in the above embodiments, the value of the pump current Ip2 changes according to the NOx concentration when the NOx concentration in the measured gas changes constantly. Therefore, during the start-up pump control process, when the NOx concentration in the measured gas changes, a stable region for the pump current Ip2 may not be apparent. Therefore, it is preferable that the CPU 92 determines whether the end condition of the start-up pump control process has been met based on whether the pump current Ip2 has stabilized, assuming that the NOx concentration in the measured gas is considered to be stable. The assumption that the NOx concentration in the measured gas is considered to be stable also includes the assumption that there is no NOx in the measured gas. Specific examples of assuming that the NOx concentration in the measured gas is considered to be stable include: low-load operation of the internal combustion engine, idling, and deceleration of a vehicle equipped with the gas sensor 100. Furthermore, in the case of a hybrid electric vehicle equipped with the gas sensor 100, the assumption that the NOx concentration in the measured gas is stable is also given when the hybrid electric vehicle is in operation (when the engine is stopped). CPU92 can determine whether the NOx concentration in the measured gas is considered to be stable (e.g., whether it belongs to any of the specific examples mentioned above) based on information obtained from the engine ECU (not shown) of the internal combustion engine, or determine whether the pump current Ip2 has stabilized if the determination is not affirmative.

[0147] Alternatively, the CPU92 can combine the following processes: determining whether the end condition of the start-up measurement pump control process has been met based on whether the oxygen concentration in the third internal cavity 61 has stabilized, and determining whether the end condition of the start-up measurement pump control process has been met in either of the above methods. That is, the determination of whether the end condition of the start-up measurement pump control process has been met can be performed based on whether any one of multiple conditions has been met. In this way, even when it is impossible to determine whether the end condition of the start-up measurement pump control process has been met based on whether the oxygen concentration in the third internal cavity 61 has stabilized (e.g., when the NOx concentration in the measured gas changes), it can still be determined based on whether other conditions have been met (e.g., as described above). Figure 3 The determination in step S130 is performed to switch from the pump control process for measurement during startup to the pump control process for measurement during normal operation. Additionally, in this case, the determination of whether the NOx concentration in the measured gas is considered stable can be omitted.

[0148] An example is given of a case where multiple decisions are combined to determine whether the termination condition of the pump control process at startup has been met. Figure 12 This is a flowchart illustrating an example of the startup control processing of a modified example. Figure 12 In the middle, to and Figure 3The same processing, marking and Figure 3 The same step numbers are used, and their descriptions are omitted. In Figure 12 In the startup control process, after the startup measurement pump control process begins in step S120, the CPU 92 determines whether the oxygen concentration in the measurement chamber (here, the third internal cavity 61) has stabilized (step S125). For example, if the CPU 92 determines that the pump current Ip2 has stabilized based on at least one of its first and second derivative values ​​after it has increased once, then the oxygen concentration in the third internal cavity 61 has stabilized. If the pump current Ip2 is increasing, or before it begins to decrease after increasing, or if the pump current Ip2 is not stable, in step S125, the oxygen concentration in the third internal cavity 61 is determined to be unstable, and the process in step S130 is performed. If step S130 is a negative determination, the process in step S125 is executed. If either step S125 or step S130 is a positive determination, step S140 is executed, and the process transitions to normal control. Figure 12 In the startup control process, if a stable region of pump current Ip2 is observed, the process can transition to normal operation control via step S125. Therefore, the switch from startup measurement pump control process to normal operation measurement pump control process can be appropriately performed. Furthermore, even if a stable region of pump current Ip2 is not observed, the process can transition to normal operation control at time t3 via step S130, thus ensuring a reliable transition to normal operation control. Figure 12 In this process, although steps S125 and S130 are combined to determine whether the end condition of the pump control process at startup has been met, steps S125 and S130 can also be combined. Figure 5 Step S230 can also be combined with steps S125, S130, and S230. Figure 12 The startup control process can also include an option to determine whether the NOx concentration in the measured gas is considered stable. For example, the CPU92 can... Figure 12After step S120, the following steps are performed: determining whether the NOx concentration in the measured gas is considered stable. If the NOx concentration is considered stable, step S125 is performed; otherwise, step S130 is performed. Furthermore, if the determination in step S125 or S130 is negative, the CPU92 can again perform the following steps: determining whether the NOx concentration in the measured gas is considered stable. If the determination in step S125 or S130 is positive, step S140 is performed. In other words, if the NOx concentration in the measured gas is considered stable, step S130 can be omitted. Thus, if the pump current Ip1 stabilizes near the target current Ip1* too early, using step S130 would prematurely switch from the pump control process for startup to the pump control process for normal operation. Even in this case, if step S125 is performed only when the NOx concentration is stable, the switch can be performed at a more appropriate time.

[0149] In the voltage V1 (an example of an auxiliary pump voltage) detected by the oxygen partial pressure detection sensor unit 81 (an example of an auxiliary pump voltage detection sensor unit) in the above embodiment, in addition to the electromotive force based on the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42, it also includes a thermoelectric potential based on the temperature difference between the auxiliary pump electrode 51 and the reference electrode 42. Therefore, in the above-described normal control process, a correction taking into account the thermoelectric potential contained in the voltage V1 can be performed. Specifically, in the initial stage of the normal control process, a correction process can be performed to correct the target value V1* of the voltage V1 to a higher value compared to the period after the initial stage. Here, the thermoelectric potential contained in the voltage V1 will be explained first. Figure 13 This is a graph showing an example of the time-varying voltage V1 caused by thermoelectric potential. Figure 13 The time t0 and Figure 4 The time t0 shown is the same. Additionally, in Figure 13To facilitate understanding of the time-varying voltage V1 caused by the thermoelectric potential, the following diagram illustrates the voltage V1 when the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42 is constant. At time t0, when the heater control process begins, both the auxiliary pump electrode 51 and the reference electrode 42 are heated and their temperatures rise. After a sufficient period, the temperatures of the auxiliary pump electrode 51 and the reference electrode 42 stabilize, and the thermoelectric potential between the two electrodes also stabilizes at a near-constant value. However, during the period until the temperatures of the two electrodes stabilize, the temperature difference between the two electrodes sometimes temporarily increases due to the difference in their heating rates. When the temperature difference between the two electrodes is temporarily large, the thermoelectric potential contained in the voltage V1 between the two electrodes also temporarily increases. Therefore, for example, even when the electromotive force based on the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42 is constant, the voltage V1 remains constant. Figure 13As shown by the solid line, voltage V1 temporarily becomes high after heater control processing begins at time t0. Furthermore, as time progresses and the temperature difference between the two electrodes decreases, voltage V1 decreases, reaching a stable value A at time te when the thermoelectric potential has stabilized. Value A includes: the electromotive force based on the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42, and the thermoelectric potential between the two electrodes in a state where a small temperature difference between them is sufficient for stability. Therefore, for example, at time td before time te, voltage V1, in addition to value A, also includes a value B based on the temporarily larger thermoelectric potential between the auxiliary pump electrode 51 and the reference electrode 42. Thus, voltage V1 becomes a value that increases by a quantity corresponding to value B. Therefore, at time td, the actual value of voltage V1 (=A+B) differs from the desired electromotive force, which is the electromotive force based on the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42 (almost equal to value A), by a value of B. Thus, when the deviation between the actual voltage V1 and the electromotive force based on the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42 temporarily increases, even with the aforementioned auxiliary pump control processing, it may be impossible to control the oxygen concentration around the auxiliary pump electrode 51 with high precision. Specifically, even when the voltage Vp1 of the variable power supply 52 is controlled by feedback in the auxiliary pump control processing to achieve the target value V1*, the voltage V1 contains a temporarily large thermoelectric potential. Therefore, the oxygen concentration difference between the periphery of the auxiliary pump electrode 51 and the periphery of the reference electrode 42 will be controlled to be less than the originally desired oxygen concentration difference. As a result, the oxygen concentration around the auxiliary pump electrode 51 will be controlled to be higher than the originally desired target concentration (closer to the oxygen concentration around the reference electrode 42 than the target concentration). Moreover, when the oxygen concentration around the auxiliary pump electrode 51 is controlled to be higher than the target concentration, the amount of NOx reduced in the second internal cavity 40 changes, and the amount of NOx reaching the third internal cavity 61 also changes. Specifically, when the oxygen concentration around the auxiliary pump electrode 51 is controlled to the target concentration, although NOx in the measured gas is slightly reduced in the second internal cavity 40, the amount of NOx reduction decreases when the oxygen concentration around the auxiliary pump electrode 51 is controlled to a value higher than the target concentration. As a result, the amount of NOx reaching the third internal cavity 61 sometimes increases. Accordingly, the pump current Ip2 flowing through the pump control process under normal conditions increases, thus causing errors in the detected value of NOx concentration. Figure 14 This is a graph showing an example of the time variation of the pump current Ip2 caused by the thermoelectric potential contained in the voltage V1. Figure 14 The times t0, td, te, and Figure 13 The times shown are the same. Additionally, in Figure 14In order to easily understand the time change of pump current Ip2 caused by thermoelectric potential, the state of pump current Ip2 when the NOx concentration in the measured gas is constant is shown. Figure 13 As shown by the solid line, when the value of voltage V1 temporarily increases due to thermoelectric electromotive force, such as Figure 14 The solid line shown will also temporarily increase the pump current Ip2 for the reasons mentioned above, due to the error caused by the NOx concentration in the gas being measured, which was originally intended to be determined. Therefore, for example, even when the NOx concentration in the gas being measured is constant, such as... Figure 14 As shown, the pump current Ip2 temporarily becomes high after the heater control process begins at time t0. Furthermore, as time progresses and the thermoelectric potential decreases, the pump current Ip2 decreases, and at time te when the thermoelectric potential stabilizes, the pump current Ip2 becomes its stable value D (the pump current Ip2 value corresponding to the NOx concentration in the gas to be measured). Therefore, for example, at time td before time te, as... Figure 13 As shown by the solid line, the voltage V1 includes the value B caused by the thermoelectric potential. Therefore, the pump current Ip2 becomes a value greater than the value D. Because of the amount corresponding to this value, an error occurs in the detected value of NOx concentration, and the detection accuracy of NOx concentration is reduced.

[0150] Therefore, as described above, in the initial stage of normal control processing, a correction process is performed to adjust the target value V1* of voltage V1 to a higher value compared to periods after the initial stage. By increasing the target value V1* of voltage V1 in the initial stage of normal control processing, the effects of the temporarily large thermoelectric potential contained in voltage V1 can be reduced. Thus, compared to the case without correction processing, high-precision control of the oxygen concentration around the auxiliary pump electrode 51 is possible even when the thermoelectric potential contained in voltage V1 is temporarily large. For example, if in Figure 13 If the target value V1* is corrected to a value B higher than its original value at time td, the effect of the voltage V1 temporarily exceeding the value B can be offset by the thermoelectric potential, thereby controlling the oxygen concentration in the second internal cavity 40 to the target concentration. As a result, it is possible to suppress Figure 14 The temporary increase in pump current Ip2 shown in the figure can suppress the decrease in the detection accuracy of NOx concentration.

[0151] The correction of the target value V1* can be performed based on a predetermined correction pattern that tends to decrease over time. As mentioned above, the temperature difference between the auxiliary pump electrode 51 and the reference electrode 42 tends to decrease over time. Therefore, the thermoelectric potential contained in the voltage V1 also tends to decrease over time. Therefore, by correcting the target value V1* of the voltage V1 based on a predetermined correction pattern that tends to decrease over time, the effects of a temporary increase in the thermoelectric potential contained in the voltage V1 can be further reduced. For example, the correction pattern can be determined in advance through experiments according to... Figure 13 The correction mode is shown as a curve of the time change of voltage V1, represented by a solid line. This allows the correspondence between time (e.g., time elapsed since time t0) and correction amount (or the corrected target value V1*) to be stored in the storage unit 94. Furthermore, the CPU 92 can derive the correction amount corresponding to the current time based on this correspondence, and derive the corrected target value V1*. Thus, it is possible to offset... Figure 13 The temporary increase in voltage V1 (the deviation from the value A) is shown by the solid line in the figure. Figure 14 As shown by the dashed line representing the pump current Ip2 in the corrected state, compared to the pump current Ip2 in the uncorrected state shown by the solid line, the deviation between the pump current Ip2 and the value D can be reduced. Furthermore, Figure 14 The pump current Ip2, shown by the dashed line in the calibration state, deviates slightly from the value D, but ideally, this deviation can be corrected to zero. Regarding... Figure 13 The time-varying pattern of voltage V1, shown by the solid line, which is also the time-varying pattern of the thermoelectric potential between the auxiliary pump electrode 51 and the reference electrode 42, will be substantially the same as the time-varying pattern of heater 72 in the heater control process, provided that the heating pattern is the same. Therefore, the correction pattern can be determined experimentally in advance. Furthermore, by using such a pre-prepared correction pattern, the target value V1* can be appropriately corrected without measuring the thermoelectric potential between the auxiliary pump electrode 51 and the reference electrode 42.

[0152] Furthermore, "there is a trend of the correction amount decreasing over time" includes, for example, the correction amount decreasing linearly, the correction amount decreasing curvilinearly, and the correction amount decreasing as a step function. For example, as mentioned above, it is possible to use... Figure 13 The correction mode shown by the dashed line, which reduces the step function, is used instead of the correction mode based on... Figure 13The correction mode is the curve of the time change of voltage V1 shown by the solid line. In this case, it is preferable to determine the correction mode in such a way that the difference between the correction mode shown by the dashed line and the actual time change of voltage V1 shown by the solid line (e.g., the value C at time td) is not too large (e.g., within 10mV). Alternatively, a correction mode based on an approximate straight line based on the curve can be used instead of the correction mode based on the solid line. Figure 13 The correction mode of the curve showing the time variation of voltage V1, represented by a solid line.

[0153] An example is given when correcting the target value V1* based on such a predetermined correction pattern. Figure 15 This is a flowchart illustrating an example of the correction process. (At the beginning) Figure 3 , 5 During the normal control process shown in step S140 of section 12, this correction process is performed. When the correction process begins, CPU 92 derives the correction amount ΔV1* of the target value V1* based on the correction mode (step S310). For example, when the correction process is performed according to... Figure 13 When the correction mode of the curve shown by the solid line is stored in the storage unit 94, the CPU 92 derives the correction amount ΔV1* corresponding to the current time (e.g., the time elapsed since the start of heater control processing t0) from the correction mode. For example, if the current time is... Figure 13 When the time td is reached, CPU 92 derives value B as the correction amount ΔV1*. Next, CPU 92 corrects the target value V1* based on the derived correction amount ΔV1* (step S320). For example, CPU 92 derives the corrected target value V1* by adding the correction amount ΔV1* to the original target value V1*. Next, CPU 92 determines whether the correction period for the target value V1* has ended (step S330). For example, if the current time has exceeded the last time of the correction mode stored in the storage unit 94, or if a predetermined time has been exceeded, CPU 92 determines that the correction period has ended. For example, if the current time has exceeded the last time of the correction mode stored in the storage unit 94, or if a predetermined time has been exceeded, CPU 92 determines that the correction period has ended. Figure 13 The situation at time te, or the time has exceeded the threshold for being negligible. Figure 13When the difference between the solid line and value A is of a certain magnitude (slightly earlier than the specified time te), the CPU92 determines that the calibration period has ended. If the CPU92 determines in step S330 that the calibration period has not ended, it executes the process of step S310. Thus, during the period until the end of the calibration period, based on the calibration mode, the calibrated target value V1* is set in a manner that the calibration amount tends to decrease over time. Moreover, if the CPU92 determines in step S330 that the calibration period has ended, it ends the calibration process. By doing so, since the auxiliary pump control process is performed based on the calibrated target value V1* during the initial stage of the normal control process, that is, from the start of the normal control process until the end of the calibration period, as described above, even when the thermoelectric potential contained in the voltage V1 is temporarily large, the oxygen concentration around the auxiliary pump electrode 51 can be controlled with high precision. As a result, the temporary increase of the pump current Ip2 can be suppressed, thereby suppressing the decrease in the detection accuracy of NOx concentration.

[0154] The target value V1* can be corrected by means of a predetermined correction mode instead of by means of a predetermined correction mode. That is, in the correction process, the CPU92 considers that, assuming the pump current Ip0 (an example of the main pump current) flowing through the main pump unit 21 in the main pump control process is stable, the target value V1* in the correction process can be corrected with the following trend: the larger the deviation between the voltage Vref derived from the pump current Ip0 and corresponding to the oxygen concentration in the gas being measured around the sensor element 101 (i.e., the calculated reference voltage Vrefs) and the voltage Vref detected by the sensor unit 83 (an example of a reference voltage detection sensor unit), i.e., the measured reference voltage Vrefa), the larger the correction amount. Here, the main pump control process is, as described above, a process that controls the main pump unit 21 so that the pump current Ip1 reaches the target current Ip1*. The pump current Ip0 flowing when adjusting the oxygen concentration in the first internal cavity 20 through the main pump control process is correlated with the oxygen concentration in the gas being measured around the sensor element 101. Furthermore, the voltage Vref (an example of a reference voltage) is the voltage between the outer pump electrode 23 (an example of a gas-side electrode) outside the sensor element 101 and the reference electrode 42. Therefore, it is correlated with the oxygen concentration in the gas being measured around the sensor element 101. That is, the pump current Ip0 is correlated with the oxygen concentration in the gas being measured around the sensor element 101, and the oxygen concentration in the gas being measured around the sensor element 101 is correlated with the voltage Vref. Thus, assuming that the pump current Ip0 has stabilized, the voltage Vref corresponding to the oxygen concentration in the gas being measured around the sensor element 101 can be derived based on the pump current Ip0, i.e., the reference voltage Vrefs can be calculated. The calculated reference voltage Vrefs is a value equivalent to an electromotive force, which is an electromotive force based on the difference in oxygen concentration between the gas being measured around the sensor element 101 and the reference gas around the reference electrode 42. On the other hand, the voltage Vref actually detected by the sensor unit 83, i.e., the measured reference voltage Vrefa, also includes the thermoelectric potential between the outer pump electrode 23 and the reference electrode 42. Therefore, when the temperature difference between the two electrodes is temporarily large, the thermoelectric potential included in the measured reference voltage Vrefa is also temporarily large. Thus, the larger the thermoelectric potential included in the measured reference voltage Vrefa, the greater the deviation between the calculated reference voltage Vrefs derived from the main pump current Ip0 and the measured reference voltage Vrefa actually detected by the sensor unit 83. In addition, when the thermoelectric potential between the outer pump electrode 23 and the reference electrode 42 is large, the thermoelectric potential between the auxiliary pump electrode 51 and the reference electrode 42 is also usually large.Therefore, by applying the trend that the larger the deviation between the calculated reference voltage Vrefs and the measured reference voltage Vrefa, the larger the correction amount, the target value V1* in the correction process is corrected. This reduces the impact of the temporarily large thermoelectric potential contained in voltage V1. Accordingly, similar to the correction mode described above, compared to the case without correction, it is possible to control the oxygen concentration around the auxiliary pump electrode 51 with high precision even when the thermoelectric potential contained in voltage V1 is temporarily large. As a result, the temporary increase in pump current Ip2 can be suppressed, thereby suppressing the decrease in the detection accuracy of NOx concentration.

[0155] For example, the correspondence between the pump current Ip0 and the calculated reference voltage Vrefs is pre-stored in the storage unit 94. The CPU 92 can derive the calculated reference voltage Vrefs based on this correspondence and the value of the pump current Ip0 flowing through the main pump unit 21. The calculated reference voltage Vrefs is a value equivalent to the measured value of the voltage Vref, which is the measured value of the voltage Vref after sufficient time has elapsed since the start of heater control processing, allowing the temperature difference between the outer pump electrode 23 and the reference electrode 42 to decrease, thereby stabilizing the thermoelectric potential between the two electrodes. Therefore, by measuring the combination of the measured value of the voltage Vref after the thermoelectric potential stabilizes and the value of the pump current Ip0 in the main pump control when the oxygen concentration in the gas being measured around the sensor element 101 changes, such a correspondence can be predetermined. The correspondence is as follows: the larger the value of the pump current Ip0 (i.e., the higher the oxygen concentration around the sensor element 101), the smaller the calculated reference voltage Vrefs (i.e., the smaller the oxygen concentration difference between the measured gas and the reference gas around the sensor element 101).

[0156] An example is given of how the target value V1* is corrected based on the calculated reference voltage Vrefs and the measured reference voltage Vrefa. Figure 16 It shows the relationship with Figure 15 A flowchart illustrating an example of different correction processes. Figure 16 In the middle, to and Figure 15 The same processing, marking and Figure 15 The same step numbers are used, and detailed explanations are omitted. Begin... Figure 3 , 5 During the normal control process of step S140 shown in section 12, the following steps are executed: Figure 16The calibration process begins. When the calibration process begins, the CPU 92 determines whether the pump current Ip0 flowing through the main pump control process has stabilized; in other words, it determines whether the oxygen concentration of the gas being measured around the sensor element 101 has stabilized (step S300). For example, the CPU 92 repeatedly measures the pump current Ip0 at predetermined intervals, and determines that the pump current Ip0 has stabilized if the difference between the current measurement value and the previous measurement value is within a predetermined range. Alternatively, the CPU 92 can determine whether the pump current Ip0 has stabilized based on the first or second derivative value of the pump current Ip0, similar to the determination of whether the pump current Ip2 has stabilized described above. If the CPU 92 determines that the pump current Ip0 has not stabilized in step S300, it performs... Figure 15 The processing in step S310, as described above, derives a correction amount ΔV1* based on the correction mode pre-stored in the storage unit 94. On the other hand, if it is determined in step S300 that the pump current Ip0 has stabilized, the CPU 92 calculates the reference voltage Vrefs based on the current pump current Ip0 and the aforementioned correspondence (step S312). Next, the CPU 92 derives the correction amount ΔV1* for the target value V1* based on the derived calculated reference voltage Vrefs and the current voltage Vref detected by the sensor unit 83, i.e., the measured reference voltage Vrefa (step S314). For example, the CPU 92 can derive the correction amount ΔV1* based on the difference between the measured reference voltage Vrefa and the calculated reference voltage Vrefs. The difference between the measured reference voltage Vrefa and the calculated reference voltage Vrefs corresponds to the temporary increase in the thermoelectric potential between the outer pump electrode 23 and the reference electrode 42. Therefore, it can be considered that the difference is the same as the temporary increase in thermoelectric potential between the auxiliary pump electrode 51 and the reference electrode 42, and thus the value of the difference itself is used as the correction amount ΔV1*. Alternatively, the correction amount ΔV1* can also be derived by multiplying the difference between the measured reference voltage Vrefa and the calculated reference voltage Vrefs by a predetermined coefficient. When the correction amount ΔV1* is derived in step S310 or step S314, the CPU92 performs step S320 and performs correction based on the target value V1* of the correction amount ΔV1*. Moreover, if the CPU92 determines in step S330 that the correction period has not ended, it performs the processing of step S300; if it determines that the correction period has ended, it ends the correction processing. In step S330, the correction period can be determined to have ended when the correction amount ΔV1* derived in step S314 is a small value that is considered to be zero (for example, a value less than a predetermined threshold). By performing this... Figure 16The correction process can correct the target value V1* based on the calculated reference voltage Vrefs and the measured reference voltage Vrefa when the pump current Ip0 is stable. On the other hand, when the pump current Ip0 is not stable, the target value V1* can be corrected based on a predetermined correction mode. Even when the correction amount ΔV1* is derived in either step S310 or S314, a correction that takes into account the thermoelectric potential contained in the voltage V1 can be performed.

[0157] Furthermore, the temperatures of the auxiliary pump electrode 51 and the reference electrode 42 are not yet stable in the initial stage of normal control processing, such as Figure 13 As shown, voltage V1 contains a temporarily increased thermoelectric electromotive force, thus, as Figure 14 As shown, the pump current Ip2 temporarily increases, thus the sensor element 101 ignites when the thermoelectric potential has stabilized (e.g., when the thermoelectric potential has stabilized). Figure 14 (te) in the middle. Thus, for example, in from Figure 4 If normal time control processing begins at time t3, then time t3 is: Figure 14 At time td, without correction processing, the pump current Ip2 has an error from time t3 (time td) to time te, and therefore does not ignite, sometimes resulting in a longer actual ignition time. In contrast, by performing correction processing, the temporary increase in pump current Ip2 is suppressed, thereby enabling, for example, the sensor element 101 to ignite immediately at or after time td, thus shortening the ignition time.

[0158] Furthermore, the main body of sensor element 101, as described above, is an elongated shape having two ends along its long side, namely a front end and a rear end. Additionally, as... Figure 1As shown, the auxiliary pump electrode 51 and the reference electrode 42 are disposed at the front end of the main body of the element (specifically, at the front end relative to the center in the front-rear direction), and the reference electrode 42 is disposed at a position further away from the front end in the front-rear direction than the auxiliary pump electrode 51 (i.e., rearward). When the auxiliary pump electrode 51 and the reference electrode 42 are disposed in this positional relationship, during the period from when the sensor element 101 is heated by the heater 72 until the temperature of the two electrodes stabilizes, a difference in the heating rate between the auxiliary pump electrode 51 and the reference electrode 42 will occur, and the temperature difference between the two electrodes will easily become temporarily large. Therefore, the above-mentioned correction process is of great significance. In addition, generally, since the inner pump electrode 22 of each electrode of the sensor element 101 is located at the front end, the main pump unit 21 releases more oxygen than the auxiliary pump unit 50 and the measuring pump unit 41. Therefore, in most cases, the heater 72 is disposed so that the inner pump electrode 22 of each electrode reaches the highest temperature. Therefore, it can be cited that the reason why the temperature difference between the auxiliary pump electrode 51 and the reference electrode 42 tends to temporarily increase is that the auxiliary pump electrode 51 is positioned closer to the inner pump electrode 22 than the reference electrode 42 in the front-back direction.

[0159] Furthermore, the outer pump electrode 23 is disposed at the front end of the main body of the sensor element 101 (specifically, at the front end relative to the center in the front-rear direction), and the reference electrode 42 is disposed at a position further away from the front end in the front-rear direction than the outer pump electrode 23 (i.e., rearward). When the outer pump electrode 23 and the reference electrode 42 are disposed in this positional relationship, when the temperature difference between the auxiliary pump electrode 51 and the reference electrode 42 temporarily increases, the temperature difference between the outer pump electrode 23 and the reference electrode 42 also tends to temporarily increase. Therefore, with such electrode positional relationship, the greater the deviation between the calculated reference voltage Vrefs and the measured reference voltage Vrefa, the greater the thermoelectric potential contained in the voltage V1 tends to be, thus making it suitable for correction based on the above deviation. In addition, as Figure 1 As shown, it can also be cited that the reason why the temperature difference between the outer pump electrode 23 and the reference electrode 42 tends to temporarily increase is that the outer pump electrode 23 is positioned closer to the inner pump electrode 22 than the reference electrode 42 in the front-back direction.

[0160] In addition, in the above embodiment, the outer pump electrode 23 also serves as: the gas to be measured side electrode and other electrodes (e.g., the outer main pump electrode of the main pump unit 21). The gas to be measured side electrode is part of the sensor unit 83 and is disposed on the outside of the element body of the sensor element 101 in contact with the gas to be measured, but is not limited thereto. The gas to be measured side electrode and the outer pump electrode 23 can be disposed separately on the outside of the element body of the sensor element 101.

[0161] In the above embodiment, although the CPU92 performs pump control processing for startup measurement and then transfers to normal operation control processing, it may also skip the startup pump control processing. In this case, it can start heater control processing first, and then start normal operation control processing. For example, the CPU92 can... Figure 3 , Figure 5 , Figure 12 If the determination in step S110 is positive, normal control processing begins. In this case, by performing the aforementioned correction processing at the beginning of the normal control processing, the impact of the temporarily large thermoelectric potential contained in voltage V1 can be reduced, thereby suppressing the decrease in the detection accuracy of a specific gas concentration.

[0162] Alternatively, the CPU92 can also perform the aforementioned correction process during the auxiliary pump control process, either before the start of the normal control process or during the startup control process. However, since the startup control process does not detect the specific gas concentration based on the pump current Ip2, the necessity for performing the correction process is low.

[0163] The gas sensor of the present invention can be configured as follows.

[0164] The gas sensor of the present invention includes: a sensor element, a pump unit control unit, and a specific gas concentration detection unit.

[0165] The sensor element has the following characteristics:

[0166] The main body of the element includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside to introduce and circulate the gas to be measured.

[0167] The measuring pump unit has an outer measuring electrode disposed on the outside of the main body of the component in a manner that contacts the gas to be measured, and an inner measuring electrode disposed in the measuring chamber of the gas to be measured, and draws oxygen from the periphery of the inner measuring electrode to the periphery of the outer measuring electrode.

[0168] A reference electrode is disposed inside the main body of the element in such a way that it is in contact with a reference gas, which serves as a reference for detecting the concentration of a specific gas, in the gas being measured; and

[0169] The voltage detection sensor unit for measurement detects the voltage for measurement between the reference electrode and the inner measuring electrode.

[0170] During normal operation of the sensor element, the pump unit control unit performs the following: Normal operation pump control processing, which controls the measuring pump unit to draw oxygen from the measuring chamber by ensuring the measuring voltage reaches a normal target value; During startup of the sensor element prior to normal operation, the pump unit performs the following startup pump control processing, which controls the measuring pump unit to draw oxygen from the measuring chamber by ensuring the measuring voltage reaches a startup target value higher than the normal target value.

[0171] The aforementioned specific gas concentration detection unit detects the concentration of a specific gas in the gas being measured based on the measuring pump current flowing through the measuring pump unit via the aforementioned normal measuring pump control process.

[0172] In this gas sensor, during normal operation of the sensor element, a normal operation measurement pump control process is performed: controlling the measurement pump unit to draw oxygen from the measurement chamber by ensuring the measurement voltage reaches a normal target value. Furthermore, the concentration of a specific gas in the measured gas is detected based on the measurement pump current flowing through the measurement pump unit during the normal operation measurement pump control process. Additionally, during startup of the sensor element prior to normal operation, a startup measurement pump control process is performed: controlling the measurement pump unit to draw oxygen from the measurement chamber by ensuring the measurement voltage reaches a startup target value higher than the normal target value. That is, during startup measurement pump control, the target value of the oxygen concentration in the measurement chamber is lower than the value during normal operation, and oxygen is drawn from the measurement chamber. Therefore, compared to the case where normal operation measurement pump control begins from the startup of the sensor element, oxygen present in the measurement chamber before the sensor element is started can be rapidly removed from the measurement chamber. Thus, the ignition time of the sensor element is shortened. Here, oxygen that is already present in the measurement chamber before the sensor element is activated can be exemplified by, for example, oxygen molecules (O2) present in the space inside the measurement chamber, oxygen molecules (O2) attached to the surface of the inner measurement electrode, and oxygen bonded to the constituent material of the inner measurement electrode (causing oxidation of the constituent material).

[0173] The gas sensor of the present invention may include: a heater for heating the main body of the aforementioned element, and a heater control unit for performing heater control processing. The heater control processing involves energizing the heater to heat it up in a manner that the temperature of the heater or the main body of the element, i.e., the temperature of the sensor element, reaches a predetermined target temperature. The pump unit control unit begins the start-up measurement pump control processing when the heater control processing begins and the temperature of the sensor element reaches a predetermined threshold below the target temperature. In this way, the start time of the start-up measurement pump control processing can be appropriately determined based on the sensor element temperature. The predetermined threshold can be a value less than the target temperature. Here, "energizing the heater to heat it up in a manner that the temperature of the sensor element reaches a predetermined target temperature" includes: controlling the heater based on the sensor element temperature itself, and controlling the heater based on a value that can be converted into the sensor element temperature (e.g., the resistance value of the heater, the resistance value of a circuit containing a solid electrolyte, etc.). Examples of the resistance value of a circuit containing a solid electrolyte include, for example, the resistance value of a measuring pump unit, the resistance value of a measuring voltage detection sensor unit, etc.

[0174] In the gas sensor of the present invention, the sensor element includes an adjustment pump unit that adjusts the oxygen concentration in an oxygen concentration adjustment chamber upstream of the measuring chamber, which is located within the gas flow section to be measured. When the sensor element is started, the pump unit control unit performs adjustment pump control processing to activate the adjustment pump unit. If, based on the activation of the adjustment pump unit, it is determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, a switch can be made between the start-up measurement pump control processing and the normal measurement pump control processing. Here, before the sensor element is started, not only the measuring chamber but also the upstream oxygen concentration adjustment chamber is in a state where a large amount of oxygen (not from a specific gas) is present (e.g., atmospheric atmosphere). When the sensor element is started, the pump unit control unit performs adjustment pump unit control processing, thereby removing the oxygen already present in the oxygen concentration adjustment chamber before the sensor element is started. Furthermore, since the oxygen concentration adjustment chamber is connected to the measuring chamber, the oxygen in the measuring chamber can also be removed by activating the adjustment pump unit. Furthermore, as described above, the oxygen concentration adjustment chamber is connected to the measurement chamber, so even when the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, sufficient oxygen can be drawn from the measurement chamber. Therefore, when it is determined, based on the operation of the adjustment pump unit, that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, a switch is made from the start-up measurement pump control process to the normal operation measurement pump control process, thereby enabling an appropriate switch from the start-up measurement pump control process to the normal operation measurement pump control process. Here, "switching from the start-up measurement pump control process to the normal operation measurement pump control process when it is determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized" includes: switching immediately when it is determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, and switching after the time when it is determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized. Examples of the latter include switching after a predetermined time has elapsed after it has been determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized, and other situations where switching is performed only when other conditions besides the determination that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized are met.

[0175] In this case, the aforementioned adjustment pump unit may include: an inner adjustment pump electrode disposed in the oxygen concentration adjustment chamber, and an outer adjustment pump electrode disposed on the outside of the main body of the component, the portion of which is exposed to the gas being measured.

[0176] In the gas sensor of the present invention, which includes an adjustment pump unit, the oxygen concentration adjustment chamber has a first internal cavity and a second internal cavity disposed further downstream than the first internal cavity and further upstream than the measurement chamber. The adjustment pump unit includes a main pump unit for adjusting the oxygen concentration of the first internal cavity and an auxiliary pump unit for adjusting the oxygen concentration of the second internal cavity. The adjustment pump control process includes an auxiliary pump control process that controls the auxiliary pump unit to achieve a target oxygen concentration in the second internal cavity, and a main pump control process that controls the main pump unit to achieve a target current in the auxiliary pump unit through the auxiliary pump control process. The pump unit control unit can switch from the start-up measurement pump control process to the normal operation measurement pump control process when it is determined that the auxiliary pump current has stabilized near the target current. That is, it can be determined that the oxygen concentration in the oxygen concentration adjustment chamber has stabilized when the auxiliary pump current is stable near the target current. In this way, the switching from pump control processing for measurement during startup to pump control processing for measurement during normal operation can be appropriately performed based on the auxiliary pump current.

[0177] In this configuration, the main pump unit may include an inner main pump electrode disposed in the first internal cavity and an outer main pump electrode disposed on the outside of the component body, with a portion exposed to the gas to be measured. The auxiliary pump unit may include an inner auxiliary pump electrode disposed in the second internal cavity and an outer auxiliary pump electrode disposed on the outside of the component body, with a portion exposed to the gas to be measured.

[0178] In the gas sensor of the present invention, the pump unit control unit can switch from the start-up pump control process to the normal operation pump control process when the measuring voltage (i.e., the release measuring voltage) reaches or exceeds a predetermined threshold without controlling the flow of current through the inner measuring electrode and the reference electrode. The release measuring voltage is a value corresponding to the oxygen concentration in the measuring chamber; therefore, by comparing this release measuring voltage with the threshold, it is possible to appropriately determine whether sufficient oxygen has been drawn out of the measuring chamber. Thus, the switch from the start-up pump control process to the normal operation pump control process can be appropriately performed.

[0179] This application takes priority based on Japanese Patent Application No. 2020-204045, filed on December 9, 2020, the entire contents of which are incorporated herein by reference.

[0180] Industrial availability

[0181] This invention relates to a gas sensor that can be used to detect the concentration of specific gases such as NOx in measured gases such as automobile exhaust.

[0182] Symbol Explanation

[0183] 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, 20 First internal cavity, 21 Main pump unit, 22 Inner pump electrode, 22a Top electrode, 22b Bottom electrode, 23 Outer pump electrode, 24 Variable 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, 45 Fourth diffusion rate control unit, 46 Variable power supply, 48 Atmosphere inlet layer. 50 Auxiliary pump unit, 51 Auxiliary pump electrode, 51a Top electrode section, 51b Bottom electrode section, 52 Variable power supply, 60 Fourth diffusion rate control section, 61 Third internal cavity, 70 Heater section, 71 Connecting electrode, 72 Heater, 73 Through hole, 74 Heater insulation layer, 75 Pressure diffusion hole, 76 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 section, 92 CPU, 94 Storage section, 100 Gas sensor, 101, 201 Sensor element.

Claims

1. A gas sensor, comprising a sensor element, a heater control unit, a pump unit control unit, and a specific gas concentration detection unit, wherein, The sensor element has: The main body of the element includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside to introduce and circulate the gas to be measured. The measuring pump unit has an outer measuring electrode disposed on the outside of the main body of the element in a manner that contacts the gas to be measured, and an inner measuring electrode disposed in the measuring chamber of the gas to be measured, and draws oxygen from the periphery of the inner measuring electrode to the periphery of the outer measuring electrode. A reference electrode is disposed inside the element body in such a way that it is in contact with a reference gas, which serves as a reference for detecting the concentration of a specific gas in the gas being measured. A voltage detection sensor unit for measuring voltage, which detects the voltage for measuring voltage between the reference electrode and the inner measuring electrode; The main pump unit adjusts the oxygen concentration in the first internal cavity, wherein the first internal cavity is located in the gas flow section being measured at a position further upstream than the measuring chamber. An auxiliary pump unit has an inner auxiliary pump electrode disposed in a second internal cavity, and adjusts the oxygen concentration of the second internal cavity. The second internal cavity is located in the gas flow section being measured at a position that is further downstream than the first internal cavity and further upstream than the measuring chamber. An auxiliary pump voltage detection sensor unit detects the auxiliary pump voltage between the reference electrode and the inner auxiliary pump electrode; and A heater that heats the main body of the component; The heater control unit performs heater control processing to energize the heater and cause it to heat up. After initiating the heater control process, the pump unit control unit performs a normal operation control process, which includes: a main pump control process for controlling the main pump unit; an auxiliary pump control process for controlling the auxiliary pump unit to achieve a target voltage; and a normal operation measurement pump control process for controlling the measurement pump unit to achieve a normal operation target voltage and drawing oxygen from the measurement chamber. The specific gas concentration detection unit detects the concentration of a specific gas in the gas being measured based on the measuring pump current flowing through the measuring pump unit via the normal measuring pump control process. In the initial stage of the normal control process, the pump unit control unit performs a correction process to adjust the target value of the auxiliary pump voltage to a higher value compared to subsequent periods. In the correction process, the pump unit control unit corrects the target value of the auxiliary pump voltage based on a correction mode predetermined in advance, in a manner that shows a tendency for the correction amount to decrease over time.

2. The gas sensor according to claim 1, wherein, The gas sensor includes a reference voltage detection sensor unit, which detects the reference voltage between the gas-to-be-measured side electrode, which is disposed on the outside of the element body in a manner that contacts the gas to be measured, and the reference electrode. The main pump control process is a process of controlling the main pump unit so that the auxiliary pump current flowing through the auxiliary pump unit reaches the target current through the auxiliary pump control process. In the calibration process, the pump unit control unit, assuming that the main pump current flowing through the main pump unit in the main pump control process is stable, corrects the target value of the auxiliary pump voltage in the calibration process according to the trend that the larger the deviation between the reference voltage derived from the main pump current and the oxygen concentration in the gas being measured around the sensor element, the larger the correction amount will be.

3. The gas sensor according to claim 1, wherein, The pump unit control unit performs the following during normal operation of the sensor element: normal operation control processing; and during startup of the sensor element prior to normal operation: startup pump control processing, which controls the measuring pump unit to draw oxygen from the measuring chamber in such a way that the measuring voltage reaches a startup target value higher than the normal operation target value.

4. The gas sensor according to claim 3, wherein, The heater control process is as follows: the heater is energized to generate heat in a manner that ensures the temperature of the heater or the main body of the component, i.e., the temperature of the sensor element, reaches a predetermined target temperature. When the pump unit control unit starts the heater control process and the temperature of the sensor element reaches or exceeds a predetermined threshold below the target temperature, the start-up measurement pump control process is initiated.

5. The gas sensor according to claim 3, wherein, When the sensor element is activated, the pump unit control unit performs the auxiliary pump control processing and the main pump control processing. The main pump control process is a process of controlling the main pump unit in such a way that the auxiliary pump current flowing through the auxiliary pump unit reaches the target current through the auxiliary pump control process. When the pump unit control unit determines that the auxiliary pump current has stabilized near the target current, it switches from the pump control process for startup measurement to the pump control process for normal operation measurement and begins the normal operation control process.

6. The gas sensor according to claim 3, wherein, When the measurement voltage, i.e. the release measurement voltage, reaches or exceeds a predetermined threshold in a state where current is not controlled to flow through the inner measurement electrode and the reference electrode, the pump unit control unit performs the following: switching from the start-up measurement pump control process to the normal-time measurement pump control process, and begins the normal-time control process.

7. The gas sensor according to claim 3, wherein, The inner measuring electrode comprises at least one of Pt and Rh.

8. The gas sensor according to claim 3, wherein, The volume C of the inner measuring electrode is 8 × 10⁻⁶. -3 mm 3 Above and 32×10 -3 mm 3 the following, The difference ΔV between the target value at startup and the target value under normal conditions is greater than 120mV and less than 200mV.

9. The gas sensor according to claim 3, wherein, When the pump unit control unit determines that the oxygen concentration in the measuring chamber has stabilized based on the operation of the measuring pump unit, it switches from the start-up measuring pump control process to the normal-time measuring pump control process and begins the normal-time control process.

10. The gas sensor according to claim 9, wherein, When the current flowing through the measuring pump unit in the measuring pump unit, which is controlled by the measuring pump during startup, has stabilized, the pump unit control unit determines that the oxygen concentration in the measuring chamber has stabilized.

11. The gas sensor according to claim 10, wherein, The pump unit control unit determines whether the measuring pump current has stabilized based on the first derivative of the measuring pump current flowing through the measuring pump unit through the starting measuring pump control process.

12. The gas sensor according to claim 10, wherein, The pump unit control unit determines whether the measuring pump current has stabilized based on the second derivative of the measuring pump current flowing through the measuring pump unit through the starting measuring pump control process.

Images