Gas sensors and their control methods

Abstract

This invention provides a gas sensor and a control method for the gas sensor, which shortens the ignition time and suppresses cracking of the sensor element. The gas sensor detects the target gas in the measured gas and includes: a sensor element comprising an adjustment pump unit and a measurement pump unit; and a control device comprising a pump control unit, which performs start-up pump control when the sensor element is started, and stable drive pump control during stable drive after the start-up. In the start-up pump control, a start-up voltage of the adjustment pump unit is applied between the inner and outer pump electrodes of the adjustment pump unit, which is higher than the voltage applied in the stable drive pump control. Similarly, a start-up voltage of the measurement pump unit is applied between the inner and outer measurement electrodes of the measurement pump unit, which is higher than the voltage applied in the stable drive pump control but lower than the start-up voltage of the adjustment pump unit.

Description

Technical Field

[0001] This invention relates to a gas sensor and a control method for the gas sensor. Background Technology

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

[0003] As such gas sensors, those using oxygen ion-conducting solid electrolytes such as zirconium oxide (ZrO2) are known. For example, Japanese Patent No. 4903895 discloses a gas sensor comprising: a first oxygen pump unit for adjusting the oxygen concentration of a target gas introduced into a first measuring chamber, and a second oxygen pump unit for detecting the concentration of a specific gas introduced into a second measuring chamber.

[0004] In addition, Japanese Patent No. 4903895 discloses that, before the start of drive control, a preparatory control is performed to supply a constant current to the second oxygen pump unit for a certain period of time in order to reduce the start-up time deviation of the gas sensor.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 4903895 Summary of the Invention

[0008] Gas sensors using solid electrolytes require a period of time from startup to the point where they can measure the concentration of the target gas. This time is called the ignition time.

[0009] With stricter regulations on vehicle emissions, there is a need for vehicle engines to activate their exhaust purification systems within a shorter time after startup. Therefore, this requires gas sensors to have shorter ignition times.

[0010] For example, as described above, Japanese Patent No. 4903895 discloses that, in a gas sensor equipped with a first oxygen pump unit and a second oxygen pump unit, a preparatory control is performed before the start of drive control to supply a constant current to the second oxygen pump unit for a certain period of time, in order to reduce the deviation of the gas sensor's start-up time (ignition time). It also discloses that the voltage applied to the second oxygen pump unit during the preparatory control is greater than the voltage applied to the second oxygen pump unit during drive control.

[0011] However, in gas sensors configured with two or more pump units connected in series starting from the inlet of the gas being measured, as will be explained in detail below, the ignition time sometimes becomes longer.

[0012] Furthermore, it is known that if the voltage applied to the pump unit is too high, the oxygen in the solid electrolyte contained within the pump unit will move, and the strength of the solid electrolyte may sometimes decrease. As a result, cracks may sometimes occur in the internal structure of the sensor element.

[0013] Therefore, the object of the present invention is to provide a gas sensor with a short ignition time and to suppress cracking of the internal structure of the sensor element.

[0014] The inventors of this invention conducted in-depth research and discovered that the following invention prevents the internal structure of the sensor element from cracking and shortens the ignition time.

[0015] This invention includes the following inventions.

[0016] (1) A gas sensor that detects the target gas in the gas to be measured.

[0017] Includes: a sensor element, and a control device for controlling the sensor element.

[0018] The gas sensor is characterized in that...

[0019] The sensor element includes:

[0020] A long, plate-shaped substrate containing a solid electrolyte layer that is oxygen ion conductive;

[0021] The gas flow section to be measured is formed from one end of the base portion in the longitudinal direction;

[0022] An adjustment pump unit includes an inner pump electrode disposed on the inner surface of the gas flow section to be measured, and an outer pump electrode disposed at a position on the base portion corresponding to the inner pump electrode, which is different from the gas flow section to be measured. This adjustment pump unit is used to adjust the oxygen concentration in the gas to be measured to a desired level.

[0023] A measuring pump unit includes an inner measuring electrode disposed at one end of the inner surface of the gas flow section, further away from the base in the longitudinal direction than the inner pump electrode, and an outer measuring electrode disposed at a different position on the base corresponding to the inner measuring electrode, and is used to detect the target gas in the gas being measured.

[0024] The control device includes a pump control unit that controls the operation of the adjustment pump unit and the measuring pump unit.

[0025] The pump control unit performs pump control during startup when the sensor element is started, and stable drive pump control during stable drive of the sensor element after startup.

[0026] In the pump start-up control, a start-up voltage of the adjusting pump unit is applied between the inner and outer pump electrodes of the adjusting pump unit. This voltage is higher than the voltage applied to the adjusting pump unit in the stable drive pump control. Similarly, a start-up voltage of the measuring pump unit is applied between the inner and outer measuring electrodes of the measuring pump unit. This voltage is higher than the voltage applied to the measuring pump unit in the stable drive pump control but lower than the start-up voltage of the adjusting pump unit.

[0027] In the stable drive pump control, the oxygen in the gas to be measured is adjusted to the desired concentration using the adjustment pump unit, and the target gas in the gas to be measured is detected using the measurement pump unit.

[0028] (2) The gas sensor described in (1) above, characterized in that,

[0029] The sensor element also includes an auxiliary pump unit.

[0030] The auxiliary pump unit includes an inner auxiliary pump electrode disposed at one end of the inner surface of the gas flow section, which is further away from the base in the longitudinal direction than the inner pump electrode, and an outer auxiliary pump electrode disposed at a position on the base that corresponds to the inner auxiliary pump electrode, which is different from the gas flow section. It is used to further adjust the oxygen concentration in the gas being measured.

[0031] In the pump start-up control, a start-up voltage of the auxiliary pump unit is also applied between the inner and outer auxiliary pump electrodes of the auxiliary pump unit. This voltage is higher than the voltage applied to the auxiliary pump unit in the stable drive pump control, lower than the start-up voltage of the adjustment pump unit, and higher than the start-up voltage of the measurement pump unit.

[0032] In the stable drive pump control, the oxygen in the gas to be measured is adjusted to the desired concentration using the adjustment pump unit, and the oxygen concentration in the gas to be measured after adjustment using the adjustment pump unit is further adjusted using the auxiliary pump unit. Finally, the gas to be measured is detected using the measuring pump unit.

[0033] (3) The gas sensor according to (1) or (2) above, characterized in that,

[0034] The sensor element includes a heater that heats the substrate.

[0035] The control device includes:

[0036] A heater control unit that controls the heater; and

[0037] The determination unit determines the start and end of the pump control during startup.

[0038] The heater control unit performs heater control as follows: it heats the base portion using the heater, raising the temperature of the base portion from the initial temperature controlled by the pump at startup to a predetermined stable driving temperature, and then maintains the temperature of the base portion at the stable driving temperature.

[0039] When the determination unit determines that the temperature of the base portion has reached the start temperature of the start-up pump control, the pump control unit starts the start-up pump control.

[0040] (4) The gas sensor described in (3) above, characterized in that,

[0041] When the determination unit determines that the pump current flowing through the measuring pump unit in the start-up pump control is below a predetermined threshold, the pump control unit switches from the start-up pump control to the stable drive pump control.

[0042] (5) The gas sensor according to (3) above, characterized in that,

[0043] The sensor element includes a reference electrode, which is configured to contact a reference gas inside the substrate.

[0044] When the determination unit determines that the electromotive force between the inner measuring electrode and the reference electrode in the start-up pump control is above a predetermined threshold, the pump control unit switches from the start-up pump control to the stable drive pump control.

[0045] (6) The gas sensor described in any one of (1) to (5) above, characterized in that,

[0046] The starting voltage of the adjustment pump unit is above 1.5V and below 3.0V.

[0047] (7) The gas sensor described in any one of (1) to (6) above, characterized in that,

[0048] The starting voltage of the pump unit used for measurement is between 0.5V and 1.45V.

[0049] (8) The gas sensor described in any one of (1) to (7) above, characterized in that,

[0050] The voltage ratio of the starting voltage of the adjustment pump unit to the starting voltage of the measurement pump unit is 1.03 or more and 6.00 or less.

[0051] (9) A control method for a gas sensor, the gas sensor being used to detect the target gas in a gas to be measured.

[0052] The control method for the gas sensor is characterized in that...

[0053] The gas sensor includes: a sensor element, and a control device for controlling the sensor element.

[0054] The sensor element includes:

[0055] A long, plate-shaped substrate containing a solid electrolyte layer that is oxygen ion conductive;

[0056] The gas flow section to be measured is formed from one end of the base portion in the longitudinal direction;

[0057] An adjustment pump unit includes an inner pump electrode disposed on the inner surface of the gas flow section to be measured, and an outer pump electrode disposed at a position on the base portion corresponding to the inner pump electrode, which is different from the gas flow section to be measured. This adjustment pump unit is used to adjust the oxygen concentration in the gas to be measured to a desired level.

[0058] A measuring pump unit includes an inner measuring electrode disposed at one end of the inner surface of the gas flow section, further away from the base in the longitudinal direction than the inner pump electrode, and an outer measuring electrode disposed at a different position on the base corresponding to the inner measuring electrode, and is used to detect the target gas in the gas being measured.

[0059] The control device includes a pump control unit that controls the operation of the adjustment pump unit and the measuring pump unit.

[0060] The control method includes: a startup pump control step executed when the sensor element is started, and a subsequent stable drive pump control step.

[0061] In the pump control step during startup, the pump control unit applies a startup voltage of the adjustment pump unit between the inner and outer pump electrodes of the adjustment pump unit. This voltage is higher than the voltage applied to the adjustment pump unit in the stable drive pump control. Conversely, the pump control unit applies a startup voltage of the measurement pump unit between the inner and outer measurement electrodes of the measurement pump unit. This voltage is higher than the voltage applied to the measurement pump unit in the stable drive pump control but lower than the startup voltage of the adjustment pump unit.

[0062] In the stable drive pump control step, the pump control unit uses the adjustment pump unit to adjust the oxygen in the gas to be measured to the desired concentration, and uses the measurement pump unit to detect the target gas in the gas to be measured.

[0063] (10) The control method described in (9) above is characterized in that,

[0064] The sensor element also includes an auxiliary pump unit.

[0065] The auxiliary pump unit includes an inner auxiliary pump electrode disposed at one end of the inner surface of the gas flow section, which is further away from the base in the longitudinal direction than the inner pump electrode, and an outer auxiliary pump electrode disposed at a position on the base that corresponds to the inner auxiliary pump electrode, which is different from the gas flow section. It is used to further adjust the oxygen concentration in the gas being measured.

[0066] In the pump control step during startup, the pump control unit further applies a startup voltage of the auxiliary pump unit between the inner and outer auxiliary pump electrodes. This voltage is higher than the voltage applied to the auxiliary pump unit in the stable drive pump control, lower than the startup voltage of the adjustment pump unit, and higher than the startup voltage of the measurement pump unit.

[0067] In the stable drive pump control step, the pump control unit uses the adjustment pump unit to adjust the oxygen in the gas to be measured to the desired concentration, further adjusts the oxygen concentration in the gas to be measured using the auxiliary pump unit after adjustment by the adjustment pump unit, and uses the measuring pump unit to detect the target gas in the gas to be measured.

[0068] (11) The control method described in (9) or (10) above is characterized in that,

[0069] The sensor element includes a heater that heats the substrate.

[0070] The control device includes:

[0071] A heater control unit that controls the heater; and

[0072] The determination unit determines the start and end of the pump control during startup.

[0073] The control method performs the following heater control steps: the heater control unit uses the heater to heat the substrate, raising the temperature of the substrate from the initial temperature controlled by the pump at startup to a predetermined stable driving temperature, and maintaining the temperature of the substrate at the stable driving temperature.

[0074] Furthermore, when the determination unit determines that the temperature of the substrate reaches the start temperature controlled by the start-up pump, the start-up pump control step is initiated.

[0075] (12) The control method described in (11) above is characterized in that,

[0076] The control method performs the heater control steps.

[0077] Furthermore, when the determination unit determines that the pump current flowing through the measuring pump unit during the start-up pump control is below a predetermined threshold, the start-up pump control step ends and the stable drive pump control step begins.

[0078] (13) The control method described in (11) above is characterized in that,

[0079] The sensor element includes a reference electrode, which is configured to contact a reference gas inside the substrate.

[0080] The control method performs the heater control steps.

[0081] Furthermore, when the determination unit determines that the electromotive force between the inner measuring electrode and the reference electrode in the start-up pump control is above a predetermined threshold, the start-up pump control step ends and the stable drive pump control step begins.

[0082] (14) The control method described in any one of (9) to (13) above is characterized in that,

[0083] The starting voltage of the adjustment pump unit is above 1.5V and below 3.0V.

[0084] (15) The control method described in any one of (9) to (14) above is characterized in that,

[0085] The starting voltage of the pump unit used for measurement is between 0.5V and 1.45V.

[0086] (16) The control method described in any one of (9) to (15) above is characterized in that,

[0087] The voltage ratio of the starting voltage of the adjustment pump unit to the starting voltage of the measurement pump unit is 1.03 or more and 6.00 or less.

[0088] Invention Effects

[0089] According to the present invention, a gas sensor with short ignition time and suppression of cracking in the internal structure of the sensor element can be provided. Attached Figure Description

[0090] Figure 1 This is a schematic diagram of a vertical cross-section along the length of an example of the general configuration of a gas sensor 100.

[0091] Figure 2 This is a block diagram showing the electrical connections between the control device 90 and the pump units 21, 50, 41, sensor units 80, 81, 82, 83, and heater section 70 of the sensor element 101.

[0092] Figure 3 This is a flowchart illustrating an example of the startup process in the gas sensor 100.

[0093] Figure 4 This is a flowchart illustrating a modified example of the startup process in the gas sensor 100.

[0094] Symbol Explanation

[0095] 1…First substrate layer, 2…Second substrate layer, 3…Third substrate layer, 4…First solid electrolyte layer, 5…Isolation layer, 6…Second solid electrolyte layer, 10…Gas inlet, 11…First diffusion rate control unit, 12…Buffer space, 13…Second diffusion rate control unit, 15…Measured gas flow section, 20…First internal cavity, 21…Main pump unit, 22…Inner main pump electrode, 22a…Top electrode section (of the inner main pump electrode), 22b…Bottom electrode section (of the inner main pump electrode), 23…Outer pump electrode, 24…Variable power supply (of the main pump unit), 30…Third diffusion rate control unit, 40…Second internal cavity, 41…Pump unit for current measurement, 42…Reference electrode, 43…Reference gas inlet space, 44…Measurement electrode, 46…Variable power supply (of the measurement pump unit), 47…Switching unit, 48…Atmosphere inlet layer, 50… …Auxiliary pump unit, 51…Auxiliary pump electrode, 51a…(Top electrode of auxiliary pump electrode), 51b…(Bottom electrode of auxiliary pump electrode), 52…(Variable power supply of auxiliary pump unit), 60…Fourth diffusion rate control unit, 61…Third internal cavity, 70…Heater unit, 71…Heater electrode, 72…Heater, 73…Through hole, 74…Heater insulation layer, 75…Pressure relief hole, 76…Heater lead, 77…Heater power supply, 80…Oxygen partial pressure detection sensor unit for main pump control, 81…Oxygen partial pressure detection sensor unit for auxiliary pump control, 82…Electromotive force detection sensor unit, 83…Sensor unit, 90…Control device, 91…Control unit, 92…Heater control unit, 93…Pump control unit, 94…Concentration calculation unit, 95…Determination unit, 100…Gas sensor, 101…Sensor element, 102…Substrate. Detailed Implementation

[0096] The gas sensor of the present invention includes: a sensor element and a control device for controlling the sensor element.

[0097] The gas sensor of the present invention includes sensor elements comprising:

[0098] A long, plate-shaped substrate containing a solid electrolyte layer that is oxygen ion conductive;

[0099] The gas flow section to be measured is formed from one end of the base portion in the longitudinal direction;

[0100] An adjustment pump unit includes an inner pump electrode disposed on the inner surface of the gas flow section to be measured, and an outer pump electrode disposed at a position on the base portion corresponding to the inner pump electrode, which is different from the gas flow section to be measured. This adjustment pump unit is used to adjust the oxygen concentration in the gas to be measured to a desired level.

[0101] A measuring pump unit includes an inner measuring electrode disposed at one end of the inner surface of the gas flow section being measured, which is further away from the base in the length direction than the inner pump electrode, and an outer measuring electrode disposed at a position on the base that is different from the gas flow section being measured, corresponding to the inner measuring electrode, and is used to detect the target gas in the gas being measured.

[0102] The gas sensor of the present invention includes a control device comprising a pump control unit that controls the operation of the adjustment pump unit and the measurement pump unit. The pump control unit is configured to perform startup pump control when the sensor element is started, and stable drive pump control when the sensor element is stably driven after startup.

[0103] The startup time of a gas sensor element refers to the period from when the gas sensor is turned on until the detection (measurement) of the target gas can be performed. It is also called the gas sensor startup time. Conversely, the stable drive time of the sensor element refers to the period during which the detection (measurement) of the target gas can be performed. It is also called the gas sensor stable drive time. After the startup time ends, the stable drive time begins. Typically, the stable drive time is the period from when the gas sensor is turned on until it is turned off, excluding the startup time. The detection of the target gas includes the measurement of its concentration.

[0104] Hereinafter, an example of an embodiment of the gas sensor of the present invention will be described in detail.

[0105] [Overview of the structure of a gas sensor]

[0106] The gas sensor of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a schematic cross-sectional view along the length of an example showing the general configuration of a gas sensor 100 including sensor element 101. Hereinafter, [the following will be described using...] Figure 1 Based on the benchmark, the so-called upper and lower will Figure 1 Set the top side as top, and set the bottom side as bottom. Figure 1 The left side is designated as the front-end side, and the right side is designated as the back-end side.

[0107] Figure 1 In the example of gas sensor 100, an example of a NOx sensor is shown that monitors NOx in the gas to be measured and measures its concentration through sensor element 101.

[0108] In addition, the gas sensor 100 includes a control device 90 for controlling the sensor element 101. Figure 2 This is a block diagram showing the electrical connection between the control device 90 and the sensor element 101.

[0109] (Sensor element)

[0110] The sensor element 101 is a strip-shaped element, including a substrate 102 having a structure formed by stacking multiple oxygen ion-conducting solid electrolyte layers. The strip shape is also called a plate-shaped or strip-shaped structure. The substrate 102 has a structure formed by stacking six layers from bottom to top in the following order: 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, formed from oxygen ion-conducting solid electrolyte layers such as zirconium oxide (ZrO2). The solid electrolyte forming these six layers is a dense and gas-tight solid electrolyte. The six layers can all be of the same thickness, or each layer can have a different thickness. The layers are bonded together by an adhesive layer containing the solid electrolyte, which is included in the substrate 102. Figure 1 The example shown illustrates a layer structure including the six layers described above. However, the layer structure in this invention is not limited to this, and any number of layers and layer structure can be used.

[0111] The sensor element 101 is manufactured by, for example, performing prescribed processing and printing circuit patterns on ceramic green sheets corresponding to each layer, then stacking them and firing them to achieve integration.

[0112] A gas inlet 10 is formed at one end (hereinafter referred to as the front end) of the sensor element 101 along its length and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The gas flow section 15 is formed by connecting the first diffusion rate control section 11, the buffer space 12, the second diffusion rate control section 13, the first internal cavity 20, the third diffusion rate control section 30, the second internal cavity 40, the fourth diffusion rate control section 60, and the third internal cavity 61 adjacent to each other in the order described above, starting from the gas inlet 10.

[0113] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are the internal spaces of the sensor element 101 provided by hollowing out the isolation layer 5. The upper part of the internal space is divided by the lower surface of the second solid electrolyte layer 6, the lower part is divided by the upper surface of the first solid electrolyte layer 4, and the side part is divided by the side of the isolation layer 5.

[0114] The first diffusion velocity control unit 11, the second diffusion velocity control unit 13, and the third diffusion velocity control unit 30 are all configured as two horizontally elongated slits. Figure 1In the diagram, the direction perpendicular to the drawing constitutes the length direction of the opening. The first diffusion rate control unit 11 and the second diffusion rate control unit 13 can both be shaped to apply the desired diffusion resistance, and their shapes are not limited to the slit.

[0115] The fourth diffusion velocity control unit 60 uses a horizontally elongated slit ( Figure 1 The fourth diffusion rate control unit 60 is disposed between the isolation layer 5 and the second solid electrolyte layer 6 in such a way that the opening is formed in the direction perpendicular to the attached drawing (the length direction of the opening). The fourth diffusion rate control unit 60 can be shaped to apply the desired diffusion resistance, and its shape is not limited to the slit.

[0116] Furthermore, a reference gas introduction space 43 is provided at a location further away from the front end than the gas flow section 15, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position defined by the side of the first solid electrolyte layer 4. The reference gas introduction space 43 has an opening at the other end of the sensor element 101 (hereinafter referred to as the rear end). For example, atmospheric air is introduced into the reference gas introduction space 43 as a reference gas for measuring NOx concentration.

[0117] The atmosphere introduction layer 48 is a layer composed of porous alumina, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43. In addition, the atmosphere introduction layer 48 is formed to cover the reference electrode 42.

[0118] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, an atmospheric inlet layer 48 communicating with the reference gas inlet space 43 is provided around it. That is, the reference electrode 42 is configured to contact the reference gas through the porous atmospheric inlet layer 48 and the reference gas inlet space 43. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a Pt and ZrO2 metal-ceramic electrode).

[0119] In the gas flow section 15, the gas inlet 10 is open relative to the external space, and the gas to be measured is introduced from the external space into the sensor element 101 through the gas inlet 10.

[0120] In this embodiment, the gas to be measured flow section 15 is configured such that the gas to be measured is introduced through a gas inlet 10 that is open at the front end face of the sensor element 101. However, the present invention is not limited to this configuration. For example, the gas to be measured flow section 15 may not have a recess in the gas inlet 10. In this case, the first diffusion rate control section 11 is essentially the gas inlet.

[0121] Alternatively, for example, the gas to be measured flow section 15 may have an opening on the side of the base portion 102 along the length direction, communicating with the buffer space 12 or the first internal cavity 20 near the buffer space 12. In this case, the gas to be measured is introduced from the side of the base portion 102 along the length direction through the opening.

[0122] Alternatively, for example, the gas flow section 15 can be configured such that the gas to be measured is introduced through a porous body.

[0123] The first diffusion rate control unit 11 is a part that applies a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10.

[0124] The buffer space 12 is a space provided for guiding the measured gas introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13.

[0125] The second diffusion rate control unit 13 is a part that applies a predetermined diffusion resistance to the gas being measured introduced from the buffer space 12 into the first internal cavity 20.

[0126] The amount of gas to be measured introduced into the first internal cavity 20 only needs to be within a specified range. That is, a specified diffusion resistance needs to be applied to the entire length from the front end of the sensor element 101 to the second diffusion rate control unit 13. For example, the first diffusion rate control unit 11 can be directly connected to the first internal cavity 20, i.e., there is no buffer space 12 and the second diffusion rate control unit 13.

[0127] The buffer space 12 is a space provided to mitigate the impact of pressure changes on the measured value when the pressure of the gas being measured changes.

[0128] When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, it is rapidly introduced into the sensor element 101 from the gas inlet 10 due to the pressure change of the gas in the external space (in the case of automobile exhaust, the pulsation of exhaust pressure). However, the gas to be measured is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure change of the gas to be measured is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure change of the gas to be measured introduced into the first internal space is almost negligible.

[0129] The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust this oxygen partial pressure.

[0130] The sensor element 101 includes an adjustment pump unit, which comprises an inner pump electrode disposed on the inner surface of the gas flow section 15 to be measured, and an outer pump electrode disposed on the base portion 102 at a position different from the gas flow section 15 to be measured, corresponding to the inner pump electrode, for adjusting the oxygen concentration in the gas to be measured to a desired level. In this embodiment, the main pump unit 21 functions as the adjustment pump unit. Additionally, the inner main pump electrode 22 functions as the inner pump electrode, and the outer pump electrode 23 functions as the outer pump electrode. In this embodiment, the sensor element 101 is configured such that, in addition to the main pump unit 21 including the adjustment pump unit, it also includes an auxiliary pump unit 50 for further adjusting the oxygen concentration in the gas to be measured, thereby adjusting the oxygen concentration with higher precision.

[0131] The main pump unit 21 is an electrochemical pump unit including an inner main pump electrode 22 and an outer pump electrode 23. The inner main pump electrode 22 is disposed on the inner surface of the gas flow section 15, and the outer pump electrode 23 is disposed at a position on the substrate 102 different from that of the gas flow section 15. Figure 1 The outer pump electrode 23 is the outer surface of the substrate 102 and corresponds to the inner main pump electrode 22. "Corresponds to the inner main pump electrode 22" means that the outer pump electrode 23 is configured such that a second solid electrolyte layer 6 is sandwiched between it and the inner main pump electrode 22.

[0132] That is, the main pump unit 21 is an electrochemical pump unit consisting of an inner main pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between the inner main pump electrode 22 and the outer pump electrode 23. The inner main pump electrode 22 has a top electrode portion 22a on the lower surface of the second solid electrolyte layer 6, which is disposed on the entire surface 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 it to the external space.

[0133] The inner main pump electrode 22 is formed across the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that define the first internal cavity 20, and the isolation layer 5 that forms the sidewall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that forms the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that forms the bottom surface. Furthermore, side electrode portions (not shown) are formed on the sidewall surface (inner surface) of the isolation layer 5 that forms the two sidewall portions of the first internal cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b, thereby forming a tunnel-shaped structure at the location where the side electrode portions are arranged.

[0134] The inner main pump electrode 22 and the outer pump electrode 23 are porous metal-ceramic electrodes (electrodes in which metal and ceramic components coexist). There are no particular limitations on the ceramic component, but it is preferable to use a solid electrolyte with oxygen ion conductivity, similar to the substrate 102. For example, ZrO2 can be used as the ceramic component.

[0135] The inner main pump electrode 22, which is in contact with the gas being measured, is formed using a material whose reducing ability against NOx in the gas being measured is weakened. The inner main pump electrode 22 may contain a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) and a noble metal (e.g., Au, Ag, etc.) that reduces the catalytic activity of the catalytically active noble metal against the target gas (NOx in this embodiment). In this embodiment, the inner main pump electrode 22 is a porous metal-ceramic electrode containing 1% Au, Pt, and ZrO2.

[0136] The outer pump electrode 23 may contain the aforementioned catalytically active noble metal. Similarly, the reference electrode 42 may also contain the aforementioned catalytically active noble metal. In this embodiment, the outer pump electrode 23 is a porous metal-ceramic electrode made of Pt and ZrO2.

[0137] In the main pump unit 21, the desired pump voltage Vp0 is applied between the inner main pump electrode 22 and the outer pump electrode 23 by the variable power supply 24, so that the pump current Ip0 flows between the inner main pump electrode 22 and the outer pump electrode 23 in the positive or negative direction. Thus, oxygen in the first internal cavity 20 can be drawn out to the external space, or oxygen in the external space can be drawn into the first internal cavity 20.

[0138] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 80 for main pump control, is composed of the inner main 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.

[0139] By measuring the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) within the first internal cavity 20 can be determined. Furthermore, during stable operation of the gas sensor 100, feedback control is applied to the pump voltage Vp0 of the variable power supply 24 to maintain a constant electromotive force V0, thereby controlling the pump current Ip0. Thus, the oxygen concentration within the first internal cavity 20 can be maintained at a predetermined constant value.

[0140] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20, and guides the gas to be measured into the second internal cavity 40.

[0141] The second internal cavity 40 is configured as a space for more precise adjustment of the oxygen partial pressure in the gas to be measured, which is introduced through the third diffusion rate control unit 30. This oxygen partial pressure is adjusted by operating the auxiliary pump unit 50. A configuration without the second internal cavity 40 and the auxiliary pump unit 50 is also possible. From the viewpoint of adjusting the oxygen partial pressure with precision, the presence of the second internal cavity 40 and the auxiliary pump unit 50 is more preferable.

[0142] In the second internal cavity 40, the oxygen concentration (oxygen partial pressure) of the gas to be measured, which has been pre-adjusted in the first internal cavity 20 and then introduced through the third diffusion rate control unit, is further adjusted using the auxiliary pump unit 50. This allows the oxygen concentration within the second internal cavity 40 to be kept constant with high precision, thus enabling the high-precision measurement of NOx concentration in such a gas sensor 100.

[0143] The auxiliary pump unit 50 is an electrochemical pump unit including an inner auxiliary pump electrode (auxiliary pump electrode 51 in this embodiment) and an outer auxiliary pump electrode. The inner auxiliary pump electrode is disposed on the inner surface of the gas flow section 15, at a position further away from the front end of the base portion 102 in the length direction than the inner pump electrode (inner main pump electrode 22 in this embodiment). The outer auxiliary pump electrode is disposed at a position on the base portion 102 different from that of the gas flow section 15. Figure 1 The outer surface of the substrate 102 (in the middle) corresponds to the inner auxiliary pump electrode. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the substrate 102 also functions as an outer auxiliary pump electrode. "Corresponding to the inner auxiliary pump electrode" means that the outer pump electrode 23 is configured such that a second solid electrolyte layer 6 is sandwiched between it and the auxiliary pump electrode 51.

[0144] That is, 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 that is generally disposed on the lower surface of the second solid electrolyte layer 6 and facing the second internal cavity 40.

[0145] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner main pump electrode 22 previously disposed in the first internal cavity 20. That is, a top electrode portion 51a is formed on the lower surface of the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the upper surface of the first solid electrolyte layer 4 constituting 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 respectively formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40, thereby forming a tunnel-shaped structure.

[0146] Furthermore, the auxiliary pump electrode 51, like the inner main pump electrode 22, is formed using a material that weakens the reducing ability for NOx components in the gas being measured. The auxiliary pump electrode 51, like the inner main pump electrode 22, comprises a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) and a noble metal (e.g., Au, Ag, etc.) that reduces the catalytic activity of the catalytically active noble metal for the target gas (NOx in this embodiment). In this embodiment, the auxiliary pump electrode 51, like the inner main pump electrode 22, is a porous metal-ceramic electrode composed of Pt and ZrO2 containing 1% Au.

[0147] In the auxiliary pump unit 50, a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23 using a variable power supply 52. ​​This allows oxygen in the atmosphere inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn from the external space into the second internal cavity 40.

[0148] 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.

[0149] It should be noted that during stable operation of the gas sensor 100, the auxiliary pump unit 50 pumps using a variable power supply 52, which controls the voltage based on the electromotive force V1 detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. As a result, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a relatively low partial pressure that has no substantial impact on NOx measurement.

[0150] Additionally, the pump current Ip1 is used to control the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and its electromotive force V0 is controlled to ensure that the gradient of oxygen partial pressure in the gas to be measured, introduced from the third diffusion rate control unit 30 into the second internal cavity 40, remains constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm due to the action of the main pump unit 21 and the auxiliary pump unit 50.

[0151] The fourth diffusion rate control unit 60 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled to be lower in the second internal cavity 40 by the operation of the auxiliary pump unit 50, and guides the gas to be measured to the third internal cavity 61.

[0152] The third internal cavity 61 is configured as a space for measuring the concentration of nitrogen oxides (NOx) in the gas to be measured, which is introduced through the fourth diffusion rate control unit 60. The NOx concentration is measured by the operation of the measuring pump unit 41.

[0153] The measuring pump unit 41 is an electrochemical pump unit including an inner measuring electrode (measuring electrode 44 in this embodiment) and an outer measuring electrode. The inner measuring electrode is disposed on the inner surface of the gas flow section 15, at a position further away from the base portion 102 in the longitudinal direction than the inner pump electrode (inner main pump electrode 22 in this embodiment). The outer measuring electrode is disposed on the base portion 102 at a position different from the gas flow section 15 and corresponds to the inner measuring electrode. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the base portion 102 also functions as an outer measuring electrode. "Corresponds to the inner measuring electrode" means that the outer pump electrode 23 is configured such that a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4 are sandwiched between it and the measuring electrode 44. In this embodiment, the measuring electrode 44 is disposed on the inner surface of the gas flow section 15, at a position further away from the base portion 102 in the longitudinal direction than the inner main pump electrode 22 and the auxiliary pump electrode 51.

[0154] That is, the measuring pump unit 41 is an electrochemical pump unit composed of a measuring electrode 44, 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), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4, facing the third internal cavity 61. The measuring pump unit 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61.

[0155] The measuring electrode 44 is a porous metal-ceramic electrode. The measuring electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere within the third internal cavity 61. The measuring electrode 44 is an electrode containing at least one catalytically active noble metal (e.g., Pt, Rh, Ir, Ru, Pd). Preferably, it does not contain noble metals (e.g., Au, Ag, etc.) that would reduce the catalytic activity of the catalytically active noble metal for the target gas (NOx in this embodiment). In this embodiment, the measuring electrode 44 is a porous metal-ceramic electrode made of Pt, Rh, and ZrO2.

[0156] In addition, to detect the oxygen partial pressure around the measuring electrode 44, an electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 82 for measuring pump control, is constructed from the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. During stable operation of the gas sensor 100, the variable power supply 46 is controlled based on the electromotive force V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control.

[0157] 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 pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the control voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control remains constant. The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured; therefore, the concentration of nitrogen oxides in the gas to be measured is calculated using the measuring pump current Ip2 in the measuring pump unit 41.

[0158] 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 Vref can be obtained by using the sensor unit 83, and the oxygen partial pressure in the gas to be measured outside the sensor can be detected by using the electromotive force Vref.

[0159] In addition, the sensor element 101 also includes a heater section 70, which is responsible for heating and maintaining the temperature of the sensor element 101 to improve the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes: a heater electrode 71, a heater 72, a heater lead 76, a through hole 73, a heater insulation layer 74, and a pressure relief hole 75.

[0160] The heater electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to the heater power supply 77, which is an external power source, power can be supplied to the heater section 70 from the outside.

[0161] The heater 72 is a resistive element formed by sandwiching the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater electrode 71 via the heater lead 76 and the through hole 73. It is powered from the outside through the heater electrode 71 to generate heat and heat and keep the solid electrolyte forming the sensor element 101 warm. The heater lead 76 is connected to the heater 72 and extends to the rear end of the sensor element 101 in the longitudinal direction.

[0162] Furthermore, the heater 72 is embedded throughout the entire area from the first internal cavity 20 to the third internal cavity 61, enabling the sensor element 101 to be adjusted to the temperature at which the solid electrolyte is activated. The temperature can be adjusted in a manner that allows the main pump unit 21, auxiliary pump unit 50, and measuring pump unit 41 to operate. It is not necessary to adjust the entire area to the same temperature; a temperature distribution can be achieved within the sensor element 101.

[0163] In the sensor element 101 of this embodiment, the heater 72 is embedded in the substrate 102, but it is not limited to this method. The heater 72 is configured to heat the substrate 102. That is, the heater 72 can heat the sensor element 101 to the degree that exhibits the oxygen ion conductivity required for the operation of the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41. For example, it can be embedded in the substrate 102 as in this embodiment. Alternatively, for example, the heater portion 70 can be formed as a separate heater substrate from the substrate 102 and disposed adjacent to the substrate 102.

[0164] The heater insulation layer 74 is an insulation layer formed on the upper and lower surfaces of the heater 72 and the heater lead 76 using an insulator such as alumina. 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 the heater lead 76, and electrical insulation between the third substrate layer 3 and the heater 72 and the heater lead 76.

[0165] The pressure relief hole 75 is formed to penetrate the third substrate layer 3, thereby connecting the heater insulation layer 74 and the reference gas introduction space 43. The pressure relief hole 75 can mitigate the increase in internal pressure associated with a temperature rise within the heater insulation layer 74. It should be noted that a configuration without the pressure relief hole 75 is also possible.

[0166] The aforementioned sensor element 101 is assembled in the gas sensor 100 such that the front end of the sensor element 101 is in contact with the gas to be measured and the rear end of the sensor element 101 is in contact with the reference gas.

[0167] (Control device)

[0168] The gas sensor 100 of this embodiment includes: the sensor element 101 described above, and a control device 90 for controlling the sensor element 101. In the gas sensor 100, each electrode 22, 23, 51, 44, 42 of the sensor element 101 is electrically connected to the control device 90 via leads (not shown). Figure 2This is a block diagram showing the electrical connections between the control device 90 and the pump units 21, 50, 41, sensor units 80, 81, 82, 83, and heater unit 70 of the sensor element 101. The control device 90 includes the aforementioned variable power supplies 24, 46, 52, heater power supply 77, and control unit 91. Control unit 91 includes a heater control unit 92, a pump control unit 93, a concentration calculation unit 94, and a determination unit 95.

[0169] The control unit 91 is implemented using a general-purpose or dedicated computer, and utilizes the CPU, memory, etc., mounted on the computer to perform the functions of the heater control unit 92, pump control unit 93, concentration calculation unit 94, and determination unit 95. It should be noted that when the gas sensor 100 measures NOx contained in the exhaust gas from the automobile engine, and the sensor element 101 is installed in the exhaust path, some or all of the functions of the control device 90 (especially the control unit 91) can be implemented by the ECU (Electronic Control Unit) mounted on the automobile.

[0170] The control unit 91 is configured to acquire the electromotive forces (V0, V1, V2, Vref) in each sensor unit 80, 81, 82, 83 of the sensor element 101, the pump currents (Ip0, Ip1, Ip2) in each pump unit 21, 50, 41, and the heater voltage Vh and heater current Ih in the heater unit 70. Furthermore, the control unit 91 is configured to output control signals to the variable power supplies 24, 52, 46 and the heater power supply 77.

[0171] The heater control unit 92 is configured to control the heater in such a way that it heats the base portion 102 using the heater 72, raising the temperature of the base portion 102 (further than the initial temperature controlled by the pump during startup, described later) to a predetermined stable driving temperature, and then maintains the temperature of the base portion 102 at the predetermined stable driving temperature. The temperature of the base portion 102 is approximately the same as the temperature of the sensor element 101. For example, the temperature of the base portion 102 (or the sensor element 101) itself can be controlled to be maintained at the stable driving temperature. Furthermore, by controlling the heater 72 to be maintained at a predetermined temperature, the base portion 102 can be maintained at the stable driving temperature. In this embodiment, the heater control unit 92 heats the heater 72 and maintains the temperature of the heater 72 at a predetermined temperature (referred to as the set temperature Th). SET ).

[0172] Various known control methods can be used to heat the heater 72. For example, a certain voltage can be applied to the heater 72 for heating. The output of the heater power supply 77 can also be controlled based on the resistance value of the heater 72. Alternatively, the output of the heater power supply 77 can be controlled based on at least one of the resistance values ​​in the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41.

[0173] For example, the heater control unit 92 performs feedback control on the control signal output to the heater power supply 77 based on the heater resistance value Rh (=Vh / Ih) calculated according to the heater voltage Vh and heater current Ih in the heater 72, so that the heater 72 reaches the target temperature.

[0174] The pump control unit 93 is configured to control the operation of the adjustment pump unit (main pump unit 21 in this embodiment) and the measurement pump unit 41. In this embodiment, the pump control unit 93 also controls the operation of the auxiliary pump unit 50.

[0175] The pump control unit 93 is configured to perform start-up pump control when the sensor element 101 (gas sensor 100) is started, and stable drive pump control when the sensor element 101 (gas sensor 100) is stably driven after the start-up.

[0176] As described above, the startup time of sensor element 101 refers to the period from when gas sensor 100 is turned on until the detection (measurement) of the target gas can be performed. It is also called the startup time of gas sensor 100. Furthermore, the stable driving time of sensor element 101 refers to the period during which the detection (measurement) of the target gas can be performed. It is also called the stable driving time of gas sensor 100. After the startup time ends, the stable driving time begins. Generally, the stable driving time is the period from when the gas sensor is turned on until it is turned off, excluding the startup time.

[0177] That is, the start-up of sensor element 101 (gas sensor 100) refers to the period from when heater control unit 92 starts heating heater 72 until the solid electrolyte forming sensor element 101 is activated by the heating of heater 72, and pump control unit 93 is able to measure the target gas. Furthermore, stable drive refers to the state where heater control unit 92 maintains the temperature of heater 72 (or the temperature of sensor element 101) at the desired temperature, and pump control unit 93 measures the target gas.

[0178] First, the stable drive pump control executed during stable operation after the gas sensor 100 is activated will be described. The stable drive pump control involves adjusting the oxygen concentration in the gas to be measured to the desired level using the adjustment pump unit (main pump unit 21 in this embodiment), and then using the measurement pump unit 41 to detect the target gas in the gas being measured. In this embodiment, in addition to the main pump unit 21, an auxiliary pump unit 50 is also used for adjusting the oxygen concentration in the gas being measured.

[0179] In the stable drive pump control, the pump control unit 93 keeps the electromotive force V0 in the oxygen partial pressure detection sensor unit 80 for main pump control at a constant value (referred to as the set value V0). SET The pump voltage Vp0 of the variable power supply 24 in the main pump unit 21 is controlled by feedback. The pump voltage Vp0 varies in direction and value depending on the oxygen concentration in the gas being measured, the concentration of reducing gases such as hydrocarbons (HC), the configuration of the gas sensor 100, and its intended use; however, as an absolute value, it can be in the range of approximately 1V or less. The electromotive force V0 represents the oxygen partial pressure near the inner main pump electrode 22; therefore, keeping the electromotive force V0 constant means keeping the oxygen partial pressure near the inner main pump electrode 22 constant. As a result, the pump current Ip0 in the main pump unit 21 changes accordingly to the oxygen concentration in the gas being measured.

[0180] The oxygen partial pressure in the gas being measured is higher than the set value V0. SET Under a given oxygen partial pressure, oxygen is discharged from the first internal cavity 20 in the main pump unit 21. On the other hand, if the oxygen partial pressure in the gas being measured is lower than the set value V0... SET Under certain oxygen partial pressure conditions (e.g., when hydrocarbons such as HC are present), oxygen is drawn into the first internal cavity 20 from the space outside the sensor element 101 in the main pump unit 21. Therefore, the pump current Ip0 can take all values, both positive and negative.

[0181] Pump control unit 93 keeps the electromotive force V1 in the oxygen partial pressure detection sensor unit 81 for auxiliary pump control at a constant value (referred to as set value V1). SET The pump voltage Vp1 of the variable power supply 52 in the auxiliary pump unit 50 is controlled by feedback in a manner that allows for feedback control. The pump voltage Vp1 can vary depending on the configuration and intended use of the gas sensor 100, and can be in the range of approximately 0.8V or less. The electromotive force V1 represents the partial pressure of oxygen near the auxiliary pump electrode 51; therefore, keeping the electromotive force V1 constant means keeping the partial pressure of oxygen near the auxiliary pump electrode 51 constant. (Set value V1) SET The setting is: the oxygen partial pressure (oxygen concentration) in the atmosphere within the second internal cavity 40 is a low partial pressure (oxygen concentration) that has no substantial effect on the determination of NOx.

[0182] In addition, at the same time, the pump current Ip1 in the auxiliary pump unit 50 is kept constant (referred to as the set value Ip1). SET The electromotive force V0 is set based on the pump current Ip1 using the following method. SET Feedback control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and its electromotive force V0 is controlled to a set value V0 based on the pump current Ip1. SET This ensures that the gradient of the oxygen partial pressure in the gas being measured, introduced from the third diffusion rate control unit 30 into the second internal cavity 40, remains constant. (Set value V0) SET The oxygen concentration in the first internal cavity 20 is set to a predetermined low concentration. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm through the operation of the main pump unit 21 and the auxiliary pump unit 50. That is, it is assumed that the oxygen concentration in the gas to be measured introduced from the fourth diffusion rate control unit 60 into the third internal cavity 61 is maintained at a constant value of approximately 0.001 ppm.

[0183] The pump control unit 93 ensures that the electromotive force V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control is a constant value (referred to as the target value V2). SET The pump voltage Vp2 of the variable power supply 46 in the measuring pump unit 41 is controlled by feedback. The pump voltage Vp2 varies depending on the concentration of the target gas in the measured gas (NOx concentration in this embodiment), the configuration of the gas sensor 100, and its intended use, and can be approximately 0.2V to 0.4V. At the measuring electrode 44, nitrogen oxides in the measured gas are reduced (2NO→N2+O2) to generate oxygen. The pump control unit 93 pumps the generated oxygen out using the measuring pump unit 41, so that the electromotive force V2 reaches the set value V2. SET Setting value V2 SET It can be set to a value that substantially decomposes all NOx at the measuring electrode 44. This is achieved by setting the value V2 in this way. SETThe system is configured so that virtually all NOx in the gas to be measured is detected as the measuring pump current Ip2 in the measuring pump unit 41. Specifically, the measuring pump current Ip2 includes: the current from the low concentration of oxygen controlled by the main pump unit 21 and the auxiliary pump unit 50, and the current from the oxygen originating from NOx in the gas to be measured. By maintaining a constant oxygen level in the gas to be measured reaching the measuring electrode 44 as described above, the measuring pump current Ip2 can accurately measure the oxygen originating from NOx in the gas to be measured. As a result, the measuring pump current Ip2 can be detected as a current value corresponding to the NOx concentration.

[0184] It should be noted that the setting value V0 SET Ip1 SET V1 SET and V2 SET The control values ​​(target values) are stored as control values ​​in the memory of the control unit 91, which functions as the pump control unit 93. Based on these control values, the CPU of the control unit 91, which functions as the pump control unit 93, performs stable drive pump control for the gas sensor 100.

[0185] Next, the start-up pump control performed when the gas sensor 100 is started will be described. The pump control unit 93 performs start-up pump control during the period included when the gas sensor 100 is started. The start-up pump control may start simultaneously with the start-up of the gas sensor 100, or it may start later after the gas sensor 100 is started. In addition, after the pump control unit 93 ends the start-up pump control, it enters the stable drive pump control.

[0186] The pump control during startup is as follows: a startup voltage of the adjustment pump unit is applied between the inner pump electrode (inner main pump electrode 22) and the outer pump electrode (outer pump electrode 23) of the adjustment pump unit (main pump unit 21 in this embodiment), which is higher than the voltage applied to the adjustment pump unit in the stable drive pump control; and a startup voltage of the measurement pump unit 41 is applied between the inner measurement electrode (measurement electrode 44) and the outer measurement electrode (outer pump electrode 23) of the measurement pump unit 41, which is higher than the voltage applied to the measurement pump unit in the stable drive pump control and lower than the startup voltage of the adjustment pump unit.

[0187] That is, in the pump control during startup of this embodiment, the pump control unit 93 applies the startup voltage of the main pump unit 21 (referred to as the main pump startup voltage Vp0) between the inner main pump electrode 22 and the outer pump electrode 23 of the main pump unit 21. INITIALThis voltage is higher than the pump voltage Vp0 applied in the stable drive pump control, and the start-up voltage of the measuring pump unit 41 (referred to as the starting voltage Vp2 of the measuring pump) is applied between the measuring electrode 44 and the outer pump electrode 23 of the measuring pump unit 41. INITIAL This voltage is higher than the pump voltage Vp2 applied during stable drive and higher than the main pump startup voltage Vp0. INITIAL Low.

[0188] Furthermore, during pump control at startup, the pump control unit 93 may apply a startup voltage of the auxiliary pump unit 50 between the inner auxiliary pump electrode (auxiliary pump electrode 51) and the outer auxiliary pump electrode (outer pump electrode 23). This voltage is higher than the voltage applied to the auxiliary pump unit during the stable drive pump control, and is lower than the startup voltage of the adjustment pump unit, but higher than the startup voltage of the measurement pump unit.

[0189] That is, during pump control at startup, the pump control unit 93 can apply the startup voltage of the auxiliary pump unit 50 (referred to as the auxiliary pump startup voltage Vp1) between the auxiliary pump electrode 51 and the outer pump electrode 23. INITIAL This voltage is higher than the pump voltage Vp1 applied to the auxiliary pump unit 50 in the stable drive pump control, and is also higher than the starting voltage of the main pump unit 21 (main pump starting voltage Vp0). INITIAL Below, and compared to the starting voltage of the measuring pump unit 41 (the starting voltage of the measuring pump Vp2) INITIAL High. It should be noted that the starting voltage of the auxiliary pump unit 50 (auxiliary pump starting voltage Vp1) is high. INITIAL The voltage is lower than the starting voltage of the main pump unit 21 (main pump starting voltage Vp0). INITIAL In the case of ), the starting voltage of the auxiliary pump unit 50 (the starting voltage of the auxiliary pump Vp1) INITIAL ) and the starting voltage of the measuring pump unit 41 (the starting voltage of the measuring pump Vp2) INITIAL They can be equal.

[0190] Before the gas sensor 100 is activated, the gas flow section 15 contains the gas atmosphere surrounding the gas sensor 100 (e.g., atmospheric atmosphere). Therefore, before the gas sensor 100 is activated, the oxygen concentration in the third internal cavity 61 is usually higher than the oxygen concentration during stable operation of the gas sensor 100. That is, the area near the measuring electrode 44 has more oxygen compared to stable operation. When the gas sensor 100 is activated under such conditions, more oxygen needs to be drawn out of the measuring pump unit 41 during activation compared to stable operation.

[0191] The gas sensor 100 requires a period of time from startup to the point where the concentration of the target gas can be measured. This required time is called the ignition time. The ignition time is the time required from when the heater 72 of the gas sensor 100 is turned on until the detection (measurement) of the target gas can be performed. In other words, the ignition time is the time required from when the heater 72 starts heating until the oxygen concentration in the target gas in the gas flow section 15 is controlled to a stable driving state by the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41.

[0192] During startup pump control, a higher startup voltage than that applied during stable drive pump control is applied to the main pump unit 21, auxiliary pump unit 50, and measuring pump unit 41. As a result, larger pump currents Ip0, Ip1, and Ip2 can flow through each pump unit 21, 50, and 41, thus efficiently extracting oxygen present in the measured gas flow section 15 before the gas sensor 100 is started, as well as oxygen continuously flowing in from the gas inlet 10. Therefore, the oxygen concentration in the measured gas within the measured gas flow section 15 can be controlled to the stable drive concentration earlier. That is, the oxygen concentration in the measured gas reaching the measuring electrode 44 can be controlled to the stable drive concentration earlier. As a result, the ignition time can be shortened.

[0193] In sensor element 101, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are connected in series in this order from the front end of sensor element 101. The main pump unit 21 draws oxygen from the first internal cavity 20, the auxiliary pump unit 50 draws oxygen from the second internal cavity 40, and the measuring pump unit 41 draws oxygen from the third internal cavity. In this sensor element 101, when a pump voltage is applied to each pump unit 21, 50, 41, the oxygen concentration is highest in the first internal cavity 20 closest to the gas inlet 10, and decreases further away from the gas inlet 10, i.e., in the order of the second internal cavity 40 and the third internal cavity 61.

[0194] When the oxygen concentration difference between the first internal cavity 20 and / or the second internal cavity and the third internal cavity 61 is large, a small amount of oxygen will flow into the third internal cavity 61 due to the concentration gradient caused by this oxygen concentration difference. As a result, it can be seen that sometimes it takes time for the oxygen concentration in the third internal cavity 61, that is, the oxygen concentration near the measuring electrode 44, to reach the concentration required for stable driving.

[0195] According to the inventors' research, by applying a higher main pump start-up voltage Vp0 to the main pump unit 21 INITIALThis allows for faster extraction of oxygen from the first internal cavity 20, which is closest to the gas inlet 10. In other words, it allows the oxygen concentration in the first internal cavity 20 to decrease more quickly. Consequently, it reduces the oxygen concentration difference between the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, thereby reducing oxygen inflow into the third internal cavity 61 due to the concentration gradient. Therefore, it has been found that the time required for the oxygen concentration near the measuring electrode 44 to reach a stable driving concentration can be shortened.

[0196] In each pump unit 21, 50, and 41, the higher the applied pump voltage, the greater the pump current. Therefore, the higher the applied pump voltage, the earlier the oxygen in the gas flow section 15 can be drawn out. However, it has been found that if the pump voltage applied to the pump unit is too high, cracks may sometimes occur in the internal structure of the sensor element 101.

[0197] When a pump voltage is applied to the pump unit, oxygen in the gas to be measured is drawn out from the internal cavity corresponding to that pump voltage. However, if the pump voltage is too high, sometimes the pump voltage applied to the pump unit is higher than the pump voltage required to draw out virtually all the oxygen in the gas to be measured. In this case, oxygen in the solid electrolyte (e.g., zirconium oxide ZrO2) contained in the pump unit migrates. As a result, an oxygen-deficient region can form in the solid electrolyte. This phenomenon is also called blackening. The oxygen-deficient region in the solid electrolyte is less intense than that in a typical solid electrolyte. As a result, it is believed that cracking sometimes occurs in the internal structure of the sensor element 101, particularly in the oxygen-deficient region of the solid electrolyte.

[0198] As described above, the oxygen concentration is highest in the first internal cavity 20 closest to the gas inlet 10, and decreases further away from the gas inlet 10, in the order of the second internal cavity 40 and the third internal cavity 61. Therefore, the amount of oxygen that each pump unit 21, 50, and 41 can draw from each internal cavity 20, 40, and 61 decreases sequentially from the main pump unit 21, the auxiliary pump unit 50, and the measuring pump unit 41. The inventors of this invention discovered that during pump control at startup, the starting voltage Vp2 applied to the measuring pump unit 41, which draws out less oxygen, is... INITIAL The voltage applied during stable drive pump control is higher than the voltage Vp0 applied during main pump startup. INITIAL The small size can suppress the movement of oxygen that constitutes the solid electrolyte. As a result, blackening can be suppressed, thereby suppressing cracking of the internal structure of the sensor element 101.

[0199] During pump startup control, a higher pump startup voltage Vp0 is applied to the main pump unit 21, which draws oxygen from the first internal cavity 20 closest to the gas inlet 10, than the pump voltage Vp0 applied to the main pump unit 21 during stable drive pump control. INITIAL That's all (Vp0) INITIAL >Vp0 in the stable drive pump control). The specific voltage value can be appropriately set according to the desired ignition time and the intended use of the gas sensor 100.

[0200] Voltage Vp0 when main pump starts INITIAL The lower limit value should be greater than the pump voltage Vp0 applied in the stable drive pump control. Accordingly, oxygen can be extracted from the first internal cavity 20 faster than with stable drive pump control. The pump voltage Vp0 applied in the stable drive pump control, as described above, is approximately 1V at its maximum. The voltage Vp0 when the main pump starts... INITIAL The lower limit can be, for example, above 1.1V, above 1.2V, above 1.5V, above 1.8V, etc. The main pump starts at voltage Vp0. INITIAL The upper limit can be set at a range where the oxygen atoms in the solid electrolyte itself will not move. For example, it could be below 3.0V, below 2.8V, below 2.5V, etc. The main pump starts at voltage Vp0. INITIAL It can be, for example, above 1.5V and below 3.0V.

[0201] During pump start-up, the pump voltage Vp2 applied to the measuring pump unit 41, which draws oxygen from the third internal cavity 61 where the oxygen concentration is relatively low, is higher than that applied to the measuring pump unit 41 during stable drive pump control and higher than the main pump start-up voltage Vp0. INITIAL Small measurement of pump start-up voltage Vp2 INITIAL That's all (Vp0) INITIAL >Vp2 INITIAL >Vp2 in the stable drive pump control). The specific value can be set appropriately according to the desired ignition time and the intended use of the gas sensor 100.

[0202] The voltage Vp2 of the pump during startup was measured. INITIAL The lower limit value should be greater than the pump voltage Vp2 applied in the stable drive pump control. Based on this, oxygen can be extracted from the third internal cavity 61 faster than with stable drive pump control. The pump voltage Vp2 applied in the stable drive pump control, as described above, is approximately 0.3V at most. The voltage Vp2 is measured when the pump starts. INITIAL The lower limit can be, for example, above 0.4V, above 0.5V, above 0.6V, above 0.7V, etc. The voltage Vp2 is measured when the pump starts. INITIALThe upper limit can be set at a range where the oxygen atoms in the solid electrolyte itself will not move. For example, this could be below 1.5V, 1.45V, 1.3V, or 1.2V. However, it must be lower than the main pump startup voltage Vp0. INITIAL The voltage Vp2 during pump startup was measured. INITIAL It can be, for example, above 0.5V and below 1.45V.

[0203] In this embodiment, an auxiliary pump unit 50 is formed between the main pump unit 21 and the measuring pump unit 41. During pump control at startup, an auxiliary pump startup voltage Vp1 is applied to the auxiliary pump unit 50, which draws oxygen from the second internal cavity 40. INITIAL The voltage applied to the auxiliary pump unit 50 in the stable drive pump control is higher than the voltage Vp0 when the main pump starts. INITIAL The following is a comparison of the voltage Vp2 when the pump is started. INITIAL The voltage should be high. That is, the voltage Vp0 when the main pump starts. INITIAL Voltage Vp1 when auxiliary pump starts INITIAL and the voltage Vp2 when the pump is started. INITIAL The relationship is Vp0 INITIAL =Vp1 INITIAL >Vp2 INITIAL Vp0 INITIAL >Vp1 INITIAL >Vp2 INITIAL That's fine. Alternatively, you can use Vp0. INITIAL >Vp1 INITIAL =Vp2 INITIAL The specific value can be set appropriately according to the desired ignition time and the intended use of the gas sensor 100.

[0204] Voltage Vp1 when auxiliary pump starts INITIAL The lower limit value should be greater than the pump voltage Vp1 applied in the stable drive pump control. Based on this, oxygen can be extracted from the second internal cavity 40 faster than with stable drive pump control. The pump voltage Vp1 applied in the stable drive pump control, as described above, is approximately 0.8V at its maximum. The auxiliary pump starts at voltage Vp1... INITIAL The lower limit value is conditional upon being higher than the pump voltage Vp1 applied in the stable drive pump control, for example, it can be 0.5V or higher, 0.6V or higher, 0.8V or higher, 0.9V or higher, 1.0V or higher, etc. Preferably, the voltage Vp2 used to measure the pump startup is selected. INITIAL That's all. The voltage Vp1 when the auxiliary pump starts is... INITIAL The upper limit can be defined as the range where the oxygen atoms in the solid electrolyte itself will not move. For example, it can be below 3.0V, below 2.8V, below 2.5V, below 2.0V, below 1.5V, etc. Preferably, the voltage Vp0 at the start of the main pump is [value missing].INITIAL The following is the voltage Vp1 when the auxiliary pump starts. INITIAL It can be, for example, above 0.6V and below 3.0V.

[0205] In the case of three or more pump units connected in series, the starting voltage applied in the pump control during startup can be gradually reduced in stages from the pump unit closest to the gas inlet 10 to the pump unit furthest from the gas inlet 10.

[0206] The first start-up voltage (main pump start-up voltage Vp0) applied to the main pump unit 21 closest to the gas inlet 10 INITIAL The second startup voltage (startup voltage Vp2 of the measuring pump) applied relative to the measuring pump unit 41 furthest from the gas inlet 10 INITIAL The ratio of (Vp0) INITIAL / Vp2 INITIAL The value can be appropriately determined within a range greater than 1. For example, it can be between 1.03 and 6.00.

[0207] It should be noted that the voltage Vp0 when the main pump starts is... INITIAL Voltage Vp1 when auxiliary pump starts INITIAL and the voltage Vp2 when the pump is started. INITIAL The control values ​​(set values) are stored as control values ​​in the memory of the control unit 91, which functions as the pump control unit 93. Based on these control values, the CPU of the control unit 91, which functions as the pump control unit 93, performs pump control when the gas sensor 100 is started.

[0208] The concentration calculation unit 94 is configured to calculate and output the NOx concentration in the gas being measured.

[0209] The concentration calculation unit 94 acquires the pump current Ip2 in the measuring pump unit 41, and calculates the NOx concentration in the measured gas based on a pre-stored conversion parameter (current-concentration conversion parameter) between the pump current Ip2 and the NOx concentration in the measured gas, outputting the measured value as a value from the gas sensor 100. The current-concentration conversion parameter is pre-stored in the memory of the control unit 91, which functions as the concentration calculation unit 94. Those skilled in the art can appropriately determine the current-concentration conversion parameter for the gas sensor 100 beforehand through experiments, etc. The current-concentration conversion parameter can be, for example, the coefficient of an approximate formula (linear function, etc.) obtained experimentally, or it can be a mapping representing the correspondence between the measuring pump current Ip2 and the NOx concentration in the measured gas. The current-concentration conversion parameter can be a parameter inherent to each gas sensor 100, or it can be a parameter shared by multiple gas sensors.

[0210] The determination unit 95 is configured to determine the start and end of pump control during startup.

[0211] For example, when the determination unit 95 determines that the heating of the heater 72 by the heater control unit 92 has caused the base portion 102 (sensor element 101) to reach a predetermined start determination threshold (start temperature of pump control at startup), the pump control unit 93 starts the pump control at startup. The determination that the base portion 102 (sensor element 101) has reached the start temperature can be based on the temperature of the base portion 102 body or on the temperature of the heater 72.

[0212] The specified start-up threshold (the starting temperature of pump control at startup) can be appropriately set within a range below the stable drive temperature. For example, it can be above the lower limit required to activate the solid electrolytes (in this embodiment, the second solid electrolyte layer 6, the isolation layer 5, and the first solid electrolyte layer 4) contained in each pump unit 21, 50, and 41, that is, to make the oxygen ion conductivity of the solid electrolytes manifest. For example, when the determination is based on the temperature Th of the heater 72, the relationship between the temperature of the substrate 102 (more specifically, the temperature of the solid electrolytes contained in each pump unit 21, 50, and 41) and the temperature of the heater 72 can be determined in advance through experiments, etc. For example, the temperature Th of the heater 72 can be a set temperature Th. SET More than 50%, 60%, 70%, 80%, 90%, etc.

[0213] The determination unit 95 can, for example, end the start-up pump control and begin stable drive pump control when the oxygen concentration near the measuring electrode 44 reaches the target oxygen concentration.

[0214] For example, the determination unit 95 may switch from the start-up pump control to the stable drive pump control when it determines that the pump current Ip2 flowing through the measuring pump unit 41 in the start-up pump control is below a predetermined threshold. The predetermined threshold (end determination threshold) of the pump current Ip2 can be appropriately set according to the intended use of the gas sensor 100. For example, it can be 0.1 μA to 5.0 μA.

[0215] Alternatively, the determination unit 95 may switch from the start-up pump control to the stable drive pump control when it determines that the electromotive force V2 between the inner measuring electrode 44 and the reference electrode 42 in the start-up pump control is above a predetermined threshold. The predetermined threshold (end determination threshold) of the electromotive force V2 can be appropriately set according to the intended use of the gas sensor 100. For example, it can be 0.3V to 1.0V.

[0216] [Pump control during gas sensor startup]

[0217] Next, the start-up pump control, from the start of the gas sensor 100 until stable pump control is achieved, will be explained in detail when the concentration of the target gas in the gas to be measured is determined using the gas sensor 100.

[0218] The control method for the gas sensor in this embodiment includes: a startup pump control step executed when the sensor element is started, and a subsequent stable drive pump control step.

[0219] In the pump control step during startup, the pump control unit 93 applies a startup voltage of the adjustment pump unit (inner main pump electrode 22) to the inner pump electrode (main pump unit 21 in this embodiment) and the outer pump electrode 23 of the adjustment pump unit (main pump unit 21 in this embodiment). This voltage is higher than the voltage applied in the stable drive pump control. Similarly, the pump control unit 93 applies a startup voltage of the measurement pump unit 41 to the inner measurement electrode (measurement electrode 44) and the outer measurement electrode (outer pump electrode 23 in this embodiment) of the measurement pump unit 41. This voltage is higher than the voltage applied in the stable drive pump control but lower than the startup voltage of the adjustment pump unit.

[0220] In the stable drive pump control step, the pump control unit uses the adjustment pump unit to adjust the oxygen in the gas to be measured to the desired concentration, and uses the measurement pump unit 41 to detect the target gas in the gas to be measured.

[0221] The startup process of the gas sensor 100 in this embodiment will be described in detail below. Figure 3 This is a flowchart illustrating an example of the startup process of the gas sensor 100.

[0222] For the gas sensor 100, for example, it is activated when it receives a start signal (Dew point). When the gas sensor 100 is mounted in a vehicle or similar device, the start signal (Dew point) is, for example, a signal sent to the gas sensor 100 from the vehicle's ECU, exhaust gas treatment system, or similar source. It can also be activated, for example, by manually turning on the power to the control device 90.

[0223] When the gas sensor 100 is activated, the heater control unit 92 of the control unit 91 begins to energize the heater 72 to achieve heater control (step S10), heating the heater 72 to a stable driving temperature (e.g., around 800°C) for accurate NOx concentration measurement after solid electrolyte activation, and maintains this stable driving temperature. In this embodiment, the heater control unit 92 controls the heating of the heater 72 to a set temperature Th. SETThis heats the substrate 102 (sensor element 101) to a stable driving temperature.

[0224] After the heater control unit 92 starts heater control in step S10, the determination unit 95 performs a start determination of pump control at startup (step S11). When the heater control unit 92 starts heater control, the heater 72 is heated, and the temperature of the base 102 (sensor element 101) rises. The determination unit 95 determines whether the temperature of the base 102 has reached the start temperature of pump control at startup. In this embodiment, it determines whether the temperature Th of the heater 72 corresponding to the temperature of the base 102 is above or above the start determination threshold. Furthermore, as an example, the start determination threshold is set to the temperature of the heater 72 during stable operation (set temperature Th). SET 70% of the temperature.

[0225] If the determination unit 95 determines that the temperature Th of the heater 72 is above the start determination threshold, it instructs the pump control unit 93 to start pump control. The pump control unit 93 receives the instruction from the determination unit 95 and starts pump control (step S12). If the determination unit 95 determines that the temperature Th of the heater 72 is below the start determination threshold, step S11 is repeated until the temperature Th of the heater 72 reaches or exceeds the start determination threshold.

[0226] In step S12, the pump control unit 93 begins pump control upon startup. That is, the pump control unit 93 applies the main pump startup voltage Vp0 between the inner main pump electrode 22 and the outer pump electrode 23 in the main pump unit 21. INITIAL In the auxiliary pump unit 50, the auxiliary pump start-up voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23. INITIAL In the measuring pump unit 41, the measuring pump start-up voltage Vp2 is applied between the measuring electrode 44 and the outer pump electrode 23. INITIAL The voltage Vp0 when the main pump starts INITIAL Voltage Vp1 when auxiliary pump starts INITIAL and the voltage Vp2 when the pump is started. INITIAL The voltages are 2.0V, 1.0V, and 0.6V, respectively. It should be noted that after pump control begins during startup, the heater control unit 92 continues to control the heater, causing the temperature of the base portion 102 to rise further from the initial temperature controlled by the pump during startup to the stable drive temperature. Furthermore, the temperature of the base portion 102 is maintained at the stable drive temperature.

[0227] It is assumed that before the gas sensor 100 is activated, the gas flow section 15 contains the same gas atmosphere as the gas being measured. Upon activation, after pump control begins, oxygen O2 present in the first internal cavity 20 before the gas sensor 100 is activated is drawn out by the main pump unit 21; oxygen O2 present in the second internal cavity 40 before the gas sensor 100 is activated is drawn out by the auxiliary pump unit 50; and oxygen O2 present in the third internal cavity 61 before the gas sensor 100 is activated, along with oxygen originating from NOx, is drawn out by the measuring pump unit 41. Furthermore, the gas being measured is continuously introduced through the gas inlet 10. The oxygen O2 in the continuously introduced gas is primarily drawn out through the main pump unit 21 from the first internal cavity 20, which is closest to the gas inlet 10. Accordingly, oxygen present in the gas flow section 15 before the gas sensor 100 is activated and oxygen continuously flowing in from the gas inlet 10 are efficiently drawn out from each of the internal cavities 20, 40, and 61.

[0228] Next, the determination unit 95 performs an end determination of the pump control during startup (step S13). In this embodiment, the determination unit 95 determines whether the pump current Ip2 flowing through the measuring pump unit 41 during pump control during startup is below a predetermined threshold (end determination threshold). As an example, the end determination threshold for the pump current Ip2 is set to 3.0 μA.

[0229] If the determination unit 95 determines that the pump current Ip2 is below the end determination threshold, it instructs the pump control unit 93 to switch from start-up pump control to stable drive pump control. Additionally, the determination unit 95 instructs the concentration calculation unit 94 to calculate and output the NOx concentration in the gas being measured based on the pump current Ip2. The pump control unit 93 receives the instruction from the determination unit 95 and ends the start-up pump control, then begins stable drive pump control (step S14). The concentration calculation unit 94 receives the instruction from the determination unit 95 and begins calculating the NOx concentration. If the determination unit 95 determines that the pump current Ip2 is greater than the end determination threshold, step S13 is repeated until the pump current Ip2 falls below the end determination threshold.

[0230] In this embodiment, the temperature of the base portion 102 (sensor element 101) does not directly affect the termination determination of pump control during startup. However, typically, after the temperature of the base portion 102 (sensor element 101) reaches a stable driving temperature, the pump current Ip2 may be below the termination determination threshold.

[0231] The ignition time is the time required from the start of the gas sensor 100 to the point where the concentration of the target gas can be measured. Typically, the concentration of the target gas can be measured at the moment when the pump control at startup ends and the pump control at startup stabilizes. In this case, the ignition time is the time required from the start of the gas sensor 100 to the end of the pump control at startup. Depending on the intended use of the gas sensor 100, sometimes the concentration of the target gas can be measured at the moment when the pump control at startup stabilizes and the pump current Ip2 reaches a predetermined value lower than the threshold value for determining the end of the pump control at startup. In this case, the ignition time can be a predetermined time from the start of the gas sensor 100 to the start of the pump control at startup.

[0232] Figure 4 This is a flowchart illustrating a modified example of the startup process of the gas sensor 100. Figure 4 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 4 In the startup process of the modified example shown, the determination unit 95 performs the startup pump control end determination and... Figure 3 The difference lies in the startup process of the modified example. The determination unit 95 determines whether the electromotive force V2 between the measuring electrode 44 and the reference electrode 42 in the pump control is above a predetermined threshold (end determination threshold) during startup (step S23). As an example, the end determination threshold for the electromotive force V2 is set to 0.5V.

[0233] If the determination unit 95 determines that the electromotive force V2 is above the end determination threshold, it instructs the pump control unit 93 to switch from start-up pump control to stable drive pump control. The pump control unit 93 receives the instruction from the determination unit 95 and ends start-up pump control and begins stable drive pump control (step S14). If the determination unit 95 determines that the electromotive force V2 is below the end determination threshold, it repeats step S23 until the electromotive force V2 reaches or exceeds the end determination threshold.

[0234] The above examples, as embodiments of the present invention, illustrate a gas sensor 100 for detecting the NOx concentration in a measured gas; however, the present invention is not limited to this embodiment. In the present invention, if the objective of shortening ignition time and suppressing cracking in the internal structure of the sensor element is to be achieved, gas sensors comprising various types of sensor elements and control devices may be included.

[0235] In the above embodiments, the gas sensor 100 detects the NOx concentration in the gas to be measured; however, the gas to be measured is not limited to NOx. For example, the gas to be measured can be other oxide gases besides NOx (e.g., carbon dioxide CO2, water H2O, etc.). When the gas to be measured is an oxide gas, similar to the embodiment for detecting NOx concentration described above, the gas to be measured, including the oxide gas itself, is introduced into the third internal cavity 61. At the measuring electrode 44, the oxide gas in the gas to be measured is reduced to generate oxygen. The generated oxygen can be used as the measuring pump current Ip2 of the measuring pump unit 41 to detect the gas to be measured.

[0236] Alternatively, the target gas can be a non-oxide gas such as ammonia (NH3). When the target gas is a non-oxide gas, it is converted into an oxide gas (e.g., NO in the case of ammonia (NH3)). The target gas containing the converted oxide gas is introduced into the third internal cavity 61. At the measuring electrode 44, the converted oxide gas in the target gas is reduced to generate oxygen. The generated oxygen can be used as the measuring pump current Ip2 of the measuring pump unit 41 to detect the target gas. The conversion of the non-oxide gas into an oxide gas can be achieved by at least one of the inner main pump electrode 22 and the auxiliary pump electrode 51 acting as a catalyst.

[0237] In the above embodiment, the determination unit 95 determines the start of pump control based on the heater temperature Th, but is not limited to this. The temperature of the sensor element 101 (substrate 102) itself can be detected, and the determination can be based on the detected temperature. Alternatively, the principle that the resistance of the solid electrolyte decreases corresponding to a rise in the temperature of the sensor element 101 (substrate 102) can be employed. For example, the resistance value of any pump unit in the main pump unit 21 (inner main pump electrode 22 and outer pump electrode 23), auxiliary pump unit 50 (auxiliary pump electrode 51 and outer pump electrode 23), and measuring pump unit 41 (measuring electrode 44 and outer pump electrode 23), or the resistance value of any sensor unit in the main pump control oxygen partial pressure detection sensor unit 80 (inner main pump electrode 22 and reference electrode 42), auxiliary pump control oxygen partial pressure detection sensor unit 81 (auxiliary pump electrode 51 and reference electrode 42), and measuring pump control oxygen partial pressure detection sensor unit 82 (measuring electrode 44 and reference electrode 42), can be detected. When the detected resistance value is below a specified threshold, the pump control is started.

[0238] In the above-described embodiments, the determination unit 95 determines the end of pump control during startup based on the pump current Ip2 or the electromotive force V2, but is not limited thereto. For example, when the pump current Ip0 of the main pump unit 21 or the pump current Ip1 of the auxiliary pump unit 50 is determined to be below a predetermined end determination threshold, a switch from startup pump control to stable drive pump control may be performed. Alternatively, for example, when the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control or the electromotive force V1 of the oxygen partial pressure detection sensor unit 81 for auxiliary pump control is determined to be above a predetermined end determination threshold, a switch from startup pump control to stable drive pump control may be performed. Furthermore, the end determination may be based on multiple end determination thresholds.

[0239] Furthermore, the determination unit 95 can determine the start and / or end of the start-up pump control based on the elapsed time calculated from the start of the gas sensor 100. For example, the start-up pump control can start simultaneously with the start of the gas sensor 100, or it can start after a predetermined time has elapsed since the start of the gas sensor 100. Additionally, the determination unit 95 can determine the end of the start-up pump control based on the elapsed time calculated from the start of the start-up pump control.

[0240] In the above embodiments, during pump startup control, a predetermined startup voltage (main pump startup voltage Vp0) higher than the voltage applied during stable drive pump control is applied to the main pump unit 21, auxiliary pump unit 50, and measuring pump unit 41. INITIAL Voltage Vp1 when auxiliary pump starts INITIAL and the voltage Vp2 when the pump is started. INITIAL However, this is not the only possibility. During pump startup control, as a result, a higher startup voltage than that applied in the stable drive pump control can be applied. For example, feedback control similar to that in the stable drive pump control case can be performed. Specifically, for example, the pump control unit 93 of the control unit 91 can make the electromotive force V1 of the oxygen partial pressure detection sensor unit 81 for auxiliary pump control reach the startup set value V1a. SET The pump voltage Vp1 of the auxiliary pump unit 50 is controlled by feedback. Alternatively, the pump current Ip1 of the auxiliary pump unit 50 can be set to the startup setpoint Ip1a. SET The method is based on setting the start-up set value V0a of the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control according to the pump current Ip1. SET And make the electromotive force V0 the set value V0a at startup. SET The pump voltage Vp0 of the main pump unit 21 is controlled by feedback. Furthermore, the electromotive force V2 of the oxygen partial pressure detection sensor unit 82 for pump control can be set to the startup setpoint V2a. SETThe pump voltage Vp2 of the measuring pump unit 41 is controlled by feedback in this manner. In this case, the set value V1a at startup... SET Startup setting value Ip1a SET Startup setting value V0a SET and startup setting value V2a SET The setpoint V1 is set separately for the stable drive pump control. SET Setting value Ip1 SET , setting value V0 SET and setting value V2 SET A higher value. Accordingly, during pump startup control, a higher startup voltage can be applied than that applied during stable drive pump control.

[0241] In the above embodiments, during the stable drive pump control, the pump control unit 93 of the control unit 91 sets the pump current Ip1 of the auxiliary pump unit 50 to a set value Ip1. SET The method is based on the pump current Ip1 to set the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control to a set value V0. SET And make the electromotive force V0 the set value V0 SET The pump voltage Vp0 of the variable power supply 24 of the main pump unit 21 is controlled by feedback in this manner; however, the control method is not limited to this. For example, the pump control unit 93 can set the pump current Ip1 of the auxiliary pump unit 50 to a set value Ip1. SET The pump voltage Vp0 of the variable power supply 24 of the main pump unit 21 is controlled by feedback in this manner. That is, the pump control unit 93 can directly control the pump voltage Vp0 based on the pump current Ip1, without acquiring and setting the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control. SET The settings.

[0242] In the gas sensor 100 of the above-described embodiments, such as Figure 1 As shown, the sensor element 101 has a structure comprising three internal cavities: a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61. An inner main pump electrode 22, an auxiliary pump electrode 51, and a measuring electrode 44 are respectively disposed in each internal cavity, but this is not limited to this. For example, it can have a structure comprising two internal cavities: a first internal cavity 20 and a second internal cavity 40. The inner main pump electrode 22 is disposed in the first internal cavity 20, and the auxiliary pump electrode 51 and the measuring electrode 44 are respectively disposed in the second internal cavity 40. In this case, for example, a porous protective layer covering the measuring electrode 44 can be formed as a diffusion rate control unit between the auxiliary pump electrode 51 and the measuring electrode 44.

[0243] In the gas sensor 100 of the above-described embodiment, the outer pump electrode 23 serves as three electrodes: the outer main pump electrode of the main pump unit 21, the outer auxiliary pump electrode of the auxiliary pump unit 50, and the outer measuring electrode of the current measuring pump unit 41. However, it is not limited to these three electrodes. For example, the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode can be formed as other electrodes. For example, any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode can be configured to contact the gas to be measured separately on the outer surface of the substrate 102, distinct from the outer pump electrode 23. Alternatively, the reference electrode 44 can serve as any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measuring electrode.

[0244] As described above, according to the present invention, the ignition time of the gas sensor can be shortened and cracking of the internal structure of the sensor element can be suppressed by reducing the blackening of the sensor element.

Claims

1. A gas sensor that detects the target gas in a measured gas. include: A sensor element, and a control device for controlling the sensor element. The gas sensor is characterized in that... The sensor element includes: A long, plate-shaped substrate containing a solid electrolyte layer that is oxygen ion conductive; The gas flow section to be measured is formed from one end of the base portion in the longitudinal direction; An adjustment pump unit includes an inner pump electrode disposed on the inner surface of the gas flow section to be measured, and an outer pump electrode disposed at a position on the base portion corresponding to the inner pump electrode, which is different from the gas flow section to be measured. This adjustment pump unit is used to adjust the oxygen concentration in the gas to be measured to a desired level. A measuring pump unit includes an inner measuring electrode disposed at one end of the inner surface of the gas flow section, further away from the base in the longitudinal direction than the inner pump electrode, and an outer measuring electrode disposed at a different position on the base corresponding to the inner measuring electrode, and is used to detect the target gas in the gas being measured. The control device includes a pump control unit that controls the operation of the adjustment pump unit and the measuring pump unit. The pump control unit performs pump control during startup when the sensor element is started, and stable drive pump control during stable drive of the sensor element after startup. In the pump start-up control, a start-up voltage of the adjusting pump unit is applied between the inner and outer pump electrodes of the adjusting pump unit. This voltage is higher than the voltage applied to the adjusting pump unit in the stable drive pump control. Similarly, a start-up voltage of the measuring pump unit is applied between the inner and outer measuring electrodes of the measuring pump unit. This voltage is higher than the voltage applied to the measuring pump unit in the stable drive pump control but lower than the start-up voltage of the adjusting pump unit. In the stable drive pump control, the oxygen in the gas to be measured is adjusted to the desired concentration using the adjustment pump unit, and the target gas in the gas to be measured is detected using the measurement pump unit.

2. The gas sensor according to claim 1, characterized in that, The sensor element also includes an auxiliary pump unit. The auxiliary pump unit includes an inner auxiliary pump electrode disposed at one end of the inner surface of the gas flow section, which is further away from the base in the longitudinal direction than the inner pump electrode, and an outer auxiliary pump electrode disposed at a position on the base that corresponds to the inner auxiliary pump electrode, which is different from the gas flow section. It is used to further adjust the oxygen concentration in the gas being measured. In the pump start-up control, a start-up voltage of the auxiliary pump unit is also applied between the inner and outer auxiliary pump electrodes of the auxiliary pump unit. This voltage is higher than the voltage applied to the auxiliary pump unit in the stable drive pump control, lower than the start-up voltage of the adjustment pump unit, and higher than the start-up voltage of the measurement pump unit. In the stable drive pump control, the oxygen in the gas to be measured is adjusted to the desired concentration using the adjustment pump unit, and the oxygen concentration in the gas to be measured after adjustment using the adjustment pump unit is further adjusted using the auxiliary pump unit. Finally, the gas to be measured is detected using the measuring pump unit.

3. The gas sensor according to claim 1 or 2, characterized in that, The sensor element includes a heater that heats the substrate. The control device includes: A heater control unit that controls the heater; and The determination unit determines the start and end of the pump control during startup. The heater control unit performs heater control as follows: it heats the base portion using the heater, raising the temperature of the base portion from the initial temperature controlled by the pump at startup to a predetermined stable driving temperature, and then maintains the temperature of the base portion at the stable driving temperature. When the determination unit determines that the temperature of the base portion has reached the start temperature of the start-up pump control, the pump control unit starts the start-up pump control.

4. The gas sensor according to claim 3, characterized in that, When the determination unit determines that the pump current flowing through the measuring pump unit in the start-up pump control is below a predetermined threshold, the pump control unit switches from the start-up pump control to the stable drive pump control.

5. The gas sensor according to claim 3, characterized in that, The sensor element includes a reference electrode, which is configured to contact a reference gas inside the substrate. When the determination unit determines that the electromotive force between the inner measuring electrode and the reference electrode in the start-up pump control is above a predetermined threshold, the pump control unit switches from the start-up pump control to the stable drive pump control.

6. The gas sensor according to claim 1, characterized in that, The starting voltage of the adjustment pump unit is above 1.5V and below 3.0V.

7. The gas sensor according to claim 1, characterized in that, The starting voltage of the pump unit used for measurement is between 0.5V and 1.45V.

8. The gas sensor according to claim 1, characterized in that, The voltage ratio of the starting voltage of the adjustment pump unit to the starting voltage of the measurement pump unit is 1.03 or more and 6.00 or less.

9. A control method for a gas sensor, the gas sensor being used to detect the target gas in a measured gas. The control method for the gas sensor is characterized in that... The gas sensor includes: A sensor element, and a control device for controlling the sensor element. The sensor element includes: A long, plate-shaped substrate containing a solid electrolyte layer that is oxygen ion conductive; The gas flow section to be measured is formed from one end of the base portion in the longitudinal direction; An adjustment pump unit includes an inner pump electrode disposed on the inner surface of the gas flow section to be measured, and an outer pump electrode disposed at a position on the base portion corresponding to the inner pump electrode, which is different from the gas flow section to be measured. This adjustment pump unit is used to adjust the oxygen concentration in the gas to be measured to a desired level. A measuring pump unit includes an inner measuring electrode disposed at one end of the inner surface of the gas flow section, further away from the base in the longitudinal direction than the inner pump electrode, and an outer measuring electrode disposed at a different position on the base corresponding to the inner measuring electrode, and is used to detect the target gas in the gas being measured. The control device includes a pump control unit that controls the operation of the adjustment pump unit and the measuring pump unit. The control method includes: a startup pump control step executed when the sensor element is started, and a subsequent stable drive pump control step. In the pump control step during startup, the pump control unit applies a startup voltage of the adjustment pump unit between the inner and outer pump electrodes of the adjustment pump unit. This voltage is higher than the voltage applied to the adjustment pump unit in the stable drive pump control. Conversely, the pump control unit applies a startup voltage of the measurement pump unit between the inner and outer measurement electrodes of the measurement pump unit. This voltage is higher than the voltage applied to the measurement pump unit in the stable drive pump control but lower than the startup voltage of the adjustment pump unit. In the stable drive pump control step, the pump control unit uses the adjustment pump unit to adjust the oxygen in the gas to be measured to the desired concentration, and uses the measurement pump unit to detect the target gas in the gas to be measured.

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