Gas concentration detector

Abstract

In a gas concentration detection device (1), a voltage control unit controls a pump voltage that is a voltage applied to a pump cell (4). The gas concentration detection device (1) is configured so as to be able to execute, before starting NOx concentration detection of a gas to be measured, two processing modes, namely a first processing mode and a second processing mode. The first processing mode is a processing mode for applying a pump voltage higher than the pump voltage applied at the time of NOx concentration detection. The second processing mode is a processing mode for applying a pump voltage lower than the pump voltage applied at the time of NOx concentration detection. On the basis of the time for which an internal combustion engine is stopped, the gas concentration detection device (1) selects both the first processing mode and the second processing mode, or, only the first processing mode from between the first processing mode and the second processing mode, and the gas concentration detection device then executes the selected processing mode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-036838 filed on March 9, 2023, the contents of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a gas concentration detection device. [Background technology]

[0003] For example, as disclosed in Patent Document 1, a gas concentration detector is known that applies a removal voltage to a pump cell that is higher than the normal voltage applied during gas concentration detection to remove oxygen stored in a sensor electrode, thereby decomposing water in a measurement gas chamber to generate hydrogen. This gas concentration detector reacts the generated hydrogen with oxygen stored in the sensor electrode, removing the oxygen from the sensor electrode, thereby achieving early activation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-070922 Summary of the Invention

[0005] The early activation process performed by the gas concentration detection device described in Patent Document 1 does not take into consideration the removal of VOCs (i.e., volatile organic compounds) adsorbed to the sensor electrode. In other words, depending on the length of time an internal combustion engine equipped with a gas concentration detection device is out of operation, there is a risk that VOCs will be adsorbed to the sensor electrode in addition to oxygen being stored in the sensor electrode. Therefore, the process performed by the gas concentration detection device described in Patent Document 1 alone may not be sufficient to efficiently remove VOCs from the sensor electrode, and there is a risk that it will take a long time for the sensor cell output to stabilize when the gas concentration detection device is started. Therefore, it can be said that the gas concentration detection device described in Patent Document 1 has room for further improvement in terms of early activation.

[0006] The present disclosure aims to provide a gas concentration detection device that can be activated efficiently, reliably, and quickly.

[0007] One aspect of the present disclosure is a gas concentration detection device that includes a sensor element and a voltage control unit and is mounted on an internal combustion engine, The sensor element is a measurement gas chamber into which a measurement gas is introduced; a sensor cell having a solid electrolyte body having oxygen ion conductivity and a pair of electrodes provided on the solid electrolyte body, the sensor cell detecting the concentration of NOx in the measurement gas in the measurement gas chamber; a pump cell having the solid electrolyte body and a pair of electrodes provided on the solid electrolyte body, and configured to adjust the concentration of oxygen in the measurement gas in the measurement gas chamber, the sensor cell has a sensor electrode disposed in the measurement gas chamber; the pump cell has a pump electrode disposed in the measurement gas chamber; the voltage control unit controls a pump voltage that is a voltage applied to the pump cell; The device is configured to be able to execute two processing modes, namely, a first processing mode in which a pump voltage higher than the pump voltage applied during NOx concentration detection is applied before starting detection of the NOx concentration of the measurement gas, and a second processing mode in which a pump voltage lower than the pump voltage applied during NOx concentration detection is applied, The gas concentration detection device selects both the first processing mode and the second processing mode based on the operation stop time of the internal combustion engine, or selects only the first processing mode from the first processing mode and the second processing mode, and executes the selected processing mode.

[0008] The gas concentration detection device selects both the first treatment mode and the second treatment mode, or selects only the first treatment mode from the first and second treatment modes, based on the operation stop time of the internal combustion engine, and executes the selected treatment mode. Therefore, oxygen occluded in the sensor electrode and VOCs adsorbed to the sensor electrode can be efficiently removed. As a result, early activation can be achieved efficiently and reliably.

[0009] As described above, according to the above aspect, it is possible to provide a gas concentration detection device that can be activated efficiently and reliably at an early stage. Note that the symbols in parentheses in the claims indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0010] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a block diagram of a gas concentration detection device according to a first embodiment; [Figure 2] FIG. 2 is a cross-sectional view of a tip portion of a sensor element according to the first embodiment; [Figure 3] FIG. 3 is a graph showing the relationship between the operation suspension time and the amount of oxygen stored in the sensor electrode and the amount of VOC adsorbed in the sensor electrode in the first embodiment; [Figure 4] FIG. 4 is a graph showing the pump cell temperature required for hydrogen generation and the sensor cell temperature required for reduction of the sensor electrode in the first embodiment; [Figure 5] FIG. 5 is a flowchart showing a flow up to execution of a selected processing mode in the first embodiment. [Figure 6] FIG. 6 is a graph showing the relationship between the water vapor concentration in the measurement gas and activation time in the first embodiment; [Figure 7]FIG. 7 is a graph showing the relationship between the oxygen concentration in the measurement gas and activation time in the first embodiment; [Figure 8] FIG. 8 is a graph showing the relationship between the operation suspension time and the activation time in Experimental Example 1; [Figure 9] FIG. 9 is a graph showing the relationship between the operation suspension time and the accuracy of NOx concentration detection in Example 1 and Comparative Example 1 in Experimental Example 2; [Figure 10] FIG. 10 is a block diagram of a gas concentration detection device according to a third embodiment; [Figure 11] FIG. 11 is a graph showing the relationship between the amount of water remaining in the exhaust pipe and the detection accuracy of the NOx concentration. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Embodiment 1) An embodiment of a gas concentration detection device will be described with reference to FIGS. 1, the gas concentration detecting device 1 of this embodiment includes a sensor element 11 and a voltage control unit 71, and is mounted on an internal combustion engine (not shown). As shown in FIG. 2, the sensor element 11 includes a measurement gas chamber 10 into which a measurement gas is introduced, a sensor cell 3, and a pump cell 4.

[0012] The sensor cell 3 has a solid electrolyte body 2 having oxygen ion conductivity and a pair of electrodes 21, 22 provided on the solid electrolyte body 2. The sensor cell 3 detects the concentration of NOx (i.e., nitrogen oxides) in the measurement gas in the measurement gas chamber 10. The pump cell 4 has a solid electrolyte body 2 and a pair of electrodes 23, 22 provided on the solid electrolyte body 2. The pump cell 4 adjusts the concentration of oxygen in the measurement gas in the measurement gas chamber 10. The sensor cell 3 also has a sensor electrode 21 disposed in the measurement gas chamber 10. The pump cell 4 also has a pump electrode 23 disposed in the measurement gas chamber 10.

[0013] The voltage control unit 71 controls the pump voltage applied to the pump cell 4. The gas concentration detection device 1 is configured to be able to execute two processing modes, a first processing mode and a second processing mode, before starting to detect the NOx concentration of the measurement gas. The first processing mode is a processing mode in which a pump voltage higher than the pump voltage applied when detecting the NOx concentration is applied. The second processing mode is a processing mode in which a pump voltage lower than the pump voltage applied when detecting the NOx concentration is applied.

[0014] 3, the gas concentration detection device 1 selects both the first treatment mode and the second treatment mode, or selects only the first treatment mode from the first and second treatment modes, based on the operation stop time T1 of the internal combustion engine, and executes the selected treatment mode. The first treatment mode is a treatment mode in which the pump cell 4 decomposes water contained in the measurement gas to generate hydrogen. The second treatment mode is a treatment mode in which oxygen contained in the measurement gas is allowed to flow toward the sensor electrode 21.

[0015] In this specification, the term "active state" refers to a state in which the solid electrolyte body 2 and the sensor electrode 21 are at temperatures suitable for detecting NOx, as well as a state in which the amounts of oxygen occluded in the sensor electrode 21 and VOCs adsorbed on the sensor electrode 21 are sufficiently small, making the sensor electrode 21 suitable for detecting NOx. In this specification, the term "active time T2" ​​refers to the time from the start of operation of the gas concentration detection device 1 until the sensor electrode 21 enters an active state after the occluded oxygen and adsorbed VOCs have been sufficiently removed, and the detection accuracy of the NOx concentration by the gas concentration detection device 1 becomes stable.

[0016] The gas concentration detecting device 1 of this embodiment can be mounted on a vehicle, for example, and used as a means for measuring the concentration of NOx contained in exhaust gas. The gas concentration detecting device 1 can measure the concentration of NOx contained in exhaust gas by being attached, for example, to an exhaust pipe (not shown) of an internal combustion engine of the vehicle.

[0017] In the gas concentration detecting device 1, the sensor element 11 is formed in an elongated shape. As shown in FIG. 2 , the sensor cell 3, the pump cell 4, the measurement gas chamber 10, etc. are provided at one longitudinal end of the sensor element 11. The end of the sensor element 11 where the sensor cell 3, etc. are provided is covered with an element cover (not shown) and placed in an exhaust pipe, and is exposed to exhaust gas, which is the measurement gas. The end of the sensor element 11 opposite to the end placed in the exhaust pipe (not shown) is exposed to the atmosphere, which is the reference gas, described below. In this embodiment, the sensor element 11 is configured as a limiting current sensor element. In this specification, the longitudinal direction Z of the sensor element 11 is referred to as the Z direction as appropriate. In the Z direction, the side of the sensor element 11 located in the exhaust pipe is referred to as the tip side, and the opposite side is referred to as the base side. In addition, the stacking direction Y of the pair of electrodes 21, 22 and the solid electrolyte body 2 in the sensor cell 3 is referred to as the Y direction as appropriate. In addition, in the Y direction, the side of the solid electrolyte body 2 on which the measurement gas chamber 10 is located is referred to as the upper side, and the opposite side is referred to as the lower side.

[0018] The sensor cell 3 has a sensor electrode 21 and a reference electrode 22. The sensor electrode 21 and the reference electrode 22 are disposed on both sides of the solid electrolyte body 2 in the Y direction so as to face each other. The sensor electrode 21 is disposed on the surface of the solid electrolyte body 2 facing the measurement gas chamber 10. The reference electrode 22 is disposed on the surface of the solid electrolyte body 2 facing the reference gas chamber 100 (described later). The sensor electrode 21 is located closer to the base end in the Z direction than the pump electrode 23 and downstream of the pump electrode 23 in the flow of the measurement gas introduced into the measurement gas chamber 10. In this embodiment, the sensor electrode 21 is made of a porous cermet electrode containing Pt (i.e., platinum) and Rh (i.e., rhodium) and has strong reducing properties for NOx. In this embodiment, the reference electrode 22 is made of a porous cermet electrode containing a precious metal such as Pt.

[0019] The pump cell 4 has a pump electrode 23 and a reference electrode 22. The pump electrode 23 is disposed on the surface of the solid electrolyte body 2 facing the measurement gas chamber 10. In this embodiment, the pump electrode 23 is made of a porous cermet electrode containing Au (i.e., gold) and Pt. In this embodiment, the reference electrode 22 of the pump cell 4 and the reference electrode 22 of the sensor cell 3 are integrated into one common electrode.

[0020] The solid electrolyte body 2 is a plate-shaped member made of a solid electrolyte material having oxygen ion conductivity. The solid electrolyte body 2 is activated by heating with a heater 6, which will be described later. That is, the solid electrolyte body 2 is configured to have oxygen ion conductivity at a predetermined activation temperature. In this embodiment, the solid electrolyte body 2 is made of yttria-stabilized zirconia. In this embodiment, the solid electrolyte body 2 is common to both the sensor cell 3 and the pump cell 4.

[0021] An insulator 52 is laminated on the upper surface of the solid electrolyte body 2 in the Y direction via a first spacer 51 made of insulating ceramics such as alumina. The solid electrolyte body 2, the first spacer 51, and the insulator 52 surround the solid electrolyte body 2, forming a measurement gas chamber 10. An inlet 530 for the measurement gas is formed at the tip of the first spacer 51. A diffusion resistor 53 made of a porous material is embedded in the inlet 530. The measurement gas that has passed through the diffusion resistor 53 is introduced into the measurement gas chamber 10. In this embodiment, the diffusion resistor 53 is made of gas-permeable porous ceramics. The insulator 52 is made of insulating ceramics such as alumina.

[0022] A heater substrate layer 61 is laminated on the lower surface in the Y direction of the solid electrolyte body 2, with a second spacer 54 made of insulating ceramics interposed therebetween. The heater substrate layer 61 constitutes a part of the heater 6, which will be described later. A reference gas chamber 100 is formed by being surrounded by the solid electrolyte body 2, the second spacer 54, and the heater substrate layer 61. A reference gas is introduced into the reference gas chamber 100. The reference gas is a gas that serves as a reference for oxygen concentration. In this embodiment, the reference gas is atmospheric air. The reference gas chamber 100 is configured so that atmospheric air is introduced through an opening (not shown).

[0023] The heater 6 has a heater substrate layer 61 made of insulating ceramics and a heater electrode 62 embedded inside the heater substrate layer 61. The heater 6 is disposed opposite the solid electrolyte body 2 in the Y direction across the reference gas chamber 100.

[0024] The heater electrode 62 is configured to generate heat when energized. The heater 6 heats the sensor cell 3 and the pump cell 4 to temperatures suitable for detecting the NOx concentration. In this embodiment, the heater 6 heats the pump cell 4 to a temperature of 500°C or higher. The heater 6 also heats the sensor cell 3 to a temperature of 400°C or higher. In this embodiment, during NOx concentration detection, the heater 6 heats the pump cell 4 to a temperature in the range of 700°C to 800°C, and heats the sensor cell 3 to a temperature in the range of 500°C to 700°C.

[0025] Next, measurement of the NOx concentration in the measurement gas by the gas concentration detection device 1 will be described. The measurement gas flowing through the exhaust pipe of an internal combustion engine passes through the diffusion resistor 53 and enters the measurement gas chamber 10. The pump cell 4 then discharges oxygen from the measurement gas chamber 10 to the reference gas chamber 100 to adjust the oxygen concentration of the measurement gas. Specifically, when a predetermined pump voltage is applied between the pump electrode 23 and the reference electrode 22, the oxygen contained in the measurement gas in the measurement gas chamber 10 is reduced and decomposed by the pump electrode 23 to form oxygen ions. The oxygen ions flow through the solid electrolyte 2 toward the reference electrode 22, where oxygen is generated and discharged from the reference gas chamber 100 to the atmosphere. Since the inflow of the measurement gas into the measurement gas chamber 10 is limited by the diffusion resistor 53, the current flowing through the pump cell 4 exhibits a limiting current characteristic that depends on the oxygen concentration in the measurement gas. Therefore, by setting the pump voltage so that it is in the limiting current region of oxygen, the oxygen concentration and air-fuel ratio A / F of the measured gas can be determined from the current flowing through the pump cell 4, using the air introduced into the reference gas chamber 100 as a reference.

[0026] Next, the measurement gas after oxygen has been discharged by the pump cell 4 reaches the sensor electrode 21, which is located downstream of the pump electrode 23 in the flow of the measurement gas. When a voltage is applied between the sensor electrode 21 and the reference electrode 22, NOx in the measurement gas is ionized at the sensor electrode 21 and discharged into the reference gas chamber 100 through the solid electrolyte body 2. In this embodiment, the current flowing at this time is detected, and the detected value is used to calculate the NOx concentration.

[0027] Furthermore, in the pump cell 4 during NOx concentration detection, the pump voltage during NOx concentration detection decomposes oxygen in the measurement gas, but does not decompose water in the measurement gas. In contrast, in the pump cell 4 during the first processing mode, a pump voltage higher than the pump voltage during NOx concentration detection decomposes not only oxygen in the measurement gas, but also water in the measurement gas. The hydrogen produced by the decomposition of water is then used to remove oxygen occluded in the sensor electrode 21. The pump voltage applied during NOx concentration detection can be, for example, 0.4 V.

[0028] In the second processing mode, the pump voltage is intentionally set lower than the pump voltage used for detecting the NOx concentration, thereby reducing the amount of oxygen removed from the measurement gas by the pump cell 4 compared to when detecting the NOx concentration. This allows oxygen to flow into the sensor electrode 21.

[0029] Next, the sensor control unit 7 that controls the operation of the sensor element 11 will be described. 1, the gas concentration detection device 1 has a sensor control unit 7. The sensor control unit 7 is electrically connected to a sensor element 11 and controls the operation of the sensor element 11. The sensor control unit 7 also includes a processor and a memory, and calculates the NOx concentration and oxygen concentration in the measurement gas.

[0030] The sensor control unit 7 also includes a voltage control unit 71, a current detection unit 74, and an element temperature control unit 73. The voltage control unit 71 controls the pump voltage applied in the first treatment mode to 0.5 V or higher, and controls the pump voltage applied in the second treatment mode to 0.32 V or lower. In this embodiment, the voltage control unit 71 controls the pump voltage applied in the first treatment mode to 0.5 to 1.2 V, and controls the pump voltage applied in the second treatment mode to 0.20 to 0.32 V. The voltage control unit 71 can also change the magnitude of the pump voltage in the first treatment mode and the pump voltage in the second treatment mode within the above-mentioned pump voltage ranges, for example, depending on the amount of oxygen stored in the sensor electrode 21 and the amount of VOCs adsorbed by the sensor electrode 21.

[0031] The current detection unit 74 is configured to detect the current flowing through the sensor cell 3 and the current flowing through the pump cell 4. The sensor control unit 7 calculates the NOx concentration of the measurement gas based on the current flowing through the sensor cell 3 detected by the current detection unit 74. The sensor control unit 7 also calculates the oxygen concentration of the measurement gas based on the current flowing through the pump cell 4 detected by the current detection unit 74.

[0032] The element temperature control unit 73 controls the temperature of the sensor element 11 by controlling the operation of the heater 6. Specifically, the element temperature control unit 73 controls the amount of heat generated by the heater 6 by controlling the power supplied to the heater 6. For example, the element temperature control unit 73 can control the operation of the heater 6 based on temperature information of the sensor element 11 so that the sensor element 11 is in a state suitable for detecting the NOx concentration. In this embodiment, the element temperature control unit 73 controls the operation of the heater 6 based on cell temperature information detected by a cell temperature detection unit (not shown) that detects the temperatures of the sensor cell 3 and the pump cell 4. Here, the cell temperature detection unit can be configured to detect the temperature of only one of the sensor cell 3 and the pump cell 4 and estimate the temperature of the other cell based on the detected temperature information.

[0033] The sensor control unit 7 is also configured to be able to communicate data with an ECU (Engine Control Unit) that controls the internal combustion engine. Detection results such as NOx concentration by the gas concentration detection device 1 are output from the sensor control unit 7 to the ECU (not shown) and used for controlling an exhaust gas purification system, etc. Information on an operation downtime T1 of the internal combustion engine is output from the ECU to the sensor control unit 7 and used to select a processing mode. In this specification, the operation downtime T1 means the time from when the operation of the internal combustion engine is stopped to when the operation of the internal combustion engine is started again.

[0034] Furthermore, when the gas concentration detection device 1 is started, the element temperature control unit 73 commands the heater 6 to heat the sensor element 11 after the ECU sends a drive permission signal to the sensor control unit 7, as indicated by the arrow in the graph in FIG. 4 . The temperature of the pump cell 4 required for the pump electrode 23 to decompose water and generate hydrogen is different from the temperature of the sensor cell 3 required to remove oxygen stored in the sensor electrode 21 using hydrogen. In this embodiment, the pump cell 4 can generate a sufficient amount of hydrogen by decomposing water when its temperature is raised to 500°C or higher. Furthermore, the sensor cell 3 can remove oxygen stored in the sensor electrode 21 using hydrogen when its temperature is raised to 400°C or higher. In this embodiment, the first and second processing modes are executed when the pump cell 4 temperature is 500°C or higher and the sensor cell 3 temperature is 400°C or higher.

[0035] Next, a flow of operations performed by the gas concentration detection device 1 from selecting a processing mode to executing the processing mode will be described with reference to the flowchart of FIG. First, the sensor control unit 7 receives information on the operation downtime T1 of the internal combustion engine from the ECU. Then, in step S1, the sensor control unit 7 determines whether the operation downtime T1 is equal to or greater than a predetermined threshold T1th. If the operation downtime T1 is equal to or greater than the threshold T1th, the process proceeds to step S2, where the first processing mode and the second processing mode are selected as processing modes to be executed. On the other hand, if the operation downtime T1 is less than the threshold T1th, the process proceeds to step S5, where only the first processing mode is selected as the processing mode to be executed. In other words, the gas concentration detection device 1 of this embodiment executes only the first processing mode out of the first processing mode and the second processing mode when the operation downtime T1 is less than the predetermined threshold T1th. Furthermore, the gas concentration detection device 1 executes both the first processing mode and the second processing mode when the operation downtime T1 is equal to or greater than the threshold T1th. In this embodiment, when both the first processing mode and the second processing mode are executed, the first processing mode is executed after the second processing mode is executed.

[0036] Furthermore, the threshold value T1th can be set, for example, to the shortest outage period T1 among the periods of outage period T1 during which the amount of adsorbed VOCs is likely to affect the early activation of the sensor electrode 21. In this embodiment, the threshold value T1th is set just before the amount of adsorbed VOCs in the sensor electrode 21 exceeds the amount of stored oxygen. The threshold value T1th can be set, for example, to an outage period T1 within a range of 2 to 3 months.

[0037] Next, after selecting a processing mode in step S2, the process proceeds to step S3, where an execution time for at least one of the first processing mode and the second processing mode is determined. Furthermore, after selecting the first processing mode in step S5, the process proceeds to step S6, where an execution time for the first processing mode is determined. More specifically, when executing both the first processing mode and the second processing mode, the gas concentration detection device 1 changes the execution time for at least one of the first processing mode and the second processing mode in accordance with the operation downtime T1. Furthermore, when executing only the first processing mode out of the first processing mode and the second processing mode, the gas concentration detection device 1 changes the execution time for the first processing mode in accordance with the operation downtime T1. In this embodiment, when executing both the first processing mode and the second processing mode, the execution time for both the first processing mode and the second processing mode is changed in accordance with the operation downtime T1.

[0038] Here, the amount of oxygen stored in the sensor electrode 21 and the amount of VOCs adsorbed by the sensor electrode 21 tend to increase as the operation suspension time T1 increases, as shown in the graph of Fig. 3. Therefore, in this embodiment, the operation times of the first treatment mode and the second treatment mode are extended as the operation suspension time T1 increases.

[0039] 3, when the downtime T1 is relatively short, the amount of oxygen stored in the sensor electrode 21 and the amount of adsorbed VOCs tend to increase relatively easily, but once the downtime T1 reaches a certain level, the amounts of oxygen stored and VOCs increase substantially. Therefore, in this embodiment, taking into consideration the fact that the amount of oxygen stored and the amount of VOCs adsorbed reach a plateau, the execution times of the first treatment mode and the second treatment mode are each set to 120 seconds or less.

[0040] In this embodiment, the execution time of each processing mode is shorter than the operation pause time T1. The execution times of the first processing mode and the second processing mode are each 1 to 120 seconds. If the duration of one application of the pump voltage is set to a fixed time by the voltage control unit 71, the execution time of each processing mode can be changed by changing the number of times the pump voltage is applied in the first processing mode and the second processing mode. In other words, the execution time of the selected processing mode can be extended by increasing the number of times the pump voltage is applied.

[0041] 5, after determining the execution time of the processing mode in step S3, the process proceeds to step S4, where the first processing mode and the second processing mode are executed. Also, after determining the execution time of the first processing mode in step S6, the process proceeds to step S7, where the first processing mode is executed.

[0042] In this embodiment, the gas concentration detection device 1 starts the first processing mode when an air-fuel mixture containing fuel is combusted in the internal combustion engine. In addition, when both the first processing mode and the second processing mode are executed, the second processing mode is started when the internal combustion engine is not combusting an air-fuel mixture containing fuel.

[0043] Next, the gas concentration detecting device 1 executes the selected processing mode in step S4 or step S7, and then starts detecting the NOx concentration of the measurement target gas.

[0044] Next, the effects of this embodiment will be described. The gas concentration detection device 1 selects both the first treatment mode and the second treatment mode, or selects only the first treatment mode from the first and second treatment modes, based on the operation downtime T1 of the internal combustion engine, and executes the selected treatment mode. Therefore, oxygen occluded in the sensor electrode 21 and VOCs adsorbed to the sensor electrode 21 can be efficiently removed. As a result, early activation can be achieved efficiently and reliably.

[0045] As shown in FIG. 3 , when the downtime T1 is relatively short, the increase rate of the stored oxygen is faster than the increase rate of the adsorbed VOCs at the sensor electrode 21. Furthermore, it is generally desirable for a gas concentration detection device to be activated as soon as possible after startup. Therefore, the gas concentration detection device 1 of this embodiment selects both the first treatment mode and the second treatment mode, or selects only the first treatment mode from the first and second treatment modes, based on the downtime T1, and executes the selected treatment mode. This allows the sensor electrode 21 to be activated efficiently and quickly. That is, when the downtime T1 is relatively short, the amount of adsorbed VOCs is small, and the activation of the sensor electrode 21 is likely to be mainly influenced by the stored oxygen. On the other hand, when the downtime T1 is relatively long, both the stored oxygen and the adsorbed VOCs are likely to affect the activation of the sensor electrode 21. Therefore, when the downtime T1 is less than the threshold T1th, the gas concentration detection device 1 of this embodiment executes only the first treatment mode from the first treatment mode and the second treatment mode. Furthermore, when the operation suspension time T1 is equal to or greater than the threshold value T1th, both the first processing mode and the second processing mode are executed. This allows the activation processing to be performed according to the state of the sensor electrode 21, and enables the early activation of the sensor electrode 21 to be efficiently performed. Therefore, the NOx detection accuracy can be improved relatively soon after the gas concentration detection device 1 is started.

[0046] The first treatment mode is a treatment mode in which the pump cell 4 decomposes water contained in the measurement gas to generate hydrogen. The hydrogen generated by the first treatment mode spreads within the measurement gas chamber 10 and flows to the sensor electrode 21. This causes the generated hydrogen to react with oxygen occluded in the sensor electrode 21, allowing the oxygen to be quickly removed from the sensor electrode 21. The second treatment mode is a treatment mode in which oxygen contained in the measurement gas is allowed to flow toward the sensor electrode 21. By performing the second treatment mode, the inflowing oxygen can quickly remove VOCs adsorbed to the sensor electrode 21. As a result, early activation can be achieved.

[0047] Furthermore, the longer the operation suspension time T1, the greater the amount of oxygen stored and the amount of adsorbed VOCs in the sensor electrode 21. Therefore, when the gas concentration detection device 1 executes both the first treatment mode and the second treatment mode, it varies the time for which at least one of the first treatment mode and the second treatment mode is executed, depending on the operation suspension time T1. Furthermore, when the gas concentration detection device 1 executes only the first treatment mode of the first treatment mode and the second treatment mode, it varies the time for which the first treatment mode is executed, depending on the operation suspension time T1. In other words, the longer the operation suspension time T1, the longer the execution time of the selected treatment mode. This allows the stored oxygen and adsorbed VOCs in the sensor electrode 21 to be efficiently removed. As a result, early activation can be achieved more efficiently and reliably.

[0048] The concentration of water vapor contained in the measurement gas, which is exhaust gas, tends to be relatively high when hydrocarbon fuel is being burned in an internal combustion engine. As shown in the graph of FIG. 6, when the concentration of water vapor contained in the measurement gas is above a certain level, the activation time T2 when the first processing mode is executed tends to be short. Therefore, the gas concentration detection device 1 of this embodiment starts the first processing mode when a fuel-containing mixture is being burned in the internal combustion engine. This makes it easy to generate a sufficient amount of hydrogen by executing the first processing mode. As a result, early activation of the sensor electrode 21 can be reliably achieved.

[0049] When both the first and second processing modes are executed, the second processing mode is initiated when the internal combustion engine is not combusting a fuel-containing mixture. Therefore, when the second processing mode is executed, a sufficient amount of oxygen is likely to flow toward the sensor electrode 21. As a result, VOCs are efficiently removed from the sensor electrode 21, facilitating early activation of the sensor electrode 21. In other words, because an internal combustion engine consumes oxygen when combusting a fuel-containing mixture, the amount of oxygen contained in the measured gas when the internal combustion engine is combusting the mixture tends to be low. On the other hand, the measured gas when the internal combustion engine is not combusting the mixture, such as during a fuel cut that stops the fuel supply to the internal combustion engine, tends to have a high oxygen concentration. Furthermore, as shown in FIG. 7 , when the oxygen concentration in the measured gas is above a certain level, the activation time T2 when the second processing mode is executed tends to be short. Therefore, the gas concentration detection device 1 of this embodiment starts the second processing mode when the internal combustion engine is not combusting the mixture. This allows efficient removal of VOCs adsorbed to the sensor electrode 21. As a result, the sensor electrode 21 can be reliably activated early.

[0050] The voltage control unit 71 controls the applied pump voltage to 0.5 V or higher in the first treatment mode, and controls the applied pump voltage to 0.32 V or lower in the second treatment mode. Therefore, by performing the first treatment mode, a sufficient amount of hydrogen can be reliably generated, and by performing the second treatment mode, a sufficient amount of oxygen can be reliably introduced into the sensor electrode 21. This ensures that the oxygen stored in the sensor electrode 21 and the adsorbed VOCs are reliably removed. As a result, early activation can be achieved more reliably.

[0051] In this embodiment, the pump voltage applied in the first processing mode is controlled to 0.5 to 1.2 V, and the pump voltage applied in the second processing mode is controlled to 0.20 to 0.32 V. Therefore, when the first processing mode is performed, a sufficient amount of hydrogen can be reliably generated, and deterioration of the solid electrolyte body 2 due to excessively high voltage can be reliably suppressed. As a result, early activation can be more reliably achieved, and the life of the sensor element 11 can be extended. Furthermore, when the second processing mode is performed, a sufficient amount of oxygen can be allowed to flow toward the sensor electrode 21 while reliably suppressing oxidation of the sensor electrode 21 due to an excessive amount of oxygen flowing toward the sensor electrode 21. As a result, early activation can be more reliably achieved.

[0052] In this embodiment, when both the first treatment mode and the second treatment mode are executed, the first treatment mode is executed after the second treatment mode is executed, so that oxygen stored in the sensor electrode 21 can be more reliably removed, and early activation can be more reliably achieved.

[0053] The active time T2 is shorter than the non-operation time T1, so that the sensor electrode 21 can be reliably activated early.

[0054] The execution time of the first treatment mode and the second treatment mode is 1 to 120 seconds, respectively. Therefore, the activation treatment can be reliably performed according to the amount of oxygen stored in the sensor electrode 21 and the amount of VOCs adsorbed thereon, and early activation can be reliably achieved.

[0055] As described above, according to this embodiment, it is possible to provide a gas concentration detecting device 1 that can be activated efficiently, reliably, and quickly.

[0056] In the above-described first embodiment, when both the first processing mode and the second processing mode are executed, the first processing mode is executed after the second processing mode is executed. However, when both the first processing mode and the second processing mode are executed, the second processing mode may be executed after the first processing mode is executed.

[0057] (Experimental Example 1) In this example, the gas concentration detection device shown in the first embodiment was used to examine the relationship between the operation suspension time T1 and the activation time T2 of the gas concentration detection device, as shown in the graph of Fig. 8. In this example, the activation time T2 is the activation time T2 when the second treatment mode is executed. In other words, in this example, the activation time T2 when VOCs adsorbed to the sensor electrode were removed was examined, rather than when oxygen occluded in the sensor electrode was removed.

[0058] The amount of VOCs adsorbed to the sensor electrode increases as the downtime T1 increases. Therefore, as shown in the graph in FIG. 8, the longer the downtime T1, the longer the activation time T2. Specifically, when the downtime T1 is 5 minutes, the activation time T2 is 1 second; when the downtime T1 is 1 day, the activation time T2 is 60 seconds; and when the downtime T1 is 6 months, the activation time T2 is 120 seconds. Furthermore, even when the downtime T1 is longer than a certain level, the activation time T2 does not exceed 120 seconds, peaking out at 120 seconds. These results suggest that adjusting the execution time of the second processing mode between 1 and 120 seconds based on the downtime T1 can ensure early activation of the gas concentration detection device.

[0059] (Experimental Example 2) In this example, as shown in the graph of Fig. 9, the relationship between the operation suspension time T1 and the measurement accuracy of the gas concentration detection device was investigated using a gas concentration detection device of Example 1 having the same basic structure as that of Embodiment 1, and a gas concentration detection device of Comparative Example 1 having the same basic structure as that of Embodiment 1 but in which the content of the activation treatment for the sensor electrode is constant. In this example, Comparative Example 1 is configured to execute only the first treatment mode.

[0060] The conditions for the first treatment mode performed in Comparative Example 1 were a pump voltage of 1.2 V and an execution time of 50 seconds throughout the entire downtime T1. On the other hand, the activation treatment conditions in Example 1 varied the pump voltage and execution time depending on the downtime T1. Specifically, in Example 1, when the downtime T1 was time Tn, the pump voltage was set to 1.2 V and the execution time of the first treatment mode was set to 50 seconds, similar to Comparative Example 1. Furthermore, in Example 1, when the downtime T1 was time Tn-1, which was shorter than time Tn, the pump voltage was set to 1.2 V and the execution time of the first treatment mode was set to 30 seconds. Furthermore, in Example 1, when the downtime was time Tn+1 and time Tn+2, which were longer than time Tn, in addition to the first treatment mode similar to the treatment mode performed when the downtime T1 was time Tn, a second treatment mode with a pump voltage of 0.3 V and an execution time of 60 seconds was also performed.

[0061] The accuracy on the vertical axis of the graph in Fig. 9 represents the detection accuracy of the NOx concentration of the gas concentration detection device immediately after the processing mode is executed. The accuracy on the vertical axis of the graph in Fig. 9 is expressed as a ratio, with the accuracy at time Tn in Example 1 being set to 1.0. In other words, when the accuracy value is less than 1.0, it means that the detection accuracy is lower than the accuracy at time Tn in Example 1.

[0062] As shown in the graph of Figure 9, when the operation downtime T1 is time Tn and Tn-1, Example 1 and Comparative Example 1 have equivalent accuracy. Here, when the operation downtime T1 is time Tn-1, Comparative Example 1 executes the first treatment mode for 50 seconds, while Example 1 executes the first treatment mode for 30 seconds. Furthermore, since the operation downtime T1 is shorter, it is thought that the amount of oxygen stored in the sensor electrode is less at time Tn-1 than at time Tn. From these facts, it is thought that Example 1 was able to activate the sensor electrode more efficiently than Comparative Example 1.

[0063] Furthermore, when the downtime T1 is at time Tn+1 and time Tn+2, Example 1 has the same accuracy as at time Tn, whereas Comparative Example 1 has lower accuracy compared to time Tn. Furthermore, in Comparative Example 1, the accuracy is lower at time Tn+2 than at time Tn+1. Here, as the downtime T1 becomes longer, the amount of oxygen stored in the sensor electrode increases, and the amount of adsorbed VOCs is also likely to increase. Furthermore, in Comparative Example 1, the content of the treatment mode is the same regardless of the downtime T1. Therefore, it is thought that Comparative Example 1 was unable to sufficiently remove adsorbed VOCs from the sensor electrode when the downtime T1 is at time Tn+1 and time Tn+2, resulting in lower accuracy compared to time Tn. On the other hand, Example 1 executes the second treatment mode in addition to the first treatment mode when the downtime is at time Tn+1 and time Tn+2. This suggests that Example 1 was able to efficiently remove VOCs adsorbed to the sensor electrode. Therefore, it is considered that in Example 1, even when the operation suspension time T1 is time Tn+1 or time Tn+2, the accuracy is equivalent to that when it is time Tn. In other words, the gas concentration detection device of Example 1 can be efficiently and reliably activated early.

[0064] (Embodiment 2) The gas concentration detection device 1 of this embodiment is configured to change the execution time of the selected processing mode based on temperature-related information related to the temperature of the sensor element 11.

[0065] When the gas concentration detection device 1 of this embodiment executes both the first processing mode and the second processing mode, it changes the execution time of at least one of the first processing mode and the second processing mode based on temperature-related information related to the temperature of the sensor element 11. When the gas concentration detection device 1 executes only the first processing mode out of the first processing mode and the second processing mode, it changes the execution time of the first processing mode based on the temperature-related information. In this embodiment, when the gas concentration detection device 1 executes both the first processing mode and the second processing mode, it changes the execution times of both the first processing mode and the second processing mode based on the temperature-related information.

[0066] The temperature-related information may be, for example, the temperature of the sensor element 11, the temperature of the pump cell 4, the temperature of the sensor cell 3, or the operating state of the internal combustion engine, such as the load on the internal combustion engine and the rotation speed of the internal combustion engine. In this embodiment, the temperature-related information is the operating state of the internal combustion engine.

[0067] In this embodiment, the execution time of the selected processing mode is changed based on the temperature-related information while being changed in accordance with the operation downtime T1. When determining the execution time of the selected processing mode, the weighting of the operation downtime T1 and the temperature-related information can be determined arbitrarily according to various purposes. Other aspects are the same as those of embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0068] The temperature rise rate of the sensor element 11 tends to vary depending on the operating conditions of the internal combustion engine, such as the load on the internal combustion engine and the engine speed. Furthermore, the activation efficiency of the sensor electrode 21 tends to vary depending on the temperature of the sensor element 11. That is, when the temperature of the sensor element 11 is relatively low, the execution time of the processing mode required to activate the sensor electrode 21 tends to be longer than when the temperature of the sensor element 11 is sufficiently high. Therefore, when the gas concentration detection device 1 executes both the first processing mode and the second processing mode, it changes the execution time of at least one of the first processing mode and the second processing mode based on the temperature-related information. Furthermore, when the gas concentration detection device 1 executes only the first processing mode of the first processing mode and the second processing mode, it changes the execution time of the first processing mode based on the temperature-related information. That is, the sensor control unit 7 can adjust the execution time of the selected processing mode based on information on the operating conditions of the internal combustion engine, which is the temperature-related information received from the ECU. Therefore, the activation process time can be controlled depending on the temperature condition of the sensor element 11. As a result, early activation can be more reliably achieved. In addition, the same effects as those of the first embodiment are achieved.

[0069] (Embodiment 3) The gas concentration detection device 1 of this embodiment is configured to adjust the timing for executing a selected processing mode based on the dryness state of the exhaust pipe of the internal combustion engine.

[0070] As shown in FIG. 10 , the gas concentration detection device 1 includes a dryness determination unit 81 that determines the dryness state of the exhaust pipe of the internal combustion engine, and an element temperature control unit 73 that controls the temperature of the sensor element 11. The dryness determination unit 81 is configured to perform a dryness determination to determine that the state of the exhaust pipe of the internal combustion engine is dry, and a non-dryness determination to determine that the state of the exhaust pipe of the internal combustion engine is not dry. The element temperature control unit 73 controls the temperature of the sensor element 11 to be lower than the temperature at which the NOx concentration is detected during a non-dry period in which the dryness determination unit 81 performs a non-dryness determination. After the dryness determination unit 81 performs a dryness determination, the element temperature control unit 73 controls the temperature of the sensor element 11 to be the temperature at which the NOx concentration is detected. After the dryness determination, the gas concentration detection device 1 executes a processing mode and changes the time for executing the first processing mode depending on the time from when the internal combustion engine starts operating until the dryness determination unit 81 performs a dryness determination. That is, in this embodiment, the longer the time from when the internal combustion engine starts to when the dryness determination unit 81 makes the dryness determination, the longer the time for which the first processing mode is executed.

[0071] In this embodiment, as shown in Fig. 10, the ECU 8 that controls the internal combustion engine has a dryness determination unit 81. The dryness determination unit 81 makes a dryness determination or a non-dryness determination based on information such as combustion in the internal combustion engine, the temperature of exhaust gas in the exhaust pipe, and the flow velocity of exhaust gas in the exhaust pipe. The dryness determination unit 81 is configured to output the determination result as a signal to the sensor control unit 7. The sensor control unit 7 controls the driving state of the sensor based on the dryness state determination result received from the dryness determination unit 81.

[0072] Furthermore, the element temperature control unit 73 controls the temperature of the sensor element 11 during the non-drying period so that the temperature will not crack even if the sensor element 11 is exposed to water. Specifically, the element temperature control unit 73 can control the upper limit temperature of the sensor element 11 to be 150 to 450°C during the non-drying period, for example.

[0073] In addition, in this embodiment, the execution time of the first treatment mode is changed in accordance with the operation pause time T1, and the execution time of the first treatment mode is changed in accordance with the time from the start of operation of the internal combustion engine until the dryness determination unit 81 makes a dryness determination. When determining the execution time of the first treatment mode, the weighting of the operation pause time T1 and the time from the start of operation of the internal combustion engine until the dryness determination unit 81 makes a dryness determination can be determined arbitrarily in accordance with various purposes. The rest is the same as in the first embodiment.

[0074] In general, in an internal combustion engine, condensed water may occur in the exhaust pipe due to condensation or the like during periods when the engine is not in operation. It is assumed that the greater the amount of water remaining in the exhaust pipe, the greater the likelihood that the sensor element of the gas concentration detection device will be exposed to condensed water in the exhaust pipe when the gas concentration detection device is driven. Therefore, the gas concentration detection device 1 of this embodiment executes the selected processing mode after determining that the exhaust pipe is dry. Therefore, the selected processing mode can be executed when the exhaust pipe is sufficiently dry. This reliably prevents damage to the sensor element 11 due to exposure to water.

[0075] Furthermore, during the non-drying period, the element temperature control unit 73 controls the temperature of the sensor element 11 to be lower than the temperature at which the NOx concentration is detected. Furthermore, after the dryness determination unit 81 makes a dryness determination, the element temperature control unit 73 controls the temperature of the sensor element 11 to be the temperature at which the NOx concentration is detected. Therefore, even if the sensor element 11 is exposed to water during the non-drying period, damage to the sensor element 11 can be more reliably suppressed.

[0076] In this embodiment, the execution time of the first processing mode is changed depending on the time from the start of operation of the internal combustion engine until the dryness determination unit 81 makes a dryness determination. This allows the execution time of the first processing mode to be adjusted depending on the time the sensor electrode 21 is exposed to high-humidity measurement gas. This allows the sensor electrode 21 to be activated efficiently. In other words, generally, the greater the amount of water remaining in the exhaust pipe, the longer the sensor electrode is likely to have been exposed to high-humidity measurement gas, and the longer it will take for the exhaust pipe to dry. Furthermore, the longer the exposure time to high-humidity measurement gas, the more likely OH groups will adhere to the sensor electrode. As shown in FIG. 11 , this may result in a decrease in the accuracy of NOx concentration detection. Therefore, in this embodiment, the execution time of the first processing mode is extended depending on the time it takes for the exhaust pipe to dry. Therefore, the OH groups adhered to the sensor electrode 21 can be reliably removed by the hydrogen generated in the first processing mode. As a result, the sensor electrode 21 can be reliably activated early.

[0077] During the non-drying period, the element temperature control unit 73 controls the upper limit temperature of the sensor element 11 to be 150 to 450°C. In other words, during the non-drying period, the element temperature control unit 73 can maintain the temperature of the sensor element 11 at a temperature that will not crack the sensor element 11 even if it is exposed to water, while still maintaining the temperature higher than a predetermined temperature. Therefore, after determining that the sensor element 11 is dry, the temperature of the sensor element 11 can be raised to the temperature at which the NOx concentration is detected in a relatively short time. As a result, early activation can be more reliably achieved. In addition, the same effects as those of the first embodiment are achieved.

[0078] In the above-described first to third embodiments, the gas concentration detecting device 1 includes a pump cell 4 and a sensor cell 3. However, in addition to the pump cell and the sensor cell, the gas concentration detecting device may also include a monitor cell that measures the concentration of residual oxygen in the measurement gas after the oxygen concentration has been adjusted by the pump cell. In this case, even if the pump cell cannot completely discharge oxygen, the NOx concentration can be calculated more accurately.

[0079] Furthermore, if the operation downtime is short and the amount of oxygen stored in the sensor electrode and the amount of VOC adsorbed do not affect the accuracy of NOx detection, it is possible to configure the system so that neither the first treatment mode nor the second treatment mode is executed.

[0080] The present disclosure is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the spirit of the present disclosure.

[0081] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0082] <Other> The features of the present disclosure are as follows: [Section 1] A gas concentration detection device (1) that includes a sensor element (11) and a voltage control unit (71) and is mounted on an internal combustion engine, The sensor element is a measurement gas chamber (10) into which a measurement gas is introduced; a sensor cell (3) having an oxygen ion conductive solid electrolyte (2) and a pair of electrodes (21, 22) provided on the solid electrolyte, the sensor cell detecting the concentration of NOx in the measurement gas in the measurement gas chamber; a pump cell (4) having the solid electrolyte body and a pair of electrodes (23, 22) provided on the solid electrolyte body, and adjusting the concentration of oxygen in the measurement gas in the measurement gas chamber, The sensor cell has a sensor electrode (21) disposed in the measurement gas chamber, The pump cell has a pump electrode (23) disposed in the measurement gas chamber, the voltage control unit controls a pump voltage that is a voltage applied to the pump cell; The device is configured to be able to execute two processing modes, namely, a first processing mode in which a pump voltage higher than the pump voltage applied during NOx concentration detection is applied before starting detection of the NOx concentration of the measurement gas, and a second processing mode in which a pump voltage lower than the pump voltage applied during NOx concentration detection is applied, A gas concentration detection device that selects both the first processing mode and the second processing mode based on the operation stop time (T1) of the internal combustion engine, or selects only the first processing mode from the first processing mode and the second processing mode, and executes the selected processing mode. [Section 2] When both the first treatment mode and the second treatment mode are executed, a time for executing at least one of the first treatment mode and the second treatment mode is changed according to the operation suspension time, Item 1. A gas concentration detection device according to item 1, wherein, when only the first processing mode is executed out of the first processing mode and the second processing mode, the time for executing the first processing mode is changed depending on the operation downtime. [Section 3] the first treatment mode is a treatment mode in which the pump cell decomposes water contained in the measurement target gas to generate hydrogen, and the second treatment mode is a treatment mode in which oxygen contained in the measurement target gas is caused to flow into the sensor electrode side; When both the first processing mode and the second processing mode are executed, a time period for executing at least one of the first processing mode and the second processing mode is changed based on temperature-related information related to a temperature of the sensor element; 3. The gas concentration detection device according to claim 1, wherein, when only the first processing mode is executed out of the first processing mode and the second processing mode, the time for executing the first processing mode is changed based on the temperature-related information. [Section 4] 4. The gas concentration detection device according to any one of items 1 to 3, wherein the first processing mode is started when an air-fuel mixture containing fuel is combusted in the internal combustion engine. [Section 5] A gas concentration detection device as described in any one of items 1 to 4, wherein, when both the first processing mode and the second processing mode are executed, the second processing mode is started when the internal combustion engine is not burning a mixture containing fuel. [Section 6] 6. The gas concentration detection device according to any one of items 1 to 5, wherein when the operation suspension time is less than a predetermined threshold (T1th), only the first processing mode of the first processing mode and the second processing mode is executed, and when the operation suspension time is equal to or greater than the threshold, both the first processing mode and the second processing mode are executed, and the voltage control unit controls the pump voltage applied in the first processing mode to be 0.5 V or more, and controls the pump voltage applied in the second processing mode to be 0.32 V or less. [Section 7] the exhaust system includes a dryness determination unit (81) that determines a dryness state of an exhaust pipe of the internal combustion engine, and an element temperature control unit (73) that controls a temperature of the sensor element, the dryness determination unit being configured to perform a dryness determination that determines that the state of the exhaust pipe is dry, and a non-dryness determination that determines that the state of the exhaust pipe is not dry, the element temperature control unit controls the temperature of the sensor element to be lower than the temperature at the time of detecting the NOx concentration during a non-dry period in which the dryness determination unit makes the non-dryness determination, and controls the temperature of the sensor element to be the temperature at the time of detecting the NOx concentration after the dryness determination unit makes the dryness determination, The gas concentration detection device according to any one of items 1 to 6, wherein after the dryness determination, the processing mode is executed, and the time for executing the first processing mode is changed depending on the time from when the internal combustion engine starts operating until the dryness determination unit makes the dryness determination.

Claims

1. A gas concentration detection device (1) having a sensor element (11) and a voltage control unit (71) and mounted on an internal combustion engine, The sensor element is a measurement gas chamber (10) into which a measurement gas is introduced; a sensor cell (3) having a solid electrolyte body (2) having oxygen ion conductivity and a pair of electrodes (21, 22) provided on the solid electrolyte body, for detecting the concentration of NOx in the measurement gas in the measurement gas chamber; a pump cell (4) having the solid electrolyte body and a pair of electrodes (23, 22) provided on the solid electrolyte body, and adjusting the concentration of oxygen in the measurement gas in the measurement gas chamber, The sensor cell has a sensor electrode (21) disposed in the measurement gas chamber, The pump cell has a pump electrode (23) disposed in the measurement gas chamber, the voltage control unit controls a pump voltage that is a voltage applied to the pump cell; The device is configured to be able to execute two processing modes, namely, a first processing mode in which a pump voltage higher than the pump voltage applied during NOx concentration detection is applied before starting detection of the NOx concentration of the measurement gas, and a second processing mode in which a pump voltage lower than the pump voltage applied during NOx concentration detection is applied, A gas concentration detection device that selects both the first processing mode and the second processing mode based on the operation stop time (T1) of the internal combustion engine, or selects only the first processing mode from the first processing mode and the second processing mode, and executes the selected processing mode.

2. When both the first treatment mode and the second treatment mode are executed, a time for executing at least one of the first treatment mode and the second treatment mode is changed according to the operation suspension time, 2. The gas concentration detection device according to claim 1, wherein, when only the first processing mode is executed out of the first processing mode and the second processing mode, the time for executing the first processing mode is changed depending on the operation downtime.

3. the first treatment mode is a treatment mode in which the pump cell decomposes water contained in the measurement target gas to generate hydrogen, and the second treatment mode is a treatment mode in which oxygen contained in the measurement target gas is caused to flow into the sensor electrode side; When both the first processing mode and the second processing mode are executed, a time period for executing at least one of the first processing mode and the second processing mode is changed based on temperature-related information related to a temperature of the sensor element; 3. The gas concentration detection device according to claim 1, wherein when only the first processing mode is executed out of the first processing mode and the second processing mode, the time for executing the first processing mode is changed based on the temperature-related information.

4. 3. The gas concentration detection device according to claim 1, wherein the first processing mode is initiated when an air-fuel mixture containing fuel is combusted in the internal combustion engine.

5. 3. The gas concentration detection device according to claim 1, wherein, when both the first processing mode and the second processing mode are executed, the second processing mode is started when the internal combustion engine is not combusting a mixture containing fuel.

6. 3. The gas concentration detection device according to claim 1, wherein when the operation suspension time is less than a predetermined threshold (T1th), only the first processing mode of the first processing mode and the second processing mode is executed, and when the operation suspension time is equal to or greater than the threshold, both the first processing mode and the second processing mode are executed, and the voltage control unit controls the pump voltage applied in the first processing mode to be 0.5 V or more and controls the pump voltage applied in the second processing mode to be 0.32 V or less.

7. the exhaust pipe includes a dryness determination unit (81) that determines a dryness state of the exhaust pipe of the internal combustion engine, and an element temperature control unit (73) that controls the temperature of the sensor element, the dryness determination unit being configured to perform a dryness determination that determines that the state of the exhaust pipe is dry, and a non-dryness determination that determines that the state of the exhaust pipe is not dry, the element temperature control unit controls the temperature of the sensor element to be lower than the temperature at the time of detecting the NOx concentration during a non-dry period in which the dryness determination unit makes the non-dryness determination, and controls the temperature of the sensor element to be the temperature at the time of detecting the NOx concentration after the dryness determination unit makes the dryness determination, 3. The gas concentration detection device according to claim 1, wherein the processing mode is executed after the dryness determination, and the time for executing the first processing mode is changed depending on the time from when the internal combustion engine starts operating until the dryness determination unit makes the dryness determination.

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