JP7800766B2 - Gas concentration detector - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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

The present disclosure relates to a gas concentration detection device.

For example, as disclosed in Patent Document 1, a gas concentration detection device is known that applies a removal voltage to a pump cell that is higher than the normal voltage applied during gas concentration detection in order to remove oxygen stored in the sensor electrode, thereby decomposing water in the measurement gas chamber to generate hydrogen. This gas concentration detection device aims for early activation by reacting the generated hydrogen with the oxygen stored in the sensor electrode and removing the oxygen from the sensor electrode.

Japanese Patent Application Laid-Open No. 2016-070922

The early activation process performed by the gas concentration detection device described in Patent Document 1 does not take into account the removal of VOCs (i.e., volatile organic compounds) adsorbed to the sensor electrode. In other words, depending on the length of time the internal combustion engine equipped with the gas concentration detection device is out of operation, there is a risk that VOCs may 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 it may 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.

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

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.

The gas concentration detection device selects both the first and second treatment modes based on the engine's downtime, or selects only the first treatment mode from the first and second treatment modes, and executes the selected treatment mode. This allows for efficient removal of oxygen occluded in the sensor electrode and VOCs adsorbed to the sensor electrode. As a result, early activation can be achieved efficiently and reliably.

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.

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:
FIG. 1 is a block diagram of a gas concentration detection device according to a first embodiment; FIG. 2 is a cross-sectional view of a tip portion of a sensor element according to the first embodiment; 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; 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; FIG. 5 is a flowchart showing a flow up to execution of a selected processing mode in the first embodiment. FIG. 6 is a graph showing the relationship between the concentration of water vapor in the measurement gas and activation time in the first embodiment; FIG. 7 is a graph showing the relationship between the oxygen concentration in the measurement gas and activation time in the first embodiment; FIG. 8 is a graph showing the relationship between the operation suspension time and the activation time in Experimental Example 1; 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; FIG. 10 is a block diagram of a gas concentration detection device according to a third embodiment; 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.

(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.

The sensor cell 3 has a solid electrolyte body 2 with 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 has a pump electrode 23 disposed in the measurement gas chamber 10.

The voltage control unit 71 controls the pump voltage, which is the voltage applied to the pump cell 4. The gas concentration detection device 1 is also 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 measured 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.

As shown in Figure 3, the gas concentration detection device 1 selects both the first and second treatment modes, or selects only the first treatment mode from the first and second treatment modes, based on the engine's operation downtime T1, 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 measured gas to generate hydrogen. The second treatment mode is a treatment mode in which oxygen contained in the measured gas flows into the sensor electrode 21.

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 amount of oxygen occluded in the sensor electrode 21 and the amount of VOCs adsorbed to 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 when the gas concentration detection device 1 starts operating until the sensor electrode 21 enters an active state after the occluded oxygen and adsorbed VOCs have been sufficiently removed, and the NOx concentration detection accuracy of the gas concentration detection device 1 stabilizes.

The gas concentration detection 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 detection device 1 can be attached, for example, to the exhaust pipe (not shown) of the vehicle's internal combustion engine, to measure the concentration of NOx contained in exhaust gas.

In the gas concentration detection device 1, the sensor element 11 is formed in an elongated shape. As shown in FIG. 2 , the sensor cell 3, pump cell 4, 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 the exhaust pipe, where it is exposed to the exhaust gas being measured. The end of the sensor element 11 opposite the end placed in the exhaust pipe (not shown) is exposed to the atmosphere, which serves as 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.

The sensor cell 3 includes a sensor electrode 21 and a reference electrode 22. The sensor electrode 21 and the reference electrode 22 are disposed opposite each other on both sides of the solid electrolyte body 2 in the Y direction. 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 a porous cermet electrode containing Pt (i.e., platinum) and Rh (i.e., rhodium) and has strong NOx reduction properties. In this embodiment, the reference electrode 22 is a porous cermet electrode containing a precious metal such as Pt.

The pump cell 4 has a pump electrode 23 and a reference electrode 22. The pump electrode 23 is installed 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 a single common electrode.

The solid electrolyte body 2 is a plate-shaped member made of a solid electrolyte material with oxygen ion conductivity. The solid electrolyte body 2 is activated by heating using the heater 6, which will be described later. In other words, 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.

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, first spacer 51, and insulator 52 surround the 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.

A heater substrate layer 61 is laminated on the lower surface of the solid electrolyte body 2 in the Y direction, with a second spacer 54 made of insulating ceramics interposed between them. The heater substrate layer 61 forms part of the heater 6, which will be described later. The 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 to allow atmospheric air to be introduced through an opening (not shown).

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 positioned opposite the solid electrolyte body 2 in the Y direction across the reference gas chamber 100.

The heater electrode 62 is configured to generate heat when current is applied. The heater 6 heats the sensor cell 3 and pump cell 4 so that they reach temperatures suitable for detecting NOx concentrations. 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, when detecting NOx concentrations, 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.

Next, the measurement of the NOx concentration of 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, adjusting 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 body 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.

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 measurement gas flow. When a voltage is applied between the sensor electrode 21 and the reference electrode 22, the NOx in the measurement gas is ionized at the sensor electrode 21 and discharged through the solid electrolyte body 2 into the reference gas chamber 100. In this embodiment, the current that flows at this time is detected, and the detected value is used to calculate the NOx concentration.

In addition, when detecting NOx concentration, the pump cell 4 decomposes the oxygen in the measured gas due to the pump voltage applied during NOx concentration detection, but does not decompose the water in the measured gas. In contrast, when the first processing mode is being executed, the pump cell 4 applies a pump voltage higher than the pump voltage applied during NOx concentration detection, which not only decomposes the oxygen in the measured gas, but also decomposes the water in the measured gas. The hydrogen produced by this decomposition of water is then used to remove the oxygen stored in the sensor electrode 21. The pump voltage applied during NOx concentration detection can be, for example, 0.4 V.

In addition, in the second processing mode, the pump voltage is intentionally set lower than the pump voltage used when detecting NOx concentration, thereby reducing the amount of oxygen removed from the measured gas by the pump cell 4 compared to when detecting NOx concentration. This allows oxygen to flow toward the sensor electrode 21.

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 the sensor element 11 and controls the operation of the sensor element 11. The sensor control unit 7 also has a processor and a memory, and calculates the NOx concentration and oxygen concentration in the measurement gas.

The sensor control unit 7 also has 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 pump voltage range, for example, depending on the amount of oxygen stored in the sensor electrode 21 and the amount of VOC adsorbed by the sensor electrode 21.

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 measured 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 measured gas based on the current flowing through the pump cell 4 detected by the current detection unit 74.

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. The element temperature control unit 73 can control the operation of the heater 6, for example, based on temperature information about the sensor element 11, so that the sensor element 11 is in a state suitable for detecting NOx concentrations. 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 or the pump cell 4, and estimate the temperature of the other cell based on the detected temperature information.

The sensor control unit 7 is also configured to be able to communicate data with the ECU (Engine Control Unit) that controls the internal combustion engine. The detection results of the NOx concentration, etc., by the gas concentration detection device 1 are output from the sensor control unit 7 to the ECU (not shown) and used for controlling the exhaust gas purification system, etc. Information on the 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, 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.

Furthermore, when the gas concentration detection device 1 starts up, 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 Figure 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 at which the oxygen stored in the sensor electrode 21 can be removed by 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 sufficiently remove the oxygen stored in the sensor electrode 21 by 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.

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 the 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.

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

Next, after selecting a processing mode in step S2, the process proceeds to step S3, where the 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 the 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 varies 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 and second processing modes, the gas concentration detection device 1 varies 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 varied in accordance with the operation downtime T1.

Here, as shown in the graph in Figure 3, 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 downtime T1 increases. Therefore, in this embodiment, the operation time of the first treatment mode and the second treatment mode is configured to increase as the operation downtime T1 increases.

Furthermore, as shown in the graph in Figure 3, when the operation 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 operation downtime T1 exceeds a certain level, they plateau and barely increase. Therefore, in this embodiment, taking into account the fact that the amount of stored oxygen and the amount of adsorbed VOCs plateau, the execution times for the first processing mode and the second processing mode are each set to 120 seconds or less.

In addition, in this embodiment, the execution time of each processing mode is shorter than the operation pause time T1. Furthermore, the execution times of the first processing mode and the second processing mode are each 1 to 120 seconds. Furthermore, if the application time of one 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.

Next, as shown in the flowchart of Figure 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.

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

Next, the gas concentration detection device 1 executes the selected processing mode in step S4 or step S7, and then begins detecting the NOx concentration of the measured gas.

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 treatment mode and the second treatment mode, 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.

As shown in Figure 3, when the operation downtime T1 is relatively short, the increase rate of stored oxygen is faster than the increase rate of 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 and second treatment modes, or selects only the first treatment mode from the first and second treatment modes, based on the operation downtime T1, and executes the selected treatment mode. This allows for efficient and early activation of the sensor electrode 21. In other words, when the operation 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 operation downtime T1 is relatively long, both the stored oxygen and adsorbed VOCs are likely to affect the activation of the sensor electrode 21. Therefore, when the operation downtime T1 is less than the threshold value T1th, the gas concentration detection device 1 of this embodiment executes only the first treatment mode from the first and second treatment modes. Furthermore, when the operation suspension time T1 is equal to or greater than the threshold value T1th, both the first treatment mode and the second treatment mode are executed. This allows the activation process to be performed according to the state of the sensor electrode 21, and efficiently activates the sensor electrode 21 early. Therefore, the NOx detection accuracy can be improved relatively early after the gas concentration detection device 1 is started.

The first treatment mode is a treatment mode in which the pump cell 4 decomposes water contained in the measured gas to generate hydrogen. The hydrogen generated by the first treatment mode spreads within the measured gas chamber 10 and flows to the sensor electrode 21. This causes the generated hydrogen to react with the oxygen stored 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 measured gas flows toward the sensor electrode 21. By executing 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.

Furthermore, the longer the operation suspension time T1, the greater the amount of oxygen stored and adsorbed VOCs in the sensor electrode 21. Therefore, when the gas concentration detection device 1 executes both the first and second treatment modes, it varies the time for which at least one of the first and second treatment modes is executed, depending on the operation suspension time T1. Furthermore, when the gas concentration detection device 1 executes only the first 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, earlier activation can be achieved more efficiently and reliably.

The concentration of water vapor contained in the measurement gas (exhaust gas) tends to be relatively high when hydrocarbon fuel is being burned in an internal combustion engine. As shown in the graph in Figure 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 an internal combustion engine. This makes it easier 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 ensured.

When both the first and second processing modes are implemented, 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 implemented, 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 during combustion of an air-fuel mixture, the amount of oxygen contained in the measured gas during combustion of the air-fuel mixture in the internal combustion engine tends to be low. On the other hand, the measured gas when the internal combustion engine is not combusting the air-fuel mixture, such as during a fuel cut that stops fuel supply to the internal combustion engine, tends to have a high oxygen concentration. Furthermore, as shown in Figure 7, when the oxygen concentration in the measured gas is above a certain level, the activation time T2 when the second processing mode is implemented tends to be short. Therefore, the gas concentration detection device 1 of this embodiment initiates the second processing mode when the internal combustion engine is not combusting the air-fuel mixture. This allows for efficient removal of VOCs adsorbed to the sensor electrode 21. As a result, the sensor electrode 21 can be reliably activated early.

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. Therefore, by executing the first treatment mode, it is easy to reliably generate a sufficient amount of hydrogen, and by executing the second treatment mode, it is possible to reliably flow a sufficient amount of oxygen into the sensor electrode 21. This ensures that the occluded oxygen and adsorbed VOCs in the sensor electrode 21 are reliably removed. As a result, early activation can be achieved more reliably.

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 executed, 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 executed, a sufficient amount of oxygen can be allowed to flow into the sensor electrode 21 while reliably suppressing oxidation of the sensor electrode 21 due to an excessive amount of oxygen flowing into the sensor electrode 21. As a result, early activation can be more reliably achieved.

In addition, in this embodiment, when both the first and second treatment modes are executed, the second treatment mode is executed first, followed by the first treatment mode. This makes it possible to more reliably remove oxygen stored in the sensor electrode 21, thereby enabling more reliably early activation.

The activation time T2 is shorter than the operation pause time T1. Therefore, early activation of the sensor electrode 21 can be ensured.

The execution time for the first and second processing modes is 1 to 120 seconds, respectively. This ensures that activation processing is carried out in accordance with the amount of oxygen stored in the sensor electrode 21 and the amount of VOCs adsorbed, and ensures early activation.

As described above, this embodiment provides a gas concentration detection device 1 that can be activated efficiently and reliably and quickly.

In the above-mentioned embodiment 1, 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 configuration may also be such that the first processing mode is executed after the second processing mode is executed.

(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. That is, in this example, the activation time T2 when VOCs adsorbed on the sensor electrode were removed was examined, rather than the removal of oxygen occluded on the sensor electrode.

The amount of VOC adsorbed to the sensor electrode increases as the downtime T1 increases. Therefore, as shown in the graph in Figure 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 never exceeds 120 seconds, peaking out at 120 seconds. Based on these results, it is believed 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.

(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 was constant. In this example, Comparative Example 1 is configured to execute only the first treatment mode.

The conditions for the first treatment mode implemented in Comparative Example 1 were a pump voltage of 1.2 V and an execution time of 50 seconds for all operation downtimes T1. On the other hand, the activation treatment conditions for Example 1 varied the pump voltage and execution time depending on the operation downtime T1. Specifically, when operation downtime T1 was time Tn, Example 1, like Comparative Example 1, implemented a pump voltage of 1.2 V and an execution time of the first treatment mode of 50 seconds. Furthermore, when operation downtime T1 was time Tn-1, which was shorter than time Tn, Example 1 implemented a pump voltage of 1.2 V and an execution time of the first treatment mode of 30 seconds. Furthermore, when operation downtimes Tn+1 and Tn+2 were longer than time Tn, Example 1 implemented a second treatment mode with a pump voltage of 0.3 V and an execution time of 60 seconds, in addition to the first treatment mode, which was the same as the treatment mode implemented when operation downtime T1 was time Tn.

The accuracy on the vertical axis of the graph in Figure 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 Figure 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.

As shown in the graph in 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, because 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.

Furthermore, when the downtime T1 is time Tn+1 and time Tn+2, Example 1 has the same accuracy as when it is time Tn, while Comparative Example 1 has lower accuracy compared to when it is time Tn. Furthermore, in Comparative Example 1, accuracy is lower at time Tn+2 than at time Tn+1. Here, the longer the downtime T1, the more oxygen is absorbed by the sensor electrode and the more likely adsorbed VOCs are to increase. Furthermore, in Comparative Example 1, the treatment mode is the same regardless of the downtime T1. Therefore, when the downtime T1 is time Tn+1 and time Tn+2, Comparative Example 1 is unable to sufficiently remove adsorbed VOCs from the sensor electrode, resulting in lower accuracy compared to when it is time Tn. On the other hand, Example 1 executes the second treatment mode in addition to the first treatment mode when the downtime is time Tn+1 and time Tn+2. As a result, Example 1 is believed to have been able to efficiently remove VOCs adsorbed to the sensor electrode. Therefore, it is considered that in Example 1, even when the operation downtime 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.

(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.

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 of the first and second processing modes, 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 time of both the first processing mode and the second processing mode based on the temperature-related information.

Temperature-related information can be, for example, the temperature of the sensor element 11, the temperature of the pump cell 4, the temperature of the sensor cell 3, and 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.

In this embodiment, the execution time of the selected processing mode is changed in accordance with the operation downtime T1, and the execution time of the selected processing mode is changed based on the temperature-related information. 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.
Others are the same as in 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 in the previous embodiments, unless otherwise specified.

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. In other words, 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 obtained.

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

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 exhaust pipe of the internal combustion engine is in a dry state, and a non-dryness determination to determine that the exhaust pipe of the internal combustion engine is not in a dry state. 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 the non-dry period when the dryness determination unit 81 performs the non-dryness determination. Furthermore, after the dryness determination unit 81 performs the 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 the processing mode and varies the time for executing the first processing mode depending on the time from the start of operation of the internal combustion engine to the time when the dryness determination unit 81 performs the 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.

In this embodiment, as shown in Figure 10, the ECU 8 that controls the internal combustion engine has a dryness determination unit 81. The dryness determination unit 81 makes dryness determination and non-dryness determination based on information such as the combustion of the internal combustion engine, the temperature of the exhaust gas in the exhaust pipe, and the flow rate of the 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.

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 between 150 and 450°C during the non-drying period, for example.

In this embodiment, the execution time of the first treatment mode is changed in accordance with the operation pause time T1, and is also 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.

In general, in internal combustion engines, condensed water may form in the exhaust pipe due to condensation or other factors during periods when the engine is not in operation. Furthermore, it is expected 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 operated. 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.

In addition, the element temperature control unit 73 controls the temperature of the sensor element 11 during the non-drying period so that it is 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 so that it is 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.

In addition, 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 for efficient activation of the sensor electrode 21. 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, which may result in a decrease in the accuracy of NOx concentration detection, as shown in Figure 11. Therefore, in this embodiment, the execution time of the first processing mode is extended as the time until the exhaust pipe dries increases. 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, early activation of the sensor electrode 21 can be reliably achieved.

During the non-drying period, the element temperature control unit 73 controls the upper limit temperature of the sensor element 11 to be between 150 and 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 a 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 obtained.

In the above embodiments 1 to 3, the gas concentration detection device 1 has a pump cell 4 and a sensor cell 3. However, in addition to the pump cell and sensor cell, the gas concentration detection device can also be equipped with 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.

In addition, 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, the system can be configured to not execute either the first treatment mode or the second treatment mode.

This disclosure is not limited to the above embodiments and can be applied to various embodiments without departing from the spirit of the present disclosure.

While the present disclosure has been described with reference to certain embodiments, it is understood that the present disclosure is not limited to those embodiments or structures. The present disclosure also encompasses various modifications and equivalent variations. In addition, various combinations and forms, including only one element, more, or less than one element, are also within the scope and spirit of the present disclosure.

<Others>
The features of the present disclosure are as follows:
[Section 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.
[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,
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.
[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]
5. A gas concentration detection device according to any one of claims 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 claims 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 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,
7. The gas concentration detection device according to any one of claims 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 (7)

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. 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. 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. A gas concentration detection device as described in claim 1 or 2, wherein the first processing mode is initiated when a mixture containing fuel is combusted in the internal combustion engine. A gas concentration detection device as described in claim 1 or 2, 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. A gas concentration detection device as described in claim 1 or 2, 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 0.5 V or more and the pump voltage applied in the second processing mode to 0.32 V or less. 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.