JP6187439B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device capable of detecting the concentration of sulfur oxide contained in exhaust gas (test gas) of an internal combustion engine or determining the presence or absence of the sulfur oxide.

Conventionally, in order to control an internal combustion engine, an air-fuel ratio sensor (A / F sensor) that acquires an air-fuel ratio (A / F) of an air-fuel mixture in a combustion chamber based on the concentration of oxygen (O ₂ ) contained in exhaust gas ) Is widely used. One type of such an air-fuel ratio sensor is a limiting current type gas sensor.

  A limiting current type gas sensor used as an air-fuel ratio sensor as described above is an electrochemical cell including a solid electrolyte body having oxide ion conductivity and a pair of electrodes fixed to the surface of the solid electrolyte body. A pumping cell is provided. One of the pair of electrodes is exposed to the exhaust gas of the internal combustion engine as the test gas introduced through the diffusion resistance portion, and the other is exposed to the atmosphere. Furthermore, when detecting the air-fuel ratio, the solid electrolyte body is heated to a predetermined temperature that is equal to or higher than a temperature at which oxide ion conductivity is exhibited (hereinafter, sometimes referred to as “activation temperature”). The

In the above state, when one of the electrodes is used as a cathode and the other electrode is used as an anode, a voltage higher than the voltage at which oxygen decomposition starts (decomposition start voltage) is applied between the pair of electrodes. Oxygen contained in is reduced and decomposed at the cathode to become oxide ions (O ²⁻ ). The oxide ions are conducted to the anode through the solid electrolyte body, become oxygen, and are discharged into the atmosphere. Such movement of oxygen by conduction of oxide ions through the solid electrolyte body from the cathode side to the anode side is referred to as “oxygen pumping action”.

  A current flows between the pair of electrodes by conduction of oxide ions accompanying the oxygen pumping action. The current flowing between the pair of electrodes in this way is referred to as “electrode current”. This electrode current has a tendency to increase as the voltage applied between the pair of electrodes (hereinafter, sometimes simply referred to as “applied voltage”) increases. However, since the flow rate of the test gas reaching the one electrode (cathode) is limited by the diffusion resistance section, the oxygen consumption rate accompanying the oxygen pumping action eventually exceeds the oxygen supply rate to the cathode. . That is, the oxygen reductive decomposition reaction at the cathode is in a diffusion-controlled state.

  In the diffusion-controlled state, the electrode current does not increase even when the applied voltage is increased, and becomes substantially constant. Such a characteristic is referred to as a “limit current characteristic”, and a range of an applied voltage in which the limit current characteristic is manifested (observed) is referred to as a “limit current region”. Furthermore, the electrode current in the limit current region is referred to as “limit current”, and the magnitude of the limit current (limit current value) corresponds to the supply rate of oxygen to the cathode. Since the flow rate of the test gas reaching the cathode is maintained constant by the diffusion resistance portion as described above, the oxygen supply rate to the cathode corresponds to the concentration of oxygen contained in the test gas.

  Therefore, in the limit current type gas sensor used as an air-fuel ratio sensor, the electrode current (limit current) when the applied voltage is set to “predetermined voltage in the limit current region” corresponds to the concentration of oxygen contained in the test gas. To do. In this way, using the limiting current characteristic of oxygen, the air-fuel ratio sensor can detect the concentration of oxygen contained in the exhaust gas as the test gas and acquire the air-fuel ratio of the air-fuel mixture in the combustion chamber based on the detected concentration. it can.

The limiting current characteristics as described above are not limited to oxygen gas alone. Specifically, in the gas containing oxygen atoms in the molecule (hereinafter, sometimes referred to as “oxygen-containing gas”), the limit current is determined by appropriately selecting the applied voltage and the configuration of the cathode. There is something that can express the characteristics. Examples of such oxygen-containing gas include sulfur oxide (SOx), water (H ₂ O), carbon dioxide (CO ₂ ), and the like.

  Incidentally, a small amount of sulfur (S) component is contained in the fuel (for example, light oil and gasoline) of the internal combustion engine. In particular, a fuel also called a poor fuel may contain a sulfur component at a relatively high content. When the content rate of sulfur components in the fuel (hereinafter, sometimes simply referred to as “sulfur content rate”) is high, deterioration and / or failure of components of the internal combustion engine, poisoning of the exhaust purification catalyst, exhaust gas There is an increased risk of problems such as the generation of white smoke. For this reason, the content rate of the sulfur component in the fuel is acquired, and the acquired sulfur content rate is used, for example, to change the control of the internal combustion engine, issue a warning about a failure of the internal combustion engine, It is desirable to help improve self-diagnosis diagnosis (OBD).

  When the fuel of the internal combustion engine contains a sulfur component, sulfur oxide is contained in the exhaust discharged from the combustion chamber. Furthermore, the higher the content of sulfur component in the fuel (the sulfur content), the higher the concentration of sulfur oxide contained in the exhaust (hereinafter sometimes referred to simply as “SOx concentration”). Therefore, if the SOx concentration in the exhaust gas can be accurately acquired, it is considered that the sulfur content can be accurately acquired based on the acquired SOx concentration.

  Therefore, in this technical field, an attempt has been made to acquire the concentration of sulfur oxide contained in the exhaust gas of the internal combustion engine by the limiting current type gas sensor using the oxygen pumping action described above. Specifically, a limiting current type gas sensor (2 cells) having two pumping cells arranged in series so that the cathode faces an internal space through which the exhaust gas of the internal combustion engine as the test gas is guided through the diffusion resistance unit. The limiting current type gas sensor) is used.

  In this sensor, by applying a relatively low voltage between the electrodes of the upstream pumping cell, oxygen contained in the test gas is removed by the oxygen pumping action of the upstream pumping cell. Further, by applying a relatively high voltage between the electrodes of the downstream pumping cell, the downstream pumping cell causes the sulfur oxide contained in the test gas to be reduced and decomposed at the cathode, and the resulting oxidation. Conducts physical ions to the anode. Based on the change in the electrode current (decomposition current) value resulting from this oxygen pumping action, the concentration of sulfur oxide contained in the test gas is acquired (see, for example, Patent Document 1).

JP-A-11-190721

  However, the present inventor correctly detects the sulfur oxide when performing the detection again after detecting the sulfur oxide contained in the test gas (exhaust gas) based on the decomposition current of the sulfur oxide. I noticed that sometimes I couldn't. Specifically, it is detected even though the concentration of sulfur oxide contained in the test gas is actually low, or sulfur oxidation is not performed even though the test gas contains no sulfur oxide. Sometimes it is determined that an object is included. In this specification, “detection (measurement) of the concentration of sulfur oxide contained in the test gas and determination of the presence or absence of the sulfur oxide” is referred to as “detection of sulfur oxide contained in the test gas. ". Furthermore, “detection (measurement) of content of sulfur component contained in fuel and determination of presence or absence of sulfur component” is collectively referred to as “detection of sulfur component contained in fuel”.

  The cause of the above-mentioned erroneous detection is the decomposition product of sulfur oxide adsorbed on the cathode of the electrochemical cell (for example, sulfur (S) and sulfur (S)) in the previous “detection of sulfur oxide contained in the test gas”. It is considered that at least a part of the sulfur compound or the like) remains adsorbed on the cathode even during the current detection. Therefore, in order to prevent the above-described erroneous detection, the decomposition product of the sulfur oxide adsorbed on the cathode of the electrochemical cell when the gas detection operation for detecting the sulfur oxide contained in the test gas is started. Must be removed from the cathode.

  The present invention has been made to address the above-described problems. That is, the present invention removes sulfur oxide decomposition products adsorbed on the cathode from the cathode by combining the temperature of the electrochemical cell and the applied voltage in an appropriate combination, and thus sulfur contained in the test gas. One object is to provide a gas detection device capable of accurately detecting oxides.

  As a result of further studies, the present inventor can desorb the decomposition product of sulfur oxide adsorbed on the cathode as described above by raising the temperature of the electrochemical cell to a predetermined temperature or higher. I found out that I can do it. Specifically, when the gas detection operation is not performed, the rate at which the decomposition product of the sulfur oxide contained in the test gas is desorbed from the cathode than the rate at which the decomposition product is adsorbed on the cathode. The applied voltage and temperature of the electrochemical cell are controlled so as to be larger. It has been found that by maintaining this state for a predetermined period or longer, decomposition products of sulfur oxide adsorbed on the cathode can be removed from the cathode.

  A gas detection apparatus according to the present invention (hereinafter, sometimes referred to as “the present invention apparatus”) will be described below. The device of the present invention is a gas detection device having the same configuration as that of a limiting current gas sensor including an electrochemical cell having an oxygen pumping action. That is, the apparatus of the present invention is based on the detected value corresponding to the electrode current when water and sulfur oxide are decomposed at a predetermined applied voltage in an electrochemical cell (pumping cell) having an oxygen pumping action. It is a gas detection apparatus which detects the sulfur oxide contained in.

Specifically, the device of the present invention includes an element unit, a heater, a voltage application unit, a temperature adjustment unit, and a measurement control unit.
The element section includes a first electrochemical cell including a solid electrolyte body having oxide ion conductivity and a first electrode and a second electrode formed on the surface of the solid electrolyte body, a dense body, and a diffusion resistance section. And comprising. Further, in the element portion, exhaust gas of an internal combustion engine as a test gas is introduced into the internal space defined by the solid electrolyte body, the dense body, and the diffusion resistance portion via the diffusion resistance portion. An electrode is exposed to the internal space, and the second electrode is exposed to a first separate space that is a space different from the internal space.
The heater generates heat when energized to heat the element unit.
The electron applying unit applies a voltage between the first electrode and the second electrode.
The temperature adjusting unit controls the temperature of the element unit by controlling an energization amount to the heater.
The measurement control unit controls the voltage application unit and the temperature adjustment unit and acquires a first detection value corresponding to a current flowing between the first electrode and the second electrode.

Further, the first electrode has a first predetermined temperature equal to or higher than an activation temperature at which the element portion has a temperature at which the oxide ion conductivity of the solid electrolyte body is expressed, and the first electrode and the second electrode. In a first state in which a first predetermined voltage is applied between the electrodes, water (H ₂ O) and sulfur oxide (SOx) contained in the test gas can be decomposed. It is comprised so that it may become.
The measurement control unit uses the temperature adjustment unit to match the temperature of the element unit with the first predetermined temperature and is applied between the first electrode and the second electrode using the voltage application unit. The first state is realized by matching a first applied voltage that is a voltage to be equal to the first predetermined voltage, and is included in the test gas based on the first detection value acquired in the first state It is configured to perform a gas detection operation for detecting the concentration of sulfur oxide to be detected or determining the presence or absence of the sulfur oxide.

  In addition, the measurement control unit controls the temperature of the element unit using the temperature adjustment unit and performs the first application voltage using the voltage application unit when the gas detection operation is not being performed. Control. Thereby, the measurement control unit removes the decomposition product from the first electrode more than the adsorption rate, which is the rate at which the decomposition product of sulfur oxide contained in the test gas is adsorbed to the first electrode. The desorption rate, which is the separation rate, is made larger. The measurement control unit performs a poisoning recovery operation in which a combination of the first applied voltage and the temperature of the element unit realizing such a state is maintained for a predetermined first period or more. Configured to do.

  According to the apparatus of the present invention, the decomposition product is desorbed from the first electrode rather than the rate at which the decomposition product of sulfur oxide contained in the test gas is adsorbed to the first electrode (that is, the adsorption rate). The combination of the first applied voltage and the temperature of the element portion is maintained so that the speed (that is, the desorption speed) is higher. Therefore, the device of the present invention can remove from the cathode the “decomposition product of sulfur oxide adsorbed on the first electrode (cathode) during the gas detection operation”. As a result, the sulfur oxide decomposition product is not adsorbed on the cathode the next time the gas detection operation is performed. Therefore, according to this invention apparatus, the density | concentration of the sulfur oxide contained in test gas can be detected correctly, or the presence or absence of the sulfur oxide can be determined correctly.

  The combination of the first applied voltage and the temperature of the element unit suitable for execution of the poisoning recovery operation (the desorption rate is larger than the adsorption rate) can be specified by the following preliminary experiment, for example. it can. First, a gas detection operation is performed over a predetermined period to adsorb sulfur oxide decomposition products to the first electrode. Thereafter, a test gas containing sulfur oxide in various combinations of the first applied voltage and the temperature of the element portion is supplied to the internal space over a predetermined period, and the first sulfur oxide decomposition product is supplied. Measure the increase or decrease in the amount of adsorption to the electrode. The combination of the first applied voltage at which the amount of adsorption of the decomposition products to the first electrode is reduced and the temperature of the element portion is suitable for the execution of the poisoning recovery operation (the desorption rate is higher than the adsorption rate). This is specified as a combination of the first applied voltage and the temperature of the element portion. The increase / decrease in the amount of adsorption of the decomposition product to the first electrode can be measured, for example, by measuring the mass of the first electrode or analyzing the surface of the first electrode.

  Furthermore, with regard to the length of the first period, which is the duration of the poisoning recovery operation, for example, the decomposition of sulfur oxides in the combination of the first applied voltage and the temperature of the element portion specified by the preliminary experiment as described above. The rate of decrease in the amount of adsorption of the product to the first electrode and the amount of adsorption of the decomposition product assumed in the gas detection operation to the first electrode can be determined as appropriate.

  By the way, when the gas detection operation is not performed, the device according to the present invention is suitable for performing the poisoning recovery operation (the desorption rate is larger than the adsorption rate) and the first applied voltage and the temperature of the element unit. By maintaining this, the decomposition product of the sulfur oxide adsorbed on the first electrode is desorbed. As will be described in detail later, in principle, the higher the first applied voltage, the higher the adsorption rate, and the higher the temperature of the element portion, the higher the desorption rate. Therefore, in order to effectively desorb the decomposition product of the sulfur oxide adsorbed on the first electrode, it is desirable that the first applied voltage is sufficiently low and the temperature of the element portion is sufficiently high. On the other hand, when the gas detection operation is performed, the temperature of the element portion is raised to the first predetermined temperature.

  Therefore, in the gas detection device according to another aspect of the present invention, the measurement control unit performs the gas detection operation, and then maintains the temperature of the element unit at the activation temperature or higher. By reducing the first applied voltage to a non-decomposable voltage that is a voltage at which sulfur oxides contained in the test gas are not decomposed even if the temperature of the part is equal to or higher than the activation temperature, the poisoning It is configured to perform a recovery operation. In the gas detection device according to this aspect, the measurement control unit performs the gas detection operation, and then stops applying the voltage between the first electrode and the second electrode, thereby preventing the indecomposable voltage. The first applied voltage may be reduced to

  The gas detection apparatus according to the above aspect does not increase the temperature of the element unit from a low temperature such as room temperature, for example, but does not greatly decrease the temperature of the element unit that is increased during the execution of the gas detection operation (that is, gas The poisoning recovery operation is performed by lowering the first applied voltage to a non-decomposable voltage while maintaining the activation temperature close to or higher than the first predetermined temperature during the detection operation. Therefore, the amount of energy for raising the temperature of the element portion for the poisoning recovery operation can be reduced, which is desirable from the viewpoint of improving energy efficiency. The indecomposable voltage is a voltage at which the sulfur oxide contained in the test gas is not decomposed even when the temperature of the element portion is equal to or higher than the activation temperature. In other words, the non-decomposable voltage can be said to be a voltage lower than the minimum voltage at which the sulfur oxide is decomposed in a state where the temperature of the element portion is maintained at the activation temperature or higher.

  Furthermore, when the poisoning recovery operation is performed by reducing the first applied voltage to a non-decomposable voltage as described above, and by stopping the application of the voltage between the first electrode and the second electrode. When the poisoning recovery operation is performed by reducing the first applied voltage to a non-decomposable voltage, the first applied voltage is lowered to a voltage at which sulfur oxides cannot be decomposed. That is, there is no possibility that the decomposition product of the sulfur oxide is further adsorbed on the first electrode, so after performing the poisoning recovery operation, it is not necessary to maintain the temperature of the element portion at the first predetermined temperature or higher. From the viewpoint of improving energy efficiency and the like, it is desirable to stop heating the element portion immediately after performing the poisoning recovery operation. Therefore, in these cases, the measurement control unit stops heating the element unit by the heater by stopping energization of the heater by the temperature adjusting unit after executing the poisoning recovery operation. Can be configured.

  Incidentally, in order to execute the gas detection operation, as described above, it is necessary to raise the temperature of the element portion to the first predetermined temperature. Therefore, when the temperature of the element portion is raised to the first predetermined temperature in order to execute the gas detection operation, the poisoning recovery operation may be executed by maintaining a sufficiently low first applied voltage.

  Therefore, in the gas detection device according to still another aspect of the present invention, the measurement control unit sets the first applied voltage to a temperature equal to or higher than the activation temperature before performing the gas detection operation. While maintaining the non-decomposable voltage, which is a voltage at which the sulfur oxide contained in the test gas is not decomposed even at the temperature of the above, by raising the temperature of the element portion to a temperature equal to or higher than the activation temperature, The poisoning recovery operation is configured to be executed. In the gas detection device according to this aspect, the measurement control unit prevents the voltage application unit from applying a voltage between the first electrode and the second electrode before performing the gas detection operation. The device may be configured to raise the temperature of the element unit to a temperature equal to or higher than the activation temperature while maintaining the first applied voltage at the non-decomposable voltage.

  The gas detection device according to the above aspect does not increase the temperature of the element unit from a low temperature such as room temperature, for example, in order to perform the poisoning recovery operation, but instead of the element unit raised to perform the gas detection operation. Since poisoning recovery operation is performed using temperature, it is desirable from the viewpoint of improving energy efficiency.

  By the way, the gas detection apparatus according to the above aspect raises the temperature of the element portion to a temperature equal to or higher than the activation temperature before performing the gas detection operation. Thereafter, since the gas detection device performs a gas detection operation, it is not desirable from the viewpoint of improving energy efficiency or the like to lower the temperature of the element portion below the activation temperature after completing the execution of the poisoning recovery operation. .

  Therefore, from this point of view, in the gas detection device according to the above aspect, the measurement control unit lowers the temperature of the element unit to a temperature lower than the activation temperature after performing the poisoning recovery operation. The gas detection operation may be performed by matching the first predetermined temperature without increasing the first applied voltage to the first predetermined voltage. As a result, the gas detection operation is performed without greatly decreasing the temperature of the element portion that has been raised to the activation temperature or higher by performing the poisoning recovery operation (that is, while maintaining the temperature at the activation temperature or higher). Execute. Therefore, the amount of energy for raising the temperature of the element portion for the gas detection operation can be reduced, which is desirable from the viewpoint of improving energy efficiency.

  Other objects, other features, and attendant advantages of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

It is typical sectional drawing which shows an example of a structure of the element part with which the gas detection apparatus (1st apparatus) which concerns on 1st Embodiment of this invention is provided. Schematic showing the relationship between the voltage (applied voltage) Vm1 applied between the first electrode and the second electrode constituting the first electrochemical cell provided in the first device, and the electrode current Im1 flowing between these electrodes It is a typical graph. Applied voltage Vm1 in the first device is a schematic graph showing the relationship between the concentration of sulfur dioxide (SO ₂₎ contained in the size and the test gas in the electrode current Im1 of time is 1.0 V. It is a flowchart which shows the gas detection operation and poisoning recovery operation which a 1st apparatus performs. It is typical sectional drawing which shows an example of a structure of the element part with which the gas detection apparatus (2nd apparatus) which concerns on 2nd Embodiment of this invention is provided.

<First Embodiment>
Hereinafter, a gas detection device (hereinafter, may be referred to as “first device”) according to a first embodiment of the present invention will be described. The first device is a two-cell type gas sensor (gas detection device) including two electrochemical cells. In the first apparatus, the second electrochemical cell (pumping cell) on the upstream side decomposes and discharges oxygen and nitrogen oxides in the exhaust gas as the test gas, and the first electrochemical cell (sensor cell) on the downstream side Decompose and detect water and sulfur oxides in the sample gas.

(Constitution)
As shown in FIG. 1, the element unit 10 included in the first device includes a first solid electrolyte body 11s, a second solid electrolyte body 12s, a first alumina layer 21a, a second alumina layer 21b, a third alumina layer 21c, 4a alumina layer 21d, 5th alumina layer 21e, 6th alumina layer 21f, diffusion resistance part (diffusion rate-limiting layer) 32, and heater (electric heater) 41 are provided.
The solid electrolyte body 11s is a thin plate body containing zirconia or the like and having oxide ion conductivity. The zirconia forming the solid electrolyte body 11s may contain elements such as scandium (Sc) and yttrium (Y). The second solid electrolyte body 12s is the same as the solid electrolyte body 11s.
The first to sixth alumina layers 21a to 21f are dense (gas impermeable) layers (dense bodies) containing alumina.
The diffusion resistance portion 32 is a porous diffusion-controlling layer, and is a gas permeable layer (thin plate).
The heater 41 is a cermet thin plate including, for example, platinum (Pt) and ceramics (for example, alumina), and is a heating element that generates heat when energized.

  The layers of the element unit 10 are, from below, the fifth alumina layer 21e, the fourth alumina layer 21d, the third alumina layer 21c, the first solid electrolyte body 11s, the diffusion resistance unit 32, the second alumina layer 21b, and the second solid electrolyte. The body 12s, the sixth alumina layer 21f, and the first alumina layer 21a are laminated in this order.

  The internal space 31 is a space defined by the first solid electrolyte body 11 s, the second solid electrolyte body 12 s, the diffusion resistance portion 32 and the second alumina layer 21 b, and the test gas via the diffusion resistance portion 32 therein. The exhaust of the internal combustion engine is introduced. That is, in the element unit 10, the internal space 31 communicates with the inside of an exhaust pipe (none of which is shown) of the internal combustion engine via the diffusion resistance unit 32. Therefore, the exhaust gas in the exhaust pipe is guided into the internal space 31 as the test gas.

  The first atmosphere introduction path 51 is defined by the first solid electrolyte body 11s, the third alumina layer 21c, and the fourth alumina layer 21d, and is open to the atmosphere outside the exhaust pipe. The first air introduction path 51 corresponds to a first separate space. The second atmosphere introduction path 52 is defined by the second solid electrolyte body 12s, the first alumina layer 21a, and the sixth alumina layer 21f, and is open to the atmosphere outside the exhaust pipe. The second atmosphere introduction path 52 corresponds to a second separate space.

  The first electrode 11a is a cathode, and the second electrode 11b is an anode. The first electrode 11a is fixed to the surface on one side of the first solid electrolyte body 11s (specifically, the surface of the first solid electrolyte body 11s that defines the internal space 31). On the other hand, the second electrode 11b is fixed to the surface on the other side of the first solid electrolyte body 11s (specifically, the surface of the first solid electrolyte body 11s that defines the first air introduction path 51). The first electrode 11a and the second electrode 11b are arranged to face each other with the solid electrolyte body 11s interposed therebetween. The first electrode 11a, the second electrode 11b, and the first solid electrolyte body 11s constitute a first electrochemical cell 11c having an oxygen discharge capability by an oxygen pumping action.

  The third electrode 12a is a cathode, and the fourth electrode 12b is an anode. The third electrode 12a is fixed to the surface of one side of the second solid electrolyte body 12s (specifically, the surface of the second solid electrolyte body 12s that defines the internal space 31). On the other hand, the fourth electrode 12b is fixed to the surface on the other side of the second solid electrolyte body 12s (specifically, the surface of the second solid electrolyte body 12s that defines the second air introduction path 52). The third electrode 12a and the fourth electrode 12b are disposed so as to face each other with the solid electrolyte body 12s interposed therebetween. The third electrode 12a, the fourth electrode 12b, and the second solid electrolyte body 12s constitute a second electrochemical cell 12c having an oxygen discharge capability by an oxygen pumping action. The first electrochemical cell 11c and the second electrochemical cell 12c are heated by the heater 41 and maintained at a desired temperature.

  Each of the first solid electrolyte body 11s, the second solid electrolyte body 12s, and the first to sixth alumina layers 21a to 21f is formed into a sheet by, for example, a doctor blade method, an extrusion method, or the like. The first electrode 11a, the second electrode 11b, the third electrode 12a, the fourth electrode 12b, and the wiring for energizing these electrodes are formed by, for example, a screen printing method. By laminating and firing these sheets as described above, the element portion 10 having the above-described structure is integrally manufactured.

  The first electrode 11a is a porous cermet electrode that contains an alloy of platinum (Pt) and rhodium (Rh) as a main component, and the second electrode 11b is a porous cermet electrode that contains platinum (Pt) as a main component. is there. However, the material constituting the first electrode 11a is a test sample introduced into the internal space 31 through the diffused resistor 32 when a predetermined voltage is applied between the first electrode 11a and the second electrode 11b. There is no particular limitation as long as water and sulfur oxides contained in the gas can be reduced and decomposed. Preferably, the material constituting the first electrode 11a contains a platinum group element such as platinum (Pt), rhodium (Rh), palladium (Pd) or an alloy thereof as a main component. More preferably, the first electrode 11a is a porous cermet electrode containing as a main component at least one selected from the group consisting of platinum (Pt), rhodium (Rh), and palladium (Pd). Further, the material constituting the second electrode 11b is not limited to the above, and can be appropriately selected from various materials widely used as the anode material of the electrochemical cell utilizing the oxygen pumping action.

  On the other hand, the third electrode 12a and the fourth electrode 12b are porous cermet electrodes containing platinum (Pt) as a main component. However, the material constituting the first electrode 12a is a voltage capable of decomposing oxygen contained in the test gas between the third electrode 12a and the fourth electrode 12b (specifically, about 0.1 V or more). Typically, there is no particular limitation as long as oxygen contained in the test gas introduced to the internal space 31 through the diffusion resistance portion 32 can be reduced and decomposed when about 0.4 V) is applied. . Further, the material constituting the fourth electrode 12b is not limited to the above, and can be appropriately selected from various materials widely used as the anode material of the electrochemical cell utilizing the oxygen pumping action.

  In the example shown in FIG. 1, the second electrochemical cell 12c includes a second solid electrolyte body 12s separate from the first solid electrolyte body 11s constituting the first electrochemical cell 11c. However, the second electrochemical cell 12c may share the first solid electrolyte body 11s with the first electrochemical cell 11c. In this case, the first atmosphere introduction path 51 functions as a first separate space and a second separate space.

The first device further includes a power source 61, an ammeter 71, and an ECU (electric control unit) (not shown). The power supply 61 and the ammeter 71 are connected to the ECU.
The power supply 61 can apply a predetermined voltage between the first electrode 11a and the second electrode 11b so that the potential of the second electrode 11b is higher than the potential of the first electrode 11a. The operation of the power supply 61 is controlled by the ECU.
The ammeter 71 measures the magnitude of the electrode current, which is the current flowing between the first electrode 11a and the second electrode 11b (therefore, the current flowing through the first solid electrolyte body 11s), and the measured value is measured by the ECU. To output.

In addition, the first device further includes a power source 62 and an ammeter 72. The power source 62 and the ammeter 72 are connected to the ECU.
The power source 62 can apply a predetermined voltage between the third electrode 12a and the fourth electrode 12b so that the potential of the fourth electrode 12b is higher than the potential of the third electrode 12a. The operation of the power source 62 is controlled by the ECU.
The ammeter 72 measures the magnitude of the electrode current which is the current flowing between the third electrode 12a and the fourth electrode 12b (and hence the current flowing through the second solid electrolyte body 12s), and the measured value is measured by the ECU. To output.

  As described above, the first electrochemical cell 11 c and the second electrochemical cell 12 c are heated by the heater 41. The resulting temperature of the element unit 10 is detected based on the impedance when a high-frequency voltage is applied between the third electrode 12a and the fourth electrode 12b. The ECU controls the power supplied to the heater 41 based on the detected temperature to control the temperature of the element unit 10. However, the temperature of the element unit 10 may be detected based on the impedance when a high frequency voltage is applied between the first electrode 11a and the second electrode 11b, or may be detected by providing a separate temperature sensor. May be.

  The ECU is a microcomputer including a CPU, a ROM that stores programs executed by the CPU, a map, and the like, and a RAM that temporarily stores data (none of which are shown). The ECU is connected to an actuator (not shown) of the internal combustion engine (fuel injection valve, throttle valve, EGR valve, etc.). The ECU sends drive (instruction) signals to these actuators to control the internal combustion engine.

  The ECU can control a first applied voltage that is a voltage applied between the first electrode 11a and the second electrode 11b. That is, the power supply 61 and the ECU constitute a first voltage application unit. Further, the ECU can receive a signal corresponding to the electrode current flowing from the ammeter 71 and flowing through the first electrochemical cell 11c. That is, the ammeter 71 and the ECU constitute a first measurement control unit. In addition, the ECU can control the voltage applied between the third electrode 12a and the fourth electrode 12b. That is, the power source 62 and the ECU constitute a second voltage application unit. Further, the ECU can receive a signal corresponding to the electrode current flowing in the second electrochemical cell 12 c output from the ammeter 72. That is, the ammeter 72 and the ECU constitute a second measurement control unit. In addition, the ECU can control the temperature of the element unit 10 by controlling the energization amount to the heater 41. That is, the heater 41 and the ECU constitute a temperature adjustment unit.

  In the example shown in FIG. 1, the first and second voltage application units are included as separate voltage application units. However, these voltage application units may be configured as one voltage application unit as long as an intended applied voltage can be applied between the intended electrodes. Similarly, the example shown in FIG. 1 includes the first and second measurement control units as separate measurement control units. However, these measurement control units may be configured as one measurement control unit as long as it is possible to acquire each of the desired detection values from the intended electrodes.

(Gas detection operation)
The CPU provided in the above-described ECU (hereinafter sometimes simply referred to as “CPU”) heats the element portion 10 to the first predetermined temperature that is equal to or higher than the activation temperature by the heater 41. The activation temperature is the “temperature of the element unit 10” at which the oxide ion conductivity of the solid electrolyte (the first solid electrolyte body 11s and the second solid electrolyte body 12s) is manifested. In this state, the CPU applies a voltage (for example, 0.4 V) corresponding to the limiting current region of oxygen between these electrodes so that the third electrode 12a and the fourth electrode 12b become a cathode and an anode, respectively. . Thereby, oxygen and nitrogen oxides are decomposed at the third electrode 12a, and the generated oxide ions (O ²⁻ ) are discharged from the internal space 31 to the second atmosphere introduction path 52 by the oxygen pumping action. In this way, the CPU substantially eliminates oxygen and nitrogen oxides contained in the test gas in the internal space 31 using the second electrochemical cell 12c.

  On the other hand, in the state in which the element unit 10 is heated to the first predetermined temperature by the heater 41, the CPU performs a first predetermined interval between these electrodes so that the first electrode 11a and the second electrode 11b become a cathode and an anode, respectively. A voltage (eg, 1.1 V) is applied. Thereby, not only the water contained in the test gas but also the sulfur oxide contained in the test gas is decomposed in the first electrode 11a. As a result, the first detection value corresponding to the electrode current when the first predetermined voltage is applied between the first electrode 11a and the second electrode 11b depends on the concentration of sulfur oxide contained in the test gas. Change. In this way, the CPU detects the concentration of sulfur oxide contained in the test gas.

(Detection principle)
Here, the principle of the gas detection operation performed in the first device will be specifically described. FIG. 2 is a schematic graph showing the relationship between the applied voltage Vm1 and the electrode current Im1 when the applied voltage Vm1 is gradually increased (step-up sweep) in the first electrochemical cell 11c. This measurement was performed in a state in which the element unit 10 was heated by the heater 41 to “a first predetermined temperature not lower than the activation temperature that is a temperature at which the oxide ion conductivity of the first solid electrolyte body 11 s is developed”. Furthermore, in this example, four different test gases having concentrations of sulfur dioxide (SO ₂ ) as sulfur oxide contained in the test gas of 0, 100, 300, and 500 ppm were used. In addition, the concentrations of oxygen and nitrogen oxide contained in the test gas reaching the first electrode 11a (cathode) of the first electrochemical cell 11c are arranged on the upstream side of the first electrochemical cell 11c. The second electrochemical cell 12c is maintained constant (substantially 0 (zero) ppm) in any sample gas.

  First, a solid curve L1 indicates the relationship between the applied voltage Vm1 and the electrode current Im1 when the concentration of sulfur dioxide contained in the test gas is 0 (zero) ppm. As described above, since the oxygen and nitrogen oxides contained in the test gas in the internal space 31 are substantially removed by the second electrochemical cell 12c, in the region where the applied voltage Vm1 is less than about 0.6V. The electrode current Im1 does not flow (Im1 = 0 μA). When the applied voltage Vm1 becomes about 0.6 V or more, the electrode current Im1 starts to increase. The increase in the electrode current Im1 is caused by the start of water decomposition in the first electrode 11a.

  Next, a dotted curve L2 shows the relationship between the applied voltage Vm1 and the electrode current Im1 when the concentration of sulfur dioxide contained in the test gas is 100 ppm. Also in this case, when the applied voltage Vm1 is less than the voltage at which water decomposition at the first electrode 11a begins (decomposition start voltage) (about 0.6 V), the relationship between the applied voltage Vm1 and the electrode current Im1 is a curve L1 (covered). This is the same as the case where the concentration of sulfur dioxide contained in the detected gas is 0 (zero) ppm. That is, the electrode current Im1 does not flow in a region where the applied voltage Vm1 is less than about 0.6V. On the other hand, when the applied voltage Vm1 is equal to or higher than the water decomposition start voltage (about 0.6 V) in the first electrode 11a, the electrode current Im1 flows due to water decomposition. However, the electrode current Im1 is small compared to the curve L1, and the increase rate of the electrode current Im1 with respect to the applied voltage Vm1 is also small compared to the curve L1 (the slope is small).

  Further, curves L3 and L4 represented by the alternate long and short dash line and the broken line show the relationship between the applied voltage Vm1 and the electrode current Im1 when the concentration of sulfur dioxide contained in the test gas is 300 ppm and 500 ppm, respectively. . Also in these cases, the electrode current Im1 does not flow when the applied voltage Vm1 is lower than the water decomposition start voltage (about 0.6 V) in the first electrode 11a. On the other hand, when the applied voltage Vm1 is equal to or higher than the water decomposition start voltage (about 0.6 V) in the first electrode 11a, the electrode current Im1 flows due to water decomposition. However, the higher the concentration of sulfur dioxide contained in the test gas, the smaller the electrode current Im1, and the higher the increase rate of the electrode current Im1 relative to the applied voltage Vm1, the smaller the concentration of sulfur dioxide contained in the test gas ( (Slope is small).

  As described above, the magnitude of the electrode current Im1 when the applied voltage Vm1 is equal to or higher than the water decomposition start voltage (about 0.6 V) in the first electrode 11a is the sulfur oxide contained in the test gas. Varies depending on the concentration of sulfur dioxide. For example, when the magnitude of the electrode current Im1 in the curves L1 to L4 when the applied voltage Vm1 in the graph shown in FIG. 2 is 1.0 V is plotted against the concentration of sulfur dioxide contained in the test gas, FIG. The graph shown in 3 is obtained. As shown by the dotted curve in FIG. 3, the magnitude of the electrode current Im1 at a specific applied voltage Vm1 (in this case, 1.0 V) varies depending on the concentration of sulfur dioxide contained in the test gas. To do. Therefore, if the electrode current Im1 (corresponding first detection value) at a specific applied voltage Vm1 (a predetermined voltage equal to or higher than the water decomposition start voltage and also referred to as “first predetermined voltage”) is obtained, The concentration of sulfur oxide corresponding to the electrode current Im1 (corresponding to the first detection value) can be acquired.

  The specific values of the applied voltage Vm1 shown on the horizontal axis of the graph shown in FIG. 2, the electrode current Im1 shown on the vertical axis, and the applied voltage Vm1 described in the above description are as follows. The value of the applied voltage Vm1 and the electrode current Im1 may vary depending on the conditions of the experiment performed to obtain the graph shown in FIG. 2 (for example, the concentration of various components contained in the test gas). Is not always the above-mentioned value.

  By the way, the element unit 10 is heated to the first predetermined temperature as described above, and is acquired in the first state in which the first predetermined voltage is applied between the first electrode 11a and the second electrode 11b. The details of the mechanism by which the detected first detection value changes according to the concentration of sulfur oxide in the test gas is unknown. However, in the first state, not only the water contained in the test gas but also the sulfur oxide contained in the test gas is decomposed at the first electrode 11a which is the cathode. As a result, sulfur oxide decomposition products (for example, sulfur (S) and sulfur compounds) are adsorbed on the first electrode 11a, and the area of the first electrode 11a that can contribute to water decomposition decreases. Conceivable. For this reason, it is considered that the first detection value (corresponding to the electrode current) in the first state changes according to the concentration of sulfur oxide contained in the test gas.

(Poison recovery action)
As described above, as a result of the gas detection operation, at least a part of the sulfur oxide decomposition products (for example, sulfur (S) and sulfur compounds) is adsorbed to the first electrode 11a (cathode). Therefore, if the gas detection operation is executed again in this state, a first detection value smaller than the original value is acquired, and the concentration of sulfur oxide contained in the test gas is detected to be higher than the original value.

  Therefore, the first device controls the first applied voltage, which is a voltage applied between the first electrode 11a and the second electrode 11b, and the temperature of the element unit 10 when the gas detection operation is not performed. Then, the poisoning recovery operation is executed, and the decomposition product of the sulfur oxide adsorbed on the first electrode 11a (cathode) is desorbed from the first electrode 11a.

  Specifically, when the gas detection operation is not being performed, the first device has the decomposition product that is higher than the adsorption rate, which is the rate at which the decomposition product of sulfur oxide is adsorbed on the first electrode 11a. The first applied voltage and the temperature of the element unit 10 are controlled so that the desorption rate, which is the rate of desorption from the one electrode 11a, becomes larger. By continuing such a state in which the combination of the first applied voltage and the temperature of the element unit 10 is maintained for a predetermined first period or longer, the first device is adsorbed on the first electrode 11a (cathode). Remove decomposition products of sulfur oxide (perform poisoning recovery operation).

(Recovery principle)
Here, the principle of the poisoning recovery operation executed by the first device will be described. In principle, the higher the first applied voltage, the more sulfur oxide is decomposed per unit time, so the adsorption rate of sulfur oxide decomposition products to the first electrode 11a is higher. However, the case where the first applied voltage is excessive and the element portion is deteriorated such as decomposition of the solid electrolyte body or the case where the first applied voltage reaches the limit current region of the sulfur oxide is excluded. Conversely, the lower the first applied voltage, the lower the adsorption rate of the decomposition products to the first electrode 11a. In particular, when the first applied voltage is less than the decomposition start voltage of sulfur oxide (the lowest voltage (the minimum voltage) at which sulfur oxide can be decomposed) (that is, the first applied voltage is a “non-decomposable voltage”). ), The adsorption rate of the decomposition product of the sulfur oxide to the first electrode 11a is substantially 0 (zero).

  On the other hand, in principle, the higher the temperature of the element unit 10, the higher the desorption rate of the decomposition product of the sulfur oxide from the first electrode 11a. Conversely, the lower the temperature of the element unit 10, the lower the desorption rate of the decomposition product from the first electrode 11a. This phenomenon is because the molecular kinetic energy of the decomposition product adsorbed on the first electrode 11a increases as the temperature of the element unit 10 increases, and becomes higher than the binding (adsorption) energy to the first electrode 11a. It is thought to happen.

  Therefore, when the decomposition product of the sulfur oxide is adsorbed on the first electrode 11a, the first applied voltage is decreased or the temperature of the element unit 10 is increased to increase the first decomposition product. The adsorption rate to the electrode 11a can be decreased, and the desorption rate of the decomposition product from the first electrode 11a can be increased. Thus, a state in which the desorption rate is higher than the adsorption rate is realized, and the decomposition product can be removed from the first electrode 11a by maintaining this state over a predetermined first period. .

(Specific operation)
Here, the gas detection operation and poisoning recovery operation executed by the first device will be described more specifically. FIG. 4 is a flowchart illustrating an example of a gas detection operation and a poisoning recovery operation performed by the CPU of the ECU using the element unit 10. In this example, the first device executes the poisoning recovery operation 1 before the gas detection operation and the poisoning recovery operation 2 after the gas detection operation. Here, “perform the poisoning recovery operation 1 before the gas detection operation” means “execute the gas detection operation subsequent to the poisoning recovery operation 1”. On the other hand, “perform poisoning recovery operation 2 after gas detection operation” means “perform poisoning recovery operation 2 following the gas detection operation”. However, at least one of the poisoning recovery operations 1 and 2 may be performed at an unrelated time that is not continuous with the gas detection operation. In the following description, the gas detection operation and poisoning recovery operation executed by the first device are collectively referred to as “SOx sensor control routine”.

  First, the CPU starts the “SOx sensor control routine” from step S01 at a predetermined timing after the internal combustion engine is started, and proceeds to step S02. When the internal combustion engine is started, no voltage is applied between the first electrode 11a and the second electrode 11b, and the heater 41 is not energized.

  In step S02, the CPU determines whether or not there is a request (SOx detection request) for detecting sulfur oxide contained in the test gas. The SOx detection request is generated, for example, when a fuel tank is filled with fuel in a vehicle equipped with an internal combustion engine to which the first device is applied. Further, after the fuel is filled in the fuel tank, the “SOx sensor control routine” is executed, and the detection process of sulfur oxide contained in the test gas (ie, “gas detection operation”) is acquired. If there is a history, the SOx concentration acquisition request may be canceled.

  If it is determined in step S02 that there is a SOx detection request (step S02: Yes), the CPU proceeds to the next step S03, and determines whether the internal combustion engine to which the first device is applied is in a steady state. The CPU, for example, when the difference between the maximum value and the minimum value of the load within a predetermined period is less than the threshold value, or when the difference between the maximum value and the minimum value of the accelerator operation amount within the predetermined period is less than the threshold value, It is determined that the internal combustion engine is in a steady state.

  If it is determined in step S03 that the internal combustion engine is in a steady state (step S03: Yes), the CPU proceeds to the next step S04 and performs poisoning recovery operation 1. Specifically, the heater 41 is energized while the first applied voltage, which is the voltage applied between the first electrode 11a and the second electrode 11b, is lower than the sulfur oxide decomposition start voltage. The element unit 10 is heated, and the temperature of the element unit 10 is set to a temperature (for example, 700 ° C.) higher than the activation temperature (for example, 500 ° C.) of the first solid electrolyte body 11s, and this state is set to a predetermined first period. To continue.

  If the voltage is not applied between the first electrode 11a and the second electrode 11b when the poisoning recovery operation 1 is performed, for example, immediately after the internal combustion engine is started, the first applied voltage is 0. In the state of (zero) V, the heater unit 41 may be energized to heat the element unit 10. On the other hand, when a voltage is applied between the first electrode 11a and the second electrode 11b when performing the poisoning recovery operation 1, a predetermined voltage (for example, 0) less than the sulfur oxide decomposition start voltage is applied. .4 V) may be applied to the heater 41 in a state where the first applied voltage is set to heat the element unit 10.

  In the above state, since the first applied voltage is lower than the sulfur oxide decomposition start voltage, the sulfur oxide contained in the test gas is not decomposed at the first electrode 11a. That is, the decomposition product of sulfur oxide is not further adsorbed on the first electrode 11a. On the other hand, since the temperature of the element unit 10 is sufficiently higher than the activation temperature of the first solid electrolyte body 11s, even if the decomposition product of sulfur oxide is adsorbed on the first electrode 11a, the decomposition product is Desorbed from the first electrode 11a. Accordingly, in the above state, the rate at which the decomposition product of sulfur oxide contained in the test gas is desorbed from the first electrode 11a than the adsorption rate at which the decomposition product is adsorbed on the first electrode 11a. The desorption rate is greater. That is, the above state corresponds to a state in which the combination of the first applied voltage suitable for the poisoning recovery operation and the temperature of the element unit 10 is maintained.

  Next, the CPU proceeds to step S05 to execute a gas detection operation. Specifically, the CPU sets the temperature of the element unit 10 to the first predetermined temperature (for example, 600 ° C.) by the heater 41 and sets the first applied voltage to the first predetermined voltage (for example, 1.1 V) by the voltage application unit. To do. In this state, the CPU acquires the electrode current flowing between the first electrode 11a and the second electrode 11b as the first detection value, and refers to the data map as shown in FIG. The concentration of sulfur oxide corresponding to the detected value is acquired.

  At least during the execution of the gas detection operation, the CPU substantially excludes oxygen and nitrogen oxides contained in the test gas in the internal space 31 using the second electrochemical cell 12c. Thereby, the change of the 1st detection value resulting from the change of the density | concentration of oxygen and nitrogen oxide contained in test gas can be reduced. As a result, it is possible to accurately detect sulfur oxides contained in the test gas. On the other hand, during the execution of the poisoning recovery operations 1 and 2, from the viewpoint that the decomposition product of the sulfur oxide adsorbed on the first electrode 11a can be desorbed from the first electrode 11a by reoxidation, the internal space 31 is not necessarily required. It is not necessary to exclude oxygen and nitrogen oxides contained in the sample gas.

  Next, the CPU proceeds to step S06, and determines whether or not the concentration of sulfur oxide obtained in step S05 is equal to or higher than a predetermined value. This predetermined value is a threshold value for determining whether or not a significant amount of decomposition products are adsorbed to the first electrode 11a by executing the gas detection operation. Such a predetermined value can be appropriately determined based on, for example, the fluctuation range and / or detection accuracy of the first detection value obtained by a preliminary experiment.

  When it determines with the density | concentration of sulfur oxide being more than a predetermined value in the said step S06 (step S06: Yes), CPU progresses to following step S07 and performs poisoning recovery operation 2. Specifically, the first applied voltage is applied to a voltage lower than the decomposition start voltage of sulfur oxide while energizing the heater 41 to heat the element unit 10 and maintain the temperature of the element unit 10 at a temperature equal to or higher than the activation temperature. This state is continued for a predetermined first period. This state also corresponds to a state in which the combination of the first applied voltage suitable for the poisoning recovery operation and the temperature of the element unit 10 is maintained.

  Next, the CPU proceeds to step S08, stops the first applied voltage and the supply voltage to the heater 41, and ends the routine in the next step S09. In this way, the first device accurately detects sulfur oxides contained in the test gas by executing the gas detection operation, and sulfur oxides adsorbed on the first electrode 11a by executing the poisoning recovery operation. The decomposition product of can be removed. As a result, the sulfur oxide contained in the test gas can be detected with high accuracy even in the execution of the gas detection operation from the next time.

  By the way, when it is determined in step S02 that there is no SOx detection request (step S02: No) and in step S03, it is determined that the internal combustion engine is not in a steady state (step S03: No), the CPU proceeds to step S09. Proceed and end the routine. When it determines with the density | concentration of sulfur oxide being less than predetermined value in the said step S06 (step S06: No), CPU skips following step S07 and does not perform the poisoning recovery operation 2.

  A program for causing the CPU to execute the routine as described above can be stored in a data storage device (for example, ROM) provided in the ECU. Further, the correspondence between the electrode current as the first detection value and the concentration of sulfur oxide contained in the test gas when the first applied voltage is the first predetermined voltage (1.1 V in the first device) Can be obtained in advance by a preliminary experiment using a test gas having a known sulfur oxide concentration. A data table (for example, a data map) representing the correspondence relationship is stored in a data storage device (for example, a ROM) provided in the ECU, and can be referred to by the CPU in step S05.

  As described above, in the first device, the poisoning recovery operation 1 is executed before the gas detection operation, and the gas detection operation is performed only when a significant amount of sulfur oxide is detected by the execution of the gas detection operation. After that, poisoning recovery operation 2 is executed. However, the poisoning recovery operation may always be executed both before and after the gas detection operation. Alternatively, the poisoning recovery operation may be executed without fail before or after the gas detection operation. Further, when a significant amount of sulfur oxide is not detected by execution of the gas detection operation, the poisoning recovery operation may not be executed.

  Furthermore, in the first device, the poisoning recovery operation was performed in a state where the first applied voltage was a voltage (0.4 V) lower than the sulfur oxide decomposition start voltage. However, the first applied voltage when performing the poisoning recovery operation is not limited to the above. In other words, the first applied voltage and the temperature of the element unit 10 when performing the poisoning recovery operation are the adsorption speed at which the decomposition product of sulfur oxide contained in the test gas is adsorbed on the first electrode 11a. As long as it is possible to realize a state in which the desorption rate, which is the rate at which the decomposition product is desorbed from the first electrode 11a, can be realized, any combination may be used. For example, the poisoning recovery operation may be executed in a state where the temperature of the element unit 10 is equal to or higher than the first predetermined temperature and no voltage is applied between the first electrode 11a and the second electrode 11b. .

  On the other hand, when the gas detection operation is executed, the first predetermined voltage is set to 1.1 V in the first device as described above. However, as described above, when the first electrode 11a is used as a cathode and the second electrode 11b is used as an anode, the first predetermined voltage is applied between these electrodes, so that water contained in the test gas can be obtained. As long as it is a predetermined voltage capable of decomposing sulfur oxides, there is no particular limitation. As described above, the voltage at which the decomposition of water starts is about 0.6V. Therefore, the first predetermined voltage can be a predetermined voltage of 0.6 V or more.

  Furthermore, in the first device, as described above, the magnitude of the electrode current when the first applied voltage is the specific first predetermined voltage (1.1 V) is acquired as the first detection value. Based on the detected value, the concentration of sulfur oxide contained in the test gas was detected. However, the first detection value is particularly limited as long as it is a value corresponding to the electrode current flowing between the first electrode 11a and the second electrode 11b in the first state (for example, a voltage value, a current value, a resistance value, etc.). Not. In addition, as described above, the first detection value is not limited to a value corresponding to the electrode current when the first applied voltage is the specific first predetermined voltage (1.1 V).

  For example, a specific voltage band capable of decomposing water and sulfur oxide contained in the test gas (however, a voltage band in which the adsorption rate of the decomposition product of sulfur oxide is larger than the desorption rate of the decomposition product) The first applied voltage may be raised and lowered at a predetermined sweep speed, and a value corresponding to the difference (difference and / or ratio) in the electrode current between when it is raised and when it is lowered may be used as the first detection value. Such a difference in electrode current is considered to be caused by the fact that more decomposition products of sulfur oxide are adsorbed to the first electrode 11a when the first applied voltage is lower than when the first applied voltage is increased. . Furthermore, the integrated value of the magnitude of the electrode current in the specific voltage band capable of decomposing water and sulfur oxide contained in the test gas may be set as the first acquired value, or at the time of rising and falling The integrated value of the difference in electrode current between the first and second acquired values may be used as the first acquired value.

The first device may take various modes as listed below.
(A) After the gas detection operation, the measurement control unit maintains the temperature of the element unit 10 at the activation temperature or higher, and the temperature of the element unit is equal to or higher than the activation temperature. Even so, the poisoning recovery operation may be performed by reducing the first applied voltage to a non-decomposable voltage that is a voltage at which sulfur oxides contained in the test gas are not decomposed.
(B) After performing the gas detection operation, the measurement control unit stops applying the voltage between the first electrode 11a and the second electrode 11b, thereby reducing the first voltage up to the non-decomposable voltage. It can be configured to reduce the applied voltage.
(C) The measurement control unit stops heating the element unit 10 by the heater 41 by stopping energization of the heater 41 by the temperature adjustment unit after executing the poisoning recovery operation. Can be configured.

(D) The measurement control unit applies the first applied voltage to the test gas even when the temperature of the element unit 10 is equal to or higher than the activation temperature before executing the gas detection operation. The poisoning recovery operation is performed by raising the temperature of the element unit 10 to a temperature equal to or higher than the activation temperature while maintaining a non-decomposable voltage that is a voltage at which the contained sulfur oxide is not decomposed. Can be done.
(E) The measurement control unit does not cause the voltage application unit to apply a voltage between the first electrode 11a and the second electrode 11b before performing the gas detection operation. Can be configured to increase the temperature of the element unit 10 to a temperature equal to or higher than the activation temperature while maintaining the voltage at the non-decomposable voltage.
Gas detection device.
(F) After performing the poisoning recovery operation, the measurement control unit matches the first predetermined temperature without reducing the temperature of the element unit 10 to a temperature lower than the activation temperature, and The gas detection operation may be performed by increasing one applied voltage to the first predetermined voltage.

Second Embodiment
The first device was a two-cell type gas sensor (gas detection device) including two electrochemical cells. On the other hand, the gas detection device according to the second embodiment of the present invention (hereinafter may be referred to as “second device”) has a second electrochemical cell (pumping cell) on the upstream side of the first device. ) Is a 1-cell type gas sensor.

(Constitution)
FIG. 5 shows a configuration of a one-cell type gas sensor according to the second device. The element unit 10 included in the gas sensor includes a second electrochemical cell 12c (a third electrode 12a, a fourth electrode 12b, and a second solid electrolyte body 12s), a second element from the element unit 10 included in the first device illustrated in FIG. 6 Alumina layer 21f, second atmosphere introduction path 52 (second separate space 52), power supply 62 and ammeter 72 are excluded. Therefore, in the element portion 10 provided in the gas sensor, the internal space 31 is formed by the first alumina layer 21a, the solid electrolyte body 11s, the diffusion resistance portion 32, and the second alumina layer 21b.

(Specific operation)
Since the SOx sensor control routine executed in this gas sensor is the same as the SOx sensor control routine executed in the first device described above, a detailed description thereof is omitted here. However, since this gas sensor does not include the second electrochemical cell 12c, it is not possible to detect the temperature of the element unit 10 based on the impedance when a high frequency voltage is applied between the third electrode 12a and the fourth electrode 12b. Can not. Therefore, the temperature of the element unit 10 included in the gas sensor is detected based on the impedance when a high frequency voltage is applied between the first electrode 11a and the second electrode 11b, or a separate temperature sensor is provided. It needs to be detected.

  By the way, the decomposition start voltage of oxygen in an electrochemical cell is generally lower than the decomposition start voltage of water. Since the second device is a 1-cell type gas sensor, the electrode current corresponding to the first detection value is determined by the decomposition current caused by oxygen in addition to the decomposition current caused by water and the decomposition current caused by sulfur oxide. Including. Therefore, when the concentration of oxygen contained in the test gas changes, the first detection value also changes. Therefore, when the gas detection operation is performed in the second device, the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is a specific value (the concentration of oxygen contained in the exhaust gas is a specific value). Value) is preferably constant.

  In the above, for the purpose of explaining the present invention, several embodiments and modifications having specific configurations have been described with reference to the accompanying drawings. However, the scope of the present invention is not limited to these illustrative examples. It should be understood that the present invention should not be construed as being limited to the embodiments and the modifications, and that appropriate modifications can be made within the scope of the matters described in the claims and the specification.

  DESCRIPTION OF SYMBOLS 10 ... Element part, 11a and 12a ... Electrode (cathode), 11b and 12b ... Electrode (anode), 11s and 12s ... 1st and 2nd solid electrolyte body, 11c and 12c ... Pumping cell (1st electrochemical cell and 1st 2 electrochemical cells), 21a, 21b, 21c, 21d, 21e and 21f ... first to sixth alumina layers, 31 ... internal space, 32 ... diffusion resistor, 41 ... heaters, 51 and 52 ... first and second Air introduction path, 61 and 62 ... power source, 71 and 72 ... ammeter.

Claims (7)

A first electrochemical cell including a solid electrolyte body having oxide ion conductivity and a first electrode and a second electrode respectively formed on the surface of the solid electrolyte body; a dense body; and a diffusion resistance section. The exhaust gas of the internal combustion engine as the test gas is introduced into the internal space defined by the solid electrolyte body, the dense body, and the diffusion resistance portion via the diffusion resistance portion, and the first electrode is connected to the internal space. And an element portion configured to be exposed to a first separate space that is a space different from the internal space and the second electrode is exposed to
A heater that generates heat when energized to heat the element unit;
A voltage applying unit that applies a voltage between the first electrode and the second electrode;
A temperature adjusting unit that controls the temperature of the element unit by controlling the amount of current supplied to the heater;
A measurement control unit for controlling the voltage application unit and the temperature adjustment unit and acquiring a first detection value corresponding to a current flowing between the first electrode and the second electrode;
And the first electrode has a first predetermined temperature not lower than an activation temperature at which the oxide ion conductivity of the solid electrolyte body is exhibited, and the first electrode and the first electrode, in the first state is a state where the first predetermined voltage is applied between the second electrode, wherein that degrade the water contained in the gas to be detected (H 2 _O) and sulfur oxides (SOx) Configured to be possible,
The measurement control unit uses the temperature adjustment unit to match the temperature of the element unit with the first predetermined temperature and is applied between the first electrode and the second electrode using the voltage application unit. The first state is realized by matching a first applied voltage that is a voltage to be equal to the first predetermined voltage, and is included in the test gas based on the first detection value acquired in the first state Configured to perform a gas detection operation for detecting a concentration of sulfur oxide to be detected or determining the presence or absence of the sulfur oxide,
A gas detection device comprising:
The measurement control unit controls the temperature of the element unit using the temperature adjustment unit and the first application voltage using the voltage application unit when the gas detection operation is not performed. By this, the decomposition product of the decomposition product of sulfur oxide contained in the test gas is desorbed at a rate at which the decomposition product is desorbed from the first electrode than the adsorption rate at which the decomposition product is adsorbed on the first electrode. It is configured to perform a poisoning recovery operation that continues a state in which a combination of the first applied voltage and the temperature of the element unit, in which the speed is increased, is maintained over a predetermined first period,
Gas detection device. The gas detection device according to claim 1,
After the gas detection operation is performed, the measurement control unit maintains the temperature of the element unit at or above the activation temperature, and the temperature of the element unit is equal to or higher than the activation temperature. The poisoning recovery operation is performed by lowering the first applied voltage to a non-decomposable voltage that is a voltage at which sulfur oxides contained in the test gas are not decomposed.
Gas detection device. The gas detection device according to claim 2,
The measurement control unit lowers the first applied voltage to the non-decomposable voltage by stopping the application of the voltage between the first electrode and the second electrode after performing the gas detection operation. Configured as
Gas detection device. In the gas detection device according to claim 2 or 3,
The measurement control unit is configured to stop heating of the element unit by the heater by stopping energization of the heater by the temperature adjustment unit after performing the poisoning recovery operation.
Gas detection device. The gas detection device according to claim 1,
The measurement control unit is a voltage at which the sulfur oxide contained in the test gas is not decomposed even when the temperature of the element unit is equal to or higher than the activation temperature before the gas detection operation is performed. The poisoning recovery operation is performed by increasing the temperature of the element unit to a temperature equal to or higher than the activation temperature while maintaining the first applied voltage at a non-decomposable voltage.
Gas detection device. The gas detector according to claim 5, wherein
The measurement control unit does not cause the voltage application unit to apply a voltage between the first electrode and the second electrode before performing the gas detection operation, thereby reducing the first applied voltage to the non-decomposable voltage. Configured to increase the temperature of the element portion to a temperature equal to or higher than the activation temperature,
Gas detection device. The gas detection device according to claim 5 or 6,
The measurement control unit, after executing the poisoning recovery operation, matches the first predetermined voltage without reducing the temperature of the element unit to a temperature lower than the activation temperature, and sets the first applied voltage. The gas detection operation is configured to increase to the first predetermined voltage,
Gas detection device.

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