JP2016217863A - Gas concentration detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration detection device capable of accurately detecting (obtaining) concentration of a sulfur oxide (SOx)contained in an exhaust gas of an internal combustion engine.SOLUTION: A limit current type gas sensor having a monitor cell controls a heater power so that a detection value by the monitor cell when applied with a predetermined voltage coincides with a standard detection value corresponding to the concentration of water contained in a gas to be detected at this point of time, and the value corresponding to the heater power when the detection value coincides with the standard detection value is stored as a target power index. In this way, a change in decomposition of activity for a sulfur oxide is reduced. As a result, even when the decomposition of activity of the sensor for the sulfur oxide is changed, the concentration of the sulfur oxide (SOx) contained in the gas to be detected can be more accurately detected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas concentration detection device capable of accurately detecting (acquiring) the concentration of sulfur oxide (SOx) contained in exhaust gas of an internal combustion engine.

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. When one of the electrodes is used as a cathode and the other electrode is used as an anode, when a voltage equal to or higher than the voltage at which oxygen begins to decompose (decomposition start voltage) is applied between the pair of electrodes, oxygen contained in the test gas Is reduced and decomposed into 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. Thus, the air-fuel ratio sensor can detect the concentration of oxygen contained in the test gas by using the limiting current characteristic of oxygen, and can acquire the air-fuel ratio of the air-fuel mixture in the combustion chamber based on the oxygen concentration.

The limiting current characteristics as described above are not limited to oxygen gas only. 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. Therefore, the content rate of sulfur component in the fuel is acquired, and the acquired sulfur content rate is reflected in, for example, control of the internal combustion engine, a warning about the failure of the internal combustion engine is issued, or the self-diagnosis diagnosis of the exhaust purification catalyst It is desirable to make use of it for improving (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 detected (acquired) with high accuracy, it is considered that the sulfur content can be detected (acquired) with high accuracy based on the acquired SOx concentration.

  Therefore, in this technical field, a limiting current type comprising two electrochemical cells arranged in series so that the cathode faces the internal space through which the exhaust gas of the internal combustion engine as the test gas is guided through the diffusion resistance portion A gas sensor (a two-cell limiting current type gas sensor) is known. In this gas sensor, by applying a relatively low voltage between the electrodes of the upstream electrochemical cell, oxygen contained in the test gas is removed by the oxygen pumping action of the upstream electrochemical cell. That is, the upstream electrochemical cell functions as a so-called “pump cell”. On the other hand, by applying a relatively high voltage between the electrodes of the downstream electrochemical cell, sulfur oxide contained in the test gas is reduced and decomposed at the cathode by the downstream electrochemical cell. The resulting oxide ions are conducted to the anode. Based on the change in the electrode current value resulting from the oxygen pumping action, the concentration of sulfur oxide contained in the test gas is acquired. That is, the upstream electrochemical cell functions as a so-called “sensor cell” (see, for example, Patent Document 1).

JP-A-11-190721

  As described above, in this technical field, an attempt is made to detect the concentration of sulfur oxide contained in the exhaust gas of an internal combustion engine by a limiting current type gas sensor using an oxygen pumping action. However, since the concentration of sulfur oxide contained in the exhaust gas is extremely low and the decomposition current of sulfur oxide is extremely small, it is difficult to accurately detect the decomposition current of sulfur oxide itself.

  Therefore, as a result of diligent research, the present inventor has found that the electrode current when decomposing water and sulfur oxide at a predetermined applied voltage in an electrochemical cell having an oxygen pumping action is in the exhaust of an internal combustion engine as a test gas. It has been found that it varies depending on the concentration of sulfur oxides. According to this, the concentration of sulfur oxide contained in the test gas can be detected based on the change in the water decomposition current larger than the sulfur oxide decomposition current. Therefore, the concentration of sulfur oxide contained in the test gas can be accurately detected based on the change in the decomposition current of water and sulfur oxide in the limiting current gas sensor.

  Furthermore, in addition to the electrochemical cell (sensor cell) capable of decomposing water and sulfur oxides, the present inventor further provides an electrochemical cell (monitor cell) having a decomposition activity (reduction ability) for sulfur oxides lower than that of the sensor cell. Thus, it was found that the concentration of sulfur oxide can be detected with higher accuracy. Specifically, at a predetermined element temperature and applied voltage, the electrode current of the sensor cell when decomposing water and sulfur oxide by the sensor cell, and the electrode current of the monitor cell when decomposing water and sulfur oxide by the monitor cell, Based on the difference, the concentration of sulfur oxide contained in the test gas can be detected with higher accuracy.

  However, due to individual differences in each sensor and deterioration over time, for example, the activity of the electrode (cathode) and / or the oxide ion conductivity of the solid electrolyte body with respect to the reductive decomposition of the oxygen-containing gas contained in the test gas changes. Equally, the activity of a sensor having a normal activity (that is, a reference sensor; a sensor whose sensor activity is a median of design tolerances) may be different. Thus, when the activity as a sensor (sensor activity) is changing, the concentration of sulfur oxide contained in the test gas is adjusted even if the sensor is controlled to have a predetermined element temperature and applied voltage. It is difficult to detect accurately with a sensor.

  In particular, when detecting the concentration of sulfur oxide contained in the test gas based on changes in the decomposition current of water and sulfur oxide at an applied voltage less than the limit current region of water in a limiting current gas sensor, The reductive decomposition reaction of water and sulfur oxide in is not in a diffusion-controlled state. In this case, the decomposition rate of water and sulfur oxide at the cathode is not sufficiently high relative to the rate at which the test gas (water and sulfur oxide contained therein) reaches the cathode.

  Therefore, the magnitude of water and sulfur oxide decomposition current at the cathode is greatly influenced by the rate of reductive decomposition reaction of water and sulfur oxide at the cathode. That is, since the detection value by the sensor is greatly influenced by the sensor activity, the concentration of sulfur oxide contained in the test gas is controlled by the sensor even if it is controlled to have a predetermined element temperature and applied voltage. Therefore, it is extremely difficult to detect with high accuracy.

  Therefore, the present invention reduces the change in the detected value caused by the change in the sensor activity even if the sensor activity has changed as described above, so that the concentration of sulfur oxide contained in the exhaust gas of the internal combustion engine can be accurately adjusted. It is an object to provide a gas concentration detection device that can detect well.

  As a result of diligent research to achieve the above object, the present inventor controls the power supplied to the heater (heater power) for adjusting the temperature of the element portion constituting the sensor, thereby detecting the value detected by the sensor. We found that the size can be changed. That is, even if the sensor activity has changed, the inventor can control the element temperature by appropriately controlling the heater power to reduce the change in the detected value due to the change in the sensor activity, and It has been found that a detection value equivalent to a detection value by a sensor (that is, a reference) can be obtained. For example, for a sensor having a sensor activity lower than that of a normal sensor due to individual differences and / or aging, substantial sensor activity (i.e., including Increase the ability to reduce and decompose oxygen gas. Thereby, the fall of the detection value resulting from the fall of the sensor activity in the said sensor can be reduced.

  More specifically, in a limiting current type gas sensor having a monitor cell, the detection value by the monitor cell when a predetermined voltage is applied corresponds to the reference detection corresponding to the concentration of water contained in the test gas at that time. The heater power is controlled to match the value. Thereby, even if the sensor activity of the limit current type gas sensor is changed, it is possible to reduce a change in the detection value due to the change in the sensor activity and obtain a normal detection value.

  In view of the above points, a gas concentration detection device according to the present invention (hereinafter sometimes referred to as “the device of the present invention”) includes an element unit, a power source, a heater, a detection unit, and a control. A section.

The element part includes a first electrochemical cell, a second electrochemical cell, a dense body, and a diffusion resistance part.
The first electrochemical cell includes a first solid electrolyte body having oxide ion conductivity, and a first electrode and a second electrode formed on the surface of the first solid electrolyte body, respectively.
The second electrochemical cell includes a second solid electrolyte body having oxide ion conductivity and a third electrode and a fourth electrode respectively formed on the surface of the second solid electrolyte body.

  The first solid electrolyte body and the second solid electrolyte body may be the same (integrated) solid electrolyte body, or may be separate solid electrolyte bodies. Typically, the first solid electrolyte body and the second solid electrolyte body are the same (integrated) solid electrolyte body.

Exhaust gas of the internal combustion engine as a test gas is introduced into the internal space defined by the first solid electrolyte body, the second solid electrolyte body, the dense body, and the diffusion resistance portion through the diffusion resistance portion. .
The first 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 third electrode is exposed in the internal space, and the fourth electrode is exposed in a second separate space that is a space different from the internal space.

  The first separate space and the second separate space may be the same space (communication with each other inside the element portion) or separate spaces (independent of each other within the element portion). Typically, the first separate space and the second separate space are the same space (communication with each other inside the element portion).

  The first electrode and the third electrode have a first predetermined temperature that is equal to or higher than an activation temperature, which is a temperature at which the oxide ion conductivity of the solid electrolyte body is developed, when the temperature of the element portion is the first temperature. The first decomposition rate is configured to be higher than the second decomposition rate. The first decomposition rate refers to the amount of sulfur oxide in the first electrode when a first predetermined voltage that is equal to or higher than the water decomposition start voltage is applied between the first electrode and the second electrode. Decomposition rate. The second decomposition rate is the amount of sulfur oxide in the third electrode when a second predetermined voltage that is a voltage equal to or higher than the water decomposition start voltage is applied between the third electrode and the fourth electrode. Decomposition rate. Accordingly, the sulfur oxide decomposition rate (first decomposition rate) by the first electrochemical cell under the above conditions is higher than the sulfur oxide decomposition rate (second decomposition rate) by the second electrochemical cell under the above conditions. Is also expensive. That is, in the device of the present invention, the first electrochemical cell is a sensor cell, and the second electrochemical cell is a monitor cell.

  As described above, the first electrode is capable of decomposing water at a predetermined applied voltage (first predetermined voltage) and decomposes sulfur oxide at a relatively high decomposition rate (first decomposition rate). Configured to be possible. Such a 1st electrode can be produced by selecting suitably the kind of substance which comprises electrode material, the conditions of the heat processing at the time of producing an electrode, etc., for example. Such a material constituting the first electrode decomposes water and sulfur oxide contained in the test gas when, for example, a first predetermined voltage is applied between the first electrode and the second electrode. A substance (for example, a noble metal) having an activity capable of Typically, the first electrode desirably includes at least one selected from the group consisting of platinum (Pt), rhodium (Rh), and palladium (Pd).

  On the other hand, as described above, the third electrode can decompose water at a predetermined applied voltage (second predetermined voltage), and sulfur oxide at a relatively low decomposition rate (second decomposition rate). It is comprised so that it can be decomposed | disassembled. Such a third electrode can also be produced by appropriately selecting, for example, the types of substances constituting the electrode material and the conditions for the heat treatment in producing the electrode. Such a material constituting the third electrode is, for example, an activity capable of decomposing at least water contained in the test gas when a second predetermined voltage is applied between the third electrode and the fourth electrode. (For example, noble metals). Typically, the third electrode desirably includes platinum (Pt).

  Furthermore, the first predetermined voltage and the second predetermined voltage may be the same or different. Typically, the first predetermined voltage and the second predetermined voltage are equal.

The power source is configured to apply a voltage between the first electrode and the second electrode and between the third electrode and the fourth electrode.
The heater is configured to heat the element unit.
The detection unit corresponds to a first detection value which is a detection value corresponding to a current flowing between the first electrode and the second electrode and a current flowing between the third electrode and the fourth electrode. The second detection value that is the detection value is configured to be detected.

  The control unit controls the power source to apply the first predetermined voltage between the first electrode and the second electrode, and to apply the second predetermined voltage between the third electrode and the fourth electrode. Apply voltage. In addition, the control unit controls heater power, which is power supplied to the heater, to set the temperature of the element unit to the first predetermined temperature. The control unit executes a detection operation for detecting a concentration of sulfur oxide contained in the test gas based on the first detection value and the second detection value detected by the detection unit at this time. .

  Specific examples of the method for detecting the concentration of sulfur oxide contained in the test gas based on the first detection value and the second detection value include the following methods. The correspondence relationship between the magnitude of the difference obtained by subtracting the second detection value from the first detection value in the device of the present invention and the concentration of sulfur oxide contained in the test gas is obtained in advance, and data related to the correspondence relationship is obtained. For example, it is stored as a map (data table) in a data storage device (for example, ROM) provided in the control unit. And the density | concentration of the sulfur oxide contained in test gas is specified based on the said correspondence from the difference of the 1st detection value actually detected by detection operation, and a 2nd detection value. However, the above method is merely an example, and the specific method for detecting the concentration of sulfur oxide contained in the test gas based on the first detection value and the second detection value is not limited to the above.

  That is, the device of the present invention is a limiting current type SOx sensor that detects the concentration of sulfur oxide contained in a test gas based on detection values by a sensor cell and a monitor cell at a predetermined element temperature and applied voltage.

  However, in the device of the present invention, the first predetermined temperature does not necessarily indicate a specific temperature, but the oxygen content in which the first electrochemical cell and the second electrochemical cell constituting the device of the present invention are contained in the test gas. The temperature of the element part which can express the activity with respect to reductive decomposition of gas, or the range of temperature is pointed out. Therefore, when the activity of the first electrochemical cell and the second electrochemical cell constituting the device of the present invention is in a normal state, the first predetermined temperature is set to a predetermined temperature for the device of the present invention in the normal state. By setting the temperature, it is possible to accurately detect the concentration of sulfur oxide contained in the test gas based on the detection values obtained by the sensor cell and the monitor cell.

  However, as described above, when the sensor activity of the device of the present invention has changed, the sensor activity can be maintained even if the first predetermined temperature is set to a predetermined temperature for the device of the present invention in a normal state. The detection value changes due to the change of the gas, and it is difficult to accurately detect the concentration of sulfur oxide contained in the test gas.

  Therefore, in the device of the present invention, the control unit stores in advance data related to the correspondence relationship between the concentration of water contained in the test gas and the reference detection value that is the reference value of the second detection value. ing.

  Further, the control unit performs a learning operation. Specifically, in the learning operation, the control unit detects the second detection detected by the detection unit when the second predetermined voltage is applied between the third electrode and the fourth electrode. Get the value. And the said control part controls the said heater electric power so that the acquired 2nd detection value corresponds with a reference | standard detection value. This reference detection value is a reference detection value that is specified based on the correspondence relationship from the concentration of water contained in the test gas at that time.

  When the second detection value matches the reference detection value by controlling the heater power in this way, the substantial sensor activity (reduction ability) of the device of the present invention is that of a normal sensor (reference sensor). Equivalent to sensor activity. In other words, at this time, the sensor activity changed due to individual differences or aging deterioration is adjusted to the normal (standard) sensor activity by adjusting the element temperature. Therefore, the control unit stores (learns) a value corresponding to the heater power when the second detection value matches the reference detection value as a target power index.

  The target power index is not particularly limited as long as it is a value corresponding to the heater power when the second detection value matches the reference detection value as described above. Specifically, as the target power index, for example, the heater power when the second detection value matches the reference detection value, the temperature of the element unit, and the first detection value when the second detection value matches the reference detection value. Various values such as impedance between the three electrodes and the fourth electrode can be adopted.

  In addition, the control unit may be configured to control the heater power so as to achieve the target power index in the detection operation performed after execution of the learning operation. Specifically, for example, when the heater power when the second detection value matches the reference detection value is used as the target power index, in the detection operation executed after the learning operation is performed, the control unit May be configured to control the heater power to match the target power index.

  Alternatively, for example, when the temperature of the element unit when the second detection value matches the reference detection value is used as the target power index, in the detection operation executed after the learning operation is performed, the control unit It may be configured to control the heater power so that the temperature matches the target power index.

  Alternatively, for example, when the impedance between the electrodes of any electrochemical cell constituting the element unit when the second detection value coincides with the reference detection value is used as the target power index, it is executed after the execution of the learning operation. In the detection operation, the control unit may be configured to control the heater power so that the impedance between the electrodes of the electrochemical cell matches the target power index.

  Based on the above, the control unit can accurately detect the concentration of sulfur oxide contained in the test gas by reducing the change in the detection value caused by the change in the sensor activity even if the sensor activity is changed. The operation of controlling the heater power can be performed reliably and simply so that it can be performed. As a result, even if the sensor activity has changed, the device of the present invention reliably and easily reduces the change in the detection value caused by the change in the sensor activity, and the concentration of sulfur oxide contained in the test gas. Can be detected with high accuracy.

  The heater power control based on the target power index learned as described above is executed in a detection operation that is executed after the execution of the learning operation. Therefore, when the learning operation execution condition (for example, the element temperature and the applied voltage) matches the detection operation execution condition (for example, the element temperature and the applied voltage), the second detection value is the reference detection value in the learning operation. The detection operation may be executed when the values match.

  By the way, as described above, as the target power index, for example, when the second detection value matches the reference detection value, the heater power and the temperature of the element unit, and when the second detection value matches the reference detection value Various values, such as the impedance between the electrodes of any electrochemical cell constituting the element part, can be adopted. Of these various values, the impedance between the electrodes of the electrochemical cell is particularly suitable as the target power index because it has a more direct relationship with the sensor activity of the device of the present invention.

  Therefore, the gas concentration detection apparatus according to another embodiment of the present invention is the apparatus of the present invention, further comprising an impedance detection unit that detects an impedance between electrodes of any electrochemical cell constituting the element unit. The impedance detection unit is not particularly limited as long as it can detect the impedance between the electrodes of any electrochemical cell constituting the element unit.

  Specifically, the impedance detection unit is configured to calculate the impedance based on an electrode current detected when a predetermined high-frequency voltage is applied between the third electrode and the fourth electrode, for example. It can be implemented as a control unit. Such an impedance detection unit calculates the temperature of the element unit based on the impedance calculated based on the electrode current detected when a predetermined high-frequency voltage is applied between the third electrode and the fourth electrode. When the control unit is configured as described above, it can be conveniently implemented without adding special components.

  Furthermore, in the gas concentration detection device according to this embodiment, the control unit stores the impedance when the second detection value matches the reference detection value as the target power index in the learning operation. In addition, the control unit may be configured to control the heater power so that the impedance matches the target power index in the detection operation performed after execution of the learning operation.

  As described above, the gas concentration detection device according to the present embodiment reliably and easily reduces the change in the detection value caused by the change in the sensor activity even if the sensor activity is changed, and is included in the test gas. The concentration of sulfur oxide to be detected can be detected with higher accuracy.

  Incidentally, as described above, the control unit is configured such that the second detection value acquired in the learning operation is specified based on the correspondence described above from the concentration of water contained in the test gas at that time. A value corresponding to the heater power when it matches the detected value is stored (learned) as a target power index. That is, in order to execute the learning operation, it is necessary to acquire the concentration of water contained in the test gas at that time.

  The method for obtaining the concentration of water contained in the test gas in the apparatus of the present invention is not particularly limited. The concentration of the water can be appropriately acquired from various state quantities related to the concentration of water contained in the test gas that can be detected in the internal combustion engine, for example. Alternatively, the learning operation may be executed in a state where the concentration of water contained in the test gas is known.

  In the latter case, for example, the control unit determines the concentration of water contained in the atmosphere when a fuel cut is performed in which fuel is not supplied to the combustion chamber of the internal combustion engine. The learning operation may be performed using the concentration. As is well known to those skilled in the art, for example, a fuel cut means that a vehicle equipped with an internal combustion engine as a power source is traveling in a state where the accelerator opening is 0 (zero) for the purpose of improving fuel efficiency. This is a process of automatically stopping the supply of fuel when the rotational speed of the internal combustion engine is higher than a predetermined threshold value.

  According to this, since the learning operation can be executed when the fuel cut is being executed, it is possible to achieve both improvement in detection accuracy of the sulfur oxide concentration and improvement in fuel consumption of the internal combustion engine by the device of the present invention. . Furthermore, in this case, the concentration of water contained in the test gas is equal to the concentration of water contained in the atmosphere. Therefore, in the learning operation, the control unit may control the heater power so that the second detection value matches the reference detection value corresponding to the concentration of water contained in the atmosphere.

  For example, a predetermined fixed value determined in advance may be adopted as the concentration of water contained in the atmosphere. In this case, the control unit transmits the air as the “predetermined fixed value” as data related to the correspondence relationship between the concentration of water contained in the test gas and the reference detection value that is the reference value of the second detection value. Only the reference detection value corresponding to the concentration of water contained therein needs to be stored in advance. Therefore, in this case, the storage capacity that should be ensured by the data storage device included in the control unit can be reduced.

  However, more strictly, as the concentration of water contained in the atmosphere, it is desirable to adopt the concentration of water actually contained in the atmosphere at that time instead of the predetermined fixed value as described above.

  Therefore, the device of the present invention may further include an intake humidity sensor that detects intake humidity, which is a concentration of water contained in intake air supplied to the combustion chamber of the internal combustion engine. The intake humidity sensor is not particularly limited as long as the intake humidity can be detected. Typically, the intake humidity sensor is a so-called “humidity sensor”.

  In the above case, the control unit is configured to use the detected intake humidity as the concentration of water contained in the test gas at that time in the learning operation. According to this, even if the intake humidity varies, the reference detection value corresponding to the concentration of water contained in the test gas can be specified with higher accuracy. As a result, it is possible to reliably and easily reduce the change in the detection value caused by the change in the sensor activity, and to detect the concentration of sulfur oxide contained in the test gas with higher accuracy.

  By the way, the decomposition start voltage of oxygen in an electrochemical cell is generally lower than the decomposition start voltage of water. Therefore, each electrode current corresponding to the first detection value and the second detection value in the detection operation includes not only the water decomposition current and the sulfur oxide decomposition current but also the oxygen decomposition current. Therefore, when the concentration of oxygen contained in the test gas changes, the first detection value and the second detection value also change. Therefore, the detection of the concentration of sulfur oxide contained in the test gas based on these detection values. There is a risk that the accuracy may decrease. Therefore, in order to increase the detection accuracy of the concentration of sulfur oxide contained in the test gas based on these detection values, it is desirable to reduce the amount of oxygen contained in the test gas.

  In addition, the amount of oxygen contained in the test gas is very large compared to the amount of sulfur oxide. Therefore, in each electrode current corresponding to the first detection value and the second detection value in the detection operation, the ratio of the oxygen decomposition current is compared with the ratio of the water decomposition current and the sulfur oxide decomposition current. Very big. Therefore, it is desirable to reduce the amount of oxygen contained in the test gas in order to increase the SN ratio in detecting the concentration of sulfur oxide contained in the test gas based on these detection values.

  Therefore, a gas concentration detection device according to another embodiment of the present invention is a gas concentration detection device according to any of the various embodiments described above, and includes a first electrochemical cell (sensor cell) and a second electrochemical cell. A third electrochemical cell (pump cell) that reduces the amount of oxygen contained in the test gas before reaching the (monitor cell) is provided.

  Specifically, in the gas concentration detection apparatus according to the present embodiment, the element unit further includes a third electrochemical cell. The third electrochemical cell includes a third solid electrolyte body having oxide ion conductivity, and a fifth electrode and a sixth electrode formed on the surface of the third solid electrolyte body, respectively. The third solid electrolyte body and the first solid electrolyte body and / or the second solid electrolyte body described above may be the same (integrated) solid electrolyte body, or may be separate solid electrolyte bodies. . Typically, the third solid electrolyte body, the first solid electrolyte body, and the second solid electrolyte body are separate solid electrolyte bodies.

  Further, the fifth electrode is exposed to the internal space, and the sixth electrode is exposed to a third separate space that is a space different from the internal space. The third separate space and the first separate space and / or the second separate space may be the same space (communication with each other inside the element portion) or may be separate (independent of each other within the element portion). It may be a space. Typically, the third separate space, the first separate space, and the second separate space are separate spaces (independent of each other inside the element portion). In addition, the fifth electrode is formed at a position closer to the diffusion resistance portion than the first electrode and the third electrode.

  The fifth electrode corresponds to a limit current region of oxygen between the fifth electrode and the sixth electrode when the temperature of the element portion is the first predetermined temperature, and starts decomposition of water. Configured to be capable of decomposing and exhausting oxygen contained in the test gas when the third predetermined voltage, which is a voltage lower than the voltage, is applied.

  The fifth electrode as described above can be produced, for example, by appropriately selecting the type of substance constituting the electrode material and the conditions of the heat treatment when producing the electrode. Such a material constituting the fifth electrode has, for example, an activity capable of decomposing oxygen contained in the test gas when a third predetermined voltage is applied between the fifth electrode and the sixth electrode. The substance (for example, noble metal) which has. Typically, the fifth electrode desirably includes at least one selected from the group consisting of platinum (Pt), gold (Au), lead (Pb), and silver (Ag).

  Further, the power source is configured to apply a voltage between the fifth electrode and the sixth electrode.

  In addition, the control unit is configured to perform an oxygen discharge operation at least in a period during which the detection operation is performed. Specifically, in the oxygen discharging operation, the control unit controls the power source to apply the third predetermined voltage between the fifth electrode and the sixth electrode. Thereby, the control unit decomposes oxygen contained in the test gas and discharges it from the internal space.

  As described above, the gas concentration detection apparatus according to the present embodiment reduces the amount of oxygen contained in the test gas before reaching the first electrochemical cell (sensor cell) and the second electrochemical cell (monitor cell). A third electrochemical cell (pump cell). Thereby, the gas concentration detection apparatus which concerns on this embodiment can raise the detection accuracy and SN ratio of the density | concentration of the sulfur oxide contained in the test gas based on a 1st detection value and a 2nd detection value.

  On the other hand, as described above, the concentration of water contained in the test gas is appropriately acquired from various state quantities related to the concentration of water contained in the test gas that can be detected in the internal combustion engine, for example. Can do. Specifically, the water concentration can be calculated based on, for example, an air-fuel ratio detected by an air-fuel ratio sensor.

  Therefore, the gas concentration detection apparatus according to still another embodiment of the present invention further includes an air-fuel ratio sensor for detecting an air-fuel ratio in the air-fuel mixture supplied to the combustion chamber of the internal combustion engine. Since the configuration of the air-fuel ratio sensor is well known to those skilled in the art, a description thereof is omitted here. The air-fuel ratio sensor may be an air-fuel ratio sensor provided for the purpose of controlling the internal combustion engine. Alternatively, as will be described later, when the apparatus of the present invention further includes a component capable of detecting the limiting current value of oxygen such as a pump cell that discharges oxygen from the internal space, the component is used as an air-fuel ratio sensor. May be.

  Further, in the learning operation, the control unit is configured to calculate the concentration of water contained in the test gas at that time based on the detected air-fuel ratio. As known to those skilled in the art, if the air-fuel ratio in the air-fuel mixture is known, the amount of water produced as a result of the combustion of the fuel can be calculated from the amounts of fuel and oxygen contained in the air-fuel mixture. Therefore, the concentration of water contained in the exhaust gas of the internal combustion engine as the test gas can be calculated based on the air-fuel ratio.

  By the way, the control unit may be configured to execute the learning operation when the air-fuel ratio is a value within a predetermined range including a specific value. According to this, in the learning operation, the control unit adjusts the concentration of water contained in the exhaust gas (test gas) of the internal combustion engine when the air-fuel ratio is a value within a predetermined range including a specific value. The heater power may be controlled so that the second detection value matches the corresponding reference detection value. That is, the control unit detects the reference detection corresponding to the concentration of the water as data related to the correspondence relationship between the concentration of water contained in the test gas and the reference detection value that is the reference value of the second detection value. Only the value needs to be stored in advance. Therefore, it is possible to reduce the storage capacity to be secured by the data storage device provided in the control unit.

  In the above, the air-fuel ratio which is the specific value can be set as the stoichiometric air-fuel ratio. In this case, the control unit may be configured to execute the learning operation when the air-fuel ratio is a value within a predetermined range including the stoichiometric air-fuel ratio. According to this, for example, in the recent gasoline engine having a high frequency of burning fuel by controlling the air-fuel ratio in the vicinity of the theoretical air-fuel ratio for the purpose of effectively functioning the three-way catalyst for exhaust purification, the above learning is performed. Opportunities for performing operations can be increased.

  As described above, the concentration of water contained in the exhaust gas of the internal combustion engine as the test gas can be calculated based on the air-fuel ratio. However, the test gas includes not only water generated as a result of fuel combustion but also water contained in the intake air supplied to the combustion chamber of the internal combustion engine. The amount of water contained in the intake air is negligible compared to the amount of water produced as a result of fuel combustion.

  However, when the air-fuel ratio is large (lean) and when the fuel cut is performed, the amount of water generated as a result of fuel combustion compared to the case where the air-fuel ratio is small (rich) or the stoichiometric air-fuel ratio. Is less. That is, when the air-fuel ratio is lean and when the fuel cut is executed, it is included in the test gas of water contained in the intake air as compared with the case where the air-fuel ratio is rich or the stoichiometric air-fuel ratio. The proportion of water is relatively high. Accordingly, even in such a case, in order to strictly acquire the concentration of water contained in the test gas, not only the concentration of water generated as a result of the combustion of fuel but also the combustion chamber of the internal combustion engine is supplied. It is also desirable to consider the concentration of water contained in the intake air.

  Therefore, as described above, the apparatus of the present invention that calculates the concentration of water contained in the test gas based on the air-fuel ratio detected by the air-fuel ratio sensor is also included in the intake air supplied to the combustion chamber of the internal combustion engine. An intake humidity sensor that detects intake humidity, which is the concentration of contained water, may be further provided. In this case, in the learning operation, the control unit is configured to calculate the concentration of water contained in the test gas at that time based on the detected air-fuel ratio and the detected intake humidity. The Thus, in the gas concentration detection device according to this embodiment, not only the concentration of water generated as a result of fuel combustion but also the concentration of water contained in the intake air supplied to the combustion chamber of the internal combustion engine is considered. Thus, the concentration of water contained in the test gas is acquired with higher accuracy. As a result, the gas concentration detection device according to the present embodiment can specify the reference detection value corresponding to the concentration of water contained in the test gas with higher accuracy even if the intake humidity varies. . As a result, it is possible to reliably and easily reduce the change in the detection value caused by the change in the sensor activity, and to detect the concentration of sulfur oxide contained in the test gas with higher accuracy.

  By the way, in the present invention apparatus (including the present invention apparatus further provided with an intake humidity sensor) that calculates the concentration of water contained in the test gas based on the air-fuel ratio detected by the air-fuel ratio sensor as described above. In order to improve the detection accuracy and SN ratio of the concentration of sulfur oxide contained in the test gas, it is desirable to reduce the amount of oxygen contained in the test gas.

  Therefore, a gas concentration detection device according to another embodiment of the present invention is a gas concentration detection device according to any of the various embodiments described above, and includes a first electrochemical cell (sensor cell) and a second electrochemical cell. A third electrochemical cell (pump cell) that reduces the amount of oxygen contained in the test gas before reaching the (monitor cell) is provided. About the structure of the said 3rd electrochemical cell, since it already mentioned above, description is not repeated here.

  By the way, in the oxygen discharging operation, the control unit controls the power source to apply the third predetermined voltage between the fifth electrode and the sixth electrode. As described above, the third predetermined voltage corresponds to the limiting current region of oxygen and is a voltage lower than the water decomposition start voltage. Accordingly, a limit current of oxygen flows between the fifth electrode and the sixth electrode during the period in which the oxygen discharging operation is being performed. As described at the beginning, the magnitude of the limit current (limit current value) corresponds to the concentration of oxygen contained in the test gas.

  Therefore, if a detection value corresponding to the current flowing between the fifth electrode and the sixth electrode is detected while the oxygen discharge operation is being executed, the detection gas is included in the test gas based on the detection value. It is possible to detect the oxygen concentration and / or the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine. That is, the third electrochemical cell can function as the air-fuel ratio sensor described above.

  Therefore, in the device of the present invention according to the embodiment further including the third electrochemical cell as described above, the detection unit has a detection value corresponding to the current flowing between the fifth electrode and the sixth electrode. It may also be configured to detect the third detection value. In this case, the control unit detects the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine corresponding to the test gas based on the third detection value when the oxygen discharge operation is being performed. Thus, the third electrochemical cell is configured to be used as the air-fuel ratio sensor.

  According to this, the device of the present invention is not only a gas concentration detection device (SOx sensor) for detecting the concentration of sulfur oxide contained in the test gas, but also of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine. It can also function as an air-fuel ratio sensor that detects the air-fuel ratio. Accordingly, there is no need to provide a separate air-fuel ratio sensor for the purpose of controlling the internal combustion engine, and therefore, for example, the manufacturing cost of equipment (for example, a vehicle) on which the internal combustion engine is mounted can be reduced.

  Further, in the learning operation described above, the concentration of water contained in the test gas can be calculated based on the air-fuel ratio detected by the third electrochemical cell as the air-fuel ratio sensor. Accordingly, it is not necessary to provide a separate air-fuel ratio sensor for the purpose of calculating the concentration of water contained in the test gas, so that, for example, the manufacturing cost of equipment (for example, a vehicle) equipped with an internal combustion engine is reduced. can do.

  In addition, the impedance detection unit may acquire the impedance between the electrodes of the third electrochemical cell. In this case, the impedance detection unit is, for example, a control unit configured to calculate impedance based on an electrode current detected when a predetermined high-frequency voltage is applied between the fifth electrode and the sixth electrode. Can be implemented. Such an impedance detection unit calculates the temperature of the element unit based on the impedance calculated based on the electrode current detected when a high frequency voltage is applied between the fifth electrode and the sixth electrode. When the control unit is configured, it is advantageous because it can be implemented without adding special components.

  By the way, the 3rd electrochemical cell which functions as a pump cell in this way applies a high frequency voltage in order to acquire impedance compared with the 1st electrochemical cell and 2nd electrochemical cell which function as a sensor cell and a monitor cell, respectively. It is difficult to see the effects of this. Therefore, when the apparatus of the present invention includes the third electrochemical cell that functions as a pump cell, it is desirable that the impedance detection unit is configured to acquire the impedance between the electrodes of the third electrochemical cell.

  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 concentration detection apparatus (1st apparatus) which concerns on one Embodiment of this invention is provided. It is a typical graph which shows the difference by the sensor activity of the relationship between an applied voltage and an electrode current. 4 is a schematic graph showing a correspondence relationship between an air-fuel ratio of an air-fuel mixture in a combustion chamber of an internal combustion engine corresponding to a test gas and a concentration of water contained in the test gas. It is a typical graph which shows the correspondence of the density | concentration of the water contained in to-be-tested gas, and the normal value (reference | standard detection value) of the 2nd detection value detected from a monitor cell. It is a flowchart which shows the "heater electric power control routine" which the control part with which a 1st apparatus is provided performs.

  Hereinafter, a gas concentration detection apparatus (hereinafter, may be referred to as a “first apparatus”) according to an embodiment of the present invention will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1A, the element unit 10 included in the first device includes a first solid electrolyte body 11s, a third solid electrolyte body 13s, a first alumina layer 21a, a second alumina layer 21b, and a third alumina. A layer 21c, a fourth alumina layer 21d, a fifth alumina layer 21e, a sixth alumina layer 21f, a diffusion resistance portion (diffusion-controlling layer) 32, and a heater 41;
The first solid electrolyte body 11s and the third solid electrolyte body 13s are thin plate bodies containing zirconia and the like and having oxide ion conductivity. The zirconia forming the first solid electrolyte body 11s and the third solid electrolyte body 13s may contain elements such as scandium (Sc) and yttrium (Y), for example.
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, for example, a thin plate body of cermet of 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 third solid electrolyte. The body 13s, the sixth alumina layer 21f, and the first alumina layer 21a are laminated in this order.

  The internal space 31 is a space formed by the first solid electrolyte body 11 s, the third solid electrolyte body 13 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 portion 10, the internal space 31 communicates with the inside of the exhaust pipe (none of which is shown) of the internal combustion engine via the diffusion resistance portion 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 formed 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 formed by the third solid electrolyte body 13s, the sixth alumina layer 21f, and the first alumina layer 21a, and is open to the atmosphere outside the exhaust pipe. The second atmosphere introduction path 52 corresponds to a third 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, the second electrode 11b, and the first solid electrolyte body 11s constitute a first electrochemical cell 11c that functions as a sensor cell that detects the concentration of sulfur oxide contained in the test gas.

  The fifth electrode 13a is a cathode, and the sixth electrode 13b is an anode. The fifth electrode 13a is fixed to the surface on one side of the third solid electrolyte body 13s (specifically, the surface of the third solid electrolyte body 13s that defines the internal space 31). On the other hand, the sixth electrode 13b is fixed to the surface on the other side of the third solid electrolyte body 13s (specifically, the surface of the third solid electrolyte body 13s that defines the second air introduction path 52). The fifth electrode 31a, the sixth electrode 31b, and the third solid electrolyte body 13s constitute a third electrochemical cell 13c that functions as a pump cell that discharges oxygen contained in the test gas from the internal space 31.

  FIG. 1B is a cross-sectional view of the element portion 10 taken along a plane including the line segment AA shown in FIG. In the example shown in FIG. 1B, the first device further includes a second electrochemical cell 12c (monitor cell) provided in the vicinity of the first electrochemical cell 11c. Here, “near” refers to a region where a test gas containing water having a concentration equal to the concentration of water contained in the test gas reaching the first electrochemical cell 11c reaches. Specifically, in the first apparatus, the first electrochemical cell 11c and the second electrochemical cell 12c are separated from the third electrochemical cell 13c disposed on the upstream side by the same distance to the downstream side. It is arranged.

  The second electrochemical cell 12c shares the first solid electrolyte body 11s with the first electrochemical cell 11c and has a third electrode 12a and a fourth electrode 12b which are a pair of electrodes disposed on the surface thereof. That is, the second solid electrolyte body 12s shown in FIG. 1B is the same (integrated) solid electrolyte body as the first solid electrolyte body 11s. In the example shown in FIG. 1, the third electrode 12 a is disposed so as to face the internal space 31, and the fourth electrode 12 b is disposed so as to face the first atmosphere introduction path 51. That is, in this case, the first atmosphere introduction path 51 also functions as a third separate space.

  The first electrochemical cell 11c to the third electrochemical cell 13c are heated to the activation temperature by the heater 41.

  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. On the other hand, the third electrode 12a and the fifth electrode 13a are porous cermet electrodes mainly containing an alloy of platinum (Pt) and gold (Au), and the fourth electrode 12b and the sixth electrode 13b are made of platinum ( It is a porous cermet electrode containing Pt) as a main component.

  The 1st electrode 11a and the 3rd electrode 12a are produced so that the 1st decomposition rate may become higher than the 2nd decomposition rate. As described above, the first decomposition rate is a voltage equal to or higher than the decomposition start voltage of water between the first electrode 11a and the second electrode 11b when the temperature of the element unit 10 is the first predetermined temperature. This is the decomposition rate of sulfur oxide in the first electrode 11a when the first predetermined voltage is applied. On the other hand, when the temperature of the element unit 10 is the first predetermined temperature, the second decomposition rate is a second predetermined rate that is a voltage equal to or higher than the water decomposition start voltage between the third electrode 12a and the fourth electrode 12b. It is the decomposition rate of sulfur oxide in the third electrode 12a when a voltage is applied.

  In the first device, the first decomposition speed when the first predetermined temperature is 700 ° C. and the first predetermined voltage and the second predetermined voltage are both 1.0 V is greater than the second decomposition speed, and the first The 1st electrode 11a and the 3rd electrode 12a were constituted so that 2 decomposition speed might become 0 (zero) substantially.

  Each of the first solid electrolyte body 11s (second solid electrolyte body 12s), the third solid electrolyte body 13s, and the first to sixth alumina layers 21a to 21f is formed into a sheet shape by, for example, a doctor blade method or an extrusion molding method. Can be molded. The first electrode 11a and the second electrode 11b, the third electrode 12a and the fourth electrode 12b, the fifth electrode 13a and the sixth electrode 13b, and the wiring for energizing these electrodes are formed by, for example, a screen printing method or the like. can do. By laminating and firing these sheets as described above, the element portion 10 having the above structure can be integrally manufactured.

The first device further includes power supplies 61 to 63, ammeters 71 to 73, and an ECU (electronic control unit) not shown. The power supplies 61 to 63 and ammeters 71 to 73 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 that is the current flowing between the first electrode 11a and the second electrode 11b (and hence the current flowing through the first solid electrolyte body 11s), and the measured value is One detection value is output 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 that is the current flowing between the third electrode 12a and the fourth electrode 12b (and hence the current flowing through the first solid electrolyte body 11s (second solid electrolyte body 12s)). Then, the measurement value is output to the ECU as the second detection value.
The power source 63 can apply a predetermined voltage between the fifth electrode 13a and the sixth electrode 13b so that the potential of the sixth electrode 13b is higher than the potential of the fifth electrode 13a. The operation of the power supply 63 is controlled by the ECU. The ammeter 73 measures the magnitude of the electrode current that is the current flowing between the fifth electrode 13a and the sixth electrode 13b (and hence the current flowing through the third solid electrolyte body 13s), and the measured value is 3 is output to the ECU as a detected value.

  As described above, the power sources 61 to 63 correspond to the power source included in the device of the present invention, and the ammeters 71 to 73 correspond to the detection unit included in the device of the present invention. The ECU controls the power source to apply a first predetermined voltage between the first electrode 11a and the second electrode 11b, and applies a second predetermined voltage between the third electrode 12a and the fourth electrode 12b, A third predetermined voltage is applied between the fifth electrode 13a and the sixth electrode 13b.

  Further, in the first device, the temperature of the element unit 10 based on the impedance calculated based on the electrode current detected when a predetermined high-frequency voltage is applied between the fifth electrode 13a and the sixth electrode 13b. The ECU is configured to calculate. The ECU increases the heater power when the temperature of the element unit 10 thus calculated is lower than the first predetermined temperature, and decreases the heater power when the temperature of the element unit 10 is higher than the first predetermined temperature. Let Thus, the ECU controls the heater power, which is the power supplied to the heater 41, to heat the temperature of the element unit 10 to the first predetermined temperature.

  That is, the ECU corresponds to a control unit provided in the device of the present invention. In the first device, the first predetermined voltage and the second predetermined voltage were set to 1.0V, and the third predetermined voltage was set to 0.4V. Furthermore, the initial set value of the first predetermined temperature was 700 ° C. However, as described above, the first predetermined voltage and the second predetermined voltage may be the same or different. Even if the first predetermined voltage and the second predetermined voltage are different, they are included in the gas to be detected by performing the detection operation as long as they are kept constant in the category satisfying the above-described conditions. The concentration of sulfur oxide can be detected. Similarly, even if the first predetermined voltage and the second predetermined voltage are different, if each of them is maintained constant in a category that satisfies the above-described conditions, the target power index is set by executing the learning operation. Can learn.

(Detection operation)
A third predetermined voltage (0.4V) is applied between the fifth electrode 13a and the sixth electrode 13b constituting the third electrochemical cell 13c functioning as a pump cell. Thereby, oxygen contained in the test gas is reduced and decomposed at the fifth electrode 13 a and discharged from the internal space 31.

  A second predetermined voltage (1.0 V) is applied between the third electrode 12a and the fourth electrode 12b constituting the second electrochemical cell 12c functioning as a monitor cell. As described above, the sulfur oxide decomposition rate (second decomposition rate) in the third electrode 12a is substantially 0 (zero). Therefore, water contained in the test gas from which oxygen has been discharged by the pump cell is reduced and decomposed at the third electrode 12a, and a second detection value corresponding to the water decomposition current is detected.

  On the other hand, a first predetermined voltage (1.0 V) is applied between the first electrode 11a and the second electrode 11b constituting the first electrochemical cell 11c functioning as a sensor cell. As described above, the sulfur oxide decomposition rate (first decomposition rate) in the first electrode 11a is higher than the second decomposition rate. Therefore, water and sulfur oxides contained in the test gas from which oxygen has been discharged by the pump cell are reduced and decomposed at the first electrode 11a, and a first detection value corresponding to the decomposition current of water and sulfur oxides is detected.

  The ECU functioning as the control unit acquires the first detection value and the second detection value detected as described above, and calculates the difference between the first detection value and the second detection value. Specifically, the ECU detects the value of the electrode current (first detection) when a first predetermined voltage (1.0 V) is applied between the first electrode 11a and the second electrode 11b of the first electrochemical cell 11c. Value), and the value of the electrode current (second detection value) when a second predetermined voltage (1.0 V) is applied between the third electrode 12a and the fourth electrode 12b of the second electrochemical cell 12c, Is obtained by the current difference detection circuit 81.

  On the other hand, as described above, the data storage device provided in the ECU relates to the correspondence between the magnitude of the difference between the first detection value and the second detection value and the concentration of sulfur oxide contained in the test gas. Data is stored in advance. Therefore, the ECU applies the magnitude of the difference between the first detection value and the second detection value calculated as described above to the correspondence relationship, so that the concentration of sulfur oxide contained in the test gas is increased. Is identified.

  In the first device, as described above, the first electrode 11a and the third electrode 12a are set so that the first decomposition rate is higher than the second decomposition rate and the second decomposition rate is substantially 0 (zero). Is configured. Accordingly, the decomposition product of sulfur oxide adsorbed on the first electrode 11a is more than the decomposition product of sulfur oxide adsorbed on the third electrode 12a, and the decomposition product of sulfur oxide adsorbed on the third electrode 12a. The amount of the object is substantially 0 (zero). As a result, the reaction area of the first electrode 11a is smaller than the reaction area of the third electrode 12a, and the first detection value is smaller than the second detection value.

(Learning action)
As described above, based on the electrode currents of the sensor cell and monitor cell at a predetermined element temperature and applied voltage, the concentration of sulfur oxide contained in the test gas can be detected with higher accuracy. However, as described at the beginning of the present specification, the activity of the electrode (cathode) and / or the solid due to the reductive decomposition of the oxygen-containing gas contained in the test gas, for example, due to individual differences in each sensor and aging The sensor activity may be different from that of a normal sensor because the oxide ion conductivity of the electrolyte body changes.

  For example, as shown in FIG. 2, when the sensor activity changes due to individual differences or aging deterioration in individual sensors, the magnitude of the electrode current with respect to the applied voltage is compared with the case where the sensor activity is normal (solid line), When the sensor activity is high, it is higher (broken line), and when the sensor activity is low, it is lower (dotted line), so that each is detected. As described above, when the sensor activity is changed, the concentration of sulfur oxide contained in the test gas can be accurately measured by the sensor even if the sensor element is controlled to have a predetermined element temperature and applied voltage. It is difficult to detect.

  Therefore, in the first device, the control unit determines the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine corresponding to the test gas based on the third detection value detected from the third electrochemical cell 13c (pump cell). An air-fuel ratio detection operation to be detected is executed. That is, in the first device, the third electrochemical cell 13c is used as an air-fuel ratio sensor to detect the air-fuel ratio. Then, the control unit identifies the concentration of water contained in the test gas based on the correspondence between the air-fuel ratio and the concentration of water contained in the test gas as shown in FIG. To do. Further, the control unit determines the concentration of water contained in the test gas as shown in FIG. 4 and the normal value of the second detection value detected from the second electrochemical cell 12c (monitor cell) from the concentration of the water. Based on this correspondence relationship, the normal second detection value at the concentration of the water is specified as the reference detection value.

  Then, the control unit controls the heater power so that the second detection value detected from the monitor cell matches the reference detection value. Then, the CPU stores the impedance between the electrodes of the pump cell when the second detection value matches the reference detection value as a target power index. Data such as the map (data table) representing the various correspondences described above and the target power index are stored in a data storage device provided in the ECU functioning as a control unit.

(Specific operation)
In the first device, the above-described detection operation or learning operation is executed according to the heater power control routine shown in the flowchart of FIG. For example, a CPU provided in the above-described ECU (hereinafter may be simply referred to as “CPU”) starts processing from step 500 at a predetermined timing, and proceeds to step 510.

  First, in step 510, the CPU determines whether or not a sensor drive condition that is a condition for normally operating the first device as a sensor is satisfied. In the first device, as described above, the CPU sets the first predetermined voltage and the second predetermined voltage to 1.0 V, sets the third predetermined voltage to 0.4 V, and sets an initial set value of the first predetermined temperature to 700 ° C. The power supply and the heater are controlled so that Therefore, in the first device, the sensor driving condition is that the temperature of the element unit 10 is stable at the first predetermined temperature, and the applied voltages of the first electrochemical cell 11c to the third electrochemical cell 13c are respectively This is established when the first predetermined voltage to the third predetermined voltage are stable.

  If it is determined in step 510 that the sensor driving condition is not satisfied (step 510: No), the CPU proceeds to step 390 without executing any special processing, and once ends the routine.

  On the other hand, when it is determined in step 510 that the sensor driving condition is satisfied (step 510: Yes), the CPU proceeds to the next step 520 to determine whether or not the learning condition for the target power index is satisfied. To do. The learning condition of the target power index is established when the concentration of water contained in the test gas is known or can be acquired, and a predetermined period has elapsed since the previous learning operation was performed.

  However, the learning condition of the target power index can be appropriately set according to the use of the equipment (for example, a vehicle or the like) equipped with the internal combustion engine to which the first device is applied. For example, when the equipment is a vehicle, the learning condition is that the concentration of water contained in the test gas is known or can be acquired, and the vehicle has a predetermined distance from the execution of the previous learning operation. You may set so that it may be materialized when it runs. Alternatively, learning of the target power index is turned off after the ignition key of the vehicle is turned on when the concentration of water contained in the test gas is known or can be acquired. It may be set to be executed a predetermined number of times (for example, once) within a period until it becomes.

  When it is determined in step 520 that the learning condition for the target power index is satisfied (step 520: Yes), the CPU proceeds to the next step 530 to execute the learning operation described above. Specifically, the CPU detects the reference corresponding to the concentration of water contained in the test gas calculated as described above based on a map stored in advance in a data storage device provided in the ECU as the control unit. Identify the value.

  Then, the CPU controls the heater power so that the second detection value detected from the monitor cell matches the reference detection value, and the impedance between the electrodes of the pump cell when the second detection value matches the reference detection value. Is stored as a target power index. Thereafter, the CPU proceeds to the next step 590 to end the routine once.

  On the other hand, when it is determined in step 520 that the learning condition for the target power index is not satisfied (step 520: No), the CPU proceeds to the next step 540 and executes the above-described detection operation. Specifically, the CPU controls the heater power so that the impedance between the electrodes of the pump cell matches the target power index stored by the learning operation. In this state, the CPU detects a first detection value and a second detection value by applying a predetermined applied voltage between the electrodes of the first electrochemical cell 11c and the second electrochemical cell 12c. As described above, the CPU detects the concentration of sulfur oxide (SOx) contained in the test gas based on the first detection value and the second detection value thus detected. Thereafter, the CPU proceeds to the next step 590 to end the routine once.

  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.

  As described above, in the first device, the impedance between the electrodes of the pump cell (third electrochemical cell) when the second detection value matches the reference detection value is adopted as the target power index. However, as described above, the target power index is not particularly limited as long as it is a value corresponding to the heater power when the second detection value matches the reference detection value. Specifically, as the target power index, for example, the heater power and the temperature of the element unit when the second detection value matches the reference detection value, and the element unit when the second detection value matches the reference detection value Various values such as the impedance between the electrodes of any of the electrochemical cells constituting 10 can be adopted.

  For example, when the heater power when the second detection value matches the reference detection value is used as the target power index, in the detection operation executed after execution of the learning operation, the control unit determines that the heater power is the target power index. Can be configured to control the heater power to match. Alternatively, for example, when the temperature of the element unit when the second detection value matches the reference detection value is used as the target power index, in the detection operation executed after the learning operation is performed, the control unit The heater power may be controlled such that the temperature of the heater matches the target power index.

  In the first device, as described above, the air / fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine corresponding to the test gas is detected by using the third electrochemical cell 13c as the air / fuel ratio sensor. Based on the air-fuel ratio, the concentration of water contained in the test gas was obtained. However, as described above, the air-fuel ratio may be detected by an air-fuel ratio sensor separate from the third electrochemical cell 13c.

  Further, in the first device, as described above, the reference detection value is specified based on the correspondence relationship described above from the concentration of water acquired based on an arbitrary air fuel ratio detected by the air fuel ratio sensor. However, as described above, when the air-fuel ratio is a value within a predetermined range including a specific value such as a theoretical air-fuel ratio, for example, the learning operation is executed, and the concentration of the specific water corresponding to the air-fuel ratio is determined. A reference detection value may be specified.

  In addition, as described above, the gas concentration detection device according to the present invention may further include an intake humidity sensor that detects intake humidity that is the concentration of water contained in the intake air supplied to the combustion chamber of the internal combustion engine. it can. In this case, in the learning operation, the control unit calculates the concentration of water contained in the test gas at that time by using the detected intake humidity and the air-fuel ratio detected as described above (the water calculated from the above). It can be calculated based on (concentration).

  On the other hand, as described above, the control unit sets the concentration of water contained in the atmosphere as the concentration of water contained in the test gas when fuel cut is being performed in which fuel is not supplied to the combustion chamber of the internal combustion engine. May be used to perform a learning operation. In this case, the reference detection value is specified from the concentration of water contained in the atmosphere.

  In this case as well, as described above, the gas concentration detection device according to the present invention further includes an intake humidity sensor that detects the intake humidity, which is the concentration of water contained in the intake air supplied to the combustion chamber of the internal combustion engine. Can do. In this case, in the learning operation, the control unit can calculate the concentration of water contained in the test gas at that time based on the detected intake humidity.

  Further, as described above, the first device includes the third electrochemical cell 13c as a pump cell. However, the element unit included in the gas concentration detection device according to the present invention has only the first electrochemical cell as the sensor cell and the second electrochemical cell as the monitor cell without the third electrochemical cell as the pump cell. You can also.

  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, 12a and 13a ... Electrode (cathode), 11b, 12b and 13b ... Electrode (anode), 11s, 12s and 13s ... 1st thru | or 3rd solid electrolyte body, 11c, 12c and 13c ... 1st Thru | or 3rd electrochemical cell, 21a, 21b, 21c, 21d, 21e and 21f ... 1st thru | or 6th alumina layer, 31 ... internal space, 32 ... diffusion resistor, 41 ... heater, 51 and 52 ... 1st and 1st 2 air introduction paths, 61, 62 and 63 ... power source, 71, 72 and 73 ... ammeter, and 81 ... current difference detection circuit.

Claims (11)

In a gas concentration detection device comprising an element unit, a power source, a heater, a detection unit, and a control unit,
The element portion includes a first electrochemical cell, a second electrochemical cell, a dense body, and a diffusion resistance portion.
The first electrochemical cell includes a first solid electrolyte body having oxide ion conductivity, and a first electrode and a second electrode formed on the surface of the first solid electrolyte body,
The second electrochemical cell includes a second solid electrolyte body having oxide ion conductivity, and a third electrode and a fourth electrode formed on the surface of the second solid electrolyte body, respectively.
Exhaust gas of the internal combustion engine as a test gas is introduced into the internal space defined by the first solid electrolyte body, the second solid electrolyte body, the dense body, and the diffusion resistance portion through the diffusion resistance portion,
The first electrode is exposed to the internal space, the second electrode is exposed to a first separate space that is a space different from the internal space,
The third electrode is exposed to the internal space, the fourth electrode is exposed to a second separate space that is a space different from the internal space,
The first electrode and the third electrode, when the temperature of the element portion is a first predetermined temperature equal to or higher than an activation temperature, which is a temperature at which oxide ion conductivity of the solid electrolyte body is expressed, A first decomposition rate that is a decomposition rate of sulfur oxide at the first electrode when a first predetermined voltage that is equal to or higher than a water decomposition start voltage is applied between the first electrode and the second electrode. Is the decomposition rate of sulfur oxide at the third electrode when a second predetermined voltage, which is a voltage equal to or higher than the decomposition start voltage of water, is applied between the third electrode and the fourth electrode. 2 higher than the decomposition rate,
Is configured as
The power source is configured to apply a voltage between the first electrode and the second electrode and between the third electrode and the fourth electrode, respectively.
The heater is configured to heat the element portion;
The detection unit corresponds to a first detection value which is a detection value corresponding to a current flowing between the first electrode and the second electrode and a current flowing between the third electrode and the fourth electrode. It is configured to detect a second detection value that is a detection value,
The control unit controls the power source to apply the first predetermined voltage between the first electrode and the second electrode, and to apply the second predetermined voltage between the third electrode and the fourth electrode. The first detection value detected by the detection unit when the voltage is applied and the heater power that is the power supplied to the heater is controlled to set the temperature of the element unit to the first predetermined temperature, and It is configured to perform a detection operation for detecting the concentration of sulfur oxide contained in the test gas based on a second detection value.
A gas concentration detection device comprising:
The controller is
Data related to the correspondence between the concentration of water contained in the gas to be detected and a reference detection value that is a reference value of the second detection value is stored in advance;
The second detection value detected by the detector when the second predetermined voltage is applied between the third electrode and the fourth electrode is water contained in the test gas at that time. The heater power is controlled so as to coincide with a reference detection value specified based on the correspondence relationship from the concentration of the second value, and a value corresponding to the heater power when the second detection value matches the reference detection value is determined. Execute learning operation to memorize as target power index,
Configured as
Gas concentration detector. The gas concentration detection device according to claim 1,
An impedance detection unit for detecting impedance between electrodes of any electrochemical cell constituting the element unit;
The controller is
In the learning operation, the impedance when the second detection value matches the reference detection value is stored as the target power index.
Configured as
Gas concentration detector. In the gas concentration detection apparatus according to claim 1 or 2,
The control unit uses the concentration of water contained in the atmosphere as the concentration of water contained in the test gas when a fuel cut is performed in which fuel is not supplied to the combustion chamber of the internal combustion engine. Configured to perform actions,
Gas concentration detector. In the gas concentration detection apparatus according to claim 3,
An intake air humidity sensor that detects an intake air humidity that is a concentration of water contained in the intake air supplied to the combustion chamber of the internal combustion engine;
The controller is configured to use the detected intake humidity as the concentration of water contained in the test gas at that time in the learning operation.
Gas concentration detector. The gas concentration detection device according to any one of claims 1 to 4,
The element unit further includes a third electrochemical cell,
The third electrochemical cell includes a third solid electrolyte body having oxide ion conductivity, and a fifth electrode and a sixth electrode formed on the surface of the third solid electrolyte body, respectively.
The fifth electrode is exposed to the internal space, the sixth electrode is exposed to a third space that is different from the internal space,
The fifth electrode is formed at a position closer to the diffusion resistance portion than the first electrode and the third electrode,
The fifth electrode corresponds to a limit current region of oxygen between the fifth electrode and the sixth electrode when the temperature of the element portion is the first predetermined temperature, and starts decomposition of water. When a third predetermined voltage that is a voltage lower than the voltage is applied, it is possible to decompose oxygen contained in the test gas and discharge it from the internal space.
Is configured as
The power source is configured to apply a voltage between the fifth electrode and the sixth electrode,
The control unit controls the power source and applies the third predetermined voltage between the fifth electrode and the sixth electrode at least during a period during which the detection operation is performed, so that the test target is detected. Configured to perform an oxygen discharge operation of decomposing oxygen contained in the gas and discharging it from the internal space,
Gas concentration detector. The gas concentration detection device according to claim 1 or 2,
An air-fuel ratio sensor for detecting an air-fuel ratio in an air-fuel mixture supplied to the combustion chamber of the internal combustion engine;
In the learning operation, the control unit is configured to calculate the concentration of water contained in the test gas at that time based on the detected air-fuel ratio.
Gas concentration detector. The gas concentration detection device according to claim 6,
The control unit is configured to execute the learning operation when the air-fuel ratio is a value within a predetermined range including a specific value.
Gas concentration detector. The gas concentration detection device according to claim 7,
The control unit is configured to execute the learning operation when the air-fuel ratio is a stoichiometric air-fuel ratio.
Gas concentration detector. The gas concentration detection device according to any one of claims 6 to 8,
An intake air humidity sensor that detects an intake air humidity that is a concentration of water contained in the intake air supplied to the combustion chamber of the internal combustion engine;
In the learning operation, the control unit is configured to calculate the concentration of water contained in the test gas at that time based on the detected air-fuel ratio and the detected intake humidity.
Gas concentration detector. A gas concentration detection device according to any one of claims 6 to 9,
The element unit further includes a third electrochemical cell,
The third electrochemical cell includes a third solid electrolyte body having oxide ion conductivity, and a fifth electrode and a sixth electrode formed on the surface of the third solid electrolyte body, respectively.
The fifth electrode is exposed to the internal space, the sixth electrode is exposed to a third space that is different from the internal space,
The fifth electrode is formed at a position closer to the diffusion resistance portion than the first electrode and the third electrode,
The fifth electrode corresponds to a limit current region of oxygen between the fifth electrode and the sixth electrode when the temperature of the element portion is the first predetermined temperature, and starts decomposition of water. When a third predetermined voltage that is a voltage lower than the voltage is applied, it is possible to decompose oxygen contained in the test gas and discharge it from the internal space.
Is configured as
The power source is configured to apply a voltage between the fifth electrode and the sixth electrode,
The control unit controls the power source and applies the third predetermined voltage between the fifth electrode and the sixth electrode at least during a period during which the detection operation is performed, so that the test target is detected. Configured to perform an oxygen discharge operation of decomposing oxygen contained in the gas and discharging it from the internal space,
Gas concentration detector. The gas concentration detection device according to claim 10,
The detection unit is also configured to detect a third detection value that is a detection value corresponding to a current flowing between the fifth electrode and the sixth electrode,
The control unit detects the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine corresponding to the test gas based on the third detection value when performing the oxygen discharge operation. Using a third electrochemical cell as the air-fuel ratio sensor;
Configured as
Gas concentration detector.

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