JP2017020825A - Gas concentration detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration detector capable of acquiring (detecting) a concentration of sulfur oxides contained in exhaust gas as gas to be detected with accuracy as much as possible by using a limit current type gas sensor.SOLUTION: In a limit current type gas sensor comprising a first electrochemical cell 11c and a second electrochemical cell 12c, one (a negative electrode) 11a of a pair of electrodes provided to the first electrochemical cell 11C is constituted of a material capable of decomposing sulfur oxides (SOx). A decomposition rate of SOx by one (a negative electrode) of a pair of electrodes of the second electrochemical cell 12C is made slower than that of the negative electrode of the first electrochemical cell. Further, a SOx concentration in gas to be detected is obtained by using output of the first electrochemical cell and the second electrochemical cell at the time of detection of SOx and correction coefficients Km and Ks for correcting inherent detection errors of the first electrochemical cell and the second electrochemical cell.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas concentration detection device that can more accurately acquire the concentration of sulfur oxide (SOx) contained in exhaust gas of an internal combustion engine.

Conventionally, a limiting current type gas sensor is known as one of air-fuel ratio sensors. The limiting current type gas sensor includes a pumping cell which 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. 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 due to conduction of oxide ions 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 that reaches the one electrode (cathode) is limited by the diffusion resistance portion, 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 alone. Specifically, in the gas containing oxygen atoms in the molecule (hereinafter, sometimes referred to as “oxygen-containing gas”), the limit current is determined by appropriately selecting the applied voltage and the configuration of the cathode. There is something that can express the characteristics. Examples of such oxygen-containing gas include, for example, sulfur oxide (hereinafter sometimes referred to as “SOx”), water (hereinafter sometimes referred to as “H ₂ O”) and carbon dioxide (hereinafter referred to as “SOx”). May be referred to as “CO ₂ ”).

  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 generation of white smoke. Therefore, it is desired to acquire the content rate of the sulfur component in the fuel and reflect the acquired sulfur content rate in the control of the vehicle. As an example thereof, reflection in internal combustion engine control, reflection in internal combustion engine failure warning control, and exhaust purification catalyst self-failure diagnosis (OBD) are assumed.

  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 sulfur content in the fuel, the higher the concentration of sulfur oxide contained in the exhaust (hereinafter sometimes referred to simply as “SOx concentration”). Therefore, if the SOx concentration in the exhaust gas can be accurately acquired, it is considered that the sulfur content in the fuel can be accurately acquired based on the acquired SOx concentration.

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

  In this sensor, by applying a relatively low voltage between the electrodes of the upstream pumping cell, oxygen contained in the test gas is removed by the oxygen pumping action of the upstream pumping cell.

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

JP-A-11-190721

  As described above, an attempt has been made to acquire the concentration of sulfur oxide contained in the exhaust gas of an internal combustion engine using a limiting current gas sensor that utilizes an oxygen pumping action. However, the concentration of sulfur oxide contained in the exhaust gas is extremely low, and the current (decomposition current) resulting from the decomposition of sulfur oxide is also extremely small. Furthermore, a decomposition current caused by oxygen-containing gas other than sulfur oxide (for example, water and carbon dioxide) can also flow between the electrodes. Therefore, for example, when the concentration of water in the exhaust gas changes, the concentration of sulfur oxide cannot be detected with high accuracy.

  Furthermore, the limiting current type gas sensor has individual differences in manufacturing, and furthermore, its output characteristics change with time. Therefore, in order to accurately detect the concentration of sulfur oxide, it is necessary to compensate for these individual differences and changes in the output value due to changes over time.

  The present invention has been made to address the above-described problems. That is, one of the objects of the present invention is to provide a gas concentration detection device capable of acquiring (detecting) the concentration of sulfur oxide contained in the exhaust gas as the test gas as accurately as possible using the limiting current type gas sensor. Is to provide.

  Generally speaking, the gas concentration detection apparatus according to the present invention (hereinafter referred to as “the present invention apparatus”) is in contact with the test gas (exhaust gas of the internal combustion engine) that has flowed into the internal space through the diffusion resistance layer. 1 electrochemical cell (sensor cell) and second electrochemical cell (monitor cell) ”.

  The first electrochemical cell and the second electrochemical cell can decompose water contained in the test gas when a voltage equal to or higher than the water decomposition start voltage is applied. On the other hand, the sulfur oxide decomposition rate when a specific voltage equal to or higher than the water decomposition start voltage is applied to the second electrochemical cell is the sulfur oxide decomposition rate when the specific voltage is applied to the first electrochemical cell. It is comprised so that it may become lower.

The device according to the present invention provides a current value (SOx detection first current) flowing between the electrodes of the first electrochemical cell when a voltage equal to or higher than the water decomposition start voltage is applied to the first electrochemical cell and the second electrochemical cell. 1 detection value) and a current value flowing between the electrodes of the second electrochemical cell (second detection value for SOx detection) are acquired. The second detection value for SOx detection, which is a detection value corresponding to the electrode current of the second electrochemical cell, mainly includes the value of the current due to the decomposition of water, but substantially affects the influence of the decomposition product of SOx. I don't accept it. Therefore, by obtaining the difference Δ between the first detection value for SOx detection of the first electrochemical cell and the second detection value for SOx detection of the second electrochemical cell, the concentration fluctuation of the water contained in the test gas is obtained. Can be reduced. In other words, the difference Δ is highly sensitive to the SOx concentration.

  Furthermore, as described above, the detection values (current values) of the first and second electrochemical cells include output errors due to individual differences and changes over time. In view of this, the apparatus according to the present invention, first, in the case where the oxygen concentration of the test gas in the internal space is a specific constant concentration (for example, when the operation state of the internal combustion engine is the fuel cut operation state), A voltage is applied to the second electrochemical cell, and a ratio of a predetermined reference output value determined in advance to a detection value (detection monitor cell value) of the second electrochemical cell at that time is obtained as a monitor cell correction value (Km). The reference output value is that when the oxygen concentration of the test gas in the internal space is a specific constant concentration, the voltage in the limiting current region of oxygen is applied to the electrochemical cell. This is the detection value shown when applied. Therefore, hereinafter, the value obtained by multiplying the second detection value for SOx detection by the monitor cell correction value (Km) is the SOx detection shown when the second electrochemical cell has the same characteristics as the reference second electrochemical cell. It becomes equal to the second detection value.

  Furthermore, the device according to the present invention applies a voltage equal to or higher than the lower limit voltage of the oxygen limit current region to the first and second electrochemical cells when the operation state of the internal combustion engine is a fuel cut operation state, or the internal combustion engine. When the operation state is not the fuel cut operation state, a voltage in the limiting current region of oxygen is applied to the first and second electrochemical cells. Then, the ratio of the “product of the detection value of the second electrochemical cell at that time and the monitor cell correction value (Km)” to the “detection value of the first electrochemical cell at that time” is used as the sensor cell correction value (Ks). Ask. According to the inventor's experiment, this ratio (that is, the sensor cell correction value (Ks)) is the first and second values when the operation state of the internal combustion engine is not the fuel cut operation state (that is, when fuel is being injected). When “a voltage higher than a voltage higher than the limiting current region of oxygen (for example, a voltage equal to or higher than the water decomposition start voltage)” is applied to the electrochemical cell, “the detected value of the first electrochemical cell” Is substantially equal to the ratio of the product of the detected value of the second electrochemical cell and the monitor cell correction value (Km) ". Therefore, hereinafter, the value obtained by multiplying the first detection value for SOx detection by the sensor cell correction value (Ks) has the same characteristics as the second electrochemical cell as a reference, and the second This is equal to the first detection value for SOx detection obtained when one electrochemical cell has the same characteristics as the first reference electrochemical cell.

  The device according to the present invention has a value corresponding to a difference between a product of the second detection value for SOx detection and the monitor cell correction value and a product of the first detection value for SOx detection and the sensor cell correction value. Based on this, the concentration of sulfur oxide in the test gas is determined. As described above, the device of the present invention can detect the SOx concentration with high accuracy.

  More specifically, the device of the present invention includes a first electrochemical cell (11c), a second electrochemical cell (12c), a dense body (21a to 21f), and a diffusion resistance portion (32). It has an element part (10) provided.

The first electrochemical cell (11c) includes a first solid electrolyte body (11s) having oxide ion conductivity, and a first electrode (11a) and a second electrode formed on the surface of the first solid electrolyte body, respectively. An electrode (11b).
The second electrochemical cell (12c) includes a third electrode (12a) and a fourth electrode (12b) respectively formed on the surface of the second solid electrolyte body (11s) having oxide ion conductivity. .

Furthermore, the element portion (10) includes the diffusion resistance portion in a first internal space (31) defined by the first solid electrolyte body, the second solid electrolyte body, the dense body, and the diffusion resistance portion. The exhaust gas of the internal combustion engine is introduced as a test gas via the first electrode, the third electrode is exposed to the first internal space, and the second electrode and the fourth electrode are the first internal space. It is configured to be exposed to a different first separate space (51).
The first separate space in which the second electrode is located and the first separate space in which the fourth electrode is located may be the same space or different spaces as long as they are different from the first internal space. Good.

In addition, the device of the present invention
A voltage application unit (61, 62) for applying a voltage between the first electrode and the second electrode and between the third electrode and the fourth electrode;
A first detection value corresponding to a current value flowing between the first electrode and the second electrode when a voltage is applied between the first electrode and the second electrode; An acquisition unit (71, 72, 81) for acquiring a second detection value corresponding to a current value flowing between the third electrode and the fourth electrode when a voltage is applied between the four electrodes;
Have

The first electrode decomposes water (H ₂ O) contained in the test gas when a voltage equal to or higher than a water decomposition start voltage is applied between the first electrode and the second electrode. It is configured to be possible.
The third electrode decomposes water (H ₂ O) contained in the test gas when a voltage equal to or higher than a water decomposition start voltage is applied between the third electrode and the fourth electrode. Is configured to be possible.

  Further, the first electrode and the third electrode apply the same voltage that is equal to or higher than the water decomposition start voltage between the first electrode and the second electrode and between the third electrode and the fourth electrode. In this case, the sulfur oxide (SOx) decomposition rate (monitor cell decomposition rate) by the third electrode is configured to be lower than the sulfur oxide decomposition rate (sensor cell decomposition rate) by the first electrode. Specifically, it is desirable that the monitor cell decomposition rate is a rate that can be regarded as substantially zero with respect to the sensor cell decomposition rate.

In addition, the acquisition unit
When it is determined that the oxygen concentration of the test gas in the first internal space is a specific constant concentration, a voltage in a limiting current region of oxygen is applied between the third electrode and the fourth electrode, A ratio of a predetermined reference output value determined in advance to the detected monitor cell value that is the second detected value at that time is obtained as a monitor cell correction value (Km) (steps 530 to 560),
When the operation state of the internal combustion engine is a fuel cut operation state, a voltage equal to or higher than the lower limit voltage of the limit current region of oxygen is applied between the first electrode and the second electrode and between the third electrode and the fourth electrode. First voltage application control (steps 640 to 670) to be applied using the voltage application unit during the period of time, and when the operation state of the internal combustion engine is not a fuel cut operation state, the voltage in the limiting current region of oxygen is Of the second voltage application control (steps 730 to 1020 in FIG. 10) to be applied using the voltage application unit between one electrode and the second electrode and between the third electrode and the fourth electrode And at least one of
A ratio of a product of the second detection value and the monitor cell correction value with respect to the first detection value when at least one of the first voltage application control and the second voltage application control is being executed. Obtained as a sensor cell correction value (Ks) (steps 680 and 1030),
When the operation state of the internal combustion engine is not a fuel cut operation state, a voltage equal to or higher than a water decomposition start voltage is applied between the first electrode and the second electrode and between the third electrode and the fourth electrode. And applying the first detection value and the second detection value at that time as a first detection value for SOx detection and a second detection value for SOx detection, respectively (steps 730 to 750 in FIG. 7);
Based on a value corresponding to a difference between a product of the second detection value for SOx detection and the monitor cell correction value and a product of the first detection value for SOx detection and the sensor cell correction value, The concentration of sulfur oxide is obtained (steps 760 to 780).

  As described above, the apparatus of the present invention applies the voltage in the limiting current region of oxygen to the second electrochemical cell while the oxygen concentration is a specific constant concentration (for example, during fuel cut operation). Ask. Therefore, the detection monitor cell value is not affected by the concentration of the water and SOx of the test gas, and is a value corresponding to the inherent pumping function of the second electrochemical cell. Therefore, the monitor cell correction value (Km), which is the ratio of the reference output value to the detected monitor cell value (= detected monitor cell value / reference output value), is a value that accurately reflects the inherent error of the second electrochemical cell.

  Furthermore, the device according to the present invention provides the second detection value and the monitor cell correction value with respect to the first detection value when at least one of the first voltage application control and the second voltage application control is executed. The ratio (= Km · first detection value / second detection value) of the product of is calculated as a sensor cell correction value (Ks).

  Further, when the operating state of the internal combustion engine is not a fuel cut operating state, a voltage equal to or higher than a water decomposition start voltage is applied to the first electrochemical cell and the second electrochemical cell, and a first detection value for SOx detection and The second detection value for SOx detection is acquired.

  In addition, the device according to the present invention provides a difference (SOx concentration detection parameter P) between the product of the second detection value for SOx detection and the monitor cell correction value and the product of the first detection value for SOx detection and the sensor cell correction value. The concentration of sulfur oxide in the test gas is detected based on the value corresponding to the above. This difference (P) is a value that compensates for the inherent error of the first and second electrochemical cells.

  Therefore, according to this invention apparatus, the density | concentration of the sulfur oxide contained in test gas can be detected accurately. Furthermore, the apparatus of the present invention can detect the concentration of sulfur oxide contained in the test gas with higher accuracy than when the detection error inherent to the first electrochemical cell and the second electrochemical cell is not taken into consideration. Can do.

The device of the present invention
The first solid electrolyte body and the second solid electrolyte body are the same common solid electrolyte body (11s),
The element portion includes a third solid electrolyte body (12s) having oxide ion conductivity, a fifth electrode (13a) and a sixth electrode (13b) formed on the surface of the third solid electrolyte body, A third electrochemical cell (13c) comprising
The first internal space (31) is defined by the common solid electrolyte body, the dense body (21b), the diffusion resistance portion (32), and the third solid electrolyte,
The fifth electrode is exposed to the first internal space and the sixth electrode is exposed to a second separate space (52) different from the first internal space,
The voltage application unit (61 to 63) is configured to apply a voltage between the fifth electrode and the sixth electrode,
The fifth electrode and the sixth electrode discharge oxygen (O ₂ ) from the first internal space when a voltage in a limiting current region of oxygen is applied between the fifth electrode and the sixth electrode. Constructed to demonstrate oxygen pumping function,
The acquisition unit
When the operation state of the internal combustion engine is a fuel cut operation state, it is determined that the oxygen concentration of the test gas in the first internal space is the specific constant concentration (step 530),
When obtaining the monitor cell correction value, the application of the voltage using the voltage application unit between the fifth electrode and the sixth electrode is stopped to stop the oxygen pumping function,
When acquiring the first detection value for SOx detection and the second detection value for SOx detection, the voltage application unit applies a voltage in the limiting current region of oxygen between the fifth electrode and the sixth electrode. The oxygen pumping function may be exhibited by applying the voltage using a voltage application unit.

If comprised in this way, even if the density | concentration of the oxygen contained in test gas changes, when acquiring the 1st detection value for SOx detection, and the 2nd detection value for SOx detection, the 3rd electrochemical cell With the oxygen pumping function, the oxygen concentration in the first internal space can be kept constant. Therefore, it is possible to effectively reduce the influence of the change in the oxygen concentration on the first detection value for SOx detection and the second detection value for SOx detection.
Therefore, compared with the case where oxygen pumping by the third electrochemical cell is not performed, the concentration of sulfur oxide in the test gas can be detected more accurately by the first electrochemical cell and the second electrochemical cell.
On the other hand, when the monitor cell correction value is obtained, the oxygen pumping function by the third electrochemical cell is stopped. Accordingly, since the detected monitor cell value is obtained in a state where a sufficient amount of oxygen is present in the first internal space, the monitor cell correction value can be obtained more accurately.

The acquisition unit
A voltage using the voltage application unit between the fifth electrode and the sixth electrode during execution of the first voltage application control while obtaining the sensor cell correction value by executing the first voltage application control May be configured to stop the oxygen pumping function.

The acquisition unit
The second voltage application control is executed when the difference between the maximum value and the minimum value of the change amount of the oxygen concentration of the test gas in the first internal space in a predetermined time is equal to or less than a predetermined change amount threshold value. The sensor cell correction value may be obtained.

  In this way, when the sensor cell correction value (Ks) is obtained based on the first detection value and the second detection value while executing the second voltage application control, the oxygen concentration of the first and second detection values is determined. The effect of change can be reduced. Therefore, the sensor cell correction value (Ks) can be obtained with higher accuracy.

The acquisition unit
The difference (P) between the product (Imc) of the second detection value for SOx detection and the monitor cell correction value and the product (Isc) of the first detection value for SOx detection and the sensor cell correction value, and the SOx Even if it is configured to obtain the concentration of sulfur oxide of the test gas based on a look-up table (two-dimensional map) using as an argument the product (Imc) of the second detection value for detection and the monitor cell correction value. Good (steps 760 to 780).

  In this way, the concentration of sulfur oxide contained in the test gas can be accurately detected without being affected by the concentration of water in the exhaust gas.

The first electrode and the third electrode include platinum (Pt),
The first electrode may be configured to include at least one of rhodium (Rh) and palladium (Pd) more than the third electrode.

  Rhodium (Rh) and palladium (Pd) can decompose SOx, and platinum (Pt) cannot decompose SOx. Therefore, the SOx decomposition rate of the first electrode can be easily increased from the SOx decomposition rate of the third electrode.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached to the configuration of the invention corresponding to the embodiments in parentheses, but each constituent element of the invention is the reference numeral. It is not limited to the embodiment defined by. Other objects, other features and attendant advantages of the present invention will be readily understood from the description of the embodiments of the present invention described with reference to the following drawings.

(A) is typical sectional drawing which shows an example of a structure of the element part with which the gas concentration detection apparatus which concerns on 1st Embodiment of this invention is equipped, (b) follows the AA arrow line of (a). It is sectional drawing. It is a typical graph which shows the relationship between the voltage (applied voltage) Vm1 applied between the 1st electrode which comprises a 1st electrochemical cell, and a 2nd electrode, and the electrode electric current Im1 which flows between these electrodes. . Applied voltage Vm1 to the first electrochemical cell is a schematic graph showing the relationship between the concentration of sulfur dioxide (SO ₂₎ contained in the size and the test gas in the electrode current Im1 of time is 1.0 V. Schematic showing the relationship between the water concentration and the electrode current when the same voltage equal to or higher than the water decomposition start voltage is applied to the first electrochemical cell and the second electrochemical cell when the test gas does not contain SOx. It is a typical graph. It is a flowchart which shows the acquisition process routine of the correction coefficient (monitor cell correction value) Km. It is a flowchart which shows the acquisition process routine of correction coefficient Ks (sensor cell correction value). It is a flowchart which shows the density | concentration calculation processing routine of the sulfur oxide using the correction coefficients Km and Ks. It is a figure which shows the two-dimensional map for SOx density | concentration calculation. It is a typical graph which shows the relationship between the density | concentration of water, the parameter for SOx density | concentration detection, and a correction | amendment 2nd detection value. It is a flowchart which shows the acquisition process routine of the correction coefficient Ks which concerns on 2nd Embodiment of this invention.

1. First embodiment (configuration)
Hereinafter, a gas concentration detection apparatus (hereinafter, may be referred to as “first detection apparatus”) according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 9. The first detection device is a device that detects the sulfur oxide concentration in the gas passing through the “exhaust pipe of the internal combustion engine mounted on the vehicle” (not shown).

  The 1st detection apparatus is provided with the element part 10, as shown to Fig.1 (a) and (b). The element unit 10 includes a first electrochemical cell 11c that is a pumping cell, and a second electrochemical cell 12c that is a pumping cell provided near the first electrochemical cell 11c.

  The element unit 10 includes a solid electrolyte body 11s, a solid electrolyte body 12s, a first alumina layer 21a, a second alumina layer 21b, a third alumina layer 21c, a fourth alumina layer 21d, a fifth alumina layer 21e, and a sixth alumina layer 21f. , A diffusion resistance portion (diffusion rate limiting layer) 32 and a heater 41 are provided. The solid electrolyte body 11s is sometimes referred to as a first solid electrolyte body or a second solid electrolyte body, and the solid electrolyte body 12s is referred to as a third solid electrolyte body.

The solid electrolyte body 11s is a thin plate body having oxide ion conductivity containing zirconia or the like. The zirconia forming the solid electrolyte body 11s may contain elements such as scandium (Sc) and yttrium (Y).
The solid electrolyte body 12s is also a thin plate body having oxide ion conductivity containing zirconia or the like. The zirconia forming the solid electrolyte body 12s may contain elements such as scandium (Sc) and yttrium (Y), for example.

Each of the first to sixth alumina layers 21a to 21f is a dense layer (dense body) that contains alumina and does not allow gas to pass therethrough.
The diffusion resistance portion 32 is a porous diffusion rate limiting layer. That is, the diffusion resistance portion 32 is a gas permeable layer (thin plate).
The heater 41 is a thin plate-like cermet having, for example, platinum (Pt) and ceramics (for example, alumina or the like), and generates heat when electric power of a power source (not shown) is energized under the control of the ECU 81 described later.

  Each layer of the element unit 10 includes, from below, the fifth alumina layer 21e, the fourth alumina layer 21d, the third alumina layer 21c, the solid electrolyte body 11s, the diffusion resistance unit 32 and the second alumina layer 21b, the solid electrolyte body 12s, The 6 alumina layers 21f and the first alumina layer 21a are laminated in this order.

  The first internal space 31 is a space formed by the solid electrolyte body 11s, the diffusion resistance portion 32, the second alumina layer 21b, and the solid electrolyte body 12s. The exhaust gas of the internal combustion engine is introduced into the first internal space 31 as a test gas via the diffusion resistance portion 32. That is, the first internal space 31 communicates with the inside of the exhaust pipe of the internal combustion engine via the diffusion resistance portion 32.

  A first air introduction path 51 is formed by the solid electrolyte body 11s, the third alumina layer 21c, and the fourth alumina layer 21d. The first atmosphere introduction path 51 communicates with the atmosphere outside the exhaust pipe. Note that the first air introduction path 51 corresponds to a first separate space.

  A second air introduction path 52 is defined by the solid electrolyte body 12s, the sixth alumina layer 21f, and the first alumina layer 21a. The second atmosphere introduction path 52 communicates with the atmosphere outside the exhaust pipe. The second atmosphere introduction path 52 corresponds to a second separate space.

The first electrochemical cell 11c includes a solid electrolyte body 11s, a first electrode 11a, and a second electrode 11b. The first electrochemical cell 11 c is heated to the activation temperature by the heater 41.
The first electrode 11a that is a cathode is fixed to the surface on one side of the solid electrolyte body 11s (specifically, the surface of the solid electrolyte body 11s that defines the first internal space 31). The first electrode 11a is a porous cermet electrode containing an alloy of platinum (Pt) and rhodium (Rh) as a main component. The first electrode 11a may contain palladium (Pd).
The second electrode 11b, which is an anode, defines the surface (specifically, the first air introduction path 51) on the other side of the solid electrolyte body 11s so as to face the first electrode 11a across the solid electrolyte body 11s. To the surface of the solid electrolyte body 11s. The second electrode 11b is a porous cermet electrode containing platinum (Pt) as a main component. The second electrode 11b contains neither rhodium (Rh) nor palladium (Pd).

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

The first detection device further includes a power supply 61, an ammeter 71, and an ECU 81 (electronic control unit, controller). The power supply 61 and the ammeter 71 are connected to the ECU 81.
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 81.
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 solid electrolyte body 11s of the first electrochemical cell 11c).

  The ECU 81 is a microcomputer including a CPU, a ROM that stores programs executed by the CPU, a map, and the like, a RAM that temporarily stores data, a backup RAM, and the like (all not shown). As is well known, the backup RAM continues to store the stored data while the vehicle is not driving. The ECU 81 can control the applied voltage Vm1 applied between the first electrode 11a and the second electrode 11b using the power supply 61. Further, the ammeter 71 acquires the electrode current Im1 flowing through the first electrochemical cell 11c and outputs the acquired information to the ECU 81. That is, the ammeter 71 and the ECU 81 constitute an acquisition unit.

  Further, the ECU 81 is connected to an actuator (not shown) (fuel injection valve, throttle valve, EGR valve, etc.) of the internal combustion engine. The ECU 81 sends drive (instruction) signals to these actuators to control the internal combustion engine.

  The second electrochemical cell 12c includes a solid electrolyte body 11s shared with the first electrochemical cell 11c, and a third electrode 12a and a fourth electrode 12b which are a pair of electrodes provided on the surface of the solid electrolyte body 11s. Have. The second electrochemical cell 12c is also heated to the activation temperature by the heater 41.

The third electrode 12 a serving as a cathode is disposed so as to face the first internal space 31. The third electrode 12a is provided in the vicinity of the first electrode 11a. In other words, when the test gas reaches the first internal space 31, oxygen, water, and sulfur oxides contained in each of the test gas that contacts the first electrode 11a and the test gas that contacts the third electrode 12a ( The concentrations of SOx) are equal to each other. The third electrode 12a is a porous cermet electrode containing an alloy of platinum (Pt) and gold (Au) as a main component. The third electrode 12a contains neither rhodium (Rh) nor palladium (Pd).
In addition, although you may comprise the 3rd electrode 12a so that any one of rhodium (Rh) and palladium (Pd) may be comprised, in that case, content is decreased rather than the 1st electrode 11a. However, the third electrode 12a preferably does not contain either rhodium (Rh) or palladium (Pd).

  The 4th electrode 12b which is an anode is arrange | positioned so that the 1st air introduction path 51 may be faced so that 11 s of solid electrolytes may be pinched | interposed. The fourth electrode 12b is a porous cermet electrode containing platinum (Pt) as a main component. The fourth electrode 12b contains neither rhodium (Rh) nor palladium (Pd).

  The third electrode 12a is “a voltage applied between the third electrode 12a and the fourth electrode 12b and equal to or higher than the water decomposition start voltage” is “between the first electrode 11a and the second electrode 11b. Even when the voltage is equal to the voltage applied to the first electrode 11a, the SOx decomposition rate is extremely low as compared with the first electrode 11a. Specifically, the rate at which SOx is decomposed in the third electrode 12a is substantially 0 (zero).

The first detection device further includes a “power supply 62 and an ammeter 72”, all of which are connected to the ECU 81.
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 81.
The ammeter 72 measures an electrode current that is a current that flows between the third electrode 12a and the fourth electrode 12b (thus, a current that flows through the solid electrolyte body 11s of the second electrochemical cell 12c).
The ECU 81 can control the applied voltage Vm2 applied between the third electrode 12a and the fourth electrode 12b using the power source 62. Further, the ammeter 72 acquires the electrode current Im2 flowing through the second electrochemical cell 12c, and outputs the acquired information to the ECU 81.
That is, the ammeter 72 and the ECU 81 constitute an acquisition unit.

  As shown in FIG. 1A, the element unit 10 is a pumping cell disposed on the upstream side (the diffused resistor unit 32 side) of the “first electrochemical cell 11c and the second electrochemical cell 12c”. A three-electrochemical cell 13c is further provided. In other words, the 1st electrochemical cell 11c and the 2nd electrochemical cell 12c are arrange | positioned in the position away from the 3rd electrochemical cell 13c in the downstream by the same distance. As will be described later, the third electrochemical cell 13c discharges oxygen in the first space 31 to the atmosphere by exerting an oxygen pumping function (action).

The third electrochemical cell 13c includes a solid electrolyte body 12s, a fifth electrode 13a, and a sixth electrode 13b. The third electrochemical cell 13c is also heated to the activation temperature by the heater 41.
The fifth electrode 13a is fixed to the surface on one side of the solid electrolyte body 12s (specifically, the surface of the solid electrolyte body 12s that defines the first internal space 31). The fifth electrode 13a is disposed at a position closer to the diffused resistor portion 32 than the first electrode 11a and the third electrode 12a. The fifth electrode 13a is a porous cermet electrode containing platinum (Pt) as a main component. The fifth electrode 13a contains neither rhodium (Rh) nor palladium (Pd).
The sixth electrode 13b has a surface on the other side of the solid electrolyte body 12s (specifically, a solid electrolyte that defines the second air introduction path 52 so as to face the fifth electrode 13a across the solid electrolyte body 12s). The surface of the body 12s). The sixth electrode 13b is also a porous cermet electrode containing platinum (Pt) as a main component. The sixth electrode 13b contains neither rhodium (Rh) nor palladium (Pd).

The first detection device further includes a “power source 63 and an ammeter 73”, all of which are connected to the ECU 81.
The power source 63 can apply a voltage between the fifth electrode 13a and the sixth electrode 13b so that one of the fifth electrode 13a and the sixth electrode 13b has a higher potential with respect to the other. It has become. The operation of the power supply 63 is controlled by the ECU 81. That is, the ECU 81 can control the applied voltage Vm3 applied to the fifth electrode 13a and the sixth electrode 13b.
The ammeter 73 measures an electrode current Im3, which is a current flowing between the fifth electrode 13a and the sixth electrode 13b (and hence a current flowing through the solid electrolyte body 12s of the third electrochemical cell 12c), and measures the measurement. The value is output to the ECU 81.
That is, the ammeter 73 and the ECU 81 constitute an acquisition unit.

<Operation of the first electrochemical cell 11c>
Next, the operation of the first electrochemical cell 11c will be described.
In the first electrochemical cell 11c, a voltage equal to or higher than the water decomposition starting 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 ( For example, 1.0V) is applied. Thus, not only water contained in the test gas but also SOx contained in the test gas is decomposed in the first electrode 11a, and an electrode current flows between the first electrode 11a and the second electrode 11b. The decomposition product of SOx (for example, sulfur or sulfur compound) is adsorbed on the first electrode 11a, and it is considered that the decomposition product of SOx reduces the area of the first electrode 11a that can contribute to the decomposition of water. . The SOx decomposition products adsorbed on the first electrode 11a are separated from the first electrode 11a at a certain rate. As a result, the amount of the decomposition product of SOx adsorbed on the first electrode 11a increases as the concentration of SOx contained in the test gas increases. Therefore, when the oxygen and water concentrations are constant, the electrode current Im1 of the first electrochemical cell 11c when a voltage equal to or higher than the water decomposition start voltage is applied between the first electrode 11a and the second electrode 11b. , And changes depending on the concentration of SOx contained in the test gas (the higher the SOx concentration, the smaller the electrode current Im1). The value of the electrode current Im1 when a voltage is applied to the first electrochemical cell 11 may be hereinafter referred to as “first detection value”.

  Here, a voltage (applied voltage Vm1) applied between the first electrode 11a and the second electrode 11b of the first electrochemical cell 11c and a current (electrode) flowing between the first electrode 11a and the second electrode 11b. The relationship with the current Im1) will be described more specifically.

FIG. 2 is a schematic graph showing the relationship between the applied voltage Vm1 and the electrode current Im1 when the applied voltage Vm1 for the first electrochemical cell 11c is gradually increased (step-up sweep). In this example, four different test gases having concentrations of 0, 100, 300, and 500 ppm of sulfur dioxide (SO ₂ ) as SOx contained in the test gas were used. However, the concentrations of oxygen and water contained in the test gas are kept constant in any test gas. Furthermore, in this example, the limiting current value of oxygen is displayed as 0 (zero) μA.

  First, a solid curve L1 indicates the relationship between the applied voltage Vm1 and the electrode current Im1 when the concentration of sulfur dioxide contained in the test gas is 0 (zero) ppm. In the region where the applied voltage Vm is less than about 0.2 V, the electrode current Im1 also increases as the applied voltage Vm1 increases. In this region, as the applied voltage Vm1 increases, the oxygen decomposition rate at the first electrode 11a (cathode) also increases. However, in the region where the applied voltage Vm1 is about 0.2 V or more, the electrode current Im1 hardly increases even when the applied voltage Vm1 increases, and is substantially constant. That is, the limit current characteristic of oxygen described above is manifested. Thereafter, when the applied voltage Vm1 becomes about 0.6 V or more, the electrode current Im1 starts increasing again. This increase in the electrode current Im1 is caused by the start of the decomposition of water in the first electrode 11a. Thereafter, the electrode current Im1 increases as the applied voltage Vm1 increases in the range of 0.6 V or more.

  Next, a dotted curve L2 shows the relationship between the applied voltage Vm1 and the electrode current Im1 when the concentration of sulfur dioxide contained in the test gas is 100 ppm. Also in this case, when the applied voltage Vm1 is less than the voltage at which the water decomposition at the first electrode 11a begins (decomposition start voltage) (about 0.6 V), the relationship between the applied voltage Vm1 and the electrode current Im1 is the same as that of the curve L1. It is. However, when the applied voltage Vm1 is equal to or higher than the water decomposition start voltage (about 0.6 V), the electrode current Im1 indicated by the curve L2 is smaller than the electrode current Im1 indicated by the curve L1. That is, when a voltage equal to or higher than the water decomposition start voltage is applied, the increase rate of the electrode current Im1 indicated by the curve L2 with respect to the applied voltage Vm1 is higher than the increase rate of the electrode current Im1 indicated by the curve L1 with respect to the applied voltage Vm1. Small (small tilt).

  Furthermore, curves L3 and L4 represented by a dashed line and a broken line show the relationship between the applied voltage Vm1 and the electrode current Im1 when the concentrations of sulfur dioxide contained in the test gas are 300 ppm and 500 ppm, respectively. . Also in these cases, when the applied voltage Vm1 is less than the water decomposition start voltage (about 0.6V) at the first electrode 11a, the relationship between the applied voltage Vm1 and the electrode current Im1 is those indicated by the curve L1. Same as relationship. However, when the applied voltage Vm1 is equal to or higher than the water decomposition start voltage (about 0.6 V) in the first electrode 11a, the electrode current Im1 decreases as the concentration of sulfur dioxide contained in the test gas increases. That is, when a voltage equal to or higher than the water decomposition start voltage is applied, the increase rate of the electrode current Im1 indicated by the curve L4 with respect to the applied voltage Vm1 is higher than the increase rate of the electrode current Im1 indicated by the curve L3 with respect to the applied voltage Vm1. Small (small tilt). Furthermore, the increasing rate of the electrode current Im1 indicated by the curve L3 with respect to the applied voltage Vm1 is smaller than the increasing rate of the electrode current Im1 indicated by the curve L2 with respect to the applied voltage Vm1 (the slope is small).

As described above, the magnitude of the electrode current Im1 when the applied voltage Vm1 is equal to or higher than the water decomposition start voltage in the first electrode 11a varies depending on the concentration of sulfur dioxide as SOx contained in the test gas. To do. For example, the magnitude of the electrode current Im1 indicated by the curves L1 to L4 when the applied voltage Vm1 in the graph shown in FIG. 2 is 1.0 V is plotted against the concentration of sulfur dioxide contained in the test gas. Then, the graph shown in FIG. 3 is obtained. As shown by the dotted curve in FIG. 3, the magnitude of the electrode current Im1 with respect to the applied voltage Vm1 (1.0 V in this case), which is a specific voltage higher than the water decomposition start voltage, is It changes according to the concentration of sulfur dioxide contained in (it becomes smaller as the concentration of sulfur dioxide is higher). Therefore, if the electrode current Im1 when the applied voltage Vm1 is set to a voltage equal to or higher than the water decomposition start voltage is obtained, if the concentrations of oxygen and water contained in the test gas are known, the electrode current Im1 ( That is, the SOx concentration can be acquired based on the first detection value.
Therefore, if the oxygen concentration and the water concentration are constant, the first detection device can detect the concentration of SOx contained in the test gas based only on the first detection value of the first electrochemical cell 11c. . Thus, since the 1st electrochemical cell 11c is used as a sensor which acquires the density | concentration of SOx contained in test gas, it may be called a "sensor cell."

  It should be noted that individual specifics such as the applied voltage Vm1 shown on the horizontal axis of the graph shown in FIG. 2, the electrode current Im1 shown on the vertical axis, and the applied voltage Vm1 described in the above description. The value may vary depending on experimental conditions (for example, concentrations of various components contained in the test gas, electrode composition, electrode area, etc.).

<Operation of Second Electrochemical Cell 12c>
Next, the operation of the second electrochemical cell 12c will be described.
As described above, the concentration of SOx contained in the test gas can be detected only by the first electrochemical cell 11c. However, if the detection result of the second electrochemical cell 12c is used in addition to the detection result of the first electrochemical cell 11c, the concentration of SOx in the test gas can be detected with higher accuracy as described below. .

  As described above, when an applied voltage (for example, 1.0 V) equal to or higher than the applied voltage to the first electrochemical cell 11c is applied to the second electrochemical cell 12c, The contained SOx is decomposed at a rate much lower than that of the first electrochemical cell 11c. Specifically, the rate at which SOx is decomposed at the third electrode 12a (second decomposition rate, monitor cell decomposition rate) is higher than the rate at which SOx is decomposed at the first electrode 11a (first decomposition rate, sensor cell decomposition rate). Is extremely low and substantially 0 (zero). That is, the second detection value, which is a detection value corresponding to the electrode current of the second electrochemical cell 12c, mainly includes a current value resulting from water decomposition, but is not affected by the decomposition product of SOx. Therefore, by obtaining the difference Δ between the first detection value corresponding to the electrode current of the first electrochemical cell 11c and the second detection value corresponding to the electrode current of the second electrochemical cell 12c, The influence of the concentration variation of the contained water can be reduced. In other words, the difference Δ is highly sensitive to the SOx concentration. Therefore, since the second electrochemical cell 12c has a function of monitoring the concentration of water, it may be referred to as “monitor cell 12c”.

As understood from the above, in principle, the first detection device performs the steps described below, and uses the first electrochemical cell 11c and the second electrochemical cell 12c in the test gas. The concentration of SOx contained is detected.
(1) The first detection device includes an applied voltage Vm1 (voltage between the first electrode 11a and the second electrode 11b) and a second applied voltage Vm2 (voltage between the third electrode 12a and the fourth electrode 12b). Is set to a voltage equal to or higher than the water decomposition start voltage. It is desirable that the applied voltage Vm1 and the applied voltage Vm2 are equal to each other.
(2) The first detection device is configured such that the difference between the electrode current Im1 (first detection value) of the first electrochemical cell 11c and the electrode current Im2 (second detection value) of the second electrochemical cell 12c at this time Δ (Δ = Im2−Im1) is acquired by the ECU 81. This difference Δ may also be referred to as a SOx concentration detection parameter. In practice, as will be described later, the electrode currents Im1 and Im2 are corrected and then the difference Δ is obtained.
(3) The first detection device detects the concentration of SOx contained in the test gas based on the relationship between this difference Δ and “data indicating the correlation between the difference Δ and the SOx concentration” stored in advance. To do. In practice, the first detection device detects the SOx concentration using the difference Δ and the electrode current Im2.

  According to this detection method, the influence of fluctuations in the concentration of water contained in the test gas can be reduced, so that the concentration of SOx in the test gas is higher than when only the first electrochemical cell 11c is used. Can be detected with higher accuracy. However, as will be described later, the first detection value and the second detection value are corrected so as to reduce the influence of individual differences, and based on the corrected values (corrected first detection value and corrected second detection value). Preferably, the SOx concentration is detected.

<Operation of Third Electrochemical Cell 13c>
Next, the operation of the third electrochemical cell 13c will be described.
The concentration of oxygen contained in the exhaust gas discharged from the internal combustion engine varies depending on, for example, the air-fuel ratio (A / F) of the air-fuel mixture burned in the combustion chamber of the internal combustion engine. When the concentration of oxygen contained in the test gas changes, the magnitude of the current flowing between the electrodes of the first electrochemical cell 11c and the second electrochemical cell 12c also changes. Since the test gas is exhaust gas from an internal combustion engine, the fluctuation in oxygen concentration is extremely large compared to the fluctuation in SOx concentration. Therefore, the fluctuation of the oxygen concentration may greatly reduce the detection accuracy of the SOx concentration using the first electrochemical cell 11c and the second electrochemical cell 12c. Therefore, when the first detection device detects the SOx concentration, the oxygen concentration reaching the first electrochemical cell 11c and the second electrochemical cell 12c is extremely reduced by using the oxygen pumping action of the third electrochemical cell 13c. Use a low concentration (substantially zero). The third electrochemical cell 13c may be referred to as an “oxygen pumping cell”.

  More specifically, in the first detection device, the fifth electrode 13a and the sixth electrode 13b become a cathode and an anode, respectively, between the fifth electrode 13a and the sixth electrode 13b of the third electrochemical cell 13c. Thus, the voltage of the limiting current flow region of oxygen is applied. As a result, oxygen is discharged from the first internal space 31 to the second air introduction path 52. As a result, even if the concentration of oxygen contained in the test gas changes, the oxygen concentration in the first internal space 31 is reduced by discharging oxygen from the first internal space 31 by the third electrochemical cell 13c. Can be kept low and constant. In the present embodiment, the concentration of oxygen in the first internal space 31 is adjusted to approximately 0 (zero) ppm by the third electrochemical cell 13c.

  Accordingly, the first detection device can reduce “the influence of the concentration of oxygen contained in the test gas on the first detection value and the second detection value”. As a result, compared with the case where oxygen pumping by the third electrochemical cell 13c is not executed, the SOx concentration in the test gas is detected with higher accuracy using the first electrochemical cell 11c and the second electrochemical cell 12c. be able to.

  In addition, the 1st electrochemical cell 11c, the 2nd electrochemical cell 12c, and the 3rd electrochemical cell 13c can be utilized also as an air fuel ratio sensor. That is, a voltage corresponding to the limiting current region of oxygen is applied between the electrodes of any one of the electrochemical cells, and the concentration of oxygen contained in the exhaust gas of the internal combustion engine based on the detected value corresponding to the electrode current at that time Can be detected. Based on the detected oxygen concentration in the exhaust gas, the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine can be detected. The first detection device uses the third electrochemical cell 13c as an air-fuel ratio sensor.

<Correction of individual difference between first electrochemical cell 11c and second electrochemical cell 12c>
By the way, as described above, theoretically, if the detection results (first detection value and second detection value) of the first electrochemical cell 11c and the second electrochemical cell 12c are used, the SOx in the gas to be detected is detected. It should be possible to detect the concentration with high accuracy. However, the first electrochemical cell 11c and / or the second electrochemical cell 12c have individual differences in manufacturing, and the output characteristics change with time. Therefore, if the inherent detection error of the first electrochemical cell 11c and / or the second electrochemical cell 12c is large, it is obvious that the SOx concentration in the test gas cannot be detected with high accuracy. Therefore, the first detection device corrects the detection error specific to the first electrochemical cell 11c and the detection error specific to the second electrochemical cell 12c by the following methods.

<< Calculation of Correction Factor Km for Detection Error Specific to Second Electrochemical Cell >>
First, a method for correcting the inherent detection error of the second electrochemical cell (monitor cell) 12c will be described. In the following, the “specific detection error of the second electrochemical cell 12c” means the difference between the detection value of the second electrochemical cell 12c and the detection value of the reference electrochemical cell. The reference electrochemical cell is, for example, an electrochemical cell that has the same specifications as the second electrochemical cell 12c and can exhibit standard performance as an electrochemical cell of this specification. That is, for example, an electrochemical cell having the same specifications as the “second electrochemical cell 12c manufactured according to the design value and having a design central output characteristic expected in design” is used as the reference electrochemical cell.

  Then, when the same voltage is applied to the “reference electrochemical cell and second electrochemical cell 12 c” arranged in the same test gas, the difference between the two electrode currents (detected values) is “second electrochemical cell”. 12c inherent detection error ". The first detection device obtains a correction coefficient (monitor cell correction value) Km for correcting the second detection value of the second electrochemical cell 12c as follows so that this detection error is eliminated. Hereinafter, the detection value (second detection value) of the second electrochemical cell 12c when compared with the detection value of the reference electrochemical cell is referred to as “detection monitor cell value” and corresponds to the electrode current of the reference electrochemical cell. The detected value is referred to as a “reference cell value”.

  When the internal combustion engine is in a fuel cut (hereinafter referred to as “F / C”) operation state, the first detection device detects the voltage Vm2 applied to the second electrochemical cell 12c by “specifying within the limiting current range of oxygen”. The detected monitor cell value Im2 is acquired after setting the voltage to Vms (for example, 0.4 V). Since the atmospheric oxygen concentration is about 20 percent, when the operating state of the internal combustion engine is in the F / C state, the oxygen concentration of the test gas in the first internal space 31 is also about 20 percent (that is, a certain constant value). Concentration) is retained. On the other hand, the applied voltage Vms is “the voltage within the limiting current region of oxygen” and is therefore smaller than the water decomposition start voltage. Therefore, the detection monitor cell value Im2 is not affected by the concentration of atmospheric water and becomes a limit current value with respect to the oxygen concentration in the atmosphere. The temperature of the second electrochemical cell 12c is maintained at a predetermined specific activation temperature.

  On the other hand, the reference cell value Ist is obtained in advance by the following method and stored in the ROM in the ECU 81 of the first detection device. That is, the “element portion 10 having the reference electrochemical cell” is disposed in the exhaust pipe of the internal combustion engine. Further, the operation state of the internal combustion engine is set to the F / C operation state in a state where the temperature of the reference electrochemical cell is maintained at the specific activation temperature. And the reference cell value Ist is acquired after setting the applied voltage with respect to the reference | standard electrochemical cell to the said "specific voltage Vms in the limiting current region of oxygen". Like the detection monitor cell value Im2, the reference cell value Ist is not affected by the concentration of atmospheric water and becomes a limit current value for the oxygen concentration in the atmosphere.

Therefore, the difference D1 between the detection monitor cell value Im2 and the reference cell value Ist is a value corresponding to the “detection error unique to the second electrochemical cell 12c”. Therefore, the first detection device obtains a correction coefficient Km that satisfies the following expression (1). The correction coefficient Km is also referred to as “monitor cell correction value”.

(Detection monitor cell value Im2) · Km = reference cell value Ist (1)

  The first detection device acquires, as the corrected second detection value, a value obtained by multiplying the second detection value by the correction coefficient Km when detecting the SOx concentration. The first detection device detects the SOx concentration using the corrected second detection value. The corrected second detection value is substantially equal to the second detection value obtained when the second electrochemical cell 12c has the same characteristics as the reference electrochemical cell.

<< Calculation of Correction Factor Ks for Detection Error Specific to First Electrochemical Cell >>
Next, a method for correcting a detection error unique to the first electrochemical cell (sensor cell) 11c will be described.

  After the correction coefficient Km is acquired, the first detection device sets the first electrochemical cell 11c and the second electrochemical cell 12c to “the water decomposition start voltage or higher” when the operation state of the internal combustion engine is in the F / C operation state. The same voltage (for example, 1.0 V) ”is applied. This voltage control is referred to as “first voltage application control” for convenience.

In this state, the first detection device acquires a first detection value Im1 corresponding to the electrode current of the first electrochemical cell 11c and a second detection value Im2 corresponding to the electrode current of the second electrochemical cell 12c. To do. Hereinafter, the first detection value Im1 of the first electrochemical cell 11c at this time will be referred to as “Ks calculation sensor cell value Isks”, and the second detection value Im2 of the second electrochemical cell 12c will be referred to as “Ks calculation monitor cell”. May be referred to as “value Imks”. Then, the first detection device obtains a correction coefficient (sensor cell correction value) Ks that satisfies the following expression (2).

Imks · Km = Isks · Ks (2)

  The first detection device acquires the corrected first detection value by multiplying the first detection value by the correction coefficient Ks when detecting the SOx concentration. The corrected first detection value is an ideal characteristic in which the second electrochemical cell 12c (monitor cell) is a reference electrochemical cell, and the first electrochemical cell (sensor cell) 11c is a sensor cell (center specification in design). Is substantially equal to the first detection value obtained when Therefore, the first detection device detects the SOx concentration using the above-described corrected second detection value and the corrected first detection value.

  By the way, in the first detection device, when the SOx concentration is detected using the first electrochemical cell 11c and the second electrochemical cell 12c, the first electrochemical cell 11c and the second electrochemical cell 12c decompose water. A voltage above the starting voltage is applied so that they break down the water. Therefore, when the correction coefficient Ks is obtained, the same voltage higher than the water decomposition start voltage is applied to the first electrochemical cell 11c and the second electrochemical cell 12c, thereby the first electrochemical cell 11c and the second electrochemical cell. The cell 12c can be placed in a situation similar to that at the time of detecting the SOx concentration. In other words, when an applied voltage (for example, a voltage in the limiting current region of oxygen) that does not decompose water is applied to the first electrochemical cell 11c and the second electrochemical cell 12c, the environment is different from that at the time of detecting the SOx concentration. Thus, “the correction coefficient Ks for correcting the detection error unique to the first electrochemical cell (sensor cell) 11c” is obtained. Therefore, as described above, the first detection device applies “the same voltage equal to or higher than the water decomposition start voltage” to the first electrochemical cell 11c and the second electrochemical cell 12c when determining the correction coefficient Ks.

Furthermore, when a voltage equal to or higher than the water decomposition start voltage is applied to the first electrochemical cell 11c and the second electrochemical cell 12c, the electrode currents of both the cells 11c and 12c resulting from the decomposition of SOx Very small compared to the resulting electrode current. Therefore, even when the operating state of the internal combustion engine is in the F / C operating state (that is, when SOx does not flow into the first internal space 31), the first electrochemical cell 11c and the second electrochemical cell 12c The electrode voltage of the first electrochemical cell 11c and the second electrochemical cell 12c is obtained by applying the same voltage that is equal to or higher than the water decomposition start voltage, and the correction coefficient Ks is set based on the electrode current as described above. If calculated, the correction coefficient Ks becomes a correction coefficient that is effective (high correction accuracy) even when the first detection device actually detects the SOx concentration.
However, when obtaining the correction coefficient Ks, a voltage (for example, 0.4 V which is the voltage in the limit current region of oxygen) higher than the lower limit voltage (for example, 0.2 V) in the limit current region of oxygen may be applied. In this case as well, the correction coefficient Ks can be obtained with appropriate accuracy.

  As described above, the correction coefficient Km uses the electrode current of the second electrochemical cell 12c when a voltage (for example, 0.4 V) smaller than the water decomposition start voltage is applied to the second electrochemical cell 12c. This is the coefficient obtained. Therefore, the magnitude of the applied voltage to the second electrochemical cell 12c when obtaining the correction coefficient Km is different from the magnitude of the applied voltage to the second electrochemical cell 12c when obtaining the correction coefficient Ks.

  However, according to the inventors' investigation, for example, the ratio when the applied voltage is 0.4 V = (the detected value of the first electrochemical cell 11c / the detected value of the second electrochemical cell 12c) and the applied voltage are The magnitude of the ratio when 1.0 V = (detected value of the first electrochemical cell 11c / detected value of the second electrochemical cell 12c) is substantially the same. That is, when the applied voltage is equal to or higher than the lower limit voltage of the limit current region of oxygen, the ratio = (detected value of the first electrochemical cell 11c / detected value of the second electrochemical cell 12c) regardless of the magnitude of the applied voltage. The size is a substantially constant value.

  Therefore, it can be said that the correction coefficient Ks obtained using the correction coefficient Km is a coefficient that accurately compensates for the detection error of the second electrochemical cell 12c.

  It should be noted that the concentration of water in the test gas located in the first internal space 31 is also made constant by performing the F / C operation and executing oxygen pumping by the third electrochemical cell 13c. I can't. That is, the concentration of water in the test gas located in the first internal space 31 when the correction coefficient Ks is obtained may change.

  However, according to the inventor's experiment, as shown in FIG. 4, even when the concentration of water is changed, the first electrochemical cell 11c and the second electrochemical cell 12c have a water decomposition start voltage or higher. It was found that the ratio when the same voltage was applied = (detected value of the first electrochemical cell 11c / detected value of the second electrochemical cell 12c) was substantially constant. Therefore, even when the correction coefficient Ks is obtained and the SOx concentration is detected, even if the concentration of water in the test gas located in the first internal space 31 is different, the correction coefficient Ks is the first electric current when the SOx concentration is detected. It is possible to accurately correct the detection value of the chemical cell 11c.

  Then, the first detection device corrects the first detection value (first detection value for SOx detection) of the first electrochemical cell 11c at the time of SOx detection by the correction coefficient Ks and the second electrochemical at the time of SOx detection. The SOx concentration is obtained based on the value obtained by correcting the second detection value (second detection value for SOx detection) of the cell 12c with the correction coefficient Km.

(Actual operation)
Next, the “SOx concentration acquisition processing routine” executed by the ECU 81 (actually the CPU) of the first detection device will be specifically described with reference to the flowcharts of FIGS.

  When the internal combustion engine starts operating by operating an ignition key switch (not shown) of the vehicle on which the internal combustion engine is mounted, the ECU 81 repeats the routine shown in the flowchart of FIG. 5 every time a predetermined time elapses. It is supposed to run.

  The third electrochemical cell 13c that also functions as an air-fuel ratio sensor detects the oxygen concentration in the first internal space 31 every time a predetermined time elapses while the internal combustion engine is operating. The oxygen concentration is transmitted to the ECU 81. The ECU 81 detects the air-fuel ratio of the exhaust gas based on the signal.

  When the ECU 81 starts the process in step 500, it determines in step 510 whether or not the correction coefficient Km has been newly calculated after the current internal combustion engine is started. If the correction coefficient Km is not newly calculated after the start of the internal combustion engine this time, the ECU 81 makes a “No” determination at step 510 and proceeds to step 520.

  In step 520, the ECU 81 determines “whether the internal combustion engine has been warmed up” based on a cooling water temperature detected by a water temperature sensor (not shown) of the internal combustion engine, and closes to the heater 41 of the element unit 10. Based on information from the provided temperature sensor (not shown), it is determined whether or not all of the first to third electrochemical cells 11c, 12c, and 13c are activated. Instead of the information from the temperature sensor, the ECU 81 detects the impedances of the solid electrolyte body 11s and the solid electrolyte body 12s, and “whether or not the first to third electrochemical cells are activated” based on the impedances. May be determined.

  When the ECU 81 determines “Yes” in step 520, the ECU 81 determines whether or not the F / C operation is performed in step 530. More specifically, the ECU 81 determines “whether a predetermined time (for example, 3 seconds) has elapsed since the start of the F / C operation and whether the F / C operation is still in progress”. By this step 530, the ECU 81 determines whether or not the oxygen concentration of the test gas in the first internal space 31 is a specific constant concentration. The ECU 81 executes an engine control routine (not shown) to perform an F / C operation for stopping fuel injection from the fuel injection valve when the vehicle is in a deceleration state. When it is determined that the condition of Step 530 (hereinafter referred to as “F / C operation execution condition”) is satisfied, the atmosphere has reached the element unit 10 through the exhaust pipe. It can be presumed that SOx is not contained in the test gas flowing into the internal space 31.

  When the ECU 81 determines that the FC execution condition is satisfied, in step 530, the ECU 81 further indicates that “the respective temperatures of the first electrochemical cell 11c, the second electrochemical cell 12c, and the third electrochemical cell 13c are predetermined appropriate. Whether or not the temperature is within the temperature range is determined based on the information (or the impedance) of the temperature sensor. The appropriate temperature range is, for example, a range including the temperature of the solid electrolyte of the reference electrochemical cell when the above-described “reference cell value” is acquired using the reference electrochemical cell.

  When it is determined that “the temperature of each of the first electrochemical cell 11c, the second electrochemical cell 12c, and the third electrochemical cell 13c is within a predetermined appropriate temperature range”, the ECU 81 determines “Yes” in step 530. In step 540, the application of voltage to the third electrochemical cell (oxygen pumping cell) 13c is stopped, thereby stopping the oxygen pumping function of the third electrochemical cell 13c. As a result, the oxygen concentration of the test gas flowing in the first internal space 31 is maintained at about 20 percent (specific constant concentration), which is the same as the atmosphere. In this case, the operation of the third electrochemical cell 13c as an air-fuel ratio sensor is also temporarily stopped.

  Subsequently, in step 550, the ECU 81 applies 0.4 V, which is a voltage in the limiting current region of oxygen, to the second electrochemical cell (monitor cell) 12c.

  Subsequently, in step 560, the ECU 81 obtains the detection value (second detection value) of the second electrochemical cell 12c as the detection monitor cell value Im2. Further, in step 560, the ECU 81 stores in advance a “detection value of the reference electrochemical cell (reference cell value Ist) acquired in an environment where the oxygen concentration is 20%” stored in the ROM, a detection monitor cell value Im2, and Is applied to the above equation (1) to calculate the correction coefficient Km (= Im2 / Ist). Then, the ECU 81 stores the acquired correction coefficient Km in the backup RAM. When the correction coefficient Km is already stored in the backup RAM, the correction coefficient Km is overwritten on the correction coefficient Km acquired this time. At this time, an average value of the correction coefficient Km already stored in the backup RAM and the correction coefficient Km acquired this time may be stored in the backup RAM as a new correction coefficient Km. In addition, the detected monitor cell value Im2 used when calculating the correction coefficient Km in this step may be an average value of the detected monitor cell values Im2 acquired multiple times including the current time after the current engine start.

  Subsequently, the ECU 81 proceeds to step 570, and “a voltage is applied to the third electrochemical cell (oxygen pumping cell) 13c, thereby causing the third electrochemical cell 13c to exhibit an oxygen pumping function. In step 595, this routine is temporarily terminated.

  On the other hand, if the ECU 81 determines “YES” in step 510 or determines “No” in any of the steps 520 and 530, the ECU 81 proceeds directly to step 570 from each step, and then proceeds to step 595. Proceed to to end the present routine.

  Further, the ECU 81 repeatedly executes the routine shown in the flowchart of FIG. 6 every time a predetermined time elapses.

  When the ECU 81 starts the process in step 600, it determines in step 610 whether or not the correction coefficient Km has been newly calculated after the current internal combustion engine is started. If the correction coefficient Km has been newly calculated after the start of the internal combustion engine this time, the ECU 81 makes a “Yes” determination at step 610 and proceeds to step 620.

  In step 620, the ECU 81 determines whether or not the correction coefficient Ks has been newly calculated after the current internal combustion engine is started. If the correction coefficient Ks is not newly calculated after the start of the internal combustion engine this time, the ECU 81 makes a “No” determination at step 620 to proceed to step 630.

  Steps 630 and 640 are steps for performing the same processes as those in steps 520 and 530 described above. The ECU 81 proceeds to step 640 when it determines “Yes” at step 630, and proceeds to step 650 when it determines “Yes” at step 640.

  In step 650, the ECU 81 determines whether or not the third electrochemical cell (pumping cell) 13c is performing oxygen pumping (whether or not it exhibits an oxygen pumping function). When the ECU 81 makes a “Yes” determination at step 650, the ECU 81 proceeds to step 660 to “stop the application of voltage to the third electrochemical cell (oxygen pumping cell) 13c, whereby the third electrochemical cell 13c. Then, the ECU 81 proceeds to step 670. On the other hand, when the ECU 81 makes a “No” determination at step 650, the ECU 81 proceeds directly to step 670.

  In step 670, the ECU 81 applies 1.0 V, which is a voltage equal to or higher than the water decomposition start voltage, to the first electrochemical cell 11c and the second electrochemical cell 12c. In step 670, the ECU 81 may apply a “voltage in the limiting current region of oxygen (eg, 0.4 V)” to the first electrochemical cell 11c and the second electrochemical cell 12c.

  Thereafter, in step 680, the ECU 81 acquires the detection value (first detection value) of the first electrochemical cell 11c as the sensor cell value Isks for Ks calculation, and the detection value (second detection value) of the second electrochemical cell 12c. ) As the monitor cell value Imks for Ks calculation. Further, in step 680, the ECU 81 applies the correction coefficient Km, the sensor cell value Isks for Ks calculation, and the monitor cell value Imks for Ks calculation stored in the backup RAM to the above equation (2), thereby correcting the correction coefficient Ks ( = Imks · Km / Isks). Then, the ECU 81 stores the acquired correction coefficient Ks in the backup RAM.

  When the correction coefficient Ks is already stored in the backup RAM, the correction coefficient Ks is overwritten on the correction coefficient Ks acquired this time. At this time, an average value of the correction coefficient Ks already stored in the backup RAM and the correction coefficient Ks acquired this time may be stored in the backup RAM as a new correction coefficient Ks. In addition, the “Ks calculation sensor cell value Isks and the Ks calculation monitor cell value Imks” used when calculating the correction coefficient Ks in this step are acquired “Ks” several times including the current time after the current engine start. It may be an average value of each of the calculation sensor cell value Isks and the Ks calculation monitor cell value Imks.

  Subsequently, the ECU 81 proceeds to step 690, and “a voltage is applied to the third electrochemical cell (oxygen pumping cell) 13c, thereby causing the third electrochemical cell 13c to exhibit an oxygen pumping function. In step 695, this routine is once ended.

  On the other hand, if the ECU 81 determines “No” in any of the steps 610, 630, and 640 and “Yes” in step 620, the ECU 81 proceeds directly to step 690 from each step. Thereafter, the routine proceeds to step 695, where the present routine is temporarily terminated.

  Further, the ECU 81 repeatedly executes the routine shown in the flowchart of FIG. 7 every time a predetermined time elapses.

  In step 710 following step 700, the ECU 81 determines whether both the correction coefficient Ks and the correction coefficient Km are stored in the backup RAM. When both the correction coefficient Ks and the correction coefficient Km are stored in the backup RAM, the ECU 81 determines “Yes” in step 710 and proceeds to step 720. Step 720 is a step for performing the same processing as step 520. If the ECU 81 determines “Yes” in step 720, the ECU 81 proceeds to step 730.

  In step 730, the ECU 81 determines that “a predetermined time (for example, 3 seconds) has elapsed since the F / C operation was stopped (that is, the fuel injection was resumed), and the F / C operation is still stopped ( It is determined whether or not fuel is being injected. The ECU 81 executes an engine control routine (not shown) to stop the F / C operation and restart the fuel injection when the vehicle returns from the deceleration state to the acceleration state or the steady state. When it is determined that the determination condition of the step 730 (hereinafter referred to as “fuel injection execution condition”) is satisfied, the exhaust gas has reached the element portion 10 through the exhaust pipe. It can be estimated that the sample gas flowing into the space 31 may contain SOx.

  When the ECU 81 determines that the condition during execution of fuel injection is satisfied, the ECU 81 further determines that the temperature of each of the first electrochemical cell 11c, the second electrochemical cell 12c, and the third electrochemical cell 13c has been described above in step 730. Whether or not it is within a predetermined appropriate temperature range is determined based on the information (or the impedance) of the temperature sensor.

  When it is determined that “the temperatures of the first electrochemical cell 11c, the second electrochemical cell 12c, and the third electrochemical cell 13c are within a predetermined appropriate temperature range”, the ECU 81 determines “Yes” in step 730. In step 740, 1.0V, which is a voltage equal to or higher than the water decomposition start voltage, is applied to the first electrochemical cell (sensor cell) 11c and the second electrochemical cell (monitor cell) 12c.

  Next, the ECU 81 proceeds to step 750, where the first detection value of the first electrochemical cell (sensor cell) 11c (the first detection value in this case is also referred to as “the first detection value Im1sd for SOx detection)” and the second electricity. A second detection value of the chemical cell (monitor cell) 12c (the second detection value in this case is also referred to as “second detection value Im2md for SOx detection”) is acquired.

  Next, the ECU 81 proceeds to step 760, corrects the first detection value Im1sd with the correction coefficient Ks, and corrects the second detection value Im2md with the correction coefficient Km. More specifically, the ECU 81 obtains the corrected first detection value Isc by multiplying the first detection value Im1sd by the correction coefficient Ks, and corrects the second correction value by multiplying the second detection value Im2md by the correction coefficient Km. The detection value Imc is acquired.

  Next, the ECU 81 proceeds to step 770 and obtains the SOx concentration detection parameter P (= Imc−Isc) by subtracting the corrected first detected value Isc from the corrected second detected value Imc.

  Subsequently, the ECU 81 proceeds to step 780, and the SOx concentration detection parameter P and the corrected second detection value (SOx concentration detection parameter Q) Imc acquired in step 770 are shown in FIG. The SOx concentration in the test gas is acquired (detected) by applying it to a lookup table (interpolating as necessary). The ECU 81 stores the SOx concentration in the RAM and the backup RAM, and uses the stored SOx concentration for control of the internal combustion engine and self-diagnosis. Thereafter, the ECU 81 proceeds to step 795 to end the present routine tentatively.

The loop-up table in FIG. 8 is a two-dimensional map that uses the SOx concentration detection parameter P (Imc−Isc) and the corrected second detection value Imc as arguments.
For example, when using a one-dimensional map in which only the SOx concentration detection parameter P is used as an argument instead of the two-dimensional map, as shown in the graph of FIG. 9, the detected value (mA) of the SOx concentration detection parameter P is used. ) Is, for example, the value IA, there is a possibility that both the “H ₂ O concentration is a and the SOx concentration is 200 ppm” and “H ₂ O concentration is b and the SOx concentration is 100 ppm”. Can not do it. On the other hand, as can be understood from the graph of FIG. 9, the corrected second detection value Imc (mA) has a one-to-one correspondence with the H 2 O concentration. Therefore, if the corrected second detection value Imc is, for example, IB, when the SOx concentration detection parameter P is the value IA, it can be uniquely specified that the H ₂ O concentration is a and the SOx concentration is 200 ppm. Therefore, a two-dimensional map as shown in FIG. 8 is used.

  If the ECU 81 makes a “No” determination at any of step 710, step 720, and step 730, the ECU 81 proceeds directly to step 795 to end the present routine tentatively.

As described above, the first detection device can accurately detect the concentration of sulfur oxide contained in the test gas. Furthermore, the apparatus of the present invention can detect the concentration of sulfur oxide contained in the test gas with higher accuracy than when the detection error inherent to the first electrochemical cell 11c and the second electrochemical cell 12c is not taken into consideration. can do.
Note that the ECU 81 may determine in step 530 of FIG. 5 that the oxygen concentration is a specific constant concentration by using the third electrochemical cell 13c as an air-fuel ratio sensor.

2. Second Embodiment Next, a detection apparatus according to a second embodiment of the present invention (hereinafter may be referred to as a “second detection apparatus”) will be described with reference to FIG. The second detection device is different from the first detection device only in that the method of obtaining the correction coefficient Ks is different from the method of obtaining the correction coefficient Ks of the first detection device.

  The first detection device obtains correction coefficients Km and Ks during the F / C operation. However, the F / C operation may end within an extremely short time. In such a case, there is a possibility that both the correction coefficient Km and the correction coefficient Ks cannot be calculated during the F / C operation. Furthermore, even if the ECU 81 can calculate the correction coefficient Km, it may not be able to calculate the correction coefficient Ks and may not be able to obtain the correction coefficient Ks until the next F / C operation. For this reason, it takes a long time to newly calculate the correction coefficient Ks after the start of the current engine, and as a result, it is highly likely that a long time will be required to accurately detect the SOx concentration.

  Therefore, the second detection device obtains the correction coefficient Km in the F / C as in the first detection device, while not performing the F / C operation on the correction coefficient Ks (that is, during the fuel injection operation). Ask for. Hereinafter, a method for obtaining the correction coefficient Ks by the second detection device will be described in detail.

  First, when the F / C is not executed, the same voltage (a voltage equal to or higher than the water decomposition start voltage (eg, 1.0 V)) is applied to the first electrochemical cell 11c and the second electrochemical cell 12c, Consider a case where the correction coefficient Ks is obtained based on the detection values of the cells 11c and 12c at this time. This voltage control is referred to as “second voltage application control” for convenience.

  When the correction coefficient Ks is obtained by the second voltage application control, since the F / C operation is not being performed, the test gas decomposed by the first electrochemical cell 11c and the second electrochemical cell 12c includes not only water but also SOx. May be included. Further, as described above, the second electrochemical cell 12c has a lower SOx decomposition capability than the first electrochemical cell 11c. Therefore, if the same voltage (for example, 1.0 V) equal to or higher than the water decomposition start voltage is applied to the first electrochemical cell 11c and the second electrochemical cell 12c, the detection values of both the cells 11c and 12c are obtained. The first detection value of the electrochemical cell 11c is affected by SOx, but the second detection value of the second electrochemical cell 12c is hardly affected by SOx. Therefore, it is difficult to immediately obtain the correction coefficient Ks for correcting the inherent detection error of the first electrochemical cell 11 based on these first and second detection values.

  On the other hand, if a voltage in the limiting current region of oxygen is applied to the first electrochemical cell 11c and the second electrochemical cell 12c, water and SOx are not decomposed in these cells. Therefore, the “first detection value and second detection value” when such a voltage is applied is a value indicating the output characteristics of the first electrochemical cell 11c and the second electrochemical cell 12c with appropriate accuracy.

  Therefore, the second detection apparatus is identical to the first electrochemical cell 11c and the second electrochemical cell 12c in the case where the F / C operation is not performed, and “the voltage in the limiting current region of oxygen (eg, 0.4 V)”. And the correction coefficient Ks is acquired based on the “first detection value and second detection value” obtained in that state.

  However, when “the voltage in the limiting current region of oxygen (for example, 0.4 V)” is applied to the first electrochemical cell 11c and the second electrochemical cell 12c when the oxygen concentration in the test gas varies greatly, Since the first detection value and the second detection value are greatly affected by the oxygen concentration, there is a high possibility that the correction coefficient Ks cannot be obtained with high accuracy.

  Therefore, when it is determined that the oxygen concentration of the test gas flowing into the first internal space 31 is “substantially constant”, the second detection device 11c and the second electrochemical cell The same voltage in the limiting current region of oxygen is applied to 12c, and the correction coefficient Ks is obtained based on the first detection value and the second detection value obtained at that time.

When the second detection device determines that the oxygen concentration of the test gas is substantially constant, the voltage in the limiting current region of oxygen with respect to the first electrochemical cell 11c and the second electrochemical cell 12c. The correction coefficient Ks is calculated using the first detection value of the first electrochemical cell 11c and the second detection value of the second electrochemical cell 12c when. Hereinafter, the first detection value of the first electrochemical cell 11c at this time will be referred to as “Ks calculation sensor cell value Isks”, and the second detection value of the second electrochemical cell 12c will be referred to as “Ks calculation monitor cell value Imks”. Sometimes called. And the 2nd detection apparatus calculates | requires the correction coefficient Ks using the following (3) Formula which is the same as said (2) Formula.

Imks · Km = Isks · Ks (3)

  As described above, the correction coefficient Km is a coefficient obtained by using the detected value of the second electrochemical cell 12c when 0.4V, which is a voltage smaller than the water decomposition start voltage, is applied to the second electrochemical cell 12c. It is. Further, the correction coefficient Ks is also applied to the first electrochemical cell 11c and the second electrochemical cell when 0.4V, which is a voltage smaller than the water decomposition start voltage, is applied to the first electrochemical cell 11c and the second electrochemical cell 12c. This is a coefficient obtained using the detected value of the cell 12c. Therefore, it can be said that the correction coefficient Ks obtained using the correction coefficient Km accurately represents the correlation between the detection values of the first electrochemical cell 11c and the second electrochemical cell 12c.

(Actual operation)
Next, the “routine for obtaining the correction coefficient Ks” executed by the ECU 81 (actually the CPU) of the second detection apparatus will be specifically described with reference to the flowchart of FIG. Note that the second detection device calculates the correction coefficient Km and detects the SOx concentration in the same manner as the first detection device. That is, the second detection apparatus executes the routines shown in FIGS.

  When the internal combustion engine starts operation by operating the ignition key switch, the ECU 81 of the second detection device repeatedly executes the routine shown in the flowchart of FIG. 10 every time a predetermined time elapses. . The steps already described in this routine are denoted by the same reference numerals as the steps already described.

If the ECU 81 determines “Yes” in Step 610 following Step 1000, “No” in Step 620, “Yes” in Step 630, and “Yes” in Step 730, the ECU 81 proceeds to Step 1010. That is, the ECU 81 proceeds to step 1010 when all of the following conditions are satisfied.
(1) The correction coefficient km is newly calculated after the current engine start (step 610).
(2) The correction coefficient ks is not newly calculated after the current engine start (step 620).
(3) Warm-up of the internal combustion engine has been completed, and each electrochemical cell has been activated (step 630).
(4) Conditions during execution of fuel injection are satisfied, and the temperatures of the first electrochemical cell 11c, the second electrochemical cell 12c, and the third electrochemical cell 13c are within the predetermined appropriate temperature range described above. (Step 730).

  In step 1010, the ECU 81 determines whether or not the oxygen concentration of the test gas flowing into the first internal space 31 is “substantially constant” based on the detection value of the third electrochemical cell 13c (air-fuel ratio sensor). Judgment. More specifically, the ECU 81 determines that the magnitude of the difference between the maximum value and the minimum value of the oxygen concentration obtained based on the electrode current of the third electrochemical cell 13c for a predetermined time is equal to or less than a predetermined change amount threshold value. In this case, it is determined that the oxygen concentration of the test gas is “substantially constant”.

  If the ECU 81 determines “Yes” in step 1010, the ECU 81 proceeds to step 1020, and the voltage in the limiting current region of oxygen (for example, with respect to the first electrochemical cell (sensor cell) 11 c and the second electrochemical cell (monitor cell) 12 c (for example, 0.4V) is applied.

  Next, the ECU 81 proceeds to step 1030 to acquire the detection value (first detection value) of the first electrochemical cell 11c as the sensor cell value Isks for Ks calculation and the detection value (second detection value) of the second electrochemical cell 12c. Is obtained as the monitor cell value Imks for Ks calculation. Further, in step 1030, the ECU 81 applies the correction coefficient Km, the sensor cell value Isks for Ks calculation, and the monitor cell value Imks for Ks calculation stored in the backup RAM to the above equation (3), thereby obtaining the correction coefficient Ks. calculate. Then, the ECU 81 stores the acquired correction coefficient Ks in the backup RAM. Thereafter, the ECU 81 proceeds to step 1095 to end the present routine tentatively.

  When the correction coefficient Ks is already stored in the backup RAM, the correction coefficient Ks is overwritten on the correction coefficient Ks acquired this time. At this time, an average value of the correction coefficient Ks already stored in the backup RAM and the correction coefficient Ks acquired this time may be stored in the backup RAM as a new correction coefficient Ks. In addition, the “sensor cell value for Ks calculation and monitor cell value for Ks calculation” used when calculating the correction coefficient Ks in this step is the “Ks calculation for Ks calculation” acquired several times after the engine start. The average value of the “sensor cell value and Ks calculation monitor cell value” may be used.

  On the other hand, if the ECU 81 determines “No” in any of Step 610, Step 630, Step 730, and Step 1010, and determines “Yes” in Step 620, the ECU 81 performs the steps from the respective steps. Proceed directly to 1095 to end the present routine tentatively.

  In this way, the second detection device can acquire the correction coefficient Ks when the F / C operation is not being performed (while fuel injection is being performed). Therefore, even when the F / C operation at the time of acquiring the correction coefficient Km is completed in a very short time, the correction coefficient Ks can be acquired in a relatively short time. It can be detected with high accuracy.

Furthermore, as with the first detection device, the second detection device uses the correction coefficients Km and Ks, and therefore, compared with the case where the SOx concentration is detected without using the correction coefficients Km and Ks, It becomes possible to obtain the SOx concentration with higher accuracy.
In addition, although the 2nd detection apparatus is making the 3rd electrochemical cell 13c exhibit the oxygen pumping function during 2nd voltage application control, you may make it not exhibit the same function.

  As mentioned above, although this invention was demonstrated based on said each embodiment, this invention is not limited to said each embodiment, A various change is possible unless it deviates from the objective of this invention.

  For example, the first detection device may apply a voltage in the limiting current region of oxygen to the first electrochemical cell 11c and the second electrochemical cell 12c when obtaining the correction coefficient Ks (during the first voltage application control). Good. That is, the first detection device may obtain the correction coefficient Ks by applying a voltage equal to or higher than the lower limit voltage of the oxygen limit current region.

  The voltage (applied voltage Vm) applied to the first electrochemical cell 11c and the second electrochemical cell 12c for decomposing water and SOx is higher than the decomposition start voltage of water and less than the limit current region of water. If there is, it is not necessary to be 1.0V.

That is, when the applied voltage Vm becomes excessively high, decomposition of other components (for example, carbon dioxide (CO ₂ ), etc.) contained in the test gas is started, or the solid electrolyte body 11s and the solid electrolyte body There is a possibility of causing 12s decomposition. Therefore, it is desirable that the applied voltage Vm for decomposing water and SOx is a predetermined voltage lower than the lower limit voltage in the limit current region of water.

  The magnitude of the electrode current flowing between the first electrode 11a and the second electrode 11b when a voltage is applied between the first electrode 11a and the second electrode 11b was taken as the first detection value. Similarly, when the voltage is applied between the third electrode 12a and the fourth electrode 12b, the magnitude of the electrode current flowing between the third electrode 12a and the fourth electrode 12b is set as the second detection value. . However, as described above, the first detection value and the second detection value are not particularly limited as long as they are values of some signal corresponding to the electrode current (for example, a voltage value, a current value, a resistance value, etc.).

  In addition, the first electrode 11a is a porous cermet electrode containing an alloy of platinum (Pt) and rhodium (Rh) as a main component, and the second electrode 11b is a porous electrode containing platinum (Pt) as a main component. It is a cermet electrode. However, the material constituting the first electrode 11a is a test sample that is guided to the first internal space 31 through the diffusion resistance portion 32 when a voltage is applied between the first electrode 11a and the second electrode 11b. It is not particularly limited as long as water and SOx contained in the gas can be reduced and decomposed. Preferably, the material constituting the first electrode 11a contains a platinum group element such as platinum (Pt), rhodium (Rh), palladium (Pd) or an alloy thereof as a main component. More preferably, the first electrode 11a is a porous cermet electrode containing as a main component at least one selected from the group consisting of platinum (Pt), rhodium (Rh), and palladium (Pd).

In the first and second embodiments, the first electrochemical cell 11c and the second electrochemical cell 12c share the solid electrolyte body 11s. However, the first electrochemical cell 11c and the second electrochemical cell 12c may be formed on separate solid electrolyte bodies. That is, the first electrode 11a and the second electrode 11b of the first electrochemical cell 11c are disposed on one of the solid electrolyte 11s and the solid electrolyte body 12s that define the first internal space 31, and the second electrochemical cell 12c. The third electrode 12 a and the fourth electrode 12 b may be disposed on either one of the solid electrolyte 11 s and the solid electrolyte body 12 s that define the first internal space 31.
Further, the third electrochemical cell 13c may share the solid electrolyte body 11s with the first electrochemical cell 11c and / or the second electrochemical cell 12c.
Furthermore, if the first separate space where the second electrode 11b is located and the first separate space where the fourth electrode 12b is located are different from the first internal space 31, they are different from each other even if they are the same space. It may be a space.

  Oxygen is supplied to the first internal space 31 by the oxygen pumping action of the third electrochemical cell 13c to maintain the oxygen concentration in the first internal space 31 at a specific constant concentration (however, a concentration higher than 0 percent). The correction coefficient Km may be calculated in the state.

  Further, the second electrochemical cell 12c is disposed in the vicinity of the first electrochemical cell 11c. However, as long as the concentration of SOx contained in the sample gas can be detected based on the difference between the first detection value and the second detection value acquired from these cells, the positional relationship between these cells is particularly It is not limited.

In the first and second detection devices, the first detection value for SOx detection and the second detection value for SOx detection are detected using the first electrochemical cell 11c and the second electrochemical cell 12c. The same voltage (1.0 V) is applied to the first electrochemical cell 11c and the second electrochemical cell 12c.
However, the voltages applied to the first electrochemical cell 11c and the second electrochemical cell 12c at this time may be different from each other as long as the voltages are equal to or higher than the water decomposition start voltage. In this case, the data of the lookup table shown in FIG. 8 is acquired in advance according to the voltage applied to each cell.

  Furthermore, in the first and second detection devices, the third electrode 12a is a porous cermet electrode containing an alloy of platinum (Pt) and gold (Au) as a main component, and the fourth electrode 12b is platinum. It is a porous cermet electrode containing (Pt) as a main component. However, the material constituting the third electrode 12a is the first internal space via the diffusion resistance portion 32 when a voltage equal to or higher than the water decomposition start voltage is applied between the third electrode 12a and the fourth electrode 12b. There is no particular limitation as long as water contained in the test gas led to 31 can be reduced and decomposed and SOx cannot be substantially decomposed. Preferably, the material constituting the third electrode 12a includes a metal element such as platinum (Pt), gold (Au), lead (Pb), silver (Ag), or an alloy thereof as a main component. More preferably, the third electrode 12a is a porous cermet electrode containing as a main component at least one selected from the group consisting of platinum (Pt), gold (Au), lead (Pb), and silver (Ag).

  The speed at which SOx is decomposed in the third electrode 12a (second decomposition speed) is substantially 0 (zero). However, the second decomposition rate may not be 0 as long as it is lower than the first decomposition rate.

  Furthermore, although the first and second detection devices detect the SOx concentration using the SOx concentration detection parameter P and the corrected second detection value Imc, the SOx concentration is detected using only the SOx concentration detection parameter P. It may be detected. In this case, the first and second detection devices detect the SOx concentration and the SOx concentration when the detected value of the reference electrochemical cell is a specific value (for example, 4 mA or a value within a minute current range including 4 mA). The relationship with the parameter P is stored in the ROM in the form of a one-dimensional map (lookup table). The first and second detection devices determine whether the corrected second detection value Imc is the specific value after the stage where the correction coefficients Km and Ks are acquired, and the corrected second detection value Im. The SOx concentration may be detected by applying the SOx concentration detection parameter P actually obtained when is the specific value to the one-dimensional map. Furthermore, the detection device is further provided with a water concentration sensor that detects the concentration of water contained in the exhaust gas, and the SOx concentration detection parameter is only provided when the water concentration detected by the water concentration sensor is within a predetermined range. The SOx concentration may be detected by applying P to “a one-dimensional map that defines the relationship between the detection parameter P and the SOx concentration when the water concentration is within a predetermined range”.

  DESCRIPTION OF SYMBOLS 10 ... Element part, 11a, 12a and 13a ... Electrode, 11b, 12b and 13b ... Electrode, 11s and 12s ... Solid electrolyte body, 11c, 12c and 13c ... Pumping cell (1st thru | or 3rd electrochemical cell), 21a, 21b, 21c, 21d, 21e and 21f ... 1st to 6th alumina layers, 31 ... internal space, 32 ... diffusion resistance part, 41 ... heater, 51 and 52 ... 1st and 2nd atmosphere introduction path, 61, 62 and 63 ... Power supply, 71, 72 and 73 ... Ammeter, 81 ... ECU.

Claims (6)

A first electrochemical cell including a first solid electrolyte body having oxide ion conductivity and a first electrode and a second electrode respectively formed on a surface of the first solid electrolyte body; and having oxide ion conductivity A second electrochemical cell including a third electrode and a fourth electrode respectively formed on a surface of the second solid electrolyte body; a dense body; and a diffusion resistance portion; and the first solid electrolyte body and the first electrode The exhaust gas of the internal combustion engine is introduced as a test gas into the first internal space defined by the two solid electrolyte body, the dense body, and the diffusion resistance portion via the diffusion resistance portion, and the first electrode and the third electrode An element portion configured such that an electrode is exposed to the first internal space and the second electrode and the fourth electrode are exposed to a first separate space different from the first internal space;
A voltage applying unit that applies a voltage between the first electrode and the second electrode and between the third electrode and the fourth electrode;
A first detection value corresponding to a current value flowing between the first electrode and the second electrode when a voltage is applied between the first electrode and the second electrode; An acquisition unit for acquiring a second detection value corresponding to a current value flowing between the third electrode and the fourth electrode when a voltage is applied between the four electrodes;
In a gas concentration detection device having
The first electrode decomposes water (H ₂ O) contained in the test gas when a voltage equal to or higher than a water decomposition start voltage is applied between the first electrode and the second electrode. Configured to be possible,
When the third electrode is applied with a voltage equal to or higher than the decomposition start voltage of water between the third electrode and the fourth electrode using the voltage application unit, water (H ₂ O) can be decomposed,
The first electrode and the third electrode are applied with the same voltage equal to or higher than the water decomposition start voltage between the first electrode and the second electrode and between the third electrode and the fourth electrode. , The sulfur oxide decomposition rate by the third electrode is configured to be lower than the sulfur oxide decomposition rate by the first electrode,
The acquisition unit
When it is determined that the oxygen concentration of the test gas in the first internal space is a specific constant concentration, a voltage in a limiting current region of oxygen is applied between the third electrode and the fourth electrode, A ratio of a predetermined reference output value determined in advance to the detected monitor cell value that is the second detected value at that time is obtained as a monitor cell correction value (Km),
When the operation state of the internal combustion engine is a fuel cut operation state, a voltage equal to or higher than the lower limit voltage of the limit current region of oxygen is applied between the first electrode and the second electrode and between the third electrode and the fourth electrode. A first voltage application control applied using the voltage application unit between the first electrode and the second electrode when the operating state of the internal combustion engine is not a fuel cut operating state. Performing at least one of second voltage application control applied between the electrodes and between the third electrode and the fourth electrode using the voltage application unit, and the first voltage application control and A sensor cell correction value (Ks) is a ratio of the product of the second detection value and the monitor cell correction value to the first detection value when at least one of the second voltage application controls is executed. Seeking
When the operation state of the internal combustion engine is not a fuel cut operation state, a voltage equal to or higher than a water decomposition start voltage is applied between the first electrode and the second electrode and between the third electrode and the fourth electrode. Applying using the voltage application unit, and obtaining the first detection value and the second detection value at that time as a first detection value for SOx detection and a second detection value for SOx detection, respectively,
Based on a value corresponding to a difference between a product of the second detection value for SOx detection and the monitor cell correction value and a product of the first detection value for SOx detection and the sensor cell correction value, Configured to determine the concentration of sulfur oxides,
Gas concentration detector. The gas concentration detection apparatus according to claim 1,
The first solid electrolyte body and the second solid electrolyte body are the same common solid electrolyte body,
The element portion includes a third electrochemical cell including 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 first internal space is defined by the common solid electrolyte body, the dense body, the diffusion resistance portion, and the third solid electrolyte,
The fifth electrode is exposed to the first internal space, and the sixth electrode is exposed to a second separate space different from the first internal space,
The voltage application unit is configured to apply a voltage between the fifth electrode and the sixth electrode,
The fifth electrode and the sixth electrode discharge oxygen (O ₂ ) from the first internal space when a voltage in a limiting current region of oxygen is applied between the fifth electrode and the sixth electrode. Constructed to demonstrate oxygen pumping function,
The acquisition unit
When the operation state of the internal combustion engine is a fuel cut operation state, it is determined that the oxygen concentration of the test gas in the first internal space is the specific constant concentration,
When obtaining the monitor cell correction value, the application of the voltage using the voltage application unit between the fifth electrode and the sixth electrode is stopped to stop the oxygen pumping function,
When the first detection value for SOx detection and the second detection value for SOx detection are acquired, the voltage application unit is used between the fifth electrode and the sixth electrode to set the voltage in the limiting current region of oxygen. Configured to exert the oxygen pumping function by applying
Gas concentration detector. The gas concentration detection apparatus according to claim 2,
The acquisition unit
A voltage using the voltage application unit between the fifth electrode and the sixth electrode during execution of the first voltage application control while obtaining the sensor cell correction value by executing the first voltage application control Is configured to stop the oxygen pumping function by stopping the application of
Gas concentration detector. The gas concentration detection apparatus according to claim 1,
The acquisition unit
The sensor cell is configured to execute the second voltage application control when the difference between the maximum value and the minimum value of the oxygen concentration of the test gas in the first internal space in a predetermined time is equal to or less than a predetermined change amount threshold value. Configured to determine the correction value,
Gas concentration detector. In the gas concentration detection apparatus according to any one of claims 1 to 4,
The acquisition unit
The difference between the product of the second detection value for SOx detection and the monitor cell correction value, the product of the first detection value for SOx detection and the sensor cell correction value, and the second detection value for SOx detection and the monitor cell Based on the product of the correction value and a look-up table with the argument as an argument, the sulfur oxide concentration of the test gas is determined.
Gas concentration detector. In the gas concentration detection apparatus according to any one of claims 1 to 5,
The first electrode and the third electrode include platinum (Pt),
The first electrode includes at least one of rhodium (Rh) and palladium (Pd) more than the third electrode;
Gas concentration detector.

Images