JP2017072565A - Sulfur component detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sulfur component detection method for properly detecting a content of a sulfur component contained in fuel even when an air-fuel ratio of exhaust gas changes during detection of the sulfur component.SOLUTION: A sulfur component detection device 1 comprises: a first electrochemical cell 51 that includes a solid electrolyte layer 11 having an oxide ion conductibility, a first electrode 41, and second electrode 42; a diffusion-rate controlling layer 16; and a measurement object gas chamber 30. The first electrode is arranged in the measurement object gas chamber, and the second electrode is arranged so as to be exposed to an atmosphere. In detection of a content of a sulfur component in a fuel, a voltage equal to or larger than a decomposition start voltage of the SOx is applied to the first electrochemical cell over a time equal to or longer than a prescribed time, and then, a voltage equal to or larger than a decomposition start voltage of water is applied thereto, and an inter-electrode current is acquired to detect a sulfur component on the basis of the inter-electrode current. In detection of the sulfur component in the fuel, when the acquired inter-electrode current is a value within a first area, it is judged that the content of the sulfur component is low in comparison with a case in which the acquired inter-electrode current is a value within a second area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sulfur component detection method for detecting the content of a sulfur component contained in fuel.

  A trace amount of sulfur (S) component is contained in the fuel used for the internal combustion engine, particularly in the fossil fuel. Thus, the sulfur component contained in the fuel causes deterioration of components in the exhaust system of the internal combustion engine. Further, frequent control of suppressing deterioration of the component due to the sulfur component and control of regenerating the deteriorated component cause deterioration of fuel consumption. Therefore, it is desired to accurately detect the content of the sulfur component in the fuel in order to minimize deterioration of the component parts while minimizing deterioration of fuel consumption and the like.

  When the sulfur component is contained in the fuel used for the internal combustion engine, sulfur oxide (SOx) is contained in the exhaust gas discharged from the combustion chamber. Further, the higher the content ratio of the sulfur component in the fuel, the higher the concentration of SOx contained in the exhaust gas. Therefore, if the SOx concentration contained in the exhaust gas can be accurately detected, the content of the sulfur component in the fuel can be accurately detected.

  Thus, an exhaust gas sensor that detects the concentration of an oxygen-containing gas component such as SOx contained in the exhaust gas has been proposed (see, for example, Patent Document 1). This exhaust gas sensor has a measured gas chamber into which exhaust gas is introduced through a diffusion-controlled layer, a first electrochemical cell, and a second electrochemical cell. In the first electrochemical cell, a relatively low voltage is applied between the electrodes constituting the first electrochemical cell, and as a result, the SOx in the measured gas chamber is decomposed by the oxygen pumping action of the first electrochemical cell. And oxygen in the measured gas chamber is removed. On the other hand, in the second electrochemical cell, a relatively high voltage is applied between the electrodes constituting the second electrochemical cell, whereby SOx contained in the exhaust gas after oxygen is removed by the first electrochemical cell. Is disassembled. In addition, the oxide ions generated by the decomposition of the SOx are discharged from the measured gas chamber by the oxygen pumping action of the second electrochemical cell, and the decomposition current flowing along with the discharge of the oxide ions is detected to detect the SOx. Concentration is detected.

JP-A-11-190721

  By the way, the concentration of SOx contained in the exhaust gas is extremely low, so that the decomposition current detected by the exhaust gas sensor as described above is also extremely small. For this reason, it is difficult to accurately detect the SOx decomposition current using the exhaust gas sensor as described above. In addition, the exhaust gas contains water, and a decomposition current is generated by the decomposition of the water. Of the decomposition currents generated by the decomposition of water and SOx, it is difficult to detect only the decomposition current generated by the decomposition of SOx, and this also makes it difficult to accurately detect the decomposition current of SOx.

  On the other hand, the inventor of the present application applies a voltage that can cause decomposition of water and SOx in an electrochemical cell having an oxygen pumping action to include decomposition current in the exhaust gas when water and SOx are decomposed. It has been found that the concentration varies depending on the SOx concentration. The specific principle that causes such a phenomenon is not necessarily clear, but is considered to be caused by the following mechanism.

  That is, when a decomposition voltage is applied between the electrodes of the electrochemical cell, water and SOx contained in the gas to be measured are decomposed on the electrodes. Thus, decomposition products (for example, sulfur and sulfur compounds) generated by the decomposition of SOx are adsorbed on the electrode, and as a result, the surface area on the electrode that can contribute to the decomposition of water is reduced. When the concentration of SOx contained in the measured gas is high, the decomposition products adsorbed on the electrodes increase, and as a result, the water flowing between the electrodes is decomposed when a decomposition voltage is applied between the electrodes of the electrochemical cell. The current becomes smaller. Conversely, when the concentration of SOx contained in the measured gas is low, the decomposition products adsorbed on the electrodes are reduced, and as a result, when a decomposition voltage is applied between the electrodes of the electrochemical cell, they flow between the electrodes. Water decomposition current increases. Thus, the magnitude of the decomposition current of the water flowing between the electrodes changes according to the concentration of SOx contained in the measured gas.

  Therefore, if the phenomenon as described above is used, the concentration of SOx contained in the exhaust gas can be detected based on the decomposition current of water when a decomposition voltage is applied to the electrochemical cell. In addition, the content of the sulfur component contained in the fuel can be detected based on the concentration of SOx contained in the exhaust gas.

  By the way, even if the content rate of the sulfur component in the fuel is constant, the SOx concentration in the exhaust gas is not necessarily constant, and changes depending on, for example, the change in the air-fuel ratio of the exhaust gas. For this reason, it is detected that the air-fuel ratio of the exhaust gas changes while applying the SOx decomposition voltage between the electrodes of the electrochemical cell, that is, while the SOx decomposition products are adsorbed on the electrodes. Based on the SOx concentration, the content of the sulfur component in the fuel cannot be accurately detected. Therefore, in order to accurately detect the sulfur component content in the fuel, the air-fuel ratio of the exhaust gas is kept constant throughout the period in which the SOx decomposition voltage is applied to detect the SOx concentration. It is desirable to do. However, during actual operation of the internal combustion engine, it may be difficult to keep the air-fuel ratio of the exhaust gas constant over a certain period.

  Accordingly, in view of the above problems, an object of the present invention is to detect a sulfur component contained in fuel appropriately even if the air-fuel ratio of the exhaust gas changes during the detection of the sulfur component. It is to provide a detection method.

  The present invention has been made to solve the above problems, and the gist thereof is as follows.

  (1) A solid electrolyte layer having oxide ion conductivity, a first electrode disposed on one side surface of the solid electrolyte layer, and a second electrode disposed on the other side surface of the solid electrolyte layer, A first electrochemical cell comprising: a diffusion rate-limiting layer that performs diffusion rate-limiting of the gas to be measured passing therethrough; and a gas chamber to be measured that is partitioned into the solid electrolyte layer and the diffusion rate-limiting layer, Sulfur component for detecting the content of sulfur component contained in the fuel by a sulfur component detector arranged so that one electrode is arranged in the measured gas chamber and the second electrode is exposed to the atmosphere In the detection method, a first voltage equal to or higher than a sulfur oxide decomposition start voltage is applied between the first electrode and the second electrode until the value of the integration parameter reaches a predetermined value or more. Following the step and applying the first voltage, A step of applying a second voltage equal to or higher than a water decomposition start voltage between the first electrode and the second electrode, and obtaining a value of a current correlation parameter correlated with an interelectrode current flowing between the electrodes; And a step of detecting the content rate of the sulfur component in the fuel based on the value of the acquired current correlation parameter, wherein the integration parameter increases the value of the sulfur oxide in the exhaust gas as the integration parameter value increases. In the step of detecting the sulfur component in the fuel, when the acquired current correlation parameter value is a value in the first region, the acquired parameter value is a parameter that increases the integrated flow rate. The sulfur component detection method of determining that the content rate of the sulfur component in a fuel is low compared with when it is a value in the 2nd area | region which is all areas | domains other than said 1st area | region.

  (2) In the step of acquiring the value of the current correlation parameter, when the amount of change per unit time of the value of the current correlation parameter is less than or equal to the predetermined change amount, or less than the predetermined change amount The sulfur component detection method according to (1) above, wherein the value of the current correlation parameter is acquired.

  (3) When the time until the current correlation parameter value is acquired after the step of applying the first voltage is relatively long, the first region is narrower than when the time is relatively short. The sulfur component detection method according to (2), wherein the second region is widened.

  (4) The sulfur component detection method according to any one of (1) to (3), wherein the magnitude of the first voltage is equal to the magnitude of the second voltage.

  (5) The current correlation parameter is a current flowing between the first electrode and the second electrode, the first region is a region equal to or greater than a predetermined reference current, and the second region is the The sulfur component detection method according to any one of the above (1) to (4), which is a region less than a predetermined reference current.

  (6) The sulfur component detection device includes a solid electrolyte layer having oxide ion conductivity, a third electrode disposed on one side surface of the solid electrolyte layer, and on the other side surface of the solid electrolyte layer. A second electrochemical cell having a fourth electrode disposed, wherein the third electrode is disposed in the measured gas chamber and the fourth electrode is disposed to be exposed to the atmosphere. One electrode and the third electrode are the first electrode when the first voltage is applied between the first electrode and the second electrode and between the third electrode and the fourth electrode. The sulfur oxide decomposition rate at the third electrode is configured to be faster than the sulfur oxide decomposition rate at the third electrode, and the current correlation parameter is between the electrodes flowing between the first electrode and the second electrode. Current flows between the third electrode and the fourth electrode The difference between the current between the electrodes, the first region is a region below a predetermined reference value, and the second region is a region larger than the predetermined reference value. The sulfur component detection method according to any one of (4).

  ADVANTAGE OF THE INVENTION According to this invention, even if the air fuel ratio of exhaust gas changes during the detection of a sulfur component, the sulfur component detection method which can detect appropriately the content rate of the sulfur component contained in a fuel is provided.

FIG. 1 is a schematic cross-sectional view showing the configuration of the sulfur component detection device according to the first embodiment. FIG. 2 is a diagram showing the relationship between the applied voltage between the electrodes of the first electrochemical cell and the interelectrode current flowing between these electrodes. FIG. 3 is a diagram showing the relationship between the magnitude of the interelectrode current when the applied voltage is 1.0 V and the concentration of sulfur dioxide contained in the measured gas. FIG. 4 is a diagram showing the time transition of the interelectrode current when an applied voltage of 1.1 V is continuously applied to the first electrochemical cell. FIG. 5 is a flowchart illustrating an example of a sulfur component detection process executed by the ECU. FIG. 6 is a schematic cross-sectional view showing the configuration of the sulfur component detection device according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to similar components.

<First embodiment>
First, with reference to FIG. 1, the detection method of the sulfur component using the sulfur component detection apparatus 1 which concerns on 1st embodiment of this invention is demonstrated. The sulfur component detection device 1 of the present embodiment is disposed in an exhaust pipe (not shown) of an internal combustion engine, and detects the content of sulfur components in the fuel (hereinafter also simply referred to as “sulfur component detection”). Do.

<Configuration of sulfur component detection device>
As shown in FIG. 1, the sulfur component detection apparatus 1 according to the first embodiment includes an element unit 10 having two electrochemical cells, a first circuit 60 connected to one electrochemical cell, and the other A third circuit 70 connected to the electrochemical cell and an electronic control unit (ECU) 80 are provided.

  As shown in FIG. 1, the element unit 10 is configured by laminating a plurality of layers. Specifically, the first solid electrolyte layer 11, the second solid electrolyte layer 12, the diffusion rate limiting layer 16, The first opaque layer 21, the second opaque layer 22, the third opaque layer 23, the fourth opaque layer 24, the fifth opaque layer 25, and the sixth opaque layer 26 are provided.

The solid electrolyte layers 11 and 12 are thin plate bodies having oxide ion conductivity. The solid electrolyte layers 11 and 12 are sintered, for example, by using ZrO ₂ (zirconia), HfO ₂ , ThO ₂ , Bi ₂ O ₃ or the like as a stabilizer with CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ or the like as a stabilizer. It is formed by the body. The diffusion-controlling layer 16 is a thin plate having gas permeability. The diffusion control layer 16 is formed of a porous sintered body of a heat resistant inorganic material such as alumina, magnesia, silica, spinel, mullite, and the like. The impermeable layers 21 to 26 are gas impermeable thin plates, and are formed, for example, as layers containing alumina.

  Each layer of the element part 10 is, from the lower side of FIG. The layer 24, the second solid electrolyte layer 12, the fifth impermeable layer 25, and the sixth impermeable layer 26 are laminated in this order.

  A gas chamber 30 to be measured is defined by the first solid electrolyte layer 11, the second solid electrolyte layer 12, the diffusion rate limiting layer 16, and the fourth impermeable layer 24. In the measured gas chamber 30, the exhaust gas of the internal combustion engine (measured gas) flows into the measured gas chamber 30 via the diffusion-controlled layer 16 when the sulfur component detection device 1 is disposed in the exhaust pipe. It is configured. That is, the sulfur component detection device 1 is disposed in the exhaust pipe so that the diffusion rate controlling layer 16 is exposed to the exhaust gas. As a result, the measured gas chamber 30 communicates with the inside of the exhaust passage through the diffusion rate controlling layer 16. doing. The measured gas chamber 30 may be configured in any manner as long as it is partitioned by the first solid electrolyte layer 11, the second solid electrolyte layer 12, and the diffusion-controlling layer 16.

  The first atmospheric chamber 31 is partitioned by the first solid electrolyte layer 11, the second impermeable layer 22, and the third impermeable layer 23. As can be seen from FIG. 1, the first atmospheric chamber 31 is disposed on the opposite side of the measured gas chamber 30 with the first solid electrolyte layer 11 interposed therebetween. The first atmosphere chamber 31 is open to the atmosphere outside the exhaust pipe. Therefore, atmospheric gas flows into the first atmospheric chamber 31. The first atmospheric chamber 31 may be configured in any manner as long as it is partitioned by the first solid electrolyte layer 11.

  In addition, a second atmospheric chamber 32 is defined by the second solid electrolyte layer 12, the fifth impermeable layer 25, and the sixth impermeable layer 26. As can be seen from FIG. 1, the second atmospheric chamber 32 is disposed on the opposite side of the measured gas chamber 30 with the second solid electrolyte layer 12 interposed therebetween. The second atmospheric chamber 32 is open to the atmosphere outside the exhaust pipe. Therefore, the atmospheric gas also flows into the second atmospheric chamber 32. The second atmospheric chamber 32 may be configured in any manner as long as it is at least partially partitioned by the second solid electrolyte layer 12.

  In addition, the element unit 10 includes a first electrode 41, a second electrode 42, a fifth electrode 45, and a sixth electrode 46. The first electrode 41 is disposed on the surface of the first solid electrolyte layer 11 on the measured gas chamber 30 side. Therefore, the first electrode 41 is exposed to the gas in the measured gas chamber 30. On the other hand, the second electrode 42 is disposed on the surface of the first solid electrolyte layer 11 on the first atmospheric chamber 31 side. Therefore, the second electrode 42 is exposed to the gas (atmosphere) in the first atmospheric chamber 31. The first electrode 41 and the second electrode 42 are disposed so as to face each other with the first solid electrolyte layer 11 interposed therebetween. The first electrode 41, the first solid electrolyte layer 11, and the second electrode 42 constitute a first electrochemical cell 51.

  The fifth electrode 45 is disposed on the surface of the second solid electrolyte layer 12 on the measured gas chamber 30 side. Therefore, the fifth electrode 45 is exposed to the gas in the measured gas chamber 30. On the other hand, the sixth electrode 46 is disposed on the surface of the second solid electrolyte layer 12 on the second atmospheric chamber 32 side. Therefore, the sixth electrode 46 is exposed to the gas (atmosphere) in the second atmospheric chamber 32. The fifth electrode 45 and the sixth electrode 46 are arranged to face each other with the second solid electrolyte layer 12 interposed therebetween. The fifth electrode 45, the second solid electrolyte layer 12, and the sixth electrode 46 constitute a third electrochemical cell 53.

  The fifth electrode 45 is disposed closer to the diffusion rate controlling layer 16 than the first electrode 41 in the measured gas chamber 30. Therefore, the measured gas that has flowed into the measured gas chamber 30 via the diffusion-controlled layer 16 first flows around the fifth electrode 45 and then flows around the first electrode 41.

  In the present embodiment, the material constituting the first electrode 41 includes a platinum group element such as platinum (Pt), rhodium (Rh) and palladium (Pd), or an alloy thereof as a main component. Preferably, the first electrode 41 is a porous cermet electrode containing at least one of platinum (Pt), rhodium (Rh) and palladium (Pd) as a main component. However, the material constituting the first electrode 41 is not necessarily limited to the above material, and when a predetermined voltage is applied between the first electrode 41 and the second electrode 42, the measured gas chamber 30. Any material may be used as long as water and SOx contained in the gas to be measured can be reduced and decomposed.

  In the present embodiment, the second electrode 42 is a porous cermet electrode containing platinum (Pt) as a main component. However, the material constituting the second electrode 42 is not necessarily limited to the above material, and when a predetermined voltage is applied between the first electrode 41 and the second electrode 42, Any material may be used as long as the oxide ions can be moved between the second electrode 42.

  On the other hand, the fifth electrode 45 and the sixth electrode 46 are porous cermet electrodes containing platinum (Pt) as a main component. However, the material constituting the fifth electrode 45 is not necessarily limited to the above material, and when a predetermined voltage is applied between the fifth electrode 45 and the sixth electrode 46, the measured gas chamber 30. Any material may be used as long as oxygen contained in the gas to be measured can be reduced and decomposed. In addition, the material constituting the sixth electrode 46 is not necessarily limited to the above material, and when a predetermined voltage is applied between the fifth electrode 45 and the sixth electrode 46, the fifth electrode 45. Any material may be used as long as the oxide ions can be moved between the electrode 6 and the sixth electrode 46.

  In the above embodiment, the third electrochemical cell 53 includes the second solid electrolyte layer 12 that is different from the first solid electrolyte layer 11 that constitutes the first electrochemical cell 51. However, the first solid electrolyte layer and the second solid electrolyte layer may be the same solid electrolyte layer. That is, the first solid electrolyte layer 11 of FIG. 1 also functions as the second solid electrolyte layer, and thus the third electrochemical cell 53 may be configured to include the first solid electrolyte layer 11. In this case, the fifth electrode 45 is disposed on the surface of the first solid electrolyte layer 11 on the first atmospheric chamber 31 side, and the sixth electrode 46 is on the surface of the first solid electrolyte layer 11 on the measured gas chamber 30 side. Be placed.

  Further, the element unit 10 includes a heater (electric heater) 55. In the present embodiment, the heater 55 is disposed between the first impermeable layer 21 and the second impermeable layer 22 as shown in FIG. The heater 55 is a cermet thin plate including, for example, platinum (Pt) and ceramics (for example, alumina), and is a heating element that generates heat when energized. The heater 55 can heat the first electrochemical cell 51 and the third electrochemical cell 53 to an activation temperature or higher.

  As shown in FIG. 1, the first circuit 60 includes a first power supply 61 and a first ammeter 62. The first power supply 61 and the first ammeter 62 are connected to an electronic control unit (ECU) 80. The first power supply 61 applies a voltage between the first electrode 41 and the second electrode 42 such that the potential of the second electrode 42 is higher than the potential of the first electrode 41. The magnitude of the voltage applied by the first power supply 61 is controlled by the ECU 80.

  On the other hand, the first ammeter 62 detects the magnitude of the interelectrode current, which is the current flowing between the first electrode 41 and the second electrode 42 (that is, the current flowing in the first solid electrolyte layer 11). The detected value of the interelectrode current by the first ammeter 62 is input to the ECU 80.

  As shown in FIG. 1, the third circuit 70 includes a third power source 71 and a third ammeter 72. The third power source 71 and the third ammeter 72 are connected to the ECU 80. The third power source 71 applies a voltage between the fifth electrode 45 and the sixth electrode 46 such that the potential of the sixth electrode 46 is higher than the potential of the fifth electrode 45. The magnitude of the voltage applied by the third power supply 71 is controlled by the ECU 80.

  On the other hand, the third ammeter 72 detects the magnitude of the interelectrode current that is the current flowing between the fifth electrode 45 and the sixth electrode 46 (that is, the current flowing in the second solid electrolyte layer 12). The detected value of the interelectrode current by the third ammeter 72 is input to the ECU 80.

  The ECU 80 is a digital computer including a CPU that performs arithmetic processing, a ROM that stores programs executed by the CPU, a RAM that temporarily stores data, and the like. The ECU is connected to various actuators (fuel injection valve, throttle valve, etc.) of the internal combustion engine and controls the operation of these actuators.

  The ECU 80 can control the first applied voltage applied between the first electrode 41 and the second electrode 42 by the first power supply 61 by controlling the first power supply 61. In addition, the ECU 80 can control the second applied voltage applied between the fifth electrode 45 and the sixth electrode 46 by the third power source 71 by controlling the third power source 71. Therefore, the ECU 80, the first power supply 61, and the third power supply 71 apply inter-electrode voltages between the first electrode 41 and the second electrode 42 and between the fifth electrode 45 and the sixth electrode 46, and It functions as a voltage application device that can control the voltage between the electrodes.

  In addition, the ECU 80 receives a signal corresponding to the magnitude of the electrode current flowing between the first electrode 41 and the second electrode 42 detected by the first ammeter 62. Therefore, the ECU 80 and the first ammeter 62 function as a detection unit that detects an interelectrode current flowing between the first electrode 41 and the second electrode 42. In addition, a signal corresponding to the magnitude of the electrode current flowing between the fifth electrode 45 and the sixth electrode 46 detected by the third ammeter 72 is input. Therefore, the ECU 80 and the third ammeter 72 function as a detection unit that detects an interelectrode current flowing between the fifth electrode 45 and the sixth electrode 46.

<Basic sulfur component detection principle>
Next, the detection principle of SOx by the sulfur component detection apparatus according to this embodiment will be described.
In describing the SOx detection principle, first, the limiting current characteristic of oxygen in the element unit 10 configured as described above will be described. In the element unit 10 configured as described above, when a voltage is applied between the electrodes on the measured gas chamber 30 side as a cathode and the electrodes on the atmospheric gas chamber side as an anode, they are included in the measured gas. Oxygen is reduced and decomposed into oxide ions. The oxide ions are conducted to the anode side through the solid electrolyte layers 11 and 12 of the electrochemical cells 51 and 52, become oxygen, and are discharged into the atmosphere. Hereinafter, the movement of oxygen by conduction of oxide ions from the cathode side to the anode side through the solid electrolyte layer is referred to as “oxygen pumping action”.

  Due to the conduction of oxide ions accompanying such oxygen pumping action, an interelectrode current flows between the electrodes constituting the electrochemical cells 51 and 52. This interelectrode current increases as the applied voltage applied between the electrodes constituting each electrochemical cell 51, 52 increases. This is because the higher the applied voltage, the greater the amount of oxide ion conduction.

  However, when the applied voltage is gradually increased to a certain value or more, the interelectrode current is maintained at a certain value without increasing further. Such a characteristic is referred to as an oxygen limiting current characteristic, and a voltage region in which the oxygen limiting current characteristic occurs is referred to as an oxygen limiting current region. In such a limiting current characteristic of oxygen, the conduction velocity of oxide ions that can be conducted in the solid electrolyte layers 11 and 12 is introduced into the measured gas chamber 30 via the diffusion-controlling layer 16 in accordance with the voltage application. This is caused by exceeding the oxygen introduction rate. That is, it occurs when the oxygen reductive decomposition reaction at the cathode is in a diffusion-controlled state.

  Accordingly, the interelectrode current (limit current) when a voltage in the oxygen limit current region is applied in the electrochemical cells 51 and 52 corresponds to the concentration of oxygen contained in the measured gas. Thus, by utilizing the limiting current characteristic of oxygen, it is possible to detect the concentration of oxygen contained in the measured gas and to detect the air-fuel ratio of the exhaust gas based on it.

By the way, the oxygen pumping action as described above is not an action that appears only in oxygen contained in the gas to be measured. Among gases containing oxygen atoms in the molecule, there are gases that can exhibit an oxygen pumping action. Such gases include SOx and water (H ₂ O). Therefore, by applying a voltage equal to or higher than the decomposition start voltage of SOx and water between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51, the water and SOx contained in the measured gas are reduced. Disassembled. Oxide ions generated by the decomposition of SOx and water are conducted from the first electrode 41 to the second electrode 42 by the oxygen pumping action, and accordingly, an interelectrode current flows between these electrodes.

  However, the concentration of SOx contained in the exhaust gas is extremely low, and the interelectrode current generated due to the decomposition of SOx is also extremely small. In particular, the exhaust gas contains a large amount of water, and an interelectrode current is generated due to the decomposition of the water. For this reason, it is difficult to accurately detect and detect the interelectrode current caused by the decomposition of SOx.

  On the other hand, when a predetermined first voltage equal to or higher than the SOx decomposition start voltage is applied between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51, the gas is included in the measured gas as described above. SOx is decomposed. As a result, decomposition products of SOx (for example, sulfur and sulfur compounds) are adsorbed on the first electrode 41 that is the cathode. When the amount of adsorption of the decomposition product of SOx on the first electrode 41 increases, the surface of the first electrode 41 is covered by the decomposition product correspondingly, which may contribute to the decomposition of water. It is considered that the area of the first electrode 41 that can be reduced. For this reason, in a state where the area of the first electrode 41 that can contribute to the decomposition of water is reduced in this way, a predetermined first voltage higher than the water decomposition start voltage between the first electrode 41 and the second electrode 42 is obtained. When two voltages are applied, the interelectrode current flowing between the electrodes 41 and 42 decreases. That is, as the SOx concentration contained in the measured gas increases, the amount of decomposition products adsorbed on the surface of the first electrode 41 increases, and as a result, when a second voltage higher than the water decomposition start voltage is applied. Current between the electrodes decreases. Therefore, the concentration of SOx contained in the measured gas can be detected based on the interelectrode current when a second voltage equal to or higher than the water decomposition start voltage is applied.

  Here, the decomposition start voltage of water and the decomposition start voltage of SOx vary depending on the measurement conditions and the like, and the relationship between the measurement conditions and the decomposition start voltage has not necessarily been elucidated. However, the water decomposition starting voltage is about 0.6 V to about 0.8 V, although fluctuations are observed depending on the measurement conditions and the like. In addition, the decomposition start voltage of SOx is about the same as or slightly lower than the decomposition start voltage of water. Therefore, the second voltage that is equal to or higher than the water decomposition start voltage is a voltage of 0.6 V to 0.8 V or higher. Similarly, the first voltage that is equal to or higher than the SOx decomposition start voltage is also 0.6 to 0.8 V or higher. The first voltage may be a voltage equal to or higher than the water decomposition start voltage. Further, the first voltage and the second voltage may be the same voltage.

  On the other hand, when the applied voltage between the first electrode 41 and the second electrode 42 is increased from 0.6 V, the water decomposition rate on the first electrode 41 increases accordingly. For this reason, the inter-electrode current flowing between the first electrode 41 and the second electrode 42 increases as the applied voltage increases. However, when the applied voltage between the first electrode 41 and the second electrode 42 is equal to or higher than the lower limit voltage of the limit current region of water, the decomposition rate of water that can be decomposed at the first electrode 41 is determined by the diffusion rate limiting layer. The rate of introduction of water introduced into the measured gas chamber 30 via 16 is exceeded. That is, the limiting current characteristic of water comes to manifest. In such a case, the interelectrode current flowing between the first electrode 41 and the second electrode 42 changes according to the concentration of water, and the SOx concentration contained in the measured gas is changed based on the interelectrode current. It becomes difficult to detect with high accuracy. In addition, when the applied voltage is excessively high, the first solid electrolyte layer 11 may be decomposed. In this case as well, the concentration of SOx contained in the gas to be measured is accurately determined based on the interelectrode current. It becomes difficult to detect.

  Therefore, in this embodiment, even when a voltage equal to or higher than the above-described water decomposition start voltage or SOx decomposition start voltage is applied to the first electrochemical cell 51, the voltage is the lower limit voltage in the limit current region of water. The voltage is less than. The lower limit voltage in the limit current region of water is about 2.0 V, although some variation is observed depending on the measurement conditions and the like. Therefore, in the present embodiment, the first voltage and the second voltage described above are both less than 2.0V.

The relationship between the applied voltage and the interelectrode current will be specifically described. FIG. 2 is a schematic graph showing the relationship between the applied voltage and the interelectrode current when the applied voltage is gradually increased (step-up sweep) in the first electrochemical cell 51. In the illustrated example, four types of measured gases (0 ppm, 100 ppm, 300 ppm, and 500 ppm) having different concentrations of SO ₂ (ie, SOx) contained in the measured gas were used. In addition, the concentration of oxygen contained in the gas to be measured that reaches the first electrode (cathode) 41 of the first electrochemical cell 51 is the third electrochemical cell arranged on the upstream side of the first electrochemical cell 51. 53, it is maintained constant (almost 0 ppm) in any measured gas.

First, the solid line L1 shows the relationship between the applied voltage and the interelectrode current when the concentration of SO ₂ contained in the measured gas is 0 ppm. As can be seen from FIG. 2, the interelectrode current is almost zero in the region where the applied voltage is less than about 0.6V. This is because the oxygen contained in the measured gas in the measured gas chamber 30 is removed by the third electrochemical cell 53 as will be described later. On the other hand, when the applied voltage is about 0.6 V or more, the interelectrode current starts to increase as the applied voltage increases. This increase in inter-electrode current results from the start of water decomposition at the first electrode 41.

Next, the broken line L2 shows the relationship between the applied voltage and the interelectrode current when the concentration of SO ₂ contained in the measured gas is 100 ppm. Even in this case, in the region where the applied voltage is less than about 0.6 V, the inter-electrode current is almost zero as in the case of the solid line L1. On the other hand, when the applied voltage is about 0.6 V or more, an interelectrode current flows due to water decomposition. However, the interelectrode current at this time (broken line L2) is smaller than that of the solid line L1, and the rate of increase of the interelectrode current with respect to the applied voltage (slope in FIG. 2) is also smaller than that of the solid line L1.

Furthermore, the alternate long and short dash line L3 and the alternate long and two short dashes line L4 indicate the relationship between the applied voltage and the interelectrode current when the concentration of SO ₂ contained in the measured gas is 300 ppm and 500 ppm. Also in these cases, in the region where the applied voltage is less than about 0.6 V, the inter-electrode current is almost zero as in the case of the solid line L1 and the broken line L2. On the other hand, when the applied voltage is about 0.6 V or more, an interelectrode current flows due to water decomposition. However, the higher the concentration of SO ₂ contained in the measured gas, the smaller the interelectrode current, and the higher the concentration of SO ₂ contained in the measured gas, the higher the increase rate of the interelectrode current with respect to the applied voltage (FIG. 2). The slope at () is also small.

Thus, also from the example shown in FIG. 2, the magnitude of the interelectrode current when the applied voltage is about 0.6 V or more, which is the SOx and water decomposition start voltage, is the SO _It can be seen that it varies depending on the concentration of ₂ (ie, SOx). For example, when the magnitude of the electrode current in the lines L1 to L4 when the applied voltage in the graph shown in FIG. 2 is 1.0 V is plotted against the concentration of SO ₂ contained in the measured gas, FIG. The graph shown is obtained.

As can be seen from FIG. 3, the magnitude of the interelectrode current when a predetermined voltage (1.0 V in the example shown in FIG. 3) is applied is SO ₂ (ie, SOx) contained in the measured gas. Varies depending on the concentration. Therefore, as described above, the concentration of SOx can be detected based on the interelectrode current when a predetermined voltage equal to or higher than the decomposition start voltage of water and SOx is applied.

<Problem>
By the way, when the sulfur component is contained in the fuel used for the internal combustion engine, SOx is contained in the exhaust gas discharged from the combustion chamber of the internal combustion engine. The concentration of SOx contained in the exhaust gas increases as the content of the sulfur component in the fuel increases. Therefore, as described above, by detecting the concentration of SOx based on the interelectrode current by the sulfur component detection device 1, the content rate of the sulfur component in the fuel can be basically detected.

  However, when the SOx concentration is detected by the above-described method, the SOx concentration varies not only with the content of the sulfur component in the fuel but also with the air-fuel ratio of the exhaust gas. In particular, when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, the ratio of fuel to air decreases as the lean degree of the air-fuel ratio of the exhaust gas increases (the air-fuel ratio increases). Therefore, in this case, the SOx concentration in the exhaust gas decreases as the lean degree of the air-fuel ratio of the exhaust gas increases even if the content of the sulfur component contained in the fuel is constant.

  For this reason, in order to accurately detect the content of the sulfur component in the fuel, it is necessary to maintain the air-fuel ratio of the exhaust gas constant over the entire SOx detection period by the sulfur component detection device 1. That is, in the sulfur component detection device 1, it is necessary to keep the air-fuel ratio of the exhaust gas constant over the entire period in which the first voltage is applied to the first electrochemical cell 51. However, even if the fuel injection amount or the like is controlled so that the air-fuel ratio of the exhaust gas is maintained constant, in the internal combustion engine, the air-fuel ratio of the exhaust gas varies with changes in engine load and engine speed. . For this reason, during actual operation of the internal combustion engine, it is difficult to keep the air-fuel ratio of the exhaust gas constant over a certain period. For this reason, it is difficult to detect the content of the sulfur component in the fuel with high accuracy.

<Sulfur component detection principle>
By the way, when the concentration of SOx contained in the exhaust gas, that is, the concentration of SOx contained in the measured gas is, for example, about 0 ppm to several ppm, the first electrochemical cell 51 has a predetermined value equal to or higher than the decomposition start voltage of SOx. Even if the first voltage is continuously applied over a long period of time, SOx decomposition products are hardly adsorbed on the first electrode 41. As a result, after the first voltage is continuously applied to the first electrochemical cell 51 for a long period of time, a second voltage that is equal to or higher than the water decomposition start voltage is applied to the first electrochemical cell 51 to generate an interelectrode current. When detected, the interelectrode current takes a relatively large value.

  On the other hand, when the concentration of SOx contained in the exhaust gas is a certain level or higher, if the first voltage is continuously applied to the first electrochemical cell 51 over a long period of time, the first electrode 41 will eventually decompose and form. It will be covered with things. As a result, after the first voltage is continuously applied to the first electrochemical cell 51 for a long time, the second voltage is applied to the first electrochemical cell 51 to detect the interelectrode current of the first electrochemical cell 51. Then, the interelectrode current becomes a relatively small value.

FIG. 4 is a diagram showing a time transition of the interelectrode current when an applied voltage of 1.1 V is continuously applied to the first electrochemical cell 51. Similarly to FIG. 2, the solid line L1, the broken line L2, and the alternate long and short dash line L3 indicate the time transition of the interelectrode current when the concentrations of SO ₂ contained in the measured gas are 0 ppm, 100 ppm, and 300 ppm, respectively. In the example shown in FIG. 4, the applied voltage is made less than 0.6V before time t ₁ and the applied voltage is made 1.1V after time t ₁ .

As shown in FIG. 4, when the concentration of SO ₂ contained in the gas to be measured is 0 ppm (solid line L1), that is, when the content rate of the sulfur component in the fuel is 0, at time t ₁ , When a voltage of 1.1 V (more than the decomposition start voltage of SOx and more than the decomposition start voltage of water) is applied to one electrochemical cell 51, the interelectrode current in the first electrochemical cell 51 increases rapidly. This is because water is decomposed on the first electrode 41 after time t ₁ . Thereafter, the interelectrode current converges to a constant value with almost no decrease. This is because SOx decomposition products are not adsorbed on the first electrode 41.

When the concentration of SO ₂ contained in the measured gas is 100 ppm (broken line L2), that is, when the content of the sulfur component in the fuel is medium, 1.1 V is applied to the electrochemical cell 51 at time t ₁ . Is applied, the interelectrode current in the first electrochemical cell 51 increases rapidly. Thereafter, since the decomposition product of SOx is adsorbed on the first electrode 41, the interelectrode current gradually decreases and finally converges to a constant value. The value that converges at this time is smaller than the value that the solid line L1 converges. This is because the decomposition product of SOx adsorbed on the first electrode 41 covers, and eventually no further decomposition product can be adsorbed on the first electrode 41 (the decomposition product on the first electrode 41). Adsorption is saturated).

When the concentration of SO ₂ contained in the measured gas is 300 ppm (one-dot chain line L3), that is, when the content of the sulfur component in the fuel is high, a voltage of 1.1 V is applied to the electrochemical cell 51 at time t ₁ . Is applied, the interelectrode current in the first electrochemical cell 51 increases rapidly. Thereafter, since the decomposition product of SOx is adsorbed on the first electrode 41, the interelectrode current gradually decreases and finally converges to a constant value. In this case, since the concentration of SO ₂ contained in the measured gas is high and the adsorption rate of the decomposition products to the first electrode 41 is high, the rate of decrease of the interelectrode current in the alternate long and short dash line L3 is the electrode in the broken line L2. It is faster than the current decrease rate. Further, the value at which the one-dot chain line L3 converges is equal to the value at which the broken line L2 converges. This is because, even when the concentration of SO ₂ contained in the measured gas is 300 ppm, the decomposition product of SOx covers the first electrode 41 as in the case where this concentration is 100 ppm. This is because the adsorption of the decomposition product on one electrode 41 is saturated.

  Such a tendency basically does not change even if the air-fuel ratio of the exhaust gas changes. When the sulfur component content in the fuel is extremely low, if a predetermined first voltage equal to or higher than the SOx decomposition start voltage is continuously applied to the first electrochemical cell 51 over a long period of time, the air-fuel ratio of the exhaust gas is reduced during that period. Even if it fluctuates, the decomposition product of SOx hardly adsorbs on the first electrode 41. As a result, in this case, even if the air-fuel ratio of the exhaust gas fluctuates during the application of the first voltage, the inter-electrode current when the second voltage equal to or higher than the water decomposition start voltage is applied as shown by the solid line L1 in FIG. It converges to a similar value.

  On the other hand, if the content of the sulfur component in the fuel is moderate or higher, if the first voltage is continuously applied to the first electrochemical cell 51 for a long time, the air-fuel ratio of the exhaust gas may fluctuate during that time. A large amount of SOx decomposition products are adsorbed on the first electrode 41. As a result, the adsorption of decomposition products on the first electrode 41 is eventually saturated. Therefore, in this case, even if the air-fuel ratio of the exhaust gas fluctuates during the application of the first voltage, the interelectrode current when the second voltage is applied thereafter is the same value as the broken line L2 and the alternate long and short dash line L3 in FIG. Converge to.

<Sulfur component detection processing>
Therefore, in the present embodiment, the sulfur component detection process is performed according to the following procedure. First, a first voltage equal to or higher than the decomposition start voltage of SOx is applied between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51 (time t _{1 in} FIG. 4). Thereafter, the first voltage is continuously applied between the electrodes 41 and 42 for a predetermined duration Δt. As a result, when the content of the sulfur component in the fuel is medium or higher, a large amount of SOx decomposition products are adsorbed on the first electrode 41. On the other hand, when the content rate of the sulfur component in the fuel is extremely low, the decomposition product of SOx is hardly adsorbed on the first electrode 41.

Thereafter, at time t ₂ when the elapsed time from the start of application of the first voltage (time t ₁ ) is equal to or longer than a predetermined duration Δt, the first electrode 41 and the second electrode 42 of the first electrochemical cell 51 In the meantime, a second voltage equal to or higher than the water decomposition start voltage is applied. At this time, if the content of the sulfur component in the fuel is small, the amount of SOx decomposition products adsorbed on the first electrode 41 is small, so the interelectrode current when the second voltage is applied is a predetermined reference. It becomes the current It or more. Therefore, when the interelectrode current when the second voltage is applied is equal to or greater than a predetermined reference current It, it is determined that the content of the sulfur component in the fuel is equal to or less than a predetermined reference content.

  On the contrary, when the content rate of the sulfur component in the fuel is high, the interelectrode current when the second voltage is applied is less than a predetermined reference current It. Therefore, when the interelectrode current when the second voltage is applied is less than a predetermined reference current It, it is determined that the sulfur content in the fuel is higher than the reference content.

  Here, a current region equal to or greater than the reference current It is defined as a first region, and a current region less than the reference current It is defined as a second region. Therefore, it can be said that the second region is all current regions other than the first region. In the present embodiment, when the interelectrode current when the second voltage is applied to the first electrochemical cell 51 is a value in the first region, the content of the sulfur component in the fuel is determined to be equal to or less than the reference content. The On the other hand, when the current between the electrodes when the second voltage is applied to the first electrochemical cell 51 is a value in the second region, the content rate of the sulfur component in the fuel is determined to be higher than the reference content rate. . Therefore, in the present embodiment, when the magnitude of the interelectrode current when the second voltage is applied is a value in the first region, sulfur in the fuel is larger than when the value is in the second region. It is determined that the component content is low.

  Thus, by detecting the content rate of the sulfur component in the fuel, it is possible to detect whether the content rate of the sulfur component in the fuel is less than the reference content rate regardless of the air-fuel ratio of the exhaust gas. . In particular, it is possible to distinguish when the content of the sulfur component in the fuel is very small and when the content of the sulfur component in the fuel is moderate or higher.

Here, as described above, the first voltage is preferably equal to the second voltage. In this case, the applied voltage from time t ₁ to time t ₂ is equal to the applied voltage after time t ₂ . In this way, by setting the first voltage and the second voltage to be equal, it is not necessary to switch the voltage at time t ₂ , so that the control of the applied voltage can be simplified. Moreover, in decomposing SOx and water, decomposition of SOx and water is promoted when a voltage higher than a decomposition start voltage (0.6 V to 0.8 V) is applied. Thus, for example, the first voltage and the second voltage are 1.1V.

  However, the first voltage and the second voltage are not necessarily equal. Therefore, the second voltage may be higher than the first voltage. As described above, since the decomposition start voltage of SOx is considered to be lower than the decomposition start voltage of water, the first voltage applied to decompose SOx can be a relatively low voltage. As a result, the power consumption accompanying the detection of the sulfur component can be suppressed, and the deterioration of fuel consumption can be suppressed. Conversely, the first voltage may be higher than the second voltage. In this case, decomposition of SOx can be promoted during application of the first voltage.

  In the above embodiment, the first voltage is applied between the electrodes of the first electrochemical cell 51 for a predetermined duration Δt. The duration Δt is decomposed onto the first electrode 41 when the first voltage is applied to the first electrochemical cell 51 over the duration Δt when the content of the sulfur component in the fuel is a predetermined value or more. The time is set so that the adsorption of the product is saturated. Therefore, in other words, the duration Δt is such that the cumulative flow rate of SOx in the exhaust gas flowing through the exhaust pipe during this duration Δt is constant when the sulfur component content in the fuel is equal to or greater than a predetermined value. Is set to be

  Moreover, in the said embodiment, the 1st voltage is applied between the electrodes of the 1st electrochemical cell 51 over predetermined duration (DELTA) t. However, during the period in which the first voltage is applied between the electrodes of the first electrochemical cell 51, a parameter that increases the integrated flow rate of SOx in the exhaust gas as the parameter value increases (hereinafter referred to as “integrated parameter”). If so, it may be determined based on parameters other than time. Therefore, as such an integration parameter, in addition to “time”, “an integrated value of the amount of intake air taken into the combustion chamber of the internal combustion engine” or “a fuel injection valve of the internal combustion engine supplied to the combustion chamber” “Integrated value of fuel supply amount” can be considered.

  In the sulfur component detection process, the first voltage is applied between the electrodes of the first electrochemical cell 51 until the value of the integration parameter becomes a predetermined value or more. The predetermined value at this time is that when the first voltage is applied to the first electrochemical cell 51 until the value of the integration parameter reaches the predetermined value when the content of the sulfur component in the fuel is equal to or higher than the predetermined value. The value is set such that the adsorption of the decomposition product on the first electrode 41 is saturated.

<Pump cell>
By the way, in the first electrochemical cell 51, as described above, SOx is generated on the first electrode 41 by applying a first voltage equal to or higher than the SOx decomposition start voltage between the first electrode 41 and the second electrode 42. While decomposing, the interelectrode current accompanying the decomposition of the water on the 1st electrode 41 is detected by applying the 2nd voltage more than the decomposition start voltage of water. However, when oxygen is contained in the gas to be measured that reaches the first electrochemical cell 51, oxygen is decomposed (ionized) on the first electrode 41, and oxide ions generated thereby are generated. It flows from the first electrode 41 to the second electrode 42. As described above, if a decomposition current flows between the first electrode 41 and the second electrode 42 due to the decomposition of oxygen, the SOx concentration cannot be accurately detected based on the interelectrode current.

  Here, as described above, when a voltage in the limiting current region of oxygen is applied to the third electrochemical cell 53, the conduction velocity of oxide ions that can be conducted by the third electrochemical cell 53 in accordance with the voltage application is It becomes faster than the introduction speed of oxygen introduced into the measured gas chamber 30 through the diffusion control layer 16. Therefore, when a voltage in the limiting current region of oxygen is applied to the third electrochemical cell 53, most of the oxygen contained in the measured gas that has flowed into the measured gas chamber 30 through the diffusion rate controlling layer 16. Can be removed.

  Therefore, in the present embodiment, the voltage in the limiting current region of oxygen is applied to the third electrochemical cell 53 disposed closer to the diffusion rate controlling layer 16 than the first electrochemical cell 51. The limiting current region of oxygen is a region of a lower limit voltage (for example, 0.1 V) or more at which the interelectrode current hardly changes even when the applied voltage is further increased. In addition, the voltage applied to the third electrochemical cell 53 is set to a voltage lower than the decomposition start voltage (about 0.6 V) of SOx and water. When the voltage applied to the third electrochemical cell 53 is set in this way, oxygen contained in the gas to be measured can be decomposed and removed via the second solid electrolyte layer 12. In addition, since the voltage applied to the third electrochemical cell 53 is lower than the SOx and water decomposition start voltage, the decomposition of water and SOx does not occur on the fifth electrode 45 of the third electrochemical cell 53. Therefore, the third electrochemical cell 53 functions as a pump cell that discharges oxygen from the measured gas chamber 30 without discharging water and SOx.

<Specific control>
With reference to FIG. 5, the specific control which performs the detection process of the sulfur component mentioned above is demonstrated. FIG. 5 is a flowchart illustrating an example of the sulfur component detection process executed by the ECU 80. In the present embodiment, the applied voltage to the third electrochemical cell 53 is always 0.4 V, for example.

  First, as shown in step S11, the ECU 80 determines whether or not a sulfur component detection condition is satisfied. Specifically, for example, after the start of the internal combustion engine (or after the ignition key is turned on or after the previous fuel supply), when the detection process of the sulfur component is completed, the detection of the sulfur component is performed. It is determined that the condition is not satisfied. That is, the content rate of the sulfur component in the fuel does not change unless fuel is supplied. Therefore, once the detection of the sulfur component is completed, it is not necessary to perform the sulfur component detection process so frequently. For this reason, when the detection process of a sulfur component is completed, it determines with the detection conditions of a sulfur component not being satisfied.

  If it is determined in step S11 that the SOx detection condition is not satisfied, the process proceeds to step S12. In step S12, the ECU 80 sets the applied voltage to the first electrochemical cell 51 to 0.30V. Thus, when the applied voltage to the first electrochemical cell 51 is less than 0.45 V, the first electrochemical cell 51 is slightly oxygen-excessive on the first electrode 41 of the first electrochemical cell 51. Oxide ions move through the solid electrolyte layer 11 of the cell 51. As a result, when the decomposition product of SOx is adsorbed on the first electrode 41, the decomposition product is released.

  On the other hand, if it is determined in step S11 that the sulfur component detection condition is satisfied, the process proceeds to step S13. In step S13, the ECU 80 sets the voltage applied to the first electrochemical cell 51 to 1.1 V (first voltage). For this reason, the decomposition product of SOx is gradually adsorbed on the first electrode 41 in accordance with the SOx concentration contained in the measured gas.

  Next, in step S14, the ECU 80 determines whether or not an elapsed time after the applied voltage to the first electrochemical cell 51 is 1.1 V is equal to or longer than a predetermined duration Δt. If it is determined that the elapsed time is less than the predetermined duration Δt, the process returns to step S11. On the other hand, if it is determined in step S14 that the elapsed time since the applied voltage to the first electrochemical cell 51 is 1.1 V is equal to or longer than the predetermined duration Δt, the process proceeds to step S15. In the example shown in FIG. 5, the applied voltage to the first electrochemical cell 51 is 1.1 V (second voltage) even after it is determined in step S14 that the elapsed time is equal to or longer than the predetermined duration Δt. Is maintained.

  In step S <b> 15, the ECU 80 acquires the interelectrode current of the first electrochemical cell 51. Next, in step S16, the ECU 80 determines whether or not the interelectrode current acquired in step S15 is greater than or equal to the reference current It. If it is determined that the interelectrode current is greater than or equal to the reference current It, the process proceeds to step S17. In step S17, the ECU 80 determines that the content rate of the sulfur component in the fuel is lower than the reference content rate, and then the routine proceeds to step S19. On the other hand, if it is determined in step S16 that the interelectrode current is equal to or less than the reference current It, the process proceeds to step S18. In step S18, the ECU 80 determines that the content ratio of the sulfur component in the fuel is also high, and then the routine proceeds to step S19. In step S19, the ECU 80 sets the applied voltage to the first electrochemical cell 51 to 0.30 V, and the control routine ends.

  The detection process shown in FIG. 5 shows a case where both the first voltage and the second voltage are set to 1.1V. If the first voltage and the second voltage are different from each other, after the first cell applied voltage is set to the first voltage in step S13 and it is determined in step S14 that it is equal to or longer than the predetermined duration Δt. The first cell applied voltage is set to the second voltage.

<Second embodiment>
Next, with reference to FIG. 6, the detection method of the sulfur component by the sulfur component detection apparatus 2 which concerns on 2nd embodiment of this invention is demonstrated. FIG. 6A is a schematic cross-sectional view similar to FIG. 1 of the sulfur component detection device according to the present embodiment. FIG. 6B is a schematic cross-sectional view of the sulfur component detection device according to the present embodiment as viewed along line AA shown in FIG. Below, about the sulfur component detection apparatus 2 which concerns on 2nd embodiment, a different part from the sulfur component detection apparatus 1 which concerns on 1st embodiment is mainly demonstrated.

<Configuration of sulfur component detection device>
As shown in FIG. 6B, the sulfur component detection device 2 according to the second embodiment further includes a second electrochemical cell 52 provided near the first electrochemical cell 51. As can be seen from FIGS. 6A and 6B, the second electrochemical cell 52 has a distance from the diffusion-controlling layer 16 and the third electrochemical cell 53 equal to that of the first electrochemical cell 51. Are arranged side by side with the first electrochemical cell 51.

  Specifically, in the present embodiment, the element unit 10 further includes a third electrode 43 and a fourth electrode 44. The third electrode 43 is disposed on the surface of the first solid electrolyte layer 11 on the measured gas chamber 30 side. Therefore, the third electrode 43 is exposed to the gas in the measured gas chamber 30. On the other hand, the fourth electrode 44 is disposed on the surface of the first solid electrolyte layer 11 on the first atmospheric chamber 31 side. Therefore, the fourth electrode 44 is exposed to the gas (atmosphere) in the first atmospheric chamber 31. The third electrode 43 and the fourth electrode 44 are disposed so as to face each other with the first solid electrolyte layer 11 interposed therebetween. The third electrode 43, the first solid electrolyte layer 11, and the fourth electrode 44 constitute a second electrochemical cell 52. Therefore, the third electrode 43 is arranged side by side with the first electrode 41 so that the distance from the diffusion-controlling layer 16 and the third electrochemical cell 53 is equal to the first electrode 41.

  In the present embodiment, the material constituting the third electrode 43 includes a metal element such as platinum (Pt), gold (Au), lead (Pb), silver (Ag), or an alloy thereof as a main component. Preferably, the third electrode 43 is a porous cermet electrode containing at least one of platinum (Pt), gold (Au), lead (Pb), and silver (Ag) as a main component. The fourth electrode 44 is a porous cermet electrode containing platinum (Pt) as a main component. Note that the material constituting the third electrode 43 is not necessarily limited to the above-described material. Even if the applied voltage is equal, the electrode is formed so that the decomposition rate of SOx is lower than that of the first electrode 41. Any material can be used as long as it is configured. In particular, in the present embodiment, the material constituting the third electrode 43 is preferably a material that substantially eliminates the rate at which SOx is decomposed in the third electrode 43. The material constituting the fourth electrode 44 is not necessarily limited to the above material, and when a predetermined voltage is applied between the first electrode 41 and the second electrode 42, Any material may be used as long as the oxide ions can be moved between the second electrode 42.

  The sulfur component detection device according to the second embodiment includes a second circuit 90. The second circuit 90 includes a second power source 91 and a second ammeter 92. The second power source 91 and the second ammeter 92 are connected to the ECU 80. The second power supply 91 applies a voltage between the third electrode 43 and the fourth electrode 44 so that the potential of the fourth electrode 44 is higher than the potential of the third electrode 43. The magnitude of the voltage applied by the second power source 91 is controlled by the ECU 80.

  On the other hand, the second ammeter 92 detects the magnitude of the interelectrode current, which is the current flowing between the third electrode 43 and the fourth electrode 44 (that is, the current flowing in the first solid electrolyte layer 11). The detected value of the interelectrode current by the second ammeter 92 is input to the ECU 80.

  The ECU 80 can control the third applied voltage applied between the third electrode 43 and the fourth electrode 44 by the second power source 91 by controlling the second power source 91. Therefore, the ECU 80 and the second power supply 91 function as a voltage application device that can apply an interelectrode voltage between the third electrode 43 and the fourth electrode 44 and control the interelectrode voltage. Further, the ECU 80 receives a signal corresponding to the magnitude of the interelectrode current flowing between the third electrode 43 and the fourth electrode 44 detected by the second ammeter 92. Therefore, the ECU 80 and the second ammeter 92 function as a detection unit that detects the value of the current correlation parameter that correlates with the current flowing between the third electrode 43 and the fourth electrode 44.

<Detection principle>
As described above, in the second electrochemical cell 52, even when the same applied voltage as that in the first electrochemical cell 51 is applied, the rate of decomposing SOx contained in the measured gas is higher than that in the first electrochemical cell 51. Is too slow. Specifically, the rate at which SOx is decomposed at the third electrode 43 is extremely slower than the rate at which SOx is decomposed at the first electrode 41, and is substantially zero. Therefore, the rate at which the decomposition products of SOx contained in the measured gas are adsorbed on the electrode is also slower on the third electrode 43 than on the first electrode 41. Specifically, the SOx decomposition product is not substantially adsorbed on the third electrode 43. Therefore, the rate of decrease in activity for water decomposition in the third electrode 43 is slower than the rate of decrease in activity for water decomposition in the first electrode 41. Specifically, the activity for water decomposition in the third electrode 43 is not substantially reduced. As a result, the interelectrode current in the second electrochemical cell 52 is not affected by the decomposition of SOx. For this reason, the interelectrode current in the second electrochemical cell 52 is larger than the interelectrode current in the first electrochemical cell 51, and the difference between these interelectrode currents is higher in the concentration of SOx contained in the measured gas. It gets bigger.

  Therefore, the sulfur component detection device 2 of the present embodiment is configured such that the interelectrode current when a predetermined voltage is applied between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51, and the second electrochemical cell. The ECU 80 calculates the difference from the interelectrode current when the same predetermined voltage is applied between the third electrode 43 and the fourth electrode 44 of the 52, and detects the sulfur component contained in the fuel based on this difference Like to do. Thus, the concentration of water contained in the gas to be measured in detecting the concentration of SOx by taking the difference between the interelectrode current of the first electrochemical cell 51 and the interelectrode current of the second electrochemical cell 52. The influence of fluctuation can be reduced.

  In the example shown in FIG. 6, the second electrochemical cell 52 shares the first solid electrolyte layer 11 with the first electrochemical cell 51. However, the second electrochemical cell 52 may include a solid electrolyte layer different from the first solid electrolyte layer 11 constituting the first electrochemical cell 51.

  In the above embodiment, the applied voltage to the first electrochemical cell 51 and the applied voltage to the second electrochemical cell 52 are the same voltage. However, if the voltage applied to the second electrochemical cell 52 is a voltage that can decompose water contained in the gas to be measured when applied between the electrodes and is less than the lower limit value of the limit current region of water, A voltage different from the voltage applied to one electrochemical cell 51 may be used.

<Sulfur component detection processing>
Based on the above-described detection principle of the sulfur component, in the present embodiment, the sulfur component detection process is performed as follows.

  In addition, in the present embodiment, the ECU 80 applies a first voltage to the first electrochemical cell 51 and the second electrochemical cell 52 when detecting the sulfur component contained in the fuel. Thereafter, the first voltage is continuously applied to both electrochemical cells 51 and 52 for a predetermined duration Δt. As a result, when the content of the sulfur component in the fuel is medium or higher, a large amount of SOx decomposition products are adsorbed on the first electrode 41. On the other hand, even in this case, the decomposition product of SOx is not adsorbed on the third electrode 43.

  Thereafter, when the elapsed time from the start of application of the first voltage becomes equal to or longer than the predetermined duration Δt, the second voltage is applied to the first electrochemical cell 51 and the second electrochemical cell 52. At this time, if the content of the sulfur component in the fuel is small, the amount of SOx decomposition products adsorbed on the first electrode 41 is small, so the interelectrode current of the first electrochemical cell 51 and the second electrochemical cell 52 are reduced. The difference between the inter-electrode currents t is equal to or less than a predetermined reference value. Therefore, when the difference in the interelectrode current when the second voltage is applied is equal to or less than a predetermined reference value, the content of the sulfur component in the fuel is determined to be equal to or less than the predetermined reference content.

  On the contrary, when the content rate of the sulfur component in the fuel is high, the difference in the interelectrode current when the second voltage is applied becomes larger than a predetermined reference value. Therefore, when the difference in the interelectrode current when the second voltage is applied is greater than a predetermined reference value, it is determined that the sulfur content in the fuel is greater than the reference content.

  Here, the difference area of the interelectrode current below the reference value is defined as a first area, and the difference area of the interelectrode current larger than the reference value is defined as a second area. Therefore, it can be said that the second region is all current regions other than the first region. In the present embodiment, when the difference between the currents when the second voltage is applied to the first electrochemical cell 51 is a value within the first region, the sulfur content in the fuel is equal to or less than the reference content. Determined. On the other hand, when the current between the electrodes when the second voltage is applied to the first electrochemical cell 51 is a value in the second region, the content rate of the sulfur component in the fuel is determined to be higher than the reference content rate. . Therefore, in the present embodiment, when the difference between the electrodes when the second voltage is applied is a value in the first region, the sulfur component in the fuel is larger than that in the second region. Is determined to be low.

  In the first embodiment, the sulfur component content in the fuel is detected based on the interelectrode current flowing between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51. In the second embodiment, the interelectrode current flowing between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51 and the third electrode 43 and the fourth electrode 44 of the second electrochemical cell 52 are also described. The content rate of the sulfur component in the fuel is detected based on the difference between the currents flowing between the electrodes. Therefore, in these embodiments, the SOx contained in the measured gas is detected based on the current correlation parameter that correlates with the interelectrode current flowing between the first electrode 41 and the second electrode 42 of the first electrochemical cell 51. It can be said that.

  Further, as such a current correlation parameter, not only the inter-electrode current and the difference between the electrodes, but also the inter-electrode current and a voltage or a resistance value that changes according to the difference may be used.

DESCRIPTION OF SYMBOLS 1, 2 Sulfur component detection apparatus 10 Element part 11 1st solid electrolyte layer 12 2nd solid electrolyte layer 16 Diffusion-controlling layer 41 1st electrode 42 2nd electrode 43 3rd electrode 44 4th electrode 45 5th electrode 46 6th electrode 51 First Electrochemical Cell 52 Second Electrochemical Cell 53 Third Electrochemical Cell 60 First Circuit 70 Third Circuit 80 Electronic Control Unit (ECU)
90 Second circuit

Claims (6)

A first electrode having a solid electrolyte layer having oxide ion conductivity, a first electrode disposed on one side surface of the solid electrolyte layer, and a second electrode disposed on the other side surface of the solid electrolyte layer. An electrochemical cell; a diffusion rate-determining layer that performs diffusion rate-limiting of the gas to be measured; and a gas chamber to be measured that is partitioned into the solid electrolyte layer and the diffusion rate-limiting layer, wherein the first electrode is A sulfur component detection method for detecting a content rate of sulfur components contained in fuel by a sulfur component detection device disposed in the measured gas chamber and disposed so that the second electrode is exposed to the atmosphere. There,
A step of applying a first voltage equal to or higher than a decomposition start voltage of sulfur oxide between the first electrode and the second electrode until the value of the integration parameter reaches a predetermined value or more;
Subsequent to the step of applying the first voltage, a second voltage equal to or higher than the water decomposition start voltage is applied between the first electrode and the second electrode, and an interelectrode current flowing between these electrodes is applied. Obtaining values of correlated current correlation parameters;
A step of detecting the content of the sulfur component in the fuel based on the value of the acquired current correlation parameter,
The cumulative parameter is a parameter such that the cumulative flow rate of sulfur oxide in the exhaust gas increases as the value of the cumulative parameter increases,
In the step of detecting the sulfur component in the fuel, when the acquired current correlation parameter value is a value in the first region, the acquired parameter value is in all regions other than the first region. The sulfur component detection method which determines with the content rate of the sulfur component in a fuel being low compared with when it is a value in a certain 2nd area | region.   In the step of obtaining the value of the current correlation parameter, when the amount of change in the air-fuel ratio of the exhaust gas per unit time is less than or equal to the predetermined change amount, the current correlation parameter is obtained. The sulfur component detection method according to claim 1, wherein a parameter value is acquired.   When the time of applying the second voltage is relatively short after the step of applying the first voltage is completed and until the value of the current correlation parameter is obtained 3. The sulfur component detection method according to claim 2, wherein the first region is narrowed and the second region is widened.   The sulfur component detection method according to claim 1, wherein the magnitude of the first voltage is equal to the magnitude of the second voltage.   The current correlation parameter is a current flowing between the first electrode and the second electrode, the first region is a region equal to or greater than a predetermined reference current, and the second region is the predetermined The sulfur component detection method according to claim 1, wherein the sulfur component detection region is a region less than a reference current. The sulfur component detection device is disposed on a solid electrolyte layer having oxide ion conductivity, a third electrode disposed on one side surface of the solid electrolyte layer, and the other side surface of the solid electrolyte layer. A second electrochemical cell having a fourth electrode, wherein the third electrode is disposed in the measured gas chamber and the fourth electrode is disposed to be exposed to the atmosphere,
When the first voltage is applied between the first electrode and the second electrode and between the third electrode and the fourth electrode, the first electrode and the third electrode are The sulfur oxide decomposition rate at one electrode is configured to be faster than the sulfur oxide decomposition rate at the third electrode,
The current correlation parameter is a difference between an interelectrode current flowing between the first electrode and the second electrode and an interelectrode current flowing between the third electrode and the fourth electrode, The sulfur component detection according to any one of claims 1 to 4, wherein one area is an area that is equal to or smaller than a predetermined reference value and the second area is an area that is larger than the predetermined reference value. Method.

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