JP2016099317A - Control apparatus for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control apparatus for an internal combustion engine, the apparatus capable of easily determining presence of sulfur oxide, as a test object gas, contained in an exhaust gas by using a limiting current gas sensor even in the case of the density of water contained in the exhaust gas being unknown.SOLUTION: In a state where an air-fuel ratio (A/F) of an air-fuel mixture supplied to a combustion chamber of an internal combustion engine is held constant, a voltage applied across electrodes of an electrochemical cell (a pumping cell) that has an oxygen pumping action over a range of voltages enabling decomposition of water (HO) and sulfur oxide (SOx) contained in an exhaust gas as a test object gas is increased and decreased gradually. Here, based on a difference in an electrode current between increasing the applied voltage and decreasing it, whether or not to execute a specific action corresponding to a determination that the fuel supplied to the engine contains a sulfuric component of first percentage content or higher is switched.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine that determines whether or not a sulfur component is contained in a fuel used in an internal combustion engine having a gas detection means.

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

A limiting current type gas sensor used as an air-fuel ratio sensor as described above is an electrochemical cell including a solid electrolyte body having oxide ion conductivity and a pair of electrodes fixed to the surface of the solid electrolyte body. A pumping cell is provided. One of the pair of electrodes is exposed to the exhaust gas of the internal combustion engine as the test gas introduced through the diffusion resistance portion, and the other is exposed to the atmosphere. When one of the electrodes is used as a cathode and the other electrode is used as an anode, when a voltage equal to or higher than the voltage at which oxygen begins to decompose (decomposition start voltage) is applied between the pair of electrodes, oxygen contained in the test gas Is reduced and decomposed into oxide ions (O ²⁻ ). The oxide ions are conducted to the anode through the solid electrolyte body, become oxygen, and are discharged into the atmosphere. Such movement of oxygen by conduction of oxide ions through the solid electrolyte body from the cathode side to the anode side is referred to as “oxygen pumping action”.

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

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

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

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

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

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

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

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

JP-A-11-190721

  As described above, in this technical field, 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, it is difficult to accurately distinguish and detect only the decomposition current caused by sulfur oxide.

  Therefore, the present inventor has been studying a technique for acquiring the SOx concentration in the exhaust gas using a limiting current type gas sensor and acquiring the sulfur content in the fuel based on the acquired SOx concentration. As a result, the present inventor has found that an electrode current generated when water and sulfur oxide are decomposed at a predetermined applied voltage in an electrochemical cell having an oxygen pumping action (pumping cell) is exhausted from an internal combustion engine as a test gas. It has been found that it varies depending on the concentration of sulfur oxides.

  However, when the concentration of water contained in the exhaust gas of the internal combustion engine changes, the magnitude of the decomposition current caused by water also changes, and the magnitude of the electrode current also changes. Therefore, in order to obtain the concentration of sulfur oxide contained in the exhaust based on the electrode current, the concentration of water contained in the exhaust needs to be known. However, since the concentration of water contained in the exhaust gas of the actual internal combustion engine changes with changes in the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine, for example, It is difficult to obtain the concentration of contained sulfur oxides.

  On the other hand, even if the concentration of sulfur oxide contained in the exhaust gas cannot be obtained, if the presence or absence of sulfur oxide can be determined, the result is reflected in the control of the internal combustion engine, for example, or the internal combustion engine Can be issued, and can be used to improve self-diagnosis (OBD) of the exhaust purification catalyst. The present invention has been made based on such a viewpoint. That is, the present invention uses the limiting current type gas sensor to detect the presence or absence of sulfur oxide contained in the exhaust gas as the test gas even when the concentration of water contained in the exhaust gas as the test gas is unknown. An object of the present invention is to provide a control device for an internal combustion engine that easily determines the engine speed and executes control according to the result.

  In view of the above points, as a result of intensive research, the present inventor has applied voltage between the electrodes of the pumping cell within a voltage range in which water and sulfur oxide contained in the test gas can be decomposed. It was found that when the gas was gradually raised and lowered, if the test gas contained sulfur oxide, a difference in the electrode current occurred between when it was raised and when it was lowered. The reason for this phenomenon will be described later. At this time, the magnitude of the electrode current varies depending on the concentration of water in the test gas. However, if the concentration of water during the period in which the applied voltage is raised and lowered is constant, the presence or absence of sulfur oxide contained in the test gas can be determined based on the difference in the electrode current.

  Therefore, the control device for a gas internal combustion engine according to the present invention (hereinafter sometimes referred to as “the present invention device”) has the same configuration as that of a limiting current gas sensor including an electrochemical cell having an oxygen pumping action. The present invention is applied to an internal combustion engine having gas detection means. That is, the gas detection means provided in the internal combustion engine to which the device of the present invention is applied has an element part, a voltage application part, and an acquisition part.

  The element section includes a first electrochemical cell including a solid electrolyte body having oxide ion conductivity and a first electrode and a second electrode formed on the surface of the solid electrolyte body, a dense body, and a diffusion resistance section. And comprising. Further, in the element portion, exhaust gas of an internal combustion engine as a test gas is introduced into the internal space defined by the solid electrolyte body, the dense body, and the diffusion resistance portion via the diffusion resistance portion. An electrode is exposed to the internal space, and the second electrode is exposed to a first separate space that is a space different from the internal space. The voltage application unit applies a voltage between the first electrode and the second electrode. The acquisition unit acquires a first detection value corresponding to a current flowing between the first electrode and the second electrode.

The first electrode contains water (H ₂ O) and sulfur oxide (SOx) contained in the test gas when a first predetermined voltage is applied between the first electrode and the second electrode. It is configured to be disassembled. Such a 1st electrode can be produced by selecting suitably the kind of substance which comprises electrode material, the conditions of the heat processing at the time of producing an electrode, etc., for example.

  The voltage applying unit applies a first applied voltage, which is a voltage applied between the first electrode and the second electrode, in a first voltage band that is a voltage range including the first predetermined voltage. A boost sweep is performed to increase at the first boost speed. Further, the voltage application unit is configured to execute a step-down sweep that lowers the first applied voltage at a predetermined first step-down speed in the first voltage band after the step-up sweep is performed.

The first predetermined voltage is a voltage range equal to or higher than the “voltage at which water decomposition starts (water decomposition start voltage)” higher than the “voltage at which sulfur oxide decomposition starts (sulfur oxide decomposition start voltage)”. It is a predetermined voltage included in (voltage band). Therefore, when the first applied voltage corresponds to the first predetermined voltage during the period in which the step-up sweep or the step-down sweep is performed in the first voltage band, the decomposition of water and sulfur oxide contained in the test gas is performed. An electrode current resulting from is flowing between the first electrode and the second electrode. That is, the first applied voltage becomes a specific voltage (specific voltage) at which water (H ₂ O) can be decomposed at the first electrode during the period in which the step-up sweep or the step-down sweep is performed in the first voltage band. Electrode current caused by decomposition of water and sulfur oxide contained in the test gas flows between the first electrode and the second electrode.

The device of the present invention includes a control means. In the state where the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is constant, the control means is executing the boost sweep and the first applied voltage is A first boost detection value that is the first detection value acquired by the acquisition unit when water (H ₂ O) is a specific voltage that can be decomposed at the first electrode, and the step-down sweep is being executed. And a first detection value difference that is a value corresponding to a difference from the first step-down detection value that is the first detection value acquired by the acquisition unit when the first applied voltage is the specific voltage is predetermined. If it is equal to or higher than the first threshold value, the specific operation corresponding to the determination that the fuel supplied to the internal combustion engine contains a sulfur component equal to or higher than the first content rate is executed. In this case, the control means determines whether or not the first detection value difference is greater than or equal to the first threshold based on whether or not the difference between the first boost detection value and the first buck detection value is greater than or equal to the threshold. Alternatively, the determination may be made based on whether the ratio between the first boost detection value and the first buck detection value is equal to or greater than a threshold value.

  In the state where the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is constant as described above, the concentration of water generated as a result of fuel combustion is also constant. On the other hand, it is unlikely that the concentration (humidity) of water contained in the air will change abruptly in an extremely short time. Therefore, if the air-fuel ratio (A / F) of the air-fuel mixture is constant during the period in which the pressure-up sweep and the pressure-down sweep are executed, the concentration of water contained in the exhaust gas of the internal combustion engine is regarded as substantially constant. Can do.

Therefore, if the test gas does not contain sulfur oxides, the first applied voltage is a specific voltage at which the first electrode can decompose water (H ₂ O) while the boosting sweep is being performed. And a first detection value (first step-down detection value) when the step-down sweep is being executed and the first applied voltage is the specific voltage. And match. Therefore, the first detection value difference that is a value corresponding to the difference is substantially 0 (zero). On the other hand, if the test gas contains sulfur oxide, the first pressure increase detection value and the first pressure decrease detection value do not match, and the first detection value difference corresponding to the difference between them does not match. It becomes larger than 0 (zero).

  Therefore, the control means performs an operation according to whether or not the first detection value difference is equal to or greater than a predetermined first threshold value. Specifically, the control means determines that the fuel supplied to the internal combustion engine contains a sulfur component equal to or higher than a first content when the first detection value difference is equal to or greater than a predetermined first threshold. Perform the corresponding specific action. “Specific operation” means, for example, lighting a lamp indicating that a sulfur component is contained in the fuel, storing in the storage device that the sulfur component is contained in the fuel, and an exhaust purification catalyst. Including air-fuel ratio control to cope with sulfur poisoning. Details of the first threshold and the first content will be described later in detail.

  As described above, according to the apparatus of the present invention, even when the concentration of water contained in the exhaust gas as the test gas is unknown, it is contained in the exhaust gas as the test gas using the limiting current type gas sensor. It is possible to easily determine the presence or absence of sulfur oxide and to perform an operation according to the result.

  By the way, as described above, the first predetermined voltage is higher than the “voltage at which the decomposition of water starts (the decomposition start voltage of sulfur oxide)” and the “voltage at which the decomposition of water starts (the decomposition start voltage of water). ) ”Is a predetermined voltage included in the above voltage range (voltage band). For example, some fluctuations are observed depending on the concentration of oxygen contained in the test gas and measurement conditions, but the water decomposition start voltage is about 0.6V. Therefore, it is desirable that the lower limit of the first voltage band is a predetermined voltage of 0.6V or more. Therefore, the voltage application unit may be configured to perform the step-up sweep and the step-down sweep with the lower limit of the first voltage band set to 0.6V. By performing the step-up sweep and the step-down sweep in such a first voltage band, not only the water contained in the test gas but also the sulfur oxide contained in the test gas can be reliably decomposed. As a result, when sulfur oxide is contained in the test gas, the first detection value difference can be reliably detected.

  By the way, when the applied voltage (first applied voltage) between the first electrode and the second electrode becomes equal to or higher than the lower limit voltage of the limit current region of water, it reaches the first electrode (cathode) via the diffusion resistance portion. The water decomposition rate of the first electrode exceeds the water supply rate. That is, in this case, since the first applied voltage is in the limit current region of water, the limit current characteristic of water comes to appear. In the limit current region of water, substantially all of the water that reaches the first electrode via the diffusion resistance portion is decomposed. Therefore, since a large amount of water is decomposed compared to sulfur oxide, the amount of sulfur oxide decomposed at the first electrode is relatively small.

  On the other hand, when the voltage application unit performs the step-up sweep and the step-down sweep, the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is constant. Therefore, in both the step-up sweep and the step-down sweep, the period in which the first applied voltage is in the limit current region of water is between the first electrode and the second electrode even if sulfur oxide is contained in the exhaust gas. The magnitude of the current flowing through the water becomes substantially constant at the limit current value of water, and there is no substantial difference between the first step-up detection value and the first step-down detection value. Therefore, from the viewpoint of detecting the first detection value difference, it is not necessary to raise the first applied voltage to the limit current region of water.

Furthermore, when the first applied voltage exceeds the limit current region of water and becomes a higher voltage, the electrode current is caused by decomposition of other components (for example, carbon dioxide (CO ₂ ), etc.) contained in the test gas. May begin to flow. Furthermore, when the first applied voltage is excessively high, the solid electrolyte body may be decomposed. In such a case, the electrode current may change due to factors other than the decomposition current caused by water and sulfur oxide contained in the test gas. As a result, the first boost detection value and the first buck detection value It may be difficult to detect correctly.

  Therefore, it is desirable that the upper limit of the first voltage band is a predetermined voltage lower than the lower limit voltage of the limit current region of water. In other words, it is desirable that the upper limit of the first voltage band is a predetermined voltage that is less than the lower limit of the voltage band in which the limit current characteristic of water is manifested (observed). For this reason, the voltage application unit may be configured to perform the step-up sweep and the step-down sweep with the upper limit of the first voltage band as a predetermined voltage lower than the lower limit voltage of the limit current region of water. By executing the step-up sweep and the step-down sweep in such a first voltage band, it is possible to avoid the first applied voltage from being raised to an excessively high voltage as described above. For example, a slight variation is observed depending on the concentration of water contained in the test gas, measurement conditions, and the like, but the lower limit voltage of the limit current region of water is about 2.0V.

  Incidentally, the first detection value acquired by the acquisition unit is a value of some signal corresponding to the electrode current flowing between the first electrode and the second electrode (for example, voltage value, current value, resistance value, etc.). As long as it is not particularly limited. Typically, the first detection value is a magnitude of a current flowing between the first electrode and the second electrode. In other words, the acquisition unit may be configured to acquire the magnitude of a current flowing between the first electrode and the second electrode as the first detection value.

  Further, the first electrode can decompose water and sulfur oxide contained in the test gas when a first predetermined voltage is applied between the first electrode and the second electrode. If it is comprised so that it may become, it will not specifically limit. Such a material constituting the first electrode decomposes water and sulfur oxide contained in the test gas when, for example, a first predetermined voltage is applied between the first electrode and the second electrode. A substance (for example, a noble metal) having an activity capable of Typically, the first electrode desirably includes at least one selected from the group consisting of platinum (Pt), rhodium (Rh), and palladium (Pd).

  By the way, the decomposition start voltage of oxygen in an electrochemical cell is generally lower than the decomposition start voltage of water. Therefore, the electrode current corresponding to the first detection value includes a decomposition current caused by oxygen in addition to a decomposition current caused by water and a decomposition current caused by sulfur oxide. Accordingly, when the concentration of oxygen contained in the test gas changes, the first detection value also changes.

  For example, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is large (lean) when performing the above-described pressure-up sweep and pressure-down sweep, the exhaust gas as the test gas is exhausted. The concentration of oxygen contained is also high. Therefore, since the limit current value of oxygen increases as the air-fuel ratio of the air-fuel mixture increases (lean), the first detection value also increases. As a result, compared with the case where the air-fuel ratio of the air-fuel mixture is small (rich) and the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio (stoichiometric), The value corresponding to the difference between the first detection values (first detection value difference) is relatively small with respect to the first detection value. That is, since the signal-to-noise ratio (S / N ratio) of the first detection value difference is lowered, there is a possibility that the detection accuracy of the sulfur oxide contained in the test gas is lowered.

  Therefore, in the gas detection means provided in the internal combustion engine to which the control device for an internal combustion engine according to one aspect of the present invention is applied, the element section includes the solid electrolyte body or a solid electrolyte body separate from the solid electrolyte body. A second electrochemical cell including a third electrode and a fourth electrode respectively formed on the surface of the solid electrolyte body may be further provided. In this case, the third electrode is exposed to the internal space, and the fourth electrode is exposed to a second separate space that is a space different from the internal space, and the third electrode is the first electrode. Rather than the diffused resistor portion. That is, in the internal space, the third electrode that is the cathode of the second electrochemical cell is formed on the upstream side of the first electrode that is the cathode of the first electrochemical cell.

Furthermore, the third electrode is capable of discharging oxygen (O ₂ ) from the internal space when a second predetermined voltage is applied between the third electrode and the fourth electrode, and sulfur oxidation. An object (SOx) cannot be decomposed, and the voltage application unit is configured to apply the second predetermined voltage between the third electrode and the fourth electrode. . In addition, when the voltage application unit performs the step-up sweep and the step-down sweep, the control means includes the second predetermined voltage between the third electrode and the fourth electrode in the second electrochemical cell. Is applied to adjust the oxygen concentration in the internal space below a predetermined concentration.

  According to the above configuration, even when the air-fuel ratio of the air-fuel mixture at the time of executing the pressure increase sweep and the pressure decrease sweep is large, the concentration of oxygen contained in the test gas reaching the first electrode in the internal space is the first concentration. It is adjusted below a predetermined concentration by the oxygen pumping action of two electrochemical cells. Therefore, the increase in the first detection value due to the oxygen decomposition current can be reduced. As a result, it is possible to reduce the possibility that the signal-to-noise ratio (S / N ratio) of the first detection value difference is lowered and the detection accuracy of the sulfur oxide contained in the test gas is lowered as described above. .

By the way, as described above, the second predetermined voltage can discharge oxygen (O ₂ ) from the internal space when the voltage is applied between the third electrode and the fourth electrode, and sulfur oxidation. It is a voltage at which it is impossible to decompose the object (SOx). Specifically, the second predetermined voltage is applied between these electrodes when the third electrode is a cathode and the fourth electrode is an anode, so that the oxygen contained in the test gas is reduced by an oxygen pumping action. This is a predetermined voltage that can be discharged from the internal space to the second separate space. That is, the second predetermined voltage is preferably a predetermined voltage that is equal to or higher than the oxygen decomposition start voltage. However, as will be described in detail later, the third electrode is configured so that it is substantially impossible to decompose the sulfur oxide (SOx). Such a 3rd electrode is a porous cermet electrode etc. which contain platinum (Pt) as a main component, for example.

  On the other hand, for example, when the third electrode is a cathode and the fourth electrode is an anode, if the applied voltage between these electrodes is equal to or higher than the water decomposition start voltage, the water contained in the test gas is second. Decomposed by electrochemical cell. In this case, the concentration of water contained in the test gas that reaches the first electrode, which is the cathode of the first electrochemical cell located downstream of the second electrochemical cell, decreases. As a result, since the first detection value changes, it becomes difficult to accurately determine the presence or absence of sulfur oxide contained in the test gas based on the first pressure increase detection value and the first pressure decrease detection value. There is a fear. Therefore, it is desirable that the second predetermined voltage is a predetermined voltage lower than the water decomposition start voltage.

  From the above, it is desirable that the second predetermined voltage is a predetermined voltage that is equal to or higher than the oxygen decomposition start voltage and lower than the water decomposition start voltage. For this reason, the voltage application unit may be configured to apply a predetermined voltage that is equal to or higher than the oxygen decomposition start voltage and lower than the water decomposition start voltage as the second predetermined voltage. Thereby, the concentration of oxygen contained in the test gas reaching the first electrode, which is the cathode of the first electrochemical cell, can be adjusted to be lower than the predetermined concentration, and the first, which is the cathode of the first electrochemical cell. It is possible to avoid changing the concentration of water contained in the test gas that reaches the electrode. As a result, it is possible to more accurately determine the presence or absence of sulfur oxide contained in the test gas, and to perform an operation corresponding to the result.

  In another aspect of the present invention, the voltage application unit applies a first electrode pair composed of the first electrode and the second electrode during a period when neither the step-up sweep nor the step-down sweep is performed. A fourth predetermined voltage that is a predetermined voltage corresponding to the limiting current region of oxygen may be applied. In this case, the control means mixes the air-fuel mixture in the combustion chamber of the internal combustion engine based on the first detection value acquired by the acquisition unit when the fourth predetermined voltage is applied to the first electrode pair. The air-fuel ratio (A / F) is detected.

  Alternatively, when the element unit includes a second electrochemical cell, the voltage application unit has a second electrode pair including the third electrode and the fourth electrode. A fourth predetermined voltage that is a voltage may be applied. In this case, the acquisition unit is configured to acquire a second detection value corresponding to a current flowing between the third electrode and the fourth electrode. Further, the control means is configured to control the mixture in the combustion chamber of the internal combustion engine based on the second detection value acquired by the acquisition unit when the fourth predetermined voltage is applied to the first electrode pair. The air-fuel ratio (A / F) is configured to be detected.

  In any of the above cases, it is possible to determine the presence or absence of sulfur oxides contained in the exhaust gas using an air-fuel ratio sensor that is normally provided in a vehicle equipped with an internal combustion engine, without adding a dedicated detection device. It becomes possible.

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

1 is a schematic diagram illustrating an example of a configuration of an internal combustion engine (engine 110) to which an internal combustion engine control device (first control device) according to a first embodiment of the present invention is applied. It is typical sectional drawing which shows an example of a structure of the element part with which the gas detection means (gas sensor 140) with which the internal combustion engine with which a 1st control apparatus is applied is provided is provided. A voltage (applied voltage) Vm applied between a first electrode and a second electrode constituting a first electrochemical cell included in an internal combustion engine to which the first control device is applied, and an electrode current flowing between these electrodes It is a typical graph which shows the relationship with Im. It is a flowchart which shows the "SOx detection routine" which the control means with which a 1st control apparatus is provided performs. It is typical sectional drawing which shows an example of a structure of the element part of the gas detection means with which the internal combustion engine with which the control apparatus (2nd control apparatus) of the internal combustion engine which concerns on 2nd Embodiment of this invention is applied is provided.

<First Embodiment>
Hereinafter, a control device for an internal combustion engine according to a first embodiment of the present invention (hereinafter may be referred to as a “first control device”) will be described.

(Constitution)
The first control device is applied to the internal combustion engine 110 shown in FIG. The engine 110 employs a “one-cell limiting current gas sensor” as a gas detection means. The engine 110 is a diesel engine and includes an intake port 112, an exhaust port 113, and a combustion chamber 122.

  The intake valve 124 is disposed in the cylinder head portion, and is driven by an intake camshaft (not shown) so as to open and close a communication portion between the intake port 112 and the combustion chamber 122. The exhaust valve 125 is disposed in the cylinder head portion, and is driven by an exhaust camshaft (not shown) so as to open and close the communication portion between the exhaust port 113 and the combustion chamber 122. The fuel injection valve 126 is disposed in the cylinder head portion so that fuel can be injected into the combustion chamber 122. The fuel injection valve 126 directly injects fuel into the combustion chamber 122 in accordance with an instruction from the ECU 130 described later.

  An intake pipe 121 is connected to the end of the intake port 112 opposite to the combustion chamber 122. An exhaust pipe 123 is connected to the end of the exhaust port 113 opposite to the combustion chamber 122.

  The ECU 130 is a microcomputer including a CPU 133, a ROM 134 that stores programs executed by the CPU 133, a data map, and the like, and a RAM 135 that temporarily stores data. ECU 130 is connected to various actuators (fuel injection valve 126 and the like) of engine 110. ECU 130 sends drive (instruction) signals to these actuators to control engine 110. Further, the ECU 130 is connected to various sensors described below.

  The gas sensor 140 is a one-cell limiting current type gas sensor, and is disposed in an exhaust pipe 123 that constitutes an exhaust path of the engine 110. The gas sensor 140 is disposed upstream of an unillustrated exhaust purification catalyst (or an exhaust purification device such as a DPF) interposed in the exhaust pipe 123. The configuration and operation of the gas sensor 140 will be described in detail later.

  The air flow meter 141 measures a mass flow rate (intake air amount) Ga of intake air (fresh air) passing through the intake pipe 121 constituting the intake path, and generates a signal corresponding to the measured intake air amount Ga. . Crank angle sensor 143 generates a signal corresponding to the rotational position of a crankshaft (not shown) of engine 110. ECU 130 calculates engine speed NE of engine 110 based on a signal from crank angle sensor 143.

Next, the configuration of the gas sensor 140 will be described with reference to FIG. As shown in FIG. 2, the element unit 10 included in the gas sensor 140 includes a solid electrolyte body 11s, a first alumina layer 21a, a second alumina layer 21b, a third alumina layer 21c, a fourth alumina layer 21d, and a fifth alumina layer 21e. , A diffusion resistance portion (diffusion rate limiting layer) 32 and a heater 41 are provided.
The solid electrolyte body 11s is a thin plate body containing zirconia or the like and having oxide ion conductivity. The zirconia forming the solid electrolyte body 11s may contain elements such as scandium (Sc) and yttrium (Y).
The first to fifth alumina layers 21a to 21e are dense (gas impermeable) layers (dense bodies) containing alumina.
The diffusion resistance portion 32 is a porous diffusion-controlling layer, and is a gas permeable layer (thin plate).
The heater 41 is a cermet thin plate including, for example, platinum (Pt) and ceramics (for example, alumina), and is a heating element that generates heat when energized.

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

  The internal space 31 is a space formed by the first alumina layer 21a, the solid electrolyte body 11s, the diffusion resistance portion 32, and the second alumina layer 21b, and an internal combustion as a test gas via the diffusion resistance portion 32 therein. Engine exhaust is introduced. That is, the internal space 31 communicates with the inside of the exhaust pipe 123 of the engine 110 via the diffusion resistance portion 32. Accordingly, the exhaust gas in the exhaust pipe 123 is guided into the internal space 31 as the test gas. The first atmosphere introduction path 51 is formed by the solid electrolyte body 11s, the third alumina layer 21c, and the fourth alumina layer 21d, and is open to the atmosphere outside the exhaust pipe. The first air introduction path 51 corresponds to a first separate space.

  The first electrode 11a is a cathode, and the second electrode 11b is an anode. The first electrode 11a is fixed to the surface on one side of the solid electrolyte body 11s (specifically, the surface of the solid electrolyte body 11s that defines the internal space 31). On the other hand, the second electrode 11b is fixed to the surface on the other side of the solid electrolyte body 11s (specifically, the surface of the solid electrolyte body 11s that defines the first air introduction path 51). The first electrode 11a and the second electrode 11b are arranged to face each other with the solid electrolyte body 11s interposed therebetween. That is, the first electrode 11a, the second electrode 11b, and the solid electrolyte body 11s constitute a first electrochemical cell 11c having an oxygen discharge capability by an oxygen pumping action. The first electrochemical cell 11c is heated to the activation temperature by the heater 41.

  Each of the solid electrolyte body 11s and the first to fifth alumina layers 21a to 21e is formed into a sheet by, for example, a doctor blade method or an extrusion method. The first electrode 11a, the second electrode 11b, and wiring for energizing these electrodes are formed by, for example, a screen printing method. By laminating and firing these sheets as described above, the element portion 10 having the above-described structure is integrally manufactured. In the first control device, the first electrode 11a is a porous cermet electrode containing an alloy of platinum (Pt) and rhodium (Rh) as a main component. On the other hand, the second electrode 11b is a porous cermet electrode containing platinum (Pt) as a main component.

  The material constituting the first electrode 11a is not limited to the above. For example, the material is selected from materials containing platinum group elements such as platinum (Pt), rhodium (Rh), palladium (Pd), or alloys thereof as main components. can do. 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). However, the material constituting the first electrode 11a diffuses when a first predetermined voltage (specifically, a voltage of about 0.6 V or more) is applied between the first electrode 11a and the second electrode 11b. There is no particular limitation as long as water and sulfur oxides contained in the test gas guided to the internal space 31 through the resistance portion 32 can be reduced and decomposed.

The gas sensor 140 further includes a power supply 61 and an ammeter 71. The power supply 61 and the ammeter 71 are connected to the ECU 130 described above.
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 130.
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), and outputs the measured value to the ECU 130. It is supposed to be.

  The ECU 130 can control the applied voltage Vm applied to the first electrode 11a and the second electrode 11b. That is, the power supply 61 and the ECU 130 constitute a voltage application unit. Further, the ECU 130 can receive a signal (first detection value) corresponding to the electrode current Im flowing through the first electrochemical cell 11 c output from the ammeter 71. That is, the ammeter 71 and the ECU 130 constitute an acquisition unit. In addition, the ECU 130 can execute an operation based on a first detection value difference described later. That is, the ECU 130 constitutes a control means.

  As will be described in detail later, in the first control device, the first electrochemical cell 11c is used as a sensor for determining (detecting) the presence or absence of sulfur oxide contained in the test gas. The electrochemical cell 11c may be referred to as a “sensor cell 11c”. That is, the first electrode 11a, the second electrode 11b, and the solid electrolyte body 11s constitute a sensor cell 11c.

(Function)
When the first predetermined voltage is applied 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 gas is included in the test gas. Not only the water that is contained, but also the sulfur oxides contained in the test gas are decomposed at the first electrode 11a. As a result, an electrode current Im resulting from the decomposition of water and sulfur oxide flows between the first electrode 11a and the second electrode 11b of the first electrochemical cell 11c. The acquisition unit acquires a first detection value corresponding to the electrode current Im.

  The first control device increases (boosts sweep) and decreases the voltage (first applied voltage Vm) applied between the first electrode 11a and the second electrode 11b in the first voltage band including the first predetermined voltage. (Step-down sweep) At this time, if sulfur oxide is contained in the test gas, a difference occurs in the electrode current Im (first detection value) between the boost sweep and the buck sweep. Therefore, the first control device is included in the test gas based on a value (first detection value difference) corresponding to the difference between the first detection value during the boost sweep and the first detection value during the step-down sweep. It is possible to accurately determine the presence or absence of sulfur oxide and execute an operation according to the result.

  The first voltage band is not limited to a specific voltage range as long as it includes the first predetermined voltage. For example, the first voltage band range during the step-up sweep and the first voltage band range during the step-down sweep. May be the same or different.

(Measurement principle)
Here, the relationship between the applied voltage Vm and the electrode current Im will be described more specifically. FIG. 3 shows that in the sensor cell 11c (single-cell limit current type gas sensor provided in the first control device), the applied voltage Vm is gradually lowered (step-down sweep) and then the applied voltage Vm is gradually lowered (step-down). It is a typical graph which shows the relationship between the applied voltage Vm and electrode current Im when it swept.

In this example, _two different kinds of test gases having concentrations of 0 and 300 ppm of sulfur dioxide (SO ₂ ) as sulfur oxide contained in the test gas were used. Furthermore, actual detection (measurement) is performed in a state where the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber 122 of the engine 110 is constant, so that oxygen contained in the test gas and The concentration of water was kept constant in any sample gas. In FIG. 3, the limiting current value of oxygen is displayed as 0 (zero) mA.

  First, the solid curve L1 shows the relationship between the applied voltage Vm and the electrode current Im 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 the water decomposition start voltage (about 0.6 V), the electrode current Im does not increase to 0 (zero) mA even when the applied voltage Vm increases, and is almost constant. Yes. In this region, the above-described limiting current characteristics of oxygen are manifested. When the applied voltage Vm is about 0.6 V or more, the electrode current Im starts to increase. This increase in the electrode current Im is caused by the start of water decomposition in the first electrode 11a. Thereafter, as indicated by the white arrow, as the applied voltage Vm rises to about 1.2 V (step-up sweep), the electrode current Im also increases.

  When the applied voltage Vm reaches about 1.2 V due to the step-up sweep, the step-down sweep is executed as indicated by the black arrow. Specifically, the applied voltage Vm is lowered to about 0.6 V (step-down sweep). Accordingly, the electrode current Im also decreases. When the applied voltage Vm becomes less than about 0.6 V again, the electrode current Im remains 0 (zero) mA and is almost constant even if the applied voltage Vm further decreases. As shown in FIG. 3, when the concentration of sulfur dioxide contained in the test gas is 0 (zero) ppm (solid line L1), the electrode current Im (open arrow) during the upward sweep and the step-down sweep No difference is observed between the electrode current Im (black arrow).

  On the other hand, a broken line L2 indicates the relationship between the applied voltage Vm and the electrode current Im when the concentration of sulfur dioxide contained in the test gas is 300 ppm. Also in this case, when the applied voltage Vm is less than about 0.6 V, the relationship between the applied voltage Vm and the electrode current Im is the curve L1 (the concentration of sulfur dioxide contained in the test gas is 0 (zero) ppm. Case). However, in the region where the applied voltage Vm is about 0.6 V or more (the voltage region where water decomposition occurs), the curve L1 in both the step-up sweep (open arrow) and the step-down sweep (black arrow). The electrode current Im is small as compared with the applied voltage Vm, and the increase rate of the electrode current Im with respect to the applied voltage Vm is also small compared with the curve L1 (the inclination is small). Further, in the dashed curve L2, the electrode current Im during the step-down sweep (black arrow) is lower than the electrode current Im during the step-up sweep (outlined arrow).

As described above, when sulfur dioxide is contained in the test gas, a difference is generated between the electrode current Im during the step-up sweep and the electrode current Im during the step-down sweep. For example, in the graph shown in FIG. 3, the difference between the electrode current Im during the step-up sweep and the electrode current Im during the step-down sweep when the applied voltage Vm is 1.0 V is the curve L1 (SO ₂ = 0 (zero). ) Ppm) is almost 0 (zero) mA, whereas the curve L2 (SO ₂ = 300 ppm) is about 0.1 mA. Thus, a value (first detection value difference) corresponding to the difference between the electrode current Im (corresponding to the first detection value) during the step-up sweep and the electrode current Im (corresponding to the first detection value) during the step-down sweep. ), It can be determined whether or not sulfur dioxide is contained in the test gas.

  The specific values of the applied voltage Vm shown on the horizontal axis of the graph shown in FIG. 3, the electrode current Im shown on the vertical axis, and the applied voltage Vm described in the above description are as follows. The value of the applied voltage Vm and the electrode current Im may vary depending on the conditions of the experiment conducted to obtain the graph shown in FIG. 3 (for example, the concentration of various components contained in the test gas). Is not always the above-mentioned value.

By the way, when sulfur oxide is contained in the test gas as described above, details of the mechanism in which the electrode current flowing between the first electrode 11a and the second electrode 11b is reduced in the step-up sweep and / or the step-down sweep. Is unknown. Furthermore, a first detection value (first boost) acquired when a boost sweep is being performed and the first applied voltage is a specific voltage at which water (H ₂ O) can be decomposed at the first electrode. Detection value) and a first detection value (first step-down detection value) acquired when the step-down sweep is being executed and the first applied voltage is the specific voltage. The details of are also unclear.

  However, as described above, the water decomposition start voltage is higher than the sulfur oxide decomposition start voltage. Therefore, when the first applied voltage is a specific voltage during the boost sweep, not only the water contained in the test gas but also the sulfur oxide contained in the test gas is decomposed. As a result, sulfur oxide decomposition products (for example, sulfur (S) and sulfur compounds) are adsorbed on the first electrode 11a, which is the cathode, and can contribute to the decomposition of water. Is thought to decrease. For this reason, when sulfur oxide is contained in the test gas, the first pressure increase detection value is considered to be smaller than when the test gas does not contain sulfur oxide.

  In addition, when the first applied voltage is a specific voltage during the step-down sweep, not only the water contained in the test gas but also the sulfur oxide contained in the test gas is decomposed. As a result, also at this time, the decomposition product of the sulfur oxide is further adsorbed on the first electrode 11a which is the cathode, and the decomposition product is deposited on the first electrode 11a, which can contribute to the decomposition of water. It is considered that the area of the first electrode 11a is further reduced. For this reason, it is considered that the first step-down detection value is smaller than the first step-up detection value, and a difference is generated between these first detection values.

  Note that if the lengths of the pressure-up sweep and the pressure-down sweep vary, it becomes difficult to accurately determine the presence or absence of sulfur oxide contained in the test gas based on the first detection value difference. That is, in order to accurately determine the presence or absence of sulfur oxide contained in the test gas based on the first detection value difference, a voltage capable of decomposing sulfur oxide in each of the step-up sweep and the step-down sweep. It is desirable that the length of the period applied between the first electrode 11a and the second electrode 11b is always the same (between individual detection opportunities).

  Furthermore, the first detection value acquired by the acquisition unit when the speed at which the voltage applied between the first electrode and the second electrode (first applied voltage) increases and decreases in the step-up sweep and the step-down sweep changes, respectively. Will also change. Accordingly, it is desirable that the speed at which the first applied voltage is increased and decreased, respectively, in the step-up sweep and the step-down sweep is also always the same (between individual detection opportunities). For this reason, the voltage application unit increases the first applied voltage over the first voltage band at a predetermined first step-up speed in the step-up sweep, and then performs the first application at the predetermined first step-down speed in the step-down sweep. The voltage is decreased over the first voltage band.

  The magnitudes of the first step-up speed and the first step-down speed are preferably determined so that the first detection value and its change can be detected easily and accurately in the step-up sweep and the step-down sweep, respectively. Specifically, the magnitudes of the first step-up speed and the first step-down speed are, for example, the accuracy and responsiveness of the control of the first applied voltage by the voltage application unit, and the response of the first detection value to the change in the first applied voltage. It can be determined as appropriate according to the characteristics and the accuracy and responsiveness of the detection of the first detection value by the acquisition unit. More specifically, in the apparatus of the present invention, an experiment for detecting the first detection value at various first step-up speeds and first step-down speeds can be performed, and the first detection value and its change can be detected easily and accurately. The magnitudes of the first step-up speed and the first step-down speed can be specified. However, the first step-up speed and the first step-down speed may be constant or may not be constant (that is, the first step-up speed and the first step-down speed may change during the sweep period). Furthermore, the first step-up speed and the first step-down speed may be the same or different.

(Specific operation)
Here, the sulfur oxide (SOx) detection routine executed in the first control device will be described more specifically. FIG. 4 is a flowchart showing an “SOx detection routine” executed by the ECU 130 as the control means using the element unit 10. The CPU 133 provided in the ECU 130 (hereinafter may be simply referred to as “CPU”) starts processing from step 400 at a predetermined timing, and proceeds to step 410.

  First, in step 410, the CPU determines whether or not there is a request (SOx detection request) for determining the presence or absence of sulfur oxide contained in the test gas. The SOx detection request is generated, for example, when a fuel tank is filled with fuel in a vehicle on which the engine 110 to which the first control device is applied is mounted. Further, when there is a history in which the SOx detection routine is executed after the fuel tank has been filled and the presence or absence of sulfur oxide contained in the test gas is determined, the SOx detection request is canceled. It may be.

  When it is determined in step 410 that there is a request for SOx detection (step 410: Yes), the CPU proceeds to the next step 420, and a condition (SOx detection) for determining the presence or absence of sulfur oxide contained in the test gas. It is determined whether (condition) is satisfied. At this time, specifically, the CPU determines that the operating state of the engine 110 is constant in the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber 122 of the engine 110 (here, the stoichiometric air-fuel ratio is constant). ) Is determined. More specifically, the CPU determines whether or not the engine 110 to which the first control device is applied is in a steady state. The CPU, for example, when the difference between the maximum value and the minimum value of the load on the engine 110 within a predetermined period is less than the threshold value, or the difference between the maximum value and the minimum value of the accelerator operation amount within the predetermined period is less than the threshold value. At some time, it is determined that the engine 110 is in a steady state.

  If it is determined in step 420 that the SOx detection condition is satisfied (step 420: Yes), the CPU proceeds to the next step 430 to execute the above-described step-up sweep and step-down sweep. In the first control device, a voltage in the range from 0.6V to 1.2V is defined as the first voltage band. This “0.6 V” corresponds to the water decomposition start voltage, and “1.2 V” is a predetermined voltage less than the lower limit voltage (about 2.0 V) in the limit current region of water. Then, the CPU executes step-up sweep and step-down sweep, and the electrode current Im when the applied voltage Vm is the specific voltage Vdet for detection (specifically, 1.0 V) in each of the step-up sweep and the step-down sweep. Are obtained as the first boost detection value (Iu) and the first buck detection value (Id), respectively. As described above, the specific voltage Vdet is a voltage at which water and sulfur oxide can be decomposed in the first electrode 11a. Next, the CPU proceeds to step 440, where a value (first detection value difference) corresponding to the difference between the first boost detection value (Iu) and the first buck detection value (Id) is a predetermined first threshold (TH1). It is determined whether it is above.

  As described above, in the first control apparatus, the difference (Iu) between the first boost detection value (Iu) and the first buck detection value (Id) when the applied voltage Vm is the specific voltage Vdet (1.0 V). -Id) was adopted as the first detection value difference. However, the first voltage step-up over a specific range of the voltage included in the first voltage band (the voltage range including the range of the applied voltage in which water and sulfur oxide included in the test gas are decomposed at the first electrode 11a). An integrated value of the difference between the detection value (Iu) and the first step-down detection value (Id) may be adopted as the first detection value difference. Such an integrated value is, for example, as an area surrounded by a curve indicating the transition of the electrode current Im with respect to the increase in the applied voltage Vm in the step-up sweep and a curve indicating the transition of the electrode current Im with respect to the decrease in the applied voltage Vm in the step-down sweep. Can be defined. The first detection value difference (ΔD1) as the integral value is, for example, the difference (Iu−Id) between the first boost detection value (Iu) and the first buck detection value (Id) in the first voltage band. It can be calculated by the following equation (1) that integrates over the whole.

  Incidentally, the first detection value difference is a value corresponding to the difference between the first step-up detection value (Iu) and the first step-down detection value (Id). Therefore, in the above, whether or not the difference (Iu−Id) between the first boost detection value (Iu) and the first buck detection value (Id) or the integral value (ΔD1) of the difference is equal to or greater than the first threshold value TH1. It was judged. However, based on the comparison between the threshold value and the ratio between the first boost detection value (Iu) and the first buck detection value (Id), it is determined whether or not the first detection value difference is greater than or equal to the first threshold TH1. May be. That is, the first detection value difference may be a difference between the first boost detection value (Iu) and the first buck detection value (Id), or may be a ratio thereof. In other words, the method for determining whether or not the first detection value difference is greater than or equal to the first threshold value TH1 is not particularly limited.

  On the other hand, the first threshold value TH1 is the magnitude of the first detected value difference that serves as a reference for determining whether or not the fuel supplied to the engine 110 contains a sulfur component equal to or higher than a predetermined content rate (first content rate). It is. Therefore, the specific value of the first threshold value TH1 is determined when, for example, a sulfur oxide having a concentration to be determined to contain the sulfur component in the fuel is included in the test gas by a preliminary experiment or the like. It can be determined as appropriate based on the magnitude of the obtained first detection value difference.

  For example, it is a problem whether the engine 110 is supplied with fuel that is so bad that it immediately causes problems such as deterioration and / or failure of components of the engine 110, poisoning of the exhaust purification catalyst and generation of white smoke in the exhaust. Is set to a relatively large value as the first content rate. In this case, the first threshold value TH1 is also set to a relatively large value. On the other hand, if the problem is whether or not fuel that is so bad as to cause problems such as those described above is being supplied to the engine 110, a relatively small value is set as the first content rate. To do. In this case, the first threshold value TH1 is also set to a relatively small value.

  By the way, even when a fuel having the same sulfur component content is used, if the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber 122 of the engine 110 is different, the fuel is burned. The amount of sulfur oxide generated is also different. As a result, the first detection values (first boost detection value Iu and first step-down detection value Id) acquired in step 430 and the first detection value difference (= Iu−Id) calculated in step 440 are also different. Therefore, a different value depending on the air-fuel ratio (A / F) of the air-fuel mixture may be adopted as the first threshold value TH1. In this case, the first threshold value TH1 is set to a smaller value as the air-fuel ratio (A / F) of the air-fuel mixture is larger (lean). Such a correspondence relationship between the air-fuel ratio (A / F) of the air-fuel mixture and the first threshold value TH1 is stored as electronic data such as a data map in the ROM 134 as a data storage device provided in the ECU 130, for example, and the execution of the routine is executed. Sometimes the CPU 133 can refer to it.

  When it is determined in step 440 that the first detection value difference (= Iu−Id) is greater than or equal to the predetermined first threshold value TH1 (step 440: Yes), the CPU proceeds to the next step 450 and is supplied to the engine 110. The specific operation corresponding to the determination that the fuel contains a sulfur component equal to or higher than the first content rate is executed.

  The above-mentioned “specific operation” means, for example, recording of information indicating that the fuel contains a sulfur component equal to or higher than the first content (for example, storing in a data storage device such as a backup RAM), and a warning indicating the same information. And control for recovering poisoning due to the sulfur component of the exhaust purification catalyst (see, for example, Japanese Patent Application Laid-Open No. 2012-57576 and Japanese Patent Application Laid-Open No. 2014-15921. The disclosure of this patent document is incorporated herein by reference) Etc.). In step 450 shown in FIG. 4, the CPU determines that the concentration of sulfur oxide (SOx concentration) contained in the test gas is equal to or higher than a predetermined value. Then, the CPU proceeds to step 470 and ends the routine. Thus, the 1st control apparatus can determine the presence or absence of the sulfur oxide contained in test gas with high precision, and can control the engine 110 according to the result.

  By the way, if it is determined in step 410 that there is no SOx detection request (step 410: No), and if it is determined in step 420 that the SOx detection condition is not satisfied (step 420: No), the CPU performs step Proceeding to 470, the routine ends. Furthermore, when it is determined in step 440 that the first detection value difference is less than the first threshold value TH1 (step 440: No), the CPU proceeds to the next step 460, where the fuel supplied to the engine 110 contains the first content. It is determined that the sulfur component is not included or more than the rate, or normal control is executed in the engine 110. In step 460 shown in FIG. 4, the CPU determines that the concentration of sulfur oxide (SOx concentration) contained in the test gas is less than a predetermined value. Then, the CPU proceeds to step 470 and ends the routine.

  As described above, the first control device executes the SOx detection routine to accurately determine the presence or absence of sulfur oxide contained in the test gas, and to control the engine 110 according to the result. Can do. A program for causing the CPU to execute the SOx detection routine can be stored in, for example, a data storage device (eg, ROM 134) provided in the ECU 130.

  By the way, as described above, when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is kept constant, for example, when the internal combustion engine is in a steady operation, the first control device performs the pressure increase sweep and the pressure decrease sweep. To determine whether the first detection value difference (= Iu−Id) is equal to or greater than a predetermined first threshold value TH1. However, the control means may execute control to positively keep the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber constant when executing the pressure increase sweep and the pressure decrease sweep.

Second Embodiment
Hereinafter, a control device for an internal combustion engine according to a second embodiment of the present invention (hereinafter sometimes referred to as a “second control device”) will be described with reference to FIG.

(Constitution)
The element unit 20 included in the gas detection unit 140 included in the internal combustion engine to which the second control device is applied is a second unit disposed on the upstream side (the diffusion resistance unit 32 side) of the first electrochemical cell (pumping cell 11c). An electrochemical cell (pumping cell 12c) is further provided. Except for this point, the element unit 20 has the same configuration as the element unit 10 included in the gas detection unit 140 provided in the internal combustion engine to which the first control device is applied. Therefore, in the following description, the configuration of the second control device will be described by paying attention to differences from the first control device.

  As shown in FIG. 5, in the element portion 20, a second solid electrolyte body 12s is disposed instead of the first alumina layer 21a in the element portion 10 shown in FIG. The second atmosphere introduction path 52 is defined by the sixth alumina layer 21f and the first alumina layer 21a laminated on the side). The second atmosphere introduction path 52 corresponds to a second separate space. The second solid electrolyte body 12s is also a thin plate body that contains zirconia or the like and has oxide ion conductivity. The zirconia forming the second solid electrolyte body 12s may contain elements such as scandium (Sc) and yttrium (Y), for example. The sixth alumina layer 21f is a dense (gas impermeable) layer (thin plate) containing alumina.

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

  The second electrochemical cell 12c is disposed on the upstream side (the diffused resistor 32 side) of the first electrochemical cell 11c. More specifically, the third electrode 12a is disposed so as to face the internal space 31 at a position closer to the diffusion resistance portion 32 than the first electrode 11a. The third electrode 12a and the fourth electrode 12b are porous cermet electrodes containing platinum (Pt) as a main component. That is, the third electrode 12a decomposes oxygen and discharges it from the internal space when a second predetermined voltage is applied between the third electrode 12a and the fourth electrode 12b, but decomposes sulfur oxide. It is configured not to be able to.

  The power source 62 applies an applied 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 ammeter 72 outputs a signal corresponding to the electrode current flowing through the second electrochemical cell 12c to the ECU (not shown). The ECU can control the applied voltage applied to the third electrode 12a and the fourth electrode 12b. That is, the power source 62 and the ECU constitute a voltage application unit. Further, the ECU can receive a signal corresponding to the electrode current flowing through the second electrochemical cell 12 c output from the ammeter 72. That is, the ammeter 72 and the ECU constitute an acquisition unit.

(Function)
As described above, for example, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is large (lean) when performing the above-described pressure-up and pressure-down sweeps, the test gas The concentration of oxygen contained in the exhaust gas is also high. Therefore, the higher the air-fuel ratio of the air-fuel mixture (the leaner it is), the greater the limit current value of oxygen, so the first detection value also increases. As a result, compared with the case where the air-fuel ratio of the air-fuel mixture is small (rich) and the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio (stoichiometric), The value corresponding to the difference between the first detection values (first detection value difference) is relatively small with respect to the first detection value. That is, since the signal-to-noise ratio (S / N ratio) of the first detection value difference is lowered, there is a possibility that the detection accuracy of the sulfur oxide contained in the test gas is lowered.

  However, in the element part 20, when a predetermined voltage is applied between the third electrode 12a and the fourth electrode 12b, oxygen can be discharged from the internal space 31 by an oxygen pumping action. More specifically, when a voltage is applied between these electrodes so that the third electrode 12a and the fourth electrode 12b become a cathode and an anode, respectively, oxygen is discharged from the internal space 31 to the second atmosphere introduction path 52. Is done. Thus, in the element part 20, the density | concentration of oxygen in the internal space 31 can be adjusted to less than predetermined concentration with the 2nd electrochemical cell (pumping cell) 12c.

  That is, in the element unit 20, even if the concentration of oxygen contained in the test gas changes, oxygen is supplied from the internal space 31 by the oxygen pumping action of the second electrochemical cell (pumping cell) 12c as described above. By discharging, the concentration of oxygen in the internal space 31 can be adjusted low (typically, approximately 0 (zero) ppm). Therefore, when the CPU of the second control device executes the boosting sweep and the bucking sweep (in other words, when acquiring the first boosting detection value and the first bucking detection value), the third electrode 12a and the fourth electrode 12b A second predetermined voltage (a voltage that is equal to or higher than the oxygen decomposition start voltage and lower than the water decomposition start voltage) is applied. Therefore, even if the concentration of oxygen contained in the test gas changes, the second control device supplies the electrode current Im (first detection value) detected in the first electrochemical cell (pumping cell) 11c. The influence can be effectively reduced. As a result, according to the second control device, the presence or absence of sulfur oxide contained in the test gas can be determined with higher accuracy.

  In the example shown in FIG. 5, the second electrochemical cell (pumping cell 12c) includes a second solid electrolyte body 12s separate from the solid electrolyte body 11s constituting the first electrochemical cell (pumping cell 11c). . However, the second electrochemical cell (pumping cell 12c) may share the solid electrolyte body 11s with the first electrochemical cell (pumping cell 11c). In this case, the first atmosphere introduction path 51 functions as a first separate space and a second separate space.

(Modification)
By the way, as described above, at least one of the above-described first electrochemical cell and second electrochemical cell (when the element unit is provided) can be used as an air-fuel ratio sensor. In this case, the applied voltage in at least one of the electrochemical cells is set to a voltage (fourth predetermined voltage) corresponding to the limiting current region of oxygen. Based on the detection value corresponding to the electrode current at that time, the concentration of oxygen contained in the exhaust gas of the internal combustion engine as the test gas is detected. Based on the oxygen concentration in the exhaust gas thus detected, the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine can be detected.

  In this case, in order to detect the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine based on the detection value acquired in at least one of the electrochemical cells, as described above, the electrochemical cell has an oxygen limit. It is necessary to apply an applied voltage (for example, 0.4 V) corresponding to the current region. Therefore, basically, it is desirable that the CPU of the modified example detects the air-fuel ratio when the SOx detection routine is not executed. However, when the element portion includes the second electrochemical cell and an applied voltage corresponding to the limiting current region of oxygen is applied in the second electrochemical cell, the SOx detection routine by the device of the present invention is executed. Even at times, the air-fuel ratio of the air-fuel mixture can be detected.

  In any case, for example, the detected value (for example, the magnitude of the electrode current) and the mixing in the combustion chamber when the applied voltage is a predetermined voltage (fourth predetermined voltage) corresponding to the limiting current region of oxygen. A correspondence relationship with the air-fuel ratio of the air is obtained in advance by a preliminary experiment or the like. A data table (for example, a data map or the like) representing this correspondence can be stored in a data storage device (for example, a ROM) provided in the ECU, and can be referred to by the CPU at the time of the detection. Thereby, the air-fuel ratio of the air-fuel mixture can be specified from the detected value. Alternatively, the oxygen concentration in the test gas is once obtained from the detected value, and the correspondence relationship between the oxygen concentration in the test gas and the air-fuel ratio of the air-fuel mixture is referred to from the oxygen concentration in the test gas. The air-fuel ratio of the air-fuel mixture may be specified.

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

  DESCRIPTION OF SYMBOLS 10 and 20 ... Element part, 11a and 12a ... Electrode (cathode), 11b and 12b ... Electrode (anode), 11s and 12s ... 1st and 2nd solid electrolyte body, 11c and 12c ... Pumping cell (1st electrochemical cell) And the second electrochemical cell), 21a, 21b, 21c, 21d, 21e, and 21f ... first to sixth alumina layers, 31 ... internal space, 32 ... diffusion resistor, 41 ... heater, 51 and 52 ... first and Second atmosphere introduction path, 61 and 62 ... power source, 71 and 72 ... ammeter, 110 ... engine, 112 ... intake port, 113 ... exhaust port, 121 ... intake pipe, 122 ... combustion chamber, 123 ... exhaust pipe, 124 ... Intake valve, 125 ... exhaust valve, 126 ... fuel injection valve, 130 ... ECU, 133 ... CPU, 134 ... ROM, 135 ... RAM, 140 ... gas sensor, 141 ... air flow meter , As well as 143 ... crank angle sensor.

Claims (9)

A first electrochemical cell including a solid electrolyte body having oxide ion conductivity and a first electrode and a second electrode respectively formed on the surface of the solid electrolyte body; a dense body; and a diffusion resistance section. The exhaust gas of the internal combustion engine as the test gas is introduced into the internal space defined by the solid electrolyte body, the dense body, and the diffusion resistance portion via the diffusion resistance portion, and the first electrode is connected to the internal space. And an element portion configured to be exposed to a first separate space that is a space different from the internal space and the second electrode is exposed to
A voltage applying unit that applies a voltage between the first electrode and the second electrode;
An acquisition unit for acquiring a first detection value corresponding to a current flowing between the first electrode and the second electrode;
Applied to an internal combustion engine comprising a gas detection means having a control means,
A control device for an internal combustion engine,
The first electrode contains water (H ₂ O) and sulfur oxide (SOx) contained in the test gas when a first predetermined voltage is applied between the first electrode and the second electrode. Configured to be disassembled,
The voltage applying unit applies a first applied voltage, which is a voltage applied between the first electrode and the second electrode, in a first voltage band that is a voltage range including the first predetermined voltage. After the step-up sweep for increasing at the first step-up speed is executed, the step-down sweep for decreasing the first applied voltage at the predetermined first step-down speed in the first voltage band is executed.
In the state where the air-fuel ratio (A / F) of the air-fuel mixture supplied to the combustion chamber of the internal combustion engine is constant, the control means is executing the boost sweep and the first applied voltage is A first boost detection value that is the first detection value acquired by the acquisition unit when water (H ₂ O) is a specific voltage that can be decomposed at the first electrode, and the step-down sweep is being executed. And a first detection value difference that is a value corresponding to a difference from the first step-down detection value that is the first detection value acquired by the acquisition unit when the first applied voltage is the specific voltage is predetermined. When the fuel is supplied to the internal combustion engine, the specific operation corresponding to the determination that the sulfur component is equal to or higher than the first content rate is executed.
Configured as
Control device for internal combustion engine. The control apparatus for an internal combustion engine according to claim 1,
The voltage application unit is configured to execute the step-up sweep and the step-down sweep with a lower limit of the first voltage band set to 0.6V.
Control device for internal combustion engine. The control device for an internal combustion engine according to claim 1 or 2,
The voltage application unit is configured to execute the step-up sweep and the step-down sweep, with the upper limit of the first voltage band being a predetermined voltage less than the lower limit voltage of the limit current range of water.
Control device for internal combustion engine. The control device for an internal combustion engine according to any one of claims 1 to 3,
The acquisition unit is configured to acquire a magnitude of a current flowing between the first electrode and the second electrode as the first detection value.
Control device for internal combustion engine. The control device for an internal combustion engine according to any one of claims 1 to 4,
The first electrode includes at least one selected from the group consisting of platinum (Pt), rhodium (Rh), and palladium (Pd).
Control device for internal combustion engine. A control device for an internal combustion engine according to any one of claims 1 to 5,
The element portion further includes a second electrochemical cell including a solid electrolyte body separate from the solid electrolyte body or the solid electrolyte body and a third electrode and a fourth electrode formed on the surface of the solid electrolyte body, respectively. And the third electrode is exposed to the internal space and the fourth electrode is exposed to a second separate space that is a space different from the internal space. The third electrode is formed from the first electrode. Is formed at a position close to the diffused resistor portion,
The third electrode can discharge oxygen (O ₂ ) from the internal space when a second predetermined voltage is applied between the third electrode and the fourth electrode, and sulfur oxide ( SOx) is configured to be impossible to decompose,
The voltage application unit is configured to apply the second predetermined voltage between the third electrode and the fourth electrode,
The control means applies the second predetermined voltage between the third electrode and the fourth electrode in the second electrochemical cell when the voltage application unit performs the step-up sweep and the step-down sweep. Configured to adjust the concentration of oxygen in the internal space below a predetermined concentration,
Control device for internal combustion engine. The control apparatus for an internal combustion engine according to claim 6,
The voltage application unit is configured to apply a predetermined voltage that is equal to or higher than an oxygen decomposition start voltage and lower than a water decomposition start voltage as the second predetermined voltage.
Control device for internal combustion engine. A control device for an internal combustion engine according to any one of claims 1 to 7,
The voltage application unit has a predetermined range corresponding to a limiting current region of oxygen in the first electrode pair including the first electrode and the second electrode during a period in which neither the step-up sweep nor the step-down sweep is performed. Configured to apply a fourth predetermined voltage, which is a voltage;
The control means is configured to determine the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine based on the first detection value acquired by the acquisition unit when the fourth predetermined voltage is applied to the first electrode pair. Configured to detect (A / F),
Control device for internal combustion engine. A control device for an internal combustion engine according to claim 6 or 7,
The voltage application unit is configured to apply a fourth predetermined voltage, which is a predetermined voltage corresponding to a limiting current region of oxygen, to the second electrode pair including the third electrode and the fourth electrode,
The acquisition unit is configured to acquire a second detection value corresponding to a current flowing between the third electrode and the fourth electrode,
The control means is based on the second detection value acquired by the acquisition unit when the fourth predetermined voltage is applied to the second electrode pair, and the air-fuel ratio of the air-fuel mixture in the combustion chamber of the internal combustion engine Configured to detect (A / F),
Control device for internal combustion engine.

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