JP5969433B2 - SOx concentration detection device for internal combustion engine - Google Patents

Description

The present invention relates to an SOx concentration detection device for an internal combustion engine.

A sensor for measuring the relative amount of oxygen-containing gas in a gas mixture is described in US Pat. This sensor has two pump cells. These pump cells are arranged in series. In this sensor, by applying a low voltage to the upstream pump cell, part of the oxygen-containing gas (especially O ₂ ) in the gas mixture is eliminated, and by applying a high voltage to the downstream pump sensor. , The relative amounts of the remaining oxygenated gases (especially H ₂ O and CO ₂ ) in the gas mixture are measured.

JP-A-2-122255 JP 2002-349250 A JP 2008-255952 A JP 7-27738 A JP-A-11-230931 JP 2009-244279 A

By the way, a limit current type sensor is known. In this sensor, when detecting the SOx concentration in the exhaust gas discharged from the internal combustion engine , a certain voltage is generally applied. However, in the application method of such voltage, the easier the SOx concentration that can not be accurately detected.

However, the inventors' research has revealed that the SOx concentration that could not be detected with high accuracy can be detected with high accuracy by using the limiting current type of sensor, if the method of applying a voltage to the limiting current type sensor is elaborated. .

Based on the knowledge of the inventors of the present application, an object of the present invention is to detect the SOx concentration in the exhaust discharged from the internal combustion engine with a limit current sensor with high accuracy.

One invention of the present application relates to an SOx concentration detection device for an internal combustion engine having a limiting current type sensor capable of detecting an oxygen concentration in exhaust gas. The SOx concentration detection device according to the present invention provides an output current (hereinafter simply referred to as “output current”) output from the sensor while a voltage applied to the sensor (hereinafter simply referred to as “application voltage”) is lowered from a predetermined voltage. ) To detect the SOx concentration in the exhaust gas, and to detect the oxygen concentration in the exhaust gas using the output current of the sensor when a voltage lower than the predetermined voltage is applied to the sensor Have Further, the output current for detecting the SOx concentration is changed when the absolute value of the output current increases while the voltage applied to the sensor is decreased from the predetermined voltage. This is a current that is opposite to the direction of change of the output current when the absolute value of the output current increases while the voltage applied to is increased to the predetermined voltage.

According to this, the SOx concentration can be detected using a sensor that can be used for detecting the oxygen concentration in the exhaust gas. In particular, the influence of SOx on the output current when the applied voltage is maintained at a constant voltage, or the influence of SOx on the output current when the applied voltage is increased is another component of the output current. If the influence of SOx on the output current while the applied voltage is reduced from the predetermined voltage is large compared to the influence of other components on the output current, The SOx concentration can be detected with high accuracy using a sensor that can be used to detect the oxygen concentration in the inside.

The detection unit preferably uses a peak value of the output current while the applied voltage is lowered from the predetermined voltage as the output current for detecting the SOx concentration. The peak value is the smallest output current (or the largest output current) among the output currents when the applied voltage is decreasing. Therefore, it can be said that the peak value is an output current that accurately corresponds to the SOx concentration. Therefore, the SOx concentration can be detected with higher accuracy by using the peak value as the output current for detecting the SOx concentration.

Further, the detection unit applies a voltage lower than the predetermined voltage before applying the predetermined voltage, increases the applied voltage to the predetermined voltage, and then decreases the applied voltage from the predetermined voltage. The output current between them may be used as the output current for detecting the SOx concentration. In this case, the voltage applied to the sensor before the start of the decrease in the applied voltage is lower than the predetermined voltage. For this reason, compared with the case where the voltage to be applied to the sensor before the start of the decrease in the applied voltage is the predetermined voltage, the power consumed for the SOx concentration detection can be reduced.

The predetermined voltage is preferably 0.8 V or more. According to this, it is possible to obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

Moreover, it is preferable that the applied voltage at the end of the decrease in the applied voltage from the predetermined voltage is a voltage of 0.7 V or less. According to this, it is possible to obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

Further, the detecting unit, the applied voltage at a rate less rate of 100Hz the voltage change may be Unishi by Ru lowers from the predetermined voltage. According to this, it is possible to reliably obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

In addition, the detection unit applies a voltage lower than the predetermined voltage at a speed equal to or lower than a voltage change rate of 100 Hz, and then increases the applied voltage to the predetermined voltage, and then decreases the applied voltage from the predetermined voltage. it may be by Ru to Unishi. According to this, it is possible to reliably obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

The internal combustion engine is, for example, a gasoline engine. The gasoline engine is operated at a stoichiometric air-fuel ratio in most engine operating ranges. Thus, the low oxygen concentration in the exhaust. For this reason, it is easy to detect the SOx concentration .

Further, the detection unit lowers the applied voltage to the sensor from the predetermined voltage, and then uses the output current of the sensor when a voltage lower than the predetermined voltage is applied to the sensor to exhaust the exhaust . It is also possible to detect the oxygen concentration. According to this, the oxygen concentration and SOx concentration in the exhaust gas can be detected by one sensor.

The detection unit may detect an oxygen concentration in the exhaust gas using an output current of the sensor while a voltage lower than the predetermined voltage is applied before the predetermined voltage is applied. According to this, the oxygen concentration and SOx concentration in the exhaust gas can be detected by one sensor.

In addition, the SOx concentration detection device is configured to detect S when the absolute value of the output current output from the sensor is lower than or equal to the first predetermined value while the applied voltage to the sensor is decreased from the predetermined voltage. You may further have a control part which performs poison recovery control. According to this, the SOx concentration is detected only when there is no possibility that the detection accuracy of the sensor is reduced due to S poisoning. For this reason, the SOx concentration can be detected with higher accuracy.

Further, the SOx concentration detecting device is configured to detect the internal combustion engine when the absolute value of the output current output from the sensor is lower than or equal to a second predetermined value while the applied voltage to the sensor is decreased from the predetermined voltage. There may be further provided a control unit that warns of abnormalities in the properties of the fuel supplied to the combustion chamber. According to this, when there is a possibility that the fuel property is abnormal, the user of the SOx concentration detection device can know that the fuel property may be abnormal.

Another invention of the present application relates to a method for detecting SOx concentration in an internal combustion engine having a limiting current type sensor capable of detecting oxygen concentration in exhaust gas. In this method, a voltage reduction step for reducing the voltage applied to the sensor from a predetermined voltage, and an output current output from the sensor while the voltage applied to the sensor is reduced in the voltage reduction step . An output current acquisition step to be acquired; and a SOx concentration detection step of detecting the SOx concentration in the exhaust gas using the output current acquired in the output current acquisition step.

According to this, the SOx concentration can be detected using a sensor that can be used for detecting the oxygen concentration in the exhaust gas. In particular, the influence of SOx on the output current when the applied voltage is maintained at a constant voltage, or the influence of SOx on the output current when the applied voltage is increased is another component of the output current. If the influence of SOx on the output current while the applied voltage is reduced from the predetermined voltage is large compared to the influence of other components on the output current, The SOx concentration can be detected with high accuracy using a sensor that can be used to detect the oxygen concentration in the inside.

In the output current acquisition step, it is preferable to acquire a peak value of the output current of the sensor. The peak value is the smallest output current (or the largest output current) among the output currents when the applied voltage is decreasing. Therefore, it can be said that the peak value is an output current that accurately corresponds to the SOx concentration . Thus, by using the peak value as output current for SOx concentration detection can be more accurately detected SOx concentration.

Further, the above method is a voltage increasing step in which a voltage lower than the predetermined voltage is applied before the predetermined voltage is applied, and the applied voltage is increased to the predetermined voltage, and is executed before the voltage decreasing step. The step of increasing the voltage may be further included. In this case, the voltage applied to the sensor before the start of the decrease in the applied voltage is lower than the predetermined voltage. For this reason, compared with the case where the voltage applied to the sensor before the start of the decrease in applied voltage is the predetermined voltage, the power consumed for SOx concentration detection can be reduced.

Moreover, in the said method, it is preferable in the said predetermined voltage being a voltage more than 0.8V. According to this, it is possible to obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

In the voltage drop step, it is preferable that the applied voltage at the end of the drop of the applied voltage from the predetermined voltage is a voltage of 0.7 V or less. According to this, it is possible to obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

Also, preferably the applied voltage at a rate less rate of 100Hz voltage change in the voltage drop step Ru lowers from the predetermined voltage. According to this, it is possible to reliably obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

Also, preferably the applied voltage at a rate less rate of 100Hz voltage change in the voltage increase step Ru is increased to the predetermined voltage. According to this, you are possible to reliably obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to accurately detect the concentration of SOx.

The internal combustion engine in which the above method is executed is, for example, a gasoline engine. The gasoline engine is operated at a stoichiometric air-fuel ratio in most engine operating ranges. Thus, the low oxygen concentration in the exhaust. For this reason, it is easy to detect the SOx concentration .

In addition, it is preferable that the limit current sensor of the present invention is used with the predetermined voltage set to a voltage of 0.8 V or more. According to this, it is possible to obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to provide a limiting current type sensor for accurately detecting the concentration of SOx.

Moreover, it is preferable that the voltage when the voltage is lowered from the predetermined voltage is set to a voltage of 0.7 V or less and the limiting current sensor of the present invention is used. According to this, it is possible to obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to provide a limiting current type sensor for accurately detecting the concentration of SOx.

Also, limiting current type sensor of the present invention the rate of voltage change is set to a speed hereinafter the 100Hz voltage change when decreasing the applied voltage from said predetermined voltage is preferably used. According to this, it is possible to reliably obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to provide a limiting current type sensor for accurately detecting the concentration of SOx.

Also, the speed hereinafter voltage change rate is 100Hz voltage change when decreasing the applied voltage after the predetermined voltage from the voltage lower than increasing the applied voltage to the predetermined voltage from said predetermined voltage It is preferable that the limiting current type sensor of the present invention is used after being set. According to this, it is possible to reliably obtain an output current accurately corresponding to the SOx concentration, and thus, it is possible to provide a limiting current type sensor for accurately detecting the concentration of SOx.

Further, the limiting current type sensor of the present invention may be used for detecting the SOx concentration when the internal combustion engine is a gasoline engine. The gasoline engine is operated at a stoichiometric air-fuel ratio in most engine operating ranges. Thus, the low oxygen concentration in exhaust. Therefore, it is possible to provide a limiting current type sensor that can easily detect the SOx concentration .

FIG. 1 shows one embodiment of the limiting current type sensor of the present invention (two-cell type limiting current type sensor). FIG. 2 shows the output characteristics of the limiting current type sensor of FIG. FIG. 3 shows the output characteristics of the limiting current type sensor of FIG. FIG. 4 shows the relationship between the SOx concentration and the peak value of the output current. FIG. 5 shows another embodiment of the limiting current type sensor of the present invention (one cell type limiting current type sensor). FIG. 6 shows the output characteristics of the limiting current type sensor of FIG. FIG. 7 shows an internal combustion engine equipped with a SOx concentration detection device having the limiting current type sensor of FIG. 1 or FIG. FIG. 8 is a time chart showing an output current corresponding to a change in applied voltage in the first embodiment. FIG. 9 shows the form of increase and decrease in applied voltage. FIG. 10A shows an example of a circuit adopted in the limit current type sensor of FIG. 1, and FIG. 10B shows an example of a circuit adopted in the limit current type sensor of FIG. FIG. 11 shows an example of an embodiment of the SOx concentration detection flow of the first embodiment. FIG. 12 shows an example of the SOx concentration detection flow of the second embodiment. FIG. 13 shows an example of the SOx concentration detection flow of the third embodiment. FIG. 14 shows an example of the SOx concentration / air-fuel ratio detection flow of the fourth embodiment.

An embodiment of a limiting current type sensor for detecting SOx concentration according to the present invention with reference to the drawings, and a concentration of sulfur oxide (hereinafter referred to as “SOx”) in exhaust discharged from an internal combustion engine having the limiting current type sensor An embodiment of a SOx concentration detection device for detecting the above will be described .

<Configuration of 2-cell type limiting current sensor>
FIG. 1 shows one of the limiting current type sensors according to the first embodiment of the present invention. The limiting current type sensor of FIG. 1 is a two-cell type limiting current type sensor. In FIG. 1, 10 is a limiting current sensor, 11A is a first solid electrolyte layer, 11B is a second solid electrolyte layer, 12A is a first alumina layer, 12B is a second alumina layer, 12C is a third alumina layer, and 12D is 4th alumina layer, 12E is 5th alumina layer, 12F is 6th alumina layer, 13 is diffusion control layer, 14 is heater, 15 is pump cell, 15A is 1st pump electrode, 15B is 2nd pump electrode, 15C is pump cell Voltage source, 16 is a sensor cell, 16A is a first sensor electrode, 16B is a second sensor electrode, 16C is a sensor cell voltage source, 17A is a first atmosphere introduction path, 17B is a second atmosphere introduction path, and 18 is an internal space. ing.

  The solid electrolyte layers 11A and 11B are layers made of zirconia or the like and have oxygen ion conductivity. The alumina layers 12A to 12F are layers made of alumina. The diffusion control layer 13 is a porous layer and can pass exhaust gas. In the sensor 10, the layers are arranged in the order from the bottom in FIG. 1 to the sixth alumina layer 12F, the fifth alumina layer 12E, the fourth alumina layer 12D, the second solid electrolyte layer 11B, the diffusion rate controlling layer 13 and the third alumina layer 12C, The first solid electrolyte layer 11A, the second alumina layer 12B, and the first alumina layer 12A are stacked in this order. The heater 14 is disposed between the fifth alumina layer 12E and the sixth alumina layer 12F.

The first atmosphere introduction path 17A is a space formed by the first alumina layer 12A, the second alumina layer 12B, and the first solid electrolyte layer 11A, and a part thereof is open to the atmosphere. The second atmosphere introduction path 17B is a space formed by the second solid electrolyte layer 11B, the fourth alumina layer 12D, and the fifth alumina layer 12E, and a part thereof is open to the atmosphere. The internal space 18 is a space formed by the first solid electrolyte layer 11 </ b> A, the second solid electrolyte layer 11 </ b > B , the diffusion rate limiting layer 13, and the third alumina layer 12 </ b> C. It communicates with the outside.

<Configuration of pump cell>
The first pump electrode 15A and the second pump electrode 15B are electrodes made of a platinum group element such as platinum or rhodium or an alloy thereof. The first pump electrode 15A is disposed on the wall surface on one side of the second solid electrolyte layer 11B (that is, the wall surface of the second solid electrolyte layer 11B that forms the internal space 18), and the second pump electrode 15B includes the second pump electrode 15B. It is arranged on the wall surface on the other side of the solid electrolyte layer 11B (that is, the wall surface of the second solid electrolyte layer 11B that forms the second atmosphere introduction path 17B). The electrodes 15A and 15B and the second solid electrolyte layer 11B constitute a pump cell 15. The sensor 10 is configured to be able to apply a voltage from the pump cell voltage source 15C to the pump cell 15 (specifically, between the first pump electrode 15A and the second pump electrode 15B). The first pump electrode 15A is a cathode side electrode, and the second pump electrode 15B is an anode side electrode.

<Pump cell function>
When a voltage is applied to the pump cell 15, when oxygen in the internal space 18 comes into contact with the first pump electrode 15A, this oxygen becomes oxygen ions on the first pump electrode 15A, and these oxygen ions become the second solid electrolyte. The inside of the layer 11B moves toward the second pump electrode 15B. At this time, a current proportional to the amount of oxygen ions moved through the second solid electrolyte layer 11B flows between the first pump electrode 15A and the second pump electrode 15B. When oxygen ions reach the second pump electrode 15B, the oxygen ions become oxygen at the second pump electrode 15B and are released to the second atmosphere introduction path 17B. That is, the pump cell 15 can release oxygen in the exhaust gas from the exhaust gas to the atmosphere by pumping, and reduce the oxygen concentration in the exhaust gas. The pumping capacity of the pump cell 15 is higher as the voltage applied to the pump cell 15 from the pump cell voltage source 15C is higher.

<Configuration of sensor cell>
The first sensor electrode 16A and the second sensor electrode 16B are electrodes made of a platinum group element such as platinum or rhodium or an alloy thereof. The first sensor electrode 16A is arranged on the wall surface on one side of the first solid electrolyte layer 11A (that is, the wall surface of the first solid electrolyte layer 11A forming the internal space 18), and the second sensor electrode 16B is the first sensor electrode 16B. It is arranged on the wall surface on the other side of the solid electrolyte layer 11A (that is, the wall surface of the first solid electrolyte layer 11A forming the first air introduction path 17A). The electrodes 16A and 16B and the first solid electrolyte layer 11A constitute a sensor cell 16. The sensor 10 is configured to be able to apply a voltage from the sensor cell voltage source 16C to the sensor cell 16 (specifically, between the first sensor electrode 16A and the second sensor electrode 16B). The first sensor electrode 16A is a cathode side electrode, and the second sensor electrode 16B is an anode side electrode.

<Function of sensor cell>
When a voltage is applied to the sensor cell 16, when SOx in the internal space 18 comes into contact with the first sensor electrode 16A, the SOx is decomposed on the first sensor electrode 16A, and the oxygen of SOx becomes oxygen ions. Oxygen ions move inside the first solid electrolyte layer 11A toward the second sensor electrode 16B. At this time, a current proportional to the amount of oxygen ions moved through the first solid electrolyte layer 11A flows between the first sensor electrode 16A and the second sensor electrode 16B. When oxygen ions reach the second sensor electrode 16B, the oxygen ions become oxygen at the second sensor electrode 16B and are released to the first atmosphere introduction path 17A.

<Air-fuel ratio detection function 1 of 2-cell type limit current sensor>
FIG. 2 shows the relationship between the pump cell applied voltage and the pump cell output current in the two-cell limit current sensor of the first embodiment. The pump cell applied voltage is a voltage applied to the pump cell 15 by the pump cell voltage source 15C, and the pump cell output current is a current flowing between the first pump electrode 15A and the second pump electrode 15B. In FIG. 2, a line indicated by A / F = 12 indicates a change in output current with respect to a change in pump cell applied voltage when the air-fuel ratio of the exhaust gas is 12. Similarly, A / F The lines indicated by = 13 to A / F = 18 indicate changes in the output current with respect to changes in the pump cell applied voltage when the air-fuel ratio of the exhaust gas is 13 to 18, respectively.

  As shown in FIG. 2, for example, when the air-fuel ratio of exhaust is 18, when the pump cell output voltage is a negative value within a range where the pump cell applied voltage is smaller than a certain value Vth, the pump cell applied voltage Is higher, the absolute value of the pump cell output current is smaller. When the pump cell output current is a positive value, the higher the pump cell applied voltage is, the larger the absolute value of the pump cell output current is. Further, in a certain range where the pump cell applied voltage is equal to or greater than the certain value Vth, the pump cell output current becomes a constant value regardless of the pump cell applied voltage.

  The relationship between the pump cell applied voltage and the pump cell output current is similarly established when the air-fuel ratio of the exhaust gas is 12-17. As can be seen from FIG. 2, if the pump cell output current is applied to the pump cell 15 at all air-fuel ratios to be detected, the pump cell output detected at that time is constant. The air-fuel ratio of the exhaust can be detected based on the current. That is, the two-cell type limiting current sensor 10 of the first embodiment can be used for detecting the air-fuel ratio of the exhaust gas. Since the air-fuel ratio of the exhaust gas is a parameter having a correlation with the oxygen concentration in the exhaust gas, in principle, the two-cell type limiting current type sensor of the first embodiment determines the oxygen concentration in the exhaust gas. It can be said that it can be detected.

<Air-fuel ratio detection function 2 of 2-cell type limit current type sensor>
Further, the relationship between the sensor cell applied voltage and the sensor cell output current in the two-cell type limiting current type sensor of the first embodiment is also the same as the relationship shown in FIG. Therefore, the voltage at which the sensor cell output current is constant regardless of the sensor cell applied voltage in all the air-fuel ratios to be detected in a state where the pump cell applied voltage is zero (that is, the pump cell 15 is not functioning). 16, the air-fuel ratio of the exhaust can be detected based on the sensor cell output current detected at that time. That is, the two-cell type limiting current sensor 10 of the first embodiment can be used for detecting the air-fuel ratio of the exhaust gas. The sensor cell applied voltage is a voltage applied to the sensor cell 16 by the sensor cell voltage source 16C, and the sensor cell output current is a current flowing between the first sensor electrode 16A and the second sensor electrode 16B.

<Output characteristics of 2-cell type limiting current sensor>
By the way, according to the research of the inventors of the present application, by reducing the applied voltage to the two-cell type limit current type sensor (specifically, the applied voltage from the sensor cell voltage source 16C to the sensor cell 16) from a predetermined voltage, It was newly found that a current corresponding to the SOx concentration in the exhaust gas can be obtained from this limiting current sensor. Next, this will be described. In the following description, the output current is a current output from the sensor cell 16.

  FIG. 3 shows a change in output current when the applied voltage is gradually increased from 0.1 V to 1.0 V and then gradually decreased from 1.0 V to 0.1 V. The horizontal axis in FIG. 3 is the applied voltage, and the vertical axis in FIG. 3 is the output current. While the applied voltage is changed in this way, a voltage that makes the oxygen concentration in the exhaust gas in the internal space 18 zero (or substantially zero) is applied to the pump cell 15.

  In FIG. 3, the solid line LU0 indicates the output current when the applied voltage is increased from 0.1 V to 1.0 V when SOx is not included in the exhaust (that is, the SOx concentration in the exhaust is zero). The solid line LD0 indicates the change in the output current when the applied voltage is decreased from 1.0 V to 0.1 V when SOx is not included in the exhaust gas. In FIG. 3, an alternate long and short dash line LU1 indicates a change in output current when the applied voltage is increased from 0.1 V to 1.0 V when SOx is included in the exhaust, and an alternate long and short dash line LD1 The graph shows changes in the output current when the applied voltage is decreased from 1.0 V to 0.1 V when SOx is included therein.

  When SOx is not included in the exhaust, when the applied voltage is increased from 0.1 V to about 0.2 V, the output current increases rapidly to about 4 μA as shown by the solid line LU0 in FIG. To do. Then, while the applied voltage rises from about 0.2 V to about 0.85 V, the output current is approximately constant at about 4 μA. When the applied voltage exceeds about 0.85 V, the output current starts to increase. The output current gradually increases while the applied voltage is raised from about 0.85 V to 1.0 V. When the applied voltage reaches 1.0 V, the output current reaches about 7 μA.

  After that, when the applied voltage is gradually decreased from 1.0 V to 0.4 V, the output current is gradually decreased from about 7 μA as shown by the solid line LD0 in FIG. The output current is substantially constant at about 3.5 μA until the voltage reaches about 0.4 V after the voltage drops below about 0.85 V.

On the other hand, when SOx is contained in the exhaust gas, when the applied voltage is increased from 0.1 V to about 0.2 V, the output current is about 4 μA as shown by the one-dot chain line LU1 in FIG. Rises rapidly. While the applied voltage rises from about 0.2 V to about 0.6 V, the output current is about 4 μA and is substantially constant. When the applied voltage exceeds about 0.6 V, the output current starts to increase. The output current gradually increases while the applied voltage is raised from about 0.6 V to 1.0 V, and reaches about 7 μA when the applied voltage reaches 1.0 V.

  After that, when the applied voltage is gradually decreased from 1.0 V to 0.4 V, the output current is gradually decreased from about 7 μA as shown by the one-dot chain line LD1 in FIG. Between the time when the voltage drops below about 0.8V and the time when the voltage reaches about 0.7V, the output current rapidly decreases and the direction in which the output current flows is reversed to reach about −5 μA. Then, while the applied voltage is further reduced from about 0.7V to 0.4V, the output current rapidly rises, the direction in which the output current flows returns to the original direction, and the applied voltage reaches 0.4V. Then, the output current becomes about 3.5 μA.

  Therefore, when SOx is included in the exhaust gas, the applied voltage is increased from 0.4 V to 0.8 V, and then the applied voltage is decreased when the applied voltage is decreased from 0.8 V to 0.4 V. During this period, the output current suddenly decreases and then increases rapidly. That is, when the applied voltage is decreased from 0.8 V to 0.4 V, the output current shows a change with a minimum value (that is, a peak value). Here, when the applied voltage reaches about 0.7 V, the output current has a peak value.

  When SOx is included in the exhaust gas, the output current from when the applied voltage exceeds approximately 0.6 V to 1.0 V is approximately equal to the applied voltage when SOx is not included in the exhaust gas. It is larger than the output current from reaching 0.6V after exceeding 0.6V.

<Advantages of the 2-cell type limiting current sensor of the first embodiment>
According to the research of the inventors of the present application, the peak value of the output current and the SOx concentration when the applied voltage is reduced from 0.8 V to 0.4 V as described above in the two-cell type limiting current sensor, It has been found that there is a relationship shown in FIG. That is, it has been found that the SOx concentration in the exhaust gas is higher as the difference between the reference current (that is, the output current when the applied voltage reaches 0.8 V) and the peak value is larger. The two-cell type limiting current sensor of the first embodiment can be used for detecting the oxygen concentration in the exhaust gas (and thus the air-fuel ratio of the exhaust gas). Therefore, according to the two-cell type limiting current sensor of the first embodiment, the SOx concentration is calculated (that is, detected) using the peak value by using a sensor that can be used for detecting the oxygen concentration in the exhaust gas. can do.

<Configuration of 1-cell type limiting current sensor>
FIG. 5 shows another one of the limiting current type sensors according to the first embodiment of the present invention. The limiting current type sensor of FIG. 5 is a one-cell type limiting current type sensor. In FIG. 5, 30 is a limiting current sensor, 31 is a solid electrolyte layer, 32A is a first alumina layer, 32B is a second alumina layer, 32C is a third alumina layer, 32D is a fourth alumina layer, 32E is a fifth alumina layer. Layer, 33 is a diffusion-controlled layer, 34 is a heater, 35 is a sensor cell, 35A is a first sensor electrode, 35B is a second sensor electrode, 35C is a sensor cell voltage source, 36 is an air introduction path, and 37 is an internal space. Yes.

  The solid electrolyte layer 31 is a layer made of zirconia or the like and has oxygen ion conductivity. The alumina layers 32A to 32E are layers made of alumina. The diffusion control layer 33 is a porous layer and can pass exhaust gas. In the sensor 30, the layers are arranged in the order from the bottom in FIG. 5 from the fifth alumina layer 32 E, the fourth alumina layer 32 D, the third alumina layer 32 C, the solid electrolyte layer 31, the diffusion rate controlling layer 33 and the second alumina layer 32 B, The layers 32A are stacked in this order. The heater 34 is disposed between the fourth alumina layer 32D and the fifth alumina layer 32E.

  The air introduction path 36 is a space formed by the solid electrolyte layer 31, the third alumina layer 32C, and the fourth alumina layer 32D, and a part thereof is open to the atmosphere. The internal space 37 is a space formed by the first alumina layer 32A, the solid electrolyte layer 31, the diffusion-controlling layer 33, and the second alumina layer 32B, and part of the internal space 37 communicates with the outside of the sensor via the diffusion-controlling layer 33. doing.

<Configuration of sensor cell>
The first sensor electrode 35A and the second sensor electrode 35B are electrodes made of a platinum group element such as platinum or rhodium or an alloy thereof. The first sensor electrode 35A is disposed on the wall surface on one side of the solid electrolyte layer 31 (that is, the wall surface of the solid electrolyte layer 31 forming the internal space 37), and the second sensor electrode 35B is disposed on the other side of the solid electrolyte layer 31. On the side wall (that is, the wall surface of the solid electrolyte layer 31 forming the air introduction path 36). These electrodes 35 </ b> A and 35 </ b> B and the solid electrolyte layer 31 constitute a sensor cell 35. The sensor 30 is configured to be able to apply a voltage from the sensor cell voltage source 35C to the sensor cell 35 (specifically, between the first sensor electrode 35A and the second sensor electrode 35B). The first sensor electrode 35A is a cathode side electrode, and the second sensor electrode 35B is an anode side electrode.

<Function of sensor cell>
When a voltage is applied to the sensor cell 35, when SOx in the internal space 37 comes into contact with the first sensor electrode 35A, this SOx is decomposed on the first sensor electrode 35A, and the oxygen of SOx becomes oxygen ions, Oxygen ions move inside the solid electrolyte layer 31 toward the second sensor electrode 35B. At this time, a current proportional to the amount of oxygen ions moved through the solid electrolyte layer 31 flows between the first sensor electrode 35A and the second sensor electrode 35B. When the oxygen ions reach the second sensor electrode 35B, the oxygen ions are released into the atmosphere introduction path 36 as oxygen at the second sensor electrode 35B.

<Air-fuel ratio detection function of 1-cell type limit current sensor>
The sensor cell applied voltage and the sensor cell output current in the one-cell type limiting current type sensor of the first embodiment are in the same relationship as that shown in FIG. Therefore, if a voltage at which the sensor cell output current is constant regardless of the sensor cell applied voltage is applied to the sensor cell 35 at all air-fuel ratios to be detected, the exhaust gas is detected based on the pump cell output current detected at that time. The air-fuel ratio can be detected. That is, the one-cell type limiting current type sensor 30 of the first embodiment can be used for detecting the air-fuel ratio of the exhaust gas. Since the air-fuel ratio of the exhaust gas is a parameter having a correlation with the oxygen concentration in the exhaust gas, in principle, the 1-cell type limit current sensor of the first embodiment determines the oxygen concentration in the exhaust gas. It can be said that it can be detected. The sensor cell applied voltage is a voltage applied to the sensor cell 35 by the sensor cell voltage source 35C, and the sensor cell output current is a current flowing between the first sensor electrode 35A and the second sensor electrode 35B.

<Output characteristics of 1-cell type limiting current sensor>
By the way, according to the research of the inventors of the present application, the voltage applied to the one-cell type limiting current type sensor (specifically, from the sensor cell voltage source 35C to the sensor cell 35, as in the case of the two-cell type limiting current type sensor). It has been found that a current corresponding to the SOx concentration in the exhaust gas can be obtained from this limit current sensor by reducing the applied voltage) from a predetermined voltage. Next, this will be described. In the following description, the output current is a current output from the sensor cell 35, and the oxygen concentration in the exhaust gas is constant at 1%.

  FIG. 6 shows changes in the output current when the applied voltage is gradually increased from 0.1 V to 1.0 V and then gradually decreased from 1.0 V to 0.1 V. The horizontal axis in FIG. 6 is the applied voltage, and the vertical axis in FIG. 6 is the output current.

  In FIG. 6, an alternate long and short dash line LU1 shows a change in output current when the applied voltage is increased from 0.1 V to 1.0 V when SOx is included in the exhaust, and an alternate long and short dash line LD1 The graph shows changes in the output current when the applied voltage is decreased from 1.0 V to 0.1 V when SOx is included therein.

  When SOx is contained in the exhaust, when the applied voltage is increased from 0.1 V to about 0.2 V, the output current suddenly increases to about 100 μA as shown by a one-dot chain line LU1 in FIG. To rise. Then, while the applied voltage rises from about 0.2 V to about 0.6 V, the output current is approximately constant at about 100 μA. When the applied voltage exceeds about 0.6 V, the output current starts to increase. Then, while the applied voltage is raised from about 0.6 V to 1.0 V, the output current gradually increases slightly, and reaches about 105 μA when the applied voltage reaches 1.0 V.

  Then, when the applied voltage is gradually decreased from 1.0 V to 0.4 V, the output current gradually decreases from about 105 μA as shown by the one-dot chain line LD1 in FIG. Between the time when the voltage drops below about 0.8 V and the time when the voltage reaches about 0.7 V, the output current rapidly decreases and reaches about 80 μA. Then, while the applied voltage is lowered from about 0.7 V to 0.4 V, the output current rises rapidly, and when the applied voltage reaches 0.4 V, the output current becomes about 100 μA.

  Therefore, when SOx is included in the exhaust gas, the applied voltage is increased from 0.4 V to 0.8 V, and then the applied voltage is decreased when the applied voltage is decreased from 0.8 V to 0.4 V. During this period, the output current suddenly decreases and then increases rapidly. That is, when the applied voltage is decreased from 0.8 V to 0.4 V, the output current shows a change with a minimum value (that is, a peak value). Here, when the applied voltage reaches about 0.7 V, the output current has a peak value.

<Advantages of 1-cell type limiting current type sensor according to the first embodiment>
According to the research of the inventors of the present application, the peak value of the output current and the SOx concentration when the applied voltage is reduced from 0.8 V to 0.4 V as described above in the one-cell type limiting current type sensor, It has been found that there is a relationship similar to that shown in FIG. That is, it has been found that the SOx concentration in the exhaust gas is higher as the difference between the reference current (that is, the output current when the applied voltage reaches 0.8 V) and the peak value is larger. The 1-cell type limiting current sensor of the first embodiment can be used for detecting the oxygen concentration in the exhaust gas (and thus the air-fuel ratio of the exhaust gas). Therefore, according to the one-cell type limiting current type sensor of the first embodiment, the SOx concentration is calculated (that is, detected) using the peak value by using a sensor that can be used for detecting the oxygen concentration in the exhaust gas. can do.

<SOx concentration detection apparatus of the first embodiment>
FIG. 7 shows an internal combustion engine equipped with a SOx concentration detecting device having the limiting current sensor 10 of FIG. 1 or the limiting current sensor 30 of FIG. The internal combustion engine of FIG. 7 is a spark ignition internal combustion engine (so-called gasoline engine). However, the present invention is also applicable to a compression self-ignition internal combustion engine (so-called diesel engine). Further, the internal combustion engine of FIG. 7 is operated at a stoichiometric air-fuel ratio (stoichiometric) in most engine operating regions.

<Configuration of internal combustion engine>
7, 10 or 30 is the limiting current type sensor of FIG. 1 or FIG. 5, 50 is the body of the internal combustion engine, 51 is the cylinder head, 52 is the cylinder block, 53 is the combustion chamber, 54 is the fuel injection valve, and 55 is the ignition. Plug, 56, fuel pump, 57, fuel supply pipe, 60, piston, 61, connecting rod, 62, crankshaft, 63, crank angle sensor, 70, intake valve, 71, intake port, 72, intake manifold, 73 Surge tank, 74 throttle valve, 75 intake pipe, 76 air flow meter, 77 air filter, 80 exhaust valve, 81 exhaust port, 82 exhaust manifold, 83 exhaust pipe, 90 electronic control unit (ECU) ), 91 denotes an accelerator pedal, and 92 denotes an accelerator pedal depression amount sensor.

<Configuration and function of ECU>
The fuel injection valve 54, the spark plug 55, the throttle valve 74, the crank angle sensor 63, the air flow meter 76, the accelerator pedal depression amount sensor 92, and the limit current type sensors 10 and 30 are electrically connected to the ECU 90. The ECU 90 transmits signals for operating the fuel injection valve 54, the spark plug 55, and the throttle valve 74 to these. Further, the ECU 90 receives signals from the crank angle sensor 63, the air flow meter 76, and the accelerator pedal depression amount sensor 92. A signal corresponding to the rotational speed of the crankshaft 62 is output from the crank angle sensor 63. The ECU 90 calculates the engine speed based on the signal received from the crank angle sensor 63. The air flow meter 76 outputs a signal corresponding to the flow rate of air passing therethrough (and consequently the flow rate of air sucked into the combustion chamber 53). The ECU 90 calculates the intake air amount based on the signal received from the air flow meter 76. A signal corresponding to the amount of depression of the accelerator pedal 91 is output from the accelerator pedal depression amount sensor 92. The ECU 90 calculates the engine load based on the signal received from the accelerator pedal depression amount sensor 92.

<Limit current sensor>
The limit current sensors 10 and 30 are attached to the exhaust pipe 83. Therefore, the gas to be detected by the limit current sensors 10 and 30 (that is, the test gas) is exhaust gas discharged from the combustion chamber 53. The limit current sensors 10 and 30 output a current corresponding to the SOx concentration in the exhaust that arrives there. The ECU 90 calculates the SOx concentration based on the current received from the limit current sensors 10 and 30 (details of this calculation method will be described later).

<SOx concentration detection in the first embodiment>
The SOx concentration detection of the first embodiment will be described with reference to FIG. In the first embodiment, the applied voltage is constantly maintained at 0.4 V (see the period before time T0 in FIG. 8). That is, 0.4 V is constantly applied to the sensor. In the SOx concentration detection according to the first embodiment, the applied voltage is increased from 0.4 V to 0.8 V (see the period from time T0 to time T1 in FIG. 8), and then the applied voltage is changed from 0.8 V to 0. The voltage is decreased to 4 V (see the period from time T1 to time T2 in FIG. 8). At this time, the ECU calculates (that is, detects) the SOx concentration using the peak value of the output current input to the ECU and the reference current while the applied voltage is decreased from 0.8 V to 0.4 V. . At this time, the greater the difference between the reference current and the peak value, the higher the calculated SOx concentration.

  When calculating the SOx concentration using the difference between the peak value and the reference current (hereinafter referred to as “current difference”), for example, the SOx concentration corresponding to the current difference is obtained for each current difference in advance by experiments or the like. The obtained SOx concentration is stored in the ECU in the form of a current difference function map, and the SOx concentration corresponding to the current difference calculated during the detection of the SOx concentration is read out from the map to calculate the SOx concentration.

<Advantages of the SOx concentration detection apparatus of the first embodiment>
The limiting current type sensor of the SOx concentration detection device of the first embodiment can be used for detecting the oxygen concentration in the exhaust gas (and hence the air-fuel ratio of the exhaust gas). Therefore, according to the SOx concentration detection device of the first embodiment, the SOx concentration in the exhaust gas can be detected using a sensor that can be used for detecting the oxygen concentration in the exhaust gas. That is, the effect of SOx on the output current when the applied voltage is maintained at a constant voltage (for example, 0.4 V) or the effect of SOx on the output current when the applied voltage is increased are the same. The influence of SOx on the output current when the applied voltage is reduced from a predetermined voltage (eg, 0.8 V ) is small compared to the influence of other components (eg, O ₂ and NOx) on the output current. The inventors of the present application have obtained the knowledge that the influence of other components in the output current is large. For this reason, according to the SOx concentration detection device of the first embodiment, the oxygen concentration in the exhaust gas The SOx concentration can be detected with high accuracy using a sensor that can be used for detection.

  The peak value is an output current that is most different from the output current when the SOx concentration is zero among the output currents during the decrease of the applied voltage. Therefore, it can be said that the peak value is an output current that accurately corresponds to the SOx concentration. Therefore, the SOx concentration can be detected with higher accuracy by using the peak value as the output current for detecting the SOx concentration.

  In the first embodiment, the voltage applied to the sensor before the applied voltage starts to decrease is 0.4V. Therefore, this voltage is lower than 0.8 V that is the applied voltage at the start of the decrease of the applied voltage. For this reason, according to the first embodiment, it is possible to reduce the power consumed for SOx concentration detection, compared to the case where the voltage applied to the sensor before the start of the decrease in the applied voltage is 0.8V. .

<Applicable scope of the first embodiment>
In the SOx concentration detection according to the first embodiment, the applied voltage at the start of increasing the applied voltage (that is, the applied voltage that is steadily applied to the sensor) is not limited to 0.4 V, and the applied voltage increases. Any voltage may be used as long as it causes a change in output current having a peak value when the applied voltage is lowered later. For example, the voltage may be 0.6 V or less, and preferably 0.4 V.

  In addition, the applied voltage at the end of the increase in the applied voltage is not limited to 0.8 V, and a voltage that generates a change in output current having a peak value when the applied voltage is lowered after the applied voltage is increased, or an output A voltage equal to or higher than the maximum voltage in the stable voltage range (that is, in the range where the output current is substantially constant regardless of the applied voltage when the SOx concentration is zero, for example, in the range of 0.2 V to 0.8 V). For example, it may be 0.8 V or more.

  Further, the applied voltage at the end of the decrease in the applied voltage is not limited to 0.4 V, and may be equal to or lower than the applied voltage corresponding to the peak value, for example, 0.7 V or lower. 4V. Therefore, the applied voltage at the start of application voltage increase may be the same as or different from the applied voltage at the end of decrease in applied voltage.

  In the SOx concentration detection of the first embodiment, a peak value is used. Instead, a range in which the output current rapidly decreases while the applied voltage is decreased from 0.8 V to 0.4 V or abruptly. An output current in a range that rises rapidly may be used.

<Reference current>
Note that the oxygen concentration in the exhaust gas flowing into the internal space of the sensor may change while the applied voltage is decreasing. In this case, considering that it takes a certain time to decrease the applied voltage, the output current when the applied voltage is 0.4 V is higher than the output current when the applied voltage is 0.8 V. It can be said that the oxygen concentration in the exhaust gas in the internal space of the sensor at the time of output is more accurately reflected. Therefore, in the SOx concentration detection according to the first embodiment, when the applied voltage is reduced from 0.8 V to 0.4 V, the output current (or when the applied voltage reaches 0.4 V, instead of the reference current) (or The output current after a predetermined time has elapsed from that point in time may be used as the reference current. According to this, even if the oxygen concentration in the exhaust gas changes while the applied voltage is decreasing, the SOx concentration can be detected with high accuracy.

In the first embodiment, instead of calculating the SOx concentration using the peak value and the reference current, the SOx concentration may be calculated using the peak value and the conversion coefficient. At this time, the greater the peak value in the negative direction, the higher the calculated SOx concentration. That is, when the peak value is negative, the larger the absolute value of the peak value, the higher the calculated SOx concentration, and when the peak value is positive, the absolute value of the peak value is small. The calculated SOx concentration is higher. The conversion coefficient is a coefficient for converting the peak value into the SOx concentration according to the relationship of FIG. Of course, when the peak value appears as a positive value, the calculated SOx concentration increases as the peak value increases in the positive direction.

<Sweep speed of the first embodiment>
In the SOx concentration detection of the first embodiment, if the applied voltage rises or falls (sweep speed) is too fast, even if the applied voltage is lowered, the peak value is not output, or the SOx concentration is sufficiently dealt with. The peak value to be output may not be output. Therefore, in the SOx concentration detection of the first embodiment, it is preferable to select an increase rate and a decrease rate of the applied voltage that outputs a peak value sufficiently corresponding to the SOx concentration when the applied voltage is decreased.

  Specifically, as shown in FIG. 9 (A), after the applied voltage is increased so that the applied voltage rise rate gradually decreases, the applied voltage decrease rate gradually increases. It is preferable that the applied voltage is lowered. Alternatively, as shown in FIG. 9B, after the applied voltage is increased so that the applied voltage rise rate is maintained constant, the applied voltage is applied such that the applied voltage decrease rate is maintained constant. It is preferable if the voltage is lowered.

More specifically, in the SOx concentration detection according to the first embodiment, the change in the applied voltage until the applied voltage is lowered from 0.8 V to 0.4 V after the applied voltage is raised from 0.4 V to 0.8 V. When expressed in terms of frequency, this frequency is preferably 100 Hz or less. In other words, it is preferable that the time from when the increase of the applied voltage is started to when the decrease of the applied voltage is completed is 0.01 seconds or more.

<Configuration 1 of SOx detection circuit>
When the internal combustion engine has the limit current type sensor (two-cell type limit current type sensor) shown in FIG. 1, for example, the circuit shown in FIG. 10A is employed as the SOx detection circuit. 10A, 10 is a limit current sensor (ie, the limit current sensor of FIG. 1), 14 is a heater, 15 is a pump cell, 16 is a sensor cell, 90 is an ECU, 91 is an applied voltage command unit, and 92 is A parameter calculation unit, 93 is a heater control unit, 94P and 94S are applied voltage control circuits, and 95P and 95S are output current detection circuits.

  The applied voltage command unit 91, the parameter calculation unit 92, and the heater control unit 93 are components of the ECU 90.

  The applied voltage command unit 91 transmits a command related to the applied voltage to the pump cell 15 to the applied voltage control circuit 94P, and transmits a command related to the applied voltage to the sensor cell 16 to the applied voltage control circuit 94S.

  The parameter calculation unit 92 receives a signal corresponding to the pump cell output current from the output current detection circuit 95P, calculates the pump cell output current based on the received signal, and based on the calculated output current, the air-fuel ratio ( Alternatively, the oxygen concentration in the exhaust gas) is calculated. Further, the parameter calculation unit 92 receives a signal corresponding to the sensor cell output current from the output current detection circuit 95S, calculates the sensor cell output current based on the received signal, and based on the calculated output current, The SOx concentration is calculated. Further, the parameter calculation unit 92 calculates the impedance of the circuit in the sensor 10 based on the signals received from the output current detection circuits 95P and 95S, and transmits information on the calculated impedance to the heater control unit 93. The heater control unit 93 transmits a control signal for controlling the heater 14 to the heater 14 based on the information regarding the impedance received from the parameter calculation unit 92.

  The applied voltage control circuit 94P is based on the command received from the applied voltage command unit 91 (or the command corresponding to the command received from the applied voltage command unit 91 and the pump cell output current provided from the output current detection circuit 95P. To control the pump cell applied voltage.

  The output current detection circuit 95P detects the pump cell output current, and transmits a signal corresponding to the detected output current to the parameter calculation unit 92 and the applied voltage control circuit 94P.

  The applied voltage control circuit 94S is a signal corresponding to the command received from the applied voltage command unit 91 (or the command received from the applied voltage command unit 91 and the sensor cell output current provided from the output current detection circuit 95S). To control the sensor cell applied voltage.

  The output current detection circuit 95S detects the sensor cell output current, and transmits a signal corresponding to the detected output current to the parameter calculation unit 92 and the applied voltage control circuit 94S.

<Configuration 2 of SOx detection circuit>
For example, the circuit shown in FIG. 10B is employed as the SOx detection circuit when the internal combustion engine has the limit current sensor (1-cell type limit current sensor) of FIG. In FIG. 10B, 30 is a limit current type sensor (that is, the limit current type sensor of FIG. 5), 34 is a heater, 35 is a sensor cell, 90 is an ECU, 91 is an applied voltage command unit, 92 is a parameter calculation unit, Reference numeral 93 denotes a heater control unit, 94 denotes an applied voltage control circuit, and 95 denotes an output current detection circuit.

  The applied voltage command unit 91, the parameter calculation unit 92, and the heater control unit 93 are components of the ECU 90.

  The applied voltage command unit 91 transmits a command related to the applied voltage to the sensor cell 35 to the applied voltage control circuit 94.

  The parameter calculation unit 92 receives a signal corresponding to the sensor cell output current from the output current detection circuit 95, calculates the sensor cell output current based on the received signal, and based on the calculated output current, the air-fuel ratio ( Alternatively, the oxygen concentration in the exhaust gas) or the SOx concentration in the exhaust gas is calculated. Further, the parameter calculation unit 92 calculates the impedance of the circuit in the sensor 30 based on the signal received from the output current detection circuit 95, and transmits information on the calculated impedance to the heater control unit 93. The heater control unit 93 transmits a control signal for controlling the heater 34 to the heater 14 based on the information regarding the impedance received from the parameter calculation unit 92.

  The applied voltage control circuit 94 is based on the command received from the applied voltage command unit 91 (or the command received from the applied voltage command unit 91 and the signal corresponding to the sensor cell output current provided from the output current detection circuit 95. To control the sensor cell applied voltage.

  The output current detection circuit 95 detects the sensor cell output current, and transmits a signal corresponding to the detected output current to the parameter calculation unit 92 and the applied voltage control circuit 94.

<SOx concentration detection flow>
An example of the SOx concentration detection flow of the first embodiment described above will be described. This flow is shown in FIG.

  When the flow of FIG. 11 is started, the applied voltage is maintained at 0.4V. In step 10, the applied voltage Vs is increased from 0.4V to 0.8V. Next, at step 11, it is determined whether or not the applied voltage Vs has reached 0.8V (Vs = 0.8V). Here, when it is determined that Vs = 0.8 V, the flow proceeds to step 12. On the other hand, when it is determined that Vs = 0.8 V, the flow returns to step 10. Therefore, the increase in the applied voltage Vs is continued until it is determined in step 11 that Vs = 0.8V.

  In step 12, the applied voltage Vs is decreased from 0.8V to 0.4V, and the output current Is is detected. Next, at step 13, it is judged if the applied voltage Vs has reached 0.4V (Vs = 0.4V). Here, when it is determined that Vs = 0.4 V, the flow proceeds to step 14. On the other hand, when it is determined that Vs = 0.4 V is not satisfied, the flow returns to step 12. Therefore, the decrease in the applied voltage Vs and the detection of the output current Is are continued until it is determined in step 13 that Vs = 0.4V.

  In step 14, the SOx concentration Csox is calculated based on the peak value of the output current Is detected in step 12, and the flow ends.

<Sensor element temperature>
In the SOx concentration detection of the above-described embodiment, the reason why the current corresponding to the SOx concentration is output from the sensor when the applied voltage is reduced is that a reaction related to SOx occurs in the sensor cell. Inferred. On the other hand, this reaction is greatly influenced by the temperature of the sensor cell. Therefore, considering that the SOx concentration in the exhaust gas is extremely low, it is preferable that the temperature of the sensor cell is kept constant. Therefore, in the above-described embodiment, the heater may be controlled so that the temperature of the sensor cell is kept constant when performing the SOx concentration detection. According to this, the SOx concentration is detected with higher accuracy.

<Sensor mounting position>
Further, when a catalyst for purifying components in the exhaust is provided in the exhaust pipe, SOx in the exhaust may be trapped by the catalyst. In this case, if the limit current sensor is attached to the exhaust pipe downstream of the catalyst, the SOx concentration may not be detected with high accuracy. Therefore, in the above-described embodiment, when the catalyst is provided in the exhaust pipe, it is preferable that the limit current type sensor is attached to the exhaust pipe upstream of the catalyst.

Second Embodiment
A second embodiment will be described. The configuration and control of the second embodiment not described below are the same as the configuration and control of the first embodiment, respectively, or when considering the configuration or control of the second embodiment described below. The configuration and control are naturally derived from the configuration or control of the first embodiment.

<SOx concentration detection and S poison recovery of the second embodiment>
In the second embodiment, the applied voltage is constantly maintained at 0.4V. In the SOx concentration detection according to the second embodiment, the applied voltage is increased from 0.4 V to 0.8 V, and then the applied voltage is decreased from 0.8 V to 0.4 V. At this time, the ECU determines whether or not the absolute value of the peak value of the output current input to the ECU is not less than the first predetermined value while the applied voltage is decreased from 0.8 V to 0.4 V. To do. Here, when the absolute value of the peak value is equal to or greater than the first predetermined value, the ECU executes S poisoning recovery control (details of this control will be described later). On the other hand, when the absolute value of the peak value is smaller than the first predetermined value, the ECU calculates (that is, detects) the SOx concentration using the peak value and the reference current.

<Predetermined value of the second embodiment>
Note that the first predetermined value of the second embodiment is set as follows, for example. SOx sulfur content in the exhaust gas may adhere to the first sensor electrode. It has been found by the inventors' research that the absolute value of the peak value increases as the amount of deposited S (that is, the amount of sulfur attached to the first sensor electrode) increases. And when this amount of adhesion S is very large, there is a possibility that the detection accuracy (especially the detection accuracy of SOx concentration) of the limiting current type sensor is lowered. Therefore, when the amount of attached S is large, it is preferable to remove sulfur attached to the first sensor electrode (that is, to execute S poisoning recovery control). Therefore, the first predetermined value of the second embodiment is, for example, the absolute value of the peak value when execution of S poison recovery control is required (that is, the applied voltage is reduced from 0.8 V to 0.4 V). (The absolute value of the peak value of the output current input to the ECU).

<S poison recovery control>
The S poison recovery control can be a known control, for example, a control for increasing the applied voltage to a relatively high voltage (for example, a voltage of 0.8 V or more, and in particular, 1.0 V). Can be adopted.

<Advantages of the SOx concentration detection apparatus of the second embodiment>
According to the SOx concentration detection apparatus of the second embodiment, when there is a possibility that the detection accuracy of the sensor is lowered due to S poisoning (that is, sulfur adhesion to the first sensor electrode), S poison recovery control is performed. Is executed. In other words, the SOx concentration is detected only when there is no possibility that the detection accuracy of the sensor is reduced due to S poisoning. For this reason, according to the SOx concentration detection apparatus of the second embodiment, the SOx concentration can be detected with higher accuracy.

<SOx Concentration Detection Flow of Second Embodiment>
An example of the SOx concentration detection flow of the second embodiment will be described. This flow is shown in FIG.

  When the flow of FIG. 12 is started, the applied voltage is maintained at 0.4V. In step 20, the applied voltage Vs is increased from 0.4V to 0.8V. Next, at step 21, it is determined whether or not the applied voltage Vs has reached 0.8V (Vs = 0.8V). Here, when it is determined that Vs = 0.8 V, the flow proceeds to step 22. On the other hand, when it is determined that Vs = 0.8 V, the flow returns to step 20. Therefore, the increase of the applied voltage Vs is continued until it is determined in step 21 that Vs = 0.8V.

  In step 22, the applied voltage Vs is decreased from 0.8V to 0.4V, and the output current Is is detected. Next, at step 23, it is judged if the applied voltage Vs has reached 0.4V (Vs = 0.4V). Here, when it is determined that Vs = 0.4 V, the flow proceeds to step 24. On the other hand, when it is determined that Vs = 0.4 V is not satisfied, the flow returns to step 22. Therefore, the decrease in the applied voltage Vs and the detection of the output current Is are continued until it is determined in step 23 that Vs = 0.4V.

  In step 24, it is determined whether or not the absolute value | Is | of the peak value of the output current Is detected in step 22 is larger than the first predetermined value Isth1 (| Is |> Isth1). Here, when it is determined that | Is |> Isth1, the flow proceeds to step 25, S poisoning recovery control is executed, and then the flow ends. On the other hand, when it is determined that | Is |> Isth1 is not satisfied, the flow proceeds to step 26, and the SOx concentration Csox is calculated based on the peak value of the output current Is detected at step 22, and then the flow is finish.

<Third Embodiment>
A third embodiment will be described. The configuration and control of the third embodiment not described below are the same as the configuration and control of the above embodiment, respectively, or when considering the configuration or control of the third embodiment described below. The configuration and control are naturally derived from the configuration or control of the above embodiment.

<SOx concentration detection / fuel property abnormality warning of the third embodiment>
In the third embodiment, the applied voltage is constantly maintained at 0.4V. In the SOx concentration detection according to the third embodiment, the applied voltage is increased from 0.4 V to 0.8 V, and then the applied voltage is decreased from 0.8 V to 0.4 V. At this time, the ECU determines whether or not the absolute value of the peak value of the output current input to the ECU is greater than or equal to the second predetermined value while the applied voltage is decreased from 0.8V to 0.4V. To do. Here, when the absolute value of the peak value is greater than or equal to the second predetermined value, the ECU warns of an abnormality in the fuel property. On the other hand, when the absolute value of the peak value is smaller than the second predetermined value, the ECU calculates (that is, detects) the SOx concentration using the peak value and the reference current.

<Predetermined value of the third embodiment>
Note that the second predetermined value of the third embodiment is set as follows, for example. As described above, the sulfur content of SOx in the exhaust gas may adhere to the first sensor electrode, and when the amount of deposited S increases, the absolute value of the peak value increases. It turns out. And when this amount of adhesion S is very large, there is a possibility that the detection accuracy (especially the detection accuracy of SOx concentration) of the limiting current type sensor is lowered. Here, one of the causes that the amount of attached S increases is that the SOx concentration in the exhaust gas is high. When the sulfur component concentration in the fuel is high, the SOx concentration in the exhaust gas is high. If the sulfur component concentration in the fuel is unacceptably high, and therefore there is a possibility that the fuel property may be abnormal, it is preferable to warn that.

  Therefore, the second predetermined value of the third embodiment is, for example, the peak value when the fuel property is not in an allowable range (particularly when the S concentration in the fuel is higher than the allowable concentration). The absolute value (that is, the absolute value of the peak value of the output current input to the ECU while the applied voltage is reduced from 0.8 V to 0.4 V) is set to a value selected as appropriate.

  Note that the second predetermined value of the third embodiment may be the same value as the first predetermined value of the second embodiment, or may be a different value.

<Advantages of the SOx concentration detection apparatus of the third embodiment>
According to the SOx concentration detection device of the third embodiment, when there is a possibility that the fuel property is abnormal, a warning to that effect is given, so that the user of the SOx concentration detection device may have an abnormal fuel property. You can know that there is.

<SOx Concentration Detection Flow of Third Embodiment>
An example of the SOx concentration detection flow of the third embodiment will be described. This flow is shown in FIG.

  When the flow of FIG. 13 is started, the applied voltage is maintained at 0.4V. In step 30, the applied voltage Vs is increased from 0.4V to 0.8V. Next, at step 31, it is determined whether or not the applied voltage Vs has reached 0.8V (Vs = 0.8V). Here, when it is determined that Vs = 0.8 V, the flow proceeds to step 32. On the other hand, when it is determined that Vs = 0.8 V, the flow returns to step 30. Therefore, the increase in the applied voltage Vs is continued until it is determined in step 31 that Vs = 0.8V.

  In step 32, the applied voltage Vs is decreased from 0.8V to 0.4V, and the output current Is is detected. Next, at step 33, it is judged if the applied voltage Vs has reached 0.4V (Vs = 0.4V). Here, when it is determined that Vs = 0.4 V, the flow proceeds to step 34. On the other hand, when it is determined that Vs = 0.4 V is not established, the flow returns to step 32. Therefore, the decrease in the applied voltage Vs and the detection of the output current Is are continued until it is determined in step 33 that Vs = 0.4V.

  In step 34, it is determined whether or not the absolute value | Is | of the peak value of the output current Is detected in step 32 is larger than the second predetermined value Isth2 (| Is |> Isth2). Here, when it is determined that | Is |> Isth2, the flow proceeds to step 35, a fuel property abnormality is warned, and then the flow ends. On the other hand, when it is determined that | Is |> Isth2 is not satisfied, the flow proceeds to step 36, and the SOx concentration Csox is calculated based on the peak value of the output current Is detected at step 32. finish.

<Fourth embodiment>
A fourth embodiment will be described. The configuration and control of the fourth embodiment not described below are the same as the configuration and control of the above embodiment, respectively, or when considering the configuration or control of the fourth embodiment described below. The configuration and control are naturally derived from the configuration or control of the above embodiment.

<SOx concentration detection / air-fuel ratio detection of the fourth embodiment>
In the first embodiment, the applied voltage is constantly maintained at 0.4V. That is, 0.4 V is constantly applied to the sensor cell. Here, the voltage of 0.4 V is equal to or higher than the voltage Vth shown in FIG. 2, and the sensor cell output current is constant regardless of the sensor cell applied voltage when the air-fuel ratio of the exhaust gas is constant. Is the voltage.

  In the SOx concentration / air-fuel ratio detection of the fourth embodiment, the ECU determines the air-fuel ratio from the relationship shown in FIG. 2 based on the sensor cell output current when 0.4 V is constantly applied to the sensor cell. Is calculated (ie, detected).

  On the other hand, when detection of the SOx concentration is required, the sensor cell applied voltage is increased from 0.4 V to 0.8 V, and then the sensor cell applied voltage is decreased from 0.8 V to 0.4 V. At this time, the ECU calculates (ie, detects) the SOx concentration using the peak value of the output current input to the ECU and the reference current while the sensor cell applied voltage is decreased from 0.8 V to 0.4 V. To do.

  Even after the sensor cell applied voltage is reduced from 0.8 V to 0.4 V, the ECU calculates (ie, detects) the air-fuel ratio from the relationship shown in FIG. 2 based on the sensor cell output current. Of course, at this time, the sensor cell applied voltage is maintained at 0.4V.

  In the case where a two-cell type limit current type sensor is used for SOx concentration / air-fuel ratio detection of the fourth embodiment, the applied voltage of the pump cell 15 is set to zero when detecting the air-fuel ratio. .

<Advantages of SOx Concentration Detector of Fourth Embodiment>
According to the fourth embodiment, the air-fuel ratio of exhaust gas and the SOx concentration in exhaust gas can be detected by one sensor.

<SOx concentration / air-fuel ratio detection flow of the fourth embodiment>
An example of the SOx concentration / air-fuel ratio detection flow of the fourth embodiment will be described. This flow is shown in FIG.

  When the flow of FIG. 14 is started, the applied voltage is maintained at 0.4V. In step 40, it is determined whether or not the SOx concentration detection flag Fsox is set (Fsox = 1). This flag Fsox is a flag that is set when the detection of the SOx concentration in the exhaust is requested, and is reset when the detection of the SOx concentration in the exhaust is completed. If it is determined in step 40 that Fsox = 1, the flow proceeds to step 41. On the other hand, when it is determined that Fsox = 1 is not satisfied, the flow proceeds to step 47.

  In step 47, the output current Is is detected. Next, at step 48, the air-fuel ratio A / F is calculated based on the output current Is detected at step 47, and then the flow ends.

  In step 41, the applied voltage Vs is increased from 0.4V to 0.8V. Next, at step 42, it is judged if the applied voltage Vs has reached 0.8V (Vs = 0.8V). Here, when it is determined that Vs = 0.8 V, the flow proceeds to step 43. On the other hand, when it is determined that Vs = 0.8 V, the flow returns to step 41. Therefore, the increase in the applied voltage Vs is continued until it is determined in step 42 that Vs = 0.8V.

  In step 43, the applied voltage Vs is decreased from 0.8V to 0.4V, and the output current Is is detected. Next, at step 44, it is judged if the applied voltage Vs has reached 0.4V (Vs = 0.4V). Here, when it is determined that Vs = 0.4 V, the flow proceeds to step 45. On the other hand, when it is determined that Vs = 0.4 V is not established, the flow returns to step 43. Therefore, the decrease in the applied voltage Vs and the detection of the output current Is are continued until it is determined in step 44 that Vs = 0.4V.

  In step 45, the SOx concentration Csox is calculated based on the peak value of the output current Is detected in step 43. Next, at step 46, the SOx concentration detection flag Fsox is reset, and then the flow ends.

The SOx concentration detection embodiment described above mentioned increase of the applied voltage is performed before lowering the applied voltage. However, as long as the applied voltage is lowered, the benefits of the above-described embodiments can be obtained notwithstanding that the applied voltage is not raised before that.

<Summary of Embodiment>
The SOx concentration detection device for an internal combustion engine of the above-described embodiment can be broadly expressed by reducing the voltage applied to the limit current type sensor from a predetermined voltage (for example, a voltage of 0.8 V or more, particularly 0.8 V). It can be said that this is a SOx concentration detection device for an internal combustion engine having a detection unit that detects the SOx concentration in the exhaust gas using the output current of the sensor when it is set.

More specifically, the detection unit uses a peak value of the output current of the sensor when the applied voltage to the sensor is decreased from the predetermined voltage as the output current for detecting the SOx concentration. It can be said that.

In addition, the detection unit of the SOx concentration detection device for an internal combustion engine according to the above-described embodiment can be broadly expressed by applying a voltage applied to the sensor to a predetermined voltage (for example, a voltage of 0.8 V or more, particularly ) after reducing from those voltage lower than the predetermined voltage for detecting the oxygen concentration in the exhaust with an output current of the sensor (or the air-fuel ratio of the exhaust) when it is being applied to the sensor It can be said that there is.

In addition, the detection unit of the SOx concentration detection device for an internal combustion engine according to the above-described embodiment can be broadly expressed as a predetermined voltage (for example, a voltage of 0.8 V or more, particularly 0.8 V) before the application The oxygen concentration in the exhaust gas (or the air-fuel ratio of the exhaust gas) using the output current of the sensor while applying a voltage lower than the voltage (for example, a voltage of 0.6 V or less, particularly 0.4 V). ).

  Moreover, the SOx concentration detection device for an internal combustion engine of the above-described embodiment can be broadly expressed by changing the applied voltage to the sensor from the predetermined voltage (for example, a voltage of 0.8 V or more, particularly 0.8 V). When the absolute value of the output current of the sensor at the time of reduction is equal to or greater than the first predetermined value, it can be said that the control unit (for example, ECU) that performs S poison recovery control is further included.

Moreover, the SOx concentration detection device for an internal combustion engine of the above-described embodiment can be broadly expressed by changing the applied voltage to the sensor from the predetermined voltage (for example, a voltage of 0.8 V or more, particularly 0.8 V). If the absolute value of the sensor output current when reduced is the second predetermined value or more, it can be said that those further having a control unit for warning abnormality of the fuel property.

Similarly, if expressed in a limited manner, the detection unit is a voltage lower than the predetermined voltage (for example, a voltage of 0.6 V or less before the application of the predetermined voltage) as the output current for detecting the SOx concentration . In particular, it can be said that the output current of the sensor when the applied voltage is raised to the predetermined voltage and then the applied voltage is lowered is applied. In this case, the decrease in the applied voltage is continuously performed following the increase in the applied voltage.

In addition, the SOx concentration detection device of the above-described embodiment can be broadly expressed as a voltage drop that lowers the voltage applied to the sensor from a predetermined voltage (for example, a voltage of 0.8 V or more, particularly 0.8 V). a step, the output current acquiring an output current of the sensor during the voltage drop step, the SOx concentration detection step of detecting the SOx concentration in the exhaust using the obtained output current in the output current acquisition step It can be said that the method comprising:

  Expressed more specifically, it can be said that the above method acquires the peak value of the output current of the sensor in the output current acquisition step.

  Similarly, if expressed in a limited manner, the above method applies a voltage lower than the predetermined voltage (for example, a voltage of 0.6 V or less, particularly 0.4 V) before the application of the predetermined voltage. In addition, it can be said that the method further includes a voltage increase step for increasing the applied voltage to the predetermined voltage, and a voltage increase step that is executed before the voltage decrease step. In this case, the voltage lowering step is continuously executed following the voltage increasing step.

Moreover, the limiting current type sensor of the above-described embodiment can be broadly expressed as the sensor when the applied voltage is reduced from a predetermined voltage (for example, a voltage of 0.8 V or more, particularly 0.8 V). It can be said that the sensor is a limiting current type sensor used for detecting the SOx concentration in the exhaust gas using the output current.

In more limited terms, the sensor of the above-mentioned embodiment, by using the peak value of the output current of the sensor when the applied voltage is lowered from the predetermined voltage as an output current for the SOx concentration detection SOx It can be said that the sensor is used for detecting the concentration .

Similarly, if expressed in a limited manner, the sensor of the above-described embodiment has a voltage lower than the predetermined voltage (for example, a voltage of 0.6 V or less, particularly 0.4 V) before the application of the predetermined voltage. It was applied, then the applied voltage is increased to the predetermined voltage, then the output current of the sensor when lowering the applied voltage for detecting the SOx concentration is used as the output current for the SOx concentration detection It can be said that this is a sensor used in In this case, the decrease in the applied voltage is continuously performed following the increase in the applied voltage.

  DESCRIPTION OF SYMBOLS 10 ... Limit current type sensor, 11A, 11B ... Solid electrolyte layer, 13 ... Diffusion control layer, 15 ... Pump cell, 15A, 15B ... Pump electrode, 16 ... Sensor cell, 16A, 16B ... Sensor electrode, 30 ... Limit current type sensor, 31 ... Solid electrolyte layer, 33 ... Diffusion-controlled layer, 35 ... Sensor cell, 35A, 35B ... Sensor electrode, 90 ... ECU

Claims (14)

  In a SOx concentration detection device for an internal combustion engine having a limiting current type sensor capable of detecting an oxygen concentration in exhaust gas exhausted from the internal combustion engine, an output from the sensor is performed while a voltage applied to the sensor is reduced from a predetermined voltage. The detected SOx concentration in the exhaust gas is detected using the output current, and the oxygen concentration in the exhaust gas is detected using the output current of the sensor when a voltage lower than the predetermined voltage is applied to the sensor. An SOx concentration detection device for an internal combustion engine having a detection unit that performs the operation.   The output current for detecting the SOx concentration is such that when the absolute value of the output current increases while the applied voltage to the sensor is reduced from the predetermined voltage, the change direction of the output current is the applied voltage to the sensor. 2. The SOx concentration detection device for an internal combustion engine according to claim 1, wherein the current is opposite to the direction of change of the output current when the absolute value of the output current increases while the voltage is increased to the predetermined voltage.   The said detection part uses the peak value of the output current output from the said sensor as the output current for the said SOx density | concentration detection while reducing the applied voltage to the said sensor from the said predetermined voltage. The SOx concentration detection device for an internal combustion engine according to 2.   The detection unit applies a voltage lower than the predetermined voltage before applying the predetermined voltage to the sensor, raises the applied voltage to the sensor to the predetermined voltage, and then applies the applied voltage to the sensor. The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 3, wherein an output current output from the sensor while decreasing from the predetermined voltage is used as an output current for detecting the SOx concentration.   The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 4, wherein the predetermined voltage is a voltage of 0.8 V or more.   The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 5, wherein an applied voltage at a time point when the decrease of the applied voltage to the sensor from the predetermined voltage is 0.7 V or less.   The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 6, wherein the detection unit reduces the applied voltage to the sensor from the predetermined voltage at a speed equal to or lower than a voltage change speed of 100 Hz. .   The detection unit applies a voltage lower than the predetermined voltage to the sensor at a speed equal to or lower than a voltage change rate of 100 Hz, and then increases the applied voltage to the sensor up to the predetermined voltage. The SOx concentration detection device for an internal combustion engine according to claim 4, wherein the value is decreased from the predetermined voltage.   The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 8, wherein the internal combustion engine is a gasoline engine.   The detection unit reduces the applied voltage to the sensor from the predetermined voltage, and then uses the output current of the sensor when a voltage lower than the predetermined voltage is applied to the sensor to detect oxygen in exhaust gas. The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 9, wherein the concentration is detected.   The detection unit detects an oxygen concentration in exhaust gas using an output current of the sensor while a voltage lower than the predetermined voltage is applied to the sensor before application of the predetermined voltage to the sensor. Item 5. The SOx concentration detection device for an internal combustion engine according to Item 4.   When the absolute value of the output current output from the sensor while the applied voltage to the sensor is reduced from the predetermined voltage is greater than or equal to a first predetermined value, a control unit that performs S poison recovery control The SOx concentration detection device for an internal combustion engine according to claim 1, further comprising:   When the absolute value of the output current output from the sensor while the applied voltage to the sensor is reduced from the predetermined voltage is greater than or equal to a second predetermined value, it is supplied to the combustion chamber of the internal combustion engine. The SOx concentration detection device for an internal combustion engine according to any one of claims 1 to 12, further comprising a control unit that warns of an abnormality in fuel properties. In an internal combustion engine having a limiting current type sensor capable of detecting an oxygen concentration in exhaust gas discharged from the internal combustion engine,
A voltage lowering step for lowering a voltage applied to the sensor from a predetermined voltage;
An output current acquisition step of acquiring an output current output from the sensor while lowering an applied voltage to the sensor in the voltage reduction step;
A SOx concentration detection step of detecting the SOx concentration in the exhaust gas using the output current acquired in the output current acquisition step;
A SOx concentration detection method comprising:

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