JP2013019749A - Sulfur concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly detect concentration of sulfur contained in an exhaust gas.SOLUTION: A sulfur concentration sensor (100) comprises: a substrate (221) made of a solid electrolyte; a first exhaust side electrode (222) arranged on a first substrate surface which is the surface of the substrate which comes into contact with an exhaust gas; a second exhaust side electrode (223) arranged on the first substrate surface and has different sulfur adsorption performance from the sulfur adsorption performance of the first exhaust side electrode; an atmosphere side electrode (224) arranged on a second substrate surface which is the surface of the substrate which comes into contact with the atmosphere; and sulfur concentration detecting means (21) which detects the concentration of sulfur contained in the exhaust gas according to the difference between a first voltage between the first exhaust side electrode and the atmosphere side electrode and a second voltage between the second exhaust side electrode and the atmosphere side electrode.

Description

  The present invention relates to a technical field of a sulfur concentration sensor that detects sulfur oxide (Sulfur Oxide: SOx) contained in, for example, exhaust gas discharged from an engine mounted on an automobile.

  Examples of this type of sensor include a solid electrolyte having oxide ion conductivity, a sulfate layer formed on a part of the surface of the solid electrolyte, an electrode in electrical contact with the sulfate layer, and a solid electrolyte. Has been proposed (see Patent Document 1).

  Or (i) a reference electrode containing platinum electrically connected to the surface of a solid electrolyte substrate having oxygen ion conductivity, and (ii) a sulfur dioxide provided with a sensing electrode using a combination of gold or a gold alloy and a glass component Gas sensors have been proposed. Here, in particular, the change in electromotive force when a constant current is passed between the reference electrode and the detection electrode, or the current value of the detection electrode when the voltage between the reference electrode and the detection electrode is kept constant is measured. It is described that the amount of sulfur dioxide is quantified. Further, it is described that the influence of oxygen contained in sulfur dioxide is excluded by providing an electrode for measuring oxygen concentration (see Patent Document 2).

  Alternatively, the sulfur concentration detection that detects the sulfur component in the exhaust gas from the difference between the physical property of the detection metal compound that captures sulfur in the exhaust gas and changes to sulfate, and the physical property of the reference metal compound that consists of sulfate A device has been proposed. In particular, it is described that the sulfur concentration detection device includes a heater that releases sulfur from the detection metal compound to regenerate the detection metal compound (see Patent Document 3).

  Alternatively, a working electrode formed on one side in contact with a sulfur-containing gas of a substrate formed of a solid electrolyte material in which oxygen ions can move, and a counter electrode formed on a multi-sided side in contact with the oxygen-containing gas of the substrate, There has been proposed a sulfur detection sensor including an external circuit made of a wire that electrically connects the working electrode and the counter electrode. Here, in particular, in the working electrode made of silver, when the silver forming the working electrode reacts with the sulfur component in the gas flow and the oxygen ions moving in the substrate, the working electrode is formed. Therefore, it is described that the integrated amount of the sulfur component in the gas flow is measured from the difference between the current measured value and the previous measured value of the electrical resistance value (see Patent Document 4).

JP 2004-239706 A JP-A-11-223617 JP 2009-019966 A Japanese Patent Laid-Open No. 2003-130832

  However, in the background art described above, for example, the influence of thermal deterioration of the sulfate layer used for SOx detection under a high temperature environment is relatively large, and a reduction reaction may occur in a rich atmosphere. Then, there exists a technical problem that the detection function of sulfur (concentration) may fall.

  This invention is made | formed in view of the said problem, for example, and makes it a subject to provide the sulfur concentration sensor which can detect a sulfur concentration appropriately.

  In order to solve the above problems, a sulfur concentration sensor according to the present invention is a sulfur concentration sensor that is installed in an exhaust passage of an engine and that can detect the concentration of sulfur contained in exhaust gas flowing through the exhaust passage. A substrate made of an electrolyte; a first exhaust side electrode disposed on a first substrate surface which is a surface in contact with the exhaust gas of the substrate; and a first exhaust side disposed on the first substrate surface. A second exhaust-side electrode having a sulfur adsorption performance different from the sulfur adsorption performance of the electrode; an atmosphere-side electrode disposed on a second substrate surface which is a surface in contact with the atmosphere of the substrate; and the first exhaust side Sulfur that detects the concentration of sulfur contained in the exhaust gas according to the difference between the first voltage between the electrode and the atmosphere-side electrode and the second voltage between the second exhaust-side electrode and the atmosphere-side electrode Concentration detecting means.

  According to the sulfur concentration sensor of the present invention, the sulfur concentration sensor is installed in the exhaust passage of the engine. Depending on the sulfur concentration contained in the exhaust gas detected by the sulfur concentration sensor, for example, it is possible to evaluate catalyst poisoning due to sulfur components contained in fuel such as gasoline, deterioration of engine parts, and the like.

  The sulfur concentration sensor includes a substrate made of a solid electrolyte, a first exhaust side electrode and a second exhaust side electrode disposed on a first substrate surface that is a surface in contact with the exhaust gas of the substrate, And an atmosphere-side electrode disposed on a second substrate surface that is a surface in contact with the atmosphere. Here, the first exhaust side electrode and the second exhaust side electrode are configured such that the sulfur adsorption performance of the first exhaust side electrode and the sulfur adsorption performance of the second exhaust side electrode are different from each other.

  For example, the sulfur concentration detecting means including a memory, a processor, etc. includes a first voltage that is a voltage between the first exhaust side electrode and the atmosphere side electrode, and a second voltage that is a voltage between the second exhaust side electrode and the atmosphere side electrode. The concentration of sulfur contained in the exhaust gas is detected according to the difference from the electrode (that is, corresponding to the oxygen partial pressure difference).

  As described above, in the present invention, in particular, the sulfur adsorption performance of the first exhaust side electrode and the sulfur adsorption performance of the second exhaust side electrode are different from each other. Then, among the first exhaust side electrode and the second exhaust side electrode, the voltage between the exhaust side electrode and the atmosphere side electrode having high sulfur adsorption performance (that is, one of the first voltage and the second voltage) is the exhaust gas. It shows relatively good responsiveness to changes in the sulfur concentration contained in. On the other hand, of the first exhaust side electrode and the second exhaust side electrode, the voltage between the exhaust side electrode and the atmosphere side electrode having low sulfur adsorption performance (that is, the other of the first voltage and the second voltage) is the exhaust gas. A predetermined response delay occurs with respect to the change in the sulfur concentration contained in the gas, and it has been found by the present inventors' research that the predetermined response delay is proportional to the change in the sulfur concentration.

  For this reason, if the difference between the first voltage and the second voltage is used, the sulfur concentration can be detected appropriately. In addition, since it is not necessary to use a sulfate layer for both the first exhaust side electrode and the second exhaust side electrode, the sulfur concentration can be appropriately detected even in a rich atmosphere, for example. Very advantageous.

  In one aspect of the sulfur concentration sensor of the present invention, heating means capable of heating the sulfur concentration sensor, air-fuel ratio detection means for detecting an air-fuel ratio related to the engine, and the sulfur concentration detection means are included in the exhaust gas. And a control means for controlling the heating means so as to heat the sulfur concentration sensor in accordance with the detected air-fuel ratio when the sulfur concentration is detected.

  According to this aspect, the sulfur concentration sensor includes a heating unit that can heat the sulfur concentration sensor, such as a heater, and an air-fuel ratio detection unit that detects an air-fuel ratio related to the engine, such as an air-fuel ratio sensor. And comprising.

  Here, according to the inventor's research, the following matters have been found. That is, the temperature of the sulfur concentration sensor changes due to the temperature of the exhaust gas changing depending on whether the air-fuel ratio is rich or lean. Then, the adsorption amount of, for example, SOx on each of the first exhaust side electrode and the second exhaust side electrode of the sulfur concentration sensor becomes unstable, and the detection result of the sulfur concentration by the sulfur concentration sensor may become inappropriate. is there.

  Therefore, in this aspect, when the concentration of sulfur contained in the exhaust gas is detected by the sulfur concentration detection means by the control means including, for example, a memory, a processor, etc., the sulfur is detected according to the detected air-fuel ratio. The heating means is controlled to heat the concentration sensor. Therefore, the amount of adsorption of, for example, SOx with respect to each of the first exhaust side electrode and the second exhaust side electrode is stabilized, and the reliability of the detection result of the sulfur concentration by the isotopic sulfur concentration sensor can be improved.

  In another aspect of the sulfur concentration sensor of the present invention, when the concentration of sulfur contained in the exhaust gas is detected by the sulfur concentration detection means, the time average value or integrated value of the exhaust gas, or the engine A calculation means for calculating the time average value or integrated value of the air-fuel ratio, and the calculated time average value or integrated value of the exhaust gas or the time average value or integrated value of the air-fuel ratio related to the engine Correction means for correcting the detected sulfur concentration.

  According to this aspect, the calculating means including, for example, a memory, a processor, etc., when the concentration of sulfur contained in the exhaust gas is detected by the sulfur concentration detecting means, the time average value or integrated value of the exhaust gas, or Then, the time average value or integrated value of the air-fuel ratio of the engine is calculated.

  For example, the correcting means comprising a memory, a processor, etc., calculates the calculated exhaust gas time average value or integrated value, or the sulfur concentration detected according to the engine air-fuel ratio time average value or integrated value. to correct.

  Here, it has been found by the inventor's research that the atmosphere in the exhaust gas exhausted from the engine changes sequentially depending on the intention of the user (for example, the driver of the car) who uses the engine.

  Therefore, as described above, the correction means corrects the concentration of sulfur detected according to the time average value or integrated value of the exhaust gas or the time average value or integrated value of the air-fuel ratio of the engine. The detection accuracy of the concentration of sulfur contained in the exhaust gas can be improved. Specifically, for example, if the time average value or integrated value of the exhaust gas is relatively large, the correction means corrects the detected sulfur concentration to the low concentration side. Alternatively, the correction means corrects the detected sulfur concentration to the low concentration side if the time average value or integrated value of the air-fuel ratio is relatively large.

  In another aspect of the sulfur concentration sensor of the present invention, the sulfur concentration detection means may be configured such that the difference is generated between the first voltage and the second voltage until the difference is eliminated. Based on the integrated value of the difference, the concentration of sulfur contained in the exhaust gas is detected.

  According to this aspect, the concentration of sulfur contained in the exhaust gas can be detected relatively easily, which is very advantageous in practice.

  Alternatively, in another aspect of the sulfur concentration sensor of the present invention, the sulfur concentration detection means is based on the difference after a lapse of a predetermined time after a difference occurs between the first voltage and the second voltage. The concentration of sulfur contained in the exhaust gas is detected.

  According to this aspect, the concentration of sulfur contained in the exhaust gas can be detected relatively easily, which is very advantageous in practice.

  In another aspect of the sulfur concentration sensor of the present invention, the sulfur concentration sensor further comprises: a first coating layer laminated on the first exhaust side electrode; and a second coating layer laminated on the second exhaust side electrode; The first coating layer is (i) low in porosity, (ii) thick, or (iii) low in porosity and thick as compared to the second coating layer.

  According to this aspect, the sulfur adsorption performance of the first exhaust side electrode and the sulfur adsorption performance of the second exhaust side electrode can be made different from each other relatively easily.

  In another aspect of the sulfur concentration sensor of the present invention, the first exhaust side electrode and the second exhaust side electrode are composed only of a platinum group element.

  According to this aspect, for example, in a rich atmosphere in which a reducing gas exists, compared to an exhaust-side electrode configured with a noble metal such as gold (Au) or an exhaust-side electrode having a sulfate layer. The reduction of the reduction reaction can be prevented, which is very advantageous in practice.

  In another aspect of the sulfur concentration sensor of the present invention, the first exhaust side electrode is made of palladium, the second exhaust side electrode is made of platinum, and is contained in the exhaust gas based on the second voltage. Oxygen concentration detection means for detecting the oxygen concentration is further provided.

  According to this aspect, it is possible to detect the sulfur concentration and the oxygen concentration at the same time with relatively high accuracy, which is very advantageous in practice.

  The effect | action and other gain of this invention are clarified from the form for implementing demonstrated below.

It is the schematic which shows schematic structure of the engine which concerns on 1st Embodiment. It is a block diagram which shows the structure of the sulfur concentration sensor which concerns on 1st Embodiment. It is an example of the time fluctuation of the voltage between the exhaust side electrode in the sulfur concentration sensor which concerns on 1st Embodiment, and the atmosphere side electrode. It is a conceptual diagram which shows an example of the relationship between time until the electromotive force of two cells corresponds, and the output difference of two cells, or the integrated value of this output difference. It is a block diagram which shows the structure of the sulfur concentration sensor which concerns on the modification of 1st Embodiment. It is a time chart which shows an example of the temperature control of the sulfur concentration sensor which concerns on 2nd Embodiment. It is a flowchart which shows the sulfur concentration detection process which ECU which concerns on 2nd Embodiment performs. It is an example of the map which shows the relationship between the time until the electromotive force of two cells corresponds, the average value of gas amount, and a correction coefficient. It is a flowchart which shows the sulfur concentration detection process which ECU which concerns on the 1st modification of 2nd Embodiment performs. It is an example of the map which shows the relationship until the electromotive force of two cells corresponds, the average value of an air fuel ratio, and a correction coefficient. It is a flowchart which shows the sulfur concentration detection process which ECU which concerns on the 2nd modification of 2nd Embodiment performs. It is an example of the map which shows the relationship between the average value of an air fuel ratio, and the air fuel ratio correction coefficient of sulfur concentration.

  Hereinafter, embodiments according to the sulfur concentration sensor of the present invention will be described with reference to the drawings. In the following drawings, the scales are different for each member so that each member has a size that can be recognized on the drawing.

<First Embodiment>
1st Embodiment which concerns on the sulfur concentration sensor of this invention is described with reference to FIG. FIG. 1 is a schematic diagram illustrating a schematic configuration of an engine according to the present embodiment.

  In FIG. 1, an engine 10 includes an engine body (cylinder group) 11, an intake passage 12 and an exhaust passage 13 connected to the engine body 11, and a catalyst such as a three-way catalyst disposed in the exhaust passage 13. 14.

  An air-fuel ratio sensor 23 is disposed upstream of the catalyst 14 in the exhaust passage 13. On the other hand, an air-fuel ratio sensor 24 is disposed downstream of the catalyst 14 in the exhaust passage 13. An ECU (Electronic Control Unit) 21 controls the engine 10 based on the outputs of the air-fuel ratio sensors 23 and 24.

  The sulfur concentration sensor 100 includes a sensor element 22 disposed on the upstream side of the catalyst 14 in the exhaust passage 13 and an ECU 21.

  Next, the sensor element 22 of the sulfur concentration sensor 100 according to the present embodiment will be described with reference to FIG. FIG. 2 is a configuration diagram showing the configuration of the sulfur concentration sensor according to the present embodiment.

  In FIG. 2, the sensor element 22 includes a substrate 221 made of a solid electrolyte such as yttria-stabilized zirconia (YSZ), and an exhaust-side electrode 222 disposed on a substrate surface 221a that is in contact with the exhaust gas of the substrate 221. 223, an atmosphere-side electrode 224 disposed on the substrate surface 221b of the substrate 221 in contact with the atmosphere, and a heater 225 that can heat the sensor element 22.

  Here, the exhaust side electrode 222 is made of, for example, platinum (Pt), and the exhaust side electrode 223 is made of, for example, palladium (Pd). The atmosphere side electrode 224 is made of, for example, platinum. Since palladium has higher sulfur adsorption performance than platinum, the exhaust side electrode 223 has higher sulfur adsorption performance than the exhaust side electrode 222.

  The exhaust side electrode 223 is not limited to Pd, and may be made of, for example, a palladium alloy such as Pd / Pt. For example, the exhaust side electrode 223 may be a two-layer structure electrode in which a Pd layer is laminated on a Pt layer. Good.

  The ECU 21 determines the sulfur contained in the exhaust gas flowing through the exhaust passage 13 according to the difference between the voltage V1 between the exhaust side electrode 222 and the atmosphere side electrode 224 and the voltage V2 between the exhaust side electrode 223 and the atmosphere side electrode 224. The concentration of is detected.

  Here, the output of the sensor element 22 will be described with reference to FIG. FIG. 3 is an example of the time variation of the voltage between the exhaust side electrode and the atmosphere side electrode in the sulfur concentration sensor according to the present embodiment. The upper part of FIG. 3 shows the time variation of the SOx concentration contained in the exhaust gas, and the lower part of FIG. 3 shows the voltage V1 between the exhaust side electrode 222 and the atmosphere side electrode 224 (“exhaust side Pt electrode” in the figure) and the exhaust gas. This is a time variation with respect to the voltage V2 between the side electrode 223 and the atmosphere side electrode 224 (“exhaust side Pd electrode” in the figure).

  As shown in FIG. 3, when the SOx concentration increases at time t1, first, the voltage V2 between the exhaust side electrode 223 and the atmosphere side electrode 224 having a relatively high sulfur adsorption performance changes. Thereafter, with a predetermined time delay, the voltage V1 between the exhaust-side electrode 222 and the atmosphere-side electrode 224 having a relatively low sulfur adsorption performance changes. Here, at time t2, voltage V1 and voltage V2 become equal.

  The ECU 21 determines the concentration of sulfur contained in the exhaust gas according to the period from time t1 to time t2 (that is, the period from when a difference occurs between the voltage V1 and the voltage V2 until the generated difference disappears). Is detected.

  In addition, the ECU 21 sets the integrated value from the time t1 to the time t2 of (i) the difference between the voltage V1 and the voltage V2 after the elapse of a predetermined time from the time t1, or (ii) the difference between the voltage V1 and the voltage V2. Accordingly, the concentration of sulfur contained in the exhaust gas may be detected.

  Here, a time until the electromotive forces of the two cells coincide (that is, a period from when a difference occurs between the voltage V1 and the voltage V2 until the difference is eliminated) and a predetermined time from the time t1. It is the present invention that there is a correlation as shown in FIG. 4 between the difference between the subsequent voltage V1 and voltage V2 or the integrated value from time t1 to time t2 of the difference between voltage V1 and voltage V2. Has been found by the research of the former.

  For this reason, it is not limited to a period from when the difference between the voltage V1 and the voltage V2 occurs until the generated difference disappears, and (i) according to the difference between the voltage V1 and the voltage V2 after a predetermined time has elapsed from the time t1. Alternatively, (ii) the sulfur concentration can be detected according to the integrated value from the time t1 to the time t2 of the difference between the voltage V1 and the voltage V2. FIG. 4 is a conceptual diagram showing an example of the relationship between the time until the electromotive forces of two cells match and the output difference between the two cells or the integrated value of the output difference.

  The “substrate surface 221a”, “substrate surface 221b”, “exhaust side electrode 222”, “exhaust side electrode 223”, “heater 225”, “ECU 21”, “voltage V1”, and “voltage V2” according to the present embodiment. "Is the" first substrate surface "," second substrate surface "," first exhaust side electrode "," second exhaust side electrode "," heating means "," sulfur concentration detection means "according to the present invention, respectively. , “First voltage” and “second voltage”. In the present embodiment, some of the functions of the electronic control ECU 21 are used as part of the sulfur concentration sensor 100.

<Modification>
Next, a modification of the sulfur concentration sensor according to the first embodiment will be described with reference to FIG. FIG. 5 is a configuration diagram showing a configuration of a sulfur concentration sensor according to a modification of the first embodiment having the same meaning as in FIG. 2.

  In FIG. 5, exhaust-side electrodes 222 and 223 arranged on the substrate surface 221a of the sensor element 22 are covered with coating layers 226 and 227, respectively. The coating layer 226 covering the exhaust side electrode 222 is formed to be thicker than the coating layer 227 covering the exhaust side electrode 223. In addition, the porosity of the coating layer 226 is formed to be lower than the porosity of the coating layer 227.

  With this configuration, the sulfur adsorption performance of the exhaust side electrode 222 becomes lower, so that the difference in the adsorption amount of sulfur components (for example, SOx) per unit time to the exhaust side electrodes 222 and 223 is different. Even if the concentration of sulfur contained in the exhaust gas is relatively low, the detection accuracy of the sulfur concentration can be improved.

  The “coating layer 226” and the “coating layer 227” according to the present embodiment are examples of the “first coating layer” and the “second coating layer” according to the present invention, respectively.

Second Embodiment
A second embodiment of the sulfur concentration sensor of the present invention will be described with reference to FIGS. The second embodiment is the same as the configuration of the first embodiment except that the temperature control of the sulfur concentration sensor is performed. Therefore, in the second embodiment, the description overlapping with that in the first embodiment is omitted, and the common portions in the drawings are denoted by the same reference numerals, and only FIGS. 6 to 8 are basically different only. The description will be given with reference.

  In the present embodiment, in order to repeatedly detect the concentration of sulfur contained in the exhaust gas by the sulfur concentration sensor 100, the sensor element 22 (see FIG. 2) is heated by using the heater 225 (see FIG. 2). Causes elimination of components.

  Here, the temperature control of the sensor element 22 will be specifically described with reference to the time chart of FIG.

  When the “output monitor flag” at the bottom of FIG. 6 is “ON” (that is, the period from time t2 to time t3), the ECU 21 determines the sulfur contained in the exhaust gas based on the output from the sensor element 22. Detect concentration. Therefore, at least during the period from time t2 to time t3, the temperature of the sensor element 22 is relatively low (for example, 500 degrees Celsius) as shown in the middle stage of FIG. 6 so that the sulfur component is appropriately adsorbed to the sensor element 22. The heater 225 is controlled so that

  On the other hand, when the “output monitor flag” is “OFF” (that is, the period until time t2 and the period after time t3), the sulfur component adsorbed on the sensor element 22 is desorbed as shown in FIG. As shown in the middle stage, the heater 225 is controlled so that the temperature of the sensor element 22 is relatively high (for example, 700 degrees Celsius).

  As a result, the desorption of the sulfur component adsorbed on the sensor element 22 can be surely executed at an appropriate timing.

  Next, the sulfur concentration detection process executed by the ECU 21 in the present embodiment will be described with reference to the flowchart of FIG.

  In FIG. 7, the ECU 21 determines whether (i) it is after the engine 11 has been started and (ii) whether the sulfur concentration sensor 100 has failed or not (step S101). In addition, since various well-known aspects are applicable to the failure determination of the sulfur concentration sensor 100, description is omitted here.

  When it is determined that the engine 11 has not been started, or when it is determined that the sulfur concentration sensor 100 has failed (step S101: No), the ECU 22 ends the process. On the other hand, after the engine 11 is started and when it is determined that the sulfur concentration sensor 100 has not failed (step S101: Yes), the ECU 21 sets the temperature of the sensor element 22 to, for example, 700 degrees Celsius or higher. Then, the heater 225 is controlled (step S102).

  Next, the ECU 21 determines whether or not a condition for starting the air-fuel ratio stoichiometric feedback control is established based on, for example, the temperature of the catalyst 14 detected by a temperature sensor (not shown) or the like (step S103). ). When it is determined that the condition for starting stoichiometric feedback control is not satisfied (step S103: No), the ECU 21 ends the process.

  On the other hand, when it is determined that the condition for starting the feedback control is satisfied (step S103: Yes), the ECU 21 sets the stoichiometric feedback control start flag to “ON” (see, for example, time t1 in FIG. 6), and the stoichiometric feedback. Start control. In addition, since various well-known aspects are applicable to stoichiometric feedback control, description is omitted here.

  Subsequently, the ECU 21 controls the heater 225 so that the temperature of the sensor element 22 is, for example, 500 degrees centigrade or less (step S104). At this time, it is desirable to configure the ECU 21 so as to control the temperature of the sensor element 22 based on the outputs of the air-fuel ratio sensors 23 and 24. Specifically, for example, when the air-fuel ratio is lean, it is desirable to control the heater 225 so that the temperature of the sensor element 22 is 500 degrees Celsius or less. In addition, when the air-fuel ratio is stoichiometric or rich, the heater 225 is desirably controlled so that the temperature of the sensor element 22 is 500 degrees Celsius to 700 degrees Celsius.

  Next, the ECU 21 determines whether or not the temperature of the sensor element 22 has reached the target temperature (step S105). When it is determined that the temperature of the sensor element 22 has not reached the target temperature (step S105: No), the ECU 21 executes the process of step S105 (that is, the ECU 21 sets the temperature of the sensor element 22 to the target temperature). Until you reach it).

  When it is determined that the temperature of the sensor element 22 has reached the target temperature (step S105: Yes), the ECU 21 determines the time Te (until the electromotive forces of the two cells match based on the output from the sensor element 22). That is, a period (see FIG. 3) from when the difference is generated between the voltage V1 and the voltage V2 until the generated difference disappears is detected (step S106). Subsequently, the ECU 21 calculates the concentration of sulfur contained in the exhaust gas based on the detected time Te.

  In parallel with the process of step S106, the ECU 21 calculates the average value Ag or the integrated value Sg of the gas amount (air amount) in the period until the electromotive forces of the two cells coincide with each other, for example, an air flow meter (not shown) or the like. (Step S107).

  Next, the ECU 21 is based on (i) the detected time Te, (ii) the calculated average value Ag or integrated value Sg of the gas amount, and (iii) a map as shown in FIG. 8, for example. A correction coefficient is calculated (step S108). Subsequently, the ECU 21 corrects the calculated sulfur concentration with the calculated correction coefficient to calculate a final sulfur concentration.

  FIG. 8 is an example of a map showing the relationship between the time Te, the average gas amount Ag, and the correction coefficient. When the integrated value Sg is used instead of the average gas amount Ag, a map (not shown) showing the relationship between the time Te, the integrated gas amount Sg, and the correction coefficient may be used.

  Next, the ECU 21 controls the heater 225 so that the temperature of the sensor element 22 is, for example, 700 degrees Celsius or higher in order to desorb the sulfur component adsorbed on the sensor element 22 (step S109).

  Next, the ECU 21 determines whether or not the temperature of the sensor element 22 is held at a temperature of 700 degrees Celsius or higher for a predetermined time (step S110). When it is determined that the predetermined time has been held (step S110: Yes), the ECU 21 ends the process. On the other hand, when it determines with not having hold | maintained for the predetermined time (step S110: No), ECU21 performs the process of step S110. Here, the “predetermined time” may be set as a time during which the sulfur component adsorbed on the sensor element 22 can be appropriately desorbed.

  When the sensor element 22 detects the oxygen concentration at the same time as the sulfur concentration, the electromotive force (that is, the voltage V1) relating to the exhaust-side electrode 222 that hardly adsorbs the sulfur component may be used. Note that various known modes can be applied to the method for detecting the oxygen concentration, and thus the description thereof is omitted here.

  The “ECU 21” according to the present embodiment is an example of the “calculation unit” and the “correction unit” according to the present invention. The “air-fuel ratio sensors 23 and 24” according to the present embodiment are an example of “air-fuel ratio detection means”.

<First Modification>
Next, a first modification of the sulfur concentration sensor according to the second embodiment will be described with reference to FIGS.

  In the present modified example, in parallel with the process of step S106 described above (see FIG. 7), the ECU 21 calculates the average value Aaf or the integrated value Saf of the air-fuel ratio during the period until the electromotive forces of the two cells coincide with each other. Calculation is made based on the outputs of the fuel ratio sensors 23 and 24 (step S201).

  Next, the ECU 21 is based on (i) the detected time Te, (ii) the calculated average value Aaf or integrated value Saf of the air-fuel ratio, and (iii), for example, a map as shown in FIG. A correction coefficient is calculated (step S202). Subsequently, the ECU 21 corrects the calculated sulfur concentration with the calculated correction coefficient to calculate a final sulfur concentration.

  FIG. 10 is an example of a map showing the relationship between the time Te, the average value Aaf of the air-fuel ratio, and the correction coefficient. When the integrated value Saf is used instead of the average value Aaf of the air-fuel ratio, a map (not shown) showing the relationship between the time Te, the integrated value Saf of the air-fuel ratio, and the correction coefficient may be used.

<Second Modification>
Next, a second modification of the sulfur concentration sensor according to the second embodiment will be described with reference to FIGS.

  In the present modification, in parallel with the process of step S106 described above (see FIG. 7), the ECU 21 calculates the average value Ag or integrated value of the gas amount (air amount) in the period until the electromotive forces of the two cells match. Sg is calculated (step S301).

  Next, the ECU 21 is based on (i) the detected time Te, (ii) the calculated average value Ag or integrated value Sg of the gas amount, and (iii) a map as shown in FIG. 8, for example. A correction coefficient is calculated. Subsequently, the ECU 21 corrects the calculated sulfur concentration with the calculated correction coefficient to calculate the sulfur component concentration Csi (step S302).

  The ECU 21 calculates the average value Aaf or the integrated value Saf of the air-fuel ratio in the period until the electromotive forces of the two cells coincide with each other in parallel with the process of step S106 described above. Subsequently, the ECU 21 calculates the air-fuel ratio correction coefficient Ck of the sulfur concentration based on the calculated average value Aaf or integrated value Saf of the air-fuel ratio and a map as shown in FIG. 12, for example (step S303).

  FIG. 12 is an example of a map showing the relationship between the average value Aaf of the air-fuel ratio and the air-fuel ratio correction coefficient Ck of the sulfur concentration. When the integrated value Saf is used instead of the average value Aaf of the air-fuel ratio, a map (not shown) showing the relationship between the integrated value Saf of the air-fuel ratio and the air-fuel ratio correction coefficient Ck of the sulfur concentration is used. Good.

  Next, the ECU 21 calculates the final sulfur component concentration Csr based on the sulfur component concentration Csi calculated in the process of step S302 and the air-fuel ratio correction coefficient Ck of the sulfur concentration calculated in the process of step S303. To do.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and the sulfur concentration sensor accompanying such a change. Is also included in the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Engine main body, 12 ... Intake passage, 13 ... Exhaust passage, 14 ... Catalyst, 21 ... ECU, 22 ... Sensor element, 23, 24 ... Air-fuel ratio sensor, 100 ... Sulfur concentration sensor, 221 ... Substrate, 222, 223 ... exhaust side electrode, 224 ... atmosphere side electrode, 225 ... heater

Claims (8)

A sulfur concentration sensor installed in an exhaust passage of an engine and capable of detecting a concentration of sulfur contained in exhaust gas flowing through the exhaust passage,
A substrate made of a solid electrolyte;
A first exhaust-side electrode disposed on a first substrate surface that is a surface of the substrate in contact with the exhaust gas;
A second exhaust side electrode disposed on the first substrate surface and having a sulfur adsorption performance different from the sulfur adsorption performance of the first exhaust side electrode;
An atmosphere-side electrode disposed on a second substrate surface which is a surface in contact with the atmosphere of the substrate;
According to the difference between the first voltage between the first exhaust side electrode and the atmosphere side electrode and the second voltage between the second exhaust side electrode and the atmosphere side electrode, the sulfur contained in the exhaust gas Sulfur concentration detection means for detecting the concentration;
A sulfur concentration sensor comprising: Heating means capable of heating the sulfur concentration sensor;
Air-fuel ratio detecting means for detecting an air-fuel ratio related to the engine;
Control means for controlling the heating means to heat the sulfur concentration sensor in accordance with the detected air-fuel ratio when the sulfur concentration detection means detects the concentration of sulfur contained in the exhaust gas. ,
The sulfur concentration sensor according to claim 1, further comprising: When the concentration of sulfur contained in the exhaust gas is detected by the sulfur concentration detection means, the time average value or integrated value of the exhaust gas, or the time average value or integrated value of the air-fuel ratio of the engine, A calculating means for calculating;
Correction means for correcting the detected sulfur concentration according to the calculated time average value or integrated value of the exhaust gas or the time average value or integrated value of the air-fuel ratio of the engine;
The sulfur concentration sensor according to claim 1, further comprising:   The sulfur concentration detection means is configured to detect the exhaust gas based on an integrated value of the difference in a period from when a difference occurs between the first voltage and the second voltage until the difference is eliminated. The sulfur concentration sensor according to any one of claims 1 to 3, wherein the concentration of sulfur contained in the gas is detected.   The sulfur concentration detection means detects a concentration of sulfur contained in the exhaust gas based on the difference after a predetermined time has elapsed since a difference is generated between the first voltage and the second voltage. The sulfur concentration sensor according to any one of claims 1 to 3, wherein: A first coating layer laminated on the first exhaust-side electrode;
A second coating layer laminated on the second exhaust side electrode;
Further comprising
The first coating layer is (i) low porosity, (ii) thick, or (iii) low porosity and thick compared to the second coating layer,
The sulfur concentration sensor according to any one of claims 1 to 5, wherein:   The sulfur concentration sensor according to any one of claims 1 to 6, wherein the first exhaust-side electrode and the second exhaust-side electrode are composed of only a platinum group element. The first exhaust side electrode is made of palladium,
The second exhaust side electrode is made of platinum,
The sulfur concentration sensor according to any one of claims 1 to 7, further comprising oxygen concentration detection means for detecting a concentration of oxygen contained in the exhaust gas based on the second voltage.

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