JP2016065862A - Sensor control method and sensor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-gas sensor control method and a multi-gas sensor control device capable of curbing a reduction in detection accuracy of an ammonia concentration when using a multi-gas sensor for detecting concentrations of nitrogen oxide and ammonia in measurement object gas.SOLUTION: A multi-gas sensor control device allows a CPU of a microcomputer to calculate concentrations of ammonia, NOand NO in measurement object gas by executing a gas concentration calculation process. In the gas concentration calculation process, depending on whether or not a correction permitting condition is met (S200), the multi-gas sensor control device stores: a latest corrected ammonia concentration as a NHconcentration (latest) (S170); or a NHconcentration (reference) as the NHconcentration (latest) (S210). Thus, the multi-gas sensor control device can curb a reduction in detection accuracy of the ammonia concentration when detecting the same with a multi-gas sensor.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a sensor control method and a sensor control apparatus for controlling a sensor suitable for detecting a nitrogen oxide concentration and an ammonia concentration in a gas to be measured.

In recent years, a urea SCR (selective catalytic reduction) system has attracted attention as a technology for purifying nitrogen oxides (NOx) contained in exhaust gas discharged from internal combustion engines such as gasoline engines and diesel engines. The urea SCR system purifies nitrogen oxides contained in exhaust gas by chemically reacting ammonia (NH ₃ ) and nitrogen oxides (NOx) to reduce nitrogen oxides to nitrogen (N ₂ ). System.

  In this urea SCR system, if the amount of ammonia supplied to the nitrogen oxides becomes excessive, unreacted ammonia may be discharged to the outside while being contained in the exhaust gas. In order to suppress such release of ammonia, a sensor capable of measuring a plurality of types of gas concentrations including a sensor element for measuring the concentration of ammonia contained in exhaust gas is used in the urea SCR system.

  In this urea SCR system, the amount of ammonia used for the reduction of nitrogen oxides is adjusted so that the concentration of ammonia measured by the sensor, that is, the concentration of ammonia contained in the exhaust gas is within a predetermined range. Yes.

In addition, as this sensor, what was provided with the NOx sensor part and the ammonia sensor part is mentioned. Moreover, as this sensor, the form with which a NOx sensor part and an ammonia sensor part are provided separately, and the form (multi-gas sensor) provided with a NOx sensor part and an ammonia sensor part integrally are mentioned. By using such a sensor, it is possible to detect nitric oxide (NO), nitrogen dioxide (NO ₂ ), and ammonia (NH ₃ ).

  Further, in the detection of the ammonia concentration by the ammonia sensor unit, the ammonia concentration may fluctuate due to the influence of the oxygen concentration and the detection accuracy of the ammonia concentration may be lowered. Therefore, based on the output signal of the ammonia sensor unit and the oxygen concentration. A technique for calculating a corrected ammonia concentration has been proposed (see, for example, Patent Document 1). According to such a technique for calculating the corrected ammonia concentration, the influence of the oxygen concentration in the gas to be measured can be reduced, and a decrease in the detection accuracy of the ammonia concentration can be suppressed.

JP 2011-075546 A

  However, in the configuration in which the corrected ammonia concentration is calculated based on the output signal of the ammonia sensor unit and the oxygen concentration, the correction is made when the oxygen concentration changes sharply even under the situation where the actual ammonia concentration does not change. There is a possibility that the ammonia concentration fluctuates and the detection accuracy of the ammonia concentration is lowered.

  For example, in an actual internal combustion engine, the oxygen concentration changes every moment depending on the operating conditions, so the reaction rate of the ammonia sensor unit and the sensor for calculating the oxygen concentration or the predicted value do not always synchronize with the oxygen concentration change.

  In particular, when an oxygen concentration instantaneous change such as a rich spike occurs, it is highly possible that a large error will occur in the calculation if the followability of the oxygen concentration value to the output change of the ammonia sensor is poor. Accuracy may be reduced.

  It is an object of the present invention to provide a sensor control method and a sensor control device that can suppress a decrease in detection accuracy of ammonia concentration when using a sensor that detects nitrogen oxide concentration and ammonia concentration in a gas to be measured.

  A sensor control method according to one aspect of the present invention is a sensor control method for controlling a sensor including a NOx sensor unit and an ammonia sensor unit, and includes an oxygen concentration calculation step, a corrected concentration calculation step, and an oxygen concentration change rate calculation step. And an ammonia concentration setting step.

The NOx sensor unit includes a first pumping cell and a second pumping cell.
The first pumping cell pumps or pumps oxygen in the measurement gas introduced into the measurement chamber.

The second pumping cell is configured such that the second pumping current flows in accordance with the NOx concentration in the gas to be measured whose oxygen concentration is adjusted by the first pumping cell.
The ammonia sensor unit is formed on the outer surface of the NOx sensor unit and outputs an ammonia concentration signal corresponding to the ammonia concentration in the gas to be measured.

In the oxygen concentration calculation step, the oxygen concentration in the gas to be measured is calculated based on the first pumping current flowing through the first pumping cell.
In the corrected concentration calculation step, the corrected ammonia concentration is calculated based on the oxygen concentration and the ammonia concentration signal of the ammonia sensor unit.

In the oxygen concentration change rate calculation step, an oxygen concentration change rate, which is a change rate of the oxygen concentration with time, is calculated.
In the ammonia concentration setting step, when a predetermined correction permission condition is satisfied, the corrected ammonia concentration is set as the detection result of the ammonia concentration. On the other hand, in the ammonia concentration setting step, if the correction permission condition is not satisfied, the correction ammonia concentration calculated when the correction permission condition is satisfied among the correction ammonia concentrations calculated in the past is set as the detection result of the ammonia concentration. . In the ammonia concentration setting step, when the oxygen concentration change rate is less than a predetermined reference determination value, it is determined that the correction permission condition is satisfied, and when the oxygen concentration change rate is equal to or higher than the reference determination value, correction is performed. It is determined that the permission condition is not satisfied.

  In this sensor control method, the corrected ammonia concentration is set to the detection result of the ammonia concentration depending on whether the correction permission condition is satisfied, or the corrected ammonia concentration calculated in the past (in detail, when the correction permission condition is satisfied) It is switched whether to set one of the calculated corrected ammonia concentrations) as the ammonia concentration detection result.

  When the oxygen concentration change rate is less than a predetermined reference determination value, it is determined that the correction permission condition is satisfied. In other words, the oxygen concentration change rate increases as the oxygen concentration change becomes sharper. Therefore, when the oxygen concentration change rate is equal to or higher than the reference determination value, it can be determined that the oxygen concentration has changed sharply. It can be determined that the above is not satisfied. The oxygen concentration change rate correction permission condition includes, for example, an oxygen concentration change rate at which the detection error of the ammonia concentration falls within an allowable range (± 5%, preferably ± 3%) when calculating the corrected ammonia concentration, and ammonia A boundary value between the oxygen concentration change rate at which the concentration detection error deviates from the allowable range and the boundary value are set in advance.

  In other words, when the oxygen concentration change rate is less than a predetermined reference judgment value and the correction permission condition is satisfied, the detection error of the ammonia concentration at the corrected ammonia concentration is within the allowable range, so the corrected ammonia concentration is detected as the ammonia concentration. When set as a result, the detection accuracy of the ammonia concentration does not decrease.

  On the other hand, when the oxygen concentration change rate is equal to or higher than the reference determination value and the correction permission condition is not satisfied, the ammonia concentration detection error in the corrected ammonia concentration exceeds the allowable range. When set to, the detection accuracy of ammonia concentration decreases. By setting the past corrected ammonia concentration calculated when the correction permission condition is satisfied instead of such corrected ammonia concentration as the ammonia concentration detection result, it is possible to suppress a decrease in ammonia concentration detection accuracy. .

  In other words, when the actual ammonia concentration has not changed significantly and the oxygen concentration has changed, the past corrected ammonia concentration calculated when the correction permission condition is satisfied is a value close to the actual ammonia concentration. it is conceivable that. For this reason, by setting the past corrected ammonia concentration calculated when the correction permission condition is satisfied as the detection result of the ammonia concentration, it is possible to suppress a decrease in detection accuracy of the ammonia concentration.

  Therefore, according to this sensor control method, when using the sensor for detecting the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

  In the sensor control method described above, if the correction permission condition is not satisfied in the ammonia concentration setting step, the latest corrected ammonia concentration calculated when the correction permission condition is satisfied among the corrected ammonia concentrations calculated in the past is used. You may set to the detection result of ammonia concentration.

  As described above, the past corrected ammonia concentration calculated when the correction permission condition is satisfied, and the latest corrected ammonia concentration is set as the ammonia concentration detection result, so that a decrease in detection accuracy of the ammonia concentration can be suppressed. .

  In other words, when the actual ammonia concentration has not changed significantly and the oxygen concentration has changed, the latest corrected ammonia concentration of the past corrected ammonia concentration calculated when the correction permission condition is satisfied is actually It is considered that the value is close to the ammonia concentration.

For this reason, as described above, by setting the latest corrected ammonia concentration as the detection result of the ammonia concentration, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.
In the sensor control method described above, in the ammonia concentration setting step, when the correction permission condition is not satisfied, the ammonia concentration set in the previous detection result may be set as the detection result of the current ammonia concentration.

  In other words, the numerical value set in the detection result of ammonia concentration is the corrected ammonia concentration calculated when the correction permission condition is satisfied. Therefore, the correction permission condition is also satisfied for the ammonia concentration set in the previous detection result. The corrected ammonia concentration calculated at the time. The ammonia concentration set in the previous detection result is the latest corrected ammonia concentration among the past corrected ammonia concentrations calculated when the correction permission condition is satisfied, and thus is close to the actual ammonia concentration. Conceivable.

  For this reason, as described above, by setting the ammonia concentration set in the previous detection result as the detection result of the current ammonia concentration, it is possible to suppress a decrease in detection accuracy of the ammonia concentration.

  In the sensor control method described above, in the ammonia concentration setting step, it is determined that the correction permission condition is satisfied when the oxygen concentration change rate is less than the reference determination value and the oxygen concentration exceeds a predetermined reference concentration. If at least one of the oxygen concentration change rate is equal to or higher than the reference determination value and the oxygen concentration is equal to or lower than the reference concentration, it may be determined that the correction permission condition is not satisfied.

  In this sensor control method, it is determined whether the correction permission condition is satisfied including not only the oxygen concentration change rate but also the oxygen concentration, and the corrected ammonia concentration is set as the detection result of the ammonia concentration or the correction calculated in the past is performed. Whether the ammonia concentration (specifically, the corrected ammonia concentration calculated when the correction permission condition is satisfied) is set as the ammonia concentration detection result is switched.

  Note that the oxygen concentration in the correction permission conditions is determined by whether or not the oxygen concentration exceeds a predetermined reference concentration. That is, when the oxygen concentration becomes extremely low, the error in the corrected ammonia concentration tends to increase. Therefore, when the oxygen concentration is equal to or lower than the reference concentration, it can be determined that the error in the corrected ammonia concentration is large. The reference concentration of the oxygen concentration is, for example, an oxygen concentration at which the detection error of the ammonia concentration falls within an allowable range when the corrected ammonia concentration is calculated, and an oxygen concentration at which the detection error of the ammonia concentration deviates from the allowable range. A boundary value is set in advance. For example, when the reference concentration is set to 4%, it is determined that at least the correction permission condition is not satisfied when the oxygen concentration is 4% or less.

  In this ammonia concentration setting step, the correction permission condition is set when the two conditions of “the oxygen concentration change rate is less than the reference determination value” and “the oxygen concentration exceeds the reference concentration” are both satisfied. It is determined that it satisfies. In this ammonia concentration setting step, the correction is made when at least one of the two conditions “the oxygen concentration change rate is equal to or higher than the reference determination value” and “the oxygen concentration is equal to or lower than the reference concentration” is satisfied. It is determined that the permission condition is not satisfied.

  In other words, when the correction permission condition determined based on the oxygen concentration and the oxygen concentration change rate is satisfied, the detection error of the ammonia concentration at the corrected ammonia concentration is within the allowable range, so the corrected ammonia concentration is set as the detection result of the ammonia concentration. In this case, it is possible to suppress a decrease in detection accuracy of the ammonia concentration.

  On the other hand, if the correction permission condition determined based on the oxygen concentration and the oxygen concentration change rate is not satisfied, the detection error of the ammonia concentration at the corrected ammonia concentration exceeds the allowable range. When set, the ammonia concentration detection accuracy decreases. Instead of such corrected ammonia concentration, setting the past corrected ammonia concentration calculated when the correction permission condition is satisfied in the detection result of ammonia concentration can further suppress the decrease in detection accuracy of ammonia concentration. it can.

  In other words, when the actual ammonia concentration has not changed significantly and the oxygen concentration has changed, the past corrected ammonia concentration calculated when the correction permission condition is satisfied is a value close to the actual ammonia concentration. it is conceivable that. For this reason, the fall of the detection precision of ammonia concentration can be suppressed more by setting the above-mentioned correction ammonia concentration to the detection result of ammonia concentration.

  Therefore, according to this sensor control method, in using the sensor for detecting the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, whether the correction permission condition is satisfied including not only the oxygen concentration change rate but also the oxygen concentration. Therefore, it is possible to further suppress a decrease in detection accuracy of the ammonia concentration.

  In the sensor control method described above, in the ammonia concentration setting step, it may be determined that the correction permission condition is not satisfied until a predetermined stop period elapses after it is determined that the correction permission condition is not satisfied. .

That is, when it is determined that the correction permission condition is not satisfied, the influence of the oxygen concentration remains for a certain period thereafter, and there is a high possibility that an error occurs in the corrected ammonia concentration.
Therefore, when the correction permission condition is satisfied among the corrected ammonia concentrations calculated in the past by determining that the correction permission condition is not satisfied until the stop period elapses after it is determined that the correction permission condition is not satisfied. The corrected ammonia concentration calculated in step 1 is set as the ammonia concentration detection result.

  As a result, it is possible to avoid setting the corrected ammonia concentration that is likely to cause an error as the detection result of the ammonia concentration. Therefore, according to this sensor control method, it is possible to further suppress a decrease in detection accuracy of the ammonia concentration.

In the sensor control method described above, in the oxygen concentration change rate calculating step, a value obtained by dividing the previously calculated oxygen concentration by the oxygen concentration calculated this time may be calculated as the oxygen concentration change rate.
In other words, when calculating the oxygen concentration change rate, the value calculated by dividing the previously calculated oxygen concentration by the oxygen concentration calculated this time is calculated as the oxygen concentration change rate. Large value. For this reason, since the oxygen concentration change rate greatly changes with respect to a slight change in oxygen concentration, it is easy to determine whether or not the oxygen concentration change rate has fluctuated.

Therefore, according to this sensor control method, the determination accuracy based on the oxygen concentration change rate can be improved, and the decrease in the ammonia concentration detection accuracy can be further suppressed.
In the sensor control method described above, the sensor may be a multi-gas sensor that integrally includes a NOx sensor unit and an ammonia sensor unit.

  Since such a multi-gas sensor is integrally provided with a NOx sensor part and an ammonia sensor part, it is used for detecting nitrogen oxide concentration and ammonia concentration contained in the same gas to be measured.

  Therefore, according to this sensor control method, when using the multi-gas sensor that detects the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

  In the above-described sensor control method, the sensor may be configured such that the NOx sensor unit and the ammonia sensor unit are individually provided and arranged in the exhaust path of the internal combustion engine. The exhaust path may be configured to include a plurality of spaces partitioned by a partition portion through which exhaust gas can permeate. The NOx sensor unit and the ammonia sensor unit may be arranged in the same space among a plurality of spaces.

  In such a sensor, since the NOx sensor unit and the ammonia sensor unit are arranged in the same space in the exhaust path, it is possible to detect the nitrogen oxide concentration and the ammonia concentration contained in the gas to be measured in the same space. .

  Therefore, according to this sensor control method, when using the sensor for detecting the nitrogen oxide concentration and the ammonia concentration in the gas under measurement in the same space, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

  In the above-described sensor control method in which the NOx sensor unit and the ammonia sensor unit are separately provided, the NOx sensor unit is disposed at the same position as the ammonia sensor unit or upstream of the ammonia sensor unit in the exhaust gas traveling direction. May be.

  Since the relative positional relationship between the NOx sensor unit and the ammonia sensor unit is determined in this manner, the oxygen concentration detection position is the same position or upstream side in the exhaust gas traveling direction compared to the ammonia concentration detection position. It becomes. In this case, in calculating the corrected ammonia concentration, the oxygen concentration detected at the same position as the detection position of the ammonia concentration or at the upstream side can be used. As a result, the oxygen concentration detection time is not delayed from the ammonia concentration detection time, and the corrected ammonia concentration can be calculated with high accuracy.

Therefore, according to this sensor control method, the corrected ammonia concentration can be calculated with high accuracy, so that a decrease in detection accuracy of the ammonia concentration can be suppressed.
A sensor control device according to another aspect of the present invention is a sensor control device that controls a sensor including a NOx sensor unit and an ammonia sensor unit, and includes an oxygen concentration calculation unit, a corrected concentration calculation unit, and an oxygen concentration change rate calculation unit. And an ammonia concentration setting unit.

The NOx sensor unit includes a first pumping cell and a second pumping cell.
The first pumping cell pumps or pumps oxygen in the measurement gas introduced into the measurement chamber.

The second pumping cell is configured such that the second pumping current flows in accordance with the NOx concentration in the gas to be measured whose oxygen concentration is adjusted by the first pumping cell.
The ammonia sensor unit is formed on the outer surface of the NOx sensor unit and outputs an ammonia concentration signal corresponding to the ammonia concentration in the gas to be measured.

The oxygen concentration calculation unit calculates the oxygen concentration in the measurement gas based on the first pumping current flowing through the first pumping cell.
The corrected concentration calculation unit calculates a corrected ammonia concentration based on the oxygen concentration and the ammonia concentration signal of the ammonia sensor unit.

The oxygen concentration change rate calculation unit calculates an oxygen concentration change rate that is a change rate of the oxygen concentration with time.
The ammonia concentration setting unit sets the corrected ammonia concentration as the detection result of the ammonia concentration when the predetermined correction permission condition is satisfied. On the other hand, when the correction permission condition is not satisfied, the ammonia concentration setting unit sets the corrected ammonia concentration calculated when the correction permission condition is satisfied among the corrected ammonia concentrations calculated in the past as the detection result of the ammonia concentration. . The ammonia concentration setting unit determines that the correction permission condition is satisfied when the oxygen concentration change rate is less than a predetermined reference determination value, and corrects when the oxygen concentration change rate is equal to or greater than the reference determination value. It is determined that the permission condition is not satisfied.

  Similar to the above-described sensor control method, this sensor control device can suppress a decrease in detection accuracy of ammonia concentration when using a multi-gas sensor that detects nitrogen oxide concentration and ammonia concentration in a gas to be measured.

  In the sensor control apparatus described above, the ammonia concentration setting unit, when the correction permission condition is not satisfied, out of the corrected ammonia concentrations calculated in the past, the latest correction ammonia concentration calculated when the correction permission condition is satisfied. You may set to the detection result of ammonia concentration.

  Similar to the above-described sensor control method, this sensor control device can suppress a decrease in ammonia concentration detection accuracy by setting the latest corrected ammonia concentration as the ammonia concentration detection result.

  In the above-described sensor control device, the ammonia concentration setting unit may set the ammonia concentration set in the previous detection result as the detection result of the current ammonia concentration when the correction permission condition is not satisfied.

  Similar to the above-described sensor control method, this sensor control device sets the ammonia concentration set in the previous detection result as the detection result of the current ammonia concentration, thereby suppressing a decrease in ammonia concentration detection accuracy. it can.

  In the sensor control device described above, the ammonia concentration setting unit determines that the correction permission condition is satisfied when the oxygen concentration change rate is less than the reference determination value and the oxygen concentration exceeds a predetermined reference concentration. If at least one of the oxygen concentration change rate is equal to or higher than the reference determination value and the oxygen concentration is equal to or lower than the reference concentration, it may be determined that the correction permission condition is not satisfied.

  As with the sensor control method described above, this sensor control device permits modification including not only the oxygen concentration change rate but also the oxygen concentration when using a sensor that detects the nitrogen oxide concentration and ammonia concentration in the gas under measurement. By determining whether or not the condition is satisfied, a decrease in ammonia concentration detection accuracy can be further suppressed.

In the above-described sensor control device, the sensor may be a multi-gas sensor integrally including a NOx sensor unit and an ammonia sensor unit.
Since such a multi-gas sensor is integrally provided with a NOx sensor part and an ammonia sensor part, it is used for detecting nitrogen oxide concentration and ammonia concentration contained in the same gas to be measured.

  Therefore, according to this sensor control apparatus, when using the multi-gas sensor for detecting the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

  In the above-described sensor control device, the sensor may be configured such that the NOx sensor unit and the ammonia sensor unit are individually provided and arranged in the exhaust path of the internal combustion engine. The exhaust path may be configured to include a plurality of spaces partitioned by a partition portion through which exhaust gas can permeate. The NOx sensor unit and the ammonia sensor unit may be arranged in the same space among a plurality of spaces.

  In such a sensor, since the NOx sensor unit and the ammonia sensor unit are arranged in the same space in the exhaust path, it is possible to detect the nitrogen oxide concentration and the ammonia concentration contained in the gas to be measured in the same space. .

  Therefore, according to this sensor control device, when using the sensor that detects the nitrogen oxide concentration and the ammonia concentration in the gas under measurement in the same space, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

  In the above-described sensor control device in which the NOx sensor unit and the ammonia sensor unit are separately provided, the NOx sensor unit is disposed at the same position as the ammonia sensor unit or upstream from the ammonia sensor unit in the exhaust gas traveling direction. May be.

  Since the relative positional relationship between the NOx sensor unit and the ammonia sensor unit is determined in this manner, the oxygen concentration detection position is the same position or upstream side in the exhaust gas traveling direction compared to the ammonia concentration detection position. It becomes. In this case, in calculating the corrected ammonia concentration, the oxygen concentration detected at the same position as the detection position of the ammonia concentration or at the upstream side can be used. As a result, the oxygen concentration detection time is not delayed from the ammonia concentration detection time, and the corrected ammonia concentration can be calculated with high accuracy.

  Therefore, according to this sensor control device, the corrected ammonia concentration can be calculated with high accuracy, so that a decrease in the detection accuracy of the ammonia concentration can be suppressed.

  According to the sensor control method and the sensor control apparatus of the present invention, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration when using the sensor that detects the nitrogen oxide concentration and the ammonia concentration in the gas to be measured.

It is sectional drawing which shows the internal structure of the multi gas sensor with which a multi gas sensor control apparatus is equipped. It is a block diagram explaining the structure of a multi-gas sensor control apparatus. It is an expanded view which shows the structure of an ammonia sensor part. It is a block diagram which shows the structure of the various data stored in the microcomputer of a multi gas sensor control apparatus. It is explanatory drawing which shows an example of an ammonia concentration output-ammonia concentration relational expression. It is a flowchart which shows the processing content of a gas concentration calculation process. It is explanatory drawing which shows the measurement result of the measurement test which measured ammonia concentration using the multi-gas sensor control apparatus. It is a block diagram explaining the structure of the multi-gas sensor control apparatus of the modification 1. It is sectional drawing showing the structure of the 1st ammonia sensor part in a sensor element part, and the 2nd ammonia sensor part. It is a flowchart which shows the processing content of the gas concentration calculation process in the modification 2. It is a block diagram explaining the structure of the sensor control apparatus of the modification 3. It is a block diagram explaining the structure of the sensor control apparatus of the modification 4.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
In addition, this invention is not limited to the following embodiment at all, and it cannot be overemphasized that various forms may be taken as long as it belongs to the technical scope of this invention.

[1. First Embodiment]
[1-1. overall structure]
As a first embodiment, a multi-gas sensor control device 1 provided in an internal combustion engine such as an automobile will be described.

The multi-gas sensor control device 1 is used in a urea SCR system that purifies nitrogen oxides (NOx) contained in exhaust gas (measured gas) discharged from a diesel engine. More specifically, the concentration of nitrogen monoxide (NO), nitrogen dioxide (NO ₂ ), and ammonia contained in the exhaust gas after reacting NOx contained in the exhaust gas with ammonia (urea) is measured. Is.

As shown in FIGS. 1 and 2, the multi-gas sensor control device 1 controls the multi-gas sensor 2 that is a sensor main body, and controls the multi-gas sensor 2 and performs arithmetic processing on the sensor output, so that the concentrations of NO, NO _2, and ammonia And a control unit 3 (calculation unit 3).

[1-2. Multi gas sensor]
As shown in FIG. 1, the multigas sensor 2 mainly includes a sensor element unit 10, a metal shell 110, a separator 134, and a connection terminal 138. In the following description, the side (lower side in FIG. 1) where the sensor element unit 10 of the multi-gas sensor 2 is arranged is the front end side, and the side where the connection terminal 138 is arranged (upper side in FIG. 1) is the rear end. It is written as side.

  The sensor element unit 10 has a plate shape extending in the axis O direction. Electrode terminal portions 10 </ b> A and 10 </ b> B are disposed at the rear end of the sensor element portion 10. In FIG. 1, for ease of illustration, the electrode terminal portions formed on the sensor element portion 10 are only the electrode terminal portion 10A and the electrode terminal portion 10B. A plurality of electrode terminal portions are formed according to the number of electrodes and the like that the ammonia sensor portion 21 has. A more detailed description of the sensor element unit 10 will be described later.

  The metal shell 110 is a cylindrical member in which a screw portion 111 that fixes the multi-gas sensor 2 to an exhaust pipe of a diesel engine is formed on the outer surface. The metal shell 110 is mainly provided with a through hole 112 penetrating in the axial direction and a shelf 113 projecting radially inward of the through hole 112. The shelf 113 is formed as an inwardly tapered surface having an inclination that approaches the front end side from the radially outer side of the through hole 112 toward the center.

  The metal shell 110 holds the sensor element unit 10 in a state where the front end side of the sensor element unit 10 protrudes from the through hole 112 to the front end side and the rear end side of the sensor element unit 10 protrudes to the rear end side of the through hole 112. Is.

  Inside the through-hole 112 of the metal shell 110, in order from the front end side to the rear end side, a ceramic holder 114 that is a cylindrical member surrounding the radial periphery of the sensor element unit 10, and a talc ring that is a powder-filled layer 115 and 116 and a ceramic sleeve 117 are laminated.

  A caulking packing 118 is disposed between the ceramic sleeve 117 and the end portion on the rear end side of the metal shell 110. A metal holder 119 is disposed between the ceramic holder 114 and the shelf 113 of the metal shell 110. The metal holder 119 holds the talc ring 115 and the ceramic holder 114. The end portion on the rear end side of the metal shell 110 is a portion that is crimped so as to press the ceramic sleeve 117 toward the distal end side via the crimping packing 118.

  An external protector 121 and an internal protector 122 are provided at the end of the metal shell 110 on the front end side. The external protector 121 and the internal protector 122 are cylindrical members formed of a metal material such as stainless steel whose end on the distal end side is closed. The internal protector 122 is welded to the metal shell 110 in a state where the end of the sensor element unit 10 on the front end side is covered, and the external protector 121 is welded to the metal shell 110 in a state where the internal protector 122 is covered.

  At the end on the rear end side of the metal shell 110, the end portion on the front end side of the outer cylinder 131 formed in a cylindrical shape is fixed. Furthermore, a grommet 132 that closes the opening is disposed in an opening that is an end portion on the rear end side of the outer cylinder 131.

  The grommet 132 is formed with a lead wire insertion hole 133 through which the lead wire 141 is inserted. The lead wire 141 is electrically connected to the electrode terminal portion 10A of the sensor element portion 10 and the electrode terminal portion 10B.

  The separator 134 is a cylindrical member disposed on the rear end side of the sensor element unit 10. A space formed inside the separator 134 is an insertion hole 135 penetrating in the axial direction. On the outer surface of the separator 134, a flange 136 that protrudes radially outward is formed.

The rear end portion of the sensor element portion 10 is inserted into the insertion hole 135 of the separator 134, and the electrode terminal portions 10 </ b> A and 10 </ b> B are disposed inside the separator 134.
Between the separator 134 and the outer cylinder 131, a holding member 137 formed in a cylindrical shape is disposed. The holding member 137 contacts the flange 136 of the separator 134 and also contacts the inner surface of the outer cylinder 131, thereby fixing and holding the separator 134 with respect to the outer cylinder 131.

  The connection terminal 138 is a member disposed in the insertion hole 135 of the separator 134, and electrically connects the electrode terminal portion 10A and the electrode terminal portion 10B of the sensor element portion 10 and the lead wire 141 independently of each other. It is a conductive member. In FIG. 1, only two connection terminals 138 are shown for ease of illustration.

[1-3. Sensor element section]
Here, the detail of a structure of the sensor element part 10 is demonstrated, referring FIG. For convenience of explanation, FIG. 2 shows only a schematic cross-sectional view along the longitudinal direction of the sensor element unit 10.

  The sensor element unit 10 is mainly provided with a NOx sensor unit 11 and an ammonia sensor unit 21. The NOx sensor unit 11 and the ammonia sensor unit 21 in the present embodiment have the same configuration as a known NOx sensor and the same configuration as a known ammonia sensor, respectively.

  The NOx sensor unit 11 mainly includes an insulating layer 10e, a first solid electrolyte body 12a, an insulating layer 10d, a third solid electrolyte body 16a, an insulating layer 10c, a second solid electrolyte body 18a, an insulating layer 10b, and an insulating layer 10a. However, the structure is laminated in this order. Each of the insulating layers 10a, 10b, 10c, 10d, and 10e described above is formed mainly of alumina.

  Further, in the NOx sensor unit 11, the first measurement chamber S1 is provided between the first solid electrolyte body 12a and the third solid electrolyte body 16a, and the second measurement chamber S2 corresponding to the NOx measurement chamber is provided in the first solid state. A third solid electrolyte body 16a is provided between the electrolyte body 12a and the second solid electrolyte body 18a.

  A first diffusion resistor 14 is disposed at the inlet end (left end in FIG. 2) of the first measurement chamber S1 into which the gas to be measured is introduced. A second diffusion resistor 15 that partitions the first measurement chamber S1 and the second measurement chamber S2 is disposed at the end opposite to the inlet end in the first measurement chamber S1 (the right end in FIG. 2). . The first diffusion resistor 14 and the second diffusion resistor 15 described above are made of a porous material such as alumina, and have permeability to the gas to be measured.

  The NOx sensor unit 11 further includes a heater (heater unit) that raises the NOx sensor unit 11 and the ammonia sensor unit 21 to the activation temperature and increases the conductivity of oxygen ions in the solid electrolyte bodies constituting the sensors. 19 is provided. The heater 19 is formed of platinum or an alloy containing platinum in the shape of a long plate extending along the longitudinal direction of the sensor element unit 10, and is embedded between the insulating layer 10b and the insulating layer 10a. .

In addition, the NOx sensor unit 11 is provided with a first pumping cell 12, an oxygen concentration detection cell 16, and a second pumping cell 18.
The first pumping cell 12 includes a first solid electrolyte body 12a mainly composed of zirconia having oxygen ion conductivity, an inner first pumping electrode (first electrode) 12b mainly composed of platinum, and an outer first pumping electrode (first electrode). 1 electrode) 12c.

  The inner first pumping electrode 12b is provided on the surface of the first solid electrolyte body 12a exposed to the first measurement chamber S1. Further, the inner first pumping electrode 12b has a surface on the first measurement chamber S1 side covered with a protective layer 12d made of a porous body.

  The outer first pumping electrode 12c is an electrode serving as a counter electrode for the inner first pumping electrode 12b, and is disposed with the first solid electrolyte body 12a sandwiched between the inner first pumping electrode 12b. A portion corresponding to a region where the outer first pumping electrode 12c is disposed in the insulating layer 10e is hollowed out and filled with the porous body 12e. The porous body 12e allows gas (oxygen) to enter and exit between the outer first pumping electrode 12c and the outside.

  The oxygen concentration detection cell 16 is disposed downstream of the first pumping cell 12 and upstream of the second pumping cell 18. The oxygen concentration detection cell 16 includes a third solid electrolyte body 16a mainly composed of zirconia, and a detection electrode 16b and a reference electrode 16c mainly composed of platinum and arranged with the third solid electrolyte body 16a interposed therebetween. It is mainly composed.

  The detection electrode 16b is a surface exposed to the first measurement chamber S1 of the third solid electrolyte body 16a, and is provided downstream of the inner first pumping electrode 12b, in other words, in a region on the second diffusion resistor 15 side. It has been.

  A reference electrode 16c, which is a counter electrode of the detection electrode 16b, is disposed inside a reference oxygen chamber 17 formed by cutting out the insulating layer 10c. The reference oxygen chamber 17 is filled with a porous body. In the reference oxygen chamber 17, there is oxygen sent from the first measurement chamber S1, and oxygen in the reference oxygen chamber 17 is used as an oxygen reference.

  The second pumping cell 18 includes a second solid electrolyte body 18a mainly composed of zirconia, an inner second pumping electrode (second electrode) 18b mainly composed of platinum, and a second pumping counter electrode (second electrode) 18c. Consists mainly of.

  The inner second pumping electrode 18b is provided in a region exposed to the second measurement chamber S2 in the second solid electrolyte body 18a. The second pumping counter electrode 18c is a region exposed to the reference oxygen chamber 17 in the second solid electrolyte body 18a, and is provided in a portion facing the reference electrode 16c.

Further, the inner first pumping electrode 12b, the detection electrode 16b, and the inner second pumping electrode 18b are each connected to a reference potential.
On the other hand, the ammonia sensor unit 21 is formed on the outer surface of the NOx sensor unit 11, more specifically, on the insulating layer 10e. The ammonia sensor unit 21 is disposed at substantially the same position as the reference electrode 16c in the longitudinal direction of the NOx sensor unit 11 (left and right direction in FIG. 2).

  The ammonia sensor unit 21 includes a pair of electrodes 21 a formed on the solid electrolyte body 23 for the ammonia sensor unit and a selective reaction layer 21 b that covers the pair of electrodes 21 a, and changes in electromotive force between the pair of electrodes 21 a. The ammonia concentration in the measurement gas is detected.

  A porous diffusion layer 24 (protective layer 24) is formed so as to completely cover the selective reaction layer 21b, and is configured to be capable of adjusting the diffusion rate of the gas to be measured flowing into the ammonia sensor unit 21 from the outside. Yes.

FIG. 3 is a development view showing the configuration of the ammonia sensor unit 21.
The pair of electrodes 21a includes a pair of electrodes 21a1 and 21a2 disposed on the solid electrolyte body 23 for the ammonia sensor section.

  Leads 21ax and 21ay are extended from the electrodes 21a1 and 21a2 along the longitudinal direction of the solid electrolyte body 23 for the ammonia sensor section, respectively. The leads 21ax and 21ay are covered with an insulating layer 22. However, the right ends (not shown) of the leads 21ax and 21ay are exposed without being covered with the insulating layer 22 to form predetermined electrode terminal portions, respectively.

  The electrodes 21a1 and 21a2 are spaced apart from each other along the short direction of the solid electrolyte body 23 for the ammonia sensor section. The electrode 21a1 is made of a material whose main component is gold and functions as a detection electrode, and the electrode 21a2 is made of a material whose main component is platinum and functions as a reference electrode. Since the detection electrode 21a1 is more reactive with ammonia than the reference electrode 21a2, an electromotive force is generated between the detection electrode 21a1 and the reference electrode 21a2.

Further, the solid electrolyte body 23 for the ammonia sensor portion is made of an oxygen ion conductive material such as ZrO ₂ , and the leads 21ax and 21ay are made of a material mainly containing platinum, for example.

The selective reaction layer 21b has a role of burning combustible gas components other than ammonia in the gas to be measured. When the selective reaction layer 21b is present, ammonia in the gas to be measured can be detected without being affected by the combustible gas component. The selective reaction layer 21b is usually composed of a metal oxide as a main component, but in particular, a material containing vanadium oxide (V ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ) at a predetermined ratio (for example, bismuth vanadium oxide: BiVO). ₄ ).

  Even if the selective reaction layer 21b covers only the detection electrode 21a1, the above-described effects can be exhibited. In the present embodiment, the detection electrode 21a1 and the selective reaction layer 21b are provided separately. However, the selective reaction layer 21b is not provided, and a material (for example, a metal oxide) that forms the selective reaction layer 21b on the detection electrode 21a1. ) May be included.

Examples of the diffusion layer 24 include at least one selected from the group consisting of alumina, spinel (MgAl ₂ O ₄ ), silica alumina, and mullite. The gas diffusion time reaching the selective reaction layer 21b and the electrodes 21a1 and 21a2 can be arbitrarily adjusted by appropriately adjusting the thickness, particle size, particle size distribution, porosity, blending ratio, and the like of the diffusion layer 24. .

  In this embodiment, the temperature of the oxygen concentration detection cell 16 is measured, and heating by the heater 19 is performed based on the measured temperature. In this embodiment, when the control temperature of the second solid electrolyte body 18a of the NOx sensor unit 11 is 700 ° C., the temperature of the ammonia sensor unit 21 is 650 ° C.

[1-4. Control unit]
As shown in FIG. 2, the control unit 3 of the multi-gas sensor control device 1 is electrically connected to an ECU 200 that is a vehicle-side control device of a vehicle on which the multi-gas sensor control device 1 is mounted. The ECU 200 receives data indicating the NO concentration, NO ₂ concentration and ammonia concentration in the exhaust gas calculated by the control unit 3, and executes control processing of the operating state of the diesel engine based on the received data, or the catalyst The accumulated NOx purification process is executed.

As shown in FIG. 2, the control unit 3 includes a control circuit 50 that is an analog circuit disposed on a circuit board, and a microcomputer 60.
The microcomputer 60 controls the entire control unit 3. The microcomputer 60 mainly includes a CPU 61 as a central processing unit, a RAM 62 and a ROM 63 as storage means, a signal input / output unit 64, an A / D converter 65, and a clock (not shown). Is provided. The microcomputer 60 performs various processes when the CPU 61 executes a program stored in advance in the ROM 63 or the like.

  The control circuit 50 includes a reference voltage comparison circuit 51, an Ip1 drive circuit 52, a Vs detection circuit 53, an Icp supply circuit 54, an Ip2 detection circuit 55, a Vp2 application circuit 56, a heater drive circuit 57, and an electromotive force. The detection circuit 58 is mainly provided.

  The Ip1 drive circuit 52 is electrically connected to the outer first pumping electrode 12c of the NOx sensor unit 11, and the Vs detection circuit 53 and the Icp supply circuit 54 are electrically connected to the reference electrode 16c. The Ip2 detection circuit 55 and the Vp2 application circuit 56 are electrically connected to the second pumping counter electrode 18c, and the heater drive circuit 57 is electrically connected to the heater 19.

  The electromotive force detection circuit 58 is electrically connected to the pair of electrodes 21a (the detection electrode 21a1 and the reference electrode 21a2) in the ammonia sensor unit 21. The electromotive force detection circuit 58 detects an ammonia electromotive force EMF, which is an electromotive force between the detection electrode 21a1 and the reference electrode 21a2, and outputs it to the microcomputer 60.

  The Ip1 drive circuit 52 supplies the first pumping current Ip1 between the inner first pumping electrode 12b and the outer first pumping electrode 12c, and detects the supplied first pumping current Ip1.

  The Vs detection circuit 53 detects the voltage Vs between the detection electrode 16b and the reference electrode 16c, and outputs the detected result to the reference voltage comparison circuit 51. The reference voltage comparison circuit 51 compares the reference voltage (for example, 425 mV) with the output (voltage Vs) of the Vs detection circuit 53, and outputs the comparison result to the Ip1 drive circuit 52.

  The Ip1 drive circuit 52 controls the flow direction and magnitude of the Ip1 current so that the voltage Vs becomes equal to the above-described reference voltage, and has a predetermined value that does not decompose the oxygen concentration in the first measurement chamber S1. To adjust.

  The Icp supply circuit 54 allows a weak current Icp to flow between the detection electrode 16b and the reference electrode 16c. By supplying the current Icp, oxygen is sent into the reference oxygen chamber 17 from the first measurement chamber S1. The reference electrode 16c is exposed to a predetermined oxygen concentration as a reference.

The Vp2 application circuit 56 applies a constant voltage Vp2 (for example, 450 mV) between the inner second pumping electrode 18b and the second pumping counter electrode 18c, and decomposes NOx into nitrogen and oxygen. The constant voltage Vp2 is such a voltage that the NOx gas in the gas to be measured is decomposed into oxygen and N ₂ gas.

  The Ip2 detection circuit 55 detects the second pumping current Ip2 flowing through the second pumping cell 18. The second pumping current Ip2 is a current that flows when oxygen generated by the decomposition of NOx is pumped from the second measurement chamber S2 to the second pumping counter electrode 18c side through the second solid electrolyte body 18a.

  The Ip1 drive circuit 52 outputs the detected value of the first pumping current Ip1 to the A / D converter 65, and the Ip2 detection circuit 55 supplies the detected value of the second pumping current Ip2 to the A / D converter 65. Output. The A / D converter 65 digitally converts the values of the first pumping current Ip1 and the second pumping current Ip2 and outputs them to the CPU 61 via the signal input / output unit 64.

[1-5. Control circuit]
Next, control by the control circuit 50 will be described below.
First, when the engine is started and electric power is supplied to the control circuit 50 from the outside, electric power is supplied from the heater drive circuit 57 to the heater 19. The heater 19 supplied with electric power generates heat and heats the first pumping cell 12, the oxygen concentration detection cell 16, and the second pumping cell 18 to the activation temperature.

  When the NOx sensor unit 11 is heated to a target temperature by the heater 19, the ammonia sensor unit 21 disposed on the NOx sensor unit 11 is also heated to a desired temperature and activated.

  Further, the current Icp is supplied from the Icp supply circuit 54 between the detection electrode 16b and the reference electrode 16c. Then, oxygen is sent into the reference oxygen chamber 17 from the first measurement chamber S1, and the sent oxygen becomes the oxygen reference.

  When the first pumping cell 12, the oxygen concentration detection cell 16, and the second pumping cell 18 are heated to the activation temperature, the first pumping cell 12 pumps out oxygen from the first measurement chamber S1. That is, oxygen in the gas to be measured (exhaust gas) flowing into the first measurement chamber S1 is pumped from the inner first pumping electrode 12b of the first pumping cell 12 toward the outer first pumping electrode 12c.

  The oxygen concentration in the first measurement chamber S1 is a concentration corresponding to the interelectrode voltage Vs of the oxygen concentration detection cell 16. The Ip1 drive circuit 52 controls the first pumping current Ip1 flowing through the first pumping cell 12 so that the interelectrode voltage Vs becomes the above-described reference voltage. By doing so, the oxygen concentration in the first measurement chamber S1 is adjusted to such an extent that NOx is not decomposed.

  The gas to be measured whose oxygen concentration is adjusted in the first measurement chamber S1 then flows into the second measurement chamber S2. In the second measurement chamber S2, NOx contained in the gas to be measured is decomposed into nitrogen and oxygen. That is, when a constant voltage Vp2 (for example, 450 mV) is applied from the Vp2 application circuit 56 as a voltage between the electrodes of the second pumping cell 18, NOx is decomposed into nitrogen and oxygen. The constant voltage Vp2 is such a voltage that the NOx gas in the measurement gas is decomposed into oxygen and N2 gas, and is higher than the control voltage value of the oxygen concentration detection cell 16.

  Oxygen generated by the decomposition of NOx is pumped out of the second measurement chamber S2 by the second pumping cell 18. At this time, the second pumping cell 18 is supplied with a second pumping current Ip2 to pump out oxygen. Since there is a linear proportional relationship between the second pumping current Ip2 and the NOx concentration, the second pumping current Ip2 detected by the Ip2 detection circuit 55 is a value that is linearly proportional to the NOx concentration.

  On the other hand, an electromotive force is generated between the detection electrode 21a1 and the reference electrode 21a2 of the ammonia sensor unit 21 according to the ammonia concentration contained in the gas to be measured. The electromotive force detection circuit 58 detects an electromotive force between the detection electrode 21a1 and the reference electrode 21a2 as an ammonia electromotive force.

Note that the value of the second pumping current Ip2 includes the influence of the oxygen concentration, NO ₂ concentration, and ammonia concentration of the gas to be measured in the second measurement chamber S2. Further, the ammonia electromotive force EMF output from the ammonia sensor unit 21 includes the influence of the oxygen concentration, NO concentration, NO ₂ concentration, and temperature of each sensor unit 11, 21 of the gas to be measured. In this embodiment, after removing the influence of the oxygen concentration from the second pumping current Ip2 and the ammonia electromotive force, the NO concentration, the NO ₂ concentration, and the ammonia concentration are obtained by arithmetic processing. The details of the calculation process will be described later. The oxygen concentration is obtained from the first pumping current Ip1 using a relational expression.

[1-6. Microcomputer]
Here, the ROM 63 of the microcomputer 60 stores various data described below. The CPU 61 reads various data from the ROM 63 and performs various arithmetic processes such as removing the influence of the oxygen concentration from the value of the second pumping current Ip2 and the ammonia electromotive force.

As schematically shown in FIG. 4, the ROM 63 includes a “first pumping current (Ip1) -oxygen concentration relational expression” 63a and a plurality of “ammonia concentration output (electromotive force EMF) -ammonia concentration relations set for each oxygen concentration”. 63b, “second pumping current (Ip2) -NO concentration relational expression” 63c, “negative ammonia concentration output-NO ₂ concentration relational expression” 63d, “contributing second pumping current-NO” A concentration / NO ₂ concentration relational expression 63e and a plurality of “ammonia concentration output-ammonia concentration relational expressions” 63f set for each of the oxygen concentration and the NO ₂ concentration are stored.

  In the example of FIG. 4, the various data 63a to 63f are set as predetermined relational expressions, but may be a table or the like as long as various gas concentrations are calculated from the output of the sensor. Further, the various data 63a to 63f can be values (relational expressions, tables, etc.) obtained by using a model gas whose gas concentration is known in advance.

  The “first pumping current-oxygen concentration relational expression” 63a is a first pumping current (Ip1) that flows through the first pumping cell 12 as oxygen in the measurement gas introduced into the first measurement chamber is pumped or pumped. And the relationship between the oxygen concentration in the gas to be measured. Although not shown, normally, Ip1 and the oxygen concentration are in a substantially linear relationship. Based on the “first pumping current-oxygen concentration relational expression” 63a, the oxygen concentration in the measurement gas can be calculated.

  "Ammonia concentration output-ammonia concentration relational expression" 63b is set for each oxygen concentration, and is a relational expression between the ammonia concentration output of the ammonia sensor unit and the ammonia concentration in the gas to be measured.

  FIG. 5 shows an example of an ammonia concentration output-ammonia concentration relational expression. In the present embodiment, the ammonia concentration is expressed by a cubic expression of EMF for each different oxygen concentration. Although the EMF varies depending on the oxygen concentration, it is based on the “ammonia concentration output-ammonia concentration relational expression” 63b for each oxygen concentration. "Corrected ammonia concentration") can be calculated.

  The ammonia concentration output-ammonia concentration relational expression at an unset oxygen concentration can be calculated by extrapolation from the ammonia concentration output-ammonia concentration relational expression at two oxygen concentrations sandwiching the oxygen concentration, for example. .

Further, the microcomputer 60 includes a “second pumping current (Ip2) —NO concentration relational expression” 63c, a “negative ammonia concentration output—NO ₂ concentration relational expression” 63d, “contributing second pumping current—NO concentration, NO _2. Using the “concentration relational expression” 63e and the “ammonia concentration output-ammonia concentration relational expression” 63f, the NO concentration and the NO ₂ concentration are calculated.

Incidentally, a known method for calculating the NO concentration, NO ₂ concentration, for example, because it is described in JP 2011-075546, the detailed description thereof is omitted here.
Next, a gas concentration calculation process executed in the CPU 61 of the microcomputer 60 will be described. The gas concentration calculation process is a process for calculating the concentrations (NO concentration, NO ₂ concentration and ammonia concentration) of various gas components in the measured gas using the second pumping current Ip2 and the ammonia electromotive force EMF.

  In the urea SCR system, urea water is injected according to the detection result of the multi-gas sensor 2 in order to purify NOx, but when it is determined that NOx has been purified, the urea water injection is stopped. ing. Therefore, when a certain time has elapsed since the injection of urea water was stopped, the CPU 61 considers that “the ammonia concentration in the gas to be measured is 0”.

FIG. 6 is a flowchart showing the processing content of the gas concentration calculation processing.
When the gas concentration calculation process is started, first, in S110 (S represents a step), the heater drive circuit 57 is operated to cause the heater 19 to generate heat.

In the next S120, initialization processing is performed, and the values of internal variables and internal flags used in this processing are reset.
In next S130, it is determined whether or not the multi-gas sensor 2 (first pumping cell 12, oxygen concentration detection cell 16, second pumping cell 18, and ammonia sensor unit 21) has reached the activation temperature by the heater 19. If the determination is affirmative, the process proceeds to S140. If the determination is negative, the same step is repeatedly executed to wait.

When an affirmative determination is made in S130 and the process proceeds to S140, the first pumping current Ip1, the second pumping current Ip2, and the ammonia electromotive force EMF are measured.
In the next S150, the oxygen concentration is calculated. Specifically, the calculation of the oxygen concentration is performed by calculating the relation between the first pumping current Ip1 measured in S140 and the relational expression stored in the ROM 63 (the relational expression between the first pumping current Ip1 and the oxygen concentration (for details, “first pumping This is executed using the current (Ip1) -oxygen concentration relational expression 63a)). The oxygen concentration obtained at this time is stored as “O ₂ concentration (current)”.

In the next S160, it is determined whether or not a value is stored in “O ₂ concentration (previous)” which is one of internal variables used for calculation in the CPU 61. If an affirmative determination is made, the process proceeds to S190. If a negative determination is made, the process proceeds to S170.

The “O ₂ concentration (previous)” is an internal variable whose value is stored in S180 or S250 described later. That is, in S160, it is determined whether or not the storage process of the value to “O ₂ concentration (previous)” in S180 has been executed. For this reason, after starting the gas concentration calculation process, a negative determination is made at the first execution of S160, and an affirmative determination is made at the second and subsequent executions of S160.

If a negative determination is made in S160 and the process proceeds to S170, the calculation of “NH ₃ concentration (current)”, “NO ₂ concentration (current)”, and “NO concentration (current)” is performed in S170.
Specifically, using the above-mentioned “ammonia concentration output (electromotive force EMF) -ammonia concentration relational expression” 63b, an accurate ammonia concentration that is not affected by the oxygen concentration in the gas to be measured (“correction of claims” "Ammonia concentration") is calculated, and this corrected ammonia concentration is stored as the value of "NH ₃ concentration (current)". The corrected ammonia concentration calculated at this time represents the ammonia concentration from which the influence of the oxygen concentration has been removed.

In S170, the above-mentioned “second pumping current (Ip2) -NO concentration relational expression” 63c, “negative ammonia concentration output-NO2 concentration relational expression” 63d, “contributing second pumping current-NO concentration, NO2 concentration relation”. wherein "63e," ammonia concentration output - such as the second pumping current Ip2 measured in ammonia concentration relationship "63f, S140, using, performs calculation of NO ₂ concentration and NO concentration," NO ₂ concentration (time respectively ) ”And“ NO concentration (current) ”. In addition, since the well-known method for calculating NO density | concentration and NO2 density | concentration is described in Unexamined-Japanese-Patent No. 2011-075546, detailed description here is abbreviate | omitted.

In the next S180, the value of “NH ₃ concentration (current)” is stored as the value of “NH ₃ concentration (reference)”, and the value of “NO ₂ concentration (current)” is set to “NO ₂ concentration (reference)”. As a value, the “NO concentration (current)” value is stored as the “NO concentration (reference)” value, and the “O ₂ concentration (current)” value is stored as the “O ₂ concentration (previous)” value. The process to memorize is executed.

The “NH ₃ concentration (reference)” is the corrected ammonia concentration calculated in the past, and is the latest of the corrected ammonia concentrations calculated when the correction permission condition determined based on the oxygen concentration and the oxygen concentration change rate is satisfied. Is an internal variable for storing the value of. Further, "NO ₂ concentration (reference)" is a NO ₂ concentration calculated in the past, is an internal variable for storing the latest value of the NO ₂ concentration calculated at the time that satisfies the modified permission condition . Furthermore, “NO concentration (reference)” is an internal variable for storing the latest value of the NO concentration calculated in the past and calculated when the correction permission condition is satisfied.

On the other hand, when an affirmative determination is made in S160 and the process proceeds to S190, the oxygen concentration change rate RA is calculated using “O ₂ concentration (current)” and “O ₂ concentration (previous)” in S190. Specifically, using [Equation 1], a value obtained by dividing “O ₂ concentration (previous)” by “O ₂ concentration (current)” is calculated as the oxygen concentration change rate RA.

In the next S200, it is determined whether or not the correction permission condition for correcting the ammonia concentration based on the oxygen concentration is satisfied. If an affirmative determination is made, the process proceeds to S170, and if a negative determination is made, the process proceeds to S210.

Specifically, the “O ₂ concentration (current)” exceeds a predetermined reference concentration (4% in this embodiment), and the oxygen concentration change rate is a predetermined reference determination value (this embodiment). Then, in the case of less than 1.5), it is determined that the correction permission condition is satisfied (positive determination). In addition, when the “O ₂ concentration (current)” is equal to or less than the reference concentration (4% in the present embodiment), or the oxygen concentration change rate is equal to or greater than the reference determination value (1.5 in the present embodiment). In this case, it is determined that the correction permission condition is not satisfied (negative determination).

  Note that the reference concentration, which is a condition for permitting correction of the oxygen concentration, is set in advance as a numerical range of the oxygen concentration in which the detection error of the ammonia concentration is within an allowable range when calculating the corrected ammonia concentration, for example. In addition, the reference determination value, which is a condition for permitting modification of the oxygen concentration change rate, is preset with a numerical range of the oxygen concentration change rate in which the ammonia concentration detection error is within an allowable range when calculating the corrected ammonia concentration, for example. .

After the transition to S210 is negative determination in S200, in S210, it computes the value of the "NH ₃ concentration (reference)" as the value of the "NH ₃ concentration (this)" (substituted) "NO ₂ concentration (present)" A process of calculating (substituting) the value of “NO ₂ concentration (reference)” as the value of “NO” and calculating (substituting) the value of “NO concentration (reference)” as the value of “NO concentration (current)” is executed.

In the next S220, the timer process is started and the timer count is started.
In the next S230, it is determined whether or not a predetermined stop period has elapsed with the start of the timer count in S220 as a starting point. If an affirmative determination is made, the process proceeds to S240, and if a negative determination is made, the same step is repeatedly executed. To wait. In the present embodiment, 5.0 [sec] is set as the stop period.

When an affirmative determination is made in S230 and the process proceeds to S240, the timer process is stopped and the timer count is reset in S240.
In the next S250, a process of storing the value of “O ₂ concentration (current)” as the value of “O ₂ concentration (previous)” is executed.

When the process of S180 or S250 is completed, the process proceeds to S140 again.
In this way, the CPU 61 that executes the gas concentration calculation processing is “NH ₃ concentration (current)”, “NH ₃ concentration (reference)”, “NO ₂ concentration (current)”, “NO ₂ concentration (reference)”, The values of “NO concentration (current)”, “NO concentration (reference)”, “O ₂ concentration (current)”, and “O ₂ concentration (previous)” are updated. The gas concentration calculation process ends when the internal combustion engine is stopped.

Further, in the concentration output process separately executed in the CPU 61, the value of “NH ₃ concentration (current)” is set as the ammonia concentration, the value of “NO ₂ concentration (current)” is set as the NO ₂ concentration, and “NO concentration (current)”. ”Is set as the NO concentration, and the process of outputting to the ECU 200 is executed. It should be noted that the density output process is repeatedly executed every predetermined period.

[1-7. Measurement test]
Next, the measurement result of the measurement test which measured the ammonia concentration using the multi-gas sensor control device 1 will be described.

  In this measurement test, a sample gas in which the oxygen concentration was changed while the ammonia concentration was controlled to a constant concentration was used as the gas to be measured. Further, as a comparative example, the ammonia concentration calculated when the correction using the correction permission condition is not performed was also measured.

  FIG. 7 shows the test results. FIG. 7 shows five waveforms. From the top, the waveform showing the oxygen concentration in the sample gas (O2 concentration [%]), the waveform showing the oxygen concentration change rate (O2 concentration change rate), and the NH3 sensor. Waveform (NH3 sensor output EMF [mV]) indicating output (ammonia electromotive force EMF), waveform (NH3 concentration) indicating ammonia concentration (NH3 concentration (no correction)) calculated when correction using the correction permission condition is not performed Concentration [ppm]), and a waveform (NH3 concentration [ppm] with correction) indicating the ammonia concentration (NH3 concentration (with correction)) calculated using the multi-gas sensor control device 1 of the present embodiment.

Further, in the waveforms showing the NH3 concentration (without correction) and the NH3 concentration (with correction), the ammonia concentration measured by an ammonia analyzer is also shown.
According to this measurement result, the ammonia concentration (NH3 concentration (with correction)) of this embodiment is closer to the ammonia concentration measured by the ammonia analyzer than the ammonia concentration (NH3 concentration (without correction)) of the comparative example. The waveform is shown.

  In particular, in the period where the elapsed time is 350 sec to 550 sec, the oxygen concentration has changed abruptly many times and the oxygen concentration change rate has fluctuated a lot. Therefore, the ammonia concentration (NH3 concentration ( In the case of no correction)), there are many places where the value changes instantaneously under the influence of this sharp change in oxygen concentration. On the other hand, the ammonia concentration (NH3 concentration (with correction)) of the present embodiment has an instantaneous change in the elapsed time period of 350 sec to 550 sec. It is less than the density (no correction).

  That is, by using the multi-gas sensor control device 1 of the present embodiment, it is possible to measure the ammonia concentration while suppressing the influence of a steep change in the oxygen concentration, and it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

[1-8. effect]
As described above, the multi-gas sensor control device 1 of the present embodiment is a control device that controls the multi-gas sensor 2 including the NOx sensor unit 11 and the ammonia sensor unit 21, and the CPU 61 of the microcomputer 60 performs the gas concentration calculation process. Is executed to calculate the ammonia concentration, NO ₂ concentration, and NO concentration in the gas to be measured.

  Among these, regarding the ammonia concentration, using the “ammonia concentration output (electromotive force EMF) -ammonia concentration relational expression” 63b, an accurate ammonia concentration (corrected ammonia concentration) that is not affected by the oxygen concentration in the gas to be measured is obtained. Arithmetic.

Further, in the gas concentration calculation process, whether the latest corrected ammonia concentration is calculated as the value of “NH ₃ concentration (current)” (S 170) or “NH ₃ concentration ( Whether the value of “reference)” is calculated (assigned) as the value of “NH ₃ concentration (current)” (S210).

  As the oxygen concentration correction permission condition, for example, when the corrected ammonia concentration is calculated, a numerical range of the oxygen concentration in which the detection error of the ammonia concentration is within an allowable range is set in advance. In addition, the oxygen concentration change rate correction permission condition is set in advance, for example, as a numerical range of the oxygen concentration change rate in which the ammonia concentration detection error is within an allowable range when calculating the corrected ammonia concentration.

In other words, when the correction permission condition determined based on the oxygen concentration and the oxygen concentration change rate is satisfied, the detection error of the ammonia concentration in the corrected ammonia concentration falls within an allowable range, so the corrected ammonia concentration is set to “NH ₃ concentration (current)”. When it is set to (ammonia concentration detection result), the ammonia concentration detection accuracy does not decrease.

On the other hand, at least one of, if not satisfied modification permission condition, since the detection error of the ammonia concentration in the modified ammonia concentration exceeds an allowable range, "NH ₃ concentration the corrected ammonia concentration of oxygen concentration and oxygen concentration change rate (This time) ", the detection accuracy of ammonia concentration decreases. Instead of such corrected ammonia concentration, “NH ₃ concentration (reference)” (the latest value of past corrected ammonia concentrations calculated when both oxygen concentration and oxygen concentration change rate satisfy the correction permission conditions) Is set to “NH ₃ concentration (current)”, it is possible to suppress a decrease in ammonia concentration detection accuracy.

That is, when the actual ammonia concentration has not changed greatly and the oxygen concentration has changed, the “NH ₃ concentration (reference)” is considered to be a value close to the actual ammonia concentration. For this reason, by setting “NH ₃ concentration (reference)” to “NH ₃ concentration (current)”, it is possible to suppress a decrease in ammonia concentration detection accuracy.

  Therefore, according to this multi-gas sensor control device 1, when using the multi-gas sensor 2 that detects the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

Next, in the multi-gas sensor control device 1, in S200 of the gas concentration calculation process, the oxygen concentration (“O ₂ concentration (current)”) exceeds the reference concentration, and the oxygen concentration change rate is the reference determination value (this embodiment). In the embodiment, if it is less than 1.5), it is determined that the correction permission condition is satisfied (Yes determination in S200). On the other hand, in S200 of the gas concentration calculation process, when the oxygen concentration change rate is equal to or higher than the reference determination value, or when the oxygen concentration is equal to or lower than a predetermined reference concentration, it is determined that the correction permission condition is not satisfied (S200). Negative determination).

  In other words, the oxygen concentration change rate increases as the oxygen concentration change becomes sharper. Therefore, when the oxygen concentration change rate is equal to or higher than the reference determination value, it can be determined that the oxygen concentration has changed sharply. It can be determined that the above is not satisfied. The reference determination value of the oxygen concentration change rate is, for example, an oxygen concentration change rate at which the ammonia concentration detection error falls within an allowable range (± 5%, preferably ± 3%) when calculating the corrected ammonia concentration, A boundary value between the oxygen concentration change rate at which the detection error of the ammonia concentration deviates from the permissible range is set in advance.

  In addition, when the oxygen concentration is extremely low, the error in the corrected ammonia concentration tends to increase. Therefore, when the oxygen concentration is equal to or lower than the reference concentration, it can be determined that the error in the corrected ammonia concentration is large, and the correction permission condition is satisfied. It can be determined that there is no. The reference concentration of the oxygen concentration is, for example, an oxygen concentration at which the detection error of the ammonia concentration falls within an allowable range when the corrected ammonia concentration is calculated, and an oxygen concentration at which the detection error of the ammonia concentration deviates from the allowable range. A boundary value is set in advance.

That is, in the multi-gas sensor control device 1, when the oxygen concentration change rate is equal to or higher than the reference determination value or when the oxygen concentration is equal to or lower than the reference concentration, it is determined that the correction permission condition is not satisfied, and “NH ₃ “Concentration (reference)” is set to “NH ₃ concentration (current)”.

  Therefore, according to the multi-gas sensor control device 1, when the oxygen concentration change rate is equal to or higher than the reference determination value, or when the oxygen concentration is equal to or lower than the reference concentration, it is determined that the correction permission condition is not satisfied, A decrease in density detection accuracy can be suppressed.

Next, in the multi-gas sensor control device 1, the correction is made until it is determined that the correction permission condition is not satisfied in S200 of the gas concentration calculation process (No determination in S200) until a predetermined stop period elapses. It is determined that the permission condition is not satisfied. Specifically, the update of “NH ₃ concentration (current)” is stopped until the stop period elapses after the negative determination is made in S200, so that “NH ₃ concentration (reference)” becomes “NH ₃ concentration ( The state set to “This time” is maintained.

  That is, when it is determined that at least one of the oxygen concentration and the oxygen concentration change rate does not satisfy the correction permission condition, the influence of the oxygen concentration remains for a certain period thereafter, and there is a high possibility of an error in the corrected ammonia concentration.

Therefore, it is determined that the correction permission condition is not satisfied until at least one of the oxygen concentration and the oxygen concentration change rate does not satisfy the correction permission condition, and the “NH ₃ concentration (standard ) ”Is set to“ NH ₃ concentration (current) ”.

As a result, it is possible to avoid setting the corrected ammonia concentration at which an error is likely to occur to “NH ₃ concentration (current)”. Therefore, according to the multi-gas sensor control device 1, it is possible to further suppress a decrease in the detection accuracy of the ammonia concentration.

  Next, in the multi-gas sensor control device 1, in S190 of the gas concentration calculation process, a value obtained by dividing the previously calculated oxygen concentration by the oxygen concentration calculated this time is calculated as the oxygen concentration change rate.

In other words, in calculating the oxygen concentration change rate, the value obtained by dividing “O ₂ concentration (previous)” (previously calculated oxygen concentration) by “O ₂ concentration (current)” (currently calculated oxygen concentration) is used. By calculating as a rate, the oxygen concentration change rate becomes a large value when the oxygen concentration decreases. For this reason, since the oxygen concentration change rate greatly changes with respect to a slight change in oxygen concentration, it is easy to determine whether or not the oxygen concentration change rate has fluctuated.

Therefore, according to the multi-gas sensor control device 1, it is possible to improve the determination accuracy based on the oxygen concentration change rate, and to further suppress the decrease in the ammonia concentration detection accuracy.
[1-9. Correspondence with Claims]
Here, the correspondence of the words in the claims and the present embodiment will be described.

  The first pumping cell 12 corresponds to an example of a first pumping cell, the second pumping cell 18 corresponds to an example of a second pumping cell, the NOx sensor unit 11 corresponds to an example of a NOx sensor unit, and the ammonia sensor unit 21 Corresponds to an example of an ammonia sensor unit, the multi-gas sensor 2 corresponds to an example of a multi-gas sensor, and the multi-gas sensor control device 1 corresponds to an example of a sensor control device.

  S150 of the gas concentration calculation process corresponds to an example of an oxygen concentration calculation step, S170 of the gas concentration calculation process corresponds to an example of a corrected concentration calculation step, and S190 of the gas concentration calculation process corresponds to an example of an oxygen concentration change rate calculation step. Correspondingly, S200, S180, S210, S220, S230, and S240 of the gas concentration calculation process correspond to an example of the ammonia concentration setting step.

  The microcomputer 60 that executes S150 of the gas concentration calculation process corresponds to an example of an oxygen concentration calculation unit, and the microcomputer 60 that executes S170 of the gas concentration calculation process corresponds to an example of a correction concentration calculation unit, and the gas concentration calculation process. The microcomputer 60 that executes S190 corresponds to an example of an oxygen concentration change rate calculation unit. The microcomputer 60 that executes S200, S180, S210, S220, S230, and S240 of the gas concentration calculation processing corresponds to an example of an ammonia concentration setting unit.

[2. Variant 1]
Next, variant 1 of the present invention will be described. The multi-gas sensor control device 201 according to the first modification differs from the multi-gas sensor control device 1 according to the first embodiment in the configuration of the sensor element unit 10 (particularly, the configuration of the ammonia sensor unit 21). The data stored in the control unit 3 and the ROM 63 of the microcomputer 60 due to the difference in the configuration of 21 are different.

  In the following description of the multi-gas sensor control device 201 according to the first modification, differences from the multi-gas sensor control device 1 according to the first embodiment will be described, and the same points as the multi-gas sensor control device 1 according to the first embodiment will be described. Description will be made using the same reference numerals as those in the first embodiment, or description thereof will be omitted.

[2-1. Sensor element section]
FIG. 8 shows only a schematic cross-sectional view along the longitudinal direction of the sensor element unit 10 of the multi-gas sensor control device 201 of the first modification.

  The sensor element unit 10 is mainly provided with a NOx sensor unit 11, a first ammonia sensor unit 221, and a second ammonia sensor unit 222. Since the NOx sensor unit 11 of the first modification has the same configuration as that of the first embodiment, the description thereof is omitted.

  The first ammonia sensor unit 221 and the second ammonia sensor unit 222 are arranged at substantially the same position as the reference electrode 16c in the longitudinal direction of the NOx sensor unit 11 (left and right direction in FIG. 8) (in the width direction of FIG. They are arranged in parallel so that their positions in the depth direction are different from each other.

  FIG. 9 is a cross-sectional view illustrating the configuration of the first ammonia sensor unit 221 and the second ammonia sensor unit 222. The left-right direction in FIG. 9 corresponds to the width direction of the NOx sensor unit 11.

  As shown in FIGS. 8 and 9, the first ammonia sensor part 221 and the second ammonia sensor part 222 are formed on the outer surface of the NOx sensor part 11, more specifically, on the insulating layer 10e. In the first ammonia sensor unit 221, a first reference electrode 221a is formed on the insulating layer 10e, and a first solid electrolyte body 221b is formed so as to cover an upper surface and a side surface of the first reference electrode 221a. Further, a first detection electrode 221c is formed on the surface of the first solid electrolyte body 221b. The ammonia concentration in the gas to be measured is detected by the change in electromotive force between the first reference electrode 221a and the first detection electrode 221c.

  Similarly, in the second ammonia sensor unit 222, a second reference electrode 222a is formed on the insulating layer 10e, and a second solid electrolyte body 222b is formed to cover the upper surface and the side surface of the second reference electrode 222a. Further, a second detection electrode 222c is formed on the surface of the second solid electrolyte body 222b.

  The first detection electrode 221c and the second detection electrode 222c can be formed from a material containing Au as a main component (for example, 70% by mass or more). The first reference electrode 221a and the second reference electrode 222a can be made of Pt alone or a material containing Pt as a main component (for example, 70% by mass or more). The first solid electrolyte body 221b and the second solid electrolyte body 222b are made of, for example, partially stabilized zirconia (YSZ).

  A porous diffusion layer 24 (protective layer 24) is formed so as to completely cover the first detection electrode 221c, the first solid electrolyte body 221b, the second detection electrode 222c, and the second solid electrolyte body 222b, The diffusion rate of the gas to be measured flowing into the first ammonia sensor unit 221 and the second ammonia sensor unit 222 from the outside can be adjusted.

The diffusion layer 24 is exemplified by at least one selected from the group of alumina, spinel (MgAl ₂ O ₄ ), silica alumina, and mullite, as in the first embodiment.
[2-2. Control unit]
The control circuit 50 of the control unit 3 of the multi-gas sensor control device 201 includes a reference voltage comparison circuit 51, an Ip1 drive circuit 52, a Vs detection circuit 53, an Icp supply circuit 54, an Ip2 detection circuit 55, and a Vp2 application circuit 56. And a heater drive circuit 57, a first electromotive force detection circuit 58a, and a second electromotive force detection circuit 58b. Among the modified control circuits 50, the reference voltage comparison circuit 51, the Ip1 drive circuit 52, the Vs detection circuit 53, the Icp supply circuit 54, the Ip2 detection circuit 55, the Vp2 application circuit 56, and the heater drive circuit 57. Since the configuration is the same as that of the first embodiment, description thereof is omitted.

  The first electromotive force detection circuit 58a is electrically connected to the first detection electrode 221c and the first reference electrode 221a in the first ammonia sensor unit 221. The second electromotive force detection circuit 58b is electrically connected to the second detection electrode 222c and the second reference electrode 222a in the second ammonia sensor unit 222. The first electromotive force detection circuit 58a detects a first ammonia electromotive force EMF, which is an electromotive force between the first detection electrode 221c and the first reference electrode 221a, and outputs it to the microcomputer 60. The second electromotive force detection circuit 58b detects a second ammonia electromotive force EMF, which is an electromotive force between the second detection electrode 222c and the second reference electrode 222a, and outputs it to the microcomputer 60.

[2-3. Microcomputer]
Various data (relational expressions) described below are stored in the ROM 63 of the microcomputer 60. The CPU 61 reads the various data from the ROM 63 and performs various arithmetic processes from the value of the first pumping current Ip1, the value of the second pumping current Ip2, the first ammonia electromotive force, and the second ammonia electromotive force.

The ROM 63 includes “first ammonia concentration output (electromotive force EMF) —first ammonia concentration relational expression”, “second ammonia concentration output (electromotive force EMF) —second ammonia concentration relational expression”, “first pumping current ( "Ip1) -oxygen concentration relational expression", "second pumping current (Ip2) -NOx concentration relational expression", "first ammonia concentration & second ammonia concentration & oxygen concentration-corrected ammonia concentration relational expression" (correction formula (1) : See below), "First ammonia concentration & second ammonia concentration & oxygen concentration output-corrected NO ₂ concentration relational expression" (correction formula (2)), "NOx concentration & corrected ammonia concentration & corrected NO ₂ concentration-corrected “NO concentration relational expression” (correction expression (3)) is stored.

  The various data may be set as a predetermined relational expression as described above, or may be set as a table, for example, as long as various gas concentrations are calculated from the output of the sensor. In addition, values (relational expressions, tables, etc.) obtained using a gas model whose gas concentration is known in advance may be used.

  The “first ammonia concentration output-first ammonia concentration relational expression” and the “second ammonia concentration output-second ammonia concentration relational expression” are output from the first ammonia sensor unit 221 and the second ammonia sensor unit 222. It is a formula showing the relationship between the ammonia concentration output and the ammonia concentration in the gas to be measured.

  The “first pumping current-oxygen concentration relational expression” is an expression representing the relation between the first pumping current and the oxygen concentration in the gas to be measured. The “second pumping current-NOx concentration relational expression” is an expression representing the relation between the second pumping current and the NOx concentration in the gas to be measured.

"The first ammonia concentration & second ammonia concentration and the oxygen concentration - Fixed ammonia concentration relationship", the oxygen concentration and NO ₂ concentration ammonia concentration affected (first, second) and, oxygen concentration and NO ₂ concentration It is a formula showing the relationship of the correction | amendment ammonia concentration output which remove | eliminated the influence of (3). In addition, the “first ammonia concentration & second ammonia concentration & oxygen concentration−corrected NO ₂ concentration relational expression” has removed the NO ₂ concentration affected by the oxygen concentration and ammonia concentration, and the influence of the oxygen concentration and ammonia concentration. is an expression that represents the corrected NO ₂ concentration output relationship. Furthermore, "NOx concentration & corrected ammonia concentration & fix NO ₂ concentration - Fixed NO concentration relationship" is a NOx concentration affected the ammonia concentration and NO ₂ concentration, removing the influence of ammonia concentration and NO ₂ concentration, modified It is a formula showing the relationship of the correct corrected NO concentration.

Next, from the first pumping current Ip1, the second pumping current Ip2, the first ammonia concentration output and the second ammonia concentration output, which are executed by the CPU 61 of the microcomputer 60, the corrected NO concentration, the corrected NO ₂ concentration and the corrected ammonia concentration are obtained. A calculation process for obtaining the above will be described.

When the first pumping current Ip1, the second pumping current Ip2, the first ammonia concentration output, and the second ammonia concentration output are input, the CPU 61 obtains the oxygen concentration, the NOx concentration, the first ammonia concentration, and the second ammonia concentration. Perform arithmetic processing. Specifically, from the ROM 63, “first ammonia concentration output-first ammonia concentration relational expression”, “second ammonia concentration output-second ammonia concentration relational expression”, “first pumping current Ip1—oxygen concentration relational expression. ”,“ Second pumping current Ip2-NOx concentration relational expression ”, and processing for calculating each concentration output using the relational expression is performed. When the oxygen concentration, the NOx concentration, the first ammonia concentration, and the second ammonia concentration are obtained, the CPU 61 performs a calculation using the correction formula described below, thereby correcting the corrected ammonia concentration, the corrected NO concentration, and the correction. Determine the NO ₂ concentration.

Correction formula (1): x = F (A, B, D)
= (EA-c) * (jB-h-fA + d) / (eA-c-iB + g) + fA-d
Correction formula (2): y = F ′ (A, B, D)
= (JB-h-fA + d) / (eA-c-iB + g)
Correction formula (3): z = C−ax + by
Here, x is the corrected ammonia concentration, is the corrected NO ₂ concentration, and z is the corrected NO concentration. A is the first ammonia concentration, B is the second ammonia concentration, C is the NOx concentration, and D is the oxygen concentration. Then, F and F ′ in the correction equations (1) and (2) indicate that x is a function of (A, B, D). Further, a and b are correction coefficients, and c, d, e, f, g, h, i, and j are coefficients calculated using the oxygen concentration D (coefficient determined by D).

By substituting and calculating the first ammonia concentration, the second ammonia concentration, the NOx concentration, and the oxygen concentration in the correction equations (1) to (3), the corrected ammonia concentration and the corrected NO ₂ concentration of the gas to be measured. , And the corrected NO concentration.

  The correction formulas (1) and (2) are formulas determined based on the characteristics of the first ammonia sensor unit 221 and the second ammonia sensor unit 222, and the correction formula (3) is based on the characteristics of the NOx sensor unit 11. It is a formula to be determined. The correction expressions (1) to (3) are merely examples of the correction expression, and other correction expressions, coefficients, and the like may be changed as appropriate according to the gas detection characteristics.

[2-4. effect]
According to the multi-gas sensor control device 201 of the first modification, similarly to the multi-gas sensor control device 1, when using the multi-gas sensor for detecting the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, the accuracy of detecting the ammonia concentration is lowered. Can be suppressed.

[3. Variation 2]
Next, variant 2 of the present invention will be described. The multi-gas sensor control device according to the second modification is different from the multi-gas sensor control device 1 according to the first embodiment in the gas concentration calculation process. In the following description of the multi-gas sensor control device according to the second modification, the differences from the multi-gas sensor control device 1 according to the first embodiment will be described, and the same points as the multi-gas sensor control device 1 according to the first embodiment will be described. The description will be made using the same reference numerals as in the embodiment, or the description will be omitted.

  FIG. 10 is a flowchart showing the processing content of the gas concentration calculation processing. Note that S110 to S170, S190 to S200, and S220 to S240 have the same configuration as that of the first embodiment, and thus description thereof is omitted.

Gas density arithmetic processing variations 2, in S180, the value of the value of the "NH ₃ concentration (this)" is stored as the value of the "NH ₃ concentration (last)", "NO ₂ concentration (this)"" NO ₂ is stored as the value of the concentration (last) "," NO concentrations stores the value of the (present) "as the value of" NO concentration (last) "," 0 ₂ concentration (present) value of "" 0 ₂ The process of storing the value of “density (previous)” is executed.

Moreover, the gas concentration calculation process variant 2, when the process proceeds to S210 are negative determination in S200, computes the value of the "NH ₃ concentration (last)" as the value of the S210, "NH ₃ concentration (this)" ( assignment) and, as the value of "NO ₂ concentration (this time)" and "NO ₂ concentration (last)" calculates the value of (assignment), as the value of "NO concentration (this)""NO concentration (last)" Executes processing to calculate (substitute) a value.

In addition, in the gas concentration calculation process according to the second modification, when the timer process is stopped and the timer count is reset in S240, the process proceeds to S180.
In the multi-gas sensor control device according to the second modification configured as described above, when the correction permission condition is satisfied (Yes in S200), the current corrected ammonia concentration is detected as the current ammonia concentration detection result (NH ₃ concentration (current time)). )) (S170). If the correction permission condition is not satisfied (No in S200), the multi-gas sensor control device uses the ammonia concentration (NH ₃ concentration (previous)) set in the previous detection result as the current ammonia concentration detection result ( NH ₃ concentration (this time)) is set (S210).

That is, the numerical value set in the ammonia concentration detection result (NH ₃ concentration (current)) is the corrected ammonia concentration calculated when the correction permission condition is satisfied, and therefore the ammonia concentration (set in the previous detection result ( The NH ₃ concentration (previous)) is also the corrected ammonia concentration calculated when the correction permission condition is satisfied. The ammonia concentration (NH ₃ concentration (previous)) set in the previous detection result is the latest corrected ammonia concentration among the past corrected ammonia concentrations calculated when the correction permission condition is satisfied. This value is close to the ammonia concentration.

Therefore, as described above, by setting the ammonia concentration (NH ₃ concentration (previous)) set in the previous detection result to the current ammonia concentration detection result (NH ₃ concentration (current)), the ammonia concentration A decrease in detection accuracy can be suppressed.

  Therefore, according to the multi-gas sensor control apparatus of the modified embodiment 2, as with the multi-gas sensor control apparatus 1, when using the multi-gas sensor for detecting the nitrogen oxide concentration and the ammonia concentration in the gas to be measured, the detection accuracy of the ammonia concentration is improved. Reduction can be suppressed.

[4. Variation 3]
Next, modification 3 of the present invention will be described. The sensor control device 301 according to the third modification is different from the multi-gas sensor control device 1 according to the first embodiment in that a separate sensor 540 is provided instead of the multi-gas sensor 2. The separation type sensor 540 includes a NOx sensor 541 and an ammonia sensor 542 separately, and the NOx sensor 541 and the ammonia sensor 542 can be separately disposed separately.

  In the following description of the sensor control device 301 according to the third modification, the differences from the multi-gas sensor control device 1 according to the first embodiment will be described, and the same points as the multi-gas sensor control device 1 according to the first embodiment will be described. The description will be made using the same reference numerals as in the embodiment, or the description will be omitted.

[4-1. Sensor control device]
FIG. 11 is a block diagram illustrating the configuration of the sensor control device 301 according to the third modification.
The sensor control device 301 is a separation type sensor 540 (NOx sensor 541, ammonia sensor 542) and a control unit 3 that calculates the concentrations of NO, NO ₂ and ammonia by controlling the sensors and calculating the sensor output. And an arithmetic unit 3).

  The separation type sensor 540 (NOx sensor 541 and ammonia sensor 542) is provided in an exhaust pipe 502 (exhaust path 502) of an engine 500 (diesel engine 500) that is an internal combustion engine of a vehicle.

Since the control part 3 is the same as that of the control part 3 of 1st Embodiment, description is abbreviate | omitted.
[4-2. Exhaust purification device]
An exhaust purification device 550 for purifying exhaust gas discharged from the engine 500 is attached in the middle of the exhaust pipe 502 of the engine 500. The exhaust purification device 550 includes an upstream side exhaust purification device 510 (also referred to as “DPF device 510”), a downstream side exhaust purification device 520 (also referred to as “SCR device 520”), and a urea water addition nozzle 531. ing. The upstream side exhaust purification device 510 is disposed upstream of the downstream side exhaust purification device 520 in the exhaust pipe 502. The urea water addition nozzle 531 is provided between the upstream side exhaust purification device 510 and the downstream side exhaust purification device 520.

The DPF device 510 includes, in order from the upstream side, an oxidation catalyst 512 (Diesel Oxidation Catalyst, hereinafter referred to as “DOC512”) and a particulate filter 514 (Diesel Particulate Filter, hereinafter referred to as “DPF514”). It is arranged and arranged in the casing. The DPF 514 includes, for example, a porous filter (for example, a ceramic filter) that collects particulate matter (PM). The DOC 512 is formed by supporting a catalyst material that oxidizes NO into NO ₂ on a honeycomb-shaped carrier made of metal, ceramics, or the like. Then, the DOC 512 oxidizes NO in the exhaust gas into NO ₂ , and the PM collected by the DPF 514 is oxidized and burned and removed using this NO ₂ , so that the DPF 514 can be continuously regenerated. The regeneration control of the DPF 514 is performed by the ECU 200.

The SCR device 520 exhausts, in order from the upstream side, a selective catalytic reduction catalyst 522 (Selective Catalytic Reduction, hereinafter referred to as “SCR522”) and a post-stage oxidation catalyst 524 (Clean Up Catalyst, hereinafter referred to as “CUC524”). The tube 502 is arranged in a cylindrical casing. The SCR device 520 is a catalyst for reducing NOx in the exhaust gas to N _{2 using} ammonia supplied from the upstream side as a reducing agent. For example, a zeolite-based or vanadium-based catalyst can be used. CUC524 is an oxidation catalyst that removes ammonia that has not reacted in SCR522.

  The urea water addition nozzle 531 injects urea water in the urea water tank 535 into the exhaust gas on the upstream side of the SCR 522 by the addition device 533. The urea water injected into the exhaust gas upstream of the SCR 522 is hydrolyzed into ammonia and acts as a reducing agent in the SCR 522. The ECU 200 controls the addition of urea water.

The ECU 200 receives the concentrations of NO, NO ₂ and ammonia in the exhaust gas after passing through the SCR 522 from the control unit 3, various controls of the engine, DOC 512 deterioration determination, DPF 514 regeneration control, urea water And so on. The ECU 200 includes a microcomputer including a CPU (Central Control Unit), RAM, ROM, and the like, and an electronic control unit (ECU) configured by a predetermined analog circuit, and is a computer stored in the ROM. Various processes are performed by the CPU executing the program.

  The exhaust path 502 includes a plurality of spaces partitioned by DOC 512, DPF 514, SCR 522, and CUC 524. Each of the DOC 512, DPF 514, SCR 522, and CUC 524 is configured to be able to transmit exhaust gas.

[4-3. NOx sensor and ammonia sensor]
The NOx sensor 541 and the ammonia sensor 542 are arranged in a space between the SCR 522 and the CUC 524 among a plurality of spaces provided in the exhaust path 502. The NOx sensor 541 is disposed upstream of the ammonia sensor 542 in the exhaust gas traveling direction.

Since the separation type sensor 540 is configured such that the NOx sensor 541 and the ammonia sensor 542 are arranged in the same space in the exhaust path 502, the nitrogen oxide concentration (NO concentration, NO concentration) contained in the gas to be measured in the same space. ₂ concentration) and ammonia concentration can be detected.

  Although not shown, the NOx sensor 541 mainly includes a sensor element portion, a metal shell, a separator, and a connection terminal. The sensor element part of the NOx sensor 541 is formed as a plate-shaped sensor element part having a sensor part equivalent to the NOx sensor part 11 in the first embodiment. The NOx sensor 541 can be configured by using a known NOx sensor. Since the known NOx sensor is described in, for example, Japanese Patent Application Laid-Open No. 2011-164086, detailed description thereof is omitted here.

  Although not shown, the ammonia sensor 542 mainly includes a sensor element portion, a metal shell, a separator, and a connection terminal. The sensor element portion of the ammonia sensor 542 is formed as a plate-shaped sensor element portion having a sensor portion equivalent to the ammonia sensor portion 21 in the first embodiment. For example, an ammonia sensor part can be formed by using each component shown in FIG. The ammonia sensor 542 can be configured using a known ammonia sensor. Since the known ammonia sensor is described in, for example, Japanese Patent Laid-Open No. 2013-068607, detailed description thereof is omitted here.

  The sensor element unit of the NOx sensor 541 and the sensor element unit of the ammonia sensor 542 are connected to the control unit 3 in the same manner as the NOx sensor unit 11 and the ammonia sensor unit 21 of the first embodiment.

The control unit 3 of the sensor control device 301 is provided with a control circuit 50 and a microcomputer 60 as in the control unit 3 of the first embodiment. Then, the control unit 3, by processing the outputs of the sensors to control the NOx sensor 541 and the ammonia sensor 542, NO, calculates the respective concentrations of NO ₂ and ammonia.

[4-4. effect]
As described above, the sensor control device 301 is different from the multi-gas sensor control device 1 of the first embodiment in that the sensor control device 301 includes the separation type sensor 540 instead of the multi-gas sensor 2. By executing the concentration calculation process, the calculation is common in the ammonia concentration, NO ₂ concentration, and NO concentration in the gas to be measured.

  Among the separated sensors 540, the NOx sensor 541 and the ammonia sensor 542 are arranged in the same space among the plurality of spaces in the exhaust path 502, and the NOx sensor 541 is upstream of the ammonia sensor 542 in the exhaust gas traveling direction. Arranged on the side. In such a separate sensor 540, since the NOx sensor 541 and the ammonia sensor 542 are disposed in the same space in the exhaust path 502, the concentration of nitrogen oxides contained in the gas to be measured (in the exhaust gas) in the same space And ammonia concentration can be detected.

  Therefore, the sensor control device 301 uses the separation type sensor 540 having the NOx sensor 541 and the ammonia sensor 542, so that the nitrogen in the measured gas in the same space is the same as the multi-gas sensor control device 1 of the first embodiment. In detecting the oxide concentration and the ammonia concentration, it is possible to suppress a decrease in the detection accuracy of the ammonia concentration.

  The NOx sensor 541 is disposed upstream of the ammonia sensor 542 in the exhaust gas traveling direction. Since the relative positional relationship between the NOx sensor 541 and the ammonia sensor 542 is determined in this way, the oxygen concentration detection position is upstream in the exhaust gas traveling direction as compared with the ammonia concentration detection position. In this case, when calculating the corrected ammonia concentration, the oxygen concentration detected upstream of the ammonia concentration detection position can be used. As a result, the oxygen concentration detection time is not delayed from the ammonia concentration detection time, and the corrected ammonia concentration can be calculated with high accuracy.

Therefore, according to the sensor control device 301, the corrected ammonia concentration can be calculated with high accuracy, so that a decrease in the detection accuracy of the ammonia concentration can be suppressed.
Further, the ECU 200 receives the concentrations of NO, NO ₂ and ammonia in the exhaust gas after passing through the SCR 522 from the control unit 3, various controls of the engine, DOC 512 deterioration determination, DPF 514 regeneration control, Perform urea water addition control. Thus, the ECU 200 can appropriately determine the state of the exhaust gas based on the detection results (NO, NO ₂ and ammonia concentrations) in the control unit 3, various controls of the engine, DOC 512 deterioration determination, and regeneration of the DPF 514. Control, urea water addition control, etc. can be executed appropriately.

[4-5. Correspondence with Claims]
Here, the correspondence of the words in the claims and the present embodiment will be described.
The separation type sensor 540 corresponds to an example of a sensor, the NOx sensor 541 corresponds to an example of a NOx sensor unit, the ammonia sensor 542 corresponds to an example of an ammonia sensor unit, and the sensor control device 301 corresponds to an example of a sensor control device. To do. The exhaust pipe 502 (exhaust path 502) corresponds to an example of an exhaust path, and the oxidation catalyst 512, the particulate filter 514, the selective reduction catalyst 522, and the post-stage oxidation catalyst 524 correspond to an example of a partition part.

[5. Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  For example, the first embodiment and the second modification are configured to determine whether or not a predetermined stop period has elapsed by executing S220, S230, and S240 in the gas concentration calculation process. A configuration in which S220, S230, and S240 are omitted as steps in the density calculation processing may be used.

That is, the calculation of the corrected ammonia concentration and the update of the “NH ₃ concentration (current)” are not stopped until the stop period elapses after the negative determination is made in S200, but the calculation of the corrected ammonia concentration and the “NH ₃ concentration ( You may continue to update this time. As a result, the calculation of the corrected ammonia concentration is repeatedly executed, and the update of “NH ₃ concentration (current)” is continued according to the determination result in S200, thereby suppressing a decrease in detection accuracy of the ammonia concentration. it can.

  In the first embodiment and the second modification, S160 is executed in the gas concentration calculation process, and S170 is executed when a negative determination is made in S160. However, S150 is executed as a step in the gas concentration calculation process. After that, S170 may be executed, and then S160 may be executed.

That is, after the oxygen concentration is calculated in S150, the process proceeds to S170, and first, “NH ₃ concentration (current)”, “NO ₂ concentration (current)”, and “NO concentration (current)” are calculated. Thereafter, the flow proceeds to S160, the value in the one of the internal variable "0 ₂ concentration (last)" used for the operation in the CPU61 may determine whether it has been stored. In this gas concentration calculation process, if a negative determination is made in S160 or a positive determination is made in S200, the process proceeds to S180.

  Moreover, in the said 1st Embodiment and the modification 2, although the correction permission conditions in S200 of gas concentration calculation processing were the structures determined based on oxygen concentration and oxygen concentration change rate, it is restricted to such a structure. There is no. For example, the correction permission condition may be determined based only on the oxygen concentration change rate. Specifically, in S200, when the oxygen concentration change rate is less than a predetermined reference determination value, it is determined that the correction permission condition is satisfied (positive determination), and the oxygen concentration change rate is equal to or greater than the reference determination value. In this case, it may be determined that the correction permission condition is not satisfied (negative determination).

  In other words, the oxygen concentration change rate increases as the oxygen concentration change becomes sharper. Therefore, when the oxygen concentration change rate is equal to or higher than the reference determination value, it can be determined that the oxygen concentration has changed sharply. It can be determined that the above is not satisfied. Therefore, even if the correction permission condition is determined based only on the oxygen concentration change rate, it is possible to determine whether or not the ammonia concentration detection error is within the allowable range when calculating the corrected ammonia concentration.

  The engine to which the multi-gas sensor control device of the present invention is applied is not limited to the diesel engine described above, but can be applied to a gasoline engine, and the type of the engine is not particularly limited.

  Next, in the third modification, the NOx sensor 541 is arranged upstream of the ammonia sensor 542 in the exhaust gas traveling direction as a configuration including the separation type sensor 540 in which the NOx sensor 541 and the ammonia sensor 542 are individually provided. Although the structure arrange | positioned in was demonstrated, it is not restricted to such a structure.

  For example, as in Modification 4 shown in FIG. 12, the NOx sensor 541 may be arranged at the same position as the ammonia sensor 542 in the exhaust gas traveling direction. Even in this case, the NOx sensor 541 and the ammonia sensor 542 are arranged in the same space in the exhaust path 502.

  Since the relative positional relationship between the NOx sensor 541 and the ammonia sensor 542 is determined in this manner, the oxygen concentration detection position is the same position in the exhaust gas traveling direction as compared with the ammonia concentration detection position. In this case, when calculating the corrected ammonia concentration, the oxygen concentration detected at the same position as the ammonia concentration detection position can be used. As a result, the oxygen concentration detection time is not delayed from the ammonia concentration detection time, and the corrected ammonia concentration can be calculated with high accuracy.

  Therefore, according to this sensor control device, the corrected ammonia concentration can be calculated with high accuracy, so that a decrease in the detection accuracy of the ammonia concentration can be suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Multi gas sensor control apparatus, 2 ... Multi gas sensor, 3 ... Control part (calculation part), 10 ... Sensor element part, 11 ... NOx sensor part, 12 ... 1st pumping cell, 12a ... 1st solid electrolyte body, 12b ... Inner first pumping electrode, 12c ... outer first pumping electrode, 16 ... oxygen concentration detection cell, 16a ... third solid electrolyte body, 16b ... detection electrode, 16c ... reference electrode, 18 ... second pumping cell, 18a ... second Solid electrolyte body, 18b ... Inner second pumping electrode, 18c ... Second pumping counter electrode, 19 ... Heater, 21 ... Ammonia sensor part, 21a ... Electrode, 21a1 ... Detection electrode, 21a2 ... Reference electrode, 60 ... Microcomputer, 61 ... CPU, 62 ... RAM, 63 ... ROM, 64 ... signal input / output unit, 301 ... sensor control device, 540 ... separate sensor, 54 ... NOx sensor, 542 ... ammonia sensor.

Claims (16)

A first pumping cell that pumps or pumps oxygen in the gas to be measured introduced into the measurement chamber, and a second gas according to the NOx concentration in the gas to be measured whose oxygen concentration is adjusted in the first pumping cell. A NOx sensor unit comprising: a second pumping cell through which a pumping current flows;
An ammonia sensor part that is formed on the outer surface of the NOx sensor part and outputs an ammonia concentration signal corresponding to the ammonia concentration in the gas under measurement;
A sensor control method for controlling a sensor comprising:
An oxygen concentration calculating step of calculating an oxygen concentration in the measurement gas based on a first pumping current flowing in the first pumping cell;
A corrected concentration calculating step for calculating a corrected ammonia concentration based on the oxygen concentration and the ammonia concentration signal of the ammonia sensor unit;
An oxygen concentration change rate calculating step for calculating an oxygen concentration change rate that is a change rate of the oxygen concentration with time;
If the predetermined correction permission condition is satisfied, the correction ammonia concentration is set to the detection result of the ammonia concentration, and if the correction permission condition is not satisfied, the correction ammonia concentration calculated in the past, An ammonia concentration setting step for setting the corrected ammonia concentration calculated when the correction permission condition is satisfied in the detection result of the ammonia concentration;
Have
In the ammonia concentration setting step, when the oxygen concentration change rate is less than a predetermined reference determination value, it is determined that the correction permission condition is satisfied, and the oxygen concentration change rate is greater than or equal to the reference determination value Determining that the modification permission condition is not satisfied,
A sensor control method characterized by the above. In the ammonia concentration setting step, when the correction permission condition is not satisfied, the latest corrected ammonia concentration calculated when the correction permission condition is satisfied among the corrected ammonia concentrations calculated in the past is set to the ammonia concentration. To set the detection result,
The sensor control method according to claim 1. In the ammonia concentration setting step, when the correction permission condition is not satisfied, the ammonia concentration set in the previous detection result is set as the detection result of the current ammonia concentration;
The sensor control method according to claim 1. In the ammonia concentration setting step, when the oxygen concentration change rate is less than the reference determination value and the oxygen concentration exceeds a predetermined reference concentration, it is determined that the correction permission condition is satisfied, and the oxygen concentration Determining that the correction permission condition is not satisfied when at least one of the rate of change in concentration is equal to or higher than the reference determination value and the oxygen concentration is equal to or lower than a predetermined reference concentration. ,
The sensor control method according to any one of claims 1 to 3, wherein: In the ammonia concentration setting step, it is determined that the correction permission condition is not satisfied until a predetermined stop period elapses after it is determined that the correction permission condition is not satisfied.
The sensor control method according to claim 1, wherein: In the oxygen concentration change rate calculating step, a value obtained by dividing the previously calculated oxygen concentration by the oxygen concentration calculated this time is calculated as the oxygen concentration change rate;
The sensor control method according to any one of claims 1 to 5, wherein: The sensor is a multi-gas sensor integrally including the NOx sensor unit and the ammonia sensor unit;
The sensor control method according to any one of claims 1 to 6, wherein: The sensor is provided with the NOx sensor unit and the ammonia sensor unit separately, and is disposed in an exhaust path of the internal combustion engine,
The exhaust path is configured to include a plurality of spaces partitioned by a partition portion through which exhaust gas can permeate.
The NOx sensor unit and the ammonia sensor unit are disposed in the same space among the plurality of spaces;
The sensor control method according to any one of claims 1 to 6, wherein: The NOx sensor unit is disposed at the same position as the ammonia sensor unit or upstream of the ammonia sensor unit in the direction of travel of the exhaust gas;
The sensor control method according to claim 8. A first pumping cell that pumps or pumps oxygen in the gas to be measured introduced into the measurement chamber, and a second gas according to the NOx concentration in the gas to be measured whose oxygen concentration is adjusted in the first pumping cell. A NOx sensor unit comprising: a second pumping cell through which a pumping current flows;
An ammonia sensor part that is formed on the outer surface of the NOx sensor part and outputs an ammonia concentration signal corresponding to the ammonia concentration in the gas under measurement;
A sensor control device for controlling a sensor comprising:
An oxygen concentration calculator that calculates an oxygen concentration in the gas under measurement based on a first pumping current flowing through the first pumping cell;
Based on the oxygen concentration and the ammonia concentration signal of the ammonia sensor unit, a corrected concentration calculating unit that calculates a corrected ammonia concentration;
An oxygen concentration change rate calculating unit that calculates an oxygen concentration change rate that is a change rate of the oxygen concentration over time;
If the predetermined correction permission condition is satisfied, the correction ammonia concentration is set to the detection result of the ammonia concentration, and if the correction permission condition is not satisfied, the correction ammonia concentration calculated in the past, An ammonia concentration setting unit for setting the corrected ammonia concentration calculated when the correction permission condition is satisfied in the detection result of the ammonia concentration;
Have
The ammonia concentration setting unit determines that the correction permission condition is satisfied when the oxygen concentration change rate is less than a predetermined reference determination value, and the oxygen concentration change rate is greater than or equal to the reference determination value Determining that the modification permission condition is not satisfied,
A sensor control device. The ammonia concentration setting unit, when the correction permission condition is not satisfied, out of the corrected ammonia concentrations calculated in the past, the latest correction calculated when the oxygen concentration change rate satisfies the correction permission condition Setting the ammonia concentration to the detection result of the ammonia concentration;
The sensor control device according to claim 10. If the ammonia concentration setting unit does not satisfy the correction permission condition, the ammonia concentration set in the previous detection result is set as the detection result of the current ammonia concentration;
The sensor control device according to claim 10. The ammonia concentration setting unit determines that the correction permission condition is satisfied when the oxygen concentration change rate is less than the reference determination value and the oxygen concentration exceeds a predetermined reference concentration; Determining that the correction permission condition is not satisfied when at least one of the rate of change in concentration is equal to or higher than the reference determination value and the oxygen concentration is equal to or lower than a predetermined reference concentration. ,
The sensor control device according to any one of claims 10 to 12, wherein The sensor is a multi-gas sensor integrally including the NOx sensor unit and the ammonia sensor unit;
The sensor control device according to any one of claims 10 to 13, characterized by: The sensor is provided with the NOx sensor unit and the ammonia sensor unit separately, and is disposed in an exhaust path of the internal combustion engine,
The exhaust path is configured to include a plurality of spaces partitioned by a partition portion through which exhaust gas can permeate.
The NOx sensor unit and the ammonia sensor unit are disposed in the same space among the plurality of spaces;
The sensor control device according to any one of claims 10 to 13, characterized by: The NOx sensor unit is disposed at the same position as the ammonia sensor unit or upstream of the ammonia sensor unit in the direction of travel of the exhaust gas;
The sensor control device according to claim 15.