JP2013221931A - Multi-gas sensor and multi-gas sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-gas sensor and a multi-gas sensor device which can suppress deterioration of measurement accuracy of NO concentration, NOconcentration, and NHconcentration.SOLUTION: A multi-gas sensor comprises: an NOx sensor part 11 for measuring concentration of nitrogen oxide contained in gas to be measured; a first ammonia sensor part 21 and a second ammonia sensor part 22 for measuring ammonia contained in the gas to be measured; and a heater part 19 for heating the NOx sensor part 11, the first ammonia sensor part 21 and the second ammonia sensor part 22. The first ammonia sensor part 21 and the second ammonia sensor part 22 consist of the same components, and the second ammonia sensor part 22 is disposed in an area inside a sensor element part 10 where its temperature is lower than that of the first ammonia sensor part 21.

Description

  The present invention relates to a multi-gas sensor and a multi-gas sensor device used for measuring the concentration of nitrogen oxide and the concentration of ammonia contained 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 an internal combustion engine such as a diesel engine. 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 multi-gas sensor capable of measuring a plurality of types of gas concentrations including a sensor element that measures the concentration of ammonia contained in exhaust gas is used in the urea SCR system (for example, (See Patent Documents 1 and 2). 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 multi-gas sensor, that is, the concentration of ammonia contained in the exhaust gas is within a predetermined range. .

JP 2011-075546 A US Patent Application Publication No. 2010/0161242

The multi-gas sensor described in Patent Document 1 described above is a NOx sensor provided with an NH ₃ detection cell. In this multi-gas sensor, only the measurement signal output from the NOx sensor and the measurement signal output from the NH ₃ detection cell can be obtained. Therefore, when there are three gas types to be measured, for example, in the case of nitric oxide (NO), nitrogen dioxide (NO ₂ ), and ammonia (NH ₃ ), it is difficult to calculate the exact concentrations of the three gas types. There is a possibility that only a concentration with insufficient accuracy can be obtained.

The multi-gas sensor described in Patent Document 2 described above is a combination of an NH ₃ detection cell, an NO ₂ detection cell, and an NOx cell, a measurement signal of the NH ₃ detection cell, a measurement signal of the NO ₂ detection cell, and Based on the measurement signal of the NOx cell, the respective concentrations of ammonia, nitric oxide and nitrogen dioxide are calculated.

However, in the multi-gas sensor described in Patent Document 2, the electrode of the NH ₃ detection cell and the electrode of the NO ₂ detection cell are formed from different materials. Therefore, it was necessary to take measures to ensure reliability for each of the NH ₃ detection cell and the NO ₂ detection cell. That is, there is a possibility that the degree of deterioration of the electrodes may be different, and if the use period of the multi-gas sensor is extended, there is a problem that the difference in the degree of deterioration of the electrodes increases and the measurement accuracy of the concentration of the gas species may deteriorate .

  The present invention has been made to solve the above-described problem, and is capable of suppressing deterioration in measurement accuracy of the concentration of nitric oxide, the concentration of nitrogen dioxide, and the concentration of ammonia, and a multigas sensor device. The purpose is to provide.

In order to achieve the above object, the present invention provides the following means.
The multi-gas sensor of the present invention includes a NOx sensor unit that measures the concentration of nitrogen oxides contained in the gas to be measured, an ammonia sensor unit that measures the concentration of ammonia contained in the gas to be measured, the NOx sensor unit, and the A heater unit for heating the ammonia sensor unit is a multi-gas sensor having a sensor element unit integrally provided and extending in the axial direction, wherein the ammonia sensor unit includes the first ammonia sensor unit and the same component It has a 2nd ammonia sensor part, and the 2nd ammonia sensor part is arranged in the field where temperature is lower than the 1st ammonia sensor part among the sensor element parts.

  According to the multi-gas sensor of the present invention, since there is a temperature difference between the first ammonia sensor part and the second ammonia sensor part at the time of measurement, nitrogen monoxide and dioxide dioxide in the first ammonia sensor part and the second ammonia sensor part. Differences in the degree of reaction to nitrogen occur. Therefore, different values of output can be obtained from each of the NOx sensor unit, the first ammonia sensor unit, and the second ammonia sensor unit. By calculating using these three outputs, the concentrations of nitric oxide, nitrogen dioxide and ammonia can be obtained.

  In addition, Preferably, the temperature difference between the first ammonia sensor unit and the second ammonia sensor unit is set to 50 ° C. or more, so that the output difference between the first ammonia sensor unit and the second ammonia sensor unit is sufficient. Can be secured. Therefore, the output of three different values can be reliably ensured, and the accuracy of the nitrogen monoxide concentration, the nitrogen dioxide concentration, and the ammonia concentration obtained by calculation can be more easily ensured.

  Further, as a specific calculation method, the output of the NOx sensor unit including the influence of ammonia (output value of the nitrogen oxide concentration), the first ammonia including the influence of nitrogen oxides (nitrogen monoxide and nitrogen dioxide) From the output of the sensor unit (ammonia concentration output value) and the output of the second ammonia sensor unit (ammonia concentration output value), which also includes the influence of nitrogen oxides, the effects of ammonia and nitrogen dioxide The concentration of removed nitrogen monoxide, the concentration of nitrogen dioxide from which the effects of ammonia and nitric oxide have been removed, and the concentration of ammonia from which the effects of nitrogen monoxide and nitrogen dioxide have been removed can be calculated.

  Here, even if the first ammonia sensor unit disposed in the high temperature region and the second ammonia sensor unit disposed in the low temperature region have the same components, the temperature of the region disposed (that is, the temperature of the sensor unit). ) Are different, the degree of influence of nitrogen oxides on the output changes. In other words, the influence of nitrogen oxides on the output depends on the temperature of the sensor unit. Therefore, the output of the first ammonia sensor unit and the output of the second ammonia sensor unit can be treated as different outputs, and three different outputs obtained by adding the output of the NOx sensor unit to this are used for the nitric oxide. The concentration of nitrogen dioxide and ammonia can be determined.

  In addition, by making the elements constituting the first ammonia sensor unit and the second ammonia sensor unit the same, the degree of deterioration with time of the first ammonia sensor unit and the second ammonia sensor unit becomes the same. Therefore, as compared with the case where the first ammonia sensor unit and the second ammonia sensor unit are configured using separate components, the output relationship between the first ammonia sensor unit and the second ammonia sensor unit is kept constant. Easy to do. In other words, the necessity of calibrating the outputs of the first ammonia sensor unit and the second ammonia sensor unit is reduced, and the accuracy of the nitric oxide concentration, the nitrogen dioxide concentration, and the ammonia concentration is easily maintained.

  Note that “the same constituent elements” means that the first ammonia sensor unit and the second ammonia sensor unit have the same configuration made of the same material. For example, as is well known, the ammonia sensor unit is a solid electrolyte body. , And a pair of electrodes provided on the surface thereof, the first ammonia sensor part and the second ammonia sensor part are each formed of a solid electrolyte body and a pair of electrodes (configuration), And this solid electrolyte body and a pair of electrodes point out that it is the same material.

  Furthermore, it is preferable that the lower limit of the temperature on the low temperature side among the temperatures of the NOx sensor unit, the first ammonia sensor unit, and the temperature of the second ammonia sensor unit is 500 ° C., and the upper limit of the temperature on the high temperature side is 800 ° C. It is preferable. Thus, by setting the lower limit of the temperature on the low temperature side to 500 ° C., the sensors of the NOx sensor unit, the first ammonia sensor unit, and the second ammonia sensor unit can be activated, and the upper limit of the temperature on the high temperature side is set to 800. By setting it to ° C., it is possible to suppress a decrease in ammonia detection performance of the NOx sensor unit, the first ammonia sensor unit, and the second ammonia sensor unit.

  In the above invention, the sensor element unit is provided with a temperature detection unit that measures a temperature used to control heating of the NOx sensor unit, and the first ammonia sensor unit includes the sensor element unit of the sensor element unit. It is preferable that the second ammonia sensor unit is disposed at a position closer to the temperature detection unit than the second ammonia sensor unit.

  Thus, the temperature of the first ammonia sensor unit can be accurately controlled by arranging the first ammonia sensor unit arranged in the high temperature region at a position close to the temperature detection unit. In particular, when the temperature of the first ammonia sensor unit is controlled to a temperature close to the above-described upper limit temperature of 800 ° C., it is easy to suppress a decrease in detection performance of the first ammonia sensor unit due to exceeding the upper limit temperature. .

  In the above invention, the NOx sensor unit includes a first solid electrolyte body and a pair of first electrodes provided on the first solid electrolyte body and positioned inside and outside the first measurement chamber, A first pumping cell for pumping or pumping oxygen in the gas to be measured introduced into the measurement chamber, a second solid electrolyte body, and the second solid electrolyte body; A pair of second electrodes located outside, and a second pumping current corresponding to the NOx concentration in the gas flowing into the second measurement chamber after the oxygen concentration is adjusted in the first measurement chamber. A second pumping cell that flows between the second electrodes of the first pumping cell, and the temperature detector is provided downstream of the first pumping cell and upstream of the second pumping cell, The ammonia sensor unit is the sensor An outer surface of the terminal portion, it is preferably provided at the same position as the temperature detection portion in the axial direction.

  Thus, when the NOx sensor unit is formed with the above-described configuration, the NOx sensor unit is provided by providing the temperature detection unit on the downstream side of the first pumping cell and on the upstream side of the second pumping cell. Can be measured, and the heating of the NOx sensor unit can be well controlled. Moreover, the temperature of the first ammonia sensor unit can be more accurately controlled by providing the first ammonia sensor unit on the outer surface of the sensor element unit and at the same position as the temperature detection unit in the axial direction.

  In the said invention, it is preferable that the said 1st ammonia sensor part and the said 2nd ammonia sensor part are comprised using the common reference electrode.

  Thus, by making the reference electrode of the 1st ammonia sensor part and the reference electrode of the 2nd ammonia sensor part into a common electrode, the deterioration of the measurement accuracy in a multi gas sensor can be controlled. Specifically, since the degree of deterioration of the reference electrode of the first ammonia sensor unit matches the degree of deterioration of the reference electrode of the second ammonia sensor unit, the degree of deterioration is lower than when the reference electrode is provided separately. The deterioration of measurement accuracy due to the difference is suppressed.

  The multi-gas sensor device of the present invention is based on the multi-gas sensor of the present invention, the output of the NOx sensor unit, the output of the first ammonia sensor unit, and the output of the second ammonia sensor unit. And an arithmetic unit for calculating concentrations of nitrogen monoxide, nitrogen dioxide, and ammonia contained in the battery.

  According to the multi-gas sensor device of the present invention, since the multi-gas sensor of the present invention is provided, calculation is performed based on outputs of different values from the NOx sensor unit, the first ammonia sensor unit, and the second ammonia sensor unit. And output concentrations of nitric oxide, nitrogen dioxide and ammonia.

According to the multi-gas sensor and the multi-gas sensor device of the present invention, by providing a temperature difference between the first ammonia sensor unit and the second ammonia sensor unit at the time of measurement, the NOx sensor unit, the first ammonia sensor unit, and the second Different values of output can be obtained from each of the ammonia sensor units. By calculating the NO concentration, the NO ₂ concentration, and the NH ₃ concentration by calculation based on these three outputs having different values, it is possible to suppress deterioration in measurement accuracy of the concentration of nitrogen monoxide, the concentration of nitrogen dioxide, and the concentration of ammonia. There is an effect.

It is sectional drawing which follows the longitudinal direction explaining the structure of the multi-gas sensor which concerns on one Embodiment of this invention. It is a block diagram explaining the structure of the multi-gas sensor apparatus which concerns on one Embodiment of this invention. It is an expanded view explaining the structure of the 1st and 2nd ammonia sensor part. It is a figure explaining the detection characteristic of a 1st and 2nd ammonia sensor part, and a NOx sensor part. It is a figure explaining the detection characteristic of a 1st and 2nd ammonia sensor part, and a NOx sensor part. It is a figure explaining the detection characteristic of a 1st and 2nd ammonia sensor part, and a NOx sensor part. It is a figure explaining the detection characteristic of a 1st and 2nd ammonia sensor part, and a NOx sensor part. NO concentration before and after performing the correction processing of this embodiment, is a diagram explaining a difference in NO ₂ concentration and NH ₃ concentration. NO concentration before and after performing the correction processing of this embodiment, is a diagram explaining a difference in NO ₂ concentration and NH ₃ concentration.

A multi-gas sensor device 1 according to an embodiment of the present invention will be described with reference to FIGS. The multi-gas sensor device 1 of this embodiment is used for a urea SCR system that purifies nitrogen oxides (NOx) contained in exhaust gas (gas to be measured) 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.

  Note that the engine to which the multi-gas sensor device 1 of the present embodiment is applied may be the above-described diesel engine or can be applied to a gasoline engine, and the type of the engine is not particularly limited.

As shown in FIGS. 1 and 2, the multi-gas sensor device 1 controls the multi-gas sensor 2 which is a sensor main body, and controls the multi-gas sensor 2 and computes the sensor output to obtain concentrations of NO, NO ₂ and ammonia. And a control unit (calculation unit) 3 for calculating.

  As shown in FIG. 1, the multi-gas sensor 2 is mainly provided with 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 in accordance with the number of electrodes and the like that the first ammonia sensor portion 21 and the second ammonia sensor portion 22 have. 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.

As shown in FIG. 2, the control unit 3 of the multigas sensor device 1 is electrically connected to an ECU 200 that is a vehicle-side control device of a vehicle on which the multigas sensor 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.

  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 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, a first ammonia sensor unit 21, and a second ammonia sensor unit 22. The NOx sensor unit 11, the first ammonia sensor unit 21, and the second ammonia sensor unit 22 in the present embodiment have the same configuration as the known NOx sensor and the same configuration as the 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, and insulating layers 10b and 10a. 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.

  Further, the NOx sensor unit 11 further increases the temperature of the NOx sensor unit 11, the first ammonia sensor unit 21, and the second ammonia sensor unit 22 to the activation temperature, and oxygen ions in the solid electrolyte bodies constituting the respective sensors. A heater (heater part) 19 is provided to increase the conductivity of the heater. 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 disposed 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 first ammonia sensor part 21 and the second ammonia sensor part 22 are formed on the outer surface of the NOx sensor part 11, more specifically, on the insulating layer 10e. The first ammonia sensor unit 21 is disposed substantially at the same position in the direction of the axis O as the reference electrode 16c in the NOx sensor unit 11 (for example, the upper side in FIG. 2), and the second ammonia sensor unit 22 On the other hand, it is arranged adjacent to the rear end side.

  In the present invention, the temperature of the oxygen concentration detection cell 16 is measured (corresponding to the temperature detection unit of the present invention), and the heater 19 is heated based on the measured temperature. Moreover, the 1st ammonia sensor part 21 is arrange | positioned in the position where the temperature of the 1st ammonia sensor part 21 becomes 650 degreeC. In the present embodiment, the second ammonia sensor unit 22 is disposed at a position where the temperature is 100 ° C. lower than the first ammonia sensor unit 21.

  As shown in FIGS. 2 and 3, the first ammonia sensor unit 21 includes a first reference electrode (reference electrode) 21a mainly composed of platinum, a solid electrolyte body 23 for ammonia mainly composed of zirconia, cobalt oxide and The first intermediate layer 21b mainly composed of zirconia and the first ammonia electrode 21c mainly composed of gold are mainly configured. The second ammonia sensor unit 22 includes a second reference electrode (reference electrode) 22a mainly composed of platinum, a solid electrolyte body 23 for ammonia, a second intermediate layer 22b mainly composed of cobalt oxide and zirconia, and mainly composed of gold. And the second ammonia electrode 22c. Furthermore, the first ammonia sensor portion 21 and the second ammonia sensor portion 22 are integrally covered with a porous protective layer 24.

  The first reference electrode 21a and the second reference electrode 22a are rectangular electrodes disposed on the outer surface (the upper surface in FIG. 3) of the insulating layer 10e, and are arranged in the longitudinal direction (the horizontal direction in FIG. 3) of the insulating layer 10e. ), And is integrally formed by a reference electrode lead 25 mainly composed of platinum. The end portion on the rear end side (right side in FIG. 3) of the reference electrode lead 25 forms an electrode terminal portion.

  The ammonia solid electrolyte body 23 is made of an oxygen ion conductive material such as yttria stabilized zirconia (YSZ), and sandwiches the first reference electrode 21a and the second reference electrode 22a between the insulating layer 10e. It is arranged by. In other words, the ammonia solid electrolyte body 23 is common to the first ammonia sensor unit 21 and the second ammonia sensor unit 22.

The first intermediate layer 21b and the second intermediate layer 22b are layers formed of a material containing cobalt oxide (Co ₃ O ₄ ). The first intermediate layer 21b and the second intermediate layer 22b are solid electrolyte bodies for ammonia. 23, which are arranged at positions facing the first reference electrode 21a and the second reference electrode 22a, respectively.

  The 1st ammonia electrode 21c and the 2nd ammonia electrode 22c are electrodes formed from the material which has gold as a main component, and work as a detection electrode. The first ammonia electrode 21c and the second ammonia electrode 22c are respectively disposed on the outer surfaces of the first intermediate layer 21b and the second intermediate layer 22b. In other words, the first ammonia electrode 21c is disposed with the solid electrolyte for ammonia 23 and the first intermediate layer 21b interposed between the first reference electrode 21a and the second ammonia electrode 22c. The ammonia solid electrolyte body 23 and the second intermediate layer 22b are disposed between the reference electrode 22a and the reference electrode 22a.

  A first ammonia electrode lead 21d is formed on the first ammonia electrode 21c so as to extend from the first ammonia electrode 21c toward the rear end side, and a second ammonia electrode lead 22d is formed on the second ammonia electrode 22c with the second ammonia. It extends from the electrode 22c toward the rear end side. The first ammonia electrode lead 21d and the second ammonia electrode lead 22d are formed of a material whose main component is platinum. Further, the end portions on the rear end side of the first ammonia electrode lead 21d and the second ammonia electrode lead 22d form electrode terminal portions.

  The first ammonia electrode 21c and the second ammonia electrode 22c are highly reactive with ammonia. Therefore, an electromotive force (potential difference) is generated between the first ammonia electrode 21c and the first reference electrode 21a and between the second ammonia electrode 22c and the second reference electrode 22a.

  In the present embodiment, the first ammonia electrode 21c and the second ammonia electrode 22c are provided separately from the first ammonia electrode 21c and the second ammonia electrode 22c, although the first intermediate layer 21b and the second intermediate layer 22b are provided separately. In addition, cobalt oxide contained in the first intermediate layer 21b and the second intermediate layer 22b may be included, and the first intermediate layer 21b and the second intermediate layer 22b may be omitted.

The protective layer 24 prevents adherence of poisonous substances to the first ammonia electrode 21c and the second ammonia electrode 22c, and prevents the gas to be measured flowing into the first ammonia sensor unit 21 and the second ammonia sensor unit 22 from the outside. It adjusts the diffusion rate. Examples of the material for forming the protective layer 24 include at least one material selected from the group consisting of alumina (aluminum oxide), spinel (MgAl ₂ O ₄ ), silica alumina, and mullite. The diffusion rate of the gas to be measured by the protective layer 24 is adjusted by adjusting the thickness, particle size, particle size distribution, porosity, blending ratio, etc. of the protective layer 24.

  The protective layer 24 may be provided as in the above-described embodiment, or the first ammonia electrode 21c, the second ammonia electrode 22c, etc. may be exposed without providing the protective layer 24, which is particularly limited. is not.

  The first ammonia sensor unit 21 and the second ammonia sensor unit 22 described above can be manufactured as described below.

  First, a material for forming the first reference electrode 21a and the second reference electrode 22a is disposed on the insulating layer 10e by using a method similar to printing (hereinafter, referred to as “printing method”), and the material is formed thereon. The material for forming the solid electrolyte body 23 for ammonia is arranged by a printing method. Thereafter, the first reference electrode 21a, the second reference electrode 22a, and the ammonia solid electrolyte body 23 are formed by firing at 1500 ° C.

  Next, the material for forming the first intermediate layer 21b and the second intermediate layer 22b is arranged on the solid electrolyte body 23 for ammonia by a printing method. Then, the 1st intermediate | middle layer 21b and the 2nd intermediate | middle layer 22b are formed by baking at 1000 degreeC.

  Further, materials for forming the first ammonia electrode 21c and the second ammonia electrode 22c are arranged on the first intermediate layer 21b and the second intermediate layer 22b, respectively, and are fired at a predetermined temperature (for example, 1000 ° C.). Thus, the first ammonia electrode 21c and the second ammonia electrode 22c are arranged. Finally, to cover the first reference electrode 21a, the second reference electrode 22a, the solid electrolyte body 23 for ammonia, the first intermediate layer 21b, the second intermediate layer 22b, the first ammonia electrode 21c and the second ammonia electrode 22c, The protective layer 24 is formed by arranging a paste containing alumina or the like by screen printing and firing at a predetermined temperature (for example, 1000 ° C.). Thus, the first ammonia sensor unit 21 and the second ammonia sensor unit 22 are completed.

  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 a first drive circuit. The electromotive force detection circuit 58 and the second electromotive force detection circuit 59 are mainly configured.

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

  The first electromotive force detection circuit 58 is electrically connected to the first reference electrode 21 a and the first ammonia electrode 21 c in the first ammonia sensor unit 21, and the second electromotive force detection circuit 59 is in the second ammonia sensor unit 22. The second reference electrode 22a and the second ammonia electrode 22c are electrically connected. Further, the first electromotive force detection circuit 58 detects a first ammonia electromotive force EMF, which is an electromotive force between the first reference electrode 21 a and the first ammonia electrode 21 c, and outputs it to the microcomputer 60. Similarly, the second electromotive force detection circuit 59 detects a second ammonia electromotive force EMF, which is an electromotive force between the second reference electrode 22a and the second ammonia electrode 22c, 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.

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 the target temperature by the heater 19, the first ammonia sensor unit 21 and the second ammonia sensor unit 22 arranged on the NOx sensor unit 11 are also brought to their desired temperatures. The temperature is raised.

  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 in the first measurement chamber S1. Is called. 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 first reference electrode 21a and the first ammonia electrode 21c of the first ammonia sensor unit 21 according to the ammonia concentration contained in the gas to be measured. The first electromotive force detection circuit 58 detects an electromotive force between the first reference electrode 21a and the first ammonia electrode 21c as a first ammonia electromotive force. Similarly, an electromotive force is generated between the second reference electrode 22a and the second ammonia electrode 22c of the second ammonia sensor unit 22 according to the ammonia concentration. The second electromotive force detection circuit 59 detects an electromotive force between the second reference electrode 22a and the second ammonia electrode 22c as a second ammonia concentrated 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. The first ammonia electromotive force EMF output from the first ammonia sensor unit 21 and the second ammonia electromotive force EMF output from the second ammonia sensor unit 22 include the oxygen concentration, NO concentration, NO _{2 of the} gas to be measured. The influence of the concentration and the temperature of each sensor unit 11, 21, 22 is also included. In this embodiment, after removing the influence of the oxygen concentration from the second pumping current Ip2, the first ammonia electromotive force, and the second 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.

  Here, the ROM 63 of the microcomputer 60 stores various data described below. The CPU 61 reads the 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, the first ammonia electromotive force, and the second ammonia electromotive force.

  The ROM 63 stores “ammonia electromotive force-ammonia concentration output relational expression”, “ammonia concentration output-corrected ammonia concentration output relational expression”, and “second pumping current Ip2-NOx concentration output relational expression”.

  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 “ammonia electromotive force-ammonia concentration output relational expression” is a relationship between the ammonia electromotive force output from the first ammonia sensor unit 21 and the second ammonia sensor unit 22 and the ammonia concentration output related to the ammonia concentration of the gas to be measured. Is an expression.

  The “ammonia concentration output-corrected ammonia concentration output relational expression” is set for each oxygen concentration, and the first ammonia concentration output affected by the oxygen concentration, the corrected ammonia concentration output from which the influence of the oxygen concentration is removed, and And an expression representing the relationship between the second ammonia concentration output affected by the oxygen concentration and the corrected ammonia concentration output from which the influence of the oxygen concentration has been removed.

  Note that an ammonia concentration output-corrected ammonia concentration output relational expression at a predetermined oxygen concentration that is not set in the "ammonia concentration output-corrected ammonia concentration output relational expression" can be obtained as follows. That is, "ammonia concentration output-corrected ammonia concentration output relational expression" at a set oxygen concentration lower than a predetermined oxygen concentration and "ammonia concentration output-corrected ammonia concentration output relationship" at a high oxygen concentration set From the equation, an ammonia concentration output-corrected ammonia concentration output relational expression at a predetermined oxygen concentration can be obtained using an extrapolation method.

  The “second pumping current Ip2-NOx concentration output relational expression” is an expression representing the relationship between the second pumping current Ip2 and the NOx concentration of the gas to be measured.

Next, calculation processing executed by the CPU 61 of the microcomputer 60 to obtain the NO concentration, the NO ₂ concentration, and the ammonia concentration from the second pumping current Ip2, the first ammonia electromotive force EMF, and the second ammonia electromotive force EMF will be described. .

  When the second pumping current Ip2, the first ammonia electromotive force, and the second ammonia electromotive force are input, the CPU 61 performs arithmetic processing for obtaining the first ammonia concentration output and the second ammonia concentration output. Specifically, the “ammonia electromotive force-ammonia concentration output relational expression” is called from the ROM 63, and the first ammonia concentration output and the second ammonia concentration output are calculated using the relational expression.

  Next, a calculation process for obtaining a corrected first ammonia concentration output and a corrected second ammonia concentration output by removing the influence of the oxygen concentration from the first ammonia concentration output and the second ammonia concentration output is performed. Specifically, the “ammonia concentration output−corrected ammonia concentration output relational expression” is called from the ROM 63, and the correction first ammonia concentration output and the corrected second ammonia concentration output are calculated using the relational expression.

  Further, a calculation process for obtaining a NOx concentration output from the second pumping current Ip2 is performed. Specifically, the “second pumping current Ip2-NOx concentration output relational expression” is called from the ROM 63, and the NOx concentration output is calculated using the relational expression.

When the NOx concentration output, the corrected first ammonia concentration output, and the corrected second ammonia concentration output are obtained, the CPU 61 performs an operation using the correction equation (1) to the correction equation (3) described below, thereby performing the calculation. The NO concentration, NO ₂ concentration and NH ₃ concentration of the measurement gas are obtained.

x = (1 + ay) (1 + bz) A + cz (1)
x = (1 + dy + ez) B + fz (2)
C = y + 0.8z + 1.2x (3)
Here, x is the NH ₃ concentration, y is the NO concentration, and z is the NO ₂ concentration. A is the first ammonia concentration output, B is the second ammonia concentration output, and C is the NOx concentration output. Further, a, b, c, e, and f are correction coefficients.

  The correction formula (1) is determined based on the characteristics of the first ammonia sensor unit 21, the correction formula (2) is determined based on the characteristics of the second ammonia sensor unit 22, and the correction formula (3) is determined based on the characteristics of the NOx sensor unit 11. This is a formula determined based on the characteristics of Note that (1) to (3) show examples of correction equations, and other correction equations, coefficients, and the like may be changed as appropriate in accordance with the gas detection characteristics.

The calculation procedure of the NO concentration y, the NO ₂ concentration z and the NH ₃ concentration x based on the above correction equations (1) to (3) is as follows.
1. From the correction equations (2) and (3), the equation is transformed into the form of x = ... z, y = ... z.
2. The above equation is substituted into the correction equation (1) to obtain a quadratic equation for z.
3. For quadratic equation of the obtained NO ₂ concentration z, determining the value of the NO ₂ concentration z using the formula of the solution. In addition, when the coefficient of the quadratic term of z is 0, the NH ₃ concentration x is set to 0.
4). The NO concentration y is calculated from the correction equations (1) and (3) and the value of z.
5. The NH ₃ concentration x is calculated by inputting the NO concentration y and the NO ₂ concentration z into the correction formula (3).

Next, while referring to FIGS. 4 to 9, the detection characteristics of the first ammonia sensor unit 21, the second ammonia sensor unit 22, and the NOx sensor unit 11 will be described, and the NO before and after performing the correction process of the present embodiment. Differences in concentration, NO ₂ concentration, and NH ₃ concentration will be described.

First, detection characteristics of the first ammonia sensor unit 21, the second ammonia sensor unit 22, and the NOx sensor unit 11 with respect to single NO, NO _2, and NH ₃ will be described with reference to FIG. 4A is a graph for explaining the detection characteristic of the first ammonia sensor unit 21, FIG. 4B is a graph for explaining the detection characteristic of the second ammonia sensor unit 22, and FIG. ) Is a graph for explaining the detection characteristics of the NOx sensor unit 11. In each graph, the graphs indicated by white diamonds (◇) are graphs showing the output density from the sensor when only NH ₃ is input, and the white triangles (Δ) are only NO. Is a graph representing the output density at the time of the measurement, and a white circle (◯) is a graph representing the output density from the sensor when only NO ₂ is charged.

Looking at the first ammonia sensor unit 21 arranged on the high temperature side, it can be seen that only the NH ₃ is outputting an accurate output concentration proportional to the input concentration. There is no output for NO, and for NO ₂ , the output concentration decreases as the input concentration increases. Also, the second ammonia sensor unit 22 arranged on the low temperature side has substantially the same output concentration as the first ammonia sensor unit 21.

Looking at the NOx sensor unit 11, the output concentration increases as the input concentration increases with respect to NO, NO ₂ and NH ₃ . Of particular note is that the NOx sensor unit 11 is sensitive to NH ₃ as well as NO and NO ₂ .

Next, referring to FIG. 5, the first ammonia sensor unit 21 and the second ammonia when the concentration of NH ₃ input to the measurement gas containing NO is changed (NO ₂ is not included). The detection characteristics of the sensor unit 22 and the NOx sensor unit 11 will be described. Note that the NO concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) in each graph represent the case where the NO concentration is 0 ppm, and are white triangles. (Δ) represents the case of 20 ppm, and the white circle (◯) represents the case of 50 ppm.

Looking at the first ammonia sensor unit 21 shown in FIG. 5A, it can be seen that an accurate output concentration proportional to the input NH ₃ concentration is output regardless of whether the NO concentration is high or low. In other words, it can be seen that the first ammonia sensor unit 21 is hardly affected by the NO concentration.

Further, when looking at the second ammonia sensor unit 22 shown in FIG. 5B, as the NO concentration increases, an output concentration lower than the input NH ₃ concentration is output, and the slope of the graph changes. I know that In other words, it can be seen that the detection sensitivity of the second ammonia sensor unit 22 decreases as the NO concentration increases.

Further, when viewing the NOx sensor unit 11 shown in FIG. 5C, an output concentration having a value proportional to the input NH ₃ concentration is output, and the output concentration is shown as the NO concentration increases. It can be seen that the graph translates (offsets) to the high density side.

Next, referring to FIG. 6, the first ammonia sensor unit 21 and the second ammonia when the concentration of NH ₃ introduced into the measurement gas containing NO ₂ is changed (NO is not included). The detection characteristics of the sensor unit 22 and the NOx sensor unit 11 will be described. Note that the NO ₂ concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) in each graph represent the case where the NO ₂ concentration is 0 ppm, and white The open triangle (Δ) represents the case of 20 ppm, and the open circle (◯) represents the case of 50 ppm.

Looking at the first ammonia sensor unit 21 shown in FIG. 6A, the influence of the NO ₂ concentration on the change in the value of the output concentration with respect to the change in the NH ₃ concentration to be input is small, but the NH to be input It can be seen that the output density value itself becomes smaller with respect to the _three density changes. That is, it can be seen that although the change in the slope of the output density graph is small, the graph moves parallel to the low density side. In other words, it can be seen that when the NO ₂ concentration increases, the first ammonia sensor unit 21 mainly offsets the output concentration to the low concentration side.

Looking at the second ammonia sensor unit 22 shown in FIG. 6B, it can be seen that the influence of the NO ₂ concentration on the change in the value of the output concentration with respect to the change in the input NH ₃ concentration is large. That is, it can be seen that the change in the slope of the output density graph is large. On the other hand, the parallel movement of the graph is smaller than that of the first ammonia sensor unit 21. In other words, it can be seen that when the NO ₂ concentration increases, the second ammonia sensor unit 22 mainly decreases in detection sensitivity.

Looking at the NOx sensor unit 11 shown in FIG. 6C, a graph showing an output concentration with a value proportional to the input NH ₃ concentration and an output concentration as the NO ₂ concentration increases. It can be seen that is translated (offset) to the high density side.

Next, referring to FIG. 7, the first ammonia sensor unit 21 and the second ammonia when the concentration of NO ₂ input to the measurement gas containing NO is changed (NH ₃ is not included). The detection characteristics of the sensor unit 22 and the NOx sensor unit 11 will be described. Note that the NO concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) in each graph represent the case where the NO concentration is 0 ppm, and are white triangles. (Δ) represents the case of 20 ppm, and the white circle (◯) represents the case of 50 ppm.

Looking at the first ammonia sensor unit 21 shown in FIG. 7A, the value of the output concentration decreases as the input NO ₂ concentration increases, and the output concentration is affected by the high or low NO concentration. It turns out that it has hardly received.

Looking at the second ammonia sensor unit 22 shown in FIG. 7 (b), as with the first ammonia sensor unit 21, the value of the output concentration decreases as the concentration of NO ₂ input increases, and It can be seen that the output concentration is hardly affected by the high or low NO concentration.

Looking at the NOx sensor unit 11 shown in FIG. 7 (c), a graph showing an output concentration with a value proportional to the input NO ₂ concentration and an output concentration as the NO concentration increases is shown. It can be seen that it is translated (offset) to the high density side.

Next, the difference in the NO concentration, the NO ₂ concentration, and the NH ₃ concentration before and after performing the correction processing of the present embodiment will be described with reference to FIGS. FIG. 8A shows the calculated NH ₃ before correction when the concentration of NH ₃ introduced into the measurement gas containing NO as an interfering gas is changed (NO ₂ is not included). is a graph showing the concentration, the NH ₃ concentration after correction.

Note that the NO concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) and black diamonds (◆) in each graph have a NO concentration of 0 ppm. The white triangle (Δ) and the black triangle (▲) represent the case of 20 ppm, and the white circle (◯) and the black circle (●) represent the case of 50 ppm. Furthermore, the graphs indicated by white marks (◇, △, ○) indicate the NH ₃ concentration before correction, and the graphs indicated by black marks (◆, ▲, ●) indicate the NH ₃ concentration after correction. Represents.

Looking at the NH ₃ concentration before correction shown in FIG. 8A, it can be seen that as the NO concentration increases, the obtained NH ₃ concentration decreases and the sensitivity decreases. In other words, it can be seen that the obtained NH ₃ concentration includes the influence of the NO concentration. On the other hand, when the NH ₃ concentration after correction is viewed, it can be seen that an NH ₃ concentration that correctly represents the input NH ₃ concentration is obtained regardless of the NO concentration. In other words, it can be seen that an NH ₃ concentration in which the influence of the NO concentration is eliminated is required.

FIG. 8B shows the obtained NO concentration before correction when the concentration of NO introduced into the measurement gas containing NH ₃ that is an interfering gas is changed (NO ₂ is not included). And a corrected NO concentration.

The NH ₃ concentration contained in the gas to be measured is fixed to a predetermined constant value. The graphs indicated by white diamonds (◇) and black diamonds (◆) in each graph are NH ₃ concentrations. Represents a case of 0 ppm, a white triangle (Δ) and a black triangle (▲) represent a case of 20 ppm, and a white circle (◯) and a black circle (●) represent a case of 50 ppm. Furthermore, the graphs represented by white marks (◇, △, ○) represent the NO concentration before correction, and the graphs represented by black marks (◆, ▲, ●) represent the NO concentration after correction. Yes.

Looking at the NO concentration before correction shown in FIG. 8B, it can be seen that as the NH ₃ concentration increases, the obtained NO concentration increases and the value of the NO concentration is offset. In other words, it can be seen that the obtained NO concentration includes the influence of the NH ₃ concentration. On the other hand, when the corrected NO concentration is viewed, it can be seen that although the obtained NO concentration value is offset, the offset width is reduced as compared with that before the correction. In other words, it can be seen that the influence of the NH ₃ concentration on the determined NO concentration is suppressed.

FIG. 8 (c) shows the calculated NO ₂ before correction when the concentration of NO ₂ input to the gas to be measured containing NH ₃ that is an interference gas is changed (NO is not included). is a graph showing the concentration, the NO ₂ concentration after correction.

The NH ₃ concentration contained in the gas to be measured is fixed to a predetermined constant value. The graphs indicated by white diamonds (◇) and black diamonds (◆) in each graph are NH ₃ concentrations. Represents a case of 0 ppm, a white triangle (Δ) and a black triangle (▲) represent a case of 20 ppm, and a white circle (◯) and a black circle (●) represent a case of 50 ppm. Furthermore, the graphs represented by white marks (◇, △, ○) represent the NO ₂ concentration before correction, and the graphs represented by black marks (◆, ▲, ●) represent the NO ₂ concentration after correction. Represents.

Looking at the uncorrected NO ₂ concentration shown in FIG. 8C, it can be seen that as the NH ₃ concentration increases, the obtained NO ₂ concentration increases and the value of the NO ₂ concentration is offset. . In other words, it can be seen that the obtained NO ₂ concentration includes the influence of the NH ₃ concentration. On the other hand, when the corrected NO ₂ concentration is seen, it can be seen that the offset width is reduced as compared with that before the correction, although the obtained NO ₂ concentration value is offset. In other words, it can be seen that the influence of the NH ₃ concentration on the determined NO ₂ concentration is suppressed.

FIG. 9A shows the calculated NH ₃ before correction when the concentration of NH ₃ introduced into the measurement gas containing NO ₂ that is an interfering gas is changed (NO is not included). is a graph showing the concentration, the NH ₃ concentration after correction.

Note that the NO ₂ concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) and black diamonds (◆) in each graph are NO ₂ concentrations. Represents a case of 0 ppm, a white triangle (Δ) and a black triangle (▲) represent a case of 20 ppm, and a white circle (◯) and a black circle (●) represent a case of 50 ppm. Furthermore, the graphs indicated by white marks (◇, △, ○) indicate the NH ₃ concentration before correction, and the graphs indicated by black marks (◆, ▲, ●) indicate the NH ₃ concentration after correction. Represents.

Looking at the NH ₃ concentration before correction shown in FIG. 9A, as the NO ₂ concentration increases, the change in the calculated NH ₃ concentration value with respect to the change in the NH ₃ concentration to be input decreases. It can be seen that the obtained NH ₃ concentration value also decreases. In other words, it can be seen that the slope of the graph becomes smaller and the graph is offset to the low density side. On the other hand, when the corrected NH ₃ concentration is seen, it can be seen that the influence of the NO ₂ concentration on the obtained NH ₃ concentration is greatly suppressed.

FIG. 9B shows the obtained NO concentration before correction when the concentration of NO input to the measurement gas containing NO ₂ that is an interfering gas is changed (NH ₃ is not included). And a corrected NO concentration.

Note that the NO ₂ concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) and black diamonds (◆) in each graph are NO ₂ concentrations. Represents a case of 0 ppm, a white triangle (Δ) and a black triangle (▲) represent a case of 20 ppm, and a white circle (◯) and a black circle (●) represent a case of 50 ppm. Furthermore, the graphs represented by white marks (◇, △, ○) represent the NO concentration before correction, and the graphs represented by black marks (◆, ▲, ●) represent the NO concentration after correction. Yes.

Looking at the NO concentration before correction shown in FIG. 9B, it can be seen that as the NO ₂ concentration increases, the obtained NO concentration increases and the value of the NO concentration is offset. In other words, it can be seen that the obtained NO concentration includes the influence of the NO ₂ concentration. On the other hand, looking at the corrected NO concentration, it can be seen that the influence of the NO ₂ concentration on the obtained NO concentration is greatly suppressed.

FIG. 9 (c) shows the calculated NO ₂ before correction when the concentration of NO ₂ input to the gas to be measured containing NO as an interfering gas is changed (NH ₃ is not included). is a graph showing the concentration, the NO ₂ concentration after correction.

Note that the NO concentration contained in the gas to be measured is fixed at a predetermined constant value, and the graphs indicated by white diamonds (◇) and black diamonds (◆) in each graph have a NO concentration of 0 ppm. The white triangle (Δ) and the black triangle (▲) represent the case of 20 ppm, and the white circle (◯) and the black circle (●) represent the case of 50 ppm. Furthermore, the graphs represented by white marks (◇, △, ○) represent the NO ₂ concentration before correction, and the graphs represented by black marks (◆, ▲, ●) represent the NO ₂ concentration after correction. Represents.

When the NO ₂ concentration before correction shown in FIG. 9B is seen, it can be seen that as the NO concentration increases, the obtained NO ₂ concentration increases and the value of the NO concentration is offset. In other words, it can be seen that the obtained NO ₂ concentration includes the influence of the NO concentration. On the other hand, when the corrected NO ₂ concentration is seen, it can be seen that the influence of the NO concentration on the obtained NO ₂ concentration is greatly suppressed.

According to the multi-gas sensor device 1 configured as described above, since there is a temperature difference between the first ammonia sensor unit 21 and the second ammonia sensor unit 22 during measurement, the first ammonia sensor unit 21 and the second ammonia sensor unit 22 are used. There is a difference in the detection sensitivity for NO and NO ₂ . Therefore, different output concentrations can be obtained from the NOx sensor unit 11, the first ammonia sensor unit 21, and the second ammonia sensor unit 22, respectively. By calculating using these three output concentrations, the concentrations of nitric oxide, nitrogen dioxide and ammonia can be obtained.

As a specific calculation method, the output concentration of the NOx sensor unit 11 including the influence of NH ₃ (output concentration of NO concentration), the first ammonia sensor unit 21 including the influence of NOx (NO and NO ₂ ). output density (output density of NH ₃ concentrations), and, likewise three output density of the output density of the second ammonia sensor section 22 (output density of NH ₃ concentrations) which includes the effect of NOx, NH ₃ and NO ₂ the concentration of NO removal of the influence of the concentration of NO ₂ to effect removal of the NH ₃ and NO, and it is possible to calculate the concentration of NH ₃ removal of the effects of NO and NO _2.

Here, even if the first ammonia sensor unit 21 arranged in the high temperature region and the second ammonia sensor unit 22 arranged in the low temperature region have the same constituent elements, the temperature of the arranged region (that is, the sensor unit). The degree of the influence of NOx on the output concentration changes. In other words, the degree of influence of NOx on the output concentration also depends on the temperature of the sensor unit. Therefore, the output concentration of the first ammonia sensor unit 21 and the output concentration of the second ammonia sensor unit 22 can be handled as different output concentrations, and three different output concentrations obtained by adding the output of the NOx sensor unit 11 to this. Can be used to determine the concentrations of NO, NO ₂ and NH ₃ .

Further, by making the elements constituting the first ammonia sensor unit 21 and the second ammonia sensor unit 22 the same, the degree of deterioration with time of the first ammonia sensor unit 21 and the second ammonia sensor unit 22 is also about the same. It becomes. Therefore, compared with the case where the first ammonia sensor unit 21 and the second ammonia sensor unit 22 are configured using separate components, the output concentration between the first ammonia sensor unit 21 and the second ammonia sensor unit 22 is reduced. It is easy to keep the relationship constant. In other words, the necessity of calibrating the output concentrations of the first ammonia sensor unit 21 and the second ammonia sensor unit 22 is reduced, and the accuracy of the NO, NO _2, and NH ₃ concentrations can be easily maintained.

  In the present embodiment, the first ammonia sensor unit 21 includes an ammonia solid electrolyte body 23, a first reference electrode 21a, a first intermediate layer 21b, a first ammonia electrode 21c, and a protective layer 24. The ammonia sensor unit 22 includes an ammonia solid electrolyte body 23, a second reference electrode 22a, a second intermediate layer 22b, a second ammonia electrode 21c, and a protective layer 24, and has the same configuration. The first reference electrode 21a and the second reference electrode 22a, the first intermediate layer 21b and the second intermediate layer 22b, and the first ammonia electrode 21c and the second ammonia electrode 22c are made of the same material.

  By arranging the first ammonia sensor unit 21 arranged in the high temperature region at a position close to the oxygen concentration detection cell 16 corresponding to the temperature detection unit, the temperature of the first ammonia sensor unit 21 can be accurately controlled. . In particular, when the temperature of the first ammonia sensor unit 21 is controlled to a temperature close to the above-described upper limit temperature of 800 ° C., a decrease in detection performance of the first ammonia sensor unit 21 due to exceeding the upper limit temperature is suppressed. It becomes easy.

  And the temperature of the 1st ammonia sensor part 21 is controlled more correctly by providing the 1st ammonia sensor part 21 in the outer surface of the sensor element part 10, and the same position as the oxygen concentration detection cell 16 in the axis O direction. can do. The “same position” indicates that the oxygen concentration detection cell 16 and the first ammonia sensor unit 21 are arranged so as to overlap in the axis O direction.

  Furthermore, by using the first reference electrode 21a of the first ammonia sensor unit 21 and the second reference electrode 22a of the second ammonia sensor unit 22 as a common electrode, the measurement accuracy in the multi-gas sensor 2 and the multi-gas sensor device 1 is deteriorated. Can be suppressed. Specifically, since the degree of deterioration of the first reference electrode 21a and the degree of deterioration of the second reference electrode 22a coincide with each other, the measurement accuracy is deteriorated due to the difference in degree of deterioration as compared with the case where the reference electrodes are provided separately. Is suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Multi gas sensor apparatus, 2 ... Multi gas sensor, 3 ... Control part (calculation part), 11 ... NOx sensor part, 12 ... 1st pumping cell, 12a ... 1st solid electrolyte body, 12b ... Inner 1st pumping electrode (1st 1 electrode), 12c ... outer first pumping electrode (first electrode), 18 ... second pumping cell, 18a ... second solid electrolyte body, 18b ... inner second pumping electrode (second electrode), 18c ... second pumping Counter electrode (second electrode), 19 ... heater (heater part), 21 ... first ammonia sensor part, 21a ... first reference electrode (reference electrode), 22 ... second ammonia sensor part, 22a ... second reference electrode ( Reference electrode), S1 ... first measurement chamber, S2 ... second measurement chamber

Claims (5)

A NOx sensor unit for measuring the concentration of nitrogen oxides contained in the gas to be measured;
An ammonia sensor unit for measuring the concentration of ammonia contained in the gas to be measured;
A heater unit for heating the NOx sensor unit and the ammonia sensor unit;
Is a multi-gas sensor having a sensor element part integrally provided and extending in the axial direction,
The ammonia sensor unit has a first ammonia sensor unit and a second ammonia sensor unit made of the same components,
The second ammonia sensor section is arranged in a region of the sensor element section where the temperature is lower than that of the first ammonia sensor section. The sensor element unit is provided with a temperature detection unit that measures a temperature used to control heating of the NOx sensor unit,
2. The multi-gas sensor according to claim 1, wherein the first ammonia sensor unit is disposed at a position closer to the temperature detection unit than the second ammonia sensor unit in the sensor element unit. The NOx sensor unit is
A gas to be measured having a first solid electrolyte body and a pair of first electrodes provided on the first solid electrolyte body and located inside and outside the first measurement chamber and introduced into the first measurement chamber A first pumping cell for pumping or pumping oxygen therein;
A second solid electrolyte body and a pair of second electrodes provided on the second solid electrolyte body and located outside and inside the second measurement chamber, the oxygen concentration being adjusted in the first measurement chamber A second pumping cell in which a second pumping current corresponding to the NOx concentration in the gas flowing into the second measurement chamber flows between the pair of second electrodes;
With
The temperature detector is provided on the downstream side of the first pumping cell and on the upstream side of the second pumping cell;
The multi-gas sensor according to claim 2, wherein the first ammonia sensor unit is an outer surface of the sensor element unit, and is provided at the same position as the temperature detection unit in the axial direction.   The multi-gas sensor according to claim 1, wherein the first ammonia sensor unit and the second ammonia sensor unit are configured using a common reference electrode. A multi-gas sensor according to any one of claims 1 to 4,
Based on the output of the NOx sensor unit, the output of the first ammonia sensor unit, and the output of the second ammonia sensor unit, the concentrations of nitrogen monoxide, nitrogen dioxide and ammonia contained in the gas to be measured are calculated. An arithmetic unit;
A multi-gas sensor device comprising:

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