JP2022089377A - Gas concentration detector - Google Patents

Abstract

To provide a gas concentration detector that can increase the accuracy of detecting a mixed potential.SOLUTION: A gas concentration detector 1 includes: a sensor element unit 2 with a plurality of detection electrodes 22A and 22B; a plurality of detection units 51A and 51B; and an operation unit 52. The detection electrodes 22A and 22B are arranged in positions that a heat generator 41 heats to different temperatures. The detection units 51A and 51B are formed to detect a mixed potential based on ammonia and oxygen for the detection electrodes 22A and 22B separately. The operation unit 52 determines a sensor output by combining mixed potentials of the detection units 51A and 51B, which are different according to the heating temperatures of the detection electrodes 22A and 22B.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas concentration detecting device.

The gas concentration detecting device uses a gas sensor arranged in the exhaust pipe or the like of the internal combustion engine of the vehicle, and detects the specific gas concentration, the oxygen concentration, etc. in the detection target gas by using the exhaust gas flowing through the exhaust pipe as the detection target gas. .. Some gas concentration detectors detect specific gases such as ammonia gas and hydrocarbon gas, in addition to those that detect air fuel ratio, NOx (nitrogen oxide), and the like. Some gas concentration detecting devices for detecting the specific gas detect the mixed potential of the specific gas and the oxygen gas by using a detection electrode having catalytic activity on the specific gas and the oxygen gas.

As a gas sensor that outputs a mixed potential of ammonia gas and oxygen gas, for example, there is one described in Patent Document 1. In the gas sensor of Patent Document 1, a mixed potential type first sensor unit that outputs a mixed potential signal corresponding to the ammonia concentration and a second sensor unit that outputs a current signal corresponding to the NOx concentration are used. Then, in order to increase the detection sensitivity of the mixed potential, the distance between the electrode center of the first detection electrode of the first sensor unit and the heat generation center of the heat generating portion of the heater is set to the electrode center of the second detection electrode of the second sensor unit. Is larger than the distance between the heater and the heat generating center of the heater.

Japanese Unexamined Patent Publication No. 2019-203834

In the gas concentration detecting device that detects the concentration of a specific gas such as ammonia gas by the mixed potential, the following findings have been obtained by the research of the inventors of the present application. The sensitivity of the mixed potential is higher when the temperature of the detection electrode exposed to the detection target gas for detecting the mixed potential is lowered to about 350 to 450 ° C. within the limit of having catalytic activity. Further, when the concentration of a specific gas such as ammonia gas becomes high, the sensitivity of the mixed potential becomes saturated. Further, the higher the temperature of the detection electrode, the more easily the specific gas such as ammonia gas is oxidized and disappears on the surface of the detection electrode.

Saturation of the sensitivity of the mixed potential occurs as a phenomenon in which the detection range, which is the ratio of the minimum value to the maximum value of the detectable signal, is narrowed. The inventors of the present application have found a configuration for maintaining a wide detection range in a wide range of a specific gas concentration and improving the detection accuracy of the mixed potential in the mixed potential type gas concentration detecting device having the above-mentioned properties. In Patent Document 1, no countermeasure is taken for the sensitivity of the mixed potential to be saturated, and there is room for improvement in order to improve the detection accuracy of the mixed potential.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas concentration detecting device capable of improving the detection accuracy of a mixed potential.

One aspect of the present invention is
A solid electrolyte body having ionic conductivity (21), a plurality of detection electrodes (22A, 22B) provided on the first surface (201) of the solid electrolyte body and exposed to the detection target gas (G), and the solid electrolyte body. On the second surface (202) of the above, it is embedded in a reference electrode (23) provided at a position facing the plurality of detection electrodes and an insulator (3) laminated on the solid electrolyte body, and generates heat by energization. Sensor element unit (2) having a heating element (41) and
A plurality of detection units (51A, 51B) for detecting a mixed potential based on a specific gas and an oxygen gas generated between the plurality of detection electrodes and the reference electrode for each detection electrode.
A calculation unit (52) for performing calculation processing on the mixed potential in the plurality of detection units to obtain a sensor output of the concentration of the specific gas is provided.
The plurality of detection electrodes are arranged at positions where the heating temperatures of the heating elements are different from each other.
The calculation unit is configured to obtain the sensor output by combining the mixed potentials of the plurality of detection units, which differ depending on the difference in the heating temperature of the plurality of detection electrodes, in the gas concentration detection device (1). be.

Another aspect of the present invention is
A solid electrolyte body having ionic conductivity (21), a plurality of detection electrodes (22A, 22B) provided on the first surface (201) of the solid electrolyte body and exposed to the detection target gas (G), and the solid electrolyte body. On the second surface (202) of the above, it is embedded in a reference electrode (23) provided at a position facing the plurality of detection electrodes and an insulator (3) laminated on the solid electrolyte body, and generates heat by energization. Sensor element unit (2) having a heating element (41) and
A plurality of detection units (51A, 51B) for detecting a mixed potential based on a specific gas and an oxygen gas generated between the plurality of detection electrodes and the reference electrode for each detection electrode.
A calculation unit (52) for performing calculation processing on the mixed potential in the plurality of detection units to obtain a sensor output of the concentration of the specific gas is provided.
At least one of the plurality of detection electrodes is provided with a porous layer (222) for decomposing the specific gas so that the concentrations of the specific gas in the plurality of detection electrodes are different from each other.
The calculation unit is in a gas concentration detection device configured to obtain the sensor output by combining mixed potentials in the plurality of detection units, which differ depending on the difference in the concentration of the specific gas in the plurality of detection electrodes. ..

(One aspect of gas concentration detection device)
The gas concentration detection device of the above aspect has a sensor element unit having a plurality of detection electrodes exposed to the gas to be detected, a plurality of detection units that detect a mixed potential for each detection electrode, and a mixed potential in the plurality of detection units. It is provided with an arithmetic unit that performs arithmetic processing and obtains a sensor output of a specific gas concentration. The plurality of detection electrodes are arranged at positions where the heating temperatures of the heating elements are different from each other, and the calculation unit combines mixed potentials in the plurality of detection units, which differ depending on the difference in the heating temperature of the plurality of detection electrodes. Find the sensor output.

In the detection electrode arranged on the side where the heating temperature is relatively low, the sensitivity of the mixed potential is high, and the detection range is widened when the concentration of the specific gas is low. On the other hand, in the detection electrode arranged on the side where the heating temperature is relatively low, when the concentration of the specific gas is high, the sensitivity of the mixed potential is saturated and the detection range is narrowed. On the other hand, in the detection electrode arranged on the side where the heating temperature is relatively high, a part of the specific gas is decomposed and disappears on the surface of the detection electrode, so that the concentration of the specific gas is low. The detection range becomes narrower. On the other hand, in the detection electrode arranged on the side where the heating temperature is relatively high, the sensitivity of the mixed potential is difficult to saturate even if the concentration of the specific gas is high, and the concentration of the specific gas is relatively high. The detection range becomes wider.

In the calculation unit, when the concentration of the specific gas is low, the mixed potential in the detection unit corresponding to the detection electrode on the side where the heating temperature is relatively low is preferentially adopted, and the concentration of the specific gas is relatively low. When it is high, the mixed potential in the detection unit corresponding to the detection electrode on the side where the heating temperature becomes relatively high may be preferentially adopted. This makes it possible to maintain a wide detection range and improve the detection accuracy of the mixed potential in a wide concentration range from a low concentration state to a relatively high concentration state of the specific gas.

Therefore, according to the gas concentration detecting device of the above aspect, it is possible to maintain a wide detection range in a wide range of the concentration of the specific gas and improve the detection accuracy of the mixed potential.

(Gas concentration detection device of another aspect)
The gas concentration detection device of the other aspect includes the same sensor element unit, a plurality of detection units, and a calculation unit as in the case of the one aspect. At least one of the plurality of detection electrodes is provided with a porous layer for decomposing the specific gas so that the concentrations of the specific gas in the plurality of detection electrodes are different from each other, and a plurality of calculation units are provided. The sensor output is obtained by combining the mixed potentials in a plurality of detection units, which differ depending on the difference in the concentration of the specific gas in the detection electrode of.

In the detection electrode in which the porous layer is not provided or the specific gas is hardly decomposed by the porous layer, the sensitivity of the mixed potential is high and the detection range is widened when the concentration of the specific gas is low. On the other hand, in this detection electrode, when the concentration of the specific gas becomes high, the sensitivity of the mixed potential becomes saturated and the detection range becomes narrow. On the other hand, in the detection electrode provided with the porous layer, a part of the specific gas is decomposed and disappears in the porous layer, so that the detection range is narrowed when the concentration of the specific gas is low. On the other hand, in this detection electrode, when the concentration of the specific gas becomes high, the specific gas is appropriately decomposed and disappears by the porous layer, so that the sensitivity of the mixed potential is less likely to be saturated and the concentration of the specific gas is relative. The detection range becomes wider when the temperature is high.

In the calculation unit, when the concentration of the specific gas is low, the mixed potential in the detection unit corresponding to the detection electrode on which the porous layer is not provided or the specific gas is hardly decomposed by the porous layer is preferentially adopted. When the concentration of the specific gas is relatively high, the mixed potential in the detection unit corresponding to the detection electrode provided with the porous layer may be preferentially adopted. This makes it possible to maintain a wide detection range and improve the detection accuracy of the mixed potential in a wide concentration range from a low concentration state to a relatively high concentration state of the specific gas.

Therefore, the gas concentration detecting device of the other aspect can also maintain a wide detection range in a wide range of the concentration of the specific gas and improve the detection accuracy of the mixed potential.

The reference numerals in parentheses of each component shown in each aspect of the present invention indicate the correspondence with the reference numerals in the figure in the embodiment, but each component is not limited to the content of the embodiment.

An explanatory diagram showing a gas concentration detecting device according to the first embodiment. FIG. II is a view taken along the line II of FIG. 1, showing a sensor element unit according to the first embodiment. FIG. 3 is a sectional view taken along line III-III of FIG. 1, showing a gas concentration detection device and a sensor element unit according to the first embodiment. An explanatory diagram showing an internal combustion engine in which a gas concentration detecting device is used according to the first embodiment. The graph which shows the mixed potential generated in each detection electrode which concerns on Embodiment 1. FIG. The graph which shows the mixed potential generated in each detection electrode when the ammonia concentration changes, which concerns on Embodiment 1. FIG. The graph which shows the mixed potential generated in each detection electrode when the oxygen concentration changes, which concerns on Embodiment 1. FIG. The graph which shows the relationship between the heating temperature of a detection electrode and the sensitivity of a mixed potential in a detection electrode which concerns on Embodiment 1. FIG. The graph which shows the relationship between the concentration of ammonia and the sensitivity of the mixed potential in each detection electrode which concerns on Embodiment 1. FIG. FIG. 9 is a graph showing the concentration of ammonia in FIG. 9 on a logarithmic scale according to the first embodiment. The flowchart which shows an example of the method of detecting the concentration of ammonia by the gas concentration detection apparatus which concerns on Embodiment 1. FIG. 2 is a diagram corresponding to the arrow II view of FIG. 1, showing the sensor element unit according to the second embodiment. FIG. 2 is a diagram corresponding to a cross-sectional view taken along the line III-III of FIG. 1, showing a gas concentration detection device and a sensor element unit according to the second embodiment. The graph which shows the relationship between the concentration of ammonia and the sensitivity of the mixed potential in each detection electrode which concerns on Embodiment 2 on the logarithmic scale of the concentration of ammonia. The flowchart which shows an example of the method of detecting the concentration of ammonia by the gas concentration detection apparatus which concerns on Embodiment 2.

A preferred embodiment of the gas concentration detector described above will be described with reference to the drawings.
<Embodiment 1>
As shown in FIGS. 1 to 3, the gas concentration detection device 1 of the present embodiment includes a sensor element unit 2, a plurality of detection units 51A and 51B, and a calculation unit 52. The sensor element 2 includes a solid electrolyte 21 having ionic conductivity, a plurality of detection electrodes 22A and 22B provided on the first surface 201 of the solid electrolyte 21 and exposed to the detection target gas G, and the solid electrolyte 21. The heating element 41, which is embedded in the reference electrode 23 provided at a position facing the plurality of detection electrodes 22A and 22B on the second surface 202 and the insulator 3 laminated on the solid electrolyte body 21, and generates heat by energization. And have.

Each of the detection units 51A and 51B detects a mixed potential generated between the plurality of detection electrodes 22A and 22B and the reference electrode 23 based on the specific gas and oxygen gas (simply referred to as oxygen) for each detection electrode 22A and 22B. It is configured as. The calculation unit 52 is configured to perform calculation processing on the mixed potential in each of the detection units 51A and 51B to obtain the sensor output As of the concentration of the specific gas. The plurality of detection electrodes 22A and 22B are arranged at positions where the heating temperatures of the heating element 41 are different from each other. The calculation unit 52 is configured to obtain the sensor output As by combining the mixed potentials of the plurality of detection units 51A and 51B, which are different depending on the difference in the heating temperature of the plurality of detection electrodes 22A and 22B.

Hereinafter, the gas concentration detecting device 1 of the present embodiment will be described in detail.
(Gas concentration detector 1)
As shown in FIG. 1, the gas concentration detecting device 1 of the present embodiment is of a mixed potential type. The specific gas detected by the gas concentration detecting device 1 is ammonia gas (NH ₃ ) (simply referred to as ammonia). In addition to ammonia, the specific gas includes carbon monoxide (CO), water (H ₂ O), hydrogen (H ₂ ), hydrocarbons, nitric oxide (NO), nitrogen dioxide (NO ₂ ), and nitrous oxide. It may be nitrogen (N ₂ O).

The gas concentration detecting device 1 detects a mixed potential based on the concentration of ammonia and the concentration of oxygen, corrects the mixed potential by the concentration of oxygen, and detects the concentration of ammonia. In each of the detection units 51A and 51B, a reduction current due to an electrochemical reduction reaction of oxygen (hereinafter, simply referred to as a reduction reaction) and an oxidation current due to an electrochemical oxidation reaction of ammonia (hereinafter, simply referred to as an oxidation reaction). It is configured to detect the potential difference ΔV between the plurality of detection electrodes 22A and 22B and the reference electrode 23, which occurs when the two are equal to each other, as a mixed potential.

Although not shown, the oxygen concentration used for correcting the ammonia concentration may be detected by an oxygen sensor different from the gas concentration detection device 1. It is assumed that the oxygen sensor is arranged around the gas sensor 10 having the sensor element portion 2 in the exhaust pipe 71. Then, in each of the detection units 51A and 51B, the mixed potential is corrected by using the oxygen concentration by the oxygen sensor, and in the calculation unit 52, the sensor output As indicating the concentration of ammonia based on the corrected mixed potential. Ask for.

Further, although not shown, the gas concentration detecting device 1 may have a function of detecting the oxygen concentration. In this case, the sensor element unit 2 includes a solid electrolyte 21 provided with a pair of electrodes for detecting the oxygen concentration, a gas chamber into which the detection target gas G is introduced via the diffusion resistance unit, and the like. Is provided. Further, in this case, the gas concentration detecting device 1 includes, as another detecting unit, an oxygen detecting unit that detects the current flowing between the electrodes to which the DC voltage is applied.

(Internal combustion engine 7)
As shown in FIG. 4, the gas concentration detection device 1 includes a gas sensor 10 having a sensor element unit 2, and the gas sensor 10 is arranged and used in an exhaust pipe 71 of an internal combustion engine (engine) 7 of a vehicle. .. The detection target gas G supplied to the gas concentration detection device 1 is exhaust gas exhausted from the internal combustion engine 7 to the exhaust pipe 71. The gas concentration detecting device 1 is arranged in the exhaust pipe 71 at a position on the downstream side of the exhaust gas flow of the catalyst 72 that reduces NOx, and detects the concentration of ammonia flowing out from the catalyst 72. .. The internal combustion engine 7 of this embodiment is mounted on a vehicle.

(Catalyst 72)
As shown in FIG. 4, the exhaust pipe 71 is provided with a catalyst 72 for reducing NOx and a reducing agent supply device 73 for supplying the reducing agent K containing ammonia to the catalyst 72. In the catalyst 72, ammonia as a reducing agent K of NOx is attached to the catalyst carrier. The amount of ammonia adhered to the catalyst carrier of the catalyst 72 decreases with the reduction reaction of NOx. Then, when the amount of ammonia adhered to the catalyst carrier is reduced, ammonia is newly replenished from the reducing agent supply device 73 to the catalyst carrier. The reducing agent supply device 73 is arranged in the exhaust pipe 71 at a position upstream of the exhaust gas flow from the catalyst 72, and supplies ammonia generated by injecting urea water to the exhaust pipe 71. Ammonia is produced by hydrolyzing urea water. A urea water tank 731 is connected to the reducing agent supply device 73.

The internal combustion engine 7 of this embodiment is a diesel engine that performs combustion operation by utilizing self-ignition of light oil. Further, the catalyst 72 is a selective reduction catalyst (SCR) that chemically reacts NOx (nitrogen oxide) with ammonia (NH ₃ ) to reduce it to nitrogen (N ₂ ) and water (H ₂ O).

Although not shown, an oxidation catalyst (DOC) that converts NO to NO ₂ (oxidation), CO, HC (hydrocarbon), etc. is reduced at the upstream position of the catalyst 72 in the exhaust pipe 71. , A filter (DPF) for collecting fine particles may be arranged. Further, the gas concentration detecting device 1 may detect the ammonia contained in the detection target gas G by using the exhaust gas flowing through the exhaust pipe 71 of the gasoline engine as the detection target gas G.

(Sensor element unit 2)
As shown in FIGS. 1 to 3, in the sensor element unit 2, a solid electrolyte 21 provided with a plurality of detection electrodes 22A and 22B and a reference electrode 23 and an insulator 3 in which a heating element 41 is embedded are laminated. Is formed. The sensor element portion 2 is formed in a long shape. The portion of the tip side X1 of the sensor element portion 2 in the longitudinal direction X is arranged in the exhaust pipe 71 in a state of being housed in the cover constituting the gas sensor 10. In the sensor element portion 2, the direction in which the solid electrolyte 21 and the insulator 3 are laminated at right angles to the longitudinal direction X is called the lamination direction D, and the direction orthogonal to both the longitudinal direction X and the lamination direction D is the width. It is called direction W.

(Solid electrolyte 21)
As shown in FIGS. 1 to 3, the solid electrolyte 21 is formed in a plate shape and is made of a zirconia material having a property of conducting oxygen ions (oxide ions) at a predetermined temperature. .. The zirconia material is composed of various materials containing zirconia (zirconium dioxide) as a main component. As the zirconia material, stabilized zirconia or partially stabilized zirconia in which a part of zirconia is replaced with a rare earth metal element such as yttria (yttrium oxide) or an alkaline earth metal element is used.

The first surface 201 of the solid electrolyte body 21 exposed to the detection target gas G forms the outermost surface of the sensor element portion 2. The detection electrodes 22A and 22B provided on the first surface 201 are formed in a state in which the detection target gas G can easily come into contact with the detection electrodes 22A and 22B. The surfaces of the detection electrodes 22A and 22B of this embodiment are not provided with a protective layer made of a porous body of ceramics or the like. Then, the detection target gas G comes into contact with the detection electrodes 22A and 22B without being diffusion-controlled. A protective layer may be provided on the surfaces of the detection electrodes 22A and 22B so as not to reduce the flow velocity of the detection target gas G as much as possible.

The reference electrode 23 provided on the second surface 202 and the second surface 202 of the solid electrolyte 21 is exposed to the atmosphere as the reference gas A. A reference gas duct (atmospheric duct) 24 into which the atmosphere is introduced is formed adjacent to the second surface 202 of the solid electrolyte body 21.

(Detection electrodes 22A, 22B)
As shown in FIGS. 1 to 3, the detection electrodes 22A and 22B are provided on the first surface 201 of the solid electrolyte body 21 exposed to the detection target gas G containing oxygen and ammonia. The detection electrodes 22A and 22B contain a noble metal having catalytic activity for ammonia and oxygen, and a zirconia material which is a co-material when sintering with the solid electrolyte 21. As the noble metal constituting the detection electrodes 22A and 22B, gold (Au), platinum (Pt) -gold alloy, platinum-palladium (Pd) alloy, palladium-gold alloy and the like are used. Further, the detection electrodes 22A and 22B may contain a metal oxide or an oxide having a perovskite structure (perovskite type oxide) in addition to the noble metal and the zirconia material, or instead of the noble metal.

As shown in FIGS. 1 and 2, two detection electrodes 22A and 22B of this embodiment are arranged side by side in the longitudinal direction X of the sensor element unit 2. The two detection electrodes 22A and 22B are formed to have the same size (surface area). The two detection electrodes 22A and 22B are provided on the first surface 201 of the solid electrolyte 21 with a predetermined gap. Further, the first surface 201 is provided with a lead portion 221 connected to the detection electrodes 22A and 22B. The lead portions 221 of the detection electrodes 22A and 22B are connected to the detection portions 51A and 51B formed in the sensor control unit 5 via separate connection terminals, lead wires and the like. The size (surface area) of each of the detection electrodes 22A and 22B may be the same or different.

The distance between the center Oa of one of the two detection electrodes 22A and 22B and the heat generation center O of the heat generating portion 411 of the heating element 41 is the center Ob of the other of the two detection electrodes 22A and 22B and the heating element. It is longer than the distance between the heat generating portion 411 of 41 and the heat generating center O. The detection electrode 22A located farther from the heat generation center O is the low temperature detection electrode 22A which is the detection electrode 22A arranged at the position where the heating temperature is the lowest. The detection electrode 22B located near the heat generation center O is a high temperature detection electrode 22B which is a detection electrode 22B arranged at a position where the heating temperature is higher than the low temperature detection electrode 22A. In other words, the distance between the center Oa of the low temperature detection electrode 22A and the heat generation center O is longer than the distance between the center Ob of the high temperature detection electrode 22B and the heat generation center O.

Although not shown, the detection electrodes may be formed in a state where three or more detection electrodes are lined up in the longitudinal direction X of the sensor element unit 2. In this case, at least one of the low temperature detection electrode 22A and the high temperature detection electrode 22B may be configured by a plurality of detection electrodes.

(Reference electrode 23)
As shown in FIGS. 1 to 3, the reference electrode 23 is provided on the second surface 202 of the solid electrolyte body 21 opposite to the first surface 201. The reference electrode 23 provided on the second surface 202 and the second surface 202 is exposed to the atmosphere as the reference gas A. The reference electrode 23 contains a noble metal having catalytic activity for oxygen and a zirconia material which is a co-material when sintering with the solid electrolyte 21. Platinum (Pt) or the like can be used as the noble metal constituting the reference electrode 23.

One reference electrode 23 of the present embodiment is commonly formed at a position facing the entire plurality of detection electrodes 22A and 22B via the solid electrolyte body 21. Further, the reference electrode 23 may be individually formed at a position facing the detection electrodes 22A and 22B via the solid electrolyte 21. The second surface 202 of the solid electrolyte 21 is provided with a lead portion 231 connected to the reference electrode 23.

In the sensor element portion 2, oxide ions are conducted by the detection electrodes 22A and 22B, the reference electrode 23, and the portion of the solid electrolyte 21 sandwiched between the detection electrodes 22A and 22B and the reference electrode 23. A detection cell is formed. The temperature of the sensor element unit 2 due to the heat generated by the heat generating unit 411 of the heating element 41 is controlled so that the temperature of the detection cell becomes a predetermined operating temperature.

(Insulator 3)
As shown in FIGS. 1 to 3, the insulator 3 is formed by a spacer insulator portion 31 provided with a notch portion forming a reference gas duct 24 and a heater insulator portion 32 in which a heating element 41 is embedded. Has been done. The insulator 3 is made of an insulating ceramic material such as alumina (aluminum oxide). The reference gas duct 24 is formed from the position where the reference electrode 23 is arranged to the position of the proximal end side X2 in the longitudinal direction X. In the reference gas duct 24, the atmosphere as the reference gas A is introduced from the opening 241 formed at the position of the proximal end side X2 in the longitudinal direction X.

(Heating element 41)
As shown in FIGS. 1 to 3, a heating element 41 that generates heat by energization is embedded in the heater insulator portion 32 of the insulator 3. The heating element 41 is formed by a heating element 411 and a heating element lead portion 412 connected to the heating element 411. The heat generating portion 411 is arranged at a position facing each of the detection electrodes 22A and 22B and the reference electrode 23 in the stacking direction D. An energization control unit 53 for energizing the heating element 41 is connected to the heating element 41. The energization control unit 53 is formed in the sensor control unit 5, and is formed by using a drive circuit or the like that applies a voltage controlled by PWM (pulse width modulation) or the like to the heating element 41.

The heat generating portion 411 is formed by a linear conductor portion meandering by a straight portion and a curved portion. The straight portion of the heat generating portion 411 of the present embodiment is formed parallel to the longitudinal direction X. The heating element lead portion 412 is formed by a linear conductor portion. The resistance value per unit length of the heating element 411 is larger than the resistance value per unit length of the heating element lead unit 412. The heating element lead portion 412 is pulled out to the portion of the proximal end side X2 in the longitudinal direction X. The heating element 41 contains a conductive metal material.

The cross-sectional area of the heating element 411 is smaller than the cross-sectional area of the heating element lead portion 412, and the resistance value per unit length of the heating element 411 is higher than the resistance value per unit length of the heating element lead portion 412. This cross-sectional area means the cross-sectional area in a plane orthogonal to the extending direction of the heating element 411 and the heating element lead portion 412. When a voltage is applied to the pair of heating element lead portions 412, the heating unit 411 generates heat due to Joule heat, and the heat generation causes the detection electrodes 22A and 22B, the reference electrode 23, and the electrodes 22A, 22B and 23. The portion of the solid electrolyte 21 located around the above is heated.

The heat generation center O of the heat generation unit 411 of the present embodiment is arranged at a position facing the high temperature detection electrode 22B in the stacking direction D of the sensor element unit 2. In other words, the high temperature detection electrode 22B is arranged at a position where the heat generation center O of the heat generation unit 411 is projected in the stacking direction D.

(Detection units 51A, 51B)
As shown in FIG. 1, the detection units 51A and 51B of the gas concentration detection device 1 detect based on the potential difference (voltage) ΔV as a mixed potential generated between the detection electrodes 22A and 22B and the reference electrode 23. The concentration of ammonia in the target gas G is detected. As shown in FIG. 5, each of the detection electrodes 51A and 51B occurs when the reduction current due to the reduction reaction of oxygen and the oxidation current due to the oxidation reaction of ammonia in the detection electrodes 22A and 22B become equal to each other. The potential difference ΔV between the 22B and the reference electrode 23 is detected. The potential difference ΔV generated between the detection electrodes 22A and 22B and the reference electrode 23 indicates the mixed potential generated in the detection electrodes 22A and 22B by the detection target gas G containing ammonia and oxygen.

Each of the detection units 51A and 51B is formed in a sensor control unit 5 connected to the engine control unit 50 of the vehicle. Each of the detection units 51A and 51B corrects the potential difference ΔV by the potential difference detection circuit 511 and the potential difference detection circuit 511 for detecting the potential difference ΔV generated between the detection electrodes 22A and 22B and the reference electrode 23 according to the oxygen concentration, and oxygen. It has an oxygen correction unit 512 or the like for obtaining a corrected ammonia concentration (or a mixed potential after oxygen correction). The oxygen correction unit 512 uses a relationship map in which the relationship between the potential difference ΔV and the oxygen concentration (or the mixed potential after oxygen correction) is obtained using the oxygen concentration as a parameter, and the potential difference ΔV and the oxygen concentration are added to the relationship map. It is configured to collate and obtain the oxygen concentration after oxygen correction (or the mixed potential after oxygen correction).

In the detection electrodes 22A and 22B, when ammonia and oxygen are present in the detection target gas G in contact with the detection electrodes 22A and 22B, the oxidation reaction of ammonia and the reduction reaction of oxygen proceed at the same time. The oxidation reaction of ammonia is typically represented by 2NH ₃ + 3O ^2- → N ₂ + 3H ₂ O + ^6e- . The oxygen reduction reaction is typically represented by O ₂ + ^4e- → 2O ^2- . The mixed potential of ammonia and oxygen at each of the detection electrodes 22A and 22B is the potential when the oxidation reaction (rate) of ammonia and the reduction reaction (rate) of oxygen at each of the detection electrodes 22A and 22B become equal. Occurs.

FIG. 5 is a diagram for explaining the mixed potential generated in each of the detection electrodes 22A and 22B. In FIG. 5, the horizontal axis represents the potential (potential difference ΔV) of each of the detection electrodes 22A and 22B with respect to the reference electrode 23, and the vertical axis represents the current flowing between the detection electrodes 22A and 22B and the reference electrode 23. The method of changing the mixed potential is shown. Further, in FIG. 5, the first line L1 showing the relationship between the potential and the current when the oxidation reaction of ammonia is carried out at the detection electrodes 22A and 22B, and the oxygen reduction reaction are carried out at the detection electrodes 22A and 22B. The second line L2 showing the relationship between the potential and the current is shown. Both the first line L1 and the second line L2 are indicated by an upward-sloping line.

When the potential (potential difference ΔV) is 0 (zero), it indicates that the potentials of the detection electrodes 22A and 22B are the same as the potentials of the reference electrode 23. The mixed potential is the potential when the positive current on the first line L1 showing the oxidation reaction of ammonia and the negative current on the second line L2 showing the reduction reaction of oxygen are balanced. Then, the mixed potential at each of the detection electrodes 22A and 22B is detected as a potential on the negative side with respect to the reference electrode 23.

Further, as shown in FIG. 6, when the concentration of ammonia in the detection target gas G becomes high, the slope θa of the first line L1 showing the oxidation reaction of ammonia becomes steep. At this time, the potential at which the positive current on the first line L1 and the negative current on the second line L2 are balanced shifts to the negative side. As a result, as the concentration of ammonia increases, the potentials of the detection electrodes 22A and 22B with respect to the reference electrode 23 increase to the negative side. In other words, the higher the concentration of ammonia, the larger the potential difference (mixed potential) ΔV between the detection electrodes 22A and 22B and the reference electrode 23. Therefore, the higher the concentration of ammonia, the larger the potential difference ΔV, and by detecting the potential difference ΔV, it becomes possible to detect the concentration of ammonia in the detection target gas G.

Further, as shown in FIG. 7, when the oxygen concentration in the detection target gas G becomes high, the slope θs of the second line L2 showing the oxygen reduction reaction becomes steep. At this time, the potential at which the positive current on the first line L1 and the negative current on the second line L2 are balanced shifts to a position closer to zero on the negative side. As a result, the higher the oxygen concentration, the smaller the potential on the negative side of each of the detection electrodes 22A and 22B with respect to the reference electrode 23. In other words, the higher the oxygen concentration, the smaller the potential difference (mixed potential) ΔV between the detection electrodes 22A and 22B and the reference electrode 23. Therefore, the higher the oxygen concentration, the higher the potential difference ΔV or the correction to increase the ammonia concentration, so that the detection accuracy of the ammonia concentration can be improved.

(Relationship between the heating temperature of each detection electrode 22A, 22B and the sensitivity of the mixed potential of each detection electrode 22A, 22B)
FIG. 8 shows an example of the relationship between the heating temperature of each of the detection electrodes 22A and 22B and the sensitivity of the mixed potential of each of the detection electrodes 22A and 22B. The sensitivity of the mixed potential in the figure is the sensitivity of the mixed potential after oxygen correction, which indicates the concentration of ammonia after oxygen correction, which is corrected by the oxygen concentration. The heating temperature of each of the detection electrodes 22A and 22B is shown as an average temperature of each of the detection electrodes 22A and 22B heated by the heating unit 411 of the heating element 41.

The temperature of each of the detection electrodes 22A and 22B may fluctuate in response to a change in the temperature of the detection target gas G. However, the heating temperature of each of the detection electrodes 22A and 22B is determined by the heating state by the heat generating portion 411. The sensitivity of the mixed potential of the detection electrodes 22A and 22B is the potential difference between the detection electrodes 22A and 22B and the reference electrode 23 when the detection target gas G containing ammonia is supplied to the detection electrodes 22A and 22B. It is indicated by the difference between ΔV and the potential difference ΔV between each of the detection electrodes 22A and 22B and the reference electrode 23 when the detection target gas G containing no ammonia is supplied to the detection electrodes 22A and 22B.

In FIG. 8, when the detection target gas G containing ammonia having concentrations of 10 ppm, 50 ppm, 100 ppm, and 200 ppm is supplied to the detection electrodes 22A and 22B, the difference in heating temperature between the detection electrodes 22A and 22B is obtained. It is shown how much the sensitivity of the mixed potential of each detection electrode 22A, 22B changes by. In the present embodiment, the low temperature detection electrode 22A is heated to a heating temperature of 400 ° C. by the heat generating portion 411 of the heating element 41, and the high temperature detection electrode 22B is heated to a heating temperature of 500 ° C. by the heating unit 411 of the heating element 41. It shall be heated.

When the heating temperature of the low temperature detection electrode 22A is as low as 400 ° C. and ammonia having a concentration of less than 100 ppm is supplied to the low temperature detection electrode 22A, the sensitivity of the mixed potential of the low temperature detection electrode 22A is good, and ammonia can be detected. The range R1 is wide. Further, when the heating temperature of the low temperature detection electrode 22A is as low as 400 ° C. and ammonia having a concentration of 100 ppm or more and less than 200 ppm is supplied to the low temperature detection electrode 22A, the sensitivity of the mixed potential of the low temperature detection electrode 22A is saturated. The state is reached, and the ammonia detection range R2 is narrowed.

On the other hand, when the heating temperature of the high temperature detection electrode 22B is as high as 500 ° C. and ammonia having a concentration of less than 100 ppm is supplied to the high temperature detection electrode 22B, a large amount of ammonia is decomposed on the surface of the high temperature detection electrode 22B ( (Oxidation) and disappearing, the sensitivity of the mixed potential of the high temperature detection electrode 22B is poor, and the ammonia detection range R1 is narrow. Further, when the heating temperature of the high temperature detection electrode 22B is as high as 500 ° C. and ammonia having a concentration of 100 or more and less than 200 ppm is supplied to the high temperature detection electrode 22B, a part of ammonia is present on the surface of the high temperature detection electrode 22B. Is decomposed and disappears, but the ammonia detection range R2 is widened by the appropriate amount of ammonia remaining.

Here, the detection ranges R1 and R2 refer to dynamic ranges that are the ratio of the minimum value and the maximum value of identifiable signals. In FIG. 8, it can be seen that the detection ranges R1 and R2 are wide due to the wide range of sensitivity of the mixed potential in the range of the predetermined ammonia concentration.

When the heating temperature of the detection electrodes 22A and 22B is an intermediate temperature between 400 ° C. and 500 ° C., the detection range has properties intermediate between the case of 450 ° C. and the case of 500 ° C. The heating temperature of the low temperature detection electrode 22A is, for example, a temperature of 350 ° C. or higher and lower than 450 ° C. On the other hand, the heating temperature of the high temperature detection electrode 22B is, for example, a temperature of 450 ° C. or higher and lower than 550 ° C.

The target operating temperature of the detection cell including the detection electrodes 22A and 22B of the sensor element 2 and the reference electrode 23, which is controlled by energizing the heating element 41, is set as a specific temperature within the temperature range of 350 ° C to 550 ° C. Set. The temperature of the detection electrodes 22A and 22B (detection cell) is controlled so as to reach the target operating temperature by the amount of energization of the heating element 41 by the energization control unit 53. However, in the transitional period of detection or the like, the temperatures of the detection electrodes 22A and 22B (detection cells) change within the operating temperature due to the influence of changes in the temperature of the detection target gas G, the flow velocity, and the like.

(Relationship between ammonia concentration and sensitivity of mixed potential of each detection electrode 22A, 22B)
FIG. 9 shows an example of the relationship between the concentration of ammonia supplied to each of the detection electrodes 22A and 22B and the sensitivity of the mixed potential of each of the detection electrodes 22A and 22B for the low temperature detection electrode 22A and the high temperature detection electrode 22B. Is shown. The sensitivity of the mixed potential in FIG. 9 is the sensitivity of the mixed potential after oxygen correction, which is corrected by the concentration of oxygen. In FIG. 9, when the sensitivity of the mixed potential of the high temperature detection electrode 22B is good, it is shown by the fact that the range of change in the sensitivity of the mixed potential with respect to the change in the concentration of ammonia is large. Further, in FIG. 9, the low temperature detection electrode 22A is shown as a low temperature detection unit 51A, and the high temperature detection electrode 22B is shown as a high temperature detection unit 51B.

In the low temperature detection electrode 22A, the sensitivity of the mixed potential is high when the concentration of the supplied ammonia is less than 100 ppm, and the sensitivity of the mixed potential is low when the concentration of the supplied ammonia is 100 ppm or more. On the other hand, in the high temperature detection electrode 22B, when the concentration of the supplied ammonia is less than 100 ppm, a mixed potential is hardly obtained. In the high temperature detection electrode 22B, the sensitivity of the mixed potential is high in the range where the concentration of the supplied ammonia is 100 ppm or more and less than 200 ppm, but the sensitivity of the mixed potential is high when the concentration of the supplied ammonia exceeds 200 ppm. Will be low.

FIG. 10 shows the relationship between the concentration of ammonia in FIG. 9 and the sensitivity of the mixed potentials of the detection electrodes 22A and 22B on a logarithmic scale of the concentration of ammonia. In FIG. 10, the low temperature detection electrode 22A is shown as a low temperature detection unit 51A, and the high temperature detection electrode 22B is shown as a high temperature detection unit 51B. In FIG. 10, the sensitivity of the mixed potential of the low temperature detection electrode 22A changes linearly with a constant slope according to the concentration of ammonia, and the sensitivity of the mixed potential of the high temperature detection electrode 22B is such that the concentration of ammonia is 200 ppm. It changes linearly with a two-step inclination with the vicinity of the boundary as the boundary. In FIG. 10, when the sensitivity of the mixed potential of the high temperature detection electrode 22B is good, the inclination of the mixed potential line is larger than that of the low temperature detection electrode 2A.

(Gas sensor 10)
As shown in FIG. 4, the gas sensor 10 holds the sensor element portion 2 by a housing, and also has a front end cover that protects the sensor element portion 2 in the housing and a base end that protects a wiring portion connected to the sensor element portion 2. It is configured with a side cover and the like. Each of the detection electrodes 22A and 22B and the reference electrode 23 are arranged in the portion of the sensor element portion 2 on the tip side X1 in the longitudinal direction X, and the portion of the tip side X1 is in a state of protruding from the housing and is covered on the tip side. Protected by.

(Sensor control unit 5)
As shown in FIG. 4, the detection units 51A and 51B, the calculation unit 52, the energization control unit 53, and the like of the present embodiment are formed in the sensor control unit 5 electrically connected to the gas sensor 10. The gas concentration detection device 1 is composed of a mechanical component as a gas sensor 10 including a sensor element unit 2 and an electrical component as a sensor control unit 5. The sensor control unit 5 is composed of a computer, a control circuit, and the like. The sensor control unit 5 is electrically connected to the engine control unit 50 of the vehicle and can operate in response to a command from the engine control unit 50.

(Calculation unit 52)
As shown in FIGS. 1 and 9, when the concentration of ammonia is a low concentration shown as, for example, less than 100 ppm, the calculation unit 52 of the present embodiment is electrically connected to the low temperature detection electrode 22A for low temperature detection. The sensor output As is obtained based on the mixed potential of the unit 51A, and when the concentration of ammonia is a medium concentration shown as, for example, 100 ppm or more and less than 200 ppm, the high temperature detection unit 51B electrically connected to the high temperature detection electrode 22B. The sensor output As is obtained based on the mixed potential of. Further, when the concentration of ammonia is a high concentration shown as, for example, 200 ppm or more, the calculation unit 52 determines the sensor output As based on the mixed potential in at least one of the low temperature detection unit 51A and the high temperature detection unit 51B. Ask for.

More specifically, the calculation unit 52 has a first concentration region N1 in which the concentration of ammonia in the detection target gas G is less than a predetermined low concentration, and the concentration of ammonia in the detection target gas G is a predetermined low concentration or more. Sensors in the three concentration regions N1, N2, N3 of the second concentration region N2, which is less than the predetermined medium concentration, and the third concentration region N3, where the concentration of ammonia in the detection target gas G is equal to or higher than the predetermined medium concentration. The method of obtaining the output As is different. The three concentration regions N1, N2, and N3 are set to widen the detection range of the ammonia concentration by the gas concentration detection device 1.

As shown in FIG. 9, the arithmetic unit 52 of the present embodiment has a switching threshold value v1 and a switching difference value Δs in order to determine whether the ammonia concentration is in the first to third concentration regions N1, N2, N3. Is used. The switching threshold value v1 indicates the value of the hybrid potential when a small amount of ammonia is detected, in other words, the value of the hybrid potential when the concentration of ammonia becomes a minute concentration. The switching difference value Δs indicates the difference between the mixed potentials of the plurality of detection units 51A and 51B.

In the high temperature detection unit 51B, when the concentration of ammonia in the detection target gas G is low, the ammonia is decomposed and disappears on the surface of the high temperature detection electrode 22B, so that the mixed potential is not detected. In the high temperature detection unit 51B, the mixed potential is detected only when the concentration of ammonia becomes a predetermined medium concentration or higher. Taking advantage of this, when the mixed potential by the high temperature detection unit 51B is less than the switching threshold value v1 indicating that the concentration of ammonia is less than the medium concentration, the calculation unit 52 of the present embodiment has a second ammonia concentration. Recognize that it is in the 1 concentration region N1.

The mixed potential by the high temperature detection unit 51B rises sharply with an increase in the concentration of ammonia, for example, in a medium concentration region where the concentration of ammonia is shown as a concentration of 100 ppm or more and less than 200 ppm, while the concentration of ammonia is, for example, 200 ppm. In the high concentration region shown above, the concentration gradually increases as the concentration of ammonia increases. The switching difference value Δs between the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B is large in the medium concentration region, but small in the high concentration region. Taking advantage of this, the calculation unit 52 of the present embodiment has a mixed potential by the high temperature detection unit 51B having a switching threshold value v1 or more indicating that the concentration of ammonia is medium concentration or higher, and the low temperature detection unit 51A. When the difference between the mixed potential by the high temperature detection unit 51B and the mixed potential by the high temperature detection unit 51B is the switching difference value Δs or more, it is recognized that the concentration of ammonia is in the second concentration region N2. Further, utilizing this fact, in the calculation unit 52 of the present embodiment, the mixed potential by the high temperature detection unit 51B is equal to or higher than the switching threshold value v1, and the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B are mixed. When the difference from the potential is less than the switching difference value Δs, it is recognized that the concentration of ammonia is in the third concentration region N3.

In the first concentration region N1, the sensitivity of the mixed potential by the low temperature detection unit 51A is high, and if the mixed potential by the low temperature detection unit 51A is used, the detection range of the ammonia concentration becomes the widest. Therefore, the calculation unit 52 obtains the sensor output As in the first concentration region N1 based on the mixed potential by the low temperature detection unit 51A.

In the second concentration region N2, the sensitivity of the mixed potential by the high temperature detection unit 51B is high, and if the mixed potential by the high temperature detection unit 51B is used, the detection range of the ammonia concentration becomes the widest. Therefore, the calculation unit 52 obtains the sensor output As in the second concentration region N2 based on the mixed potential by the high temperature detection unit 51B.

In the third concentration region N3, the sensitivity of both the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B is low. From this, in the third concentration region N3, there is no significant difference in the detection range of the ammonia concentration regardless of whether the mixed potential by the low temperature detection unit 51A or the mixed potential by the high temperature detection unit 51B is used. In the third concentration region N3, the calculation unit 52 of the present embodiment obtains the sensor output As based on the average value of the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B.

In the third concentration region N3, the calculation unit 52 may obtain the sensor output As based on the mixed potential of the low temperature detection unit 51A, and may obtain the sensor output As based on the mixed potential of the high temperature detection unit 51B. You may ask.

The calculation unit 52 of the present embodiment sets the sensor output As so that the values are continuous at the boundary between the first concentration region N1 and the second concentration region N2 and the boundary between the second concentration region N2 and the third concentration region N3. It is configured to ask. Since the detection units 51A and 51B used to obtain the sensor output As are different in each of the concentration regions N1, N2, and N3, the sensor output As is not changed abruptly at each boundary.

Specifically, when determining the sensor output As [ppm] indicating the concentration of ammonia after oxygen correction, the calculation unit 52 performs the following calculation processing. The mixed potential by the low temperature detection unit 51A is A1 [V], and the mixed potential by the high temperature detection unit 51B is A2 [V]. Further, the mixed potential in the low temperature detection unit 51A corresponding to the maximum concentration in the second concentration region N2 (for example, indicated as 200 ppm) is set to A1x [V], and the high temperature corresponding to the maximum concentration in the second concentration region N2. The mixed potential in the detection unit 51B is A2x [V]. Further, α and β are coefficients for matching the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B.

Then, the calculation unit 52 obtains the sensor output As [ppm], which is the mixed potential after oxygen correction, by the relational expression of K1 and A1 in the first concentration region N1, and K1 and A1 + K2 in the second concentration region N2.・ Obtained by the relational expression of α ・ A2, and in the third concentration region N3, the relational expression of K1 ・ A1 + K2 ・ α ・ A2 + β ・ (K1 ・ A1-K1 ・ A1x + K2 ・ α ・ A2-K2 ・ α ・ A2x) / 2 Asked by. Here, K1, K2, and K3 are coefficients for converting the mixed potential [V] into the concentration [ppm] of ammonia. The sensor output As may be a voltage, and in this case, K1, K2, and K3 are coefficients that convert the mixed potential [V] into the voltage of the sensor output As. By using the relational expression for obtaining the sensor output As of the calculation unit 52, the sensor output at the boundary between the first concentration region N1 and the second concentration region N2 and the boundary between the second concentration region N2 and the third concentration region N3. The continuity of As values is maintained.

The relationship between the oxygen-corrected mixed potentials A1 and A2 and the sensor output As indicating the concentration of ammonia may be formed as a relationship map in the calculation unit 52.

(Method of detecting gas concentration by gas concentration detecting device 1)
Next, an example of a method of detecting the concentration of ammonia by the gas concentration detecting device 1 will be described with reference to the flowchart of FIG. After the internal combustion engine 7 of the vehicle is started and the gas concentration detection device 1 is started, the low temperature detection unit 51A and the high temperature detection unit 51B of the sensor control unit 5 are used for the low temperature detection electrode 22A and the high temperature detection electrode. The mixed potential generated when the detection target gas G is supplied to 22B is detected (step S101). Further, the receiving unit of the sensor control unit 5 receives the oxygen concentration in the detection target gas G from the oxygen sensor (step S102). Next, the calculation unit 52 of the sensor control unit 5 determines whether or not the mixed potential by the high temperature detection unit 51B is equal to or higher than the switching threshold value v1 (step S103).

When the mixed potential by the high temperature detection unit 51B is less than the switching threshold value v1, the calculation unit 52 recognizes that the concentration of ammonia in the detection target gas G is in the first concentration region N1 (step S104). Then, the calculation unit 52 corrects the mixed potential by the low temperature detection unit 51A by the oxygen concentration to obtain the oxygen-corrected mixed potential A1, and the sensor output As indicating the ammonia concentration by the relational expression of K1 and A1. (Step S105). When the mixed potential by the high temperature detection unit 51B is equal to or higher than the switching threshold value v1, the calculation unit 52 determines that the difference between the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B is the switching difference value Δs. It is determined whether or not it is the above (step S106).

When the difference between the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B is equal to or greater than the switching difference value Δs, the calculation unit 52 determines that the concentration of ammonia in the detection target gas G is the second concentration. Recognize that it is in the region N2 (step S107). Then, the calculation unit 52 corrects the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B according to the oxygen concentration, and mixes by the low temperature detection unit 51A and the high temperature detection unit 51B after oxygen correction. The potentials A1 + α ・ A2 are obtained, and the sensor output As indicating the concentration of ammonia is obtained by the relational expression of K1 ・ A1 + K2 ・ α ・ A2 (step S108).

When the difference between the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B is less than the switching difference value Δs, the calculation unit 52 determines that the concentration of ammonia in the detection target gas G is the third concentration. Recognize that it is in the region N3 (step S109). Then, the calculation unit 52 corrects the mixed potential by the low temperature detection unit 51A and the mixed potential by the high temperature detection unit 51B according to the oxygen concentration, and the oxygen-corrected mixed potential A1 + α ・ A2 + β ・ (A1-A1x + α ・ A2-). α ・ A2x) / 2 is obtained, and the sensor output indicating the concentration of ammonia by the relational expression of K1, A1 + K2, α, A2 + β, (K1, A1-K1, A1x + K2, α, A2-K2, α, A2x) / 2. As is obtained (step S110).

After that, the calculation unit 52 repeats steps S101 to S110 until the detection stop signal is sent from the engine control unit 50 to the sensor control unit 5 (step S111).

(Action effect)
In the gas concentration detection device 1 of the present embodiment, the mixed potentials A1 and A2 of the low temperature detection electrode 22A and the high temperature detection electrode 22B arranged at positions where the heating temperatures of the heating elements 41 are different from each other are set to the low temperature detection unit 51A and the low temperature detection unit 51A. The high temperature detection unit 51B detects each, and the calculation unit 52 appropriately combines the mixed potentials A1 and A2 of the detection units 51A and 51B to obtain the sensor output As indicating the concentration of ammonia.

In the gas concentration detection device 1 of the present embodiment, when the concentration of ammonia in the detection target gas G is in the first concentration region N1, the sensor output As is obtained based on the mixed potential A1 by the low temperature detection unit 51A. It is possible to maintain a wide range for detecting the concentration of ammonia in one concentration region N1. Further, when the concentration of ammonia in the detection target gas G is in the second concentration region N2, the concentration of ammonia in the second concentration region N2 is determined by obtaining the sensor output As based on the mixed potential A2 by the high temperature detection unit 51B. The detection range can be widened.

In this way, the calculation unit 52 can maintain a wide detection range in the first concentration region N1 where the concentration of ammonia is low, and widen the detection range even in the second concentration region N2 where the concentration of ammonia is relatively high. can. This makes it possible to maintain a wide detection range and improve the detection accuracy of the mixed potential in a wide concentration range from a low concentration state to a relatively high concentration state of ammonia in the detection target gas G.

Therefore, according to the gas concentration detecting device 1 of the present embodiment, it is possible to maintain a wide detection range and improve the detection accuracy of the mixed potential in a wide range of the ammonia concentration.

In the present embodiment, three or more detection electrodes may be arranged on the first surface 201 of the solid electrolyte 21 at positions where the heating temperatures of the heating elements 41 are different from each other. In this case, the mixed potential is detected by the detection unit corresponding to each of the three or more detection electrodes. Further, in this case, the detection unit corresponding to the detection electrode having a higher heating temperature has a wider detection range when the concentration of ammonia is high. Then, the calculation unit 52 can utilize the difference in the detection range of the mixed electrode by the three or more detection electrodes in the same manner as in the case of the two detection electrodes 22A and 22B.

<Embodiment 2>
In this embodiment, instead of making the heating temperatures of the plurality of detection electrodes 22A and 22B different, a porous layer 222 for decomposing ammonia is provided on one of the two detection electrodes 22C and 22D, and each detection electrode 22C is provided. , 22D shows a gas concentration detecting device 1 in which the concentrations of ammonia are different from each other. In the first embodiment, when the heating temperature of the detection electrodes 22C and 22D becomes high, a part of ammonia is decomposed (oxidized) and disappears on the surface of the detection electrodes 22C and 22D. This phenomenon that a part of ammonia is decomposed and disappears can also be obtained by lengthening the time that ammonia stays in the vicinity of the detection electrodes 22C and 22D. In this embodiment, by providing the porous layer 222 on one of the detection electrodes 22C and 22D, it is utilized that ammonia is decomposed and disappears in the porous layer 222.

(Detection electrodes 22C, 22D and porous layer 222)
As shown in FIGS. 12 and 13, the two detection electrodes 22C and 22D of this embodiment are arranged side by side in the width direction W on the first surface 201 of the solid electrolyte body 21. The distances from the heat generating center of the heat generating portion 411 of the heating element 41 to the centers of the two detection electrodes 22C and 22D are substantially the same. The two detection electrodes 22C and 22D of the present embodiment are composed of a first detection electrode 22C in which the porous layer 222 is not provided on the surface and a second detection electrode 22D in which the porous layer 222 is provided on the surface. There is.

The porous layer 222 is made of a ceramic material such as alumina in which a large number of pores through which the detection target gas G passes are formed. The porous layer 222 may be composed of a large number of ceramic particles, and the large number of pores may be gaps formed between the ceramic particles. The porosity of the porous layer 222 refers to the ratio of the volume of the pores to the total volume of the porous layer 222. The porosity of the porous layer 222 is increased by increasing the number, volume, and the like of the pores contained in the porous layer 222.

When the detection target gas G passes through the porous layer 222, a part of the ammonia contained in the detection target gas G stays in the porous layer 222 and is decomposed into nitrogen and hydrogen and disappears. Since the porous layer 222 also has a function of protecting the second detection electrode 22D, it can also be called a protective layer. The porous layer 222 may carry an oxidation catalyst for oxidizing ammonia. In this case, the burning of ammonia in the porous layer 222 is promoted. For this oxidation catalyst, for example, NiO (nickel oxide) may be used.

(1st detection unit 51C and 2nd detection unit 51D)
As shown in FIG. 13, the two detection units 51C and 51D of the present embodiment are provided with the first detection unit 51C corresponding to the first detection electrode 22C to which the porous layer 222 is not provided, and the porous layer 222. It is composed of a second detection unit 51D corresponding to the second detection electrode 22D. In the first detection electrode 22C, similarly to the low temperature detection electrode 22A, the sensitivity of the mixed potential when the concentration of ammonia in the detection target gas G is low is high, while the sensitivity of the mixed potential when the concentration of ammonia is relatively high is high. The sensitivity is low. In the second detection electrode 22D, as in the high temperature detection electrode 2B, the sensitivity of the mixed potential when the concentration of ammonia in the detection target gas G is low is low, while the sensitivity of the mixed potential when the concentration of ammonia is relatively high is low. The sensitivity is high.

(Calculation unit 52)
As shown in FIG. 14, the calculation unit 52 of the present embodiment has a first concentration region N1 in which the concentration of ammonia in the detection target gas G is less than a predetermined low concentration, and a predetermined low concentration of ammonia in the detection target gas G. In the two concentration regions N1 and N2 with the second concentration region N2 which is equal to or higher than the concentration, the method of obtaining the sensor output As is different. The two concentration regions N1 and N2 are set to widen the detection range of the ammonia concentration by the gas concentration detection device 1. The calculation unit 52 of the present embodiment determines whether or not the concentration of ammonia is at least a predetermined low concentration, depending on whether or not the mixed potential in the second detection unit 51D is at least the switching threshold value v1.

In the first concentration region N1, the sensitivity of the mixed potential by the first detection unit 51C is high, and if the mixed potential by the first detection unit 51C is used, the detection range of the ammonia concentration becomes the widest. Therefore, the calculation unit 52 obtains the sensor output As in the first concentration region N1 based on the mixed potential by the first detection unit 51C.

In the second concentration region N2, the sensitivity of the mixed potential by the second detection unit 51D is high, and if the mixed potential by the second detection unit 51D is used, the detection range of the ammonia concentration becomes the widest. Therefore, the calculation unit 52 obtains the sensor output As in the second concentration region N2 based on the mixed potential by the second detection unit 51D.

Also in this embodiment, the calculation unit 52 is configured to obtain the sensor output As so that the values are continuous at the boundary between the first concentration region N1 and the second concentration region N2, as in the case of the first embodiment. ing. When obtaining the sensor output Aa, the relational expression of K1 and A1 is used with the mixed potential of the first detection unit 51C as A1 in the first concentration region N1, and the second detection unit 51D is used in the second concentration region. The relational expression of K1, A1 + K2, α, and A2 is used, where the mixed potential of is A2.

FIG. 14 shows an example of the relationship between the concentration of ammonia and the sensitivity of the mixed potentials of the detection electrodes 22C and 22D on a logarithmic scale of the concentration of ammonia. In FIG. 14, the first detection electrode 22C is shown as the first detection unit 51C, and the second detection electrode 22D is shown as the second detection unit 51D. In FIG. 14, the sensitivity of the mixed potential of the first detection electrode 22C changes linearly with a constant slope as the concentration of ammonia increases from the vicinity of 0 ppm. On the other hand, the sensitivity of the mixed potential of the second detection electrode 22D changes linearly with a constant slope as the concentration of ammonia increases from the vicinity of 100 ppm.

In the porous layer 222, the smaller the porosity (the more dense ceramic material is used), the longer the time that ammonia stays, and the larger the amount of ammonia that is decomposed and disappears. The smaller the porosity of the porous layer 222 provided on the second detection electrode 22D, the more difficult it is for ammonia to reach the second detection electrode 22D, and the higher the concentration at which ammonia can be detected.

In FIG. 14, in the second detection electrode 22D, a mixed potential cannot be obtained when the concentration of ammonia is less than about 100 ppm, and a mixed potential is obtained when the concentration of ammonia is about 100 pp or more. Further, since the inclination of the mixed potential line by the second detection electrode 22D is larger than the inclination of the mixed potential line by the first detection electrode 22C, the sensitivity of the mixed potential by the second detection electrode 22D becomes higher than that of the first detection electrode 22C. It turns out that it is better than the sensitivity of the mixed potential by. As the porosity of the porous layer 222 provided on the second detection electrode 22D increases, the concentration at which ammonia can be detected decreases, as shown by the broken line in FIG.

As for the mixed potential by the first detection unit 51C, as in the case of the low temperature detection unit 51A of the first embodiment, when the concentration of ammonia is high, the sensitivity of the mixed potential is saturated and the detection range is narrowed. On the other hand, the mixed potential by the second detection unit 51D detects, for example, low-concentration ammonia of less than 100 ppm by partially decomposing and disappearing in the porous layer 222 provided on the second detection electrode 22D. Can't. However, in the second detection electrode 22D, when the concentration of ammonia becomes high, for example, to 100 ppm or more, the ammonia is appropriately decomposed and disappears by the porous layer 222, so that it is compared with the first detection electrode 22C. The sensitivity of the mixed potential is less likely to be saturated, and the detection range when the concentration of ammonia is relatively high becomes wider than that of the first detection electrode 22C.

(Method of detecting gas concentration by gas concentration detecting device 1)
Next, an example of a method of detecting the concentration of ammonia by the gas concentration detecting device 1 of the present embodiment will be described with reference to the flowchart of FIG. After the internal combustion engine 7 of the vehicle is started and the gas concentration detection device 1 is started, the first detection unit 51C and the second detection unit 51D of the sensor control unit 5 detect the gas G as the first detection electrode 22C. And the mixed potential generated when the second detection electrode 22D is supplied is detected (step S201). Further, the receiving unit of the sensor control unit 5 receives the oxygen concentration in the detection target gas G from the oxygen sensor (step S202). Next, the calculation unit 52 of the sensor control unit 5 determines whether or not the mixed potential by the second detection unit 51D is equal to or higher than the switching threshold value v1 (step S203).

When the mixed potential by the second detection unit 51D is less than the switching threshold value v1, the calculation unit 52 recognizes that the concentration of ammonia in the detection target gas G is in the first concentration region N1 (step S204). Then, the calculation unit 52 corrects the mixed potential by the first detection unit 51C by the oxygen concentration to obtain the oxygen-corrected mixed potential A1, and the sensor output As indicating the ammonia concentration by the relational expression of K1 and A1. (Step S205).

When the mixed potential by the second detection unit 51D is equal to or higher than the switching threshold value v1, the calculation unit 52 recognizes that the concentration of ammonia in the detection target gas G is in the second concentration region N2 (step S206). Then, the calculation unit 52 corrects the mixed potential by the first detection unit 51C and the mixed potential by the second detection unit 51D according to the oxygen concentration, and the mixing by the first detection unit 51C and the second detection unit 51D after oxygen correction. The potentials A1 + α ・ A2 are obtained, and the sensor output As indicating the concentration of ammonia is obtained by the relational expression of K1 ・ A1 + K2 ・ α ・ A2 (step S207).

After that, the calculation unit 52 repeats steps S201 to S207 until a detection stop signal is sent from the engine control unit 50 to the sensor control unit 5 (step S208).

(Action effect)
In the gas concentration detection device 1 of the present embodiment, the second detection electrode 22D is used to decompose ammonia so that the concentration of ammonia in the first detection electrode 22C and the concentration of ammonia in the second detection electrode 22D are different from each other. A porous layer 222 is provided. The calculation unit 52 obtains the sensor output As by combining the mixed potentials A1 and A2 in the detection units 51C and 51D, which differ depending on the difference in the concentration of ammonia in the detection electrodes 22C and 22D.

In the gas concentration detection device 1 of the present embodiment, when the concentration of ammonia in the detection target gas G is in the first concentration region N1, the sensor output As is obtained based on the mixed potential A1 by the first detection unit 51C. It is possible to maintain a wide range for detecting the concentration of ammonia in one concentration region N1. Further, when the concentration of ammonia in the detection target gas G is in the second concentration region N2, the concentration of ammonia in the second concentration region N2 is determined by obtaining the sensor output As based on the mixed potential A2 by the second detection unit 51D. The detection range can be widened. This makes it possible to maintain a wide detection range and improve the detection accuracy of the mixed potential in a wide concentration range from a low concentration state to a relatively high concentration state of ammonia in the detection target gas G.

Therefore, even with the gas concentration detecting device 1 of the present embodiment, it is possible to maintain a wide detection range in a wide range of ammonia concentration and improve the detection accuracy of the mixed potential.

Also in this embodiment, the two detection electrodes 22C and 22D may be arranged side by side in the longitudinal direction X on the first surface 201 of the solid electrolyte body 21. In this case, the distances from the heat generating center of the heat generating portion 411 of the heating element 41 to the centers of the two detection electrodes 22C and 22D may be substantially the same, and the two detection electrodes from the heat generating center of the heat generating portion 411 of the heating element 41 may be substantially the same. The distances to the centers of 22C and 22D may be different from each other.

(Other configurations)
The porous layer 222 may be provided on each of the first detection electrode 22C and the second detection electrode 22D in a state where the porosities are different from each other. For example, the first detection electrode 22C is provided with a porous layer 222 having a large porosity, and the second detection electrode 22D has a smaller porosity than the porous porosity provided in the first detection electrode 22C. A porous layer 222 is provided. In this case, the sensitivity of the mixed potential by the first detection electrode 22C is shown by the other second detection unit 51D by the wavy line in FIG. 14, and the sensitivity of the mixed potential by the second detection electrode 22D is the solid line in FIG. It is shown by the second detection unit 51D by.

In this case, the calculation unit 52 has the porous layer 222 having the largest porosity in the first concentration region N1 in which the mixed potential in the second detection unit 51D corresponding to the second detection electrode 22D is less than the switching threshold value v1. The sensor output As is obtained based on the mixed potential in the first detection unit 51C corresponding to the provided first detection electrode 22C. On the other hand, the calculation unit 52 is a porous layer having a relatively small porosity in the second concentration region N2 in which the mixed potential in the second detection unit 51D (or both detection units 51C and 51D) is equal to or higher than the switching threshold value v1. The sensor output As is obtained based on the mixed potential in the second detection unit 51D corresponding to the second detection electrode 22D provided with 222.

In this case, it is effective when the detection when the concentration of ammonia is as low as less than 10 ppm is unnecessary. In this case, the sensitivity of the mixed potential when the concentration of ammonia is low may be increased by the first detection unit 51A.

Other configurations, actions and effects, etc. of the gas concentration detecting device of this embodiment are the same as those of the first embodiment, such as the configurations, actions and effects, and the like. Further, also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those of the first embodiment.

The present invention is not limited to each embodiment, and further different embodiments can be configured without departing from the gist thereof. In addition, the present invention includes various modifications, modifications within a uniform range, and the like. Further, combinations, forms, etc. of various components assumed from the present invention are also included in the technical idea of the present invention.

1 Gas concentration detector 2 Sensor element 21 Solid electrolyte 22A, 22B Detection electrode 23 Reference electrode 3 Insulator 41 Heat generator 51A, 51B Detection unit 52 Calculation unit

Claims (9)

A solid electrolyte body having ionic conductivity (21), a plurality of detection electrodes (22A, 22B) provided on the first surface (201) of the solid electrolyte body and exposed to the detection target gas (G), and the solid electrolyte body. On the second surface (202) of the above, it is embedded in a reference electrode (23) provided at a position facing the plurality of detection electrodes and an insulator (3) laminated on the solid electrolyte body, and generates heat by energization. Sensor element unit (2) having a heating element (41) and
A plurality of detection units (51A, 51B) for detecting a mixed potential based on a specific gas and an oxygen gas generated between the plurality of detection electrodes and the reference electrode for each detection electrode.
A calculation unit (52) for performing calculation processing on the mixed potential in the plurality of detection units to obtain a sensor output of the concentration of the specific gas is provided.
The plurality of detection electrodes are arranged at positions where the heating temperatures of the heating elements are different from each other.
The calculation unit is configured to obtain the sensor output by combining the mixed potentials of the plurality of detection units, which differ depending on the difference in the heating temperature of the plurality of detection electrodes (1). The arithmetic unit
In the first concentration region (N1) where the mixed potential in at least one of the plurality of detection units is less than the switching threshold value (v1), the detection electrode is arranged at the position where the heating temperature is the lowest. The sensor output is obtained based on the mixed potential in the detection unit corresponding to a certain low temperature detection electrode (22A).
On the other hand, in the second concentration region (N2) where the mixed potentials in the plurality of detection units are equal to or higher than the switching threshold and the difference between the mixed potentials in the plurality of detection portions is equal to or higher than the switching difference value (Δs), the low temperature is used. The present invention is configured to obtain the sensor output based on the mixed potential in the detection unit corresponding to the high temperature detection electrode (22B) which is the detection electrode arranged at a position where the heating temperature is higher than the detection electrode. The gas concentration detection device according to 1. The gas concentration detecting device according to claim 2, wherein the calculation unit is configured to obtain the sensor output so that the values are continuous at the boundary between the first concentration region and the second concentration region. The arithmetic unit
In the third concentration region (N3) where the mixed potentials of the plurality of detection units are equal to or higher than the switching threshold value and the difference between the mixed potentials of the plurality of detection units is less than the switching difference value, the low temperature detection electrode is supported. The gas concentration detecting device according to claim 2, wherein the sensor output is obtained based on a mixed potential in at least one of the detection unit and the detection unit corresponding to the high temperature detection electrode. The calculation unit is configured to obtain the sensor output so that the values are continuous at the boundary between the first concentration region and the second concentration region and the boundary between the second concentration region and the third concentration region. The gas concentration detecting apparatus according to claim 4. A solid electrolyte body having ionic conductivity (21), a plurality of detection electrodes (22A, 22B) provided on the first surface (201) of the solid electrolyte body and exposed to the detection target gas (G), and the solid electrolyte body. On the second surface (202) of the above, it is embedded in a reference electrode (23) provided at a position facing the plurality of detection electrodes and an insulator (3) laminated on the solid electrolyte body, and generates heat by energization. Sensor element unit (2) having a heating element (41) and
A plurality of detection units (51A, 51B) for detecting a mixed potential based on a specific gas and an oxygen gas generated between the plurality of detection electrodes and the reference electrode for each detection electrode.
A calculation unit (52) for performing calculation processing on the mixed potential in the plurality of detection units to obtain a sensor output of the concentration of the specific gas is provided.
At least one of the plurality of detection electrodes is provided with a porous layer (222) for decomposing the specific gas so that the concentrations of the specific gas in the plurality of detection electrodes are different from each other.
The calculation unit is a gas concentration detecting device configured to obtain the sensor output by combining mixed potentials in the plurality of detection units, which differ depending on the difference in the concentration of the specific gas in the plurality of detection electrodes. The arithmetic unit
In the first concentration region (N1) where the mixed potential in at least one of the plurality of detection units is less than the switching threshold value (v1), the detection electrode is not provided with the porous layer. The sensor output is obtained based on the mixed potential in the detection unit.
On the other hand, in the second concentration region (N2) where the mixed potentials in the plurality of detection units are equal to or higher than the switching threshold value, the mixed potentials in the detection units corresponding to the detection electrodes provided with the porous layer are used. The gas concentration detecting device according to claim 6, which is configured to obtain the sensor output. The porous layer is provided on each of the plurality of detection electrodes, and the porosities of the plurality of the porous layers are different from each other.
The arithmetic unit
In the first concentration region (N1) where the mixed potential in at least one of the plurality of detection units is less than the switching threshold (v1), the porous layer having the largest porosity is provided. The sensor output is obtained based on the mixed potential in the detection unit corresponding to the first detection electrode, which is the detection electrode.
On the other hand, in the second concentration region (N2) where the mixed potential in the plurality of detection units is equal to or higher than the switching threshold, the porosity is smaller than the porosity of the porous layer provided in the first detection electrode. The gas concentration detecting apparatus according to claim 6, wherein the sensor output is obtained based on the mixed potential in the detection unit corresponding to the second detection electrode which is the detection electrode provided with the porous layer. The gas concentration detecting device according to claim 7 or 8, wherein the calculation unit is configured to obtain the sensor output so that the values are continuous at the boundary between the first concentration region and the second concentration region. ..

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