JP2022153760A - Sensor element and gas sensor - Google Patents

Abstract

To suppress a decrease in response properties of detection of a specific oxide gas concentration in a measured gas.SOLUTION: A sensor element 101 includes: an element body 101a in which a measured gas circulation part 9 for introducing and circulating a measured gas is provided inside; a main pump cell 21 having an inner pump electrode 22; a measurement electrode 44 for detecting a specific oxide gas concentration in a measured gas; a mixed potential cell 55 that has a detection electrode 56 and generates an electromotive voltage corresponding to an ammonia concentration in a measured gas; and a heater 72. Area of the measured gas circulation part 9 in a section is set to a sectional area Sf when the measured gas circulation part 9 and the detection electrode 56 are seen from the section vertical to a circulation direction of a measured gas, and an area ratio R as a value obtained by dividing a sectional area Sp by the sectional area Sf when area that the detection electrode 56 occupies in the sectional area Sf is the sectional area Sp is equal to or less than 0.5. The detection electrode 56 has length Lp in a circulation direction of 2 mm or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to sensor elements and gas sensors.

2. Description of the Related Art Conventionally, there is known a gas sensor that detects concentrations of multiple components such as NOx and ammonia in a gas to be measured such as automobile exhaust gas. For example, Patent Literature 1 describes a gas sensor including a structure composed of an oxygen ion-conducting solid electrolyte layer, a mixed potential electrode, a main pump electrode, a measurement electrode, and a reference electrode. The structure is formed with a gas introduction port into which the gas to be measured is introduced, and a preliminary chamber, an oxygen concentration adjustment chamber, and a measurement chamber communicating with the gas introduction port. A mixed potential electrode is arranged in the auxiliary chamber, a main pump electrode is arranged in the oxygen concentration adjusting chamber, and a measuring electrode is arranged in the measuring chamber. This gas sensor controls the oxygen concentration in the oxygen concentration adjustment chamber based on the voltage of the main pump electrode, and measures the NO concentration in the measurement chamber based on the pump current of the measurement electrode. Also, the ammonia concentration is measured based on the mixed potential of the mixed potential electrode. A gas sensor that detects the concentration of NOx without a mixed potential electrode is also known (for example, Patent Document 2).

JP 2019-219177 A JP 2016-188853 A

By the way, in a sensor element in which a mixed potential electrode (also referred to as a detection electrode) is arranged inside the sensor element as in Patent Document 1, the NOx concentration There was a case where the responsiveness of the detection of

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem, and its main object is to suppress the decrease in responsiveness in detecting the specific oxide gas concentration in the gas to be measured.

The present invention employs the following means in order to achieve the above main object.

The sensor element of the present invention is
an element main body having an oxygen ion-conducting solid electrolyte layer, a measuring gas flow section for introducing and circulating a measuring gas, and having a longitudinal direction;
an adjustment pump cell having an adjustment pump electrode disposed in the oxygen concentration adjustment chamber of the gas flow portion to be measured, and adjusting the oxygen concentration in the oxygen concentration adjustment chamber;
A sensor for detecting a concentration of a specific oxide gas in the gas to be measured, disposed on the inner peripheral surface of a measurement chamber provided downstream of the oxygen concentration adjustment chamber in the gas flow section to be measured. a measuring electrode;
a mixed potential cell having a detection electrode disposed upstream of the adjustment pump electrode in the gas flow portion to be measured and generating an electromotive force corresponding to the concentration of ammonia in the gas to be measured;
a heater for heating the element body;
with
When the measured gas flow portion and the detection electrode are viewed in a cross section perpendicular to the flow direction of the measured gas, the area of the measured gas flow portion in the cross section is defined as a cross-sectional area Sf, and the cross-sectional area Sf is When the area occupied by the detection electrode is defined as the cross-sectional area Sp, the area ratio R, which is the value obtained by dividing the cross-sectional area Sp by the cross-sectional area Sf, is 0.5 or less,
The detection electrode has a length Lp of 2 mm or less in the flow direction,
It is.

Using this sensor element, it is possible to detect specific oxide gas concentration and ammonia concentration contained in the gas to be measured, for example, as follows. First, the adjustment pump cell is operated to adjust the oxygen concentration of the gas to be measured introduced into the gas flow section to be measured. As a result, the gas to be measured whose oxygen concentration has been adjusted reaches the measurement chamber. Then, a detection value corresponding to the oxygen generated in the measurement chamber due to the specific oxide gas (oxygen generated when the specific oxide gas is reduced in the measurement chamber) is obtained, and the obtained detection value is A specific oxide gas concentration in the gas to be measured is detected based on the above. Further, since a mixed potential corresponding to the ammonia concentration in the gas to be measured is generated in the mixed potential cell, the ammonia concentration is detected based on this mixed potential. Since the above detection value may be affected by ammonia in the gas to be measured, the specific oxide gas concentration may be corrected based on the ammonia concentration in the gas to be measured. In this sensor element, the detection electrode is disposed upstream of the adjustment pump electrode and the measurement electrode in the measured gas flow section provided inside the element body. Further, when the measured gas circulation part and the detection electrode are viewed in a cross section perpendicular to the direction of flow of the measured gas, the area of the measured gas circulation part in the cross section is defined as a cross-sectional area Sf, and the detection is performed within the cross-sectional area Sf. The area occupied by the electrodes is defined as a cross-sectional area Sp. At this time, the area ratio R, which is the value obtained by dividing the cross-sectional area Sp by the cross-sectional area Sf, is 0.5 or less. Moreover, the detection electrode has a length Lp of 2 mm or less in the flow direction. When the area ratio R is 0.5 or less and the length Lp is 2 mm or less, the detection electrode is less likely to block the flow of the gas to be measured in the gas flow part to be measured. Arrival of the gas to be measured to the arranged measurement electrodes is less likely to be delayed. Therefore, in this sensor element, it is possible to suppress a decrease in responsiveness in detecting the concentration of oxide gas. The area ratio R may be greater than 0, and may be 0.1 or more.

In the sensor element of the present invention, a distance D in the direction of flow from a gas introduction port, which is an entrance of the gas flow portion to be measured, to the detection electrode may be 4 mm or less. Here, when the sensor element is used, the element body is heated by the heater to a high temperature. Therefore, when the gas to be measured comes into contact with the sensor element, the ammonia in the gas to be measured burns, and the sensitivity of detecting the concentration of ammonia may decrease. On the other hand, if the distance D is 4 mm or less, the measured gas introduced from the gas inlet into the measured gas circulation section reaches the detection electrode in a short time. is difficult to burn. Therefore, it is possible to suppress a decrease in sensitivity in detecting the concentration of ammonia in the gas to be measured.

In the sensor element of the present invention, a slit-shaped gap or a diffusion rate-determining section made of a porous material is disposed between the gas introduction port, which is the entrance of the gas flow section to be measured, and the detection electrode. It doesn't have to be. With this configuration, the gas to be measured introduced into the gas-to-be-measured flow passage from the gas inlet reaches the detection electrode in a short time, so ammonia is less likely to burn before reaching the detection electrode. Therefore, it is possible to suppress a decrease in sensitivity in detecting the concentration of ammonia in the gas to be measured.

In the sensor element of the present invention, the longitudinal direction is defined as the front-rear direction, and the gas introduction port, which is the entrance of the measured gas circulation portion, opens in the front end surface of the element main body. The flow path may extend in the front-rear direction from the gas inlet to the measurement electrode, and the distance C in the front-rear direction between the detection electrode and the measurement electrode may be 11 mm or less. When the distance C is 11 mm or less, the time required for the gas to be measured to pass through the periphery of the sensing electrode and reach the periphery of the measurement electrode is relatively short. The responsiveness of ammonia concentration detection becomes comparable. That is, the response time for detecting the oxide gas concentration and the response time for detecting the ammonia concentration are relatively close to each other. Therefore, even if the composition of the gas to be measured changes from moment to moment, for example, the deviation in detection timing of the oxide gas concentration and the ammonia concentration is reduced.

In the sensor element of the present invention, the measured gas flow portion has a rectangular cross section perpendicular to the flow direction, and the detection electrode forms the four sides of the measured gas flow portion. may be disposed on one or more of the four inner peripheral surfaces of the . In this case, the sensing electrode may have a tunnel shape disposed on any one of the four inner peripheral surfaces of the measured gas flow portion.

A gas sensor according to the present invention includes the sensor element according to any one of the aspects described above. Therefore, this gas sensor can obtain the same effect as the sensor element of the present invention described above, for example, the effect of being able to suppress the decrease in responsiveness in detecting the specific oxide gas concentration in the gas to be measured.

FIG. 2 is a schematic cross-sectional view of the gas sensor 100; FIG. 2 is a partially enlarged view of FIG. 1; FIG. 3 is a partial cross-sectional view showing a part of the AA cross section of FIG. 2; FIG. 2 is a block diagram showing the electrical connection relationship between a control device 90 and each cell; FIG. 11 is an enlarged cross-sectional view showing the arrangement of detection electrodes 156 of a modified example; FIG. 6 is a partial cross-sectional view showing a part of the BB cross section of FIG. 5; The cross-sectional schematic diagram of the sensor element 201 of a modification.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional schematic diagram schematically showing an example of the configuration of a gas sensor 100 that is an embodiment of the present invention. 2 is a partially enlarged view of FIG. 1. FIG. 3 is a partial cross-sectional view showing a part of the AA cross section of FIG. 2. FIG. FIG. 4 is a block diagram showing electrical connections between the control device 90 and each cell. This gas sensor 100 is attached to a pipe such as an exhaust gas pipe of an internal combustion engine such as a gasoline engine or a diesel engine. The gas sensor 100 detects the concentration of a specific oxide gas (here, NOx) in the gas under measurement and the concentration of ammonia in the gas under measurement, using exhaust gas from an internal combustion engine as the gas under measurement.

The gas sensor 100 includes a sensor element 101 and a control device 90 that controls the gas sensor 100 as a whole. The sensor element 101 includes an element body 101a having an elongated rectangular parallelepiped shape, cells 21, 41, 50, 55, 80 to 83 configured to include part of the element body 101a, and covering the element body 101a. and a porous protective layer 85 . As shown in FIG. 1, the longitudinal direction of the element body 101a is the front-rear direction, and the thickness direction of the element body 101a is the vertical direction. Also, the width direction of the element main body 101a (the direction perpendicular to the longitudinal direction and the thickness direction) is defined as the left-right direction.

The sensor element 101 includes a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, and a first solid electrolyte layer 4 each made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). , a spacer layer 5, and a second solid electrolyte layer 6 are laminated in this order from the lower side in the view of the drawing (element main body 101a). Also, the solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured by, for example, performing predetermined processing and circuit pattern printing on ceramic green sheets corresponding to each layer, laminating them, and firing them to integrate them.

Between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4 on the front end side (left end side in FIG. 1) of the element main body 101a, a gas introduction port 10 and a buffer space 12 are provided. , the diffusion rate-controlling portion 13, the first internal space 20, the diffusion rate-controlling portion 30, the second internal space 40, the diffusion rate-controlling portion 60, and the third internal space 61 communicate in this order. are formed adjacent to each other.

The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are provided in the upper part provided by hollowing out the spacer layer 5. The space inside the element body 101a is defined by the lower surface of the second solid electrolyte layer 6, the upper surface of the first solid electrolyte layer 4 in the lower portion, and the side surface of the spacer layer 5 in the lateral portion.

Both the diffusion rate-controlling part 13 and the diffusion rate-controlling part 30 are provided as two horizontally long slits (the openings of which have the longitudinal direction in the direction perpendicular to the drawing). Diffusion control part 60 is provided as one laterally long slit (the opening has its longitudinal direction in the direction perpendicular to the drawing) formed as a gap with the lower surface of second solid electrolyte layer 6 . A portion extending from the gas introduction port 10 to the third internal space 61 is referred to as a gas flow portion 9 to be measured. The gas introduction port 10 is an inlet of the measured gas circulation portion 9 and opens at the front end surface of the element main body 101a. Further, the measured gas circulation portion 9 is a channel extending in the front-rear direction, and is arranged so as to extend rearward from the gas introduction port 10 . Therefore, the gas to be measured introduced from the gas inlet 10 into the gas-to-be-measured circulation portion 9 moves backward. That is, in the present embodiment, the flow direction of the gas to be measured in the gas flow part 9 to be measured is along the front-rear direction. In the measured gas flow section 9, a detection electrode 56, an inner pump electrode 22, an auxiliary pump electrode 51, and a measurement electrode 44 are arranged in this order from the gas inlet 10 side. The measured gas circulation part 9 is a flow path extending in the front-rear direction from the gas introduction port 10 to the measurement electrode 44 .

Further, at a position farther from the front end side than the measured gas circulation portion 9, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, a side portion of the first solid electrolyte layer 4 is provided. A reference gas introduction space 43 is provided at a position defined by . For example, atmospheric air is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

The atmosphere introduction layer 48 is a layer made of porous ceramics, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43 . Also, the atmosphere introduction layer 48 is formed so as to cover the reference electrode 42 .

The reference electrode 42 is an electrode formed in a manner sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, is connected to the reference gas introduction space 43 around it. An atmosphere introduction layer 48 is provided. In addition, as will be described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20, the second internal space 40, and the third internal space 61. It is possible. The reference electrode 42 is formed as a porous cermet electrode (eg, a Pt and ZrO ₂ cermet electrode).

In the measured gas circulation portion 9, the gas introduction port 10 is a portion opened to the external space, and the gas to be measured is taken into the element main body 101a from the external space through the gas introduction port 10. ing. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the gas introduction port 10 to the diffusion control section 13 . A front end portion of the buffer space 12 serves as a gas introduction port 10 . The diffusion control portion 13 is a portion that imparts a predetermined diffusion resistance to the gas under measurement introduced from the buffer space 12 into the first internal space 20 . When the gas to be measured is introduced into the first internal space 20 from the outside of the element main body 101a, the pressure fluctuation of the gas to be measured in the external space (if the gas to be measured is the exhaust gas of an automobile, the exhaust pressure) The gas to be measured that is rapidly taken into the element main body 101a through the gas inlet 10 due to pulsation is not introduced directly into the first internal space 20, but passes through the buffer space 12 and the diffusion control section 13 to be measured. The gas is introduced into the first internal cavity 20 after the pressure fluctuations have been canceled. As a result, pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 are almost negligible. The first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the diffusion control section 13 . The oxygen partial pressure is adjusted by operating the main pump cell 21 .

The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode portion 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and an upper surface of the second solid electrolyte layer 6. This is an electrochemical pump cell composed of an outer pump electrode 23 provided in a region corresponding to the ceiling electrode portion 22a and a second solid electrolyte layer 6 sandwiched between these electrodes. The outer pump electrode 23 is provided outside the element main body 101a so as to be in contact with the gas to be measured. Specifically, in this embodiment, the outer pump electrode 23 is provided on the upper surface of the element main body 101a.

The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that define the first internal cavity 20 and the spacer layer 5 that provides side walls. there is Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal cavity 20, and a bottom electrode portion 22a is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. A spacer layer in which electrode portions 22b are formed, and side electrode portions (not shown) constitute both side wall portions of the first internal cavity 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b. 5, and arranged in a tunnel-shaped structure at the arrangement portion of the side electrode portion.

The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, cermet electrodes of Pt and ZrO ₂ containing 1% Au). The inner pump electrode 22 that comes into contact with the gas to be measured is made of a material that has a weakened ability to reduce NOx components in the gas to be measured.

In the main pump cell 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 to generate a positive or negative pump current between the inner pump electrode 22 and the outer pump electrode 23. By flowing Ip0, it is possible to pump oxygen in the first internal space 20 to the external space, or to pump oxygen in the external space into the first internal space 20 .

In order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 , the third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 80 for main pump control.

By measuring the electromotive force (voltage V0) in the oxygen partial pressure detection sensor cell 80 for controlling the main pump, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be known. Furthermore, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value. Thereby, the oxygen concentration in the first internal space 20 can be kept at a predetermined constant value.

The diffusion control section 30 applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and converts the gas to be measured into the second gas. It is a portion that leads to the internal cavity 40 .

In the second internal space 40 , the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal space 20 , and then oxygen is added by the auxiliary pump cell 50 to the gas to be measured introduced through the diffusion control section 30 . It is provided as a space for adjusting the partial pressure. As a result, the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, so that the gas sensor 100 can measure the NOx concentration with high accuracy.

The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40, and an outer pump electrode 23 (outer pump electrode 23 and a second solid electrolyte layer 6, which is an auxiliary electrochemical pump cell.

The auxiliary pump electrode 51 is arranged in the second internal space 40 in the same tunnel-like structure as the inner pump electrode 22 provided in the first internal space 20 . That is, the ceiling electrode portion 51a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40 has , bottom electrode portions 51b are formed, and side electrode portions (not shown) connecting the ceiling electrode portions 51a and the bottom electrode portions 51b are formed on the spacer layer 5 that provides the sidewalls of the second internal cavity 40. It has a tunnel-like structure formed on both walls. As with the inner pump electrode 22, the auxiliary pump electrode 51 is also made of a material having a weakened ability to reduce NOx components in the gas to be measured.

In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere inside the second internal cavity 40 is pumped out to the external space, or It is possible to pump from the space into the second internal cavity 40 .

In order to control the oxygen partial pressure in the atmosphere inside the second internal space 40, the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte The layer 4 and the third substrate layer 3 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump.

The auxiliary pump cell 50 performs pumping with the variable power source 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detecting sensor cell 81 for controlling the auxiliary pump. Thereby, the oxygen partial pressure in the atmosphere inside the second internal cavity 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

Along with this, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for controlling the main pump, and by controlling the above-described target value of the voltage V0, the pump current Ip1 is transferred from the diffusion rate-determining section 30 to the second internal The gradient of the oxygen partial pressure in the gas to be measured introduced into the space 40 is controlled so as to be constant. When used as a NOx sensor, the main pump cell 21 and the auxiliary pump cell 50 work to keep the oxygen concentration in the second internal cavity 40 at a constant value of approximately 0.001 ppm.

The diffusion control section 60 applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal space 40, and converts the gas to be measured into the third gas. This is a portion that leads to the internal space 61 . The diffusion control section 60 serves to limit the amount of NOx flowing into the third internal cavity 61 .

After the oxygen concentration (oxygen partial pressure) is adjusted in advance in the second internal space 40 , the third internal space 61 is introduced through the diffusion control section 60 to the gas under test, and the nitrogen in the gas under test is It is provided as a space for performing processing related to measurement of oxide (NOx) concentration. The NOx concentration is measured mainly in the third internal space 61 by operating the measuring pump cell 41 .

The measuring pump cell 41 measures the NOx concentration in the gas to be measured in the third internal space 61 . The measurement pump cell 41 includes a measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61 , an outer pump electrode 23 , a second solid electrolyte layer 6 and a spacer layer 5 . , and the first solid electrolyte layer 4 . The measurement electrode 44 is a porous cermet electrode made of a material having a higher ability to reduce NOx components in the gas to be measured than the inner pump electrode 22 . The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere inside the third internal cavity 61 .

In the measurement pump cell 41, oxygen generated by decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 can be pumped out, and the amount of oxygen generated can be detected as a pump current Ip2.

Also, in order to detect the oxygen partial pressure around the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44 and the reference electrode 42 form an electrochemical sensor cell, i.e. An oxygen partial pressure detection sensor cell 82 for controlling the measuring pump is configured. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the measuring pump controlling oxygen partial pressure detecting sensor cell 82 .

The measured gas guided into the second internal space 40 reaches the measurement electrode 44 in the third internal space 61 through the diffusion control section 60 under the condition that the oxygen partial pressure is controlled. Nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N ₂ +O ₂ ) to generate oxygen. The generated oxygen is pumped by the measurement pump cell 41. At this time, the voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 is kept constant (target value). , the voltage Vp2 of the variable power supply 46 is controlled. Since the amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the pump current Ip2 in the pump cell 41 for measurement is used to measure the nitrogen oxides in the gas to be measured. The concentration will be calculated.

An electrochemical sensor cell 83 is composed of the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The electromotive force (voltage Vref) obtained by the sensor cell 83 can be used to detect the partial pressure of oxygen in the gas to be measured outside the sensor.

In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect NOx measurement). A gas to be measured is supplied to the measuring pump cell 41 . Therefore, the NOx concentration in the gas to be measured is determined based on the pump current Ip2 that flows when the oxygen generated by the reduction of NOx is pumped out of the measuring pump cell 41 in substantially proportion to the concentration of NOx in the gas to be measured. It is possible to know.

A detection electrode 56 is arranged on the element main body 101a. The detection electrode 56 is arranged in the gas-to-be-measured circulation portion 9 inside the element main body 101a. The detection electrode 56 is disposed on the upstream side (here, forward) of the inner pump electrode 22 in the measured gas circulation section 9 . The sensing electrode 56 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that partition the buffer space 12 and the spacer layer 5 that provides side walls. Specifically, a ceiling electrode portion 56a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the buffer space 12, and the upper surface of the first solid electrolyte layer 4 that provides the bottom surface of the buffer space 12 has a A bottom electrode portion 56b is formed. Side electrode portions 56c and 56d (see FIG. 3) form side wall surfaces (inner peripheral portions) of the spacer layer 5 forming both side wall portions of the buffer space 12 so as to connect the ceiling electrode portion 56a and the bottom electrode portion 56b. surface). The side electrode portion 56 c is arranged on the left side of the buffer space 12 , and the side electrode portion 56 d is arranged on the right side of the buffer space 12 . In this way, the detection electrode 56 is provided with the ceiling electrode portion 56a, the bottom electrode portion 56b, and the side electrode portions 56c and 56d, so that it can be arranged on any of the four inner peripheral surfaces of the buffer space 12, namely, the upper, lower, left, and right sides. It has a tunnel shape. As described above, the front end portion of the buffer space 12 serves as the gas introduction port 10, and the diffusion control portion 13, A diffusion rate-determining portion composed of slit-shaped gaps such as 30 and 60 is not provided.

The detection electrode 56, the reference electrode 42, and the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer 3, which are solid electrolyte layers between both electrodes, form a mixed potential cell. 55 are configured. In the mixed potential cell 55 , a mixed potential (electromotive force EMF) is generated at the detection electrode 56 according to the concentration of ammonia in the gas to be measured. Then, the value of the electromotive force EMF between the detection electrode 56 and the reference electrode 42 is used to detect the concentration of ammonia in the gas to be measured. The detection electrode 56 is mainly composed of a material that generates a mixed potential corresponding to the concentration of ammonia and has detection sensitivity to the concentration of ammonia. The detection electrode 56 may be composed mainly of a noble metal such as gold (Au), or may be composed mainly of a conductive oxide. When the main component is a noble metal, the detection electrode 56 preferably contains an Au--Pt alloy as the main component. Here, the main component means the component with the largest abundance (atm %, atomic weight ratio) among all the components contained. In this embodiment, the sensing electrode 56 is a porous cermet electrode of Au--Pt alloy and zirconia.

Further, the sensor element 101 includes a heater section 70 that plays a role of temperature adjustment for heating the element body 101a to keep it warm in order to increase the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes heater connector electrodes 71 , heaters 72 , through holes 73 , heater insulating layers 74 , and pressure dissipation holes 75 .

The heater connector electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1 . By connecting the heater connector electrode 71 to an external power source, power can be supplied to the heater section 70 from the outside.

The heater 72 is an electric resistor that is sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connector electrode 71 through the through hole 73, and generates heat by being supplied with power from the outside through the heater connector electrode 71, thereby heating the solid electrolyte forming the element main body 101a and keeping it warm. .

Further, the heater 72 is embedded over the entire area from the first internal space 20 to the third internal space 61, and it is possible to adjust the entire element body 101a to a temperature at which the solid electrolyte is activated. ing.

The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 with an insulator such as alumina. The heater insulating layer 74 is formed for the purpose of providing electrical insulation between the second substrate layer 2 and the heater 72 and electrical insulation between the third substrate layer 3 and the heater 72 .

The pressure dissipation hole 75 is a portion that is provided so as to penetrate the third substrate layer 3 and the atmosphere introduction layer 48 and communicate with the reference gas introduction space 43 . It is formed for the purpose of alleviating

Here, the portion of the sensor element 101 that is mainly used for detecting the oxide gas concentration (here, the NOx concentration) (the cells 21, 41, 50, 80 to 83 in this embodiment) is used for oxide gas detection. section (NOx detection section in this embodiment). A portion of the sensor element 101 that is mainly used to detect the concentration of ammonia (the mixed potential cell 55 in this embodiment) is also called an ammonia detection portion. Both the NOx detection unit and the ammonia detection unit are disposed on the front side of the element body 101a, that is, in a region closer to the front end of the element body 101a than the center of the element body 101a in the front-rear direction. Accordingly, the electrodes 22, 23, 42, 44, 51, and 56 included in the NOx detection section and the ammonia detection section are also arranged on the front side of the element main body 101a.

Here, when the measured gas flow portion 9 and the detection electrode 56 are viewed in a cross section perpendicular to the flow direction of the measured gas, the area of the measured gas flow portion 9 in the cross section is defined as a cross-sectional area Sf. Moreover, the area occupied by the detection electrode 56 in the cross-sectional area Sf is assumed to be a cross-sectional area Sp. In the sensor element 101 of this embodiment, the area ratio R (=Sp/Sf), which is the value obtained by dividing the cross-sectional area Sp by the cross-sectional area Sf, is 0.5 or less. The area ratio R is the ratio of the cross-sectional area Sp of the detection electrode 56 to the cross-sectional area Sf of the gas flow part 9 to be measured. Furthermore, the detection electrode 56 has a length Lp of 2 mm or less along the flow direction of the gas to be measured. When the area ratio R is 0.5 or less and the length Lp is 2 mm or less, the detection electrode 56 is less likely to block the flow of the gas to be measured in the gas flow part 9 to be measured. A decrease in responsiveness of NOx concentration detection can be suppressed.

In this embodiment, the flow direction of the gas to be measured passing near the detection electrode 56 in the gas to be measured circulating portion 9 is along the front-rear direction. Therefore, the cross-sectional area Sf and the cross-sectional area Sp are determined based on the shapes of the measured gas flow portion 9 and the detection electrode 56 appearing in a cross section perpendicular to the front-rear direction, that is, a cross section parallel to the vertical and horizontal directions. For example, the cross section shown in FIG. 3 is the AA cross section in FIG. 2 and is a cross section perpendicular to the front-rear direction. The shape of the measured gas circulation portion 9 appearing in this cross section is a rectangular shape with a width of W in the left and right direction and a height of H in the top and bottom directions. Therefore, the product of the width W and the height H corresponds to the cross-sectional area Sf. Note that the height H corresponds to the thickness of the spacer layer 5 . The cross-sectional area Sf is the cross-sectional area Sp of the detection electrode 56 and the cross-sectional area Sa of the space portion of the gas-to-be-measured flow section 9 through which the gas to be measured can flow (in FIG. area) and Therefore, in the cross section shown in FIG. 3, R=Sp/Sf=Sp/(W×H)=Sp/(Sp+Sa). The cross-sectional area Sp of the detection electrode 56 corresponds to the sum of the cross-sectional areas of the ceiling electrode portion 56a, the bottom electrode portion 56b, and the side electrode portions 56c and 56d appearing in the cross section shown in FIG. The area ratio R is preferably 0.4 or less, more preferably 0.2 or less. Also, the area ratio R may be greater than 0, and may be 0.1 or more. The area ratio R can be adjusted by changing the thickness of the sensing electrode 56, for example.

When actually calculating the area ratio R, an image (SEM image) obtained by observation using a scanning electron microscope (SEM) is used for measurement as follows. First, with reference to the front and rear ends of the detection electrode 56 (both ends along the flow direction of the gas to be measured), three cross-sections that equally divide the detection electrode 56 into four are determined. Each of these three cross-sections is a cross-section perpendicular to the flow direction of the gas to be measured, as in FIG. Next, the sensor element 101 is cut so that each of these three cross-sections serves as an observation surface, and each cut surface is filled with resin and polished to obtain an observation material. Subsequently, the observation surface of the observation sample is photographed with the magnification of the SEM set to 100 times to 500 times to obtain SEM images of each of the three cross sections. Next, the number of pixels corresponding to the sensing electrode 56 is counted for each of the three cross-sectional SEM images, and the cross-sectional area Sp is calculated based on the average value thereof. Similarly, for each of the SEM images of the three cross-sections, the number of pixels in the measured gas flow portion 9 (the number of pixels corresponding to the space portion of the measured gas flow portion 9 and the number of pixels corresponding to the detection electrode 56 ) is calculated, and the cross-sectional area Sf is calculated based on the average value thereof. Then, the area ratio R (=Sp/Sf) is calculated from the calculated cross-sectional area Sp and cross-sectional area Sf.

As described above, the flow direction of the gas to be measured passing near the detection electrode 56 in the gas-to-be-measured flow section 9 is along the front-rear direction. Therefore, the length Lp of this embodiment is the length in the front-rear direction from the front end of the detection electrode 56 to the rear end of the detection electrode 56 (see FIG. 2). Note that even if the length of the detection electrode 56 differs depending on the part of the detection electrode 56, for example, the length in the front-rear direction differs between the ceiling electrode part 56a and the bottom electrode part 56b, the front end of the detection electrode 56 as a whole (in the direction of flow of the gas to be measured) The length from the most upstream portion) to the rear end (the most downstream portion in the flow direction of the gas to be measured) is the length Lp. More preferably, the length Lp is 1 mm or less. Moreover, the length Lp may be 0.5 mm or more.

The sensing electrode 56 of the mixed potential cell 55 , the inner pump electrode 22 of the main pump cell 21 , and the heater 72 are arranged such that when the sensing electrode 56 and the inner pump electrode 22 are heated by the heater 72 , the inner pump electrode 22 becomes the sensing electrode. It is preferably arranged to be hotter than 56 . Moreover, it is preferable that the distance A in the front-rear direction between the detection electrode 56 and the inner pump electrode 22 shown in FIG. 2 is 1 mm or more. As a result, when the sensing electrode 56 and the inner pumping electrode 22 are heated by the heater 72, a sufficient temperature difference can be generated between the electrodes 56, 22, and both the mixed potential cell 55 and the main pumping cell 21 can be appropriately heated. can be operated.

A specific example of the temperatures of the sensing electrode 56 and the inner pump electrode 22 will be described. The sense electrode 56 of the mixed potential cell 55 and the inner pump electrode 22 of the main pump cell 21 preferably meet a first temperature condition when heated by the heater 72 . The first temperature condition is that the temperature of the sensing electrode 56 is within the range of 550° C. or higher and 700° C. or lower, and the minimum temperature of the inner pump electrode 22 is 725° C. or higher. By satisfying the first temperature condition, both the mixed potential cell 55 and the main pump cell 21 can be properly operated, so it is preferable to satisfy the first temperature condition. In other words, the first temperature condition is that the minimum temperature of the inner pump electrode 22 is 725° C. or higher when the heater 72 heats the detection electrode 56 to a temperature in the range of 550° C. or higher and 700° C. or lower. means That the temperature of the detection electrode 56 is within the range of 550° C. or more and 700° C. or less means that the temperature of any part of the detection electrode 56 is within the range of 550° C. or more and 700° C. or less. That the lowest temperature of the inner pump electrode 22 is 725° C. or higher means that the temperature of any portion of the inner pump electrode 22 is 725° C. or higher. When the distance A is 1 mm or more, a sufficient temperature difference can be generated between the electrodes 56 and 22. Since it is easy to maintain, it is easy to satisfy the first temperature condition.

It is not limited to the case where the lowest temperature of the inner pump electrode 22 is always 725° C. or higher when the heater 72 heats the detection electrode 56 so that the temperature of the detection electrode 56 is in the range of 550° C. or higher and 700° C. or lower. If such heating is possible, it can be said that the first temperature condition is satisfied. For example, when the temperature of the detection electrode 56 is in the range of 550° C. or more and less than 600° C., even if the lowest temperature of the inner pump electrode 22 does not reach 725° C. or more, the temperature of the detection electrode 56 is 600° C. or more and 700° C. If the lowest temperature of the inner pump electrode 22 is 725° C. or higher within the following range, the sensing electrode 56 and the inner pump electrode 22 are arranged so as to satisfy the first temperature condition.

Moreover, the distance A described above is preferably 4 mm or less. When the distance A is 4 mm or less, the temperature difference between the detection electrode 56 and the inner pump electrode 22 when heated by the heater 72 does not become too large, so the sensor element 101 is resistant to thermal shock. cracks can be suppressed. The distance A may be 3 mm or less.

A specific example in which the temperature difference between the sensing electrode 56 and the inner pump electrode 22 does not become too large will be described. Sensing electrode 56 and inner pump electrode 22 preferably meet a second temperature condition when heated by heater 72 . The second temperature condition is that the difference between the lowest temperature of the detection electrode 56 and the highest temperature of the inner pump electrode 22 is 400° C. or less. By satisfying the second temperature condition, the temperature difference between the detection electrode 56 and the inner pump electrode 22 when heated by the heater 72 is small. Cracks can be suppressed. The second temperature condition is easily satisfied because the distance A is 4 mm or less. Moreover, it is more preferable that the difference between the lowest temperature of the sensing electrode 56 and the highest temperature of the inner pump electrode 22 is 350° C. or less.

By adjusting the mutual positional relationship between the heater 72, the detection electrode 56, and the inner pump electrode 22, the inner pump electrode 22 becomes hotter than the detection electrode 56 when heated by the heater 72. can be done. For example, by arranging the inner pump electrode 22 directly above the center of heat generation of the heater 72 (the portion that reaches the highest temperature, for example, the center of the front, back, left, and right of the heater 72), the temperature of the inner pump electrode 22 can be detected by the detection electrode 56. easy to raise. Also, the distance A can be adjusted by adjusting the positional relationship between the detection electrode 56 and the inner pump electrode 22 .

Moreover, it is preferable that the distance L in the front-rear direction from the gas inlet 10 to the measurement electrode 44 shown in FIG. 2 is 13 mm or less. Since the distance L is 13 mm or less, it is possible to suppress a decrease in responsiveness of NOx concentration detection. More preferably, the distance L is 11 mm or less.

The detection electrode 56 is arranged in front of the outer pump electrode 23, as shown in FIG. Further, in the present embodiment, the outer pump electrode 23 is arranged so as to have substantially the same size and position as the inner pump electrode 22 in top view. Therefore, the distance in the front-rear direction between the detection electrode 56 and the outer pump electrode 23 has the same value as the distance A described above.

The sensor element 101 comprises a buffer layer 84, as shown in FIG. The buffer layer 84 is a porous body, is disposed on the surface of the element body 101a, and serves to bond the protective layer 85 and the element body 101a. The buffer layer 84 includes an upper buffer layer 84a covering at least part of the upper surface of the second solid electrolyte layer 6 and a lower buffer layer 84b covering at least part of the lower surface of the first substrate layer 1. there is Upper buffer layer 84 a also covers outer pump electrode 23 . Each of the upper buffer layer 84a and the lower buffer layer 84b extends from the front end of the element main body 101a to the rear of the electrodes 22, 23, 42, 44, 51, 56 included in the NOx detection section and the ammonia detection section. exists in Also, the upper buffer layer 84 a and the lower buffer layer 84 b each exist to the rear of the rear end of the measured gas circulation portion 9 and the rear end of the protective layer 85 . The buffer layer 84 is made of porous ceramics such as alumina, zirconia, spinel, cordierite and magnesia. The main component of buffer layer 84 is preferably the same as that of protective layer 85 . In this embodiment, the buffer layer 84 is made of porous ceramics made of alumina.

The protective layer 85 is a porous body and covers the periphery of the front end portion of the element body 101a, more specifically, the periphery of the area where the NOx detection section and the ammonia detection section are present. The protective layer 85 covers the entire front end surface of the element body 101a and partially covers the top, bottom, left, and right surfaces of the element body 101a. The protective layer 85 is arranged outside the buffer layer 84 and covers the upper surface of the upper buffer layer 84a and the lower surface of the lower buffer layer 84b. The protective layer 85 exists to the rear of the rear end of the measured gas circulation section 9 . The protective layer 85 plays a role of suppressing cracks in the element main body 101a due to adhesion of moisture or the like in the gas to be measured, for example. The protective layer 85 is made of porous ceramics such as alumina, zirconia, spinel, cordierite and magnesia. In this embodiment, the protective layer 85 is made of porous ceramics made of alumina. Since the protective layer 85 is a porous body, the gas to be measured can flow through the inside of the protective layer 85 and reach the gas inlet 10 . Moreover, since the protective layer 85 and the buffer layer 84 are porous bodies, the gas to be measured can flow through the protective layer 85 and the buffer layer 84 to reach the outer pump electrode 23 . Note that the sensor element 101 does not have to include the buffer layer 84 and the protective layer 85 .

The control device 90 includes the above-described variable power sources 24, 46, and 52 and a control section 91, as shown in FIG.

The control unit 91 is a microprocessor including a CPU 92, a RAM (not shown), a storage unit 94, and the like. The storage unit 94 is a rewritable nonvolatile memory such as an EEPROM, and is a device that stores various data. The control unit 91 controls the electromotive force EMF detected by the mixed potential cell 55, the voltage V0 detected by the oxygen partial pressure detection sensor cell 80 for controlling the main pump, and the voltage V0 detected by the oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump. voltage V1 detected by the measuring pump controlling oxygen partial pressure detection sensor cell 82; voltage Vref detected by the sensor cell 83; pump current Ip0 detected by the main pump cell 21; The detected pump current Ip1 and the pump current Ip2 detected by the measuring pump cell 41 are input. The control unit 91 also controls the voltages Vp0, Vp1 and Vp2 output by the variable power supplies 24, 46 and 52, thereby controlling the main pump cell 21, the measurement pump cell 41 and the auxiliary pump cell 50. FIG. The storage unit 94 also stores target values V0*, V1*, V2*, etc., which will be described later. The CPU 92 of the control unit 91 controls each cell 21, 41, 50 with reference to these target values V0*, V1*, V2*. The control unit 91 also controls a heater power supply (not shown) that supplies power to the heater 72 to control the power that the heater power supply supplies to the heater 72 .

The control unit 91 feeds back the pump voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes a target value (referred to as a target value V0*) (that is, so that the oxygen concentration in the first internal space 20 becomes the target concentration). Control. Therefore, the pump current Ip0 changes according to the oxygen concentration of the gas to be measured. Therefore, the control section 91 can detect the oxygen concentration in the gas under measurement based on the pump current Ip0. For example, a relational expression, map, or the like representing the correspondence between the pump current Ip0 and the oxygen concentration in the gas to be measured is prepared in advance by experiments and stored in the storage unit 94 . Then, the control unit 91 uses the pump current Ip0 and this correspondence relationship to detect the oxygen concentration in the gas to be measured.

In addition, the control unit 91 controls the voltage V1 to a constant value (referred to as a target value V1*) (that is, the oxygen concentration in the second internal space 40 is set to a predetermined low oxygen concentration that does not substantially affect the measurement of NOx). The voltage Vp1 of the variable power supply 52 is feedback-controlled so as to obtain the concentration. Along with this, the control unit 91 sets the target value V0* of the electromotive force V0 based on the pump current Ip1 (feedback control) so that the pump current Ip1 flowing by the voltage Vp1 becomes a constant value (referred to as the target value Ip1*). )do. As a result, the gradient of the partial pressure of oxygen in the gas to be measured introduced into the second internal space 40 from the diffusion control section 30 is always constant. Also, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that has substantially no effect on NOx measurements. The target value V0* is set to a value such that the oxygen concentration in the first internal space 20 is higher than 0% and is low.

Furthermore, the control device 90 controls the variable power supply 46 so that the electromotive force V2 becomes a constant value (referred to as a target value V2*) (that is, so that the oxygen concentration in the third internal space 61 becomes a predetermined low concentration). feedback control of the voltage Vp2. As a result, oxygen is pumped out of the third internal space 61 so that the amount of oxygen generated by reduction of NOx in the gas under measurement in the third internal space 61 is substantially zero. Then, the control device 90 obtains a pump current Ip2 as a detected value corresponding to oxygen generated in the third internal cavity 61 due to a specific oxide gas (here, NOx), and determines the pump current Ip2. Based on this, the NOx concentration in the measured gas is derived.

Further, the control unit 91 acquires the electromotive force EMF of the mixed potential cell 55 and detects the concentration of ammonia in the gas to be measured based on the electromotive force EMF. Since the electromotive force EMF is also affected by oxygen in the gas under measurement, the control unit 91 uses the electromotive force EMF and the concentration of oxygen in the gas under measurement derived based on the pump current Ip0 to determine the concentration of oxygen in the gas under measurement. is preferably detected. For example, a relational expression or a map representing the correspondence between the oxygen concentration in the gas to be measured (or the pump current Ip0 as a value representing the oxygen concentration), the electromotive force EMF, and the ammonia concentration is created in advance by experiments and stored in the storage unit 94. store in Then, the control unit 91 detects the concentration of ammonia in the gas to be measured using the oxygen concentration in the gas to be measured, the electromotive force EMF, and their corresponding relationship. Thereby, the control unit 91 can derive the ammonia concentration in which the error in the electromotive force EMF due to the oxygen concentration is corrected.

Pump current Ip2 is also affected by ammonia in the gas to be measured. This is for the following reasons. When ammonia is contained in the gas to be measured, the ammonia reacts with oxygen in the gas-to-be-measured flow passage 9 to generate NO, and oxygen is generated in the third internal space 61 from the NO. Therefore, the oxygen pumped by the measurement pump cell 41 contains such oxygen derived from ammonia. Therefore, the value of the pump current Ip2 also changes depending on the concentration of ammonia in the gas to be measured. Therefore, the control unit 91 preferably detects the NOx concentration in the gas under measurement using the pump current Ip2 and the ammonia concentration in the gas under measurement derived based on the electromotive force EMF described above. For example, a relational expression, a map, or the like representing the correspondence between the pump current Ip2, the ammonia concentration, and the NOx concentration is created in advance through experiments and stored in the storage unit 94 . Then, the controller 91 uses the pump current Ip2, the ammonia concentration in the gas to be measured, and the corresponding relationship to derive the NOx concentration in the gas to be measured. Thereby, the control unit 91 can derive the NOx concentration in which the error of the pump current Ip2 due to the ammonia concentration is corrected.

A usage example of the gas sensor 100 configured in this manner will be described below. The CPU 92 of the control unit 91 first controls the heater power source to supply power to the heater 72 so that the temperature of the heater 72 reaches a target temperature (for example, 900° C.). The CPU 92 acquires, for example, a value that can be converted to the temperature of the heater 72 (for example, the resistance value or the current value of the heater 72), and feedback-controls the heater power supply based on the value, thereby controlling the temperature of the heater 72. do. The target temperature of the heater 72 is predetermined as a value that activates the solid electrolyte of each cell 21, 41, 50, 55, 80-83. Moreover, the target temperature of the heater 72 is preferably determined so that the detection electrode 56 and the inner pump electrode 22 satisfy at least one of the first temperature condition and the second temperature condition described above. In this embodiment, the target temperature of the heater 72 is determined as a value that satisfies both the first temperature condition and the second temperature condition.

When the temperature of the heater 72 reaches the target temperature (or near the target temperature), the CPU 92 controls the pump cells 21, 41, and 50 described above, and the voltages V0, V1, V2, Acquisition of Vref and acquisition of the electromotive force EMF from the mixed potential cell 55 are started. In this state, when the gas to be measured is introduced from the gas inlet 10, the gas to be measured reaches the detection electrode 56 in the buffer space 12, and the mixed potential cell 55 generates an electromotive force EMF. Also, the gas to be measured passes through the buffer space 12 and the diffusion control section 13 and reaches the first internal space 20 . Then, the oxygen concentration of the gas to be measured is adjusted by the main pump cell 21 and the auxiliary pump cell 50 in the first internal space 20 and the second internal space 40, and the gas to be measured after adjustment reaches the third internal space 61. . Then, the CPU 92 derives the concentration of ammonia and the concentration of NOx in the gas to be measured based on the pump current Ip0, the electromotive force EMF, the pump current Ip2, and various correspondences stored in the storage section 94 as described above. . The CPU 92 transmits the derived ammonia concentration and NOx concentration to the engine ECU, for example. The CPU 92 may only use the ammonia concentration for correction when calculating the NOx concentration, and only the NOx concentration may be finally transmitted to the engine ECU.

When the control device 90 detects the ammonia concentration and the NOx concentration using the sensor element 101 in this way, the sensor element 101 of the present embodiment uses the cross-sectional area Sp of the detection electrode 56 as described above. 9 is 0.5 or less, and the length Lp of the sensing electrode 56 is 2 mm or less. Here, when the area ratio R is large, the detection electrode 56 closes a larger portion of the cross section of the flow path of the measured gas circulation portion 9, thereby impeding the flow of the measured gas. On the other hand, when the area ratio R is 0.5 or less, the detection electrode 56 is less likely to block the flow of the gas to be measured in the gas flow section 9 to be measured. In addition, when the length Lp of the detection electrode 56 is long, there are many portions of the gas flow portion to be measured (here, the buffer space 12) where the cross section of the flow path is narrowed by the detection electrode 56. Gas flow is obstructed. On the other hand, when the length Lp of the detection electrode 56 is 2 mm or less, the part where the cross section of the flow path is narrowed by the detection electrode 56 in the measurement gas circulation portion is small. It is difficult to obstruct the flow of For these reasons, if the area ratio R is 0.5 or less and the length Lp is 2 mm or less, the gas to be measured is less likely to reach the measurement electrode 44 downstream of the detection electrode 56 . Therefore, even if the detection electrode 56 is arranged in the measurement gas circulation section 9, the responsiveness of the sensor element 101 to detect the NOx concentration is less likely to deteriorate.

Further, as described above, the sensing electrode 56, the inner pump electrode 22, and the heater 72 are arranged so that the inner pump electrode 22 becomes hotter than the sensing electrode 56 when heated by the heater 72. . A distance A in the front-rear direction between the detection electrode 56 and the inner pump electrode 22 is 1 mm or more. As a result, when the sensing electrode 56 and the inner pump electrode 22 are heated by the heater 72, a sufficient temperature difference can be generated between both electrodes. At this time, the solid electrolyte forming the main pump cell 21 is sufficiently activated, and the oxygen pumping capacity of the main pump cell 21 is sufficiently increased. For example, as described above as the first temperature condition, it is preferable to set the lowest temperature of the inner pump electrode 22 of the main pump cell 21 to 725° C. or higher. On the other hand, if the temperature of the sensing electrode 56 is too high, the ammonia around the sensing electrode 56 may burn and the ammonia concentration detection accuracy may drop. For example, as described above as the first temperature condition, the temperature of the detection electrode 56 is preferably 700° C. or lower. In the sensor element 101 of this embodiment, both the electrodes 22 and 56 and the heater 72 are arranged such that the inner pump electrode 22 has a higher temperature than the detection electrode 56, and the distance A is 1 mm or more. The sensor element 101 can be used with the temperature of 21 sufficiently high and the temperature of the sensing electrode 56 not too high. As a result, both the mixed potential cell 55 and the inner pump electrode 22 can be appropriately operated, and the NOx concentration and the ammonia concentration in the gas to be measured can be detected with high accuracy.

Furthermore, in the sensor element 101 of this embodiment, the distance L in the front-rear direction from the gas inlet 10 to the measurement electrode 44 is 13 mm or less. As described above, the measured gas circulation portion 9 is a flow path extending in the front-rear direction from the gas introduction port 10 to the measurement electrode 44 , and the distance L is the distance from the gas introduction port 10 to the measured gas flowing into the measured gas circulation portion 9 . There is a correlation with the time required for the gas to reach the measuring electrode 44 . Therefore, the distance L has a correlation with the responsiveness of NOx concentration detection. If the distance L is too large, the responsiveness of detecting the NOx concentration may decrease, but if the distance L is 13 mm or less, the decrease in responsiveness can be suppressed.

From the above, in the sensor element 101 of this embodiment, it is preferable that the distance A is 1 mm or more and the distance L is 13 mm or less. As a result, the NOx concentration and the ammonia concentration in the gas to be measured can be detected with high accuracy, and a decrease in responsiveness in detecting the NOx concentration can be suppressed. Note that when the ammonia concentration is used to derive the NOx concentration as described above, the NOx concentration detection accuracy also improves due to the improvement in the ammonia concentration detection accuracy.

Also, if the distance B from the front end of the inner pump electrode 22 to the front end of the measurement electrode 44 shown in FIG. The leakage current flowing through the electrode 44 may cause the pump current Ip2 to become an excessive value, and the NOx concentration may be detected to be higher than the actual value. Therefore, it is preferable to ensure that the distance B is at least a certain length (for example, 5 mm or more). When the distance B is set to a certain length or longer, increasing the distance A tends to increase the distance L (>distance A+distance B). However, if the distance L is too long, the responsiveness of NOx concentration detection decreases as described above. is preferred. Also, if the distance B is too large, the temperature of the measurement electrode 44 becomes low, and the function of the measurement electrode 44 as a NOx reduction catalyst is reduced, and the NOx concentration may be detected lower than the actual value. For example, it is preferably 10 mm or less.

The distance C between the detection electrode 56 and the measurement electrode 44 in the front-rear direction is preferably 11 mm or less. Distance C is equal to the sum of distance A and distance B, as shown in FIG. When the distance C is 11 mm or less, the time required for the gas to be measured to reach the periphery of the measurement electrode 44 after passing through the periphery of the detection electrode 56 is relatively short. and the responsiveness of ammonia concentration detection become comparable. That is, the response time for detecting the NOx concentration and the response time for detecting the ammonia concentration are relatively close to each other. Specifically, the response time for detecting the NOx concentration is the time until the detected value (here, the pump current Ip2) representing the NOx concentration in the detection unit 23 changes in accordance with the change in the NOx concentration in the gas to be measured. is. Similarly, the response time for detection of ammonia concentration means that the detection value (here, electromotive force EMF) representing the ammonia concentration in the mixed potential cell 55 changes in response to changes in the ammonia concentration in the gas to be measured. It is time to Since the response time for detecting the NOx concentration and the response time for detecting the ammonia concentration are relatively close, the sensor element 101 detects the NOx concentration and the ammonia concentration even when the composition of the gas to be measured changes from moment to moment. detection timing deviation becomes smaller. The distance C is more preferably 9 mm or less, and even more preferably 7 mm or less.

The detection electrode 56 is preferably arranged at a position where the distance D from the gas introduction port 10 to the detection electrode 56 along the flow direction of the gas to be measured is 4 mm or less. The distance D in this embodiment is a distance along the front-rear direction, like the length Lp (see FIG. 2). Here, when the sensor element 101 is used, the element main body 101a is heated by the heater 72 to a high temperature as described above. Therefore, when the gas to be measured comes into contact with the sensor element 101, the ammonia in the gas to be measured burns, and the sensitivity of ammonia concentration detection may decrease. In other words, the accuracy of ammonia concentration detection may decrease. On the other hand, if the distance D is 4 mm or less, the gas to be measured introduced from the gas introduction port 10 into the gas flow part 9 to be measured reaches the detection electrode 56 in a short time. Ammonia is difficult to burn until. Therefore, it is possible to suppress a decrease in sensitivity in detecting the concentration of ammonia in the gas to be measured. The distance D is more preferably 2 mm or less, and even more preferably less than 1 mm.

Of the first temperature conditions described above, "the temperature of the detection electrode 56 is 550° C. or higher" will be supplemented. When the temperature of the sensing electrode 56 is 550° C. or higher, the ammonia adsorbed on the surface of the sensing electrode 56 burns due to the catalytic action of the sensing electrode 56. However, when the temperature of the sensing electrode 56 is less than 550° C., the ammonia becomes difficult to burn and is detected. Ammonia remaining on the surface of the electrode 56 may reduce the responsiveness of the mixed potential (electromotive force EMF) to changes in ammonia concentration. By setting the temperature of the detection electrode 56 to 550° C. or higher, such a decrease in responsiveness can be suppressed. If the target temperature of the heater 72 is raised, both the temperatures of the sensing electrode 56 and the inner pump electrode 22 can be raised, so the temperature of the sensing electrode 56 can be raised to 550° C. or higher. Further, if the distance A is 4 mm or less, the temperature difference between the detection electrode 56 and the inner pump electrode 22 does not become too large as described above, so the temperature of the detection electrode 56 can be easily raised to 550° C. or higher.

Of the first temperature conditions described above, "the minimum temperature of the inner pump electrode 22 is 725° C. or higher" will be supplemented. Besides the main pump cell 21 , the auxiliary pump electrode 51 and the measuring pump cell 41 also pump oxygen, the first internal cavity 20 being located upstream of the second internal cavity 40 and the third internal cavity 61 . , the amount of oxygen pumped by the main pump cell 21 is much greater than the amount of oxygen pumped by the auxiliary pump electrode 51 and the measuring pump cell 41 . Therefore, among the main pump cell 21, the auxiliary pump electrode 51 and the measurement pump cell 41, the main pump cell 21 in particular needs to have a sufficiently high pumping capacity. Therefore, the auxiliary pump electrode 51 of the auxiliary pump cell 50 and the measurement electrode 44 of the measurement pump cell 41 do not need to be as hot as the inner pump electrode 22 .

An example of a method for manufacturing such a gas sensor 100 will be described below. When manufacturing the sensor element 101 of the gas sensor 100, first, a plurality (here, six sheets) of unfired ceramic green sheets corresponding to the element main body 101a are prepared. In this green sheet, a plurality of sheet holes used for positioning at the time of printing or stacking, necessary through holes, etc. are formed in advance. In addition, the green sheet that will be the spacer layer 5 is previously provided with a space that will be the gas flow part 9 to be measured by a punching process or the like. Then, corresponding to each of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6, each A pattern printing process and a drying process are performed to form various patterns on the ceramic green sheet. Specifically, the patterns to be formed are, for example, patterns of the above-described electrodes, wirings connected to the electrodes, the atmosphere introduction layer 48, the heater section 70, and the like. Pattern printing is carried out by applying a pattern forming paste prepared according to the characteristics required for each object to be formed onto the green sheet using a known screen printing technique. The pattern to be the detection electrode 56 includes a pattern to be the ceiling electrode portion 56a provided on the lower surface of the second solid electrolyte layer 6, a pattern to be the bottom electrode portion 56b provided on the upper surface of the first solid electrolyte layer 4, and a spacer layer. 5, patterns to be the side electrode portions 56c and 56d provided on the left and right side surfaces of the portion to be the buffer space 12 are separately formed. The pattern for the side electrode portion 56c and the side electrode portion 56d can be formed, for example, by known through-hole printing. Specifically, first, a paste pattern for the side electrode portion 56c and the side electrode portion 56d is formed by screen-printing a space (punched hole) that will be the buffer space 12 on the upper surface of the green sheet that will be the spacer layer 5. formed around the Then, the lower surface side of the green sheet to be the spacer layer 5 is set to a negative pressure to flow the paste into the space to be the buffer space 12 , and the paste is applied to the left and right side surfaces of the buffer space 12 . As a result, a pattern that becomes the side electrode portion 56c and the side electrode portion 56d is formed. The drying treatment is also performed using a known drying means. After pattern printing and drying, an adhesive paste for laminating and bonding the green sheets corresponding to each layer is printed and dried. Then, the green sheets on which the adhesive paste is formed are laminated in a predetermined order while being positioned by the sheet holes, and are crimped under predetermined temperature and pressure conditions to form a laminate. The laminate thus obtained includes a plurality of sensor elements 101 . The laminate is cut into pieces of the size of the sensor element 101 . Then, the cut laminate is fired at a predetermined firing temperature to obtain the sensor element 101 .

After obtaining the sensor element 101 in this manner, a sensor assembly is manufactured by incorporating the sensor element 101 into an element sealing body (not shown), a protective cover or the like is attached, and the sensor element 101 and the control device 90 are electrically connected. By doing so, the gas sensor 100 is obtained.

Here, correspondence relationships between the components of the present embodiment and the components of the present invention will be clarified. The measured gas circulation part 9 of the present embodiment corresponds to the measured gas circulation part of the present invention, the element main body 101a corresponds to the element main body, the first internal space 20 corresponds to the oxygen concentration adjustment chamber, and the inner pump. The electrode 22 corresponds to the adjustment pump electrode, the main pump cell 21 corresponds to the adjustment pump cell, the third internal cavity 61 corresponds to the measurement chamber, the measurement electrode 44 corresponds to the measurement electrode, and the detection electrode 56 corresponds to the detection. It corresponds to an electrode, the mixed potential cell 55 corresponds to a mixed potential cell, and the heater 72 corresponds to a heater.

According to the gas sensor 100 of the present embodiment described above, the area ratio R, which is the value obtained by dividing the cross-sectional area Sp of the detection electrode 56 of the sensor element 101 by the cross-sectional area Sf of the gas flow portion 9 to be measured, is 0.5 or less. In addition, since the detection electrode 56 has a length Lp of 2 mm or less in the flow direction of the gas flow portion 9 to be measured, the detection electrode 56 is less likely to block the flow of the gas to be measured in the gas flow portion 9 to be measured. Therefore, it is possible to suppress the deterioration of the NOx concentration detection responsiveness of the sensor element 101 .

Furthermore, since the distance D in the flow direction of the measured gas from the gas introduction port 10, which is the entrance of the measured gas circulation portion 9, to the detection electrode 56 is 4 mm or less, The gas to be measured introduced inside reaches the detection electrode 56 in a short time. This makes it difficult for the ammonia in the gas to be measured to burn until it reaches the detection electrode 56 . Therefore, it is possible to suppress a decrease in the sensitivity of detection of the concentration of ammonia in the gas under test in the sensor element 101 .

Furthermore, no diffusion rate-determining section constituted by a slit-like gap is provided between the gas introduction port 10 and the detection electrode 56 in the measured gas circulation section 9 . As a result, the measured gas introduced into the measured gas circulation section 9 from the gas inlet 10 reaches the detection electrode 56 in a short period of time. is difficult to burn. Therefore, it is possible to suppress a decrease in the sensitivity of detection of the concentration of ammonia in the gas under test in the sensor element 101 .

Since the distance C between the detection electrode 56 and the measurement electrode 44 in the front-rear direction is 11 mm or less, the time required for the gas to be measured to reach the circumference of the measurement electrode 44 after passing through the circumference of the detection electrode 56 is relatively short. As a result, the responsiveness of the sensor element 101 in detecting the NOx concentration and the responsiveness in detecting the ammonia concentration are approximately the same. The difference between the detection timings of concentration and ammonia concentration is reduced.

It goes without saying that the present invention is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

For example, in the above-described embodiment, the measured gas flow section 9 has a rectangular cross section perpendicular to the flow direction of the measured gas, and the detection electrode 56 forms the four sides of the rectangular shape. Although they are arranged on any of the four inner peripheral surfaces of the portion 9, the present invention is not limited to this. The detection electrode 56 may be arranged on one or more of the four inner peripheral surfaces of the measured gas circulation section 9 . In other words, the detection electrode 56 includes the ceiling electrode portion 56a, the bottom electrode portion 56b, and the side electrode portions 56c and 56d in the above-described embodiment, but may include one or more of these. For example, the modified detection electrode 156 shown in FIGS. 5 and 6 includes only the ceiling electrode portion 56a. FIG. 5 is an enlarged cross-sectional view showing the arrangement of detection electrodes 156 of a modified example, and FIG. 6 is a partial cross-sectional view showing a part of the BB cross section of FIG. Also in this case, as in the above-described embodiment, the area ratio R, which is the value obtained by dividing the cross-sectional area Sp of the detection electrode 156 by the cross-sectional area Sf of the gas flow part 9 to be measured, is 0.5 or less, and If the length Lp is 2 mm or less, it is possible to suppress a decrease in the NOx concentration detection responsiveness of the sensor element 101 . In the examples of FIGS. 5 and 6, the cross-sectional area Sp of the sensing electrode 156 is approximately equal to the product of the thickness of the ceiling electrode portion 56a and the left and right widths.

In the above-described embodiment, no diffusion control section is provided between the gas introduction port 10 and the detection electrode 56 in the measured gas circulation section 9, but a diffusion control section may be provided. However, as described above, it is preferable that no diffusion rate-limiting section is provided because it is possible to suppress a decrease in the sensitivity for detecting the concentration of ammonia in the gas to be measured.

In the above-described embodiments, the diffusion control portions 13, 30, and 60 are all configured as slit-shaped gaps, but the present invention is not limited to this. For example, one or more of the diffusion control sections 13, 30 and 60 are porous bodies (for example, alumina (Al ₂ O ₃ ) may be configured as a ceramic porous body). In this case, the diffusion resistance of the diffusion control section can be adjusted by adjusting the porosity and pore diameter of the porous body. It should be noted that it is preferable that no diffusion control section is provided between the gas introduction port 10 and the detection electrode 56, regardless of whether it is a slit-like gap or a porous body.

In the above-described embodiment, one reference electrode 42 is provided in the element main body 101a, and the reference electrode 42 serves as both the reference electrode of the NOx detection section and the reference electrode of the ammonia detection section, but the present invention is not limited to this. . For example, the reference electrode 42 may be the reference electrode for the NOx detection section, and the reference electrode included in the mixed potential cell 55 of the ammonia detection section may be provided separately from the reference electrode 42 .

In the above-described embodiment, the outer pumping electrode 23 is a part of the main pumping cell 21 and is disposed on the outside of the sensor element 101 in contact with the gas to be measured, and a part of the auxiliary pumping cell 50 and an outer auxiliary pump electrode disposed in a portion of the sensor element 101 that contacts the gas to be measured, and a part of the measuring pump cell 41 that is disposed in a portion of the sensor element 101 that contacts the gas to be measured. Although it also serves as the provided outer measurement electrode, it is not limited to this. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be provided outside the sensor element 101 separately from the outer pump electrode 23 .

In the embodiment described above, the sensor element 101 of the gas sensor 100 is provided with the first internal space 20, the second internal space 40, and the third internal space 61, but it is not limited to this. For example, like the sensor element 201 in FIG. 7, the third internal cavity 61 may not be provided. In the sensor element 201 of the modified example shown in FIG. 7, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the gas introduction port 10, the buffer space 12, the diffusion control portion 13, a first internal space 20, a diffusion control portion 30, and a second internal space 40 are formed adjacent to each other in a manner communicating with each other in this order. Further, the measurement electrode 44 is arranged on the upper surface of the first solid electrolyte layer 4 inside the second internal cavity 40 . The measurement electrode 44 is covered with a diffusion control portion 45 . The diffusion control portion 45 is a film made of a porous ceramic material such as alumina (Al ₂ O ₃ ). The diffusion control section 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, like the diffusion control section 60 of the above-described embodiment. In addition, the diffusion control section 45 also functions as a protective film for the measurement electrode 44 . A ceiling electrode portion 51 a of the auxiliary pump electrode 51 is formed up to just above the measurement electrode 44 . Even with the sensor element 201 having such a configuration, the NOx concentration can be detected based on, for example, the pump current Ip2 as in the above-described embodiment. In this case, the area around the measuring electrode 44 functions as a measuring chamber.

In the above-described embodiment, the element body 101a of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6), but it is not limited to this. The element main body 101a only needs to include at least one oxygen ion conductive solid electrolyte layer and to have the measurement gas flow section 9 provided therein. For example, layers 1 to 5 other than the second solid electrolyte layer 6 in FIG. 1 may be structural layers made of a material other than the solid electrolyte (for example, layers made of alumina). In this case, each electrode of sensor element 101 may be arranged on second solid electrolyte layer 6 . For example, the measurement electrode 44 in FIG. 1 may be arranged on the bottom surface of the second solid electrolyte layer 6 . Further, the reference gas introduction space 43 is provided in the spacer layer 5 instead of the first solid electrolyte layer 4, and the air introduction layer 48 is provided in the second solid electrolyte layer 4 instead of providing it between the first solid electrolyte layer 4 and the third substrate layer 3. It may be provided between the electrolyte layer 6 and the spacer layer 5 , and the reference electrode 42 may be provided behind the third internal space 61 and on the lower surface of the second solid electrolyte layer 6 .

In the above-described embodiment, the gas sensor 100 detects the NOx concentration as the specific oxide gas concentration, but the specific oxide gas concentration may be other oxide concentrations without being limited to this. When measuring the specific oxide gas concentration, oxygen is generated when the specific oxide gas itself is reduced in the third internal space 61 as in the above-described embodiment. can be obtained to detect a specific oxide gas concentration. Also in this case, correction of the oxide gas concentration based on the ammonia concentration can be performed in the same manner as in the above-described embodiment.

In the above-described embodiment, the CPU 92 performs feedback control of the voltage Vp2 of the variable power supply 46 so that the electromotive force V2 becomes the target value V2* as the measurement pump control processing. Although the NOx concentration in the measured gas was detected based on Ip2), it is not limited to this. For example, as the measurement pump control process, the CPU 92 controls the measurement pump cell 41 (for example, controls the voltage Vp2) so that the pump current Ip2 becomes a constant target value Ip2*, and the detected value (electromotive force V2 ) may be used to detect the NOx concentration. By controlling the measuring pump cell 41 so that the pump current Ip2 becomes the target value Ip2*, oxygen is pumped out of the third internal cavity 61 at a substantially constant flow rate. Therefore, the oxygen concentration in the third internal space 61 changes according to the amount of oxygen generated by reduction of NOx in the gas to be measured in the third internal space 61, thereby changing the electromotive force V2. . Therefore, the electromotive force V2 becomes a value corresponding to the NOx concentration in the gas to be measured. Therefore, the NOx concentration can be calculated based on this electromotive force V2. For example, the correspondence relationship between the electromotive force V2 and the NOx concentration may be stored in the storage unit 94 in advance.

In the above-described embodiment, the control unit 91 sets the target value V0* of the electromotive force V0 based on the pump current Ip1 (feedback control) so that the pump current Ip1 becomes the target value Ip1*. Although the pump voltage Vp0 is feedback-controlled so as to achieve the target value V0*, other processing may be performed. For example, the control unit 91 may feedback-control the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1*. That is, the control unit 91 omits acquisition of the electromotive force V0 from the oxygen partial pressure detection sensor cell 80 for main pump control and setting of the target value V0*, and directly controls the pump voltage Vp0 based on the pump current Ip1. (and thus control the pump current Ip0).

In the above-described embodiment, the control unit 91 performs feedback control of the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*, acquires the pump current Ip2 at this time as the detected value, and obtains the detected value. Although the NOx concentration in the measured gas was detected based on the detected value, the present invention is not limited to this. For example, the control unit 91 controls the measurement pump cell 41 (for example, controls the voltage Vp2) so that the pump current Ip2 becomes a constant target value Ip2*, acquires the voltage V2 at this time as a detection value, and obtains the voltage V2 at this time as a detection value. The value may be used to detect NOx concentration. By controlling the measuring pump cell 41 so that the pump current Ip2 becomes the target value Ip2*, oxygen is pumped out of the third internal cavity 61 at a substantially constant flow rate. Therefore, the oxygen concentration in the third internal space 61 changes according to the amount of oxygen generated by reduction of NOx in the gas under measurement in the third internal space 61, thereby changing the voltage V2. Therefore, the voltage V2 has a value corresponding to the NOx concentration in the gas to be measured. Therefore, the NOx concentration can be calculated based on this voltage V2. Also in this case, the correction of the NOx concentration based on the ammonia concentration can be performed in the same manner as in the above-described embodiment. For example, a relational expression, a map, or the like representing the correspondence between the voltage V2, the ammonia concentration, and the NOx concentration may be prepared in advance through experiments and stored in the storage unit 94 .

Specific examples of the gas sensor will be described below as examples. Experimental Examples 1 to 5, 8 to 11 and 14 to 27 correspond to the examples of the present invention, and Experimental Examples 6, 7, 12 and 13 correspond to comparative examples. In addition, the present invention is not limited to the following examples.

[Experimental example 1]
The gas sensor 100 shown in FIGS. 1 to 4 was manufactured by the manufacturing method described above, and was designated as Experimental Example 1. FIG. In fabricating the sensor element 101, the ceramic green sheet was formed by mixing zirconia particles to which 4 mol % of yttria as a stabilizer was added, an organic binder, and an organic solvent, and forming the mixture by tape forming. The pattern for the detection electrode 56 was formed using a paste prepared by mixing coating powder obtained by coating Pt powder with Au, zirconia powder, and a binder. The measurement electrode 44 was a porous cermet electrode of Pt and zirconia. A pattern for the measurement electrode 44 was formed using a paste prepared by mixing Pt powder, zirconia powder, a binder, and a pore-forming material. When the area ratio R of the sensor element 101 of Experimental Example 1 was measured by the method described above, it was 0.1. Also, the length Lp of the detection electrode 56 was 1 mm.

[Experimental Examples 2 to 7, 8 to 13]
Experimental Examples 2 to 7 were prepared by manufacturing the same gas sensor 100 as in Experimental Example 1 except that the area ratio R was variously changed as shown in Table 1 below. Further, the same gas sensor 100 as that of Experimental Example 1 was manufactured except that the area ratio R was 0.3 and the length Lp was variously changed as shown in Table 2 below, and designated as Experimental Examples 8 to 13.

[Evaluation of Responsiveness of NOx Concentration Detection]
Each of Experimental Examples 1 to 13 was evaluated for NOx concentration detection responsiveness. Specifically, first, the gas sensor 100 of Experimental Example 1 is attached to a pipe, and the controller 91 controls the temperature of the heater 72 so that the heater 72 reaches a predetermined target temperature. A state in which the pump cells 21, 41, 50 are controlled, the voltages V0, V1, V2, Vref are obtained from the sensor cells 80 to 83, and the electromotive force EMF is obtained from the mixed potential cell 55. did. In this state, a model gas having a nitrogen base gas and a NOx concentration of 0 ppm was used as the gas to be measured. Then, the temporal change in the value of the pump current Ip2 was investigated when the NOx concentration of the gas to be measured flowing through the pipe was changed from 0 ppm to 500 ppm. When the value of the pump current Ip2 exceeds 10%, where the value of the pump current Ip2 immediately before the NOx concentration is changed is 0%, and the value when the pump current Ip2 changes and stabilizes after the NOx concentration is changed is 100%. The elapsed time from when the concentration exceeded 90% was defined as the response time [sec] of the NOx concentration detection. It means that the shorter the response time, the higher the responsiveness of the sensor element 101 in detecting the NOx concentration. If the NOx concentration detection response time is 1.1 sec or less, the NOx concentration detection responsiveness is determined as "A (excellent)", and if the NOx concentration detection response time is 1.2 sec or less, the NOx concentration detection responsiveness is determined. was determined as "B (possible)", and when it exceeded 1.2 sec, the responsiveness of NOx concentration detection was determined as "F (impossible)". For Experimental Examples 2 to 13, the response time for NOx concentration detection was measured in the same manner as in Experimental Example 1 to evaluate the responsiveness. Tables 1 and 2 collectively show the area ratio R, the length Lp, the NOx concentration detection response time, and the responsiveness evaluation results in each of Experimental Examples 1 to 7 and 8 to 13.

As shown in Tables 1 and 2, it was confirmed that the smaller the area ratio R and the length Lp, the shorter the response time for NOx concentration detection. Specifically, in Experimental Examples 1 to 5 and 8 to 11 in which the area ratio R is 0.5 or less and the length Lp is 2 mm or less, the NOx concentration detection response time is 1.2 sec or less. The quality evaluation was "A (excellent)" or "B (acceptable)". In particular, in Experimental Examples 1 to 4 and 8 to 11, in which the area ratio R is 0.4 or less and the length Lp is 2 mm or less, the NOx concentration detection response time is 1.1 sec or less, and the responsiveness is evaluated. was "A (excellent)". On the other hand, in Experimental Examples 5 to 7 in which the area ratio R exceeds 0.5 and in Experimental Examples 12 and 13 in which the length Lp exceeds 2 mm, the NOx concentration detection response time is 1.3 sec. Responsiveness evaluation was "F (failure)". From these results, it was confirmed that when the area ratio R is 0.5 or less and the length Lp is 2 mm or less, a decrease in the responsiveness of NOx concentration detection can be suppressed. Moreover, from the results of Table 1, it is considered that the area ratio R is preferably 0.4 or less, more preferably 0.2 or less. From the results of Table 2, it is considered that the length Lp is preferably 1 mm or less.

[Experimental Examples 14 to 20]
Experimental examples 14 to 20 were prepared by manufacturing the same gas sensor 100 as in experimental example 3 (area ratio R: 0.3, length Lp: 1 mm) except that the distance D shown in FIG.

[Evaluation of ammonia concentration detection sensitivity]
For each of Experimental Examples 14 to 20, the sensitivity of ammonia concentration detection by the sensing electrode 56 was examined. Specifically, first, the gas sensor 100 of Experimental Example 14 was attached to the pipe, and the control unit 91 was in a state of controlling the above-described pump cells and the like. In this state, a model gas having a nitrogen base gas and an ammonia concentration of 500 ppm is used as the gas to be measured. A value representing the sensitivity of ammonia concentration detection. The smaller the value (electromotive force EMF) representing the sensitivity of ammonia concentration detection, the lower the ammonia concentration detection accuracy of the mixed potential cell 55 . Then, when the electromotive force EMF was 140 mV or more, the ammonia concentration detection accuracy using the mixed potential cell 55 was determined as "A (excellent)", and when the electromotive force EMF was 100 mV or more, the ammonia concentration The detection accuracy was determined as "B (acceptable)", and when it was less than 100 mV, the ammonia concentration detection accuracy was determined as "F (impossible)". Table 3 summarizes the distance D, the ammonia concentration detection sensitivity (electromotive force EMF), and the detection sensitivity evaluation in each of Experimental Examples 14 to 20.

As shown in Table 3, it was confirmed that the smaller the distance D, the higher the sensitivity of ammonia concentration detection. Specifically, in Experimental Examples 14 to 18 in which the distance D is 4 mm or less, the electromotive force EMF of the mixed potential cell 55 representing the sensitivity of ammonia concentration detection is all 100 mV or more, and the evaluation of the ammonia concentration detection sensitivity is It was "A (excellent)" or "B (fair)". In particular, in Experimental Example 14 in which the distance D was 0 mm, the electromotive force EMF was 140 mV and the detection sensitivity was evaluated as "A (excellent)". On the other hand, in Experimental Examples 19 and 20 in which the distance D exceeded 4 mm, the electromotive force EMF decreased to 90 mV or less, and the ammonia concentration detection accuracy was evaluated as "F (impossible)". From these results, it was confirmed that if the distance D is 4 mm or less, the detection sensitivity of the ammonia concentration using the detection electrode 56 is increased. Moreover, it is considered that the distance D is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0 mm.

[Experimental Examples 21 to 27]
Experimental Examples 21 to 27 were prepared by manufacturing gas sensors 100 with various distances C shown in FIG. In Experimental Examples 21 to 27, the area ratio R was 0.3, the length Lp was 1 mm, and the distance D was 0.65 mm.

[Evaluation of difference between response time of ammonia concentration detection and response time of NOx concentration detection]
For each of Experimental Examples 21 to 27, the difference between the NOx concentration detection response time and the ammonia concentration detection response time was examined. Specifically, a model gas having a nitrogen base gas and an ammonia concentration of 0 ppm is used as the gas to be measured. We waited until the value of the current Ip2 stabilized. Then, changes over time in the value of the electromotive force EMF and the value of the pump current Ip2 were examined when the ammonia concentration of the gas to be measured flowing through the pipe was changed from 0 ppm to 500 ppm. When the value of the electromotive force EMF exceeds 10%, where the value of the electromotive force EMF immediately before the ammonia concentration is changed is 0%, and the value when the electromotive force EMF changes and stabilizes after the ammonia concentration is changed is 100%. A response time [sec] for detection of the ammonia concentration was defined as the elapsed time from when the concentration exceeded 90%. In a similar manner, the elapsed time from when the value of the pump current Ip2 exceeded 10% to when it exceeded 90% was defined as the NOx concentration detection response time [sec]. As described above, when the ammonia concentration in the gas under measurement changes, the pump current Ip2 also changes. can be examined. Then, the difference between the two obtained response times was calculated. The smaller the difference in response time, the smaller the difference in detection timing of the NOx concentration and the ammonia concentration by the sensor element 101 . Then, if the difference in response time is 0.8 sec or less, the difference in response time is determined as "A (difference is very small)", and if it is 0.9 sec or less, the difference in response time is determined as " The difference in response time was determined as "B (small difference)", and when it exceeded 0.9 sec, the difference in response time was determined as "F (large difference)". Table 4 summarizes the distance C, the response time for ammonia concentration detection, the response time for NOx concentration detection, the difference in response time, and the evaluation of the difference in response time in each of Experimental Examples 21 to 27. show.

As shown in Table 4, it was confirmed that the smaller the distance C, the smaller the difference between the ammonia concentration detection response time and the NOx concentration detection response time. Specifically, in Experimental Examples 21 to 26 in which the distance C is 11 mm or less, the difference in response time is 0.9 sec or less, and the evaluation of the difference in response time is "A (difference is very small). )” or “B (small difference)”. In particular, in Experimental Examples 21 to 24 in which the distance C was 9 mm or less, the difference in response time was 1.1 sec or less, and the evaluation of the difference in response time was "A (very small difference)". . On the other hand, in Experimental Example 27 in which the distance C exceeds 11 mm, the difference in response time was 1.3 sec, and the evaluation of the difference in response time was "F (large difference)". From these results, it was confirmed that when the distance C is 11 mm or less, the deviation in detection timing of the NOx concentration and the ammonia concentration becomes small. Moreover, it is considered that the distance C is preferably 9 mm or less, and more preferably 7 mm or less.

REFERENCE SIGNS LIST 1 first substrate layer 2 second substrate layer 3 third substrate layer 4 first solid electrolyte layer 5 spacer layer 6 second solid electrolyte layer 9 measured gas flow portion 10 gas introduction port 12 buffer space, 13 diffusion rate-limiting part, 20 first internal space, 21 main pump cell, 22 inner pump electrode, 22a ceiling electrode part, 22b bottom electrode part, 23 outer pump electrode, 24 variable power supply, 30 diffusion rate-limiting part, 40 second second Internal cavity 41 Measurement pump cell 42 Reference electrode 43 Reference gas introduction space 44 Measurement electrode 45 Diffusion control section 46 Variable power supply 48 Atmosphere introduction layer 50 Auxiliary pump cell 51 Auxiliary pump electrode 51a Ceiling electrode section , 51b bottom electrode portion, 52 variable power source, 55 mixed potential cell, 56 detection electrode, 56a ceiling electrode portion, 56b bottom electrode portion, 56c, 56d side electrode portions, 60 diffusion rate-limiting portion, 61 third internal space, 70 Heater part 71 Heater connector electrode 72 Heater 73 Through hole 74 Heater insulating layer 75 Pressure dissipation hole 80 Oxygen partial pressure detection sensor cell for main pump control 81 Oxygen partial pressure detection sensor cell for auxiliary pump control 82 For measurement Pump control oxygen partial pressure detection sensor cell 83 sensor cell 84 buffer layer 84a upper buffer layer 84b lower buffer layer 85 protective layer 90 controller 91 controller 92 CPU 94 storage 100 gas sensor 101 , 201 sensor element, 101a element body, 156 detection electrode.

Claims (5)

an element main body having an oxygen ion-conducting solid electrolyte layer, a measuring gas flow section for introducing and circulating a measuring gas, and having a longitudinal direction;
an adjustment pump cell having an adjustment pump electrode disposed in the oxygen concentration adjustment chamber of the gas flow portion to be measured, and adjusting the oxygen concentration in the oxygen concentration adjustment chamber;
A sensor for detecting a concentration of a specific oxide gas in the gas to be measured, disposed on the inner peripheral surface of a measurement chamber provided downstream of the oxygen concentration adjustment chamber in the gas flow section to be measured. a measuring electrode;
a mixed potential cell having a detection electrode disposed upstream of the adjustment pump electrode in the gas flow portion to be measured and generating an electromotive force corresponding to the concentration of ammonia in the gas to be measured;
a heater for heating the element body;
with
When the measured gas flow portion and the detection electrode are viewed in a cross section perpendicular to the flow direction of the measured gas, the area of the measured gas flow portion in the cross section is defined as a cross-sectional area Sf, and the cross-sectional area Sf is When the area occupied by the detection electrode is defined as the cross-sectional area Sp, the area ratio R, which is the value obtained by dividing the cross-sectional area Sp by the cross-sectional area Sf, is 0.5 or less,
The detection electrode has a length Lp of 2 mm or less in the flow direction,
sensor element. The distance D in the direction of flow from the gas introduction port, which is the entrance of the gas flow part to be measured, to the detection electrode is 4 mm or less.
A sensor element according to claim 1 . No slit-like gap or a diffusion rate-limiting portion made of a porous material is provided between the gas introduction port, which is the entrance of the gas flow portion to be measured, and the detection electrode.
3. A sensor element according to claim 1 or 2. With the longitudinal direction as the front-rear direction, a gas introduction port, which is an inlet of the measured gas flow portion, opens in the front end surface of the element main body,
the measured gas flow portion is a flow path extending in the front-rear direction from the gas introduction port to the measurement electrode;
The distance C between the detection electrode and the measurement electrode in the front-rear direction is 11 mm or less,
The sensor element according to any one of claims 1-3. A gas sensor comprising the sensor element according to any one of claims 1 to 4.

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