JP2022153759A - Sensor element and gas sensor - Google Patents

Abstract

To precisely detect a specific oxide gas concentration and an ammonium concentration in a measured gas, and to suppress a decrease in response properties of detection of the oxide gas concentration.SOLUTION: A sensor element includes: an element body having a longitudinal direction; an inner pump electrode 22; a measurement electrode 44; a detection electrode 56; and a heater. With a longitudinal direction of the element body as a fore-and-aft direction, the inner pump electrode 22 and the measurement electrode 44 are arranged in a front side of the element body. The detection electrode 56 is arranged in a front side of the inner pump electrode 22. The detection electrode 56, the inner pump electrode 22, and the heater are disposed such that the inner pump electrode 22 becomes hotter than the detection electrode 56 when being heated by the heater. Distance A in a fore-and-aft direction between the detection electrode 56 and the inner pump electrode 22 is equal to or more than 1 mm, and distance L in a fore-and-aft direction from a gas introduction port 10 as an entrance to a measured gas circulation part to the measurement electrode 44 is equal to or less than 13 mm.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.

JP 2019-219177 A

By the way, in such a gas sensor, there is a demand for improving the detection accuracy of oxide gas concentration such as NOx and the detection accuracy of ammonia concentration. was desired. In addition, depending on the position of the measurement electrode, the responsiveness of detecting the oxide gas concentration may be lowered, and there has been a demand to suppress such a decrease in responsiveness.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and is capable of accurately detecting a specific oxide gas concentration and ammonia concentration in a gas to be measured, and preventing a decrease in responsiveness in detecting the oxide gas concentration. The main purpose is to suppress

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 on the element body 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
With the longitudinal direction of the element body as the front-rear direction, the adjustment pump electrode and the measurement electrode are disposed on the front side of the element body,
The detection electrode is disposed in front of the adjustment pump electrode in the element body,
The detection electrode, the adjustment pump electrode, and the heater are arranged so that the adjustment pump electrode becomes hotter than the detection electrode when heated by the heater,
The distance A in the front-rear direction between the detection electrode and the adjustment pump electrode is 1 mm or more,
The distance L in the front-rear direction from the gas introduction port, which is the entrance of the gas flow part to be measured, to the measurement electrode is 13 mm or less.
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 adjusting pump electrode of the adjusting pump cell and the measuring electrode in the measuring chamber are arranged on the front side of the element body, and the detection electrode of the mixed potential cell is further forward than the adjusting pump electrode. are placed in The sensing electrode, the adjusting pump electrode, and the heater are arranged so that the adjusting pump electrode becomes hotter than the sensing electrode when the sensing electrode and the adjusting pump electrode are heated by the heater. A distance A in the front-rear direction between the detection electrode and the adjustment pump electrode is 1 mm or more. As a result, a sufficient temperature difference can be generated between the detection electrode and the adjustment pump electrode when the heater heats the electrodes. Here, since the oxygen pumping capacity of the adjustment pump cell is sufficiently high, it is preferable to set the temperature of the adjustment pump electrode to a relatively high temperature. On the other hand, if the temperature of the sensing electrode is too high, the ammonia around the sensing electrode may burn and the ammonia concentration detection accuracy may drop. Therefore, the temperature of the sensing electrode is preferably not too high. In the sensor element of the present invention, both electrodes and the heater are arranged so that the temperature of the adjustment pump electrode is higher than that of the detection electrode, and the distance A is 1 mm or more, so that the temperature of the adjustment pump cell is sufficiently high and The sensor element can be used without the temperature of the sensing electrode becoming too high. As a result, both the mixed potential cell and the adjustment pump cell can be appropriately operated, and the specific oxide gas concentration and ammonia concentration in the gas to be measured can be accurately detected. Furthermore, in the sensor element of the present invention, the distance L in the front-rear direction from the gas introduction port, which is the entrance of the gas flow part to be measured, to the measurement electrode is 13 mm or less. If the distance L is too large, it takes a long time for the gas to be measured that has flowed into the gas flow part to be measured from the gas introduction port to reach the measuring electrode, which may reduce the responsiveness of oxide gas concentration detection. However, when the distance L is 13 mm or less, the decrease in responsiveness can be suppressed. As described above, the sensor element of the present invention can accurately detect the specific oxide gas concentration and ammonia concentration in the gas to be measured, and can suppress a decrease in the responsiveness of detecting the oxide gas concentration.

In the sensor element of the present invention, the distance A may be 4 mm or less. This prevents the temperature difference between the detection electrode and the adjustment pump electrode when heated by the heater from becoming too large. Therefore, the sensor element is resistant to thermal shock, and cracking of the sensor element due to thermal shock can be suppressed. A thermal shock applied to the sensor element is caused, for example, by adhesion of moisture in the gas to be measured.

In the sensor element of the present invention, the detection electrode may be arranged outside the element main body so as to be in contact with the gas to be measured. With this configuration, the detection electrode is arranged in front of the adjustment pump electrode and outside the element body, that is, the detection electrode is arranged near the front end of the element body and outside the element body, so that the gas to be measured can be measured. It becomes easier to reach the detection electrode, and the responsiveness of ammonia concentration detection is improved.

In the sensor element of the present invention, the detection electrode may be provided on the upstream side of the oxygen concentration adjustment chamber in the measurement gas circulation section.

In the sensor element of the present invention in which the detection electrode is provided on the upstream side of the oxygen concentration adjustment chamber in the gas flow section to be measured, the distance C between the detection electrode and the measurement electrode in the front-rear direction is 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 gas introduction port is open to the front end surface of the element main body, and the measurement target gas circulation portion is a flow path extending in the front-rear direction from the gas introduction port to the measurement electrode. good too.

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 has the same effects as the sensor element of the present invention described above, for example, it can accurately detect a specific oxide gas concentration and ammonia concentration in the gas to be measured, and the responsiveness of oxide gas concentration detection is reduced. can be obtained.

FIG. 2 is a schematic cross-sectional view of the gas sensor 100; FIG. 2 is a partially enlarged view of FIG. 1; 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; 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. FIG. 3 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.

A gas inlet 10 and a first diffusion a rate-controlling portion 11, a buffer space 12, a second diffusion rate-controlling portion 13, a first internal space 20, a third diffusion rate-controlling portion 30, a second internal space 40, a fourth diffusion rate-controlling portion 60, The third internal space 61 is adjacently formed in a manner communicating with the third internal space 61 in this order.

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.

Each of the first diffusion rate-controlling part 11, the second diffusion rate-controlling part 13, and the third diffusion rate-controlling part 30 is provided as two horizontally long slits (the openings of which have the longitudinal direction in the direction perpendicular to the drawing). . Further, the fourth diffusion rate-controlling part 60 is provided as one horizontally long slit (the opening has its longitudinal direction in the direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6 . A portion from the gas introduction port 10 to the third internal space 61 is also referred to as a measured gas flow portion. The gas introduction port 10 is the inlet of the measured gas circulation portion, and is open at the front end surface of the element main body 101a. Further, the measured gas circulation portion is a flow path 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 introduction port 10 into the gas-to-be-measured circulation portion moves backward. Inside the measured gas circulation portion, the inner pump electrode 22, the auxiliary pump electrode 51, and the measuring electrode 44 are arranged in this order from the gas inlet 10 side. The measured gas flow portion 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 part, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, the side part is the side surface of the first solid electrolyte layer 4. A reference gas introduction space 43 is provided at a partitioned position. 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, the gas inlet port 10 is a portion that is open to the external space, and the gas to be measured is taken into the element main body 101a from the outer space through the gas inlet port 10. there is The first diffusion control portion 11 is a portion that imparts a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10 . The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate controlling section 11 to the second diffusion rate controlling section 13 . The second diffusion control portion 13 is a portion that imparts a predetermined diffusion resistance to the gas to be measured 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 directly introduced into the first internal space 20, but is passed through the first diffusion rate-determining portion 11, the buffer space 12, After pressure fluctuations of the gas to be measured are canceled out through the second diffusion control section 13 , the gas is introduced into the first internal cavity 20 . 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 second 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 third diffusion rate controlling section 30 applies a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal cavity 20, thereby reducing the gas under measurement. It is a portion that leads to the second internal space 40 .

After the oxygen concentration (oxygen partial pressure) has been adjusted in the first internal space 20 in advance, the second internal space 40 is provided with the auxiliary pump cell 50 for the measurement gas introduced through the third diffusion control section 30 . It is provided as a space for adjusting the oxygen partial pressure by 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 the above-described target value of the voltage V0 is controlled, whereby the third diffusion rate-determining section 30 2 The gradient of the oxygen partial pressure in the gas to be measured introduced into the internal space 40 is controlled 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 fourth diffusion rate control section 60 applies a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal space 40, thereby reducing the gas under measurement. It is a portion that leads to the third internal space 61 . The fourth diffusion control section 60 serves to limit the amount of NOx flowing into the third internal space 61 .

After the oxygen concentration (oxygen partial pressure) has been adjusted in the second internal space 40 in advance, the third internal space 61 allows the measurement gas introduced through the fourth diffusion control section 60 to It is provided as a space for performing processing related to measurement of nitrogen 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 fourth 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 outside the element main body 101a so as to be in contact with the gas to be measured. More specifically, the detection electrode 56 is arranged on the upper surface of the element main body 101a. Further, the detection electrode 56 is arranged in front of the inner pump electrode 22 in the element main body 101a. 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.

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 arranged so that it becomes hotter than 56. Further, 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 .

In addition, the distance L in the front-rear direction from the gas introduction port 10 shown in FIG. 2 to the measurement electrode 44 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 sensing electrode 56 and 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 Further, each of the upper buffer layer 84a and the lower buffer layer 84b extends to the rear of the rear end of the measured gas flow portion and the rear end of the protective layer 85. As shown in FIG. 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 extends to the rear of the rear end of the measured gas circulation section. 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 and the detection electrode 56 . 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 voltage V0 based on the pump current Ip1 so that the pump current Ip1 flowing by the voltage Vp1 becomes a constant value (referred to as the target value Ip1*) (feedback control). do. As a result, the gradient of the oxygen partial pressure in the gas to be measured introduced into the second internal space 40 from the third 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.

Further, the control device 90 controls the variable power supply 46 so that the voltage 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). The voltage Vp2 is feedback-controlled. 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 flow part to be measured 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 reaches the detection electrode 56, the mixed potential cell 55 generates an electromotive force EMF. Further, when the gas to be measured is introduced from the gas inlet 10 , the gas to be measured passes through the first diffusion rate controlling portion 11 , the buffer space 12 and the second diffusion rate controlling portion 13 and reaches the first inner space 20 . do. 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 controller 90 uses the sensor element 101 to detect the ammonia concentration and the NOx concentration in this way, the sensor element 101 of the present embodiment, as described above, is heated by the heater 72 to cause the inner pump electrode 22 to The sensing electrode 56 , the inner pump electrode 22 , and the heater 72 are positioned such that the inner electrode 56 is hotter than the sensing electrode 56 . 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 is a flow path extending in the longitudinal direction from the gas introduction port 10 to the measurement electrode 44, and the distance L is the length of the measured gas flowing from the gas introduction port 10 into the measured gas circulation portion. There is a correlation with the time required 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.

As described above, the sensor element 101 of the present embodiment can accurately detect the NOx concentration and the ammonia concentration in the gas to be measured, and can suppress a decrease in the responsiveness of NOx concentration detection. 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. This is very important. 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.

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 detection electrode 56 is 550° C. or higher, the ammonia adsorbed on the surface of the detection electrode 56 burns due to the catalytic action of the detection electrode 56. However, when the temperature of the detection electrode 56 is lower 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 increased, the temperatures of both 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 sensing electrode 56 and the inner pump electrode 22 does not become too large as described above, so the temperature of the sensing 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 .

Here, correspondence relationships between the components of the present embodiment and the components of the present invention will be clarified. The element body 101a of this embodiment corresponds to the element body of the present invention, the first internal cavity 20 corresponds to the oxygen concentration adjustment chamber, the inner pump electrode 22 corresponds to the adjustment pump electrode, and the main pump cell 21 is adjusted. The third internal cavity 61 corresponds to the measuring chamber, the measuring electrode 44 corresponds to the measuring electrode, the detection electrode 56 corresponds to the detection electrode, and the mixed potential cell 55 corresponds to the mixed potential cell. , the heater 72 corresponds to the heater.

According to the gas sensor 100 of the present embodiment described above, the sensing electrode 56 , the inner pump electrode 22 and the heater 72 of the sensor element 101 are heated by the heater 72 when the sensing electrode 56 and the inner pump electrode 22 are heated. The electrode 22 is arranged to have a higher temperature than the detection electrode 56, and the distance A between the detection electrode 56 and the inner pump electrode 22 in the front-rear direction is 1 mm or more. Thereby, the specific oxide gas concentration and ammonia concentration in the gas to be measured can be detected with high accuracy. Furthermore, since the distance L in the front-rear direction from the gas inlet 10 to the measurement electrode 44 is 13 mm or less, it is possible to suppress a decrease in responsiveness in detecting the NOx concentration. As described above, the gas sensor 100 of the present embodiment can accurately detect the NOx concentration and the ammonia concentration in the gas to be measured, and can suppress the deterioration of the NOx concentration detection responsiveness.

Further, since 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. Therefore, the sensor element 101 is resistant to thermal shock, and cracking of the sensor element 101 due to thermal shock can be suppressed. A thermal shock applied to the sensor element 101 is caused, for example, by adhesion of moisture in the gas to be measured.

Furthermore, the detection electrode 56 is provided forward of the inner pump electrode 22 and outside the element main body 101a so as to be in contact with the gas to be measured. That is, the detection electrode 56 is provided near the front end of the element body 101a and outside the element body 101a. This makes it easier for the gas to be measured to reach the detection electrode 56 and improves the responsiveness of ammonia concentration detection, compared to the case where the detection electrode 56 is disposed in the gas flow portion to be measured.

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 detection electrode 56 is arranged outside the element body 101a, but may be arranged inside the element body 101a. For example, the sensing electrode 56 may be provided on the upstream side of the first internal cavity 20 in the measured gas circulation section. FIG. 4 is an enlarged cross-sectional view showing the arrangement of detection electrodes 156 of a modified example. A detection electrode 156 is provided in the buffer space 12 upstream of the second diffusion rate-limiting section 13 . Also, the sensing electrode 156 has a tunnel-like structure in the buffer space 12 , similar to the inner pump electrode 22 and the auxiliary pump electrode 51 . Specifically, the sensing electrode 156 consists of a ceiling electrode portion 156a formed on the lower surface of the second solid electrolyte layer 6, which is the ceiling surface of the buffer space 12, and the first solid electrolyte layer 4, which is the bottom surface of the buffer space 12. It has a bottom electrode portion 156b formed on the upper surface and a side electrode portion (not shown) formed to connect the ceiling electrode portion 156a and the bottom electrode portion 156b. Even when the detection electrode 156 is arranged in this way, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer, which are the solid electrolyte layers between the detection electrode 156 and the reference electrode 42, and the solid electrolyte layers therebetween, 3 constitute a mixed potential cell 55 . Then, the detection electrode 156 produces a mixed potential corresponding to the ammonia concentration. Therefore, the concentration of ammonia in the gas to be measured can be detected based on the electromotive force EMF of the mixed potential cell 55, as in the above-described embodiment. In addition, in the example of FIG. 4, the element main body 101a does not include the first diffusion control portion 11 unlike the embodiment described above, and the opening area of the gas introduction port 10 is larger than that in the embodiment described above. This makes it easier for the gas to be measured to reach the detection electrode 156 , thereby improving the responsiveness of detection of the ammonia concentration by the detection electrode 156 . Therefore, it is preferable to omit the first diffusion control section 11 as shown in FIG. FIG. 4 also shows the distance A between the sensing electrode 156 and the inner pump electrode 22 and the distance B from the front end of the inner pump electrode 22 to the front end of the measuring electrode 44 . Note that the sensing electrode 156 may be arranged on either the bottom surface of the second solid electrolyte layer 6 or the top surface of the first solid electrolyte layer 4 without having a tunnel structure. Also, the first diffusion rate-limiting section 11 may not be omitted.

When the detection electrode 156 is provided on the upstream side of the first internal space 20 in the gas flow part to be measured as shown in FIG. The following are preferable. 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 around the detection electrode 156 is relatively short, so the responsiveness of the sensor element 101 to detect the NOx concentration is reduced. 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.

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. 5, the third internal cavity 61 may not be provided. In the sensor element 201 of the modified example shown in FIG. 5, 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 first diffusion control section 11, The buffer space 12, the second diffusion rate-controlling portion 13, the first internal space 20, the third diffusion rate-controlling portion 30, and the second internal space 40 are formed adjacently in a manner communicating in this order. . Also, 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 fourth diffusion control portion 45 . The fourth diffusion control portion 45 is a film made of a ceramic porous material such as alumina (Al ₂ O ₃ ). The fourth diffusion rate-controlling part 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, like the fourth diffusion rate-controlling part 60 of the above-described embodiment. Further, the fourth diffusion rate-limiting part 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 may include at least one oxygen ion-conducting solid electrolyte layer, and may be provided with a gas flow portion to be measured 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 voltage V2 becomes the target value V2* as the measurement pump control processing. ), the NOx concentration in the gas to be measured is detected, but the present invention 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 (voltage V2) at this time 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 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. For example, the correspondence relationship between the voltage 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 voltage V0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1* (feedback control), and the voltage V0 reaches the target value Ip1*. Although the pump voltage Vp0 is feedback-controlled so as to be 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 voltage 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 ( Consequently, the pump current Ip0 may be controlled).

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 2 to 6 and 9 to 13 correspond to examples of the present invention, and Experimental Examples 1, 7, 8 and 14 correspond to comparative examples. In addition, the present invention is not limited to the following examples.

[Experimental Examples 1 to 7]
Experimental Examples 1 to 7 were obtained by changing the distance A and the distance L of the sensor element 101 of the gas sensor 100 shown in FIGS. 1 to 3 as shown in Table 2 below. For each of Experimental Examples 1 to 7, whether or not the sensor element 101 can be heated by the heater 72 so as to achieve both the pumping ability of the inner pump electrode 22 and the detection accuracy of the ammonia concentration using the detection electrode 56. examined. 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, an evaluation of the pumping capacity of the inner pump electrode 22, which will be described later, and an evaluation of the ammonia concentration detection accuracy using the detection electrode 56 were performed, and it was examined whether or not both evaluations were "excellent." . If at least one of the evaluations is not "excellent", is it possible to change the target temperature of the heater 72 and heat the sensor element 101 with the heater 72 so that both evaluations are "excellent"? I checked whether For each of the gas sensors 100 of Experimental Examples 2 to 7, similarly to Experimental Example 1, it was examined whether or not the sensor element 101 could be heated by the heater 72 so that both evaluations would be "excellent."

Evaluation of the pumping capacity of the inner pump electrode 22 was performed as follows. While the control unit 91 is performing the above-described control, a model gas having a nitrogen base gas and a NOx concentration of 500 ppm is used as the gas to be measured. The value of the pump current Ip2 after this was examined. Based on the correct pump current Ip2 value corresponding to the NOx concentration of 500 ppm as a reference (100%), the obtained value of the pump current Ip2 expressed in percentage was calculated as the NOx concentration detection sensitivity (%) value. . Then, when the sensitivity of NOx concentration detection exceeds 95%, the pumping ability of the inner pump electrode 22 is judged to be "excellent", and when it is 95% or less, the pumping ability of the inner pumping electrode 22 is judged to be "impossible". I judged. Here, if the oxygen pumping capacity of the inner pump electrode 22 is low, the amount of oxygen pumped out of the first internal space 20 by the main pump cell 21 will be insufficient, and the voltage V0 will not easily reach the target value V0*. As a result, the controller 91 controls the variable power supply 24 so as to increase the pump voltage Vp0. If the pump voltage Vp0 is too high, the NOx in the gas to be measured is likely to be decomposed in the first internal space 20, so the value of the pump current Ip2 becomes smaller than the correct value corresponding to the actual NOx concentration. That is, the sensitivity of NOx concentration detection is lowered. Therefore, the oxygen pumping ability of the inner pump electrode 22 can be evaluated by the sensitivity of NOx concentration detection.

Evaluation of the detection accuracy of the ammonia concentration was performed as follows. While the controller 91 is performing the above-described control, a model gas having a nitrogen base gas and an ammonia concentration of 500 ppm is used as the gas to be measured. We waited until the value of The value of the electromotive force EMF after stabilization was used as 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 using the detection electrode 56 . Then, when the electromotive force EMF was 170 mV or more, the ammonia concentration detection accuracy was determined as "excellent", and when the electromotive force EMF was less than 170 mV, the ammonia concentration detection accuracy was determined as "poor".

Also, for each of Experimental Examples 1 to 7, the relationship between the distance L and the responsiveness of NOx concentration detection was examined. Specifically, first, in a state where the control unit 91 is performing the above-described control, a model gas having a base gas of nitrogen and a NOx concentration of 0 ppm is used as the gas to be measured. We waited until the value of the current Ip2 stabilized. 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)".

Further, for each of Experimental Examples 1 to 7, the difference between the minimum temperature of the detection electrode 56 and the maximum temperature of the inner pump electrode 22 was examined when the heater 72 reached the target temperature.

Table 1 shows the distance A and the distance L in each of Experimental Examples 1 to 7, and the determination result of whether or not the pumping capacity of the inner pump electrode 22 and the detection accuracy of the ammonia concentration using the detection electrode 56 are compatible. , NOx concentration detection response time, responsiveness evaluation, and the difference between the minimum temperature of the detection electrode 56 and the maximum temperature of the inner pump electrode 22 are shown together.

As shown in Table 1, in Experimental Examples 2 to 7 in which the distance A was 1 mm or more, both the pumping ability of the inner pump electrode 22 and the detection accuracy of the ammonia concentration using the detection electrode 56 were compatible. On the other hand, in Experimental Example 1 in which the distance A was 0 mm, both were not possible. Specifically, in Experimental Example 1, when the target temperature of the heater 72 is lowered, the evaluation of the pumping ability of the inner pumping electrode 22 becomes "impossible" and the evaluation of the pumping ability of the inner pumping electrode 22 becomes "excellent". When the target temperature was increased, the evaluation of the ammonia concentration detection accuracy using the detection electrode 56 was "impossible". From the results of Experimental Examples 1 to 7, it was confirmed that both the main pump cell 21 and the mixed potential cell 55 can be properly operated when the distance A is 1 mm or more.

Also, it was confirmed that the smaller the distance L, the shorter the response time for NOx concentration detection. Specifically, in Experimental Examples 1 to 6 in which the distance L is 13 mm or less, the response time for NOx concentration detection is all 1.2 sec or less, and the responsiveness is evaluated as "A (excellent)" or " B (acceptable)”. In particular, in Experimental Examples 1 to 4 in which the distance L was 11 mm or less, the NOx concentration detection response time was 1.1 sec or less, and the responsiveness was evaluated as "A (excellent)." On the other hand, in Experimental Example 7, in which the distance L exceeds 13 mm, the NOx concentration detection response time was 1.3 sec or longer, and the responsiveness was evaluated as "F (impossible)." From these results, it was confirmed that if the distance L is 13 mm or less, it is possible to suppress a decrease in the responsiveness of NOx concentration detection.

From the above results, if the distance A is 1 mm or more and the distance L is 13 mm or less as in Experimental Examples 2 to 6, the NOx concentration and ammonia concentration in the gas to be measured can be accurately detected, and the NOx concentration detection response It was confirmed that the decrease in sex can be suppressed.

Further, in Experimental Examples 1 to 5 in which the distance A was 4 mm or less, the difference between the lowest temperature of the detection electrode 56 and the highest temperature of the inner pump electrode 22 was 400° C. or less. It was confirmed that the temperature difference did not become too large.

[Experimental Examples 8 to 14]
As shown in FIG. 4, regarding the sensor element 101 in which the detection electrode 156 is arranged inside the element body 101a, the distance C, the distance A, and the distance L are variously changed as shown in Table 2 below. , respectively, as Experimental Examples 8 to 14. In Experimental Examples 8 to 14, the distance B was set to 6 mm. For each of Experimental Examples 8 to 14, 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 2 shows distance C, distance A, distance L, ammonia concentration detection response time, NOx concentration detection response time, difference in response time, and response time difference in each of Experimental Examples 8 to 14. are shown collectively.

As shown in Table 2, it was confirmed that the smaller the distance C, the smaller the difference between the response time for detecting the ammonia concentration and the response time for detecting the NOx concentration. Specifically, in Experimental Examples 8 to 13 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 8 to 11 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 14 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.

In Experimental Examples 8 to 14, the distance A and the distance L were changed in the same manner as in Experimental Examples 1 to 7, and the same results as in Table 1 were obtained for Experimental Examples 8 to 14 as well. For example, in Experimental Examples 9 to 13 in which the distance A is 1 mm or more and the distance L is 13 mm or less, it is possible to achieve both the pumping ability of the inner pump electrode 22 and the ammonia concentration detection accuracy using the detection electrode 156, and NOx The evaluation of concentration detection responsiveness was "excellent (A)" or "fair (B)".

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 10 gas inlet 11 first diffusion control section 12 buffer space, 13 second diffusion rate-limiting section, 20 first internal cavity, 21 main pump cell, 22 inner pump electrode, 22a ceiling electrode section, 22b bottom electrode section, 23 outer pump electrode, 24 variable power supply, 30 third diffusion rate-limiting section , 40 second internal cavity, 41 measurement pump cell, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 45 fourth diffusion rate-limiting section, 46 variable power source, 48 atmosphere introduction layer, 50 auxiliary pump cell, 51 auxiliary pump Electrode 51a Ceiling electrode portion 51b Bottom electrode portion 52 Variable power source 55 Mixed potential cell 56 Detection electrode 60 Fourth diffusion rate-determining portion 61 Third internal space 70 Heater portion 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 oxygen partial pressure detection sensor cell for measurement pump control 83 Sensor cell 84 Buffer layer 84a Upper buffer layer 84b Lower buffer layer 85 Protective layer 90 Control device 91 Control unit 92 CPU 94 Storage unit 100 Gas sensor 101, 201 Sensor element 101a Element body 156 Sensing electrode, 156a ceiling electrode portion, 156b bottom electrode portion.

Claims (7)

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 on the element body 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
With the longitudinal direction of the element body as the front-rear direction, the adjustment pump electrode and the measurement electrode are disposed on the front side of the element body,
The detection electrode is disposed in front of the adjustment pump electrode in the element body,
The detection electrode, the adjustment pump electrode, and the heater are arranged so that the adjustment pump electrode becomes hotter than the detection electrode when heated by the heater,
The distance A in the front-rear direction between the detection electrode and the adjustment pump electrode is 1 mm or more,
The distance L in the front-rear direction from the gas introduction port, which is the entrance of the gas flow part to be measured, to the measurement electrode is 13 mm or less.
sensor element. The distance A is 4 mm or less,
A sensor element according to claim 1 . The sensing electrode is arranged outside the element body so as to be in contact with the gas to be measured.
3. A sensor element according to claim 1 or 2. The detection electrode is provided on the upstream side of the oxygen concentration adjustment chamber in the measurement gas circulation section,
3. A sensor element according to claim 1 or 2. The distance C between the detection electrode and the measurement electrode in the front-rear direction is 11 mm or less,
5. A sensor element according to claim 4. The gas introduction port is open to the front end surface of the element 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 sensor element according to any one of claims 1-5. A gas sensor comprising the sensor element according to any one of claims 1 to 6.

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