JP7124644B2 - gas sensor element - Google Patents

Description

The present invention relates to a gas sensor element that detects a specific gas contained in a gas to be measured.

2. Description of the Related Art Conventionally, a gas sensor installed in an exhaust system of an internal combustion engine has been used to control combustion of the internal combustion engine, control of an exhaust gas purifier, and the like. Such a gas sensor includes a gas sensor element having an oxygen ion-conducting solid electrolyte layer, and utilizes the movement of oxygen ions through an electrode formed on the surface of the solid electrolyte layer to detect a specific gas (e.g., oxygen, NOx, etc.).

For example, Patent Document 1 discloses a pump cell that consists of a pair of electrodes provided on the surface of a solid electrolyte layer, respectively, for adjusting the oxygen concentration in the gas to be measured, a sensor cell for detecting the NOx concentration in the gas to be measured, A gas sensor element is disclosed comprising: A measured gas chamber into which a measured gas is taken is provided inside the gas sensor element, and a pair of electrodes of the pump cell and the sensor cell are arranged such that one faces the measured gas chamber.

In the gas sensor element configured as described above, a diffusion resistance layer is provided at the gas inlet to the gas chamber to be measured, and the gas to be measured has a predetermined diffusion resistance and is introduced into the gas chamber to be measured. At this time, if the diffusion resistance is reduced in order to improve the responsiveness, on the other hand, the detection accuracy of the gas sensor element tends to decrease. Therefore, in Patent Document 1, in order to achieve both responsiveness and detection accuracy, the product of the ratio of the diffusion length to the cross-sectional area in the diffusion resistance layer and the ratio of the diffusion length to the cross-sectional area in the gas chamber to be measured is set to a predetermined value. The dimensions of the gas sensor element are defined so as to be within the range.

JP 2016-028226 A

The gas sensor element having the above structure usually has a built-in heater, and the energization is controlled so that each cell has a temperature equal to or higher than the activation temperature. However, it has been found that when the heater is energized, for example, in the insulator layer between which the gas chamber to be measured is provided between the solid electrolyte layer, the temperature tends to become non-uniform, and the element cracks easily occur due to thermal stress. On the other hand, for example, it has been studied to narrow the temperature distribution by reducing the width of the gas chamber to be measured. There is a risk that the amount of gas taken in from the diffusion resistance layer will decrease, resulting in a decrease in detection accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a gas sensor element capable of suppressing element cracking due to thermal stress, suppressing a decrease in gas intake, and maintaining good detection performance. It is.

One aspect of the present invention is
a measured gas chamber (2) into which the measured gas is introduced;
a porous diffusion resistance layer (21) arranged at a gas introduction port to the gas chamber to be measured;
an oxygen ion conductive solid electrolyte layer (11) forming the bottom wall (2a) of the gas chamber to be measured;
an insulating layer (12) forming the sidewall (2b) and the top wall (2c) of the gas chamber to be measured;
an oxygen sensing cell (3) having an oxygen sensing electrode (31) disposed on the surface of said bottom wall;
a heater (4) comprising a heating element (41);
The measured gas chamber has a width direction Y in a plane parallel to the bottom wall, and a direction perpendicular to the gas flow direction X in the measured gas chamber. The width W1 of the gas chamber to be measured and the width W2 of the end surface (21a) of the diffusion resistance layer on the gas introduction side have a relationship of W1<W2, and the width W1<W2 of the gas flow direction upstream side of the gas flow direction. The gas sensor element (1) has a relationship of h1>h2 between the height h1 of the gas chamber to be measured and the height h2 of the diffusion resistance layer at the end .
Another aspect of the present invention is
a measured gas chamber (2) into which the measured gas is introduced;
a porous diffusion resistance layer (21) arranged at a gas introduction port to the gas chamber to be measured;
an oxygen ion conductive solid electrolyte layer (11) forming the bottom wall (2a) of the gas chamber to be measured;
an insulating layer (12) forming the sidewall (2b) and the top wall (2c) of the gas chamber to be measured;
an oxygen sensing cell (3) having an oxygen sensing electrode (31) disposed on the surface of said bottom wall;
a heater (4) comprising a heating element (41);
The measured gas chamber has a width direction Y in a plane parallel to the bottom wall, and a direction perpendicular to a gas flow direction X in the measured gas chamber. The width W1 of the chamber and the width W2 of the diffusion resistance layer have a relationship of W1<W2,
In the plane parallel to the bottom wall, both corners (211, 212) in the width direction of the end face (21a) of the diffusion resistance layer on the gas introduction side and the width of the opening of the gas chamber to be measured on the gas introduction side The intersection (P) of the extension lines (L1, L2) of the line segments connecting both corners (111, 112) of the direction is the line segment (L3) passing through the center position of the oxygen detection electrode in the width direction. Located above, in the gas sensor element (1).

In the gas sensor element, the width W2 of the diffusion resistance layer serving as the gas introduction port to the gas chamber to be measured is larger than the width W1 of the bottom wall of the gas chamber to be measured. Even in this case, it is possible to secure the amount of the gas to be measured that is taken into the gas chamber to be measured, and to suppress the deterioration of the detection accuracy of the oxygen detection cell. In addition, by increasing the width, the gas to be measured can be easily introduced into the entire oxygen detecting electrode, and the risk of crushing during the manufacturing process is smaller than when the electrode is increased in the height direction.

Therefore, according to the above aspect, it is possible to provide a gas sensor element capable of suppressing element cracking due to thermal stress, suppressing a decrease in gas intake, and maintaining good detection performance.
It should be noted that the symbols in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the embodiments described later, and limit the technical scope of the present invention. not a thing

FIG. 3 is a longitudinal sectional view of the tip portion and a sectional view along the line AA thereof, schematically showing the basic structure of the gas sensor element and the flow of gas introduced into the gas chamber to be measured according to the first embodiment; FIG. 2 is a lateral cross-sectional view of the distal end portion showing the basic structure of the gas sensor element in the first embodiment; 1 is an overall cross-sectional view of a gas sensor incorporating a gas sensor element according to Embodiment 1. FIG. FIG. 2 is a longitudinal cross-sectional view of the distal end portion showing the detailed structure of the gas sensor element in the first embodiment; FIG. 5 is a longitudinal cross-sectional view of the distal end portion showing the detailed structure of the gas sensor element in Embodiment 1, and is a cross-sectional view taken along the line BB of FIG. 4; 4A and 4B are schematic views of the surface of the solid electrolyte layer on the side of the measured gas chamber and the surface on the side of the reference gas chamber, showing an example of arrangement of the lead portions of the gas sensor element in the first embodiment; FIG. 10 is a longitudinal sectional view of the distal end portion showing the basic structure of the gas sensor element in Embodiment 2; 4 is a diagram showing the relationship between the difference (W2−W1) between the width of the diffusion resistance layer of the gas sensor element and the width of the gas chamber to be measured and the A/F detection accuracy in Test Example 1. FIG. FIG. 10 is a diagram showing the relationship between the width W2 of the diffusion resistance layer and the A/F detection accuracy in Test Example 1; 4 is a diagram showing the relationship between the height h2 of the diffusion resistance layer and the A/F detection accuracy in Test Example 1. FIG. 4 is a diagram showing the relationship between the height h2 of the diffusion resistance layer and the A/F detection accuracy and A/F responsiveness in Test Example 1. FIG.

(Embodiment 1)
Embodiment 1 of the gas sensor element will be described below with reference to FIGS. 1 to 6. FIG.
The gas sensor element 1 of the present embodiment, the basic structure of which is shown in FIGS. 1 and 2, is a laminated sensor element, which is incorporated in the gas sensor S shown in FIG. 3 and detects the concentration of a specific gas contained in the gas to be measured. The gas to be measured is, for example, exhaust gas emitted from an internal combustion engine, and the gas sensor S is installed in the exhaust gas passage of the internal combustion engine. The fuel ratio, NOx concentration, etc. are detected.

In FIGS. 1 and 2, the gas sensor element 1 is
a measured gas chamber 2 into which the measured gas is introduced;
a porous diffusion resistance layer 21 arranged at a gas introduction port to the gas chamber 2 to be measured;
an oxygen ion conductive solid electrolyte layer 11 forming the bottom wall 2a of the gas chamber 2 to be measured;
an insulator layer 12 forming the side wall 2b and the top wall 2c of the gas chamber 2 to be measured;
an oxygen detection cell (eg, oxygen pump cell 3) having an oxygen detection electrode (eg, oxygen pump electrode 31) disposed on the surface of bottom wall 11a;
and a heater 4 having a heating element 41 .

Here, in the plane parallel to the bottom wall of the measured gas chamber 2, the direction perpendicular to the gas flow direction X in the measured gas chamber 2 is defined as the width direction Y, which is expressed by the width of the bottom wall 2a. The width W1 of the gas chamber 2 to be measured and the width W2 of the diffusion resistance layer 21 have a relationship of W1<W2 (for example, see the upper diagram of FIG. 1). The end face 21a on the gas introduction side of the diffusion resistance layer 21 is positioned on the outer surface of the gas sensor element 1 and is exposed to the exhaust gas, and the end face 21b on the gas outlet side faces the gas chamber 2 to be measured.

At this time, in the gas sensor element 1, since the width W2 of the diffusion resistance layer 21 serving as an intake port for the exhaust gas is larger than the width W1 of the measured gas chamber 2 located downstream in the gas flow direction X, the diffusion resistance layer 21 can easily secure the intake amount of exhaust gas. Since the exhaust gas is introduced from the entire width direction Y onto the surface of the oxygen pump electrode 31 of the oxygen pump cell 3 formed on the bottom wall 2a, the pumping action is accelerated and the detection accuracy can be improved. .

Such a gas sensor element 1 can be configured as a laminated element in which an insulator layer 12 and a heater 4 are laminated with a solid electrolyte layer 11 interposed therebetween (see FIG. 2, for example).
The gas chamber 2 to be measured is composed of a solid electrolyte layer 11 and an insulating layer 12 having recesses formed thereon to form side walls 2b and a top wall 2c. In the stacking direction Z (for example, the vertical direction in the lower diagram of FIG. 1), the diffusion resistance layer 21 is arranged between the insulator layer 12 and the bottom wall 2a, and constitutes part of the side wall 2b rising from the bottom wall 2a. ing.
Preferably, the height h1 of the measured gas chamber at the upstream end in the gas flow direction X and the height h2 of the diffusion resistance layer 21 have a relationship of h1>h2.

The oxygen detection cell can be configured, for example, as an oxygen pump cell 3 with oxygen pumping action. The oxygen pump cell 3 has an oxygen pump electrode 31 as an oxygen detection electrode and a reference electrode (not shown) on the surface of the solid electrolyte layer 11 . Oxygen is pumped so as to exhaust or introduce oxygen into the gas chamber 2 to be measured. The pump current flowing at that time exhibits limiting current characteristics according to the oxygen concentration in the gas chamber 2 to be measured, and has a correlation with the air-fuel ratio (A/F) of the exhaust gas. of the air-fuel ratio can be detected.

Further, the gas sensor element 1 may have a plurality of cells including the oxygen pump cell 3 arranged in the gas chamber 2 to be measured.
For example, as will be described later, when the gas sensor S is applied to a NOx sensor or the like, a sensor cell 5 for detecting a specific gas such as NOx is provided in addition to the oxygen pump cell 3 (for example, see FIG. 4). The sensor cell 5 has a sensor electrode 51 arranged on the surface of the bottom wall 11 a , the sensor electrode 51 being arranged downstream of the oxygen pump electrode 31 in the direction X of gas flow. At this time, the oxygen pump cell 3 pumps oxygen in the exhaust gas introduced into the gas chamber 2 to be measured to adjust the oxygen concentration in the exhaust gas introduced into the downstream sensor cell 5 .

Next, detailed configurations of the gas sensor element 1 and the gas sensor S will be described.
3, the gas sensor S comprises a cylindrical housing 101 in which the gas sensor element 1 is held, an element cover 102 and an atmospheric side cover 103 fixed to the housing 101, and a control circuit section 104 connected to the gas sensor element 1. have The gas sensor element 1 is inserted into and held by a tubular insulator 105 housed inside the housing 101 , and the tip side projecting from the housing 101 (for example, the lower end side in FIG. 3 ) is fixed to the tip side of the housing 101 . It is housed within the element cover 102 . Also, the base end side projecting from the housing 101 (for example, the upper end side in FIG. 3) is accommodated in an atmosphere side cover 103 fixed to the base end side of the housing 101 .

The gas sensor element 1 is an elongated plate-like body whose longitudinal direction is the axial direction of the gas sensor S (for example, the vertical direction in FIG. 3). ) is formed. The gas sensor S is inserted through and fixed to an exhaust gas passage wall (not shown) so that the tip side of the gas sensor element 1 covered with the element cover 102 is exposed to the exhaust gas. The element cover 102 has, for example, a double cover structure consisting of a container-like inner cover 102a and an outer cover 102b. to reach

One end of lead portion 106 is connected to the proximal end of gas sensor element 1 , and the other end of lead portion 106 is connected to control circuit portion 104 . The control circuit unit 104 controls energization of the gas sensor element 1 to the oxygen pump cell 3 and the like, and also includes a detection control circuit for calculating a specific gas concentration such as an oxygen concentration based on the output from the gas sensor element 1, a heater A heater control circuit or the like is provided for controlling the energization of the gas sensor element 1 to a predetermined temperature.

The control circuit unit 104 may be provided integrally with an electronic control unit (ECU) (not shown) that controls the internal combustion engine based on the detection result from the gas sensor S, or may be provided separately so that the ECU Alternatively, each part of the gas sensor element 1 may be energized based on the control signal of , or the specific gas concentration may be calculated and output to the ECU.

4 and 5 show a detailed configuration example of the gas sensor element 1. Here, it is configured as a NOx sensor element for examining the NOx concentration in exhaust gas. The NOx sensor element has a three-cell structure in which a NOx sensor cell 5 and a monitor cell 6 as sensor cells are provided in addition to the oxygen pump cell 3 inside the gas sensor element 1 . The oxygen pump electrode 31 of the oxygen pump cell 3, the sensor electrode 51 of the NOx sensor cell 5, and the monitor electrode 61 of the monitor cell 6 are arranged on the surface of the solid electrolyte layer 11 that forms the bottom wall 2a of the gas chamber 2 to be measured.

The gas sensor element 1 is composed of a rectangular parallelepiped ceramic laminate obtained by laminating a plurality of flat ceramic layers. The plurality of ceramic layers are a solid electrolyte layer 11, an insulator layer 12 laminated on one surface thereof, and a heater-side insulator layer 13 laminated on the other surface. An integrated ceramic laminate is obtained by molding into an external shape, stacking and firing.
The solid electrolyte layer 11 is made of a solid electrolyte having oxygen ion conductivity, and may be made of a zirconia-based solid electrolyte such as stabilized zirconia or partially stabilized zirconia in which a stabilizer such as yttria is dissolved. can.
The insulator layer 12 and the heater-side insulator layer 13 are made of an insulating material that does not permeate the gas to be measured, such as alumina.

Inside the gas sensor element 1 , the measured gas chamber 2 is arranged on one surface side of the solid electrolyte layer 11 , and the exhaust gas is introduced through the porous diffusion resistance layer 21 . The measured gas chamber 2 is a flat rectangular parallelepiped chamber-like space provided between the solid electrolyte layer 11 and the insulator layer 12, and the longitudinal direction and the lateral direction of the measured gas chamber 2 are the gas sensor element 1 coincides with the longitudinal direction and the transverse direction.

A reference gas chamber 7 and a heater 4 are stacked in this order on the other surface side of the solid electrolyte layer 11 . The reference gas chamber 7 is a duct-shaped space provided between the solid electrolyte layer 11 and the heater-side insulator layer 13, and extends from a position facing the gas chamber 2 to be measured in the stacking direction Z to the base end side. longitudinally extending toward. Air, which serves as a reference gas, is introduced into the reference gas chamber 5 from an opening on the proximal side (not shown).

The heater 4 has a heater base layer 42 forming a part of the heater-side insulator layer 13 and a heating element 41 embedded in the heater base layer 42 . The heating element 41 is provided corresponding to the formation position of the gas chamber 2 to be measured, and a heater lead 43 is connected to the base end side of the heating element 41 . The heater 4 can heat the oxygen pump cell 3 and the like having electrodes arranged on the surface of the solid electrolyte layer 11 by energizing the heating element 41 through the heater lead 43 .

The diffusion resistance layer 21 is embedded in the tip portion of the gas sensor element 1, and the tip end face 21a, which is the end face on the gas introduction side, is flush with the tip face of the gas sensor element 1, and is the end face on the gas lead-out side. The proximal end surface 21b is positioned to face the gas chamber 2 to be measured, and constitutes a gas introduction port to the gas chamber 2 to be measured.
At this time, the gas flow direction X inside the gas chamber 2 to be measured is the longitudinal direction of the gas chamber 2 to be measured and the gas sensor element 1, and the direction perpendicular to the gas flow direction X is the width direction of the gas chamber 2 to be measured ( That is, the lateral direction) becomes Y. The exhaust gas passes through the diffusion resistance layer 21 on the front end side of the gas chamber 2 to be measured, and flows in the longitudinal direction (for example, the left-right direction in FIGS. 4 and 5) from the upstream side to the downstream side in the gas flow direction X. flow.

The solid electrolyte layer 11 constitutes the bottom wall 2a of the gas chamber 2 to be measured, and the insulator layer 12 constitutes the side wall 2b and the top wall 2c of the gas chamber 2 to be measured. The insulator layer 12 has a two-layer structure. In the stacking direction Z, the first insulator layer 12a, which is the outermost layer of the gas sensor element 1, faces the gas chamber 2 to be measured. 2c. The second insulator layer 12b arranged between the first insulator layer 12a and the solid electrolyte layer 11 has a rectangular punched hole at a position corresponding to the gas chamber 2 to be measured, and the inner wall of the punched hole is covered. It serves as a side wall 2 b of the measurement gas chamber 2 .

The solid electrolyte layer 11 constitutes the top wall 7c of the reference gas chamber 7, and the heater-side insulator layer 13 constitutes the bottom wall 7a and side walls 7b of the reference gas chamber 7. As shown in FIG. The heater-side insulator layer 13 has a two-layer structure, and includes a heater base layer 42 forming the heater 4 and a third insulator layer 13 a arranged between the solid electrolyte layer 11 and the heater base layer 42 . In the third insulator layer 13 a , a punched groove opening toward the base end is formed at a position corresponding to the reference gas chamber 7 , and the inner wall of the punched groove serves as the side wall 7 b of the reference gas chamber 7 . The surface of the heater base layer 42 facing the reference gas chamber 7 serves as the bottom wall 7 a of the reference gas chamber 7 .

On the surface of the solid electrolyte layer 11 that forms the bottom wall 2a of the gas chamber 2 to be measured, the oxygen pump electrode 31 of the oxygen pump cell 3 is arranged upstream in the gas flow direction X, and the NOx sensor cell 5 is arranged downstream thereof. The sensor electrode 51 and the monitor electrode 61 of the monitor cell 6 are arranged side by side in the width direction Y. As shown in FIG. The oxygen pump electrode 31, the sensor electrode 51, and the monitor electrode 61 are all rectangular with the gas flow direction X as the longitudinal direction and the width direction Y as the lateral direction, and the sensor electrode 51 and the monitor electrode 61 are substantially identical. It has a shape.
The electrode area of the oxygen pump electrode 31 is sufficiently large with respect to the sensor electrode 51 and the monitor electrode 61, and the longitudinal length L11 of the oxygen pump electrode 31 is longer than the longitudinal length L21 of the sensor electrode 51 and the monitor electrode 61. . The same applies to the length in the lateral direction. Thus, in a one-chamber structure in which the oxygen pump electrode, the sensor electrode 51 and the monitor electrode 61 are arranged upstream and downstream of the same gas chamber 2 to be measured, the oxygen concentration can be well adjusted by the oxygen pump cell 3 .

On the other hand, on the surface of the solid electrolyte layer 11 that forms the top wall 7c of the reference gas chamber 7, a common reference electrode 71 is arranged at a position facing the oxygen pump electrode 31, the sensor electrode 51 and the monitor electrode 61. As a result, the oxygen pump cell 3 comprising a pair of the oxygen pump electrode 31 and the reference electrode 71 facing each other with the solid electrolyte layer 11 interposed therebetween is formed. Similarly, a NOx sensor cell 5 consisting of the solid electrolyte layer 11 and a pair of sensor electrodes 51 and a reference electrode 71, and a monitor cell 6 consisting of the solid electrolyte layer 11 and a pair of monitor electrodes 61 and a reference electrode 71 are formed.

A pump electrode lead 32 connected to the proximal side of the oxygen pump electrode 31 is formed on the surface of the solid electrolyte layer 11 and extends to the proximal side of the solid electrolyte layer 11 . Similarly, a sensor electrode lead 52 and a monitor electrode lead 62 are connected to the base end sides of the sensor electrode 51 and the monitor electrode 61 and extend to the base end side of the solid electrolyte layer 11 . The same applies to the reference electrode 71 (not shown).

The oxygen pump electrode 31 and the reference electrode 71 are made of an electrode material containing noble metal as a main component. Preferably, the oxygen pump electrode 31 is an electrode with low NOx decomposition activity, such as a porous cermet electrode containing Pt and Au, to suppress the decomposition of NOx in the exhaust gas. At this time, by applying a predetermined voltage between the pair of electrodes of the oxygen pump cell 3, the oxygen in the exhaust gas reaching the oxygen pump electrode 31 is reduced to become oxygen ions, which permeate the solid electrolyte layer 11 and pass through the reference It is discharged to the electrode 71 side. By this pumping action, oxygen is discharged from the side of the oxygen pump electrode 31 facing the gas chamber 2 to be measured to the side of the reference electrode 71 facing the reference gas chamber 7, thereby increasing the oxygen concentration in the exhaust gas passing through the oxygen pump cell 3. , to a concentration suitable for NOx detection in the NOx sensor cell 5 .

The sensor electrode 51 and the monitor electrode 61 are made of an electrode material containing noble metal as a main component. Preferably, the sensor electrode 51 is an electrode with high NOx decomposition activity in the exhaust gas, such as a porous cermet electrode containing Pt and Rh, and the monitor electrode 61 is an electrode with low NOx decomposition activity, such as Pt and Au. A reference electrode 71 serving as a common electrode for the oxygen pump cell 3, the NOx sensor cell 5, and the monitor cell 6 is made of, for example, a porous cermet electrode containing Pt as a main component.

At this time, by applying a predetermined voltage between the pair of electrodes of the NOx sensor cell 5, the oxygen and NOx in the exhaust gas reaching the NOx sensor cell 5 are decomposed on the sensor electrode 51, and oxygen ions are converted into solids by a pumping action. It passes through the electrolyte layer 11 and is discharged to the reference electrode 71 side. The current flowing at that time is based on the concentrations of oxygen and NOx contained in the exhaust gas.
On the other hand, in the monitor cell 6, the oxygen reaching the monitor electrode 61 is decomposed and discharged to the reference electrode 71 side, and the current flowing at that time is based on the oxygen remaining in the exhaust gas.
Since the monitor cell 6 is located at the same position as the NOx sensor cell 5 in the gas flow direction X in the measured gas chamber 2, the NOx concentration can be accurately calculated from the output difference between the NOx sensor cell 5 and the monitor cell 6. Further, based on the output of the monitor cell 6, the voltage applied to the oxygen pump cell 3 may be controlled so that the residual oxygen concentration after passing through the oxygen pump cell 3 becomes a desired value.

Although the NOx sensor cell 5 and the monitor cell 6 here detect the pump current flowing between the pair of electrodes when a voltage is applied, they may detect the electromotive force generated between the pair of electrodes.

Here, the diffusion resistance layer 21 has an elongated rectangular parallelepiped shape in the width direction Y of the gas chamber 2 to be measured, and has a flat cross-sectional shape in which the length in the stacking direction Z is shorter than the length in the gas flow direction X. is doing. The diffusion resistance layer 21 is embedded between the solid electrolyte layer 11 and the second insulator layer 12b of the insulator layer 12 at the tip of the gas sensor element 1, and is positioned on the porous side wall 2b of the gas chamber 2 to be measured. and form a gas introduction port to the gas chamber 2 to be measured.

The width W2 of the diffusion resistance layer 21 is the length of the diffusion resistance layer 21 in the width direction Y, and as shown in FIG. be. The width W1 of the measured gas chamber 2 is represented by the length of the bottom wall 2a in the width direction Y, that is, the distance between the side walls 2b in the width direction Y. As shown in FIG. In this embodiment, since the gas chamber 2 to be measured has a rectangular parallelepiped shape, the cross-sectional shape in the stacking direction Z is constant (that is, a rectangular shape having the same shape as the bottom wall 2a), and the width W1 of the gas chamber 2 to be measured is It is substantially constant regardless of the position in the stacking direction Z or the gas flow direction X.
The width W2 of the diffusion resistance layer 21 is appropriately set within the range of the width W3 of the gas sensor element 1 or less. The width W3 of the gas sensor element 1 is the length in the width direction Y of the gas sensor element 1 in a plane parallel to the bottom wall 2a.

The diffusion resistance layer 21 is positioned in contact with the bottom wall 2a at the upstream end in the gas flow direction X, and forms part of the side wall 2b rising from the bottom wall 2a. At this time, as shown in FIG. 1, the height h2 of the diffusion resistance layer 21 is such that h1>h2 with respect to the height h1 of the measured gas chamber 2 at the upstream end in the gas flow direction X. in a relationship. The height h1 of the measured gas chamber 2 is the distance between the bottom wall 2a and the top wall 2c. It is approximately constant.

The diffusion resistance layer 21 can be made of the same insulating material as the insulator layer 12, and its porosity is adjusted so as to provide a predetermined diffusion resistance. At this time, by making the width W2 of the diffusion resistance layer 21 larger than the width W1 of the gas chamber 2 to be measured in the width direction Y, the exhaust gas passing through the diffusion resistance layer 21 is directed to the front end side of the gas chamber 2 to be measured. It is possible to take in a sufficient amount over the entirety of the width direction Y. In addition, by making the height h2 of the diffusion resistance layer 21 lower than the height h1 of the gas chamber 2 to be measured in the stacking direction Z, the diffusion resistance layer 21 is brought closer to the bottom wall 2a of the gas chamber 2 to be measured. The exhaust gas can easily pass through the vicinity of the oxygen pump electrode 31 arranged on the surface of the bottom wall 2a.

Therefore, the amount of gas taken into the gas chamber 2 to be measured can be ensured, and the entire oxygen pump cell 3 can be efficiently used to adjust the oxygen concentration to a desired value. Detection accuracy can be improved. Also, the diffusion distance of the exhaust gas is shortened, so the NOx responsiveness is improved.
As a result, even when the width W1 of the measured gas chamber 2 is reduced in order to relax the thermal stress during heating by the heater 4, the amount of gas taken in can be reduced by increasing the width W2 of the diffusion resistance layer 21. can be maintained, and good detection performance can be realized while suppressing element cracking.

When the width W1 of the gas chamber 2 to be measured becomes smaller than the conventional width, the widths of the oxygen pump electrode 31 of the oxygen pump cell 3, the sensor electrode 51 of the NOx sensor cell 5, and the monitor electrode 61 of the monitor cell 6 also become smaller. It is desirable that the impedance of the electrode section including the lead section does not change significantly. For example, if the width of each electrode is reduced and thus the electrode area is reduced, the width of the electrode lead connected to each electrode is set to be relatively large, and the electrode impedance is adjusted to a predetermined value. It is possible.

Specifically, as shown in FIG. 6, an oxygen pump electrode 31 is arranged on the front end side of the surface of the solid electrolyte layer 11 that forms the bottom portion 2a of the gas chamber 2 to be measured, and an oxygen pump electrode 31 is arranged on the base end side thereof. A sensor electrode 51 and a monitor electrode 61 having an electrode area smaller than that of the electrode 31 are arranged. In addition, the pump electrode lead 32 connected to the proximal side edge portion of the oxygen pump electrode 31 extends to the proximal side along the side of the sensor electrode 51 and the monitor electrode 61, and the sensor electrode lead 32 connected to the sensor electrode 51 extends to the proximal side. It is arranged in parallel with the monitor electrode lead 62 connected to the lead 52 and the monitor electrode 61 with a predetermined insulation distance.
At this time, the sensor electrode lead 52 and the monitor electrode lead 62 have approximately the same width, and the width W4 of the pump electrode lead 32 and the width W5 of the sensor electrode lead 52 and the monitor electrode 61 have a relationship of W4>W5. It is in.

Similarly, on the surface of the solid electrolyte layer 11 that forms the top portion 7c of the reference gas chamber 7, a reference electrode 71 is arranged on the distal end side, and a reference electrode lead 72 is arranged on the proximal end side. Also in this case, the width of the reference electrode lead 72 is set to be relatively large while the width of the reference electrode 71 is small. They are roughly equivalent.
The width W6 of the reference electrode lead 72, the width W4 of the pump electrode lead 32, and the width W5 of the sensor electrode lead 52 and the monitor electrode 61 have a relationship of W6>W4>W5.

(Embodiment 2)
A second embodiment of the gas sensor element will be described with reference to FIG.
In Embodiment 1, the gas sensor element 1 is configured as a NOx sensor element with a 3-cell structure, but in this embodiment, it is configured as an air-fuel ratio sensor element with a 1-cell structure. The basic configuration of the gas sensor element 1 and the gas sensor S using the gas sensor element 1 is the same as that of the first embodiment, and the differences will be mainly described below.
Note that, of the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

As shown in FIG. 7, in this embodiment, the gas sensor element 1 has a one-cell structure including an oxygen pump cell 3. , the oxygen pump electrode 31 of the oxygen pump cell 3 is arranged on the tip side. As in the first embodiment, the other surface of the solid electrolyte layer 11 constitutes the top wall 7c of the reference gas chamber 7 (not shown), and the reference electrode 71 is arranged opposite the oxygen pump electrode 31 .

In this configuration, when a voltage is applied between the pair of electrodes of the oxygen pump cell 3, oxygen in the exhaust gas taken into the gas chamber 2 to be measured through the diffusion resistance layer 21 is transferred from the oxygen pump electrode 31 side to the reference electrode. 71 side, or oxygen is pumped from the reference electrode 71 side to the oxygen pump electrode 31 side. Since the pump current that flows at this time changes according to the air-fuel ratio of the exhaust gas, the air-fuel ratio can be detected by detecting this as the output of the oxygen pump cell 3 .

Also in this embodiment, the width W2 of the diffusion resistance layer 21 is larger than the width W1 of the gas chamber 2 to be measured, and the relation is W1<W2. Further, the width W2 of the diffusion resistance layer 21 is smaller than the width W3 of the gas sensor element 1, and the relationship is W2<W3.
The diffusion resistance layer 21 is arranged in contact with the bottom wall 2a of the solid electrolyte layer 11, and as described above, the height h2 of the diffusion resistance layer 21 is There is a relationship of h1>h2 (see, for example, FIG. 1).

Specifically, as shown in Test Example 1 described later, the difference W2-W1 between the width W2 of the diffusion resistance layer 21 and the width W1 of the gas chamber 2 to be measured is larger than 0.5 mm (that is, W2-W1 >0.5 mm), preferably 0.6 mm or more (ie W2-W1≧0.6 mm). Thus, when the width W2 of the diffusion resistance layer 21 is larger than the width W1 of the gas chamber 2 to be measured, the gas flows from the both ends of the diffusion resistance layer 21 to the diffusion resistance layer 21 from various angles. By forming a flow to the inside of the gas chamber 2 to be measured, a sufficient amount of gas can be taken in.

Preferably, the size and arrangement of the diffusion resistance layer 21 are similar to those of the oxygen pump electrode 31 of the gas chamber 2 to be measured, as indicated by the phantom lines in FIG. It is preferable that they are set so as to have a predetermined relationship. Specifically, both corners 211 and 212 in the width direction Y of the end surface 21a on the gas introduction side of the diffusion resistance layer 21 and both corners 111 and 112 in the width direction Y of the opening on the gas introduction side of the gas chamber 2 to be measured. , the intersection point P of the extension lines L1 and L2 of the line segments is located on the line segment L3 passing through the central position of the oxygen pump electrode 31 in the width direction Y.
That is, the extension line L1 is a line segment that passes through the corner portion 211 on the gas introduction side of the diffusion resistance layer 21 and the corner portion 111 serving as the opening end of the gas chamber 2 to be measured on one side in the width direction Y. The extension line L2 is a line segment passing through the corner portion 212 of the diffusion resistance layer 21 on the gas introduction side and the corner portion 112 serving as the opening end of the gas chamber 2 to be measured on the other side in the width direction Y.

More preferably, the intersection point P is located on the upstream side of the central position C of the oxygen pump electrode 31 in the gas flow direction X.
By making the width W2 of the diffusion resistance layer 21 larger than the width W1 of the gas chamber 2 to be measured in this manner, for example, the exhaust gas is also introduced from the directions of the extension lines L1 and L2, and the gas is taken in. contribute to the increase in volume. At this time, since the intersection point P is positioned on the line segment L3, the exhaust gas to be introduced gathers at the place of the oxygen pump electrode 31 where the oxygen discharge capacity is the highest (that is, the temperature is the highest). becomes. Furthermore, by setting the intersection point P upstream of the central position C, the electrode area used for oxygen discharge can be increased, and the oxygen pump cell 3 can be effectively functioned. can be stabilized.

(Test example 1)
For the gas sensor element 1 having the configuration of the second embodiment, a plurality of test elements were produced by changing the width W1 of the gas chamber 2 to be measured or the width W2 of the diffusion resistance layer 21, and the relationship between element cracking and detection characteristics was investigated. Examined.
First, a plurality of samples were prepared by changing the difference between the width W1 of the gas chamber 2 to be measured and the width W2 of the diffusion resistance layer 21, and an air-fuel ratio detection test was performed on each sample using a test model gas. The width W1 of the measured gas chamber 2 is constant (W1≦2.5 mm), and the width W2 of the diffusion resistance layer 21 is changed so that the difference W2−W1 is in the range of 0 mm to 0.74 mm. The test results are shown in FIG. 8 for comparison. The air-fuel ratio detection test was performed a predetermined number of times for each test element, and the rate of detection variation with respect to the air-fuel ratio of the model gas was calculated, and the average value was taken as the A/F detection accuracy (unit: %).

As is clear from FIG. 8, the A/F detection accuracy is improved by changing W2-W1 from 0 mm to 0.2 mm. The larger W2-W1 is, the more the A/F detection accuracy is improved, especially in the range where W2-W1 is larger than 0.5 mm (eg, 0.52 mm, 0.74 mm), the A/F detection accuracy is further improved. is doing. Therefore, W2-W1 is preferably greater than 0.5 mm, more preferably 0.6 mm or greater.

Further, as shown in Table 1, the width W1 of the gas chamber 2 to be measured was changed in the range of 0.5 mm to 3.5 mm (that is, test elements 1 to 9). The presence or absence of element cracks was examined by performing a heating test using . The width W3 of the gas sensor element 1 was set constant (eg, 4.2 mm).
The heating test was performed by applying a voltage (for example, 14 V for 5 seconds) to the heaters 4 of the test elements 1 to 9 in still air to raise the temperature of the test elements. After completion of the heating test, a dyeing test was performed by immersing each test element in a dyeing solution, and the presence or absence of element cracks was determined visually.

As is clear from Table 1, no element cracks occurred in the test elements 1 to 7 in which the width W1 of the gas chamber 2 to be measured was 2.5 mm or less. On the other hand, element cracks were found in the test elements 8 and 9 in which the width W1 of the gas chamber 2 to be measured was larger than 2.5 mm. This is because when the gas sensor element 1 is heated by the heater 4, a difference occurs in heat transfer to the insulating layer 12 forming the wall of the gas chamber 2 to be measured. It is presumed that when σ increases, element cracking is more likely to occur due to thermal stress.
Therefore, by setting the width W1 of the gas chamber 2 to be measured 2 within the range of 0.5 mm to 2.5 mm, the thermal stress due to the difference in heat transfer can be alleviated, thereby suppressing element cracking. be done.

As shown in Table 1, FIG. 9 shows the width W2 of the diffusion resistance layer 21 and the A/F when the width W2 of the diffusion resistance layer 21 is decreased as the width W1 of the measured gas chamber 2 is decreased. The relationship between detection accuracy is shown. As shown in the figure, when the width W2 of the diffusion resistance layer 21 is 1.5 mm or more, good A/F detection accuracy is obtained regardless of the width W1 of the gas chamber 2 to be measured.
Therefore, the width W2 of the diffusion resistance layer 21 preferably has a width W1 of the gas chamber 2 to be measured within a range in which the lower limit is 1.5 mm and the width W3 of the gas sensor element 1 is the upper limit (for example, 4.2 mm). should be set to be greater than

FIG. 10 shows the relationship between the height h2 of the diffusion resistance layer 21 and the A/F detection accuracy. As shown, good A/F detection accuracy is obtained when the height h2 of the diffusion resistance layer 21 is in the range of 0.005 mm to 0.05 mm. It is presumed that this is because the amount of gas introduced from the diffusion resistance layer 21 into the measured gas chamber 2 is insufficient when the height h2 of the diffusion resistance layer 21 is less than 0.005 mm. Also, in the range higher than 0.05 mm, it is presumed that the porous diffusion resistance layer 21 is likely to be crushed in the lamination process when manufacturing the gas sensor element 1, and the amount of gas taken into the gas chamber 2 to be measured is reduced. Insufficient A/F detection accuracy may not be obtained.

FIG. 11 shows the relationship between the height h2 of the diffusion resistance layer 21 and the A/F detection accuracy and A/F responsiveness. A/F responsiveness is measured by performing an air-fuel ratio detection test using a test model gas, and when the reference gas is switched to a model gas with a predetermined air-fuel ratio, the test element detects a predetermined air-fuel ratio. It was evaluated by the response time up to
As shown, good A/F responsiveness is obtained when the height h2 of the diffusion resistance layer 21 is 0.04 mm or less. /F responsiveness tends to improve. It is presumed that this is because when the height h2 of the diffusion resistance layer 21 increases, the exhaust gas introduced into the measured gas chamber 2 becomes less likely to come into contact with the surface of the oxygen pump electrode 31 arranged on the bottom wall 2a. Above 0.04 mm, the A/F response sharply decreases.

Therefore, it is preferable that the height h2 of the diffusion resistance layer 21 is 0.05 mm or less, more preferably 0.04 mm or less, so that the amount of gas taken into the measured gas chamber 2 can be secured. Thus, it is desirable to appropriately set the width W1 of the diffusion resistance layer 21 and the like.

Even when the gas sensor element 1 is configured as the NOx sensor element shown in the first embodiment, the same tendency is observed in the NOx detection characteristics. That is, when the height h2 of the diffusion resistance layer 21 is lower than a certain height, the amount of gas taken in is insufficient and the NOx detection accuracy is lowered. NOx responsiveness tends to decrease.
In particular, in the case of the NOx sensor element, higher detection accuracy (for example, ppm order) is required than that of the air-fuel ratio sensor element. , 0.010 mm to 0.03 mm. As a result, both NOx detection accuracy and NOx responsiveness can be achieved, and excellent detection performance can be obtained.

The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the scope of the invention.
For example, in the above embodiment, the gas sensor element 1 is applied to the gas sensor S installed in the exhaust system of an internal combustion engine. It can be used for component detection. In the above embodiment, the three-cell structure gas sensor element 1 is described as a NOx sensor element for detecting NOx contained in exhaust gas, but the specific gas component is not limited to NOx, and may be SOx or the like.

1 gas sensor element 11 solid electrolyte layer 12 insulator layer 2 measured gas chamber 21 diffusion resistance layer 3 oxygen pump cell 31 oxygen pump electrode (oxygen detection electrode)
4 heater 5 sensor cell 51 sensor electrode

Claims (7)

a measured gas chamber (2) into which the measured gas is introduced;
a porous diffusion resistance layer (21) arranged at a gas introduction port to the gas chamber to be measured;
an oxygen ion conductive solid electrolyte layer (11) forming the bottom wall (2a) of the gas chamber to be measured;
an insulating layer (12) forming the sidewall (2b) and the top wall (2c) of the gas chamber to be measured;
an oxygen sensing cell (3) having an oxygen sensing electrode (31) disposed on the surface of said bottom wall;
a heater (4) comprising a heating element (41);
The measured gas chamber has a width direction Y in a plane parallel to the bottom wall, and a direction perpendicular to the gas flow direction X in the measured gas chamber. The width W1 of the gas chamber to be measured and the width W2 of the end surface (21a) of the diffusion resistance layer on the gas introduction side have a relationship of W1<W2, and the width W1<W2 of the gas flow direction upstream side of the gas flow direction. A gas sensor element (1) , wherein the height h1 of the gas chamber to be measured and the height h2 of the diffusion resistance layer at the end have a relationship of h1>h2 . The gas chamber to be measured is constructed by stacking the insulator layer on the solid electrolyte layer, the insulator layer having the side wall and the concave portion serving as the top wall.
2. The diffusion resistance layer is disposed between the insulator layer and the bottom wall at the upstream end in the gas flow direction, and constitutes part of the side wall rising from the bottom wall. The gas sensor element according to . 3. The gas sensor element according to claim 1, wherein the height h1 of the gas chamber to be measured and the width W1 of the gas chamber to be measured are constant in the gas flow direction. The oxygen detection cell has an oxygen pump electrode serving as the oxygen detection electrode and a reference electrode (71) on the surface of the solid electrolyte layer, and is an oxygen pump cell that pumps oxygen by applying a voltage between both electrodes. The gas sensor element according to any one of claims 1 to 3, wherein the gas sensor element is composed of A sensor electrode (41) disposed on the surface of the bottom wall on the downstream side of the oxygen detection electrode in the direction of gas flow is provided in the gas chamber to be measured to detect the concentration of a specific gas in the gas to be measured. The gas sensor element according to any one of claims 1 to 4, further comprising a sensor cell (4) for detection. a measured gas chamber (2) into which the measured gas is introduced;
a porous diffusion resistance layer (21) arranged at a gas introduction port to the gas chamber to be measured;
an oxygen ion conductive solid electrolyte layer (11) forming the bottom wall (2a) of the gas chamber to be measured;
an insulating layer (12) forming the sidewall (2b) and the top wall (2c) of the gas chamber to be measured;
an oxygen sensing cell (3) having an oxygen sensing electrode (31) disposed on the surface of said bottom wall;
a heater (4) comprising a heating element (41);
The measured gas chamber has a width direction Y in a plane parallel to the bottom wall, and a direction perpendicular to a gas flow direction X in the measured gas chamber. The width W1 of the chamber and the width W2 of the diffusion resistance layer have a relationship of W1<W2,
In the plane parallel to the bottom wall, both corners (211, 212) in the width direction of the end face (21a) of the diffusion resistance layer on the gas introduction side and the width of the opening of the gas chamber to be measured on the gas introduction side The intersection (P) of the extension lines (L1, L2) of the line segments connecting both corners (111, 112) of the direction is the line segment (L3) passing through the center position of the oxygen detection electrode in the width direction. Overlying, gas sensor element (1) . 7. The gas sensor element according to claim 6, wherein the intersection point (P) is located upstream of the central position (C) of the oxygen detecting electrodes in the direction of gas flow.

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