WO2022239645A1

WO2022239645A1 - Gas sensor

Info

Publication number: WO2022239645A1
Application number: PCT/JP2022/018954
Authority: WO
Inventors: 大樹市川
Original assignee: 株式会社デンソー
Priority date: 2021-05-12
Filing date: 2022-04-26
Publication date: 2022-11-17
Also published as: JPWO2022239645A1; JP7495012B2

Abstract

[Solution] The present invention provides a gas sensor (1) comprising a first solid electrolyte (11) and a second solid electrolyte (12) facing each other across a gas chamber to be measured (2), a first reference gas introduction path (31) and a second reference gas introduction path (32) into which a reference gas (A) containing oxygen is introduced, a pump cell (4) having a pump electrode (41) and a first reference electrode (42), a sensor cell (5) having a sensor electrode (51) and a second reference electrode (52), and an early activation control unit (101) for controlling the pump cell (4), at the time of sensor startup, to a startup voltage (V2) higher than the normal control voltage (V1). The second reference gas introduction path (32) is formed so that the oxygen limit current value indicating, as a current value flowing through the second solid electrolyte (12), the limit value for oxygen fed from the second reference gas introduction path (32) to the sensor electrode (51), at the time of sensor startup, is 20 μA or above.

Description

gas sensor

Cross-reference to related applications

This application is based on Patent Application No. 2021-080944 filed on May 12, 2021, and the contents thereof are incorporated herein.

The present disclosure relates to a gas sensor that detects the concentration of a specific gas in gas to be measured.

For example, in gas sensors for vehicles, early activation of the gas sensor element using a solid electrolyte body is required in order to start gas detection promptly at startup. The gas sensor element includes a pump cell for adjusting the oxygen concentration in the gas to be measured and a sensor cell for detecting a specific gas such as NOx. It is heated using a built-in heater or the like so as to reach the temperature.

In addition, it is known that when the electrode material of the sensor cell contains rhodium, the sensor output fluctuates due to oxygen being occluded by the electrode material before starting. Therefore, in order to stabilize the sensor output, it has been proposed to perform early activation control using a pump cell. For example, in Patent Document 1, when a sensor that detects gas concentration is started, the voltage applied to the pump cell is set to a removal voltage for removing occluded oxygen. A pump cell controller is disclosed for generating a reducing gas such as hydrogen.

JP 2016-70922 A

In Patent Literature 1, the pump cell control unit adjusts, for example, the application time of the voltage for removal, and controls such that enough reducing gas is generated to remove oxygen. In that case, the reducing gas generated in the pump cell will contain surplus gas in addition to the gas consumed by the reaction with oxygen occluded by the electrodes of the sensor cell. Excess reducing gas is usually removed by reaction with oxygen supplied from the reference electrode side through the solid electrolyte body.

On the other hand, a gas sensor is known in which a sensor cell and a pump cell are formed on different solid electrolyte bodies. In this configuration, the reference gas introduction path for introducing the oxygen-containing reference gas arranged on the reference electrode side of the sensor cell and the reference gas introduction path on the reference electrode side of the pump cell are separately provided. In that case, the thickness of the element is restricted from the viewpoint of element assembly, and the reference gas introduction path on the sensor cell side with a smaller output becomes smaller than that on the pump cell side. However, it has been found that if the above-described early activation control is applied to this sensor configuration, it will take time to remove the reducing gas from the sensor electrode, which may cause a delay in the start of NOx detection.

An object of the present disclosure is to provide a gas sensor capable of quickly removing reducing gas generated in early activation control and starting detection of a specific gas without delay.

One aspect of the present disclosure is
A gas sensor that detects the concentration of a specific gas contained in a gas to be measured,
a gas chamber to be measured into which the gas to be measured is introduced;
a first solid electrolyte body and a second solid electrolyte body facing each other with the gas chamber to be measured interposed therebetween;
a first reference gas introduction path and a second reference gas introduction path into which a reference gas containing oxygen is introduced;
The first solid electrolyte body has a pump electrode on the surface thereof facing the gas chamber to be measured, and a first reference electrode on the surface thereof facing the first reference gas introduction path. a pump cell for adjusting oxygen concentration;
a sensor electrode on the surface facing the gas chamber to be measured of the second solid electrolyte body, a second reference electrode on the surface facing the second reference gas introduction path, and an output based on the specific gas a sensor cell that produces
The voltage applied to the pump cell when the sensor is started is controlled to a starting voltage higher than the normal control voltage, and the reducing gas generated in the measured gas chamber by the decomposition of the water contained in the measured gas is used. and an early activation control unit for removing oxygen occluded in the sensor electrode,
The second reference gas introduction path is configured to indicate a limit amount of oxygen supplied from the second reference gas introduction path toward the sensor electrode when the sensor is started, as a current value flowing through the second solid electrolyte body. The gas sensor is formed to have a limit current value of 20 μA or more.

In the gas sensor configured as described above, when a start-up voltage higher than the normal control voltage is applied to the pump cell of the gas sensor by the early activation control section, reducing gas is generated due to decomposition of water in the gas chamber to be measured. The reducing gas is supplied to the sensor cell and consumed to reduce and remove oxygen stored in the sensor electrode. The excess reducing gas is sequentially removed by ionizing the oxygen in the second reference gas introduction path at the second reference electrode and supplying the ionized gas through the second solid electrolyte. At this time, while sufficient reducing gas is supplied to remove the occluded oxygen, if the second reference gas introduction passage becomes small due to restrictions on the element thickness, etc., the amount of oxygen supplied from the second reference gas introduction passage becomes It was found that the activation was delayed due to the shortage of the generated amount. It is considered that this is because the oxygen concentration in the second reference gas introduction passage decreases and the reducing gas stays in the sensor electrode.

In the gas sensor having the above configuration, the second reference gas introduction path has an oxygen limit current value of 20 μA or more, which indicates the limit amount of oxygen supplied to the sensor electrode when the sensor is started, as a current value flowing through the second solid electrolyte body. As a result, the amount of oxygen corresponding to the amount of reducing gas generated can be supplied from the second reference gas introduction passage. As a result, it is possible to suppress the retention of the reducing gas, so that the generated reducing gas can be removed and activation can be achieved early, and the detection of the specific gas in the gas to be measured can be started promptly. .

As described above, according to the above aspect, it is possible to provide a gas sensor capable of quickly removing reducing gas generated in early activation control and starting detection of a specific gas without delay.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing is
1 is a longitudinal cross-sectional view showing a schematic configuration of a sensor element and a sensor control unit, which are main parts of a gas sensor, in Embodiment 1; 2 is a longitudinal sectional view showing the overall configuration of the gas sensor in Embodiment 1, FIG. 3 is a diagram showing the relationship between the oxygen supply amount and the activation time during early activation control of the gas sensor in the first embodiment; FIG. 4 is a diagram showing the relationship between the amount of hydrogen generated and the activation time during early activation control of the gas sensor in Embodiment 1; FIG. 5 is a diagram showing the temporal transition of the pump current value flowing during early activation control of the gas sensor in the first embodiment; 6 is a longitudinal cross-sectional view showing the detailed configuration of the sensor element in Embodiment 1, and is a cross-sectional view taken along line aa in FIG. 7 is a cross-sectional view in the direction perpendicular to the axis showing the detailed configuration of the sensor element in Embodiment 1, 8 is a diagram showing the time transition of the NOx output during early activation control of the gas sensor in Embodiment 1, 9 is a diagram showing the time transition of the NOx output during early activation control of the gas sensor in Embodiment 1, FIG. 10 is a diagram showing the relationship between the oxygen supply amount and the activation time during early activation control of the gas sensor in Embodiment 1; FIG. 11 is a diagram showing changes in NOx output over time during early activation control based on the amount of hydrogen generated by the gas sensor in the first embodiment; 12 is a flow chart showing the procedure of sensor control by the sensor control unit in the first embodiment, FIG. 13 is a cross-sectional view in the width direction showing the main configuration of the sensor element in Embodiment 2; 14 is a longitudinal cross-sectional view showing a schematic configuration of a sensor element in

Embodiment

3, 15 is a longitudinal cross-sectional view showing a schematic configuration of a sensor element in a modification of Embodiment 3, FIG. 16 is an end view showing the configuration of the main parts of the sensor element and a longitudinal cross-sectional view of the bb line cross-sectional view thereof in a modification of Embodiment 3; 17A and 17B are an end view and a longitudinal cross-sectional view taken along the line cc of the sensor element in a modified example of the third embodiment.

(Embodiment 1)
A first embodiment of a gas sensor will be described with reference to FIGS. 1 to 12. FIG.
As shown in FIGS. 1 and 2, the gas sensor 1 of the present embodiment is installed, for example, in an exhaust gas passage of an internal combustion engine such as a vehicle engine, and detects the concentration of a specific gas contained in the gas to be measured. Configured as a sensor. The gas to be measured in this case is the exhaust gas G flowing through the exhaust gas passage, and the concentration of NOx (that is, nitrogen oxides) in the exhaust gas G, for example, is detected as the specific gas. The exhaust gas G introduced into the gas sensor 1 contains, for example, water present in the exhaust gas passage.

In FIG. 1, the gas sensor 1 includes a measured gas chamber 2 into which exhaust gas G is introduced as a measured gas, a first solid electrolyte body 11 and a second solid electrolyte body 12 facing each other across the measured gas chamber 2, A first reference gas introduction passage 31 and a second reference gas introduction passage 32 into which the atmosphere A is introduced as a reference gas, a pump cell 4 formed using the first solid electrolyte body 11, and a second solid electrolyte body 12 are used. A sensor element 1</b>A having a sensor cell 5 formed by

As indicated by the arrow in FIG. 1, in the longitudinal direction X of the sensor element 1A (that is, the horizontal direction in the figure), the exhaust gas G flows from the tip side of the sensor element 1A (that is, the left end side in the figure) to the atmosphere A. is introduced into the inside of the sensor element 1A from the base end side (that is, the right end side in the figure). The direction of gas flow in the measured gas chamber 2 is the same as the direction in which the exhaust gas G is introduced.

Preferably, the sensor element 1A is provided with a heater 6 so that the pump cell 4 and the sensor cell 5 can be heated to temperatures suitable for detection. The sensor control unit 10 is provided with a detection control unit 102 for controlling the operation of the sensor element 1A during normal detection, and is provided with a heater control unit 103 for controlling the operation of the heater 6. It has become.

The pump cell 4 is composed of the first solid electrolyte body 11 and a pair of

electrodes

41 and 42 on its surface. Specifically, a pump electrode 41 is provided on the surface of the first solid electrolyte body 11 facing the gas chamber 2 to be measured, and a first reference electrode 42 is provided on the surface facing the first reference gas introduction passage 31. , to adjust the oxygen concentration in the gas chamber 2 to be measured. The sensor cell 5 is composed of the second solid electrolyte body 12 and a pair of

electrodes

51 and 52 on the surface thereof. Specifically, a sensor electrode 51 is provided on the surface of the second solid electrolyte body 12 facing the gas chamber 2 to be measured, and a second reference electrode 52 is provided on the surface facing the second reference gas introduction path 32. , produces an output based on the NOx in the exhaust gas G.

The first solid electrolyte body 11 is arranged between the measured gas chamber 2 and the first reference gas introduction path 31, and the second solid electrolyte body 12 is disposed between the measured gas chamber 2 and the second reference gas introduction path. It is located between 32. In the pump cell 4 and the sensor cell 5, the measured gas chamber 2 and the first reference gas introduction path 31 or the second reference gas introduction path 32 are connected via the first solid electrolyte body 11 or the second solid electrolyte body 12, which is an ion conductor. It is possible to adjust the gas concentration or detect the gas concentration by conducting ionic conduction between and.

In the pump cell 4, a predetermined voltage is applied to the pair of

electrodes

41 and 42, so that oxygen (ie, O ₂ ) in the exhaust gas G is decomposed into oxide ions (ie, O ²⁻ ) at the pump electrode 41. Then, it passes through the first solid electrolyte body 11 and moves toward the first reference electrode 42 , becomes oxygen again, and is discharged to the first reference gas introduction passage 31 . Due to this pumping action, the inside of the gas chamber 2 to be measured is adjusted to a predetermined low oxygen concentration, and the influence of oxygen on the sensor cell 5 located downstream of the pump cell 4 can be eliminated or minimized. In the sensor cell 5, NOx reaching the sensor electrode 51 is decomposed into nitrogen (that is, N ₂ ) and oxygen, and a predetermined voltage is applied between the pair of

electrodes

51 and 52 to decompose and ionize the oxygen. . These oxide ions permeate the second solid electrolyte body 12 , move toward the second reference electrode 52 , become oxygen again, and are discharged to the second reference gas introduction passage 32 . At this time, the current output of the sensor cell 5 corresponds to the NOx concentration, and based on this relationship, the concentration of the specific gas can be detected.

The sensor element 1A preferably includes a monitor cell 50 arranged in parallel with the sensor cell 5 in addition to the pump cell 4 and the sensor cell 5, and can be configured to detect oxygen remaining in the exhaust gas G. The monitor cell 50 has a monitor electrode 53 on the surface of the second solid electrolyte body 12 facing the gas chamber 2 to be measured as a pair of

electrodes

53 and 52 formed on the surface of the second solid electrolyte body 12. It has a second reference electrode 52 common to the sensor cell 5 on the surface facing the two-reference gas introduction path 32 . In the monitor cell 50, NOx is not decomposed, and a current caused only by residual oxygen flows.

Prior to such normal specific gas detection control, the sensor control unit 10 uses the early activation control unit 101 to perform early activation control. The early activation control unit 101 controls the voltage applied to the pump cell 4 at the time of starting the sensor to a starting voltage V2 higher than the normal control voltage V1. With this early activation control, the oxygen stored in the sensor electrode 51 can be quickly removed by using the reducing gas generated in the gas chamber 2 under measurement due to the decomposition of the water contained in the gas under measurement. During sensor start-up, the early activation control is controlled to generate sufficient reducing gas to remove the occluded oxygen. At that time, the second reference gas introduction path 32 is configured such that the reducing gas does not stay in the sensor electrode 51 and is removed by oxygen supply from the second reference electrode 52 side.

Specifically, the second reference gas introduction path 32 has a limit amount of oxygen supplied from the second reference gas introduction path 32 toward the sensor electrode 51 (hereinafter referred to as the oxygen supply amount as appropriate) when the sensor is started. is formed to be 20 μA or more. As will be described later, the oxygen limiting current value indicating the oxygen supply amount is determined based on, for example, the channel structure of the second reference gas introduction channel 32 and the like. As a result, even when the oxygen supply from the second reference gas introduction passage 32 is restricted, the reducing gas remaining in the measurement gas chamber 2 without being used for removing oxygen is prevented from the second reference electrode. Sufficient oxygen is supplied from the 52 side, making it possible to suppress retention of the reducing gas.

At this time, as shown in FIG. 3, the activation time (unit: seconds) indicating the time required for element activation is reduced, and the removal of oxygen and the removal of reducing gas during early activation control can be performed in a well-balanced manner. . If the oxygen limiting current value, which indicates the amount of oxygen supplied when the sensor is started, is less than 20 μA, the supply of oxygen for removing the reducing gas is insufficient, and the reducing gas stays, resulting in a longer activation time and premature activation. may not be done well. Specifically, the activation time can be the time required from the start of the early activation control until the sensor output converges within a predetermined threshold range, as will be described later.

Preferably, the second reference gas introduction path 32 is configured so that the oxygen limiting current value, which indicates the amount of oxygen supplied when the sensor is started, is 2500 μA or less. If the oxygen limit current value exceeds 2500 μA, for example, the space portion that becomes the second reference gas introduction path 32 becomes large, and there is a possibility that the strength required in assembling the device may not be satisfied. Sufficient oxygen is supplied to the generated reducing gas by setting the amount of oxygen supplied from the second reference gas introduction passage 32 within the range defined by the upper and lower limits of the oxygen limit current value described above, It is possible to quickly remove the reducing gas and achieve early activation while suppressing a decrease in element strength.

During early activation control, oxygen contained in the exhaust gas G is decomposed at the pump electrode 41 of the pump cell 4, and, for example, water vapor contained in the exhaust gas G is decomposed to generate hydrogen (that is, H ₂ ) as a reducing gas. . Oxygen stored in the sensor electrode 51 reacts with hydrogen supplied from the pump cell 4 to become water (that is, H ₂ O) and is removed. The generated reducing gas is consumed in the sensor electrode 51 by reaction with oxygen stored therein, and is removed as water by reaction with oxygen supplied through the second solid electrolyte body 12 .

As shown in FIGS. 4 and 5, the amount of coulombs indicating the total amount of hydrogen generated when the sensor is started (hereinafter referred to as the amount of hydrogen generated as appropriate) has a correlation with the activation time. The operation of the pump cell 4 is controlled so that sufficient hydrogen is generated to remove the oxygen present. Preferably, the pump cell 4 is controlled so that the amount of hydrogen generated in the pump cell 4 is in the range of 2000 μA·s to 11000 μA·s. By controlling the amount of hydrogen generation to be 2000 μA s or more, the amount of hydrogen required to remove the occluded oxygen is generated, and by setting it to 11000 μA s or less, it takes time to remove excess hydrogen. delay in active time can be avoided. The amount of hydrogen generated can be controlled, for example, by adjusting the start-up voltage V2 applied to the pump cell 4 and its application time.

In FIG. 5, due to the application of the start-up voltage V2 during early activation control, the pump current value (unit: μA) flowing through the pump cell 4 is generated together with the output based on the oxygen contained in the exhaust gas G and the decomposition of water vapor. It appears as the sum of the outputs based on oxygen. The output based on the latter of these continues until the control voltage is switched to the normal control voltage V1 at the timing when the early activation control ends (for example, time (t1) in the figure), and the total amount of hydrogen generated during that time, that is, , The amount of hydrogen generated at the start of the sensor can be calculated as a coulomb amount (unit: μA×s) corresponding to the hatched area in the figure (that is, the integrated value of the pump current value per unit time).

As shown by Equation 1 in FIG. 3 shows limiting current characteristics dependent on the amount of oxygen passing through the gas introduction passage 32 and reaching the second reference electrode 52. FIG. At this time, the limit amount of oxygen supplied to the sensor electrode 51 when the sensor is started is defined as an oxygen limit current value IL (unit: μA) using the current value flowing through the second solid electrolyte body 12 . From Equation 1, the oxygen limiting current value IL, which indicates the oxygen supply amount at the time of starting the sensor, is governed by the movement of oxygen due to diffusion in the second reference gas introduction passage 32, and there is no change in environmental conditions such as oxygen concentration and temperature. At this time, the oxygen supply amount (IL) is determined according to the channel cross-sectional area S or the channel length L indicating the channel structure of the second reference gas introduction channel 32 .
Formula 1: IL=(4FP/RT).D.(S/L) _.Ln [1-(PO2/P)]×10 ⁶
IL: oxygen supply amount ≈ oxygen limit current value (μA)
F: Faraday constant P: atmospheric pressure (atm)
R: gas constant D: diffusion coefficient T: temperature (K)
S: Channel cross-sectional area (m ² )
L: channel length (m)
_PO2 : Oxygen partial pressure (atm)

Specifically, the oxygen supply amount (IL) increases as the ratio between the channel cross-sectional area S and the channel length L of the second reference gas introduction channel 32 increases. Among these, the flow path length L is restricted by the length of the sensor element 1A, etc., so that the desired oxygen supply amount (IL) is obtained within the range of the flow path length L in the normal sensor element 1A. , the size of the cross-sectional area S of the flow path, etc. are preferably adjusted. As a result, it is possible to achieve both a sufficient amount of oxygen supply corresponding to the amount of hydrogen generated and the strength of the device.

In this manner, in the configuration in which the sensor element 1A of the gas sensor 1 has a plurality of

solid electrolyte bodies

11 and 12 and a plurality of reference

gas introduction paths

31 and 32, the amount of oxygen supplied from the second reference electrode 52 side of the sensor cell 5 is By setting the value within the predetermined range, the early activation control by the early activation control unit 101 can be performed satisfactorily.

Details of the configuration and control of the gas sensor 1 will be described below.
In FIG. 2, a gas sensor 1 as a NOx sensor has a cylindrical housing H, a sensor element 1A inserted and held inside the housing H, an element cover C1 and an atmosphere cover C2. Both ends of the sensor element 1A protrude outward from the housing H with the axial direction of the housing H being the longitudinal direction X (that is, the vertical direction in FIG. 2). It is housed inside the cover C2. The element cover C1 is arranged to cover the outer peripheral side of the sensor element 1A on the distal end side (that is, the lower end side in FIG. 2), and the atmosphere cover C2 is arranged to cover the proximal end side of the sensor element 1A (that is, the upper end side in FIG. 2). ) is arranged to cover the outer peripheral side of the

The housing H is fixed to the passage wall of the exhaust gas passage (not shown), and the sensor element 1A projects into the exhaust gas passage on the tip side accommodated in the element cover C1. The element cover C1 has, for example, a double-cylinder structure having a bottom surface. is provided with a gas flow hole C133. Further, a plurality of gas flow holes C21 are provided on the side surface of the cylindrical atmosphere cover C2. As a result, the exhaust gas G flowing through the exhaust gas passage is taken into the element cover C1 and reaches the tip side of the sensor element 1A, and the air A taken into the atmosphere cover C2 is the base of the sensor element 1A. reach the end.

The sensor element 1A has a front end housed in the element cover C1, which serves as a detection part exposed to the exhaust gas G, which is the gas to be measured, and uses the air A taken in from the base end housed in the atmosphere cover C2 as a reference gas. NOx in exhaust gas is detected. A control signal or a detection signal to the detection section is input or output from an external sensor control section 10 via a lead wire L1 electrically connected to a terminal section on the base end side of the sensor element 1A. The base end side of the sensor element 1A is clamped by a spring terminal portion L2 provided at the end portion of the lead wire L1.

In FIG. 1, the sensor element 1A is provided with a pump cell 4 and a sensor cell 5 as well as a monitor cell 50 in the detection section of the sensor element 1A, whose operation is controlled by the sensor control section 10. The pump cell 4 is exposed to the exhaust gas G introduced into the measured gas chamber 2 and the atmosphere A introduced into the first reference gas introduction passage 31. The sensor cell 5 and the monitor cell 50 are introduced into the measured gas chamber 2. and the atmosphere A introduced into the second reference gas introduction passage 32 . Further, the sensor element 1A has a built-in heater 6 whose operation is controlled by the sensor control section 10 so that the portion corresponding to the detection section can be heated to a predetermined temperature.

The sensor control unit 10 has an early activation control unit 101 that performs early activation control when the sensor is started, a detection control unit 102 that performs NOx detection control, and a heater control unit 103 that performs energization control of the heater 6. It controls the operation of element 1A. Specifically, as shown in FIG. 2, the detection control section 102 has a pump cell control section 102A, a sensor cell detection section 102B, and a monitor cell detection section 102C. 102 A of pump cell control parts detect the electric current which the pump cell 4 outputs while controlling the voltage applied to the pump cell 4 normally. The sensor cell detector 102B detects the current output by the sensor cell 5, and the monitor cell detector 102C detects the current output by the monitor cell 50. FIG. Control by these units of the sensor control unit 10 will be described later.

As shown in detail in FIGS. 6 and 7, the sensor element 1A is made of a laminate of ceramic layers. A protective layer 15 is formed. The sensor element 1A has a shielding layer 14, a second solid electrolyte body 12, a spacer layer 13, and a first solid electrolyte body 11, with the direction orthogonal to the longitudinal direction X (that is, the vertical direction in FIGS. 6 and 7) as the stacking direction. , and a heater insulating layer 61 constituting the heater 6 are arranged in this order. The first solid electrolyte body 11 and the second solid electrolyte body 12 face each other across a spacer layer 13 in which a space forming the gas chamber 2 to be measured is formed. A space that serves as the first reference gas introduction path 31 is formed in the layer 61 . A space that serves as the second reference gas introduction path 32 is formed in the shielding layer 14 arranged outside the second solid electrolyte body 12 .

In FIG. 6, the measured gas chamber 2 is separated from the space in the element cover C1 (for example, see FIG. 2 above) in which the exhaust gas G exists through the diffusion resistance portion 21 embedded in the tip side of the spacer layer 13. are in communication. The diffusion resistance portion 21 serving as a gas introduction portion is a porous body made of an insulating ceramic material such as alumina, and is adjusted so that the exhaust gas G is introduced under a predetermined diffusion resistance.

The first solid electrolyte body 11 and the second solid electrolyte body 12 are composed of a zirconia-based solid electrolyte material having oxide ion conductivity. As the zirconia-based solid electrolyte material, for example, partially stabilized zirconia or stabilized zirconia containing a stabilizer such as yttria can be used. A pump electrode 41 of the pump cell 4 is formed on the surface of the first solid electrolyte body 11 facing the gas chamber 2 to be measured. , the first reference electrode 42 of the pump cell 4 is formed. A sensor electrode 51 of the sensor cell 5 is formed on the surface of the second solid electrolyte body 12 facing the gas chamber 2 to be measured. A second reference electrode 52 of the sensor cell 5 is formed on the surface.

The spacer layer 13, the shield layer 14, and the heater insulating layer 61 are made of an insulating ceramic material such as alumina. The porous protective layer 15 is for protecting the detection portion of the sensor element 1A from poisonous components and the like, and is made of porous ceramics adjusted to a porosity that does not hinder the introduction of the exhaust gas G. be able to.

A heating element 62 that generates heat when energized is embedded inside the heater insulating layer 61 that serves as the passage wall of the first reference gas introduction path 31 to constitute the heater 6 . The heating elements 62 are arranged corresponding to the portions where the electrodes of the pump cell 4, the sensor cell 5 and the monitor cell 50 are formed, and are capable of heating the entire front end side of the element serving as the detection portion.

The second reference gas introduction path 32, in which the second reference electrode 52 is arranged, extends to the base end side of the sensor element 1A (that is, the right end side in FIG. 6), and the second reference gas introduction port opens at the end face thereof. 321 communicates with the space within the element cover C1 (see, for example, FIG. 2 above) where the atmosphere A is present. Similarly, the first reference gas introduction passage 31, in which the first reference electrode 42 of the pump cell 4 is arranged, extends to the base end side of the sensor element 1A, and through a first reference gas introduction port 311 opened at the end surface thereof, is in communication with the atmosphere A.

Terminal portions

71 and 72 are provided on both surfaces in the stacking direction at the base end portion of the sensor element 1A. Specifically, the surface on the side of the second reference gas introduction path 32 (that is, the upper surface in FIG. 6) and the surface on the side of the first reference gas introduction path 31 (that is, the lower surface in FIG. 6) each have A plurality of

terminal portions

71 and 72 are arranged and electrically connected to the spring terminal portion L2 (for example, see FIG. 2 described above) inside the atmosphere cover C2. Each terminal of the

terminal portions

71 and 72 is electrically connected to an electrode constituting each cell of the detection portion or to the positive and negative terminals of the heating element 62 of the heater 6 via a lead portion. As a result, a control signal to each cell or a detection signal from each cell is input/output from the sensor control unit 10, and energization control of the heater 6 becomes possible. The number and arrangement of terminals constituting the

terminal portions

71 and 72 and the connection structure can be changed as appropriate.

In the measured gas chamber 2, the pump electrode 41 of the pump cell 4 is arranged on the upstream side in the gas flow direction of the exhaust gas G, and the sensor electrode 51 of the sensor cell 5 is arranged on the downstream side of the pump electrode 41. . The first reference electrode 42 of the pump cell 4 is positioned opposite the pump electrode 41 with the first solid electrolyte body 11 interposed therebetween, and the second reference electrode 52 of the sensor cell 5 is positioned with the second solid electrolyte body 12 interposed therebetween. It is located at a position facing the sensor electrode 51 . Also, the monitor electrode 53 of the monitor cell 50 is located at the same position as the sensor electrode 51 of the sensor cell 5 in the gas flow direction.

As shown in FIG. 7, the sensor electrode 51 of the sensor cell 5 and the monitor electrode 53 of the monitor cell 50 are arranged adjacent to each other in a cross section orthogonal to the gas flow direction. The second reference electrode 52 is common to the sensor cell 5 and the monitor cell 50 and arranged to face both the sensor electrode 51 and the monitor electrode 53 . The heating element 62 of the heater 6 is embedded in the bottom wall of the first reference gas introduction passage 31 facing the first solid electrolyte body 11, forms a predetermined heater pattern, and can evenly heat the entire detection section. It's becoming

The electrodes of the pump cell 4, sensor cell 5 and monitor cell 50 can be porous cermet electrodes containing a noble metal or noble metal alloy material and a zirconia-based solid electrolyte. The sensor electrode 51 of the sensor cell 5 can be constructed using an electrode material having decomposition activity for NOx to be detected. Such a sensor electrode 51 is, for example, an electrode containing platinum and rhodium (hereinafter appropriately referred to as a Pt--Rh electrode), and has oxygen and NOx decomposition activity.

The pump electrode 41 of the pump cell 4 and the monitor electrode 53 of the monitor cell 50 are made of an electrode material that has oxygen decomposition activity but does not have NOx decomposition activity. electrodes). Also, the first reference electrode 42 and the second reference electrode 52 can be configured as, for example, electrodes containing platinum (hereinafter, appropriately referred to as Pt electrodes).

It should be noted that the sensor electrode 51 is not limited to the Pt--Rh electrode, and may be formed of an electrode material having a similar action. As such an electrode material, for example, an alloy material obtained by mixing platinum with a metal such as palladium (Pd), iron (Fe), cobalt (Co), or nickel (Ni) is used.

Here, when the sensor is started before detection by the gas sensor 1, the oxygen concentration of the exhaust gas G introduced into the gas chamber 2 to be measured is high. It is desirable to Moreover, each cell of the sensor element 1A is in a low activation state, and it is desired to quickly raise the temperature to a predetermined activation temperature. On the other hand, when the sensor electrode 51 of the sensor cell 5 is a Pt—Rh electrode, rhodium is known to occlude oxygen. At the same time, the pump cell 4 is used to generate hydrogen as a reducing gas, thereby performing early activation control to remove the stored oxygen.

In the early activation control, a starting voltage V2 higher than the normal control voltage V1 is applied to the pair of

electrodes

41 and 42 of the pump cell 4. At this time, at the pump electrode 41, oxygen in the exhaust gas G present in the gas chamber 2 to be measured is decomposed, and the water vapor is decomposed to generate hydrogen as a reducing gas. The generated hydrogen is supplied to the sensor cell 5 located on the downstream side of the gas flow and consumed in the reaction with the oxygen occluded in the sensor electrode 51 . Oxygen generated together with hydrogen by the decomposition of water vapor is decomposed at the pump electrode 41 . The oxygen ionized at the pump electrode 41 moves inside the first solid electrolyte body 11 and is discharged from the first reference electrode 42 to the first reference gas introduction passage 31 .

In the early activation control, the start-up voltage V2 applied to the pair of

electrodes

41 and 42 of the pump cell 4 is such that the oxygen in the exhaust gas G is decomposed on the pump electrode 41 and the water vapor is decomposed to generate hydrogen which becomes a reducing gas. is set to a voltage that can be generated. At this time, oxygen generated together with hydrogen by decomposition of water vapor is decomposed on the pump electrode 41 and moves through the first solid electrolyte body 11 (for example, in FIG. 6 indicated by a solid line arrow), and is discharged to the first reference electrode 42 side.

It should be noted that the control voltage V1 during normal operation is adjusted so that the oxygen concentration in the measured gas chamber 2 is equal to or lower than a predetermined concentration. The magnitude of the control voltage V1 is, for example, 0.3 to 0.4 V, and the first solid electrolyte body 11 is the limit at which the current flowing through the pump cell 4 hardly changes even if the voltage applied to the pump cell 4 changes. It is determined within the range of voltage values that indicate current characteristics. On the other hand, the starting voltage V2 is set higher than the control voltage V1, and is set as a voltage value higher than the voltage value indicating the limit current characteristic. The startup voltage V2 of this embodiment can be set within a range of 0.5 to 2V, for example.

In this manner, a sufficient amount of hydrogen is generated as a reducing gas in the pump cell 4, and the oxygen occluded in the sensor electrode 51 of the sensor cell 5 can be removed by utilizing the reduction reaction of oxygen. can. At this time, oxygen ionized on the side of the second reference electrode 52 is supplied via the second solid electrolyte body 12 to excess hydrogen in the sensor electrode 51 (for example, indicated by a dotted arrow in FIG. 6). , is desorbed and removed by the generation of water. However, since the amount of oxygen supplied depends on the amount of oxygen that passes through the second reference gas introduction passage 32 and reaches the second reference electrode 52, if the removal of excess hydrogen does not progress, the hydrogen will be activated early. It may take longer.

As shown in FIGS. 3 to 5 above, during the early activation control, the amount of oxygen supplied to the sensor electrode 51 is expressed as the oxygen limiting current value IL defined by Equation 1, and the amount of hydrogen generation is It can be controlled based on the relationship between the pump current value flowing through the pump cell 4 and time. The amount of oxygen supply is determined, for example, by the cross-sectional area S and length L of the second reference gas introduction passage 32 in Equation 1, so that the oxygen limiting current value IL is 20 μA or more, preferably 2500 μA or less. , so that both the removal of occluded oxygen and the removal of stagnant hydrogen can be suitably carried out at a desired hydrogen generation amount. Preferably, the amount of hydrogen generated is controlled to be in the range of 2000 μA·s or more and 11000 μA·s or less, and in combination with an appropriate amount of oxygen supply, the activation time during early activation control can be shortened.

As shown in FIG. 8, the NOx concentration based on the output of the sensor cell 5 during early activation control is within a predetermined threshold range on the positive side or the negative side, and the time until it converges to approximately 0 is defined as the activation time. At this time, the NOx output waveform and activation time are correlated with the oxygen supply amount. After the waveform swings from the negative side to the positive side at the end of the early activation control (t1), it gradually decreases. time) increases. This is because hydrogen stays in the gas chamber 2 to be measured, while oxygen is depleted in the second reference gas introduction passage 32 due to the supply of oxygen to the sensor electrode 51 side, and the oxygen concentration in the second reference gas introduction passage 32 decreases. due to that. Therefore, the difference between the oxygen partial pressure in the measured gas chamber 2 and the oxygen partial pressure in the second reference gas introduction passage 32 changes, and the electromotive force between the pair of

electrodes

51 and 52 of the sensor cell 5 changes. , NOx output fluctuations.

On the other hand, as shown by the solid line in the figure, when the oxygen supply amount (oxygen limiting current value IL) is 20 μA, the convergence is achieved at time (t1) without deviating to the positive side. Therefore, the threshold on the negative side is quickly reached (that is, time (t2)), and the activation time is shortened. Preferably, as indicated by the dashed line in FIG. 9, when the oxygen supply amount (oxygen limiting current value IL) increases to 40 μA, the negative side threshold is reached more rapidly (that is, time (t11)), Active time is shorter. As shown in FIG. 10, when the oxygen supply amount (oxygen limiting current value IL) is from 20 μA to around 40 μA, the activation time is gradually shortened, and when it exceeds 40 μA, the activation time becomes substantially constant.

Therefore, the second reference gas introduction passage 32 is preferably configured so that the oxygen supply amount (oxygen limiting current value IL) is 40 μA or more, and a sufficient amount of oxygen is supplied to activate the oxygen. can save time. On the other hand, if the oxygen supply amount (oxygen limiting current value IL) increases, the spatial volume of the second reference gas introduction path 32 increases, which may reduce the strength of the element. As described above, the sensor element 1A has the

terminal portions

71 and 72 arranged at the proximal end where the second reference gas introduction path 32 opens, and is sandwiched between the spring terminal portions L2. The upper limit of the oxygen supply amount (oxygen limiting current value IL) is preferably set to 2500 μA or less, more preferably 1000 μA or less, so as to ensure the device strength.

Further, as shown in FIG. 11, when the amount of hydrogen generation changes within the above-described desired range (that is, 2000 μA·s or more and 11000 μA·s or less), a similar NOx output waveform is obtained. , the end timing of the early activation control is advanced, and the activation time is shortened. For example, when the amount of hydrogen generation is 5000 μA s, the negative threshold is reached at time (t12), whereas when the amount of hydrogen generation is 10000 μA s, it reaches a later time (t13). will reach the threshold on the negative side. Therefore, preferably, the hydrogen generation amount can be adjusted so as to achieve a desired activation time within the range of 5000 μA·s or more and 10000 μA·s or less.

Next, control by the sensor control unit 10 will be described with reference to the flowchart of FIG. The sensor control unit 10 is configured as, for example, a sensor control unit (hereinafter referred to as SCU) that controls the entire gas sensor 1, and an engine control unit (hereinafter referred to as ECU) that controls the entire vehicle engine. (referred to as ). The SCU includes an early activation control unit 101, a detection control unit 102, and a heater control unit 103 shown in FIG. 1, as well as a communication unit and a calculation unit (not shown). The NOx concentration can be detected by going there, and the detection result can be output to the ECU at any time.

In FIG. 8, when the sensor control unit 10 starts control, first, in step S1, it is determined whether or not sensor activation is permitted, and if sensor activation is permitted, the process proceeds to step S2 and subsequent steps. Step S2 corresponds to heater control by heater control section 103, and steps S3 to S5 correspond to early activation control by early activation control section 101. FIG. Steps S5 to S7 correspond to NOx detection control by the detection control section 102, step S6 corresponds to the pump cell control section 102A, and step S7 corresponds to the sensor cell detection section 102B and the monitor cell detection section 102C. In step S1, the state of the sensor element 1A is checked before performing these controls, thereby preventing damage to the sensor element 1A and erroneous detection.

Specifically, at low temperatures when condensed water tends to adhere to the sensor element 1A, there is a risk of damage due to heater energization. False detection may occur due to Therefore, it is possible to check the temperature of the sensor element 1A and the presence or absence of abnormality based on another control flow, and output the permission signal only when it is determined that normal operation is possible. If the determination in step S1 is affirmative, the SCU is activated, the process proceeds to step S2, and energization of the sensor element 1A is started. If the determination in step S1 is negative, the process ends without starting the SCU.

In step S2, energization control to the heater 6 is started, and the temperature of the solid electrolyte body and electrodes of the sensor element 1A is raised to a predetermined activation temperature. This energization control can be performed by utilizing the fact that the impedance of each cell of the sensor element 1A changes with temperature, and controlling the amount of energization so that the detected impedance becomes a predetermined value. Specifically, until the impedance of the pump cell 4 reaches the activation determination impedance corresponding to a predetermined activation temperature, the energization duty of the heater 6 is set large (for example, 100%). can be performed by PI-controlling the energization duty of the heater 6 based on the deviation of . Impedance detection is not limited to the pump cell 4, and can be performed for other cells and the heater 6 as well.

After the power supply control to the heater 6 is started in step S2, the process proceeds to step S3, and early activation control by the early activation control unit 101 is started. Specifically, the voltage applied to the pair of

electrodes

41 and 42 of the pump cell 4 is raised to the preset starting voltage V2. Next, in step S4, it is determined whether or not a predetermined time has elapsed. If the determination in step S4 is affirmative, the process proceeds to step S5, and if the determination in step S4 is negative, step S4 is repeated until a predetermined period of time elapses.

The starting voltage V2 applied to the pair of

electrodes

41 and 42 of the pump cell 4 is set higher (eg, 0.5 to 2 V) than the normal control voltage V1 (eg, 0.3 to 0.4 V). ). As a result, on the pump electrode 41, the oxygen in the exhaust gas G is decomposed and the water vapor is decomposed to generate hydrogen as a reducing gas. The generated hydrogen spreads in the gas chamber 2 to be measured, reaches the sensor cell 5, reacts with the oxygen occluded in the sensor electrode 51, and is removed.

The predetermined time in step S4 corresponds to the time from the start of the early activation control to the end of the early activation control (t1) in FIGS. become more. In addition, as shown in FIG. 11, the more hydrogen generated, the longer the activation time. Therefore, it is desirable to set in advance in consideration of the desired hydrogen generation amount and activation time. Alternatively, it is also possible to set the heating time until a predetermined activation temperature is reached in the power supply control to the heater 6 in step S2 within the range in which the desired hydrogen generation amount and activation time can be obtained. The lower limit of the predetermined time is, for example, 5 seconds or more, and may be, for example, 10 seconds or more so as to more reliably reach the activation temperature. The upper limit of the predetermined time is a time that can be secured as a preparation time until the start of detection, for example, 30 seconds or less. good.

In step S4, after a predetermined period of time has elapsed, the process proceeds to step S5, where the control by the early activation control unit 101 ends and the detection control unit 102 switches to normal control. Specifically, in step S6, the pump cell control unit 102A is used to lower the startup voltage V2 applied to the pair of

electrodes

41 and 42 of the pump cell 4 to a lower control voltage V1. As a result, in the pump cell 4, a current due to decomposition of oxygen in the gas chamber 2 to be measured flows, and the output current of the pump cell 4 can be detected and controlled to a predetermined low concentration.

Next, proceeding to step S6, the output current of the sensor cell 5 is detected using the sensor cell detection section 102B, and the output current of the monitor cell 50 is detected using the monitor cell detection section 102C. A predetermined voltage indicating limiting current characteristics is applied to the sensor cell 5 and the monitor cell 50. From the output current of the sensor cell 5 based on the residual oxygen and NOx in the gas chamber 2 to be measured, the output current of the monitor cell 50 based only on residual oxygen is determined. By subtracting the output current, the NOx concentration corrected for the influence of residual oxygen can be calculated.

As described above, according to the configuration of this embodiment, it is possible to suppress the delay in the early activation control when the sensor is started, and to promptly start detecting the specific gas.

(Embodiment 2)
A second embodiment of the gas sensor will be described with reference to FIG.
Since the basic configuration of the gas sensor 1 of this embodiment is the same as those shown in FIGS. 1 and 2, illustration and description thereof are omitted, and FIG. ing. The following description will focus on the differences.
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. 13, in the present embodiment, the monitor cell 50 in the first embodiment is not provided, and the sensor electrode 51 and the second reference electrode 52 of the sensor cell 5 sandwich the second solid electrolyte body 12 and are equivalent to each other. located opposite to each other. The sensor electrode 51 is arranged on the surface of the second solid electrolyte body 12 facing the gas chamber 2 to be measured. 41 are placed.

During normal detection, the sensor current based on residual oxygen and NOx in the sensor cell 5 is very small compared to the pump current based on oxygen discharged from the gas chamber 2 to be measured to the first reference gas introduction passage 31 by the pump cell 4. . Therefore, by providing the second reference gas introduction path 32 separately from the first reference gas introduction path 31, there are advantages such as being less susceptible to concentration fluctuations due to the discharge of oxygen. From the point of view, when the spatial volume of the second reference gas introduction passage 32 becomes small, as described above, there is a possibility that the oxygen supply amount during the early activation control cannot be sufficiently secured. Further, when the spatial volume of the first reference gas introduction passage 31 increases, the strength of the sensor element 1A may decrease as described above.

Therefore, the second reference gas introduction path 32 is configured such that the cross-sectional shape of the flow path is a flat shape in which the height of the flow path (that is, the length in the stacking direction) is sufficiently small relative to the width of the flow path. This makes it easier to introduce the atmosphere A onto the second reference electrode 52 while suppressing the element thickness in the stacking direction. Further, it is desirable to sufficiently reduce the ratio of the channel height h of the second reference gas introduction path 32 to the thickness t of the shielding layer 14 in which the second reference gas introduction path 32 is formed. As a result, the thickness of the shielding layer 14, which serves as the channel wall of the second reference gas introduction channel 32, is secured, and the channel cross-sectional area S required for early activation control is secured while maintaining the element strength. of oxygen can be supplied.

In order to keep the oxygen supply amount (IL) based on the above-mentioned formula 1 within the desired range during the early activation control, it is preferable that the flow passage cross-sectional area S of the second reference gas introduction passage 32 is 0.007 mm ² or more. It is desirable to be configured to be The cross-sectional area S of the flow path is represented by a region surrounded by a dotted line in FIG. Defined as cross-sectional areas in orthogonal directions. As a result, in a normal NOx sensor configuration (for example, see FIG. 2), it is possible to achieve a configuration that satisfies the lower limit value of 20 μA or more of the oxygen supply amount (IL) in FIG. 3 described above.

Moreover, it is preferable that the cross-sectional area S of the second reference gas introduction path 32 is set to 80 mm ² or less. As a result, the upper limit value of the oxygen supply amount (IL) in FIG. 3 described above, 2500 μA or less, can be satisfied. In addition, when calculating the oxygen supply amount (IL) based on Equation 1, for the entire channel length L from the distal end side to the proximal end side of the second reference gas introduction channel 32, the same channel cross-sectional area S Also, the oxygen supply amount is obtained for each block with different temperature conditions, etc., and the total oxygen supply amount (IL) is calculated as the sum of them. In addition, it is desirable that the channel length L is configured to be, for example, 20 mm or more and 40 mm or less.

Further, the ratio (h/t) between the channel height h of the second reference gas introduction channel 32 and the thickness t of the shielding layer 14 in which the second reference gas introduction channel 32 is formed is, specifically, (h/t)<1/4, preferably (h/t)<1/5. At this time, the thickness t of the shielding layer 14 at the position where the second reference gas introduction path 32 is formed is four to five times or more the height h of the flow path. Sufficient element strength can be obtained even in a configuration in which is opened. From the viewpoint of highly satisfying the required cross-sectional area S of the flow path and the strength of the element required when assembling the element, it is preferable that 0.03<(h/t)<0.13. Preferably, it can be constructed so as to satisfy the relationship of 0.04<(h/t)<0.11.

(Embodiment 3)
A third embodiment of the gas sensor will be described with reference to FIGS. 14 to 17. FIG.
Since the basic structure of the gas sensor 1 of this embodiment is the same as that shown in FIGS. 1 and 2, illustration and description thereof will be omitted, and differences will be mainly described below. As shown in FIG. 14, in the present embodiment, in the configuration of the sensor element 1A in Embodiment 1, instead of opening the second reference gas introduction path 32 in the end surface on the base end side, which is one end side, the second A second reference gas introduction port 321 is formed at the base end of the reference gas introduction path 32 so as to penetrate through the shielding layer 14 in the stacking direction.

The second reference gas introduction port 321 is formed at a position adjacent to the terminal portion 71 arranged on the surface of the shielding layer 14 on the proximal side, and is located at the flow path end portion on the proximal side of the second reference gas introduction passage 32 . connected to. At this time, since the sensor element 1A does not have a space at the base end portion where the terminal portion 71 is arranged, it is possible to secure the element strength required when assembling the element. In addition, the channel length L of the second reference gas introduction channel 32 is shorter than the configuration in which the second reference gas introduction port 321 opens at the end surface on the proximal end side, and the channel cross-sectional area S and the flow Since the ratio (S/L) of the path length L is increased, it becomes easier to secure the oxygen supply amount. In this embodiment, the cross-sectional area of the through hole is used for the portion passing through the second reference gas introduction port 321, and the cross-sectional area of the through hole and the cross section of the second reference gas introduction passage 32 are used as the flow passage cross-sectional area S. The area is used to calculate the oxygen supply amount.

As shown in FIG. 15 as a modified example, in the configuration of the sensor element 1A in the first embodiment, a diffusion layer (hereinafter referred to as a A configuration in which a porous diffusion layer 33 is formed can also be used. In this case, even if the second reference gas introduction port 321 of the second reference gas introduction path 32 is open at the end surface on the proximal side, the element strength can be improved by the porous diffusion layer 33 . can.

Since the diffusion resistance of the second reference gas introduction passage 32 is increased by arranging the porous diffusion layer 33, the oxygen supply amount in the above equation 1 is calculated as follows: It will be reduced compared to the case of the space portion. If it is desired to increase the amount of oxygen supplied, the cross-sectional area S of the second reference gas introduction passage 32 can be increased, or the portion filled with the porous diffusion layer 33 can be reduced. In the latter case, the porous diffusion layer 33 may be arranged so as to include at least the base end portion where the terminal portion 71 is formed from the base end surface where the second reference gas introduction port 321 opens. It is possible to improve the ease of assembly by reinforcing the proximal end portion that is held during assembly.

Alternatively, as shown in FIG. 16 as a modified example, the passage wall of the second reference gas introduction passage 32 may be provided with a reinforcing portion 34 in which a columnar reinforcing member is embedded. Specifically, the reinforcing portion 34 is formed to reduce the flow of the second reference gas introduction passage 32 from the vicinity of the base end surface where the second reference gas introduction port 321 opens to the portion including the base end portion where the terminal portion 71 is formed. Can be placed within the width of the road. Also in this way, it is possible to reinforce the base end part that is held when assembling the sensor element 1A, thereby improving the assembling efficiency.

The reinforcement part 34 has, for example, a higher strength than the shielding layer 14 that forms the flow path wall, and may be formed so that the strength at the end of the second reference gas introduction path 32 is improved. It may be the same ceramic material as or a different material. Further, here, the reinforcing member embedded in the reinforcing portion 34 is formed in a flat rectangular plate shape, but the shape, size, etc. can be changed as appropriate. Moreover, although the reinforcing member is embedded inside the flow path wall, for example, a configuration in which a part of the reinforcing member is exposed at the end surface where the second reference gas inlet 321 is formed may be employed.

Furthermore, as shown in FIG. 17 as a modification, a plurality of second reference gas introduction ports 321 may be opened in the width direction wall of the second reference gas introduction passage 32 . The second reference gas introduction path 32 is not formed at the proximal end portion where the terminal portion 71 (see, for example, FIG. 15) is arranged, and the space portion serving as the second reference gas introduction path 32 is formed at the proximal end. It branches into two from the part and communicates with a plurality of second reference gas introduction ports 321 opened in both side walls. The bifurcated path obliquely penetrates both side walls toward the base end, and the vicinity of the second reference gas inlet 321 is filled with the porous diffusion layer 33 .

Even in this way, no space is provided in the proximal end portion that is sandwiched during assembly of the sensor element 1A, and the plurality of second reference gas introduction ports 321 are reinforced by the porous diffusion layer 33. Therefore, the strength of the element is improved, and the ease of assembly can be improved. The porous diffusion layer 33 may be filled in the entire second reference gas introduction path 32, or the configuration may be such that the porous diffusion layer 33 is not filled. When calculating the oxygen supply amount for these configurations, for the bifurcated path, the oxygen supply amount corresponding to the cross-sectional area and the arrangement of the porous diffusion layer 33 is obtained and reflected in the overall oxygen supply amount. be able to.

In this embodiment, the porous diffusion layer 33 can be applied not only to the second reference gas introduction passage 32 shown in FIGS. 14 and 16, but also to the second reference gas introduction passage 32 shown in FIG. 14 or FIG. In that case, the porous diffusion layer 33 is provided at least at the second reference gas introduction port 321 and its vicinity, so that the strength of the opening can be improved. Moreover, the flow path shape of the second reference gas introduction path 32 is not limited to the illustrated one, and can be changed as appropriate.

In the above embodiments, the gas sensor 1 is used as a NOx sensor. Moreover, the configuration and shape of each part of the gas sensor 1 and the sensor element 1A are not limited to those shown in the drawings, and can be changed as appropriate.

The present disclosure is not limited to the above embodiments, and can be applied to various embodiments without departing from the scope of the present disclosure.

Although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to such embodiments or structures. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and configurations, as well as other combinations and configurations, including single elements, more, or less, are within the scope and spirit of this disclosure.

Claims

A gas sensor (1) for detecting the concentration of a specific gas contained in a gas (G) to be measured,
a measured gas chamber (2) into which the measured gas is introduced;
a first solid electrolyte body (11) and a second solid electrolyte body (12) facing each other with the gas chamber to be measured interposed therebetween;
a first reference gas introduction passage (31) and a second reference gas introduction passage (32) through which a reference gas (A) containing oxygen is introduced;
Having a pump electrode (41) on the surface facing the gas chamber to be measured of the first solid electrolyte body, and having a first reference electrode (42) on the surface facing the first reference gas introduction path, a pump cell (4) for adjusting the oxygen concentration in the gas chamber to be measured;
Having a sensor electrode (51) on the surface facing the gas chamber to be measured of the second solid electrolyte body, and having a second reference electrode (52) on the surface facing the second reference gas introduction path, a sensor cell (5) that produces an output based on the specific gas;
The voltage applied to the pump cell when the sensor is started is controlled to a starting voltage (V2) higher than the normal control voltage (V1). an early activation control unit (101) that removes oxygen occluded in the sensor electrode using the generated reducing gas,
The second reference gas introduction path is configured to indicate a limit amount of oxygen supplied from the second reference gas introduction path toward the sensor electrode when the sensor is started, as a current value flowing through the second solid electrolyte body. A gas sensor formed to have a limiting current value of 20 μA or more.
The gas sensor according to claim 1, wherein the oxygen limiting current value is 2500 μA or less.
The early activation control unit applies the start-up voltage and the start-up voltage so that the coulomb amount indicating the total amount of the reducing gas generated when the sensor is started is in the range of 2000 μA s or more and 11000 μA s or less. 3. The gas sensor according to claim 1, which controls time.
The gas sensor according to any one of claims 1 to 3, wherein the second reference gas introducing passage has a flow passage cross-sectional area of 0.007 mm 2 or more at the portion where the second reference electrode is formed.
The gas sensor according to any one of claims 1 to 4, wherein the second reference gas introducing passage has a flow passage cross-sectional area of 0.80 mm 2 or less at the portion where the second reference electrode is formed.
A sensor element (1A) in which the pump cell and the sensor cell are formed,
A first reference gas introduction port (311) for introducing the reference gas into the first reference gas introduction passage and the reference The second reference gas introduction ports (321) for introducing gas are respectively open,
6. The oxygen limiting current value according to any one of claims 1 to 5, wherein the magnitude of the oxygen limiting current value is determined depending on the flow channel structure of the second reference gas introduction passage from the second reference gas introduction port to the second reference electrode. 2. The gas sensor according to item 1.
The gas sensor according to claim 6, wherein a reinforcing portion (34) is formed on at least a portion of the channel wall surrounding the second reference gas inlet.
The second reference gas introduction port is formed at the one end side of the sensor element by a through hole penetrating in the stacking direction through a flow channel wall of the second reference gas introduction passage extending in the longitudinal direction. 8. The gas sensor according to 6 or 7.
A plurality of the second reference gas introduction ports are open at the one end side of the sensor element, and the plurality of the second reference gas introduction ports are arranged on both sides of the second reference gas introduction path extending in the longitudinal direction. 8. The gas sensor according to claim 6 or 7, provided through a wall.
A diffusion layer (33) filled with a porous material is formed in at least a part of the second reference gas introduction passage leading to the second reference gas introduction port. The gas sensor described in .