JP2021085665A - Gas sensor and method for detecting crack - Google Patents

Abstract

To provide a gas sensor and a method for detecting a crack that can detect a crack when a measurement target gas contains oxygen in a high concentration.SOLUTION: A gas sensor 100 applies a predetermined pump voltage Vp3 for which current flowing between a reference electrode 42 and an inside pump electrode 22 is a limitation current, between the reference electrode 42 and the inside pump electrode 22 to take oxygen from around the reference electrode 42 to around the inside pump electrode 22, acquires a pump current Ip3 flowing between the reference electrode 42 and the inside pump electrode 22 when the pump voltage Vp3 is applied, and detects a crack in the element body on the basis of the acquired pump current Ip3.SELECTED DRAWING: Figure 6

Description

The present invention relates to a gas sensor and a crack detection method.

Conventionally, as a gas sensor that detects a specific gas concentration such as oxygen or NOx in a gas to be measured such as an automobile exhaust gas, a gas sensor using a solid electrolyte such as stabilized zirconia is known. For example, in Patent Document 1, it is sandwiched between the first electrode provided in the exhaust chamber through which the gas to be measured flows, the second electrode provided in the atmospheric duct into which the reference gas is introduced, and the first and second electrodes. Described is a gas sensor having a sensor element having a solid electrolyte layer and generating a sensor output according to the oxygen concentration in the gas to be measured. Further, in Patent Document 1, a predetermined voltage is applied between both electrodes so as to supply oxygen from the second electrode side to the first electrode side, and the rate of change of the current between both electrodes caused by oxygen supply is shown. It is described that the parameters are calculated and the cracks in the solid electrolyte layer are detected based on the velocity parameters. In Patent Document 1, when a crack occurs in the solid electrolyte layer, a gas to be measured having a low oxygen concentration flows into the atmosphere chamber, the oxygen concentration around the second electrode becomes low, and the oxygen concentration from the second electrode side to the first electrode side is reduced. Cracks in the solid electrolyte layer are detected by utilizing the fact that it becomes difficult for current to flow.

Japanese Unexamined Patent Publication No. 2014-235107

However, Patent Document 1 has a problem that cracks cannot be detected when the oxygen concentration of the gas to be measured is high. Therefore, a gas sensor and a crack detection method capable of detecting cracks when the oxygen concentration of the gas to be measured is high have been desired.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a gas sensor capable of detecting cracks when the oxygen concentration of the gas to be measured is high and a crack detecting method.

The present invention has taken the following measures to achieve the above-mentioned main object.

The gas sensor of the present invention
An element body having an oxygen ion conductive solid electrolyte layer and an internal measurement gas flow section for introducing and circulating the measurement gas, and an element body.
The electrode to be measured gas side arranged in the gas flow unit to be measured and the electrode to be measured
A reference electrode arranged inside the element body and
A reference gas introduction unit that introduces a reference gas that serves as a reference for detecting the specific gas concentration of the gas to be measured from the reference gas inlet and distributes the reference gas to the reference electrode and imparts diffusion resistance to the reference gas.
A predetermined detection voltage is applied between the reference electrode and the gas-measured gas-side electrode so that the current flowing between the reference electrode and the gas-measured gas-side electrode becomes a limit current, and the reference electrode is applied. Oxygen is pumped from the periphery of the electrode to the gas side electrode to be measured, and the detection current flowing between the reference electrode and the gas side electrode to be measured is acquired when the detection voltage is applied. A crack detecting means for detecting a crack in the element body based on the detection current, and
It is equipped with.

In this gas sensor, the reference gas introduction portion is formed so as to impart diffusion resistance to the reference gas. Therefore, a predetermined detection voltage is applied between both electrodes so that the current flowing between the reference electrode and the gas-side electrode to be measured becomes the critical current, and the circumference of the reference electrode to the periphery of the gas-measured gas-side electrode is measured. When oxygen is pumped into the electrode, a detection current corresponding to the amount of oxygen introduced into the reference gas introduction section flows. At this time, for example, if there is a crack between the part of the element body on the gas side to be measured that comes into contact with the gas to be measured and the part on the side of the reference gas that comes into contact with the reference gas, oxygen around the part to be measured gas cracks. It is introduced into the reference gas introduction section via. Therefore, when there is a crack, the amount of oxygen introduced into the reference gas introduction portion increases, and the detection current becomes larger than when there is no crack. In particular, the greater the oxygen present around the portion to be measured, the greater the difference in the detection current depending on the presence or absence of cracks. Therefore, the higher the oxygen concentration of the gas to be measured, the more accurately the cracks are detected based on the detection current. it can. Therefore, in the present invention, when the oxygen concentration of the gas to be measured is high, cracks in the element body can be detected based on the detection current. The predetermined detection voltage may be a value empirically determined using a gas sensor having the same structure.

In the gas sensor of the present invention, the crack detecting means may determine that the crack is formed when the detecting current exceeds a predetermined detection threshold value.

The gas sensor of the present invention includes a heater provided inside the element body, a heater portion arranged so as to cover the heater and having a porous heater insulating layer capable of gas flow, and a reference gas introduction portion. A connecting portion that connects the portion inside the reference gas inlet and the heater portion in a state in which gas can flow may be provided. In a gas sensor having a heater inside the element body, the temperature gradient of the part between the heater and the gas flow part to be measured tends to be large when the heater is heated, and cracks may occur in that part due to thermal stress. Such cracks can be detected if the heater insulating layer and the connecting portion are provided. For example, when there is a crack in the part of the element body between the heater part and the gas flow part to be measured, oxygen in the gas flow part to be measured enters the reference gas introduction part through the crack, the heater insulating layer and the connecting part. Since the detection current is larger than that in the case where the crack is not introduced, the crack can be detected based on the detection current.

The gas sensor of the present invention includes a plurality of the electrode to be measured, and the crack detecting means is individually placed between the reference electrode and the electrode to be measured for each of the electrodes to be measured. A predetermined detection voltage such that the flowing current becomes the limit current is applied between the reference electrode and the electrode to be measured, and oxygen is transferred from the periphery of the reference electrode to the periphery of the gas side electrode to be measured. The detection is performed, and the detection current flowing between the reference electrode and the gas-measured gas-side electrode when the detection voltage is applied is acquired, and the detection is individually acquired for each of the gas-measured gas-side electrodes. The position of the crack may be estimated based on the working current. When oxygen is pumped from around the reference electrode to around each gas-side electrode to be measured, the closer the electrode to be measured is to the crack, the more oxygen pumped around the gas-to-measure electrode reaches the crack. It is easy to reach the reference gas introduction part through the crack. Therefore, when a detection voltage is applied between the reference electrode and the electrode on the gas side to be measured that is close to the crack, the detection current when there is a crack tends to increase. Therefore, the position of the crack can be estimated based on the detection current measured individually for each of the electrodes on the gas side to be measured.

The crack detection method of the present invention
An element body having an oxygen ion conductive solid electrolyte layer and an internal measurement gas flow section for introducing and circulating the measurement gas, and an element body.
The electrode to be measured gas side arranged in the gas flow unit to be measured and the electrode to be measured
A reference electrode arranged inside the element body and
A reference gas introduction unit that introduces a reference gas that serves as a reference for detecting the specific gas concentration of the gas to be measured from the reference gas inlet and distributes the reference gas to the reference electrode and imparts diffusion resistance to the reference gas.
It is a crack detection method of a sensor element equipped with
A predetermined detection voltage is applied between the reference electrode and the gas-measured gas-side electrode so that the current flowing between the reference electrode and the gas-measured gas-side electrode becomes a limit current, and the reference electrode is applied. Oxygen is drawn from the periphery of the electrode to the gas side electrode to be measured, and the detection current flowing between the reference electrode and the gas side electrode to be measured is acquired when the detection voltage is applied. A crack in the element body is detected based on the detection current.
It is a thing.

In this crack detection method, similarly to the gas sensor described above, a crack in the element body can be detected by utilizing the fact that the detection current increases when there is a crack.

A vertical sectional view of the gas sensor 100. FIG. 6 is a schematic cross-sectional view schematically showing an example of the configuration of the sensor element 101. The block diagram which shows the electrical connection relationship between a control device 95 and each cell. The flowchart which shows an example of a crack detection process. FIG. 6 is a VI curve showing an example of the relationship between the pump voltage Vp3 and the pump current Ip3. Explanatory drawing which shows the flow of oxygen at the time of a crack detection process. The graph which shows an example of the relationship between the oxygen concentration of the measured gas and the critical current value of Ip3. FIG. 6 is a schematic cross-sectional view of the sensor element 201 of the modified example.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view schematically showing an example of the configuration of the sensor element 101 included in the gas sensor 100. FIG. 3 is a block diagram showing an electrical connection relationship between the control device 95 and each cell. The sensor element 101 has a long rectangular body shape, the longitudinal direction of the sensor element 101 (horizontal direction in FIG. 2) is the front-rear direction, and the thickness direction of the sensor element 101 (vertical direction in FIG. 2) is up and down. The direction. Further, the width direction (direction perpendicular to the front-rear direction and the vertical direction) of the sensor element 101 is defined as the left-right direction.

As shown in FIG. 1, the gas sensor 100 includes a sensor element 101, a protective cover 130 that protects the front end side of the sensor element 101, a sensor assembly 140 including a connector 150 that conducts with the sensor element 101, and a control device 95 ( (See FIG. 3). As shown in the figure, the gas sensor 100 is attached to a pipe 190 such as an exhaust gas pipe of a vehicle and is used to measure the concentration of a specific gas such _{as NOx or O 2 contained in the exhaust gas as a gas to be measured.} .. In the present embodiment, the gas sensor 100 measures the NOx concentration as a specific gas concentration.

The protective cover 130 includes a bottomed tubular inner protective cover 131 that covers the front end of the sensor element 101, and a bottomed tubular outer protective cover 132 that covers the inner protective cover 131. The inner protective cover 131 and the outer protective cover 132 are formed with a plurality of holes for allowing the gas to be measured to flow into the protective cover 130. The sensor element chamber 133 is formed as a space surrounded by the inner protective cover 131, and the front end of the sensor element 101 is arranged in the sensor element chamber 133.

The sensor assembly 140 is provided on the surface (upper and lower surfaces) of the element sealing body 141 for sealing and fixing the sensor element 101, the bolt 147 attached to the element sealing body 141, the outer cylinder 148, and the rear end of the sensor element 101. It includes a connector 150 that is in contact with and electrically connected to the formed connector electrodes (only the heater connector electrode 71, which will be described later, is shown in FIG. 2).

The element sealing body 141 is sealed in a tubular main metal fitting 142, a tubular inner cylinder 143 that is coaxially welded and fixed to the main metal fitting 142, and inside through holes of the main metal fitting 142 and the inner cylinder 143. It includes ceramics supporters 144a to 144c, green compacts 145a and 145b, and a metal ring 146. The sensor element 101 is located on the central axis of the element encapsulant 141 and penetrates the element encapsulant 141 in the front-rear direction. The inner cylinder 143 has a reduced diameter portion 143a for pressing the green compact 145b in the central axis direction of the inner cylinder 143, ceramics supporters 144a to 144c, and compacts 145a and 145b forward via a metal ring 146. A reduced diameter portion 143b for pressing is formed. The green compacts 145a and 145b are compressed between the main metal fitting 142 and the inner cylinder 143 and the sensor element 101 by the pressing force from the reduced diameter portions 143a and 143b, so that the green compacts 145a and 145b are protected by the protective cover 130. The sensor element chamber 133 inside and the space 149 inside the outer cylinder 148 are sealed, and the sensor element 101 is fixed.

The bolt 147 is fixed coaxially with the main metal fitting 142, and a male screw portion is formed on the outer peripheral surface. The male threaded portion of the bolt 147 is inserted into a fixing member 191 welded to the pipe 190 and provided with a female threaded portion on the inner peripheral surface. As a result, the gas sensor 100 is fixed to the pipe 190 with the front end of the sensor element 101 and the portion of the protective cover 130 of the gas sensor 100 protruding into the pipe 190.

The outer cylinder 148 covers the periphery of the inner cylinder 143, the sensor element 101, and the connector 150, and a plurality of lead wires 155 connected to the connector 150 are pulled out from the rear end. The lead wire 155 is electrically connected to each electrode (described later) of the sensor element 101 via the connector 150. The gap between the outer cylinder 148 and the lead wire 155 is sealed by a rubber stopper 157. The space 149 in the outer cylinder 148 is filled with a reference gas (atmosphere in this embodiment). The rear end of the sensor element 101 is arranged in this space 149.

As shown in FIG. 2, the sensor element 101 includes a first substrate layer 1, a second substrate layer 2, and a third substrate layer 3 _{, each of which is composed of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO 2).} , The six layers of the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 are laminated in this order from the bottom in the drawing. Further, the solid electrolyte forming these six layers is a dense and airtight one. The sensor element 101 is manufactured, for example, by performing predetermined processing, printing of a circuit pattern, or the like on a ceramic green sheet corresponding to each layer, laminating them, and further firing and integrating them.

At one end of the sensor element 101 (on the left side in FIG. 2), between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas introduction port 10 and a first diffusion rate-determining unit 11 are located. , The buffer space 12, the second diffusion rate-determining section 13, the first internal space 20, the third diffusion rate-determining section 30, the second internal space 40, the fourth diffusion rate-determining section 60, and the third interior. The vacant space 61 is formed adjacent to each other in this order.

The gas introduction port 10, the buffer space 12, the first internal space 20, the second internal space 40, and the third internal space 61 have an upper portion provided in a manner in which the spacer layer 5 is hollowed out. The space inside the sensor element 101 is defined by the lower surface of the second solid electrolyte layer 6, the lower portion is the upper surface of the first solid electrolyte layer 4, and the side portion is partitioned by the side surface of the spacer layer 5.

The first diffusion rate-determining section 11, the second diffusion rate-determining section 13, and the third diffusion rate-determining section 30 are all provided as two horizontally long slits (openings have a longitudinal direction in the direction perpendicular to the drawing). .. Further, the fourth diffusion rate-determining portion 60 is provided as one horizontally long slit (the opening has a longitudinal direction in the direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. The portion from the gas introduction port 10 to the third internal space 61 is also referred to as a gas distribution section to be measured.

An atmosphere introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The atmosphere introduction layer 48 is a porous body made of ceramics such as alumina. The rear end surface of the atmosphere introduction layer 48 is an inlet portion 48c, and the inlet portion 48c is exposed on the rear end surface of the sensor element 101. The entrance portion 48c is exposed in the space 149 of FIG. 1 (see FIG. 1). A reference gas for measuring the NOx concentration is introduced into the atmosphere introduction layer 48 from the inlet portion 48c. The reference gas was the atmosphere (atmosphere in the space 149 of FIG. 1) in the present embodiment. Further, the atmosphere introduction layer 48 is formed so as to cover the reference electrode 42. The atmosphere introduction layer 48 introduces the reference gas introduced from the inlet portion 48c into the reference electrode 42 while imparting a predetermined diffusion resistance.

The reference electrode 42 is an electrode formed so as to be sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, the atmosphere introduction layer 48 is provided around the reference electrode 42. ing. The reference electrode 42 is formed directly on the upper surface of the third substrate layer 3, and the portion other than the portion in contact with the upper surface of the third substrate layer 3 is covered with the atmosphere introduction layer 48. However, at least a part of the reference electrode 42 may be covered with the atmosphere introduction layer 48. Further, as will be described later, it is possible to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20, the second internal space 40, and the third internal space 61 using the reference electrode 42. It has become. The reference electrode 42 is formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO ₂ ).

In the gas distribution section to be measured, the gas introduction port 10 is a portion that is open to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas introduction port 10. There is. The first diffusion rate-determining unit 11 is a portion that imparts a predetermined diffusion resistance to the gas to be measured taken in from the gas introduction port 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate-determining unit 11 to the second diffusion rate-determining unit 13. The second diffusion rate-determining unit 13 is a portion that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from the outside of the sensor element 101 to the inside of the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (if the gas to be measured is the exhaust gas of an automobile, the pulsation of the exhaust pressure). ) Suddenly taken into the inside of the sensor element 101 from the gas introduction port 10), the gas to be measured is not directly introduced into the first internal space 20, but the first diffusion rate-determining unit 11, the buffer space 12, and the second. After the pressure fluctuation of the gas to be measured is canceled through the diffusion rate-determining unit 13, the gas is introduced into the first internal space 20. As a result, the pressure fluctuation of the gas to be measured introduced into the first internal space 20 becomes almost negligible. The first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate-determining unit 13. The oxygen partial pressure is adjusted by operating the main pump cell 21.

The main pump cell 21 has an inner pump electrode 22 having a ceiling electrode portion 22a provided on substantially the entire lower surface of the lower surface of the second solid electrolyte layer 6 facing the first internal space 20, and an upper surface of the second solid electrolyte layer 6. An outer pump electrode 23 provided in a region corresponding to the ceiling electrode portion 22a so as to be exposed to an external space (sensor element chamber 133 in FIG. 1), and a second solid electrolyte layer 6 sandwiched between these electrodes. It is an electrochemical pump cell composed of.

The inner pump electrode 22 is formed so as to straddle the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that partition the first internal space 20 and the spacer layer 5 that provides the side wall. There is. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal space 20, and a bottom portion is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. The electrode portion 22b is directly formed, and the side electrode portion (not shown) constitutes both side wall portions of the first internal space 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b. It is formed on the side wall surface (inner surface) of the spacer layer 5, and is arranged in a structure in the form of a tunnel at the arrangement portion of the side electrode portion.

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

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

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

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

The third diffusion rate-determining unit 30 imparts a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and applies the gas to be measured. It is a part leading to the second internal space 40.

In the second internal space 40, after the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal space 20, the auxiliary pump cell 50 is further applied to the gas to be measured introduced through the third diffusion rate-determining unit 30. It is provided as a space for adjusting the oxygen partial pressure. As a result, the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, so that the gas sensor 100 can measure the NOx concentration with high accuracy.

The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, and an outer pump electrode 23 (outer pump electrode 23). It is an auxiliary electrochemical pump cell composed of a suitable electrode on the outside of the sensor element 101) and a second solid electrolyte layer 6.

The auxiliary pump electrode 51 is arranged in the second internal space 40 in a structure having a tunnel shape similar to that of the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and the upper surface of the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40. The bottom electrode portion 51b is directly formed, and the side electrode portion (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b provides a side wall of the second internal space 40. It has a tunnel-like structure formed on both wall surfaces of the spacer layer 5. The auxiliary pump electrode 51 is also formed by using a material having a weakened reducing ability for the NOx component in the gas to be measured, similarly to the inner pump electrode 22.

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

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

The auxiliary pump cell 50 pumps with a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. As a result, the partial pressure of oxygen in the atmosphere in the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for controlling the main pump. Specifically, the pump current Ip1 is input to the oxygen partial pressure detection sensor cell 80 for controlling the main pump as a control signal, and the voltage V0 is controlled so that the third diffusion rate control unit 30 to the second internal space 40 The gradient of the oxygen partial pressure in the gas to be measured introduced into the pump is controlled to be constant at all times. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

The fourth diffusion rate-determining unit 60 imparts a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal space 40, and transfers the gas to be measured. It is a part leading to the third internal space 61. The fourth diffusion rate-determining unit 60 plays a role of limiting the amount of NOx flowing into the third internal space 61.

The third internal space 61 is in the gas to be measured with respect to the gas to be measured introduced through the fourth diffusion rate-determining unit 60 after the oxygen concentration (oxygen partial pressure) is adjusted in advance in the second internal space 40. It is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration of the above. The measurement of the NOx concentration is mainly performed by the operation of the measurement pump cell 41 in the third internal space 61.

The measurement pump cell 41 measures the NOx concentration in the gas to be measured in the third internal space 61. The measurement pump cell 41 includes a measurement electrode 44 provided directly on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61, an outer pump electrode 23, a second solid electrolyte layer 6, and a spacer layer. It is an electrochemical pump cell composed of 5 and a 1st solid electrolyte layer 4. _{The measurement electrode 44 is a porous cermet electrode (for example, a cermet electrode of Pt and ZrO 2} ) made of a material having a reduction ability for a NOx component in the gas to be measured higher than that of the inner pump electrode 22. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx existing in the atmosphere in the third internal space 61.

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

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

The gas to be measured guided into the second internal space 40 reaches the measurement electrode 44 in the third internal space 61 through the fourth diffusion rate-determining unit 60 under the condition that the oxygen partial pressure is controlled. .. Nitrogen oxides in the gas to be measured around the measurement electrode 44 are reduced (2NO → N ₂ + O ₂ ) to generate oxygen. Then, the generated oxygen is pumped by the measurement pump cell 41, and at that time, the variable power supply 46 is set so that the voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 becomes constant. The voltage Vp2 of is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the nitrogen oxides in the gas to be measured are used by using the pump current Ip2 in the measurement pump cell 41. The concentration will be calculated.

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

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

Further, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are used to form an electrochemical pump cell, that is, a reference electrode 42. A first detection pump cell 85 is configured. The first pump cell for detection 85 pumps oxygen by causing a pump current Ip3 to flow by a pump voltage Vp3 applied by a variable power source 86 connected between the reference electrode 42 and the inner pump electrode 22. As a result, the detection first pump cell 85 draws oxygen from the space around the reference electrode 42 (atmosphere introduction layer 48) to the space around the inner pump electrode 22 (first internal space 20).

Further, the auxiliary pump electrode 51, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 form an electrochemical pump cell, that is, a reference electrode 42. A second detection pump cell 87 is configured. The second pump cell for detection 87 pumps oxygen by causing a pump current Ip4 to flow by a pump voltage Vp4 applied by a variable power source 88 connected between the reference electrode 42 and the auxiliary pump electrode 51. As a result, the detection second pump cell 87 draws oxygen from the space around the reference electrode 42 (atmosphere introduction layer 48) to the space around the auxiliary pump electrode 51 (second internal space 40).

Further, the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 constitute an electrochemical pump cell cell, that is, a third pump cell 89 for detection. The detection third pump cell 89 pumps oxygen by causing a pump current Ip5 to flow by a pump voltage Vp5 applied by a variable power source 90 connected between the reference electrode 42 and the measurement electrode 44. As a result, the detection third pump cell 89 draws oxygen from the space around the reference electrode 42 (atmosphere introduction layer 48) to the space around the measurement electrode 44 (third internal space 61).

Further, the sensor element 101 includes a heater unit 70 that plays a role of temperature adjustment for heating and keeping the sensor element 101 warm in order to increase the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure dissipation hole 75.

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

The heater 72 is an electric resistor formed in a manner of being sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connector electrode 71 via a through hole 73, and generates heat when power is supplied from the outside through the heater connector electrode 71 to heat and retain heat of the solid electrolyte forming the sensor element 101. ..

Further, the heater 72 is embedded in the entire area from the first internal space 20 to the third internal space 61, and the entire sensor element 101 can be adjusted to a temperature at which the solid electrolyte is activated. ing.

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

The pressure dissipation hole 75 is a portion provided so as to penetrate the third substrate layer 3 and the atmosphere introduction layer 48, and is formed for the purpose of alleviating an increase in internal pressure due to a temperature increase in the heater insulating layer 74. .. The pressure dissipation hole 75 connects a portion of the atmosphere introduction layer 48 inside the inlet of the reference gas (here, the inlet portion 48c) and the heater portion 70 in a state in which gas can flow. ..

The variable power supplies 24, 46, 52, 86, 88, 90 and the like shown in FIG. 2 are actually via lead wires (not shown) formed in the sensor element 101 and the connectors 150 and lead wires 155 of FIG. It is connected to each electrode.

The control device 95 includes the above-mentioned variable power supplies 24, 46, 52, 86, 88, 90 and a control unit 91. The control unit 91 is a microprocessor including a CPU 92, a storage unit 94, and the like. The storage unit 94 is a device that stores various programs and various data. The control unit 91 detects the voltage V0 detected by the main pump control oxygen partial pressure detection sensor cell 80, the voltage V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81, and the measurement pump control oxygen partial pressure detection. The voltage V2 detected by the sensor cell 82, the voltage Vref detected by the sensor cell 83, the pump current Ip0 detected by the main pump cell 21, the pump current Ip1 detected by the auxiliary pump cell 50, and the measurement pump cell 41. The detected pump current Ip2, the pump current Ip3 detected by the first detection pump cell 85, the pump current Ip4 detected by the second detection pump cell 87, and the pump current detected by the third detection pump cell 89. Enter Ip5. Further, the control unit 91 outputs a control signal to the variable power supplies 24, 46, 52, 86, 88, 90, and the voltages Vp0, Vp1, Vp2, output by the variable power supplies 24, 46, 52, 86, 88, 90 are output. It controls Vp3, Vp4, and Vp5, thereby controlling the main pump cell 21, the measurement pump cell 41, the auxiliary pump cell 50, the detection first pump cell 85, the detection second pump cell 87, and the detection third pump cell 89. The storage unit 94 also stores target values V0 *, V1 *, V2 *, etc., which will be described later. The CPU 92 of the control unit 91 controls the cells 21, 41, and 50 with reference to these target values V0 *, V1 *, and V2 *, and performs NOx concentration detection processing described later. Further, the storage unit 94 also stores set values Vsp3, Vsp4, Vsp5 and the like, which will be described later. The CPU 92 of the control unit 91 controls each cell 85, 87, 89 with reference to these set values Vsp3, Vsp4, Vsp5, and performs a crack detection process described later. The control unit 91 controls the variable power supplies 86, 88, 90 so as not to operate the cells 85, 87, 89, that is, to output the voltages Vp3, Vp4, Vp5 when performing the NOx concentration detection process. To do.

Next, an example of the NOx concentration detection process for detecting the NOx concentration in the gas to be measured using the gas sensor 100 will be described. When the NOx concentration detection process is started, the control unit 91 of the control device 95 sets the voltage V0 to the target value (referred to as the target value V0 *) (that is, the oxygen concentration in the first internal space 20 is the target concentration). The pump voltage Vp0 of the variable power supply 24 is feedback-controlled. The pump current Ip0 changes according to the oxygen concentration of the gas to be measured and the air-fuel ratio (A / F) of the gas to be measured.

Further, the control unit 91 sets a predetermined low oxygen so that the voltage V1 becomes a constant value (referred to as a target value V1 *) (that is, the oxygen concentration of the second internal space 40 does not substantially affect the measurement of NOx). The voltage Vp1 of the variable power supply 52 is feedback-controlled (so that the concentration becomes high). At the same time, the control unit 91 sets the target value V0 * of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 flowing by the voltage Vp1 becomes a constant value (referred to as the target value Ip1 *) (feedback control). To do. As a result, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate-determining unit 30 into the second internal space 40 is always constant. Further, the partial pressure of oxygen in the atmosphere in the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx. The target value V0 * is set to a value such that the oxygen concentration of the first internal space 20 is higher than 0% and the oxygen concentration is low.

Further, the control unit 91 controls the variable power supply 46 so that the voltage V2 becomes a constant value (referred to as a target value V2 *) (that is, the oxygen concentration in the third internal space 61 becomes a predetermined low concentration). The voltage Vp2 is feedback-controlled. As a result, oxygen is pumped out from the third internal space 61 so that the oxygen generated by the reduction of NOx in the gas to be measured in the third internal space 61 becomes substantially zero. Then, the control unit 91 acquires the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal space 61 derived from the specific gas (NOx in this case), and is measured based on the pump current Ip2. Calculate the NOx concentration in the gas. In this way, oxygen derived from the specific gas in the gas to be measured introduced into the sensor element 101 is pumped out, and the specific gas concentration is based on the amount of oxygen pumped out (based on the pump current Ip2 in this embodiment). The method of detecting the above is called the limit current method.

The storage unit 94 stores a relational expression (for example, an expression of a linear function), a map, or the like as a correspondence relationship between the pump current Ip2 and the NOx concentration. Such a relational expression or map can be obtained experimentally in advance. The CPU 92 of the control unit 91 detects the NOx concentration in the gas to be measured based on the acquired pump current Ip2 and the correspondence relationship stored in the storage unit 94.

Next, an example of the crack detection process in the gas sensor 100 will be described with reference to FIG. FIG. 4 is a flowchart showing an example of the crack detection process. This process is executed at a predetermined crack detection timing, for example, at regular time intervals. Here, a case where the crack detection process is performed following the NOx concentration detection process described above will be described.

When the crack detection process is started, the control unit 91 first acquires the oxygen concentration information of the gas to be measured (S100). Here, the control unit 91 inputs the pump current Ip0 detected by the above-mentioned NOx concentration detection process as the oxygen concentration information. It is assumed that the storage unit 94 stores a relational expression (for example, a linear function expression) or a map as a correspondence relationship between the pump current Ip0 and the oxygen concentration of the gas to be measured, and the CPU 92 of the control unit 91 has acquired the pump. The oxygen concentration of the gas to be measured may be derived based on the correspondence between the current Ip0 and the correspondence stored in the storage unit 94. When the oxygen concentration information of the gas to be measured is acquired, the control unit 91 stops applying the pump voltages Vp0, Vp1 and Vp2 (S110), and temporarily interrupts the NOx concentration detection process. Subsequently, the control unit 91 controls the variable power supply 86 of the detection first pump cell 85 so as to apply the pump voltage Vp3 set to the set value Vsp3 (S120). As a result, oxygen is pumped from the periphery of the reference electrode 42 to the space around the inner pump electrode 22 (first internal space 20), and the pump current Ip3 flows. Then, the control unit 91 inputs the pump current Ip3 at this time (S130), and stops applying the pump voltage Vp3 (S140). Subsequently, the control unit 91 controls the variable power supply 88 of the second detection pump cell 87 so as to apply the pump voltage Vp4 set to the set value Vsp4 (S150). As a result, oxygen is pumped from the periphery of the reference electrode 42 into the space (second internal space 40) around the auxiliary pump electrode 51, and the pump current Ip4 flows. Then, the control unit 91 inputs the pump current Ip4 at this time (S160), and stops applying the pump voltage Vp4 (S170). Subsequently, the control unit 91 controls the variable power supply 90 of the detection third pump cell 89 so as to apply the pump voltage Vp5 set to the set value Vsp5 (S180). As a result, oxygen is pumped from the periphery of the reference electrode 42 into the space around the measurement electrode 44 (third internal space 61), and the pump current Ip5 flows. Then, the control unit 91 inputs the pump current Ip5 at this time (S190), and stops applying the pump voltage Vp5 (S200). When the pump currents Ip3 to Ip5 are input in this way, the control unit 91 detects whether the pump current Ip3 is equal to or higher than the detection threshold value Tp3 or the pump current Ip4 is detected based on the detection threshold values Tp3 to Tp5 stored in the storage unit 94. It is determined whether or not one or more of the threshold value Tp4 or more and the pump current Ip5 is one or more of the detection threshold value Tp5 or more is satisfied (S210). If the above-mentioned 1 or more is satisfied in S210, the control unit 91 determines that the sensor element 101 has a crack and performs a process of estimating the position of the crack (S220). Details of S220 will be described later. After that, the control unit 91 outputs the crack detection signal and the crack position to the outside (S230), terminates this routine, and restarts the NOx concentration detection process if necessary. On the other hand, if the control unit 91 does not satisfy the above-mentioned 1 or more in S210, the control unit 91 terminates this routine as it is, and restarts the NOx concentration detection process if necessary.

For the set value Vsp3 of the pump voltage Vp3 and the detection threshold Tp3 of the pump current Ip3, an experiment was conducted in advance to obtain a VI curve showing the relationship between the pump voltage Vp3 and the pump current Ip3, and the obtained VI curve. Can be set based on. The same applies to the set values Vsp4 and Vsp5 and the detection threshold values Tp4 and Tp5. Here, first, as an example of an experiment for acquiring a VI curve, an experiment for acquiring a VI curve showing the relationship between the pump voltage Vp3 and the pump current Ip3 will be described. First, a sensor element 101 with cracks and a sensor element 101 without cracks are prepared. The sensor element 101 with cracks may form cracks inside the sensor element 101, for example, by rapidly raising the temperature of the element. The crack is formed between the first internal space 20 and the heater portion 70, for example, as shown in FIG. 6 described later. Next, for each sensor element 101, the gas introduction port 10 side of the sensor element 101 is arranged in a predetermined gas to be measured (here, a model gas), and the inlet portion 48c side of the atmosphere introduction layer 48 is arranged in the atmosphere. A gas sensor 100 is arranged in the heater 72, and the heater 72 is energized to heat the sensor element 101 to a predetermined driving temperature (for example, 850 ° C.). The variable power supplies 24, 52, 46, 86, 88, and 90 are all in a state where no voltage is applied. After the temperature of the sensor element 101 stabilizes, oxygen is drawn from the periphery of the reference electrode 42 to the periphery of the inner pump electrode 22 by the variable power supply 86 between the reference electrode 42 and the inner pump electrode 22. A pump voltage Vp3 is applied. The pump voltage Vp3 is applied while gradually increasing (for example, 2 mV / sec). Then, the pump current Ip3 flowing at this time is measured, and a VI curve showing the relationship between the pump voltage Vp3 and the pump current Ip3 is obtained. For the VI curve showing the relationship between the pump voltage Vp4 and the pump current Ip4 and the VI curve showing the relationship between the pump voltage Vp5 and the pump current Ip5, the electrodes for measuring the pump current by applying the pump voltage are changed. Except for this, it may be acquired in the same manner as the VI curve showing the relationship between the pump voltage Vp3 and the pump current Ip3.

FIG. 5 shows an example of a VI curve showing the relationship between the pump voltage Vp3 and the pump current Ip3. As shown in FIG. 5, while the pump voltage Vp3 is low, the pump current Ip3 increases as the pump voltage Vp3 increases, but when the pump voltage Vp3 increases, the pump current Ip3 does not increase even if the pump voltage Vp3 increases. Will be saturated with. The saturation value that saturates without increasing the pump current even if the pump voltage increases is called the limit current value. As shown in FIG. 5, the limit current value of the pump current Ip3 is higher in the sensor element 101 with cracks than in the sensor element 101 without cracks. The reason for this can be inferred as follows.

When the crack detection process is started in the gas sensor 100 and the pump voltage Vp3 is applied, oxygen is pumped from the space around the reference electrode 42 to the space around the inner pump electrode 22 as shown in FIG. It is said. Here, if the sensor element 101 has a crack, the oxygen contained in the measured gas introduced from the sensor element chamber 133 (see FIG. 1) into the measured gas flow section and the pump current Ip3 cause the surrounding of the inner pump electrode 22 to be cracked. At least one of the oxygen pumped into the space reaches the heater insulating layer 74 through the crack, and reaches the periphery of the reference electrode 42 through the heater insulating layer 74, the pressure dissipation hole 75, and the air introduction layer 48. Therefore, the amount of oxygen around the reference electrode 42 increases. Therefore, when the sensor element 101 has a crack, the limit current value of the pump current Ip3 becomes larger than when there is no crack. Therefore, the gas sensor 100 can detect cracks based on the pump current Ip3. Similar to Ip3, the pump currents Ip4 and Ip5 also have a larger critical current value when there is a crack than when there is no crack. Therefore, the gas sensor 100 can detect cracks based on the pump current Ip4 and the pump current Ip5.

The set value Vsp3 of the pump voltage Vp3 may be selected from the voltage range of the pump voltage Vp3 (for example, the limit current range of FIG. 5) such that the pump current Ip3 becomes the limit current. The set values Vsp4 and Vsp5 of the pump voltages Vp4 and Vp5 may be set in the same manner as the set values Vsp3 of the pump voltage Vp3. The set values Vsp3, Vsp4, and Vsp5 may all be the same value, or one or more of Vsp3, Vsp4, and Vsp5 may be different values. Further, the detection threshold Tp3 of the pump current Ip3 is higher than the pump current Ip3 without cracks and lower than the pump current Ip3 with cracks when the pump voltage Vp3 set to the set value Vsp3 is applied. It may be selected from the current range, and the pump current Ip3 when there is no crack and the pump current Ip3 when there is a crack may be defined so as to be distinguishable. For example, as shown in FIG. 5, the pump current Ip3 without cracks may be Np3, and the pump current Ip3 with cracks may be Cp3, which may be selected from the current range between Np3 and Cp3. In addition, in FIG. 5, in determining the detection threshold value Tp3, the case where one sensor element 101 with a crack and one without a crack are prepared has been described, but a plurality of each of the sensor elements 101 are prepared, and a VI curve is obtained for each of them. The detection threshold Tp3 may be selected from the current range between the maximum value of Np3 and the minimum value of Cp3. The detection threshold values Tp4 and Tp5 of the pump currents Ip4 and Ip5 may be set in the same manner as the detection threshold values Tp3 of the pump currents Ip3.

By the way, as described above, in the gas sensor 100, oxygen existing in the gas flow section to be measured, for example, oxygen contained in the gas to be measured introduced into the gas flow section to be measured reaches the periphery of the reference electrode 42 through a crack. To do. Therefore, when the sensor element 101 has a crack, as shown by the broken line in FIG. 7, the limit current value of the pump current Ip3 increases as the oxygen concentration of the gas to be measured increases. On the other hand, when the sensor element 101 has no cracks, the oxygen existing in the gas flow section to be measured does not reach the periphery of the reference electrode 42. Therefore, when there are no cracks in the sensor element 101, the limit current value of the pump current Ip3 is substantially constant regardless of the oxygen concentration of the gas to be measured, as shown by the solid line in FIG. As described above, in the gas sensor 100, the higher the oxygen concentration of the gas to be measured, the larger the difference between the limit current values of the pump currents Ip3, Ip4, and Ip5 between the case where there is a crack and the case where there is no crack. Therefore, here, the detection threshold value Tp3 is changed so that the higher the oxygen concentration of the gas to be measured, the higher the threshold value Tp3. The detection threshold Tp3 may be changed linearly or stepwise so that the relationship with the oxygen concentration of the gas to be measured becomes a linear function, for example, as shown by the alternate long and short dash line in FIG. .. The detection threshold Tp3 may be changed so that the ratio of the difference between Cp3 minus Tp3 and the difference between Tp3 minus Np3 is substantially constant at each oxygen concentration as shown by the alternate long and short dash line in FIG. In order to change the detection threshold Tp3 in association with the oxygen concentration of the gas to be measured, the storage unit 94 may store an expression or a map showing the correspondence between the detection threshold Tp3 and the oxygen concentration of the gas to be measured. Good. In that case, the control unit 91 may derive the detection threshold value Tp3 by using the oxygen concentration of the gas to be measured acquired in S100 and the formula or map stored in the storage unit 94. The same applies to the detection thresholds Tp4 and Tp5.

Next, the estimation of the crack position of S220 will be described. In the gas sensor 100, of the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44, the electrode close to the crack easily reaches the crack, and the pumped oxygen easily reaches the reference electrode 42 through the crack. , The limit current value of the pump current tends to increase. The control unit 91 uses this to estimate the position of the crack. In the process of estimating the position of the crack, for example, it may be estimated that the crack is formed around the electrode having the largest difference between the input pump currents Ip3, Ip4, and Ip5 minus the respective detection threshold values. Further, for example, when there is only one of the input pump currents Ip3, Ip4, and Ip5 that is equal to or higher than the detection threshold value, a crack is formed around the electrode in which the input pump current is equal to or higher than the detection threshold value. It may be presumed that it is.

Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5 and the second solid electrolyte layer 6 of the present embodiment correspond to the element body of the present invention, and the gas Introduction port 10, first diffusion rate-determining section 11, buffer space 12, second diffusion rate-determining section 13, first internal space 20, third diffusion rate-determining section 30, second internal space 40, fourth diffusion rate-determining section 60, and The third internal space 61 corresponds to the gas flow section to be measured, the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 each correspond to the gas side electrode to be measured, and the reference electrode 42 corresponds to the reference electrode. The atmosphere introduction layer 48 corresponds to the reference gas introduction portion, the inlet portion 48c corresponds to the reference gas inlet, and the gas sensor 100 corresponds to the gas sensor. Further, when the pump voltage Vp3 set in the set value Vsp33, the pump voltage Vp4 set in the set value Vsp44, and the pump voltage Vp5 set in the set value Vsp5 correspond to the detection voltage, and each detection voltage is applied. Each of the pump currents Ip3, Ip4, and Ip5 corresponds to the detection current, and the control unit 91 corresponds to the crack detecting means. Further, the detection thresholds Tp3, Tp4, and Tp5 correspond to the detection thresholds. Further, the heater 72 corresponds to the heater, the heater insulating layer 74 corresponds to the heater insulating layer, the heater portion 70 corresponds to the heater portion, and the pressure dissipation hole 75 corresponds to the connecting portion. Further, the sensor element 101 corresponds to the sensor element. Further, in the above-described embodiment, an example of the crack detection method of the present invention is also clarified by explaining the operation of the gas sensor 100.

In the gas sensor 100 of the present embodiment described in detail above, as described above, when the pump current Ip3 when the pump voltage Vp3 set to the set value Vsp3 is applied and the pump voltage Vp4 set to the set value Vsp4 are applied. A crack in the element body can be detected based on any one or more of the pump current Ip4 and the pump current Ip5 when the pump voltage Vp5 set to the set value Vsp5 is applied. In particular, in the gas sensor 100, as described above, the higher the oxygen concentration of the gas to be measured, the larger the difference between the limit current values of the pump currents Ip3, Ip4, and Ip5 between the case where there is a crack and the case where there is no crack. The higher the oxygen concentration of the gas, the more accurately the crack can be detected. In the gas sensor 100, oxygen is drawn from the periphery of the reference electrode 42 to the vicinity of the electrode to be measured (inner pump electrode 22, auxiliary pump electrode 51, measurement electrode 44), so that the gas to be measured itself contains oxygen. Even if it is not contained, oxygen is present in the gas flow section to be measured, and this oxygen reaches the periphery of the reference electrode 42 through the crack. Therefore, even when the gas to be measured does not contain oxygen, cracks in the element body can be detected based on the pump currents Ip3, Ip4, and Ip5. Further, in the gas sensor 100, if the gas to be measured contains oxides such as NOx, they are reduced by the electrode to be measured on the gas side (for example, the measurement electrode 44 made of a material having an enhanced reducing ability with respect to NOx). Oxygen is generated, and the generated oxygen reaches the periphery of the reference electrode 42 through the crack. Therefore, even when the gas to be measured does not contain oxygen, cracks in the element body can be detected based on the pump currents Ip3, Ip4, and Ip5.

Further, since the gas sensor 100 includes the heater insulating layer 74 and the pressure dissipation hole 75, cracks between the gas flow section to be measured and the heater section 70 can be detected.

Further, since the gas sensor 100 acquires the pump currents Ip3, Ip4, Ip5, the crack position can be estimated based on the pump currents Ip3, Ip4, Ip5.

It goes without saying that the present invention is not limited to the above-described embodiment, and can be implemented in various aspects as long as it belongs to the technical scope of the present invention.

In the above-described embodiment, the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 are used as the measurement gas side electrodes, but one or two of them may not be used as the measurement gas side electrodes. Good. That is, the control unit 91 processes and measures S120 to S140 using the first detection pump cell 85 including the inner pump electrode 22, and processes and measures S150 to S170 using the second detection pump cell 87 including the auxiliary pump electrode 51. It is not necessary to perform one or two of the treatments of S180 to S200 using the detection third pump cell 89 including the electrode 44. In that case, of the detection first pump cell 85 and the variable power supply 86 connected to it, the detection second pump cell 87 and the variable power supply 88 connected to it, the detection third pump cell 89 and the variable power supply 90 connected to it. One or two may be omitted. For example, as in the gas sensor 200 of FIG. 8 described later, the first pump cell for detection 85 and the variable power supply 86 connected to the first pump cell 85 for detection are provided, the second pump cell 87 for detection and the variable power supply 88 connected to the second pump cell 87 for detection, and the third detection power supply 88. The pump cell 89 and the variable power supply 90 connected to the pump cell 89 may not be provided. Further, the control unit 91 may perform the above-described processing of S120 to S140, processing of S150 to S170, and processing of S180 to S200 in a different order.

Further, in the above-described embodiment, the control unit 91 collectively determines whether or not one or more of the pump currents Ip3, Ip4, and Ip5 is equal to or more than the detection threshold value after all the processes of S120 to S200 are performed. Each time the processing of S120 to S140, the processing of S150 to S170, and the processing of S180 to S200 are performed, it may be individually determined whether or not the pump current is equal to or higher than the detection threshold value. In that case, if the pump current is equal to or higher than the detection threshold, the crack detection signal is output to the outside and this routine is terminated without performing the remaining processing. If the pump current is less than the detection threshold, the remaining processing is continued. You may go. In this way, the crack may be detected only without estimating the position of the crack.

In the above-described embodiment, the detection threshold value Tp3 is changed so that the higher the oxygen concentration of the measurement gas is, the higher the detection threshold value Tp3 is. However, the detection threshold value Tp3 may be a constant value regardless of the oxygen concentration of the measurement gas. Good. As described above, when the sensor element 101 has cracks, the higher the oxygen concentration of the gas to be measured, the larger the limit current value of the pump current Ip3, while when the sensor element 101 has no cracks, the measured gas has a crack. The limit current value of the pump current Ip3 is substantially constant regardless of the oxygen concentration. Therefore, if the detection threshold Tp3 is set so that the pump current Ip3 without cracks and the pump current Ip3 with cracks can be distinguished when the oxygen concentration of the gas to be measured is low, the oxygen of the gas to be measured is oxygenated. Cracks can be detected even when the concentration is higher than that. The same applies to the detection thresholds Tp4 and Tp5.

In the above-described embodiment, the set value Vsp3 may be constant regardless of the oxygen concentration of the gas to be measured, or may be changed according to the oxygen concentration of the gas to be measured. The set value Vsp3 may be changed so that it tends to increase as the oxygen concentration of the gas to be measured increases. For example, the set value Vsp3 may be changed linearly so that the relationship with the oxygen concentration of the gas to be measured becomes a linear function. , May be changed step by step. In order to change the set value Vsp3 in association with the oxygen concentration of the gas to be measured, the storage unit 94 may store an expression or a map showing the correspondence between the set value Vsp3 and the oxygen concentration of the gas to be measured. In that case, the control unit 91 may derive the set value Vsp3 by using the oxygen concentration of the gas to be measured acquired in S100 and the formula or map stored in the storage unit 94. The same applies to the set values Vsp4 and Vsp5.

In the above-described embodiment, the control unit 91 has acquired the oxygen concentration information of the gas to be measured in S100. For example, when the oxygen concentration of the gas to be measured is known or for detection regardless of the oxygen concentration of the gas to be measured. When the threshold values Tp3, Tp4, Tp5 and the set values Vsp3, Vsp4, Vsp5 are set to constant values, S100 may be omitted.

In the above-described embodiment, the control unit 91 may perform a process after S100 to determine whether or not the oxygen concentration of the gas to be measured is contained in a predetermined high concentration region. If the oxygen concentration of the gas to be measured is contained in the predetermined high concentration region in this treatment, the control unit 91 performs the processing after S110, while the oxygen concentration of the gas to be measured is contained in the predetermined high concentration region. If not, the control unit 91 may end this routine as it is and restart the NOx concentration detection process if necessary. As described above, in the gas sensor 100, the higher the oxygen concentration of the gas to be measured, the more accurately the crack can be detected based on the pump currents Ip3, Ip4 and Ip5. Therefore, when the oxygen concentration of the gas to be measured is high, the cracks in the element body can be efficiently detected by performing the process of detecting the cracks based on the pump currents Ip3, Ip4, and Ip5. In the process of determining whether or not the oxygen concentration of the gas to be measured is included in the predetermined high concentration region, a predetermined high concentration region may be set according to the required crack detection accuracy. For example, a region having an oxygen concentration of 1% or more, a region having an oxygen concentration of 3% or more, a region having an oxygen concentration of 5% or more, and the like may be defined as a predetermined high concentration region. In the process of determining whether or not the oxygen concentration of the gas to be measured is included in the predetermined high concentration region, the control unit 91 sets the oxygen of the gas to be measured when the pump current Ip0 input in S100 is equal to or higher than the predetermined threshold value. It may be determined that the concentration is included in a predetermined high concentration region. The predetermined threshold value may be the lower limit value of the pump current Ip0 such that the oxygen concentration of the gas to be measured is included in the predetermined high concentration region, and is derived in advance from the correspondence relationship between the pump current Ip0 and the oxygen concentration of the gas to be measured. , May be stored in the storage unit 94.

In the above-described embodiment, the control unit 91 may perform a process after S100 to determine whether or not the oxygen concentration of the gas to be measured is contained in a predetermined low concentration region. If the oxygen concentration of the gas to be measured is contained in the predetermined low concentration region in this treatment, the control unit 91 performs the processing after S110 as it is, while the oxygen concentration of the gas to be measured is contained in the predetermined low concentration region. If not, the control unit 91 omits the process of estimating the crack position (S220) and omits the output of the crack position to the outside in S230 and only detects the crack when performing the process after S110. You may. As described above, in S220, the position of the crack is estimated by utilizing the fact that the oxygen pumped in the electrode close to the crack among the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 easily reaches the crack. Therefore, the position of the crack can be estimated more accurately as the ratio of the oxygen taken in from the oxygen existing in the gas flow section to be measured increases, that is, the oxygen concentration of the gas to be measured decreases. Therefore, the crack position of the element body can be estimated accurately by performing the process of estimating the crack position when the oxygen concentration of the gas to be measured is low. In the process of determining whether or not the oxygen concentration of the gas to be measured is included in the predetermined low concentration region, a predetermined low concentration region may be set according to the required estimation accuracy of the crack position. For example, as a region where the ratio of the pumped oxygen to the oxygen existing in the gas flow section to be measured is sufficiently large, an oxygen concentration of 5% or less, a region of 3% or less, a region of 1% or less, etc. May be set as a predetermined low concentration region. Further, the predetermined low concentration region may be a region having a lower oxygen concentration than the above-mentioned high concentration region. In the process of determining whether or not the oxygen concentration of the gas to be measured is included in the predetermined low concentration region, the control unit 91 determines the oxygen of the gas to be measured when the pump current Ip0 input in S100 is equal to or less than a predetermined threshold value. It may be determined that the concentration is contained in a predetermined low concentration region. The predetermined threshold value may be an upper limit value of the pump current Ip0 such that the oxygen concentration of the gas to be measured is included in the predetermined low concentration region, and is derived in advance from the correspondence relationship between the pump current Ip0 and the oxygen concentration of the gas to be measured. , May be stored in the storage unit 94.

In the above-described embodiment, the control unit 91 inputs the pump current Ip0 detected by the NOx concentration detection process when acquiring the oxygen concentration information, but the present invention is not limited to this. For example, when acquiring the oxygen concentration information, the control unit 91 may perform only a process of detecting the oxygen concentration separately from the NOx concentration detection process. In that case, the control unit 91 may feedback-control the pump voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0 *, and input the pump current Ip0 at that time. Further, the control unit 91 may acquire the oxygen concentration information measured by another gas sensor when acquiring the oxygen concentration information. When acquiring the oxygen concentration information measured by another gas sensor, the other gas sensor may be a gas sensor of the same type as itself (here, a NOx sensor) or a different type of gas sensor. The other gas sensor may be, for example, a limit current detection type oxygen sensor or a potential detection type oxygen sensor (lambda sensor). When the oxygen concentration information is acquired by a method other than the NOx concentration detection process, it is not necessary to perform the crack detection process following the NOx concentration detection process.

In the above-described embodiment, the detection of cracks between the first internal space 20 and the heater portion 70 has been described, but other cracks can also be detected. For example, a crack between the gas flow unit to be measured other than the first internal space 20 (for example, the buffer space 12, the second internal space 40, the third internal space 61) and the heater unit 70 can be detected. Further, for example, a crack between the gas flow section to be measured and the atmosphere introduction layer 48 can be detected. Even if there is such a crack, the oxygen caused by the measured gas introduced into the measured gas flow unit from the sensor element chamber 133 (see FIG. 1) (for example, the oxygen contained in the measured gas itself or the measured gas) At least one of the oxygen (oxygen generated by reducing the contained oxide) and the oxygen drawn into the gas flow section to be measured by the detection current reaches the periphery of the reference electrode 42 through the crack, and the reference electrode 42 The amount of oxygen around the body increases. Therefore, the gas sensor 100 can detect cracks based on the pump currents Ip3, Ip4, and Ip5. Further, when oxygen is contained in the gas to be measured, cracks between the portion of the outside of the element main body arranged in the sensor element chamber 133 and the heater portion 70 or the atmosphere introduction layer 48 can be detected. Even if there is such a crack, oxygen contained in the gas to be measured reaches the periphery of the reference electrode 42 from the sensor element chamber 133 through the crack, and the amount of oxygen around the reference electrode 42 increases, so that the gas sensor 100 Then, cracks can be detected based on the pump currents Ip3, Ip4, and Ip5.

In the above-described embodiment, the atmosphere introduction layer 48 is arranged from the reference electrode 42 to the rear end surface of the sensor element 101 in the longitudinal direction, but the present invention is not limited to this. FIG. 8 is a schematic cross-sectional view of the sensor element 201 of the modified example in this case. As shown in FIG. 8, the sensor element 201 has a reference gas introduction space 43 above the atmosphere introduction layer 248. The reference gas introduction space 43 is a space arranged between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5 at a position where the side portion is partitioned by the side surface of the first solid electrolyte layer 4. .. The rear end of the reference gas introduction space 43 is open to the rear end surface of the sensor element 201. The reference gas introduction space 43 is arranged in the front-rear direction to the front of the pressure dissipation hole 75, and the pressure dissipation hole 75 is open to the reference gas introduction space 43. Unlike the atmosphere introduction layer 48, the atmosphere introduction layer 248 is not arranged up to the rear end of the sensor element 201. Therefore, the atmosphere introduction layer 248 is not exposed on the rear end surface of the sensor element 201. Instead, a part of the upper surface of the atmosphere introduction layer 248 is exposed to the reference gas introduction space 43. This exposed portion is the inlet portion 48c of the atmosphere introduction layer 248. The reference gas is introduced into the atmosphere introduction layer 248 from the inlet portion 48c through the reference gas introduction space 43. In the sensor element 201, the rear end of the atmosphere introduction layer 248 may be arranged up to the rear end of the sensor element 201. In the aspect of FIG. 8, the atmosphere introduction layer 248 and the reference gas introduction space 43 correspond to the reference gas introduction portion, and the opening on the rear end side of the reference gas introduction space 43 corresponds to the reference gas inlet. In the aspect of FIG. 8, the pressure dissipation hole 75 may be provided at a position where it abuts on the first solid electrolyte layer 4 instead of opening in the reference gas introduction space 43. In this way, oxygen that has reached the pressure dissipation hole 75 through the crack and the heater insulating layer 74 is less likely to be released into the atmosphere and easily reaches the periphery of the reference electrode 42, and is therefore based on the pump currents Ip3, Ip4, and Ip5. The crack can be detected accurately.

In the above-described embodiment, the sensor element 101 of the gas sensor 100 includes a first internal space 20, a second internal space 40, and a third internal space 61, but is not limited thereto. For example, as in the sensor element 201 of FIG. 8 described above, the third internal space 61 may not be provided. In the modified example sensor element 201 shown in FIG. 8, a gas introduction port 10 and a first diffusion rate-determining portion 11 are provided between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The buffer space 12, the second diffusion rate-determining section 13, the first internal space 20, the third diffusion rate-determining section 30, and the second internal space 40 are formed adjacent to each other in this order. .. Further, the measurement electrode 44 is arranged on the upper surface of the first solid electrolyte layer 4 in the second internal space 40. The measurement electrode 44 is covered with a fourth diffusion rate-determining portion 45. The fourth diffusion rate-determining unit 45 is a film made of a ceramic porous body such as _{alumina (Al 2} O _3). The fourth diffusion rate-determining unit 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, similarly to the fourth diffusion rate-determining unit 60 of the above-described embodiment. The fourth diffusion rate-determining unit 45 also functions as a protective film for the measurement electrode 44. The ceiling electrode portion 51a of the auxiliary pump electrode 51 is formed up to directly above the measurement electrode 44. Even with the sensor element 201 having such a configuration, the NOx concentration can be detected by the measurement pump cell 41 as in the above-described embodiment. In the sensor element 201 of FIG. 8, the periphery of the measurement electrode 44 plays the same role as the third internal space 61.

In the above-described embodiment, the surface of the front side (the portion exposed to the sensor element chamber 133) of the sensor element 101 including the outer pump electrode 23 may be coated with a porous protective layer made of ceramics such as alumina.

In the above-described embodiment, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for measuring pump control becomes constant, and the pump current Ip2 at this time is used to cover the voltage Vp2. The nitrogen oxide concentration in the measurement gas is calculated, but if the specific gas concentration in the measurement gas is detected based on the voltage between the reference electrode 42 and the measurement electrode 44, this is used. Not limited. For example, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detecting means as an electrochemical sensor cell, the measurement electrode A voltage corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around 44 and the amount of oxygen around the reference electrode 42 can be detected as the voltage V2, thereby in the gas to be measured. The concentration of the NOx component of can be determined.

In the above-described embodiment, the reference gas is the atmosphere, but the gas is not limited to this as long as it is a gas that serves as a reference for detecting the concentration of the specific gas in the gas to be measured. For example, a gas adjusted to a predetermined oxygen concentration (> oxygen concentration of the gas to be measured) may be filled in the space 149 as a reference gas.

In the above-described embodiment, the sensor element 101 detects the NOx concentration in the gas to be measured, but the present invention is not limited to this as long as it detects the concentration of the specific gas in the gas to be measured. For example, not only NOx but also other oxide concentrations may be used as the specific gas concentration. When the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced in the third internal space 61 as in the above-described embodiment, so that the measurement pump cell 41 has a detection value corresponding to the oxygen. (For example, pump current Ip2) can be acquired to detect a specific gas concentration. Further, the specific gas may be a non-oxide such as ammonia. When the specific gas is non-oxide, by converting the specific gas to oxide (for example, if it is ammonia, it is converted to NO), oxygen is released when the converted gas is reduced in the third internal space 61. Since it is generated, the measurement pump cell 41 can acquire a detected value (for example, pump current Ip2) corresponding to this oxygen and detect a specific gas concentration. For example, when the inner pump electrode 22 of the first internal space 20 functions as a catalyst, ammonia can be converted to NO in the first internal space 20.

In the above-described embodiment, the element body of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6), but the present invention is not limited to this. The element body of the sensor element 101 may include at least one oxygen ion conductive solid electrolyte layer. For example, in FIG. 2, the layers 1 to 5 other than the second solid electrolyte layer 6 may be a layer made of a material other than the solid electrolyte layer (for example, a layer made of alumina). In this case, each electrode of the sensor element 101 may be arranged on the second solid electrolyte layer 6. For example, the measurement electrode 44 of FIG. 2 may be arranged on the lower surface of the second solid electrolyte layer 6. Further, instead of providing the atmosphere introduction layer 48 between the first solid electrolyte layer 4 and the third substrate layer 3, it is provided between the second solid electrolyte layer 6 and the spacer layer 5, and the reference electrode 42 is provided in the third internal space. It may be provided behind the place 61 and on the lower surface of the second solid electrolyte layer 6.

In the above-described embodiment, the inner pump electrode 22 is _{a cermet electrode of Pt containing 1% Au and ZrO 2} , but is not limited thereto. The inner pump electrode 22 is a noble metal having catalytic activity (for example, at least one of Pt, Rh, Ir, Ru, and Pd) and a noble metal having a catalytic activity-suppressing ability to suppress the catalytic activity of the noble metal having catalytic activity with respect to a specific gas. (For example, Au) and may be included. Similar to the inner pump electrode 22, the auxiliary pump electrode 51 may also contain a noble metal having catalytic activity and a noble metal having an ability to suppress catalytic activity. The outer pump electrode 23, the reference electrode 42, and the measurement electrode 44 may each contain the noble metal having the above-mentioned catalytic activity. Each of the electrodes 22, 23, 42, 44, 51 is preferably a cermet containing a noble metal and an oxide having oxygen ion conductivity (for example, ZrO ₂ ), but one or more of these electrodes are cermets. It does not have to be. Each of the electrodes 22, 23, 42, 44, 51 is preferably a porous body, but one or more of these electrodes may not be a porous body.

In the above-described embodiment, the pump current Ip1 is used for controlling the voltage V0 of the oxygen partial pressure detection sensor cell 80 for controlling the main pump, but the present invention is not limited to this. For example, the pump voltage Vp0 may be feedback-controlled based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1 *. That is, the control of the voltage V0 based on the pump current Ip1 may be omitted, and the pump voltage Vp0 may be directly controlled (and thus the pump current Ip0) based on the pump current Ip1.

1 1st substrate layer, 2 2nd substrate layer, 3 3rd substrate layer, 4 1st solid electrolyte layer, 5 spacer layer, 6 2nd solid electrolyte layer, 10 gas inlet, 11 1st diffusion rate controlling part, 12 buffer Space, 13 2nd diffusion rate control section, 20 1st internal space, 21 main pump cell, 22 inner pump electrode, 22a ceiling electrode section, 22b bottom electrode section, 23 outer pump electrode, 24 variable power supply, 30 3rd diffusion rate control section , 40 2nd internal space, 41 measurement pump cell, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 45 4th diffusion rate control part, 46 variable power supply, 48, 248 atmosphere introduction layer, 48c inlet part, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode part, 51b Bottom electrode part, 52 Variable power supply, 60 4th diffusion rate control part, 61 3rd internal space, 70 Heater part, 71 Heater connector electrode, 72 Heater, 73 Thru Hall, 74 Heater insulation layer, 75 Pressure dissipation hole, 80 Main pump control oxygen partial pressure detection sensor cell, 81 Auxiliary pump control oxygen partial pressure detection sensor cell, 82 Measurement pump control oxygen partial pressure detection sensor cell, 83 sensor cell, 85 1st pump cell for detection, 86 variable power supply, 87 2nd pump cell for detection, 88 variable power supply, 89 3rd pump cell for detection, 90 variable power supply, 91 control unit, 92 CPU, 94 storage unit, 95 control device, 100 gas sensor, 101, 201 sensor element, 130 protective cover, 131 inner protective cover, 132 outer protective cover, 133 sensor element chamber, 140 sensor assembly, 141 element sealant, 142 main metal fitting, 143 inner cylinder, 143a, 143b reduced diameter part , 144a to 144c supporters, 145a, 145b green compact, 146 metal rings, 147 bolts, 148 outer cylinders, 149 spaces, 150 electrodes, 155 lead wires, 157 rubber stoppers, 190 pipes, 191 fixing members.

Claims (5)

An element body having an oxygen ion conductive solid electrolyte layer and an internal measurement gas flow section for introducing and circulating the measurement gas, and an element body.
The electrode to be measured gas side arranged in the gas flow unit to be measured and the electrode to be measured
A reference electrode arranged inside the element body and
A reference gas introduction unit that introduces a reference gas that serves as a reference for detecting the specific gas concentration of the gas to be measured from the reference gas inlet and distributes the reference gas to the reference electrode and imparts diffusion resistance to the reference gas.
A predetermined detection voltage is applied between the reference electrode and the gas-measured gas-side electrode so that the current flowing between the reference electrode and the gas-measured gas-side electrode becomes a limit current, and the reference electrode is applied. Oxygen is pumped from the periphery of the electrode to the gas side electrode to be measured, and the detection current flowing between the reference electrode and the gas side electrode to be measured is acquired when the detection voltage is applied. A crack detecting means for detecting a crack in the element body based on the detection current, and
Gas sensor equipped with. The gas sensor according to claim 1, wherein the crack detecting means determines that the crack is formed when the detecting current exceeds a predetermined detection threshold value. The gas sensor according to claim 1 or 2.
A heater provided inside the element body, a heater portion arranged so as to cover the heater and having a porous heater insulating layer capable of flowing gas, and a heater portion.
A connecting portion that connects a portion of the reference gas introduction portion inside the reference gas inlet and the heater portion in a state in which gas can flow.
With, gas sensor. A plurality of electrodes on the gas side to be measured are provided.
The crack detecting means individually applies a predetermined detection voltage to each of the electrodes to be measured so that the current flowing between the reference electrode and the electrode to be measured becomes a limit current. It is applied between the reference electrode and the gas side electrode to be measured to draw oxygen from the periphery of the reference electrode to the periphery of the gas side electrode to be measured, and when the detection voltage is applied, the reference electrode and the said The detection current flowing between the electrode to be measured and the electrode to be measured is acquired, and the position of the crack is estimated based on the detection current individually acquired for each of the electrodes to be measured.
The gas sensor according to any one of claims 1 to 3. An element body having an oxygen ion conductive solid electrolyte layer and an internal measurement gas flow section for introducing and circulating the measurement gas, and an element body.
The electrode to be measured gas side arranged in the gas flow unit to be measured and the electrode to be measured
A reference electrode arranged inside the element body and
A reference gas introduction unit that introduces a reference gas that serves as a reference for detecting the specific gas concentration of the gas to be measured from the reference gas inlet and distributes the reference gas to the reference electrode and imparts diffusion resistance to the reference gas.
It is a crack detection method of a sensor element equipped with
A predetermined detection voltage is applied between the reference electrode and the gas-measured gas-side electrode so that the current flowing between the reference electrode and the gas-measured gas-side electrode becomes a limit current, and the reference electrode is applied. Oxygen is drawn from the periphery of the electrode to the gas side electrode to be measured, and the detection current flowing between the reference electrode and the gas side electrode to be measured is acquired when the detection voltage is applied. A crack in the element body is detected based on the detection current.
Crack detection method.

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