JP2023089945A - Gas sensor and diagnostic method for moisture absorption state of gas sensor - Google Patents

Abstract

To diagnose a moisture absorption state around a reference electrode.SOLUTION: A gas sensor 100 comprises a sensor element 101 and a controller. The sensor element 101 includes: an element body (layers 1 to 6) inside which a gas-to-be-measured flow portion is provided; a measurement electrode 44 disposed on the gas-to-be-measured flow portion; an outer pump electrode 23 provided on the element body to be in contact with gas to be measured; a reference electrode 42 disposed inside the element body; a reference gas introduction portion 49 that causes reference gas to flow from outside of the element body to the reference electrode 42; and a reference gas adjustment pump cell 90 configured to include the outer pump electrode 23 and the reference electrode 42. The controller performs moisture absorption state diagnostic processing for diagnosing a moisture absorption state around the reference electrode 42 on the basis of a pump current Ip3 flowing through the reference gas adjustment pump cell 90 when controlling the reference gas adjustment pump cell 90 to pump oxygen out from around the reference electrode 42 to around the outer pump electrode 23.SELECTED DRAWING: Figure 2

Description

The present invention relates to a gas sensor and a method for diagnosing a moisture absorption state of the gas sensor.

2. Description of the Related Art Conventionally, a sensor element used for a gas sensor for detecting the concentration of a specific gas such as NOx in a gas to be measured such as automobile exhaust gas is known. For example, Patent Document 1 discloses an element main body having an oxygen ion-conducting solid electrolyte layer and a measurement gas circulation portion for introducing and circulating a measurement gas, and an element main body inside the measurement gas circulation portion. A measurement electrode disposed on the peripheral surface, a reference electrode disposed inside the element body, and a reference gas (e.g., atmospheric air) serving as a reference for detecting the specific gas concentration of the gas to be measured is introduced into the reference electrode. A sensor element is described with a reference gas inlet for circulating to. The reference gas introduction part has a porous reference gas introduction layer. The specific gas concentration in the gas to be measured can be detected based on the electromotive force generated between the reference electrode and the measurement electrode of this sensor element.

JP 2020-094899 A

By the way, there is a case where the reference gas introduction part adsorbs external water, for example, while the sensor element is not driven. Since the sensor element is heated when the drive starts, the water in the reference gas introduction portion becomes gas and escapes from the reference gas introduction portion to the outside. The oxygen concentration in the surrounding area is reduced. As a result, the detection accuracy of the specific gas concentration may decrease until the water is removed. Therefore, there is a demand for diagnosing the moisture absorption state around the reference electrode.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and its main object is to diagnose the moisture absorption state around the reference electrode.

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

The gas sensor of the present invention is
A gas sensor for detecting a specific gas concentration in a gas to be measured,
an element body including a solid electrolyte layer with oxygen ion conductivity and having therein a measured gas flow section for introducing and circulating the measured gas;
a measuring electrode disposed in the measured gas flow portion;
a measured gas side electrode provided on the element body so as to be in contact with the measured gas;
a reference electrode disposed inside the element body;
a reference gas introduction section for circulating a reference gas serving as a reference for detecting the concentration of the specific gas in the gas to be measured from the outside of the element main body to the reference electrode;
a reference gas adjustment pump cell including the measured gas side electrode and the reference electrode;
a sensor element having
a moisture absorption state around the reference electrode based on a pump current flowing through the reference gas adjustment pump cell when the reference gas adjustment pump cell is controlled to pump oxygen from around the reference electrode to around the electrode on the side of the gas to be measured; A control unit that performs moisture absorption state diagnosis processing for diagnosing
is provided.

In this gas sensor, the control section controls the reference gas adjustment pump cell to pump oxygen from around the reference electrode to around the electrode on the side of the gas to be measured based on the pump current that flows through the reference gas adjustment pump cell. Diagnose the moisture absorption state of the surroundings. Here, the pump current that flows when the reference gas adjustment pump cell pumps oxygen from the surroundings of the reference electrode to the surroundings of the measured gas side electrode changes depending on the amount of water around the reference electrode. Therefore, the moisture absorption state around the reference electrode can be diagnosed based on this pump current. In the moisture absorption state diagnosis process, the control unit may determine whether or not there is a large amount of moisture around the reference electrode.

In the gas sensor of the present invention, in the moisture absorption state diagnosis process, the control unit applies a predetermined control voltage higher than the voltage in the limiting current region of the reference gas adjustment pump cell between the measured gas side electrode and the reference electrode. A moisture absorption state around the reference electrode may be diagnosed based on the pump current when applied to the reference electrode. If a voltage higher than the voltage in the limiting current region is applied, the moisture around the reference electrode is likely to be decomposed, so the amount of moisture around the reference electrode is likely to affect the pump current. Therefore, by using the pump current when such a voltage is applied, the moisture absorption state of the reference electrode can be more appropriately diagnosed.

In this case, in the moisture absorption state diagnosis process, the control unit may diagnose the moisture absorption state around the reference electrode based on a comparison between the pump current and the limit current of the reference gas adjustment pump cell. As the amount of moisture around the reference electrode increases, the difference between the pump current and the limiting current increases. By comparing these, the moisture absorption state around the reference electrode can be more appropriately diagnosed. In this case, in the moisture absorption state diagnosis process, the control unit may diagnose the moisture absorption state around the reference electrode based on the difference or ratio between the pump current and the limit current.

In the gas sensor of the present invention in which the pump current and the limit current are compared, the control unit includes a storage unit that stores the value of the limit current, and the control unit controls the pump current in the moisture absorption state diagnosis process. may be compared with the limit current stored in the storage unit. This eliminates the need to measure the limit current in the moisture absorption state diagnosis process.

In the gas sensor of the present invention, the pump current and the limit current are compared. may be compared with the limit current. By doing this, not only the pump current but also the limit current is measured in the moisture absorption state diagnosis process, so that the diagnosis can be made with higher accuracy.

In the gas sensor of the present invention, the predetermined control voltage may be 0.8V or more and 1.5V or less. If the control voltage has a value of 0.8 V or more, the pump current when a voltage in this range is applied is likely to change depending on the amount of moisture around the reference electrode, which is suitable for performing moisture absorption state diagnosis processing. . When the control voltage is 1.5 V or less, blackening of the sensor element can be suppressed.

In the gas sensor of the present invention, a heater for heating the element main body is provided, and the control section performs the moisture absorption state diagnosis process after the heater is energized and the temperature of the heater reaches a predetermined temperature or higher. good. In this way, since the moisture absorption state diagnosis processing is performed after the temperature of the heater rises, the reference gas adjustment pump cell can be operated in a state in which the solid electrolyte layer is activated and oxygen ion conductivity is exhibited. Therefore, the moisture absorption state diagnosis process can be executed at appropriate timing.

The method for diagnosing the moisture absorption state of the gas sensor of the present invention comprises:
A method for diagnosing a moisture absorption state of a gas sensor for detecting a specific gas concentration in a gas to be measured, comprising:
The gas sensor is
an element body including a solid electrolyte layer with oxygen ion conductivity and having therein a measured gas flow section for introducing and circulating the measured gas;
a measuring electrode disposed in the measured gas flow portion;
a measured gas side electrode provided on the element body so as to be in contact with the measured gas;
a reference electrode disposed inside the element body;
a reference gas introduction section for circulating a reference gas serving as a reference for detecting the concentration of the specific gas in the gas to be measured from the outside of the element main body to the reference electrode;
a reference gas adjustment pump cell including the measured gas side electrode and the reference electrode;
a sensor element having
a moisture absorption state around the reference electrode based on a pump current flowing through the reference gas adjustment pump cell when the reference gas adjustment pump cell is controlled to pump oxygen from around the reference electrode to around the electrode on the side of the gas to be measured; moisture absorption state diagnosis processing to diagnose the
includes.

In this method for diagnosing the moisture absorption state of the gas sensor, the moisture absorption state around the reference electrode can be diagnosed in the same manner as the gas sensor described above. In this method for diagnosing the moisture absorption state of a gas sensor, various aspects of the gas sensor described above may be adopted, and processing for realizing each function of the gas sensor described above may be added.

FIG. 2 is a longitudinal sectional view of the gas sensor 100; FIG. 2 is a schematic cross-sectional view schematically showing an example of the configuration of the sensor element 101. FIG. FIG. 3 is a block diagram showing the electrical connection relationship between a control device 95 and each cell; 4 is a graph showing the relationship between the voltage Vp3 of the reference gas regulation pump cell 90 and the pump current Ip3; 4 is a flow chart showing an example of a control routine; 4 is a graph showing the relationship between time t and voltage V2open; FIG. 10 is a schematic cross-sectional view showing the configuration around a reference gas introduction portion 249 of a modified example; The cross-sectional schematic diagram of the sensor element 201 of a modification.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a vertical cross-sectional view of a gas sensor 100 that is one 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. As shown in FIG. FIG. 3 is a block diagram showing electrical connections between the control device 95 and each cell. The sensor element 101 has a long rectangular parallelepiped shape, and 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 the vertical direction. direction. Also, the width direction of the sensor element 101 (the direction perpendicular to the front-back direction and the up-down direction) is defined as the left-right direction.

As shown in FIG. 1 , gas sensor 100 includes sensor element 101 , protective cover 130 that protects the front end side of sensor element 101 , and sensor assembly 140 including connector 150 electrically connected to sensor element 101 . This gas sensor 100 is attached to a pipe 190 such as an exhaust gas pipe of a vehicle, as shown in the figure, and used to measure the concentration of specific gases such as NOx and O ₂ contained in the exhaust gas as the gas to be measured. . In this embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration.

The protective cover 130 includes a bottomed cylindrical inner protective cover 131 that covers the front end of the sensor element 101 and a bottomed cylindrical outer protective cover 132 that covers the inner protective cover 131 . A plurality of holes are formed in the inner protective cover 131 and the outer protective cover 132 for circulating the gas to be measured into the protective cover 130 . A 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 this sensor element chamber 133 .

The sensor assembly 140 includes an element sealing body 141 for enclosing and fixing the sensor element 101 , bolts 147 and an outer cylinder 148 attached to the element sealing body 141 , and rear end surfaces (upper and lower surfaces) of the sensor element 101 . and a connector 150 which is in contact with and electrically connected to connector electrodes (not shown) formed (only a heater connector electrode 71, which will be described later, is shown in FIG. 2).

The element sealing body 141 includes a cylindrical metal shell 142, a cylindrical inner cylinder 143 welded and fixed coaxially with the metal shell 142, and enclosed in a through hole inside the metal shell 142 and the inner cylinder 143. It has ceramic supporters 144a to 144c, powder compacts 145a and 145b, and a metal ring 146. The sensor element 101 is positioned on the central axis of the element sealing body 141 and penetrates the element sealing body 141 in the front-rear direction. The inner cylinder 143 has a diameter-reduced portion 143a for pressing the green compact 145b in the central axis direction of the inner cylinder 143, ceramic supporters 144a to 144c via a metal ring 146, and the green compacts 145a and 145b forward. A reduced diameter portion 143b for pressing is formed. The compressed powder bodies 145a and 145b are compressed between the metal shell 142 and the inner cylinder 143 and the sensor element 101 by the pressing force from the diameter-reduced parts 143a and 143b. It seals the space between the inner sensor element chamber 133 and the space 149 in the outer cylinder 148 and fixes the sensor element 101 .

The bolt 147 is coaxially fixed to the metal shell 142 and has a male threaded portion on its outer peripheral surface. A 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 thereof. As a result, the gas sensor 100 is fixed to the pipe 190 with the front end of the sensor element 101 and the protective cover 130 of the gas sensor 100 protruding into the pipe 190 .

The outer cylinder 148 covers 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 led 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 . A gap between the outer cylinder 148 and the lead wire 155 is sealed with a rubber plug 157 . A space 149 within the outer cylinder 148 is filled with a reference gas (atmosphere in this embodiment). The rear end of the sensor element 101 is arranged within 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 made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). , a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, which are stacked in this order from the bottom as viewed in the drawing. Also, the solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured by, for example, performing predetermined processing and circuit pattern printing on ceramic green sheets corresponding to each layer, laminating them, and firing them to integrate them.

At one end (left side in FIG. 2) of the sensor element 101 and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10 and a first diffusion control section 11 are provided. , buffer space 12 , second diffusion rate-limiting portion 13 , first internal space 20 , third diffusion rate-limiting portion 30 , second internal space 40 , fourth diffusion rate-limiting portion 60 , third internal space The voids 61 are formed adjacently in a manner communicating with each other in this order.

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

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

The sensor element 101 has a reference gas introduction part 49 for passing a reference gas from outside the sensor element 101 to the reference electrode 42 when measuring the NOx concentration. The reference gas introduction section 49 has a reference gas introduction space 43 and a reference gas introduction layer 48 . The reference gas introduction space 43 is a space provided inward from the rear end surface of the sensor element 101 . The reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5 at a position defined by the side surface of the first solid electrolyte layer 4 . The reference gas introduction space 43 is open on the rear end surface of the sensor element 101 , and this opening functions as an inlet portion 49 a of the reference gas introduction portion 49 . The inlet portion 49a is exposed in the space 149 (see FIG. 1). A reference gas is introduced into the reference gas introduction space 43 from the inlet 49a. The reference gas introduction part 49 introduces the reference gas introduced from the inlet part 49 a into the reference electrode 42 while imparting a predetermined diffusion resistance to the reference gas. In this embodiment, the reference gas is the air (atmosphere in the space 149 in FIG. 1).

The reference gas 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 reference gas introduction layer 48 is a porous body made of ceramics such as alumina. A portion of the upper surface of the reference gas introduction layer 48 is exposed inside the reference gas introduction space 43 . A reference gas introduction layer 48 is formed to cover the reference electrode 42 . The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42 .

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

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

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

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

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

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

In order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 , the third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 80 for controlling the 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. Furthermore, the pump current Ip0 is controlled by feedback-controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value. Thereby, the oxygen concentration in the first internal space 20 can be maintained at a predetermined constant value.

The third diffusion control section 30 applies a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, thereby reducing the gas under measurement. It is a portion that leads to the second internal space 40 .

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

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

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

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

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

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

Along with this, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for controlling the main pump, and the above-described target value of the voltage V0 is controlled, whereby the third diffusion rate-determining section 30 2 The gradient of the oxygen partial pressure in the gas to be measured introduced into the internal space 40 is controlled to be constant. When used as a NOx sensor, the main pump cell 21 and the auxiliary pump cell 50 work to keep the oxygen concentration in the second internal cavity 40 at a constant value of approximately 0.001 ppm.

The fourth diffusion rate control section 60 applies a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal space 40, thereby reducing the gas under measurement. It is a portion that leads to the third internal space 61 . The fourth diffusion control section 60 serves to limit the amount of NOx flowing into the third internal space 61 .

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

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

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

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

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

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

Further, an electrochemical reference gas regulation pump cell 90 is formed from 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. is configured. In this reference gas adjustment pump cell 90, a control current (pump current Ip3) flows due to a control voltage (voltage Vp3) applied by a power supply circuit 92 connected between the outer pump electrode 23 and the reference electrode 42, thereby generating oxygen. Do pumping. As a result, the reference gas adjustment pump cell 90 can pump oxygen from the space around the outer pump electrode 23 (sensor element chamber 133 in FIG. 1) to the periphery of the reference electrode 42 and to pump oxygen from the periphery of the reference electrode 42 to the outside. It is possible to pump oxygen around the pump electrode 23 .

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

Further, the sensor element 101 is provided with a heater section 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 section 70 includes heater connector electrodes 71 , heaters 72 , through holes 73 , heater insulating layers 74 , pressure dissipation holes 75 , and lead wires 76 .

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 supply, power can be supplied to the heater section 70 from the outside.

The heater 72 is an electric resistor that is sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connector electrode 71 via a lead wire 76 and a through hole 73, and is supplied with power from the outside through the heater connector electrode 71 to generate heat to heat the solid electrolyte forming the sensor element 101. and keep warm.

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

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

The pressure dissipation hole 75 is a portion provided so as to penetrate the third substrate layer 3 and the reference gas introduction layer 48, and is formed for the purpose of alleviating an increase in internal pressure accompanying a temperature rise in the heater insulating layer 74. Become.

The control device 95 includes the variable power sources 24, 46 and 52 described above, the heater power source 78, the power supply circuit 92 described above, and a control section 96, as shown in FIG. The control unit 96 is a microprocessor including a CPU 97, a RAM (not shown), a storage unit 98, and the like. The storage unit 98 is a nonvolatile memory, and is a device that stores various programs and various data, for example. The control unit 96 inputs the voltages V0 to V2 and the voltage Vref of the sensor cells 80 to 83, respectively. The controller 96 inputs the pump currents Ip0 to Ip2 and the pump current Ip3 that flow through the pump cells 21, 50, 41, and 90, respectively. The control unit 96 controls the voltages Vp0 to Vp3 output by the variable power sources 24, 46, 52 and the power circuit 92 by outputting control signals to the variable power sources 24, 46, 52 and the power circuit 92. It controls the pump cells 21, 41, 50, 90. The control unit 96 outputs a control signal to the heater power supply 78 to control the power supplied from the heater power supply 78 to the heater 72 , thereby adjusting the temperature of the sensor element 101 . The storage unit 98 stores target values V0*, V1*, V2*, a target current Ip1*, and the like, which will be described later. The CPU 97 of the control unit 96 controls each cell 21, 41, 50 with reference to these target values V0*, V1*, V2* and target current Ip1*.

The control unit 96 performs auxiliary pump control processing for controlling the auxiliary pump cell 50 so that the oxygen concentration in the second internal space 40 reaches the target concentration. Specifically, the control unit 96 controls the auxiliary pump cell 50 by feedback-controlling the voltage Vp1 of the variable power supply 52 so that the voltage V1 becomes a constant value (referred to as a target value V1*). The target value V1* is determined as a value such that the oxygen concentration in the second internal space 40 becomes a predetermined low concentration that does not substantially affect the measurement of NOx.

The control unit 96 controls the main pump cell 21 so that the pump current Ip1 that flows when the auxiliary pump cell 50 adjusts the oxygen concentration in the second internal space 40 by the auxiliary pump control process becomes a target current (referred to as target current Ip1*). main pump control processing for controlling the Specifically, the control unit 96 sets the target value of the voltage V0 (referred to as the target value V0*) based on the pump current Ip1 so that the pump current Ip1 flowing by the voltage Vp1 becomes a constant target current Ip1*. (feedback control). Then, the control unit 96 feedback-controls the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (that is, so that the oxygen concentration in the first internal space 20 becomes the target concentration). Due to this main pump control process, the gradient of the partial pressure of oxygen in the gas to be measured introduced from the third diffusion control section 30 into the second internal space 40 is always constant. The target value V0* is set to a value such that the oxygen concentration in the first internal space 20 is higher than 0% and is low. Further, the pump current Ip0 that flows during this main pump control process changes according to the oxygen concentration of the measured gas flowing into the measured gas flow section from the gas inlet 10 (that is, the measured gas surrounding the sensor element 101). do. Therefore, the control section 96 can also detect the oxygen concentration in the gas under measurement based on the pump current Ip0.

The above-described main pump control process and auxiliary pump control process are also collectively referred to as adjustment pump control process. Also, the first internal space 20 and the second internal space 40 are collectively referred to as an oxygen concentration adjustment chamber. The main pump cell 21 and the auxiliary pump cell 50 are also collectively referred to as adjustment pump cells. The adjustment pump cell adjusts the oxygen concentration in the oxygen concentration adjustment chamber by the control unit 96 performing the adjustment pump control process.

Furthermore, the control unit 96 controls the measurement pump cell 41 so that the voltage V2 becomes a constant value (target value) (that is, so that the oxygen concentration in the third internal space 61 becomes a predetermined low concentration). perform pump control processing. Specifically, the control unit 96 controls the measurement pump cell 41 by feedback-controlling the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*. Oxygen is pumped out of the third internal space 61 by this measurement pump control process.

By performing the measurement pump control process, the pressure inside the third internal space 61 is reduced so that the amount of oxygen generated by the reduction of NOx in the gas to be measured in the third internal space 61 becomes substantially zero. Oxygen is pumped out of Then, the control unit 96 acquires the pump current Ip2 as a detected value corresponding to the oxygen generated in the third internal space 61 due to the specific gas (here, NOx), and based on this pump current Ip2, the measured value is measured. Calculate the NOx concentration in the gas.

The storage unit 98 stores a relational expression (for example, a linear function or a quadratic function), a map, etc. as the correspondence between the pump current Ip2 and the NOx concentration. Such a relational expression or map can be obtained in advance by experiments.

The control unit 96 controls the power supply circuit 92 so that the voltage Vp3 is applied to the reference gas adjustment pump cell 90, thereby causing the reference gas adjustment pump cell 90 to flow the pump current Ip3. The control unit 96 controls the magnitude and direction of flow of the pump current Ip3 by changing the magnitude and positive/negative of the voltage Vp3. Thereby, the control unit 96 controls the direction of movement of oxygen between the reference electrode 42 and the outer pump electrode 23 (pumping oxygen to the periphery of the reference electrode 42 or pumping oxygen from the periphery of the reference electrode 42). or control the amount of oxygen transfer. In the present embodiment, the voltage Vp3 is set to a DC voltage such that the pump current Ip3 becomes a predetermined value (constant DC current).

The control unit 96 performs a reference gas adjustment process that controls the reference gas adjustment pump cell 90 so as to pump oxygen from around the outer pump electrode 23 to around the reference electrode 42 to adjust the oxygen concentration around the reference electrode 42 . . Here, the gas to be measured is introduced from the sensor element chamber 133 shown in FIG. On the other hand, the reference gas (atmosphere) in the space 149 shown in FIG. The sensor element chamber 133 and the space 149 are partitioned by the sensor assembly 140 (particularly, the powder compacts 145a and 145b) and are sealed so that gas does not flow between them. However, when the pressure of the gas to be measured is high, the gas to be measured may slightly enter the space 149 and the oxygen concentration in the space 149 may decrease. At this time, if the oxygen concentration around the reference electrode 42 is lowered, the reference potential, which is the potential of the reference electrode 42, will change. By performing the reference gas adjustment process, such a decrease in oxygen concentration around the reference electrode 42 can be compensated for.

Incidentally, the control device 95 including the variable power sources 24, 46, 52 and the power supply circuit 92 shown in FIG. It is connected to each electrode inside the sensor element 101 via a lead wire 155 .

By the way, the reference gas introduction part 49 may adsorb water outside the sensor element 101 (here, inside the space 149) while the sensor element 101 is not driven. In relation to this, the inventors investigated the relationship between the moisture absorption state of the reference gas introduction section 49 and the pump current Ip3 flowing through the reference gas adjustment pump cell 90 . First, the sensor element 101 was driven by the controller 95 . Specifically, with the gas sensor 100 placed in the atmosphere, the heater 72 was energized from the heater power source 78 to heat the sensor element 101, and the temperature of the sensor element 101 was maintained at 800.degree. After waiting for 0.5 hours to pass in this state, the gas sensor 100 in which the amount of moisture absorbed by the reference gas introduction portion 49 is small is obtained. Subsequently, the value of the pump current Ip3 was measured when the voltage Vp3 applied to the reference gas adjustment pump cell 90 by the power supply circuit 92 was gradually changed from 0 mV to 1000 mV with the gas sensor 100 placed in the atmosphere. A voltage Vp3 was applied in a direction in which the reference gas regulating pump cell 90 pumps oxygen from around the reference electrode 42 to around the outer pump electrode 23 . FIG. 4 shows the relationship between the voltage Vp3 and the pump current Ip3 in the gas sensor 100 in the state where the moisture absorption amount is small, which is measured as a solid line graph L1. Next, the gas sensor 100 was stored in a constant temperature/humidity chamber at a temperature of 40° C. and a humidity of 85% for one week to cause the reference gas introduction part 49 to adsorb water, thereby making the gas sensor 100 in a state of a large amount of moisture absorption. This gas sensor 100 was placed in the atmosphere, and the temperature of the sensor element 101 was maintained at 800° C. by the heater 72 . In this state, the value of the pump current Ip3 was measured when the voltage Vp3 was gradually changed from 0 mV to 1000 mV in the same manner as described above. FIG. 4 shows the relationship between the voltage Vp3 and the pump current Ip3 in the gas sensor 100 with a large amount of moisture absorption thus measured as a dashed line graph L2.

As shown in FIG. 4, in both the graphs L1 and L2, the pump current Ip3 remains substantially constant even if the voltage Vp3 increases in the range of the voltage Vp3 from 100 mV to 700 mV. That is, the pump current Ip3 has become the limit current. The value of the limiting current is determined by, for example, the diffusion resistance of the reference gas introducing section 49 . A region in which the pump current Ip3 hardly changes even when the voltage Vp3 changes (for example, a region where the voltage Vp3 is 100 mV to 700 mV in FIG. 4) is called a limit current region. In both graphs L1 and L2, in the region where the voltage Vp3 is higher than the limit current region, the pump current Ip3 tends to increase as the voltage Vp3 increases. This is because the higher the voltage Vp3, the more the moisture in the reference gas introduction part 49, especially around the reference electrode 42, is decomposed to generate oxygen, and this oxygen is also pumped out from around the reference electrode 42. Conceivable. Also, in both the limit current region and the region where the voltage Vp3 is higher than the limit current region, the value of the pump current Ip3 was larger in the graph L2 than in the graph L1. That is, it was confirmed that the value of the pump current Ip3 tends to be greater in the gas sensor 100 in which the amount of moisture absorbed by the reference gas introduction portion 49 is greater. Therefore, even when the voltage Vp3 in the limiting current region is applied, it is considered that the moisture around the reference electrode 42 is decomposed. In particular, in the region where the voltage Vp3 is higher than the limit current region (for example, the region where the voltage Vp3 is 800 mV or higher in FIG. 4), the difference in the value of the pump current Ip3 between the graph L2 and the graph L1 is more pronounced. For example, when the voltage Vp3 is 400 mV in the limit current region, the difference (=A2-A1) between the value A1 of the pump current Ip3 in the graph L1 and the value A2 of the pump current Ip3 in the graph L2 is 1000 mV. The difference (=B2-B1) between the value B1 of the pump current Ip3 in the graph L1 and the value B2 of the pump current Ip3 in the graph L2 in a certain case was larger.

Thus, the pump current Ip3 that flows when the reference gas regulating pump cell 90 pumps oxygen from around the reference electrode 42 to around the outer pump electrode 23 varies with the amount of moisture around the reference electrode 42 . Specifically, as the amount of water around the reference electrode 42 increases, the pump current Ip3 increases. Therefore, the control unit 96 of the present embodiment performs moisture absorption state diagnosis processing for diagnosing the moisture absorption state around the reference electrode 42 based on this pump current Ip3. More specifically, the control unit 96 of the present embodiment performs, as an example of moisture absorption state diagnosis processing, moisture determination processing that determines whether or not there is a large amount of moisture around the reference electrode 42 based on the pump current Ip3. Details of the moisture determination process will be described later.

Next, an example of processing for measuring the NOx concentration by the control unit 96 of the gas sensor 100 will be described. FIG. 5 is a flowchart showing an example of a control routine executed by the control section 96. As shown in FIG. The control unit 96 stores this routine in the storage unit 98, for example. The control unit 96 starts this control routine, for example, when a start command is input from an engine ECU (not shown).

When the control routine is started, the CPU 97 of the control unit 96 first outputs a control signal to the heater power supply 78 to perform heater control processing to control the temperature of the heater 72 to a target temperature (eg, 800° C.). is started (step S100). Here, the temperature of the heater 72 can be represented by a linear function expression of the resistance value of the heater 72 . Therefore, in the heater control process of the present embodiment, the CPU 97 calculates the resistance value of the heater 72 as a value that can be regarded as the temperature of the heater 72 (a value that can be converted to temperature), and the calculated resistance value is the target resistance value (target temperature The heater power supply 78 is feedback-controlled so as to obtain a resistance value corresponding to . The CPU 97 can acquire, for example, the voltage of the heater 72 and the current flowing through the heater 72, and calculate the resistance value of the heater 72 based on the acquired voltage and current. The CPU 97 may calculate the resistance value of the heater 72 by, for example, a three-terminal method or a four-terminal method. The CPU 97 outputs a control signal to the heater power supply 78 so that the calculated resistance value of the heater 72 becomes the target resistance value, and feedback-controls the power supplied by the heater power supply 78 . When energizing the heater 72 , the heater power supply 78 adjusts the power supplied to the heater 72 by changing the value of the voltage applied to the heater 72 , for example.

Subsequently, the CPU 97 determines whether or not the heater temperature has reached a predetermined temperature or higher by the heater control process (step S110). This predetermined temperature is predetermined and stored in the storage unit 98 as a value equal to or lower than the target temperature of the heater control process described above. The predetermined temperature is determined in advance as a temperature at which the solid electrolyte of the sensor element 101 is activated so that the reference gas adjustment pump cell 90 can pump oxygen. The predetermined temperature may be a value less than the target temperature. The predetermined temperature may be 80% or more or 90% or more of the target temperature. In this embodiment, the predetermined temperature is 90% of the target temperature. In this embodiment, the CPU 97 uses the resistance value as the value representing the temperature of the heater 72 as described above, so the determination in step S110 is also performed using the resistance value of the heater 72 .

If the determination in step S110 is negative, the CPU 97 repeats step S110 and waits until the determination is positive. That is, it waits until the temperature of the heater 72 reaches a predetermined temperature or higher. If the determination in step S110 is affirmative, the CPU 97 performs the following steps S120 and S130 as moisture determination processing.

In the moisture determination process, the CPU 97 first applies the voltage Vp3 to the reference gas adjustment pump cell 90 and acquires the pump current Ip3 that flows at that time (step S120). The value of the voltage Vp3 applied at this time is denoted as voltage Vha, and the value of the acquired pump current Ip3 is denoted as pump current Iph. Voltage Vha is applied in a direction that causes reference gas regulation pump cell 90 to pump oxygen from around reference electrode 42 to around outer pump electrode 23 . The value of the voltage Vha may be a value within the range of the limit current region described with reference to FIG. 4, but is preferably a voltage higher than the limit current region. Voltage Vha is preferably 0.8 V or more, for example. The voltage Vha may be 1.5 V or less. In this embodiment, the voltage Vha is set to 1.0V.

Subsequently, the CPU 97 determines the moisture absorption state around the reference electrode 42 based on the acquired pump current Iph, specifically, determines whether or not there is much moisture around the reference electrode 42 (step S130). . In the present embodiment, the CPU 97 makes this determination based on a comparison of the pump current Iph and the limit current Iprim of the reference gas regulation pump cell 90 . More specifically, the CPU 97 determines whether or not the reference electrode 42 has a large amount of moisture depending on whether or not the difference ΔI between the pump current Iph and the limit current Iprim is greater than the threshold value Iref. The limiting current Iprim of the reference gas regulating pump cell 90 applies a voltage Vp3 in the direction in which the reference gas regulating pump cell 90 pumps oxygen from the periphery of the reference electrode 42 to the periphery of the outer pump electrode 23, like the limiting current described in FIG. is the limit current when In the present embodiment, the limit current value (for example, the value A1 in FIG. 4) of the sensor element 101 in a state where the reference gas introduction portion 49 absorbs a small amount of moisture, which is measured in advance by experiment, is stored in the storage unit 98 as the limit current Iprim. It is assumed that Therefore, the CPU 97 calculates the difference ΔI between the pump current Iph acquired in step S120 and the limit current Iprim stored in the storage unit 98, and determines whether the difference ΔI is equal to or greater than the threshold value Iref. As described above, the larger the amount of water around the reference electrode 42, the larger the pump current Iph, and hence the larger the difference ΔI. Therefore, for example, a threshold value Iref is set as the value of the difference ΔI when the amount of water around the reference electrode 42 is the upper limit amount that can be regarded as having no effect on the detection accuracy of the NOx concentration. For example, in the example of FIG. 4, when the water content around the reference electrode 42 is large, the difference ΔI=B2−A1, and when the water content around the reference electrode 42 is small, the difference ΔI=B1−A1. A threshold value Iref is determined so as to have a value in between.

If the determination in step S130 is affirmative, the CPU 97 executes a water concentration reduction process for controlling the reference gas adjustment pump cell 90 so as to reduce the water concentration around the reference electrode 42 (step S140). In the moisture concentration lowering process of the present embodiment, the CPU 97 applies a voltage Vp3 to the reference gas adjustment pump cell 90 in a direction to pump oxygen from the periphery of the reference electrode 42 to the periphery of the outer pump electrode 23 . The value of voltage Vp3 at this time is expressed as voltage Vhc. As described above, applying voltage Vp3 to reference gas regulating pump cell 90 to pump oxygen around reference electrode 42 can decompose moisture around reference electrode 42, thereby causing the reference electrode to Moisture concentration around 42 can be reduced. The value of voltage Vhc may be a value within the range of the limit current region, or may be a voltage higher than the limit current region. For example, voltage Vhc may be 0.3 V or more and 1.5 V or less. Voltage Vhc may be 0.8 V or higher. Voltage Vhc may be 1.0 V or less. The voltage Vhc may be the same value as the voltage Vha in the moisture determination process described above. In this embodiment, the voltage Vhc is set to 1.0V. It is preferable that the execution time of the water concentration lowering process is 5 seconds or more and 300 seconds or less.

If the determination in step S130 is negative, or after executing the water concentration lowering process in step S140, the CPU 97 starts the normal time control process, which is the control process for measuring the NOx concentration in the normal time (step S150). . Specifically, the CPU 97 starts the above-described main pump control process, auxiliary pump control process, measurement pump control process, and reference gas adjustment process, and ends this routine. After starting the normal control process, the CPU 97 acquires the value of the pump current Ip2 at predetermined time intervals, for example, and based on the acquired pump current Ip2 and the correspondence stored in the storage unit 98, to derive the NOx concentration of The CPU 97 outputs the derived NOx concentration value to the engine ECU or stores it in the storage unit 98 .

An example of the case where the water concentration lowering process of step S140 is performed in an air atmosphere will be described with reference to FIG. FIG. 6 is a graph showing the relationship between time t and voltage V2open when the time when the temperature of heater 72 reaches the predetermined temperature in step S110 is time t=0 seconds. The voltage V2open is the value of the voltage V2 in a state in which no current is controlled to flow through the measurement electrode 44 and the reference electrode 42, that is, in an open state. The graph of the example indicated by the solid line in FIG. 6 was obtained as follows. First, similarly to the measurement of graph L2 in FIG. 4, the gas sensor 100 with the reference gas introduction part 49 having a large amount of moisture absorbed was prepared and placed in the atmosphere. Then, the heater control process was started, and the water concentration reduction process was started at the timing (time t=0) when the temperature of the heater 72 reached the predetermined temperature in step S110, and was executed until time t=t1 in FIG. The period from time t=0 to time t=t1, that is, the execution time of the water concentration lowering process is a predetermined time of 5 seconds or more and 300 seconds or less. The voltage Vhc was set to 1.0V. After time t=t1, the reference gas adjustment pump cell 90 was not operated and the connection between the measurement electrode 44 and the reference electrode 42 was kept open. Then, the voltage V2open was measured every 0.1 seconds after the time t=0 to obtain the graph of the example indicated by the solid line in FIG. From time t=0 to time t=t1, the water concentration lowering process was momentarily stopped and the voltage V2open was measured. The same measurement as in the example was performed except that the reference gas adjustment pump cell 90 was not operated at all and the gap between the measurement electrode 44 and the reference electrode 42 was kept open. got the graph.

As can be seen from FIG. 6, in both the example and the comparative example, it was confirmed that the voltage V2open decreased as time passed from time t=0, and then the voltage V2open stabilized. However, in the comparative example in which the water concentration lowering process was not performed, the stabilization of the voltage V2open was slower than in the example. Also, in the comparative example, the voltage V2open temporarily took a negative value. It is considered that this is because the moisture around the reference electrode 42 is heated by the heater 72 to become gas, and the oxygen concentration around the reference electrode 42 is temporarily lower than the oxygen concentration in the atmosphere. . In such a state, since the potential (reference potential) of the reference electrode 42 is unstable, an error occurs in the values of the voltages V0, V1, and V2 measured with reference to the reference potential. descend. In contrast, in the example in which the water concentration reduction process was performed, the voltage V2open stabilized earlier than in the comparative example. This is because the moisture around the reference electrode 42 is decomposed by the moisture concentration lowering process from time t=0 to time t=t1, so that the oxygen concentration around the reference electrode 42 decreases due to evaporation of the moisture. This is probably because it is suppressed. In this case, since the reference potential is quickly stabilized, the deterioration of the detection accuracy of the NOx concentration is suppressed as compared with the comparative example. In both the working example and the comparative example, the reason why the voltage V2open decreases as time elapses from time t=0 is that the thermoelectromotive force between the reference electrode 42 and the measuring electrode 44 is applied to the voltage V2open. It is considered that this thermoelectromotive force decreases with the lapse of time. For example, if there is temperature variation within each of the reference electrode 42 and the measurement electrode 44, the thermoelectromotive force between the reference electrode 42 and the measurement electrode 44 will increase. As the temperature in each electrode becomes uniform with the lapse of time, the thermoelectromotive force becomes smaller.

Here, correspondence relationships 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 this embodiment correspond to the element body of the present invention, and the measurement The electrode 44 corresponds to the measurement electrode, the outer pump electrode 23 corresponds to the measured gas side electrode, the reference electrode 42 corresponds to the reference electrode, the reference gas introduction section 49 corresponds to the reference gas introduction section, and the reference gas adjustment is performed. The pump cell 90 corresponds to the reference gas adjustment pump cell, the sensor element 101 corresponds to the sensor element, and the controller 96 corresponds to the controller. Also, the heater 72 corresponds to the heater, and the storage section 98 corresponds to the storage section. In this embodiment, an example of a method for diagnosing the moisture absorption state of the gas sensor of the present invention is clarified by explaining the operation of the control device 95 .

According to the gas sensor 100 of the present embodiment described in detail above, the controller 95 controls the reference gas adjustment pump cell 90 to pump oxygen from around the reference electrode 42 to around the outer pump electrode 23. Based on the pump current Iph flowing through the pump cell 90, the moisture absorption state around the reference electrode 42 is diagnosed. As described above, the pump current Ip3 (=Iph) that flows when the reference gas regulating pump cell 90 pumps oxygen from around the reference electrode 42 to around the outer pump electrode 23 depends on the amount of water around the reference electrode 42. Since it changes, the moisture absorption state around the reference electrode 42 can be diagnosed based on the pump current Iph. Further, the control device 95 performs moisture determination processing for determining whether or not there is a large amount of moisture around the reference electrode 42 as the moisture absorption state diagnosis processing. Then, the control device 95 performs the water concentration reduction process when it is determined in the water content determination process that the water content is high. By doing so, it is possible to appropriately determine whether or not to perform the moisture concentration lowering process based on the diagnosis result of the moisture absorption state diagnosis process. Moreover, since the moisture concentration around the reference electrode 42 can be quickly lowered by performing the moisture concentration lowering process, it is possible to suppress a decrease in detection accuracy of the concentration of the specific gas due to the moisture around the reference electrode 42 . .

In addition, the control device 95 applied a predetermined control voltage (voltage Vha) higher than the voltage in the limiting current region of the reference gas adjustment pump cell 90 between the outer pump electrode 23 and the reference electrode 42 in the moisture absorption state diagnosis process. The moisture absorption state around the reference electrode 42 is diagnosed based on the pump current Iph at the time. When a voltage Vha higher than the voltage in the limiting current region is applied to the reference gas adjustment pump cell 90, the moisture around the reference electrode 42 is likely to be decomposed, so the amount of moisture around the reference electrode 42 is likely to affect the pump current Iph. . Therefore, by using the pump current Iph when such a voltage Vha is applied, the moisture absorption state around the reference electrode 42 can be more appropriately diagnosed.

Furthermore, in the moisture absorption state diagnosis process, the control device 95 diagnoses the moisture absorption state around the reference electrode 42 based on the comparison between the pump current Iph and the limit current Iprim of the reference gas adjustment pump cell 90 . When a voltage Vha higher than the voltage in the limiting current region is applied to the reference gas regulating pump cell 90, the difference between the pump current Iph and the limiting current Iprim increases as the amount of moisture around the reference electrode 42 increases. Accordingly, the moisture absorption state around the reference electrode 42 can be diagnosed more appropriately.

Furthermore, the control device 95 compares the pump current Iph with the limit current Iprim stored in the storage unit 98 in the moisture absorption state diagnosis process. This eliminates the need to measure the limit current Iprim in the moisture absorption state diagnosis process.

If the voltage Vha is a value of 0.8 V or more, the pump current Iph when a voltage in this range is applied is likely to change depending on the amount of moisture around the reference electrode 42. Therefore, the moisture absorption state diagnosis process is performed. Suitable for If the voltage Vha is higher than 1.5 V, oxygen ions in the solid electrolyte of the sensor element 101 are depleted, electron conduction occurs in the solid electrolyte, and the sensor element 101 may blacken and become unusable. , the voltage Vha is 1.5 V or less, blackening of the sensor element 101 can be suppressed.

After the heater 72 is energized and the temperature of the heater 72 reaches a predetermined temperature or higher, the control device 95 performs the moisture absorption state diagnosis process. In this way, since the moisture absorption state diagnosis processing is performed after the temperature of the heater 72 rises, the reference gas adjustment pump cell 90 can be operated in a state in which the solid electrolyte layer is activated and the oxygen ion conductivity is exhibited. . Therefore, the moisture absorption state diagnosis process can be executed at appropriate timing.

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

For example, in the above-described embodiment, the limit current Iprim stored in advance in the storage unit 98 is used in the moisture absorption state diagnosis process, but the present invention is not limited to this. For example, in the moisture absorption state diagnosis process, the control device 95 may apply a voltage Vp3 in the limit current region to the reference gas adjustment pump cell 90 and measure the pump current Ip3 flowing at this time as the limit current Iprim. The value of the voltage Vp3 applied at this time is expressed as voltage Vhb. Voltage Vhb may be predetermined as a value within the range of the limit current region (for example, a value within the range of 100 mV to 700 mV in the example of FIG. 4). Alternatively, in the moisture absorption state diagnosis process, the control device 95 measures the value of the pump current Ip3 while gradually changing the value of the voltage Vhb, and measures the value when the pump current Ip3 can be considered to have stopped changing as the limiting current Iplim. You may In this manner, if not only the pump current Iph but also the limit current Iprim is measured in the moisture absorption state diagnosis process, the determination can be made with higher accuracy.

In the above-described embodiment, the moisture absorption state around the reference electrode 42 is diagnosed based on the difference between the pump current Iph and the limit current Iprim, but the present invention is not limited to this. Diagnosis may be made by comparing the pump current Iph and the limit current Iprim, and for example, the diagnosis may be made based on the ratio between the pump current Iph and the limit current Iprim. Further, the diagnosis may be performed based on the pump current Iph, and the limit current Iprim may not be used for the diagnosis. For example, the pump current Iph may be compared with a predetermined threshold, and if the pump current Iph exceeds the threshold, it may be determined that there is a large amount of moisture around the reference electrode 42 .

In the above-described embodiment, the control device 95 performed the moisture absorption state diagnosis process when the temperature of the heater 72 reached the predetermined temperature or higher in step S110. After the temperature of the heater 72 reaches a predetermined temperature or higher and a predetermined time has elapsed, the moisture absorption state diagnosis processing may be performed. Further, the control device 95 does not determine whether or not the temperature of the heater 72 has reached a predetermined temperature or higher, and even if the moisture absorption state diagnosis process is executed after a predetermined time has elapsed since the start of energization of the heater 72. good.

In the above-described embodiment, the control device 95 performs moisture determination processing for determining whether or not there is a large amount of moisture around the reference electrode 42 as the moisture absorption state diagnosis processing. Diagnose the moisture absorption state. For example, the control device 95 may calculate the amount of moisture around the reference electrode 42 based on the pump current Iph to diagnose the moisture absorption state. For example, the relationship between the pump current Iph and the water content of the reference electrode 42 or the relationship between the difference ΔI and the water content of the reference electrode 42 is experimentally investigated in advance and stored in the storage unit 98. , the water content may be calculated based on the pump current Iph and the relationship stored in the storage unit 98 .

In the above-described embodiment, the control device 95 uses the diagnosis result of the moisture absorption state diagnosis process to determine whether or not to perform the moisture concentration lowering process. good. For example, since the potential (reference potential) of the reference electrode 42 changes depending on the amount of water around the reference electrode 42, the change in the reference potential is predicted based on this amount of water. You can change the controls. Specifically, the control device 95 calculates the moisture content around the reference electrode 42 in the moisture absorption state diagnosis process, and selects one or more of the target values V0*, V1*, V2* according to the calculated moisture content. Alternatively, the voltage Vp3 applied to the reference gas adjustment pump cell 90 in the reference gas adjustment process may be changed.

In the embodiment described above, the control device 95 starts the normal control process in step S150 after executing the moisture absorption state diagnosis process in steps S120 and S130, but the present invention is not limited to this. The control device 95 may execute the moisture absorption state diagnosis process after starting the normal time control process. For example, the control device 95 may execute the moisture absorption state diagnosis process every time a predetermined period of time has elapsed. In this case, the normal time control process may be temporarily stopped during the execution of the moisture absorption state diagnosis process.

In the above-described embodiment, the voltage Vp3 is a DC voltage, but it is not limited to this and may be a voltage that is repeatedly turned on and off, such as a pulse voltage. Even in this way, the control device 95 can perform the moisture absorption state diagnosis process, the moisture concentration reduction process, and the reference gas adjustment process. When the voltage Vp3 is a voltage that is repeatedly turned on and off, the control device 95 measures the voltages V0, V1, and V2 during the period when the voltage Vp3 is off (in other words, during the period when the pump current Ip3 does not flow), It may be used for control processing. By doing so, the moisture absorption state diagnosis process and the normal control process can be performed in parallel without temporarily stopping the normal control process during execution of the moisture absorption state diagnosis process.

In the embodiment described above, the control device 95 does not have to perform the reference gas adjustment process.

In the above-described embodiment, the reference gas introduction part 49 includes the reference gas introduction space 43 and the reference gas introduction layer 48. However, if at least one of the reference gas introduction space 43 and the reference gas introduction layer 48 is provided, good. Since the reference gas introduction layer 48 easily absorbs moisture, it is highly significant to perform the moisture absorption state diagnosis processing of the present invention when the reference gas introduction part 49 is provided with the reference gas introduction layer 48 . For example, in the above-described embodiment, instead of the reference gas introduction part 49, a reference gas introduction part 249 shown in FIG. 7 may be adopted. The reference gas introduction part 249 does not have the reference gas introduction space 43 but has the reference gas introduction layer 48 . The reference gas introduction layer 48 in FIG. 7 is arranged from the periphery of the reference electrode 42 to the rear end surface of the element body of the sensor element 101 . A portion of the reference gas introduction layer 48 shown in FIG. The inlet portion 49 a is exposed in the space 149 outside the sensor element 101 .

In the above-described embodiment, the sensor element 101 of the gas sensor 100 is provided with the first internal space 20, the second internal space 40, and the third internal space 61, but it is not limited to this. For example, like the sensor element 201 of the modified example shown in FIG. 8, the third internal space 61 may not be provided. In the sensor element 201 of the modified example shown in FIG. 8, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the gas introduction port 10, the first diffusion control section 11, The buffer space 12, the second diffusion rate-controlling portion 13, the first internal space 20, the third diffusion rate-controlling portion 30, and the second internal space 40 are formed adjacently in a manner communicating in this order. . Also, the measurement electrode 44 is arranged on the upper surface of the first solid electrolyte layer 4 inside the second internal cavity 40 . The measurement electrode 44 is covered with a fourth diffusion control portion 45 . The fourth diffusion control portion 45 is a film made of a ceramic porous material such as alumina (Al ₂ O ₃ ). The fourth diffusion control section 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, like the fourth diffusion control section 60 of the above-described embodiment. Further, the fourth diffusion rate-limiting part 45 also functions as a protective film for the measurement electrode 44 . A ceiling electrode portion 51 a of the auxiliary pump electrode 51 is formed up to just above the measurement electrode 44 . Even with the sensor element 201 having such a configuration, the NOx concentration can be detected by the measuring pump cell 41 as in the above-described embodiment. In the sensor element 201 of FIG. 8, the area around the measuring electrode 44 functions as a measuring chamber. That is, the circumference of the measuring electrode 44 plays the same role as the third internal space 61 .

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

In the embodiment described above, the sensor element 101 detects the NOx concentration in the gas to be measured, but is not limited to this as long as it detects the concentration of a specific gas in the gas to be measured. For example, the concentration of oxides other than NOx 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. (for example, pump current Ip2) can be obtained to detect the specific gas concentration. Also, the specific gas may be a non-oxide such as ammonia. When the specific gas is a non-oxide, the specific gas is converted to an oxide (for example, ammonia is converted to NO), so that when the gas after conversion is reduced in the third internal space 61, oxygen is generated. Therefore, the measuring pump cell 41 can acquire a detection value (for example, pump current Ip2) corresponding to this oxygen and detect the specific gas concentration. For example, ammonia can be converted to NO in the first internal cavity 20 by the inner pump electrode 22 of the first internal cavity 20 acting as a catalyst.

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 it 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 structural layers made of a material other than the solid electrolyte layer (for example, layers made of alumina). In this case, each electrode of sensor element 101 may be arranged on second solid electrolyte layer 6 . For example, the measurement electrode 44 in FIG. 2 may be arranged on the bottom surface of the second solid electrolyte layer 6 . Further, the reference gas introduction space 43 is provided in the spacer layer 5 instead of the first solid electrolyte layer 4, and the reference gas introduction layer 48 is provided between the first solid electrolyte layer 4 and the third substrate layer 3 instead of the second solid electrolyte layer 4. It may be provided between the solid electrolyte layer 6 and the spacer layer 5 , and the reference electrode 42 may be provided behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6 .

In the above-described embodiment, the outer pump electrode 23 is part of the main pump cell 21 and is arranged in the part exposed to the gas to be measured outside the sensor element 101, and part of the auxiliary pump cell 50. and an outer auxiliary pump electrode disposed in a portion exposed to the gas to be measured outside the sensor element 101, and a part of the measuring pump cell 41 and disposed in a portion exposed to the gas to be measured outside the sensor element 101. and the measured gas side electrode which is a part of the reference gas adjustment pump cell 90 and which is disposed outside the sensor element 101 and exposed to the measured gas. is not limited to Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, the outer measurement electrode, and the measured gas side electrode may be provided outside the sensor element 101 separately from the outer pump electrode 23 . The electrode on the side of the gas to be measured of the reference gas adjustment pump cell 90 may be provided on the sensor element 101 so as to be in contact with the gas to be measured. More specifically, it may be disposed in the measured gas circulation portion of the sensor element 101 . For example, the inner pump electrode 22 serves as both the electrode (inner main pump electrode) of the main pump cell 21 and the measured gas side electrode of the reference gas adjustment pump cell 90 , and the reference gas adjustment pump cell 90 surrounds the inner pump electrode 22 and the reference electrode. Oxygen may be pumped to and from the surroundings of electrode 42 .

The present inventors investigated the relationship between the voltage Vhc and execution time of the water concentration reduction process and the time until the reference potential stabilizes as follows. First, the sensor element 101 and the gas sensor 100 of the embodiment described above with reference to FIGS. 1 to 3 were prepared. This gas sensor 100 was stored in a constant temperature/humidity chamber at a temperature of 40° C. and a humidity of 85% for one week to cause the reference gas introduction layer 48 to adsorb water. Next, the gas sensor 100 was attached to the pipe. A model gas was prepared with nitrogen as the base gas, an oxygen concentration of 0%, and an NO concentration of 1500 ppm. In this state, the controller 95 drives the sensor element 101 to execute the heater control process and the water concentration reduction process. The water concentration lowering process was executed from the timing (time t=0) when the temperature of the heater 72 reached a predetermined temperature after starting the heater control process to time t=t1. The water concentration reduction process was performed by controlling the reference gas regulation pump cell 90 to pump oxygen from around the reference electrode 42 . After the water concentration lowering process is completed, the control device 95 executes the normal control process to continuously control each pump cell and acquire each voltage V0, V1, V2, Vref from each sensor cell. state. Thereafter, the normal control process was continued until 60 minutes after the start of driving (starting of heating) of the sensor element 101, during which the pump current Ip2 was continuously measured. Using the value of the pump current Ip2 after 60 minutes from the start of driving the sensor element 101 as a reference value (100%), the rate of change of the value of the pump current Ip2 after 10 minutes from the start of driving the sensor element 101 with respect to the reference value is Calculated. As shown in Table 1, the calculation of the rate of change in the above procedure was performed by changing the voltage Vhc and the execution time of the water concentration lowering process, and Experimental Examples 1 to 14 were obtained. The voltage Vhc was variously changed in the range of 0.3V to 1.5V. The execution time of the water concentration lowering process (time from time t=0 to time t=t1) was variously changed within the range of 5 seconds or more and 300 seconds or less. Experimental example 15 was obtained by calculating the rate of change of the pump current Ip2 in the same manner as in experimental examples 1 to 14, except that the normal control process was started from time t=0 without executing the water concentration lowering process. . Note that in any of Experimental Examples 1 to 15, the reference gas adjustment pump cell 90 was not operated during the normal control process, that is, the reference gas adjustment process was not executed. Here, as described above, if moisture exists around the reference electrode 42, the moisture is heated by the heater 72 and turns into gas, causing the potential of the reference electrode 42 to temporarily become unstable. Therefore, until the potential of the reference electrode 42 is stabilized, the pump current Ip2 is not stabilized even if the NOx concentration of the measured gas is constant. It is considered that the smaller the rate of change of the pump current Ip2, the less moisture around the reference electrode 42 and the more stable the potential of the reference electrode 42 after 10 minutes from the start of driving. Therefore, the length of the stabilization time, which is the time from the start of driving the sensor element 101 to the stabilization of the potential of the reference electrode 42, can be evaluated depending on the magnitude of the change rate of the pump current Ip2. The shorter the stabilization time, the better. Therefore, for each of Experimental Examples 1 to 15, when the calculated rate of change was 3% or less, it was determined that the stabilization time was extremely short (“A”). When the calculated rate of change was more than 3% and 5% or less, it was determined that the stabilization time was short (“B”). When the calculated rate of change exceeded 5%, it was determined that the stabilization time was long (“F”). Table 1 shows evaluation results of voltage Vhc, execution time, and stabilization time for each of Experimental Examples 1-15. As shown in Table 1, it was confirmed that Experimental Examples 1 to 14, in which the water concentration lowering process was performed, could shorten the stabilization time compared to Experimental Example 15, in which the water concentration lowering process was not performed. Further, from the results of Experimental Examples 1 to 14, it was confirmed that the higher the voltage Vhc of the water concentration reduction process and the longer the execution time, the shorter the stabilization time.

In this specification, the technical idea of changing "the gas sensor according to any one of claims 2 to 4" to "the gas sensor according to any one of claims 2 to 6" in claim 7 as originally filed. , the technical idea of changing "the gas sensor according to any one of claims 1 to 4" to "the gas sensor according to any one of claims 1 to 7" in claim 8 originally filed, or In the original claim 15, "the method for diagnosing the state of moisture absorption of the gas sensor according to any one of claims 9 to 12" was changed to "the method for diagnosing the state of moisture absorption of the gas sensor according to any one of claims 9 to 14." ” is also disclosed.

INDUSTRIAL APPLICABILITY The present invention can be used as a gas sensor for detecting the concentration of a specific gas such as NOx in gas to be measured such as automobile exhaust gas.

REFERENCE SIGNS LIST 1 first substrate layer 2 second substrate layer 3 third substrate layer 4 first solid electrolyte layer 5 spacer layer 6 second solid electrolyte layer 10 gas introduction port 11 first diffusion control section 12 buffer space, 13 second diffusion rate-limiting section, 20 first internal cavity, 21 main pump cell, 22 inner pump electrode, 22a ceiling electrode section, 22b bottom electrode section, 23 outer pump electrode, 24 variable power supply, 30 third diffusion rate-limiting section , 40 second internal cavity, 41 measurement pump cell, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 45 fourth diffusion rate control section, 46 variable power source, 48 reference gas introduction layer, 49, 249 reference gas introduction Section 49a Inlet Section 50 Auxiliary Pump Cell 51 Auxiliary Pump Electrode 51a Ceiling Electrode Section 51b Bottom Electrode Section 52 Variable Power Source 60 Fourth Diffusion Control Section 61 Third Internal Space 70 Heater Section 71 Heater Connector Electrode 72 Heater 73 Through hole 74 Heater insulating layer 75 Pressure dissipation hole 76 Lead wire 78 Heater power supply 80 Oxygen partial pressure detection sensor cell for main pump control 81 Oxygen partial pressure detection sensor cell for auxiliary pump control 82 Oxygen partial pressure detection sensor cell for controlling pump for measurement, 83 sensor cell, 90 reference gas adjustment pump cell, 92 power supply circuit, 95 control device, 96 control section, 97 CPU, 98 storage section, 100 gas sensor, 101, 201 sensor element, 130 protection Cover 131 inner protective cover 132 outer protective cover 133 sensor element chamber 140 sensor assembly 141 element sealing body 142 metal shell 143 inner cylinder 143a, 143b reduced diameter portion 144a to 144c ceramic supporter 145a , 145b green compact, 146 metal ring, 147 bolt, 148 outer cylinder, 149 space, 150 connector, 155 lead wire, 157 rubber plug, 190 pipe, 191 fixing member.

Claims (15)

A gas sensor for detecting a specific gas concentration in a gas to be measured,
an element body including a solid electrolyte layer with oxygen ion conductivity and having therein a measured gas flow section for introducing and circulating the measured gas;
a measuring electrode disposed in the measured gas flow portion;
a measured gas side electrode provided on the element body so as to be in contact with the measured gas;
a reference electrode disposed inside the element body;
a reference gas introduction section for circulating a reference gas serving as a reference for detecting the concentration of the specific gas in the gas to be measured from the outside of the element main body to the reference electrode;
a reference gas adjustment pump cell including the measured gas side electrode and the reference electrode;
a sensor element having
a moisture absorption state around the reference electrode based on a pump current flowing through the reference gas adjustment pump cell when the reference gas adjustment pump cell is controlled to pump oxygen from around the reference electrode to around the electrode on the side of the gas to be measured; a control unit that performs moisture absorption state diagnosis processing for diagnosing
gas sensor with In the moisture absorption state diagnosing process, the control unit controls the control voltage when a predetermined control voltage higher than the voltage in the limiting current region of the reference gas adjustment pump cell is applied between the measured gas side electrode and the reference electrode. diagnosing a moisture absorption state around the reference electrode based on the pump current;
The gas sensor according to claim 1. In the moisture absorption state diagnosis process, the control unit diagnoses the moisture absorption state around the reference electrode based on a comparison between the pump current and the limit current of the reference gas adjustment pump cell.
The gas sensor according to claim 2. In the moisture absorption state diagnosis process, the control unit diagnoses the moisture absorption state around the reference electrode based on the difference or ratio between the pump current and the limit current.
The gas sensor according to claim 3. The control unit includes a storage unit that stores the value of the limit current,
The control unit compares the pump current with the limit current stored in the storage unit in the moisture absorption state diagnosis process.
The gas sensor according to claim 3 or 4. In the moisture absorption state diagnosis process, the control unit compares the pump current with the limit current measured by applying a voltage in the limit current region to the reference gas adjustment pump cell.
The gas sensor according to claim 3 or 4. The predetermined control voltage is a voltage of 0.8 V or more and 1.5 V or less.
The gas sensor according to any one of claims 2-4. The gas sensor according to any one of claims 1 to 4,
a heater for heating the element body;
with
The control unit performs the moisture absorption state diagnosis process after the heater is energized and the temperature of the heater reaches a predetermined temperature or higher.
gas sensor. A method for diagnosing a moisture absorption state of a gas sensor for detecting a specific gas concentration in a gas to be measured, comprising:
The gas sensor is
an element body including a solid electrolyte layer with oxygen ion conductivity and having therein a measured gas flow section for introducing and circulating the measured gas;
a measuring electrode disposed in the measured gas flow portion;
a measured gas side electrode provided on the element body so as to be in contact with the measured gas;
a reference electrode disposed inside the element body;
a reference gas introduction section for circulating a reference gas serving as a reference for detecting the concentration of the specific gas in the gas to be measured from the outside of the element main body to the reference electrode;
a reference gas adjustment pump cell including the measured gas side electrode and the reference electrode;
a sensor element having
a moisture absorption state around the reference electrode based on a pump current flowing through the reference gas adjustment pump cell when the reference gas adjustment pump cell is controlled to pump oxygen from around the reference electrode to around the electrode on the side of the gas to be measured; moisture absorption state diagnosis processing to diagnose the
A method for diagnosing a moisture absorption state of a gas sensor, comprising: In the moisture absorption state diagnosis process, based on the pump current when a predetermined control voltage higher than the voltage in the limiting current region of the reference gas adjustment pump cell is applied between the measured gas side electrode and the reference electrode. , diagnosing the moisture absorption state around the reference electrode;
A method for diagnosing a moisture absorption state of a gas sensor according to claim 9 . In the moisture absorption state diagnosis process, the moisture absorption state around the reference electrode is diagnosed based on a comparison between the pump current and the limit current of the reference gas adjustment pump cell.
The method for diagnosing the moisture absorption state of the gas sensor according to claim 10. In the moisture absorption state diagnosis process, the moisture absorption state around the reference electrode is diagnosed based on the difference or ratio between the pump current and the limit current.
A method for diagnosing a moisture absorption state of a gas sensor according to claim 11. The gas sensor includes a storage unit that stores the value of the limiting current,
comparing the pump current with the limit current stored in the storage unit in the moisture absorption state diagnosis process;
A method for diagnosing a moisture absorption state of a gas sensor according to claim 11 or 12. In the moisture absorption state diagnosis process, the pump current is compared with the limit current measured by applying a voltage in the limit current region to the reference gas adjustment pump cell.
A method for diagnosing a moisture absorption state of a gas sensor according to claim 11 or 12. A method for diagnosing a moisture absorption state of a gas sensor according to any one of claims 9 to 12,
The gas sensor includes a heater that heats the element body,
After the heater is energized and the temperature of the heater reaches a predetermined temperature or higher, the moisture absorption state diagnosis process is performed.
A method for diagnosing the moisture absorption state of a gas sensor.

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