JP2007278732A - Device and method for determining deterioration of sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for determining deterioration of a sensor element capable of determining the deterioration state of a gas sensor element with various cells. <P>SOLUTION: In a gas sensor control device 190, in S170 in sensor diagnosis processing, an oxygen partial pressure control state in the first measuring chamber 159 relative to a current-carrying state into an oxygen partial pressure detection cell 112 is detected, and in S180, it is determined whether a NOx gas sensor element 10 is in a normal state or in a deteriorated state by determining whether the detected oxygen partial pressure control state is within a normal range determined beforehand. The gas sensor control device 190 can determined whether the NOx gas sensor element 10 can control properly the oxygen partial pressure in the first measuring chamber 159, and can determine the deterioration state of the NOx gas sensor element 10 with various cells. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sensor element deterioration determination apparatus and a sensor element deterioration determination method for determining a deterioration state of a gas sensor element.

Conventionally, a gas sensor element including a first measurement chamber, a first oxygen ion pump cell, a second measurement chamber, a second oxygen ion pump cell, a reference oxygen chamber, and an oxygen partial pressure detection cell is known.
As a device for determining the state of such a gas sensor element, the current value flowing through various cells constituting the gas sensor element, the voltage value output from the cell, the impedance of the cell, etc. are measured, and these measurement results are obtained. There has been proposed a method for determining a failure state of a gas sensor element based on whether it is within an allowable range (for example, see Patent Document 1 and Patent Document 2).
Japanese Patent Laid-Open No. 11-014589 International Publication No. 03/083465 Pamphlet

  However, in the above-mentioned conventional apparatus, it is possible to determine a fatal failure state such as a disconnection or a short circuit among various states of the gas sensor element, but until the deterioration state of the gas sensor element such as the sensitivity of the cell is deteriorated. There was a problem that it could not be judged.

  That is, in a gas sensor element that has reached a fatal failure state, the values of current, voltage, impedance, etc. of various cells show numerical values in a range clearly different from that of a gas sensor element in a normal state. From this, it is possible to determine the failure state of the gas sensor element by using the conventional apparatus.

  In contrast, in a gas sensor element in a deteriorated state, values such as current values, voltage values, and impedances of various cells indicate numerical values that are included in substantially the same range as the gas sensor element in a normal state. It is difficult to distinguish between the normal state and the deteriorated state based on the value, and it is difficult to determine the deteriorated state of the gas sensor element in the conventional apparatus.

  Since the gas detection characteristics of the gas sensor element in the deteriorated state change compared to the gas sensor element in the normal state, the same gas detection result as that of the gas sensor element in the normal state cannot be obtained, and the gas detection accuracy may be reduced. There is.

  Therefore, the present invention has been made in view of these problems, and an object thereof is to provide a sensor element deterioration determination apparatus and a sensor element deterioration determination method that can determine a deterioration state in a gas sensor element including various cells.

  The invention according to claim 1, which has been made to achieve the above object, includes a first measurement chamber into which a measurement target gas is introduced via the first diffusion resistance portion, an oxygen ion conductor, and the oxygen ion conductor. A first oxygen ion for pumping or pumping oxygen to a measurement target gas introduced into the first measurement chamber, wherein one of the pair of electrodes is disposed in the first measurement chamber. A pump cell, a second measurement chamber into which a measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced via a second diffusion resistance unit, an oxygen ion conductor, and the oxygen ion conductor A second oxygen ion pump cell having a pair of electrodes formed thereon, wherein one of the pair of electrodes is disposed in the second measurement chamber, and a current corresponding to a specific gas concentration in the second measurement chamber flows; Reference oxygen partial pressure atmosphere It has a set reference oxygen chamber, an oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, one of the pair of electrodes is disposed in the first measurement chamber, and the other electrode is a reference oxygen An oxygen partial pressure detection cell arranged in a chamber, the sensor element deterioration determination device for determining a deterioration state of a gas sensor element, wherein the oxygen partial pressure detection cell is a reference oxygen according to the magnitude of an energized current. The gas sensor element is configured so that the oxygen partial pressure in the first measurement chamber is determined based on the reference oxygen partial pressure in the reference oxygen chamber, and the oxygen partial pressure is detected. An oxygen partial pressure control state detecting means for detecting an oxygen partial pressure control state in the first measurement chamber with respect to an energized state of the cell; and determining whether the oxygen partial pressure control state is within a predetermined normal range; Partial pressure control state is positive A deterioration determining means that determines that the gas sensor element is in a normal state when it is within a range and determines that the gas sensor element is in a deteriorated state when the oxygen partial pressure control state deviates from the normal range. This is a characteristic sensor element deterioration determination device.

  In order to achieve the above object, the invention method according to claim 8 includes a first measurement chamber into which a gas to be measured is introduced via a first diffusion resistance portion, an oxygen ion conductor, and the oxygen ions. A first electrode having a pair of electrodes formed on the conductor, wherein one of the pair of electrodes is disposed in the first measurement chamber, and pumps or pumps oxygen into the measurement target gas introduced into the first measurement chamber; 1 oxygen ion pump cell; a second measurement chamber into which a measurement target gas from which oxygen has been pumped or pumped in the first measurement chamber is introduced via a second diffusion resistance unit; an oxygen ion conductor and the oxygen A second oxygen ion pump having a pair of electrodes formed on an ion conductor, one of the pair of electrodes being disposed in the second measurement chamber, and a current corresponding to the specific gas concentration in the second measurement chamber flowing Cell and reference oxygen content A reference oxygen chamber set in an atmosphere; an oxygen ion conductor; and a pair of electrodes formed on the oxygen ion conductor. One of the pair of electrodes is disposed in the first measurement chamber, and the other electrode is A sensor element deterioration determination method for determining a deterioration state of a gas sensor element provided with an oxygen partial pressure detection cell disposed in a reference oxygen chamber, wherein the oxygen partial pressure detection cell is in accordance with the magnitude of an energized current. The oxygen pumping amount to the reference oxygen chamber is configured to be changeable, and the gas sensor element is configured to determine the oxygen partial pressure of the first measurement chamber based on the reference oxygen partial pressure of the reference oxygen chamber. An oxygen partial pressure control state detecting step for detecting an oxygen partial pressure control state in the first measurement chamber with respect to an energized state of the pressure detection cell; and if the oxygen partial pressure control state is within a predetermined normal range, the gas sensor element is normal And a deterioration determination step for determining that the gas sensor element is in a deteriorated state when the oxygen partial pressure control state deviates from a normal range. .

  First, the gas sensor element to be determined has a configuration in which the oxygen partial pressure of the reference oxygen chamber (in other words, the reference oxygen partial pressure) can be set according to the magnitude of the current flowing to the oxygen partial pressure detection cell. The gas sensor element is configured to control the oxygen partial pressure in the first measurement chamber to a target value with reference to the reference oxygen partial pressure in the reference oxygen chamber.

  Such a gas sensor element can appropriately control the oxygen partial pressure in the first measurement chamber to the target value in a normal state in which each cell can operate properly, but in a degraded state in which any cell cannot operate normally. If so, the oxygen partial pressure in the first measurement chamber may not be controlled to the target value.

  In other words, the gas sensor element in the normal state and the gas sensor element in the deteriorated state have different oxygen partial pressure control states in the first measurement chamber with respect to the energized state of the oxygen partial pressure detection cell (normal range or deviate from the normal range). Any of the ranges). From this, it is possible to determine whether or not the gas sensor element is in a deteriorated state based on the oxygen partial pressure control state in the first measurement chamber with respect to the energized state of the oxygen partial pressure detection cell.

Here, the energization state is a concept including states such as the magnitude of the current value and the energization amount per unit time.
In the sensor element deterioration state determination apparatus and the sensor element deterioration determination method of the present invention, the oxygen partial pressure control state in the first measurement chamber is detected with respect to the energization state of the oxygen partial pressure detection cell, and the detected oxygen partial pressure control is performed. By determining whether or not the state is in a predetermined normal range, it is determined whether the gas sensor element is in a normal state or a deteriorated state.

  By performing the determination using the oxygen partial pressure control state in this way, the gas sensor element is in a normal state in which the oxygen partial pressure in the first measurement chamber can be properly controlled, or the oxygen partial pressure in the first measurement chamber is appropriate. It is possible to appropriately determine whether the deterioration state cannot be controlled.

  Therefore, according to the sensor element deterioration determination apparatus and the sensor element deterioration determination method of the present invention, it can be determined whether or not the gas sensor element can properly control the oxygen partial pressure in the first measurement chamber. The deterioration state can be determined.

  In the sensor element deterioration determining apparatus, the oxygen partial pressure control state detecting means is configured to detect the second when the predetermined current for determination is supplied to the oxygen partial pressure detecting cell. A current value flowing through the second oxygen ion pump cell in accordance with the oxygen partial pressure in the measurement chamber is detected as a second pump current offset value, and the deterioration determining means is an offset value determined for determining the deterioration state of the gas sensor element. And the second pump current offset value is compared, and when the second pump current offset value is equal to or greater than the offset value deterioration determination threshold, it is determined that the gas sensor element is in a normal state, and the second pump current offset value is determined. When the value is smaller than the offset value deterioration determination threshold, the gas sensor element is determined to be in a deteriorated state.

  The gas sensor element to be determined is configured such that the oxygen partial pressure in the first measurement chamber can be controlled to a target value based on the reference oxygen partial pressure in the reference oxygen chamber. Further, the gas sensor element has a configuration in which the measurement target gas from which oxygen has been pumped or pumped in the first measurement chamber is introduced into the second measurement chamber via the second diffusion resistance unit. The oxygen partial pressure is determined in accordance with the oxygen partial pressure in the first measurement chamber.

  The second pump current offset value is a current value flowing through the second oxygen ion pump cell in accordance with the oxygen partial pressure in the second measurement chamber, and thus indicates a value in accordance with the oxygen partial pressure in the second measurement chamber. In addition, a value corresponding to the oxygen partial pressure in the first measurement chamber is shown.

  That is, the change state of the second pump current offset value with respect to the determination current that is supplied to the oxygen partial pressure detection cell reflects the oxygen partial pressure control state in the first measurement chamber with respect to the supply state of the oxygen partial pressure detection cell. Is.

  Note that the second pump current offset value increases as the oxygen partial pressure in the second measurement chamber increases, and decreases as the oxygen partial pressure in the second measurement chamber decreases. From this, an offset value deterioration determination threshold value for determining the deterioration state of the gas sensor element is determined, and the gas sensor element is compared with the second pump current offset value and the offset value deterioration determination threshold value. It can be determined whether or not the oxygen partial pressure in the measurement chamber can be properly controlled.

  That is, when the second pump current offset value is greater than or equal to the offset value deterioration determination threshold, it can be determined that the gas sensor element is in a normal state, and when the second pump current offset value is smaller than the offset value deterioration determination threshold. It can be determined that the gas sensor element is in a deteriorated state.

  In the present invention, the oxygen partial pressure control state detection means detects the second pump current offset value for the determination current, and the deterioration determination means determines the offset value deterioration determination threshold value and the second pump current offset value. In comparison, it is determined whether the gas sensor element is in a normal state or a deteriorated state.

  Therefore, the sensor element deterioration determination apparatus of the present invention can determine whether or not the gas sensor element can properly control the oxygen partial pressure in the first measurement chamber, and can determine the deterioration state of the gas sensor element including various cells. .

  The offset value deterioration determination threshold value can be determined based on, for example, a measurement result using an actual gas sensor element. As an example, using a gas sensor element in an unused state, a second pump current offset value is measured when a current for determination is supplied to the oxygen partial pressure detection cell, and the second pump current offset value at that time is measured. A value obtained by multiplying a predetermined deterioration coefficient (a value less than 1, for example, 0.9, etc.) can be used as an offset value deterioration determination threshold value.

  In the sensor element deterioration determination device that detects the second pump current offset value, as described in claim 3, the gas sensor element includes an oxygen reference in which an energization current to the oxygen partial pressure detection cell is predetermined. A configuration in which the reference oxygen chamber is controlled to the reference oxygen partial pressure atmosphere when the generation current is used, and the determination current has the same current value as the oxygen reference generation current is adopted. Can do.

  In this way, by setting the determination current to the same current value as the oxygen reference generation current, it is necessary to change the setting of the energization current to the oxygen partial pressure detection cell when shifting from the specific gas detection state to the deterioration determination state. Disappear.

Thereby, the trouble of setting and changing the energization current to the oxygen partial pressure detection cell can be omitted, and the complexity associated with the deterioration determination can be reduced.
Further, in the above sensor element deterioration determination device that detects the second pump current offset value, the voltage applied to the second oxygen ion pump cell cannot be dissociated and the oxygen gas cannot be dissociated as described in claim 4. Comprises a degradation determination voltage setting means for setting a degradation determination voltage value that can be dissociated, and the oxygen partial pressure control state detection means uses the degradation determination voltage setting means to determine whether the voltage applied to the second oxygen ion pump cell is degradation degradation. A configuration characterized by detecting the second pump current offset value in a state where the voltage value is set can be employed.

  Thus, by setting the voltage applied to the second oxygen ion pump cell to the voltage value for deterioration determination, the second oxygen ion pump cell is in a state in which dissociation of the specific gas is impossible and oxygen can be dissociated. It becomes. That is, if the second oxygen ion pump cell is in such a state, even if the specific gas exists in the second measurement chamber, the current flowing through the second oxygen ion pump cell is affected by the specific gas. It becomes a value according to the oxygen partial pressure of the 2nd measurement chamber without.

  Therefore, according to the present invention, it is possible to prevent the value of the current flowing through the second oxygen ion pump cell from fluctuating due to the influence of the specific gas, and the second pump current offset value can be detected with high accuracy, thereby improving the degradation determination accuracy. .

The deterioration determination voltage value is a voltage value smaller than a voltage value (detection voltage value) that can dissociate the specific gas.
Next, in the sensor element deterioration determination device according to claim 1, as described in claim 5, the oxygen partial pressure control state detection means supplies a predetermined first determination current to the oxygen partial pressure detection cell. Is detected as a second pump current first offset value according to the oxygen partial pressure in the second measurement chamber, and a predetermined second determination current is detected. When the oxygen partial pressure detection cell is energized, the current value flowing through the second oxygen ion pump cell according to the oxygen partial pressure in the second measurement chamber is detected as the second pump current second offset value, and the second pump current An offset change amount that is a difference between the one offset value and the second pump current second offset value is detected, and the deterioration determination means determines a deterioration determination threshold for change amount and an offset determined to determine a deterioration state of the gas sensor element. When the offset change amount is equal to or greater than the change amount deterioration determination threshold value, it is determined that the gas sensor element is in a normal state, and when the offset change amount is smaller than the change amount deterioration determination threshold value, the gas sensor element is deteriorated. It is possible to adopt a configuration characterized in that it is determined to be a state.

  As described above, the change state of the second pump current offset value with respect to the determination current supplied to the oxygen partial pressure detection cell reflects the oxygen partial pressure control state in the first measurement chamber with respect to the supply state of the oxygen partial pressure detection cell. It is what is done.

  In the present invention, when the oxygen partial pressure control state detection means supplies the first determination current and the second determination current to the oxygen partial pressure detection cell, the current value flowing through the second oxygen ion pump cell A second pump current first offset value and a second pump current second offset value are detected, respectively, and an offset change amount that is a difference between the second pump current first offset value and the second pump current second offset value is detected. To do.

  This offset change amount is the change amount of the second pump current offset value with respect to the change amount of the determination current, and reflects the oxygen partial pressure control state in the first measurement chamber with respect to the energization state of the oxygen partial pressure detection cell. It is.

  The offset change amount increases as the oxygen partial pressure change amount in the second measurement chamber corresponding to the determination current change amount increases, and the offset change amount decreases as the oxygen partial pressure change amount in the second measurement chamber decreases. Indicates the value. For this reason, the deterioration determination threshold value for change amount for determining the deterioration state of the gas sensor element is determined, and the gas sensor element is compared with the deterioration determination threshold value for change amount so that the gas sensor element can detect oxygen in the first measurement chamber. It can be determined whether or not the partial pressure can be properly controlled.

  That is, when the offset change amount is equal to or greater than the change amount deterioration determination threshold value, it can be determined that the gas sensor element is in a normal state, and when the offset change amount is smaller than the change amount deterioration determination threshold value, it is determined that the gas sensor element is in a deteriorated state. it can.

  In the present invention, the oxygen partial pressure control state detection unit detects the offset change amount, and the deterioration determination unit compares the change amount deterioration determination threshold with the offset change amount to determine whether the gas sensor element is in a normal state. It is determined whether it is in a degraded state.

  Therefore, the sensor element deterioration determination apparatus of the present invention can determine whether or not the gas sensor element can properly control the oxygen partial pressure in the first measurement chamber, and can determine the deterioration state of the gas sensor element including various cells. .

  Note that the change amount deterioration determination threshold value can be determined based on, for example, a measurement result using an actual gas sensor element. As an example, an offset change amount is measured using an unused gas sensor element, and the offset change amount at that time is multiplied by a predetermined deterioration coefficient (a value less than 1, for example, 0.9). The value obtained in this manner can be used as the change amount deterioration determination threshold value.

  In the sensor element deterioration determination device that detects the offset change amount, as described in claim 6, the gas sensor element includes an oxygen reference generation current in which an energization current to the oxygen partial pressure detection cell is predetermined. The reference oxygen chamber is controlled to a reference oxygen partial pressure atmosphere, and each current value of the first determination current and the second determination current is equal to or less than the current value of the oxygen reference generation current. The structure characterized by this can be taken.

  That is, in the gas sensor element, when there is no means for pumping out oxygen from the reference oxygen chamber, the oxygen partial pressure in the reference oxygen chamber is determined at the time of deterioration determination (when the first determination current and the second determination current are applied). If it rises, it may take a long time to lower the oxygen partial pressure in the reference oxygen chamber to the target value when shifting from the deterioration determination state to the specific gas detection state.

  On the other hand, as in the present invention, by setting the current values of the first determination current and the second determination current to be equal to or less than the current value of the oxygen reference generation current, the deterioration determination time (the first determination current and It is possible to prevent the oxygen partial pressure detection cell from excessively pumping oxygen into the reference oxygen chamber when the second determination current is applied. The gas sensor element is configured to allow oxygen to be pumped by the oxygen partial pressure detection cell.

  For this reason, the present invention increases the oxygen partial pressure in the reference oxygen chamber to the target value by the oxygen partial pressure detection cell performing an oxygen pumping operation when shifting from the deterioration determination state to the specific gas detection state. Can be shortened.

Therefore, according to the present invention, it is possible to shorten the time required for shifting from the deterioration determination state to the specific gas detection state.
Note that either the first determination current or the second determination current may have the same current value as the oxygen reference generation current.

  For example, when the first determination current is set to the same current value as the oxygen reference generation current, oxygen shifts from the specific gas detection state to the deterioration determination state (in particular, the state in which the second pump current first offset value is detected). There is no need to change the setting of the energization current to the partial pressure detection cell. Thereby, the trouble of setting and changing the energization current to the oxygen partial pressure detection cell can be omitted, and the complexity associated with the deterioration determination can be reduced. Therefore, by adopting such a configuration, it is possible to reduce the complexity when shifting from the specific gas detection state to the deterioration determination state (particularly, the state in which the second pump current first offset value is detected).

  Next, in the sensor element deterioration determination device according to claim 1, as described in claim 7, the oxygen partial pressure control state detection means stops pumping or pumping oxygen by the first oxygen ion pump cell. In addition, the energization to the oxygen partial pressure detection cell is stopped, and then the energization stop voltage value generated in the oxygen partial pressure detection cell when the energization is stopped is detected, and the deterioration determination means determines the deterioration state of the gas sensor element. Compared to the voltage degradation judgment threshold value determined for the current and the energization stop voltage value, if the energization halt voltage value is less than the voltage degradation judgment threshold value, it is determined that the gas sensor element is in a normal state, and the energization is stopped. When the hourly voltage value is equal to or greater than the voltage deterioration determination threshold, it is possible to adopt a configuration characterized in that it is determined that the gas sensor element is in a deteriorated state.

  In the gas sensor element to be judged, the oxygen partial pressure detection cell is energized in order to set the reference oxygen chamber to the reference oxygen partial pressure atmosphere. There is a possibility that the partial pressure of oxygen in the first measurement chamber cannot be accurately detected due to the influence of the voltage drop due to the resistance component in the path.

  On the other hand, since the influence of the voltage drop in the energization path can be suppressed by stopping the energization to the oxygen partial pressure detection cell as in the present invention, the oxygen partial pressure in the first measurement chamber can be accurately detected. It becomes possible to do.

  Then, the oxygen partial pressure control state detecting means detects the voltage value at the time of stopping the energization of the oxygen partial pressure detection cell after stopping the pumping or pumping of oxygen by the first oxygen ion pump cell. From this, the voltage value at the time of energization stop of the oxygen partial pressure detection cell detected by the oxygen partial pressure control state detection means of the present invention reflects the oxygen partial pressure control state of the first measurement chamber immediately before the energization stop. Is. Therefore, the voltage value at the time of stopping energization of the oxygen partial pressure detection cell indicates a value corresponding to the oxygen partial pressure in the first measurement chamber.

  In addition, the voltage value at the time of stopping energization of the oxygen partial pressure detection cell shows a smaller value as the oxygen partial pressure in the first measurement chamber becomes higher, and shows a larger value as the oxygen partial pressure in the first measurement chamber becomes lower. From this, a voltage deterioration determination threshold value for determining the deterioration state of the gas sensor element is determined, and the gas sensor element in the first measurement chamber is compared by comparing the energization stop voltage value with the voltage deterioration determination threshold value. It can be determined whether or not the oxygen partial pressure can be properly controlled.

  That is, the gas sensor element can be determined to be in a normal state when the energization stop voltage value is less than the voltage deterioration determination threshold value, and the gas sensor element is deteriorated when the energization stop voltage value is equal to or greater than the voltage deterioration determination threshold value. It can be determined that it is in a state.

  In the present invention, the oxygen partial pressure control state detecting means detects the voltage value at the time of stopping the energization of the oxygen partial pressure detection cell, and the deterioration determining means compares the voltage value at the time of stopping the energization with the voltage deterioration determining threshold value. Then, it is determined whether the gas sensor element is in a normal state or a deteriorated state.

  Therefore, the sensor element deterioration determination apparatus of the present invention can determine whether or not the gas sensor element can properly control the oxygen partial pressure in the first measurement chamber, and can determine the deterioration state of the gas sensor element including various cells. .

  The voltage deterioration determination threshold can be determined based on, for example, a measurement result using an actual gas sensor element. As an example, immediately after setting the reference oxygen chamber to the reference oxygen partial pressure atmosphere using the unused gas sensor element, the voltage value at the time of stopping the energization of the oxygen partial pressure detection cell is measured, and at that time the energization is stopped The voltage value can be used as a voltage deterioration determination threshold.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram showing a schematic configuration of a gas detection device 1 including a gas sensor control device 190 to which the present invention is applied.

  The gas detection device 1 includes a gas sensor control device 190 and a NOx gas sensor element 10, and a specific gas (NOx in this embodiment) in exhaust gas from various combustion equipment such as an internal combustion engine of a car or a boiler. Used for detection purposes.

  The gas sensor control device 190 is mainly composed of a microcomputer including a central processing unit (CPU), RAM, ROM, signal input / output unit and the like. And the gas sensor control device 190 is a sensor for determining the deterioration state of the NOx gas sensor element 10, a process for controlling the driving of the NOx gas sensor element 10, a process for detecting a specific gas in the exhaust gas based on a detection signal from the NOx gas sensor element 10. Diagnosis processing (On Board Diagnosis processing (OBD processing)) and the like are executed.

  In FIG. 1, the NOx gas sensor element 10 is shown as a cross-sectional view showing the internal structure. In the following description, the left side of the NOx gas sensor element 10 shown in FIG. 1 will be described as the front end side, and the right side will be described as the rear end side. Further, FIG. 1 shows the internal configuration of the front end portion of the NOx gas sensor element 10, and the rear end portion is not shown.

First, the NOx gas sensor element 10 will be described.
The NOx gas sensor element 10 has a structure in which a first pump cell 111, an oxygen partial pressure detection cell 112, and a second pump cell 113 are stacked via insulating layers 114 and 115 mainly composed of alumina. In the NOx gas sensor element 10, the heater unit 180 is stacked on the second pump cell 113 side.

  Among these, the first pump cell 111 includes a first solid electrolyte layer 131 made of zirconia having oxygen ion conductivity, a first electrode for first pump 135 disposed so as to sandwich the first solid electrolyte layer 131, and a first pump cell 111. The first porous electrode 121 including the second electrode for pump 137 is formed. The first pump first electrode 135 and the first pump second electrode 137 are made of platinum, platinum alloy, cermet containing platinum and ceramics (for example, a solid electrolyte body), and the like. The protective layer 122 made of a porous body is formed.

  The oxygen partial pressure detection cell 112 includes a detection solid electrolyte layer 151 made of zirconia having oxygen ion conductivity, a detection electrode 155 disposed so as to sandwich the detection solid electrolyte layer 151, and a reference electrode 157. And a porous detection electrode 123. The detection electrode 155 and the reference electrode 157 are made of platinum, a platinum alloy, cermet containing platinum and ceramics (for example, a solid electrolyte body), or the like.

  The second pump cell 113 includes a second solid electrolyte layer 141 made of zirconia having oxygen ion conductivity, and a first second pump pump disposed on the surface of the second solid electrolyte layer 141 facing the insulating layer 115. An electrode 145 and a second porous electrode 125 including a second pump second electrode 147 are formed.

  The second pump first electrode 145 and the second pump second electrode 147 are made of platinum, platinum alloy, cermet containing platinum and ceramics (for example, a solid electrolyte body), or the like.

  A first measurement chamber 159 into which a measurement target gas is introduced is formed inside the NOx gas sensor element 10. A measurement target gas is introduced into the first measurement chamber 159 from the outside through the first diffusion resistor 116 disposed between the first pump cell 111 and the oxygen partial pressure detection cell 112.

  The first diffusion resistor 116 is formed of a porous body, and is disposed in the measurement target gas introduction path 14 from the opening on the tip side of the NOx gas sensor element 10 to the first measurement chamber 159 to perform the first measurement. The introduction amount (passage amount) of the measurement target gas per unit time into the chamber 159 is limited.

  The introduction path 14 is a region on the tip side (left side in the drawing) of the first measurement chamber 159 in the space surrounded by the first pump cell 111 and the oxygen partial pressure detection cell 112. The first pump first electrode 135 of the first pump cell 111 (specifically, the first pump first electrode 135 covered with the protective layer 122) and the detection electrode 155 of the oxygen partial pressure detection cell 112 are The first measurement chamber 159 is disposed so as to face.

  Further, a second diffusion resistor 117 made of a porous body is provided on the rear end side (right side in the drawing) of the first measurement chamber 159, and the second pump first electrode 145 and the second diffusion resistor are provided. A second measurement chamber 161 is formed between the first measurement chamber 117 and the second measurement chamber 161. The second measurement chamber 161 is formed so as to penetrate the oxygen partial pressure detection cell 112 in the stacking direction.

  Further, in the inside of the NOx gas sensor element 10, in addition to the second measurement chamber 161, between the detection solid electrolyte layer 151 of the oxygen partial pressure detection cell 112 and the second solid electrolyte layer 141 of the second pump cell 113. A reference oxygen chamber 118 is formed. The second measurement chamber 161 and the reference oxygen chamber 118 are formed along the second pump cell 113 in this order from the rear end side to the front end side. The reference oxygen chamber 118 is surrounded by the detection solid electrolyte layer 151 of the oxygen partial pressure detection cell 112, the second solid electrolyte layer 141 of the second pump cell 113, and the insulating layer 115. Thereby, the reference oxygen chamber 118 can be set to a predetermined oxygen partial pressure atmosphere (oxygen partial pressure atmosphere serving as a reference for concentration detection).

The reference electrode 157 of the oxygen partial pressure detection cell 112 and the second pump second electrode 147 of the second pump cell 113 are arranged so as to face the reference oxygen chamber 118.
The heater unit 180 is configured by laminating sheet-like insulating layers 171 and 173 made of insulating ceramics such as alumina. The heater unit 180 includes a heater 175 mainly composed of Pt between the insulating layers 171 and 173.

  The NOx gas sensor element 10 configured as described above can pump (pump out) the oxygen present in the first measurement chamber 159 by the first pump cell 111, and the oxygen partial pressure detection cell 112 can The oxygen concentration difference (oxygen partial pressure difference) between the reference oxygen chamber 118 and the first measurement chamber 159 whose concentration (oxygen partial pressure) is controlled to be constant, that is, the oxygen concentration (oxygen partial pressure) inside the first measurement chamber 159 is set. It can be measured.

  The NOx gas sensor element 10 is driven by a separately provided gas sensor control device 190. The gas sensor control device 190 controls the voltage applied to the heater 175 (heater applied voltage Vh) (in other words, the heater 175). Are driven to heat each cell (first pump cell 111, second pump cell 113, oxygen partial pressure detection cell 112) to the activation temperature.

  The gas sensor control device 190 drives and controls the heater 175 to heat the NOx gas sensor element 10 to the activation temperature (for example, 750 ° C.), and in this state, the detection voltage detected as the voltage across the oxygen partial pressure detection cell 112. The first pump current Ip1 flowing through the first pump cell 111 is controlled so that the value Vs becomes a preset constant voltage (for example, 425 mV).

  The gas sensor control device 190 causes the reference oxygen chamber 118 to flow by passing a small self-generated current Icp for pumping oxygen from the first measurement chamber 159 to the reference electrode 157 to the oxygen partial pressure detection cell 112. Is functioning as an internal oxygen reference source. The current value (current value for oxygen reference generation) of the self-generated current Icp at this time is such that the oxygen partial pressure (oxygen concentration) in the reference oxygen chamber 118 is set to the target value (reference value) by pumping oxygen in the oxygen partial pressure detection cell 112. (Oxygen partial pressure) is controlled in advance.

  The gas sensor controller 190 controls the first pump current Ip1 and applies a predetermined second pump voltage Vp2 (for example, 450 mV) to the second pump cell 113. As a result, in the second measurement chamber 161, NOx is dissociated (reduced) by the catalytic action of the second porous electrode 125 constituting the second pump cell 113, and oxygen ions obtained by the dissociation are converted into the second pump second electrode. The second pump current Ip2 flows by moving the second solid electrolyte layer 141 between the first electrode 145 and the second pump second electrode 147. That is, the second pump cell 113 dissociates the specific gas component (NOx (nitrogen oxide)) present in the second measurement chamber 161 and pumps oxygen from the second measurement chamber 161 to the reference oxygen chamber 118.

The oxygen ions (O ²⁻ ) dissociated at the second pump first electrode 145 in the second measurement chamber 161 move to the second pump second electrode 147 through the second solid electrolyte layer 141, In the second pump second electrode 147, the oxygen (O ₂ ) is released into the reference oxygen chamber 118.

  In other words, the gas sensor control device 190 adjusts the oxygen concentration (oxygen partial pressure) in the first measurement chamber 159 by the pumping operation of the first pump cell 111 while being connected to the NOx gas sensor element 10, and The oxygen concentration (oxygen partial pressure) is set to a concentration for NOx detection capable of detecting NOx, and processing for detecting NOx is performed based on the magnitude and integrated value of the second pump current Ip2.

  Next, processing contents of the sensor diagnosis process (On Board Diagnosis process (OBD process)) executed by the gas sensor control device 190 will be described. FIG. 2 shows a flowchart showing the processing contents of the sensor diagnosis processing.

  When the sensor diagnosis process is started, first, in S110 (S represents a step), the oxygen concentration of the measurement target gas is high (oxygen concentration equivalent to that in the atmosphere. In this embodiment, it is set to 20% or more. ), If the determination is affirmative, the process proceeds to S160, and if the determination is negative, the process proceeds to S120.

  Note that the oxygen concentration of the measurement target gas is the first pump current Ip1 that flows in the first pump cell 111 (specifically, the first pump current Ip1 that flows to adjust the oxygen concentration (oxygen partial pressure) in the first measurement chamber 159). ). That is, since the energization state (current value, current integral value, energization direction, etc.) of the first pump current Ip1 changes according to the oxygen concentration of the measurement target gas, the measurement target gas is based on the first pump current Ip1. The oxygen concentration inside can be determined.

  The gas sensor control device 190 according to the present embodiment uses the first pump current Ip1 that flows through the first pump cell 111 to adjust the oxygen concentration in the first measurement chamber 159 in an oxygen concentration determination process that is separately performed as an internal process. Based on the detected energization state (current value, energization direction, etc.) of the detected first pump current Ip1, the oxygen concentration of the measurement target gas is determined.

  For this reason, in S110, the determination result (oxygen concentration of the measurement target gas) in the oxygen concentration determination process is read, and the oxygen concentration of the measurement target gas is included in the high concentration range (in this embodiment, a range of 20% or more). If the oxygen concentration of the measurement target gas is included in the high concentration range, an affirmative determination is made, and if the oxygen concentration of the measurement target gas deviates from the high concentration range, a negative determination is made.

  Note that the measurement target gas in which the oxygen concentration of the measurement target gas is in the high concentration range contains almost no NOx. Therefore, if the determination in S110 is affirmative, the measurement target gas contains almost NOx. In other words, NOx does not exist in the first measurement chamber 159 and the second measurement chamber 161.

  When a negative determination is made in S110 and the process proceeds to S120, in S120, the voltage value of the second pump voltage Vp2 applied to the second pump cell 113 is set to a voltage value for NOx dissociation that enables dissociation of NOx (for example, 450 [mV]). Therefore, the process of setting the voltage value for oxygen dissociation (in this embodiment, 250 [mV]) capable of dissociating oxygen, although dissociation of NOx is impossible is executed.

In addition, the voltage value for oxygen dissociation can set any numerical value within the range of 250 [mV]-350 [mV], for example.
Before the voltage value is changed, NOx and oxygen (O ₂ ) are dissociated (reduced) in the second measurement chamber 161 by the catalytic action of the second porous electrode 125 constituting the second pump cell 113. In contrast, after the voltage value is changed, oxygen (O ₂ ) is dissociated (reduced), but NOx is not dissociated.

That is, after the voltage value is changed, the second pump current Ip2 flows due to the movement of oxygen ions obtained by the dissociation of oxygen (O ₂ ), and the second pump current Ip2 at this time is the second measurement. The current value according to the oxygen concentration (oxygen partial pressure) in the second measurement chamber 161 is shown instead of the current value according to the specific gas concentration (NOx concentration) in the chamber 161.

  Note that immediately after the voltage change, the second pump current Ip2 may increase due to the influence of oxygen ions obtained by dissociation of NOx before the change. Therefore, the effects of NOx can be reduced by executing the processing in the next S130 to S150 and waiting for a certain time until the second pump current Ip2 is stabilized.

First, in S130, timer processing for measuring elapsed time is started.
In subsequent S140, it is determined whether or not the stabilization waiting time has elapsed from the start of time measurement by the timer process. If the determination is affirmative, the process proceeds to S150, and if the determination is negative, the same step is repeated. Wait by executing.

In the present embodiment, 1.0 [sec] is set as a stabilization waiting time until the second pump current Ip2 is stabilized after the second pump voltage Vp2 is changed.
When an affirmative determination is made in S140 and the process proceeds to S150, the timer process for measuring the elapsed time is stopped in S150.

  When an affirmative determination is made in S110 or the processing of S150 ends, the process proceeds to S160, and in S160, a process of reading a predetermined offset value deterioration determination threshold K from a predetermined storage device (such as an internal memory) is executed. To do.

  The offset value deterioration determination threshold value K is a determination value used for determination processing (processing for determining deterioration of the NOx gas sensor element 10) in S180, which will be described later, and is based on a measurement result using the actual NOx gas sensor element 10. Can be determined. For example, the current value (initial value) of the second pump current Ip2 when the self-generated current Icp set to the oxygen reference generation current value is supplied to the oxygen partial pressure detection cell 112 using the unused NOx gas sensor element 10. Second pump current offset value α) is measured, and this initial second pump current offset value α is multiplied by a predetermined deterioration coefficient J (a value less than 1, for example, 0.9). The value (= α × J) can be determined as the offset value deterioration determination threshold K (= α × J).

In the next S170, a process of detecting the current value of the second pump current Ip2 flowing through the second pump cell 113 as the second pump current offset value β (Ip2 offset value β) is executed.
The second pump current Ip2 detected at this time does not indicate a current value according to the concentration of the specific gas (NOx), but a current value flowing through the second pump cell 113 according to the oxygen partial pressure in the second measurement chamber 161. It becomes.

  That is, if the determination in S110 is affirmative, NOx is not present in the second measurement chamber 161, and therefore the second pump current Ip2 detected in S170 is equal to the oxygen partial pressure in the second measurement chamber 161. The corresponding current value is shown. If the negative determination is made in S110, since the second pump voltage Vp2 is set to the oxygen dissociation voltage value in S120, the specific gas (NOx) cannot be dissociated, so the second detected in S170. The pump current Ip2 indicates a current value corresponding to the oxygen partial pressure in the second measurement chamber 161.

  For this reason, the second pump current offset value β is determined according to the oxygen partial pressure in the second measurement chamber 161 when the self-generated current Icp flowing through the oxygen partial pressure detection cell 112 is the oxygen reference generation current value. The current value flowing through the pump cell 113 is obtained.

Here, FIG. 3 shows an explanatory diagram showing the correlation between the self-generated current Icp supplied to the oxygen partial pressure detection cell 112 and the second pump current offset value.
In FIG. 3, the solid line indicates the correlation when the NOx gas sensor element 10 is in a normal state (initial state that is not deteriorated), and the NOx gas sensor element 10 is in a deteriorated state (the oxygen partial pressure in the first measurement chamber 159 is The correlation when the deterioration state is lower than the target value is indicated by a one-dot chain line. Further, in FIG. 3, the correlation between the two is shown in a coordinate plane in which the vertical axis is the second pump current offset value (Ip2 offset) and the horizontal axis is the self-generated current Icp.

  Note that the deterioration state in which the oxygen partial pressure in the first measurement chamber 159 is lower than the target value is a state in which the pumping of oxygen from the first measurement chamber 159 is excessively performed. Not only the specific gas (NOx) may be pumped out of the first measurement chamber 159.

  According to FIG. 3, even if the self-generated current Icp has the same current value, the second pump current offset value in the deteriorated NOx gas sensor element 10 is the second pump current offset in the normal state NOx gas sensor element 10. The value is smaller than the value. From this, it can be seen that the correlation between the second pump current offset value (Ip2 offset) and the self-generated current Icp changes according to the state (normal state, deteriorated state) of the NOx gas sensor element 10.

  That is, a specific current value (determination current value) is determined in advance as the self-generated current Icp, and the second pump current offset value β when the determination current is supplied to the oxygen partial pressure detection cell 112 is detected. Then, by determining whether or not the detected second pump current offset value β is included in the normal range, it is possible to determine whether the NOx gas sensor element 10 is in a normal state or in a deteriorated state.

  Next, returning to the flowchart of FIG. 2, in S180, the deterioration judgment threshold value for offset value K read in S160 is compared with the second pump current offset value β detected in S170, and the second pump current offset value β is offset. It is determined whether or not the deterioration determination threshold value K is greater than or equal to the value. If the determination is affirmative, the process proceeds to S190. If the determination is negative, the process proceeds to S200.

  That is, in S180, when the second pump current offset value β is equal to or greater than the offset value deterioration determination threshold K, it is determined that the NOx gas sensor element 10 is in a normal state, and the second pump current offset value β is the offset value. If it is less than the use deterioration determination threshold K, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  The offset value deterioration determination threshold value K used for the determination in S180 is set to a value obtained by multiplying the initial second pump current offset value α and the deterioration coefficient J as described above. For example, when the deterioration coefficient J is “0.9”, if the detected second pump current offset value β is 90% or more of the initial second pump current offset value α, the normal state is determined and detected. If the second pump current offset value β is less than 90% of the initial second pump current offset value α, it is determined that the state is deteriorated.

  For the NOx gas sensor element 10 that is positively determined in S180 when the deterioration coefficient J is “0.9”, the control error of the oxygen partial pressure (oxygen concentration) in the first measurement chamber 159 and the second measurement chamber 161 is 10 In applications where the control error can be up to 10%, it is possible to determine that NOx detection is not possible (deterioration state), but NOx detection is possible (normal state).

The deterioration coefficient J is not limited to “0.9”, and by appropriately setting a value according to the allowable range of the control error, it is possible to appropriately determine the deterioration according to the application.
When an affirmative determination is made in S180 and the process proceeds to S190, it is determined in S190 that the NOx gas sensor element 10 is in a normal state, and the voltage value of the second pump voltage Vp2 applied to the second pump cell 113 can be dissociated from NOx. A process for setting a voltage value for dissociating NOx is executed.

  The voltage change process in S190 is intended to return the voltage value of the second pump voltage Vp2 that was negatively determined in S110 and changed in S120 to the voltage value before the change. Therefore, when an affirmative determination is made in S110, the voltage value of the second pump voltage Vp2 is not changed to the voltage value for oxygen dissociation and remains the voltage value for NOx dissociation. The pump voltage Vp2 is not changed, and the same voltage value is maintained.

  That is, by performing the process in S190, the gas dissociation ability in the second pump cell 113 is set to a level at which NOx can be dissociated (reduced), and the NOx gas sensor element 10 can detect NOx. Set to

  The gas sensor control device 190 detects the second pump current Ip2 of the NOx gas sensor element 10 by executing the NOx detection process as an internal process different from the sensor diagnosis process, and based on the detected second pump current Ip2. NOx detection is performed.

  When a negative determination is made in S180 and the process proceeds to S200, in S200, it is determined that the NOx gas sensor element 10 is in a deteriorated state, and an abnormality occurrence signal indicating that the NOx gas sensor element 10 is in a deteriorated state is sent to the gas sensor control device 190. Processing to output to an external device from an output terminal (not shown) is performed.

  Then, the external device that has received the abnormality occurrence signal performs processing for notifying the user that the NOx gas sensor element 10 is in a deteriorated state. Specific processing includes, for example, processing for turning on a warning lamp indicating that the NOx gas sensor element 10 is in a deteriorated state, processing for outputting a voice message indicating that the NOx gas sensor element 10 is in a deteriorated state, and the like. be able to.

When S190 or S200 ends, this control process (sensor diagnosis process) ends.
As described above, in the gas sensor control device 190 provided in the gas detection device 1 of the present embodiment, when the self-generated current Icp is supplied to the oxygen partial pressure detection cell 112, the oxygen partial pressure in the second measurement chamber 161 is set. Accordingly, the current value flowing through the second pump cell 113 is detected as the second pump current offset value β.

  The NOx gas sensor element 10 has a configuration in which the oxygen partial pressure in the first measurement chamber 159 is determined based on the reference oxygen partial pressure in the reference oxygen chamber 118. In addition, the NOx gas sensor element 10 has a configuration in which the measurement target gas from which oxygen is pumped or pumped in the first measurement chamber 159 is introduced into the second measurement chamber 161 via the second diffusion resistor 117. The oxygen partial pressure in the second measurement chamber 161 is determined according to the oxygen partial pressure in the first measurement chamber 159.

  The second pump current offset value β is a current value that flows through the second pump cell 113 in accordance with the oxygen partial pressure in the second measurement chamber 161. Therefore, the second pump current offset value β is a value in accordance with the oxygen partial pressure in the second measurement chamber 161. In addition, a value corresponding to the oxygen partial pressure in the first measurement chamber 159 is shown.

  That is, the change state of the second pump current offset value β with respect to the self-generated current Icp supplied to the oxygen partial pressure detection cell 112 is the first measurement chamber 159 relative to the current supply state of the self-generated current Icp to the oxygen partial pressure detection cell 112. This reflects the oxygen partial pressure control state.

  Note that the second pump current offset value β indicates a larger value as the oxygen partial pressure in the second measurement chamber 161 becomes higher, and a smaller value as the oxygen partial pressure in the second measurement chamber 161 becomes lower. From this, by setting a deterioration determination threshold value K for offset value for determining the deterioration state of the NOx gas sensor element 10, and comparing the second pump current offset value β and the deterioration determination threshold value K for offset value, It can be determined whether or not the NOx gas sensor element 10 can properly control the oxygen partial pressure in the first measurement chamber 159.

  Then, the gas sensor control device 190 detects the second pump current offset value β with respect to the self-generated current Icp in S170 in the sensor diagnosis process. In S180 in the sensor diagnosis process, the gas sensor control device 190 detects the offset value deterioration determination threshold K and the second value. The pump current offset value β is compared to determine whether the NOx gas sensor element 10 is in a normal state or a deteriorated state. In S180, when the second pump current offset value β is equal to or greater than the offset value deterioration determination threshold value K, it is determined that the NOx gas sensor element 10 is in a normal state, and the second pump current offset value β is determined as the offset value deterioration determination threshold value. When it is smaller than K, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  That is, the gas sensor control device 190 of the present embodiment detects the oxygen partial pressure control state in the first measurement chamber 159 relative to the energized state of the oxygen partial pressure detection cell 112, and the detected oxygen partial pressure control state is determined in advance. It is determined whether the NOx gas sensor element 10 is in a normal state or in a deteriorated state by determining whether or not it is in the normal range.

  Thus, by making a determination using the oxygen partial pressure control state, the NOx gas sensor element 10 is in a normal state in which the oxygen partial pressure in the first measurement chamber 159 can be properly controlled, or the oxygen in the first measurement chamber 159 It is possible to appropriately determine whether or not the partial pressure cannot be properly controlled.

  Therefore, the gas sensor control device 190 of the present embodiment can determine whether or not the NOx gas sensor element 10 can appropriately control the oxygen partial pressure in the first measurement chamber 159, and determine the deterioration state of the NOx gas sensor element 10 including various cells. It can be judged.

  Further, in the present embodiment, the current value (current value for determination) of the self-generated current Icp that is energized to the oxygen partial pressure detection cell 112 when performing deterioration determination, and the oxygen partial pressure detection cell 112 that is energized when detecting a specific gas. The current value (oxygen reference generation current) of the self-generated current Icp is the same current value.

  In this way, by setting the current value for determination and the current value for oxygen reference generation to the same current value, the current applied to the oxygen partial pressure detection cell 112 is changed when shifting from the specific gas detection state to the deterioration determination state. There is no need to do.

  As a result, in the sensor diagnosis process, it is not necessary to execute the step of changing the setting of the current supplied to the oxygen partial pressure detection cell 112, and the labor for executing such a step can be omitted. The accompanying process can be simplified.

  Further, in this embodiment, if a negative determination is made in S110, the voltage value of the second pump voltage Vp2 applied to the second pump cell 113 is changed to a NOx dissociation voltage value (for example, NOx dissociation capable of dissociating NOx) in S120. , 450 [mV]), the process of setting the voltage value for oxygen dissociation to which dissociation of NOx is impossible but oxygen can be dissociated is executed. When the voltage value of the second pump voltage Vp2 is thus set, in S170, the second pump voltage Vp2 applied to the second pump cell 113 is set to the oxygen dissociation voltage value in the second state. A process of detecting the pump current offset value β is executed.

  When the oxygen concentration of the measurement target gas is high (the same oxygen concentration as in the atmosphere), the measurement target gas has almost no specific gas (NOx), but the oxygen concentration of the measurement target gas When is not a high concentration, there is a high possibility that the specific gas (NOx) exists in the measurement target gas.

  That is, the gas sensor control device 190 of the present embodiment sets the voltage applied to the second pump cell 113 to the oxygen dissociation voltage value (degradation determination voltage value), so that the second pump cell 113 can dissociate the specific gas. Impossible and oxygen can be dissociated. Thereby, even when the specific gas (NOx) is present in the second measurement chamber 161, the current flowing through the second pump cell 113 is not affected by the specific gas (NOx), and the current in the second measurement chamber 161 is not affected. The value depends on the oxygen partial pressure.

  Therefore, according to the present embodiment, the current value flowing through the second pump cell 113 can be prevented from fluctuating due to the influence of the specific gas (NOx), and the second pump current offset value β can be accurately detected. Can be improved.

  In the present embodiment, the gas sensor control device 190 that executes sensor diagnosis processing corresponds to the sensor element deterioration determination device described in the claims, the NOx gas sensor element 10 corresponds to the gas sensor element, and the first pump cell 111. Corresponds to the first oxygen ion pump cell, the second pump cell 113 corresponds to the second oxygen ion pump cell, and the oxygen partial pressure detection cell 112 corresponds to the oxygen partial pressure detection cell. The first diffusion resistor 116 corresponds to the first diffusion resistor part, and the second diffusion resistor 117 corresponds to the second diffusion resistor part.

  Further, the gas sensor control device 190 that executes S170 of the sensor diagnosis process corresponds to the oxygen partial pressure control state detection means, and the gas sensor control device 190 that executes S180 of the sensor diagnosis process corresponds to the deterioration determination means. The gas sensor control device 190 that executes S120 corresponds to the voltage setting means for deterioration determination.

  As described above, the embodiment of determining the deterioration state of the NOx gas sensor element 10 based on the second pump current offset value β (hereinafter also referred to as the first embodiment) has been described as an embodiment of the present invention. The form is not limited to the above embodiment.

  Next, as a second embodiment, an embodiment in which the deterioration state of the NOx gas sensor element 10 is determined based on an offset change amount which is a difference between the second pump current first offset value and the second pump current second offset value. Will be described.

  In addition, the gas detection apparatus 1 in 2nd Embodiment is provided with the gas sensor control apparatus 190 and NOx gas sensor element 10 similarly to 1st Embodiment, and the block diagram which shows schematic structure is the same as that of FIG.

  Compared to the first embodiment, the second embodiment is different from the first embodiment in that the sensor diagnostic process (On Board Diagnosis process (OBD process)) executed by the gas sensor control device 190 is different, so that the second embodiment is executed in the second embodiment. The contents of the second sensor diagnosis process will be mainly described.

FIG. 4 is a flowchart showing the processing contents of the second sensor diagnosis processing.
When the second sensor diagnosis process is started, first, in S310 (S represents a step), the oxygen concentration of the measurement target gas is high (oxygen concentration equivalent to that in the atmosphere. In the present embodiment, it is 20% or more). If the determination is affirmative, the process proceeds to S360. If the determination is negative, the process proceeds to S320.

  Note that the oxygen concentration of the measurement target gas is the first pump current Ip1 that flows in the first pump cell 111 (specifically, the first pump current Ip1 that flows to adjust the oxygen concentration (oxygen partial pressure) in the first measurement chamber 159). ). That is, since the energization state (current value, current integral value, energization direction, etc.) of the first pump current Ip1 changes according to the oxygen concentration of the measurement target gas, the measurement target gas is based on the first pump current Ip1. The oxygen concentration inside can be determined.

  The gas sensor control device 190 according to the present embodiment uses the first pump current Ip1 that flows through the first pump cell 111 to adjust the oxygen concentration in the first measurement chamber 159 in an oxygen concentration determination process that is separately performed as an internal process. Based on the detected energization state (current value, energization direction, etc.) of the detected first pump current Ip1, the oxygen concentration of the measurement target gas is determined.

  For this reason, in S310, the determination result (oxygen concentration of the measurement target gas) in the oxygen concentration determination process is read, and the oxygen concentration of the measurement target gas is included in the high concentration range (in this embodiment, the range of 20% or more). If the oxygen concentration of the measurement target gas is included in the high concentration range, an affirmative determination is made, and if the oxygen concentration of the measurement target gas deviates from the high concentration range, a negative determination is made.

  Note that the measurement target gas in which the oxygen concentration of the measurement target gas is in the high concentration range contains almost no NOx. Therefore, if the determination in S310 is affirmative, the measurement target gas contains almost NOx. In other words, NOx does not exist in the first measurement chamber 159 and the second measurement chamber 161.

  When a negative determination is made in S310 and the process proceeds to S320, in S320, the voltage value of the second pump voltage Vp2 applied to the second pump cell 113 is set to a voltage value for NOx dissociation that enables dissociation of NOx (for example, 450 [mV]). Therefore, the process of setting the voltage value for oxygen dissociation (in this embodiment, 250 [mV]) capable of dissociating oxygen, although dissociation of NOx is impossible is executed.

In addition, the voltage value for oxygen dissociation can set any numerical value within the range of 250 [mV]-350 [mV], for example.
Before the voltage value is changed, NOx and oxygen (O ₂ ) are dissociated (reduced) in the second measurement chamber 161 by the catalytic action of the second porous electrode 125 constituting the second pump cell 113. In contrast, after the voltage value is changed, oxygen (O ₂ ) is dissociated (reduced), but NOx is not dissociated.

That is, after the voltage value is changed, the second pump current Ip2 flows due to the movement of oxygen ions obtained by the dissociation of oxygen (O ₂ ), and the second pump current Ip2 at this time is the second measurement. The current value according to the oxygen concentration (oxygen partial pressure) in the second measurement chamber 161 is shown instead of the current value according to the specific gas concentration (NOx concentration) in the chamber 161.

  Note that immediately after the voltage change, the second pump current Ip2 may increase due to the influence of oxygen ions obtained by dissociation of NOx before the change. Therefore, the following processes in S330 to S350 are executed, and the influence of NOx is surely avoided by waiting for a certain period of time until the second pump current Ip2 is stabilized.

First, in S330, timer processing for measuring elapsed time is started.
In subsequent S340, it is determined whether or not the stabilization waiting time has elapsed from the time measurement start time by the timer process. If the determination is affirmative, the process proceeds to S350, and if the determination is negative, the same step is repeated. Wait by executing.

In the present embodiment, 1.0 [sec] is set as a stabilization waiting time until the second pump current Ip2 is stabilized after the second pump voltage Vp2 is changed.
When an affirmative determination is made in S340 and the process proceeds to S350, the timer process for measuring the elapsed time is stopped in S350.

  When an affirmative determination is made in S310 or the processing of S350 ends, the process proceeds to S360, and in S360, the current value of the second pump current Ip2 flowing through the second pump cell 113 is detected as the second pump current first offset value β1. At the same time, a process of detecting the current value of the self-generated current Icp (hereinafter also referred to as the first determination current value Icp1) that is energized in the oxygen partial pressure detection cell 112 is executed.

  The second pump current Ip2 detected in S360 does not indicate a current value according to the concentration of the specific gas (NOx), but a current value flowing through the second pump cell 113 according to the oxygen partial pressure in the second measurement chamber 161. It becomes.

  That is, if the determination in S310 is affirmative, NOx is not present in the second measurement chamber 161, and therefore the second pump current Ip2 detected in S360 is equal to the oxygen partial pressure in the second measurement chamber 161. The corresponding current value is shown. If the negative determination is made in S310, since the second pump voltage Vp2 is set to the oxygen dissociation voltage value in S320, the specific gas (NOx) cannot be dissociated, so the second detected in S360. The pump current Ip2 indicates a current value corresponding to the oxygen partial pressure in the second measurement chamber 161.

  For this reason, the second pump current first offset value β1 detected in S360 is the value of the second measurement chamber 161 when the self-generated current Icp flowing through the oxygen partial pressure detection cell 112 is the first determination current value Icp1. The current value flowing through the second pump cell 113 is determined according to the oxygen partial pressure.

  In addition, the self-generated current Icp detected in S360 controls the oxygen partial pressure (oxygen concentration) in the reference oxygen chamber 118 to the target value (reference oxygen partial pressure) by pumping in oxygen from the oxygen partial pressure detection cell 112. The oxygen reference generation current value is determined in advance. That is, the first determination current value Icp1 detected in S360 is the oxygen reference generation current value.

  In next S370, a process of changing the current value of the self-generated current Icp energized to the oxygen partial pressure detection cell 112 to the second determination current value Icp2 different from the oxygen reference generation current value is executed. The second determination current value Icp2 is set to a current value smaller than the oxygen reference generation current value.

  Since the oxygen concentration (oxygen partial pressure) in the reference oxygen chamber 118 immediately after the current change is substantially equal to that before the current change, the oxygen concentration in the reference oxygen chamber 118 is the second determination current after the current change. It is desirable to wait until the concentration reaches the value Icp2. Therefore, the processing in the next S380 to S400 is executed, and the process waits for a certain period of time until the oxygen concentration in the reference oxygen chamber 118 becomes a concentration corresponding to the second determination current value Icp2 after the current change.

First, in S380, timer processing for measuring elapsed time is started.
In subsequent S390, it is determined whether or not the detection standby time has elapsed from the start of time measurement by the timer process. If the determination is affirmative, the process proceeds to S400, and if the determination is negative, the same step is repeatedly executed. To wait.

  In the present embodiment, after the self-generated current Icp is changed to the second determination current value Icp2, the detection standby time until the oxygen concentration in the reference oxygen chamber 118 becomes a concentration corresponding to the second determination current value Icp2. Is set to 5.0 [sec].

When an affirmative determination is made in S390 and the process proceeds to S400, the timer process for measuring the elapsed time is stopped in S400.
When the process of S400 is completed, the process proceeds to S410. In S410, the current value of the second pump current Ip2 flowing through the second pump cell 113 is detected as the second pump current second offset value β2, and the oxygen partial pressure detection cell 112 is detected. Is executed to detect the current value (second determination current value Icp2) of the self-generated current Icp that is energized to the current.

  In the next S420, a process of calculating a difference value between the second pump current first offset value β1 and the second pump current second offset value β2 as an offset change amount ΔIp2 (= β1-β2) is performed. In S430, a process of calculating a difference value between the first determination current value Icp1 and the second determination current value Icp2 as a determination current change amount ΔIcp (= ΔIcp1-ΔIcp2) is performed.

In subsequent S440, a process of reading a predetermined change amount deterioration determination threshold A from a predetermined storage device (such as an internal memory) is executed.
The change amount deterioration determination threshold A is a determination value used in a determination process in S450 described later (a process for determining deterioration of the NOx gas sensor element 10), and is based on a measurement result using the actual NOx gas sensor element 10. Can be determined.

  For example, using the unused NOx gas sensor element 10, the first determination current value Icp1 and the second determination current value Icp2 are supplied to the oxygen partial pressure detection cell 112 as the self-generated current Icp, Current values of the second pump current Ip2 (second pump current first offset value β1 and second pump current second offset value β2) are measured. Then, the difference value (offset change amount B) between the second pump current first offset value β1 and the second pump current second offset value β2 at this time, the first determination current value Icp1 and the second determination at this time A difference value (determination current change amount C) from the current value Icp2 for calculation is calculated, and a value obtained by dividing the offset change amount B by the determination current change amount C is used as an initial offset change amount D (= B / C). Further, a value obtained by multiplying the initial offset change amount D (= B / C) by a predetermined deterioration coefficient E (a value less than 1, for example, 0.9) is used as a change amount deterioration determination threshold A. (= D × E).

  Here, the correlation between the self-generated current Icp supplied to the oxygen partial pressure detection cell 112 and the second pump current offset value is shown, and an explanatory diagram for explaining the offset change amount ΔIp2 and the determination current change amount ΔIcp. Is shown in FIG.

  In FIG. 5, the solid line indicates the correlation when the NOx gas sensor element 10 is in a normal state (an initial state that is not deteriorated), and the NOx gas sensor element 10 is in a deteriorated state (the oxygen partial pressure in the first measurement chamber 159 is The correlation when the deterioration state is lower than the target value is indicated by a one-dot chain line. Further, in FIG. 5, the correlation between the two is shown in a coordinate plane in which the vertical axis is the second pump current offset value (Ip2 offset) and the horizontal axis is the self-generated current Icp.

  Further, FIG. 5 illustrates a determination current change amount ΔIcp, which is a difference between the first determination current value Icp1 and the second determination current value Icp2, and the offset change amounts ΔIp2 (in the initial state and the deteriorated state). The initial ΔIp2 and the deterioration ΔIp2) are illustrated.

  Note that the deterioration state in which the oxygen partial pressure in the first measurement chamber 159 is lower than the target value is a state in which the pumping of oxygen from the first measurement chamber 159 is excessively performed. Not only the specific gas (NOx) may be pumped out of the first measurement chamber 159.

  According to FIG. 5, even if the self-generated current Icp has the same current value, the second pump current offset value in the deteriorated NOx gas sensor element 10 is the second pump current offset in the normal state NOx gas sensor element 10. The value is smaller than the value. From this, it can be seen that the correlation between the second pump current offset value (Ip2 offset) and the self-generated current Icp changes according to the state (normal state, deteriorated state) of the NOx gas sensor element 10.

  Furthermore, even if the current change amount for determination ΔIcp is the same, the offset change amount ΔIp2 (initial time ΔIp2, deterioration time ΔIp2) is different in the initial state and the deterioration state, and “initial time ΔIp2> deterioration time” The relationship is “ΔIp2”. That is, it can be seen that the correlation between the determination current change amount ΔIcp and the offset change amount ΔIp2 changes according to the state (normal state, deteriorated state) of the NOx gas sensor element 10.

  Thus, two determination current values (first determination current value Icp1 and second determination current value Icp2) for specifying the determination current change amount ΔIcp are determined in advance, and the determination current change amount ΔIcp is determined. By detecting the offset change amount ΔIp2 with respect to, and determining whether or not the value (ΔIp2 / ΔIcp) obtained by dividing the detected offset change amount ΔIp2 by the determination current change amount ΔIcp is included in the normal range, It can be determined whether the NOx gas sensor element 10 is in a normal state or a deteriorated state.

  Next, returning to the flowchart of FIG. 4, in S450, a value obtained by dividing the offset change amount ΔIp2 obtained in S420 by the determination current change amount ΔIcp obtained in S430 (corrected offset change amount ΔIp2 / ΔIcp). Is compared with the change amount deterioration determination threshold A read in S440, and it is determined whether or not the correction offset change amount ΔIp2 / ΔIcp is greater than or equal to the change amount deterioration determination threshold A. Shifts to S460, and shifts to S500 if a negative determination is made.

  That is, in S450, when the correction offset change amount ΔIp2 / ΔIcp is equal to or greater than the change amount deterioration determination threshold A, it is determined that the NOx gas sensor element 10 is in the normal state, and the correction offset change amount ΔIp2 / ΔIcp is the change amount. When it is less than the use deterioration determination threshold A, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  Then, the change amount deterioration determination threshold A used for the determination in S450 is the initial offset change amount D (= B / C) obtained by dividing the offset change amount B by the determination current change amount C as described above. A value obtained by multiplying the deterioration coefficient E by the value is set.

  For example, when the deterioration coefficient E is “0.9”, if the detected correction offset change amount ΔIp2 / ΔIcp is 90% or more of the initial offset change amount D, the normal state is determined, and the detected correction is detected. If the offset change amount ΔIp2 / ΔIcp is less than 90% of the initial offset change amount D, it is determined that the deterioration state has occurred.

  For the NOx gas sensor element 10 that is determined to be affirmative in S450 when the deterioration coefficient E is “0.9”, the control error of the oxygen partial pressure (oxygen concentration) in the first measurement chamber 159 and the second measurement chamber 161 is 10 In applications where the control error can be up to 10%, it is possible to determine that NOx detection is not possible (deterioration state), but NOx detection is possible (normal state).

Note that the deterioration coefficient E is not limited to “0.9”, and by appropriately setting a value corresponding to the allowable range of the control error, it is possible to appropriately determine the deterioration according to the application.
When an affirmative determination is made in S450 and the process proceeds to S460, in S460, it is determined that the NOx gas sensor element 10 is in a normal state, and the current value of the self-generated current Icp is changed from the second determination current value Icp2 to the first determination current value. A process of changing the setting to Icp1 is executed.

  The current change process in S460 is for the purpose of returning the self-generated current Icp changed in S370 to the current value before the change (first determination current value Icp1, in other words, oxygen reference generation current value). Yes. That is, by performing the process in S460, the oxygen partial pressure (oxygen concentration) in the reference oxygen chamber 118 is controlled to the target value (reference oxygen partial pressure) by pumping oxygen in the oxygen partial pressure detection cell 112. Is set to the state.

  Since the oxygen concentration (oxygen partial pressure) in the reference oxygen chamber 118 immediately after the current change is substantially equal to that before the current change, the oxygen concentration in the reference oxygen chamber 118 is the first determination current after the current change. It is desirable to wait until the concentration reaches the value Icp1 (oxygen reference generation current value). Therefore, the processing in the next S470 to S490 is executed, and the process waits for a certain period of time until the oxygen concentration in the reference oxygen chamber 118 becomes a concentration corresponding to the first determination current value Icp1 after the current change.

First, in S470, timer processing for measuring elapsed time is started.
In subsequent S480, it is determined whether or not the return waiting time has elapsed since the start of the time measurement by the timer process. If the determination is affirmative, the process proceeds to S490, and if the determination is negative, the same step is repeated. To wait.

  In the present embodiment, after the self-generated current Icp is changed to the first determination current value Icp1, the return waiting time until the oxygen concentration in the reference oxygen chamber 118 becomes a concentration corresponding to the first determination current value Icp1. Is set to 1.0 [sec].

If an affirmative determination is made in S480 and the process proceeds to S490, the timer process for measuring the elapsed time is stopped in S490.
On the other hand, when a negative determination is made in S450 and the process proceeds to S500, in S500, it is determined that the NOx gas sensor element 10 is in a deteriorated state, and an abnormality occurrence signal indicating that the NOx gas sensor element 10 is in a deteriorated state is sent to the gas sensor control device. A process of outputting to an external device from the output terminal 190 (not shown) is performed.

  Then, the external device that has received the abnormality occurrence signal performs processing for notifying the user that the NOx gas sensor element 10 is in a deteriorated state. Specific processing includes, for example, processing for turning on a warning lamp indicating that the NOx gas sensor element 10 is in a deteriorated state, processing for outputting a voice message indicating that the NOx gas sensor element 10 is in a deteriorated state, and the like. be able to.

When S490 or S500 ends, the present control process (second sensor diagnostic process) ends.
As described above, in the gas sensor control device 190 provided in the gas detection device 1 of the second embodiment, when the first determination current Icp1 and the second determination current Icp2 are respectively supplied to the oxygen partial pressure detection cell 112. In addition, the second pump current first offset value β1 and the second pump current second offset value β2 are detected as current values flowing in the second pump cell 113, respectively, and the second pump current first offset value β1 and the second pump current are detected. An offset change amount ΔIp2 that is a difference from the second offset value β2 is detected.

  This offset change amount ΔIp2 is a change amount of the second pump current offset value with respect to the change amount of the determination current (determination current change amount ΔIcp), and the first measurement chamber 159 corresponding to the energization state of the oxygen partial pressure detection cell 112. This reflects the oxygen partial pressure control state.

  The offset change amount ΔIp2 shows a larger value as the change amount of the oxygen partial pressure in the second measurement chamber corresponding to the determination current change amount ΔIcp is larger, and the smaller the change amount of the oxygen partial pressure in the second measurement chamber is. Indicates a small value.

  Further, the corrected offset change amount ΔIp2 / ΔIcp obtained by dividing the offset change amount ΔIp2 by the determination current change amount ΔIcp changes according to the offset change amount ΔIp2 if the determination current change amount ΔIcp is the same value. . Therefore, the correction offset change amount ΔIp2 / ΔIcp shows a larger value as the change amount of the oxygen partial pressure in the second measurement chamber 161 becomes higher under the condition that the determination current change amount ΔIcp becomes the same value, and the second measurement The smaller the amount of change in the oxygen partial pressure of the chamber, the smaller the value.

  For this reason, a change amount deterioration determination threshold value A for determining the deterioration state of the NOx gas sensor element 10 is determined, and the correction offset change amount ΔIp2 / ΔIcp is compared with the change amount deterioration determination threshold value A. It can be determined whether or not the gas sensor element 10 can properly control the oxygen partial pressure in the first measurement chamber 159.

  That is, when the correction offset change amount ΔIp2 / ΔIcp is equal to or greater than the change amount deterioration determination threshold A, it can be determined that the NOx gas sensor element 10 is in a normal state, and the correction offset change amount ΔIp2 / ΔIcp is the change amount deterioration determination threshold A. When it is smaller than that, it can be determined that the NOx gas sensor element 10 is in a deteriorated state.

  In this embodiment, the offset change amount ΔIp2 is calculated in S420, the determination current change amount ΔIcp is calculated in S430, and in S450, the offset change amount ΔIp2 is calculated as the determination current change amount ΔIcp. The correction offset change amount ΔIp2 / ΔIcp is obtained by division, and the correction offset change amount ΔIp2 / ΔIcp is compared with the change amount deterioration determination threshold A to determine whether the NOx gas sensor element 10 is in a normal state or in a deteriorated state. judge.

  Therefore, the gas sensor control device 190 of the second embodiment can determine whether or not the NOx gas sensor element 10 can properly control the oxygen partial pressure in the first measurement chamber 159, and the deterioration state of the NOx gas sensor element 10 including various cells. Can be determined.

  In the second embodiment, the first determination current value Icp1 is set to a voltage value equal to the oxygen reference generation current, and the second determination current value Icp2 is smaller than the oxygen reference generation current. Is set to

  That is, in the NOx gas sensor element 10, when there is no means for pumping out oxygen from the reference oxygen chamber, the oxygen in the reference oxygen chamber 118 is determined at the time of deterioration determination (when the first determination current and the second determination current are energized). When the partial pressure is increased, there is a possibility that the time for reducing the oxygen partial pressure in the reference oxygen chamber 118 to the target value becomes longer when shifting from the deterioration determination state to the specific gas detection state.

  In contrast, as in the second embodiment, the first determination current value Icp1 is set equal to the oxygen reference generation current, and the second determination current value Icp2 is set smaller than the oxygen reference generation current. Thus, it is possible to prevent the oxygen partial pressure detection cell 112 from excessively pumping oxygen into the reference oxygen chamber 118 during the deterioration determination (when the first determination current and the second determination current are energized). .

  The NOx gas sensor element 10 is configured such that oxygen can be pumped by the oxygen partial pressure detection cell 112. For this reason, the gas sensor control device 190 changes the oxygen partial pressure of the reference oxygen chamber 118 to the target value by the oxygen partial pressure detection cell 112 performing the oxygen pumping operation when shifting from the deterioration determination state to the specific gas detection state. The time for raising to can be shortened.

Therefore, according to the gas sensor control apparatus 190 of 2nd Embodiment, the time at which it transfers to a specific gas detection state from a deterioration determination state can be shortened.
In the second embodiment, the gas sensor control device 190 that executes the second sensor diagnostic process corresponds to the sensor element deterioration determination device described in the claims, the NOx gas sensor element 10 corresponds to the gas sensor element, One pump cell 111 corresponds to a first oxygen ion pump cell, the second pump cell 113 corresponds to a second oxygen ion pump cell, and the oxygen partial pressure detection cell 112 corresponds to an oxygen partial pressure detection cell. The first diffusion resistor 116 corresponds to the first diffusion resistor part, and the second diffusion resistor 117 corresponds to the second diffusion resistor part.

  Further, the gas sensor control device 190 that executes S360, S410, S420, and S430 of the second sensor diagnostic processing corresponds to the oxygen partial pressure control state detection means, and the gas sensor control device 190 that executes S450 of the second sensor diagnostic processing is deteriorated. This corresponds to the determination means.

  In the second embodiment, since ΔIcp is constant, it is possible to determine deterioration based only on the offset change amount ΔIp2 without calculating “ΔIp2 / ΔIcp”. In this case, for the change amount deterioration determination threshold A, the deterioration determination is performed by setting a value calculated using the offset change amount ΔIp2 instead of “ΔIp2 / ΔIcp”.

  As mentioned above, although embodiment (1st Embodiment and 2nd Embodiment) which determines the deterioration state of NOx gas sensor element 10 based on 2nd pump electric current offset value was described as embodiment of this invention, implementation of this invention is demonstrated. The form is not limited to the above embodiment.

  Next, as a third embodiment, an embodiment in which the deterioration state of the NOx gas sensor element 10 is determined based on the both-ends voltage of the oxygen partial pressure detection cell 112 when the self-generated current Icp is stopped (voltage value when the current is stopped). explain.

  In addition, the gas detection apparatus 1 in 3rd Embodiment is provided with the gas sensor control apparatus 190 and NOx gas sensor element 10 similarly to 1st Embodiment, and the block diagram which shows schematic structure is the same as that of FIG.

  Compared with the first embodiment, the third embodiment is different from the first embodiment in that the sensor diagnostic process (On Board Diagnosis process (OBD process)) executed by the gas sensor control device 190 is different, and thus the third embodiment is executed in the third embodiment. The contents of the third sensor diagnosis process will be mainly described.

FIG. 6 shows a flowchart showing the processing contents of the third sensor diagnosis processing.
When the third sensor diagnostic process is started, first, in S610 (S represents a step), the supply of the self-generated current Icp to the oxygen partial pressure detection cell 112 is stopped, and the first pump current to the first pump cell 111 is stopped. A process of stopping the control of Ip1 is executed.

  When the control of the first pump current Ip1 for the first pump cell 111 is stopped, the pumping (pumping and pumping) of oxygen from the first measurement chamber 159 is stopped. For this reason, during the period until oxygen is introduced through the first diffusion resistor 116, the oxygen partial pressure (oxygen concentration) in the first measurement chamber 159 maintains the state before the control of the first pump current Ip1 is stopped. Is done.

In the next S620, timer processing for measuring the elapsed time is started.
In subsequent S630, it is determined whether or not the stop standby time has elapsed from the start of time measurement by the timer process. If the determination is affirmative, the process proceeds to S640, and if the determination is negative, the same step is repeatedly executed. To wait.

  In the present embodiment, after stopping the energization of the self-generated current Icp and the control stop of the first pump current Ip1, the stop waiting time until the both-ends voltage of the oxygen partial pressure detection cell 112 becomes stable is 100 [mSec. ] Is set. This stop standby time is set longer than the time required until the voltage across the oxygen partial pressure detection cell 112 reaches a voltage value corresponding to the oxygen concentration in the first measurement chamber 159.

  When an affirmative determination is made in S630 and the process proceeds to S640, in S640, it is determined whether or not the elapsed time from the time measurement start time by the timer processing is within the allowable stop time. If the determination is negative and the determination is negative, the process proceeds to S700.

  In addition, after oxygen pumping by the first pump cell 111 is stopped by stopping the control of the first pump current Ip1, oxygen partial pressure in the first measurement chamber 159 is obtained when oxygen is introduced through the first diffusion resistor 116. (Oxygen concentration) changes. Therefore, in order to determine whether or not the NOx gas sensor element 10 is in a deteriorated state (a deteriorated state in which the oxygen partial pressure in the first measurement chamber 159 is lower than the target value), the oxygen content in the first measurement chamber 159 is determined. Before the pressure (oxygen concentration) changes, it is necessary to determine the deterioration.

  Accordingly, a permissible stop time during which the oxygen partial pressure (oxygen concentration) in the first measurement chamber 159 does not fluctuate is determined, and it is determined in S640 whether or not it is within the permissible stop time range. For example, the process proceeds to a step (S650 to S690) for determining the deterioration of the gas sensor element. If the allowable stop time is exceeded, the process proceeds to the timer stop step (S700) without performing the deterioration determination. In the present embodiment, 500 [mSec] is set as the allowable stop time.

When an affirmative determination is made in S640 and the process proceeds to S650, in S650, a process of reading a predetermined voltage deterioration determination threshold value M from a predetermined storage device (such as an internal memory) is executed.
Note that the voltage deterioration determination threshold M is a determination value used for determination processing (processing for determining deterioration of the NOx gas sensor element 10) in S670, which will be described later, and is based on a measurement result using the actual NOx gas sensor element 10. Can be determined.

  For example, the self-generated current Icp set to the oxygen reference generation current value is supplied to the oxygen partial pressure detection cell 112 using the unused NOx gas sensor element 10, and the oxygen partial pressure (oxygen concentration) in the reference oxygen chamber 118 ) Is set to the target value (reference oxygen partial pressure), the control of the first pump current Ip1 for the first pump cell 111 is stopped, and the energization of the self-generated current Icp to the oxygen partial pressure detection cell 112 is stopped. Thereafter, the both-end voltage generated in the oxygen partial pressure detection cell 112 when the energization is stopped can be detected, and the detected both-end voltage value can be determined as the voltage deterioration determination threshold M.

  In the present embodiment, the voltage deterioration determination threshold value M is set to 423 mV. Note that the voltage degradation determination threshold M of the present embodiment is a voltage drop on the line caused by energization of the self-generated current Icp, compared to the target both-end voltage value (425 mV) of the oxygen partial pressure detection cell 112 in the specific gas detection state. It is set to a value substantially equal to a value (420 to 423 mV) obtained by subtracting minutes (2 to 5 mV).

  Here, assuming that the voltage across the oxygen partial pressure detection cell 112 is the oxygen concentration electromotive force Vemf and the voltage drop in the energization path is the path drop voltage Vr, the gas sensor control device 190 uses the voltage across the oxygen partial pressure detection cell 112 as the voltage across the oxygen partial pressure detection cell 112. Specifically, the detected voltage value Vsk to be detected can be expressed as [Equation 1] because it is the sum of the oxygen concentration electromotive force Vemf and the path drop voltage Vr.

また、通電経路の抵抗成分による抵抗値を経路抵抗値Ｒａ、センサ素子内部のバルク抵抗成分による抵抗値をバルク抵抗値Ｒｂ、三層界面（電極−ジルコニア−酸素）部分の抵抗成分による抵抗値を界面抵抗値Ｒｃとし、酸素分圧検知セル１１２への通電電流値をＩｃｐとすると、通電経路での電圧降下分を経路降下電圧Ｖｒは、［数２］のように表すことができる。

Further, the resistance value due to the resistance component of the energization path is the path resistance value Ra, the resistance value due to the bulk resistance component inside the sensor element is the bulk resistance value Rb, and the resistance value due to the resistance component at the three-layer interface (electrode-zirconia-oxygen) portion. When the interface resistance value Rc and the energization current value to the oxygen partial pressure detecting cell 112 are Icp, the voltage drop in the energization path can be expressed as [Equation 2].

つまり、これらの数式によれば、通電経路での各抵抗成分（Ｒａ、Ｒｂ、Ｒｃ）が変化するとガスセンサ制御装置１９０での検出電圧値Ｖｓｋが変動することが判る。このため、酸素分圧検知セル１１２に自己生成電流Ｉｃｐを通電した状態で第１測定室１５９の酸素分圧を検出する場合には、通電経路での各抵抗成分（Ｒａ、Ｒｂ、Ｒｃ）の変化に起因して、検出精度が低下する虞がある。

That is, according to these mathematical expressions, it can be seen that the detected voltage value Vsk in the gas sensor control device 190 changes when each resistance component (Ra, Rb, Rc) in the energization path changes. For this reason, when the oxygen partial pressure in the first measurement chamber 159 is detected in a state where the self-generated current Icp is supplied to the oxygen partial pressure detection cell 112, each resistance component (Ra, Rb, Rc) in the current supply path is detected. Due to the change, the detection accuracy may decrease.

  In contrast, if the self-generated current Icp is not supplied to the oxygen partial pressure detection cell 112 (Icp = 0), the path drop voltage Vr at the detection voltage value Vsk in the gas sensor control device 190 is determined. The component becomes 0. That is, by stopping energization of the self-generated current Icp to the oxygen partial pressure detection cell 112, the detection voltage value Vsk in the gas sensor control device 190 becomes equal to the voltage Vemf across the oxygen partial pressure detection cell 112. Accordingly, the gas sensor control device 190 can accurately detect the oxygen partial pressure in the first measurement chamber 159 while suppressing the influence of the voltage drop in the energization path.

  It should be noted that the both-end voltage Vemf generated in the oxygen partial pressure detection cell 112 shows a smaller value as the oxygen partial pressure in the first measurement chamber 159 is higher, and shows a larger value as the oxygen partial pressure in the first measurement chamber 159 is lower. There is.

  For this reason, the both-ends voltage Vemf generated in the oxygen partial pressure detection cell 112 is the NOx gas sensor element when the NOx gas sensor element 10 is in a deteriorated state (a deteriorated state in which the oxygen partial pressure in the first measurement chamber is lower than the target value). 10 indicates a larger value than when it is in a normal state (an initial state that has not deteriorated).

  That is, the gas sensor control device 190 detects the detected voltage value Vsk detected when the energization of the self-generated current Icp is stopped as the energization stop voltage value Vs (specifically, the both-ends voltage Vemf generated in the oxygen partial pressure detection cell 112). Then, by comparing the detected energization stop voltage value Vs with the voltage deterioration determination threshold value M, it is possible to determine whether the NOx gas sensor element 10 is in a normal state or in a deterioration state.

  Note that the deterioration state in which the oxygen partial pressure in the first measurement chamber 159 is lower than the target value is a state in which the pumping of oxygen from the first measurement chamber 159 is excessively performed. Not only the specific gas (NOx) may be pumped out of the first measurement chamber 159.

In the next S660, a process of detecting the detected voltage value Vsk as the energization stop voltage value Vs is executed.
As described above, since the supply of the self-generated current Icp to the oxygen partial pressure detection cell 112 is stopped, the gas sensor control device 190 and the NOx gas sensor element 10 (specifically, the oxygen partial pressure detection cell 112) are connected. In the energization path to be connected, a voltage drop due to energization of the self-generated current Icp does not occur. Therefore, the energization stop voltage value Vs detected by the gas sensor control device 190 by the process in S660 is a voltage value that does not include the voltage drop in the energization path, and is the oxygen partial pressure in the first measurement chamber 159. Accordingly, it becomes equal to the both-ends voltage value Vemf generated in the oxygen partial pressure detection cell 112.

  In S670, the voltage deterioration determination threshold value M read in S650 is compared with the energization stop voltage value Vs detected in S660, and it is determined whether or not the energization stop voltage value Vs is smaller than the voltage deterioration determination threshold value M. If the determination is affirmative, the process proceeds to S680. If the determination is negative, the process proceeds to S690.

  That is, in S670, when the energization stop voltage value Vs is smaller than the voltage deterioration determination threshold value M, it is determined that the NOx gas sensor element 10 is in a normal state, and the energization stop voltage value Vs is the voltage deterioration determination threshold value M. When it is above, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  The voltage degradation determination threshold M used for the determination in S670 is, as described above, measured by measuring the voltage at both ends generated in the oxygen partial pressure detection cell 112 using the unused NOx gas sensor element 10, and measuring the measured both ends. The voltage value is set as the voltage degradation determination threshold value M.

  For this reason, the NOx gas sensor element 10 in which the energization stop voltage value Vs detected in S660 is equal to or higher than the voltage deterioration determination threshold value M is compared with the NOx gas sensor element 10 in the unused state (initial state) in the first measurement chamber 159. It can be determined that the oxygen partial pressure is lower than the target value, and it can be determined as a deteriorated state.

When an affirmative determination is made in S670 and the process proceeds to S680, a process of determining that the NOx gas sensor element 10 is in a normal state is executed in S680.
When a negative determination is made in S670 and the process proceeds to S690, in S690, it is determined that the NOx gas sensor element 10 is in a deteriorated state, and an abnormality occurrence signal indicating that the NOx gas sensor element 10 is in a deteriorated state is sent to the gas sensor control device 190. Processing to output to an external device from an output terminal (not shown) is performed.

  Then, the external device that has received the abnormality occurrence signal performs processing for notifying the user that the NOx gas sensor element 10 is in a deteriorated state. Specific processing includes, for example, processing for turning on a warning lamp indicating that the NOx gas sensor element 10 is in a deteriorated state, processing for outputting a voice message indicating that the NOx gas sensor element 10 is in a deteriorated state, and the like. be able to.

When a negative determination is made in S640, or when S680 or S690 ends, the process proceeds to S700, and in S700, the timer process for measuring the elapsed time is stopped.
In the next S710, a process of starting (resuming) the self-generated current Icp for the oxygen partial pressure detection cell 112 and starting (restarting) the control of the first pump current Ip1 for the first pump cell 111 is executed.

  Thereby, the gas sensor control device 190 starts (restarts) the process of controlling the oxygen partial pressure (oxygen concentration) of the reference oxygen chamber 118 to the target value (reference oxygen partial pressure), and performs the first measurement by the first pump cell 111. Start (restart) oxygen pumping into chamber 159.

When S710 ends, the present control process (sensor diagnosis process) ends.
As described above, the gas sensor control device 190 provided in the gas detection device 1 of the third embodiment stops the pumping or pumping of oxygen by the first pump cell 111 and the oxygen sensor S610 in the third sensor diagnostic process. Processing to stop energization of the partial pressure detection cell 112 is executed. Thereafter, in S660, the gas sensor control device 190 executes a process of detecting the energization stop voltage value Vs generated in the oxygen partial pressure detection cell 112 when energization is stopped. Further, in S670, the voltage deterioration determination threshold value M is compared with the energization stop voltage value Vs. When the energization stop voltage value Vs is less than the voltage deterioration determination threshold value M, the NOx gas sensor element 10 is in a normal state. When the energization stop voltage value Vs is equal to or greater than the voltage deterioration determination threshold M, it is determined that the NOx gas sensor element 10 is in a deteriorated state. In the NOx gas sensor element 10 to be determined, the reference oxygen chamber 118 is In order to set the reference oxygen partial pressure atmosphere, the oxygen partial pressure detection cell 112 is energized (the self-generated current Icp is energized). When the self-generated current Icp is energized as described above, the gas sensor control device 190 reduces the oxygen partial pressure in the first measurement chamber 159 due to the influence of the voltage drop (path drop voltage Vr) due to the resistance component in the energization path. There is a possibility that it cannot be detected accurately.

  On the other hand, as in this embodiment, by stopping the supply of the self-generated current Icp to the oxygen partial pressure detection cell 112, the first measurement chamber 159 is suppressed while suppressing the influence of the voltage drop in the energization path. It is possible to accurately detect the oxygen partial pressure.

  In the third embodiment, after the pumping-in or pumping-out of oxygen by the first pump cell 111 is stopped, the oxygen content is reduced until the stop allowable time elapses (in other words, during the period in which an affirmative determination is made in S640). The voltage value Vs at the time of stopping energization of the pressure detection cell 112 is detected. The energization stop voltage value Vs detected during such a period indicates a value corresponding to the oxygen partial pressure control state of the first measurement chamber 159 immediately before the energization stop.

  Note that the energization stop voltage value Vs of the oxygen partial pressure detection cell 112 shows a smaller value as the oxygen partial pressure in the first measurement chamber 159 becomes higher, and shows a larger value as the oxygen partial pressure in the first measurement chamber 159 becomes lower. . Therefore, when the energization stop voltage value Vs is less than the voltage deterioration determination threshold M, it can be determined that the NOx gas sensor element 10 is in a normal state, and the energization stop voltage value Vs is equal to or greater than the voltage deterioration determination threshold M. When it is, it can be determined that the NOx gas sensor element 10 is in a deteriorated state.

  In this embodiment, the energization stop voltage value Vs of the oxygen partial pressure detection cell 112 is detected in the process in S660, and in the process in S670, the energization stop voltage value Vs and the voltage deterioration determination threshold value M are determined. Are compared to determine whether the NOx gas sensor element 10 is in a normal state or in a deteriorated state.

  Therefore, the gas sensor control device 190 of the present embodiment can determine whether or not the NOx gas sensor element 10 can appropriately control the oxygen partial pressure in the first measurement chamber 159, and determine the deterioration state of the NOx gas sensor element 10 including various cells. It can be judged.

  In the third embodiment, the gas sensor control device 190 that executes the third sensor diagnostic process corresponds to the sensor element deterioration determination device described in the claims, the NOx gas sensor element 10 corresponds to the gas sensor element, One pump cell 111 corresponds to a first oxygen ion pump cell, the second pump cell 113 corresponds to a second oxygen ion pump cell, and the oxygen partial pressure detection cell 112 corresponds to an oxygen partial pressure detection cell. The first diffusion resistor 116 corresponds to the first diffusion resistor part, and the second diffusion resistor 117 corresponds to the second diffusion resistor part.

  Further, the gas sensor control device 190 that executes S610 and S660 of the third sensor diagnosis processing corresponds to the oxygen partial pressure control state detection means, and the gas sensor control device 190 that executes S670 of the third sensor diagnosis processing corresponds to the deterioration determination means. is doing.

  The embodiments of the present invention have been described above. However, the embodiments of the present invention are not limited to the above-described embodiments, and various forms can be taken as long as they belong to the technical scope of the present invention. Nor.

For example, the numerical value of each waiting time in the above embodiment is not limited to the above numerical value, and an arbitrary numerical value can be set according to the application.
Further, in the first embodiment and the second embodiment, the execution time of the sensor diagnosis process (in other words, the deterioration determination time) is the same as the first measurement chamber and the first measurement chamber when the oxygen concentration in the measurement target gas is detected as the specific gas. It may be set when the concentration is higher than the target oxygen concentration of the two measurement chambers.

  That is, when the oxygen concentration in the measurement target gas is lower than the target oxygen concentration at the time of detecting the specific gas, the amount of oxygen introduced into the second measurement chamber through the first measurement chamber decreases and the second oxygen ion pump The amount of oxygen dissociated in the cell is reduced, and the value of the current flowing through the second oxygen ion pump cell is reduced. That is, if the second pump current offset value decreases due to an insufficient oxygen amount, even if the gas sensor element is not actually deteriorated, it may be erroneously determined as a deteriorated state.

  On the other hand, when the oxygen concentration in the measurement target gas is high, there is sufficient oxygen, so the current value flowing through the second oxygen ion pump cell (second pump current offset value) is the deterioration state of the gas sensor element. Therefore, the deterioration state can be appropriately determined based on the second pump current offset value. In addition, when the oxygen concentration in the measurement target gas is high, the specific gas concentration is relatively low, so that fluctuations in the second pump current offset value due to the influence of the specific gas can be suppressed.

  Therefore, by setting the deterioration determination timing when the oxygen concentration in the measurement target gas is higher than the target oxygen concentration at the time of detecting the specific gas, erroneous determination can be suppressed and the determination accuracy of deterioration determination can be improved.

  Furthermore, in the third embodiment, the numerical value of the voltage deterioration determination threshold value M is not limited to the case where the both-end voltage generated in the oxygen partial pressure detection cell 112 at the time of stopping energization is applied as it is. A value obtained by multiplying the value L by a predetermined deterioration coefficient G (a value equal to or greater than 1, for example, 1.1) may be defined as the voltage deterioration determination threshold M (= L × G). By setting the voltage deterioration determination threshold value M using the deterioration coefficient G in this way, deterioration determination can be performed while allowing a certain range of deterioration according to the deterioration coefficient G.

It is a block diagram which shows schematic structure of a gas detection apparatus provided with the gas sensor control apparatus to which this invention was applied. It is a flowchart showing the processing content of a sensor diagnostic process. It is explanatory drawing showing the correlation of the self-generated electric current Icp supplied with an oxygen partial pressure detection cell, and a 2nd pump current offset value. It is a flowchart showing the processing content of a 2nd sensor diagnostic process. It is explanatory drawing for demonstrating correlation with the self-generated electric current Icp supplied with an oxygen partial pressure detection cell, and the 2nd pump current offset value, and explaining offset variation | change_quantity (DELTA) Ip2 and determination electric current variation | change_quantity (DELTA) Icp. It is a flowchart showing the process content of a 3rd sensor diagnostic process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gas detection apparatus, 10 ... NOx gas sensor element, 111 ... 1st pump cell, 112 ... Oxygen partial pressure detection cell, 113 ... 2nd pump cell, 116 ... 1st diffusion resistor, 117 ... 2nd diffusion resistor, 118 ... Reference oxygen chamber, 121 ... first porous electrode, 123 ... detecting porous electrode, 125 ... second porous electrode, 131 ... first solid electrolyte layer, 135 ... first pump first electrode, 137 ... first Second electrode for pump, 141 ... second solid electrolyte layer, 145 ... first electrode for second pump, 147 ... second electrode for second pump, 151 ... solid electrolyte layer for detection, 155 ... electrode for detection, 157 ... Reference electrode, 159... First measurement chamber, 161... Second measurement chamber, 190.

Claims (8)

A first measurement chamber into which a gas to be measured is introduced via the first diffusion resistance unit;
The measurement having an oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, wherein one of the pair of electrodes is disposed in the first measurement chamber and introduced into the first measurement chamber A first oxygen ion pump cell for pumping or pumping oxygen to the target gas;
A second measurement chamber into which the measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced via a second diffusion resistance unit;
An oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, wherein one of the pair of electrodes is disposed in the second measurement chamber, and a specific gas concentration in the second measurement chamber is obtained. A second oxygen ion pump cell in which a corresponding current flows;
A reference oxygen chamber set in a reference oxygen partial pressure atmosphere;
An oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, wherein one of the pair of electrodes is disposed in the first measurement chamber and the other electrode is disposed in the reference oxygen chamber; An oxygen partial pressure detection cell;
A sensor element deterioration determination device for determining a deterioration state of a gas sensor element comprising:
The oxygen partial pressure detection cell is configured to be able to change the amount of oxygen pumped into the reference oxygen chamber according to the magnitude of a current to be energized,
The gas sensor element is configured to determine an oxygen partial pressure of the first measurement chamber with reference to a reference oxygen partial pressure of the reference oxygen chamber,
Oxygen partial pressure control state detection means for detecting an oxygen partial pressure control state in the first measurement chamber with respect to the energization state of the oxygen partial pressure detection cell;
It is determined whether the oxygen partial pressure control state is a predetermined normal range, and when the oxygen partial pressure control state is the normal range, it is determined that the gas sensor element is in a normal state, Deterioration determining means for determining that the gas sensor element is in a deteriorated state when the oxygen partial pressure control state deviates from the normal range;
A sensor element deterioration determination device comprising: The oxygen partial pressure control state detection means flows to the second oxygen ion pump cell in accordance with the oxygen partial pressure in the second measurement chamber when a predetermined determination current is supplied to the oxygen partial pressure detection cell. Detecting the current value as the second pump current offset value;
The deterioration determination means compares a deterioration determination threshold for an offset value determined for determining a deterioration state of the gas sensor element with the second pump current offset value, and the second pump current offset value is the offset value. It is determined that the gas sensor element is in a normal state when it is greater than or equal to a deterioration determination threshold value for use, and it is determined that the gas sensor element is in a deteriorated state when the second pump current offset value is smaller than the deterioration determination threshold value for offset value. thing,
The sensor element deterioration determination apparatus according to claim 1. The gas sensor element is configured such that the reference oxygen chamber is controlled to the reference oxygen partial pressure atmosphere when an energization current to the oxygen partial pressure detection cell is a predetermined oxygen reference generation current.
The determination current has the same current value as the oxygen reference generation current;
The sensor element deterioration determination apparatus according to claim 2. A voltage setting means for determining deterioration, which sets a voltage applied to the second oxygen ion pump cell to a voltage value for determining deterioration that the specific gas cannot dissociate and oxygen can dissociate;
The oxygen partial pressure control state detection means is configured to set the second pump current offset value in a state where the voltage applied to the second oxygen ion pump cell is set to the deterioration determination voltage value by the deterioration determination voltage setting means. Detecting,
The sensor element deterioration determination apparatus according to claim 2 or claim 3, wherein The oxygen partial pressure control state detecting means is configured to detect the second oxygen ion pump cell according to an oxygen partial pressure in the second measurement chamber when a predetermined first determination current is supplied to the oxygen partial pressure detection cell. Is detected as a second pump current first offset value, and when a predetermined second determination current is passed through the oxygen partial pressure detection cell, the oxygen partial pressure in the second measurement chamber is determined. A current value flowing through the second oxygen ion pump cell is detected as a second pump current second offset value, and is a difference between the second pump current first offset value and the second pump current second offset value. Detect offset change amount,
The deterioration determination means compares the change amount deterioration determination threshold determined for determining the deterioration state of the gas sensor element with the offset change amount, and the offset change amount is equal to or greater than the change amount deterioration determination threshold. Determining that the gas sensor element is in a normal state at a certain time, and determining that the gas sensor element is in a deteriorated state when the offset change amount is smaller than the change deterioration deterioration determination threshold;
The sensor element deterioration determination apparatus according to claim 1. The gas sensor element is configured such that the reference oxygen chamber is controlled to the reference oxygen partial pressure atmosphere when an energization current to the oxygen partial pressure detection cell is a predetermined oxygen reference generation current.
Each current value of the first determination current and the second determination current is equal to or less than the current value of the oxygen reference generation current,
The sensor element deterioration determination apparatus according to claim 5. The oxygen partial pressure control state detection means stops the pumping or pumping of oxygen by the first oxygen ion pump cell, stops energization of the oxygen partial pressure detection cell, and then stops the oxygen at the time of energization stop. Detects the voltage value at the time of energization stop generated in the partial pressure detection cell,
The deterioration determination means compares a voltage deterioration determination threshold determined to determine a deterioration state of the gas sensor element with the energization stop voltage value, and the energization stop voltage value is the voltage deterioration determination threshold. Determining that the gas sensor element is in a normal state when it is less than, and determining that the gas sensor element is in a deterioration state when the energization stop voltage value is equal to or greater than the voltage deterioration determination threshold;
The sensor element deterioration determination apparatus according to claim 1. A first measurement chamber into which a gas to be measured is introduced via the first diffusion resistance unit;
The measurement having an oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, wherein one of the pair of electrodes is disposed in the first measurement chamber and introduced into the first measurement chamber A first oxygen ion pump cell for pumping or pumping oxygen to the target gas;
A second measurement chamber into which the measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced via a second diffusion resistance unit;
An oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, wherein one of the pair of electrodes is disposed in the second measurement chamber, and a specific gas concentration in the second measurement chamber is obtained. A second oxygen ion pump cell in which a corresponding current flows;
A reference oxygen chamber set in a reference oxygen partial pressure atmosphere;
An oxygen ion conductor and a pair of electrodes formed on the oxygen ion conductor, wherein one of the pair of electrodes is disposed in the first measurement chamber and the other electrode is disposed in the reference oxygen chamber; An oxygen partial pressure detection cell;
A sensor element deterioration determination method for determining a deterioration state of a gas sensor element comprising:
The oxygen partial pressure detection cell is configured to be able to change the amount of oxygen pumped into the reference oxygen chamber according to the magnitude of a current to be energized,
The gas sensor element is configured to determine an oxygen partial pressure of the first measurement chamber with reference to a reference oxygen partial pressure of the reference oxygen chamber,
An oxygen partial pressure control state detection step of detecting an oxygen partial pressure control state in the first measurement chamber with respect to the energization state of the oxygen partial pressure detection cell;
When the oxygen partial pressure control state is in a predetermined normal range, it is determined that the gas sensor element is in a normal state, and when the oxygen partial pressure control state is out of the normal range, the gas sensor element is A deterioration determination step for determining that the state is a deterioration state;
A sensor element deterioration determination method characterized by comprising:

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