JP4805734B2 - Sensor element deterioration determination device and sensor element deterioration determination method - Google Patents

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 such an object, includes a first measurement chamber into which a measurement target gas is introduced via the first diffusion resistance section, and pumping or pumping oxygen in the first measurement chamber. A second measurement chamber into which the gas to be measured is introduced through the second diffusion resistance unit, a reference oxygen chamber set in a reference oxygen partial pressure atmosphere, an oxygen ion conductor , and the oxygen ion conductor A pair of first pump electrodes , wherein one of the pair of first pump electrodes is disposed in the first measurement chamber, and the other of the pair of first pump electrodes is outside the first measurement chamber and second. A first oxygen ion pump cell which is arranged outside the measurement chamber and outside the reference oxygen chamber and pumps or pumps oxygen into the measurement target gas introduced into the first measurement chamber ; an oxygen ion conductor; and the oxygen Formed on ionic conductor A pair of second pumping electrodes, are arranged on the other the reference oxygen chamber of the pair of second pumping electrodes with one of the pair of the second pump electrode is arranged in the second measuring chamber, second measuring chamber Identification and second oxygen ion pump cell Le the current corresponding to the gas concentration, a pair of detection electrodes formed on the oxygen-ion conductor and said oxygen ion conductor on the body, one of the pair of detection electrodes in Is a sensor element deterioration determination device that determines a deterioration state of a gas sensor element including an oxygen partial pressure detection cell in which the other electrode is disposed in a reference oxygen chamber, wherein the gas sensor element includes: The first oxygen ion pump cell pumps or pumps oxygen into the first measurement chamber so that the voltage across the oxygen partial pressure detection cell becomes a predetermined target value based on the reference oxygen partial pressure in the reference oxygen chamber. And a second pump that flows to the second oxygen ion pump cell when the second cell applied voltage applied to the second oxygen ion pump cell is a predetermined detection voltage value for detecting the specific gas. Based on the current, the specific gas concentration in the second measurement chamber is detected. The detection state determining means for determining whether or not the specific gas is present in the second measurement chamber, and the second measurement chamber by the detection state determining means. If it is determined that a specific gas is present in the battery, a deterioration determination voltage setting unit that sets the second cell applied voltage to a deterioration determination voltage value different from the detection voltage value in a gas detection voltage range in which the specific gas can be detected; Among the second pump current detection means for detecting the second pump current and the second pump current detected by the second pump current detection means, at least the second cell applied voltage is a deterioration determination voltage value. And a deterioration determining means for determining whether or not the gas sensor element is in a deteriorated state using the second pump current at the time of determination.

The invention method according to claim 12 made to achieve the above object includes a first measurement chamber into which a gas to be measured is introduced through the first diffusion resistance section, and pumping out oxygen in the first measurement chamber. Alternatively, the second measurement chamber into which the pumped measurement target gas is introduced via the second diffusion resistance unit, the reference oxygen chamber set in a reference oxygen partial pressure atmosphere, the oxygen ion conductor , and the oxygen ion A pair of first pump electrodes formed on the conductor, wherein one of the pair of first pump electrodes is disposed in the first measurement chamber and the other of the pair of first pump electrodes is outside the first measurement chamber; And a first oxygen ion pump cell which is arranged outside the second measurement chamber and outside the reference oxygen chamber and pumps or pumps oxygen into the measurement target gas introduced into the first measurement chamber, and an oxygen ion conductor And on the oxygen ion conductor A pair of second pumping electrodes formed, is disposed on the other the reference oxygen chamber of the pair of second pumping electrodes with one of the pair of the second pump electrode is arranged in the second measuring chamber, the 2 and a second oxygen ion pump cell Le which current corresponding to a specific gas concentration in the measurement chamber, a pair of detection electrodes which oxygen ion conductor and formed on the oxygen-ion conductor, a pair of detection A sensor element deterioration determination method for determining a deterioration state of a gas sensor element, comprising: an oxygen partial pressure detection cell in which one of electrodes is disposed in a first measurement chamber and the other electrode is disposed in a reference oxygen chamber. In the element, the first oxygen ion pump cell pumps or pumps oxygen in the first measurement chamber so that the voltage across the oxygen partial pressure detection cell becomes a predetermined target value based on the reference oxygen partial pressure in the reference oxygen chamber. Enter And when the second cell applied voltage applied to the second oxygen ion pump cell is a predetermined detection voltage value for detecting the specific gas, the second oxygen ion pump cell flows through the second oxygen ion pump cell. Based on the pump current, the specific gas concentration in the second measurement chamber is detected. The detection state determination step for determining whether or not the specific gas exists in the second measurement chamber, and the second measurement in the detection state determination step Deterioration determination voltage setting step of setting the second cell applied voltage to a deterioration determination voltage value different from the detection voltage value in the gas detection voltage range in which the specific gas can be detected when it is determined that the specific gas is present in the chamber Among the second pump current detection step for detecting the second pump current and the second pump current detected in the second pump current detection step, at least the second cell applied voltage is the degradation determination voltage value. And a deterioration determination step of determining whether or not the gas sensor element is in a deteriorated state using the second pump current at the time of determination.

  First, the second pump current flowing through the second oxygen ion pump cell has a different current value depending on whether the gas sensor element is in a normal state or a deteriorated state even if the specific gas concentration in the second measurement chamber is constant. In the deteriorated state, the current value varies depending on the progress of deterioration. From this, it is possible to determine whether or not the gas sensor element is in a deteriorated state by using the second pump current.

  Further, the gas sensor element in the normal state has the second gas concentration when the specific gas concentration in the second measurement chamber is constant and the second cell applied voltage is set to a gas detection voltage range in which the specific gas can be detected. Even when the magnitude of the cell applied voltage changes, the second pump current has a characteristic (limit current characteristic) indicating a substantially constant current value corresponding to the specific gas concentration.

  However, in the gas sensor element in a deteriorated state, the limit current characteristic is unclear, so the specific gas concentration in the second measurement chamber is constant, and the second cell applied voltage is set in the gas detection voltage range. Even in such a case, the current value of the second pump current changes as the magnitude of the voltage applied to the second cell changes.

From this, it can be seen that it is possible to determine whether or not the gas sensor element is in a deteriorated state by using the second pump current.
Note that the change in the second pump current due to the deterioration does not occur only when the second cell applied voltage is the detection voltage value, but the deterioration is caused if the gas detection voltage range in which the specific gas can be detected. A change in the second pump current is occurring. Therefore, in determining whether the gas sensor element is in a deteriorated state using the second pump current, the second pump current used for the determination is the second pump current when the second cell applied voltage is the detection voltage value. The pump current is not limited to two pump currents, and the second pump current when the second cell applied voltage is other than the detection voltage value can be used.

  That is, among the second pump currents detected by the second pump current detection means, the gas sensor element is deteriorated by using the second pump current at the time of determination when at least the second cell applied voltage is the deterioration determination voltage value. It can be determined whether or not it is in a state.

Therefore, according to the sensor element deterioration determination apparatus and the sensor element deterioration determination method of the present invention, it is possible to determine the deterioration state of the gas sensor element including various cells.
And as said sensor element deterioration determination apparatus which performs deterioration determination using the 2nd pump current at the time of determination, for example, as described in claim 2, the deterioration determination means, the second cell applied voltage is for deterioration determination The second pump current at the time of determination, which is the second pump current detected by the second pump current detection means when it is a voltage value, and a current reference value for deterioration determination predetermined for deterioration determination of the gas sensor element If the second pump current at the time of determination is equal to or greater than the current reference value for deterioration determination, it is determined that the gas sensor element is in a normal state, and the second pump current at the time of determination is smaller than the current reference value for deterioration determination In this case, it is possible to adopt a configuration in which a current deterioration determination unit that determines that the gas sensor element is in a deteriorated state is provided.

  Even if the specific gas concentration is constant, the value of the second pump current tends to decrease as the gas sensor element deteriorates. Therefore, the second pump current at the time of determination causes the gas sensor element to deteriorate. The smaller the value, the smaller the value.

  Therefore, a current reference value for deterioration determination for determining deterioration of the gas sensor element is determined in advance, and the gas sensor element is in a deteriorated state by comparing the second pump current and the current reference value for deterioration determination. It can be determined whether or not.

  That is, when the second pump current at the time of determination is greater than or equal to the current reference value for deterioration determination, it is determined that the gas sensor element is in a normal state, and the second pump current at the time of determination is smaller than the current reference value for deterioration determination Is provided with a current deterioration determining means for determining that the gas sensor element is in a deteriorated state, whereby it can be determined whether or not the gas sensor element is in a deteriorated state.

Therefore, according to the present invention, by performing the deterioration determination using the second pump current at the time of determination, it is possible to determine the change tendency of the second pump current and to determine the deterioration of the gas sensor element.
Note that the current reference value for deterioration determination can be set based on, for example, a measurement result using an actual gas sensor element.

  As an example, as described in claim 3, the second pump current detected by the second pump current detection means when the second cell applied voltage is a detection voltage value is used as the second pump current at the time of detection. In this case, the deterioration reference current reference value is detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 95% with respect to the second pump current at the time of detection in the gas sensor element when not in use. Detected by the gas sensor element that is equal to or less than the second pump current at the time of detection and the second pump current at the time of detection is reduced to a value equivalent to 50% of the second pump current at the time of detection in the unused gas sensor element. It is possible to adopt a configuration in which the value is greater than or equal to the second pump current at the time of determination.

  In other words, the gas sensor element in which the second pump current at the time of detection is reduced to a value equivalent to 50% when not in use is in a deteriorated state in which it is difficult to detect a specific gas (a fatal deteriorated state). It is necessary to determine that the gas sensor element is in a deteriorated state before it is in a deteriorated state.

Further, the second pump current at the time of determination tends to decrease as the gas sensor element deterioration state deteriorates.
For this reason, a value equal to or higher than the second pump current at the time of detection detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 50% when not in use is set as the current reference value for deterioration determination. Thus, it is possible to determine that the gas sensor element is in a deteriorated state before the gas sensor element is in a fatal deteriorated state.

  Further, the gas sensor element in which the second pump current at the time of detection does not decrease to a value equivalent to 95% when not in use has a small amount of change in current value deterioration of the second pump current at the time of detection, and can detect a specific gas. Therefore, the current reference value for deterioration determination is detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 95% with respect to the second pump current at the time of detection in the gas sensor element when not in use. It may be set to a value less than the second pump current.

  In applications where the gas sensor element in which the second pump current at the time of detection has been reduced to a value equivalent to 90% when not used is determined as a deteriorated state, the second pump current at the time of detection has been reduced to a value equivalent to 90% when not used. The second pump current at the time of determination may be detected using the gas sensor element in the state, and the detected current value of the second pump current at the time of determination may be set as the current reference value for deterioration determination. Alternatively, when the gas sensor element in which the second pump current at the time of detection is reduced to a value equivalent to 70% when not used is determined to be in a deteriorated state, the second pump current at the time of detection is reduced to a value equivalent to 70% when not used. It is preferable to adopt a configuration in which the current value of the second pump current at the time of determination detected by the gas sensor element in the state is set as the current reference value for deterioration determination.

  Note that the amount of change in the second pump current (current value deterioration change amount) that occurs when the gas sensor element changes from the normal state to the deteriorated state varies depending on the voltage applied to the second cell. Then, as the current value deterioration change amount accompanying deterioration increases, the current value deterioration change amount increases even in a mild deterioration state, so that the determination accuracy of deterioration determination can be improved.

  For this reason, when performing the deterioration determination with the current deterioration determination means, the current value deterioration change amount is larger than the current value deterioration change amount when the second cell applied voltage is the detection voltage value. It is desirable to set the voltage value to be the degradation determination voltage value.

  Therefore, in the above-described sensor element deterioration determination device provided with the current deterioration determination means, as described in claim 4, the deterioration determination voltage value is smaller than the detection voltage value. Can do.

  That is, by setting the deterioration determination voltage value in this way, the current value deterioration change amount with respect to the progress of the deterioration state is smaller than the current value deterioration change amount when the second cell applied voltage is the detection voltage value. Therefore, when performing the deterioration determination based on the second pump current at the time of determination, it is possible to accurately determine the deterioration state even when the degree of progress of the deterioration state is small.

  Further, as the above-described sensor element deterioration determination device that performs the deterioration determination using the second pump current at the time of determination, for example, as described in claim 5, the deterioration determination means is configured such that the second cell applied voltage is a detection voltage. Second pump current at the time of detection, which is a second pump current detected by the second pump current detection means when it is a value, and second pump current detection means when the second cell applied voltage is a voltage value for deterioration determination A second pump current change amount detecting means for detecting a second pump current change amount that is an absolute value of a difference between the second pump current at the time of determination, which is the second pump current detected in step S, and a second pump current change amount. Is compared with a predetermined reference value for deterioration determination for determining the deterioration of the gas sensor element. If the second pump current change amount is equal to or less than the reference value for deterioration determination, the gas sensor element is normal. It is determined that 2 when the pump current change amount is greater than the determination change amount reference value deterioration, it may take a configuration that includes a determining variation degradation determining means and the gas sensing element is in a degraded state, the.

  Since the second pump current change amount, which is the absolute value of the difference between the second pump current at the time of detection and the second pump current at the time of determination, is determined according to the second pump current at the time of determination, the gas sensor element is in a deteriorated state. It can be used to determine whether or not there is.

  Further, the amount of change in the second pump current is determined based on each current value in two types of second pump currents having different voltages applied to the second cell (second pump current at detection, second pump current at determination). From this, the deterioration determination using the second pump current change amount can determine the change tendency of the second pump current more accurately than the deterioration determination using only one type of the second pump current. The deterioration state of the gas sensor element can be accurately determined.

  A deterioration determination change reference value for determining deterioration of the gas sensor element is determined in advance, and the gas sensor element is in a deteriorated state by comparing the second pump current change amount and the deterioration determination change reference value. It can be determined whether or not.

  That is, when the second pump current change amount is equal to or less than the deterioration determination change reference value, it is determined that the gas sensor element is in a normal state, and the second pump current change amount is smaller than the deterioration determination change reference value. If larger, it is possible to determine whether or not the gas sensor element is in a deteriorated state by providing a change amount deterioration determining means for determining that the gas sensor element is in a deteriorated state.

  Therefore, according to the present invention, by making a determination using the second pump current change amount, the change tendency of the second pump current can be determined with high accuracy, and the determination accuracy in determining the deterioration of the gas sensor element can be improved.

  The second pump current change amount tends to increase as the deterioration state of the gas sensor element deteriorates. And the variation reference value for deterioration determination can be set based on, for example, a measurement result using an actual gas sensor element.

  As an example, as described in claim 6, when the change reference value for deterioration determination is equal to a value equivalent to 95% of the second pump current at the time of detection with respect to the second pump current at the time of detection in the gas sensor element when not in use. The value is equal to or greater than the amount of change in the second pump current detected by the gas sensor element in the lowered state, and the second pump current at detection corresponds to 50% of the second pump current at detection in the gas sensor element when not in use. It is possible to adopt a configuration in which the value is equal to or less than the second pump current change amount detected by the gas sensor element in a state of being lowered to the value.

  That is, the gas sensor element in which the second pump current at the time of detection is reduced to a value equivalent to 50% when not in use is a deteriorated state in which detection of a specific gas is difficult (a fatal deteriorated state). Before entering a fatal deterioration state, it is necessary to determine that the gas sensor element is in a deterioration state.

  Then, a value equal to or smaller than the second pump current change amount detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 50% when not used is set as the change reference value for deterioration determination. Thus, it is possible to determine that the gas sensor element is in a deteriorated state before the gas sensor element is in a fatal deteriorated state.

  Further, the gas sensor element in which the second pump current at the time of detection does not decrease to a value equivalent to 95% when not in use has a small amount of change in current value deterioration of the second pump current at the time of detection, and can detect a specific gas. Therefore, the change reference value for deterioration determination is detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 95% with respect to the second pump current at the time of detection in the gas sensor element when not in use. It is good to set to the value more than the 2nd pump current change amount.

  When the gas sensor element in which the output of the second pump current at the time of detection is reduced by 10% compared to the gas sensor element at the time of non-use is determined to be in a deteriorated state, the second pump current at the time of detection is up to a value equivalent to 90% of that at the time of non-use. By detecting the second pump current change amount using the gas sensor element in the lowered state and setting the second pump current change amount as the deterioration determination change reference value, it is possible to determine the deterioration of the gas sensor element. Alternatively, when the gas sensor element in which the second pump current at the time of detection is reduced to a value equivalent to 70% when not used is determined to be in a deteriorated state, the second pump current at the time of detection is reduced to a value equivalent to 70% when not used. A configuration may be adopted in which the second pump current change amount is detected using the gas sensor element in the state, and the second pump current change amount is set as the deterioration determination change reference value.

  Further, as the above-described sensor element deterioration determination device that performs deterioration determination using the second pump current at the time of determination, for example, as described in claim 7, the deterioration determination means includes a second cell applied voltage that is a detection voltage. Second pump current at the time of detection, which is a second pump current detected by the second pump current detection means when it is a value, and second pump current detection means when the second cell applied voltage is a voltage value for deterioration determination A second pump current change rate detecting means for detecting a second pump current change rate that is a ratio of the second pump current at the time of determination, which is the second pump current detected in step, and a second pump current change rate and a gas sensor element When the second pump current change rate is included in the deterioration determination change rate reference range, the gas sensor element is in a normal state. And the second When the lamp current change rate deviates from the rate of change reference range for determining degradation may take the configuration that includes a determining change rate deterioration determining means and the gas sensing element is in a degraded state, the.

  Since the second pump current change rate, which is the ratio of the second pump current at the time of detection and the second pump current at the time of determination, is determined according to the second pump current at the time of determination, whether or not the gas sensor element is in a deteriorated state. It can be used for the determination.

  The second pump current change rate is determined based on each current value in two types of second pump currents having different voltages applied to the second cell (second pump current at detection, second pump current at determination). From this, the deterioration determination using the second pump current change rate can determine the change tendency of the second pump current more accurately than the deterioration determination using only one type of second pump current. The deterioration state of the gas sensor element can be accurately determined.

  A deterioration determination change rate reference range for determining deterioration of the gas sensor element is determined in advance, and the gas sensor element is in a deteriorated state by comparing the second pump current change rate with the deterioration determination change rate reference range. It can be determined whether or not.

  That is, when the second pump current change rate is included in the deterioration determination change rate reference range, it is determined that the gas sensor element is in a normal state, and the second pump current change rate deviates from the deterioration determination change rate reference range. In this case, it is possible to determine whether or not the gas sensor element is in a deteriorated state by providing a change rate deterioration determining unit that determines that the gas sensor element is in a deteriorated state.

  Therefore, according to the present invention, by performing determination using the second pump current change rate, it is possible to accurately determine the change tendency of the second pump current, and it is possible to improve the determination accuracy in determining the deterioration of the gas sensor element.

  The second pump current change rate tends to increase as the deterioration state of the gas sensor element deteriorates. The deterioration determination change rate reference range can be set based on, for example, a measurement result using an actual gas sensor element.

  As an example, as described in claim 8, the change rate reference range for deterioration determination is detected in the unused gas sensor element from the value of the second pump current change rate detected in the unused gas sensor element. The second pump current is included in the range of the second pump current change rate detected by the gas sensor element in a state where the second pump current is reduced to a value equivalent to 50% with respect to the second pump current. Can be taken.

  That is, the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 50% when not in use is in a deteriorated state (fatal deteriorated state) in which it is difficult to detect a specific gas. It is necessary to determine that the gas sensor element is in a deteriorated state.

  Therefore, the change rate reference range for deterioration determination is a state in which the second pump current change rate value detected by the gas sensor element when not used is reduced to a value equivalent to 50% when the second pump current is not used. The second pump current change rate value detected by the gas sensor element is set so as to fall within the range.

  By setting the change rate reference range for deterioration determination in this way, it is possible to determine that the gas sensor element in the state where the second pump current at the time of detection is lower than the value equivalent to 50% when not in use is in a deteriorated state. .

  When the gas sensor element in which the output of the second pump current at the time of detection is reduced by 10% compared to the gas sensor element at the time of non-use is determined to be in a deteriorated state, the second pump current at the time of detection is up to a value equivalent to 90% of that at the time of non-use. It is preferable to detect the second pump current change rate using the gas sensor element in a lowered state, and set the change rate reference range for deterioration determination using the detected second pump current change rate. That is, a state in which the change rate reference range for deterioration determination is reduced from a value of the second pump current change rate detected by the gas sensor element when not used to a value corresponding to 90% when the second pump current is not used. This is set to a range up to the value of the second pump current change rate detected by the gas sensor element.

  Alternatively, when it is determined that the gas sensor element whose output of the second pump current is 30% lower than that of the unused gas sensor element is in a deteriorated state, the second pump current at the time of detection is up to a value equivalent to 70% of the unused value. It is preferable to detect the second pump current change rate using the gas sensor element in a lowered state, and set the change rate reference range for deterioration determination using the detected second pump current change rate. That is, the deterioration determination change rate reference range is reduced from the value of the second pump current change rate detected by the gas sensor element when not in use to the value corresponding to 70% when the second pump current is not used. This is set to a range up to the value of the second pump current change rate detected by the gas sensor element.

  Next, in the above-described sensor element deterioration determination device provided with the change amount deterioration determination means or the change rate deterioration determination means, as described in claim 9, the deterioration determination voltage value is a value larger than the detection voltage value. It is possible to adopt a configuration that

  First, when the degradation determination voltage value is set to a value smaller than the detection voltage value, the amount of dissociation of the specific gas in the second oxygen ion pump cell is reduced, so the specific gas concentration in the second measurement chamber is The value is higher than the specific gas concentration in the second measurement chamber during normal detection for detecting the specific gas. As described above, when the specific gas concentration in the second measurement chamber is increased, the second cell applied voltage is changed from the deterioration determination voltage value to the detection voltage value, and then the specific gas concentration in the second measurement chamber is normally detected. It may take a long time to reach the concentration.

  In contrast, when the deterioration determination voltage value is set to a value larger than the detection voltage value, the specific gas concentration in the second measurement chamber is higher than the specific gas concentration during normal detection. Therefore, after changing the voltage applied to the second cell from the voltage value for determination of deterioration to the voltage value for detection, the specific gas concentration in the second measurement chamber can be set to the concentration at the time of normal detection at an early stage.

  Therefore, according to the sensor element deterioration determination device of the present invention, it is possible to obtain an operational effect that it is possible to return to the normal detection state (detection state of the specific gas) at an early stage after the deterioration determination.

  Next, in the sensor element deterioration determination device described above, the gas detection voltage range of the specific gas includes a specific gas and a voltage value at which the second cell applied voltage is lower than the detection voltage value. The dissociation amount of the low-voltage dissociation gas and the dissociation amount of the specific gas when dissociating the low-voltage dissociation gas and the specific gas with the same amount of oxygen atoms, respectively, Of these ratios, when the value obtained by dividing the dissociation amount of the specific gas by the dissociation amount of the low voltage dissociation gas is defined as the low voltage side dissociation ratio, the low voltage side dissociation ratio is at least included in the voltage range of 50% or more. In addition, for the specific gas and the high-voltage dissociation gas that is dissociated when the voltage applied to the second cell is higher than the detection voltage value, the high-voltage dissociation gas and the specific gas having the same amount of oxygen atoms Each Of the ratio between the dissociation amount of the high-voltage dissociation gas and the dissociation amount of the specific gas when dissociated, the value obtained by dividing the dissociation amount of the high-voltage dissociation gas by the dissociation amount of the specific gas is used as the high-voltage side dissociation ratio The high voltage side dissociation ratio is at least included in the voltage range of 50% or less.

  By setting the deterioration determination voltage value in the gas detection voltage range of the specific gas specified in this way, the second pump current (specifically, the second pump current at the time of determination) associated with the dissociation of the specific gas can be generated. Therefore, it can be avoided that the voltage applied to the second cell is set to a voltage range in which the specific gas cannot be dissociated and the deterioration determination of the gas sensor element becomes impossible.

  Therefore, according to the sensor element deterioration determination device in which the gas detection voltage range is set as described above, it is possible to generate the second pump current at the time of determination accompanying the dissociation of the specific gas, and use the second pump current at the time of determination. It can be determined whether or not the gas sensor element is in a deteriorated state.

  Next, in the sensor element deterioration determination device described above, the detection state determination means is detected by the second pump current detection means when the second cell applied voltage is a detection voltage value. The second pump current at the time of detection, which is the second pump current to be detected, is compared with the reference range for detection state determination predetermined in the numerical range that can be taken by the second pump current at the time of detection when the specific gas is present. When the detection second pump current is included in the detection state determination reference range, it is determined that the specific gas is present in the second measurement chamber, and the detection second pump current is included in the detection state determination reference range. If there is no specific gas, it can be determined that the specific gas is not present in the second measurement chamber.

  That is, since the current value of the second pump current at the time of detection changes according to the specific gas in the second measurement chamber, whether or not the specific gas exists in the second measurement chamber by using the second pump current at the time of detection. Can be determined.

  A detection state determination reference range is determined in advance based on a numerical range that can be taken by the detection second pump current when a specific gas is present, and the detection second pump current and the detection state determination reference range are It is possible to determine whether or not a specific gas is present in the second measurement chamber.

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 and pump in) oxygen present in the first measurement chamber 159 by the first pump cell 111 to which the first pump voltage Vp1 is applied. The oxygen concentration difference (oxygen partial pressure difference) between the reference oxygen chamber 118 and the first measurement chamber 159 in which the oxygen concentration (oxygen partial pressure) is controlled to be constant by the oxygen partial pressure detection cell 112, that is, the inside of the first measurement chamber 159. The oxygen concentration (oxygen partial pressure) 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.

  Further, the gas sensor control device 190 controls the first pump current Ip1 and detects the second pump voltage Vp2 (also referred to as the second cell applied voltage Vp2) applied to the second pump cell 113 in order to detect NOx. It is set to a predetermined detection voltage value Vp2a (for example, 450 mV). 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 same applies hereinafter), a process of detecting the second pump current Ip2 flowing in the second pump cell 113 as the second pump current α at the time of detection is executed. To do.

  At this time, since the second pump voltage Vp2 applied to the second pump cell 113 is a detection voltage value Vp2a that is predetermined for detecting NOx, the second pump current α at the time of detection is The second pump current Ip2 that flows through the second pump cell 113 when the two pump voltage Vp2 is the detection voltage value Vp2a.

Next, in S120, a process for determining whether NOx exists in the second measurement chamber 161 using the second pump current α at the time of detection is executed.
Specifically, it is determined whether or not the detection-time second pump current α is included in the detection state determination reference range Rth, and the detection-time second pump current α is included in the detection state determination reference range Rth. In this case, it is determined that NOx is present in the second measurement chamber 161 (affirmative determination), the process proceeds to S130, and when the second pump current α at the time of detection is not included in the detection state determination reference range Rth, 2 It is determined that NOx does not exist in the measurement chamber 161 (negative determination), and waits by repeatedly executing the same step until an affirmative determination is made.

  The detection state determination reference range Rth is set in advance to a numerical range that can be taken by the second pump current α at the time of detection when NOx exists in the second measurement chamber 161 based on the actual measurement data. By comparing the two-pump current α and the detection state determination reference range Rth, it is possible to determine whether or not NOx exists in the second measurement chamber 161.

When an affirmative determination is made in S120 and the process proceeds to S130, a process of changing the second pump voltage Vp2 to the deterioration determination voltage value Vp2b is executed in S130.
The degradation determination voltage value Vp2b is a voltage different from the detection voltage value Vp2a in the gas detection voltage range Rgs (for example, a range of 100 [mV] to 1200 [mV]) in which NOx can be detected in the second pump cell 113. This value is set to 500 mV in this embodiment.

The NOx gas detection voltage range Rgs includes the dissociation amount of oxygen (O ₂ ) (hereinafter also referred to as oxygen dissociation amount M1) and the dissociation amount of NOx (hereinafter also referred to as NOx dissociation amount M2) in the second pump cell 113. Among these ratios, the value obtained by dividing the NOx dissociation amount M2 by the oxygen dissociation amount M1 (hereinafter also referred to as the low voltage side dissociation ratio RL (= M2 / M1)) is at least included in the voltage range of 50% or more. Is set. The amounts of oxygen (O ₂ ) and NOx used to specify the gas detection voltage range Rgs are determined so that the oxygen atoms are the same amount.

Further, the gas detection voltage range Rgs is determined by water (H ₂ O in the second pump cell 113). ) Dissociation amount (hereinafter also referred to as water dissociation amount M3) and NOx dissociation amount M2 divided by NOx dissociation amount M2 (hereinafter referred to as high voltage side dissociation ratio RH (= M3). / M2)) is set so as to be at least included in a voltage range of 50% or less. Note that NOx and water (H ₂ O used for specifying the gas detection voltage range Rgs are used. ) Are determined so that oxygen atoms are the same amount.

Here, a specific example of a method for setting the NOx gas detection voltage range Rgs will be described.
Regarding the low voltage side dissociation ratio RL (= M2 / M1), first, the NOx gas sensor element 10 in which the element temperature is set to the normal control temperature (for example, 750 [° C.]) is converted into oxygen atoms in terms of the NOx current measurement. the same amount of oxygen (e.g., NO: If the 100 [ppm], oxygen _{(O 2): 50 [ppm} ]) are arranged in the adjusted atmosphere (e.g., in a chamber of a model gas system). Then, the entire inside of the NOx gas sensor element 10 (the first measurement chamber and the second measurement chamber) is in a state of only certain oxygen (O ₂ ) (for example, oxygen: 50 [ppm]). Next, a NOx current measurable voltage (for example, 450 [mV]) is applied to the second pump cell 113, and the current value flowing through the second pump cell 113 is set as an oxygen dissociation current value (a numerical value corresponding to the oxygen dissociation amount M1). To detect. Subsequently, the same operation is performed in an atmosphere adjusted to the same amount of NOx in terms of oxygen atoms with respect to the above oxygen concentration (for example, NO: 100 [ppm]), so that the second pump cell 113 flows. The current value is detected as a NOx dissociation current value (a numerical value corresponding to the NOx dissociation amount M2).

  Using the oxygen dissociation current value (oxygen dissociation amount M1) and the NOx dissociation current value (NOx dissociation amount M2) thus obtained, the low voltage side dissociation ratio RL (= M2 / M1) is calculated, and the low voltage side A second pump voltage Vp2 is determined when the dissociation ratio RL is 50%. The second pump voltage Vp2 determined in this way is set as the lower limit value of the NOx gas detection voltage range Rgs.

Regarding the high voltage side dissociation ratio RH (= M3 / M2), first, the NOx gas sensor element 10 whose element temperature is set to the normal control temperature (for example, 750 [° C.]) In terms of the same amount of water concentration (for example, NO: 100 [ppm], water (H ₂ O ): 100 [ppm]) (for example, in the chamber of the model gas apparatus). Then, the entire interior of the NOx gas sensor element 10 (the first measurement chamber and the second measurement chamber) is in a certain amount of water (H ₂ O ) (For example, water: 100 [ppm]). Next, a NOx current measurable voltage (for example, 450 [mV]) is applied to the second pump cell 113, and the current value flowing through the second pump cell 113 is set as a water dissociation current value (a numerical value corresponding to the water dissociation amount M3). To detect. Subsequently, the same operation is performed in an atmosphere adjusted to the same amount of NOx concentration (for example, NO: 100 [ppm]) in terms of oxygen atoms with respect to the water concentration, thereby flowing to the second pump cell 113. The current value is detected as a NOx dissociation current value (a numerical value corresponding to the NOx dissociation amount M2).

  Using the water dissociation current value (water dissociation amount M3) and NOx dissociation current value (NOx dissociation amount M2) thus obtained, the high voltage side dissociation ratio RH (= M3 / M2) is calculated, and the high voltage side A second pump voltage Vp2 is determined when the dissociation ratio RH is 50%. The second pump voltage Vp2 determined in this way is set as the upper limit value of the NOx gas detection voltage range Rgs.

  Here, in FIG. 4, regarding the NOx gas sensor element 10, an unused NOx gas sensor element (hereinafter also referred to as an unused sensor) and a NOx gas sensor element (hereinafter also referred to as a deterioration sensor) that has deteriorated due to use for a certain period of time. An explanatory view showing the correlation between the 2nd pump voltage Vp2 applied to the 2nd pump cell, and the 2nd pump current Ip2 which flows into the 2nd pump cell is shown.

As shown in FIG. 4, for the unused sensor, the waveform representing the correlation between the second pump voltage Vp2 and the second pump current Ip2 has a certain voltage for each of oxygen (O ₂ ), NOx, and water. In the range, even when the magnitude of the second pump voltage Vp2 changes, the second pump current Ip2 shows a waveform that has a substantially constant current value corresponding to each gas concentration. In addition, as shown in FIG. 4, the gas detection voltage range Rgs in which NOx detection is possible is a range of 100 [mV] to 1200 [mV].

  That is, the unused sensor shows a waveform in which the correlation waveform clearly represents the limit current characteristic, and even when the second pump voltage Vp2 is changed from 450 [mV] to 500 [mV] The magnitude of the second pump current Ip2 has not changed. For this reason, the current difference value between the second pump current Ip2 when the second pump voltage Vp2 is 450 [mV] and the second pump current Ip2 when the second pump voltage Vp2 is 500 [mV] (hereinafter referred to as “the second pump current Ip2”). , Also referred to as second pump current change amount ΔIp2) is 0 [mV].

  On the other hand, for the deterioration sensor, the second pump current Ip2 changes as the magnitude of the second pump voltage Vp2 changes even if the waveform representing the correlation is in the gas detection voltage range Rgs where NOx detection is possible. Waveform to be shown.

  That is, the deterioration sensor shows a waveform in which the correlation waveform does not clearly represent the limit current characteristic. When the second pump voltage Vp2 is changed from 450 [mV] to 500 [mV], the deterioration sensor The current value of the two pump current Ip2 is changing. For this reason, the second pump current change amount ΔIp2 of the deterioration sensor shows a value different from the second pump current change amount ΔIp2 of the unused sensor. The second pump current change amount ΔIp2 tends to show a larger value as the deterioration state of the gas sensor element gets worse.

Returning to the flowchart of FIG. 2, in the next step S140, timer processing for measuring the elapsed time is started.
In subsequent S150, 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 S160, and if the determination is negative, the same step is repeated. Wait by executing.

  Note that a time difference (time lag) until the dissociation of NOx occurs immediately after the voltage change in S130, and therefore it may take a certain time for the second pump current Ip2 to increase. Thus, the detection error of the second pump current Ip2 can be suppressed by executing the determination process in S150 and waiting for a certain time until the second pump current Ip2 is stabilized.

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.
If an affirmative determination is made in S150 and the process proceeds to S160, the timer process for measuring the elapsed time is stopped in S160.

In the next S170, a process of detecting the second pump current Ip2 flowing through the second pump cell 113 as the second pump current β at the time of determination is executed.
At this time, since the second pump voltage Vp2 applied to the second pump cell 113 is the degradation determination voltage value Vp2b, the second pump current Vp during the determination is determined by the second pump voltage Vp2 being the degradation determination voltage. This is the second pump current Ip2 that flows through the second pump cell 113 when the value is Vp2b.

In the next S180, a deterioration determination process is executed as a subroutine process.
FIG. 3 is a flowchart showing the contents of the deterioration determination process.
When the deterioration determination process is started, first, in S210, a process of reading a predetermined deterioration determination change reference value K1 from a predetermined storage device (such as an internal memory) is executed.

  The deterioration determination variation reference value K1 is a determination value used for determination processing (processing for determining deterioration of the NOx gas sensor element 10) in S230, which will be described later, and is a measurement result using the actual NOx gas sensor element 10. Can be determined based on.

  For example, in the present embodiment, the NOx gas sensor element 10 in which the second pump current α at the time of detection is reduced to a value equivalent to 70% when not in use is used for the purpose of determining the deterioration state. The second pump current change amount ΔIp2 is detected using the NOx gas sensor element 10 that has been reduced to a value equivalent to 70% when not in use, and the second pump current change amount ΔIp2 is set as the deterioration determination change reference value K1. Has been.

  Since the second pump current change amount ΔIp2 tends to increase as the deterioration state of the NOx gas sensor element 10 deteriorates, the second pump current change amount ΔIp2 is larger than the deterioration determination change amount reference value K1. When it becomes larger, it can be determined that the NOx gas sensor element 10 is in a deteriorated state.

In the next S220, a process of calculating the second pump current change amount ΔIp2 is executed.
Specifically, the current difference value between the second pump current α detected at S110 and the second pump current β detected at S170 is calculated, and the absolute value of the current difference value is calculated as the second pump current change. It is calculated as an amount ΔIp2 (= | β−α |).

  In the next S230, the deterioration determination variation reference value K1 read in S210 is compared with the second pump current variation ΔIp2 calculated in S220, and the second pump current variation ΔIp2 is determined as a deterioration determination variation criterion. It is determined whether or not the value is equal to or less than the value K1. If the determination is affirmative, the process proceeds to S240, and if the determination is negative, the process proceeds to S250.

  That is, in S230, when the second pump current change amount ΔIp2 is equal to or less than the deterioration determination change reference value K1, it is determined that the NOx gas sensor element 10 is in a normal state, and the second pump current change amount ΔIp2 is deteriorated. When it is larger than the determination change reference value K1, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  As described above, the second pump current change amount ΔIp2 tends to indicate a larger value as the deterioration state of the gas sensor element deteriorates. Therefore, the second pump current change amount ΔIp2 and the deterioration determination change amount reference value K1. It is possible to determine whether or not the NOx gas sensor element 10 is in a deteriorated state based on the comparison result.

  When an affirmative determination is made in S230 and the process proceeds to S240, in S240, it is determined 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 is determined for NOx detection. A process of setting to a predetermined detection voltage value Vp2a is executed.

  In addition, the voltage change process in S240 is a state for detecting the specific gas in the exhaust gas from the state for determining the deterioration of the NOx gas sensor element 10 (deterioration determination state) from the state for operating the gas detection device 1. This is performed to shift to the (gas detection state). That is, by executing the process in S240, the second cell applied voltage Vp2 is changed from the deterioration determination voltage value Vp2b to the detection voltage value Vp2a, and the operating state of the gas detection device 1 is changed from the deterioration determination state. Transition to the gas detection state.

  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 S230 and the process proceeds to S250, it is determined in S250 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 S240 or S250 ends, the deterioration determination process as a subroutine process ends and the sensor diagnosis process ends.
As described above, the gas sensor control device 190 provided in the gas detection device 1 of the present embodiment compares the second pump current change amount ΔIp2 with the deterioration determination change reference value K1, and based on the comparison result, NOx. It is configured to determine whether or not the gas sensor element 10 is in a deteriorated state.

  The second pump current Ip2 flowing through the second pump cell 113 has a current value depending on whether the NOx gas sensor element 10 is in a normal state or a deteriorated state even if the NOx gas concentration in the second measurement chamber 161 is constant. In the deteriorated state, the current value varies depending on the degree of progress of deterioration. From this, it is possible to determine whether or not the NOx gas sensor element 10 is in a deteriorated state by using the second pump current Ip2.

  Further, when the NOx gas sensor element 10 is in a normal state, as shown in FIG. 4, the NOx gas concentration in the second measurement chamber 161 is constant and the second cell applied voltage Vp2 can detect NOx. When the detection voltage range Rgs is set, the second pump current Ip2 exhibits a substantially constant current value corresponding to the NOx gas concentration (limit) even when the magnitude of the second cell applied voltage Vp2 changes. Current characteristics).

  However, in the deteriorated NOx gas sensor element 10, the limit current characteristics are unclear, so the NOx gas concentration in the second measurement chamber 161 is constant, and the second cell applied voltage Vp2 is within the gas detection voltage range Rgs. Even when the second pump current Ip2 is set, the current value changes as the magnitude of the second cell applied voltage Vp2 changes.

That is, it can be seen that it is possible to determine whether or not the NOx gas sensor element 10 is in a deteriorated state by using the second pump current Ip2.
Note that the change in the second pump current Ip2 due to the deterioration does not occur only when the second cell applied voltage Vp2 is the detection voltage value Vp2a, but in the gas detection voltage range Rgs in which NOx can be detected. The second pump current Ip2 changes due to deterioration. Therefore, in determining whether or not the NOx gas sensor element 10 is in a deteriorated state using the second pump current Ip2, the second cell applied voltage Vp2 is a voltage value for detection. The second pump current α at the time of detection when Vp2a is not limited, and the second pump current Ip2 when the second cell applied voltage Vp2 is other than the detection voltage value Vp2a (for example, the second pump current at determination) β) can be used.

  The second pump current change amount ΔIp2 that is the absolute value of the difference between the second pump current α at the time of detection and the second pump current β at the time of determination is the second pump current whose value changes as the NOx gas sensor element 10 deteriorates. Since the value is determined according to Ip2, it can be used to determine whether or not the NOx gas sensor element 10 is in a deteriorated state.

  Further, the second pump current change amount ΔIp2 is based on each current value in two types of second pump currents Ip2 (second pump current α at detection, second pump current β at determination) having different second cell applied voltages Vp2. The value is determined. Therefore, the deterioration determination using the second pump current change amount ΔIp2 can more accurately determine the change tendency of the second pump current Ip2 than the deterioration determination using only one type of second pump current Ip2. As a result, the deterioration state of the NOx gas sensor element 10 can be accurately determined.

  Further, the gas sensor control device 190 of the present embodiment previously determines a deterioration determination change amount reference value K1 for performing deterioration determination of the NOx gas sensor element 10, and the second pump current change amount ΔIp2 and the deterioration determination change amount. By comparing with the reference value K1, it is determined whether or not the NOx gas sensor element 10 is in a deteriorated state.

  That is, the gas sensor control device 190 determines that the NOx gas sensor element 10 is in a normal state when the second pump current change amount ΔIp2 is equal to or less than the deterioration determination change reference value K1 (when affirmative determination is made in S230). When the second pump current change amount ΔIp2 is larger than the deterioration determination change amount reference value K1 (when a negative determination is made in S230), a determination process is performed to determine that the NOx gas sensor element 10 is in a deteriorated state. By performing, it can be determined whether the NOx gas sensor element 10 is in a deteriorated state.

  Therefore, according to the gas sensor control device 190 of the present embodiment, by performing the deterioration determination using the second pump current change amount ΔIp2, the change tendency of the second pump current Ip2 can be accurately determined, and the NOx gas sensor element 10 It is possible to improve the determination accuracy in determining deterioration.

  Further, in this embodiment, the deterioration determination change reference value K1 is set in order to determine that the NOx gas sensor element 10 in which the second pump current α at the time of detection has decreased to a value equivalent to 70% when not in use is in a deteriorated state. ing. As described above, the second pump current change amount ΔIp2 tends to increase as the deterioration state of the NOx gas sensor element 10 deteriorates.

  In other words, the deterioration determining change reference value K1 of the present embodiment is such that the detected second pump current α is reduced to a value equivalent to 50% with respect to the detected second pump current α in the NOx gas sensor element 10 when not in use. The value is equal to or less than the second pump current change amount ΔIp2 detected by the NOx gas sensor element 10 in a state (a fatal deterioration state).

  Therefore, the gas sensor control device 190 of the present embodiment can determine that the NOx gas sensor element 10 in which the second pump current α at the time of detection has decreased to a value equivalent to 70% when not in use is in a deteriorated state, and it is difficult to detect NOx. It is possible to detect the deterioration state of the NOx gas sensor element 10 before reaching a bad deterioration state (a fatal deterioration state).

  In the gas sensor control device 190 of the present embodiment, the gas detection voltage range Rgs is a voltage range in which the low voltage side dissociation ratio RL is 50% or more and a voltage in which the high voltage side dissociation ratio RH is 50% or less. It is set to be at least included in the range. That is, the gas detection voltage range Rgs is a voltage range in which NOx can be reliably dissociated.

  By setting the deterioration determination voltage value Vp2b in such a gas detection voltage range Rgs, it is possible to generate the second pump current Ip2 (specifically, the second pump current β during determination) that accompanies the dissociation of NOx. . As a result, the gas sensor control device 190 can avoid that the second cell applied voltage Vp2 is set to a voltage range in which NOx cannot be dissociated and the deterioration determination of the NOx gas sensor element 10 becomes impossible.

  Further, the gas sensor control device 190 executes a process (S120) for determining whether or not NOx exists in the second measurement chamber 161 using the second pump current α at the time of detection, and deteriorates when NOx exists. The determination process (S180) is performed. Thus, by performing the deterioration determination process when NOx is present in the second measurement chamber 161, it is possible to prevent an erroneous determination due to the absence of NOx from occurring in the deterioration determination process.

  That is, when NOx is not present in the second measurement chamber 161, the second pump current Ip2 is not generated, so the second pump current change amount ΔIp2 does not indicate a value corresponding to the deterioration state of the NOx gas sensor element 10. become. When the deterioration determination is performed using the second pump current change amount ΔIp2, the deterioration state of the NOx gas sensor element 10 cannot be appropriately determined.

  In contrast, since the gas sensor control device 190 performs the deterioration determination process (S180) when NOx exists, it is possible to prevent an erroneous determination caused by the absence of NOx from occurring in the deterioration determination process. it can.

  In determining whether or not NOx exists in the second measurement chamber 161, it is possible to determine NOx without adding a NOx detection cell or the like to the second measurement chamber 161 by using the second pump current Ip2. There is an advantage that it can be determined whether or not there is.

  In addition, since the deterioration determination voltage value Vp2b is set to a value larger than the detection voltage value Vp2a, the gas sensor control device 190 enters the normal detection state (NOx detection state) early after the deterioration determination. There is an advantage of being able to return.

  That is, when the degradation determination voltage value Vp2b is set to a value smaller than the detection voltage value Vp2a, the NOx dissociation amount in the second pump cell 113 decreases, and therefore the NOx concentration in the second measurement chamber 161 is NOx. This is a higher value than the NOx concentration in the second measurement chamber 161 at the time of normal detection for detecting. As described above, when the NOx concentration in the second measurement chamber 161 is increased, the NOx concentration in the second measurement chamber 161 is normally changed after the second cell applied voltage Vp2 is changed from the deterioration determination voltage value Vp2b to the detection voltage value Vp2a. It may take a long time to obtain the concentration at the time of detection.

  On the other hand, when the degradation determination voltage value Vp2b is set to a value larger than the detection voltage value Vp2a, the NOx concentration in the second measurement chamber 161 is higher than the NOx concentration during normal detection. In order to avoid this, after changing the second cell applied voltage Vp2 from the deterioration determination voltage value Vp2b to the detection voltage value Vp2a, the NOx concentration in the second measurement chamber 161 is set to the normal detection concentration early. Can do.

Therefore, the gas sensor control device 190 can return to the normal detection state (NOx detection state) early after the deterioration determination.
In this embodiment, the gas sensor control device 190 corresponds to the sensor element deterioration determination device in the claims, the first pump cell 111 corresponds to the first oxygen ion pump cell, and the second pump cell 113 corresponds to the second oxygen cell. The first diffusion resistor 116 corresponds to a first diffusion resistor portion, and the second diffusion resistor 117 corresponds to a second diffusion resistor portion.

  Further, the gas sensor control device 190 that executes the processing of S120 corresponds to the detection state determination means, and the gas sensor control device 190 that executes the processing of S130 corresponds to the voltage setting means for deterioration determination, and executes the processing of S110 and S170. The gas sensor control device 190 corresponds to the second pump current detection means, and the gas sensor control device 190 that executes the processing of S180 corresponds to the deterioration determination means.

  Further, the gas sensor control device 190 that executes the process of S220 corresponds to the second pump current change amount detecting means, and the gas sensor control device 190 that executes the process of S230 corresponds to the change amount deterioration determining means.

  Further, the execution time of S120 corresponds to the detection state determination step, the execution time of S130 corresponds to the voltage setting step for deterioration determination, the execution times of S110 and S170 correspond to the second pump current detection step, and the execution of S180 Time corresponds to the deterioration determination step.

  As described above, according to the embodiment of the present invention, the deterioration state of the NOx gas sensor element 10 is determined using the second pump current change amount ΔIp2 that is the absolute value of the difference between the detection-time second pump current α and the determination-time second pump current β. Although the embodiment for determining (hereinafter also referred to as the first embodiment) has been described, the embodiment of the present invention is not limited to the above embodiment.

  Therefore, as the second embodiment, the deterioration of the NOx gas sensor element 10 is performed using the second pump current change rate AIp2 (= β / α), which is the ratio of the second pump current α during detection to the second pump current β during determination. An embodiment for determining the state 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 processing content of the deterioration determination process (the process in S180 of the sensor diagnosis process) executed in the gas sensor control device 190 is different. The contents of the second deterioration determination process will be mainly described.

FIG. 5 is a flowchart showing the processing content of the second deterioration determination processing.
When the second deterioration determination process is started, first, in S510 (S represents a step), a process of reading a predetermined deterioration determination change rate reference range K2 from a predetermined storage device (such as an internal memory) is executed. To do.

  Note that the deterioration determination change rate reference range K2 is a determination value used for determination processing (processing for determining deterioration of the NOx gas sensor element 10) in S530, which will be described later, and is based on a measurement result using the actual NOx gas sensor element 10. Can be determined based on.

  For example, in the present embodiment, the NOx gas sensor element 10 in which the second pump current α at the time of detection is reduced to a value equivalent to 50% when not in use is used to determine that the NOx gas sensor element 10 is in a deteriorated state. The second pump current change rate AIp2 (= β / α) is detected using the NOx gas sensor element 10 that has been reduced to a value equivalent to 50% when not used, and the deterioration is determined using the second pump current change rate AIp2. A change rate reference range K2 is set.

  In other words, the deterioration determination change rate reference range K2 is based on the value of the second pump current change rate AIp2 (= β / α) detected by the NOx gas sensor element 10 when not in use. The value is set in a range up to the value of the second pump current change rate AIp2 (= β / α) detected by the NOx gas sensor element 10 in a state of being reduced to a value equivalent to 50% of the hour.

  When the deterioration determination voltage value Vp2b is larger than the detection voltage value Vp2a, the second pump current change rate AIp2 tends to increase as the deterioration state of the NOx gas sensor element 10 deteriorates. There is. Therefore, in the present embodiment, when the second pump current change rate AIp2 is larger than the deterioration determination change rate reference range K2, the second pump current change rate AIp2 deviates from the deterioration determination change rate reference range K2. By determining that the NOx gas sensor element 10 has been deteriorated, it can be determined that the NOx gas sensor element 10 is in a deteriorated state.

  On the other hand, if the deterioration determination voltage value Vp2b is smaller than the detection voltage value Vp2a, the second pump current change rate AIp2 decreases as the deterioration state of the NOx gas sensor element 10 deteriorates. Tend to be. From this, when the deterioration determination voltage value Vp2b is a voltage value smaller than the detection voltage value Vp2a, when the second pump current change rate AIp2 is smaller than the deterioration determination change rate reference range K2, By determining that the second pump current change rate AIp2 has deviated from the deterioration determination change rate reference range K2, it can be determined that the NOx gas sensor element 10 is in a deteriorated state.

In the next S520, a process of calculating the second pump current change rate AIp2 is executed.
Specifically, in the sensor diagnosis process (FIG. 2), the ratio between the second pump current α detected at S110 detected at S110 and the second pump current β determined at S170 detected at the second pump current change rate AIp2 (= (β / α) is calculated.

  In next S530, the deterioration determination change rate reference range K2 read in S510 is compared with the second pump current change rate AIp2 calculated in S520, and the second pump current change rate AIp2 is determined as the deterioration determination change rate reference. It is determined whether or not it is included in the range K2. If the determination is affirmative, the process proceeds to S540, and if the determination is negative, the process proceeds to S550.

  That is, in S530, when the second pump current change rate AIp2 is included in the deterioration determination change rate reference range K2, it is determined that the NOx gas sensor element 10 is in a normal state, and the second pump current change rate AIp2 is deteriorated. When deviating from the change rate reference range K2 for determination, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  As described above, the second pump current change rate AIp2 of the present embodiment tends to indicate a larger value as the deterioration state of the gas sensor element deteriorates. Therefore, the second pump current change rate AIp2 and the deterioration determination change Based on the comparison result with the rate reference range K2, it can be determined whether or not the NOx gas sensor element 10 is in a deteriorated state.

  When an affirmative determination is made in S530 and the process proceeds to S540, in S540, it is determined 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 is determined for NOx detection. A process of setting to a predetermined detection voltage value Vp2a is executed.

  In addition, the voltage change process in S540 is a state for detecting the specific gas in the exhaust gas from the state for determining the deterioration of the NOx gas sensor element 10 (deterioration determination state) from the operation state of the gas detection device 1. This is performed to shift to the (gas detection state). That is, by executing the process in S540, the second cell applied voltage Vp2 is changed from the deterioration determination voltage value Vp2b to the detection voltage value Vp2a, and the operation state of the gas detection device 1 is changed from the deterioration determination state. Transition to the gas detection state.

  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 S530 and the process proceeds to S550, in S550, 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 S540 or S550 ends, the deterioration determination process as a subroutine process ends and the sensor diagnosis process ends.
As described above, the gas sensor control device 190 provided in the gas detection device 1 of the second embodiment compares the second pump current change rate AIp2 with the deterioration determination change rate reference range K2, and based on the comparison result. It is configured to determine whether or not the NOx gas sensor element 10 is in a deteriorated state.

  The second pump current change rate AIp2, which is the ratio of the second pump current α at the time of detection and the second pump current β at the time of determination, is a value according to the second pump current Ip2 whose value changes as the NOx gas sensor element 10 deteriorates. Therefore, it can be used to determine whether or not the NOx gas sensor element 10 is in a deteriorated state.

  Further, the second pump current change rate AIp2 is based on each current value in two types of second pump currents Ip2 (second pump current α at detection, second pump current β at determination) having different second cell applied voltages Vp2. The value is determined. Therefore, the deterioration determination using the second pump current change rate AIp2 can determine the change tendency of the second pump current Ip2 more accurately than the deterioration determination using only one type of second pump current Ip2. As a result, the deterioration state of the NOx gas sensor element 10 can be accurately determined.

  In addition, the gas sensor control device 190 of the second embodiment predetermines a deterioration determination change rate reference range K2 for determining deterioration of the NOx gas sensor element 10, and the second pump current change rate AIp2 and the deterioration determination change. By comparing with the rate reference range K2, it is determined whether or not the NOx gas sensor element 10 is in a deteriorated state.

  That is, the gas sensor control device 190 determines that the NOx gas sensor element 10 is in a normal state when the second pump current change rate AIp2 is included in the deterioration determination change rate reference range K2 (when an affirmative determination is made in S530). When the second pump current change rate AIp2 deviates from the deterioration determination change rate reference range K2 (when a negative determination is made in S530), a determination process is performed to determine that the NOx gas sensor element 10 is in a deteriorated state. By performing, it can be determined whether the NOx gas sensor element 10 is in a deteriorated state.

  Therefore, according to the gas sensor control device 190 of the second embodiment, by performing the deterioration determination using the second pump current change rate AIp2, the change tendency of the second pump current Ip2 can be accurately determined, and the NOx gas sensor element. Determination accuracy in 10 deterioration determinations can be improved.

  In the second embodiment, the change rate reference range K2 for deterioration determination is set to determine that the NOx gas sensor element 10 in which the second pump current α at the time of detection has decreased to a value equivalent to 50% when not in use is in a deteriorated state. Has been. For this reason, the gas sensor control apparatus 190 of 2nd Embodiment can detect the NOx gas sensor element 10 used as the deterioration state (fatal deterioration state) where it is difficult to detect NOx.

  In the second embodiment, the gas sensor control device 190 that executes the process of S520 corresponds to the second pump current change rate detecting means in the claims, and the gas sensor control device 190 that executes the process of S530 is the change rate. It corresponds to a deterioration determination means.

Although two embodiments have been described as the embodiments of the present invention, the embodiments of the present invention are not limited to the above embodiments.
Next, as a third embodiment, an embodiment in which the deterioration state of the NOx gas sensor element 10 is determined using the second pump current β during determination will be described.

  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 content of the deterioration determination process (the process in S180 of the sensor diagnosis process) executed by the gas sensor control device 190 is different. The contents of the third deterioration determination process will be mainly described.

FIG. 6 is a flowchart showing the contents of the third deterioration determination process.
When the third deterioration determination process is started, first, in S610 (S represents a step), a process of reading a predetermined deterioration determination current reference value K3 from a predetermined storage device (such as an internal memory) is executed. .

  The deterioration determination current reference value K3 is a determination value used for determination processing (processing for determining deterioration of the NOx gas sensor element 10) in S620, 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, in the present embodiment, the NOx gas sensor element 10 in which the second pump current α at the time of detection is reduced to a value equivalent to 50% when not in use is used to determine that the NOx gas sensor element 10 is in a deteriorated state. The second pump current β is detected at the time of determination using the NOx gas sensor element 10 that has been reduced to a value equivalent to 50% when not in use, and the current reference value K3 for deterioration determination is determined using the second pump current β at the time of determination. Is set.

  In other words, the deterioration determination current reference value K3 is set to the value of the determination second pump current β detected by the NOx gas sensor element 10 in a state where the detection second pump current is reduced to a value equivalent to 50% when not used. Has been.

  Note that the value of the second pump current β during determination tends to decrease as the deterioration state of the NOx gas sensor element 10 worsens. From this, in the present embodiment, it can be determined that the NOx gas sensor element 10 is in the deteriorated state when the second pump current β at the time of determination is smaller than the current reference value K3 for deterioration determination.

  In the next S620, the deterioration determination current reference value K3 read in S610 is compared with the determination second pump current β detected in S170 of the sensor diagnosis process, and the determination second pump current β is used for deterioration determination. It is determined whether or not the current value is equal to or greater than the current reference value K3. If the determination is affirmative, the process proceeds to S630, and if the determination is negative, the process proceeds to S640.

  That is, in S620, when the determination second pump current β is equal to or greater than the deterioration determination current reference value K3, it is determined that the NOx gas sensor element 10 is in a normal state, and the determination second pump current β is determined to be deteriorated. When it is less than the current reference value K3, it is determined that the NOx gas sensor element 10 is in a deteriorated state.

  When an affirmative determination is made in S620 and the process proceeds to S630, it is determined in S630 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 is determined for NOx detection. A process of setting to a predetermined detection voltage value Vp2a is executed.

  In addition, the voltage change process in S630 is a state for detecting the specific gas in the exhaust gas from the state for determining the deterioration of the NOx gas sensor element 10 from the state for determining the deterioration of the NOx gas sensor element 10 (deterioration determination state). This is performed to shift to the (gas detection state). That is, by executing the process in S630, the second cell applied voltage Vp2 is changed from the deterioration determination voltage value Vp2b to the detection voltage value Vp2a, and the operating state of the gas detection device 1 is changed from the deterioration determination state. Transition to the gas detection state.

  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 S620 and the process proceeds to S640, in S640, 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 S630 or S640 ends, the deterioration determination process as a subroutine process ends, and the sensor diagnosis process ends.
As described above, the gas sensor control device 190 provided in the gas detection device 1 of the third embodiment compares the second pump current β at the time of determination with the current reference value K3 for deterioration determination, and NOx based on the comparison result. It is configured to determine whether or not the gas sensor element 10 is in a deteriorated state.

  Since the second pump current Ip2 tends to decrease as the deterioration state of the NOx gas sensor element 10 progresses even if the NOx concentration is constant, the second pump current β at the time of determination is determined as the NOx gas sensor element 10. The value decreases as the degradation state of the progresses.

  From this, by determining in advance the deterioration determination current reference value K3 for performing the deterioration determination of the NOx gas sensor element 10, and comparing the second pump current β and the deterioration determination current reference value K3 at the time of determination, It can be determined whether or not the NOx gas sensor element 10 is in a deteriorated state.

  Therefore, according to the gas sensor control device 190 of the present embodiment, by performing the deterioration determination using the second pump current β at the time of determination, the change tendency of the second pump current Ip2 can be determined, and the NOx gas sensor element 10 is deteriorated. Judgment is possible.

  Further, the gas sensor control device 190 of the present embodiment is configured to perform the deterioration determination by comparing the detected second pump current β detected and the current reference value K3 for deterioration determination, and the second pump current β at the time of determination is determined. The process of calculating other numerical values (second pump current change amount ΔIp2, second pump current change rate AIp2) by using them becomes unnecessary. Thereby, the gas sensor control apparatus 190 of this embodiment has the advantage that the processing content of a deterioration determination process can be simplified.

  As shown in the explanatory diagram of FIG. 4, the change amount of the second pump current Ip2 (current value deterioration change amount ΔU) generated when the NOx gas sensor element 10 changes from the normal state to the deteriorated state is applied to the second cell. The voltage Vp2 is different for each voltage. Then, as the current value deterioration change amount ΔU accompanying deterioration increases, the current value deterioration change amount ΔU increases even in a light deterioration state, so that the determination accuracy of deterioration determination can be improved.

  For this reason, in the configuration in which the determination is made by comparing the second pump current β at the time of determination with the current reference value K3 for deterioration determination, the current value deterioration when the second cell applied voltage Vp2 is the detection voltage value Vp2a. It is desirable to set a voltage value at which the current value deterioration change amount ΔU is larger than the change amount ΔU as the deterioration determination voltage value Vp2b.

  That is, by setting the deterioration determination voltage value Vp2b in this way, the current value with respect to the progress of the deterioration state compared to the current value deterioration change amount ΔU when the second cell applied voltage Vp2 is the detection voltage value Vp2a. Since the deterioration change amount ΔU becomes large, it is possible to accurately determine the deterioration state even when the degree of progress of the deterioration state is small when performing the deterioration determination based on the second pump current β at the time of determination.

According to FIG. 4, the current value deterioration change amount ΔU tends to show a larger value as the second cell applied voltage Vp <b> 2 becomes smaller.
For this reason, in the configuration in which the determination is made by comparing the second pump current β at the time of determination with the current reference value K3 for deterioration determination, the value of the deterioration determination voltage value Vp2b set in S130 is determined from the detection voltage value Vp2a. By setting to a small value, it is possible to improve the determination system for deterioration determination.

In the third embodiment, the gas sensor control device 190 that executes the process of S620 corresponds to the current deterioration determination means in the claims.
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 values of the detection voltage value Vp2a and the deterioration determination voltage value Vp2b in the above embodiment are not limited to the above numerical values, and may be gas sensor elements as long as they are within a gas detection voltage range in which a specific gas can be detected. Arbitrary numerical values can be set in accordance with various conditions such as the type and use of each.

  In the above embodiment, as a method for determining whether or not the specific gas exists in the second measurement chamber, a determination method using the second pump cell (specifically, a determination using the second pump current flowing through the second pump cell). Method), but is not limited to this determination method. For example, a method for determining the presence or absence of a specific gas by providing a separate independent cell in the second measurement chamber, or whether there is a specific gas in the first measurement chamber using the first pump cell by adjusting the first cell applied voltage By determining whether or not, a determination method for indirectly determining whether or not the specific gas exists in the second measurement chamber may be employed.

  Further, the gas sensor element to be determined to be in a deteriorated state is a gas sensor element in which the second pump current is reduced to a value equivalent to 70% at the time of detection, or a gas sensor element in which the second pump current is reduced to a value equivalent to 50% in the detection. It is not limited to.

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 a flowchart showing the processing content of a deterioration determination process. It is explanatory drawing showing the correlation of 2nd pump voltage Vp2 applied to a 2nd pump cell, and 2nd pump current Ip2 which flows into a 2nd pump cell regarding an unused sensor and a deterioration sensor. It is a flowchart showing the processing content of a 2nd deterioration determination process. It is a flowchart showing the process content of a 3rd deterioration determination 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 (12)

A first measurement chamber into which a gas to be measured is introduced via the first diffusion resistance unit;
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;
A reference oxygen chamber set in a reference oxygen partial pressure atmosphere;
It has an oxygen ion conductor and said oxygen ion conductive pair of first pumping electrodes formed on the body, the first of the pair with one of the pair of first pumping electrodes are arranged on the first measurement chamber The other pump electrode is arranged outside the first measurement chamber, outside the second measurement chamber, and outside the reference oxygen chamber, and pumps out oxygen to the measurement target gas introduced into the first measurement chamber or A first oxygen ion pump cell for pumping ;
An oxygen ion conductor and a pair of second pump electrodes formed on the oxygen ion conductor, and one of the pair of second pump electrodes is disposed in the second measurement chamber and the pair of second pump electrodes . the other second pump electrode is arranged in the reference oxygen chamber, and a second oxygen ion pump cell Le which current corresponding to a specific gas concentration in the second measuring chamber flows,
An oxygen ion conductor and a pair of detection electrodes formed on the oxygen ion conductor, wherein one of the pair of detection electrodes is disposed in the first measurement chamber, and the other electrode is the reference oxygen chamber An oxygen partial pressure detection cell disposed in
A sensor element deterioration determination device for determining a deterioration state of a gas sensor element comprising:
The gas sensor element includes the first oxygen ion pump cell in the first measurement chamber so that a voltage across the oxygen partial pressure detection cell becomes a predetermined target value based on a reference oxygen partial pressure in the reference oxygen chamber. Pumping out or pumping in oxygen, and when the second cell applied voltage applied to the second oxygen ion pump cell is a voltage value for detection predetermined for detecting the specific gas, Based on the second pump current flowing through the second oxygen ion pump cell, the specific gas concentration in the second measurement chamber is detected,
Detection state determination means for determining whether or not the specific gas is present in the second measurement chamber;
When it is determined by the detection state determination means that the specific gas exists in the second measurement chamber, the deterioration determination voltage value different from the detection voltage value in the gas detection voltage range in which the specific gas can be detected. Degradation determination voltage setting means for setting the second cell applied voltage;
Second pump current detection means for detecting the second pump current;
Among the second pump currents detected by the second pump current detection means, the gas sensor element uses the second pump current at the time of determination when at least the second cell applied voltage is the voltage value for deterioration determination Deterioration determining means for determining whether or not is in a deteriorated state;
A sensor element deterioration determination device comprising: The deterioration determining means includes
A second pump current at the time of determination which is the second pump current detected by the second pump current detection means when the applied voltage of the second cell is the voltage value for deterioration determination, and deterioration determination of the gas sensor element Therefore, when the second pump current at the time of determination is equal to or greater than the current reference value for deterioration determination, it is determined that the gas sensor element is in a normal state. And a current deterioration determination means for determining that the gas sensor element is in a deteriorated state when the second pump current at the time of determination is smaller than the current reference value for deterioration determination.
The sensor element deterioration determination apparatus according to claim 1. In the case where the second pump current detected by the second pump current detection means when the second cell applied voltage is the detection voltage value is the second pump current at the time of detection,
The current reference value for deterioration determination is detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 95% with respect to the second pump current at the time of detection in the gas sensor element when not in use. The value of the second pump current at the time of determination is a value equal to or lower than the second pump current, and the second pump current at the time of detection is reduced to a value equivalent to 50% of the second pump current at the time of detection in the gas sensor element when not in use A value greater than or equal to the second pump current at the time of determination detected by a gas sensor element;
The sensor element deterioration determination apparatus according to claim 2. The deterioration determination voltage value is smaller than the detection voltage value;
The sensor element deterioration determination apparatus according to claim 2 or claim 3, wherein The deterioration determining means includes
The second pump current during detection, which is the second pump current detected by the second pump current detection means when the second cell applied voltage is the detection voltage value, and the second cell applied voltage is the A second pump current change amount that is an absolute value of a difference from the second pump current at the time of determination that is the second pump current detected by the second pump current detection means when the voltage value is for deterioration determination is detected. A second pump current change amount detecting means;
The second pump current change amount is compared with a deterioration determination change reference value that is predetermined for deterioration determination of the gas sensor element, and the second pump current change amount is equal to or less than the deterioration determination change reference value. If the gas sensor element is in a normal state, and the second pump current change amount is larger than the deterioration determination change reference value, the gas sensor element is in a deteriorated state. A change amount deterioration determining means for determining,
The sensor element deterioration determination apparatus according to claim 1. The change criterion value for deterioration determination is
More than the amount of change in the second pump current detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 95% with respect to the second pump current at the time of detection in the gas sensor element when not in use. And the second detected by the gas sensor element in a state where the second pump current at the time of detection is reduced to a value equivalent to 50% of the second pump current at the time of detection in the gas sensor element when not in use. The value must be less than the pump current change amount,
The sensor element deterioration determination apparatus according to claim 5. The deterioration determining means includes
The second pump current during detection, which is the second pump current detected by the second pump current detection means when the second cell applied voltage is the detection voltage value, and the second cell applied voltage is the A second pump current change rate that is a ratio of the second pump current at the time of determination, which is the second pump current detected by the second pump current detection means when the voltage value is for deterioration determination, is detected. A pump current change rate detecting means;
The second pump current change rate is compared with a deterioration determination change rate reference range predetermined for determining the deterioration of the gas sensor element, and the second pump current change rate falls within the deterioration determination change rate reference range. If included, it is determined that the gas sensor element is in a normal state, and if the second pump current change rate deviates from the deterioration determination change rate reference range, the gas sensor element is in a deteriorated state. A change rate deterioration determining means for determining,
The sensor element deterioration determination apparatus according to claim 1. The deterioration determining change rate reference range is determined based on the second pump current change rate detected by the gas sensor element when not in use and the second pump current when detected by the gas sensor element when not used. The second pump current at the time of detection is included in a range up to a value of the second pump current change rate detected by the gas sensor element in a state where the second pump current has been reduced to a value equivalent to 50%
The sensor element deterioration determination apparatus according to claim 7. The deterioration determination voltage value is larger than the detection voltage value;
The sensor element deterioration determination apparatus according to any one of claims 5 to 8. The gas detection voltage range of the specific gas is
The low-voltage dissociation gas having the same amount of oxygen atoms as the specific gas and the low-voltage dissociation gas dissociated even when the voltage applied to the second cell is lower than the voltage value for detection. And a value obtained by dividing the dissociation amount of the specific gas by the dissociation amount of the low-voltage dissociation gas among the ratio of the dissociation amount of the low-voltage dissociation gas and the dissociation amount of the specific gas when the specific gas is dissociated. And the low voltage side dissociation ratio is at least included in the voltage range in which the low voltage side dissociation ratio is 50% or more,
The high-voltage dissociation gas having the same amount of oxygen atoms as the specific gas and the high-voltage dissociation gas dissociated when the voltage applied to the second cell is higher than the voltage value for detection. Of the ratio between the dissociation amount of the high-voltage dissociation gas and the dissociation amount of the specific gas when the specific gas is dissociated, a value obtained by dividing the dissociation amount of the high-voltage dissociation gas by the dissociation amount of the specific gas. When the high voltage side dissociation ratio is set, the high voltage side dissociation ratio is at least included in a voltage range of 50% or less,
The sensor element deterioration determination apparatus according to claim 1, wherein: The detection state determination means includes
When the second gas at the time of detection, which is the second pump current detected by the second pump current detection means when the voltage applied to the second cell is the detection voltage value, and when the specific gas exists When the detection state determination reference range is compared with a predetermined detection state determination reference range in a numerical range that can be taken by the detection second pump current, and the detection second pump current is included in the detection state determination reference range When it is determined that the specific gas is present in the second measurement chamber, and the second pump current at the time of detection is not included in the detection state determination reference range, the specific gas is present in the second measurement chamber. To decide not to,
The sensor element deterioration determination apparatus according to any one of claims 1 to 10, wherein: A first measurement chamber into which a gas to be measured is introduced via the first diffusion resistance unit;
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;
A reference oxygen chamber set in a reference oxygen partial pressure atmosphere;
It has an oxygen ion conductor and said oxygen ion conductive pair of first pumping electrodes formed on the body, the first of the pair with one of the pair of first pumping electrodes are arranged on the first measurement chamber The other pump electrode is arranged outside the first measurement chamber, outside the second measurement chamber, and outside the reference oxygen chamber, and pumps out oxygen to the measurement target gas introduced into the first measurement chamber or A first oxygen ion pump cell for pumping ;
An oxygen ion conductor and a pair of second pump electrodes formed on the oxygen ion conductor, and one of the pair of second pump electrodes is disposed in the second measurement chamber and the pair of second pump electrodes . the other second pump electrode is arranged in the reference oxygen chamber, and a second oxygen ion pump cell Le which current corresponding to a specific gas concentration in the second measuring chamber flows,
An oxygen ion conductor and a pair of detection electrodes formed on the oxygen ion conductor, wherein one of the pair of detection electrodes is disposed in the first measurement chamber, and the other electrode is the reference oxygen chamber An oxygen partial pressure detection cell disposed in
A sensor element deterioration determination method for determining a deterioration state of a gas sensor element comprising:
The gas sensor element includes the first oxygen ion pump cell in the first measurement chamber so that a voltage across the oxygen partial pressure detection cell becomes a predetermined target value based on a reference oxygen partial pressure in the reference oxygen chamber. Pumping out or pumping in oxygen, and when the second cell applied voltage applied to the second oxygen ion pump cell is a voltage value for detection predetermined for detecting the specific gas, Based on the second pump current flowing through the second oxygen ion pump cell, the specific gas concentration in the second measurement chamber is detected,
A detection state determination step of determining whether or not the specific gas exists in the second measurement chamber;
When it is determined in the detection state determination step that the specific gas is present in the second measurement chamber, the deterioration determination voltage value that is different from the detection voltage value is selected from the gas detection voltage range in which the specific gas can be detected. Degradation determination voltage setting step for setting the second cell applied voltage;
A second pump current detecting step for detecting the second pump current;
Among the second pump currents detected in the second pump current detection step, the gas sensor element using the second pump current at the time of determination when at least the second cell applied voltage is the voltage value for deterioration determination A deterioration determination step for determining whether or not is in a deteriorated state;
A sensor element deterioration determination method comprising: