JP6573567B2 - Method for determining light-off abnormality of sensor element and method for manufacturing gas sensor - Google Patents

Description

  The present invention relates to a light-off abnormality determination method for a sensor element and a method for manufacturing a gas sensor.

  Conventionally, a gas sensor including a sensor element that detects a specific gas concentration such as NOx in a gas to be measured such as an exhaust gas of an automobile is known. For example, Patent Document 1 discloses a laminate in which oxygen ion conductive solid electrolyte layers are laminated, an outer pump electrode arranged on the upper surface of the laminate, a measurement electrode arranged in the laminate, and a laminate. The sensor element provided with the heater arrange | positioned inside is described. In this sensor element, a specific gas in the measurement gas is introduced based on the current flowing between the outer pump electrode and the measurement electrode when the measurement gas is introduced around the measurement electrode and oxygen in the measurement gas is pumped out. Detect concentration. The heater heats the sensor element to a temperature at which the solid electrolyte layer is activated and keeps the temperature.

  Further, such a sensor element takes time from when the heater is energized until the specific gas concentration can be correctly detected, and this time is called a light-off time. The light-off time is the time it takes for the heater to activate the solid electrolyte and the oxygen existing around the measurement electrode before use (oxygen not derived from a specific gas) is pumped out to the extent that it does not affect the measurement accuracy. It is a time based on the time required for.

  It is known that the light-off time is measured by the method described in Patent Document 2, for example. FIG. 5 is an explanatory diagram of a conventional method for measuring the light-off time. Specifically, first, a gas sensor having a sensor element is installed in a predetermined atmosphere, and the heater is energized. In addition, the time change of the pump current when pumping out oxygen around the measurement electrode is measured. Then, the value of the pump current 30 minutes (1800 seconds) after the start of heater energization is regarded as the saturation value Is, and the time tL when the pump current becomes a value of Is ± 10 ppm is set as the light-off time.

Japanese Patent Laid-Open No. 2015-200633 JP 2009-300428 A (FIG. 3)

  By the way, for example, as an inspection of the manufactured sensor element, there is a case where the presence or absence of abnormality is determined by measuring the light-off time. In this case, conventionally, the light-off time is derived based on the value that the pump current can be regarded as saturated as described above, and it is determined that there is an abnormality when the derived light-off time exceeds a predetermined threshold value. . However, there is a problem that it takes time to determine abnormality of the light-off time, for example, it takes 30 minutes to obtain the saturation value Is.

  The present invention has been made to solve such a problem, and a main object thereof is to make it possible to determine an abnormality in the light-off time of a sensor element in a short time.

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

The sensor element light off abnormality determination method of the present invention,
A substrate comprising an oxygen ion conductive solid electrolyte and having a gas flow part for introducing a gas to be measured provided therein;
A first measuring electrode disposed facing the gas flow part;
A second measurement electrode disposed outside the gas circulation part;
A heater for heating the substrate;
A light-off abnormality determination method for determining an abnormality in a light-off time of a sensor element comprising:
(A) The sensor element is exposed to an oxygen-existing atmosphere, the heater is energized, and a voltage is applied between the first and second measurement electrodes to pump out oxygen around the first measurement electrode. Control is started, and a predetermined measurement time in which the elapsed time from the reference time exceeds 0 second and is 65 seconds or less with the later one of the heating start time of the heater and the control start time at which the control is started as the reference time Obtaining a measurement value based on a pump current flowing between the first and second measurement electrodes based on the voltage, or a measurement value based on the potential of the first measurement electrode;
(B) determining an abnormality in the light-off time of the sensor element based on the measured value obtained in step (a) and a predetermined threshold;
Is included.

  In this light-off abnormality determination method, the pump current at a predetermined measurement time at which the elapsed time from the reference time exceeds 0 second and is 65 seconds or less with the later of the heater temperature rise completion time and the control start time as the reference time or A measurement value based on the potential of the first measurement electrode is obtained. In a normal sensor element, oxygen around the first measurement electrode is pumped out as time elapses from the reference time. Therefore, the pump current or the potential of the first measurement electrode changes as time elapses from the reference time. To go. However, in the sensor element having an abnormality (prolongation) in the light-off time, the rate of decrease in the oxygen concentration around the first measurement electrode is slow, so that the slope of the change in the pump current or the potential of the first measurement electrode after the reference time Becomes moderate. Therefore, a sensor element having an abnormality in the light-off time tends to have a different pump current value or potential value of the first measurement electrode at the measurement time as compared with a normal sensor element. Therefore, since the measured value based on the pump current or the potential of the first measurement electrode has a correlation with the presence or absence of the abnormality in the light-off time, the abnormality in the light-off time can be determined based on this measured value and the threshold value. . In the light-off abnormality determination method of the present invention, it is only necessary to obtain a measurement value at a measurement time where the elapsed time from the reference time is greater than 0 seconds and less than 65 seconds, and the pump current is measured as in the conventional light-off time measurement. There is no need to wait for it to drop and stabilize sufficiently (eg 30 minutes). Therefore, an abnormality in the light-off time can be determined in a short time. By setting the measurement time to be later than the reference time (elapsed time exceeds 0 second), it is possible to obtain an appropriate measurement value in a state where the pump cell is activated and oxygen is pumped out. In addition, if the oxygen concentration around the first measurement electrode is lowered and sufficiently stabilized, the difference in measured values due to the presence or absence of abnormality in the light-off time may be reduced and the accuracy of abnormality determination may be reduced. By setting the elapsed time from the time to 65 seconds or less, it is possible to accurately determine an abnormality.

  In the light-off abnormality determination method of the present invention, the temperature rise completion time is a pump cell including the first measurement electrode, the second measurement electrode, and a solid electrolyte layer between the first and second measurement electrodes. It may be the time when is activated. The temperature rise completion time is at least one of a time when a predetermined time has elapsed from the start of energization of the heater and a time when a predetermined waiting time has elapsed after the resistance value of the heater has reached a predetermined value. It is good. The step (a) may be performed in a state where a control circuit is connected to the sensor element. In this case, the control circuit includes a temperature increase completion determination unit that determines whether or not the temperature increase of the heater has been completed. It may be the time when it is determined that the temperature increase has been completed. Further, the temperature increase completion determination means determines that the temperature increase of the heater has been completed when a predetermined time has elapsed from the start of energization of the heater, or after the resistance value of the heater has reached a predetermined value. It may be a means for determining whether the heating of the heater is completed when a predetermined waiting time has elapsed.

  In the light-off abnormality determination method of the present invention, the control start time may be a time after the temperature increase completion time. In this case, the control start time becomes the reference time.

  In the light-off abnormality determination method of the present invention, the second measurement electrode may be an outer electrode disposed outside the substrate. Further, in the light-off abnormality determination method of the present invention, the base has an internal reference gas space into which a reference gas serving as a reference for detecting a specific gas concentration in the gas to be measured is not communicated with the gas circulation part. The second measurement electrode may be a reference electrode disposed facing the reference gas space.

  In the light-off abnormality determination method of the present invention, in the step (a), the measurement time may be a timing at which an elapsed time from the reference time is 5 seconds or more. When the elapsed time is 5 seconds or more, the difference in the measured value at the measurement time due to the presence or absence of abnormality in the light-off time becomes larger, so that abnormality in the light-off time can be determined with higher accuracy.

  In the light-off abnormality determination method of the present invention, in the step (a), the measurement time may be a timing at which the elapsed time from the reference time is 35 seconds or less. When the elapsed time is 35 seconds or less, the measured value based on the pump current before changing and stabilizing or the potential of the first measurement electrode can be obtained more reliably, and therefore the abnormality in the light-off time can be determined with higher accuracy.

  In the light-off abnormality determination method of the present invention, the oxygen presence atmosphere may be an air atmosphere. In this way, the measured value can be acquired more easily.

  In the light-off abnormality determination method of the present invention, the step (a) may be performed on a sensor element that is not assembled as a gas sensor. In this way, for example, an abnormality can be determined before the gas sensor assembly operation is performed, so that it is possible to reduce the case where the assembly operation is wasted or the entire gas sensor needs to be discarded when the abnormality is determined.

The manufacturing method of the gas sensor of the present invention includes:
A determination step of determining an abnormality in the light-off time of the sensor element by performing the light-off abnormality determination method of the sensor element of any one of the aspects described above,
A manufacturing process for manufacturing a gas sensor using a sensor element that has not been determined to be abnormal in the determination process;
Is included.

  In this gas sensor manufacturing method, since the gas sensor is manufactured using the sensor element that is not determined to be abnormal by performing the above-described sensor element light-off abnormality determination method of the present invention, the yield of the gas sensor is improved. In addition, since the conventional measurement of the light-off time is performed after the gas sensor is assembled, if the measured light-off time is abnormal, the assembly work may be wasted or the entire gas sensor may need to be discarded. Although there is such a thing, it can be reduced.

FIG. 3 is a schematic cross-sectional view schematically showing an example of the configuration of the gas sensor 100. Explanatory drawing of abnormality determination of the light-off time of the sensor element 101. FIG. The cross-sectional schematic diagram which showed schematically an example of the structure of the gas sensor 100 of a modification. The graph which shows the relationship between measurement time Tm and distribution of the measured value A of the some sensor element 101. FIG. Explanatory drawing of the measuring method of the conventional light-off time.

  Next, embodiments of the present invention will be described with reference to the drawings. First, a sensor element to be subjected to the light-off abnormality determination method of the present embodiment and a gas sensor equipped with the sensor element will be described. FIG. 1 is a schematic cross-sectional view schematically illustrating an example of a configuration of a gas sensor 100 including a sensor element 101. The sensor element 101 has a long rectangular parallelepiped shape. The longitudinal direction (the left-right direction in FIG. 1) of the sensor element 101 is the front-rear direction, and the thickness direction of the sensor element 101 (up-down direction in FIG. 1) is the up-down direction. The direction. The width direction of sensor element 101 (the direction perpendicular to the front-rear direction and the up-down direction) is the left-right direction.

The sensor element 101 includes a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, and a first solid electrolyte layer 4 each made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). The spacer layer 5 and the second solid electrolyte layer 6 are elements having a structure in which the layers are laminated in this order from the bottom in the drawing. The solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured, for example, by performing predetermined processing and circuit pattern printing on a ceramic green sheet corresponding to each layer, stacking them, and firing and integrating them.

  One end of the sensor element 101, and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, is a gas inlet 10, a first diffusion rate limiting unit 11, and a buffer space. 12, the second diffusion rate limiting unit 13, the first internal space 20, the third diffusion rate limiting unit 30, the second internal space 40, the fourth diffusion rate limiting unit 60, and the third internal space 61. Are formed adjacent to each other in this order.

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

  Each of the first diffusion rate controlling unit 11, the second diffusion rate controlling unit 13, and the third diffusion rate controlling unit 30 is provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). . The fourth diffusion rate controlling part 60 is provided as one horizontally long slit (the opening has a longitudinal direction in a direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. In addition, the site | part from the gas inlet 10 to the 3rd internal space 61 is also called a gas distribution part.

  Further, at a position farther from the front end side than the gas circulation part, the side part is partitioned by the side surface of the first solid electrolyte layer 4 between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5. The reference gas introduction space 43 is provided at the position. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

  The air introduction layer 48 is a layer made of porous ceramics, and a reference gas is introduced into the air introduction layer 48 through the reference gas introduction space 43. The air introduction layer 48 is formed so as to cover the reference electrode 42.

  The reference electrode 42 is an electrode formed in such a manner that it is sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, the reference electrode 42 leads to the reference gas introduction space 43. An air introduction layer 48 is provided. As will be described later, the oxygen concentration (oxygen partial pressure) in the first internal space 20, the second internal space 40, and the third internal space 61 can be measured using the reference electrode 42. It is possible.

  In the gas circulation part, the gas inlet 10 is a part opened to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion control unit 11 is a part that provides a predetermined diffusion resistance to the gas to be measured taken from the gas inlet 10. The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate controlling unit 11 to the second diffusion rate controlling unit 13. The second diffusion rate limiting unit 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from the outside of the sensor element 101 to the inside of the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (exhaust pressure pulsation if the gas to be measured is an automobile exhaust gas) ), The gas to be measured that is suddenly taken into the sensor element 101 from the gas inlet 10 is not directly introduced into the first internal space 20, but the first diffusion control unit 11, the buffer space 12, the second After the concentration variation of the gas to be measured is canceled through the diffusion control unit 13, the gas is introduced into the first internal space 20. As a result, the concentration fluctuation of the gas to be measured introduced into the first internal space 20 becomes almost negligible. The first internal space 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate limiting unit 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

  The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode portion 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20, and an upper surface of the second solid electrolyte layer 6. An electrochemical pump cell comprising an outer pump electrode 23 provided in a manner exposed to the external space in a region corresponding to the ceiling electrode portion 22a, and a second solid electrolyte layer 6 sandwiched between these electrodes. is there.

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

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

  In the main pump cell 21, a desired pump voltage Vp 0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and the pump current is positive or negative between the inner pump electrode 22 and the outer pump electrode 23. By flowing Ip0, oxygen in the first internal space 20 can be pumped into the external space, or oxygen in the external space can be pumped into the first internal space 20.

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

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

  The third diffusion control unit 30 provides a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and the gas under measurement is supplied to the gas under measurement. This is the part that leads to the second internal space 40.

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

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

  The auxiliary pump electrode 51 is disposed in the second internal space 40 in the same tunnel configuration as the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51 a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40 is formed on the first solid electrolyte layer 4. The bottom electrode part 51b is formed, and the side electrode part (not shown) connecting the ceiling electrode part 51a and the bottom electrode part 51b is provided on the spacer layer 5 that provides the side wall of the second internal space 40. It has a tunnel-type structure formed on both wall surfaces. Note that the auxiliary pump electrode 51 is also formed using a material having a reduced reducing ability with respect to the NOx component in the gas to be measured, like the inner pump electrode 22.

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

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

  The auxiliary pump cell 50 performs pumping by the variable power source 52 that is voltage-controlled based on the electromotive force V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. Specifically, the pump current Ip1 of the auxiliary pump cell 50 is controlled by feedback controlling the pump voltage Vp1 of the variable power source 52 so that the electromotive force V1 becomes a predetermined target value V1 * (approaching). . Thereby, the oxygen partial pressure in the atmosphere in the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

  At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input to the main pump control oxygen partial pressure detection sensor cell 80 as a control signal, and the electromotive force V0 is controlled. More specifically, based on the value of the pump current Ip1, the target value V0 * of the electromotive force V0 when the above-described voltage Vp0 is feedback controlled is determined. As a result, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion control unit 30 into the second internal space 40 is controlled to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

  The fourth diffusion control unit 60 gives a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal space 40, and causes the gas to be measured to flow. This is the part that leads to the third internal space 61. The fourth diffusion control unit 60 plays a role of limiting the amount of NOx flowing into the third internal space 61.

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

  The measurement pump cell 41 measures the NOx concentration in the gas to be measured in the third internal space 61. The measurement pump cell 41 includes a measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61, the outer pump electrode 23, the second solid electrolyte layer 6, and the spacer layer 5. An electrochemical pump cell constituted by the first solid electrolyte layer 4. The measurement electrode 44 is a porous cermet electrode. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the third internal space 61.

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

  In order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, a first solid electrolyte layer 4, a third substrate layer 3, a measurement electrode 44, and a reference electrode 42, that is, A measurement pump control oxygen partial pressure detection sensor cell 82 is configured. The variable power supply 46 is controlled on the basis of the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82.

The gas to be measured introduced into the second internal space 40 reaches the measurement electrode 44 in the third internal space 61 through the fourth diffusion rate-determining unit 60 under the condition where the oxygen partial pressure is controlled. . Nitrogen oxide in the gas to be measured around the measurement electrode 44 is reduced (2NO → N ₂ + O ₂ ) to generate oxygen. The generated oxygen is pumped by the measurement pump cell 41. At this time, the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 becomes a predetermined target value V2 *. Thus, the voltage Vp2 of the variable power supply 46 is feedback-controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxide in the gas to be measured, the nitrogen oxide in the gas to be measured using the pump current Ip2 in the measurement pump cell 41. The concentration will be calculated.

  If the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detecting means as an electrochemical sensor cell, the measurement electrode The electromotive force according to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around 44 and the amount of oxygen contained in the reference atmosphere can be detected, whereby the NOx component in the gas to be measured It is also possible to determine the concentration of.

  The second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42 constitute an electrochemical sensor cell 83. The oxygen partial pressure in the gas to be measured outside the sensor can be detected by the electromotive force Vref obtained by the sensor cell 83.

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

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

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

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

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

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

  The pressure dissipating hole 75 is a portion that is provided so as to penetrate the third substrate layer 3 and communicate with the reference gas introduction space 43, and is for the purpose of alleviating the increase in internal pressure accompanying the temperature increase in the heater insulating layer 74. Formed.

  The sensor element 101 is provided with lead wires (not shown) connected to the respective electrodes and connector electrodes (not shown) located on the upper and lower surfaces of the rear end of the sensor element 101. A voltage or a current is applied to each electrode (the inner pump electrode 22, the outer pump electrode 23, the reference electrode 42, the measurement electrode 44, and the auxiliary pump electrode 51) of the sensor element 101 from outside through these lead wires and connector electrodes. The voltage and current of each electrode can be measured. The application of voltage by the above-described variable power supply 24, variable power supply 46, variable power supply 52, and detection of pump currents Ip1, Ip2, electromotive forces V0, V1, V2, Vref, etc. are actually performed through these lead wires and connector electrodes. Done.

  Although not shown, the gas sensor 100 includes a protective cover that protects the front end side of the sensor element 101, a connector that is attached to the rear end side of the sensor element 101 and is electrically connected to the connector electrode, and a rear end side of the sensor element. And an outer cylinder that covers the connector, an element sealing body that encloses and fixes the sensor element 101 and separates the space on the front end side (in the protective cover) and the space on the rear end side (in the outer cylinder). And a lead wire connected to the connector and drawn out from the outer cylinder. In addition, the structure of such a gas sensor 100 whole is well-known, For example, it describes in the patent document 1 mentioned above.

  Next, the light-off abnormality determination method of the present embodiment that is performed on the sensor element 101 of the gas sensor 100 configured as described above will be described. FIG. 2 is an explanatory diagram of the abnormality determination of the light-off time of the sensor element 101.

The light-off abnormality determination method of this embodiment is
(A) The sensor element 101 is exposed to an oxygen-existing atmosphere, the heater 72 is energized, and the voltage Vp2 is applied between the outer pump electrode 23 and the measurement electrode 44 to pump out oxygen around the measurement electrode 44. The later of the temperature rise completion time T1 of the heater 72 and the control start time T2 at which the control is started is defined as a reference time Tref, and a predetermined time with an elapsed time from the reference time Tref exceeding 0 seconds and 65 seconds or less Obtaining a measurement value A based on the pump current Ip2 flowing between the outer pump electrode 23 and the measurement electrode 44 based on the voltage Vp2 at the measurement time Tm of
(B) determining an abnormality in the light-off time of the sensor element 101 based on the measured value A obtained in step (a) and the predetermined threshold value Aref;
including.

  In the present embodiment, the light-off abnormality determination method is performed on the sensor element 101 that is not assembled as the gas sensor 100, for example, the sensor element 101 alone. First, as preparation before step (a), the voltage applied to each electrode (inner pump electrode 22, outer pump electrode 23, reference electrode 42, measurement electrode 44, auxiliary pump electrode 51) and heater 72 of sensor element 101 or A predetermined control circuit is connected so that the current can be controlled and the voltage and current of each electrode can be measured. In the present embodiment, the control circuit as shown in FIG. 1 is connected as in the case of using as the gas sensor 100. More specifically, the variable power sources 24, 46, 52, the detectors for the pump currents Ip 1, Ip 2, the electromotive forces V 0, V 1, V 2, Vref, and the control unit that controls the feedback control and the heater 72 described above. A control circuit provided with the above is connected. The sensor element 101 and the control circuit are connected via the connector electrode of the sensor element 101 described above. Further, the connector electrode and the control circuit may be connected using a connector or a lead wire used as a part of the gas sensor 100.

Next, step (a) described above is performed. First, the sensor element 101 is exposed to an oxygen-existing atmosphere. Here, the oxygen-existing atmosphere is an atmosphere in which molecules containing oxygen (O) in a chemical formula are present, such as O ₂ , CO, CO ₂ , NOx, and H ₂ O. In this embodiment, the oxygen atmosphere is an air atmosphere. In the present embodiment, an atmospheric atmosphere at normal temperature (for example, 20 ° C.) and normal pressure is used. Next, a process of energizing the heater 72 from the control circuit and a process of starting control of the sensor element 101 by the control circuit are performed. In the present embodiment, energization of the heater 72 is the time for the heater 72 to reach a predetermined target temperature (for example, 800 ° C.) for activating the pump cells 21, 41, 50 and the sensor cells 80 to 83 from the start of energization. Was performed in accordance with a temperature rising pattern determined in advance so as to be 85 seconds. That is, the heater 72 is energized such that the time when 85 seconds have elapsed from the start of energization of the heater 72 is the temperature increase completion time. In addition, the process for starting the control of the sensor element 101 includes at least control for applying the voltage Vp <b> 2 between the outer pump electrode 23 and the measurement electrode 44 to pump out oxygen around the measurement electrode 44. In this embodiment, each feedback control mentioned above is performed, and the same control as the case where it uses as the gas sensor 100 shall be started.

  In FIG. 2, the time T at which the heater 72 is energized is indicated as 0 seconds, the time T after 85 seconds from when the heater 72 is energized is indicated as the temperature rise completion time T1, and the time when the control of the sensor element 101 is started. T is shown as the control start time T2. As shown in FIG. 2, in this embodiment, the control start time T2 is the same as the temperature rise completion time T1. However, the present invention is not limited to this, and the control start time T2 may be before or after the temperature increase completion time T1. Further, the control of the sensor element 101 may be started before the heater 72 is energized. The timing at which the sensor element 101 is exposed to the oxygen-existing atmosphere may be before or after the start of energization of the heater 72, but at least the timing at which the oxygen-existing atmosphere reaches around the measurement electrode 44 at the control start time T2. It is preferable that Alternatively, the sensor element 101 may be exposed to an oxygen-existing atmosphere from the above-described preparatory work such as connection of a control circuit.

  Next, based on the voltage Vp2 at a predetermined measurement time Tm in which the elapsed time from the reference time Tref is 0 second and 65 seconds or less with the later of the temperature increase completion time T1 and the control start time T2 as the reference time Tref. Then, a measurement value A based on the pump current Ip2 flowing between the outer pump electrode 23 and the measurement electrode 44 is obtained. In this embodiment, since the temperature rise completion time T1 and the control start time T2 are the same time, T1 = T2 = Tref. Further, the range in which the elapsed time from the reference time Tref exceeds 0 second and 65 seconds or less is a range in which the time T exceeds 85 seconds and 150 seconds or less with reference to the time when the heater 72 is energized. The measurement time Tm is preferably set to a timing at which the elapsed time from the reference time Tref is 5 seconds or more (in this embodiment, the time T is 90 seconds or more). The measurement time Tm is preferably set to a timing at which the elapsed time from the reference time Tref is 35 seconds or less (in this embodiment, the time T is 120 seconds or less). In the present embodiment, the measurement time Tm is set to a timing at which the elapsed time from the reference time Tref is 15 seconds (time T is 100 seconds). In this embodiment, the value of the pump current Ip2 is obtained as it is as the measured value A. As shown in FIG. 2, since the oxygen around the measurement electrode 44 is pumped out as time elapses from the reference time Tref, the pump current Ip2 decreases as time elapses from the reference time Tref. . The measured value A at the measurement time Tm is a value based on the decreasing pump current Ip2.

  When step (a) is performed as described above, in step (b), an abnormality in the light-off time of the sensor element 101 is determined based on the obtained measurement value A and the predetermined threshold value Aref. In the present embodiment, if the measured value A is equal to or less than the threshold value Aref, it is determined that the light-off time is normal, and if it exceeds the threshold value Aref, it is determined that the light-off time is abnormal.

  The reason why the light-off time abnormality can be determined by the above method will be described. In a normal sensor element (normal product), as shown in FIG. 2, oxygen around the measurement electrode 44 is pumped out as time elapses from the reference time Tref, so that the time elapses from the reference time Tref. The pump current Ip2 changes (decreases). However, in the sensor element 101 (abnormal product) having an abnormality (prolongation) in the light-off time, the rate of decrease in the oxygen concentration around the measurement electrode 44 is slow, so that the pump after the reference time Tref as shown in FIG. The slope of the change (decrease) in the current Ip2 becomes gentle compared to the normal product. This is due to the following reasons. First, the cause of the abnormality in the light-off time is the presence of an oxygen supply source such as an unnecessary space (oxygen pool) in the sensor element 101, or the solid electrolyte (first solid) between the outer pump electrode 23 and the measurement electrode 44. There is an abnormality in the pumping capacity of oxygen of the measuring pump cell 41 composed of the electrolyte layer 4, the spacer layer 5 and the second solid electrolyte layer 6) (the pumping capacity is low). More specific reasons for the pumping capacity abnormality include the case where the activity of the measurement pump cell 41 is still low even when the temperature is raised by the heater 72, or the adhering matter is at least one of the outer pump electrode 23 and the measurement electrode 44. There are some cases. For example, when there is a supply source of oxygen, even if the measurement pump cell 41 pumps out oxygen, oxygen is supplied to the periphery of the measurement electrode 44. Therefore, the change (decrease) in the pump current Ip2 after the reference time Tref The inclination becomes gentle. Further, when the pumping capacity of the measurement pump cell 41 is low, the amount of oxygen pumped around the measurement electrode 44 per unit time is reduced, so that the slope of the change (decrease) in the pump current Ip2 after the reference time Tref is reduced. Be gentle. From the above, the sensor element 101 having an abnormality in the light-off time has a gentler slope of the change (decrease) in the pump current Ip2 than the normal sensor element 101, and as a result, the pump current Ip2 at the measurement time Tm. The values tend to be different (large). Thus, since the measured value A based on the pump current Ip2 has a correlation with the presence or absence of abnormality in the light-off time, the abnormality in the light-off time can be determined based on the measured value A and the threshold value Aref. In the present embodiment, as shown in FIG. 2, the measurement value A exceeds the threshold value Aref by preliminarily determining a threshold value Aref that can discriminate between the measurement value A1 of the normal product and the measurement value A2 of the abnormal product. Whether or not the light is off can be determined depending on whether or not the light is off.

  In the light-off abnormality determination method according to the present embodiment, the measurement value A based on the pump current is obtained at the measurement time Tm where the elapsed time from the reference time Tref is greater than 0 seconds and less than 65 seconds. Therefore, unlike the conventional measurement of the light-off time described with reference to FIG. 5, there is no need to wait for the pump current Ip2 to decrease and stabilize sufficiently (for example, 30 minutes). Therefore, an abnormality in the light-off time can be determined in a short time. By setting the measurement time Tm to be after the reference time Tref (elapsed time exceeds 0 second), an appropriate measurement value A in a state where the pump cell 41 for measurement is activated and oxygen is pumped out is obtained. You can get it. Further, when the oxygen concentration around the measurement electrode 44 is lowered and sufficiently stabilized, that is, when the pump current Ip2 is lowered and sufficiently stabilized, the difference in the pump current Ip2 due to the presence or absence of abnormality in the light-off time is reduced, and the abnormality determination accuracy is reduced. However, if the elapsed time from the reference time Tref is 65 seconds or less, the abnormality can be accurately determined.

Next, a method for manufacturing the gas sensor 100 will be described below. The manufacturing method of the gas sensor 100 of this embodiment is as follows.
A determination step of determining a light-off time abnormality of the sensor element 101 by performing the light-off abnormality determination method of the sensor element described above;
A manufacturing process for manufacturing the gas sensor 100 using the sensor element 101 that is not determined to be abnormal in the determination process;
including.

  First, a preparation process for preparing the sensor element 101 is performed before the determination process. In the preparation step, the already manufactured sensor element 101 may be prepared, or may be prepared by manufacturing the sensor element 101. For example, the sensor element 101 is manufactured as follows.

  First, six green ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconia as a ceramic component are prepared. In this green sheet, a plurality of sheet holes and necessary through holes used for positioning during printing and lamination are formed in advance. In addition, the green sheet to be the spacer layer 5 and the green sheet to be the first solid electrolyte layer 4 are respectively provided with a space serving as a gas circulation part and a space serving as the reference gas introduction space 43 by a punching process or the like in advance. And each corresponding to each of the 1st substrate layer 1, the 2nd substrate layer 2, the 3rd substrate layer 3, the 1st solid electrolyte layer 4, the spacer layer 5, and the 2nd solid electrolyte layer 6, A pattern printing process and a drying process for forming various patterns on the ceramic green sheet are performed. Specifically, the pattern to be formed is, for example, the above-described electrodes, lead wires connected to the respective electrodes, connector electrodes, the air introduction layer 48, the heater unit 70, and the like. Pattern printing is performed by applying a pattern forming paste prepared according to the characteristics required for each object to be formed on a green sheet using a known screen printing technique. The drying process is also performed using a known drying means. When pattern printing / drying is completed, printing / drying processing of an adhesive paste for laminating / bonding the green sheets corresponding to each layer is performed. Then, the green sheets on which the adhesive paste is formed are stacked in a predetermined order while being positioned by the sheet holes, and are pressed by applying predetermined temperature and pressure conditions, thereby performing a pressing process to form a single laminate. The laminated body thus obtained includes a plurality of sensor elements 101. The laminated body is cut and cut into the size of the sensor element 101. Then, the cut laminate is fired at a predetermined firing temperature to obtain the sensor element 101.

  When the sensor element 101 is prepared in the preparation process, a determination process is performed. In the determination step, the light-off abnormality determination method described above is performed to determine whether the sensor element 101 is abnormal based on the measured value A and the threshold value Aref. In the manufacturing process, the gas sensor 100 incorporating the sensor element 101 is assembled using the sensor element 101 that is not determined to be abnormal in the determination process. Specifically, an element sealing body is attached and sealed to the sensor element 101, and a connector and lead wires are attached. In addition, a protective cover is attached to the tip side of the sensor element 101 in the element sealing body. Also. An outer cylinder is attached to the rear end side of the sensor element 101 in the element sealing body, and a lead wire is pulled out from the outer cylinder. In addition, the process of assembling such a sensor element 101 and assembling the gas sensor 100 is publicly known, and is described in, for example, Japanese Patent Application Laid-Open No. 2015-178988.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. Each layer 1-6 of this embodiment is equivalent to the base | substrate of this invention, the measurement electrode 44 is equivalent to a 1st measurement electrode, the outer side pump electrode 23 is equivalent to a 2nd measurement electrode and an outer side electrode, and the heater 72 is a heater. Equivalent to.

  In the light-off abnormality determination method for the sensor element 101 according to the present embodiment described in detail above, a substrate (each layer 1 to 6) made of an oxygen ion conductive solid electrolyte and provided with a gas flow part for introducing a gas to be measured therein. ), A measurement electrode 44 disposed facing the gas circulation part, an outer pump electrode 23 disposed outside the gas circulation part (outside the base), and a heater 72 for heating the base. An abnormality in the light-off time of the sensor element 101 is determined. Specifically, the sensor element 101 is exposed to an oxygen-existing atmosphere, and the measurement value A based on the pump current Ip2 at the measurement time Tm at which the elapsed time from the reference time Tref exceeds 0 seconds and is 65 seconds or less is acquired and measured. An abnormality in the light-off time of the sensor element 101 is determined based on the value A and the threshold value Aref. Thereby, abnormality of the light-off time of the sensor element 101 can be determined in a short time.

  In addition, the measurement time Tm is a timing at which the elapsed time from the reference time Tref is 5 seconds or more. When the elapsed time is 5 seconds or more, the difference in the measured value A (pump current Ip2) at the measurement time Tm due to the presence / absence of an abnormality in the light-off time becomes larger. The measurement time Tm is set to a timing at which the elapsed time from the reference time Tref is 35 seconds or less. If the elapsed time is 35 seconds or less, the measured value A based on the pump current Ip2 before being changed (decreased) and stabilized can be obtained more reliably, so that the abnormality in the light-off time can be determined with higher accuracy. Furthermore, the measurement value A can be acquired more easily by making the oxygen presence atmosphere an air atmosphere. Furthermore, step (a) is performed on the sensor element 101 that is not assembled as the gas sensor 100. As a result, for example, an abnormality can be determined before the gas sensor assembly operation (such as the above-described manufacturing process) is performed. Therefore, when it is determined that there is an abnormality, the assembly operation is wasted or the entire gas sensor 100 needs to be discarded. Can be reduced.

  In addition, according to the method for manufacturing the gas sensor 100 of the present embodiment, the gas sensor 100 is manufactured using the sensor element 101 that is not determined to be abnormal by performing the light-off abnormality determination method for the sensor element 101 of the present embodiment. The yield of the gas sensor 100 is improved. In addition, since the conventional measurement of the light-off time is performed after the gas sensor 100 is assembled, if the measured light-off time is abnormal, the assembly work becomes useless or the entire gas sensor 100 needs to be discarded. In some cases, this can be reduced.

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

  For example, in the above-described embodiment, the measurement value A in step (a) is obtained for the sensor element 101 that is not assembled as the gas sensor 100. However, the present invention is not limited to this. The measurement value A may be acquired after the gas sensor 100 is assembled. In addition, the “state not assembled as the gas sensor 100” means a state before the assembly as the gas sensor 100 is completed, for example, one of a protective cover, a connector, an element sealing body, a lead wire, and an outer cylinder. This includes a state during assembly such as a state in which the part is attached to the sensor element 101. The “state not assembled as the gas sensor 100” includes a state before the gas sensor 100 is assembled and a state where the gas sensor 100 is disassembled after the assembly.

  In the embodiment described above, the temperature increase completion time T1 is the time when 85 seconds have elapsed from the start of energization of the heater 72, but is not limited thereto. The temperature increase completion time T1 may be a time when a predetermined time has elapsed since the start of energization of the heater 72. The predetermined time may be a predetermined time of 85 seconds or less, may be a time determined in the range of 40 to 85 seconds, or may be a predetermined time exceeding 85 seconds. When a predetermined temperature increase pattern is used so that the heater 72 reaches a predetermined target temperature when a predetermined time has elapsed from the start of energization of the heater 72, the time when the predetermined time has elapsed is the temperature increase completion time T1. It becomes. Further, the temperature increase completion time T1 is not limited to the time at which a predetermined time has elapsed from the start of energization of the heater 72. The temperature rise completion time T1 is between the first measurement electrode (measurement electrode 44 in the embodiment described above), the second measurement electrode (outer pump electrode 23 in the embodiment described above), and the first and second measurement electrodes. What is necessary is just the time (including the time which can be considered to be activated) when the pump cell (the measurement pump cell 41 in the above-described embodiment) provided with the solid electrolyte layer (the layers 4 to 6 in the above-described embodiment) is activated. That is, the temperature rise completion time T1 includes a time at which a voltage can be applied between the first and second measurement electrodes and oxygen around the first measurement electrode can be pumped out (a time that can be regarded as possible). ). For example, a time at which a predetermined waiting time has elapsed after the resistance value of the heater 72 reaches a predetermined value may be set as the temperature increase completion time T1. This predetermined value can be determined in advance as a resistance value when the temperature of the heater 72 reaches a predetermined target temperature (for example, 800 ° C.) for activating the pump cell. The predetermined value may be expressed as a resistance value itself, or may be expressed as a ratio (a multiple) of the resistance value of the heater 72 at a predetermined temperature (for example, 25 ° C.). The predetermined waiting time may be 0 seconds, or may be a predetermined value greater than 0 seconds. When the control circuit is connected to the sensor element 101 and step (a) is performed, the control circuit determines whether or not the heating of the heater 72 has been completed (detects completion of the heating). You may provide the determination means. In this case, the time when the temperature increase completion determination unit determines that the temperature increase of the heater 72 has been completed may be set as the temperature increase completion time T1. The temperature increase completion determination unit may be a unit that determines that the temperature increase is completed when a predetermined time has elapsed from the start of energization of the heater 72. The temperature increase completion determination unit may be a unit that determines that the temperature increase is completed when a predetermined waiting time elapses after the resistance value of the heater 72 reaches a predetermined value. In this case, the temperature increase completion determination unit may acquire the voltage applied to the heater 72 and the current flowing through the heater 72, and derive the resistance value of the heater 72 based on the acquired value to perform the determination. In addition, the control circuit may include measurement electrode control means for starting control for pumping out oxygen around the first measurement electrode when the temperature increase completion determination means determines that the temperature increase is completed. In this case, since the control start time T2 is a time after the temperature rise completion time T1, the control start time T2 is always the reference time Tref.

  In the above-described embodiment, the control performed in step (a) is the same control as that used in the gas sensor 100, but is not limited thereto. The control of the sensor element 101 in step (a) only needs to include at least control for pumping out oxygen around the measurement electrode 44 by applying the voltage Vp2 between the outer pump electrode 23 and the measurement electrode 44. For example, at least a part of each feedback control described above may not be performed. For example, at least the process of performing feedback control of the voltage Vp2 of the variable power supply 46 so that the electromotive force V2 becomes a predetermined target value V2 * may be performed, and the other feedback control described above may not be performed. Alternatively, the voltage Vp2 of the variable power supply 46 may be controlled to be constant without performing feedback control, and the measurement value A based on the pump current Ip2 at the measurement time Tm may be acquired.

  In the embodiment described above, the measurement value A based on the pump current Ip2 flowing between the measurement electrode 44 and the outer pump electrode 23 is obtained in the step (a), but the present invention is not limited to this. The measurement value A may be a value based on the oxygen concentration around the measurement electrode 44. For example, a value based on the potential of the measurement electrode 44 may be obtained as the measurement value A. When measuring the electric potential of the measurement electrode 44, you may measure the voltage between the measurement electrode 44 and the electrode arrange | positioned other than a gas distribution | circulation part. For example, a value based on the voltage (electromotive force V2) between the measurement electrode 44 and the reference electrode 42 may be obtained as the measurement value A. In this case, for example, at the control start time T2, the feedback control of the voltage Vp2 is started so that the pump current Ip2 becomes the predetermined target value Ip2 *, or the control to make the voltage Vp2 constant is started, and the measurement electrode 44 Peripheral oxygen is pumped out, and a measured value A (for example, the value of the electromotive force V2 itself) based on the electromotive force V2 at the measurement time Tm may be obtained. Also in this case, the electromotive force V2 changes with the passage of time from the reference time Tref, and the slope of this change tends to vary depending on whether the light-off time of the sensor element 101 is abnormal. Therefore, even when the measurement value A based on the electromotive force V2 is obtained, the abnormality in the light-off time can be determined based on the measurement value A and the predetermined threshold as in the above-described embodiment.

  In the above-described embodiment, the control for applying the voltage Vp2 between the measurement electrode 44 and the outer pump electrode 23 is started at the control start time T2. That is, the first measurement electrode was used as the measurement electrode 44 and the second measurement electrode was used as the outer pump electrode 23, and control was performed to apply a voltage therebetween. However, the present invention is not limited to this, and it is only necessary to control the pumping of oxygen from the periphery of the first measurement electrode (measurement electrode 44) by applying a voltage between the first and second measurement electrodes. Therefore, the second measurement electrode is not limited to the outer pump electrode 23 as long as the second measurement electrode is an electrode disposed other than the gas flow part. For example, the second measurement electrode does not communicate with the gas flow part, and is arranged facing the reference gas space into which a reference gas (for example, the atmosphere or an atmosphere containing oxygen having a predetermined partial pressure) is introduced. It may be. For example, the second measurement electrode may be the reference electrode 42 disposed facing the atmosphere introduction layer 48 in the above-described embodiment. In this case, the control to apply the voltage V between the measurement electrode 44 and the reference electrode 42 is started at the control start time T2, the oxygen around the measurement electrode 44 is pumped into the atmosphere introduction layer 48, and the measurement at the measurement time Tm is performed. A measured value A based on the pump current I between the electrode 44 and the reference electrode 42 (for example, the value of the pump current I itself) may be obtained. In this case, the control for applying the voltage V between the measurement electrode 44 and the reference electrode 42 is performed, for example, so that the voltage V3 between the measurement electrode 44 and the outer pump electrode 23 becomes a predetermined target value V3 *. Alternatively, the voltage V may be feedback controlled by a variable power supply, or the voltage V may be controlled to be constant. Also in this case, the pump current I changes with the passage of time from the reference time Tref, and the slope of this change tends to differ depending on whether the light-off time of the sensor element 101 is abnormal. Therefore, even if the measurement value A based on the pump current I is obtained, the abnormality of the light-off time can be determined based on the measurement value A and the predetermined threshold value as in the above-described embodiment. Further, the control for applying the voltage V between the measurement electrode 44 and the reference electrode 42 is started at the control start time T2, the oxygen around the measurement electrode 44 is pumped into the atmosphere introduction layer 48, and the measurement electrode at the measurement time Tm is measured. A measured value A based on 44 potentials may be obtained. Specifically, for example, a value based on the voltage V3 between the measurement electrode 44 and the outer pump electrode 23 (for example, the value of the voltage V3 itself) may be obtained as the measurement value A. In this case, for example, the control for applying the voltage V between the measurement electrode 44 and the reference electrode 42 is such that the pump current I between the measurement electrode 44 and the reference electrode 42 becomes a predetermined target value I *. Alternatively, the voltage V may be feedback controlled by a variable power supply, or the voltage V may be controlled to be constant. Also in this case, the voltage V3 changes with the passage of time from the reference time Tref, and the slope of this change tends to vary depending on whether the light-off time of the sensor element 101 is abnormal. Therefore, even when the measurement value A based on the voltage V3 is obtained, the abnormality in the light-off time can be determined based on the measurement value A and the predetermined threshold value as in the above-described embodiment.

  In the embodiment described above, the oxygen-existing atmosphere is an air atmosphere. However, the present invention is not limited to this, and any atmosphere including molecules containing oxygen (O) in the chemical formula notation may be used as described above. For example, the oxygen presence atmosphere may be an atmosphere that simulates exhaust gas (for example, an atmosphere containing at least NOx). Note that, for example, compared with an atmosphere simulating exhaust gas, since the oxygen concentration is higher in the air atmosphere, the slope of the decrease in the pump current Ip2 from the reference time Tref shown in FIG. 2 is normal and abnormal. It tends to be moderate. Therefore, in the air atmosphere, the difference between the pump current Ip2 at the measurement time Tm between the normal product and the abnormal product tends to be large, and it is easy to determine the abnormality using the threshold value Aref. The same applies to the case where the measurement value A based on other values (for example, the above-described electromotive force V2, current I, voltage V3) other than the pump current Ip2 is obtained.

  In the embodiment described above, the value of the pump current Ip2 is obtained as it is as the measured value A, but the measured value A may be a value based on the pump current Ip2. For example, the measured value A may be a value corresponding to the NOx concentration [ppm] derived based on the pump current Ip2. Further, based on a value obtained by multiplying the pump current Ip2 by a predetermined coefficient, a value obtained by substituting the pump current Ip2 into a predetermined formula, and a predetermined map or table representing the correspondence relationship between the pump current Ip2 and the measured value A. The derived value or the value derived based on the reciprocal of the pump current Ip2 may be used as the measured value A. The same applies to the case where the measurement value A based on other values (for example, the above-described electromotive force V2, current I, voltage V3) other than the pump current Ip2 is obtained.

  In the above-described embodiment, after the manufacturing process of the gas sensor 100, for example, the conventional light-off time measurement as shown in FIG. 5 may or may not be performed. In addition, the time can be shortened by not performing the measurement of the conventional light-off time. Further, when a plurality of gas sensors 100 are manufactured, the measurement of the light-off time may be omitted for some gas sensors 100.

In the embodiment described above, the sensor element 101 of the gas sensor 100 includes the first internal space 20, the second internal space 40, and the third internal space 61, but is not limited thereto. For example, the third internal space 61 may not be provided. FIG. 3 is a schematic cross-sectional view schematically showing an example of the configuration of the sensor element 101 of the gas sensor 100 according to the modification in this case. As shown in the figure, in the gas sensor 100 of this modified example, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion rate controlling part 11, The buffer space 12, the second diffusion rate limiting unit 13, the first internal space 20, the third diffusion rate limiting unit 30, and the second internal space 40 are formed adjacent to each other in this order. . The measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 in the second internal space 40. The measurement electrode 44 is covered with a fourth diffusion rate controlling part 45. The fourth diffusion control part 45 is a film made of a ceramic porous body such as alumina (Al ₂ O ₃ ). The fourth diffusion rate limiting unit 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, similarly to the fourth diffusion rate limiting unit 60 of the embodiment described above. The fourth diffusion rate controlling part 45 also functions as a protective film for the measurement electrode 44. The ceiling electrode portion 51 a of the auxiliary pump electrode 51 is formed up to just above the measurement electrode 44. Even with the gas sensor 100 having such a configuration, an abnormality can be determined in a short time using the light-off time abnormality determination method of the above-described embodiment.

  In the embodiment described above, the sensor element 101 may include a porous protective layer that covers at least a part of the base (for example, the tip side). The porous protective layer may include, for example, ceramic particles of at least one of alumina, zirconia, spinel, cordierite, titania, and magnesia as constituent particles. The porous protective layer may also cover the outer pump electrode 23.

  In the embodiment described above, the sensor element 101 detects the NOx concentration in the gas to be measured. However, the sensor element 101 is not limited to this as long as it detects the concentration of the specific gas in the gas to be measured. For example, the oxygen concentration in the gas to be measured may be detected.

  Hereinafter, an example in which the light-off abnormality determination method for the sensor element of the present invention is performed will be described as an example. In addition, this invention is not limited to a following example.

[Production of sensor element]
A plurality of sensor elements 101 shown in FIG. 1 were produced according to the preparation steps of the method for manufacturing the gas sensor 100 of the above-described embodiment. The sensor element 101 has a length in the front-rear direction of 67.5 mm, a width in the left-right direction of 4.25 mm, and a thickness in the vertical direction of 1.45 mm. In producing the sensor element 101, the ceramic green sheet was formed by mixing zirconia particles to which 4 mol% of a stabilizer yttria was added, an organic binder, and an organic solvent, and then forming a tape.

[Acquisition of measured value A]
About each of the some sensor element 101 produced above, the light-off abnormality determination method of the sensor element 101 mentioned above was performed, and the measured value A was acquired. The measured value A was the same as the pump current Ip2. Further, the temperature rise completion time T1, the control start time T2, and the reference time Tref are the same time T = 85 seconds as in FIG. 2, and the measurement time Tm is 90 seconds to 160 seconds (the elapsed time from the reference time Tref is 5 seconds to 75 seconds). The measured value A was acquired 10 times for each sensor element 101 (measured 80 times for each sensor element 101).

[Measurement of light-off time]
The gas sensor 100 was assembled using each of the plurality of sensor elements 101 after obtaining the measurement value A, and the conventional light-off time described with reference to FIG. 5 was measured for each of the plurality of gas sensors 100 after assembly. The atmosphere at the time of measurement was an atmosphere simulating exhaust gas. In order to simulate the exhaust gas burned with excess oxygen, specifically, the atmosphere was adjusted to an oxygen concentration of 10%, a NOx concentration of 100 ppm, a moisture content of 9%, and a gas temperature of 125 ° C. Also, unlike FIG. 5, the value of the pump current Ip2 15 minutes (900 seconds) after the start of heater energization is regarded as the saturation value Is, and the time when the pump current becomes Is ± 30 ppm is derived as the light-off time. did. The derived sensor element 101 having a light-off time of 100 seconds or less was determined to be normal, and the sensor element 101 exceeding 100 seconds was determined to be abnormal.

[Evaluation of relationship between presence / absence of light-off time and measured value A]
Four gas sensors 100 with normal light-off times (100 seconds or less) are extracted from the plurality of gas sensors 100 whose light-off times have been measured as described above. 1-No. It was set to 4. And about the sample of these four sensor elements 101, the value of the measured value A measured before the assembly of the gas sensor 100 as mentioned above is totaled, and the maximum value of the measured value A, an average value, minimum The value was derived. In addition, each result when the measurement time Tm is changed in units of 10 seconds from 90 seconds to 160 seconds is aggregated separately, and the maximum value, the average value, and the minimum value of the measurement value A are calculated for each value of the measurement time Tm. Derived. For example, when the measurement time Tm is 90 seconds, the maximum value, the average value, and the minimum value are obtained by totaling 10 times each of the four sensor elements 101 (data of 40 measurement values A in total). Derived. Similarly, eight gas sensors 100 having an abnormal light-off time (exceeding 100 seconds) are extracted, and the sensor element 101 of the gas sensor 100 is referred to as sensor element No. 5-No. It was set to 12. For these eight sensor element 101 samples, the results when the measurement time Tm is changed in units of 10 seconds from 90 seconds to 160 seconds are divided and summed up for each value of the measurement time Tm. The maximum value, average value, and minimum value of the measured value A were derived.

  Sensor element No. 1-No. Table 1 shows the light-off time measured after assembling 12 and the determination results of normality and abnormality. Sensor element No. with normal light-off time 1-No. Table 2 shows the relationship between the measurement time Tm 4 and the maximum, average, and minimum values of the measurement value A. Sensor element No. with abnormal light-off time 5-No. Table 3 shows the relationship between the twelve measurement times Tm and the maximum, average, and minimum values of the measurement value A. In Tables 2 and 3, the elapsed time from the reference time Tref (= 85 seconds) is also shown together with the measurement time Tm. FIG. 4 is a graph showing the relationship between the measurement time Tm and the distribution of the measurement values A of the plurality of sensor elements 101. FIG. 4 is a graph showing the relationship between the maximum value, the average value, and the minimum value of the measured value A of the normal product shown in Table 2 with a solid line, and the maximum value of the measured value A of the abnormal product shown in Table 3. A graph showing the relationship between the average value and the minimum value is shown by a broken line.

  As can be seen from Tables 2 and 3 and FIG. 4, it was confirmed that the abnormal product tended to have a larger measured value A (pump current Ip2) than the normal product. Further, when the measurement time Tm is 160 seconds (the elapsed time from the reference time Tref is 75 seconds), the maximum value of the measurement value A of the normal product exceeds the minimum value of the measurement value A of the abnormal product. The range of measured value A and the range of measured value A of the abnormal product partially overlapped, but the measurement time Tm was 90 seconds to 150 seconds (the elapsed time from the reference time Tref was 5 seconds to 65 seconds) ), The range of both did not overlap. Therefore, when the measurement time Tm is 150 seconds or less (the elapsed time from the reference time Tref is 65 seconds or less), the threshold value Aref for discriminating between the measurement value A of the normal product and the measurement value A of the abnormal product is between the ranges. It was confirmed that the presence or absence of abnormality can be determined based on the measured value A and the threshold value Aref. In addition, the smaller the measurement time Tm (the smaller the elapsed time from the reference time Tref), the larger the difference between the maximum value of the normal product measurement value A and the minimum value of the abnormal product measurement value A tends to increase. It was. This difference is particularly large when the measurement time Tm is 120 seconds or less (the elapsed time from the reference time Tref is 35 seconds or less). By setting the measurement time Tm to 35 seconds or less from the reference time Tref, It is considered that an abnormality in the light-off time can be determined with higher accuracy.

  DESCRIPTION OF SYMBOLS 1 1st board | substrate layer, 2nd board | substrate layer, 3rd board | substrate layer, 4th 1st solid electrolyte layer, 5 spacer layer, 6 2nd solid electrolyte layer, 10 gas inlet, 11 1st diffusion control part, 12 buffer Space, 13 Second diffusion limiting part, 20 First internal space, 21 Main pump cell, 22 Inner pump electrode, 22a Ceiling electrode part, 22b Bottom electrode part, 23 Outer pump electrode, 24 Variable power supply, 30 Third diffusion limiting part , 40 Second internal space, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 46 Variable power source, 48 Air introduction layer, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode part, 51b Bottom electrode portion, 52 Variable power source, 60 Fourth diffusion rate limiting portion, 61 Third internal space, 70 Heater portion, 71 Heater connector electrode, 72 Heater, 73 Through Hall, 74 Heater insulation layer, 75 Pressure diffusion hole, 80 Oxygen partial pressure detection sensor cell for main pump control, 81 Oxygen partial pressure detection sensor cell for auxiliary pump control, 82 Oxygen partial pressure detection sensor cell for measurement pump control, 83 Sensor cell, 100 Gas sensor, 101 sensor element.

Claims (6)

A substrate comprising an oxygen ion conductive solid electrolyte and having a gas flow part for introducing a gas to be measured provided therein;
A first measuring electrode disposed facing the gas flow part;
A second measurement electrode disposed outside the gas circulation part;
A heater for heating the substrate;
A light-off abnormality determination method for determining an abnormality in a light-off time of a sensor element comprising:
(A) The sensor element is exposed to an oxygen-existing atmosphere, the heater is energized, and a voltage is applied between the first and second measurement electrodes to pump out oxygen around the first measurement electrode. Control is started, and a predetermined measurement time in which the elapsed time from the reference time exceeds 0 second and is 65 seconds or less with the later one of the heating start time of the heater and the control start time at which the control is started as the reference time Obtaining a measurement value based on a pump current flowing between the first and second measurement electrodes based on the voltage, or a measurement value based on the potential of the first measurement electrode;
(B) determining an abnormality in the light-off time of the sensor element based on the measured value obtained in step (a) and a predetermined threshold;
A sensor element light-off abnormality determination method including: In the step (a), the measurement time is set to a timing at which an elapsed time from the reference time is 5 seconds or more.
The sensor element light-off abnormality determination method according to claim 1. In the step (a), the measurement time is set to a timing at which the elapsed time from the reference time is 35 seconds or less.
The sensor element light-off abnormality determination method according to claim 1 or 2. The oxygen presence atmosphere is an air atmosphere.
The light-off abnormality determination method for the sensor element according to claim 1. The step (a) is performed on a sensor element that is not assembled as a gas sensor.
The light-off abnormality determination method of the sensor element of any one of Claims 1-4. A determination step of determining an abnormality in the light-off time of the sensor element by performing the light-off abnormality determination method of the sensor element according to any one of claims 1 to 5.
A manufacturing process for manufacturing a gas sensor using a sensor element that has not been determined to be abnormal in the determination process;
The manufacturing method of the gas sensor containing this.