Gas sensor

Abstract

The gas sensor 100 includes the sensor element 101 and a control device. The control device determines whether or not the update of the sensor element 101 is required based on at least one of the undershoot and the overshoot of the pump current Ip2. In addition, the control device performs the update processing including at least either one of the update-time adjustment pump control processing of controlling the adjustment pump unit (the main pump unit 21 or the auxiliary pump unit 50) in a manner of sucking out more oxygen of the oxygen concentration adjustment chamber (the first internal cavity 20 and the second internal cavity 40) than the usual-time adjustment pump control processing and the update-time measurement pump control processing of controlling the measurement pump unit 41 in a manner of sucking out more oxygen of the third internal cavity 61 than the usual-time measurement pump control processing, in a case where it is determined that the update is required.

Description

Technical Field

[0001] This invention relates to gas sensors. Background Technology

[0002] Previously, gas sensors were known for detecting the concentration of specific gases such as NOx in gases such as automobile exhaust. For example, the NOx sensor described in Patent Document 1 includes an electrochemical pump unit configured to include a solid electrolyte with oxygen ion conductivity and a measuring electrode with NOx reduction capability. This NOx sensor converts NOx gas in the gas to be measured into O2 gas at the measuring electrode, and outputs the NOx concentration in the gas to be measured based on a pump current flowing through the electrochemical pump unit that changes in proportion to the concentration of the converted O2 gas.

[0003] Furthermore, Patent Document 1 describes that in the aforementioned NOx sensor, when the NOx concentration becomes zero, for example, during a fuel cut-off that stops fuel supply to the engine, the output signal of the NOx concentration experiences a temporary, excessively low undershoot compared to the ideal signal. If such an undershoot occurs, the accuracy of NOx concentration measurement easily deteriorates, thus it is undesirable. Patent Document 2 describes that the above phenomenon is caused by changes in the moisture content of the gas being measured. Additionally, Patent Document 1 describes that by subjecting the NOx sensor's sensor element to a fuel-rich atmosphere at a temperature of 500°C or higher for at least 15 minutes, the undershoot can be suppressed. This fuel-rich atmosphere is a hydrocarbon-containing gas atmosphere with an NO concentration of 0.05% to 1.0% by volume and an excess air ratio (λ) of 0.80 to 0.9999.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-190939

[0007] Patent Document 2: International Publication No. 2008 / 038773 Summary of the Invention

[0008] However, even for gas sensors that do not experience the aforementioned pump current undershoot during manufacturing, undershoot can sometimes increase with use. Similarly, overshoot can sometimes increase with the use of gas sensors.

[0009] The present invention was made to solve the above-mentioned problems, and its main objective is to suppress the increase in undershoot and overshoot of the measuring pump current that occurs with the use of gas sensors.

[0010] The present invention employs the following means to achieve the aforementioned main objectives.

[0011] [1] The gas sensor of the present invention includes: a sensor element, a specific gas concentration detection unit, a do-or-not determination unit, and an update control unit.

[0012] The sensor element has:

[0013] The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and has a gas flow section inside for introducing and circulating the gas to be measured.

[0014] A measuring pump unit has an outer measuring electrode disposed on the outside of the main body of the component in a manner that contacts the gas to be measured, and an inner measuring electrode disposed in a measuring chamber in the gas flow section, wherein oxygen is drawn out from the periphery of the inner measuring electrode to the periphery of the outer measuring electrode.

[0015] An adjustment pump unit is provided to adjust the oxygen concentration in an oxygen concentration adjustment chamber located upstream of the measuring chamber in the gas flow section being measured.

[0016] A reference electrode, disposed inside the element body in such a manner as to contact a detection reference, i.e., a reference gas, of a specific gas concentration in the gas being measured; and

[0017] A voltage detection sensor unit for measuring voltage is provided, which detects the measuring voltage between the reference electrode and the inner measuring electrode.

[0018] The specific gas concentration detection unit performs normal-time adjustment pump control processing to operate the adjustment pump unit, and normal-time measurement pump control processing to control the measurement pump unit to draw oxygen from the measurement chamber in a manner that makes the measurement voltage of the sensor element reach a target value. Based on the measurement pump current flowing through the measurement pump unit through this normal-time measurement pump control processing, the concentration of the specific gas in the gas to be measured is detected.

[0019] The update determination unit performs update determination processing, that is, it determines whether the sensor element needs to be updated based on at least one of undershoot and overshoot when the current of the measuring pump changes abruptly.

[0020] When the update control unit determines that an update is required using the update-need-to-update determination process, it performs an update process, which includes at least one of the following: an update-time adjustment pump control process that controls the adjustment pump unit to draw out more oxygen from the oxygen concentration adjustment chamber compared to the normal time adjustment pump control process, and an update-time measurement pump control process that controls the measurement pump unit to draw out more oxygen from the measurement chamber compared to the normal time measurement pump control process.

[0021] This gas sensor performs normal adjustment pump control processing to operate the adjustment pump unit, and normal measurement pump control processing to control the measurement pump unit to draw oxygen from the measurement chamber in a manner that makes the measurement voltage of the sensor element reach a target value. Furthermore, based on the measurement pump current flowing through the measurement pump unit through the normal measurement pump control processing, the concentration of a specific gas in the gas being measured is detected. When the gas sensor is used for detecting a specific gas concentration in this way, the undershoot and overshoot during sudden changes in the measurement pump current sometimes increase with use. Therefore, this gas sensor performs an update-needs determination process based on at least one of the undershoot and overshoot during sudden changes in the measurement pump current to determine whether the sensor element needs to be updated; if it is determined that an update is needed, an update process is performed. The update process includes at least one of the following: an update-time adjustment pump control process that controls the adjustment pump unit to draw more oxygen from the oxygen concentration adjustment chamber compared to the normal adjustment pump control process, and an update-time measurement pump control process that controls the measurement pump unit to draw more oxygen from the measurement chamber compared to the normal measurement pump control process. The inventors of this invention have discovered that by performing the above-described update process, it is possible to reduce the undershoot and overshoot that increase with the use of the gas sensor. In this gas sensor, if it is determined that an update is necessary, the update process is performed, thereby suppressing the increase in undershoot and overshoot of the measurement pump current that accompanies the use of the gas sensor.

[0022] Here, the update determination process is not limited to processes based on the measuring pump current itself, but also includes processes based on values ​​that can be converted into or considered as measuring pump current. For example, the update determination process can be performed based on at least one of undershoot and overshoot when the value of a specific gas concentration detected according to the measuring pump current changes abruptly. Furthermore, the specific gas concentration detection unit preferably does not perform the normal operating pump control process during the update process, and more preferably, it does not perform the normal operating adjustment pump control process. During the update process, it is preferable not to perform control such as the measuring pump unit drawing oxygen into the measuring chamber, and more preferably, it does not perform control such as the adjustment pump unit drawing oxygen into the oxygen concentration adjustment chamber.

[0023] [2] Based on the gas sensor described above (the gas sensor described in [1] above), the update process may include the update-time adjustment pump control process. Compared with the update-time measurement pump control process, the update-time adjustment pump control process is more effective in updating the sensor element. Therefore, by performing at least the update-time adjustment pump control process in the update process, the effect of suppressing undershoot and overshoot of the measurement pump current can be improved, and the update process can be performed in a shorter time. In this case, the update process may not include the update-time measurement pump control process.

[0024] [3] In this case (based on the gas sensor described in [2] above), the oxygen concentration adjustment chamber may have: a first internal cavity and a second internal cavity configured to be downstream of the first internal cavity and upstream of the measuring chamber; the adjustment pump unit may have: a main pump unit for adjusting the oxygen concentration of the first internal cavity and an auxiliary pump unit for adjusting the oxygen concentration of the second internal cavity; the update adjustment pump control process may include at least one of the following: a process of controlling the main pump unit to draw out more oxygen from the first internal cavity than the normal adjustment pump control process, and a process of controlling the auxiliary pump unit to draw out more oxygen from the second internal cavity than the normal adjustment pump control process.

[0025] [4] Based on the gas sensor described above (the gas sensor described in any one of [1] to [3] above), the gas to be measured may be exhaust gas from an internal combustion engine, and the update determination unit may perform the update determination process based on the behavior of the measuring pump current when the fuel cut-off of the internal combustion engine occurs. Undershoot and overshoot of the measuring pump current are prone to occur when the H2O concentration (moisture) in the gas to be measured changes abruptly. Furthermore, the H2O concentration is more likely to change abruptly when the fuel cut-off of the internal combustion engine occurs. Therefore, by determining the update requirement based on the behavior (at least one of undershoot or overshoot) of the measuring pump current when the fuel cut-off of the internal combustion engine occurs, it is possible to more appropriately determine whether an update is needed.

[0026] [5] Based on the gas sensor described above (the gas sensor described in any one of [1] to [4] above), the determination unit may determine that the update is required when at least one of the undershoot and overshoot during the sudden change of the pump current deviates from the allowable range. Accordingly, it is possible to appropriately determine whether an update is required based on at least one of the undershoot and overshoot.

[0027] [6] Based on the gas sensor described above (the gas sensor described in any of [1] to [5] above), the update control unit may perform the update process when it is considered that the gas to be measured in the gas flow section contains carbon. Here, the update process needs to be performed when the gas to be measured contains carbon. Therefore, by performing the update process when it is considered that the gas to be measured in the gas flow section contains carbon, the update can be performed effectively. Accordingly, for example, it is less likely that even if the update process is performed, the undershoot and overshoot will not decrease and a new update process is required. Here, "the gas to be measured contains carbon" also includes the case where the gas to be measured contains molecules containing carbon. For example, if the gas to be measured contains one or more of carbon (C), carbon monoxide (CO), carbon dioxide (CO2), and hydrocarbons (HC), it can be said that the gas to be measured contains carbon.

[0028] [7] Based on the gas sensor described above (the gas sensor described in any of [1] to [6] above), the processing time of the update process can be 1 second or more and 10 seconds or less. By making the processing time 1 second or more, the sensor element can be updated more reliably. In addition, even if the update process is performed for a long period of time, the update effect does not increase much, and the update effect is relatively high in the first 10 seconds from the start. In addition, the specific gas concentration cannot be correctly detected during the update process, so the processing time of the update process is preferably shorter. By making the processing time 10 seconds or less, the time during which the specific gas concentration cannot be correctly detected can be shortened, and the sensor element can be updated efficiently. Attached Figure Description

[0029] Figure 1 This is a cross-sectional schematic diagram of the gas sensor 100.

[0030] Figure 2 This is a block diagram showing the electrical connections between the control device 90 and each unit and heater 72.

[0031] Figure 3 It is a graph showing the undershoot and overshoot of the pump current Ip2.

[0032] Figure 4 It is a graph showing the increase in undershoot and overshoot of the pump current Ip2 in sensor element 101.

[0033] Figure 5 It is a graph showing the undershoot and overshoot before and after the update process.

[0034] Figure 6 It is a graph showing the relationship between the processing time of the update process and the effect of reducing the downstroke.

[0035] Figure 7 This is a flowchart illustrating an example of a control routine.

[0036] Figure 8 This is a schematic cross-sectional view of the sensor element 201 as an example.

[0037] Figure 9 It is a graph showing the relationship between the processing time of the update process and the effect of reducing the downstroke. Detailed Implementation

[0038] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a schematic cross-sectional view showing an example of the structure of a gas sensor 100 as one embodiment of the present invention. Figure 2 This is a block diagram showing the electrical connections between the control device 90, each unit, and the heater 72. The gas sensor 100 is installed in piping such as the exhaust pipe of an internal combustion engine, such as a gasoline engine or a diesel engine. The gas sensor 100 detects the concentration of specific gases such as NOx in the exhaust gas of the internal combustion engine. The gas sensor 100 includes: a sensor element 101, which is a long rectangular parallelepiped; units 21, 41, 50, 80-83, which are configured as part of the sensor element 101; a heater unit 70 disposed inside the sensor element 101; and a control device 90 that controls the entire gas sensor 100.

[0039] The sensor element 101 is a stacked element comprising six layers arranged in the following order from bottom to top in the accompanying drawings: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an insulating layer 5, and a second solid electrolyte layer 6, each containing an oxygen ion-conducting solid electrolyte such as zirconium oxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense and gas-tight solid electrolyte. For example, the sensor element 101 is manufactured by performing a prescribed process and printing circuit patterns on ceramic green sheets corresponding to each layer, then stacking them, and finally firing them to achieve integration.

[0040] At the front end side of sensor element 101 ( Figure 1 The gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, the second diffusion rate control unit 13, the first internal cavity 20, the third diffusion rate control unit 30, the second internal cavity 40, the fourth diffusion rate control unit 60, and the third internal cavity 61 are formed adjacently in a connected manner in this order between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4.

[0041] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are spaces inside the sensor element 101 provided by cutting through the isolation layer 5. The upper part of the space is formed by the lower surface of the second solid electrolyte layer 6, the lower part of the space is formed by the upper surface of the first solid electrolyte layer 4, and the side part of the space is formed by the side of the isolation layer 5.

[0042] The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are all configured as two horizontally elongated slits (the length direction of the opening is perpendicular to the drawing). Furthermore, the fourth diffusion rate control unit 60 is configured as a single horizontally elongated slit (the length direction of the opening is perpendicular to the drawing) formed as a gap between itself and the lower surface of the second solid electrolyte layer 6. Additionally, the portion from the gas inlet 10 to the third internal cavity 61 is referred to as the measured gas flow section.

[0043] Furthermore, a reference gas introduction space 43 is provided at a position further away from the front end of the gas flow section, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position where the side is divided by the side of the first solid electrolyte layer 4. For example, atmospheric air is introduced into the reference gas introduction space 43 as a reference gas for NOx concentration measurement.

[0044] The atmosphere introduction layer 48 is a layer made of porous ceramic, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43. In addition, the atmosphere introduction layer 48 is formed to cover the reference electrode 42.

[0045] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, an atmospheric inlet layer 48 communicating with the reference gas inlet space 43 is provided around it. Furthermore, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) within the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a Pt and ZrO2 metal-ceramic electrode).

[0046] Regarding the gas flow section, the gas inlet 10 is an opening relative to the external space through which the gas to be measured enters the sensor element 101 from the external space. The first diffusion rate control unit 11 is a section that applies a predetermined diffusion resistance to the gas to be measured entering from the gas inlet 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13. The second diffusion rate control unit 13 is a section that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas that rapidly enters the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (in the case of exhaust gas from a car, the fluctuations in exhaust pressure) is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 only after the pressure fluctuations are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the pressure fluctuations of the gas introduced into the first internal cavity 20 are negligible. The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust this oxygen partial pressure.

[0047] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between these electrodes. The inner pump electrode 22 has a top electrode portion 22a disposed on the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20. The outer pump electrode 23 is disposed such that the area on the upper surface of the second solid electrolyte layer 6 corresponding to the top electrode portion 22a is exposed to the external space.

[0048] The inner pump electrode 22 is formed as follows: a solid electrolyte layer (a second solid electrolyte layer 6 and a first solid electrolyte layer 4) spanning the upper and lower parts of the first internal cavity 20, and an isolation layer 5 forming the sidewall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 forming the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 forming the bottom surface. Furthermore, side electrode portions (not shown) are formed on the sidewall surfaces (inner surfaces) of the isolation layers 5 forming the two sidewall portions of the first internal cavity 20. The top electrode portion 22a and the bottom electrode portion 22b are connected, and the side electrode portions are arranged in a tunnel-like structure.

[0049] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous metal-ceramic electrodes (e.g., metal-ceramic electrodes of Pt and ZrO2 containing 1% Au). It should be noted that the inner pump electrode 22, which is in contact with the gas being measured, is formed using a material whose reducing ability against NOx components in the gas being measured is weakened.

[0050] Regarding the main pump unit 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, causing the pump current Ip0 to flow between the inner pump electrode 22 and the outer pump electrode 23 in either a positive or negative direction. This allows oxygen in the first internal cavity 20 to be drawn out to the external space, or oxygen in the external space to be drawn into the first internal cavity 20.

[0051] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, namely the main pump control oxygen partial pressure detection sensor unit 80, is composed of the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0052] The oxygen concentration (oxygen partial pressure) within the first internal cavity 20 is determined by measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control. Furthermore, the pump voltage Vp0 of the variable power supply 24 is controlled by feedback to ensure that the voltage V0 reaches a target value, thereby controlling the pump current Ip0. Thus, the oxygen concentration within the first internal cavity 20 can be maintained at a predetermined constant value.

[0053] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20, thereby guiding the gas to be measured into the second internal cavity 40.

[0054] The second internal cavity 40 is configured as a space for performing the following process: for the gas to be measured, which has had its oxygen concentration (oxygen partial pressure) pre-adjusted in the first internal cavity 20 and then introduced through the third diffusion rate control unit 30, the oxygen partial pressure is further adjusted using the auxiliary pump unit 50. As a result, the oxygen concentration within the second internal cavity 40 can be kept constant with high precision, thus enabling the gas sensor 100 to achieve high-precision measurement of NOx concentration.

[0055] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit consisting of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode outside the sensor element 101), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a disposed on the lower surface of the second solid electrolyte layer 6 and facing the second internal cavity 40.

[0056] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner pump electrode 22 previously disposed in the first internal cavity 20. Specifically, a top electrode portion 51a is formed relative to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Side electrode portions (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b are formed on the two wall surfaces of the isolation layer 5 constituting the sidewall of the second internal cavity 40, thereby forming a tunnel-shaped structure. Furthermore, similar to the inner pump electrode 22, the auxiliary pump electrode 51 is also formed using a material that reduces the reducing power of NOx components in the measured gas.

[0057] Regarding the auxiliary pump unit 50, a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23, thereby enabling oxygen in the atmosphere within the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn in from the external space into the second internal cavity 40.

[0058] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 81 for auxiliary pump control, is constructed from the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, and the third substrate layer 3.

[0059] Furthermore, the auxiliary pump unit 50 utilizes a variable power supply 52 for pumping, and the voltage of this variable power supply 52 is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. As a result, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that substantially has no impact on NOx measurement.

[0060] In addition, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and its voltage V0 is controlled to the aforementioned target value, thereby controlling the gradient of oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 to remain constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

[0061] The fourth diffusion rate control unit 60 is configured to apply a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled in the second internal cavity 40 by the operation of the auxiliary pump unit 50, and to guide the gas to be measured into the third internal cavity 61. The fourth diffusion rate control unit 60 is responsible for limiting the amount of NOx flowing into the third internal cavity 61.

[0062] The third internal cavity 61 is configured as a space for performing the following process: measuring the concentration of nitrogen oxides (NOx) in a gas to be measured, which has had its oxygen concentration (oxygen partial pressure) pre-adjusted in the second internal cavity 40 and then introduced through the fourth diffusion rate control unit 60. The NOx concentration is primarily measured in the third internal cavity 61 by the operation of the measuring pump unit 41.

[0063] The measuring pump unit 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61. The measuring pump unit 41 is an electrochemical pump unit composed of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4, facing the third internal cavity 61. The measuring electrode 44 is a porous metal-ceramic electrode made of a material with improved reduction capability for NOx components in the gas to be measured compared to the inner pump electrode 22. The measuring electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere within the third internal cavity 61.

[0064] Specifically, the measuring electrode 44 is an electrode containing at least one of Pt and Rh, which are noble metals with catalytic activity. The measuring electrode 44 is preferably an electrode formed of a cermet containing at least one of Pt and Rh and an oxide (here, ZrO2) with oxygen ion conductivity. Furthermore, the measuring electrode 44 is preferably a porous material. In this embodiment, the measuring electrode 44 is a porous cermet electrode of Pt, Rh, and ZrO2.

[0065] Regarding the measuring pump unit 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 can be drawn out and its generation amount can be detected as pump current Ip2.

[0066] In addition, in order to detect the oxygen partial pressure around the measuring electrode 44, an electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 82 for measuring pump control, is constructed from the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control.

[0067] The gas to be measured, introduced into the second internal cavity 40, reaches the measuring electrode 44 in the third internal cavity 61 through the fourth diffusion rate control unit 60 under controlled oxygen partial pressure. Nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. This generated oxygen is pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled in a manner that keeps the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control constant (target value). The amount of oxygen generated around the measuring electrode 44 is directly proportional to the concentration of nitrogen oxides in the gas to be measured; therefore, the concentration of nitrogen oxides in the gas to be measured is calculated using the pump current Ip2 in the measuring pump unit 41.

[0068] In addition, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23 and the reference electrode 42. The oxygen partial pressure in the gas to be measured outside the sensor can be detected based on the electromotive force (voltage Vref) obtained by the sensor unit 83.

[0069] Regarding the gas sensor 100 with such a structure, the gas to be measured, which operates the main pump unit 21 and the auxiliary pump unit 50 to keep the oxygen partial pressure at a constant low value (a value that has no substantial effect on the determination of NOx), is supplied to the measuring pump unit 41. Therefore, the NOx concentration in the gas to be measured can be determined based on the pump current Ip2, which is approximately proportional to the NOx concentration in the gas to be measured and flows due to the absorption of oxygen generated by the reduction of NOx by the measuring pump unit 41.

[0070] In addition, the sensor element 101 includes a heater section 70, which performs temperature regulation functions to heat and maintain the sensor element 101, thereby improving the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulation layer 74, and a pressure relief hole 75.

[0071] The heater connector electrode 71 is formed in a manner that contacts 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 section 70 from the outside.

[0072] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from the top and bottom. The heater 72 is connected to the heater connector electrode 71 via a through-hole 73, and receives power from the heater power supply 76 (see reference 76) through this heater connector electrode 71. Figure 2 The power supply generates heat, thereby heating and keeping the solid electrolyte forming the sensor element 101 warm.

[0073] In addition, the heater 72 is embedded in the entire area from the first internal cavity 20 to the third internal cavity 61, which can adjust the entire sensor element 101 to the temperature that activates the solid electrolyte.

[0074] The heater insulation layer 74 is an insulation layer formed on the upper and lower surfaces of the heater 72 by an insulator such as alumina. The purpose of forming the heater insulation layer 74 is to achieve 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.

[0075] The pressure relief hole 75 is a portion that is configured to penetrate the third substrate layer 3 and the atmospheric inlet layer 48 and communicate with the reference gas inlet space 43. The purpose of forming the pressure relief hole 75 is to mitigate the increase in internal pressure that accompanies the temperature rise in the heater insulation layer 74.

[0076] like Figure 2As shown, the control device 90 includes: the aforementioned variable power supplies 24, 46, and 52, the heater power supply 76, and a control unit 91. The control unit 91 is a microprocessor equipped with a CPU 92 and a storage unit 94. The storage unit 94 is, for example, a device capable of storing various programs and various data. The control unit 91 is input to the voltage V0 detected by the oxygen partial pressure detection sensor unit 80 for main pump control, the voltage V1 detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control, the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control, the voltage Vref detected by the sensor unit 83, the pump current Ip0 detected by the main pump unit 21, the pump current Ip1 detected by the auxiliary pump unit 50, and the pump current Ip2 detected by the measuring pump unit 41. In addition, the control unit 91 outputs control signals to the variable power supplies 24, 46, and 52, thereby controlling the pump voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 46, and 52, and thus controlling the main pump unit 21, the measuring pump unit 41, and the auxiliary pump unit 50. The control unit 91 also outputs control signals to the heater power supply 76, thereby controlling the power supplied by the heater power supply 76 to the heater 72. The storage unit 94 also stores target values ​​V0*, V0r*, V1*, V1r*, V2*, and V2r*, which will be described later. The CPU 92 of the control unit 91 refers to these target values ​​V0*, V0r*, V1*, V1r*, V2*, and V2r* to control each unit 21, 41, and 50.

[0077] The control unit 91 performs normal auxiliary pump control processing on the auxiliary pump unit 50 to ensure that the oxygen concentration in the second internal cavity 40 reaches a target concentration. Specifically, the control unit 91 performs feedback control on the voltage Vp1 of the variable power supply 52 to ensure that the voltage V1 reaches a constant value (referred to as the target value V1*), thereby controlling the auxiliary pump unit 50. The target value V1* is defined as a value in which the oxygen concentration in the second internal cavity 40 reaches a specified low concentration that has no substantial impact on the determination of NOx.

[0078] The control unit 91 performs normal-time main pump control processing on the main pump unit 21 so that the pump current Ip1 flowing through the auxiliary pump unit 50 adjusts the oxygen concentration in the second internal cavity 40 using normal-time auxiliary pump control processing reaches a target current (referred to as target current Ip1*). Specifically, the control unit 91 sets a target value (referred to as target value V0*) of voltage V0 based on the pump current Ip1 so that the pump current Ip1 flowing due to voltage Vp1 reaches a constant target current Ip1* (feedback control). Furthermore, the control unit 91 performs feedback control on the pump voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0* (that is, so that the oxygen concentration in the first internal cavity 20 reaches the target concentration). Through this normal-time main pump control processing, the gradient of oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 remains constant. The target value V0* is set to a value where the oxygen concentration in the first internal cavity 20 is higher than 0% and is a low oxygen concentration. Furthermore, the pump current Ip0 flowing in the main pump control process under normal conditions changes accordingly with the oxygen concentration of the gas to be measured (i.e., the gas to be measured around the sensor element 101) flowing into the gas to be measured from the gas inlet 10. Therefore, the control unit 91 can also detect the oxygen concentration in the gas to be measured based on the pump current Ip0.

[0079] The aforementioned normal-time main pump control processing and normal-time auxiliary pump control processing are collectively referred to as normal-time adjustment pump control processing. Furthermore, the first internal cavity 20 and the second internal cavity 40 are collectively referred to as oxygen concentration adjustment chambers. The main pump unit 21 and the auxiliary pump unit 50 are collectively referred to as adjustment pump units. The normal-time adjustment pump control processing, performed by the control unit 91, causes the adjustment pump units to adjust the oxygen concentration in the oxygen concentration adjustment chambers.

[0080] Furthermore, the control unit 91 performs normal-time measurement pump control processing on the measurement pump unit 41 in a manner that makes the voltage V2 reach a constant value (referred to as the target value V2*) (that is, in a manner that makes the oxygen concentration in the third internal cavity 61 reach a predetermined low concentration). Specifically, the control unit 91 performs feedback control on the voltage Vp2 of the variable power supply 46 in a manner that makes the voltage V2 reach the target value V2*, thereby controlling the measurement pump unit 41. Through this normal-time measurement pump control processing, oxygen is drawn out from the third internal cavity 61.

[0081] Oxygen is drawn out of the third internal cavity 61 by performing a pump control process for normal measurement, such that the oxygen generated by the reduction of NOx in the measured gas in the third internal cavity 61 is substantially zero. Furthermore, the control unit 91 acquires a pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 from a specific gas (in this case, NOx), and calculates the NOx concentration in the measured gas based on the pump current Ip2.

[0082] The memory 94 stores formulas (e.g., linear functions) and mappings that represent the correspondence between pump current Ip2 and NOx concentration. These formulas or mappings can be determined experimentally in advance.

[0083] Next, the undershoot and overshoot of the pump current Ip2 of sensor element 101 will be explained. Figure 3 It is a graph showing the undershoot and overshoot of the pump current Ip2. Figure 3 The solid line illustrates an example of the pump current Ip2 behavior when the internal combustion engine's fuel is cut off midway through the measurement of the NOx concentration in the gas being measured by the gas sensor 100. The dashed line illustrates the behavior of the ideal pump current Ip2.

[0084] When fuel cutoff begins, the NOx concentration in the measured gas decreases sharply to approximately zero; when fuel cutoff ends, the NOx concentration in the measured gas rises sharply again. Therefore, in principle, as... Figure 3 As shown by the dashed line, the value corresponding to the NOx concentration, i.e., the pump current Ip2, should quickly follow suit and change to the corresponding value when the fuel cut-off begins. Figure 3 (The change from I1 to I0). Furthermore, when the fuel cut-off ends, it should follow suit and change to the corresponding value ( Figure 3 In the middle, the change from I0 to I1). However, in reality, as... Figure 3 As shown by the solid line, the pump current Ip2 exhibits excessive output fluctuations that differ from the actual NOx concentration changes. Specifically, at the start of fuel cutoff, the pump current Ip2 experiences an excessive decrease followed by a rise to a value corresponding to the actual NOx concentration, followed by a falloff. Conversely, at the end of fuel cutoff, the pump current Ip2 experiences an excessive increase followed by a falloff to a value corresponding to the actual NOx concentration, followed by a falloff. For example, such overshoots and undershoots of the pump current Ip2 may not occur in the newly manufactured gas sensor 100; however, as the gas sensor 100 is used, there is a trend towards increasing overshoots and undershoots. For example, as the gas sensor 100 is used, there are... Figure 3The trend of increasing undershoot and overshoot is shown. In particular, such increased undershoot and overshoot is more likely to occur if sensor element 101 is heated to a high temperature by heater 72 and exposed to atmospheric conditions when the vehicle is stationary. It should be noted that undershoot can be calculated, for example, as the difference between the lowest value when pump current Ip2 excessively decreases and the value when pump current Ip2 stabilizes. Overshoot can be calculated, for example, as the difference between the highest value when pump current Ip2 excessively increases and the value when pump current Ip2 stabilizes. Alternatively, undershoot and overshoot can also be calculated as the maximum difference between the value of pump current Ip2 when it experiences excessive output variation and the ideal value of pump current Ip2.

[0085] The inventors of this invention have discovered that by controlling the sensor element 101 to draw out more oxygen from the flow section of the gas being measured compared to when measuring a specific gas concentration (normally), it is possible to reduce the undershoot and overshoot that increase with the use of the gas sensor 100. This process is referred to as a refresh process. Specifically, the refresh process includes at least one of the following: a refresh-time adjustment pump control process that controls the adjustment pump unit to draw out more oxygen from the oxygen concentration adjustment chamber compared to the normal adjustment pump control process, and a refresh-time measurement pump control process that controls the measurement pump unit 41 to draw out more oxygen from the third internal cavity 61 compared to the normal measurement pump control process.

[0086] Regarding the pump control process for update, in this embodiment, the voltage Vp2 of the variable power supply 46 is feedback-controlled so that the voltage V2 reaches a target value V2r* higher than the aforementioned target value V2*. Otherwise, it is the same as the pump control process for normal operation. The voltage V2 is a value related to the oxygen concentration difference between the area around the reference electrode 42 and the third internal cavity 61. The lower the oxygen concentration in the third internal cavity 61, the greater the oxygen concentration difference, and the higher the voltage V2 becomes. Therefore, a target value V2r* higher than the target value V2* means that when performing the pump control process for update, the target value of the oxygen concentration in the third internal cavity 61 is set to a lower value compared to performing the pump control process for normal operation. Therefore, in this pump control process for update, the pump unit 41 is controlled to draw out more oxygen from the third internal cavity 61 compared to the pump control process for normal operation.

[0087] The pump control processing during the update includes at least one of the following: a main pump control processing during the update that controls the main pump unit 21 to draw more oxygen from the first internal cavity 20 compared to the normal main pump control processing, and an auxiliary pump control processing during the update that controls the auxiliary pump unit 50 to draw more oxygen from the second internal cavity 40 compared to the normal auxiliary pump control processing. Regarding the main pump control processing and the auxiliary pump control processing during the update, in this embodiment, similar to the pump control processing for measurement during the update, the target value of the feedback control is set to a higher value than in the normal case. Specifically, the main pump control processing during the update is a process of feedback control of the pump voltage Vp0 of the variable power supply 24 to achieve a predetermined target value V0r* higher than the aforementioned target value V0*. It should be noted that in the normal main pump control processing, the target value V0* is set (changed) based on the pump current Ip1; however, in the main pump control processing during the update, the target value V0r* is not changed based on the pump current Ip1 but uses a predetermined value. During the update, the auxiliary pump control process performs feedback control on the voltage Vp1 of the variable power supply 52 in such a way that the voltage V1 reaches a specified target value V1r* higher than the target value V1*. Otherwise, it is the same as the auxiliary pump control process in normal operation.

[0088] During the update process, it is preferable not to perform the normal measurement pump control process, and more preferably not to perform the normal adjustment pump control process. During the update process, it is preferable not to perform control such as the measurement pump unit 41 drawing oxygen into the third internal cavity 61, and more preferably not to perform control such as the main pump unit 21 drawing oxygen into the first internal cavity 20 or the auxiliary pump unit 50 drawing oxygen into the second internal cavity 40. For example, if the update-time measurement pump control process is performed, the normal measurement pump control process cannot be performed; however, it is preferable not to perform the normal adjustment pump control process either. For example, if the update-time measurement pump control process is performed, it is preferable that the variable power supply 24 and variable power supply 52 are not energized, and the main pump unit 21 and auxiliary pump unit 50 are in an inactive state. Similarly, if the update-time main pump control process is performed, it is preferable that the variable power supply 52 and variable power supply 46 are not energized, and the auxiliary pump unit 50 and measurement pump unit 41 are in an inactive state. When auxiliary pump control is being performed during an update, it is preferable that variable power supplies 24 and 46 are not energized, and the main pump unit 21 and the measuring pump unit 41 are in a non-operational state. Thus, regarding the pump units in the main pump unit 21, auxiliary pump unit 50, and measuring pump unit 41 that are not used for update processing, it is preferable that normal pump control processing and oxygen intake control are not performed, and preferably that the pump units are not operated.

[0089] Figure 4This is a graph showing the increase in undershoot and overshoot of the pump current Ip2 in the actual sensor element 101. The graph is obtained as follows. The sensor element 101 is installed in the piping. Using a model gas device, a model gas (the gas to be measured) is circulated through the piping. In this state, the control device 90 controls the sensor element 101 to measure the NOx concentration. As the model gas, firstly, a first model gas (NO concentration 500 ppm, H2O concentration 12%, oxygen concentration 0%, base gas nitrogen) is circulated; secondly, a second model gas (NO concentration 0 ppm, H2O concentration 0%, oxygen concentration 21%, base gas nitrogen) is circulated; then, the first model gas is circulated again, thereby causing a sudden change in the NO, H2O, and oxygen concentrations of the gas to be measured, simulating a fuel cut-off state. The flow rate of the model gas is 100 L / min, and the temperature is 120°C. Then, the time change of the pump current Ip2 during this period is measured. Figure 4 The dashed line represents the time variation of the pump current Ip2 in the sensor element 101 in the initial state (right after manufacturing). Figure 4 The solid line represents the time variation of the pump current Ip2 in sensor element 101, simulating its state after use from its initial state. The heater 72 is energized and maintained at approximately 700°C to 800°C. Under this condition, sensor element 101 in its initial state is placed in the atmosphere for 5 minutes, thus preparing to simulate the state of sensor element 101 after use. Figure 4 As shown, almost no overshoot or undershoot occurs in the sensor element 101 in the initial state. In contrast, in the sensor element 101 in the simulated state after use, overshoot and undershoot increase.

[0090] Next, for the sensor element 101, which has been simulated to be in a post-use state as described above, an update process is performed as follows. A model gas with a CO2 concentration of 15%, an H2O concentration of 15%, and nitrogen as the base gas is used as the gas to be measured, and it is circulated through the piping on which the sensor element 101 is installed. In this state, as an update process, the main pump control process described above is performed. The target value V0r* for the main pump control process during the update is 1000mV, and the processing time is 300 seconds. During the update process, no voltage is applied to the variable power supply 46 and the variable power supply 52, and the measuring pump unit 41 and the auxiliary pump unit 50 are in an inactive state. For the sensor element 101 after the update process, and... Figure 4 Similarly, the time variation of the pump current Ip2 was measured when simulating a fuel cut-off state. The results are shown below. Figure 5 . Figure 5 The solid line represents the time variation of the pump current Ip2 in sensor element 101 before the update process. Figure 5 The dashed line represents the time variation of the pump current Ip2 in sensor element 101 after the update process. For example... Figure 5 As shown, by performing an update process, undershoot and overshoot are reduced, thereby restoring sensor element 101 to its normal state. Figure 4 The sensor element 101 in the initial state shown is in a state that is substantially the same. It should be noted that, since the undershoot and overshoot are caused by the waveform of the pump current Ip2, the sensor element 101, especially the measuring electrode 44, is updated through an update process.

[0091] Next, with Figure 5 Similarly, when the main pump control is updated as part of the update process, the processing time differs from that of the update process. Figure 5 Similarly, the time variation of pump current Ip2 was measured to investigate the relationship between processing time and the reduction effect on downstroke. Furthermore, the relationship between processing time and the reduction effect on downstroke was similarly investigated for both the auxiliary pump control process during replacement and the measurement pump control process during replacement. The results are presented below. Figure 6 And Table 1. It should be noted that the target value V1r* during the auxiliary pump control processing during the update is 1000mV. During this processing, the main pump unit 21 and the measuring pump unit 41 are in an inactive state. The target value V2r* during the measuring pump control processing during the update is 1000mV. During this processing, the main pump unit 21 and the auxiliary pump unit 50 are in an inactive state. Regarding... Figure 6 The vertical axis is defined by the initial value of the undershoot of sensor element 101 in its initial state (a small value close to zero), and the difference ΔUS between the initial value and the updated undershoot is expressed as a percentage of the initial value. The closer the difference ΔUS is to 0%, the more it means that the undershoot has decreased and sensor element 101 has recovered (updated) to the same state as the initial state. Figure 6 In the diagram, the data processed by the main pump control during the update is represented by a solid line (referred to as "V0" in the example), the data processed by the auxiliary pump control during the update is represented by a dashed line (referred to as "V1" in the example), and the data processed by the measurement pump control during the update is represented by a single-dot dashed line (referred to as "V2" in the example).

[0092] [Table 1]

[0093]

[0094] Depend on Figure 6As shown in Table 1, for sensor element 101 with a processing time of 0 seconds during the update process, i.e., the sensor element 101 simulating the state after use, the difference ΔUS is approximately -450% (the undershoot is approximately 5.5 times the initial value). In contrast, the following trend was confirmed: the longer the processing time, the closer the difference ΔUS is to 0%. Furthermore, it was confirmed that: compared to the case where pump control processing was performed during the update (… Figure 6 Compared to the data represented by "V2" in the explanatory notes of Table 1, the cases where main pump control processing was performed during the update and the cases where auxiliary pump control processing was performed during the update are compared. Figure 6 The difference ΔUS between the data represented by "V0" and "V1" in the examples of Table 1 and the data therein approaches 0% for a short time. That is, it is confirmed that the update-time adjustment pump control process (here, the update-time main pump control process and the update-time auxiliary pump control process) is more effective at updating the sensor element 101 than the update-time measurement pump control process. Therefore, the update process preferably includes the update-time adjustment pump control process. Furthermore, from Figure 6 As shown in Table 1, the following trend was observed: when the processing time is less than 10 seconds, the difference ΔUS approaches 0% sharply, and then approaches 0% relatively slowly. Therefore, it can be concluded that even if the update process is performed for a long time, the update effect does not increase much, and the update effect is relatively high in the first 10 seconds. Therefore, it can be concluded that performing multiple short update processes can efficiently update the sensor element 101 compared to performing a single update process over a long period of time. In addition, the processing time of the update process is preferably more than 1 second.

[0095] Here, the update process needs to be performed in a state where the gas being measured contains carbon within the gas flow section. "The gas being measured contains carbon" also includes cases where the gas being measured contains molecules containing carbon. For example, if the gas being measured contains one or more of carbon (C), carbon monoxide (CO), carbon dioxide (CO2), and hydrocarbons (HC), it can be said that the gas being measured contains carbon. For example, in the above example, the update process was performed using a model gas with a CO2 concentration of 15%, an H2O concentration of 15%, and nitrogen as the base gas. However, when the update process was performed using a model gas that does not contain CO2, no reduction effect on undershoot and overshoot was observed. Furthermore, when the update process was performed using a model gas containing ethylene (C2H4) instead of a model gas that does not contain CO2, a reduction effect on undershoot and overshoot was confirmed.

[0096] The rationale for the effectiveness of the refresh treatment in cases where the measured gas contains carbon is as follows. First, in the initial state (freshly manufactured), the sensor element 101 has at least one of carbon (C), carbon monoxide (CO), and hydrocarbons (HC) adhering to the measuring electrode 44, thus preventing undershoot and overshoot, or reducing undershoot and overshoot. Furthermore, it is believed that as the sensor element 101 is used, the aforementioned substances adhering to the measuring electrode 44 decrease, and undershoot and overshoot increase. Here, if the refresh treatment is performed, more oxygen in the measured gas within the measured gas flow section is adsorbed compared to normal conditions, creating a reducing atmosphere. Accordingly, carbon dioxide (CO2) in the measured gas is reduced to produce carbon (C) and carbon monoxide (CO), or the oxidation of carbon (C) and carbon monoxide (CO) in the measured gas to produce carbon dioxide (CO2) is suppressed. Therefore, it is believed that by performing the refresh treatment, at least one of carbon (C) and carbon monoxide (CO) is easily adsorbed onto the measuring electrode 44. As a result, it was found that the measuring electrode 44 could be restored (renewed) to the same state as its initial state, reducing undershoot and overshoot. Furthermore, when hydrocarbons (HC) are present in the measured gas, by performing the renewal process as described above, the measured gas becomes a reducing atmosphere, thus suppressing the oxidation of hydrocarbons (HC) to produce water (H2O) and carbon dioxide (CO2). Therefore, it was found that by performing the renewal process, hydrocarbons (HC) readily adhere to the measuring electrode 44. Therefore, in this case, it is also possible to restore (renew) the measuring electrode 44 to the same state as its initial state, reducing undershoot and overshoot.

[0097] Furthermore, during the pump control process for updating the measurement, it is believed that: compared to normal conditions, more oxygen is drawn from the periphery of the measuring electrode 44. For example, some of the oxygen generated from the water (H2O) in the measured gas oxidizes the carbon (C) and carbon monoxide (CO) around the measuring electrode 44 to generate carbon dioxide (CO2). In contrast, during the adjustment pump control process for updating, it is believed that: since the measured gas, after oxygen has been drawn out, reaches the measuring electrode 44, almost no carbon dioxide (CO2) is generated around the measuring electrode 44. It can be considered that: this difference results in less carbon (C) and carbon monoxide (CO) adhering to the measuring electrode 44 compared to the adjustment pump control process during updating. Based on this reasoning, it is believed that: Figure 6 As shown, the pump control processing for updating improves the updating effect of sensor element 101 compared to the pump control processing for updating measurement.

[0098] Next, an example of measuring and updating the NOx concentration in the control unit 91 of the gas sensor 100 will be described. Figure 7This is a flowchart illustrating an example of a control routine executed by the control unit 91. The control unit 91 stores this routine in, for example, a storage unit 94. The control unit 91 controls, for example, the power supplied by the heater power supply 76 to the heater 72, and starts the control routine when the temperature of the heater 72 reaches a target temperature (e.g., 800°C).

[0099] When the CPU 92 of the control unit 91 starts the control routine, it first begins the normal-time control process for measuring NOx concentration (step S100). In the normal-time control process, the CPU 92 performs the aforementioned normal-time adjustment pump control process (normal-time main pump control process and normal-time auxiliary pump control process), and also performs the aforementioned normal-time measurement pump control process. Then, the CPU 92 calculates the NOx concentration in the gas being measured based on the pump current Ip2 flowing through the normal-time measurement pump control process.

[0100] Next, the CPU 92 determines whether it is a time to determine whether the sensor element 101 needs to be updated (step S110). The time to determine whether to update refers to a time when the pump current Ip2 is likely to undershoot or overshoot. As described in Patent Document 2, undershoot and overshoot are likely to occur when the H2O concentration in the gas being measured changes. Therefore, it is preferable to set the time to determine whether to update as a time when the H2O concentration in the gas being measured changes abruptly within the gas flow section. In this embodiment, the time to determine whether to update is the start of fuel cutoff of the internal combustion engine. When fuel cutoff begins, the gas being measured is in the same state as the atmospheric atmosphere, and the possibility of a sudden change in H2O concentration is high, thus making it suitable as a time to determine whether to update. It should be noted that when fuel cutoff begins, the NOx concentration in the gas being measured also changes abruptly. For example, the control unit 91 detects the start of fuel cutoff based on fuel cutoff execution information obtained from the engine ECU (not shown) of the internal combustion engine. For example, the CPU92 determines at each specified time whether it has obtained fuel cut-off execution information from the engine ECU, which is intended to indicate that fuel cut-off has been performed. When the fuel cut-off execution information is obtained, fuel cut-off is started. Therefore, the determination is the timing of whether to make a determination.

[0101] If step S110 determines whether a decision is needed, CPU 92 calculates the downswing of pump current Ip2 and performs update decision processing to check if the calculated value is within the allowable range (step S120). In this embodiment, the decision is made when fuel cut-off begins; therefore, after that, pump current Ip2 immediately follows the fuel cut-off... Figures 3-5The current decreases sharply as shown. The CPU 92 calculates the downstroke based on the behavior (waveform) of the pump current Ip2 at this time. Regarding the determination in step S120, it can be determined by comparing the calculated downstroke itself with the allowable range, or by comparing the difference between the downstroke (initial value) of the sensor element 101 in its initial state and the calculated downstroke with the allowable range. For example, the upper limit of the allowable range can be preset to the value of the pump current Ip2 corresponding to a NOx concentration of 5 ppm. If the downstroke itself exceeds this upper limit, it is determined to be a deviation from the allowable range. Alternatively, it can be determined to be a deviation from the allowable range if the difference between the initial value and the current downstroke exceeds this upper limit. The information of the allowable range and the initial value can be stored in the storage unit 94 in advance. When the downstroke deviates from the allowable range in step S120, the CPU 92 determines that an update process is required and sets the flag F to the value 1 (step S130). Flag F is set to 1 when an update is required, and to 0 when no update is required or at the start of a control routine.

[0102] After step S130, if it is determined in step S110 that it is not an opportunity to determine whether to update, or if the downswing in step S120 is within the allowable range, the CPU92 determines whether it is an opportunity to execute the update process (step S140). The opportunity to execute the update process refers to a time when the gas being measured is considered to contain carbon in the gas flow section. In this embodiment, the execution time is set to the operation of the internal combustion engine (except when fuel is cut off). If it is not during fuel cut-off, the gas being measured essentially contains carbon (especially CO2), and therefore, it is suitable for update processing. For example, the CPU92 determines whether it is an opportunity to execute the update process based on fuel cut-off execution information obtained from the engine ECU (not shown). For example, the CPU92 determines at each predetermined time whether it has obtained fuel cut-off execution information from the engine ECU indicating that fuel cut-off has been performed. If no fuel cut-off execution information is obtained, it determines that the current operation is other than during fuel cut-off, i.e., an opportunity to execute the update process.

[0103] When step S140 determines that it is time to execute an update process, CPU 92 determines whether flag F is 1 (step S150). If it is 1, the normal control process started in step S100 is stopped (step S160), and the update process is executed (step S170). That is, when it is determined that it is time to execute an update process and an update is required (flag F is 1), CPU 92 performs the update process. For example, as an update process, CPU 92 performs a 10-second update main pump control process. In this case, since the normal control process is stopped in step S160, the normal auxiliary pump control process and the normal measurement pump control process are not performed during the update process. Then, when the update process ends, CPU 92 sets flag F to 0 (step S180) and restarts the normal control process (step S190), thereby starting the NOx concentration detection.

[0104] After the normal control process begins in step S190, when it is determined in step S140 that it is not the execution time for update processing, or when flag F is not 1 in step S150, CPU 92 executes the processing after step S110. This is performed by CPU 92 as described above. Figure 7 The control routine is capable of measuring NOx concentration and updating it as needed. Thus, the updating process of the present invention is not limited to the manufacturing or maintenance of the gas sensor 100, but can also be performed when the gas sensor 100 is in use (e.g., during the operation of an internal combustion engine).

[0105] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is clarified. The stacked body obtained by sequentially stacking the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6 in this embodiment corresponds to the main body of the component of the present invention. The outer pump electrode 23 corresponds to the outer measuring electrode, the third internal cavity 61 corresponds to the measuring chamber, the measuring electrode 44 corresponds to the inner measuring electrode, the measuring pump unit 41 corresponds to the measuring pump unit, the first internal cavity 20 and the second internal cavity 40 correspond to the oxygen concentration adjustment chamber, the main pump unit 21 and the auxiliary pump unit 50 correspond to the adjustment pump unit, the reference electrode 42 corresponds to the reference electrode, the oxygen partial pressure detection sensor unit 82 for measuring pump control corresponds to the measuring voltage detection sensor unit, the sensor element 101 corresponds to the sensor element, the pump current Ip2 corresponds to the measuring pump current, and the control device 90 corresponds to the specific gas concentration detection unit, the decision unit, and the update control unit.

[0106] According to the gas sensor 100 of this embodiment described in detail above, the control device 90 performs a determination process based on the undershoot of the pump current Ip2 when determining whether the sensor element 101 needs to be updated. If it is determined that an update is needed, an update process is performed. The update process includes at least one of the following: an update-time adjustment pump control process that controls the adjustment pump unit (here, the main pump unit 21 and the auxiliary pump unit 50) to draw out more oxygen from the oxygen concentration adjustment chamber (here, the first internal cavity 20 and the second internal cavity 40) compared to the normal adjustment pump control process, and an update-time measurement pump control process that controls the measurement pump unit 41 to draw out more oxygen from the third internal cavity 61 compared to the normal measurement pump control process. By performing such an update process, the undershoot and overshoot of the pump current Ip2 that accompany the use of the gas sensor 100 can be suppressed.

[0107] In addition, the update process includes pump control processing for adjustment during update. Compared with pump control processing for measurement during update, the pump control processing for adjustment during update is more effective in updating the sensor element 101. Therefore, by performing at least the pump control processing for adjustment during update in the update process, the effect of suppressing undershoot and overshoot of pump current Ip2 can be improved, and the update process can be performed in a shorter time.

[0108] Furthermore, the oxygen concentration adjustment chamber includes a first internal cavity 20 and a second internal cavity 40 positioned downstream of the first internal cavity 20 and upstream of the third internal cavity 61. Additionally, the adjustment pump unit includes a main pump unit 21 for adjusting the oxygen concentration in the first internal cavity 20 and an auxiliary pump unit 50 for adjusting the oxygen concentration in the second internal cavity 40. Moreover, the adjustment pump control process during renewal includes at least one of the following: a process that controls the main pump unit 21 to extract more oxygen from the first internal cavity 20 compared to the normal adjustment pump control process, and a process that controls the auxiliary pump unit 50 to extract more oxygen from the second internal cavity 40 compared to the normal adjustment pump control process.

[0109] Furthermore, since the gas being measured is exhaust gas from an internal combustion engine, the control unit 91 performs a refresh determination process based on the behavior of the pump current Ip2 during a sudden change associated with fuel cutoff from the internal combustion engine. As mentioned above, the undershoot of pump current Ip2 is more likely to occur during a sudden change in H2O concentration in the measured gas than during a sudden change in NOx concentration. Moreover, when the fuel is cut off from the internal combustion engine, the measured gas is temporarily in a state similar to atmospheric conditions, thus the likelihood of a sudden change in H2O concentration is higher. Therefore, by determining the refresh requirement based on the behavior of the pump current Ip2 during a sudden change associated with fuel cutoff, a more appropriate determination can be made regarding whether a refresh is needed. For example, even if a sudden change occurs in NOx concentration but not in H2O concentration, in reality, even if the sensor element 101 is in a state requiring refresh processing, the undershoot and overshoot of pump current Ip2 may not be very large. In such cases, if a refresh determination process is performed, it may be determined that a refresh is not needed, which may sometimes make the refresh determination inappropriate. In contrast, by performing a fuel replacement decision when the H2O concentration is likely to change abruptly during fuel cutoff, it is possible to more appropriately determine whether a replacement is needed.

[0110] Furthermore, if the undershoot deviates from the allowable range when the pump current Ip2 changes abruptly, the control device 90 determines that the sensor element 101 needs to be updated. Therefore, it is possible to appropriately determine whether an update is necessary based on the undershoot.

[0111] Furthermore, the control device 90 performs an update process when the measured gas in the gas flow section is considered to contain carbon. Since the update process needs to be performed when the measured gas contains carbon, by performing the update process when the measured gas in the gas flow section is considered to contain carbon, the update can be performed effectively. Accordingly, it is less likely that a situation will arise where, even after the update process is performed, the undershoot and overshoot do not decrease, requiring another update process.

[0112] Furthermore, the update processing time is between 1 second and 10 seconds. By making the processing time more than 1 second, the sensor element 101 can be updated more reliably. Also, even if the update processing is performed for a long period, the update effect does not improve much; the update effect is higher in the first 10 seconds. Additionally, NOx concentration cannot be accurately detected during the update processing; therefore, the update processing time is preferably shorter. By making the processing time less than 10 seconds, the time during which NOx concentration cannot be accurately detected is shortened, and the sensor element 101 can be updated efficiently. It should be noted that by making the update processing time less than 10 seconds, the undershoot and overshoot of the pump current Ip2 may not be sufficiently reduced in a single update process. However, in this case, a decision on whether to proceed with the next update (e.g., to perform...) needs to be made. Figure 7In step S120 (following step S170), it is determined that an update process is needed, and the update process is executed again. Therefore, the update process is executed repeatedly until the update-need-or-not-determined process determines that no update process is needed, and finally the undershoot and overshoot are reduced to the level at which it is determined that no update process is needed.

[0113] Furthermore, by reducing the update processing time to less than 10 seconds, the ignition time of the sensor element 101 can be shortened. For example, Figure 7 In step S190, after the normal control process begins, it sometimes takes time for the pump current Ip2 to reach the value corresponding to the NOx concentration. This time is called the ignition time, and the NOx concentration cannot be accurately measured before the ignition time has elapsed. Furthermore, there is a trend that the longer the update process time, the longer the ignition time. By reducing the update process time to less than 10 seconds, the ignition time of the sensor element 101 can be shortened, thereby enabling rapid initiation of NOx concentration measurement after the update process.

[0114] It should be noted that the present invention is not limited to any of the above embodiments. Of course, as long as it falls within the technical scope of the present invention, it can be implemented in various ways.

[0115] For example, in the above embodiments, Figure 7 In step S120, the CPU92 determines whether to perform update processing based on the undershoot of the pump current Ip2, but it is not limited to this; it can determine whether to perform update processing based on the undershoot of the pump current Ip2. For example, it can determine whether to perform update processing based on the minimum value of the undershoot of the pump current Ip2. Alternatively, it can determine whether to perform update processing based on the time from when the pump current Ip2 reaches the minimum value of the undershoot until the pump current Ip2 stabilizes, i.e., the undershoot time. In addition, the CPU92 can also determine whether to perform update processing based on the overshoot of the pump current Ip2. For example, it can determine whether to perform update processing based on the overshoot amount of the pump current Ip2. It can also determine whether to perform update processing based on the maximum value of the overshoot of the pump current Ip2. Alternatively, it can determine whether to perform update processing based on the time from when the pump current Ip2 reaches the maximum value of the overshoot until the pump current Ip2 stabilizes, i.e., the overshoot time. In addition, the CPU92 can determine whether to perform update processing based on both the undershoot and overshoot of the pump current Ip2.

[0116] When determining whether to perform update processing based on the overshoot of pump current Ip2, the timing for determining whether to perform the update process in step S110 can be a time when overshoot is likely to occur, such as when the fuel cutoff ends. Regarding the end of the fuel cutoff, it can be detected based on the aforementioned fuel cutoff execution information, just as it is at the start of the fuel cutoff. For example, the CPU92 pre-determines at predetermined intervals whether it has obtained fuel cutoff execution information from the engine ECU indicating that fuel cutoff has been performed. If no fuel cutoff execution information is obtained for the first time after obtaining the fuel cutoff execution information, the fuel cutoff ends; therefore, this can be determined as the timing for determining whether to perform the update process.

[0117] In the above embodiment, the decision to update is based on the undershoot of the pump current Ip2. However, it is not limited to the case where the decision is based on the pump current Ip2 itself. The decision can also be based on a value that can be converted into or regarded as the pump current Ip2. For example, the decision to update can be based on the behavior of the NOx concentration [ppm] value obtained from the pump current Ip2 (at least one of undershoot and overshoot).

[0118] In the above embodiment, the update process in step S170 is the main pump control process during update. However, as described above, the update process can include at least one of the adjustment pump control process and the measurement pump control process during update. Therefore, in step S170, it is sufficient to perform at least one of the main pump control process, the auxiliary pump control process, and the measurement pump control process during update. However, if using Figure 6 As illustrated in Table 1, the update efficiency is higher when adjusting the pump control process during the update than when measuring the pump control process during the update. Therefore, the update process preferably includes at least one of the main pump control process and the auxiliary pump control process during the update.

[0119] In the above embodiments, the main pump control processing, auxiliary pump control processing, and measurement pump control processing during the update are all processes that increase the target value compared to normal operation. However, they can be processes that control the flow of the measured gas to draw out more oxygen than normal. For example, the control processing during the update can be a process of constant pressure control of the pump unit without feedback control using the target value, or a process of constant current control of the pump unit. For example, the main pump control processing during the update can be a process where the CPU 92 controls the variable power supply 24 to a predetermined constant voltage higher than the value in the normal main pump control processing without feedback control. Alternatively, the main pump control processing during the update can be a process where the CPU 92 controls the variable power supply 24 to a predetermined constant current higher than the value in the normal main pump control processing. The same applies to the auxiliary pump control processing and the measurement pump control processing during the update.

[0120] In the above embodiments, the execution timing for the update process is exemplified as operation other than when the fuel of the internal combustion engine is cut off. However, it is not limited to any timing where the measured gas in the gas flow section is considered to contain carbon. For example, if the vehicle equipped with the gas sensor 100 is a hybrid vehicle, the execution timing can be set as when the hybrid vehicle is electrically running (when the engine is stopped) and the exhaust gas is still (when exhaust gas remains around the sensor element 101). Alternatively, the execution timing can be set as when the measured gas is considered not to be atmospheric air. Alternatively, the update process can be performed without determining whether it is an execution timing, i.e., whether the measured gas in the gas flow section is considered to contain carbon. For example, the sensor element 101 is subjected to... Figure 7 The control routine is generally performed while the internal combustion engine is running, which allows for the effect of refueling. Therefore, step S140 can be omitted. In this case, refueling may sometimes be performed, for example, during fuel cut-off rather than during operation, resulting in the inability to reduce the undershoot and overshoot of pump current Ip2. However, in this case, if the next refueling determination process determines that refueling is required, and the refueling process is executed again, the effect of refueling can be achieved if the internal combustion engine is running. In this way, even without determining whether it is the right time to perform refueling, by performing refueling multiple times, undershoot and overshoot can eventually be reduced. However, as mentioned above, the NOx concentration cannot be accurately measured during refueling; therefore, in order to minimize such time, it is preferable to determine whether it is the right time to perform the refueling.

[0121] In the above embodiment, the CPU 92 detects the start of fuel cut-off or other times besides fuel cut-off based on fuel cut-off execution information. However, it can also detect these times based on the pump current Ip0. As described above, the pump current Ip0 flowing in the main pump control process normally changes according to the oxygen concentration of the gas to be measured (i.e., the gas around the sensor element 101) flowing into the gas to be measured from the gas inlet 10. Furthermore, when the gas to be measured is exhaust gas from an internal combustion engine, the oxygen concentration in the gas to be measured is the same as the oxygen concentration in the atmosphere at the time of fuel cut-off. Therefore, the CPU 92 can determine whether fuel cut-off is occurring based on whether the pump current Ip0 flowing in the main pump control process normally corresponds to a concentration within a specified range (e.g., 20-22%) that is considered to be the same as the oxygen concentration in the atmosphere. Therefore, for example, the CPU 92 can determine whether fuel cut-off has started based on the pump current Ip0 in step S110, and if it has started, determine whether to determine the timing. Alternatively, CPU92 can determine whether fuel cutoff is in progress based on pump current Ip0 in step S140. If fuel cutoff is not in progress, it determines that it is time to execute the update process. In step S120, when determining whether to perform the update process based on the overshoot of pump current Ip2, CPU92 can determine whether fuel cutoff has ended based on pump current Ip0 in step S110. If it has ended, it determines that it is time to determine whether to perform the update process.

[0122] Although not described in the above embodiments, fuel cutoff may sometimes be initiated during the update process in step S170. In this case, the update process can be terminated without waiting for the processing time (10 seconds in the above embodiments) to elapse.

[0123] In the above embodiment, the oxygen concentration adjustment chamber has a first internal cavity 20 and a second internal cavity 40, but is not limited thereto. For example, the oxygen concentration adjustment chamber may further include another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above embodiment, the adjustment pump unit has a main pump unit 21 and an auxiliary pump unit 50, but is not limited thereto. For example, the adjustment pump unit may further include another pump unit, or one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, if the oxygen concentration of the gas to be measured can be sufficiently low using only the main pump unit 21, the auxiliary pump unit 50 may be omitted. In this case, as a normal adjustment pump control process, the CPU 92 may perform, for example, a process to control the main pump unit 21 in a way that makes the oxygen concentration of the oxygen concentration adjustment chamber (first internal cavity 20) reach a target concentration. More specifically, a target value V0* can be predetermined, and the CPU92 performs feedback control on the pump voltage Vp0 of the variable power supply 24 in a manner that makes the voltage V0 reach the target value V0* (that is, in a manner that makes the oxygen concentration in the first internal cavity 20 reach the target concentration), thereby controlling the main pump unit 21.

[0124] In the above embodiments, the outer pump electrode 23 serves as: an outer main pump electrode disposed as part of the main pump unit 21 and in contact with the gas to be measured outside the sensor element 101; an outer auxiliary pump electrode disposed as part of the auxiliary pump unit 50 and in contact with the gas to be measured outside the sensor element 101; and an outer measuring electrode disposed as part of the measuring pump unit 41 and in contact with the gas to be measured outside the sensor element 101, but is not limited thereto. Alternatively, any one or more of the outer main pump electrode, outer auxiliary pump electrode, and outer measuring electrode may be disposed independently of the outer pump electrode 23 and separately disposed on the outside of the sensor element 101.

[0125] In the above embodiment, the outer pump electrode 23 is exposed on the outside of the sensor element 101, but it is not limited to this. As long as the outer pump electrode 23 is disposed on the outside of the element body (layers 1 to 6) in a manner that allows it to contact the gas being measured. For example, the sensor element 101 may also have a porous protective layer covering the element body (layers 1 to 6), and the outer pump electrode 23 may also be covered by the porous protective layer.

[0126] In the above embodiments, the sensor element 101 of the gas sensor 100 includes a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited thereto. For example, it can also be like... Figure 8 The sensor element 201 does not have a third internal cavity 61. Figure 8In the modified sensor element 201 shown, the gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, the second diffusion rate control unit 13, the first internal cavity 20, the third diffusion rate control unit 30, and the second internal cavity 40 are formed adjacently between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, connected in this order. Furthermore, the measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The measuring electrode 44 is covered by a fourth diffusion rate control unit 45. The fourth diffusion rate control unit 45 is a membrane composed of a porous ceramic material such as alumina (Al2O3). Similar to the fourth diffusion rate control unit 60 in the above embodiment, the fourth diffusion rate control unit 45 serves to limit the amount of NOx flowing into the measuring electrode 44. Additionally, the fourth diffusion rate control unit 45 also functions as a protective film for the measuring electrode 44. The top electrode portion 51a of the auxiliary pump electrode 51 is formed directly above the measuring electrode 44. Even with this sensor element 201, it is possible to detect NOx concentration based on, for example, the pump current Ip2, in the same manner as in the embodiments described above. In this case, the area around the measuring electrode 44 functions as a measuring chamber.

[0127] In the above embodiments, the main body of the sensor element 101 is a laminate having multiple solid electrolyte layers (layers 1 to 6), but is not limited thereto. The main body of the sensor element 101 only needs to include at least one oxygen ion-conductive solid electrolyte layer and have a flow passage for the gas to be measured inside. For example, Figure 1 Layers 1 to 5, other than the second solid electrolyte layer 6, can also be structural layers made of a material other than the solid electrolyte layer (e.g., layers made of aluminum oxide). In this case, each electrode of the sensor element 101 only needs to be disposed within the second solid electrolyte layer 6. For example, Figure 1 The measuring electrode 44 can be disposed on the lower surface of the second solid electrolyte layer 6. Alternatively, it can be formed as follows: the reference gas introduction space 43 is disposed in the isolation layer 5 instead of the first solid electrolyte layer 4; the atmospheric introduction layer 48 is disposed between the second solid electrolyte layer 6 and the isolation layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3; and the reference electrode 42 is disposed behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0128] In the above embodiment, during normal main pump control processing, the control device 90 sets a target value V0* for voltage V0 based on pump current Ip1 to achieve a target current Ip1* (feedback control), and performs feedback control on pump voltage Vp0 to achieve the target value V0*. However, other control methods are also possible. For example, during normal main pump control processing, the control device 90 can perform feedback control on pump voltage Vp0 based on pump current Ip1 to achieve a target current Ip1*. That is, the control device 90 can also omit obtaining voltage V0 from the oxygen partial pressure detection sensor unit 80 for main pump control and omit setting the target value V0*, and directly control pump voltage Vp0 based on pump current Ip1 (and thus control pump current Ip0).

[0129] In the above embodiment, the gas sensor 100 detects the NOx concentration as the specific gas concentration, but it is not limited to this; other oxide concentrations can also be set as the specific gas concentration. When the specific gas is an oxide, similar to the above embodiment, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61. Therefore, the CPU 92 can detect the specific gas concentration based on the detection value corresponding to this oxygen. Alternatively, the specific gas can also be a non-oxide such as ammonia. When the specific gas is a non-oxide, the specific gas is converted into an oxide (for example, if it is ammonia, it is oxidized to NO) in, for example, the first internal cavity 20. The converted oxide is reduced in the third internal cavity 61 to generate oxygen. Therefore, the CPU 92 can obtain the detection value corresponding to this oxygen and detect the specific gas concentration. In this way, whether the specific gas is an oxide or a non-oxide, the gas sensor 100 can detect the specific gas concentration based on the oxygen generated in the third internal cavity 61 from the specific gas.

[0130] In the above embodiment, the target value V0r* in the main pump control processing during the update is a value higher than the target value V0*. Figure 6 In this context, the target value V0r* is 1000mV. This target value V0r* is preferably greater than 700mV and less than 1100mV. The inventors of this invention investigated the relationship between the update processing time and the reduction effect of the downswing when the target value V0r* is within the range of 700mV to 1100mV. The results are shown below. Figure 9 . Figure 9 The horizontal and vertical axes and Figure 6 The horizontal and vertical axes are the same. Figure 9 In the curve graph, make the target value V0r* different, otherwise, make it similar to Figure 6 The curve represented by the solid line (referred to as "V0" in the examples) is measured under the same conditions. Figure 9The results are shown when the target value V0r* is varied by five different values: 700mV, 800mV, 900mV, 1000mV, and 1100mV. Figure 9 In the middle, the result when the target value V0r* is 1000mV ( Figure 9 The double-dotted line curve (the value of which is 1000mV, the same as the target value V0r*) is shown. Figure 6 The result is roughly the same as the curve plot of the solid line. Figure 9 It is known that the larger the target value V0r*, the faster the difference ΔUS approaches 0%, confirming a higher effect on updating the sensor element 101. Furthermore, if the target value V0r* is 700mV, the effect on updating the sensor element 101 is almost negligible; therefore, it is considered that the target value V0r* is preferably greater than 700mV, more preferably 800mV or more. Additionally, the higher the target value V0r*, the higher the voltage Vp0 during the main pump control process during updating. Furthermore, if the voltage Vp0 is too high, the solid electrolyte (here, zirconium oxide) of the sensor element 101 may sometimes undergo reduction. Therefore, the target value V0r* is preferably 1100mV or less. Regarding the target values ​​V1r* for the auxiliary pump control process during updating and V2r* for the measurement pump control process during updating, similarly, they are preferably greater than 700mV and less than 1100mV, more preferably 800mV or more.

[0131] This application is based on Japanese Patent Application No. 2021-137094, filed on August 25, 2021, the entire contents of which are incorporated herein by reference.

[0132] Industrial availability

[0133] This invention relates to a gas sensor capable of detecting the concentration of specific gases such as NOx in measured gases such as automobile exhaust.

[0134] Symbol Explanation

[0135] 1 First substrate layer, 2 Second substrate layer, 3 Third substrate layer, 4 First solid electrolyte layer, 5 Isolation layer, 6 Second solid electrolyte layer, 10 Gas inlet, 11 First diffusion rate control unit, 12 Buffer space, 13 Second diffusion rate control unit, 20 First internal cavity, 21 Main pump unit, 22 Inner pump electrode, 22a Top electrode, 22b Bottom electrode, 23 Outer pump electrode, 24 Variable power supply, 30 Third diffusion rate control unit, 40 Second internal cavity, 41 Measurement pump unit, 42 Reference electrode, 43 Reference gas inlet space, 44 Measurement electrode, 45 Fourth diffusion rate control unit, 46 Variable power supply, 48 Atmosphere inlet layer, 50 Auxiliary pump unit, 51 Auxiliary pump electrode, 51a Top electrode, 51b Bottom electrode, 52 Variable power supply, 60 Fourth diffusion rate control unit, 61 Third internal cavity, 70 Heater section, 71 Connector electrode, 72 Heater, 73 Through hole, 74 Heater insulation layer, 75 Pressure relief hole, 76 Heater power supply, 80 Oxygen partial pressure detection sensor unit for main pump control, 81 Oxygen partial pressure detection sensor unit for auxiliary pump control, 82 Oxygen partial pressure detection sensor unit for measuring pump control, 83 Sensor unit, 90 Control device, 91 Control unit, 92 CPU, 94 Storage unit, 100 Gas sensor, 101, 201 Sensor element.

Claims

1. A gas sensor comprising: a sensor element, a specific gas concentration detection unit, a do / no determination unit, and an update control unit. The sensor element has: The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and has a gas flow section inside for introducing and circulating the gas to be measured. A measuring pump unit has an outer measuring electrode disposed on the outside of the main body of the component in a manner that contacts the gas to be measured, and an inner measuring electrode disposed in a measuring chamber in the gas flow section, wherein oxygen is drawn out from the periphery of the inner measuring electrode to the periphery of the outer measuring electrode. An adjustment pump unit is provided to adjust the oxygen concentration in an oxygen concentration adjustment chamber located upstream of the measuring chamber in the gas flow section being measured. A reference electrode is disposed inside the main body of the element in such a way that it is in contact with a reference gas, which is used as a detection reference for a specific gas concentration in the gas being measured. as well as A voltage detection sensor unit for measuring voltage is provided, which detects the measuring voltage between the reference electrode and the inner measuring electrode. The specific gas concentration detection unit performs normal-time adjustment pump control processing to operate the adjustment pump unit, and normal-time measurement pump control processing to control the measurement pump unit to draw oxygen from the measurement chamber in a manner that makes the measurement voltage of the sensor element reach a target value. Based on the measurement pump current flowing through the measurement pump unit through this normal-time measurement pump control processing, the concentration of the specific gas in the gas to be measured is detected. The update determination unit performs update determination processing, that is, it determines whether the sensor element needs to be updated based on at least one of undershoot and overshoot when the current of the measuring pump changes abruptly. When the update control unit determines that an update is required using the update-need-to-be-updated determination process, it performs an update process. This update process includes at least one of the following: an update-time adjustment pump control process that controls the adjustment pump unit to extract more oxygen from the oxygen concentration adjustment chamber compared to the normal time adjustment pump control process, and an update-time measurement pump control process that controls the measurement pump unit to extract more oxygen from the measurement chamber compared to the normal time measurement pump control process. The update control unit performs the update process when it considers that the measured gas in the measured gas flow section contains carbon.

2. The gas sensor according to claim 1, wherein, The update process includes the pump control process for adjusting during the update.

3. The gas sensor according to claim 2, wherein, The oxygen concentration adjustment chamber has: a first internal cavity, and a second internal cavity configured to be located downstream of the first internal cavity and upstream of the measuring chamber. The adjustment pump unit includes: a main pump unit for adjusting the oxygen concentration of the first internal cavity, and an auxiliary pump unit for adjusting the oxygen concentration of the second internal cavity. The update-time adjustment pump control process includes at least one of the following: a process of controlling the main pump unit to extract more oxygen from the first internal cavity compared to the normal adjustment pump control process, and a process of controlling the auxiliary pump unit to extract more oxygen from the second internal cavity compared to the normal adjustment pump control process.

4. The gas sensor according to any one of claims 1 to 3, wherein, The gas being measured is the exhaust gas from an internal combustion engine. The decision-making unit performs the update decision-making process based on the behavior of the measuring pump current when the fuel cut-off of the internal combustion engine occurs.

5. The gas sensor according to any one of claims 1 to 3, wherein, The determination unit determines that the update is required if at least one of the undershoot and overshoot during the sudden change in the pump current deviates from the allowable range.

6. The gas sensor according to any one of claims 1 to 3, wherein, The processing time for the update is more than 1 second and less than 10 seconds.

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