Gas sensor and concentration measuring method using gas sensor

Abstract

The adjustment pump unit executes a first suction operation for sucking out oxygen such that H2O and CO2 in the gas to be measured introduced into the first cavity are all reduced, the first measurement pump unit selectively oxidizes H2 in the gas to be measured introduced into the second cavity, the second measurement pump unit oxidizes CO in the gas to be measured introduced into the third cavity, and the adjustment pump unit executes a second suction operation for sucking out oxygen such that H2O and CO2 in the gas to be measured introduced into the third cavity are all reduced. The H2O concentration is determined on the basis of the suction current toward the second cavity, the CO2 concentration is determined on the basis of the suction current toward the third cavity, and the adjustment pump unit can further execute a second suction operation for sucking oxygen from the first cavity within a range in which H2O and CO2 are not reduced during the first suction operation. The second suction operation is started and the reduction of H2O and CO2 in the first cavity is interrupted, whereby H2O and CO2 generated in the second cavity or the third cavity are discharged to the outside of the element.

Description

Technical Field

[0001] The present invention relates to a multi-gas sensor capable of monitoring a plurality of types of monitoring target gas components and measuring their concentrations. Background Art

[0002] As for the measurement for managing the emission amount from automobile exhaust gas, there are known technologies for measuring the concentration of water vapor (H2O) and carbon dioxide (CO2) (for example, see Patent Documents 1 to 3). The gas sensors disclosed in Patent Documents 1 and 2 can measure the water vapor (H2O) component and the carbon dioxide (CO2) component at the same time. In addition, the gas sensor disclosed in Patent Document 3 can also measure the water vapor (H2O) component with good accuracy when the measured gas contains carbon dioxide (CO2).

[0003] In addition, there is also known a carbon dioxide detection device, in which an air-fuel ratio detection electrode and a carbon dioxide detection electrode are arranged in parallel, and by using an electric current flowing between each electrode and a reference electrode, a correction taking into account the influence of the air-fuel ratio can be performed and the concentration of carbon dioxide can be measured, and a correction taking into account the influence of water concentration can be further performed (for example, see patent document 4).

[0004] In the three-chamber gas sensor disclosed in Patent Document 1, first, the main pump unit, which is a pump unit for the first internal cavity, operates to suck out O2 contained in the measured gas introduced into the first internal cavity, and H2O and CO2 also contained in the measured gas are temporarily reduced to generate H2 and CO. The measured gas containing H2 and CO is introduced into the second and third internal cavities. Next, O2 is sucked in by the first measuring pump unit, which is a pump unit for the second internal cavity, so that H2 is selectively oxidized to generate H2O, and further, O2 is sucked in by the second measuring pump unit, which is a pump unit for the third internal cavity, so that CO is oxidized to generate CO2. And, based on the magnitude of the pump current flowing in the first measuring pump unit and the second measuring pump unit respectively when the H2 and CO are oxidized, the concentrations of H2O and CO2 in the measured gas are measured.

[0005] The generated H2O and CO2 are basically retained in the second and third internal cavities. However, it is known that as the measurement continues, the following phenomenon may occur, that is, the H2O and CO2 flow back to the first internal cavity and are reduced again, and the generated H2 and CO are re-oxidized by the first and second measurement pump units sucking oxygen into the second and third internal cavities.

[0006] If the above phenomenon occurs, the current associated with the re-oxidation related to the pump current flowing through the first measuring pump unit and the second measuring pump unit according to the amount of H2O and CO2 contained in the measured gas is superimposed, and the concentration of H2O and CO2 is measured based on the magnitude of these pump currents. This leads to a decrease in the measurement accuracy of the gas sensor involved in Patent Document 1, so it is not ideal.

[0007] In addition, in the gas sensor disclosed in Patent Document 4, carbon dioxide is decomposed into carbon and oxygen by a carbon dioxide detection unit, and on the other hand, the electromotive force of the air-fuel ratio detection unit is controlled in such a way that it becomes a constant value corresponding to the oxygen concentration of the exhaust gas. However, in this gas sensor, similarly, CO and oxygen generated by the carbon dioxide detection unit react in the air-fuel ratio detection unit that adjusts the oxygen concentration to generate CO2, which is repeatedly monitored by the carbon dioxide detection unit. Therefore, the measurement accuracy may be reduced.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent No. 5918177

[0011] Patent Document 2: Japanese Patent No. 6469464

[0012] Patent Document 3: Japanese Patent No. 6469462

[0013] Patent Document 4: Japanese Patent Application Publication No. 2020-67432 Summary of the invention

[0014] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a gas sensor in which a decrease in measurement accuracy due to the presence of a substance generated in connection with concentration measurement is well suppressed.

[0015] In order to solve the above-mentioned problems, a first scheme of the present invention is a gas sensor capable of measuring the concentrations of multiple monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide, characterized in that it comprises: a sensor element having a structure composed of a solid electrolyte with oxygen ion conductivity; and a controller, which controls the operation of the gas sensor, the sensor element comprising: a gas inlet port for introducing the measured gas; a plurality of cavities, the plurality of cavities being connected in sequence from the gas inlet port via different diffusion rate control units; and a heater, which heats the sensor element. Two of the plurality of cavities are a first measurement cavity and a second measurement cavity, the second measurement cavity being the innermost cavity of the plurality of cavities from the gas inlet, and the first measurement cavity being a cavity in front of the second measurement cavity, and the sensor element further comprises: an oxygen absorption mechanism, which can perform a first absorption action of aspirating oxygen contained in the measured gas in a manner that water vapor and carbon dioxide contained in the measured gas are substantially completely reduced during the period when the measured gas introduced from the gas inlet reaches the first measurement cavity; and a first measurement pump unit, which is formed by a first measurement pump unit facing the first measurement cavity. The first measuring pump unit is composed of a first measuring electrode formed facing the second measuring cavity, an out-of-cavity pump electrode arranged at a position other than the plurality of cavities, and the solid electrolyte existing between the first measuring electrode and the out-of-cavity pump electrode; and a second measuring pump unit, which is composed of a second measuring electrode formed facing the second measuring cavity, the out-of-cavity pump electrode, and the solid electrolyte existing between the second measuring electrode and the out-of-cavity pump electrode, and the first measuring pump unit is configured to: by sucking oxygen into the first measuring cavity, the water vapor contained in the measured gas introduced into the first measuring cavity due to the first suction action can be removed The hydrogen generated by the reduction is selectively oxidized in the first measuring cavity; the second measuring pump unit is configured to: by sucking oxygen into the second measuring cavity, the carbon monoxide generated by the reduction of carbon dioxide accompanying the first suction action contained in the measured gas introduced into the second measuring cavity can be oxidized in the second measuring cavity, and the controller has: a water vapor concentration determining mechanism, which determines the concentration of water vapor contained in the measured gas based on the magnitude of the current flowing between the first measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the first measuring cavity by the first measuring pump unit;and a carbon dioxide concentration determination mechanism that determines the concentration of carbon dioxide contained in the gas to be measured based on the magnitude of the current flowing between the second measurement electrode and the pump electrode outside the cavity when oxygen is sucked into the second measurement cavity by the second measurement pump unit, wherein the oxygen suction mechanism is configured to further perform a second suction operation for a predetermined time to suction oxygen contained in the gas to be measured within a range where water vapor and carbon dioxide contained in the gas to be measured before reaching the first measurement cavity are not reduced during the first suction operation, and the reduction of water vapor and carbon dioxide by the oxygen suction mechanism is interrupted by the start of the second suction operation, so that water vapor generated in the first measurement cavity and carbon dioxide generated in the second measurement cavity are discharged to the outside of the sensor element. ;

[0016] A second scheme of the present invention is based on the gas sensor involved in the first scheme, and is characterized in that the multiple cavities are a first cavity, a second cavity as the first measuring cavity, and a third cavity as the second measuring cavity, and the sensor element also has an adjustment pump unit as the oxygen absorption mechanism, the adjustment pump unit is composed of an adjustment electrode formed facing the first cavity, the cavity outer pump electrode, and the solid electrolyte existing between the adjustment electrode and the cavity outer pump electrode, and the adjustment pump unit is configured to: as the first absorption action, it is possible to perform a suction operation in the gas to be measured introduced into the first cavity. The invention also provides an action of sucking out oxygen from the first cavity in such a manner that the water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are substantially completely reduced, and as the second sucking out action, the action of sucking out oxygen from the first cavity within a range in which the water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are not reduced is performed. During a specified time during which the first sucking out action is performed, the second sucking out action is started by the adjustment pump unit, so that the reduction of the water vapor and carbon dioxide in the first cavity is interrupted, and the water vapor generated in the second cavity and the carbon dioxide generated in the third cavity are discharged to the outside of the sensor element via the first cavity.

[0017] The third scheme of the present invention is based on the gas sensor involved in the second scheme, and is characterized in that the adjustment pump unit alternately and periodically performs the first suction action and the second suction action, and according to the first suction action and the second suction action of the adjustment pump unit, the first measuring pump unit is used to suck oxygen into the second cavity and the second measuring pump unit is used to suck oxygen into the third cavity periodically.

[0018] A fourth aspect of the present invention is the gas sensor according to the third aspect, wherein the oxygen intake into the second cavity by the first measuring pump unit and the oxygen intake into the third cavity by the second measuring pump unit are synchronized with the second suction operation of the adjustment pump unit.

[0019] The fifth scheme of the present invention is based on the gas sensor involved in the third scheme, and is characterized in that the use of the first measuring pump unit to absorb oxygen into the second cavity and the use of the second measuring pump unit to absorb oxygen into the third cavity are performed from the middle of the first suction action of the adjustment pump unit to the middle of the second suction action.

[0020] A sixth scheme of the present invention is based on the gas sensor involved in any one of the second to fifth schemes, characterized in that the sensor element further includes: a reference electrode, which is in contact with a reference gas; a sensor unit for a first cavity, which is composed of the adjustment electrode, the reference electrode, and the solid electrolyte present between the adjustment electrode and the reference electrode, and generates an electromotive force V0 corresponding to the oxygen concentration of the first cavity between the adjustment electrode and the reference electrode; a second sensor unit for a second cavity, which is composed of the first measuring electrode, the reference electrode, and the solid electrolyte present between the first measuring electrode and the reference electrode, and generates an electromotive force V1 corresponding to the oxygen concentration of the second cavity between the first measuring electrode and the reference electrode; and a third sensor unit for a third cavity, which is composed of the second measuring electrode, the reference electrode, and the solid electrolyte present between the second measuring electrode and the reference electrode, and generates an electromotive force V2 corresponding to the oxygen concentration of the third cavity between the second measuring electrode and the reference electrode. The controller comprises: an adjustment pump unit control mechanism, which controls the voltage applied between the adjustment electrode and the cavity external pump electrode in the adjustment pump unit in such a way that the electromotive force V0 in the first cavity sensor unit is maintained at a specified target value within the range of 1000mV to 1500mV during the first suction action and is maintained at a specified target value within the range of 400mV to 700mV during the second suction action; and a first measuring ...400mV to 700mV during the second suction action. The voltage applied between the first measuring electrode and the pump electrode outside the cavity in the first measuring pump unit is controlled in such a way that the electromotive force V1 in the cavity sensor unit is maintained at a specified target value within the range of 250mV to 450mV; and a second measuring pump unit control mechanism, which controls the voltage applied between the second measuring electrode and the pump electrode outside the cavity in the second measuring pump unit in such a way that the electromotive force V2 in the third cavity sensor unit is maintained at a specified target value within the range of 100mV to 300mV.

[0021] The seventh scheme of the present invention is a method for measuring the concentrations of multiple monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide using a gas sensor, characterized in that the gas sensor includes a sensor element, the sensor element has a structure composed of a solid electrolyte with oxygen ion conductivity, and the sensor element includes: a gas inlet port for introducing the measured gas; a plurality of cavities, the plurality of cavities are connected in sequence from the gas inlet port via different diffusion rate control units; and a heater, the heater heats the sensor element, two of the plurality of cavities are a first measurement cavity and a second measurement cavity. The sensor element further comprises: an oxygen absorption mechanism, which can perform a first absorption action to absorb oxygen contained in the measured gas in a manner that substantially all of the water vapor and carbon dioxide contained in the measured gas are reduced during the period when the measured gas introduced from the gas inlet port reaches the first measuring cavity; and a first measuring pump unit, which is composed of a first measuring electrode formed facing the first measuring cavity, The method comprises the following steps: a) the oxygen absorption mechanism performs the first absorption action; b) the first measurement pump unit absorbs oxygen into the first measurement cavity, thereby removing the measured gas introduced into the first measurement cavity; and c) the oxygen absorption mechanism performs the first absorption action; and c) the oxygen absorption mechanism performs the first absorption action; and c) the second measuring pump unit oxidizes the carbon monoxide generated by the reduction of carbon dioxide accompanied by the first suction action contained in the measured gas introduced into the second measuring cavity by sucking oxygen into the second measuring cavity; d) the concentration of water vapor contained in the measured gas is determined based on the magnitude of the current flowing between the first measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the first measuring cavity by the first measuring pump unit;and e) determining the concentration of carbon dioxide contained in the gas to be measured based on the magnitude of the current flowing between the second measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the second measuring cavity by the second measuring pump unit, wherein during the step a), the oxygen suction mechanism performs a second suction operation of suctioning oxygen contained in the gas to be measured within a range where water vapor and carbon dioxide contained in the gas to be measured before reaching the first measuring cavity are not reduced for a predetermined time, thereby interrupting the reduction of water vapor and carbon dioxide by the oxygen suction mechanism, thereby discharging water vapor generated in the first measuring cavity and carbon dioxide generated in the second measuring cavity to the outside of the sensor element. ;

[0022] The eighth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the seventh scheme, and is characterized in that the multiple cavities are a first cavity, a second cavity serving as the first measurement cavity, and a third cavity serving as the second measurement cavity, and the sensor element also has an adjustment pump unit serving as the oxygen absorption mechanism, the adjustment pump unit being composed of an adjustment electrode formed facing the first cavity, the cavity outer pump electrode, and the solid electrolyte existing between the adjustment electrode and the cavity outer pump electrode, and in the step a), with respect to the adjustment pump unit, as the first absorption action, performing The invention further comprises an action of sucking out oxygen from the first cavity in such a manner that water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are substantially completely reduced, and as the second sucking-out action, the action of sucking out oxygen from the first cavity within a range in which water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are not reduced is performed for a specified time during the first sucking-out action, thereby interrupting the reduction of water vapor and carbon dioxide in the first cavity, so that water vapor generated in the second cavity and carbon dioxide generated in the third cavity are discharged to the outside of the sensor element through the first cavity.

[0023] The ninth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the eighth scheme, and is characterized in that in the step a), the adjustment pump unit alternately and periodically performs the first suction action and the second suction action, and according to the first suction action and the second suction action of the adjustment pump unit in the step a), the step b) of inhaling oxygen into the second cavity using the first measuring pump unit and the step c) of inhaling oxygen into the third cavity using the second measuring pump unit are periodically performed respectively.

[0024] The tenth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the ninth scheme, and is characterized in that the use of the first measuring pump unit in the step b) to absorb oxygen into the second cavity and the use of the second measuring pump unit in the step c) to absorb oxygen into the third cavity are performed synchronously with the second suction action of the adjustment pump unit in the step a).

[0025] The eleventh scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the ninth scheme, and is characterized in that the oxygen suction into the second cavity using the first measuring pump unit in the step b) and the oxygen suction into the third cavity using the second measuring pump unit in the step c) are performed from the middle of the first suction action of the adjustment pump unit in the step a) to the middle of the second suction action.

[0026] The twelfth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in any one of the eighth to eleventh schemes, and is characterized in that the sensor element also has a reference electrode, which is in contact with a reference gas, and in the step a), the voltage applied between the adjustment electrode and the pump electrode outside the cavity in the adjustment pump unit is adjusted in such a way that the electromotive force V0 generated between the adjustment electrode and the reference electrode corresponding to the oxygen concentration in the first cavity is maintained at a specified target value in the range of 1000mV to 1500mV during the first suction action and is maintained at a specified target value in the range of 400mV to 700mV during the second suction action. Control is performed, in the step b), the voltage applied between the first measuring electrode and the pump electrode outside the cavity in the first measuring pump unit is controlled in such a way that the electromotive force V1 generated between the first measuring electrode and the reference electrode corresponding to the oxygen concentration in the second cavity is maintained at a specified target value within the range of 250mV to 450mV, and in the step c), the voltage applied between the second measuring electrode and the pump electrode outside the cavity in the second measuring pump unit is controlled in such a way that the electromotive force V2 generated between the second measuring electrode and the reference electrode corresponding to the oxygen concentration in the third cavity is maintained at a specified target value within the range of 100mV to 300mV.

[0027] According to the first to twelfth aspects of the present invention, a decrease in the measurement accuracy of the gas sensor caused by the re-reduction of water vapor and carbon dioxide generated by the oxidation of hydrogen and carbon monoxide is well suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram schematically showing an example of the configuration of the gas sensor 100 .

[0029] Figure 2 It is a block diagram showing components of functions implemented in the controller 110 .

[0030] Figure 3 Schematic diagram showing basic gas inflow and outflow in three cavities included in the sensor element 101 of the gas sensor 100 .

[0031] Figure 4 This is a diagram for explaining a malfunction that occurs when the gas sensor 100 continues to perform measurement based on the basic operation.

[0032] Figure 5 This is a diagram for explaining a malfunction that occurs when the gas sensor 100 continues to perform measurement based on the basic operation.

[0033] Figure 6 This is a diagram showing the time changes of the target values ​​of the electromotive forces V0, V1, and V2 during the generated gas discharge operation.

[0034] Figure 7 This is a schematic diagram showing how gases enter and exit the three cavities during the generated gas discharge operation.

[0035] Figure 8 This is a diagram showing another example of the generated gas discharge operation. DETAILED DESCRIPTION

[0036] <Gas sensor configuration>

[0037] Figure 1 1 is a diagram schematically showing an example of the configuration of the gas sensor 100 involved in the present embodiment. The gas sensor 100 is a multi-gas sensor that monitors a plurality of gas components and measures their concentrations through a sensor element 101. In the present embodiment, at least water vapor (H2O) and carbon dioxide (CO2) are the main monitoring target gas components in the gas sensor 100. The gas sensor 100 is used in a manner such as being installed in an exhaust path of an internal combustion engine such as an engine of an automobile and using the exhaust gas flowing through the exhaust path as the measured gas. Figure 1 A vertical cross-sectional view along the length direction of the sensor element 101 is included.

[0038] The sensor element 101 comprises: a long plate-shaped structure (base part) 14 formed of a solid electrolyte having oxygen ion conductivity; a first diffusion rate control part 11 formed at one end (the left end in the drawing) of the structure 14 and also serving as a gas inlet 10 for introducing the measured gas; and a buffer space 12, a first cavity 20, a second cavity 40 and a third cavity 61 formed in the structure 14 and connected in sequence from the gas inlet 10 (first diffusion rate control part 11). The buffer space 12 is connected to the gas inlet 10 (first diffusion rate control part 11). The first cavity 20 is connected to the buffer space 12 via the second diffusion rate control part 13. The second cavity 40 is connected to the first cavity 20 via the third diffusion rate control part 30. The third cavity 61 is connected to the second cavity 40 via the fourth diffusion rate control part 60.

[0039] The structure 14 is formed by laminating a plurality of substrates formed of, for example, ceramics. Specifically, the structure 14 has a structure in which six layers are laminated in this order from the bottom, namely, a first substrate 1, a second substrate 2, a third substrate 3, a first solid electrolyte layer 4, a separator 5, and a second solid electrolyte layer 6. Each layer is formed of a solid electrolyte having oxygen ion conductivity, such as zirconium oxide (ZrO2).

[0040] The first diffusion rate control part 11, the buffer space 12, the second diffusion rate control part 13, the first cavity 20, the third diffusion rate control part 30, the second cavity 40, the fourth diffusion rate control part 60 and the third cavity 61, which also serve as the gas introduction port 10, are formed in this order on one end side of the structure 14, and are formed between the lower surface 6b of the second solid electrolyte layer 6 and the upper surface 4a of the first solid electrolyte layer 4. The portion from the gas introduction port 10 to the third cavity 61 is also referred to as a gas flow portion.

[0041] The buffer space 12, the first cavity 20, the second cavity 40 and the third cavity 61 are formed so as to penetrate the isolation layer 5 in the thickness direction. In the above-mentioned cavities, the lower surface 6b of the second solid electrolyte layer 6 is exposed in the upper part in the drawings, and the upper surface 4a of the first solid electrolyte layer 4 is exposed in the lower part in the drawings. The side of the above-mentioned cavities is divided by the isolation layer 5 or any diffusion rate control part. The length (dimension in the element length direction) of the first cavity 20, the second cavity 40 and the third cavity 61 is, for example, 0.3 mm to 1.0 mm, the width (dimension in the element width direction) is, for example, 0.5 mm to 30 mm, and the height (dimension in the element thickness direction) is, for example, 50 μm to 200 μm. However, the dimensions of each cavity do not need to be the same and can be different.

[0042] The gas inlet 10 may also be formed to penetrate the spacer layer 5 in the thickness direction, separately from the first diffusion rate control portion 11. In this case, the first diffusion rate control portion 11 is formed adjacent to the gas inlet 10 at a position inside.

[0043] The first diffusion rate control unit 11, the second diffusion rate control unit 13, the third diffusion rate control unit 30, and the fourth diffusion rate control unit 60 are each provided with two horizontally long slits. That is, the upper and lower parts in the drawing have openings extending long in a direction perpendicular to the drawing. The length of the slit (dimension in the element length direction) is, for example, 0.2 mm to 1.0 mm, the width of the opening (dimension in the element width direction) is, for example, 0.5 mm to 30 mm, and the height of the opening (dimension in the element thickness direction) is, for example, 5 μm to 30 μm.

[0044] In addition, a reference gas introduction space 43 is provided at the other end (right end in the drawing) of the sensor element 101 on the opposite side of the end provided with the gas introduction port 10. The reference gas introduction space 43 is formed between the upper surface 3a of the third substrate 3 and the lower surface 5b of the isolation layer 5. In addition, the side portion of the reference gas introduction space 43 is partitioned by the side surface of the first solid electrolyte layer 4. For example, oxygen (O2) and the atmosphere are introduced into the reference gas introduction space 43 as the reference gas.

[0045] The gas inlet port 10 (first diffusion rate control unit 11 ) is a portion open to the external space, and the gas to be measured is introduced from the external space into the sensor element 101 through the gas inlet port 10 .

[0046] The first diffusion rate control unit 11 is a portion that provides a predetermined diffusion resistance to the introduced gas to be measured.

[0047] The buffer space 12 is provided to eliminate the concentration fluctuation of the gas to be measured caused by the pressure fluctuation of the gas to be measured in the external space. Examples of the pressure fluctuation of the gas to be measured include the pulsation of the exhaust pressure of automobile exhaust gas.

[0048] The second diffusion rate control unit 13 is a portion that provides a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first cavity 20 .

[0049] The first cavity 20 is provided as a space for absorbing oxygen from the gas to be measured introduced through the second diffusion rate control unit 13, and further, with the absorption, H2O and CO2 are reduced (decomposed) to generate hydrogen (H2) and carbon monoxide (CO), so that the gas to be measured does not substantially contain oxygen, H2O and CO2. The absorption of oxygen is achieved by adjusting the operation of the pump unit 21.

[0050] The adjustment pump cell 21 is an electrochemical pump cell composed of an inner pump electrode (adjustment electrode) 22 , an outer pump electrode (outer-cavity pump electrode) 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between these two electrodes.

[0051] In the adjustment pump unit 21, a voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 by using a variable power supply 24 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip0. As a result, the oxygen in the first cavity 20 can be sucked out to the external space. It should be noted that in this embodiment, the direction of the oxygen pump current Ip0 when sucking oxygen from the first cavity 20 is set to the positive direction of the oxygen pump current Ip0.

[0052] The inner pump electrode 22 is provided as a top electrode portion 22a and a bottom electrode portion 22b respectively on substantially the entire lower surface 6b of the second solid electrolyte layer 6 and substantially the entire upper surface 4a of the first solid electrolyte layer 4 defining the first cavity 20. The top electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion not shown.

[0053] The inner pump electrode 22 is provided as a porous cermet electrode having a rectangular shape in a plan view and containing at least one of platinum and rhodium (Rh) as a metal component.

[0054] The outer pump electrode 23 is provided as a porous cermet electrode having platinum or an alloy of platinum and gold (Pt—Au alloy) as a metal component, for example, platinum or a Pt—Au alloy and zirconium oxide and having a rectangular shape in plan view.

[0055] In the sensor element 101, the first cavity sensor cell 80 is formed by the inner pump electrode 22, the reference electrode 42, and the solid electrolyte present in the portion sandwiched by these two electrodes in the structure 14. The first cavity sensor cell 80 is an electrochemical sensor cell for grasping the oxygen partial pressure in the atmosphere in the first cavity 20.

[0056] The reference electrode 42 is an electrode formed between the first solid electrolyte layer 4 and the third substrate 3 and is provided as, for example, a porous cermet electrode containing platinum and zirconium oxide and having a rectangular shape in a plan view.

[0057] A reference gas introduction layer 48 formed of porous alumina and connected to the reference gas introduction space 43 is provided around the reference electrode 42. The reference gas in the reference gas introduction space 43 is introduced into the surface of the reference electrode 42 via the reference gas introduction layer 48. That is, the reference electrode 42 is always in contact with the reference gas.

[0058] In the first cavity sensor unit 80, an electromotive force (Nernst electromotive force) V0 is generated between the inner pump electrode 22 and the reference electrode 42. The electromotive force V0 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the first cavity 20 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, so the electromotive force V0 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the first cavity 20.

[0059] The third diffusion rate control unit 30 is a portion that provides a predetermined diffusion resistance to the measured gas that does not substantially contain oxygen, H 2 O, and CO 2 and is introduced from the first cavity 20 to the second cavity 40 .

[0060] The second cavity 40 is provided as a space for selectively oxidizing all H2 contained in the gas to be measured and H2 in CO introduced through the third diffusion rate control unit 30 to generate H2O again. The generation of H2O by oxidation of H2 is achieved by the operation of the first measurement pump unit 50.

[0061] The first measuring pump cell 50 is an electrochemical pump cell composed of a first measuring electrode 51 , an outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between these two electrodes.

[0062] In the first measuring pump unit 50, a voltage Vp1 is applied between the first measuring electrode 51 and the outer pump electrode 23 by a variable power supply 52 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip1. Thus, oxygen can be sucked from the external space into the second cavity 40. It should be noted that in this embodiment, the direction of the oxygen pump current Ip1 when oxygen is sucked out from the second cavity 40 is set to the positive direction of the oxygen pump current Ip1.

[0063] The first measuring electrode 51 is provided as a top electrode portion 51a and a bottom electrode portion 51b respectively on substantially the entire lower surface 6b of the second solid electrolyte layer 6 and substantially the entire upper surface 4a of the first solid electrolyte layer 4 defining the second cavity 40. The top electrode portion 51a and the bottom electrode portion 51b are connected by a conductive portion (not shown).

[0064] The first measuring electrode 51 is provided as a porous metal ceramic electrode having a rectangular shape in a plan view and containing a Pt-Au alloy as a metal component, for example, the Pt-Au alloy and zirconium oxide. The Au concentration in the Pt-Au alloy is preferably 1 wt% or more and 50 wt% or less, and more preferably 10 wt% or more and 30 wt% or less. In this case, the selective oxidation property of H2 in the first measuring electrode 51, that is, the property that only H2 is selectively oxidized by the oxygen sucked by the first measuring pump unit 50 and CO is not oxidized when H2 and CO coexist in the second cavity 40, is better exhibited.

[0065] In the sensor element 101, the first measuring electrode 51, the reference electrode 42, and the solid electrolyte present in the portion sandwiched between the two electrodes in the structure 14 constitute the second cavity sensor cell 81. The second cavity sensor cell 81 is an electrochemical sensor cell for grasping the oxygen partial pressure in the atmosphere in the second cavity 40.

[0066] In the second cavity sensor unit 81, an electromotive force (Nernst electromotive force) V1 is generated between the first measuring electrode 51 and the reference electrode 42. The electromotive force V1 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the second cavity 40 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, so the electromotive force V1 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the second cavity 40.

[0067] The fourth diffusion rate control unit 60 is a portion that provides a predetermined diffusion resistance to the measured gas containing H 2 O and CO and substantially containing no CO 2 and oxygen, which is introduced from the second cavity 40 into the third cavity 61 .

[0068] The third cavity 61 is provided as a space for oxidizing all CO contained in the gas to be measured introduced through the fourth diffusion rate control unit 60 to generate CO 2 again. The oxidation of CO to generate CO 2 is achieved by the operation of the second measurement pump unit 41.

[0069] The second measuring pump cell 41 is an electrochemical pump cell composed of the second measuring electrode 44 , the outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between the two electrodes.

[0070] In the second measuring pump unit 41, a voltage Vp2 is applied between the second measuring electrode 44 and the outer pump electrode 23 by a variable power supply 46 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip2. Thus, oxygen can be sucked from the external space into the third cavity 61. It should be noted that in this embodiment, the direction of the oxygen pump current Ip2 when oxygen is sucked out from the third cavity 61 is set to the positive direction of the oxygen pump current Ip2.

[0071] The second measuring electrode 44 is provided on substantially the entire upper surface 4 a of the first solid electrolyte layer 4 defining the third cavity 61 .

[0072] The second measuring electrode 44 is provided as a porous cermet electrode having Pt as a metal component and having a rectangular shape in a plan view, for example, containing Pt and zirconium oxide.

[0073] In the sensor element 101, the second measuring electrode 44, the reference electrode 42, and the solid electrolyte present in the portion sandwiched between the two electrodes in the structure 14 constitute the third cavity sensor cell 82. The third cavity sensor cell 82 is an electrochemical sensor cell for grasping the oxygen partial pressure in the atmosphere in the third cavity 61.

[0074] In the third cavity sensor unit 82, an electromotive force (Nernst electromotive force) V2 is generated between the second measuring electrode 44 and the reference electrode 42. The electromotive force V2 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the third cavity 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. The oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, so the electromotive force V2 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the third cavity 61.

[0075] In addition, the sensor element 101 further includes an electrochemical sensor unit 83 composed of an outer pump electrode 23, a reference electrode 42, and a solid electrolyte present in a portion sandwiched between these two electrodes in the structure 14. The electromotive force Vref generated between the outer pump electrode 23 and the reference electrode 42 in the sensor unit 83 is a value corresponding to the oxygen partial pressure of the measured gas present outside the sensor element 101.

[0076] In addition to the above components, the sensor element 101 includes a heater unit 70 that performs a temperature adjustment function of heating and keeping the sensor element 101 warm in order to improve the oxygen ion conductivity of the solid electrolyte constituting the structure 14 .

[0077] The heater unit 70 mainly includes a heater electrode 71, a heater member 72, a heater lead 72a, a through hole 73, a heater insulating layer 74, and Figure 1 The heater resistance detection lead wire shown in the figure is omitted.

[0078] The heater 72 is provided in a manner of being sandwiched between the second substrate 2 and the third substrate 3, and generates heat by supplying power from the outside through the heater electrode 71, the through hole 73, and the heater lead 72a provided on the lower surface 1b of the first substrate 1. The heater 72 is implanted in the entire area ranging from the buffer space 12 to the third cavity 61, and can heat the sensor element 101 to a predetermined temperature and keep the temperature.

[0079] The heater 72 is set so that when heating, the vicinity of the first cavity 20 (the vicinity of the adjustment electrode 22) becomes the highest temperature, and the temperature decreases as it moves away from the first cavity 20 in the element length direction. In this embodiment, the temperature of the range from one end of the sensor element 101 where the gas inlet 10 is located to the third cavity 61 when the gas sensor 100 is used (when the sensor element 101 is driven) is referred to as the element driving temperature. The heater 72 heats in such a manner that the element driving temperature is within the range of 750°C to 950°C.

[0080] A heater insulating layer 74 made of alumina or the like is formed above and below the heater 72 for the purpose of obtaining electrical insulation from the second substrate 2 and the third substrate 3. In addition, the heater portion 70 is provided with a pressure release hole 75. The pressure release hole 75 is provided so as to penetrate the third substrate 3 and communicate with the reference gas introduction space 43. The purpose of providing the pressure release hole 75 is to mitigate the internal pressure increase associated with the temperature increase in the heater insulating layer 74.

[0081] The gas sensor 100 further includes a controller 110 that controls the operation of the sensor element 101 and performs processing for determining the concentration of a monitoring target gas component based on the current flowing through the sensor element 101 .

[0082] Figure 2 This is a block diagram showing the components of the functions implemented in the controller 110. The controller 110 is composed of one or more electronic circuits such as one or more CPUs (central processing units) and a storage device. The electronic circuit is also a software function unit that implements a component of a specified function by executing a specified program stored in a storage device, for example, by the CPU. Of course, it can also be composed of an integrated circuit such as an FPGA (Field-Programmable Gate Array) obtained by connecting multiple electronic circuits according to the function.

[0083] It should be noted that when the gas sensor 100 is installed in the exhaust path of a car engine and the exhaust gas flowing through the exhaust path is used as the measured gas, part or all of the functions of the controller 110 can be implemented by the car's ECU (electronic control unit).

[0084] The controller 110 includes, as components for implementing functions by executing a prescribed program in the CPU, an element operation control unit 120 for controlling the operation of each part of the sensor element 101, and a concentration determination unit 130 for determining the concentration of the monitored gas component contained in the measured gas.

[0085] The element action control unit 120 mainly includes: an adjustment pump unit control unit 121, which controls the action of the adjustment pump unit 21; a first measuring pump unit control unit 122a, which controls the action of the first measuring pump unit 50; a second measuring pump unit control unit 122b, which controls the action of the second measuring pump unit 41; and a heater control unit 123, which controls the heating action of the heater 72.

[0086] On the other hand, the concentration determination unit 130 mainly includes a water vapor concentration determination unit 130H and a carbon dioxide concentration determination unit 130C for respectively determining the concentrations of H 2 O and CO 2 , which are main monitoring target gas components in the gas sensor 100 .

[0087] The water vapor concentration determination unit 130H determines the concentration of H 2 O contained in the gas to be measured based on the value of the oxygen pump current Ip1 flowing through the first measuring pump cell 50 acquired by the first measuring pump cell control unit 122 a .

[0088] The carbon dioxide concentration determination unit 130C determines the concentration of CO 2 contained in the gas to be measured based on the value of the oxygen pump current Ip2 flowing through the second measuring pump cell 41 acquired by the second measuring pump cell control unit 122 b .

[0089] The concentration determination unit 130 further includes an oxygen concentration determination unit 130A that determines the concentration of oxygen contained in the gas to be measured. The oxygen concentration determination unit 130A determines the concentration of oxygen contained in the gas to be measured based on the value of the oxygen pump current Ip0 flowing through the adjustment pump unit 21 obtained by the adjustment pump unit control unit 121, the value of the oxygen pump current Ip1 flowing through the first measurement pump unit 50 obtained by the first measurement pump unit control unit 122a, and the value of the oxygen pump current Ip2 flowing through the second measurement pump unit 41 obtained by the second measurement pump unit control unit 122b. That is, in the gas sensor 100 involved in this embodiment, in addition to the main monitoring target gas components, that is, H2O and CO2, oxygen is also monitored as an additional monitoring target gas component.

[0090] <Basic thinking method for multi-gas monitoring and concentration determination>

[0091] Next, the basic concept of monitoring multiple gas types (multi-gas monitoring) and determining the concentration of the monitored gas implemented in the gas sensor 100 having the above-mentioned configuration will be described. Hereinafter, the gas to be measured is exhaust gas containing oxygen, H2O, and CO2.

[0092] Figure 3 Schematic diagram showing basic gas inflow and outflow patterns in three cavities (internal cavities) provided in the sensor element 101 of the gas sensor 100 .

[0093] First, in the sensor element 101 of the gas sensor 100 according to the present embodiment, as described above, the gas to be measured is introduced into the first cavity 20 through the gas introduction port 10 (first diffusion rate control unit 11), the buffer space 12, and the second diffusion rate control unit 13. In the first cavity 20, the pump unit 21 is adjusted to operate, and oxygen contained in the introduced gas to be measured is sucked out, and H2O and CO2 are reduced. That is, the pump unit 21 is adjusted to operate, oxygen is sucked out from the gas to be measured introduced into the first cavity 20, and a reduction (decomposition) reaction (2H2O→2H2+O2, 2CO2→2CO+O2) of H2O and CO2 contained in the gas to be measured is performed, and H2O and CO2 are substantially all decomposed into hydrogen (H2), carbon monoxide (CO), and oxygen.

[0094] The above-mentioned oxygen absorption and reduction (decomposition) of H2O and CO2 are carried out as follows, that is, the adjustment pump unit control unit 121 of the controller 110 sets the target value (control voltage) of the electromotive force V0 in the first cavity sensor unit 80 to a value in the range of 1000mV to 1500mV (preferably 1000mV), and based on the difference between the actual electromotive force V0 and the target value, the voltage Vp0 applied by the variable power supply 24 to the adjustment pump unit 21 is feedback-controlled in such a way that the electromotive force V0 is maintained at the target value.

[0095] By adjusting the pump unit 21 to operate in this manner, the oxygen partial pressure in the first cavity 20 is maintained at a sufficiently low value that oxygen is considered to be substantially absent. For example, in the case of V0=1000 mV, it is 10 －20 Therefore, the measured gas does not substantially contain H2O, CO2 and oxygen.

[0096] The measured gas containing H 2 and CO and substantially containing no H 2 O, CO 2 , and oxygen is introduced into the second cavity 40 .

[0097] In the second cavity 40 , the first measuring pump unit 50 is operated so that oxygen is sucked in and only H 2 contained in the introduced gas to be measured is selectively oxidized.

[0098] The above-mentioned oxygen inhalation is carried out as follows: the first measuring pump unit control section 122a of the controller 110 sets the target value (control voltage) of the electromotive force V1 in the second cavity sensor unit 81 to a value within the range of 250mV to 450mV (preferably 350mV), and based on the difference between the actual value of the electromotive force V1 and the target value, feedback control is performed on the voltage Vp1 applied by the variable power supply 52 to the first measuring pump unit 50 to keep the electromotive force V1 at the above-mentioned target value.

[0099] By operating the first measuring pump unit 50 in this manner, the oxidation (combustion) reaction of 2H2+O2→2H2O is promoted in the second cavity 40, and H2O is regenerated in an amount correlated with the H2O introduced from the gas inlet port 10. It should be noted that in this embodiment, the amount of H2O is correlated means that the amount of H2O introduced from the gas inlet port 10 and the amount of H2O regenerated by oxidation of H2 generated by the decomposition of the H2O are the same, or are within a certain error range allowed in terms of measurement accuracy.

[0100] By setting the target value of the electromotive force V1 to a value within the range of 250 mV to 450 mV, the oxygen partial pressure in the second cavity 40 is maintained within a range where H2 is almost completely oxidized but CO is not oxidized. For example, when V1 = 350 mV, the oxygen partial pressure in the second cavity 40 is maintained within a range where H2 is almost completely oxidized but CO is not oxidized. －7 Around atm.

[0101] In addition, as described above, providing the first measuring electrode 51 as a cermet electrode containing, as a metal component, a Pt—Au alloy having an Au concentration of 1 wt % or more and 50 wt % or less also contributes to improving the selective oxidation property of H 2 .

[0102] At this time, the oxygen pump current Ip1 (hereinafter also referred to as the water vapor detection current Ip1) flowing through the first measurement pump unit 50 is approximately proportional to the concentration of H2O generated by the combustion of H2 in the second cavity 40 (the water vapor detection current Ip1 and the concentration of the generated H2O have a linear relationship). The amount of H2O generated by the combustion is correlated with the amount of H2O in the measured gas that is introduced from the gas inlet 10 and then temporarily decomposed in the first cavity 20. Accordingly, by detecting the water vapor detection current Ip1 in the first measurement pump unit control unit 122a, the H2O in the measured gas can be monitored. Therefore, the second cavity 40 is also referred to as the first measurement cavity.

[0103] In addition, a linear relationship is established between the water vapor detection current Ip1 and the water vapor concentration in the measured gas. Data (water vapor characteristic data) indicating this linear relationship is predetermined using a model gas whose water vapor concentration is known, and is held in the water vapor concentration determination unit 130H. In the gas sensor 100 according to the present embodiment, the water vapor concentration determination unit 130H acquires the value of the water vapor detection current Ip1 detected by the first measuring pump unit control unit 122a. The water vapor concentration determination unit 130H refers to the water vapor characteristic data and determines the value of the water vapor concentration corresponding to the acquired water vapor detection current Ip1. Thus, the water vapor concentration in the measured gas is determined.

[0104] If H2O does not exist in the measured gas introduced from the gas inlet 10, H2O will not be decomposed in the first cavity 20, and therefore, no H2 will be introduced into the second cavity 40, so the water vapor detection current Ip1 is substantially zero.

[0105] H2 is oxidized to become H2O, so that the measured gas contains H2O and CO and substantially does not contain CO2 and oxygen. The measured gas is introduced into the third cavity 61. In the third cavity 61, the second measuring pump unit 41 is operated, so that oxygen is sucked in and CO contained in the introduced measured gas is oxidized.

[0106] The above-mentioned oxygen inhalation is carried out as follows: the second measuring pump unit control unit 122b of the controller 110 sets the target value (control voltage) of the electromotive force V2 in the third cavity sensor unit 82 to a value in the range of 100mV to 300mV (preferably 200mV), and based on the difference between the actual value of the electromotive force V2 and the target value, the voltage Vp2 applied by the variable power supply 46 to the second measuring pump unit 41 is feedback controlled to keep the electromotive force V2 at the above-mentioned target value.

[0107] As the second measuring pump unit 41 operates in the above-described manner, the oxidation (combustion) reaction of 2CO+O 2 →2CO 2 is promoted in the third cavity 61 , and CO 2 in an amount correlated with the amount of CO 2 introduced from the gas inlet port 10 is generated again.

[0108] By setting the target value of the electromotive force V2 to a value within the range of 100 mV to 300 mV, the oxygen partial pressure in the third cavity 61 is maintained within a range where almost all CO is oxidized. For example, in the case of V2 = 200 mV, the oxygen partial pressure in the third cavity 61 is 10 －4 Atm or so.

[0109] At this time, the oxygen pump current Ip2 (hereinafter also referred to as the carbon dioxide detection current Ip2) flowing through the second measuring pump unit 41 is approximately proportional to the concentration of CO2 generated by the combustion of CO in the third cavity 61 (the carbon dioxide detection current Ip2 and the concentration of the generated CO2 have a linear relationship). The amount of CO2 generated by the combustion is correlated with the amount of CO2 in the measured gas that is introduced from the gas inlet 10 and then temporarily decomposed in the first cavity 20. Therefore, by detecting the carbon dioxide detection current Ip2 in the second measuring pump unit control unit 122b, the CO2 in the measured gas can be monitored. Therefore, the third cavity 61 is also referred to as the second measurement cavity.

[0110] In addition, a linear relationship is established between the carbon dioxide detection current Ip2 and the carbon dioxide concentration in the measured gas. Data representing the linear relationship (carbon dioxide characteristic data) is predetermined using a model gas with a known carbon dioxide concentration, and is maintained in the carbon dioxide concentration determination unit 130C. In the gas sensor 100 involved in this embodiment, the carbon dioxide concentration determination unit 130C obtains the value of the carbon dioxide detection current Ip2 detected by the second measurement pump unit control unit 122b. The carbon dioxide concentration determination unit 130C refers to the carbon dioxide characteristic data and determines the value of the carbon dioxide concentration corresponding to the obtained carbon dioxide detection current Ip2. In this way, the carbon dioxide concentration in the measured gas is determined.

[0111] It should be noted that if CO 2 does not exist in the measured gas introduced from the gas inlet 10 , CO 2 will not be decomposed in the first cavity 20 , and therefore no CO will be introduced into the third cavity 61 , so the carbon dioxide detection current Ip2 is substantially zero.

[0112] The following will also be based on Figure 3 The operation mode of the gas sensor 100 described above is called a basic operation.

[0113] In addition, the gas sensor 100 according to the present embodiment can also determine the concentration of oxygen contained in the measured gas, although indirectly. In summary, the difference between the concentration of oxygen sucked out from the first cavity 20 (referred to as C0) and the concentration of oxygen sucked into the second cavity 40 and the third cavity 61 (referred to as C1 and C2, respectively) is

[0114] C=C0-C1-C2····(1)

[0115] It is equivalent to the concentration of oxygen in the measured gas introduced from the gas inlet port 10. C0, C1, and C2 are values ​​that are approximately proportional to the oxygen pump currents Ip0, Ip1, and Ip2, respectively. In the gas sensor 100, the relationship between C0 and Ip0, the relationship between C1 and Ip1, and the relationship between C2 and Ip2 (proportional constant) are predetermined and stored in the oxygen concentration determination unit 130A. When the measurement of the measured gas is started, the oxygen concentration determination unit 130A obtains the detection values ​​of the oxygen pump currents Ip0, Ip1, and Ip2 from the adjustment pump unit control unit 121, the first measurement pump unit control unit 122a, and the second measurement pump unit control unit 122b, respectively, and calculates the concentration of oxygen in the measured gas based on the above detection values, the above proportional constant, and formula (1).

[0116] <Concentration determination considering continuous use>

[0117] Figure 4 and Figure 5 This is a diagram for explaining a malfunction that may occur when the gas sensor 100 continues to perform measurement based on the above-mentioned basic operation.

[0118] When the gas sensor 100 measures the concentrations of H2O and CO2 and the concentration of oxygen in the measured gas according to the above-mentioned basic operation, the H2O generated in the second cavity 40 is basically introduced into the third cavity 61 or retained in the second cavity 40. In addition, the CO2 generated in the third cavity 61 is basically retained in the third cavity 61. Therefore, as the measurement continues, the amount of H2O and CO2 generated in the second cavity 40 and the third cavity 61 increases.

[0119] Therefore, when the concentration of the gas to be measured newly introduced from the first diffusion rate control unit 11 (gas introduction port 10) is relatively low, Figure 4 As shown, in the gas flow portion from the gas inlet 10 to the third cavity 61, a concentration gradient can be formed in which the concentrations of H 2 O and CO 2 increase as they go from the gas inlet 10 to the innermost cavity, that is, the third cavity 61 .

[0120] As a result of the concentration gradient, H2O and CO2 in the third cavity 61 or the second cavity 40 can diffuse and move from the third cavity 61 and the second cavity 40 toward the first cavity 20. That is, H2O and CO2 can flow back toward the first cavity 20.

[0121] As described above, in the first cavity 20, the pump unit 21 is adjusted to operate, and oxygen is continuously sucked out and H2O and CO2 are reduced. Figure 5As shown, when H2O and CO2 flow back from the third cavity 61 and the second cavity 40, they are indistinguishable from the original measurement objects at this moment, i.e., H2O and CO2 contained in the measured gas introduced from the gas inlet 10, and are (re)reduced to H2 and CO.

[0122] When the above-mentioned re-reduction occurs, H2 generated by re-reduction is included in H2 oxidized by oxygen sucked into the second cavity 40 through the first measuring pump cell 50, and CO generated by re-reduction is included in CO oxidized by oxygen sucked into the third cavity 61 through the second measuring pump cell 41. Therefore, the currents derived from the re-reduced H2O and CO2 are superimposed on the water vapor detection current Ip1 flowing through the first measuring pump cell 50 and the carbon dioxide detection current Ip2 flowing through the second measuring pump cell 41. That is, the values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 do not correspond to the concentrations of H2O and CO2 originally contained in the measured gas, and as a result, the measurement accuracy is reduced.

[0123] In the gas sensor 100 according to the present embodiment, the operation of each pump unit is controlled in such a manner that the measurement accuracy is not reduced due to the backflow of H2O and CO2. In summary, the measurement accuracy is ensured by performing an operation of discharging the H2O and CO2 that flow back toward the first cavity 20 to the outside of the sensor element 101 without suppressing the backflow of H2O and CO2 generated in the second cavity 40 and the third cavity 61. This operation mode is also referred to as a generated gas discharge operation.

[0124] Figure 6 : is a graph showing the time variation of the target values ​​of the electromotive force V0, V1 and V2 in the generated gas discharge operation. Figure 7 This is a schematic diagram showing how gases enter and exit the three cavities (inner cavities) during the generated gas discharge operation.

[0125] As described above, in the basic operation, the target value of the electromotive force V0 in the first cavity sensor unit 80 is set to a value within the range of 1000 mV to 1500 mV, and the voltage Vp0 applied to the adjustment pump unit 21 is feedback-controlled so that the electromotive force V0 is maintained at the target value.

[0126] In contrast, in the generated gas discharge operation, Figure 6 As shown in (a), the target value (set value) of the electromotive force V0 in the first cavity sensor unit 80 is temporarily changed from the stable value V0a to the value V0b at an appropriate timing.

[0127] Here, the value V0a is a value in the range of 1000 mV to 1500 mV, similarly to the target value of the electromotive force V0 in the basic operation. The value V0a can be set to the same value as the target value of the electromotive force V0 in the basic operation.

[0128] While the target value of the electromotive force V0 is set to the value V0a, the adjustment pump unit 21 absorbs oxygen from the first cavity 20 to the outside so that H2O and CO2 contained in the measured gas are substantially completely reduced, as in the basic operation.

[0129] On the other hand, the value V0b is a value within a range of 400 mV to 700 mV (preferably 400 mV) which is smaller than the value V0a.

[0130] When the target value of the electromotive force V0 is set to the above-mentioned value V0b, the adjustment pump unit 21 is adjusted to absorb the oxygen present in the first cavity 20 to the outside within a range in which the reduction of H2O and CO2 contained in the measured gas does not occur. That is, although the operation of the adjustment pump unit 21 as an oxygen absorption mechanism is maintained, the reduction of H2O and CO2 in the first cavity 20 is temporarily interrupted. In this case, the oxygen partial pressure in the first cavity 20 is maintained at a sufficiently low value within a range in which the reduction of H2O and CO2 contained in the measured gas does not occur. For example, in the case of V0 = 400 mV, it is 10 －8 Atm or so.

[0131] That is, in the generated gas discharge action, the adjustment pump unit 21 performs an absorption action (second absorption action) of aspirating oxygen from the first cavity 20 within a range in which the water vapor and carbon dioxide contained in the measured gas introduced into the first cavity 20 are not reduced, during an absorption action (first absorption action) of aspirating oxygen from the first cavity 20 in a manner in which the water vapor and carbon dioxide contained in the measured gas are substantially completely reduced.

[0132] On the other hand, the target values ​​of electromotive force V1 and electromotive force V2 are set similarly to the basic operation. Specifically, the target value of electromotive force V1 is set to a value within the range of 250mV to 450mV (preferably 350mV), and the target value of electromotive force V2 is set to a value within the range of 100mV to 300mV (preferably 200mV).

[0133] In this case, the operation of the gas sensor 100 during the period when the target value of the electromotive force V0 is set to the value V0a is the same as that during the basic operation. However, when the target value of the electromotive force V0 is set to the value V0b, only the oxygen contained in the introduced measured gas is absorbed in the first cavity 20, and H2O and CO2 are not reduced. Therefore, as a result of the retention of H2O and CO generated in the second cavity 40 and the third cavity 61, Figure 4The concentration gradient shown in FIG. 1 is the same as that shown in FIG. 1 , even when H2O and CO2 flow backward toward the first cavity 20. Figure 7 As shown in FIG. 1 , the H2O and CO2 that flowed back are not reduced again in the first cavity 20, but are directly discharged to the outside of the element. As a result, the concentration gradient is weakened, and as a result, it is not easy for the H2O and CO2 that flowed back to be reduced again after the target value of the electromotive force V0 is set to the value V0a again. That is, in the gas sensor 100 involved in this embodiment, by starting the second suction operation, the H2O and CO2 generated by the selective oxidation of H2 and CO are well discharged to the outside of the element through the first cavity 20 according to the concentration gradient generated in the gas flow portion inside the sensor element 101.

[0134] The second suction operation can be performed at any time, or at a predetermined time. Alternatively, it can be performed when a specified condition is met. For example, the longer the measured values ​​of H2O and CO2 in the gas sensor 100 are large, the more H2O and CO2 are generated in the second cavity 40 and the third cavity 61, and the second suction operation is performed based on the integral value of the measured value.

[0135] The target value of the electromotive force V0 is set to the value V0b and the time for the second suction action is preferably within the range of 1ms to 1s. When the set time is shorter than 1ms, the diffusion of H2O and CO2 from the second cavity 40 or the third cavity 61 is not sufficiently carried out, so the concentration gradient is not sufficiently weakened, and the situation of reduced measurement accuracy may continue, which is not ideal. In addition, when the set time is longer than 1s, the time for reducing H2O and CO2 contained in the newly introduced measured gas becomes longer, that is, the time for which the concentration measurement cannot be carried out becomes longer, so the responsiveness is reduced, which is not ideal.

[0136] Alternatively, by periodically changing the target value of the electromotive force V0, the first suction action and the second suction action are alternately and periodically performed in the adjustment pump unit 21, thereby periodically stopping the reduction of H2O and CO2. In addition, the target values ​​(set values) of the electromotive force V1 in the second cavity sensor unit 81 and the electromotive force V2 in the third cavity sensor unit 82 may also be as follows: Figure 6 As shown in (b), it is periodically changed in synchronization with the periodic change of the target value of the electromotive force V0. That is, the oxygen intake by the first measuring pump unit 50 and the second measuring pump unit 41 can be synchronized with the second suction operation.

[0137] The target values ​​of the electromotive force V1 and the electromotive force V2 are set to 0 during the period when the target value of the electromotive force V0 is set to the value V0a, and are set to values ​​within the same range as during the basic operation only during the period when the target value of the electromotive force V0 is set to the value V0b. In this case, the first measuring pump unit 50 and the second measuring pump unit 41 operate only during the period when the adjustment pump unit 21 performs the second suction operation, and do not operate during the period when the adjustment pump unit 21 performs the first suction operation. It should be noted that Figure 6 In (b), both are shown in one graph for simplicity of illustration, but in reality, the electromotive force V1 and the electromotive force V2 are set to different values.

[0138] In this case, the reduction of H2O and CO2 in the first cavity 20 and the selective oxidation of H2 and CO in the second cavity 40 and the third cavity 61 are performed at different times. That is, during the period when H2 and CO are reoxidized in the second cavity 40 and the third cavity 61, only the oxygen contained in the introduced measured gas is absorbed in the first cavity 20, and H2O and CO2 are not reduced. In this case, the H2O and CO2 generated in the second cavity 40 and the third cavity 61 are retained, and even if Figure 4 As shown in the concentration gradient, H2O and CO2 flowing back into the first cavity 20 will not be reduced again in the first cavity 20, but will be directly discharged to the outside of the element.

[0139] In this case, the time during which the target value of the electromotive force V0 is set to the value V0a is preferably within a range of 1 ms to 1 s.

[0140] in addition, Figure 8 is a diagram showing another example of the generated gas discharge operation. Figure 8 As shown in (a), the periodic change of the target value of the electromotive force V0 is Figure 6 (a) is the same as above, and if Figure 8 As shown in (b), the phase (timing) of the periodic change of the target values ​​of the electromotive force V1 and the electromotive force V2 is relative to Figure 6 More specifically, the start of oxygen inhalation to the second cavity 40 and the third cavity 61 is advanced to the middle of the first inhalation action, and the inhalation is ended in the middle of the second inhalation action. The degree of the early start time is set to be less than 50% of the time (time for setting the target value of the electromotive force V0 to the value V0a) Δt for the first inhalation action.

[0141] As described above, according to this embodiment, oxygen contained in the measured gas is sucked out and H2O and CO2 are reduced in the first cavity, H2 and CO generated by the reduction are oxidized in the second cavity and the third cavity, respectively, and the concentrations of H2O and CO2 contained in the measured gas are obtained based on the magnitude of the oxygen pump current sucked into the second cavity and the third cavity during the oxidation. In this gas sensor, the reduction of H2O and CO2 in the first cavity is temporarily or periodically stopped, so that H2O and CO2 generated by the oxidation of H2 and CO are discharged from the first cavity to the outside of the sensor element using their concentration gradient. As a result, the reduction of H2O and CO2 generated by the oxidation of H2 and CO is reduced again, which is caused by the reduction of H2O and CO, and the decrease in measurement accuracy is well suppressed.

[0142] <Modification>

[0143] In the above-mentioned embodiment, the generated gas discharge operation of H2O and CO2 generated by oxidation of H2 and CO is targeted for concentration measurement. The H2 and CO are generated by reduction of H2O and CO2 contained in the measured gas in the gas sensor 100 having the sensor element 101 with a three-chamber structure. However, it is not essential that the process of reducing H2O and CO2 contained in the measured gas to generate H2 and CO is performed only in one cavity. If the generated gas discharge operation similar to that in the above-mentioned embodiment can be performed, the sensor element may have another structure.

Claims

1. A gas sensor capable of measuring the concentrations of a plurality of monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide, The gas sensor is characterized in that it has: A sensor element having a structure composed of an oxygen ion conductive solid electrolyte; and a controller, the controller controlling the action of the gas sensor, The sensor element comprises: A gas inlet port, the gas inlet port is used to introduce the measured gas; a plurality of cavities, the plurality of cavities being sequentially connected from the gas inlet via different diffusion rate control parts; and a heater for heating the sensor element, Two of the plurality of cavities are a first measurement cavity and a second measurement cavity, the second measurement cavity is the innermost cavity from the gas inlet among the plurality of cavities, and the first measurement cavity is a cavity in front of the second measurement cavity. The sensor element further comprises: an oxygen suction mechanism capable of performing a first suction operation of suctioning oxygen contained in the gas to be measured in such a manner that water vapor and carbon dioxide contained in the gas to be measured are substantially completely reduced while the gas to be measured introduced from the gas inlet reaches the first measurement cavity; a first measuring pump cell including a first measuring electrode formed facing the first measuring cavity, an out-of-cavity pump electrode provided at a portion other than the plurality of cavities, and the solid electrolyte present between the first measuring electrode and the out-of-cavity pump electrode; and a second measuring pump cell, the second measuring pump cell comprising a second measuring electrode formed facing the second measuring cavity, the cavity outer pump electrode, and the solid electrolyte existing between the second measuring electrode and the cavity outer pump electrode, The first measuring pump unit is configured to selectively oxidize hydrogen generated by reduction of water vapor included in the gas to be measured introduced into the first measuring cavity in the first measuring cavity by sucking oxygen into the first measuring cavity; The second measuring pump unit is configured to oxidize carbon monoxide generated by reduction of carbon dioxide accompanying the first suction operation contained in the measured gas introduced into the second measuring cavity in the second measuring cavity by sucking oxygen into the second measuring cavity. The controller has: a water vapor concentration determining mechanism for determining the concentration of water vapor contained in the measured gas based on the magnitude of a current flowing between the first measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the first measuring cavity by the first measuring pump unit; and a carbon dioxide concentration determining mechanism for determining the concentration of carbon dioxide contained in the gas to be measured based on the magnitude of the current flowing between the second measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the second measuring cavity by the second measuring pump unit, The oxygen suction mechanism is configured to further perform a second suction operation for suctioning oxygen contained in the measured gas within a range where water vapor and carbon dioxide contained in the measured gas before reaching the first measurement cavity are not reduced for a predetermined time during the first suction operation. The start of the second suction operation interrupts the reduction of water vapor and carbon dioxide by the oxygen suction mechanism, so that water vapor generated in the first measurement cavity and carbon dioxide generated in the second measurement cavity are discharged to the outside of the sensor element.

2. The gas sensor according to claim 1, characterized in that The plurality of cavities are a first cavity, a second cavity as the first measurement cavity, and a third cavity as the second measurement cavity. The sensor element further includes an adjustment pump unit as the oxygen suction mechanism. The adjustment pump unit is composed of an adjustment electrode formed facing the first cavity, the cavity-external pump electrode, and the solid electrolyte existing between the adjustment electrode and the cavity-external pump electrode. The adjustment pump unit is configured to perform, as the first suction operation, an operation of sucking oxygen from the first cavity in such a manner that water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are substantially completely reduced, and, as the second suction operation, an operation of sucking oxygen from the first cavity within a range in which water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are not reduced, for a predetermined time during the first suction operation. The second suction operation is started by the adjustment pump unit to interrupt the reduction of water vapor and carbon dioxide in the first cavity, so that water vapor generated in the second cavity and carbon dioxide generated in the third cavity are discharged to the outside of the sensor element through the first cavity.

3. The gas sensor according to claim 2, characterized in that: The adjustment pump unit performs the first suction action and the second suction action alternately and periodically, According to the first suction operation and the second suction operation of the adjustment pump unit, the first measuring pump unit sucks oxygen into the second cavity and the second measuring pump unit sucks oxygen into the third cavity periodically.

4. The gas sensor according to claim 3, characterized in that: The oxygen intake into the second cavity by the first measuring pump unit and the oxygen intake into the third cavity by the second measuring pump unit are synchronized with the second suction operation of the adjustment pump unit.

5. The gas sensor according to claim 3, characterized in that: The oxygen intake into the second cavity by the first measuring pump unit and the oxygen intake into the third cavity by the second measuring pump unit are performed from the middle of the first suction operation of the adjustment pump unit to the middle of the second suction operation.

6. The gas sensor according to any one of claims 2 to 5, characterized in that: The sensor element further comprises: a reference electrode in contact with a reference gas; a first cavity sensor unit, the first cavity sensor unit comprising the adjustment electrode, the reference electrode, and the solid electrolyte between the adjustment electrode and the reference electrode, and generating an electromotive force V0 corresponding to the oxygen concentration of the first cavity between the adjustment electrode and the reference electrode; a second cavity sensor unit, the second cavity sensor unit comprising the first measuring electrode, the reference electrode, and the solid electrolyte between the first measuring electrode and the reference electrode, and generating an electromotive force V1 corresponding to the oxygen concentration of the second cavity between the first measuring electrode and the reference electrode; as well as a third cavity sensor unit, the third cavity sensor unit comprising the second measuring electrode, the reference electrode, and the solid electrolyte between the second measuring electrode and the reference electrode, generating an electromotive force V2 corresponding to the oxygen concentration of the third cavity between the second measuring electrode and the reference electrode, The controller has: an adjustment pump unit control mechanism for controlling the voltage applied between the adjustment electrode and the cavity external pump electrode in the adjustment pump unit in such a manner that the electromotive force V0 in the first cavity sensor unit is maintained at a specified target value within a range of 1000 mV to 1500 mV during the first suction operation and is maintained at a specified target value within a range of 400 mV to 700 mV during the second suction operation; a first measuring pump unit control mechanism for controlling a voltage applied between the first measuring electrode and the cavity outer pump electrode in the first measuring pump unit so that the electromotive force V1 in the second cavity sensor unit is maintained at a predetermined target value within a range of 250 mV to 450 mV; as well as and a second measuring pump unit control mechanism for controlling the voltage applied between the second measuring electrode and the cavity outer pump electrode in the second measuring pump unit so that the electromotive force V2 in the third cavity sensor unit is maintained at a predetermined target value within a range of 100 mV to 300 mV.

7. A concentration measurement method using a gas sensor, comprising measuring the concentrations of a plurality of monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide using the gas sensor, The concentration determination method is characterized in that The gas sensor includes a sensor element having a structure composed of an oxygen ion conductive solid electrolyte. The sensor element comprises: A gas inlet port, the gas inlet port is used to introduce the measured gas; a plurality of cavities, the plurality of cavities being sequentially connected from the gas inlet via different diffusion rate control parts; and a heater for heating the sensor element, Two of the plurality of cavities are a first measurement cavity and a second measurement cavity, the second measurement cavity is the innermost cavity from the gas inlet among the plurality of cavities, and the first measurement cavity is a cavity in front of the second measurement cavity. The sensor element further comprises: an oxygen suction mechanism capable of performing a first suction operation of suctioning oxygen contained in the gas to be measured in such a manner that water vapor and carbon dioxide contained in the gas to be measured are substantially completely reduced while the gas to be measured introduced from the gas inlet reaches the first measurement cavity; a first measuring pump cell including a first measuring electrode formed facing the first measuring cavity, an out-of-cavity pump electrode provided at a portion other than the plurality of cavities, and the solid electrolyte present between the first measuring electrode and the out-of-cavity pump electrode; and a second measuring pump cell, the second measuring pump cell comprising a second measuring electrode formed facing the second measuring cavity, the cavity outer pump electrode, and the solid electrolyte existing between the second measuring electrode and the cavity outer pump electrode, The concentration determination method comprises the following steps: a) the oxygen suction mechanism performs the first suction action; b) the first measuring pump unit sucks oxygen into the first measuring cavity, thereby selectively oxidizing hydrogen generated by reduction of water vapor contained in the gas to be measured introduced into the first measuring cavity in the first measuring cavity; c) the second measuring pump unit absorbs oxygen into the second measuring cavity, thereby oxidizing carbon monoxide in the second measuring cavity that is generated by the reduction of carbon dioxide accompanying the first suction operation and contained in the measured gas introduced into the second measuring cavity; d) determining the concentration of water vapor contained in the measured gas based on the magnitude of the current flowing between the first measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the first measuring cavity by the first measuring pump unit; and e) determining the concentration of carbon dioxide contained in the gas to be measured based on the magnitude of the current flowing between the second measuring electrode and the pump electrode outside the cavity when oxygen is sucked into the second measuring cavity by the second measuring pump unit, During the process a), the oxygen absorption mechanism performs a second absorption action for a predetermined time to absorb oxygen contained in the gas to be measured within a range where water vapor and carbon dioxide contained in the gas to be measured are not reduced before reaching the first measuring cavity, thereby interrupting the reduction of water vapor and carbon dioxide performed by the oxygen absorption mechanism, thereby discharging water vapor generated in the first measuring cavity and carbon dioxide generated in the second measuring cavity to the outside of the sensor element.

8. The concentration measurement method using a gas sensor according to claim 7, characterized in that: The plurality of cavities are a first cavity, a second cavity as the first measurement cavity, and a third cavity as the second measurement cavity. The sensor element further includes an adjustment pump unit as the oxygen suction mechanism. The adjustment pump unit is composed of an adjustment electrode formed facing the first cavity, the cavity-external pump electrode, and the solid electrolyte existing between the adjustment electrode and the cavity-external pump electrode. In the step a), with respect to the adjustment pump unit, as the first suction action, an action of sucking oxygen from the first cavity is performed in such a way that substantially all of the water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are reduced, and as the second suction action, the action of sucking oxygen from the first cavity within a range in which the water vapor and carbon dioxide contained in the measured gas introduced into the first cavity are not reduced is performed for a specified time during the first suction action, thereby interrupting the reduction of the water vapor and carbon dioxide in the first cavity, so that the water vapor generated in the second cavity and the carbon dioxide generated in the third cavity are discharged to the outside of the sensor element via the first cavity.

9. The concentration measurement method using a gas sensor according to claim 8, characterized in that: In the step a), the adjustment pump unit performs the first suction operation and the second suction operation alternately and periodically. According to the first suction operation and the second suction operation of the adjustment pump unit in the step a), the oxygen is sucked into the second cavity by the first measuring pump unit in the step b) and the oxygen is sucked into the third cavity by the second measuring pump unit in the step c).

10. The concentration measurement method using a gas sensor according to claim 9, characterized in that: The suction of oxygen into the second cavity by the first measuring pump unit in the step b) and the suction of oxygen into the third cavity by the second measuring pump unit in the step c) are performed synchronously with the second suction operation of the adjustment pump unit in the step a).

11. The concentration measurement method using a gas sensor according to claim 9, characterized in that: The oxygen suction into the second cavity by the first measuring pump unit in the step b) and the oxygen suction into the third cavity by the second measuring pump unit in the step c) are performed from the middle of the first suction operation of the adjustment pump unit in the step a) to the middle of the second suction operation.

12. The concentration measurement method using a gas sensor according to any one of claims 8 to 11, characterized in that: The sensor element further includes a reference electrode, the reference electrode being in contact with a reference gas. In the step a), the voltage applied between the adjustment electrode and the pump electrode outside the cavity in the adjustment pump unit is controlled in such a manner that the electromotive force V0 generated between the adjustment electrode and the reference electrode in accordance with the oxygen concentration in the first cavity is maintained at a predetermined target value within a range of 1000 mV to 1500 mV during the first suction operation and is maintained at a predetermined target value within a range of 400 mV to 700 mV during the second suction operation. In the step b), the voltage applied between the first measuring electrode and the pump electrode outside the cavity in the first measuring pump unit is controlled in such a manner that the electromotive force V1 generated between the first measuring electrode and the reference electrode in accordance with the oxygen concentration in the second cavity is maintained at a predetermined target value within a range of 250 mV to 450 mV. In the step c), the voltage applied between the second measuring electrode and the pump electrode outside the cavity in the second measuring pump unit is controlled in such a manner that the electromotive force V2 generated between the second measuring electrode and the reference electrode in accordance with the oxygen concentration in the third cavity is maintained at a specified target value within the range of 100 mV to 300 mV.

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