Gas sensor and method for controlling gas sensor

Abstract

And a low-concentration gas to be measured can be measured with good precision. Provided are a gas sensor 100 and a control method therefor, the gas sensor 100 comprising a sensor element 101 and a control device, the sensor element 101 being provided with: a base part 102; a cavity (15) through which the gas to be measured flows; the oxygen pump unit 21 comprises an in-cavity oxygen pump electrode 22 and an out-cavity oxygen pump electrode 23; a decomposition pump unit (50) comprising an in-cavity decomposition pump electrode (51) and an out-cavity decomposition pump electrode (23); an in-cavity detection electrode 44; and a reference electrode 42 that is disposed so as to be in contact with a reference gas, the control device being provided with: a pump control unit that operates the decomposition pump unit 50 so that the voltage between the in-cavity detection electrode 44 and the reference electrode 42 reaches a prescribed value, thereby decomposing at least a portion of the gas to be measured among the gas to be measured; oxygen generated by decomposition is sucked out; and a concentration calculation unit that calculates the concentration of the gas to be measured in the gas to be measured on the basis of the value of the voltage between the decomposition pump electrode (51) and the reference electrode (42) in the cavity.

Description

Technical Field

[0001] The present invention relates to a gas sensor and a control method of the gas sensor. This application claims priority to Japanese Patent Application No. 2022-144890 filed in Japan on September 12, 2022, the contents of which are incorporated herein by reference. Background Art

[0002] In various fields such as combustion control of internal combustion engines such as automobile engines, exhaust gas control, environmental control, medicine, biotechnology, and agriculture and industry, it is required to measure the concentration of target gas components (oxygen O2, water vapor H2O, carbon dioxide CO2, nitrogen oxides NOx, ammonia NH3, hydrocarbons HC, etc.) in the measured gas. Various measuring devices are used to measure the concentration, but as an example, a limiting current gas sensor using a solid electrolyte with oxygen ion conductivity such as zirconium dioxide (ZrO2) is known.

[0003] For example, Japanese Patent No. 5918177 and Japanese Patent No. 6469464 disclose a gas sensor that determines the concentration of water vapor and carbon dioxide in a measured gas based on a current flowing in a solid electrolyte. Also, for example, Japanese Patent No. 6469462 discloses a gas sensor that determines the concentration of water vapor in a measured gas based on a current flowing in a solid electrolyte.

[0004] In addition, for example, Japanese Patent No. 5323752 discloses a NOx sensor having a main pump unit and an auxiliary pump unit for adjusting oxygen concentration, and a measuring pump unit including a measuring electrode for detecting NOx. In the NOx sensor, first, the oxygen partial pressure in the measured gas is controlled to a low partial pressure that has substantially no effect on the measurement of NOx by the main pump unit and the auxiliary pump unit. NOx in the measured gas with the controlled oxygen partial pressure is reduced at the measuring electrode, and the generated oxygen is sucked out by the measuring pump unit and detected in the form of a current value.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 5918177

[0008] Patent Document 2: Japanese Patent No. 6469464

[0009] Patent Document 3: Japanese Patent No. 6469462

[0010] Patent Document 4: Japanese Patent No. 5323752 Summary of the invention

[0011] With the strengthening of various environmental restrictions such as automobile exhaust gas restrictions and the diversification of usage environments, gas sensors are also required to accurately measure lower concentrations of the measurement target gas. Here, the desired concentration range of low concentration may vary depending on the type of measurement target gas and the usage environment of the gas sensor. When the measurement target gas is water vapor H2O or carbon dioxide CO2, low concentration refers to, for example, a concentration of less than 10%, less than 5%, less than 3%, or less than 1%. When the measurement target gas is nitrogen oxide NOx, ammonia NH3, etc., low concentration refers to a concentration of less than 500ppm, less than 400ppm, less than 300ppm, less than 200ppm, or less than 100ppm.

[0012] In the conventional limiting current gas sensor, the concentration of the measured gas is measured based on the current flowing in the solid electrolyte. For example, the above-mentioned Japanese Patent No. 5918177 and Japanese Patent No. 6469464 disclose that: in the main electrochemical pump unit, the water vapor H2O and carbon dioxide CO2 of the measured gas are substantially completely decomposed, in the first electrochemical pump unit for measurement, the hydrogen H2 produced by the decomposition of the water vapor H2O is burned, and in the second electrochemical pump unit for measurement, the carbon monoxide CO produced by the decomposition of the carbon dioxide CO2 is burned. In addition, it is disclosed that: based on the magnitude of each current flowing at this time, the concentrations of the water vapor component and the carbon dioxide component are determined respectively. In addition, for example, Japanese Patent No. 5323752 discloses that: in the measurement pump unit, the oxygen produced by the reduction of the measured gas (such as NOx) is detected in the form of current. The magnitude of the current is a value corresponding to the concentration of the measured gas.

[0013] However, the above-mentioned current is not zero even when there is no measurement target gas in the measured gas, and a small current flows in the above-mentioned first measurement electrochemical pump unit and the second measurement electrochemical pump unit, or the measurement pump unit (measurement pump unit, etc.). This small current is called bias current. Bias current is generated regardless of the concentration of the measurement target gas. Therefore, when the current value of the bias current changes due to some reasons, regardless of the concentration of the measurement target gas, the current value detected in the measurement pump unit, etc. is offset by the change in the bias current value. In the case of measuring a measurement target gas with a low concentration, there is the following trend: the current value detected in the measurement pump unit, etc. corresponding to the measurement target gas concentration is relatively small, and therefore, the change in the current value caused by the change in the bias current value becomes relatively large, and the influence on the measurement accuracy becomes larger.

[0014] Therefore, an object of the present invention is to accurately measure a low-concentration measurement target gas. In other words, an object of the present invention is to accurately measure a measurement target gas in a wide concentration range including a low-concentration measurement target gas.

[0015] The inventors of the present invention have conducted intensive research and found that by configuring the gas sensor to include:

[0016] an oxygen pump unit that adjusts the oxygen concentration in the gas being measured;

[0017] a decomposition pump unit including an intracavity decomposition pump electrode for decomposing at least a portion of a measurement target gas in a measurement target gas whose oxygen concentration is adjusted;

[0018] an intracavity detection electrode for detecting the oxygen concentration in the gas to be measured after the oxygen concentration has been adjusted and at least a portion of the gas to be measured has been decomposed; and

[0019] a reference electrode, which is in contact with the reference gas,

[0020] Even when the concentration of the measurement target gas is low, the measurement target gas can be measured with high accuracy.

[0021] The present invention is based on a new finding that the concentration of a measurement target gas in a measurement gas can be calculated based on the voltage between a decomposition pump electrode and a reference electrode in a cavity when the voltage between a detection electrode and a reference electrode in a cavity reaches a predetermined value.

[0022] The present invention is based on the finding that a decomposition pump unit including an intra-cavity decomposition pump electrode disposed upstream of the intra-cavity detection electrode is operated so that a voltage between the intra-cavity detection electrode and a reference electrode reaches a predetermined value.

[0023] The present invention is based on the following new insight: a decomposition pump unit including an intra-cavity decomposition pump electrode arranged upstream of an intra-cavity detection electrode is operated in such a way that the voltage between the intra-cavity detection electrode and the reference electrode reaches a specified value; based on the voltage between the intra-cavity decomposition pump electrode and the reference electrode at this time, the concentration of the measured object gas in the measured gas can be calculated.

[0024] The present invention includes the following inventions.

[0025] (1) A gas sensor comprising a sensor element and a control device for controlling the sensor element, the sensor element detecting a measurement target gas in a measurement target gas,

[0026] The gas sensor is characterized in that

[0027] The sensor element comprises:

[0028] A long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer;

[0029] a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion;

[0030] An oxygen pump unit, the oxygen pump unit comprising an intra-cavity oxygen pump electrode disposed in the measured gas circulation cavity, and an extra-cavity oxygen pump electrode disposed at a position of the base body different from the measured gas circulation cavity and corresponding to the intra-cavity oxygen pump electrode, for adjusting the oxygen concentration in the measured gas;

[0031] a decomposition pump unit, the decomposition pump unit comprising an intra-cavity decomposition pump electrode disposed in the measured gas circulation cavity at a position farther from the one end portion in the length direction of the base portion than the intra-cavity oxygen pump electrode, and an extra-cavity decomposition pump electrode disposed at a position of the base portion different from the measured gas circulation cavity and corresponding to the intra-cavity decomposition pump electrode, to decompose a measurement target gas in the measured gas;

[0032] an intra-cavity detection electrode disposed in the measured gas flow cavity at a position farther from the one end in the length direction of the base portion than the intra-cavity decomposition pump electrode; and

[0033] a reference electrode disposed inside the base body so as to be in contact with a reference gas,

[0034] The control device comprises:

[0035] a pump control unit that controls the operations of the oxygen pump unit and the decomposition pump unit; and

[0036] a concentration calculating unit for calculating the concentration of the measurement target gas in the measured gas;

[0037] The pump control unit operates the oxygen pump unit to adjust the oxygen concentration in the measured gas to a predetermined concentration, and operates the decomposition pump unit in such a manner that the voltage between the detection electrode in the cavity and the reference electrode reaches a predetermined value, thereby decomposing at least a portion of the measurement target gas in the measured gas at the decomposition pump electrode in the cavity of the decomposition pump unit, and sucking out oxygen generated by the decomposition of the measurement target gas by using the decomposition pump unit.

[0038] The concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the value of the voltage between the intra-cavity decomposition pump electrode and the reference electrode.

[0039] (2) The gas sensor according to (1) above, characterized in that:

[0040] The pump control unit adjusts the voltage between the intra-cavity decomposition pump electrode and the reference electrode in such a manner that the voltage between the intra-cavity detection electrode and the reference electrode reaches the specified value, thereby decomposing at least a portion of the measurement target gas in the measured gas at the intra-cavity decomposition pump electrode of the decomposition pump unit, and sucking out oxygen generated by the decomposition of the measurement target gas using the decomposition pump unit.

[0041] The concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the adjusted value of the voltage between the intra-cavity decomposition pump electrode and the reference electrode.

[0042] (3) The gas sensor according to (1) or (2) above, characterized in that:

[0043] The sensor element further includes a pump unit for current measurement.

[0044] The current measuring pump unit includes: the cavity detection electrode and the cavity detection electrode outside the cavity provided at a position of the base body different from the cavity through which the gas to be measured flows and corresponding to the cavity detection electrode.

[0045] The control device further comprises a switching unit,

[0046] The switching unit switches whether or not to allow current to flow through the current measuring pump unit.

[0047] (4) The gas sensor according to (3) above, characterized in that:

[0048] The control device includes a measurement mode switching unit,

[0049] The measurement mode switching unit switches between a voltage measurement mode and a current measurement mode. In the voltage measurement mode, the concentration of the measurement target gas in the measurement target gas is calculated based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity. In the current measurement mode, the concentration of the measurement target gas in the measurement target gas is calculated based on the current value flowing through the current measurement pump unit.

[0050] The measurement mode switching unit switches the switching means so that current does not flow through the current measuring pump unit when switching to the voltage measurement mode, and switches the switching means so that current flows through the current measuring pump unit when switching to the current measurement mode.

[0051] (5) The gas sensor according to (4) above, characterized in that:

[0052] The measurement mode switching unit switches to the voltage measurement mode when it is determined that the concentration of the measurement target gas detected in the current measurement mode is lower than a predetermined first concentration threshold value C1.

[0053] When it is determined that the concentration of the measurement target gas detected in the voltage measurement mode is higher than a predetermined second concentration threshold value C2, switching to the current measurement mode is performed.

[0054] (6) The gas sensor according to (5) above, characterized in that:

[0055] The first concentration threshold C1 is a concentration lower than the second concentration threshold C2.

[0056] (7) The gas sensor according to any one of (4) to (6) above, characterized in that:

[0057] In the current measurement mode, the value of the current flowing through the current measurement pump cell is controlled so that the voltage between the intra-cavity detection electrode and the reference electrode reaches a predetermined value.

[0058] (8) The gas sensor according to any one of (1) to (7) above, characterized in that:

[0059] The measurement target gas is selected from the group consisting of water vapor H2O, carbon dioxide CO2 and nitrogen oxides NOx.

[0060] (9) A method for controlling a gas sensor for detecting a measurement target gas in a measured gas,

[0061] The gas sensor control method is characterized in that:

[0062] The gas sensor includes a sensor element and a control device for controlling the sensor element.

[0063] The sensor element comprises:

[0064] A long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer;

[0065] a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion;

[0066] An oxygen pump unit, the oxygen pump unit comprising an intra-cavity oxygen pump electrode disposed in the measured gas circulation cavity, and an extra-cavity oxygen pump electrode disposed at a position of the base body different from the measured gas circulation cavity and corresponding to the intra-cavity oxygen pump electrode, for adjusting the oxygen concentration in the measured gas;

[0067] a decomposition pump unit, the decomposition pump unit comprising an intra-cavity decomposition pump electrode disposed in the measured gas circulation cavity at a position farther from the one end portion in the length direction of the base portion than the intra-cavity oxygen pump electrode, and an extra-cavity decomposition pump electrode disposed at a position of the base portion different from the measured gas circulation cavity and corresponding to the intra-cavity decomposition pump electrode, to decompose a measurement target gas in the measured gas;

[0068] an intra-cavity detection electrode disposed in the measured gas flow cavity at a position farther from the one end in the length direction of the base portion than the intra-cavity decomposition pump electrode; and

[0069] a reference electrode disposed inside the base body so as to be in contact with a reference gas,

[0070] The control device comprises:

[0071] a pump control unit that controls the operations of the oxygen pump unit and the decomposition pump unit; and

[0072] a concentration calculating unit for calculating the concentration of the measurement target gas in the measured gas;

[0073] The control method comprises:

[0074] a pump control step in which the oxygen concentration in the measured gas is adjusted to a predetermined concentration by operating the oxygen pump unit through the pump control unit, and the decomposition pump unit is operated in such a manner that the voltage between the detection electrode in the cavity and the reference electrode reaches a predetermined value, thereby decomposing at least a part of the measurement target gas in the measured gas at the decomposition pump electrode in the cavity of the decomposition pump unit, and oxygen generated by the decomposition of the measurement target gas is sucked out by the decomposition pump unit; and

[0075] A concentration calculation step in which the concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity.

[0076] (10) The control method according to (9) above is characterized in that:

[0077] The sensor element further includes a pump unit for current measurement.

[0078] The current measuring pump unit includes: the cavity detection electrode and the cavity detection electrode outside the cavity provided at a position of the base body different from the cavity through which the gas to be measured flows and corresponding to the cavity detection electrode.

[0079] The control device further comprises a switching unit,

[0080] The switching unit switches whether to allow current to flow through the current measuring pump unit.

[0081] In the control method, the voltage measurement mode and the current measurement mode are switched by the switching unit while the measurement is performed.

[0082] In the voltage measurement mode, the pump control step and the concentration calculation step are performed, and the concentration of the measurement target gas in the measurement target gas is calculated based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity. In the current measurement mode, the oxygen pump unit, the decomposition pump unit and the current measurement pump unit are operated, and the concentration of the measurement target gas in the measurement target gas is calculated based on the current value flowing through the current measurement pump unit.

[0083] Effects of the Invention

[0084] According to the present invention, it is also possible to accurately measure a low-concentration measurement target gas. That is, according to the present invention, a wide concentration range of measurement target gases including low-concentration measurement target gases can be accurately measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 1 is a schematic vertical cross-sectional view in the longitudinal direction showing an example of the schematic configuration of the gas sensor 100 .

[0086] Figure 2 1 is a block diagram showing the electrical connection relationship between the control device 90 and each pump unit 21 , 50 , each sensor unit 80 , 81 , 82 , 83 , and the heater unit 70 of the sensor element 101 in the gas sensor 100 .

[0087] Figure 3 1 is a conceptual diagram showing the principle of water vapor measurement in the gas sensor 100 .

[0088] Figure 4 2 is a diagram showing an example of the relationship between the voltage V1 and the voltage V2 in the gas sensor 100. The horizontal axis represents the voltage V1 (mV), and the vertical axis represents the voltage V2 (mV).

[0089] Figure 5: is a graph showing an example of the relationship between the H2O concentration and the voltage V1 in the gas sensor 100. The horizontal axis represents the H2O concentration (%), and the vertical axis represents the voltage V1 (mV) when the voltage V2 reaches 450 mV.

[0090] Figure 6 1 is a schematic vertical cross-sectional view in the longitudinal direction showing an example of a schematic configuration of a gas sensor 200 according to a modified example.

[0091] Figure 7 1 is a block diagram showing the electrical connection relationship between the control device 290 and each pump unit 21 , 50 , 41 , each sensor unit 80 , 81 , 82 , 83 and the heater unit 70 of the sensor element 201 in the gas sensor 200 of the modified example.

[0092] Figure 8 1 is a schematic diagram showing an example of time change of the H2O concentration detection value output by the gas sensor 200 of the modified example and switching of the measurement mode. The horizontal axis represents time (seconds) and the vertical axis represents the H2O concentration detection value (%) output by the gas sensor 200.

[0093] Fig. 9 1 is a flowchart showing an example of H 2 O concentration detection processing in the gas sensor 200 according to the modified example.

[0094] Fig.10 This is a diagram showing an example of the relationship between the CO2 concentration and the voltage V1 in the gas sensor according to another embodiment. The horizontal axis represents the CO2 concentration (%), and the vertical axis represents the voltage V1 (mV) when the voltage V2 reaches 450 mV.

[0095] Fig.11 1 is a conceptual diagram showing the nitrogen oxide measurement principle when the nitrogen oxide is measured using the gas sensor 100 . DETAILED DESCRIPTION

[0096] A gas sensor according to the present invention includes a sensor element and a control device for controlling the sensor element.

[0097] The sensor element included in the gas sensor of the present invention comprises:

[0098] A long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer;

[0099] a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion;

[0100] An oxygen pump unit, the oxygen pump unit comprising an intra-cavity oxygen pump electrode disposed in the measured gas circulation cavity, and an extra-cavity oxygen pump electrode disposed at a position of the base body different from the measured gas circulation cavity and corresponding to the intra-cavity oxygen pump electrode, for adjusting the oxygen concentration in the measured gas;

[0101] a decomposition pump unit, the decomposition pump unit comprising an intra-cavity decomposition pump electrode disposed in the measured gas circulation cavity at a position farther from the one end portion in the length direction of the base portion than the intra-cavity oxygen pump electrode, and an extra-cavity decomposition pump electrode disposed at a position of the base portion different from the measured gas circulation cavity and corresponding to the intra-cavity decomposition pump electrode, to decompose a measurement target gas in the measured gas;

[0102] an intra-cavity detection electrode disposed in the measured gas flow cavity at a position farther from the one end in the length direction of the base portion than the intra-cavity decomposition pump electrode; and

[0103] A reference electrode is disposed inside the base portion so as to be in contact with a reference gas.

[0104] The control device included in the gas sensor of the present invention includes:

[0105] a pump control unit that controls the operations of the oxygen pump unit and the decomposition pump unit; and

[0106] a concentration calculating unit for calculating the concentration of the measurement target gas in the measured gas;

[0107] The pump control unit operates the oxygen pump unit to adjust the oxygen concentration in the measured gas to a predetermined concentration, and operates the decomposition pump unit in such a manner that the voltage between the detection electrode in the cavity and the reference electrode reaches a predetermined value, thereby decomposing at least a portion of the measurement target gas in the measured gas at the decomposition pump electrode in the cavity of the decomposition pump unit, and sucking out oxygen generated by the decomposition of the measurement target gas by using the decomposition pump unit.

[0108] The concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the value of the voltage between the intra-cavity decomposition pump electrode and the reference electrode.

[0109] Hereinafter, an example of an embodiment of the gas sensor of the present invention will be described in detail.

[0110] [General structure of gas sensor]

[0111] Hereinafter, the gas sensor of the present invention will be described with reference to the drawings. Figure 1 FIG. 1 is a schematic vertical cross-sectional view in the longitudinal direction showing an example of the schematic structure of a gas sensor 100 including a sensor element 101. Figure 1 As a benchmark, the so-called up and down Figure 1 Set the upper side of the Figure 1 The left side of is set as the front end side, and the right side thereof is set as the rear end side.

[0112] Figure 1 In FIG. 1 , the gas sensor 100 is an example of a water vapor sensor (H 2 O sensor) that monitors water vapor H 2 O in a measured gas using a sensor element 101 and measures the concentration thereof.

[0113] (Sensor element)

[0114] The sensor element 101 is a long strip-shaped element, which includes: a substrate 102 having a structure obtained by stacking multiple oxygen ion conductive solid electrolyte layers. The long strip-shaped is also called a long plate or a strip. The substrate 102 has: starting from the bottom in the accompanying drawings, the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5 and the second solid electrolyte layer 6 are stacked in this order. The solid electrolyte forming these six layers is a dense and airtight solid electrolyte. The six layers can be all of the same thickness, or each layer can be of different thickness. The layers are bonded to each other by means of an adhesive layer containing a solid electrolyte, and the adhesive layer is included in the substrate 102. Figure 1 In the embodiment, the layer structure composed of the six layers is exemplified; however, the layer structure in the present invention is not limited thereto, and any number of layers and layer structure may be employed.

[0115] The sensor element 101 is manufactured by, for example, subjecting ceramic green sheets corresponding to the respective layers to predetermined processing and printing of circuit patterns, stacking them, and further sintering them to integrate them.

[0116] A gas inlet 10 is formed at one end (hereinafter referred to as the front end) in the longitudinal direction of the sensor element 101 and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measured gas flow section 15, that is, the measured gas flow section is formed such that, starting from the gas inlet 10, in the longitudinal direction, the first diffusion rate control section 11, the buffer space 12, the second diffusion rate control section 13, the first internal cavity 20, the third diffusion rate control section 30, the second internal cavity 40, the fourth diffusion rate control section 60, and the third internal cavity 61 are adjacently formed in a manner that they are sequentially connected in the above order.

[0117] The gas inlet port 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61 are: the internal space of the sensor element 101 arranged in a manner of hollowing out the isolation layer 5, wherein the upper part of the internal space is divided by the lower surface of the second solid electrolyte layer 6, the lower part is divided by the upper surface of the first solid electrolyte layer 4, and the side part is divided by the side surface of the isolation layer 5.

[0118] The first diffusion rate control unit 11, the second diffusion rate control unit 13 and the third diffusion rate control unit 30 are all provided with two horizontally long slits ( Figure 1 In the figure, the direction perpendicular to the drawing constitutes the length direction of the opening.) The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 may be in any form as long as they apply a desired diffusion resistance, and their forms are not limited to the slits.

[0119] The fourth diffusion rate control unit 60 has a horizontally long slit ( Figure 1 The fourth diffusion rate control unit 60 is provided between the separator 5 and the second solid electrolyte layer 6 in a manner that the direction perpendicular to the drawing constitutes the length direction of the opening. The fourth diffusion rate control unit 60 may be in a form that provides a desired diffusion resistance, and its form is not limited to the slit.

[0120] In addition, a reference gas introduction space 43 is provided at a position farther from the front end side than the measured gas flow cavity 15, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position partitioned by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 has an opening at the other end (hereinafter referred to as the rear end) of the sensor element 101. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the H2O concentration.

[0121] The atmosphere introduction layer 48 is a layer formed of porous alumina, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43. The atmosphere introduction layer 48 is formed so as to cover the reference electrode 42.

[0122] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, an atmosphere introduction layer 48 connected to the reference gas introduction space 43 is provided around it. That is, the reference electrode 42 is configured to be in contact with the reference gas by means of the porous atmosphere introduction layer 48 and the reference gas introduction space 43. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 can be formed as a porous metal ceramic electrode (for example, a metal ceramic electrode of Pt and ZrO2).

[0123] In the measured gas flow cavity 15 , a gas introduction port 10 is open to the external space, and the measured gas enters the sensor element 101 from the external space through the gas introduction port 10 .

[0124] In this embodiment, the measured gas flow cavity 15 is a form in which the measured gas is introduced from the gas inlet 10 which is open at the front end surface of the sensor element 101, but the present invention is not limited to this form. For example, there may be no concave part of the gas inlet 10 in the measured gas flow cavity 15. In this case, the first diffusion rate control unit 11 is essentially a gas inlet.

[0125] In addition, for example, the measured gas flow cavity 15 may be in the form of an opening on the side surface along the length direction of the base portion 102 that is connected to the buffer space 12 or a position of the first internal cavity 20 close to the buffer space 12. In this case, the measured gas is introduced from the side surface along the length direction of the base portion 102 through the opening.

[0126] In addition, for example, the measured gas flow cavity 15 may be configured such that the measured gas is introduced through a porous body.

[0127] The first diffusion rate control unit 11 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10 .

[0128] The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13 .

[0129] The second diffusion rate control unit 13 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20 .

[0130] As a result, the amount of the measured gas introduced into the first internal cavity 20 only needs to be within a predetermined range. In other words, a predetermined diffusion resistance can be applied to the entirety from the tip of the sensor element 101 to the second diffusion rate control unit 13. For example, the first diffusion rate control unit 11 may be directly connected to the first internal cavity 20, that is, the buffer space 12 and the second diffusion rate control unit 13 may not exist.

[0131] The buffer space 12 is a space provided to mitigate the influence of the pressure change on the detection value when the pressure of the gas to be measured changes.

[0132] When the measured gas is introduced from the outside of the sensor element 101 into the first internal cavity 20, it is rapidly introduced into the sensor element 101 from the gas introduction port 10 due to the pressure change of the measured gas in the external space (when the measured gas is automobile exhaust gas, it is the pulsation of exhaust pressure). However, the measured gas is not introduced directly into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure change of the measured gas is eliminated by passing through the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure change of the measured gas introduced into the first internal space is almost negligible.

[0133] The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust the oxygen partial pressure. That is, in the present embodiment, the main pump unit 21 functions as an oxygen pump unit for adjusting the oxygen concentration in the gas to be measured.

[0134] The main pump unit 21 includes an inner main pump electrode 22 of the cavity oxygen pump electrode disposed on the inner surface of the measured gas flow cavity 15, and a position ( Figure 1 In the electrochemical pump unit, an outer pump electrode 23 of the cavity outer oxygen pump electrode corresponding to the inner main pump electrode 22 is provided on the outer surface of the base portion 102. "Corresponding to the inner main pump electrode 22" means that the outer pump electrode 23 and the inner main pump electrode 22 are provided with the second solid electrolyte layer 6 therebetween.

[0135] That is, the main pump unit 21 is an electrochemical pump unit composed of an inner main pump electrode 22, an outer pump electrode 23 and a second solid electrolyte layer 6 clamped by these electrodes, wherein the inner main pump electrode 22 has: a top electrode portion 22a arranged on substantially the entire surface of the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is arranged on the upper surface of the second solid electrolyte layer 6 in an area corresponding to the top electrode portion 22a in a manner exposed in the external space.

[0136] The inner main pump electrode 22 is formed across: the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that partition the first internal cavity 20, and the isolation layer 5 that constitutes the side wall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that constitutes the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that constitutes the bottom surface, and a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the isolation layer 5 that constitutes the two side wall portions of the first internal cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b, so that the side electrode portion is arranged in a tunnel-shaped structure.

[0137] The inner main pump electrode 22 and the outer pump electrode 23 are porous metal ceramic electrodes (electrodes in the form of a mixture of metal components and ceramic components). As the metal component, it is sufficient to contain a noble metal with catalytic activity (for example, at least one of Pt, Rh, Ir, Ru, and Pd). As the ceramic component, there is no particular limitation, and it is preferred to use a solid electrolyte with oxygen ion conductivity as with the base portion 102. The inner main pump electrode 22 and the outer pump electrode 23 can be metal ceramic electrodes of, for example, Pt and ZrO2.

[0138] In the main pump unit 21, a variable power supply 24 is used to apply a pump voltage Vp0 between the inner main pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner main pump electrode 22 and the outer pump electrode 23 in a positive direction or a negative direction. As a result, the oxygen in the first internal cavity 20 can be absorbed into the external space, or the oxygen in the external space can be absorbed into the first internal cavity 20.

[0139] In addition, the inner main pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a main pump control oxygen partial pressure detection sensor unit 80. In the main pump control oxygen partial pressure detection sensor unit 80, due to the oxygen concentration difference between the atmosphere in the first internal cavity 20 and the reference gas in the reference gas introduction space 43, an electromotive force (voltage V0) is generated between the inner main pump electrode 22 and the reference electrode 42.

[0140] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is obtained by measuring the voltage V0 of the oxygen partial pressure detection sensor unit 80 for main pump control. In addition, the pump voltage Vp0 of the variable power supply 24 is feedback-controlled so that the voltage V0 is constant, thereby controlling the pump current Ip0. Thus, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined value.

[0141] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20 , and guides the gas to be measured to the second internal cavity 40 .

[0142] The second internal cavity 40 is provided as a space for reducing (decomposing) water vapor in the gas to be measured introduced by the third diffusion rate control unit 30. The reduction of water vapor is performed by the operation of the decomposition pump unit 50.

[0143] The decomposition pump unit 50 is an electrochemical pump unit including an intra-cavity decomposition pump electrode 51 disposed at a position on the inner surface of the measured gas circulation cavity 15 that is farther from the front end portion in the length direction of the base portion 102 than the inner main pump electrode 22, and an extra-cavity decomposition pump electrode corresponding to the decomposition pump electrode 51 disposed at a position on the base portion 102 that is different from the measured gas circulation cavity 15. In the present embodiment, the outer pump electrode 23 disposed on the outer surface of the base portion 102 also functions as an extra-cavity decomposition pump electrode. "Corresponding to the decomposition pump electrode 51" means that the outer pump electrode 23 and the decomposition pump electrode 51 are disposed with the second solid electrolyte layer 6 therebetween.

[0144] That is, the decomposition pump unit 50 is an electrochemical pump unit consisting of a decomposition pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode arranged at a position different from the measured gas flow cavity 15), and a second solid electrolyte layer 6, wherein the decomposition pump electrode 51 has: a top electrode portion 51a arranged on the lower surface of the second solid electrolyte layer 6 and facing the second internal cavity 40 in a substantially entirety.

[0145] The decomposition pump electrode 51 is arranged in the second internal cavity 40 in the same tunnel-shaped structure as the inner main pump electrode 22 previously arranged in the first internal cavity 20. That is, a top electrode portion 51a is formed with respect to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40, and a side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed in a tunnel-shaped structure respectively formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40.

[0146] The decomposition pump electrode 51 is an electrode having catalytic activity for decomposing water vapor. It is a porous metal ceramic electrode similar to the inner main pump electrode 22. As a metal component, it can contain a noble metal having catalytic activity (for example, at least one of Pt, Rh, Ir, Ru, and Pd). As a ceramic component, there is no particular limitation, and it is preferred to use a solid electrolyte with oxygen ion conductivity similar to the base part 102. For example, it can be a metal ceramic electrode of Pt and ZrO2.

[0147] In the decomposition pump unit 50, a voltage Vp1 is applied between the decomposition pump electrode 51 and the outer pump electrode 23 using a variable power supply 52, thereby allowing a pump current Ip1 to flow between the decomposition pump electrode 51 and the outer pump electrode 23, thereby being able to decompose (reduce) at least a portion of the water vapor at the decomposition pump electrode 51 (2H2O→2H2+O2), and to absorb the oxygen generated by the decomposition of the water vapor from the second internal cavity 40 to the external space.

[0148] In addition, the decomposition pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4 and the third substrate layer 3 constitute an electrochemical sensor unit, that is, a decomposition pump control oxygen partial pressure detection sensor unit 81. In the decomposition pump control oxygen partial pressure detection sensor unit 81, due to the oxygen concentration difference between the atmosphere in the second internal cavity 40 and the reference gas in the reference gas introduction space 43, an electromotive force (voltage V1) is generated between the decomposition pump electrode 51 and the reference electrode 42.

[0149] The oxygen concentration (oxygen partial pressure) in the second internal cavity 40 is determined by measuring the voltage V1 of the decomposition pump control oxygen partial pressure detection sensor cell 81. Based on the voltage V1 detected by the decomposition pump control oxygen partial pressure detection sensor cell 81, the pump voltage Vp1 of the variable power supply 52 is feedback controlled.

[0150] The fourth diffusion rate control unit 60 is a portion that applies a predetermined diffusion resistance to the gas to be measured including hydrogen gas generated by decomposition of at least a portion of water vapor in the second internal cavity 40 , and guides the gas to be measured to the third internal cavity 61 .

[0151] The third internal cavity 61 is provided as a space for measuring the oxygen partial pressure in the gas to be measured introduced by the fourth diffusion rate control unit 60. The oxygen partial pressure is measured by the electromotive force detection sensor unit 82.

[0152] The electromotive force detection sensor unit 82 is an electrochemical sensor unit composed of the detection electrode 44 of the cavity detection electrode, the reference electrode 42, the first solid electrolyte layer 4, and the third substrate layer 3. In the electromotive force detection sensor unit 82, an electromotive force (voltage V2) is generated between the detection electrode 44 and the reference electrode 42 due to the oxygen concentration difference between the atmosphere in the third internal cavity 61 and the reference gas in the reference gas introduction space 43. It should be noted that hydrogen is a reducing gas, and therefore acts in a manner that increases the oxygen concentration difference.

[0153] The detection electrode 44 is an electrode disposed in the measured gas flow cavity 15 at a position farther from the one end portion in the longitudinal direction of the base portion 102 than the decomposition pump electrode 51 .

[0154] The detection electrode 44 is a porous metal ceramic electrode disposed on the upper surface of the first solid electrolyte layer 4 in the third internal cavity 61. The detection electrode 44 may contain a noble metal with catalytic activity (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) as a metal component. There is no particular limitation on the ceramic component, but it is preferred to use a solid electrolyte with oxygen ion conductivity as in the base portion 102. For example, it may be a metal ceramic electrode of Pt and ZrO2.

[0155] The detection electrode 44 may further include Au (gold). Alternatively, it may include only Au as a metal component. It is believed that Au is active against hydrogen H2, but inactive against carbon monoxide CO. When carbon dioxide CO2 is present in the measured gas, the carbon dioxide may decompose at the decomposition pump electrode 51 to produce carbon monoxide CO. However, it is believed that when the detection electrode 44 includes Au, carbon monoxide CO is not detected at the detection electrode 44, and only hydrogen H2 produced by the decomposition of water vapor H2O can be detected with better accuracy. Since the influence of carbon dioxide CO2 can be reduced, the water vapor concentration can be measured with higher accuracy. The metal component of the detection electrode 44 can be appropriately selected according to the type of the measured gas.

[0156] The oxygen concentration (oxygen partial pressure) in the third internal cavity 61 is obtained by measuring the electromotive force (voltage V2) between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82. The lower the oxygen concentration, the greater the voltage V2. In addition, in the presence of hydrogen as a reducing gas, the following trend is presented: the higher the concentration of hydrogen, the greater the voltage V2. The following feedback control is performed: Based on the voltage V2 detected by the electromotive force detection sensor unit 82, the value of the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42 in the above-mentioned oxygen partial pressure detection sensor unit 81 for decomposition pump control is adjusted.

[0157] In addition, the electrochemical sensor unit 83 composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23 and the reference electrode 42 can be used to obtain the electromotive force Vref, and the electromotive force can be used to detect the oxygen partial pressure in the measured gas outside the sensor.

[0158] In addition, the sensor element 101 further includes a heater unit 70, which has a temperature adjustment function of heating and keeping the sensor element 101 warm so as to improve the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater electrode 71, a heater 72, a heater lead 76, a through hole 73, a heater insulating layer 74, and a pressure release hole 75.

[0159] The heater electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to a heater power source 77 as an external power source, power can be supplied to the heater unit 70 from the outside.

[0160] The heater 72 is a resistor formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater electrode 71 via a heater lead 76 and a through hole 73, and is supplied with power from a heater power source 77 through the heater electrode 71 to generate heat, thereby heating and keeping the solid electrolyte forming the sensor element 101 warm. The heater lead 76 is connected to the heater 72 and extends to the rear end side of the sensor element 101 in the longitudinal direction.

[0161] In addition, the heater 72 is buried in the entire region from the first internal cavity 20 to the third internal cavity 61, and the entire sensor element 101 can be adjusted to the temperature at which the solid electrolyte is activated. The temperature can be adjusted in such a manner that the main pump unit 21 and the decomposition pump unit 50 can operate and the main pump control oxygen partial pressure detection sensor unit 80, the decomposition pump control oxygen partial pressure detection sensor unit 81, the electromotive force detection sensor unit 82, and the sensor unit 83 can be detected. It is not necessary to adjust the entire region to the same temperature, and the sensor element 101 can have a temperature distribution.

[0162] In the sensor element 101 of the present embodiment, the heater 72 is embedded in the base portion 102, but the present invention is not limited to this embodiment. The heater 72 only needs to be arranged to heat the base portion 102. That is, the heater 72 only needs to be able to heat the sensor element 101 to a degree that the oxygen ion conductivity of the main pump unit 21 and the decomposition pump unit 50 described above can work. For example, it can be embedded in the base portion 102 as in the present embodiment. Alternatively, for example, the heater portion 70 can also be formed as another heater substrate different from the base portion 102 and arranged at an adjacent position of the base portion 102.

[0163] The heater insulating layer 74 is an insulating layer formed by an insulator such as alumina on the upper and lower surfaces of the heater 72 and the heater lead 76. The purpose of forming the heater insulating layer 74 is to obtain electrical insulation between the second substrate layer 2 and the heater 72 and the heater lead 76, and electrical insulation between the third substrate layer 3 and the heater 72 and the heater lead 76.

[0164] The pressure release hole 75 is formed to penetrate the third substrate layer 3 so as to communicate the heater insulating layer 74 with the reference gas introduction space 43. The pressure release hole 75 can alleviate the internal pressure increase associated with the temperature increase in the heater insulating layer 74. It should be noted that the pressure release hole 75 may not exist.

[0165] The sensor element 101 described above is embedded in the gas sensor 100 in such a manner that the front end of the sensor element 101 contacts the gas to be measured and the rear end of the sensor element 101 contacts the reference gas.

[0166] (Control device)

[0167] The gas sensor 100 of this embodiment includes the sensor element 101 described above and a control device 90 that controls the sensor element 101. In the gas sensor 100, the electrodes 22, 23, 51, 44, and 42 of the sensor element 101 are electrically connected to the control device 90 via lead wires (not shown). Figure 21 is a block diagram showing the electrical connection relationship between the control device 90 and each pump unit 21, 50, each sensor unit 80, 81, 82, 83 and the heater unit 70 of the sensor element 101. The control device 90 includes: the above-mentioned variable power supply 24, 52 and heater power supply 77, and a control unit 91. The control unit 91 includes: a heater control unit 92, a pump control unit 93 and a concentration calculation unit 94.

[0168] The control unit 91 is implemented by a general-purpose or dedicated computer, and uses a CPU, memory, etc. mounted on the computer to implement the functions of the heater control unit 92, the pump control unit 93, and the concentration calculation unit 94. It should be noted that the gas sensor 100 uses water vapor H2O contained in the exhaust gas from the engine of the automobile as the measurement target gas, and when the sensor element 101 is installed in the exhaust path, part or all of the functions of the control device 90 (especially the control unit 91) can be implemented by the ECU (Electronic Control Unit: electronic control unit) mounted on the automobile.

[0169] The control unit 91 is configured to obtain the electromotive force (voltage V0, V1, V2, Vref) of each sensor unit 80, 81, 82, 83 of the sensor element 101, the pump current (Ip0, Ip1) of each pump unit 21, 50, and the heater voltage Vh and heater current Ih of the heater unit 70. In addition, the control unit 91 is configured to output a control signal to the variable power supply 24, 52 and the heater power supply 77.

[0170] The heater control unit 92 may be configured to control the heater unit 70 (particularly the heater 72). The heater control unit 92 heats the heater 72 and maintains the temperature of the heater 72 at a desired temperature.

[0171] In order to heat the heater 72, various well-known control methods can be used. For example, a certain voltage can be applied to the heater 72 to heat it. The output of the heater power supply 77 can also be controlled based on the resistance value of the heater 72. Alternatively, the output of the heater power supply 77 can also be controlled based on at least one of the resistance values ​​in the main pump unit 21 and the decomposition pump unit 50. In addition, the output of the heater power supply 77 can also be controlled based on at least one of the resistance values ​​in the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen partial pressure detection sensor unit 81 for decomposition pump control, the electromotive force detection sensor unit 82, and the sensor unit 83.

[0172] For example, the heater control unit 92 performs feedback control on the control signal output to the heater power supply 77 so that the heater 72 reaches the target temperature based on the heater resistance value Rh (=Vh / Ih) calculated from the heater voltage Vh and the heater current Ih in the heater 72 .

[0173] The pump control unit 93 is configured to control the operations of the main pump unit 21 and the decomposition pump unit 50 so that the gas sensor 100 can measure the concentration of the measurement target gas (water vapor H 2 O in the present embodiment).

[0174] The pump control unit 93 is configured to adjust the oxygen concentration in the measured gas to a predetermined concentration using the oxygen pump unit (main pump unit 21). In this embodiment, the pump control unit 93 adjusts the oxygen concentration in the measured gas to a predetermined concentration so that the voltage V0 in the oxygen partial pressure detection sensor unit 80 for main pump control reaches a constant value (referred to as the set value V0). SET ) to feedback control the pump voltage Vp0 of the variable power supply 24 in the main pump unit 21. SET For example, the oxygen partial pressure in the atmosphere in the first internal cavity 20 may be set to a low oxygen partial pressure that has substantially no effect on the measurement of H2O. For example, the oxygen partial pressure may be set to an oxygen partial pressure at which H2O in the measurement target gas is substantially not decomposed. The voltage V0 represents the oxygen partial pressure near the inner main pump electrode 22, and therefore, making the voltage V0 constant means making the oxygen partial pressure near the inner main pump electrode 22 constant. As a result, the pump current Ip0 in the main pump unit 21 changes in accordance with the oxygen concentration in the measured gas.

[0175] The oxygen partial pressure in the measured gas is higher than the set value V0 SET When the oxygen partial pressure is equal to or lower than the set value V0, oxygen is discharged from the first internal cavity 20 in the main pump unit 21. On the other hand, the oxygen partial pressure in the measured gas is lower than the set value V0. SET When the oxygen partial pressure is considerable (for example, when hydrocarbons HC are contained), the main pump unit 21 draws oxygen from the space outside the sensor element 101 into the first internal cavity 20. Therefore, the pump current Ip0 can take any positive or negative value.

[0176] The pump control unit 93 is configured to operate the decomposition pump unit 50 in such a manner that the voltage V2 between the detection electrode (detection electrode 44) in the cavity of the electromotive force detection sensor unit 82 and the reference electrode 42 reaches a specified value, and to decompose at least a portion of the measurement object gas in the measured gas at the decomposition pump electrode (decomposition pump electrode 51) in the cavity of the decomposition pump unit 50, and to suck out oxygen generated by the decomposition of the measurement object gas using the decomposition pump unit 50.

[0177] The pump control unit 93 may also be configured to adjust the voltage V1 between the intra-cavity decomposition pump electrode (decomposition pump electrode 51) and the reference electrode 42 in the decomposition pump control oxygen partial pressure detection sensor unit 81 in such a manner that the voltage V2 between the intra-cavity detection electrode (detection electrode 44) and the reference electrode 42 in the electromotive force detection sensor unit 82 reaches a specified value, thereby decomposing at least a portion of the measurement target gas in the measured gas at the intra-cavity decomposition pump electrode (decomposition pump electrode 51) of the decomposition pump unit 50, and utilizing the decomposition pump unit 50 to absorb oxygen generated by the decomposition of the measurement target gas.

[0178] In this embodiment, the pump control unit 93 performs the following feedback control so that the voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 reaches a target value (referred to as a set value V2 SET ) is used to determine the target value (referred to as the set value V1) of the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control. SET ) is adjusted. Then, the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control reaches the adjusted target value (set value V1 SET ) is used to feedback control the pump voltage Vp1 of the variable power supply 52 in the decomposition pump unit 50. Setting value V2 SET The setting value V2 can be appropriately set according to the type and concentration range of the gas to be measured by the gas sensor 100. Although it may differ depending on the gas to be measured, when measuring water vapor, it can be about 300mV to 600mV, for example. More preferably, it can be about 400mV to 500mV. Setting value V2 SET It may be, for example, 450 mV.

[0179] The concentration calculation unit 94 is configured to calculate the concentration of the measurement target gas (H 2 O concentration in the present embodiment) in the measurement target gas.

[0180] The concentration calculation unit 94 obtains the voltage V1 between the decomposition pump electrode (decomposition pump electrode 51) in the cavity and the reference electrode 42 in the decomposition pump control oxygen partial pressure detection sensor unit 81, and calculates the H2O concentration in the measured gas based on the conversion parameter (voltage-concentration conversion parameter) between the voltage V1 and the H2O concentration in the measured gas stored in advance. In addition, the calculated H2O concentration is output as a measurement value of the gas sensor 100. The voltage-concentration conversion parameter is pre-stored in the storage unit of the control unit 91 that functions as the concentration calculation unit 94 as data representing the relationship between the voltage V1 described later and the H2O concentration in the measured gas. Regarding the gas sensor 100, those skilled in the art can appropriately determine the voltage-concentration conversion parameter in advance by experiments or the like. The voltage-concentration conversion parameter can be, for example, a coefficient of an approximate formula (logarithmic function, etc.) obtained by experiment, or a map representing the correspondence between the voltage V1 and the H2O concentration in the measured gas. The voltage-concentration conversion parameter may be a parameter specific to each gas sensor 100 , or may be a parameter common to a plurality of gas sensors.

[0181] The concentration calculation unit 94 may be further configured to calculate the oxygen concentration in the measured gas based on the pump current Ip0 flowing through the main pump unit 21. If configured in this way, the concentration of the measured gas (H2O concentration in this embodiment) and the oxygen concentration in the measured gas can be simultaneously measured using the gas sensor 100.

[0182] (Measurement of gas concentration)

[0183] Next, a method for measuring the water vapor concentration (H 2 O concentration) in the gas to be measured using the gas sensor 100 having the above-described configuration will be described.

[0184] The control method of the gas sensor of the present invention comprises:

[0185] a pump control step in which the oxygen concentration in the measured gas is adjusted to a predetermined concentration by operating the oxygen pump unit through the pump control unit, and the decomposition pump unit is operated in such a manner that the voltage between the detection electrode in the cavity and the reference electrode reaches a predetermined value, thereby decomposing at least a part of the measurement target gas in the measured gas at the decomposition pump electrode in the cavity of the decomposition pump unit, and oxygen generated by the decomposition of the measurement target gas is sucked out by the decomposition pump unit; and

[0186] A concentration calculation step in which the concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity.

[0187] The gas sensor 100 is installed on a gas pipe or the like in such a way that the tip of the sensor element 101 contacts the measured gas containing water vapor. It should be noted that the measured gas often also contains oxygen. The gas sensor 100 receives, for example, a start signal (Dew point ) and start. Start signal (Dew point ) is: when the gas sensor 100 is mounted in a car or the like, for example, a signal transmitted to the gas sensor 100 from the ECU, exhaust gas treatment system, etc. of the car. The gas sensor 100 can be started by, for example, manually turning on the power of the control device 90.

[0188] When the gas sensor 100 is activated, the heater control unit 92 of the control unit 91 heats the heater 72 to maintain the temperature of the heater 72 at a desired temperature. Thus, the sensor element 101 is maintained at a driving temperature (e.g., about 800° C.) at which the solid electrolyte is activated and the H2O concentration can be measured accurately.

[0189] Next, the pump control unit 93 controls the main pump unit 21 and the decomposition pump unit 50 as described above. The pump control unit 93 may start control after the sensor element 101 reaches the driving temperature, or may start control at a temperature lower than the driving temperature.

[0190] Figure 3 FIG. 1 is a conceptual diagram showing the principle of water vapor measurement in the gas sensor 100. The behavior of water vapor H2O and oxygen O2 in the measured gas is focused on. Figure 3 Only water vapor H2O and oxygen O2 are shown in the figure. Figure 3 The structure of the sensor element 101 is simplified in the figure, so the following also refers to Figure 1 The measured gas is introduced from the gas inlet 10, passes through the first diffusion rate control section 11, the buffer space 12 and the second diffusion rate control section 13 in order, and reaches the first internal cavity 20. And, the oxygen concentration is adjusted to a specified concentration by the operation of the main pump unit 21. Thus, it is sufficient to adjust the oxygen concentration in the first internal cavity 20, that is, the oxygen concentration in the measured gas to be introduced into the second internal cavity 40, to a low concentration that has substantially no effect on the measurement of water vapor H2O. For example, it is sufficient to adjust in such a way that almost all of the oxygen in the measured gas is absorbed and the water vapor in the measured gas is substantially not decomposed. Thereafter, the measured gas whose oxygen concentration is adjusted to a specified concentration passes through the third diffusion rate control section 30 and is introduced into the second internal cavity 40.

[0191] In the second internal cavity 40, at least a portion of the water vapor H2O contained in the measured gas that reaches is decomposed (reduced) at the decomposition pump electrode 51 to generate hydrogen and oxygen (2H2O→2H2+O2). The oxygen generated by the decomposition of the water vapor is sucked out from the second internal cavity 40 by the decomposition pump unit 50. In addition, the measured gas containing hydrogen H2 generated by the decomposition of the water vapor passes through the fourth diffusion rate control unit 60 and is introduced into the third internal cavity 61 to reach the detection electrode 44. It should be noted that the measured gas that reaches the detection electrode 44 also contains water vapor H2O that is not decomposed at the decomposition pump electrode 51.

[0192] As described above, the pump control unit 93 controls the voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 to reach a predetermined value (set value V2 SET ). As described above, the voltage V2 is an electromotive force generated according to the concentration of oxygen and hydrogen in the atmosphere around the detection electrode 44. It should be noted that it is considered that the water vapor H2O itself has no effect on the value of the voltage V2. As described above, the oxygen concentration in the measured gas has been adjusted to a specified concentration by the operation of the main pump unit 21. Therefore, it is considered that the so-called control in a manner that makes the voltage V2 reach a specified value can be said to be controlled in a manner that makes the amount (number) of hydrogen in the measured gas reaching the detection electrode 44 reach a specified amount (number).

[0193] That is, the pump control unit 93 operates the decomposition pump unit 50 in such a manner that the amount of hydrogen in the measured gas reaching the detection electrode 44 reaches a predetermined amount, thereby controlling the decomposition of water vapor at the decomposition pump electrode 51 to generate the predetermined amount of hydrogen. That is, the decomposition pump electrode 51 is controlled to decompose a predetermined amount of water vapor regardless of the water vapor concentration in the measured gas. For example, when the water vapor concentration in the measured gas is high, the water vapor is decomposed at a low decomposition rate at the decomposition pump electrode 51, and when the water vapor concentration in the measured gas is low, the water vapor is decomposed at a high decomposition rate at the decomposition pump electrode 51.

[0194] Figure 4 1 is a diagram showing an example of the relationship between the voltage V1 in the decomposition pump control oxygen partial pressure detection sensor cell 81 and the voltage V2 in the electromotive force detection sensor cell 82. The horizontal axis represents the voltage V1 (mV), and the vertical axis represents the voltage V2 (mV). Figure 4The relationship between voltage V1 and voltage V2 when the water vapor concentration is H2O = 1%, 5%, and 10% (volume basis. The same applies below) is shown in the figure. It can be seen that at any concentration, there is a region where the change in voltage V1 is smaller than the change in voltage V2. In addition, in this region, when the voltage V1 is compared at the same voltage V2 (for example, when voltage V2 = 450mV), the following insight is obtained: it can be seen that the lower the water vapor concentration, the larger the voltage V1.

[0195] It is considered that when the value of V2 is the same, as described above, the amount of water vapor decomposed at the decomposition pump electrode 51 is the same regardless of the water vapor concentration in the measured gas. Therefore, it is considered that the lower the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42 in the decomposition pump control oxygen partial pressure detection sensor unit 81, the lower the decomposition rate of water vapor at the decomposition pump electrode 51, and the higher the voltage V1, the higher the decomposition rate of water vapor at the decomposition pump electrode 51.

[0196] Figure 5 : is a diagram showing an example of the relationship between the H2O concentration in the measured gas and the voltage V1 in the gas sensor 100. The horizontal axis represents the H2O concentration (%), and the vertical axis represents the voltage V1 (mV) when the voltage V2 reaches 450mV. It can be seen that there is a correlation between the H2O concentration and the voltage V1. The concentration calculation unit 94 can calculate the water vapor concentration in the measured gas based on the voltage V1 using this correlation.

[0197] In addition, if Figure 5 As shown in FIG. 1 , the lower the H2O concentration in the measured gas, the greater the change in voltage V1 with respect to the change in H2O concentration. That is, there is a tendency that the lower the H2O concentration in the measured gas, the greater the change in voltage V1 with respect to a small change in H2O concentration, and thus the resolution of the measurement is higher. Therefore, it is considered that when measuring a measured gas containing low-concentration water vapor H2O, the H2O concentration can be measured with particularly high measurement accuracy.

[0198] [Modifications]

[0199] Hereinafter, another embodiment of the gas sensor of the present invention will be described.

[0200] The sensor element further includes a pump unit for current measurement.

[0201] The current measuring pump unit includes: the cavity detection electrode and the cavity detection electrode outside the cavity provided at a position of the base body different from the cavity through which the gas to be measured flows and corresponding to the cavity detection electrode.

[0202] The control device further comprises a switching unit,

[0203] The switching unit switches whether or not to allow current to flow through the current measuring pump unit.

[0204] In the gas sensor 100 described above, the H2O concentration in the measured gas is calculated based on the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42. In the gas sensor 200 of the modified example, the measurement is performed while switching between a voltage measurement mode and a current measurement mode. In the voltage measurement mode, the H2O concentration in the measured gas is calculated based on the voltage V1 as in the case of the gas sensor 100. In the current measurement mode, the H2O concentration in the measured gas is calculated based on the pump current flowing through the current measurement pump unit.

[0205] Figure 6 1 is a schematic vertical cross-sectional view in the longitudinal direction showing an example of a schematic configuration of a gas sensor 200 including a modified example of a sensor element 201 . Figure 6 In, with Figure 1 The same components are denoted by the same reference numerals, and therefore, description thereof will be omitted. Figure 7 2 is a block diagram showing the electrical connection relationship between the control device 290 and the sensor element 201 in the gas sensor 200 . Figure 7 In, with Figure 2 The same components are denoted by the same reference numerals, and thus description thereof will be omitted. The control device 290 includes a switching unit 47 that switches whether or not to allow current to flow through the current measuring pump unit 41 .

[0206] In the gas sensor 200, the switching unit 47 only needs to have a mechanism for switching whether to allow the current to flow through the current measurement pump unit 41. For example, the switching unit 47 may be Figure 6 The switch 47 illustrated in the figure, or a mechanism including a switch. The switch can be a contact switch that mechanically opens and closes contacts provided on a circuit, or a switch that uses a switching element that turns on / off the current flowing in the circuit. Switching elements include diodes, thyristors, transistors, MOSFETs, etc. Those skilled in the art can appropriately determine the composition of the switch. By setting the switch to OFF, it is possible to switch to disconnect the conduction of the current measuring pump unit 41 without allowing the current to flow. By setting the switch to ON, it is possible to switch to turn on the current measuring pump unit 41 to allow the current to flow.

[0207] In addition, for example, the switching unit 47 may be a variable power supply 46, or a mechanism including a variable power supply 46. By making the voltage of the variable power supply 46 zero, it is possible to switch to not applying a voltage to the current measuring pump unit and not allowing a current to flow. By making the voltage of the variable power supply 46 a predetermined value, it is possible to switch to applying a voltage to the current measuring pump unit and allowing a current to flow.

[0208] The sensor element 201 includes a current measuring pump cell 41. The current measuring pump cell 41 is an electrochemical pump cell including an in-cavity detection electrode (in this embodiment, the detection electrode 44) arranged at a position farther from the front end of the length direction of the base part 102 than the in-cavity decomposition pump electrode (in this embodiment, the decomposition pump electrode 51) in the measured gas circulation cavity 15, and an out-cavity detection electrode corresponding to the in-cavity detection electrode arranged at a position of the base part 102 different from the measured gas circulation cavity 15. In the gas sensor 200, the outer pump electrode 23 arranged on the outer surface of the base part 102 also functions as an out-cavity detection electrode. "Corresponding to the in-cavity detection electrode" means that the outer pump electrode 23 and the detection electrode 44 are arranged with the second solid electrolyte layer 6, the isolation layer 5 and the first solid electrolyte layer 4 interposed therebetween.

[0209] That is, the current measuring pump unit 41 is an electrochemical pump unit consisting of a detection electrode 44, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode arranged at a position different from the measured gas flow cavity 15), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4, and the detection electrode 44 is arranged at a position on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61.

[0210] In the current measuring pump cell 41 , the variable power supply 46 applies a voltage Vp2 between the detection electrode 44 and the outer pump electrode 23 , so that the pump current Ip2 flows between the detection electrode 44 and the outer pump electrode 23 , thereby allowing oxygen to be drawn from the external space into the third internal cavity 61 .

[0211] The current measuring pump unit 41 is configured such that whether or not to allow current to flow through the current measuring pump unit 41 is switched by the switching unit 47. Figure 6 , the switching unit 47 is taken as an example to explain the situation where the switching unit 47 is a switch. Figure 6 The circuit symbol of the contact switch is schematically shown in FIG. 4 , but the switching unit 47 may also be a switch using a switch element. In addition, the setting position of the switching unit 47 is not limited to Figure 6 The position shown may be set at any position as long as it is on the circuit of the current measuring pump unit 41 .

[0212] When the switching unit 47 is turned OFF, the electrical connection of the current measuring pump unit 41 is disconnected, so that no current flows through the current measuring pump unit 41. No current flows means that the current value in the current measuring pump unit 41 is zero or substantially zero.

[0213] In this case, feedback control is performed to adjust the value of voltage V1 in the decomposition pump control oxygen partial pressure detection sensor unit 81 based on voltage V2 detected by the electromotive force detection sensor unit 82. In addition, a voltage measurement mode is executed to calculate the H2O concentration in the measured gas based on voltage V1.

[0214] When the switching unit 47 is turned on, the current measuring pump unit 41 is electrically connected, and thus current flows through the current measuring pump unit 41 .

[0215] In this case, the pump voltage Vp2 of the variable power supply 46 is controlled based on the voltage V2 detected by the electromotive force detection sensor unit 82. As a result, the pump current Ip2 flows through the current measurement pump unit 41. Then, the current measurement mode is executed to calculate the H2O concentration in the measured gas based on the pump current Ip2.

[0216] Thus, in the gas sensor 200, the value of the voltage V2 is fed back to different objects in the case where the switching unit 47 is turned OFF (voltage measurement mode) and in the case where the switching unit 47 is turned ON (current measurement mode). That is, the value of the voltage V2 is fed back to the voltage V1 in the voltage measurement mode, and is fed back to the pump voltage Vp2 in the current measurement mode. Figure 6 The feedback switching unit 85 in FIG. 8 schematically shows that the object to which the value of the voltage V2 is fed back is switched according to the measurement mode, and does not exist as an entity. The object to which the value of the voltage V2 is fed back is set in the control program of each measurement mode performed by the pump control unit 293 described later.

[0217] Figure 7 1 is a block diagram showing the electrical connection relationship between the control device 290 and each pump unit 21, 50, 41, each sensor unit 80, 81, 82, 83 and the heater unit 70 of the sensor element 201 in the gas sensor 200 of the modified example. In the gas sensor 200 of the modified example, the control device 290 includes: variable power supplies 24, 46, 52; a switching unit 47 that switches whether to allow current to flow through the current measurement pump unit 41; and a control unit 291. The control unit 291 includes: a heater control unit 92, a pump control unit 293, a concentration calculation unit 294, and a measurement mode switching unit 95. The switching unit 47 is a component that receives a control signal from the measurement mode switching unit 95 and switches whether to allow current to flow through the current measurement pump unit 41. Figure 7 In, with Figure 2 The same components are denoted by the same reference numerals, and thus description thereof will be omitted.

[0218] The pump control unit 293 includes:

[0219] Pump control in the voltage measurement mode, which calculates the H2O concentration in the measured gas based on the voltage V1 between the pump electrode 51 and the reference electrode 42; and

[0220] The pump control in the current measurement mode calculates the H 2 O concentration in the gas to be measured based on the pump current Ip2 flowing through the current measurement pump cell 41 .

[0221] The pump control unit 293 adjusts the oxygen concentration in the gas to be measured to a predetermined concentration using the oxygen pump unit (main pump unit 21 ) regardless of the measurement mode, similarly to the pump control unit 93 of the gas sensor 100 described above.

[0222] In the voltage measurement mode, the pump control unit 293 performs the same operation as the pump control unit 93 of the gas sensor 100 described above so that the voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 reaches the target value (set value V2 SET ) is used to determine the target value (set value V1) of the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control. SET ) is adjusted by feedback control. Then, the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control reaches the adjusted target value (set value V1 SET ) method to feedback control the pump voltage Vp1 of the variable power supply 52 in the decomposition pump unit 50.

[0223] In the current measurement mode, the pump control unit 293 sets the voltage V1 of the oxygen partial pressure detection sensor unit 81 for decomposition pump control to a target value (referred to as a set value V1a). SET ) is used to feedback control the pump voltage Vp1 of the variable power supply 52 in the decomposition pump unit 50. Setting value V1a SET The value V1a can be set to a value such that substantially all of the water vapor in the gas to be measured is decomposed (reduced) at the decomposition pump electrode 51. Setting value V1a SET Normally, it is set to be higher than the set value V0 in the control of the above-mentioned main pump unit 21. SET Oxygen generated by decomposition of water vapor is sucked out by passing the pump current Ip1 through the decomposition pump unit 50 . Also, the measured gas including hydrogen generated by decomposition of water vapor is introduced into the third internal cavity 61 .

[0224] In the current measurement mode, the pump control unit 293 sets the voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 to a target value (referred to as a set value V2a). SET ) is used to feedback control the pump voltage Vp2 of the variable power supply 46 in the current measurement pump unit 41. Setting value V2a SET The value may be set to a value at which substantially all of the hydrogen generated by decomposition of water vapor at the decomposition pump electrode 51 is burned (oxidized) at the detection electrode 44. The pump control unit 293 causes the pump current Ip2 to flow through the current measurement pump unit 41, thereby sucking in an amount of oxygen that substantially all of the hydrogen generated by decomposition of water vapor at the detection electrode 44 is burned (oxidized). Therefore, the pump current Ip2 becomes a value corresponding to the amount (concentration) of hydrogen generated by decomposition of water vapor.

[0225] When the water vapor in the measured gas is substantially completely decomposed (reduced) at the decomposition pump electrode 51 (2H2O→2H2+O2), hydrogen is generated in direct proportion to the amount (concentration) of water vapor in the measured gas. The amount of oxygen sucked in in the form of pump current Ip2 in order to substantially completely burn the hydrogen at the detection electrode 44 is proportional to the amount of hydrogen. Therefore, there is a linear relationship between the H2O concentration in the measured gas and the pump current Ip2, in which the magnitude (absolute value) of the pump current Ip2 increases in accordance with the H2O concentration. Based on this linear relationship, regardless of the H2O concentration, it is possible to measure with high decomposition capability.

[0226] In the current measurement mode, even when the H2O concentration in the measured gas is zero, the pump current Ip2 is not zero, and a small current flows. This small current is called the bias current Ip2offset. The bias current Ip2offset is a small current that flows regardless of the H2O concentration in the measured gas and is affected by the control in the main pump unit 21 and the decomposition pump unit 50. When the current value of the bias current Ip2offset changes for some reason, the pump current Ip2 detected in the current measurement pump unit 41 is offset by the change ΔIp2offset of the bias current Ip2offset regardless of the H2O concentration in the measured gas. It is considered that the bias current Ip2offset can change according to, for example, the change in the electrode temperature caused by the change in the temperature of the measured gas and the resulting change in the output of the heater power supply 77.

[0227] When measuring a gas to be measured containing a high concentration of H2O, the magnitude (absolute value) of the pump current Ip2 detected in the current measurement pump unit 41 is relatively large, and therefore, the change in the pump current Ip2 caused by the change ΔIp2offset of the bias current Ip2offset is relatively small. Thus, even if the bias current Ip2offset changes, the H2O concentration can be measured with higher measurement accuracy. That is, if the current measurement mode is used, when measuring a gas to be measured containing a high concentration of water vapor H2O, the H2O concentration can be measured with higher measurement accuracy.

[0228] On the other hand, as described above, the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42 in the voltage measurement mode is as follows: Figure 5 As shown in FIG. 1 , the lower the H2O concentration in the measured gas, the greater the change in voltage V1 with respect to the change in H2O concentration. That is, there is a tendency that the lower the H2O concentration in the measured gas, the greater the change in voltage V1 with respect to a small change in H2O concentration, and thus the resolution of the measurement is higher. Therefore, it is considered that if the voltage measurement mode is used, when measuring the measured gas containing low-concentration water vapor H2O, the H2O concentration can be measured with higher measurement accuracy.

[0229] The concentration calculation unit 294 is configured to calculate the concentration of the measurement target gas in the measured gas (the H 2 O concentration in the gas sensor 100 of the modified example).

[0230] In the voltage measurement mode, the concentration calculation unit 294 obtains the voltage V1 between the decomposition pump electrode (decomposition pump electrode 51) in the cavity and the reference electrode 42 in the decomposition pump control oxygen partial pressure detection sensor unit 81, and calculates the H2O concentration in the measured gas based on the conversion parameter (voltage-concentration conversion parameter) between the voltage V1 and the H2O concentration in the measured gas stored in advance. In addition, the calculated H2O concentration is output as the measurement value of the gas sensor 200.

[0231] In the current measurement mode, the concentration calculation unit 294 obtains the pump current Ip2 flowing through the current measurement pump unit 41, and calculates the H2O concentration in the measured gas based on the conversion parameter (current-concentration conversion parameter) between the pump current Ip2 and the H2O concentration in the measured gas stored in advance. In addition, the calculated H2O concentration is output as the measurement value of the gas sensor 200. The current-concentration conversion parameter is pre-stored in the storage unit of the control unit 291 that functions as the concentration calculation unit 294. Regarding the gas sensor 200, those skilled in the art can appropriately determine the current-concentration conversion parameter in advance by experiments, etc. The current-concentration conversion parameter can be, for example, a coefficient of an approximate formula (linear function, etc.) obtained by experiment, or a mapping that represents the correspondence between the pump current Ip2 and the H2O concentration in the measured gas. The current-concentration conversion parameter can be a parameter inherent to each gas sensor 200, or a parameter common to multiple gas sensors.

[0232] The measurement mode switching unit 95 is configured to switch between the voltage measurement mode and the current measurement mode described above.

[0233] When switching from the current measurement mode to the voltage measurement mode, the measurement mode switching unit 95 switches the switching unit 47 so that the current does not flow through the current measurement pump unit 41 or substantially does not flow through the current measurement pump unit 41. In the gas sensor 200 of the modified example, a control signal set to OFF is output to the switching unit 47 (switching switch). In addition, the measurement mode switching unit 95 gives an instruction to the pump control unit 293 to control in the voltage measurement mode. In this case, the pump control unit 293 performs the following feedback control: based on the voltage V2 detected by the above-mentioned electromotive force detection sensor unit 82, the value of the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42 in the above-mentioned decomposition pump control oxygen partial pressure detection sensor unit 81 is adjusted. The measurement mode switching unit 95 gives an instruction to the concentration calculation unit 294 to obtain the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42 and calculate the H2O concentration based on the voltage-concentration conversion parameter.

[0234] When switching from the voltage measurement mode to the current measurement mode, the measurement mode switching unit 95 switches the switching unit 47 so that current flows through the current measurement pump unit 41. In the gas sensor 200 of the modified example, a control signal set to ON is output for the switching unit 47 (switching switch). In addition, the measurement mode switching unit 95 gives an instruction to the pump control unit 293 to control in the current measurement mode. In this case, the pump control unit 293 performs feedback control on the pump voltage Vp2 of the variable power supply 46 of the above-mentioned current measurement pump unit 41, and detects the pump current Ip2 in the current measurement pump unit 41. The measurement mode switching unit 95 gives an instruction to the concentration calculation unit 294 to obtain the pump current Ip2 in the current measurement pump unit 41 and calculate the H2O concentration based on the current-concentration conversion parameter.

[0235] The switching between the voltage measurement mode and the current measurement mode can be performed based on the concentration of the measurement target gas output by the concentration calculation unit 294 (the H2O concentration in the gas sensor 200). The first concentration threshold C1 for switching the current measurement mode to the voltage measurement mode and the second concentration threshold C2 for switching the voltage measurement mode to the current measurement mode can be recorded in advance in the measurement mode switching unit 95 (more specifically, the storage unit that functions as the measurement mode switching unit 95 in the control unit 291). The measurement mode switching unit 95 can obtain the H2O concentration output by the concentration calculation unit 294 continuously or at a predetermined interval.

[0236] The measurement mode switching unit 95 can be: in the current measurement mode, the H2O concentration output by the concentration calculation unit 294 is obtained, and when it is determined that the H2O concentration is in a low concentration region lower than a specified first concentration threshold C1, the voltage measurement mode is switched; when it is determined that the H2O concentration is above the specified first concentration threshold C1, the current measurement mode is maintained.

[0237] In addition, in the voltage measurement mode, the H2O concentration output by the concentration calculation unit 294 can also be obtained. When it is determined that the H2O concentration is in a high concentration area higher than the specified second concentration threshold C2, switching to the current measurement mode is performed. When it is determined that the H2O concentration is below the specified second concentration threshold C2, the voltage measurement mode is maintained.

[0238] Regarding the first concentration threshold C1 of the threshold for switching the current measurement mode to the voltage measurement mode, those skilled in the art can appropriately set it. The first concentration threshold C1 can be a value that is different according to the concentration range of H2O in the assumed gas to be measured, or the measurement accuracy required by the gas sensor 200. The first concentration threshold C1 can be the lower limit value of the H2O concentration that obtains the desired measurement accuracy when measured in the current measurement mode. The first concentration threshold C1 can be, for example, the lower limit value of the H2O concentration within the allowable range of the value of the bias current Ip2offset relative to the measurement accuracy. Or, for example, it can be the lower limit value of the H2O concentration within the allowable range of the value of the assumed bias current change ΔIp2offset relative to the measurement accuracy. The first concentration threshold C1 can be, for example, in the range of 0.1% to 10%. For example, it can be 3%.

[0239] Regarding the second concentration threshold C2 of the threshold for switching the voltage measurement mode to the current measurement mode, those skilled in the art can appropriately set it. The second concentration threshold C2 can be a concentration range of H2O in the assumed gas to be measured, or a value that varies according to the measurement accuracy required by the gas sensor 200. The second concentration threshold C2 can be an upper limit value of the H2O concentration that obtains the desired measurement accuracy when measuring in the voltage measurement mode. The second concentration threshold C2 can also be, for example, an upper limit value of the H2O concentration within a range that can be tolerated as the decomposition capacity of the measurement, where the change in the voltage V1 relative to the change in the H2O concentration. The second concentration threshold C2 can be, for example, in the range of 0.1% to 10%. For example, it can be 5%.

[0240] The first concentration threshold C1 and the second concentration threshold C2 may be the same value or different values. When the first concentration threshold C1 and the second concentration threshold C2 are the same value, the voltage measurement mode may be executed in a low concentration region lower than the first concentration threshold C1 (= second concentration threshold C2), and the current measurement mode may be executed in a high concentration region higher than the first concentration threshold C1 (= second concentration threshold C2).

[0241] It is more preferable that the first concentration threshold value C1 is a concentration lower than the second concentration threshold value C2. In other words, it is more preferable to use two threshold values ​​having a concentration range.

[0242] Figure 8 1 is a schematic diagram showing an example of the time change of the H2O concentration detection value output by the gas sensor 200 and the switching of the measurement mode. The horizontal axis represents time (seconds), and the vertical axis represents the H2O concentration detection value output by the gas sensor 200 (%).

[0243] like Figure 8As shown, when the H2O concentration in the measured gas (i.e., the H2O concentration output by the gas sensor 200) is lower than the first concentration threshold C1, the measurement mode switching unit 95 switches to the voltage measurement mode. After switching to the voltage measurement mode, even if the H2O concentration in the measured gas sometimes changes in concentration near the first concentration threshold C1 and exceeds the first concentration threshold C1, it will not switch to the current measurement mode, but continue the voltage measurement mode until the H2O concentration in the measured gas exceeds the second concentration threshold C2. Thereafter, when the H2O concentration in the measured gas exceeds the second concentration threshold C2, it switches to the current measurement mode. After switching to the current measurement mode, even if the H2O concentration in the measured gas sometimes changes in concentration near the second concentration threshold C2 and becomes lower than the second concentration threshold C2, it will not switch to the voltage measurement mode, but continue the current measurement mode until the H2O concentration in the measured gas becomes lower than the first concentration threshold C1.

[0244] In this way, when the first concentration threshold C1 is set to a concentration lower than the second concentration threshold C2, the concentration range (intermediate concentration range) between the first concentration threshold C1 and the second concentration threshold C2 plays a role as a buffer area for maintaining the previous measurement mode without switching the measurement mode. That is, it can be adjusted so that when the H2O concentration in the measured gas changes frequently near the first concentration threshold C1 and the second concentration threshold C2, the switching of the measurement mode is not too frequent. When switching the measurement mode, by changing the control of the current measurement pump unit 41, the gas sensor 200 may be in a state where the H2O concentration cannot be measured temporarily. By setting a buffer area between the first concentration threshold C1 and the second concentration threshold C2, it can be adjusted so that the switching of the measurement mode does not occur too frequently. As a result, the gas sensor 200 can measure the H2O concentration more continuously and with good accuracy.

[0245] For example, the first concentration threshold C1 may be 0.1 to 5%, and the second concentration threshold C2 may be 5 to 10%. For example, the first concentration threshold C1 may be 3%, and the second concentration threshold C2 may be 5%.

[0246] The measurement mode may also be switched in the buffer region between the first concentration threshold C1 and the second concentration threshold C2. For example, the measurement mode may be switched based on the time variation of the H2O concentration detection value ( Figure 8 The H2O concentration detection value is predicted and switched based on the slope of the curve in ( ). For example, the switching can be performed based on the time when the H2O concentration detection value is in the buffer area.

[0247] (Detection of Concentration of Gas to be Measured in Modified Example)

[0248] Next, a method of measuring the concentration of the measurement target gas in the measurement target gas using the gas sensor 200 will be described.

[0249] In the control method of the gas sensor of the modified example, the measurement is performed while switching between the voltage measurement mode and the current measurement mode using the switching unit. In the voltage measurement mode, the pump control step and the concentration calculation step are performed to calculate the concentration of the measurement target gas in the measurement gas based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity. In the current measurement mode, the oxygen pump unit, the decomposition pump unit, and the current measurement pump unit are operated to calculate the concentration of the measurement target gas in the measurement gas based on the current value flowing through the current measurement pump unit. By always executing any measurement mode, the concentration can be detected continuously.

[0250] Hereinafter, the H 2 O concentration detection process of the gas sensor 200 according to the modified example will be described in detail. Fig. 9 1 is a flowchart showing an example of H 2 O concentration detection processing in the gas sensor 200 according to the modified example.

[0251] For example, when the gas sensor 200 receives a start signal (Dew point ), the H2O concentration detection process starts. point ) is: when the gas sensor 200 is mounted in a car or the like, a signal sent from, for example, the ECU of the car, the exhaust gas treatment system, etc. to the gas sensor 200. It may also be started by, for example, manually turning on the power of the control device 290.

[0252] When the H2O concentration detection process starts, the heater control unit 92 of the control unit 291 first energizes the heater 72 to start heating the heater 72 (step S10), and maintains the sensor element 201 at a driving temperature (e.g., about 800°C) at which the solid electrolyte is activated and the H2O concentration is measured with good accuracy.

[0253] Next, the pump control unit 293 starts controlling the main pump unit 21 (step S11). That is, the main pump unit 21 is controlled based on the set value V0. SET Step S11 may be performed after the sensor element 101 reaches the driving temperature, or may be performed at a temperature lower than the driving temperature.

[0254] Next, the measurement mode switching unit 95 of the control unit 291 switches to the current measurement mode (step S13). Specifically, the measurement mode switching unit 95 outputs a control signal to turn on the switching unit 47. In addition, the measurement mode switching unit 95 gives an instruction to the pump control unit 293 to control in the current measurement mode. In this case, the pump control unit 293 performs a control operation based on the set value V1a on the decomposition pump unit 50. SET The feedback control is performed based on the set value V2a for the pump voltage Vp2 of the variable power supply 46 of the current measurement pump unit 41. SET The pump current Ip2 in the current measuring pump cell 41 is detected by feedback control. The measurement mode switching unit 95 gives an instruction to the concentration calculation unit 294 to obtain the pump current Ip2 in the current measuring pump cell 41 and calculate the H2O concentration based on the current-concentration conversion parameter. In the current measurement mode, the pump current Ip2 corresponding to the H2O concentration flows in the current measuring pump cell 41 as described above. Step S13 can be performed simultaneously with the above-mentioned step S11.

[0255] Next, the concentration calculation unit 294 obtains the pump current Ip2 in the current measurement pump unit 41, and calculates the H2O concentration in the measured gas based on the conversion parameter (current-concentration conversion parameter) between the pump current Ip2 and the H2O concentration in the measured gas stored in advance (step S14). The calculated H2O concentration is output as the detection value of the gas sensor 200. After step S14, the measurement mode switching unit 95 obtains the H2O concentration calculated by the concentration calculation unit 294, and determines whether the obtained H2O concentration is lower than the first concentration threshold C1 (step S15). As the first concentration threshold C1, for example, the lower limit value of the H2O concentration that obtains the desired measurement accuracy when measuring in the current measurement mode is pre-set.

[0256] In step S15, when the H2O concentration obtained from the concentration calculation unit 294 is greater than or equal to the first concentration threshold C1, the processing after step S14 is performed. That is, when the H2O concentration is greater than or equal to the first concentration threshold C1, the measurement mode switching unit 95 does not switch the measurement mode, and the pump control unit 293 and the concentration calculation unit 294 continue the current measurement mode.

[0257] In step S15, when the H2O concentration obtained from the concentration calculation unit 294 is a value lower than the first concentration threshold value C1, the measurement mode switching unit 95 switches to the voltage measurement mode (step S23). Specifically, the measurement mode switching unit 95 outputs a control signal set to OFF to the switching unit 47. In addition, the measurement mode switching unit 95 gives an instruction to the pump control unit 293 to control in the voltage measurement mode. In this case, the pump control unit 293 performs the following feedback control: based on the set value V2 of the voltage V2 in the electromotive force detection sensor unit 82 ... SET , the setting value V1 of the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control SET The measurement mode switching unit 95 instructs the concentration calculation unit 294 to obtain the voltage V1 of the decomposition pump control oxygen partial pressure detection sensor unit 81 and calculate the H2O concentration based on the voltage-concentration conversion parameter. In the voltage measurement mode, no pump current Ip2 flows through the current measurement pump unit 41.

[0258] Next, the concentration calculation unit 294 obtains the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control, and calculates the H2O concentration in the measured gas based on the conversion parameter (voltage-concentration conversion parameter) between the voltage V1 and the H2O concentration in the measured gas stored in advance (step S24). The calculated H2O concentration is output as the detection value of the gas sensor 200. After step S24, the measurement mode switching unit 95 obtains the H2O concentration calculated by the concentration calculation unit 294, and determines whether the obtained H2O concentration is higher than the second concentration threshold C2 (step S25). As the second concentration threshold C2, for example, the upper limit value of the H2O concentration that obtains the desired measurement accuracy when measuring in the voltage measurement mode is pre-set.

[0259] In step S25, when the H2O concentration obtained from the concentration calculation unit 294 is less than the second concentration threshold C2, the processing after step S24 is performed. That is, when the H2O concentration is less than the second concentration threshold C2, the measurement mode switching unit 95 does not switch the measurement mode, and the pump control unit 293 and the concentration calculation unit 294 continue the voltage measurement mode.

[0260] In step S25, when the H2O concentration obtained from the concentration calculation unit 294 is a value higher than the second concentration threshold value C2, the measurement mode switching unit 95 switches to the current measurement mode (step S13), and performs the processing after step S14.

[0261] In this way, the control unit 291 determines which of the current measurement mode and the voltage measurement mode to use based on the H2O concentration obtained from the concentration calculation unit 294 in the measurement mode switching unit 95, and as a result, detects the H2O concentration using one of the measurement modes. By making good use of the voltage measurement mode that can more accurately measure the measured gas containing low-concentration H2O and the current measurement mode that can more accurately measure the measured gas containing high-concentration H2O, the H2O concentration can be more accurately measured in a wide concentration range including low concentrations.

[0262] In step S13, when the measurement mode switching unit 95 switches from the voltage measurement mode to the current measurement mode, the water vapor in the measured gas is substantially completely decomposed at the decomposition pump electrode 51, and the hydrogen produced by the decomposition is substantially completely burned at the detection electrode 44. Therefore, the atmosphere near the detection electrode 44 is controlled to be in a state where substantially no hydrogen derived from water vapor exists. After the H2O concentration is measured in the current measurement mode at least once in this state (step S14), the mode is switched to the voltage measurement mode (step S23). In addition, in step S23, when the measurement mode switching unit 95 switches from the current measurement mode to the voltage measurement mode, the current is not allowed to flow through the current measurement pump unit 41, so that the voltage V2 detected by the electromotive force detection sensor unit 82 reaches the set value V2 SET The pump current Ip1 is passed through the decomposition pump unit 50 in a manner to decompose a part of the water vapor in the measured gas. Furthermore, the state is controlled so that a predetermined amount of hydrogen derived from the water vapor exists in the atmosphere near the detection electrode 44. After measuring the H2O concentration in the voltage measurement mode at least once (step S24) in this state, switching to the current measurement mode is performed (step S13).

[0263] When the measurement mode is switched in this way, after the atmosphere near the detection electrode 44 is controlled to be in a state where the H2O concentration can be measured, the next measurement mode switching is determined. Regarding the switching of the measurement mode, in most cases, it is usually performed with an interval of more than 1 second. It is not intended to perform switching based on the on-off of the pump current Ip2 in such a short time that the above-mentioned switching of the atmosphere near the monitoring electrode 44 cannot be achieved, or so-called on-off control based on pulse current.

[0264] In step S13, immediately after the measurement mode switching unit 95 switches from the voltage measurement mode to the current measurement mode, the control of the decomposition pump unit 50 and the current measurement pump unit 41 is changed, and therefore, the pump current Ip2 may be unstable. Therefore, the concentration calculation unit 94 may perform step S14 after a predetermined standby time has passed. In addition, in step S23, immediately after the measurement mode switching unit 95 switches from the current measurement mode to the voltage measurement mode, the control of the decomposition pump unit 50 and the current measurement pump unit 41 is also changed, and therefore, the voltage V1 may be unstable. Therefore, the concentration calculation unit 94 may perform step S24 after a predetermined standby time has passed.

[0265] As described above, the gas sensor 100 and the gas sensor 200 for detecting the H2O concentration in the measured gas are shown as examples of the embodiments of the present invention, but the present invention is not limited to these embodiments. In the present invention, as long as the purpose of the present invention is to accurately measure the measured gas in a wide concentration range including the low concentration measured gas, the gas sensor having various forms of sensor elements and control devices can be included.

[0266] In the above-mentioned embodiment, the gas sensor 100 and the gas sensor 200 detect the H2O concentration in the measured gas, but the measured gas is not limited to H2O. For example, the measured gas may be an oxide gas such as carbon dioxide CO2, nitrogen oxide NOx, or a non-oxide gas such as ammonia NH3 in addition to H2O.

[0267] For example, the case where carbon dioxide CO2 is detected as the measured gas is described. When carbon dioxide CO2 is decomposed (reduced), carbon monoxide CO and oxygen O2 (2CO2→2CO+O2) are generated. Carbon monoxide CO is a reducing gas like hydrogen H2. Therefore, when carbon dioxide CO2 is detected, the CO2 concentration in the measured gas can be calculated based on the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42, as in the above-mentioned gas sensor 100. Fig.10 This is a graph showing an example of the relationship between CO2 concentration and voltage V1. The horizontal axis represents CO2 concentration (%), and the vertical axis represents voltage V1 (mV) when voltage V2 reaches 450mV. Figure 5 The concentration calculation unit can use the H2O concentration and the voltage V1 to obtain the same correlation. Fig.10 The carbon dioxide concentration in the gas to be measured is calculated based on the voltage V1 by using the correlation shown in FIG.

[0268] For example, refer to Figure 1 and Fig.11 , a case where nitrogen oxides NOx are detected as the measurement target gas will be described. Fig.11 1 is a conceptual diagram showing the nitrogen oxide measurement principle when the nitrogen oxide is measured using the gas sensor 100 . Fig.11 In FIG. 4 , only nitrogen oxides NO and oxygen O2 are shown as gas components in the measured gas. When the nitrogen oxides NOx are decomposed (reduced), nitrogen N2 and oxygen O2 (2NO→N2+O2) are generated. Nitrogen N2 is a chemically stable inactive gas. When the nitrogen oxides NOx are detected, a voltage V2 between the detection electrode 44 and the reference electrode 42 is generated in accordance with the NOx that is not decomposed at the decomposition pump electrode 51. Therefore, at the decomposition pump electrode 51, control is performed in such a way that a predetermined amount of NOx is not decomposed regardless of the NOx concentration in the measured gas. That is, when the NOx concentration in the measured gas is high, NOx is decomposed at a high decomposition rate at the decomposition pump electrode 51. On the other hand, when the NOx concentration in the measured gas is low, NOx is decomposed at a low decomposition rate at the decomposition pump electrode 51. As a result, regardless of the NOx concentration in the measured gas, a predetermined amount of NOx is not decomposed and remains. The measured gas containing a predetermined amount of NOx that has not been decomposed is introduced into the third internal cavity 61 and reaches the detection electrode 44. Therefore, it is considered that there is the following trend: unlike the case of H2O and CO2, the higher the NOx concentration in the measured gas, the higher the voltage V1. The concentration calculation unit can use the correlation between the NOx concentration and the voltage V1 in the same way as the case of the gas sensor 100, and calculate the NOx concentration in the measured gas based on the voltage V1. In addition, the measurement can be performed while switching between the voltage measurement mode and the current measurement mode. In the current measurement mode, it is sufficient as long as the NOx is not substantially decomposed at the decomposition pump electrode 51 and the NOx is substantially completely decomposed at the detection electrode 44. For example, in the current measurement mode, the pump current Ip1 can be prevented from flowing through the decomposition pump unit 50.

[0269] For example, the case of detecting ammonia NH3 as the measurement target gas will be described. When ammonia NH3 is detected, ammonia NH3 is decomposed and converted into nitrogen oxides NO at the oxygen pump electrode (inner main pump electrode 22) in the cavity of the oxygen pump unit (main pump unit 21). By measuring NO converted from ammonia NH3 in the same way as in the above-mentioned case of measuring NOx, the concentration of ammonia NH3 can be measured.

[0270] When measuring the H2O concentration and CO2 concentration, for example, the setting value V0 for control of the main pump unit 21 is SETIt can be set to about 300mV to 800mV. More preferably, the setting value V0 SET It can be set to about 350mV to 500mV. In the main pump unit 21, H2O and CO2 are not substantially decomposed. It should be noted that when NOx exists in the measured gas, NOx can be decomposed in the main pump unit 21. In this case, the inner main pump electrode 22 can contain, for example, Rh as a metal component. In addition, when detecting the NOx concentration and NH3 concentration, for example, the setting value V0 for the control of the main pump unit 21 SET It can be set to about 150mV to 450mV. In the main pump unit 21, it is made not to substantially decompose NOx. In this way, the control setting value V0 of the main pump unit 21 can be appropriately set according to the type of the measured gas. SET That's it.

[0271] The voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 is made to reach the set value V2 SET In the case of feedback control for adjusting the voltage V1 in the decomposition pump control oxygen partial pressure detection sensor unit 81 in the manner of adjusting the voltage V1 in the decomposition pump control oxygen partial pressure detection sensor unit 81, the set value V2 can be adjusted according to the type of the measurement target gas. SET When measuring CO2 concentration, the setting value V2 is similar to the above-mentioned case of measuring H2O concentration. SET For example, it can be set to about 300mV to 600mV. More preferably, it can be set to about 400mV to 500mV. When detecting the NOx concentration and the NH3 concentration, the setting value V2 SET For example, it can be set to about 300 mV to 600 mV, and more preferably, it can be set to about 400 mV to 500 mV.

[0272] In the current measurement mode, the setting value V1a for controlling the decomposition pump unit 50 is SET , the setting value V2a for controlling the current measuring pump unit 41 SET Similarly, it only needs to be appropriately set according to the type of gas to be measured.

[0273] By appropriately setting each setting value as described above, the influence of gases other than the desired measurement target gas can be reduced, thereby enabling the desired measurement target gas to be measured with higher accuracy.

[0274] In the above-described embodiment, the pump control unit 93 of the control unit 91 performs the operation so that the voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 reaches the set value V2. SETThe pump control unit 93 may adjust the voltage V1 in the oxygen partial pressure detection sensor unit 81 for decomposition pump control in a feedback control manner, but the control method is not limited to this. For example, the pump control unit 93 may adjust the voltage V2 between the detection electrode 44 and the reference electrode 42 in the electromotive force detection sensor unit 82 to a set value V2. SET The pump voltage Vp1 of the variable power supply 52 in the decomposition pump unit 50 is feedback-controlled in a manner. Furthermore, the concentration calculation unit 94 can calculate the concentration of the measurement target gas in the measured gas based on the voltage V1 between the decomposition pump electrode 51 and the reference electrode 42 in the decomposition pump control oxygen partial pressure detection sensor unit 81 as the control result.

[0275] In the gas sensor 100 of the above embodiment, Figure 1 As shown, the sensor element 101 has the following structure: it has three internal cavities, namely, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, and the inner main pump electrode 22, the decomposition pump electrode 51, and the monitoring electrode 44 are respectively arranged in each internal cavity, but it is not limited thereto. For example, it can also be set as follows: it has two internal cavities, namely, the first internal cavity 20 and the second internal cavity 40, and the inner main pump electrode 22 is arranged in the first internal cavity 20, and the decomposition pump electrode 51 and the monitoring electrode 44 are arranged in the second internal cavity 40. In this case, for example, as a diffusion rate control unit between the decomposition pump electrode 51 and the monitoring electrode 44, a porous body protective layer covering the monitoring electrode 44 can be formed.

[0276] In the gas sensor 100 and the gas sensor 200 of the above-mentioned embodiment, the outer pump electrode 23 has the functions of two or three electrodes: the outer-cavity oxygen pump electrode in the oxygen pump unit (main pump unit 21), the outer-cavity decomposition pump electrode in the decomposition pump unit 50, and the outer-cavity detection electrode in the current measurement pump unit 41 (in the case of the gas sensor 200), but is not limited to this. For example, the outer-cavity oxygen pump electrode, the outer-cavity decomposition pump electrode, and the outer-cavity detection electrode may also be formed as another electrode respectively. For example, any one or more of the outer-cavity oxygen pump electrode, the outer-cavity decomposition pump electrode, and the outer-cavity detection electrode may be provided on the outer surface of the base 102 in a manner different from the outer pump electrode 23 so as to contact the measured gas. Alternatively, the reference electrode 42 may also be used as any one or more of the outer-cavity oxygen pump electrode, the outer-cavity decomposition pump electrode, and the outer-cavity detection electrode.

[0277] In the above-mentioned gas sensor 200, a switch is provided as an example of the switching unit 47, however, the present invention is not limited to this form. For example, the variable power supply 46 may also be used as the switching unit 47. The measurement mode switching unit 95 may be: in switching to the voltage measurement mode, the pump voltage Vp2 of the variable power supply 46 is made zero without applying a voltage to the current measurement pump unit 41, thereby switching to not allowing current to flow; in switching to the current measurement mode, the pump voltage Vp2 of the variable power supply 46 is made a prescribed value and a prescribed voltage is applied to the current measurement pump unit 41, thereby switching to allowing current to flow. It should be noted that in the current measurement mode, as in the case of the above-mentioned gas sensor 200, the voltage V2 as the control voltage detected by the electromotive force detection sensor unit 82 may reach the set value V2 SET The pump voltage Vp2 of the variable power supply 46 in the current measuring pump unit 41 is feedback controlled in a manner.

[0278] In the above-described gas sensor 200 , after step S12 , the measurement mode switching unit 95 first switches to the current measurement mode in step S13 . However, after step S12 , the mode may first switch to the voltage measurement mode in step S23 .

[0279] Alternatively, when the gas sensor 200 is activated, the control device 290 may be preset to be in the current measurement mode or in the voltage measurement mode.

[0280] In the above-described gas sensor 200 , the measurement mode switching unit 95 switches between the voltage measurement mode and the current measurement mode based on the H 2 O concentration calculated by the concentration calculating unit 294 , but the present invention is not limited thereto.

[0281] As a threshold for switching the current measurement mode to the voltage measurement mode, a person skilled in the art may appropriately set the lower limit value of the pump current Ip2 that obtains the desired measurement accuracy when measuring in the current measurement mode instead of the first concentration threshold value C1. As a threshold for switching the voltage measurement mode to the current measurement mode, a person skilled in the art may appropriately set the upper limit value of the voltage V1 that obtains the desired measurement accuracy when measuring in the voltage measurement mode instead of the second concentration threshold value C2.

[0282] The switching between the voltage measurement mode and the current measurement mode may be performed based on a signal from another device such as the ECU of the vehicle or the exhaust gas treatment device.

[0283] As described above, according to the present invention, the voltage between the decomposition pump electrode and the reference electrode in the cavity is measured when the voltage between the detection electrode and the reference electrode in the cavity reaches a specified value, so that the measurement target gas in a wide concentration range including the measurement target gas at a low concentration can be measured with good accuracy. In addition, by switching between the voltage measurement mode with higher measurement accuracy at low concentrations and the current measurement mode with higher measurement accuracy at high concentrations while measuring, the measurement target gas in a wide concentration range including the measurement target gas at a low concentration can be measured with further good accuracy. In the case of water vapor and carbon dioxide, the measurement target gas in a wide concentration range of, for example, 0.01 to 30% can be measured with good accuracy, and in the case of NOx and NH3, the measurement target gas in a wide concentration range of, for example, 10 to 5000 ppm can be measured with good accuracy.

[0284] Explanation of symbols

[0285] 1. First substrate layer

[0286] 2 Second substrate layer

[0287] 3 Third substrate layer

[0288] 4 First solid electrolyte layer

[0289] 5 Isolation layer

[0290] 6 Second solid electrolyte layer

[0291] 10 Gas inlet

[0292] 11. First diffusion rate control unit

[0293] 12 Buffer Space

[0294] 13. Second diffusion rate control unit

[0295] 15 Cavity for the gas to be measured

[0296] 20 first inner cavity

[0297] 21 Main pump unit

[0298] 22 Inner main pump electrode

[0299] 22a Top electrode portion (of the inner main pump electrode)

[0300] 22b Bottom electrode portion (of the inner main pump electrode)

[0301] 23 Outer pump electrode

[0302] 24 Variable power supply (of main pump unit)

[0303] 30 Third diffusion rate control unit

[0304] 40 Second inner cavity

[0305] 41 Pump unit for current measurement

[0306] 42 Reference electrode

[0307] 43 Reference gas introduction space

[0308] 44 Detection electrode

[0309] 46 Variable power supply (for pump unit for current measurement)

[0310] 47 Switching unit

[0311] 48 Atmospheric introduction layer

[0312] 50 Disassemble the pump unit

[0313] 51 Decomposition pump electrode

[0314] 51a Top electrode portion (of the decomposed pump electrode)

[0315] 51b Bottom electrode portion (of decomposed pump electrode)

[0316] 52 Variable power supply (for decomposition pump unit)

[0317] 60 Fourth diffusion rate control unit

[0318] 61 Third internal cavity

[0319] 70 Heater section

[0320] 71 Heater electrode

[0321] 72 Heater

[0322] 73 Through Holes

[0323] 74 Heater insulation layer

[0324] 75 Pressure relief hole

[0325] 76 Heater lead

[0326] 77 Heater power supply

[0327] 80 Main pump control oxygen partial pressure detection sensor unit

[0328] 81 Decomposition pump control oxygen partial pressure detection sensor unit

[0329] 82 Electromotive force detection sensor unit

[0330] 83 Sensor unit

[0331] 85 Feedback switching unit

[0332] 90, 290 Control Device

[0333] 91, 291 Control Department

[0334] 92 Heater control unit

[0335] 93, 293 Pump control unit

[0336] 94, 294 Concentration calculation unit

[0337] 95 Measurement mode switching section

[0338] 100, 200 Gas Sensor

[0339] 101, 201 sensor element

[0340] 102 Base part

Claims

1. A gas sensor comprising a sensor element and a control device for controlling the sensor element, for detecting a measurement target gas in a measured gas, The gas sensor is characterized in that The sensor element comprises: A long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion; An oxygen pump unit, the oxygen pump unit comprising an intra-cavity oxygen pump electrode disposed in the measured gas circulation cavity, and an extra-cavity oxygen pump electrode disposed at a position of the base body different from the measured gas circulation cavity and corresponding to the intra-cavity oxygen pump electrode, for adjusting the oxygen concentration in the measured gas; a decomposition pump unit, the decomposition pump unit comprising an intra-cavity decomposition pump electrode disposed in the measured gas circulation cavity at a position farther from the one end portion in the length direction of the base portion than the intra-cavity oxygen pump electrode, and an extra-cavity decomposition pump electrode disposed at a position of the base portion different from the measured gas circulation cavity and corresponding to the intra-cavity decomposition pump electrode, to decompose a measurement target gas in the measured gas; an intra-cavity detection electrode disposed in the measured gas flow cavity at a position farther from the one end in the length direction of the base portion than the intra-cavity decomposition pump electrode; as well as a reference electrode disposed inside the base body so as to be in contact with a reference gas, The control device comprises: a pump control unit that controls the operations of the oxygen pump unit and the decomposition pump unit; as well as a concentration calculating unit for calculating the concentration of the measurement target gas in the measured gas; The pump control unit operates the oxygen pump unit to adjust the oxygen concentration in the measured gas to a predetermined concentration, and operates the decomposition pump unit in such a manner that the voltage between the detection electrode in the cavity and the reference electrode reaches a predetermined value, thereby decomposing at least a portion of the measurement target gas in the measured gas at the decomposition pump electrode in the cavity of the decomposition pump unit, and sucking out oxygen generated by the decomposition of the measurement target gas by using the decomposition pump unit. The concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the value of the voltage between the intra-cavity decomposition pump electrode and the reference electrode.

2. The gas sensor according to claim 1, characterized in that The pump control unit adjusts the voltage between the intra-cavity decomposition pump electrode and the reference electrode in such a manner that the voltage between the intra-cavity detection electrode and the reference electrode reaches the specified value, thereby decomposing at least a portion of the measurement target gas in the measured gas at the intra-cavity decomposition pump electrode of the decomposition pump unit, and sucking out oxygen generated by the decomposition of the measurement target gas using the decomposition pump unit. The concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the adjusted value of the voltage between the intra-cavity decomposition pump electrode and the reference electrode.

3. The gas sensor according to claim 1, characterized in that: The sensor element further includes a pump unit for current measurement. The current measuring pump unit includes: the cavity detection electrode and the cavity detection electrode outside the cavity provided at a position of the base body different from the cavity through which the gas to be measured flows and corresponding to the cavity detection electrode. The control device further comprises a switching unit, The switching unit switches whether or not to allow current to flow through the current measuring pump unit.

4. The gas sensor according to claim 3, characterized in that: The control device includes a measurement mode switching unit, The measurement mode switching unit switches between a voltage measurement mode and a current measurement mode. In the voltage measurement mode, the concentration of the measurement target gas in the measurement target gas is calculated based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity. In the current measurement mode, the concentration of the measurement target gas in the measurement target gas is calculated based on the current value flowing through the current measurement pump unit. The measurement mode switching unit switches the switching means so that current does not flow through the current measuring pump unit when switching to the voltage measurement mode, and switches the switching means so that current flows through the current measuring pump unit when switching to the current measurement mode.

5. The gas sensor according to claim 4, characterized in that: The measurement mode switching unit switches to the voltage measurement mode when it is determined that the concentration of the measurement target gas detected in the current measurement mode is lower than a predetermined first concentration threshold value C1. When it is determined that the concentration of the measurement target gas detected in the voltage measurement mode is higher than a predetermined second concentration threshold value C2, switching to the current measurement mode is performed.

6. The gas sensor according to claim 5, characterized in that: The first concentration threshold C1 is a concentration lower than the second concentration threshold C2.

7. The gas sensor according to claim 4, characterized in that: In the current measurement mode, the value of the current flowing through the current measurement pump cell is controlled so that the voltage between the intra-cavity detection electrode and the reference electrode reaches a predetermined value.

8. The gas sensor according to claim 1, characterized in that The measurement target gas is selected from the group consisting of water vapor H2O, carbon dioxide CO2 and nitrogen oxides NOx.

9. A method for controlling a gas sensor for detecting a measurement target gas in a measured gas, The gas sensor control method is characterized in that: The gas sensor includes a sensor element and a control device for controlling the sensor element. The sensor element comprises: A long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion; An oxygen pump unit, the oxygen pump unit comprising an intra-cavity oxygen pump electrode disposed in the measured gas circulation cavity, and an extra-cavity oxygen pump electrode disposed at a position of the base body different from the measured gas circulation cavity and corresponding to the intra-cavity oxygen pump electrode, for adjusting the oxygen concentration in the measured gas; a decomposition pump unit, the decomposition pump unit comprising an intra-cavity decomposition pump electrode disposed in the measured gas circulation cavity at a position farther from the one end portion in the length direction of the base portion than the intra-cavity oxygen pump electrode, and an extra-cavity decomposition pump electrode disposed at a position of the base portion different from the measured gas circulation cavity and corresponding to the intra-cavity decomposition pump electrode, to decompose a measurement target gas in the measured gas; an intra-cavity detection electrode disposed in the measured gas flow cavity at a position farther from the one end in the length direction of the base portion than the intra-cavity decomposition pump electrode; as well as a reference electrode disposed inside the base body so as to be in contact with a reference gas, The control device comprises: a pump control unit that controls the operations of the oxygen pump unit and the decomposition pump unit; and a concentration calculating unit for calculating the concentration of the measurement target gas in the measured gas; The control method comprises: a pump control step, in which the oxygen concentration in the measured gas is adjusted to a predetermined concentration by operating the oxygen pump unit through the pump control unit, and the decomposition pump unit is operated in such a manner that the voltage between the detection electrode in the cavity and the reference electrode reaches a predetermined value, thereby decomposing at least a part of the measurement target gas in the measured gas at the decomposition pump electrode in the cavity of the decomposition pump unit, and oxygen generated by the decomposition of the measurement target gas is sucked out by the decomposition pump unit; and A concentration calculation step in which the concentration calculation unit calculates the concentration of the measurement target gas in the measurement target gas based on the value of the voltage between the decomposition pump electrode and the reference electrode in the cavity.

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