Gas sensor and gas sensor control method

Abstract

To shorten light-off time and suppress occurrence of cracks in a sensor element.SOLUTION: A gas sensor for detecting a measurement object gas in a gas to be measured and its control method include: a sensor element 101 including an adjusting pump cell 21 and a measuring pump cell 41; and a controller 90 including a pump control unit 93. The pump control unit 93 performs start-up pump control when the sensor element 101 is started and steady-state drive pump control during steady-state driving after the start-up, and in the start-up pump control, applies to an adjusting pump cell 21 a start-up voltage that is higher than the voltage applied between an inner pump electrode 22 and an outer pump electrode 23 of the adjustment pump cell 21 in the steady-state drive pump control, and applies to the measuring pump cell 41 a start-up voltage that is higher than the voltage applied between an inner measuring electrode 44 and an outer measuring electrode 23 of the measuring pump cell 41 in the steady driving pump control and lower than the start-up voltage of the adjusting pump cell 21.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor and a method for controlling a gas sensor. [Background technology]

[0002] Gas sensors are used to detect and measure the concentration of target gas components (oxygen O2, nitrogen oxides NOx, ammonia NH3, hydrocarbons HC, carbon dioxide CO2, etc.) in gases to be measured, such as automobile exhaust gases. For example, the concentration of target gas components in automobile exhaust gases is measured, and the exhaust gas purification system installed in the automobile is optimally controlled based on the measured value.

[0003] Known examples of such gas sensors include gas sensors that use an oxygen ion conductive solid electrolyte such as zirconia (ZrO2). For example, Japanese Patent No. 4903895 discloses a gas sensor that includes a first oxygen pump cell that adjusts the oxygen concentration of a target gas introduced into a first measurement chamber, and a second oxygen pump cell that detects the concentration of a specific gas introduced into a second measurement chamber.

[0004] Furthermore, Japanese Patent No. 4903895 discloses that in order to reduce variations in the start-up time of the gas sensor, preliminary control is performed in which a constant current is supplied to the second oxygen pump cell for a certain period of time before drive control is started. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4903895 Summary of the Invention [Problem to be solved by the invention]

[0006] Gas sensors using solid electrolytes require a certain amount of time from startup until they can measure the concentration of the target gas. This time is called the light-off time.

[0007] As automobile exhaust gas regulations become stricter, there is a demand for exhaust gas purification systems to function more quickly after the engine starts. To achieve this, gas sensors must have a shorter light-off time.

[0008] For example, as mentioned above, Japanese Patent No. 4903895 discloses that in a gas sensor having a first oxygen pump cell and a second oxygen pump cell, preliminary control is performed to supply a constant current to the second oxygen pump cell for a fixed period of time before starting drive control in order to reduce variations in the start-up time (light-off time) of the gas sensor. It is disclosed that the voltage applied to the second oxygen pump cell during preliminary control is higher than that during drive control.

[0009] However, it has been found that in a gas sensor in which two or more pump cells are arranged in series from an inlet for a gas to be measured, the light-off time may become long, as will be described in detail later.

[0010] Furthermore, it was found that excessive voltage applied to the pump cell can cause the oxygen in the solid electrolyte in the pump cell to migrate, weakening the solid electrolyte and potentially causing cracks in the internal structure of the sensor element.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas sensor that has a short light-off time and that suppresses the occurrence of cracks in the internal structure of the sensor element. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have found that the following invention can prevent cracks from occurring in the internal structure of the sensor element and shorten the light-off time.

[0013] The present invention includes the following inventions. (1) A gas sensor including a sensor element and a control device that controls the sensor element, The sensor element is a long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measurement gas flow portion formed at one end of the base portion in the longitudinal direction; an adjusting pump cell including an inner pump electrode disposed on an inner surface of the measurement target gas flow portion and an outer pump electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner pump electrode, the adjusting pump cell adjusting the oxygen concentration in the measurement target gas to a desired concentration; a measurement pump cell for detecting a measurement target gas in the measurement gas, the measurement pump cell including: an inner measurement electrode disposed on an inner surface of the measurement target gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer measurement electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner measurement electrode; Including, The control device a pump control unit that controls operations of the adjustment pump cell and the measurement pump cell, The pump control unit performing a startup pump control at the startup of the sensor element and a steady drive pump control during steady drive of the sensor element after the startup; In the startup pump control, a startup voltage of the adjustment pump cell that is higher than the voltage applied to the adjustment pump cell in the steady drive pump control is applied between the inner pump electrode and the outer pump electrode of the adjustment pump cell, and a startup voltage of the measurement pump cell that is higher than the voltage applied to the measurement pump cell in the steady drive pump control and lower than the startup voltage of the adjustment pump cell is applied between the inner measurement electrode and the outer measurement electrode of the measurement pump cell, In the steady-state drive pump control, the oxygen concentration in the measurement gas is adjusted to a desired concentration by the adjustment pump cell, and the measurement pump cell detects the measurement target gas in the measurement gas.

[0014] (2) The sensor element further comprises: an auxiliary pump cell including an inner auxiliary pump electrode disposed on an inner surface of the measurement gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer auxiliary pump electrode disposed at a position different from the measurement gas flow portion of the base portion and corresponding to the inner auxiliary pump electrode, for further adjusting the oxygen concentration in the measurement gas; The startup pump control further includes: a startup voltage for the auxiliary pump cell is applied between the inner auxiliary pump electrode and the outer auxiliary pump electrode of the auxiliary pump cell, the startup voltage being higher than the voltage applied to the auxiliary pump cell in the steady drive pump control, not higher than the startup voltage of the adjustment pump cell, and higher than the startup voltage of the measurement pump cell; The gas sensor according to (1) above, wherein in the steady-state drive pump control, the oxygen concentration in the measurement gas is adjusted to a desired concentration by the adjustment pump cell, the oxygen concentration in the measurement gas adjusted by the adjustment pump cell is further adjusted by the auxiliary pump cell, and the measurement target gas in the measurement gas is detected by the measurement pump cell.

[0015] (3) The sensor element includes a heater that heats the base portion, The control device a heater control unit that controls the heater; Further, a determination unit that determines the start and end of the startup pump control, the heater control unit heats the base unit with the heater, raises the temperature of the base unit to a predetermined steady-state driving temperature through the start temperature of the startup pump control, and performs heater control to maintain the temperature of the base unit at the steady-state driving temperature; The gas sensor according to (1) or (2), wherein the determination unit causes the pump control unit to start the startup pump control when it determines that the temperature of the base unit has reached the start temperature of the startup pump control.

[0016] (4) The gas sensor according to (3), wherein the determination unit causes the pump control unit to switch from the startup pump control to the steady-state drive pump control when it determines that the pump current flowing through the measurement pump cell during the startup pump control is equal to or less than a predetermined threshold.

[0017] (5) The sensor element includes a reference electrode disposed inside the base portion so as to be in contact with a reference gas; The gas sensor according to (3) above, wherein the determination unit causes the pump control unit to switch from the startup pump control to the steady-state drive pump control when it determines that the electromotive force between the inner measurement electrode and the reference electrode is equal to or greater than a predetermined threshold value during the startup pump control.

[0018] (6) The gas sensor according to any one of (1) to (5) above, wherein the startup voltage of the adjustment pump cell is 1.5 V or more and 3.0 V or less.

[0019] (7) The gas sensor according to any one of (1) to (6) above, wherein the startup voltage of the measuring pump cell is 0.5 V or more and 1.45 V or less.

[0020] (8) The gas sensor according to any one of (1) to (7) above, wherein a voltage ratio of the startup voltage of the adjustment pump cell to the startup voltage of the measurement pump cell is 1.03 or more and 6.00 or less.

[0021] (9) A method for controlling a gas sensor for detecting a target gas in a measurement gas, comprising: The gas sensor comprises: a sensor element and a control device that controls the sensor element; The sensor element is a long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measurement gas flow portion formed at one end of the base portion in the longitudinal direction; an adjusting pump cell including an inner pump electrode disposed on an inner surface of the measurement target gas flow portion and an outer pump electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner pump electrode, the adjusting pump cell adjusting the oxygen concentration in the measurement target gas to a desired concentration; a measurement pump cell for detecting a measurement target gas in the measurement gas, the measurement pump cell including: an inner measurement electrode disposed on an inner surface of the measurement target gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer measurement electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner measurement electrode; Including, The control device a pump control unit that controls operations of the adjustment pump cell and the measurement pump cell, The control method includes: a startup pump control step executed when the sensor element is started, and a steady drive pump control step executed thereafter; In the startup pump control step, a pump control unit applies a startup voltage of the adjustment pump cell between the inner pump electrode and the outer pump electrode of the adjustment pump cell, the startup voltage being higher than a voltage applied to the adjustment pump cell in the steady drive pump control, and applies a startup voltage of the measurement pump cell between the inner measurement electrode and the outer measurement electrode of the measurement pump cell, the startup voltage being higher than the voltage applied to the measurement pump cell in the steady drive pump control and lower than the startup voltage of the adjustment pump cell; a pump control unit that adjusts the oxygen concentration in the measurement target gas to a desired concentration using the adjustment pump cell and detects the measurement target gas in the measurement target gas using the measurement pump cell in the steady-state drive pump control step.

[0022] (10) The sensor element further comprises: an auxiliary pump cell including an inner auxiliary pump electrode disposed on an inner surface of the measurement gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer auxiliary pump electrode disposed at a position different from the measurement gas flow portion of the base portion and corresponding to the inner auxiliary pump electrode, for further adjusting the oxygen concentration in the measurement gas; In the startup pump control step, a pump control unit applies a startup voltage for the auxiliary pump cell between the inner auxiliary pump electrode and the outer auxiliary pump electrode of the auxiliary pump cell, the startup voltage being higher than the voltage applied to the auxiliary pump cell in the steady drive pump control, not higher than the startup voltage of the adjustment pump cell, and higher than the startup voltage of the measurement pump cell; The control method according to (9) above, wherein in the steady drive pump control step, the pump control unit adjusts the oxygen concentration in the measurement gas to a desired concentration using the adjustment pump cell, further adjusts the oxygen concentration in the measurement gas adjusted by the adjustment pump cell using the auxiliary pump cell, and detects the measurement target gas in the measurement gas using the measurement pump cell.

[0023] (11) The sensor element includes a heater that heats the base portion, The control device a heater control unit that controls the heater; Further, a determination unit that determines the start and end of the startup pump control, The control method includes: the heater control unit performs a heater control step of heating the base unit with the heater, raising the temperature of the base unit to a predetermined steady-state driving temperature through the start temperature of the startup pump control, and maintaining the temperature of the base unit at the steady-state driving temperature; The control method described in (9) or (10) above, wherein the determination unit starts the startup pump control step when it determines that the temperature of the base unit has reached the start temperature of the startup pump control.

[0024] (12) The control method comprises: While performing the heater control step, The control method described in (11) above, wherein when the judgment unit determines that the pump current flowing through the measurement pump cell during the startup pump control is equal to or less than a predetermined threshold, the startup pump control step is terminated and the steady-state drive pump control step is started.

[0025] (13) The sensor element includes a reference electrode disposed inside the base portion so as to be in contact with a reference gas, The control method includes: While performing the heater control step, The control method described in (11) above, wherein when the judgment unit determines that the electromotive force between the inner measurement electrode and the reference electrode during the startup pump control is greater than or equal to a predetermined threshold, the startup pump control step is terminated and the steady-state drive pump control step is started.

[0026] (14) The control method according to any one of (9) to (13) above, wherein the startup voltage of the regulation pump cell is 1.5 V or more and 3.0 V or less.

[0027] (15) The control method according to any one of (9) to (14) above, wherein the startup voltage of the measurement pump cell is 0.5 V or more and 1.45 V or less.

[0028] (16) The control method according to any one of (9) to (15) above, wherein a voltage ratio of the start-up voltage of the adjustment pump cell to the start-up voltage of the measurement pump cell is 1.03 or more and 6.00 or less. [Effects of the Invention]

[0029] According to the present invention, it is possible to provide a gas sensor that has a short light-off time and that suppresses the occurrence of cracks in the internal structure of the sensor element. [Brief explanation of the drawings]

[0030] [Figure 1]1 is a schematic vertical cross-sectional view showing an example of the schematic configuration of a gas sensor 100 in the longitudinal direction. [Figure 2] 1 is a block diagram showing the electrical connection relationship between a control device 90 and each of pump cells 21, 50, 41, each of sensor cells 80, 81, 82, 83 of a sensor element 101, and a heater section 70. FIG. [Figure 3] 4 is a flowchart showing an example of a startup process in the gas sensor 100. [Figure 4] 10 is a flowchart showing a modified example of the start-up process in the gas sensor 100. DETAILED DESCRIPTION OF THE INVENTION

[0031] The gas sensor of the present invention includes a sensor element and a control device that controls the sensor element.

[0032] The sensor element included in the gas sensor of the present invention is a long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measurement gas flow portion formed at one end of the base portion in the longitudinal direction; an adjusting pump cell including an inner pump electrode disposed on an inner surface of the measurement target gas flow portion and an outer pump electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner pump electrode, the adjusting pump cell adjusting the oxygen concentration in the measurement target gas to a desired concentration; a measurement pump cell for detecting a measurement target gas in the measurement gas, the measurement pump cell including: an inner measurement electrode disposed on an inner surface of the measurement target gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer measurement electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner measurement electrode; Includes:

[0033] The control device included in the gas sensor of the present invention includes a pump control unit that controls the operations of the adjustment pump cell and the measurement pump cell, and is configured to perform startup pump control when the sensor element is started up and steady-state drive pump control when the sensor element is in steady-state drive after the startup.

[0034] The startup period of the sensor element refers to the period from when the gas sensor is turned on until it is able to detect (measure) the gas to be measured. This is also referred to as the startup period of the gas sensor. The steady-state operation period of the sensor element refers to the period from when the gas sensor is turned on until it is able to detect (measure) the gas to be measured. This is also referred to as the steady-state operation period of the gas sensor. Once the startup period ends, the gas sensor transitions to the steady-state operation period. Normally, the steady-state operation period is the period from when the gas sensor is turned on until it is turned off, excluding the startup period. The detection of the gas to be measured includes measuring the concentration of the gas to be measured.

[0035] An example of an embodiment of the gas sensor of the present invention will be described in detail below.

[0036] [Outline of gas sensor configuration] The gas sensor of the present invention will be described below with reference to the drawings. Fig. 1 is a schematic vertical cross-sectional view in the longitudinal direction showing an example of the general configuration of a gas sensor 100 including a sensor element 101. In the following, with Fig. 1 as the reference, the upper side of Fig. 1 will be referred to as the top, the lower side as the bottom, the left side of Fig. 1 as the leading end side, and the right side as the rear end side.

[0037] In FIG. 1, a gas sensor 100 is an example of a NOx sensor that detects NOx in a measurement gas by a sensor element 101 and measures its concentration.

[0038] The gas sensor 100 also includes a control device 90 that controls the sensor element 101. Figure 2 is a block diagram showing the electrical connection between the control device 90 and the sensor element 101.

[0039] (sensor element) The sensor element 101 is a long, plate-like element including a base portion 102 having a structure in which multiple oxygen-ion conductive solid electrolyte layers are stacked. The long, plate-like shape is also referred to as a long plate shape or a strip shape. The base portion 102 has a structure in which six layers are stacked in this order from bottom to top as viewed in the drawing: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, each of which is made of an oxygen-ion conductive solid electrolyte layer such as zirconia (ZrO). The solid electrolyte forming these six layers is dense and airtight. The six layers may all have the same thickness or may have different thicknesses. The layers are bonded together via adhesive layers made of solid electrolyte, and the base portion 102 includes the adhesive layers. While FIG. 1 illustrates a layer structure consisting of six layers, the layer structure of the present invention is not limited to this and any number and layer structure may be used.

[0040] The sensor element 101 is manufactured by, for example, laminating ceramic green sheets corresponding to each layer after performing predetermined processing and printing a circuit pattern on them, and then firing the sheets to integrate them.

[0041] A gas inlet 10 is formed at one longitudinal end (hereinafter referred to as the tip) of the sensor element 101, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measurement gas flow section 15 includes, in the longitudinal direction from the gas inlet 10, a first diffusion-controlling section 11, a buffer space 12, a second diffusion-controlling section 13, a first internal space 20, a third diffusion-controlling section 30, a second internal space 40, a fourth diffusion-controlling section 60, and a third internal space 61, which are adjacently formed and communicate with each other in this order.

[0042] The gas inlet 10, the buffer space 12, the first internal space 20, the second internal space 40, and the third internal space 61 are spaces inside the sensor element 101, which are defined by hollowing out the spacer layer 5, with an upper portion defined by the underside of the second solid electrolyte layer 6, a lower portion defined by the upper surface of the first solid electrolyte layer 4, and sides defined by the side surfaces of the spacer layer 5.

[0043] The first diffusion rate-controlling section 11, the second diffusion rate-controlling section 13, and the third diffusion rate-controlling section 30 are each provided as two horizontally elongated slits (the openings have their longitudinal direction perpendicular to the plane of the drawing in FIG. 1). The first diffusion rate-controlling section 11 and the second diffusion rate-controlling section 13 may have any shape that provides a desired diffusion resistance, and the shape is not limited to the slits.

[0044] The fourth diffusion rate-controlling portion 60 is provided as a single horizontally elongated slit (the opening has its longitudinal direction perpendicular to the plane of the drawing in FIG. 1 ) between the spacer layer 5 and the second solid electrolyte layer 6. The fourth diffusion rate-controlling portion 60 may have any shape that provides a desired diffusion resistance, and the shape is not limited to the slit.

[0045] Furthermore, a reference gas introduction space 43 is provided at a position farther from the tip side than the measurement gas flow section 15, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, and at a position defined at its side 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, air is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

[0046] The air introduction layer 48 is a layer made of porous alumina, and a reference gas is introduced into the air introduction layer 48 through the reference gas introduction space 43. The air introduction layer 48 is also formed so as to cover the reference electrode 42.

[0047] The reference electrode 42 is an electrode formed in a manner sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, the air introduction layer 48, which is connected to the reference gas introduction space 43, is provided around the reference electrode 42. That is, the reference electrode 42 is disposed so as to come into contact with the reference gas via the porous air introduction layer 48 and the reference gas introduction space 43. As will be described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20, the second internal space 40, and the third internal space 61. The reference electrode 42 is formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO).

[0048] In the measurement gas flow section 15, the gas inlet 10 is open to the external space, and the measurement gas is introduced into the sensor element 101 from the external space through the gas inlet 10.

[0049] In this embodiment, the measurement gas flow section 15 is configured such that the measurement gas is introduced through the gas inlet 10 opening at the tip end surface of the sensor element 101, but the present invention is not limited to this configuration. For example, the measurement gas flow section 15 does not need to have a recess for the gas inlet 10. In this case, the first diffusion rate-controlling section 11 essentially serves as the gas inlet. Furthermore, for example, the measurement gas flow part 15 may have an opening in a side surface along the longitudinal direction of the base part 102, the opening communicating with the buffer space 12 or a position in the first internal space 20 close to the buffer space 12. In this case, the measurement gas is introduced from the side surface along the longitudinal direction of the base part 102 through the opening. Furthermore, for example, the measurement gas flow portion 15 may be configured so that the measurement gas is introduced through a porous body.

[0050] The first diffusion rate-controlling part 11 is a part that applies a predetermined diffusion resistance to the measurement gas taken in through the gas inlet 10.

[0051] The buffer space 12 is a space provided for guiding the measurement gas introduced from the first diffusion rate-controlling part 11 to the second diffusion rate-controlling part 13 .

[0052] The second diffusion rate-controlling portion 13 is a portion that applies a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 into the first internal space 20 .

[0053] It is sufficient that the amount of the measurement gas introduced into the first internal space 20 is within a predetermined range. That is, it is sufficient that a predetermined diffusion resistance is imparted to the entire area from the tip of the sensor element 101 to the second diffusion-controlling section 13. For example, it is also possible that the first diffusion-controlling section 11 directly communicates with the first internal space 20, that is, the buffer space 12 and the second diffusion-controlling section 13 do not exist.

[0054] The buffer space 12 is a space provided to mitigate the influence of pressure fluctuations on the detected value when the pressure of the gas to be measured fluctuates.

[0055] When the measurement gas is introduced from the outside of the sensor element 101 into the first internal space 20, the measurement gas is suddenly taken into the sensor element 101 from the gas inlet 10 due to pressure fluctuations of the measurement gas in the external space (exhaust pressure pulsations if the measurement gas is automobile exhaust gas), but is not introduced directly into the first internal space 20, but is introduced into the first internal space 20 after the pressure fluctuations of the measurement gas are canceled out through the first diffusion rate-controlling section 11, buffer space 12, and second diffusion rate-controlling section 13. As a result, the pressure fluctuations of the measurement gas introduced into the first internal space become almost negligible.

[0056] The first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the measurement gas introduced through the second diffusion-controlling part 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

[0057] The sensor element 101 includes an inner pump electrode disposed on the inner surface of the measurement gas flow portion 15 and an outer pump electrode corresponding to the inner pump electrode disposed at a position on the base portion 102 different from the measurement gas flow portion 15, and includes an adjustment pump cell that adjusts the oxygen concentration in the measurement gas to a desired concentration. In this embodiment, the main pump cell 21 functions as the adjustment pump cell. The inner main pump electrode 22 functions as the inner pump electrode, and the outer pump electrode 23 functions as the outer pump electrode. In this embodiment, the sensor element 101 includes, in addition to the main pump cell 21, which is an adjustment pump cell, an auxiliary pump cell 50 that further adjusts the oxygen concentration in the measurement gas, thereby adjusting the oxygen concentration with higher precision.

[0058] The main pump cell 21 is an electrochemical pump cell including an inner main pump electrode 22 disposed on the inner surface of the measurement gas flow section 15, and an outer pump electrode 23 disposed at a position of the base section 102 different from the measurement gas flow section 15 (on the outer surface of the base section 102 in FIG. 1 ) and corresponding to the inner main pump electrode 22. The phrase "corresponding to the inner main pump electrode 22" means that the outer pump electrode 23 is provided on the inner main pump electrode 22 with a second solid electrolyte layer 6 interposed therebetween.

[0059] That is, the main pump cell 21 is an electrochemical pump cell including an inner main pump electrode 22 having a ceiling electrode portion 22a provided on almost the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20, an outer pump electrode 23 provided on the upper surface of the second solid electrolyte layer 6 in a region corresponding to the ceiling electrode portion 22a so as to be exposed to the external space, and the second solid electrolyte layer 6 sandwiched between these electrodes.

[0060] 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 define the first internal space 20 and the spacer layer 5 that provides the side walls. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal space 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. Side electrode portions (not shown) are formed on the side wall surfaces (inner surfaces) of the spacer layer 5 that configure both side wall portions of the first internal space 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and are arranged in a tunnel-like structure at the locations where the side electrode portions are provided.

[0061] The inner main pump electrode 22 and the outer pump electrode 23 are porous cermet electrodes (electrodes in which a metal component and a ceramic component are mixed). The ceramic component is not particularly limited, but it is preferable to use an oxygen ion conductive solid electrolyte, similar to the base portion 102. For example, ZrO2 can be used as the ceramic component.

[0062] The inner main pump electrode 22, which comes into contact with the measurement gas, is formed using a material with reduced reduction capability for the NOx component in the measurement gas. The inner main pump electrode 22 preferably contains a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) and a noble metal (e.g., Au, Ag, etc.) that reduces the catalytic activity of the catalytically active noble metal for the measurement target gas (NOx in this embodiment). In this embodiment, the inner main pump electrode 22 is a porous cermet electrode made of Pt containing 1% Au and ZrO2.

[0063] The outer pump electrode 23 may contain any noble metal having catalytic activity as described above. Similarly, the reference electrode 42 may contain any noble metal having catalytic activity as described above. In this embodiment, the outer pump electrode 23 is a porous cermet electrode of Pt and ZrO2.

[0064] In the main pump cell 21, by applying a desired pump voltage Vp0 between the inner main pump electrode 22 and the outer pump electrode 23 using a variable power supply 24 and flowing a pump current Ip0 in a positive or negative direction between the inner main pump electrode 22 and the outer pump electrode 23, it is possible to pump oxygen from the first internal space 20 out to the external space or pump oxygen from the external space into the first internal space 20.

[0065] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, an inner main pump electrode 22 and a second solid electrolyte layer 6, a spacer layer 5, and a first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 constitute an electrochemical sensor cell, that is, a main pump control oxygen partial pressure detection sensor cell 80.

[0066] By measuring the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be determined. Furthermore, during steady-state operation of the gas sensor 100, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power supply 24 so that the electromotive force V0 is constant. Place 2 The oxygen concentration within 0 can be maintained at a predetermined constant value.

[0067] The third diffusion control section 30 is a section that imparts a predetermined diffusion resistance to the measurement gas whose oxygen concentration (oxygen partial pressure) has been controlled by the operation of the main pump cell 21 in the first internal space 20, and guides the measurement gas to the second internal space 40.

[0068] The second internal space 40 is provided as a space for adjusting with higher precision the oxygen partial pressure in the measurement gas introduced through the third diffusion-controlling section 30. The oxygen partial pressure is adjusted by the operation of the auxiliary pump cell 50. The second internal space 40 and the auxiliary pump cell 50 may be omitted. From the viewpoint of the accuracy of adjusting the oxygen partial pressure, it is more preferable to have the second internal space 40 and the auxiliary pump cell 50.

[0069] In the second internal space 40, the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal space 20, and then the measurement gas introduced through the third diffusion-controlling part is further subjected to adjustment of the oxygen partial pressure by the auxiliary pump cell 50. This makes it possible to keep the oxygen concentration in the second internal space 40 constant with high precision, thereby enabling the gas sensor 100 to measure the NOx concentration with high precision.

[0070] The auxiliary pump cell 50 is an electrochemical pump cell including an inner auxiliary pump electrode (auxiliary pump electrode 51 in this embodiment) disposed on the inner surface of the measurement gas flow section 15 at a position farther from the longitudinal end of the base section 102 than the inner pump electrode (in this embodiment, the inner main pump electrode 22) is, and an outer auxiliary pump electrode disposed on the base section 102 at a position different from the measurement gas flow section 15 (on the outer surface of the base section 102 in FIG. 1 ) and corresponding to the inner auxiliary pump electrode. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the base section 102 also functions as the outer auxiliary pump electrode. The phrase "corresponding to the inner auxiliary pump electrode" means that the outer pump electrode 23 is provided on the auxiliary pump electrode 51 with a second solid electrolyte layer 6 interposed therebetween.

[0071] That is, the auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, and an outer pump electrode 23 (not limited to the outer pump electrode 23, but also the sensor element 101 of The auxiliary electrochemical pump cell is composed of a first electrode (any suitable outer electrode will suffice) and a second solid electrolyte layer 6.

[0072] The auxiliary pump electrode 51 is disposed in the second internal space 40 in a tunnel-shaped structure similar to the inner main pump electrode 22 disposed in the first internal space 20. That is, a ceiling electrode portion 51a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and a bottom electrode portion 51b is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40. Side electrodes (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b are formed on both wall surfaces of the spacer layer 5 that provide the side walls of the second internal space 40, forming a tunnel-shaped structure.

[0073] Like the inner main pump electrode 22, the auxiliary pump electrode 51 is also formed using a material with a weakened ability to reduce the NOx component in the measurement gas. Like the inner main pump electrode 22, the auxiliary pump electrode 51 preferably contains a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) and a noble metal (e.g., Au, Ag, etc.) that reduces the catalytic activity of the catalytically active noble metal for the measurement gas (NOx in this embodiment). In this embodiment, the auxiliary pump electrode 51 is a porous cermet electrode of Pt containing 1% Au and ZrO2, like the inner main pump electrode 22.

[0074] In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23 using a variable power supply 52, it is possible to pump oxygen from the atmosphere in the second internal space 40 into the external space or pump oxygen from the external space into the second internal space 40.

[0075] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal space 40, an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump, is configured by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer 3.

[0076] During steady-state operation of the gas sensor 100, the auxiliary pump cell 50 performs pumping using the variable power supply 52 whose voltage is controlled based on the electromotive force V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. This allows the oxygen partial pressure in the atmosphere within the second internal space 40 to be controlled to a low level that does not substantially affect the measurement of NOx.

[0077] In addition, the pump current Ip1 is used to control the electromotive force V0 of the main pump control oxygen partial pressure detection sensor cell 80. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor cell 80, and by controlling the electromotive force V0, the gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion-controlling part 30 into the second internal space 40 is controlled to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of approximately 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

[0078] The fourth diffusion rate-controlling section 60 is a section that imparts a predetermined diffusion resistance to the measurement gas whose oxygen concentration (oxygen partial pressure) has been further controlled to a lower level by the operation of the auxiliary pump cell 50 in the second internal space 40, and guides the measurement gas to the third internal space 61.

[0079] The third internal space 61 is provided as a space for measuring the concentration of nitrogen oxides (NOx) in the measurement gas introduced through the fourth diffusion-controlling section 60. The NOx concentration is measured by the operation of the measurement pump cell 41.

[0080] The measurement pump cell 41 is an electrochemical pump cell including an inner measurement electrode (measurement electrode 44 in this embodiment) disposed on the inner surface of the measurement gas flow section 15 at a position farther from the longitudinal end of the base section 102 than the inner pump electrode (in this embodiment, the inner main pump electrode 22), and an outer measurement electrode disposed on the base section 102 at a position different from the measurement gas flow section 15 and corresponding to the inner measurement electrode. In this embodiment, the outer pump electrode 23 disposed on the outer surface of the base section 102 also functions as the outer measurement electrode. "Corresponding to the inner measurement electrode" means that the outer pump electrode 23 is provided via the measurement electrode 44, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. In this embodiment, the measurement electrode 44 is disposed on the inner surface of the measurement gas flow section 15 at a position farther from the longitudinal end of the base section 102 than the inner main pump electrode 22 and the auxiliary pump electrode 51.

[0081] That is, the measurement pump cell 41 is an electrochemical pump cell that includes a measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any appropriate electrode on the outside of the sensor element 101 will suffice), the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The measurement pump cell 41 measures the NOx concentration in the measurement gas within the third internal space 61.

[0082] The measurement electrode 44 is a porous cermet electrode. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the third internal space 61. The measurement electrode 44 is an electrode containing a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd). It is preferable that the measurement electrode 44 does not contain a noble metal (e.g., Au, Ag, etc.) that reduces the catalytic activity of the catalytically active noble metal with respect to the measurement target gas (NOx in this embodiment). In this embodiment, the measurement electrode 44 is a porous cermet electrode of Pt, Rh, and ZrO2.

[0083] In addition, in order to detect the oxygen partial pressure around the measuring electrode 44, a second solid-state Solution The solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 82 for controlling the measurement pump. During steady-state operation of the gas sensor 100, the variable power supply 46 is controlled based on the electromotive force V2 detected by the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump.

[0084] The measurement gas introduced into the second internal space 40 reaches the measurement electrode 44 in the third internal space 61 through the fourth diffusion-controlling part 60 under conditions where the oxygen partial pressure is controlled. Nitrogen oxides in the measurement gas around the measurement electrode 44 are reduced (2NO → N2 + O2) to generate oxygen. The generated oxygen is then pumped by the measurement pump cell 41, and the voltage Vp2 of the variable power supply 46 is controlled so that the control voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 remains constant. Because the amount of oxygen generated around the measurement electrode 44 is proportional to the nitrogen oxide concentration in the measurement gas, the measurement pump current Ip2 in the measurement pump cell 41 is used to calculate the nitrogen oxide concentration in the measurement gas.

[0085] In addition, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42 constitute an electrochemical sensor cell 83, and the electromotive force Vref obtained by this sensor cell 83 makes it possible to detect the oxygen partial pressure in the measurement gas outside the sensor.

[0086] Furthermore, in order to enhance the oxygen ion conductivity of the solid electrolyte, the sensor element 101 is provided with a heater section 70 that adjusts the temperature by heating and maintaining the temperature of the sensor element 101. The heater section 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.

[0087] The heater electrode 71 is an electrode formed in a manner to contact the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to a heater power supply 77, which is an external power supply, it is possible to supply power to the heater section 70 from the outside.

[0088] The heater 72 is an electrical resistor 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 that is connected to the heater 72 and extends to the rear end side of the sensor element 101 in the longitudinal direction, and a through hole 73. The heater 72 generates heat when power is supplied from the outside through the heater electrode 71, thereby heating and keeping warm the solid electrolyte that forms the sensor element 101.

[0089] The heater 72 is embedded throughout the entire area from the first internal space 20 to the third internal space 61, making it possible to adjust the entire sensor element 101 to a temperature at which the solid electrolyte is activated. The temperature needs to be adjusted so that the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41 can operate. It is not necessary to adjust these entire areas to the same temperature, and the sensor element 101 may have a temperature distribution.

[0090] In the sensor element 101 of this embodiment, the heater 72 is embedded in the base portion 102, but the present invention is not limited to this. The heater 72 may be disposed so as to heat the base portion 102. That is, the heater 72 may be capable of heating the sensor element 101 to an extent that the sensor element 101 exhibits oxygen ion conductivity that enables the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41 to operate. For example, the heater 72 may be embedded in the base portion 102 as in this embodiment. Alternatively, the heater portion 70 may be formed as a heater substrate separate from the base portion 102 and disposed adjacent to the base portion 102.

[0091] The heater insulating layer 74 is an insulating layer made of an insulator such as alumina and formed on the upper and lower surfaces of the heater 72 and heater lead 76. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and heater lead 76, and between the third substrate layer 3 and the heater 72 and heater lead 76.

[0092] The pressure release hole 75 penetrates the third substrate layer 3 and is formed so as to connect the heater insulating layer 74 and the reference gas introduction space 43. The pressure release hole 75 can mitigate an increase in internal pressure that accompanies an increase in temperature within the heater insulating layer 74. Note that the pressure release hole 75 may be omitted.

[0093] The above-described sensor element 101 is incorporated into 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.

[0094] (Control device) The gas sensor 100 of this embodiment includes the above-described sensor element 101 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). FIG. 2 is a block diagram showing the electrical connections between the control device 90 and the pump cells 21, 50, and 41 of the sensor element 101, the sensor cells 80, 81, 82, and 83, and the heater unit 70. The control device 90 includes the above-described variable power supplies 24, 46, and 52, the heater power supply 77, and a control unit 91. The control unit 91 includes a heater control unit 92, a pump control unit 93, a concentration calculation unit 94, and a determination unit 95.

[0095] The control unit 91 is realized by a general-purpose or dedicated computer, and functions as a heater control unit 92, a pump control unit 93, a concentration calculation unit 94, and a determination unit 95 are realized by a CPU, memory, etc. mounted on the computer. Note that when the gas sensor 100 measures NOx contained in exhaust gas from an automobile engine and the sensor element 101 is attached to an exhaust path, some or all of the functions of the control device 90 (particularly the control unit 91) may be realized by an ECU (Electronic Control Unit) mounted on the automobile.

[0096] The control unit 91 is configured to acquire the electromotive forces (V0, V1, V2, Vref) in the sensor cells 80, 81, 82, 83 of the sensor element 101, the pump currents (Ip0, Ip1, Ip2) in the pump cells 21, 50, 41, and the heater voltage Vh and heater current Ih in the heater unit 70. The control unit 91 is also configured to output control signals to the variable power supplies 24, 52, 46 and the heater power supply 77.

[0097] The heater control section 92 is configured to heat the base section 102 with the heater 72, raise the temperature of the base section 102 (through the starting temperature of the startup pump control described below) to a predetermined steady-state driving temperature, and perform heater control to maintain the temperature of the base section 102 at the steady-state driving temperature. The temperature of the base section 102 is approximately the temperature of the sensor element 101. For example, the temperature of the base section 102 (or the sensor element 101) itself may be controlled to be maintained at the steady-state driving temperature. Also, for example, the base section 102 may be maintained at the steady-state driving temperature as a result of controlling the heater 72 to be maintained at a predetermined temperature. In this embodiment, the heater control section 92 heats the heater 72 and also controls the temperature of the heater 72 to be maintained at a predetermined temperature (set temperature Th SET The Company decided to hold the information in the "Public Information" section (hereinafter referred to as the "Public Information").

[0098] Various known control methods can be used to heat the heater 72. For example, the heater 72 can be heated by applying a constant voltage to 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 be controlled based on at least one of the resistance values ​​of the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41.

[0099] For example, the heater control unit 92 feedback-controls the control signal output to the heater power supply 77 based on the heater resistance value Rh (=Vh / Ih) calculated from the heater voltage Vh and heater current Ih in the heater 72 so that the heater 72 reaches the target temperature.

[0100] The pump control unit 93 is configured to control the operation of the adjustment pump cell (the main pump cell 21 in this embodiment) and the measurement pump cell 41. In this embodiment, the pump control unit 93 also controls the operation of the auxiliary pump cell 50.

[0101] The pump control unit 93 is configured to perform startup pump control when the sensor element 101 (gas sensor 100) is started up, and steady-state drive pump control when the sensor element 101 (gas sensor 100) is in steady-state drive after the startup.

[0102] As described above, the startup of the sensor element 101 refers to the period from when the gas sensor 100 is turned on until it becomes possible to detect (measure) the gas to be measured. This is also referred to as the startup of the gas sensor 100. Furthermore, the steady-state operation of the sensor element 101 refers to the period during which it becomes possible to detect (measure) the gas to be measured. This is also referred to as the steady-state operation of the gas sensor 100. Once the startup period ends, the gas sensor transitions to the steady-state operation period. Usually, the steady-state operation period is the period from when the gas sensor is turned on until it is turned off, excluding the startup period.

[0103] That is, the startup of the sensor element 101 (gas sensor 100) refers to the period from when the heater control unit 92 starts heating the heater 72 until the solid electrolyte forming the sensor element 101 is heated and activated by the heater 72 and the pump control unit 93 is able to measure the gas to be measured. Furthermore, the steady-state operation refers to the state in which the heater control unit 92 maintains the temperature of the heater 72 (or the temperature of the sensor element 101) at a desired temperature and the pump control unit 93 is measuring the gas to be measured.

[0104] First, we will explain the steady-state drive pump control that is executed during steady-state drive after startup of the gas sensor 100. The steady-state drive pump control is a control that adjusts the oxygen concentration in the measurement gas to a desired concentration using the adjustment pump cell (main pump cell 21 in this embodiment) and detects the target gas to be measured in the measurement gas using the measurement pump cell 41. In this embodiment, in addition to the main pump cell 21, the auxiliary pump cell 50 is used to adjust the oxygen concentration in the measurement gas.

[0105] In the steady drive pump control, the pump control unit 93 controls the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump to a constant value (set value V0 SET The pump voltage Vp0 of the variable power supply 24 in the main pumping cell 21 is feedback-controlled so that the pump current Ip0 is equal to the oxygen concentration in the measured gas, the concentration of reducing gases such as hydrocarbons (HC), the configuration and intended use of the gas sensor 100, and the like. The direction and value of the pump voltage Vp0 vary depending on the oxygen concentration in the measured gas, the concentration of reducing gases such as hydrocarbons (HC), the configuration and intended use of the gas sensor 100, and the like, but the absolute value of the pump voltage Vp0 may be approximately within a range of 1 V or less. Since the electromotive force V0 indicates the oxygen partial pressure near the inner main pump electrode 22, maintaining the electromotive force V0 constant means maintaining the oxygen partial pressure near the inner main pump electrode 22 constant. As a result, the pump current Ip0 in the main pumping cell 21 changes depending on the oxygen concentration in the measured gas.

[0106] When the oxygen partial pressure in the measurement gas reaches the set value V0 SET On the other hand, when the oxygen partial pressure in the measurement gas is higher than the set value V0SET When the oxygen partial pressure is lower than the oxygen partial pressure corresponding to (for example, when hydrocarbons HC, etc. are contained), the main pump cell 21 pumps oxygen from the space outside the sensor element 101 into the first internal space 20. Therefore, the pump current Ip0 can take either a positive or negative value.

[0107] The pump control unit 93 controls the auxiliary pump control oxygen partial pressure detection sensor cell 81 so that the electromotive force V1 is a constant value (set value V1 SET The pump voltage Vp1 of the variable power supply 52 in the auxiliary pump cell 50 is feedback-controlled so that the set value Vp1 is equal to the set value Vp1 (referred to as "set value Vp1"). The pump voltage Vp1 may vary depending on the configuration and intended use of the gas sensor 100, but may be in the range of approximately 0.8 V or less. Since the electromotive force V1 indicates the oxygen partial pressure in the vicinity of the auxiliary pump electrode 51, keeping the electromotive force V1 constant means keeping the oxygen partial pressure in the vicinity of the auxiliary pump electrode 51 constant. SET is set to a value that makes the oxygen partial pressure (oxygen concentration) in the atmosphere inside the second internal space 40 low enough to have no substantial effect on the measurement of NOx.

[0108] At the same time, the pump current Ip1 in the auxiliary pump cell 50 is set to a constant value (set value Ip1 SET The set value V0 of the electromotive force V0 is set based on the pump current Ip1 so that the SET Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for controlling the main pump, and the electromotive force V0 is adjusted to a set value V0 set based on the pump current Ip1. SET By controlling the set value V0 SETis set to a value that will cause the oxygen concentration in the first internal space 20 to become a predetermined low concentration. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of approximately 0.001 ppm by the actions of the main pump cell 21 and the auxiliary pump cell 50. In other words, it is considered that the oxygen concentration in the measurement gas introduced from the fourth diffusion-controlling section 60 to the third internal space 61 is maintained at a constant value of approximately 0.001 ppm.

[0109] The pump control unit 93 controls the electromotive force V2 detected by the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump to be a constant value (target value V2 SET The pump voltage Vp2 of the variable power supply 46 in the measuring pump cell 41 is feedback-controlled so that the pump voltage Vp2 is equal to the target gas concentration (NOx concentration in this embodiment) in the measurement gas. The pump voltage Vp2 may be approximately 0.2 V to 0.4 V, although the voltage value varies depending on the concentration of the gas to be measured (NOx concentration in this embodiment) in the measurement gas, the configuration and intended use of the gas sensor 100, etc. pole 4 In 4, nitrogen oxides in the measurement gas are reduced (2NO → N2 + O2) to generate oxygen. The pump control unit 93 pumps the generated oxygen to a pressure of 1000 kJ / s at a pressure of 1000 kJ / s. SET The measurement pump cell 41 is used to pump out the set value V2. SET can be set to a value that substantially completely decomposes NOx at the measuring electrode 44. SET By setting the above, substantially all of the NOx in the measurement gas is detected as the measurement pump current Ip2 in the measurement pump cell 41. To be precise, the measurement pump current Ip2 includes a current due to low-concentration oxygen after being controlled by the main pump cell 21 and the auxiliary pump cell 50, and a current due to oxygen derived from the NOx in the measurement gas. pole 4 By keeping the oxygen in the measurement gas that reaches the pump 4 constant as described above, the measurement pump current Ip2 can accurately measure the oxygen derived from NOx in the measurement gas. As a result, the measurement pump current Ip2 can be detected as a current value corresponding to the NOx concentration.

[0110] In addition, the set value V0 SET, Ip1 SET , V1 SET and V2 SET are stored as control values ​​(target values) in the memory of the control unit 91 functioning as the pump control unit 93. Based on these control values, the CPU of the control unit 91 functioning as the pump control unit 93 performs steady drive pump control of the gas sensor 100.

[0111] Next, a description will be given of startup pump control that is executed when the gas sensor 100 is started. The pump control unit 93 executes the startup pump control during a period that is included in the startup of the gas sensor 100. The startup pump control may be started simultaneously with the startup of the gas sensor 100, or may be started after a delay from the startup of the gas sensor 100. Furthermore, when the startup pump control ends, the pump control unit 93 transitions to steady-state pump control.

[0112] The startup pump control is a control in which a startup voltage of the adjustment pump cell that is higher than the voltage applied to the adjustment pump cell in the steady-state drive pump control is applied between the inner pump electrode (inner main pump electrode 22) and the outer pump electrode (outer pump electrode 23) of the adjustment pump cell (in this embodiment, the main pump cell 21) and a startup voltage of the measurement pump cell 41 that is higher than the voltage applied to the measurement pump cell in the steady-state drive pump control and lower than the startup voltage of the adjustment pump cell are applied between the inner measurement electrode (measurement electrode 44) and the outer measurement electrode (outer pump electrode 23) of the measurement pump cell 41.

[0113] That is, in the startup pump control in this embodiment, the pump control unit 93 sets a startup voltage (main pump startup voltage Vp0) of the main pump cell 21 that is higher than the pump voltage Vp0 applied between the inner main pump electrode 22 and the outer pump electrode 23 of the main pump cell 21 in the steady drive pump control. INITIAL ) is applied between the measurement electrode 44 of the measurement pump cell 41 and the outer pump electrode 23 during steady-state operation. Po Higher than the pump voltage Vp2 and the main pump startup voltage Vp0 INITIALLower start-up voltage of the measuring pump cell 41 (measurement pump start-up voltage Vp2 INITIAL ) is applied.

[0114] Furthermore, in the startup pump control, the pump control unit 93 may further apply a startup voltage of the auxiliary pump cell between the inner auxiliary pump electrode (auxiliary pump electrode 51) and the outer auxiliary pump electrode (outer pump electrode 23) of the auxiliary pump cell 50, the startup voltage being higher than the voltage applied to the auxiliary pump cell in the steady-state drive pump control, lower than the startup voltage of the adjustment pump cell, and higher than the startup voltage of the measurement pump cell.

[0115] That is, in the startup pump control, the pump control unit 93 applies a startup voltage (main pump startup voltage Vp0) of the main pump cell 21 between the auxiliary pump electrode 51 and the outer pump electrode 23 that is higher than the pump voltage Vp1 applied to the auxiliary pump cell 50 in the steady drive pump control. INITIAL ) or less, and the starting voltage of the measuring pump cell 41 (the starting voltage of the measuring pump Vp2 INITIAL ) is higher than the auxiliary pump cell 50 startup voltage (auxiliary pump startup voltage Vp1 INITIAL The auxiliary pump cell 50 may be supplied with a startup voltage (referred to as auxiliary pump startup voltage Vp1 INITIAL ) is the start-up voltage of the main pump cell 21 (main pump start-up voltage Vp0 INITIAL ), the auxiliary pump cell 50 startup voltage (auxiliary pump startup voltage Vp1 INITIAL ) and the start-up voltage of the measurement pump cell 41 (measurement pump start-up voltage Vp2 INITIAL ) may be equal.

[0116] Before the gas sensor 100 is started up, the measurement gas flow portion 15 contains the gas atmosphere (e.g., the air atmosphere) surrounding the gas sensor 100. Therefore, before the gas sensor 100 is started up, the third internal space 61 usually contains a higher oxygen concentration than the oxygen concentration during steady operation of the gas sensor 100. In other words, more oxygen is present near the measuring electrode 44 than during steady operation. If the gas sensor 100 is started up in this state, the measuring pump cell 41 needs to pump out more oxygen during start-up than during steady operation.

[0117] It takes time from the start-up (start-up) of the gas sensor 100 until the concentration of the measurement target gas can be measured. This required time is called the light-off time. The light-off time is the time required from the turn-on of the heater 72 of the gas sensor 100 until the detection (measurement) of the measurement target gas is possible. In other words, the light-off time is the time required from the start of heating of the heater 72 until the oxygen concentration of the measurement target gas in the measurement target gas flow section 15 is controlled by the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41 to the state during steady operation.

[0118] In the startup pump control, a startup voltage higher than that applied in the steady-state drive pump control is applied to each of the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41. As a result, relatively large pump currents Ip0, Ip1, and Ip2 can flow through the pump cells 21, 50, and 41, respectively. This allows oxygen that has been present in the measurement gas flow section 15 before the gas sensor 100 was started and oxygen that continuously flows in through the gas inlet 10 to be efficiently pumped out. This allows the oxygen concentration in the measurement gas in the measurement gas flow section 15 to be more quickly controlled to the concentration during steady-state drive. In other words, the oxygen concentration in the measurement gas reaching the measuring electrode 44 can be more quickly controlled to the concentration during steady-state drive. As a result, the light-off time can be shortened.

[0119] In the sensor element 101, the first internal space 20, the second internal space 40, and the third internal space 61 are arranged in series in this order from the tip of the sensor element 101. The main pump cell 21 pumps oxygen from the first internal space 20, the auxiliary pump cell 50 pumps oxygen from the second internal space 40, and the measurement pump cell 41 pumps oxygen from the third internal space 61. 61 In such a sensor element 101, when a pump voltage is applied to each pump cell 21, 50, 41, the oxygen concentration is highest in the first internal space 20 closest to the gas inlet 10, and the oxygen concentration decreases with increasing distance from the gas inlet 10, that is, in the second internal space 40 and the third internal space 61.

[0120] In the first internal cavity 20 and / or the second internal cavity 40 When there is a large difference in oxygen concentration between the oxygen concentration in the third internal space 61 and the oxygen concentration in the third internal space 62, a concentration gradient caused by the difference in oxygen concentration causes a small amount of oxygen to flow into the third internal space 61. As a result, it has been found that it may take some time for the oxygen concentration in the third internal space 61, i.e., the oxygen concentration near the measurement electrode 44, to reach the concentration during steady-state operation.

[0121] According to the study by the inventors, the main pump cell 21 has a high main pump startup voltage Vp0 INITIAL By applying this voltage, oxygen in the first internal space 20 closest to the gas inlet 10 can be pumped out more quickly. In other words, the oxygen concentration in the first internal space 20 can be reduced more quickly. As a result, the difference in oxygen concentration between the oxygen concentration in the first internal space 20 and the oxygen concentrations in the second internal space 40 and the third internal space 61 can be reduced, and the inflow of oxygen into the third internal space 61 due to the concentration gradient can be reduced. Therefore, it has been found that the time required for the oxygen concentration near the measuring electrode 44 to reach the concentration during steady-state operation can be shortened.

[0122] The higher the pump voltage applied to each of the pump cells 21, 50, and 41, the larger the pump current. Therefore, the higher the pump voltage applied, the faster oxygen can be pumped out of the measurement gas flow section 15. However, it has been found that an excessively high pump voltage applied to the pump cell can cause cracks in the internal structure of the sensor element 101.

[0123] When a pump voltage is applied to the pump cell, oxygen in the measurement gas is pumped out of the internal cavity in response to the pump voltage. However, if the pump voltage becomes excessively large, a pump voltage higher than the pump voltage required to pump out substantially all of the oxygen in the measurement gas may be applied to the pump cell. In this case, oxygen constituting the solid electrolyte (e.g., zirconia ZrO2) contained in the pump cell may migrate. As a result, an oxygen-deficient region is formed in the solid electrolyte. This phenomenon is also called blackening. The oxygen-deficient region in the solid electrolyte has lower strength than a normal solid electrolyte. As a result, cracks may occur in the internal structure of the sensor element 101, particularly in the oxygen-deficient region in the solid electrolyte.

[0124] As described above, the oxygen concentration is highest in the first internal space 20 closest to the gas inlet 10, and the oxygen concentration decreases in the second internal space 40 and the third internal space 61 as the distance from the gas inlet 10 increases. Therefore, the amount of oxygen that each pump cell 21, 50, 41 can pump out from each internal space 20, 40, 61 decreases in the order of the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41. The inventors have determined that, in the startup pump control, the measurement pump startup voltage Vp2 applied to the measurement pump cell 41, which can pump out the least amount of oxygen, is INITIAL is set to a value higher than that applied in the steady drive pump control and set to the main pump start-up voltage Vp0 INITIAL It has been found that by making the thickness smaller than 1 / 2 mm, the movement of oxygen constituting the solid electrolyte can be suppressed, which in turn can suppress blackening and the occurrence of cracks in the internal structure of the sensor element 101.

[0125] In the startup pump control, the main pump cell 21 that pumps out oxygen in the first internal space 20 closest to the gas inlet 10 is supplied with a main pump startup voltage Vp0 higher than the pump voltage Vp0 applied to the main pump cell 21 in the steady drive pump control. INITIAL is applied (Vp0 INITIAL (Vp0 in steady drive pump control) The specific voltage value may be appropriately set depending on the desired light-off time and the purpose of using the gas sensor 100.

[0126] Main pump startup voltage Vp0 INITIAL The lower limit of the main pump start-up voltage Vp0 should be greater than the pump voltage Vp0 applied in the steady drive pump control. This allows oxygen to be pumped out of the first internal space 20 more quickly than in the steady drive pump control. The pump voltage Vp0 applied in the steady drive pump control is approximately 1 V at most, as described above. INITIAL The lower limit of the main pump startup voltage Vp0 may be, for example, 1.1 V or more, 1.2 V or more, 1.5 V or more, 1.8 V or more, etc. INITIAL The upper limit of the main pump start-up voltage Vp0 may be within a range in which oxygen atoms in the solid electrolyte itself do not migrate. For example, the upper limit may be 3.0 V or less, 2.8 V or less, or 2.5 V or less. INITIAL may be, for example, 1.5V or more and 3.0V or less.

[0127] In the start-up pump control, the measurement pump cell 41 that pumps out oxygen in the third internal space 61 having a low oxygen concentration is supplied with a pump voltage Vp0 that is higher than the pump voltage Vp2 applied to the measurement pump cell 41 in the steady-state drive pump control and is equal to or lower than the main pump start-up voltage Vp0. INITIAL The measured pump start-up voltage Vp2 is smaller than INITIAL is applied (Vp0 INITIAL >Vp2 INITIAL (Vp2 in steady drive pump control) The specific value may be appropriately set depending on the desired light-off time and the purpose of using the gas sensor 100.

[0128] Measurement pump startup voltage Vp2 INITIALThe lower limit of the pump voltage Vp2 for measurement should be larger than the pump voltage Vp2 applied in the steady drive pump control. This allows oxygen to be pumped out of the third internal space 61 more quickly than in the steady drive pump control. As mentioned above, the pump voltage Vp2 applied in the steady drive pump control is approximately 0.3 V at most. INITIAL The lower limit of the measurement pump start-up voltage Vp2 may be, for example, 0.4 V or more, 0.5 V or more, 0.6 V or more, 0.7 V or more, etc. INITIAL The upper limit of the voltage Vp0 at the start of the main pump may be set within a range in which oxygen atoms in the solid electrolyte itself do not migrate. For example, the upper limit may be set to 1.5 V or less, 1.45 V or less, 1.3 V or less, or 1.2 V or less. INITIAL The voltage at the start of the measurement pump Vp2 must be smaller than INITIAL may be, for example, 0.5V or more and 1.45V or less.

[0129] In this embodiment, an auxiliary pump cell 50 is formed between the main pump cell 21 and the measurement pump cell 41. In the startup pump control, an auxiliary pump startup voltage Vp1 is applied to the auxiliary pump cell 50 that pumps out oxygen from the second internal space 40. INITIAL is higher than the voltage applied to the auxiliary pump cell 50 in the steady drive pump control, and the main pump start-up voltage Vp0 INITIAL The following is the voltage Vp2 when the pump is started for measurement: INITIAL The higher the voltage, the better. That is, the main pump startup voltage Vp0 INITIAL , auxiliary pump start-up voltage Vp1 INITIAL , and measurement pump start-up voltage Vp2 INITIAL The relationship is Vp0 INITIAL =Vp1 INITIAL >Vp2 INITIAL , Vp0 INITIAL >Vp1 INITIAL >Vp2 INITIAL Alternatively, Vp0 INITIAL >Vp1 INITIAL =Vp2 INITIAL The specific value may be appropriately set depending on the desired light-off time and the purpose of using the gas sensor 100.

[0130] Auxiliary pump startup voltage Vp1 INITIAL The lower limit of the auxiliary pump start-up voltage Vp1 should be greater than the pump voltage Vp1 applied in the steady drive pump control. This allows oxygen to be pumped out of the second internal space 40 more quickly than in the steady drive pump control. The pump voltage Vp1 applied in the steady drive pump control is approximately 0.8 V at maximum, as described above. INITIAL The lower limit of the pump voltage Vp2 for measurement may be, for example, 0.5 V or more, 0.6 V or more, 0.8 V or more, 0.9 V or more, 1.0 V or more, provided that the lower limit is higher than the pump voltage Vp1 applied in the steady drive pump control. INITIAL It is preferable that the auxiliary pump startup voltage Vp1 is equal to or greater than the above. INITIAL The upper limit of the voltage Vp0 at the start of the main pump may be within a range in which oxygen atoms in the solid electrolyte itself do not migrate. For example, the upper limit may be 3.0 V or less, 2.8 V or less, 2.5 V or less, 2.0 V or less, 1.5 V or less, etc. INITIAL It is preferable that the auxiliary pump start-up voltage Vp1 is equal to or less than the above. INITIAL may be, for example, 0.6V or more and 3.0V or less.

[0131] In this way, when three or more pump cells are formed in series, the startup voltage applied during startup pump control should be set to gradually decrease from the pump cell closest to the gas inlet 10 to the pump cell farthest from the gas inlet 10.

[0132] The first startup voltage (main pump startup voltage Vp0) applied to the main pump cell 21 closest to the gas inlet 10 INITIAL ) to be applied to the measurement pump cell 41 farthest from the gas inlet 10 (measurement pump startup voltage Vp2 INITIAL ) to the ratio (Vp0 INITIAL / Vp2 INITIAL ) may be appropriately determined in a range greater than 1. For example, it may be 1.03 or more and 6.00 or less.

[0133] In addition, the main pump startup voltage Vp0INITIAL , auxiliary pump start-up voltage Vp1 INITIAL , and measurement pump start-up voltage Vp2 INITIAL are stored as control values ​​(set values) in the memory of the control unit 91 functioning as the pump control unit 93. Based on these control values, the CPU of the control unit 91 functioning as the pump control unit 93 controls the pump at the start of the gas sensor 100.

[0134] The concentration calculation unit 94 is configured to calculate and output the NOx concentration in the measurement gas.

[0135] The concentration calculation unit 94 acquires the pump current Ip2 in the measurement pump cell 41, calculates the NOx concentration in the measurement gas based on a pre-stored conversion parameter (current-concentration conversion parameter) between the pump current Ip2 and the NOx concentration in the measurement gas, and outputs the calculated value as a measurement value of the gas sensor 100. The current-concentration conversion parameter is pre-stored in the memory of the control unit 91 that functions as the concentration calculation unit 94. The current-concentration conversion parameter can be appropriately determined for the gas sensor 100 in advance through experiments or the like by a person skilled in the art. The current-concentration conversion parameter may be, for example, a coefficient of an approximate equation (such as a linear function) obtained through experiments, or may be a map showing the correspondence between the measurement pump current Ip2 and the NOx concentration in the measurement gas. The current-concentration conversion parameter may be a parameter unique to each gas sensor 100, or a parameter commonly used by multiple gas sensors.

[0136] The determination unit 95 is configured to determine the start and end of startup pump control.

[0137] For example, the determination unit 95 Heater control unit 92When it is determined that the base part 102 (sensor element 101) has reached a predetermined start determination threshold (start temperature of startup pump control), the heater 72 is heated by the heater 72, and the pump control part 93 is caused to start the startup pump control. The determination that the base part 102 (sensor element 101) has reached the start temperature may be made based on the temperature of the base part 102 itself, or may be made based on the temperature of the heater 72.

[0138] The predetermined start determination threshold (start temperature of the start-up pump control) may be set appropriately within a range equal to or lower than the steady-state driving temperature. For example, it may be equal to or higher than the lower limit required to activate the solid electrolyte (in this embodiment, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4) contained in each pump cell 21, 50, 41, i.e., to develop oxygen ion conductivity of the solid electrolyte. For example, when the start determination is made based on the temperature Th of the heater 72, the relationship between the temperature of the base portion 102 (more specifically, the temperature of the solid electrolyte contained in each pump cell 21, 50, 41) and the temperature of the heater 72 may be determined in advance by experiment or the like. For example, the start determination threshold may be set based on the temperature Th of the heater 72, and the set temperature Th SET It may be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, etc.

[0139] For example, when the oxygen concentration near the measuring electrode 44 reaches a target oxygen concentration, the determining unit 95 may end the startup pump control and start the steady drive pump control.

[0140] For example, when the determining unit 95 determines that the pump current Ip2 flowing through the measurement pump cell 41 during the startup pump control is equal to or less than a predetermined threshold, the determining unit 95 may switch from the startup pump control to the steady drive pump control. The predetermined threshold (termination determination threshold) for the pump current Ip2 may be set appropriately depending on the intended use of the gas sensor 100. For example, it may be 0.1 μA to 5.0 μA.

[0141] Alternatively, the determination unit 95 may switch from the startup pump control to the steady drive pump control when it determines that the electromotive force V2 between the inner measurement electrode 44 and the reference electrode 42 is equal to or greater than a predetermined threshold during the startup pump control. The predetermined threshold (termination determination threshold) for the electromotive force V2 may be set appropriately depending on the intended use of the gas sensor 100. For example, it may be 0.3 V to 1.0 V.

[0142] [Pump control at gas sensor startup] Next, a detailed description will be given of startup pump control from startup of the gas sensor 100 to steady drive pump control when the gas sensor 100 is used to measure the concentration of a gas to be measured in a measurement gas.

[0143] The gas sensor control method of this embodiment includes the steps of: a startup pump control step executed when the sensor element is started, and a steady drive pump control step executed thereafter; In the startup pump control step, the pump control unit 93 applies a startup voltage of the adjustment pump cell between the inner pump electrode (inner main pump electrode 22) and the outer pump electrode 23 of the adjustment pump cell (in this embodiment, the main pump cell 21), the startup voltage being higher than the voltage applied in the steady drive pump control, and applies a startup voltage of the measurement pump cell 41 between the inner measurement electrode (measurement electrode 44) and the outer measurement electrode (in this embodiment, the outer pump electrode 23) of the measurement pump cell 41, the startup voltage being higher than the voltage applied in the steady drive pump control and lower than the startup voltage of the adjustment pump cell; In the steady drive pump control step, the pump control section adjusts the oxygen concentration in the measurement gas to a desired concentration using the adjustment pump cell, and detects the measurement target gas in the measurement gas using the measurement pump cell 41.

[0144] The startup process of the gas sensor 100 of this embodiment will be described in detail below. FIG.

[0145] The gas sensor 100 is activated, for example, when the gas sensor 100 receives a dew point signal. When the gas sensor 100 is mounted on an automobile or the like, the dew point signal is a signal sent to the gas sensor 100 from, for example, an ECU or an exhaust gas treatment system of the automobile. The gas sensor 100 may be activated, for example, by manually turning on the power of the control device 90.

[0146] When the gas sensor 100 is activated, the heater control unit 92 of the control unit 91 starts heater control by energizing the heater 72 (step S10), and heats the sensor element 101 to a steady-state operating temperature (for example, about 800°C) at which the solid electrolyte is activated and the NOx concentration is accurately measured, and maintains the steady-state operating temperature. In this embodiment, the heater control unit 92 sets the temperature Th of the heater 72 to a set temperature Th SET By controlling the heating temperature to a temperature above 1000 K, the base portion 102 (sensor element 101) is heated to a steady-state operating temperature.

[0147] In step S10, the heater control unit 92 but After starting heater control, the determination unit 95 determines whether to start startup pump control (step S11). When the heater control unit 92 starts heater control, the heater 72 is heated, and the temperature of the base unit 102 (sensor element 101) rises. The determination unit 95 determines whether the temperature of the base unit 102 has reached the start temperature of startup pump control. In this embodiment, it is determined whether the temperature Th of the heater 72 corresponding to the temperature of the base unit 102 is equal to or higher than the start determination threshold. In addition, the start determination threshold is, for example, the temperature of the heater 72 during steady operation (set temperature Th SET ) and the temperature was set to 70% of that.

[0148] If the determination unit 95 determines that the temperature Th of the heater 72 is equal to or higher than the start determination threshold, it instructs the pump control unit 93 to start the startup pump control. The pump control unit 93 starts the startup pump control upon receiving the instruction from the determination unit 95 (step S12). If the determination unit 95 determines that the temperature Th of the heater 72 is lower than the start determination threshold, the determination unit 95 repeats step S11 until the temperature Th of the heater 72 becomes equal to or higher than the start determination threshold.

[0149] In step S12, the pump control unit 93 starts the start-up pump control. That is, the pump control unit 93 applies a main pump start-up voltage Vp0 between the inner main pump electrode 22 and the outer pump electrode 23 in the main pump cell 21. INITIAL In the auxiliary pump cell 50, an auxiliary pump startup voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23. INITIAL is applied between the measurement electrode 44 and the outer pump electrode 23 in the measurement pump cell 41, and a measurement pump start-up voltage Vp2 INITIAL Apply the voltage Vp0 when the main pump starts up. INITIAL , auxiliary pump start-up voltage Vp1 INITIAL , and measurement pump start-up voltage Vp2 INITIAL were set to 2.0 V, 1.0 V, and 0.6 V, respectively. Even after the start-up pump control is initiated, the heater control unit 92 continues to perform heater control, and raises the temperature of the base unit 102 from the start temperature of the start-up pump control to the steady-state driving temperature. The temperature of the base unit 102 is also maintained at the steady-state driving temperature.

[0150] Before the gas sensor 100 is activated, the measurement gas flow section 15 is considered to be in the same gas atmosphere as the measurement gas. When the startup pump control is initiated, the oxygen O2 that was present in the first internal space 20 before the gas sensor 100 was activated is pumped out by the main pump cell 21, the oxygen O2 that was present in the second internal space 40 before the gas sensor 100 was activated is pumped out by the auxiliary pump cell 50, and the oxygen O2 and NOx-derived oxygen that were present in the third internal space 61 before the gas sensor 100 was activated are pumped out by the measurement pump cell 41. Furthermore, the measurement gas is successively introduced through the gas inlet 10. The oxygen O2 in the measurement gas that is successively introduced is mainly pumped out by the main pump cell 21 from the first internal space 20 closest to the gas inlet 10. In this way, the oxygen that has been present in the measurement gas flow portion 15 before the gas sensor 100 is activated and the oxygen that flows in succession from the gas inlet 10 are efficiently pumped out from the internal spaces 20, 40, and 61.

[0151] Next, the determination unit 95 determines whether to terminate the startup pump control (step S13). In this embodiment, the determination unit 95 determines whether the pump current Ip2 flowing through the measurement pump cell 41 during the startup pump control is equal to or less than a predetermined threshold (termination threshold). The termination threshold for the pump current Ip2 is set to 3.0 μA, for example.

[0152] If the determination unit 95 determines that the pump current Ip2 is equal to or less than the termination threshold, it instructs the pump control unit 93 to switch from startup pump control to steady drive pump control. The determination unit 95 also instructs the concentration calculation unit 94 to start calculating and outputting the NOx concentration in the measurement gas based on the pump current Ip2. In response to the instruction from the determination unit 95, the pump control unit 93 ends the startup pump control and starts steady drive pump control (step S14). In response to the instruction from the determination unit 95, the concentration calculation unit 94 starts calculating the NOx concentration. If the determination unit 95 determines that the pump current Ip2 is greater than the termination threshold, the determination unit 95 repeatedly performs step S13 until the pump current Ip2 becomes equal to or less than the termination threshold.

[0153] In this embodiment, the temperature of the base part 102 (sensor element 101) does not directly affect the determination of the termination of the startup pump control. However, usually, after the temperature of the base part 102 (sensor element 101) reaches the steady-state operating temperature, the pump current Ip2 will often become equal to or less than the termination determination threshold.

[0154] The light-off time is the time from the startup (start-up) of the gas sensor 100 until the concentration of the target gas can be measured. Usually, the measurement of the target gas concentration becomes possible when the startup pump control ends and the steady drive pump control starts. In this case, the light-off time is the time required from the startup of the gas sensor 100 until the startup pump control ends. Depending on the purpose of use of the gas sensor 100, the measurement of the target gas concentration may become possible when the steady drive pump control starts and the pump current Ip2 reaches a predetermined value lower than the threshold for determining the end of the startup pump control. In this case, the light-off time may be a predetermined time point after the startup of the gas sensor 100 and the start of the steady drive pump control.

[0155] 4 is a flowchart showing a modified example of the startup process in the gas sensor 100. In FIG. 4, the same steps as in FIG. 3 are assigned the same step numbers, and their description will be omitted. In the startup process of the modified example shown in FIG. 4, the determination unit 95 makes a termination determination of the startup pump control, which differs from that in FIG. 3. In the startup process of the modified example, the determination unit 95 determines whether the electromotive force V2 between the measurement electrode 44 and the reference electrode 42 during the startup pump control is equal to or greater than a predetermined threshold (termination determination threshold) (step S23). The termination determination threshold for the electromotive force V2 is set to 0.5 V, for example.

[0156] If the determination unit 95 determines that the electromotive force V2 is equal to or greater than the termination determination threshold, it instructs the pump control unit 93 to switch from startup pump control to steady drive pump control. In response to the instruction from the determination unit 95, the pump control unit 93 ends the startup pump control and starts steady drive pump control (step S14). If the determination unit 95 determines that the electromotive force V2 is smaller than the termination determination threshold, the determination unit 95 repeatedly performs step S23 until the electromotive force V2 becomes equal to or greater than the termination determination threshold.

[0157] Although the gas sensor 100 for detecting the NOx concentration in a measurement gas has been described above as an example of an embodiment of the present invention, the present invention is not limited to this embodiment. The present invention may include gas sensors including various configurations of sensor elements and control devices, as long as the object of the present invention, which is to shorten the light-off time and suppress the occurrence of cracks in the internal structure of the sensor element, is achieved.

[0158] In the above-described embodiment, the gas sensor 100 detects the NOx concentration in the measurement gas, but the measurement gas is not limited to NOx. For example, the measurement gas may be an oxide gas other than NOx (e.g., carbon dioxide CO2, water HO, etc.). When the measurement gas is an oxide gas, the measurement gas containing the oxide gas itself is introduced into the third internal space 61, as in the above-described embodiment for detecting the NOx concentration, and the oxide gas in the measurement gas is reduced at the measurement electrode 44 to generate oxygen. The generated oxygen can be obtained as the measurement pump current Ip2 in the measurement pump cell 41, and the measurement gas can be detected.

[0159] Alternatively, the measurement target gas may be a non-oxide gas such as ammonia (NH3). When the measurement target gas is a non-oxide gas, the non-oxide gas is converted to an oxide gas (for example, ammonia (NH3) is converted to NO), and the measurement target gas containing the converted oxide gas is introduced into the third internal space 61. The converted oxide gas in the measurement target gas is reduced at the measurement electrode 44 to generate oxygen. The generated oxygen can be detected by acquiring the measurement pump current Ip2 in the measurement pump cell 41. The non-oxide gas can be converted to an oxide gas by at least one of the inner main pump electrode 22 and the auxiliary pump electrode 51 functioning as a catalyst.

[0160] In the above-described embodiment, the determining unit 95 determines whether to start the startup pump control based on the heater temperature Th, but this is not limiting. The temperature of the sensor element 101 (base portion 102) itself may be detected, and the determination may be based on the detected temperature. Alternatively, the fact that the resistance value of the solid electrolyte decreases as the temperature of the sensor element 101 (base portion 102) increases may be used. For example, the main pump cell 21 (inner main pump electrode 22 and outer pump electrode 23), auxiliary pump cell 50 (auxiliary pump electrode 51 and outer pump electrode 23), measurement pump cell 41 (measurement electrode 44 and outer pump electrode 23), or the resistance value of any of the pump cells, or the oxygen partial pressure detection sensor cell 80 for controlling the main pump (inner main pump electrode 22 The resistance value of any of the sensor cells among the auxiliary pump control oxygen partial pressure detection sensor cell 81 (auxiliary pump electrode 51 and reference electrode 42), the auxiliary pump control oxygen partial pressure detection sensor cell 82 (measurement electrode 44 and reference electrode 42), and the measurement pump control oxygen partial pressure detection sensor cell 82 (measurement electrode 44 and reference electrode 42) may be detected, and startup pump control may be started if the detected resistance value is equal to or less than a predetermined threshold value.

[0161] In the above-described embodiment, the determination unit 95 determines whether to terminate the startup pump control based on the pump current Ip2 or the electromotive force V2. However, this is not limiting. For example, the determination unit 95 may switch from the startup pump control to the steady-state drive pump control when it determines that the pump current Ip0 in the main pump cell 21 or the pump current Ip1 in the auxiliary pump cell 50 is equal to or less than a predetermined termination threshold. Alternatively, the determination unit 95 may switch from the startup pump control to the steady-state drive pump control when it determines that the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump or the electromotive force V1 in the oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump is equal to or greater than a predetermined termination threshold. The termination determination may also be based on multiple termination thresholds.

[0162] The determination unit 95 may also determine the start and / or end of the startup pump control based on the elapsed time from the start-up of the gas sensor 100. For example, the startup pump control may be started simultaneously with the start-up of the gas sensor 100, or may be started when a predetermined time has elapsed since the start-up of the gas sensor 100. The determination unit 95 may also determine the end of the startup pump control based on the elapsed time from the start-up of the startup pump control.

[0163] In the above-described embodiment, in the start-up pump control, a predetermined start-up voltage (main pump start-up voltage Vp0 INITIAL , auxiliary pump start-up voltage Vp1 INITIAL , and measurement pump start-up voltage Vp2 INITIAL ) is applied, but the present invention is not limited to this. In the startup pump control, it is sufficient that a startup voltage higher than that applied in the steady drive pump control is applied as a result. For example, a feedback control similar to that in the steady drive pump control may be performed. Specifically, for example, the pump control section 93 of the control section 91 may perform a feedback control such that the electromotive force V1 in the oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump is equal to the startup set value V1a SETThe pump voltage Vp1 in the auxiliary pump cell 50 may be feedback-controlled so that the pump current Ip1 in the auxiliary pump cell 50 is equal to the startup set value Ip1a. SET The starting set value V0a of the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump is set based on the pump current Ip1 so as to be SET Set the electromotive force V0 to the startup set value V0a SET The pump voltage Vp0 in the main pump cell 21 may be feedback-controlled so that the electromotive force V2 in the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump is equal to or greater than the startup set value V2a SET The pump voltage Vp2 in the measuring pump cell 41 may be feedback-controlled so that the start-up set value V1a SET , startup setting value Ip1a SET , startup setting value V0a SET , and startup setting value V2a SET are the set values ​​V1 SET , setting value Ip1 SET , set value V0 SET , and set value V2 SET By doing so, a higher startup voltage can be applied in the startup pump control than in the steady drive pump control.

[0164] In the above-described embodiment, in the steady drive pump control, the pump control unit 93 of the control unit 91 controls the pump current Ip1 in the auxiliary pump cell 50 to be equal to or greater than the set value Ip1 SET The set value V0 of the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump is set based on the pump current Ip1 so as to be SET When the electromotive force V0 is set to the set value V0 SET However, the control method is not limited to this. For example, the pump control unit 93 may be configured to feedback control the pump voltage Vp0 of the variable power supply 24 in the main pump cell 21 so that the pump current Ip1 in the auxiliary pump cell 50 is equal to or greater than the set value Ip1. SETIn other words, the pump control unit 93 may obtain the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump and adjust the set value V0 SET Instead of setting the pump voltage Vp0, the pump voltage Vp0 may be directly feedback-controlled based on the pump current Ip1.

[0165] 1 , the sensor element 101 has three internal cavities, namely, the first internal cavities 20, the second internal cavities 40, and the third internal cavities 61, and the inner main pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 are respectively disposed in the internal cavities. However, the present invention is not limited to this. For example, the sensor element 101 may have two internal cavities, namely, the first internal cavities 20 and the second internal cavities 40, and the inner main pump electrode 22 is disposed in the first internal cavities 20, and the auxiliary pump electrode 51 and the measurement electrode 44 are disposed in the second internal cavities 40. In this case, for example, a porous protective layer covering the measurement electrode 44 may be formed as a diffusion rate-controlling part between the auxiliary pump electrode 51 and the measurement electrode 44.

[0166] In the gas sensor 100 of the above-described embodiment, the outer pump electrode 23 functions as three electrodes: the outer main pump electrode in the main pump cell 21, the outer auxiliary pump electrode in the auxiliary pump cell 50, and the outer measurement electrode in the current measurement pump cell 41. However, this is not limiting. For example, the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be formed as separate electrodes. For example, one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be provided separately from the outer pump electrode 23 on the outer surface of the base portion 102 so as to be in contact with the gas to be measured. Alternatively, one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be used as a reference electrode. 42 It may also serve as both.

[0167] As described above, according to the present invention, the light-off time of the gas sensor can be shortened and the occurrence of cracks in the internal structure of the sensor element can be suppressed by reducing the blackening of the sensor element. [Explanation of symbols]

[0168] 1 First board layer 2 Second board layer 3 Third board layer 4 First solid electrolyte layer 5 Spacer layer 6 Second solid electrolyte layer 10 Gas inlet 11 First diffusion-controlled section 12 Buffer space 13 Second diffusion-controlled section 15 Measurement gas flow section 20 1st internal void 21 Main pump cell 22 Inner main pump electrode 22a (Inner main pump electrode) ceiling electrode part 22b Bottom electrode part (of inner main pump electrode) 23 Outer pump electrode 24 Variable power supply (for main pump cell) 30 Third diffusion-controlled section 40 Second internal void 41 Current measurement pump cell 42 Reference electrode 43 Reference gas introduction space 44 Measuring electrode 46 Variable power supply (for measuring pump cell) 47 Switching Unit 48 Atmospheric introduction layer 50 Auxiliary pump cell 51 Auxiliary pump electrode 51a (auxiliary pump electrode) ceiling electrode part 51b (auxiliary pump electrode) bottom electrode part 52 Variable power supply (for auxiliary pump cell) 60 4th diffusion-controlled section 61 3rd internal void 70 Heater section 71 Heater electrode 72 Heater 73 through holes 74 Heater insulator 75 Pressure relief hole 76 Heater lead 77 Heater power supply 80 Oxygen partial pressure detection sensor cell for main pump control 81 Oxygen partial pressure detection sensor cell for auxiliary pump control 82 Electromotive force detection sensor cell 83 Sensor Cell 90 Control device 91 Control Unit 92 Heater control unit 93 Pump control section 94 Concentration calculation section 95 Judgment section 100 Gas Sensor 101 Sensor element 102 Base

Claims

1. A gas sensor including a sensor element and a control device that controls the sensor element, The sensor element is a long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measurement gas flow portion formed at one end of the base portion in the longitudinal direction; an adjusting pump cell including an inner pump electrode disposed on an inner surface of the measurement target gas flow portion and an outer pump electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner pump electrode, the adjusting pump cell adjusting the oxygen concentration in the measurement target gas to a desired concentration; a measurement pump cell for detecting a measurement target gas in the measurement gas, the measurement pump cell including: an inner measurement electrode disposed on an inner surface of the measurement target gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer measurement electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner measurement electrode; a heater for heating the base portion; Including, The control device a pump control unit that controls operations of the adjustment pump cell and the measurement pump cell, The pump control unit performing a startup pump control at the startup of the sensor element and a steady drive pump control during steady drive of the sensor element after the startup; In the startup pump control, a startup voltage of the adjustment pump cell that is higher than the voltage applied to the adjustment pump cell in the steady drive pump control is applied between the inner pump electrode and the outer pump electrode of the adjustment pump cell, and a startup voltage of the measurement pump cell that is higher than the voltage applied to the measurement pump cell in the steady drive pump control and lower than the startup voltage of the adjustment pump cell is applied between the inner measurement electrode and the outer measurement electrode of the measurement pump cell, In the steady-state drive pump control, the oxygen concentration in the measurement gas is adjusted to a desired concentration by the adjustment pump cell, and the measurement pump cell detects the measurement target gas in the measurement gas.

2. The sensor element further comprises: an auxiliary pump cell including an inner auxiliary pump electrode disposed on an inner surface of the measurement gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer auxiliary pump electrode disposed at a position different from the measurement gas flow portion of the base portion and corresponding to the inner auxiliary pump electrode, for further adjusting the oxygen concentration in the measurement gas; The startup pump control further includes: a startup voltage for the auxiliary pump cell is applied between the inner auxiliary pump electrode and the outer auxiliary pump electrode of the auxiliary pump cell, the startup voltage being higher than the voltage applied to the auxiliary pump cell in the steady drive pump control, not higher than the startup voltage of the adjustment pump cell, and higher than the startup voltage of the measurement pump cell; 2. The gas sensor according to claim 1, wherein, in the steady-state drive pump control, the oxygen concentration in the measurement gas is adjusted to a desired concentration by the adjustment pump cell, the oxygen concentration in the measurement gas adjusted by the adjustment pump cell is further adjusted by the auxiliary pump cell, and the measurement target gas in the measurement gas is detected by the measurement pump cell.

3. The control device a heater control unit that controls the heater; Further, a determination unit that determines the start and end of the startup pump control, the heater control unit heats the base unit with the heater, raises the temperature of the base unit to a predetermined steady-state driving temperature through the start temperature of the startup pump control, and performs heater control to maintain the temperature of the base unit at the steady-state driving temperature; 3. The gas sensor according to claim 1, wherein the determining unit causes the pump control unit to start the startup pump control when it determines that the temperature of the base unit has reached the start temperature of the startup pump control.

4. 4. The gas sensor according to claim 3, wherein the determination unit causes the pump control unit to switch from the startup pump control to the steady-state drive pump control when it determines that the pump current flowing through the measurement pump cell during the startup pump control is equal to or less than a predetermined threshold.

5. the sensor element includes a reference electrode disposed inside the base portion so as to be in contact with a reference gas; 4. The gas sensor according to claim 3, wherein the determination unit causes the pump control unit to switch from the startup pump control to the steady-state drive pump control when it determines that the electromotive force between the inner measurement electrode and the reference electrode is equal to or greater than a predetermined threshold value during the startup pump control.

6. 6. The gas sensor according to claim 1, wherein the startup voltage of the adjustment pump cell is 1.5 V or more and 3.0 V or less.

7. 7. The gas sensor according to claim 1, wherein the startup voltage of the measuring pump cell is 0.5 V or more and 1.45 V or less.

8. 8. The gas sensor according to claim 1, wherein a voltage ratio of the startup voltage of the adjustment pump cell to the startup voltage of the measurement pump cell is 1.03 or more and 6.00 or less.

9. 1. A method for controlling a gas sensor for detecting a measurement target gas in a measurement target gas, comprising: The gas sensor comprises: a sensor element and a control device that controls the sensor element; The sensor element is a long plate-shaped substrate including an oxygen ion conductive solid electrolyte layer; a measurement gas flow portion formed at one end of the base portion in the longitudinal direction; an adjusting pump cell including an inner pump electrode disposed on an inner surface of the measurement target gas flow portion and an outer pump electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner pump electrode, the adjusting pump cell adjusting the oxygen concentration in the measurement target gas to a desired concentration; a measurement pump cell for detecting a measurement target gas in the measurement gas, the measurement pump cell including: an inner measurement electrode disposed on an inner surface of the measurement target gas flow portion at a position farther from the one longitudinal end of the base portion than the inner pump electrode; and an outer measurement electrode disposed on the base portion at a position different from the measurement target gas flow portion and corresponding to the inner measurement electrode; a heater for heating the base portion; Including, Including, The control device a pump control unit that controls operations of the adjustment pump cell and the measurement pump cell, The control method includes: a startup pump control step executed when the sensor element is started, and a steady drive pump control step executed thereafter; In the startup pump control step, a pump control unit applies a startup voltage of the adjustment pump cell between the inner pump electrode and the outer pump electrode of the adjustment pump cell, the startup voltage being higher than a voltage applied to the adjustment pump cell in the steady drive pump control, and applies a startup voltage of the measurement pump cell between the inner measurement electrode and the outer measurement electrode of the measurement pump cell, the startup voltage being higher than the voltage applied to the measurement pump cell in the steady drive pump control and lower than the startup voltage of the adjustment pump cell; a pump control unit that adjusts the oxygen concentration in the measurement target gas to a desired concentration using the adjustment pump cell and detects the measurement target gas in the measurement target gas using the measurement pump cell in the steady-state drive pump control step.

Images