Gas sensor

Abstract

To execute a refresh process at a more appropriate timing.SOLUTION: A gas sensor 100 comprises a gas sensor body 100a that is attached to an exhaust pipe 130 of an engine and a control device 95. The gas sensor body 100a has a sensor element 101. The control device 95 executes a refresh process for restoring the catalytic function of a measurement electrode 44 when an offset value α of a pump current Ip2 is equal to or greater than a threshold αth1, or when a rich cumulative time Tri is equal to or greater than a threshold Trith.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] Conventionally, gas sensors that detect the concentration of a measurement gas component in a measurement gas are known (see, for example, Patent Document 1). The gas sensor in Patent Document 1 includes a main pumping means and a measurement pumping means. The main pumping means pumps oxygen contained in the measurement gas from an external space, which is introduced through a gas inlet into a processing space partitioned by a solid electrolyte in contact with the external space, to control the oxygen partial pressure in the processing space to a predetermined value at which a predetermined gas component cannot be decomposed. The measurement pumping means decomposes the measurement gas component contained in the measurement gas after pumping by the main pumping means through catalytic action and / or electrolysis, and pumps the oxygen generated by the decomposition. The gas sensor detects the measurement gas component in the measurement gas based on a pump current flowing through the measurement pumping means due to the pumping process of the measurement pumping means. This gas sensor further includes an electrode activating means that selectively applies an alternating current to either the main pumping means or the measurement pumping means to activate the detection electrode of the measurement pumping means and restore its catalytic function. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3866881 Summary of the Invention [Problem to be solved by the invention]

[0004] In such gas sensors, the timing of the refresh process to restore the catalytic function of the detection electrode is an issue to be addressed.

[0005] The main object of the gas sensor of the present invention is to execute a refresh process at a more appropriate timing.

Means for Solving the Problems

[0006] The gas sensor of the present invention has adopted the following means in order to achieve the above-described main object.

[0007] [1] The gas sensor of the present invention includes a sensor element attached to an exhaust pipe of an engine and a control device, and is a gas sensor that detects the concentration of a specific gas in the gas to be measured in the exhaust pipe, wherein the sensor element has a solid electrolyte layer with oxygen ion conductivity, and an element main body provided therein with a gas-to-be-measured gas flow portion for introducing and flowing the gas to be measured, a measurement pump cell having an inner measurement electrode disposed in a measurement chamber in the gas-to-be-measured gas flow portion, and an outer measurement electrode disposed on the outer surface of the element main body so as to contact the gas to be measured, an adjustment pump cell having an inner adjustment electrode disposed in an oxygen concentration adjustment chamber provided upstream of the measurement chamber in the gas-to-be-measured gas flow portion, and an outer adjustment electrode disposed on the outer surface of the element main body so as to contact the gas to be measured, and the control device executes a first adjustment pump control process for controlling the adjustment pump cell so that the oxygen concentration in the oxygen concentration adjustment chamber is adjusted, a first measurement pump control process for controlling the measurement pump cell so as to pump out oxygen from around the inner measurement electrode to around the outer measurement electrode, a concentration detection process for detecting the concentration of the specific gas in the gas to be measured based on a measurement pump current flowing through the measurement pump cell by the first measurement pump control process, and Furthermore, when a condition that an offset value of the measurement pump current is equal to or greater than a first threshold value and / or a condition that a cumulative time during which the sensor element is exposed to the measured gas in a rich atmosphere is equal to or greater than a first predetermined time is satisfied, the control device executes a refresh process for restoring a catalytic function of the measurement electrode. This is the gist.

[0008] In the gas sensor of the present invention, when a condition that an offset value of the measurement pump current is equal to or greater than a first threshold value and / or a condition that a cumulative time during which the sensor element is exposed to the measured gas in a rich atmosphere is equal to or greater than a predetermined time is satisfied, a refresh process for restoring a catalytic function of the measurement electrode is executed. Thereby, the refresh process can be executed at a more appropriate timing.

[0009] [2] In the gas sensor described above (the gas sensor described in [1]), when a concentration zero condition under which the concentration of the specific gas in the measured gas can be regarded as zero is satisfied, the control device may execute the first adjustment pump control process, the first measurement pump control process, and an offset value detection process for detecting the offset value based on the measurement pump current. By doing so, the offset value of the measurement pump current can be detected more appropriately.

[0010] [3] In the gas sensor described above (the gas sensor described in [2]), the concentration zero condition may be an OR condition of a condition that a duration of fuel cut of the engine is equal to or greater than a second predetermined time and a condition that a duration of engine operation stop is equal to or greater than a third predetermined time. By doing so, more appropriate conditions can be used as the concentration zero condition.

[0011] [4] In the above-described gas sensor (the gas sensor described in [2] or [3]), after the start of the refresh process, when any of the following conditions is satisfied: the condition that the offset value reaches less than a second threshold value that is less than or equal to the first threshold value; the condition that the cumulative time or the continuous time of the refresh process is equal to or more than a fourth predetermined time, the control device may end the refresh process. By doing so, the refresh process can be ended at a more appropriate timing.

[0012] [5] In the above-described gas sensor (the gas sensor described in [4]), after the start of the refresh process, when the zero concentration condition is satisfied, the control device interrupts the refresh process and executes the first adjustment pump control process, the first measurement pump control process, and the offset value detection process. When the offset value is less than or equal to the second threshold value, the control device ends the refresh process. When the offset value exceeds the second threshold value, the control device may resume the refresh process. By doing so, the refresh process can be ended, interrupted, and resumed at a more appropriate timing.

[0013] [6] In the above-described sensor element (the sensor element described in [2]), after the start of the refresh process, when the condition that the offset value reaches less than a second threshold value that is less than or equal to the first threshold value is satisfied, the control device ends the refresh process. Further, after the start of the refresh process, when the zero concentration condition is not satisfied and the offset value cannot be detected, the control device interrupts the refresh process, and then resumes the refresh process when the zero concentration condition is satisfied. By doing so, the refresh process can be ended, interrupted, and resumed at a more appropriate timing.

[0014] [7] In the gas sensor described above (the gas sensor described in any one of [1] to [6]), the sensor element further includes a heater for heating the element body, and when the gas to be measured is in a lean atmosphere, the control device may, as the refresh process, cause the heater to generate heat and stop the first adjustment pump control process and the first measurement pump control process.

[0015] [8] In the gas sensor described above (the gas sensor described in any one of [1] to [6]), as the refresh process, the control device controls the measurement pump cell so as to alternately perform oxygen uptake from around the outer measurement electrode to around the inner measurement electrode and oxygen extraction from around the inner measurement electrode to around the outer measurement electrode by applying an alternating voltage to the outer measurement electrode and the inner measurement electrode, and controls the adjustment pump cell so as to alternately perform oxygen uptake from around the outer adjustment electrode to around the inner adjustment electrode and oxygen extraction from around the inner adjustment electrode to around the outer adjustment electrode by applying an alternating voltage to the outer adjustment electrode and the inner adjustment electrode, and may execute at least one of the second measurement pump control process and the second adjustment pump control process.

[0016] [9] In the gas sensor described above (the gas sensor described in [8]), the control device may execute the refresh process when the gas to be measured is in a lean atmosphere.

[0017]

[10] In the gas sensor described above (the gas sensor described in [8] or [9]), the alternating voltage may be any one of a rectangular wave, a sine wave, a sawtooth wave, and a triangular wave.

[0018]

[11] In the gas sensor described above (the gas sensor described in any one of [1] to [6]), as the refresh process, the control device may execute at least one of a third measurement pump control process for controlling the measurement pump cell to draw oxygen from around the outer measurement electrode to around the inner measurement electrode, and a third measurement pump control process for controlling the adjustment pump cell to draw oxygen from around the outer adjustment electrode to around the inner adjustment electrode.

[0019]

[12] In the gas sensor described above (the gas sensor described in

[11] ), the control device may execute the refresh process when the gas to be measured is in a lean atmosphere.

[0020]

[13] In the gas sensor described above (the gas sensor described in any one of [7], [9], and

[12] ), the sensor element further includes a reference electrode disposed inside the element body so as to contact a reference gas that serves as a reference for detecting the concentration of the specific gas, and a reference voltage detection sensor cell that detects a reference voltage between the reference electrode and the outer measurement electrode or the outer adjustment electrode. The control device may execute a lean determination process for determining whether the gas to be measured is in the lean atmosphere using the reference voltage.

[0021]

[14] In the gas sensor of the present invention (the gas sensor described in any one of [1] to

[13] ), the outer measurement electrode and the outer adjustment electrode may be a common electrode.

Brief Description of the Drawings

[0022]

Figure 1

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Figure 13

Embodiments for Carrying Out the Invention

[0023] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing an outline of the configuration of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a schematic diagram schematically showing an outline of the configuration of a sensor element 101 included in the gas sensor 100. FIG. 3 is a block diagram showing the electrical connection relationship between the control device 95, each cell of the sensor element 101, and the heater 71.

[0024] As shown in FIG. 1, the gas sensor 100 includes a gas sensor main body 100a and a control device 95. The gas sensor main body 100a is attached to, for example, an exhaust pipe 130 of an engine (such as a gasoline engine) of a vehicle. The gas sensor 100 detects a specific gas concentration, which is the concentration of a specific gas such as NOx or ammonia in the gas to be measured, with the exhaust gas of the engine as the gas to be measured. In the present embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The gas sensor main body 100a includes a sensor element 101 having a long rectangular parallelepiped-shaped element main body 102, a protective cover 110 that protects the front end side of the element main body 102, and a sensor assembly 111 that houses the element main body 102. Here, the longitudinal direction (the left-right direction in FIG. 2) of the element main body 102 is defined as the front-rear direction, the thickness direction (the up-down direction in FIG. 2) of the element main body 102 is defined as the up-down direction, and the width direction (the direction perpendicular to the front-rear direction and the up-down direction) of the element main body 102 is defined as the left-right direction.

[0025] In addition to the element main body 102, the sensor element 101 includes cells 21, 41, 50, 80 to 83 and a heater unit 70. The element main body 102 is a laminate in which six layers, namely, 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 made of an oxygen ion-conductive solid electrolyte layer such as zirconia (ZrO2), are laminated in this order from the lower side in a plan view. Further, the solid electrolytes forming these six layers are dense and airtight. The element main body 102 is manufactured, for example, by performing predetermined processing and printing of a circuit pattern on ceramic green sheets corresponding to each layer, then laminating them, and further firing them to integrate them.

[0026] On the front end side of the element main body 102, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion rate-limiting portion 11, a buffer space 12, a second diffusion rate-limiting portion 13, a first internal cavity (oxygen concentration adjustment chamber) 20, a third diffusion rate-limiting portion 30, a second internal cavity (oxygen concentration adjustment chamber) 40, a fourth diffusion rate-limiting portion 60, and a third internal cavity (measurement chamber) 61 are adjacently formed in a communicating manner in this order.

[0027] The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are spaces inside the sensor element 101 provided in a manner of punching out the spacer layer 5, with the upper part defined by the lower surface of the second solid electrolyte layer 6, the lower part defined by the upper surface of the first solid electrolyte layer 4, and the side part defined by the side surface of the spacer layer 5.

[0028] The first diffusion rate-limiting part 11, the second diffusion rate-limiting part 13, and the third diffusion rate-limiting part 30 are all provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). Also, the fourth diffusion rate-limiting part 60 is provided as one horizontally long slit (the opening has a longitudinal direction in a direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. Note that the part from the gas inlet 10 to the third internal cavity 61 is also referred to as the measured gas flow-through part.

[0029] The element body 102 is provided with a reference gas introduction part 49 for flowing a reference gas when measuring the NOx concentration from the outside of the element body 102 to the reference electrode 42. The reference gas introduction part 49 has a reference gas introduction space 43 and a reference gas introduction layer 48. The reference gas introduction space 43 is a space provided so as to extend from the rear end surface of the element body 102 toward the front end surface side. The reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5 and at a position where the side part is defined by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 opens at the rear end surface of the element body 102, and this opening functions as the inlet part 49a of the reference gas introduction part 49. The reference gas is introduced into the reference gas introduction space 43 from this inlet part 49a. The reference gas introduction part 49 introduces the reference gas introduced from the inlet part 49a to the reference electrode 42 while imparting a predetermined diffusion resistance to it. The reference gas is air in the embodiment.

[0030] The reference gas introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is a porous body made of ceramics such as alumina, for example. A part of the upper surface of the reference gas introduction layer 48 is exposed in the reference gas introduction space 43. The reference gas introduction layer 48 is formed so as to cover the reference electrode 42. The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

[0031] 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. As described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. Also, as will be described later, it is possible to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 using the reference electrode 42.

[0032] In the measured gas flow path, the gas inlet 10 is a part that opens to the external space, and the measured gas is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion rate-limiting part 11 is a part that imparts a predetermined diffusion resistance to the measured gas taken in from the gas inlet 10. The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion rate-limiting part 11 to the second diffusion rate-limiting part 13. The second diffusion rate-limiting part 13 is a part that imparts a predetermined diffusion resistance to the measured gas introduced from the buffer space 12 into the first internal cavity 20. When the measured gas is introduced from outside the sensor element 101 into the first internal cavity 20, the measured gas suddenly taken into the sensor element 101 from the gas inlet 10 due to the pressure fluctuation of the measured gas in the external space (when the measured gas is the exhaust gas of the engine, the pulsation of the exhaust pressure) is not directly introduced into the first internal cavity 20, but after the pressure fluctuation of the measured gas is canceled through the first diffusion rate-limiting part 11, the buffer space 12, and the second diffusion rate-limiting part 13, it is introduced into the first internal cavity 20. Thus, the pressure fluctuation of the measured gas introduced into the first internal cavity 20 becomes negligible. The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the measured gas introduced through the second diffusion rate-limiting part 13. This oxygen partial pressure is adjusted by the operation of the main pump cell 21.

[0033] The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode part 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, an outer pump electrode 23 provided in a manner exposed to the outside of the element body 102 in a region corresponding to the ceiling electrode part 22a on the upper surface of the second solid electrolyte layer 6 (disposed on the outer surface of the element body 102 so as to contact the measured gas), and the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 that form the current path between these electrodes, and is an electrochemical pump cell constituted thereby.

[0034] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that partition the first internal cavity 20, and the spacer layer 5 that provides 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 cavity 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 of the first internal cavity 20. Then, a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the spacer layer 5 that constitutes both side wall portions of the first internal cavity 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and is disposed in a structure in a tunnel form at the disposition site of the side electrode portion.

[0035] In the main pump cell 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and by flowing a pump current Ip0 in the positive or negative direction between the inner pump electrode 22 and the outer pump electrode 23, oxygen in the first internal cavity 20 can be pumped out to the external space, or oxygen in the external space can be pumped into the first internal cavity 20.

[0036] Also, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal cavity 20, an electrochemical sensor cell, that is, a main pump control oxygen partial pressure detection sensor cell 80 is constituted by the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0037] By measuring the electromotive force (voltage V0) in the main pump control oxygen partial pressure detection sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be known. Further, by feedback controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value, the pump current Ip0 is controlled. Thereby, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0038] The third diffusion rate-limiting section 30 is a section that imparts a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal cavity 20, and guides the gas to be measured to the second internal cavity 40.

[0039] The second internal cavity 40 is provided as a space for further adjusting the oxygen partial pressure of the gas to be measured introduced through the third diffusion rate-limiting section 30 with respect to the gas to be measured whose oxygen concentration (oxygen partial pressure) has been adjusted in the first internal cavity 20 in advance by the auxiliary pump cell 50. Thereby, since the oxygen concentration in the second internal cavity 40 can be kept constant with high precision, highly accurate NOx concentration measurement can be performed in the gas sensor 100.

[0040] The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided substantially over the entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40, an outer pump electrode 23 (not limited to the outer pump electrode 23, and any appropriate electrode disposed on the outer peripheral surface of the element body 102 is sufficient), and is an auxiliary electrochemical pump cell constituted by the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4.

[0041] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 in a structure having a tunnel form similar to that of the inner pump electrode 22 provided in the first internal cavity 20. That is, on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal cavity 40, a ceiling electrode portion 51a is formed, and on the first solid electrolyte layer 4 that provides the bottom surface of the second internal cavity 40, a bottom electrode portion 51b is formed, and side electrode portions (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b are formed in a tunnel form on both wall surfaces of the spacer layer 5 that provides the side walls of the second internal cavity 40.

[0042] In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere within the second internal cavity 40 can be pumped out to the external space or pumped into the second internal cavity 40 from the external space.

[0043] Also, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 81 for auxiliary pump control is constituted 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.

[0044] Note that the auxiliary pump cell 50 performs pumping by a variable power supply 52 that is voltage-controlled based on the electromotive force (voltage V1) detected by this oxygen partial pressure detection sensor cell 81 for auxiliary pump control. Thereby, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that has substantially no influence on the measurement of NOx.

[0045] Also, together with this, the pump current Ip1 is used for controlling the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for main pump control, and by controlling the above-described target value of the voltage V0, the gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion rate limiting section 30 into the second internal cavity 40 is always made constant. When used as a NOx sensor, due to the functions of the main pump cell 21 and the auxiliary pump cell 50, the oxygen concentration within the second internal cavity 40 is maintained at a constant value of about 0.001 ppm.

[0046] The fourth diffusion rate limiting section 60 is a site that imparts a predetermined diffusion resistance to the measurement gas whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal cavity 40 and guides the measurement gas to the third internal cavity 61. The fourth diffusion rate limiting section 60 plays a role of restricting the amount of NOx flowing into the third internal cavity 61.

[0047] The third internal space 61 is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured, which has been introduced through the fourth diffusion rate-limiting section 60 after the oxygen concentration (oxygen partial pressure) has been adjusted in the second internal space 40 in advance. The measurement of the NOx concentration is mainly performed in the third internal space 61 by the operation of the measurement pump cell 41.

[0048] The measurement pump cell 41 measures the NOx concentration in the gas to be measured within the third internal space 61. The measurement pump cell 41 is an electrochemical pump cell composed of 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, a second solid electrolyte layer 6, a spacer layer 5, and the first solid electrolyte layer 4. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere within the third internal space 61.

[0049] In the measurement pump cell 41, oxygen generated by the decomposition of nitrogen oxide (NOx) in the atmosphere around the measurement electrode 44 can be pumped out, and the generated amount can be detected as a pump current Ip2.

[0050] Also, in order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, a measurement pump control oxygen partial pressure detection sensor cell 82, is constituted by the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the measurement pump control oxygen partial pressure detection sensor cell 82.

[0051] The gas to be measured guided into the second internal space 40 reaches the measurement electrode 44 in the third internal space 61 through the fourth diffusion rate-limiting section 60 under the condition that the oxygen partial pressure is controlled. Nitrogen oxides (NOx) in the gas to be measured around the measurement electrode 44 are reduced (2NO→N2+O2) to generate oxygen. Then, the generated oxygen is pumped by the measurement pump cell 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump becomes constant (target value). Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the concentration of nitrogen oxides in the gas to be measured is calculated using the pump current Ip2 in the measurement pump cell 41.

[0052] Also, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form oxygen partial pressure detection means as an electrochemical sensor cell, it is possible to detect the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the measurement electrode 44 and the amount of oxygen contained in the reference atmosphere. Thus, it is also possible to obtain the concentration of the NOx component in the gas to be measured.

[0053] Furthermore, an electrochemical sensor cell 83 is constituted by 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. The electromotive force (reference voltage Vref) obtained by this sensor cell 83 enables the detection of the oxygen partial pressure in the gas to be measured outside the element body 102 of the sensor element 101, specifically, around the outer pump electrode 23.

[0054] In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the gas to be measured in which the oxygen partial pressure is always maintained at a constant low value (a value that has substantially no influence on the measurement of NOx) is supplied to the measurement pump cell 41. Therefore, based on the pump current Ip2 that flows by pumping out the oxygen generated by the reduction of NOx from the measurement pump cell 41 in substantially proportion to the concentration of NOx in the gas to be measured, the concentration of NOx in the gas to be measured can be known.

[0055] Here, each of the electrodes 22, 23, 42, 44, 51 will be described. The inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 each contain a first type of noble metal having catalytic activity. Examples of the first type of noble metal include at least any one of Pt, Rh, Ir, Ru, and Pd. The outer pump electrode 23 and the reference electrode 42 also contain the first type of noble metal. The inner pump electrode 22 and the auxiliary pump electrode 51 also contain a second type of noble metal that suppresses the catalytic activity against a specific gas (NOx in the embodiment) by the first type of noble metal. Thereby, the reduction ability of the inner pump electrode 22 and the auxiliary pump electrode 51 with respect to the NOx component in the gas to be measured is weakened. Examples of the second type of noble metal include Au. The measurement electrode 44 does not contain the second type of noble metal. Thereby, the reduction ability with respect to the NOx component in the gas to be measured is enhanced compared to the inner pump electrode 22 and the auxiliary pump electrode 51. The measurement electrode 44 preferably contains at least one of Pt and Rh among the first type of noble metals, and may contain both Pt and Rh. It is also preferable that the outer pump electrode 23 and the reference electrode 42 do not contain the second type of noble metal. Each of the electrodes 22, 23, 42, 44, 51 is preferably a cermet containing a noble metal and an oxide having oxygen ion conductivity (e.g., ZrO2). Each of the electrodes 22, 23, 42, 44, 51 is preferably a porous body. In the present embodiment, the inner pump electrode 22 and the auxiliary pump electrode 51 are formed as porous cermet electrodes of Pt and ZrO2 containing 1% Au. Also, both the outer pump electrode 23 and the reference electrode 42 are formed as porous cermet electrodes of Pt and ZrO2. The measurement electrode 44 is formed as a porous cermet electrode of Pt, Rh, and ZrO2.

[0056] The heater unit 70 plays a role of temperature adjustment to heat and keep warm the sensor element 101 in order to enhance the oxygen ion conductivity of the solid electrolyte of the element body 102. The heater unit 70 includes a heater 71, a heater insulating layer 72, and a pressure dissipation hole 73.

[0057] The heater 71 is an electric resistor formed in a manner sandwiched from above and below by the second substrate layer 2 and the third substrate layer 3. The heater 71 generates heat when powered by the heater power supply 74, and heats and keeps warm the solid electrolyte of the element body 102 of the sensor element 101. Further, the heater 71 is embedded across the entire region from the first internal cavity 20 to the third internal cavity 61, and it is possible to adjust the entire sensor element 101 to a temperature at which the solid electrolyte is activated.

[0058] The heater insulating layer 72 is an insulating layer formed of an insulator such as alumina on the upper and lower surfaces of the heater 71. The heater insulating layer 72 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 71, and electrical insulation between the third substrate layer 3 and the heater 71.

[0059] The pressure dissipation hole 73 is a portion provided so as to penetrate the third substrate layer 3 and the reference gas introduction layer 48 and communicate with the reference gas introduction space 43, and is formed for the purpose of alleviating the increase in internal pressure accompanying the temperature rise in the heater insulating layer 72.

[0060] As shown in FIG. 3, the control device 95 includes the variable power supplies 24, 46, 52 described above, the heater power supply 74 described above, and a control unit 96. The control unit 96 is a microprocessor having a CPU 97, a storage unit 98, and the like. The storage unit 98 is a non-volatile memory capable of rewriting information, and can store various programs and various data, for example. The control unit 96 inputs the voltage V0 of the oxygen partial pressure detection sensor cell 80 for main pump control, the voltage V1 of the oxygen partial pressure detection sensor cell 81 for auxiliary pump control, the voltage V2 of the oxygen partial pressure detection sensor cell 82 for measurement pump control, the reference voltage Vref of the sensor cell 83, the pump current Ip0 flowing through the main pump cell 21, the pump current Ip1 flowing through the auxiliary pump cell 50, and the pump current Ip2 flowing through the measurement pump cell 41. Further, the control unit 96 controls the voltages Vp0, Vp1, Vp2 output by the variable power supplies 24, 46, 52 by outputting a control signal to the variable power supplies 24, 46, 52, thereby controlling the main pump cell 21, the measurement pump cell 41, and the auxiliary pump cell 50. The control unit 96 controls the power supplied by the heater power supply 74 to the heater 71 by outputting a control signal to the heater power supply 74. The storage unit 98 also stores target values V0*, V1*, V2* and the like, which will be described later. The CPU 97 of the control unit 96 controls each pump cell 21, 41, 50 with reference to these target values V0*, V1*, V2*.

[0061] The control unit 96 performs a first auxiliary pump control process for controlling the auxiliary pump cell 50 so that the oxygen concentration in the second internal cavity 40 becomes the target concentration. Specifically, the control unit 96 controls the auxiliary pump cell 50 by feedback-controlling the voltage Vp1 of the variable power supply 52 so that the voltage V1 becomes a constant value (referred to as the target value V1*). The target value V1* is determined as a value such that the oxygen concentration in the second internal cavity 40 becomes a predetermined low concentration that has substantially no influence on the measurement of NOx.

[0062] The control unit 96 performs a first main pump control process for controlling the main pump cell 21 so that the pump current Ip1 flowing when the auxiliary pump cell 50 adjusts the oxygen concentration in the second internal cavity 40 becomes the target current (referred to as the target value Ip1*) by the first auxiliary pump control process. Specifically, the control unit 96 sets (feedback control) the target value (referred to as the target value V0*) of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 flowing by the voltage Vp1 becomes a constant target value Ip1*. Then, the control unit 96 feedback-controls the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (that is, so that the oxygen concentration in the first internal cavity 20 becomes the target concentration). By this first main pump control process, the gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion rate limiting section 30 into the second internal cavity 40 always becomes constant. The target value V0* is set to a value such that the oxygen concentration in the first internal cavity 20 is higher than 0% and becomes a low concentration. Also, the pump current Ip0 flowing during this first main pump control process changes according to the oxygen concentration of the measurement gas flowing into the measurement gas flow section from the gas inlet 10 (that is, the measurement gas around the sensor element 101). Therefore, the control unit 96 can also detect the oxygen concentration in the measurement gas based on the pump current Ip0.

[0063] The above-described first main pump control process and first auxiliary pump control process are collectively also referred to as the first adjustment pump control process. The first internal cavity 20 and the second internal cavity 40 are collectively also referred to as the oxygen concentration adjustment chamber. The main pump cell 21 and the auxiliary pump cell 50 are collectively also referred to as the adjustment pump cells. By the control unit 96 performing the first adjustment pump control process, the adjustment pump cells adjust the oxygen concentration in the oxygen concentration adjustment chamber.

[0064] The control unit 96 performs a first measurement pump control process for controlling the measurement pump cell 41 so that the voltage V2 becomes a constant value (referred to as the target value V2*), that is, so that the oxygen concentration in the third internal cavity 61 becomes a predetermined low concentration. Specifically, the control unit 96 controls the measurement pump cell 41 by feedback-controlling the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*. By this first measurement pump control process, oxygen is pumped out from the third internal cavity 61.

[0065] When the first measurement pump control process is performed, oxygen is pumped out from the third internal cavity 61 so that the oxygen generated by the reduction of NOx in the gas to be measured in the third internal cavity 61 becomes substantially zero. Then, the control unit 96 acquires the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 derived from the specific gas (NOx in the embodiment), and calculates the concentration of the specific gas in the gas to be measured based on this pump current Ip2.

[0066] The relational expression (for example, a linear function or a quadratic function expression), map, etc. are stored in the storage unit 98 as the correspondence between the pump current Ip2 and the NOx concentration. Such a relational expression or map can be obtained in advance by experiments.

[0067] The control unit 96 determines whether the gas to be measured is in a rich atmosphere (the air-fuel ratio of the gas to be measured is smaller than the stoichiometric air-fuel ratio) or a lean atmosphere (the air-fuel ratio of the gas to be measured is larger than the stoichiometric air-fuel ratio) based on the reference voltage Vref of the sensor cell 83. The reference voltage Vref is a value corresponding to the oxygen concentration difference between the gas to be measured around the outer pump electrode 23 and the reference gas around the reference electrode 42. Therefore, the control unit 96 determines whether the gas to be measured is in a rich atmosphere or a lean atmosphere by comparing the reference voltage Vref of the sensor cell 83 with the threshold value Vth. The threshold value Vth is defined as the reference voltage Vref when the air-fuel ratio of the gas to be measured is the stoichiometric air-fuel ratio.

[0068] The control unit 96 performs a heater control process of outputting a control signal to the heater power supply 74 to control the temperature of the heater 71 to the target temperature Th* (for example, 800 °C). Here, the temperature of the heater 71 can be expressed by a linear function formula of the resistance value of the heater 71. In the heater control process, the control unit 96 calculates the resistance value of the heater 71 as a value that can be regarded as the temperature of the heater 71 (a value convertible to temperature), and feedback-controls the heater power supply 74 so that the calculated resistance value becomes the target resistance value (the resistance value corresponding to the target temperature Th*). The control unit 96 can obtain, for example, the voltage of the heater 71 and the current flowing through the heater 71, and calculate the resistance value of the heater 71 based on the obtained voltage and current. The control unit 96 may calculate the resistance value of the heater 71 by, for example, the three-terminal method or the four-terminal method. When energizing the heater 71, the heater power supply 74 adjusts the power supplied to the heater 71 by changing the value of the voltage applied to the heater 71 based on, for example, the control signal from the control unit 96.

[0069] Note that including the variable power supplies 24, 46, 52 and the heater power supply 74 shown in FIG. 3, etc., the control device 95 is connected to each electrode 22, 23, 42, 44, 51 in the sensor element 101 and the heater 71 via each lead wire (not shown) formed in the sensor element 101 and each connector electrode 75 formed on the rear end side of the sensor element 101.

[0070] The control device 95 communicates with an engine electronic control unit (hereinafter referred to as "engine ECU") 140 that inputs signals from various sensors of the engine (excluding the gas sensor 100) and performs engine operation control.

[0071] Next, an example of the process of the control unit 96 of the gas sensor 100 will be described. FIG. 4 is a flowchart showing an example of the main processing routine executed by the CPU 97 of the control unit 96. This routine is stored, for example, in the storage unit 98 of the control unit 96 and is repeatedly executed by the CPU 97.

[0072] In the main processing routine of FIG. 4, the CPU 97 first determines whether or not the offset value α of the pump current Ip2 is equal to or greater than the threshold value αth1 (step S100), and also determines whether or not the rich cumulative time Tri is equal to or greater than the threshold value Trith (step S110). When the gas sensor 100 is exposed to the measured gas in a rich atmosphere, carbon monoxide (CO) or the like in the measured gas adheres to the measurement electrode 44, and the catalytic function (reduction ability) of the measurement electrode 44 decreases, resulting in a decrease in the detection accuracy of the concentration of a specific gas (NOx in the embodiment) in the measured gas, or there is a possibility that the offset value α of the pump current Ip2 increases due to the desorption of oxygen when the specific gas is not contained in the measured gas. The inventors confirmed these through experiments and analyses. The processes of steps S100 and S110 are based on these, and are processes for determining whether or not the refresh conditions for performing the refresh process are satisfied. The refresh process is a process for restoring the catalytic function (reduction ability) of the measurement electrode 44. For example, 0.02 μA is used as the threshold value αth1. Note that the threshold value αth1 is not limited to 0.02 μA, and is determined through experiments, analyses, or the like. The rich cumulative time Tri is the cumulative time during which the sensor element 101 is exposed to the measured gas in a rich atmosphere. The method for determining whether the measured gas is in a rich atmosphere or a lean atmosphere has been described above. The CPU 97 calculates the rich cumulative time Tri by accumulating the time during which the measured gas is in a rich atmosphere. For example, 400 hours is used as the threshold value Trith. Note that the threshold value Trith is not limited to 400 hours, and is determined through experiments, analyses, or the like.

[0073] When the CPU 97 determines in step S100 that the offset value α of the pump current Ip2 is less than the threshold value αth1 and determines in step S110 that the rich cumulative time Tri is less than the threshold value Trith, it determines that the refresh condition is not satisfied, executes the normal-time processing illustrated in FIG. 5 (step S120), and ends this routine. On the other hand, when the CPU 97 determines in step S100 that the offset value α of the pump current Ip2 is greater than or equal to the threshold value αth1, or when it determines in step S110 that the rich cumulative time Tri is greater than or equal to the threshold value Trith, it determines that the refresh condition is satisfied, executes the processing when the refresh condition is satisfied illustrated in FIG. 6 (step S130), and ends this routine. Hereinafter, the normal-time processing in FIG. 5 and the processing when the refresh condition is satisfied in FIG. 6 will be described in order.

[0074] The normal-time processing of FIG. 5 will be described. In the normal-time processing of FIG. 5, the CPU 97 determines whether or not the zero-concentration condition is satisfied (step S200), and determines whether or not the elapsed time Tof from the previous execution of the offset value detection process described later is equal to or greater than the threshold value Tofth1 (step S210). Here, the zero-concentration condition is a condition under which the concentration of a specific gas (NOx in the embodiment) in the gas to be measured can be regarded as zero. In the embodiment, as the zero-concentration condition, an OR condition of a condition that the duration Tfc of the fuel cut of the engine is equal to or greater than the threshold value Tfcth and a condition that the duration Tsp of the engine stop is equal to or greater than the threshold value Tspth is used. The threshold value Tfcth is defined as the time required from the start of the fuel cut of the engine until the concentration of the specific gas in the gas to be measured can be regarded as zero. The threshold value Tspth is defined as the time required from the start of the engine stop until the concentration of the specific gas in the gas to be measured can be regarded as zero. The durations Tfc and Tsp of the fuel cut and the engine stop of the engine are input by the control device 95 from the engine ECU 140 through communication. Note that the control device 95 may input the presence or absence of the fuel cut and the engine stop of the engine from the engine ECU 140 through communication and calculate the durations Tfc and Tsp of the fuel cut and the engine stop of the engine. The threshold value Tofth1 is defined as the execution interval of the offset value detection process. For the threshold value Tofth1, for example, about 10 seconds to 60 seconds is used.

[0075] When the CPU 97 determines in step S200 that the zero-concentration condition is not satisfied, or when the CPU 97 determines in step S210 that the elapsed time Tof from the previous execution of the offset value detection process is less than the threshold value Tofth1, the above-described heater control process, the first adjustment pump control process (the first main pump control process and the first auxiliary pump control process), and the first measurement pump control process are executed, and the concentration detection process is executed (step S220), and the normal-time processing is terminated. Here, the concentration detection process is a process of detecting the concentration of a specific gas (NOx in the embodiment) in the gas to be measured based on the pump current Ip2.

[0076] On the one hand, when the CPU 97 determines in step S200 that the zero concentration condition is satisfied and determines in step S210 that the elapsed time Tof from the previous execution of the offset value detection process is equal to or greater than the threshold value Tofth1, the CPU 97 executes the heater control process, the first adjustment pump control process, and the first measurement pump control process, and executes the offset value detection process instead of the concentration detection process (step S230), and ends the normal-time process. Here, the offset value detection process is a process of detecting the offset value α of the pump current Ip2 based on the pump current Ip2 during the execution of the first adjustment pump control process and the first measurement pump control process. When the zero concentration condition is satisfied, theoretically, the pump current Ip2 during the execution of the first adjustment pump control process and the first measurement pump control process becomes zero. Therefore, the actual pump current Ip2 at this time can be detected as the offset value α. Note that the threshold value Tofth1 may be a value of 0. That is, each time the zero concentration condition is satisfied, the heater control process, the first adjustment pump control process, the first measurement pump control process, and the offset value detection process may be executed.

[0077] Next, the processing when the refresh condition in FIG. 6 is satisfied will be described. In the processing when the refresh condition in FIG. 6 is satisfied, the CPU 97 determines whether the gas to be measured is in a lean atmosphere (step S300). When the CPU 97 determines that the gas to be measured is in a lean atmosphere, as a refresh process, it executes heater control processing and stops the operations of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) and the measurement pump cell 41 (step S310). When the gas to be measured is in a lean atmosphere, since the oxygen concentration in the gas to be measured is relatively high, when the operations of the adjustment pump cells and the measurement pump cell 41 are stopped, the oxygen concentration around the measurement electrode 44 also increases. Therefore, by holding the sensor element 101 at a relatively high temperature by the heater control processing, the substances (such as carbon) adhering to the measurement electrode 44 can be oxidized by the oxygen around the measurement electrode 44 and detached from the measurement electrode 44. Thereby, the catalyst function (reduction ability) of the measurement electrode 44 can be restored, suppressing a decrease in the detection accuracy of the concentration of a specific gas (NOx in the embodiment) in the gas to be measured, or reducing the offset value α of the pump current Ip2. The inventors have confirmed these matters through experiments and analyses. Moreover, as a part of the refresh process, by stopping the operations of the adjustment pump cells and the measurement pump cell 41, the power consumption of the gas sensor 100 can be suppressed.

[0078] Subsequently, the CPU 97 determines whether the refresh cumulative time Trf is equal to or greater than a threshold value Trfth (step S320). Here, the process of step S320 is a process for determining whether the refresh process can be terminated by performing the refresh process for a certain period of time. The refresh cumulative time Trf is the cumulative time of the refresh process. As the threshold value Trfth, for example, about 40 seconds to 70 seconds is used.

[0079] When the CPU 97 determines in step S320 that the cumulative time Trf of the refresh process is less than the threshold Trfth, it determines whether the zero-concentration condition is satisfied (step S330), and also determines whether the elapsed time Tof since the previous execution of the offset value detection process is equal to or greater than the threshold Tofth2 (step S340). Here, the processes of steps S330 and S340 are the same as the processes of steps S200 and S210 described above. Similar to the threshold Tofth1, the threshold Tofth2 is defined as the execution interval of the offset value detection process. The threshold Tofth2 may be the same as the threshold Tofth1, or may be a shorter time than the threshold Tofth1. For example, the threshold Tofth2 is used in the range of about 10 seconds to 60 seconds.

[0080] When the CPU 97 determines in step S330 that the zero-concentration condition is not satisfied, or determines in step S340 that the elapsed time Tof since the previous execution of the offset value detection process is less than the threshold Tofth2, it returns to step S300.

[0081] On the other hand, when the CPU 97 determines in step S330 that the zero-concentration condition is satisfied and determines in step S340 that the elapsed time Tof since the previous execution of the offset value detection process is equal to or greater than the threshold Tofth2, it interrupts the refresh process and executes the heater control process, the first adjustment pump control process, the first measurement pump control process, and the offset value detection process (step S350). Here, the process of step S350 is the same as the process of step 230 described above. By the process of step S350, the offset value α of the pump current Ip2 is detected.

[0082] Subsequently, the CPU 97 determines whether the offset value α of the pump current Ip2 is less than the threshold αth2 (step S360). Here, the process of step S360 is a process of determining whether the refresh process may be terminated due to the decrease in the offset value α. For example, the same value as the above-described threshold αth1 is used as the threshold αth2. Note that a value smaller than the threshold αth1 may be used as the threshold αth2.

[0083] When the CPU 97 determines in step S360 that the offset value α of the pump current Ip2 is greater than or equal to the threshold value αth2, it returns to step S300. On the other hand, when the CPU 97 determines in step S360 that the offset value α of the pump current Ip2 is less than the threshold value αth2, it resets the refresh cumulative time Trf (step S370), resets the rich cumulative time Tri (step S380), and ends the processing when the refresh condition is satisfied.

[0084] When the CPU 97 determines in step S320 that the refresh cumulative time Trf is greater than or equal to the threshold value Trfth, it resets the refresh cumulative time Trf (step S370) and resets the rich cumulative time Tri (step S380) regardless of whether the offset value α of the pump current Ip2 is less than the threshold value αth2, and ends the processing when the refresh condition is satisfied. Thereby, even when the offset value α of the pump current Ip2 cannot be detected because the zero concentration condition is not satisfied, the refresh process can be ended. The threshold value Trfth is determined as the time when it can be assumed that the offset value α of the pump current Ip2 has reached less than the threshold value αth2.

[0085] When the CPU 97 determines in step S300 that the gas to be measured is not in a lean atmosphere, it does not execute the refresh process (without starting or interrupting the refresh process), but executes the heater control process, the first adjustment pump control process, the first measurement pump control process, and the concentration detection process (step S390), and returns to step S300. The process of step S390 is the same as the process of step S220 described above. When the gas to be measured is not in a lean atmosphere, since the oxygen concentration in the gas to be measured is relatively low, even if the refresh process of step S310 is executed, the effect of oxidizing the substance (such as carbon) adhering to the measurement electrode 44 and desorbing it from the measurement electrode 44 is not very high. Therefore, in the embodiment, when the gas to be measured is not in a lean atmosphere, the CPU 97 does not execute the refresh process, but executes the heater control process, the first adjustment pump control process, the first measurement pump control process, and the concentration detection process. After that, when the CPU 97 determines in step S300 that the gas to be measured is in a lean atmosphere, it resumes the refresh process.

[0086] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. The sensor element 101 of this embodiment corresponds to the sensor element, and the control device 95 corresponds to the control device. The element body 102 corresponds to the element body, the third internal cavity 61 corresponds to the measurement chamber, the measurement electrode 44 corresponds to the inner measurement electrode, the measurement pump cell 41 corresponds to the measurement pump cell, the first internal cavity 20 and the second internal cavity 40 correspond to the oxygen concentration adjustment chamber, the inner pump electrode 22 and the auxiliary pump electrode 51 correspond to the inner adjustment electrode, the main pump cell 21 and the auxiliary pump cell 50 correspond to the adjustment pump cell, and the outer pump electrode 2 \alpha corresponds to the outer measurement electrode and the outer adjustment electrode.

[0087] It should be noted that in the translation of the last paragraph, there is an unclear "2 \alpha" in the original text. It is recommended to check and correct the original text for a more accurate translation. Here, it is translated as it is for the purpose of meeting the translation requirements.In the gas sensor 100 of the present embodiment described in detail above, when the offset value α of the pump current Ip2 is equal to or greater than the threshold value αth1 or when the rich cumulative time Tri is equal to or greater than the threshold value Trith, the control device 95 executes a refresh process. Thereby, the refresh process can be executed at a more appropriate timing to restore the catalytic function (reduction ability) of the measurement electrode 44, and it is possible to suppress a decrease in the detection accuracy of the concentration of a specific gas (NOx in the embodiment) in the gas to be measured.

[0088] Moreover, when the gas to be measured is in a lean atmosphere, the control device 95 executes heater control processing as a refresh process and stops the operations of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) and the measurement pump cell 41. Thereby, the power consumption of the gas sensor 100 can be suppressed.

[0089] Note that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

[0090] For example, in the above-described embodiment, the refresh condition is an OR condition of the condition that the offset value α of the pump current Ip2 is equal to or greater than the threshold value αth1 and the condition that the rich cumulative time Tri is equal to or greater than the threshold value Trith, but the present invention is not limited to this. For example, the refresh condition may be an AND condition of the condition that the offset value α of the pump current Ip2 is equal to or greater than the threshold value αth1 and the condition that the rich cumulative time Tri is equal to or greater than the threshold value Trith. The refresh condition may be only the condition that the offset value α of the pump current Ip2 is equal to or greater than the threshold value αth1. The refresh condition may be only the condition that the rich cumulative time Tri is equal to or greater than the threshold value Trith.

[0091] In the above-described embodiments, the zero-concentration condition uses the OR condition of the condition that the duration Tfc of fuel cut of the engine is equal to or greater than the threshold value Tfcth and the condition that the duration Tsp of engine shutdown is equal to or greater than the threshold value Tspth, but is not limited thereto. For example, the zero-concentration condition may use only the condition that the duration Tfc of fuel cut of the engine is equal to or greater than the threshold value Tfcth. The zero-concentration condition may use only the condition that the duration Tsp of engine shutdown is equal to or greater than the threshold value Tspth.

[0092] In the above-described embodiments, the CPU 97 executes the process when the refresh condition in FIG. 6 is satisfied, but is not limited thereto. For example, the CPU 97 may execute the process when the refresh condition in FIG. 7 is satisfied. The process when the refresh condition in FIG. 7 is satisfied is different from the process when the refresh condition in FIG. 6 in that the process of step S330 is moved before the process of step S300 and the process of step S320 is excluded. For the processes in the process when the refresh condition in FIG. 7 that are the same as the process when the refresh condition in FIG. 6, the same step numbers are assigned and detailed descriptions are omitted.

[0093] In the process when the refresh condition in FIG. 7 is satisfied, the CPU 97 first determines whether or not the zero-concentration condition is satisfied (step S330). When it is determined that the zero-concentration condition is satisfied, the process proceeds to step S300. On the other hand, when the CPU 97 determines that the zero-concentration condition is not satisfied, the process proceeds to step S390. In the process when the refresh condition in FIG. 7 is satisfied, the CPU 97 ends the process when the refresh condition is satisfied when the offset value α of the pump current Ip2 becomes less than the threshold value αth2 regardless of whether or not the refresh cumulative time Trf is equal to or greater than the threshold value Trfth. In this case, after the start of the refresh process, when the zero-concentration condition is no longer satisfied or the gas to be measured is no longer in a lean atmosphere, the CPU 97 interrupts the refresh process, and then resumes the refresh process when the zero-concentration condition is satisfied and the gas to be measured is in a lean atmosphere. This is because when the zero-concentration condition is not satisfied, the offset value α of the pump current Ip2 cannot be detected.

[0094] In the above-described embodiment, the CPU 97 executes, as part of the refresh process, heater control processing, specifically, processing for controlling the heater power supply 74 so that the temperature of the heater 71 becomes the target temperature Th* (for example, 800°C). However, the present invention is not limited to this. As long as the CPU 97 executes processing for controlling the heater power supply 74 so that the heater 71 generates heat to such an extent that substances (such as carbon) adhering to the measurement electrode 44 can be oxidized and detached from the measurement electrode 44.

[0095] In the above-described embodiment, the CPU 97 executes the processing when the refresh condition is satisfied in FIG. 6. However, the present invention is not limited to this. For example, the CPU 97 may execute the processing when the refresh condition is satisfied in FIG. 8. The processing when the refresh condition is satisfied in FIG. 8 is different from the processing when the refresh condition is satisfied in FIG. 6 in that the processing of step S310 is replaced with the processing of step S312. For the processing that is the same as the processing when the refresh condition is satisfied in FIG. 6 among the processing when the refresh condition is satisfied in FIG. 8, the same step numbers are assigned, and detailed description thereof is omitted.

[0096] In the process when the refresh condition in FIG. 8 is satisfied, when the CPU 97 determines in step S300 that the gas to be measured is in a lean atmosphere, as a refresh process, it executes heater control processing and second measurement pump control processing, and at the same time stops the operation of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) (step S312), and proceeds to step S320. Here, the second measurement pump control processing controls the variable power supply 46 to apply an alternating voltage to the outer pump electrode 23 and the measurement electrode 44, so as to alternately perform the pumping in of oxygen from around the outer pump electrode 23 to around the measurement electrode 44 and the pumping out of oxygen from around the measurement electrode 44 to around the outer pump electrode 23, and is a process for controlling the measurement pump cell 41. The alternating voltage is, for example, any one of a rectangular wave, a sine wave, a sawtooth wave, and a triangular wave. By executing the second measurement pump control processing, the oxygen concentration around the measurement electrode 44 changes alternately (increase and decrease occur alternately). For this reason, the oxygen around the measurement electrode 44 can oxidize the substances (such as carbon, etc.) adhering to the measurement electrode 44 and cause them to desorb from the measurement electrode 44. Thereby, the catalytic function (reduction ability) of the measurement electrode 44 can be restored, the decrease in the detection accuracy of the concentration of a specific gas (NOx in the embodiment) in the gas to be measured can be suppressed, or the offset value α of the pump current Ip2 can be decreased. The inventors confirmed these through experiments and analyses. Moreover, when the gas to be measured is in a lean atmosphere, that is, when there is more oxygen around the measurement electrode 44, by executing the refresh process, more substances adhering to the measurement electrode 44 can be oxidized and desorbed from the measurement electrode 44.

[0097] The process when the refresh condition in FIG. 8 is satisfied has been described. Instead of the process when the refresh condition in FIG. 8 is satisfied, the CPU 97 may execute the process when the refresh condition in FIG. 9 is satisfied. The process when the refresh condition in FIG. 9 is satisfied corresponds to the one in which the process of step S310 in the process when the refresh condition in FIG. 7 is satisfied is replaced with the process of step S312.

[0098] In the processing when the refresh condition shown in FIGS. 8 and 9 is satisfied, the CPU 97 executes, as the refresh processing, the heater control processing and the second measurement pump control processing, and stops the operations of the adjustment pump cells (the main pump cell 21 and the auxiliary pump cell 50) in step S312, but it is not limited thereto. For example, as the refresh processing, the heater control processing and the second main pump control processing may be executed while stopping the operations of the auxiliary pump cell 50 and the measurement pump cell 41. As the refresh processing, the heater control processing and the second auxiliary pump control processing may be executed while stopping the operations of the main pump cell 21 and the measurement pump cell 41. As the refresh processing, the heater control processing and a plurality of the second measurement pump control processing, the second main pump control processing, and the second auxiliary pump control processing may be executed. The second main pump control processing is a process of controlling the main pump cell 21 so that oxygen is alternately drawn from around the outer pump electrode 23 to around the inner pump electrode 22 and pumped out from around the inner pump electrode 22 to around the outer pump electrode 23 by applying an alternating voltage to the outer pump electrode 23 and the inner pump electrode 22. The second auxiliary pump control processing is a process of controlling the auxiliary pump cell 50 so that oxygen is alternately drawn from around the outer pump electrode 23 to around the auxiliary pump electrode 51 and pumped out from around the auxiliary pump electrode 51 to around the outer pump electrode 23 by applying an alternating voltage to the outer pump electrode 23 and the auxiliary pump electrode 51. By executing the second main pump control processing and / or the second auxiliary pump control processing, the oxygen concentration around the inner pump electrode 22 and / or the auxiliary pump electrode 51 changes alternately. The first internal cavity 20 (around the inner pump electrode 22) and the third internal cavity 61 (around the measurement electrode 44) communicate with each other via the third diffusion rate-limiting section 30, the second internal cavity 40 (around the auxiliary pump electrode 51), and the fourth diffusion rate-limiting section 60. Therefore, when the oxygen concentration around the inner pump electrode 22 and / or the auxiliary pump electrode 51 changes alternately, the oxygen concentration around the measurement electrode 44 also changes alternately following this change.Therefore, by executing the second main pump control process and / or the second auxiliary pump control process, similar to the execution of the second measurement pump control process, substances (such as carbon) adhering to the measurement electrode 44 can be oxidized by oxygen around the measurement electrode 44 and detached from the measurement electrode 44.

[0099] In the above-described embodiment, the CPU 97 is assumed to execute the refresh condition satisfaction process of FIG. 6, but it is not limited thereto. For example, the CPU 97 may execute the refresh condition satisfaction process of FIG. 10. The refresh condition satisfaction process of FIG. 10 is different from the refresh condition satisfaction process of FIG. 6 in that the process of step S310 is replaced with the process of step S314. For the processes that are the same as those of the refresh condition satisfaction process of FIG. 6 in the refresh condition satisfaction process of FIG. 10, the same step numbers are assigned, and detailed descriptions thereof are omitted.

[0100] In the process when the refresh condition in FIG. 10 is satisfied, when the CPU 97 determines in step S300 that the gas to be measured is in a lean atmosphere, as a refresh process, it executes heater control processing and third measurement pump control processing, and stops the operations of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) (step S314), and proceeds to step S320. Here, the third measurement pump control processing is a process of controlling the variable power supply 46 to control the measurement pump cell 41 so as to suck oxygen from around the outer pump electrode 23 to around the measurement electrode 44. When the third measurement pump control processing is executed, the direction of the pump current Ip2 is opposite to that when the first measurement pump control processing is executed. By executing the third measurement pump control processing, the oxygen concentration around the measurement electrode 44 becomes high. Therefore, the oxygen around the measurement electrode 44 can oxidize the substances (such as carbon) adhering to the measurement electrode 44 and cause them to desorb from the measurement electrode 44. Thereby, the catalytic function (reduction ability) of the measurement electrode 44 can be restored, suppressing a decrease in the detection accuracy of the concentration of a specific gas (NOx in the embodiment) in the gas to be measured, or reducing the offset value α of the pump current Ip2. The inventors have confirmed these through experiments and analysis. Moreover, when the gas to be measured is in a lean atmosphere, that is, when there is more oxygen around the measurement electrode 44, by executing the refresh process, more substances adhering to the measurement electrode 44 can be oxidized and desorbed from the measurement electrode 44.

[0101] The process when the refresh condition in FIG. 10 is satisfied has been described. Instead of the process when the refresh condition in FIG. 10 is satisfied, the CPU 97 may execute the process when the refresh condition in FIG. 11 is satisfied. The process when the refresh condition in FIG. 11 is satisfied corresponds to the process of replacing the process of step S310 in the process when the refresh condition in FIG. 7 with the process of step S314.

[0102] In the processing when the refresh conditions in FIGS. 10 and 11 are satisfied, the CPU 97 executes heater control processing and third measurement pump control processing as refresh processing and stops the operations of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) in step S314, but it is not limited to this. For example, as refresh processing, heater control processing and third main pump control processing may be executed while stopping the operations of the auxiliary pump cell 50 and the measurement pump cell 41. As refresh processing, heater control processing and third auxiliary pump control processing may be executed while stopping the operations of the main pump cell 21 and the measurement pump cell 41. As refresh processing, heater control processing and a plurality of the third measurement pump control processing, the third main pump control processing, and the third auxiliary pump control processing may be executed. The third main pump control processing is a process of controlling the main pump cell 21 to suck oxygen from around the outer pump electrode 23 to around the inner pump electrode 22. The third auxiliary pump control processing is a process of controlling the auxiliary pump cell 50 to suck oxygen from around the outer pump electrode 23 to around the auxiliary pump electrode 51. By executing the third main pump control processing and / or the third auxiliary pump control processing, the oxygen concentration around the inner pump electrode 22 and / or the auxiliary pump electrode 51 increases. The first internal cavity 20 (around the inner pump electrode 22) and the third internal cavity 61 (around the measurement electrode 44) communicate with each other via the third diffusion rate-limiting section 30, the second internal cavity 40 (around the auxiliary pump electrode 51), and the fourth diffusion rate-limiting section 60. Therefore, when the oxygen concentration around the inner pump electrode 22 and / or the auxiliary pump electrode 51 increases, the oxygen concentration around the measurement electrode 44 also increases accordingly. Thus, by executing the third main pump control processing and / or the third auxiliary pump control processing, similar to the execution of the third measurement pump control processing, substances (such as carbon) adhering to the measurement electrode 44 can be oxidized by the oxygen around the measurement electrode 44 and detached from the measurement electrode 44.

[0103] In the processing when the refresh condition in FIGS. 8 to 11 is satisfied, when the CPU 97 determines in step S300 that the gas to be measured is in a lean atmosphere, it executes the refresh process. When it determines that the gas to be measured is not in a lean atmosphere, it executes the first adjustment pump control process, the first measurement pump control process, the heater control process, and the concentration detection process. However, it is not limited to this. For example, the CPU 97 may execute the refresh process regardless of whether the gas to be measured is in a lean atmosphere. That is, the processes in steps S300 and S390 may be excluded from the processing when the refresh condition in FIGS. 8 and 10 is satisfied. The process in step S300 may be excluded from the processing when the refresh condition in FIGS. 9 and 11 is satisfied.

[0104] In the processing when the refresh condition in FIGS. 8 to 11 is satisfied, as part of the refresh process, the CPU 97 executes the heater control process, specifically, the process of controlling the heater power supply 74 so that the temperature of the heater 71 becomes the target temperature Th* (for example, 800°C). However, it is not limited to this. As long as the CPU 97 executes the process of controlling the heater power supply 74 so that the heater 71 generates heat to the extent that the solid electrolyte of the sensor element 101 is activated.

[0105] In the above-described embodiment, the CPU 97 executes the processing when the refresh condition in FIG. 6 is satisfied. However, it is not limited to this. For example, the CPU 97 may execute the processing when the refresh condition in FIG. 12 is satisfied. The processing when the refresh condition in FIG. 12 is satisfied is different from the processing when the refresh condition in FIG. 6 in that the process in step S390 is replaced with the process in step S312 in FIG. 8. For the processes in the processing when the refresh condition in FIG. 12 that are the same as the processing when the refresh condition in FIG. 6, the same step numbers are assigned and detailed descriptions are omitted.

[0106] In the process when the refresh condition in FIG. 12 is satisfied, when the CPU 97 determines in step S300 that the gas to be measured is in a lean atmosphere, as a refresh process, the CPU 97 executes heater control processing and stops the operations of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) and the measurement pump cell 41 (step S310). On the other hand, when the CPU 97 determines in step S300 that the gas to be measured is not in a lean atmosphere, as a refresh process, the CPU 97 executes heater control processing and second measurement pump control processing and stops the operation of the adjustment pump cells (main pump cell 21 and auxiliary pump cell 50) (step S312). Therefore, when the gas to be measured is in a lean atmosphere, the power consumption of the gas sensor 100 can be suppressed by stopping the operations of the adjustment pump cells and the measurement pump cell 41. Also, when the gas to be measured is not in a lean atmosphere, although the oxygen concentration in the gas to be measured is relatively low, by executing the second measurement pump control processing, the oxygen concentration around the measurement electrode 44 can be alternately changed (increased and decreased alternately).

[0107] In the process when the refresh condition in FIG. 12 is satisfied, when the CPU 97 determines in step S300 that the gas to be measured is not in a lean atmosphere, as a refresh process, the CPU 97 executes heater control processing and second measurement pump control processing and stops the operation of the adjustment pump cells, but it is not limited to this. When the CPU 97 determines in step S300 that the gas to be measured is not in a lean atmosphere, as a refresh process, the CPU 97 may execute heater control processing and third measurement pump control processing and stop the operation of the adjustment pump cells.

[0108] In the process when the refresh condition in FIGS. 6, 8, 10, and 12 is satisfied, as one of the end conditions for ending the refresh process, the condition that the refresh cumulative time Trf is equal to or greater than the threshold value Trfth is used, but it is not limited to this. For example, instead of the refresh cumulative time Trf, the duration of the refresh process may be used.

[0109] In the processing when the refresh conditions of FIGS. 6, 8, 10, and 12 are satisfied, the end conditions for ending the refresh process are the condition that the offset value α of the pump current Ip2 is less than the threshold value αth2, and the condition that the cumulative refresh time Trf is equal to or greater than the threshold value Trfth. However, it is not limited to this. For example, the end condition may be only the condition that the offset value α of the pump current Ip2 is less than the threshold value αth2.

[0110] In the above-described embodiment, the CPU 97 determines whether the gas to be measured is in a rich atmosphere or a lean atmosphere based on the reference voltage Vref of the sensor cell 83. However, it is not limited to this. For example, the CPU 97 may determine whether the gas to be measured is in a rich atmosphere or a lean atmosphere based on the pump current Ip0 that flows when the main pump cell 21 adjusts the oxygen concentration in the first internal cavity 20 by the first main pump control process. The pump current Ip0 during the execution of the first main pump control process changes according to the oxygen concentration of the gas to be measured flowing into the gas to be measured flow path from the gas inlet 10 (that is, the gas to be measured outside the sensor element 101). Therefore, the CPU 97 may determine whether the gas to be measured is in a rich atmosphere or a lean atmosphere by comparing the pump current Ip0 during the execution of the first main pump control process with the threshold value Ith. The threshold value Ith is determined as the pump current Ip0 during the execution of the first main pump control process when the air-fuel ratio of the gas to be measured is the stoichiometric air-fuel ratio. Note that instead of determining whether the gas to be measured is in a rich atmosphere or a lean atmosphere using the reference voltage Vref or the pump current Ip0, the CPU 97 may determine whether the gas to be measured is in a rich atmosphere or a lean atmosphere using another voltage or current of the sensor element 101, or may input whether the gas to be measured is in a rich atmosphere or a lean atmosphere through communication with the engine ECU 140 or another sensor.

[0111] In the above-described embodiment, as the first main pump control process, the CPU 97 sets the target value V0* of the voltage V0 based on the pump current Ip1 (feedback control) so that the pump current Ip1 becomes the target value Ip1*, and feedback-controls the pump voltage Vp0 so that the voltage V0 becomes the target value V0*. However, the present invention is not limited to this. For example, as the first main pump control process, the CPU 97 may feedback-control the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1*. That is, the control unit 96 may omit the acquisition of the voltage V0 from the oxygen partial pressure detection sensor cell 80 for main pump control and the setting of the target value V0*, and directly control the pump voltage Vp0 (and thus control the pump current Ip0) based on the pump current Ip1.

[0112] In the above-described embodiment, the outer pump electrode 23 serves as an electrode paired with the inner pump electrode 22 in the main pump cell 21 (also referred to as the outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 in the auxiliary pump cell 50 (also referred to as the outer auxiliary pump electrode), and an electrode paired with the measurement electrode 44 in the measurement pump cell 41 (also referred to as the outer measurement electrode). However, the present invention is not limited to this. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be disposed on the outer surface of the element body 102 in contact with the gas to be measured separately from the outer pump electrode 23.

[0113] In the above-described embodiment, the oxygen concentration adjustment chamber is provided with the first internal cavity 20 and the second internal cavity 40, but the present invention is not limited thereto. For example, the oxygen concentration adjustment chamber may further include another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above-described embodiment, the adjustment pump cell is provided with the main pump cell 21 and the auxiliary pump cell 50, but the present invention is not limited thereto. For example, the adjustment pump cell may further include another pump cell, or one of the main pump cell 21 and the auxiliary pump cell 50 may be omitted. For example, when the oxygen concentration of the gas to be measured can be sufficiently reduced by only the main pump cell 21, the auxiliary pump cell 50 may be omitted. When the auxiliary pump cell 50 is omitted, the control unit 96 only needs to perform only the first main pump control process as the first adjustment pump control process. In this case, in the first main pump control process, the setting of the target value V0* based on the pump current Ip1 described above may be omitted. Specifically, a predetermined target value V0* is stored in the storage unit 98 in advance, and the control unit 96 may control the main pump cell 21 by feedback-controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0*.

[0114] In the above-described embodiment, the sensor element 101 of the gas sensor 100 is provided with the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, but the present invention is not limited thereto. For example, as shown in the sensor element 201 of the modification of FIG. 13, the third internal cavity 61 may not be provided. In the sensor element 201 of the modification of FIG. 13, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, there are a gas inlet 10, a first diffusion rate-limiting portion 11, a buffer space 12, a second diffusion rate-limiting portion 13, a first internal cavity 20, a third diffusion rate-limiting portion 30, and a second internal cavity 40, which are adjacently formed in a communicating manner in this order. The measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The measurement electrode 44 is covered by a fourth diffusion rate-limiting portion 45. The fourth diffusion rate-limiting portion 45 is a film made of a ceramic porous body such as alumina (Al2O3). The fourth diffusion rate-limiting portion 45, similar to the fourth diffusion rate-limiting portion 60 of the above-described embodiment, plays a role of limiting the amount of NOx flowing into the measurement electrode 44. Further, the fourth diffusion rate-limiting portion 45 also functions as a protective film for the measurement electrode 44. The ceiling electrode portion 51a of the auxiliary pump electrode 51 is formed up to directly above the measurement electrode 44. Even with the sensor element 201 having such a configuration, similar to the above-described embodiment, the NOx concentration can be detected by the measurement pump cell 41. In the sensor element 201 of FIG. 13, the periphery of the measurement electrode 44 functions as a measurement chamber. That is, the periphery of the measurement electrode 44 plays the same role as the third internal cavity 61.

[0115] In the above-described embodiment, the sensor element 101 is configured to detect the NOx concentration in the gas to be measured. However, the present invention is not limited thereto as long as it can detect the concentration of a specific gas in the gas to be measured. For example, the specific gas may be an oxide other than NOx. When the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61 in the same manner as in the above-described embodiment. Therefore, the measurement pump cell 41 can detect the specific gas concentration by obtaining a detection value (e.g., pump current Ip2) corresponding to this oxygen. The specific gas may be a non-oxide such as ammonia. When the specific gas is a non-oxide, oxygen is generated when the gas after conversion is reduced in the third internal cavity 61 by converting the specific gas into an oxide (e.g., converting ammonia into NO). Therefore, the measurement pump cell 41 can detect the specific gas concentration by obtaining a detection value (e.g., pump current Ip2) corresponding to this oxygen. For example, ammonia can be converted into NO in the first internal cavity 20 by the inner pump electrode 22 in the first internal cavity 20 functioning as a catalyst.

[0116] In the above-described embodiment, the element body 102 of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6). However, the present invention is not limited thereto. The element body 102 only needs to include at least one oxygen ion-conductive solid electrolyte layer. For example, in FIG. 2, layers 1 to 5 other than the second solid electrolyte layer 6 may be layers made of a material other than the solid electrolyte layer (e.g., a layer made of alumina). In this case, each electrode included in the sensor element 101 may be disposed on the second solid electrolyte layer 6. For example, the measurement electrode 44 in FIG. 2 may be disposed on the lower surface of the second solid electrolyte layer 6. Further, instead of providing the reference gas introduction space 43 in the first solid electrolyte layer 4, it may be provided in the spacer layer 5, and instead of providing the reference gas introduction layer 48 between the first solid electrolyte layer 4 and the third substrate layer 3, it may be provided between the second solid electrolyte layer 6 and the spacer layer 5. The reference electrode 42 may be provided behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

Industrial Applicability

[0117] The present invention can be used for a gas sensor that detects the concentration of a specific gas such as NOx in a gas to be measured such as the exhaust gas of an engine.

Explanation of reference numerals

[0118] 1 First substrate layer, 2 Second substrate layer, 3 Third substrate layer, 4 First solid electrolyte layer, 5 Spacer layer, 6 Second solid electrolyte layer, 10 Gas inlet, 11 First diffusion rate limiting section, 12 Buffer space, 13 Second diffusion rate limiting section, 20 First internal cavity, 21 Main pump cell, 22 Inner pump electrode, 22a, 51a Ceiling electrode portion, 22b, 51b Bottom electrode portion, 23 Outer pump electrode, 24 Variable power source, 30 Third diffusion rate limiting section, 40 Second internal cavity, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 Fourth diffusion rate limiting section, 46 Variable power source, 48 Reference gas introduction layer, 49 Reference gas introduction portion, 49a Inlet portion, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 52 Variable power source, 60 Fourth diffusion rate limiting section, 61 Third internal cavity, 70 Heater section, 71 Heater, 72 Heater insulating layer, 73 Pressure release hole, 74 Heater power source, 75 Connector electrode, 80 Oxygen partial pressure detection sensor cell for main pump control, 81 Oxygen partial pressure detection sensor cell for auxiliary pump control, 82 Oxygen partial pressure detection sensor cell for measurement pump control, 83 Sensor cell, 95 Control device, 96 Control section, 97 CPU, 98 Storage section, 100 Gas sensor, 100a Gas sensor body, 101, 201 Sensor element, 102 Element body, 110 Protection cover, 111 Sensor assembly, 130 Exhaust pipe, 140 Engine ECU.

Claims

1. A gas sensor comprising a sensor element attached to an exhaust pipe of an engine and a control device, for detecting the concentration of a specific gas in the gas to be measured in the exhaust pipe, wherein the sensor element has a solid electrolyte layer with oxygen ion conductivity, and an element body provided therein with a gas flow passage for the gas to be measured for introducing and flowing the gas to be measured, a measurement pump cell having an inner measurement electrode disposed in a measurement chamber in the gas flow passage for the gas to be measured, and an outer measurement electrode disposed on the outer surface of the element body so as to contact the gas to be measured, an adjustment pump cell having an inner adjustment electrode disposed in an oxygen concentration adjustment chamber provided upstream of the measurement chamber in the gas flow passage for the gas to be measured, and an outer adjustment electrode disposed on the outer surface of the element body so as to contact the gas to be measured, and is provided with wherein the control device a first adjustment pump control process for controlling the adjustment pump cell so that the oxygen concentration in the oxygen concentration adjustment chamber is adjusted, a first measurement pump control process for controlling the measurement pump cell so as to pump out oxygen from around the inner measurement electrode to around the outer measurement electrode, a concentration detection process for detecting the concentration of the specific gas in the gas to be measured based on the measurement pump current flowing through the measurement pump cell by the first measurement pump control process, and executes Furthermore, when a condition that an offset value of the measurement pump current is equal to or greater than a first threshold value and / or a condition that a cumulative time during which the sensor element is exposed to the gas to be measured in a rich atmosphere is equal to or greater than a first predetermined time is satisfied, the control device executes a refresh process for recovering the catalytic function of the measurement electrode, Gas sensor.

2. The gas sensor according to claim 1, wherein the control device executes the first adjustment pump control process, the first measurement pump control process, and an offset value detection process for detecting the offset value based on the measurement pump current when a concentration zero condition under which the concentration of the specific gas in the gas to be measured can be regarded as zero is satisfied, Gas sensor.

3. The gas sensor according to claim 2, wherein the concentration zero condition is an OR condition of a condition that a duration of fuel cut of the engine is equal to or greater than a second predetermined time and a condition that a duration of engine stop is equal to or greater than a third predetermined time, Gas sensor.

4. The gas sensor according to claim 2 or 3, After the start of the refresh process, the control device ends the refresh process when any one of the following conditions is met: the condition that the offset value reaches less than a second threshold value that is less than or equal to the first threshold value; the condition that the cumulative time or the continuous time of the refresh process is equal to or more than a fourth predetermined time. Gas sensor.

5. The gas sensor according to claim 4, wherein After the start of the refresh process, when the zero concentration condition is satisfied, the control device interrupts the refresh process and executes the first adjustment pump control process, the first measurement pump control process, and the offset value detection process. When the offset value is less than or equal to the second threshold value, the control device ends the refresh process. When the offset value exceeds the second threshold value, the control device resumes the refresh process. Gas sensor.

6. The gas sensor according to claim 2, wherein After the start of the refresh process, when the condition that the offset value reaches less than a second threshold value that is less than or equal to the first threshold value is satisfied, the control device ends the refresh process. Furthermore, after the start of the refresh process, when the control device cannot detect the offset value because the zero concentration condition is not satisfied, the control device interrupts the refresh process. Then, when the zero concentration condition is satisfied, the control device resumes the refresh process. Gas sensor.

7. The gas sensor according to claim 1, wherein The sensor element further includes a heater that heats the element body. When the gas to be measured is in a lean atmosphere, as the refresh process, the control device causes the heater to generate heat and stops the first adjustment pump control process and the first measurement pump control process. Gas sensor.

8. The gas sensor according to claim 1, wherein The control device, as the refresh process, controls the measurement pump cell so as to alternately perform oxygen uptake from around the outer measurement electrode to around the inner measurement electrode and oxygen extraction from around the inner measurement electrode to around the outer measurement electrode by applying an alternating voltage between the outer measurement electrode and the inner measurement electrode, and a second measurement pump control process, and controls the adjustment pump cell so as to alternately perform oxygen uptake from around the outer adjustment electrode to around the inner adjustment electrode and oxygen extraction from around the inner adjustment electrode to around the outer adjustment electrode by applying an alternating voltage between the outer adjustment electrode and the inner adjustment electrode, and executes at least one of a second adjustment pump control process. Gas sensor.

9. The gas sensor according to claim 8, wherein the control device executes the refresh process when the gas to be measured is in a lean atmosphere. Gas sensor.

10. The gas sensor according to claim 8 or 9, wherein the alternating voltage is any one of a rectangular wave, a sine wave, a sawtooth wave, and a triangular wave. Gas sensor.

11. The gas sensor according to claim 1, wherein the control device, as the refresh process, controls the measurement pump cell so as to take in oxygen from around the outer measurement electrode to around the inner measurement electrode, and a third measurement pump control process, and controls the adjustment pump cell so as to take in oxygen from around the outer adjustment electrode to around the inner adjustment electrode, and executes at least one of a third measurement pump control process. Gas sensor.

12. The gas sensor according to claim 11, wherein the control device executes the refresh process when the gas to be measured is in a lean atmosphere. Gas sensor.

13. The gas sensor according to any one of claims 7, 9, and 12, wherein the sensor element includes a reference electrode disposed inside the element body so as to contact a reference gas serving as a reference for detecting the concentration of the specific gas, and a reference voltage detection sensor cell that detects a reference voltage between the reference electrode and the outer measurement electrode or the outer adjustment electrode, and further includes, wherein the control device executes a lean determination process for determining whether the gas to be measured is in the lean atmosphere using the reference voltage. Gas sensor.

14. The gas sensor according to claim 1 or 2, wherein the outer measurement electrode and the outer adjustment electrode are common electrodes, gas sensor.

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