JP2016080684A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor which has a gas detection accuracy that does not decrease due to rapid change in the electromotive force of cells caused by change in the atmosphere of a measurement target gas and which has a solid electrolyte layer with maintained characteristics.SOLUTION: There is provided a gas sensor 1 including a sensor element 100 having a cell 140 and a porous layer 113a, the cell 140 having a plate-like solid electrolyte layer 111 and an electrode 110 on a surface of the solid electrolyte layer, and the porous layer 113a being on a surface of the electrode and being capable of exchanging gas between the electrode and the outside. The outer periphery of the electrode is located inner than the outer periphery of the porous layer when seen from the direction in which the porous layer is deposited on the electrode, and a ventilatory resistor 150 is formed in the gas sensor 1, which is on or in the porous layer, is separated from the electrode, and overlaps with a part of an overlapping region S of the electrode and the porous layer when viewed from the direction of the deposition.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a gas sensor suitably used for detecting the gas concentration of a specific gas contained in combustion gas or exhaust gas of, for example, a combustor or an internal combustion engine.

Conventionally, a gas sensor for detecting the concentration of a specific component in the exhaust gas of an internal combustion engine (oxygen, NO _x, etc.) have been used (Patent Documents 1 and 2). For example, in the case of the gas sensor described in Patent Document 1, as shown in FIG. 13, the gas sensor has a sensor element 1000 inside, and the sensor element 1000 has two cells 1300 and 1400.
Among these, the cell 1400 has electrodes 1080 and 1100 formed on both surfaces of the solid electrolyte layer 1090, and the electrode 1100 pumps or pumps oxygen in the exhaust gas between the outside through the porous layer 1130. It is a pumping cell to perform. On the other hand, the cell 1300 is an oxygen concentration detection cell that faces the measurement chamber 1070 and outputs an output voltage (electromotive force) corresponding to the oxygen concentration in the exhaust gas in the measurement chamber 1070. Then, a voltage (Vp voltage) is applied to the pumping cell 1400 so that the output voltage becomes constant, a pump current Ip is supplied, and the oxygen concentration in the exhaust gas corresponding to the pump current Ip is detected. Yes.

JP 2012-173146 A Japanese Patent No. 4966266

Incidentally, as shown in FIG. 14, when the air-fuel ratio (A / F) in the exhaust gas in the measurement chamber 1070 changes from rich to lean, the output voltage of the oxygen concentration detection cell 1300, which is a λ sensor, changes abruptly. Accordingly, the Vp voltage applied to the pumping cell 1400 also changes abruptly. Then, an extra pulsating current Ri called an overshoot phenomenon (ripple phenomenon) is superimposed on the pump current Ip output from the pumping cell 1400, and the detected value of the oxygen concentration becomes inaccurate. .
As shown in FIG. 15, this is because a capacitor circuit is formed between the solid electrolyte layer 1090 of the pumping cell 1400 and the electrode 1100, and the voltage between the capacitor electrodes (Vp voltage) changes with time. Probably, this is because the electric charge flows between the electrodes of the capacitor in proportion to the time. That is, the capacitance C of the capacitor in this capacitor circuit, the change in charge ΔQ of the capacitor, and the change ΔVp in the Vp voltage between the electrodes of the capacitor are in the relationship of the following equation (1).
ΔQ = C × ΔVp (1)
Since ΔQ = Ri,
Ri = C × ΔVp (2)
It becomes. From equation (2), the pulsating current (overshoot current) Ri is reduced as ΔVp, which is the time change of the Vp voltage, is reduced.
On the other hand, as shown in FIG. 16, when the air-fuel ratio (A / F) in the exhaust gas does not cross the stoichiometric point, the output voltage of the oxygen concentration detection cell 1300 and thus the Vp voltage do not change abruptly. The pulsating current Ri is not superimposed on Ip.

Then, as a measure to reduce ΔVp, it is considered that the change in electromotive force of the pumping cell 1400 is prevented, that is, (1) the ventilation resistance of the porous layer 1130 is increased, and (2) the electrode reaction at the electrode 1100 is delayed. It is done.
Among these, for (1), there are measures to make the porous layer 1130 dense or to reduce its size. However, since the porous layer 1130 is generally manufactured by firing insulator particles, there is a limit to making the pore distribution and thickness constant. For this reason, even if the porous layer 1130 is made dense or small, the porosity and size vary locally, and it is difficult to obtain a stable effect, and the production of the porous layer 1130 becomes difficult. is there.
As for (2), measures can be taken to make the electrode 1100 dense or thick. However, when the thickness of the electrode 1100 is increased, the amount of noble metal (Pt or the like) that is an electrode material increases, leading to an increase in cost of the electrode. Further, when the electrode 1100 is made dense, the three-phase interface between the electrode 1100, the solid electrolyte layer 1090, and the gas phase is reduced, and the electrode resistance (internal resistance of the sensor element) is increased, and as a result, the operating voltage of the sensor element is increased. There is a problem that blackening described later and restrictions on the electric circuit occur. Further, in a rich atmosphere, the electrode 1100 pumps oxygen from an oxygen source (H 2 O, CO 2, etc. in the exhaust gas) to the measurement chamber 1070, but the gas reaching the electrode 1100 decreases when the electrode 1100 is made dense or thick. As a result, the measurement range on the rich side becomes narrow.

On the other hand, the present inventor, regarding (1), while making the porosity and size of the porous layer 1130 equivalent to the conventional one, it overlaps with a part of the porous layer 1130, so that the porous layer 1130 is externally passed through the porous layer 1130. A measure for reducing the amount of oxygen source (exhaust gas) reaching the electrode 1100 was examined. In this case, the above problems (1) and (2) can be suppressed.
However, it has been found that depending on the position overlapping the porous layer 1130, characteristic deterioration of the solid electrolyte layer 1090 called blackening occurs. Blackening is a phenomenon in which the metal oxide in the solid electrolyte layer 1090 is reduced due to a lack of oxygen in the solid electrolyte layer 1090 in a state where an electrode reaction occurs through the solid electrolyte layer 1090. When blackening occurs, the characteristics (ion conductivity) of the solid electrolyte layer 1090 deteriorate, and the pumping performance decreases.
For example, as shown in FIG. 17, when a ventilation resistance layer 1200 is provided between the porous layer 1130 and the electrode 1100 so as to be in contact with the outer peripheral side of the porous layer 1130, the solid electrolyte layer overlapping the ventilation resistance layer 1200 is provided. Blackening may occur at the 1090 site Br. In other words, in the portion Br, although the supply of the oxygen source (exhaust gas G) from the porous layer 1130 is hindered by the ventilation resistance layer 1200, the electrodes 1100 and 1080 sandwiching the solid electrolyte layer 1090 from the solid electrolyte layer 1090. An electrode reaction that forcibly moves oxygen ions occurs, resulting in a shortage of oxygen in the solid electrolyte layer 1090.

  Therefore, the present invention suppresses a decrease in gas detection accuracy due to a sudden change in cell electromotive force in accordance with a change in the atmosphere of a gas to be measured, and a gas sensor that suppresses deterioration in characteristics of the solid electrolyte layer. For the purpose of provision.

  In order to solve the above problems, a gas sensor according to the present invention comprises a cell having a plate-shaped solid electrolyte layer and an electrode disposed on the surface of the solid electrolyte layer, and is laminated on the surface of the electrode. A gas sensor having a porous layer through which gas can flow in and out, wherein the outer peripheral edge of the electrode is positioned inside the outer peripheral edge of the porous layer when viewed from the stacking direction. In addition, a ventilation resistor is provided on the surface or inside of the porous layer so as to be separated from the electrode and overlap a part of an overlapping region of the electrode and the porous layer when viewed from the stacking direction.

According to this gas sensor, the amount of oxygen source in the gas that reaches the electrode from the outside through the porous layer decreases as the ventilation resistor becomes the ventilation resistance, and the gas exchange rate on the electrode is slow. Become. Thereby, the time change of the voltage in the cell which performs oxygen pumping becomes small, the pulsation current (overshoot current) superimposed on a pump current can be reduced, and the fall of the detection accuracy of gas can be controlled. In addition, the air flow resistance can be stably increased and the production of the porous layer becomes difficult as compared with the case where the air resistance is realized by making the porous layer itself dense or small in size. Is also avoided. Similarly, since it is not necessary to make the electrode itself dense or thick, it suppresses the cost increase of the electrode and suppresses the occurrence of blackening due to the increase in electrode resistance (internal resistance of the sensor element). It can also be suppressed that the measurement range on the side becomes narrow.
In addition, when the ventilation resistor is formed by printing and applying an insulating paste, the dimensional accuracy by printing is high, so the dimensional accuracy of the ventilation resistor is also high, and the above effects can be stably exhibited. it can.

  Also, the gas sensor of the present invention comprises a cell having a plate-like solid electrolyte layer and an electrode disposed on the surface of the solid electrolyte layer, and is laminated on the surface of the electrode, and gas is passed between the electrode and the outside. A gas sensor having a sensor element comprising a porous layer capable of entering and exiting, wherein the electrode and the porous layer when viewed from the stacking direction while being separated from the electrode on the surface or inside of the porous layer A gas sensor having a ventilation resistor that overlaps a part of the overlapping region with the porous layer, the sensor element having the cell and the porous layer, and not having the ventilation resistor is used as a reference gas sensor, and the reference When the Ip value when the output of the gas sensor is stabilized is 100% and the maximum value of the overshoot current is represented by (100 + X)%, the maximum value of the overshoot current of the gas sensor is (100 + X / 2)%. It is below. However, the overshoot current is output from the cell functioning as a pumping cell that pumps or pumps oxygen in the gas introduced into the measurement chamber when the air-fuel ratio in the gas changes from rich to lean. This is the maximum value of the pulsating current superimposed on the pump current Ip.

According to this gas sensor, the amount of oxygen source in the gas that reaches the electrode from the outside through the porous layer decreases as the ventilation resistor becomes the ventilation resistance, and the gas exchange rate on the electrode is slow. Become. Thereby, the time change of the voltage in the cell which performs oxygen pumping becomes small, the pulsation current (overshoot current) superimposed on a pump current can be reduced, and the fall of the detection accuracy of gas can be controlled. In addition, the air flow resistance can be stably increased and the production of the porous layer becomes difficult as compared with the case where the air resistance is realized by making the porous layer itself dense or small in size. Is also avoided. Similarly, since it is not necessary to make the electrode itself dense or thick, it suppresses the cost increase of the electrode and suppresses the occurrence of blackening due to the increase in electrode resistance (internal resistance of the sensor element). It can also be suppressed that the measurement range on the side becomes narrow.
In addition, when the ventilation resistor is formed by printing and applying an insulating paste, the dimensional accuracy by printing is high, so the dimensional accuracy of the ventilation resistor is also high, and the above effects can be stably exhibited. it can.

The ventilation resistor may be gas impermeable.
According to this gas sensor, the ventilation resistor functions as a ventilation resistor that reliably reduces the amount of oxygen source in the gas that reaches the electrode from the outside via the porous layer.

When viewed from the stacking direction, the ventilation resistor may overlap with an area of 25.0 to 97.5% of the overlapping region.
According to this gas sensor, the above-described effect as the ventilation resistance of the ventilation resistor is exhibited, the ventilation resistance is excessively increased due to the overlapping region, the electrode resistance (internal resistance of the sensor element) is increased, and blackening is caused. It is possible to eliminate problems that occur or pump current hardly flows.

The sensor element includes, as the cell, a pumping cell that pumps or pumps oxygen in the measurement gas introduced into the measurement chamber, and further outputs according to the oxygen concentration in the measurement gas in the measurement chamber An oxygen sensor element having an oxygen concentration detection cell for outputting a voltage, wherein a pump current is passed through the pumping cell so that the output voltage is constant, and the oxygen concentration in the gas to be measured according to the pump current It may be an oxygen sensor element that detects.
According to this gas sensor, the present invention can be applied to an oxygen sensor element.

The sensor element includes, as the cell, a first pumping cell that pumps or pumps oxygen in a measurement gas introduced into a measurement chamber and adjusts the oxygen concentration in the measurement chamber, and further adjusts the oxygen concentration. the may be a NO _x sensor element having a second pumping cell pumping current corresponding to the concentration of NO _x in the measurement gas which is.
According to this gas sensor, the present invention can be applied to a NO _x sensor element.

The electrode may contain 50% by mass or more of Pt and Au in total.
According to this gas sensor, the gas reaction on the electrode can be moderated, the overshoot or reverse shoot of the pump current at approximately λ = 1 can be reduced, and the detection accuracy can be improved.
The electrode contains Pt and Au in the form of a Pt—Au alloy, a mixture of Pt and Au (a paste containing Pt and Au particles that does not become an alloy), and Au plating on the surface of Pt. The layer structure obtained by impregnating Pt with Au is exemplified. The electrode preferably contains 0.1 to 10% by mass of Au. This is because in the case of a layer structure in which the surface of Pt is Au-plated, the Au plating is extremely thin and functions even when the Au content is 0.1% by mass. As a method for impregnating Pt with Au, there is a method in which a Pt substrate is impregnated with an Au salt (for example, HAuCl ₄ ) and then baked to thermally decompose the salt to leave Au.

  According to the present invention, there is provided a gas sensor that suppresses a rapid change in the electromotive force of a cell due to a change in the atmosphere of a gas to be measured and decreases the gas detection accuracy, and suppresses deterioration in characteristics of the solid electrolyte layer. can get.

It is sectional drawing which follows the longitudinal direction of the gas sensor (oxygen sensor) which concerns on embodiment of this invention. It is a model exploded perspective view of a sensor element. It is a partial expanded sectional view of the front end side of a sensor element. It is sectional drawing orthogonal to the axial direction of a sensor element. It is the top view seen from the lamination direction which shows the positional relationship of a 4th electrode and a porous layer. It is sectional drawing which follows the AA line of FIG. It is a schematic diagram which shows the effect | action by a ventilation resistance layer separating from the 4th electrode. It is a schematic diagram which shows the effect | action by the ventilation resistance layer being in contact with the 4th electrode. It is sectional drawing orthogonal to the axial direction which shows the modification of a ventilation resistance layer. It is sectional drawing orthogonal to the axial direction which shows another modification of a ventilation resistance layer. It is a cross-sectional view taken along the longitudinal direction of the NO _x sensor element. It is a figure which shows the time change of the pump current Ip of an oxygen pump cell when the overlap ratio is 75% and the air-fuel ratio (A / F) in the gas is changed from rich to lean. It is sectional drawing orthogonal to the axial direction of the sensor element in the conventional gas sensor. It is a figure which shows the time change of the pump current Ip of an oxygen pumping cell when changing the air fuel ratio (A / F) in gas from rich to lean. It is a figure which shows the equivalent circuit of an oxygen pumping cell. It is a figure which shows the time change of the pump current Ip of an oxygen pumping cell when the air fuel ratio (A / F) in exhaust gas does not straddle the stoichiometric point. It is sectional drawing which shows generation | occurrence | production of blackening at the time of providing a ventilation resistance layer between the porous layer and electrode of an oxygen pumping cell.

Hereinafter, embodiments of the present invention will be described.
1 is a cross-sectional view taken along the longitudinal direction (axis L direction) of a gas sensor (oxygen sensor) 1 according to an embodiment of the present invention, FIG. 2 is a schematic exploded perspective view of a sensor element 100, and FIG. 3 is an axis L of the sensor element 100. 4 is a cross-sectional view orthogonal to the direction of the axis L of the sensor element 100. FIG.

  As shown in FIG. 1, the gas sensor 1 includes a sensor element 100, a metal shell (housing) 30 that holds the sensor element 100 and the like inside, a protector 24 that is attached to the tip of the metal shell 30, and the like. The sensor element 100 is arranged so as to extend in the direction of the axis L.

The sensor element 100 includes a heater unit 200 and a detection element unit 300.
As shown in FIG. 2, the heater unit 200 includes a first base 101 and a second base 103 mainly composed of alumina, and a heating element 102 mainly composed of platinum sandwiched between the first base 101 and the second base 103. have. The heating element 102 has a heating part 102a located on the tip side and a pair of heater lead parts 102b extending from the heating part 102a along the longitudinal direction of the first base 101. The terminal of the heater lead portion 102b is electrically connected to the heater side pad 120 via a conductor formed in the heater side through hole 101a provided in the first base 101. A laminate of the first substrate 101 and the second substrate 103 corresponds to the insulating ceramic body.

  The detection element unit 300 includes two cells, an oxygen concentration detection cell 130 and an oxygen pump cell 140. The oxygen concentration detection cell 130 is formed of a first solid electrolyte layer 105 and a first electrode 104 and a second electrode 106 formed on both surfaces of the first solid electrolyte 105. The first electrode 104 is formed of a first electrode portion 104 a and a first lead portion 104 b extending from the first electrode portion 104 a along the longitudinal direction of the first solid electrolyte layer 105. The second electrode 106 is formed of a second electrode portion 106 a and a second lead portion 106 b extending from the second electrode portion 106 a along the longitudinal direction of the first solid electrolyte layer 105.

  The terminals of the first lead portion 104b are first through holes 105a provided in the first solid electrolyte layer 105, second through holes 107a provided in the insulating layer 107 described later, and second terminals provided in the second solid electrolyte layer 109. The detection element side pads 121 are electrically connected through conductors formed in the four through holes 109a and the sixth through holes 111a provided in the insulating protective layer 111, respectively. On the other hand, the end of the second lead portion 106b is a third through hole 107b provided in the insulating layer 107 described later, a fifth through hole 109b provided in the second solid electrolyte layer 109, and a seventh through hole provided in the insulating protective layer 111. The detection element side pad 121 is electrically connected through a conductor formed in each of the holes 111b.

  On the other hand, the oxygen pump cell 140 is formed of the second solid electrolyte layer 109 and the third electrode 108 and the fourth electrode 110 formed on both surfaces of the second solid electrolyte layer 109. The third electrode 108 is formed of a third electrode portion 108 a and a third lead portion 108 b extending from the third electrode portion 108 a along the longitudinal direction of the second solid electrolyte layer 109. The fourth electrode 110 is formed of a fourth electrode portion 110 a and a fourth lead portion 110 b extending from the fourth electrode portion 110 a along the longitudinal direction of the second solid electrolyte layer 109.

  And the terminal of the 3rd lead part 108b is a detection element via the conductor formed in each of the 5th through hole 109b provided in the 2nd solid electrolyte layer 109, and the 7th through hole 111b provided in the insulating protection layer 111. It is electrically connected to the side pad 121. On the other hand, the end of the fourth lead portion 110b is electrically connected to the detection element side pad 121 via a conductor formed in an eighth through hole 111c provided in an insulating protective layer 111 described later. The second lead portion 106b and the third lead portion 108b are at the same potential.

The first solid electrolyte layer 105 and the second solid electrolyte layer 109 are partially stabilized zirconia sintered bodies obtained by adding yttria (Y ₂ O ₃ ) or calcia (CaO) as a stabilizer to zirconia (ZrO ₂ ). It is composed of

  The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 can be formed of a platinum group element. Pt, Rh, Pd etc. can be mentioned as a suitable platinum group element which forms these, These can also be used individually by 1 type, and can also use 2 or more types together.

  However, the heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 are mainly composed of Pt in consideration of heat resistance and oxidation resistance. It is even more preferable to form it. Furthermore, the heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 include ceramic components in addition to the main platinum group element. It is preferable to contain. This ceramic component is preferably the same component as the main material on the laminated side (for example, the main component of the first solid electrolyte layer 105 and the second solid electrolyte layer 109) from the viewpoint of fixation. .

  An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130. The insulating layer 107 includes an insulating portion 114 and a diffusion rate controlling portion 115. In the insulating portion 114 of the insulating layer 107, a hollow gas detection chamber 107c is formed at a position corresponding to the second electrode portion 106a and the third electrode portion 108a. The gas detection chamber 107c communicates with the outside in the width direction of the insulating layer 107, and the communication portion has a diffusion rate-determining method that realizes gas diffusion between the outside and the gas detection chamber 107c under a predetermined rate-limiting condition. Part 115 is arranged.

  The insulating part 114 is not particularly limited as long as it is an insulating ceramic sintered body, and examples thereof include oxide ceramics such as alumina and mullite.

  The diffusion control part 115 is a porous body made of alumina. The diffusion rate-determining unit 115 performs rate-limiting when the detection gas flows into the gas detection chamber (measurement chamber) 107c.

An insulating protective layer 111 is laminated on the surface of the second solid electrolyte layer 109 so as to sandwich the fourth electrode 110. A substantially rectangular through hole 112a is provided on the front end side of the insulating protective layer 111 so as to surround the fourth electrode portion 110a, and a porous layer 113a is embedded in the through hole 112a. The porous layer 113a covers the fourth electrode portion 110a, protects the fourth electrode portion 110a from poisoning, and is exposed to the outside so that gas is passed between the fourth electrode portion 110a and the outside via the porous layer 113a. Can enter and exit.
Further, on the surface facing the outside of the porous layer 113a, a rectangular annular insulating insulating resistance layer 150 is formed, covering the outer peripheral side of the porous layer 113a and opening the central portion of the porous layer 113a. .
The sensor element 100 of the present embodiment flows between the electrodes of the oxygen pump cell 140 so that the Vs voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130 becomes a predetermined value (for example, 450 mV). The direction and magnitude of the current (Ip current) are adjusted, and this corresponds to an oxygen sensor element that linearly detects the oxygen concentration in the gas to be measured corresponding to the Ip current flowing through the oxygen pump cell 140.
Further, as shown in FIG. 3, a porous protective layer 20 is provided to cover the entire circumference of the sensor element 100 on the tip side.

  The oxygen pump cell 140 corresponds to a “pumping cell” in the claims. In addition, the fourth electrode 110 (more precisely, the fourth electrode portion 110a), the second solid electrolyte layer 109, and the ventilation resistance layer 150 are respectively referred to as "electrode", "solid electrolyte layer", and "ventilation resistor" in the claims. Is equivalent to.

For example, an insulating ceramic sintered body can be used as the insulating protective layer 111, and examples thereof include oxide ceramics such as alumina and mullite.
An example of the porous layer 113a is a porous body made of ceramic such as alumina or mullite. The porous layer 113a can be manufactured, for example, by burning off the carbon when firing the mixed paste of the ceramic and carbon particles. In addition, as shown in FIGS. 3 to 5 described later, in the present embodiment, the outer peripheral edge of the fourth electrode 110 (fourth electrode portion 110a) is located inside the outer peripheral edge of the porous layer 113a. In this case, the outer shape of the fourth electrode 110 formed on the surface of the second solid electrolyte layer 109 is made smaller than the outer shape of the through-hole 112a, so that when the paste that becomes the porous layer 113a is embedded in the through-hole 112a, the through-hole is penetrated. The porous layer 113a is also formed on the surface of the second solid electrolyte layer 109 between the hole 112a and the fourth electrode 110.

The ventilation resistance layer 150 can be formed by applying (printing) an oxide ceramic paste such as alumina or mullite. In particular, it is preferable that the ventilation resistance layer 150 has the same composition as that of the porous layer 113a because adhesion to the porous layer 113a is improved.
The ventilation resistance layer 150 only needs to have a larger gas ventilation resistance than the porous layer 113a. Further, the ventilation resistance layer 150 does not necessarily have insulating properties as long as it does not contact the fourth electrode 110 and the second solid electrolyte layer 109. As the ventilation resistance layer 150 having no insulating property, a metal and partially stabilized zirconia similar to the second solid electrolyte layer 109 can be used. However, when the ventilation resistance layer 150 is in contact with the fourth electrode 110 or the second solid electrolyte layer 109, it is necessary to have insulation.
Further, the airflow resistance of the airflow resistance layer 150 may be appropriately adjusted so as to exhibit the effect of reducing the pulsating current (overshoot current) superimposed on the pump current.

  Returning to FIG. 1, the metal shell 30 is made of SUS430, and has a male screw portion 31 for attaching the gas sensor to the exhaust pipe, and a hexagonal portion 32 to which an attachment tool is applied at the time of attachment. Further, the metal shell 30 is provided with a metal side step portion 33 protruding radially inward, and this metal side step portion 33 supports a metal holder 34 for holding the sensor element 100. . Inside the metal holder 34, a ceramic holder 35 and a talc 36 are arranged in this order from the tip side. The talc 36 includes a first talc 37 disposed in the metal holder 34 and a second talc 38 disposed over the rear end of the metal holder 34. The sensor element 100 is fixed to the metal holder 34 by compressing and filling the first talc 37 in the metal holder 34. In addition, the second talc 38 is compressed and filled in the metal shell 30, thereby ensuring a sealing property between the outer surface of the sensor element 100 and the inner surface of the metal shell 30. An alumina sleeve 39 is disposed on the rear end side of the second talc 38. The sleeve 39 is formed in a multi-stage cylindrical shape, is provided with a shaft hole 39a along the axis, and the sensor element 100 is inserted therein. The caulking portion 30 a on the rear end side of the metal shell 30 is bent inward, and the sleeve 39 is pressed to the front end side of the metal shell 30 through the stainless steel ring member 40.

  Further, a metal protector 24 having a plurality of gas intake holes 24a is attached to the outer periphery on the front end side of the metallic shell 30 by covering the distal end portion of the sensor element 100 protruding from the distal end of the metallic shell 30 by welding. . This protector 24 has a double structure, a cylindrical outer protector 41 having a uniform outer diameter on the outer side, and an outer diameter of the rear end part 42a on the inner side from the outer diameter of the front end part 42b. An inner protector 42 having a bottomed cylindrical shape that is formed to be larger is also arranged.

  On the other hand, on the rear end side of the metal shell 30, the front end side of the outer tube 25 made of SUS430 is inserted. The outer cylinder 25 has a distal end portion 25a whose diameter is enlarged on the distal end side fixed to the metal shell 30 by laser welding or the like. A separator 50 is disposed inside the rear end side of the outer cylinder 25, and a holding member 51 is interposed in a gap between the separator 50 and the outer cylinder 25. The holding member 51 is fixed by the outer cylinder 25 and the separator 50 by engaging a protrusion 50 a of the separator 50 described later and caulking the outer cylinder 25.

  The separator 50 is provided with through holes 50b for inserting the lead wires 11 to 15 for the detection element unit 300 and the heater unit 200 from the front end side to the rear end side (note that the lead wires 14, 15 is not shown). The connection holes 16 that connect the lead wires 11 to 15 to the detection element side pads 121 of the detection element unit 300 and the heater side pads 120 of the heater unit 200 are accommodated in the through holes 50b. Each lead wire 11-15 is connected to a connector (not shown) outside. Electric signals are input and output between the external devices such as the ECU and the lead wires 11 to 15 through this connector. Moreover, although not shown in detail in each lead wire 11-15, it has the structure which showed the conducting wire with the insulating film which consists of resin.

  Further, a substantially cylindrical rubber cap 52 for closing the opening 25 b on the rear end side of the outer cylinder 25 is disposed on the rear end side of the separator 50. The rubber cap 52 is fixed to the outer cylinder 25 by caulking the outer periphery of the outer cylinder 25 toward the radially inner side in a state where the rubber cap 52 is mounted in the rear end of the outer cylinder 25. The rubber cap 52 is also provided with through holes 52a for inserting the lead wires 11 to 15 from the front end side to the rear end side.

As shown in FIGS. 3 and 4, the ventilation resistance layer 150 is formed on the surface of the porous layer 113 a and covers the outer peripheral portion of the porous layer 113 a while being separated from the fourth electrode 110. Therefore, the ventilation resistance layer 150 will be described in detail below with reference to FIGS.
As shown in FIGS. 3 and 4, the porous protective layer 20 includes the front end surface of the sensor element 100, is formed to extend to the rear end side along the axis L direction, and the sensor element 100 (laminated layer). 4) on the front and back surfaces and both side surfaces of the body.

Next, the ventilation resistance layer 150 will be described.
5 is a plan view seen from the stacking direction showing the positional relationship between the fourth electrode 110 and the porous layer 113a, FIG. 6 is a cross-sectional view taken along line AA in FIG. 5, and FIG. FIG. 7 is a schematic view showing the action of the ventilation resistance layer 150 being separated from the fourth electrode 110, and FIG. 8 is a schematic view showing the action of the ventilation resistance layer 150 in the first layer. FIG. 4 is a schematic diagram showing an action by being in contact with four electrodes 110.

As shown in FIG. 5, in this embodiment, the outer periphery of the 4th electrode 110 (4th electrode part 110a) is located inside the outer periphery of the porous layer 113a.
Here, the 4th electrode 110 is formed from the 4th electrode part 110a and the 4th lead part 110b, and the 4th electrode part 110a acts as an electrode which contributes to an electrode reaction among these. Therefore, the “outer periphery” of the fourth electrode 110 represents the outer periphery of the fourth electrode part 110a that contributes to the electrode reaction, and is defined as follows so as to exclude the fourth lead part 110b. That is, the “outer periphery” of the fourth electrode 110 refers to an outer periphery excluding a portion of the fourth electrode 110 that contacts the fourth lead portion 110b when viewed from the stacking direction. Further, “the portion of the fourth electrode 110 in contact with the fourth lead portion 110b” is tangent lines M1 and M2 passing through the sides (two sides in this example) of the fourth electrode portion 110a connected to the fourth lead portion 110b. When the fourth electrode 110 is cut, it means a boundary line between the fourth lead portion 110b and the fourth electrode portion 110a represented by tangent lines M1 and M2.
Therefore, in the example of FIG. 5, the “outer periphery” of the fourth electrode 110 includes (1) the actual outer periphery of the fourth electrode part 110a at a portion not connected to the fourth lead part 110b, and (2) the tangent line M1, It consists of the fourth lead part 110b represented by M2 and the boundary line of the fourth electrode part 110a. Further, for example, when the intersection of the tangent lines M1 and M2 is located outside the outer peripheral edge of the porous layer 113a, the intersection is “the portion of the fourth electrode 110 that contacts the fourth lead portion 110b”. 110 does not correspond to the “outer periphery”. Therefore, also in this case, as long as the outer peripheral edge of the fourth electrode 110 excluding the intersection and the boundary line is located inside the outer peripheral edge of the porous layer 113a, the “outside of the fourth electrode 110 (fourth electrode portion 110a)”. The peripheral edge is located inside the outer peripheral edge of the porous layer 113a ".
Further, the overlapping region S between the fourth electrode portion 110a and the porous layer 113a is a region surrounded by the outer periphery of the fourth electrode 110 (cross-hatched portion in FIG. 5).

Next, the effect | action by the ventilation resistance layer 150 is demonstrated.
As shown in FIG. 6, the ventilation resistance layer 150 covers the outer periphery of the porous layer 113 a while being separated from the fourth electrode 110, and the porous layer 113 a is exposed from the central opening Op of the ventilation resistance layer 150. Therefore, the amount of oxygen source (exhaust gas) that reaches the fourth electrode 110 from the outside via the porous layer 113a (opening Op) decreases as the ventilation resistance layer 150 becomes ventilation resistance, The gas exchange speed on the four electrodes 110 becomes slow. Thereby, the time change (ΔVp) of the Vp voltage in the oxygen pump cell 140 is reduced, and the pulsating current (overshoot current) Ri can be reduced to suppress the deterioration of the gas detection accuracy. Further, since it is not necessary to make the porous layer 113a dense or reduce its size, it is possible to stably increase the airflow resistance and to avoid the difficulty in manufacturing the porous layer. . Similarly, since it is not necessary to make the fourth electrode 110 dense or thick, it suppresses the cost increase of the electrode and suppresses the occurrence of blackening due to the increase in electrode resistance (internal resistance of the sensor element). And it can also suppress that the measurement range of a rich side becomes narrow.
Further, when the ventilation resistance layer 150 is formed by printing and applying an insulating paste, since the dimensional accuracy by printing is high, the dimensional accuracy of the ventilation resistance layer 150 is also increased, and the above effects are stably exhibited. be able to.

  As shown in FIG. 5, when viewed from the stacking direction, the outer peripheral edge of the fourth electrode 110 (fourth electrode portion 110 a) does not protrude outward from the outer peripheral edge of the porous layer 113 a and is positioned inside. Therefore, even if the ventilation resistance layer 150 covers the portion T outside the fourth electrode 110 in the porous layer 113a, it does not function as the ventilation resistance of the oxygen source (exhaust gas) reaching the fourth electrode 110. That is, the ventilation resistance layer 150 needs to cover a part of the overlapping region S between the fourth electrode part 110a and the porous layer 113a, which is a part that actually functions as an electrode in the porous layer 113a.

Further, the overlapping ratio of the overlapping region S by the ventilation resistance layer 150 can be obtained from Equation 1.
Equation 1: Overlap ratio (%) = [{(area of overlap region S) − (area of opening Op)} / (area of overlap region S)] × 100. Each area is an area when projected in the stacking direction as shown in FIG. Here, the area of the opening Op corresponds to an area of the overlapping region S that does not overlap with the ventilation resistance layer 150, that is, an area that is not blocked in the stacking direction by the ventilation resistance layer 150.
The overlap ratio is preferably 25.0 to 97.5%.
When the overlap ratio is less than 25.0%, the effect of the ventilation resistance layer 150 described above as the ventilation resistance is reduced, and it may be difficult to reduce the pulsating current Ri. If the overlap ratio exceeds 97.5%, the effect as ventilation resistance becomes too great, the electrode resistance (internal resistance of the sensor element) increases, blackening may occur, or the Ip current may hardly flow. .

Next, the operation of separating the ventilation resistance layer 150 from the fourth electrode 110 will be described.
As shown in FIG. 7, when the ventilation resistance layer 150 is separated from the fourth electrode 110, the ventilation resistance layer 150, the fourth electrode 110, and the like are also formed in the portion where the ventilation resistance layer 150 covers the fourth electrode 110. Since the oxygen source (exhaust gas) is supplied to the fourth electrode 110 and the second solid electrolyte layer 109 below the fourth electrode 110 from the gap, blackening can be suppressed.
On the other hand, as shown in FIG. 8, when the ventilation resistance layer 150 is in contact with the fourth electrode 110, the oxygen source (exhaust gas) is supplied to the fourth electrode at a portion where the ventilation resistance layer 150 covers the fourth electrode 110. 110 and the second solid electrolyte layer 109 underneath are not supplied, and there is a risk of blackening. In particular, when the overlapping rate is 25.0% or more as described above, the second solid electrolyte layer 109 adjacent to the portion where the ventilation resistance layer 150 covers the fourth electrode 110 overlaps the ventilation resistance layer 150. The supply of oxygen source (exhaust gas) to the part Br of the solid electrolyte layer 109 cannot catch up, and unlike FIG. 6, there is a high possibility that blackening will occur.

It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention.
For example, in the above embodiment, the opening Op is formed in the center of the ventilation resistance layer 150, and the overlapping region S is not closed in the opening Op portion. However, the shape, arrangement position, number, and the like of the ventilation resistance layer 150 are not limited to this. It is not limited to. That is, as shown in FIG. 9, the ventilation resistance layer 152 may be provided on the surface of the porous layer 113 a corresponding to the central portion of the overlapping region S, and the porous layer 113 a may be exposed around the ventilation resistance layer 152.
As shown in FIG. 10, a plurality of ventilation resistance layers 153 and 154 may be provided corresponding to a plurality of positions of the overlapping region S. In the example of FIG. 10, a plurality of ventilation resistance layers 153 and 154 are embedded in the porous layer 113 a, and the gaps between the ventilation resistance layers 153 and 154 are configured not to overlap the overlapping region S. The embedding positions of the ventilation resistance layers 153 and 154 may be different in the stacking direction.
In the above embodiment, the insulating protective layer 111 having the through hole 112a is laminated on the surface of the second solid electrolyte layer 109 so as to sandwich the fourth electrode 110, and the porous layer 113a is formed in the through hole 112a. However, the porous layer 113 a may be directly stacked on the fourth electrode 110 without providing the insulating protective layer 111.

  The present invention also provides a sensor element comprising a cell having an electrode disposed on the surface of a solid electrolyte layer, and a porous layer disposed on the surface of the electrode and allowing gas to enter and exit between the electrode and the outside. The present invention can be applied to any gas sensor having the above and can be applied to the oxygen sensor (oxygen sensor element) of the present embodiment, but is not limited to these uses, and various modifications and equivalents included in the concept and scope of the present invention. Needless to say, it extends to things. For example, the present invention may be applied to a NOx sensor (NOx sensor element) that detects the NOx concentration in the gas to be measured, an HC sensor (HC sensor element) that detects the HC concentration, and the like.

FIG. 11 is a cross-sectional view of the NO _x sensor element 100B, which is a sensor element, cut along the longitudinal direction.
The NO _x sensor element 100B is generally a long plate-like body, and is configured by laminating solid electrolyte layers 2c, 6c, and 4c in this order. Further, an insulating layer 63 is interposed between the solid electrolyte layers 2c and 6c, an insulating layer 65 is interposed between the solid electrolyte layers 6c and 4c, and the outside of the solid electrolyte layer 2c (the insulating layer 63). The insulating protective layer 61 is laminated on the opposite side of the solid electrolyte layer 4c, and the insulating layers 18 and 19 are laminated in this order on the outside of the solid electrolyte layer 4c (on the opposite side to the insulating layer 65).
Here, since a first counter electrode 2b of the first pumping cell 2 described later is exposed to the outside through the porous layer 79, it corresponds to an “electrode” in the claims.
Furthermore, a heater 20 is embedded between the insulating layers 68 and 69 so as to extend along the longitudinal direction of the NO _x sensor element and raise the NO _x sensor to the activation temperature.

The insulating layer 63 is cut out in a U shape in plan view, and is arranged so that the U-shaped opening faces the left in FIG. Thereby, the cut-out portion of the insulating layer 63 becomes a gap, and an internal space is formed by the surface of the solid electrolyte layer 6c (upper surface in FIG. 11), the back surface of the solid electrolyte layer 2c (lower surface in FIG. Is done. In addition, a diffusion rate-determining portion 70 having a diffusion resistance is provided in the opening (the left end of the solid electrolyte layers 2c and 6c in FIG. 11), which is an inlet for the gas to be measured from the outside. On the other hand, a diffusion-controlling unit 71 that divides the internal space in the direction of the paper of FIG. 11 is disposed at a predetermined position from the center from the right end in the internal space, and the internal space between the diffusion-controlling units 70 and 71 is the first measurement chamber. S1.
A first inner electrode 2a having a substantially rectangular shape in plan view is disposed on the back surface of the solid electrolyte layer 2c facing the first measurement chamber S1, and the surface of the solid electrolyte layer 2c is disposed at a position facing the first inner electrode 2a. A first counter electrode 2b is disposed. And the 1st pumping cell 2 is comprised by the 1st inner side electrode 2a, the 1st counter electrode 2b, and the solid electrolyte layer 2c. The insulating protective layer 61 includes a through-hole 61a cut out in a substantially rectangular shape in plan view so that the first counter electrode 2b in contact with the solid electrolyte layer 2c is disposed inside, and the inside of the through-hole 61a is porous. Layer 79 is filled.

Furthermore, an insulating ventilation resistance layer 156 is provided on the surface of the porous layer 79 so as to overlap a part of the overlapping region between the first counter electrode 2 b and the porous layer 79.
Note that also in the NO _x sensor element 100B, the outer peripheral edge of the first counter electrode 2b is positioned inside the outer peripheral edge of the porous layer 79. The ventilation resistance layer 156 is formed so as to cover the outer peripheral portions of the porous layer 79 and the first counter electrode 2b, and the central portion of the ventilation resistance layer 156 opens in a substantially rectangular shape. In addition, the 1st counter electrode 2b is arrange | positioned inside the through-hole cut out by the insulating protective layer 30b as the same layer as the insulating protective layer 30b.

On the other hand, the surface of the solid electrolyte layer 6c facing the first measurement chamber S1 has a first rectangular shape in a substantially rectangular shape in plan view at a position slightly to the left of the diffusion rate controlling portion 71 and to the right of the right end of the first inner electrode 2a. A detection electrode 6a smaller than the inner electrode 2a is arranged. A reference electrode 6b having the same size as the detection electrode is disposed on the back surface of the solid electrolyte layer 6c at a position facing the detection electrode 6a. The detection electrode 6a, the reference electrode 6b, and the solid electrolyte layer 6c constitute an oxygen concentration detection cell 6. The reference electrode 6b is in contact with the solid electrolyte layer 6c through a substantially rectangular cutout in plan view of the insulating layer 65, and the back surface (cutout portion) of the reference electrode 6b is a filled layer made of a porous material or an insulator. 75 is filled, and the filling layer 75 can be filled with oxygen at a predetermined partial pressure.
Note that oxygen is filled in the filling layer 75 on the reference electrode 6b side by flowing a weak current Icp through the oxygen concentration detection cell 6 in advance.

The solid electrolyte layer 6c and the insulating layer 65 are cut out in a rectangular shape in plan view on the right side of the diffusion rate controlling portion 71, and these cut out portions are positioned so as to overlap the right end of the internal space. As a result, a gap extending downward from the right end of the internal space is formed, and the NO _x measurement chamber S2 is defined by this gap and the portion of the internal space on the right side of the diffusion rate controlling portion 71.
Then, the gas to be measured introduced from the outside through the diffusion rate controlling unit 70 flows from the left to the right in FIG. 11 in the first measuring chamber S1, and then flows to the NO _x measuring chamber S2 through the diffusion controlling unit 71. It is like that.

On the surface of the solid electrolyte layer 4c facing the NO _x measurement chamber S2, a second inner electrode 4a having a substantially rectangular shape in plan view is disposed. A second outer electrode 4b serving as an outer electrode of the second inner electrode is disposed on the surface of the solid electrolyte layer 4c facing the filling layer 75. A second pumping cell 4 is configured by the second inner electrode 4a, the second outer electrode 4b, and the solid electrolyte layer 4c.

For each of the insulating protective layers 61 to 69, the porous layer 79, the solid electrolyte layers 2 c, 4 c and 6 c, each of the electrodes 2 a to 6 b, and the heater 20, the same material as the sensor element 100 can be used.
In particular, the first inner electrode 2a and the detection electrodes 6a in contact with the measurement gas, (no or reduced capacity) is low reduction ability to NO _x components in the measurement gas is preferably used materials such La ₃ CuO It is preferable to use a compound having a perovskite structure such as ₄ or the like, a cermet of a metal having a low catalytic activity such as Au and ceramics, or a cermet of a metal having a low catalytic activity such as Au, a Pt group metal and ceramics. Furthermore, when an alloy of Au and a Pt group metal is used as an electrode material, the Au content is preferably 0.03 to 35 vol% of the entire alloy. As the second inner electrode 4a, it can be exemplified a porous cermet consisting of Rh and ZrO _2.

  The diffusion rate-determining part is not limited as long as the rate-determining part is controlled when the gas to be measured flows in. In addition to the slit, a porous body or the like can be used, and a porous body made of alumina or the like can be exemplified. . The diffusion rate controlling unit stabilizes the oxygen concentration around the electrodes in the sensor by blocking gas from entering and exiting the sensor while blocking direct contact between the inside of the sensor and the outside air (or the spaces defined by the diffusion rate controlling unit).

The NO _x sensor (element) is configured as described above and operates, for example, as follows. First, the heater is activated to heat the sensor to the activation temperature. The gas to be measured (exhaust gas) flows into the first measurement chamber S1 through the diffusion rate controlling unit 70, and the first pumping cell 2 removes excess oxygen in the exhaust gas in the first measurement chamber S1 from the first inner electrode 2a. Pump toward the first counter electrode 2c.
The gas from which oxygen is pumped flows downstream of the first measurement chamber S1 and reaches the oxygen concentration detection cell 6 (electrode 6a). Therefore, by monitoring the voltage Vs across the oxygen concentration detection cell 6, the oxygen concentration in the first measurement chamber S1 can be detected. Then, by Vs to control the first voltage between electrodes pumping cell 2 (terminal voltage) Vp1 to a predetermined voltage, the oxygen concentration in the first measurement chamber S1 is NO _x managed so as not to decompose .

The exhaust gas (NO _x gas) in which the oxygen concentration is controlled flows through the diffusion rate controlling part 71 toward the second pumping cell 4 (second inner electrode 4a) in the NO _x measurement chamber S2. Therefore, by applying a voltage to the second pumping cell 4 so that the NO _x gas is decomposed into oxygen and N ₂ gas, oxygen generated by the decomposition of the NO _x gas can be pumped out from the NO _x measurement chamber S2. . In this case, between the second pump current Ip2 and NO _x gas concentration flowing through the second pumping cell 4 because there is a proportional relationship, it is possible to detect the concentration of NO _x in the measurement gas by detecting the Ip2 .
The oxygen pumped out by the second pumping cell 4 is filled into the filling layer 75 from the second counter electrode 4c. Moreover, when an electrode having a catalytic function such as porous rhodium is used as the second inner electrode 4a, decomposition of NO _x gas can be promoted.

Also in the NO _x sensor element 100B, the ventilation resistance layer 156 becomes a ventilation resistance, and the gas exchange rate on the first counter electrode 2b becomes slow. Thereby, the time change (ΔVp) of the Vp voltage is reduced, and the pulsating current (overshoot current) Ri can be reduced to suppress a decrease in the gas detection accuracy.

The gas sensor 1 having the sensor element (oxygen sensor element) 100 shown in FIGS. 1 to 5 was manufactured. A gas sensor in which the size of the overlap region S between the fourth electrode part 110a and the porous layer 113a is made constant, and the size of the opening Op of the ventilation resistance layer 150 is variously changed so that the overlap rate is between 0 and 99.0%. Several were manufactured. The ventilation resistance layer 150 was formed by applying (printing) alumina paste on the outer peripheral portions of the insulating protective layer 111 and the porous layer 113a of the porous layer 113a, and then firing the sensor element 100 at the same time.
The overlap ratio (%) = [{(area of overlap region S) − (area of opening Op)} / (area of overlap region S)] × 100.

Using the gas sensor obtained as described above, the suppression effect of the pulsating current (overshoot current) Ri and the limiting current of the oxygen pump cell 140 were measured.
The effect of suppressing the pulsating current (overshoot current) Ri is that each gas sensor is attached to an exhaust pipe connected to a parallel 4-cylinder engine with a displacement of 2000 cc, sensor control is performed, and then the λ of the exhaust gas at an engine speed of 3000 rpm. It was evaluated whether or not the pulsating current Ri shown in FIG. 14 was generated in the pump current Ip of the oxygen pump cell 140 when the (air-fuel ratio) was switched from 0.95 to 1.05. Specifically, when the Ip value at the time of stable output in a reference gas sensor (a gas sensor with an overlap rate of 0.0% in Table 1) made of a conventional product not provided with the ventilation resistance layer 150 is 100%, the overshoot current Ri The maximum value is expressed as (100 + X)% based on the Ip value. On the other hand, if the maximum value of the overshoot current Ri in the gas sensor of each example was equal to or less than (100 + X / 2)% with respect to the Ip value, the evaluation was “good”. For example, when the maximum value of Ri of the reference gas sensor is 110%, the evaluation is good if the maximum value of Ri of the gas sensor of the example is 105% or less.
The limit current was evaluated as “good” when the air-fuel ratio (A / F) of the model gas was an extremely rich atmosphere with A / F = 10 and Vs could be controlled to 450 mV.
The obtained results are shown in Table 1.

As is apparent from Table 1, when the overlap ratio was 25.0 to 97.5%, the pulsation current Ri was reduced, and a sufficient Ip current was obtained, and there was no problem in the operation of the gas sensor.
When the overlap ratio is less than 25.0%, it is difficult to reduce the pulsating current Ri. When the overlap ratio exceeded 97.5%, the electrode resistance (internal resistance of the sensor element) increased and the Ip current became small, which hindered the operation of the gas sensor and was inappropriate.
FIG. 12 shows the time change of the pump current Ip of the oxygen pump cell 140 when the overlap ratio is 75% and the air-fuel ratio (A / F) in the gas is changed from rich to lean. It can be seen that the pulsating current Ri is suppressed.

DESCRIPTION OF SYMBOLS 1 Gas sensor 100, 100B Sensor element 109, 2c Solid electrolyte layer 110, 2b Electrode 113a, 79 Porous layer 130, 4 cells (oxygen concentration detection cell, 2nd pumping cell)
140, 2 cells (pumping cell, first pumping cell)
150, 152, 153, 154, 156 Ventilation resistor (ventilation resistance layer)
S electrode overlap region with porous layer 107c, S1 measurement chamber

Claims (7)

A cell having a plate-like solid electrolyte layer and an electrode disposed on the surface of the solid electrolyte layer;
A porous layer that is laminated on the surface of the electrode and allows gas to enter and exit between the electrode and the outside;
A gas sensor having a sensor element comprising:
When viewed from the stacking direction, the outer peripheral edge of the electrode is located inside the outer peripheral edge of the porous layer,
A gas sensor having a ventilation resistor on a surface or inside of the porous layer, which is separated from the electrode and overlaps a part of an overlapping region of the electrode and the porous layer when viewed from the stacking direction. A cell having a plate-like solid electrolyte layer and an electrode disposed on the surface of the solid electrolyte layer;
A porous layer that is laminated on the surface of the electrode and allows gas to enter and exit between the electrode and the outside;
A gas sensor having a sensor element comprising:
On the surface or inside of the porous layer, having a ventilation resistor that is separated from the electrode and overlaps a part of the overlapping region of the electrode and the porous layer when viewed from the stacking direction,
A gas sensor having a sensor element having the cell and the porous layer and not having the ventilation resistor is a reference gas sensor, the Ip value when the output of the reference gas sensor is stable is 100%, and the overshoot current is A gas sensor in which the maximum value of the overshoot current of the gas sensor is (100 + X / 2)% or less when the maximum value of is expressed as (100 + X)%.
However, the overshoot current is output from the cell functioning as a pumping cell that pumps or pumps oxygen in the gas introduced into the measurement chamber when the air-fuel ratio in the gas changes from rich to lean. This is the maximum value of the pulsating current superimposed on the pump current Ip.   The gas sensor according to claim 1, wherein the ventilation resistor is gas impermeable.   The gas sensor according to any one of claims 1 to 3, wherein the ventilation resistor overlaps an area of 25.0 to 97.5% of the overlapping region when viewed from the stacking direction. The sensor element is
A pumping cell for pumping or pumping oxygen in the gas to be measured introduced into the measurement chamber is provided as the cell,
Furthermore, an oxygen sensor element comprising an oxygen concentration detection cell for outputting an output voltage corresponding to the oxygen concentration in the measurement gas in the measurement chamber,
5. The oxygen sensor element according to claim 1, wherein a pump current is passed through the pumping cell so that the output voltage is constant, and the oxygen sensor element detects an oxygen concentration in the gas to be measured according to the pump current. The gas sensor according to item. The sensor element is
A first pumping cell for pumping or pumping oxygen in the measurement gas introduced into the measurement chamber and adjusting the oxygen concentration in the measurement chamber is provided as the cell;
Further, the oxygen concentration is NO _x sensor element having a second pumping cell pumping current corresponding to the concentration of NO _x in the measurement gas is adjusted, according to any one of claims 1-4 Gas sensor.   The gas sensor according to any one of claims 1 to 6, wherein the electrode contains 50 mass% or more of Pt and Au in total.

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