JP6517613B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor suitably used to detect 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 sides of the solid electrolyte layer 1090, and the electrode 1100 pumps out or pumps in oxygen in the exhaust gas with 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 measuring chamber 1070 and outputs an output voltage (electromotive force) according to the oxygen concentration in the exhaust gas in the measuring chamber 1070. Then, a voltage (Vp voltage) is applied to the pumping cell 1400 so that the output voltage becomes constant, and the pump current Ip flows, and the oxygen concentration in the exhaust gas according to the pump current Ip is detected. There is.

JP 2012-173146 A 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 rapidly Accordingly, the Vp voltage applied to the pumping cell 1400 also changes rapidly. Then, an extra pulsating current Ri referred to as an overshoot phenomenon (ripple phenomenon) is superimposed on the pump current Ip output from the pumping cell 1400, and there is a problem that the detected value of the oxygen concentration becomes inaccurate. .
This is because, as shown in FIG. 15, when a capacitor circuit is formed between the solid electrolyte layer 1090 of the pumping cell 1400 and the electrode 1100, and the voltage (Vp voltage) between the electrodes of the capacitor changes with time, It is considered that the charge between the electrodes of the capacitor changes temporally in proportion to current flow. That is, the capacitance C of the capacitor in the capacitor circuit, the change ΔQ in the charge of the capacitor, and the change ΔVp in the voltage Vp between the electrodes of the capacitor have a relationship of the following equation (1).
ΔQ = C × ΔVp (1)
Since ΔQ = Ri,
Ri = C × ΔVp (2)
It becomes. From the equation (2), the pulsation current (overshoot current) Ri is reduced as the time change ΔVp 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 hence the Vp voltage do not change rapidly, so the pump current The pulsating current Ri is not superimposed on Ip.

Then, as a measure to reduce ΔVp, it is considered that the electromotive force change of the pumping cell 1400 is hindered, that is, (1) the air flow resistance of the porous layer 1130 is increased, (2) the electrode reaction at the electrode 1100 is delayed. Be
Among them, as to (1), there is a method of densifying the porous layer 1130 or reducing its size. However, since the porous layer 1130 is generally manufactured by firing insulator particles, there is a limit in making the distribution and thickness of pores constant. For this reason, even if the porous layer 1130 is made dense or small, the porosity and the size locally vary, and it is difficult to obtain a stable effect, and it becomes difficult to manufacture the porous layer 1130. is there.
As for (2), there is a method of densifying the electrode 1100 or increasing its thickness. However, if the thickness of the electrode 1100 is increased, the amount of use of noble metal (Pt or the like) which is an electrode material is increased, which leads to an increase in cost of the electrode. In addition, when the electrode 1100 is made dense, the three-phase interface between the electrode 1100, the solid electrolyte layer 1090 and the gas phase decreases, the electrode resistance (the internal resistance of the sensor element) increases, and the operating voltage of the sensor element increases. However, there are problems such as the occurrence of blackening, which will be described later, and restrictions on the electric circuit. Furthermore, in a rich atmosphere, the electrode 1100 pumps oxygen from the oxygen source (H 2 O, CO 2 in exhaust gas, etc.) to the measurement chamber 1070, but if the electrode 1100 is made dense or thick, the gas reaching the electrode 1100 decreases. As a result, there is a problem that the measurement range on the rich side becomes narrow.

On the other hand, with regard to (1), while making the porosity and the size of the porous layer 1130 equal to those of the conventional one, the present inventor overlaps from part of the porous layer 1130, thereby making the porous layer 1130 from the outside. A strategy for reducing the amount of oxygen source (exhaust gas) reaching the electrode 1100 was examined. In this case, the problems (1) and (2) described above can be suppressed.
However, it has been found that depending on the position overlapping with the porous layer 1130, characteristic deterioration of the solid electrolyte layer 1090 referred to as blackening occurs. Blacking is a phenomenon in which oxygen deficiency occurs in the solid electrolyte layer 1090 and the metal oxide in the solid electrolyte layer 1090 is reduced in a state where an electrode reaction occurs via the solid electrolyte layer 1090. When blackening occurs, the characteristics (ion conductivity) of the solid electrolyte layer 1090 are degraded, and the pumping performance is degraded.
For example, as shown in FIG. 17, when a flow resistance layer 1200 is provided between the porous layer 1130 and the electrode 1100 so as to contact the outer peripheral side of the porous layer 1130, a solid electrolyte layer overlapping the flow resistance layer 1200 is provided. Blacking may occur at a site Br of 1090. That is, in the portion Br, although the supply of the oxygen source (exhaust gas G) from the porous layer 1130 is prevented by the air flow 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, and a lack of oxygen occurs in the solid electrolyte layer 1090.

  Therefore, the present invention is a gas sensor that suppresses the deterioration of gas detection accuracy due to a rapid change of the cell's electromotive force with the change of the atmosphere of the measurement gas, and suppresses the characteristic deterioration of the solid electrolyte layer. The purpose is to provide.

In order to solve the above problems, the gas sensor of the present invention is disposed on the surface of a measurement chamber, a plate-like solid electrolyte layer , and the solid electrolyte layer , and faces the first electrode and the measurement chamber facing the measurement chamber. a second electrode which is not, a pumping cell for pumping or pump-priming insertion of oxygen in the gas said measuring chamber, is laminated on a surface of the second electrode, the gas between the second electrode and the outside A gas sensor having a sensor element provided with an accessible porous layer, wherein the outer peripheral edge of the second electrode is located inside the outer peripheral edge of the porous layer when viewed from the stacking direction, The porous resistor has a flow resistance member which overlaps with a part of the overlapping region of the second electrode and the porous layer when viewed from the stacking direction while being separated from the second electrode on the surface or inside of the porous layer.

According to this gas sensor, the amount of oxygen source in the gas that reaches the electrode from the outside through the porous layer per hour decreases due to the flow resistance becoming flow resistance, and the gas exchange rate on the electrode decreases. Become. Thereby, the time change of the voltage in the cell which performs oxygen pumping becomes small, and it is possible to reduce the pulsation current (overshoot current) superimposed on the pump current and to suppress the decrease in the detection accuracy of the gas. In addition, compared with the case where the porous layer itself is made dense or the size thereof is reduced to realize the air flow resistance, the air flow resistance can be stably increased and manufacturing of the porous layer becomes difficult. Is also avoided. Similarly, since it is not necessary to make the electrode itself compact or to increase its thickness, the cost increase of the electrode is suppressed, and the occurrence of blackening due to the increase of the electrode resistance (the internal resistance of the sensor element) is suppressed. It is also possible to suppress the narrowing of the measurement range on the side.
Furthermore, when the ventilation resistor is formed by printing and coating the insulator paste, the dimensional accuracy by printing is high, so the dimensional accuracy of the ventilation resistor is also high, and the above effect can be stably exhibited. it can.

Further, the gas sensor of the present invention comprises a measuring chamber, a plate-like solid electrolyte layer , and a first electrode disposed on the surface of the solid electrolyte layer and facing the measuring chamber and a second electrode not facing the measuring chamber. A porous cell which is laminated on the surface of the second electrode and has a pumping cell through which the gas can flow between the second electrode and the outside. And the outer peripheral edge of the second electrode is located inside the outer peripheral edge of the porous layer when viewed from the stacking direction, and the surface of the porous layer or within, the while spaced apart from the second electrode, wherein said second electrode when viewed from the laminating direction has a ventilation resistor that overlaps a portion of the overlap region between the porous layer, the cell and the It has a porous layer and does not have the ventilation resistor When a gas sensor provided with a sensor element is used as a reference gas sensor, the Ip value when the output of the reference gas sensor is stabilized is 100%, and the maximum overshoot current is represented by (100 + X)%, the overshoot current of the gas sensor The gas sensor has a maximum value of (100 + X / 2)% or less. However, the overshoot current, when the air-fuel ratio of the gas is changed from rich to lean, the Ru output pumping cell or found to perform pumping or pumping in of oxygen in the gas to be introduced into the measurement chamber It is the maximum value of the pulsating current.

According to this gas sensor, the amount of oxygen source in the gas that reaches the electrode from the outside through the porous layer per hour decreases due to the flow resistance becoming flow resistance, and the gas exchange rate on the electrode decreases. Become. Thereby, the time change of the voltage in the cell which performs oxygen pumping becomes small, and it is possible to reduce the pulsation current (overshoot current) superimposed on the pump current and to suppress the decrease in the detection accuracy of the gas. In addition, compared with the case where the porous layer itself is made dense or the size thereof is reduced to realize the air flow resistance, the air flow resistance can be stably increased and manufacturing of the porous layer becomes difficult. Is also avoided. Similarly, since it is not necessary to make the electrode itself compact or to increase its thickness, the cost increase of the electrode is suppressed, and the occurrence of blackening due to the increase of the electrode resistance (the internal resistance of the sensor element) is suppressed. It is also possible to suppress the narrowing of the measurement range on the side.
Furthermore, when the ventilation resistor is formed by printing and coating the insulator paste, the dimensional accuracy by printing is high, so the dimensional accuracy of the ventilation resistor is also high, and the above effect can be stably exhibited. it can.

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

The flow resistance may overlap an area of 25.0 to 97.5% of the overlapping area when viewed from the stacking direction.
According to this gas sensor, the above-mentioned effect as the ventilation resistance of the ventilation resistor is exhibited, and the ventilation resistance becomes too large overlapping in the overlapping region, the electrode resistance (the internal resistance of the sensor element) rises, and blacking occurs It is possible to solve the problem that occurs or the pump current hardly flows.

The sensor element further, an oxygen sensor element having an oxygen concentration detection cell for outputting an output voltage corresponding to the oxygen concentration of the measurement gas in the measurement chamber, so that the output voltage becomes constant It may be an oxygen sensor element which supplies a pump current to the pumping cell and detects the oxygen concentration in the gas to be measured according to the pump current.
According to this gas sensor, the present invention can be applied to the oxygen sensor element.

The sensor element may further be a NO _x sensor element having a second pumping cell pumping current oxygen concentration corresponding to the concentration of NO _x of the measurement gas which is adjusted to flow.
According to this gas sensor, the present invention can be applied to the NO _x sensor element.

The electrode may contain 50% by mass or more in total of Pt and Au.
According to this gas sensor, it is possible to moderate the gas reaction on the electrode, reduce overshoot or reverse shoot of the pump current at approximately λ = 1, and improve detection accuracy.
In addition, as a form in which the electrode contains Pt and Au, a Pt-Au alloy, a mixture of Pt and Au (a paste containing particles of Pt and Au is fired to form no alloy), and Au plating on the surface of Pt A layered structure, one in which Pt is impregnated with Au, is exemplified. Moreover, it is preferable that an electrode contains 0.1-10 mass% of Au. In the case of a layer structure in which the surface of Pt is plated with Au, the Au plating is extremely thin, and even when the content of Au is 0.1% by mass, it functions. Further, as a method of impregnating Pt with Au, there is a method of impregnating a Pt base with a salt of Au (for example, HAuCl ₄ ) and baking it to thermally decompose the salt to leave Au.

  According to the present invention, the gas sensor suppresses the deterioration of the detection accuracy of the gas due to the rapid change of the electromotive force of the cell with the change of the atmosphere of the measurement gas, and the deterioration of the characteristics of the solid electrolyte layer. can get.

It is a sectional view which meets a longitudinal direction of a gas sensor (oxygen sensor) concerning an embodiment of the present invention. It is a model disassembled perspective view of a sensor element. It is a partial expanded sectional view of the tip 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 in alignment with the AA of FIG. It is a schematic diagram which shows the effect | action by a ventilation resistance layer separating with a 4th electrode. It is a schematic diagram which shows the effect | action by the ventilation resistance layer being in contact with a 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. FIG. 2 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 at the time of making an overlap rate into 75% and changing the air fuel ratio (A / F) in gas 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 the air fuel ratio (A / F) in gas is changed 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 cross a stoichiometry point. It is sectional drawing which shows generation | occurrence | production of the blackening at the time of providing a ventilation resistance layer between the porous layer of an oxygen pumping cell, and an electrode.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a 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. FIG. 4 is a cross-sectional view orthogonal to the direction of the axis L of the sensor element 100.

  As shown in FIG. 1, the gas sensor 1 includes a sensor element 100, a metal shell (housing) 30 for holding the sensor element 100 and the like inside, and a protector 24 mounted on the tip of the metal shell 30. The sensor element 100 is arranged 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 is sandwiched between a first base 101 and a second base 103 mainly composed of alumina, and the first base 101 and the second base 103, and a heating element 102 mainly composed of platinum. have. The heat generating body 102 has a heat generating portion 102 a located on the tip end side, and a pair of heater lead portions 102 b extending along the longitudinal direction of the first base 101 from the heat generating portion 102 a. The terminal of the heater lead portion 102 b is electrically connected to the heater side pad 120 through a conductor formed in the heater side through hole 101 a provided in the first base 101. A stack of the first base 101 and the second base 103 corresponds to the insulating ceramic body.

  The detection element unit 300 includes two cells of 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 first and second electrodes 104 and 106 formed on both sides 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 along the longitudinal direction of the first solid electrolyte layer 105 from the first electrode portion 104 a. The second electrode 106 is formed of a second electrode portion 106 a and a second lead portion 106 b extending along the longitudinal direction of the first solid electrolyte layer 105 from the second electrode portion 106 a.

  The end of the first lead portion 104 b is formed by a first through hole 105 a provided in the first solid electrolyte layer 105, a second through hole 107 a provided in the insulating layer 107 described later, and a second solid electrolyte layer 109. It is electrically connected to the detection element side pad 121 through a conductor formed in each of the fourth through holes 109 a and the sixth through holes 111 a provided in the insulating protection layer 111. On the other hand, the terminal 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 provided in the insulating protection layer 111. It electrically connects with the detection element side pad 121 via the 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 sides 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 along the longitudinal direction of the second solid electrolyte layer 109 from the third electrode portion 108 a. The fourth electrode 110 is formed of a fourth electrode portion 110 a and a fourth lead portion 110 b extending along the longitudinal direction of the second solid electrolyte layer 109 from the fourth electrode portion 110 a.

  The terminal of the third lead portion 108 b is a detection element through a conductor formed in each of the fifth through hole 109 b provided in the second solid electrolyte layer 109 and the seventh through hole 111 b provided in the insulating protection layer 111. It electrically connects with the side pad 121. On the other hand, the terminal of the fourth lead portion 110 b is electrically connected to the detection element side pad 121 via a conductor formed in an eighth through hole 111 c provided in the insulating protection layer 111 described later. The second lead portion 106 b and the third lead portion 108 b 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 consists 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, in consideration of heat resistance and oxidation resistance, 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 Pt. It is even more preferable to form it. Furthermore, the heat generating 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 contain a ceramic component in addition to the main platinum group element. It is preferable to contain. It is preferable that this ceramic component is the same component as the material (for example, the component which is the main component of the first solid electrolyte layer 105 and the second solid electrolyte layer 109) which is the main component of the side to be stacked. .

  An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130. The insulating layer 107 includes the insulating portion 114 and the diffusion control 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 is in communication with the outside in the width direction of the insulating layer 107, and in the communication portion, diffusion-limited to realize gas diffusion between the outside and the gas detection chamber 107c under predetermined rate-limiting conditions The part 115 is arranged.

  The insulating portion 114 is not particularly limited as long as it is a ceramic sintered body having an insulating property, and examples thereof include oxide-based ceramics such as alumina and mullite.

  The diffusion controlling portion 115 is a porous body made of alumina. The diffusion limiting portion 115 performs rate limiting when the detection gas flows into the gas detection chamber (measurement chamber) 107 c.

Further, the insulating protection layer 111 is stacked 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 tip end side of the insulating and 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 to allow gas to pass through the porous layer 113a between the fourth electrode portion 110a and the outside. Are accessible.
Furthermore, on the surface of the porous layer 113a facing the outside, a rectangular annular insulating ventilation resistance layer 150 is laminated, in which the central portion of the porous layer 113a opens while covering the outer peripheral side of the porous layer 113a. .
The sensor element 100 according to the present embodiment flows between the electrodes of the oxygen pump cell 140 such 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 the magnitude of the current (Ip current) are adjusted, which corresponds to an oxygen sensor element that linearly detects the oxygen concentration in the measurement gas according to the Ip current flowing to 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 tip end of the sensor element 100.

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

For example, a ceramic sintered body having an insulating property can be used for the insulating and protective layer 111, and an oxide-based ceramic such as alumina or mullite can be exemplified.
As the porous layer 113a, a porous body made of ceramic such as alumina or mullite can be exemplified. The porous layer 113a can be produced, for example, by burning away carbon when firing the mixed paste of the ceramic and the carbon particles. In addition, as shown in FIGS. 3-5 mentioned later, in this embodiment, the outer periphery of 4th electrode 110 (4th electrode part 110a) is located inside the outer periphery of the porous layer 113a. In this case, the outer diameter of the fourth electrode 110 formed on the surface of the second solid electrolyte layer 109 is smaller than the outer diameter of the through hole 112a, whereby the paste to be the porous layer 113a is embedded in the through hole 112a. The porous layer 113 a is also formed on the surface of the second solid electrolyte layer 109 between the hole 112 a and the fourth electrode 110.

The air flow resistance layer 150 can be formed by applying (printing) a paste of an oxide ceramic such as alumina or mullite. In particular, it is preferable to make the gas permeation resistance layer 150 the same composition as the porous layer 113a because the adhesion with the porous layer 113a is improved.
The gas flow resistance layer 150 may have a gas flow resistance higher than that of the porous layer 113a. Also, the air flow resistance layer 150 may not necessarily have insulation unless it is in contact with the fourth electrode 110 and the second solid electrolyte layer 109. As the air flow resistance layer 150 having no insulating property, metal and partially stabilized zirconia similar to the second solid electrolyte layer 109 can be used. However, when the flow 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 flow resistance of the flow resistance layer 150 may be appropriately adjusted so as to exert 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 an externally threaded portion 31 for attaching the gas sensor to the exhaust pipe, and a hexagonal portion 32 for attaching an attachment tool at the time of attachment. Further, the metal shell 30 is provided with a metal fitting side step 33 projecting radially inward, and the metal fitting side step 33 supports a metal holder 34 for holding the sensor element 100. . A ceramic holder 35 and a talc 36 are arranged in this order from the front end side inside the metal holder 34. The talc 36 comprises a first talc 37 disposed within the metal holder 34 and a second talc 38 disposed across the rear end of the metal holder 34. By compression-loading the first talc 37 in the metal holder 34, the sensor element 100 is fixed to the metal holder 34. In addition, since the second talc 38 is compressed and filled in the metal shell 30, the sealability between the outer surface of the sensor element 100 and the inner surface of the metal shell 30 is secured. A sleeve 39 made of alumina is disposed on the rear end side of the second talc 38. The sleeve 39 is formed in a multistage cylindrical shape, and an axial hole 39a is provided along the axis, and the sensor element 100 is inserted inside. The crimped portion 30a 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 via the ring member 40 made of stainless steel.

  Further, a metal protector 24 having a plurality of gas intake holes 24 a is attached by welding to the outer periphery on the front end side of the metal shell 30 while covering the front end portion of the sensor element 100 projecting from the front end of the metal shell 30. . The protector 24 has a double structure and has a bottomed cylindrical outer protector 41 having a uniform outer diameter on the outer side, and an outer diameter of the rear end 42a on the inner side than the outer diameter of the tip 42b. Also, a bottomed cylindrical inner protector 42 formed to a large size is disposed.

  On the other hand, at the rear end side of the metal shell 30, the front end side of the outer cylinder 25 made of SUS430 is inserted. The outer cylinder 25 is fixed to the metal shell 30 by laser welding or the like for the enlarged end portion 25a of the end side. 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 engages with a protrusion 50 a of the separator 50 described later, and is fixed by the outer cylinder 25 and the separator 50 by caulking the outer cylinder 25.

  In addition, through holes 50b for inserting the lead wires 11 to 15 for the detection element unit 300 and the heater unit 200 are penetrated from the front end side to the rear end side of the separator 50 (note that the lead wire 14, 15 not shown). In the through holes 50 b, connection terminals 16 for connecting the lead wires 11 to 15, 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. Each of the lead wires 11 to 15 is externally connected to a connector (not shown). Electrical signals are input / output between an external device such as an ECU and the lead wires 11 to 15 through the connector. Each of the lead wires 11 to 15 is not shown in detail, but has a structure in which the conducting wire is covered with an insulating film made of resin.

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

As shown in FIGS. 3 and 4, the flow 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. 5 to 8.
As shown in FIGS. 3 and 4, the porous protective layer 20 is formed to include the front end face of the sensor element 100 and extend to the rear end side along the axis L direction, and the sensor element 100 (laminated Body) is formed to completely surround the four sides of the front and back and both sides 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 the line A-A of FIG. FIG. 7 is a schematic view showing the function of the flow resistance layer 150 separating from the fourth electrode 110, and FIG. 8 is a plan view of the flow resistance layer 150 when the flow resistance layer 150 is positioned. It is a schematic diagram which shows the effect | action by contacting with 4 electrode 110. FIG.

As shown in FIG. 5, in the present embodiment, the outer peripheral edge of the fourth electrode 110 (fourth electrode portion 110 a) is located inside the outer peripheral edge of the porous layer 113 a.
Here, the fourth electrode 110 is formed of a fourth electrode portion 110a and a fourth lead portion 110b, among which the fourth electrode portion 110a acts as an electrode contributing to the electrode reaction. Therefore, the “outer peripheral edge” of the fourth electrode 110 represents the outer peripheral edge of the fourth electrode portion 110 a contributing to the electrode reaction, and is defined as follows so as to exclude the fourth lead portion 110 b. That is, the “outer peripheral edge” of the fourth electrode 110 refers to the outer peripheral edge of the fourth electrode 110 excluding the portion in contact with the fourth lead portion 110 b when viewed in the stacking direction. Also, "a portion of the fourth electrode 110 in contact with the fourth lead portion 110b" is a tangent M1 or M2 passing through the side (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, the boundary line between the fourth lead portion 110 b and the fourth electrode portion 110 a represented by tangent lines M 1 and M 2 is used.
Therefore, in the example of FIG. 5, the “outer peripheral edge” of the fourth electrode 110 is (1) the actual outer peripheral edge of the fourth electrode portion 110 a at a portion not connected to the fourth lead portion 110 b; It consists of the 4th lead part 110b denoted by M2, and the borderline of the 4th electrode part 110a. Also, for example, when the intersection of the tangents M1 and M2 is located outside the outer peripheral edge of the porous layer 113a, this intersection is "a portion of the fourth electrode 110 in contact with the fourth lead portion 110b". It does not correspond to the "outer periphery" of 110. Therefore, in this case as well, as long as the outer peripheral edge of the fourth electrode 110 excluding the intersection and the boundary line is positioned inside the outer peripheral edge of the porous layer 113a, “the fourth electrode 110 (fourth electrode portion 110a) The periphery is located inside the outer periphery of the porous layer 113a.
The overlapping region S between the fourth electrode portion 110a and the porous layer 113a is a region (cross hatched portion in FIG. 5) surrounded by the outer peripheral edge of the fourth electrode 110.

Next, the function of the air flow resistance layer 150 will be described.
As shown in FIG. 6, the flow resistance layer 150 is separated from the fourth electrode 110 to cover the outer periphery of the porous layer 113a, and the porous layer 113a is exposed from the central opening Op of the flow resistance layer 150. Therefore, the amount per unit time of the oxygen source (exhaust gas) reaching the fourth electrode 110 from the outside through the porous layer 113a (opening Op) is reduced by the flow resistance layer 150 becoming a flow resistance, The gas exchange rate on the four electrodes 110 is reduced. As a result, the time change (ΔVp) of the Vp voltage in the oxygen pump cell 140 is reduced, and the pulsation current (overshoot current) Ri can be reduced to suppress the decrease in gas detection accuracy. In addition, since it is not necessary to make the porous layer 113a itself compact or to reduce its size, it is possible to stably increase the air flow resistance, and it is also avoided that the production of the porous layer becomes difficult. . Similarly, since it is not necessary to make the fourth electrode 110 itself dense or thick, it is possible to suppress the cost increase of the electrode and to suppress the occurrence of blackening due to the increase of the electrode resistance (the internal resistance of the sensor element) Also, the narrow measurement range on the rich side can be suppressed.
Furthermore, when the ventilation resistance layer 150 is formed by printing and coating the insulator paste, the dimensional accuracy by printing is high, so the dimensional accuracy of the ventilation resistance layer 150 is also high, and the above effects are stably exhibited. be able to.

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

Further, the overlapping ratio of the overlapping region S due to the air flow resistance layer 150 can be obtained from Expression 1.
Formula 1: Overlap rate (%) = [{(area of overlapping area S) − (area of opening Op)} / (area of overlapping area 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 the area of the overlapping region S that does not overlap with the flow resistance layer 150, that is, the area of the portion that is not blocked by the flow resistance layer 150 in the stacking direction.
The overlap rate is preferably 25.0 to 97.5%.
If the overlapping rate is less than 25.0%, the effect as the ventilation resistance of the ventilation resistance layer 150 described above may be reduced, and it may be difficult to reduce the pulsating current Ri. If the overlap rate exceeds 97.5%, the effect as air flow resistance becomes too large, and the electrode resistance (internal resistance of the sensor element) may increase to cause blackening or cause almost no Ip current flow .

Next, the operation of separating the flow resistance layer 150 from the fourth electrode 110 will be described.
As shown in FIG. 7, when the flow resistance layer 150 is separated from the fourth electrode 110, the flow resistance layer 150 and the fourth electrode 110 can be separated from the fourth electrode 110 even at the portion where the flow 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 it from the gap between the two, it is possible to suppress the occurrence of blackening.
On the other hand, as shown in FIG. 8, when the flow resistance layer 150 is in contact with the fourth electrode 110, the oxygen source (exhaust gas) is the fourth electrode at the portion where the flow resistance layer 150 covers the fourth electrode 110. It is not supplied to the second solid electrolyte layer 109 under 110 and the lower side thereof, and blackening may occur. In particular, when the overlapping rate becomes 25.0% or more as described above, the second solid electrolyte layer 109 adjacent to the portion where the flow resistance layer 150 covers the fourth electrode 110 overlaps the flow resistance layer 150. The supply of the oxygen source (exhaust gas) to the portion Br of the solid electrolyte layer 109 does not catch up, and unlike in FIG. 6, the possibility of the occurrence of blackening is increased.

It is needless to say that the present invention is not limited to the above embodiments, 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 at 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, etc. of the ventilation resistance layers 150 are not limited. It is not limited to. That is, as shown in FIG. 9, the flow resistance layer 152 may be provided on the surface of the porous layer 113a corresponding to the central portion of the overlapping region S, and the porous layer 113a may be exposed around the flow resistance layer 152.
Further, as shown in FIG. 10, a plurality of ventilation resistance layers 153, 154 may be provided corresponding to a plurality of positions in the overlapping region S. In the example of FIG. 10, a plurality of flow resistance layers 153 and 154 are embedded in the porous layer 113a, and the gap between the flow resistance layers 153 and 154 is configured not to overlap the overlapping region S. The embedding position 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 holes 112a is stacked 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 on the through holes 112a. Although it has been embedded, the porous layer 113a may be laminated directly on the fourth electrode 110 without providing the insulating protective layer 111.

  Further, the present invention provides a sensor element including 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 capable of entering and exiting a gas between the electrode and the outside. The present invention is applicable to any gas sensor having the same and applicable to the oxygen sensor (oxygen sensor element) of the present embodiment, but is not limited to these applications, and various modifications and equivalents included in the spirit and scope of the present invention It goes without saying that 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, or 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 in the form of a generally long plate, and is formed by laminating solid electrolyte layers 2c, 6c, 4c in this order. Further, an insulating layer 63 is interposed between the solid electrolyte layers 2c and 6c, and an insulating layer 65 is interposed between the solid electrolyte layers 6c and 4c. The insulating protection layer 61 is stacked on the opposite side of the above, and the insulating layers 18 and 19 are stacked in this order on the outer side of the solid electrolyte layer 4c (the opposite side to the insulating layer 65).
Here, since the 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 the "electrode" in the claims.
Furthermore, a heater 20 is embedded between the insulating layers 68 and 69 and extends along the longitudinal direction of the NO _x sensor element to raise the NO _x sensor to the activation temperature.

The insulating layer 63 is cut out in a U-shape in plan view, and the U-shaped opening is arranged to face the left in FIG. Thus, the cut-out portion of the insulating layer 63 becomes an air gap, and an inner 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. 11), and the side surface of the insulating layer 63. Be done. Further, a diffusion control 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 introduction port of the measurement gas from the outside. On the other hand, a diffusion control portion 71 is provided at a predetermined position from the right end to the center in the internal space, which divides the internal space in the direction of the paper of FIG. 11. The internal space between the diffusion control portions 70 and 71 is the first measurement chamber It becomes S1.
The 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 opposed to the first inner electrode 2a. The first counter electrode 2 b 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 has 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 porous inside of the through hole 61a is provided. Layer 79 is filled.

Furthermore, on the surface of the porous layer 79, an insulating flow-resistant layer 156 overlapping a part of the overlapping region of the first counter electrode 2b and the porous layer 79 is provided.
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 air flow resistance layer 156 is formed to cover the outer peripheral portions of the porous layer 79 and the first counter electrode 2b, and the central portion of the air flow resistance layer 156 opens in a substantially rectangular shape. The first opposing electrode 2b is disposed in the through hole cut out in 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 substantially rectangular shape in plan view at a position slightly to the left of the diffusion control 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 disposed. Further, on the back surface of the solid electrolyte layer 6c, a reference electrode 6b having substantially the same size as the detection electrode is disposed at a position facing the detection electrode 6a. And the oxygen concentration detection cell 6 is comprised by the detection electrode 6a, the reference electrode 6b, and the solid electrolyte layer 6c. The reference electrode 6b is in contact with the solid electrolyte layer 6c through the cutout portion substantially rectangular in plan view of the insulating layer 65, and the back surface (cutout portion) of the reference electrode 6b is a filling layer made of a porous body or an insulator. 75 is filled so that 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 side of the reference electrode 6 b by supplying a weak current Icp in advance to the oxygen concentration detection cell 6.

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 control portion 71, and these cut out portions are positioned to overlap the right end of the internal space. As a result, an air gap extending downward from the right end of the inner space is formed, and the NO _X measurement chamber S2 is defined by the air gap and a portion of the inner space to the right of the diffusion control portion 71.
Then, the gas to be measured introduced from the outside through the diffusion control unit 70 flows from the left to the right in FIG. 11 in the first measurement chamber S1, and then flows into the NO _x measurement chamber S2 through the diffusion control unit 71. It is supposed to be.

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

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

  The diffusion-limited portion may be any as long as the rate-determining is performed when the gas to be measured flows in, and 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 control unit allows gas to enter and leave the sensor while blocking direct contact between the inside of the sensor and the outside air (or the spaces defined by the diffusion control unit), thereby stabilizing the oxygen concentration around the electrodes in the sensor.

Configured the NO _x sensor (element) as described above, for example, operates 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 control unit 70, and the first pumping cell 2 generates excess oxygen in the exhaust gas in the first measurement chamber S1 from the first inner electrode 2a. It pumps out toward the 1st 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. By Vs to control the first inter-electrode voltage of the 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 .

Exhaust gas oxygen concentration was controlled (NO _x gas) flows toward the second pumping cell 4 (second inner electrodes 4a) in the NO _x measurement housing S2 through the diffusion control part 71. Therefore, by NO _x gas into the second pumping cell 4 applies a voltage of about decomposes into oxygen and N ₂ gas, the oxygen generated by the decomposition of the NO _x gas can be pumped out from the NO _x measurement housing 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 in the filling layer 75 from the second opposing electrode 4c. In addition, when an electrode having a catalytic function such as porous rhodium is used as the second inner electrode 4a, the decomposition of the NO _x gas can be promoted.

Also in the NO _x sensor element 100B, the gas flow resistance layer 156 becomes a gas flow resistance, and the gas exchange speed on the first counter electrode 2b becomes slow. As a result, the time change (ΔVp) of the Vp voltage is reduced, and the pulsation current (overshoot current) Ri can be reduced to suppress the decrease in 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 having an overlap ratio of 0 to 99.0% by changing the size of the opening Op of the flow resistance layer 150 variously while keeping the size of the overlap region S between the fourth electrode portion 110a and the porous layer 113a constant. Several were manufactured. The air flow resistance layer 150 was formed by applying (printing) an alumina paste on the outer peripheral portion of the insulating protective layer 111 and the porous layer 113a of the porous layer 113a, and firing it simultaneously with the sensor element 100.
Note that the overlap ratio (%) = [{(area of overlapping area S) − (area of opening Op)} / (area of overlapping area S)] × 100.

The suppression effect of the pulsation current (overshoot current) Ri and the limit current of the oxygen pump cell 140 were measured using the gas sensor obtained as described above.
The effect of suppressing the pulsation current (overshoot current) Ri is to attach each gas sensor to an exhaust pipe connected to a parallel 4-cylinder engine with a displacement of 2000 cc and perform sensor control, and then λ of exhaust gas at an engine speed of 3000 rpm. When (air-fuel ratio) was switched from 0.95 to 1.05, 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. Specifically, assuming that the Ip value at the time of stable output in a reference gas sensor (a gas sensor with an overlap ratio of 0.0% in Table 1) consisting of a conventional product without the ventilation resistance layer 150 is 100%, the overshoot current Ri The maximum value is represented by (100 + X)% based on the above Ip value. On the other hand, when the maximum value of the overshoot current Ri in the gas sensor of each example was (100 + X / 2)% or less based on the above-mentioned Ip value, it was evaluated as ○. For example, when the maximum value of Ri of the reference gas sensor is 110%, the evaluation is で あ れ ば if the maximum value of Ri in the gas sensor of the embodiment is 105% or less.
The limiting current was evaluated as ○ if the air-fuel ratio (A / F) of the model gas was set to a pole rich atmosphere of A / F = 10 and Vs could be controlled to 450 mV.
The obtained results are shown in Table 1.

As apparent from Table 1, when the overlap rate is set to 25.0 to 97.5%, the pulsating current Ri is reduced, and a sufficient Ip current is obtained, and there is no problem in the operation of the gas sensor.
When the overlapping rate is less than 25.0%, it has become difficult to reduce the pulsating current Ri. When the overlapping rate exceeds 97.5%, the electrode resistance (internal resistance of the sensor element) is increased, the Ip current is decreased, and the operation of the gas sensor is not suitable.
FIG. 12 shows the time change of the pump current Ip of the oxygen pump cell 140 when the air-fuel ratio (A / F) in the gas is changed from rich to lean with an overlap rate of 75%. It can be seen that the pulsating current Ri is suppressed.

Reference Signs List 1 gas sensor 100, 100B sensor element 109, 2c solid electrolyte layer 110, 2b electrode 113a, 79 porous layer 130, 4 cell (oxygen concentration detection cell, second pumping cell)
140, 2 cells (pumping cell, first pumping cell)
150, 152, 153, 154, 156 vent resistor (vent resistor layer)
Overlap area 107c of S electrode and porous layer, S1 measuring chamber

Claims (7)

Measurement room,
A plate-like solid electrolyte layer , and a first electrode disposed on the surface of the solid electrolyte layer and facing the measurement chamber and a second electrode not facing the measurement chamber, wherein oxygen in the gas in the measurement chamber A pumping cell for pumping out or pumping in;
Laminated on the surface of the second electrode, wherein the gas and the porous layer capable and out between the second electrode and the outside,
A gas sensor having a sensor element provided with
When viewed from the stacking direction, the outer peripheral edge of the second electrode is located inside the outer peripheral edge of the porous layer,
On or within the porous layer, while apart from the second electrode, having a ventilation resistance material overlapping portion of the second electrode and the overlapping region of the porous layer when viewed from the stacking direction Gas sensor. Measurement room,
A plate-like solid electrolyte layer , and a first electrode disposed on the surface of the solid electrolyte layer and facing the measurement chamber and a second electrode not facing the measurement chamber, wherein oxygen in the gas in the measurement chamber A pumping cell for pumping out or pumping in;
Laminated on the surface of the second electrode, wherein the gas and the porous layer capable and out between the second electrode and the outside,
A gas sensor having a sensor element provided with
When viewed from the stacking direction, the outer peripheral edge of the second electrode is located inside the outer peripheral edge of the porous layer,
Yes on or within the porous layer, while apart from the second electrode, the ventilation resistor that overlaps a portion of the overlap region between the porous layer and the second electrode when viewed from the stacking direction And
A gas sensor provided with a sensor element having the cell and the porous layer and not having the ventilation resistor is used as a reference gas sensor, the Ip value when the output of the reference gas sensor is stabilized is 100%, and the overshoot current 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 represented by (100 + X)%.
However, the overshoot current, when the air-fuel ratio of the gas is changed from rich to lean, the Ru output pumping cell or found to perform pumping or pumping in of oxygen in the gas to be introduced into the measurement chamber It is the maximum value of the pulsating current.   The gas sensor according to claim 1 or 2, wherein the ventilation resistor is gas impermeable.   The gas sensor according to any one of claims 1 to 3, wherein the flow resistance resistor overlaps an area of 25.0 to 97.5% of the overlapping region when viewed from the stacking direction. Said sensor element,
Furthermore, the oxygen sensor element has an oxygen concentration detection cell that outputs an output voltage according to the oxygen concentration in the measurement gas in the measurement chamber,
The oxygen sensor element according to any one of claims 1 to 4, wherein a pump current is supplied to the pumping cell such that the output voltage becomes constant, and the oxygen concentration in the gas to be measured according to the pump current is detected. The gas sensor as described in a term. Said sensor element,
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% by mass or more in total of Pt and Au.

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