JP6979387B2 - Sensor element and gas sensor - Google Patents

Description

The present invention relates to a sensor element and a gas sensor that detect the concentration of the gas to be detected.

Conventionally, a gas sensor for detecting the concentration of a specific component (oxygen, etc.) in the exhaust gas of a combustor, an internal combustion engine, or the like has been used. The gas sensor has a sensor element comprising a cell having a solid electrolyte and a pair of electrodes arranged on the solid electrolyte. This cell has a function of detecting the concentration of a specific component in the exhaust gas and performing an oxygen pump for pumping or pumping oxygen from the internal space (measurement chamber or the like) of the element. Further, in order to heat the solid electrolyte body of the cell to the activation temperature, a heater that generates heat by energization is laminated on the sensor element.
By the way, in recent years, early activity for shortening the activation time of the gas sensor has been required, but if the heating rate of the heater is increased, the thermal stress in the vicinity of the heater becomes large, and the element may be cracked. Therefore, the heating element of the heater is formed as close as possible to the end (side end and tip) of the element (heater substrate), and the end of the heater substrate in which the heating element is not embedded and the heating element are embedded. A technique for reducing the temperature difference (thermal stress) from the portion has been developed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2002-228626

However, in the case of the gas sensor described in Patent Document 1, as shown in FIG. 9, when the conductive component (carbon soot) or water 1200 in the exhaust gas adheres to the end surface (side end surface in FIG. 9) of the sensor element 1000, the heater There is a problem that the leakage current from the heating element 1150 flows to each of the electrodes 1110 and 1120 and the solid electrolyte layer 1100, and the detection accuracy and the oxygen pumping ability are deteriorated.
This is because the end face of the solid electrolyte layer 1100 is exposed, so that a current path CP is formed between the water 1200 adhering to the end face of the solid electrolyte layer 1100 and the solid electrolyte layer 1100, and the heater heating element 1150 and the current. The insulation between the path CP is maintained only by a slight gap G between the heater substrate 1160 and the side end of the heating element 1150, but the gap G is easily destroyed when the heating element 1150 is energized. it is conceivable that.

The present invention has been made in view of the current situation, and is a sensor element that realizes early activity, stably secures insulation between the heater and the solid electrolyte, and suppresses deterioration of detection accuracy and the like. And to provide gas sensors.

The sensor element of the present invention includes one or more cells having a composite layer in which a solid electrolyte is arranged in a through hole provided in an insulating layer, and a pair of electrodes formed on the surface of the solid electrolyte. A sensor element extending in the axial direction, comprising a heater substrate arranged in the stacking direction of the composite layer, and a heater provided on the heater substrate and provided with a heat generating portion for heating at least one cell. The heat generating portion includes a pair of outer linear portions extending in the axial direction, a pair of inner linear portions arranged between the outer linear portions, and an adjacent outer linear portion. A heating element comprising a first connecting portion connecting the tip of the portion and the tip of the inner linear portion, and a second connecting portion connecting the rear ends of the pair of the inner linear portions, and a pair of the outer side. It is configured to include a pair of lead portions connected to the rear end of the linear portion, and the minimum distance A between the side end portion of the heater substrate and the side end portion of the outer linear portion is 0.15 mm ≦. A ≦ 0.35 mm, the minimum distance B between the tip of the heater substrate and the tip of the first connection is 0.25 mm ≦ B ≦ 0.85 mm, and the insulating layer in the composite layer The total length of the minimum distance G2 between the side end portion and the side end portion of the solid electrolyte and the minimum distance A is 0.3 mm or more, and the inner linear portion is the pair of electrodes and the solid electrolyte. It is characterized in that it overlaps with the overlapping region with the above in the stacking direction and is formed so as to straddle the front end or the rear end of the overlapping region.

According to this sensor element, by setting the minimum distances A and B between the side end portion and the tip portion of the heater substrate and the heat generating portion within an appropriate range, the side end portion and the tip portion of the heater substrate (and thus the sensor element) can be covered. The heat generating portion can be brought closer, and even if the heating rate of the heater is increased, the increase in thermal stress in the vicinity of the heater can be suppressed, the element cracking can be suppressed, and early activity can be realized. Further, since the heat generating portion is not brought too close to the side end portion and the tip portion, the insulation between the heater and the solid electrolyte body can be ensured.
Further, since the solid electrolyte is embedded in the insulating layer, when the conductive component (carbon soot) or water in the exhaust gas adheres to the end of the insulating layer, the conductive component or water and the solid electrolyte Since the insulating layer insulates between the body and the body, the insulation between the heater and the solid electrolyte body can be stably ensured in combination with the above-mentioned gaps A and B between the heater substrate and the heat generating portion.
Further, since the pair of inner linear portions overlap with the overlapping region of the cell in the stacking direction and are formed so as to straddle the front end or the rear end of the overlapping region, the inner linear portion is formed in the overlapping region which is an effective portion of the cell. The heat can be reliably transferred, early activity can be realized more reliably, and the temperature difference (thermal stress) from the end of the heater substrate can be further reduced.

In the sensor element of the present invention, the outer linear portion may be arranged on the side end side of the solid electrolyte body at a distance from the solid electrolyte body.
According to this sensor element, early activity can be realized more reliably, and the temperature difference (thermal stress) from the end of the heater substrate can be further reduced.

In the sensor element of the present invention, the inner linear portion may be formed so as to straddle the front end and the rear end of the overlapping region of the pair of electrodes.
According to this sensor element, since the inner linear portion overlaps to the tip and the back of the overlapping region of the cells, the heat of the inner linear portion can be more reliably transferred to the overlapping region.

The gas sensor of the present invention is a gas sensor including a sensor element for detecting a specific gas in a gas to be measured and a main metal fitting for holding the sensor element, and the sensor element is any one of claims 1 to 3. The sensor element according to item 1 is provided.

According to the present invention, it is possible to realize early activity of the gas sensor, stably secure insulation between the heater and the solid electrolyte, and suppress deterioration of detection accuracy and the like.

It is sectional drawing of the gas sensor which concerns on embodiment of this invention. It is a schematic disassembled perspective view of a sensor element. It is a top view which shows the heat generation part. It is a top view which shows the positional relationship between a heat generating part, a pump cell and a heater substrate. It is a top view which shows the positional relationship between a heat generating part, a detection cell, and a heater substrate. It is a cross-sectional view in the width direction which shows the insulation state between a solid electrolyte body and a heating element when water adheres to a side end surface of a sensor element. It is a figure which shows the relationship between the voltage of a heating element and the minimum distance A when the failure rate by a crack is 0.1%. It is a figure which shows the relationship between the voltage of a heating element and the minimum distance B when the failure rate by a crack is 0.1%. It is a cross-sectional view in the width direction which shows the insulation state between a solid electrolyte body and a heating element when water adheres to a side end surface of a conventional sensor element.

Embodiments of the present invention will be described in detail with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view of the gas sensor 1 according to the embodiment of the present invention along the axis O direction, FIG. 2 is a schematic exploded perspective view of the sensor element 19, and FIG. 3 is a plan view showing a heat generating portion 146.

In FIG. 1, the gas sensor (all-region air-fuel ratio gas sensor) 1 is a holder (ceramic holder) 30 having a sensor element 19, a through hole 32 penetrating in the axis O direction through which the sensor element 19 is inserted, and a ceramic holder 30. It is provided with a main metal fitting 11 that surrounds the radial circumference.
Of the sensor element 19, the portion near the tip where the detection unit 22 is formed protrudes from the ceramic holder 30 to the tip. The sensor element 19 passed through the through hole 32 in this way has a sealing material (talc in this example) 41 arranged on the rear end surface side (upper side in the drawing) of the ceramic holder 30, a sleeve 43 made of an insulating material, and a ring washer. By compressing in the front-rear direction via the 45, the airtightness is maintained and fixed in the front-rear direction inside the main metal fitting 11.
The portion near the rear end including the rear end 19e of the sensor element 19 protrudes rearward from the sleeve 43 and the main metal fitting 11, and the sensor pad portions 13 to 15 and the heater pad portion 16 formed on the portion near the rear end. A terminal fitting 75 provided at the tip of each lead wire 71 drawn out to the outside through the sealing material 85 is pressure-welded to 17 and electrically connected. Further, the portion near the rear end of the sensor element 19 including the sensor pad portions 13 to 15 and the heater pad portions 16 and 17 is covered with the outer cylinder 81. Hereinafter, it will be described in more detail.

The sensor element 19 extends in the O-axis direction and is composed of an electrode to be measured on the gas side to be measured such as an electrode 155 (see FIG. 2) on the tip side (lower side in the drawing) facing the measurement target, and detects a specific gas component in the gas to be detected. It has a strip-shaped shape (plate-shaped) provided with a detection unit 22. The cross section of the sensor element 19 forms a rectangle (rectangle) of a certain size in the front and rear, and is formed as an elongated one mainly composed of a ceramic (solid electrolyte or the like).
In this sensor element 19, a detection cell layer 151 forming a detection unit 22 and a pair of electrodes 153 and 155 (see FIG. 2) are arranged at a portion near the tip, and a detection output is taken out at a portion connected to the detection cell layer 15 near the rear end. Sensor pads 14 and 15 (see FIG. 2) for connecting the lead wire 71 of the above are exposed.

In this example, a pump cell layer 161 (see FIG. 2) for pumping oxygen is provided inside the portion near the tip of the sensor element 19, and a sensor for connecting a lead wire 71 for pump cell control is provided at the portion near the rear end. Pad portions 13 and 15 (see FIG. 2) are exposed and formed.
That is, in this example, the sensor element 19 includes two cells, a detection cell 150 and a pump cell 160.

Further, in this example, a heater 145 (see FIG. 2) including a heat generating portion 146 is provided below the portion near the tip of the sensor element 19, and a lead wire for applying a heater voltage is provided at the portion near the rear end. The heater pad portions 16 and 17 (see FIG. 2) for connecting 71 are exposed and formed.

The sensor pad portions 13 to 15 and the heater pad portions 16 and 17 are formed in a vertically long rectangular shape. For example, in a portion near the rear end of the sensor element 19, the sensor pad portion 13 is formed on the wide surface of the strip as shown in FIG. ~ 15 are arranged side by side, and two heater pad portions 16 and 17 are arranged side by side on the opposite surface.
Further, the detection unit 22 of the sensor element 19 is coated with a porous protective layer 23 made of alumina, spinel, or the like.

The main metal fitting 11 has a cylindrical shape having concentric and different diameters at the front and rear, and has a small diameter on the tip side, and is a cylindrical annular portion (hereinafter, also referred to as a cylindrical portion) for externally fitting and fixing the protectors 51 and 61 described later. 12 is provided, and a screw 13 for fixing to the exhaust pipe of the engine having a larger diameter is provided on the outer peripheral surface behind the 12 (upper side in the drawing). A polygonal portion 14 for screwing the sensor 1 by the screw 13 is provided behind the screw 13.
Further, behind the polygonal portion 14, a cylindrical portion 11e to which a protective cylinder (outer cylinder) 81 covering the rear of the gas sensor 1 is fitted and welded is continuously provided, and the outer diameter thereof is smaller than that behind the cylindrical portion 11e. It is provided with a small and thin-walled caulking cylindrical portion 16. In FIG. 1, the caulking cylindrical portion 16 is bent inward for post-caulking. A gasket 21 for sealing at the time of screwing is attached to the lower surface of the polygonal portion 14.
On the other hand, the main metal fitting 11 has an inner hole 18 penetrating in the axis O direction. The inner peripheral surface of the inner hole 18 has a tapered step portion 11d that tapers inward in the radial direction from the rear end side to the tip side.

Inside the main metal fitting 11, a ceramic holder 30 made of an insulating ceramic (for example, alumina) and formed in a substantially short cylindrical shape is arranged. The ceramic holder 30 has a tip facing surface 30a formed in a tapered shape that tapers toward the tip. Then, the ceramic holder 30 is positioned in the main metal fitting 11 by pressing the ceramic holder 30 from the rear end side with the sealing material 41 while the portion of the tip facing surface 30a near the outer circumference is locked to the step portion 11d. And it is fitted in the gap.
On the other hand, the through hole 32 is provided in the center of the ceramic holder 30 and is a rectangular opening having substantially the same dimensions as the cross section of the sensor element 19 so that the sensor element 19 can pass through without a gap.

The sensor element 19 is passed through a through hole 32 of the ceramic holder 30, and the tip of the sensor element 19 is projected beyond the tip 12a of the ceramic holder 30 and the main metal fitting 11.
On the other hand, the tip portion of the sensor element 19 has a two-layer structure in this embodiment, and is covered with bottomed cylindrical protectors (protective covers) 51 and 61, both of which have ventilation holes (holes) 56 and 67, respectively. .. Of these, the rear end of the inner protector 51 is fitted and welded to the cylindrical portion 12 of the main metal fitting 11. It should be noted that the ventilation holes 56 are provided at, for example, eight places in the circumferential direction on the rear end side of the protector 51. On the other hand, on the tip side of the protector 51, for example, four discharge holes 53 are provided in the circumferential direction.
Further, the outer protector 61 is fitted onto the inner protector 51 and is welded to the cylindrical portion 12 at the same time. The vent holes 67 of the outer protector 61 are provided at, for example, eight places in the circumferential direction near the tip, and the discharge holes 69 are also provided at the center of the bottom of the tip of the protector 61.

Further, as shown in FIG. 1, each of the sensor pad portions 13 to 15 and the heater pad portions 16 and 17 formed in the portion near the rear end of the sensor element 19 has lead wires drawn out through the sealing material 85 to the outside. Each terminal fitting 75 provided at the tip of the 71 is pressure-welded by its springiness and electrically connected. In the gas sensor 1 of this example, the terminal fittings 75 including the pressure contact portion are provided in opposite arrangements in each accommodating portion provided in the insulating separator 91 arranged in the outer cylinder 81. .. The separator 91 is restricted from moving in the radial direction and toward the tip side via a holding member 82 that is caulked and fixed in the outer cylinder 81. Then, the tip of the outer cylinder 81 is fitted onto the cylindrical portion 11e of the portion near the rear end of the main metal fitting 11 and welded, so that the rear of the gas sensor 1 is airtightly covered.
The lead wire 71 is pulled out to the outside through a sealing material (for example, rubber) 85 arranged inside the rear end portion of the outer cylinder 81, and the small diameter cylinder portion 83 of the outer cylinder 81 is crimped. By compressing the sealing material 85 of the lever, the airtightness of this portion is maintained.

Incidentally, a stepped portion 81d having a large diameter at the tip side is formed on the rear end side of the outer cylinder 81 slightly from the center in the axis O direction, and the inner surface of the stepped portion 81d supports the rear end of the separator 91 so as to push it forward. do. On the other hand, in the separator 91, a flange 93 formed on the outer periphery thereof is supported on a holding member 82 fixed to the inside of the outer cylinder 81, and the separator 91 is oriented in the axis O direction by the stepped portion 81d and the holding member 82. It is held in.

Next, the configuration of the sensor element 19 will be described with reference to FIG.
The sensor element 19 is formed by laminating an outer ceramic layer 183, a pump cell 160, an intermediate ceramic layer 170, a detection cell 150, and a heater 145 in order from the upper side of FIG. 2 in the thickness direction (stacking direction). Each layer 145, 150 to 183 is made of an insulating ceramic such as alumina, and has a rectangular plate shape having the same external dimensions (at least width and length).

The outer ceramic layer 183 constitutes the outer surface (upper surface of FIG. 2) of the sensor element 19, and the sensor pad portions 13 to 15 are arranged at the rear end thereof. Further, a penetrating portion 183h that opens in a substantially rectangular shape is provided on the tip end side (left side in FIG. 2) of the outer ceramic layer 183, and a substantially rectangular porous layer 182 is filled so as to be embedded in the penetrating portion 183h. There is. The outer ceramic layer 183 protects and covers the following pump cell layer 161 and the porous layer 182 covers the pump electrode 163 in the pump cell 160.
The porous layer 182 is exposed on the upper surface of the sensor element 19, and oxygen can be pumped and pumped between the pump electrode 163 and the outside through the upper surface of the porous layer 182.

The pump cell 160 includes a pump cell layer 161 provided with a first insulating layer 161a and a substantially rectangular plate-shaped solid electrolyte body 162, and the above-mentioned pump electrodes 163 and counter electrodes 165 provided on the front and back surfaces of the solid electrolyte body 162, respectively. I have. A penetrating portion 161h that opens in a substantially rectangular shape is provided on the tip end side (left side of FIG. 2) of the first insulating layer 161a, and the solid electrolyte body 162 is arranged so as to be embedded in the penetrating portion 161h. The pump electrode 163 is composed of a pump electrode portion 163E and a lead portion 163L extending from the pump electrode portion 163E toward the rear end side, and the counter electrode 165 is rearward from the counter electrode portion 165E and the counter electrode portion 165E. It consists of a lead portion 165L extending toward the end side.
The solid electrolyte body 162, the pump electrode 163 and the counter electrode 165 constitute an oxygen pump cell for pumping and pumping oxygen in the gas to be measured in the measurement chamber 171 described later, and the counter electrode 165 faces the measurement chamber 171. The pump electrode 163 communicates with the outside via the porous layer 182.

The lead portion 163L is electrically connected to the sensor pad portion 13 via a through hole provided in the outer ceramic layer 183. Further, the lead portion 165L is electrically connected to the sensor pad portion 15 via a through hole provided in the pump cell layer 161 and the outer ceramic layer 183.
Then, the direction and magnitude of the current flowing between the pump electrode 163 and the counter electrode 165 are controlled by an external device from the two lead wires 71 via the sensor pad portions 13 and 15 according to the oxygen concentration in the measurement chamber 171. And oxygen is pumped.

A measurement chamber 171 is rectangularally opened on the tip end side (left side in FIG. 2) of the intermediate ceramic layer 170. Further, on both side surfaces on the long side of the intermediate ceramic layer 170, a diffusion porous layer 173 that partitions the measurement chamber 171 from the outside is arranged. On the other hand, on the front end side and the rear end side of the measurement chamber 171, the ceramic insulating layer 175 forming the side wall of the measurement chamber 171 is arranged.
The measurement chamber 171 communicates with the outside through the diffusion porous layer 173, and the diffusion porous layer 173 realizes gas diffusion between the outside and the measurement chamber 171 under a predetermined rate-determining condition.

The detection cell 150 includes a detection cell layer 151 having a second insulating layer 151a and a substantially rectangular plate-shaped solid electrolyte body 152, a reference gas side electrode 153 provided on the front and back surfaces of the solid electrolyte body 152, and a gas to be measured. It is provided with a side electrode 155. A penetrating portion 151h that opens in a substantially rectangular shape is provided on the tip end side (left side of FIG. 2) of the second insulating layer 151a, and the solid electrolyte 152 is arranged so as to be embedded in the penetrating portion 151h. The reference gas side electrode 153 includes a reference gas side electrode portion 153E and a lead portion 153L extending from the reference gas side electrode portion 153E toward the rear end side, and the measured gas side electrode 155 is a measured gas side electrode. It is composed of a portion 155E and a lead portion 155L extending from the measured gas side electrode portion 155E toward the rear end side.
The solid electrolyte 152, the reference gas side electrode 153, and the measured gas side electrode 155 constitute a detection cell for the oxygen concentration in the measured gas, and the measured gas side electrode portion 155E faces the measurement chamber 171. On the other hand, the reference gas side electrode portion 153E is ventilated to the outside through the lead portion 153L and the through hole.

The lead portion 153L is electrically connected to the sensor pad portion 14 via through holes provided in the detection cell layer 151, the intermediate ceramic layer 170, the pump cell layer 161 and the outer ceramic layer 183. Further, the lead portion 155L is electrically connected to the sensor pad portion 15 via through holes provided in the intermediate ceramic layer 170, the pump cell layer 161 and the outer ceramic layer 183.
Then, the detection signals of the reference gas side electrode 153 and the measured gas side electrode 155 are output from the sensor pad portions 14 and 15 to the outside via the two lead wires 71, and the oxygen concentration is detected.

The detection cell 150 and the pump cell 160 correspond to the "cells" in the claims, respectively. The reference gas side electrode 153 and the measured gas side electrode 155, and the pump electrode 163 and the counter electrode 165 each correspond to the "pair of electrodes" in the claims.
Further, the first insulating layer 161a and the second insulating layer 151a correspond to the "insulating layer" in the claims. The detection cell layer 151 and the pump cell layer 161 correspond to the "composite layer" in the claims.

In the sensor element 19, the direction and magnitude of the current flowing between the electrodes of the pump cell 160 are adjusted so that the voltage (electromotive force) generated between the electrodes of the detection cell 150 becomes a predetermined value (for example, 450 mV). It constitutes an oxygen sensor element that linearly detects the oxygen concentration in the measured gas according to the current flowing through the pump cell 160.

The heater 145 includes a first heater substrate 145a made of ceramic, a second heater substrate 145b made of ceramic, and a heat generating portion 146 arranged between the first heater substrate 145a and the second heater substrate 145b. The first heater substrate 145a faces the detection cell layer 151. The heating element 146 includes a heating element 146 m (see FIG. 3) having a meandering pattern, and a pair of lead portions 146 L extending from the heating element 146 m toward the rear end side.
The lead portion 146L is electrically connected to the heater pad portions 16 and 17 via a through hole provided in the second heater substrate 145b. Then, by energizing the heat generating portion 146 from the heater pad portions 16 and 17 via the two lead wires 71, the heat generating portion 146 generates heat and activates the solid electrolyte bodies 152 and 162.
The heat generating portion 146 (heater 145) is arranged on one side (lower side in FIG. 2) in the stacking direction with respect to the detection cell 150 and the pump cell 160.
The first heater substrate 145a and the second heater substrate 145b correspond to the "heater substrate" in the claims.

Next, the heat generating portion 146 will be described with reference to FIG.
As shown in FIG. 3, the heating element 146 includes a heating element 146m and a pair of lead portions 146L extending from the heating element 146 to the rear end side.
The heating element 146m includes a pair of outer linear portions 146m1 extending in the axis O direction, a pair of inner linear portions 146m2 arranged between the outer linear portions 146m1 and extending in the axis O direction, and adjacent outer linear portions 146m1. Two U-shaped first connecting portions 146j1 connecting the tip of the inner linear portion 146m2 and one U-shaped second connecting portion connecting the rear ends of the pair of inner linear portions 146m2. It consists of 146j2.
Further, each of the pair of lead portions 146L is connected to the rear end 146e of the outer linear portion 146m1.
In the present embodiment, the heating element 146 m of the heating unit 146 overlaps the detection cell 150 and the pump cell 160 in the stacking direction (see FIGS. 4 and 5), and heats both cells 150 and 160.
The rear end 146e of the outer linear portion 146m1 is the rearmost end portion of the portion where the width D1 of the outer linear portion 146m1 is constant, and is connected to the lead portion 146L having a width D2 (D2> D1) wider than the width D1. It is a boundary part.

Next, with reference to FIGS. 4 to 6, the positional relationship between the heat generating portion 146 (heater 145), the cells 150 and 160, and the heater substrates 145a and 145b will be described. FIG. 4 is a plan view showing the positional relationship between the heat generating portion 146 and the pump cell 160 and the heater substrates 145a and 145b, and FIG. 5 is a positional relationship between the heating unit 146 and the detection cell 150 and the heater substrates 145a and 145b. It is a plan view which shows.

First, as shown in FIGS. 4 and 5, assuming that the minimum distance between the side end portion of the heater substrate 145a and 145b and the side end portion of the outer linear portion 146m1 is A, 0.15 mm ≦ A ≦ 0.35 mm. be. Further, assuming that the minimum distance between the tip of the heater substrates 145a and 145b and the tip of the first connection portion 146j1 is B, 0.25 mm ≦ B ≦ 0.85 mm.

Next, as shown in FIG. 4, the overlapping region of the pump electrode portion 163E, the counter electrode portion 165E, and the solid electrolyte body 162 in the pump cell 160 is defined as S1. Here, when the overlapping region S1 is obtained, among the pair of electrodes 163 and 165 of the pump cell 160, the pump electrode portion 163E and the counter electrode portion 165E that effectively contribute to the electrode reaction as cells are targeted, and the lead portion 163L. Exclude 165L. Further, the boundary 163B between the pump electrode portion 163E and the lead portion 163L is the most advanced portion of the outer lead portion 163L of the solid electrolyte body 162 in which the width D3 is constant. The same applies to the boundary 165B between the counter electrode portion 165E and the lead portion 165L.
At this time, the pair of inner linear portions 146m2 overlap with the overlapping region S1 in the stacking direction, and are formed so as to straddle the rear end of the overlapping region S1.

Similarly, for the detection cell 150 of FIG. 5, the overlapping region of the reference gas side electrode portion 153E, the measured gas side electrode portion 155E, and the solid electrolyte body 152 of the detection cell 150 is defined as S2. The method for obtaining the boundary 153B and 155B between the reference gas side electrode portion 153E and the measured gas side electrode portion 155E and the lead portions 153L and 155L when the overlapping region S2 is obtained is also as described above.
At this time, the pair of inner linear portions 146m2 overlap with the overlapping region S2 in the stacking direction, and are formed so as to straddle the rear end of the overlapping region S2.
In the pump cell 160, since the pump electrode portion 163E and the counter electrode portion 165E are located inside the solid electrolyte body 162, the overlapping region S1 is the overlapping portion of the pump electrode portion 163E and the counter electrode portion 165E. On the other hand, in the detection cell 150, the reference gas side electrode portion 153E and the measured gas side electrode portion 155E are located outside the solid electrolyte body 152 in the width direction, so that the overlapping region S2 is the reference gas side electrode portion in the width direction. It is inside the 153E and the electrode portion 155E on the gas side to be measured.

As described above, by setting the minimum distances A and B between the side end portions and the tip portions of the heater substrates 145a and 145b and the heat generating portion 146 within an appropriate range, the side of the heater substrates 145a and 145b (and by extension, the sensor element 19) The heat generating portion 146 can be brought close to the end portion and the tip portion, and even if the heating rate of the heater 145 is increased, the increase in thermal stress in the vicinity of the heater 145 can be suppressed, the element cracking can be suppressed, and early activity can be realized. Further, since the heat generating portion 146 is not brought too close to the side end portion and the tip portion, the insulation between the heater 145 and the solid electrolyte bodies 162 and 152 can be ensured.

When 0.15 mm> A or 0.25 mm> B, when the conductive component (carbon soot) or water in the exhaust gas adheres to the side end or the tip of the heater substrates 145a and 145b, these are conducted. The insulation distance, which is the gap between the component or water and the heat generating portion 146, becomes short, and when the heat generating portion 146 is energized, the gap is easily broken down. As a result, the leak current from the heat generating portion 146 flows to the electrodes and the solid electrolyte of the cells 150 and 160, and the detection accuracy and the oxygen pumping ability are lowered. Further, since the temperature near the end of the element becomes high and the material strength decreases, cracks occur in the element even with a small stress. Further, the heat generating portion 146 may not be sufficiently embedded in the heater substrates 145a and 145b, and the heating portion 146 may be exposed on the end face.
When 0.35 mm <A or 0.85 mm <B, the heat generating portion 146 moves away from the side end portion or the tip portion of the heater substrates 145a and 145b, and when the heating rate of the heater 145 is increased, the thermal stress in the vicinity of the heater 145 is increased. May increase and cause element cracking.

Further, in the present embodiment, the solid electrolytes 162 and 152 are embedded in the first insulating layer 161a and the second insulating layer 151a, respectively. Therefore, when the conductive component (carbon soot) or water in the exhaust gas adheres to the side end portion or the tip portion of the first insulating layer 161a and the second insulating layer 151a, these conductive components or water and the solid electrolyte Since the first insulating layer 161a and the second insulating layer 151a insulate between the bodies 162 and 152, the heater 145 and the heater 145 are combined with the above-mentioned gaps A and B between the heater substrate 145a and 145b and the heat generating portion 146. Stable insulation can be ensured between the solid electrolytes 162 and 152.
That is, as shown in FIG. 6, even if the water 200 adheres to the end surface (side end surface) of the sensor element 19, the second insulating layer 151a insulates between the water 200 and the solid electrolyte 152 via the gap G2. At the same time, the space A between the water 200 and the heat generating portion 146 is insulated. As a result, a current path is not formed between the solid electrolyte body 152 and the heat generating portion 146, so that the gaps A and G2 are suppressed from dielectric breakdown, and insulation can be stably secured. Although the solid electrolyte 152 is shown in FIG. 6, the same applies to the solid electrolyte 162.

Further, a pair of inner linear portions 146 m2 overlap with the overlapping regions S1 and S2 in the stacking direction, respectively, and are formed so as to straddle the front end or the rear end (rear end in the examples of FIGS. 4 and 5) of the overlapping regions S1 and S2. Has been done.
As a result, the heat of the inner linear portion 146 m2 can be reliably transferred to the overlapping regions S1 and S2, which are the effective portions of the cells 160 and 150, and early activity can be more reliably realized, and the heater substrates 145a and 145b can be realized. The temperature difference (thermal stress) from the end can be further reduced.

As shown in FIGS. 4 and 5, in the present embodiment, the outer linear portion 146m1 is arranged on the side end side of the solid electrolyte body 162, 152 at a distance from the solid electrolyte body 162, 152. ..
By doing so, early activity can be realized more reliably, and the temperature difference (thermal stress) from the end portion of the heater substrate can be further reduced.

Further, when the length of the heating element 146 m shown in FIG. 3 in the axis O direction (the length from the tip of the first connecting portion 146j1 to the rear end 146e of the outer linear portion 146m1) is 4 to 10 mm, the heat generation range is set. The thermal stress does not increase too much due to the concentration of heat, and it is possible to suppress a decrease in the heating rate of the element and an increase in power consumption.
If the length is less than 4 mm, the thermal stress may increase due to the concentration of heat generation ranges. If the length exceeds 10 mm, the rate of temperature rise of the element may decrease and the power consumption may increase.
Further, when the total length of the gap A and the gap (minimum gap) G2 shown in FIG. 6 is 0.3 mm or more, the insulation between the heater 145 and the solid electrolyte bodies 162 and 152 can be secured more stably.

The structure and configuration of the sensor element and gas sensor of the present invention can be appropriately redesigned and embodied without departing from the gist of the present invention.
For example, in the above embodiment, the through hole provided in the insulating layer is filled with the paste of the solid electrolyte and embedded, but even in the embodiment in which the sheet-shaped solid electrolyte is inserted and arranged in the through hole of the insulating layer. good.
Further, in each cell, the pair of electrodes may protrude outside the solid electrolyte.
Further, the sensor element is not limited to the one that measures the oxygen concentration as long as it has one or more cells, but the one that measures the concentration of nitrogen oxides (NOx), hydrocarbons (HC), and the like. May be used.
Further, as shown in FIGS. 4 and 5, in the above embodiment, in all the cells of the sensor element, the inner linear portion overlaps with the overlapping region in the stacking direction and is formed so as to straddle the front end or the rear end of the overlapping region. However, it may be formed so as to overlap with the overlapping region of at least one cell in the stacking direction and to straddle the front end or the rear end of the overlapping region.

<Example 1>
As the sensor element 19 shown in FIGS. 2 to 5, a heating element 146 m having a resistance of 1.75 ± 0.05 Ω and having various changes in the value of A were manufactured. The value of B was constant at 1 mm. An initial voltage of 10 V is applied to the heating element 146 m of each sensor element 19, the element temperature is raised to 900 ° C., and then the cycle of quenching to room temperature is repeated for 100 cycles. The presence or absence of was visually determined.
When there were no cracks, the voltage was increased by 0.5 V to determine the presence or absence of cracks after performing the same cycle test, and this was repeated until cracks occurred, and the voltage at the time of cracks was determined.
Ten sensor elements 19 each having A and B as predetermined values were manufactured, the cycle test was performed on the ten sensor elements 19, and the failure rate of 0.1% was obtained by Weibull analysis for the ten data. The voltage of the heating element 146 m at that time was obtained. The higher the voltage, the higher the heating rate of the heater without causing cracks in the sensor element 19 (without increasing the thermal stress). When the voltage is 12 V or more, it can be considered that early activity can be realized by increasing the heating rate of the heater.

<Example 2>
In the same manner as in Example 1, the value of B is variously changed, the sensor elements 19 in which the value of A is constant at 0.2 mm are manufactured, and the cycle test is performed in the same manner when the failure rate is 0.1%. The voltage of the heating element 146 m was obtained.

The obtained results are shown in FIGS. 7 and 8, respectively.
As is clear from FIGS. 7 and 8, if 0.15 mm ≤ A ≤ 0.35 mm and 0.25 mm ≤ B ≤ 0.85 mm, the voltage of the heating element 146 m when the failure rate is 0.1% is 12 V. It can be seen that the above can be achieved and early activity can be realized without causing cracks in the sensor element 19.
When 0.15 mm> A or 0.25 mm> B, the thermal stress decreases, but the material strength also decreases for the above reason, and it is considered that cracks occur even with a small stress. Therefore, the method of making a judgment based on the voltage at which a crack occurs in this experiment is also suitable for determining the lower limits of A and B.

1 Gas sensor 11 Main metal fittings 19 Sensor element 145 Heater 145a, 145b Heater substrate (1st heater substrate, 2nd heater substrate)
146 Heating element 146m Heating element 146m1 Outer linear part 146m2 Inner linear part 146j1 First connection part 146j2 Second connection part 146e Rear end of outer linear part 146L Lead part 160,150 Cell (pump cell, detection cell)
161 and 151 composite layer (pump cell layer, detection cell layer)
161a, 151a Insulation layer (first insulation layer, second insulation layer)
161h, 151h Through hole 162,152 Solid electrolyte 153 and 155, 163 and 165 Pair of electrodes O-axis S1, S2 Overlapping region

Claims (4)

One or more cells having a composite layer in which a solid electrolyte is arranged in a through hole provided in the insulating layer, and a pair of electrodes formed on the surface of the solid electrolyte.
A heater substrate arranged in the stacking direction of the composite layer, and a heater provided on the heater substrate and provided with a heat generating portion for heating at least one cell.
Is a sensor element that extends in the axial direction.
The heat generating portion includes a pair of outer linear portions extending in the axial direction, a pair of inner linear portions arranged between the outer linear portions, and an adjacent outer linear portion. A heating element consisting of a first connecting portion connecting the tip and the tip of the inner linear portion, and a second connecting portion connecting the rear ends of the pair of inner linear portions, and a pair of the outer linear portions. Consists of a pair of lead sections connected to the rear end of the section,
The minimum distance A between the side end portion of the heater substrate and the side end portion of the outer linear portion is 0.15 mm ≦ A ≦ 0.35 mm.
The minimum distance B between the tip end portion of the heater substrate and the tip end portion of the first connection portion is 0.25 mm ≦ B ≦ 0.85 mm.
The total length of the minimum distance G2 between the side end portion of the insulating layer and the side end portion of the solid electrolyte in the composite layer and the minimum distance A is 0.3 mm or more.
The inner linear portion overlaps the overlapping region of the pair of electrodes and the solid electrolyte body in the stacking direction, and is formed so as to straddle the front end or the rear end of the overlapping region. .. The sensor element according to claim 1, wherein the outer linear portion is arranged on the side end side of the solid electrolyte body at a distance from the solid electrolyte body. The sensor element according to claim 1 or 2, wherein the inner linear portion is formed so as to straddle the front end and the rear end of the overlapping region of the pair of electrodes. A gas sensor including a sensor element for detecting a specific gas in a gas to be measured and a main metal fitting for holding the sensor element.
A gas sensor including the sensor element according to any one of claims 1 to 3, as the sensor element.

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