JP2019207134A - Gas sensor - Google Patents

Abstract

To provide a gas sensor which can be down-sized while securing responsiveness, and can suppress a water splash to a detection element.SOLUTION: In a gas sensor having a plate-shaped detection element having a detection part 22, a main metal fixture, and a protector fixed to the main metal fixture while accommodating the detection part of the detection element therein, the protector has a cylindrical inside protector 51 and a cylindrical outside protector 61 which are arranged with an interval from the detection part, and the inside protector has an inside gas discharge hole 53 which can derive a measured gas G to the outside at its own bottom part, and an inside gas introduction hole 56 which can introduce the measured gas therein at a rear end side rather than the inside gas discharge hole. The inside gas introduction hole further has a louver 55 which is arranged at a tip side rather than a tip 21e of the detection element, contacts with a tip of the inside gas introduction hole, and extends toward the detection part so that an extension line EL of its own rear-end directed face 55e intersects with the detection part.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a gas sensor including a detection element and a protector.

  Conventionally, a gas sensor is known in which a plate-shaped detection element is assembled to a cylindrical metal shell and the tip side of the detection element is protected by a protector (Patent Document 1). This gas sensor has a double structure consisting of an inner cover and an outer cover as a protector. The inner cover has an inner introduction opening for introducing a gas to be measured, and an inner cover from the tip of the inner introduction opening in the axial direction. And a louver portion bent inside. The louver portion adjusts the flow of the gas to be measured introduced into the inner introduction opening and introduces it into the inner cover.

JP 2014-122876 A

By the way, with the demand for downsizing the dimensions of the gas sensor, it is desired to shorten the detection element. However, in the case of the gas sensor described in Patent Document 1, the detection element is arranged on the tip side from the inner introduction opening. If the detection element is shortened, there is no room for moving the inner introduction opening to the rear end side, and the size cannot be reduced. In this gas sensor, if the detection element is simply arranged on the rear end side, it does not match the gas flow of the louver provided in the inner introduction opening, and the detection element is not sufficiently exposed to the gas to be measured. Responsiveness may be reduced.
In the case of the gas sensor described in Patent Document 1, since the detection element is arranged on the tip side from the inner introduction opening, the detection element is submerged when water enters from the inner introduction opening. There is also a problem that it is easy.

  This invention is made | formed in view of this present condition, Comprising: It aims at providing the gas sensor which can suppress a water | moisture content of a detection element while being able to miniaturize a gas sensor, ensuring responsiveness.

  The gas sensor of the present invention includes a plate-like detection element that extends in the axial direction and has a detection unit for detecting a specific gas component in the gas to be measured on its tip side, and the detection unit protrudes from its tip. However, in the gas sensor comprising: a cylindrical metal shell surrounding the periphery of the detection element in the radial direction; and a protector fixed to the metal shell while accommodating the detection portion of the detection element therein A cylindrical inner protector disposed across the detector and a gap, and a cylindrical outer protector disposed radially outward of the inner protector, the inner protector externally passing a gas to be measured An inner gas discharge hole which can be led out to the bottom of the inner gas discharge hole, and an inner gas introduction hole which can introduce the gas to be measured into the inside thereof at a rear end side of the inner gas discharge hole. The gas introduction hole is disposed on the front side of the detection element, is in contact with the front end of the inner gas introduction hole, and faces the detection unit so that an extension line of the rear end surface thereof intersects the detection unit. And a louver extending further.

According to this gas sensor, since the extension line of the louver rearward facing surface intersects the detection unit, the gas to be measured introduced from the inner gas introduction hole into the inner protector is guided by the louver toward the detection unit. Flowing.
For this reason, when the detection element is shortened and the gas sensor is downsized, the detection unit is sufficiently exposed to the gas G to be measured by the louver even if the inner gas introduction hole is closer to the tip side than the tip of the detection element. The gas sensor can be downsized while ensuring responsiveness.
In addition, since the inner gas introduction hole is located on the front end side with respect to the front end of the detection element, even if water enters from the inner gas introduction hole, the detection element can be prevented from being wet.

In the gas sensor of the present invention, the outer protector has an outer gas introduction hole through which the gas to be measured can be introduced into itself, and the outer gas introduction hole is disposed on a tip side of the inner gas introduction hole. May be.
According to this gas sensor, even if water enters the inside from the outer gas introduction hole, it is difficult for water to enter the inside gas introduction hole 56, and the detection element 21 can be further prevented from being wet.

In the gas sensor of the present invention, the inner gas introduction hole may be provided in a tapered wall that is narrowed toward the tip.
According to this gas sensor, since the flow direction of the gas to be measured from the outside toward the inner gas introduction hole is directed toward the oblique rear end, the gas to be measured (on the rear end side) is detected in combination with the action of the louver. It is possible to guide more reliably toward.

In the gas sensor according to the present invention, the length of the louver toward the detection unit may be 1/2 or more of a circle-equivalent diameter of the outer gas introduction hole.
According to this gas sensor, the length of the louver is sufficient with respect to the flow rate of the gas to be measured introduced from the outer gas introduction hole, and hence the inner gas introduction hole, and the gas to be measured is more reliably guided toward the detection unit. be able to.

  According to the present invention, it is possible to obtain a gas sensor that can reduce the size of the gas sensor while ensuring the responsiveness and can suppress the moisture of the detection element.

It is sectional drawing of the gas sensor concerning embodiment of this invention. It is a partial expanded sectional view of the front end side of a detection element. It is a partial expanded sectional view of FIG. It is a fragmentary perspective view which shows the external appearance of the inner side gas introduction hole vicinity of an inner side protector. It is a figure which shows the modification of an inner side gas introduction hole.

  An embodiment of the present invention will be described in detail with reference to FIGS. 1 is a cross-sectional view of a gas sensor 1 according to an embodiment of the present invention, FIG. 2 is a partial enlarged cross-sectional view of a front end side of a detection element 21, FIG. 3 is a partial enlarged cross-sectional view of FIG. FIG. 6 is a partial perspective view showing an external appearance in the vicinity of an inner gas introduction hole 56.

In FIG. 1, a gas sensor (full-range air-fuel ratio gas sensor) 1 includes a detection element 21, a holder (ceramic holder) 30 having a through hole 32 that passes through the detection element 21 through the axis O direction, and a ceramic holder 30. And a metal shell 11 surrounding the periphery in the radial direction.
In the detection element 21, a portion closer to the tip where the detection unit 22 is formed protrudes from the ceramic holder 30 to the tip. The detection element 21 thus passed through the through-hole 32 is made up of a sealing material 41 (talc in this example) disposed on the rear end surface side (the upper side in the figure) 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 45, the airtightness is fixed in the front-rear direction inside the metal shell 11 and fixed.
The portion near the rear end 29 including the rear end 29 of the detection element 21 protrudes rearward from the sleeve 43 and the metal shell 11, and the electrode terminal 24 formed at the portion closer to the rear end 29 is connected to the outside through the grommet 85. A terminal metal fitting 75 provided at the tip of each lead wire 71 drawn out is pressed and electrically connected. Further, a portion near the rear end 29 including the electrode terminal 24 is covered with an outer cylinder 81. This will be described in more detail below.

The detection element 21 extends in the direction of the axis O, and includes a detection electrode or the like (see FIG. 2) on the tip side (lower side in the drawing) directed toward the measurement object, and detects a specific gas component in the detected gas. It has a strip shape (plate shape) with The cross section of the detection element 21 is formed as a long and narrow rectangle (rectangular shape). The detection element 21 itself is the same as a conventionally known one, and a pair of detection electrodes forming the detection unit 22 is arranged near the front end of the solid electrolyte (member), and the detection electrode 21 is connected to this near the rear end. The electrode terminal 24 for connecting the lead wire 71 for taking out the detection output is exposed.
Further, in this example, a heater (not shown) is provided in the vicinity of the tip of the detection element 21, and the lead wire 71 for applying a voltage to the heater is connected to the vicinity of the rear end. The electrode terminal 24 is exposed and formed. Although not shown, these electrode terminals 24 are formed in a vertically long rectangle. For example, three or two electrode terminals are arranged side by side on the wide surface (both sides) of the strip at a portion near the rear end 29 of the detection element 21. It is out.
The detection portion 22 of the detection element 21 is covered with a porous protective layer 23 made of alumina or spinel.

The metal shell 11 has a cylindrical shape with concentric and different diameters at the front and the rear, a tip end side having a small diameter, and a cylindrical annular portion (hereinafter also referred to as a cylindrical portion) 12 for externally fitting and fixing a protector 50 described later. A screw 13 for fixing to an engine exhaust pipe having a larger diameter is provided on the outer peripheral surface behind (upward in the drawing). In addition, a polygonal portion 14 for screwing the sensor 1 with the screw 13 is provided behind it. Further, behind the polygonal portion 14, a cylindrical portion 15 for externally fitting and welding a protective cylinder (outer cylinder) 81 that covers the back of the gas sensor 1 is provided, and the outer diameter is provided behind it. A small and thin caulking cylindrical portion 16 is provided. The caulking cylindrical portion 16 is bent inward in FIG. 1 after caulking. A gasket 19 for sealing at the time of screwing is attached to the lower surface of the polygonal portion 14.
On the other hand, the metal shell 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 17 that tapers radially inward from the rear end side toward the front end side.

A ceramic holder 30 made of an insulating ceramic (for example, alumina) and formed in a substantially short cylindrical shape is disposed inside the metal shell 11. The ceramic holder 30 has a tip-facing surface 30a that is tapered toward the tip. Then, the ceramic holder 30 is positioned in the metal shell 11 by pressing the ceramic holder 30 from the rear end side with the sealing material 41 while the portion near the outer periphery of the front-facing surface 30a is locked to the stepped portion 17. And the gap is fitted.
On the other hand, the through-hole 32 is provided at the center of the ceramic holder 30 and is a rectangular opening having substantially the same size as the cross section of the detection element 21 so that the detection element 21 passes through with almost no gap.

The detection element 21 is passed through the through hole 32 of the ceramic holder 30, and the tip of the detection element 21 is protruded further forward than the tip 12 a of the ceramic holder 30 and the metal shell 11.
On the other hand, the tip portion of the detection element 21 is covered with a bottomed cylindrical protector (protective cover) 50 having a double structure of a cylindrical inner protector 51 and an outer protector 61. Among these, the rear end of the inner protector 51 is externally fitted and welded to the cylindrical portion 12 of the metal shell 11. Further, the outer protector 61 is externally fitted to the inner protector 51 and is welded to the cylindrical portion 12 at the same time.
The inner protector 51 is disposed with a gap from the detection unit 22 and has an inner gas introduction hole 56 and an inner gas discharge hole 53. The outer protector 61 is disposed on the radially outer side of the inner protector 51 and has an outer gas introduction hole 66 and an outer water draining hole 63.
For example, six inner gas introduction holes 56 are provided in the circumferential direction of the inner protector 51, and one inner gas discharge hole 53 is provided at the center of the bottom of the inner protector 51.
For example, six outer gas introduction holes 66 are provided in the circumferential direction of the outer protector 61, and one outer drain hole 63 is provided at the center of the bottom of the outer protector 61.
The detailed configuration of the protector 50 will be described later.

Further, as shown in FIG. 1, each electrode terminal 24 formed near the rear end 29 of the detection element 21 has each terminal fitting provided at the tip of each lead wire 71 drawn out through a grommet 85 to the outside. 75 is pressed by its spring property and is electrically connected. And in this gas sensor 1 of this example, each terminal metal fitting 75 containing this press-contact part is each provided in each accommodating part provided in the insulating separator 91 arrange | positioned in the outer cylinder 81 by opposing arrangement | positioning. Yes. In addition, the movement of the separator 91 in the radial direction and the distal end side is restricted via a holding member 82 that is caulked and fixed in the outer cylinder 81. The rear end of the gas sensor 1 is covered in an airtight manner by fitting the front end portion of the outer cylinder 81 to the cylindrical portion 15 near the rear end of the metal shell 11 and welding it.
The lead wire 71 is pulled out through a grommet (for example, rubber) 85 disposed inside the small-diameter cylindrical portion 83 located at the rear end of the outer cylinder 81, and the small-diameter cylindrical portion 83 is reduced in diameter. By compressing the grommet 85 of the caulking lever, the airtightness of this portion is maintained.

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

  Next, the detection element 21 will be described with reference to FIG. For the sake of easy understanding, FIG. 2 shows an exaggerated dimension in the thickness direction of the detection element 21.

The detection element 21 includes an oxygen concentration detection cell 130, an oxygen pump cell 140, and a heater 200.
The oxygen concentration detection cell 130 is formed of a first solid electrolyte body 105 and a first electrode 104 and a second electrode 106 formed on both surfaces of the first solid electrolyte 105. The oxygen pump cell 140 includes a second solid electrolyte body 109 and a third electrode 108 and a fourth electrode 110 formed on both surfaces of the second solid electrolyte body 109.
The heater 200 includes a first base 101 and a second base 103 mainly composed of alumina, and a heating element 102 mainly composed of platinum sandwiched between the first base 101 and the second base 103.

An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130. A hollow gas detection chamber 107 c is formed at a position corresponding to the second electrode 106 and the third electrode 108 in the insulating layer 107. The gas detection chamber 107c communicates with the outside in the width direction of the insulating layer 107, and the communication portion has a diffusion rate-determining method that realizes gas diffusion between the outside and the gas detection chamber 107c under a predetermined rate-limiting condition. Part 115 is arranged.
The diffusion control part 115 is a porous body made of alumina. The diffusion rate-determining unit 115 performs rate-limiting when the detection gas flows into the gas detection chamber 107c.
A portion where the flow hole through which the gas detection chamber 107 c and the outside such as the diffusion rate controlling portion 115 circulate is exposed to the outer surface of the detection element 21 is regarded as the “detection portion 22”. This is because the region where the gas to be measured guided to the detection element 21 by the louver 55 described later flows into the detection element 21 is the diffusion rate limiting unit 115.

  A protective layer 111 is formed on the surface of the second solid electrolyte body 109, and a portion of the protective layer 111 that covers the fourth electrode 110 is porous for allowing oxygen to enter and exit between the fourth electrode 110 and the outside air. A quality part 113a is provided. The detection element 21 has a direction and a magnitude of a current flowing between the electrodes of the oxygen pump cell 140 so that a voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130 becomes a predetermined value (for example, 450 mV). Is adjusted, and the oxygen concentration in the gas to be measured corresponding to the current flowing through the oxygen pump cell 140 is linearly detected.

Next, the protector 50 will be described with reference to FIGS.
The inner protector 51 is formed in a bottomed cylindrical shape with the tip end closed, and has an inner gas discharge hole 53 at the center of the bottom. The outer protector 61 is also formed in a bottomed cylindrical shape with the tip end closed, and has an outer drain hole 63 at the center of the bottom.
The outer drain hole 63 is larger in diameter than the outer diameter of the tip portion of the inner protector 51, and the tip of the outer protector 61 and the tip of the inner protector 51 are flush with each other inside the outer drain hole 63. When the distal end portion of the inner protector 51 is disposed on the inner surface, a ring-shaped gap Cv is formed between the inner surface of the outer drain hole 63 and the outer surface of the distal end portion of the inner protector 51, and the outer protector 61 and the inner protector are formed from the gap Cv. The water accumulated between 51 and 51 can be discharged.
On the other hand, the gas G to be measured is introduced from the outer gas introduction hole 66 into the inner protector 51 through the inner gas introduction hole 56 and then discharged from the inner gas discharge hole 53 to the outside.

In addition, a tapered wall 51t that narrows toward the tip is provided at the central portion in the axis O direction of the inner protector 51, and the inner protector 51 has a larger diameter on the rear end side than the tapered wall 51t. The tapered wall 51t is provided with a rectangular inner gas introduction hole 56 (see FIG. 4).
Further, as shown in FIG. 4, a louver 55 is provided that contacts the tip 56 f of the inner gas introduction hole 56 and extends radially inward toward the detection unit 22. In the present embodiment, the louver 55 is formed by cutting out the tapered wall 51t in a U-shape so that the tip remains, and cutting the cut-out piece radially inward. Further, the cut-out portion becomes a rectangular inner gas introduction hole 56. In this way, the distal end 56f of the inner gas introduction hole 56 and the proximal end of the louver 55 are integrally connected (contacted).

Returning to FIG. 3, the louver 55 extends so that the extension line EL of the rear end facing surface 55 e of the louver 55 intersects the detection unit 22. Further, the inner gas introduction hole 56 is disposed on the front end side of the front end 21 e of the detection element 21. Further, the inner gas introduction hole 56 is disposed on the rear end side with respect to the inner gas discharge hole 53.
Further, in the present embodiment, the outer gas introduction hole 66 is disposed on the tip side of the inner gas introduction hole 56. Further, the length L1 (see FIG. 4) of the louver 55 toward the detection unit 22 is 1/2 or more of the equivalent circle diameter of the outer gas introduction hole 66.
Here, the tip 21 e of the detection element 21 is the forefront of the detection element 21, but when the protective layer 23 covers the surface of the detection element 21, it is the tip of the protective layer 23.
Further, the inner gas introduction hole 56 is disposed on the rear end side with respect to the inner gas discharge hole 53. The front end of the inner gas introduction hole 56 is located on the rear end side with respect to the rear end of the inner gas discharge hole 53. This does not include the case where the inner gas introduction hole 56 and the inner gas discharge hole 53 partially overlap in the direction of the axis O. The outer gas introduction hole 66 is disposed on the front end side with respect to the inner gas introduction hole 56, and similarly, the rear end of the outer gas introduction hole 66 is located on the front end side with respect to the front end of the inner gas introduction hole 56.

As described above, the extension line EL of the rear end facing surface 55 e of the louver 55 intersects the detection unit 22, so that the measured gas G introduced into the inner protector 51 from the inner gas introduction hole 56 is guided to the louver 55. And flows toward the detection unit 22.
Therefore, when the detection element 21 is shortened to reduce the size of the gas sensor, the detection unit 22 is sufficiently measured gas by the louver 55 even if the inner gas introduction hole 56 is closer to the front end side than the front end 21e of the detection element 21. Since it is exposed to G, the gas sensor can be miniaturized while ensuring responsiveness.
Further, since the inner gas introduction hole 56 is located on the tip side of the tip 21e of the detection element 21, even if water enters from the inner gas introduction hole 56, the detection element 21 can be prevented from being wet. .
The reason why the extended line EL is based on the rear end facing surface 55e of the louver 55 is that the gas to be measured G is affected by gravity, and therefore the flow of the gas to be measured G is guided from under the gas to be measured G. It is necessary.

Further, in the present embodiment, the outer gas introduction hole 66 is disposed on the tip side of the inner gas introduction hole 56. Accordingly, even if water enters from the outer gas introduction hole 66, it is difficult for water to enter the inside gas introduction hole 56, and the detection element 21 can be further prevented from being wet.
In the present embodiment, the inner gas introduction hole 56 is provided in the tapered wall 51t that is narrowed toward the tip. As a result, the flow direction of the measurement gas G from the outside (outer gas introduction hole 66) toward the inner gas introduction hole 56 is inclined rearward, so that the measurement gas G is combined with the action of the louver 55. It is possible to guide more reliably toward the detection unit 22 (on the rear end side).
In the present embodiment, the length L1 of the louver 55 toward the detection unit 22 is ½ or more of the equivalent circle diameter of the outer gas introduction hole 66. As a result, the length L1 of the louver 55 is sufficient with respect to the flow rate of the gas to be measured G introduced from the outer gas introduction hole 66, and hence the inner gas introduction hole 56, and the measurement gas G is more directed toward the detection unit 22. It can be surely guided.

The gas sensor of the present invention can be embodied by appropriately changing the structure and configuration without departing from the gist of the present invention.
For example, in the above embodiment, the inner gas introduction hole 56 is rectangular, but as shown in FIG. 5, for example, the tip 76f of the inner gas introduction hole 76 may be linear and the other part may be semicircular. In this case, the louver 75 may also be semicircular on the tip side.
For example, in the above-described embodiment, the inner gas introduction hole 56 is provided in the tapered wall 51t of the inner protector 51. However, the present invention is not limited to this, and the inner gas introduction hole 56 may be provided on the side surface of the inner protector 51.
For example, in the above-described embodiment, the outer gas introduction hole 66 is disposed on the front end side with respect to the inner gas introduction hole 56, but not limited thereto, the outer gas introduction hole 66 may be disposed on the rear end side with respect to the inner gas introduction hole 56.
The numbers of the inner gas introduction holes 56, the inner gas discharge holes 53, and the outer gas introduction holes 66 are not limited.
For example, when the diffusion control unit 115 is provided on the tip-facing surface of the detection element 21, the position of the detection unit 22 is considered to be on the tip-facing surface.

  Moreover, the shape of the whole protector is not limited to the said embodiment, For example, the outside drain hole 63 of the outside protector 61 may be eliminated. Further, an outer gas discharge hole communicating with the inner gas discharge hole 53 may be provided at the bottom of the outer protector 61.

DESCRIPTION OF SYMBOLS 1 Gas sensor 11 Main metal fitting 21 Detection element 21e The front-end | tip of a detection element 22 Detection part 50 Protector 51 Inner protector 51t Tapered wall 53 Inner gas discharge hole 55, 75 Louver 55e Rear end facing surface 56, 76 Inner gas introduction hole 56f, 76f End of inner gas introduction hole 61 Outer protector 66 Outer gas introduction hole O Axis G Gas to be measured EL Extension line L1 Length toward louver detector

Claims (4)

A plate-like detection element that extends in the axial direction and has a detection unit for detecting a specific gas component in the gas to be measured on its tip side;
A cylindrical metal shell that surrounds the periphery of the detection element in the radial direction while projecting the detection unit from its tip,
A protector fixed to the metal shell while accommodating the detection unit of the detection element inside,
In a gas sensor comprising:
The protector includes a cylindrical inner protector disposed via the detection unit and a gap, and a cylindrical outer protector disposed on a radially outer side of the inner protector,
The inner protector has an inner gas discharge hole at its bottom that can lead the measurement gas to the outside, and an inner gas introduction hole that can introduce the measurement gas into the inside of the inner protector than the inner gas discharge hole. On the rear end side,
The inner gas introduction hole is disposed on the tip side of the tip of the detection element,
A gas sensor, further comprising a louver that is in contact with a tip of the inner gas introduction hole and extends toward the detection unit such that an extension line of a surface facing the rear end thereof intersects the detection unit.   The said outer protector has the outer gas introduction hole which can introduce | transduce the said to-be-measured gas in its inside, The said outer gas introduction hole is arrange | positioned in the front end side rather than the said inner gas introduction hole. Gas sensor.   The gas sensor according to claim 1, wherein the inner gas introduction hole is provided in a tapered wall that narrows toward a tip.   The gas sensor according to any one of claims 1 to 3, wherein a length of the louver toward the detection unit is 1/2 or more of a circle-equivalent diameter of the outer gas introduction hole.

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