JPH10177005A - Gas concentration detection element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration detection element that has a high temperature preservation property, is prevented from adhesion and deposition of particulates and hence is prevented from occurrence of detection error, and is capable of obtaining a sufficient responsiveness. SOLUTION: The element has a gas concentration detector 2 for detecting, for example, the concentration of oxygen in an exhaust gas and a cover body 3 in double cylinder shape for surrounding a part that is exposed to the exhaust gas. A plurality of gas circulation holes 33, 34 are provided at the tip part in the direction of the axial line of the cover body 3 so that one of them functions as a port for introducing the exhaust gas and the other functions to allow a gas to be exchanged smoothly. The side part of the cover body 3 is made of a closed wall part without any opening, thus preventing the exhaust gas to cool the cover body 3 and the gas concentration detector 2 easily, improving a temperature preservation property, and preventing particulates from being adhered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration detecting element for detecting a concentration of a specific gas component in a gas to be measured, and more particularly to a gas concentration detecting element suitable for detecting an oxygen concentration or the like in an exhaust gas of an internal combustion engine. is there.

[0002]

2. Description of the Related Art A gas concentration detecting element is provided on an exhaust pipe wall of an internal combustion engine to detect oxygen concentration and the like in exhaust gas, and to perform feedback control of a fuel injection amount and an EGR amount of an exhaust gas recirculation (EGR) system. Has been done. FIG. 10 shows an example of this type of gas concentration detecting element. The gas concentration detecting element has a housing 92 fixed to an exhaust pipe P wall of an internal combustion engine at a flange 91, and has a tubular gas concentration detecting element therein. The detection body 93 is housed. The gas concentration detector 93 has a lower half protruding from the housing 92 and located in the exhaust pipe P, and its periphery is protected by a cover body 94. The gas concentration detector 93 is formed by forming electrodes such as platinum on the inner and outer surfaces of a tubular portion made of a solid electrolyte such as zirconia, and has a built-in heater 95 for heating the electrodes to improve detection sensitivity. .

The cover 94 is provided with a gas concentration detector 93.
Is kept warm and protected from mechanical shock, and usually has a double structure of an inner cylinder 94a and an outer cylinder 94b as shown in the figure. The inner cylinder 94a and the outer cylinder 94b are alternately provided with gas circulation holes 941 and 942 at a plurality of locations on the side wall, respectively, to protect the electrodes by reducing the flow velocity of the inflowing exhaust gas. In the drawing, reference numeral 96 denotes an upper cover that covers the upper half of the gas concentration detection element, and 97 denotes a gas concentration detector 93.
Is a terminal connected to the electrode through a lead wire.

The gas concentration detecting element having the above structure is used for controlling the fuel injection amount of a gasoline engine.
It is also used for controlling quantity. Gas concentration detector 93
As is well known, since the oxygen ion conductivity depends on the temperature, the heater 95 heats the gas concentration detector 93 when the exhaust gas temperature is low.

However, the heat supplied to the gas concentration detector 93 is radiated from the outer surface of the gas concentration detector 93 into the exhaust gas. As is well known, a diesel engine has a lower exhaust gas temperature and a higher exhaust gas flow rate than a gasoline engine. Therefore, when such an exhaust gas collides with the outer surface of the gas concentration detector 93, the The concentration detector 93 is rapidly cooled. In order to prevent the cooling of the gas concentration detector 93 as much as possible, the tip of the gas concentration detector 93 which is exposed to the exhaust gas is designed so that the exhaust gas does not directly collide with the outer surface of the gas concentration detector 93. It is conceivable that the portion is surrounded by a cover body 94 and the cover body 94 improves the heat retention of the gas concentration detector 93.

[0006]

However, in the conventional gas concentration detecting element for a gasoline engine, gas flow holes 941 and 942 are formed in the cover 94 in a direction in which the exhaust gas collides directly with the peripheral wall. Therefore, the exhaust gas flows through the cover body 94 through the gas circulation holes 941 and 942 and without a gas flow velocity being reduced so much.

For this reason, when the gas concentration detecting element having the above-described cover 94 is applied to a diesel engine, the heat retention of the gas concentration detector 93 by the cover 94 is not sufficient, and the surface of the gas concentration The temperature of the cover body 94 and the temperature of the cover body 94 itself are also lowered, and the particulates in the exhaust gas of the diesel engine easily adhere to and accumulate on these surfaces. Particulate is soot
(Soot), containing SOF (soluble organic component)
OF has a high viscosity and mediates the adhesion of Soot, but the lower the surface temperature of the gas concentration detector 93 and the cover 94, the less the SOF volatilizes, and therefore the more easily the particulates adhere to the surface.

When a part of the attached and deposited particulates is burned by high-temperature exhaust gas during high-power operation of the engine, the component concentration (oxygen concentration) of the exhaust gas around the gas concentration detector 93 is changed and detected. This may cause an error. Further, the gas flow holes 941 and 942 may be clogged by particulates, and the flow of the exhaust gas may be deteriorated, resulting in a decrease in detection responsiveness or erroneous detection. To avoid this, there are problems that the load on the heater 95 increases and the amount of power required for heating increases.

In Japanese Utility Model Application Laid-Open No. 53-103784, a heat mass having a large heat capacity is provided at a closed portion at the tip of the cover body so as to enhance the heat-retaining effect of the gas-sensitive portion with respect to the temperature fluctuation of the exhaust gas. An oxygen concentration sensor is disclosed. However, in the above configuration, since the gas flow holes are formed in the side portions of the cover body, the same problem as described above occurs.

As a countermeasure against this, the present inventor has proposed that, for example, without forming a gas flow hole on the side of the cover, the amount of exhaust gas which is formed at the tip of the cover and comes into contact with the gas concentration detector It is considered that the cooling of the cover is suppressed by reducing the flow rate and avoiding the gas flow flowing across the gas concentration detector and the cover. U.S. Pat. No. 5,073,247 discloses a prior art for such a concept. Although this conventional example does not disclose a direct idea of suppressing the cooling of the gas concentration detector and the cover, the gas concentration detector and the cover are formed at the tip without forming a gas flow hole on the side of the cover. They are structurally signed in terms of points.

However, in this conventional example, since there is only one gas flow hole provided at the tip of the cover, the inflow and outflow of exhaust gas into the inside of the cover proceed simultaneously in the same gas flow hole. Therefore, gas exchange via the gas flow holes is not performed smoothly. As a result, there is a problem that the detection response is poor.

It is an object of the present invention to provide a gas concentration detecting element which can enhance the heat retention, prevent the deposition and accumulation of particulates, prevent the occurrence of a detection error and the like, and obtain a sufficient response. With the goal.

[0013]

According to a first aspect of the present invention, there is provided a gas concentration detecting element for detecting a concentration of a gas component in a gas to be measured. And a cover body surrounding a portion of the portion exposed to the gas to be measured. The cover body has a plurality of openings at the tip end in the axial direction, each of which functions as an inlet or outlet for the gas to be measured, and the side of the cover body excluding the tip has an opening. There are no closed walls.

In the above configuration, the opening is provided only at the tip end in the axial direction of the cover, so that the cover or the gas concentration detecting unit due to the inflow and outflow of the exhaust gas is different from the conventional configuration having the opening at the side. Is suppressed. Therefore, the heat retention is improved without increasing the load on the heater, and the occurrence of a detection error due to the attachment of particulates can be prevented. Further, since the opening is provided at the distal end, the flow of the exhaust gas does not directly hit the opening, so that the opening is not easily clogged. Further, since a plurality of the openings are provided, one of the openings functions as an inlet for the gas to be measured, and one of the openings functions as an outlet. Therefore, the flow of the exhaust gas is made smoother than in the case where the number of the openings is one, and the detection response is greatly improved.

Alternatively, one opening is provided at the axial end of the cover body, and the opening has a shape having a plurality of holes and a narrow portion communicating with the plurality of holes. The plurality of holes may be configured to function as an inlet or outlet for the gas to be measured (claim 2). It is the same as claim 1 that no opening is provided on the side of the cover except for the tip.

Also in this case, the same effect as that of the first aspect can be obtained by providing the opening only at the front end. Although only one opening is provided, one of the plurality of holes communicating with the narrow portion functions as an inlet for the gas to be measured and one of the holes functions as an outlet, so that the exhaust gas can flow smoothly. Therefore, a sufficiently high detection response can be realized.

The cover body may have a double cylinder structure in which an inner cylinder and an outer cylinder having different diameters are arranged concentrically. As described above, by double protecting the periphery of the gas concentration detector, the heat insulating effect of the cover can be further enhanced. Alternatively, the cover body has an inner cylinder having a different diameter, a triple cylinder structure in which the middle cylinder and the outer cylinder are concentrically arranged, or a plurality of cylinders arranged between the inner cylinder and the outer cylinder to further increase A multi-cylinder structure may be adopted (claim 4).

In the case where the cover body has a double or more multi-cylinder structure, the plurality of openings are formed by providing a tip portion only in the innermost inner cylinder, and the outer cylinder body may be open at the tip. Good (claim 5). At this time, since the outer cylinder is open at the tip, the heat of the opening serving as the inlet or outlet of the gas to be measured does not escape to the outer cylinder and is released from the side. Can be prevented. Therefore, the temperature near the opening can be maintained at a high temperature, and the heat retention can be improved.

In the case where the cover body has a double or more multi-cylinder structure, the tip of the inner cylinder may not be in contact with the tip of the cylinder located outside the inner cylinder. ). Even if the outer cylinder of the inner cylinder is not open at the tip,
By arranging the distal end of the outer cylinder not to contact the distal end of the inner cylinder, it is possible to prevent heat from escaping from the distal end of the inner cylinder to the distal end of the outer cylinder. Therefore, the temperature near the opening can be maintained at a high temperature, and the heat retention can be improved.

The inner cylinder may be tapered so that the diameter decreases toward the tip. At this time, since the inner volume of the inner cylinder is reduced, gas exchange in the inner cylinder is performed more smoothly, which is effective in improving responsiveness.

[0021]

FIG. 1 shows an example in which the present invention is applied to an oxygen concentration detecting element mounted on an exhaust pipe wall of a diesel engine. In the figure, the oxygen concentration detecting element has a cylindrical housing 1 penetrating through an exhaust pipe P wall of a diesel engine, and is fixed to the exhaust pipe P wall by a flange portion P1 provided on the outer periphery of the housing 1. I have. A cylindrical gas concentration detector 2 as a concentration detector is inserted and held in the housing 1.

The gas concentration detector 2 has an upper half held and fixed in the housing 1 and a lower half protruding from the housing 1 and extending into the exhaust pipe P. The lower half of the gas concentration detector 2 is accommodated in a cover 3 described in detail later, and a heater 4 is built in the hollow interior. A ceramic lid 5 is disposed above the gas concentration detector 2, and the outer periphery of the upper half of the lid 5 is covered with a metal cover 51. The upper end opening of the cover 51 is sealed with an electric insulating member 52.

The gas concentration detector 2 includes an oxygen ion conductive solid electrolyte 2a such as zirconia formed into a tubular shape,
It is composed of electrodes 2b and 2c of platinum or the like provided in the vicinity of the distal end at opposing positions of the inner and outer peripheral surfaces. The solid electrolyte 2a
A diffusion resistance layer (not shown) made of porous alumina or the like is formed on the outer surface of the first electrode, and the exhaust gas passing through the diffusion resistance layer reaches the outer electrode 2c. The electrodes 2b and 2c are connected to lead wires 61 and 62 through leads formed on the surface of the electrolyte 2a. The other ends of these lead wires 61 and 62 are
Are connected to the terminals 71 and 72 held at the terminals.

Ceramic cylindrical lid 5 and cover 5
A metal tube 81 is disposed between the two. The upper end of the tube 81 is in contact with the lower end of the ceramic cylinder 11, and the lower end of the tube 81 is located inside the housing 1. The housing 1 below the tube 81 is filled with an insulating member 12.

The lower end of the tube 81 is the gas concentration detector 2
Caulking 8 used when fixing the housing and the housing 1
The tube 81 is fixed to the housing 1 by swaging the upper end of the housing 1 through the ring 80.

A coil spring 82 is disposed between the upper end of the tube 81 and the lid 5. And
The upper end of the cover 51 is caulked and fixed to an elastic electric insulating member 52 such as rubber, and the position of the electric insulating member 52 is determined. The lid 5 is pressed and fixed to the upper end of the gas concentration detector 2 by an elastic reaction force due to the compression acting on the lid 5. A guide ring 83 is fixed above the heater 4, and the elastic reaction force acts on the upper end of the guide ring 83 via the lower end of the lid 5, so that the heater 4 moves its position. Fixed.

A small gap is formed between the lower end of the cover 51 and the tube 81. Therefore, through this gap, the atmosphere is contacted between the cylindrical body 11 and the upper end of the tube 81, the inner space of the cylindrical body 11, the inner space of the lid 5, the guide ring 83 of the heater 4 and the gas concentration detector 2. Is guided to the inside of the detection body 2 through a fitting gap with

A heater 4 is provided in the hollow portion of the solid electrolyte 2a.
Is housed. The heater 4 includes the gas concentration detector 2
The heating portion 41 is formed by burying a nichrome wire or the like in a bar-like body made of alumina or the like at a position facing the electrodes 2b and 2c. The heater 4 is connected to a terminal 73 held by the electric insulating member 52.

The cover body 3 has a double-cylinder structure.
(A), as shown in (b), made of stainless steel or the like,
An inner cylinder 31 and an outer cylinder 32 having different diameters are arranged concentrically.
The distal ends (lower ends in the figure) of the inner cylinder 31 and the outer cylinder 32 in the axial direction are closed, and the distal surfaces of the inner and outer cylinders 31 and 32 are in close contact. The upper end of the inner cylinder 31 that is bent outward is connected to the outer cylinder 3.
2 is abutted against the inner peripheral wall, and the upper end of the outer cylinder 32 is fixed to the lower end of the housing 1 (FIG. 1).

Each of the inner cylinder 31 and the outer cylinder 32 has two gas flow holes 33,
4 are formed so as to be arranged in the flow direction of the exhaust gas (indicated by an arrow in FIG. 2). The gas flow holes 33 and 34 have the same shape (circular shape), and one functions as a gas introduction hole and the other functions as a gas outlet hole. No openings are formed in the side walls of the inner cylinder 31 and the outer cylinder 32, and the exhaust gas enters and exits the cover body 3 only through the gas flow holes 33 and 34.

Next, the operation of the gas concentration detecting element having the above configuration will be described. As shown in FIG. 1, when the oxygen concentration detecting element is fixed to the wall of the exhaust pipe P, the exhaust gas flows into the cover 3 from the gas flow holes 33 or 34 and reaches the surface of the gas concentration detector 2. Atmosphere is introduced into the hollow portion of the gas concentration detector 2. Therefore, the gas concentration detector 2 is heated to a predetermined temperature by the heater 4, and the electrodes 2b and 2b are heated.
When a predetermined voltage is applied to the solid electrolyte 2a, oxygen in the exhaust gas passes through the diffusion resistance layer on the surface of the solid electrolyte 2a, and the outer electrode 2
c, and further passes through the inside of the solid electrolyte 2a to reach the inner peripheral electrode 2b. Due to this movement of oxygen, a limit current proportional to the oxygen concentration in the exhaust gas flows between the electrodes 2b and 2c. By detecting this, the oxygen concentration in the exhaust gas can be detected.

In the present invention, the gas concentration holes are not formed in the side portions of the cover body 3 and the gas circulation holes 33 and 34 are provided only in the axial end portion.
And the inner cylinder 31 is not directly exposed to the exhaust gas.
Therefore, a decrease in the surface temperature of the cover 3 and the gas concentration detector 2 due to the inflow and outflow of the exhaust gas is suppressed, and the cover 3 has a double-cylinder structure including the inner and outer cylinders 31 and 32, so that the heat retention is improved. Further improve. Therefore, particulates adhere to the cover 3 or the gas concentration detector 2,
Accumulation can be prevented, and occurrence of a detection error can be prevented.

Further, since the gas circulation holes are not suitable for the flow of the exhaust gas, the gas circulation holes 33 and 34 are less likely to be clogged, and deterioration of the exhaust gas circulation can be prevented. Further, since two exhaust gas circulation holes 33 and 34 having the same shape are provided in the flow direction of the exhaust gas, one is divided into a discharge gas introduction hole and the other is a discharge hole. Therefore, the outflow and inflow of the exhaust gas are performed more smoothly as compared with the case where the number of the gas circulation holes is one, and the gas exchange speed in the cover body 3 is increased. In addition, cover body 3
Since the tip surfaces of the inner and outer cylinders 31 and 32 are in close contact with each other, stagnation of exhaust gas between the inner and outer cylinders 31 and 32 is suppressed,
These greatly improve the responsiveness of detection.

Here, an oxygen concentration detecting element having the above-described structure was actually manufactured on a trial basis, and exposed to exhaust gas during idling operation of a diesel engine to examine the effect of improving heat retention. The cover 3 has an axial length of 20 mm, an inner cylinder diameter of 7 mm, and an outer cylinder diameter of 9 m.
m, and the diameter of the gas flow holes 33 and 34 is 2.5 m
m. As a result, FIG.
0, the surface temperature of the gas concentration detector 2 is increased by 75 ° C., and the inner surface of the cover 3 (the surface closest to the gas concentration detector 2) is increased by 45 ° C. with the same heater power. Thus, the adhesion and deposition of particulates could be greatly reduced.

Next, a 63% response speed when the oxygen concentration in the exhaust gas is suddenly changed from 5% to 10% using the cover body 3 (a 63% concentration change is detected from a sudden change point of the oxygen concentration). Of the gas flow hole), which was 63% of that of a single gas flow hole (2.5 mm in diameter).
The response speed was greatly improved from 400 ms to 180 ms.

FIG. 3 shows a second embodiment of the present invention. In this embodiment, a single gas flow hole 35 is provided.
The shape was such that two circular holes 35a and 35b arranged in the flow direction of the exhaust gas were partially overlapped. At this time, the narrow portion 35c formed at the overlapping portion of the two circular holes 35a and 35b divides the role of one circular hole into a gas introduction hole and the other circular hole into a gas outlet hole with the narrow portion 35c interposed therebetween. Therefore, the same effects as in the first embodiment can be obtained. The diameter of each hole 35a, 35b is actually 2.5 mm
The cover 3 having the structure shown in FIG. 3 was fabricated as a prototype, and its response was examined. As a result, the 63% response speed was 400 ms to 270 ms compared to the case where the number of gas flow holes was one (diameter 2.5 mm).
And greatly improved.

As described above, it is not always necessary to provide a plurality of gas flow holes, and a narrow portion is provided in the middle, and one side of the narrow hole functions as a gas inlet and the other side functions as a gas outlet. What is necessary is just to be comprised. In addition, the shape is not limited to a shape in which two circles are overlapped, and may be a shape in which three or more circles are overlapped, or a shape in which an oval or polygon other than a circle is overlapped. It is to be noted that the number is not limited to two, and may be three or more. Of course, one or more of them may function as gas introduction holes and the other one or more may function as gas outlet holes. Is obtained.

FIG. 4 shows a third embodiment of the present invention. As shown in FIG.
A space may be provided between the two end surfaces, and three gas flow holes 36a to 36c and 37a to 37c may be provided in each of the spaces so as to be staggered. The gas flow holes 36a to 36c and 37a to 37c of both the inner and outer cylinders 31 and 32 are circular (diameter 2 m).
In m), each hole is positioned at the vertex of an equilateral triangle, and the position of the center of the triangle matches the center of the tip surface. The positions of the centers of the gas circulation holes 36a to 36c and 37a to 37c are respectively 2 mm away from the center of the distal end surface, and the gas circulation holes 36a to 36c of the inner cylinder 31 and the gas circulation holes 37a to 37c of the outer cylinder 32 are located at the center of the distal end surface. At a position that is relatively rotated by 60 ° with respect to the center. Also, the inner cylinder 31 and the outer cylinder 3
The distal end surface of the inner cylinder 2 is separated by 2 mm so that exhaust gas can be introduced to the inside of the inner cylinder 32.

As described above, the gas flow holes 36a of the inner cylinder 31
By displacing the positions of the gas flow holes 37a to 37c of the outer cylinder 32 with the position of the gas flow holes 37a to 37c, the heat retaining property is further improved. In particular,
In comparison with the case where the gas concentration detector 2 is not shifted (three gas flow holes, diameter 2 mm), the outer surface temperature of the gas concentration detector 2 is 30 ° C. and the inner surface of the cover 3 (the surface closest to the gas concentration detector 2) is 15 °. ° C could be raised. Moreover, in the above configuration,
Since the tip surfaces of the inner cylinder 31 and the outer cylinder 32 are not in contact with each other, the outer cylinder 32 is exposed to the exhaust gas flow and has a lower temperature.
Heat can be prevented from escaping from the distal end surface of the inner cylinder 31, and the effect of improving heat retention can be further enhanced.

Further, the gas exchange rate in the cover body 3 is not largely changed even if the positions of the gas flow holes 36a to 36c and the gas flow holes 37a to 37c are shifted because the three gas flow holes are provided. The 63% response speed when abruptly changed was 220 ms compared to 180 ms without shifting.
It can be seen that a sufficiently fast response speed can be maintained.

As in the fourth embodiment of the present invention shown in FIG. 5, no space is provided between the end surfaces of the inner cylinder 31 and the outer cylinder 32 of the cover body 3 and the gas in the inner cylinder 31 is changed. Distribution hole 36
The gas flow holes 37a and 37b of the outer cylinder 32 may slightly overlap with the gas flow holes 37a and 36b, and the same effect of improving the heat retaining property can be obtained by shifting the positions of the gas flow holes.

FIG. 6 shows a fifth embodiment of the present invention. In this embodiment, the inner cylinder 31 of the cover body 3 is tapered so as to reduce its diameter toward the tip. The outer cylinder 32 has the same shape as the above embodiments, and the inner cylinder 31 and the outer cylinder 3
2 and the three gas flow holes 38a-3
8c are provided at the vertices of the equilateral triangle. Gas flow holes 38a-38c are circular (diameter 2mm)
The position of each center is 2 mm away from the center of the front end surface of the cover 3.

In the above configuration, since the inner cylinder 31 is tapered, the inner cylinder volume is reduced, and the gas exchange time can be further shortened. For this reason, 63% when the oxygen concentration is suddenly changed
The response speed was changed from 180 ms to 150 ms as compared with the case where the inner cylinder 31 was not tapered, and the responsiveness could be improved.

FIG. 7 shows a sixth embodiment of the present invention. In the first embodiment, the contact portions at the distal end and the upper end of the inner cylinder 31 and the outer cylinder 32 of the cover body 3 are shown. Welding and joining (in the figure, the black circles indicate the joints)
The space between the outer tube 2 and the outer tube 31 is filled with a filler 8 such as ceramic powder.

In the above configuration, the heat insulating property is further improved by the heat insulating effect of the filler 8. In addition, since the inner and outer cylinders 31 and 32 are welded to each other, exhaust gas does not enter between them and stay there, thereby improving responsiveness.

FIG. 8 shows a seventh embodiment of the present invention. In this embodiment, the cover 3 is attached to the inner cylinder 31.
And an outer cylinder 32 and a middle cylinder 39 between them. The gas flow holes 33 and 34 are formed only on the front end surface of the inner cylinder 31, and the outer cylinder 32 and the middle cylinder 39 are open at the front ends.

In the above configuration, the heat retention can be further improved by forming the cover body 3 in a triple structure. As a result, the temperature in the vicinity of the gas flow holes 33 and 34 is increased by 80 ° C. as compared with a structure having a front end face in which the gas flow holes 33 and 34 are formed in both the inner cylinder 31 and the outer cylinder 32 in the double cylinder structure. I was able to. Further, since the middle cylinder 39 and the outer cylinder 32 do not have a front end surface, the heat of the gas flow holes 33 and 34 is prevented from escaping to the middle cylinder 39 and the outer cylinder 32 and being released to the exhaust gas through these. can do. Thereby, the gas flow holes 3
The temperature around 3 and 34 can be kept high, which is particularly effective for preventing the gas flow holes 33 and 34 from being clogged.

FIG. 9 shows an eighth embodiment of the present invention. In the present embodiment, the cover body 3 has a double cylinder structure of an inner cylinder 31 and an outer cylinder 32, and two gas flow holes 33 and 34 are formed in the distal end surface of the inner cylinder 31.
An opening 321 is provided on the front end surface of the second. Here, the opening 321 is formed sufficiently large so that the tip of the outer cylinder 32 does not contact the tip of the inner cylinder 31. As described above, even if the inner cylinder 31 has a shape having a distal end surface, the distal end surface of the inner cylinder 31 is prevented from contacting the outer cylinder 32, so that the temperature is reduced by being exposed to the exhaust gas. Outer cylinder 32
In addition, it is possible to prevent the heat of the gas flow holes 33 and 34 from escaping and being released to the exhaust gas through the side surfaces thereof.
Therefore, since the temperature near the gas circulation holes 33 and 34 can be kept high, it is particularly effective to prevent the gas circulation holes 33 and 34 from being clogged.

Further, in each of the above embodiments, the gas concentration detector 2 is cylindrical, but may be of a so-called laminated structure in which a solid electrolyte plate and an electric insulating plate are laminated.

[Brief description of the drawings]

FIG. 1 is an overall cross-sectional view of a gas concentration detecting element according to a first embodiment of the present invention.

2A is a longitudinal sectional view of a cover body according to the first embodiment, and FIG. 2B is a transverse sectional view.

FIGS. 3A and 3B show a second embodiment of the present invention, wherein FIG. 3A is a longitudinal sectional view of a cover body, and FIG.

4A and 4B show a third embodiment of the present invention, wherein FIG. 4A is a longitudinal sectional view of a cover body, and FIG. 4B is a sectional view taken along line AA of FIG.

FIG. 5 is a longitudinal sectional view of a cover body according to a fourth embodiment of the present invention.

FIGS. 6A and 6B show a fifth embodiment of the present invention, in which FIG. 6A is a longitudinal sectional view of a cover body, and FIG. 6B is a sectional view taken along line BB of FIG.

FIG. 7 is a longitudinal sectional view of a cover body according to a sixth embodiment of the present invention.

FIGS. 8A and 8B show a seventh embodiment of the present invention, wherein FIG. 8A is a longitudinal sectional view of a cover body, and FIG.

9A and 9B show an eighth embodiment of the present invention, wherein FIG. 9A is a longitudinal sectional view of a cover body, and FIG. 9B is a transverse sectional view.

FIG. 10 is an overall sectional view of a conventional gas concentration detecting element.

[Explanation of symbols]

 Reference Signs List 1 housing 11 cylindrical body 12 insulating member 2 gas concentration detector (concentration detector) 2a solid electrolyte 2b electrode 2c electrode 3 cover body 31 inner cylinder 32 outer cylinder 321 opening 33 to 38 gas flow hole 39 middle cylinder 4 heater 41 heating section 5 Lid 51 Metal cover 52 Insulating member 61, 62 Lead wire 71, 72, 73 Terminal 80 Ring 81 Tube 82 Coil spring P Exhaust pipe P1 Flange

Continued on the front page (72) Inventor Michihiro Wakimoto 14 Iwatani Shimowa Kakucho, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Taisuke Makino 14 Iwatani Shimowa Kakumachi Nishio City, Aichi Prefecture Japan Motor Corporation Inside the Parts Research Laboratory (72) Inventor Hideomi Kawachi 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Toshihiro Sakawa 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation

Claims (7)

[Claims] 1. A gas concentration detecting element comprising: a concentration detector for detecting a gas component concentration in a gas to be measured; and a cover surrounding a portion of the concentration detector exposed to the gas to be measured. At the axial end of the cover, a plurality of openings are provided, each functioning as an inlet or outlet for the gas to be measured, and the side of the cover except for the end has no opening. A gas concentration detecting element, characterized in that the wall has a curved wall. 2. A gas concentration detecting element comprising: a concentration detector for detecting a gas component concentration in a gas to be measured; and a cover surrounding a portion of the concentration detector exposed to the gas to be measured. One opening is provided at the axial end of the cover body, and the opening has a shape having a plurality of holes and a narrow portion communicating the plurality of holes. A gas characterized in that it is configured to function as an inlet or outlet for the gas to be measured, and that a side portion of the cover body except for the tip portion is a closed wall having no opening. Concentration detection element. 3. The gas concentration detecting element according to claim 1, wherein the cover body has a double cylinder structure in which an inner cylinder and an outer cylinder having different diameters are arranged concentrically. 4. The cover body has a triple-cylinder structure in which an inner cylinder having a different diameter, a middle cylinder and an outer cylinder are concentrically arranged, or a multi-cylinder structure in which a plurality of cylinders are arranged between an inner cylinder and an outer cylinder. The gas concentration detecting element according to claim 1 or 2, wherein: 5. The cover body having a double or multiple tube structure, wherein the plurality of openings are provided only at the distal end of the inner cylinder, and the outer cylindrical body is open at the distal end. Or the gas concentration detecting element according to 4. 6. The cover according to claim 3, wherein in the cover having a double or multiple tube structure, the distal end of the inner cylinder does not contact the distal end of the cylindrical body located outside the inner cylinder. Gas concentration detection element. 7. The gas concentration detecting element according to claim 3, wherein the inner cylinder has a tapered shape whose diameter decreases toward the tip.