JPH1010084A - Gas concentration sensor - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To prevent deterioration of a sensor due to adhesion of dirt to a gas concentration detection unit, and to sufficiently increase a flow rate of a measured gas passing through the surface of the gas concentration detection unit to respond The balance between performance and durability at a high level. SOLUTION: A sensor element 2 having a gas concentration detecting portion 21 protruding into an exhaust pipe is inserted into and held in a housing 1 fixed to an exhaust pipe wall of an internal combustion engine. Is covered with a protective cover 3. Protective cover 3
As a double structure of the inner cover 32 and the outer cover 31,
In the inner cover 32 and the outer cover 31, gas flow holes 31 a and 32 a facing the flow of the gas to be measured are provided on the peripheral walls above the gas concentration detecting section 21 of the sensor element 2, while the lower peripheral walls are provided with: Gas flow holes 32 in the inner cover
b and 32c are gas flow holes 31e to 31h of the outer cover.
It is provided so as to be located between them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a gas concentration sensor for detecting the concentration of a specific gas component in a gas to be measured, for example, an air-fuel ratio sensor for detecting an air-fuel ratio from the concentration of oxygen contained in exhaust gas of an internal combustion engine. And a gas concentration sensor to be used.

[0002]

2. Description of the Related Art An example of this type of gas concentration sensor is shown in FIG.
Shown in FIG. 10A shows a main part of a gas concentration sensor, which is an exhaust pipe of an internal combustion engine (not shown).
The housing 1 includes a housing 1 fixed to a wall and a sensor element 2 inserted and held in the housing 1. The sensor element 2 has a distal end having a gas concentration detecting portion 21 protruding from the housing 1 and positioned in the exhaust pipe. A protective cover 3 is provided around the distal end to cover the distal end. It is.

[0003] The protective cover 3 is in the form of a container, and is usually provided with a heat insulating effect to maintain the sensor element 2 at a high temperature.
As shown, the outer cover 31 and the inner cover 32 have a double structure. These outer cover 31 and inner cover 32
In the upper and lower positions of the gas concentration detector 21 of the sensor element 2, four gas flow holes 31 are provided on the peripheral wall.
1 and 321 are provided respectively (FIG. 10A,
(B), the gas flow holes 311 and the gas flow holes 321 are arranged in the same plane and alternately.

[0004]

The above-mentioned conventional gas concentration sensor has gas flow holes 311 and 321 so that the exhaust gas does not directly hit the gas concentration detector 21 of the sensor element 2.
Is formed so as to avoid the position opposed to the gas concentration detecting section 21 to prevent soot and dirt contained in the exhaust gas from adhering to the gas concentration detecting section 21 to prevent the sensor from deteriorating and reducing the durability. I have. However, in this configuration, the flow of the exhaust gas introduced into the inner cover 31 via the gas flow holes 311 and 321 flows along the outer periphery of the sensor element 2 as shown by arrows in FIGS. From the upstream side to the downstream side, or from the downstream side to the upstream side (FIG. 12 (a),
(B)), flowing on the same plane. That is, the exhaust gas mainly flows above or below the gas concentration detection unit 21,
The flow passing through the surface of the gas concentration detector 21 located between them is small. On the other hand, since the responsiveness of the sensor is generally proportional to the flow rate, in the above configuration, a sufficient flow rate that passes through the surface of the gas concentration detection unit 21 cannot be obtained, and the responsiveness may be reduced.

Accordingly, an object of the present invention is to prevent the sensor from being deteriorated due to the adhesion of dirt to the gas concentration detecting section 21,
In addition, it is an object of the present invention to provide a gas concentration sensor that can sufficiently increase the flow rate of the gas to be measured passing through the surface of the gas concentration detection section 21 to achieve both high responsiveness and high durability.

[0006]

In order to solve the above problems, a gas concentration sensor according to the first aspect of the present invention comprises:
A housing fixed to a flow path wall through which the gas to be measured flows, and a sensor element inserted and held in the housing and having a tip portion having a gas concentration detection section protruding into the flow path; The periphery of the distal end portion is covered with a protective cover, and a gas flow hole is provided in the protective cover so that the gas to be measured can flow therethrough. The protective cover has a double structure of an inner cover and an outer cover, and the inner cover and the outer cover have one of a distal end side and a proximal end side with respect to the gas concentration detecting section of the sensor element. At least one gas circulation hole facing the flow of the gas to be measured is formed on the peripheral wall of the gasket, and a plurality of gas circulation holes are formed on the other peripheral wall. It is provided so as to be located between the circulation holes.

In the above configuration, the gas to be measured is introduced into the inside through the gas flow holes facing the flow of the gas to be measured, which are disposed opposite to the inner cover and the outer cover.
The gas to be measured that has reached the space around the sensor element passes through the surface of the gas concentration detection section of the sensor element and reaches the opposite side to the gas flow hole facing the flow of the gas to be measured. In the space between the outer covers, a flow of the gas to be measured flowing between a plurality of gas circulation holes provided in the outer cover is formed. For this reason, a negative pressure is generated on the surface of the gas flow hole of the inner cover located in the middle of the gas flow, and the gas in the inner cover is easily sucked out.

As described above, the gas flow hole is formed so that the flow of the gas to be measured is easy to enter on one side and the flow is easy to exit on the other side across the surface of the gas concentration detecting section. In the inside cover, a flow in a certain direction that passes through the gas concentration detector is generated. Therefore, a sufficient amount of the gas to be measured can be introduced into the gas concentration detecting section, and the response is improved. In addition, since the gas flow holes are formed at positions not opposed to the gas concentration detection section, it is possible to prevent contamination of the gas to be measured from adhering to the gas concentration detection section, and to achieve a high level of responsiveness and durability. It is possible to achieve both.

Alternatively, at least one gas flow hole facing the flow of the gas to be measured is formed on one of the peripheral walls of the protective cover on the distal end side or the base end side of the gas concentration detecting section of the sensor element. The protective cover is formed on the other peripheral wall to have a double structure of an inner cover and an outer cover, and the inner cover and the outer cover have a plurality of gas flow holes, respectively, It may be provided so as to be located between the gas circulation holes of the cover (claim 2).

As described above, at the position where the gas flow hole facing the flow of the gas to be measured is formed, the protective cover may have a single-layer structure. In this case, the same effect is obtained.

In the protective cover according to the second aspect, the portion of the sensor element facing the gas concentration detecting section may have a double structure of an inner cover and an outer cover. As described above, by double-protecting the periphery of the gas concentration detecting portion of the sensor element, the heat insulating effect of the protective cover can be enhanced, and the sensor sensitivity is improved.

The plurality of gas flow holes of the inner cover and the plurality of gas flow holes of the outer cover are preferably provided on the same plane (claim 4), and gas can easily flow between the gas flow holes. In addition, the gas is more preferably sucked out from the inner cover.

[0013] Specifically, the plurality of gas flow holes of the outer cover are provided in a space between the outer cover and the inner cover, the gas flow holes being upstream of the gas flow holes on the upstream side with respect to the flow of the gas to be measured. It is arranged to form a flow of the gas to be measured toward the gas flow hole on the side. At this time, each of the plurality of gas flow holes of the inner cover is arranged in the middle of the flow of the gas to be measured.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1A, a housing 1 of a gas concentration sensor has a through hole 11 in a center portion through which a sensor element 2 is inserted and held, and a plurality of mounting holes 12 provided in an outer peripheral flange portion, for example, an internal combustion engine. It is fixed to the exhaust pipe wall of the engine. FIG. 2 shows a state in which the gas concentration sensor of FIG. 1 is mounted on the wall of the exhaust pipe P of the internal combustion engine, and a bolt 13 is inserted through the mounting hole 12 so that the mounting member P1 is welded and fixed to the wall of the exhaust pipe P. It is fixed.

The sensor element 2 has a base end (upper end in the figure) held and fixed in the through hole 11 of the housing 1, and a distal end (lower end in the figure) protrudes from the housing 1 and extends downward in the figure. And is located in the exhaust pipe P through which the exhaust gas to be measured flows. The sensor element 2 includes:
As shown in FIG. 3, electrodes 23 and 24 made of platinum or the like are disposed on the inner and outer peripheral surfaces of an oxygen ion conductive solid electrolyte 22 such as stabilized zirconia formed into a tubular shape, respectively. A diffusion resistance layer 241 made of a porous layer is formed on the surface of the electrode 24.

The outer surface of the sensor element 2 is covered with a coating layer 25 except for a part, and a part from the tip where the coating layer 25 is not formed detects the concentration of a specific gas component in the gas to be measured. Function as a gas concentration detector 21. In the gas concentration detecting section 21, a predetermined voltage is applied between the inner peripheral electrode 23 and the outer electrode 24, and the application of this voltage causes oxygen in the exhaust gas to diffuse into the diffusion resistance layer 241 and the solid electrolyte 22. Through the hollow space 26 in the solid electrolyte. At this time, since a limit current flows between the electrodes 23 and 24 due to the movement of oxygen, the oxygen concentration in the exhaust gas can be detected from the limit current value.

A protective cover 3 made of stainless steel or the like is fixed to the lower surface of the housing 1 (FIG. 1) to protect the periphery of the tip of the gas concentration detecting element 2. The protective cover 3 has a double structure, in which a cylindrical outer cover 31 and an inner cover 32 whose upper end is open and whose lower end is closed are concentrically arranged, and the bottom facing surface is fixed by welding. The upper edge of the outer cover 31 is embedded and fixed in the housing 1, and the inner cover 32 has its upper edge bent outward to abut on the inner peripheral wall of the outer cover 31.

At the base end side of the gas concentration detecting section 21 of the sensor element 2, that is, at the upper position in the figure, the outer cover 31 is provided with four gas flow holes 3 at equal intervals at the peripheral wall.
1a to 31d are formed (FIG. 1B). One of the gas flow holes 31a faces the flow of the exhaust gas (indicated by an arrow in FIG. 1A), and the inner cover 32 faces the gas flow hole 31a. A gas flow hole 32a is formed at the position.

On the other hand, on the tip side of the gas concentration detecting portion 21 of the sensor element 2, that is, at a position below the drawing, gas flow holes 31e to 31h are formed in the outer cover 31 at four positions on the peripheral wall at equal intervals. (FIG. 1 (c)). At this time, these gas circulation holes 31e to 31h are at positions rotated by 45 ° with respect to the gas circulation holes 31a to 31d. The inner cover 32 has gas flow holes 32b and 32c formed at equal intervals at two locations on the peripheral wall. The gas flow hole 32b is provided between the gas flow hole 31e and the gas flow hole 31f of the outer cover 31. The gas flow hole 32c is provided between the gas flow hole 31g and the gas flow hole 31h of the outer cover 31.

Next, the operation of the gas concentration sensor having the above configuration will be described. When the gas concentration sensor of the present invention is fixed to the wall of the exhaust pipe P such that the gas flow holes 31a and 32a provided on the base end side of the protective cover 3 face the flow of exhaust gas as shown in FIG. The exhaust gas flows into the outer cover 31 through the gas circulation hole 31a, and further receives the dynamic pressure of the exhaust gas, and most of the exhaust gas is introduced into the inner cover 32 through the opposed gas circulation hole 32a. Excess exhaust gas is discharged into the exhaust pipe P through the gas flow holes 31b to 31d of the outer cover 31.

On the tip side of the protective cover 3,
As shown in FIG. 4, the exhaust gas flows into the outer cover 31 from the gas circulation holes 31 e and 31 h located on the upstream side, and the exhaust gas entering from the gas circulation hole 31 e is a downstream gas circulation hole. The flow mainly flows toward 31f, and the flow along the outer surface of the inner cover 32 occurs as shown by the arrow in the figure. Therefore, the inner cover 3 located in the middle of this flow
2, a negative pressure is generated in the gas flow hole 32b, and the exhaust gas in the inner cover 32 is sucked out from the gas flow hole 32b (arrow in the figure) and joins the flow toward the gas flow hole 31f. Similarly, the exhaust gas that has entered through the gas flow holes 31h mainly flows toward the gas flow holes 31g downstream of the gas flow holes 31h, and the negative pressure generated in the gas flow holes 32c of the internal cover 32 located in the middle of this flow causes Exhaust gas in the inner cover 32 is sucked out from the gas flow holes 32c.

Thus, in the space between the sensor element 2 and the inner cover 32, as shown in FIG. 5, the gas flow holes 32b, 3b below the upper gas flow hole 32a are provided.
An exhaust gas flow toward 2c is generated. Therefore, the flow of the exhaust gas always passes through the surface of the gas concentration detecting section 21 of the sensor element 2 located between them,
On the surface of one, the exhaust gas will always flow in one direction from top to bottom. As a result, a sufficient amount of exhaust gas is introduced into the gas concentration detector 21 and is constantly replaced with new exhaust gas, so that the response of the sensor is greatly improved.

Further, an outer cover 31, an inner cover 32
The gas flow holes 31a to 31h and 32a to 32c are provided at positions that do not face the gas concentration detection unit 21 of the sensor element 2, so that the exhaust gas does not directly contact the gas detection unit 21. Therefore, the sensor element is not contaminated by soot or the like in the gas reaching the surface of the protective cover 3 and the performance is not deteriorated, and the durability is greatly improved.

Further, in the present embodiment, the outlet side gas flow holes 31e to 31h and 32b to 32c are located at the tip end side, that is, near the center of the exhaust pipe P where the flow rate of the exhaust gas is large. The flow velocity of the exhaust gas flowing between the gas flow holes 31e to 31h is increased. Accordingly, the gas flow holes 3
Suction of gas from 2b to 32c is accelerated, the flow rate of gas passing through the surface of the gas concentration detection unit 21 is increased, and responsiveness can be further improved.

As shown in FIG. 6 as a second embodiment of the present invention, the gas flow holes 31e to 31h on the outlet side,
32b to 32c at the upper position in the drawing, that is, at the base end side,
Of course, the gas flow holes 31a and 32a on the introduction side can be formed at the lower position in the figure, that is, at the tip end side. Also in this case, the same effect of improving the responsiveness by forming the flow of the gas to be measured passing through the surface of the gas detection unit 21 can be obtained.

In the above embodiments, the gas flow holes of the outer cover 31 are provided at four locations on the peripheral wall, and the gas flow holes of the inner cover 32 are provided at two locations on the peripheral wall. However, the present invention is not limited to this, and may be any number as long as it is more than one. For example, the present embodiment can be realized by providing two gas flow holes at the peripheral wall of the outer cover 31, one at a position facing the flow of exhaust gas and the other at a position axially symmetric to the exhaust gas. Similarly, by forming two flows from the upstream to the downstream in the outer cover 31 and providing the gas flow holes of the inner cover 32 in the middle of these flows, the same effect can be obtained. The arrangement of the gas circulation holes is not particularly limited, either.
It is only necessary that the gas flow hole of the inner cover 32 is located in the middle of the flow of the measured gas so that the flow of the measured gas is formed between the first cover 1 and the inner cover 32.

In each of the above embodiments, the entire protective cover has an inner / outer double structure. However, as in the third embodiment of the present invention shown in FIG. It is not necessary to necessarily have a double configuration. In the figure,
The protective cover 3 includes a cylindrical outer cover 31 having both ends opened.
Inside, a cylindrical internal cover 32 whose upper end is open and whose lower end is closed is fitted and fixed, and below the gas concentration detecting portion 21 of the sensor element 2, only the internal cover 32 has a single structure. . The front end of the inner cover 32 protruding from the lower end opening of the outer cover 31 is formed with the gas flow holes 32a facing the flow direction of the exhaust gas (FIG. 7B). Gas flow holes 31e to 31h, 32b are formed in the peripheral walls of the cover 31 and the inner cover 32.
To 32c are formed in the same arrangement as in the above embodiments (FIG. 7C).

According to the above configuration, the exhaust gas is also supplied to the inner cover 3 through the gas passage hole 32a below the protective cover 3.
2 and is sucked out by the negative pressure generated in the upper gas flow holes 32b and 32c. Therefore, the sensor element 2
The gas flow rate passing through the gas detection unit 21 increases, and the responsiveness of the sensor improves. Further, since the protective cover 3 is configured to be double inside and outside at the position facing the gas concentration detecting section 21 to enhance the heat insulating effect, the sensor element is maintained at a high temperature to improve the detection sensitivity.

FIG. 8 shows a third embodiment of the present invention. In each of the above embodiments, the gas concentration sensor using the tubular sensor element 2 has been described, but the present invention can be applied to a gas concentration sensor using the stacked sensor element 2 as shown in the figure. FIG. 9A shows the details of the stacked sensor element 2. The plate-shaped oxygen conductive solid electrolyte 22 has electrodes 23 and 24 on both surfaces, and a porous surface is provided on the left electrode 23 in the figure. A diffusion resistance layer 241 made of layers is formed by lamination. A heater layer 28 is laminated on the right electrode 24 via a support member 27 forming a hollow portion 26. As shown in FIG. 9B, the heating layer 281
And has a function of quickly heating to a high temperature at which the sensor element 2 can detect.

The left electrode 23 of the sensor element 2 is covered with a coating layer except for a part serving as a gas concentration detecting section 21 (see FIG. 8) (not shown in FIG. 9). In the gas concentration detecting section 21, the sensor element 2 detects the oxygen concentration in the exhaust gas based on the limiting current value between the electrodes 23 and 24 as described in the first embodiment.

Also in the present embodiment, a sufficient amount of exhaust gas is introduced into the gas concentration detecting section 21 of the sensor element 2 by the gas flow holes provided at two places above and below the peripheral wall of the protective cover 3 to improve the responsiveness. A similar effect of improving is obtained.

[Brief description of the drawings]

FIGS. 1A and 1B show a first embodiment of the present invention, wherein FIG. 1A is a schematic sectional view of a gas concentration sensor, and FIG.
FIG. 2C is a sectional view taken along line Ib, and FIG. 2C is a sectional view taken along line Ic-Ic in FIG.

FIG. 2 is a diagram showing a state in which the gas concentration sensor of the present invention is attached to an exhaust pipe wall of an internal combustion engine.

FIG. 3 is a partially enlarged cross-sectional view of a sensor element.

FIG. 4 is a view showing the operation of the gas concentration sensor of the present invention, and is a cross-sectional view of the gas concentration sensor.

FIG. 5 is a view showing the operation of the gas concentration sensor of the present invention, and is a longitudinal sectional view of the gas concentration sensor.

FIGS. 6A and 6B show a second embodiment of the present invention, wherein FIG. 6A is a schematic sectional view of a gas concentration sensor, and FIG.
b-VIb sectional view, (c) is VIc-VIc of (a)
It is a line sectional view.

FIGS. 7A and 7B show a third embodiment of the present invention, in which FIG. 7A is a schematic sectional view of a gas concentration sensor, and FIG.
Ib-VIIb line sectional view, (c) is VIIc- of (a)
It is a VIIc line sectional view.

8A and 8B show a fourth embodiment of the present invention, wherein FIG. 8A is a schematic sectional view of a gas concentration sensor, and FIG.
IIb-VIIIb sectional view, (c) is VII of (a)
It is Ic-VIIIc line sectional drawing.

FIG. 9A is a schematic cross-sectional view of a sensor element, and FIG.
FIG. 2 is a sectional view taken along line IXb-IXb of FIG.

FIG. 10A is a schematic sectional view of a conventional gas concentration sensor, and FIG. 10B is a sectional view taken along line Xb-Xb of FIG.

FIG. 11A is a diagram showing a gas flow state in a conventional gas concentration sensor, and is a partial schematic cross-sectional view of the gas concentration sensor;
(B) is a sectional view taken along line XIb-XIb of (a).

FIG. 12A is a diagram showing a gas flow state in a conventional gas concentration sensor, and is a partial schematic cross-sectional view of the gas concentration sensor;
(B) is a sectional view taken along line XIIb-XIIb of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 11 Through-hole 12 Mounting hole 2 Sensor element 21 Gas concentration detection part 22 Solid electrolyte 23, 24 Electrode 241 Diffusion resistance layer 25 Coating layer 26 Hollow part 3 Protective cover 31 External cover 31a-31h Gas circulation hole 32 Internal cover 31a- 31c Gas flow hole

Continued on the front page (72) Inventor Nobuaki Ando 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Prefecture Inside Japan Automotive Parts Research Institute (72) Inventor Norihiko Takagi 1-Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Corporation Inside

Claims (5)

[Claims] 1. A housing fixed to a flow path wall through which a gas to be measured flows, and a sensor element which is inserted and held in the housing and has a gas concentration detecting portion and a tip end protruding into the flow path, A gas concentration sensor in which a periphery of the sensor element is covered with a protective cover, and a gas flow hole is provided in the protective cover so that a gas to be measured can be introduced into the sensor. A double structure of a cover and an outer cover is provided.The inner cover and the outer cover are provided on one of the peripheral walls on the distal end side or the proximal end side with respect to the gas concentration detecting section of the sensor element, and the gas to be measured is provided. At least one gas flow hole facing the flow is formed oppositely, and a plurality of gas flow holes are respectively formed on the other peripheral wall, and the gas flow hole of the inner cover is located between the gas flow holes of the outer cover. A gas concentration sensor, characterized in that the gas concentration sensor is provided. 2. A housing fixed to a flow path wall through which a gas to be measured flows, and a sensor element inserted and held in the housing and having a gas concentration detecting portion and a tip protruding into the flow path, A gas concentration sensor that covers the periphery of the tip of the sensor element with a protective cover, and is provided with a gas flow hole in the protective cover so that a gas to be measured can be introduced therein. At least one gas flow hole facing the flow of the gas to be measured is formed in one of the peripheral walls of the sensor element on the distal end side or the base end side with respect to the gas concentration detection section, and the protective cover is formed on the other peripheral wall. Is formed into a double structure of an inner cover and an outer cover, and a plurality of gas circulation holes are respectively formed in the inner cover and the outer cover. A gas concentration sensor provided so as to be located between through holes. 3. The gas concentration sensor according to claim 2, wherein a portion of the protective cover facing the gas concentration detecting portion of the sensor element has a double structure of an inner cover and an outer cover. 4. The gas concentration sensor according to claim 1, wherein the plurality of gas flow holes of the inner cover and the plurality of gas flow holes of the outer cover are on the same plane. 5. The method according to claim 5, wherein the plurality of gas flow holes of the outer cover are provided in a space between the outer cover and the inner cover.
Each of the plurality of gas flow holes of the inner cover is disposed so as to form a flow of the gas to be measured toward the gas flow hole located downstream from the gas flow hole located upstream of the flow path. 5. A gas concentration sensor according to claim 1, wherein the gas concentration sensor is disposed in the middle of the flow of the gas to be measured.