JPH09145668A - Oxygen-concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent clogging of an exhaust-gas flowing port with the soot in exhaust gas in an oxygen-concentration detector, wherein an oxygen- concentration detecting part coated with a cover body in which the exhaust-gas flowing port is formed is protruding into the exhaust pipe in an internal combustion engine and operated at high temperature. SOLUTION: A cover body 5A is constituted of first, second and third cover bodies 51, 52 and 53 in three layers at the inside and outside. A third exhaust- gas flowing port 531 of the third cover body 53 is formed in a trumpet shape at a position facing a second exhaust-gas flowing port 521 of the second cover body 52. At the same time, the diameter of the opening end of the port 531 is made larger than that of the second exhaust-gas flowing port 521 so as to suppress the clogging by soot. The above described opening end is made to approach around the second exhaust-gas flowing port 521 so than the part between the second cover body 52 and the third cover body 53 is substantially closed. Thus, the heat deprivation by the exhaust gas in the second cover body 52 is suppressed, and the clogging with the soot of the second exhaust-gas flowing port 521 is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration detecting device, and more particularly to an oxygen concentration detecting device provided in an exhaust pipe of an internal combustion engine to detect the oxygen concentration in exhaust gas discharged from the internal combustion engine.

[0002]

2. Description of the Related Art An oxygen concentration detecting device is provided in an exhaust pipe of an internal combustion engine to detect the oxygen concentration in exhaust gas and feedback control the air-fuel ratio.

In the oxygen concentration detecting device, as shown in FIG. 4, an oxygen concentration detecting element 92 is inserted into a substantially cylindrical housing 91 provided so as to penetrate the wall of the exhaust pipe 7 of the internal combustion engine, and the oxygen concentration detecting element 92 is inserted into the exhaust pipe 7. The protruding tip portion is the oxygen concentration detecting portion 93, and the base portion is the casing 9 provided outside the wall of the exhaust pipe 7.
4. The oxygen concentration detector 93 is composed of a sensing cell 931 and a protective layer 932 thereof. One side of the sensing cell 931 is in contact with exhaust gas and the other side is in contact with reference gas (atmosphere) such as ZrO2. A solid electrolyte layer is provided, and an electromotive force is generated between the two surfaces according to the difference in oxygen concentration between the exhaust gas serving as the gas to be detected and the reference gas. The generated electromotive force is taken out from the lead terminal 97 provided on the upper end of the casing 94.

The oxygen concentration detecting section 93 is covered with cover bodies 94 and 95 made of stainless steel or the like, and exhaust gas flows through exhaust gas flow holes 941 and 951 formed in the peripheral walls thereof. Further, the oxygen concentration detection unit 93 is heated to a temperature higher than the exhaust gas by a heater built in the sensing cell 931 and the cover body 94, 95 is doubled inside and outside to increase the heat insulation effect to raise the temperature. It is retained so that the detection sensitivity of oxygen concentration is increased.

[0005]

By the way, in the above-mentioned oxygen concentration detecting device, since the cover bodies 94 and 95 are dual inside and outside, the radiant heat from the oxygen concentration detecting portion 93 does not reach the outside cover body 95, The temperature of the outer cover body 95 exposed to the exhaust gas flow is low.

It is known that in this type of cover body, soot contained in the exhaust gas is more likely to adhere and accumulate at lower temperatures, and such an oxygen concentration detecting device is used for soot in the exhaust gas as compared with a gasoline engine. When it is mounted on a diesel engine containing a large amount of soot, the exhaust gas circulation holes 951 of the outer cover body 95, which has a low temperature and is easily attached with soot, are clogged with soot in the exhaust gas. As a result, there is a problem that the exhaust gas flow becomes poor and the detection response is delayed. When the exhaust gas flow hole 951 is widened so that the exhaust gas flow hole 951 is not clogged, the oxygen concentration detection unit 9
3 increases the amount of exhaust gas flowing into the oxygen concentration detector 9
3. The inner cover body 94 is easily cooled, and the burden on the heater increases. As in the oxygen sensor described in Japanese Utility Model Laid-Open No. 6-74960, there is a case where a trap layer that traps soot is formed on the surface of the inner cover body at a position facing the exhaust gas flow hole of the outer cover body. Although it is effective to prevent clogging of the exhaust gas flow holes of the inner cover body and the above-mentioned protective layer of the oxygen concentration detection part, exhaust gas flow of the outer cover body where soot is likely to adhere and accumulate at low temperature Soot adhesion to the holes cannot be reduced.

[0007] Therefore, it is an object of the present invention to provide an oxygen concentration detecting device which has a good exhaust gas flow and which requires less burden on the heater.

[0008]

According to the present invention, as shown in FIG. 1, an oxygen concentration detecting section 2 projecting into an exhaust pipe 7 of an internal combustion engine is operated at a high temperature by heating a heater to detect the oxygen concentration. In the apparatus, a cover body 5A that covers the oxygen concentration detection unit 2 and has a large number of exhaust gas circulation holes is configured in an inner and outer triple, and the exhaust gas circulation holes 511 of the innermost first cover body 51 and the first cover are formed. The exhaust gas circulation holes 521 of the second cover body 52 provided around the body 51 are formed at positions not facing each other, and the exhaust gas circulation holes 521 of the second cover body 52 and the second cover body 52 are formed. The exhaust gas circulation holes 531 of the third cover body 53 provided around the exhaust gas are formed at positions facing each other, and the exhaust gas circulation holes 531 are formed.
Has a diameter larger than that of the exhaust gas flow hole 521, and an opening end on the side of the exhaust gas flow hole 521 is positioned close to the periphery of the exhaust gas flow hole 521 so that the outer periphery of the second cover body 52 and the third The structure is such that a space S is formed between the cover body 53 and the inner circumference thereof (claim 1).

By making the exhaust gas flow hole 531 of the outermost third cover body 53 having a low temperature larger than the exhaust gas flow hole 521, it is possible to reduce the attachment of soot in the exhaust gas.
The open end of the exhaust gas flow hole 531 is the exhaust gas flow hole 521.
Since the space S is close to the surroundings, the space S is substantially closed and the inflow of exhaust gas is suppressed, and most of the exhaust gas that has entered from the exhaust gas flow hole 531 of the third cover body 53 is directly in the first space. Into the exhaust gas circulation hole 521 of the second cover body 52. Therefore, heat removal of the second cover body 52 is prevented and the second cover body 52 is kept at a high temperature, so that the soot adhesion in the exhaust gas circulation hole 521 is small. Further, since the exhaust gas flow holes 521 and 511 of the second and first cover bodies 52 and 51 are located at alternate positions, the low temperature exhaust gas is not directly blown to the oxygen concentration detection unit 2.

Further, in the present invention, as shown in FIG. 2, the cover body 5B for covering the oxygen concentration detecting section 2 is constructed in a double structure, and a large number of exhaust gas circulation holes 541 are formed in the inner cover body 54, and the outer cover body 54 is formed outside. In the cover body 55, an opening 551 is formed on the upstream side of the exhaust gas flow in the exhaust pipe 7, and an exhaust gas outlet 552 having an opening area smaller than that of the opening 551 is formed on the downstream side of the exhaust gas flow. A cover plate 56 is provided inside the opening 551 to cover a portion of the inner cover body 54 facing the opening 551 (claim 2).

A large amount of exhaust gas entering through the opening 551 of the outer cover body 55 is throttled at the exhaust gas exhaust port 552 to accelerate the flow velocity, so that soot is prevented from adhering to the exhaust gas exhaust port 552. It Further, the exhaust gas flowing in through the opening 551 is prevented from directly hitting the inner cover body 54 and absorbing heat from the inner cover body 54.

Further, in the present invention, as shown in FIG. 3, the housing 4 of the cover bodies 57 and 58 constituting the cover body 5C.
On the first side, slit-shaped elongated holes 572 and 582 are formed along the edge of the housing 41 (claim 3). Cover body 5
Since the paths of heat escaping from 7, 58 to the housing 41 are blocked by the long holes 572, 582, the cover bodies 57, 58
Cooling is prevented.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows a first oxygen concentration detecting device of the present invention. A housing 41 having a flange 43 welded and fixed to the upper end of the exhaust pipe 7 of an internal combustion engine is provided. The housing 41 is connected to the wall of the exhaust pipe 7 via a flange 43 by a bolt (not shown). A through hole 42 is formed in the housing 41, and the tubular member 31 with the tip closed of the oxygen concentration detecting element 1 is inserted therein. Tubular member 31
Has a tip portion protruding into the exhaust pipe 7, a base portion housed in a casing 61 provided outside the exhaust pipe 7, and a hollow portion 110 thereof communicates with the atmosphere at the base end. The tubular member 31 is held by hollow cylindrical hold members 63, 64, 65 inserted in the housing 41 and the casing 61.

A sensing cell 21 is formed on a part of the peripheral wall at the tip of the tubular member 31. Sensing cell 21
Is a plate-shaped solid electrolyte made of a material such as ZrO2, on which electrodes such as porous platinum are formed on both front and back surfaces, and a porous protective layer 22 made of a heat-resistant ceramic material is formed on the surface. The oxygen concentration detecting section 2 is formed. One of the electrodes faces the inside of the exhaust pipe 7, the exhaust gas as the gas to be measured reaches the sensing cell 21 through the protective layer 22, and passes through the platinum electrode of the sensing cell 21 to the solid electrolyte. It is coming. The other of the electrodes faces the hollow portion of the tubular member 31 so that the atmosphere can reach the solid electrolyte through the porous platinum electrode. That is, the sensing cell 21 acts as a battery that generates an electromotive force between the electrodes depending on the concentration of oxygen partial pressure between the exhaust gas and the atmosphere.

A lead wire is arranged along an unillustrated vertical groove formed on the surface of the tubular member 31, and is connected to the electrode at one end and extends to the lead connection 33 at the other end 32.
In the lead connection 33, the other end 32 of the lead wire
And the terminal 34 whose tip projects outside the casing 61 is electrically connected. The lead connection 33 is penetrated and held by a holding member 66 inserted in the casing 61,
The terminal 34 is penetrated and held by a holding member 67 inserted in the casing 61.

A packing 62 is provided in the gap between the tubular member 31 and the housing 41 so as to maintain airtightness between the inside and outside of the exhaust pipe 7.

The sensing cell 21 has a heater 120.
Is built in, and power is supplied from a terminal (not shown) different from the terminal 34 by a lead wire arranged along the vertical groove of the tubular member 31, and heats the entire oxygen concentration detection unit 2. It is like this.

A cover unit 5A made of a material such as stainless steel is fitted inside the exhaust pipe 7 of the housing 41 to cover the periphery of the oxygen concentration detecting section 2. Cover unit 5
A is a bottomed, substantially cylindrical cover body 51, 52, 53 that is formed in an inner and outer triple layer, and is integrally welded on the base side. A large number of exhaust gas circulation holes 511 are formed at axially symmetric positions on the peripheral wall of the first cover body 51 provided closest to the oxygen concentration detection unit 2. In the second cover body 52 provided around the first cover body 51, the exhaust gas circulation hole 5
An exhaust gas flow hole 521 having substantially the same diameter as the exhaust gas flow hole 511 is formed at a position not facing 11. Outermost third
An exhaust gas flow hole 531 is formed in the cover body 53 so as to face the exhaust gas flow hole 521. The exhaust gas flow hole 531 has a trumpet shape around the hole, and the opening end facing the exhaust gas flow hole 521 has a diameter slightly larger than that of the exhaust gas flow hole 521. The exhaust gas flow hole 531 has an open end that is made close to the second cover body 52 around the exhaust gas flow hole 521, and is a space S surrounded by the third cover body 53 and the second cover body 52. Are substantially occluded.

The operation of the oxygen concentration detecting device will be described.
The exhaust gas flowing through the exhaust pipe 7 is covered by the cover bodies 51, 52, 53.
Of the exhaust gas flow holes 511, 521 and 531 in order to flow into the oxygen concentration detection unit 2, pass through the protective layer 22 and reach the sensing cell 21, and between the electrodes of the sensing cell 21, the oxygen concentration with the atmosphere. Generate an electromotive force according to the difference.
The electromotive force is output to the terminal 34 via the lead wire as an oxygen concentration detection signal.

The heater 120 holds the oxygen concentration detector 2 at a high temperature to enhance the detection sensitivity and heats the first cover body 51 by the radiant heat from the oxygen concentration detector 2. The second cover body 52 is heated by the radiant heat from the first cover body 51. The third cover body 53 is heated by radiant heat from the second cover body 52, but is further deprived of heat by the flow of exhaust gas hitting the surface thereof.

Exhaust gas flows from around the exhaust gas passage hole 531 of the third cover body 53 toward the open end along the tapered surface. Since the exhaust gas flow hole 531 has a larger diameter than the exhaust gas flow holes 511 and 521 of the other cover bodies 51 and 52, soot attachment can be reduced.

The second cover body 52 and the third cover body 53
Since the space S surrounded by is substantially closed, the inflow of exhaust gas into the space S is suppressed and the second cover body 52 is prevented.
The second cover body 52 is effectively kept at a high temperature by the radiant heat from the first cover body 51. Therefore, the exhaust gas flow hole 521 is not clogged with soot, and the exhaust gas circulates through the exhaust gas flow hole 521 satisfactorily.

The first cover body 51 is effectively kept at a high temperature by the radiant heat from the oxygen concentration detecting section 2. Therefore, the exhaust gas flow hole 511 is not clogged with soot, and the exhaust gas satisfactorily flows into the exhaust gas flow hole 511,
The protective layer 22 of the oxygen concentration detector 2 is reached. Further, since the exhaust gas flow hole 511 and the exhaust gas flow hole 521 do not face each other, the exhaust gas flowing from the exhaust gas flow hole 531 through the exhaust gas flow hole 521 does not directly hit the oxygen concentration detector 2. The heat removal by the exhaust gas in the oxygen concentration detection unit 2 is suppressed.

(Second Embodiment) FIG. 2 shows a main part of a second oxygen concentration detecting device of the present invention. The cover body of the oxygen concentration detection device of FIG. 1 is changed to another cover body, and the difference will be mainly described. The cover unit 5B fitted in the housing 41 of the oxygen concentration detector has a substantially cylindrical cover body 54,
55 is a double inner and outer structure, and is integrally welded on the base side. The inner cover body 54 has a cylindrical shape with a bottom, and a large number of exhaust gas flow holes 541 are formed on its peripheral wall at axially symmetric positions.
It is formed by being distributed to the upstream side and the downstream side of the exhaust gas flow. The outer cover body 55 is a bottomed cylinder with an elliptical cross section,
On the upstream side of the exhaust gas flow, an exhaust gas introduction port 551, which is an opening having a width approximately the same as the diameter of the inner cover body 54 and opening from the tip to the base, is formed, and on the downstream side, a little from the exhaust gas flow hole 541. A plurality of large-diameter exhaust gas outlets 552 are vertically formed in a line. A partition-shaped cover plate 56 is provided so as to face the exhaust gas introduction port 551 so as to be along the peripheral wall of the inner cover body 54. The outer shape of the cover plate 56 is the exhaust gas introduction port 55 of the outer cover body 55.
It is almost the same as the open end shape of No. 1. Inner cover 54
The cover plate 56 is welded to the outer cover body 55 on the base side (not shown).

The operation of the above oxygen concentration detector will be described.
The exhaust gas flowing from the upstream of the exhaust gas flow from the exhaust gas inlet 551 of the outer cover body 55 is divided into left and right by the cover plate 56 and is divided into the inner cover body 54 and the outer cover body 55.
Flows toward the downstream side in the space between them, and a part of the oxygen concentration detection unit 2 enters the inside cover body 54 through the exhaust gas flow hole 541 formed on the upstream side of the exhaust gas flow of the inside cover body 54. To reach the outside of the inner cover body 54 through the exhaust gas flow hole 541 formed on the downstream side of the exhaust gas flow. The inner and outer cover bodies 5 do not enter the inner cover body 54.
The exhaust gas flowing between the four and 55 is merged and exhausted from the exhaust gas exhaust port 551 of the outer cover body 55.

In the above-mentioned oxygen concentration detecting device, the opening area of the exhaust gas inlet 551 is much larger than the total opening area of the exhaust gas outlet 552, so that the exhaust gas is rapidly ejected from the exhaust gas outlet 552. The exhaust gas exerts a shearing force on the soot existing around the exhaust gas exhaust port 552, so that the adherence of the soot can be reduced. Further, since the exhaust gas introduction port 551 has a large opening, clogging due to soot does not occur. Since the cover plate 56 guides the exhaust gas flowing from the exhaust gas introduction port 551 to the left and right, the exhaust gas flow does not directly hit the inner cover body 54 and the inner cover body 54 absorbs heat by the exhaust gas. Can be suppressed.

(Third Embodiment) FIG. 3 shows an essential part of a third oxygen concentration detecting device of the present invention. The cover body of the oxygen concentration detection device of FIG. 1 is changed to another cover body, and the difference will be mainly described. The cover unit 5C fitted in the housing 41 of the oxygen concentration detection device has a substantially cylindrical cover body 57,
The double-sided structure of 58 is integrally welded on the base side (not shown). Exhaust gas circulation holes 571, 581 are formed in the respective cover bodies 57, 58 so that the exhaust gas can flow. A plurality of slit-shaped long holes 572 and 582 are formed in the cover bodies 57 and 58 along the edge of the housing 41 side.

Since the housing 41 is in contact with the outside air at about room temperature outside the wall of the exhaust pipe 7, there is a high temperature gradient between the cover body 5C and the housing 41 on the cover body 5C side.
Therefore, the long holes 572 and 582 are formed to form the cover body 5.
By reducing the heat transfer cross-sectional area from 7, 58 to the housing 41 side, heat conduction is suppressed, and the cover body 57,
A heat insulating effect between 58 and the housing 41 is produced. However, in the inner cover body 57, the heat dissipated from the cover body 57 to the housing 41 is suppressed, and it is effectively heated by the radiant heat from the oxygen concentration detection unit 2 and kept at a high temperature. The outer cover body 58 suppresses the heat dissipated from the cover body 58 to the housing 41, and receives the radiant heat from the inner cover body 57 which is kept at a high temperature, so that the outer cover body 58 is also kept at a high temperature. To be done. Therefore, it is possible to reduce the attachment of soot to the exhaust gas circulation holes 571, 581.

The radial temperature distribution in the exhaust pipe 7 forms a transition layer near the wall of the exhaust pipe 7 in contact with the outside air, and the vicinity of the wall of the exhaust pipe 7 is lower than the center of the exhaust pipe 7. . The long holes 572 and 582 are preferably located closer to the center of the exhaust pipe 7 than the transition layer.

Further, the present invention can be applied to an oxygen concentration detection unit having a structure in which a solid electrolyte is formed into a tube shape and a rod-shaped heater is arranged inside the tube.

[Brief description of the drawings]

FIG. 1A is an overall sectional view of an oxygen concentration detection device of the present invention, and FIG. 1B is a sectional view taken along line IB-IB of FIG.

FIG. 2A is a perspective view of a main part of another oxygen concentration detection device of the present invention, and FIG. 2B is a sectional view taken along line IIB-IIB of FIG.

FIG. 3A is a partial cross-sectional side view of a main part of still another oxygen concentration detection device of the present invention, and FIG.
It is sectional drawing which follows the B-III B line.

FIG. 4 is a partial cross-sectional side view of a conventional oxygen concentration detection device.

[Explanation of symbols]

1 Oxygen concentration detection element 2 Oxygen concentration detection part 41 Housing 5A, 5B, 5C Cover unit (cover body) 51, 52, 53, 54, 55, 57, 58 Cover body 511, 521, 531, 541, 571, 581 Exhaust Gas distribution hole 551 Exhaust gas inlet (opening) 552 Exhaust gas outlet 56 Cover plates 572, 582 Long hole 7 Exhaust pipe S Space

Claims (3)

[Claims] 1. An oxygen concentration detecting element is inserted into a housing provided penetrating an exhaust pipe wall of an internal combustion engine so that the oxygen concentration detecting portion projects into the exhaust pipe. In an oxygen concentration detecting device which is covered with a cover body so as to be flowable and is adapted to operate the oxygen concentration detecting section at a high temperature by heating the oxygen concentration detecting section with a heater, the cover body is configured in inner and outer triple layers. A plurality of exhaust gas passage holes are formed in the innermost first cover body, and a second cover body provided around the first cover body is provided with an exhaust gas passage hole of the first cover body. Exhaust gas flow holes are formed at positions that do not face each other, and the third cover body provided around the second cover body is provided with the exhaust gas flow holes so as to face the exhaust gas flow holes of the second cover body. Formed, the exhaust gas flow hole, The diameter of the exhaust gas passage is larger than that of the exhaust gas passage of the second cover body, and the opening end of the exhaust gas passage hole of the third cover body on the exhaust gas passage hole side of the second cover body is the second end. By locating the cover body close to the periphery of the exhaust gas circulation hole, a space is formed between the outer periphery of the second cover body and the inner periphery of the third cover body. Oxygen concentration detector. 2. An oxygen concentration detecting element is inserted into a housing provided through an exhaust pipe wall of an internal combustion engine so that the oxygen concentration detecting portion projects into the exhaust pipe. In an oxygen concentration detecting device which is covered with a cover body so as to be flowable and which is adapted to operate the oxygen concentration detecting section at a high temperature by heating the oxygen concentration detecting section with a heater, the cover body is configured in double. Forming a large number of exhaust gas flow holes in the inner cover body, and forming an opening in the outer cover body for introducing the exhaust gas upstream of the exhaust gas flow in the exhaust pipe, and downstream of the exhaust gas flow An exhaust gas outlet having an opening area smaller than that of the opening is formed, and a cover plate is provided inside the opening to cover a portion of the inner cover body facing the opening. Tosu Oxygen concentration detector. 3. An oxygen concentration detecting element is inserted through a housing provided through an exhaust pipe wall of an internal combustion engine so that the oxygen concentration detecting portion projects into the exhaust pipe. An oxygen concentration detecting device which is covered with a cover body so as to be flowable and which is adapted to operate the oxygen concentration detecting section at a high temperature by heating the oxygen concentration detecting section with a heater, wherein the housing side of the peripheral wall of the cover body is provided. An oxygen concentration detecting device, characterized in that a slit-shaped long hole is formed along the edge of the housing on the exhaust pipe side.