JP3434170B2 - Gas concentration sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration sensor for detecting oxygen concentration in exhaust gas.

[0002]

2. Description of the Related Art The concentration of oxygen in exhaust gas discharged from an internal combustion engine is detected and the fuel injection amount and the like are feedback-controlled. The gas concentration sensor used in this case has a rod-shaped gas concentration detection element, and the tip of the gas concentration detection element, which is the part sensitive to gas, projects into the exhaust pipe to keep the gas concentration detection element warm and operate. It is surrounded by a ventilation cover to stabilize it. Ventilation holes for leading in and out exhaust gas are formed in the peripheral wall of the ventilation cover body.

Exhaust gas contains a large amount of water vapor. There is a problem in that this gas condenses into water droplets and enters the inside of the ventilation cover body, and the gas concentration detection element covers the gas and erroneously detects it. In particular, if the gas concentration detection element uses the principle of an oxygen concentration battery, an electric heater is built in to increase the detection sensitivity and the temperature is high. There is a problem that the detection element is cracked. In order to solve these problems, in the oxygen concentration measuring device described in Japanese Utility Model Laid-Open No. 61-187455, the ventilation cover body is surrounded by a cylindrical partition having the same length as this, and the ventilation hole is formed in the ventilation cover body. The surrounding wall is prevented from being directly exposed to the exhaust gas flow, and the water droplets that have collided with the partition are evaporated by being heated by an electric heater embedded in the partition.

[0004]

However, the oxygen concentration measuring device described in Japanese Utility Model Laid-Open No. 61-187455 has a certain effect of preventing the gas concentration detecting element from getting wet, but the partition is a ventilation cover body. Since it obstructs the flow of the exhaust gas through the vent hole, it cannot follow the change in the oxygen concentration in the exhaust gas and the detection response becomes poor.

Therefore, it is an object of the present invention to provide a gas concentration sensor which prevents the gas concentration detection element from getting wet and has a good detection response.

[0006]

Means for Solving the Problems As a result of intensive experiments and researches on the behavior of water vapor contained in a gas to be measured flowing through a gas flow path, the inventors have found that the water condensed from water vapor is mostly in the gas flow path. We found that few things move along the inner surface of the wall and fly in the gas flow path. Based on this finding, in the invention according to claim 1, the tip portion of the gas concentration detecting element is made to project into the gas flow passage, and the tip portion is surrounded by a ventilation cover body having a large number of ventilation holes. In a gas concentration sensor adapted to let gas in and out of the inside, a tubular waterproof cover body surrounding the outer periphery of the base end portion of the ventilation cover body is provided on the inner surface of the gas flow path wall, and at least the waterproof cover of the ventilation cover body is provided. The front end side of the cover body has a double structure including an outer cover body and an inner cover body. In addition, the vent holes of these cover bodies are formed at positions displaced from each other in the circumferential direction and the axial direction of the cover body.

By providing the waterproof cover body, some of the water droplets propagating on the inner surface of the gas flow path wall and the water droplets flying near the inner surface are carried by the exhaust gas flow to the rear of the gas concentration sensor, and some of them are waterproof. The gas concentration detecting element is not covered by the water drops flowing down the surface of the cover body and dripping from the tip of the waterproof cover body. On the other hand, even if water droplets fly to the tip of the ventilation cover body exposed from the waterproof cover body, the ventilation holes of the outer cover body and the inner cover body are formed at positions displaced from each other, so that Almost no water droplets flying in the center enter the inside of the ventilation cover body, and the gas concentration detection element
It does not get so wet that it affects the detection value.

Therefore, the gas concentration detecting element is prevented from being erroneously detected due to water.

Moreover, the gas flowing through the gas flow channel flows better through the vent hole formed in the exposed tip portion of the ventilation cover body and reaches the gas concentration detecting element, so that a good detection response is obtained. can get.

In order to prevent water droplets that have flowed down to the tip of the ventilation cover body from dripping toward the ventilation cover body side, in the invention according to claim 2, a brim portion is formed at the peripheral edge of the tip end portion of the waterproof cover body, and the ventilation cover body is formed. Make sure that water droplets drip from a position further away from.

Alternatively, as in the third aspect of the present invention, by forming the waterproof cover body in a tapered shape that expands in diameter in the front end direction, water droplets outward from a position further away from the ventilation cover body. Try to drip towards it.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the findings obtained by the inventors will be described. The inventors conducted a visualization test in a gas flow path such as an exhaust pipe connected to an internal combustion engine, and obtained the following findings from the observation results regarding the behavior of water vapor contained in the measured gas flowing in the gas flow path. .
There are two types of modes in which water droplets in which water vapor is condensed move in the gas flow passage: traveling along the inner surface of the gas flow passage and flying in the gas flow passage. The former occupies the majority, and the latter is Turned out to be relatively small. It is recognized that this is caused by condensation of water vapor, which is mostly taken by the inner surface of the low temperature gas passage wall. The present invention has been made based on such findings.

(First Embodiment) FIG. 1 shows an example in which the present invention is applied to an oxygen concentration sensor for detecting the oxygen concentration in exhaust gas discharged from an internal combustion engine. The oxygen concentration sensor 2 which is a gas concentration sensor is attached to the exhaust pipe 1 which is a gas flow path connected to an exhaust port of an internal combustion engine. A through hole 11a for mounting is formed in the exhaust pipe wall 11,
The rod-shaped gas concentration detecting element 3 of the oxygen concentration sensor 2 is inserted through this, and the tip portion 3a thereof projects into the exhaust pipe 1.
The gas concentration detecting element 3 is fixed to the exhaust pipe wall 11 via a flange portion 4 provided on the outer surface of the exhaust pipe wall 11.

The flange portion 4 has a plate-shaped first flange 41 through which the gas concentration detecting element 3 penetrates and is held, and an annular second flange 42 welded to the exhaust pipe wall 11.
The first flange 41 has a plurality of embedded screws 43 screwed to the second flange 42 and a nut 44 to form a second
The gas concentration detecting element 3 is fixed to the exhaust pipe wall 11 by being fixed to the flange 42.

The gas concentration detecting element 3 is formed by forming an oxygen ion conductive solid electrolyte material such as zirconia into a cylindrical shape with its tip closed, and providing a pair of electrodes (not shown) inside and outside thereof. The outer electrode is exposed to the exhaust gas in the exhaust pipe 1 and the inner electrode is exposed to the atmosphere as the reference gas, so that an electromotive force proportional to the oxygen concentration difference between these electrodes is generated between both electrodes. .

The ventilation cover body 5 surrounds the tip portion 3a of the gas concentration detecting element 3. The ventilation cover body 5 has a double structure including an outer cover body 51 and an inner cover body 52 each having a cylindrical shape with a bottom, and an upper opening edge of the outer cover body 51 is embedded and fixed in a lower end portion of the first flange 41. . Inner cover body 5
2 is concentrically arranged in the outer cover body 51, and the upper end opening edge is bent outward and elastically contacts the inner peripheral wall of the outer cover body 51 to be integrated with the outer cover body 51. Inner cover body 52
The bottom surface of is close to the bottom surface of the outer cover body 51.

Outer cover body 51 and inner cover body 52
Has a plurality of ventilation holes 51a and 52a on its peripheral wall.
a is formed. These ventilation holes 51a, 52a are formed at substantially equal intervals in the axial direction and the circumferential direction. In the illustrated example, the ventilation holes 51 are provided at four locations in the axial direction and at eight locations in the circumferential direction.
a and 52a are formed, and there are 32 places in total. The vent holes 51a of the outer cover body 51 and the inner cover body 5
The second ventilation holes 52a are arranged at positions displaced in the axial direction and the circumferential direction of the cover bodies 51, 52.

Between the annular second flange 42 and the ventilation cover body 5, a cylindrical waterproof cover body 6 is fitted coaxially therewith, and closely adheres to the side surface of the through hole 11a formed in the exhaust pipe wall 11. ing. The waterproof cover body 6 has a length that projects into the exhaust pipe 1, and is approximately half of the ventilation cover body 5 and is the base end portion 5.
It surrounds the outer circumference of b. The front half of the waterproof cover body 6 excluding the fitting portion is thinly formed, and an annular space 7 is formed between the waterproof cover body 6 and the ventilation cover body 5.

By providing such a waterproof cover body 6, two rows of ventilation holes 5 formed in the tip portion 5a of the ventilation cover body 5 are provided.
Exhaust gas is directly distributed in 1a and 52a, and exhaust gas is distributed through the space 7 in the two rows of vent holes 51a and 52a formed in the base end portion 5b.

The operation of the oxygen concentration sensor 2 will be described. The water vapor in the exhaust gas is cooled by the inner surface 1a of the exhaust pipe wall 11 and the like to condense into water droplets. Of these, the exhaust pipe wall 1
The one that propagates along the inner surface 1a of 1 flows down the surface of the waterproof cover body 6 from the inner surface 1a, and a part thereof is blown to the side of the exhaust gas flow by the waterproof cover body 6 and downstream of the oxygen concentration sensor 2, The waterproof cover body 6 is prevented from entering the inside. Further, the remaining part drops from the tip of the waterproof cover body 6. Therefore, these water droplets are not covered by the gas concentration detecting element 3 located at a position apart from the ventilation cover body 5.

The water droplets flying in the exhaust pipe 1 and those near the inner surface 1a of the exhaust pipe wall 11 are blocked by the waterproof cover body 6 in the same manner as the water droplets propagating on the inner surface 1a of the exhaust pipe wall 11. Further, the water droplets flying on the center side of the exhaust pipe 1 reach the tip portion 5 a of the ventilation cover body 5 without being blocked by the waterproof cover body 6. However, since the ventilation holes 51a and 52a of the ventilation cover body 5 are formed at positions displaced from each other between the outer cover body 51 and the inner cover body 52, even if the ventilation holes 51a of the outer cover body 51 are passed through, the inner cover body 52 will be hit. , Does not reach the oxygen concentration detection element 3. Since the amount of water drops flying in the exhaust pipe 1 is originally small, the amount of water drops reaching the gas concentration detecting element 3 is a very small amount that does not affect the detected value of oxygen concentration.

Therefore, the gas concentration detecting element 3 is prevented from getting wet.

The exhaust gas flowing from the upstream side of the oxygen concentration sensor 2 reaches the tip portion 5a of the ventilation cover body 5 exposed from the waterproof cover body 6. Exhaust gas is at the tip 5a
Of the outer cover body 5 formed to face the exhaust gas flow
1 vent hole 51a and inner cover body 52 vent hole 52
It flows into the inside of the ventilation cover body 5 from a, diffuses quickly, and flows out from the other ventilation holes 51a and 52a. Therefore, the tip portion 3a of the gas concentration detecting element 3 is exposed to the same exhaust gas as the exhaust gas flowing outside the oxygen concentration sensor 2, and good detection response is obtained.

(Second Embodiment) FIG. 2 shows a second gas concentration sensor of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIG. 1 are substantially the same, and therefore the differences from the first embodiment will be mainly described. Flange 42A of the present embodiment
Is an annular member that constitutes the flange portion 4 together with the first flange 41 and the like, and is substantially equivalent to the flange 42 in FIG. 1, and the inner peripheral edge portion extends toward the inside of the exhaust pipe 1. The extending portion 6 is in close contact with the side surface of the through hole 11a formed in the exhaust pipe wall 11 and surrounds the outer periphery of the base end portion 5b of the ventilation cover body 5 to form a waterproof cover body 6. As described above, by forming the second flange 42 and the waterproof cover body 6 in FIG. 1 into the integrated flange 42A, the number of parts is reduced and the assembling work can be simplified.

(Third Embodiment) In the gas concentration sensor of FIGS. 1 and 2, the waterproof cover has a simple cylindrical shape, but in order to prevent the oxygen concentration detecting element from being more effectively covered with water, the waterproof cover has a shape. An improved waterproof cover body may be used. FIG. 3 shows a third gas concentration sensor of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIGS. 1 and 2 are substantially the same, so that the first and second embodiments are the same. The differences will be mainly described. The waterproof cover body 6A of the present embodiment has a shape in which a brim portion 601 protruding outward is formed on the peripheral edge of the tip end portion. With such a shape, the water droplets that have flowed down to the tip of the waterproof cover body 6A are dropped from a position further away from the ventilation cover body 5, and the water droplets dropped by the ventilation cover body 5 from the tip of the waterproof cover body 6A. It can be effectively prevented from being covered.

(Fourth Embodiment) FIG. 4 shows a fourth gas concentration sensor of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIGS. 1 and 2 are substantially the same, and therefore the differences from the first embodiment will be mainly described. The waterproof cover body 6B of the present embodiment is a waterproof cover body having an improved shape in order to more effectively prevent the oxygen concentration detection element 3 from being exposed to water, and is formed in a tapered shape that expands in diameter in the distal direction. . With such a shape, the water droplets that have flown down to the tip of the waterproof cover body 6B drop outward from a position further away from the ventilation cover body 5, and the ventilation cover body 5 has the tip end of the waterproof cover body 6B. It is possible to effectively prevent water droplets dripping from the cover.

The length of the waterproof cover body is not limited to that of each of the above-mentioned embodiments, but the tip end of the ventilation cover body is exposed from the waterproof cover body, and at least one row of vent holes is formed in the peripheral wall of the tip end portion. Should be formed.

The ventilation cover body has a double structure from the tip to the base end, but the inner cover body is constructed as a short-sized cover body and only the tip side of the waterproof cover body has a double structure. It may be.

The arrangement of the ventilation holes is not limited to the arrangement of 4 rows in the axial direction and 8 rows in the circumferential direction, and may be changed as appropriate.

The present invention is not limited to the gas concentration detecting element using the oxygen ion conductive solid electrolyte material such as zirconia, but can be suitably applied to other detecting methods. The type of gas to be detected is not limited to oxygen. In addition to the gas concentration sensor attached to the exhaust pipe,
Any gas concentration sensor used for detecting the components of the gas flowing through the gas flow path can be suitably applied.

[Brief description of drawings]

FIG. 1A is an overall vertical sectional view of a first gas concentration sensor of the present invention, and FIG. 1B is a sectional view taken along line IB-IB in FIG.

FIG. 2 is an overall vertical sectional view of a second gas concentration sensor of the present invention.

FIG. 3 is an overall vertical sectional view of a third gas concentration sensor of the present invention.

FIG. 4 is an overall vertical sectional view of a fourth gas concentration sensor of the present invention.

[Explanation of symbols]

1 Exhaust pipe (gas flow path) 11 Exhaust pipe wall (gas channel wall) 1a inner surface 2 Oxygen concentration sensor (gas concentration sensor) 3 Gas concentration detection element 3a tip 4 Flange part 5 Ventilation cover body 5a tip 5b base end 51 Outer cover body 52 Inner cover body 51a, 52a Vent hole 6,6A, 6B Waterproof cover body 6a Tip 601 collar part

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Nakamura 1 Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Corporation (56) Reference JP-A-6-235714 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/409

Claims (3)

(57) [Claims] 1. A gas concentration detecting element having a tip protruding into a gas flow path, and a ventilation cover body surrounding the tip of the gas concentration detecting element, wherein the ventilation cover body has a gas flow path inside the gas flow path. In a gas concentration sensor having a large number of vent holes for letting in and out the gas, a cylindrical waterproof cover body surrounding the outer periphery of the base end portion of the vent cover body is provided on the inner surface of the gas passage wall, and the vent cover is provided. At least the front end side of the waterproof cover body is made to have a double structure composed of an outer cover body and an inner cover body, and the ventilation holes of these cover bodies are displaced from each other in the circumferential direction and the axial direction of the cover body. A gas concentration sensor characterized by being formed at a position. 2. The gas concentration sensor according to claim 1, wherein the waterproof cover body has a brim portion projecting outward at a peripheral edge of a front end portion. 3. The gas concentration sensor according to claim 1, wherein the waterproof cover body is formed in a taper shape whose diameter is expanded in a tip direction.