JPH10282042A - Gas concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a drop in the performance of gas concentration detectors by fast draining water infiltrated into a cover body to block the cooling of the element as caused by water splashing over it. SOLUTION: A gas concentration detector 2 is inserted and hold into a housing 1 and the tip part of the gas concentration detector 2 positioned in a gas passage is wrapped by a cover body 3. The cover body 3 is a double structure of an external cover 31 and an internal cover 32 which have air poles 31a and 32a respectively to guide a gas into or out of the covers. Water repelling films 41 and 42 are formed respectively on the internal surface of the external cover 31 and the external surface of the internal cover 32 and water infiltrated between both the covers 31 and 32 is quickly discharged outside from the air hole 31a on the backwash side without being accumulated in a clearance therebetween.

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, for example, the concentration of oxygen in exhaust gas, and more particularly to the structure of a cover body.

[0002]

2. Description of the Related Art For example, a gas concentration sensor is mounted on an exhaust pipe wall of an internal combustion engine to detect an oxygen concentration in exhaust gas and to perform a feedback control of a fuel injection amount and the like. An example of this type of gas concentration sensor is shown in FIG.
As shown in FIG. 1B, a cylindrical sensor housing 1 is fixed to an exhaust pipe (not shown) wall of an internal combustion engine by a flange 11, and a tubular gas concentration detecting element 2 is provided in the cylinder.
Is inserted and held. The gas concentration detecting element 2 has a lower half protruding from the housing 1, and its periphery is protected by a cover body 3.

The cover 3 keeps the gas concentration detecting element 2 warm and protects it from contaminants and the like, and usually has a double structure of an outer cover 31 and an inner cover 32 as shown in the figure. In the outer cover 31 and the inner cover 32, ventilation holes 31a and 32a are provided alternately at a plurality of positions on the side surface, so that the exhaust gas flowing in does not directly hit the gas concentration detection element 2.

[0004]

However, in the gas concentration sensor having the above structure, the water generated in the exhaust pipe collides with the cover body 3 and enters the inside of the cover body 3, enters the inside cover 32, and causes the gas. There was a problem that the concentration detecting element 2 was wet. This will be described with reference to FIG.
In the configuration of the conventional cover body 3 described above, since the gap between the outer cover 31 and the inner cover 32 is narrow, the resistance due to the viscosity of water is large, and once the water enters the outer cover 31, it is difficult for the water to go outside. Therefore, water that has entered the outer cover 31 accumulates between the outer cover 31 and the inner cover 32,
The accumulated water may be pushed out into the inner cover 32 to rapidly cool the gas concentration detecting element 2 and reduce the responsiveness of the element.

SUMMARY OF THE INVENTION It is an object of the present invention to quickly discharge water that has entered a cover body, prevent cooling of a gas concentration detecting element due to being wet, and prevent deterioration of element performance. It is to provide a gas concentration sensor.

[0006]

In order to solve the above problems, a gas concentration sensor according to the first aspect of the present invention comprises:
A gas concentration detection element which is inserted into and held in the housing and has a tip located in the gas flow path; and a cover body which surrounds the tip of the gas concentration detection element so as to allow gas flow. . The cover body has a double structure of an outer cover and an inner cover, and each of the outer cover and the inner cover has a vent hole for introducing and discharging gas in the gas flow path. A water-repellent coating is formed on at least the inner surface of the outer cover and the outer surface of the inner cover.

In the above configuration, at least the water repellent coating is provided on the inner surface of the outer cover and the outer surface of the inner cover. It is quickly discharged to the outside through the ventilation hole. For this reason, water does not enter the inside of the inner cover, thereby preventing cooling of the gas concentration detection element and improving the responsiveness of the element.

[0008] In the configuration of the second aspect, the gap between the outer cover and the inner cover is set to be equal to or larger than the diameter of the ventilation hole of the outer cover and equal to or larger than 1/8 of the outer diameter of the outer cover. By increasing the gap between the two covers to a value equal to or greater than the above-mentioned set value, the resistance due to the viscosity of the water is reduced, and the water is hardly accumulated between the two covers. Therefore, the above-described effect of the water-repellent coating is further enhanced, and the device performance can be greatly improved.

[0009]

1A and 1B show an example in which the present invention is applied to an oxygen concentration sensor attached to an exhaust pipe wall of an internal combustion engine. In the figure, an oxygen concentration sensor is a cylindrical housing 1 penetrating an exhaust pipe wall of an internal combustion engine.
And is fixed to an exhaust pipe wall (not shown) by a flange portion 11 provided on the outer periphery of the housing 1. A rod-shaped gas concentration detecting element 2 is inserted and held in the housing 1.

The gas concentration detecting element 2 is formed by molding an oxygen ion conductive solid electrolyte such as zirconia into a hollow body, and providing a pair of electrodes (not shown) inside and outside of the solid electrolyte. The exhaust gas in the tube is exposed to the atmosphere as the reference gas at the inner electrode, so that an electromotive force is generated between the two electrodes in proportion to the difference in oxygen concentration between these gases.

The lower half of the gas concentration detecting element 2 projects from the housing 1 and is located in an exhaust pipe (not shown), and the periphery thereof is covered with a container-like cover body 3. . The cover body 3 has a double structure of the outer cover 31 and the inner cover 32, and the upper opening edge of the outer cover 31 is embedded and fixed to the lower end of the housing 1. The inner cover 32 is disposed concentrically inside the outer cover 31, and has an upper end edge bent outward to abut and support the inner peripheral wall of the outer cover 32. The bottom surface of the inner cover 32 is in close contact with the bottom surface of the outer cover 31.

The outer cover 31 and the inner cover 32
Has a large number of ventilation holes 31a, 32
a is formed. These ventilation holes 31a and 32a are formed at substantially equal intervals in the axial or circumferential direction.
At four locations in the axial direction, eight ventilation holes 3 are provided in the circumferential direction.
1a and 32a are formed to make a total of 32 places. In addition, these ventilation holes 31a and 32a are
1 and the inner cover 32 are arranged so as to be staggered.

In the present invention, the inner peripheral surface of the outer cover 31 and the outer peripheral surface of the inner cover 32 are each subjected to a water-repellent surface treatment to form coatings 41 and 42. As the coatings 41 and 42, those coated with molybdenum sulfide, for example, are preferable because they have water repellency and heat resistance up to 900 ° C. It is also effective to apply hard chromium plating to reduce surface roughness and improve water repellency, and a coating having higher heat resistance of 1000 ° C. or higher can be obtained.

Next, the operation of the oxygen concentration sensor having the above configuration will be described. In FIG. 2, the moisture in the exhaust gas is cooled by the exhaust pipe wall and condensed, forming water droplets on the cover 3.
, The water droplets enter the inside of the outer cover 31 through the ventilation holes 31a. Here, in the present invention, the outer cover 3
Since the water-repellent films 41 and 42 are formed on the inner peripheral surface of the first cover 1 and the outer peripheral surface of the inner cover 32, the outer cover 31
Even if water enters inside, the water is quickly discharged to the outside through the vent hole 31a on the downstream side, and the stagnation of water between the covers 31 and 32 can be suppressed. Therefore, water does not enter the inside of the inner cover 32, and a decrease in element responsiveness due to cooling of the gas concentration detection element 2 can be prevented.

Here, in order to make the functions of the water repellent films 41 and 42 more effective, the outer cover 31 is used.
The gap between the inner cover 32 and the inner cover 32 may be set larger than usual. Specifically, as shown in FIG. 3, the diameter (φb) of the ventilation hole 31a of the outer cover 31 and the outer cover 31
It is preferable that the gap (a) between the covers 31 and 32 satisfies the following formulas (1) and (2) with respect to the outer diameter (φD). a ≧ b (1) a ≧ D / 8 (2) The gap (a) is set to be equal to or larger than the diameter (φb) of the ventilation hole 31a, that is, equal to or larger than the diameter of a water droplet that enters the outer cover 31. By making the outer diameter (φD) of the outer cover 31 １ ／ or more, the resistance due to the viscosity of water is reduced,
Water can hardly be held between the 32.

FIG. 4 shows the relationship between the amount of water generated in the exhaust pipe and the generation of water by the sensor, based on the outer diameter (φD) of the outer cover 31.
This was examined by changing the ratio of the gap (a) to. As shown in the figure, as the ratio between the gap (a) and the outer diameter (φD) increases, the amount of condensed water in the exhaust pipe where water is generated increases, and the amount of condensed water generated in the exhaust pipe when the engine starts. Is usually about 60cc,
It can be seen that it is only necessary to satisfy a ≧ D / 8 in order to prevent flooding. On the other hand, in the conventional cover body 3, this gap (a)
Is usually set to about 1/16 of the outer diameter (φD). In this case, water is generated when the amount of condensed water in the exhaust pipe is 40 cc.

FIG. 5 shows the gap (a) between the inner and outer covers.
7 shows the effect of the magnification on the responsiveness of the sensor. In the figure, T ₉₀
Indicates the rise time until the sensor output reaches 90% of the saturation value when the oxygen concentration in the gas to be measured is changed. In normal engine control system, responsive required for the sensor, T ₉₀ is equal to or less than 200 msec, even expanding the ratio of the gap (a) between the outer diameter ([phi] D) 1/8, ratio 1 It is almost the same as the conventional sensor of / 16 and is within the allowable range. Therefore, the response of the sensor is not reduced, and the controllability of the engine is not adversely affected. However, as the ratio of the gap (a) between the outer diameter ([phi] D) is increased, since the T ₉₀ is increased, preferably, the ratio preferably set to 3/8 or less.

As described above, it is effective to widen the gap (a) and to set the gap to an appropriate value, which is effective in generating water. By combining this with the water-repellent coatings 41 and 42,
Water generation can be reliably prevented, and the element performance can be improved.

[Brief description of the drawings]

FIGS. 1A and 1B show an embodiment of the present invention, wherein FIG. 1A is an overall schematic sectional view of a gas concentration sensor, and FIG. 1B is a sectional view taken along line AA of FIG.

FIG. 2 is a cross-sectional view of the gas concentration sensor for explaining the operation of the present invention.

FIG. 3 is an overall schematic cross-sectional view of a gas concentration sensor for explaining a relationship between a gap between inner and outer covers and generation of water.

FIG. 4 is a diagram showing a relationship between enlargement of a gap between inner and outer covers and occurrence of water by a sensor.

FIG. 5 is a diagram showing a relationship between enlargement of a gap between inner and outer covers and responsiveness of a sensor.

6A is a schematic cross-sectional view of a conventional gas concentration sensor, and FIG. 6B is a cross-sectional view taken along line BB of FIG.

FIG. 7 is a cross-sectional view for explaining the operation of a conventional gas concentration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 11 Flange 2 Gas concentration detection element 3 Cover body 31 Outer cover 32 Inner cover 31a, 32a Vent hole 41, 42 Coating

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasunori Nakamura 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kazuya Mizusawa 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation

Claims (2)

[Claims] 1. A housing, a gas concentration detecting element inserted into and held in the housing and having a tip located in a gas flow path, and a cover body surrounding the tip of the gas concentration detecting element so that gas can flow therethrough. In the gas concentration sensor having the above, the cover body has a double structure of an outer cover and an inner cover, and the outer cover and the inner cover are each provided with a vent hole for introducing and introducing gas in the gas flow path. A gas concentration sensor wherein at least the inner surface of the outer cover and the outer surface of the inner cover are covered with a water-repellent coating. 2. The gas concentration sensor according to claim 1, wherein a gap between the outer cover and the inner cover is set to be equal to or larger than a diameter of a ventilation hole of the outer cover and equal to or larger than ８ of an outer diameter of the outer cover.