JP3010636B2 - Oxygen sensor - Google Patents

Description

The present invention relates to an oxygen sensor for detecting the concentration of oxygen in exhaust gas of an internal combustion engine or the like, and more particularly to a detection characteristic, For example, the present invention relates to an oxygen sensor having an oxygen concentration detecting unit whose resistance value changes.

[Prior Art] Conventionally, this type of oxygen sensor has been disclosed in
There is one as shown in FIG.

That is, the rear end of the detection element 1 provided with the gas sensing layer 8 at the front end is adhesively fixed to a ceramic holder 3 in advance, and the holder 3 is assembled to a mounting housing 5. In addition, a part of the detection element 1 having the gas sensing layer 8 is exposed in the exhaust gas through the hole of the cover 11,
In order to exhibit the oxygen concentration detecting function of the gas sensing layer 8,
A heater for heating the gas sensing layer 8 is built in the detection element 1.

[Problems to be solved by the invention]

However, in the oxygen sensor having the above configuration, since a part of the detection element 1 having the gas sensing layer 8 is exposed in the exhaust gas, the gas sensing layer 8 is heated to a high temperature ( Even if heated to 900 ° C)
It is cooled by the exhaust gas (usually 200 ° C. to 800 ° C.), whereby the temperature of the gas sensing layer 8 changes greatly.

Therefore, in an oxygen sensor utilizing the characteristic that the gas sensing layer 8 changes its resistance according to the oxygen concentration, such as TiO ₂ , for example, the resistance of the TiO ₂ gas sensing layer 8 changes even with the temperature. Therefore, a large temperature change of the gas sensing layer 8 lowers the detection accuracy of a feedback signal of an air-fuel ratio (hereinafter referred to as A / F) determined by the oxygen concentration in the exhaust gas, thereby deteriorating the emission. There's a problem.

The present invention has been made in view of the above circumstances, and has a structure in which a portion of a detection element exposed in exhaust gas is hardly subjected to a cooling action of the exhaust gas, thereby reducing a temperature change of the gas sensing layer due to the exhaust gas. It is another object of the present invention to provide an oxygen sensor capable of performing stable A / F control.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an oxygen sensor comprising an oxygen concentration detecting section having a characteristic that varies according to the oxygen concentration in exhaust gas, and wherein the characteristic varies with temperature. A detection element in the form of a plate in which the oxygen concentration detection section and the electrode electrically connected to the oxygen concentration detection section are stacked and integrated, and the oxygen concentration detection section is heated. Provided is an oxygen sensor including a heater, a holder that supports and fixes a rear end of the detection element, and a cylindrical part that is protruded from the holder and is made of ceramic that covers at least a part of the detection element via a space. Is what you do.

In addition, it is desirable from the viewpoint of manufacturing that the holder and the cylindrical portion are integrally formed of ceramic.

Further, the sectional area S of the space interposed between the holder and the detecting element is equal to the sectional area A of the detecting element.
It is possible to obtain a more effective heat retaining action when the value is not more than three times the value.

Furthermore, an effective heat retaining action can be obtained when the length b of the cylindrical portion of the holder is at least 1/3 times the protruding length a of the detection element.

[Action]

According to the above-described means, at least a part of the portion of the detection element that protrudes from the holder is covered with the ceramic cylindrical portion having a low thermal conductivity, and thus exists in the space formed by the cylindrical portion and the detection element. The temperature of the exhaust gas is set higher than the temperature of the external exhaust gas to keep the detection element warm.

Therefore, the oxygen concentration detecting section heated by the heater provided in the detecting element is less likely to be cooled by the exhaust gas due to the warming action of the detecting element by providing such a ceramic tubular portion. Temperature change can be suppressed.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the oxygen sensor of the present invention.

In FIG. 1, reference numeral 1 denotes a plate-shaped detection element, which is formed in a T-shape by laminating and integrating a heater and electrodes (both not shown) on an alumina sheet (not shown) by pattern printing. At the tip of the detection element 1, a TiO ₂ layer whose resistance varies according to the oxygen concentration is formed as a gas sensing layer 8, and the other end is used for heating a heater, extracting an oxygen concentration output, and applying a voltage. The four lead wires 9a to 9b are connected.

The detection element 1 configured as described above has a square hole 2 at the center.
Ceramic holder 3 made of alumina porcelain etc.
Is inserted and positioned in the square hole 2 and fixed by an inorganic adhesive applied to the gap between the detection element 1 and the square hole 2 of the holder 3 and a part of the lead wires 9a to 9b side is used for lead insulation. At the same time as the insulator 10 made of a ceramic material, it is hermetically fixed by the glass seal 4.

Here, as shown in FIG. 2, the holder 3, which is a main part of the present invention, has legs 20 exposed to the exhaust gas side, and extends further from the square hole 2 of the holder 3. A cylindrical portion 21 is formed so as to cover a part of the detecting element 1, and in order to exhibit a heat retaining effect described later, FIGS. 3 (a) and 3 (b).
The cylindrical portion between the length b of the cylindrical portion 21 shown in FIG.
The spatial cross-sectional area S of 21 is set to a significant dimension.

As shown in FIG. 1, the holder 3 holding the detecting element 1 has a double cover 11 made of stainless steel or the like for protecting the detecting element 1 and a flange made of stainless steel for mounting to the engine. 12 is inserted together with a washer packing 13 into a housing 5 made of stainless steel or the like having 12;
It is fixed by the lower ring 14. Further, after connecting the four lead wires 15a to 15d for extension, an upper ring 16, a protection cover 7 made of stainless steel or the like, a spacer 17 for electrical insulation of the lead, via a powder filling layer 6 made of talc or the like.
It is assembled together by a spring together with the spring 18,
Finally, the rubber bush 19 is attached to the protection cover 7 to form an oxygen sensor.

In such a configuration, as described above, the detection element 1 heated above the gas temperature by the heater built in the detection element 1
(See the area c in FIG. 2)
It is cooled by the new gas flowing into 11. In order to prevent the temperature change from being given to the gas sensing layer 8 by the heat conduction by this, the leg 20 exposed to the exhaust gas side of the alder 3 as shown in FIG. Therefore, there is a feature of the present invention in that a ceramic cylindrical portion 21 for shielding a new gas is formed.
The length b of the cylindrical portion 21 in FIGS. 3 (a) and 3 (b) and the cylindrical portion
This means that the sectional area S of the space 21 was set significantly according to the experimental results.

Hereinafter, a description will be given based on experimental results. The experiment was carried out on an actual engine.
The exhaust gas temperature was changed in the range of 200 ° C. to 800 ° C. by changing the engine conditions, and the temperature near the gas sensing layer 8 (the temperature at the tip of the detecting element 1) at that time was measured. As shown in FIG. Tip temperature change width Δt of detecting element 1 in temperature range
According to the method of seeking.

That is, according to the present experimental results, the length b of the cylindrical portion 21
Is, as shown in FIG. 5, 1 / 3a or more with respect to the protruding length a of the detecting element 1, and the spatial sectional area S of the cylindrical portion 21 between the detecting element 1 and the detecting element 1 is as shown in FIG. By setting the cross-sectional area A of the detection element 1 to 3 A or less, the tip temperature change width Δt of the detection element 1 is such that the cylindrical portion 21 is not formed as schematically shown in FIG. Smaller than. In other words, the formation of the ceramic cylindrical portion 21 having a small thermal conductivity has the effect of preventing cooling by a new gas and improving the heat retention.

Therefore, particularly, the gas sensing layer 8 has large temperature dependency.
In the case of TiO ₂ , the A / F detection accuracy is improved, and stable A / F control becomes possible, so that good emission is obtained.

Next, in this embodiment, the holder 3 and the cylindrical portion 21 are integrally formed of ceramic, but as shown in FIG.
Holder 3a for supporting and fixing detection element 1, and this holder
It may be configured separately from a holder 3b that covers a portion of the detection element 1 protruding from 3a. In this case, the holder 3a may be made of metal instead of ceramic, and the metal preferably has a coefficient of thermal expansion close to that of the detection element 1.

In the present embodiment, the ceramic cylindrical portion 21 has a cylindrical shape. However, the cylindrical portion 21 may have, for example, a rectangular cylindrical shape or an elliptical cylindrical shape.

In the present embodiment, the detection element 1 is a square pole,
For example, the column may be a column or an ellipse, and the point is that the column can be manufactured.

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are obtained.

(1) In the gas sensing layer in which the detection characteristics change depending on the oxygen concentration and the temperature, the temperature change due to the exhaust gas becomes small due to the heat retaining action of the ceramic cylinder, so that the error fluctuation of the detection characteristics due to the temperature change becomes small. With this, A / F
The detection accuracy of the feedback signal is improved, so that stable A / F control can be performed over a wide operating range, and emission can be stabilized.

(2) Further, by integrally forming the holder for supporting and fixing the detecting element and the cylindrical portion covering the detecting element with ceramic, the number of parts is reduced and the assembling becomes easy.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of the oxygen sensor of the present invention,
FIG. 2 is a sectional view showing a main part of FIG. 1, and FIG.
(B) is a cross-sectional view showing the main part dimensions and main part area in FIG. 2 by reference numerals, FIG. 4 is a view showing the relationship between the exhaust gas temperature and the temperature of the detecting element tip, and FIGS. FIG. 7 is a view showing an experimental result of a relationship between the temperature change width of the tip of the detection element and FIG. 7 is a sectional view of a main part showing another embodiment of the oxygen sensor of the present invention, and FIG. FIG. 1 ... Detector element, 3 ... Holder, 5 ... Housing, 8 ...
Gas sensing layer (oxygen concentration detecting section), 11 ... cover, 21 ... ceramic cylinder.

Continuation of the front page (56) References JP-A-58-82150 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12

Claims (4)

(57) [Claims] 1. An oxygen sensor comprising an oxygen concentration detecting section having a characteristic that varies according to the oxygen concentration in exhaust gas, and wherein the characteristic varies with temperature. A detection element in the form of a plate in which the oxygen concentration detection section and an electrode electrically connected to the oxygen concentration detection section are laminated and integrated; a heater for heating the oxygen concentration detection section; An oxygen sensor, comprising: a holder for supporting and fixing an end portion; and a cylindrical portion made of ceramic that projects from the holder and covers at least a part of the detection element via a space. 2. The oxygen sensor according to claim 1, wherein said holder and said cylindrical portion are integrally formed of ceramic. 3. The oxygen sensor according to claim 1, wherein a sectional area S of said space interposed between said holder and said detecting element is not more than three times a sectional area A of said detecting element. 4. The oxygen sensor according to claim 1, wherein the length b of the cylindrical portion of the holder is at least 1/3 times the protruding length a of the detection element.