JPH0755758A - Detecting device of air-fuel ratio - Google Patents

Abstract

PURPOSE:To obtain a detecting device of air-fuel ratio having a detecting part which is excellent in a mechanical strength and an insulation strength and also ensures high airtightness between inspection fluids. CONSTITUTION:A detecting device of air-fuel ratio having a detecting part 10 prepared by laminating an exhaust-side electrode 12 and a protective film 14 sequentially on a first surface 111 of a flat-plate-shaped solid electrolyte 11 and laminating an atmosphere-side electrode 13, a flat-plate-shaped support 20 made of alumina, an electric heater 15 and an insulating sheet 16 sequentially on a second surface 112 thereof and by integrating them together. As for the flat-plate-shaped support 20, a ventilating passage 21 communicating with the atmosphere is bored therein and also an atmosphere chamber 22 opening toward the second surface 112 is formed therein. It is preferable that the plate thickness (d) of the flat-plate-shaped support 20 is made 1 to 5mm and the content of alumina 9wt.% or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio detecting device for an internal combustion engine for a vehicle, and more particularly to an air-fuel ratio detecting device excellent in mechanical strength and insulation strength of a detecting portion.

[0002]

2. Description of the Related Art If the air-fuel ratio of an internal combustion engine for a vehicle is not appropriate, exhaust gas pollution due to generation of soot, unburned fuel discharge due to misfire,
A problem such as a decrease in output occurs. Therefore, adjustment of the air-fuel ratio in the internal combustion engine is extremely important, and therefore the air-fuel ratio is detected.

As the above-mentioned air-fuel ratio detecting device, a device in which an electrochemical cell is constituted by providing electrodes on both sides of a solid electrolyte which is an oxygen ion conductor is often used. Then, the exhaust gas is introduced into one of the electrodes and the atmosphere into the other, and the air-fuel ratio of the internal combustion engine is detected from the potential difference between the electrodes caused by the difference in oxygen concentration between the two.

Further, in the case of detecting the air-fuel ratio in a wide range, there is a method in which a constant voltage is applied between the electrodes to cause an oxygen ion current to flow in the solid electrolyte and the diffusion resistance layer controls the current to measure the limiting current. Used. A high temperature (about 650 ° C. or higher) is required to generate oxygen ion conduction in the fixed electrolyte, and therefore the cell is heated by using an electric heater.

Further, in the air-fuel ratio detecting device for a vehicle, it is necessary to activate the air-fuel ratio detecting device as soon as possible immediately after the engine is started. Therefore, the electrothermal heater heats the detecting portion in a short time. There is a need to.

Detection unit (cell unit) of a conventional air-fuel ratio detection device
90 (FIG. 4) is a solid electrolyte 91 as shown in FIG.
Electrodes 921 and 922 are provided on both upper and lower surfaces of 1,912, and the electrodes 921 and 922 are connected to lead terminals 931 and 932. One of the solid electrolytes 911 and 912 is 912.
A ventilation groove 923 extending in the longitudinal direction is formed in the.
The upper surface 913 of the solid electrolyte 911 has a protective film 94.
Contact with the exhaust air through.

The protective film 94 is made of a porous material, or is provided with air permeability by a method such as providing a window 941 (FIG. 3). Also,
Atmosphere is introduced into the lower surface 914 of the solid electrolyte 911 from the ventilation groove 923 formed by the solid electrolytes 911 and 912 and the substrate 95.

Then, an electric heater 97 is attached to the lower surface of the substrate 95 through an alumina insulating tank 96. The electric heater 97 includes a heating element 971 and a zirconia insulating layer 97.
2 and the zirconia protective layer 973. The reason why the alumina insulating layer 96 is required is that the resistivity of zirconia is significantly reduced at high temperature.

The above-mentioned members are sequentially laminated as shown in FIG. 3 and then fired to be integrated with the detection section 90 as a laminated body shown in FIG. Incidentally, PSZ (partially stabilized zirconia) is generally used as zirconia used as the solid electrolyte, and this zirconia has a characteristic thermal hysteresis characteristic. Therefore, in order to enable integration by firing, the metal members such as electrodes and the laminated members except the alumina insulating layer 96 are formed of a zirconia-based material.

This is because when members having different thermal expansion characteristics are integrated, thermal stress may cause delamination. For the same reason, the alumina insulating layer 96 sandwiched between the zirconia insulating layer 972 and the substrate 95 is used.
Is formed of a thin alumina plate (about 0.02 mm).

[0011]

However, the detecting section 90 of the above conventional air-fuel ratio detecting device has the following problems. The first point is the problem of electrical insulation strength between the heating element 971 of the electric heater 97 and the atmosphere-side electrode 922.

That is, as described above, the alumina insulating layer 96
Since its thickness cannot be increased, the dielectric strength at high temperature heating is not sufficient. Therefore, the heating element 971
There may be a case where the electric potential between the atmosphere side electrode and the atmosphere side electrode 922 fluctuates due to electrical leakage.

The second problem is the problem of airtightness of the ventilation groove 923 for introducing the atmosphere. If the airtightness of the ventilation groove 923 is insufficient, the surrounding exhaust gas enters the ventilation groove 923 and mixes with the atmosphere, resulting in a measurement error. However, the ventilation groove 923 is formed in the zirconia solid electrolyte 912 which is not so rigid. Therefore, when the whole is laminated and thermocompression-bonded, fine cracks may occur in the solid electrolyte 912.

The solid electrolyte 912 has a ventilation groove 92.
3 is formed, the pressure applied to the solid electrolytes 911 and 912 during thermocompression bonding is unbalanced between the ventilation groove 923 and other portions. Therefore, there is a problem that the solid electrolytes 911 and 912 are deformed or cracked, and as a result, the airtightness of the ventilation groove 923 is impaired.

The third problem is the mechanical strength of the entire detector 90. As described above, in order to shorten the rise time of the air-fuel ratio detection device, the electric heater 97 needs to heat the detection unit 90 quickly. For this reason, the detection unit 90 is formed by stacking thin plate laminated bodies in order to enhance thermal conductivity, and the laminated bodies are mainly composed of zirconia whose strength is not so great.

Therefore, the strength of the detection unit 90 is not always sufficient for vibration and shock in the environment of use of the vehicle, and there is a problem that it is sometimes broken. In view of the above conventional problems, the present invention is to provide an air-fuel ratio detection device having a detection portion which is excellent in mechanical strength and insulation strength and has high airtightness between test fluids.

[0017]

The present invention is directed to an internal combustion engine in which an electrochemical cell is formed by providing an exhaust side electrode on a first surface of a solid electrolyte which is an oxygen ion conductor and an atmosphere side electrode on a second surface facing the solid electrolyte. The air-fuel ratio detecting device of claim 1, wherein an exhaust side electrode and a protective film are sequentially laminated on the first surface of the flat plate-shaped solid electrolyte,
On the other hand, below the second surface of the solid electrolyte, an atmosphere-side electrode, an alumina flat plate-like support, an electric heater, and an insulating seed are sequentially laminated, and the flat plate-like support communicates with the atmosphere. The air-fuel ratio detecting device for an internal combustion engine is characterized in that an air chamber is formed to communicate with the air passage and is opened to the second surface of the solid electrolyte.

What is most noticeable in the present invention is that a flat plate-shaped support made of alumina is arranged between the second surface of the solid electrolyte and the electric heater, and the flat plate-shaped support is the second solid electrolyte. It has an atmosphere chamber open to the surface, and this atmosphere chamber communicates with the atmosphere through an air passage formed in the flat support. The ventilation passage is not a groove-like open passage as in the conventional detecting portion, but a tunnel-like closed passage formed in a flat plate-like support.

It is preferable that the plate-like support has a plate thickness of 1 to 5 mm. This is because if the plate thickness is less than 1 mm, the strength decreases and the dielectric strength in the plate thickness direction also decreases. On the other hand, if the plate thickness exceeds 5 mm, the thermal conductivity from the electric heater to the solid electrolyte decreases, and the startup time of the air-fuel ratio detection device becomes long.

The flat plate-like support preferably has an alumina content of 90% by weight or more. This is because the content of alumina must be 90% by weight or more in order to secure a sufficient electric insulation strength (high resistivity) in the flat plate-shaped support.

[0021]

FUNCTION AND EFFECT In the air-fuel ratio detecting device of the present invention, between the electric heater and the solid electrolyte, a flat plate-shaped support body of alumina having an air chamber and a ventilation passage is provided.
The flat plate-shaped support is an alumina plate provided with an air chamber and a ventilation path, and has a remarkably large thickness as compared with a sheet-shaped alumina insulating layer (reference numeral 96 in FIG. 3) in a conventional detection unit. .

Therefore, the insulation resistance between the electrothermal heater and the solid electrolyte is greatly increased, and there is no possibility that a leak current will flow from the electrothermal heater to the atmosphere-side electrode of the solid electrolyte. On the other hand, since the thermal conductivity of alumina is much higher than that of zirconia (about twice), the thermal conductivity from the electric heater to the solid electrolyte is good.

The ventilation passage provided on the flat support is
Since it is provided inside the flat plate-like support, its airtightness is perfect, and there is no possibility that exhaust gas will enter the ventilation passage unlike the ventilation groove (923 in FIG. 3) of the conventional device. Therefore,
The airtightness of the air introduction part may be secured only in the periphery of the air chamber provided in the flat support. Also, since alumina has a large strength, there is no fear of cracks and the like even if the pressure bonding strength is increased, and it is easy to secure its airtightness.

Further, the strength of the detecting portion is greatly increased by the flat plate-shaped support made of alumina, which has high strength. That is,
In the conventional apparatus, the strength was uncertain because it was a laminated body centered on a zirconia member, but in the present invention, the strength is significantly increased by using a flat plate-shaped support made of alumina. As described above, according to the present invention, it is possible to provide an air-fuel ratio detection device having a detection portion that is excellent in mechanical strength and insulation strength and has high airtightness between test fluids.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An air-fuel ratio detecting device according to an embodiment of the present invention will be described with reference to FIGS. In this example, as shown in FIG. 1, the first of the solid electrolyte 11 which is an oxygen ion conductor is used.
The exhaust side electrode 12 is provided on the surface 111, and the second surface 1 facing the exhaust side electrode 12 is provided.
1 is an air-fuel ratio detection device 1 for an internal combustion engine in which an atmosphere-side electrode 13 is provided in 12 to form an electrochemical cell.

An exhaust side electrode 12 and a protective film 14 are sequentially laminated on the first surface 111 of the flat plate-shaped solid electrolyte 11. On the other hand, below the second surface 112 of the solid electrolyte 11, the atmosphere-side electrode 13, the flat plate-shaped support body 20 made of alumina, the electric heater 15, and the insulating sheet 16 are sequentially laminated.

The plate-like support 20 has a ventilation passage 21 communicating with the atmosphere and an atmosphere chamber 22 communicating with the ventilation passage 21 and opening toward the second surface 112 of the solid electrolyte 11. Has been formed.

The plate-shaped support 20 has a plate thickness d of 3.0 mm, which is a value between 1 and 5 mm. Further, the content rate of alumina in the flat plate-shaped support 20 is 100%.

Each of these will be described in detail below. In this example,
As shown in FIG. 2, the detection unit 10 is provided inside the housing 40.
Is an air-fuel ratio detection device 1 having a lead wire 41 that accommodates the The housing 40 has a body portion 42 provided with a flange 43 in a substantially central portion, and has an exhaust cover 44 inserted into the exhaust passage below the body portion 42,
An atmosphere cover 45 that is in contact with the atmosphere is provided above the body 42.

As shown in FIG. 2, the exhaust cover 44 has an inner cover 441 and an outer cover 442 made of stainless steel, and both covers 441 and 442 have exhaust ports 443 and 44.
4 is provided. On the other hand, the atmosphere cover 45 has a main cover 451 attached to the body 42 and a sub-cover 452 covering the rear end of the main cover 451. 45
3,454 are provided.

The atmosphere ports 453 and 454 communicate with the ventilation passage 21 of the detecting section 10. And both atmosphere ports 453, 4
A water repellent filter 46 for waterproofing is inserted between 54. The detector 10 is sandwiched between the insulating members 421 and housed in the body 42. In addition, the detection unit 10
The lead wire 41 connected to is composed of a pair of signal wires for taking out the cell electromotive force and a pair of heater wires for supplying electric power to the electrothermal heater.

As shown in FIG. 1, the detection unit 10 includes an exhaust side electrode 12 made of platinum or the like, lead terminals 121 and 131, and an exhaust side electrode 12 on the first surface 111 of the solid electrolyte 11.
A protective film 14 covering the above is sequentially laminated. The exhaust side electrode 12 is connected to one of the lead terminals 121. On the other hand, on the second surface 112 of the solid electrolyte 11, the atmosphere side electrode 13, the flat plate-shaped support 20, the electrothermal heater 15,
The insulating sheet 16 is sequentially laminated.

The atmosphere-side electrode 13 is connected to the lead terminal 131 on one side on the first surface 111 via a connecting member 132 penetrating the solid electrolyte 11. The electric heater 15 includes a heat generating portion 151 covered with an insulating sheet 16 and bent in a zigzag shape, and a lead terminal 152.

The plate-like support 20 has a bottomed atmosphere chamber 22 that opens to the solid electrolyte 11 and a tunnel-shaped ventilation path 21 that communicates with the atmosphere chamber 22. The members 11 to 16 and 20 are laminated and fired integrally (see FIG. 4).
2), the housing 40 of the air-fuel ratio detection device 1 shown in FIG.
Housed in.

Next, the function and effect of the air-fuel ratio detecting device 1 of this embodiment will be described. The thickness of the alumina flat plate-shaped support 20 in the detection unit 10 is 3.0 mm, and has a much higher insulation resistance than the conventional alumina insulating layer (reference numeral 96 in FIG. 3).

Therefore, the potential of the electrothermal heater 15 does not affect the potential of the atmosphere-side electrode 13 due to electrical leakage, and highly accurate measurement is possible. On the other hand, alumina has a remarkably large thermal conductivity as compared with zirconia, and therefore has a good heat transfer property to the electrothermal heater 15 or the solid electrolyte 11.

Further, the ventilation passage 21 of the flat plate-shaped support 20 is
Since it is a closed tunnel structure, there is no concern about airtightness. Therefore, the airtightness of the air introduction part should be ensured by the air chamber 22.
It is only necessary to reliably and reliably perform the surroundings of. On the other hand, alumina has much higher strength than zirconia, so even if pressure is applied, cracks and deformation do not cause clearance, etc., and it is easy to secure airtightness.

As described above, the strength of the entire detection unit 10 is greatly improved by the flat plate-shaped support 20. As described above, according to this example, it is possible to provide the air-fuel ratio detection device 1 that has the detection unit 10 that is excellent in mechanical strength and insulation strength and has high airtightness between the exhaust gas and the atmosphere.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a detection unit of an air-fuel ratio detection device according to a first embodiment.

FIG. 2 is a sectional view of an air-fuel ratio detection device according to an embodiment.

FIG. 3 is an exploded perspective view of a detection unit of a conventional air-fuel ratio detection device.

FIG. 4 is a perspective view of a detection unit of a conventional air-fuel ratio detection device.

[Explanation of symbols]

 10. ． ． Detection unit, 11. ． ． Solid electrolyte, 111. ． ． First surface, 112. ． ． Second surface, 12. ． ． Exhaust side electrode, 13. ． ． Atmosphere side electrode, 14. ． ． Protective film, 15. ． ． Electric heater, 16. ． ． Insulating sheet, 20. ． ． A plate-like support, 21. ． ． Air passage, 22. ． ． Atmosphere chamber,

Front page continued (72) Inventor Hiromi Sano 1-1, Showa-cho, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor Masatoshi 1-1-1-1, Showa-cho, Kariya city, Aichi prefecture, Nippon Denso Co., Ltd. (72) Inventor Hiroshi Furuhashi 1-1-1, Showa-cho, Kariya city, Aichi prefecture Nihon Denso Co., Ltd.

Claims (3)

[Claims] 1. An air-fuel ratio detection device for an internal combustion engine in which an exhaust-side electrode is provided on a first surface of a solid electrolyte which is an oxygen ion conductor, and an atmosphere-side electrode is provided on a second surface facing the solid electrolyte, thereby forming an electrochemical cell. The exhaust side electrode and the protective film are sequentially laminated on the first surface of the flat solid electrolyte, while the atmosphere side electrode and the alumina flat plate are under the second surface of the solid electrolyte. A support body, an electric heater, and an insulating sheet are sequentially laminated, and the flat support body has a vent passage communicating with the atmosphere, and the second support of the solid electrolyte communicates with the vent passage. An air-fuel ratio detection device for an internal combustion engine, characterized in that an air chamber that opens toward the surface is formed. 2. The air-fuel ratio detecting device for an internal combustion engine according to claim 1, wherein the plate-shaped support has a plate thickness of 1 to 5 mm. 3. The air-fuel ratio detection device for an internal combustion engine according to claim 1, wherein the flat plate-shaped support has an alumina content of 90% by weight or more.