JPH06229976A - Air fuel ratio detector - Google Patents

Abstract

PURPOSE:To provide an air fuel ratio detector of an internal combustion engine which is shorter in the rising time after the closing of a power source with a better heating efficiency of an electric heater. CONSTITUTION:This air fuel ratio detector has an exhaust side electrode 13 on one surface of a solid electrolyte 11 and an atmosphere side electrode 12 on the other surface thereof. An atmospheric air chamber 32 is arranged communicating with an atmospheric air duct 28 at a position facing the atmosphere side electrode 12 and an electric heater 20 contacting the atmosphere side electrode 12 between the atmospheric air chamber 32 and the atmosphere side electrode 12 through an insulation sheet 30. The insulation sheet 30 and an insulation plate 35 of the electric heater 20 have air holes 31 made avoiding the electric heater 20.

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 a vehicle internal combustion engine, and more particularly to a structure of an electric heater having excellent thermal efficiency and responsiveness.

[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 is introduced 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 electrodes. Further, in the case of detecting the air-fuel ratio in a wide range, a method is used 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.

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 using an electric heater. For example, as shown in FIGS. 10 and 11, the detection unit (cell unit) 90 of the air-fuel ratio detection device is provided with electrodes 91 and 92 on the upper and lower surfaces 111 and 112 of the solid electrolyte 11 and introduces exhaust gas into the upper surface 111. The atmosphere 51 is introduced into the lower surface 112 through the duct 93.

Then, as shown in FIG.
An electric heater 951 embedded in the insulating member 94 is disposed on the lower surface of the (type A). Alternatively, as shown in FIG. 11, an electrothermal heater 952 is provided between the solid electrolyte 11 and the duct 93 and on the side of the electrode 92 (type B). The electric heater 952 is also embedded in the insulating member 94.

The detecting portion (cell portion) 90 of the air-fuel ratio detecting device shown in FIGS. 10 and 11 is housed in a cover made of stainless steel or the like (see FIG. 3) and mounted in the exhaust passage of the engine. In an air-fuel ratio detecting device for a vehicle, it is necessary to operate the air-fuel ratio detecting device as soon as possible immediately after the engine is started.
1,952 needs to heat the said detection part 90 within a short time.

[0007]

However, the above conventional air-fuel ratio detecting device has the following problems. That is, in the conventional air-fuel ratio detection device, the electric heater 951 heats the reaction part (electrode part) through the duct 93 (see FIG. 10).
The type A) and the electric heater 952 heat the reaction part from the side of the reaction part (electrode part) (FIG. 11 type B).

Therefore, there are problems that heat loss increases, heating efficiency is poor, and power consumption is high. In addition, the response characteristic of the temperature rise is relatively poor compared to the power consumption, and the start-up of the air-fuel ratio detection device after the power is turned on is delayed. The present invention is
In view of such conventional problems, it is an object of the present invention to provide an air-fuel ratio detection device for an internal combustion engine, which has good heating efficiency of the electric heater and has a short rise time after power-on.

[0009]

According to the present invention, an empty space of an internal combustion engine in which an electrochemical cell is formed by providing an exhaust side electrode on one surface of a solid electrolyte which is an oxygen ion conductor and an atmosphere side electrode on the other surface opposite thereto. In the fuel ratio detection device, an atmosphere chamber communicating with an atmosphere duct is arranged at a position facing the atmosphere side electrode, and an atmosphere side is interposed between the atmosphere chamber and the atmosphere side electrode via an insulating sheet. An air-fuel ratio detecting device for an internal combustion engine is provided, in which an electrothermal heater is provided in contact with the electrodes, and the insulating sheet has a vent hole formed while avoiding the electrothermal heater.

What is most noticeable in the present invention is that the atmosphere side electrode is provided with an electric heater via an insulating sheet, and the insulating sheet has a ventilation hole formed by avoiding the electric heater. It is configured as follows. An atmosphere chamber communicating with the atmosphere duct is arranged at a position facing the atmosphere side electrode, and the electrothermal heater is arranged between the atmosphere side electrode and the atmosphere chamber.

[0011]

In the air-fuel ratio detection device of the present invention,
The electric heater is in contact with the atmosphere-side electrode through the insulating sheet and heats the atmosphere-side electrode, which is the reaction part, from close up. Therefore, the electric heater directly heats the atmosphere-side electrode without heating extra parts such as the side of the atmosphere-side electrode (FIG. 11) and the duct (FIG. 10, reference numeral 93) unlike the conventional device. Therefore, the heating efficiency is high.

Further, since an insulating sheet is interposed between the electric heater and the atmosphere side electrode, electrical insulation between them is also secured. Then, since an extremely thin insulating sheet is sufficient for ensuring insulation between the two, the atmosphere-side electrode is immediately heated. Therefore, the cell can be operated and the air-fuel ratio detection device can be activated in a very short time.
That is, it is possible to obtain an air-fuel ratio detection device with good thermal efficiency and start response.

Since the insulating sheet is provided with a ventilation hole, the atmosphere can be introduced into the atmosphere side electrode through the ventilation hole. As described above, according to the present invention, it is possible to provide an air-fuel ratio detection device for an internal combustion engine in which the heating efficiency of the electric heater is good and the rise time after power-on is short.

[0014]

【Example】

Embodiment 1 An air-fuel ratio detection device according to an embodiment of the present invention will be described with reference to FIGS. In this example, as shown in FIG. 1, an upper surface 1 which is one surface of a solid electrolyte 11 which is an oxygen ion conductor.
An air-fuel ratio detection device 1 for an internal combustion engine for a vehicle in which an exhaust side electrode 13 is provided at 11 and an atmosphere side electrode 12 is provided at a lower surface 112 which is the other surface opposite to the exhaust side electrode 13 to form a detection unit 10 which is an electrochemical cell (Fig. 3).

The atmosphere-side electrode 12 of the detection unit 10
An atmosphere chamber 32 communicating with the atmosphere duct 38 is disposed at a position facing the atmosphere side electrode 32, and the atmosphere side electrode 1 is interposed between the atmosphere chamber 32 and the atmosphere side electrode 12 via an electrically insulating sheet 30.
2 is provided with an electric heater 20 in contact with the insulating sheet 3
0 is a ventilation hole 31 formed by avoiding the electric heater 20.
have.

Each of these will be described in detail below. In this example,
As shown in FIG. 3, the detecting 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. 3, the exhaust cover 44 has an inner cover 441 and an outer cover 442 made of stainless steel, and both covers 441, 442 have exhaust ports 443, 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 atmosphere duct 38 of the detecting section 10 which will be described later. A water-repellent filter 46 for waterproofing is provided between the atmosphere ports 453 and 454.
Has been inserted. Then, the detection unit 10 includes the insulating member 4
It is sandwiched by 21 and housed in the body 42. The lead wire 41 connected to the detection unit 10 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.

The detection unit 10 of the air-fuel ratio detection device 1 of this example is
As shown in FIG. 1, a platinum exhaust side electrode 13 is provided on the upper surface 111 of a zirconia sheet which is a solid electrolyte 11, and a lower surface 11 is provided.
2 is provided with a platinum atmosphere-side electrode 12. An air duct 38 made of zirconia or mullite having a low thermal conductivity is arranged below the solid electrolyte 11, and an air chamber 32 is formed. In addition, solid electrolyte 1
An electric heater 20 sandwiched between an insulating sheet 30 and an insulating plate 35 is attached to the lower surface 112 of No. 1.

The insulating plate 35 has a thickness of 20 μm as shown in FIG.
A ceramic sheet of alumina or the like having the above thickness, and an electrothermal heater 20 having a white metal metal paste printed thereon is formed on the upper surface thereof. Then, an insulating sheet 30 made of ceramic such as alumina having a thickness of 20 μm or more is attached to the upper surface of the electric heater 20.

A large number of vent holes 31 are formed through the insulating plate 35 and the insulating sheet 30 while avoiding the electric heater 20. The ventilation hole 31 is a cylindrical ventilation hole having an outer diameter of 100 μm or more so that the detection gas is molecular diffusion controlled, and the atmosphere 51 (FIG. 1) in the atmosphere chamber 32 is in contact with the atmosphere-side electrode 12.

As shown in FIG. 2, the atmosphere-side electrode 12 and the exhaust-side electrode 13 are composed of wide reaction portions 121 and 131, and an elongated linear portion 122 connected to the signal line of the lead wire 41.
And 132. The electric heater 20 has a wide lead portion 2 connected to the heater wire of the lead wire 41.
01 and a thin line-shaped heat generating portion 202.

The reaction section 121 of the atmosphere-side electrode 12 is
Area S ₁ of the electric heater 20 and the area S ₂ of the heat generating portion 202 of the electric heater 20.
And 0.1S ₁ ≤S ₂ ≤0.5S ₁ . That is, the area S ₂ of the heat generating portion 202 is between 10% and 50% of the area S ₁ of the reaction portion 121 of the atmosphere-side electrode 121.

The reason is that the area S ₂ of the heat generating portion 202 must be 50% or less of the area S ₁ of the reaction portion 121 in order to obtain the necessary electric resistance by forming the ventilation hole 31.
This is because it becomes difficult to form the heat generating portion 202 on the surface 5.

On the other hand, if the area S ₂ of the heat generating portion 202 is too small, the temperature distribution becomes non-uniform, and the heat lost by the insulating sheet 30 and the insulating plate 35, which are insulating members, becomes large and the electric heater 20 The heating efficiency of the atmosphere-side electrode 12 is reduced. Therefore, the area S ₂ is equal to the atmosphere side electrode 12
10% or more of the area S ₁ of the reaction section 121 is required.

The width of the projection of the heat generating portion 202 on the solid electrolyte 11 is smaller than the width of the reaction portion 121. This is because it is possible to reduce the heating loss caused by heating the part other than the reaction part 121.

The sum S ₃ of the contact areas of the vent holes 31 with the atmosphere-side electrode 12 is determined by the reaction portion 12 of the atmosphere-side electrode 12 described above.
20% or more and 50% or less with respect to the area S _{1 of 1} (0.2S ₁ ≦ S ₃ ≦ 0.5S ₁ ). The reason is as follows. First, the sum of the area S ₂ of the heat generating portion 202 of the electric heater 20 and the area S ₃ of the ventilation hole 31 (S
₂ + S ₃ ) is useless if these do not overlap with the reaction part of the atmosphere-side electrode 12, so the reaction part area is S ₁ or less (S ₂ + S ₃ ≦ S ₁ ). On the other hand, as described above, since the heating portion area S ₂ is 50% of the reaction portion area S ₁ at maximum,
Based on this time, the vent hole area S ₃ is the reaction area area S
₁ is 50% or less _{(S 3 ≦ 1 / 2S 1} ).

If the area S ₃ of the vent hole 31 becomes too small, the area in contact with the atmosphere, that is, the reaction area of the cell, becomes small, and the current capacity of the cell is lowered, resulting in a detection error when a detection signal is taken out from the cell. growing. Therefore,
The vent hole area S ₃ needs to be 20% or more of the reaction area area S ₁ (S ₃ ≧ 1 / 5S ₁ ).

Various shapes can be considered as the shapes of the heat generating portion 202 and the vent hole 31 of the electric heater 20. For example, as shown in FIG. 4, the heat generating portion 202 is formed in a zigzag shape in the front-rear direction, and the ventilation hole 31 has a uniform circular cross-sectional shape. Further, as shown in FIG. 5, the ventilation hole 31 may have an oval cross section.

Further, as shown in FIG. 6, the heat generating portion 202 may be formed so as to meander in the left and right directions, and the cross-sectional shape of the ventilation hole 31 may be circular with different sizes. Further, as shown in FIG. 7, the cross-sectional shape of the ventilation hole 31 may be square. Moreover, the cross-sectional shape of the vent hole 31 may be a triangle or a polygon having five or more pentagons.

Next, a method of manufacturing the detection unit 10 of this example will be described. First, the insulating plate 35 made of alumina green sheet
A paste containing platinum as a main component is applied to the top by a method such as screen printing and dried to form the electric heater 20.

Next, the insulating sheet 30 made of an alumina green sheet is bonded and integrated on the surface of the insulating plate 35 on which the electric heater 20 is formed. Subsequently, a ventilation hole 31 penetrating the integrated insulating sheet 30 and insulating plate 35 is formed using a punching machine to complete a heater unit.

On the other hand, the air duct 38 is formed by injection molding, press molding, or the like using zirconia or mullite as a main component. In addition, the zirconia-based solid electrolyte 11
A paste containing platinum as a main component is applied to both surfaces of the green sheet by a method such as screen printing and dried to form the atmosphere side electrode 12 and the exhaust side electrode 13 to complete the cell unit.

Next, the heater unit is attached to the upper end of the air duct 38 using a binder. Further, the cell unit is laminated thereon with a binder, and the whole is co-fired.

Then, a platinum wire is embedded and connected to the linear parts 122 and 132 of the atmosphere side electrode 12 and the exhaust side electrode 13 and the lead part 201 of the electric heater 20 to form a connection part to the lead wire 41. . Alternatively, the linear portion 12
2, 132 and the lead portion 201 are extended to form the lead wire 4
There is also a method of forming a connection part with 1.

Next, the function and effect of the air-fuel ratio detection device 1 of this example will be described. In the air-fuel ratio detection device 1 of this example,
The electric heater 20 in the detection unit 10 is in contact with the atmosphere-side electrode 12 via the insulating sheet 30. Further, the insulating sheet 30 is extremely thin, and the electrothermal heater 20 is connected to the atmosphere side electrode 12
Since it is heated from near, heat is not taken away by the excess and the heating efficiency is good.

Further, since the atmosphere-side electrode 12 is directly heated through the thin insulating sheet 30, the temperature of the atmosphere-side electrode 12 portion can be raised within an extremely short time. FIG. 8 shows an example of the conventional apparatus of type A (FIG. 10) and type B (FIG. 1).
It shows the heating efficiency of the electric heater in comparison with 1). As is known from FIG. 8, the heating efficiency of this example was increased to 2-3 times that of the conventional device.

Further, as shown in FIG. 9, the temperature rising characteristics of the air-fuel ratio detecting device of this example are as shown in FIG.
And the heating time is 1/3 to 1 as compared with the type B (FIG. 11).
It was shortened to / 5. As described above, according to this example, it is possible to provide the air-fuel ratio detection device for an internal combustion engine, which has good heating efficiency of the electric heater and has a short rise time after power-on.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a detection unit of an air-fuel ratio detection device according to an embodiment.

FIG. 2 is an exploded perspective view of the detection unit shown in FIG.

FIG. 3 is a cross-sectional view of the air-fuel ratio detection device according to the embodiment.

FIG. 4 is an explanatory view showing an example of the shape and arrangement of an electric heater and a vent hole according to the embodiment.

FIG. 5 is another explanatory view showing the shapes and arrangement examples of the electric heater and the ventilation holes according to the embodiment.

FIG. 6 is another explanatory view showing the shapes and arrangement examples of the electric heater and the ventilation holes according to the embodiment.

FIG. 7 is another explanatory view showing the shapes and arrangement examples of the electric heater and the ventilation holes according to the embodiment.

FIG. 8 is a thermal efficiency comparison diagram of the electric heaters of the air-fuel ratio detection devices of the example and the conventional example.

FIG. 9 is a comparison diagram of temperature rising characteristics of the air-fuel ratio detection devices of the example and the conventional example.

FIG. 10 is a sectional view of a detection portion of an air-fuel ratio detection device (type A) of a conventional example.

FIG. 11 is a sectional view of a detection portion of another conventional air-fuel ratio detection device (type B).

[Explanation of symbols]

 1. ． ． Air-fuel ratio detection device, 10. ． ． Detection unit, 11. ． ． Solid electrolyte, 12. ． ． Atmosphere side electrode, 13. ． ． Exhaust side electrode, 20. ． ． Electric heater, 30. ． ． Insulating sheet, 31. ． ． Ventilation holes, 32. ． ． Atmosphere chamber, 38. ． ． Atmosphere duct, 41. ． ． Lead,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi 1-1 1-1 Showa-cho, Kariya city, Aichi prefecture Nihon Denso Co., Ltd.

Claims (1)

[Claims] 1. An air-fuel ratio detecting device for an internal combustion engine, wherein an exhaust side electrode is provided on one surface of a solid electrolyte which is an oxygen ion conductor, and an atmosphere side electrode is provided on the other surface facing the solid electrolyte, thereby forming an electrochemical cell. And an atmosphere chamber communicating with the atmosphere duct is disposed at a position facing the atmosphere side electrode, and an electric heater that is in contact with the atmosphere side electrode via an insulating sheet is provided between the atmosphere chamber and the atmosphere side electrode. And an air-fuel ratio detecting device for an internal combustion engine, wherein the insulating sheet has a vent hole formed by avoiding an electric heater.