JP3110848B2 - Air-fuel ratio detector - Google Patents

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 in which an oxygen pump cell and a sensing cell are formed via an insulating layer.

[0002]

2. Description of the Related Art Conventionally, an air-fuel ratio sensor comprising an oxygen sensor using an oxygen ion-conductive solid electrolyte has been known for measuring the air-fuel ratio of an internal combustion engine or the like. this is,
A configuration in which one of the solid electrolytes is brought into contact with a gas to be measured, the other is brought into contact with a reference gas having a known oxygen concentration, and the oxygen concentration is measured from a current generated according to oxygen ions passing through the solid electrolyte based on the difference in the oxygen concentration. It has become. As an improved type thereof, there is known an air-fuel ratio detecting device in which an oxygen pump cell having electrodes provided on both surfaces of a solid electrolyte plate made of, for example, zirconia and a sensing cell having a similar configuration are integrally formed.

In recent years, an air-fuel ratio detecting device having an oxygen pump cell and a sensing cell sufficiently insulated inside a sensor element has been developed in order to prevent leakage current and achieve stable measurement in the air-fuel ratio detecting device having the above configuration. This is known, for example, from JP-A-1-262458. FIG. 5 is a diagram showing an example of a longitudinal section of the above-described air-fuel ratio detection device. In FIG. 5, the oxygen pump cell 31 and the sensing cell 41 are integrally formed with an insulating layer 51 interposed therebetween, and a heating heater 52 is provided on the sensing cell 41 side.
Is also provided integrally.

The oxygen pump cell 31 has a gap 53
Solid electrolyte plate 33 having through hole 32 at a position corresponding to
And electrodes 34-1 and 34-2 provided around the through holes 32 on both surfaces of the solid electrolyte plate 33. Then, an oxygen pump current Ip composed of a direct current is supplied using the electrode 34-1 as a positive electrode and the electrode 34-2 as a negative electrode. Further, the sensing cell 41 includes the solid electrolyte plate 4
2 and a measurement electrode 43-1 provided facing the gap 53 of the solid electrolyte plate 42, and a reference electrode 43-2 provided facing the other surface, the space 54 to which the reference gas is supplied. Have been. Then, the voltage between the two electrodes is measured using the measurement electrode 43-1 as a negative electrode and the reference electrode 42-2 as a positive electrode.

[0005]

However, in the air-fuel ratio detecting device having the structure disclosed in Japanese Patent Application Laid-Open No. 1-262458, the oxygen pump cell 31 and the sensing cell 41 are completely insulated by the insulating layer 51. Therefore, the electrode 34-2 of the oxygen pump cell 31 facing the gap 53
And the measurement electrode 44-1 of the sensing cell 41 are likely to have a difference in oxygen concentration, and transmission delay is likely to occur. Therefore, during transient response, overshoot or hunting of the oxygen pump current Ip occurs, and stable measurement cannot be performed. At the same time, the solid electrolyte plate 32 in contact with the electrodes 34-1 and 34-2 of the oxygen pump cell 31 is easily oxidized and blackened, and there is a problem in durability.

On the other hand, the applicant of the present invention has disclosed Japanese Patent Laid-Open No. 3-167467.
In the publication, the oxygen pump cell and the sensing cell are related to an air-fuel ratio detection device in which the sensor cell is not insulated inside the sensor element. However, in order to improve output accuracy and stability over time, which are problematic, A technique for controlling the amount of current leak to a cell is disclosed. However, in the air-fuel ratio detection device of the type in which the oxygen pump cell and the sensing cell which are the objects of the present invention are insulated inside the sensor element, no leak current from the oxygen pump cell to the sensing cell is generated at all. There was a problem that technology could not be applied.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an air-fuel ratio detection device capable of obtaining high output accuracy and stability over time.

[0008]

An air-fuel ratio detecting device according to the present invention comprises an oxygen pump cell having electrodes provided on both surfaces of a solid electrolyte plate and a sensing cell integrated via an insulating layer. , Wherein the oxygen pump cell and the sensing cell are connected via an external circuit, and a part of the pump cell current of the oxygen pump cell flows to the sensing cell.

[0009]

In the above-described configuration, an external circuit for flowing a part ip of the pump cell current Ip of the oxygen pump cell to the sensing cell is provided, so that the current ip enables auxiliary pumping of the measurement electrode side of the sensing cell. Overshoot and hunting of the response waveform can be eliminated, and the change in the pump cell current Ip can be reduced. As a result, an air-fuel ratio detection device having high output accuracy and stability over time can be obtained.

[0010]

FIG. 1 is a diagram showing an example of a longitudinal section of an air-fuel ratio detecting device according to the present invention. In FIG. 1, the oxygen pump cell 1 and the sensing cell 11 are integrally formed with an insulating layer 21 interposed therebetween, and a heater 22 for heating is integrally provided on the sensing cell 11 side. The oxygen pump cell 1 includes a solid electrolyte plate 3 having a through hole 2 at a position corresponding to a gap 23 generated when assembled, and a hollow disk-shaped electrode provided around the through holes 2 on both surfaces of the solid electrolyte plate 3. 4
-1, 4-2. Then, the electrode 4-1 is used as a positive electrode and the electrode 4-2 is used as a negative electrode, and an oxygen pump current Ip of direct current is supplied between the electrodes 4-1 and 4-2. The sensing cell 11 includes a solid electrolyte plate 12 made of zirconia or the like and a hollow disk-shaped measurement electrode 13-1 provided facing a gap 23 of the solid electrolyte plate 12.
And a reference electrode 13-2 provided facing the space 24 to which the reference gas is supplied, which is the other surface of the solid electrolyte plate 12. The voltage between the two electrodes is measured using the measurement electrode 13-1 as a negative electrode and the reference electrode 13-2 as a positive electrode.

The above-described configuration is no different from the conventional air-fuel ratio detecting device. What is important in the present invention is that the electrode 4-1 provided outside the solid electrolyte plate 3 constituting the oxygen pump cell 1 and the sensing cell 11 The point is that the solid electrolyte plate 12 is connected via an external circuit 25 to a reference electrode 13-2 provided on the side facing the space 24 of the solid electrolyte plate 12. With such a configuration, a part of the pump cell current Ip can flow to the sensing cell 11 side as the current ip via the external circuit 25, and the auxiliary pumping can be performed by the measurement electrode 13-1. The current ip passing through the external circuit 25 is preferably about 0.1 to 1% of the pump cell current Ip. This is because if ip is less than 0.1% of Ip, there is a case where there is no point in leaking current, and if it exceeds 1%, there is a problem that Ip changes with time.

FIG. 2 is a diagram showing a configuration of an example of the external circuit 25 used in the present invention. As shown in FIG. 2, a differential amplifier 2 is provided between the oxygen pump cell 1 and the sensing cell 11.
6. By connecting the diodes 27-1, 27-2 and the resistor 28, the current ip shown in FIG. 1 is configured not to flow backward. That is, in lean gas,
The current ip flows in the direction of the arrow as shown in FIG.
In the rich gas, the current ip flows in the opposite direction and consumes the reference gas of the sensing cell 11, so that it is configured to prevent this.

In order to examine the effect of the present invention, hunting and overshoot of the response waveform when the leak current ip is changed by using the air-fuel ratio detection device having the external circuit shown in FIG. 2 and having the structure shown in FIG. And the results are schematically shown in FIG. In FIG. 3, it can be seen that the sensor 1 in which the hunting of the waveform is examined has the leak current ip of 0, that is, the hunting generated in the conventional example is eliminated by flowing the ip. Similarly, it can be seen from the sensor 2 that the waveform overshoot is examined that the leak current ip is 0, that is, the overshoot generated in the conventional example is gradually eliminated by flowing the ip. Further, FIG.
Is the pump cell current I when the leak current ip is changed
The relationship between the change rate of p and the elapsed time is shown. 3 and 4
From the result, it is found that the leak current ip is 5 times the pump cell current Ip.
%, The change with time of Ip becomes large, so that it is preferable to be 1% or less as described above.

[0014]

As is apparent from the above description, according to the present invention, in an air-fuel ratio detecting device in which an oxygen pump cell and a sensing cell are integrated via an insulating layer, an external circuit is provided to provide a pump cell of the oxygen pump cell. Part i of current Ip
By flowing p to the sensing cell, overshoot and hunting of the response waveform can be eliminated, and the change in the pump cell current Ip can be reduced, resulting in air-fuel ratio detection having high output accuracy and stability over time. A device can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a longitudinal section of an air-fuel ratio detection device of the present invention.

FIG. 2 is a diagram showing a configuration of an example of an external circuit used in the air-fuel ratio detection device of the present invention.

FIG. 3 is a diagram illustrating the effect of reducing hunting and overshoot of a response waveform.

FIG. 4 is a graph showing a relationship between a change rate of a pump cell current and an elapsed time.

FIG. 5 is a diagram showing an example of a longitudinal section of a conventional air-fuel ratio detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxygen pump cell 3 Solid electrolyte board 4-1 and 4-2 electrode 11 Sensing cell 12 Solid electrolyte 13-1 Measurement electrode 13-2 Reference electrode 21 Insulating layer 25 External circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/419

Claims (2)

(57) [Claims] 1. An air-fuel ratio detection device in which an oxygen pump cell having electrodes provided on both sides of a solid electrolyte plate and a sensing cell are integrated via an insulating layer, wherein the oxygen pump cell and the sensing cell are connected to an external circuit. Connect through and
An air-fuel ratio detecting device, wherein a part of a pump cell current of the oxygen pump cell is caused to flow to the sensing cell. 2. The air-fuel ratio detecting device according to claim 1, wherein a part of the pump cell current is 0.1 to 1% of the pump cell current.