JPH05256817A - Air-fuel ratio detecting device - Google Patents

Abstract

PURPOSE:To obtain an air-fuel ratio detecting device having high output accuracy and aging stability. CONSTITUTION:In the air-fuel ratio detecting device which is constituted by integrating an oxygen pump cell 1 and sensing cell 11 respectively provided with electrodes 4-1 and 4-2 and 13-1 and 13-s on both surfaces of solid electrolytic plates 3 and 12 with an insulating layer 21 in between, the cells l and 11 are connected to each other through an external circuit 25. Then the detecting device is constituted so that part of the pump cell current Ip of the cell 1 can be made to flow to the cell 11.

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 with an insulating layer in between.

[0002]

2. Description of the Related Art Conventionally, an air-fuel ratio sensor including an oxygen sensor using a solid electrolyte having oxygen ion conductivity is 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 the gas to be measured, the other is brought into contact with a reference gas whose oxygen concentration is known, and the oxygen concentration is measured from a current generated according to oxygen ions passing through the solid electrolyte based on the difference in oxygen concentration. Has become. As an improved type, there is known an air-fuel ratio detection device in which an oxygen pump cell having electrodes on both sides of a solid electrolyte plate made of zirconia or the like and a sensing cell having the same structure are integrally formed.

Furthermore, in recent years, there has been developed an air-fuel ratio detecting device in which the oxygen pump cell and the sensing cell are sufficiently insulated inside the sensor element so that a leak current can be prevented and stable measurement can be achieved in the air-fuel ratio detecting device having the above-mentioned structure. For example, it is known from Japanese Patent Laid-Open No. 1-262458. FIG. 5 is a diagram showing an example of a vertical cross 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 via an insulating layer 51, and a heater 52 for heating is further provided on the sensing cell 41 side.
Is also integrated.

The oxygen pump cell 31 has a gap 53.
Solid electrolyte plate 33 having through holes 32 at positions 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, the electrode 34-1 is used as a positive electrode and the electrode 34-2 is used as a negative electrode, and an oxygen pump current Ip of direct current is supplied. In addition, the sensing cell 41 includes the solid electrolyte plate 4
2 and the measurement electrode 43-1 provided facing the gap 53 of the solid electrolyte plate 42, and the reference electrode 43-2 provided on the other surface facing the space 54 to which the reference gas is supplied. Has been done. The measurement electrode 43-1 is used as the negative electrode and the reference electrode 43-2 is used as the positive electrode, and the voltage between both electrodes is measured.

[0005]

However, in the air-fuel ratio detecting device having the structure disclosed in JP-A-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 a measurement electrode 44-1 of the sensing cell 41 easily generate an oxygen concentration difference and a transmission delay easily occurs. Therefore, during the 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 terms of durability.

[0006] On the other hand, the applicant of the present invention is disclosed in Japanese Patent Application Laid-Open No. 3-167467.
In the publication, although the oxygen pump cell and the sensing cell are technologies related to an air-fuel ratio detection device of a type in which the sensor element is not insulated inside the sensor element, in order to improve the problematic output accuracy and stability over time, sensing is performed from the oxygen pump cell. A technique for controlling the amount of current leakage to the cell is disclosed. However, in the air-fuel ratio detection device of the type in which the oxygen pump cell and the sensing cell targeted by the present invention are insulated inside the sensor element, since the leak current from the oxygen pump cell to the sensing cell does not occur at all, this is kept as it is. There was a problem that the technology could not be applied.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide an air-fuel ratio detecting device that can obtain high output accuracy and stability over time.

[0008]

SUMMARY OF THE INVENTION An air-fuel ratio detecting device of the present invention is an air-fuel ratio detecting device in which an oxygen pump cell having electrodes on both sides of a solid electrolyte plate and a sensing cell are integrated via an insulating layer. In the third aspect, 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 is made to flow to the sensing cell.

[0009]

In the above-described structure, since the external circuit for flowing a part ip of the pump cell current Ip of the oxygen pump cell to the sensing cell is provided, it becomes possible to auxiliary pump the measuring electrode side of the sensing cell by this current ip. It is possible to eliminate the overshoot and hunting of the response waveform, reduce the change in the pump cell current Ip, and as a result, it is possible to obtain an air-fuel ratio detection device having high output accuracy and stability over time.

[0010]

FIG. 1 is a diagram showing an example of a vertical cross section of an air-fuel ratio detecting device of the present invention. In FIG. 1, the oxygen pump cell 1 and the sensing cell 11 are integrally configured via an insulating layer 21, and a heater 22 for heating is also 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 hollow disk-shaped electrodes provided around the through hole 2 on both surfaces of the solid electrolyte plate 3. Four
-1 and 4-2. Then, with the electrode 4-1 as a positive electrode and the electrode 4-2 as a negative electrode, an oxygen pump current Ip composed of direct current is supplied between the electrodes 4-1 and 4-2. Further, the sensing cell 11 includes a solid electrolyte plate 12 made of zirconia and a hollow disk-shaped measuring 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, which is the other surface of the solid electrolyte plate 12, into which the reference gas is supplied. Then, the measurement electrode 13-1 is used as a negative electrode and the reference electrode 13-2 is used as a positive electrode, and the voltage between both electrodes is measured.

The above-described structure is no different from the conventional air-fuel ratio detecting device. What is important in the present invention is the electrode 4-1 provided outside the solid electrolyte plate 3 constituting the oxygen pump cell 1 and the sensing cell 11. This is the point where the solid electrolyte plate 12 and the reference electrode 13-2 provided on the side facing the space 24 are connected via an external circuit 25. With this configuration, a part of the pump cell current Ip can be made to flow to the sensing cell 11 side as the current ip via the external circuit 25, and the measurement electrode 13-1 can perform auxiliary pumping. 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, it may be meaningless to leak current, and if it exceeds 1%, there is a problem that the change over time of Ip becomes large.

FIG. 2 is a diagram showing the 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, the diodes 27-1, 27-2 and the resistor 28 are connected so that the current ip shown in FIG. 1 does not flow backward. That is, normally in lean gas
As shown in, the current ip flows in the direction of the arrow,
In the rich gas, the current ip flows in the opposite direction, and the reference gas of the sensing cell 11 is consumed, so this is prevented.

In order to investigate the effect of the present invention, the hunting and overshoot of the response waveform when the leak current ip is changed by using the air-fuel ratio detecting device having the structure shown in FIG. 1 having the external circuit shown in FIG. Was examined and the results are shown schematically in FIG. In FIG. 3, it can be seen that in the sensor 1 in which the hunting of the waveform is examined, the leak current ip is 0, that is, the hunting that occurs in the conventional example is eliminated by flowing ip. Also, in the sensor 2 in which the overshoot of the waveform is examined, similarly, it can be seen that the leak current ip is 0, that is, the overshoot occurring in the conventional example is gradually eliminated by flowing ip. Furthermore, FIG.
Is the pump cell current I when the leak current ip is changed.
The relationship between the rate of change of p and the elapsed time is shown. 3 and 4
As a result, the leak current ip is 5 of the pump cell current Ip.
%, The change with time of Ip becomes large, so that it is preferable that it is 1% or less as described above.

[0014]

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

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a vertical cross 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 for explaining an effect of reducing hunting and overshoot of a response waveform.

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

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

[Explanation of symbols]

 1 Oxygen Pump Cell 3 Solid Electrolyte Plate 4-1 4-2 Electrode 11 Sensing Cell 12 Solid Electrolyte 13-1 Measuring Electrode 13-2 Reference Electrode 21 Insulating Layer 25 External Circuit

Claims (2)

[Claims] 1. An air-fuel ratio detecting device in which an oxygen pump cell having electrodes on both sides of a solid electrolyte plate and a sensing cell are integrated through an insulating layer, wherein the oxygen pump cell and the sensing cell are connected to an external circuit. Connect through
An air-fuel ratio detection device, wherein a part of the pump cell current of the oxygen pump cell is made 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.