JP3113373B2 - Reference oxygen supply method for air-fuel ratio sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference oxygen supply method for an air-fuel ratio sensor comprising an oxygen pump and an oxygen concentration cell.

[0002]

2. Description of the Related Art Conventionally, in order to control the combustion state of an engine or the like, it is necessary to measure the air-fuel ratio of a mixture of gasoline or the like and air. For this purpose, an air-fuel ratio sensor has been used. As an example of this air-fuel ratio sensor, an element is conventionally prepared in which a pair of electrodes are provided on both surfaces of a plate-shaped body made of a solid electrolyte such as zirconia, and this element is stacked with a gap therebetween, and one element is set as a reference. An oxygen pump for supplying oxygen, and the other element is configured as an oxygen concentration cell,
For example, it is known from JP-A-59-178354.

In these conventional air-fuel ratio sensors, there are a case where the oxygen concentration is obtained from the output of the oxygen pump based on the oxygen concentration cell side and a case where the oxygen concentration is obtained from the output of the oxygen concentration cell based on the oxygen pump side. . In the case where the oxygen concentration cell side is used as a reference, the reference oxygen generation current supplied between the electrodes provided on both surfaces of the element forming the conventional oxygen concentration cell is, for example, about 30 μA, and a constant current value from the time of startup is constant. For example, 100%
It had to meet the standard reference air O _2. This is because the accuracy until the output at the time of rising immediately after turning on the power became constant did not matter so much.
On the other hand, if the value is about 30 μA, the level is such that the solid electrolyte forming the element is not destroyed even if the supply to the element is continued for a long time.

[0004]

However, in the above-described conventional reference oxygen supply method, the current of about 30 μA is constant from the start-up time, so that a stabilization time of the reference oxygen concentration is required for about 30 seconds. And the pump cell current value I _p at the stoichiometric point of the air-fuel ratio λ = 1 becomes approximately −20 to 30 in the steady state.
There was a problem that the value shifted to the negative side of μA and did not approach the desirable value of I _p = 0.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a reference oxygen supply method for an air-fuel ratio sensor that can obtain a highly accurate measurement value from the time of startup when power is turned on.

[0006]

A reference oxygen supply method for an air-fuel ratio sensor according to the present invention is a reference oxygen supply method for an air-fuel ratio sensor comprising an oxygen pump and an oxygen concentration cell. In the first stage immediately after the rise, the reference oxygen is quickly generated as a large current value, and thereafter, the required minimum current value is set to a small current value.A more preferable example is a temperature of the air-fuel ratio sensor. 650 ° C. or higher, and then performing the above step.

[0007]

In the above-described configuration, the reference oxygen generation current supplied to the oxygen concentration cell is set to be larger than the conventional current at the time of startup immediately after the power is turned on. Since the current is smaller, the load on the element can be reduced after stabilization, and a longer life can be achieved. Further, when the element is at a low temperature and a current larger than the conventional reference oxygen generation current is supplied as in the present invention, the element may be broken or blackened.
It is preferable to carry out the above process by turning on the power while heating to a temperature of about 0 ° C.

[0008]

FIG. 1 is a sectional view showing the structure of an example of an air-fuel ratio sensor for implementing a reference oxygen supply method according to the present invention. FIG.
In the example shown in FIG. 1, the air-fuel ratio sensor 1 is connected to the oxygen concentration cell 2, the oxygen pump 3 and the protection cover 4, the gap 5 is provided between the protection cover 4 and the oxygen concentration cell 2, and the oxygen concentration cell 2 and the oxygen pump 3 are connected to each other. A gap 6 is provided by the gas diffusion layer 8 between
It is configured by being integrally laminated. The oxygen concentration cell 2 is a plate-shaped sensing cell 1 made of a solid electrolyte such as zirconia.
1 is provided with a pair of electrodes 12-1 and 12-2 on both surfaces. The oxygen pump 3 has a pair of electrodes 22 on both surfaces of a plate-like pumping cell 21 also made of a solid electrolyte.
-1, 22-2. In this embodiment, the heater 7 is provided outside the oxygen pump 3 so that the air-fuel ratio sensor 1 can be heated to a temperature of, for example, about 650 ° C. However, the heater 7 may not be provided in some cases. .

In the air-fuel ratio sensor 1 having the structure shown in FIG. 1, an electrode is connected between the electrodes 12-1 and 12-2 as shown, and a predetermined reference oxygen generation current is applied to the electrodes 12-1 and 12-2.
To generate the reference air composed of 100% O ₂ in the gap 5, while the oxygen in the gas to be measured supplied into the gap 6 and the oxygen in the reference air in the gap 5 are generated. Is about to be balanced, the pumping current _Ip flowing through the pumping cell 21 is measured to determine the oxygen concentration. This operation is no different from the conventional air-fuel ratio sensor.

What is important in the present invention is that in the air-fuel ratio sensor shown in FIG. 1, the reference oxygen generation current is initially set to a current of more than 30 μA, preferably 40 to 60 μA, for a predetermined short period of time at the first time. After the elapse of a short time, the point is to switch to 5 to 15 μA, preferably 10 to 15 μA, which is smaller than the conventional 30 μA. An example of a circuit for that purpose is shown in FIGS. In the circuit shown in FIG. 2A, the sensing cell 11, the power supply 13, and the resistors 14-1 and 14-2 connected in parallel have the large resistance value R of the resistor 14-1 and the resistance of the resistor 14-2. Switch 1 with small value
5 and the switch 15 is switched to set the reference oxygen generation current _Icp to a large value at the beginning of rising, and thereafter to the small reference oxygen generation current _Icp .
Further, in the circuit shown in FIG.
The power supply 13, the capacitor 16, and the resistors 14-1 and 14-2 connected in parallel are connected via the switch 15, and when the switch 15 is turned on, as shown in FIG. Initially, it is large _Icp and then gradually smaller _Icp .

The air-fuel ratio sensor 1 having the structure shown in FIG.
FIG. 4 shows the relationship between the reference oxygen generation current _Icp and the reference oxygen stabilization time, that is, the time until the gap 5 is filled with 100% O ₂ , when the measured gas is air and I _P = 5 mA is output. It is shown in FIG. From FIG. 4, it is found that the reference oxygen generation current _Icp is stabilized in about 10 seconds at 50 μA,
From this figure, the switching timing of _Icp can be determined. Further, FIG. 5 the relationship between the reference oxygen generating current I _cp and the reference oxygen by generating electromotive force in the rich gas as an example
Shown in From Figure 5 it was found that the obtained occurrence electromotive force unchanged as in the more I _cp Lowest 5μA about reference oxygen generating current I _cp, I _cp of after switching is sufficient larger than 5μA I understand. FIG. 6 shows the relationship between the reference oxygen generation current _Icp and the pump current _{Ip at} the stoichiometric point where λ = 1 in the same sensor. From FIG. 6, when the reference oxygen current is 5 μA, I _{p at the} stoichiometric point
Is about −3 μA, that is, the O ₂ output = −0.01%, and it can be seen that there is no practical problem even without performing the zero point adjustment.

Further, in the generation current switching step of the present invention, when the temperature of the air-fuel ratio sensor 1 is low and a current larger than the conventional reference oxygen generation current is supplied, the air-fuel ratio sensor 1 is broken or blackened. May occur. Therefore, when the power is turned on and the above-described process is performed while the air-fuel ratio sensor 1 is heated to a certain high temperature, that is, a temperature of about 650 ° C. by the heater 7, destruction and blackening of the air-fuel ratio sensor 1 can be prevented. preferable.

[0013]

As is clear from the above description, according to the present invention, the reference oxygen generation current supplied to the oxygen concentration cell is set to be larger than the conventional current at the rise immediately after the power is turned on. Since the reference oxygen can be generated quickly and the current is reduced to a necessary minimum current after that, the load on the element can be reduced after stabilization, and a longer life can be achieved. It is preferable that the power supply be turned on while the element is heated to a certain high temperature, that is, a temperature of about 650 ° C., and the above steps be performed, because destruction and blackening of the element can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of an example of an air-fuel ratio sensor for implementing a reference oxygen supply method of the present invention.

FIG. 2A is a diagram showing an example of a circuit for implementing the reference oxygen supply method of the present invention, and FIG. 2B is a graph for explaining the operation.

3A is a diagram showing another example of a circuit for implementing the reference oxygen supply method of the present invention, and FIG. 3B is a graph for explaining the operation.

FIG. 4 is a graph showing a relationship between a reference oxygen generation current and a reference oxygen stabilization time.

FIG. 5 is a graph showing a relationship between a reference oxygen generation current in a rich gas and an electromotive force generated by the reference oxygen.

FIG. 6 is a graph showing a relationship between a reference oxygen generation current and a pump current at a stoichiometric point.

[Explanation of symbols]

 1 air-fuel ratio sensor 11 oxygen concentration cell 21 oxygen pump

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/419 G01N 27/409

Claims (3)

(57) [Claims] 1. A reference oxygen supply method for an air-fuel ratio sensor comprising an oxygen pump and an oxygen concentration cell, wherein the reference oxygen generation current supplied to the oxygen concentration cell is set to a large current value in the first stage immediately after the start-up. A reference oxygen supply method for an air-fuel ratio sensor, wherein the reference current is generated early, and then the current value is reduced to a minimum necessary value. 2. The method according to claim 1, wherein said first large current value is 40 to 60 μm.
A, and the required minimum current value is 5 to 15
2. The reference oxygen supply method for an air-fuel ratio sensor according to claim 1, wherein the reference oxygen supply is μA. 3. A reference oxygen supply method for an air-fuel ratio sensor, comprising: performing the process according to claim 1 after raising the temperature of the air-fuel ratio sensor to 650 ° C. or higher.