JPH0249566Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an oxygen concentration detector, and particularly to an oxygen concentration detector that utilizes the pumping action of a solid electrolyte.

The oxygen pump type oxygen concentration detector was published in Japanese Patent Application Laid-Open No. 1983-
It is disclosed in Publication No. 166039. However, it is necessary to maintain the solid electrolyte at a high temperature, and if the standard oxygen concentration is set to the atmosphere, heat dissipation will be large and the heater capacity will be large. There is also a method of using it as exhaust gas, but it has the disadvantage that the electromotive force is small at the stoichiometric air-fuel ratio due to the catalytic action of the electrode.

An object of the present invention is to provide an inexpensive oxygen concentration detector that eliminates the above-mentioned drawbacks.

The present invention reduces the catalytic action of the electrode on the reference oxygen concentration side and makes use of the oxygen remaining even near the stoichiometric air-fuel ratio, making it possible to measure the air-fuel ratio even near the stoichiometric air-fuel ratio.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, an oxygen concentration detector 13 is attached to an exhaust pipe 25. A diffused resistor 41 having an orifice 48 in a cover 43 having a vent inlet 44 and outlets 45a and 45b and a porous solid electrolyte 40 having a chamber 53 made of glass (ceramics may also be used) 42
It is crimped with. The solid electrolyte 40 and the diffusion resistor 41 are suspended within the cover 53 by a lead wire 46 of the heating resistor and an electrode lead wire 47 of the solid electrolyte 40 . Lead wires 46a, 47a,
47b is insulated with insulators 52a, 52b, and 52c and drawn out to the outside, but the lead wire 46b
is directly earthed. The electric circuit 17 includes a constant current circuit that flows current into the solid electrolyte 40 and a circuit that measures the electromotive force of the solid electrolyte 40. The heating circuit 22 is a power source that heats the diffused resistor 41 .
In this detection operation, air flowing from the vent entrance 44 near the center of the exhaust pipe is heated by the diffusion resistor 41 and rises, and is discharged from the vent exits 45a and 45b.A part of the air flows into the chamber 53 through the orifice 48 and diffuses into the chamber 53. The temperature becomes the same as the surrounding temperature. Oxygen in this chamber 53 is pumped out through the solid electrolyte 40 in proportion to the current applied to the solid electrolyte 40. Therefore, the oxygen concentration within the chamber 53 decreases and an electromotive force is generated in the solid electrolyte 40.

FIG. 2a is a plan view of the solid electrolyte 40 of the present invention. In FIG. 2a, the lead wire 47b has a thick electrode 54 on the outer periphery on the reference oxygen concentration (exhaust gas) side and a porous electrode 55 in the center. This electrode 54,
55 is made of a metal with low catalytic activity, such as gold (nickel, etc.). FIG. 2b is a cross-sectional view thereof. In FIG. 2b, the chamber 53 side of the solid electrolyte 40 includes a lead wire 47a made of platinum, a thick electrode 50,
It consists of a porous electrode 51, and the electrode 50 and lead wire 47a are welded to each other in a state of low electrical resistance.

FIG. 3a is a plan view of the diffused resistor 41 on the solid electrolyte 40 side. In Figure 3a a resistor 49 is printed. Lead wires 46a and 46b are fixed to resistor 49. FIG. 3b is a cross-sectional view of the same, in which the resistor 49 is only on one side.

FIG. 4 shows a characteristic diagram of the present invention, and FIG. 5 shows a characteristic diagram of a conventional device. Both FIGS. 4 and 5 show similar characteristics when λ=1 or more. For I=7mA, in both FIGS. 4 and 5, the electromotive force decreases when λ=1.2.
This is because λ becomes larger and the oxygen concentration in the exhaust gas becomes higher than when the amount of oxygen discharged from the chamber 53 due to the pumping action of the solid electrolyte is greater than the amount supplied by diffusion from the exhaust gas through the orifice 48. This is because the amount of oxygen supplied from the orifice 48 is greater than the amount discharged by the pump action, so the amount of oxygen in the chamber 53 increases. When λ=1.4 or more, the amount supplied from the orifice 48 increases, and almost no electromotive force is generated.

On the other hand, even when λ is close to 1, about 0.5 to 1.0% of oxygen remains in the exhaust gas, but in the case of FIG. 4, the exhaust gas that has flowed into the chamber 53 almost disappears due to the temperature of 800° C. and the catalytic action of platinum. However, since the electrode on the reference oxygen concentration side is made of gold, which has less catalytic activity, oxygen remains and the electromotive force is maintained. On the other hand, in the case of FIG. 5, since both electrodes are made of platinum, there is no oxygen near the solid electrolyte 40, and no electromotive force is generated. As described above, according to the present invention, the electromotive force can be maintained until λ=0.7.

According to the present invention, the electromotive force can be maintained even near the stoichiometric air-fuel ratio, so the air-fuel ratio detection range is widened.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figure 2 a
3 is a plan view of the solid electrolyte of the present invention, b is a cross-sectional view, and FIG. 3a is a plan view of a diffused resistor.
b is the same cross-sectional view, Fig. 4 is the characteristic diagram, and Fig. 5 is the same sectional view.
The figure is a characteristic diagram of a conventional device. 13...Oxygen concentration detector, 25...Exhaust pipe, 4
0...Solid electrolyte, 41...Diffusion resistor.

Claims (1)

[Claims for Utility Model Registration] (a) A solid electrolyte; (b) A first electrode having a catalytic action provided on one side of the solid electrolyte; (c) Covering the first electrode and coming into contact with exhaust gas. (d) a second electrode with a small catalytic action that is provided on the other side of the solid electrolyte and contacts the exhaust gas; (e) a variable current that corresponds to the measured air-fuel ratio to the first electrode and the second electrode; The oxygen concentration detector consists of an electric circuit that flows through a current and outputs a stepwise output voltage corresponding to this variable current as the sensor output.