JPS58158553A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To enable continuous detection of a theoretical an air-fuel ratio and an air-fuel ratio on the lean side by providing one oxygen sensor with two functions of a concentration cell type and a limited current type. CONSTITUTION:An oxygen sensor element section A is mounted to an exhaust tube as exposed to an exhaust gas. The element section A is heated up to a specified temperature with a heater inserted thereinto and a lead wire connected to internal and external electrodes 2 and 3 in the element section A is connected to a measuring device through a selector switch 35. When the exhaust gas contacting the outer surface of the element section A is near a theoretical air-fuel ratio, the selector switch 35 is connected to the point B to measure an electromotice force generated between electrodes with a voltometer 31. When the air- fuel ratio is on the lean side, the selector switch 35 is connected to the point C to measure a limited current flowing between the electrodes of the element section A with an ammeter 35.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen sensor that can detect the air-fuel ratio of an automobile engine over a wide range.

Oxygen sensors used in air-fuel ratio control systems for automobile engines utilize changes in the voltage generated by the sensor near the stoichiometric air-fuel ratio (A/F = 146), and are mainly intended for exhaust gas purification systems using three-way catalysts. It has been put into practical use as

Oxygen sensors that have been put into practical use to date are of the so-called concentration cell type, in which electrode layers are provided on the inner and outer surfaces of a cylinder made of an oxygen ion-permeable solid electrolyte with one end closed. When exhaust gas is brought into contact with the outer surface of an oxygen sensor element containing a standard gas such as The stoichiometric sudden combustion ratio is detected by measuring the . However, although this oxygen concentration cell type oxygen sensor can accurately detect the vicinity of the stoichiometric air-fuel ratio, it has been unable to detect other oxygen concentration regions. In recent years, in response to social demands for lower fuel consumption in automobiles, engines have been improved to achieve oxygen excess (lean side) than the stoichiometric air-fuel ratio under specific conditions.
However, the concentration cell type oxygen sensor described above is not suitable for use in this system.

On the other hand, a so-called lean sensor has been developed that can continuously detect the oxygen concentration of exhaust gas from a low range to a high range. In this lean sensor, electrode layers are provided on both sides of a substrate made of an oxygen ion permeable solid electrolyte, and at least one electrode layer is coated with an inorganic material so that the sensor element portion comes into contact with exhaust gas. When it is attached to the exhaust pipe and a constant voltage is applied to the two poles, a limit box, method 1., flows between the two poles depending on the degree of oxygen W in the exhaust gas. It is possible to detect the air-fuel ratio of the engine.However,
This lean sensor is capable of detecting an air-fuel ratio that is higher than the stoichiometric air-fuel ratio, that is, an air-fuel ratio on the oxygen-excess side.

By combining the strained cell type acid accumulation sensor and the sensor, the present invention continuously and accurately adjusts not only the stoichiometric air-fuel ratio of the C engine but also the lean side air-fuel ratio. An object of the present invention is to provide an oxygen sensor that can be used for one cycle in an air-fuel ratio control system in which the air-fuel ratio required by operating conditions changes continuously.

That is, the oxygen sensor of the present invention includes a cylindrical element body with one end closed made of an oxygen ion permeable solid electrolyte, an inner electrode and an outer electrode provided on the inner surface and outer surface of the element body, and at least the outer electrode. When the exhaust gas that contacts the outer surface of the element is discharged near the stoichiometric air-fuel ratio, the concentration of oxygen introduced into the exhaust gas and the inside of the element is known. A change in the electromotive force generated in the VC between the inner electrode and the outer electrode is detected based on the oxygen concentration difference between the element and the standard gas, and the exhaust gas that contacts the outer surface of the element is discharged in an oxygen-excess region than the stoichiometric air-fuel ratio. The present invention is characterized by comprising a circuit that applies a constant voltage to both the inner and outer electrodes and detects changes in the current flowing between the inner and outer electrodes.

Below) 1 The oxygen sensor of the present invention will be explained based on the drawings.

FIG. 1 is a cross-sectional view showing an example of the oxygen sensor of the present invention, blood line U.
A porous ceramic solute, for example, Zr@, Hf0, covers the character-shaped element body 1, the electrode layers 2, 3 provided on the inner and outer peripheral surfaces of the element body 1, and the stiff electrodes N2, 3.
t, 'rho,, OeO,, Bi, (Y, 0 in etc.
．． It is a dense sintered body containing OaO, MgO, Yb2O3, etc. as a solid solution. The element main body 1 has a tapered part 1a on its upper inner periphery which becomes narrower toward the closed end [7], and a shoulder part 1b projecting outward on its outer periphery. An electrode (hereinafter referred to as an inner electrode layer or simply an inner electrode) provided on the inner circumferential surface of the element body 1 is formed at the open end O of the element 1, and an electrode (hereinafter referred to as an inner electrode layer) provided on the outer circumferential surface of the element body 1 is formed at the open end O of the element 1. The outer electrode layer (d) 3 (simply referred to as outer electrode) is formed to reach at least the upper surface of the shoulder portion 1b of the element body 1. Both electrodes 2 and 5 may be formed over the entire inner and outer surfaces of the element body 1, or may be formed only on a portion thereof. Among the porous ceramic layers 4.5, the ceramic layer 4 that covers the inner electrode (anode) 2 is thin to protect the electrode and the -! The ceramic layer 5 covering the outer electrode (cathode) 3 is made thick in order to limit the amount of oxygen flowing into the outer electrode 3.

Reference numeral 6 denotes a generally cylindrical housing, which has a flange 6a on its outer periphery for mounting an exhaust pipe, and has a flange 6a on its lower inner periphery that abuts the lower surface of the shoulder 1b of the element body 1 to attach the element body 1. It has a tapered portion 6b that can be locked. Housing 6
The lower end Ktrf of is connected to the looper 7, and the louver 7 has holes 7a, 7a, . . . for inflowing the gas to be measured.
... are drilled in large numbers.

To attach the element body 1 to the housing 6, place a heat-resistant seal ring 10 made of graphite or the like on the tapered part 6b of the housing 6, and insert the element body 1 into the housing 6 from the closing part side. , the lower surface of the element body shoulder 1b is
This is done by bringing it into contact with the upper surface of the tapered portion 6b of the housing 6.

8 is a ceramic heater, which is a long cylindrical body having a heat generating metal layer (not shown). Eight ceramic heaters are housed and attached to the inside of the element body 1 via locking tools 9 fitted to the outer periphery of the two parts.

The locking tool 9 has an inner shape that corresponds to the outer shape of the ceramic heater 8, and whose outer shape corresponds to the inner shape of the opening end of the element body 1, and the ceramic heater 8 is attached by crimping or the like. The lower surface of the shoulder portion 9a of the locking tool 9 is brought into contact with the upper surface of the tapered portion 1a of the element main body 1 while being fixed to the inner circumference thereof,
As a result, the locking tool 9 to which the ceramic heater 8 is attached is attached to the open end of the element body 1. ceramic heater 8
It has a length such that its lower end reaches almost the bottom of the element body 1, and air from the outside is introduced into the element body 1 through a hollow portion 8a penetrating in the axial direction.

Reference numeral 11 denotes a metal tube for taking out a first outer electrode (hereinafter referred to as a lower outer tube) fitted on the outer circumference above the shoulder of the element body 1.
It is. At the lower end of the lower outer tube is a flange portion 1 that spreads outward.
1a is provided, and this flange portion 11a is connected to the element body 1.
It is placed on the upper surface of the shoulder portion 1b and is in contact with the upper surface of the shoulder portion 1b via a heat-resistant cushion ring 30. The lower outer tube 11 includes an outer electrode 3 formed on the outer peripheral surface of the element body 1.
is in contact with the lower inner circumferential surface of the outer tube.

Reference numeral 12 denotes an outer insulating tube fitted around the outer periphery of the lower outer tube 11. The outer insulating tube 12 has a thick lower portion, and the thick lower opening surface is placed on the upper surface of the shoulder portion 1b of the element body 1 via the flange portion 11a of the lower outer tube 11. Reference numeral 13 indicates a filler made of a heat-resistant inorganic substance such as talc, which is filled in the gap between the housing 6 and the outer insulating tube 12;

15Vi, a circular tubular lower holder connected to the upper part of the housing B, with 7 langes 1 provided at the lower end of the lower holder 15.
5a is in contact with the upper surface of the presser ring 14. By caulking the outer periphery of the tip of the housing 6, the housing 6 and the lower holder 15 are integrated.

16 is a metal tube for taking out the inner electrode (hereinafter referred to as the inner tube)
It is. The inner tube 16 has a flange portion 16a extending outward at its lower end, and is mounted on the locking device 9 by abutting the flange portion 16a against the upper surface of the locking device 9.

The flange portion 16a of the inner tube 16 is in contact with the inner electrode via the locking tool 9.

18F:r, an insulating cylindrical body fitted inside the inner tube 16, with a through hole for passing two lead wires 19 (one not shown) therein and an atmosphere from the outside. It has a conduction through hole (not shown) 7. Insulating cylindrical body 1
The lower surface of the ceramic heater 8 is in contact with the upper surface of the ceramic heater 8, and is connected to the ceramic heater 8 at the lower end of the lead wire 19.

An inner insulating tube 20 is fitted around the outer periphery of the inner tube 16. The lower part of the inner insulating tube 20 has a thick wall, and the open end surface of the thick lower part is connected to the upper surface of the lock JEi, 9 via the flange 16a of the inner tube 16 L4. Inner insulation tube 2
The length is such that the inner tube 16 protrudes further upward from its upper end.

A second outer electrode extraction metal tube (hereinafter referred to as an upper outer tube) 21 is fitted into the second row of the inner insulating tubes 20. The upper outer tube 21 has a flange portion 21a projecting outward at its lower end, and a spring 2 provided on the outer periphery of the inner insulating tube 20 is attached to the lower surface of the 7 flange portion 21a.
The upper ends of 2 are in contact with each other. A filler 29 is provided on the lower outer periphery of the upper outer tube 21 to fill the gap with the lower holder 15.
−) It is flowing.

The spring 22 has its lower end in contact with a cushioning material 23 and a press plate 24 provided on the upper surface of the lower thick-walled portion of the inner insulating tube 20, and its −F end contacts the flange portion 21 of the upper outer tube 21.
a Still in contact with the bottom surface.

It has appropriate elasticity and is provided on the outer periphery of the inner insulating tube 20. The lower part of the spring 22 comes into contact with the inner circumference of the lower outer tube 11. This spring 22 applies a downward pressing force to the thick wall portion of the inner insulating tube 2o, and as a result, the inner tube 16 is brought into good pressure contact with the locking tool 9, and the locking tool 9
The opening of the element body 1 can be securely attached, and the element body 1 can be firmly attached to the housing 6.

At the same time, since the lower part of the spring 22 is in contact with the inner peripheral surface of the lower outer tube 11, the lower outer tube 11 and the upper outer tube 21 are electrically connected by the spring 22.

25 is an upper holder, the lower end of which is connected to the lower holder 15;
It fits around the outer periphery of the upper end. The upper holder 25 and the lower holder 15 are integrally assembled by caulking the mutually overlapping portions from the outside.

26 is a lead wire connected to the inner tube 16, and 27 is a lead wire connected to the upper outer tube 21.

Each of the lead wires 26 and 27 has its outer periphery coated with an insulating material, and together with the ceramic heater heating lead wire 19, it is partially coated with insulation.

Reference numeral 28 denotes an insulating layer provided on the inner periphery of the upper holder 25, which completely ensures electrical insulation between the upper holder 25, the upper outer tube 21, and the lead wire 27.

In the oxygen sensor configured as described above, the inner electrode 2 provided in the sensor element portion is electrically connected to the lead wire 26 via the locking tool 9 and the inner tube 16, and the outer electrode 3 is connected to the lower outer tube 11, It is electrically connected to a lead wire 27 via the spring 22 and the upper outer tube 21. In order to prevent the outer electrode 3 from coming into contact with the housing 6, a notch is provided in the shoulder portion 1b in the axial direction, for example, as shown by the broken line in FIG. You can do it like this. Further, the inside of the element body 1 is in communication with the outside air through the through hole of the insulating cylindrical body and the hollow portion 8a of the ceramic heater 8.

The principle of measuring oxygen concentration in the oxygen sensor having the above configuration will be explained using FIGS. 3(a), 3(b) and FIG.

The mark in Figure 3 is a measurement circuit diagram when the oxygen sensor element A is used as a concentration battery type. Atmosphere (standard gas) is introduced into the inside of the element 1, and exhaust gas is in contact with the outside of the element 1. When the inner electrode 2 and outer electrode 3 of this element A are connected, a potential difference is generated between the inner and outer electrodes 2 and 5 due to the ratio of the oxygen partial pressure in the atmosphere inside the element to the oxygen partial pressure in the exhaust gas.

This is measured as an electromotive force using a voltmeter 31. This electromotive force fluctuates greatly near the stoichiometric air-fuel ratio, as shown by curve I in Figure 4, so the stoichiometric air-fuel ratio (A, /F = 14
6) can be detected.

On the other hand, FIG. 3(b) is a measurement circuit diagram when oxygen sensor element A is used as a limiting current type.
is connected to the anode side of the constant voltage power supply 32, and the outer electrode 3 of the element 1 is connected to the cathode side of the constant voltage power supply 32.

In this measurement circuit, since the constant voltage power supply 32 is used, a limiting current of an amount corresponding to the oxygen concentration in the exhaust gas in contact with the outer electrode 3 is generated in the element body 1. This is measured with an ammeter 33. Since this limiting current is in a proportional relationship with the lean side air-fuel ratio as shown by the broken line (■) in FIG. 4, by measuring the limiting current of element A, the lean side air-fuel ratio can be detected.

Next, a specific example of the operation of the oxygen sensor having the configuration shown in FIG. 1 will be described.

First, the oxygen sensor having the configuration shown in FIG.
Install it in the exhaust pipe so that it is exposed to the exhaust gas. The element A is heated to a predetermined temperature by operating a ceramic heater 8 inserted inside. Lead wires connected to the inner and outer electrodes of element A are drawn out to the outside of the oxygen sensor and constitute, for example, a circuit shown in FIG. 5. In the figure, 35 is a changeover switch. When using element A as a concentration cell type, move it upwards in the figure and connect it to point B, and when using element A as a limiting current type, move it downwards in the figure. Move and connect to point 0.

In the oxygen sensor having the circuit shown in FIG.
When F=14 to 15), the selector switch 55 connects to point B, forming the circuit shown in FIG. 3(a). 19. As described above, since the electromotive force generated between the inner and outer electrodes of element A can be measured with the voltmeter 31, the stoichiometric air-fuel ratio can be accurately detected from fluctuations in this electromotive force. On the other hand, when the air-fuel ratio is on the lean side (A/F is 15 or more), the selector switch 35 is connected to the 0 point, as shown in Fig. 3 (b).
The circuit shown in is formed.

Thereby, the limiting current flowing between the inner and outer electrodes of the device can be measured by the ammeter 33 as described above, and the lean side air-fuel ratio can be continuously detected based on this limiting current value.

As described above, the oxygen sensor of the present invention has two functions, concentration cell type and limiting current type, in one oxygen sensor, so it can accurately measure both the stoichiometric air-fuel ratio and the lean side air-fuel ratio. It has the advantage of being able to detect continuously. Further, since the oxygen sensor of the present invention is structurally almost the same as the conventional one, it has the advantage that the manufacturing and installation methods and the equipment used therefor are almost the same as before.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an example of the oxygen sensor of the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Figs. 3 (a) and (b) are the measurement principle of the oxygen sensor. 4 is a graph showing the output characteristics of the oxygen sensor of the present invention. FIG. 5 is a circuit diagram showing the measurement principle of the oxygen sensor of the present invention. In the figure, 1...Element body, 2...Inner electrode, 3...Outer electrode, 4.5...Porous ceramic layer, 8...Ceramic heater, 11...First outer side Metal tube for taking out the electrode (lower outer tube), 16...Metal tube for taking out the inner electrode, 2
1...Second outer 4F411 electrode extraction metal tube (upper outer tube) Patent applicant Toyota Motor Corporation Patent Attorney Yumi Sagi (and 1 other person) 27 Figure 8 6 q 1 2 2 123 15a 35 4 ! 3 A

Claims (1)

[Claims] (1) A cylindrical element body with one end closed made of an oxygen ion permeable solid electrolyte, an inner electrode and an outer electrode provided on the inner and outer surfaces of the element body, and an inorganic material layer covering at least the outer electrode. an oxygen sensor element consisting of;
When the exhaust gas that comes into contact with the outer surface of the element is discharged at an air-fuel ratio close to that of the air-fuel ratio, the inside A change in the electromotive force generated between the electrode and the outer electrode is detected, and if the exhaust gas in contact with the outer surface of the element is discharged in an oxygen excess region than the stoichiometric air-fuel ratio, a constant voltage is applied to both the inner and outer electrodes. An oxygen sensor for automobile exhaust gas, comprising: a circuit that detects changes in the current applied between the inner and outer electrodes;