JPS604850A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To realize the proper control of an air-fuel ratio A/F by obtaining stable current output in combustion gas of which the flow rate is remarkably varied, by arranging the hot junction of a thermocouple in the vicinity of the outer surface electrode of a plate shaped solid electrolyte for conducting the detection of an oxygen concn. while compensating the influence of gas flow by the output of the hot junction. CONSTITUTION:An oxygen concn. detecting cell (detection cell)1 and an oxygen pumping-up cell (pump cell) 2 are arranged in opposed relationship so as to leave a gap or a cavity part between the inner sides of electrodes P formed to both surfaces of each of the cells 1, 2 by a spacer 3 while the hot junction 7 of a chromelalumel (CA) thermocouple is positioned at the center of the outer surface of the detection cell 1 to be fixed thereto by a heat resistant adhesive and connected to the detection cell 1 in series to regulate the pumping-up current Ip of the pump cell 2 so as to set the total voltage of the electromotive force E of CA and the electromotive force V of the detection cell 1 to a certain constant value. By this method, the influence of the flow rate of combustion exhaust gas can be compensated.

Description

Detailed Description of the Invention (Technical Field) Oxygen a1 in gas atmosphere in general, especially in automobile exhaust gas
Various solid-state electrochemical devices using oxygen ion conductive solid electrolytes have been developed to measure the air-fuel ratio of internal combustion engines. Regarding the solution to the problem that the output of the device is affected depending on the load difference between high-speed operation such as driving and low-speed operation such as during idle fishing, this specification will be described below. The technical content described in this book is related to an oxygen sensor suitable for combustion control in internal combustion engines, etc., which are severely affected by load fluctuations.

(Prior art) Conventional oxygen sensors, for example, λ sensors, only utilize the operation near the λ point, and the correction of the output on the leaner side than the 2 points is based on the Nernst's equation shown below. At the temperature T shown by d'3 in the equation, J,
This is limited to compensation for the impact of For example, JP-A DB 53-12
As seen in 9091, the chemical composition of the Zr02 solid electrolyte contains Feze3, which is an electronically conductive component.
It is known to attempt to reduce the temperature dependence by adding -C. However, this type of output correction cannot easily eliminate the effect of temperature 1- on the output shown by the above Nernst equation, and it is difficult to eliminate the influence of temperature 1- on the output as shown by the above Nernst equation. It is essentially not possible to compensate for the influence of such gas flow on the oxygen sensor.

Internal combustion engines have a wide range of operating speeds, from several hundred revolutions per minute during idling to several thousand revolutions per minute at high speeds, and the speed depends on the load. Engine d: The exhaust gas flow rate fluctuates significantly depending on the force, and as a result, the current output for use in controlling the air-fuel ratio A/F for the oxygen sensor, which is easily influenced by the gas flow in the outside world, is It had the disadvantage of being significantly affected by changes in engine output due to changes in exhaust gas flow velocity. An overview of the prior art in this regard is as follows.

Figure 1 <a), (b), and (C) show an oxygen concentration detection cell (hereinafter simply referred to as a detection cell) 1, an oxygen pumping cell (also abbreviated as a pump cell) 2, etc. The main structure of an oxygen sensor is such that the inner electrodes P formed on both sides of the electrode P face each other across a spacer 3 with a gap or cavity in between, and when this oxygen sensor is placed in a combustion gas atmosphere, the detection The superpower V generated in Hill 1 should normally be read by a voltage meter, for example, 20+n V.
Under the control of the oxygen pumping current by a variable resistor 6 of the current of the power supply 5 of the pump cell 2, the current output 1p, under the influence of the engine power and the current output 1o in a similar setting, a constant gas flow bottom. The effect of gas temperature was shown.

Originally, in this type of measurement method using this type of oxygen sensor,
Since the detection cell and the pump cell are provided separately and separated from each other, the temperature dependence of the current output of the sensor is compensated for. As shown in Figure 1 (C), the dependence on temperature itself is extremely small. ! The lp characteristic at I[ is shown by the α curve, whereas the lp characteristic at low engine speed such as idling is shown by the α curve. As shown in the comparison of Ip characteristics under relatively low temperature and low combustion gas flow velocity conditions with β curve C, the inflow of combustion gas into the gap between detection cell 1 and pump cell 2, which is originally unfavorable, It is unavoidable to avoid including errors in the A/F value that should be represented by the current output I13 (see arrow γ) due to fluctuations in the flow of exhaust gas whose amount varies depending on the engine output. There wasn't.

(Objective of the invention) To effectively eliminate the so-called combustion gas flow rate dependence of the output current I11 described above, in other words, to effectively eliminate the dependence of the output current I11 on the combustion gas flow rate. We propose an oxygen sensor that can accurately obtain a stable current output in a combustion gas atmosphere where the flow rate of dregs fluctuates significantly, thereby improving the air-fuel ratio A/F.
It is an object of this invention to realize control.

(Structure of the Invention) According to the present invention, the above object is advantageously achieved by a mechanism that has the following points as its main points.

A pair of plate-shaped solid electrolytes used for acid depth detection and oxygen pumping are placed in the inner and outer parts of each plate-shaped solid electrolyte, separated by a gap or cavity that communicates with the combustion gas atmosphere. The formed electrodes are fixed facing each other on the inside, and the hot junction of the thermocouple is arranged near the outer surface electrode of the plate-shaped solid electrolyte that controls oxygen 13 degree detection, and between the inner and outer electrodes of the solid electrolyte and Oxygen sensor-0 is equipped with a connection that detects the sum of electromotive forces generated in a thermal lightning pair and a connection that conducts an oxygen pumping current between the outer electrodes of the plate-shaped solid electrolyte that controls oxygen pumping. In this oxygen sensor, at least the electrode facing the gap or cavity is made of a porous layer containing a porous refractory metal that exhibits oxygen diffusion resistance, or is made of a porous layer containing a porous refractory metal. It is recommended as an embodiment to provide a porous coating with.

This oxygen sensor consists of a pair of plate-shaped solid electrolytes, separated by a gap or cavity that communicates with the combustion gas atmosphere, with electrodes formed on the inner and outer surfaces of each plate-shaped solid electrolyte facing each other. Then, one side is used as an oxygen temperature detection cell and the other as an oxygen pumping cell, and if the sum of the electromotive force of the detection cell and the electromotive force of the thermal lightning pair placed near the outer surface of its outer electrode is constant, In addition to controlling the current of the oxygen pumping cell, the current value is used to measure the acidity in the combustion gas, which is independent of the load fluctuation of the above-mentioned detection cell output characteristics. .

By the way, as mentioned above, the combustion gas flow rate changes depending on the product of engine speed and load. The influence of this engine output on the combustion exhaust gas temperature has a nearly linear relationship as shown in Figure 2.

On the other hand, for the oxygen sensor shown in Figure 1(a) again, while keeping the ambient temperature constant, the superpower V of Le 1 was increased to 20
Under the regulation of the oxygen pumping current of the pump cell 2, which increases from m V to, for example, 50 m V, the effect of the unprecedented ratio A / F on the current output 1 +1, with the electromotive force V as a parameter, is determined by the third The relationship is as shown in the figure.

Focusing on these relationships, the outer surface potential 46P of the detection cell 1
For example, a chromel-alumel type thermal lightning pair (hereinafter abbreviated as CA) is arranged and connected in series with the detection cell 1 so that the hot junction approaches or partially contacts the electromotive force E of the detection cell. The wave output current 1 of the pump cell 2 is adjusted so that the combined voltage with the electromotive force V of 1 becomes a constant value, for example, 50 mV.
By adjusting p, the following relationship is derived (there is pC).

CA electromotive force F when the combustion gas is relatively low temperature
On the other hand, when the temperature is high, the CA electromotive force becomes high. Therefore, the value of the electromotive force of detection cell 1, which corresponds to the difference from the combined voltage of 50 mV assumed above, is high when the combustion scum is low. , becomes low at high temperatures. Therefore, the sum of the electromotive force V of the detection cell 1 and the CA electromotive force is, for example, 50 mV.With the current output of the oxygen pumping current 111 of the pump cell 2, the air-fuel ratio Δ/Fail III is determined. This is to compensate for the influence of combustion exhaust gas flow velocity, which was unavoidable in the past.

Figure 4 shows the appearance of the oxygen sensor according to the present invention, and Figure 5 shows the appearance of the oxygen sensor according to the present invention.
The cross section is illustrated in figures (a> and (b) together with the main parts of the detection cell 1 in figure (c)).

In the figure, 1 is a detection cell, 2 is a pump cell, 3 is an adhesive layer such as a spacer, 4 is a voltmeter, 5 is a power supply, and 6 is a variable resistor, which is almost the same as shown in Figure 1 (a). In addition to Inl, 7 is the hot junction of CA, 8 is also the cold junction, 9 is the thermocouple wire, and CA is the already mentioned J, sea urchin detection cell 1.
In series, one side of CA is connected to η, that is, the + side of detection cell 1, and one side of detection cell 1 and the + side of CA are connected to voltage gt 4 via lead wire 10.

% (+) 11 is the lead wire of the pump cell 2 and is connected to the power supply 5 and the resistor 6, and 12 is the lead wire of the pump cell 2.
A heater placed along the back side of the heater is connected to a preheating power source 5' via a lead wire 13.

Each of the above elements is held inside the cylindrical sensor body 14 by a heat-resistant filler and adhesive 15, and is enabled to come into contact with the combustion gas atmosphere communicated through the through hole 17 of the protective tube 16 placed over the sensor body 14. .

Connecting tubes 18 and 19 are connected to the sensor body 14, and the lead wires 10 to 13 are held together with their connection terminals by a filling adhesive 20, and a closing member 21 is caulked to the end of the connecting tube 19. Pull out each lead wire to the outside. NaJ
322 is a mounting screw.

Both the detection cell 1 and the pump cell 2 have electrodes made of a porous material containing a porous metal having resistance to oxygen diffusion, or electrodes made of a porous material containing a porous metal having resistance to oxygen diffusion, on both sides of a provisional body made of an oxygen ion conductive solid electrolyte such as stabilized zirconia porcelain. The electrodes P are covered with a porous refractory material having diffusion resistance, and their inner sides are joined together by a spacer 3 with a gap between them.
．． CA made of alumel-chromel wire of 32 ++ mφ
The thermal contact point 7 is positioned and fixed using a heat-resistant adhesive or the like.

The thermal electromotive force F of CA has a total voltage E + V with the electromotive force V of detection cell 1 -C1 Utilizes the relationship A/t-1p with the voltage of detection cell 1 as a puff meter, which was already mentioned in Figure 3. This is useful for correcting the error explained in FIG. 1(b).

For example, when the hot junction temperature is 800°C, the cold junction temperature is 4.
00°C, and when the former is 300°C, the latter has a temperature gradient of 100°C. Therefore, the electromotive force E of CA, which corresponds to the difference in electromotive force generated at each temperature C between the hot junction 7 and the cold junction 8, is The length of the thermocouple wire 9 is determined by °C, and depending on the error γ in Fig. 1 (1), which should be corrected by CA, by lengthening the gap when it is large and shortening it when it is small, All necessary corrections will be made.

The oxygen sensor described above, together with a conventional sensor that differs only in the absence of a CA arrangement, was operated as follows in a combustion exhaust gas atmosphere under balanced conditions, as shown in FIG. I'Ip
-A/F characteristics were obtained.

First, set the air-fuel ratio A/F to 15, then set the A/F ratio to 15.
Air was sequentially mixed into the waste residue until A/F reached 20, and then A/F was measured using a λ scan waste analyzer.

The exhaust gas flow rate corresponding to υ1 gas temperature J3 and A/F is as shown in the following table: J3.

Note that 14 V was applied to the heater 12 to equalize the measurement temperature environment.

In Figure 6, the conventional sensor has a significant error between the α curve at high temperature and large flow rate corresponding to high engine output, and the β curve at relatively low temperature and small flow corresponding to low engine output. On the other hand, with the oxygen sensor according to the present invention, it is clear that almost no difference can be obtained from the influence of the exhaust gas flow rate, as in the α' and β' curves, which have a small difference in a relationship that is almost the same as the above.

The table below is a summary of the comparison with the conventional one.

Furthermore, the characteristic error ΔA/F can be reduced by adjusting the electromotive force of the GA by changing the position of the cold junction.

(Effects of the Invention) According to the present invention, by using the algebraic sum of the electromotive force of the thermal lightning pair and the electromotive force of the detection sensor, the relationship between the air-fuel ratio Δ/F and the oxygen pumping current of the pump cell can be determined. It is possible to advantageously eliminate engine output dependence represented by the exhaust gas flow rate, which has a negative influence on the engine, and to effectively realize appropriate air-fuel ratio control using extremely simple means.

[Brief explanation of drawings]

Figures 1 (a), (b), and (c) are the main parts of the oxygen sensor 4 and their characteristic diagrams, Figure 2 is the relationship diagram between engine output and exhaust gas temperature, and Figure 3 is the oxygen This is a graph showing the relationship between the pumping current and the air-fuel ratio using the detection cell electromotive force as a parameter. FIG. 4 is an external view of the oxygen sensor according to the present invention, FIGS. Figure 5 (C) is a side view of the main parts, and Figure 6 is a performance comparison graph. 1... Plate solid electrolyte for oxygen m degree detection (detection cell) 2
... Plate solid electrolyte for oxygen pumping (pump cell) 3.
...Spacer 7...CA hot junction 8...CA cold junction 10.11...Lead wires Fig. 1 (a) (b) Q 4 (C) Fig. 2 Fig. 3■ Engine output Figure 4 Figure 5 (,b) (C') Procedural amendment April 19, 1980 1, Indication of case 1981 Patent order/No. 111951 2, Title of invention Oxygen sensor 3, Amendment Relation to the case of the patent applicant (+54) NGK Spark Plug Co., Ltd. The scope of claims on page 1, line 8 to page 2, line 3 of the 1 specification is amended as follows. [2. Claim L A pair of plate-shaped solid electrolytes for detecting oxygen concentration and pumping out oxygen are separated by a gear or a cavity that communicates with the combustion gas atmosphere, and of each plate-shaped solid electrolyte,
The electrodes formed on both outer surfaces are fixed facing each other on the inside, and the hot junction of the thermocouple is arranged near the outer electrode of the plate-shaped solid electrolyte that controls oxygen concentration detection. or the electrode facing the cavity,
The sensor according to claim 1, comprising a porous layer containing a porous heat-resistant metal having oxygen diffusion resistance. 8. The sensor according to claim 1, wherein at least one of the electrodes facing the gear or the cavity is coated with a porous layer of a porous refractory material having resistance to oxygen diffusion. ” 2. “Internal combustion engine” on page 2, line 10 of the specification is 1.
- One of these is an oxygen sensor such as that described in Japanese Patent Application Laid-Open No. 58-158155, in which a pair of plate-shaped solid electrolytes are connected to each other via an interlayer for detecting oxygen concentration, pumping out or pumping in oxygen, and providing Q. Regarding oxygen sensors fixed facing each other inside electrodes formed on both the inner and outer surfaces of the electrodes, such oxygen sensors are corrected to "Internal combustion engine", and "Regarding the solution" in line 14 of the same page is changed to "Regarding the solution". Correct. 8. Delete page 2, line 19 to page 8, line 1404
, (-oxygen sensor) in the first line of page 4 is corrected to [this type of oxygen sensor]. 5. "The solid electrolyte --- "Oxygen sensor." is corrected as follows: "An oxygen sensor characterized by compensating for the influence of gas flow by the output of the thermal junction." 6, page 7, line 19, "Oxygen sensor."
Correct "combustion gas flow velocity" to "combustion gas temperature". On the 20th line of the same page, [varies depending on the product. Correct "Now" as follows. "It changes according to the product, that is, the engine output." 7, same No. 8
Correct "superpower" in lines 4 and 5 of the page to "electromotive force". 8 Illustrated on page 9, line 9. " is corrected to "Illustrated for one example." 9 Correct "electrode P" on page 10, line 17 of the same to "electrode." 10 Add the following between the 8th and 7th lines from the bottom of page 18. [Next, FIGS. 7(a) and 7(b) show another example, in which the influence of the gas flow already mentioned is compensated for! At the same time, the feedback control circuit 23 controls Ip so that the output via the lead wire lOI of the detection cell 1 is always constant.
is controlled, and an output corresponding to this process can be taken out from the terminal 24 as the oxygen concentration indicating output of this sensor. In the figure, 25 is a compensation circuit, 26, 27 and 28 are amplifiers, and 29 is an adder. 11, page 14, line 11, graph 1. ” is corrected as follows. "The graph, Figures 7 (a) and (b) are cross-sectional views showing other examples." 1 stone outside, - 4, □I+, /

Claims (1)

[Scope of Claims] 1. A single plate-shaped solid electrolyte is provided for oxygen concentration detection and oxygen pumping, respectively, with a gap or cavity communicating with the combustion gas atmosphere separated from each plate-shaped solid electrolyte. Inside,
The hot junction of the thermocouple is arranged near the outer electrode of the plate-shaped solid electrolyte that controls oxygen concentration detection, and the electrodes are fixed facing each other inside the electrodes formed on the outer surfaces. , a connection that detects the sum of each electromotive force generated between the outer electrodes and the thermocouple, and a plate-shaped solid electrolyte that controls oxygen pumping, and controls the oxygen pumping current between the outer electrodes.
Oxygen sensor with wire connections. 2. The sensor according to claim 1, wherein among the electrodes, at least the electrode located in the gap or cavity is made of a porous layer containing a porous heat-resistant metal having oxygen diffusion resistance. 3. The sensor according to claim 1, wherein at least one of the electrodes facing the gap or cavity is coated with a porous layer of a porous refractory material having resistance to oxygen diffusion.