JPS6034062B2 - Air fuel ratio detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio detection device using an oxygen ion conductive solid electrolyte, and particularly to an air-fuel ratio detection device that has less anomaly with respect to a gas flow to be detected and has excellent responsiveness.

Attempts to detect the air-fuel ratio (ratio of air and fuel) and control combustion conditions using oxygen ion-conducting solid electrolytes have been actively conducted in the field of various combustion equipment, including internal combustion engines for automobiles. ing.

Various types of air-fuel ratio detection devices have been developed, and FIG. 1 shows one example.

That is, an electron conductive layer 2, a gas-permeable oxygen ion conductive solid electrolyte layer 3, and an electron conductive layer 4 are sequentially laminated on an insulating substrate 1 having a rectangular planar shape to form an oxygen sensor having an overall substantially flat shape. A DC power supply device 6 is provided which forms the main body and forces a direct current to flow between the electronically conductive layers 2 and 4 via a lead wire 5, and also controls the electromotive force generated in the electronically conductive layers 2 and 4. The structure includes a voltage measuring device 7 for detecting the voltage. In such an air-fuel ratio detection device, when a direct current is passed from the electron conductive layer 2 to the electron conductive layer 4 by the DC power supply device 6, the direct current flows from the electron conductive layer 4 to the electron conductive layer 2. Oxygen ions flow through the solid electrolyte layer 3, and oxygen molecules formed at the interface between the electronically conductive layer 2 and the collective electrolyte layer 3 diffuse through the gas-permeable solid electrolyte layer 3, causing the inflow of the oxygen ions and the oxygen A high oxygen partial pressure balanced with molecular diffusion is maintained at the interface, and the output voltage corresponding to the difference between this standard oxygen partial pressure and the oxygen partial pressure in the test gas is This occurs between the magnetic layers 2 and 4, which makes it possible to detect the air-fuel ratio.

Although the oxygen sensor having such a structure is superior in that the main body can be made compact with a relatively simple structure, it has been found that the following problems remain.

In other words, (1) the electron conductive layer 2, the solid electrolyte layer 3, and the electron conductive layer 4 are sequentially laminated on one side of the substrate 1, which has a rectangular planar shape, and the oxygen sensor body has a flat shape as a whole; Different characteristics are produced depending on the direction in which the oxygen sensor body is placed with respect to the gas flow.

In other words, the response is best when the gas flow to be detected flows in a direction perpendicular to the laminated surface of the flat oxygen sensor body (direction of arrow A in Figure 1). When the test gas flows in the direction of arrow B in Figure 1), its responsiveness decreases. Therefore, when installing the oxygen sensor body, the direction must be carefully considered.
(2) Since the insulating substrate 1 is used as the structural base, there is a limit to the responsiveness.

That is, based on the principle of an oxygen sensor, only the solid electrolyte layer 3 and the electron conductive layers 2 and 4 on both sides generate an electromotive force, and only these three layers have good responsiveness to the temperature and the gas atmosphere to be detected. However, in reality, a structural substrate is required, and it requires an insulating substrate such as alumina.
is used, resulting in a limit to heat capacity and a limit to responsiveness. (2) Since the insulator substrate 1 having a planar rectangular shape is used as a structural base, the oxygen sensor body becomes somewhat large.

That is, while the thermocouple used on the thermometer side can be easily applied even in very narrow areas, the one shown in FIG. 1 has a limit to the application of oxygen concentration measurement in very narrow areas. SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio detection device that has a small anisotropy with respect to a gas flow to be detected, can be made into a 4-type device with a very simple structure, and has excellent responsiveness.

The air-fuel ratio detection device of the present invention includes an electronically conductive wire made of Au, Ag, and a platinum group element or an alloy.
A gas permeable oxygen ion conductive solid electrolyte layer is provided in direct contact with the electron conductive wire, an electron conductive layer is provided in direct contact with the solid electrolyte layer around the solid electrolyte layer, and the electron conductive layer is provided with an electron conductive layer in direct contact with the solid electrolyte layer. contact with the exposed gas directly or indirectly through a protective layer or the like, and further comprising a voltage measuring device for detecting the electromotive force generated between the electron conductive wire and the electron conductive layer. The present invention is characterized in that it is provided with a DC power supply device for forcing a current to flow between the electron conductive wire and the electron conductive layer, if necessary.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a schematic vertical cross-sectional explanatory diagram of an air-fuel ratio detection device according to an embodiment of the present invention, in which the area around the electronically conductive wire (circular or square cross section) 12 is in direct contact with the electronically conductive wire 12. A gas permeable oxygen ion conductive solid electrolyte layer 13 is provided, an electron conductive layer 14 is provided around the solid electrolyte layer 13 in direct contact with the solid electrolyte layer 13, and the electron conductive Sexual line 12 and electronic conductive layer 14
A voltage measuring device 17 for detecting the electromotive force generated between the two is connected by a lead wire 15.

In such a structure, the oxygen partial pressure at the interface between the oxygen ion conductive solid electrolyte layer 13 and the electron conductive wire 12 is used as a reference, and when the oxygen partial pressure in the test gas, that is, the exhaust gas fluctuates greatly, e.g. The transition period occurs when rich gas (exhaust gas on the excess fuel side) with a very low oxygen partial pressure and lean gas (exhaust gas on the excess air side) with a very high oxygen partial pressure flow alternately, such as the exhaust gas from an automobile internal combustion engine. It generates an output at , making it possible to detect the stoichiometric air-fuel ratio.

FIG. 3 shows another embodiment of the present invention, in which a DC power supply device 16 for forcing a current to flow between the electron conductive wire 12 and the electron conductive layer 14 is provided. in this way,
Electron conduction between the solid electrolyte layer 13 and the solid electrolyte layer 13 is established by connecting a DC power source, preferably a constant current DC power source, to forcibly generate a flow of oxygen ions and to cause diffusion of oxygen molecules within the gas-permeable solid electrolyte layer 13. The oxygen partial pressure at the interface with the sex wire 12 can be made more constant, and stable electromotive force characteristics can be obtained. FIG. 4 shows still another embodiment of the present invention, in which the electron conductive layer 14 is in the form of a coil, whereas in the ones shown in FIGS. 2 and 3, it is in the form of a coil. be.

In this way, there is no need to directly connect a lead wire to the electron conductive layer 14 as shown in FIGS. 2 and 3. As mentioned above, in the present invention, the electron conductive wire (circular or square cross section) 12 is used as the structural base, and the solid electrolyte layer 13 and the electron conductive layer 14 are provided around it, so that the wire is particularly thin in the circumferential direction. There is no anomaly,
Similar electromotive force characteristics can be obtained regardless of the direction of the gas flow to be detected. In addition, since it does not use an insulating substrate as shown in Figure 1, the heat capacity of the oxygen sensor body can be further reduced, and it has excellent responsiveness as an oxygen sensor, in other words, the ability to follow the test gas atmosphere and temperature. It becomes something. In this regard, the thickness of the electron conductive wire 12 is preferably as small as possible within a range that maintains its strength as a structural base, for example, in the case of a circular cross section, it is desirable to have a diameter of 0.5 or less, and the thickness of the solid electrolyte layer 13 is 0.1
It is preferable to keep it below the ribs. In this way, a very small oxygen sensor body serving as an oxygen gas detection section can be obtained, which can provide versatility comparable to that of conventional thermocouples. The above-mentioned electronic conductive wire 12 is made of Au, A
It is preferable to use stable metal pongee wires that do not form oxides at high temperatures, such as platinum group elements such as g and platinum group elements such as Pt and Pd.

Or Au, Ag such as Ag-Pd, Au-Pd
It may also be an alloy of platinum group elements. Further, as the oxygen ion solid electrolyte layer 13, Ca0, Y203, Sr0,
Z2 stabilized with Mg0, Tho2, W03, Ta205, etc. or Nb205, S, W03, Ta2
Bi203 stabilized with 05, Y203, etc., or known materials such as Tho2-Y203, Ca○-Y203, etc. can be used as the material, and sputtering or ion plating can be used to form it around the electron conductive line 12. A physical vapor deposition method such as, an electrochemical method, a high temperature firing method using a paste, etc. can be used. Further, as the electron conductive layer 14, Au, Ag and SIC without catalytic action, or Tj02, Coo,
Oxide semiconductors such as C3 or catalytic R
The material can be a single platinum group element such as Pd, Rh, 0s, lr, or Pt, an alloy thereof, or an alloy of a platinum group element and a base metal element, and is formed around the solid electrolyte layer 13. For this purpose, physical vapor deposition methods such as sputtering and ion plating, electrochemical methods such as plating, or high-temperature firing methods using paste can be used. You can also wrap the Tsumugi wire into a coil.

Furthermore, it is also desirable to provide a protective layer on the surface of the oxygen sensor body, and in this case, the protective layer may be Ca○-Zr.
02 (calcium zirconate), Yama 202 (alumina), spinel, etc., deposited by immersion firing or plasma spraying can be used. In addition,
Since the oxygen ion conductivity of the solid electrolyte deteriorates at low temperatures, it is also desirable to provide a conductor within the protective layer to enable heat generation, or to place the oxygen sensor body in a heat generating atmosphere.

Experimental Example 1 FIGS. 5 to 7 show an air-fuel ratio detection device manufactured in Experimental Example 1 of the present invention.

In manufacturing, first, a platinum wire having a diameter of 0.2 ribs and a length of 3 ribs used as the electronic conductive wire 12 is immersed between two legs on one end side in a mass electrolyte paste. The solid electrolyte paste used at this time was a mixture of 5 mol% Y203-Zr02 powder and lacquer at a weight ratio of 1:1, kneaded, and then adjusted to a viscosity of approximately 80,000 centipoise with thinner. . After the above bond immersion, 100o
It was dried at OX for 1 hour. Solid electrolyte layer 1 obtained here
The film thickness of No. 3 (unfired) was approximately 50 rm. Next, a platinum paste as the electron conductive layer 14 is attached to the surface of the solid electrolyte layer 13 by bonding without directly contacting the platinum wire, and then a platinum paste with a diameter of 0.2 ribs and a length to be used as the lead wire 18 is applied. A 30 mm platinum wire was pressed against the platinum wire paste film and dried for 1 hour at 10,000 mm.

Thereafter, the collective electrolyte paste membrane and the platinum paste membrane were fired at 1400 oo x 3 hours. The temperature increase rate at this time is 60% from room temperature to 140,000℃.
00/hr. The obtained solid electrolyte layer 13 was gas permeable and had a thickness of about 30 meters, and the thickness of the electron conductive layer (platinum) 14 was 7 to 8 meters.

Furthermore, Ca○-Zr02 (calcium zirconate) was deposited as a protective layer 19 by plasma spraying to manufacture the oxygen sensor body 20. Note that the thickness of the protective layer 19 was approximately 50 mm. Figures 6 and 7 show an example of the oxygen sensor main body 20 attached with silk, and the oxygen sensor main body 20 is housed in a stainless steel louver 21 to prevent it from being directly exposed to the gas to be detected. The test gas passes through the hole 21a formed in the louver 21, reaches the two oxygen sensor bodies, and is then discharged.

The oxygen sensor main body 20 is bonded to an alumina insulating tube 23 by a ceramic adhesive 22 made of Si02, and the adhesive 22 also serves as a gas seal. Also,
The insulating tube 23 has holes 23a and 23b to prevent the platinum wires 12 and 18 from being short-circuited. Furthermore, insulation tube 2
In order to prevent the louver 3 from being damaged, a holder 24 made of stainless steel is placed over the outside of the louver 21, and the louver 21 is fixed by welding via a ring 25 also made of stainless steel.
The platinum wires 12 and 18 are connected to nickel wires 27 and 27, respectively, at the welding portion 2-6, and the nickel wires 27 and
The holes 23a and 23b through which the cylindrical member 27 passes are filled with a ceramic adhesive for gas sealing.

Further, the holder 24 is joined to another holder 28 by welding, and the holder 28 holds alumina powder 29. This alumina powder 29 prevents the nickel wire 27 from shorting. The holder 28 is connected to a stainless steel tube 31 by forming a roll caulking portion 30, and the alumina powder 29 is prevented from leaking into the stainless steel tube 31, and the nickel wire 27 and the copper wire 32 are inserted into the stainless steel tube 31. A silicone rubber separator 33 is inserted to prevent short circuits.

The nickel wire 27 and the copper wire 32 are joined by a silver soldered portion 34. Further, the copper wires 32 are prevented from shorting each other by the silicone rubber 35, and the silicone rubber 35
A shield wire 36 is provided around the stainless steel tube 31 and the shield wire 36 is fixed by a roll caulking portion 37.

A nut 38 is loosely attached to the outside of the shield wire 36, and the nut 38 can be moved in the direction of the arrow up to the ring 25 and fixed to, for example, an exhaust pipe.

Next, an evaluation test was conducted using the air-fuel ratio detection device having the structure described above.

That is, at a temperature of 600[deg.] C., rich gas (oxygen partial pressure of about 10-atm) and lean gas (oxygen partial pressure of about 10-3 atm) were alternately flowed at intervals of two inkstones to examine changes in output voltage. Note that here, the positive side of the voltage measuring device 17 was connected to the electron conductive layer 14 side. The results are shown in the 8th section.
As shown in the figure. In this experiment, when the exhaust gas is kept in a fuel-rich state, the oxygen partial pressure in the exhaust gas is equal to the oxygen partial pressure at the interface between the electronic conductive wire 12 and the solid electrolyte layer 13. , the output voltage is 0.

However, the next time excess air (lean) gas flows in, at that moment, according to Nernst's equation, E = Hirotaka Obi = 7
An output of 4 dishes v is generated.

However, since the lean gas enters the interface between the electron conductive wire 12 and the solid electrolyte layer 13 through the electron conductive layer 14 and the solid electrolyte layer 13, the oxygen partial pressure at the interface and the oxygen partial pressure in the exhaust gas decrease. Since these become equal, the output voltage approaches zero. Next, when fuel excess (rich) gas flows in, at that moment an output of E = band n special mention 〒 - chest v is generated, and as the rich gas diffuses through the solid electrolyte layer 13, the output voltage becomes 0 again. As it approaches, the electromotive force characteristics become as shown in FIG.

In this way, if the stoichiometric air-fuel ratio is cut when switching from rich gas to lean gas, a positive electromotive force is generated, and if the stoichiometric air-fuel ratio is cut when switching from lean gas to rich gas, a negative electromotive force is generated. Note that if the connection polarity of the voltage measuring device 17 is reversed, the positive and negative electromotive force will also be reversed, but in any case, the stoichiometric air-fuel ratio can be detected. Experimental Example 2 In this experiment, an evaluation test was conducted using almost the same air-fuel ratio detection device as described in Experimental Example 1.

That is, the difference from Experimental Example 1 is that the electron conductive wire 1
The difference is that 2 and the electron conductive layer 14 are connected to a DC power supply 16 (see FIG. 3), and a current is forced to flow between them. Here, a constant current DC power source was used as the DC power supply device 16, and its negative electrode was connected to the electron conductive layer 14 side, and its positive electrode was connected to the electron conductive wire 12 side. Therefore, while a constant current of 5 A was constantly flowing at a temperature of 60,000, as in Experimental Example 1, rich gas and lean gas were alternately flowed at two axes and intervals to examine the output characteristics.

Note that here, the electronic conductive wire 12 side is connected to the voltage measuring device 17.
The measured impedance is IM.
It was O. The results are shown in FIG. In this case, since the current is forced to flow, oxygen ions are constantly flowing between the electron conductive wire 12 and the solid electrolyte layer 1 through the solid electrolyte layer 13.
Since the oxygen molecules flowing into the interface with 3 and generated at this interface are diffusing through the solid electrolyte layer 13, the oxygen partial pressure at the interface is in a state where the inflow of oxygen ions and the diffusion of oxygen molecules are balanced. It's getting expensive.

For this reason, a high output voltage is generated when the oxygen partial pressure in the exhaust gas is low, such as in rich gas, and conversely, when the oxygen partial pressure in the exhaust gas is high, as in lean gas, the output voltage is low. Furthermore, even when using the same rich gas, measurements were performed with the air-fuel ratio changed, and the results shown in FIG. 10 were obtained. on the other hand,
The test was conducted by reversing the connection to the constant current DC power supply 16, connecting the positive electrode to the electron conductive layer 14 side, and connecting the negative electrode to the electron conductive wire 12 side.

In this case, contrary to the situation shown in FIG. 9, a high output voltage is generated when the exhaust gas is a lean gas with a high oxygen partial pressure,
The output voltage was low when the exhaust gas was a rich gas with a low oxygen partial pressure. Further, even though the same lean gas was used, the results shown in FIG. 11 were obtained when the air-fuel ratio was further changed. Experimental Example 3 FIG. 12 shows the oxygen sensor main body 20 of the air-fuel ratio detection device manufactured in Experimental Example 3 of the present invention.

In manufacturing, first, a platinum wire having a diameter of 0.2 mm and a length of 30 willow used as the electronic conductive wire 12 is immersed in a solid electrolyte paste between one end and two sides.

The solid electrolyte paste used at this time was 5 mol% Y20
The two powders of 3-Z and lacquer were mixed at a weight ratio of 1:1, kneaded, and then the viscosity was adjusted to about 80,000 centipoise with thinner. After the above-mentioned soaking, drying was carried out for 1 hour at 100 pm. The thickness of the solid electrolyte layer 13 (unfired) thus obtained was about 50 m (see FIG. 12a). Next, the solid electrolyte layer 13 shown in FIG.
A coiled electronically conductive layer 14 was formed by winding it around the . Incidentally, when winding one end of the platinum wire into a coil, the end of the electronically conductive wire 12 may be folded back and wound, and then both may be cut.
Subsequently, in order to sinter the solid electrolyte layer 13,
Firing was performed for 3 hours.

The temperature increase rate at this time is 600 from room temperature to 140,000
It was 0/hr. Obtained solid electrolyte layer 13 after firing
The film had a thickness of about 30 mm and was porous enough to allow oxygen gas to pass through. Thereafter, Cao-Z 2 was further deposited as a protective layer 19 by plasma spraying to form the oxygen sensor body 2.
0 was manufactured. Therefore, the oxygen sensor main body 20 is
An evaluation test was carried out by placing the electron conductive wire 12 and the electron conductive layer 14 made of platinum wire in a louver 21 as shown in the figure and connecting them to a nickel wire 27. A similar test was carried out in which rich gas and lean gas were alternately flowed at 600°C at intervals of two inkstones, as shown in FIG. In tests using the same machine, we were able to obtain the electromotive force characteristics shown in Figure 9.

Comparative example Figure 13 shows the conventional flat plate oxygen sensor body (see Figure 1)
FIG. 13 is an explanatory diagram showing the manufacturing process for forming an electron conductive layer 2 as shown by diagonal lines in FIG. 13 b on an alumina substrate 1 (5×4×0.6 ribs) shown in FIG. 13 a. A platinum paste was printed, dried at 10,000 x 1 hour, and then fired at 1,300 qo x 1 hour in the air.

The thickness of the electron conductive layer 2 obtained here was 5 to 6 meters. Next, in order to form the solid electrolyte layer 3, as shown in FIG.
Solid electrolyte paste was applied to the shaded area.
Then, after drying at 10,000 x 1 hour, 1,400
Firing was performed for 3 hours. The solid electrolyte layer 3 obtained here had a thickness of about 50 m and had gas permeability. Furthermore, in order to form an electron conductive layer 4, platinum base was printed on the shaded area in FIG.
After drying at 0 and 0x for 1 hour, dry at 130p and 0x in the air.
Firing was performed for 1 hour. The thickness of the electron conductive layer 4 obtained here was 5 to 6 meters. Thereafter, as shown in FIG. 13e, the lead wire 5 was taken out by crimping, assembled into an alumina protection tube, and subjected to an evaluation test. Therefore, the product a of the present invention described in Experimental Example 1 and the product b using the conventional product shown in FIG. Regarding c, where the test gas is flowed in the direction opposite to arrow A (arrow B in Figure 1),
A comparative test was conducted on the output response when the exhaust gas suddenly changed from lean (excess air) to rich (excess fuel).

In either case, the negative electrode of the constant current power supply device 6 or 16 was connected to the exhaust gas side electron conductive layer 4 or 14 side, respectively, and a constant current of 5 A was applied. The results are shown in FIG. In addition, if a in Fig. 14 is 70000, then b
is the measured value in the case of 50,000, and c is the measured value in the case of 35,000, with the vertical axis representing the rate of change in output and the horizontal axis representing time. As shown in Fig. 15, the output change rate F (%) is the output voltage VR in a stable state in a rich atmosphere, the output voltage VL in a stable state in a lean atmosphere, and the output voltage VL in a stable state in a lean atmosphere, and the output voltage VL in a stable state in a lean atmosphere, and the output voltage VL in a stable state in a lean atmosphere, and the output voltage VL in a stable state in a lean atmosphere, as shown in Fig. 15. When the output voltage is V, it is expressed as F = Bisanshi X1oo (%), and as is clear from Fig. 14, the responsiveness of both the invention product a and the conventional products b and c decreases as the temperature increases. It is excellent.

In addition, in the case of the same temperature, the present invention product a and the conventional products b and c
There is a considerable difference in responsiveness between the two, and the effect of not using the insulating substrate 1 as in the conventional case is very large. Furthermore, even with the same conventional product, there is a considerable difference in response between b and c, and in the flat plate type shown in Figure 1, the flow of the gas to be detected is in the direction of arrow A. It is clear that good responsiveness cannot be obtained unless it is used. As described above, according to the present invention, since no structural base such as an insulating substrate is used, it is possible to obtain a very simple and compact product, and of course, it is possible to reduce the weight of parts. Due to its small heat capacity, it has excellent responsiveness, and can be used as well as conventional thermocouples even in tight installation spaces, making it extremely versatile, and eliminates anisotropy in performance. Since it is possible to do this, there is no problem of having to consider the mounting direction individually, and it has very excellent effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory vertical cross-sectional view of a conventional air-fuel ratio detection device, FIGS. 2 to 4 are schematic vertical cross-sectional views of an air-fuel ratio detection device in each embodiment of the present invention, and Figure 7 is an enlarged cross-sectional view of the oxygen sensor main body, an enlarged cross-sectional view of the oxygen sensor main body mounting part, and a partial cross-sectional view of the oxygen sensor mounting device, respectively, of an air-fuel ratio detection device in an experimental example of the present invention. Graphs showing the relationship between time and output voltage in each experimental example of the invention, FIGS. 10 and 11 are graphs showing the relationship between air-fuel ratio and output voltage, and FIGS. 12a and b
13A to 13E are cross-sectional explanatory views of the manufacturing process of the air-fuel ratio detection device and cross-sectional explanatory views of the oxygen sensor body, respectively, which are used in other experimental examples of the present invention. Explanatory diagram showing the manufacturing process of the oxygen sensor body, No. 14
Figures a, b, and c are graphs showing the relationship between time and the rate of change in output for the present invention and the conventional product, and Figure 15 is a graph showing the relationship between excess air ratio and output voltage to explain the rate of change in output. be. 12...Electron conductive wire, 13...Oxygen ion conductive solid electrolyte layer, 14...Electron conductive layer, 16...DC power supply device, 17...
・Voltage measurement device. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Boat Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15

Claims (1)

[Claims] 1. A gas-permeable oxygen ion conductive collective electrolyte layer is provided around an electron conductive wire made of a single substance or an alloy of Au, Ag, and platinum group elements, and is in direct contact with the electron conductive wire. , providing an electron conductive layer in direct contact with the solid electrolyte layer around the solid electrolyte layer, making the electron conductive layer contactable with the gas to be detected; An air-fuel ratio detection device characterized by comprising a voltage measurement device for detecting an electromotive force generated between the two. 2. The air-fuel ratio detection device according to claim 1, wherein the electron conductive layer is in the form of a film. 3 Claim 1 in which the electron conductive layer is coiled
The air-fuel ratio detection device described in . 4. The air-fuel ratio detection device according to claim 1, 2, or 3, comprising a DC power supply device that allows current to flow between the electron conductive wire and the electron conductive layer.