JPS58746A - Gaseous component detector - Google Patents

Abstract

PURPOSE:To detect an air-fuel ratio with high accuracy without having any influence of the temperature of waste gas, by using a gaseous component detection element made of a transition metallic oxide and carrying a catalyst on this detection element. CONSTITUTION:The first and the second lead wires 8 and 9 are inserted into a lower holding body 2 and an upper holding body 5 of a housing 1 and electrodes 10 and 11 are connected to the tip ends of the wires 8 and 9. A gaseous component detection element 13 made of a transition metallic oxide such as titanium oxide etc. is provided between the electrodes 10 and 11 and a catalyst 14 such as platinum is stuck to its surface. On occasion of detecting the gas, characteristic for an air-fuel ratio of an electric resistance value of the element 13 is varied suddently by the action of the catalyst 14 bordering on some air-fuel ratio and accordingly, the detection is carried out with high accuracy without making compensation for a temperature of waste gas by decreasing a detection error of the air-fuel ratio in very small. Also, a response property is improved by the catalyst 14 even when the temperature is low.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for detecting 0.00. A gas component detector that can detect changes in the concentration of components such as (oxygen), 00 (-carbon oxide), and HC (hydrocarbons) as changes in the overall atmosphere with good responsiveness, especially for internal combustion engine exhaust gas. It is.

Gas component detectors are generally widely used, but in recent years,
In connection with exhaust gas countermeasures for internal combustion engines, it has come to be used as a means for detecting the air-fuel ratio of the air-fuel mixture used for combustion in the internal combustion engine.

In other words, when using a catalyst for exhaust gas purification, for example, as a countermeasure against exhaust gas from an internal combustion engine, it is necessary to ensure that the catalyst performs its maximum function (although it is necessary to always maintain the air-fuel ratio of the air-fuel mixture at an appropriate value). In the case of a carburetor in a normal engine or an injection device in a fuel injection type engine, even if the air-fuel ratio of the air-fuel mixture is set to be constant, the welfare air-fuel ratio actually changes significantly. In order to maintain this, it is necessary to detect the actual air-fuel ratio by some method and feed that signal back to the carburetor or injection device.

However, in contrast to detecting the air-fuel ratio using a gas component detector, this gas component detector directly uses the fact that changes in the concentration of each exhaust gas component are closely related to the air-fuel ratio of the air-fuel mixture to detect the air-fuel ratio. Detects fuel ratio. In this case, as is well known, the temperature of the exhaust gas and the concentration of gas components change rapidly and significantly, and therefore, an accurate detector that takes this point into account is desired.

Conventionally, the air-fuel ratio of internal combustion engines has been detected using a solid electrolyte such as zirconia, which acts as an oxygen concentration battery.
This is done by detecting changes in electromotive force, or by using transition metal oxides and detecting changes in their electrical resistance.

However, in the former method, ion conduction in the solid electrolyte occurs due to the movement of ions through thermal vibrations in ion defects existing in the interstitial space, and therefore an electromotive force is generated. Therefore, when the temperature of the solid electrolyte is as low as 400° C. or lower, no electromotive force is generated, and therefore, the response is significantly reduced when starting an internal combustion engine with a low exhaust gas temperature.

On the other hand, in the latter method, the 171st! ! ! Since the slope of the characteristic curve is gentler than that of the former method, this method has the disadvantage that the accuracy is extremely low when attempting to detect the air-fuel ratio at a certain point. Furthermore, since the electrical resistance value also changes depending on the exhaust gas temperature, it is not possible to control an arbitrary air-fuel ratio without temperature compensation, and temperature compensation causes a delay in response.

The present invention uses a gas component detection element made of the latter 11-transfer metal oxide, and by supporting a catalyst on this gas component detection element, the required air-fuel ratio can be determined accurately without being affected by the temperature of the detected gas. The purpose is to detect.

Further, the present invention provides an electrode for detecting changes in electrical resistance of the gas component detection element, a lead wire is electrically connected to this electrode, a terminal is electrically connected to this lead wire, and these lead wires are electrically connected to a terminal. By inserting and fixing the terminal into the through hole of the electrically insulating holder and fixing the mounting housing to the outside of this holder, it is easy to attach and detach the gas to be detected from the wall that separates it from the outside world. The purpose is to simplify the electrical connection for operation.

A first embodiment in which the gas component detector of the present invention is used as means for detecting the air-fuel ratio of an internal combustion engine will be described below. In FIGS. 1, 2, and 8, l is a housing made of metal with good electrical conductivity, and has a threaded portion 1m and a tightening portion 1b for attachment to an exhaust pipe of an internal combustion engine, etc.
has. The lower end of the housing l is made of electrically insulating ceramic.

A lower holding body 2 is housed in a disc-like shape having a tapered portion 2a at the lower end, and this lower holding body 2 has a packing waffle Vya 8 interposed between the upper mm and the housing 1, and has a tapered portion 2a. A metal ring 4 having good electrical conductivity is interposed between the portion 2a and the lower end of the housing 1, and the lower end of the housing 1 is fixed by heat caulking inward. Further, at the upper end of the housing 1, an upper holder 5 made of electrically insulating ceramic and having a cylindrical shape and a tapered part 5a at the upper end is provided, like the lower holder 2, with a packing washer between it and the housing 1. 6 and metal ring 7
It is heat caulked with a

The lower holding body 2 and the upper holding body 5 each have two through holes 2b, 2c, 5b, and 5c in the axial direction, and one through hole 2b of the lower holding body 2 and the upper holding body 5, respectively. , 5b, the first lead 818 is connected to the through hole 2 of the lower holder 2 and the upper holder 5, respectively.
The second lead wires 9 are inserted into the C+ 50 respectively. Each of the IJ-domains 8 and 9 is made of a heat-resistant metal with good electrical conductivity, such as 8U842 or Inconel 600 (trade name).

The lower holder 2 has a thin film-like first electrode IO in a portion corresponding to one of the through holes 2b on its lower end surface, and a thin film-like first electrode IO in a portion corresponding to the other through hole 2C. A second electrode 11 is provided respectively. The electrodes 10, 11 are arranged by depositing a metal having excellent heat and corrosion resistance, such as gold (MUR) or platinum (Pt), on the surface of the lower holder 2 by vacuum deposition, sputtering, or the like. And the above-mentioned 1. The second electrodes 10 and 114 are the first and second electrodes 10 and 114, respectively. It is connected to the second lead wires 8 and 9 by a method such as thermal caulking and plasma welding. Reference numeral 18 denotes a gas component detection element made of a thin film of transfer gold jlN fluoride. The surface of the gas component detection element 18 is coated with platinum (pt), paddillam (
A catalyst 14 such as Pd) or rhodium (Rh) is attached and supported. How to attach the catalyst 14 For example, if the gas component detection element 18 is a thin film, the catalyst 14 is attached to the gas component detection element 13 by a method such as vacuum deposition. On the other hand, if the gas component detection element 18 is a sintered body as described later, it is impregnated in, for example, chloroplatinate (H!PtCl4.6n,o), reduced and fired in a hydrogen stream, and Pt is is attached to the gas component detection element 13. However, the catalyst 14 is the first one. It must not be deposited on the gas component detection element 13 in such a large amount that electrical continuity occurs between the second electrodes 10 and 11. Thus, the gas component detection element 13 is disposed on the lower end surface of the lower holder 2 between the first and second electrodes 10 and 11.
゜They are electrically connected to the second electrodes 10 and 11, respectively. As a transition metal oxide, titanium oxide (Tie)
, nickel oxide (Nip), cobal oxide) (Cod
), manganese oxide (MnO), zinc (ZmO), copper oxide (C!uO), chimi oxide (T iOz ),
The gas component detection element 18 is arranged on the lower end surface of the lower holder 2 by selecting an appropriate transition metal oxide from among these oxides, and applying a method such as vacuum evaporation or electron beam evaporation to the lower end surface of the lower holder 2. This is done by attaching a thin film with a thickness of 100 μm to 1 (11 μm) to the top of the upper holding body 6. are also formed quite large, and tubular first and second terminals 16.1 are provided in these portions, respectively.
6 is for storage.

1st. Second terminal 15.160 lower j! # is provided with boxwood 15 & 11681 respectively. Second terminal 15.
16 is held in each of the through holes 5b and 5c of the upper holding body by rings 17, 18 and K which are press-fitted above the boxwoods 15al and 16&, respectively, and is connected to the boxwoods 15m and 16m and the rings 17 and 18 and the upper part. The spaces formed by the through holes 5b and 5c of the holder 5 are filled and fixed with glass seals 19, ff1ot, etc., respectively.

Then, the first O lead I18 is inserted into the first terminal lb, and its upper end is welded to the upper end of the first terminal 1M, and
The second glue i19#i is inserted into the second terminal 16, and its upper end is welded to the upper end of the second terminal 16. In addition,
21 is a gasket.

The operation of the above configuration will be explained. The gas component detector housing 1 having the above structure is attached to the exhaust pipe of an internal combustion engine, so that the gas component detection element 18 is exposed to exhaust gas. Exhaust gas is well known (): and <, OHrNOit
,,00. H.C.H.

CO,,N! The concentration line of each component varies depending on the air-fuel ratio of the mixture before combustion. The transition metal oxide constituting the gas component detection element 18 is mainly affected by the concentration or partial pressure of o, co, nc, a, etc. among the above gas components, and moreover, The resistance value corresponds to the change in the overall atmosphere caused by the change rather than the change in resistance.

However, in the present invention, since the catalyst 14 is attached to the surface of the gas component detection element 18α on the side exposed to gas components, the reactivity to gas components such as O, CO, H(!, H, etc.) is reduced. 01 around the gas component detection element 18.
It is possible to increase the characteristic that the electrical resistance value of the gas component detection element 18 changes due to a change in partial pressure, and to obtain a rapid change in electrical resistance in response to a change in partial pressure. The reason for this is thought to be as follows. That is, if 01 and combustible gas components such as CjO, HC, H, etc. are present near the surface of the transition metal oxide on the side exposed to the gas components, the action of the catalyst 14 K L
”) Teco-1-1/20.-CO,,HC+IO
,→F e Ox 1”* 0 * Hz +-!-o
z ”m o etc. O anti-R5b = occurs. However, when the air-fuel ratio of the mixture before combustion is richer than the stoichiometric air-fuel ratio, all of the gas components 08 are subjected to reactions such as co and nc, and - (mona >co, nc company remains, so it is inferred that almost no Ol exists on the surface of the gas component detection element 18 due to the above reaction.On the other hand, the air-fuel ratio of the air-fuel mixture before combustion is lower than the stoichiometric air-fuel ratio. On the thin side, even if O2 is subjected to reaction with the combustible gas component, 0! still remains, so it is inferred that a large amount of OI exists on the surface of the gas component detection element 18.

In other words, it is understood that there are only two possible conditions on the surface of the gas component detection element 13: 08 exists or not. It is thought that due to the action of the catalyst 14, the electrical resistance value of the I-sulfur component detection element 18 changes rapidly at or near the air-fuel ratio afMe.

Figure 1O shows the results of measuring changes in electrical resistance when using the gas component detector having the above configuration (in which TELO1, which is an N-type semiconductor, is used as the gas component detection element 13). As can be seen, the electrical resistance value of the gas component detection element 18 changes rapidly around the stoichiometric air-fuel ratio.The vertical axis of the figure shows the electrical resistance value (KΩ) of the detection element 18.
is expressed on a logarithmic scale, and the air-fuel ratio (mu/F) is expressed on an equal scale on the horizontal axis. - In this Figure 1O, if the detection level of the gas is set at an exhaust gas temperature of 400°C, if the electrical resistance value of the gas component detection element 13 is larger than the detection level, air-fuel combustion (lean mixture) occurs; If the resistance value is smaller than the detection level, it can be determined that the air-fuel ratio is low (rich mixture). Therefore, the air-fuel ratio (gas component) can be detected near the stoichiometric air-fuel ratio point, and the air-fuel ratio is controlled based on this. be able to. Furthermore, it can be seen from FIG. 10 that if the detection level is set accurately, compensation for the exhaust gas temperature is not necessary. Therefore, it is extremely convenient for automatic exhaust gas O air-fuel ratio control, which has large temperature reversals depending on operating conditions.

Here, two gas component detectors having the structures shown in FIGS. 1 to 8 were prepared. The catalyst 14 is attached to one side, and the catalyst 14 is not attached to the other side.

The internal combustion engine exhaust gas temperature δ of these two gas component detectors
The first characteristic of the electrical resistance value with respect to the air-fuel ratio at OO℃ is
Shown in Figure 1. In addition, as the gas component detection element 18, Tie,
was used. In FIG. 11, it is assumed that the air-fuel ratio is controlled at a predetermined detection level. In this case, the electrical resistance value detected by the detector will vary from A1 due to the overall delay such as the response of the detection circuit and the delay until the exhaust gas whose air-fuel ratio has changed due to feedback to the internal combustion engine reaches the detector. It is thought to take a value between Maro. For this reason, when looking at the air-fuel ratio, an error occurs in the detected air-fuel ratio of the BL glass in the conventional detector (Pi) to which the catalyst 14 is not attached. In addition, the detector with the catalyst 14 attached←) is also Hatake! Although an error occurs in the detected air-fuel ratio of al, it can be seen that the error range is small. Further examining this result shows that the smaller the slope of the characteristic curve of the electrical resistance value of the detector versus the air-fuel ratio, the smaller the error in the detected air-fuel ratio. Therefore, it can be seen that if the catalyst 14 is not provided, the slope of the characteristic curve described above will be large, the detected air-fuel ratio O error will be large, and the system is not suitable for controlling a desired air-fuel ratio at a certain point.

In particular, it is necessary to keep the error in the air-fuel ratio within a certain range due to the purification performance of the catalytic converter, and from this point of view as well, it is desirable that the error in the detected air-fuel ratio be small.

By the way, as mentioned above, the catalyst 14 is attached to the surface of the gas component detection element 18, and when gas components such as O2 and CO, O, and He react with each other due to the action of this catalyst 140, reaction heat is generated. This reaction heat causes the surface temperature of the I-sulfur component detection element 180 to rise! Therefore, even when the exhaust gas temperature is low, such as when starting the internal combustion engine, the responsiveness of the gas component detection element 18 is improved.

In addition, 1. FIG. 16 shows the relationship between the position of the second electrode 10.11 on the gas component detection element 13 and the response time of a change in electrical resistance with respect to a change in gas component concentration. As can be seen from FIG. 16, f! of the gas component detection element 13 on the surface of the gas component detection element 18 exposed to the gas component or in the vicinity of this surface as in this embodiment. E
By locating the Kth 1.1g2 voltage [jlO, 11, it is possible to speed up the response time of the electrical resistance value change of the gas component detection element 18 in response to a change in the gas component concentration.

4 and 5, a TiO,O sintered body which is a transition metal oxide is used as the gas component detection element 13, and first and second electrodes are placed on the surface of the sintered body. 10.
This shows a second embodiment in which a catalyst 14 such as Pt is attached so that 11 is not electrically conductive, and the other structure is the same as the first embodiment.

FIG. 6 shows a first example in which a TiO□O sintered body, which is a transition metal oxide, is used as the gas component detection element 18, and the change in electrical resistance of the gas component detection element 13 is extracted. Second electrode 10
．． 11 is embedded several microns inside the surface of the detection element 18 exposed to the gas component, and furthermore, the surface of the gas component detection element 13 exposed to the gas component [the present invention with a catalyst 14 such as Pt attached] is embedded. This shows the third embodiment, and the other structure is the same as the above-mentioned 11j! Same as the example. According to this eighth embodiment, the first. Since the second electrode 10, 1lti is embedded inside the gas component detection element 18, impurities in the gas (for example, carbon, etc.) may adhere to the surface of the gas component detection element 18 on the side exposed to the gas components. But first. Second
Electrode 10. lluThe impurities will not have an adverse effect.0 Also, as is clear from FIG. Second
Merely embedding the electrodes 10 and 11 does not increase the response time of the electrical resistance value change of the gas component detection element 13.

7vli and FIG. 8 are the fourth embodiment of the present invention corresponding to the first embodiment and the second embodiment, respectively. Fifth! l! This example shows an example in which # is applied to the surface of the gas component detection element 18 which is made of a 2'h t Oz thin film or sintered body of transition metal oxide and is exposed to the gas component.
In order to prevent impurities in the gas from adhering, the surface of the gas component detection element 13 is coated with a coating material 80 (for example, gamma alumina) that is electrically insulating and has pores large enough to allow gas to pass through, so as to cover the catalyst 14 as well. It is attached to.

FIG. 9 shows a gas component detection element 18 using a sintered body of Tie, which is a transition metal oxide, as a gas component detection element 18.
A first electric current [10] is attached to the surface of f9 exposed to the gas component, and the change in electrical resistance of the gas component detection element 130 is measured by the first electrode.
a lead wire 8 that is electrically connected and conductive to the electrode 10;
This shows a sixth embodiment of the present invention in which the second electric current fi 111 is taken out between the howling l which is electrically connected via the metal ring 4, and the other structure is as follows. This is the same as the first embodiment.

Next, in the gas component detector having the structure of the gth embodiment, ZnO is used as the gas component detection element 18.

8+aO mushroom, Niobium oxide (NbsOs),
1211 to 15 show the characteristics of the electrical resistance value of the gas component detection element 13 with respect to the air-fuel ratio and temperature when NiO and NiO are used, respectively. As is clear from Figures 12 to 16, the electrical resistance value changes rapidly near the stoichiometric air-fuel ratio, and the electrical resistance value does not change depending on the exhaust gas temperature near the stoichiometric air-fuel ratio. Recognize.

In the first to sixth embodiments described above, the catalyst 14 is attached to the surface of the gas component detection element 18 on the side exposed to the gas component; however, the present invention is not limited to this; The catalyst 14 may be dispersed inside the detection element 18. In this case, the leads [8, 9 or the first . It is necessary to prevent the second electrodes 10.11 from shorting each other.

As detailed above, in the present invention, since a catalyst is supported on the gas component detection element made of a transition metal oxide, the effect of the catalyst causes the electric resistance value of the gas component detection element to have a certain air-fuel ratio. Therefore, the detection error of the desired air-fuel ratio is extremely small, and the desired air-fuel ratio can be detected with high accuracy. Furthermore, this can be done without being affected by the temperature O of the detection gas.

Further, the present invention provides an electrode for detecting changes in electrical resistance of the gas component detection element, a lead wire is electrically connected to the electrode, a terminal is electrically connected to the lead wire, and a terminal is electrically connected to the lead wire, and a terminal is electrically connected to the lead wire. By inserting and fixing the wires and terminals into the through holes of the electrically insulating holder, and fixing the mounting housing to the outside of this holder, it is easy to attach and detach the detected gas from the wall that separates it from the outside world. The electrical connections for operation of this detector are simple.

[Brief explanation of the drawing]

1st v! J is a cross-sectional front view showing the first embodiment of the gas component detector according to the present invention; ! Figure 1 is a cross-sectional front view showing in detail the vicinity of the gas component detection element of the illustrated detector of the present invention, Figure 3 is a bottom view of Figure 2, and Figure 4 is a view of the second embodiment of the detector of the present invention. A cross-sectional front view showing the vicinity of the gas component detection element in detail;
FIG. 5 is a bottom view of FIG. 4, and FIG. 6 is a bottom view of the detector of the present invention.
7g is a sectional front view showing in detail the vicinity of the gas component detection element of the fourth embodiment of the present invention detector; FIG. 8 is a sectional front view showing the vicinity of the gas component detection element of the fourth embodiment of the present invention; FIG. Figure 11!9 is a cross-sectional front view showing in detail the vicinity of the gas component detection element of the fifth embodiment of the detector, and Figure 11!9 is a cross-sectional front view showing the vicinity of the gas component detection element of the sixth embodiment of the detector of the present invention in detail. , FIG. 1O is provided for explanation of the present invention, and FIG. , Tei0. Figures 12 to 15 are characteristic diagrams of electrical resistance versus air-fuel ratio, comparing gas component detection elements with and without a catalyst attached.
The figure shows ZnO as the gas component detection element in the detector of the second embodiment. 8 m O,, N b, 0. , Characteristic diagram of electrical resistance value versus air-fuel ratio when using N i O, 16th
The figure serves to explain the present invention, and shows the relationship between the response time of the electrical resistance value and the depth of the electrode from the surface of the gas component detection element. FIG. 3 is a characteristic diagram showing output changes with respect to a ZrO□ element, which is a solid electrolyte, and an O air-fuel ratio. l...Housing, 5...Holding body, 8, 9...Lead wire, 10.11--Electrode, 18...Gas component detection element, 14--Catalyst, 15.16--Terminal . Representative Patent Attorney Osamu Okabe @1 Figure 2 Figure 93 Figure 4 Figure 6 Figure 5 Figure 5 1417/I Naoga ■ 7th Figure 8 Figure 9 Figure 10 Figure 1 1-(Al/ F) The 110th is a comparison (A/F) The 12th figure is sophistry (lyF) The 13th figure is the electric mome field yoko) The 14th figure is the comparison (fear) The 15th figure is the I! ! Hiroo (masu) Figure 16

Claims (1)

[Claims] A gas component detection element made of a transition metal oxide that exhibits an electrical resistance value depending on the gas component, a catalyst supported on the gas component detection element, an electrode for detecting changes in electrical resistance of the gas component detection element, and the electrode. a lead wire electrically connected to the lead wire, a terminal electrically connected to the lead wire, an electrically insulating holder having a through hole into which the lead wire and the terminal are inserted and fixed, and an outside of the holder. A gas component detector comprising: a mounting housing fixed to a mounting housing;