JPS5810641A - Sensor for detecting combustion state - Google Patents

Abstract

PURPOSE:To allow a combustion state sensor to be independent of the change in temperature of exhaust gas, by providing on one surface of a heat-resistant insulating substrate a metallic oxide semiconductor to contact a gas to be inspected, while providing on the other surface a metallic oxide semiconductor to contact a reference gas. CONSTITUTION:A recess 2 is formed in one surface at the distal end of an aluminum heat-resistant insulating substrate 1 and filled with semiconductor 3 of a metallic oxide, such as SnO2, TiO2 or the like, to form a detecting element. In this case, it is desirable to mix into the semiconductor 3 a substance having the same thermal expansion coeffcient as that of the substrate l1 in order to prevent failure of the semiconductor 3. In addition, a recess 1 is formed also in the other surface of the substrate 1 and filled with a semiconductor 12 having resistance temperature characteristics corresponding to those of the above-mentioned semiconductor 3 to form a compensating element. Then thus constituted sensor is mounted in a combustion chamber or an exhaust pipe so that the semiconductor 3 will contact a gas to be inspected, while the semiconductor 12 will contact a reference gas. Thereby, the change in resistance value of the semiconductor 3 is compensated by the change in resistance value of the semiconductor 12 to detect a combustion state independently of the change in temperature of the exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a combustion state detection sensor that utilizes the fact that the resistance value of a metal oxide semiconductor changes depending on the gas composition of the surrounding atmosphere. More specifically, the temperature dependence of the resistance value of the metal oxide semiconductor is compensated for, and the combustion state can be accurately detected even when the temperature of the atmospheric gas changes.

A combustion state detection sensor is attached to a combustion chamber or an exhaust pipe of an internal combustion engine or combustion equipment to detect the composition of exhaust gas or the like. High temperature exhaust gas or the like is used to heat the sensor. However, the temperature of exhaust gas and the like is not constant. Furthermore, the resistance value of the semiconductor used in the sensor also changes depending on the temperature. For this reason, detection accuracy decreases due to temperature changes in the exhaust gas and the like.

This invention compensates for the temperature coefficient of resistance of the semiconductor, thereby eliminating the influence of temperature changes from exhaust gas, etc.
It is an object of the present invention to provide a sensor capable of accurately detecting combustion conditions.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Figures 1 to 3 show the most basic embodiment of the present invention, with Figure 1 showing its front view and showing the first surface and detection element of the sensor. Figure 2 is its rear view, showing the second side of the sensor and the compensation element;
FIG. 3 is a sectional view taken along the line AA in FIG. 1.

First, the first aspect and the detection and output elements will be explained.

f1+ is a heat-resistant insulating substrate made of alumina as a base, and a first depression (2) is provided at the tip thereof. A first metal oxide semiconductor (3) is filled and housed inside the recess (2). The metal oxide semiconductor (3) includes Sn
O2, TlO2, Fe201, Z n01MgFe2O
4, Co2O, etc. can be widely used. Furthermore, due to the difference in thermal expansion between the semiconductor (3) and the substrate m, the semiconductor (
In order to avoid damage to the semiconductor (3), a substance having the same coefficient of thermal expansion as the substrate is mixed into the semiconductor (3), so that the coefficient of thermal expansion is lower than that of the substrate (1).
) is desirable. In order to improve the sensitivity of the semiconductor (3) to gas and speed up the response, the semiconductor (:1
), add a noble metal catalyst such as ruthenium oxide or rhodium. A porous catalyst layer (4) is provided on the surface of the semiconductor (3). The porous catalyst layer (4) includes:
A heat-resistant catalyst carrier such as alumina or phosphoric acid supported on palladium or platinum is used. The catalyst layer (4) is provided in order to remove poisonous components in the combustion gas, such as sulfur content, by adsorbing them to a carrier such as alumina, and to remove unreacted components in the combustion gas by burning them. It is. The semiconductor (3) has a first pair of electrodes (5a) made of a noble metal wire such as a platinum wire or a platinum-rhodium alloy wire.
, (5b) are buried and detect the resistance value of the semiconductor (3).

In this way, the semiconductor (3) and the electrodes (5a), (5b
) constitute a detection element.

(6a) and (6b) are a pair of first grooves provided in the substrate (1), and the noble metal wires used for the electrodes (5a) and (5b) are housed at the bottom of the screen, and a dense inorganic adhesive is used. Protect the precious metal wire by filling it with a chemical agent. The ends of the noble metal wires are welded to a first pair of metal rods (7a) and (7b) housed in through holes provided in the substrate, and transmit the resistance value of the detection element to the outside.

Next, the second aspect and the compensation element will be explained. The l river is a second recess provided in the substrate DJ opposite to the first recess (2), and the second semiconductor (12) is filled and accommodated therein. A second pair of electrodes (18a) and (18b) made of a pair of noble metal wires are embedded in the semiconductor 02) to constitute a compensation element. The second semiconductor (12) may have a resistance temperature characteristic that is almost the same as the first semiconductor (3), but it is better to use the same material as the first semiconductor (3). . Further, it is desirable that the distance between the first recessed portion (2) and the second recessed portion 110g be as thin as possible. A pair of second grooves (14a) and (14b) accommodate the noble metal wires used for the second pair of electrodes (18a) and (18b), and are protected by a dense inorganic adhesive. (15a) and (15b) are a second pair of metal rods,
It is fixed to the substrate i11 and connected to the second noble metal wire to transmit the resistance value of the compensation element to the outside.

(16a) and (16b) are through holes for fixing the substrate tl) to the outside by bolts and nuts.

In addition, in this example, there are two recesses (2) in the substrate H.
, 111) are provided to accommodate the detection element and the compensation element, however, the semiconductor may be formed in a layer on the substrate +1) without providing the recess. In this case, the thickness of the substrate +1+ is
Since this is the distance between the two elements, the substrate should be made thinner and the temperature of the two elements should be made the same.

Further, in this embodiment, the two elements are provided facing each other, but they may be provided offset within a range where the heating temperature of each element can be maintained equally. Further, the catalyst layer (4) may not be provided.

Next, the functions of this embodiment will be explained.

The sensor is attached to the combustion chamber or exhaust pipe so that the first surface of the sensor is in contact with the test gas and the second surface is in contact with the reference gas. Here, as the gas to be tested, the gas being combusted in the combustion chamber or the exhaust gas after combustion is used. Further, as the reference gas, ambient air is desirable, but other gases may be used as long as the composition is constant. When an internal combustion engine or combustion equipment is operated, the sensor comes into contact with high-temperature exhaust gas and heats up to its operating temperature. The composition of the gas to be detected is detected by the resistance value of the first semiconductor (3) in the detection element. Since the sensor is heated by the high-temperature test gas, the temperature of the sensor fluctuates irregularly. Furthermore, the temperature dependence of the resistance value of semiconductors is extremely complicated.

For this reason, the resistance value of the semiconductor (3) in the detection element also varies in a complicated manner.

A compensation element is used to compensate for the resistance temperature dependence of the detection element. Since the compensation element is provided facing the detection element, their temperatures are approximately equal. Although the resistance temperature dependence of semiconductors is complicated, it is easy to make the temperature dependencies of two semiconductors equal. The compensation element therefore makes it possible to accurately compensate for the temperature dependence of the detection element.

4 and 5 illustrate other embodiments,
FIG. 4 is an axial sectional view thereof, and FIG. 5 is a left side side view based on FIG. 4.

In the figure, (1) is a cylindrical base with a bottom, the outer circumferential surface of which is the first surface, and the inner cylindrical surface thereof which is the second surface. Substrate (
A recessed portion 12υ is provided near the tip of the outer circumferential surface of 1), and the first semiconductor (a) is filled and housed inside the recessed portion 12υ. The semiconductor (a) has a pair of noble metal wires (28a),
(28b) (only (28a) is shown as a perspective view),
is buried as an electrode, and the semiconductor and electrode constitute a detection element. The other part of the precious metal wire (23a) is embedded in a pair of grooves (only one of which is shown as (24a) in a perspective view) with a dense inorganic adhesive, and the tip of the precious metal wire is exposed to the outside. The resistance value of the detection element is transmitted to the outside.

A second semiconductor (E) is placed at the tip of the inner cylindrical portion of the base f1+.
A pair of noble metal wires (26a) and (26b) are connected to form a compensation element. The depth of the inner cylindrical portion of the base (1) is adjusted so that the first semiconductor wire and the second semiconductor (c) face each other with the base in between. A pair of protective tubes (27a) and (27b) are provided in the inner cylindrical portion of the base body +11 to accommodate noble metal wires (26a) and (26b). Further, a flange (c) with a threaded portion is provided at the bottom of the base fl l so that the sensor can be attached to a combustion chamber or the like.

In addition, in this example, the materials of semiconductors (a) and (c),
The materials of the electrode wires (28a), (26a), and (26b) are the same as those in the embodiments shown in FIGS. 1 to 3, so their explanations are omitted.

The effects of this invention will be explained below.

FIG. 6 shows an example of a detection circuit suitable for the sensor of the present invention. In the figure, SI) is a detection element, (ψ is a compensation element, and (to) is an amplifier. It is driven by the output of the engine, and is used to stop combustion and control the air-fuel ratio.

FIG. 7 shows an example of the sensor of the present invention attached to a wick type kerosene stove. 141 in the figure)
(6) is the stove body, (6) is its oil tank, (2) is the wick, (2) is the primary combustion chamber with many small through holes, and (2) is the secondary combustion chamber. The sensor (47) is attached to the upper part of the inner wall of the primary combustion chamber. Alternatively, the sensor η may be attached to the outer wall of the primary combustion chamber, and the combustion gas may come into contact with the sensor 17) through the small through hole (2). For cell/cell 1'I), those of the embodiments shown in FIGS. 1 to 8 were used. In this case,
Both the detection element and the compensation element are made of 50% by weight of 0.5% by weight of ruthenium oxide and 49.5% by weight of stannic oxide.
The catalyst layer (4) was removed and tested. (G) is a mixer, which consists of an impeller-like swirler and two plates with many through holes arranged one after the other, and the concentration distribution of the gas composition in the direction perpendicular to the flow path of the combustion gas. This is something that cannot be solved.

The fuel evaporated from the wick burns while mixing with air supplied from a through hole (c) provided in the wall of the primary combustion chamber, and combustion is completed in the secondary combustion chamber. In this case, when the indoor oxygen concentration decreases, a large amount of CO is generated as shown by curve B in FIG. This mechanism can be thought of as follows. During normal combustion, there is some unreacted fuel in the combustion chamber, but its concentration is low and almost constant, so the resistance value of the sensor θ is also almost constant. On the other hand, when the indoor oxygen concentration decreases, the concentrations of dO and H2 increase together with unreacted fuel. The resistance value of the sensor 17) changes depending on each of these components. Since the concentration ratio of each of these components is unknown and only CO is a harmful gas, the following explanation will focus on CO. At this time, the temperature of the sensor 1 force also drops rapidly, as shown by curve C in FIG. These are caused by the following process. When the indoor oxygen concentration decreases, incomplete combustion occurs,
-The temperature of the fire combustion chamber (b) decreases. Air is introduced through the through hole (c) due to the negative pressure associated with combustion, so
- When the temperature of the secondary combustion chamber decreases, the amount of air supplied through the through holes also decreases. - When the temperature in the secondary combustion chamber decreases, the amount of evaporation from the wick also decreases. At this time, since the amount of air supplied is also decreasing, incomplete combustion is not resolved and the temperature in the secondary combustion chamber further decreases.

In this way, the temperature of the sensor @η changes as the combustion state changes, so the resistance value of the detection element changes in a complicated manner as shown by the curved line in FIG. In other words, when the indoor oxygen concentration decreases from 21% to 17.8%, 800%
Even though Co of approximately PPm is generated, its resistance value increases. This is because the sensor is more affected by the temperature drop than by the change in atmosphere due to the generation of CO. As the indoor oxygen concentration further decreases, the resistance value of the sensor @ also decreases, but the resistance value at an indoor oxygen concentration of 16.7% and the resistance value at an indoor oxygen concentration of 21% become equal, and the indoor oxygen concentration becomes 16.5%. %, the resistance value decreases enough to be detectable.

On the other hand, curve E in FIG. 9 shows the result of the present invention in which the resistance value of the detection element is compensated by the resistance value of the compensation element. In this case, the detection circuit shown in FIG. 6 was used, and the circuit power supply was set to 0.7 volts. It can be seen that the output of the circuit rises from an indoor oxygen concentration of about 19%, and the combustion state can be detected without being affected by the temperature change of sensor 0.

In this test example, the sensor 1't) was installed in the upper part of the primary combustion chamber 1, but it may be installed in another position. However, in the vicinity of the core, there is a large amount of unreacted fuel in the atmosphere, which becomes a gas that interferes with CO detection, and the ambient temperature is too low to heat up the carbon dioxide sufficiently. do not have.

In the above explanation, an example was taken of a wick-type oil stove in which the temperature of exhaust gas changes depending on changes in the amount of oxygen supplied.
The present invention can be suitably implemented in any internal combustion engine or combustion device in which the temperature of exhaust gas or the like changes irregularly during combustion.

[Brief explanation of the drawing]

1 to 8 show a first embodiment of the present invention, and FIG.
The figure is a front view showing the first surface and the detection element, FIG. 2 is a rear view showing the second surface and the compensation element, and FIG.
It is a sectional view in the ' direction. 4 and 5 show an embodiment of a cormorant. FIG. 4 is an axial sectional view with a partially transparent view, and FIG. 5 is a left side view based on FIG. 4. FIG. 6 shows an example of a detection circuit using the sensor of the present invention.
FIG. 7 shows an example of a kerosene stove using the sensor of the present invention. FIG. 8 shows the relationship between the indoor oxygen concentration, the amount of CO generated, and the sensor in the kerosene stove of FIG. 7, and FIG. 9 shows the detection results of the kerosene stove of FIG. 7. (11...substrate, (3), 4...first semiconductor, (1 (c)...second semiconductor. 1ml 2aa 3s 4th figure 5m 6th figure 7 figure

Claims (1)

[Claims] 1. A heat-resistant insulating substrate is provided with a first surface in contact with the test gas and a second surface in contact with the reference gas; (2) the first surface is provided with a gas (3) A detection element with a pair of electrodes connected is provided to the first metal oxide semiconductor whose resistance value changes depending on the temperature of the first metal oxide semiconductor; a second metal oxide semiconductor having
A combustion state detection sensor characterized by having a compensation element connected to a pair of electrodes. 2. The combustion state detection sensor as set forth in claim 1, wherein the heat-resistant insulating substrate has a flat plate shape, and its front and back surfaces are respectively a first surface and a second surface. . 3. The combustion according to claim 1, wherein the heat-resistant insulating substrate has a cylindrical shape with a bottom, and the outer circumferential surface thereof is the first surface, and the inner cylindrical surface thereof is the second surface. Sensor for status detection.