JP2000065783A - Explosion-proof type gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an explosion-proof type gas sensor capable of preventing the ignition of combustible gas or the propagation of a flame and capable of detecting a combustion gas with high accuracy over a wide concn. range. SOLUTION: A solid electrolyte type combustible gas sensor element 2 detecting the concn. of a combustible gas by measuring the amt. of oxygen after the combustible gas in the gas to be measured introduced from the introducing port 11 of the gas to be measured is reacted with oxygen is housed in the case 1 provided with the introducing port 11 of the gas to be measured. The temp. rise of the outer surface of the case l is prevented by the heat insulating members 41, 42, 43 arranged along the inner wall of the case l and an explosion-proof metal net 6 of a double metal net structure is provided so as to cover the introducing port 11 of the gas to be measured to prevent the propagation of a flame to the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can detect a combustible gas such as hydrogen, a hydrocarbon such as methane or propane, or a combustible gas such as carbon monoxide in a wide concentration range, and can detect heat or a flame due to combustion of the combustible gas. The present invention relates to a gas sensor having an explosion-proof structure for preventing leakage to the outside.

[0002]

2. Description of the Related Art Conventionally, as a sensor for detecting a combustible gas, for example, a contact combustion type gas sensor and a semiconductor type gas sensor are mainly used. The former has a platinum wire coil coated with a platinum catalyst together with an alumina carrier, has a sintered gas detection element, and contacts a combustible gas to its surface,
By detecting the temperature rise at the time of burning, the flammable gas concentration can be detected. In the latter, the concentration of the flammable gas is detected from the change in electric resistance when the flammable gas is adsorbed on the surface of the metal oxide semiconductor.

[0003] However, these conventional flammable gas sensors have the advantage that they can directly detect flammable gas, but have the problem that the detection concentration range is limited. For example, a contact combustion type gas sensor accurately detects a temperature rise below the lower explosion limit, but cannot detect a temperature rise properly when the flammable gas becomes high in concentration and enters the explosion range. Further, in a semiconductor gas sensor, since the amount of adsorption on the semiconductor surface is limited, the detection output decreases when the number of adsorption sites decreases as the concentration of combustible gas increases.

[0004]

On the other hand, there is a limiting current type oxygen sensor utilizing the oxygen ion conductivity of a zirconia solid electrolyte, and it is known that the oxygen concentration can be accurately detected in a wide concentration range. . Therefore, the application of this limiting current type oxygen sensor was examined to detect flammable gas from the residual oxygen concentration after oxidizing the flammable gas. However, in this method, the sensor element portion is
Usually, it is necessary to heat the sensor to several hundred degrees Celsius or more, so that the temperature on the outer surface of the sensor is likely to be high, and if the concentration is high, flammable gas may be ignited. Further, there is a possibility that the flame due to the ignition on the surface of the sensor element portion may leak out of the sensor.

Accordingly, the present invention provides an explosion-proof gas sensor capable of preventing the ignition of a combustible gas and the propagation of a flame, and capable of detecting the combustible gas with high accuracy in a wide concentration range. With the goal.

[0006]

In order to solve the above-mentioned problems, a gas sensor according to a first aspect of the present invention is introduced into a case provided with an inlet for a gas to be measured from the inlet for the gas to be measured. After reacting the flammable gas in the gas to be measured with oxygen, a flammable gas sensor element for detecting the flammable gas concentration by measuring the amount of oxygen is housed, and the inlet of the gas to be measured is provided. It is characterized in that a heat-resistant flame spread prevention member having a large number of ventilation holes is provided so as to cover.

When the flammable gas is ignited on the surface of the flammable gas sensor element, the flame tends to propagate to the outside of the sensor. It is blocked by the member and does not propagate further. Therefore, even if the flammable gas sensor element is heated to a high temperature of several hundred degrees Celsius or more, it can accurately and safely detect flammable gas in a wide concentration range while preventing ignition of flammable gas and diffusion of flame. can do.

According to a second aspect of the present invention, a heat insulating member is provided between the case and the combustible gas sensor element to prevent a temperature rise on the outer surface of the case. Depending on the position and configuration of the heater that heats the combustible gas sensor element, the temperature of the sensor outer surface may easily become high. In such a case, by disposing the heat insulating member between the case and the flammable gas sensor element, the temperature of the outer surface of the case is prevented from rising, and the ignition point of the flammable gas is not exceeded. can do. Thereby, the effect of preventing the ignition of the combustible gas and the diffusion of the flame can be enhanced.

According to a third aspect of the present invention, the flame propagation preventing member is made of a double wire mesh, porous ceramic or sintered metal. By using these, it is possible to prevent the propagation of the flame by removing heat due to the ignition of the combustible gas while securing the air permeability.

According to a fourth aspect of the present invention, there is provided a protection member for protecting the periphery of the flame propagation preventing member. Accordingly, when a force is applied to the sensor from the outside, the flame propagation preventing member can be prevented from being damaged, and the reliability is improved.

According to a fifth aspect of the present invention, the flammable gas is
Hydrogen, hydrocarbon, or carbon monoxide. The explosion-proof sensor according to the present invention is particularly effective in detecting these combustible gases, which have conventionally been difficult to detect in a wide range of concentrations.

According to a sixth aspect of the present invention, in the flammable gas sensor element, a pair of electrodes is formed on a surface of an oxygen ion conductive solid electrolyte, and one of the pair of electrodes is measured via diffusion resistance means. It has a limiting current type oxygen sensor structure exposed to the internal space where the gas is introduced, and detects the flammable gas concentration by measuring the oxygen concentration in the gas to be measured after the oxidation reaction of the flammable gas And

When a predetermined voltage is applied between the pair of electrodes, a limiting current flows according to the oxygen concentration in the internal space. At this time, if the gas to be measured contains a flammable gas, the residual oxygen concentration after the flammable gas has undergone an oxidation reaction will be detected, and the amount of change in the oxygen in the gas to be measured The flammable gas concentration can be detected. This oxygen sensor of the limiting current type has an oxygen concentration of approximately 0 to 100.
% Of the flammable gas can be detected in the atmosphere until oxygen containing about 20.9% is completely consumed in the atmosphere. And can be accurately detected.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall cross-sectional view of an explosion-proof gas sensor for detecting a combustible gas in a gas to be measured, for example, hydrogen, hydrocarbon, carbon monoxide, etc., and the lower end opening is an inlet 11 for the gas to be measured. It has a cylindrical case 1 and an elongated flat combustible gas sensor element 2 housed in the case 1. The case 1 is made of a material having resistance to the combustible gas to be detected, for example, stainless steel, and the lower half is inserted and arranged in the space where the gas to be measured exists. The case 1 has a screw portion for attachment formed on the outer periphery of a lower portion, and a cover body 3 having an atmosphere port 31 is covered at an upper end opening.

The middle part of the case 1 is filled with cylindrical heat insulating members 41 and 42.
The combustible gas sensor element 2 is inserted and held in the cylinder 42. A heat insulating member 43 having a predetermined thickness is also provided on the inner peripheral surface of the case 1 above the heat insulating member 42, and the heat insulating members 41 to 43 suppress a temperature rise on the outer surface of the case 1. . These heat insulating members 41 to 43
Can be usually made of porous ceramics represented by refractory bricks, for example, alumina. Also,
A gas seal material 5 is interposed between the heat insulating members 41 and 42 so that the gas to be measured introduced into the lower space of the case 1 does not leak to the upper space of the case 1. Usually, talc is suitably used as the gas seal material 5.

The heat insulating member is arranged as necessary so that the temperature of the outer surface of the case 1 is lower than the ignition point of the flammable gas. In the present embodiment, the heat insulating member is not provided on the inner peripheral surface of the lower end portion of the case 1 which is relatively close to the measured gas inlet 11 and is relatively easy to radiate heat, but depending on the type of combustible gas and the sensor shape. Alternatively, a configuration in which a heat insulating member is provided may be adopted. For example, in the case of hydrogen that is most easily ignited, the temperature rise limit of the outer surface of the case 1 is 320 ° C., and the installation site and the thickness of the heat insulating member may be appropriately changed so as not to exceed 320 ° C. The thickness of the heat insulating members 41 to 43 varies depending on the type of the flammable gas and the location of the flammable gas, but may be usually 1 mm or more.
Like the reference numerals 1 and 42, the portion that becomes the holding portion of the combustible gas sensor element 2 is formed to be slightly thicker.

An explosion-proof wire mesh 6 as a flame propagation preventing member is provided at the inlet 11 at the lower end of the case 1. The explosion-proof wire mesh 6 is hemispherical and has a double structure of, for example, a stainless steel (SUS316) wire mesh of 100 mesh or less. The heat of the flame tends to spread to the outside through the hole of the explosion-proof wire mesh 6 serving as an outlet. To prevent this, it is necessary to appropriately set the size and distance of the hole. here,
By making the explosion-proof wire mesh 6 100 mesh or less, it effectively deprives the heat energy of the flame, and by making it a double structure,
A space is formed between the inner and outer wire meshes to prevent the spread of the flame. Further, because of the double structure, even if the surface temperature of the inner wire mesh rises by removing heat, the temperature rise of the outer wire mesh is suppressed, and the outermost surface temperature can be maintained below the ignition point. . In order to prevent the explosion-proof wire mesh 6 from being damaged, the periphery of the explosion-proof wire mesh 6 is protected by a cylindrical protective member 7 extending from the lower end opening of the case 1.

The flame spread preventing member is not limited to the explosion proof wire mesh 6, but gas permeable porous ceramics or sintered metal can be used, and the same effect can be obtained.

As the flammable gas sensor element 2, an element having a limiting current type oxygen sensor structure utilizing oxygen ion conductivity of a solid electrolyte is preferably used. A lead wire 8 for extracting output is connected to the rear end of the combustible gas sensor element 2, and the lead wire 8 extends through the cover body 3 to the outside.

FIG. 2 shows such a combustible gas sensor element 2.
In the figure, a pair of electrodes 21a and 21b made of platinum or the like are formed on the upper and lower surfaces of a flat zirconia solid electrolyte 21 by screen printing or the like. The upper electrode 21a faces the internal space A formed in the spacer 22 laminated on the solid electrolyte 21. An insulating plate 23 made of alumina or the like is laminated on the spacer 22.
3 through a communication hole 23a as a diffusion resistance means.
The gas to be measured in the lower space of the case 1 of FIG. 1 is introduced into the internal space A. The upper surface of the communication hole 23a is covered with a protective film 24 made of porous alumina or the like.

The lower electrode 21b is connected to an air passage B formed in a spacer 25 laminated on the lower surface of the solid electrolyte 21.
Faces. The atmosphere passage B communicates with the upper space of the case 1 shown in FIG. Below the spacer 25, a substrate 26a made of alumina or the like is placed.
A heater section 26 is provided which includes a heater electrode 26b formed on the surface of the heater electrode 6a by screen printing or the like, and an insulating layer 26c of alumina or the like covering the heater electrode 26b.

The principle of detection of the combustible gas sensor element 2 having the above configuration will be described with reference to FIG. The gas to be measured is in communication hole 2
It is introduced into the internal space A through 3a and reaches the electrode 21a facing the internal space A. On the other hand, the electrode 21b
Faces the atmosphere passage B and is in contact with the atmosphere, which is a reference oxygen concentration gas. When a predetermined voltage is applied between the electrodes 21a and 21b, the solid electrolyte 21
A limiting current according to the oxygen concentration in the internal space A flows,
This makes it possible to know the oxygen concentration in the gas to be measured.

When a flammable gas is mixed into the gas to be measured, the flammable gas is oxidized at the electrode 21a and oxygen is consumed. Therefore, the detected oxygen concentration is determined after the flammable gas undergoes an oxidation reaction. Of the residual oxygen concentration. Therefore, by detecting the amount of change in oxygen at this time, the concentration of the combustible gas can be known.

When there is a possibility that the oxygen concentration in the gas to be measured changes, or when the gas to be measured contains a plurality of flammable gases, a plurality of electrodes having the above-described configuration in which a pair of electrodes are formed on the surface of the solid electrolyte are used. It is also possible to provide a sensor section and change the oxidizing activity of the electrode facing the internal space to compare the outputs of both sensor sections. For example, if one electrode is made to have a high oxidizing activity and the other electrode is made to be oxidatively inactive only for the flammable gas to be detected, the output difference between the two electrodes becomes the flammable gas to be detected. It depends only on the gas concentration, and the effects of other gases can be eliminated.

As described above, according to the above configuration, even if the flammable gas sensor element 2 is heated to several hundred degrees Celsius or more, the heat-insulating members 41 to 43 suppress the temperature rise on the outer surface of the sensor. 6, the propagation of the flame can be prevented, so that the concentration of the flammable gas can be measured safely and accurately.

FIG. 3 shows a second embodiment of the present invention. In the present embodiment, the shape of the protective member 7 is changed so that the lower end is closed and the cylindrical body covers not only the side surface but also the lower surface of the explosion-proof wire mesh 6. A plurality of ventilation holes 7 are provided on the side and bottom surfaces of the protection member 7.
1 is formed, and the gas to be measured is taken into the sensor from the vent 71. Other configurations are the same as those of the first embodiment. By doing so, the strength of the protection member 7 can be improved, and the effect of preventing the explosion-proof wire mesh 6 from being damaged can be enhanced.

FIG. 4 shows a third embodiment of the present invention. In each of the above embodiments, the combustible gas sensor element 2 having a configuration in which the plate-shaped solid electrolytes are laminated is used. However, as shown in FIG.
The flammable gas sensor element 2 using 7 can also be used. Hereinafter, the details of the present embodiment will be described focusing on the differences from the configurations of the above embodiments. In the present embodiment,
A cylindrical housing 1a having a mounting flange on the outer periphery as a case for housing the combustible gas sensor element 2
And a cylindrical case 1b fixed to the lower end thereof. Both the housing 1a and the cylindrical case 1b are made of a material having resistance to the combustible gas to be detected, for example, stainless steel.

The flammable gas sensor element 2 has an upper half held and fixed in a housing 1a via an insulating member 51, and a lower half protruding from the housing 1 to form a cylindrical case 1b.
Housed within. The cylindrical case 1b has a lower end opening serving as an inlet 11 for the gas to be measured. As shown in FIG. 4B, the inlet 11 is provided with an explosion-proof wire mesh 6 as a flame propagation preventing member. The explosion-proof wire mesh 6 has the same double wire mesh structure as that of the first embodiment, and also protects the periphery of the explosion-proof wire mesh 6 to prevent breakage, as in the case of the first embodiment. A cylindrical protection member 7 is provided extending from the lower end opening of FIG. 1 (FIG. 4A).

A lid 31 made of ceramics is provided so as to cover the upper end of the combustible gas sensor element 2, and the lower end of the lid 31 is fixed to the upper end opening of the housing 1. The outer periphery of the lid 31 is covered with a cylindrical metal cover 1 c, and the upper end opening of the metal cover 1 c is sealed with an insulating member 52. A cylindrical body 32 made of ceramic is disposed below the insulating member 52, and a lower end of the cylindrical body 32 and the lid 3
1 by means of a coil spring 9 disposed between
Are pressed downward.

The flammable gas sensor element 2 is composed of a zirconia solid electrolyte 27 formed in a test tube and electrodes 27a and 27b of platinum or the like provided near the inner and outer peripheral surfaces in the vicinity of the tip. A diffusion resistance layer (not shown) made of porous alumina or the like is formed on the outer surface of the solid electrolyte 27 as diffusion resistance means.
The gas to be measured that has passed through the diffusion resistance layer reaches 7b. In the hollow portion of the solid electrolyte 27,
The air introduced from a ventilation hole (not shown) provided in the metal cover 1c is guided through a ventilation path formed by a minute gap or the like formed between the members, and the air is introduced to the inner electrode 27a. It has become.

A heater 2 is provided in the hollow portion of the solid electrolyte 27.
8 are accommodated. The heating portion 28a of the heater 28 faces the electrodes 27a and 27b of the solid electrolyte 27.
The electrodes 27a and 27b are connected to lead wires 81 and 82 through leads (not shown) formed on the surface of the solid electrolyte 27a.
2 are connected to the terminals 8a and 8b held in the terminal 2. The heater 28 is connected to the terminal 8 held by the insulating member 52.
c.

The operation of the flammable gas sensor element 2 having the above-described configuration is the same as that of each of the above-described embodiments. In this embodiment, the same effect can be obtained by providing the explosion-proof wire mesh 6 and the protection member 7. In the configuration using the test tubular solid electrolyte 27 as in the present embodiment, the heater 28 is held in the hollow portion of the solid electrolyte 27 via an air layer, and the heat of the heater 28 is radiated to the outside. It is hard to be done. For this reason, the temperature of the sensor outer surface is unlikely to increase, and it is not always necessary to provide a heat insulating member between the sensor and the case as in the first and second embodiments.

FIG. 5 shows a fourth embodiment of the present invention. In the present embodiment, in the configuration of the third embodiment using the test tubular solid electrolyte 27, the shape of the protection member 7 is changed as in the second embodiment. That is, the protective member 7 is a cylindrical body having a closed lower end and covers the side and lower surfaces of the explosion-proof wire mesh 6 as shown in FIG.
A plurality of vents 71 are formed as in (a) and (b). Thereby, the strength of the protection member 7 is improved, and the effect of preventing the explosion-proof wire mesh 6 from being damaged can be enhanced.

It is needless to say that the gas sensor of the present invention is a gas sensor capable of measuring at least one of a rich atmosphere and a lean atmosphere in which the oxygen concentration in the gas to be measured after the oxidation reaction of the combustible gas is performed.

[Brief description of the drawings]

FIG. 1 is an overall sectional view of an explosion-proof gas sensor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part of the gas sensor according to the first embodiment.

FIG. 3 is an overall sectional view of an explosion-proof gas sensor according to a second embodiment of the present invention.

FIG. 4A is an overall sectional view of an explosion-proof gas sensor according to a third embodiment of the present invention, and FIG.
It is a principal part downward view of (a).

FIG. 5A is an overall sectional view of an explosion-proof gas sensor according to a fourth embodiment of the present invention, and FIG.
It is a principal part downward view of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 11 Gas inlet 2 Flammable gas sensor element 3 Cover body 41, 42, 43 Heat insulating member 5 Gas seal 6 Explosion-proof wire mesh (flame propagation preventing member) 7 Protecting member

Continued on the front page (72) Inventor Yoshimasa Kodama 14 Iwatani, Shimowasumi-cho, Nishio, Aichi Prefecture Inside Japan Automobile Parts Research Institute (72) Inventor Kazuhiko 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Japan Inside the Automotive Parts Research Institute (72) Inventor Susumu Ukita 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Masanori Iwase 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kazuo Toshima 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hidetaka Hayashi 1-1-1 Showa Town, Kariya City, Aichi Prefecture Inside DENSO Corporation

Claims (6)

[Claims] An amount of oxygen is measured after a combustible gas in a gas to be measured introduced from an inlet for the gas to be measured is reacted with oxygen in a case provided with an inlet for the gas to be measured. A heat-resistant flame propagation preventing member having a large number of ventilation holes is provided so as to cover a gas-injecting port for the gas to be measured, and to accommodate a combustible gas sensor element for detecting a combustible gas concentration. Explosion-proof gas sensor. 2. The explosion-proof gas sensor according to claim 1, further comprising a heat insulating member disposed between the case and the flammable gas sensor element to prevent a temperature rise on the outer surface of the case. 3. The explosion-proof gas sensor according to claim 1, wherein the flame propagation preventing member is made of a double wire mesh, a porous ceramic, or a sintered metal. 4. The explosion-proof gas sensor according to claim 1, further comprising a protection member for protecting a periphery of the flame propagation prevention member. 5. The explosion-proof gas sensor according to claim 1, wherein the combustible gas is hydrogen, hydrocarbon, or carbon monoxide. 6. The flammable gas sensor element has a pair of electrodes formed on a surface of an oxygen ion conductive solid electrolyte, and one of the pair of electrodes is supplied with a gas to be measured via diffusion resistance means. 4. A sensor according to claim 1, further comprising a limiting current type oxygen sensor structure exposed in the internal space, wherein the flammable gas concentration is detected by measuring the oxygen concentration in the gas to be measured after the oxidizable reaction of the flammable gas. 6. The explosion-proof gas sensor according to any one of 5.