JP6335518B2 - Gas sensor filter and gas sensor - Google Patents

Description

  The present invention relates to a gas sensor filter and a gas sensor.

  Conventionally, a catalytic combustion type CO sensor composed of a sensor element and a temperature compensation element has been proposed. In this CO sensor, the sensor element is coated with an oxidation catalyst on the heating resistor, and reacts with the carbon monoxide gas in contact to increase the resistance of the heating resistor in the sensor element. On the other hand, since the temperature compensation element includes a filter that selectively oxidizes carbon monoxide gas in an explosion-proof wire mesh provided around the temperature compensation element, the carbon monoxide gas is burned and removed by the filter, and the heating resistor in the temperature compensation element The resistance value of this will change only minutely. This CO sensor detects carbon monoxide gas based on such a change in resistance value (see Patent Document 1).

  A gas sensor having a sintered filter and a silicon trap filter provided for the sensor element has also been proposed. In this gas sensor, catalyst poisoning of the sensor element by a silicon compound is prevented by a silicon trap filter (see Patent Document 2).

JP-A-8-226908 JP 2004-20377 A

  However, the filters as described above (the filter of Patent Document 1 and the sintered filter of Patent Document 2) exhibit a filter function for a specific gas in a normal temperature and humidity environment. For this reason, there is a possibility that a sufficient filter function cannot be exhibited in a high temperature and high humidity environment. Therefore, it is conceivable to provide another filter as in the silicon trap filter described in Patent Document 2, but if a silicon trap filter is further provided, it only exhibits a filter function for silicon compounds. The filter function is not sufficient, and the sensor element is poisoned.

  In particular, in recent years, a demand for a low power consumption type sensor has been increased from the viewpoint of energy saving, and there has been a problem that the durability of the element itself decreases as the sensor element becomes smaller.

  The present invention has been made to solve such a conventional problem, and the object of the present invention is to prevent the sensor element from being poisoned more accurately and to use the sensor element even when a small element is used. An object of the present invention is to provide a gas sensor filter and a gas sensor capable of improving the durability of the gas sensor.

The gas sensor filter of the present invention is a gas sensor filter that covers at least a sensor element that covers a heating resistor with an oxidation catalyst and outputs a signal corresponding to the concentration of the gas to be detected. The sensor element is mounted thereon. A casing that covers the outer periphery of the sensor element together with a base and has an opening formed in a part thereof, and a silicone that is provided between the opening and the sensor element of the casing and is a poisoning target of the sensor element A filter part that adsorbs both a gas and a sulfur-based gas, the filter part comprising: a first filter part made of at least one of activated carbon, activated clay, mesoporous silica, alumina, and zeolite; and palladium or platinum. A second filter portion comprising any of a precious metal simple substance and a ceramic carrier carrying at least one of palladium and platinum , Have a, the first filter unit is characterized in that is provided to both the second the opening side and the opening opposite the filter portion.

According to this gas sensor filter, the first filter portion made of at least one of activated carbon, activated clay, mesoporous silica, alumina and zeolite, palladium or platinum noble metal alone, and ceramic supporting at least one of palladium and platinum. And a second filter portion made of any one of the carriers, so that both the silicone gas and the sulfur-based gas are adsorbed by the first filter portion in a normal temperature and normal humidity environment, and in a high temperature and high humidity environment. When the adsorption performance of both poisoning gases in the first filter unit is lowered, both poisoning gases are adsorbed by the second filter unit. For this reason, the sensor element will be protected from both poisoning gases in a normal temperature and normal humidity environment to a high temperature and high humidity environment, and when a small element is used to prevent catalyst poisoning of the sensor element more accurately. The durability of the sensor element can also be improved. Moreover, since a part of 1st filter part is provided in the opening part side rather than the 2nd filter part, both poison gas is first adsorbed by the 1st filter part, and the trace amount poison gas which was not able to adsorb | suck completely Will be adsorbed by the second filter portion. Thereby, the fall of the filter function in a high temperature, high humidity environment can be suppressed, and durability of a sensor element can be improved more.

  Moreover, the gas sensor of this invention is equipped with the filter for gas sensors as described in any one of said, and the said sensor element accommodated in the casing of the said filter for gas sensors, It is characterized by the above-mentioned.

  According to this gas sensor, since it is a gas sensor including the gas sensor filter and a sensor element housed in the casing of the gas sensor filter, even if a small sensor element is used, it is surely durable. It can be improved.

  According to the present invention, it is possible to provide a gas sensor filter and a gas sensor that can more accurately prevent catalyst poisoning of a sensor element and improve the durability of the sensor element even when a small element is used. .

It is a figure which shows the circuit model containing the gas sensor which concerns on embodiment of this invention. It is sectional drawing of the gas sensor which concerns on embodiment of this invention. It is sectional drawing of a sensor element. It is sectional drawing of the gas sensor which concerns on the 1st modification of this embodiment. It is sectional drawing of the gas sensor which concerns on the 2nd modification of this embodiment. It is sectional drawing of the gas sensor which concerns on the 3rd modification of this embodiment. It is a graph which shows the methane sensitivity deterioration rate of the gas sensor which concerns on a 1st modification, and the conventional gas sensor.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments. FIG. 1 is a diagram illustrating a circuit model including a gas sensor according to an embodiment of the present invention.

  As shown in FIG. 1, the gas sensor 1 according to the present embodiment has a sensor element F1 used as one element of a so-called catalytic combustion type gas sensor. This sensor element F1 is arranged on the first side E1 constituting the bridge circuit. A reference element F2 is arranged on the second side E2 connected in series to the first side E1, and the third and fourth sides E3 and E4 connected in parallel to the first side E1 are arranged. Are arranged with a first fixed resistor R1 and a second fixed resistor R2, respectively.

  The sensor element F1 is coated with an oxidation catalyst that burns a detection target gas (methane gas (CH4), propane gas (C3H8), butane (C4H10), etc.), and is heated by combustion heat that the detection target gas burns on the oxidation catalyst. A change occurs in the resistance value of the heating resistor. The reference element F2 is processed so that the detection target gas does not undergo catalytic combustion.

  When such a catalytic combustion type gas sensor is exposed to the detection target gas, the resistance value of the sensor element F1 changes according to the concentration of the detection target gas, while the resistance value of the reference element F2 does not change substantially. The potential difference signal generated between the elements F1 and F2 can be detected as a concentration signal of the detection target gas.

  FIG. 2 is a cross-sectional view of the gas sensor 1 according to the embodiment of the present invention. The gas sensor 1 includes a gas sensor filter 10 and a sensor element F1 accommodated in a casing of the gas sensor filter 10.

  FIG. 3 is a cross-sectional view showing the sensor element F1. As shown in FIG. 3, the sensor element F <b> 1 includes a heating resistor 101 patterned with platinum (Pt), and an oxidation catalyst 102 coated on the heating resistor 101 through a protective film, from the upper surface of the substrate 103. It is formed on the thin film diaphragm D straddling the formed recess 104. At both ends of the heating resistor 101, connection pad portions are formed integrally with the heating resistor 101, and the pad portions are bonded to the lead terminals 106 penetrating the stem 105 shown in FIG.

  The oxidation catalyst 102 is composed of a single noble metal such as palladium or platinum, or a ceramic support supporting at least one of palladium and platinum (several wt% to several tens wt%).

  The sensor filter 10 includes a casing 11, a filter portion 12, and a support member 13. The casing 11 covers the outer periphery of the sensor element F1 together with a stem (base) 105 on which the sensor element F1 is mounted, and an opening 11b is formed in a top plate (part) 11a facing the stem 105. Yes. The opening 11b is configured to have a plurality of air holes, for example. The stem 105 is also mounted with respect to the reference element F2. That is, the sensor filter 10 according to the present embodiment is configured to cover not only the sensor element F1 but also the reference element F2.

  The filter unit 12 is provided between the opening 11b of the casing 11 and the sensor element F1, and adsorbs both the silicone gas and the sulfur-based gas that are to be poisoned by the sensor element F1.

  Such a filter part 12 is comprised from the 1st filter part 12a and the 2nd filter part 12b, and all the 1st filter parts 12a are provided in the opening part 11b side rather than the 2nd filter part 12b. It has been.

  The first filter part 12a is composed of at least one of activated carbon, activated clay, mesoporous silica, alumina, and zeolite, and has good adsorption performance for both silicone gas and sulfur-based gas in a normal temperature and humidity environment. Is shown.

  The second filter portion 12b is composed of any of a noble metal simple substance of palladium or platinum and a ceramic support supporting at least one of palladium and platinum (several wt% to several tens wt%), and includes silicone gas and sulfur. It exhibits good adsorption performance under high temperature and high humidity environment for both system gases.

  The support member 13 is a member that supports the filter unit 12 from below the filter unit 12, and is configured by a wire mesh or the like.

  The gas sensor 1 may be configured as follows. 4-6 is sectional drawing of the gas sensor which concerns on the 1st-3rd modification of this embodiment. As shown in FIG. 4, the gas sensor 2 according to the first modified example has a three-layer structure in which the second filter portion 12b is sandwiched between the first filter portion 12a. For this reason, a part of the first filter part 12a is provided on the opening part 11b side with respect to the second filter part 12b, and the remaining part is provided on the stem 105 side with respect to the second filter part 12b. .

  As shown in FIG. 5, the gas sensor 3 according to the second modification has a two-layer structure in which the first filter portion 12a is provided closer to the stem 105 than the second filter portion 12b. Further, in the gas sensor 4 according to the third modification shown in FIG. 6, the first filter portion 12a and the second filter portion 12b are mixed to form one adsorption member.

  According to the gas sensors 1 to 4 according to the present embodiment and the respective modifications as described above, even if the silicone gas and the sulfur-based gas that are poisonous gases flow into the casing 11 together with the detection target gas from the opening 11b, In a normal temperature and humidity environment, the first filter portion 12a adsorbs the catalyst element and the progress of catalyst poisoning of the sensor element F1 is suppressed. On the other hand, in a high-temperature and high-humidity environment, silicone gas and sulfur-based gas are adsorbed by the second filter portion 12b. For this reason, the progress of catalyst poisoning of the sensor element F1 is suppressed even in a high temperature and high humidity environment. Furthermore, according to the present embodiment and the gas sensors 1 and 2 according to the first modification, all or a part of the first filter portion 12a is provided closer to the opening portion 11b than the second filter portion 12b. Both poisoning gases are first adsorbed by the first filter part 12a, and a trace amount of poisoning gas that could not be adsorbed is adsorbed by the second filter part 12b. Thereby, the fall of the filter function in a high temperature, high humidity environment can be suppressed.

  FIG. 7 is a graph showing the methane sensitivity deterioration rate between the gas sensor 2 according to the first modification and the conventional gas sensor. In FIG. 7, the gas sensor 2 according to the first modified example has a sensor element F1 having a size of about 0.1 mm and relatively low durability. Further, activated carbon was used for the first filter part 12a, and a ceramic carrier carrying platinum was used for the second filter part 12b. On the other hand, the gas sensor according to the related art is the same as the gas sensor 2 according to the first modification except that only activated carbon is used as a filter.

  As shown in FIG. 7, as a result of exposing a conventional gas sensor to a high temperature and high humidity environment (temperature 35 ° C., humidity 80%) for 450 days in an energized state, the methane sensitivity deteriorates by about 20% in 100 days, It deteriorated by more than 40% at 300 days. Furthermore, it deteriorated by about 50% at the time of 450 days.

  On the other hand, as a result of exposing the gas sensor 2 according to the first modified example to a high temperature and high humidity environment (temperature 35 ° C., humidity 80%) for 450 days in an energized state, the methane sensitivity exceeds about 10% in 100 days. Deteriorated and deteriorated by over 20% at 300 days. Furthermore, it deteriorated by about 25% at the time of 450 days.

  Thus, it was confirmed that the gas sensor 2 which concerns on a 1st modification has durability about 2 times compared with the conventional gas sensor.

  Thus, according to the gas sensor filter 10 according to the present embodiment, the first filter portion 12a made of at least one of activated carbon, activated clay, mesoporous silica, alumina, and zeolite, and a noble metal simple substance of palladium or platinum, And a second filter portion 12b made of any one of a ceramic carrier supporting at least one of palladium and platinum, so that the poison gas of both the silicone gas and the sulfur-based gas is removed from the first filter in a normal temperature and humidity environment. In addition to being adsorbed by the part 12a, both poisoning gases are adsorbed by the second filter part 12b when the adsorption performance of both poisoning gases of the first filter part 12a deteriorates in a high temperature and high humidity environment. For this reason, the sensor element F1 is protected from both poisoning gases in a normal temperature and normal humidity environment to a high temperature and high humidity environment, and more accurately prevents catalyst poisoning of the sensor element F1 and uses a small element. Even when the sensor element F1 is damaged, the durability of the sensor element F1 can be improved.

  Further, since all or part of the first filter portion 12a is provided closer to the opening than the second filter portion 12b, both poisoning gases are first adsorbed by the first filter portion 12a and cannot be completely adsorbed. A very small amount of poisoning gas is adsorbed by the second filter portion 12b. Thereby, the fall of the filter function in a high temperature, high humidity environment can be suppressed, and durability of the sensor element F1 can be improved more.

  Moreover, since the 1st filter part 12a and the 2nd filter part 12b are mixed and it is made into 1 adsorption | suction member, compared with the case where the 1st filter part 12a and the 2nd filter part 12b are comprised by another component. Thus, the number of parts can be reduced, and the number of man-hours for attaching the filter portion 12 to the casing 11 can be reduced.

  Furthermore, according to the gas sensors 1 to 4 according to the present embodiment, since the gas sensors 1 to 4 include the gas sensor filter 10 and the sensor element F1 housed in the casing 11 of the gas sensor filter 10, the gas sensors 1 to 4 are small. Even if the sensor element F1 is used, the durability can be reliably improved.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention. For example, in the present embodiment, the sensor filter 10 accommodates both the sensor element F1 and the reference element F2, but is not limited thereto, and may be configured to accommodate only the sensor element F1.

  Moreover, in the said embodiment, although the sensor element F1 is formed on the diaphragm D straddling the recessed part 104 formed from the upper surface of the board | substrate 103, a recessed part may be formed from the board | substrate lower surface side. Furthermore, the sensor element F1 is not limited to a small element formed on a substrate.

  The first filter portion 12a is not limited to any one of activated carbon, activated clay, mesoporous silica, alumina and zeolite, and may be composed of two or more, and the second filter portion 12b is also palladium. Or it is not restricted to any one of the noble metal single substance of platinum and the ceramic support body which carry | supported at least one of palladium and platinum, You may be comprised from 2 or more.

DESCRIPTION OF SYMBOLS 1-4 ... Gas sensor 10 ... Sensor filter 11 ... Casing 11a ... Top plate 11b ... Opening part 12 ... Filter part 12a ... 1st filter part 12b ... 2nd filter part 13 ... Support member 101 ... Heating resistor 102 ... Oxidation catalyst DESCRIPTION OF SYMBOLS 103 ... Board | substrate 104 ... Concave 105 ... Stem 106 ... Lead terminal 107 ... Wire D ... Thin film diaphragm F1 ... Sensor element F2 ... Reference element

Claims (2)

A gas sensor filter that covers at least a sensor element that coats an oxidation catalyst on a heating resistor and outputs a signal corresponding to the concentration of a gas to be detected,
A casing that covers the outer periphery of the sensor element together with a base on which the sensor element is mounted, and in which an opening is formed in part.
A filter unit that is provided between the opening of the casing and the sensor element and that adsorbs both the silicone gas and the sulfur-based gas that are to be poisoned by the sensor element;
The filter part includes a first filter part made of at least one of activated carbon, activated clay, mesoporous silica, alumina, and zeolite, a noble metal simple substance of palladium or platinum, and a ceramic carrier supporting at least one of palladium and platinum. possess a second filter section consisting of either a,
The gas filter according to claim 1, wherein the first filter part is provided on both the opening part side and the opening part opposite side of the second filter part . The gas sensor filter according to claim 1 ;
The sensor element housed in a casing of the gas sensor filter;
A gas sensor comprising:

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