JP4575846B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor placed in a high humidity environment.

  In general, a solid polymer membrane fuel cell is formed by sandwiching both sides of a solid polymer electrolyte membrane between a fuel electrode and an oxygen electrode to form a single cell, and a plurality of single cells are stacked to form one fuel cell stack. Yes. The fuel electrode is supplied with hydrogen as a fuel, the oxygen electrode is supplied with air as an oxidant, and hydrogen ions generated by a catalytic reaction at the fuel electrode pass through the solid polymer electrolyte membrane and pass through the oxygen electrode. The hydrogen ions and oxygen cause an electrochemical reaction to generate electricity.

  In such a solid polymer membrane fuel cell, conventionally, a hydrogen detector (gas sensor) is provided in the discharge system on the oxygen electrode side of the fuel cell, and the hydrogen on the fuel electrode side is removed from the solid polymer electrolyte membrane by this hydrogen detector. There is known a technique for detecting leakage to the oxygen electrode side through (see Patent Document 1). Specifically, in this technology, the hydrogen intake port (gas flow part) of the hydrogen detector is directed downward in the vertical direction, and the hydrogen detector is provided on the upper wall of the exhaust pipe. The structure is such that light hydrogen can be taken into the hydrogen detector well. In addition, in such a technology, by providing a water repellent filter at the hydrogen intake port, water droplets in the gas are removed by the water repellent filter before high-humidity gas enters the hydrogen detector to detect hydrogen. It is also considered to prevent water droplets from adhering to the gas detection element in the vessel.

JP2003-294675A (paragraphs 0008 to 0010, FIG. 4)

  However, in the above-described technique, in a state where the water vapor contained in the high-humidity gas has not yet become water droplets, the water vapor passes through the water-repellent filter, and thus the water vapor enters the hydrogen detector. When the gas detection element enters and the surroundings are in a low temperature state, there is a problem that water vapor is condensed around the gas detection element. And if water vapor adheres to the gas detection element due to the dew condensation around the gas detection element in this way, there is a possibility of affecting the subsequent sensing.

  Accordingly, an object of the present invention is to provide a gas sensor that can suppress condensation around the gas detection element.

The invention according to claim 1 of the present invention that solves the above problems includes a gas detection element that detects a gas to be detected contained in a gas, an element storage portion that stores the gas detection element, and the element storage portion. A gas sensor provided on a wall of the flow path with the gas flow part facing the inside of the flow path through which the gas flows. A communication passage is provided for communicating the element housing portion with a low humidity region having a lower humidity than in the flow path, and the gas introduced into the element housing portion from the gas flow portion is It is discharged to the low humidity region through a passage .

  According to the first aspect of the present invention, since the communication path that communicates the inside of the element housing portion with the low humidity region where the humidity is lower than that in the flow path is provided, the high humidity is provided from the gas flow portion to the inside of the element housing portion. Even if the gas enters, moisture (water) in the gas is released to the low humidity region through the communication path. Therefore, dew condensation around the gas detection element in the element housing portion can be suppressed.

  The invention described in claim 2 is the gas sensor according to claim 1, wherein the low humidity region is a region connected to the atmosphere.

According to the second aspect of the present invention, for example, when the outside of the flow path is the atmosphere, it is possible to dehumidify the inside of the element housing portion simply by providing the communication path so as to pass from the inside of the element housing portion to the outer surface of the gas sensor. Therefore, the structure becomes simple and the manufacturing cost can be reduced. According to the third aspect of the present invention, by providing the water repellent filter in the communication path, the entry of water from the outside into the element housing portion is suppressed.

  According to the first aspect of the present invention, by providing the communication path that allows the inside of the element housing portion to communicate with the low humidity region, moisture in the high-humidity gas that has entered the element housing portion from the gas flow portion communicates. Since it is discharged to the low humidity region through the passage, dew condensation around the gas detection element in the element housing portion can be suppressed.

According to the second aspect of the present invention, for example, when the outside of the flow path is the atmosphere, it is possible to dehumidify the inside of the element housing portion simply by providing the communication path so as to pass from the inside of the element housing portion to the outer surface of the gas sensor. Therefore, the structure becomes simple and the manufacturing cost can be reduced. According to the invention described in claim 3, by providing the water repellent filter in the communication path, it is possible to suppress water from entering the element housing portion from the outside.

[First Embodiment]
Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the drawings to be referred to, FIG. 1 is a schematic configuration diagram showing a fuel cell system provided with a hydrogen sensor according to the first embodiment.

  As shown in FIG. 1, a hydrogen sensor (gas sensor) 1 according to the first embodiment is incorporated in a fuel cell system S in order to detect hydrogen in air off-gas discharged from the fuel cell 2. . Hereinafter, the fuel cell system S will be briefly described, and then the details of the hydrogen sensor 1 will be described.

The fuel cell system S mainly includes a fuel cell 2, an inlet side pipe 3 and an outlet side pipe 5 on the fuel electrode (anode) side, and an inlet side pipe 4 and an outlet side pipe 6 on the oxygen electrode (cathode) side. Yes.
The fuel cell 2 includes a single cell (not shown) in which an electrolyte membrane electrode structure in which a solid polymer electrolyte membrane made of, for example, a cation exchange membrane is sandwiched between a fuel electrode and an oxygen electrode is further sandwiched between a pair of separators. It consists of a stack composed of a large number of sets.

In this fuel cell 2, for example, hydrogen is supplied to the fuel electrode as a fuel via a fuel supply side inlet side pipe 3 from a hydrogen supply device (not shown) including a high-pressure hydrogen tank or the like, and an oxygen electrode is supplied by a compressor 21. Air is supplied to the oxygen electrode as an oxidant through the side inlet side pipe 4. On the catalyst electrode of the fuel electrode, hydrogen is ionized by the catalytic reaction, and the generated hydrogen ion passes through the appropriately polymerized solid polymer electrolyte membrane and moves to the oxygen electrode. Then, electrons generated during this period are taken out to an external circuit and used as direct current electric energy. Since oxygen-containing air is supplied to the oxygen electrode, hydrogen ions, electrons, and oxygen react electrochemically by the action of the catalyst of the oxygen electrode to generate water. .
Then, so-called off-gas containing unreacted reaction gas (for example, hydrogen or air) is discharged from the outlet side pipe 5 on the fuel electrode side and the outlet side pipe (flow channel) 6 on the oxygen electrode side.

Here, the hydrogen off-gas (anode off-gas) containing unreacted hydrogen is discharged from the outlet side pipe 5 on the fuel electrode side of the fuel cell 2 to the hydrogen circulation path 22 and through the ejector 23 to the inlet side pipe on the fuel electrode side. 3 is supplied to the fuel electrode of the fuel cell 2 again.
On the other hand, the air off gas (cathode off gas) containing a large amount of moisture in the reacted air is discharged to the atmosphere through the diluter 26 and the outlet side pipe 6.

Further, a hydrogen discharge path 25 is connected to the outlet side pipe 5 on the fuel electrode side of the fuel cell 2 via a purge valve 24, and a diluter 26 is connected to the hydrogen discharge path 25. The hydrogen off-gas can be discharged to the hydrogen discharge path 25 via the purge valve 24 and can be introduced to the diluter 26 through the hydrogen discharge path 25.
The diluter 26 is configured to dilute the hydrogen off gas taken from the hydrogen discharge passage 25 with an appropriate magnification by the air off gas discharged from the fuel cell 2 and discharge it as a diluted gas.
A gas catalytic combustion type hydrogen sensor 1 is disposed downstream of the diluter 26, and the hydrogen concentration of the diluted gas is monitored by this. Here, the hydrogen sensor 1 is arranged at the upper part in the vertical direction of the outlet side pipe 6 arranged so that the flow direction of the air off gas is the horizontal direction.

  Next, details of the hydrogen sensor 1 will be described with reference to FIGS. 2 and 3. In the drawings to be referred to, FIG. 2 is a cross-sectional view showing the inside of the hydrogen sensor according to the first embodiment.

  As shown in FIG. 2, the hydrogen sensor 1 includes a rectangular parallelepiped case 30 in which a control board CB is incorporated. The case 30 is made of, for example, polyphenylene sulfide, and includes flange portions 31 at both ends in the longitudinal direction. A collar 32 is attached to the flange portion 31, and a bolt 33 is inserted into the collar 32, so that the flange portion 31 is attached to an outlet seat (flow path) 6 on the oxygen electrode side. (Wall) It is fastened and fixed to 6a.

  A gas detection element 50 and a heater 60 connected to the control board CB are provided on the lower end surface of the case 30, and a bottomed cylindrical element receiving portion 34 for receiving these protrudes downward. It is provided as follows. Further, the case 30 has a communication path 80 that communicates the inside of the element accommodating portion 34 and the outside (atmosphere; a low humidity region where the humidity is lower than that in the outlet side pipe 6) from the lower end surface of the case 30 to the upper end surface. It is provided so that it may penetrate.

  The gas detection element 50 detects hydrogen (a gas to be detected) contained in the dilution gas (gas). Specifically, the gas detection element 50 is arranged on the front side of the figure and on the back side thereof. The temperature compensation element 52 is configured as a pair. The detection element 51 is a well-known element, and is formed by coating a coil of metal wire containing platinum or the like having a high temperature coefficient with respect to electric resistance with a carrier such as alumina carrying a catalyst. The catalyst is made of a noble metal active against hydrogen. The temperature compensation element 52 is inactive with respect to hydrogen, and is formed, for example, by coating the surface of a coil equivalent to the detection element 51 with a carrier such as alumina.

  When the detection element 51 becomes hot due to the reaction heat generated when hydrogen comes into contact with the catalyst, a difference occurs in the resistance value between the detection element 51 and the temperature compensation element 52, so that the hydrogen concentration can be detected from this difference. It can be done. Note that the change in electrical resistance value due to the ambient temperature is offset by using the temperature compensation element 52.

  The heater 60 heats the inside of the element accommodating portion 34 (hereinafter, this internal space is also referred to as “gas detection chamber R”), and thereby, the occurrence of condensation in the gas detection element 50 is suppressed.

  The element accommodating portion 34 is fitted into a through hole 6 c formed in the outlet side pipe 6, and is formed so that the lower surface of the bottom wall 34 c is flush with the inner surface 6 b of the outlet side pipe 6. ing. The bottom wall 34c is provided with a gas flow portion 70 so that the diluent gas is taken into the gas detection chamber R from the gas flow portion 70 that faces the outlet side pipe 6. It has become.

  The gas flow part 70 includes an opening 71 formed on the bottom wall 34 c of the element housing part 34, a water repellent filter 72 provided on the opening 71, and an explosion-proof filter 73 provided on the water repellent filter 72. And is configured. Thereby, water contained in the wet dilution gas is repelled by the water repellent filter 72 so as not to enter the gas detection chamber R, and explosion-proof property is also ensured.

  In addition, a predetermined groove 34b is formed in the circumferential wall 34a of the element housing portion 34 along the circumferential direction, and a seal member 35 is provided in the groove 34b. Thereby, when the hydrogen sensor 1 is attached to the outlet side pipe 6, the seal member 35 is brought into close contact with the inner peripheral surface of the through hole 6 c of the outlet side pipe 6 and the groove 34 b of the element accommodating portion 34. Ensuring airtightness between.

  The communication path 80 is a cylindrical pipe formed in a straight line, and is arranged such that its axial direction is along the vertical direction. The communication path 80 has one end opened in the gas detection chamber R and the other end opened to the outside, and the gas flow section 70 described above is formed in the opening on the other end side. A water repellent filter 82 and an explosion proof filter 83 similar to the water repellent filter 72 and the explosion proof filter 73 are provided. This prevents water from entering the gas detection chamber R from the outside.

Next, the operation of the hydrogen sensor 1 will be described.
As shown in FIG. 2, the high-humidity diluted gas flowing in the outlet side pipe 6 enters the gas detection chamber R from the gas flow part 70. And the high-humidity diluted gas that has entered the gas detection chamber R in this way does not stay in the gas detection chamber R for a long time due to the dilution gas that newly enters the gas detection chamber R. It will be pushed out through the communication path 80. Further, when the flow of the dilution gas disappears in the outlet side pipe 6 (for example, when the fuel cell 2 is stopped), the high-humidity dilution gas may remain in the gas detection chamber R. Even in this case, moisture (moisture) in the dilution gas is released into the atmosphere having low humidity via the communication path 80.

According to the above, the following effects can be obtained in the first embodiment.
Since moisture in the dilution gas in the gas detection chamber R is released into the atmosphere via the communication path 80, dew condensation around the gas detection element 50 in the gas detection chamber R can be suppressed.

The present invention is not limited to the first embodiment, and can be implemented in various forms.
In the first embodiment, the communication path 80 is formed in a linear shape, but the present invention is not limited to this, and may be formed in, for example, a curved shape or a shape bent multiple times.

[Second Embodiment]
The second embodiment of the present invention will be described below. Since this embodiment is obtained by partially changing the structure of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. In the drawings to be referred to, FIG. 3 is a cross-sectional view showing the inside of the hydrogen sensor according to the second embodiment, and FIG. 4 is a cross-sectional view taken along line AA of FIG.

As shown in FIG. 3, the hydrogen sensor 1 ′ according to the second embodiment includes an element housing portion 37 having a shape different from that of the first embodiment.
The element accommodating portion 37 has a shape and structure similar to that of the element accommodating portion 34 of the first embodiment, while the portion fitted to the outlet side piping 6 is an upper portion (outside the outlet side piping 6). And a lower portion (portion protruding into the outlet side pipe 6) are different from each other. Specifically, as shown in FIG. 4, a substantially cylindrical communication passage 90 that protrudes substantially horizontally toward the outside is formed in the upper peripheral wall 37 a of the element housing portion 37. A water repellent filter 82 and an explosion proof filter 83 similar to those in the first embodiment are provided in the opening on the front end side of the communication path 90. The case 30 is appropriately formed with an escape portion for accommodating the upper portion including the communication passage 90 of the element accommodating portion 37.

  Moreover, the peripheral wall 37a of the lower part of the element accommodating portion 37 is formed in a tapered shape that inclines inward as it goes downward. As a result, the cross-sectional area of the element accommodating portion 37 in a plane orthogonal to the flow direction of the dilution gas becomes smaller than that in the case where the element housing portion 37 is not formed in a tapered shape. It is like that. Further, as shown in FIG. 3, the inclined peripheral wall 37a of the element accommodating portion 37 is similar to the first embodiment in the upstream portion and the downstream portion (positions overlapping when viewed from the flow direction) in the flow direction of the dilution gas. Are provided one by one.

  Further, a drain hole 37d for discharging water liquefied in the gas detection chamber R to the outside is provided at an appropriate position on the bottom wall 37c of the element housing portion 37, and water is passed through the drain hole 37d. The same explosion-proof filter 73 as that of the first embodiment is provided. Further, a drainage channel 36 is provided in the lower part of the drainage hole 37d, and the drainage hole 36 is formed so that the lower part of the drainage channel 36 is bent toward the downstream side in the flow direction of the dilution gas. The dilution gas is prevented from entering the gas detection chamber R from 37d. Incidentally, since the element housing portion 37 protrudes from the inner surface 6 b of the outlet side pipe 6, the cross-sectional area of the outlet side pipe 6 at that portion is reduced, and therefore the flow rate of the dilution gas flowing below the element housing portion 37. Therefore, the discharge of water from the drain hole 37d is promoted by the action of the negative pressure.

According to the above, the following effects can be obtained in the second embodiment.
Since the opening of the communication passage 90 faces substantially in the horizontal direction, even if water adheres to the water repellent filter 82 provided in the opening, water can be removed from the water repellent filter 82 by gravity, so that the water is repelled by the water repellent filter 82. It is possible to suppress the water repellent filter 82 from being clogged up.
Since the inside of the gas detection chamber R communicates with the outside through the lateral communication passage 90, a through hole is formed in the control board CB compared to the structure in which the communication passage is communicated through the vertical communication passage 80 according to the first embodiment. There is no need. That is, since it is not necessary to make the control board CB into a special shape, the manufacturing cost can be reduced.

  Since the two gas flow portions 70 are provided so as to overlap each other when viewed from the flow direction of the dilution gas, the dilution gas smoothly passes through the element housing portion 37. Can be suppressed, and the element housing portion 37 protruding from the inner surface 6b of the outlet side pipe 6 can be prevented from becoming resistant to the flow of the dilution gas as much as possible.

By providing the gas flow part 70 on the peripheral wall 37a of the element housing part 37, even if the water liquefied in the gas detection chamber R adheres to the gas flow part 70, it flows downward due to gravity, and the gas flow part Accumulation at 70 is suppressed. Therefore, clogging of the gas flow part 70 (water repellent filter 72) can be suppressed.
Since the element accommodating portion 37 is provided with the drain hole 37d and the drainage channel 36 bent to the downstream side, the water accumulated inside can be drained well.

  By tilting the peripheral wall 37a of the element accommodating portion 37, the cross-sectional area of the element accommodating portion 37 (the surface directly exposed to the dilution gas) in the plane orthogonal to the flow of the dilution gas is reduced. Resistance to the gas flow can be suppressed as much as possible. In addition, as a result, the air off-gas discharged from the fuel cell 2 flows out smoothly, so that it is possible to suppress the energy consumption of the air supply.

The present invention is not limited to the second embodiment, and can be implemented in various forms.
In the second embodiment, the opening at the front end of the communication path 90 is oriented substantially horizontally, but the present invention is not limited to this. For example, the front end of the communication path 90 is projected downward from the side wall of the outlet side pipe 6. The opening may be directed downward by bending it into a circle. According to this, similarly to the second embodiment, even if water adheres to the water repellent filter 82 provided at the opening of the communication passage 90 from the outside, the water can be removed by gravity.

  In the second embodiment, the entire lower half of the element accommodating portion 37 is formed in a tapered shape (conical frustum shape). However, the present invention is not limited to this, and at least the side portion of the element accommodating portion 37 (the dilution gas) It is sufficient that only the portion that lies directly beside the flow is tilted.

  Further, in the second embodiment having a structure having a drain hole 37d, a substance having a small specific heat such as a metal may be provided in the element housing portion 37 so as to positively condense with the substance. As a specific example of this structure, as shown in FIG. 5, a metal plate M1 is provided on the inner surface of the peripheral wall 37a of the element housing portion 37, and a metal plate M2 having a drain hole M21 is provided on the bottom wall 37c. Just do it. Specifically, a position at which the water droplet W condensed on the surface of the metal plate M1 provided above the gas flow part 70 can reach only the peripheral wall 37a to the bottom wall 37c (the condensed water droplet W is a gas). The metal plate M <b> 2 may be disposed below the gas flow part 70. According to this, dew condensation around the gas flow part 70 is suppressed, and it is also possible to prevent water condensed by the metal plates M1 and M2 from adhering to the gas flow part 70.

Further, the present invention is not limited to the above-described two embodiments (first and second embodiments), and can be implemented in various forms.
In the above embodiment, the gas to be detected is hydrogen, but the present invention is not limited to this, and may be another gas such as carbon monoxide or hydrogen sulfide. Furthermore, in the above-described embodiment, the contact combustion type gas sensor is adopted as the gas sensor. However, the present invention may be any gas sensor provided with a gas detection chamber. For example, other types such as a semiconductor type gas sensor may be used. It may be a gas sensor.

  In the above embodiment, the gas detection chamber R communicates with the atmosphere via the communication passages 80 and 90. However, the present invention is not limited to this, and may be in a low humidity region where the humidity is lower than that in the outlet side pipe 6. You can communicate anywhere. Specifically, for example, a humidifier for connecting the outlet of the communication path into a pipe upstream of the compressor 21 shown in FIG. 1 or humidifying dry air supplied from the compressor 21 to the fuel cell 2. You may connect the exit of a communicating path to the moisture supply side. However, in the said embodiment, since the exit of the communicating paths 80 and 90 is only open | released to air | atmosphere, the structure can be simplified.

  In the embodiment described above, a cylindrical pipe-shaped passage is used as the communication path. However, the present invention is not limited to this. For example, when the gas detection chamber R and the outside are separated by a single wall, it is formed on the wall. Such holes may be used as communication paths. Further, when the communication path is constituted by piping, it is not necessary to be cylindrical as in the above-described embodiment, and any shape may be used as long as it is cylindrical.

It is a schematic structure figure showing a fuel cell system provided with a hydrogen sensor concerning a 1st embodiment. It is sectional drawing which shows the inside of the hydrogen sensor which concerns on 1st Embodiment. It is sectional drawing which shows the inside of the hydrogen sensor which concerns on 2nd Embodiment. It is AA sectional drawing of FIG. It is sectional drawing which shows the modification of 2nd Embodiment.

Explanation of symbols

1,1 'Hydrogen sensor (gas sensor)
6 Outlet piping (flow path)
6a Mounting seat (wall)
6b Inner surface 34, 37 Element housing part 50 Gas detection element 70 Gas flow part 71 Opening part 72 Water repellent filter 73 Explosion-proof filter 80,90 Communication path 82 Water-repellent filter 83 Explosion-proof filter R Gas detection chamber

Claims (3)

A gas detection element for detecting a gas to be detected contained in the gas;
An element accommodating portion for accommodating the gas detecting element;
A gas flow part for flowing the gas into and out of the element housing part,
A gas sensor provided on a wall of the flow path with the gas flow portion facing the flow path through which the gas flows,
A communication path is provided that communicates the element accommodating portion with a low humidity region that has a lower humidity than in the flow path .
The gas sensor, wherein the gas introduced into the element housing portion from the gas flow portion is released to the low humidity region through the communication path .   The gas sensor according to claim 1, wherein the low humidity region is a region connected to the atmosphere. The gas sensor according to claim 1, wherein a water repellent filter is provided in the communication path.

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