JP4571002B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor such as a catalytic combustion type hydrogen sensor mounted on a fuel cell vehicle.

Conventionally, for example, a polymer electrolyte fuel cell is a stack formed by laminating a plurality of cells to a cell formed by sandwiching a polymer electrolyte membrane between a fuel electrode and an oxygen electrode from both sides (hereinafter referred to as a stack). (Referred to as a fuel cell), hydrogen is supplied to the fuel electrode as fuel, air is supplied to the oxygen electrode as oxidant, and hydrogen ions generated by a catalytic reaction at the fuel electrode are converted into a solid polymer electrolyte membrane. It passes through to the oxygen electrode and generates electricity by causing an electrochemical reaction with oxygen at the oxygen electrode.
In such a fuel cell such as a solid polymer membrane fuel cell, conventionally, for example, a hydrogen detector (gas sensor) is provided in the discharge system on the oxygen electrode side of the fuel cell, and hydrogen on the fuel electrode side is provided by this hydrogen detector. A protection device that shuts off the supply of fuel when it is detected that leakage has occurred to the oxygen electrode side through the solid polymer electrolyte membrane is known (see, for example, Patent Document 1).
The hydrogen detector includes a pair of a gas detection element made of a catalyst such as platinum and a temperature compensation element, for example, and the gas detection element is relatively moved by heat generated by combustion when hydrogen comes into contact with the catalyst such as platinum. Gas contact combustion type that detects the concentration of hydrogen gas according to the difference in electrical resistance that occurs between the temperature compensation element in a relatively low temperature state, such as under ambient temperature, for example There are known hydrogen detectors.
JP-A-6-223850

By the way, in a fuel cell such as the above-described solid polymer membrane fuel cell, in order to maintain the ionic conductivity of the solid polymer electrolyte membrane, a reaction gas (for example, hydrogen or air) supplied to the fuel cell is used. Since water (humidified water) is mixed by a humidifier or the like, and reaction product water is generated by an electrochemical reaction when the fuel cell is operated, the exhaust gas of the fuel cell, particularly the exhaust gas on the oxygen electrode side is It is a highly humid gas.
For this reason, in the fuel cell protection device according to the above-described prior art, dew condensation may occur in a hydrogen detector or the like disposed in the flow path of the off gas due to the highly humid off gas discharged from the fuel cell. In this case, the hydrogen detector may be deteriorated or damaged. In particular, in the solid polymer membrane fuel cell described above, the normal operating temperature is lower than the vaporization temperature of water, and the offgas is discharged as a gas with a high humidity and a large amount of moisture. There is a problem that it is easy to do. When the above-described gas catalytic combustion type hydrogen detector is provided in the exhaust system on the oxygen electrode side of the fuel cell, etc., when energization is performed with humidified water, reaction product water, etc. attached to the gas detection element, In addition, local non-uniform temperature distribution occurs on the element surface, which may cause element destruction and sensitivity reduction.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas sensor capable of preventing the gas sensor from being damaged, deteriorated, and lowered in detection accuracy.

  In order to solve the above problems and achieve the object, the gas sensor of the present invention according to claim 1 is a gas detection chamber into which a gas to be inspected is introduced (for example, a gas detection chamber 27 in an embodiment described later). ) Is a gas sensor that detects a gas concentration of a gas to be detected included in the inspection target gas based on an electric resistance value of a detection element (for example, a detection element 31 in an embodiment described later), A heater that covers at least one of the inner surfaces of the gas detection chamber (for example, the second heater 36b in the embodiment described later) and an introduction in which the detected gas is introduced into the detection element in the gas detection chamber. A dehumidifying material (for example, a dehumidifying material in an embodiment described later) that is reversibly adsorbed and desorbed on the side opposite to the position of the portion (for example, the gas introduction portion 29 in the embodiment described later). 1 Dehumidifier 38 ) Is characterized by comprising a.

According to the gas sensor having the above-described configuration, even when moisture enters the gas detection chamber due to, for example, an inspection target gas having a high relative humidity, the gas is detected by the heater that covers the inner surface of the gas detection chamber, particularly at least one of the inner wall surfaces. The relative humidity in the detection chamber can be reduced.
Moreover, the position on the back side of the detection element where condensation is relatively likely to occur, and the generated condensation is relatively likely to stagnate, that is, the position opposite to the position of the introduction part where the gas to be detected is introduced with respect to the detection element By placing a dehumidifying material at the position, the generated condensed water can be adsorbed, and the detection accuracy of the gas concentration of the gas to be detected will be reduced, for example, the state where water has adhered to the surface of the detection element It is possible to prevent the element from being damaged or deteriorated by being energized.

Furthermore , as the heater, a cylindrical heater (for example, a second heater 36b in an embodiment described later) covering an inner wall surface of the gas detection chamber, and an annular heater (for example, a first heater in an embodiment described later) 36a), and the cylindrical heater and the annular heater are arranged so as to sandwich the dehumidifying material from both sides by the cylindrical heater and the annular heater.

  According to the gas sensor having the above configuration, it is possible to ensure a desired amount of water that can be adsorbed with respect to the dehumidifying material disposed at a position where condensation is relatively likely to occur and the generated condensation is relatively likely to stagnate. Can do.

Furthermore, the gas sensor of the present invention according to claim 2 is a second dehumidifying material (for example, described later) capable of reversibly adsorbing and desorbing water between the detection element in the gas detection chamber and the introduction portion. The second dehumidifying material 38b) in the embodiment is provided.

  According to the gas sensor having the above configuration, the relative humidity of the atmospheric gas to which the surface of the detection element is exposed can be reduced, and condensation can be prevented from occurring on the surface of the detection element.

Furthermore, the gas sensor of the present invention according to claim 3 is characterized in that the dehumidifying material and the second dehumidifying material are arranged so as to sandwich the heater from both sides by the dehumidifying material and the second dehumidifying material. It is said.

  According to the gas sensor having the above configuration, the dehumidifying material and the second dehumidifying material can be heated and dried (that is, dehumidified) by the heater, and the amount of water that can be adsorbed to the dehumidifying material and the second dehumidifying material. Can be secured.

According to the gas sensor of the first aspect of the present invention, even when moisture has entered the gas detection chamber, the heaters covering at least one of the inner surfaces of the gas detection chamber, particularly the inner wall surface, are relatively Humidity can be reduced.
In addition, condensation is relatively likely to occur, and the generated condensation is relatively likely to stagnate. By arranging the dehumidifying material at the position, the generated dew condensation water can be adsorbed, and the detection accuracy of the gas concentration of the gas to be detected will be reduced, for example in the state where water has adhered to the surface of the detection element It is possible to prevent the element from being damaged or deteriorated by being energized.
Furthermore , it is possible to ensure a desired amount of water that can be adsorbed with respect to the dehumidifying material disposed at a position where condensation is relatively likely to occur and the generated condensation is relatively likely to stagnate.
Furthermore, according to the gas sensor of the present invention as set forth in claim 2 , the relative humidity of the atmospheric gas to which the surface of the detection element is exposed can be reduced, and condensation is prevented from occurring on the surface of the detection element. be able to.
Furthermore, according to the gas sensor of the present invention described in claim 3 , the dehumidifying material and the second dehumidifying material can be heated and dried (that is, dehumidified) by the heater. A desired amount of water that can be adsorbed can be secured.

  Hereinafter, a gas sensor according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  The gas sensor 1 according to the present embodiment is, for example, a hydrogen sensor that detects hydrogen. For example, as shown in FIG. 1, a control device 2, a storage device 3, an alarm device 4, and a fuel that is used as a vehicle power source. In the fuel cell system 10 including the battery 5 and the pipes 6, 7, 8, and 9 connected to the fuel cell 5 and supplying the reaction gas, the fuel cell system 10 is provided on the upper side in the gravity direction of the outlet side pipe 9 on the oxygen electrode side, This is for confirming that hydrogen is not discharged from the outlet side pipe 9.

  The control device 2 is connected to the gas sensor 1 attached to the outlet side pipe 9 on the oxygen electrode side. For example, the detection signal output from the gas sensor 1 is compared with a predetermined determination threshold value stored in the storage device 3. According to the result, it is determined whether or not an abnormal state of the fuel cell 5 has occurred. When it is determined that the fuel cell 5 is in an abnormal state, the alarm device 4 outputs an alarm or the like. Here, the storage device 3 stores a map or the like of a predetermined determination threshold for the detection value of the gas sensor 1 according to the operating state of the fuel cell 5, for example, the inter-electrode differential pressure, the operating pressure, or the like.

The fuel cell 5 is mounted on a vehicle as a power source of, for example, an electric vehicle, and further includes a pair of electrolyte electrode structures 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. A large number of fuel battery cells (not shown) sandwiched between the separators are stacked.
Hydrogen is ionized on the catalyst electrode of the fuel electrode by a fuel gas such as hydrogen supplied from the inlet side pipe 6 to the fuel electrode, and moves to the oxygen electrode through a solid polymer electrolyte membrane that is appropriately humidified. Electrons generated in the meantime are taken out to an external circuit and used as direct current electric energy. For example, since an oxidant gas such as oxygen or air is supplied to the oxygen electrode through the inlet-side pipe 7, water is generated by reaction of hydrogen ions, electrons, and oxygen at the oxygen electrode. . Then, so-called off-gas that has been reacted is discharged out of the system from the outlet side pipes 8 and 9 on both the fuel electrode side and the oxygen electrode side.
Here, even if the moisture contained in the off-gas on the oxygen electrode side is cooled by the gas sensor 1 being attached to the upper side in the gravity direction of the outlet side pipe 9 on the oxygen electrode side, Is discharged downward in the direction of gravity.

For example, as shown in FIGS. 2 to 4, the gas sensor 1 includes a case 21 having a rectangular shape that is long in the longitudinal direction of the outlet side pipe 9 extending in the horizontal direction, that is, in the horizontal direction. The case 21 is made of, for example, polyphenylene sulfide, and includes flange portions 22 at both ends in the longitudinal direction. A collar 23 is attached to the flange portion 22. For example, as shown in FIG. 3, a bolt 24 is inserted into the collar 23, so that the flange portion 22 is provided in the outlet side pipe 9 on the oxygen electrode side. The mounting seat 25 is fastened and fixed.
For example, as shown in FIGS. 3 and 4, a cylindrical portion 26 is formed on the end surface of the case 21 in the thickness direction. For example, a bottomed cylindrical cylindrical base end portion 26 a and a cylindrical cylindrical tip end portion 26 b are coaxially connected to each other along the thickness direction of the gas sensor 1. The inside of this cylindrical part 26 is formed as a gas detection chamber 27, a flange part 28 is formed inward on the inner side surface of the cylindrical part 26, and the inner peripheral part of the flange part 28 is a gas inlet. An opening is formed as the portion 29.
A sealing material 35 is attached to the outer peripheral surface of the cylindrical portion 26, and the sealing material 35 is in close contact with the inner peripheral wall of the through hole 9a of the outlet side pipe 9 to ensure airtightness.

A circuit board 30 sealed with resin is provided in the case 21, and a plurality of, for example, four, detection elements 31 and temperature compensation elements 32 disposed in the gas detection chamber 27 are connected to the circuit board 30. It is connected to the circuit board 30 by a stay 33 for energization and a lead wire 33a.
In the gas detection chamber 27, together with the detection element 31 and the temperature compensation element 32, the base portion 34 of the cylindrical base end portion 26 a, the first heater 36 a and the second heater 36 b, and the temperature in the gas detection chamber 27 A sensor 37 for detecting humidity and the like, a first dehumidifying material 38a and a second dehumidifying material 38b, a structure 39, a sintered filter 40, and a water repellent filter 41 are arranged.
The four energizing stays 33 are substantially disk-shaped base portions that are sequentially arranged from the base end portion toward the tip end portion along the thickness direction of the gas sensor 1 from the bottom surface 27A of the gas detection chamber 27. 34, a substantially disc-shaped first dehumidifying material 38a, and a substantially disc-shaped structure 39 are fixed by, for example, the base portion 34.
Note that an appropriate coating for preventing corrosion is provided on the surface of the stay 33.

Then, for example, a concave portion 39a that is recessed by one step toward the base end portion is formed at the distal end portion of the substantially disc-shaped structure 39 made of polyphenylene sulfide or phenol resin, and the base portion 34 and the first dehumidifying material 38a and A substantially annular plate-like stay cover 33b is arranged so as to cover the entire exposed portions of the four energizing stays 33 that penetrate the structure 39 and are exposed in the recesses 39a.
Each element 31, 32 is formed, for example, by a lead wire 33 a connected to each stay 33 in a space formed by the recess 39 a of the structure 39 and the stay cover 33 b and communicating with the gas detection chamber 27. In a position separated from the gas sensor 1 by a predetermined distance in the thickness direction of the gas sensor 1, the gas sensor 1 is disposed so as to form a pair with a predetermined interval.

For example, as shown in FIG. 4, as a heater that covers at least one of the inner surfaces of the gas detection chamber 27, a first heater 36a made of, for example, a substantially annular ceramic heater is placed on the bottom surface 27A of the gas detection chamber 27A. The inner periphery of the first heater 36a is set so as to be opposed to the outer periphery of the substantially disc-shaped base portion 34 disposed on the bottom surface 27A of the gas detection chamber 27A.
As a heater that covers at least one of the inner surfaces of the gas detection chamber 27, a second heater 36b made of, for example, a substantially cylindrical ceramic heater is disposed on the inner wall surface 27B of the gas detection chamber 27, and the outer periphery of the second heater 36b. The surface is set so as to cover the inner wall surface 27 </ b> B of the gas detection chamber 27. And the inner peripheral part of the 2nd heater 36b is opposingly arranged by the outer peripheral part of the structure 39 and the stay cover 33b.

In addition, one surface of the first heater 36a is in contact with the bottom surface 27A of the gas detection chamber 27A, and the other surface of the first heater 36a and one end surface of the second heater 36b are used. The first dehumidifying material 38a is arranged so as to be sandwiched from both sides in the thickness direction. A substantially annular plate-like second dehumidifying material 38b is disposed so as to contact the other end surface of the second heater 36b.
Each of the heaters 36a and 36b is, for example, a ceramic heater having a conductive ceramic itself as a heating element, or a ceramic heater having a conductive metal resistor on a nonconductive ceramic, for example, and is parallel to each other. It is set to heat the gas detection chamber 27 and each element 31, 32 and each dehumidifying material 38a, 38b by being energized by the connected circuit board 30. For example, for each dehumidifying material 38a, 38b, The first heater 36a heats the first dehumidifying material 38a, and heats the first dehumidifying material 38a and the second dehumidifying material 38b.

And between the other end surface of the 2nd heater 36b and the gas introducing | transducing part 29, a substantially annular plate-shaped 2nd dehumidification material is sequentially followed from a base end part to a front-end | tip part along the thickness direction of the gas sensor 1. FIG. 38b, a substantially disc-shaped sintered filter 40, and a water-repellent filter 41 covering the gas introducing portion 29 are arranged.
Each dehumidifier 38a, 38b is made of an adsorbent that physically adsorbs water according to the humidity state of the atmospheric gas, such as silica gel, zeolite, activated carbon, activated alumina, water-absorbing polymer, zirconium oxide, etc., and adsorbs water. The dehumidifying materials 38a and 38b are heated by the heaters 36a and 36b, etc., so that the adsorbed water can be desorbed and evaporated into the atmospheric gas of the dehumidifying materials 38a and 38b. It is made into the adsorbent which has.
Further, the sintered filter 40 and the water repellent filter 41 are capable of permeating the gas to be inspected, and the off-gas flowing through the outlet side pipe 9 passes through at least the sintered filter 40 and the water repellent filter 41 and is in the gas detection chamber. 27 circulates in the inside.

The detection element 31 is a well-known element. For example, as shown in FIG. 5, the surface of the coil 31a of the metal wire containing platinum or the like having a high temperature coefficient with respect to the electric resistance is against the hydrogen to be detected gas. It is formed by being coated with a carrier such as alumina carrying a catalyst 31b made of an active noble metal or the like.
The temperature compensation element 32 is inactive with respect to the gas to be detected. For example, the surface of the coil 32a equivalent to the detection element 31 is covered with a carrier such as alumina.
And the detection element 31 which became high temperature by the heat_generation | fever of the combustion reaction produced when hydrogen which is to-be-detected gas contacts the catalyst 31b of the detection element 31, and the combustion reaction by a to-be-detected gas does not generate | occur | produce rather than the detection element 31. By utilizing the fact that a difference in electrical resistance value occurs between the temperature compensation element 32 and the low temperature compensation element 32, it is possible to detect the hydrogen concentration by offsetting the change in the electrical resistance value due to the ambient temperature.

  For example, as shown in FIG. 5, a branch side in which a detection element 31 (resistance value R4) and a temperature compensation element 32 (resistance value R3) are connected in series, a fixed resistance 41 (resistance value R1), and a fixed resistance 42 (resistance value) In a bridge circuit in which a branch edge having a value R2) connected in series is connected in parallel to a reference voltage generation circuit 44 that applies a predetermined reference voltage based on a voltage supplied from an external power supply 43 The detection circuit 45 for detecting the voltage between the connection points PS and PR is connected between the connection point PS between the detection element 31 and the temperature compensation element 32 and the connection point PR between the fixed resistors 41 and 42. Furthermore, an output circuit 46 is connected to the detection circuit 45.

  Here, when hydrogen, which is a gas to be detected, does not exist in the inspection target gas introduced into the gas detection chamber 27, the bridge circuit is balanced and is in a state of R1 × R4 = R2 × R3. Output is zero. On the other hand, when hydrogen is present, hydrogen burns in the catalyst 31b of the detection element 31, the temperature of the coil 31a rises, and the resistance value R4 increases. On the other hand, in the temperature compensation element 32, hydrogen does not burn and the resistance value R3 does not change. As a result, the balance of the bridge circuit is broken and an appropriate voltage is applied to the detection circuit 45 that changes in an increasing trend in response to an increasing change in the hydrogen concentration. The detection value of the voltage output from the detection circuit 45 is output to the output circuit 46, and the output circuit 46 outputs the input detection value to the control device 2. In the control device 2, the hydrogen concentration is calculated based on a hydrogen concentration map or the like set in advance according to the change in the detected voltage value.

  A heater voltage generation circuit 47 that applies an appropriate voltage to the first heater 36a and the second heater 36b is connected to the external power supply 43 to which the reference voltage generation circuit 44 is connected, and the first heater 36a and the second heater 36a are connected to the second heater 36b. The heaters 36b are connected to the heater voltage generation circuit 47 in parallel with each other.

The control device 2 is connected to the sensor 37 and the heaters 36 a and 36 b in the gas detection chamber 27. For example, the temperature state and humidity state of the atmospheric gas in the gas detection chamber 27 output from the sensor 37, the load of the fuel cell 5. The operating states of the elements 31 and 32 and the heaters 36a and 36b, for example, the timing of starting and stopping energization, the energizing amount, and the like are controlled according to the state and the operating state. At this time, the control device 2 performs, for example, feedback control on the current value energized to each heater 36a, 36b, chopper control based on, for example, on / off operation of the switching element (that is, on / off switching control) To control the energization amount to each heater 36a, 36b.
For example, the control device 2 controls energization of the heaters 36a and 36b based on the detection temperature of the sensor 37, and the temperature in the gas detection chamber 27 detected from the sensor 37 is a predetermined temperature that is at least higher than the dew point temperature. The relative humidity in the gas detection chamber 27 detected by the sensor 37 is set according to, for example, the relative humidity in a predetermined humidity range or the temperature state in the gas detection chamber 27 created in advance, for example. The energization start and energization stop timings and energization amounts of the heaters 36a and 36b are controlled so that the relative humidity search value obtained from the relative humidity map or the like is obtained.

Further, in addition to the temperature state in the gas detection chamber 27 detected by the sensor 37, the control device 2, for example, the operation state of the fuel cell 5 (that is, the operation state including the start and stop of operation of the fuel cell 5) For example, a load state during operation of the fuel cell 5, for example, a power generation command (FC output command value) for the fuel cell 5, a current value of the output current of the fuel cell 5 detected by, for example, an output current sensor (not shown), For example, each heater 36a is determined according to the power generation state of the fuel cell 5 calculated based on the detected value of the flow rate of air supplied to the fuel cell 5 from an air compressor (not shown) detected by a flow rate sensor (not shown) or the like. , 36b is controlled.
For example, when the load state of the fuel cell 5 changes to a high load state, for example, the control device 2 increases the flow rate of the off gas flowing in the outlet side pipe 9 on the oxygen electrode side and is exposed to the off gas. When the temperature in the gas detection chamber 27 decreases or the relative humidity in the gas detection chamber 27 increases due to, for example, an increase in the amount of generated water generated in the fuel cell 5 and included in the off-gas. By increasing the energization amount to each of the heaters 36a and 36b and raising the temperature in the gas detection chamber 27, it is possible to prevent condensation from occurring in the gas detection chamber 27. On the other hand, when the load state of the fuel cell 5 changes to a low load state or the like, the control device 2 suppresses excessive energy consumption by reducing the energization amount to the heaters 36a and 36b.

Further, when the operation of the fuel cell 5 is stopped, for example, the control device 2 increases the flow rate of off-gas flowing through the outlet side pipes 8 and 9 to discharge water remaining in the fuel cell system to the outside. When the purge process is performed, the amount of current supplied to the heaters 36a and 36b is increased, and the temperature in the gas detection chamber 27 is temporarily raised, so that saturated water vapor of the atmospheric gas in the gas detection chamber 27 is obtained. The amount is increased to prevent condensation in the gas detection chamber 27.
In addition, when the operation of the fuel cell 5 is started, the control device 2 prior to the start of the off-gas flow in the outlet side pipe 9 on the oxygen electrode side, the elements 31 and 32 of the gas sensor 1, the heaters 36 a and 36 b, When the fuel cell 5 is stopped and the operation of the fuel cell 5 is stopped, the flow of the off gas in the outlet side pipe 9 on the oxygen electrode side is stopped, and then the elements 31 and 32 of the gas sensor 1 and the heaters 36a and 36b are connected. Stop energization.

Next, the operation of the gas sensor 1 according to the above-described embodiment will be described.
The dehumidifying materials 38 a and 38 b arranged in the gas detection chamber 27 adsorb or desorb water according to the humidity state of the atmospheric gas in the gas detection chamber 27.
For example, when the heaters 36a and 36b are energized during the operation of the gas sensor 1, the relative humidity in the gas detection chamber 27 increases as the temperature in the gas detection chamber 27 becomes relatively high. The dehumidifying materials 38a and 38b are in a state where water is desorbed, that is, a state where the amount of adsorbable water is increased.
When the flow of the off gas in the outlet pipe 9 on the oxygen electrode side is stopped along with the stop of the operation of the fuel cell 5, the temperature in the gas detection chamber 27 is stopped when the energization to the heaters 36 a and 36 b is stopped. As the temperature decreases, the relative humidity in the gas detection chamber 27 increases. At this time, each dehumidifying material 38a, 38b adsorbs water containing water vapor in the atmospheric gas in the gas detection chamber 27 according to the amount of adsorbable water. This prevents dew condensation in the gas detection chamber 27, that is, prevents the relative humidity in the gas detection chamber 27 from reaching 100% or the temperature in the gas detection chamber 27 from dropping below the dew point temperature. In addition, for example, even when the temperature locally falls below the dew point temperature and dew condensation occurs in the gas detection chamber 27, the generated dew condensation water is adsorbed by the dehumidifying materials 38a and 38b. be able to.

In particular, in the gas detection chamber 27, the position between the elements 31 and 32, that is, the position between the upper region in the direction of gravity where the condensation is relatively likely to occur and the generated condensation is relatively stagnant, that is, the gas detection chamber. 27, the first dehumidifying material 38a disposed at a position opposite to the position of the gas introducing portion 29 where the off gas is introduced is heated by the first heater 36a and the second heater 36b. As a result, the water can be dried (that is, dehumidified), and a desired amount of water that can be adsorbed can be secured. For example, the occurrence of dew condensation at the upper part in the vertical direction of the elements 31 and 32 can be suppressed. .
Further, the second dehumidifier disposed between the elements 31 and 32 in the gas detection chamber 27 and the gas introduction part 29 is shifted to the gas introduction part 29 side from the position where the second heater 36b is arranged. 38b can reduce the relative humidity of the atmospheric gas to which the surfaces of the elements 31 and 32 are exposed, and can prevent condensation on the surfaces of the elements 31 and 32.
In addition, the second heater 36b is disposed so as to cover the inner wall surface 27B of the gas detection chamber 27, so that dew condensation is caused by being formed of a metal having a relatively high thermal conductivity in the gas detection chamber 27. It is possible to suppress the occurrence of condensation on the inner wall surface 27B in the vicinity of the cylindrical portion 26 that is likely to generate water.

As described above, according to the gas sensor 1 of the present embodiment, the heater 36a, which can change the temperature state and humidity state of the atmospheric gas in the gas detection chamber 27, and the temperature state of the surfaces of the elements 31, 32 can be changed. Even when the ambient gas and the temperature of the surfaces of the elements 31 and 32 are lowered as the operation of 36b is stopped, the water vapor in the atmospheric gas in the gas detection chamber 27 by the dehumidifying materials 38a and 38b. Water can be adsorbed, the relative humidity of the atmospheric gas in the gas detection chamber 27 is reduced, and the temperature of the atmospheric gas in the gas detection chamber 27 and the surfaces of the elements 31 and 32 are reduced below the dew point temperature. It is possible to suppress the occurrence of condensation in the gas detection chamber 27.
Further, for example, even when dew condensation occurs due to a local temperature decrease due to the operation stop of each heater 36a, 36b, the generated dew condensation water can be adsorbed by each dehumidifying material 38a, 38b, It is possible to prevent condensation from occurring in the gas sensor 1 at the start of the next operation, and it is possible to reduce the relative humidity in the gas detection chamber 27 in preparation for the start of the next operation. .

Further, even when moisture enters the gas detection chamber 27 due to, for example, off-gas having a high relative humidity, the relative humidity in the gas detection chamber 27 is set by the second heater 36b that covers the inner wall surface 27B of the gas detection chamber 27. Can be reduced.
In addition, the position of the elements 31 and 32 on the back side where the condensation is relatively easy to occur and the generated condensation is relatively stagnant, that is, the gas introduction part into which the off gas is introduced to the elements 31 and 32. By arranging the first dehumidifying material 28a at a position opposite to the position 29, the generated dew condensation water can be adsorbed, and the detection accuracy of the gas concentration of hydrogen, which is the gas to be detected, may be reduced. For example, the element can be prevented from being damaged or deteriorated by being energized with water attached to the surfaces of the elements 31 and 32.

  In addition, the configuration of the circuit system can be simplified by supplying electric power from the common power supply 43 to the detection units including the elements 31 and 32 and the resistors 41 and 42 and the heaters 36a and 36b. Can do.

In the above-described embodiment, the gas sensor 1 is a hydrogen sensor. However, the present invention is not limited to this, and may be a gas sensor that detects other gases, for example, combustible gases such as carbon monoxide and methane.
In the above-described embodiment, the gas sensor 1 is a contact combustion type sensor. However, the gas sensor 1 is not limited to this, and may be a sensor of another type such as a semiconductor type.
In the above-described embodiment, the circuit formed by connecting the elements 31 and 32 is a bridge circuit. However, the circuit is not limited to this, and may be another circuit such as a series circuit. As a state quantity related to the resistance value R4 of 31, a detection value of a voltage or current between predetermined contacts may be output to the control device 2.

It is a principal part block diagram of a fuel cell system provided with the gas sensor which concerns on one Embodiment of this invention. It is sectional drawing of the gas sensor shown in FIG. It is a schematic sectional drawing which follows the AA line shown in FIG. FIG. 4 is a detailed cross-sectional view of the gas detection chamber shown in FIG. 3. It is a circuit diagram of the gas sensor shown in FIG.

Explanation of symbols

1 Gas sensor 27 Gas detection chamber 29 Gas introduction part (introduction part)
31 Detection element 36a First heater (annular heater)
36b Second heater (heater, cylindrical heater)
38a First dehumidifying material (dehumidifying material)
38b Second dehumidifying material (second dehumidifying material)

Claims (3)

A gas sensor that detects a gas concentration of a gas to be detected included in the inspection target gas based on an electric resistance value of a detection element arranged in a gas detection chamber into which the inspection target gas is introduced,
A heater covering at least one of the inner surfaces of the gas detection chamber;
A dehumidifying material that is disposed at a position opposite to the position of the introduction part where the detection gas is introduced with respect to the detection element in the gas detection chamber, and that can reversibly adsorb and desorb water ,
As the heater, a cylindrical heater that covers the inner wall surface of the gas detection chamber, and an annular heater,
The gas sensor , wherein the cylindrical heater and the annular heater are arranged so as to sandwich the dehumidifying material from both sides by the cylindrical heater and the annular heater . 2. The gas sensor according to claim 1, further comprising a second dehumidifying material capable of reversibly adsorbing and desorbing water between the detection element in the gas detection chamber and the introduction unit . The gas sensor according to claim 2 , wherein the dehumidifying material and the second dehumidifying material are arranged so as to sandwich the heater from both sides by the dehumidifying material and the second dehumidifying material .

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