JP2007309905A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector capable of obtaining stable detection results, by preventing detection gas from dew condensing in the detection space. <P>SOLUTION: The detection space comprises an outside plane of the element case 20 and the inside side plane of the accommodation case 40, in the accommodation forming surface 58 for forming the accommodation space 59 that accommodates the circuit substrate 41; the heating elements 50 and 51 for heating the element case 20 for forming the detection space 39 are fixed. The heat, generated from the heating elements 50 and 51, is conducted to the element case 20 and accommodation case 40 composing the accommodation formation surface 58, the inside surface of the element case 20 forming the detection space 39 is prevented from being cooled from the outside. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas detector, and more particularly to a gas detector used for concentration measurement, leakage detection, and the like of various combustible gases such as hydrogen, carbon monoxide, and hydrocarbon-based gas. In particular, the present invention relates to a hydrogen gas leak detector installed in a pipe on the air electrode side of a solid polymer fuel cell unit.

  In recent years, research on fuel cells has been actively conducted as a high-efficiency and clean power source amid global environmental deterioration. Among them, polymer electrolyte fuel cells (PEFC) are expected for automobiles and households due to the advantages of low temperature operation and high power density. In such a fuel cell, a thin solid polymer electrolyte membrane is used, and when the electrolyte membrane is damaged, fuel gas leaks from the fuel electrode side to the air electrode side, leading to a decrease in power generation efficiency. Therefore, a gas detector that is installed in the air electrode side pipe and detects leakage of fuel gas is required. As a gas sensor (gas detection element) of such a gas detector that detects the concentration of combustible gas, a reaction part including a catalyst for combusting combustible gas is provided, and the amount of heat generated when combustible gas is combusted by the catalyst. Based on this, a contact combustion type gas sensor (gas detection element) for detecting a combustible gas is known. However, since the PEFC described above does not exhibit proton conductivity unless it is a humid environment, the gas flowing through the fuel cell needs to be kept at a high humidity. Further, in order to improve cooling efficiency and use waste heat, the temperature of the circulating gas is usually operated at 50 ° C. to 80 ° C., and the gas detector is also exposed to such a wet gas environment to be detected. Become.

In such a gas detector, when the temperature in the detection space where the gas detection element is installed is lower than the temperature of the gas to be detected, the gas to be detected is cooled in the detection space and water droplets are generated. . Further, since the output of the gas detection element depends on the temperature of the gas to be detected, a stable detection result cannot be obtained when the temperature of the gas to be detected fluctuates. For this reason, in the conventional gas detector, a heating element is provided in the vicinity of the gas detection element, and the heat generation element is energized to heat the gas detection element, thereby preventing condensation and stabilizing the output of the gas detection element. (For example, refer to Patent Document 1).
JP 2004-93473 A

  However, in the gas detector shown in Patent Document 1, since the heating element is provided in the detection space, the temperature of the test gas in the vicinity of the heating element rises, but the temperature of the inner surface of the member forming the detection space is increased. If the temperature difference between the outside air existing outside the pipe where the gas detector is installed and the gas to be detected is large, the temperature of the inner surface of the member forming the detection space is low. There is a problem in that it is cooled by the outside air or the like and falls below the dew point of the gas to be detected. For this reason, the gas to be detected is cooled on the inner surface of the member forming the detection space, and there is a possibility that water droplets are generated in the detection space or the output of the gas detection element becomes unstable.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a gas detector that can prevent the detection target gas from condensing in the detection space and obtain a stable detection result. And

  In order to solve the above problems, a gas detector according to a first aspect of the present invention includes a gas detection element that detects a gas to be detected, and an inlet that houses the gas detection element and introduces the gas to be detected. An element case that forms a detection space into which the gas to be detected is introduced, and a circuit board that is electrically connected to the gas detection element, and at least a part of the element case is contained therein A housing case having a holding portion that holds the housing in a state of being disposed; and a housing space forming surface that is configured by an inner surface of the housing case and an outer surface of the element case and forms a housing space for housing the circuit board. The gas detector includes a heating element that is fixed to the housing space forming surface and that heats the element case that forms the detection space. Note that “detection” in the present invention is not limited to determining the presence or absence of a specific gas contained in the gas to be detected, but includes calibrating the concentration of the specific gas contained in the gas to be detected. .

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the heating element is provided on an outer surface of the element case that constitutes the housing space forming surface. .

  In addition to the configuration of the invention according to claim 1 or 2, the gas detector of the invention according to claim 3 is characterized in that the heating element is an inner side surface of the housing case constituting the housing space forming surface. It is provided on the surface having the holding portion.

  According to a fourth aspect of the present invention, in addition to the configuration of the first aspect of the present invention, at least a part of the outer surface of the element case is in contact with the gas to be detected. It is characterized by.

  In addition to the configuration of the invention according to any one of claims 1 to 4, the gas detector of the invention according to claim 5 is a heat conduction type gas detection element or a catalytic combustion type gas detection element. It is characterized by being.

  According to the gas detector of the first aspect of the invention, the element case is heated via the housing case constituting the gas detector or directly by the heating element fixed to the housing space forming surface. It is possible to prevent the inner side surface of the element case to be formed from being cooled by outside air or the like existing outside the gas detector. Therefore, when the inner side surface of the element case forming the detection space is below the dew point of the gas to be detected, the gas detection element may be wetted, resulting in poor sensitivity. It is possible to prevent the detected gas in the space from condensing. As a result, it is possible to prevent the detection accuracy from being lowered due to the catalyst layer and the like being wet.

  Further, according to the gas detector of the invention according to claim 2, in addition to the effect of the invention of claim 1, since the heating element is provided on the outer surface of the element case constituting the accommodation space forming surface, The heat of the heating element is easily conducted to the element case forming the detection space, and the element case forming the detection space can be efficiently heated. Therefore, it is possible to prevent the inner side surface of the element case forming the detection space from being cooled below the dew point by outside air or the like existing outside the gas detector.

  According to the gas detector of the invention according to claim 3, in addition to the effect of the invention according to claim 1 or 2, the element case among the inner side surfaces of the housing case in which the heating element forms the housing space forming surface. Since the heat of the heating element is easily conducted to the element case forming the detection space, the element case forming the detection space can be efficiently heated. Therefore, it is possible to prevent the inner side surface of the element case forming the detection space from being cooled below the dew point by outside air or the like existing outside the gas detector.

  According to the gas detector of the invention of claim 4, in addition to the effect of the invention of any of claims 1 to 3, at least a part of the outer surface of the element case is in contact with the gas to be detected. The area of the surface of the element case that comes into contact with the gas to be detected can be increased. For this reason, since the amount of heat conducted from the gas to be detected to the element case increases, the element case forming the detection space is heated by the gas to be detected, and the atmospheric temperature in the detection space and the gas detector are attached. It is possible to reduce the temperature difference from the ambient temperature in the piping and the like, and to more reliably prevent the detected gas from condensing.

  Further, according to the gas detector of the invention according to claim 5, in addition to the effect of the invention according to any one of claims 1 to 4, an element that forms a detection space by a heating element fixed to the accommodation space forming surface Since the case is heated to prevent the gas to be detected from condensing in the detection space, the gas detection element stabilizes the sensitivity of the gas detector equipped with a heat conduction type gas detection element or a catalytic combustion type gas detection element. Can be made.

  Hereinafter, an embodiment of a gas detector 10 embodying a gas detector according to the present invention will be described with reference to the drawings. The gas detector 10 exemplified as the present embodiment includes a gas detection element 60 that is a contact combustion type gas detection element, and utilizes the fact that the electric resistance value changes as the combustible gas contained in the detection target gas burns. The gas detector detects the concentration of the combustible gas. FIG. 1 is a longitudinal sectional view showing a state in which the gas detector 10 is disposed in the pipe 200. As shown in FIG. 1, the gas detector 10 is mounted on a pipe 200 provided in a fuel cell unit of an automobile, for example, for the purpose of detecting hydrogen contained in a gas to be detected discharged in the direction of an arrow 300. Used for.

  FIG. 2 is a longitudinal sectional view of the gas detector 10. As shown in FIG. 2, the gas detector 10 includes an element case 20 that houses a gas detection element 60 that detects a gas to be detected, and supports the element case 20 and is electrically connected to the gas detection element. The housing case 40 is configured to house the circuit board 41. In FIG. 2, the vertical direction is referred to as the vertical direction, and the horizontal direction is referred to as the horizontal direction.

  First, the configuration of the housing case 40 will be described with reference to FIG. The housing case 40 includes a case body 42 and a case lid 44 that is a lid that covers an opening provided at the upper end of the case body 42. The housing case 40 includes therein a circuit board 41, a microcomputer 94, and heating elements 50 and 51 which are important components of the present invention. Hereinafter, each member which comprises the storage case 40 is explained in full detail.

  The case body 42 is a container having an opening on the upper surface and the lower surface and having a predetermined height, a holding portion 46 that holds the collar portion 38 of the element case 20 in an opening provided on the lower surface, and a peripheral edge of the circuit board 41. Circuit board holding part 45 for holding the part. Further, the opening provided on the upper surface is provided with a case lid 44 made of synthetic resin to close the opening.

  The case main body 42 includes a flow path forming portion 43 formed in the lower center of the case main body 42 and a connector 55 formed on a side portion of the case main body 42 for external power feeding. Molded. The flow path forming portion 43 accommodates an introduction portion 35 (see FIG. 3) of the element case 20 for introducing and discharging a gas to be detected, which will be described later with reference to FIG. As described above, the element case 20 is held by the holding portion 46 in a state where a part of the element case 20 is disposed inside the housing case 40. Further, a seal member 47 that seals between the flow path of the gas to be detected and the housing case 40 is provided between the collar portion 38 and the holding portion 46 of the element case 20. In addition, since the flow path forming portion 43 is a member that is in direct contact with the gas to be detected, it is preferable that the portion in contact with the gas to be detected is formed from a resin having high chemical resistance in order to prevent deterioration of strength over time. . Moreover, in order to avoid being cooled by the outside air etc. which exist outside the piping 200 in which the gas detector 10 is installed, the flow path forming unit 43 is preferably formed of a resin having low thermal conductivity.

  The connector 55 is for supplying electricity to the circuit board 41 and the microcomputer 94, and is assembled to the outer surface of the case body 42. Inside the connector 55, a plurality of connector pins 56 and 57 projecting from the side wall of the case body 42 are provided. The connector pins 56 and 57 are electrically connected to the circuit board 41 and the microcomputer 94 via wiring (not shown) embedded in the side wall of the case main body 42, respectively.

  The circuit board 41 is a plate-like board having a predetermined thickness, the sensor output circuit 90 (see FIG. 6) for detecting the combustible gas contained in the gas to be detected, and the temperatures of the heating elements 50 and 51. And a temperature control circuit (not shown) for controlling. The sensor output circuit 90 is electrically connected to the electrodes 85, 87, 88 and the ground electrodes 86, 89 of the gas detection element 60 through connection terminals 24 to 28, respectively. Further, the temperature control circuit and the heating elements 50 and 51 are electrically connected by lead wires 52 and 53. Although not shown, there are two lead wires 52 and 53, respectively. The sensor output circuit 90 provided on the circuit board 41 will be described later with reference to FIG.

  The microcomputer 94 provided on the lower surface of the circuit board 41 calculates the concentration of the combustible gas contained in the gas to be detected based on the output of the sensor output circuit, and based on the output of the temperature control circuit, The amount of generated heat (temperature) 51 is controlled. The microcomputer 94 includes at least a storage device that stores a program for executing the sensor output calculation and the temperature control of the heating elements 50 and 51, and a CPU that executes the program stored in the storage device. Yes.

  The accommodation space 59 for accommodating the circuit board 41 is surrounded by the inner side surface of the accommodation case 40 and the outer side surface of the element case 20 and is a space for accommodating the circuit board 41 and is resin-molded with a filler. By using a resin having low thermal conductivity as a filler for filling the accommodation space 59, the heat retaining effect in the accommodation space 59 can be enhanced.

  Next, the heating elements 50 and 51, which are important components of the present invention, will be described with reference to FIG. The heating elements 50 and 51 are for heating the element case 20 through the housing case 40 or directly, and maintaining the temperature of the inner surface of the element case 20 at a temperature higher than the dew point, and are used in electronic parts, for example. A resistor or a film heater is used. The heating elements 50 and 51 are composed of an inner surface of the housing case 40 and an outer surface of the element case 20 in order to efficiently heat the inner surface of the element case 20 forming the detection space 39, and Of the accommodation space forming surface 58 constituting the accommodation space 59 to be accommodated, it is preferably fixed to a portion capable of transferring heat to a member that contacts the detection space 39. Therefore, it is preferable that the element case 20 that is a member in contact with the detection space 39 is fixed to a portion where heat can be efficiently transmitted. For example, the accommodation space forming surface 58 of the element case 20 in the accommodation space forming surface 58 Among the inner side surfaces of the housing case constituting the housing space forming surface 58, the surface is provided on the surface having the holding portion 46 that holds the element case 20 close to the element case 20. In addition, as the fixing method of the heating elements 50 and 51, a fixing method capable of fixing at least a part of the heating element in close contact with the accommodation space forming surface 58 can be adopted. For example, the heating elements 50 and 51 can be fixed by screw fixing or adhesive fixing. The

  The amount of heat generated by the heating elements 50 and 51 is preferably set so that the temperature of the inner surface of the element case 20 forming the detection space 39 is higher than the dew point of the gas to be detected. As a result, the gas to be detected is cooled below the dew point of the gas to be detected on the inner surface of the element case 20, and it is possible to prevent dew condensation in the detection space 39. Moreover, since the gas to be detected usually has a temperature higher than the dew point, it is more preferable to set the temperature of the heating elements 50 and 51 to be equal to or higher than the temperature of the gas to be detected. By setting such a temperature, it is possible to prevent the detected gas from being cooled on the inner side surface of the element case 20 that forms the detection space 39, and to prevent the temperature of the detected gas from becoming unstable. For this reason, the influence of the temperature characteristic of the gas detection element 60 according to the temperature of the gas to be detected can be reduced, and the combustible gas contained in the gas to be detected can be detected with higher accuracy.

  The heating elements 50 and 51 are controlled by, for example, known constant voltage control, constant power control, or PWM control (pulse width modulation control). In addition, the same control method may be employ | adopted for the control method at the time of providing a several heat generating body like the heat generating bodies 50 and 51, and you may make it employ | adopt a mutually different control method. Moreover, the program which prescribed | regulated the control method of the heat generating bodies 50 and 51 is memorize | stored in the memory | storage device with which the microcomputer 94 is provided, and is performed by CPU.

  Since the heating elements 50 and 51 are provided in the housing case 40 separated from the detection space 39, the heating elements 50 and 51 have the following advantages compared to the case where the heating element is installed in the detection space 39.

  First, when the gas detector 10 is cooled by outside air or the like existing outside the pipe 200, such as when the gas detector 10 is installed in the pipe 200 shown in FIG. 1, the detection space 39 of the gas detector 10 is used. Since the temperature of the inner side surface of the element case 20 forming the lower than the temperature of the gas to be detected may cause condensation in the gas to be detected, according to the present embodiment, the gas detector 10 It is possible to avoid such a situation by heating from the side close to the outside of the installed pipe 200. In other words, the outer surface of the element case is a part where cold air outside the gas detector 10 is conducted to the element case 20 through the accommodation case 40 or the accommodation space 59, and therefore, detection is performed by heating the part. The heat retention effect of the inner side surface of the element case 20 forming the space 39 can be enhanced, and the inner side surface of the element case 20 can be prevented from being cooled by outside air or the like existing outside the gas detector 10 and the pipe 200. Therefore, when the gas to be detected has a temperature higher than the dew point, the element case 20 is heated by the heating elements 50 and 51 when the gas detector 10 is started up, and the inner side surface of the element case 20 is higher than the dew point. Once the temperature rises to a higher temperature, the heat generation amount of the heating elements 50 and 51 is adjusted to a heat generation amount that cancels the cooling heat generated by the outside air. It is possible to keep the temperature higher than the dew point.

  Further, since the heating elements 50 and 51 are fixed inside the housing case 40, even when the gas detector 10 is installed at the vibration location, there is no problem such as the installation position of the heating element being shifted. Moreover, since it is installed outside the detection space 39 that does not come into contact with the gas to be detected, it does not hinder the flow rate of the combustible gas from being lowered. Moreover, since it is not corroded by the corrosive gas contained in to-be-detected gas, it is not necessary to provide the coating | cover etc. for preventing corrosion. Moreover, when installing in the detection space 39, there are restrictions on the shape and size so as not to hinder the detection, but since it is provided in the storage case 40 separated from the detection space 39, such a case. There are no restrictions. Furthermore, since it is provided in the housing case 40, it is not necessary to separately wire a lead wire in the element case 20, and the configuration can be simplified.

  Next, the element case 20 constituting the gas detector 10 will be described with reference to FIG. FIG. 3 is an enlarged longitudinal sectional view of the periphery of the element case 20 of the gas detector 10. In FIG. 3, the vertical direction is referred to as the vertical direction, and the horizontal direction is referred to as the horizontal direction.

  As shown in FIG. 3, the element case 20 holds the connection terminal extraction base 21 where the gas detection element 60 is installed and the peripheral edge of the connection terminal extraction base 21 toward the introduction port for introducing the detection gas. And a detection space forming member 22 having a cylindrical wall surface. A sealing member 48 that seals between the flow path of the gas to be detected and the element case 20 is provided on the periphery of the connection terminal extraction base 21 of the element case 20. A space surrounded by the connection terminal extraction base 21 and the detection space forming member 22 is a detection space 39 for introducing the gas to be detected.

  The connection terminal extraction base 21 is a member for supporting the gas detection element 60, and at least a part thereof is formed of a member having thermal conductivity that conducts heat of the heating element 50 provided on the outer surface. It is preferable. Particularly suitable materials for the connection terminal extraction base 21 will be described later. A gas detection element 60 is provided on the inner surface of the connection terminal extraction base 21 via a spacer 23. The spacer 23 is made of a resin having no thermal conductivity so that the heat of the heating element 50 provided on the outer surface of the connection terminal extraction base 21 is not directly conducted to the gas detection element 60. Further, the connection terminal take-out base 21 is provided with insertion holes for individually inserting the connection terminals 24 to 28, and the periphery of each insertion hole is covered with an insulating member.

  The connection terminals 24 to 28 are members for electrically connecting a gas detection element 60 (to be described later with reference to FIGS. 4 and 5) and a circuit provided on the circuit board 41, and are pinned by a conductive member. It is formed in a shape. One end of each connection terminal is inserted through an insertion hole provided in the connection terminal extraction base 21 and is supported perpendicular to the connection terminal extraction base 21.

  Further, the detection space forming member 22 has an outer cylinder 36 that comes into contact with the gas to be detected on the outer surface, an extraction table support portion 37 that holds the peripheral edge of the connection terminal extraction table 21, and a collar portion 38 supported by the housing case 40. It has. In addition, an introduction port 34 that is an opening for introducing a gas to be detected into the detection space 39 is provided at the lower end of the detection space forming member 22. At least a part of the detection space forming member 22 is preferably formed of a member having thermal conductivity that conducts heat of the heating elements 50 and 51 or heat of the gas to be detected. Particularly suitable materials for the detection space forming member 22 will be described later.

  In the vicinity of the introduction port 34, an introduction portion 35 is provided that forms a flow path for introducing and discharging the gas to be detected from the introduction port 34 to and from the gas detection element 60. The introduction portion 35 is loaded with a water repellent filter 29, a spacer 30, and two metal meshes 31, 32 in order from the introduction port. These members are sandwiched and fixed by the detection space forming member 22 and the filter fixing member 33. Hereinafter, members constituting each introduction portion 35 will be described in detail.

  The water repellent filter 29 is a filter attached at a position closest to the introduction port 34 and is a thin film having water repellency for removing water droplets contained in the gas to be detected. Accordingly, it is possible to prevent the gas detection element 60 from getting wet even in a humid environment where water droplets or the like fly. The water repellent filter 29 may be any filter that removes water droplets by physical adsorption. For example, a filter using polytetrafluoroethylene (PTFE) can be applied.

  The spacer 30 is provided on the inner peripheral wall of the filter fixing member 33, and is a ring-shaped member in plan view having an opening through which the gas to be detected is introduced. By having a predetermined thickness, the water repellent filter 29 and the metal mesh 31, The position with 32 is adjusted.

  The metal nets 31 and 32 have a predetermined thickness and a predetermined opening, and the temperature of the heating resistor provided in the gas detection element 60 is higher than the ignition temperature of hydrogen gas contained in the gas to be detected. Even when it ignites, it functions as a flame arrester that prevents the flame from going outside.

  The filter fixing member 33 is a member for sandwiching and fixing the water repellent filter 29, the spacer 30, and the two metal nets 31, 32, and has a cylindrical wall surface that comes into contact with the inner wall surface of the detection space forming member 22. The projection protrudes in the axial direction of the wall surface and includes a convex portion for fixing the filter.

  The connection terminal take-out base 21, the detection space forming member 22, the water repellent filter 29, the spacer 30, the two metal meshes 31 and 32, and the filter fixing member 33, which are described above, are detected in the present invention. These are members that form the inner surface of the element case 20 that forms a space, and these members have high thermal conductivity so that they are heated to a temperature higher than the dew point of the gas to be detected by the heating elements 50 and 51 described above. It is preferably formed of a material. Moreover, since it is a member which contacts a to-be-detected gas, it is preferable to use a member with high corrosion resistance. For this reason, it is preferably formed of austenitic steel or austenitic-ferritic dual phase steel, more preferably SUS300 steel that is easily available and easy to mold, or SUS329J4L having high corrosion resistance, and is particularly preferable. Is formed of SUS316L having a low carbon content and excellent corrosion resistance and moldability. The thickness of each member may be set in consideration of the strength of each member.

  Further, at least a part of the connection terminal extraction base 21 and the detection space forming member 22 may be an aspect in which a member having thermal conductivity is used as at least a part of the material of the member. In addition to coating with a material, the above-described material may be inserted into the member in a line shape.

  Further, since the connection terminal extraction base 21 and the detection space forming member 22 are members that are in direct contact with the gas to be detected, at least a part of the members is formed of a member that conducts heat generated from the heating elements 50 and 51. Thus, it is possible to prevent the gas to be detected from being cooled to a dew point or less by the member and causing condensation. Moreover, the heat of the said member can be efficiently conducted to the introducing | transducing part 35 comprised from the member which has heat conductivity.

  In addition, since the introduction part 35 is a part into which the gas to be detected is introduced into the gas detector 10, when the temperature of the gas detector 10 is lower than the temperature of the gas to be detected, the gas to be detected is introduced into the introduction part. Condensation to 35. On the other hand, the detected gas is introduced by configuring the member with a member having thermal conductivity so that the heat generated from the heating elements 50 and 51 is conducted to the member constituting the introducing portion 35. It can be cooled to below the dew point by the members constituting the part 35, and condensation can be prevented. When the water repellent filter 29, the spacer 30, the two metal nets 31, 32, and the filter fixing member 33 constituting the introduction part 35 are formed of a material having high thermal conductivity as described above, the housing case 40 is used. The heat of the heating elements 50 and 51 fixed to the housing space forming surface 58 can be efficiently conducted to the introducing portion 35.

  In addition, when the member is cooled by outside air or the like, the detected gas introduced into the detection space 39 is cooled, and thus the temperature of the detected gas may become unstable. In the gas detector 10, the temperature of the member can be kept higher than the dew point of the gas to be detected by the heat conducted to the connection terminal extraction base 21, the detection space forming member 22, and the introducing portion 35. For this reason, the influence of the temperature characteristic of the gas detection element 60 according to the temperature of the gas to be detected can be reduced, and the combustible gas contained in the gas to be detected can be detected with high accuracy.

  Further, the connection terminal take-out base 21, the detection space forming member 22, the water repellent filter 29, the spacer 30, the two metal nets 31, 32, and the filter fixing member 33 constituting the introduction portion 35 are formed of a highly corrosion-resistant member. In this case, even when a corrosive gas is contained in the gas to be detected, it is possible to prevent these members from being corroded by the corrosive gas. For this reason, it is possible to avoid problems such as poor sensitivity due to corrosion of the members constituting the detection space 39.

  Next, the configuration of the gas detection element 60 provided in the connection terminal extraction base 21 will be described with reference to FIGS. 4 and 5. 4 is a schematic plan view for explaining the arrangement state of the detection element 70 and the reference element 75 of the gas detection element 60, and FIG. 5 is a diagram for explaining the arrangement state of the detection element 70 and the reference element 75. It is an arrow directional cross-sectional view in the AA line of 4. FIG. In FIG. 5, the upper side is the upper side, the lower side is the lower side, and in FIGS. 4 and 5, the left-right direction is the left-right direction.

  As shown in FIG. 4, the gas detection element 60 is a catalytic combustion type gas detection element having a rectangular planar shape with a length of 3 mm and a width of 5 mm. As shown in FIGS. 4 and 5, the gas detection element 60 is formed on a plate-like silicon substrate 61 and the surface of the silicon substrate 61, and includes a heating resistor 71 and a reference heating resistor 76, respectively. The layer 65 and the protective layer 64 formed with a predetermined thickness on the insulating layer 65 are provided. The gas detection element 60 is formed by, for example, a micromachining technique. Hereinafter, each member which comprises the gas detection element 60 is explained in full detail.

  The silicon substrate 61 is a silicon flat plate having a predetermined thickness. The silicon substrate 61 includes a pair of cavities 62 and 63 in which a part of the silicon substrate 61 is removed in an opening at a portion located below the heating resistor 71 and the reference heating resistor 76. A part of the insulating layer 65 is exposed at the upper portions of the cavities 62 and 63. With such a configuration, the heating resistor 71 and the reference heating resistor 76 are insulated from the surroundings by the cavities 62 and 63, so that the temperature rises or falls in a short time. For this reason, the heat capacity of the gas detection element 60 can be reduced.

On the upper surface of the silicon substrate 61, an insulating layer 65 having insulating properties is formed in a layer shape with a predetermined thickness. A part of the lower surface of the insulating layer 65 is exposed to the cavities 62 and 63 in which a part of the silicon substrate 61 is removed in an opening shape. A heating resistor 71 and a reference heating resistor 76 are included in regions corresponding to the cavities 62 and 63, respectively. In addition, wiring films 711, 712, 761 and wirings 713, 714, 762, 763 formed on the same plane as the plane on which the heating resistor 71 and the reference heating resistor 76 are formed are respectively included in the insulating layer 65. Yes. The insulating layer 65 is formed of an insulating material, and for example, silicon oxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) is used. The insulating layer 65 may be formed of a single material, or a plurality of layers may be formed using different materials.

  The protective layer 64 is formed in a layer shape having a predetermined thickness on the upper surface of the insulating layer 65, and is formed of the same material as the insulating layer 65. The protective layer 64 is disposed so as to cover the heating resistor 71, the reference heating resistor 76, the wiring films 711, 712, and 761, and the wirings 713, 714, 762, and 763, thereby preventing these contaminations and damages. It is preventing.

  The heating resistor 71 included in the insulating layer 65 constitutes the detection element 70 together with the catalyst layer 72, and is a resistor whose resistance value changes according to its own temperature change. The heating resistor 71 is covered at its upper part by a catalyst layer 72 described later, and the temperature of the gas to be detected and the amount of heat generated when the combustible gas contained in the gas to be detected is burned by the action of the catalyst. As a result, the heating resistor 71 is heated or cooled, and its own resistance value changes. That is, the resistance value of the heating resistor 71 changes based on the temperature of the gas to be detected and the amount of heat generated when the combustible gas is burned by the action of the catalyst. By using an output value that changes in accordance with the change in gas, it is possible to detect the combustible gas contained in the gas to be detected. The output value that changes in accordance with the change in the resistance value of the heating resistor 71 will be described later in detail with reference to FIG.

  The heating resistor 71 is formed in a spiral shape in a plan view at a portion corresponding to the upper portion of the flat cavity 62 parallel to the silicon substrate 61, and is included in the insulating layer 65. The heating resistor 71 is formed of a conductive member having a large temperature resistance coefficient, and is formed of, for example, platinum (Pt), polysilicon, or the like.

Further, a catalyst layer 72 is formed on the upper surface of the insulating layer 65 and above the heat generating resistor 71 so as to cover a part of the heat generating resistor 71. The catalyst layer 72 includes a catalyst that is heated by the heating resistor 71 and promotes combustion of combustible gas, and a material can be appropriately selected depending on the combustible gas to be detected. For example, noble metals such as platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir) and ruthenium (Ru) can be adopted as a catalyst applied to many combustible gases such as hydrogen gas. As the catalyst layer 72, a single layer film of the catalyst or a catalyst in which the catalyst is supported on aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), or zirconia (ZrO ₂ ) can be used. In order to improve the adhesion strength between the protective layer 64 and the catalyst layer 72, the adhesion layer can be provided below the catalyst layer 72. As a material for forming the adhesion layer, for example, glass or a mixture of glass and a catalyst layer material is used.

  The left end of the heating resistor 71 constituting the detection element 70 is included in the insulating layer 65 and is electrically connected to the electrode 85 via a wiring 713 and a wiring film 711 formed integrally with the heating resistor 71. . On the other hand, the right end of the heating resistor 71 is included in the insulating layer 65 and is electrically connected to the ground electrode 86 via a wiring 714 and a wiring film 712 formed integrally with the heating resistor 71. The electrode 85 and the ground electrode 86 are the lead-out portions of the wiring connected to the heating resistor 71 and are exposed through the contact holes. As the material of the electrode 85 and the ground electrode 86, for example, aluminum (Al) or gold (Au) is used.

  On the other hand, the reference heating resistor 76 constitutes a reference element 75 for correcting the output of the detection element 70 due to the temperature change of the gas to be detected, and is a resistor whose resistance value changes due to its own temperature change. . Since the reference heating resistor 76 changes its resistance value depending on the temperature of the gas to be detected, if the output value that changes according to the change in the resistance value of the reference heating resistor 76 is used, the heating resistor described above is used. Among the output values that change according to the change in the resistance value 71, the output value corresponding to the change in the resistance value of the heating resistor 71 based on the temperature change of the gas to be detected can be corrected. The output value that changes in accordance with the change in the resistance value of the reference heating resistor 76 will be described later in detail with reference to FIG.

  Similar to the heat generating resistor 71, the reference heat generating resistor 76 is formed in a spiral shape in plan view above the flat cavity 63 parallel to the silicon substrate 61, and is included in the insulating layer 65. The reference heating resistor 76 is usually made of the same material as the heating resistor 71, and is made of, for example, platinum (Pt), polysilicon, or the like.

  The left end of the reference heating resistor 76 is included in the insulating layer 65 and is electrically connected to the ground electrode 86 via a wiring 762 and a wiring film 712 that are integrally formed with the reference heating resistor 76. On the other hand, the right end of the reference heating resistor 76 is included in the insulating layer 65 and is electrically connected to the electrode 87 via a wiring 763 and a wiring film 761 formed integrally with the reference heating resistor 76. The ground electrode 86 and the electrode 87 are wiring lead portions connected to the reference heating resistor 76, and are exposed through contact holes. As the material of the ground electrode 86 and the electrode 87, for example, aluminum (Al) or gold (Au) is used.

  The resistance temperature detector 80 is for detecting the temperature of the gas to be detected existing in the detection space 39, and is on a plane parallel to the silicon substrate 61 between the insulating layer 65 and the protective layer 64. Is formed. The resistance temperature detector 80 is made of a metal whose electric resistance value changes in proportion to the temperature, for example, platinum (Pt). Since the resistance temperature detector 80 constitutes the gas detection element 60 together with the detection element 70 and the reference element 75, a resistance temperature detector for detecting the temperature of the gas to be detected is provided separately from the gas detection element 60. In comparison, the detection space 39 can be reduced in size.

  The resistance temperature detector 80 is electrically connected to the electrode 88 and the ground electrode 89. The electrode 88 and the ground electrode 89 are exposed through the contact hole. As the material of the electrode 88 and the ground electrode 89, for example, aluminum (Al) or gold (Au) is used.

  Next, an outline of the sensor output circuit 90 provided on the circuit board 41 will be described with reference to FIG. FIG. 6 is an explanatory diagram for explaining a sensor output circuit 90 for processing a detection signal of the gas detection element 60. As shown in FIG. 6, the sensor output circuit 90 includes a detection circuit 91, a reference circuit 92, and a temperature measurement circuit 93. Hereinafter, each circuit provided in the sensor output circuit 90 will be described in detail.

  The detection circuit 91 is provided in the Wheatstone bridge 911 including the heating resistor 71 provided in the gas detection element 60 and the fixed resistors 95 to 97 provided in the circuit board 41, and the circuit board 41. An operational amplifier 912 that amplifies the potential difference obtained from the Wheatstone bridge 911 is provided. When a resistor whose resistance value increases as the temperature rises is used as the heating resistor 71, the operational amplifier 912 has a temperature of the heating resistor 71 of a predetermined temperature (for example, 200 ° C.). When the temperature of the heating resistor 71 rises, the output voltage is lowered, and when the temperature of the heating resistor 71 is lowered, the output voltage is raised. To do. Since the output of the operational amplifier 912 is connected to the Wheatstone bridge 911, when the combustible gas contained in the gas to be detected is burned by the action of the catalyst and the temperature of the heating resistor 71 rises, the heat is generated. In order to lower the temperature of the resistor 71, the voltage output from the operational amplifier 912 decreases, and the voltage applied to the Wheatstone bridge 911 decreases. At this time, the voltage of the electrode 85 constituting the end of the Wheatstone bridge 911 is detected by the microcomputer 94 as the output of the detection circuit 91, and the output value detected by the microcomputer 94 is included in the gas to be detected and is combustible. It is subjected to arithmetic processing for detecting sex gases.

  Similarly, the reference circuit 92 includes a reference heating resistor 76 provided in the gas detection element 60, a Wheatstone bridge 921 configured by fixed resistors 98 to 100 provided in the circuit board 41, and a circuit board 41. And an operational amplifier 922 that amplifies the potential difference obtained from the Wheatstone bridge 921. The output of the operational amplifier 922 operates so that the temperature of the reference heating resistor 76 is maintained at a predetermined temperature (for example, 200 ° C.), and is connected to the Wheatstone bridge 921. The output of the electrode 85 constituting the end of the Wheatstone bridge 921 is detected by the microcomputer 94, and the output value detected by the microcomputer 94 is included in the detected gas for calculation processing for detecting the combustible gas. Provided.

  The temperature measuring circuit 93 is provided in the circuit board 41 and the Wheatstone bridge 931 configured by the resistance temperature detector 80 provided in the gas detection element 60, the fixed resistors 101 to 103 provided in the circuit board 41. And an operational amplifier 932 for amplifying the potential difference obtained from the Wheatstone bridge 931. The output of the operational amplifier 932 is detected by the microcomputer 94, and the output value detected by the microcomputer 94 is used to measure the temperature of the gas to be detected, and further detects the combustible gas contained in the gas to be detected. It is used for arithmetic processing.

  Based on the output value of the sensor output circuit 90 having the above configuration, the process of calculating the concentration of the combustible gas executed by the microcomputer 94 is performed as follows. First, the CPU provided in the microcomputer 94 is based on the potential difference obtained from the output value of the detection circuit 91 and the output value of the reference circuit 92 based on a program stored in a storage device (not shown) provided in the microcomputer 94. A first output value approximately proportional to the combustible gas concentration is output. Since this first output value includes an output change due to an ambient temperature change in the detection space 39, subsequently, a second output value obtained by correcting the first output value based on the output from the temperature measuring circuit 93 is output. To do. Further, the microcomputer 94 determines the concentration of the combustible gas contained in the detected gas based on the relationship between the second output value stored in the storage device (not shown) of the microcomputer 94 and the concentration of the combustible gas. Output. Thus, since the 1st output value is amended based on the output of temperature measuring circuit 93, combustible gas can be detected with sufficient accuracy.

  According to the gas detector 10 described above, even when the temperature of the gas to be detected is higher than the temperature of the outside air of the gas detector 10, the element case 20 is heated by the heating elements 50 and 51, and the element case 20 The members constituting the inner surface, that is, the connection terminal extraction base 21 of the element case 20, the detection space forming member, the water repellent filter 29 constituting the introducing portion 35, the spacer 30, the two metal meshes 31, 32, and the filter fixing The member 33 is prevented from being cooled below the dew point of the gas to be detected by outside air or the like. For this reason, it is possible to prevent the gas to be detected from being cooled below the dew point by the gas detector 10. For this reason, it is possible to prevent the gas to be detected from being cooled below the dew point by the gas detector 10 and dew condensation in the detection space 39.

  Further, by adjusting the amount of heat generated by the heating elements 50 and 51, it is possible to control the detected gas to have a predetermined temperature, and the temperature of the detected gas can be stabilized. Therefore, the detection sensitivity can be kept good.

  Further, the heating element 50 is provided on the outer surface of the element case constituting the accommodation space forming surface 58, and the element case 20 among the inner side surfaces of the accommodation case 40 constituting the accommodation space forming surface 58. Since the heat of the heating element is easily conducted to the inner side surface of the element case forming the detection space 39, the inner side surface can be efficiently heated.

  In addition, since the outer surface of the detection space forming member 22 constituting the element case 20 is in contact with the gas to be detected, the area of the surface of the element case 20 that is in contact with the gas to be detected can be increased. For this reason, since the amount of heat conducted from the gas to be detected to the element case increases, the element case forming the detection space can be heated by the gas to be detected, and further, the gas to be detected can be more reliably condensed. Can be prevented. Further, since the temperature of the gas to be detected can be stabilized, the sensitivity of the gas detector can be stabilized.

  The gas detector described above is not limited to the above-described embodiment, and various modifications may be made without departing from the gist of the present invention. First, in the above-described embodiment, the case where the gas detection element is a catalytic combustion type gas detection element has been described as an example of the gas detector. However, the present invention is not limited to this. For example, the gas detection element of the gas detector may be another detection element in addition to the heat conduction type gas detection element.

  Moreover, in this embodiment, although the gas detector 10 was mounted in the fuel cell unit of a motor vehicle, for example, it was illustrated that it was used for the purpose of detecting the leak of hydrogen, etc., the installation location and application of the gas detector 10 are Various selections are possible, and the present invention is not limited to this. For example, you may apply this invention to the gas detection apparatus used for the leak detection and density | concentration detection of combustible gas, such as city gas.

  Moreover, the structure of the gas detection element 60 which is a contact combustion type gas detection element should just be a thing which detects the density | concentration of combustible gas using the electrical resistance value changing with combustion of combustible gas. The present embodiment is not limited to this. Therefore, for example, instead of the resistance temperature detector 80 of the present embodiment, a resistance temperature detector separate from the gas detection element 60 and other temperature sensors may be employed.

  In the present embodiment, the two heating elements fixed to the accommodation space forming surface 58 are the heating elements 50 and 51. The number of heating elements depends on the heating characteristics of the heating elements, the desired temperature, etc. However, the present invention is not limited to this. Further, the fixing position of the heating element can adopt a surface constituting the accommodation space forming surface, and is not limited to the fixing position of the present embodiment. In order to efficiently conduct the heat of the heating element to the element case forming the detection space, it is preferable that the element case is fixed to a member in contact with the gas to be detected, that is, a position close to the element case.

2 is a longitudinal sectional view showing a state where a gas detector 10 is disposed in a pipe 200. FIG. 1 is a longitudinal sectional view of a gas detector 10. FIG. FIG. 3 is an enlarged longitudinal sectional view of the periphery of an element case 20 of the gas detector 10. It is a schematic plan view for explaining the arrangement state of the detection element 70 and the reference element 75 of the gas detection element 60, FIG. 5 is a cross-sectional view in the direction of the arrows along line AA in FIG. 4 for explaining the arrangement state of the detection element 70 and the reference element 75. It is explanatory drawing explaining the sensor output circuit 90 for processing the detection signal of the gas detection element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas detector 20 Element case 39 Detection space 40 Storage case 41 Circuit board 46 Holding | maintenance part 50 Heat generating body 51 Heat generating body 58 Storage space formation surface 59 Storage space 60 Gas detection element

Claims (5)

A gas detection element for detecting a gas to be detected;
An element case that houses the gas detection element and has an introduction port for introducing the detection gas, and forms a detection space into which the detection gas is introduced,
A housing case that houses a circuit board that is electrically connected to the gas detection element, and that has a holding portion that holds at least a part of the element case in an internal state,
A gas detector comprising an inner surface of the housing case and an outer surface of the element case, and a housing space forming surface that forms a housing space for housing the circuit board,
A gas detector, comprising: a heating element fixed to the housing space forming surface and for heating the element case forming the detection space.   The gas detector according to claim 1, wherein the heating element is provided on an outer surface of the element case constituting the housing space forming surface.   3. The gas detector according to claim 1, wherein the heating element is provided on a surface having the holding portion of an inner surface of the housing case constituting the housing space forming surface.   The gas detector according to claim 1, wherein at least a part of an outer surface of the element case is in contact with the gas to be detected.   The gas detector according to any one of claims 1 to 4, wherein the gas detection element is a heat conduction type gas detection element or a contact combustion type gas detection element.

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