JP2009014395A - Thermocouple for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermocouple having an insulated and waterproof surface and a diameter not larger than 0.014 mm for measuring a temperature by being inserted into a cell of a fuel cell, and to set a voltage rise per cell in the target fuel cell to be about 5V or less. <P>SOLUTION: A plus side thermocouple wire and a minus side thermocouple wire of a thermocouple is arranged linearly, and each abutting portion of the tip of the plus side thermocouple wire and the tip of the thermocouple wire facing each other is bonded by welding to form a temperature measuring junction, and polyimide is coated on the surface of the plus side thermocouple wire and the minus side thermocouple wire, to thereby form this thermocouple for the fuel cell. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermocouple for a fuel cell.

  A fuel cell has a structure in which power generation units called cells are stacked in multiple layers. In order to measure the temperature of an electrolyte membrane of a fuel cell testing machine, monitor the temperature of a practical machine, control the temperature, etc., there is a demand for an extremely thin thermocouple that can be inserted into a cell to measure the temperature. The present invention relates to this thermocouple.

  Conventional small-diameter thermocouples include those shown in Patent Documents 1 and 2. The one shown in Patent Document 1 has an elliptical cross section and a minor axis of about 0.3 mm, and the one shown in Patent Document 2 has a circular sectional type diameter of about 0.1 mm and an elliptical sectional type short. The diameter is also about 0.1 mm.

  Thermocouples that are inserted into the cell to measure temperature must have an insulated surface so that no current flows through the thermocouple wire due to potential differences depending on the location in the fuel cell. Yes, when the strands are immersed in the moisture of the electrolyte membrane or the moisture generated after the fuel is used, the portion of the strands immersed in the moisture is close to the same potential, and the thermoelectromotive force of the thermocouple changes. Since an error occurs in the measurement temperature, it is necessary that the wire is protected against moisture.

The thermocouple for a fuel cell satisfies these conditions, and preferably has a diameter as small as possible in order to reduce the influence on the components of the fuel cell. The thermocouple is thinner than 0.1 mm. Is required.
JP 2007-078421 A JP 2007-078333 A

  It is an object of the present invention to provide a thermocouple having a diameter of 0.014 mm or less whose surface is insulated and waterproof, which is inserted into a fuel cell to measure temperature. The target fuel cell has a voltage increase of about 5 V or less per cell. For example, a solid polymer fuel cell of an electric vehicle has a maximum voltage increase of about 1.2 V per cell, It is contained in the use object of the thermocouple by this invention.

  Therefore, in view of the above circumstances, the present invention provides a thermocouple having a diameter of 0.014 mm or less whose surface is insulated and waterproof for insertion into a fuel cell and measuring the temperature. In order to measure a fuel cell whose voltage rise per sheet is about 5 V or less, a plus side strand (hereinafter referred to as “+ side thermocouple strand”) and a minus side strand (hereinafter referred to as “− side thermoelectric”) ”Paired strands”) are arranged in a straight line, and the portion where the tip of the facing + side thermocouple strand contacts the tip of the − side thermocouple strand is welded to form a temperature measuring contact, and the + side thermocouple A thermocouple for a fuel cell in which polyimide was coated on the surface of the strand and the negative side thermocouple strand was obtained.

  Further, in the present invention, specifically, the strand diameter of the + side thermocouple strand and the minus side thermocouple strand is 13 μm or less, the polyimide coating thickness is 0.5 μm or less, and the outer diameter is 14 μm or less. The fuel cell thermocouple.

  Furthermore, the present invention is for a fuel cell in which a polyimide coating is formed on the surface of a thermocouple element of a + side thermocouple element and a − side thermocouple element by repeating application of polyimide with a brush and solidification by heating. A thermocouple was used.

  In the present invention, the + side thermocouple strand and the − side thermocouple strand of the thermocouple are arranged in a straight line, and the tip of the facing + side thermocouple strand and the − side thermocouple strand are in contact with each other. It is a thermocouple for fuel cells in which polyimide is coated on the surface of the + side thermocouple strand and the − side thermocouple strand by joining by welding to make a temperature measuring contact. A thermocouple having a diameter of 0.014 mm or less whose surface is insulated and waterproof for measurement can be provided, and a fuel cell whose voltage rise per cell is about 5 V or less can be measured.

  Further, in the present invention, specifically, the strand diameter of the + side thermocouple strand and the minus side thermocouple strand is 13 μm or less, the polyimide coating thickness is 0.5 μm or less, and the outer diameter is 14 μm or less. The fuel cell thermocouple.

  Furthermore, the present invention is for a fuel cell in which a polyimide coating is formed on the surface of a thermocouple element of a + side thermocouple element and a − side thermocouple element by repeating application of polyimide with a brush and solidification by heating. A thermocouple was used.

  Specific embodiments of the present invention are illustrated in the accompanying drawings and are described in detail below.

1. The structure of the thermocouple according to the present invention The structure of the thermocouple according to the present invention is shown in FIG.

  The + side thermocouple strand 1 and the − side thermocouple strand 2 are arranged in a straight line, and the tip of the thin portion 3 of the + side thermocouple strand and the tip of the narrow portion 4 of the − side thermocouple strand Are connected by welding, and the + side thermocouple wire 1 and the − side thermocouple wire 2 of normal thickness are connected to the other ends of the respective wires. The strands 1 and 2 having the normal thickness are wired as lead wires to the thermocouple receiver. The welded portion of the small diameter portion 3 of the + side thermocouple wire and the thin diameter portion 4 of the − side thermocouple wire becomes the temperature measuring contact 5, and the temperature at this position becomes the output temperature of the thermocouple.

  The thin thermocouple element is coated with polyimide, and the polyimide coating 6 is applied in a range longer than the width B of the cell whose temperature is to be measured.

2. Diameter of thermocouple As the thin diameter portions 3 and 4 of the thermocouple wire, a strand having an outer diameter of φ0.013 mm (13 μm) or less is used, and the following steps are repeated several times to form a polyimide coating 6. To do.

(1) Applying polyimide with a brush
(2) Solidification of applied polyimide by heating This process prevents the ingress of moisture without pinholes, and the polyimide coating has a thickness of 0.0005 mm (0.5 μm) or less with a withstand voltage of DC 5 V as an insulating material. 6 is obtained. The outer diameter of the thermocouple is φ14 μm or less when the wires 3 and 4 and the polyimide coating 6 are combined.

3. 2. Description of Use State FIG. 2 shows the use state of the thermocouple according to the present invention. The thermocouple according to the present invention is inserted to measure the temperature of, for example, the electrolyte membrane in the fuel cell 7 and measures the temperature at the position of the temperature measuring contact 5 shown in FIG. Although the illustrated cell is one, the cells are actually stacked in multiple layers. The cell is composed of an anode, a cathode, an electrolyte membrane, a separator, etc., but these are not individually shown in FIG.

  The normal thickness thermocouple wires 1 and 2 connected to the thin diameter portions 3 and 4 of the thermocouple wires are wired as lead wires to the floating input type thermocouple receiver 8. In the thermocouple receiver, the electromotive force of the thermocouple is measured, converted into a temperature, and output from the thermocouple receiver as a measured temperature.

  Since the polyimide coating portion is longer than the cell width B, the portion of the thermocouple in the cell is electrically insulated from the cell by the polyimide coating 6 and prevents moisture from entering the strand. Moreover, although not shown in figure, the normal insulation coating is given to the thermocouple element | wire of the part which the polyimide coating of the small diameter part and the normal thickness are not given. Since these portions are not limited in diameter, a normal insulating coating may be used.

4). Features The features of the present invention are summarized as follows.

  (1) By the following, a thermocouple having an outer surface with an outer diameter of φ14 μm or less was insulated.

    i. In the conventional thermocouple, the + side strand 101 and the − side strand 102 are arranged in parallel as shown in FIG. 3 and bundled as shown in FIG. -The side strands were linearly arranged and joined, and the strand diameter was made as narrow as φ13 µm or less.

   ii. A polyimide coating with an electrical insulation thickness of 0.5 μm or less was applied to the surface of the thermocouple by repeatedly applying polyimide with a brush and solidifying by heating several times.

      With this realization, it became possible to measure the temperature inside the cell of the fuel cell in a state in which the influence due to the attachment to the cell structure or the like was suppressed compared to the conventional case. In addition, if the coated part is installed between the cells, the temperature between the two cells of the fuel cell can be adjusted so that the fuel provided in the spacer between the cells and the passage of products such as water generated after the fuel is used. It has also become possible to measure in a state that is less disturbing than before.

  (2) Since the polyimide coating has an electric dielectric strength of 5V, it can be applied to a fuel cell in which the voltage rise of one cell is 5V or less.

      When a large number of cells are stacked, the ground voltage of the cell increases with the number of cells, but this ground height can be increased if a floating input type receiver is used and the potential of the thermocouple wire is not fixed. Not affected by voltage. What is required of thermocouples is that the electrical insulation of the polyimide coating is not broken by this potential difference when there are parts with different voltages depending on the location in the cell environment where the thermocouple is installed. When insulation of the polyimide coating is lost, current flows through the thermocouple wire between the parts with a potential difference, and the performance of the cell deteriorates. If the voltage rise of one cell is 5V or less, the voltage difference due to the location in the cell and between adjacent cells will not exceed this voltage, so this thermocouple will raise the voltage rise of one cell to 5V or less. It can be used for fuel cells.

  (3) Polyimide is a waterproof material. The polyimide coating on the thermocouple surface has been confirmed by surface inspection and submerged electrical insulation test to have no openings such as pinholes and prevent moisture from entering the strands. In fuel cells, there are places where the water content of the electrolyte membrane and the hydrogen of the fuel exist, but the insulation of the thermocouple surface is maintained even in the water and it is waterproof. It is also possible to measure.

      In addition, since polyimide has a heat resistance of 350 ° C., it can be used for fuel cells of solid polymer type, phosphoric acid type, alkaline type and the like whose operating temperature is lower than this.

  (4) With regard to the selection of the temperature measurement position, the front-rear direction in FIG. 2 can be selected by the front-rear position where the thermocouple is installed, and the left-right direction position in FIG. This can be done by creating a temperature measuring junction at the position in the left-right direction that you want to measure. Therefore, if there is no restriction on the structure of the fuel cell, it is possible to measure the temperature at any desired position.

      Even if the thermocouple cannot be placed in a straight line due to structural limitations of the fuel cell, the thermocouple is flexible and can be installed in a bent state.

  An embodiment of the present invention is shown in FIG.

Thermocouple type: JIS C 1602 type K
Thin diameter thermocouple wire diameter: φ12.7μm
Small diameter part thermocouple + side strand length: 210mm
Small diameter part thermocouple-side strand length: 210mm
Joining of small-diameter portion thermocouple + side strand and -side strand: laser welding Formation of polyimide coating: Forming by applying polyimide with a brush and solidifying by heating 4 times.

Polyimide coating length: 400mm
Polyimide coating thickness: 0.15 μm
Thermocouple outer diameter (elementary wire and polyimide coating): φ13μm
Withstand voltage of polyimide coating: DC5V or more (confirmed by inspection)
Polyimide coating hole: None (confirmed by surface magnifier inspection and absence of insulation degradation in water)
Joining of thermocouple strands of small diameter and lead wires: Laser welding

  Although the present invention has been described with respect to a thermocouple used for a fuel cell, it has a small diameter and does not take an installation place, so that it may be installed in a hydrogen gas engine or the like.

It is a figure which shows the whole structure of the small diameter thermocouple of this invention. It is a figure which shows the use condition of this invention. It is a figure which shows the conventional thermocouple strand arrangement | positioning. It is a figure which shows the dimension of the Example of this invention.

Explanation of symbols

1 ... + thermocouple wire (lead wire)
2 ...- side thermocouple wire (lead wire)
3 ... + thermocouple wire (small diameter part)
4 ...- side thermocouple wire (thin diameter part)
5 ... Temperature measuring contact 6 ... Polyimide coating

Claims (3)

  Place the + side thermocouple strand of the thermocouple and the – side thermocouple strand in a straight line, and join the tip of the facing + side thermocouple strand and the tip of the – side thermocouple strand by welding. A thermocouple for a fuel cell in which a temperature measuring contact is used and polyimide is coated on the surface of the + side thermocouple strand and the-side thermocouple strand.   2. The fuel cell thermoelectric device according to claim 1, wherein the wire diameter of the + side thermocouple wire and the − side thermocouple wire is 13 μm or less, the thickness of the polyimide coating is 0.5 μm or less, and the outer diameter is 14 μm or less. versus.   The polyimide coating of Claim 1 and Claim 2 which formed the polyimide coating on the thermocouple strand surface of + side thermocouple strand by repeating application | coating by the brush of polyimide, and solidification by heating. Fuel cell thermocouple.

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