Fuel cell separator and welding method for fuel cell separator

Abstract

To provide a fuel cell separator capable of preventing leakage between a gas and a cooling medium via a welded part.SOLUTION: A fuel cell separator comprises: a first thin plate having a first surface facing a first gas flow path through which a first reaction gas flows, and a second surface facing a cooling medium flow path through which a cooling medium flows; and a second thin plate having a first surface facing a second gas flow path through which a second reaction gas flows, and a second surface facing the cooling medium flow path. The second surface of the first thin plate and the second surface of the second thin plate are welded while facing each other. The first thin plate and the second thin plate have a welded part extending along an annular weld line so as to form the cooling medium flow path between the second surface of the first thin plate and the second surface of the second thin plate. A start edge and an end edge of the welded part are positioned on opposite sides of the cooling medium flow path via the weld line.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fuel cell separator formed by welding a pair of thin plates together, and a method for welding a fuel cell separator. [Background technology]

[0002] In recent years, technological development has been conducted on fuel cells that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. A conventionally known technology related to this type of fuel cell is a laser welding method in which a pair of thin plates are welded together by irradiating them with a laser beam (see, for example, Patent Document 1). In the method described in Patent Document 1, when multiple workpieces are stacked and irradiated with a laser beam, the irradiation positions are shifted between the start and end of the irradiation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6735898 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when welding by irradiating a laser beam or the like, the energy density tends to be particularly high at the start and end of irradiation. Therefore, even if the irradiation position is shifted between the start and end as in the method described in Patent Document 1, holes may be formed at the start or end of the workpiece, and leakage may occur between the cooling medium and the gas through the holes. [Means for solving the problem]

[0005] A fuel cell separator according to one aspect of the present invention comprises a first thin plate having a first surface facing a first gas flow path through which a first reactant gas flows and a second surface facing a coolant flow path through which a coolant flows, and a second thin plate having a first surface facing a second gas flow path through which a second reactant gas flows and a second surface facing the coolant flow path, the first thin plate and the second thin plate being welded together so that the second surface of the first thin plate faces the second surface of the second thin plate. The first thin plate and the second thin plate have a weld extending along an annular weld line to form the coolant flow path between the second surface of the first thin plate and the second surface of the second thin plate, with the start and end of the weld located on opposite sides of the weld line from the coolant flow path.

[0006] Another aspect of the present invention is a method for welding a fuel cell separator, which includes welding a first thin plate having a first surface facing a first gas flow path through which a first reactant gas flows and a second surface facing a coolant flow path through which a coolant flows, to a second thin plate having a first surface facing a second gas flow path through which a second reactant gas flows and a second surface facing the coolant flow path, the method including the steps of: arranging the second surface of the first thin plate and the second surface of the second thin plate so as to face each other; and welding the first thin plate and the second thin plate along an annular weld line to form a coolant flow path between the second surface of the first thin plate and the second surface of the second thin plate. The welding step includes welding such that a start end and a finish end of the weld are located on opposite sides of the coolant flow path relative to the weld line. [Effects of the Invention]

[0007] According to the present invention, leakage between the gas and the cooling medium through the welded portion can be prevented. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view schematically showing the overall configuration of a fuel cell stack having a fuel cell separator according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a perspective view showing a schematic configuration of an electrode assembly included in the fuel cell stack of FIG. [Figure 4]FIG. 2 is a rear view of a fuel cell separator according to an embodiment of the present invention. [Figure 5] 5 is a cross-sectional view taken along line VV in FIG. 4. [Figure 6] FIG. 5 is an enlarged view of the main part of FIG. 4. [Figure 7A] FIG. 7 is a diagram showing a modification of FIG. 6. [Figure 7B] FIG. 7 is a diagram showing another modified example of FIG. 6. [Figure 8] FIG. 7 is a diagram showing a reference example of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 8. A fuel cell separator according to an embodiment of the present invention is incorporated into a fuel cell stack to form a fuel cell. The fuel cell is mounted on, for example, a vehicle and generates electric power for driving the vehicle. First, the configuration of the fuel cell stack will be described.

[0010] FIG. 1 is a perspective view showing a schematic overall configuration of a fuel cell stack 100 having a fuel cell separator according to an embodiment of the present invention. For convenience, the three mutually orthogonal axial directions shown in the figure are defined as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part will be described in accordance with these definitions. The front-rear direction corresponds to the stacking direction of the fuel cell stack 100. The front-rear direction, the left-right direction, and the up-down direction are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle.

[0011] As shown in Fig. 1, the fuel cell stack 100 has a cell stack 101 formed by stacking a plurality of power-generating cells 1 in the front-to-rear direction, and end units 102 arranged at both front and rear ends of the cell stack 101, and has a generally rectangular parallelepiped shape as a whole. Although not shown in the figure, the cell stack 101 is surrounded by a generally rectangular parallelepiped case. The length of the cell stack 101 in the left-to-right direction is longer than the length in the up-to-down direction. For convenience, only a single power-generating cell 1 is shown in Fig. 1.

[0012] The power-generating cell 1 has a unitized electrode assembly 2 (UEA) having a membrane electrode assembly including an electrolyte membrane and electrodes, and separators 3, 3 arranged on both the front and rear sides of the unitized electrode assembly 2 to sandwich the unitized electrode assembly 2. The unitized electrode assemblies 2 and the separators 3 are arranged alternately in the front-to-rear direction. The unitized electrode assembly 2 can also be called a membrane electrode structure or a membrane electrode member.

[0013] FIG. 2 is a cross-sectional view of a main portion of the cell stack 101 at the center in the left-right direction (a cross-sectional view taken along line II-II in FIG. 1). As shown in FIG. 2, the separator 3 has a front plate 3F and a rear plate 3R, which are a pair of front and rear metal thin plates with a corrugated cross section. The front plate 3F extends in the vertical and horizontal directions and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends in the vertical and horizontal directions and has a front surface 3Ra and a rear surface 3Rb. The opposing front plate 3F and rear plate 3R are joined by welding at their outer peripheral edges, thereby joining the two together. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0014] A cooling flow path PAw through which a coolant flows is formed inside the separator 3 surrounded by the front plate 3F and the rear plate 3R, i.e., between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R. The flow of the coolant cools the power generation surface of the power generation cell 1. Water, for example, can be used as the coolant. The surface of the separator 3 facing the integrated electrode assembly 2 (the front surface 3Fa and the rear surface 3Rb) is formed unevenly by press molding or the like to form a gas flow path between the separator 3 and the integrated electrode assembly 2. More specifically, the separator 3 has a pair of front and rear protrusions 31 that protrude toward the integrated electrode assembly 2, and a pair of front and rear recesses 32 that are connected to the pair of front and rear protrusions 31 and are formed in a concave shape.

[0015] The pair of front and rear protrusions 31 abut against the front surface 2a and rear surface 2b of the integrated electrode assembly 2. A compressive load F is applied to the cell stack 101 in the front-to-rear direction during assembly of the fuel cell stack 100, and this compressive load F is maintained after assembly of the fuel cell stack 100 is complete. As a result, a predetermined surface pressure due to the compressive load F acts on the integrated electrode assembly 2 in the front-to-rear direction via the protrusions 31.

[0016] An anode flow path PAa through which a fuel gas flows is formed by a recess 32 between the front surface 2a of the integrated electrode assembly 2 and the rear plate 3R of the separator 3 facing this front surface 2a. A cathode flow path PAc through which an oxidizer gas flows is formed by a recess 32 between the rear surface 2b of the integrated electrode assembly 2 and the front plate 3F of the separator 3 facing this rear surface 2b. The fuel gas is a gas containing hydrogen, and hydrogen gas can be used, for example. The oxidizer gas is a gas containing oxygen, and air can be used, for example. The fuel gas and the oxidizer gas are sometimes referred to as reactant gases without being distinguished from each other.

[0017] Fig. 3 is a perspective view showing a schematic configuration of the integrated electrode assembly 2. As shown in Fig. 3, the integrated electrode assembly 2 has a substantially rectangular membrane electrode assembly (MEA) 20 and a frame 21 that supports the membrane electrode assembly 20. As shown in the detailed view of part A in Fig. 2, the membrane electrode assembly 20 has an electrolyte membrane 23, an anode electrode 24 provided on a front surface 23f of the electrolyte membrane 23, and a cathode electrode 25 provided on a rear surface 23r of the electrolyte membrane 23.

[0018] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing water can be used. The electrolyte membrane 23 is not limited to a fluorine-based electrolyte membrane, and a hydrocarbon-based electrolyte membrane can also be used.

[0019] The anode 24 is formed on the front surface 23f of the electrolyte membrane 23 and includes an electrode catalyst layer 241 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 242 that is provided in front of the electrode catalyst layer 241 and diffuses and supplies a fuel gas. An intermediate layer (base layer) may be provided between the electrode catalyst layer 241 and the gas diffusion layer 242. Only the electrode catalyst layer 241 may be referred to as the anode 24.

[0020] The cathode electrode 25 is formed on the rear surface 23r of the electrolyte membrane 23 and includes an electrode catalyst layer 251 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 252 that is provided on the rear surface of the electrode catalyst layer 251 and diffuses and supplies an oxidant gas. An intermediate layer (base layer) may be provided between the electrode catalyst layer 251 and the gas diffusion layer 252. Only the electrode catalyst layer 251 may be referred to as the cathode electrode 25.

[0021] At the anode electrode 24, the fuel gas (hydrogen) supplied via the anode flow path PAa is ionized by the action of a catalyst and moves toward the cathode electrode side through the electrolyte membrane 23. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode 25, the oxidant gas (oxygen) supplied via the cathode flow path PAc reacts with the hydrogen ions introduced from the anode electrode 24 and the electrons moved from the anode electrode 24, producing water. The produced water (referred to as "produced water") provides an appropriate humidity to the electrolyte membrane 23, and excess water is discharged to the outside of the integrated electrode assembly 2 along the gas flow. The produced water on the cathode side also flows toward the anode side by reverse diffusion through the electrolyte membrane 23. Therefore, produced water exists in both the anode flow path PAa and the cathode flow path PAc.

[0022] 3, the frame 21 is a thin plate having a substantially rectangular shape and is made of insulating resin, rubber, or the like. A substantially rectangular opening 21a is provided in the center of the frame 21. The membrane electrode assembly 20 is provided so as to cover the entire opening 21a, and the peripheral edge of the membrane electrode assembly 20 is supported by the frame 21.

[0023] Three through holes 201 to 203 are aligned vertically and penetrate the frame 21 in the front-to-rear direction on the left side of the opening 21a of the frame 21. Three through holes 204 to 206 are aligned vertically and penetrate the frame 21 in the front-to-rear direction on the right side of the opening 21a. In Fig. 3, for convenience, the through holes 201 to 206 are shown as being substantially rectangular, but the shape and arrangement of the through holes 201 to 206 are not limited to this.

[0024] As shown in FIG. 1, the front and rear separators 3 of the integrated electrode assembly 2 are provided with through-holes 301 to 306, respectively, which penetrate the separators 3 in the front-rear direction at positions corresponding to the through-holes 201 to 206 of the frame 21. The through-holes 301 to 306 are connected to the through-holes 201 to 206 of the frame 21, respectively. A collection of these mutually communicating through-holes 201 to 206 and 301 to 306 form flow paths PA1 to PA6 (indicated by arrows for convenience) which penetrate the cell stack 101 and extend in the front-rear direction. The flow paths PA1 to PA6 are sometimes called manifolds. The flow paths PA1 to PA6 are connected to a manifold external to the fuel cell stack 100. In FIG. 1, the through-holes 301 to 306 are shown as being substantially rectangular for convenience, but the shape and arrangement of the through-holes 301 to 306 are not limited thereto.

[0025] Although not shown in the figures, the front and rear end units 102 of the cell stack 101 each have a plurality of plates stacked in the front-to-rear direction. That is, the end unit 102 has a terminal plate arranged adjacent to the cell stack 101, an insulating plate arranged on the outer side of the terminal plate in the front-to-rear direction, and an end plate arranged on the outer side of the insulating plate in the front-to-rear direction.

[0026] The rear end unit 102 is a wet-side end unit through which the reactant gas and the cooling medium pass, and the front end unit 102 is a dry-side end unit through which the reactant gas and the cooling medium do not pass. The rear end unit 102 has a plurality of through holes 102a-102f that penetrate the end unit 102 in the front-rear direction at positions corresponding to the through holes 201-206, 301-306 of the cell stack 101. In FIG. 1, the through holes 102a-102f are shown as being substantially rectangular for convenience, but the shape and arrangement of the through holes 102a-102f are not limited to this.

[0027] Fuel gas is supplied to the fuel cell stack 100 via the through-hole 102a along the solid-line flow path PA1. This fuel gas is guided to the anode flow path PAa between the integrated electrode assembly 2 and the rear plate 3R of the separator 3 via the through-holes 201 and 301. After passing through the anode flow path PAa, the fuel gas (fuel exhaust gas) is discharged from the through-hole 102f via the through-holes 206 and 306 and along the solid-line flow path PA6.

[0028] The oxidant gas is supplied to the fuel cell stack 100 via the through-hole 102d along the dotted flow path PA4. This oxidant gas is guided via the through-holes 204 and 304 to the cathode flow path PAc between the integrated electrode assembly 2 and the front plate 3F of the separator 3. After passing through the cathode flow path PAc, the oxidant gas (oxidant exhaust gas) is discharged from the through-hole 102c via the through-holes 203 and 303 and along the dotted flow path PA3.

[0029] A cooling medium is supplied to the fuel cell stack 100 via the through-hole 102e along the flow path PA5 shown in dashed dotted line. This cooling medium is guided to the cooling flow path PAw between the front plate 3F and the rear plate 3R of the separator 3 via the through-holes 205 and 305. After passing through the cooling flow path PAw, the cooling medium is discharged from the through-hole 102b via the through-holes 202 and 302 along the flow path PA2 shown in dashed dotted line. The above is a schematic configuration of the fuel cell stack 100.

[0030] The configuration of the fuel cell separator 3 according to this embodiment will be described in more detail. FIG. 4 is a rear view (view from behind) of the separator 3. That is, FIG. 4 is a view showing the rear surface 3Rb (FIG. 2) of the rear plate 3R, which faces the anode electrode 24 on the front surface 2a of the integrated electrode assembly 2. Point P in the figure is the midpoint of the separator 3 in the left-right direction and the midpoint in the up-down direction, and is referred to as the center point. Hereinafter, the side toward the center point may be referred to as the inside or inner side, and the side away from the center point may be referred to as the outside or outward side. The left-right direction and the up-down direction in FIG. 4 correspond to the longitudinal and lateral directions of the separator 3, respectively.

[0031] In Fig. 4, the region of the integrated electrode assembly 2 facing the membrane electrode assembly 20, i.e., the region AR1 facing the power generation surface, is called the active region of the separator 3, and the region AR2 other than the active region is called the inactive region. As shown in Figs. 2 and 4, although some are not shown, the active region AR1 of the separator 3 has a plurality of protrusions 31 (Fig. 2) protruding rearward at equal intervals in the vertical direction over almost the entire area. Each of the plurality of protrusions 31 extends in a meandering manner in the horizontal direction, and a recess 32 (Fig. 2) is provided between adjacent protrusions 31 in the vertical direction. An anode flow path PAa is formed between the plurality of recesses 32 and the front surface 2a of the membrane electrode assembly 20.

[0032] 4, a rear surface 3Rb of the separator 3 (rear plate 3R) is provided with a plurality of bead portions for sealing, i.e., metal bead seals, protruding rearward toward the frame 21. The plurality of bead portions includes an overall bead portion 331 and a plurality of individual bead portions 332.

[0033] The individual bead portions 332 each have a substantially rectangular shape and individually surround the through holes 301 to 306. The overall bead portion 331 extends in the left-right direction above and below the active area AR1 along the upper and lower edges of the separator 3, and also extends in a zigzag pattern, passing on the outsides of the individual bead portions 332 around the through holes 301, 303, 304, and 306 in the left-right direction and on the insides of the individual bead portions 332 around the through holes 302 and 305 in the left-right direction.

[0034] In the inactive region AR2 of the separator 3 (rear plate 3R) on the left-right outer side of the active region AR1, guide portions 333 are provided to protrude rearward, extending from the through-holes 301 to the entire inlet area at the left end of the anode flow channel PAa and from the entire outlet area at the right end of the anode flow channel PAa to the through-holes 306. Along these guide portions 333, fuel gas can be uniformly guided from the through-holes 301 to the anode flow channel PAa and from the anode flow channel PAa to the through-holes 306. Instead of the guide portions 333, substantially cylindrical embossed portions protruding rearward may be provided. The protrusions 31, recesses 32, metal bead seals (overall bead portions 331 and individual bead portions 332), and guide portions 333 are formed by press-forming the rear plate 3R.

[0035] Although not shown, a plurality of protrusions 31 and recesses 32, metal bead seals (overall bead portions 331 and individual bead portions 332), and guide portions 333 are similarly formed on the front surface 3Fa of the separator 3 (front plate 3F) by press-forming the front plate 3F. As a result, a cathode flow path PAc is formed between the plurality of recesses 32 and the rear surface 2b of the membrane electrode assembly 20.

[0036] The front plate 3F and rear plate 3R of the separator 3 are welded together at a weld. As shown by the dotted line in FIG. 4 , the weld includes an overall weld 341 extending along the outer edge of the separator 3 and a plurality of individual welds 342. The overall weld 341 has a generally rectangular shape and surrounds all of the individual bead portions 332. The plurality of individual welds 342 each have a generally rectangular shape and individually surround the individual bead portions 332 around the through holes 301, 303, 304, and 306 inside the overall bead portion 331.

[0037] The welds 341, 342 are formed by, for example, using a laser welding machine (not shown) to irradiate a laser beam along the weld line. Using a laser welding machine reduces welding distortion and enables high-speed welding. Note that the front plate 3F and the rear plate 3R can also be welded together by a method other than laser welding.

[0038] The rear surface 3Fb (FIG. 2) of the front plate 3F and the front surface 3Ra (FIG. 2) of the rear plate 3R are abutted and joined without any gaps at the welded portions 341, 342. Therefore, the welded portions 341, 342 function as seals that seal the cooling medium in the cooling flow passages PAw between the pair of plates 3F, 3R.

[0039] Tunnel portions 41 to 44 are provided between the through holes 301, 303, 304, 306 and the individual welded portion 342, intersecting with inner portions in the left-right direction of the individual bead portion 332. The tunnel portions 41 to 44 extend in the left-right direction perpendicular to the individual bead portion 332. Fig. 5 is a cross-sectional view taken along line VV in Fig. 4, showing the configuration of the tunnel portion 41.

[0040] 5, a tunnel portion 41 is provided on the front plate 3F so as to protrude forward, and a tunnel portion 41 is provided on the rear plate 3R so as to protrude rearward. The amount of protrusion of the tunnel portion 41 in the front-rear direction is smaller than the amount of protrusion of the individual bead portion 332 in the front-rear direction. Although not shown in the figure, the tunnel portion 41 has a substantially rectangular or trapezoidal cross section, and a communication flow path PA11 is formed between the front and rear tunnel portions 41, 41.

[0041] The left end of the tunnel portion 41 is located on the periphery of the through hole 301, and the left end of the communicating flow path PA11 is open facing the through hole 301. A tapered portion 411 is provided at the right end of the tunnel portion 41 beyond the individual bead portion 332, so that the amount of protrusion gradually decreases toward the right. At the right end of the tunnel portion 41, the amount of protrusion in the front-to-rear direction becomes zero, the communicating flow path PA11 is closed, and the front plate 3F and the rear plate 3R abut against each other. An individual weld 342 is provided at this abutment portion.

[0042] A fuel gas inlet 410 is opened in the tapered portion 411 of the rear plate 3R. This allows the through-hole 301 to communicate with the anode flow channel PAa at the rear of the rear plate 3R via the tunnel portion 41, that is, via the communication channel PA11 and the inlet 410. Therefore, the fuel gas flowing through the through-hole 301 can be supplied to the anode flow channel PAa via the communication channel PA11 and the inlet 410, as shown by the arrow in FIG. 5 .

[0043] Although detailed illustration is omitted, as shown in FIG. 4 , the tunnel portion 42 is configured bilaterally symmetrical to the tunnel portion 41. That is, the tunnel portion 42 has a fuel gas outlet 420 opened in a tapered portion at the left end of the rear plate 3R, and the fuel gas that has flowed through the anode flow channel PAa can be discharged to the outside via the outlet 420 and the tunnel portion 42. The tunnel portion 43 also has an outlet 430 provided in a tapered portion at the right end of the front plate 3F, and the tunnel portion 44 also has an inlet 440 provided in a tapered portion at the left end of the front plate 3F. This allows the oxidant gas that has flowed through the through-holes 304 to be supplied to the cathode flow channel PAc via the tunnel portion 44 and the inlet 440. The oxidant gas that has flowed through the cathode flow channel PAc can be discharged to the outside via the outlet 430 and the tunnel portion 43.

[0044] This embodiment is characterized by the configuration of individual welded portion 342. Fig. 6 is an enlarged view of the vicinity of through hole 301 in Fig. 4, showing the detailed configuration of individual welded portion 342. For convenience, Fig. 6 exaggerates the width of welded portion 342. Although not shown, individual welded portions 342 around other through holes 303, 304, and 306 are also configured in the same manner as Fig. 6.

[0045] As shown in Fig. 6, laser welding is performed along a substantially rectangular weld line 3420 (dotted line) that surrounds the individual bead portion 332 and the tunnel portion 41. More specifically, in the method of welding the separator, first, the bead seals (overall bead portion 331, individual bead portion 332) of the front plate 3F and the rear plate 3R are arranged in abutting contact with each other (arrangement step). Next, a laser beam is continuously irradiated along the weld line 3420, for example, from the rear surface 3Rb of the rear plate 3R (welding step). As a result, a continuous weld portion 342 is formed around the entire circumference of the through hole 301.

[0046] The welding process is performed by continuously irradiating a laser beam from a starting point 3421 to a terminal end 3422, as shown by the arrows in FIG. 6 . The welded portion 342 has an intersection 3423 between the starting point 3421 and the terminal end 3422, where the irradiation paths of the laser beam intersect. In this embodiment, the starting point 2421 and the terminal end 3422 are set inside the weld line 3420, in other words, inside the intersection 3423 (on the through hole 301 side). The weld line 3420 is a line that defines the welded portion 342 of the pair of plates 3F, 3R. More specifically, the weld line 3420 is a continuous, circular, closed line (a substantially rectangular line in FIG. 6 ) without any borders, and does not include the starting point 3421 and the terminal end 3422 that protrude from the intersection 3423.

[0047] The amount of heat input during laser welding at the starting point 3421, which is the starting point of laser irradiation, and the ending point 3422, which is the ending point, tends to be large due to the relationship between welding speed and power. For this reason, there is a risk of weld holes penetrating the thin separator 3 (e.g., the rear plate 3R) being formed at the starting point 3421 and the ending point 3422. Taking this into consideration, in this embodiment, the starting point 3421 and the ending point 3422 of the laser weld are set inside the substantially rectangular weld line 3420, more specifically, between the weld line 3420 and the individual bead portion 332.

[0048] As a result, even if a weld hole is formed in at least one of the starting end 3421 and the ending end 3422, the space (cooling flow path PAw) between the pair of plates 3F, 3R on the outside of the weld 342 (the opposite side of the through hole 301) will not communicate with the space on the rear surface side of the rear plate 3R and the space on the front surface side of the front plate 3F. As a result, it is possible to prevent cross leakage, which is leakage of reactant gas into the cooling flow path PAw or leakage of coolant from the cooling flow path PAw.

[0049] 8, if the starting end 3421 and the ending end 3422 are located outside the weld line 3420, there is a risk that the cooling channel PAw will communicate with the spaces on the rear surface side of the rear plate 3R and the front surface side of the front plate 3F when a weld hole is formed in at least one of the starting end 3421 and the ending end 3422. As a result, there is a risk of cross-leakage occurring between the cooling channel PAw and the gas channels PAa and PAc.

[0050] 6, laser welding is performed around the entire circumference of the weld line 3420 in one pass, but laser welding may be performed in multiple passes along the weld line 3420, as schematically shown in, for example, FIG. 7A. In this case, it is sufficient that multiple starting ends 3421 and multiple ending ends 3422 of the welded portion 342 are all positioned inside the weld line 3420.

[0051] 6, the intersection 3423 of the weld 342 is located near a straight portion of the weld line 3420, but it may also be located near a corner of the weld line 3420, as shown schematically in FIG. 7B. In this case, too, the start end 3421 and the end end 3422 of the weld 342 should be located inside the weld line 3420. Note that in FIGS. 7A, 7B, and 8, the weld line 3420 (dotted line) is shown shifted from the weld 342 for convenience in order to clearly show the weld line 3420.

[0052] According to this embodiment, the following effects can be achieved. (1) The fuel cell separator 3 includes a rear plate 3R having a rear surface 3Rb facing the anode flow channel PAa through which fuel gas flows and a front surface 3Ra facing the cooling flow channel PAw through which a coolant flows, and a front plate 3F having a front surface 3Fa facing the cathode flow channel PAc through which oxidizer gas flows and a rear surface 3Fb facing the cooling flow channel PAw. The front surface 3Ra of the rear plate 3R and the rear surface 3Fb of the front plate 3F are welded together in a facing relationship ( FIG. 2 ). The rear plate 3R and the front plate 3F have a weld 342 extending along an annular weld line 3420 to form the cooling flow channel PAw between the front surface 3Ra of the rear plate 3R and the rear surface 3Fb of the front plate 3F ( FIG. 6 ). The start end 3421 and end end 3422 of the weld 342 are located on the opposite side of the weld line 3420 from the cooling flow channel PAw (on the through-hole 301 side) ( FIG. 6 ).

[0053] In this way, by positioning the start end 3421 and the end end 3422 of the weld 342 on opposite sides (inside) of the cooling channel PAw across the weld line 3420, it is possible to prevent communication between the cooling channel PAw and the space on the rear surface side of the rear plate 3R and the space on the front surface side of the front plate 3F, even if a weld hole is opened by heat during welding at the start end 3421 or the end end 3422. As a result, it is possible to prevent leakage between the reaction gas and the cooling medium via the weld 342, i.e., cross leakage.

[0054] (2) The rear plate 3R and the front plate 3F are respectively provided with gas supply / discharge through-holes 301, 303, 304, and 306 through which fuel gas and oxidizer gas pass, and coolant supply / discharge through-holes 302 and 305 through which a coolant passes (FIG. 1). A weld line 3420 is provided around the gas supply / discharge through-holes 301, 303, 304, and 306 (FIGS. 4 and 6). The start end 3421 and the end end 3422 of the weld 342 are located inside the weld line 3420. This effectively prevents cross-leakage between the reactant gases (fuel gas and oxidizer gas) and the coolant, even if excessive heat is input to the start end 3421 or the end end 3422 of the weld 342, causing a weld hole.

[0055] (3) The rear plate 3R has an individual bead portion 332 protruding from the opposite side of the front plate 3F to seal the anode flow path PAa (FIGS. 4 and 5). The front plate 3F has an individual bead portion 332 protruding from the opposite side of the rear plate 3R to seal the cathode flow path PAc (FIGS. 4 and 5). These individual bead portions 332 are provided inside the weld lines 3420 (FIG. 6). This prevents cross-leakage between the coolant and the reactant gas, while allowing the individual bead portions 332 and the weld lines 342 to perform their respective functions of sealing the reactant gas and the coolant.

[0056] (4) The start end 3421 and the end end 3422 of the welded portion 342 are located between the weld line 3420 and the individual bead portion 332 (FIG. 6). This allows the individual bead portion 332 to maintain a sufficient sealing function even if a weld hole occurs in the start end 3421 or the end end 3422.

[0057] (5) A welding method for a fuel cell separator includes welding a rear plate 3R having a rear surface 3Rb facing the anode flow channel PAa through which a fuel gas flows and a front surface 3Ra facing the cooling flow channel PAw through which a coolant flows, and a front plate 3F having a front surface 3Fa facing the cathode flow channel PAc through which an oxidizer gas flows and a rear surface 3Fb facing the cooling flow channel PAw, and includes a step of arranging the front surface 3Ra of the rear plate 3R and the rear surface 3Fb of the front plate 3F so that they face each other (arranging step), and a step of welding the rear plate 3R and the front plate 3F along an annular weld line 3420 to form a cooling flow channel PAw between the front surface 3Ra of the rear plate 3R and the rear surface 3Fb of the front plate 3F (welding step). The welding step includes welding such that a starting end 3421 and an ending end 3422 of a weld 342 are positioned on opposite sides of the weld line 3420 from the cooling flow channel PAw ( FIG. 6 ). This prevents leakage between the reaction gas and the cooling medium through the welded portion 342 .

[0058] The above embodiment can be modified in various ways, and some modifications will be described below. In the above embodiment, serpentine-shaped gas flow paths PAa and PA are provided on the rear plate 3R as the first thin plate and the front plate 3F as the second thin plate, which are provided with through holes 301, 303, 304, 306 (first through holes) through which the reactant gas passes and through holes 302, 305 (second through holes) through which the cooling medium passes. However, the first thin plate may have any configuration as long as it has a rear surface 3Rb (first surface) facing the anode flow path PAa (first gas flow path) through which the fuel gas (first reactant gas) flows and a front surface 3Ra (second surface) facing the cooling flow path PAw (cooling medium flow path) through which the cooling medium flows. The second thin plate may have any configuration as long as it has a front surface 3Fa (first surface) facing the cathode flow path PAc (second gas flow path) through which the oxidant gas (second reactant gas) flows and a rear surface 3Fb (second surface) facing the cooling flow path PAw.

[0059] In the above embodiment, the positional relationship between the start end 3421 and the end end 3422 relative to the weld line 3420 is applied to the individual welded portion 342, and the start end 3421 and the end end 3422 of the welded portion 342 are positioned inside the weld line 3420. However, this can also be applied to the overall welded portion 341. Therefore, the start end 3421 and the end end 3422 of the welded portion 342 may be located outside the weld line 3420. In other words, the positions of the start end 3421 and the end end 3422 of the welded portion 342 are not limited to those described above, as long as they are located on the opposite side of the cooling flow path PAw across the weld line 3420. In the above embodiment, the individual bead portion 332 protrudes rearward from the rear plate 3R to seal the anode flow path PAa, and the individual bead portion 332 protrudes forward from the front plate 3F to seal the cathode flow path PAc. However, the configurations of the first seal portion and the second seal portion are not limited to those described above.

[0060] In the above embodiment, the welded portion 342 is formed by laser welding, but the welded portion may be formed by a method other than laser welding. In the above embodiment, an example in which the fuel cell stack 100 is applied to a vehicle is described, but a fuel cell stack having a power generating cell of the present invention can also be applied to moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0061] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other.

[0062] 3 Separator, 3F Front plate, 3R Rear plate, 3Fa Front surface, 3Fb Rear surface, 3Ra Front surface, 3Rb Rear surface, 301-306 Through holes, 331 Overall bead portion, 332 Individual bead portion, 342 Weld portion, 3420 Weld line, 3421 Starting end, 3422 End portion, PAa Anode flow path, PAc Cathode flow path, PAw Cooling flow path

Claims

1. a first thin plate having a first surface facing a first gas flow path through which a first reaction gas flows and a second surface facing a coolant flow path through which a coolant flows; a second thin plate having a first surface facing a second gas flow path through which a second reaction gas flows and a second surface facing the coolant flow path; a fuel cell separator configured by welding the second surface of the first thin plate and the second surface of the second thin plate in a state where they face each other, the first thin plate and the second thin plate have a weld portion extending along an annular weld line to form the coolant flow path between the second surface of the first thin plate and the second surface of the second thin plate; A fuel cell separator, wherein the start and end of the weld are located on opposite sides of the weld line to the coolant flow field.

2. 2. The fuel cell separator according to claim 1, the first thin plate and the second thin plate are provided with a first through-hole through which the first reactive gas and the second reactive gas pass and a second through-hole through which a cooling medium passes, respectively; the welding line is provided around the first through hole, A fuel cell separator, wherein the start and end of the welded portion are located inside the weld line.

3. The fuel cell separator according to claim 2, the first thin plate has a first seal portion protruding from an opposite side of the second thin plate so as to seal the first gas flow path; the second thin plate has a second seal portion protruding from an opposite side of the first thin plate so as to seal the second gas flow path; A fuel cell separator, wherein the first seal portion and the second seal portion are provided inside the weld line.

4. The fuel cell separator according to claim 3, A fuel cell separator, wherein the start and end of the welded portion are located between the weld line and the first seal portion and the second seal portion.

5. A welding method for a fuel cell separator, comprising welding a first thin plate having a first surface facing a first gas flow path through which a first reactant gas flows and a second surface facing a coolant flow path through which a coolant flows, to a second thin plate having a first surface facing a second gas flow path through which a second reactant gas flows and a second surface facing the coolant flow path, a step of arranging the second surface of the first thin plate and the second surface of the second thin plate so as to face each other; welding the first thin plate and the second thin plate along an annular weld line to form the coolant flow path between the second surface of the first thin plate and the second surface of the second thin plate; A welding method for a fuel cell separator, characterized in that the welding step includes welding so that a start end and an end end of the weld are positioned on opposite sides of the coolant flow path across the weld line.

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