Fuel cell unit

A second flange is separated from at least one of ribs located at one end and the other end out of a plurality of ribs of a plurality of first cases which are located next to each other in a second direction, and is fixed to one of the ribs except for the at least one of the ribs.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2019-147424 filed on Aug. 9, 2019 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to fuel cell units.

2. Description of Related Art

There are cases where a fuel cell stack is integrated with a power converter for converting electric power of the fuel cell stack by fixing a case accommodating the power converter to a case accommodating the fuel cell stack with the fuel cell stack being electrically connected to the power converter (e.g., Japanese Patent Application Publication No. 2017-073199).

SUMMARY

The case accommodating the fuel cell stack has an opening so that a conductive member that electrically connects the fuel cell stack and the power converter can extend through the opening. The fuel cell stack has a stack in which a plurality of single cells are stacked. In order to obtain, e.g., satisfactory electrical connection between the single cells, a compressive load is applied by the case to the stack in the direction in which the single cells are stacked. This compressive load therefore acts as a tensile load on the case accommodating the fuel cell stack. In other words, this case has a function to retain the compressive load applied to the stack. It is therefore desired that the case have high rigidity. However, since such a case has an opening as described above, the case may have reduced rigidity. When the case has reduced rigidity, a sufficient compressive load may not be applied to the stack.

The number of stacked single cells can be increased in order to ensure output power. As the number of stacked single cells increases, the overall weight of the stack increases accordingly, and the single cells may be more likely to be displaced from each other when an external impact etc. is applied to the stack in a direction crossing the direction in which the single cells are stacked. In order also to prevent such displacement of the single cells, it is desirable to apply a sufficient compressive load to the stack. However, when the case has reduced rigidity, a sufficient compressive load may not be applied to the stack as described above. One possible solution is to integrate a plurality of fuel cell stacks with the power converter rather than increasing the number of stacked single cells of a single fuel cell stack. In this case, the overall device size may be increased when the case accommodating the power converter is fixed to cases accommodating the fuel cell stacks.

The disclosure provides a fuel cell unit in which a case accommodating a fuel cell stack has sufficient rigidity and which has a reduced size while ensuring output power.

Such a fuel cell unit is achieved by a fuel cell unit including: a plurality of fuel cell stacks; a plurality of first cases each accommodating a corresponding one of the fuel cell stacks; a power converter that converts electric power of the fuel cell stacks; a second case accommodating the power converter and fixed to the first cases; and a conductive member unit that electrically connects the fuel cell stacks to the power converter in the first cases and the second case, wherein each of the fuel cell stacks includes a stack including a plurality of single cells stacked in a first direction, the stack is subjected to a compressive load in the first direction applied by a corresponding one of the first cases, each of the first cases includes a wall facing the second case, a first flange projecting from the wall toward the second case, and a first opening formed in the wall so as to be surrounded by the first flange, the second case includes a second flange fixed to the first flanges of the first cases so as to surround the first openings of the first cases, and a second opening formed so as to be surrounded by the second flange and communicating with the first openings, the conductive member unit extends from each of the first openings through the second opening into the second case, each of the first flanges includes at least three ribs extending in the first direction and located next to each other in a second direction crossing the first direction, the first cases are arranged such that the at least three ribs of each of the first cases extend in the first direction and are located next to each other in the second direction, a length of the second case in the second direction is smaller than an overall length of the first cases in the second direction, and the second flange is separated from at least one of the ribs located at a first end and a second end out of the at least three ribs of the first cases which are located next to each other in the second direction, and is fixed to two of the at least three ribs except for the at least one of the ribs. In this specification, the power converter may be a converter or an inverter.

The at least three ribs may include at least four ribs. The second flange may be separated from both of the ribs located at the first end and the second end out of the at least four ribs of the first cases which are located next to each other in the second direction, and may be fixed to two of the at least four ribs except for the both of the ribs.

The second flange may be fixed to the rib located closest to the first opening in at least one of the first cases.

The stack may include first and second terminal plates between which the single cells are sandwiched and that are separated from each other in the first direction. The first opening may have a shape that is longer in the first direction than in the second direction. The conductive member unit may include first and second conductive members connected to the first and second terminal plates through the first opening, respectively.

The second case may include a plurality of the second flanges each fixed to a corresponding one of the first flanges of the first cases, and a plurality of the second openings each surrounded by a corresponding one of the second flanges.

The second case may include a tub-shaped body and a lid fixed to the tub-shaped body. The tub-shaped body may include a third flange and a third opening surrounded by the third flange. The lid may include the second flanges, the second openings, a fourth flange fixed to the third flange, and a fourth opening surrounded by the fourth flange. Each of the third and fourth flanges may be larger than the second flange.

The disclosure thus provides a fuel cell unit in which a case accommodating a fuel cell stack has sufficient rigidity and which has a reduced size while ensuring output power.

DETAILED DESCRIPTION OF EMBODIMENTS

General Configuration of Fuel Cell Unit1

FIG. 1is a perspective view of a fuel cell unit1.FIG. 2is an exploded perspective view of the fuel cell unit1.FIGS. 3 and 4are sectional views of the fuel cell unit1. The fuel cell unit1includes two stack cases10a,10b, fuel cell stacks100a,100b, a boost converter500, and a converter case40. The fuel cell stacks100a,100bare accommodated in the stack cases10a,10b, respectively. The boost converter500is electrically connected to the fuel cell stacks100a,100b. The boost converter500is accommodated in the converter case40. As described in detail later, the converter case40includes a body50and a lid70. An X direction, a Y direction, and a Z direction that are orthogonal to each other are shown in the figures. The Z direction is an example of a direction in which the stack cases10a,10bare arranged next to each other. As described in detail later, the X direction is an example of a direction in which single cells106of each fuel cell stack100a,100bare stacked. The two stack cases10a,10band the converter case40overlap in the Z direction.FIG. 3illustrate a section of the fuel cell unit1parallel to the XY plane.FIG. 4illustrates a section of the fuel cell unit1parallel to the YZ plane. InFIGS. 3 and 4, the boost converter500is illustrated in a simplified manner by dashed line.

The stack cases10a,10bare the same members, but are denoted by different reference signs for convenience. The fuel cell stacks100a,100bare also the same members, but are denoted by different reference signs for convenience. The boost converter500accommodated in the converter case40boosts the output voltage of the fuel cell stacks100a,100band outputs the boosted voltage to an external device. The boost converter500is an example of the power converter that converts the output power of the fuel cell stacks100a,100b. The power converter is not limited to the boost converter and may be any of a buck converter, a buck boost converter that can serve as both a boost converter and a buck converter, and an inverter that converts DC power to AC power. The power converter may be the other converter or inverter. Since the fuel cell unit1includes the two fuel cell stacks100a,100b, output power is ensured.

General Configuration of Stack Cases10a,10b

The stack case10ais made of a highly rigid material like a metal material such as an aluminum alloy. The stack case10aincludes side walls11,13, and14, an upper wall15, and a bottom wall16. The side wall11is parallel to the YZ plane. The side walls13,14are separated from each other in the Z direction and are substantially parallel to the XY plane. The upper wall15and the bottom wall16are separated from each other in the Y direction. The bottom wall16is parallel to the XZ plane, but the upper wall15is tilted with respect to the XZ plane as described in detail later. The stack case10ahas an opening rather than a wall at a position facing the side wall11in the −X direction. An end plate12a, described later, is fixed to the stack case10aby bolts, not shown, so as to close the opening. Like the side wall11, the end plate12ais parallel to the YZ plane. The upper wall15is actually tilted with respect to the XZ plane such that the end on the end plate12aside of the upper wall15is located higher in the Y direction than the end on the side wall11side of the upper wall15. However, the disclosure is not limited to this.

Similarly, the stack case10bincludes side walls11,13, and14, an upper wall15, and a bottom wall16, and an end plate12ais fixed to the stack case10b. As shown inFIGS. 1, 2, and 4, the stack cases10a,10band the converter case40are fixed together such that the side wall14of the stack case10aand the side wall13of the stack case10bface each other and the end plates12afixed to the stack cases10a,10bface the same direction. The stack cases10a,10bare an example of the plurality of first cases.

Detailed Configuration of Flange18

Each of the stack cases10a,10bhas a flange18on the upper wall15. The flange18projects in the +Y direction from the upper wall15and has a predetermined height from the upper wall15in the +Y direction. In other words, the flange18projects toward the converter case40. The upper end face of the flange18is parallel to the XZ plane. The flange18includes lateral ribs181,182, outer longitudinal ribs183,184, and inner longitudinal ribs185,186. The lateral ribs181,182extend in the Z direction and are separated from each other in the X direction. The outer longitudinal ribs183,184extend in the X direction and are separated from each other in the Z direction. The outer longitudinal rib183is continuous with one end of the lateral rib181and one end of the lateral rib182. The outer longitudinal rib184is continuous with the other end of the lateral rib181and the other end of the lateral rib182. The lateral rib181, the lateral rib182, the outer longitudinal rib183, and the outer longitudinal rib184are located near the side wall11, the end plate12a, the side wall13, and the side wall14, respectively.

The inner longitudinal ribs185,186are located between the outer longitudinal ribs183,184and extend in the X direction like the outer longitudinal ribs183,184. The inner longitudinal ribs185,186are continuous with the lateral ribs181,182. The inner longitudinal ribs185,186are continuous with the outer longitudinal ribs183,184via the lateral ribs181,182. The outer longitudinal rib183, the inner longitudinal rib185, the inner longitudinal rib186, and the outer longitudinal rib184are located next to each other in this order in +Z direction. Each of the ribs such as the lateral ribs181is shaped as follows. Each of the ribs projects in the +Y direction from the upper wall15and has a predetermined height from the upper wall15in the +Y direction. Each of the ribs extend in a predetermined direction on the upper wall15, and the thickness of each rib in a direction perpendicular to the direction in which the rib extends is smaller than the length of the rib in the direction in which the rib extends. The stack cases10a,10bare disposed such that the outer longitudinal ribs183,184and the inner longitudinal ribs185,186of each flange18extend in the X direction and are located next to each other in the Z direction. The flange18is an example of the first flange.

The flange18is an inward flange having a plurality of protrusions that protrude inward from the inner side surface of the flange18and are substantially evenly spaced apart in the circumferential direction of the flange18. Each of the protrusions has an internally threaded hole, not shown. Specifically, each of the lateral ribs181,182and the outer longitudinal ribs183,184has a plurality of protrusions that protrude inward from its inner side surface. Each of the inner longitudinal ribs185,186also has a plurality of protrusions. The protrusions of each of the inner longitudinal ribs185,186protrude inward, namely toward the other inner longitudinal rib185,186, from its inner surface in the region surrounded by the inner longitudinal ribs185,186and the lateral ribs181,182.

The upper wall15has an opening15asurrounded by the flange18. Specifically, the upper wall15has the opening15abetween the inner longitudinal ribs185,186. The opening15ais longer in the X direction than in the Z direction. InFIG. 2, a terminal plate101and a plurality of single cells106which form a part of the fuel cell stack100aare exposed from the opening15a. The opening15ais an example of the first opening. An insulating sheet etc. may be provided between the single cells106and the opening15aso that the single cells106are not directly exposed from the opening15a.

General Configuration of Fuel Cell Stacks100a,100b

As shown inFIG. 3, the fuel cell stack100aincludes a stack107in which a plurality of plate-like members are stacked. Specifically, the stack107includes the plurality of single cells106, the terminal plate101, an insulator103, a pressure plate105, a terminal plate102, an insulator104, and the end plate12a. The plurality of single cells106are stacked in the X direction. The terminal plate101, the insulator103, and the pressure plate105are disposed on one end side of the plurality of single cells106and stacked in this order on the one end of the plurality of single cells106. The terminal plate102, the insulator104, and the end plate12aare disposed on the other end side of the plurality of single cells106and stacked in this order on the other end of the plurality of single cells106. Since the pressure plate105is biased toward the end plate12aby a spring109disposed between the pressure plate105and the side wall11, and the end plate12ais fixed to the stack case10a, a compressive load in the X direction is applied to the stack107. The stack107is thus subjected to a compressive load in the X direction applied by the stack case10avia the spring109.

The single cell106is a polymer electrolyte fuel cell that is supplied with oxidant gas and fuel gas to generate electric power. The oxidant gas is air containing oxygen, and the fuel gas is hydrogen gas. The single cell106includes a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly therebetween. The membrane electrode assembly is a power generator composed of an electrolyte membrane and electrodes disposed on both sides of the electrolyte membrane. The electrolyte membrane is a solid polymer membrane that is made of a hydrocarbon resin material having a sulfonate group or fluororesin material having a sulfonate group. The electrolyte membrane exhibits satisfactory proton conductivity when in a wet state. Each of the electrodes include a carbon support and an ionomer that is a solid polymer having a sulfonate group and that exhibits satisfactory proton conductivity when in a wet state. A catalyst for facilitating a power generation reaction (e.g., platinum, a platinum-cobalt alloy, etc.) is supported on the carbon support. Each of the separators is a thin plate-like member made of a conductive material having gas barrier properties, namely made of a metal such as press-formed stainless steel, titanium, or a titanium alloy.

The terminal plates101,102are plates made of a conductive material like a metal such as copper, aluminum, or an alloy containing copper and aluminum, or dense carbon. The insulators103,104are plates made of an insulating material such as rubber or resin. The end plate12aand the pressure plate105are made of a highly rigid material like a metal material such as stainless steel or an aluminum alloy. The end plate12ahas supply holes and discharge holes for supplying and discharging the oxidant gas, the fuel gas, and cooling water to and from the fuel cell stack100a. Supply pipes and discharge pipes are connected to the supply holes and the discharge holes.

In the fuel cell unit1, both of the end plates12aof the stack cases10a,10bare disposed on the same side, the supply and discharge pipes for supplying and discharging the oxidant gas, the fuel gas, and the cooling water, which are connected to the end plates12a, can be disposed on the same side with respect to the fuel cell unit1. The fuel cell unit1thus has improved mountability.

As shown inFIG. 3, each of the terminal plates101,102of the fuel cell stack100ahas a projecting portion that projects beyond the plurality of single cells106in the +Y direction and that is exposed from the opening15a. As shown inFIGS. 2, 3, and 4, the plurality of single cells106of each fuel cell stack100a,100bare electrically connected to the boost converter500by the terminal plates101,102, a relay bus bar111, connection bus bars112,113. The relay bus bar111and the connection bus bars112,113are made of a metal having low electrical resistivity such as copper, aluminum, or an alloy containing copper and aluminum. That is, the relay bus bar111and the connection bus bars112,113are conductive. The relay bus bar111and the connection bus bars112,113are an example of the conductive member unit.

The relay bus bar111has its one end connected to the projecting portion of the terminal plate102of the fuel cell stack100a. The relay bus bar111extends from the terminal plate102side through the opening15aof the stack case10aand an opening781aof the lid70, described later, and extends above a bottom wall73of the lid70from the stack case10aside to the stack case10bside. The relay bus bar111has the other end connected to the projecting portion of the terminal plate101of the fuel cell stack100bthrough an opening781bof the lid70, described later, and an opening15aof the stack case10b. The plurality of single cells106of the fuel cell stack100aand the plurality of single cells106of the fuel cell stack100bare thus electrically connected in series with each other by the relay bus bar111.

The connection bus bar112has its one end connected to the projecting portion of the terminal plate102of the fuel cell stack100b. The connection bus bar112extends from the terminal plate102side to the converter case40side through the openings15a,781band an opening56. The connection bus bar112has the other end connected to the boost converter500. The connection bus bar113has its one end connected to the projecting portion of the terminal plate101of the fuel cell stack100a. The connection bus bar113extends from the terminal plate101side to the converter case40side through the openings15a,781a, and56. The connection bus bar113has the other end connected to the boost converter500. The plurality of single cells106of the fuel cell stack100aand the plurality of single cells106of the fuel cell stack100bare thus electrically connected to the boost converter500by the connection bus bars112,113. The other ends of the connection bus bars112,113and the boost converter500are connected by a conductive member, not shown, such as a bus bar or a cable. The boost converter500is composed of a plurality of electronic components such as a capacitor, an intelligent power module (IPM), a current sensor, and a reactor.

Detailed Configuration of Body50of Converter Case40

The converter case40includes the body50and the lid70. The body50and the lid70are made of a highly rigid material like a metal material such as an aluminum alloy. The lid70and the body50are placed next to each other in this order in the +Y direction. The body50includes side walls51to54and an upper wall55. The side walls51,52are separated from each other in the X direction and are parallel to the YZ plane. The side walls53,54are separated from each other in the Z direction and are parallel to the XY plane. The upper wall55is parallel to the XZ plane. The length in the Z direction of each of the side walls51,52is larger than that in the X direction of each of the side walls53,54. The side walls51,52have service holes511,521, described later, respectively. As shown inFIGS. 1 and 4, the length in the Z direction of each of the side walls51,52is smaller than the overall length in the Z direction of the stack cases10a,10blocated next to each other in the Z direction. The length in the X direction of each of the side walls53,54is substantially the same as that in the X direction of each of the side walls13,14of the stack cases10a,10b.

The body50does not have a wall parallel to and facing the upper wall55, but has the opening56. In other words, the body50has a tub shape with the upper wall55as its bottom. The opening56faces the stack cases10a,10bvia the lid70.

The body50has a flange59around the peripheral edge of the opening56. In other words, the flange59surrounds the opening56. The flange59is an outward flange having a plurality of protrusions that protrude outward from the outer side surface of the flange59and are substantially evenly spaced apart in the circumferential direction of the flange59. Each of the protrusions has a bolt hole, not shown. The lower end face of the flange59is parallel to the XZ plane. The flange59has a different shape from the flanges18of the stack cases10a,10bdescribed above. Accordingly, the flanges18of the stack cases10a,10bcannot be directly fixed to the flange59of the body50. The converter case40is an example of the second case. The flange59is an example of the third flange. The opening56is an example of the third opening.

Detailed Configuration of Lid70of Converter Case40

The lengths in the X and Z directions of the lid70are substantially the same as those in the X and Z directions of the body50, respectively. The lid70includes a peripheral wall71, the bottom wall73, and flanges78a,78b, and79. The peripheral wall71has a predetermined height in the Y direction and has a generally rectangular frame shape about the Y direction. Each of the flanges78a,78b, and79has a generally rectangular frame shape. The lid70has the opening781a, the opening781b, and an opening791which are surrounded by the inner peripheral edges of the flanges78a,78b, and79, respectively. The peripheral wall71continuously extends from the two flanges78a,78bto the flange79. In other words, the two flanges78a,78bare formed at the end on the −Y direction side of the peripheral wall71. The two flanges78a,78bhave the same shape and size, but are denoted by different reference signs for convenience of explanation. The flanges78a,78bare separated from each other in the Z direction. The bottom wall73is formed between the adjacent flanges78a,78b, is continuous with the peripheral wall71, and extends parallel to the XZ plane. The connection bus bar112is connected to the boost converter500via the opening781b, and the connection bus bar113is connected to the boost converter500via the opening781a. The flanges78a,78bare an example of the plurality of second flanges. The openings781a,781bare an example of the plurality of second openings. The flange79is an example of the fourth flange. The opening791is an example of the fourth opening. The bottom wall73is an example of an extended wall.

The flanges78a,78bare inward flanges like the flanges18of the stack cases10a,10b. The flange79is an outward flange like the flange59of the body50. The lower end faces of the flanges78a,78band the upper end face of the flange79are parallel to the XZ plane. The flange79is larger than the overall size of the flanges78a,78b. That is, the opening791is larger than the overall size of the openings781a,781b. The shape and size of the flange79correspond to those of the flange59of the body50, and the flange79is an outward flange like the flange59. The flanges79,59are fastened together by bolts. The body50and the lid70are fixed together in this manner.

The flange78ahas a plurality of bolt holes that are substantially evenly spaced apart from each other in the circumferential direction of the flange78a. The positions of the plurality of bolt holes of the flange78acorrespond to those of the plurality of internally threaded holes that are formed in the inner longitudinal ribs185,186of the flange18of the stack case10a, a part of the lateral rib181which is located between the inner longitudinal ribs185,186, and a part of the lateral rib182which is located between the inner longitudinal ribs185,186. The flange78aand the flange18of the stack case10aare fastened together by bolts. The lower end face of the flange78aand the upper end face of the flange18thus abut on each other and are fixed together. That is, the flange78adoes not correspond to the overall shape and size of the lateral ribs181,182and the outer longitudinal ribs183,184which form the outermost peripheral wall of the flange18, but corresponds to the shape and size of the peripheral wall that is defined by the inner longitudinal ribs185,186, the part of the lateral rib181, and the part of the lateral rib182. The flange78ais fixed to the flange18so as to surround the opening15aformed between the inner longitudinal ribs185,186. The same applies to the flange78band the flange18of the stack case10b. With the flanges78a,78bfixed to the flanges18of the stack cases10a,10b, respectively, the bottom wall73extends so as to close the clearance between the stack cases10a,10b.

The stack cases10a,10b, the lid70, and the body50are fixed together in this manner, whereby the fuel cell stacks100a,100bis integrated with the boost converter500. Since the peripheral wall71and the bottom wall73of the lid70are continuous between the flanges78a,78band the flange79, the lid70together with the body50and the stack cases10a,10bforms an outer wall of a case for the entire fuel cell unit1. These cases can thus be combined together and sealed. The body50and the lid70may be formed as a single-piece member. However, in view of ease of mounting of the electronic components of the boost converter500, the relay bus bar111, etc., it is preferable that the body50and the lid70be separate members. It is preferable to place a rubber gasket or a liquid gasket for improving sealing properties between the end faces of the flanges which are fixed together.

Rigidity of Stack Cases10a,10b

As shown inFIG. 3, the plurality of single cells106are stacked in the X direction, and a compressive load in the X direction is applied between the end plate12aand the pressure plate105by the spring109. The end plate12ais fixed to the stack case10a, and the spring109is disposed between the pressure plate105and the side wall11of the stack case10a. Accordingly, the plurality of single cells106is subjected to the compressive load in the X direction, but the stack case10ais subjected to a tensile load in the X direction. In other words, the stack case10aserves as a member for retaining the compressive load applied to the plurality of single cells106. For example, when the stack case10ahas low rigidity, the stack case10ais extended in the X direction, and a sufficient compressive load cannot be applied to the plurality of single cells106. In this case, conductive properties between the single cells106may be reduced. In the present embodiment, as shown inFIG. 2, the flange18of the stack case10ahas the four longitudinal ribs extending in the X direction, namely the outer longitudinal ribs183,184and the inner longitudinal ribs185,186. Accordingly, the stack case10ahas sufficient rigidity against the load in the X direction. A sufficient compressive load can therefore be applied to the plurality of single cells106. The same applies to the stack case10b.

Especially in the present embodiment, the stack case10ahas the opening15a, and reduction in rigidity of the stack case10adue to the opening15ais compensated for by the outer longitudinal ribs183,184and the inner longitudinal ribs185,186. As shown inFIG. 3, the opening15ais long in the X direction so as not to interfere with the terminal plates102,103, the relay bus bar111, and the connection bus bar113. Since the stack case10has such a large opening15a, the stack case10atends to have reduced rigidity. However, the outer longitudinal ribs183,184and the inner longitudinal ribs185,186increase the rigidity of the stack case10a, so that the stack case10ahas necessary rigidity. The same applies to the stack case10b.

The flange78ais connected to the inner longitudinal ribs185,186located closest to the opening15aout of the outer longitudinal ribs183,184and the inner longitudinal ribs185,186of the flange18of the stack case10a. Since the inner longitudinal ribs185,186are connected to the flange78a, the inner longitudinal ribs185,186and the flange78aare combined together, whereby rigidity of the inner longitudinal ribs185,186is further increased. Since the rigidity of the inner longitudinal ribs185,186located closest to the opening15athat can cause reduction in rigidity of the stack case10ais thus increased, the rigidity of the stack case10ais more effectively increased.

In the present embodiment, as shown inFIGS. 2 and 3, the opening15aextends in the X direction along substantially the entire length of the upper wall15. For example, one possible way to increase rigidity is to form in the upper wall15separate minimum required openings that expose the terminal plates102,103. In this case, however, it may be difficult to insert the fuel cell stack100ainto the stack case10ain the manufacturing process of the fuel cell unit1. Specifically, in the manufacturing process of the fuel cell unit1, the fuel cell stack100aassembled in advance is inserted into the stack case10ain the +X direction. However, in the case where the upper wall15has only two minimum required openings as described above, the projecting portion of the terminal plate101and the upper wall15may interfere with each other during insertion of the fuel cell stack100ainto the stack case10a, making it difficult to insert the fuel cell stack100ainto the stack case10a. The stack case10ais molded by casting or die casting. Accordingly, forming two openings in the upper wall15of the stack case10arequires a mold with a more complicated structure, which may increase the manufacturing cost of the stack case10a. In the present embodiment, the opening15aextends in the X direction. Accordingly, the fuel cell stack100ais more easily inserted into the stack case10a, and the manufacturing cost is reduced.

Reduction in Size of Converter Case40

As shown inFIGS. 1 and 4, the length in the Z direction of the converter case40is smaller than the overall length in the Z direction of the stack cases10a,10bdisposed next to each other in the Z direction. The converter case40is separated from the outer longitudinal rib183of the stack case10aand the outer longitudinal rib184of the stack case10band is fixed to the inner longitudinal ribs185,186of the stack cases10a,10b. In other words, the converter case40is located inward of the outer longitudinal rib183of the stack case10a, and is located inward of the outer longitudinal rib184of the stack case10b. The overall size of the fuel cell unit1is thus reduced.

The size in the Y direction of the converter case40is also smaller than that in the Y direction of each of the stack cases10a,10b, and the size in the X direction of the converter case40is substantially the same as that in the X direction of each of the stack cases10a,10b. The overall size of the fuel cell unit1is thus reduced. The outer longitudinal rib183of the stack case10aand the outer longitudinal rib184of the stack case10bare located at one end and the other end of all of the outer longitudinal ribs183,184and the inner longitudinal ribs185,186of the flanges18of the stack cases10a,10bwhich are located next to each other in the Z direction. That is, the outer longitudinal rib183of the stack case10aand the outer longitudinal rib184of the stack case10bare the two outermost ribs of the plurality of ribs of the stack cases10a,10bin a second direction crossing the direction in which the single cells106are stacked.

Use of Same Stack Case10ain Different Fuel Cell Unit

FIG. 5is a perspective view showing the appearance of a fuel cell unit1a.FIG. 6is an exploded perspective view of the fuel cell unit1a. Regarding the fuel cell unit1a, the same or similar configurations as those of the fuel cell unit1are denoted by the same or similar reference signs, and description thereof will not be repeated. The fuel cell unit1aincludes the stack case10aused in the fuel cell unit1, the fuel cell stack100aaccommodated in the stack case10a, and a converter case50adifferent from the converter case40, and a boost converter, not shown, accommodated in the converter case50a. The converter case50ais smaller than the converter case40, and the boost converter accommodated in the converter case50ais also smaller than the boost converter500. The boost converter accommodated in the converter case50ais a boost converter for the single fuel cell stack100a, and the size of the components of the boost converter such as a reactor is smaller than in the boost converter500. The stack107of the fuel cell stack100ais electrically connected to the boost converter by the terminal plates101,102and the connection bus bars112,113.

A side wall52aof the converter case50aand a side wall, not shown, of the converter case50awhich faces the side wall52aand which is separated in the X direction from, and parallel to, the side wall52a, have substantially the same size in the Z direction as the stack case10a. A side wall53aof the converter case50aand a side wall, not shown, of the converter case50awhich faces the side wall53aand which is separated in the Z direction from, and parallel to, the side wall53ahave substantially the same size in the X direction as the stack case10a. A flange59aof the converter case50ais an inward flange and is directly fixed to the lateral ribs181,182and the outer longitudinal ribs183,184of the flange18. By using the outer longitudinal ribs183,184that are not used in the fuel cell unit1, the converter case50aaccommodating the boost converter for the single fuel cell stack100acan be fixed to the single stack case10a. The stack case10aused for the fuel cell unit1can thus also be used for the fuel cell unit1a. The manufacturing cost of the fuel cell stack100aand the fuel cell unit1ais therefore reduced. Since the stack case10bis the same member as the stack case10aas described above, the manufacturing cost of the fuel cell unit1is also reduced.

The flange59aof the converter case50ais not limited to being connected to the lateral ribs181,182and the outer longitudinal ribs183,184. For example, the flange59amay be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib184, and the inner longitudinal rib185or a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib183, and the inner longitudinal rib186so as to surround the opening15aof the stack case10a. Since the stack case10ahas not only the outer longitudinal ribs183,184but also the plurality of inner longitudinal ribs185,186, a plurality of converter cases having different sizes can be fixed to the stack case10a.

Others

The converter case40of the fuel cell unit1shown inFIGS. 1 to 4may be fixed to any of the ribs except for the outer longitudinal rib183of the stack case10a. In this case, the flange78bof the converter case40may be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib184, and either the outer longitudinal rib183or the inner longitudinal rib185of the stack case10bso as to surround the opening15aof the stack case10b. The converter case40may be fixed to any of the ribs except for the outer longitudinal rib184of the stack case10b. In this case, the flange78aof the converter case40may be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib183, and either the outer longitudinal rib184or the inner longitudinal rib186of the stack case10aso as to surround the opening15aof the stack case10a.

The flange78aof the converter case40of fuel cell unit1is fixed to the frame-shaped region defined by the lateral ribs181,182and the inner longitudinal ribs185,186of the flange18of the stack case10a. However, the disclosure is not limited to this. For example, the flange78amay be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib184, and the inner longitudinal rib185of the stack case10a. Similarly, the flange78bof the converter case40of the fuel cell unit1may be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib183, and the inner longitudinal rib186of the stack case10b.

The opening15aof the stack case10ais formed between the inner longitudinal ribs185,186. However, the disclosure is not limited to this. The opening15aof the stack case10amay be formed between, e.g., the outer longitudinal rib184and the inner longitudinal rib186as long as the fuel cell stacks100a,100bcan be electrically connected to the boost converter500. In this case, the flange78amay be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib184, and the inner longitudinal rib185or186so as to surround the opening15a. Similarly, the opening15aof the stack case10bmay be formed between, e.g., the outer longitudinal rib183and the inner longitudinal rib185. In this case, the flange78bmay be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib183, and the inner longitudinal rib185or186so as to surround the opening15a.

The stack cases10a,10bare not limited to the members having the same shape and size. For example, the opening15aof the stack case10amay be formed between the outer longitudinal rib184and the inner longitudinal rib186as described above, and the opening15aof the stack case10bmay be formed between the inner longitudinal ribs185,186as shown inFIG. 2or may be formed between the outer longitudinal rib183and the inner longitudinal rib185as described above. The opening15aof the stack case10amay be formed between the inner longitudinal ribs185,186as shown inFIG. 2, and the opening15aof the stack case10bmay be formed between the outer longitudinal rib183and the inner longitudinal rib185as described above.

The flange18includes a total of four ribs extending in the X direction, that is, the outer longitudinal ribs183,184and the inner longitudinal ribs185,186. However, the flange18need only include three or more ribs extending in the X direction. For example, the inner longitudinal rib186may be omitted from the flange18of the stack case10a. In this case, the flange78aof the lid70of the fuel cell unit1may be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib184, and the inner longitudinal rib185of the flange18of the stack case10a. Similarly, the inner longitudinal rib185may be omitted from the flange18of the stack case10b. In this case, the flange78bof the lid70of the fuel cell unit1may be fixed to a frame-shaped region defined by the lateral ribs181,182, the outer longitudinal rib183, and the inner longitudinal rib186of the flange18of the stack case10b.

In the fuel cell unit1, the fuel cell stacks100a,100bare electrically connected in series with each other by the relay bus bar111. However, the disclosure is not limited to this. For example, the two fuel cell stacks100a,100bmay be electrically connected in parallel to the boost converter that is a power converter by a connection bus bar.

The converter case40of the fuel cell unit1is composed of the tub-shaped body50and the frame-shaped lid70. However, the disclosure is not limited to this. For example, the outer longitudinal rib184of the stack case10aand the outer longitudinal rib183of the stack case10b, which are located adjacent to each other in the Z direction, may be in contact with each other, the entire upper end faces of the flanges18of the stack cases10a,10bmay be located on the same XZ plane, and these upper end faces may be directly fixed to the lower end face of the flange59of the body50. This configuration reduces the number of components required. In this case, the flange59of the body50needs to be changed to an inward flange so as to correspond to the flange18. The flange59may be located inward of both the outer longitudinal rib183of the stack case10aand the outer longitudinal rib184of the stack case10b, may not be fixed to the outer longitudinal rib184of the stack case10aand the outer longitudinal rib183of the stack case10b, and may be fixed to a frame-shaped area defined by the inner longitudinal rib185of the stack case10a, the inner longitudinal rib186of the stack case10b, and the lateral ribs181,182of the stack cases10a,10b. In this case, the opening56of the body50is an example of the second opening.

The stack case10aapplies a compressive load in the X direction to the stack107via the spring109. However, the disclosure is not limited to this. For example, a compressive load in the X direction may be applied to the stack107with the pressure plate105being in direct contact with the side wall11of the stack case10awith no spring109therebetween and with the end plate12abeing fixed to the stack case10a. Alternatively, an adjusting screw may be provided on the side wall11, and a compressive load in the X direction may be applied to the stack107using the adjusting screw. In this case, the amount by which the adjusting screw projects from the side wall11toward the pressure plate105varies depending on how much the adjusting screw is turned, and a compressive load in the X direction is applied to the stack107by pressing the pressure plate105toward the end plate12afixed to the stack case10aby the adjusting screw. In either case, a compressive load in the X direction is applied to the stack107by the stack case10a.

The fuel cell unit1may be mounted on a vehicle etc. with the bottom walls16of the stack cases10a,10bfacing downward in the direction of gravity. However, the fuel cell unit1may be mounted on a vehicle etc. in other orientations. For example, the fuel cell unit1may be mounted on a vehicle etc. with the end plates12aof the stack cases10a,10bfacing downward in the direction of gravity. In this case, liquid water is more easily drained from the fuel cell stacks100a,100b, so that flooding during power generation and freezing of residual water in the fuel cell stacks100a,100bafter power generation is stopped can be prevented. Accordingly, the power generation capability of the fuel cell stacks100a,100bis less likely to be reduced. The fuel cell unit1may be mounted on a vehicle etc. with the upper wall55of the body50facing downward in the direction of gravity. The same applies to the fuel cell unit1a.

In the fuel cell unit1, the converter case40is fixed to the two stack cases10a,10b. However, the disclosure is not limited to this. For example, a single converter case may be fixed to three or more stack cases. In this case, with the three or more stack cases being disposed next to each other in, e.g., the Y direction, the converter case need only be located inward of at least one of a rib region located at one end of a plurality of rib regions of these stack cases which extend in the X direction and a rib region located at the other end of the plurality of rib regions.

Although the embodiments of the disclosure are described in detail above, the disclosure is not limited to such specific embodiments, and various modifications and variations can be made.