Fuel cell system

A group of fuel gas system devices are provided at a first end plate of a fuel cell system through a block member. A cover member is provided at the first end plate to cover the group of the fuel gas system devices. Support rod members are provided at the first end plate. The support rod members protrude outward in a stacking direction to support the cover member at the front ends of the support rod members.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2013-121720 filed on Jun. 10, 2013 and No. 2014-103218 filed on May 19, 2014, the contents all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell system including a fuel cell stack formed by stacking a plurality of fuel cells in a stacking direction and end plates provided at both ends of the fuel cell stack in the stacking direction. Each of the fuel cells generates electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas.

2. Description of the Related Art

For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, the electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair separators to form a power generation cell. In use, in the fuel cell, generally, a predetermined number of power generation cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.

In the case where the fuel cell stack is used, in particular, in a vehicle as an in-vehicle fuel cell stack, it is desired to provide components such as fuel gas (e.g., hydrogen gas) system devices and oxygen-containing gas (e.g., air) system devices in a small space efficiently. In this case, it is necessary to protect the fuel gas system device preferentially against possible collisions of the vehicle.

For this purpose, for example, piping structure of a fuel cell disclosed in Japanese Patent No. 3671864 is known. In the piping structure, the stack is placed in a casing to mount the fuel cell stack in a vehicle. In the casing, fuel gas pipes, oxygen-containing gas pipes, and coolant pipes connected to the stack are provided. In comparison with the oxygen-containing gas pipes and the coolant pipes, inlet side fuel gas pipe and outlet side fuel gas pipes as the fuel gas pipes are provided closely to the stack, at positions closest to the stack in the stacking direction of cells.

In the piping structure, coolant pipes for supplying a coolant into or discharging the coolant from a coolant manifold in the fuel cell stack, and gas pipes for supplying reactant gases into or discharging the reactant gases from gas manifolds in the fuel cell stack are connected to an end plate provided at one end of the fuel cell stack. The gas pipes include fuel gas pipes for supplying a fuel gas into or discharging the fuel gas from a fuel gas manifold in the fuel cell stack, and oxygen-containing gas pipes for supplying an oxygen-containing gas into or discharging the oxygen-containing gas from an oxygen-containing gas manifold in the fuel cell stack. Further, among the fuel gas pipes, the oxygen-containing gas pipes, and the coolant pipes, the fuel gas pipes are provided at the innermost positions of the vehicle.

SUMMARY OF THE INVENTION

In the technique, the above fuel cell stack is placed in the casing, and the fuel gas pipes, the oxygen-containing gas pipes, and the coolant pipes attached to one of the end plates are covered by the case. However, when a large external load is applied to the casing due to a collision of the vehicle, the casing may be deformed toward the end plate. At this time, the coolant pipes and the oxygen-containing gas pipes may be damaged by the deformed casing. Further, the fuel gas pipes may be damaged undesirably.

As a possible approach to address the problem, it has been suggested to improve the rigidity of the casing itself. However, in this approach, the casing itself becomes thick, heavy, and large. Therefore, the efficiency of handling the casing becomes low, and the casing is not economical.

The present invention has been made to solve the problem of this type, and an object of the present invention is to provide a fuel cell system having lightweight and compact structure in which the external load can be received reliably, and damages of, in particular, fuel gas system devices can be suppressed as much as possible.

The present invention relates to a fuel cell system including a fuel cell stack formed by stacking a plurality of fuel cells in a stacking direction and end plates provided at both ends of the fuel cell stack in the stacking direction. Each of the fuel cells generates electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas.

In this fuel cell system, a plurality of fuel gas system devices are provided at one of end plates, and a cover member is provided to cover the fuel gas system devices. A support rod member is provided at the one of the end plates, and the support rod member protrudes outward in the stacking direction to support the cover member at a front end of the support rod member.

In the present invention, the cover member covering the fuel gas system devices is supported by the front end of the support rod member provided at the end plate to protrude in the stacking direction. In the structure, when an external load is applied to the cover member, the external load is transmitted to the end plate through the support rod member.

Therefore, it becomes possible to suppress deformation of the cover member suitably. With the lightweight and compact structure, it is possible to reliably receive the external road. Accordingly, in particular, it becomes possible to suppress damages of the fuel gas system devices as much as possible.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG. 1, a fuel cell system10according to a first embodiment of the present invention is an in-vehicle fuel cell system mounted in a fuel cell vehicle12such as a fuel cell electric automobile. In the fuel cell system10, a fuel cell stack14is provided in a motor room18adjacent to front wheels16f,16f. A hydrogen tank90described later is provided between rear wheels16r,16r.

As shown inFIG. 2, the fuel cell system10includes the fuel cell stack14and a fuel gas supply apparatus20for supplying a fuel gas to the fuel cell stack14. Though not shown, the fuel cell system10further includes an oxygen-containing gas supply apparatus for supplying an oxygen-containing gas to the fuel cell stack14and a coolant supply apparatus for supplying a coolant to the fuel cell stack14.

As shown inFIG. 3, the fuel cell stack14is formed by stacking a plurality of fuel cells22in a horizontal direction indicated by an arrow B or in a direction of gravity indicated by an arrow C. At one end of the stacked fuel cells22in the stacking direction, a first terminal plate24ais provided. A first insulating plate26ais provided outside the first terminal plate24a, and a first end plate (one of end plates)28ais provided outside the first insulating plate26a. At the other end of the stacked fuel cells22in the stacking direction, a second terminal plate24bis provided. A second insulating plate26bis provided outside the second terminal plate24b, and a second end plate28bis provided outside the second insulating plate26b. In the fuel cell stack14, the fuel cells22are stacked together in the vehicle width direction indicated by the arrow B, and the first end plate28aand the second end plate28bare provided at both ends in the vehicle width direction.

A first power output terminal30aextends from a central position of the laterally-elongated first end plate28a. The first power output terminal30ais connected to the first terminal plate24a. A second power output terminal30bextends from a central position of the laterally-elongated second end plate28b. The second power output terminal30bis connected to the second terminal plate24b. Both ends of coupling bars32are fixed to intermediate positions of the respective sides of the first end plate28aand the second end plate28busing screws34. By the coupling bars32, a tightening load in the stacking direction indicated by the arrow B is applied to the stacked fuel cells22.

As shown inFIG. 4, the fuel cell22has a laterally elongated rectangular shape, and the fuel cell22is formed by sandwiching a membrane electrode assembly36between a first separator38and a second separator40. For example, the first separator38and the second separator40are metal separators such as steel plates, stainless steel plates, aluminum plates, or plated steel sheets. Alternatively, the first separator38and the second separator40are carbon separators.

At one end of the fuel cell22in the horizontal direction indicated by an arrow A inFIG. 4, an oxygen-containing gas supply passage42aand a fuel gas discharge passage44bare arranged in a vertical direction indicated by an arrow C. The oxygen-containing gas supply passage42aand the fuel gas discharge passage44bextend through the fuel cells22in the stacking direction indicated by the arrow B. An oxygen-containing gas (hereinafter also referred to as air) is supplied through the oxygen-containing gas supply passage42a, and a fuel gas such as a hydrogen-containing gas (hereinafter also referred to as the hydrogen gas) is discharged through the fuel gas discharge passage44b.

At the other end of the fuel cell22in the direction indicated by the arrow C, a fuel gas supply passage44afor supplying the fuel gas and an oxygen-containing gas discharge passage42bfor discharging the oxygen-containing gas are arranged in the direction indicated by the arrow C. The fuel gas supply passage44aand the oxygen-containing gas discharge passage42bextend through the fuel cell22in the direction indicated by the arrow B.

A pair of coolant supply passages46afor supplying a coolant are provided at an upper end of the fuel cell22in the direction indicated by the arrow C. A pair of coolant discharge passages46bfor discharging the coolant are provided at a lower end of the fuel cell22in the direction indicated by the arrow C. Instead of proving the pair of coolant supply passages46aand the pair of coolant discharge passages46b, one coolant supply passage46aand one coolant discharge passage46bmay be provided.

The first separator38has an oxygen-containing gas flow field48on its surface38afacing the membrane electrode assembly36. The oxygen-containing gas flow field48is connected to the oxygen-containing gas supply passage42aand the oxygen-containing gas discharge passage42b.

The second separator40has a fuel gas flow field50on its surface40afacing the membrane electrode assembly36. The fuel gas flow field50is connected to the fuel gas supply passage44aand the fuel gas discharge passage44b.

A coolant flow field52is formed between a surface38bof the first separator38of one of adjacent fuel cells22and a surface40bof the second separator40of the other of the adjacent fuel cells22. The coolant flow field52is connected to the coolant supply passage46aand the coolant discharge passage46b.

Seal members54,56, are formed integrally with the first separator38and the second separator40, respectively. Alternatively, as the seal members54,56, members separate from the first separator38and the second separator40may be provided on the first separator38and the second separator40, respectively. Each of the seal members54,56is made of seal material, cushion material, or packing material such as an EPDM (ethylene propylene diene monomer) rubber, an NBR (nitrile butadiene rubber), a fluoro rubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, or an acrylic rubber.

The membrane electrode assembly36includes a solid polymer electrolyte membrane58, and a cathode60and an anode62sandwiching the solid polymer electrolyte membrane58. The solid polymer electrolyte membrane58is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example. In the illustrated embodiment, though the surface size of the solid polymer electrolyte membrane58is larger than the surface sizes of the cathode60and the anode62, the present invention is not limited in this respect.

Each of the cathode60and the anode62has a gas diffusion layer such as a carbon paper, and an electrode catalyst layer of porous carbon particles supporting platinum alloy thereon. The carbon particles are deposited uniformly on the surface of the gas diffusion layer. The electrode catalyst layer of the cathode60and the electrode catalyst layer of the anode62are fixed to both surfaces of the solid polymer electrolyte membrane58, respectively.

As shown inFIG. 3, the oxygen-containing gas supply passage42a, the oxygen-containing gas discharge passage42b, the fuel gas supply passage44a, and the fuel gas discharge passage44bare formed in the first end plate28a. Though not shown, the coolant supply passages46aand the coolant discharge passages46bare formed in the second end plate28b.

Some of a group of fuel gas system devices (a plurality of fuel gas system devices)66are provided on the outer surface (surface opposite to the stack body of the fuel cells22) of the first end plate28ausing a block member64. The group of fuel gas system devices66attached to the block member64at least include any of an ejector96, a hydrogen pump106, a liquid-gas separator (tank)104, a purge valve108, and a check valve102described later. Though not shown, for example, the group of fuel gas system devices66may include an injector.

Though not shown, a channel68for supplying the fuel gas to and discharging the fuel gas from predetermined devices are formed in the block member64. Pipes70a,70bconnected to the fuel gas supply passage44aand the fuel gas discharge passage44bare formed integrally with the block member64. Alternatively, as the pipes70a,70b, pipes separate from the block member64may be attached to the block member64. The block member64is fixed to the first end plate28a, e.g., using screws.

A cover member72is provided at the first end plate28ato cover the group of fuel gas system devices66. The cover member72has a box shape having an opening at one end. A plurality of holes74are formed along the outer periphery of the cover member72around the opening. A predetermined number of screw holes76, i.e., corresponding to the holes74are formed in four sides of the first end plate28a. Screws78are inserted into the holes74, and front ends of the screws78are screwed into the screw holes76to fix the cover member72to the first end plate28a(seeFIGS. 3 and 5).

Support rod members80are provided at the first end plate28a. Each of the support rod members80protrudes outward in the stacking direction to support the cover member72at its front end. At least two, e.g., four support rod members80are provided at positions where the first end plate28ais deformed significantly, i.e., at positions spaced from the coupling bars32when the first end plate28ais viewed from the stacking direction. As shown inFIG. 5, a small diameter threaded portion80tis provided at one end of each of the support rod members80, and the threaded portion80tis screwed into a screw hole76aformed in a plate surface of the first end plate28a. A shoulder portion80sis provided at the other end of the support rod member80, and a small diameter threaded portion80ais formed at the other end of each of the support rod members80through the shoulder portion80s.

Four holes82are formed in the cover member72at positions corresponding to the support rod members80. As necessary, four holes (through holes)84are formed in the block member64at positions corresponding to the support rod members80. Each of the threaded portions80aof the support rod members80passes through the hole84of the block member64and the hole82at the bottom of the cover member72, and protrudes to the outside. The threaded portion80aof the support rod member80is screwed into a nut86through a washer83(seeFIG. 5).

As shown inFIG. 2, the fuel gas supply apparatus20includes the hydrogen tank90for storing high pressure hydrogen. This hydrogen tank90is connected to the fuel gas supply passage44aof the fuel cell stack14through a hydrogen supply channel92. In the hydrogen supply channel92, a pressure reducing valve93, a shutoff valve94, the ejector96, and a hydrogen circulation channel98are provided.

A hydrogen gas is supplied from the hydrogen tank90to the ejector96, and the ejector96supplies the hydrogen gas to the fuel cell stack14through the hydrogen supply channel92. Further, the ejector96sucks an exhaust gas containing a hydrogen gas which has not been consumed in the fuel cell stack14from the hydrogen circulation channel98to supply the exhaust gas as the fuel gas, again to the fuel cell stack14.

An off gas channel100is connected to the fuel gas discharge passage44b. The hydrogen circulation channel98is connected to a position somewhere in the off gas channel100, and the check valve102is provided in the hydrogen circulation channel98. The gas-liquid separator104and the hydrogen pump106are provided on the upstream side of the off gas channel100, and the purge valve108is connected to the gas-liquid separator104.

Operation of the fuel cell system10will be described below.

Firstly, when the fuel cell system10is operated, as shown inFIG. 2, in the fuel gas supply apparatus20, the shutoff valve94is opened for guiding hydrogen gas from the hydrogen tank90. Then, after the pressure of the hydrogen gas is reduced by the pressure reducing valve93, the hydrogen gas is supplied to the hydrogen supply channel92. This hydrogen gas is supplied through the hydrogen supply channel92into the fuel gas supply passage44aof the fuel cell stack14.

As shown inFIG. 4, the hydrogen gas flows from the fuel gas supply passage44ainto the fuel gas flow field50of the second separator40. The hydrogen gas moves in the direction indicated by the arrow A, and the hydrogen gas is supplied to the anode62of the membrane electrode assembly36.

In the meanwhile, the oxygen-containing gas (air) from the oxygen-containing gas supply apparatus (not shown) flows into the oxygen-containing gas supply passage42aof the fuel cell stack14. The oxygen-containing gas flows from the oxygen-containing gas supply passage42ainto the oxygen-containing gas flow field48of the first separator38. The oxygen-containing gas moves in the direction indicated by the arrow A, and the oxygen-containing gas is supplied to the cathode60of the membrane electrode assembly36.

Thus, in the membrane electrode assembly36, the hydrogen gas supplied to the anode62and the air supplied to the cathode60are partially consumed in electrochemical reactions at catalyst layers of the anode62and the cathode60for generating electricity.

As shown inFIG. 2, the partially-consumed hydrogen gas is discharged from the fuel gas discharge passage44binto the off gas channel100, and the hydrogen gas is supplied into the gas-liquid separator104. After the water in the liquid state is removed from the hydrogen gas at the gas-liquid separator104, the hydrogen gas is sucked into the ejector96through the hydrogen circulation channel98, and supplied again to the fuel cell stack14as the fuel gas. In the meanwhile, as shown inFIG. 4, the partially-consumed air is discharged from the oxygen-containing gas discharge passage42bto the outside of the fuel cell stack14.

Further, the coolant is supplied from the coolant supply apparatus (not shown) to the pair of coolant supply passages46a. After the coolant flows into the coolant flow field52between the first separator38and the second separator40, the coolant flows in the direction indicated by the arrow C. After the coolant cools the membrane electrode assembly36, the coolant flows through the pair of coolant discharge passage46b, and the coolant is discharged into the coolant circulation system.

In the first embodiment, as shown inFIG. 3, the group of fuel gas system devices66are provided on the outer surface of the first end plate28ausing the block member64. Specifically, the ejector96, the hydrogen pump106, the gas-liquid separator104, the purge valve108, and the check valve102are attached to the block member64.

Further, the cover member72is provided at the first end plate28ato cover the group of fuel gas system devices66. Further, the support rod members80are screwed into the first end plate28a. Each of the support rod members80protrudes outward in the stacking direction, and supports the cover member72at its front end. That is, the cover member72covering the group of fuel gas system devices66is supported by the front ends of the support rod member80provided at the first end plate28ato protrude in the stacking direction.

Therefore, as shown inFIG. 5, after the external load is applied to the cover members72, the external load is transmitted to the first end plate28athrough the support rod members80. Then, the external load is transmitted to the second end plate28bthrough the coupling bars32.

In the structure, it becomes possible to suppress deformation of the cover member72suitably. Further, the external load is not directly applied to the fuel gas system devices66such as the ejector96, the hydrogen pump106, the gas-liquid separator104, the purge valve108, and the check valve102.

Further, the holes84are formed in the block member64, and the threaded portions80aof the support rod members80are inserted into the holes84of the block member64and the holes82of the cover member72. Therefore, the block member64can be fixed by the support rod members80at a precise position suitably.

Accordingly, in the first embodiment, with the lightweight and compact structure, it is possible to reliably receive the external road. In particular, it becomes possible to suppress damages of the group of fuel gas system devices66as much as possible.

FIG. 6is a partial exploded perspective view showing a fuel cell stack112of a fuel cell system110according to a second embodiment of the present invention. The constituent elements that are identical to those of the fuel cell stack14of the fuel cell system10according to the first embodiment are labeled with the same reference numerals and descriptions thereof will be omitted.

As shown inFIGS. 6 and 7, support rod members114as separate components are provided at the first end plate28aadjacent to respective ends of coupling bars32a. The support rod members114extend outward in the direction indicated by the arrow B. As shown inFIG. 7, a small diameter threaded portion114tis provided at one end of each of the support rod members114, and the threaded portion114tis screwed into a screw hole76aformed in a plate surface of the first end plate28a. Preferably, the support rod member114includes a portion overlapped with an end of each coupling bar32aas viewed in the stacking direction. The support rod member114may be formed integrally with the coupling bar32a. Alternatively, as the support rod member114, a member separate from the coupling bar32amay be joined to the end of the coupling bar32atogether, e.g., by welding. A shoulder portion114sis provided at the other end of each of the support rod members114, and a small diameter threaded portion114ais formed through the shoulder portion114s.

A block member64ais provided for the group of fuel gas system devices66a, and for example, four holes (through holes)84aare formed in the block member64aat positions corresponding to the support rod members114, i.e., coaxially with the support rod members114. The threaded portion114aof each support rod member114extends through the hole84aof the block member64aand a hole82aat the bottom of the cover member72ato protrude to the outside, and the threaded portion114aof the support rod member114is screwed into a nut86through a washer83.

In the second embodiment, with the lightweight and compact structure, it is possible to reliably receive the external load. Thus, the same advantages as in the case of the first embodiment are obtained. For example, in particular, it becomes possible to suppress damages of the group of fuel gas system devices66aas much as possible.

Further, in the second embodiment, the support rod members114are provided adjacent to the ends of the coupling bars32aof the first end plate28a. Therefore, as shown inFIG. 7, when an external load is applied to the cover members72a, the external load is transmitted from the support rod members114to the coupling bars32a. Accordingly, by the external load applied to the cover member72a, it is possible to further reliably suppress deformation of the first end plate28a.

While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the scope of the invention as defined by the appended claims.