Fuel cell system

In a fuel cell system, a humidifier is attached to an end plate. A pipe connector of a fluid pipe provided at the end plate such as an oxygen-containing gas inlet manifold and a pipe connector of a fluid pipe of the humidifier such as a humidified air supply pipe are connected through a substantially ring-shaped intermediate pipe. O-rings are attached to annular grooves in the outer circumferential portions of the intermediate pipe. One of the O-rings tightly contacts the inner circumferential surface of the pipe connector of the oxygen-containing gas inlet manifold, and the other of the O-rings tightly contacts the inner circumferential surface of the pipe connector of the humidified air supply pipe.

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 power generation cells, and a humidifier for humidifying at least one of reactant gases supplied to the fuel cell stack using humidified fluid.

2. Description of the Related Art

For example, a polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte) comprising a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (electrolyte electrode assembly). The membrane electrode assembly is sandwiched between separators to form a power generation cell. In use, normally, a predetermined number of power generation cells are stacked together to form a fuel cell stack.

In the fuel cell, in order to achieve the desired ion conductivity, it is necessary to maintain the desired humidified state of the electrolyte membrane. For this purpose, in general, the oxygen-containing gas and the fuel gas are humidified through a humidifier before these gases are supplied to the fuel cell.

For example, a fuel cell humidification system disclosed in Japanese Laid-Open patent publication No. 2001-216983 includes a stack1and a humidification unit2as shown inFIG. 8. A connection surface1aof the stack1and a connection surface2aof the humidification unit2are overlapped with each other to connect the stack1and the humidification unit2together into one piece.

A fuel gas inlet port3aand a fuel gas outlet port3bare formed at positions along one diagonal line on the connection surface1aof the stack1, and a supply gas inlet port4aand a supply gas outlet port4bare provided at positions along the other diagonal line on the connection surface1a. Further, a coolant water inlet port5aand a coolant water outlet port5bare formed at substantially central positions on the left and right sides.

On the connection surface2aof the humidification unit2, in correspondence with the ports of the stack1, a fuel gas discharge port3c, a fuel gas intake port3d, a supply gas discharge port4c, an off gas intake port4d, a coolant water discharge port5c, and a coolant water intake port5dare formed.

As described above, the humidification unit2and the stack1are combined together into one piece. Therefore, it is possible to easily simplify the structure and reduce the overall size and weight of the apparatus.

However, in the fuel cell humidification system, at the time of overlapping and connecting the connection surface1aof the stack1and the connection surface2aof the humidification unit2, the pipes of the stack1and the pipes of the humidification unit2need to be accurately positioned in alignment with each other.

For example, by accurately positioning the fuel gas inlet port3aof the stack1and the fuel gas discharge port3cof the humidification unit2coaxially, the smooth flow of the fuel gas is achieved.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the needs mentioned above, and an object of the present invention is to provide a fuel cell system which makes it possible to suitably and highly accurately connect fluid pipes of a fuel cell stack and fluid pipes of a humidifier with simple structure.

The present invention relates to a fuel cell system including a fuel cell stack formed by stacking a plurality of power generation cells, and a humidifier for humidifying at least one of reactant gases supplied to the fuel cell stack using humidified fluid. In the fuel cell system, a fluid pipe provided for the fuel cell stack and a fluid pipe provided for the humidifier are connected by a separate intermediate pipe.

In the present invention, since the fluid pipe of the fuel cell stack and the fluid pipe of the humidifier are connected by the intermediate pipe, even if there is an axial misalignment between the fluid pipes, by tilting of the intermediate pipe, the axial misalignment can be absorbed reliably. Thus, with the simple structure, it is possible to connect the fluid pipe of the fuel cell stack and the fluid pipe of the humidifier suitably and highly accurately, and the smooth flow of the reactant gases is achieved reliably.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is side view schematically showing a fuel cell vehicle12equipped with a fuel cell system10according to an embodiment of the present invention.FIG. 2is a diagram schematically showing structure of the fuel cell system10. For the purpose of explanation, the positions of after-mentioned constituent elements shown inFIG. 2are different from actual positions of the constituent elements. The actual positions of the constituent elements are shown inFIG. 1.

The fuel cell system10includes a fuel cell stack14, a coolant supply mechanism16for supplying a coolant to the fuel cell stack14, an oxygen-containing gas supply mechanism18for supplying an oxygen-containing gas (reactant gas) to the fuel cell stack14, and a fuel gas supply mechanism20for supplying a fuel gas (reactant gas) to the fuel cell stack14.

The fuel cell stack14is provided at the center in a lateral direction of the fuel cell vehicle12, and components of the fuel cell stack14are stacked in a longitudinal direction (hereinafter also referred to as the stacking direction) of the fuel cell vehicle12indicated by an arrow L. For example, the fuel cell stack14is provided in a center console22.

As shown inFIGS. 1 and 2, the coolant supply mechanism16includes a radiator24provided on the front side in a traveling direction (indicated by an arrow L1inFIG. 1) of the fuel cell vehicle12. The radiator24is connected to a coolant supply pipe28through a coolant pump26, and connected to a coolant discharge pipe30. The coolant supply pipe28and the coolant discharge pipe30are provided on the front side in the traveling direction of the fuel cell vehicle12from the fuel cell stack14.

The oxygen-containing gas supply mechanism18has an air pump32provided near the coolant pump26. One end of an air supply pipe34is connected to the air pump32, and the other end of the air supply pipe34is connected to a humidifier36. The humidifier36is connected to the fuel cell stack14through a humidified air supply pipe38. An off gas supply pipe40for supplying the consumed oxygen-containing gas (hereinafter referred to as the off gas) as humidified fluid is connected to the fuel cell stack14and the humidifier36. The humidifier36has a back pressure valve42on a side where the off gas supplied through the off gas supply pipe40is discharged (seeFIG. 2).

The fuel gas supply mechanism20includes a fuel gas tank (fuel tank)44where a hydrogen gas is stored as a fuel gas. One end of a fuel gas pipe45is connected to the fuel gas tank44, and a fuel gas supply pipe51is connected to the fuel gas pipe45through a shut-off valve46, a regulator48, and an ejector50. Further, the fuel gas supply pipe51is connected to the fuel cell stack14.

An exhaust fuel gas pipe52for discharging the consumed fuel gas is connected to the fuel cell stack14. The exhaust fuel gas pipe52is connected to the ejector50through a return pipe54, and also connected to a purge valve56.

The fuel cell stack14is formed by stacking a plurality of power generation cells60horizontally in the longitudinal direction indicated by an arrow A. Metal end plates62a,62bare provided through terminal plates and insulating plates (not shown) at both ends of the fuel cell stack14in the stacking direction. Power output terminals63a,63bprotrude outwardly from the end plates62a,62bin the stacking direction. The power output terminals63a,63bare connected to a travel motor and auxiliary devices (not shown).

The fuel cell stack14has a casing64including end plates62a,62b. The end plates62a,62bare formed in a rectangular shape having long sides in a vertical direction indicated by an arrow C.

As shown inFIG. 3, each of the power generation cells60includes a membrane electrode assembly (electrolyte electrode assembly)66and thin corrugated first and second metal separators68,70sandwiching the membrane electrode assembly66. Each of the power generation cells60is elongated in the longitudinal direction. Instead of the first and second metal separators68,70, for example, carbon separators may be used.

At one end of the power generation cell60in the longitudinal direction indicated by the arrow C, an oxygen-containing gas supply passage72afor supplying an oxygen-containing gas and a fuel gas supply passage76afor supplying a fuel gas such as a hydrogen-containing gas are provided. The oxygen-containing gas supply passage72aand the fuel gas supply passage76aextend through the power generation cell60in the direction indicated by the arrow A.

At the other end of the power generation cell60in the longitudinal direction, an oxygen-containing gas discharge passage72bfor discharging the oxygen-containing gas and a fuel gas discharge passage76bfor discharging the fuel gas are provided. The oxygen-containing discharge passage72band the fuel gas discharge passage76bextend through the power generation cell60in the direction indicated by the arrow A.

At one end of the power generation cell60in the lateral direction indicated by the arrow B, a coolant supply passage74afor supplying a coolant and a coolant discharge passage74bfor discharging the coolant are provided. The coolant supply passage74aand the coolant discharge passage74bare elongated in the longitudinal direction.

The membrane electrode assembly66includes an anode80, a cathode82, and a solid polymer electrolyte membrane78interposed between the anode80and the cathode82. The solid polymer electrolyte membrane78is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example.

The first metal separator68has a fuel gas flow field84on its surface68afacing the membrane electrode assembly66. The fuel gas flow field84is connected to the fuel gas supply passage76aand the fuel gas discharge passage76b. For example, the fuel gas flow field84comprises a plurality of grooves extending in the direction indicated by the arrow C. Further, a coolant flow field86is formed on a surface68bof the first metal separator68. The coolant flow field86is connected to the coolant supply passage74aand the coolant discharge passage74b. The coolant flow field86comprises grooves extending in the direction indicated by the arrow B.

The second metal separator70has an oxygen-containing gas flow field88on its surface70afacing the membrane electrode assembly66. The oxygen-containing gas flow field88comprises grooves extending in the direction indicated by the arrow C. The oxygen-containing gas flow field88is connected to the oxygen-containing gas supply passage72aand the oxygen-containing gas discharge passage72b. A surface70bof the second metal separator70is overlapped with the surface68bof the first metal separator68to form a coolant flow field86. Though not shown, seal members are provided on the first and second metal separators68,70as necessary.

As shown inFIG. 4, the casing64includes end plates62a,62b, four panel members90ato90dprovided on sides of the stacked power generation cells60, angle members92for coupling the adjacent ends of the panel members90ato90dtogether by bolts91, coupling pins94a,94bhaving different lengths for coupling the end plates62a,62band the panel members90ato90d. The panel members90ato90dare thin metal plates.

As shown inFIG. 2, a coolant inlet manifold96aand a coolant outlet manifold96bare provided at the end plate62a. The coolant inlet manifold96ais connected to the coolant supply passage74a, and the coolant outlet manifold96bis connected to the coolant discharge passage74b. Further, the coolant inlet manifold96aand the coolant outlet manifold96bare connected to the radiator24through the coolant supply pipe28and the coolant discharge pipe30.

As shown inFIG. 4, an oxygen-containing gas inlet manifold98a, a fuel gas inlet manifold100a, an oxygen-containing gas outlet manifold98b, and a fuel gas outlet manifold100bare provided at the end plate62b. The oxygen-containing gas inlet manifold98ais connected to the oxygen-containing supply passage72a. The fuel gas inlet manifold100ais connected to the fuel gas supply passage76a. The oxygen-containing gas outlet manifold98bis connected to the oxygen-containing gas discharge passage72b. The fuel gas outlet manifold100bis connected to the fuel gas discharge passage76b.

The oxygen-containing gas inlet manifold98a, the fuel gas inlet manifold100a, the oxygen-containing gas outlet manifold98b, and the fuel gas outlet manifold100bhave pipe connectors102a,103a,102band103beach having a thin cylindrical shape. The pipe connectors102a,103a,102band103bprotrude outwardly from the surface of the end plate62bin the stacking direction.

As shown inFIG. 5, the metal casing104of the humidifier36is fixed to the end plate62bof the fuel cell stack14. For example, the casing104is formed by molding. A plurality of bolts108are inserted into a flange106which contacts the end plate62b. The bolts108are threaded into the end plate62bto fix the casing104to the end plate62b.

In the casing104, first and second humidifier sections110a,110bare arranged vertically. The first humidifier section110aand the second humidifier section110bare connected to the air supply pipe34and the humidified air supply pipe38. For example, the first humidifier section110aand the second humidifier section110badopt hollow fiber humidifier structure. Auxiliary devices of the fuel gas supply mechanism20such as the shut-off valve46, the regulator48, the ejector50, and the back pressure valve42are provided integrally with the casing104.

As shown inFIG. 6, pipe connectors112a,112b,114a, and114beach having a thin cylindrical shape are provided at ends of the humidified air supply pipe38, the off gas supply pipe40, the fuel gas supply pipe51, and the exhaust fuel gas pipe52. The pipe connectors112a,112b,114a, and114bare connected to the pipe connectors102a,102b,103a, and103bof the oxygen-containing gas inlet manifold98a, the oxygen-containing gas outlet manifold98b, the fuel gas inlet manifold100a, and the fuel gas outlet manifold100bthrough intermediate pipes116, respectively.

As shown inFIG. 7, the intermediate pipe116has a substantially cylindrical shape. O-rings120a,120bare attached to annular grooves118a,118bat opposite ends in the outer circumferential portions of the intermediate pipe116. The inner diameter of the pipe connector102aof the oxygen-containing gas inlet manifold98aand the inner diameter of the pipe connector112aof the humidified air supply pipe38are substantially the same. A predetermined space S is formed between the inner surface of the pipe connectors102aand the outer surface of the intermediate pipe116for absorbing the axial misalignment between the pipe connectors102a,112aby tilting of the intermediate pipe116. The inner surfaces of the pipe connectors102a,112ainclude tapered portions122a,122bat front ends.

In the intermediate pipe116, the O-ring120aslidingly contacts the inner surface of the pipe connector102a, and the other O-ring120bslidingly contacts the inner surface of the pipe connector112ato connect the oxygen-containing gas inlet manifold98aand the humidified air supply pipe38. The inner diameter of the intermediate pipe116is the same as the inner diameter of the oxygen-containing gas inlet manifold98a, i.e., the inner diameters of the oxygen-containing gas supply passage72aand the humidified air supply pipe38.

The relationship between the oxygen-containing gas outlet manifold98band the off gas supply pipe40, the relationship between the fuel gas inlet manifold100aand the fuel gas supply pipe51, and the relationship between the fuel gas outlet manifold100band the exhaust fuel gas pipe52are the same as the relationship between the oxygen-containing gas inlet manifold98aand the humidified air supply pipe38, and detailed description thereof will be omitted.

As shown inFIG. 4, a predetermined number of positioning knock pins122are provided in the end plate62b. As shown inFIG. 6, a predetermined number of knock holes124are provided on the surface of the casing104joined to the end plate62bfor fitting the knock pins122into the knock holes124.

In the embodiment, as shown inFIG. 2, a branch pipe with a purge valve (not shown) may be provided between the air supply pipe34of the oxygen-containing gas supply mechanism18and a position downstream of the ejector50of the fuel gas supply mechanism20for purging the fuel gas remaining in the fuel gas flow field system of the fuel cell stack14.

Next, operation of the fuel cell system10will be described below.

Firstly, as shown inFIG. 2, the air pump32of the oxygen-containing gas supply mechanism18is operated to suck the external air as the oxygen-containing gas, and the air is supplied into the air supply pipe34. The air flows from the air supply pipe34into the humidifier36, and is supplied to the humidified air supply pipe38through the first and second humidifier sections110a,110b.

At this time, as descried later, the oxygen-containing gas consumed in reaction (off gas) is supplied to the off gas supply pipe40. Thus, water in the off gas moves to the air before consumption, and humidifies the air. The humidified air flows from the humidified air supply pipe38to the oxygen-containing gas supply passage72ain the fuel cell stack14through the end plate62b.

In the fuel gas supply mechanism20, the shut-off valve46is opened, and the pressure of the fuel gas (hydrogen-gas) in the fuel gas tank44is decreased by the regulator48. Thereafter, the fuel gas flows through the ejector50, and flows from the fuel gas supply pipe51to the end plate62b. Thus, the fuel gas is supplied to the fuel gas supply passage76ain the fuel cell stack14.

Further, in the coolant supply mechanism16, by operation of the coolant pump26, the coolant flows from the coolant supply pipe28to the end plate62a. Thus, the coolant is supplied into the coolant supply passage74ain the fuel cell stack14.

As shown inFIG. 3, after the air is supplied to each of the power generation cells60in the fuel cell stack14, the air flows from the oxygen-containing gas supply passage72ato the oxygen-containing gas flow field88of the second metal separator70, and flows along the cathode82of the membrane electrode assembly66for inducing an electrochemical reaction at the cathode82. The fuel gas flows from the fuel gas supply passage76ato the fuel gas flow field84of the first metal separator68, and flows along the anode80of the membrane electrode assembly66for inducing an electrochemical reaction at the anode80.

Thus, in each of the membrane electrode assemblies66, the oxygen in the air supplied to the cathode82, and the fuel gas (hydrogen) supplied to the anode80are consumed in the electrochemical reactions at catalyst layers of the cathode82and the anode80for generating electricity.

The air consumed at the cathode82flows along the oxygen-containing gas discharge passage72b, and is discharged as the off gas from the end plate62bto the off gas supply pipe40(seeFIG. 2).

Likewise, the fuel gas consumed at the anode80flows along the fuel gas discharge passage76b, and is discharged as the exhaust fuel gas from the end plate62bto the exhaust fuel gas pipe52. The exhaust fuel gas discharged to the exhaust fuel gas pipe52partially flows through the return pipe54, and returns to the fuel gas supply pipe51by sucking operation of the ejector50. The exhaust fuel gas is mixed with the fresh fuel gas, and then, supplied from the fuel gas supply pipe51to the fuel cell stack14. The remaining exhaust fuel gas is discharged when the purge valve56is opened.

Further, as shown inFIG. 3, the coolant flows from the coolant supply passage74ato the coolant flow field86between the first and second metal separators68,70, and flows in the direction indicated by the arrow B. After the coolant cools the membrane electrode assembly66, the coolant flows through the coolant discharge passage74b, and the coolant is discharged from the coolant outlet manifold96bat the end plate62ato the coolant discharge pipe30. As shown inFIG. 2, after the coolant is cooled by the radiator24, by operation of the coolant pump26, the coolant is supplied from the coolant supply pipe28to the fuel cell stack14.

In the embodiment, the humidifier36is attached to the end plate62bof the fuel cell stack14. The fluid pipes of the fuel cell stack14and the fluid pipes of the humidifier36are connected by the intermediate pipes116.

Specifically, the intermediate pipes116are provided between the pipe connectors102a,102b,103a, and103bof the oxygen-containing gas inlet manifold98a, the oxygen-containing gas outlet manifold98b, the fuel gas inlet manifold100a, and the fuel gas outlet manifold100bat the end plate62bas shown inFIG. 4and the pipe connectors112a,112b,114a, and114bof the humidified air supply pipe38, the off gas supply pipe40, the fuel gas supply pipe51, and the exhaust fuel gas pipe52of the humidifier36as shown inFIG. 6.

As shown inFIG. 7, the predetermined space S is formed between the outer circumference of the intermediate pipe116and the inner circumference of the pipe connectors102a,112a, and the O-rings120a,120bare fitted to the outer circumference of the intermediate pipe116through the annular grooves118a,118b. The O-rings120a,120btightly contact the inner circumferential surface of the pipe connector102aof the oxygen-containing gas inlet manifold98aand the inner circumferential surface of the pipe connector112aof the humidified air supply pipe38.

In the structure, since the pipe connectors102a,112aare coupled through the intermediate pipe116, even if there is an axial misalignment between the pipe connectors102a,112a, for example, by tilting of the intermediate pipe116, the axial misalignment can be absorbed reliably.

Thus, in the embodiment, with the simple structure, it is possible to suitably connect the fluid pipes of the fuel cell stack14and the fluid pipes of the humidifier36with a high degree of accuracy. As a result, the oxygen-containing gas and the fuel gas flow smoothly and reliably.

Further, using the intermediate pipes116, it is possible to reliably and easily position the fuel cell stack14and the humidifier36with respect to each other. At this time, by fitting the predetermined number of the knock pins122into the predetermined number of the knock holes124, operation of positioning the fuel cell stack14and the humidifier36is further simplified.

Since the intermediate pipes116can be utilized as positioning members, for example, at least two intermediate pipes116may be used, and mating (spigot) structure may be adopted for the other fluid pipes that are not connected by the intermediate pipes116.

Further, in the embodiment, the inner diameter of the intermediate pipe116is the same as the inner diameter of the humidified air supply pipe38and the inner diameter of the oxygen-containing gas inlet manifold98a. Thus, the humidified air smoothly and suitably flows from the humidified air supply pipe38to the oxygen-containing gas inlet manifold98athrough the intermediate pipe116.

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