Fuel cell system and vehicle with fuel cell system mounted thereon

The voltage application unit first applies voltages (+,+,0,−,−,0) respectively to the electrostatic delivery electrodes 37 belonging to the phase ‘a’, the phase ‘b’, the phase ‘c’, the phase ‘d’, the phase ‘e’, and the phase ‘f’, and then successively applies voltages (0,+,+,0,−,−), voltages (−,0,+,+,0,−), voltages (−,−,0,+,+,0), voltages (0,−,−,0,+,+), and voltages (+,0,−,−,0,+). The voltage application unit repeats this cycle multiple times to apply the voltages to the phase ‘a’ through the phase ‘f’. The water droplets flocculated in the oxidizing gas conduits 36 are charged by electrostatic induction and travel in the direction from the inlet to the outlet of the oxidizing gas conduits 36 while being repelled or attracted by the electrostatic delivery electrodes 37 in the vicinity of the water droplets in the course of the positive-negative variation of the voltage in the cycle.

This is a 371 national phase application of PCT/JP2004/002016 filed 20 Feb. 2004, claiming priority to Japanese Patent Application No. 2003-140987 filed 19 May 2003, the contents of which are incorporated herein by reference.

BACKGROUND ART

A proposed fuel cell system includes: fuel cells that generate electric power through electrochemical reactions of oxygen included in an oxidizing gas, which is flown through oxidizing gas conduits provided on a cathode side of respective electrolyte membranes, with hydrogen included in a fuel gas, which is flown through fuel gas conduits provided on an anode side of the electrolyte membranes; piezoelectric elements that are located in the oxidizing gas conduits and are displaced by a driving voltage; and vibrators that are also located in the oxidizing gas conduits and vibrate with the displacement of the piezoelectric elements (for example, see Patent Laid-Open Gazette No. 2002-184430). In this fuel cell system, water produced by the electrochemical reactions on the cathode side may be flocculated to water droplets and prevent the smooth flow of the oxidizing gas. In such cases, the piezoelectric element is displaced to trigger vibration of the vibrator. The vibration atomizes the water content on the surface of the cathode, thereby removing the water content.

This prior art fuel cell system is, however, required to locate the piezoelectric elements and the vibrators functioning as the movable members in the restricted space of the gas conduit. This undesirably complicates the structure. Another problem is that atomization of the water droplets flocculated in the gas conduits may take a relatively long time.

DISCLOSURE OF THE INVENTION

By taking into account the drawbacks of the prior art technique discussed above, the object of the present invention is to provide a fuel cell system that effectively removes the water content from the gas conduit by the simple structure. The object of the invention is also to provide a fuel cell system that delivers water droplets intact out of the gas conduit. The object of the invention is further to provide a vehicle having these fuel cell systems mounted thereon.

In order to achieve at least part of aforementioned objects, the fuel cell system and the vehicle having the fuel cell system mounted thereon are constructed as follows.

A fuel cell system of the present invention includes: a fuel cell that generates electric power through electrochemical reactions of oxygen included in an oxidizing gas, which is flown through an oxidizing gas conduit provided on a cathode side of an electrolyte membrane, with hydrogen included in a fuel gas, which is flown through a fuel gas conduit provided on an anode side of the electrode membrane; and an electrostatic delivery module that is provided in at least one of the fuel gas conduit and the oxidizing gas conduit and effectuates electrostatic delivery of water droplets flocculated in the at least one gas conduit to deliver the water droplets out of the gas conduit.

This fuel cell system effectuates electrostatic delivery of water droplets flocculated in the gas conduit and thereby delivers the water droplets out of the gas conduit. Namely the technique utilizes the electrostatic force to remove the water content from the gas conduit. This simple structure effectively removes the water content from the gas conduit without placing any movable member like a vibrator in the gas conduit and without atomizing the water droplets flocculated in the gas conduit. The water produced by the electrochemical reaction is readily flocculated in the oxidizing gas conduit. It is thus preferable that the electrostatic delivery module is provided in the oxidizing gas conduit. The electrostatic delivery module may electrostatically deliver the water droplets flocculated in the gas conduit toward its outlet or toward its inlet.

A fuel cell system of the present invention includes: a fuel cell that generates electric power through electrochemical reactions of oxygen included in an oxidizing gas, which is flown through an oxidizing gas conduit provided on a cathode side of an electrolyte membrane, with hydrogen included in a fuel gas, which is flown through a fuel gas conduit provided on an anode side of the electrode membrane; multiple electrodes that are arranged in at least one of the fuel gas conduit and the oxidizing gas conduit and are covered with an insulator layer; and a voltage application module that applies a voltage to the multiple electrodes to effectuate electrostatic delivery of water droplets flocculated in the at least one gas conduit and thereby deliver the water droplets out of the gas conduit.

This fuel cell system applies the voltage to the multiple electrodes, which are arranged in the gas conduit, to effectuate electrostatic delivery of the water droplets flocculated in the gas conduit and thereby remove the water content from the gas conduit. Namely the technique utilizes the electrostatic force to remove the water content from the gas conduit. This simple structure effectively removes the water content from the gas conduit without placing any movable member like a vibrator in the gas conduit and without atomizing the water droplets flocculated in the gas conduit. The water produced by the electrochemical reaction is readily flocculated in the oxidizing gas conduit. It is thus preferable that the electrostatic delivery module is provided in the oxidizing gas conduit. The voltage application module may apply the voltage to the multiple electrodes to effectuate electrostatic delivery of the water droplets flocculated in the gas conduit toward its outlet or to effectuate electrostatic delivery of the water droplets flocculated in the gas conduit toward its inlet.

In this fuel cell system of the invention, it is preferable that the voltage application module applies the voltage to the multiple electrodes to make an apparent positive-negative variation in voltage toward either the outlet or the inlet of the gas conduit. This arrangement efficiently leads the water droplets flocculated in the gas conduit toward either its outlet or its inlet. The voltage application module may apply the voltage to the multiple electrodes to make an apparent positive-negative variation in voltage toward one of the outlet and the inlet of the gas conduit, which is located below the other. This structure desirably takes advantage of the force of gravity acting on the water droplets.

In the fuel cell system of the invention, the multiple electrodes may be placed at a specific position of the gas conduit having a high potential for flocculation to water droplets. The multiple electrodes may be located in the whole oxidizing gas conduit or in the whole fuel gas conduit. It is, however, preferable to place the multiple electrodes at any specific position having a high potential for flocculation to water droplets, because of the structural characteristic of the fuel cell. This arrangement does not place the electrodes at a position having a low potential for flocculation to water droplets and thereby desirably saves the electrode resource.

In one preferable embodiment of the fuel cell system of the invention, the fuel cell has a membrane electrode assembly that includes the anode and the cathode arranged across the electrolyte membrane, and a pair of electrically conductive separators that are placed across the membrane electrode assembly. The oxidizing gas conduit is defined by the cathode and a groove formed in one of the pair of electrically conductive separators. The fuel gas conduit is defined by the anode and a groove formed in the other of the pair of electrically conductive separators. The multiple electrodes are placed in the groove of at least one of the fuel gas conduit and the oxidizing gas conduit. In this structure, the multiple electrodes covered with the insulator layer are arranged in the groove formed in the electrically conductive separator, which is not in contact with the anode or the cathode. Such positioning of these electrodes does not damage the electric conductivity between the anode or the cathode and the electrically conductive separator.

In another preferable embodiment, the fuel cell system of the invention further includes: a driving state detection module that detects a driving state of the fuel cell; and a voltage application control module that determines actuation or non-actuation of the voltage application module to apply or not to apply the voltage to the multiple electrodes, based on the detected driving state of the fuel cell. The voltage application module may be controlled to continuously apply the voltage to the multiple electrodes and thereby effectuate electrostatic delivery of the water droplets during an operation of the fuel cell. The determination of application or non-application of the voltage to the multiple electrodes according to the driving state of the fuel cell, however, desirably saves the power consumption.

The fuel cell system of this preferable embodiment may further include a driving state specification module that determines whether the driving state of the fuel cell detected by the driving state detection module reaches a predetermined driving state having a high potential for flocculation to water droplets in the gas conduit. The voltage application control module actuates the voltage application module to apply the voltage to the multiple electrodes, when the driving state specification module determines that the detected driving state of the fuel cell reaches the predetermined driving state. The arrangement starts application of the voltage to the multiple electrodes for electrostatic delivery of the water droplets out of the gas conduit, when the gas conduit falls into the state having a high potential for flocculation to water droplets. This prevents unnecessary power consumption. Here the ‘driving state of the fuel cell’ may be, for example, any of a power demand to the fuel cell and an output power, an integral power, and an output voltage of the fuel cell. The fuel cell system of this preferable embodiment may still further include a driving state specification module that determines whether the driving state of the fuel cell detected by the driving state detection module represents an excess water content. The voltage application control module actuates the voltage application module to apply the voltage to the multiple electrodes, when the driving state specification module determines that the detected driving state of the fuel cell represents the excess water content.

In still another preferable embodiment, the fuel cell system of the invention further includes a voltage application control module that controls the voltage application module to continuously apply the voltage to the multiple electrodes and thereby effectuate electrostatic delivery of the water droplets during an operation of the fuel cell.

A vehicle of the present invention has the fuel cell system of any of the above arrangements mounted thereon. The fuel cell system of any arrangement discussed above effectively removes the water content from the gas conduit without placing any movable member like a vibrator in the gas conduit and without atomizing the water droplets flocculated in the gas conduit. The vehicle with this fuel cell system mounted thereon naturally exerts the equivalent functions and effects to those of the fuel cell system discussed above.

BEST MODES FOR CARRYING OUT THE INVENTION

One mode of carrying out the invention is discussed below with reference to the drawings.FIG. 1schematically illustrates the construction of a vehicle10with a fuel cell system12mounted thereon.FIG. 2is a decomposed perspective view showing a unit fuel cell30.FIG. 3is a plan view showing a separator with oxidizing gas conduits formed thereon, andFIG. 4is a sectional view taken on the line A-A ofFIG. 3.FIG. 5shows a voltage application pattern.

As shown inFIG. 1, the vehicle10of this embodiment includes a fuel cell system12, an actuation mechanism14that converts a supply of electric power from the fuel cell system12into driving force and rotates driving wheels18,18via a reduction gear16with the driving force, and an electronic control unit80that controls the whole vehicle10. The fuel cell system12has a fuel cell stack20, which is a stack of multiple unit fuel cells30generating electric power through electrochemical reactions of hydrogen and oxygen, supply manifolds M1and M2to feed supplies of an oxidizing gas and a gaseous fuel to the respective unit fuel cells30, and exhaust manifolds M3and M4to lead exhausts of the oxidizing gas and the gaseous fuel, which have passed through the respective unit fuel cells30, out of the fuel cell stack20. The vehicle10of the embodiment also has multiple electrostatic delivery electrodes37(seeFIG. 3) that function to electrostatically deliver water droplets in a direction from the inlet to the outlet of the oxidizing gas conduits36, and a voltage application unit70that applies voltages to these electrostatic delivery electrodes37.

The fuel cell stack20is manufactured by stacking a plurality of the unit fuel cells30as base units and sequentially arranging a pair of collector plates21and22, a pair of insulator plates23and24, and a pair of end plates25and26on respective ends of the stack of the unit fuel cells30. The collector plates21and22are composed of a gas-impermeable electric conductive material, such as dense carbon or copper. The insulator plates23and24are composed of an insulating material, such as rubber or resin. The end plates25and26are composed of a metal having rigidity, such as steel. The collector plates21and22respectively have output terminals21aand22ato output an electromotive force generated by the fuel cell stack20. A holder mechanism (not shown) causes the end plates25and26to hold the respective unit cells30under pressure applied in its stacking direction.

As shown inFIG. 2, each of the unit fuel cells30has a membrane electrode assembly (MEA)34including an anode32and a cathode33arranged across an electrolyte membrane31, and a pair of separators40,40disposed on both ends of the MEA34. The electrolyte membrane31has good proton conductivity in its wet state. A Nafion membrane manufactured by DuPont is preferably applied for the electrolyte membrane31. Each of the anode32and the cathode33has a catalyst electrode with platinum or an alloy of platinum and another metal carried thereon and a gas diffusion electrode of carbon cloth, which is a woven fabric of carbon fibers. The MEA34is obtained by integrating the anode32, the electrolyte membrane31, and the cathode33by thermo compression. Each of the separators40is composed of a gas-impermeable electric conductive material, for example, mold carbon obtained by compressing carbon to be gas impermeable. As shown inFIG. 2, an oxidizing gas supply port41and an oxidizing gas exhaust port43penetrating the separator40are formed on the approximate centers of a left side and a right side of the separator40. A gaseous fuel supply port42and a gaseous fuel exhaust port44penetrating the separator40are also formed on the approximate centers of an upper side and a lower side of the separator40. Circular apertures45through48penetrating the separator40for circulation of cooling water are also formed on four corners of the separator40. Multiple grooves36b(SeeFIG. 4) going from the oxidizing gas supply port41to the oxidizing gas exhaust port43form an oxidizing gas conduit36on one face of the separator40. Similarly multiple grooves going from the gaseous fuel supply port42to the gaseous fuel exhaust port44form a gaseous fuel conduit38on the other face of the separator40. The multiple electrostatic delivery electrodes37are interposed between a lower insulator layer37aand an upper insulator layer37bon the bottom of grooves36b, which define the oxidizing gas conduits36, and are arrayed along the path going from the inlet to the outlet, as shown inFIG. 4.

Gaskets50are interposed between the MEA34and the respective separators40, as shown inFIG. 2. The gaskets50are arranged across the electrolyte membrane31to restrain leakage of the gaseous fuel and the oxidizing gas and to prevent the flow of the oxidizing gas from being mixed with the flow of the gaseous fuel in the space between the separators40,40. Each of the gaskets50has slots51through54perforated to face the oxidizing gas supply port41, the gaseous fuel supply port42, the oxidizing gas exhaust port43, and the gaseous fuel exhaust port44of the separator40respectively, circular apertures55through58perforated to face the circular apertures45through48respectively (the circular aperture55is omitted from the illustration), and a square hole formed in a size to receive the anode32or the cathode33therein.

Among the supply manifolds, the oxidizing gas supply manifold M1is a hollow space of connecting the oxidizing gas supply port41of the separator40with the slot51of the gasket50in the respective unit fuel cells30in the stacking direction of the fuel cell stack20. A supply of the air as the oxidizing gas is fed from an air compressor60via a flow control valve62, is humidified by a non-illustrated humidifier, and is flown into the oxidizing gas supply manifold M1. The gaseous fuel supply manifold M2is a hollow space of connecting the gaseous fuel supply port42of the separator40with the slot52of the gasket50in the respective unit fuel cells30in the stacking direction of the fuel cell stack20. A supply of gaseous hydrogen as the gaseous fuel is fed from a hydrogen tank64via a flow control valve66, is humidified by a non-illustrated humidifier, and is flown into the gaseous fuel supply manifold M2. Cooling water inflow manifolds M5and M6are respectively hollow spaces of connecting the circular apertures45and46of the separator40with the circular apertures55and56of the gasket50in the respective unit fuel cells30in the stacking direction of the fuel cell stack20. A flow of cooling water as the coolant is fed from a non-illustrated pump and is flown into the cooling water inflow manifolds M5and M6.

Among the exhaust manifolds, the oxidizing gas exhaust manifold M3is a hollow space of connecting the oxidizing gas exhaust port43of the separator40with the slot53of the gasket50in the respective unit fuel cells30in the stacking direction of the fuel cell stack20. The exhaust of the oxidizing gas, which has passed through the oxidizing gas conduits36of the respective unit fuel cells30, is collectively led out of the fuel cell stack20. The gaseous fuel exhaust manifold M4is a hollow space of connecting the gaseous fuel exhaust port44of the separator40with the slot54of the gasket50in the respective unit fuel cells30in the stacking direction of the fuel cell stack20. The exhaust of the gaseous fuel, which has passed through the gaseous fuel conduits38of the respective unit fuel cells30, is collectively led out of the fuel cell stack20. The exhaust of the gaseous fuel still includes non-reacted hydrogen and may thus be re-circulated into the gaseous fuel supply manifold M2. Cooling water outflow manifolds M7and M8are respectively hollow spaces of connecting the circular apertures47and48of the separator40with the circular apertures57and58of the gasket50in the respective unit fuel cells30in the stacking direction of the fuel cell stack20. The hot flow of cooling water, which has passed through cooling water conduits formed in cooling water separators (not shown) disposed at intervals of several unit fuel cells30in the fuel cell stack20, is collectively led out of the fuel cell stack20. The hot flow of cooling water is cooled down by means of a non-illustrated radiator and is re-circulated into the cooling water inflow manifolds M5and M6.

The multiple electrostatic delivery electrodes37are arrayed along the path going from the inlet to the outlet of the respective oxidizing gas conduits36, as shown inFIGS. 3 and 4. The electrostatic delivery electrodes37are placed on the lower insulator layer37a, which covers the bottom surface of the grooves36bof the respective oxidizing gas conduits36, and are covered with the upper insulator layer37b. These electrostatic delivery electrodes37are linear electrodes of 0.2 mm in width (where the width represents the length along the conduit) and are arranged at pitches of 0.5 to 1 mm. The electrostatic delivery electrodes37are divided into six phases, phases ‘a’ through ‘f’, according to a voltage pattern applied thereto. The wires of the electrostatic delivery electrodes37in each phase are joined to one wiring, which is connected to the voltage application unit70. For example, the known printed wiring board production technique is applied to prepare the electrostatic delivery electrodes37and their wiring pattern.

The voltage application unit70applies voltages to the multiple electrostatic delivery electrodes37according to a voltage application pattern shown inFIG. 5. The voltage application unit70applies an identical voltage to plural electrostatic delivery electrodes37belonging to an identical phase among the phases ‘a’ through ‘f’.

The actuation mechanism14(seeFIG. 1) has a power converter to convert the d.c. power generated by the fuel cell stack20into a.c. power and a traction motor driven and rotated with the converted a.c. power, although not being specifically illustrated.

Referring back toFIG. 1, the electronic control unit80is constructed as a microprocessor including a CPU82, a ROM84that stores processing programs, a RAM86that temporarily stores data, and an input-output port (not shown). The electronic control unit80receives, as inputs via the input port, an accelerator pedal opening signal AP sent from an accelerator pedal sensor (not shown), a vehicle speed signal V sent from a vehicle speed sensor (not shown), a measurement of integral power of the fuel cell detected by and sent from a wattmeter72, and an input-output voltage signal of the power converter included in the actuation mechanism14. The electronic control unit80outputs control signals to the voltage application unit70, as well as to the power converter and the traction motor included in the actuation mechanism14via the output port.

The operations of the vehicle10of the embodiment having the above construction are described below. The description first regards the process of electrostatic delivery of water droplets flocculated in the oxidizing gas conduits36in the direction from their inlet to their outlet. According to the voltage application pattern shown inFIG. 5, the voltage application unit70first applies voltages (+,+,0,−,−,0) respectively to the electrostatic delivery electrodes37belonging to the phase ‘a’, the phase ‘b’, the phase ‘c’, the phase ‘d’, the phase ‘e’, and the phase ‘f’ (No.1ofFIG. 5). The voltage application unit70then successively applies voltages (0,+,+,0,−,−) (No.2ofFIG. 5), voltages (−,0,+,+,0,−) (No.3ofFIG. 5), voltages (−,−,0,+,+,0) (No.4ofFIG. 5), voltages (0,−,−,0,+,+) (No.5ofFIG. 5), and voltages (+,0,−,−,0,+) (No.6ofFIG. 5). The structure of this embodiment repeats this cycle of No.1to No.6multiple times to apply the voltages to the phase ‘a’ through the phase ‘f’. Namely the voltage application unit70applies voltages of 6-phase rectangular waves. As clearly shown by the positive-negative change of the voltage in the cycle of No.1to No.6ofFIG. 5, an apparent positive-negative variation in voltage proceeds in the direction from the inlet to the outlet of the oxidizing gas conduits36with elapse of time. The water droplets flocculated in the oxidizing gas conduits36are charged by electrostatic induction and travel in the direction from the inlet to the outlet of the oxidizing gas conduits36while being repelled or attracted by the electrostatic delivery electrodes37in the vicinity of the water droplets in the course of the positive-negative variation of the voltage in the cycle of No.1to No.6shown inFIG. 5. In this manner, the voltage application unit70applies the voltages to the multiple electrostatic delivery electrodes37according to the voltage application pattern ofFIG. 5. This effectuates electrostatic delivery of the water droplets flocculated in the oxidizing gas conduits36in the direction from their inlet to their outlet.

The water droplets flocculated in the oxidizing gas conduits36during a run of the vehicle are removed as discussed below.FIG. 6is a flowchart showing an electrostatic delivery routine executed by the CPU82of the electronic control unit80. This routine is stored in the ROM84and is repeatedly executed by the CPU82at preset time intervals (for example, at every several msec). When this routine starts, the CPU82first compares an electric power demand to the fuel cell stack20with a preset threshold value T1to determine whether a high power output is demanded to the fuel cell stack20(step S110). The electric power demand to the fuel cell stack20is calculated from a vehicle power demand to the drive wheels18,18, which is specified corresponding to current inputs of a vehicle speed signal V and an accelerator pedal opening signal AP by referring to a non-illustrated map stored in the ROM84. The threshold value T1is empirically set in advance. The higher output of the fuel cell stack20causes the more vigorous electrochemical reaction to produce a large amount of water. The large amount of water is readily flocculated in the oxidizing gas conduits36to interfere with the smooth flow of the oxidizing gas. The procedure experimentally determines the relation between the amount of flocculated water in the oxidizing gas conduits36and the output power of the fuel cell stack20and sets the output power of the fuel cell stack20at the time when the amount of flocculated water possibly interferes with the smooth flow of the oxidizing gas, to the threshold value T1.

When it is determined at step S110that the electric power demand to the fuel cell stack20does not exceed the preset threshold value T1, the CPU82resets a high output flag F to ‘0’ (step S120) and immediately terminates this routine. When it is determined at step S110that the electric power demand to the fuel cell stack20exceeds the preset threshold value T1, on the other hand, the CPU82subsequently determines whether the high output flag F is set equal to ‘1’ (step S130). When the high output flag F is not equal to ‘1’, the CPU82sets the value ‘1’ to the high output flag F to indicate the status of a high power demand to the fuel cell stack20(step S140). The CPU82then resets the measurement of integral power on a wattmeter72and starts power integration (step S150), before terminating this routine.

When it is determined at step S130that the high output flag F is equal to ‘1’, this means that the high power output has already been demanded to the fuel cell stack20in the previous cycle of this routine. In this case, the CPU82inputs the measurement of integral power from the wattmeter72(step S160) and compares the input measurement of integral power with a preset threshold value T2(step S170). Even when it is determined at step S110that the electric power demand exceeds the threshold value T1, the electric power demand may soon become lower than the threshold value T1. This means that the measurement of integral power does not reach a specific level, after the electric power demand has once exceeded the threshold value T1. In this case, the electrochemical reaction becomes vigorous only temporarily and does not cause flocculation of water. In another case, the electric power demand continuously exceeds the threshold value T1for a relatively long time period. This means that the measurement of integral power reaches the specific level, while the electric power demand exceeds the threshold value T1. This state often leads to flocculation of water. This specific level of the integral power is thus determined experimentally and is set to the threshold value T2.

When it is determined at step S170that the measurement of integral power does not exceed the preset threshold value T2, the CPU82immediately exits from this routine. When it is determined at step S170that the measurement of integral power exceeds the preset threshold value T2, on the other hand, there is a possibility of flocculation of water. The CPU82accordingly outputs a voltage application start signal to the voltage application unit70(step S180), before exiting from this routine. The voltage application unit70receives the voltage application start signal and applies the voltages to the multiple electrostatic delivery electrodes37according to the voltage application pattern shown inFIG. 5for a preset time period. Such voltage application induces electrostatic delivery of the flocculated water in the oxidizing gas conduits36in the direction from their inlet to their outlet by the mechanism discussed above.

As described above, the simple structure of this embodiment utilizes the electrostatic force to effectively remove the flocculated water from the oxidizing gas conduits36without locating any movable members like vibrators in the oxidizing gas conduits36and without atomizing the water flocculated in the oxidizing gas conduits36. The voltage application unit70applies the voltages to the multiple electrostatic delivery electrodes37to make an apparent positive-negative variation in voltage toward the outlet of the oxidizing gas conduits36. This arrangement efficiently leads the flocculated water in the oxidizing gas conduits36to the oxidizing gas exhaust manifold M3. The multiple electrostatic delivery electrodes37are arrayed on the bottom of the grooves36bof the oxidizing gas conduits36formed on the separator40, which are not to be in contact with the cathode33, and are covered with the lower insulator layer37aand the upper insulator layer37b. The presence of these electrostatic delivery electrodes37does not reduce the contact area of the separator40with the cathode33(that is, the area of a convex face36aof the separator40), thus keeping the sufficient electric conductivity. The voltage application unit70is controlled to apply the voltages to the multiple electrostatic delivery electrodes37only when there is a high possibility of producing flocculated water in the oxidizing gas conduits36(that is, only when the electric power demand exceeds the threshold value T1and the measurement of integral power reaches the specific level). This arrangement desirably saves the power consumption, compared with the structure of unconditionally applying voltages even when there is no need of electrostatic delivery. Another possible technique raises the pressure of the oxidizing gas supply to the oxidizing gas supply manifold M1and blows off the flocculated water. This method, however, requires a large capacity of the air compressor60, which occupies a large space. The arrangement of the embodiment, on the other hand, does not need to blow off the flocculated water by the increased pressure of the oxidizing gas supply, thus desirably reducing the required size and capacity of the air compressor60. The technique of the invention may, however, be combined with the structure of blowing off the flocculated water, according to the requirements.

The embodiment discussed above is to be considered in all aspects as illustrative and not restrictive. There may be many other modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. All changes within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

For example, in the structure of the embodiment, the voltage application unit70is controlled to apply the voltages to the multiple electrostatic delivery electrodes37only when the electric power demand exceeds the threshold value T1and the measurement of integral power reaches the specific level. In one possible modification, the voltage application unit70may be controlled to apply the voltages to the multiple electrostatic delivery electrodes37when the electric power demand exceeds the threshold value T1. In another possible modification, the voltage application unit70may be controlled to apply the voltages to the multiple electrostatic delivery electrodes37every time the measurement of integral power reaches a preset value (this is determined empirically as a value of power integration when flocculation of water occurs). The electrostatic delivery consumes extremely small power, so that the voltage application unit70may be controlled to continuously apply the voltages to the multiple electrostatic delivery electrodes37. Another modified structure determines whether the water content in the oxidizing gas conduits36is an excess level and controls the voltage application unit70to apply the voltages to the multiple electrostatic delivery electrodes37under the condition of the excess water content. The level of the water content in the oxidizing gas conduits36may be determined by the following procedure. A voltage sensor is attached to each unit fuel cell30to measure its output voltage. A behavior of the output voltage under the condition of the excess water content in the oxidizing gas conduits36is specified experimentally and is set in advance. The procedure compares the preset behavior of the output voltage with the current behavior of the output voltage of the respective unit fuel cells30to determine the level of the water content.

In the structure of the embodiment discussed above, the electrostatic delivery electrodes37are placed in all the oxidizing gas conduits36. In one modified structure, the electrostatic delivery electrodes37may be placed in only part of the oxidizing gas conduits36having the high potential for flocculation of water. In an illustrated example ofFIG. 7, the oxidizing gas conduits36are extended in the horizontal direction. Due to the force of gravity, water tends to be flocculated in the lower oxidizing gas conduits36. The electrostatic delivery electrodes37may be provided only in such places. This desirably saves the electrode resource.

In the structure of the embodiment discussed above, the air compressor60is used as the oxidizing gas supply device. A blower may replace the air compressor60, since there is no need of significantly heightening the inlet pressure (supply pressure) of the oxidizing gas supply to blow off flocculated water by the heightened pressure of the oxidizing gas supply. The technique of electrostatic delivery for removal of flocculated water may, however, be combined with the technique of raising the inlet pressure of the oxidizing gas supply to blow off and remove flocculated water. In this case, the air compressor60is required to have the capacity of sufficiently raising the pressure of the oxidizing gas supply to blow off flocculated water.

The procedure of the above embodiment adopts the voltage application pattern shown inFIG. 5. Any other voltage application pattern may be used instead, to effectuate electrostatic delivery of flocculated water in the oxidizing gas conduits36to their outlet.

In the structure of the embodiment discussed above, the oxidizing gas conduits36are formed as linear grooves going from the oxidizing gas supply port41to the oxidizing gas exhaust port43. The oxidizing gas conduits36may be formed as curved grooves or a serpentine groove. Another possible structure may mount small cubes or small rectangular parallelepipeds at preset intervals on the surface of the separator40and set the gaps defined by the cubes or rectangular parallelepipeds as the oxidizing gas conduits36.

The structure of the embodiment utilizes the technique of electrostatic delivery to deliver the water droplets flocculated in the oxidizing gas conduits36to their outlet or the oxidizing gas exhaust manifold M3. One modified structure may alternatively deliver the water droplets flocculated in the oxidizing gas conduits36to their inlet or the oxidizing gas supply manifold M1by electrostatic delivery. For example, when the inlet of the oxidizing gas conduits36is located below their outlet, it is preferable to take advantage of the force of gravity acting on the water droplets flocculated in the oxidizing gas conduits36and lead the water droplets to their inlet, instead of their outlet.

In the structure of the embodiment discussed above, the electrostatic delivery electrodes37are located in the oxidizing gas conduits36. Another possible modification may place similar electrostatic delivery electrodes in the fuel gas conduits38to effectuate electrostatic delivery of water droplets flocculated in the fuel gas conduits38, in addition to or in place of the above structure.

In the embodiment discussed above, the fuel cell system12is mounted on the vehicle10. The fuel cell system12may be mounted on any other vehicles and transportation machines like trains and aircraft, and may be incorporated in any cogeneration systems installed for domestic applications and industrial applications. In any case, the fuel cell system12and its applications exert the equivalent functions and effects to those discussed above.

INDUSTRIAL APPLICABILITY

The technique of the invention is applicable to various transportations including automobiles, trains, and aircraft.