Fuel cell system

Abstract

Fuel cell system (9), comprising: a first fuel cell stack (10a) configured to generate electrical power through a chemical reaction of reaction gas, the first fuel cell stack (10a) having a discharge manifold (101a) configured to discharge the reaction gas; a second fuel cell stack (10b) configured to generate electrical power through a chemical reaction of reaction gas, the second fuel cell stack (10b) having a discharge manifold (101b) configured to discharge the reaction gas; a first auxiliary device (30a, 36a) used to generate power from the first fuel cell stack (10a); a second auxiliary device (30b, 36b) used to generate power from the second fuel cell stack (10b); a control device (1) configured to control an operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b); and a first detector (93) configured to detect an inclination of the discharge direction of the first fuel cell stack (10a) or the second fuel cell stack (10b) relative to the vertically downward direction, wherein the control device (1) is configured to control the operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) such that a fuel cell stack of the first fuel cell stack (10a) and the second fuel cell stack (10b), the discharge direction of which the reaction gas discharged from the discharge manifold forms a smaller angle with a vertically downward direction, starts generating power earlier than the other fuel cell stack of the first fuel cell stack (10a) and the second fuel cell stack (10b) after the power generation of the first fuel cell stack (10a) and the second fuel cell stack (10b) is stopped, and wherein the control device (1) is configured to determine, based on the inclination detected by the first detector (93), which of the first fuel cell stack (10a) and the second fuel cell stack (10b) has the discharge direction that forms a smaller angle with the vertically downward direction.

Description

Background of the invention 1. Field of the invention

[0001] The invention relates to a fuel cell system. 2. Description of the related prior art

[0002] A fuel cell stack generates water when it generates electrical power using hydrogen gas and air. If water remains in the fuel cell stack when the fuel cell stack stops generating power, the water can freeze and block gas flow in a flow channel when the fuel cell stack resumes generating power, for example, at a temperature below freezing.

[0003] Therefore, when the operation of the fuel cell stack is stopped, a purging operation is performed to discharge water from the flow channel by supplying purge gas from, for example, an air pump into the fuel cell stack (see, for example, JP 2005-276 529 A).

[0004] Furthermore, JP 2009-259408 A discloses a fuel cell system mounted on a fuel cell vehicle, comprising a first fuel cell system and a second fuel cell system that are independently controlled. A control unit controls the power of a first fuel cell stack of the first fuel cell system to a specified power when a power demand of the fuel cell vehicle is a specified value or more, and controls the power of a second fuel cell stack of the second fuel cell system so that the power of the entire fuel cell system becomes the power demand or more. When the power demand is less than the specified value, the operation of the first fuel cell stack is stopped, and the power of the second fuel cell stack is controlled so that the power of the second fuel cell stack becomes equal to or more than the power demand.

[0005] JP 2009-134907 A discloses a fuel cell system comprising a pair of fuel cell stacks, each of which generates electricity through the electrochemical reaction of hydrogen gas and air, and a fuel gas-side distribution part disposed between a pair of the fuel cell stacks. Each of the fuel cell stacks is formed by laminating a plurality of unit cells of a fuel cell and is each inclined with respect to the vertical direction. A fuel gas supply passage for supplying hydrogen gas to each of the fuel cell stacks is provided in the fuel gas-side distribution part, and the supplied hydrogen gas is supplied to each of the fuel cell stacks by connecting them in parallel.

[0006] US 2010 / 0 065 359 A1 discloses a fuel cell vehicle in which a floor panel is constructed to have a center tunnel extending in a front-to-rear direction of the vehicle. A fuel cell system is at least partially arranged below the center tunnel and includes at least one fuel cell stack and a hydrogen gas supply unit constructed to supply hydrogen gas to the fuel cell stack. At least one of the front and rear ends of the center tunnel, which extends in the front-to-rear direction of the vehicle, is open to the outside of the center tunnel. The center tunnel is continuously inclined so that it has a greater height at a location closer to its at least one open end.

[0007] Furthermore, DE 11 2008 003 551 B4 discloses a fuel cell system installed in a movable body, the fuel cell system comprising: a two-part cell stack consisting of a first cell stack and a second cell stack, which form a cell stack pair and are each formed by stacking a plurality of unit cells, each of which has a fuel electrode and an oxidizing electrode; coolant inlets provided in an end portion on the lower side of the cell stack pair for introducing a coolant to be used for heat exchange with the unit cells into the first and second cell stacks;Coolant outlets provided in an upper end portion of the pair of cell stacks for discharging the coolant used for heat exchange with the unit cells from the first and second cell stacks to the outside, and reaction gas branch lines extending therethrough in a unit cell stacking direction for supplying and discharging a reaction gas used for a cell reaction in the fuel electrode and the oxidizing electrode, wherein: the first and second cell stacks are arranged symmetrically with respect to a plane perpendicular to a horizontal plane; and the first and second cell stacks are arranged such that unit cell stacking directions of the first and second cell stacks with respect to the horizontal plane are V-shaped or A-shaped when viewed from the side in the unit cell stacking direction. Summary of the invention

[0008] However, the water remaining in the fuel cell stack is not necessarily completely removed by the purging process. When two or more fuel cell stacks are used, such as in the fuel cell system described in JP 2005-276529 A, the capacity of the air pump used for the purging process may be insufficient for the volume of the flow channel in each fuel cell stack, and water may remain in the flow channel and freeze at a temperature below freezing.

[0009] In this case, when the fuel cell system is restarted, each fuel cell stack may not have sufficient power generation capacity until the freezing in the fuel cell stack disappears. Since each fuel cell stack generates power with low power generation capacity when the fuel cell system is restarted, wasteful power consumption occurs in various auxiliary devices used to generate power to the fuel cell stack, resulting in a decrease in efficiency.

[0010] Examples of auxiliary devices include an air compressor that supplies air to each fuel cell stack and an injector that injects hydrogen gas into the fuel cell stack. When the fuel cell stack starts power generation, for example, the rotational speed of a motor of the air compressor and the amount of hydrogen gas injected by the injector increase to be greater than those during a power generation stop, according to the electric power to be generated by the fuel cell stack, resulting in an increase in power consumption by the auxiliary devices.

[0011] However, when the inside of the fuel cell stack is frozen, the electric power generated by the fuel cell stack is not large enough to compensate for the increase in power consumption; therefore, wasteful power consumption increases.

[0012] This invention provides a fuel cell system that can reduce wasteful power consumption when restarting the system.

[0013] A fuel cell system according to one aspect of the invention includes a first fuel cell stack configured to generate power through a chemical reaction of reaction gas and having an exhaust manifold configured to exhaust the reaction gas, a second fuel cell stack configured to generate power through a chemical reaction of reaction gas and having an exhaust manifold configured to exhaust the reaction gas, a first auxiliary device used for power generation of the first fuel cell stack, a second auxiliary device used for power generation of the second fuel cell stack, and a control device configured to control an operation of the first auxiliary device and the second auxiliary device.The control device is configured to control the operation of the first auxiliary device and the second auxiliary device such that one of the first fuel cell stack and the second fuel cell stack, the discharge direction of which the reaction gas discharged from the discharge manifold forms a smaller angle with a vertically downward direction, starts generating power earlier than the other of the first fuel cell stack and the second fuel cell stack after the power generation of the first fuel cell stack and the second fuel cell stack is stopped.

[0014] In the fuel cell system described above, the control device may be configured to control the operation of the first auxiliary device and the second auxiliary device such that one fuel cell stack starts generating power earlier than the other fuel cell stack when an outside air temperature is lower than a first threshold.

[0015] In the fuel cell system described above, the control device may be configured to control the operation of the first auxiliary device and the second auxiliary device such that the other fuel cell stack starts generating power when a temperature of the other fuel cell stack becomes higher than a second threshold after the one fuel cell stack starts generating power.

[0016] In the fuel cell system described above, the discharge direction of one fuel cell stack may substantially coincide with the vertically downward direction.

[0017] In the fuel cell system described above, the first fuel cell stack may include a plurality of unit cells, and the second fuel cell stack may include a plurality of unit cells. The number of unit cells of one fuel cell stack may be smaller than the number of unit cells of the other fuel cell stack.

[0018] In the fuel cell system described above, the first auxiliary device may be configured to supply purge gas to the exhaust manifold of the first fuel cell stack to purge the exhaust manifold after the power generation of the first fuel cell stack is stopped, and the second auxiliary device may be configured to supply purge gas to the exhaust manifold of the second fuel cell stack to purge the exhaust manifold after the power generation of the second fuel cell stack is stopped.One auxiliary device of the first auxiliary device and the second auxiliary device that purges the exhaust manifold of the one fuel cell stack may supply the purge gas for a longer time than the other auxiliary device of the first auxiliary device and the second auxiliary device that purges the exhaust manifold of the other fuel cell stack, at substantially the same flow rate as the other auxiliary device.

[0019] In the fuel cell system described above, the first auxiliary device may be configured to supply purge gas to the exhaust manifold of the first fuel cell stack to purge the exhaust manifold after the power generation of the first fuel cell stack is stopped, and the second auxiliary device may be configured to supply purge gas to the exhaust manifold of the second fuel cell stack to purge the exhaust manifold after the power generation of the second fuel cell stack is stopped. One of the first auxiliary device and the second auxiliary device that purges the exhaust manifold of one fuel cell stack may supply the purge gas at a higher flow rate within a predetermined time than the other of the first auxiliary device and the second auxiliary device that purges the exhaust manifold of the other fuel cell stack.

[0020] In the fuel cell system described above, the first auxiliary device may be configured to supply purge gas to the exhaust manifold of the first fuel cell stack to purge the exhaust manifold after the power generation of the first fuel cell stack is stopped, and the second auxiliary device may be configured to supply purge gas to the exhaust manifold of the second fuel cell stack to purge the exhaust manifold after the power generation of the second fuel cell stack is stopped. One of the first auxiliary device and the second auxiliary device that purges the exhaust manifold of one fuel cell stack supplies the purge gas for a longer time than the other of the first auxiliary device and the second auxiliary device that purges the exhaust manifold of the other fuel cell stack, and at a higher flow rate than the other auxiliary device.

[0021] The fuel cell system according to the above aspect of the invention further includes a first detector configured to detect an inclination of the discharge direction of the first fuel cell stack or the second fuel cell stack relative to the vertically downward direction. The control device is further configured to determine which of the first fuel cell stack and the second fuel cell stack has the discharge direction that forms a smaller angle with the vertically downward direction based on the inclination detected by the first detector.

[0022] According to another aspect of the invention, the fuel cell system further comprises a second detector configured to detect an inclination of a vehicle on which the fuel cell system is installed. According to another aspect of the invention, the control device is configured to determine which of the first fuel cell stack and the second fuel cell stack has the discharge direction that forms a smaller angle with the vertically downward direction, based on the inclination detected by the second detector.

[0023] In the above-described fuel cell system according to the further aspect of the invention, the first fuel cell stack and the second fuel cell stack may be installed on a vehicle body of the vehicle such that an angle of the discharge direction of the first fuel cell stack relative to the vehicle body is substantially equal to that of the second fuel cell stack.

[0024] In the above-described fuel cell system according to the further aspect of the invention, the first fuel cell stack and the second fuel cell stack may be installed on a vehicle body of the vehicle such that an angle of the discharge direction of the first fuel cell stack relative to the vehicle body is different from that of the second fuel cell stack.

[0025] In a fuel cell system according to an illustrative aspect of the present disclosure, an angle of the discharge direction of one fuel cell stack relative to the vertically downward direction may be greater than 0 degrees and equal to or less than 180 degrees, while an angle of the discharge direction of the other fuel cell stack relative to the vertically downward direction may be greater than 0 degrees and equal to or less than 180 degrees.

[0026] According to the invention, wasteful power consumption can be reduced when the fuel cell system is restarted. Short description of the figures

[0027] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which like reference numerals designate like elements, and wherein: Fig. 1 is a configuration diagram showing an example of a fuel cell system; Fig. 2 is a flowchart illustrating an example of processing of an electronic control unit (ECU) when power generation of fuel cell stacks is stopped; Fig. 3 is a view showing a first arrangement example of fuel cell stacks; Fig. 4 is a view showing a second arrangement example of fuel cell stacks; Fig. 5 is a flowchart illustrating an example of a restart process of the fuel cell system; Fig. 6 is a view showing an arrangement example of fuel cell stacks having a different number of unit cells; Fig. 7 is a flowchart illustrating an example of a restart process of the fuel cell system; Fig. 8 is a view showing an example of the arrangement of fuel cell stacks when a vehicle body of a fuel cell vehicle on which the fuel cell system is installed is inclined from a horizontal direction; Fig. 9 is a view showing another example of the arrangement of fuel cell stacks when the vehicle body of the fuel cell vehicle on which the fuel cell system is installed is inclined from the horizontal direction; Fig. 10 is a flowchart illustrating an example of a restart process of the fuel cell system based on the inclination of the vehicle body detected by an inclination sensor; Fig. 11 is a view showing another example of the arrangement of fuel cell stacks when the vehicle body of the fuel cell vehicle on which the fuel cell system is installed is inclined from the horizontal direction; Fig. 12 is a flowchart illustrating an example of a restart process of the fuel cell system based on an angle of a discharge direction detected by a tilt sensor; and Fig. 13 is a view showing an example of the arrangement of three fuel cell stacks. Detailed description of embodimentsConfiguration example of a fuel cell system

[0028] Fig. 1 is a configuration diagram showing an example of a fuel cell system. The fuel cell system 9 is installed on a fuel cell vehicle, for example, and includes a first power generation system 9a, a second power generation system 9b, an electronic control unit (ECU) 1, an outside air temperature sensor 90, an inverter (INV) 43, a motor 44, and switches 45a, 45b. The fuel cell vehicle corresponds to an example of a vehicle.

[0029] The first power generation system 9a includes a fuel cell stack 10a, a cathode supply passage 20a, a cathode discharge passage 21a, a bypass passage 22a, an air compressor 30a, an intercooler 31a, a three-way valve 32a, a backpressure valve 33a, a humidifier 34a, an anode supply passage 25a, an anode discharge passage 23a, a tank 35a, and an injector 36a. The first power generation system 9a further includes a DC (direct current)-DC converter (FDC) 40a for the fuel cell stack 10a, a battery 42a, a DC-DC converter (BDC) 41a for the battery 42a, a coolant circulation passage 24a, and a temperature sensor 91a.

[0030] The second power generation system 9b includes a fuel cell stack 10b, a cathode supply passage 20b, a cathode discharge passage 21b, a bypass passage 22b, an air compressor 30b, an intercooler 31b, a three-way valve 32b, a backpressure valve 33b, a humidifier 34b, an anode supply passage 25b, an anode discharge passage 23b, a tank 35b, and an injector 36b. The second power generation system 9b further includes a DC-DC converter (FDC) 40b for the fuel cell stack 10b, a battery 42b, a DC-DC converter (BDC) 41b for the battery 42b, a coolant circulation passage 24b, and a temperature sensor 91b.

[0031] The cathode supply channel 20a, 20b corresponds to a conduit through which oxidizing gas flows to be supplied to the fuel cell stack 10a, 10b, and the cathode discharge channel 21a, 21b corresponds to a pipe through which oxidizing gas flows to be discharged from the fuel cell stack 10a, 10b. An example of the oxidizing gas is air.

[0032] The bypass channel 22a, 22b is connected at one end to the cathode supply channel 20a, 20b via the three-way valve 32a, 32b, and at the other end to the cathode discharge channel 21a, 21b. With this arrangement, a portion of the oxidizing gas flows from the cathode supply channel 20a, 20b via the bypass channel 22a, 22b to the cathode discharge channel 21a, 21b according to the opening of the three-way valve 32a, 32b on the bypass channel 22a, 22b side.

[0033] The anode supply channel 25a, 25b corresponds to a conduit through which the fuel gas to be supplied to the fuel cell stack 10a, 10b flows, and the anode discharge channel 23a, 23b corresponds to a conduit through which the fuel gas discharged from the fuel cell stack 10a, 10b flows. An example of the fuel gas is hydrogen gas.

[0034] The fuel cell stack 10a, 10b is a laminated body formed by laminating or stacking a plurality of polymer electrolyte unit cells. Each of the unit cells has a membrane electrode assembly (MEA) comprising a pair of electrodes with a platinum catalyst and an electrolyte membrane. It generates electrical power through an electrochemical reaction between oxygen in the oxidizing gas and hydrogen in the fuel gas in the membrane electrode assembly. The fuel cell generates both water and electrical power. The oxidizing gas and the fuel gas are examples of reaction gases.

[0035] The oxidizing gas is supplied from the cathode supply channel 20a, 20b to the fuel cell stack 10a, 10b used for power generation and is discharged from the fuel cell stack 10a, 10b into the cathode discharge channel 21a, 21b. The cathode supply channel 20a is connected to an oxidizing gas supply manifold 100a provided in the fuel cell stack 10a, and the cathode supply channel 20b is connected to an oxidizing gas supply manifold 100b provided in the fuel cell stack 10b. Each of the oxidizing gas supply manifolds 100a, 100b corresponds to a hole through which the oxidizing gas is supplied to each unit cell.

[0036] The cathode exhaust channel 21a is connected to an oxidizing gas exhaust manifold 101a provided in the fuel cell stack 10a, and the cathode exhaust channel 21b is connected to an oxidizing gas exhaust manifold 101b provided in the fuel cell stack 10b. Each of the oxidizing gas exhaust manifolds 101a, 101b corresponds to a hole through which the oxidizing gas is discharged from each unit cell.

[0037] The air compressor 30a, 30b, the intercooler 31a, 31b, the three-way valve 32a, 32b and the humidifier 34a, 34b, which are arranged in this order in a direction from the upstream side to the downstream side, are connected to the cathode supply channel 20a, 20b.

[0038] The air compressors 30a, 30b correspond to examples of the first auxiliary device and the second auxiliary device used to generate power for the fuel cell stacks 10a, 10b. Each of the air compressors 30a, 30b supplies oxidizing gas to the corresponding fuel cell stack 10a, 10b via the cathode supply channel 20a, 20b. The air compressor 30a, 30b is arranged in the cathode supply channel 20a, 20b upstream of the three-way valve 32a, 32b and the intercooler 31a, 31b.

[0039] The air compressor 30a, 30b takes in oxidizing gas from the outside and compresses it. The compressed oxidizing gas is fed to the intercooler 31a, 31b.

[0040] The ECU 1 controls the rotation of a motor (not shown) for driving the air compressor 30a, 30b. When power is generated by the fuel cell stack 10a, 10b, electricity from the fuel cell stack 10a, 10b or the battery 42a, 42b is supplied to each motor of the air compressor 30a, 30b. When the fuel cell stack 10a, 10b stops generating power, electricity from the battery 42a, 42b is supplied to the motor of the air compressor 30a, 30b.

[0041] The intercooler 31a, 31b cools the oxidizing gas, whose temperature has been increased by compression. The thus cooled oxidizing gas is fed to the three-way valve 32a, 32b.

[0042] A portion of the oxidizing gas flows from the three-way valve 32a, 32b to the bypass channel 22a, 22b and is discharged from the cathode discharge channel 21a, 21b. The remaining portion of the oxidizing gas flows to the humidifier 34a, 34b through the cathode supply channel 20a, 20b. The humidifier 34a, 34b humidifies the oxidizing gas in the cathode supply channel 20a, 20b using water contained in the oxidizing gas flowing in the cathode discharge channel 21a, 21b.

[0043] The humidifier 34a, 34b allows at least a portion of the oxidizing gas flowing in the cathode discharge channel 21a, 21b, with a relatively high humidity, to pass through a membrane 340a, 340b, formed, for example, from hollow fibers, to one side of the membrane 340a, 340b. Furthermore, the humidifier 34a, 34b allows at least a portion of the oxidizing gas flowing in the cathode supply channel 20a, 20b, with a relatively low humidity, to pass through the membrane 340a, 340b to the other side. In this way, the humidifier 34a, 34b humidifies the oxidizing gas by causing water or moisture to permeate the membrane 340a, 340b. However, the humidification method is not limited to this; other humidification methods may be used.

[0044] The humidifier 34a, 34b and the backpressure valve 33a, 33b are connected to the cathode discharge channel 21a, 21b. The humidifier 34a, 34b extracts water from the oxidizing gas flowing in the cathode discharge channel 21a, 21b for use in humidifying the oxidizing gas in the cathode supply channel 20a, 20b. The backpressure valve 33a, 33b adjusts the backpressure of the oxidizing gas.

[0045] The anode supply channel 25a is connected to the fuel gas supply manifold 102a provided in the fuel cell stack 10a, and the anode supply channel 25b is connected to the fuel gas supply manifold 102b provided in the fuel cell stack 10b. Each of the fuel gas supply manifolds 102a, 102b corresponds to a hole through which fuel gas is supplied to each unit cell.

[0046] The tank 35a, 35b and the injector 36a, 36b, arranged in a direction from the upstream side to the downstream side, are connected to the anode supply channel 25a, 25b. The tank 35a, 35b stores the fuel gas under pressure. The fuel gas in the tank 35a, 35b flows into the injector 36a, 36b.

[0047] The injectors 36a, 36b correspond to examples of the first auxiliary device and the second auxiliary device used for power generation of the fuel cell stacks 10a, 10b, respectively. Each of the injectors 36a, 36b injects the fuel gas supplied to the corresponding fuel cell stack 10a, 10b. The ECU 1 controls, for example, the amount (referred to as the "injection amount") of fuel gas injected by the injector 36a, 36b.

[0048] When power is generated by the fuel cell stack 10a, 10b, current is supplied from the fuel cell stack 10a, 10b or the battery 42a, 42b to the injector 36a, 36b. When the fuel cell stack 10a, 10b stops generating power, current is supplied from the battery 42a, 42b to the injector 36a, 36b. A pressure control valve (not shown) is provided between each injector 36a, 36b and the corresponding tank 35a, 35b.

[0049] The anode exhaust channel 23a is connected to the fuel gas exhaust manifold 103a provided in the fuel cell stack 10a, and the anode exhaust channel 23b is connected to the fuel gas exhaust manifold 103b provided in the fuel cell stack 10b. Each of the fuel gas exhaust manifolds 103a, 103b corresponds to a hole through which the fuel gas is discharged from each unit cell.

[0050] While the fuel cell stack 10a, 10b generates heat during power generation, it is cooled by coolant flowing through the coolant circulation channel 24a, 24b, thus limiting a temperature rise in the fuel cell stack 10a, 10b. Although not shown in the figures, a cooler for cooling the coolant heated in the fuel cell stack 10a, 10b and a pump for circulating the coolant through the coolant circulation channel 24a, 24b are provided in the coolant circulation channel 24a, 24b. Furthermore, a temperature sensor 91a, 91b is provided in the coolant circulation channel 24a, 24b to detect the temperature of the coolant.

[0051] The DC-DC converter 40a, 40b includes a switching device, such as a transistor, and boosts the output voltage of the fuel cell stack 10a, 10b through switching control of the switching device. The boosting operation of the DC-DC converter 40a, 40b is controlled by the ECU 1. The inverter 43 includes a transformer, transistors, etc., and converts the output current of the fuel cell stack 10a, 10b from direct current to alternating current. The motor 44 for driving wheels (not shown) of the fuel cell vehicle is connected to the inverter 43. The motor 44 rotates with the alternating current.

[0052] The inverter 43 is connected to the DC-DC converters 40a, 40b, 41a, 41b via switches 45a, 45b. The ON / OFF of the switches 45a, 45b is controlled by the ECU 1. Thus, the switch 45a electrically connects or disconnects the fuel cell stack 10a and the battery 42a to or from the inverter 43, and the switch 45b electrically connects or disconnects the fuel cell stack 10b and the battery 42b to or from the inverter 43.

[0053] While the DC-DC converters 40a, 40b, 41a, 41b and the switches 45a, 45b are each provided independently in the arrangement of this embodiment, the arrangement is not limited thereto. For example, only the DC-DC converters 40a, 40b, 41a, 41b may be provided, and the fuel cell stacks 10a, 10b and the batteries 42a, 42b may be electrically connected to or disconnected from the inverter 43 using switching devices incorporated in the DC-DC converters 40a, 40b, 41a, 41b.

[0054] The battery 42a, 42b stores excess electrical power from the fuel cell stack 10a, 10b. The DC-DC converter 41a, 41b includes a switching device, such as a transistor, and increases the output voltage of the battery 42a, 42b by switching the switching device. The power from the battery 42a, 42b is supplied to the motor 44, for example, via the inverter 43.

[0055] The ECU 1 corresponds to an example of the control device and controls the operation of the fuel cell system 9. The ECU 1 has, for example, a central processing unit (CPU) and a memory that stores programs for driving the CPU and various types of data.

[0056] The ECU 1 controls the switch 45a to the ON state when it causes the fuel cell stack 10a to start power generation, and controls the switch 45a to the OFF state when it causes the fuel cell stack 10a to stop power generation. Furthermore, the ECU 1 controls the switch 45b to the ON state when it causes the fuel cell stack 10b to start power generation, and controls the switch 45b to the OFF state when it causes the fuel cell stack 10b to stop power generation.

[0057] When each of the switches 45a, 45b is placed in the ON state, the corresponding fuel cell stack 10a, 10b is electrically connected to the inverter 43; when sufficient amounts of fuel gas and oxidant gas for the electric power to be generated by the fuel cell stack 10a, 10b (referred to as "required power") are supplied to the fuel cell stack 10a, 10b, the chemical reaction between the fuel gas and the oxidant gas begins, and the fuel cell stack 10a, 10b starts power generation. When each of the switches 45a, 45b is placed in the OFF state, the corresponding fuel cell stack 10a, 10b is electrically disconnected from the inverter 43; consequently, the chemical reaction between the fuel gas and the oxidant gas stops, and the fuel cell stack 10a, 10b stops power generation.The required power is determined, for example, based on the pedal stroke or the amount of operation of an accelerator pedal of the fuel cell vehicle.

[0058] The ECU 1 receives the coolant temperatures from the temperature sensors 91a, 91b to monitor the temperatures of the fuel cell stacks 10a, 10b. Furthermore, the ECU 1 receives the outside air temperature from the outside air temperature sensor 90 to monitor the outside air temperature.

[0059] The ECU 1 controls the rotation of the motors for driving the air compressors 30a, 30b. When the ECU 1 causes the fuel cell stack 10a to start power generation, it increases the motor speed of the air compressor 30a from a predetermined speed to a speed corresponding to the required power of the fuel cell stack 10a. As a result, the electric power consumed by the air compressor 30a increases to be greater than that during the power generation stop, and a sufficient amount of oxidizing gas for the required power is supplied to the fuel cell stack 10a.Here, the predetermined rotation speed may be zero or a rotation speed sufficient to maintain a condition where a desired pressure is applied to an oxidizing gas channel including the oxidizing gas supply manifold 100a and the oxidizing gas exhaust manifold 101a during the power generation stop of the fuel cell stack 10a. This rotation speed is lower than the rotation speed during power generation.

[0060] On the other hand, when the ECU 1 causes the fuel cell stack 10b to start power generation, it increases the rotational speed of the air compressor 30b from a predetermined speed to a speed corresponding to the required power of the fuel cell stack 10b. As a result, the electric power consumed by the air compressor 30b increases to be greater than that during the power generation stop, and a sufficient amount of oxidizing gas for the required power is supplied to the fuel cell stack 10b. When the ECU 1 causes the fuel cell stacks 10a, 10b to stop power generation, it also reduces the motor speeds of the air compressors 30a, 30b to the predetermined speed.

[0061] After the fuel cell stack 10a, 10b stops power generation, the air compressor 30a, 30b purges the cathode supply channel 20a, 20b, the cathode discharge channel 21a, 21b, the oxidizing gas supply manifold 100a, 100b, and the oxidizing gas discharge manifold 101a, 101b according to a control signal from the ECU 1. Consequently, the water remaining in the cathode supply channel 20a, 20b, the cathode discharge channel 21a, 21b, the oxidizing gas supply manifold 100a, 100b, and the oxidizing gas discharge manifold 101a, 101b is discharged.

[0062] When the ECU 1 causes the fuel cell stack 10a to start power generation, it increases the injection amount of the injector 36a from a predetermined amount to an amount corresponding to the required power of the fuel cell stack 10a. As a result, the power consumption of the injector 36a increases to be greater than that during the power generation stop, and a sufficient amount of fuel gas for the required power is supplied to the fuel cell stack 10a. Here, the predetermined amount may be zero or may correspond to an injection amount sufficient to maintain a condition in which a desired pressure is applied to a fuel gas passage including the fuel gas supply manifold 102a and the fuel gas discharge manifold 103a during the power generation stop of the fuel cell stack 10a.This injection quantity is smaller than the injection quantity during power generation.

[0063] On the other hand, when the ECU 1 causes the fuel cell stack 10b to start power generation, it increases the injection amount of the injector 36b from a predetermined amount to an amount corresponding to the required power of the fuel cell stack 10b. As a result, the power consumption of the injector 36b increases to be greater than that during the stop of power generation, and a sufficient amount of fuel gas for the required power is supplied to the fuel cell stack 10b. When the ECU 1 causes the fuel cell stacks 10a, 10b to stop power generation, it also reduces the injection amounts of the injectors 36a, 36b to the predetermined amount.

[0064] Next, the processing of ECU 1 is described. Operation of the fuel cell stack 10a, 10b after stopping power generation

[0065] Fig. 2 is a flowchart illustrating an example of processing of the ECU 1 at the time when power generation of the fuel cell stack 10a, 10b is stopped. It is assumed that the fuel cell stack 10a, 10b is generating electric power before this processing is started.

[0066] The ECU 1 determines whether there is a request to stop power generation of the fuel cell stacks 10a, 10b (step St1). If the ECU 1 receives a signal indicating, for example, that an ignition switch (not shown) is being turned off, it determines that it has received the request to stop power generation. If there is no request to stop power generation (NO in step St1), the ECU 1 executes step St1 again.

[0067] If there is a request to stop power generation (YES in step St1), the ECU 1 performs an operation to stop power generation of the fuel cell stacks 10a, 10b (step St2). At this time, the ECU 1 controls the switches 45a, 45b of the fuel cell stacks 10a, 10b to the OFF state.

[0068] Then, the ECU 1 causes the air compressors 30a, 30b to perform a purge operation (step St3). The air compressors 30a, 30b perform the purge operation by supplying air (oxidizing gas) under the purge conditions set by the ECU 1.

[0069] Then, the ECU 1 reduces the engine speeds of the air compressors 30a, 30b from the speed corresponding to the required power to the predetermined speed, and reduces the injection amounts of the injectors 36a, 36b from the injection amount corresponding to the required power to the predetermined amount (step St4). The predetermined speed and the predetermined amount may be zero. However, if it is predicted that power generation will resume shortly after the power generation is stopped, the predetermined speed and the predetermined amount may be set to low values ​​to maintain the oxidizing gas passage pressure and the fuel gas pressure in the fuel cell stacks 10a, 10b at appropriate values.

[0070] Through the above purging process, the water remaining in the cathode supply channels 20a, 20b, the cathode discharge channels 21a, 21b, the oxidizing gas supply manifolds 100a, 100b, and the oxidizing gas discharge manifolds 101a, 101b is removed. The anode supply channels 25a, 25b, the anode discharge channels 23a, 23b, the fuel gas supply manifolds 102a, 102b, and the fuel gas discharge manifolds 103a, 103b are purged in the same manner as described above using the injectors 36a, 36b or pumps (not shown).

[0071] However, the purging process does not necessarily completely remove water from the fuel cell stacks 10a, 10b. Thus, for example, water remaining in the fuel cell stacks 10a, 10b may freeze at a temperature below freezing. In this case, each fuel cell stack 10a, 10b may not exhibit favorable power generation capability until the freezing in the fuel cell stack 10a, 10b disappears when the fuel cell system 9 is restarted.

[0072] Accordingly, even when the fuel cell system 9 is restarted, each fuel cell stack 10a, 10b may generate electrical power with a low power generation capability, and wasteful power consumption may occur in various auxiliary devices around the fuel cell stack 10a, 10b, resulting in a reduction in efficiency. These auxiliary devices include, for example, the air compressors 30a, 30b and the injectors 36a, 36b.

[0073] Given the above situation, the ECU 1 provides a difference between the power generation start timing of the fuel cell stack 10a and that of the fuel cell stack 10b. Specifically, the ECU 1 controls the air compressors 30a, 30b and the injectors 36a, 36b so that one of the fuel cell stacks 10a, 10b, which has a lower water freezing degree, starts power generation earlier than the other fuel cell stack. As a result, only the aforementioned fuel cell stack of the fuel cell stacks 10a, 10b, which has the higher power generation capability, initially generates electric power, so that wasteful power consumption can be reduced.

[0074] The ECU 1 selects the fuel cell stack 10a, 10b that starts power generation earlier based on the angle of the discharge direction of the oxidizing gas discharged from the oxidizing gas discharge manifold 101a, 101b of each fuel cell stack 10a, 10b. Some examples of the arrangement of the fuel cell stacks 10a, 10b are described below. First arrangement example of the fuel cell stacks 10a, 10b

[0075] Fig. 3 shows a first arrangement example of the fuel cell stacks 10a, 10b. Fig. Figure 3 shows the fuel cell stacks 10a, 10b of the fuel cell system 9 installed on the fuel cell vehicle viewed in the horizontal direction. Fig. 3 an arrow labeled “Dg” indicates a direction vertically downwards.

[0076] First, the structure of the fuel cell stacks 10a, 10b is described. The fuel cell stacks 10a, 10b have the same size and structure.

[0077] The fuel cell stack 10a includes a pair of end plates 111a, 112a and a plurality of unit cells 110a. The end plates 111a, 112a are fixed to each other in a state where the unit cells 110a are sandwiched therebetween to compress the unit cells 110a in the stacking direction.

[0078] The oxidizing gas supply manifold 100a and the oxidizing gas discharge manifold 101a are provided in one of the end plates 112a and the unit cells 110a, so that the manifolds 100a, 101a extend in the stacking direction through the end plate 112a and the unit cells 110a. While the oxidizing gas supply manifold 100a and the oxidizing gas discharge manifold 101a in the example of Fig. 3 are provided parallel to each other, the arrangement of the distributors 100a, 101a is not limited thereto, but the distributors 100a, 101a may not be arranged parallel to each other.

[0079] The oxidizing gas flows from the cathode supply channel 20a along a supply direction Da_in into the oxidizing gas supply manifold 100a and flows through a channel in each unit cell 110a along a flow direction Da_tr into the oxidizing gas exhaust manifold 101a. At this time, the water generated by power generation in each unit cell 110a flows into the oxidizing gas exhaust manifold 101a together with the oxidizing gas.

[0080] The oxidizing gas flows from the oxidizing gas discharge manifold 101a along a discharge direction Da_out into the cathode discharge channel 21a.

[0081] Furthermore, the fuel cell stack 10b includes a pair of end plates 111b, 112b and a plurality of unit cells 110b. The end plates 111b, 112b are fixed to each other in a state where the unit cells 110b are sandwiched between them to compress the unit cells 110b in the stacking direction. The number of plates of the unit cells 110b is equal to that of the unit cells 110a of the other fuel cell stack 10a.

[0082] The oxidizing gas supply manifold 100b and the oxidizing gas discharge manifold 101b are provided in one of the end plates 112b and the unit cells 110b, so that the manifolds 100b, 101b extend through the end plate 112b and the unit cells 110b in the stacking direction. While the oxidizing gas supply manifold 100b and the oxidizing gas discharge manifold 101b in the example of Fig. 3 are provided parallel to each other, the arrangement of the distributors 100b, 101b is not limited thereto, but the distributors 100b, 101b may not be arranged parallel to each other.

[0083] The oxidizing gas flows from the cathode supply channel 20b along a supply direction Db_in into the oxidizing gas supply manifold 100b and flows through a channel in each unit cell 110b along a flow direction Db_tr into the oxidizing gas exhaust manifold 101b. At this time, the water generated by power generation in each unit cell 110b flows into the oxidizing gas exhaust manifold 101b together with the oxidizing gas.

[0084] The oxidizing gas flows from the oxidizing gas discharge manifold 101b along a discharge direction Db_out into the cathode discharge channel 21b.

[0085] The discharge direction Da_out of the oxidizing gas discharge manifold 101a of the fuel cell stack 10a forms an angle θa (0 degrees < θa ≤ 180 degrees) with the vertically downward direction Dg, and the discharge direction Db_out of the oxidizing gas discharge manifold 101b of the fuel cell stack 10b forms an angle θb (0 degrees < θb ≤ 180 degrees) with the vertically downward direction Dg. Here, the angle θa of the discharge direction Da_out is smaller than the angle θb of the discharge direction Db_out. That is, the discharge direction Da_out of the fuel cell stack 10a forms a smaller angle with the vertically downward direction Dg than the discharge direction Db_out of the fuel cell stack 10b.

[0086] Accordingly, the inclination of the oxidizing gas discharge manifold 101a is greater than that of the oxidizing gas discharge manifold 101b; therefore, the probability of water being discharged in the oxidizing gas discharge manifold 101a is higher than that in the oxidizing gas discharge manifold 101b. If the fuel cell stacks 10a, 10b are left as they are in a sub-freezing environment, for example, after the fuel cell stacks 10a, 10b stop power generation, and water in the oxidizing gas discharge manifolds 101a, 101b freezes to block the passage of the oxidizing gas, the degree of reduction in the power generation capability of one fuel cell stack 10a due to the blockage is smaller than that of the other fuel cell stack 10b.Accordingly, when the fuel cell system 9 is restarted below the freezing point, the power generation capability of the above-mentioned one fuel cell stack 10a is higher than that of the other fuel cell stack 10b.

[0087] When the fuel cell system 9 starts at normal temperatures (e.g., at 25 degrees Celsius), the power generation capacity of the fuel cell stack 10a is less likely or unlikely to be reduced by flooding compared to that of the other fuel cell stack 10b, because the amount of water in the oxidizing gas discharge manifold 101a of the fuel cell stack 10a is smaller than that in the oxidizing gas discharge manifold 101b of the other fuel cell stack 10b. Therefore, the power generation capacity of the fuel cell stack 10a is higher than that of the other fuel cell stack 10b.

[0088] Thus, the ECU 1 controls the air compressor 30a and the injector 36a so that the fuel cell stack 10a with the higher power generation capability starts power generation earlier than the other fuel cell stack 10b. At this time, for example, the ECU 1 first increases the motor speed of the air compressor 30a from a predetermined speed to a speed corresponding to the required power of the fuel cell stack 10a, and increases the injection amount of the injector 36a from a predetermined amount to an injection amount corresponding to the required power of the fuel cell stack 10a. Then, the ECU 1 puts the switch 45a of the fuel cell stack 10a into the ON state, so that the fuel cell stack 10a starts power generation.

[0089] Since the fuel cell stack 10b with the lower power generation capability starts power generation later than the fuel cell stack 10a with the higher power generation capability, the engine speed of the air compressor 30b and the injection amount of the injector 36b during the power generation stop are maintained at lower values ​​than those after the start of power generation, or at zero. Consequently, the wasteful power consumption of the air compressor 30b and the injector 36b is reduced.

[0090] When one of the fuel cell stacks 10a starts power generation, the temperature of the other fuel cell stack 10b is increased, for example, in the case where the fuel cell stacks 10a, 10b are arranged close to each other, by radiant heat generated, for example, by the power generation of the fuel cell stack 10a, or because the fuel cell stack 10b is heated by a backflow of a cooler.

[0091] Thus, the ECU 1 controls the air compressor 30b and the injector 36b so that the fuel cell stack 10b starts power generation when the temperature of the other fuel cell stack 10b is raised to a temperature level sufficient to eliminate freezing after one fuel cell stack 10a starts power generation. For example, when the temperature of the coolant of the fuel cell stack 10b reaches a predetermined temperature, the ECU 1 first increases the motor speed of the air compressor 30b from a predetermined speed to a speed corresponding to the required power of the fuel cell stack 10b, and increases the injection amount of the injector 36b from a predetermined amount to an injection amount corresponding to the required power of the fuel cell stack 10b.Then, the ECU 1 sets the switch 45b of the fuel cell stack 10b to the ON state, so that the fuel cell stack 10b starts power generation.

[0092] Since the fuel cell stack 10b can start power generation when its power generation capability becomes higher than that at the time when the fuel cell stack 10a starts power generation, the wasteful power consumption of the air compressor 30b and the injector 36b is reduced. Second arrangement example of the fuel cell stacks 10a, 10b

[0093] Fig. 4 shows a second arrangement example of the fuel cell stacks 10a, 10b. In Fig. 4 are the same components or directions as in Fig. 3 are assigned the same reference numerals or symbols, and these components or directions will not be described further.

[0094] In the example of Fig. 4, the discharge direction Da_out of the oxidizing gas discharge manifold 101a of the fuel cell stack 10a coincides with the vertically downward direction Dg. Therefore, the amount of water in the oxidizing gas discharge manifold 101a is smaller than that of the water in the oxidizing gas discharge manifold 101a of the first arrangement example. Accordingly, the power generation capability of the fuel cell stack 10a at the start of power generation is higher than that in the case of the first arrangement example.

[0095] Furthermore, the discharge direction Db_out of the oxidizing gas discharge manifold 101b of the other fuel cell stack 10b, as an example, coincides with the horizontal direction. That is, the discharge direction Db_out of the oxidizing gas discharge manifold 101b forms a right angle with the vertically downward direction Dg. Thus, the discharge direction Da_out of the oxidizing gas discharge manifold 101a forms a smaller angle with the vertically downward direction Dg than the discharge direction Db_out of the oxidizing gas discharge manifold 101b.

[0096] Accordingly, the ECU 1 causes the fuel cell stack 10a, whose discharge direction Da_out coincides with the vertically downward direction, to start power generation earlier than the fuel cell stack 10b. Since the power generation capability of the fuel cell stack 10a at the start of power generation is higher than that in the case of the first arrangement example, the wasteful power consumption of the air compressor 30b and the injector 36b is more effectively reduced. Fuel cell system restart process 9

[0097] Fig. 5 is a flowchart illustrating an example of a restart process of the fuel cell system 9. Before starting this process, the fuel cell stacks 10a, 10b stop power generation according to the Fig. 2. The arrangement of the fuel cell stacks 10a, 10b corresponds to that of the first arrangement example or the second arrangement example.

[0098] The ECU 1 determines whether there is a request to start power generation of the fuel cell stacks 10a, 10b (step St11). For example, if the ECU 1 receives a signal indicating that the ignition switch (not shown) is being turned on, it determines that it has received the request to start power generation. If there is no request to start power generation (NO in step St11), the ECU 1 executes step St11 again.

[0099] If there is a request to start power generation (YES in step St11), the ECU 1 performs an operation to start power generation of the fuel cell stack 10a (step St12). At this time, the ECU 1 increases the engine speed of the air compressor 30a and the injection amount of the injector 36a from predetermined values, respectively, and sets the switch 45a of the fuel cell stack 10a to the ON state. At this time, the ECU 1 maintains the engine speed of the air compressor 30b and the injection amount of the injector 36b at predetermined values, respectively, so that the power generation of the other fuel cell stack 10b remains stopped, and maintains the switch 45b of the fuel cell stack 10b in the OFF state.

[0100] Then, to determine whether the fuel cell stack 10b that has not been generating power can start power generation, the ECU 1 obtains the temperature Tb of its coolant from the temperature sensor 91b (step St13) and compares the temperature Tb with a predetermined temperature To (step St14). In this context, the temperature To corresponds to an example of the second threshold and is set in advance, for example, to a temperature level sufficient to eliminate the freezing of water in the oxidizing gas discharge manifold 101b of the fuel cell stack 10b. Since the coolant discharged from the fuel cell stack 10b absorbs the heat of the fuel cell stack 10b heated by the other power-generating fuel cell stack 10a, the temperature Tb of the coolant can be regarded as the temperature of the fuel cell stack 10b.

[0101] When the temperature Tb is equal to or lower than the temperature To (Tb≤To) (NO in step St14), the ECU 1 determines that water in the oxidizing gas discharge manifold 101b remains frozen and executes step St13 again. When the temperature Tb is higher than the temperature To (Tb>To) (YES in step St14), the ECU 1 determines that there is no freezing of water in the oxidizing gas discharge manifold 101b and performs the operation to start power generation of the fuel cell stack 10b (step St15). At this time, the ECU 1 increases the engine speed of the air compressor 30b and the injection amount of the injector 36b by predetermined values, respectively, and sets the switch 45b of the fuel cell stack 10b to the ON state. In this way, the restart process of the fuel cell system 9 is executed.

[0102] Therefore, after each fuel cell stack 10a, 10b stops power generation, the ECU 1 controls the operation of the air compressors 30a, 30b and the injectors 36a, 36b so that the fuel cell stack 10a, whose discharge direction Da_out of the oxidizing gas discharged from the oxidizing gas discharge manifold 101a forms a smaller angle with the vertically downward direction Dg than one of the fuel cell stacks 10a, 10b, starts power generation earlier than the other fuel cell stack 10b.

[0103] Therefore, among the fuel cell stacks 10a, 10b, the fuel cell stack 10a with a smaller amount of water in the oxidizing gas discharge manifold 101a and a higher power generation capability starts power generation earlier, while the fuel cell stack 10b with a larger amount of water in the oxidizing gas discharge manifold 101b and a lower power generation capability starts power generation with a delay. Accordingly, while the fuel cell stack 10b stops power generation, the wasteful power consumption of the air compressor 30b and the injector 36b is reduced.

[0104] When the temperature Tb of the other fuel cell stack 10b becomes higher than the predetermined temperature To after the fuel cell stack 10a with the higher power generation capability starts power generation, the ECU 1 controls the operation of the air compressor 30b and the injector 36b so that the fuel cell stack 10b starts power generation. Therefore, since the fuel cell stack 10b can start power generation when its power generation capability becomes higher than that at the start of power generation of the fuel cell stack 10a, the wasteful power consumption of the air compressor 30b and the injector 36b is reduced.

[0105] In this example, the discharge direction Da_out of the oxidizing gas discharge manifold 101a of the fuel cell stack 10a forms a smaller angle with the vertically downward direction Dg than the discharge direction Db_out of the oxidizing gas discharge manifold 101b of the fuel cell stack 10b. In contrast, the discharge direction Db_out of the oxidizing gas discharge manifold 101b may form a smaller angle with the vertically downward direction Dg than the discharge direction Da_out of the oxidizing gas discharge manifold 101a. In this case, the ECU 1 causes the fuel cell stack 10b to start power generation earlier than the fuel cell stack 10a.

[0106] In addition, the ECU 1 receives the temperature Ta of the coolant of the fuel cell stack 10a from the temperature sensor 91a and compares it with the predetermined temperature To. When the temperature Ta is higher than the temperature To (Ta > To), the ECU 1 causes the fuel cell stack 10a to start power generation.

[0107] In this case, among the fuel cell stacks 10a, 10b, the fuel cell stack 10b with a smaller water amount in the oxidizing gas discharge manifold 101b and a higher power generation capacity starts power generation earlier, while the fuel cell stack 10a with a larger water amount in the oxidizing gas discharge manifold 101a and a lower power generation capacity starts power generation with a delay. Accordingly, while the fuel cell stack 10a stops power generation, the wasteful power consumption of the air compressor 30a and the injector 36a is reduced.

[0108] In this example, the temperature of the fuel cell stack 10a that starts power generation earlier rises earlier than that of the other fuel cell stack 10b; therefore, the fuel cell stack 10a can perform a warm-up operation to the fuel cell stack 10b. The warm-up operation can be performed by supplying coolant in the coolant circulation channel 24a of the fuel cell stack 10a into the coolant circulation channel 24b of the other fuel cell stack 10b, for example, using a pump or a valve, or it can be performed by heating the other fuel cell stack 10b with a heater supplied with electric power from the fuel cell stack 10a.

[0109] In this example, the ECU 1 performs the restart process on the fuel cell system 9 when the ignition switch is turned on, but the restart process may also be performed on other occasions. For example, the ECU 1 may perform the restart process when the fuel cell system 9, which is in an idle state, is returned to a normal operating state. Number of unit cells 110a, 110b of the fuel cell stacks 10a, 10b

[0110] Fig. 6 shows an arrangement example of the fuel cell stacks 10a, 10b with different numbers of unit cells 110a, 110b. In Fig. 6 are the same components or directions as in Fig. 4 are assigned the same reference numerals or symbols, and these components or directions will not be described further.

[0111] In this example, the discharge direction Da_out of the oxidizing gas discharge manifold 101a of the fuel cell stack 10a coincides with the vertically downward direction Dg, and the discharge direction Db_out of the oxidizing gas discharge manifold 101b of the fuel cell stack 10b coincides with the horizontal direction. Furthermore, the number of unit cells 110a of the fuel cell stack 10a is smaller than that of the unit cells 110b of the fuel cell stack 10b. Here, the size of the unit cell 110a is equal to that of the unit cell 110b.

[0112] Thus, the volume of the oxidizing gas passages of the fuel cell stack 10a with the smaller number of unit cells 110a, that is, the total volume of the oxidizing gas channels in the unit cells 110a and the oxidizing gas exhaust manifold 101a, is smaller than the volume of the oxidizing gas passages of the fuel cell stack 10b with the larger number of unit cells 110b. When the oxidizing gas exhaust manifolds 101a, 101b are subjected to a purge process under the same conditions, the amount of water in the oxidizing gas exhaust manifold 101a is correspondingly smaller than that of water in the oxidizing gas exhaust manifold 101b.

[0113] Accordingly, the power generation capability of the fuel cell stack 10a at the start of power generation is higher than that of the example of Fig. 4.

[0114] Furthermore, the length La of the fuel cell stack 10a with the smaller number of unit cells 110a, measured in the stacking direction, is shorter than the length Lb of the fuel cell stack 10b with the larger number of unit cells 110b, measured in the stacking direction. Accordingly, when the fuel cell stack 10a is oriented so that the stacking direction extends vertically downward along the direction Dg, and the fuel cell stack 10b is oriented so that the stacking direction extends along the horizontal direction, the height of the fuel cell stacks 10a, 10b is reduced to be lower than that in the case of the second arrangement example. With the resulting reduced height of the fuel cell stacks 10a, 10b, the fuel cell stacks 10a, 10b can be installed under a fuel cell vehicle hood, for example.

[0115] In this context, the arrangement of the fuel cell stacks 10a, 10b is not limited to that of the example of Fig. 6, but the stacking direction of the fuel cell stack 10a may shift from the direction Dg vertically downwards and the stacking direction of the fuel cell stack 10b may shift from the horizontal direction. Purging conditions of the fuel cell stacks 10a, 10b

[0116] In the rinsing process of step St3 of Fig. 2, as described above, purge conditions of the fuel cell stack 10a may be identical to or different from those of the fuel cell stack 10b. Examples of the purge conditions include a length of time (referred to as "purge time") for which the air compressor 30a, 30b supplies air and the air flow rate.

[0117] The ECU 1 sets the purge conditions for the air compressors 30a, 30b in step St3 of Fig. 2. The ECU 1 sets, for example, a purge time longer for the air compressor 30a of the fuel cell stack 10a that starts power generation earlier than that for the air compressor 30b of the fuel cell stack 10b that starts power generation later. At this time, the ECU 1 sets the same flow rate for each air compressor 30a, 30b. This further reduces the amount of water in the oxidizing gas discharge manifold 101a of the fuel cell stack 10a that starts power generation earlier; thereby improving the power generation capability of the fuel cell stack 10a, and enabling the fuel cell stack 10a to generate sufficient power, for example, even below the freezing point.

[0118] In contrast to the above setting, the ECU 1 can set a higher flow rate for the air compressor 30a of the fuel cell stack 10a, which starts power generation earlier, than that of the air compressor 30b of the fuel cell stack 10b, which starts power generation later. At this time, if the ECU 1 sets the same purge time for the air compressors 30a, 30b, the air compressor 30a with the higher flow rate can discharge a larger amount of water than the air compressor 30b with the lower flow rate, thus achieving substantially the same effect as described above.

[0119] Furthermore, the ECU 1 can set both the purge time and the flow rate for the air compressor 30a to larger values ​​than those of the air compressor 30b. At this time, the air compressor 30a with the higher flow rate and longer purge time can discharge a larger amount of water than the air compressor 30b with the lower flow rate and shorter purge time; therefore, the above-mentioned effect becomes more pronounced.

[0120] Furthermore, for the air compressor 30b of the fuel cell stack 10b, which starts power generation later, the ECU 1 sets the purge conditions that allow the fuel cell stack 10b to generate sufficient power at normal temperatures. However, the setting of the purge conditions is not limited to this, and the purge operation may not be performed. This reduces the power consumption of the air compressors 30a, 30b required for the purge operation. Control example for starting power generation based on the outside air temperature

[0121] As described above, when the fuel cell system 9 is restarted at a subzero temperature, the power generation capacity of the fuel cell stack 10a with the smaller amount of water in the oxidizing gas discharge manifold 101a is higher than that of the fuel cell stack 10b with the larger amount of water in the oxidizing gas discharge manifold 101b. However, when the fuel cell system 9 is restarted in a high-temperature environment, the electrolyte membranes in the unit cells 110a, 110b are more likely to dry out because the amount of water in the oxidizing gas discharge manifold 101a, 101b is smaller.

[0122] Therefore, unlike the case where the system is restarted at a subfreezing temperature, the power generation capability of the fuel cell stack 10a with the smaller amount of water in the oxidizing gas discharge manifold 101a is lower than that of the fuel cell stack 10b with the larger amount of water in the oxidizing gas discharge manifold 101b. Therefore, as in the above example, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation earlier according to the outside air temperature.

[0123] Fig. 7 is a flowchart showing an example of a restart process of the fuel cell system 9. In Fig. 7 are the same steps as in Fig. 5 are assigned the same step numbers, and these steps will not be described further.

[0124] If there is a request to start power generation (YES in step St11), the ECU 1 obtains the outside air temperature Tv from the outside air temperature sensor 90 (step St11-1). Then, the ECU 1 compares the outside air temperature Tv with a threshold value T1 (step St11-2). Here, the threshold value T1, which determines whether the environment of the fuel cell system 9 is below freezing, is set to 0 degrees Celsius, for example. The threshold value T1 corresponds to an example of the first threshold value.

[0125] When the temperature Tv is below the threshold T1 (Tv < T1) (YES in step St11-2), the ECU 1 determines that the fuel cell system 9 is located in a subfreezing environment and performs an operation to start power generation of the fuel cell stack 10a whose discharge direction Da_out forms a smaller angle with the vertically downward direction Dg (step St12). Subsequently, the ECU 1 performs an operation to start power generation of the other fuel cell stack 10b (step St15). Consequently, the above effect is obtained.

[0126] If the temperature Tv is equal to or higher than the threshold T1 (Tv ≥ T1) (NO in step St11-2), the ECU 1 determines that the fuel cell system 9 is not located in a sub-freezing environment and compares the outside air temperature Tv with a threshold T2 (step St21). The threshold T2 is higher than the threshold T1 and is set to a temperature at which the electrolyte membranes in the unit cells 110a, 110b can be dried out.

[0127] When the temperature Tv is higher than the threshold T2 (Tv>T2) (YES in step St21), the ECU 1 determines that the fuel cell system 9 is in a high-temperature environment and performs an operation to start power generation of the fuel cell stack 10b whose discharge direction Db_out forms a larger angle with the vertically downward direction Dg (step St22). Since the amount of water in the oxidizing gas discharge manifold 101b of the fuel cell stack 10b is larger than that of water in the oxidizing gas discharge manifold 101a of the other fuel cell stack 10a, the unit cells 110b of the fuel cell stack 10b are less likely to be dried out in the high-temperature environment compared to the unit cells 110a of the fuel cell stack 10a.

[0128] Therefore, the power generation capability of the fuel cell stack 10b is higher than that of the fuel cell stack 10a. Accordingly, the ECU 1 can reduce the wasteful power consumption of the air compressor 30a and the injector 36a by causing the fuel cell stack 10b with the higher power generation capability to start power generation earlier than the other fuel cell stack 10a.

[0129] Then, the ECU 1 obtains the impedance Z of the fuel cell stack 10a, for example, from an impedance measuring device (not shown), to determine whether the fuel cell stack 10a that has not been generating power can start power generation (step St23). The impedance Z changes according to the dryness conditions of the electrolyte membranes of the unit cells 110a, and takes a larger value as the dryness degree is higher.

[0130] Subsequently, the ECU 1 compares the impedance Z with a predetermined impedance Zo (step St24). If the impedance Z is greater than the predetermined impedance Zo (Z > Zo) (YES in step St24), the ECU 1 determines that the electrolyte membranes of the unit cells 110a remain dry and executes step St23 again. To eliminate the dry conditions of the unit cells 110a, water generated, for example, by the power generation of the power-generating fuel cell stack 10a may be supplied to the cathode supply channel 20b of the fuel cell stack 10b that has not generated power. This shortens the time required to eliminate the dry conditions of the unit cells 110a, making it shorter than that in the case where no water is supplied to the cathode supply channel 20b.

[0131] In step St23, the ECU 1 may determine the dryness conditions of the unit cells 110a instead of the impedance Z by obtaining the humidity in the oxidizing gas supply manifold 100a of the fuel cell stack 10a that has not generated power from a hygrometer (not shown). In this case, the ECU 1 may determine that the dryness conditions of the unit cells 110a have been eliminated if the obtained humidity is higher than a predetermined threshold.

[0132] When the impedance Z is equal to or less than the predetermined impedance Zo (Z ≤ Zo) (NO in step St24), the ECU 1 determines that the electrolyte membranes of the unit cells 110a are no longer in the dry state and performs an operation to start power generation of the fuel cell stack 10a (step St25). When the freezing of water in the oxidizing gas discharge manifold 101a is eliminated, liquid water from melted ice flows from the oxidizing gas discharge manifold 101a into the humidifier 34a, so that the oxidizing gas flowing in the cathode supply channel 20a is humidified by the humidifier 34a. When the humidified oxidizing gas reaches the electrolyte membranes of the unit cells 110a, the dryness conditions of the electrolyte membranes of the unit cells 110a are eliminated, so that the power generation capability of the fuel cell stack 10a is improved.

[0133] If the temperature Tv is equal to or lower than the threshold T2 (Tv ≤ T2) (NO in step St21), the ECU 1 determines that the environment of the fuel cell system 9 is neither below freezing nor a high-temperature environment, and performs an operation to start power generation of the fuel cell stacks 10a, 10b (step St26). In this case, the ECU 1 determines that there is no substantial difference between the power generation capability of the fuel cell stack 10a and that of the fuel cell stack 10b. In this way, the restart process of the fuel cell system 9 is executed.

[0134] Therefore, when the outside air temperature Tv of the fuel cell stacks 10a, 10b is below the threshold T1, the ECU 1 controls the air compressors 30a, 30b and the injectors 36a, 36b so that one of the fuel cell stacks 10a generates power earlier than the other fuel cell stack 10b. Therefore, when the fuel cell system 9 is restarted in a sub-freezing environment, for example, the fuel cell stack 10b with the lower power generation capability starts power generation later than the fuel cell stack 10a with the higher power generation capability, thus reducing the wasteful power consumption of the air compressor 30b and the injector 36b.

[0135] Furthermore, when the outside air temperature Tv is above the threshold T2, which is higher than the threshold T1, the ECU 1 controls the operation of the air compressors 30a, 30b and the injectors 36a, 36b so that one of the fuel cell stacks 10a starts power generation later than the other fuel cell stack 10b. Therefore, when the fuel cell system 9 is restarted in a high-temperature environment, for example, the fuel cell stack 10a with the lower power generation capability starts power generation later than the fuel cell stack 10b with the higher power generation capability, so that the wasteful power consumption of the air compressor 30a and the injector 36a is reduced.

[0136] While the ECU 1 obtains the outside air temperature Tv from the outside air temperature sensor 90, the method for obtaining the temperature Tv is not limited to this. For example, the ECU 1 may obtain the coolant temperatures Ta, Tb of the fuel cell stacks 10a, 10b from the temperature sensors 91a, 91b, respectively, and estimate the outside air temperature Tv from the coolant temperatures Ta, Tb. Restart process according to the inclination of the vehicle body of the fuel cell vehicle

[0137] In each of the illustrated embodiments, the angles θa, θb of the discharge directions Da_out, Db_out of the respective fuel cell stacks 10a, 10b with respect to the vertically downward direction Dg are constant. However, the angles θa, θb can be changed. For example, the size relationship of the angles θa, θb of the oxidizing gas discharge manifolds 101a, 101b of the fuel cell stacks 10a, 10b with respect to the vertically downward direction Dg can be reversed depending on the inclination of the vehicle body of the fuel cell vehicle. Thus, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation first according to the inclination of the vehicle body.

[0138] Fig. 8 shows an example of the arrangement of the fuel cell stacks 10a, 10b when the vehicle body 8 of the fuel cell vehicle on which the fuel cell system 9 is installed is tilted from the horizontal direction Dh. In this example, the fuel cell stacks 10a, 10b are installed on the vehicle body 8 such that the angles of the discharge directions Da_out, Db_out are different relative to the vehicle body 8 of the fuel cell vehicle.

[0139] In Fig. In FIG. 8, "G1" shows a state of the fuel cell stacks 10a, 10b when the posture of the vehicle body 8 is maintained in the horizontal direction Dh, and "G2" shows a state of the fuel cell stacks 10a, 10b when the posture of the vehicle body 8 is inclined from the horizontal direction Dh (see "R"). Examples of the case where the vehicle body 8 is inclined include the case where the fuel cell vehicle is stopped on an incline.

[0140] When the posture of the vehicle body 8 is maintained in the horizontal direction Dh, the angle θa of the oxidizing gas discharge direction Da_out of the fuel cell stack 10a with respect to the vertically downward direction Dg is greater than 90 degrees, and the angle θb of the oxidizing gas discharge direction Db_out of the fuel cell stack 10b with respect to the vertically downward direction Dg is equal to 90 degrees. Thus, the relationship that the angle θa is greater than the angle θb (a>b) is satisfied.

[0141] On the other hand, when the posture of the vehicle body 8 is tilted from the horizontal direction Dh, the angle θa of the oxidizing gas discharge direction Da_out of the fuel cell stack 10a with respect to the vertically downward direction Dg is 90 degrees, and the angle θb of the oxidizing gas discharge direction Db_out of the fuel cell stack 10b with respect to the vertically downward direction Dg is greater than 90 degrees. Thus, the relationship that the angle θa is smaller than the angle θb (θa<θb) is satisfied.

[0142] Thus, when the vehicle body 8 is tilted, the relationship between the angle θa and the angle θb may be reversed. In this case, if the relationship between the angle θa and the angle θb cannot be detected, the ECU 1 cannot determine which of the fuel cell stacks 10a, 10b can start power generation earlier.

[0143] Therefore, the fuel cell system 9 is provided with a tilt sensor 92 that detects the tilt of the vehicle body 8. The tilt sensor 92, which is provided, for example, on a floor plate portion 80 of the vehicle body 8, detects, for example, an angle θv of the floor plate portion 80 relative to the vertically downward direction Dg and informs the ECU 1 of the detected angle θv. The tilt sensor 92 corresponds to an example of the second detector.

[0144] Based on the inclination of the vehicle body 8 detected by the inclination sensor 92, the ECU 1 determines which of the fuel cell stacks 10a, 10b has the discharge direction Da_out, Db_out that forms a smaller angle with the vertically downward direction Dg. Therefore, even when the vehicle body 8 is tilted, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation first according to the inclination of the vehicle body detected by the inclination sensor 92.

[0145] Even in the case where the angles of the respective fuel cell stacks 10a, 10b relative to the vehicle body 8 are equal to each other, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation first according to the inclination of the vehicle body detected by the inclination sensor 92.

[0146] Fig. Fig. 9 shows another example of the arrangement of the fuel cell stacks 10a, 10b for the case where the vehicle body 8 of the fuel cell vehicle on which the fuel cell system 9 is installed is inclined from the horizontal direction Dh. In Fig. 9 are the same components or directions as in Fig. 8 are assigned the same reference numerals or symbols, and these components or directions will not be described further.

[0147] In Fig. 9, “G11” shows a state of the fuel cell stacks 10a, 10b when the posture of the vehicle body 8 is held in the horizontal direction Dh, and “G12” shows a state of the fuel cell stacks 10a, 10b when the posture of the vehicle body 8 is inclined from the horizontal direction Dh.

[0148] In this example, the fuel cell stacks 10a, 10b are arranged such that their discharge directions Da_out, Db_out are opposite to each other, i.e., the angle formed by the discharge directions Da_out, Db_out is 180 degrees. Furthermore, the fuel cell stacks 10a, 10b are arranged such that the discharge directions Da_out, Db_out run parallel to the horizontal direction Dh.

[0149] With this arrangement, when the posture of the vehicle body 8 is maintained in the horizontal direction Dh, the angles θa, θb of the discharge directions Da_out, Db_out are both 90 degrees. That is, the relationship that the angle θa is equal to the angle θb (θa = θb) is satisfied. At this time, the ECU 1 causes both fuel cell stacks 10a, 10b to start power generation based on the angle θv of the vehicle body 8 detected by the tilt sensor 92.

[0150] On the other hand, when the posture of the vehicle body 8 is tilted from the horizontal direction Dh, the angle θa of the discharge direction Da_out becomes smaller than 90 degrees, and the angle θb of the discharge direction Db_out becomes larger than 90 degrees. Therefore, the relationship that the angle θa is smaller than the angle θb (θa < θb) is satisfied. At this time, the ECU 1 causes the fuel cell stack 10b to start power generation based on the angle θv of the vehicle body 8 detected by the tilt sensor 92 after the fuel cell stack 10a is caused to start power generation.

[0151] Fig. 10 is a flowchart illustrating an example of the restart process of the fuel cell system 9 based on the inclination of the vehicle body 8 detected by the inclination sensor 92. The ECU 1 determines whether there is a request to start power generation (step St31). If there is no request to start power generation (NO in step St31), the ECU 1 executes step St31 again.

[0152] If there is a request to start power generation (YES in step St31), the ECU 1 obtains the angle θv of the vehicle body 8 from the inclination sensor 92 (step St32). Then, the ECU 1 calculates the angles θa, θb of the discharge directions Da_out, Db_out from the angle θv of the vehicle body 8 (step St33). The angles θa, θb are calculated, for example, from map data of the correspondence relationship of the angles θa, θb, θv.

[0153] Subsequently, the ECU 1 determines whether the angle θa is smaller than the angle θb (θa < θb) (step St34). If the angle θa is smaller than the angle θb (YES in step St34), the ECU 1 causes the fuel cell stack 10a to start power generation (step St35). Subsequently, the ECU 1 obtains the temperature Tb of the coolant from the temperature sensor 91b (step St36) and compares the temperature Tb with a predetermined temperature To (step St37).

[0154] If the temperature Tb is equal to or lower than the predetermined temperature To (Tb≤To) (NO in step St37), the ECU 1 executes step St36 again. If the temperature Tb is higher than the predetermined temperature To (Tb>To) (YES in step St37), the ECU 1 causes the fuel cell stack 10b to start power generation (step St38). The tasks of steps St35 to St38 are substantially identical to those of steps St12 to St15 described above.

[0155] If the angle θa is greater than the angle θb (θa > θb) (NO in step St34, YES in step St39), the ECU 1 performs an operation to start power generation of the fuel cell stack 10b (step St40). Subsequently, the ECU 1 obtains the coolant temperature Ta from the temperature sensor 91a (step St41) and compares the temperature Ta with a predetermined temperature To (step St42).

[0156] If the temperature Ta is equal to or lower than the predetermined temperature To (Ta ≤ To) (NO in step St42), the ECU 1 executes step St41 again. If the temperature Ta is higher than the predetermined temperature To (Ta > To) (YES in step St42), the ECU 1 performs an operation to start power generation of the fuel cell stack 10a (step St43). The tasks of steps St40 to St43 are substantially identical to those of steps St22 to St25 described above.

[0157] If the angle θa is equal to the angle θb (θa = θb) (NO in step St39), the ECU 1 performs an operation to start power generation of the fuel cell stacks 10a, 10b (step St44). Thus, the restart process of the fuel cell system 9 is executed.

[0158] Therefore, based on the inclination detected by the inclination sensor 92, the ECU 1 determines which of the fuel cell stacks 10a, 10b has the discharge direction Da_out, Db_out that forms a smaller angle with the vertically downward direction Dg. Therefore, even if the vehicle body 8 of the fuel cell vehicle on which the fuel cell system 9 is installed is tilted, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation earlier.

[0159] In addition, the fuel cell stacks 10a, 10b may be installed on the vehicle body 8 such that the angles of the discharge directions Da_out, Db_out relative to the vehicle body 8 of the fuel cell vehicle are different from each other, as shown in the Fig. 8. In this case, when the vehicle body 8 is tilted, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation earlier according to the tilt detected by the tilt sensor 92, even if the magnitude relationship between the angles θa, θb of the discharge directions Da_out, Db_out is reversed relative to the vertically downward direction Dg.

[0160] In addition, the fuel cell stacks 10a, 10b may be installed on the vehicle body 8 such that the angles of the discharge directions Da_out, Db_out with respect to the vehicle body 8 of the fuel cell vehicle are equal to each other, as shown in the Fig. 9. In this case, when the vehicle body 8 is tilted, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation earlier according to the tilt detected by the tilt sensor 92, even if a difference occurs between the angles θa, θb of the discharge directions Da_out, Db_out relative to the vertically downward direction Dg.

[0161] In this example, the ECU 1 selects the fuel cell stack 10a, 10b that starts power generation earlier based on the detection result of the inclination sensor 92 that detects the inclination of the vehicle body 8. However, a tilt sensor that detects the inclination of at least one of the fuel cell stacks 10a, 10b may be used.

[0162] Fig. Fig. 11 shows another example of the arrangement of the fuel cell stacks 10a, 10b in the case where the vehicle body 8 of the fuel cell vehicle on which the fuel cell system 9 is installed is inclined from the horizontal direction Dh. In Fig. 11 are the same components or directions as in Fig. 9 are assigned the same reference numerals or symbols, and these components or directions will not be described further.

[0163] In Fig. In Fig. 11, “G21” shows a state of the fuel cell stacks 10a, 10b when the posture of the vehicle body 8 is held in the horizontal direction Dh, and “G22” shows a state of the fuel cell stacks 10a, 10b when the posture of the vehicle body 8 is inclined from the horizontal direction Dh.

[0164] In this example, the fuel cell system 9 includes a tilt sensor 93 that detects the inclination of the discharge direction Da_out of the fuel cell stack 10a relative to the vertically downward direction Dg, instead of the tilt sensor 92 that detects the inclination of the vehicle body 8. The tilt sensor 93 detects the angle θa of the discharge direction Da_out relative to the vertically downward direction Dg and informs the ECU 1 of the detected angle θa. The tilt sensor 93 corresponds to an example of the first detector.

[0165] The ECU 1 calculates the angle θb of the discharge direction Db_out of the other fuel cell stack 10b from the angle θa detected by the tilt sensor 93. In this example, the angle θb is calculated by subtracting the angle θa from 180 degrees. The ECU 1 selects the fuel cell stack 10a, 10b that starts power generation earlier from the comparison result of the angles θa, θb.

[0166] Fig. 12 is a flowchart illustrating an example of the restart process of the fuel cell system 9 based on the angle θa of the discharge direction Da_out detected by the tilt sensor 93. In Fig. 12 are the same components or directions as in Fig. 10 are assigned the same reference numerals or symbols, and these components or directions will not be described further.

[0167] If there is a request to start power generation (YES in step St31), the ECU 1 obtains the angle θa of the discharge direction Da_out from the tilt sensor 93 (step St32a). Then, the ECU 1 calculates the angle θb of the discharge direction Db_out of the other fuel cell stack 10b from the angle θa (step St33a). The angle θb is calculated from the correlation (e.g., θb = 180a-θa) of the angles θa, θb, which is determined when the fuel cell stacks 10a, 10b are installed.

[0168] Then, step St34 and subsequent steps are executed. In this way, the restart process of the fuel cell system 9 is executed.

[0169] Thus, based on the inclination detected by the inclination sensor 93, the ECU 1 determines which of the fuel cell stacks 10a, 10b has the discharge direction Da_out, Db_out that forms a smaller angle with the vertically downward direction Dg. Therefore, even if the vehicle body 8 of the fuel cell vehicle on which the fuel cell system 9 is installed is tilted, the ECU 1 can select the fuel cell stack 10a, 10b that starts power generation earlier.

[0170] While the tilt sensor 93 in this example detects the angle θa of the discharge direction Da_out of the fuel cell stack 10a, another tilt sensor that detects the angle θb of the discharge direction Db_out of the other fuel cell stack 10b may be provided in addition to the tilt sensor 93 or instead of the tilt sensor 93. If the tilt sensor is added to detect the angle θb, the task of calculating the angle θb (step St33a) is not required. Furthermore, in this case, if there is no tilt sensor 93, a task of calculating the angle θa from the angle θb is performed.

[0171] While the fuel cell stacks 10a, 10b of each example described above are arranged such that the discharge directions Da_out, Db_out point in mutually opposite directions, the arrangement is not limited to this; rather, the fuel cell stacks 10a, 10b may be arranged such that the discharge directions Da_out, Db_out face each other. Furthermore, the fuel cell stacks 10a, 10b may be arranged such that the discharge directions Da_out, Db_out form 90 degrees on a surface of the bottom plate portion 80. Example of three fuel cell stacks

[0172] While the ECU 1 controls the start of power generation of two fuel cell stacks 10a, 10b in each of the above examples, control similar to this control may be performed in a fuel cell system 9 having three fuel cell stacks.

[0173] Fig.13 shows an example of the arrangement of three fuel cell stacks 10a to 10c. The fuel cell stack 10c is included in a power generation system (not shown) similar to the first and second power generation systems 9a, 9b of the other fuel cell stacks 10a, 10b.

[0174] The discharge directions Da_out to Dc_out of the fuel cell stacks 10a to 10c form angles θa to θc with the vertically downward direction Dg, respectively. When the relationship of angles θa > θb > θc is satisfied, the ECU 1 first causes the fuel cell stack 10c with the smallest angle θc to start power generation first, then causes the fuel cell stack 10b with the angle θb to start power generation, and finally causes the fuel cell stack 10a with the largest angle θa to start power generation.

[0175] In this way, when the fuel cell system 9 is started at a temperature below freezing, for example, the fuel cell stacks 10a to 10c can start power generation in descending order of power generation capability; thereby reducing wasteful power consumption during the restart of the fuel cell system 9. In this context, the ECU 1 can cause the fuel cell stack 10b with the second largest angle θb to start power generation first. In this case, since the power generation capability of the fuel cell stack 10b is higher than that of at least the fuel cell stack 10a, wasteful power consumption during the restart of the fuel cell system 9 is reduced.

[0176] In each of the above examples, the order in which the fuel cell stacks 10a, 10b start power generation is determined according to the discharge directions Da_out, Db_out of the oxidizing gas discharge manifolds 101a, 101b. However, the manner of determining the order is not limited to this. For example, the ECU 1 may determine the order in which the fuel cell stacks 10a, 10b start power generation according to the discharge directions of the fuel gas discharged from the fuel gas discharge manifolds 103a, 103b.

[0177] Even when the purging process is performed, water remains in the fuel gas discharge manifolds 103a, 103b, just like the oxidizing gas discharge manifolds 101a, 101b. The ease of water discharge depends on the angle of the fuel gas discharge direction relative to the vertically downward direction Dg. Thus, the amount of water in the fuel gas discharge manifold 103a, 103b of one of the fuel cell stacks 10a, 10b, whose fuel gas discharge direction forms a smaller angle with the vertically downward direction Dg, is smaller than the amount of water in the fuel gas discharge manifold 103b, 103a of the other fuel cell stack 10b, 10a.

[0178] Accordingly, the power generation capability of the fuel cell stack 10a, 10b whose fuel gas discharge direction forms the smaller angle with the vertically downward direction Dg is, for example, higher than that of the other fuel cell stack at temperatures below freezing. Thus, the ECU 1 causes the fuel cell stack 10a, 10b whose fuel gas discharge direction forms the smaller angle with the vertically downward direction Dg to start power generation earlier than the other fuel cell stack 10b, 10a. Consequently, essentially the same effect as described above is achieved.

[0179] The above embodiments are preferred embodiments of the invention. However, it should be understood that the invention is not limited to the embodiments, but may be embodied with various modifications without departing from the principle of the invention.

Claims

[1] Fuel cell system (9), comprising: a first fuel cell stack (10a) configured to generate electrical power through a chemical reaction of reaction gas, the first fuel cell stack (10a) having a discharge manifold (101a) configured to discharge the reaction gas; a second fuel cell stack (10b) configured to generate electrical power through a chemical reaction of reaction gas, the second fuel cell stack (10b) having a discharge manifold (101b) configured to discharge the reaction gas; a first auxiliary device (30a, 36a) used to generate power from the first fuel cell stack (10a); a second auxiliary device (30b, 36b) used to generate power from the second fuel cell stack (10b); a control device (1) configured to control an operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b); and a first detector (93) configured to detect an inclination of the discharge direction of the first fuel cell stack (10a) or the second fuel cell stack (10b) relative to the vertically downward direction, wherein the control device (1) is configured to control the operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) such that a fuel cell stack of the first fuel cell stack (10a) and the second fuel cell stack (10b), the discharge direction of which the reaction gas discharged from the discharge manifold forms a smaller angle with a vertically downward direction, starts generating power earlier than the other fuel cell stack of the first fuel cell stack (10a) and the second fuel cell stack (10b) after the power generation of the first fuel cell stack (10a) and the second fuel cell stack (10b) is stopped, and wherein the control device (1) is configured to determine, based on the inclination detected by the first detector (93), which of the first fuel cell stack (10a) and the second fuel cell stack (10b) has the discharge direction that forms a smaller angle with the vertically downward direction. [2] The fuel cell system (9) according to claim 1, wherein the control device (1) is configured to control the operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) such that one fuel cell stack starts generating power earlier than the other fuel cell stack when an outside air temperature is lower than a first threshold. [3] The fuel cell system (9) according to claim 1 or 2, wherein the control device (1) is configured to control the operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) such that the other fuel cell stack starts generating power when a temperature of the other fuel cell stack becomes higher than a second threshold after the one fuel cell stack starts generating power. [4] Fuel cell system (9) according to one of claims 1 to 3, wherein the discharge direction of the one fuel cell stack substantially coincides with the vertically downward direction. [5] Fuel cell system (9) according to one of claims 1 to 4, wherein: the first fuel cell stack (10a) comprises a plurality of unit cells (110a); the second fuel cell stack (10b) comprises a plurality of unit cells (110b); and the number of unit cells of one fuel cell stack is smaller than the number of unit cells of the other fuel cell stack. [6] Fuel cell system (9) according to one of claims 1 to 5, wherein: the first auxiliary device (30a, 36a) is configured to supply purge gas to the exhaust manifold (101a) of the first fuel cell stack (10a) to purge the exhaust manifold (101a) after the power generation of the first fuel cell stack (10a) is stopped; the second auxiliary device (30b, 36b) is configured to supply purge gas to the exhaust manifold (101b) of the second fuel cell stack (10b) to purge the exhaust manifold (101b) after the power generation of the second fuel cell stack (10b) is stopped; and an auxiliary device of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) which purges the discharge manifold of the one fuel cell stack, supplies the purge gas for a longer time than the other auxiliary device of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) which purges the discharge manifold of the other fuel cell stack, at substantially the same flow rate as the other auxiliary device. [7] Fuel cell system (9) according to one of claims 1 to 5, wherein: the first auxiliary device (30a, 36a) is configured to supply purge gas to the exhaust manifold (101a) of the first fuel cell stack (10a) to purge the exhaust manifold (101a) after the power generation of the first fuel cell stack (10a) is stopped; the second auxiliary device (30b, 36b) is configured to supply purge gas to the exhaust manifold (101b) of the second fuel cell stack (10b) to purge the exhaust manifold (101b) after the power generation of the second fuel cell stack (10b) is stopped; and an auxiliary device of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) which purges the discharge manifold of the one fuel cell stack, supplies the purge gas within a predetermined time at a higher flow rate than the other auxiliary device of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) which purges the discharge manifold of the other fuel cell stack. [8] Fuel cell system (9) according to one of claims 1 to 5, wherein: the first auxiliary device (30a, 36a) is configured to supply purge gas to the exhaust manifold (101a) of the first fuel cell stack (10a) to purge the exhaust manifold (101a) after the power generation of the first fuel cell stack (10a) is stopped; the second auxiliary device (30b, 36b) is configured to supply purge gas to the exhaust manifold (101b) of the second fuel cell stack (10b) to purge the exhaust manifold (101b) after the power generation of the second fuel cell stack (10b) is stopped; and an auxiliary device of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) which purges the discharge manifold of the one fuel cell stack, supplies the purge gas for a longer time than the other auxiliary device of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) which purges the discharge manifold of the other fuel cell stack, at a higher flow rate than the other auxiliary device. [9] Fuel cell system (9), comprising: a first fuel cell stack (10a) configured to generate electrical power through a chemical reaction of reaction gas, the first fuel cell stack (10a) having a discharge manifold (101a) configured to discharge the reaction gas; a second fuel cell stack (10b) configured to generate electrical power through a chemical reaction of reaction gas, the second fuel cell stack (10b) having a discharge manifold (101b) configured to discharge the reaction gas; a first auxiliary device (30a, 36a) used to generate power from the first fuel cell stack (10a); a second auxiliary device (30b, 36b) used to generate power from the second fuel cell stack (10b); a control device (1) configured to control an operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b); and a second detector (92) configured to detect an inclination of a vehicle on which the fuel cell system (9) is installed, wherein the control device (1) is configured to control the operation of the first auxiliary device (30a, 36a) and the second auxiliary device (30b, 36b) such that a fuel cell stack of the first fuel cell stack (10a) and the second fuel cell stack (10b), the discharge direction of which the reaction gas discharged from the discharge manifold forms a smaller angle with a vertically downward direction, starts generating power earlier than the other fuel cell stack of the first fuel cell stack (10a) and the second fuel cell stack (10b) after the power generation of the first fuel cell stack (10a) and the second fuel cell stack (10b) is stopped, and wherein the control device (1) is configured to determine, based on the inclination detected by the second detector (92), which of the first fuel cell stack (10a) and the second fuel cell stack (10b) has the discharge direction that forms a smaller angle with the vertically downward direction. [10] The fuel cell system (9) according to claim 9, wherein the first fuel cell stack (10a) and the second fuel cell stack (10b) are installed on a vehicle body (8) of the vehicle such that an angle of the discharge direction of the first fuel cell stack (10a) relative to the vehicle body (8) is substantially equal to that of the second fuel cell stack (10b). [11] The fuel cell system (9) according to claim 9, wherein the first fuel cell stack (10a) and the second fuel cell stack (10b) are installed on a vehicle body (8) of the vehicle such that an angle of the discharge direction of the first fuel cell stack (10a) relative to the vehicle body (8) is different from that of the second fuel cell stack (10b).

Images