JP2019129141A - Fuel cell system - Google Patents

Abstract

To provide a fuel cell system determining a cause of accumulation of bubbles in a cooling water flow path of a fuel cell stack.SOLUTION: A fuel cell system includes: a fuel cell stack which includes a stacked body where a plurality of unit cells are stacked, the unit cell on one end side being located above the unit cell on the other end side in a gravity direction, a reactant gas flow path formed in the stacked body, and a cooling water flow path formed in the stacked body, and extending from a side of the unit cell on the other end side to a side of the unit cell on one end side and extending again to the side of the unit cell on the other end side; a pump that supplies cooling water to the cooling water flow path; a supply device that supplies reactant gas to the reactant gas flow path; and a control device which includes a bubble determination portion configured to determine whether or not accumulation of bubbles is caused in the cooling water flow path, and a cause determination portion configured to determine whether or not accumulation of bubbles is caused due to leakage of the reactant gas from the reactant gas flow path, when the bubble determination portion determines that accumulation of bubbles is caused.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fuel cell system.

  The fuel cell stack has a stacked body in which a plurality of unit cells are stacked, and in the stacked body, a reaction gas flow path through which a reaction gas flows and a cooling water flow path through which cooling water flows are formed. If air bubbles remain in the cooling water flow path, the cooling efficiency of the fuel cell stack may decrease and the power generation efficiency may decrease. For this reason, in patent document 1, the bubble is discharged | emitted from a cooling water flow path by changing the rotational speed of the pump which supplies cooling water to a cooling water flow path.

JP 2014-86156 A

  When air bubbles stay in this way, it is desirable to take appropriate measures depending on the cause, but determining the cause of air bubble retention has not been performed conventionally.

  An object of the present invention is to provide a fuel cell system that determines the cause of the retention of bubbles in a cooling water flow path of a fuel cell stack.

  The above object is a laminated body in which a plurality of unit cells are stacked and the unit cell on one end side is positioned on the upper side in the direction of gravity than the unit cell on the other end side; A fuel cell stack having a passage, a cooling water flow path formed in the stacked body, extending from the unit cell side on the other end side to the unit cell side on the one end side and extending again to the unit cell side on the other end side; A pump for supplying cooling water to the cooling water flow path, a supply device for supplying a reaction gas to the reaction gas flow path, an air bubble determination unit for determining presence or absence of air bubbles in the cooling water flow path, A cause determination unit that determines whether or not the cause of the bubble retention is a leak of the reaction gas from the reaction gas flow path when it is determined by the bubble determination unit that there is a bubble retention; and The present invention can be achieved by a fuel cell system provided with.

  If it is determined that the cause of the bubble retention is not a leak of the reaction gas from the reaction gas flow passage, a removal device may be provided to remove the staying bubble from the cooling water flow passage.

  The said removal apparatus may be the said pump which discharges | emits a bubble from the said cooling water flow path by increasing / decreasing a rotational speed.

  A warning device may be provided that warns when it is determined that the cause of the bubble retention is leakage of the reaction gas from the reaction gas flow path.

  When the pump is stopped and the supply device supplies the reaction gas to the reaction gas flow path, the cause determining unit is configured to increase the pressure in the cooling water flow path to a predetermined value or more. In at least one of the cases where the pressure decrease amount in the reaction gas flow channel is less than or equal to a predetermined value, it may be determined that the cause of the bubble retention is the leak of the reaction gas from the reaction gas flow channel .

  When the supply device increases the supply amount of the reaction gas to the reaction gas flow path, the cause determining unit determines that the position of the single cell having the lowest cell voltage among the plurality of single cells is directed downward in the direction of gravity. When at least one of the plurality of unit cells and the position of the unit cell having the highest temperature among the plurality of unit cells has moved downward in the direction of gravity, the cause of the bubble retention is from the reaction gas flow path. It may be determined that the reaction gas leaks.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which determines the cause of the retention of the bubble in the cooling water flow path of a fuel cell stack can be provided.

FIG. 1 is a schematic view of a fuel cell system mounted on a vehicle. FIG. 2 is a schematic view of a stack constituting the stack. FIG. 3 is a flowchart showing an example of control executed by the control device. 4A to 4C are explanatory diagrams when bubbles are not present in the cooling water flow path, and FIGS. 4D to 4F are explanatory diagrams when bubbles are retained in the cooling water flow paths. FIG. 5 is a flowchart showing an example of the bubble determination process. FIG. 6A is a flowchart showing an example of the cause determination condition confirmation process in the present embodiment, and FIG. 6B is a flowchart showing an example of the cause determination process in the present embodiment. FIG. 7 is a flowchart showing a variation of the cause determination condition confirmation process. FIG. 8A is a flowchart showing a modification of the cause determination condition confirmation process, and FIG. 8B is a flowchart showing a modification of the cause determination process. FIG. 9 is a flowchart showing a variation of the cause determination process. 10A and 10B are flowcharts of a variation of the cause determination process. FIG. 11A is a flowchart of a modification of the cause determination condition confirmation process, and FIG. 11B is a flowchart of a modification of the cause determination process. 12A to 12F are explanatory diagrams of changes in the cell voltage of a plurality of single cells.

  FIG. 1 is a schematic view of a fuel cell system 1 mounted on a vehicle. Vehicles are fuel cell vehicles, electric vehicles, hybrid vehicles and the like. However, the fuel cell system (hereinafter referred to as a system) 1 is applicable to various mobile bodies (for example, ships, airplanes, robots, etc.) other than vehicles and stationary power sources. The system 1 includes a fuel cell stack (hereinafter simply referred to as a stack) 20, a control device 30, a hydrogen gas supply system 120, an air supply system 140, and a cooling water supply system 160. The system 1 supplies the generated power of the stack 20 to a motor for traveling the vehicle.

  The control device 30 is a computer that includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The control device 30 receives sensor inputs from the ignition switch 101, the accelerator pedal AP, and the like. Perform various controls. In addition, an ignition switch 101 mounted on the vehicle is electrically connected to the control device 30. When the ignition switch 101 is turned on, the system 1 is started by the control device 30, and the ignition switch 101 is turned off. As a result, the control device 30 stops the system 1. Also, although the details will be described later, the outside air temperature detected by the outside air temperature sensor 102 is output to the control device 30. Although described in detail later, the HMI device 103 is an example of a warning device that warns a vehicle occupant in a predetermined case. The HMI device 103 includes, for example, at least one of a display capable of displaying a warning with an image and a speaker capable of outputting a warning with sound.

  The stack 20 is a solid polymer electrolyte type, a plurality of single cells are stacked, and power is generated by receiving supply of a fuel gas (for example, hydrogen) and an oxidant gas (for example, air) as reaction gases. The generated current and generated voltage of the stack 20 are detected by the current sensor 106 and the voltage sensor 107, respectively, and the detection results are output to the control device 30. The cell monitor 108 will be described later. The stack 20 includes a fuel gas passage 12 through which fuel gas flows, an oxidant gas passage 14 through which oxidant gas flows, and a cooling water passage 16 through which cooling water flows. Details of the stack 20 will be described later.

  The hydrogen gas supply system 120 supplies the stack 20 with hydrogen for power generation. Specifically, the hydrogen gas supply system 120 includes a tank 110, a hydrogen supply path 121, a circulation path 122, a discharge path 123, a tank valve 124, a pressure control valve 125, an injection valve 126, a circulation pump 127, a gas-liquid separator 128. , An on-off valve 129, and a pressure sensor 12P. The hydrogen gas supply system 120 is an example of a supply device that supplies hydrogen gas to the fuel gas flow path 12 of the stack 20.

  Hydrogen gas is supplied from the tank 110 to the fuel gas flow path 12 of the stack 20 via the hydrogen supply path 121. The tank valve 124, the pressure control valve 125, and the injection valve 126 are sequentially provided from the upstream side of the hydrogen supply path 121. The circulation path 122 circulates the fuel off-gas discharged from the fuel gas flow path 12 of the stack 20 to the hydrogen supply path 121. The supply amount of hydrogen gas is adjusted by controlling the opening / closing of various valves by the control device 30 based on the operation of the accelerator pedal AP.

  The circulation pump 127 and the gas-liquid separator 128 are provided on the circulation path 122, and the circulation pump 127 circulates the fuel off gas separated by the gas-liquid separator 128 to the hydrogen supply path 121. The water separated by the gas-liquid separator 128 and a part of the fuel off gas are discharged to the discharge path 142 through the discharge path 123 and the on-off valve 129 branched from the gas-liquid separator 128. The pressure sensor 12P is provided on the circulation path 122 between the outlet of the stack 20 and the gas-liquid separator 128, and the pressure in the fuel gas flow path 12 of the stack 20, in other words, the fuel gas flow path 12 The pressure of the fuel gas inside is detected, and the detection result is output to the control device 30.

  The air supply system 140 supplies air to the stack 20. Specifically, the air supply system 140 includes an air compressor 149, an air supply path 141, a discharge path 142, a bypass valve 145, a muffler 146, an intercooler 147, a bypass path 148, and a pressure sensor 14P. The air supply system 140 is an example of a supply device that supplies an oxidant gas to the oxidant gas flow path 14 of the stack 20.

  The air taken in from the outside through the air cleaner 144 is compressed by the air compressor 149 via the air supply path 141, cooled by the intercooler 147, and supplied to the oxidant gas flow path 14 of the stack 20.

  A bypass valve 145 is provided at a branch point where the bypass path 148 branches from the air supply path 141. The bypass valve 145 adjusts the flow rate of air supplied to the stack 20 and the flow rate of air that bypasses the stack 20 via the bypass path 148. The release passage 142 releases the oxidant off gas exhausted from the oxidant gas passage 14 of the stack 20 to the atmosphere. The pressure regulating valve 143 adjusts the flow rate of the oxidant off-gas and the back pressure on the cathode side. The pressure sensor 14P is provided in the discharge path 142 between the outlet of the oxidant gas channel 14 and the pressure regulating valve 143, and the pressure in the oxidant gas channel 14 in the stack 20, in other words, the oxidant The pressure of the oxidant gas in the gas flow channel 14 is detected, and the detection result is output to the control device 30. The supply amount of air to the stack 20 is also adjusted by controlling various devices by the control device 30 based on the operation of the accelerator pedal AP, similarly to hydrogen gas. The muffler 146 is provided in the discharge path 142 to reduce the sound generated by the air passing through the discharge path 142.

  The cooling water supply system 160 cools the stack 20 by circulating cooling water through a predetermined path. Specifically, the cooling water supply system 160 includes a radiator 150, a fan 152, a reserve tank 154, a circulation path 161, a bypass path 162, a three-way valve 163, an electric pump 164, an ion exchanger 165, a water pressure sensor 16P, and a water temperature. A sensor 16T and a distribution path 169 are provided.

  The cooling water pumped by the pump 164 flows through the circulation path 161, and heat is exchanged by the radiator 150 by air blown by the fan 152 to cool the cooling water. The cooled cooling water is supplied to the cooling water flow path 16 of the stack 20 to cool the stack 20. The water pressure sensor 16 </ b> P detects the pressure of the cooling water discharged from the cooling water flow path 16 of the stack 20 and flowing through the circulation path 161, and the detection result is output to the control device 30. Since the water pressure sensor 16P is provided in the vicinity of the outlet of the cooling water channel 16, the pressure in the cooling water channel 16 is substantially detected. The water temperature sensor 16T detects the temperature of the cooling water discharged from the cooling water flow path 16 of the stack 20 and flowing through the circulation path 161. The water temperature sensor 16 T detects the temperature of the cooling water discharged from the stack 20 and before flowing to the radiator 150, and the temperature of the cooling water substantially correlates with the temperature of the stack 20. The temperature is detected. The bypass path 162 branches from the circulation path 161 and bypasses the radiator 150, and the three-way valve 163 adjusts the flow rate of the cooling water flowing through the bypass path 162. The ion exchanger 165 is provided on the bypass path 162 so that a part of the cooling water flowing through the bypass path 162 flows.

  The reserve tank 154 is connected to the radiator 150. The reserve tank 154 is an open air container that stores cooling water. Accordingly, the pressure at the coolant level stored in the reserve tank 154 becomes atmospheric pressure. By storing surplus cooling water in the reserve tank 154, it is possible to suppress a decrease in the amount of cooling water circulating through each flow path. The reserve tank 154 has a function of separating air and liquid mixed in the cooling water.

  The distribution path 169 branches from the circulation path 161 and is connected to the intercooler 147 and is connected to the circulation path 161 again. Thereby, the cooling water is supplied to the intercooler 147 via the distribution path 169, and the air passing through the intercooler 147 is cooled by this cooling water.

  FIG. 2 is a schematic view of the stack 10 constituting the stack 20. As shown in FIG. In the laminate 10, a plurality of unit cells 10-1, 10-2... 10-n are stacked, and the direction in which these unit cells are stacked is arranged substantially along the direction of gravity. In other words, the laminate 10 is disposed in a posture in which the unit cell 10-1 on one end side is positioned above the unit cell 10-n on the other end side in the gravity direction. The n single cells are stacked. The single cell 10-1 is located on the uppermost side in the gravity direction among the plurality of single cells. The single cell 10-n is located on the lowermost side in the gravity direction among the plurality of single cells. Each single cell includes a membrane electrode gas diffusion layer assembly (MEGA), an insulating member supporting the MEGA, and a pair of separators sandwiching the MEGA and the insulating member. The MEGA has an electrolyte membrane, a catalyst layer formed on each side of the electrolyte membrane, and a pair of gas diffusion layers respectively joined to the catalyst layer. Although not shown, a pair of current collectors, a pair of insulating plates, and a pair of end plates are disposed to sandwich the plurality of unit cells. Also, the cell monitor 108 detects the cell voltage of each single cell, and outputs the detection result to the control device 30.

  The cooling water flow path 16 described above is formed inside the laminate 10. The cooling water flow passage 16 is formed between the cooling water supply manifold 16a and the cooling water discharge manifold 16b (both together referred to as a cooling water manifold) penetrating the laminate 10 in the stacking direction and the separators of adjacent single cells. And the illustrated flow path. The cooling water manifolds 16a and 16b are formed to penetrate all the single cells. The cooling water manifolds 16a and 16b are formed so as to penetrate the current collecting plate, the insulating plate, and the end plate disposed on the single cell 10-n side. The cooling water flows from the above-described circulation path 161 to the cooling water manifold 16a and is discharged from the cooling water manifold 16b to the circulation path 161 through the above-described flow path. In other words, the cooling water flow path 16 is formed in the laminate 10 and extends from the unit cell 10-n side at the other end to the unit cell 10-1 at the one end side, and is again at the unit cell 10-n side at the other end It extends to The cooling water flows in the cooling water flow path 16 formed in this manner, whereby the plurality of single cells are cooled. In the present specification, all of the cooling water manifolds 16a and 16b and the flow path formed between adjacent single cells are collectively referred to as the cooling water flow path 16 formed in the laminate 10.

  The fuel gas passage 12 of the stack 20 is also similar in configuration to the cooling water passage 16. The fuel gas flow passage 12 is formed between the fuel gas supply manifold and the fuel gas discharge manifold which penetrate the stack 10 in the stacking direction, and one of the separators of each unit cell and the membrane electrode gas diffusion layer assembly. And the illustrated flow path. Similarly, the oxidant gas flow path 14 includes an oxidant gas supply manifold and an oxidant gas discharge manifold penetrating the laminated body 10 in the lamination direction, and the other separator of each single cell and the membrane electrode gas diffusion layer assembly. And a flow path (not shown) defined therebetween. Thereby, the fuel gas and the oxidant gas are supplied to each unit cell, and the stack 20 generates power.

  As will be described in detail later, the control device 30 determines a bubble determination process for determining the retention of bubbles in the cooling water flow path 16, a cause determination condition confirmation process for confirming a precondition for executing the cause determination process, and whether or not there is a leak. Control including determination processing, bubble discharge processing for discharging bubbles from the cooling water flow path 16, and bubble discharge prohibition processing for prohibiting bubble discharge processing is executed. These processes are functionally realized by the CPU, the ROM, the RAM, and the like of the control device 30. The control which control device 30 performs below is explained.

  FIG. 3 is a flow chart showing an example of control that the control device 30 executes. This control is repeatedly executed at a predetermined cycle. First, a bubble determination process for determining whether or not bubbles are retained in the cooling water flow path 16 is performed (step S1). Such a bubble determination process is performed because the presence of the air bubbles in the cooling water flow path 16 may reduce the power generation efficiency without sufficiently cooling the stack 20. Details of the bubble determination process will be described later. In addition, as a cause of the air bubbles staying in the cooling water flow path 16, the air mixed in the cooling water supply system 160 at the time of manufacture of the system 1, at the time of cooling water exchange of the system 1, etc. It is conceivable that the reaction gas leaked from one of the gas flow channels 14 to the cooling water flow channel 16. For example, when the fuel gas leaks from the fuel gas flow path 12 to the cooling water flow path 16, the sealing performance of the seal member that seals the fuel gas flow path 12 and the cooling water flow path 16 in the stack 20 deteriorates for some reason. It is thought that it did. The same applies when the oxidant gas leaks from the oxidant gas flow path 14 to the cooling water flow path 16.

  Next, based on the result of the bubble determination process, it is determined whether or not bubbles remain (step S3). In the case of a negative determination in step S3, this control ends. If the determination in step S3 is affirmative, a cause determination condition confirmation process for confirming whether the cause determination condition is satisfied is executed (step S5). Next, based on the result of the cause determination condition confirmation process, it is determined whether or not the cause determination condition is satisfied (step S7). The cause determination condition is a precondition required to execute a cause determination process described later. The cause determination condition will be described later in detail. In the case of a negative determination in step S7, the present control ends. If the determination in step S7 is affirmative, cause determination processing is executed (step S9). In the cause determination process, a process for determining whether or not the cause of the bubble retention in the cooling water flow path 16 is due to the leakage of the reaction gas is executed.

  Next, it is determined whether there is a leak of reaction gas (step S11). In the case of a negative determination in step S11, a bubble discharge process of discharging air bubbles from the cooling water flow path 16 by increasing or decreasing the rotational speed of the pump 164 is executed (step S13). Specifically, by repeatedly switching the rotational speed of the pump 164 alternately at high speed and low speed at predetermined time intervals, the flow rate of the cooling water in the cooling water flow path 16 is repeatedly increased and decreased, whereby the cooling water flow Discharge of air bubbles from the passage 16 is promoted. Bubbles discharged from the cooling water flow path 16 are guided into the reserve tank 154 via the circulation path 161 and discharged to the outside air. Thereby, air bubbles can be discharged from the cooling water supply system 160. The pump 164 is an example of a removal device that removes the accumulated air bubbles from the cooling water flow path 16. Therefore, it is possible to suppress that the air bubbles discharged from the cooling water flow passage 16 are returned to the cooling water flow passage 16 of the stack 20 again, and the reduction of the cooling efficiency and the power generation efficiency of the stack 20 is suppressed.

  In addition, although the pump 164 was demonstrated as an example of said removal apparatus, it is not limited to this. For example, as the removing device, a vibrator that vibrates the stack 20 may be used. The vibrator can be removed by discharging air bubbles from the cooling water flow path 16 by vibrating the stack 20. The vibrator is, for example, a piezoelectric ceramic such as PZT which is an ultrasonic vibrator. For example, such a vibrator is installed on the outer wall surface of the case of the stack 20, and the stack 20 is vibrated to such an extent that a single cell is not displaced. This promotes, for example, the flow of the air bubbles remaining in the uneven flow channel grooves formed on the opposing surface sides of the separators facing each other to the cooling water manifold 16 b and discharges the air bubbles from the cooling water flow channel 16. Can promote things.

  If the determination in step S11 is affirmative, a bubble discharge prohibiting process that prohibits the bubble discharging process is executed (step S15). As described above, in the case of the positive determination in step S11, the reaction gas is leaking from the at least one of the fuel gas passage 12 and the oxidant gas passage 14 to the cooling water passage 16. For this reason, even if the bubble discharge process is executed as described above and the bubbles are discharged from the cooling water passage 16, the reaction gas may leak again into the cooling water passage 16 and the bubbles may stay in the cooling water passage 16. There is. In this case, in order to discharge the bubbles from the cooling water flow path 16, it is necessary to repeatedly execute the bubble discharge process, which increases power consumption. Therefore, in the present embodiment, when it is determined that there is a leak of the reaction gas, the power consumption by the pump 164 accompanying the execution of the bubble discharge process is suppressed by prohibiting the bubble discharge process.

  After execution of the bubble discharge prohibition process, a warning process is performed (step S17). The warning process is a process of giving a warning to a vehicle occupant by the HMI device 103. For example, the warning process is a process of displaying an image prompting the driver to check or repair the stack 20 on the display screen of the HMI device 103. Further, when it is determined that there is a leak, power generation of the stack 20 and driving of the pump 164 may be prohibited. Further, when it is determined that there is a leak, the vehicle travel mode may be switched to the retreat travel mode so that the vehicle can travel only in the retreat travel mode. The evacuation travel mode is a mode in which the vehicle can be driven by the secondary battery (not shown) while the operation of the stack 20 is stopped. The order of steps S15 and S17 does not matter.

  Note that, as described above, in the laminate 10, the single cell 10-1 on one end side is located above the single cell 10-n on the other end side in the gravity direction. For this reason, although it will be described in detail later, compared to the case where the lamination direction of the laminated body is arranged in the horizontal direction, in the present embodiment, air bubbles are hardly discharged from the cooling water flow path 16 . Therefore, in the bubble discharge process of the present embodiment, the upper limit value of the rotational speed of the pump 164 is set to be relatively high, and the power consumption is large. Therefore, it is suitable to prohibit the bubble discharge process when it is determined that there is a leak, as in the present embodiment, when the power consumption associated with the bubble discharge process is large.

  Next, the above-described air bubble determination process will be described. FIG. 4A to FIG. 4C are explanatory views in the case where there is no air bubble in the cooling water flow path 16. 4A shows the stacked body 10, FIG. 4B shows the temperature of each single cell, and FIG. 4C shows the cell voltage of each single cell. The vertical axis in FIG. 4B and FIG. 4C indicates the stacking position of each single cell, and the uppermost single cell on the vertical axis is the single cell 10-1 located most on the upper side in the gravity direction. The lowermost single cell is the single cell 10-n located on the lower side in the most gravity direction. The horizontal axis in FIG. 4B indicates the temperature of each single cell, and the horizontal axis in FIG. 4C indicates the cell voltage of each single cell. In the horizontal axis of FIG. 4B, the left side indicates low temperature and the right side indicates high temperature. In the horizontal axis of FIG. 4C, the left side indicates a low voltage and the right side indicates a high voltage. When there are no bubbles in the cooling water flow path 16, each single cell is cooled substantially uniformly by the cooling water, and the temperature of each single cell is also substantially uniform. Thereby, the power generation efficiency of each single cell is also ensured, the cell voltage of each single cell is substantially uniform, and the power generation efficiency of the entire stack 20 is ensured.

  4D to 4F are explanatory views when bubbles are retained in the cooling water flow path 16. 4D to 4F correspond to FIGS. 4A to 4C, respectively. As shown in FIG. 4D, when air bubbles are mixed in the cooling water flow path 16, the air bubbles move to the vicinity of the single cell 10-1 located on the upper side in the gravity direction by buoyancy, and the air bubbles It stagnates in the flow path between the cooling water manifolds 16a and 16b and between single cells. Further, in order for the air bubbles staying in this vicinity to be discharged from the cooling water flow path 16, the air bubbles flow downward in the gravity direction by the pressure of the cooling water against the buoyancy in the cooling water manifold 16b extending in the gravity direction. The laminated body 10 has a configuration in which air bubbles are difficult to be discharged. For example, when the stack is installed in a posture in which the stacking direction is horizontal, the cooling water manifold extends in the horizontal direction, so that bubbles are easily discharged by the pressure of the cooling water without countering buoyancy.

  Thus, when the amount of air bubbles staying near the single cell 10-1 increases in the present embodiment, the air bubbles stay not only in the single cell 10-1 but also below the single cell 10-1 in the direction of gravity. Do. Due to the presence of the bubbles, the single cells around the bubbles are not sufficiently cooled, and the temperature of the single cells around the bubbles rises. For this reason, drying proceeds in the unit cell electrolyte membrane around the bubbles. Thereby, the cell voltage of the single cell around the bubble is lower than the cell voltages of the other single cells.

  Here, as shown in FIG. 4F, the cell voltage of the unit cell 10-1 located most on the upper side in the direction of gravity is not the lowest, but the cell voltage of the unit cell 10-4 that is slightly lower than that Is the lowest. The reason is that the unit cell 10-1 is located on the outermost side of the laminate 10 and heat radiation is promoted, and along with this, the unit cell 10-1 and the unit cell 10-2 adjacent thereto are easily cooled. It is. The reason why the cell voltage of the unit cell below the unit cell 10-4 is restored is that there is no air bubble around the unit cell below the unit cell 10-4 and the cooling water It is because the cooling effect by is gradually increasing.

  In the bubble determination process, the presence or absence of the stagnation of the bubbles in the cooling water flow path 16 of the laminate 10 is determined in consideration of the characteristics of the cell voltage of each single cell as described above. FIG. 5 is a flowchart showing an example of the bubble determination process. First, it is determined whether the position of the single cell of the lowest cell voltage of the lowest cell voltages among the cell voltages of the single cells acquired by the cell monitor 108 is located on the upper side (step S101). Specifically, it is determined whether or not the single cell having the lowest cell voltage is located between the single cell 10-1 and, for example, the single cell 10- (n / 10). As described above, n indicates the total number of single cells, and single cell 10-(n / 10) is a single cell in which the number of single cells from the upper side corresponds to n / 10.

  In the case of a positive determination in step S101, it is determined whether the value obtained by subtracting the lowest cell voltage from the average cell voltage, which is the average of the cell voltages of all single cells, is equal to or greater than the threshold ΔV (step S103). The average cell voltage may be calculated by dividing the total value of the cell voltages of each single cell detected by the cell monitor 108 by the total number of single cells, or the voltage of the stack 20 detected by the voltage sensor 107 is simply calculated. It may be calculated by dividing by the number of cells. The threshold value ΔV is stored in advance in the ROM of the control device 30.

  In the case of an affirmative determination in step S103, the cell voltage of a single cell located midway between a single cell of the lowest cell voltage and the single cell 10-1 is larger than the lowest cell voltage, and the cell voltage of the single cell 10-1. It is determined whether it is less than (step S105). In the case of an affirmative determination in step S105, it is determined that bubbles remain in the cooling water flow path 16 of the laminate 10 (step S107). If a negative determination is made in any of steps S101, S103, and S105, it is determined that air bubbles do not stay in the cooling water flow path 16 (step S109). Note that it may be determined that bubbles are retained only by the position of the single cell having the lowest cell voltage positioned above the predetermined position. Alternatively, a sensor for detecting the temperature of each single cell may be provided, and it may be determined whether there is stagnation of air bubbles based on the temperature of each single cell instead of the above-described cell voltage. Alternatively, it may be determined that bubbles are retained only by the position of the single cell having the lowest temperature positioned above the predetermined position described above.

  As described above, when it is determined that bubbles remain (Yes in Step S3), a cause determination condition confirmation process is executed (Step S5), and when the cause determination condition is satisfied (Yes in Step S7). ) Cause determination processing is executed (step S9). First, the cause determination condition confirmation process will be described.

  FIG. 6A is a flowchart illustrating an example of cause determination condition confirmation processing in the present embodiment. First, it is determined whether or not the ignition is off based on the output from the ignition switch 101 (step S51). Details of this determination will be described later. In the case of a positive determination in step S51, it is determined based on the detection results of the water temperature sensor 16T and the outside air temperature sensor 102 whether the cooling water temperature has reached the outside air temperature (step S53). For example, when the difference between the cooling water temperature and the outside air temperature falls within a predetermined range that can be regarded as substantially zero, it may be determined that the cooling water temperature has reached the outside air temperature. Details of this determination will be described later.

  If the determination in step S53 is affirmative, it is determined whether or not the voltage of the stack 20 is zero (step S55). Although details will be described later, since the fuel gas and the oxidant gas remain in the stack 20 immediately after the ignition is turned off and the voltage of the stack 20 does not become zero, the process of step S55 is executed. If the determination in step S55 is affirmative, it is determined that the cause determination condition is satisfied (step S57). When a negative determination is made in any of steps S51, S53, and S55, it is determined that the cause determination condition is not satisfied (step S59).

  As described above, when it is determined that the cause determination condition is satisfied after the cause determination condition confirmation process is executed (Yes in step S7), the cause determination process is performed (step S9). FIG. 6B is a flowchart showing an example of the cause determination process in the present embodiment. The tank valve 124, the pressure control valve 125, and the injection valve 126 are controlled to supply a predetermined amount of fuel gas to the fuel gas flow path 12 in a state where the positive determination is made in steps S51, S53, and S55 described above. (Step S91). The tank valve 124, the pressure adjustment valve 125, and the injection valve 126 are an example of a supply unit that supplies fuel gas to the fuel gas flow path 12.

  Next, until a predetermined time elapses after a predetermined amount of fuel gas is supplied to the fuel gas flow channel 12, the amount of increase in pressure in the cooling water flow channel 16 is greater than or equal to the threshold A1 based on the detection result of the water pressure sensor 16P. It is determined whether it has become (step S93). The threshold value A1 is a value for determining the presence or absence of a leak, and is determined based on an experimental result of measuring the pressure in the cooling water flow path 16 after the supply of the fuel gas with and without the leak. It is stored in advance in the ROM of the control device 30. In the case of an affirmative determination in step S93, it is determined that there is a leak, assuming that a part of the fuel gas supplied to the fuel gas channel 12 has leaked to the cooling water channel 16 and the pressure in the cooling water channel 16 has increased. (Step S95). If the determination in step S93 is negative, it is determined that the fuel gas supplied to the fuel gas passage 12 does not affect the pressure in the cooling water passage 16 and that there is no leak (step S97).

  The reason for determining whether the ignition is off as in step S51 is as follows. In the state of ignition on, for example, the required power generation amount of the stack 20 is switched based on the operation amount of the accelerator pedal AP, and the rotational speed of the pump 164 is also adjusted according to the required power generation amount. That is, in the state where the ignition is on, the pressure in the cooling water flow path 16 is in a state of being easily fluctuated. Therefore, even if the leak determination is performed based on the increase in pressure in the cooling water flow passage 16 as described above in the ignition-on state, the increase in pressure in the cooling water flow passage 16 increases the rotational speed of the pump 164. It can not be determined whether it is attributable or due to a fuel gas leak. Therefore, although there is no leak, the amount of pressure increase in the cooling water flow passage 16 may become equal to or greater than the threshold A1 with the increase of the rotational speed of the pump 164, and the leak may be erroneously determined to be present. . On the other hand, since the pump 164 is stopped in the ignition-off state, the pressure in the cooling water passage 16 is not affected by the rotational speed of the pump 164. Therefore, in the present embodiment, by including that the ignition is off in the cause determination condition, the determination accuracy of the leak is improved.

  The reason for determining whether or not the cooling water temperature has become substantially the same as the outside air temperature after the ignition is turned off as in step S53 is as follows. When the ignition is turned off, the demand for power generation to the stack 20 is stopped, and the temperature of the stack 20 gradually decreases and eventually becomes substantially the same as the outside air temperature, and the cooling water temperature is also substantially the same as the outside air temperature. Become. Here, when the temperature of the stack 20 decreases, the stack 10 is thermally shrunk, and the internal volume of the cooling water flow passage 16 increases accordingly, and the pressure in the cooling water flow passage 16 decreases. That is, while the temperature of the stack 20 is decreasing, the pressure in the cooling water channel 16 is also likely to decrease. When the cause determination process is performed in such a state, even if there is no leak, the amount of pressure increase in the coolant flow passage 16 due to the leak and the coolant water flow passage 16 due to the decrease in the temperature of the stack 20 There is a possibility that the amount of decrease in pressure will be offset. As a result, although there is a leak, the amount of increase in pressure in the cooling water flow path 16 may be less than the threshold A1, and it may be erroneously determined that there is no leak. Therefore, in this embodiment, the cause determination condition includes that the cooling water temperature is substantially the same as the outside air temperature, thereby improving the leak determination accuracy. Note that instead of this process, it may be determined whether or not the rate of change of the coolant temperature has become within a predetermined threshold value, in other words, whether the coolant temperature has reached a state where it has not substantially changed.

  The reason for determining whether or not the voltage of the stack 20 is zero after the ignition is turned off as in step S55 is as follows. As described above, the power generation request to the stack 20 is stopped after the ignition is turned off, but the fuel gas and the oxidant gas may remain in the stack 20 in some cases. Due to the reaction of the remaining fuel gas and oxidant gas, the power generation of the stack 20 may continue for a predetermined period even after the ignition is turned off. If the cause determination process is executed during the continuation of the power generation of the stack 20 by the remaining reaction gas, the supplied fuel gas may be consumed by the power generation reaction with the remaining oxidant gas. . In addition, a so-called cross leak occurs in which the fuel gas permeates the electrolyte membrane and flows to the oxidant gas flow channel 14, and the fuel gas and the remaining oxidant gas react in the oxidant gas flow channel 14. Fuel gas may be consumed. For any reason, even if there is a leak of fuel gas from the fuel gas passage 12, the amount of leakage of the fuel gas to the cooling water passage 16 decreases and the amount of increase in the pressure in the cooling water passage 16 increases. Is less than the threshold value A1, and there is a possibility that it may be erroneously determined that there is no leak. Therefore, in the present embodiment, by including that the voltage of the stack 20 is zero in the cause determination condition, the leak determination accuracy is improved. Instead of this processing, it may be determined whether or not the voltage change rate of the stack 20 has become a predetermined threshold value or less.

  In the above embodiment, the order of steps S53 and S55 does not matter. Moreover, the process of step S53 is not essential. The reason is that the temperature of the stack 20 may decrease over a relatively long time after the ignition is turned off, and in this case, the fuel gas leaks even though the temperature of the stack 20 is decreasing. This is because an increase in the pressure in the cooling water passage 16 is not greatly affected, and there is a case where the leak determination accuracy is not significantly affected.

  Next, a plurality of variations of the above control will be described. In the modification, the description of the same processing as that of the above embodiment will be omitted. FIG. 7 is a flowchart showing a variation of the cause determination condition confirmation process. After step S51 described above, it is determined based on the detection result of the pressure sensor 14P whether or not the rate of change in pressure in the oxidant gas flow channel 14 is less than or equal to the threshold value α1 (step S55a). The threshold value α1 is a value that can be regarded as the disappearance of the oxidant gas remaining in the oxidant gas flow channel 14, and is acquired in advance by experiment and stored in the ROM of the control device 30. That is, it is determined whether or not the pressure in the oxidant gas flow path 14 gradually decreases and becomes substantially constant after the ignition is turned off. In the case of a positive determination in step S55a, it is determined that the cause determination condition is satisfied (step S57), and in the case of a negative determination in step S55a, the cause determination condition is determined not to be satisfied (step S59).

  The reason why it is determined whether or not the rate of change in the pressure in the oxidant gas flow path 14 is equal to or less than the threshold value α1 after the ignition is turned off as in step S55a. As described above, the oxidant gas may remain in the oxidant gas flow passage 14 immediately after the ignition is turned off. In this case, even if the fuel gas is supplied to the cooling water flow passage 16, as described above, the cross There is a possibility that a leak occurs and it is erroneously determined that there is no leak even though there is a leak of fuel gas from the fuel gas flow path 12. Therefore, in the present modification, the leak determination accuracy is improved by including the fact that the rate of change of the pressure in the oxidant gas flow channel 14 is equal to or less than the threshold value α1 in the cause determination condition. In the state where the rate of change of pressure in the oxidant gas flow passage 14 becomes equal to or less than the threshold value α1 after the ignition is turned off, the fuel gas remaining in the fuel gas flow passage 12 is already consumed and the fuel gas flow passage The pressure in 12 can be considered substantially constant. Therefore, even if the fuel gas is supplied into the oxidant gas flow channel 14, the accuracy of the leak determination is not affected. Also in the present modification, the above-described step S53 may be included in the cause determination condition.

  FIG. 8A is a flowchart showing a variation of the cause determination condition confirmation process. FIG. 8B is a flowchart showing a variation of the cause determination process. Unlike the case described above, the cause determination condition confirmation process and the cause determination process in the present modified example presuppose that the ignition is on and the process is performed during the power generation of the stack 20. As shown in FIG. 8A, it is determined whether or not the rate of change of the pressure in the cooling water channel 16 is equal to or less than a threshold value α2 (step S55b). The threshold value α2 is a value that can detect an increase in the pressure in the cooling water flow path 16 when the supply amount of a fuel gas to be described later is increased in a state where there is a leak. Stored in ROM. The case where the change rate of the pressure in the cooling water flow path 16 is equal to or less than the threshold value α2 is a case where the change rate of the required power generation amount to the stack 20 is small, for example, in an idle operation state. In such a case, since the rotation speed of the pump 164 is substantially constant, the rate of change of the pressure in the cooling water channel 16 tends to be equal to or less than the threshold value α2. In the case of a positive determination in step S55b, it is determined that the cause determination condition is satisfied (step S57). In the case of a negative determination in step S55b, it is determined that the cause determination condition is not established (step S59).

  Further, in the cause determination process according to the present modification, as shown in FIG. 8B, the stack 20 is supplied such that the pressure of the fuel gas passage 12 becomes higher than the pressure in the cooling water passage 16 as shown in FIG. The fuel gas supply amount is increased by a predetermined amount from a predetermined fuel gas supply amount according to the required power generation amount (step S91b). Next, based on the detection result of the water pressure sensor 16P, it is determined whether the amount of increase in pressure in the cooling water flow passage 16 has become equal to or greater than the threshold A2 until a predetermined time elapses after the amount of supplied fuel gas is increased. (Step S93b). The threshold value A2 is a value for determining whether or not there is a leak, and is an experimental result of measuring the pressure in the cooling water passage 16 after the increase in the supply amount of fuel gas in the case where there is a leak and in the case where there is no leak. And is stored in advance in the ROM of the control device 30. If it is determined that there is a leak in this modification, the power generation of the stack 20 may be forcibly stopped.

  Note that the following processing may be executed instead of the processing in step S93b. First, referring to the map defining the relationship between the rotational speed of the pump 164 in the normal state with no leak, the temperature of the cooling water, and the pressure in the cooling water flow path 16, the coolant flow path 16 in the normal state with no leak Calculate internal pressure (referred to as normal pressure). The normal pressure increases as the rotation speed of the pump 164 increases, and decreases as the cooling water temperature increases. Next, it is determined whether or not a value obtained by subtracting the normal pressure from the actual pressure (referred to as an actual pressure) in the cooling water flow path 16 detected by the water pressure sensor 16P is equal to or greater than a predetermined threshold. In the case of an affirmative determination, it is determined that there is a leak as the actual pressure has increased more than the normal pressure due to the increase in the supply amount of fuel gas. In the case of a negative determination, it is determined that the actual pressure is substantially equal to the normal pressure and there is no leak.

  In the modification shown in FIGS. 8A and 8B, since the ignition is executed in an on state, the bubble discharge prohibiting process in this modification is executed by stopping the power supply to the pump 164. For this reason, the power consumption by the pump 164 is suppressed. The power supply to the pump 164 is stopped, and the power generation of the stack 20 is also stopped. Further, the bubble discharge prohibiting process in the present modification may be executed by setting the upper limit guard value of the rotational speed of the pump 164 to a value smaller than the upper limit guard value when it is determined that there is no leak. Good. Thereby, the power consumption of the pump 164 accompanying the bubble discharge process is suppressed. Note that the upper limit guard value switched when it is determined that there is a leak is set to a value slower than the maximum rotation speed of the pump 164 when the bubble discharging process is performed.

  FIG. 9 is a flowchart showing a variation of the cause determination process. In this modification, as shown in FIGS. 6A and 7, it is assumed that the cause determination condition includes that the ignition is off. It is determined whether the amount of decrease in pressure in the fuel gas flow path 12 within the predetermined period after execution of step S91 is equal to or greater than the threshold A3 (step S93c). The threshold value A3 is a value for determining whether or not there is a leak, and is based on the experimental results of measuring the pressure in the fuel gas passage 12 after the fuel gas is supplied in the case where there is a leak and in the case where there is no leak. And is stored in advance in the ROM of the control device 30. The pressure in the fuel gas passage 12 rises during the supply of the fuel gas, but if there is no leak after the stop of the supply, the amount of decrease in the pressure in the fuel gas passage 12 is small, but if there is a leak The amount of decrease in pressure in the fuel gas channel 12 increases. Thus, the leak can be determined based on the amount of decrease in the pressure in the fuel gas passage 12 rather than the amount of increase in the pressure in the cooling water passage 16. Note that it may be determined that there is a leak only when both steps S93 and S93c are positively determined. This improves the accuracy of leak determination.

  FIG. 10A is a flowchart of a variation of the cause determination process. This modification is based on the cause determination conditions shown in FIGS. 6A and 7. Unlike the above-described cause determination process, instead of supplying the fuel gas to the fuel gas flow path 12, the air compressor 149 and the like are controlled to supply a predetermined amount of oxidant gas to the oxidant gas flow path 14 (step S91 d). The air compressor 149 is an example of a supply unit for supplying the oxidant gas to the oxidant gas flow channel 14. Next, the process of step S93 is performed as in the case described above. When the oxidant gas leaks from the oxidant gas flow channel 14 to the cooling water flow channel 16, the pressure increase amount in the cooling water flow channel 16 becomes equal to or more than the threshold value A1, and it is determined that there is a leak. Thus, it can be determined whether or not there is a leak due to a decrease in sealing performance between the oxidant gas flow path 14 and the cooling water flow path 16 by supplying the oxidant gas.

  FIG. 10B is a flowchart of a modification of the cause determination process. This modification is premised on the cause determination condition shown in FIG. 6A and FIG. After the predetermined amount of the oxidant gas is supplied to the oxidant gas flow channel 14 (step S91 d), it is determined whether the amount of pressure reduction in the oxidant gas flow channel 14 is equal to or greater than the threshold A4 (step S91) S93 d). The threshold value A4 is a value for determining whether or not there is a leak, and is an experimental result of measuring the pressure in the oxidant gas flow path 14 after the supply of the oxidant gas depending on whether or not there is a leak. And is stored in advance in the ROM of the control device 30. The pressure in the oxidant gas flow path 14 rises during the supply of the oxidant gas, but if there is no leak after the stop of the supply, the amount of decrease in the pressure in the oxidant gas flow path 14 is small, but there is a leak In this case, the amount of pressure reduction in the oxidant gas flow channel 14 is large. Note that it may be determined that there is a leak only when both steps S93 and S93d are positively determined. 10A and 10B, the oxidant gas is supplied to the stack 20 with almost no fuel gas in the fuel gas flow path 12. As a result, the stack 20 may become hydrogen starved and affect the power generation performance of the stack 20. Therefore, in the modification of FIG. 10A and FIG. 10B, it may be executed when there is a high possibility that there is a leak or when the remaining amount of fuel gas in the tank 110 is substantially zero.

  FIG. 11A is a flowchart of a variation of the cause determination condition confirmation process. FIG. 11B is a flowchart of a variation of the cause determination process. The cause determination process of FIG. 11B is premised on the cause determination condition confirmation process of FIG. 11A. It is determined whether the voltage of the stack 20 is other than zero (step S51e). That is, it is determined whether the stack 20 is generating power. If the determination in step S51e is affirmative, it is determined whether or not the voltage change rate of the stack 20 is equal to or less than a threshold value α3 (step S55e). That is, it is determined whether the amount of power generation is substantially constant although the stack 20 is generating power. If the determination in step S55e is affirmative, it is determined that the cause determination condition is satisfied (step S57). If a negative determination is made in either step S51e or S55e, the cause determination condition is determined not to be satisfied (step S59).

  Next, as shown in FIG. 11B, the supply amount of the fuel gas is increased by a predetermined amount (step S91b). Next, before and after the increase of the fuel gas supply amount, the position of the single cell that outputs the lowest cell voltage among the cell voltages of the plurality of single cells based on the detection result of the cell monitor 108 has moved downward in the direction of gravity. It is determined whether or not (step S93e). The process of step 93 e will be described in detail later. In the case of a positive determination in step S93 e, it is determined that there is a leak (step S95), and in the case of a negative determination, it is determined that there is no leak (step S97).

  Next, the process of step S93 e described above will be described. 12A to 12F are explanatory diagrams of changes in cell voltages of a plurality of single cells. 12A to 12C correspond to FIGS. 4D to 4F, respectively, showing the case where bubbles are retained in the cooling water flow path 16. When the supply amount of fuel gas is increased in a state where air bubbles stay in cooling water flow path 16, if there is a leak, the air bubbles that were staying in cooling water flow path 16 on the upper side in the gravity direction Bubbles resulting from the increase in the gas supply amount are further added, and the bubbles increase as shown in FIG. 12D. Accordingly, as shown in FIG. 12E, the position of the single cell having the highest temperature among the plurality of single cells moves to the lower side in the direction of gravity. Accordingly, as shown in FIG. 12F, the position of the single cell that outputs the lowest cell voltage moves to the lower side in the direction of gravity. In step S93e, the lowest cell voltage after the increase is obtained as compared with the single cell that outputs the lowest cell voltage before the increase thus obtained by acquiring the position of the single cell before and after the increase in fuel gas. It is determined whether or not the single cell outputting the signal is at the lower side in the direction of gravity. In the example of FIGS. 12C and 12F, the case where the single cell that outputs the lowest cell voltage is changed from the single cell 10-4 to the single cell 10-6 is shown. In addition, when a sensor for detecting the temperature of each single cell is provided to increase the supply amount of the fuel gas or the oxidant gas, the position of the single cell having the highest temperature moves downward in the direction of gravity to cause a leak. It may be determined that there is.

  The supply amount of the oxidant gas may be increased instead of step S91 b. Further, it may be determined that there is a leak when the positive determination is made in step S93 e and the amount of increase in pressure in the cooling water flow path 16 is higher than the threshold as in step S93 b. Further, if the determination in step S93e is affirmative and the amount of decrease in pressure in the fuel gas flow path 12 is greater than a threshold value, it may be determined that there is a leak.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. Changes are possible.

DESCRIPTION OF SYMBOLS 1 fuel cell system 10 laminated body 12 fuel gas flow path 12P pressure sensor 14 oxidant gas flow path 14P pressure sensor 16 cooling water flow path 16P water pressure sensor 20 fuel cell stack 30 control device (bubble determination unit, cause determination unit)
103 HMI device (warning device)
120 Hydrogen gas supply system (supply unit)
124 Tank valve 125 Pressure control valve 126 Injection valve 140 Air supply system (supply device)
149 Air compressor 160 Cooling water supply system 164 pump

Claims (6)

A stacked body in which a plurality of unit cells are stacked and the unit cell on one end side is positioned on the upper side in the direction of gravity than the unit cell on the other end side, a reaction gas flow path formed in the stack, the stack A fuel cell stack having a cooling water flow path formed in the body and extending from the unit cell at the other end to the unit cell at the one end and again extending to the unit cell at the other end;
A pump for supplying cooling water to the cooling water flow path;
A supply device for supplying a reaction gas to the reaction gas flow path;
A bubble determination unit that determines whether or not bubbles remain in the cooling water flow path, and the reaction from the reaction gas flow path is the cause of the bubble retention when the bubble determination unit determines that bubbles remain. A control unit that includes a cause determination unit that determines whether the gas leaks or not;
Fuel cell system equipped with   2. The fuel cell system according to claim 1, further comprising a removing device that removes the accumulated bubbles from the cooling water flow path when it is determined that the cause of the bubble retention is not leakage of the reaction gas from the reaction gas flow path. .   The fuel cell system according to claim 2, wherein the removing device is the pump that discharges bubbles from the cooling water flow path by increasing or decreasing a rotation speed.   The fuel cell system according to any one of claims 1 to 3, further comprising: a warning device that warns when it is determined that the cause of the bubble retention is a leak of the reaction gas from the reaction gas flow path.   When the pump is stopped and the supply device supplies the reaction gas to the reaction gas flow path, the cause determining unit is configured to increase the pressure in the cooling water flow path to a predetermined value or more. It is determined that the cause of the bubble retention is a leak of the reaction gas from the reaction gas flow channel in at least one of the cases where the pressure decrease amount in the reaction gas flow channel is less than or equal to a predetermined value. A fuel cell system according to any one of 1 to 4.   When the supply device increases the supply amount of the reaction gas to the reaction gas flow path, the cause determining unit determines that the position of the single cell having the lowest cell voltage among the plurality of single cells is directed downward in the direction of gravity. When at least one of the plurality of unit cells and the position of the unit cell having the highest temperature among the plurality of unit cells has moved downward in the direction of gravity, the cause of the bubble retention is from the reaction gas flow path. The fuel cell system according to any one of claims 1 to 4, wherein it is determined that the reaction gas leaks.

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