JP2012004136A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which can restrict the output of a fuel cell when air is determined to be trapped in coolant so as to suppress, in advance, heat generation by the fuel cell, thereby preventing the damage of fuel cell due to insufficient cooling.SOLUTION: A fuel cell system has a cooling system which circulates and supplies coolant to a fuel cell stack 1 by means of a coolant pump 4. Determination means in a controller 5 determines whether or not air is trapped in the coolant based on a detection result from state detection means (coolant pressure sensor 6) which detects the state of coolant. Output control means in the controller 5 restricts the output of fuel cell stack 1 if the determination means has determined that air is trapped in the coolant.

Description

  The present invention relates to a fuel cell system, and in particular, can prevent damage due to poor cooling of the fuel cell, and prevent erroneous diagnosis that the cooling mechanism based on rapid pressure fluctuations or fluctuations in the number of revolutions of the coolant pump is abnormal. The present invention also relates to a fuel cell system that can make an accurate abnormality determination.

  The fuel cell system supplies hydrogen as a fuel gas to the fuel electrode of the fuel cell, supplies air as the oxidant gas to the oxidant electrode of the fuel cell, and causes the hydrogen and oxygen in the air to react electrochemically. To obtain generated power. Such a fuel cell system is highly expected to be put into practical use, for example, as a power source for automobiles, and research and development for practical use are being actively carried out.

  As a fuel cell used in a fuel cell system. For example, a solid polymer type fuel cell is known as being suitable for mounting in an automobile. A solid polymer type fuel cell is provided with a solid polymer membrane as an electrolyte membrane between a fuel electrode and an oxidant electrode. In this solid polymer type fuel cell, the solid polymer membrane functions as an ion conductor, a reaction occurs in which hydrogen is separated into hydrogen ions and electrons at the fuel electrode, and oxygen and hydrogen in the air at the oxidant electrode. A reaction for generating water from ions and electrons is performed.

  In such a fuel cell system, a solid polymer type fuel cell has a relatively low proper operating temperature of about 80 ° C., and it is necessary to cool it when it is overheated. A liquid-type cooling mechanism for circulating the liquid to the fuel cell and the radiator is provided.

  If this cooling mechanism fails, the fuel cell cannot be maintained at an appropriate operating temperature, and the fuel cell cannot be maintained in a good power generation state. Therefore, if a failure occurs in the cooling mechanism, this is detected early and appropriate Measures need to be taken. For example, in “Failure detection method of fuel cell cooling system” of Japanese Patent Application Laid-Open No. 2004-178849, in a fuel cell cooling system in which cooling water is sent to a cooling water passage in the fuel cell by a cooling water pump to cool the fuel cell, Technology for determining that the fuel cell cooling system has failed when the difference in cooling water pressure between the cooling water inlet and the cooling water outlet of the battery continues below a threshold value determined by the number of rotations of the cooling water pump for a predetermined time. Has been proposed.

JP 2004-178849 A

  However, in the fuel cell cooling system using the cooling water disclosed in Patent Document 1 described above, there is a possibility that air may be mixed into the cooling water. In this case, the pressure sensor provided in the cooling line is temporarily used. The cooling water pressure may decrease significantly, and the cooling water pump may temporarily increase the rotational speed.

  A small amount of aerated air will not cause damage to the fuel cell stack due to poor cooling, but in a system that diagnoses cooling line abnormalities based on the cooling water pressure or the cooling water pump speed, these temporary pressure drops or There is a possibility that the fuel cell cooling system may be judged to have failed due to the increase in the rotational speed.

  Also, assuming that air is mixed into the cooling water and the system that does not determine the cooling line abnormality unless the pressure drop has elapsed for a predetermined time, if there are many bubbles, the abnormality can be determined accurately. In other words, the fuel cell stack may be adversely affected by poor cooling.

  The present invention has been made in view of the above-described conventional circumstances, and restricts the output of the fuel cell when it is determined that air is mixed in the coolant, thereby suppressing the heat generation of the fuel cell to be low. An object of the present invention is to provide a fuel cell system capable of preventing damage due to poor cooling of the fuel cell.

  Another object of the present invention is to provide a fuel cell system capable of making an accurate abnormality determination by preventing a false diagnosis that the cooling mechanism is abnormal based on sudden pressure fluctuations or fluctuations in the rotation speed of the coolant pump. There is to do.

  In order to solve the above-described object, the present invention provides a fuel cell that generates power by supplying fuel gas and oxidant gas, a cooling system that circulates coolant to the fuel cell by a coolant pump, and a state of the coolant State detecting means for detecting the air, determination means for determining whether or not air is mixed in the coolant based on the detection result of the state detecting means, and air being mixed in the cooling liquid by the determining means Output control means for limiting the output of the fuel cell when it is determined that the state detection means is a coolant temperature detection means for detecting the temperature of the coolant, and the determination means is the cooling When the actual rotational speed of the liquid pump is a predetermined time from the upper limit threshold value of the target rotational speed of the coolant pump calculated from at least one of the output of the fuel cell or the coolant temperature detection value by the coolant temperature detection means Exceeded only within, if thereafter again below the upper threshold returns to the vicinity of the target speed, characterized by determining that the air is mixed in the coolant.

  In the fuel cell system according to the present invention, the determination means determines whether air is mixed in the coolant based on the detection result of the state detection means for detecting the state of the coolant, and the output control means determines the determination means. Therefore, the output of the fuel cell is limited when it is determined that air is mixed in the coolant, so that the heat generation of the fuel cell can be suppressed to a low level and damage due to poor cooling of the fuel cell can be prevented.

1 is a configuration diagram of a fuel cell system according to an embodiment of the present invention. It is explanatory drawing explaining the relationship between air mixing in a cooling fluid, and a cooling fluid pressure (stack inlet). 6 is a flowchart for explaining a processing procedure for limiting the output of the fuel cell stack 1 when air is mixed into the coolant. It is explanatory drawing explaining the output restriction | limiting of the fuel cell stack 1 according to the air mixing amount to a cooling fluid. 6 is a timing chart for explaining the timing of output limitation of the fuel cell stack 1 performed when air is mixed into the coolant. It is explanatory drawing explaining the relationship between air mixing in a cooling fluid, and the rotation speed of the cooling fluid pump.

  Hereinafter, embodiments of the fuel cell system of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. The fuel cell system of this embodiment is used as a driving power source of a fuel cell vehicle, for example, and includes a fuel cell stack 1 that generates power by supplying hydrogen and air as shown in FIG.

  Further, as a cooling mechanism, a radiator 2, a radiator fan 2b, a coolant line 3, a coolant pump 4, a coolant pressure sensor (stack inlet) 6, a coolant temperature sensor (stack inlet) 7, and a coolant temperature sensor (stack outlet) ) 8 and a controller 5 as a control system.

  The fuel cell stack 1 includes a fuel cell to which hydrogen as a fuel gas and an oxidant electrode to which air as an oxidant gas is supplied are stacked with an electrolyte interposed therebetween. It has a stack structure in which power generation cells are stacked in multiple stages, and converts chemical energy into electrical energy by an electrochemical reaction based on hydrogen and oxygen in the air. In each power generation cell of the fuel cell stack 1, a reaction occurs in which hydrogen supplied to the fuel electrode is separated into hydrogen ions and electrons, the hydrogen ions pass through the electrolyte, and the electrons pass through an external circuit to generate electric power. , Move to the oxidizer electrode. At the oxidizer electrode, hydrogen in the supplied air reacts with hydrogen ions and electrons that have moved through the electrolyte to produce water, which is discharged to the outside.

  As the electrolyte of the fuel cell stack 1, for example, a solid polymer electrolyte membrane is used in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte membrane is made of an ion (proton) conductive polymer membrane such as a fluororesin ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water.

  In order to generate power with the fuel cell stack 1, it is necessary to supply hydrogen, which is fuel gas, or air, which is oxidant gas, to the fuel electrode or oxidant electrode of each power generation cell. As a mechanism, a hydrogen supply system (hydrogen tank, pressure control valve, hydrogen supply flow path, etc.) and an air supply system (compressor, air supply flow path, etc.) are provided, but are not directly related to the present invention. The description of the function and the like is omitted.

  A cooling mechanism for cooling the fuel cell stack 1 is also provided. For example, the solid polymer electrolyte fuel cell stack 1 has a relatively low proper operating temperature of about 80 ° C., and it is necessary to cool the heat generated by the power generation of the fuel cell stack 1 and keep the fuel cell stack 1 at an appropriate temperature. There is. The cooling mechanism has a cooling liquid line 3 and a cooling liquid pump 4 for circulating the refrigerant, and cools the fuel cell stack 1 by circulating a cooling liquid in which an antifreezing agent such as ethylene glycol is mixed in water, for example. Maintain optimal temperature.

  A radiator 2 is provided in the coolant line 3 of the cooling mechanism. The radiator 2 is operation-controlled by the controller 5, and the temperature of the coolant is adjusted by the radiator fan 2 b so that the outlet temperature of the radiator 2 becomes a desired temperature. That is, at least a temperature sensor 7 for detecting the coolant temperature at the inlet of the fuel cell stack 1 provided in the cooling line 3 or a temperature sensor 8 for detecting the coolant temperature at the outlet of the fuel cell stack 1. Using one value, the controller 5 controls the rotational speed of the radiator fan 2b of the radiator 2 and the rotational speed of the coolant pump 4 so that the fuel cell stack 1 has an appropriate temperature.

  Further, the controller 5 of the control system is configured as a microcomputer having, for example, a CPU, ROM, RAM, peripheral interface, etc., and reads various detection values of various sensors, and performs various controls according to judgments and calculation results for the detection values. A signal is output to control the operation of each part of the fuel cell system.

  The controller 5 of the present embodiment includes a determination unit and an output control unit as its components, and these units represent a functional group of programs executed on the CPU. The judging means judges whether or not air is mixed in the cooling liquid based on the detection result of the state detecting means for detecting the state of the cooling liquid (in this embodiment, the cooling liquid pressure sensor 6 corresponds), and outputs control. The means limits the output of the fuel cell stack 1 when it is determined by the determination means that air is mixed in the coolant.

  More specifically, the state detecting means is a cooling liquid pressure detecting means (cooling liquid pressure sensor 6) for detecting the pressure of the cooling liquid, and the judging means is a cooling liquid pressure detecting means (cooling liquid pressure sensor 6). When the detected coolant pressure value falls below the lower limit threshold value of the estimated coolant pressure value estimated from the number of revolutions of the coolant pump 4 within a predetermined time and then exceeds the lower limit threshold value again, air enters the coolant. Judge that

  Further, the output control means changes the output upper limit value of the fuel cell stack 1 according to the length per unit time during which the coolant pressure detection value in the determination means is below the lower limit threshold value of the coolant pressure estimation value. Let Further, when it is determined by the determination means that air is mixed in the coolant, the timing of inflow into the fuel cell stack 1 or the timing of outflow from the fuel cell stack 1 at the location where air in the coolant is mixed. At the same time, the output limitation of the fuel cell stack 1 is started or ended.

  Next, operations during operation of the fuel cell system of the present embodiment configured as described above will be described with reference to FIGS. 2, 3, 4, and 5. Here, FIG. 2 is an explanatory diagram for explaining the relationship between air mixing into the coolant and coolant pressure (stack inlet), and FIG. 3 limits the output of the fuel cell stack 1 when air is mixed into the coolant. FIG. 4 is a flowchart for explaining the processing procedure, FIG. 4 is an explanatory diagram for explaining the output restriction of the fuel cell stack 1 according to the amount of air mixed into the coolant, and FIG. 5 is the fuel that is used when air is mixed into the coolant. 4 is a timing chart for explaining output restriction timing of the battery stack 1.

  If the coolant does not circulate normally, the fuel cell stack 1 may not be able to obtain stable power, and in the worst case, the fuel cell stack 1 may be damaged. Cooling system anomalies must be constantly monitored. Therefore, in this embodiment, the coolant pressure sensor 6 for detecting the coolant pressure at the inlet of the fuel cell stack 1 provided in the coolant line 3 is used, and the value of the coolant pressure sensor 6 is the value of the coolant pump 4. If the estimated coolant pressure estimated from the rotational speed is far from the estimated value, the cooling mechanism of the fuel cell system, such as failure of the coolant pump 4, clogging of the cooling line 3, or water leakage from the cooling line 3, etc. The fuel cell system is stopped.

  However, in the cooling mechanism of the fuel cell system using the cooling liquid, there is a possibility that air is mixed into the cooling liquid. In this case, for example, as shown in FIG. 2, the cooling liquid pressure sensor 6 provided in the cooling line 3. In some cases, the coolant pressure is temporarily reduced and then recovered. Although a small amount of air does not cause damage to the fuel cell stack 1 due to poor cooling, in a system that diagnoses an abnormality in the cooling mechanism of the fuel cell system based on the pressure of the coolant, the fuel pressure is reduced by these temporary pressure drops. It may be judged that there is an abnormality in the cooling mechanism of the battery system, and the operation of the fuel cell system may be stopped.

  Therefore, in the present embodiment, the coolant pressure detection value P of the coolant pressure sensor 6 is lower than the lower limit threshold value Pmin of the coolant pressure estimated value estimated from the rotational speed of the coolant pump 4, and is lower than the lower limit threshold value Pmin. When the pressure drop time integrated value C that integrates the state time exceeds the lower limit threshold Pmin again before the predetermined time Cmax elapses, it is determined that air is mixed in the coolant, and the cooling mechanism has a failure. Do not judge. For example, in FIG. 2, the coolant pressure detection value P is lower than the lower limit threshold value Pmin of the coolant pressure estimated value during the periods T11 to T12 and T13 to T14. Since it has not elapsed, it is not determined that the cooling mechanism has failed.

  Note that the air mixed in the coolant has different effects on the cooling of the fuel cell stack 1 depending on the amount of the air. That is, the greater the amount of air mixed in, the less heat that can be taken from the fuel cell stack 1, and thus the cooling becomes disadvantageous. Therefore, in the present embodiment, as shown in FIG. 4, the output upper limit value of the fuel cell stack 1 according to the length of time (pressure drop abnormal time) during which the coolant pressure per unit time is below the lower limit threshold Pmin. Is changing. For example, in FIG. 4, until the abnormal pressure drop per unit time exceeds Tα and reaches Tβ, the output upper limit value of the fuel cell stack 1 is gradually decreased from the normal value Wmaxa to Wmaxb (in an inversely proportional relationship). If the abnormal pressure drop per unit time exceeds Tβ, the power generation is stopped and the power extraction from the fuel cell stack 1 is stopped.

  As described above, the larger the amount of air mixed in the coolant, the lower the output upper limit value of the fuel cell stack 1. Therefore, the amount of heat generated in the fuel cell stack 1 can be suppressed, and damage to the fuel cell stack 1 due to poor cooling can be prevented. it can. On the contrary, in a situation where the amount of mixed air is very small and the cooling of the fuel cell stack 1 is hardly affected, almost full output can be taken out from the fuel cell stack 1.

  Further, even when air contamination is detected in the coolant, the cooling of the fuel cell stack 1 is adversely affected only when the coolant in which air is mixed flows in the fuel cell stack 1, The air in the coolant that is not inside the fuel cell stack 1 does not affect the cooling of the fuel cell stack 1. Therefore, in this embodiment, as shown in FIG. 5, the flow rate of the coolant is obtained from the number of revolutions of the coolant pump 4 or a flow meter installed in the cooling line 3, and the time in the coolant is determined from the time when the pressure drop is detected. The time (tb−ta) until the part where the air is mixed flows into the fuel cell stack 1 (tb) is calculated, and the part where the air in the coolant is mixed flows into the fuel cell stack 1 ( The time (tc−tb) from tb) to the outflow (tc) is calculated, and the output upper limit of the fuel cell stack 1 is adjusted in accordance with the timing when the location where the air in the coolant is mixed enters and exits the fuel cell stack 1. The output is limited by changing the value. As a result, the time during which the output is limited can be shortened as much as possible, and unnecessary power shortage can be avoided.

  Next, a processing procedure for limiting the output of the fuel cell stack 1 when air is mixed into the coolant will be described with reference to the flowchart of FIG. Note that the series of processing in FIG. 3 is repeatedly executed at predetermined time intervals.

  First, it is determined whether or not the coolant pressure detection value P of the coolant pressure sensor 6 exceeds the lower limit threshold value Pmin of the coolant pressure estimated value estimated from the rotational speed of the coolant pump 4 (step S102).

  In step S102, if the detected coolant pressure value P is equal to or lower than the lower limit threshold value Pmin of the estimated coolant pressure value, it is determined that air may have entered the coolant. The pressure drop time integration value C, which integrates the time during which the fluid pressure estimated value is below the lower limit threshold Pmin, is counted up (step S107). Here, the initial value C (0) of the pressure drop time integrated value C is “0”.

  Next, it is determined whether or not the pressure drop time integrated value C is equal to or greater than a predetermined value Cmax (step S108). In step S108, when the state where the coolant pressure detection value P is below the lower limit threshold value Pmin of the coolant pressure estimated value continues for a predetermined time Cmax (the pressure drop time integrated value C is equal to or greater than the predetermined value Cmax), the fuel cell system. It is determined that a failure has occurred in the cooling mechanism, and power generation is stopped (step S109). In step S108, when the pressure drop time integrated value C has not reached the predetermined value Cmax, the output restriction processing routine is terminated.

  On the other hand, in step S102, if the detected coolant pressure value P exceeds the lower limit threshold value Pmin of the estimated coolant pressure value, the current state is normal at this time, but air is mixed into the coolant immediately before and then recovered. Since there is also a possibility, based on the pressure drop time integrated value C, it is determined whether or not it has been recovered after the coolant pressure has temporarily dropped (step S103).

  In step S103, if the pressure drop time integrated value C is "0", the process routine is terminated without restricting the output because air is not mixed in the coolant immediately before recovery.

  In step S103, if the pressure decrease time integrated value C is greater than “0”, it is determined that the coolant pressure has been recovered immediately after the temporary decrease in the coolant pressure. An output upper limit value Wmax is calculated to limit the output (step S104).

  Here, as shown in FIG. 4, the output upper limit value Wmax is a function f (C) of the pressure drop time integrated value C, and is a pressure drop abnormality per unit time obtained based on the pressure drop time integrated value C. It is calculated as a value that decreases from Wmaxa to Wmaxb according to time.

  Further, as shown in the output restriction timing chart of FIG. 5, the time from the time when the pressure drop is detected (ta) to the time when the location where the air in the coolant is mixed flows into the fuel cell stack 1 (tb). In (tb−ta), the main power limit is not performed and the output upper limit value is kept at Wmaxa, and the portion where the air in the coolant is mixed flows into the fuel cell stack 1 until it flows out from (tb) to (tc). The output is limited to the output upper limit value Wmax = f (C) at time (tc−tb). Here, times (tb-ta) and (tc-tb) are functions g1 (s) and g2 (s) of the flow rate s of the coolant, respectively.

  After performing the output restriction in step S104, the pressure drop time integrated value C is returned to the initial value “0” (step S105), and the processing routine is terminated.

  As described above, in the fuel cell system according to this embodiment, in the fuel cell system including the cooling system that circulates and supplies the coolant to the fuel cell stack 1 by the coolant pump 4, the cooling is performed by the determination unit in the controller 5. Based on the detection result of the state detection means (cooling liquid pressure sensor 6) for detecting the state of the liquid, it is determined whether or not air is mixed in the cooling liquid, and the output control means in the controller 5 uses the determination means for cooling. When it is determined that air is mixed in the liquid, the output of the fuel cell stack 1 is limited. Thereby, the heat generation of the fuel cell stack 1 can be suppressed to a low level, and damage due to poor cooling of the fuel cell stack 1 can be prevented.

  Further, in the fuel cell system of the present embodiment, the state detection means is the coolant pressure detection means (coolant pressure sensor 6) for detecting the coolant pressure, and the determination means in the controller 5 uses the coolant pressure detection means ( Cooling is detected when the detected value of the coolant pressure by the coolant pressure sensor 6) falls below the lower limit threshold of the estimated coolant pressure estimated from the number of revolutions of the coolant pump 4 within a predetermined time and then exceeds the lower limit threshold again. Judge that air is mixed in the liquid. As a result, it is possible to prevent a false diagnosis that the cooling mechanism based on abrupt pressure fluctuations due to air mixing into the cooling liquid is abnormal, and a new device for detecting air mixing in the cooling liquid. Since installation is not necessary, the apparatus cost can be kept low.

  Further, in the fuel cell system of the present embodiment, in the output control means in the controller 5, per unit time of the time during which the coolant pressure detection value in the determination means in the controller 5 is below the lower limit threshold value of the coolant pressure estimation value. The output upper limit value of the fuel cell stack 1 is changed according to the length of. As a result, when it is estimated that the estimated time of the coolant pressure value is below the lower limit threshold and the amount of air mixed in the coolant is large, the fuel cell stack 1 is set to a lower output upper limit value to reduce the fuel cell stack 1. Heat generation of the stack 1 can be suppressed to a low level, and damage due to poor cooling of the fuel cell stack 1 can be prevented. On the other hand, when the air mixing amount is estimated to be a very small amount, the maximum output can be taken out from the fuel cell stack 1, and unnecessary output limitation can be avoided.

  Furthermore, in the fuel cell system of the present embodiment, when it is determined by the determination means in the controller 5 that air is mixed in the coolant, the fuel cell stack 1 at the location where the air in the coolant is mixed. The output limitation of the fuel cell stack 1 is started or ended in accordance with the inflow timing of the fuel cell or the outflow timing from the fuel cell stack 1. As a result, it is possible to shorten the time for limiting the output to the fuel cell stack 1 as much as possible, and to minimize power shortage due to the output limitation.

(Embodiment 2)
Next, a fuel cell system according to Embodiment 2 of the present invention will be described. The fuel cell system of the second embodiment is cooled from the difference between two values of the value of the coolant pressure sensor 6 and the estimated value of the coolant pressure estimated from the rotation speed of the coolant pump 4 in the fuel cell system of the first embodiment. While the presence or absence of air mixing in the liquid is determined, the actual rotational speed of the coolant pump 4 and the target rotational speed of the coolant pump 4 calculated from at least one of the output of the fuel cell stack 1 or the temperature of the coolant. The presence or absence of air in the coolant is determined from the difference between the two.

  The configuration of the fuel cell system of Embodiment 2 is the same as that of Embodiment 1 (FIG. 1), and a specific description of each component will be omitted.

  As in the first embodiment, the controller 5 includes, as its components, a determination unit that determines whether or not air is mixed in the coolant based on the detection result of the state detection unit, Output control means for limiting the output of the fuel cell stack 1 when it is determined that air is mixed, the state detection means is a coolant temperature detection means (coolant temperature) that detects the temperature of the coolant. The sensor (stack inlet) 7 and the coolant temperature sensor (stack outlet) 8) are used, and in the judging means, the actual rotational speed of the coolant pump 4 is the output of the fuel cell stack 1 or the coolant temperature detection value by the coolant temperature detecting means. It exceeds the upper limit threshold of the target rotational speed of the coolant pump 4 calculated from at least one of them within a predetermined time, and then falls below the upper threshold again and returns to the vicinity of the target rotational speed. In case, that it is determined that air is mixed in the cooling liquid it is different from the first embodiment.

  Further, in the output control means, the output upper limit value of the fuel cell stack 1 is set according to the length per unit time in which the actual rotation speed of the coolant pump 4 in the determination means exceeds the upper limit threshold value of the target rotation speed. The point of changing is also different from the first embodiment. Furthermore, when it is determined by the determining means that air is mixed in the coolant, the inflow timing to the fuel cell stack 1 or the fuel at the location where the air in the coolant is mixed is the same as in the first embodiment. The output restriction of the fuel cell stack 1 is started or ended in accordance with the flow-out timing from the battery stack 1.

  Next, the operation during operation of the fuel cell system of the present embodiment configured as described above will be described with reference to FIG. Here, FIG. 6 is an explanatory diagram for explaining the relationship between air mixing into the coolant and the rotational speed of the coolant pump 4.

  In the cooling mechanism of the fuel cell system using the coolant, when air is mixed into the coolant, for example, as shown in FIG. 6, the actual rotational speed of the coolant pump 4 temporarily increases, and then the original target rotation. The rotational speed may return to around the number Rset. Therefore, in the present embodiment, the upper limit of the target rotational speed of the coolant pump 4 in which the actual rotational speed of the coolant pump 4 is calculated from at least one of the output of the fuel cell stack 1 or the coolant temperature detection value by the coolant temperature detection means. The rotation speed increase time integration value C that integrates the time exceeding the threshold value Rmax and exceeding the upper limit threshold value Rmax again falls below the upper limit threshold value Rmax and near the target rotation speed Rset until the predetermined time Cmax has elapsed. In the case of returning to, it is determined that air is mixed in the coolant, and it is not determined that the cooling mechanism has a failure. For example, in FIG. 6, the actual rotational speed of the coolant pump 4 exceeds the upper limit threshold value Rmax of the target rotational speed during the periods T21 to T22 and T23 to T24, but those periods have passed a predetermined time Cmax. Therefore, it is not determined that the cooling mechanism has failed.

  Further, as in the first embodiment (see FIG. 4), the length of time during which the actual rotational speed of the coolant pump 4 per unit time exceeds the upper limit threshold value Rmax of the target rotational speed (rotational speed increase abnormal time) is set. Accordingly, the output upper limit value of the fuel cell stack 1 is changed. For example, as in FIG. 4, the output upper limit value of the fuel cell stack 1 is gradually increased from the normal value Wmaxa to Wmaxb (in an inversely proportional relationship) until the rotation speed increase abnormal time per unit time exceeds Tα and reaches Tβ. ) When the rotational speed increase abnormal time per unit time exceeds Tβ, the power generation is stopped and the power extraction from the fuel cell stack 1 is stopped.

  As described above, the larger the amount of air mixed in the coolant, the lower the output upper limit value of the fuel cell stack 1. Therefore, the amount of heat generated in the fuel cell stack 1 can be suppressed, and damage to the fuel cell stack 1 due to poor cooling can be prevented. it can. On the contrary, in a situation where the amount of mixed air is very small and the cooling of the fuel cell stack 1 is hardly affected, almost full output can be taken out from the fuel cell stack 1.

  Furthermore, as in the first embodiment (see FIG. 5), the coolant flow rate is obtained from the rotational speed of the coolant pump 4 or a flow meter installed in the cooling line 3, and the time when the rotational speed increase is detected (ta) The time (tb−ta) from when the location where the air in the coolant is mixed flows into the fuel cell stack 1 (tb) is calculated, and the location where the air in the coolant is mixed is the fuel cell stack 1 The time (tc−tb) from when (tb) flows into (tc) to (tc) flow into the fuel cell is calculated, and the fuel cell is aligned with the timing when the location where the air in the coolant is mixed enters and exits the fuel cell stack 1 The output upper limit value of the stack 1 is changed to limit the output. As a result, the time during which the output is limited can be shortened as much as possible, and unnecessary power shortage can be avoided.

  As described above, in the fuel cell system according to the present embodiment, the state detecting means uses the coolant temperature detecting means (coolant temperature sensor (stack inlet) 7 and coolant temperature sensor (stack outlet)) for detecting the temperature of the coolant. 8), and in the determination means in the controller 5, the actual rotational speed of the coolant pump 4 is at least the output of the fuel cell stack 1 or the coolant temperature detection value by the coolant temperature detection means (coolant temperature sensors 7, 8). When the temperature exceeds the upper limit threshold of the target rotation speed of the coolant pump 4 calculated from one side within a predetermined time, and then falls below the upper limit threshold again and returns to the vicinity of the target rotation speed, air is mixed in the coolant. Judge. As a result, it is possible to prevent a false diagnosis that the cooling mechanism is abnormal based on a sudden change in the number of revolutions of the coolant pump caused by air mixing into the coolant, and for detecting air contamination in the coolant. Since it is not necessary to install a new device, the device cost can be kept low.

  Further, in the fuel cell system of the present embodiment, in the output control means in the controller 5, the unit time of the time when the actual rotation speed of the coolant pump 4 in the determination means in the controller 5 exceeds the upper limit threshold value of the target rotation speed The output upper limit value of the fuel cell stack 1 is changed in accordance with the per-length. Thereby, when it is estimated that the actual rotational speed of the coolant pump 4 exceeds the upper limit threshold and the amount of air mixed into the coolant is large, the output upper limit value of the fuel cell stack 1 is lowered. Therefore, the heat generation of the fuel cell stack 1 can be suppressed to a low level, and the damage due to poor cooling of the fuel cell stack 1 can be prevented. On the other hand, when the air mixing amount is estimated to be a very small amount, the maximum output can be taken out from the fuel cell stack 1, and unnecessary output limitation can be avoided.

  Furthermore, in the fuel cell system of the present embodiment, when it is determined by the determination means in the controller 5 that air is mixed in the coolant, the fuel cell stack 1 at the location where the air in the coolant is mixed. The output limitation of the fuel cell stack 1 is started or ended in accordance with the inflow timing of the fuel cell or the outflow timing from the fuel cell stack 1. As a result, it is possible to shorten the time for limiting the output to the fuel cell stack 1 as much as possible, and to minimize power shortage due to the output limitation.

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Radiator 2b Radiator fan 3 Coolant line 4 Coolant pump 5 Controller 6 Coolant pressure sensor 7 Coolant temperature sensor (stack inlet)
8 Coolant temperature sensor (stack exit)

Claims (1)

A fuel cell that generates power by supplying fuel gas and oxidant gas;
A cooling system for circulating and supplying a coolant to the fuel cell by a coolant pump;
State detecting means for detecting the state of the coolant;
Determination means for determining whether air is mixed in the coolant based on the detection result of the state detection means;
An output control means for limiting the output of the fuel cell when the determination means determines that air is mixed in the coolant;
The state detection means is a coolant temperature detection means for detecting a temperature of the coolant,
The determination means is an upper limit threshold value of the target rotation speed of the coolant pump, wherein the actual rotation speed of the coolant pump is calculated from at least one of the output of the fuel cell or the coolant temperature detection value by the coolant temperature detection means. When the fuel cell system exceeds a predetermined time and then falls below the upper threshold again and returns to the vicinity of the target rotational speed, it is determined that air is mixed in the coolant.