JP2014120386A - Cooling system for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize temperature fluctuation of cooling water caused by the opening of a thermostat valve.SOLUTION: The present invention relates to a cooling system for a fuel cell, in which a coolant passing through a radiator is cyclically supplied to a fuel cell via a thermostat valve and a flow rate adjustment mechanism. During the thermostat valve is opened, the flow rate of the coolant supplied to the fuel cell is limited to a flow rate smaller than the flow rate supplied before the thermostat valve is opened, by controlling the flow rate adjustment mechanism.

Description

  The present invention relates to a fuel cell cooling system.

  A fuel cell generates electricity by an electrochemical reaction between hydrogen as a fuel gas and oxygen as an oxidant gas, and the temperature rises due to heat generation according to the amount of power generation. For this reason, a fuel cell system using a fuel cell generally includes a cooling system for cooling the fuel cell. The cooling system circulates and supplies the cooling water cooled by the radiator to the fuel cell, and releases the heat generated by the fuel cell, thereby suppressing the temperature rise. In addition, when the fuel cell is started at a low temperature, the cooling system circulates and supplies cooling water to the fuel cell without going through the radiator so as not to release the heat generated in the fuel cell. Is performing a warm-up operation to achieve a state of high power generation efficiency.

  Patent Document 1 discloses that a thermostat device incorporating two types of thermal expansion bodies is applied to a cooling system for an internal combustion engine, thereby preventing the occurrence of thermal shock in a radiator due to a rapid inflow of high-temperature water. Have been described. In Patent Document 2, in the fuel cell cooling device (cooling system), the flow rate of the cooling water according to the switching state of the flow path switching valve detected by detecting the temperature of the cooling water in the vicinity of the flow path switching valve. It is described that the cooling water is supplied to the fuel cell without excess or deficiency in consideration of the pressure loss of the radiator that occurs when the flow path of the cooling water is switched by controlling the required flow rate. Patent Document 3 discloses that in a cooling system for an internal combustion engine, the valve opening of a thermostat is obtained based on the temperature of cooling water in the thermostat, and the flow rate of the cooling water is controlled based on the valve opening of the thermostat. Thus, it is described that the flow rate of the cooling water is adjusted so that the required flow rate is satisfied according to the pressure loss of the cooling water due to opening and closing of the valve of the thermostat.

Japanese Patent Laid-Open No. 2007-1000076 JP 2004-178826 A JP 2008-267180 A

  Here, each fuel cell constituting a stack-like fuel cell (hereinafter also referred to as “fuel cell stack”) usually exhibits the highest power generation efficiency when it is in an appropriate wet state. When some fuel cells that are not in a proper wet state are generated, the temperature of the fuel cells increases due to a decrease in power generation efficiency and an increase in power generation loss, resulting in damage to the electrolyte membrane constituting the fuel cells. In some cases, the power generation function is lost, or the fuel cell is damaged by the combustion of the fuel gas on the anode side and the oxidant gas on the cathode side. Therefore, as a cooling system for the fuel cell system, high-accuracy cooling characteristics conforming to the design are obtained so that each fuel cell maintains an appropriate wet state, and the cooling characteristics are maintained over a long period of time. It is required to do.

  Conventionally, a cooling system using a thermostat valve has been widely used as a cooling system. Thermostat valves are generally very inexpensive, but have large variations such as product variations and aging. In addition, the temperature detection response characteristic of the temperature sensing part of the thermostat valve and the valve opening / closing response characteristic have a delay characteristic, and each response characteristic has a deviation. Further, there are hysteresis and fluctuations in the valve opening temperature and the valve closing temperature, and there are fluctuations in the valve opening position and the valve closing position. Therefore, it is difficult for a cooling system using a thermostat valve to obtain highly accurate cooling characteristics according to design and to maintain the cooling characteristics for a long period of time.

  In addition, when the thermostat valve is used to switch from circulation that does not pass through the radiator to circulation that passes through the radiator, a sudden drop in temperature occurs in the cooling water supplied to the fuel cell due to the cold cooling water cooled by the radiator. There is. A sudden temperature drop causes a significant temperature fluctuation due to the response characteristics of the thermostat valve described above, causing expansion and contraction fluctuation of each member constituting the fuel cell stack, and a factor of lowering the fastening force between the fuel battery cells Can be. A decrease in the fastening force between the fuel cells causes a leak of fuel gas and oxidant gas and a leak of cooling water. In addition, the decrease in the fastening force between the fuel cells is similar to the case where some of the fuel cells that are not in the proper wet state described above are generated, and the power generation efficiency in the fuel cells is reduced and the power generation loss is increased. If the temperature rises, the power generation function is lost due to damage to the electrolyte membrane that constitutes the fuel cell, or the fuel cell is damaged due to combustion of the fuel gas on the anode side and the oxidant gas on the cathode side. There is.

  Therefore, it is not easy to apply a cooling system using a thermostat to a fuel cell cooling system. Therefore, as a conventional fuel cell cooling system, a cooling system using an electronic control valve capable of switching a valve with higher accuracy than a thermostat is often used, which causes an increase in the cost of the fuel cell system. ing.

  In addition, in the cooling system of patent document 1, as mentioned above, it describes about the point corresponding to the rapid temperature change of a cooling water. However, in addition to the thermostat design, development man-hours, and development man-hour costs that are made according to the specifications of the equipment, the cost of parts due to design changes and the man-hours in the production process associated with the assembly of complex parts The increase in cost is considered to be significant due to the increase in In addition, it is considered that characteristic adjustment is not easy. In addition, no consideration has been given to dealing with aging, and it is considered difficult to maintain high-precision cooling characteristics according to design over a long period of time. Moreover, in the cooling system of patent document 2, 3, it respond | corresponds to a pressure loss, and it does not consider at all about the response | compatibility to the rapid temperature change of a cooling water, a cost rise, and a secular change. .

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.

(1) According to an aspect of the present invention, there is provided a fuel cell cooling system in which a coolant passing through a radiator is circulated and supplied to a fuel cell via a thermostat valve and a flow rate adjusting mechanism. In this fuel cell cooling system, the flow rate of the coolant supplied to the fuel cell is controlled before the thermostat valve is opened by controlling the flow rate adjusting mechanism when the thermostat valve is opened. It is limited to a flow rate that is less than the supplied flow rate. According to the fuel cell cooling system of this embodiment, even when the thermostat valve is opened and the low-temperature coolant cooled by the radiator flows out of the thermostat valve, the flow rate of the coolant supplied to the fuel cell is reduced. By limiting, it is possible to suppress a rapid temperature fluctuation of the coolant supplied to the fuel cell. Thereby, deterioration of the member which comprises a fuel cell, and the fall of the power generation performance of a fuel cell can be suppressed. Further, since the process is executed only by limiting the flow rate of the coolant, rapid temperature fluctuations of the coolant can be suppressed regardless of the problems of the thermostat valve itself described in the problems such as product variation, aging, and response characteristics.

(2) In the fuel cell cooling system according to the above aspect, the restriction of the flow rate of the coolant is performed until the time limit duration of the coolant flow limit elapses from the timing immediately before the opening of the thermostat valve, and immediately before the valve opening. The timing and the flow rate restriction duration time are preferably determined based on the temperature of the coolant flowing out of the thermostat valve. According to the fuel cell cooling system of this embodiment, it is possible to easily determine the timing for starting the restriction of the flow rate of the coolant and the continuing time in order to suppress the rapid fluctuation of the coolant.

(3) According to another aspect of the present invention, there is provided a cooling system for a fuel cell in which a coolant passing through a radiator is circulated and supplied to the fuel cell via a thermostat valve and a circulation pump. In this fuel cell cooling system, the flow rate of the coolant supplied to the fuel cell is determined based on the differential value obtained by obtaining a differential value of the temperature of the coolant flowing out of the thermostat valve. Adjustment is performed by controlling the flow rate adjusting mechanism in accordance with a change in the amount. According to the fuel cell cooling system of this embodiment, the coolant supplied to the fuel cell is adjusted by adjusting the flow rate of the coolant according to the differential value indicating the magnitude of the temperature change of the coolant flowing out of the thermostat. Can be suppressed. Thereby, deterioration of the member which comprises a fuel cell, and the fall of the power generation performance of a fuel cell can be suppressed. In addition, since it is executed only by adjusting the flow rate of the cooling liquid according to the magnitude of the change in the temperature of the cooling liquid, similarly, the rapid temperature fluctuation of the cooling liquid is suppressed regardless of the problem of the thermostat valve described in the problem. Is possible.

  The present invention can also be realized in various forms other than the fuel cell cooling system. For example, it can be realized in the form of a fuel cell system including a fuel cell cooling system, a vehicle including a fuel cell system, and the like.

It is explanatory drawing which shows schematic structure of the cooling system of the fuel cell as 1st Embodiment of this invention. It is explanatory drawing which shows the basic concept of the flow volume restriction | limiting of the cooling water at the time of valve opening of a thermostat valve. It is a flowchart of the flow volume restriction | limiting process of the cooling water at the time of valve opening of a thermostat valve. It is a flowchart of a cooling water temperature acquisition process routine. It is a flowchart of a flow restriction start temperature detection processing routine. 7 is a flowchart of a flow rate restriction duration setting processing routine. It is a flowchart of a flow restriction start processing routine. It is a flowchart of a flow restriction end processing routine. It is explanatory drawing which shows visually about the process operation performed by each process routine of a flow volume limitation process. It is explanatory drawing which shows schematic structure of the cooling system of the fuel cell as 2nd Embodiment of this invention. It is a flowchart of the flow volume limiting process of cooling water. It is a flowchart of the flow volume limiting process of cooling water. It is a graph which shows the example of a characteristic of FC cooling water flow map at the time of warming-up. It is a graph which shows the example of a characteristic of FC cooling water negative feedback flow rate Mac. It is a graph which shows the example of a characteristic of FC cooling water raising / lowering temperature correction coefficient map. It is a graph which shows the example of a characteristic of FC cooling water radiator correction coefficient map. It is a graph which shows the example of a characteristic of a standard FC cooling water flow rate map. It is explanatory drawing which shows visually about the flow volume restriction | limiting operation | movement of FC cooling water performed by the flow volume restriction | limiting process of FIG.

A. First embodiment:
A1. Cooling system configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell cooling system according to a first embodiment of the present invention. As shown in FIG. 1A, in the cooling system 100, water as a coolant for cooling the fuel cell (hereinafter referred to as “cooling water”) is supplied to a fuel cell stack (hereinafter referred to as “cooling water”) via a radiator 50. A circulation channel LC that circulates and supplies to the FC stack 10 and a bypass circulation channel LB that circulates and supplies the FC stack 10 while bypassing the radiator 50 are provided. In order to distinguish between cooling water that passes through the radiator and cooling water that does not pass through the radiator, the cooling water that passes through the radiator is also called “cooled water”, and cooling water that does not pass through the radiator is referred to as “uncooled”. Also called “water”. In addition, as cooling water, the water to which the antifreeze liquid was added is used normally.

  The circulation channel LC includes channels L1 and L2 that connect the outlet 10b of the FC stack 10 and the inlet 50a of the radiator 50, a channel L3 that connects the outlet 50b of the radiator 50 and one inlet 40a of the thermostat valve 40, L4 which connects the outlet 40c of the thermostat valve 40 and the inlet 20a of the circulation pump 20, and the flow path L5 which connects the outlet 20b of the circulation pump 20 and the inlet 10a of the FC stack 10 are comprised. The bypass circulation flow path LB is branched at the connection positions of the flow paths L1, L4, and L5 common to the circulation flow path LC, and the flow paths L1 and L2, and is connected to the other inlet 40b of the thermostat valve 40. And a flow path L6. The flow path L4 is provided with a temperature sensor 30 for detecting the temperature (Tfc) of the cooling water flowing out from the thermostat valve 40. For the temperature sensor 30, for example, a thermistor type thermometer is used.

  The flow rate of the cooling water supplied from the inlet 10a of the FC stack 10 is controlled by a fuel cell control unit (hereinafter also referred to as “FCC unit” or “FCCU”) 70 that controls the power generation operation of the FC stack 10 by a temperature sensor. The control is performed by controlling the operation of the circulation pump 20 based on the temperature detected by 30. Therefore, the circulation pump 20 corresponds to the flow rate adjusting mechanism of the present invention. As the flow rate adjusting mechanism, not only a pump but also a flow rate adjusting valve can be applied, and various mechanisms can be applied as long as the flow rate can be adjusted.

  In addition to the cooling system 100, the fuel cell system including the FC stack 10 includes various fuel gas supply systems for supplying fuel gas and oxidant gas supply systems for supplying oxidant gas. Although an apparatus is provided, it is not an essential component in the description of the present invention, and thus illustration and description thereof are omitted.

  The thermostat valve 40 has a function of changing the opening degree of the valve (valve) 42 in accordance with the degree of expansion and contraction of the wax (not shown) of the temperature sensing part that changes in accordance with the temperature of the cooling water flowing through the thermostat valve 40. Yes. As shown on the left side of FIG. 1B, in a state where the temperature of the cooling water is lower than the valve opening temperature, the valve 42 is closed due to the shrinkage of the wax. Road LB opens. As shown on the right side of FIG. 1B, when the temperature of the cooling water is equal to or higher than the valve opening temperature, the valve 42 is opened due to the expansion of the wax, so that the bypass circulation passage LB is closed and circulated. The channel LC opens. Note that there is hysteresis in the opening and closing of the valve 42 of the thermostat valve 40, and an intermediate open state corresponding to the temperature occurs after the open state until the closed state.

  In the cooling system 100, when the temperature of the cooling water passing through the thermostat valve 40 is lower than the valve opening temperature, the circulation channel LC is closed, and the uncooled water is supplied to the FC stack 10 via the bypass circulation channel LB. Circulated and supplied. The flow of uncooled water in this case is indicated by a broken arrow in FIG. On the other hand, when the temperature of the cooling water passing through the thermostat valve 40 is equal to or higher than the valve opening temperature, the circulation channel LC is opened, and the cooled water is circulated and supplied to the FC stack 10 via the circulation channel LC. Is done.

  The flow rate of the cooling water supplied to the FC stack 10 is normally circulated according to a flow rate control value (also referred to as a “flow rate control command value”) determined according to a preset condition based on the temperature detected by the temperature sensor 30. It is controlled by operating the pump 20. In the cooling system 100 of the present embodiment, especially when the thermostat valve 40 is opened, the control of the flow rate limitation of the cooling water described below is added.

A2. Basic concept of cooling water flow restriction:
FIG. 2 is an explanatory diagram showing the basic concept of the flow rate restriction of the cooling water when the thermostat valve is opened. FIG. 2 shows that the thermostat valve 40 is opened during the warm-up operation. Moreover, the upper part of FIG. 2 shows a case where there is no restriction on the flow rate of the cooling water as a comparative example, and the lower part of FIG. 2 shows a case where there is a restriction on the flow rate of the cooling water as a basic concept.

  First, a comparative example will be described. When the fuel cell system including the FC stack 10 is started at a low temperature, particularly when the fuel cell system is started below freezing point, the FC stack 10 is required to be quickly warmed up from the viewpoint of suppressing freezing of generated water due to power generation. Normally, a reduction in power generation efficiency during warm-up operation is allowed, and the temperature generated by the power generation in the FC stack 10 increases the temperature of the cooling water circulating through the bypass circulation passage LB as shown in the upper part of FIG. Then, the FC stack 10 is rapidly warmed up. In addition, the flow rate of the cooling water circulating through the bypass circulation flow path LB is determined in advance as a flow rate that is effective for warming up in order to enable rapid warming up by circulating the cooling water whose temperature rises. The flow rate is set to a set maximum flow rate in a steady operation, a settable maximum flow rate, or the like.

  When the valve of the thermostat valve 40 starts to open, cooling water (cooled water) cooled to a state close to the outside air temperature by the radiator 50 is supplied to the FC stack 10 via the thermostat valve 40 and the circulation pump 20 (hereinafter referred to as cooling water). , Also referred to as “FC cooling water”) flows into the FC stack 10. As described above, the flow rate of the cooling water supplied to the FC stack 10 by the circulation pump 20 is set to a large flow rate for the purpose of rapid warm-up described above. For this reason, the cooling water corresponding to the larger set flow rate flows into the FC stack 10 as FC cooling water, and the temperature of the FC cooling water detected by the temperature sensor 30 is equal to the flow rate of the cooling water. Decreases accordingly. At this time, the temperature sensing part of the thermostat valve 40 is also exposed to the cooling water to detect a temperature drop. As a result, the thermostat valve 40 shifts from the open state to the closed state, and hot water (uncooled water) that is not cooled flows into the FC stack 10 as FC cooling water via the thermostat valve 40 and the circulation pump 20, The temperature of the FC cooling water detected by the sensor 30 rises again. It should be noted that the temperature sensing characteristics of the thermostat valve 40 and the response characteristics of the valve in accordance with the temperature sensing have a response delay inherent to the member being applied and variation among individuals. For this reason, the temperature of the FC cooling water detected by the temperature sensor 30 is gradually attenuated while oscillating and fluctuating (hunting) in response to the repeated opening and closing of the thermostat valve 40, and the temperature associated with warming up. Returns to the state set as the rising characteristic.

  As described in the problem, the rapid fluctuation of the temperature of the cooling water causes different expansion and contraction in a plurality of different members constituting the FC stack 10, and the stress generated in response to the expansion and contraction of the FC stack 10. This causes a reduction in fastening force for fastening each fuel cell (FC cell) constituting the stack, causing leakage of fuel gas and oxidant gas and leakage of cooling water. Further, even between the FC cells or in the same FC cell, a temperature difference occurs between the inlet and outlet of the cooling water, and the distribution of the wet state becomes non-uniform, which may cause the power generation performance to deteriorate.

  Therefore, in the present embodiment, the problem in the comparative example is solved by restricting the flow rate based on the basic concept of restricting the flow rate of cooling water described below. That is, the flow rate limitation of the cooling water in the present embodiment starts the limitation of the flow rate of the cooling water immediately before the opening timing of the thermostat valve 40 and is detected by the temperature sensor 30 as shown in the lower part of FIG. By restricting the flow rate until the temperature fluctuation (hunting) of the cooling water converges, the rapid temperature drop of the cooling water is suppressed, and the temperature fluctuation (hunting) occurring thereafter is suppressed. .

  The above concept is based on the following reasons. That is, if the flow rate of the cooling water is limited, the flow rate of the cooling water that becomes the FC cooling water is also limited by opening the thermostat valve 40. For this reason, the fluctuation | variation of the temperature fall of FC cooling water which generate | occur | produces by inflow of cooling water is suppressed. Further, the temperature rise that occurs in response to the temperature drop of the FC cooling water is also suppressed because fluctuations in the temperature drop of the base cooling water are suppressed. As a result, it is considered that temperature fluctuation (hunting) of the FC cooling water generated by opening the thermostat valve 40 is suppressed.

A3. Specific flow restriction operation:
Below, the specific operation example based on the basic concept of the flow volume restriction | limiting of the said cooling water is demonstrated. FIG. 3 is a flowchart of the flow rate limiting process for the cooling water when the thermostat valve is opened. This flow rate limiting process is repeatedly executed by the FCC unit 70 from the start to the end of the fuel cell system at a predetermined execution interval tm, for example, tm = 100 [ms]. This interval is set in consideration of the detection accuracy of the temperature variation of the cooling water, the load on the FCC unit 70 that executes the processing, and the like.

  In the cooling water flow restriction process, the cooling water temperature acquisition (step S100), the flow restriction start temperature detection (step S120), the flow restriction duration setting (step S140), the flow restriction start (step S160), and the flow restriction end. Each processing routine of (Step S180) is executed in order by the FCC unit 70.

  FIG. 4 is a flowchart of a cooling water temperature acquisition processing routine. FIG. 5 is a flowchart of a flow rate restriction start temperature detection processing routine, and FIG. 6 is a flowchart of a flow rate restriction duration setting processing routine. FIG. 7 is a flowchart of a flow rate restriction start processing routine, and FIG. 8 is a flowchart of a flow rate restriction end processing routine. FIG. 9 is an explanatory diagram visually showing the processing operation executed in each processing routine of the flow rate restriction processing.

  First, in the cooling water temperature acquisition process (step S100 in FIG. 3), as shown in FIG. 4, the temperature of the FC cooling water supplied to the FC stack 10 (FIG. 1) is detected by the temperature sensor 30, and the downstream of the thermostat Obtained and stored as the temperature tmp_ts_o (step S102). Then, the differential value of the thermostat wake temperature tmp_ts_o is calculated and stored as the thermostat wake temperature change amount dtmp_ts_o (step S104).

  Next, in the flow rate restriction start temperature detection process (step S120 in FIG. 3), as shown in FIG. 5, the acquired thermostat wake temperature tmp_ts_o is a reliable fully closed state temperature tmp_lwr (for example, 40 ° C.) to a certain fully open state temperature tmp_upr (for example, 85 ° C.) (step S122), and whether or not a temperature detection completion flag flg [ts_opn], which will be described later, is set is described. Is determined (step S124). Note that the fully closed state temperature tmp_lwr and the fully open state temperature tmp_upr are appropriately set after confirming the experiment in consideration of the specification of the thermostat valve to be applied and the secular change.

  When the thermostat wake temperature tmp_ts_o is in the above range and the temperature detection completion flag flg [ts_opn] immediately before starting the valve opening is not set, the thermostat wake temperature change amount dtmp_ts_o is determined as the valve opening start temperature detection determination. It is determined whether or not the value is smaller than a value dtmp_lwr (for example, −2 ° C./second) (step S126).

  Here, if the thermostat wake temperature change amount dtmp_ts_o is smaller than the valve opening start temperature detection determination value dtmp_lwr, the degree of change in the cooling water temperature is large, and the thermostat valve 40 is in the start state. it is conceivable that. For example, as shown in FIG. 9A, the temperature Tfc of the FC cooling water (thermostat temp_ts_o after the thermostat) increases before the thermostat valve 40 starts to open and decreases as the thermostat valve 40 opens. Then, as the thermostat valve 40 is opened and closed, the raising and lowering are repeated. At this time, as shown in FIG. 9B, the differential value dTfc of the cooling water temperature Tfc (the thermostat wake temperature change amount dtmp_ts_o) is the temperature Tfc of the cooling water when the thermostat valve 40 is opened (FIG. 9B). It changes to a negative value at the timing when a)) changes from rising to falling. Therefore, the timing at which the detection of the temperature immediately before the start of the valve opening is detected by detecting the time point when the thermostat wake flow temperature change amount dtmp_ts_o falls below the valve opening start temperature detection determination value dtmp_lwr. Note that the valve opening start temperature detection determination value dtmp_lwr is appropriately set after being experimentally confirmed in advance in consideration of various variations such as initial variation of the thermostat, aging, temperature sensor detection variation, and the like.

  When the thermostat wake temperature change amount dtmp_ts_o is smaller than the valve opening start temperature detection determination value dtmp_lwr, the maximum thermostat wake temperature tmp_ts_o [max] is calculated (step S128) and the temperature tmp_ts_on immediately before the valve opening start. Is calculated (step S130) and stored. Further, the current time time [n] is acquired and stored as the temperature detection time time_on immediately before the valve opening start (step S132), and it is assumed that the acquisition of the temperature immediately before the valve opening start and the valve opening start linear temperature detection time has been completed. A temperature detection completion flag flg [ts_opn] immediately before starting the valve is set (step S134). As the maximum thermostat wake temperature tmp_ts_o [max], the thermostat wake temperature tmp_ts_o is set. As the temperature tmp_ts_on immediately before the opening of the valve, a value obtained by subtracting the flow limit restriction start temperature tmp_ofs (for example, 3.5 ° C.) from the maximum thermostat downstream temperature tmp_ts_o [max] is set. The flow rate restriction start margin temperature tmp_ofs is appropriately set after being experimentally confirmed in advance in consideration of various variations such as initial variation of the thermostat, aging, and variation in detection of the temperature sensor.

  As described above, the flow restriction start temperature detection process is repeatedly executed at every execution interval tm as described above even after the temperature tmp_ts_on immediately before the valve opening start is calculated and the temperature detection completion flag flg [ts_opn] immediately before the valve opening start is set. Will be. However, in the flow restriction start temperature detection process in this case, since the temperature detection completion flag flg [ts_opn] immediately before the valve opening start is set (step S124), the processes of steps S126 to S134 are not executed and set. Further, the values of the temperature tmp_ts_on immediately before the valve opening start and the temperature detection time time_on immediately before the valve opening start are maintained. The reset of the temperature detection completion flag flg [ts_opn] immediately before the start of valve opening is executed when the flow rate restriction ends in a flow rate restriction end process (step S190 in FIG. 8) described later.

  Next, in the flow rate restriction duration setting process (step S140 in FIG. 3), as shown in FIG. 6, whether or not the temperature detection completion flag flg [ts_opn] just before the valve opening start is set (step S142). And whether or not a flow rate restriction duration setting completion flag flg [dtime] described later is set (step S144).

  When the temperature detection completion flag flg [ts_opn] immediately before the valve opening start and the flow rate restriction continuation time setting completion flag flg [dtime] are set, the post-thermostat temperature change amount dtmp_ts_o is larger than 0 and hunting convergence detection is performed. It is determined whether or not the range is smaller than a determination value dtmp_max (for example, 1 ° C./second) (step S146).

  Here, as shown in FIG. 9B, the timing when the thermostat wake temperature change amount dtmp_ts_o (the differential value dTfc of the cooling water temperature Tfc) changes from negative to positive as shown in FIG. 9A. The timing at which the temperature Tfc of the cooling water changes from lowering to rising is shown, and at least the timing at which the cooling water temperature Tfc deviates from the temperature decrease generated by opening the thermostat valve 40. Therefore, the hunting convergence timing is detected by detecting a time point when the thermostat wake flow temperature change amount dtmp_ts_o is in a range larger than 0 and smaller than a hunting convergence detection determination value dtmp_max (for example, 1 ° C./second). . It should be noted that the hunting convergence detection determination value dtmp_max is appropriately set after being experimentally confirmed in advance in consideration of various variations such as initial variations in the thermostat, changes over time, and variations in detection of the temperature sensor.

  When the thermostat wake temperature change amount dtmp_ts_o falls within the above range, it is determined that the hunting has converged, the flow rate restriction duration dtime is calculated and stored (step S148), and the flow rate restriction duration setting completion flag is set. flg [dtime] is set (step S150). The flow rate restriction duration time dtime is calculated by subtracting the temperature detection time time_on immediately before starting the valve opening from the current time time [n].

  Even after the flow rate restriction duration dtime is calculated and the flow rate restriction duration setting completion flag flg [dtime] is set, the flow rate restriction duration setting process is repeatedly executed at every execution interval tm as described above. It will be. However, in the flow rate restriction duration setting process in this case, since the amount restriction duration setting completion flag flg [dtime] is set (step S144), the processing from step S146 to step S150 is not executed and is set. The value of the flow restriction duration dtime is maintained. The reset of the flow rate restriction duration setting completion flag flg [dtime] is executed when the flow rate restriction is finished in a flow restriction restriction end process (step S190 in FIG. 8) described later.

  Next, in the flow rate restriction start process (step S160 in FIG. 3), as shown in FIG. 7, whether or not the flow rate restriction duration setting completion flag flg [dtime] is set (step S162) and will be described later. It is determined whether or not the anti-hunting control flag flg [Q_wtr] is set (step S164). If the flow rate restriction duration setting completion flag flg [dtime] is set, but the hunting prevention control in-progress flag flg [Q_wtr] is not yet set, the temperature tmp_ts_on immediately before starting the valve opening and the flow rate restriction duration dtime are set. Since it is obtained and stored, the opening of the thermostat valve 40 can be detected based on this, and the flow rate of the cooling water can be restricted during the flow rate restriction duration dtime. Therefore, it is determined whether or not the thermostat downstream temperature tmp_ts_o is higher than the temperature tmp_ts_on immediately before the start of valve opening (step S166).

  As shown in FIG. 9A, when the thermostat wake temperature tmp_ts_o becomes higher than the temperature tmp_ts_on immediately before the valve opening start, it is determined that the temperature immediately before the valve opening start is reached. Therefore, as shown in FIG. 9C, the flow rate restriction command value Q_wtr is set from the normal flow rate command value Q_wtr_nml to a hunting prevention flow rate command value Q_wtr_sml that is smaller than the normal flow rate command value Q_wtr_nml ( Step S168). Thereby, the flow rate of the FC cooling water by the circulation pump 20 corresponds to the hunting prevention flow rate command value Q_wtr_sml from the normal time flow rate corresponding to the normal time flow rate command value Q_wtr_nml set according to the operating conditions so far. The flow rate is limited to a hunting prevention flow rate (for example, 12 NL / min). Further, the current time time [n] at this time is acquired and set as the flow control start time time_st (step S170), and the anti-hunting control flag flg [Q_wtr] is set (step S172).

  Here, the anti-hunting flow rate is obtained in advance by experiments. For example, under an atmospheric temperature environment of −10 ° C., the power generation load of the fuel cell system is set to maximum (this state is assumed to be 1), 1/2, 1/25, each steady operation state, and each load condition The flow rate of the cooling water capable of maximizing the power generation efficiency is obtained, and each obtained flow rate is set as the “reference flow rate”. Then, after waiting until the fuel cell system reaches the atmospheric temperature, the fuel cell system is operated again under the power generation load condition. The flow rate of the cooling water at this time is tried at various flow rates larger than the “reference flow rate”, and the flow rate at which the temperature hunting width can be suppressed within 5 ° C., for example, is obtained. The obtained flow rate is the maximum value of the anti-hunting flow rate. The hunting prevention flow rate to be set is appropriately selected and set from the range of the reference value to the maximum value of the hunting prevention flow rate.

  Even after the flow restriction is started as described above and the hunting prevention controlling flag flg [Q_wtr] is set, the flow restriction start process is repeatedly executed at every execution interval tm at every execution interval tm. Become. However, in the flow rate restriction start process in this case, since the hunting prevention control in progress flag flg [Q_wtr] is set (step S124), the processes in steps S164 to S172 are not executed, and the flow rate restriction state is maintained. The The reset of the hunting prevention control flag flg [Q_wtr] is executed when the flow restriction is finished in a flow restriction completion process (step S190 in FIG. 8) described later.

  Next, in the flow restriction end processing (step S180 in FIG. 3), as shown in FIG. 8, whether or not the anti-hunting control flag flg [Q_wtr] is set and the flow restriction is in effect (step S182), and It is determined whether the elapsed time from the flow restriction start time time_st has reached the flow restriction continuation time dtime (step S184).

  As shown in FIG. 9B, when the flow rate is being restricted and the elapsed time from the flow rate restriction start time time_st has reached the flow rate restriction duration time dtime, the after-temperature change amount dtmp_ts_o of the thermostat is further increased. It is determined whether or not the hunting convergence state is in a range larger than 0 and smaller than the hunting convergence detection determination value dtmp_max (for example, 1 ° C./second) (step S186).

  When the thermostat wake temperature change amount dtmp_ts_o falls within the above range, it is determined that the hunting has converged. As a result, as shown in FIG. 9C, the flow rate restriction command value Q_wtr is returned from the hunting prevention flow rate command value Q_wtr_sml to the normal flow rate command value Q_wtr_nml (step S188). Then, the temperature detection completion flag flg [ts_opn] immediately before the start of valve opening, the flow rate restriction duration setting completion flag flg [dtime], and the anti-hunting control flag flg [Q_wtr] are reset.

  Then, calculation of the temperature immediately before the start of valve opening and the flow rate restriction duration is executed, and the flow rate restriction corresponding to the flow rate restriction duration is repeatedly executed by detecting the temperature rise of the cooling water exceeding the temperature immediately before the start of valve opening. It will be. Thereby, it is possible to intermittently and repeatedly suppress a rapid temperature drop of the FC cooling water due to the opening of the thermostat valve 40. Thereby, it is possible to suppress a rapid temperature drop and temperature fluctuation of the FC stack 10 and stably maintain a highly efficient power generation state in the FC stack 10 for a long period of time.

  In the cooling system 100 of the present embodiment, the opening timing of the thermostat valve 40 is detected regardless of various variations such as inherent variations of members such as the thermostat valve 40, individual errors, and aging. Thus, by restricting the flow rate of the FC cooling water, it is possible to suppress a rapid temperature drop of the FC cooling water and subsequent temperature fluctuations.

  It should be noted that the flow rate limiting process of the cooling water when the thermostat valve is opened is to intermittently suppress the temperature drop of the cooling water when the thermostat valve 40 is opened. Therefore, there is a possibility that the suppression effect is lower than the continuous cooling water flow rate restriction as shown in FIG. However, even if it is intermittent, the temperature drop of the cooling water can be suppressed, so that the effect of suppressing the temperature fluctuation (hunting) of the FC cooling water generated by opening the thermostat valve 40 is exhibited.

  It should be noted that at the time of initial operation or inspection of the fuel cell system including the cooling system 100 of the present embodiment, the flow rate (variation assumption) that the temperature of the cooling water is expected to fluctuate due to the opening of the thermostat valve 40. The system may be operated with the flow rate) to grasp the characteristic unique to the system, and based on the result, various values set in the flow rate limiting process of the cooling water may be set. As the fluctuation assumed flow rate, the maximum flow rate possible in the cooling system 100 may be used. This is because if the rapid temperature change of the cooling water is limited to several times, it is sufficiently possible to design an FC stack considering this.

  In the above-described cooling water flow rate limiting process, it has been described that the started flow rate limitation is simply continued until the cooling water flow rate limitation starts and ends. However, even during this period, when the differential value of the temperature of the cooling water is a value at which the decrease in the temperature of the cooling water is determined to be large, for example, when it is smaller than the valve opening start temperature detection determination value dtmp_lwr, You may make it further restrict | limit the restriction | limiting flow volume in the flow restriction | limiting period performed next time.

  The accumulated usage time of the thermostat valve 40 is managed so that each time the accumulated usage time elapses, various parameter values set in the flow restriction system process are updated according to the secular change of the thermostat valve 40. May be. The accumulated usage time is appropriately set according to the use of the applied product. For example, 1000 hours is given as an example.

  Further, the determination value of the cooling water temperature differential value (thermostat downstream flow temperature change amount dtmp_ts_o), that is, the valve opening start temperature detection determination value dtmp_lwr and the hunting convergence detection determination value dtmp_max are set in a state other than the thermostat valve opening transient state. By referring to the differential value of the temperature of the cooling water, for example, by determining the maximum value as a reference, correction control is performed using an appropriate control index value with respect to individual variations and aging, and erroneous detection and Overcorrection may be prevented.

B. Second embodiment:
B1. Cooling system configuration:
FIG. 10 is an explanatory diagram showing a schematic configuration of a fuel cell cooling system according to a second embodiment of the present invention. In the cooling system 100B of the second embodiment, in addition to the configuration of the cooling system 100 (see FIG. 1) of the first embodiment, the temperature of the cooling water (cooled water) from the radiator 50 is set near the outlet 50b of the radiator 50. The cooling system 100 is the same as the cooling system 100 except that a temperature sensor 80 to be detected is provided and the flow rate limiting process of the cooling water by the FCC unit 70 is different. Further, the basic concept of the flow rate restriction is the same as that described in the first embodiment. Therefore, in the following, description of the configuration of the cooling system 100B is omitted, and a specific operation for limiting the flow rate of the cooling water is added.

B2. Specific flow restriction operation:
11 and 12 are flowcharts of the cooling water flow rate limiting process. This flow rate limiting process is also repeatedly executed by the FCC unit 70 at a predetermined execution interval tm (for example, 100 ms) from the start to the end of the fuel cell system, as in the case of the first embodiment.

  First, the temperature Tfc of the cooling water (FC cooling water) supplied to the FC stack 10 (FIG. 10) is detected and acquired by the temperature sensor 30 (FIG. 10) (step S200). The warm-up FC coolant flow rate Qwup corresponding to the detected FC coolant temperature Tfc is a map showing the relationship between the warm-up FC coolant flow rate Qwup and the FC coolant temperature Tfc (hereinafter referred to as “warm-up time”). (Referred to as “FC cooling water flow rate map”) (step S202). Further, the FC cooling water negative feedback flow rate Qfb corresponding to the detected FC cooling water temperature Tfc is a map showing the relationship between the FC cooling water negative feedback flow rate Qfb and the FC cooling water temperature Tfc (hereinafter referred to as “FC cooling water negative feedback”). (Referred to as “flow rate map”) (step S204).

  FIG. 13 is a graph showing a characteristic example of the warm-up FC cooling water flow map. In order to promote efficient warm-up and reduce wasteful power consumption by operating various auxiliary machines such as the circulation pump 20 efficiently, the warm-up FC coolant flow Qwup is set to the FC coolant temperature Tfc. It is changed accordingly. Specifically, when the FC cooling water temperature Tfc is low, the warm-up FC cooling water flow rate Qwup is set to a substantially maximum flow rate. The warm-up FC coolant flow rate Qwup is set to be suppressed as the FC coolant temperature Tfc approaches the warm-up completion temperature Twr.

  FIG. 14 is a graph showing a characteristic example of the FC cooling water negative feedback flow rate map. For the purpose of promoting convergence to the control target temperature Tg, the FC cooling water negative feedback flow rate Qfb is set to increase as the FC cooling water temperature Tfc becomes higher than the control target temperature Tg and the deviation increases.

  Next, the obtained differential value of the FC cooling water temperature Tfc is calculated as the FC cooling water temperature change amount dTfc (step S206). Then, the FC cooling water temperature increase / decrease correction coefficient KdTfc corresponding to the calculated FC cooling water temperature change amount dTfc is a map showing the relationship between the FC cooling water temperature change amount dTfc and the FC cooling water temperature increase / decrease correction coefficient KdTfc (hereinafter, referred to as the FC cooling water temperature increase / decrease correction coefficient KdTfc It is calculated with reference to “FC cooling water rising / lowering temperature correction coefficient map” (step S208).

  FIG. 15 is a graph showing an example of the characteristics of the FC cooling water rise / fall temperature correction coefficient map. Basically, with reference to dTFc = 0 and KdTfc = 0, the FC cooling water temperature increase / decrease correction coefficient KdTfc is set to change in proportion to the change in FC cooling water temperature change amount dTfc. However, an upper limit and a lower limit are provided to prevent overcorrection. Further, the range (range 1) in which the FC cooling water temperature change amount dTfc is close to 0 is to suppress the influence of hysteresis associated with the opening and closing operations of the thermostat valve, or the introduction of disturbance and noise. The change gradient of the FC cooling water rise / fall temperature correction coefficient KdTfc is set to a cooling water flow rate fluctuation suppression range in which the change gradient is set to be smaller than the outer range. In this example, KdTfc = 0. Further, the constant range (range 2) outside the cooling water flow rate fluctuation suppression range (range 1) is a change gradient in the further outside range in order to compensate for a response delay due to the cooling water flow rate fluctuation suppression range (range 1). The correction gain increase range is set to a larger value.

  Next, the temperature Trad of cooled water (hereinafter also referred to as “radiator water”) flowing out from the radiator 50 (FIG. 10) is detected and acquired by the temperature sensor 80 (FIG. 10) (step S210). . The FC cooling water radiator correction coefficient Krad corresponding to the detected radiator water temperature Trad is a map showing the relationship between the difference between the FC cooling water temperature Tfc and the radiator water temperature Trad and the FC cooling water radiator correction coefficient Krad ( Hereinafter, it is calculated with reference to “FC cooling water radiator correction coefficient map” (step S212).

  FIG. 16 is a graph showing an example of characteristics of the FC cooling water radiator correction coefficient map. In order to reduce the width of the temperature drop when the thermostat valve 40 is opened, the FC cooling water radiator correction is performed as (Tfc−Trad) increases, that is, as the radiator water temperature Trad decreases with respect to the FC cooling water temperature Tfc. The coefficient Krad is set to be small.

  Next, estimation of the FC heat generation amount Ploss_fc is executed (step S214). The FC heat generation amount Ploss_fc is obtained, for example, from the product of the difference between the electromotive voltage obtained from the theoretical IV characteristic of the FC stack 10 and the actual voltage and the load current. A reference FC cooling water flow rate Qstd corresponding to the estimated FC heat generation amount Ploss_fc is a map indicating the relationship between the reference FC cooling water flow rate Qstd and the FC heat generation amount Ploss_fc (hereinafter referred to as a “reference FC cooling water flow rate map”). ) To calculate (step S216). The basic FC cooling water flow rate Qbase (= Qstd * Krad + KdTfc) is calculated based on the calculated reference FC cooling water flow rate Qsts, FC cooling water radiator correction coefficient Krad, and FC cooling water rising / lowering temperature correction coefficient KdTfc ( Step S218).

  FIG. 17 is a graph showing a characteristic example of the reference FC cooling water flow map. In order to improve the control responsiveness of the cooling system, the reference FC cooling water flow rate Qstd is set to increase as the heat generation loss Ploss_fc increases, and the heat dissipation efficiency improves as the heat generation loss Ploss_fc increases. The increasing gradient of the flow rate Qstd is set to decrease.

  Finally, when the FC cooling water temperature Tfc does not exceed the warm-up completion temperature Twr, the warm-up FC cooling water flow rate Qwup is calculated as the command FC cooling water flow rate Qcmd (step S222b), and the FC cooling water temperature Tfc. If the temperature exceeds the warm-up completion temperature Twr, the sum (Qbase + Qfb) of the basic FC cooling water flow rate Qbase and the FC cooling water negative feedback flow rate Qfb is calculated as the command FC cooling water flow rate Qcmd (step S222a). Then, the circulation pump 20 adjusts the flow rate of the FC cooling water according to the command FC cooling water flow rate Qcmd.

  Each of the above maps is set in advance by experimental confirmation in consideration of various variations such as initial variations and aging of thermostats and detection variations of temperature sensors.

  By repeatedly executing the above-described cooling water flow rate limiting process, a flow rate limiting operation corresponding to the temperature change of the FC cooling water is executed as described below.

  FIG. 18 is an explanatory diagram visually showing the flow restriction operation of the FC cooling water executed by the flow restriction process of FIG. In FIG. 18A, a constant flow rate required to converge to the control target temperature of the FC stack 10 is continuously supplied as the flow rate of the FC cooling water (see the one-dot chain line in FIG. 18D), and The transition of the temperature of the FC cooling water in the case where the above-described flow rate restriction processing (FIGS. 11 and 12) is not executed (hereinafter also referred to as “before correction control”) is shown. FIG. 18B shows the differential value of the FC cooling water temperature shown in FIG. 18A, that is, the magnitude of the change in the FC cooling water temperature. As can be seen from the transition of the FC cooling water temperature and its differential value, when the flow rate of the FC cooling water is not limited, the FC cooling water temperature is obtained from the radiator 50 by the opening operation of the thermostat valve 40. A rapid temperature drop occurs at the same time as the radiator cooling water (cooled water) is supplied. After that, the temperature of the FC cooling water is so-called hunting in which the rise and fall are repeated in an oscillating manner, and gradually attenuates and converges to the control target temperature.

  FIG. 18C shows the transition of the temperature of the FC cooling water when the above-described flow rate restriction processing (FIGS. 11 and 12) is executed (hereinafter also referred to as “correction control”). d) shows the transition of the flow rate of the FC cooling water during the correction control. In addition, the broken line shown in FIG.18 (c) has shown transition of the temperature of FC cooling water before correction | amendment control shown to Fig.18 (a). The change in the FC cooling water temperature can be predicted by the differential value of the FC cooling water temperature (FIG. 18B). Therefore, as described in the flow rate limiting process (FIGS. 11 and 12), when the correction control of the flow rate of the FC cooling water is executed based on the differential value of the FC cooling water temperature, the FC cooling is performed before the correction control. Until the change in the water temperature converges (see FIGS. 18A and 18B), the flow rate of the FC cooling water is limited as shown in FIG. 18D. Thereby, as shown in FIG.18 (c), the fall rate of the temperature of FC cooling water is suppressed so that it may become slow, and the subsequent temperature fluctuation which generate | occur | produced before correction | amendment control according to this is also suppressed. Note that the FC cooling water flow rate when the FC cooling water temperature converges to the control target temperature is lower than the uncorrected flow rate indicated by the broken line, as shown in FIG. This is because the opening and closing positions of the thermostat valve 40 vary depending on the operating state.

  As described above, also in the cooling system 100B of the present embodiment, it is possible to suppress a rapid temperature drop and subsequent fluctuations in the FC cooling water generated by opening the thermostat valve 40. Thereby, it is possible to suppress a rapid temperature drop and temperature fluctuation of the FC stack 10 and stably maintain a highly efficient power generation state in the FC stack 10 for a long period of time. In particular, in the cooling system 100 of the first embodiment, the rapid temperature drop of the FC cooling water due to the opening of the thermostat valve 40 is repeatedly and repeatedly suppressed, whereas in this embodiment, the temperature fluctuation converges. Until then, the restriction is continuously executed while adjusting the flow rate according to the temperature change, and the control based on the basic concept of the flow restriction is executed. Therefore, the effect of suppressing the temperature change of the FC cooling water in the present embodiment is greater than that in the first embodiment.

  Further, in the cooling system 100B according to the present embodiment, the temperature change of the cooling water is differentiated regardless of various variations such as inherent variations of members such as the thermostat valve 40, individual errors, and secular changes. By predicting based on the value and limiting the flow rate of the FC cooling water, it is possible to suppress a rapid temperature drop of the FC cooling water and subsequent temperature fluctuations.

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and the modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell (FC) stack 10a ... Inlet 10b ... Outlet 20 ... Circulation pump 20a ... Inlet 20b ... Outlet 30 ... Temperature sensor 40 ... Thermostat valve 40a ... Inlet 40b ... Inlet 40c ... Outlet 42 ... Valve 50 ... Radiator 50a ... Inlet 50b ... Outlet 80 ... Temperature sensor 100 ... Cooling system 100B ... Cooling system L1 ... Channel L2 ... Channel L3 ... Channel L4 ... Channel L5 ... Channel L6 ... Channel LB ... Bypass circulation channel LC ... Circulation channel

Claims (3)

A cooling system for a fuel cell in which a coolant passing through a radiator is circulated and supplied to the fuel cell via a thermostat valve and a flow rate adjustment mechanism,
The flow rate of the coolant supplied to the fuel cell is less than the flow rate supplied before the thermostat valve is opened by controlling the flow rate adjusting mechanism when the thermostat valve is opened. A fuel cell cooling system characterized by being limited by the flow rate. A fuel cell cooling system according to claim 1,
The restriction on the flow rate of the coolant is executed from the timing just before the thermostat valve is opened until the time limit for the flow rate of the coolant has elapsed,
The fuel cell cooling system, wherein the timing immediately before the valve opening and the flow rate restriction duration are determined based on the temperature of the coolant flowing out of the thermostat valve. A cooling system for a fuel cell in which a coolant passing through a radiator is circulated and supplied to the fuel cell via a thermostat valve and a flow rate adjustment mechanism,
As for the flow rate of the coolant supplied to the fuel cell, a differential value of the temperature of the coolant flowing out from the thermostat valve is obtained, and the flow rate according to a change in the correction amount determined based on the differential value The fuel cell cooling system, wherein the adjustment is performed by controlling the adjustment mechanism.

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