Method for operating a fuel cell system

Abstract

Method for operating a fuel cell system. The present invention relates to a method for operating a fuel cell system (1) having a cooling circuit (8) for cooling at least one fuel cell (2), wherein a coolant cooler (9) is used to cool the coolant circulating in the cooling circuit (8), and in addition, air also flows through the coolant cooler (9). The air is conveyed by a fan assembly (20). The fuel cell system (1) further includes an evaporative cooling device (13) that introduces water into the air conveyed by the fan assembly (20) upstream of the coolant cooler (9). The efficiency of the fuel cell system (1) is increased while sufficiently cooling at least one fuel cell (2) by causing the evaporative cooling device (13) to introduce water at a maximum rate (33) before the fan assembly (20) reaches its maximum air mass flow (31). The present invention also relates to such a fuel cell system (1) and a motor vehicle (25) having such a fuel cell system (1).

Description

Field of the Invention

[0001] The present invention relates to a method for operating a fuel cell system, which includes at least one fuel cell and a cooling circuit for cooling the fuel cell. The present invention also relates to such a fuel cell system and a motor vehicle having such a fuel cell system. Background Art

[0002] During the operation of a fuel cell, a cathode gas and fuel are supplied to the fuel cell in order to generate electrical energy. Heat is generated thereby. In a subordinate fuel cell system, usually a plurality of such fuel cells are assembled into a stack. Heat generation in the respective fuel cell or stack may cause damage to the fuel cell or adjacent components. Therefore, in a subordinate fuel cell system, cooling of at least one fuel cell is usually provided.

[0003] For this purpose, a cooling circuit is generally used, through which a coolant flows during operation and cools at least one fuel cell. In order to cool the coolant, a coolant cooler is generally used, through which the coolant flows during operation and which is flowed through by a cooling gas (hereinafter generally referred to as air) separately from the coolant fluid. Therefore, heat transfer from the coolant to the air occurs in the coolant cooler, thereby cooling the coolant.

[0004] Furthermore, it is known that in order to increase the cooling power of the coolant cooler, water is introduced into the air stream upstream of the coolant cooler, and the water is evaporated and causes additional cooling due to the heat of vaporization required for evaporation. This is generally achieved by means of a device hereinafter referred to as an evaporative cooling device.

[0005] In order to make the cooling of the coolant in the coolant cooler variable, it is common to make the flow of the air flowing through the coolant cooler and / or the rate of the water introduced by the evaporative cooling device variable. In order to convey the air through the coolant cooler, at least one fan is generally used. Therefore, in order to make the flow of the air through the coolant cooler variable, it is possible to operate the fan at different powers. The fan can be designed to operate between a minimum power and a maximum power here. If maximum cooling of at least one fuel cell is required, the fan operates at the maximum possible power. The maximum possible power will result in a correspondingly high energy consumption of the fan, which will lead to a reduction in the efficiency of the fuel cell system.

[0006] Since such fans are usually and increasingly driven electrically, they act as an electrical energy consuming device in the entire fuel cell system or in an application using the fuel cell system. Therefore, the operation of the fan results in a corresponding reduction in the total available electrical energy.

[0007] In the case of a mobile application, for example in a motor vehicle, the energy consumption of the fan results in a corresponding reduction in the maximum available electrical power and / or a reduction in the range. Summary of the Invention

[0008] Accordingly, it is an object of the present invention to describe improved or at least other embodiments, in particular those having higher efficiency, of a method for operating a fuel cell system of the type described at the beginning, such a fuel cell system, and a motor vehicle having such a fuel cell system.

[0009] According to the present invention, this object is solved by the method for operating a fuel cell system according to the present invention. Advantageous embodiments will be described below.

[0010] The present invention provides a method for operating a fuel cell system,

[0011] - wherein the fuel cell system has:

[0012] · at least one fuel cell,

[0013] · a cooling circuit through which a coolant circulates during operation, and the at least one fuel cell is connected into the cooling circuit for cooling the fuel cell,

[0014] · a coolant cooler through which the coolant flows during operation, and air flows through the coolant cooler separately from the coolant in order to cool the coolant,

[0015] · a fan assembly having at least one fan, the fan assembly being used to convey air through the coolant cooler, and during operation, the fan assembly conveys air with an air mass flow rate between a minimum mass flow rate and a maximum mass flow rate,

[0016] · an evaporative cooling device by means of which water can be introduced into the air conveyed by the fan assembly at an introduction rate between a minimum rate and a maximum rate upstream of the coolant cooler,

[0017] - wherein, in order to increase the cooling power of the coolant cooler, the introduction rate and the air mass flow rate are increased,

[0018] - wherein the introduction rate and the air mass flow rate are increased such that the maximum rate is reached before the maximum mass flow rate is reached.

[0019] The basic idea of the present invention is that in a fuel cell system having a cooling circuit for cooling at least one fuel cell and having a coolant cooler through which air flows and which cools the coolant circulating through the cooling circuit, in order to increase the cooling power of the cooler, the air flow through the coolant cooler by means of at least one fan is increased, and the rate of water introduced into the air by means of an evaporative cooling device is increased, wherein these increases are carried out in such a way that the maximum rate of water introduction is reached earlier than the maximum air mass flow that can be achieved by means of at least one fan. Therefore, in order to achieve the maximum cooling power of the coolant cooler, the increase in cooling power achieved by means of the evaporative cooling device is first maximally utilized before the cooling power is maximally increased by means of at least one fan as much as possible. Here, the air flow that already exists before the maximum air mass flow that can be transported by means of at least one fan is reached achieves an increase in cooling power by means of the latent heat of evaporation. Only when the cooling power achieved in this way is insufficient, is at least one fan operated to transport the maximum possible air mass flow. This results in a reduction in the total or average energy consumption of at least one fan. This leads to an increase in the efficiency of the fuel cell system, wherein at the same time damage to at least one fuel cell caused by temperature increase is avoided or at least reduced. Therefore, especially in the case of peak loads, the maximum available power of the fuel cell system is increased. In mobile applications, especially in motor vehicles, this will result in an increase in the operating time and / or the maximum available power, and an increase in the range.

[0020] According to the inventive concept, a fuel cell system comprises at least one fuel cell, a cooling circuit, a coolant cooler, at least one fan and an evaporative cooling device. Advantageously, the fuel cell system comprises at least two, in particular a plurality of fuel cells, which are combined into a stack. During operation, the coolant is circulated through the cooling circuit. At least one fuel cell is connected into the cooling circuit such that the coolant cools at least one fuel cell. During operation, the coolant flows through the coolant cooler and air flows through the coolant cooler separately from the coolant. During operation, the coolant transfers heat to the air and is thus cooled. At least one fan is used to convey air through the coolant cooler. Thus, the fuel cell system comprises a fan assembly with at least one fan. With the fan assembly, air can be conveyed between a minimum air mass flow (also referred to hereinafter as the minimum mass flow) and a maximum air mass flow (also referred to hereinafter as the maximum mass flow). During operation, the evaporative cooling device introduces water into the air conveyed by the fan assembly upstream of the coolant cooler. This is done in such a way that the water evaporates and thus extracts heat from the air and / or the coolant cooler. Here, the water can be introduced into the air at a rate also referred to hereinafter as the introduction rate. The evaporative cooling device is designed such that the water can be introduced between a minimum rate and a maximum rate (referred to hereinafter as the minimum rate and the maximum rate). Here, in order to increase the cooling power of the coolant cooler, the introduction rate and the air mass flow are increased. According to the invention, this is done in such a way that the maximum rate for introducing water into the air is reached before the maximum mass flow that the fan assembly can convey.

[0021] In principle, any means can be used to make the introduction rate variable.

[0022] It is conceivable to use at least one valve to make the introduction rate variable. Alternatively or additionally, in order to make the introduction rate variable, the power of subordinate conveying devices, such as pumps, compressors and similar conveying devices, can also be changed.

[0023] Changing the air mass flow conveyed by the fan assembly is achieved by correspondingly changing the power of the fan assembly during operation. Here, the fan assembly can operate between a minimum power and a maximum power (also referred to hereinafter as the minimum power and the maximum power). Thus, in order to convey the minimum mass flow, the fan assembly will operate at the minimum power, and in order to convey the maximum mass flow, the fan assembly will operate at the maximum power. Here, the air mass flow and the fan power are suitably substantially or approximately in a cubic relationship.

[0024] Changing the mass air flow conveyed by the fan assembly is suitably achieved by correspondingly changing the rotational speed of at least one fan. If the fan assembly has a single fan, then in order to convey the minimum mass flow, the fan operates at the minimum rotational speed (hereinafter also referred to as the minimum speed), and in order to convey the maximum mass flow, it operates at the maximum rotational speed (hereinafter also referred to as the maximum speed). If the fan assembly has two or more fans, then suitably this applies to the sum of the rotational speeds of the fans. This sum corresponds to the total rotational speed of the fans. Thus, in order to convey the minimum mass flow, the fans will operate at the minimum total rotational speed (hereinafter also simply referred to as the minimum speed), and in order to convey the maximum mass flow, they will operate at the maximum total rotational speed (hereinafter also simply referred to as the maximum speed). Similarly, the total rotational speed is hereinafter also simply referred to as the rotational speed. Here, the rotational speed or total rotational speed is suitably substantially or approximately linearly related to the mass air flow.

[0025] The fan power between the minimum power and the maximum power causes the mass air flow through the coolant cooler to increase from the minimum power to the maximum power. Similarly, the operation of the fan assembly between the minimum speed and the maximum speed causes the mass air flow through the coolant cooler to increase.

[0026] Air is conveyed actively by operating the fan assembly. It is possible here that, without using the fan assembly, for example by means of other conveying devices, such as oncoming air, air also flows through the coolant cooler.

[0027] At least one of the at least one fan is advantageously operated electrically. This in particular allows for a simple implementation and self-sufficient operation of the fuel cell system.

[0028] A preferred embodiment is that the fan assembly is put into operation before the evaporative cooling device. This generally results in a steeper switching characteristic curve for the evaporative cooling device than for the fan assembly. Thus, before the introduction of water, the fan assembly will operate at the minimum rate to convey a mass air flow that is at least equivalent to the minimum mass flow and lower than the maximum mass flow. This mass air flow is hereinafter also referred to as the threshold mass flow. The subordinate rotational speed is hereinafter also referred to as the threshold speed. Thus, it is ensured that before the introduction of water, air flow exists at the minimum rate. Thus, water staying at the fan assembly and / or the coolant cooler is avoided, or at least the residence time of the water is shortened. Thus, damage caused by water, such as that which may be caused by corrosion and / or thermal stress, is avoided or at least reduced. In addition, in this way, the water is at least partially transported by the air flow, so that the cooling achieved by the evaporative cooling device is fully achieved by the latent heat of evaporation or with higher efficiency. Thus, in this way, not only is damage at least reduced, but also the power and efficiency of the fuel cell system are increased.

[0029] In principle, the threshold mass flow can correspond to any air mass flow. The same applies to the threshold rotational speed.

[0030] Advantageously, the threshold mass flow is between 30% and 90% of the maximum mass flow. Preferably, the threshold mass flow is between 50% and 80% of the maximum mass flow. Thus, a sufficiently high air flow is achieved before introducing water at the minimum rate. Therefore, the described damage is effectively avoided and the efficiency of the fuel cell system is effectively increased.

[0031] The interdependent operation of the fan assembly and the evaporative cooling device advantageously depends on the rotational speed of the fan assembly. Since the rotational speed is an easily adjustable and / or easily monitored parameter, the operation of the fuel cell system can be achieved simply and reliably.

[0032] Before introducing at the minimum rate, the fan assembly operates at the threshold mass flow for conveyance, which is advantageously achieved by making the evaporative cooling device operate depending on a given rotational speed (i.e., the actual value of the rotational speed) or on a desired rotational speed (i.e., the rated value of the rotational speed). In other words, the introduction rate is coupled with the actual value and / or the rated value of the rotational speed. This results in simple and reliable operation of the fuel cell system.

[0033] Advantageously, the introduction rate and the rotational speed approximately have a cubic relationship. In a particularly advantageous embodiment, their correlation is at least equivalent to a cubic parabola segment in a certain region. Thus, it can be particularly taken into account that the fan power is basically in a cubic relationship with the rotational speed of at least one fan. In other words, a coupling between the air flow and the introduction rate is thus achieved, which results in effective utilization of the latent heat of evaporation to increase the cooler power and results in effective reduction of the described damage.

[0034] Here, a simplified adaptation adjustment of the introduction rate can be achieved through a proportional valve. Alternatively or additionally, an on / off valve, i.e., a valve that can be adjusted step by step, can be used. Here, the change in the amount of water supplied to the evaporative cooling device can be achieved through throttling. Alternatively or additionally, the pressure in the water container storing the reserve water can be changed and / or a variable conveyance device, such as a variable pump, can be used.

[0035] Here, a substantially sudden increase in the mass flow of the evaporated water can be achieved when reaching the threshold mass flow or the threshold rotational speed. Thus, the fuel cell system can be achieved simply and inexpensively, especially being simply and inexpensively manufactured.

[0036] The introduction rate corresponds to the amount of water introduced per unit time.

[0037] In principle, during the introduction of water at the maximum rate, the total amount of water introduced per unit time can be constant here.

[0038] It is also conceivable that during the introduction of water at the maximum rate, the total amount of water introduced per unit time is adaptively adjusted depending on the parameters of the fuel cell system and / or the environment and / or the subordinate application site. It is thus particularly possible to adjust the cooling power required separately depending on the relevant parameters (also referred to hereinafter as state parameters). This results in an improved efficiency of the fuel cell system. These state parameters include, for example, the ambient temperature, the ambient humidity, the water reservoir of the evaporated water, and the air mass flow through the coolant cooler.

[0039] Preferably, the fan assembly and / or the evaporative cooling device are only put into operation when corresponding cooling of at least one fuel cell is required. This means that only when the parameter associated with the temperature of at least one fuel cell exceeds a lower boundary value, the cooling power of the coolant cooler is increased by means of the fan assembly and / or the evaporative cooling device. This particularly avoids unnecessary operation of the fan assembly and / or the evaporative cooling device. This results in an increase in the efficiency of the fuel cell system.

[0040] Advantageously, the fan assembly is put into operation above the lower boundary value in order to convey air. Preferably, above the lower boundary value, the fan assembly conveys air between a minimum mass flow and a maximum mass flow depending on the rated value of the parameter.

[0041] Advantageously, the fan assembly is put into operation when the lower boundary value is exceeded. This means that above the lower boundary value, the fan assembly conveys air between a minimum mass flow and a maximum mass flow.

[0042] Advantageously, if below the lower boundary value, the fan assembly stops operating. Thus, after the parameter value is below the lower boundary value, the fan assembly does not convey air.

[0043] It is conceivable that when the parameter suddenly drops below the lower boundary value, the fan assembly will continue to operate for a period of time, in particular for a pre-given period of time, in order to convey air through the coolant cooler. The knowledge that a sudden drop below the lower boundary value leads to a rapid decrease in the air mass flow is utilized here. In this case, where the through-flow of the coolant cooler is thus low and no through-flow occurs, the evaporated water may remain in the coolant cooler for a long time. The result may be corrosion and / or freezing of the evaporated water. To counteract this, the fan assembly is therefore allowed to continue operating for a period of time so that the evaporated water can evaporate from the coolant cooler and / or be conveyed away. This drying process can be supported and / or accelerated by simultaneously passing the coolant through the coolant cooler.

[0044] Furthermore, it is preferably that in the case where the value of the parameter is below the lower boundary value, the evaporative cooling device does not operate, i.e., water is not actively introduced.

[0045] It is conceivable that, below the lower boundary value and / or when at least one fuel cell is switched off or deactivated, especially when the subordinate motor vehicle is stationary and / or moving slowly, the evaporative cooling device is allowed to continue operating in order to transport water out of the evaporative cooling device. The following knowledge is utilized here, namely that water remaining in the evaporative cooling device for a long time can cause damage, especially due to corrosion and / or freezing. By keeping the evaporative cooling device running, this situation is counteracted in order to expel water from the evaporative cooling device in order to prevent possible icing and / or corrosion of the water. This is done especially when the ambient temperature is below 5 °C and / or depending on weather data and / or depending on the current season and / or place of residence. For example, drainage can be effected by opening at least one valve and / or by deliberately leaking at least one valve.

[0046] In a preferred embodiment, in at least one range between the minimum mass flow and the maximum mass flow, the value to be achieved and thus the rated value of the parameter depends on the actual value of the air mass flow or on a parameter associated therewith, such as the rotational speed and / or the fan power.

[0047] In a preferred embodiment, up to the boundary mass flow between the minimum mass flow and the maximum mass flow, the rated value is substantially constant, while above the boundary mass flow the rated value increases up to the upper boundary value of the parameter. According to the above explanation, this boundary mass flow is reached at the boundary of the corresponding rotational speed, which boundary rotational speed is also referred to below as the boundary speed. This results in the air mass flow increasing from the lower boundary value of the parameter up to the boundary mass flow in order to keep the rated value substantially constant. Above the boundary mass flow, the rated value of the parameter is allowed to increase up to the upper boundary value. In other words, the range is delimited or defined by the boundary mass flow up to the maximum mass flow. Thus, especially in the case of a peak load during operation where the power generated by means of at least one fuel cell needs to reach a peak, the time to reach the maximum mass flow is delayed, whereas in the prior art, in such a case, the fan assembly would continuously transport the maximum mass flow. Thus, the maximum energy consumption of the fan assembly is delayed. This results in an increase in the energy available for other applications, especially during peak loads. Thus, the electrical energy available for subordinate applications is increased, especially during peak loads. In addition, this also results in a reduction in the average energy consumption of the fan assembly.

[0048] Preferably, when the upper boundary value of the parameter is reached, the fan assembly preferably transports air at the maximum mass flow.

[0049] In principle, the increase in the air mass flow from the boundary mass flow to the maximum mass flow can be carried out arbitrarily. In particular, the air mass flow can be increased abruptly (i.e., in one step) from the boundary mass flow to the maximum mass flow.

[0050] Preferably, the air mass flow increases up to the maximum mass flow above the boundary mass flow. In particular, it is conceivable that the air mass flow increases up to the maximum mass flow in a constant, multi-stage, continuous, etc. manner above the boundary mass flow.

[0051] In an advantageous embodiment, the boundary mass flow is between 30% and 90% of the maximum mass flow. Particularly preferably, the boundary mass flow is between 50% and 80% of the maximum mass flow. Thus, the efficiency of the fuel cell system is increased while reducing the energy consumption of the fan assembly, and damage to at least one fuel cell is avoided or at least reduced.

[0052] An advantageous embodiment is that the rated value increases linearly within this range with the air mass flow and thus the rotational speed. This means that the relationship between the rated value and the air mass flow and thus the rotational speed within this range can be represented in the form of a cubic parabola segment. This particularly takes into account that the power of the fan assembly is approximately cubic with the air mass flow and thus the rotational speed. This results in the coolant being reliably cooled, while at the same time avoiding or at least reducing damage to at least one fuel cell.

[0053] The threshold mass flow is suitably less than the boundary mass flow here. Thus, the threshold rotational speed is lower than the boundary rotational speed.

[0054] In particular, it is conceivable that the maximum rate is introduced when the boundary mass flow is reached. In other words, when the boundary mass flow is reached, the increase in the cooling power of the coolant cooler achieved by means of the evaporative cooling device is increased. This results in a smaller increase in the parameter above the boundary mass flow. Thus, the increase in the air mass flow is prevented or at least delayed. Thus, the energy required and consumed by the fan assembly is further reduced.

[0055] The fuel cell system can be designed arbitrarily for implementing the method. In particular, the fuel cell system can include a correspondingly designed control device.

[0056] The fuel cell system can be used for any purpose. In particular, it is conceivable that the fuel cell system is used for mobile applications, for example in motor vehicles. Here, the fuel cell system, in particular at least one fuel cell, can be used to drive a motor vehicle.

[0057] It should be understood that, in addition to the method, such a fuel cell system and such an application, in particular such a motor vehicle, respectively belong to the scope of the present invention.

[0058] Further important features and advantages of the present invention result from the drawings and the associated description in conjunction with the drawings.

[0059] It should be understood that the features described above and those to be explained below can be used not only in the combinations separately described, but also in other combinations or alone, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Preferred embodiments of the present invention are shown in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components.

[0061] Wherein schematically respectively:

[0062] Figure 1 A diagram showing a highly simplified wiring diagram of a fuel cell system;

[0063] Figures 2 to 6 Diagrams respectively showing simplified diagrams for explaining the method of operating a fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0064] As Figure 1 The fuel cell system 1, as shown in a highly simplified and wiring-diagram-like manner, has at least one fuel cell 2. In the illustrated embodiment, the fuel cell system 1 has a plurality of fuel cells 2 which are assembled into a stack 3. In operation, at least one fuel cell 2 requires fuel and cathode gas, such as air. The fuel is supplied to the stack 3 via a fuel supply facility 4. The cathode gas is supplied to at least one fuel cell 2 by means of a cathode gas supply facility 5. In order to transport the cathode gas to at least one fuel cell 2, the cathode gas supply facility 5 has a transport device 6, which is also referred to below as the cathode gas transport device 6. The cathode gas transport device 6 can compress the cathode gas to transport the cathode gas. During the operation of at least one fuel cell 2, water-containing exhaust gas, in particular steam, is generated. These exhaust gases are discharged by means of an exhaust gas facility 7 of the motor vehicle 25. Heat is also generated during the operation of at least one fuel cell 2, so that it may be necessary to cool at least one fuel cell 2 during the operation of the motor vehicle 25.

[0065] To cool at least one fuel cell 2, the fuel cell system 1 has a cooling circuit 8 through which coolant circulates during operation. At least one fuel cell 2 (a stack 3 in the illustrated embodiment) is connected into the cooling circuit 8 in such a way that it is cooled by the coolant during operation. To cool the coolant, the fuel cell system 1 has a cooler 9, which is also referred to below as a coolant cooler 9. The coolant cooler 9 is likewise connected into the cooling circuit 8 and is flowed through by the coolant during operation. The cooling circuit 8 suitably also has further components, which are connected into the cooling circuit 8, for example a conveying device 10 for conveying the coolant through the cooling circuit 8, which is also referred to below as a coolant conveying device 10. Thus, the flow path 11 of the coolant (also referred to below as the coolant path 11) passes through the cooling circuit 8. To cool the coolant, air is used as the cooling gas. The air flows through the coolant cooler 9 along a subordinate flow path 12 (also referred to below as the cooling gas path 12) separately from the coolant, such that the coolant transfers heat to the air separately from the coolant in the coolant cooler 9 and is thus cooled.

[0066] To improve the cooling effect of the coolant, the fuel cell system 1 also has an evaporative cooling device 13 by means of which water can be introduced into the cooling gas path 12 at the coolant cooler 9 and downstream of the coolant cooler 9. This causes evaporation of the water, which results in an improved cooling effect of the coolant in the coolant cooler 9. The evaporative cooling device 13 can introduce water into the cooling gas path 12 here between a minimum rate 32 and a maximum rate 33 (see Figure 2 ). Thus, the introduction rate 29 of the water introduced by means of the evaporative cooling device 13 (see Figure 2 ) can be adjusted between the minimum rate 32 and the maximum rate 33. In the illustrated embodiment, the water supplied to the evaporative cooling device 13 comes from a water container 14 in which water obtained from the exhaust gas is collected. The water collected in the water container 14 can be obtained from the exhaust gas, for example, by means of a water separator 19 provided in the exhaust gas facility 7. To supply water to the evaporative cooling device 13, a flow path 15 leads from the water container 14 to the evaporative cooling device 13, where this flow path 15 is also referred to below as the evaporation path 15.

[0067] To introduce water between the minimum rate 32 and the maximum rate 33 by means of the evaporative cooling device 13, pressure is applied to the water. In Figure 1In the exemplary embodiment shown in , this is done purely by way of example with the aid of the cathode gas conveyor 6. For this purpose, a flow path 16 of the cathode gas leads to the water container 14 on the pressure side of the cathode gas conveyor 6, wherein this flow path 16 is also referred to below as compressed air path 16. In order to make the introduction rate variable, at least one valve 17 of a valve device 18 can be used here. In this case, in the exemplary embodiment shown, a valve 17a is arranged in the compressed air path 16 and / or a valve 17b is arranged in the evaporation path 15.

[0068] The air conveyed through the coolant cooler 9 is conveyed by means of a fan assembly 20, which comprises at least one electrically operated fan 21. In the exemplary embodiment shown, it is assumed purely by way of example that the fan assembly 20 has a single fan 21. In order to make the flow of air through the coolant cooler 9 variable, the air mass flow 28 conveyed through the coolant cooler 9 by means of the fan assembly 20 is varied (see Figure 2 Here, the fan assembly 20 can transport air between a minimum air mass flow 30 (hereinafter also referred to as minimum mass flow 30) and a maximum air mass flow 31 (hereinafter also referred to as maximum mass flow 31). In the illustrated embodiment, the air mass flow 28 is linearly related to the rotational speed of the fan 21.

[0069] In order to make the cooling power of the coolant cooler 9 variable, the air mass flow 28 and the introduction rate 29 are made variable accordingly. Here, increasing the air mass flow 28 and / or the introduction rate 29 is used to increase the cooling power. For example, this is carried out with the help of a control device 22, which is designed accordingly and connected to the fan assembly 20 in a communication manner (not shown). In addition, the control device 22 is advantageously also connected to the valve device 18 in a communication manner. In the embodiment shown, the fuel cell system 1 also has a device 23 for determining a parameter related to the temperature of at least one fuel cell 2, wherein the device 23 is also referred to as a parameter identification device 23 below. Here, in the embodiment shown, the parameter identification device 23 is a temperature sensor 24, which determines the temperature of at least one fuel cell 2, in particular the temperature of the stack 3, and / or determines the temperature of the coolant downstream of at least one fuel cell 2 in the embodiment shown. Therefore, in the embodiment shown, the parameter is the temperature of at least one fuel cell in the at least one fuel cell 3 and / or the temperature of the coolant downstream of at least one fuel cell 2. The parameter identification device 23 is also connected to the control device 22 in a communication manner.

[0070] Will be combined below Figures 2 to 6The operation of the fuel cell system 1 is explained by means of the schematic diagrams shown, which can be used, for example, in a motor vehicle 25 not shown, in particular in order to drive the motor vehicle 25. Here, in these schematic diagrams, the introduction rate 29 and the air mass flow 28 are shown dimensionless as a percentage share of their respective maximum values.

[0071] Here, Figure 2 a schematic diagram is shown, in which the parameters mentioned are plotted along the abscissa 26, in particular the temperature of at least one fuel cell 2. The percentage quantity is plotted along the ordinate 27, where the air mass flow 28 represented as a percentage is plotted as a dashed line and the introduction rate 29 represented as a percentage is plotted as a solid line. According to Figure 2 , the air mass flow 28 thus lies between a minimum mass flow 30 of 0% and a maximum mass flow 31 of 100%. Since there is a substantially linear relationship between the air mass flow 28 and the rotational speed, the percentage curve of the air mass flow 28 shown and thus the characteristic line of the air mass flow 28 essentially corresponds to the percentage curve or characteristic line of the rotational speed. Similarly, the introduction rate 29 lies between a minimum rate 32 of 0% and a maximum rate 33 of 100%. It can be seen from Figure 2 that both the air mass flow 28 and the introduction rate 29 increase with the increase of the parameter in order to increase the cooling power of the coolant cooler 9. It can be seen from Figure 2 that the maximum rate 33 is reached earlier than the maximum mass flow 31.

[0072] Furthermore, it can be seen from Figure 2 that in the embodiment shown, the fan assembly 20 is put into operation before the evaporative cooling device 13. This means that before water is introduced at the minimum rate 32, the fan assembly 20 conveys air with an air mass flow 34 represented as a percentage that is at least equivalent to the minimum mass flow 30, where this air mass flow 34 is also referred to below as the threshold mass flow 34. Conversely, this means that only when the threshold mass flow 34 is reached does the evaporative cooling device 13 introduce water into the air at the minimum rate 32. It can be seen from Figure 2 that the resulting situation is that the characteristic line of the introduction rate 29 extends more steeply than the characteristic line of the air mass flow 28 and thus than the characteristic line of the rotational speed. It can be seen from Figure 2 that the threshold mass flow 34 lies here between 30% and 90% of the maximum mass flow 31, preferably between 50% and 80% of the maximum mass flow 31, and in this embodiment is approximately 45% of the maximum mass flow 31.

[0073] It can be seen from Figure 2It can also be seen that the cooling power enhancement achieved by means of the fan assembly 20 and the evaporative cooling device 13 is only carried out when the parameter of at least one fuel cell 2 and thus the temperature exceeds the lower boundary value 35. Here, when the lower boundary value 35 is exceeded, the fan assembly 20 operates with a minimum mass flow 30. As can be seen from the above, when the parameter reaches or exceeds the boundary value 36, the evaporative cooling device 13 is put into operation and water is introduced at a minimum rate 32. This boundary value is also referred to as the intermediate boundary value 36 below. Here, it is preferred that the fan assembly 20 operates depending on the parameter obtained. In addition, it is preferred that the evaporative cooling device 13 and thus the introduction rate 29 are adjusted depending on the air mass flow 28, advantageously depending on the rotational speed. The air mass flow 28 and thus the rotational speed are coupled to the parameter, and the introduction rate 29 is coupled to the air mass flow 28 and thus the rotational speed, and thus indirectly coupled to the parameter.

[0074] Therefore, in the case of being higher than the lower boundary value 35, the fan assembly 20 operates depending on the rated value of the parameter to convey the air mass flow 28 between the minimum mass flow 30 and the maximum mass flow 31.

[0075] Figure 3 Another simplified diagram is shown, in which the air mass flow 28 is plotted along the horizontal axis 26 in percentage representation or the rotational speed is plotted similarly, and the introduction rate 29 is plotted along the vertical axis 27. From Figure 3 it can be seen that a substantially cubic relationship appears segmentally between the air mass flow 28 represented by percentage and the introduction rate 29. Therefore, in Figure 3 the characteristic line 37 shown extends substantially as a parabolic segment in the section bounded between the threshold mass flow 34 and the maximum rate 33. This especially takes into account that the power of the fan assembly 20 and thus the rotational speed are cubic with respect to the conveyed air mass flow.

[0076] According to Figures 4 to 6 , in at least one range between the minimum mass flow 30 and the maximum mass flow 31, the value to be reached of the parameter and thus the rated value of the parameter can depend on the actual value of the air mass flow 28 and thus on the rotational speed. Here, Figure 4 a simplified diagram is shown, in which the air mass flow 28 represented by percentage is plotted along the horizontal axis 26, and the rated value of the parameter is plotted along the vertical axis 27. Figure 5 A simplified diagram is shown, in which the actual value of the parameter is plotted along the horizontal axis 26, and the air mass flow 28 is plotted along the vertical axis 27. In Figure 6 a simplified diagram can be seen, in which the actual value of the parameter is plotted along the horizontal axis 26, and the air mass flow 28 is plotted along the vertical axis 27.

[0077] InFigures 4 to 6 In the embodiment shown herein, it is provided that up to the boundary value 38 of the air mass flow 28 (also referred to hereinafter as the boundary mass flow 38), the rated value is substantially constant, and above the boundary mass flow 38, the rated value increases up to the upper boundary value 39 of the parameter. Here, the threshold mass flow 34 is suitably less than the boundary mass flow 38, and the corresponding characteristic line is shown in Figures 4 to 6 by a solid line. In Figures 4 to 6 in contrast, the comparison with the prior art is shown by a dashed line. Thus, it can be seen from Figures 4 to 6 that compared with the prior art in which the rated value of the parameter remains as constant as possible over the entire available air mass flow 28 and thus between the minimum speed 30 and the maximum speed 31, there is a delay in the time to reach the maximum mass flow 31. The upper boundary value 39 of the parameter is here related to the temperature of at least one fuel cell in at least one of the fuel cells 2, exceeding which will cause permanent damage to at least one of the fuel cells 2. The adaptation of the rated value to the air mass flow 28 in this range can be carried out with the aid of the characteristic line shown in Figure 6 and thus based on the characteristic line.

[0078] In Figures 4 to 6 it can also be seen that in the embodiment shown, when the upper boundary value 39 of the parameter is reached, the fan assembly 20 operates at the maximum mass flow 31 for conveyance. In Figure 5 in the embodiment shown, in the range between the boundary mass flow 38 and the maximum mass flow 31, there is a sectional cube root function relationship between the air mass flow 28 or the speed and the parameter.

[0079] In Figure 6 in the embodiment shown, there is a square or cubic relationship in the form of a parabolic segment between the air mass flow 28 and the actual value of the parameter in this range (i.e., between the boundary mass flow 38 and the maximum mass flow 31).

[0080] It can be seen from Figure 4 that in this range, i.e., between the boundary mass flow 38 and the maximum mass flow 31, there is preferably an approximately cubic relationship in the form of a parabolic segment between the air mass flow 28 and the rated value of the parameter. Here, through this cubic relationship, in particular, the fan power of the fan assembly 20 is considered to be approximately cubic with respect to the air mass flow 28 and with respect to the speed of the fan assembly 20.

[0081] It can be seen from Figures 4 to 6As can be seen, the boundary mass flow 38 is preferably between 30% and 90%, particularly preferably between 50% and 80% of the maximum mass flow 31 in the illustrated embodiment. In the illustrated embodiment, the boundary mass flow 38 is 70% of the maximum mass flow 31.

[0082] In the overview Figures 2 to 5 it can thus be confirmed that the threshold mass flow 34 is less than the boundary mass flow 38. The subordinate rotational speeds are accordingly the same.

[0083] In particular, from Figure 2 it can be seen that preferably, at the attainment of the boundary mass flow 38, the maximum rate 33 of the introduction rate 29 has been introduced. Thus, before the maximum mass flow 31 is reached, the increase in the cooling power of the coolant cooler 9 achieved by means of the evaporative cooling device 13 has been utilized as fully as possible. This results in a smaller increase in the parameter above the boundary mass flow 38. Thus, the stage at which the fan assembly 20 begins to convey at the maximum mass flow 31 will be further delayed or shortened. This results in a further reduction in the energy consumption of the anti-fan assembly 20.

[0084] If at least one fuel cell 2 is about to be permanently damaged within a range, it is advantageous to suspend and / or interrupt the adaptation of the rated value of the parameter according to the air mass flow 28 in order to convey air at the maximum mass flow 31. For example, this can be achieved by adjusting the rated value to a safety value that is less than the upper boundary value 39 and greater than or equal to the lower boundary value 35 (not shown). In particular, when the increase in the rated value within a range exceeds a pre-given or calculated maximum duration, and / or when the electrical power exerted by at least one of the at least one fuel cell 2 in the fuel cells drops, the rated value can be adjusted to the safety boundary value.

[0085] With this operating method, the fuel cell system 1 described, and the motor vehicle 25, reliable cooling of at least one fuel cell 2 is achieved with increased efficiency. Since the fan assembly 20 operates electrically, there is generally also more electrical energy available for the subordinate application (herein the application of the motor vehicle 25). In addition to increasing the available power, this also results in an increase in the range of the motor vehicle 25.

Claims

1. A method for operating a fuel cell system (1), - wherein the fuel cell system (1) has: · at least one fuel cell (2), · a cooling circuit (8) through which a coolant circulates during operation, and the at least one fuel cell (2) is connected into the cooling circuit for cooling the fuel cell (2), · a coolant cooler (9) through which the coolant flows during operation, and air flows through the coolant cooler separately from the coolant to cool the coolant, · a fan assembly (20) having at least one fan (21), the fan assembly being used to convey air through the coolant cooler (9), and during operation, the fan assembly conveys air with an air mass flow rate (28) between a minimum mass flow rate (30) and a maximum mass flow rate (31), · an evaporative cooling device (13) by means of which water can be introduced into the air conveyed by the fan assembly (20) with an introduction rate (29) between a minimum rate (32) and a maximum rate (33) upstream of the coolant cooler (9), - wherein, in order to increase the cooling power of the coolant cooler (9), the introduction rate (29) and the air mass flow rate (28) are increased, - wherein, the introduction rate (29) and the air mass flow rate (28) are increased such that the maximum rate (33) is reached before the maximum mass flow rate (31) is reached.

2. The method according to claim 1, characterized in that, before introducing water at the minimum rate (32), the fan assembly (20) conveys air with a threshold mass flow rate (34) which is at least equivalent to the minimum mass flow rate (30) and less than the maximum mass flow rate (31).

3. The method according to claim 2, characterized in that, the threshold mass flow rate (34) is between 30% and 90% of the maximum mass flow rate (31).

4. The method according to claim 3, characterized in that, the threshold mass flow rate (34) is between 50% and 80% of the maximum mass flow rate (31).

5. The method according to claim 2, characterized in that, water is introduced with an introduction rate (29) between the minimum rate (32) and the maximum rate (33) depending on the actual value or rated value of the air mass flow rate (28).

6. The method according to claim 1, characterized in that, the introduction rate (29) has a cubic relationship with the air mass flow rate (28) in at least one section.

7. The method according to claim 1, characterized in that, the amount of water introduced during introducing water at the maximum rate (33) depends on the state parameters of the fuel cell system (1) and / or the surrounding environment.

8. The method according to claim 1, characterized in that, - when a parameter related to the temperature of the at least one fuel cell (2) is higher than a lower boundary value (35), the fan assembly (20) is put into operation to convey air, - When above the lower boundary value (35), the fan assembly (20) conveys an air mass flow (28) between the minimum mass flow (30) and the maximum mass flow (31) depending on the rated value of the parameter. - The rated value depends on the actual value of the air mass flow (28) within at least one range between the minimum mass flow (30) and the maximum mass flow (31).

9. The method according to claim 8, characterized in that - Until the boundary mass flow (38) of the air mass flow (28) between the minimum mass flow (30) and the maximum mass flow (31) and above the threshold mass flow (34), the rated value is constant. - When above the boundary mass flow (38), the rated value increases until the upper boundary value (39) of the parameter.

10. A fuel cell system (1), the fuel cell system having: - At least one fuel cell (2), - A cooling circuit (8), in operation, coolant circulates through the cooling circuit, and the at least one fuel cell (2) is connected into the cooling circuit to cool the fuel cell (2). - A coolant cooler (9), in operation, coolant flows through the coolant cooler, and air flows through the coolant cooler separately from the coolant to cool the coolant. - A fan assembly (20) having at least one fan (21), the fan assembly conveys air through the coolant cooler (9) in operation, and with the fan assembly, air can be conveyed with an air mass flow (28) between the minimum mass flow (30) and the maximum mass flow (31). - An evaporative cooling device (13), the evaporative cooling device introduces water into the air conveyed by the fan assembly (20) at an introduction rate (29) between the minimum rate (32) and the maximum rate (33) upstream of the coolant cooler (9) in operation. - A control device (22), the control device is designed to operate the fuel cell system (1) according to the method according to any one of claims 1 to 9.

11. A motor vehicle (25), the motor vehicle having the fuel cell system (1) according to claim 10.

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