FILL LEVEL CONTROL FOR FUEL CELL COOLING SYSTEM

Abstract

The present development relates to a device and a method for determining a coolant level of a fuel cell cooling system (10), which has at least one coolant line (26, 28) that can be thermally coupled to a fuel cell (20) and through which a coolant (8) can flow, comprising the following steps: - measuring at least a first insulation resistance (36) of a first high-voltage line (16) electrically connected to the fuel cell (20) and to the coolant (8) flowing through the coolant line (26, 28), - comparing the measured first insulation resistance (36) with a first predetermined target insulation resistance or with a first insulation resistance (36') measured at an earlier time, - Determine the coolant level of the fuel cell cooling system based on the comparison performed.

Description

Technical area

[0001] The present development relates to the field of fuel cells, in particular the field of fuel cell cooling. In particular, the present development relates to a device for controlling the fill level of a fuel cell cooling system. background

[0002] Fuel cells generate electrical power by oxidizing a fuel, such as hydrogen. Fuel cells typically have a fuel cell stack, which requires active cooling during operation. Common cooling systems include a coolant circuit through which a coolant flows, allowing thermal energy generated in the area of ​​the fuel cell stack to be released into the environment in a controlled manner, ensuring proper and continuous operation of the fuel cell.

[0003] Common cooling systems for fuel cells have a separate level sensor that can be used to determine the coolant level in the fuel cell cooling system. However, if the cooling system develops a leak and / or loses coolant, potentially impairing its proper operation, the level sensor can detect such a critical operating condition. Appropriate sensor signals can be used to initiate appropriate countermeasures, such as an emergency shutdown of the fuel cell and / or a warning signal for the vehicle user.

[0004] In contrast, the objective of this further development is to simplify the determination of the coolant level in a fuel cell cooling system, to reduce the equipment required for determining the coolant level, and thus to contribute to a reduction in vehicle weight. Where possible, existing components of a motor vehicle should be used to solve this problem. Advantageous designs

[0005] This object is achieved by a method, a device, and a motor vehicle according to the features of the independent patent claims. Advantageous embodiments are the subject of dependent patent claims.

[0006] In this respect and in a first aspect, a method for determining a coolant fill level of a fuel cell cooling system is provided. The fuel cell cooling system has at least one coolant line that can be thermally coupled to a fuel cell and through which a coolant can flow. The method comprises the steps of measuring at least a first insulation resistance of a first high-voltage line that is electrically connected to the fuel cell and to the coolant flowing through the coolant line. After measuring the first insulation resistance, the measured first insulation resistance is compared with a first predetermined target insulation resistance and / or with a first insulation resistance measured at an earlier point in time. Based on the comparison performed, the coolant fill level of the fuel cell cooling system can then be determined.

[0007] The method is based on the assumption that the coolant in the coolant line contributes to the measurable insulation resistance, and that if the coolant level in the fuel cell cooling system is insufficient, the first measurable insulation resistance deviates from the specified target insulation resistance or from a first insulation resistance measured at an earlier point in time. The degree of the deviation can provide direct information about the coolant level in the fuel cell cooling system.

[0008] When the coolant level drops or decreases, a significant increase in the measurable first insulation resistance can be observed. The degree of the increase or deviation from the target insulation resistance or from a previously measured first insulation resistance can then be reliably correlated with a drop or decrease in the coolant level in the fuel cell cooling system.

[0009] The method is advantageous in that it accesses existing components of a vehicle fuel cell or vehicle electrical system. Electric vehicles are equipped as standard with hardware and / or system components that allow the insulation resistance of a high-voltage cable connected to the fuel cell to be measured. This is required and necessary for regulatory reasons alone. If, for example, the vehicle's high-voltage electrical system malfunctions, the malfunction can be precisely identified by measuring the insulation resistance.

[0010] In cases of malfunction in the motor vehicle's high-voltage system, the insulation resistance typically decreases noticeably. By also designing the method to measure an increase in insulation resistance, it can provide an expanded range of functions, for example, by inferring that an increase in the measured first insulation resistance indicates a drop in the coolant level of the fuel cell cooling system.

[0011] According to a further embodiment, the coolant level is determined based on the measured first insulation resistance. The level or magnitude of the first insulation resistance and / or its deviation from the target insulation resistance or from a first insulation resistance measured at an earlier time, which can be stored as a reference insulation resistance, for example, or stored in the system, can be used to quantitatively determine the coolant level.

[0012] In this way, by measuring the first insulation resistance and by comparing the first insulation resistance with the target insulation resistance or with a previously measured first insulation resistance, i.e. the reference insulation resistance, the fill level of the coolant in the fuel cell cooling system can be determined relatively precisely.

[0013] According to a further embodiment of the method, the coolant level is determined to be insufficient if the measured first insulation resistance deviates by more than a predetermined amount from the specified target insulation resistance or from the first insulation resistance measured at an earlier time, i.e., the first reference insulation resistance. Certain tolerances in the deviation of the first insulation resistance with respect to the specified target insulation resistance or the previously measured first reference insulation resistance can be disregarded in order to account for any measurement tolerances that may occur, for example, due to temperature or aging.

[0014] According to a further embodiment of the method, the coolant level is determined to be insufficient if the measured first insulation resistance is higher than the specified target insulation resistance, in particular if the measured first insulation resistance is higher than the specified target insulation resistance by the specified amount. Likewise, the coolant level can be determined to be insufficient if the measured first insulation resistance is higher, in particular higher by the specified amount, than the first insulation resistance measured at an earlier point in time, i.e., the first reference insulation resistance.

[0015] An increase in insulation resistance by a predetermined amount can be a direct indication of the absence of coolant in the coolant line and can therefore be detected precisely. Other malfunctions in the vehicle's electrical system typically lead to a reduction in insulation resistance. Such a reduction in insulation resistance can be distinguished in magnitude from an increase in insulation resistance caused by the absence of coolant, allowing both cases—an exceptional increase in insulation resistance caused by the absence of coolant and an exceptional decrease in insulation resistance caused by a malfunction of the electrical system—to be distinguished from one another.

[0016] According to a further embodiment of the method, a second insulation resistance of a second high-voltage line electrically connected to the fuel cell and to the coolant flowing through the coolant line is also measured. The second insulation resistance is also compared with a predetermined second target insulation resistance or with a second insulation resistance measured at an earlier time.

[0017] The first insulation resistance can be measured, for example, with respect to a first pole of a motor vehicle's high-voltage direct current system. The second insulation resistance can be measured at a second pole of the motor vehicle's high-voltage direct current system. In this respect, the insulation resistance measurement can be performed redundantly. The measurement of the second insulation resistance and its evaluation can be performed in the same way as the measurement and comparison of the first insulation resistance, which is why the above-mentioned description for the first insulation resistance can be used for the second insulation resistance, its measurement, and its evaluation.

[0018] According to a further embodiment of the method, a third insulation resistance is also measured between the first high-voltage line and the second high-voltage line. The third insulation resistance can be compared with a third target insulation resistance and / or with a third insulation resistance measured at an earlier point in time to determine the coolant level. This provides further redundancy for the measuring system. The individual poles, such as the positive pole and the negative pole of the high-voltage lines connected to the fuel cell, can each be measured separately for their insulation resistance.

[0019] Furthermore, an insulation resistance can be measured between the two poles. All measurements—the measurement of the first insulation resistance, the measurement of the second insulation resistance, and the measurement of the third insulation resistance—can be performed by an existing controller of the electrical system, such as a fuel cell controller and / or a high-voltage battery controller or a DC / DC converter.

[0020] Corresponding control components are already included in the motor vehicle, in the motor vehicle's electrical system, or in the fuel cell control system, a battery control system, or a converter control system, for example to detect a drop in insulation resistance below a predetermined minimum level. The method proposed here simply expands the functional scope of such control systems to the extent that such control systems are also designed to detect or monitor an increase in insulation resistance by a predetermined amount and, if the increase exceeds the predetermined amount or if a predetermined target insulation resistance is reached or exceeded, which is caused by a loss of coolant, to initiate a corresponding alarm or appropriate countermeasures, such as shutting down the fuel cell or the electrical system.

[0021] According to a further aspect, the present development further relates to a device for determining a coolant level of a fuel cell cooling system, which device has at least one coolant line that can be thermally coupled to a fuel cell and through which a coolant flows. The device further comprises a controller that is electrically connected to or electrically coupled to at least one first high-voltage line, which is electrically connected to the fuel cell and to the coolant flowing through the coolant line, and which is configured to measure at least a first insulation resistance of the first high-voltage line.

[0022] The controller is further configured to compare the measured first insulation resistance with a first predetermined target insulation resistance or with a first insulation resistance measured at an earlier point in time, and finally to determine the coolant level of the fuel cell cooling system based on the comparison. The device provided here, in particular its controller, is configured to practically implement and / or carry out the method described above. In this respect, all features, advantages, and effects specified with regard to the method described above also apply equally to the device and / or its controllers; and vice versa.

[0023] According to a further embodiment of the device, the controller is further configured to determine the coolant level as insufficient if the measured first insulation resistance deviates by more than a predetermined amount from the predetermined target insulation resistance or if the measured first insulation resistance deviates by the predetermined amount from the first insulation resistance measured at an earlier point in time.

[0024] In particular, and according to a further embodiment, the controller is designed to determine the coolant level as insufficient if the measured first insulation resistance is higher than the predetermined target insulation resistance or if the measured first insulation resistance is higher than the first insulation resistance measured at an earlier time.

[0025] According to further embodiments, the control of the device can further be designed not only to determine the first insulation resistance of a first high-voltage line electrically connected to the fuel cell and to the coolant located in the coolant line, but equally also to measure a second insulation resistance of a second high-voltage line electrically connected to the fuel cell and to the coolant.

[0026] Furthermore, the controller can also be designed to determine a third previously described insulation resistance between the first high-voltage line and the second high-voltage line and to compare this third insulation resistance with a third target insulation resistance in order to detect a critical drop or absence of coolant in the fuel cell cooling system and to initiate corresponding countermeasures, such as the emergency shutdown of the fuel cell and / or the electrical system of the motor vehicle.

[0027] Finally, according to a further embodiment, a motor vehicle is provided which has a fuel cell and a fuel cell cooling system thermally coupled thereto, comprising a cooling circuit. A coolant circulates in the cooling circuit. The motor vehicle further comprises a previously described device for determining a coolant fill level of the fuel cell cooling system.

[0028] In particular, the motor vehicle is configured with a controller that can be electrically coupled to at least one first high-voltage line electrically connected to the fuel cell and to the coolant. The controller is configured to measure at least a first insulation resistance of the first high-voltage line, and the controller is configured to compare the measured first insulation resistance with a first predetermined target insulation resistance or with a first insulation resistance measured at an earlier time. Furthermore, the controller is configured to determine the coolant level of the fuel cell cooling system based on the comparison performed.

[0029] Depending on the design of the motor vehicle's high-voltage electrical system, the control can be implemented, for example, in a high-voltage battery management system. If the high-voltage battery is galvanically isolated from the fuel cell, the control can also be implemented in a DC / DC converter of the high-voltage system, which is galvanically connected to the fuel cell and the fuel cell's cooling system.

[0030] The coolant line is typically designed to be electrically insulating, so that a measurement of the insulation resistance includes the coolant. In particular, the insulation resistance can be measured at a potential tap on the fuel cell. A further tap can be made at a component of the coolant circuit that is at a predetermined potential and is in electrical contact with the coolant at a predetermined distance from the fuel cell. For example, the first insulation resistance can be tapped at a positive or negative pole of the fuel cell. On the other hand, the insulation resistance can be tapped, for example, at a coolant pump connected to the vehicle body or at a coolant sensor, such as a coolant temperature sensor, which is in electrical contact with the coolant. Short description of the characters

[0031] Further objects, features, and advantageous embodiments of the method and device of the motor vehicle are explained in the following description of an exemplary embodiment with reference to the drawings. Fig. 1 a schematic representation of a motor vehicle, Fig. 2 a block diagram of a fuel cell cooling system and Fig. 3 a flowchart of the method for determining a coolant level of the fuel cell cooling system. Detailed description

[0032] The Fig. The motor vehicle 1 schematically illustrated in Figure 1 comprises a self-supporting vehicle body 2 and an interior 3 functioning as a passenger compartment. The motor vehicle 1 further comprises an electric drive 4, which can be powered by a fuel cell 20 or a high-voltage battery 12 electrically coupled thereto.

[0033] In Fig. 2 shows an associated fuel cell cooling system 10, which, in the presently illustrated embodiment, comprises two separately illustrated but fluidly connected coolant lines 26, 28, which are part of a coolant circuit 11 not explicitly shown. The coolant lines 26, 28, or the coolant circuit 11, are typically provided with an expansion tank 30, in which the coolant 8 circulating through the circuit 11 has a certain fill level. Conventional systems provide a fill level sensor in or on the expansion tank 30, which requires separate electrical contact and separate signal evaluation.

[0034] The fuel cell 20 comprises a fuel cell stack clamped between two end plates 22, 24. One or two high-voltage lines 16, 18 are provided on at least one of the end plates 22, 24, by means of which the electrical power generated at the fuel cell stack can be delivered to the high-voltage battery 12. Both high-voltage lines 16, 18 can either be directly galvanically connected to the high-voltage battery 12. A DC / DC converter 14 is typically provided between the high-voltage battery 12 and the fuel cell 20. This can either provide direct galvanic contact between the high-voltage battery 12 and the fuel cell 20 or provide galvanic isolation between the high-voltage battery 12 and the fuel cell 20.

[0035] As shown in particular in the block diagram according to Fig. As shown schematically in Figure 2, the two high-voltage lines 16, 18 are in electrical contact not only with the fuel cell 20 but also with the coolant line 26, 28 coupled to the fuel cell 20. In particular, the high-voltage lines 16, 18 are in electrical contact with the coolant 8 flowing through the fuel cell 20 as well as with the coolant lines 26, 28. The coolant 8 typically has a certain, approximately predetermined, conductivity.

[0036] The measurement of the insulation resistance, in particular a first insulation resistance 36 of the first high-voltage line 16 and a second insulation resistance 38 of the second high-voltage line 18, can be carried out in particular with regard to predetermined potentials 40. A potential 40 in the region of the coolant lines 26, 28 can be provided, for example, by a coolant pump or a coolant sensor, wherein the pump or the sensor is, for example, at the ground potential of the body 2.

[0037] The coolant lines 26, 28 themselves are typically designed to be electrically insulating, so that the measurement of the insulation resistance 36, 38 of the first high-voltage line 16 and the second high-voltage line 18 always includes the coolant 8 flowing through the coolant lines 26, 28 as well as through the fuel cell 20. The corresponding resistance can be determined in particular by the cross-section A of the coolant line and by the length I of the coolant line through which the coolant flows between the potentials 40.

[0038] Furthermore, a so-called third insulation resistance 37, 39 can be measured between the first and second high-voltage lines 16, 18. The third insulation resistance 37 can be measured, for example, by a controller 32 provided in the area of ​​or on the high-voltage battery 12. The third insulation resistance 39 can be measured, for example, by a controller 34 of the DC / DC converter 14.

[0039] The third insulation resistance 37 can be measured in particular by the battery management system of the high-voltage battery 12, which includes the controller 32 or which is formed by the controller 32.

[0040] The controller 34 can be used, in particular, to measure the third insulation resistance 39 if the DC / DC converter 14 provides galvanic isolation between the high-voltage battery 12 and the fuel cell 20. Individual contactors 42, 44 can be provided in the area of ​​the high-voltage lines 16, 18, for example, between the DC / DC converter 14 and the fuel cell 20. Likewise, further contactors 41, 43 can be provided between the DC / DC converter 14 and the high-voltage battery 12, which can be actuated by the controllers 32, 34 or by a global controller of the electrical system of the motor vehicle 1.

[0041] The contactors 41, 42, 43, 44 are designed as high-voltage switching elements and can interrupt the respective high-voltage line 16, 18 as required, for example if it should be determined that on the basis of the measurement of the insulation resistance 36, 38, 37 and / or 39 and by comparison with a predetermined target insulation resistance or by continuous temporal observation of the measured insulation resistance 36, 38, 37, 39, it should be determined that the insulation resistance in question increases approximately above a predetermined level, which would be attributable to a lack of coolant 8 in the coolant circuit 11.

[0042] When measuring a predetermined increase in the insulation resistance 36, 37, 38, 39, the controllers 32, 34 or a global controller of the electrical system of the motor vehicle 1 can be designed to open at least one of the contactors 41, 42, 43, 44 as intended in order to prevent or exclude damage to the motor vehicle, the fuel cell 20, the high-voltage battery 12 and / or a danger to the user of the motor vehicle as early as possible.

[0043] In the flowchart of the Fig. Figure 3 shows the individual method steps for determining the coolant level of the fuel cell cooling system 10. In a first step 100, at least a first insulation resistance 36 of a first high-voltage line 16 is measured, which is electrically connected to the fuel cell 20 and to the coolant in the coolant line 26, 28.

[0044] In the subsequent step 102, the measured first insulation resistance is compared with a predefined target insulation resistance. If the measured insulation resistance deviates from the target insulation resistance by more than a predefined amount, the method continues with step 104. One of the contactors 41, 42, 43, 44 shown can then be opened to protect the motor vehicle or the end user, for example, to initiate an emergency shutdown of the fuel cell.

[0045] However, if the comparison in step 102 reveals that the first insulation resistance is less than the specified target insulation resistance and / or that the measured insulation resistance is within a specified range of the target insulation resistance, the method continues with step 106. Here, the coolant level can optionally be determined based on the measured insulation resistance.

[0046] The measured coolant level can, for example, be stored in a memory and used as a reference value for a first insulation resistance measured at a later time.

[0047] The method then continues again with step 100. The loop of steps 100, 102, and 106 is executed until it is determined that the measured first insulation resistance deviates by a predetermined amount from the specified target insulation resistance or deviates from a first insulation resistance measured at an earlier time. Appropriate countermeasures are then initiated in step 104.

[0048] The illustrated embodiments merely show possible configurations of the development, for which numerous further variants are conceivable within the scope of the development. The exemplary embodiments shown are in no way to be interpreted as limiting the scope, applicability, or configuration options of the development. This description merely shows the person skilled in the art one or several possible implementations of an exemplary embodiment. Thus, a wide variety of modifications can be made to the function and arrangement of the described elements without departing from the scope of protection defined by the following claims or their equivalents. List of reference symbols 1 motor vehicle 2 Motor vehicle body 3 Interior 4 Drive 8 Coolant 10 Fuel cell cooling system 11 Cooling circuit 12 high-voltage battery 14 DC / DC converters 16 high-voltage line 18 high-voltage line 20 fuel cells 22 End plate 24 End plate 26 Coolant line 27 Coolant resistance 28 Coolant line 29 Coolant resistance 30 expansion tanks 32 Control 34 Control 36 Insulation resistance 37 Insulation resistance 38 Insulation resistance 39 Insulation resistance 40 potential 41 contactor 42 contactor 43 contactor 44 contactor

Claims

[1] Method for determining a coolant level of a fuel cell cooling system (10) which has at least one coolant line (26, 28) which can be thermally coupled to a fuel cell (20) and through which a coolant (8) can flow, comprising the following steps: - measuring at least a first insulation resistance (36) of a first high-voltage line (16) electrically connected to the fuel cell (20) and to the coolant (8) flowing through the coolant line (26, 28), - comparing the measured first insulation resistance (36) with a first predetermined target insulation resistance or with a first insulation resistance (36') measured at an earlier time, - Determine the coolant level of the fuel cell cooling system based on the comparison performed. [2] Method according to claim 1, wherein the determination of the coolant level is carried out as a function of the measured first insulation resistance (36). [3] Method according to claim 1 or 2, wherein the coolant level is determined to be insufficient if the measured first insulation resistance (36) deviates by more than a predetermined amount from the predetermined target insulation resistance or from the first insulation resistance (36') measured at an earlier time. [4] Method according to one of the preceding claims, wherein the coolant level is determined to be insufficient if the measured first insulation resistance (36) is higher than the predetermined target insulation resistance or if the measured first insulation resistance (36) is higher than the first insulation resistance (36') measured at the earlier time. [5] Method according to one of the preceding claims, wherein at least a second insulation resistance (38) of a second high-voltage line (18) electrically connected to the fuel cell (20) and to the coolant (8) flowing through the coolant line (28) is measured, and wherein the second insulation resistance (38) is compared with a predetermined second target insulation resistance or with a second insulation resistance (38') measured at an earlier time. [6] Method according to one of the preceding claims, wherein a third insulation resistance (37, 39) is measured between the first high-voltage line (16) and the second high-voltage line (18) and wherein the third insulation resistance (37, 39) is compared with a third target insulation resistance and / or with a third insulation resistance (37', 39') measured at an earlier time in order to determine the coolant level. [7] Device for determining a coolant level of a fuel cell cooling system (10), which has at least one coolant line (26, 28) which can be thermally coupled to a fuel cell (20) and through which a coolant (8) can flow, and wherein the device comprises the following: - a control (32, 34) which is electrically coupled to at least one first high-voltage line (16) which is electrically connected to the fuel cell (20) and to the coolant (8) flowing through the coolant line (26, 28) and which - is designed to measure at least a first insulation resistance (36) of the first high-voltage line (16), which - is designed to compare the measured first insulation resistance (36) with a first predetermined target insulation resistance or with a first insulation resistance (36') measured at an earlier time, and which - is designed to determine the coolant level of the fuel cell cooling system on the basis of the comparison carried out. [8] Device according to claim 7, wherein the controller (32, 34) is designed to determine the coolant level as insufficient if the measured first insulation resistance (36) deviates by more than a predetermined amount from the predetermined target insulation resistance or from the first insulation resistance (36') measured at the earlier time. [9] Device according to claim 7 or 8, wherein the controller (32, 34) is designed to determine the coolant level as insufficient if the measured first insulation resistance (36) is higher than the predetermined target insulation resistance or if the measured first insulation resistance (36) is higher than the first insulation resistance (36') measured at the earlier time. [10] Motor vehicle (1) which has a fuel cell (20) and a fuel cell cooling system (10) thermally coupled thereto, having a cooling circuit (11) in which a coolant (8) circulates, and wherein the motor vehicle has a device for determining a coolant fill level of the fuel cell cooling system (10) according to one of the following claims 7 to 9.

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