fuel cell system and vehicle with such a

Abstract

Fuel cell system (100) with a fuel cell stack (10) and with a fuel cell cooling system (40) for cooling the fuel cell stack (10), comprising a coolant path (41) in which the fuel cell stack (10) is integrated for heat transfer and at least one cooler (43) or heat exchanger is arranged, characterized in that the at least one cooler (43) is connected to a potential equalization (47), wherein at least one actuator is arranged in the connection from the at least one cooler (43) or heat exchanger to the potential equalization (47).

Description

[0001] The invention relates to a fuel cell system with a fuel cell stack and with a fuel cell cooling system for cooling the fuel cell stack, comprising a coolant path in which the fuel cell stack is integrated in a heat-transferring manner and at least one cooler or heat exchanger is arranged, as well as a vehicle.

[0002] Fuel cells utilize the chemical reaction of a fuel with oxygen to produce water, thereby generating electrical energy. As a core component, fuel cells contain the membrane electrode assembly (MEA), which consists of an ion-conducting (usually proton-conducting) membrane and an electrode (anode and cathode) positioned on either side of the membrane. Gas diffusion layers (GDLs) can also be located on either side of the MEA, on the electrodes facing away from the membrane. Typically, a fuel cell is formed by a stack of multiple MEAs, whose electrical outputs are additive. Bipolar plates (also called flux plates) are usually positioned between the individual MEAs. These plates ensure the supply of the operating fluids, i.e., the reactants, to the individual cells and also typically serve for cooling.In addition, the bipolar plates ensure an electrically conductive contact with the membrane electrode units.

[0003] During operation, the fuel cell reaction generates heat, which is why the fuel cell stack is integrated into a cooling circuit that dissipates the waste heat via a coolant. The coolant is cooled, for example, by an air cooler, or, in the case of a vehicle, typically by a radiator.

[0004] The coolant in the cooling circuit of fuel cell systems is in contact with the high-voltage potentials within the fuel cell stack. At the same time, it flows through various components whose housings are grounded, such as a high-voltage coolant pump. With high coolant conductivity, the insulation resistance between the respective high-voltage potentials and ground decreases. To maintain high insulation resistance, it is therefore essential to ensure that components with ground contact are sufficiently far from the high-voltage potentials. Simultaneously, low coolant conductivity must be ensured, for example, by using deionization filters. If the coolant conductivity becomes too high, a vehicle's insulation resistance monitoring system will detect this as an insulation fault.

[0005] In the event of an insulation fault, the vehicle is not shut down according to current technology. Therefore, it must be ensured that no one is at risk during the time between the detection of the insulation fault and its rectification. Various measures ensure high-voltage safety for high-voltage components. For example, the housing, which is grounded, cannot be opened without tools, or is secured with an interlock (a locking mechanism to prevent damage to machinery and people) and appropriate warning signs, provides touch protection to eliminate any hazard.

[0006] Similarly, in a fuel cell vehicle, the components of the cooling circuit of the fuel cell system that do not fall into the category of high-voltage components must also be considered.

[0007] These are components that do not functionally require equipotential bonding to ground and are positioned in close proximity to high-voltage potentials. They are designed or installed with electrical insulation, for example, using non-removable protective caps or similar devices, to ensure protection against accidental contact.

[0008] For components that do not functionally require equipotential bonding to ground, there are two ways to ensure touch protection, which is only necessary in the event of an insulation fault: touch protection (electrical insulation) or connection of all conductive parts to ground.

[0009] Although the radiator in the front of the vehicle does not require equipotential bonding, it is usually so easily accessible either from the outside or when opening the hood that equipotential bonding is the technically simpler and more sensible solution than ensuring complete inaccessibility to people, especially since contact protection by means of protective caps, for example, leads to a reduction in cooling performance.

[0010] However, this is countered by the fact that nowadays the radiator is made of less noble metals than the other components in the cooling circuit, so that if a potential equalization is applied, corrosion of the radiator and thus material wear, replacement costs and a permanently high input of ions into the coolant are to be expected over time.

[0011] In DE 26 31 113 A1 a fuel cell cooling system is described which provides sacrificial electrodes to protect against corrosion at the inlets and outlets of the fuel cell for a coolant.

[0012] The invention is based on the objective of providing a fuel cell system with a fuel cell cooling system that includes a cooler, in which corrosion of the cooler is significantly reduced compared to the prior art.

[0013] A fuel cell system is provided, comprising a fuel cell stack and a fuel cell cooling system for cooling the fuel cell stack. The cooling system includes a coolant path in which the fuel cell stack is integrated for heat transfer and at least one cooler or at least one heat exchanger is arranged. According to the invention, the at least one cooler or at least one heat exchanger is connected to an equipotential bonding system, with at least one actuator arranged in the connection between the at least one cooler or at least one heat exchanger and the equipotential bonding system. The actuator activates or deactivates the connection between the at least one cooler or at least one heat exchanger and the equipotential bonding system.

[0014] Where only the cooler is mentioned below, the heat exchanger is also implied. Suitable heat exchangers are known to experts.

[0015] This advantageously allows the connection duration of at least one cooler to the equipotential bonding system to be controlled. Equipotential bonding is advantageously only required at the at least one cooler when necessary. This significantly reduces corrosion, which occurs during equipotential bonding due to the typically less noble metal of the at least one cooler compared to the other components of the fuel cell system, since equipotential bonding is prevented by the at least one actuator during operating times of the fuel cell system when it is not required.

[0016] Equipotential bonding of the at least one cooler is necessary, for example, if an insulation fault occurs in the cooling system of the fuel cell system. Therefore, according to a preferred embodiment of the invention, the at least one actuator for the temporary connection of the cooler to the equipotential bonding system is controlled by a control unit, preferably a system controller, of the fuel cell system, which has means for detecting insulation faults in the cooling system. Thus, advantageously, when an insulation fault is detected in the cooling system, the at least one cooler can be connected to the equipotential bonding system, so that corrosion is only possible until the next service appointment to repair the insulation fault. Furthermore, any risk to personnel is eliminated during this time.

[0017] Potential equalization is also advantageous in other situations. For example, the conductivity of a coolant is often higher after extended periods of inactivity than during regular operation. Therefore, a system control unit can also perform potential equalization based on an evaluation of the coolant's inactivity time. Potential equalization can be deactivated after evaluating an insulation measurement, for example, once the coolant has reached its operating temperature.

[0018] Furthermore, equipotential bonding may be necessary if components of the cooling system have been replaced, as these components may exhibit increased ion release due to contamination, which in turn leads to reduced insulation resistance. The equipotential bonding can then be deactivated after evaluating the insulation resistance measurements. Thus, a temporarily increased insulation resistance can also be tolerated after maintenance work on the cooling system, which can advantageously reduce or simplify, or even eliminate, the cleaning of components before installation.

[0019] The at least one actuator is preferably an electrically switching component, which in turn is preferably a relay. Other suitable electrically switching components are known to those skilled in the art. The number of actuators to be used is determined by those skilled in the art from considering the respective fuel cell system and the cooler(s) or heat exchanger(s) arranged therein.

[0020] In a particularly preferred embodiment, the at least one cooler is additionally provided with at least one sacrificial anode, which is then connected to the equipotential bonding system together with the at least one cooler, depending on the actuator. This advantageous design of the fuel cell system according to the invention makes it possible to effectively prevent corrosion of the at least one cooler, even during operating phases in which equipotential bonding is present. Replacing the at least one sacrificial anode is more economical and simpler than replacing a corroded cooler. Since a deionization filter for the coolant is preferably provided in the fuel cell system or is arranged in the cooling system, it must be designed accordingly to accommodate the ion input from the at least one sacrificial anode into the coolant.

[0021] Another aspect of the present invention relates to a vehicle that has a fuel cell system according to the present invention. The fuel cell system serves in particular to supply electrical power to an electric drive unit of the vehicle or to charge a battery.

[0022] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0023] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0024] The invention is explained below in an exemplary embodiment with reference to the accompanying drawing. It shows: Fig. 1. A block diagram of a fuel cell system.

[0025] Fig.Figure 1 shows a fuel cell system designated as 100. The fuel cell system 100 is part of a vehicle (not shown), in particular an electric vehicle, which has an electric traction motor supplied with electrical energy by the fuel cell system 100.

[0026] The fuel cell system 100 comprises as its core component a fuel cell stack 10, which has a plurality of fuel cells 11 arranged in a stack, each of which includes an anode compartment 12 and a cathode compartment 13, separated from each other by an ion-conducting polymer electrolyte membrane 14 (see detail). A bipolar plate (also not shown) is arranged between each pair of such membrane-electrode units. This bipolar plate serves to supply the operating media to the anode and cathode compartments 12 and 13 and also establishes the electrical connection between the individual fuel cells 11. To supply the fuel cell stack 10 with the operating gases, the fuel cell system 100 has an anode supply 20 and a cathode supply 30.

[0027] The anode supply 20 comprises an anode supply path 21, which serves to supply an anode operating gas (the fuel), for example hydrogen, to the anode compartments 12 of the fuel cell stack 10. For this purpose, the anode supply path 21 connects a fuel storage reservoir 23 to an anode inlet of the fuel cell stack 10. The anode supply 20 also comprises an anode exhaust path 22, which discharges the anode exhaust from the anode compartments 12 via an anode outlet of the fuel cell stack 10. In addition, the anode supply 20 may include a fuel recirculation line (not shown) which connects the anode exhaust path 22 to the anode supply path 21. The cathode supply 30 comprises a cathode supply path 31, which supplies an oxygen-containing cathode operating gas, in particular air, to the cathode spaces 13 of the fuel cell stack 10.

[0028] The cathode supply 30 further comprises a cathode exhaust path 32, which removes the cathode exhaust (especially exhaust air) from the cathode spaces 12 of the fuel cell stack 10 and, if necessary, feeds it to an exhaust system not shown.

[0029] Furthermore, a fuel cell cooling system, designated 40 in general, is provided, which has a coolant path 41 in which the fuel cell stack 10 is integrated for heat transfer. A coolant circulating in the coolant path 41 is circulated by an electrically driven coolant pump 42. The coolant, preferably water, a water-alcohol mixture, or a water-ethylene glycol mixture, is temperature-controlled by a cooler 43, which, in the case of a vehicle installation, is typically a vehicle radiator with an air fan. The cooler 43 has a sacrificial anode 44 and is connected to a potential equalization system 47 via a relay 45, which is controlled by a control unit 46. The control of the relay 45 by the control unit 46 is dependent on the detection of an insulation fault in the fuel cell cooling system 40.The connection of the cooler 43 to the equipotential bonding system 47 can be activated or deactivated by controlling relay 45. An insulation fault is detected, for example, by measuring the conductivity of the coolant or the insulation resistance in or on the fuel cell cooling system 40, for instance, by a detection device 48. This information can also be provided by other suitable means in the fuel cell system 100, which are not shown here. Based on the result of this measurement, relay 45 is controlled.For example, if the coolant conductivity is too high—that is, if the measured value exceeds a predefined conductivity value—the relay 45 establishes a connection between the cooler 43 and the equipotential bonding system 47. This allows corrosion of the sacrificial anode 44, which protects the cooler 43 (made of a less noble metal than the other components of the fuel cell cooling system 40), to occur. To compensate for any resulting ion input from the sacrificial anode 44 into the coolant, a deionization filter 49 is also installed in the fuel cell cooling system 40. After the fault that led to the increased conductivity value has been rectified, the connection between the equipotential bonding system 47 and the cooler 43 is deactivated, for example, by the control unit 46. This can also be done manually in a workshop. The control lines of the control unit 46 are not shown.For illustrative purposes only, input 50 and output 51 for the control lines on control unit 46 are shown. Reference symbol list 100 fuel cell systems 10 fuel cell stacks 11 single cells 12 anode compartment 13 Cathode space 14 Polymer electrolyte membrane 20 anode supply 21 Anode supply path 22 Anode exhaust path 23 Fuel tank 30 Cathode supply 31 Cathode supply pathway 32 Cathode exhaust path 40 Fuel cell cooling system 41 Coolant path 42 Coolant pump 43 coolers 44 Sacrificial anode 45 relays 46 Control unit 47 Potential equalization 48 means of detection 49 Deionization filters 50 Control unit input 51 Output of the control unit

Claims

[1] Fuel cell system (100) with a fuel cell stack (10) and with a fuel cell cooling system (40) for cooling the fuel cell stack (10), comprising a coolant path (41) in which the fuel cell stack (10) is integrated in a heat-transferring manner and at least one cooler (43) or heat exchanger is arranged, characterized by that the at least one cooler (43) is connected to a potential equalization (47), wherein at least one actuator is arranged in the connection from the at least one cooler (43) or heat exchanger to the potential equalization (47). [2] Fuel cell system (100) according to claim 1, characterized by that the at least one actuator is an electrically switching component, preferably a relay (45). [3] Fuel cell system (100) according to claim 1 or 2, characterized bythat the fuel cell system (100) has a control unit (46) which is designed to control the at least one actuator or relay (45). [4] Fuel cell system (100) according to claim 3, characterized by that the control unit (46) has means for detecting (48) insulation faults in the fuel cell cooling system (40) [5] Fuel cell system (100) according to one of claims 1 to 4, characterized by that the at least one cooler (43) is connected to at least one sacrificial anode (44). [6] Fuel cell system (100) according to one of claims 1 to 5, characterized by that the fuel cell cooling system (40) has a deionization filter (49) [7] Vehicle with a fuel cell system (100) according to one of claims 1 to 6.

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