Intelligent cooling system

Abstract

A cooling system for a vehicle with a fuel cell system is provided, comprising at least one first coolant circuit, designed as a high-temperature circuit and flowing through the fuel cell system, and at least one second coolant circuit, designed as a low-temperature circuit and flowing through at least electronic components of the power electronics for controlling the fuel cells, wherein the coolant circuits can be indirectly connected to each other via a heat exchanger. A vehicle with the cooling system and a method for controlling the cooling system are also provided.

Description

The invention relates to an intelligent cooling system for a vehicle with fuel cells, a vehicle with the cooling system and a method for operating the cooling system. In fuel cells, almost all the heat generated is transferred to the cooling system. Compared to vehicles with internal combustion engines, where roughly equal amounts of waste heat are dissipated via a cooling system and an exhaust system, fuel cell vehicles therefore have more extensive cooling systems. The maximum temperature of the coolant is limited by the lifespan of the fuel cell stack. Coolant temperatures above 85 °C can lead to a reduction in the performance and lifespan of the fuel cells. Fuel cell vehicles therefore typically have large cooling systems which, positioned at the front of the vehicle, have a significant negative impact on the vehicle design, the protection of other road users (especially pedestrians), the vehicle's cost, and its aerodynamics. Alternatively, there are ways to limit the power output of the fuel cells, but this would restrict vehicle parameters such as top speed and acceleration, which is undesirable. Vehicles with fuel cells typically have a multi-circuit cooling system. A high-temperature circuit cools the fuel cells, while a low-temperature circuit cools components such as the power electronics, electronic drive system components, and the battery. Heat energy from the coolant is transferred to the vehicle's surroundings, primarily via radiators. The challenge lies in regulating the coolant temperature under adverse conditions, such as those that can occur during high power demands and / or high ambient temperatures. This problem is solved by a cooling system according to claim 1, a vehicle according to claim 6 and a method according to claim 7. A first aspect of the invention relates to a cooling system for a vehicle with a fuel cell system, wherein the cooling system comprises at least a first coolant circuit, designed as a high-temperature circuit and flowing through a fuel cell stack of the fuel cell system, and at least a second coolant circuit, designed as a low-temperature circuit and flowing through at least electronic components of the power electronics for controlling the fuel cell system. The coolant circuits can be indirectly connected to each other via a heat exchanger. The cooling system according to the invention advantageously enables the utilization of the entire cooling system's potential to dissipate heat via the coolant to the vehicle's environment. The heat exchanger facilitates indirect heat transfer. This avoids the mixing of coolants from the two circuits, which may be different. Coolants for fuel cells are characterized by low electrical conductivity and a minimal proportion of ionic additives. For other circuits, such as the coolant circuits of internal combustion engines, a simple glycol-water mixture can be used. In the cooling system according to the invention, the first coolant circuit preferably has at least one control valve by which the flow of coolant to the heat exchanger can be controlled as a function of temperature. The implementation of a control valve advantageously makes it possible to allow heat exchange only when necessary, in other words, to avoid unwanted heat transfer. Furthermore, it is preferred that the second coolant circuit has at least one control valve by which the flow of coolant to the heat exchanger can be controlled depending on the temperature. The second coolant circuit can have a corresponding control valve in addition to, or as an alternative to, the first coolant circuit. Particularly preferred is a control valve that is itself temperature-dependent. This enables efficient temperature-dependent control of coolant to the heat exchanger in the first coolant circuit and / or second coolant circuit. Furthermore, this embodiment saves space, as one valve is used instead of two. Furthermore, it is preferred if electronic components of an electronic drive system and a battery are arranged in the second coolant circuit or in at least one further coolant circuit designed as a low-temperature circuit and can be connected to the first coolant circuit by means of the heat exchanger. The second coolant circuit can also be subdivided into sub-circuits in which the aforementioned further components are arranged. A second aspect of the invention relates to a vehicle with a cooling system according to the invention. A third aspect of the invention relates to a method for controlling a cooling system according to the invention. The method comprises the following steps: - Operating a vehicle with fuel cells, - Checking the temperature of the coolant flowing in the first and second coolant circuits, - Indirectly connecting the first and second coolant circuits in the heat exchanger when the temperature of the coolant in one coolant circuit exceeds a threshold value, while the temperature of the coolant in the other coolant circuit falls below a threshold value. The advantages of the method correspond to the advantages of the cooling system according to the invention. Preferably, the two coolant circuits are connected indirectly if the temperature in the first coolant circuit exceeds a threshold value and the temperature in the second coolant circuit falls below a second threshold value. Furthermore, it is preferred that the two coolant circuits are indirectly connected when the temperature in the second coolant circuit exceeds the second threshold and the temperature of the coolant in the first coolant circuit falls below the first threshold. Furthermore, it is preferred that the two coolant circuits are not connected if the temperature in the second coolant circuit exceeds the second threshold and the temperature of the coolant in the first coolant circuit falls below the first threshold. The invention is explained in more detail with reference to the figures. Fig. 1 shows a schematic representation of a prior art cooling system. Fig. 2 shows a schematic representation of a cooling system according to one embodiment of the invention. Fig. 3 shows a schematic representation of a cooling system according to a further embodiment of the invention. Fig. 4 shows a flowchart of an embodiment of a method according to the invention. Figure 1 shows a conventional cooling system 100 for a fuel cell vehicle. The cooling system 100 is simplified to focus on the essential aspects of the invention. The cooling system 100 has two coolant circuits. A first coolant circuit 110 is designed for cooling the fuel cell and is therefore a high-temperature circuit. A second coolant circuit 120 is designed for cooling electrical and electronic components and is therefore a low-temperature circuit. The two coolant circuits 110 and 120 operate separately from each other. Water with glycol is used as the coolant in the second coolant circuit 120. The coolant used for the fuel cell is also based on a glycol-water mixture, but with other additives, and is particularly pure and specially treated to minimize electrical conductivity.The aforementioned coolants are familiar to the expert. In the first coolant circuit 110, a fuel cell stack 111, a high-temperature radiator 112 for heat dissipation, and a first pump 113 for driving the coolant flow are arranged. A first control valve 114 is arranged downstream of the fuel cell stack 111. The first control valve 114 can direct the coolant flow either via the high-temperature radiator 112 or directly back to the fuel cell stack 111. Lines lead from the fuel cell stack 111 and the high-temperature radiator 112 to a first expansion tank 115. A line leads from the first expansion tank 115 and opens into the first coolant circuit 110 between the high-temperature radiator 112 and the first pump 113. The second coolant circuit 120 contains components of the power electronics 121, electronic components of the drive system (not shown), a battery (not shown), and other possible vehicle components whose temperature is controlled. Furthermore, the second coolant circuit 120 includes a low-temperature radiator 122 for heat dissipation and a second pump 123 for driving the coolant flow. Downstream of the power electronics components 121, a line branches off to a second expansion tank 125. From the second expansion tank 125, a line leads to a second control valve 124 and into the second coolant circuit 120. A control device 140 is arranged to control the flow. The control device 140 controls the control valves 114, 124 to control their opening status, e.g., the first control valve 114 depending on a coolant temperature in the first coolant circuit 110, in order to direct the coolant via the high-temperature radiator 111 when a limit value is exceeded. In one embodiment of the invention according to Fig. 2, the cooling system 100, unlike in Fig. 1, has a heat exchanger 130. The heat exchanger 130 is designed as a liquid-to-liquid heat exchanger, in which thermal energy is transferred from the coolant in the first coolant circuit 110 to the coolant in the second coolant circuit 120 (or vice versa) without the liquids being mixed (indirect heat exchange). To control the coolant flow to the heat exchanger 130, a third control valve 134 is arranged downstream of the first control valve 114 in the first coolant circuit 110. The third control valve 134 is a temperature-controlled valve (thermostat valve) that opens or closes depending on the temperature of the coolant flowing to the heat exchanger 130. Alternatively, the third control valve 134 can also be controlled by a control device 140 to open or close depending on the coolant temperature. Specifically, in the embodiment shown in Fig. 2, the flows in the two coolant circuits 110 and 120 are controlled such that the second coolant circuit 120 always flows through the heat exchanger 130, and the first coolant circuit 110 is only controlled via the heat exchanger 130 when needed. A line leads from the heat exchanger 130 to the high-temperature radiator 112.It is also possible that in the second coolant circuit 120, an additional temperature-dependent control valve is arranged as an alternative or in addition to the third control valve 134. In the embodiment of the invention according to Fig. 3, unlike in Fig. 2, the functions of the first control valve 114 and the third control valve 134 are integrated into a single fourth control valve 144. The fourth control valve 144 can therefore also be referred to as a thermostatic valve. The fourth control valve 144 is arranged downstream of the fuel cell stack 111. Through the fourth control valve 144, the coolant flow can be directed either via the high-temperature radiator 112, directly back to the fuel cell stack 111, or to the heat exchanger 130. In a method according to Fig. 4 for controlling a cooling system 100 according to Fig. 2 or Fig. 3, a vehicle with fuel cells is operated in a first step S1. In a second step S2, the temperature of the coolant flowing in the first and second coolant circuits 110, 120 is determined and checked against threshold values. The symbols T1 for the current temperature in the first coolant circuit 110 and T1SW for a first threshold value, which is defined as the upper limit of the permissible temperature in the first coolant circuit 110, are used. Reaching the threshold value is considered an exceedance (in the sense of greater than or equal to). The threshold value is set in the range of approximately 85°C. Furthermore, the symbols T2 for the current temperature in the second coolant circuit 120 and T2SW for a second threshold value, which is defined as the upper limit of the permissible temperature in the second coolant circuit 120, are used. If the temperature T1 is above the first threshold (T1>T1SW= Y) and the temperature T2 is below the second threshold (T2 <T2SW= Y), wird in einem dritten Schritt S3 das Thermostatventil 134 bzw. 144 derart geöffnet, dass Kühlmittel des ersten Kühlmittelkreislaufs 110 zur Wärmetauscheinrichtung 130 strömt. In diesem Fall wird Wärmeenergie vom ersten Kühlmittelkreislauf 110 auf den zweiten Kühlmittelkreislauf 120 übertragen. If the temperature T1 is below the first threshold (T1>T1SW= N) (N for No), i.e., not above the first threshold, and the temperature T2 is above the second threshold (T2>T2SW= Y), then in a third step S3 the thermostatic valve 134 or 144 is opened, allowing coolant from the first coolant circuit 110 to flow to the heat exchanger 130. In this case, heat energy is transferred from the second coolant circuit 120 to the first coolant circuit 110. If the temperature T1 is above the first threshold (T1>T1SW= Y) and the temperature T2 is above the second threshold (T2 <T2SW= N), wird das Thermostatventil 134 bzw. 144 nicht in Richtung der Wärmetauscheinrichtung 130 geöffnet. In diesem Fall findet kein Wärmeaustausch statt. If the temperature T1 is below the first threshold (T1>T1SW=N) and the temperature T2 is below the second threshold (T2>T2SW=N), the thermostatic valve 134 or 144 will not open towards the heat exchanger 130. In this case, no heat exchange takes place. Reference symbol list 100 Cooling system 110 First coolant circuit 111 Fuel cell stack 112 High-temperature radiator 113 First pump 114 First control valve 115 First expansion tank 120 Second coolant circuit 121 Power electronics components 122 Low-temperature radiator 123 Second pump 124 Second control valve 125 Second expansion tank 130 Heat exchanger 134 Third control valve 140 Control unit 144 Fourth control valve

Claims

Cooling system (100) for a vehicle with a fuel cell system, wherein the cooling system has at least a first coolant circuit (110) designed as a high-temperature circuit through which a fuel cell stack (111) of the fuel cell system flows, and at least a second coolant circuit (120) designed as a low-temperature circuit through which at least electronic components of the power electronics for controlling the fuel cell system (121) flows, characterized in that the two coolant circuits (110, 120) can be indirectly connected to each other via a heat exchanger (130). Cooling system (100) according to claim 1, wherein the first coolant circuit (110) has at least one control valve by which a flow of coolant to the heat exchanger (130) can be controlled depending on the temperature. Cooling system (100) according to claim 1 or 2, wherein the second coolant circuit (120) has at least one control valve by which a flow of coolant to the heat exchanger (130) can be controlled depending on the temperature. Cooling system (100) according to one of the preceding claims, wherein the control valve itself is adjustable depending on the temperature. Cooling system (100) according to one of the preceding claims, in which electronic components of an electronic drive system and a battery are arranged in the second coolant circuit (120) or at least one further coolant circuit designed as a low-temperature circuit and can be connected to the first coolant circuit (110) by means of the heat exchange device (130). Vehicle with a cooling system (100) according to one of claims 1 to 5 . Method for controlling a cooling system (100) according to any one of claims 1 to 5, comprising the steps of: - operating a vehicle with a fuel cell system, - checking the temperature of the coolant flowing in the first coolant circuit (110) and in the second coolant circuit (120), - indirectly connecting the first coolant circuit (110) and the second coolant circuit (120) in the heat exchanger (130) when the temperature of the coolant in one coolant circuit exceeds a threshold value, while the temperature of the coolant in the other coolant circuit falls below a threshold value. Method according to claim 7, wherein the two coolant circuits (110, 120) are indirectly connected when the temperature in the first coolant circuit (110) exceeds a threshold value and the temperature in the second coolant circuit (120) falls below a second threshold value. Method according to claim 7 or 8, wherein the two coolant circuits (110, 120) are indirectly connected when the temperature in the second coolant circuit (120) exceeds the second threshold and the temperature of the coolant in the first coolant circuit (110) falls below the first threshold. Method according to claim 7, 8 or 9, wherein the two coolant circuits (110, 120) are not connected when the temperature in the second coolant circuit (120) exceeds the second threshold and the temperature of the coolant in the first coolant circuit (110) falls below the first threshold.

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