Method for operating a cooling circuit

Abstract

Method for operating a cooling circuit (100) in a motor vehicle, in which a temperature in the cooling circuit (102) is controlled, wherein the cooling circuit (100) is used to control the temperature of a device in the motor vehicle, a target temperature is specified during the control, and the target temperature is determined as a function of a dew point.

Description

[0001] The invention relates to a method for operating a cooling circuit and a control system for such a cooling circuit. State of the art

[0002] A cooling circuit, also known as a coolant circuit, is a system used to cool a self-heating device or an externally heated device, the so-called heat source, to an appropriate level. Such a cooling circuit typically includes piping, pumps, and a heat sink. During operation, a coolant circulating in the cooling circuit is guided past the heat source, heats up, and releases the absorbed heat back to the heat sink. The coolant is usually a liquid or gas that can absorb and transport heat.

[0003] Such cooling circuits are used in many technical facilities, whereby in these applications a control system is often provided so that the temperature of the facility can be regulated to a desired temperature, the target temperature, by means of the cooling circuit.

[0004] Closed-loop control is a process in which a fundamentally variable variable is automatically and regularly kept constant, or at least approximately constant. During control, the value of the variable to be kept constant is determined as the actual value, and if it deviates from a desired setpoint, it is changed so that the actual value approaches the setpoint again. Since the deviation from the setpoint is counteracted, the feedback is negative feedback. This feedback creates a closed-loop control system. This is also known as a loop.

[0005] In motor vehicles, such cooling circuits are used both to control the engine temperature and to control the temperature of electronic devices, such as control units, especially when power electronic components are used in these.

[0006] It should be noted that partially and fully autonomous driving functions in motor vehicles require significant computing power. The control units and computers installed in the vehicle for this purpose require liquid cooling for active operation. It is expected that some sensor types will only be able to be cooled to a limited extent with air cooling and will also require liquid cooling in the future.

[0007] Some of the driving functions in a partially or fully autonomous vehicle are subject to a high safety classification, such as ASIL C or even the highest level ASIL D. This means that only very low failure probabilities are acceptable, which in turn places high demands on the reliability of the cooling system.

[0008] Efficient cooling is required to enable high computing power, particularly for highly complex components such as the CPU (central processing unit), GPU (graphics processing unit), and SoC (system on chip). If their temperature limits are exceeded, these components reduce their computing power and no longer fulfill their intended range of functions. At the same time, the packaging and connection technology is stressed, which can lead to failures. Thermal and thermomechanical loads in particular are driving factors that limit reliability. In interaction with climatic loads, the humidity of the ambient air is also relevant. In combination with high temperatures, plastics and adhesives in particular are damaged. At low temperatures, condensation forms on surfaces, and this can lead to short circuits, migration, and similar failure patterns.

[0009] Current liquid cooling systems in vehicles, such as engine cooling, battery cooling, inverter cooling, and electric drive cooling, regulate the coolant temperature to a constant level. Electric drive components are kept at approximately 60°C, while engine cooling systems are kept at 80°C. This creates optimized conditions, for example, for chemical processes such as combustion. Disclosure of the invention

[0010] Against this background, a method having the features of claim 1 and a control system according to claim 11 are presented. Embodiments emerge from the dependent claims and the description.

[0011] The presented method is used to operate a cooling circuit in a motor vehicle, in which a temperature in the cooling circuit is controlled. In the method, the cooling circuit is used to control the temperature of a device or component in the motor vehicle. During the control process, a target temperature is specified. This target temperature is determined as a function of a dew point.

[0012] The dew point, also known as the dew point temperature, is the condensation point of water in air. For air with a certain absolute humidity, the dew point is the temperature below which, at constant pressure, the water contained in the air no longer remains entirely as water vapor, but precipitates as dew or mist. At the dew point, the relative humidity is 100%. The dew point therefore describes the temperature of a moist gas mixture in equilibrium, at which condensation and evaporation of the moist component are exactly balanced. If the air temperature is known, the dew point can be used to determine the absolute humidity. The dew point can be measured or determined directly with a mirror hygrometer, for example, or indirectly using other hygrometric methods.

[0013] The presented method is based on the finding that a constant cooling circuit temperature significantly increases the damaging loads over the service life. Furthermore, it is clear that, particularly in automotive applications, a very broad range of ambient temperatures must be covered. It must also be considered that each individual vehicle can be used in any climate. For example, in Europe, when considering travel activities or trade, a wide range of loads must often be considered, from the cold Alpine or Scandinavian climates in winter sports to the hot continental climate in Southern Europe. The cooling circuits should be configured to support function even under these extreme conditions.

[0014] The high stresses that impact service life are due to the fact that temperatures are largely constant during operation and that the device is operated at maximum thermal load throughout its entire lifespan. This results in a damaging, high temperature surge each time the device is turned on and off. As a result, the technological limits of the printed circuit board (PCB) and soldering load capacity are reached after just a few months. Consequently, failure is to be expected.

[0015] This presents a cooling circuit or cooling loop that is not controlled to a constant temperature, but rather to an offset from the dew point. This couples the maximum temperature to the ambient temperature. At ambient temperatures below the maximum value, full computing performance can be supported. At the same time, the operating temperature of the electronics varies more significantly. Furthermore, the periods of severe damage at high temperatures are shortened.

[0016] Thermomechanically, the loads that cause the greatest damage are otherwise imposed on the system when it is warmed up from a cold situation, such as winter parking, to the high operating temperatures. The control system presented here significantly reduces the high lift from cool starting conditions that is typical for existing methods.

[0017] It should also be noted that appropriate signals are not always available to determine the dew point. Therefore, it is also possible to use a highly simplified climate model and estimate the maximum dew point from the ambient temperature data. Even greater lifetime performance can be achieved by determining the dew point in the device and implementing additional measures, such as air drying.

[0018] Lifespan calculations show that even the simplest approach with a generous temperature offset results in a doubling of the lifetime in warm / hot climate regions and up to five times the lifetime can be predicted in regions with moderately cool climates.

[0019] The control system presented here is used for a cooling circuit in a motor vehicle and is configured to implement the method described herein. A device for determining the dew point is assigned to the control system. The setpoint to be specified during control is determined based on this dew point.

[0020] The control basically comprises a device for determining the actual temperature and a device for comparing the actual temperature with a target temperature as well as a controller that further processes the difference determined in the comparison in order to typically determine a manipulated variable.

[0021] A cooling circuit with such a control system is also presented. This cooling circuit is used to control the temperature of a device in a motor vehicle. The actual value used for the control can be the temperature in the area or in the device, or alternatively, the actual temperature of a coolant in the cooling circuit.

[0022] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention. Short description of the drawings Fig. 1 shows a flowchart of a possible sequence of the presented procedure. Fig. 2 shows a schematic, highly simplified representation of a motor vehicle with a control system of the type described herein. Fig. 3 shows a block diagram of a cooling circuit for carrying out the presented process. Embodiments of the invention

[0024] The invention is illustrated schematically in the drawings using embodiments and is described in detail below with reference to the drawings.

[0025] Fig. 1 illustrates in a flow chart an embodiment of the described method, which serves to cool a particularly technical device in a motor vehicle.

[0026] In a first step 10, the motor vehicle begins its journey. A second step 12 then determines a dew point, in particular a dew point in the device in the motor vehicle that is to be cooled or tempered. Taking this dew point into account, the temperature of the device is then regulated in a step 14. This involves comparing the actual and target temperature values, with the determined dew point being taken into account when determining the target value.

[0027] Fig. Figure 2 shows a schematic, highly simplified representation of a motor vehicle, designated overall by reference numeral 50. This motor vehicle includes a cooling circuit 52, wherein the presented method serves to regulate a temperature in the cooling circuit 52. The cooling circuit thus represents a control loop.

[0028] The illustration shows a control system 54 with a regulator 56 and a device 60 in the cooling circuit 52, which in turn includes a temperature measuring device 62. A coolant 66, in this case a liquid, flows in a coolant channel 64. In principle, the method can also be applied using a gas as the coolant, which then flows through the coolant channel 64.

[0029] Fig. Figure 3 shows a block diagram of a possible embodiment of a cooling circuit, which is designated overall by the reference numeral 100. The illustration shows a reservoir / equalization volume 102, a first switching valve 104, a first pump 106, a heating cartridge 108, a second pump 110 for an air conditioning circuit 112 for a vehicle, e.g., an air conditioning system, a second switching valve 114, a heat exchanger 116, electronics 118, e.g., a control unit (ECU: electronic control unit) with a heat sink 120, a third switching valve 122, and a cooler 124, in this case, a heat exchanger caused by airflow.

[0030] The components 104, 108, , 110, 114, 122 and 124, which are outlined with dashed lines, are switched or controlled to adjust the temperature on the heat sink.

[0031] The described application is of particular interest for computationally intensive systems in motor vehicles designed for semi- and fully autonomous driving. For this purpose, the Fig. 3. However, the method presented can also be applied to very simple cooling circuits, since only the control parameter for the desired or target temperature needs to be adjusted.

[0032] The cooling circuit can, for example, comprise two reservoirs with level monitoring. These can also be implemented as a two-chamber solution in a single component. Each loop starts from this. The separation can be improved, for example, using a three-way valve, as this also makes it possible to specifically shut off a loop. This can be used, for example, to reduce coolant loss in the event of a leak. If there are two reservoirs, this valve can also be arranged upstream of them. In this case, the flow is ensured by at least one pump per loop. A dry-run sensor in the pumps is the second signal for detecting a possible leak. The combination of the signals from the reservoir and pump increases the probability of detecting and reporting the error. This allows higher safety requirements to be met.

[0033] After the pumps, the flow passes through the coolers for the electronics. Depending on the architecture of the redundancy concept, this can mean that the loops each supply separate devices or that the devices have multiple heat sinks supplied by different loops. The concept can therefore serve different architectures. Check valves are required behind the heat sinks to prevent backflow into the leaking loop in the event of a leak. At least one check valve per loop is required. Without these valves, both loops could otherwise dry out. The two circuits are then merged, again via a three-way valve. It is also conceivable to design a valve that integrates both the switching of the cooling circuits and the check function in a single component.

[0034] The coolant, heated by the power loss of the electronic components, is then cooled. The connection to the vehicle's air conditioning circuit is established via heat exchanger 116. Furthermore, the cooling circuit 100 is continued to heat exchanger 124, which dissipates the heat to the environment via a fan. This concept is familiar from engine cooling and is preferred due to its energy efficiency. The connection to these two heat sinks provides redundancy for wider operating ranges, and at the same time, the air conditioning circuit offers the possibility of cooling extreme peaks at high ambient temperatures or due to high waste heat from the devices. In addition, the air conditioning cooling circuit can condition the cooling circuit to operating temperature before the start of a mission. This is relevant, for example, for takeoff after parking in the sun or at high ambient temperatures.

[0035] The loop is closed by returning the now cold cooling liquid to the reservoirs.

[0036] Currently, the loops are combined in the heat sink area to ensure the most homogeneous cooling of the electronics or, in electric vehicles, to utilize existing infrastructure (battery cooling circuit). Alternatively, this could be achieved via a heat exchanger between the loops, with the heat sinks each connected redundantly to two loops. This consistent separation may make the check valves unnecessary.

[0037] Valves or bypass solutions also offer the advantage that, during short off-times, the intermediate stroke can be reduced through appropriate switching. This also allows for further optimization of cooling and warm-up scenarios.

Claims

[1] Method for operating a cooling circuit (52, 100) in a motor vehicle (50), in which a temperature in the cooling circuit (102) is controlled, wherein the cooling circuit (52, 100) is used to regulate the temperature of a device (60) in the motor vehicle (50), a target temperature is specified during control, and the target temperature is determined depending on a dew point. [2] Method according to claim 1, wherein the target temperature is determined by an offset to the dew point. [3] A method according to claim 1 or 2, wherein the dew point is estimated from the ambient temperature. [4] Method according to one of claims 1 to 3, in which the dew point is determined by a temperature measuring device (62) in the device (60) whose temperature is to be controlled. [5] Method according to one of claims 1 to 4, in which the air is additionally dried in the device (60). [6] Method according to one of claims 1 to 5, with which the temperature of a computing device in the motor vehicle is controlled. [7] Method according to one of claims 1 to 6, with which the temperature of a device (60) in a motor vehicle (50) which is designed for semi-autonomous or fully autonomous operation is controlled. [8] Method according to one of claims 1 to 7, wherein the temperature in the cooling circuit (52, 100) is controlled by controlling the temperature of a coolant (66) of the cooling circuit (52, 100). [9] Method according to one of claims 1 to 8, wherein two loops are used in the cooling circuit (52, 100). [10] Method according to claim 9, wherein the two loops are coupled to one another via a three-way valve (102). [11] Control system for a cooling circuit (52, 100) which is designed for use in a motor vehicle (50) and for carrying out a method according to one of claims 1 to 10, wherein the control system (54) is assigned a device for determining the dew point. [12] Control according to claim 11, which comprises a temperature measuring device (62) to be arranged in the device (60) whose temperature is to be controlled.

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