Method for operating a thermal management system for a motor vehicle

Abstract

Method for operating a thermal management system (100) for a motor vehicle with a refrigerant circuit (10) comprising a compressor (11), an internal condenser (12), a first external heat exchanger (13), a first expansion valve (16) and an evaporator (17) which is arranged downstream of the expansion valve (16) and upstream of the compressor (11), and with a coolant circuit (40) in which a second external heat exchanger (43) is arranged and which is in heat-exchanging contact with a component (41) of an electric drive of the motor vehicle to be tempered, - wherein the first external heat exchanger (13), the second external heat exchanger (43) and a fan (35) are arranged in a front air duct (37) which communicates with the environment on the airflow side in an open position and is separated from the environment on the airflow side in a closed position, - wherein the thermal management system (100) is operated in a first cooling mode when the temperature of the component (41) of the electric drive of the motor vehicle to be cooled is greater than or equal to a specified limit temperature, wherein the front air duct (37) is operated in an open position and - the thermal management system (100) is operated in a second cooling mode when the temperature of the component (41) to be cooled of an electric drive of the motor vehicle is less than a specified limit temperature and there is no signal to provide a cooling function in the coolant circuit (40) by thermally coupling the first external heat exchanger (13) with the second external heat exchanger (43) and thermally decoupling the coupled first and second external heat exchangers (13, 43) from the environment on the air side, - wherein the vehicle speed of the motor vehicle is detected and the system switches from the second cooling mode to the first cooling mode when the vehicle speed is less than a limit speed, even though the temperature of the component to be cooled (41) is less than the specified limit temperature.

Description

[0001] The present invention relates to a method for operating a thermal management system for a motor vehicle. Thermal management systems for motor vehicles must perform a number of tasks, which include in particular the climate control of the passenger compartment, the cooling and, if necessary, temperature control of the engine, the drive system and other components, as well as the energy-efficient planning and execution of these functions.

[0002] Thermal management systems are particularly important for electric vehicles because they produce no waste heat, and energy efficiency can be used to increase the vehicle's range. Thermal management systems have become established that, in addition to a refrigerant circuit, include a coolant circuit. This coolant circuit allows for the thermal coupling of the electric drive components and enables the temporary balancing of thermal energy within the system.

[0003] DE 11 2018 006 789 T5 discloses a vehicle cooling device with reduced energy consumption, wherein heat can be transferred between a refrigerant-side external heat exchanger and a refrigerant-side radiator via a closable radiator grille, taking into account the vehicle speed. WO 2020 / 250 764 A1 discloses a thermal management system with an integrated heat exchanger that exchanges heat between two cooling circuits. DE 10 2017 115 190 A1 deals with air circulation around an integrated heat exchanger module.

[0004] The object of the present invention is to provide a method for operating a thermal management system which reveals further possibilities for realizing energy saving potentials in the operation of a motor vehicle.

[0005] This problem is solved by a method for operating a thermal management system with the features of claim 1. Advantageous further developments and refinements result from the dependent claims.

[0006] The inventive method for operating a thermal management system comprises a refrigerant circuit with a compressor, an internal condenser, a first external heat exchanger, a first expansion valve, and an evaporator, which is arranged downstream of the first expansion valve and upstream of the compressor. The thermal management system further comprises a coolant circuit with a second heat exchanger and with heat-exchanging contact to temperature-controlling components of an electric drive of the motor vehicle. The thermal management system is characterized in that the first external heat exchanger and the second external heat exchanger can be thermally coupled and, in the coupled state, thermally decoupled from the environment on the air side. This has the advantage that the heat thus stored can be used later in the system, or is stored only temporarily in the thermal management system to be released later.This is particularly useful for moderate ambient temperatures between 10°C and 30°C, when the coolant circuit and the thermal masses connected to it can absorb the excess heat in the short term without significantly heating up the vehicle itself or impairing its operation.

[0007] "Thermally decoupled" can encompass a range of measures suitable for significantly reducing or completely preventing heat exchange, as described in more detail below with examples. The first and second external heat exchangers can be insulated on the air side, in particular, by switching off their associated fans and / or closing air flaps that shield them from the airflow intended for heat exchange. Enabling the fan to be switched off, at least briefly, saves energy and reduces noise levels. The term "surroundings" of the external heat exchangers refers to both the immediate exterior area of ​​the vehicle in front of the external heat exchangers and, where applicable, the area within the vehicle immediately downstream of the airflow.

[0008] The internal condenser is typically located in an air duct of a vehicle's air conditioning system, either as a heating condenser or cabin condenser. The evaporator is also typically located in the same air duct (or alternatively, in a different air duct) of the air conditioning system. Both heat exchangers then serve to provide air conditioning for the vehicle cabin, but can alternatively be used for other air conditioning purposes, such as for refrigerated compartments or climate-controlled cargo space.

[0009] In one embodiment, the first and second external heat exchangers are thermally coupled to each other by means of heat-conducting elements. Optionally, they can also be physically integrated into one another, for example as a multi-fluid heat exchanger in which refrigerant, coolant, and an airflow can come into contact with each other to exchange heat.

[0010] The first external heat exchanger, the second external heat exchanger, and a fan are arranged in an air duct. In an open position, this duct communicates with the surrounding airflow, while in a closed position, it is sealed off from the surrounding airflow. The air duct is typically located in the front of the vehicle. A closed position can be achieved by means of air flaps within the air duct and / or a closable radiator grille in the vehicle's outer skin. In particular, the air duct may be equipped with a partition wall that allows it to be divided into at least two sub-ducts, thus enabling air circulation within the air duct by means of the fan when the duct is closed.

[0011] Depending on the design of the thermal management system, the second outdoor heat exchanger may be positioned upstream of the first heat exchanger on the airflow side. Typically, the second outdoor heat exchanger (in the coolant circuit) operates at a lower temperature than the first outdoor heat exchanger (in the refrigerant circuit) during cooling operation. To ensure subcooling in the refrigerant circuit under all circumstances, a third outdoor heat exchanger may be positioned upstream of the second, on the airflow side. This third heat exchanger can be switched on downstream of the first, on the refrigerant circuit, and has a smaller cross-section on the airflow side than the second heat exchanger, so that it does not completely obstruct the second.The third external heat exchanger typically has a cross-section that is less than half that of the second external heat exchanger. This ensures that the coolant circuit and the refrigerant circuit experience sufficient heat exchange via the airflow in all operating conditions.

[0012] According to the invention, the method for operating such a thermal management system comprises the following steps: thermally coupling the first external heat exchanger with the second heat exchanger and thermally decoupling the coupled first and second external heat exchangers from the environment on the air side. It is provided that the thermal management system operates in a first cooling mode in a manner known per se when the temperature of the component to be cooled in the electric drive of the motor vehicle is greater than or equal to a defined limit temperature, with the air duct being operated in an open position, and that the thermal management system operates in a second cooling mode according to the steps described at the beginning of this paragraph when the temperature of the component to be cooled is less than a defined limit temperature and no signal to provide a cooling function in the coolant circuit is present.This way, overheating can be avoided and energy can be saved by switching to the second cooling mode as needed.

[0013] The thermal coupling of the first external heat exchanger with the second heat exchanger is achieved via heat-conducting elements or by closing the air duct and then optionally switching on the fan located in the air duct. Advantageously, the fan can be operated in both forward and reverse directions, so that in the second cooling mode, the external heat exchanger located further inward from the vehicle's outer skin can also be supplied with air first, if necessary. This allows for greater flexibility in the heat transfer from the refrigerant circuit to the coolant circuit in the second operating mode.

[0014] Furthermore, the system is designed to detect the vehicle's speed and switch from the second cooling mode to the first if the vehicle speed falls below a certain threshold, even if the temperature of the component being cooled is below that threshold. This allows operation in the second cooling mode to be concentrated at higher vehicle speeds, as closing the radiator grille offers greater energy-saving potential at these speeds than at lower speeds. The system automatically switches back to the second cooling mode when the threshold is exceeded again.

[0015] The thermal management system operates in a first cooling mode when the temperature of the component to be cooled in the vehicle's electric drive is greater than or equal to a defined first limit temperature. Conversely, when the temperature of the component to be cooled is less than a defined second limit temperature, the thermal management system operates in a second cooling mode according to the procedure described above. The first and second limit temperatures can be the same or different. Advantageously, the first limit temperature is higher than the second limit temperature. This can potentially avoid constant switching back and forth between the two cooling modes.

[0016] The invention will now be explained in more detail using exemplary embodiments and with reference to the figures. The Fig. Figure 1 schematically shows a switching arrangement of a thermal management system in connection with the invention, the Fig. Figure 2 schematically shows the structure of a refrigerant circuit according to the state of the art. the Fig. Figure 3 schematically shows a switching arrangement of a refrigerant circuit for a thermal management system used according to a first embodiment of the invention. the Fig. Figure 4 schematically shows a coolant circuit for a thermal management system according to Fig. 3, the Fig. Figure 5 schematically shows a switching arrangement of a refrigerant circuit and an associated coolant circuit for a thermal management system, which is used according to a second embodiment of the invention. the Fig. Figure 6 schematically shows an embodiment of two coupled external heat exchangers which can be used in connection with the invention. the Fig. Figure 7 schematically shows two external heat exchangers in a lockable front air duct, which can be used in connection with the invention, and the Fig. Figure 8 schematically shows a flowchart of the method for operating a thermal management system according to an embodiment of the invention.

[0017] In the Fig. Figure 2 schematically depicts the structure of a refrigerant circuit 10 according to the state of the art, as it is used particularly for the air conditioning of motor vehicles. The refrigerant circuit 10 is driven by a compressor 11, whereby, in a cooling mode, the external heat exchanger 13 is located in the high-pressure area and dissipates excess heat by transferring it to the ambient air (indicated by the arrow). Via a downstream expansion valve 16, the refrigerant, cooled by the outside air, is expanded and thus cooled further before it can be used for a cooling function at the evaporator 17, which is located in a motor vehicle air conditioning system, in the low-pressure area.

[0018] The considerations of the present invention are based on the idea of ​​not necessarily or continuously releasing the excess heat to the environment, but instead, at least temporarily, storing it in a coolant circuit 40 via a second external heat exchanger, hereinafter referred to as radiator 43, which is arranged in the coolant circuit 40 and which can be thermally coupled to the first external heat exchanger 13. The thermal management system 100 thus designed according to Fig. In addition to the refrigerant circuit 10 and the coolant circuit 40, assembly 1 also includes a control unit 50 for controlling the thermal management system 100 in at least one first and one second cooling mode. The coolant circuit 40 is driven by at least one pump 42 and is in heat-exchanging contact with components 41, in particular an electric drive. The first external heat exchanger 13 and the radiator 43 are thermally decoupled from the environment on the air side when coupled, as will be explained further below.

[0019] With reference to the Fig. Figure 3 schematically describes the circuit arrangement of a refrigerant circuit 10 for thermal management systems 100 according to a first embodiment. The refrigerant circuit 10 comprises a compressor 11, an internal condenser 12, which, as a cabin condenser, is in heat-exchanging contact within an air duct 30 of the vehicle's air conditioning system, and a first external heat exchanger 13, which is arranged in a first refrigerant branch line 25A in the front area of ​​the vehicle. Downstream of this, a refrigerant receiver 14 is integrated, which collects liquid refrigerant and conveys it downstream via a riser line under defined conditions, and is in fluid communication downstream with the first expansion valve 16. Depending on the embodiment, the first expansion valve 16 can be a thermostatic or electronically controlled expansion valve and can optionally be fully shut off.At the first expansion valve 16, the refrigerant is expanded, evaporated in an evaporator 17, and after passing through an internal heat exchanger 18, drawn back in by the compressor 11. The evaporator 17 is also located in the air duct 30 of the vehicle's air conditioning system, upstream of the heater condenser, to provide air conditioning for the passenger compartment together with the heater condenser.

[0020] The refrigerant circuit 10 includes several other components, which are listed here as examples: Additional expansion valves 15, 20, which are fully electronically controlled and can be completely opened or closed. Furthermore, a number of shut-off valves 21A - 21C and a throttle valve 21D (with check valve) are provided, which are required for adjusting the active refrigerant branch lines for different operating modes. In addition, at least one fan 35 in the front of the vehicle and, if applicable, an air flap 31 in the air duct 30 are important in connection with the thermal management system 100.

[0021] A chiller 19 with the upstream expansion valve 20 is arranged in parallel with the evaporator 17 and can be switched on / off. The chiller 19 and a radiator 43 are integrated into the coolant circuit 40, with the radiator 43 also being located in the front area of ​​the vehicle (e.g., in relation to the airflow in front of or behind the first external heat exchanger 13). The layout of the coolant circuit 40 is shown with reference to the Fig. 4 explained in more detail.

[0022] According to the invention, the thermal management system 100 can be operated in a first and a second cooling mode. Cooling modes include all operating modes in which the evaporator 17 is not deactivated. This also includes, in a broader sense, a mixed mode (dehumidification / reheat operation) in which both the evaporator 17 and the internal condenser 12 in the air duct 30 are actively used for heat exchange. The thermal management system 100 can also be operated in other modes, which are only briefly mentioned here but are familiar to those skilled in the art. This particularly concerns a pure heating mode (heat pump operation). Heat pump operation can be achieved, for example, by using the electric expansion valve 15 with a throttling function (i.e., not fully open, as in cooling operation).In this case, the first external heat exchanger 13 in the low-pressure range, with the radiator grille 36 open, is operated as an evaporator to provide heat energy from the ambient air at a low temperature level for a heating function. For this purpose, the shut-off valve 21A is closed, and the shut-off valves 21C and 21B are opened.

[0023] In the first cooling mode, the refrigerant circuit 10 operates as follows: The refrigerant is pumped by the compressor 11 through the internal condenser 12 to the first external heat exchanger 13 with the shut-off valve 21C closed, the shut-off valve 21A open, and the electronic expansion valve 15 fully open (without throttling). The internal condenser 12 (cabin condenser) is thermally deactivated by closing the air damper 31 in the air duct 30, so that, minus minor losses, hardly any thermal energy is transferred into the air duct 30. At the first external heat exchanger 13, the excess heat is released to the environment via the open radiator grille 36, as is generally known.With shut-off valve 21B closed, the cooled and at least partially condensed refrigerant enters the refrigerant receiver 14, where the liquid refrigerant collects at the bottom. From there, it is conveyed via a riser line to the first expansion valve 16, expands, and then returns to the suction side of the compressor 11 via the evaporator 17. Simultaneously, a portion of the refrigerant is routed through the chiller 19 by controlling the electronic expansion valve 20. The mass flow rate in the two parallel lines is determined by the coordinated opening degrees of the expansion valves 16 and 20, because both lines meet before the suction side of the compressor 11, ensuring that the same pressure prevails downstream of the chiller 19 and the evaporator 17.

[0024] For the second cooling mode, thermal coupling of the first external heat exchanger 13 with the radiator 43 is provided, whereby the heat exchangers thus coupled can simultaneously be thermally decoupled from the environment. One measure for thermal decoupling is to close the closable radiator grille 36. This and further measures will be described with reference to the Fig. 6 and Fig. Section 7 is discussed in more detail. The first external heat exchanger 13 continues to be supplied with refrigerant, but its excess heat is then mainly transferred to the radiator 43.

[0025] With regard to Fig. 4 is suitable for the refrigerant circuit 10 of the Fig. 3. A coolant circuit 40 is configured in one embodiment as follows: In a first sub-circuit, components 41 of the vehicle's electric drive, here the traction battery, the chiller 19, and at least one pump 42A are arranged. In a second sub-circuit, further components 41', here the charger and inverter, the chiller 19, and another pump 42B are arranged. Both sub-circuits can be operated in various configurations, including independently and individually, via shut-off devices 44A and 44B. The shut-off devices are designed here as 3-way or 4-way valves.

[0026] In a first coolant branch line 45A, the radiator 43 is arranged as a second external heat exchanger. In the second cooling mode, at least one of the shut-off devices 44A, 44B is open, allowing coolant to flow through the radiator 43 and absorb heat via the first external heat exchanger 13. Furthermore, the operation of the pumps 42A, 42B moderates the heat transfer between the coolant circuit 40 and the refrigerant circuit 10. It should be noted that, optionally, a third coolant branch line 45C can be provided for a rapid heating function to temporarily bypass the thermal mass of the components 41 (here, the battery).

[0027] In the Fig. Figure 5 schematically depicts a circuit arrangement of a refrigerant circuit 10 and an associated coolant circuit 40 for a thermal management system 100 according to a second embodiment. Apart from the fact that the representation is generally somewhat simplified (for example, individual pipe sections and valves are not specified in detail; the air duct in the air conditioning unit is also omitted), the following discussion focuses primarily on the relevant differences from the first embodiment.

[0028] Unlike in the Fig. As shown in Figure 3, the refrigerant receiver 14 is now arranged as an accumulator in the low-pressure area near the suction side of the compressor 11. Because the radiator 43 is located upstream (i.e., towards the front of the vehicle) of the first external heat exchanger 13 on the airflow side, it can happen during operation, e.g., in the first cooling mode, that the latter does not achieve the desired heat output due to shading in the refrigerant circuit 10. For this reason, a third external heat exchanger 13A is arranged upstream of the radiator 43 on the airflow side, which is integrated downstream of the first external heat exchanger 13 in the refrigerant circuit 10. In order not to shade the radiator 43 too much, the third external heat exchanger 13A has a smaller cross-section on the airflow side than the radiator 43, so that it does not completely obstruct it. Typically, the cross-section of the third external heat exchanger is approximately half to a quarter the size of that of the radiator 43.

[0029] In the Fig. Figure 6 schematically illustrates an embodiment of the first external heat exchanger 13 coupled to the radiator 43. The two heat exchangers are arranged parallel to each other and are thermally coupled via heat-conducting elements 46, e.g., metal fins made of the same material as the heat exchangers themselves (typically aluminum). Alternatively, the first external heat exchanger 13 and the radiator 43 can also be physically integrated, e.g., manufactured in a single block as alternating layers (not shown).

[0030] In the Fig. Figure 7 schematically shows the radiator 43, the first external heat exchanger 13, and the fan 35 arranged in a lockable front air duct 37. By means of the lockable radiator grille 36 and a rear closing flap 39, the two coupled heat exchangers can communicate with the environment on the airflow side in an open position (i.e., with the radiator grille 36 and closing flap 39 open). For the second cooling mode, the radiator grille 36 and / or the closing flap 39 can be closed, so that the components arranged in the front air duct 37 are separated from the environment on the airflow side.

[0031] According to one embodiment, the front air duct 37 is divided into two sub-ducts 37A, 37B, with an optional partition 38. In the closed position, air circulation Z can be enabled by means of the fan 35, which can optionally be operated in both directions. Furthermore, the position of the partition 38 for dividing the front air duct 37 into two sub-ducts 37A, 37B can also be implemented in other, essentially arbitrary ways (not shown).

[0032] In the Fig. Figure 8 schematically illustrates a flowchart 200 of the method for operating a thermal management system 100 according to an embodiment of the invention. After the vehicle is started, a first step 210 initially checks which operating modes are possible, e.g., whether a cooling function, a heating function, or a mixed operation (reheat mode) is required. This can be done in a manner known per se based on various temperature measurements inside and outside the vehicle as well as a specific setting of the air conditioning system.

[0033] In the event that a cooling or reheating function is required, step 220 checks whether the temperature in the coolant circuit 40, in particular the temperature of the component 41 to be cooled, is greater than, equal to, or less than a defined first limit temperature T1, e.g., 60°C. If this temperature is greater than or equal to this first limit temperature T1, then in step 230 the thermal management system 100 is switched to a first cooling mode, i.e., the radiator grille 36 is opened or left open, and ambient air is drawn through the external heat exchangers by the fan 35. If this temperature is less than this first limit temperature T1, then in step 240 it is checked whether there are other cooling requirements that might necessitate a cooling function via the coolant circuit 40. If so, the system is also switched to the first cooling mode.If, on the other hand, only the cooling requirement from the refrigerant circuit 10 is present, in a step 250 the system switches to the second cooling mode, whereby the first external heat exchanger 13 is thermally coupled with the radiator 43 and both are thermally decoupled from the environment on the air side, i.e. in particular the radiator grille 36 is closed.

[0034] Depending on the design, the thermal decoupling on the air side can be achieved in various ways. Here, we refer by way of example to the description with reference to the Fig. 6 and Fig.Reference is made to section 7. Process steps 220 to 250 can be executed iteratively until the first cooling mode is activated due to exceeding the limit temperature T1, thus ending the iteration loop. Alternatively, the process can be initialized at step 210 at intervals for testing purposes (not shown). It can also be stipulated that the second cooling mode is only activated when a second limit temperature T2, lower than T1 (e.g., 55°C), is reached, in order to avoid excessively frequent switching between the two cooling modes.

[0035] In a refined version, the vehicle speed is additionally monitored when the thermal management system 100 is operating in the second cooling mode (not shown). A comparison is then made to determine whether the vehicle speed is greater than, equal to, or less than a predefined limit speed V1, e.g., 30 km / h. The system then temporarily switches from the second cooling mode to the first cooling mode even if the limit temperature T1 has not yet been reached or exceeded, but the vehicle speed is lower than the limit speed V1. Only when the limit speed V1 (or a slightly higher second limit speed V2 – to avoid frequent switching) is exceeded, is the system switched back to the second cooling mode, provided the limit temperature T1 has still not been reached. REFERENCE MARK LIST 10 Refrigerant circuit 11 Compressor 12 Inner condenser, heating heat exchanger 13 first external heat exchanger 13A Additional external heat exchanger 14 refrigerant collectors 15, 16, 20 expansion valves 17 evaporators 18 Internal heat exchanger 19 Chiller 21A - 2CL Shut-off valves 21D throttle with check valve 25A Refrigerant branch lines 30 air ducts of an air conditioner 31 Air flap 35 fans for the first and second external heat exchangers 36 lockable radiator grille 37, 37A, 37B Front air duct 38 Partition wall 39 Locking flap 40 Coolant circuit 41, 41' Components of an electric drive, in particular vehicle battery 42 Coolant pump 43 Radiator / second external heat exchanger 44A, 44B Shut-off device 45A - 45C Coolant branch lines 46 heat-conducting elements 50 Control unit 100 Thermal Management System

Claims

[1] Method for operating a thermal management system (100) for a motor vehicle with a refrigerant circuit (10) comprising a compressor (11), an internal condenser (12), a first external heat exchanger (13), a first expansion valve (16) and an evaporator (17) which is arranged downstream of the expansion valve (16) and upstream of the compressor (11), and with a coolant circuit (40) in which a second external heat exchanger (43) is arranged and which is in heat-exchanging contact with a component (41) of an electric drive of the motor vehicle to be tempered, - wherein the first external heat exchanger (13), the second external heat exchanger (43) and a fan (35) are arranged in a front air duct (37) which communicates with the environment on the airflow side in an open position and is separated from the environment on the airflow side in a closed position, - wherein the thermal management system (100) is operated in a first cooling mode when the temperature of the component (41) of the electric drive of the motor vehicle to be cooled is greater than or equal to a specified limit temperature, wherein the front air duct (37) is operated in an open position and - the thermal management system (100) is operated in a second cooling mode when the temperature of the component (41) to be cooled of an electric drive of the motor vehicle is less than a specified limit temperature and there is no signal to provide a cooling function in the coolant circuit (40) by thermally coupling the first external heat exchanger (13) with the second external heat exchanger (43) and thermally decoupling the coupled first and second external heat exchangers (13, 43) from the environment on the air side, - wherein the vehicle speed of the motor vehicle is detected and the system switches from the second cooling mode to the first cooling mode when the vehicle speed is less than a limit speed, even though the temperature of the component to be cooled (41) is less than the specified limit temperature. [2] Method for operating a thermal management system (100) according to claim 1, characterized by , that the thermal coupling of the first external heat exchanger (13) with the second external heat exchanger (43) is carried out by means of heat conducting elements (46). [3] Method for operating a thermal management system (100) according to one of claims 1 or 2, characterized by , that a closed position of the front air duct (37) is set and optionally the fan (35) arranged in the front air duct (37) is switched on.

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