Method for controlling a device for the thermal management of a motor vehicle and device therefor

Abstract

The invention relates to a method for controlling a device (1) for the thermal management of an electrically powered motor vehicle, in particular for the air conditioning of its passenger compartment, and a device (1) with a refrigerant circuit (2) comprising a compressor (5) compressing a refrigerant and at least two heat sources of different temperatures that can be connected to the refrigerant circuit (2) and provide heat. In order to increase the overall efficiency of the process underlying the heat recovery, at least one of the heat sources is connected to the refrigerant circuit (2) at a timed interval, depending on the temperature.

Description

The invention relates to a method for controlling a device for the thermal management of an electrically operated motor vehicle, in particular for the air conditioning of its passenger compartment, and to a device having a refrigerant circuit with a compressor compressing a refrigerant and at least two heat sources of different temperatures which make available heat and can be connected to the refrigerant circuit.A device and a method for the thermal management of an electrically operated motor vehicle for obtaining heat from two heat sources, namely an outer and an inner coolant circuit, which feeds heat via a so-called chiller into a refrigerant circuit, is known, for example, from the publication DE 10 2021 132 803 A1. In this case, switching over between two coolant circuits is effected by means of directional valves within the inner coolant circuit. The refrigerant circuit is fed via the chiller only by means of a single heat source.By means of the refrigerant circuit, a passenger compartment of the motor vehicle is in particular air-conditioned. At low ambient temperature, the heat requirement for heating the passenger compartment increases. In this case, owing to the high efficiency of the electrical drive of the overall system, only very little waste heat is available. The heating of the passenger compartment is therefore carried out using electrical energy which is taken from the battery, for example the traction battery, for driving the motor vehicle by means of at least one electric machine. This generally leads to a reduced range of the motor vehicle. For efficient air conditioning of the passenger compartment, refrigerant circuits with heat pump systems are frequently used, which supply heat from at least one heat source to the refrigerant circuit.The efficiency of the thermal process underlying the refrigerant circuit describes the ratio of heat output power to power input, for example as electrical power. In this case, a high degree of efficiency is sought in order to achieve a high driving performance of the motor vehicle. A high temperature level of a heat source promotes a high degree of efficiency by reducing the power of the compressor of the refrigerant circuit and thus the power consumption thereof.If the refrigerant circuit has two or more usable heat sources with different temperatures, the refrigerant must be expanded to a pressure level below the lowest temperature of all heat sources in order to be able to recover heat at all by means of a temperature difference to be adjusted accordingly. The lowest pressure / temperature level thus decisively defines the required compressor power and thus the efficiency. The potential of the heat sources with higher temperature can thus be used only to a very limited extent. If only the heat source with the highest temperature is used, the heat contributions of the heat sources with the lower temperature are eliminated.The object of the invention is the development of a method for controlling a device for the thermal management of an electrically operated motor vehicle, in particular for the air conditioning of its passenger compartment, and a device for this purpose. In particular, it is the object of the invention to use at least two heat sources of different temperatures with improved efficiency.The object is achieved by the subject matter of claims 1 and 9. The claims dependent on claims 1 and 9 represent advantageous embodiments of the subject matter of claims 1 and 9.The proposed method is used to control a device for the thermal management of an electrically operated motor vehicle, in particular for the air conditioning of its passenger compartment. In the passenger compartment, for example, an air-conditioning unit is provided, which has a cooling unit and a heating unit, through which flow takes place in a refrigerant flow as a function of a temperature setpoint value of the passenger compartment set by a driver and / or automatically, wherein corresponding throttle valves are switched in the refrigerant circuit, so that hot refrigerant liquefied under pressure is present at the heating unit and cold refrigerant expanded at the cooling unit.The refrigerant circuit additionally contains a compressor compressing and liquefying the refrigerant, for example an electrically operated compressor, optionally a separator for separating liquid and gaseous refrigerant, so that substantially gaseous refrigerant is fed into the compressor, the designated throttle valves and at least two heat sources of different temperatures which make available heat and can be connected to the refrigerant circuit. Optionally, an internal heat exchanger can be provided between an inflow of refrigerant to the compressor and the line with cooled coolant or / or a refrigerant line connected downstream of at least one heat source.The at least two heat sources are in switchable connection with the refrigerant circuit by means of heat transfer devices. For example, heat transfer devices can be designed as heat exchangers, evaporators or the like. For example, heat transfer devices can transfer the heat content of a gaseous, liquid, optionally mixed-phase, or solid heat source to the refrigerant circuit.In order to efficiently change at different temperatures of the at least two heat sources at least a portion of their higher temperature compared to the temperature of the refrigerant and without a predefined structure, in particular the design of the compressor and thus to increase the efficiency of the refrigerant circuit, at least one of the heat sources is switched on to the refrigerant circuit in a time-clocked manner depending on the temperatures of the heat sources. In this way, for example, if the heat content of a single heat source cannot be sufficiently exhausted, the passenger compartment can nevertheless be sufficiently heated at low external temperatures. Due to the time cycle of the heat source with higher temperature, a deteriorated efficiency of the warmer heat source is avoided due to the state diagram of the refrigerant, in that the refrigerant is heated by the two heat sources in a time cycle. In this case, it is advantageous if a limited amount of heat from a heat source having a higher temperature is switched off when it has dropped to a temperature range of a predefined temperature of the refrigerant, so that the temperature of the heat source can increase again and the available amount of heat can form again, so that overall a higher efficiency is achieved than in the case of continuous depletion of the amounts of heat from all heat sources. The cycle times of the switching on and off of a heat source depend, for example, on the available heat quantity of the heat sources, their temperature, the external temperature, the heat transfer coefficients of the heat transfer devices, their exchange surfaces, the refrigerant and its isochoric enthalpy available according to the state diagram, in particular during a phase change, the design of the refrigerant circuit, in particular its compressor and the like. For example, cycle times of a few minutes up to one hour may be advantageous depending on these parameters.For example, carbon dioxide, ammonia or organic refrigerants and / or mixtures thereof can be used as refrigerants.The ambient air can be provided as a first heat source, so that its heat quantity is introduced into the refrigerant circuit preferably by means of a heat transfer device provided as a heat exchanger. A coolant circuit with coolant of the motor vehicle can serve as the second heat source. For example, heat-generating components, for example one or more batteries, such as for example a traction battery, power electronics for operating at least one electric machine, for example for driving the motor vehicle, a voltage converter for a charging process, a heat transfer device, for example for dissipating heat in the exposed heating operation of the passenger compartment, optionally a water-cooled electric machine and / or the like, can be accommodated in the coolant circuit during operation and / or during a charging process. For efficient control of the individual heat flows in the coolant circuit, individual or a plurality of components can be arranged in individual coolant circuits, through which coolant flows by means of at least one pump and which can be connected to one another and disconnected from one another by means of a selector switch controlled by a control unit, for example. A heat transfer device, which is designed as a so-called chiller such as a liquid / liquid heat exchanger and is incorporated into the refrigerant circuit, is provided in the coolant circuit.In addition, a third heat source of an additional fluid circuit can be connected directly to the refrigerant circuit or to the coolant circuit as a function of a quantity of heat available in the fluid circuit. The fluid circuit can be operated with fluid from a, for example, non-aqueous lubricant such as, for example, oil, an aqueous emulsion or the like. Heat-generating components, such as at least one electric machine cooled with fluid, a transmission between an electric machine and drive wheels of the motor vehicle and / or the like, can be arranged in the fluid circuit through which the fluid flows by means of at least one pump. For example, one of the components, in particular the transmission, can be connected to the fluid circuit and disconnected from the fluid circuit as a function of a temperature of the fluid and / or an external temperature by means of a preferably continuously switchable valve.The third heat source can be connected directly, in particular in a clocked manner, by means of one of the coolant lines of the second heat source and / or the refrigerant circuit and depending on a quantity of heat present in the fluid circulation system.According to an advantageous embodiment of the method, in the case of a requested heating of the passenger compartment up to a predefined external temperature, the heating is carried out permanently exclusively with activation of the first heat source, that is to say according to a heat pump function of the refrigerant circuit, preferably without clocking. If the external temperature falls below a predefined value, the first heat source can be switched on permanently and the second heat source can be switched on in a clocked manner. Alternatively, if the predetermined external temperature is undershot, the first and the second heat source can be operated alternately in a clocked manner in time. It is understood that in the case of three and more heat sources, at least one of the heat sources can be operated in clocked fashion with a higher temperature, while the remaining heat sources are likewise operated in clocked fashion or permanently operated or switched off.The proposed apparatus for carrying out the method described contains at least two heat transfer devices which are in heat exchange connection with a refrigerant circuit and a changeover device for the clocked connection of at least one of two heat transfer devices depending on their recoverable amounts of heat. For example, a heat transfer device is provided between the ambient air and the refrigerant circuit and a second heat transfer device is provided between a coolant circuit and the refrigerant circuit. In particular, a third heat transfer device is provided between the coolant circuit and an additional fluid circuit. The third heat transfer device can alternatively be connected directly to the refrigerant circuit.The invention is explained in more detail with reference to the exemplary embodiment shown in FIGS. 1 to 3. These show: FIG. 1 shows a schematic illustration of a device having a refrigerant circuit, a coolant circuit and a fluid circuit, FIG. 2 is a diagram showing the operation of the apparatus of FIG. 1 in continuous operation; and FIG. 3 is a diagram illustrating the function of the device of FIG. 1 in time-clocked operation.The device 1 for the thermal management of an electrically operated motor vehicle is divided into the refrigerant circuit 2, the coolant circuit 3 and the fluid circuit 4.The refrigerant circuit 2 is operated by means of refrigerant, for example carbon dioxide. The compressor 5 compresses the refrigerant to the liquid state while heating. The heated refrigerant serves to heat the passenger compartment in the controllable heating unit 6, and the refrigerant cools down in the process. In the throttle valve 7, the refrigerant is expanded and further cools down. The cooled, partially still liquid refrigerant absorbs heat in the first heat transfer device 8 designed as a heat exchanger 9, which is in heat exchange connection with the ambient air as the first heat source. The fan 10 of the heat exchanger 9 is controlled by the switching device 32 so that the latter can be switched on and off.In the cooling operation, the throttle valve 11 is switched and the throttle valve 12 is blocked, so that the refrigerant is further expanded and flows via the adjustable cooling unit 13, so that the passenger compartment is cooled. In the heating operation, the throttle valve 11 blocks and the throttle valve 12 is opened and further expands the refrigerant.The heat exchanger 15 designed as a chiller is in heat exchange connection as a second heat transfer device 14 with the coolant circuit 3 serving as a second heat source. The separator 16 is arranged downstream of the heat exchanger 15, which collects any liquid refrigerant present, so that only gaseous refrigerant is supplied to the compressor 5.The internal heat exchanger 17 is connected between the heat exchanger 15 and the compressor 5, on the one hand, and the heat exchanger 9 and the heat exchanger 15, on the other hand, in order to preheat the refrigerant in advance by means of the heat exchanger 15 depending on the circuit of the heat exchangers 9, 15 and depending on the heating or cooling operation.The coolant circuit 3 is divided into a plurality of coolant circuits 19, 20 which can be connected to one another by means of the selector switch 18, for example a multiway valve and through which coolant, for example water, aqueous coolant mixtures and / or the like, flows by means of the pumps 21, 22.The external heat exchanger 23 for cooling the coolant circuit 3 as required, the third heat transfer device 24, which is designed as a heat exchanger 25 and is in heat exchange connection with the fluid circuit 4 as a third heat source, the power electronics 26 and the charging controller 27 or voltage converter are accommodated in the coolant circuit 19 with the pump 21 during charging of the battery 28. The battery 28 and the heat exchanger 15 are integrated into the coolant circuit 20 with the pump 22. An advantageous aspect before the start of the motor vehicle can result from the fact that the heat generated during charging in the charging controller 27 can already emit heat to the refrigerant circuit 2 via the heat exchanger 15 when the motor vehicle is at a standstill, so that, when the cold motor vehicle is started, the effect factor of the refrigerant circuit 2 can already be increased by heating the refrigerant above the ambient temperature, in particular if the heat supply at the heat exchanger 15 is already clocked over time.Depending on the required amount of heat available at the heat exchanger 15, heat to be dissipated via the exterior heat exchanger 23, at the heat exchanger 25, at the power electronics 26, the charge controller 27, the battery 28, the pumps 21, 22 and the selector switch 18 are controlled by the changeover device 32.The electric machine 29 and the transmission 30 are integrated and cooled in the fluid circuit 4 operated with fluid, for example with lubricant such as oil, a suspension and / or the like. The transmission 30 can be coupled and decoupled by means of the valve 31. By heating the fluid, waste heat of the electric machine 29 and / or of the transmission can be supplied to the coolant circuit 3 and thus to the refrigerant circuit 2 by means of the heat exchanger 15.FIG. 2 shows the diagram 33 with the operation of the device 1 of FIG. 1 with continuous guidance with the temperature T, the power P and the efficiency COP (coefficient of performance) over time t. During a heating operation of the device 1, the amounts of heat of the first and second heat sources are continuously transferred to the refrigerant circuit 2 via the heat transfer devices 8, 14 in accordance with the heat flows predetermined by their heat transfer coefficients and exchange surfaces and thus the available powers P 1, P 2. In this case, the refrigerant at the temperature T0is warmed up by means of the temperature T1of the ambient air at the heat exchanger 9 and the higher temperature T2at the heat exchanger 15 of the coolant circuit 3, with the result that the compressor 5 has to perform less starting from the increased temperature T0in order to heat and liquify the refrigerant and thus achieve the temperature desired in the passenger compartment. The powers P 1, P 2 in the refrigerant circuit 2 that can be achieved from the temperatures T 1, T 2 by means of the heat exchangers 9, 15 do not correspond to the required higher power P 3 for heating the passenger compartment, so that the remaining difference is compensated by consumption of electrical power of the compressor 5 from the battery 28. The ratio of the powers P 1, P 2 on the one hand and the power P 3 gives the efficiency COP(k) for the continuous operation of the refrigerant circuit 2.In contrast to the continuous operation of the refrigerant circuit 2 of FIG. 2, the diagram 34 of FIG. 3 shows the time-clocked heating operation of the device 1 of FIG. 1 with the temperature T, the power P and the efficiency COP over time t in a schematic illustration with a design not changed. When the motor vehicle is started at the time t0, the temperatures T1 and T2 of the heat exchangers 9, 15 are at ambient temperature, or when the charge controller 27 is warm, the heat exchanger 15-in a manner not shown-can already have a higher temperature T2.The heat exchanger 9 is operated via the time cycles Δt 1, Δt 3 and subsequent odd time cycles and supplies the power P 1 at the temperature T 1 at ambient temperature. Due to the generated heat of the components of the coolant circuit 3 and of the fluid circuit 4, the temperature T 1 heats up along the time cycle Δt 1 in the coolant circuit 3 when the heat exchanger 15 is not yet activated. At the time t 1, the heat exchanger 9 is switched off here-but can also be continued to be operated continuously-and the pumps 21, 22 are activated, so that the heat exchanger 15 emits heat, which is present along the time cycle Δt 2 in the coolant circuit 3 at higher temperatures T 2 than in continuous operation (FIG. 2 ), via the heat exchanger 15 to the refrigerant, the temperature T 0 of which is heated significantly higher by this amount of heat than in continuous operation. Due to the limited heat flow via the heat exchanger 15, the temperature T 2 and thus the temperature T 0 decreases again and the heat exchanger 15 is deactivated again at the time t 2 so that its temperature T 2 can increase again along the time cycle Δt 3. At the time t 3, the heat exchanger 15 is switched on again along the time cycle Δt 4 and the time cycle Δt 2 repeats. The timings Δt 2, Δt 3, Δt 4 are continuously repeated. In the exemplary embodiment shown, the heat exchangers 9, 15 are in each case alternately switched on and off at the points in time t1, t2, t3, t4 and following. In modified exemplary embodiments, the heat exchanger 9 can be operated continuously.From this clocked operation, such as heating operation, an achieved power is produced by both heat exchangers 9, 15, wherein the power P 1 is produced by the heat exchanger 9 alternately or, if appropriate, permanently and the power P 2 is produced by the heat exchanger 15 intermittently during the time cycles Δt 2, Δt 4, etc. Over time t in the time cycles Δt 1, Δt 3, etc., this results in a lower efficiency COP( 1) which is attributable exclusively to the heat exchanger 9 and which is lower than the efficiency COP(k) of the continuous operation. In the time cycles Δt2, Δt4, etc., a significantly higher efficiency COP(s) results than the efficiency COP(k) which is attributable to the quantity of heat of the heat exchanger 15 at a higher temperature T2and, if appropriate, the quantity of heat of the heat exchanger 9. Accordingly, the average efficiency COP(m) of the two efficiencies COP(1) and COP(s) is greater than the continuous operation efficiency COP(k). This leads, in particular in heating operation, to a reduced power requirement for the compressor 5 compared to continuous heating operation with the same design of the device 1, so that the compressor can be designed to be smaller and uses less electrical energy, so that the saved energy fraction benefits the range of the motor vehicle.List of reference characters1 Device 2 Refrigerant circuit 3 Coolant circuit 4 Fluid circuit 5 Compressor 6 Heat loop 7 Throttle valve 8 Heat transfer device 9 Heat exchanger 10 Fan 11 Throttle valve 12 Throttle valve 13 Cooling loop 14 Heat transfer device 15 Heat exchanger 16 Separator 17 Internal heat exchanger 18 Selector switch 19 Coolant circuit 20 Coolant circuit 21 Pump 22 Pump 23 External heat exchanger 24 Heat transfer device 25 Heat exchanger 26 Power electronics 27 Charge controller 28 Battery 29 Electric machine 30 Transmission 31 Valve 32 Switching device 33 Diagram 34 Diagram COP Efficiency COP( 1) Efficiency COP(k) Efficiency COP(m) Efficiency COP(s) Efficiency P Power P 1 Power P 2 Power P 3 Power T Temperature T 0 Temperature T 1 Temperature T 2 Temperature t Time t 0 time t 1 time t 2 time t 3 time t 4 time Δt 1 time clock Δt 2 time clock Δt 3 time clock Δt 4 time clockReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 132 803 A1

[0002]

Claims

Method for controlling a device (1) for the thermal management of an electrically operated motor vehicle, in particular for the air conditioning of its passenger compartment, having a refrigerant circuit (2) with a compressor (5) compressing a refrigerant and at least two heat sources of different temperatures (T1, T2) which make available heat and can be connected to the refrigerant circuit (2), characterized in that, depending on the temperature (T1, T2), at least one of the heat sources is connected to the refrigerant circuit (2) in a time-clocked manner.Method according to Claim 1, characterized in that the ambient air serves as the first heat source and a coolant circuit (3) with coolant of the motor vehicle serves as the second heat source.Method according to Claim 2, characterized in that a third heat source of an additional fluid circuit (4) is connected to the coolant circuit (3) or the refrigerant circuit (2) directly as a function of a quantity of heat available in the fluid circuit (4).Method according to Claim 2 or 3, characterized in that a plurality of coolant circuits (19, 20) through which coolant flows by means of at least one pump (21, 22) are connected in the coolant circuit (3) by means of a selector switch (18) as a function of the amounts of heat recoverable in the coolant circuits (19, 20).Method according to Claim 4, characterized in that the third heat source is switched on by means of one of the coolant circuits (19) of the second heat source, in particular in a clocked manner and as a function of the amount of heat present in the fluid circuit (4).Method according to one of Claims 2 to 5, characterized in that, if a predetermined external temperature is undershot, the first heat source is permanently connected and the second heat source is connected in a clocked manner in terms of time.Method according to one of Claims 2 to 5, characterized in that, if a predetermined external temperature is undershot, the first and the second heat source are operated alternately in a clocked manner in time.Method according to one of Claims 3 to 7, characterized in that, in the third heat source, a heat-generating device is connected to the fluid circuit (4) as a function of a quantity of heat which is generated by it and / or is to be supplied to it.Device (1) for carrying out the method according to one of Claims 1 to 8, having at least two heat transfer devices (8, 14) which are in heat exchange connection with a refrigerant circuit (2), and having a changeover device (32) for the time-clocked connection of at least one heat transfer device (14) as a function of the recoverable amounts of heat thereof.Device (1) according to Claim 9, characterized in that a heat transfer device (8) is provided between the ambient air and the refrigerant circuit (2) and a second heat transfer device (14) is provided between a coolant circuit (3) and the refrigerant circuit (2), wherein a third heat transfer device (24) is provided in particular between the coolant circuit (2) and an additional fluid circuit (4).

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