Thermal management system with a refrigerant circuit for a motor vehicle and motor vehicle with such a thermal management system

Abstract

The present invention relates to a thermal management system for a motor vehicle (1), in particular a motor vehicle (1) that is at least partially electrically powered, comprising a refrigerant circuit (100) with a compressor (110), an evaporator (140; 150) and an expansion element (131; 132) upstream of the evaporator (140; 150), wherein the thermal management system is configured to operate the compressor (110) in a cycle operation at low load, and wherein the thermal management system is further configured to lock the expansion element (131; 132) upstream of the evaporator (140; 150) when the compressor (110) is switched off during cycle operation, and to open it when the compressor (110) is switched on during cycle operation.

Description

The present invention relates to a thermal management system with a refrigerant circuit for a motor vehicle, in particular for a motor vehicle that is at least partially electrically powered. The present invention further relates to a motor vehicle with such a thermal management system. The invention also relates to a computer program for carrying out a method, executable on such a motor vehicle, for controlling the operation of the thermal management system. Thermal management systems for electrically powered vehicles are known in the prior art. These systems comprise a refrigerant circuit with a controllable compressor for compressing a refrigerant within the circuit. Electrically driven, speed-controlled refrigerant compressors, also known as electric air conditioning compressors (EACs), are used in these systems. The compressor's actual speed is electrically driven based on a target speed specified by the refrigerant circuit controller. Electrically driven, speed-controlled refrigerant compressors of this type typically have a minimum speed to ensure that the compressor's electric motor can drive the compressor with sufficient torque and thus maintain a stable actual speed. During low-load operation, it can happen that the target speed specified by the refrigerant circuit controller is below the compressor's minimum speed, or at least briefly falls below it. To prevent over-fulfillment of the target values ​​and inefficient operation, the prior art provides for the compressor to operate intermittently in such cases as soon as the specified target speed falls below the compressor's minimum speed. The cycling of the compressor causes pressure equalization between the high-pressure and suction sides of the refrigerant circuit, as the compressor is no longer pumping any mass flow. This pressure equalization can lead to disruptive flow noises, for example, from the evaporation of residual refrigerant in an evaporator of the refrigerant circuit. Furthermore, it can cause undesirable refrigerant shifts from the high-pressure to the suction side of the refrigerant circuit, which must first be equalized when the compressor restarts. DE 10 2018 221 280 A1 describes a refrigeration system for a vehicle with a refrigerant circuit that can be operated for both AC and heating modes. The refrigeration system comprises a first air conditioning unit with a first evaporator and a first refrigerant-to-air heat exchanger, a second air conditioning unit with a second evaporator and a second refrigerant-to-air heat exchanger, a refrigerant compressor, an external heat exchanger (as a refrigerant condenser, gas cooler, or heat pump evaporator), a first expansion element associated with the first evaporator, and a second expansion element associated with the second evaporator, wherein the first and second refrigerant-to-air heat exchangers are fluid-connected upstream to the high-pressure side of the refrigerant compressor. DE 10 2021 132 799 A1 describes a method for operating a refrigerant circuit of a motor vehicle, in which a compressor arranged in a main line of the refrigerant circuit delivers a minimum mass flow rate of refrigerant. At least one parameter is recorded, which indicates the cooling capacity of a first evaporator arranged in the main line. The first evaporator provides the cooling capacity as a result of being supplied with refrigerant expanded by means of a first expansion device. Depending on the cooling capacity provided by the first evaporator at the minimum mass flow rate, a second expansion device can be opened, which is arranged in a parallel line upstream of a second evaporator arranged in the parallel line.Depending on the cooling capacity of the first evaporator, at least one additional or alternative measure is taken, different from opening the second expansion device, which leads to an increase in heat absorption by the refrigerant. In DE 10 2021 132 799 A1, a cycling operation of the compressor in low-load operation is completely avoided, and instead a shut-off valve is opened and closed alternately in cycling operation. EP 1 469 263 A1 describes a method for reducing refrigerant diffusion in compressors and portable refrigeration and air conditioning systems with compressors, condensers and evaporators, as well as associated fans and valves, wherein the pressure in the condenser is actively reduced after the compressor has stopped. DE 10 2006 022 557 A1 describes an ejector pump circuit device with an ejector pump in which an evaporator is arranged in a refrigerant branch channel connected to a refrigerant intake port of the ejector pump. An opening / closing element is provided for opening and closing a refrigerant channel to prevent the refrigerant from flowing into the evaporator. A control unit controls the intermittent operation of a compressor. In the ejector pump circuit device, the control unit closes the opening / closing element for a period of time during which the compressor is stopped. US 2016 / 0 178 253 A1 describes an air conditioning device for a vehicle comprising a compressor that supplies a high-pressure refrigerant by drawing in and out a refrigerant, an air-heating heat exchanger that heats air to be blown into a vehicle cabin by using heat from the high-pressure refrigerant, a pressure-reducing section that expands and decompresses the high-pressure refrigerant and supplies it as an intermediate-pressure refrigerant and a low-pressure refrigerant, a first low-pressure-side heat exchanger that exchanges heat between the intermediate-pressure refrigerant and a heating medium other than air, a second low-pressure-side heat exchanger that cools the heating medium by exchanging heat between the low-pressure refrigerant and the heating medium, a first heating medium circuit through which the heating medium cooled in the second low-pressure-side heat exchanger circulates, and a heating medium-to-air heat exchanger.which causes the heating medium to absorb heat by exchanging heat between the air and the heating medium circulating through the first heating medium circuit. US 2005 / 0178150A1 describes an ejector pump circuit that includes an ejector pump which acts as a pressure reducing device for reducing the pressure of a fluid and which also acts as a pulse pump for conveying the fluid by means of a entrainment effect of an ejected high-speed working fluid, so that such an ejector pump circuit is effectively applicable to, for example, a cooling circuit of a vehicle air conditioning and cooling system that performs passenger compartment air conditioning operation and refrigeration unit cooling operation using multiple evaporators. It is an object of the present invention to provide a thermal management system with a refrigerant circuit for a motor vehicle in which improved low-load operation with higher efficiency and / or improved ease of use can be enabled, in particular avoiding or at least reducing undesirable refrigerant shifts in the refrigerant circuit and / or disturbing flow noises. To solve the aforementioned problem, a thermal management system with a refrigerant circuit for a motor vehicle according to claim 1 is proposed according to the invention. Furthermore, a motor vehicle with a thermal management system according to claim 8 and a computer program product for carrying out a method for controlling the operation of the thermal management system according to claim 9, which can be implemented on such a motor vehicle, are proposed. Advantageous exemplary embodiments can be found in the dependent claims and the description. An object of the invention is a thermal management system with a refrigerant circuit for a motor vehicle, in particular a motor vehicle that is at least partially electrically powered. The refrigerant circuit comprises a compressor, which is an electrically driven, speed-controlled refrigerant compressor, an evaporator, and an expansion element upstream of the evaporator. The thermal management system is configured to operate the compressor in a cycle mode at low load when a predetermined target speed in the compressor's normal operation falls below a minimum compressor speed, and in particular, the compressor is switched on and off in cycle mode.Furthermore, it is provided that the thermal management system is designed to at least lock the expansion device upstream of the evaporator during compressor cycling operation when the compressor is switched off, and to open it when the compressor is switched on during cycling operation. This enables efficient low-load operation, preventing the compressor from being regulated at excessively low speeds where a stable actual speed cannot be guaranteed. Furthermore, the underlying principle is that pressure equalization between the high-pressure and suction sides of the compressor, which occurs when the compressor switches off during intermittent operation at low load, can be avoided, at least at the evaporator. This allows any disruptive noises at the evaporator, for example, caused by the evaporation of residual refrigerant within the evaporator, to be avoided or at least significantly reduced. In addition, unwanted refrigerant shifts can be prevented or at least significantly reduced.By preventing unwanted refrigerant shifts when the compressor is switched off during intermittent operation, a higher efficiency of the refrigerant circuit can be advantageously achieved during intermittent operation of the compressor at low loads. Furthermore, the reduced noise at the evaporator during intermittent operation of the compressor results in improved user comfort. According to a practical exemplary embodiment, at least one evaporator can be configured to cool the interior of a motor vehicle. In this configuration, the evaporator can liquefy the refrigerant circulating in the refrigerant circuit and thereby extract heat from the surroundings. This can be advantageously used to cool ambient air, which can then be drawn into the vehicle's interior by a fan of the vehicle's air conditioning system to cool the interior. According to a convenient exemplary embodiment, the at least one evaporator can be configured as an evaporator of a chiller in the refrigerant circuit, wherein a heat exchanger of the chiller can be configured to cool a coolant in a coolant circuit of the thermal management system for cooling a traction battery of the vehicle. This enables efficient cooling of the vehicle's traction battery. According to a convenient exemplary embodiment, the refrigerant circuit can include the evaporator for cooling an interior of the motor vehicle and, in a parallel branch of the refrigerant circuit, the chiller for the coolant circuit of the thermal management system for cooling a traction battery of the motor vehicle, wherein a first expansion element can be placed upstream of the evaporator for cooling an interior of the motor vehicle and a second expansion element can be placed upstream of the chiller in the parallel branch of the refrigerant circuit. Preferably, the thermal management system is further configured to lock the first expansion element upstream of the evaporator during compressor cycling operation when the compressor is switched off, and to open it when the compressor is switched on during cycling operation. Alternatively or preferably additionally, the thermal management system is further configured to lock the second expansion element upstream of the chiller during compressor cycling operation when the compressor is switched off, and to open it when the compressor is switched on during cycling operation. According to a convenient exemplary embodiment, the expansion element upstream of the at least one evaporator, for example the first and / or the second expansion element, can be designed as an electronic expansion element, wherein the electronic expansion element can preferably include an electric actuator for opening and closing the expansion element. This enables efficient active control of the degree of opening of the expansion element and also efficient opening and closing of the expansion element during the compressor's cycling operation at low load. According to a convenient exemplary embodiment, the expansion element upstream of the at least one evaporator can be designed as a thermostatic expansion element with an actively controllable shut-off valve for opening and closing the expansion element, wherein the shut-off valve can preferably be designed as a solenoid valve. This enables efficient passive control of the opening degree of the expansion element and also efficient opening and closing of the expansion element during the compressor's cycling operation at low load. According to a convenient exemplary embodiment, the refrigerant circuit can comprise several expansion elements, wherein the thermal management system can preferably be configured to close several or preferably all expansion elements of the refrigerant circuit when the compressor is switched off during intermittent operation, and to open them when the compressor is switched on during intermittent operation. This enables a particularly advantageous avoidance of undesired refrigerant shifts in the refrigerant circuit from the high-pressure side of the compressor to the suction side of the compressor, so that restarting the compressor when switched on during intermittent operation and also when returning to normal operation can be made particularly efficient. To avoid unwanted noise, it is particularly preferred that at least all expansion devices upstream of a respective evaporator close when the compressor is switched off during cycle operation, and open when the compressor is switched on during cycle operation. According to a convenient exemplary embodiment, at least one expansion element of the refrigerant circuit can be designed as a fixed throttle with an actively controllable shut-off valve for opening and closing the expansion element, the shut-off valve preferably being designed as a solenoid valve. In this way, expansion elements designed as unregulated fixed throttles can also close when the compressor is switched off during intermittent operation and open when the compressor is switched on during intermittent operation, thus enabling particularly efficient intermittent operation of the compressor. According to a suitable exemplary embodiment, the thermal management system also comprises at least one refrigeration circuit controller and / or a control device which is configured to control and, in particular preferably, regulate the refrigerant circuit, especially directly or indirectly via one or more refrigeration circuit controllers. For example, the control device may preferably be configured to operate the compressor and the at least one expansion element in the cycle operation of the compressor, wherein the control device may in particular be configured to switch the compressor on and off in cycle operation and to lock the at least one expansion element when the compressor is switched off in cycle operation, and to open it when the compressor is switched on in cycle operation or switches to normal control operation. Furthermore, according to a subsidiary subject, a motor vehicle, in particular a motor vehicle that is at least partially electrically powered, is proposed with a thermal management system according to one of the above aspects and embodiments. According to a related subject matter, a computer program product comprising instructions of a computer program is also proposed, wherein the instructions, when executed by a computer-implemented control device of the motor vehicle or the thermal management system, cause the control device to control or preferably regulate a method for operating the thermal management system, comprising: operating the compressor of the refrigerant circuit of the thermal management system at low load in a pulsed operation when a predetermined target speed in the normal operation of the compressor falls below a minimum speed of the compressor, blocking the expansion device upstream of the at least one evaporator when the compressor is switched off in pulsed operation, and opening the expansion device upstream of the at least one evaporator when the compressor is switched on in pulsed operation. The invention also includes combinations of the features of the described embodiments. The invention therefore also includes realizations that each exhibit a combination of the features of several of the described embodiments, provided that the embodiments have not been described as mutually exclusive. The following describes some exemplary embodiments of the invention. Figure 1 shows a simplified and schematic representation of a motor vehicle according to an exemplary embodiment; Figure 2 shows a simplified and schematic representation of a thermal management system with a refrigerant circuit and a coolant circuit in a motor vehicle according to an exemplary embodiment; and Figure 3 shows a process diagram for controlling the operation of the thermal management system according to an exemplary embodiment. The following section describes in detail some examples or embodiments of the present disclosure with reference to the accompanying figures. Identical or similar elements in the figures may be designated with the same reference numerals, but sometimes they may be designated with different reference numerals. It should be emphasized that the subject matter of the present disclosure is in no way limited or restricted to the embodiments and their features described below, but also includes modifications of the embodiments, in particular those which are covered by modifications of the features of the described examples or by combining one or more of the features of the described examples within the scope of protection of the independent claims. Figure 1 schematically illustrates an exemplary embodiment of an electrically powered motor vehicle 1 with a thermal management system comprising a refrigerant circuit 100. The motor vehicle 1 in Figure 1 is, for illustrative purposes only, a purely electrically powered electric vehicle (EV). However, it should be noted that a thermal management system with a refrigerant circuit 100, as described above and below, can also be used in a so-called range-extended electric vehicle (REEV), i.e., an electric vehicle equipped with a range extender (RE). In particular, a thermal management system with a refrigerant circuit 100 according to the embodiments described above and below can be used in motor vehicles of different electrification levels, for example in BEVs (Battery Electric Vehicles), REEVs, full hybrid vehicles, plug-in hybrid vehicles and also mild hybrid vehicles in which a driving combustion engine is electrically assisted (partially electrically driven motor vehicle). The motor vehicle 1 according to Fig. 1 includes, by way of example, a rechargeable traction battery 300 and at least one electric drive (not shown) that can be powered by electrical energy from the traction battery 300 for the propulsion of the motor vehicle 1. The motor vehicle 1 according to Fig. 1 further comprises, by way of example, a refrigerant circuit 100 and a coolant circuit 200. The coolant circuit 200 is, for example, configured to cool the traction battery 300 of the motor vehicle 1 with a coolant circulating in the coolant circuit 200. The refrigerant circuit 100 is preferably configured, for example, to extract heat from the cooling circuit 200 to cool the coolant in the cooling circuit 200. Furthermore, the refrigerant circuit 100 can, for example, be configured to be used for an air conditioning system of the motor vehicle 1, for example, to cool the interior of the motor vehicle 1. Furthermore, the refrigerant circuit 100 can, for example, be configured to heat the interior of the motor vehicle 1 in a heat pump operation. The motor vehicle 1 according to Fig. 1 further comprises, by way of example, a control unit 400, which by way of example includes a processor 41 and a data storage device 42, wherein the data storage device 42 can, for example, store computer programs that can be executed by the processor 41 to control the motor vehicle 1. By way of example, the control unit 400 is connected via the signal lines shown in dashed lines in Fig. 1 at least to the refrigerant circuit 100, the coolant circuit 200 and the traction battery 100. Fig. 2 shows a simplified and schematic thermal management system with a refrigerant circuit 100 and a coolant circuit 200 in a motor vehicle according to an exemplary embodiment, for example in the motor vehicle 1 according to Fig. 1 . In preferred embodiments, the refrigerant circulating in the refrigerant circuit 100 can comprise R744 (CO2). However, the present invention is not limited to R744 as a refrigerant, and in further embodiments other refrigerants can be used in the refrigerant circuit 100, for example R1234yf, R134a, R404a, R600a, R290, R152a or R32, or mixtures of refrigerants. The refrigerant circuit 100 includes, for example, a compressor 110 for compressing the gaseous refrigerant circulating in the refrigerant circuit 100 and, on the high-pressure side, a condenser 120 or gas cooler fluidically connected to the compressor for cooling the refrigerant compressed by the compressor 110. For example, the gaseous refrigerant compressed by the compressor 110 can be liquefied at the condenser 120. The compressor 110 is designed as an electrically driven, speed-controlled refrigerant compressor (ECC). In further embodiments, it is possible that additional components or devices may be provided in series and / or in parallel on the high-pressure side of the refrigerant circuit 100. For example, pressure and / or temperature sensors may be provided on the high-pressure side. Furthermore, one or more high-pressure refrigerant receivers, high-pressure valves or mixing valves for any high-pressure parallel lines, and / or one or more high-pressure hot gas coolers or heating coils, etc., may optionally be provided. As an example, the refrigerant circuit 100 includes, on the suction side, an evaporator 140, upstream of which is a first expansion element 131 that expands the refrigerant coming from the condenser 120. At the evaporator 140, the refrigerant, expanded at the first expansion element 131, can change into a gaseous state. In this process, heat can be extracted from the surroundings. For example, the evaporator 140 can include an ambient heat exchanger of an air conditioning system of the vehicle 1, for instance, to cool the interior of the vehicle 1. For example, the refrigerant circuit 100 includes a chiller 150 on the suction side, upstream of which is a second expansion element 132 that expands the refrigerant coming from the condenser 120. At the chiller 150, the refrigerant, expanded at the second expansion element 132, can change into a gaseous state. In this process, heat can be extracted from the surroundings. For example, the chiller 150 can include an evaporator and a heat exchanger thermally connected to the evaporator for the coolant circuit 200, in order to cool the coolant circulating in the coolant circuit 200. For example, the evaporator 140 and the chiller 150 are fluidically connected to the compressor 110 on the suction side in order to supply the refrigerant to the compressor 110 for recompression. In further embodiments, additional components or devices may be provided in series and / or in parallel on the suction side of the refrigerant circuit 100. For example, pressure and / or temperature sensors may be provided on the suction side. Furthermore, one or more suction-side refrigerant receivers, suction-side valves or mixing valves for any parallel suction-side lines, etc., may optionally be provided. The coolant circuit 200 includes, for example, a pump 210 to pump the coolant circulating in the cooling circuit 200 from the heat exchanger of the chiller 150 to the drive battery 300 in order to cool the drive battery. For example, the coolant heated at the drive battery 300 is fed back into the coolant circuit 200 to the heat exchanger of the chiller 150 for further cooling. In some embodiments, water can be used as the coolant in the coolant circuit 200. In preferred embodiments, antifreeze such as glycol or alcohol can be added. A glycol-water mixture is particularly preferred as the coolant in the coolant circuit 200. In the exemplary embodiment described above according to Fig. 2, the refrigerant circuit 100 comprises, by way of example, an evaporator 140 with a first expansion element 131 upstream and, in parallel thereto, a chiller 150 with a second expansion element 132 upstream. In further exemplary embodiments, only one evaporator 140 for an air conditioning system of the motor vehicle 1 or only one chiller 150 for battery cooling may be provided. In further exemplary embodiments, additional parallel circuits with further expansion elements may also be provided. For example, the control device 400 is connected via the signal lines shown in dashed lines in Fig. 2 at least to the compressor 110 of the refrigerant circuit 100 and the expansion devices 131 and 132 of the refrigerant circuit 100. The control unit 400 can, for example, control or preferably regulate the operation of the compressor 110 directly or indirectly via an intermediate refrigeration circuit controller. For example, the control unit 400 can regulate the operation of the compressor 110 based on speed, for example by specifying a target speed for the compressor 110. The control unit 400 can preferably also be connected to several suction-side and / or high-pressure-side temperature sensors and / or pressure sensors for regulating the operation of the refrigerant circuit 100. Furthermore, the control unit 400 can control, or preferably regulate, the expansion devices 131 and 132. This can also be done directly or indirectly via a refrigeration circuit controller. Furthermore, the control device 400 is connected, by way of example, to the pump 210 of the coolant circuit 200 via the signal lines shown in dashed lines in Fig. 2 for controlling or preferably regulating the pump operation in the coolant circuit 200. The control device 400 can preferably also be connected to several temperature sensors for controlling the operation of the coolant circuit 200, in particular to detect the temperature of the coolant in the coolant circuit 200 downstream and / or upstream of the chiller 150 and / or to detect the temperature of the drive battery 300. Furthermore, it is possible that the control unit 400 detects an outside temperature via an outside temperature sensor and / or detects an inside temperature of the motor vehicle 1 via an inside temperature sensor. As mentioned above, the compressor 110 is designed as an electrically driven, in particular speed-controlled, refrigerant compressor (ECC). Such electrically driven refrigerant compressors may have a minimum speed to ensure that the electric motor of the compressor 110 can drive the compressor 110 with sufficient torque to provide a stable actual speed. During low-load operation, it can happen that the target speed specified by the refrigerant circuit controller or the control unit 400 is below the minimum speed of the compressor 110, or that the minimum speed of the compressor 110 is at least briefly undershot. To prevent over-fulfillment of the target values ​​and inefficient operation, it is provided, for example, that the compressor 110 is operated in a pulsed mode as soon as the specified target speed falls below the minimum speed of the compressor 110. To avoid the adverse pressure equalization described at the beginning during the cycling operation of compressor 110 in low-load operation, it is provided, for example, to block the flow of refrigerant at the expansion devices 131 and 132 when compressor 110 is switched off during cycling operation of compressor 110 in low-load operation. It is thus provided, by way of example, that the expansion element 131 upstream of the evaporator 140 preferably closes when the compressor 110 is switched off during low-load operation, i.e., at a compressor speed of 0 rpm, and opens again when the compressor 110 switches on again, i.e., at a compressor speed > 0 rpm. Consequently, an adverse pressure equalization between the high-pressure side and the suction side of the compressor in the refrigerant circuit can be prevented at the evaporator 140, and in particular, disruptive noise at the evaporator 140 can be avoided by preventing the evaporation of residual refrigerant in the evaporator 140 when the compressor 110 is switched off during low-load operation. Furthermore, undesirable refrigerant shifts from the high-pressure side to the suction side of the compressor at the evaporator 140 can be prevented. Since disturbing noises occur, particularly at the evaporator 140 for the air conditioning of the interior area, when the compressor 110 is operated intermittently at low load, it is advantageous in particularly beneficial embodiments that at least the expansion element 131 upstream of the evaporator 140 closes when the compressor 110 is switched off during intermittent operation at low load, i.e., at a compressor speed of 0 rpm, and opens again when the compressor 110 switches on again, i.e., at a compressor speed > 0 rpm. In this way, disturbing noises can be effectively avoided. Alternatively or additionally, it is further exemplified that the expansion device 132 upstream of the chiller 150 closes when the compressor 110 is switched off during low-load operation (i.e., at a compressor speed of 0 rpm) and opens again when the compressor 110 switches on again (i.e., at a compressor speed > 0 rpm). Consequently, an adverse pressure equalization between the high-pressure side and the suction side of the compressor in the refrigerant circuit can be prevented at the chiller 150, and in particular, disruptive noise at the chiller 150 can be avoided by preventing the evaporation of residual refrigerant in the chiller 150 or in the evaporator of the chiller 150 when the compressor 110 is switched off during low-load operation. Furthermore, undesirable refrigerant shifts from the high-pressure side to the suction side of the compressor at the chiller 150 can be prevented. Furthermore, in some embodiments, one or more additional optional expansion devices in the refrigerant circuit may also be provided to close when the compressor 110 is switched off during low-load operation, i.e., at a compressor speed of 0 rpm, and to open again when the compressor 110 is switched on again, i.e., at a compressor speed > 0 rpm. Consequently, an adverse pressure equalization between the high-pressure side and the suction side of the compressor in the refrigerant circuit can be prevented, so that undesirable refrigerant shifts from the high-pressure side to the suction side of the compressor in the refrigerant circuit can be completely avoided. For example, one or more expansion devices, in particular expansion devices 131 and / or 132, in the refrigerant circuit 100 can be designed as electronic expansion devices, which allow them to be completely closed or blocked by electrical control. For example, such an electronic expansion device can be closed by an electric actuator of the electronic expansion device when the compressor 110 is switched off during low-load operation, i.e., at a compressor speed of 0 rpm, and reopened when the compressor 110 is switched on again, i.e., at a compressor speed > 0 rpm. Alternatively or additionally, one or more expansion devices, in particular expansion devices 131 and / or 132, in the refrigerant circuit 100 can be designed as thermostatic expansion devices with an additional shut-off function. Thermostatic expansion devices are typically passive expansion devices that are preferably equipped with an actively controllable or regulated shut-off valve, for example, a solenoid valve, for the additional shut-off function. Such a shut-off valve can be integrated into the thermostatic expansion device or located upstream or downstream of it. For example, such a shut-off valve of the thermostatic expansion device can be closed when the compressor 110 is switched off during low-load operation, i.e., at a compressor speed of 0 rpm, and open again when the compressor 110 is switched on again, i.e., at a compressor speed > 0 rpm. Alternatively or additionally, one or more expansion devices in the refrigerant circuit 100 can be designed as fixed throttles with a shut-off function. Here, too, an actively controllable or adjustable shut-off valve, for example a solenoid valve, can be provided on the fixed throttle. Such a shut-off valve can be integrated into the fixed throttle or located upstream or downstream of it. For example, such a shut-off valve of the fixed throttle can be closed when the compressor 110 is switched off during low-load operation, i.e., at a compressor speed of 0 rpm, and open again when the compressor 110 is switched on again, i.e., at a compressor speed > 0 rpm. As previously described, compressor 110 switches to intermittent operation when the setpoint speed falls below the minimum speed of compressor 110, particularly during low-load operation. In intermittent operation, compressor 110 can be controlled, for example, by the discharge temperature at a fan on the evaporator 140. If the discharge temperature rises above a threshold temperature above the setpoint temperature, compressor 110 switches on in intermittent operation and off again as soon as the discharge temperature reaches the setpoint temperature. When the setpoint speed rises again to the minimum speed of compressor 110, the compressor 110 switches back to its speed-controlled normal operation. For example, it is provided that at least the expansion device 131 upstream of the evaporator 140 is blocked when the compressor 110 switches off in cycle operation, and the expansion device 131 upstream of the evaporator 140 is opened when the compressor 110 switches on in cycle operation or switches from cycle operation to normal operation. In some embodiments, the expansion element 132 upstream of the chiller 150 can also be blocked when the compressor 110 switches off in cycle operation, and opened again when the compressor 110 switches on in cycle operation or switches from cycle operation to normal operation. In some embodiments, further or all expansion devices in the refrigerant circuit can also be blocked when the compressor 110 switches off in cycling operation, and opened again when the compressor 110 switches on in cycling operation or switches from cycling operation to normal operation. For example, the one or more computer programs for controlling or regulating the thermal management system by the control device 400 in the data storage 42, for example for regulating the operation of the refrigerant circuit 100, include computer program instructions which, when executed at the control device 400, execute procedures for controlling or regulating the thermal management system of the motor vehicle 1, in particular, for example, according to the procedure described below as an example. Fig. 3 shows a process diagram for controlling the operation of the thermal management system according to an exemplary embodiment. In step S1 in Fig. 3, the thermal management system or the refrigerant circuit 100 of the thermal management system is controlled in the normal operation of the compressor 110, whereby the compressor 110 is operated at a target speed of the compressor 110 above the minimum speed of the compressor 110. In step S2, it is determined whether the target speed of compressor 110 falls below the minimum speed of compressor 110. As long as the target speed of compressor 110 does not fall below the minimum speed of compressor 110, i.e., if the target speed of compressor 110 is greater than or equal to the minimum speed of compressor 110, normal operation continues according to step S1 (step S2, No). If, in step S2, it is determined that the target speed of compressor 110 falls below the minimum speed of compressor 110 (step S2, Yes), then compressor 110 is switched to intermittent operation and operated in intermittent operation in step S3; see, for example, the intermittent operation according to steps S31 to S36 in Fig. 3. During the cycle operation (S3) of compressor 110, compressor 110 is switched off (step S32), whereby at least the expansion element 131 upstream of the evaporator 140 and optionally also the expansion element 132 upstream of the chiller 150 are blocked (S32). Any further expansion elements in the refrigerant circuit 100 may also be blocked. Step S33 determines whether a switching-on condition for cycle operation is met. This can be the case, for example, if an outlet temperature at a fan on the evaporator 140 or a coolant temperature at the outlet of the heat exchanger of the chiller 150 exceeds a limit temperature above the setpoint temperature (or the setpoint temperature itself). If the switching-on condition for the cycle operation is met (S33, Yes), the compressor 110 is switched on (S34) and the expansion device(s) blocked in step S32 are opened again (S35). Step S36 determines whether a shutdown condition for the cycle operation is met. This can occur, for example, if the outlet temperature at a fan on the evaporator 140 or the coolant temperature at the outlet of the chiller's heat exchanger 150 reaches or falls below the setpoint (or a limit temperature below the setpoint). Then, if S36 returns "yes," meaning the shutdown condition for the cycle operation is met, compressor 110 is switched off again (S31) and at least one expansion valve is closed (S32). As soon as the target speed of compressor 110 is again greater than or equal to the minimum speed of compressor 110 (S2, No), the compressor 110 switches from cycling operation to normal operation, and all expansion devices locked in S32 are also opened. Above, exemplary embodiments of a thermal management system with a refrigerant circuit for a motor vehicle, in particular a motor vehicle that is at least partially electrically powered, have been described, in which improved low-load operation can be enabled, in particular avoiding disturbing flow noises and / or undesirable refrigerant displacements in the refrigerant circuit during compressor cycle operation. It should be noted that only examples and embodiments of the present disclosure, as well as technical advantages, have been described in detail above with reference to the accompanying figures. However, the present disclosure is in no way limited or restricted to the embodiments and their features or combinations described above, but also includes modifications of these embodiments, in particular those resulting from modifications of the features of the described examples or from combinations or partial combinations of one or more of the features of the described examples within the scope of protection of the independent claims. Reference symbol list 1 Motor vehicle 100 Refrigerant circuit 110 Compressor 120 Condenser 131 First expansion element 132 Second expansion element 140 Evaporator 150 Chiller 200 Coolant circuit 210 Pump 300 Traction battery 400 Control unit 41 Processor 42 Data storage

Claims

Thermal management system for a motor vehicle (1), comprising: a refrigerant circuit (100) with an electrically driven, speed-controlled refrigerant compressor (110), at least one evaporator (140; 150) and an expansion element (131; 132) upstream of the at least one evaporator (140; 150), wherein the thermal management system is configured to operate the refrigerant compressor (110) in a cycle mode at low load when a predetermined target speed in the normal operation of the refrigerant compressor (110) falls below a minimum speed of the refrigerant compressor (110), and wherein the thermal management system is further configured to block the expansion element (131; 132) upstream of the at least one evaporator (140; 150) during the cycle operation of the refrigerant compressor (110) when the refrigerant compressor (110) is switched off in cycle operation, and to open when the refrigerant compressor (110) is switched on in cycle mode. Thermal management system according to claim 1, wherein the at least one evaporator (140) is arranged for cooling an interior of the motor vehicle (1). Thermal management system according to claim 1, wherein the at least one evaporator is configured as an evaporator of a chiller (150) of the refrigerant circuit (100), wherein a heat exchanger of the chiller (150) is configured to cool a coolant in a coolant circuit (200) of the thermal management system for cooling a traction battery (300) of the motor vehicle (1). Thermal management system according to one of the preceding claims, wherein the expansion element (131; 132) upstream of the at least one evaporator (140; 150) is designed as an electronic expansion element, wherein the electronic expansion element in particular comprises an electric actuator for opening and locking the expansion element (131; 132). Thermal management system according to one of claims 1 to 3, wherein the expansion element (131; 132) upstream of the at least one evaporator (140; 150) is designed as a thermostatic expansion element with an actively controllable shut-off valve for opening and closing the expansion element (131; 132), wherein the shut-off valve is in particular designed as a solenoid valve. Thermal management system according to one of the preceding claims, wherein the refrigerant circuit (100) comprises several expansion elements (131, 132), wherein the thermal management system is configured to lock several or all expansion elements (131, 132) of the refrigerant circuit (100) during the cycling operation of the refrigerant compressor (110) when the refrigerant compressor (110) is switched off during cycling operation, and to open them when the refrigerant compressor (110) is switched on during cycling operation. Thermal management system according to claim 6, wherein at least one expansion element of the refrigerant circuit (100) is designed as a fixed throttle with an actively controllable shut-off valve for opening and closing the expansion element (131; 132), wherein the shut-off valve is in particular designed as a solenoid valve. Motor vehicle (1) with a thermal management system according to one of the preceding claims. A computer program product comprising instructions of a computer program which, when the computer program is executed by a computer-implemented control device (400) of a motor vehicle (1) according to claim 8, cause the control device (400) to control a method for operating the thermal management system, comprising: - operating (S3) the electrically driven, speed-controlled refrigerant compressor (110) of the refrigerant circuit (100) of the thermal management system at low load in pulsed operation when a predetermined target speed in the normal operation of the refrigerant compressor (110) falls below a minimum speed of the refrigerant compressor (110), - locking (S32) the expansion element (131; 132) upstream of the at least one evaporator (140; 150) when the refrigerant compressor (110) is switched off (S31) in pulsed operation, and - opening (S35) the expansion element (131; 132) upstream of the at least one evaporator (140; 150) upstream expansion organ (131;132), when the refrigerant compressor (110) is switched on in cycle mode (S34).;

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