Method for operating a refrigerant circuit in reheating mode with demand-based fan control and motor vehicle

Abstract

The invention relates to a method for operating a refrigerant circuit (10) of a motor vehicle. In heating mode, a compressor (14) conveys compressed refrigerant to a heat exchanger (16), by means of which an airflow (18) can be heated and introduced into a passenger compartment of the motor vehicle. The refrigerant is expanded by means of at least one expansion device (24, 74), and the expanded refrigerant is supplied to at least one evaporator (22, 70). In heating mode, at least a partial flow of the refrigerant compressed by the compressor (14) is supplied to a refrigerant cooler (26) separate from the heat exchanger (16), which is supplied with ambient air (42). A control device (46) determines, based on measured values ​​acquired by sensors (58, 86, 87, 96), the excess heat introduced into the refrigerant to be dissipated at the refrigerant cooler (26).The control device (46) controls a fan (44) designed to supply the refrigerant cooler (26) with ambient air (42) depending on the excess air to be removed. The invention further relates to a motor vehicle.

Description

The invention relates to a method for operating a refrigerant circuit of a motor vehicle, in which, during heating operation of the refrigerant circuit, a compressor of the refrigerant circuit conveys compressed refrigerant to a heat exchanger of the refrigerant circuit. An airflow can be heated by means of the heat exchanger and introduced into a passenger compartment of the motor vehicle. The refrigerant is expanded by means of at least one expansion device of the refrigerant circuit, and the expanded refrigerant is supplied to at least one evaporator of the refrigerant circuit. The invention further relates to a motor vehicle with a refrigerant circuit. German patent DE 10 2021 132 039 A1 describes a method for operating a refrigerant circuit in a motor vehicle. In heating mode, a compressor circulates a refrigerant through a first condenser, which heats an airflow that can be introduced into a passenger compartment. The compressor then circulates the refrigerant through a second condenser for further cooling. At least a portion of the refrigerant flowing from the second condenser is expanded by a first expansion device and fed to a first evaporator, which reduces the humidity of the airflow. To increase the heating capacity available at the first condenser, another portion of the refrigerant is expanded by a second expansion device and fed to a second evaporator. German patent DE 10 2022 122 353 A1 describes a thermal system for an electric vehicle, comprising an external condenser, a heating condenser, an evaporator, a chiller, a compressor, flow control valves for the condensers, and expansion valves for the evaporator and chiller. A control module for the thermal system can open the flow control valve for the heating condenser and the expansion valve for the chiller, allowing refrigerant to flow through the heating condenser and chiller. Conversely, the control module closes the flow control valve for the external condenser and the expansion valve for the evaporator to prevent refrigerant flow through the external condenser and evaporator. Furthermore, in a refrigerant circuit of the type mentioned above, it is possible, during heating operation, to direct at least a portion of the refrigerant compressed by the compressor to a secondary refrigerant cooler within the circuit. This secondary cooler is supplied with ambient air. As a result, heat is dissipated from the refrigerant at both the heat exchanger and the secondary cooler. If a fan is used to supply the secondary cooler with ambient air, and this fan delivers a fixed and constant airflow through the cooler, the fan may operate inefficiently. Furthermore, it can happen that more heat is dissipated from the refrigerant at the additional refrigerant cooler than would be beneficial for heating the airflow into the passenger compartment via the heat exchanger. If the airflow is then additionally heated, for example by an electric auxiliary heater, this is inefficient with regard to the electrical energy required. The object of the present invention is to provide a method of the type mentioned at the outset which is particularly efficient, and to provide a motor vehicle with a refrigerant circuit and with a control device designed to carry out the method. This problem is solved by a method with the features of claim 1 and by a motor vehicle with the features of claim 9. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims and in the following description. In the inventive method for operating a refrigerant circuit of a motor vehicle, during heating operation, a compressor of the refrigerant circuit conveys compressed refrigerant to a heat exchanger of the refrigerant circuit. An airflow can be heated by means of the heat exchanger and introduced into a passenger compartment of the motor vehicle. The refrigerant is expanded by means of at least one expansion device of the refrigerant circuit, the expanded refrigerant being supplied to at least one evaporator of the refrigerant circuit. During heating operation, at least a partial flow of the refrigerant compressed by the compressor is supplied to a refrigerant cooler of the refrigerant circuit, which is separate from the heat exchanger and is exposed to ambient air.A vehicle control unit determines, based on sensor readings, the excess heat introduced into the refrigerant that needs to be dissipated at the refrigerant cooler. Depending on the amount of excess heat to be dissipated, the control unit activates a fan, which is designed to draw ambient air into the refrigerant cooler. In the method according to the invention, the control device determines, based on the measured values ​​acquired by the sensors, the difference in the enthalpy of the refrigerant at a refrigerant inlet and outlet of the at least one evaporator, as well as at a refrigerant inlet and outlet of the heat exchanger. For determining the excess refrigerant to be discharged, the control device takes into account the respective mass flow rate of the refrigerant passing through the at least one evaporator and through the heat exchanger. This is based on the understanding that the cooling capacity of the at least one evaporator, and thus the heat absorbed by the at least one evaporator, as well as the heating capacity of the heat exchanger, can be easily determined from the mass flow rate of the refrigerant and the enthalpy difference.This is advantageous for reliably determining the excess heat to be dissipated by the refrigerant cooler. The sensors are preferably integrated into or attached to the refrigerant circuit. For example, sensors at the respective refrigerant inlet and outlet can measure the refrigerant's pressure and temperature. Using specific refrigerant parameters, the refrigerant's enthalpy at the corresponding points in the refrigerant circuit can then be easily determined. These parameters can be graphically represented in a pressure-enthalpy diagram, from which the refrigerant's enthalpy at a given pressure and temperature can be read. Furthermore, the control unit can store relevant refrigerant parameters to facilitate easy enthalpy calculation. The cooling capacity of at least one evaporator and the heating capacity of the heat exchanger can be determined very easily by the control device via the product of the mass flow rate of the refrigerant and the enthalpy difference. By first determining the actual excess heat to be dissipated at the refrigerant cooler and then controlling the fan accordingly, the control unit can operate the fan very precisely and according to demand, ensuring that only the excess heat present in the refrigerant upon reaching the cooler is dissipated. This prevents excessive heat from being drawn from the refrigerant to the cooler. Consequently, the need for additional heating of the airflow by a separate heating device, particularly an electric one, can be largely eliminated. This contributes to the efficient operation of the process. The heat exchanger can be in direct or indirect contact with the refrigeration circuit or refrigerant circuit. In the case of direct contact, the refrigerant flows through the heat exchanger and directly heats the cabin supply airflow.In contrast, with indirect contact, the refrigerant first transfers its heat to an intermediate fluid, which then heats the airflow for the passenger compartment or the cabin's supply air flow as it subsequently flows through the heat exchanger. The control unit regulates the fan so that the refrigerant cooler is supplied with only as much ambient air as is necessary to dissipate the excess heat. This prevents the fan from operating at a higher power than required to supply the refrigerant cooler with ambient air. Consequently, the process is particularly efficient. If more heat than the excess heat to be dissipated were removed from the refrigerant cooler, less heat would be available in the refrigerant circuit to transfer to the airflow in the passenger compartment via the heat exchanger. This is largely avoidable in this case, making particularly efficient heating operation of the refrigerant circuit possible. In another application, drawing too much ambient air into the refrigerant cooler can cause the fan to generate more airflow than is actually needed for sufficient cooling. This creates an excess of cooling air, which no longer provides any additional cooling effect to an already maximally cooled refrigerant. When a vehicle or motor vehicle with a refrigerant circuit or a refrigeration system is in operation, the airflow from driving can also contribute to cooling the refrigerant in the cooler. This can be used to further reduce fan operation. Additionally or alternatively, during operation of the vehicle equipped with the refrigerant circuit, the cooling airflow can be varied by controlling a closable cooling air inlet in an air inlet area of ​​a radiator package encompassing the refrigerant cooler. This airflow is made of ambient air, allowing the refrigerant cooler to be supplied with it. This control allows the cooling potential of the refrigerant to be varied by opening, closing, or holding the closable cooling air inlet, or such a closing device, as needed. Based on the excess heat to be dissipated from the refrigerant cooler, the control unit can determine the ambient air mass flow rate required to supply the refrigerant cooler in order to dissipate the excess heat from the refrigerant.For this purpose, a characteristic curve can be stored in the control unit, for example. Preferably, the expanded refrigerant is fed to at least one evaporator designed as the interior evaporator of the refrigerant circuit, whereby the airflow is cooled and dehumidified by means of the interior evaporator before being fed to the heat exchanger. By using the interior evaporator as the at least one evaporator of the refrigerant circuit, the airflow can advantageously be conditioned before it is subsequently heated by the heat exchanger. Such a heating operation, designed as a reheat operation, is advantageous for avoiding undesirably high humidity in the passenger compartment of the motor vehicle. Preferably, the control device for determining the heat introduced into the refrigerant takes into account the compressor's power consumption, which is used to pump and compress the refrigerant. This is based on the understanding that compressing the refrigerant by the compressor involves the input of heat into the refrigerant. And although the power consumed by the compressor cannot be used for compression without loss, the heat introduced into the refrigerant by operating the compressor can be very accurately deduced from its power consumption. Considering the power consumed by the compressor contributes to a very comprehensive accounting of the heat present in the refrigerant. This is particularly true if the compressor is an electric refrigerant compressor.Accordingly, the control device can, in particular, take into account the electrical power consumption of the compressor in order to determine the heat introduced into the refrigerant. Preferably, the control unit determines the mass flow rate of the refrigerant delivered by the compressor using the compressor speed and the refrigerant density at the compressor's suction side. The density is measured by a sensor in the refrigerant circuit. This is based on the understanding that the refrigerant volume flow rate can be determined from the compressor's stroke, speed, and efficiency. By considering the refrigerant density at the compressor inlet or suction side, the control unit can calculate the refrigerant mass flow rate from the volume flow rate. The corresponding values ​​can be provided to the control unit with minimal effort.In particular, based on sensor values ​​which provide an inlet temperature and an inlet pressure of the refrigerant at the compressor using measured variables, the resulting density can be estimated or determined based on material properties. In addition to or as an alternative to measuring the cooling capacity of the at least one evaporator and the heating capacity of the heat exchanger on the refrigerant side, the amount of heat introduced into the refrigerant at the at least one evaporator and the amount of heat removed from the refrigerant at the heat exchanger can also be determined based on a flow of a respective medium that releases heat to the refrigerant or absorbs heat from the refrigerant. For example, to determine the amount of heat on the air side, the control unit can use the sensor readings to calculate the difference in air temperature between the air inlet and outlet sides of at least one evaporator and the heat exchanger. The control unit then takes this air temperature difference into account to determine the excess heat to be dissipated. This is based on the understanding that the heat input into or output from the refrigerant can be deduced from the air's heat capacity, mass flow rate, and temperature difference. If the control system also takes the air's humidity into account, the latent heat can also be considered when determining the excess refrigerant to be removed. This is advantageous. Preferably, a partial flow of the expanded refrigerant is fed to a chiller of the refrigerant circuit via at least one evaporator. A coolant flows through the chiller, and heat from the coolant is transferred to the refrigerant within the chiller. Using the evaporator as a chiller allows heat transferred to the coolant by components of the vehicle to be cooled to be used to introduce heat into the refrigerant. This is advantageous. Preferably, the control unit determines the coolant temperature difference between the coolant inlet and outlet of the chiller based on sensor readings. The control unit then uses this temperature difference to calculate the amount of excess coolant to be discharged. This approach is particularly easy to implement. In particular, the control unit can deduce the amount of heat introduced into the refrigerant at the chiller from the refrigerant flow rate and the temperature difference. The corresponding values ​​can be provided to the control unit with minimal effort. This is advantageous. The refrigerant flow rate can be derived, for example, from the pump characteristic curve of a pump unit circulating the refrigerant. Preferably, the control unit regulates the fan based on the vehicle's speed. This is based on the understanding that ambient air, in the form of airflow, can easily be used to dissipate excess heat from the refrigerant at the refrigerant cooler. Therefore, if the vehicle's speed is taken into account, the fan only needs to be activated to supply ambient air to the extent that it is available in addition to the airflow generated by the vehicle's movement. This promotes efficient fan control. In particular, at sufficiently high vehicle speeds, the fan does not need to operate at all. Additionally or alternatively, the control device can be configured to control the fan depending on the operating position of a closing device, which regulates the supply of ambient air, provided by the vehicle's airflow, to the refrigerant cooler. Such a closing device can, for example, be designed like a radiator louver or a similar device for controllable cooling air intake. In the closed position, the sealing device prevents the airflow from passing through the refrigerant cooler, while in the open position, it allows the airflow to pass through the refrigerant cooler very freely. In particular, by adjusting the sealing device to various intermediate positions, the amount of airflow that can pass through the refrigerant cooler can be precisely controlled. Particularly when considering the cooling requirements of the refrigerant cooler (designed as an ambient air heat exchanger) in the refrigeration system or the refrigerant circuit, the control signal for the fan can be influenced by the operating position of the adjustable cooling air inlet. It may be designed so that, for efficiency reasons, when cooling demand is reduced, the control signal initially reduces the fan's airflow. Subsequently, when the cooling demand of the refrigerant cooler is correspondingly low, the operating position of the closure device can be adjusted to allow less ambient air to pass through the closure device and reach the refrigerant cooler.In contrast, if the need for cooling air increases, the closing device, which is designed as a closable cooling air inlet, can first be at least partially opened before the fan is put into operation. Regardless of the chosen system configuration, this method can be used for all refrigerant circuit configurations in which the ambient air-exposed refrigerant cooler is used and is actively perfused with refrigerant. Considering the operating position of the locking mechanism contributes to the efficient operation of the vehicle. This is because when the locking mechanism is in its closed operating position, the air resistance of the moving vehicle is lower than when the locking mechanism is at least partially open. The motor vehicle according to the invention has a refrigerant circuit, wherein a compressor of the refrigerant circuit is configured to convey compressed refrigerant in heating mode to a heat exchanger of the refrigerant circuit. An airflow can be heated by means of the heat exchanger, which can then be introduced into a passenger compartment of the motor vehicle. The refrigerant can be expanded by means of at least one expansion device of the refrigerant circuit, wherein the expanded refrigerant can be supplied to at least one evaporator of the refrigerant circuit. In heating mode, at least a partial flow of the refrigerant compressed by the compressor can be supplied to a refrigerant cooler of the refrigerant circuit, which is separate from the heat exchanger and can be supplied with ambient air.A vehicle control unit is designed to determine, based on measurements acquired by the vehicle's sensors, the excess heat introduced into the refrigerant that needs to be dissipated at the refrigerant cooler. The control unit is further designed to control a fan, which supplies the refrigerant cooler with ambient air, depending on the amount of excess heat to be dissipated.The control device is designed to determine, based on the measured values ​​detectable by the sensors, the difference in the enthalpy of the refrigerant at a refrigerant inlet and outlet of the at least one evaporator, as well as at a refrigerant inlet and outlet of the heat exchanger. The control device is also designed to take into account the respective mass flow rate of the refrigerant that can be conveyed through the at least one evaporator and the heat exchanger in order to determine the excess refrigerant to be discharged. Accordingly, the motor vehicle, which incorporates the refrigerant circuit and the control device, enables the implementation of particularly efficient heating operation of the refrigerant circuit.During the operation of the refrigerant circuit or the compressor, the refrigerant can be conveyed to the heat exchanger directly or indirectly. The advantages and preferred embodiments described for the method according to the invention apply analogously to the motor vehicle according to the invention and vice versa. The invention therefore also includes further developments of the motor vehicle according to the invention, which have features as already described in connection with the further developments of the method according to the invention. For this reason, the corresponding further developments of the motor vehicle according to the invention are not described again here. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus. 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 are exemplary embodiments of the invention. Figure 1 schematically shows a refrigerant circuit of a motor vehicle, wherein, during a reheating operation of the refrigerant circuit, a fan is controlled as required, which is designed to supply a refrigerant cooler of the refrigerant circuit with ambient air; Figure 2 shows a flowchart for determining a control signal for the fan; and Figure 3 shows the motor vehicle with the refrigerant circuit according to Figure 1. The exemplary embodiments described below are preferred embodiments of the invention. In these exemplary embodiments, the described components each represent individual features of the invention, which can be considered independently of one another and each further develops the invention independently. Therefore, the disclosure is intended to include combinations of features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described. In the figures, identical reference symbols denote functionally equivalent elements. Figure 1 schematically shows a refrigerant circuit 10 as it can be used in a motor vehicle 12 (see Figure 3). The following section considers the heating operation of the refrigerant circuit 10, in which a compressor 14 delivers compressed refrigerant to a heat exchanger 16 of the refrigerant circuit 10. In heating mode, the heat exchanger 16 can heat an airflow 18, which is indicated by an arrow in Figure 1 and can be introduced into a passenger compartment 20 of the motor vehicle 12 (see Figure 3). In particular, the heating operation can be designed as a reheat operation, in which the airflow 18 is first cooled and dehumidified by means of an evaporator of the refrigerant circuit 10 before the airflow 18 is fed to the heat exchanger 16. The evaporator of the refrigerant circuit 10, by means of which the cooling and dehumidification of the airflow 18 can be effected, is designed here as an interior evaporator 22 of the refrigerant circuit 10. Accordingly, the interior evaporator 22 is designed to cool the airflow 18, which can be introduced into the interior or passenger compartment 20 of the motor vehicle 12. The interior evaporator 22 and the heat exchanger 16 can be housed in an air conditioning unit (not shown) of the motor vehicle 12, which can be arranged, in particular, within an instrument panel (not shown) of the motor vehicle 12. The refrigerant that can be introduced into the interior evaporator 22 can be expanded during reheating operation by means of an expansion device 24, which is arranged upstream of the interior evaporator 22. The following section considers a reheat operation of the refrigerant circuit 10, in which at least a partial flow of the refrigerant compressed by the compressor 14 is fed to a refrigerant cooler 26 of the refrigerant circuit 10 that is separate from the heat exchanger 16. In this operation, a first shut-off valve 28 of the refrigerant circuit 10 may be closed, so that the refrigerant coming from the heat exchanger 16 cannot directly reach the first expansion device 24. Rather, the refrigerant is supplied to the refrigerant cooler 26 via a line branch 30, wherein a valve 32 is arranged in the line branch 30, which can in particular be designed as a further expansion device of the refrigerant circuit 10. When the valve 32 is open, the refrigerant coming from the heat exchanger 16 thus flows via the line branch 30 into the refrigerant cooler 26. Depending on the refrigerant used, the refrigerant cooler 26 can be operated as a condenser or as a gas cooler. From the refrigerant cooler 26, the refrigerant, during heating operation, flows to a further valve 34, which can be configured as a further expansion device of the refrigerant circuit 10. Specifically, when the first valve 32 and the further valve 34 are fully open, the refrigerant can flow via the further valve 34 to the first expansion device 24, where it is expanded and then supplied to the interior evaporator 22. From the interior evaporator 22, the expanded refrigerant flows via a return line 36 of the refrigerant circuit 10 to a suction side 38 of the compressor 14. In this heating or reheating operation, all the refrigerant conveyed by the compressor 14 first flows through the heat exchanger 16 and then through the refrigerant cooler 26, before the refrigerant is expanded at the first expansion device 24 and fed to at least one evaporator, for example in the form of the interior evaporator 22. The refrigerant cooler 26 is located in the area of ​​the front 40 of the motor vehicle 12 (see Fig. 3) and can be supplied with ambient air 42, which is represented in Fig. 1 by a further arrow or flow arrow. A fan 44 can be operated to convey the ambient air 42 through the refrigerant cooler 26 (see Fig. 1). In this case, the fan 44 is controlled as needed by a control unit 46 of the motor vehicle 12. If, on the other hand, the fan 44 were to continuously deliver a constant mass flow of ambient air 42 during reheating operation, it could happen that more heat is dissipated from the refrigerant at the refrigerant cooler 26 than necessary. Furthermore, the mass flow of ambient air 42 might no longer have a cooling effect on the refrigerant flowing through the refrigerant cooler 26, thus resulting in an oversupply. Both scenarios would lead to inefficient operation of the fan 44. On the other hand, such operation of the fan 44 could result in insufficient heat being available at the heat exchanger 16 to heat the airflow 18, which is to be introduced into the passenger compartment 20 of the motor vehicle 12. In the present case, these disadvantages are avoided due to the demand-based control of the fan 44, which is ensured by the control device 46. The demand-based control of the fan 44 is also carried out in the present case when the refrigerant circuit 10 is used in a further heating operation, in particular in a further reheating operation, which will be explained with reference to Fig. 1. In this further heating operation, the refrigerant compressed by the compressor 14 can be divided between the heat exchanger 16 on the one hand and the refrigerant cooler 26 on the other by controlling a second shut-off valve 48 and a third shut-off valve 50. When the second shut-off valve 48 is at least partially open, a partial flow of the refrigerant supplied by the compressor 14 flows via a heating line 52 of the refrigerant circuit 10 to the heat exchanger 16. And when the third shut-off valve 50 is at least partially open, a partial flow of the refrigerant compressed by the compressor 14 flows via a connecting line 54 to the refrigerant cooler 26. In this further reheating operation, the first shut-off valve 28 is open, and the valve 32 located in the line branch 30 is closed. The first shut-off valve 28 can also be designed as an expansion valve. At a junction 56 of the refrigerant circuit 10, which is located downstream of the first shut-off valve 28 and downstream of the further valve 34, the two partial flows of the refrigerant can be recombined during the subsequent heating operation and then fed to the interior evaporator 22 via the first expansion device 24. In this subsequent reheat operation, it is also advantageous that the control device 46 controls the fan 44 as required. If only the subsequent reheat operation is to be implemented for the operation of the refrigerant circuit 10, the branch 30 with the valve 32 can be omitted from the refrigerant circuit 10. In the simplified design of the refrigerant circuit 10, where the line branch 30 and the valve 32 are omitted, the respective expansion function can be relocated to the additional valve 34 and the first shut-off valve 28, which can then be used or designed as an expansion element. As shown in Fig. 1, the additional valve 34 is located in a branch of the refrigerant circuit 10 coming from the refrigerant cooler 26 or gas cooler, and the first shut-off valve 28, designed as an expansion element, is located in a branch of the refrigerant circuit 10 coming from the heat exchanger 16. Low pressure is present upstream of the valves shown in Fig. 1, namely the first expansion device 24 and a second expansion device 74, when the further valve 34 and the first shut-off valve 28 are used as expansion elements in the reheating operation described above. The two valves arranged downstream of these expansion elements, which are referred to here as the first expansion device 24 and the second expansion device 74, can then be used to distribute the refrigerant between the interior evaporator 22 and a chiller 70 of the refrigerant circuit 10 as needed. For example, the valve upstream of the interior evaporator 22 can open fully when there is no cooling demand at the chiller 70, whereas the valve upstream of the chiller 70 can be kept completely closed. The control unit 46 determines, based on measured values ​​acquired by sensors, an excess 85 (see Fig. 2) of heat introduced into the refrigerant to be dissipated at the refrigerant cooler 26. Furthermore, the control unit 46 controls the fan 44 depending on the excess 85 to be dissipated. This ensures efficient operation, particularly of the fan 44. Specifically, no (not shown) electric auxiliary heater is required to introduce heat into the airflow 18. This is because the demand-based control of the fan 44 prevents more heat than the calculated excess 85 from being dissipated at the refrigerant cooler 26. Furthermore, it advantageously prevents the fan 44 from being controlled beyond the cooling potential of the refrigerant, thereby avoiding the generation and provision of excess cooling air. To determine the excess heat 85 to be dissipated at the refrigerant cooler 26, the control unit 46 can evaluate measured values ​​from sensors 58, which are shown schematically and arranged by way of example in Fig. 1. By cleverly positioning the sensors 58 at sections of the refrigerant circuit 10 other than those shown by way of example, the number of sensors 58 used can be reduced to a minimum. In this way, relationships such as the constancy of the enthalpy during an expansion process and / or the incorporation of characteristic curves or maps indicating a pressure drop can be taken into account. Using these sensors 58, the pressure and temperature of the refrigerant at a refrigerant inlet and at a refrigerant outlet of the respective heat exchangers can preferably be measured. For example, the difference in enthalpy between a refrigerant inlet 60 of the heating heat exchanger 16 and a refrigerant outlet 62 of the heating heat exchanger 16 can be determined using the sensors 58 arranged in the heating line 52. Similarly, the difference in enthalpy between a refrigerant inlet 64 of the interior evaporator 22 and a refrigerant outlet 66 of the interior evaporator 22 can be determined using the sensors 58 arranged in the return line 36. From the respective enthalpy difference and the mass flow rate of the refrigerant, the cooling capacity of the interior evaporator 22 and the heating capacity 68 (see Fig. 2) of the heating heat exchanger 16 can be determined. Alternatively, instead of determining the enthalpy difference on the refrigerant side, these capacities can also be determined or estimated via an air-side calculation. According to Fig. 1, the refrigerant circuit 10 can include a further evaporator, the chiller 70, which can be permeated by expanded refrigerant on one side and by a coolant on the other. The integration of the chiller 70 into a corresponding coolant circuit 72 is shown schematically in Fig. 1. To expand the refrigerant supplied to the chiller 70, the refrigerant circuit 10, according to Fig. 1, has a second expansion device 74. If, during the respective reheating operation, the additional valve 34 or the first shut-off valve 28 is open, refrigerant coming from the refrigerant cooler 26 alone, or refrigerant coming from the refrigerant cooler 26 and the heat exchanger 16, can be expanded by means of the second expansion device 74 in order to introduce a partial flow of refrigerant into the chiller 70. A corresponding refrigerant line 76 of the refrigerant circuit 10, into which the chiller 70 is integrated, connects to the return line 36 at a junction 78. When the chiller 70 is in operation, the enthalpy difference between a refrigerant inlet 80 and a refrigerant outlet 82 of the chiller 70 can be measured using additional sensors 58 arranged in the refrigerant line 76. When the chiller 70 is in operation in addition to the interior evaporator 22, the cooling capacity 84 (see Fig. 2) of the evaporators in the form of the interior evaporator 22 and the chiller 70 can be determined to calculate the excess heat 85 (see Fig. 2) to be discharged at the refrigerant cooler 26. To determine the cooling capacity 84, the mass flow rate of the refrigerant delivered by the compressor 14 can be multiplied by the enthalpy differences by the control device 46. To determine the mass flow rate of the compressor 14, the control device 46 can take into account the rotational speed, stroke, and efficiency of the compressor 14, and thus the volumetric flow rate of the refrigerant, as well as the density of the refrigerant at the suction side 38 of the compressor 14. A further sensor 87 of the refrigerant circuit 10, which can be used to determine the density of the refrigerant at the suction side 38 of the compressor 14, is shown schematically in Fig. 1. The density can be derived, in particular, from the temperature and pressure of the refrigerant at the suction side 38 of the compressor 14, these measured variables preferably being detectable by means of the further sensor 87. The cooling capacity 84 of the at least one evaporator and the heating capacity 68 (see Fig. 2) of the heat exchanger 16 can be calculated or balanced additionally or alternatively on the air side or coolant side, respectively. For example, the volume flow of air delivered by a (not shown) fan, which is schematically illustrated by the airflow 18 in Fig. 1, can be taken into account by the control device 46, as can the temperature and humidity of the airflow 18. Figure 1 schematically shows sensors in the form of temperature sensors 86, which can detect the difference in air temperature between an air inlet side 88 of the interior evaporator 22 and an air outlet side 90 of the interior evaporator 22. Furthermore, the temperature sensors 86 shown schematically in Figure 1 can determine the difference in air temperature between an air inlet side 92 of the heat exchanger 16 and an air outlet side 94 of the heat exchanger 16. This allows the control unit 46 to deduce the respective amount of heat that is introduced into the refrigerant at the interior evaporator 22 and that is transferred to the airflow 18 at the heat exchanger 16. In a manner analogous to that described for the air-side calculation, the amount of heat introduced into the refrigerant at the chiller 70 can be determined by using additional sensors 96 to measure the difference in coolant temperature between a coolant inlet 98 and a coolant outlet 100 of the chiller 70. From the coolant flow rate and the coolant temperature difference, the control unit 46 can easily determine the amount of heat introduced into the refrigerant at the chiller 70. In addition to or as an alternative to the refrigerant-side calculation of the chiller 70, the cooling capacity of the chiller 70 can therefore also be determined on the coolant side by taking into account a temperature difference of the coolant and the volume flow rate of the coolant through the chiller 70.The volume flow rate can be derived in particular from a pump characteristic curve or from a pump characteristic map of a pump or pumping device (not shown) that conveys the coolant. For the most comprehensive possible accounting of the power outputs or heat quantities to determine the excess 85 (see Fig. 2), the control device 46 preferably also takes into account a power output 102 (see Fig. 2) of the compressor 14, which is used by the compressor 14 to pump and compress the refrigerant. According to Fig. 2, the cooling capacity 84 and the power output 102 of the compressor 14 are added together, and the heating capacity 68 is subtracted from this total power output to determine the excess 85. The above-described possibilities for determining the excess 85 can be carried out as an alternative to determining a heat excess at the refrigerant cooler 26 from the enthalpy differences at the refrigerant cooler 26 and a mass flow of the refrigerant through the refrigerant cooler 26. The excess 85 (see Fig. 2) corresponds to the additional power in the refrigerant circuit 10 that is to be transferred to the external heat exchanger in the form of the refrigerant cooler 26 and is bound in the refrigerant. Based on a characteristic curve 104 (see Fig. 2), which is stored in the control unit 46, or on the basis of a corresponding characteristic map, a mass flow rate 106 of air can be determined with which the refrigerant cooler 26 can be supplied in order to dissipate the excess 85. The corresponding air flow is illustrated in Fig. 1 by the ambient air 42, shown as an arrow. When the motor vehicle 12 (see Fig. 3), which includes the refrigerant circuit 10, is in motion, airflow can reach the refrigerant cooler 26 via a radiator grille located in the area of ​​the vehicle's front 40. Therefore, it is advantageous to also consider the vehicle's speed 110 when determining a control signal 108 (see Fig. 2), with which the control unit 46 controls the fan 44 (see Fig. 2). This is because the higher the vehicle's speed 110, the more the airflow can supply the refrigerant cooler 26 with ambient air 42. Consequently, the fan 44 needs to move less ambient air 42 (or even no ambient air 42 at all) through the refrigerant cooler 26 than would be the case if the same heat dissipation were achieved with the vehicle 12 stationary. Preferably, the control device 46 also takes into account an operating position of a closing device 112 (see Fig. 1), which can be designed, for example, as a cooling louver upstream of the refrigerant cooler 26 or a similar device for a controllable cooling air inlet. This operating position can also be taken into account by the control device 46 in a characteristic curve field 114 (see Fig. 2) in order to provide the control signal 108. Figure 1 shows, by way of example, further components of the refrigerant circuit 10, the function of which need not be explained in detail here. This applies to a preferably provided internal heat exchanger 116, a refrigerant storage tank 118, check valves 120 and further shut-off valves 122. In the area of ​​the vehicle front 40 (see Fig. 3), the refrigerant radiator 26 can be part of a radiator assembly, which also includes a coolant radiator (not shown). In this configuration, the fan 44 may be operated to cool the coolant via the coolant radiator (not shown). The cooled coolant can, for example, be supplied to an electric drive unit of the vehicle 12 and / or an internal combustion engine of the vehicle 12. It may be provided that priority is given to satisfying the cooling requirements of such components of the motor vehicle 12. In this case, the fan 44 can convey a larger mass flow of ambient air 42 through the refrigerant cooler 26 than would be necessary to remove the excess 85. However, this ensures that the cooling requirements of these components of the motor vehicle 12 are met. By calculating the thermal outputs of the evaporators, namely the interior evaporator 22 and, if applicable, the chiller 70, the heat exchanger 16, and the compressor 14, the control unit 46 can estimate the output or heat quantity that should be dissipated to the environment by the refrigerant cooler 26. The fan 44 can then be controlled based on this excess output 85 or the output required. Overall, the examples show how a fan operating strategy in reheat mode can be provided via power dissipation at the refrigerant cooler 26.

Claims

Method for operating a refrigerant circuit (10) of a motor vehicle (12), wherein, in a heating mode of the refrigerant circuit (10), a compressor (14) of the refrigerant circuit (10) conveys compressed refrigerant to a heat exchanger (16) of the refrigerant circuit (10), wherein an airflow (18) can be heated by means of the heat exchanger (16), which can be introduced into a passenger compartment (20) of the motor vehicle (12), wherein the refrigerant is expanded by means of at least one expansion device (24, 74) of the refrigerant circuit (10), and wherein the expanded refrigerant is supplied to at least one evaporator (22, 70) of the refrigerant circuit (10), wherein, in the heating mode, at least a partial flow of the refrigerant compressed by the compressor (14) is supplied to a refrigerant cooler (26) of the refrigerant circuit (10) that is different from the heat exchanger (16). is supplied, whereby the refrigerant cooler (26) is supplied with ambient air (42),wherein a control device (46) of the motor vehicle (12) determines, based on measured values ​​acquired by means of sensors (58, 86, 87, 96), an excess (85) of heat introduced into the refrigerant to be discharged at the refrigerant cooler (26), and wherein the control device (46) controls a fan (44), which is designed to supply the refrigerant cooler (26) with ambient air (42), depending on the excess (85) to be discharged, characterized in that the control device (46), based on the measured values ​​acquired by means of the sensors (58), determines a difference in the enthalpy of the refrigerant at a refrigerant inlet (64, 80) and at a refrigerant outlet (66, 82) of the at least one evaporator (22, 70) as well as at a refrigerant inlet (60) and at a refrigerant outlet (62) of the heat exchanger (16) determinedwherein the control device (46) for determining the excess to be discharged (85) takes into account a respective mass flow of the refrigerant which is conveyed through the at least one evaporator (22, 70) and through the heat exchanger (16). Method according to claim 1, characterized in that the expanded refrigerant is supplied to at least one evaporator designed as an interior evaporator (22) of the refrigerant circuit (10), wherein the airflow (18) is cooled by means of the interior evaporator (22) before the airflow (18) is supplied to the heat exchanger (16). Method according to one of the preceding claims, characterized in that the control device (46) for determining the heat introduced into the refrigerant takes into account a power, in particular electrical, of the compressor (14) which is absorbed by the compressor (14) for conveying and compressing the refrigerant. Method according to one of the preceding claims, characterized in that the control device (46) determines the mass flow rate of the refrigerant delivered by the compressor (14) by taking into account a rotational speed of the compressor (14) and a density of the refrigerant present at a suction side (38) of the compressor (14), wherein the density is detected by means of a sensor (87) of the refrigerant circuit (10). Method according to one of the preceding claims, characterized in that the control device (46) determines a difference in air temperature between an air inlet side (88, 92) and an air outlet side (90, 94) of the at least one evaporator (22) and the heat exchanger (16) based on the measured values ​​which are acquired by means of the sensors (86), wherein the control device (46) takes the difference in air temperature into account for determining the excess (85) to be discharged. Method according to one of the preceding claims, characterized in that a partial flow of the expanded refrigerant is supplied to at least one evaporator and a chiller (70) of the refrigerant circuit (10), wherein the chiller (70) is supplied with a coolant, and wherein heat of the coolant is transferred to the refrigerant in the chiller (70). Method according to claim 6, characterized in that the control device (46) determines a difference in coolant temperature between a coolant inlet side (98) and a coolant outlet side (100) of the chiller based on the measured values ​​which are acquired by means of the sensors (96), wherein the control device (46) takes the difference in coolant temperature into account for determining the excess (85) to be discharged. Method according to one of the preceding claims, characterized in that the control device (46) controls the fan (44) depending on a driving speed (110) of the motor vehicle (12) and / or depending on an operating position of a closing device (112), by means of which the supply of ambient air (42) to the refrigerant cooler (26) by means of driving air can be influenced. Motor vehicle (12) with a refrigerant circuit (10), wherein a compressor (14) of the refrigerant circuit (10) is configured to convey compressed refrigerant in a heating operation of the refrigerant circuit (10) to a heat exchanger (16) of the refrigerant circuit (10), wherein an airflow (18) can be heated by means of the heat exchanger (16), which can be introduced into a passenger compartment (20) of the motor vehicle (12), wherein the refrigerant can be expanded by means of at least one expansion device (24, 74) of the refrigerant circuit (10), and wherein the expanded refrigerant can be supplied to at least one evaporator (22, 70) of the refrigerant circuit (10), wherein in the heating operation at least a partial flow of the refrigerant compressed by the compressor (14) to a refrigerant cooler (26) of the refrigerant circuit (10) that is different from the heat exchanger (16). can be supplied, wherein the refrigerant cooler (26) can be supplied with ambient air (42),wherein a control device (46) of the motor vehicle (12) is configured to determine, based on measured values ​​detectable by means of sensors (58, 86, 87, 96) of the motor vehicle (12), an excess (85) of heat introduced into the refrigerant to be discharged at the refrigerant cooler (26), and wherein the control device (46) is configured to control a fan (44), by means of which the refrigerant cooler (26) can be supplied with ambient air (42), depending on the excess (85) to be discharged, characterized in that the control device (46) is configured, based on the measured values ​​detectable by means of the sensors (58), to determine a difference in the enthalpy of the refrigerant at a refrigerant inlet (64, 80) and at a refrigerant outlet (66, 82) of the at least one evaporator (22, 70) as well as at a refrigerant inlet (60) and at a refrigerant outlet (62) of the heat exchanger (16),wherein the control device (46) is designed to take into account, for determining the excess to be discharged (85), a respective mass flow of the refrigerant which can be conveyed through the at least one evaporator (22, 70) and through the heat exchanger (16).

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