Method for controlling a multi-evaporator system installed in a motor vehicle and motor vehicle with multi-evaporator system

Abstract

In order to provide a method for controlling a multi-evaporator system arranged in a motor vehicle, by means of which cooling capacity control for different zones in the motor vehicle is enabled, a method (100) for controlling a multi-evaporator system (10) arranged in a motor vehicle (200) is proposed, wherein the multi-evaporator system (10) comprises a refrigerant circuit (11) and at least two evaporators (12, 13, 14) arranged in the refrigerant circuit (11), wherein the refrigerant circuit (11) comprises a refrigerant suitable for transcritical operation, and wherein transcritical operation is carried out, and furthermore, it is provided that high-pressure control is carried out during transcritical operation.

Description

[0001] The present invention relates to a method for controlling a multi-evaporator system arranged in a motor vehicle, wherein the multi-evaporator system comprises a refrigerant circuit and at least two evaporators arranged in the refrigerant circuit.

[0002] Furthermore, the present invention relates to a motor vehicle with a multi-evaporator system.

[0003] Multi-evaporator systems are occasionally used for air conditioning the cabins of motor vehicles, particularly electrified vehicles. Such multi-evaporator systems may include, in addition to an evaporator of an air conditioning unit for conditioning the air mass flow for a front section of the vehicle cabin, an evaporator configured as a chiller for conditioning the coolant circuit of the battery or traction components of the vehicle, as well as another evaporator for conditioning the air mass flow for a rear section of the vehicle cabin.

[0004] The evaporator for conditioning the air mass flow to the rear of the vehicle cabin is usually part of a second air conditioning unit, for example, in the rear of the vehicle. All three evaporators are combined in a refrigerant circuit.

[0005] In multi-evaporator systems, superheat control is commonly used to ensure sufficient refrigerant mass flow in the individual evaporators. This means that the refrigerant's superheat is controlled in the evaporators. In common multi-evaporator systems, which use the refrigerant R-1234yf, for example, this superheat control is usually achieved using thermal expansion valves.

[0006] US 2005 / 0 061 497 A1 discloses a temperature control device comprising a heat pump with a main refrigerant circuit that absorbs heat from a cold source and transfers it to a hot source. The cold source comprises an air-to-refrigerant heat exchanger, referred to as a first evaporator. The cold source further comprises another refrigerant-to-coolant heat exchanger, which, as a second evaporator, thermally couples the main refrigerant circuit to a secondary coolant circuit. The secondary coolant circuit is coupled to at least a first secondary heat exchanger, which exchanges heat with a first heat source of the vehicle. The first and second evaporators are connected in parallel.

[0007] DE 10 2022 102 986 A1 discloses a method for operating a refrigerant circuit for a motor vehicle, in which a control device selects function modules from a function library containing a plurality of function modules, which are assigned to respective components of the refrigerant circuit.

[0008] Furthermore, DE 10 2018 201 165 B3 discloses a method for operating a refrigerant circuit of a vehicle in AC operation with a chiller branch which has a pressure-temperature sensor connected downstream of a chiller, at least one interior evaporator branch which is connected in parallel to the chiller branch, an accumulator, a refrigerant compressor, a condenser or gas cooler, wherein the degree of superheating of the refrigerant at the refrigerant outlet of the chiller is determined by means of a control device from the measured values ​​of the pressure-temperature sensor.

[0009] Furthermore, DE 10 2018 112 333 A1 discloses a refrigerant circuit for an air conditioning system of a motor vehicle. The refrigerant circuit comprises at least one compressor, a first heat exchanger operable as a condenser / gas cooler for the refrigerant, an expansion-compression device with an expansion component and a compression component, a second heat exchanger operable as an evaporator for the refrigerant, and a first flow path and a second flow path.

[0010] DE 10 2018 209 769 A1 describes a method for operating a refrigerant circuit of a refrigeration system of a vehicle with- a chiller branch which has a chiller, a first expansion element and a first pressure-temperature sensor,- at least one interior evaporator branch which has an interior evaporator and a second expansion element and is connected in parallel to the chiller branch.

[0011] From DE 101 57 461 A1 a method is known for operating a refrigerant circuit, in particular an air conditioning system of a motor vehicle, with a refrigerant compressor for compressing essentially gaseous refrigerant, a cooler downstream of the refrigerant compressor for dissipating heat from the refrigerant, in particular an ambient air heat exchanger, a throttling means for expanding the refrigerant, and an evaporator for transferring heat to the refrigerant, wherein the pressure in the refrigerant circuit is measured on the one hand on the high-pressure side and on the other hand on the low-pressure side via a pressure measuring device.

[0012] DE 100 13 191 C1 discloses an air conditioning system, in particular for motor vehicles, with a refrigerant circuit in which refrigerant is brought into a wet vapor state, with at least one compressor and with at least one expansion machine in the form of a gear machine with helically toothed gears

[0013] The present invention is based on the object of providing a method for controlling a multi-evaporator system arranged in a motor vehicle, by means of which a cooling capacity control for different zones in the motor vehicle is made possible.

[0014] To achieve the object underlying the invention, a method for controlling a multi-evaporator system arranged in a motor vehicle is proposed, wherein the multi-evaporator system comprises a refrigerant circuit and at least two evaporators arranged in the refrigerant circuit, wherein the refrigerant circuit comprises a refrigerant which is suitable for a transcritical process control, and wherein a transcritical process control takes place, wherein it is further provided that a high-pressure control takes place during the transcritical process control.

[0015] The motor vehicle may preferably be an electrified motor vehicle, in particular an electric vehicle or a hybrid electric vehicle.

[0016] Transcritical process control is, in particular, a transcritical process control for the refrigerant. A high-pressure regulator can be provided for high-pressure control in transcritical process control.

[0017] Due to the high pressure control provided within the framework of a transcritical process control of the refrigerant in the refrigerant circuit, a cooling capacity control of the individual evaporators can be achieved.

[0018] The special feature of the method according to the invention is that high-pressure control is implemented. In contrast, in known multi-evaporator systems, which operate with the refrigerant R-1234yf, for example, superheat control is implemented. In particular, in known multi-evaporator systems, superheat is controlled at each evaporator.

[0019] It is preferably provided that for the high pressure control taking place during the transcritical process control, the high pressure to be regulated is determined by means of an empirical equation, wherein the equation is further preferably determined from an inlet temperature of a compressor of the refrigerant circuit, at least one evaporation temperature and further preferably a gas cooler outlet temperature.

[0020] The at least two evaporators can be designed as air-side heat exchangers.

[0021] Preferably, the multi-evaporator system comprises at least three evaporators.

[0022] It is further preferably provided that a first evaporator is an evaporator for conditioning an air mass flow in a front part of a vehicle cabin of the motor vehicle, and / or that a second evaporator is an evaporator for conditioning an air mass flow in a rear part of a vehicle cabin of the motor vehicle, and / or that a third evaporator is an evaporator for conditioning a battery and / or traction components of the motor vehicle.

[0023] Further preferably, the first evaporator is an evaporator of a first air conditioning unit for conditioning the air mass flow in the front part of the vehicle cabin, and / or the second evaporator is an evaporator of a second air conditioning unit for conditioning the air mass flow in the rear part of the vehicle cabin.

[0024] Furthermore, it can preferably be provided that the first evaporator is an air-refrigerant heat exchanger, and / or that the second evaporator is an air-refrigerant heat exchanger, and / or that the third evaporator is a coolant-refrigerant heat exchanger, in particular a chiller.

[0025] Another advantage is that the refrigerant is R-744.

[0026] The refrigerant R-744 is carbon dioxide (CO2). Multi-evaporator systems using CO2 (R-744) as a refrigerant must operate at extremely high pressures. The critical temperature of CO2 is very low at 31°C at 74 bar. Depending on the evaporator temperature on the high-pressure side, this requires a transcritical process with pressures well above 100 bar.

[0027] The proposed high-pressure control in a transcritical process is particularly suitable when using CO2 (R-744) as the refrigerant. However, the process can also be carried out with any other refrigerant that can be transcritically processed.

[0028] Furthermore, it can be provided that a change is made between the transcritical process control and a subcritical process control, whereby subcooling control is carried out in the subcritical process control.

[0029] The process thus also allows for subcritical process control of the refrigerant in the refrigerant circuit. If subcritical process control is present, subcooling control is implemented. A suitably designed subcooling controller can be provided for subcooling control.

[0030] Subcooling is determined by the difference between the saturation temperature of the refrigerant at a pressure p and the refrigerant temperature at the pressure p. The refrigerant must be in liquid form on the sink side.

[0031] Furthermore, it can preferably be provided that a dynamic change takes place between the subcritical process control and the transcritical process control.

[0032] The change between subcritical process control and transcritical process control can take place in both directions.

[0033] The dynamic transition between subcritical and transcritical process control can occur based on the prevailing thermodynamic ambient conditions. Furthermore, it is also possible for the dynamic transition between subcritical and transcritical process control to occur through active control.

[0034] It is preferably provided that in a transition region between the subcritical process control and the transcritical process control, the high pressure control takes place according to a transition function, wherein the transition function describes a desired high pressure, wherein the desired high pressure is preferably determined by means of a linear interpolation between a desired pressure for the subcritical process control and a desired pressure for the transcritical process control.

[0035] The use of a transition function for high pressure control ensures that sufficient cooling capacity is continuously provided when switching between subcritical process control and transcritical process control.

[0036] It is preferably provided that, if superheating of the refrigerant is detected for at least one of the evaporators, superheating is controlled to a superheat setpoint.

[0037] In particular, for the evaporator for which the superheat of the refrigerant is determined, the refrigerant is superheated to the superheat setpoint.

[0038] To determine whether the refrigerant is overheating for at least one of the evaporators, temperature sensors and / or pressure sensors are preferably provided on the evaporators, by means of which the refrigerant temperature and / or the pressure is measured, particularly preferably on the outlet side of the respective evaporator.

[0039] In particular, a refrigerant temperature is determined for at least one, preferably for several, and particularly preferably for all, evaporators. The refrigerant temperature is determined, in particular, using temperature sensors provided for this purpose.

[0040] According to the invention, it is provided that each of the evaporators is assigned an expansion valve, wherein preferably each of the expansion valves is arranged in an inlet line of the respective evaporator.

[0041] In particular, it is preferably provided that each of the expansion valves is arranged exclusively in the inlet line of the respective associated evaporator. The expansion valves are thus not arranged in a common line of the evaporators in the coolant circuit. Controlling one of the expansion valves exclusively results in high-pressure control and / or subcooling control and / or superheat control for the respective associated evaporator.

[0042] It is preferably provided that the high pressure control and / or the subcooling control and / or the superheating control is carried out by controlling at least one, preferably several, particularly preferably all, of the expansion valves.

[0043] According to the invention, the expansion valves are controlled taking into account the expected cooling capacity of the evaporators, wherein cross sections of the expansion valves are preferably pre-controlled in relation to the desired cooling capacities of the evaporators.

[0044] These target cooling capacities can be determined for the individual zones, i.e. in particular for the front part of the vehicle cabin, and / or for the rear part of the vehicle cabin and / or for the battery or for the traction components of the vehicle.

[0045] For example, it can be provided that the target cooling capacity is determined from the expected air mass flow and the temperature difference between the target supply air temperature and the air temperature flowing into the respective evaporator.

[0046] For the third evaporator, which is preferably designed as a chiller and is intended to cool the battery and / or the traction components, the target cooling capacity can be calculated from the target and actual coolant temperature and a volume flow, which can be determined, for example, via a pump control.

[0047] Furthermore, temperature sensors can be provided in the vehicle cabin of the motor vehicle. The temperature sensors can be used to determine the actual temperature in the vehicle cabin, particularly in the front part of the vehicle cabin and / or in the rear part of the vehicle cabin. Furthermore, temperature sensors are preferably arranged at the air-side outlet of the evaporators. In the event that one of the evaporators is out of operation, the temperature determined at the air-side outlet of this evaporator can be used as the initial actual temperature of the zone, for example, the front part of the vehicle cabin or the rear part of the vehicle cabin, until the evaporator starts operating.To determine the target cooling capacity of the evaporator, in particular the target cooling capacity of the first evaporator, which is preferably designed as an evaporator of a first air conditioning unit for conditioning the air mass flow in the front part of the vehicle cabin, a fan speed and an outside air temperature in partial recirculation mode can also be included.

[0048] According to the invention, if superheating of the refrigerant is determined for all of the evaporators, a mass flow proportion of the refrigerant directed to the first evaporator is increased and / or a cooling capacity of the first evaporator is increased.

[0049] By prioritizing the cooling capacity of the first evaporator, sufficient cooling capacity is available for this evaporator. This is particularly advantageous if the first evaporator is part of an air conditioning unit used to condition the air mass flow for the front part of the vehicle cabin. An overheated evaporator represents a suboptimal operating point. If refrigerant overheating is detected for all evaporators, the cooling capacity may not be sufficient for all sinks. Because the first evaporator, which is preferably intended for the front area of ​​the vehicle cabin, is prioritized, more refrigerant is routed through the first evaporator.

[0050] Superheat is preferably measured at a coupling point of all lines, especially all inlet lines, of the evaporator. For example, superheat can be measured upstream of an accumulator, also known as a liquid separator, or upstream of the compressor.

[0051] It can be provided that a reduction in the cross-section of the expansion valve assigned to the second evaporator takes place.

[0052] If superheating is detected at a suitable point, a refrigerant mass flow can be shifted to the first evaporator by moving the expansion valves, or a higher mass flow proportion of the refrigerant can be directed towards the first evaporator.

[0053] It can be further advantageously provided that the high pressure control is carried out by means of a high pressure controller, in particular a first PI controller, and / or that the superheat control is carried out by means of a superheat controller, in particular a second PI controller, wherein a controller tracking is carried out for the respective inactive high pressure controller or superheat controller.

[0054] If the two controllers, in particular the high pressure controller and the superheat controller, are active in parallel, the passive controller can be adjusted to follow the active PI controller using the integral component of the passive PI controller.

[0055] For this purpose, the integral component for the passive controller is determined from the active controller for a certain time in order to avoid a jump in the controller output at the moment the controller switches.

[0056] A further solution to the problem underlying the invention consists in providing a motor vehicle comprising a multi-evaporator system, wherein the multi-evaporator system comprises a refrigerant circuit and at least two evaporators arranged in the refrigerant circuit, wherein the refrigerant circuit comprises a refrigerant which is suitable for a transcritical process control, further comprising a high-pressure regulator, wherein the high-pressure regulator is designed to carry out a high-pressure control according to a previously described method in a transcritical process control.

[0057] All advantages, configurations and features described with regard to the method explained above can also be transferred in a corresponding manner to the motor vehicle or its multi-evaporator system.

[0058] Preferably, the multi-evaporator system comprises at least three evaporators.

[0059] Particularly preferably, a first evaporator is an evaporator for conditioning an air mass flow in a front part of a vehicle cabin of the motor vehicle, and / or a second evaporator is an evaporator for conditioning an air mass flow in a rear part of a vehicle cabin of the motor vehicle, and / or a third evaporator is an evaporator for conditioning a battery and / or traction components of the motor vehicle.

[0060] Furthermore, it can be provided that the first evaporator is an air-refrigerant heat exchanger, and / or that the second evaporator is an air-refrigerant heat exchanger, and / or that the third evaporator is a coolant-refrigerant heat exchanger, in particular a chiller.

[0061] The invention is explained in more detail below with reference to the accompanying figures. They show: Fig. 1 a schematic representation of a motor vehicle comprising a multi-evaporator system, and Fig. 2 a flow chart for a method for controlling a multi-evaporator system arranged in a motor vehicle.

[0062] A method 100 for controlling a multi-evaporator system 10 arranged in a motor vehicle 200 is described with reference to Fig. 1 and Fig. 2 explained. Fig. 1 shows a schematic representation of a motor vehicle 200 with a multi-evaporator system 10 arranged in the motor vehicle 200. The multi-evaporator system 10 comprises a refrigerant circuit 11 with at least three evaporators 12, 13, 14 arranged in the refrigerant circuit 11. A first evaporator 12 is designed as an air-refrigerant heat exchanger 12a and is part of an air conditioning unit (not shown in detail) for conditioning an air mass flow in a front part of a vehicle cabin 15 of the motor vehicle 200. A second evaporator 13 is designed as an air-refrigerant heat exchanger 13a and is part of an air conditioning unit (not shown in detail) for conditioning an air mass flow in a rear part of the vehicle cabin 15. A third evaporator 14 is designed as a chiller 14a and serves to condition a battery 16 of the motor vehicle 200.The refrigerant circuit 11 further comprises a compressor 17, a condenser 18, and an accumulator 19. Each of the evaporators 12, 13, 14 is assigned an inlet branch 20, 21, 22. In each of the inlet branches 20, 21, 22, an expansion valve 23, 24, 25 assigned to the respective evaporator 12, 13, 14 and a pressure sensor 26, 27, 28 are provided. Temperature sensors 29, 30, 31 are arranged downstream of the evaporators 12, 13, 14. A further temperature sensor 32 is arranged at a common coupling point upstream of the compressor 17. In addition, temperature sensors (not shown) are provided in the motor vehicle 200, which are arranged, for example, at the air-side outlet of the evaporators 12, 13 or on the battery 16. Furthermore, the multi-evaporator system 10 comprises at least one high-pressure regulator 33 and at least one superheat regulator 34, which control the expansion valves 23, 24, 25 via control lines 35.The refrigerant circuit 11 of the multi-evaporator system 10 contains R-744 as the refrigerant. High-pressure control is achieved by means of the high-pressure regulator 33 in a transcritical process. For this purpose, the high-pressure regulator 33 controls the cross-sections of the individual expansion valves 23, 24, and 25 to maintain an optimal high pressure.

[0063] If overheating of the refrigerant is detected in one of the evaporators 12, 13, 14 by the temperature sensor 29, 30, 31 assigned to the respective evaporator 12, 13, 14, the superheat controller 34 sets the temperature of the refrigerant in this evaporator 12, 13, 14 to a predetermined superheat setpoint. If all three evaporators 12, 13, 14 are in a superheated state, a higher mass flow proportion of the refrigerant is directed toward the first evaporator 12 by reducing the cross-section of the expansion valve 24 of the second evaporator 13. This ensures sufficient cooling capacity in the first evaporator 12, which serves to condition the air mass flow in the front part of the vehicle cabin 15.

[0064] Fig. 2 shows a flow chart for a method 100 for controlling a multi-evaporator system 10 arranged in a motor vehicle 200. The multi-evaporator system 10 can in particular be the multi-evaporator system 10 of the motor vehicle 200 according to Fig. 1. In a first process step S1, the pressures in the refrigerant circuit 11, and in particular in the evaporators 12, 13, 14, are determined using pressure sensors 26, 27, 28. Subsequently, in a second process step S2, high-pressure control takes place within the framework of a transcritical process control. List of reference symbols 100 procedures 200 motor vehicles 10 multi-evaporator system 11 Refrigerant circuit 12 First evaporator 12a Air-refrigerant heat exchanger 13 Second evaporator 13a Air-refrigerant heat exchanger 14 Third evaporator 14a Chiller 15 vehicle cabin 16 Battery 17 Compressor 18 condensers 19 Accumulator 20 inlet line 21 Inlet line 22 Inlet line 23 Expansion valve 24 Expansion valve 25 Expansion valve 26 Pressure sensor 27 Pressure sensor 28 Pressure sensor 29 Temperature sensor 30 Temperature sensor 31 Temperature sensor 32 Temperature sensor 33 high pressure regulators 34 superheat controller 35 Control line S1 Process step S2 process step

Claims

[1] Method (100) for controlling a multi-evaporator system (10) arranged in a motor vehicle (200), wherein the multi-evaporator system (10) comprises a refrigerant circuit (11) and at least two evaporators (12, 13, 14) arranged in the refrigerant circuit (11), wherein the refrigerant circuit (11) comprises a refrigerant which is suitable for a transcritical process control, and wherein a transcritical process control takes place, wherein a high-pressure control takes place in the transcritical process control, characterized bythat each of the evaporators (12, 13, 14) is assigned an expansion valve (23, 24, 25), that a control of the expansion valves (23, 24, 25) takes place taking into account an expected cooling capacity of the evaporators (12, 13, 14), and that, if an overheating of the refrigerant is determined for all of the evaporators (12, 13, 14), a mass flow proportion of the refrigerant passed to the first evaporator (12) is increased and / or a cooling capacity of the first evaporator (12) is increased, wherein a reduction in a cross section of the expansion valve (24) assigned to the second evaporator (13) takes place. [2] Method (100) according to claim 1, characterized bythat a first evaporator (12) is an evaporator (12) for conditioning an air mass flow in a front part of a vehicle cabin (15) of the motor vehicle (200), and / or that a second evaporator (13) is an evaporator (13) for conditioning an air mass flow in a rear part of a vehicle cabin (15) of the motor vehicle (200), and / or that a third evaporator (14) is an evaporator (14) for conditioning a battery (16) and / or traction components of the motor vehicle (200), wherein preferably the first evaporator (12) is an air-refrigerant heat exchanger (12a), and / or wherein the second evaporator (13) is an air-refrigerant heat exchanger (13a), and / or wherein the third evaporator (14) is a coolant-refrigerant heat exchanger, in particular a chiller (14a). [3] Method (100) according to claim 1 or 2, characterized by that the refrigerant is R-744. [4] Method (100) according to one of the preceding claims, characterized by that switching takes place between the transcritical process control and a subcritical process control, whereby subcooling control takes place in the subcritical process control, whereby switching preferably takes place dynamically between the subcritical process control and the transcritical process control. [5] Method (100) according to claim 4, characterized by that in a transition area between the subcritical process control and the transcritical process control, the high pressure control is carried out according to a transition function, wherein the transition function describes a target high pressure, wherein the target high pressure is preferably determined by means of a linear interpolation between a target pressure for the subcritical process control and a target pressure for the transcritical process control. [6] Method (100) according to one of the preceding claims, characterized bythat, if superheating of the refrigerant is detected for at least one of the evaporators (12, 13, 14), superheating is controlled to a superheat setpoint. [7] Method (100) according to one of the preceding claims, characterized by that each of the expansion valves (23, 24, 25) is arranged in an inlet branch (20, 21, 22) of the respective evaporator (12, 13, 14), and that the high-pressure control and / or the subcooling control and / or the superheating control is carried out by controlling at least one, preferably several, particularly preferably all, of the expansion valves (23, 24, 25). [8] Method (100) according to claim 7, characterized by that cross sections of the expansion valves (23, 24, 25) are pre-controlled in relation to the desired cooling capacities of the evaporators (12, 13, 14). [9] Motor vehicle (200) comprising a multi-evaporator system (10), wherein the multi-evaporator system (10) comprises a refrigerant circuit (11) and at least two evaporators (12, 13, 14) arranged in the refrigerant circuit (11), wherein the refrigerant circuit (11) comprises a refrigerant which is suitable for a transcritical process, further comprising a high-pressure regulator (33), characterized by that the high-pressure regulator (33) is designed to carry out a high-pressure control according to a method (100) according to one of the preceding claims in a transcritical process control.

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