WO2024022803A1

WO2024022803A1 - Method for operating a refrigeration system with a supercritically operating refrigerant, refrigeration system, and motor vehicle comprising a refrigeration system

Info

Publication number: WO2024022803A1
Application number: PCT/EP2023/069163
Authority: WO
Inventors: Christian Rebinger; Helmut Rottenkolber; Dirk Schroeder
Original assignee: Audi Ag
Priority date: 2022-07-26
Filing date: 2023-07-11
Publication date: 2024-02-01
Also published as: DE102022118623A1

Abstract

The invention relates to a method (500) for operating a refrigeration system (10) with a supercritically operating refrigerant, wherein the refrigeration system (10) can be operated in a first operating mode (BM1), in particular a controlled supercooling mode, or in a second operating mode (BM2), in particular a controlled high-pressure mode, wherein the method (500) comprises the following steps: setting (S501) a lower pressure limit (PGun) and an upper pressure limit (PGob) such that the absolute value of the difference (DPG) between the upper pressure limit (PGob) and the lower pressure limit (PGun) is greater than (1), in particular greater than (5), preferably approximately (10); determining or detecting (S502) a refrigerant pressure (Pkm_HD) on the high pressure side and/or a refrigerant temperature on the high pressure side; comparing (S503) the refrigerant pressure (Pkm_HD) with the lower pressure limit (PGun) or/and the upper pressure limit (PGob); operating the refrigeration system (10) in the first operating mode (BM1) or in the second operating mode (BM2) depending on the comparison (S503) of the determined or detected refrigerant pressure (Pkm_HD) with the lower pressure limit (PGun) or/and the upper pressure limit (PGob). The invention also relates to a refrigeration system comprising a control device for carrying out the method (500) and to a motor vehicle comprising such a refrigeration system.

Description

Method for operating a refrigeration system with supercritical refrigerant, refrigeration system and motor vehicle with refrigeration system

DESCRIPTION:

The invention relates to a method for operating a refrigeration system with supercritically operating refrigerant, wherein the refrigeration system can be operated in a first operating mode, in particular a regulated subcooling operation, or in a second operating mode, in particular a regulated high-pressure operation. The invention further relates to a refrigeration system that is operated according to the method and a motor vehicle with such a refrigeration system.

From WO 2018 137 783 A1 an expansion unit is known for installation in a refrigeration system that is contaminated with supercritically operating refrigerant. The expansion unit includes two expansion systems for setting different pressure levels of desired transcritical or subcooled operating states.

The object underlying the invention is to provide a method for operating a refrigeration system with supercritical refrigerant, with which efficient operation is possible and in particular an improved changeover between transcritical and subcooled operating states is achieved. Furthermore, the process should be able to be implemented with a simply constructed refrigeration system.

This task is solved by a method, a refrigeration system and a motor vehicle with the features of the respective independent patent claim. Advantageous refinements with useful further developments are specified in the dependent patent claims. What is proposed is a method for operating a refrigeration system with supercritically operating refrigerant, wherein the refrigeration system can be operated in a first operating mode, in particular a regulated subcooling operation, or in a second operating mode, in particular a regulated high-pressure operation, the method having the following steps:

Setting a lower pressure limit and an upper pressure limit such that the magnitude of the difference between the upper pressure limit and the lower pressure limit is greater than 1, in particular greater than 5, preferably about 10;

determining or detecting a high-pressure side refrigerant pressure and/or a high-pressure side refrigerant temperature;

Comparing the refrigerant pressure with the lower pressure limit and/or the upper pressure limit;

Operating the refrigeration system in the first operating mode or in the second operating mode depending on the comparison of the determined or detected refrigerant pressure with the lower pressure limit and/or the upper pressure limit.

By defining a pressure range that extends from the lower pressure limit to the upper pressure limit, a type of transition range is defined to enable optimized operation of the refrigeration system in the desired operating mode.

In the method, the refrigeration system can be operated in the first operating mode or the second operating mode at a refrigerant pressure that lies within the limits of the lower pressure limit and the upper pressure limit.

In the method, a lower comparison pressure value can be determined during the comparison by the difference between the refrigerant pressure and the lower pressure limit value. In the method, an upper comparison pressure value can be determined during the comparison by the difference between the refrigerant pressure and the upper pressure limit value.

In the method, the first operating mode can be set when the lower comparison pressure value is less than zero. This ensures that only the first operating mode is activated below the lower pressure limit.

In the method, the second operating mode can be set when the upper comparison pressure value is greater than or equal to zero. This ensures that only the second operating mode is activated when the upper pressure limit is reached or above.

Alternatively, the method can be used to decide whether a first or second operating mode should be implemented by a simple “less than” or “greater than” comparison of the determined or recorded pressure value with the specified lower and upper pressure limit values.

In the method, starting from operation in the first operating mode, the first operating mode can be maintained in a controlled manner until the upper comparison pressure value is greater than or equal to zero. This makes it possible for the refrigeration system to be operated in the first operating mode until, coming from a lower pressure level, the upper pressure limit is reached and a switch to the second operating mode can take place.

In the method, starting from operation in the second operating mode, the second operating mode can be maintained in a controlled manner until the lower comparison pressure value is less than zero. This makes it possible for the refrigeration system to be operated in the second operating mode until, coming from a higher pressure level, the lower pressure limit is reached or fallen below and a switch to the first operating mode can take place. Alternatively, a simple comparison method can also be used here between a recorded or determined pressure value and a lower pressure limit value, which switches from a second operating mode to a first as soon as a lower pressure limit value is reached or undershot. In analogy to the comparison method above, a change is made from a first operating mode to a second one as soon as an upper pressure limit is reached or exceeded.

In other words, within the transition region from the lower pressure limit to the upper pressure limit (or vice versa), a corresponding operating mode is maintained depending on how or from which pressure position the transition region is entered. A kind of hysteresis can thus be achieved in order to make the transitions between the two operating modes smooth and not abrupt.

In the method, the first operating mode and the second operating mode can be set and/or maintained by setting at least one expansion valve. The method is designed in particular in such a way that a single expansion valve is sufficient to set the desired operating modes.

The expansion valve can be adjusted in particular to achieve a specific system parameter such as high pressure and/or subcooling depending on the detected refrigerant pressure and can be carried out with a time delay. In this way, a kind of smooth or constant transition between the two operating modes can be achieved because the activation of the expansion valve is dampened so that there is no sudden change from one operating mode to the other.

The method may further include the following steps:

Comparing the recorded refrigerant pressure with a resulting target refrigerant pressure based on the estimated, determined or recorded refrigeration medium temperature; Setting or starting a target refrigerant pressure or a target subcooling via the cross-sectional adjustments of the expansion element. Monitoring the refrigerant pressure (actual pressure) and the refrigerant target pressure can be used in particular for the system operation described above.

Furthermore, a refrigeration system is proposed for a motor vehicle driven by an internal combustion engine or at least partially electrically, the refrigeration system being set up for operation with supercritically operating refrigerant and the refrigeration system comprising: a refrigerant compressor, a first heat exchanger, in particular gas cooler, a second heat exchanger, in particular evaporator, a sensor device arranged downstream of the first heat exchanger for detecting a refrigerant pressure and/or for detecting a refrigerant temperature; a controllable expansion valve arranged upstream of the second heat exchanger; a control device that is set up to operate the refrigeration system in the method described above.

The aforementioned embodiment of a refrigeration system is the simplest variant for implementing this process. Such a refrigeration system can be designed with additional heat exchangers such as additional gas coolers and/or evaporators (rear evaporator, chiller). In addition, it can have heat pump functionality.

A motor vehicle with an internal combustion engine or at least partially electric drive can be equipped with such a refrigeration system.

Further advantages and details of the invention emerge from the following description of embodiments with reference to the figures. This shows: Fig. 1 is a schematic circuit diagram of an example of a refrigeration system;

2 shows a simplified flowchart of a method for operating the refrigeration system;

Fig. 3 is a simplified diagram to illustrate the relationship between operating modes and refrigerant pressure.

Fig. 1 shows a schematic and simplified circuit diagram of a refrigeration system 10 which is contaminated with supercritically operating refrigerant, for example R744. In this exemplary configuration, the refrigeration system 10 includes a refrigerant compressor 12, a first (external or direct/indirect) heat exchanger 14, which acts as a gas cooler or condenser, a second heat exchanger 16, which acts as a (direct/indirect) evaporator, and a Refrigerant collector 18. An expansion valve AE1 is connected upstream of the second heat exchanger 16 (evaporator). The expansion valve AE1 is particularly designed to be controllable.

Furthermore, the refrigeration system 10 has an internal heat exchanger 20. In the example shown, the internal heat exchanger 20 is arranged downstream of the refrigerant collector 18 and upstream of the refrigerant compressor 12 in relation to the low-pressure side of the refrigeration system.

In the refrigeration system 10, several pressure or temperature sensors pT1, pT2, pT3 are shown as examples, which are arranged at suitable or usual positions in a refrigeration system. The sensor pT2 is arranged downstream of the first heat exchanger 14 for detecting a refrigerant pressure and/or for detecting a refrigerant temperature. Furthermore, the refrigeration system can have a sensor device Tum for detecting an ambient temperature.

The refrigerant flow in the refrigeration system 10 is illustrated by the arrow symbols along the refrigerant lines shown schematically by lines. It should be noted that in Fig. 1 only a kind of basic configuration is shown. guration of the refrigeration system 10 is shown, which can of course be supplemented with further components. The refrigeration system 10 can in particular also be set up to be operated in a heat pump mode, for example.

The refrigeration system 10 can, for example, have a third heat exchanger, not shown here, for example a chiller. In terms of flow technology, a third heat exchanger (chiller) would be arranged parallel to the second heat exchanger (evaporator). In the chiller embodiment, the third heat exchanger can be connected as an indirect heat exchanger to a coolant circuit, not shown, which can be used in particular for cooling electrical components of a motor vehicle, such as a high-voltage battery, an electric drive and the like.

The refrigeration system 10 further comprises a control device 30, which is set up to operate the refrigeration system 10 according to a method 500 described below. The control device 30 is connected to various components of the refrigeration system 10 by means of signal lines shown in dashed lines, the connections to the sensor devices pT1, pT2, pT3, Tum as well as the expansion valve AE1 and the compressor 12 being shown in FIG.

2 shows a simplified flowchart of a method 500 for operating a refrigeration system 10.

The refrigeration system 10 can be operated in a first operating mode BM1, in particular a regulated subcooling operation (also referred to as subcooling), or in a second operating mode BM2, in particular a regulated high-pressure operation.

According to the method 500, in a step S501, a lower pressure limit PGun and an upper pressure limit PGob are set such that the amount of the difference DPG between the upper pressure limit PGob and the lower pressure limit PGun is greater than 1, in particular greater than 5, preferably about 10.

According to a step S502, a high-pressure-side refrigerant pressure Pkm_HD and/or a high-pressure-side refrigerant temperature Tkm_HD is determined or detected. Based on the refrigerant temperature Tkm_HD detected or determined or estimated, in particular via the sensor pT2, a potential target pressure value is determined and can be compared with the pressure value Pkm_HD detected and present in the system at this point. If the refrigerant pressure Pkm_HD is not recorded or measured directly, it can be determined or estimated based on the recorded refrigerant temperature Tkm_HD or via pressure loss characteristic Z maps based on another pressure (temperature) sensor available in the system, such as pT1.

The further operation of the refrigeration system takes place in the first operating mode BM1 or in the second operating mode BM2 depending on the comparison carried out in step S503 of the determined or detected refrigerant pressure Pkm_HD with the lower pressure limit PGun and/or the upper pressure limit PGob.

The control device 30 acts on the expansion valve AE1 in such a way that it actively acts on the resulting subcooling of the first operating mode BM1 or on the optimal high pressure to be set in the second operating mode BM2 via the variation of its internal cross section or sets these variables, wherein at a refrigerant pressure that lies within the limits of the lower pressure limit and the upper pressure limit, the refrigeration system is operated in the first operating mode BM1 or the second operating mode BM2.

In the comparison in step S503, a lower comparison pressure value VPun is determined by the difference between the lower pressure limit PGun and the refrigerant pressure Pkm_HD, i.e

VPun = PGun - Pkm_HD During the comparison in step S503, an upper comparison pressure value VPob is alternatively or additionally determined by the difference between the upper pressure limit value PGob and the refrigerant pressure Pkm_HD, i.e

VPob = PGob - Pkm_HD.

If one assumes, for example, that the refrigeration system 10 is started or, in other words, is started up, it can be assumed that the refrigerant pressure Pkm_HD increases from a resting pressure, but is initially still below the lower pressure limit PGun.

In method 500, the first operating mode BM1 is thus set in a step S504 if the lower comparison pressure value VPun is less than zero.

Starting from the operation in the first operating mode BM, the first operating mode BM1 is maintained in a controlled manner until the upper comparison pressure value VPob is greater than or equal to zero (S505).

If it is determined in step S505 that the upper comparison pressure value VPob is greater than or equal to zero, the second operating mode BM2 is set.

Starting from the operation in the second operating mode BM2, the second operating mode BM2 is then maintained in a controlled manner until the lower comparison pressure value VPun is less than zero (S504).

In addition, it should be noted that before or when starting the refrigeration system 10, it is possible to estimate, based on the resting pressure and/or ambient temperature, which system high pressure (refrigerant pressure) is to be expected and, at least in addition, based on these variables, a forecast for the expected pressure and thus Operating mode BM1 or BM2 to be started or set can be given. If it is determined in step S504 that the lower comparison pressure value VPun is less than zero or if the lower pressure limit PGun is consequently reached or fallen below, the first operating mode BM1 is set (again).

In method 500, the first operating mode BM1 and the second operating mode BM2 are set and/or maintained by adjusting an expansion valve, in particular the expansion valve AE1.

The expansion valve AE1 can be adjusted depending on the detected refrigerant pressure Pkm_HD and can be carried out with a time delay. The setting can in particular also be carried out depending on a target refrigerant pressure to be set or achieved or a required subcooling T_SC.

It should be noted that both the detection or determination of the refrigerant pressure Pkm_HD as well as the determination of the setpoint of a refrigerant pressure Pkm_HD_Soll or the subcooling to be set T_SC_Soll takes place or is updated regularly or continuously as part of the method 500, even if this is not explicitly stated repeating process step is shown in the flow chart.

The diagram shown in Fig. 3 illustrates the method described above, which is explained below.

The refrigerant pressure Pkm_HD is entered on the x-axis of the diagram. The two operating modes BM1 and BM2 are shown on the Y axis. Furthermore, the two pressure limit values PGun and PGob are entered on the X-axis. A wider, solid line provides a simplified illustration of the pressure progression.

As a purely example, possible values for these pressure limits are given in brackets in the diagram, for example PGun = 58 bar and PGob = 68 bar. However, these concrete values should not be viewed as restrictive. means that only these values are possible. Other values that are closer together, for example 60 bar and 66 bar, are also conceivable.

In the specific example, the difference DPG between the upper pressure limit PGob and the lower pressure limit PGun results in that this is greater than 1, in particular greater than 5, and here preferably 10. In other words, a transition region comprising, for example, 10 bar is formed between the two pressure limit values PGun and PGob, which is illustrated hatched in FIG. 3.

From the diagram in FIG. 3 it can be seen that the first operating mode BM is always active when the refrigerant pressure Pkm_HD is below the lower pressure limit PGun. The second operating mode BM2 is always active when the refrigerant pressure Pkm_HD is greater than the upper pressure limit PGob.

As can be seen from FIG. 2 and described above, both operating modes BM1 or BM2 can be active in the transition area between the two pressure limit values PGun and PGob. If the refrigerant pressure Pkm_HD increases based on operation of the refrigeration system 10 in the first operating mode BM1, the operating mode BM1 is maintained within the transition range until the refrigerant pressure Pkm_HD reaches the upper pressure limit PGob. If the refrigerant pressure Pkm_HD drops due to operation of the refrigeration system 10 in the second operating mode BM2, the operating mode BM2 is maintained within the transition range until the refrigerant pressure Pkm_HD reaches the lower pressure limit PGun.

Purely by way of example, the method 500 of FIG. 2 will be described in more detail below in conjunction with the diagram of FIG. 3 using specific values. Starting from a refrigerant pressure Pkm_HD of, for example, 56 bar, which was determined or recorded in step S502, the following results from step S503:

VPun = 56 bar - 58 bar = -2

VPob = 56 bar - 68 bar = -12

VPun is therefore less than zero, so that the first operating mode BM1 is active according to step S504. Within the first operating mode, it is now continuously or repeatedly checked whether VPob is greater than zero. With a refrigerant pressure of, for example, 63 bar, the following results from the first operating mode:

VPob = 63 bar - 68 bar = -5

Accordingly, there is no switchover to the second operating mode BM2.

If the refrigerant pressure increases to, for example, 69 bar during the first operating mode BM1, the result is:

VPob = 69 bar - 68 bar = 1

Thus, VPob is greater than or equal to zero (S505) and the second operating mode BM2 is activated.

Within the second operating mode BM2, it is now continuously or repeatedly checked whether VPun becomes less than zero (S504). With a (again decreasing) refrigerant pressure of, for example, 63 bar, the following results from the second operating mode:

VPun = 63 bar - 58 bar = 5

Accordingly, there is no switchover to the first operating mode BM1.

If the refrigerant pressure drops to, for example, 57 bar during the second operating mode BM2, the result is: VPun = 57 bar - 58 bar = -1

VPun is therefore less than zero (S504) and the first operating mode BM1 is activated (again).

From the above description with the exemplary concrete pressure values it can be seen that in the method 500, starting from the operation in the first operating mode BM1, the first operating mode is maintained in a controlled manner until the upper comparison pressure value VPob is greater than or equal to zero (S505). Starting from the operation in the second operating mode BM2, the second operating mode BM2 is maintained in a controlled manner until the lower comparison pressure value VPun is less than zero (S504).

The alternative procedure for going through the process or for implementing the decision criteria as to which operating mode should be selected is based on the simple function of an actual value comparison between an existing system pressure Pkm_HD and the pressure limits PGun and PGob to be defined or specified.

Pkm_HD > or

BM2 operating mode

Pkm_HD < or

Operating mode BM1

PGun < or < Pkm_HD < or < PGob

Operating mode BM1 or operating mode BM2, whereby in the latter case it must be taken into account from which side or from which pressure range the transition area between PGun and PGob is entered.

This results in: Entry coming from area PGob into the intermediate area PGun < or < Pkm_HD < or < PGob

Operating mode BM2 remains maintained until PGun is reached or undershot.

Entry from the PGun area into the intermediate area PGun < or < Pkm_HD < or <

Operating mode BM1 is maintained until PGob is reached or exceeded. The method 500 presented is based, based on the exemplary system sketch in FIG. 1, on the interaction of the sensor device pT2 and the expansion valve AE1. The hatched transition area shown in the diagram in FIG. 3 enables a kind of sliding or constant transition between the two operating modes BM1 and BM2, whereby the activation of the expansion valve AE1 is dampened so that there is no sudden change from one operating mode to the other .

The method has been described here in general terms for a refrigeration system 10 and an ambient heat exchanger 14 operating as a gas cooler, the refrigerant temperature of which is measured downstream and the resulting target high pressure Pkm_HD_soll is used as the starting point for implementing the method. This heat exchanger 14 can implement the heat emission directly or indirectly. In addition, the method for this heat exchanger 14 in the described application for the refrigeration system 10 can also be set for a heat pump application (not outlined and described in more detail) with a heat exchanger acting, for example, as a heating register or indirect heat exchanger, based analogously on a measured temperature, a resulting high pressure setpoint Pkm_HD_soll, adjustable via an appropriately placed additional expansion element, always functioning taking into account the transfer criteria between the respective operating modes 1 and 2.

Claims

PATENT CLAIMS:

1 . Method (500) for operating a refrigeration system (10) with supercritically operating refrigerant, wherein the refrigeration system (10) can be operated in a first operating mode (BM1), in particular a regulated subcooling operation, or in a second operating mode (BM2), in particular a regulated high-pressure operation is, the method (500) having the following steps:

Setting (S501) a lower pressure limit (PGun) and an upper pressure limit (PGob), such that the magnitude of the difference (DPG) between the upper pressure limit (PGob) and the lower pressure limit (PGun) is greater than 1, in particular greater than 5 , preferably about 10;

determining or detecting (S502) a high-pressure side refrigerant pressure (Pkm_HD) and/or a high-pressure side refrigerant temperature;

Comparing (S503) the refrigerant pressure (Pkm_HD) with the lower pressure limit (PGun) and/or the upper pressure limit (PGob); Operating the refrigeration system (10) in the first operating mode (BM1) or in the second operating mode (BM2) depending on the comparison (S503) of the determined or detected refrigerant pressure (Pkm_HD) with the lower pressure limit (PGun) and/or the upper pressure limit (PGob).

2. Method (500) according to claim 1, wherein at a refrigerant pressure (Pkm_HD) which is within the limits of the lower pressure limit (PGun) and the upper pressure limit (PGob), the refrigeration system (10) is in the first operating mode (BM1). or the second operating mode (BM2).

3. Method (500) according to claim 1 or 2, wherein in the comparison (S503) a lower comparison pressure value (VPun) is determined by the Difference between the refrigerant pressure (Pkm_HD) and the lower pressure limit (PGun). Method (500) according to one of the preceding claims, wherein in the comparison (S503) an upper comparison pressure value (VPob) is determined by the difference between the refrigerant pressure (Pkm_HD) and the upper pressure limit value (PGob). Method (500) according to claim 3 or 4, wherein the first operating mode (BM1) is set when the lower comparison pressure value (VPun) is less than zero (S504). Method (500) according to one of claims 3 to 5, wherein the second operating mode (BM2) is set when the upper comparison pressure value (VPob) is greater than or equal to zero (S505). Method (500) according to claim 5 or 6, wherein, starting from the operation in the first operating mode (BM1), the first operating mode (BM1) is maintained in a controlled manner until the upper comparison pressure value (VPob) is greater than or equal to zero (S505) . Method (500) according to one of claims 5 to 7, wherein, starting from the operation in the second operating mode (BM2), the second operating mode (BM2) is maintained in a controlled manner until the lower comparison pressure value (VPun) is less than zero (S504) . Method (500) according to one of the preceding claims, wherein the setting and/or maintaining of the first operating mode (BM1) and the second operating mode (BM2) is carried out by setting at least one expansion valve (AE1), preferably setting the expansion valve (AE1) depending on the recorded refrigerant pressure (Pkm_HD) and is carried out with a time delay. The method (500) of claim 9, further comprising the steps of: comparing the sensed refrigerant pressure with a resulting target refrigerant pressure based on the determined or sensed refrigerant temperature;

Setting or starting a target refrigerant pressure or a target subcooling via the cross-sectional adjustments of the expansion element. Refrigeration system (10) for a motor vehicle powered by an internal combustion engine or at least partially electrically, wherein the refrigeration system (10) is set up for operation with supercritical refrigerant and wherein the refrigeration system (10) comprises: a refrigerant compressor (12), a first heat exchanger (14) , in particular gas cooler, a second heat exchanger (16), in particular evaporator, a sensor device (pT2) arranged downstream of the first heat exchanger (14) for detecting a pressure (Pkm_HD) and/or for detecting a refrigerant temperature; a controllable expansion valve (AE1) arranged upstream of the second heat exchanger (16); a control device (30) which is set up to operate the refrigeration system (10) in a method (500) according to the preceding claims. Motor vehicle with an internal combustion engine or at least partially electric drive with a refrigeration system (10) according to claim 11.