Defrosting method, refrigeration device and motor vehicle having such refrigeration device

Abstract

The invention relates to a method (500) for defrosting an external heat exchanger (18) of a refrigeration device (10) of a motor vehicle, the refrigeration device (10) comprising: a refrigerant compressor (12) which is connectable or connected to a main line (14) and a secondary line (16); an external heat exchanger (18) arranged in the main line (14); an evaporator (22) arranged in the main line (14); a heating regulator (26) arranged in the secondary line (16); a main line valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger, which is closed during air heat pump operation; and a main line valve (A4) arranged in the control valve (A5) to control the external heat exchanger. A secondary pipeline valve (A3) between a refrigerant compressor (12) and a heating regulator (26), which is opened during operation of an air heat pump; wherein the method comprises the following steps: closing (S502) the secondary pipeline valve (A3); opening (S503) the main pipeline valve (A4) so ​​that the refrigerant flows directly from the refrigerant compressor (12) to an external heat exchanger (18); adjusting (S504) the pressure level of the refrigerant on the inlet side of the external heat exchanger (18) to the following target pressure, which corresponds to the condensation temperature (Tkond) of the refrigerant in the following range: 2°C ≤ Tkond ≤ 20°C, in particular 4°C ≤ Tkond ≤ 10°C.

Description

Technical Field

[0001] The invention relates to a method for defrosting an external heat exchanger operated as an air heat pump evaporator of a refrigeration system for a motor vehicle, a refrigeration system and a motor vehicle having such a refrigeration system. Background Art

[0002] For air heat pumps, the heat incorporated in the ambient air is usually used to evaporate and, if necessary, heat the refrigerant, that is, to transfer heat to the refrigerant so that the refrigerant, together with the heat introduced by the compressor, can heat the air flow for the interior of the motor vehicle. Here, the refrigerant is brought to an evaporation pressure level or evaporation temperature level below the environment, so that heat can be taken away from the ambient air. Here, the ambient air is cooled, which can cause moisture to precipitate from the ambient air and condense at the air heat pump evaporator or an external heat exchanger and freeze there. Accordingly, a frost layer is formed on the external heat exchanger, which makes it difficult for the ambient air flow to flow through the heat exchanger. This has a negative impact on the evaporation power, so that the heating power of the air heat pump no longer exists or is no longer sufficient.

[0003] In order to defrost the external heat exchanger in a refrigeration system, the hot or scalding refrigerant under high pressure is conducted directly from the refrigerant compressor to the frozen external heat exchanger by means of a suitable process connection concept / process arrangement concept. Due to the pressure change and the accompanying temperature jump from the cold low-pressure level (air heat pump operation) to the warm or even hot high-pressure level, the temperature at the external heat exchanger can suddenly rise by 40K or more. Such dynamic temperature changes can lead to stresses in the external heat exchanger, so that, for example, joints, such as soldering points, are subjected to strong loads, which can shorten the service life of the external heat exchanger.

[0004] Examples of such a connection of a refrigerant device to an air heat pump can be found in EP 2 821 727 A1, DE 11 2014 003 184 T5 or DE 10 2017 110560 A1. Summary of the invention

[0005] The object of the present invention is to specify a method for defrosting an external heat exchanger operated as an air heat pump evaporator, in which the above-mentioned disadvantages, in particular large temperature jumps, can be avoided.

[0006] This object is achieved by a method having the features described below, by a refrigeration device having the features described below, and by a motor vehicle having the features described below. Advantageous embodiments with expedient developments are given below.

[0007] Therefore, a method is proposed for defrosting an external heat exchanger of a refrigeration system of a motor vehicle, which is operated as an air heat pump evaporator, wherein the refrigeration system has:

[0008] A refrigerant compressor connected or connectable to the main pipeline and the secondary pipeline;

[0009] an external heat exchanger arranged in the main line;

[0010] an evaporator arranged in the main line;

[0011] a heating regulator (Heizregister) (26) arranged in the secondary pipeline (16);

[0012] a main line valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger (18), the main line valve being closed during operation of the air heat pump;

[0013] A secondary line valve (A3) is arranged between the refrigerant compressor (12) and the heating regulator (26), and is opened during operation of the air heat pump.

[0014] Here, the method comprises the following steps:

[0015] Close the secondary pipeline valve (A3);

[0016] Opening the main line valve (A4) so ​​that the refrigerant flows directly from the refrigerant compressor (12) to the external heat exchanger;

[0017] The inlet-side pressure level of the refrigerant at the external heat exchanger is adjusted to a target pressure which corresponds to the condensation temperature (Tkond) of the refrigerant in the following range:

[0018] 2℃≤Tkond≤20℃, especially 4℃≤Tkond≤10℃.

[0019] This prevents a rapid or intense heating of the frozen external heat exchanger during defrosting. The refrigerant is regulated to a pressure level at which the condensation temperature is (significantly) above the freezing point of water, so that defrosting is achieved. However, the refrigerant pressure level and the associated temperature increase at the external heat exchanger are limited or regulated in a targeted manner, so that thermally induced stresses occurring at the external heat exchanger, which is operated as an air heat pump evaporator, can be reduced.

[0020] In the method, a closing device arranged on the air side of the external heat exchanger can be closed. Here, the closing action can be performed just before closing the secondary line valve or before opening the main line valve, or substantially simultaneously with closing the secondary line valve or opening the main line valve. In this way, the flow of ambient air into or through the external heat exchanger can be prevented on the ambient air side, so that the defrosting process can be accelerated, because little or no cooled ambient air flows into or through the external heat exchanger, which absorbs heat from the refrigerant flowing through the heat exchanger and thus delays or prevents the defrosting process.

[0021] The pressure level of the refrigerant can remain regulated to the target pressure until the refrigerant temperature (Tkm) measured at the outlet side of the external heat exchanger is greater than the condensation temperature of 0° C. for a predetermined period of time, in particular corresponds to the condensation temperature (Tkond). It can thus be ensured with a high degree of safety that the external heat exchanger is completely defrosted or thawed, since no or only little heat is output to the (originally) cold and frost-covered surfaces of the heat exchanger.

[0022] After the desired refrigerant temperature has been reached, the ventilation device can be activated in order to dry the external heat exchanger, in particular to remove condensate present on the external heat exchanger. In this case, the ventilation device can also convey ambient air to the external heat exchanger, wherein this is particularly done when the air temperature is above freezing point, in order not to directly cause the condensate to freeze again. The conveying of the air flow to the external heat exchanger can also be accompanied by at least partial opening of the air-side closure device.

[0023] During operation of the ventilation device, the pressure level of the refrigerant can be adjusted or maintained in such a way that the external surface temperature of the external heat exchanger is 4° C. or higher. This ensures that the removal of condensate and thus the drying of the external heat exchanger can be carried out effectively.

[0024] By adjusting the power consumption of the refrigerant compressor and / or by adjusting the opening of an expansion valve associated with a chiller (Chiller) operating, for example, as a water heat pump evaporator, the pressure level on the inlet side can be brought to a target pressure. Thus, the desired pressure level (target pressure) for defrosting the external heat exchanger can be adjusted taking into account at least one operating parameter of the refrigeration system.

[0025] The above object is also achieved by a refrigeration device for a motor vehicle with a heat pump function, the refrigeration device having:

[0026] a refrigerant compressor connected or connectable to the main line and the secondary line;

[0027] an external heat exchanger which operates or can be operated as an air heat pump evaporator, the external heat exchanger being arranged in the main line;

[0028] an evaporator arranged in the main line;

[0029] a heating regulator disposed in the secondary pipeline;

[0030] a main line valve disposed between the refrigerant compressor and the external heat exchanger;

[0031] A secondary line valve is arranged between the refrigerant compressor and the heating controller, wherein provision is made for the refrigeration system to be set up to operate with the above-described method for defrosting an external heat exchanger.

[0032] A motor vehicle can be equipped with such a refrigeration device. Here, the motor vehicle can be an electric vehicle in particular. In an electric vehicle, the efficient operation of the refrigeration device can save electricity, thereby enabling a greater driving range of the electric vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Other advantages and details of the present invention are apparent from the following description of embodiments with reference to the accompanying drawings.

[0034] Figure 1 A schematic simplified circuit diagram of a refrigeration system for a motor vehicle is shown;

[0035] Figure 2 In particular, by means of Figure 1 The refrigeration device described in the embodiment exemplarily implements a flow chart of a method for defrosting an external heat exchanger. DETAILED DESCRIPTION

[0036] exist Figure 1 Schematically and in a simplified manner, an embodiment of a refrigeration device 10 for a motor vehicle is shown. The refrigeration device 10 comprises a refrigerant circuit 11, which can be operated in a refrigeration device operation (referred to as AC operation) mode, a heat pump mode, and a reheating mode not described further. In the embodiment shown, the refrigeration device 10 comprises a refrigerant compressor 12, an external heat exchanger 18, an internal heat exchanger 20, an evaporator 22, and a storage or refrigerant collector 24. The external heat exchanger 18 can be configured as a condenser or a gas cooler. In particular, in the embodiment shown, the external heat exchanger 18 can be bidirectionally ventilated.

[0037] The evaporator 22 is shown here as a front evaporator for a vehicle by way of example. The evaporator 22 also represents representatively other possible evaporators in a vehicle, such as a rear evaporator, which can be arranged parallel to one another in terms of flow technology. In other words, the refrigeration device 10 therefore includes at least one evaporator 22.

[0038] A stop valve, hereinafter referred to as main line valve A4 , is arranged downstream of the compressor 12 . An expansion valve AE2 is provided upstream of the evaporator 22 .

[0039] Within the scope of the present description, in the entire refrigerant circulation circuit 11 of the refrigeration device 10 , the section from the compressor 12 to the external heat exchanger 18 , to the internal heat exchanger 20 and to the evaporator 22 is referred to as the main line 14 .

[0040] The refrigeration device 10 further comprises a heating regulator 26 (also referred to as a heating capacitor or a heating gas cooler). A shutoff valve, referred to below as a secondary line valve A3, is arranged upstream of the heating regulator 26. A shutoff valve A1 is arranged downstream of the heating regulator 26. In addition, an expansion valve AE4 is arranged downstream of the heating regulator 26.

[0041] Within the scope of the present description, in the entire refrigerant circulation circuit of the refrigeration device 10, the section from the compressor 12 to the heating regulator 26, to the expansion valve AE4 and to the branch Ab2 is referred to as the secondary line 16. The secondary line 16 includes a heating branch 16.1, which extends from the shutoff valve (secondary line valve A3) via the heating regulator 26 to the shutoff valve A1. In addition, the secondary line 16 includes a reheating branch 16.2, which can be fluidly connected to the heating regulator 26 upstream and can be fluidly connected to the external heat exchanger 18 downstream. Here, the secondary line 16 or the reheating branch 16.2 opens into the main line 14 at the branch point Ab2.

[0042] The refrigeration device 10 comprises a further evaporator designed as a refrigerator / water chiller 28. The refrigerator 28 is arranged fluidically parallel to the evaporator 22. The refrigerator 28 can be used, for example, to cool electrical components of the vehicle, but can also be used to implement a water heat pump function by utilizing the waste heat of at least one electrical component. An expansion valve AE1 is connected upstream of the refrigerator 28.

[0043] The refrigeration device 10 can also have an electric heating element 30, which is designed, for example, as a high-voltage PTC heating element. The electric heating element 30 serves as an additional heater for the supply air flow L supplied to the vehicle interior. Here, the electric heating element 30 can be accommodated in the air conditioning device 32 together with the heating regulator 26 and the evaporator 22. Here, the electric heating element 30 can be arranged downstream of the heating regulator 26.

[0044] In addition, Figure 1Check valves R1 and R2 can also be seen in the figure. A plurality of sensors pT1 to pT5 for detecting the pressure and / or temperature of the refrigerant are also shown. It should be noted that the number of sensors or their arrangement is shown here only as an example. The refrigeration device 10 can also have fewer or more sensors. In the example shown, combined pressure / temperature sensors pT1 to pT5 are shown as sensors. However, it is also conceivable that sensors independent of each other are used to measure the pressure or temperature and, if appropriate, can also be arranged in a spatially separated manner along the refrigerant line.

[0045] The refrigeration device 10 can be operated in different modes as will be briefly described below.

[0046] In AC operation of the refrigerant circuit 11, the refrigerant compressed to high pressure flows from the refrigerant compressor 12 into the external heat exchanger 18 with the main line valve A4 open and the secondary line valve A3 closed. From there, the refrigerant flows to the high-pressure section of the internal heat exchanger 20 and to the fully opened expansion valve AE3. Via the branch point Ab1, the refrigerant can flow to the expansion valve AE2 and into the interior evaporator 22 (evaporator section 22.1). In parallel or alternatively, the refrigerant can flow through the branch point Ab4 and the expansion valve AE1 into the refrigerator 28 (refrigerator section 28.1). From the evaporator 22 and / or the refrigerator 28, the refrigerant flows into the collector 24 on the low-pressure side and flows back to the compressor 12 through the low-pressure section of the internal heat exchanger 20.

[0047] In AC operation, the heating branch 16.1 or the secondary line 16 is shut off by means of a shutoff valve (secondary line valve A3), so that hot refrigerant cannot flow through the heating regulator 26. In order to recover refrigerant from the inoperative heating branch 16.1, the shutoff member A5 designed as a shutoff valve can be opened, so that the refrigerant can flow in the direction of the collector 24 through the shutoff member A5 and the non-return valve R2 while the shutoff member A2 is closed.

[0048] In the heating operation of the refrigerant circuit 11 , the main line valve A4 is closed and the secondary line valve A3 is open, so that hot refrigerant can flow into the heating branch 16 . 1 .

[0049] In order to implement the heating function by means of the refrigerator 28 to realize the water heat pump operation, the refrigerant compressed by means of the refrigerant compressor 12 flows into the heating regulator 26 via the open stop valve (secondary pipeline valve A3). At the heating regulator 26, the heat is output to the supply air flow L introduced into the vehicle interior. The refrigerant then flows via the open stop valve A1 and the branch point Ab1. The refrigerant is decompressed into the refrigerator 28 by means of the expansion valve AE1 to absorb the waste heat of the electrical components and / or electronic components arranged in the refrigerant circulation circuit 28.2. In this heating function, the expansion valves AE3 and AE4 are closed, the stop valve A5 is closed, and the stop valve A2 is opened. Here, the refrigerant discharged through the stop valve A2 in the water heat pump operation can be sucked from the two-way refrigeration line 14.1 or the main line 14 and delivered to the collector 24 through the check valve R2.

[0050] An (indirect) delta connection can be achieved by the fact that when the shut-off valve A1 is open, the refrigerant compressed by the refrigerant compressor 12 is expanded by means of the expansion valve AE1 into the refrigerator 28, wherein at the same time no mass flow occurs on the refrigerant side, i.e. in the refrigerant circuit 28.2, i.e., for example, a fluid used as refrigerant, such as water or a water-glycol mixture, remains on the refrigerant side of the refrigerator 28 or the refrigerator 28 is not actively flowed through by the refrigerant. In this connection variant, the expansion valves AE2, AE3 and AE4 remain closed.

[0051] In order to implement the heating function by means of the air heat pump operation through the external heat exchanger 18 as a heat pump evaporator, the refrigerant compressed by means of the refrigerant compressor 12 flows into the heating regulator 26 via the open stop valve (secondary line valve A3) to output heat to the supply air flow L. Subsequently, via the open stop valve A1, the refrigerant is expanded into the external heat exchanger 18 by means of the expansion valve AE3 to absorb heat from the ambient air. The refrigerant then flows to the collector 24 via the heat pump return branch 15 and returns to the refrigerant compressor 12. A stop valve A2 is provided in the heat pump return branch 15, which is open during the air heat pump operation. The expansion valves AE1, AE2 and AE4 are kept closed here like the stop valve A5. When the air heat pump is in operation, ice may occur on the external heat exchanger 18, as has been described at the beginning.

[0052] Similar to the reheating operation, the possibility of combined operation of the water heat pump connection scheme and the air heat pump connection scheme is not further explored.

[0053] The following description of the method for defrosting the external heat exchanger 18 assumes that the refrigeration system is initially in air heat pump operation, as described above.

[0054] Method 500 is referenced below Figure 2Described as an example. When it is determined during the operation of the air heat pump according to the operating parameters of the refrigeration device 10 that the external heat exchanger 18 is at least partially frozen or begins to freeze, the method 500 for defrosting the external heat exchanger is started, which is illustrated by step S501. Possible operating parameters indicating (partial) freezing can be, for example, as follows:

[0055] The amount of air passing through the ambient heat exchanger as the air heat pump evaporator is reduced, and the pressure loss increases under constant fan control;

[0056] The compressor speed and the high pressure in the refrigeration circuit continue to decrease while the heating demand and the low pressure level remain constant.

[0057] If it is determined in method 500 that external heat exchanger 18 is at least partially frozen, secondary line valve A3 is closed according to step S502. Subsequently or substantially simultaneously, main line valve A4 is opened (S503) so that refrigerant flows directly from refrigerant compressor 12 to external heat exchanger 18.

[0058] According to step S504, the inlet-side pressure level of the refrigerant on the external heat exchanger 18 is adjusted to the following target pressure, which corresponds to the condensation temperature (Tkond) of the refrigerant in the following range:

[0059] 2℃≤Tkond≤20℃, especially 4℃≤Tkond≤10℃.

[0060] According to step S505, which can be performed, for example, before step S503 or S504 or substantially simultaneously or, if necessary (immediately) after step S503 or S504, the closing device 19 ( Figure 1 ). By closing the closing device 19, the external heat exchanger 18 is prevented from being passed through by the cooled ambient air.

[0061] According to step S506, it is checked whether the refrigerant temperature Tkm on the outlet side of the external heat exchanger 18 reaches the desired target temperature Tkms. Here, the target temperature Tkms is predetermined or determined to have a temperature greater than 0°C, in particular the target temperature Tkms can be selected to be substantially equal to the condensation temperature Tkond, i.e. in the range of 2°C to 20°C, in particular in the range of 4°C to 10°C. If the target temperature is not equal to the condensation temperature, the pressure level of the refrigerant is kept at the target pressure according to step S507 until the refrigerant temperature Tkm measured on the outlet side of the external heat exchanger 18 reaches the target temperature Tkms. If the target temperature Tkms is reached, it is checked according to step S508 whether the target temperature Tkms exists during a predetermined duration. This duration can be adjusted or selected, for example, from about 10 seconds to about 120 seconds.

[0062] In order to detect the refrigerant outlet temperature Tkm on the external heat exchanger 18, it is advantageous that the external heat exchanger has a temperature measuring position for detecting the medium temperature or surface temperature downstream so as to be able to feed back the corresponding required signal value. Figure 1 ) as a combined sensor for pressure and temperature signals or as a separate temperature sensor can achieve this purpose.

[0063] After reaching the desired refrigerant temperature Tkm, wherein Tkm is substantially the same as the target temperature Tk, the ventilation device may be activated according to step S509 in order to dry the external heat exchanger 18 , in particular to remove condensate present on the external heat exchanger 18 .

[0064] During the operation of the ventilation device (S509), it is checked whether the external heat exchanger 18 has been (sufficiently) dried, which is indicated in step S510 by using the term "normal". If the drying of the external heat exchanger 18 should be performed for a longer time, the pressure level of the refrigerant is adjusted or maintained according to step S511 so that the external heat exchanger 18 has an external surface temperature of 4° C. and greater. If the drying of the external heat exchanger 18 is completed, the method 500 for defrosting the external heat exchanger 18 can be ended (S512).

[0065] The target pressure is reached by adjusting the power consumption of the refrigerant compressor 12 and / or by adjusting the opening of the expansion valve AE1 assigned to the refrigerator 28 working as a water heat pump according to the inlet side pressure level set in S504. The target pressure can be provided via a combined sensor formed by the pressure and temperature signal pT1 or a separate pressure sensor.

[0066] In a supplementary embodiment of the air heat pump evaporator, instead of implementing direct evaporation (heat transfer from air to refrigerant), the air heat pump evaporator can also have indirect evaporation (heat transfer from air to an intermediate fluid and then from the intermediate fluid to the refrigerant). For this case, the method presented here is also applicable in principle. However, in this case, the environment-intermediate fluid-heat exchanger is defrosted. Accordingly, the pressure level and therefore also the temperature above the freezing point in the refrigerant are not regulated by the refrigeration circuit, but the intermediate medium temperature is known to be heated until the intermediate medium temperature has a temperature above 0°C from the inlet to the outlet of the environment-intermediate fluid-heat exchanger. Therefore, it can also be ensured that the frost layer on the environment-intermediate fluid-heat exchanger melts.

Claims

1. A method (500) for defrosting an external heat exchanger (18) of a refrigeration system (10) of a motor vehicle, the external heat exchanger being operated as an air heat pump evaporator, wherein: The refrigeration device (10) comprises: A refrigerant compressor (12), which is connected to the main line (14) and the secondary line (16), or which can be connected to the main line (14) and the secondary line (16); an external heat exchanger (18) arranged in the main line (14); an evaporator (22) arranged in the main line (14); a heating regulator (26) arranged in the secondary pipeline (16); a main line valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger (18), the main line valve being closed during operation of the air heat pump; A secondary pipeline valve (A3) arranged between the refrigerant compressor (12) and the heating regulator (26), the secondary pipeline valve being opened during operation of the air heat pump; Wherein, the method comprises the following steps: Closing the secondary pipeline valve (A3); Opening the main line valve (A4) so ​​that the refrigerant flows directly from the refrigerant compressor (12) to the external heat exchanger (18); The inlet-side pressure level of the refrigerant at the external heat exchanger (18) is adjusted to the following target pressure, which corresponds to the condensation temperature (Tkond) of the refrigerant in the following range: 2℃≤Tkond≤20℃, The pressure level on the inlet side is brought to a target pressure by regulating the power consumption of the refrigerant compressor (12) and / or by regulating the opening of an expansion valve (AE1) associated with a refrigerator (28) operating as a water heat pump.

2. The method (500) according to claim 1, characterized in that: The closing device (19) provided on the air side of the external heat exchanger (18) is closed.

3. The method (500) according to claim 1 or 2, characterized in that: The pressure level of the refrigerant is kept set to the target pressure until the refrigerant temperature (Tkm) measured at the outlet side of the external heat exchanger (18) is greater than 0°C for a predetermined duration.

4. The method (500) according to claim 3, characterized in that: After the desired refrigerant temperature (Tkm) is reached, the ventilation device is activated in order to dry the external heat exchanger (18).

5. The method (500) according to claim 4, characterized in that: During operation of the ventilation device, the pressure level of the refrigerant is adjusted or maintained so that the external surface temperature of the external heat exchanger (18) is 4°C or higher.

6. The method (500) according to claim 1, characterized in that: The inlet-side pressure level of the refrigerant at the external heat exchanger (18) is adjusted to a target pressure corresponding to the condensation temperature (Tkond) of the refrigerant within the following range: 4°C ≤ Tkond ≤ 10°C.

7. The method (500) according to claim 3, characterized in that: The pressure level of the refrigerant is kept set to the target pressure until the refrigerant temperature (Tkm) measured at the outlet side of the external heat exchanger (18) corresponds to the condensation temperature (Tkond) during a predetermined time period.

8. The method (500) according to claim 4, characterized in that: After reaching the desired refrigerant temperature (Tkm), the ventilation device is activated in order to remove the condensate present on the external heat exchanger (18).

9. A refrigeration device (10) for a motor vehicle having a heat pump function, the refrigeration device comprising: A refrigerant compressor (12), which is connected to the main line (14) and the secondary line (16), or which can be connected to the main line (14) and the secondary line (16); an external heat exchanger (18) which operates or can operate as an air heat pump and is arranged in the main line (14); an evaporator (22) arranged in the main line (14); a heating regulator (26) arranged in the secondary pipeline (16); a main line valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger (18); A secondary pipeline valve (A3) arranged between the refrigerant compressor (12) and the heating regulator; It is characterized in that A refrigeration device (10) is configured to be operated using a method (500) for defrosting an external heat exchanger according to any one of claims 1 to 8.

10. A motor vehicle having a refrigeration device (10) according to claim 9.

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