DE102020120687A1 - Post-heating method for operating a refrigeration system for a motor vehicle, refrigeration system and motor vehicle with such a refrigeration system - Google Patents

Abstract

A post-heating method (500) for operating a refrigeration system (10) with a heat pump function for a motor vehicle is described, the refrigeration system (10) comprising: a refrigerant compressor (12); a directly or indirectly acting external heat exchanger (18); a direct or indirect acting evaporator (22); a further heat exchanger (26) acting as a heat source, which is arranged in the secondary line (16); and at least one post-heating expansion valve (AE4), which is arranged between the further heat exchanger (26) and the external heat exchanger (18). The method comprises the following steps: operating the refrigeration system (10) with two pressure levels, with the post-heating expansion valve (AE4) being open (S501) and with between the further heat exchanger (26) and the post-heating expansion valve (AE4) and between the post-heating expansion valve (AE4) and the external heat exchanger (18) are essentially at the same pressure,determining (S503) a pressure difference value (dp) between a first pressure (p4) which is at the further heat exchanger, in particular the heating register (26), is applied, and a second pressure (p3), which is applied to the external heat exchanger (18), wherein while the refrigeration system (10) is being operated with two pressure layers, the post-heating expansion valve (AE4) is closed step by step or continuously (S505) until the Pressure difference value (dp) reaches or exceeds a pressure difference limit value (dplimit) (S504).

Description

The invention relates to a post-heating method (RH III) for operating a refrigeration system with a heat pump function for a motor vehicle, a refrigeration system and a motor vehicle with such a refrigeration system.

A refrigeration system with a heat pump function usually includes a refrigerant compressor which can be connected or is connected to a primary line and a secondary line; an outer heat exchanger arranged in the primary line; an evaporator arranged in the primary line; a heating register, which is arranged in the secondary line; at least one movable temperature flap, which is arranged in front of or behind the heating register in relation to a supply air flow direction; and at least one post-heating expansion valve, which is arranged between the heating register and the external heat exchanger in the secondary line.

Such a refrigeration system with a heat pump function is, for example, in DE 10 2018 213 232.1 described. Furthermore, in the DE 10 2019 133 488.8 described a post-heating process.

Further background information on refrigeration systems or heat pumps can be found in the publications, for example EP 0 989 003 A2 , DE 10 2006 002 233 A1 and DE 10 2016 005 782 B4 .

In a post-heating process, which is also referred to in technical jargon as reheat, reheat operation, reheat process, when air conditioning a vehicle interior, the air cooled and dehumidified by the evaporator is at least partially heated by means of the heating register or a heat exchanger acting as a heat source or brought to a desired outlet temperature using an alternative heating element.

The heat exchanger or the heating register is a heat source in which the heat stored in the refrigerant is given off to another medium, such as air, water, a water-glycol mixture and the like. The heating register can be designed as a heating condenser or heating gas cooler if an air flow as cabin supply air flows directly around it, but in particular flows through it, which absorbs the emitted heat. This (cabin supply) air flow can consist of fresh air, recirculated air or a partial recirculated air flow, i.e. any mixing ratio of fresh air and recirculated air components. The heating register can be designed as a fluid heat exchanger if a fluid other than air, such as water, a water-glycol mixture or the like, flows through or around it, with the heat stored in the refrigerant being released to the fluid. In the configuration as a fluid heat exchanger, there is then a further transfer of heat from the heated fluid to the air. In this respect, air is indirectly heated as the cabin supply air flow by a fluid heat exchanger.

At least one temperature flap can be used in the air flow path between the evaporator and the heating register (i.e. upstream of the heating register), which is completely closed (0% open position or closed position) if the air is to be cooled and not heated when it is fed into the vehicle interior. When the temperature damper is fully open (100% open), essentially all of the dehumidified airflow from the evaporator is directed across the heater coil and heated. When the temperature flap is partially opened, part of the air is routed over the heating register and the other part of the air is routed around the heating register and is not heated, so that a mixture of heated and cooled air is formed downstream of the heating register, which is then distributed to the vehicle interior is forwarded. Alternatively, the adjustable temperature flap can also be arranged downstream of the heating register.

In the post-heating process, as is the case, for example, in DE 10 2019 133 488.8 has been described, it has been shown that there is further potential for optimization in system operation in a motor vehicle. In particular, it has been shown that in the post-heating process, which is referred to here as Reheat III, there is a transition from a first operating state (Reheat IIIla), in which the heat output on the heating register is sufficient and the refrigeration system works at two pressure levels (high pressure and low pressure). , to a second operating state (Reheat Illb), in which the heating output is not sufficient, is very sluggish in providing further heating output.

The dimensioning of the flow cross section of the post-heating expansion valve requires a long passage in what is known as a dead band from a fully open valve cross section to an opening cross section that causes a throttling effect for the first time, with the throttling and thus the build-up of a third pressure layer (intermediate pressure) being greatly delayed. During the transition from the first operating state (reheat IIIa) to the second operating state (reheat IIIb) and vice versa, system disturbances are therefore evident due to pressure and temperature fluctuations, which is caused by the movement of temperature flaps or changes in the fan control.

The object on which the invention is based is seen as providing a post-heating process in which the above disadvantages can be avoided.

This object is achieved by a post-heating method with the features of claim 1, by a refrigeration system with the features of claim 9 and by a motor vehicle with the features of claim 10. Advantageous configurations with useful developments are specified in the dependent claims.

• einen Kältemittelverdichter, der mit einem Primärstrang und einem Sekundärstrang verbindbar oder verbunden ist;
• einen direkt oder indirekt wirkenden äußeren Wärmeübertrager, der im Primärstrang angeordnet ist;
• einen direkt oder indirekt wirkenden Verdampfer, der im Primärstrang angeordnet ist;
• einen weiteren als Wärmequelle wirkenden Wärmeübertrager, insbesondere ein Heizregister, der im Sekundärstrang angeordnet ist;
• wenigstens eine bewegliche Temperaturklappe, die bezogen auf eine Zuluftströmungsrichtung vor oder nach (stromaufwärts oder stromabwärts) dem weiteren Wärmeübertrager, insbesondere Heizregister, angeordnet ist;
• wenigstens ein Nachheiz-Expansionsventil, das zwischen dem weiteren Wärmeübertrager, insbesondere dem Heizregister, und dem äußeren Wärmeübertrager im Sekundärstrang angeordnet ist.

A post-heating method for operating a refrigeration system with a heat pump function for a motor vehicle is therefore proposed, the refrigeration system comprising:

• a refrigerant compressor which is connectable or connected to a primary line and a secondary line;
• a directly or indirectly acting external heat exchanger, which is arranged in the primary line;
• a directly or indirectly acting evaporator, which is arranged in the primary line;
• a further heat exchanger acting as a heat source, in particular a heating register, which is arranged in the secondary line;
• at least one movable temperature flap, which is arranged upstream or downstream (upstream or downstream) of the further heat exchanger, in particular a heating register, in relation to a supply air flow direction;
• at least one post-heating expansion valve, which is arranged between the further heat exchanger, in particular the heating register, and the outer heat exchanger in the secondary line.

It is provided that the post-heating process includes the following steps:

Operating the refrigeration system with two pressure levels, with an existing expansion element in the refrigeration system already being gradually or continuously closed, in particular being throttled, during the operation of the refrigeration system with two pressure levels.

A relevant expansion element can be throttled during a first operating state without leaving the first operating state, so that a switchover to a second operating state is prepared.

In the proposed method, an expansion element is therefore already closed or throttled during operation with two pressure positions. As a result, even in this operating state, preparations are made for a possible changeover to another operating state in which, for example, the heating output is no longer sufficient. In other words, a so-called dead band, in which, despite the closing or throttling of the expansion element, there is little or no change in the two pressure positions, based on the overall system, or in the one pressure position upstream and one downstream of the valve to be moved, related to a subsystem or system section, not only run through when switching to another operation, in particular for increasing heating output. In this way, passing through the dead band can be compensated for in terms of time, so that a third pressure position (intermediate pressure) can be set as quickly as possible if the expansion element is closed again.

Depending on the presence of corresponding expansion organs, this at least third pressure action can be formed or adjusted in the high-pressure side or in the low-pressure side or in both system sections.

• Betreiben der Kälteanlage mit zwei Drucklagen, wobei das Nachheiz-Expansionsventil geöffnet ist und wobei zwischen dem weiteren Wärmeübertrager, insbesondere dem Heizregister, und dem Nachheiz-Expansionsventil sowie zwischen dem Nachheiz-Expansionsventil und dem äußeren Wärmeübertrager im Wesentlichen der gleiche Druck vorliegt,
• Bestimmen eines Druckdifferenzwerts zwischen einem ersten Druck, der am weiteren Wärmeübertrager, insbesondere dem Heizregister, anliegt, und einem zweiten Druck, der am äußeren Wärmeübertrager anliegt,

wobei während des Betreibens der Kälteanlage mit zwei Drucklagen das Nachheiz-Expansionsventil solange schrittweise oder kontinuierlich geschlossen bzw. angedrosselt wird, bis der Druckdifferenzwert einen Druckdifferenzgrenzwert erreicht oder überschreitet.The post-heating process can further include the following steps:

• Operating the refrigeration system with two pressure levels, with the post-heating expansion valve being open and with essentially the same pressure being present between the further heat exchanger, in particular the heating register, and the post-heating expansion valve and between the post-heating expansion valve and the external heat exchanger,
• Determining a pressure differential value between a first pressure that is present at the further heat exchanger, in particular the heating register, and a second pressure that is present at the outer heat exchanger,

wherein during the operation of the refrigeration system with two pressure layers, the post-heating expansion valve is closed or throttled step by step or continuously until the pressure difference value reaches or exceeds a pressure difference limit value.

In the proposed post-heating method, the post-heating expansion valve is already closed or throttled during operation in which the heat output is sufficient. As a result, even in this operating state, preparations are made for a possible changeover to an operation in which the heat output is not more is sufficient. In other words, a so-called dead band, in which there is little or no change in the two pressure positions despite the closing or throttling of the post-heating expansion valve, is not only passed through when switching to operation for increasing heating output. In this way, passing through the dead band can be compensated for in terms of time, so that a third pressure level (intermediate pressure) can be set as quickly as possible if the post-heating expansion valve closes again.

In the post-heating process, the pressure difference limit value can be defined as a function of a measured outside temperature.

The pressure difference limit can be 0.5 bar to 5 bar, preferably 1 bar to 3 bar.

The pressure difference limit can be set for outside temperatures that are 10°C to 30°C, in particular 15°C to 25°C. It must be taken into account here that a post-heating process is usually used at such outside temperatures or such outside temperatures represent a condition for the refrigeration system to be operated at all in post-heating mode.

The post-heating expansion valve can be kept in a substantially constant position as long as the pressure difference value substantially corresponds to the pressure difference limit value.

Furthermore, the activation of the implementation and setting of the pressure difference limit value described can also be made dependent on the ambient temperature, i.e. the cross-section adaptation and thus the valve cross-section reduction only starts at a point in time that can be expected that a given reheating requirement can only be covered by building up the third Pressure position can be made possible. In particular, this can be the case in an ambient temperature range below, for example, 20°C. Above this temperature threshold, the cross section can remain unaffected.

If the "refrigeration system" system also recognizes that, in addition to the interior evaporator, another evaporator, such as a chiller as a heat exchanger for conditioning a cooling medium for a high-voltage component or similar, is active, which means that the refrigerant compressor requires a higher drive power due to the increased need for refrigerant mass flow and so that more heat is introduced into the refrigeration system, the temperature threshold value and thus the point in time for the elimination of the valve deadband can be further reduced or adjusted by an upstream cross-section adjustment.

A kind of preparatory (on-) throttling of the post-heating expansion valve is brought about by the method steps described above, which has little or no influence on the then running system operation with two pressure layers. As described above, the post-heating expansion valve is closed or throttled as long as the pressure difference value is below the pressure difference limit value. If the pressure difference value reaches or exceeds the pressure difference limit value, the post-heating expansion valve is opened again until the pressure difference limit value is fallen below again. For its part, the expansion valve regulates a pressure difference limit value that does not (yet) affect the overall system behavior and ensures that it remains set.

If the pressure difference value is in the range of the pressure difference limit value, a switchover hysteresis band can be provided or used to calm the system, so that the afterheating expansion valve is not switched over within the switchover hysteresis band or has to be corrected for every small change in the pressure difference value.

In the post-heating process, when the heating requirement increases, the post-heating expansion valve can be gradually throttled further, starting from its partially closed position, which has already been kept constant, until three pressure levels have formed in the refrigeration system, wherein there is a gap between the further heat exchanger, in particular the heating register, and the post-heating Expansion valve, a high-pressure layer is formed and a medium-pressure layer is formed between the post-heating expansion valve and the external heat exchanger.

After reaching a maximum pressure and/or a maximum temperature of the refrigerant, the gradual throttling of the post-heating expansion valve can be omitted and the temperature flap can be opened further starting from a target opening position, in particular up to a maximum opening position. As an alternative or in addition to opening the temperature flaps further, an electrical heating element can be switched on, which is provided downstream of the heating register, for example. In other words, the temperature flap can be maintained in an essentially constant desired opening position and additional heating capacity can be covered by integrating an additional electric heater and/or a chiller.

The target opening position of the temperature flap can be set to a value between 60% and 90%, in particular to a value between between 70% and 85%, based on a maximum opening position of 100%.

• einem Kältemittelverdichter, der mit einem Primärstrang und einem Sekundärstrang verbindbar oder verbunden ist;
• einem direkt oder indirekt wirkenden äußeren Wärmeübertrager, der im Primärstrang angeordnet ist;
• einem direkt oder indirekt wirkenden Verdampfer, der im Primärstrang angeordnet ist;
• einem weiteren als Wärmequelle wirkenden Wärmeübertrager, insbesondere einem Heizregister, der im Sekundärstrang angeordnet ist;
• wenigstens einer beweglichen Temperaturklappe, die bezogen auf eine Zuluftströmungsrichtung vor oder nach (stromaufwärts oder stromabwärts) dem weiteren Wärmeübertrager, insbesondere dem Heizregister, angeordnet ist;
• wenigstens einem Nachheiz-Expansionsventil, das zwischen dem weiteren Wärmeübertrager, insbesondere dem Heizregister, und dem äußeren Wärmeübertrager im Sekundärstrang angeordnet ist;
• wobei die Kälteanlage dazu eingerichtet ist, in einem Nachheizbetrieb, wie er oben beschrieben worden ist, betrieben zu werden, und
• wobei in einem solchen Nachheizbetrieb das Kältemittel ausgehend vom Kältemittelverdichter nacheinander die folgenden Komponenten der Kälteanlage durchströmt: weiterer Wärmeübertrager, insbesondere Heizregister, und Nachheiz-Expansionsventil im Sekundärstrang, äußerer Wärmeübertrager und Verdampfer im Primärstrang.

A refrigeration system with a heat pump function for a motor vehicle is also proposed

• a refrigerant compressor which can be connected or is connected to a primary line and a secondary line;
• a directly or indirectly acting external heat exchanger, which is arranged in the primary line;
• a directly or indirectly acting evaporator, which is arranged in the primary line;
• a further heat exchanger acting as a heat source, in particular a heating register, which is arranged in the secondary line;
• at least one movable temperature flap which is arranged upstream or downstream (upstream or downstream) of the further heat exchanger, in particular the heating register, in relation to a supply air flow direction;
• at least one post-heating expansion valve, which is arranged between the further heat exchanger, in particular the heating register, and the outer heat exchanger in the secondary line;
• wherein the refrigeration system is set up to be operated in a post-heating mode as described above, and
• in such a post-heating operation, the refrigerant flows through the following components of the refrigeration system in succession, starting from the refrigerant compressor: further heat exchanger, in particular heating register, and post-heating expansion valve in the secondary line, external heat exchanger and evaporator in the primary line.

Depending on the system topology, the external heat exchanger can have a monodirectional or bidirectional flow, depending on the design of the refrigeration system. In a monodirectional variant, the coolant always flows through the external heat exchanger in the same direction or in the same way during refrigeration system operation and in the air heat pump mode. In a bidirectional variant, the refrigerant flows through the external heat exchanger in refrigeration system operation in a different or different direction (opposite) than in air heat pump mode. With regard to the external heat exchanger, it should also be noted that - similar to the heating register - it can give off heat to the (ambient) air or absorb it both directly (as a condenser or gas cooler) and indirectly (as a fluid heat exchanger).

A motor vehicle can be equipped with such a refrigeration system. The motor vehicle can in particular be an electric vehicle. In an electric vehicle, the efficient operation of the refrigeration system can lead to electricity savings, so that a greater range of the electric vehicle can be achieved as a result.

The method described above in more detail for the post-heating expansion valve can also be used in an analogous manner for other expansion devices and thus also for system sections of a refrigeration system.

• 1 ein schematisches und vereinfachtes Schaltbild einer Kälteanlage für ein Kraftfahrzeug;
• 2 ein Flussdiagram einer beispielhaften Umsetzung des Nachheizverfahrens in einem ersten Betriebszustand, insbesondere mittels der in 1 beschriebenen Kälteanlage;
• 3 ein Flussdiagram einer beispielhaften Umsetzung des Nachheizverfahrens in einem zweiten Betriebszustand, der sich an den ersten Betriebszustand anschließen kann, insbesondere mittels der in 1 beschriebenen Kälteanlage;
• 4 ein Flussdiagram einer beispielhaften Umsetzung des Nachheizverfahrens in einem zweiten Betriebszustand, der sich an den ersten Betriebszustand anschließen kann, insbesondere mittels der in 1 beschriebenen Kälteanlage.

Further advantages and details of the invention result from the following description of embodiments with reference to the figures. It shows:

• 1 a schematic and simplified circuit diagram of a refrigeration system for a motor vehicle;
• 2 a flowchart of an exemplary implementation of the post-heating method in a first operating state, in particular by means of in 1 described refrigeration system;
• 3 a flowchart of an exemplary implementation of the post-heating method in a second operating state, which can follow the first operating state, in particular by means of in 1 described refrigeration system;
• 4 a flow chart of an exemplary implementation of the post-heating method in a second operating state, which can follow the first operating state, in particular by means of in 1 described refrigeration system.

In 1 an embodiment of a refrigeration system 10 for a motor vehicle is shown schematically and in simplified form. The refrigeration system 10 includes a refrigerant circuit 11, which can be operated both in a refrigeration system operation (also called AC operation for short) and in a heat pump mode. In the embodiment shown, the refrigeration system 10 comprises a refrigerant compressor 12, an external heat exchanger 18, an internal heat exchanger 20, an evaporator 22 and an accumulator or refrigerant collector 24. The external heat exchanger 18 can be designed as a condenser or gas cooler. In particular, the outer heat exchanger 18 in the illustrated embodiment is bidirectional flow bar.

The evaporator 22 is shown here by way of example as a front evaporator for a vehicle. the verse evaporator 22 is also representative of other evaporators possible in a vehicle, such as rear evaporators, which can be arranged parallel to one another in terms of flow. In other words, the refrigeration system 10 includes at least one evaporator 22.

A shut-off valve A4 is arranged downstream of the compressor 12 . An expansion valve AE2 is provided upstream of the evaporator 22 .

Within the scope of this description, the section from the compressor 12 to the outer heat exchanger 18, to the inner heat exchanger 20 and to the evaporator 22 is referred to as the primary line 14 in the entire refrigerant circuit 11 of the refrigeration system 10 .

The refrigeration system 10 further includes a heating register 26 (also referred to as a heating condenser or heating gas cooler). A shut-off valve A3 is arranged upstream of the heating register 26 . A shut-off valve A1 is arranged downstream of the heating register 26 . Furthermore, an expansion valve AE4 is arranged downstream of the heating register 26 .

Within the scope of this description, the section from the compressor 12 to the heating register 26, to the expansion valve AE4 and to a branch Ab2 is referred to as the secondary branch 16 in the entire refrigerant circuit of the refrigeration system 10 . The secondary branch 16 includes a heating branch 16.1, which extends from the shut-off valve A3 via the heating register 26 to the shut-off valve A1. The secondary line 16 also includes an after-heating branch or reheat branch 16.2, which can be fluidly connected to the heating register 26 upstream and to the external heat exchanger 5 downstream. The secondary line 16 or the reheat branch 16.2 opens into the primary line 14 at a branching point Ab2.

The refrigeration system 10 includes a further evaporator or chiller 28 . The chiller 28 is provided parallel to the evaporator 22 in terms of flow. The chiller 28 can be used, for example, to cool an electrical component of the vehicle, but also to implement a water heat pump function using the waste heat from at least one electrical component. An expansion valve AE1 is connected upstream of the chiller 28 .

The refrigeration system 10 can also have an electrical heating element 30 which is designed, for example, as a high-voltage PTC heating element. The electric heating element 30 is used as an additional heater for a supply air flow L guided into the vehicle interior. The electric heating element 30 can be accommodated in an air conditioning unit 32 together with the heating register 26 and the evaporator 22 . In this case, the electrical heating element 30 can be arranged downstream of the heating register 26 .

In the 1 check valves R1 and R2 are also visible. Furthermore, some sensors pT1 to pT5 for detecting the pressure and/or temperature of the refrigerant are also shown. It is pointed out that the number of sensors and their arrangement is only shown here as an example. A refrigeration system 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 just as conceivable that sensors that are separate from one another are used for measuring pressure or temperature and, if necessary, are also arranged spatially separately from one another along the refrigerant lines.

The refrigeration system 10 can be operated in different modes, which are briefly described below.

In AC operation of the refrigerant circuit 11, the refrigerant compressed to high pressure flows from the refrigerant compressor 12 when the shut-off valve A4 is open into the outer heat exchanger 18. From there it flows to the high-pressure section of the inner heat exchanger 20 and the fully open expansion valve AE3. The refrigerant can flow to the expansion valve AE2 and into the interior evaporator 22 via a branch point Ab1 (evaporator section 22.1). In parallel or alternatively, the refrigerant can flow into the chiller 28 (chiller section 28.1) via a branch point Ab4 and the expansion valve AE1. The refrigerant flows from the evaporator 22 and/or the chiller 28 on the low-pressure side into the collector 24 and through the low-pressure section of the internal heat exchanger 20 back to the compressor 12.

In AC operation, the heating branch 16.1 or the secondary line 16 is shut off by means of the shut-off valve A3, so that hot refrigerant cannot flow through the heating register 26. To retrieve refrigerant from the inactive heating branch 16.1, the shut-off element A5, which is designed as a shut-off valve, can be opened so that the refrigerant can flow in the direction of the collector 24 via the shut-off element A5 and the non-return valve R2, with the shut-off element A2 being closed at the same time.

In the heating mode of the refrigerant circuit 11, the shut-off valve A4 is closed and the shut-off valve A3 is opened, so that hot refrigerant can flow into the heating branch 16.1.

In order to carry out the heating function by means of the chiller 28 to implement water heat pump operation, the refrigerant compressed by means of the refrigerant compressor 12 flows into the heating register 26 via the open shut-off valve A3. At the heating register 26, heat is given off to a supply air flow L guided into the vehicle interior. The refrigerant then flows via the open shut-off valve A1 and the branch point Ab1. It is expanded by means of the expansion valve AE1 in the chiller 28 to absorb waste heat from the electrical and/or electronic components arranged in a coolant circuit 28.2. With this heating function, the expansion valves AE3 and AE4 are closed, the shut-off valve A5 is closed and the shut-off valve A2 is open. In this case, via the shut-off valve A2 during water heat pump operation, refrigerant that has been removed can be sucked out of a bidirectional branch 14.1 or the primary line 14 and fed to the collector 24 via the check valve R2.

In order to carry out the heating function by means of the external heat exchanger 18 as a heat pump evaporator, the refrigerant compressed by means of the refrigerant compressor 12 flows via the open shut-off valve A3 to release heat to a supply air flow L into the heating register 26. It is then discharged via the open shut-off valve A1 by means of the expansion valve AE3 in relaxes the outer heat exchanger 18 to absorb heat from the ambient air. The refrigerant then flows via a heat pump return branch 15 to the collector 24 and back to the refrigerant compressor 12. The expansion valves AE1, AE2 and AE4 remain closed, as does the shut-off valve A5.

An indirect delta connection can be implemented in that, when the shut-off valve A1 is open, the refrigerant compressed by the refrigerant compressor 12 is expanded into the chiller 28 by means of the expansion valve AE1, with no volume flow being generated at the same time on the coolant side, i.e. in the coolant circuit 28.2, i.e. the as Coolant fluid used, such as water or water-glycol mixture, remains on the coolant side of the chiller 28 or the chiller 28 is not actively flowed through by coolant. The expansion valves AE2, AE3 and AE4 remain closed with this switching variant.

In an after-heating or reheat operation, the supply air flow L fed into the vehicle interior is first cooled by means of the evaporator 22 and thus dehumidified. With the heat transferred to the refrigerant by evaporation and dehumidification and the heat supplied to the refrigerant via the compressor 12, the supply air flow L can be completely or at least partially reheated by means of the heating register 26.

For this purpose, the refrigeration system 10 , in particular the air conditioning unit 32 , has adjustable, in particular controllable and pivotable, temperature flaps 34 between the evaporator 22 and the heating register 26 . In the illustrated example, left and right temperature doors 34L and 34R (in 1 shown schematically) arranged. The temperature doors 34L, 34R can be adjusted or pivoted between an open position, referred to as the 100% position, and a closed position, referred to as the 0% position. Alternatively, it is also possible to connect the temperature flaps 34R, 34L downstream of the heating register 26.

In the 100% position, the entire supply air flow L flowing through the evaporator 22 is guided via the heating register 26 and heated before it can flow into the passenger compartment of the vehicle. In the 0% position, the entire supply air flow L flowing through the evaporator 22 flows in the bypass around the heating register 26 without heating and thus without absorbing heat into the passenger compartment.

In an x position of the temperature flaps 34L and 34R with 0%<x<100%, these temperature flaps are only partially open, so that only a partial air flow of the supply air flow L flowing through the evaporator 22 is routed via the heating register 26. This heated partial air flow can then be mixed with the remaining, cooled and dehumidified partial air flow. The intake air flow L heated in this way is supplied to the passenger compartment of the vehicle. By way of example, a 50% position indicates that the temperature flaps 34R and 34L are only half open, ie 50%.

Post-heating or reheating operation of the refrigerant circuit 11 or the refrigeration system 10 is carried out in different ways depending on the heat balance.

An operating method 500 that is possible for post-heating or reheat operation is described below using the flow charts in FIG 2 until 4 and with reference to the in 1 illustrated refrigeration system 10 and its components explained by way of example. Such an operating method is usually implemented as a control program in a control device for the refrigeration system or for the air conditioning in a vehicle.

A post-heating operation or method 500 (Reheat III) is considered, in which the refrigerant, starting from the compressor 12 via the geö Opened shut-off valve A3 flows to another heat exchanger acting as a heat source, in particular heating register 26 (heating condenser or heating gas cooler). Shut-off valve A1 is closed and the refrigerant flows via the fully open expansion valve AE4 (S501) to the external heat exchanger 18. The refrigerant then passes through the high-pressure side internal heat exchanger 20 and reaches the evaporator 22 via the opened expansion valve AE3 and the expansion valve AE2. From there, the refrigerant returns to the compressor 12 via the refrigerant collector 24 and the low-pressure-side section of the internal heat exchanger 20. In this post-heating process, the temperature flaps 34L, 34R are moves appropriate positions, which are identified below with "TK", where TK can assume a value of 0% (temperature flaps 34L, 34R closed) to 100% (temperature flaps 34L, 34R fully open).

The post-heating method 500 is considered here based on an (initially) sufficient heat output to cover a heating requirement. This operating state within the reheating process Reheat III is subsequently addressed as RH3a (Reheat IIIa) (S502).

In the post-heating method 500, a pressure difference dp is determined in a step S503. The pressure difference dp is calculated from the difference between the pressures p4 and p3, which are recorded at the sensors pT3 and pT4, for example. In other words, the pressures present at the further heat exchanger or heating register 26 and at the outer heat exchanger are recorded and their difference is determined. It is noted that in the 1 shown position of the sensors pT3 and pT4 is shown purely as an example. It is also pointed out that the relevant pressure values p4 and p3 could also be recorded by other sensors, which are shown in the representation of the 1 are not included.

In step S504 it is checked whether the pressure difference value dp is smaller than a pressure difference limit value dplimit defined by the system. As long as the pressure difference value dp is smaller than the pressure difference limit value, the post-heating expansion valve AE4 is closed step by step or continuously in step S505. The pressure difference dp is then recalculated again in order to be able to determine what influence the gradual or continuous closing of the post-heating expansion valve has on the pressure conditions or pressure levels prevailing in the system. Steps S503, S504 and S505 are usually run through several times.

According to steps S503, S540 and S505, the post-heating expansion valve AE4 is therefore already moved in the closed direction or throttled beforehand during operation in which the heating output is sufficient. As a result, even in this operating state RH3a, a preparation is made for a possible changeover to an operation (for example RH3b) in which the heating output is no longer sufficient. In other words, a so-called dead band, in which there is little or no change in the two pressure positions (high pressure and low pressure) despite the closing or throttling of the post-heating expansion valve AE4, is not only passed through when operation for increasing heating output is initiated is switched. In this way, passing through the dead band can be compensated for in terms of time, so that if the post-heating expansion valve AE4 closes again, a third pressure position (intermediate pressure) can be set as quickly as possible.

The pressure difference limit value dplimit can in particular be 0.5 bar to 5 bar, preferably 1 bar to 3 bar. The pressure difference limit value dplimit can be defined as a function of the outside temperature. For example, respective pressure difference limit values can be assigned to different outside temperatures. In particular, the pressure difference limit value dplimit can be specified for outside temperatures of 10°C to 30°C, in particular 15°C to 25°C. It must be taken into account here that a post-heating process is usually used at such outside temperatures or such outside temperatures represent a condition for the refrigeration system to be operated at all in post-heating mode.

A purely exemplary assignment of outside temperatures and pressure difference limit value can be provided or specified as follows. Outside temperature [°C] 15 20 25 dp limit [bar] 1 2 3

Depending on the refrigerant used and/or the system structure of the refrigeration system, the pressure difference limit value dplimit can also have other values that are assigned to other outside temperatures.

If step S504 is not fulfilled, in step S506 a check is made as to which open position TK the temperature flaps 34L, 34R are in. If these are opened up to 80%, it is checked in step S507 whether the opening position corresponds to a desired opening position TKsoll. If so, the post-heating expansion valve AE4 is essentially in a kon maintained or regulated constant position, which is illustrated by the two opposite arrows.

If the opening position TK does not correspond to the desired opening position TKsoll, a check is made in step S509 to determine whether the pressure difference value dp corresponds to the pressure difference limit value dplimit. If this is the case, a branch is made to step S508. If the condition in S509 is not met, in step S510 a check is made as to whether the post-heating expansion valve AE4 is already fully (100%) open. If this is not the case, the post-heating expansion valve AE4 is further opened stepwise or continuously according to step S511. If the condition in S510 is met, according to step S512, a different operating mode is switched to, which is referred to here as Reheat IV.

Switching to the Reheat IV operating mode occurs in particular in a situation when the hot gas temperature of the refrigerant at the heating register 26 should reach a critical value when the afterheating expansion valve AE4 is open. In Reheat IV, part of the refrigerant flow can be routed directly via the external heat exchanger 18 (gas cooler) by gradually opening the shut-off element A4, so that the heating register 26 is relieved.

If it is determined in step S506 that the temperature flaps 34L, 34R are open to 80% or more or there is a requirement to open them to such a degree, a transition to the operating mode Reheat IIIb (RH3b) takes place in step S513. The RH3b mode is used when the current heating output is no longer sufficient, i.e. the heating requirement has increased.

In this context, it must be taken into account that due to the loop of steps S503, S504, S505, which is run through several times in operating mode RH3a, the post-heating expansion valve AE4 is already throttled in such a way that further closing or throttling, which occurs in operating mode RH3b ( 3 and 4 ) is carried out, leads to a third pressure layer (intermediate pressure) at the outer heat exchanger 18 .

3 shows the sequence of operating method RH3b (S513) with the optional integration of an additional electric heater 30 ( 1 ), which itself is an optional component of the refrigeration system 10.

In the operating mode RH3b (S513), in step S520 a check is made as to which open position TK the temperature flaps 34L, 34R are in. If these are opened up to 80%, it is checked in step S521 whether the open position corresponds to a desired opening position TKsoll. If this is the case, the post-heating expansion valve AE4 is essentially maintained or regulated in a constant position according to step S522, which is illustrated by the two opposite arrows.

If the opening position TK does not correspond to the desired opening position TKsetpoint, in step S523 it is checked whether the optional additional heater 30 is switched on, in particular whether it is set to a heating level greater than zero. If the additional heater is not switched on, according to step S524 the post-heating expansion valve AE4 is opened step by step or continuously.

If it is determined in S520 that the temperature flaps 34L, 34R are more than 80% open or there is a corresponding system-side request to open them further, it is checked in step S525 whether the post-heating expansion valve AE4 is throttled to a minimum permissible open position . If this is not the case, according to step S526 the post-heating expansion valve AE4 can be closed or throttled further in steps or continuously down to a minimum permissible cross section.

Starting from steps S522, S524, S525 and S526, the (re)determination of the pressure difference value dp takes place in step S527. In step S528 it is checked whether the pressure difference value dp is less than or equal to the pressure difference limit value dplimit. If not, the operating procedure RH3b is retained and starts again at step S520. Otherwise, there is a transition from step S528 back to operating mode RH3a (S502; 2 )

If it is determined in S525 that the post-heating expansion valve AE4 is already set to its minimum permissible opening position, i.e. it is throttled to the maximum possible, further heating requirements can be covered by the optional electric auxiliary heater 30. In step S529, the electric auxiliary heater can then be increased by one level, for example, which is illustrated by the arrow pointing upwards. After that, the pressure check is carried out again according to steps S527 and S528.

If the additional heater 30 has been put into operation according to S529, the check according to S523 results in step S530 being run through, in which the additional heater 30 is switched down in particular in stages, which is illustrated by the arrow pointing downwards.

In the 3 Steps S520 to S522 and S525 to S528 shown by solid lines show the basic principle of how the post-heating expansion valve AE4 is positioned or adjusted in operating mode RH3b.

This basic principle is also from 4 can be seen in which the operating mode RH3b including the chiller 28 ( 1 ) and the upstream expansion valve AE1 ( 1 ) is shown. Integrating the chiller when there is an increased heating requirement is in 4 shown instead of using an optional electric auxiliary heater.

How to 3 already explained, in the operating mode RH3b (S513) in step S520 a check is made as to which open position TK the temperature flaps 34L, 34R are in. If these are opened up to 80%, it is checked in step S521 whether the open position corresponds to a desired opening position TKsoll. If this is the case, the post-heating expansion valve AE4 is essentially maintained or regulated in a constant position according to step S522, which is illustrated by the two opposite arrows.

If the opening position TK does not correspond to the desired opening position TKsetpoint, in step S540 it is checked whether the expansion valve AE1 connected upstream of the chiller 28 is already (partially) open or not closed. If the expansion valve AE1 is still closed (AE1=0), the post-heating expansion valve AE4 is opened step by step or continuously according to step S524.

If it is determined in S520 that the temperature flaps 34L, 34R are more than 80% open or there is a corresponding system-side request to open them further, it is checked in step S525 whether the post-heating expansion valve AE4 is throttled to a minimum open position. If this is not the case, according to step S526, the post-heating expansion valve AE4 can be further closed or throttled step by step or continuously.

Starting from steps S522, S524, S525 and S526, the (re)determination of the pressure difference value dp takes place in step S527. In step S528 it is checked whether the pressure difference value dp is less than or equal to the pressure difference limit value dplimit. If not, the operating procedure RH3b is retained and starts again at step S520. Otherwise, there is a transition from step S528 back to operating mode RH3a (S502; 2 )

If it is determined in S525 that the post-heating expansion valve AE4 is already set in its minimum open position, i.e. it is throttled to the maximum possible extent, further heating requirements can be covered by integrating the chiller 28 using the upstream expansion valve AE1. In step S541 it is then checked whether the expansion valve AE1 is in a maximum opening position. If this is not the case, step S542 the expansion valve AE1 can be opened stepwise or continuously, which is illustrated by the arrow pointing upwards. After that, the pressure check is carried out again according to steps S527 and S528. If the expansion valve AE1 has already reached its maximum possible opening position, the process branches directly to S527.

If the chiller 28 has been integrated via the expansion valve AE1 according to steps S541 and S542, the check according to S540 means that step S543 is run through, in which the expansion valve AE1 is gradually or continuously closed or throttled, which is determined by the arrow directed below.

The in the 3 and 4 The options shown for the RH3b operating mode can also be combined with one another, but this is not shown in detail. In particular, the method can be structured in such a way that the (optional) electric auxiliary heater 30 is activated after the additional heating capacity has been exhausted by means of the chiller 28/expansion valve AE1. For example, step S540 ( 4 ) the step S523 ( 3 ) follow or be integrated. Likewise, step S529 ( 3 ) to step S541 if the condition there is met.

By referring to the above 2 , 3 and 4 In the method steps described, a type of preparatory throttling of the post-heating expansion valve is thus effected (S503, S504, S505), which has little or no effect on the then running system operation with two pressure layers. As described above, the post-heating expansion valve is closed or throttled as long as the pressure difference value dp is below the pressure difference limit value dplimit (S504). If the pressure difference value reaches or exceeds the pressure difference limit value dplimit, the post-heating expansion valve AE4 is opened again (S511) until the pressure difference value falls below the limit value again.

If the pressure difference value dp is in the range of the pressure difference limit value dplimit, a switchover hysteresis band can be provided or used to calm the system, so that the post-heating expansion valve AE4 within the switchover hysteresis band is not or does not have to be switched over for every small change in the pressure difference value.

The method of valve pre-throttling described above can in principle be used at any point in a refrigeration system, possibly equipped with a heat pump function, where adjustable expansion devices are provided, which on the one hand have to convert a pressure-loss-free (i.e. unthrottled) flow and on the other hand a pressure-loss-prone (i.e. throttled) flow .

Another example is the evaporator 22, which can optionally be followed by an expansion valve, in order to achieve an evaporation temperature above the freezing point, particularly at ambient temperatures below 0°C in (partial) air recirculation mode, while downstream of the expansion element there are low pressures which in turn correspond to an evaporation temperature level below 0°C. In this case, it should be noted that pressure messages or measured variables that can be transferred to a pressure value are always available in the affected system sections.

In analogy to the method described above, other expansion elements can also be throttled during a first operating state without leaving the first operating state, but preparing for switching to a second operating state. This makes it possible to implement an actual switchover from a first to a second operating state quickly if required, because a relevant expansion element is or has already been set in a preparatory manner in the first operating state. In particular, the method can also be implemented for the expansion valve AE3.

This here with reference to the 2 until 4 The post-heating process RH3a or RH3b described can be carried out using a refrigeration system 10, as described in 1 has been described as an example, are implemented. A refrigeration system 10 can be used in a motor vehicle, which is not shown in detail here.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102018213232 [0003]
• DE 102019133488 [0003, 0008]
• EP 0989003 A2 [0004]
• DE 102006002233 A1 [0004]
• DE 102016005782 B4 [0004]

Claims (12)

Post-heating method (500) for operating a refrigeration system (10) with a heat pump function for a motor vehicle, the refrigeration system (10) comprising: a refrigerant compressor (12) with a primary line (14) and a secondary strand (16) connectable or connected; a directly or indirectly acting external heat exchanger (18), which is arranged in the primary line (14); a directly or indirectly acting evaporator (22) which is arranged in the primary line (14); a further heat exchanger acting as a heat source, in particular a heating register (26), which is arranged in the secondary line (16); at least one movable temperature flap (34L, 34R) which is arranged upstream or downstream of the further heat exchanger, in particular a heating register (26), in relation to a supply air flow direction (L); at least one post-heating expansion valve (AE4) between the further heat exchanger, in particular the heating register (26), and the outer heat exchanger (18) is arranged in the secondary line (16); wherein the post-heating process comprises the following steps: Operation of the refrigeration system (10) with two pressure levels, wherein during operation of the refrigeration system (10) with two pressure levels, an expansion element present in the refrigeration system is already gradually or continuously closed, in particular throttled. procedure after claim 1 , wherein a relevant expansion element is throttled during a first operating state without leaving the first operating state, so that a switch to a second operating state is prepared. procedure after claim 1 or 2 , wherein the post-heating expansion valve (AE4) is open (S501) and between the further heat exchanger, in particular the heating register (26), and the post-heating expansion valve (AE4) and between the post-heating expansion valve (AE4) and the external heat exchanger ( 18) essentially the same pressure is present, determining (S503) a pressure difference value (dp) between a first pressure (p4), which is present at the further heat exchanger, in particular the heating register (26), and a second pressure (p3), which is present at external heat exchanger (18), wherein while the refrigeration system (10) is being operated with two pressure layers, the post-heating expansion valve (AE4) is closed step by step or continuously (S505) until the pressure difference value (dp) reaches or exceeds a pressure difference limit value (dplimit). (S504). Post-heating process (500) after claim 3 , whereby the pressure difference limit value (dp) is defined as a function of a measured outside temperature. Post-heating process (500) after claim 4 , wherein the pressure difference limit value (dp) is 0.5 bar to 5 bar, preferably 1 bar to 3 bar, Post-heating process (500) after claim 4 or 5 , wherein the pressure difference limit value (dp) is established for outside temperatures which are 10°C to 30°C, in particular 15°C to 25°C. Post-heating method (500) according to one of claims 3 until 6 , wherein the post-heating expansion valve (AE4) is held in a substantially constant position (S508) as long as the pressure difference value (dp) substantially corresponds to the pressure difference limit value (dplimit) (S509). Post-heating process (500) after claim 7 , with an increasing heating requirement, the post-heating expansion valve (AE4), starting from its already constant, partially closed position, is gradually further throttled (S526) until three pressure layers have formed in the refrigeration system (10), with between the further heat exchanger, in particular the heating register (26) and the after-heating expansion valve (AE4), a high-pressure layer is formed, and between the after-heating expansion valve (AE4) and the external heat exchanger (18) a medium-pressure layer is formed. Post-heating process (500) after claim 8 , wherein after a maximum pressure and/or a maximum temperature of the refrigerant has been reached, the gradual throttling (S526) of the post-heating expansion valve (AE4) is omitted and the temperature flap (34L, 34R) is opened further starting from a target opening position (S524), in particular up to a maximum opening position, or the temperature flap (34L, 34R) is maintained in a substantially constant target opening position and additional heating capacity is covered by incorporating (S529) an electric auxiliary heater (30) and/or a chiller (28) (S542). will. Post-heating process (500) after claim 9 , wherein the target opening position of the temperature flap (34L, 34R) is set to a value between 60% and 90%, in particular to a value between 70% and 85%, based on a maximum opening position of 100%. Refrigeration system (10) with a heat pump function for a motor vehicle, with a refrigerant compressor (12) which can be connected or is connected to a primary line (14) and a secondary line (16); a directly or indirectly acting external heat exchanger (18) which is arranged in the primary line (14); a directly or indirectly acting evaporator (22) which is arranged in the primary line (14); a further heat exchanger acting as a heat source, in particular a heating register (26) which is arranged in the secondary line (16); at least one movable temperature flap (34L, 34R) which is arranged upstream or downstream of the further heat exchanger, in particular a heating register (26), in relation to a supply air flow direction (L); at least one post-heating expansion valve (AE4), which is arranged between the further heat exchanger, in particular a heating register (26), and the outer heat exchanger (18) in the secondary line (16); wherein the refrigeration system (10) is set up to be operated in a post-heating mode (500) according to one of the preceding claims, and wherein in such a post-heating mode (500) the refrigerant, starting from the refrigerant compressor (12), successively releases the following components of the refrigeration system (10) flows through: further heat exchanger, in particular heating register (26), and post-heating expansion valve (AE4) in the secondary line, external heat exchanger (18) and evaporator (22) in the primary line (14). Motor vehicle with a refrigeration system (10). claim 11 .

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