REFRIGERATION SYSTEM

Description

[0001] The invention relates to a refrigeration system, in particular a transport refrigeration system, comprising a refrigerant circuit, in particular operating with CO2 as the refrigerant, in which a total mass flow of the refrigerant is carried, a high-pressure-side heat exchanger arranged in the refrigerant circuit and cooling the high-pressure-compressed refrigerant, an expansion element arranged in the refrigerant circuit downstream of the high-pressure-side heat exchanger, which in the active state cools the total mass flow of the refrigerant by expansion and thereby generates a main mass flow of liquid refrigerant and an additional mass flow of gaseous refrigerant, which enter an intermediate pressure collector and are separated therein into the main mass flow and the additional mass flow, at least one cooling stage,which expands the main mass flow from the intermediate pressure collector to a low pressure in at least one cooling expansion device and thereby provides cooling capacity at a low-pressure-side heat exchanger, and a refrigerant compressor unit that compresses the main mass flow from low pressure to high pressure.

[0002] Such refrigeration systems are known from the prior art. Document WO 2013 / 091899 discloses a refrigeration system and a refrigerant compressor unit with the features of the preamble of independent claims 1 and 10, respectively.

[0003] The problem with these systems is to design the refrigeration system, especially for operation as a transport refrigeration system, in a way that is as simple and efficient as possible.

[0004] This problem is solved according to the invention in a refrigeration system of the type described above by the fact that the refrigerant compressor unit has a first compressor stage for compressing the refrigerant of the main mass flow supplied at low pressure to medium pressure and a second compressor stage for compressing the refrigerant of the main mass flow compressed at medium pressure to high pressure, and that the additional mass flow from the intermediate pressure collector enters the second compressor stage of the refrigerant compressor unit for compression to high pressure.

[0005] The solution according to the invention thus provides a simple way to operate a refrigeration system with a refrigerant compressor unit in which the main mass flow and the additional mass flow can be compressed to high pressure in an optimal manner.

[0006] In particular, the refrigeration system according to the invention makes it possible to use CO2 as a refrigerant and to operate the refrigeration system optimally.

[0007] In the solution according to the invention, it is particularly advantageous if the first compressor stage of the refrigerant compressor unit is connected to a medium-pressure-side heat exchanger, which cools the main mass flow compressed to medium pressure before it enters the second compressor stage.

[0008] This solution creates the possibility – especially when using CO2 as a refrigerant – to cool down the refrigerant, which is significantly heated during compression to medium pressure, before compression to high pressure takes place.

[0009] In principle, the medium-pressure side heat exchanger could be cooled by any medium.

[0010] For example, it would be conceivable to arrange the medium-pressure side heat exchanger in such a way that it is cooled by the refrigerant flowing to the refrigerant compressor unit at low pressure.

[0011] However, a particularly simple solution proposes that the medium-pressure side heat exchanger be an external heat exchanger located outside the refrigerant compressor unit.

[0012] This external heat exchanger can be cooled by various media. Using ambient air for cooling is particularly advantageous.

[0013] Regarding the expansion of the total mass flow through the expansion element following the high-pressure side heat exchanger, it was not specified to what pressure the expansion should take place; it is merely stipulated that the expansion element expands the pressure to an intermediate pressure.

[0014] One possibility is that the intermediate pressure is higher than the mean pressure and that the additional mass flow is expanded to mean pressure by an additional mass flow expansion device and enters the second compressor stage at mean pressure.

[0015] Another advantageous possibility is that the intermediate pressure essentially corresponds to the mean pressure, so that the total mass flow can be expanded to mean pressure by the expansion element following the first external heat exchanger.

[0016] No further details were given regarding the pressure levels at which the refrigeration system operates.

[0017] One advantageous solution is that, when using CO2 as a refrigerant, the low pressure is in the range of 1 bar to 60 bar.

[0018] Furthermore, it is preferably provided that when CO2 is used as a refrigerant, the mean pressure is in the range of 20 bar to 120 bar.

[0019] Furthermore, it is preferably provided that when CO2 is used as a refrigerant, the high pressure is in the range of 50 bar to 160 bar.

[0020] No further details have yet been provided regarding the design of the refrigerant compressor unit.

[0021] Thus, an advantageous solution according to the invention provides that the refrigerant compressor unit comprises a refrigerant compressor and an electric drive motor.

[0022] According to the invention, the additional mass flow is supplied to a motor compartment of the refrigerant compressor unit for cooling the electric drive motor before entering the second compressor unit.

[0023] It is particularly advantageous if the additional mass flow enters the second compressor stage after cooling the electric drive motor in the engine compartment.

[0024] Another advantageous solution provides that the main mass flow, compressed to medium pressure, enters the engine compartment for cooling the electric drive motor after cooling through the medium-pressure side heat exchanger and before entering the second compressor stage.

[0025] It has proven particularly advantageous if the main mass flow, compressed to medium pressure and cooled by the medium-pressure side heat exchanger, enters the second compressor stage after passing through the engine compartment.

[0026] Furthermore, according to the invention, a drive chamber of the refrigerant compressor, from which the compressor stages are driven, is kept at medium pressure.

[0027] This has the advantage that the pressure difference, especially in the second compressor stage, is kept to a maximum between medium pressure and high pressure, thus minimizing the mechanical stress on the individual components of the compressor stages.

[0028] According to the invention, the drive compartment is connected to the engine compartment via a connecting channel, or the refrigerant flows through the drive compartment after cooling the electric drive motor in the engine compartment.

[0029] One particularly advantageous solution provides that the refrigerant compressor unit is designed as a semi-hermetic compressor, with both the electric drive motor and the refrigerant compressor arranged in a single housing.

[0030] Furthermore, no further details were provided regarding the design of the refrigerant compressor itself.

[0031] One advantageous solution is to design the refrigerant compressor of the refrigerant compressor unit as a piston compressor, since the pressures specified for CO2 as a refrigerant can be achieved with reasonable mechanical effort, especially with such a piston compressor.

[0032] It is particularly advantageous if the piston compressor has several cylinder units, at least one of which forms the first compressor stage and at least one the second compressor stage.

[0033] It is particularly advantageous if the two compressor stages are designed such that the ratio of the displacement volume of the first compressor stage to the displacement volume of the second compressor stage is in the range of 1.5 / 1 to 2 / 1.

[0034] In particular, it is stipulated that at least two cylinder units form the first compressor stage.

[0035] Furthermore, it is preferably provided that the at least one second cylinder unit of the second compressor stage is arranged at an angular distance relative to the at least one cylinder unit of the first compressor stage with respect to a central axis of the drive shaft of the cylinder units, so that, for example, the cylinder units of the two compressor stages can be arranged in a V-shape or in opposite directions in order to achieve, in particular, an advantageous torque distribution.

[0036] Another advantageous solution involves arranging all cylinder units of the compressor stages in a row.

[0037] Furthermore, it is preferably provided that the housing of the refrigerant compressor and in particular the overall housing of the refrigerant compressor unit is made of aluminium.

[0038] A further advantageous development provides that the overall housing of the refrigerant compressor unit has a housing sleeve and bearing covers arranged on both sides of the housing sleeve, all of which are made of aluminium.

[0039] Furthermore, it is preferably provided that the housing has cylinder heads made of aluminium.

[0040] No further details have yet been provided regarding the arrangement of the various connections on the refrigerant compressor unit.

[0041] One advantageous solution involves arranging a high-pressure connection of the refrigerant compressor unit on a cylinder head of the second compressor stage.

[0042] Another advantageous solution provides that a low-pressure connection of the refrigerant compressor unit is located on a cylinder head of the first compressor stage.

[0043] Furthermore, it is advantageously provided that a medium-pressure outlet of the refrigerant compressor unit is arranged on a cylinder head of the first compressor stage.

[0044] Furthermore, it is expedient to provide that a medium-pressure inlet of the refrigerant compressor unit is located in the area of ​​a motor housing.

[0045] Furthermore, the invention relates to a refrigerant compressor unit, in particular for compressing CO2 as a refrigerant, comprising a refrigerant compressor and an electric drive motor, wherein the refrigerant compressor has a first compressor stage for compressing refrigerant supplied at low pressure, in particular CO2, to medium pressure and a second compressor stage for compressing the refrigerant compressed at medium pressure, in particular CO2, to high pressure, and wherein in particular the refrigerant compressor unit has a medium pressure outlet connected to the first compressor stage and a medium pressure inlet connected to the second compressor stage.

[0046] The advantage of this solution is that the refrigerant compressed to medium pressure can be routed out of the refrigerant compressor through the medium pressure outlet, where it can be cooled, for example, and then fed back into the refrigerant compressor unit via the medium pressure inlet.

[0047] Furthermore, it is also possible not only to connect the medium-pressure inlet to the medium-pressure outlet, but also to feed refrigerant accumulating in a refrigerant circuit, which is also at medium pressure, into the second compressor stage via the medium-pressure inlet and to compress it to high pressure in this stage.

[0048] The refrigerant compressor according to the invention can therefore be advantageously used in particular in a refrigerant circuit with expansion of the refrigerant to an intermediate pressure, in order to compress not only the refrigerant compressed to medium pressure in the first compressor stage, but also the refrigerant expanded to an intermediate pressure back to high pressure.

[0049] In the refrigerant compressor according to the invention, the medium-pressure inlet opens into a motor compartment of the electric drive motor for cooling the same, and the refrigerant enters the second compressor stage after flowing through the motor compartment.

[0050] This means that with such a refrigerant compressor unit, it is possible to use the refrigerant supplied via the medium pressure inlet to cool the drive motor before compression in the second compressor stage.

[0051] Furthermore, in a refrigerant compressor unit according to the invention, it is provided that a drive chamber of the refrigerant compressor, from which the compressor stages are driven, is kept at medium pressure.

[0052] Such a solution has the great advantage that the presence of intermediate pressure in the drive chamber reduces the mechanical stress on the components of the compressor stages, since there is only a pressure difference between intermediate pressure and high pressure or low pressure and intermediate pressure.

[0053] To achieve this, it is preferably provided that the drive compartment is connected to the engine compartment via a connecting channel.

[0054] The connecting channel can be designed in such a way that it merely leads to a pressure equalization between the drive compartment and the engine compartment, but the connecting channel can also be designed in such a way that the refrigerant flowing through the engine compartment is supplied to the second compressor stage through it.

[0055] One particularly advantageous solution provides that the refrigerant compressor unit is designed as a semi-hermetic compressor, with both the electric drive motor and the refrigerant compressor arranged in a single housing.

[0056] This solution has the advantage of being very compact on the one hand, and on the other hand, the advantage of allowing the refrigerant to be used to cool the electric drive motor in a simple way before being fed to the second compressor stage.

[0057] One particularly advantageous solution involves designing the refrigerant compressor as a piston compressor, since a piston compressor can achieve the pressure differences required, in particular, for compressing CO2 as a refrigerant with reasonable mechanical effort.

[0058] Preferably, the piston compressor is designed such that it has several cylinder units, at least one of which forms the first compressor stage and at least one of which forms the second compressor stage.

[0059] In principle, one cylinder unit would be sufficient for each compressor stage. However, to achieve a favorable distribution of the volumes to be compressed across the cylinder units, it has proven advantageous for at least two cylinder units to form the first compressor stage.

[0060] Furthermore, for design reasons, it has proven advantageous if the at least one cylinder unit of the second compressor stage is arranged at an angular distance relative to the at least one cylinder unit of the first compressor stage with respect to a central axis of the drive shaft of the cylinder units, in order to arrange either the respective cylinder units in a V-shape or in opposite directions to each other.

[0061] Another practical solution involves arranging the cylinder units of the compressor stages in a row, resulting in a very compact design.

[0062] In connection with the previous explanation of the structure of the refrigerant compressor unit according to the invention, no further details regarding the design of the housing were given.

[0063] It is preferably provided that the housing of the refrigerant compressor, in particular the housing of the refrigerant compressor unit, is made of aluminium.

[0064] Such a housing for the refrigerant compressor unit is, on the one hand, able to withstand the high pressures and thus has sufficient stability, and on the other hand, especially when used in a portable cooling unit, has the lowest possible mass.

[0065] Particularly in the case of an overall housing, it has proven advantageous if the overall housing of the refrigerant compressor unit has a housing sleeve and bearing covers arranged on both sides of the housing sleeve, all of which are made of aluminium.

[0066] Another advantageous embodiment provides that the housing has cylinder heads made of aluminium.

[0067] No further details have yet been provided regarding the various connections for high and low pressure.

[0068] One advantageous solution involves arranging a high-pressure connection of the refrigerant compressor unit on a cylinder head of the second compressor stage.

[0069] Another advantageous solution provides that a low-pressure connection of the refrigerant compressor unit is located on a cylinder head of the first compressor stage.

[0070] Another practical solution involves arranging a medium-pressure outlet of the refrigerant compressor unit on a cylinder head of the first compressor stage.

[0071] Furthermore, it is preferably provided that a medium-pressure inlet of the refrigerant compressor unit is arranged in the area of ​​a motor housing.

[0072] Furthermore, it is specifically stipulated that when CO2 is used as a refrigerant, the low pressure will be in the range of 1 bar to 60 bar.

[0073] Furthermore, it is advisable that the mean pressure is in the range of 20 bar to 120 bar when using CO2 as a refrigerant.

[0074] Finally, it is advantageous if, when using CO2 as a refrigerant, the high pressure is in the range of 50 bar to 160 bar.

[0075] Furthermore, it is preferably provided that such a refrigerant compressor unit is arranged in a refrigeration system according to the features described above.

[0076] The drawing shows: Fig. 1 a schematic representation of a cooling unit, in particular designed as a transport cooling unit, with a refrigeration system according to the invention; Fig. 2 a schematic representation of a first embodiment of a refrigeration system according to the invention; Fig. 3 a schematic enlarged representation of a refrigerant compressor unit for the first embodiment of the refrigeration system according to the invention; Fig. 4 a schematic representation of a second embodiment of a refrigeration system according to the invention; Fig. 5 an enlarged representation of the refrigerant compressor unit of the second embodiment of the refrigeration system according to the invention; and Fig. 6 a third embodiment of a refrigeration system according to the invention.

[0077] A cooling unit designated as a whole by 10 comprises a thermally insulated housing 12 which encloses an interior space 14 in which temperature-sensitive goods 16 or temperature-sensitive cargo 16 can be stored, wherein the temperature-sensitive goods 16 or the temperature-sensitive cargo 16 is surrounded by a gaseous medium 18, in particular air, which is kept at a defined temperature level in order to keep the temperature-sensitive cargo 16 or the temperature-sensitive goods 16 within a certain temperature range.

[0078] The cooling unit 10 is preferably designed as a transportable cooling unit, for example as a superstructure for a truck or a freight wagon or as a conventional transport container for transporting temperature-sensitive cargo 16 either by truck or rail or ship.

[0079] In order to maintain a defined or predetermined temperature range for the cargo 16, a circulation flow 22 of the gaseous medium 18 runs in the interior 14, wherein an inlet flow 26 enters the interior 14 from a temperature control unit 24, flows through it and enters the temperature control unit 24 again as an outlet flow 28.

[0080] The circulation flow 22 is generated by a blower unit 32, which is arranged in the temperature control unit 24 and is kept at the desired temperature by an internal heat exchanger 34, which is arranged in the temperature control unit 24.

[0081] Preferably, the inlet flow 26 exits the temperature control unit 24 in an area near a ceiling wall 36 of the insulated housing 12, and preferably the circulation flow 22 is returned to the temperature control unit 24 near a bottom wall 38 of the insulated housing 12, thereby forming the outlet flow 28 returning to the temperature control unit 24.

[0082] In particular, the temperature control unit 24 is arranged near the ceiling wall 36 of the insulated housing 12 and, for example, near a front wall 48 or near a rear wall 48 of the same.

[0083] A unit 52 comprising a refrigerant compressor unit 54 with a refrigerant compressor 56 and an electric drive motor 58 is preferably arranged near the temperature control unit 24 on the thermally insulated housing 12, wherein the unit 52 preferably also includes a first external heat exchanger 62 and an external fan unit 64, which for example generates an airflow 66 from ambient air that passes through the first external heat exchanger 62.

[0084] As in Fig. 2 As shown, the refrigerant compressor unit 54, the internal heat exchanger 34 and the first external heat exchanger 62 are arranged in a refrigerant circuit designated as a whole by 70 of a refrigeration system 60 integrated into the cooling unit.

[0085] The refrigerant circuit 70 is connected to a high-pressure connection 72 of the refrigerant compressor unit 54, from which a supply line 74 leads to the first external heat exchanger 62, which cools a total mass flow G of refrigerant compressed to high pressure PH by the refrigerant compressor 54, in this case in particular CO2, wherein the refrigerant is in a transcritical state in the case of CO2.

[0086] The cooling of the refrigerant in the first external high-pressure side heat exchanger unit 62 can take place either through ambient air or through contact with a heat-absorbing medium of any kind, for example cooling water.

[0087] The total mass flow G supplied to the refrigerant circuit 70 at the high-pressure port 72 of the refrigerant compressor unit 54 flows through an expansion element 76 arranged in the refrigerant circuit 70 after the external heat exchanger 62, in the case of CO 2 in a transcritical state. This element expands the refrigerant to an intermediate pressure PZ and then enters an intermediate pressure collector 82, in which the total mass flow G, cooled by expansion, splits into a main mass flow H of liquid refrigerant, which settles as a liquid refrigerant bath 84 in the intermediate pressure collector 82, and an additional mass flow Z, which forms a gas bubble 86 above the liquid bath 84.

[0088] The main mass flow H of liquid refrigerant is supplied from the intermediate pressure collector 82 to a cooling stage 92, which has a cooling expansion element 94 that cools the main mass flow H by expansion to low pressure PN and from which the main mass flow H enters the internal low-pressure side heat exchanger 34, in which it is able to extract heat from the circulation flow 22 in the interior 18 of the cooling unit 10 by providing cooling capacity.

[0089] The main mass flow H, heated in the heat exchanger 34, then enters the refrigerant compressor unit 54 at low pressure PN via a low-pressure connection 102.

[0090] The refrigerant compressor 56 of the refrigerant compressor unit 54 is, as in Fig. 2 and Fig. 3 The compressor is designed as a reciprocating compressor and preferably comprises a first compressor stage 112, formed by two cylinder units 114a and 114b, each driven by a cylinder drive 115a, 115b, in particular an eccentric drive, each of which draws in the refrigerant of the main mass flow H from an inlet chamber 116a, 116b and discharges, for example, into a common outlet chamber 118. The first compressor stage 112 compresses the refrigerant supplied to it at low pressure, for example, at values ​​from 1 bar to 60 bar, from the main mass flow H to a medium pressure PM, which is, for example, in the range of 20 bar to 120 bar.

[0091] From a medium-pressure outlet 122 of the common outlet chamber 118, the main mass flow H, compressed to medium pressure PM, is then supplied to a second external medium-pressure-side heat exchanger 124, which is also arranged, for example, in the aggregate unit 52 and is also, for example, through which the external air flow 66 flows.

[0092] The second external medium-pressure side heat exchanger 124 makes it possible to cool the refrigerant of the main mass flow H, which is compressed to medium pressure PM, back down to a temperature close to the ambient temperature and to extract a significant portion of the heat supplied during compression.

[0093] From the second external medium-pressure side heat exchanger 124, the cooled and medium-pressure PM-compressed refrigerant of the main mass flow H is supplied via a medium-pressure supply line 126 to a medium-pressure inlet 128 of the refrigerant compressor unit 54, wherein the medium-pressure inlet 128 is arranged on a motor housing 132 of the refrigerant compressor unit 54.

[0094] Furthermore, the medium pressure supply line 126 is also connected to the gas bladder 86 of the intermediate pressure collector 82, so that the additional mass flow Z from the intermediate pressure collector 82 is also supplied to the medium pressure connection 128 of the refrigerant compressor unit 54 via the medium pressure supply line 126 and the medium pressure PM is adjusted so that it corresponds to the intermediate pressure PZ.

[0095] The medium-pressure inlet 128 is preferably arranged on the motor housing 132 such that the incoming refrigerant enters a motor compartment 134, passes through the motor compartment 134 while cooling the electric drive motor 58, in particular a rotor 136 and a stator 138 thereof, and then enters a second compressor stage 142 of the refrigerant compressor unit 54.

[0096] The second compressor stage 142 also comprises two cylinder units 144a and 144b, each driven by a cylinder drive 145a, 145b, in particular an eccentric drive, wherein the refrigerant compressed to medium pressure PM and supplied to the second compressor stage 142 enters the cylinder units 144a and 144b via inlet chambers 146a and 146b, is compressed in them and then exits into an outlet chamber 148 which is connected to the high-pressure port 72.

[0097] In the first embodiment of the reciprocating compressor 54 according to the invention, the cylinder units 114a and 114b of the first compressor stage 112 and the cylinder units 144a and 144b of the second compressor stage 142 are driven via a common drive shaft 152, in particular an eccentric shaft, which acts on the respective cylinder drives 115a, 115b and 145a, 145b respectively, and which is preferably coaxially and in particular integrally connected to a rotor shaft 154 of the rotor 136 and forms a total drive shaft 188 with it.

[0098] Furthermore, in the first embodiment of the refrigerant compressor unit 54, the cylinder drive chamber 156, which accommodates the drive shaft 152 and the cylinder drives 115a, 115b, 145a, 145b and is adjacent to the cylinder units 114a and 114b or 144a and 144b respectively, is connected to or merges into the engine chamber 134, so that the cylinder drive chamber 156 is at medium pressure.

[0099] This has the advantage that, particularly in the second compressor stage 142, in the cylinder units 144a and 144b, only pressure differences between medium pressure and high pressure occur, and therefore the load on cylinder drives 145a and 145b for the cylinder units 144a, 144b is lower than in the case of low pressure in the cylinder drive chamber 156.

[0100] Likewise, the load on the cylinder units 144a and 144b themselves, in particular on their pistons, is lower than in the case of low pressure in the cylinder drive chamber 156.

[0101] As in Fig. 3 As shown, in the first embodiment of the refrigerant compressor unit 54 according to the invention, this unit is designed as a semi-hermetic compressor, in which the refrigerant compressor 56 and the electric drive motor 58 are arranged in a complete housing 130, which comprises a housing sleeve 162, bearing caps 164 and 166 arranged on both sides of the housing sleeve 162, and bearing receptacles 174 and 176 formed on the bearing caps 164 and 166, which are made of aluminium, wherein rolling bearings 184 and 186 are arranged in the bearing receptacles 174 and 176, which in this case support a complete drive shaft 188, comprising the drive shaft 152 and the rotor shaft 154.

[0102] Furthermore, cylinder heads 192 and 194, which are also made of aluminium, are arranged on the housing sleeve 162, wherein the cylinder head 192 is assigned to the cylinder units 114a and 114b and has the low-pressure port 102, which is connected to the inlet chambers 116a and 116b, as well as the exhaust chamber 118, which is connected to the medium-pressure outlet 122.

[0103] The cylinder head 194 is associated with the cylinder units 144a and 144b, with the intake chambers 146a and 146b being connected to the engine compartment 134 and / or the cylinder drive compartment 156 and the exhaust chamber 148 being connected to the high-pressure port 72.

[0104] Preferably, in the first embodiment of the refrigerant compressor unit 54 according to the invention, this is arranged as a vertical compressor, i.e., that a central axis 202 of the overall drive shaft 188 runs essentially vertically, i.e., deviates from a vertical by a maximum of ± 30°.

[0105] For the purpose of conveying lubricant into the cylinder drive chamber 156, in particular to the cylinder drives 115a, 115b, 145a, 145b, for example a conveying channel 204 running obliquely to its central axis 202 is provided in the overall drive shaft 188, which conveys lubricant from a lubricant sump 206 formed above the lowest cover 166 in the direction of gravity into the cylinder drive chamber 156 due to the centrifugal force acting in the conveying channel.

[0106] Alternatively, a lubricant pump unit driven by the electric drive motor 58 is provided for conveying the lubricant into the cylinder drive chamber 156.

[0107] Furthermore, a converter 212 is provided for controlling the electric drive motor 58, which is preferably also arranged in the aggregate unit 52.

[0108] With this inverter, the electric drive motor 58 can be controlled in speed-controlled mode, and thus the cooling capacity of the refrigerant compressor unit 54 can also be continuously controlled within a specified power range.

[0109] In a second embodiment of a refrigeration system 60' according to the invention, shown in Fig. 4 and Fig. 5 Those elements that are identical to those of the first embodiment are provided with the same reference numerals, so that with regard to their description reference can be made in full to the explanations of the first embodiment.

[0110] In contrast to the first embodiment, the refrigerant compressor unit 54' is provided with a refrigerant compressor 56', which comprises two cylinder units 114a and 114b to form the first compressor stage 112, but only one cylinder unit 144 to form the second compressor stage 142, wherein all cylinder units 114a, 114b and 144 are driven by the common drive shaft 152.

[0111] The ratio of the displacement volume of the first compressor stage 112 to the displacement volume of the second compressor stage 142 is approximately in the range of 1.5 / 1 to 2 / 1.

[0112] In principle, it would be possible to arrange the cylinder units 114a, 114b and 144 at an angular distance with respect to the central axis 202 of the drive shaft 152.

[0113] However, a particularly advantageous solution provides that the cylinder units 114a, 114b and 144 are arranged in a row.

[0114] Furthermore, preferably the cylinder head 192 assigned to the first compressor stage 112 and the cylinder head 194 assigned to the second compressor stage 142 are combined to form a total cylinder head 222, in which the low-pressure port 102, the medium-pressure outlet 122 and the high-pressure port 72 are provided, while the medium-pressure inlet 128 is provided on the motor housing 132, for example on a side of the electric drive motor 58 opposite the cylinder drive chamber 156.

[0115] Preferably in the second embodiment of the refrigerant compressor unit 54', the overall drive shaft 188 is arranged such that its central axis 202 runs essentially horizontally, i.e., for example, deviates from an exactly horizontal orientation by a maximum of ± 30°, wherein a lubricant sump 206' is formed, in particular in the lowest area in the direction of gravity of the cylinder drive chamber 156, from which lubrication of the cylinder drives 115a, 115b, 145 takes place.

[0116] In a third embodiment of a refrigeration system according to the invention, shown in Fig. 6In the second embodiment, a valve 232 is provided in the intermediate pressure supply line 126 leading away from the intermediate pressure collector and to the intermediate pressure inlet 128. This valve is arranged in particular between the intermediate pressure collector 82 and an inlet of an intermediate pressure line 125 leading from the second external heat exchanger 124 to the intermediate pressure supply line 126, and thus enables the setting of an intermediate pressure PZ in the intermediate pressure collector 82 such that this intermediate pressure does not necessarily have to be identical to the intermediate pressure PM, but it is possible to keep the intermediate pressure PZ higher than the intermediate pressure PM.

[0117] If the valve 232 is designed as an expansion valve, it is possible to further cool the additional mass flow during the expansion of the additional mass flow through the expansion valve 232, resulting in an improved cooling effect when cooling the electric drive motor 58.

[0118] Furthermore, in the third embodiment, those elements that are identical to those of the preceding embodiments are also provided with the same reference numerals, so that reference is made to the explanations of the preceding embodiments.

Claims

1. A refrigeration system (60), in particular a transport refrigeration system, comprising a refrigerant circuit (70), in particular one working with CO2 as refrigerant, in which there is guided a total mass flow (G) of the refrigerant, a high-pressure side heat exchanger (62) arranged in the refrigerant circuit (70) and cooling refrigerant compressed to a high pressure (PH), an expansion element (76) arranged following the high-pressure side heat exchanger (62) in the refrigerant circuit (70), the expansion element, in the active state, cooling the total mass flow (G) of the refrigerant by expansion and thereby producing a main mass flow (H) of liquid refrigerant and an auxiliary mass flow (Z) of gaseous refrigerant, which enter an intermediate-pressure collector (82) and are separated therein into the main mass flow (H) and the auxiliary mass flow (Z), at least one cooling stage (92), which expands the main mass flow (H) from the intermediate-pressure collector in at least one cooling expansion element (94) to a low pressure (PN) and thereby provides refrigerating capacity at a low-pressure side heat exchanger (34), and a refrigerant compressor unit (54) compressing the main mass flow (H) from low pressure (PN) to high pressure (PH), wherein the refrigerant compressor unit (54) has a first compressor stage (112) for compressing the refrigerant of the main mass flow (H) guided at low pressure (PN) to medium pressure (PM) and a second compressor stage (142) for compressing the refrigerant of the main mass flow (H) compressed to medium pressure (PM) to high pressure (PH), in that the auxiliary mass flow (Z) from the intermediate-pressure collector (82) enters the second compressor stage (142) of the refrigerant compressor unit (54) for compression to high pressure (PH), characterised in that the refrigerant compressor unit (54) has a refrigerant compressor (56) and an electric drive motor (58) and in that the auxiliary mass flow (Z) before the entry into the second compressor unit (142) enters a motor chamber (134) of the refrigerant compressor unit (54) for cooling the electric drive motor (58), in that a drive chamber (156) of the refrigerant compressor (56), from which chamber a drive of the compressor stages (112, 142) is produced, is held at medium pressure (PM) and in that the drive chamber (156) is in connection with the motor chamber (134) via a connecting duct or in that the refrigerant, after cooling of the electric drive motor (58), flows through the drive chamber (156).

2. A refrigeration system according to claim 1, characterised in that the first compressor stage (112) of the refrigerant compressor unit (54) is connected to a medium-pressure side heat exchanger (124), which cools the main mass flow (H) compressed to medium pressure (PM) before it enters the second compressor stage (142).

3. A refrigeration system according to claim 2, characterised in that the medium-pressure side heat exchanger is an external heat exchanger (124) arranged outside the refrigerant compressor unit (54).

4. A refrigeration system according to any of the preceding claims, characterised in that the expansion element (76) expands the total mass flow (G) to an intermediate pressure (PZ), in that in particular the intermediate pressure (PZ) is higher than the medium pressure (PM) and in that the auxiliary mass flow (Z) is expanded to medium pressure (PM) by an additional mass flow expansion element (232) and enters the second compressor stage (142) at medium pressure (PM), or in that in particular the intermediate pressure (PZ) substantially corresponds to the medium pressure (PM), in that in particular with CO2 as refrigerant the low pressure (PN) lies at values in the range of 1 bar to 60 bar and / or in that in particular with CO2 as refrigerant the medium pressure (PM) lies in the range of 20 bar to 120 bar and / or in that in particular with CO2 as refrigerant the high pressure (PH) lies at values in the range of 50 bar to 160 bar.

5. A refrigeration system according to any of the preceding claims, characterised in that the auxiliary mass flow (Z) after cooling of the electric drive motor (58) in the motor chamber (134) enters the second compressor stage (142).

6. A refrigeration system according to any of the preceding claims, characterised in that the main mass flow (H) compressed to medium pressure (PM) after the cooling by the second heat exchanger (124) and before the entry into the second compressor stage (142) enters the motor chamber (134) for cooling the electric drive motor (58).

7. A refrigeration system according to claim 6, characterised in that the main mass flow (H) compressed to medium pressure (PM) and cooled in the second heat exchanger (124) enters the second compressor stage (142) after flowing through the motor chamber (134).

8. A refrigeration system according to any of the preceding claims, characterised in that< / b> the refrigerant compressor unit (54) is configured as a semi-hermetic compressor, wherein in an overall housing (130) thereof there are arranged both the electric drive motor (58) and the refrigerant compressor (56), in that in particular the refrigerant compressor (56) of the refrigerant compressor unit (54) is configured as a piston compressor, in that in particular the piston compressor comprises a plurality of cylinder units (114a, 114b, 144a, 144b), of which at least one (114a, 114b) forms the first compressor stage (112) at least one (144a, 144b) forms the second compressor stage (142), in that in particular at least two cylinder units (114a, 114b) form the first compressor stage (112), in that in particular the at least one cylinder unit (144a, 144b) of the second compressor stage (142) is arranged at an angular spacing relative to the at least one cylinder unit (114a, 114b) of the first compressor stage (112) in relation to a central axis (202) of a drive shaft (152) of the cylinder units (114a, 114b, 144a, 144b), or in that in particular all cylinder units (114, 144) of the compressor stages (112, 142) are arranged in a row, in that in particular the housing (130) of the refrigerant compressor (56) is constructed of aluminium, in that in particular the overall housing (130) of the refrigerant compressor unit (54) has a housing sleeve (162) and bearing covers (164, 166) arranged on both sides of the housing sleeve (162), which are all constructed of aluminium, in that in particular the housing (132) has cylinder heads (192, 194), which are constructed of aluminium.

9. A refrigeration system according to any preceding claim, characterised in that in particular a high-pressure connection (72) of the refrigerant compressor unit (54) is arranged at a cylinder head (194) of the second compressor stage (142), in that in particular a low-pressure connection (102) of the refrigerant compressor unit (54) is arranged at a cylinder head (192) of the first compressor stage (112), in that in particular a medium-pressure connection (122) of the refrigerant compressor unit (54) is arranged at a cylinder head (192) of the first compressor stage (112), in that in particular a medium-pressure inlet (128) of the refrigerant compressor unit (54) is arranged in the region of a motor housing (132).

10. A refrigerant compressor unit (54), comprising a refrigerant compressor (56) and an electric drive motor (58), wherein the refrigerant compressor (56) comprises a first compressor stage (112) for compressing refrigerant guided at low pressure (PN), in particular CO2, to medium pressure (PM) and a second compressor stage (142) for compressing the refrigerant compressed to medium pressure (PM), in particular CO2, to high pressure (PH), and wherein in particular the refrigerant compressor unit (54) comprises a medium-pressure outlet (122) connected to the first compressor stage (112) and a medium-pressure inlet (128) in connection with the second compressor stage (142), characterised in that the medium-pressure inlet (128) opens into a motor chamber (134) of the electric drive motor (58) for cooling, and the refrigerant compressed to medium pressure after flowing through the motor chamber (134) enters the second compressor stage (142), and in that a drive chamber (156) of the refrigerant compressor (56) from which there is produced a drive of the compressor stages (112, 142), is held at medium pressure (PM).

11. A refrigerant compressor unit according to claim 10, characterised in that the drive chamber (156) is in connection with the motor chamber (134) via a connecting duct.

12. A refrigerant compressor unit according to claim 10 or 11, characterised in that< / b> the refrigerant compressor unit (54) is constructed as a semi-hermetic compressor, wherein in an overall housing (130) thereof there are arranged both the electric drive motor (58) and the refrigerant compressor (56), in that in particular the refrigerant compressor (56) is configured as a piston compressor, in that in particular the piston compressor comprises a plurality of cylinder units (114a, 114b, 144a, 144b), of which at least one (114a, 114b) forms the first compressor stage (112) and at least one (144a, 144b) forms the second compressor stage (142), in that in particular at least two cylinder units (114a, 114b) form the first compressor stage (112), in that in particular the at least one cylinder unit (144a, 144b) of the second compressor stage (142) is arranged at an angular spacing relative to the at least one cylinder unit (114a, 114b) of the first compressor stage (112) in relation to a central axis (202) of a drive shaft (152) of the cylinder units (114a, 114b, 144a, 144b), or in particular in that all cylinder units (114, 144) of the compressor stages (112, 142) are arranged in a row, in that in particular the housing (130) of the refrigerant compressor (56) is constructed of aluminium, in that in particular the overall housing (130) comprises a housing sleeve (162) and bearing covers (164, 166) arranged on both sides of the housing sleeve (162), which are all constructed of aluminium, in that in particular the housing (132) has cylinder heads (192, 194) which are constructed of aluminium.

13. A refrigerant compressor unit according to any of claims 10 to 12, characterised in that in particular a high-pressure connection (72) of the refrigerant compressor unit (54) is arranged at a cylinder head (194) of the second compressor stage (142), in that in particular a low-pressure connection (102) of the refrigerant compressor unit (54) is arranged at a cylinder head (192) of the first compressor stage (112), in that particular a medium-pressure outlet (122) of the refrigerant compressor unit (54) is arranged at a cylinder head (192) of the first compressor stage (112).

14. A refrigerant compressor unit according to any of claims 10 to 13, characterised in that a medium-pressure inlet (128) of the refrigerant compressor unit (54) is arranged in the region of a motor housing (132).

15. A refrigerant compressor unit according to any of claims 10 to 14, characterised in that in particular with CO2 as refrigerant the low pressure (PN) has values in the range of 1 bar to 60 bar, in that in particular with CO2 as refrigerant the medium pressure (PM) lies in the range of 20 bar to 120 bar, in that in particular with CO2 as refrigerant the high pressure (PH) has values in the range of 50 bar to 160 bar.