Abstract:
For creating a storage unit comprising a container housing enclosing a storage volume for receiving freight and a gaseous medium surrounding said freight, said storage unit further comprising a tempering system provided with a tempering unit associated with said storage volume for maintaining a flow of said gaseous medium circulating in said storage volume and passing through said tempering unit in order to be maintained at a defined or set temperature, said tempering unit comprising an internal heat exchanger arranged in said flow of gaseous medium passing through said tempering unit, said tempering system being provided with a refrigerant circuit comprising said internal heat exchanger, an external heat exchanger exposed to ambient air surrounding said container housing which operates reliably and cost efficient under the aforementioned condition, as well as a compressor unit for compressing refrigerant, and said tempering system being further provided with an engine for driving said compressor unit in an independent power source mode and said tempering system being further provided with an electric motor/generator unit mechanically coupled to said compressor unit, and said compressor unit and said motor/generator unit being commonly driven by said engine in said independent power source mode.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application is a continuation of International application number PCT/EP2014/070062 filed on Sep. 19, 2014. 
         [0002]    This patent application claims the benefit of International application No. PCT/EP2014/070062 of Sep. 19, 2014 the teachings and disclosure of which are hereby incorporated in their entirety by reference thereto. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The invention relates to a storage unit comprising a container housing enclosing a storage volume for receiving freight and a gaseous medium surrounding said freight, that storage unit further comprising a tempering system provided with a tempering unit associated with said storage volume for maintaining a flow of said gaseous medium circulating in said storage volume and passing through said tempering unit in order to be maintained at a defined or set temperature. 
         [0004]    In particular said storage units are transport storage units used for transporting or shipping freight. 
         [0005]    Such storage units are used in a wide variety of climatic zones of the globe and under harsh conditions. 
         [0006]    The freight to be stored in such storage units is mostly perishable, such as, for example, frozen fish, meat, fruit or chocolate or flowers. 
         [0007]    It is the object of a present invention to create a storage unit which operates reliably and cost efficient under the aforementioned conditions. 
       SUMMARY OF THE INVENTION 
       [0008]    This object is solved by a storage unit comprising a container housing enclosing a storage volume for receiving freight and a gaseous medium surrounding said freight, said storage unit further comprising a tempering system provided with a tempering unit, associated with that storage volume for maintaining a flow of said gaseous medium circulating in said storage volume and passing through said tempering unit in order to be maintained at a defined or set temperature, said tempering unit comprising an internal heat exchanger arranged in said flow of gaseous medium passing through said tempering unit, said tempering system being provided with a refrigerant circuit comprising said internal heat exchanger, an external heat exchanger exposed to ambient air surrounding said container housing as well as a compressor unit for compressing refrigerant, and said tempering system being further provided with an engine for driving said compressor unit in an independent power source mode and further provided with an electric motor/generator unit mechanically coupled, in particular drive couple, to said compressor unit and said compressor unit and said motor/generator unit being commonly driven by said engine in said independent power source mode. 
         [0009]    The advantage of the present solution has to be seen in a fact that the provision of an electric motor/generator unit mechanically coupled to said compressor unit enables driving of said motor/generator unit by said engine so that the motor/generator unit can be used as a generator in said independent power source mode. 
         [0010]    In another mode the motor/generator unit can be used as a motor for driving said compressor unit, in particular in a case when the engine is not running. 
         [0011]    With respect to the mechanical coupling of said motor/generator unit and said compressor unit no further details have been given so far. 
         [0012]    For example it would be possible to couple said motor/generator unit and said compressor mechanically by a belt drive or any kind of gear. 
         [0013]    An advantageous and in particular cost efficient solution provides that said motor/generator unit and said compressor unit are directly coupled by a shaft. 
         [0014]    In this case the shaft could be a specific coupling shaft arranged between said motor/generator unit and said compressor unit. 
         [0015]    It is of particular advantage if said motor/generator unit and said compressor unit are driven by a common drive shaft, which is a shaft of said motor/generator unit as well as a shaft of said compressor unit so that the motor/generator unit and the compressor unit can be combined to one commonly driven device. 
         [0016]    In order to efficiently cool the motor/generator unit it is of particular advantage if refrigerant flowing in said refrigerant circuit is flowing through said motor/generator unit for cooling said motor/generator unit. 
         [0017]    This means that no specific fan is necessary for cooling said motor/generator unit, because the refrigerant flowing in the refrigerant circuit can be used to cool the motor/generator unit. In particular refrigerant supplied from the internal heat exchanger is used for cooling before it is compressed by said compressor. 
         [0018]    One advantageous design provides that said motor/generator unit and said compressor unit are arranged in a common housing. 
         [0019]    Arranging both units in a common housing has the advantage that the design is very cost efficient and further the arrangement of both units in a common housing enhances the mechanical stability and reliability of the concept. 
         [0020]    According to one preferred solution it is provided that said refrigerant to be compressed is flowing through a compartment within said common housing in which said motor/generator unit is arranged, before entering said compressor unit. 
         [0021]    In order to have the option to decouple the engine from said compressor unit, one preferred solution provides that a clutch unit is provided for coupling said engine to said compressor unit so that the clutch unit can be released for decoupling the compressor unit from said engine. 
         [0022]    The clutch unit can be designed in various manners. 
         [0023]    One preferred solution is to use a magnetic clutch as a clutch unit. 
         [0024]    The clutch unit can be arranged on various sides of said compressor unit. 
         [0025]    For example, the clutch unit could be arranged on a side of said motor/generator unit opposite said compressor unit. 
         [0026]    The clutch unit could also be arranged between said compressor unit and said electric motor/generator unit. 
         [0027]    One preferred solution provides that said clutch unit is arranged on a side of said compressor unit opposite to said electric motor/generator unit so that the compressor unit is arranged between the clutch unit and the electric motor/generator unit which leads to a favorable mechanical design because the compressor unit can be designed mechanically so as to be driven from one side by the clutch unit via the engine or from the other side by the electric motor/generator unit. 
         [0028]    Preferably the clutch unit is arranged on a common drive shaft of said motor/generator unit and said compressor unit. 
         [0029]    Said engine could be an engine which for example is a combustion engine or a hydraulic engine which in particular is used for driving a vehicle on which said storage unit is mounted. 
         [0030]    However in order to improve the flexibility it is of particular advantage if said engine is adapted to drive said compressor unit and said motor/generator unit only so that the engine is only used for powering the tempering system according to the present invention. 
         [0031]    In particular, said engine used for powering said tempering system could be a combustion engine or a hydraulic engine provided with pressurized hydraulic medium from another source, e.g. from a combustion engine of a vehicle. 
         [0032]    With respect to the overall design of the storage unit no further details have been given so far. 
         [0033]    For maintaining said flow of gaseous medium within said storage volume it is of advantage that at least one fan unit is provided for generating said flow of said gaseous medium within said storage volume and for having said flow passing through said tempering unit. 
         [0034]    Said at least one fan unit can be arranged on various places within said storage volume. 
         [0035]    One preferred solution provides that said at least one fan unit is comprised by said tempering unit which enables to blow said flow of gaseous medium directly on a heat exchanger unit within said tempering unit. 
         [0036]    Further at least one external fan unit is provided in order to generate a flow of ambient air through said external heat exchanger in order to cool hot refrigerant passing through said external heat exchanger. 
         [0037]    In particular said external fan unit can be used for cooling said engine. 
         [0038]    In order to be able to heat the flow of gaseous medium under certain conditions, in particular extreme low temperatures outside said storage unit, at least one heater is provided in said tempering unit in order to heat said flow of gaseous medium. 
         [0039]    In principal the heater can be arranged independent from the internal heat exchanger. 
         [0040]    However, in order to use the heater for defrosting, the internal heat exchanger one advantageous solution provides said at least one heater is connected to said internal heat exchanger so that said heater and said internal heat exchanger form a heat exchange unit. 
         [0041]    In order to run said storage unit according to the present invention a control is provided for controlling said electric motor/generator unit and said engine during operation of said storage unit. 
         [0042]    According to one solution said control controls said electric motor/generator unit and said engine to either run the engine and said motor/generator unit as a generator or to stop the engine and to run the electric motor/generator unit as a motor. 
         [0043]    Further it is of advantage if the control is adapted to connect said motor/generator unit to a mains power supply in order to drive said compressor unit by said motor/generator unit operating as a motor and being powered by said mains power supply. 
         [0044]    Another solution provides that said control is adapted to connect said mains power supply to at least one of said fan units in order to drive at least one of said fan units by said mains power supply. 
         [0045]    Further an advantageous solution provides a control for controlling the flow of refrigerant in said refrigerant circuit and therefore controlling the operation of said refrigerant circuit. 
         [0046]    This control could be different from the control mentioned before. 
         [0047]    However one preferred solution provides that the control mentioned before is the same as the control for controlling the flow of refrigerant in the refrigerant circuit. 
         [0048]    One specific solution provides that in a cooling mode said refrigerant circuit is controlled to cool said heat exchanger in order to cool said flow of gaseous medium in said storage volume. 
         [0049]    Further it is provided that in a heating mode said refrigerant circuit is controlled to heat said internal heat exchanger in order to heat said flow of gaseous medium in said storage volume. 
         [0050]    This means that in the heating mode compressed hot refrigerant is not fed to the external heat exchanger but to the internal heat exchanger to heat the internal heat exchanger of the refrigerant circuit, in this case the refrigerant circuit is heated by the heat generated by the motor/generator unit and the heat generated in the course of compression of the refrigerant and this heat is then used to heat the internal heat exchanger. 
         [0051]    Another solution provides that in a heating mode said control system controls said electric heater in order to heat said flow of gaseous medium in said storage volume. 
         [0052]    The object of the present invention is further solved by a tempering system for use in connection with a storage unit, said tempering system being provided with a tempering unit associated with a storage volume for tempering a flow of gaseous medium passing through said tempering unit in order to maintain said flow at a defined or set temperature, said tempering unit comprising an internal heat exchanger arranged within said flow of gaseous medium, said tempering system being provided with a refrigerant circuit comprising said internal heat exchanger, and an external heat exchanger exposed to ambient air, as well as a compressor unit for compressing refrigerant, said tempering unit being further provided with an engine for driving said compressor unit in an independent power source mode, and said tempering system being provided with an electric motor/generator unit mechanically coupled to said compressor unit and said compressor unit, and said motor/generator unit being commonly driven by said engine in said independent power source mode. 
         [0053]    The advantage of a tempering system as described before has to be seen in the fact that the system enables to use the electric motor/generator unit as a generator in case the compressor is driven by the engine and it further enables to use the electric motor/generator unit as an electric motor for driving the compressor unit in case the engine is not running and the mains power supply is connected. 
         [0054]    Said engine could be an engine which for example is a combustion engine or a hydraulic engine which in particular is used for driving a vehicle on which said storage unit is mounted. 
         [0055]    However in order to improve the flexibility it is of particular advantage if said engine is adapted to drive said compressor unit and said motor/generator unit only so that the engine is only used for powering the tempering system according to the present invention. 
         [0056]    In particular, said engine used for powering said tempering system could be a combustion engine or a hydraulic engine provided with pressurized hydraulic medium from another source e.g. from a combustion engine of a vehicle. 
         [0057]    In general there exist various solutions to mechanically couple the motor/generator unit and the compressor unit. 
         [0058]    One particularly simple and advantageous solution provides that said motor/generator unit and said compressor unit are directly coupled by a shaft. 
         [0059]    The shaft could be a specific coupling shaft. One preferred solution provides that said motor/generator unit and said compressor unit are driven by a common drive shaft. 
         [0060]    In this case the drive shaft of the motor/generator unit and the drive shaft of the compressor unit are formed by the same shaft so that a mechanically simple and reliable solution is provided. 
         [0061]    In order to efficiently cool said motor/generator unit and in particular to avoid a cooling fan for said motor/generator unit, according to a preferred solution refrigerant flowing in said refrigerant circuit is flowing through said motor/generator unit for cooling said motor/generator unit. 
         [0062]    The motor/generator unit and the compressor unit could be provided in different housings. 
         [0063]    One advantageous simple and therefore preferred solution provides that said motor/generator unit and said compressor unit are arranged in a common housing. 
         [0064]    In case of using a common housing it is of advantage if said refrigerant to be compressed is flowing through a compartment within said common housing in which said motor/generator unit is arranged before entering said compressor unit. 
         [0065]    In order to enable a decoupling of said engine and the compressor unit a clutch unit is provided for coupling or decoupling said engine and said compressor unit. 
         [0066]    Said clutch unit can be a mechanically operated clutch unit. One preferred solution provides that said clutch unit is a magnet clutch. 
         [0067]    With respect to the mechanical setup one preferred solution provides that said clutch unit is arranged on a side of said compressor unit opposite to said electric motor/generator unit so that the compressor unit can be driven from either side which means either by the engine via the clutch unit or by the electric motor/generator unit. 
         [0068]    It is of particular advantage if said clutch unit is arranged on a common drive shaft of said motor/generator unit and said compressor unit. 
         [0069]    Further advantages and features of the tempering system are disclosed in connection with the storage unit according to the present invention so that with respect to these features reference is made to the explanations given in connection with the storage unit according to the present invention. 
         [0070]    The invention further refers to a compressor system for a gaseous medium, in particular refrigerant, comprising a compressor unit and a motor/generator unit arranged in a common housing, said compressor unit and said motor/generator unit being mechanically drive coupled and provided with an external drive element for enabling driving of said motor/generator unit and said compressor unit by an external drive source. 
         [0071]    The advantage of the compressor system as defined before has to be seen in the fact that said compressor system can be used for compressing a gaseous medium driven either by said motor/generator unit if used as a motor and or by said external drive source and in case the compressor unit is driven by said external drive source the external drive source can be also used to drive the motor/generator unit then operated as a generator. 
         [0072]    It is also possible to use said compressor unit when provided with pressurized gaseous medium to operate as an expansion unit and to then drive said motor/generator which is in this case operating as a generator. 
         [0073]    Arranging both units in a common housing further has the advantage that the design is very cost efficient and further the arrangement of both units in a common housing enhances the mechanical stability and reliability of the concept. 
         [0074]    With respect to the mechanical coupling of said motor/generator unit and said compressor unit no further details have been given so far. 
         [0075]    For example it would be possible to couple the motor/generator unit and said compressor mechanically by a belt drive or any kind of gear. 
         [0076]    An advantageous and in particular cost efficient solution provides that said motor/generator unit and said compressor unit are directly coupled by a shaft. 
         [0077]    In this case the shaft could be a specific coupling shaft arranged between said motor generator unit and said compressor unit. 
         [0078]    It is of particular advantage if said motor/generator unit and said compressor unit are driven by a common drive shaft, which is a shaft of said motor/generator unit as well as a shaft of said compressor unit so that the motor/generator unit and the compressor unit can be combined to one commonly driven device. 
         [0079]    In order to efficiently cool the motor/generator unit it is of particular advantage if gaseous medium flowing to said compressor unit is flowing through said motor/generator unit for cooling said motor/generator unit. 
         [0080]    This means that no specific fan is necessary for cooling said motor/generator unit, because the gaseous medium flowing to the compressor unit can be used to cool the motor/generator unit. 
         [0081]    According to one preferred solution it is provided that said gaseous medium to be compressed is flowing through a compartment within said common housing in which said motor/generator unit is arranged, before entering said compressor unit. 
         [0082]    Said external drive element can be any element which enables to drive said compressor system externally, so as for example any gear element. 
         [0083]    In order to have the option to decouple the external drive source from said compressor unit, one preferred solution provides that said external drive element is a clutch unit provided for coupling said engine to said compressor unit so that the clutch unit can be released for decoupling the compressor unit from said external drive source. 
         [0084]    The clutch unit can be designed in various manners. 
         [0085]    One preferred solution is to use a magnetic clutch as a clutch unit. 
         [0086]    The clutch unit can be arranged on various sides of said compressor unit. 
         [0087]    For example, the clutch unit could be arranged on a side of said motor/generator unit opposite said compressor unit. 
         [0088]    The clutch unit could also be arranged between said compressor unit and said electric motor/generator unit. 
         [0089]    One preferred solution provides that said clutch unit is arranged on a side of said compressor unit opposite to said electric motor/generator unit so that the compressor unit is arranged between the clutch unit and the electric motor/generator unit which leads to a favorable mechanical design because the compressor unit can be designed mechanically so as to be driven from one side by the clutch unit via the external drive source or from the other side by the electric motor/generator unit. 
         [0090]    Preferably the clutch unit is arranged on a common drive shaft of said motor/generator unit and said compressor unit. 
         [0091]    Said external drive source could be an engine which for example is a stationary engine or which is used for driving a vehicle on which said compressor system is mounted. 
         [0092]    However in order to improve the flexibility it is of particular advantage if said engine is adapted to drive said compressor unit and said motor/generator unit only so that the engine is only used for powering the tempering system according to the present invention. 
         [0093]    In particular, said engine used for powering said compressor system could be a combustion engine or a hydraulic engine provided with pressurized hydraulic medium from another source, e.g. from a combustion engine. 
         [0094]    The electric motor/generator unit can be designed in different ways. 
         [0095]    One preferred design provides that said motor/generator unit is a synchronous electric machine. 
         [0096]    Another preferred solution provides that said motor/generator unit is an asynchronous permanent magnet electric machine. 
         [0097]    Further advantages and features of said compressor system are disclosed in connection with the storage unit and the tempering system as described before for which such a compressor system can be used. 
         [0098]    Further features and explanations with respect to the present invention are disclosed in connection with the detailed specification and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0099]      FIG. 1  shows as schematic arrangement of the various features of a storage unit according to the present invention; 
           [0100]      FIG. 2  shows as schematic representation of the refrigerant circuit combined with the motor/generator unit and an 
           [0101]      FIG. 3  shows a longitudinal sectional view through a compressor system comprising a compressor unit and a motor/generator unit according to the present invention; 
           [0102]      FIG. 4  shows an enlarged sectional view through the arrangement of the electric clutch and a lubricant pump of the compressor unit according to  FIG. 3 ; 
           [0103]      FIG. 5  shows a sectional view through a suction manifold and a cylinder head of a compressor unit according to the present invention; 
           [0104]      FIG. 6  shows a schematic representation of one part of an internal power distribution network together with the motor generator unit, a battery and a connection to a mains power supply and 
           [0105]      FIG. 7  shows a schematic representation of another part of the internal power distribution network together with electric heaters and fan units coupled thereto. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0106]    A storage unit  10  comprises an insulated container housing  12  enclosing a storage volume  14  within which temperature sensitive freight is received surrounded by a gaseous medium, in particular air, which is kept at a defined temperature level for maintaining said freight  16  in a defined temperature range. 
         [0107]    Said storage unit  10  is preferably adapted to be a transportable storage unit, for example for a truck trailer or a railway carriage transporting freight  16  or a conventional container for shipping freight  16  by truck, railway or ship. 
         [0108]    In order to maintain a defined or set temperature range of freight  16  a flow  22  of said gaseous medium  18  is circulating through volume  14  starting from a tempering unit  24  as a supply gas flow and entering tempering unit  24  as a return gas flow. 
         [0109]    The circulating gas flow  28  is generated by a fan unit  32  preferable arranged within tempering unit  24  and tempered by a heat exchange unit  34  arranged within tempering unit  24 . 
         [0110]    Preferably supply gas flow  26  exits from tempering unit  24  in an area close to an upper wall  36  of insulated container housing  12  and preferably returns to tempering unit  24  close to a lower wall  38  of insulated container housing  12  forming said return gas flow  28 . 
         [0111]    According to a preferred embodiment heat exchange unit  34  comprises an internal heat exchanger  42  arranged in a refrigerant circuit  44  as shown in  FIG. 2  as well as heaters  46  which are preferably electric heaters. 
         [0112]    Tempering unit  24  is arranged close to upper wall  36  of insolated container housing  12 , for example on a front wall  48  or a rear wall thereof. 
         [0113]    However, tempering unit  24  can also be arranged on upper wall  36 . 
         [0114]    An equipment box  52  comprising a compressor unit  54  a motor/generator unit  56  as well as an engine  58 , in particular a combustion engine, is preferably arranged close to tempering unit  24  on insulated container housing  12 . Equipment box  52  further comprises an external heat exchanger  62  as well as an external fan unit  64  generating an air flow  66  through external heat exchanger  72 . 
         [0115]    As can be seen from  FIG. 2  compressor  54  as well as external heat exchanger  62  are arranged in refrigerant circuit  44  in addition to internal heat exchanger  42 . 
         [0116]    The components of refrigerant circuit  44  and engine  58  as well as motor/generator unit  56  together form a tempering system  70  as shown in  FIG. 2 . 
         [0117]    In particular compressor unit  54  with its discharge port  72  is connected to a discharge line  74  of refrigerant circuit  44  guiding refrigerant compressed at compressor  54  to external heat exchanger  62  in which hot compressed refrigerant is cooled by external air flow  66 . 
         [0118]    Cooled compressed refrigerant leaves external heat exchanger  62  via high pressure lines  76  and enters a liquid receiver  82 . 
         [0119]    Preferably high pressure line  76  is provided with a valve  78  enabling to control supply of high pressure refrigerant to liquid receiver  82 . 
         [0120]    Liquid receiver  82  is further connected to expansion device  92  by liquid refrigerant line  94  guiding liquid refrigerant from liquid receiver  82  to expansion device  92 . 
         [0121]    Preferably a suction line heat exchanger  96  is arranged within liquid refrigerant line  94  in order to subcool liquid refrigerant before expansion in expansion device  92 . 
         [0122]    Expansion device  92  feeds expanded refrigerant to input port  98  of heat exchanger  42  so that in heat exchanger  42  expanded and cooled refrigerant is able to receive heat before exiting to output port  102  of heat exchanger  42  and entering suction line  104  which after passing through suction line heat exchanger  96  is connected to suction port  112  of compressor  54 . 
         [0123]    Refrigerant circuit  44  further comprises a hot gas supply line  114  branching off from discharge line  74  and being connected with input port  98  of heat exchanger  42 . 
         [0124]    Hot gas supply line  114  is further provided with hot gas supply valve  116  which enables to close our open hot gas supply line  114 . 
         [0125]    In order to control the capacity of or mass flow through compressor unit  54 , compressor unit  54  is provided with two capacity control valves  122  and  124  which enable control of the compressor capacity, for example, between 100% compressor capacity if both capacity control valves  122 ,  124  are open, 50% compressor capacity if one compressor control valve  122  is open and the other compressor control valve  124  is closed, and 0% if both compressor control valves  122 ,  124  are closed. 
         [0126]    As shown in  FIG. 2  compressor unit  54  can be driven by an internal engine  58  driving for example a belt drive  134  which then drives a clutch unit  136  connected with compressor unit  54 . 
         [0127]    As can be seen from  FIG. 3  preferably clutch unit  136  is connected with a common drive shaft  142  of said compressor unit  54  and said motor/generator unit  56  extending in a common housing  144  of said compressor unit  54  and said motor/generator unit  56  and guided by two bearing units  146  and  148  within common housing  144 . 
         [0128]    For example a first axial and radial bearing unit  146  is arranged in a bearing cover  151  mounted on said common housing  144  and receiving radial and axial forces acting on drive shaft  146 . On bearing cover  151  a front cover  152  of common housing  144  is mounted and drive shaft  142  extends through bearing cover  151  and front cover  152  with a shaft section  154 . 
         [0129]    Front cover  152  is provided with shaft seal  153  in order to prevent lubricant from leaving common housing  144  by passing along shaft section  154 . 
         [0130]    On shaft section  154  clutch unit  136  is arranged, which clutch unit  136  enables to connect or disconnect shaft section  154  with belt pulley  156  which, for example, surrounds clutch unit  136 . 
         [0131]    Preferably clutch unit  136  is held in place by front cover  152 . 
         [0132]    In particular belt pulley  156  is supported by front cover  152  via bearing  157  in order to receive the forces acting on pulley  156  by front cover  152  and avoid or reduce transverse forces acting on shaft section  154  to increase lifetime of shaft seal  153  and bearing  146 . 
         [0133]    Further front cover  152  is also carrying stationary coil unit  158  necessary for actuation of clutch unit  136  by applying magnetic force. 
         [0134]    In the preferred embodiment as shown in  FIG. 3  compressor unit  54  is a semi hermetic compressor having motor/generator unit  56  arranged within said common housing  144  and motor/generator unit  56  is arranged in a compartment  164  of common housing  144  through which refrigerant entering through suction port  112  is drawn before entering a suction manifold  166  of compressor unit  54  from which the refrigerant enters the respective compressor elements  168  of compressor unit  54  in order to be compressed. 
         [0135]    In the example shown in  FIGS. 3 and 4  compressor elements  168  are cylinders of a piston compressor, however compressor elements  168  can any kind of compressor elements such as for example scroll elements of a scroll compressor or screw elements of a screw compressor. 
         [0136]    In the embodiment shown in  FIG. 3  motor/generator unit  56  comprises a rotor  172  sitting on a shaft section  174  of common shaft  142  which extends beyond bearing unit  148  which bearing unit  148  is arranged in a central housing section  176  separating the compartment  164  receiving motor/generator unit  56  from an interior space  178  of a drive housing  182  of common housing  144  within which drives for compressor elements  168  are arranged. 
         [0137]    Rotor  172  is surrounded by a stator  192  of motor/generator unit  56  which stator  192  is fixedly arranged in common housing  144  and which stator  192  is provided with electrical windings  194  whereas rotor  172  is preferably free of windings. 
         [0138]    Motor/generator unit  56  can be designed without permanent magnets or with permanent magnets. 
         [0139]    In order to provide sufficient lubricant to various bearing locations of drive shaft  142  a pumping unit  202  is arranged on a section of drive shaft  142  extending beyond bearing unit  146  arranged in bearing cover  151  which pumping unit  202  is connected with a suction tube  204  extending into a lubricant sump  206  formed within a lower part of interior space  178 . 
         [0140]    Pumping unit  202  is pumping lubricant to a central lubricant channel  208  extending along drive shaft  142 . 
         [0141]    Within drive shaft  142  distribution channels  212  are provided which branch off from central lubricant channel  208  and guide lubricant to various bearing locations, for example to bearing units  146  and  148  as well as various cam drives  214  for driving compressor elements  168 . 
         [0142]    In particular a further distribution channel  216  is supplying lubricant to shaft seal  153  in order to cool shaft seal  153  and such lubricant is collected in a chamber  217  surrounding shaft seal  153  and guided to interior space  178  via channel  218 . 
         [0143]    Lubricant leaking through shaft seal  153  is collected in a chamber  218  arranged between front cover  152  and bearing cover  151 . 
         [0144]    As shown for example in  FIG. 5  in case of compressor elements  168  comprising cylinders capacity control valves  122  are arranged in a cylinder head  222  in order to control flow of refrigerant from suction manifold  166  into the respective suction chamber  224  of the respective cylinder head  222 . 
         [0145]    If the respective capacity control valve  122  or  124  is closed, flow of refrigerant from suction manifold  166  to the respective suction chamber  224  is interrupted so that the respective compressor element  168  is prevented from compressing refrigerant and no mass flow through said compressor element  168  occurs. 
         [0146]    As for example shown in  FIG. 6  motor/generator unit  56  is electrically connected to an internal power distribution network  232  via switching unit  234 . 
         [0147]    For example internal power distribution network  232  is a 400 Volt alternating current network having three phases and motor/generator unit  56  is also connected via a three phase line  236  to internal power distribution network  232 . 
         [0148]    Further a capacitor network  238  can be electrically connected to three phase power line  236  by closing a capacitor switching unit  242  which capacitor network  238  is used when motor/generator unit  56  is operated as a generator whereas in case motor/generator unit  56  is operated as a motor capacitor network  238  is switched off by opening by capacitor switching unit  242 . 
         [0149]    In case motor/generator unit  56  is provided with permanent magnets capacitor network  238  and capacitor switching unit  242  are not necessary. 
         [0150]    As shown in  FIG. 7  fan unit  32  can be electrically connected to internal power distribution network  232  by switching unit  252  and also external fan unit  64  can be connected to internal power distribution network  232  by switching unit  254 . 
         [0151]    Further electrical heaters  46  can be electrically connected to internal power distribution network  232  by switching unit  256 . 
         [0152]    In particular electrical heaters  46  are connected to a capacitor network  258  used to match the impedance of electrical heaters  46  to internal power distribution network  232 . 
         [0153]    Further internal power distribution network  232  can be connected to a mains power supply  262  in case storage unit  10  is operated standby power source mode so that a connection to a mains power supply  262  is possible. 
         [0154]    In addition a power converter  264  is used in order to connect internal power distribution network  232  with a battery  266  for storing electrical power. 
         [0155]    Preferably power convertor  264  can be electrically connected by a switching unit  262  to internal power distribution network  232 . 
         [0156]    Further power convertor  264  is directly connected to a power line  272  extending between mains power supply  262  and internal power distribution network  232 . 
         [0157]    In order to operate storage unit  10  a control  282  is provided which controls operation of engine  58 , clutch  136 , capacity control valves  122 ,  124 , motor/generator unit  56 , and in particular by switching units  234  and  242  as well as switching units  252 , 254  and  268 . 
         [0158]    A storage unit  10  as described before can be operated in various operation modes. 
         [0159]    In case storage unit  10  is operated in an independent power source mode and therefore independent from mains power supply  262  engine  58  is running and drives drive shaft  142  via belt drive  134  with having clutch unit  136  connecting belt drive  134  to drive shaft  142 . 
         [0160]    Since drive shaft  142  is a common drive shaft for compressor unit  54  as well as motor/generator unit  56  engine  58  drives compressor unit  54  as well as motor/generator unit  56  and in this case motor/generator unit  56  will operate as a generator. 
         [0161]    Therefore switching unit  234  connects motor/generator unit  56  with internal power distribution network  232  and capacity switching unit  242  connects capacity network  238  to motor/generator unit  162  in order to provide appropriate impedance adaption for feeding internal power distribution network  232  with electric power from motor/generator unit  56 . 
         [0162]    Electric power generated by motor/generator unit  56  is used for driving fan unit  32  for maintaining flow  22  of gaseous medium inside storage volume  14  as well as fan unit  64 . 
         [0163]    In this independent power source mode various operational modes are possible. 
         [0164]    One operational mode is the cooling mode in which refrigerant compressed by compressor unit  54  is supplied to external heat exchanger  62 , cooled therein and then supplied to liquid receiver  82  and further to expansion device  92  in order to supply expanded and cold refrigerant to input port  98  of heat exchanger  42 . Heat exchanger  42  being cooled by cold refrigerant can receive heat from circulating flow  22  of gaseous medium and cool the gaseous medium  18  circulating within storage volume  14 . In this cooling mode of refrigerant circuit  44  valve  78  is open in order to supply refrigerant under high pressure to liquid receiver  82  and hot gas supply valve  116  is closed in order to block supply of hot gas to input port  98  via hot gas supply line  114 . 
         [0165]    If however the ambient air is too cold it could be necessary to heat gaseous medium  18  within storage volume  14  in order to avoid that freight  16  is cooled down to an undesired temperature level at which freight  16  might be damaged or might perish. 
         [0166]    In this case it is necessary to heat the circulating flow  22  of gaseous medium  18  by operating tempering unit  24  in the heating mode. 
         [0167]    For operating in the heating mode there are two possibilities. 
         [0168]    One heating possibility would be to operate heaters  46  by closing switching unit  256  and to stop cooling by closing valve  78 . 
         [0169]    In order to reduce the capacity of compressor unit  54  to 0% capacity control valves  122  and  124  are closed so that no refrigerant is compressed anymore by compressor unit  54  even though this compressor unit  54  is still running. 
         [0170]    Alternatively or additionally another heating possibility would be to run compressor unit  54  with a capacity above 0%, e.g. with a capacity of 50% or 100% but to direct the compressed and heated refrigerant from discharge line  74  not to external heat exchanger  62  but by via hot gas supply line  114  to input port  98  of heat exchanger  42 . 
         [0171]    In this case the hot refrigerant, in particular heated by the compression process in compressor unit  54 , is flowing through heat exchanger  42  and therefore internal heat exchanger  42  is heated by hot refrigerant, irrespective of whether or not electric heaters  46  are operated so that the circulating flow  22  of gaseous medium is heated. 
         [0172]    For heating internal heat exchanger  42  with hot refrigerant valve  78  is closed so that no compressed refrigerant from external heat exchanger  62  enters liquid receiver  82  and further no liquid is fed to expansion device  92  which is inoperable in this case. 
         [0173]    In addition the heat generated by motor/generator unit  56  is transported by the refrigerant passing through compartment  174  to internal heat exchanger  42  by the compressed hot refrigerant outputted by compressor unit via discharge port  72 . 
         [0174]    Therefore the heat generated by motor/generator unit  56  running as a generator can be used for heating the flow  22  of gaseous medium. 
         [0175]    It is further possible to run tempering unit  24  in a defrost mode in which fan unit  32  is switched off and heat exchanger  42  can be defrosted either by using hot refrigerant, supplied via hot gas supply line  114  or by using heaters  46  for heating heat exchanger  42 . 
         [0176]    In case only heaters  46  are used for heating heat exchanger  42  capacity charge control valves  122  and  124  can be closed in order to run compressor unit  54  with 0% capacity, e.g. 0% mass flow. 
         [0177]    If control unit  282  detects that the flow  22  of gaseous medium  18  within storage volume  14  has reached its determined or set temperature, storage unit  10  can be run in an idling mode. 
         [0178]    In the idling mode one possibility is to run engine  132  at reduced or low speed in order to reduce fuel consumption. 
         [0179]    In this case engine  132  still drives compressor unit  54  as well as motor/generator unit  56 . 
         [0180]    The power generated by motor/generator unit  56  operating as a generator is used to run fan unit  32  for maintaining the circulating of the flow  22  of gaseous medium  18  within storage volume  14 . However it is possible to close both capacity control valves  122 ,  124  in order to reduce the capacity of compressor unit  54  to 0%. 
         [0181]    Further external fan unit  64  can still be active in order to cool engine  58 . 
         [0182]    In the idling mode it is also possible to stop engine  58  in case the desired or set temperature level of the flow  22  of gaseous medium  18  has been reached. In order to maintain operation of fan unit  32  for circulating flow  22  of gaseous medium  22  battery  266  can be used to supply the necessary power to fan unit  32  via power distribution network  232 . 
         [0183]    If storage unit  10  is used in a standby power source mode in which mains power supply  262  can be connected to internal power distribution network  232  engine  58  is stopped and clutch unit  136  is released in order to decouple drive shaft  142  from engine  58 . 
         [0184]    In this case motor/generator unit  56  is operated as a motor and capacitor switching unit  242  is used to decouple capacitor network  238  from motor/generator unit  56 . 
         [0185]    In this standby power source mode it is possible to operate storage unit  10  in the cooling mode, the heating mode, defrost mode and the idling mode however in this case compressor unit  54  is always driven by motor/generator unit  56  operating as a drive motor for compressor unit  54  and all the electric power necessary for the respective mode, for example for operating motor/generator unit  56 , fan unit  132 , external fan unit  62  and heaters  46 , is supplied by mains power supply  262 .