Abstract:
In order to improve a screw compressor comprising a housing, at least one screw rotor arranged in a compressor housing of the housing, a lubricant sump which is arranged on the high pressure side and in which lubricant collects, and a lubricant supply device which supplies lubricant from the lubricant sump to the at least one screw rotor, in such a manner that the amount of circulating lubricant can be kept as small as possible for adequate lubrication, it is suggested that the lubricant supply device comprise a first lubricant supply system and a second lubricant supply system, that the first lubricant supply system supply lubricant to the at least one screw rotor during operation of the screw compressor and that the second lubricant supply system additionally supply lubricant to the at least one screw rotor and thereby be activatable and deactivatable.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation of international application number PCT/EP2011/053222 filed on Mar. 3, 2011. 
     This patent application claims the benefit of International application No. PCT/EP2011/053222 of Mar. 3, 2011 and German application No. 10 2010 002 649.2 of Mar. 8, 2010, the teachings and disclosure of which are hereby incorporated in their entirety by reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a screw compressor comprising a housing, at least one screw rotor arranged in a compressor housing of the housing, a lubricant sump, which is arranged on the high pressure side and in which lubricant collects, and a lubricant supply device which supplies lubricant from the lubricant sump to the at least one screw rotor. 
     Screw compressors of this type are known from the state of the art, with which a lubricant supply device is provided which is constantly operated and is to be configured such that the lubricant circulated in it ensures an adequate discharge of heat from the housing of the screw compressor even at maximum load and so a large amount of lubricant is constantly circulating. 
     For this purpose, a lubricant cooling device, which cools the circulating lubricant, is, for example, provided. 
     The object underlying the invention is to improve a screw compressor of the type described above in such a manner that the amount of circulating lubricant can be kept as small as possible for adequate lubrication. 
     SUMMARY OF THE INVENTION 
     This object is accomplished in accordance with the invention, in a screw compressor of the type described at the outset, in that the lubricant supply device comprises a first lubricant supply system and a second lubricant supply system, that the first lubricant supply system supplies lubricant to the at least one screw rotor during operation of the screw compressor and that the second lubricant supply system additionally supplies lubricant to the at least one screw rotor and can thereby be activated and deactivated. 
     The advantage of the solution according to the invention is to be seen in the fact that the activatable and deactivatable second lubricant supply system offers the possibility of adapting the amount of circulating lubricant to the operational state of the screw compressor and, therefore, of adapting the amount of lubricant to the operational state present each time in as optimum a manner as possible. 
     In this respect, it is particularly favorable when the screw compressor can be operated in a normal load operation and in a high load operation and when the second lubricant supply system is deactivated during normal load operation and activated during high load operation. 
     The advantage of this solution is to be seen in the fact that it is possible, as a result, to increase the amount of circulating lubricant during high load operation by means of the second lubricant supply system and, therefore, to provide for sufficient cooling of the screw compressor during high load operation but to reduce the amount of circulating lubricant for normal load operation in relation to high load operation. 
     In principle, it would be conceivable to define the normal load operation and the high load operation dependent on the operational specifications for the screw compressor. 
     One particularly favorable solution provides, however, for a compressor control which recognizes whether normal load operation or high load operation is present. 
     Such a differentiation between normal load operation and high load operation can be brought about in the most varied of ways. 
     For example, it is provided for normal load operation to be present below a predeterminable threshold value for the load on the screw compressor and high load operation to be present above the threshold value for the load so that the compressor control, in particular, is able to differentiate between normal load operation and high load operation on the basis of the predeterminable threshold value. 
     Such a threshold value for the load on the screw compressor could, for example, be the input power of a drive for the screw compressor. 
     Alternatively or in addition, one advantageous solution provides for normal load operation to be carried out when a temperature measured on the high pressure side is below a predeterminable temperature threshold and high pressure operation when the measured temperature is above the temperature threshold. 
     With respect to the amount of lubricant flowing through the first lubricant supply system and the determination thereof, no further details have so far been given. 
     It would, for example, be conceivable to provide a lubricant conveyor pump, by means of which the amount of lubricant which flows through the first lubricant supply system can be determined, wherein the amount of lubricant can vary according to the speed of the screw rotor. 
     One particularly advantageous embodiment of a screw compressor according to the invention does, however, provide for the amount of lubricant flowing through the first lubricant supply system to be determined by a difference in pressure between a pressure in the lubricant sump and a pressure at a supply opening to the at least one screw rotor. 
     Such a solution has the great advantage that, on the one hand, a lubricant conveyor pump can be omitted and, on the other hand, the amount of lubricant which is required for lubrication can be determined in a simple manner. 
     In addition, it is also advantageously provided in conjunction with the second lubricant supply system for the amount of lubricant flowing through the second lubricant supply system to be determined by a difference in pressure between a pressure in the lubricant sump and a pressure at a supply opening to the at least one screw rotor. 
     As a result, the amount of lubricant through the second lubricant supply system may also be determined in a simple manner. 
     It is also possible, in particular, to determine the amount of lubricant flowing through the second lubricant supply system in that the supply opening is at a different pressure to the supply opening of the first lubricant supply system. 
     The pressure at the respective supply openings results primarily from the location of the respective screw rotor, at which the supply opening is provided for supplying lubricant to it, i.e. from the position of the respective supply opening between the high pressure side and the suction side of the screw rotor. 
     In conjunction with the preceding description of the individual embodiments, no further details have been given as to whether a targeted cooling of the amounts of lubricant should take place. 
     One advantageous solution provides for the amount of lubricant conveyed by the first lubricant supply system to be coolable by a lubricant cooling device so that heat can be discharged from the amount of lubricant circulating in the first lubricant supply system in a defined manner as a result of this lubricant cooling device. 
     A simple solution provides, in this respect, for the lubricant cooling device to constantly cool the amount of lubricant conveyed by the first lubricant supply system. 
     Alternatively thereto, it is, however, also conceivable for the lubricant cooling device to cool the amount of lubricant conveyed by the first lubricant supply system during high load operation of the compressor. 
     A further variation is for the lubricant cooling device, where applicable, to cool the amount of lubricant flowing through the first lubricant supply system during normal load operation in a controlled manner. 
     A further, advantageous solution provides for the amount of lubricant conveyed by the second lubricant supply system to be coolable by a lubricant cooling device. 
     This lubricant cooling device can be identical to the cooling device for the amount of lubricant of the first lubricant supply system. 
     It is, however, also conceivable to provide a separate lubricant cooling device for the amount of lubricant of the second lubricant supply system. 
     One particularly favorable solution provides for the amounts of lubricant of the first and second lubricant supply systems to be coolable with the lubricant cooling device. 
     Within the scope of the solution according to the invention, it has proven to be particularly advantageous when a lubricant cooling device is provided which can be operated in an active state or in an inactive state and/or in states therebetween. 
     For example, such a lubricant cooling device is designed such that it has a lubricant cooler which can be operated by way of a controllable bypass line in all possible states from the active up to the inactive state. 
     No further details have been given concerning the design of the screw compressor according to the invention. 
     One particularly advantageous solution, for example, provides for a lubricant outlet for the supply of lubricant to the lubricant supply systems as well as lubricant inlets for the supply of lubricant to the first lubricant supply system and to the second lubricant supply system to be provided on the housing. 
     As a result, the lubricant supply systems can be activated separately in a simple manner and, where applicable, the activation controlled without the housing needing to be entered for this purpose. 
     In this respect, it is particularly favorable when the lubricant outlet and the lubricant inlets open into a distributor unit which can be mounted on the housing. 
     As a result, the distribution of the lubricant to the lubricant supply systems as well as the activation, in particular, of the second lubricant supply system can be realized in a simple manner by a distributor unit provided externally to the housing. 
     Furthermore, the distributor unit may preferably be constructed such that it has connections for an external lubricant cooler so that the connection of the external lubricant cooler is also brought about via the distributor unit. 
     Furthermore, the distributor unit may preferably be designed such that lubricant fed back from the lubricant cooler can be supplied to the first lubricant supply system and the second lubricant supply system in the distributor unit. 
     Furthermore, it is preferably provided for a control valve to be provided in the distributor unit prior to the lubricant inlet of the second lubricant supply system. 
     Moreover, it is preferably provided for a bypass line located between the connections for the external lubricant cooler to be provided in the distributor unit with a control valve which offers the possibility of activating or deactivating the lubricant cooler or also setting intermediate states. 
     Additional features and advantages of the invention are the subject matter of the following description as well as the drawings illustrating several embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a longitudinal section through a first embodiment of a screw compressor according to the invention; 
         FIG. 2  shows a schematic illustration of a screw compressor according to the invention with a lubricant supply device according to the first embodiment and 
         FIG. 3  shows an illustration similar to  FIG. 2  of a lubricant supply device in a second embodiment of a screw compressor according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of a screw compressor according to the invention, illustrated in  FIG. 1 , comprises a housing which is designated as a whole as  10  and is constructed from a central section  12 , an end section  14  on the motor side and an end section  16  on the pressure side. 
     A drive motor designated as a whole as  20  is arranged in the end section  14  on the motor side and this is designed, for example, as an electric motor which comprises a stator  22  which is held in the end section  14  and surrounds a rotor  24  which is, for its part, arranged on a drive shaft  26 . 
     A compressor housing designated as a whole as  30  is formed in the central section  12  of the outer housing  10  and has rotor bores  32  and  34 , in which screw rotors  36  and  38  are arranged which are rotatable about axes parallel to one another. 
     For example, the screw rotor  36  is seated on the drive shaft  26  passing through it. 
     Bearings  42  and  44  on the low pressure side as well as bearings  46  and  48  on the high pressure side are provided for mounting the screw rotors  36  and  38  and they are arranged in corresponding bearing receptacles of the housing  10 . 
     The screw rotors  36  and  38  compress medium which is supplied via a suction chamber  50 , flows out via a high pressure outlet  52  and, in this respect, passes through, for example, a sound absorber  54  as well as a lubricant separator  56  which has the effect that lubricant is separated from the compressed medium and collects in the end section  16  on the pressure side in the form of a lubricant sump  58 . 
     Alternatively thereto, the lubricant separator and the lubricant sump can also be arranged outside the housing  10 , wherein they are always located on the high pressure side. 
     The lubricant is taken up from the lubricant sump  58  via a lubricant filter  60  and is available for lubricating the bearings  42  and  44  on the low pressure side as well as the bearings  46  and  48  on the high pressure side and the screw rotors  36  and  38  in the rotor bores  32  and  34 . 
     As illustrated schematically in  FIG. 2 , the lubricant flows from the lubricant filter  60  in a lubricant conveyor line  62  to a branch  64 , via which a first lubricant supply system  70 , illustrated in solid lines in  FIG. 2 , guides the lubricant to supply openings  72  and  74  which are associated with the rotor bores  32  and  34  and supply lubricant to the screw rotors  36  and  38  in the areas  76  and  78  which are located between suction sides  82  and  84  as well as high pressure sides  86  and  88  thereof. 
     Furthermore, the first lubricant supply system  70  comprises lubricant outlets  92  and  94  for the lubrication of the bearings  46  and  48  on the high pressure side, wherein the lubricant flowing through the bearings  46  and  48  on the high pressure side will, for example, be collected again and supplied via a collecting line  96  to an additional supply opening  98  associated, for example, with the first screw rotor  32 , wherein the supply opening  98  is located between the supply opening  72  and the suction side  82  of the screw rotor  32 . 
     A second lubricant supply system  100 , illustrated in  FIG. 2  by dash-dot lines, is provided parallel to the first lubricant supply system  70 , wherein both the first lubricant supply system  70  and the second lubricant supply system  100  proceed from a branch  102  which is connected to the branch  64  and, therefore, fed from the lubricant conveyor line  62 . The second lubricant supply system  100  guides lubricant to a supply opening  104  which is associated, for example, with the screw rotor  34  but it is certainly possible to also provide a supply opening associated with the first screw rotor  32  in the second lubricant supply system  100 . 
     Furthermore, a control valve designated as a whole as  110  is provided in the second lubricant supply system  100  and this can be controlled by a compressor control  120  and with it the second lubricant supply system  100  can be operated in a controlled manner by means of the compressor control  120 . 
     An activatable and deactivatable lubricant cooling device  130  is located between the branch  64  and the branch  102 , from which the first lubricant supply system  70  and the second lubricant supply system  100  proceed, and this lubricant cooling device comprises a lubricant cooler  136  which can be operated in the active state or in the inactive state or in intermediate states therebetween by way of a bypass line  132  with a control valve  134  provided in the bypass line  132 . 
     Furthermore, a third lubricant supply system  140  leads from the branch  64  to the bearings  42  and  44  on the low pressure side in order to supply them with lubricant. 
     Alternatively thereto, the third lubricant supply system  140  can also branch off from the branch  102  so that at least lubricant which can be cooled can likewise flow through it. 
     The housing  10  is preferably designed such that it has a lubricant outlet  152  connected to the branch  54  as well as a lubricant inlet  154  for the first lubricant supply system  70  as well as a lubricant inlet  156  for the second lubricant supply system  100 . 
     A distributor unit designated as a whole as  160  is connected to the lubricant outlet  152  and the lubricant inlets  154  and  156  and external connections  162  and  164  are provided in this distributor unit for connecting the external lubricant cooler  136  as well as the bypass line  132  to the control valve  134  and, in addition, the branch  102  is provided in this unit with a supply line  166  to the lubricant inlet  154  of the first lubricant supply system and with a supply line  168  to the lubricant inlet  156  of the second lubricant supply system  100 , wherein the control valve  110  is also arranged in the supply line  168 . 
     The distributor unit  160  is preferably mounted on the housing  10  as an external unit and borders on the lubricant outlet  152  as well as the lubricant inlets  154  and  156  in order to provide a connection to the bypass line  132  as well as the supply lines  166  and  168 . 
     The screw compressor according to the embodiment illustrated works as follows: 
     During normal load operation, i.e. a load on the screw compressor in accordance with normal operating cycles, the second lubricant supply system  100  is inactive since the compressor control  120  closes the control valve  110 . 
     In this case, lubricant will be supplied to the screw rotors  36 ,  38  and the bearings  42 ,  44 ,  46 ,  48  only via the first lubricant supply system  70  as well as the third lubricant supply system  140  and this lubricant will again be collected in the lubricant sump  58  and made available for renewed lubrication. 
     The amount of lubricant which is used during normal load operation depends on how large the difference in pressure is between the lubricant sump  58  which is subject to high pressure and essentially the supply openings  72  and  74  as well as  98  since lubricant will essentially be conveyed as a result of this difference in pressure. 
     During normal load operation, the compressor control  120  can also open the control valve  134  so that the lubricant cooler  136  does not have circulating lubricant flowing through it to any appreciable degree. 
     It is, however, also possible to close the control valve  134  or operate it in a phased or modulated manner in order to have either the entire circulating lubricant flowing through the lubricant cooler  136  or some of it flowing through the lubricant cooler  136  and, therefore, to discharge heat from the housing  10  as a result of the cooling of the lubricant. 
     If, however, the screw compressor according to the invention is working in high load operation, i.e. with a high loading, it is necessary to discharge as large an amount of heat as possible from the housing  10  for the purpose of stabilizing the temperature via the lubricant. For this reason, the control valve  134  is closed during high load operation and so the bypass line  132  is blocked and all the lubricant flowing to the branch  102  flows through the lubricant cooler  136 . 
     Furthermore, the amount of circulating lubricant will be increased considerably by activating the second lubricant supply system  100  on account of the control valve  110  being opened by the compressor control  120 , particularly since the supply opening  104  is located closer to the suction sides  82  and  84  of the screw rotors  32  and  34  than the supply openings  72  and  74  and so a greater difference in the pressure conveying the lubricant is available in the second lubricant supply system  100 . The amount of lubricant flowing through the second lubricant supply system  100  during high load operation is preferably more than 0.5 times the amount of lubricant flowing through the first lubricant supply system  70 ; this amount of lubricant can preferably stretch approximately up to the volume of the amount of lubricant flowing through the first lubricant supply system  70  so that, as a result, an efficient cooling of the screw compressor according to the invention is possible by means of the large amounts of lubricant flowing through the lubricant cooler  136 . 
     The compressor control  120  can detect high load operation in the most varied of ways. For example, it is conceivable to detect high load operation on account of the input electric power of the drive motor  20  and/or it is possible to provide a temperature sensor  170  on the high pressure side or a lubricant temperature sensor, for example arranged in the lubricant sump  58 , by means of which it is possible to ascertain when a temperature threshold is exceeded, which represents an indication for high load operation. 
     Alternatively to the mode of operation of the screw compressor according to the invention as described above, it is also possible, during normal load operation, to differentiate between a non-cooled and a cooled normal load operation, wherein during non-cooled normal load operation, for example with a very small load on the screw compressor, the control valve  134  is open whereas during cooled normal load operation, for example with a greater load on the screw compressor, the control valve  134  is closed and, therefore, the lubricant flows through the lubricant cooler  136  during cooled normal load operation, wherein the cooling capacity obtained is considerably less than during the high load operation described above on account of the smaller amount of lubricant for normal load operation. 
     In a second, simplified embodiment of a compressor according to the invention, illustrated in  FIG. 3 , the bypass line  132  and the control valve  134  are left out and so the lubricant flowing to the branch  102  always flows through the lubricant cooler  136  and will be cooled in it. 
     The high load operation by way of connecting in the second lubricant supply system  100  leads to a significant increase in the amount of lubricant cooled by the lubricant cooler  136  and so, as a result, the cooling of the screw compressor during high load operation will be improved in accordance with the invention in comparison with normal load operation.