Abstract:
In order to improve a reciprocating piston compressor for a refrigerant circuit, comprising a crankcase, in which a collecting chamber for lubricant is arranged, a cylinder housing, in which at least one reciprocating piston is movable in an oscillating manner, a valve plate which closes the cylinder housing and in which at least one inlet valve and one outlet valve are arranged, and a cylinder head, in which a suction gas duct which runs to the inlet valve and a compressed gas duct which leads away from the outlet valve are provided, in such a manner that excessive accumulations of lubricant can be avoided, it is suggested that a lubricant suction conduit be provided which has an inlet opening associated with the collecting chamber and an outlet opening associated with the suction gas duct and that the outlet opening be located in an area of the suction gas duct, in which a static pressure, which is lower than a static pressure in the collecting chamber for lubricant, prevails at least temporarily.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation of international application number PCT/EP2008/068357 filed on Dec. 30, 2008. 
     The present disclosure relates to the subject matter disclosed in international application number PCT/EP2008/068357 of Dec. 30, 2008 and German application number 10 2008 004 569.1 of Jan. 10, 2008, which are incorporated herein by reference in their entirety and for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a reciprocating piston compressor for a refrigerant circuit, comprising a crankcase, in which a collecting chamber for lubricant is arranged, a cylinder housing, in which at least one reciprocating piston is movable in an oscillating manner, a valve plate which closes the cylinder housing and in which at least one inlet valve and one outlet valve are arranged, and a cylinder head, in which a suction gas duct running to the inlet valve and a compressed gas duct leading away from the outlet valve are provided. 
     The problem with reciprocating piston compressors of this type, particularly when they are built into a refrigerant circuit as reciprocating piston compressor for one of several compressor stages, is that the amount of lubricant collected in the crankcase is larger than provided for, depending on the operating conditions. 
     The result of this is that either the amount of lubricant required altogether is greater than provided for or other components of the refrigerant circuit, for example a compressor arranged on the outlet side, do not have enough lubricant available. 
     The object underlying the invention is, therefore, to improve a reciprocating piston compressor of the generic type in such a manner that excessive accumulations of lubricant can be avoided. 
     SUMMARY OF THE INVENTION 
     This object is accomplished in accordance with the invention, in a reciprocating piston compressor of the type described at the outset, in that a lubricant suction conduit is provided which has an inlet opening associated with the collecting chamber and an outlet opening associated with the suction gas duct and that the outlet opening is located in an area of the suction gas duct, in which a static pressure, which is lower than a static pressure in the collecting chamber for lubricant, prevails at least temporarily. 
     The advantage of the solution according to the invention is to be seen in the fact that it is possible, as a result of such a configuration, to draw lubricant out of the collecting chamber by suction and supply it to the suction gas which then conveys this lubricant through the reciprocating piston compressor and conveys it further in the refrigerant circuit via the compressed gas duct to, for example, the next compressor in the refrigerant circuit. 
     As a result, it is possible, in a simple and inexpensive manner, to avoid an excessively large amount of lubricant collecting in the reciprocating piston compressor and, therefore, the problems which have already been explained occurring as a result. 
     With respect to the inlet opening in the collecting chamber, no further details have so far been given. 
     In principle, the possibility would exist of arranging the inlet opening close to a base of the collecting chamber so that it would be possible, as a result, to draw lubricant out of the collecting chamber by suction when the static pressure in the area of the suction gas duct is lower than the static pressure in the collecting chamber. 
     It is, however, even more advantageous when the inlet opening is arranged in the collecting chamber such that it predetermines a specific position of a surface level of a lubricant bath. 
     Therefore, it can already been ensured as a result of arrangement of the position of the inlet opening that too much lubricant will not be drawn out of the collecting chamber by suction but rather that an amount of lubricant which is sufficient for the respective reciprocating piston compressor will always remain in the collecting chamber. 
     This is of advantage, in particular, when the surface level of the lubricant bath falls below the inlet opening since no lubricant will be drawn off by suction in the case where the static pressure in the area of the suction gas duct is lower than the static pressure in the crankcase but only the lubricant present in any case in the crankcase will be drawn off by suction. 
     In this respect, it is particularly favorable when the inlet opening of the lubricant suction conduit predetermines a lowest surface level of the lubricant bath which can be achieved by drawing off lubricant by suction via the lubricant suction conduit. 
     With respect to the course of the lubricant suction conduit in the crankcase, no further details have so far been given. 
     One advantageous solution, for example, provides for the lubricant suction conduit to extend at least in sections through a pipe projecting into the crankcase. 
     This pipe preferably has the inlet opening and so the position of the inlet opening can also be defined by positioning the pipe in the crankcase. 
     Another advantageous solution provides for the lubricant suction conduit to extend in the crankcase at least in sections, i.e., be integrally formed in a wall of the crankcase and, therefore, for no additional pipe to be required at least for this section. 
     Furthermore, the position of the inlet opening of the lubricant suction conduit may likewise be fixed in a simple manner with this solution and, therefore, the minimum level of lubricant which can be achieved as a result of drawing off by suction can, for example, be determined. 
     In order to lower the static pressure in the area of the suction gas duct, in which the outlet opening is located, it is preferably provided for the area having the outlet opening of the lubricant suction conduit to be located in a narrow region of a nozzle. 
     As a result, a static pressure will be generated in the narrow region in the case of suction gas flowing through the nozzle and this pressure will be lower than the normal pressure in the suction gas and, therefore, a pressure gradient can be achieved between the static pressure in the crankcase, in particular in the collecting chamber, and the static pressure in the narrow region of the nozzle, as a result of which the lubricant will be drawn out of the collecting chamber by suction. 
     An alternative solution provides for the area of the suction gas duct having the outlet opening of the lubricant suction conduit to be located behind a throttling device in the suction gas duct in flow direction of the stream of suction gas. 
     Such a throttling device allows, for example, the static pressure to be reduced behind the throttling point, at least temporarily, to such an extent that a pressure gradient occurs between the collecting chamber in the crankcase and the area of the outlet opening in the suction gas duct and, therefore, lubricant will be drawn out of the collecting chamber by suction. 
     In this respect, the throttling device could be realized, for example, as a constantly active throttling point by way of, for example, a very inexpensive screen which does, however, display a constant throttling action. 
     Another advantageous solution provides for an adjustable throttling device to be provided which offers the possibility, for example, of adjusting the throttling action and, therefore, also the static pressure in the area between the throttling point and the inlet valve, depending on the size of the stream of suction gas. 
     In this respect, the adjustable throttling device can be adjustable statically, i.e. have a constant setting over a plurality of operating cycles. 
     Another solution which impairs the compressor capacity as little as possible provides for the adjustable throttling device to alternate between time intervals which are essentially free of throttling and time intervals with active throttling. 
     In this respect, the time intervals with active throttling can extend over less than one operating cycle of the reciprocating piston compressor or over several operating cycles. 
     The intervals free of throttling preferably extend over several operating cycles in order to impair the compressor capacity as little as possible. 
     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 schematic sectional view through a first embodiment with an excessively large amount of lubricant in a collecting chamber of the crankcase; 
         FIG. 2  shows a section similar to  FIG. 1  for the first embodiment with an amount of lubricant defined and reduced by lubricant being drawn off by suction; 
         FIG. 3  shows a section similar to  FIG. 1  through a second embodiment; 
         FIG. 4  shows a section similar to  FIG. 1  through a third embodiment and 
         FIG. 5  shows a section similar to  FIG. 1  through a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of a reciprocating piston compressor for refrigerant according to the invention, illustrated in  FIGS. 1 and 2 , comprises a crankcase  10 , in which a crank drive  12  is provided and which forms a collecting chamber  14  for lubricant  16 , for example, oil which collects in the collecting chamber  14  during the lubrication of the reciprocating piston compressor and forms a bath  18  of lubricant, the surface level  20  of which varies according to the amount of lubricant  16  in the lubricant bath  18 . 
     Furthermore, a cylinder housing  22 , in which a reciprocating piston  24  can be moved back and forth, driven by the crank drive  12 , is connected to the crankcase  10 , wherein a cylinder chamber  26  is available for the compression of refrigerant. 
     The cylinder chamber  26  is closed on its side located opposite the crank drive  12  by a valve plate which is designated as a whole as  30  and in which at least one inlet valve  32  as well as at least one outlet valve  34  are provided per cylinder chamber  26 . 
     A cylinder head  40 , which engages over the valve plate  30  and in which a suction gas duct  42  which reaches as far as the inlet valve  32  and a compression gas duct  44  which leads away from the outlet valve  34  are provided, is also provided on a side of the valve plate  30  located opposite the cylinder chamber  26 , wherein the suction gas duct  42  is designed as a conduit  48  which leads from a suction gas connection  46  to the inlet valve  32  and predominantly extends, for example, immediately above the valve plate  30 . 
     Refrigerant to be compressed will be supplied to the inlet valve  32  in the valve plate  30  via the suction gas duct  42  in the cylinder head  40  depending on the operating cycle of the reciprocating piston  24 , namely when the reciprocating piston  24  carries out a suction movement, or the refrigerant in the suction gas duct  42  remains essentially without flow, namely when the reciprocating piston  24  carries out a compression movement and compresses the refrigerant in the cylinder  26  and, finally, expels it into the compressed gas duct  44  via the outlet valve  34 . 
     During operation of such a reciprocating piston compressor in a complex system with a refrigerant circuit, particularly with several compressors which are arranged one after the other, there is the risk of an excessively large amount of lubricant  16  collecting in the collecting chamber  14  thereof and, therefore, of possibly too little lubricant being available in other components of the system or of an unnecessarily large amount of lubricant being needed for operation in the system in order to ensure a flow-free operation in the case of such an accumulation of lubricant in a reciprocating piston compressor. 
     In order to avoid this problem, the suction gas duct  42  in the first embodiment is provided with a nozzle  50 , in which acceleration of a stream  52  of suction gas takes place prior to it reaching the inlet valve  32 . 
     An area  54  of reduced pressure, in which a pressure P 1  can be achieved which is below a pressure P 2  in the crankcase  10 , occurs in the nozzle  50  on account of the acceleration of the stream  52  of suction gas. 
     An outlet opening  56  of a lubricant suction conduit which is designated as a whole as  60  is provided in the area  54 , the inlet opening  62  of the lubricant suction conduit being arranged in the collecting chamber  14  of the crankcase  10 , namely at a distance A from a base  64  of the collecting chamber  14  so that lubricant  16  can be drawn in through the inlet opening  62  by suction only for such a time until, as illustrated in  FIG. 2 , the surface level  20  of the lubricant bath  18  is at the height of the inlet opening  62 . 
     In this respect, the lubricant suction conduit  60  is preferably designed as a pipe  66  which reaches from the area  54  in the nozzle  50  as far as the inlet opening  62  and, as a result of the position of the inlet opening  62 , defines the position of the surface level  20  of the lubricant bath  18 , at which it is still just possible to draw in lubricant by suction via the lubricant suction conduit  60  whereas when the surface level  20  sinks further it is no longer possible to draw in lubricant by suction. 
     As a result of the fact that the pressure P 1  is lower in the area  54  than the pressure P 2  in the crankcase  10 , in particular in the collecting chamber  14 , when a stream  52  of suction gas is flowing through the nozzle  50 , it is possible to draw lubricant out of the crankcase  10  by suction via the lubricant suction conduit  60  for as long as the surface level  20  is higher than the inlet opening  62  and until such time as the surface level  20  is at the level of the inlet opening  62  of the lubricant suction conduit  60 . 
     The lubricant drawn into the nozzle  50  by suction will be supplied to the cylinder chamber  26  by the stream  52  of suction gas via the inlet valve  32  and from there be expelled with the compressed refrigerant via the outlet valve  34  and, therefore, discharged via the compressed gas duct  44 , for example conveyed with the compressed gas to the next refrigerant compressor. 
     In a second embodiment of a reciprocating piston compressor according to the invention, illustrated in  FIG. 3 , all those parts which are identical to those of the first embodiment are provided with the same reference numerals and so, with respect to their description, reference can be made in full to the explanations concerning the first embodiment. 
     In contrast to the first embodiment, the lubricant suction conduit  60 ′ is not formed by a pipe  66  but is rather integrally formed into the crankcase  10 , for example a wall area  70  thereof, so that the lubricant suction conduit  60 ′ extends in the wall area  70  as far as the inlet opening  62 , passes, in addition, through a passage  72  in the valve plate  30  and, finally, passes through a passage  74  in the nozzle  50  which reaches as far as the outlet opening  56  in the nozzle  50 . 
     In a third embodiment of a reciprocating piston compressor according to the invention, illustrated in  FIG. 4 , those parts which are identical to those of the first or second embodiments are likewise provided with the same reference numerals and so reference can be made in full to the description thereof. 
     In the third embodiment, the lubricant suction conduit  60  extends in the pipe  66 , namely from the inlet opening  62  as far as an outlet opening  56 ′ which, in this embodiment, is located in the area of a side of the valve plate  30  facing the suction gas duct  42  and so the outlet opening  56 ′ borders directly on the conduit  48  provided in the cylinder head  40 . 
     In order to generate a static pressure P 1  in the conduit  48  in the area of the outlet opening  56 ′ which is lower than the static pressure P 2  in the crankcase  10 , in particular in the collecting chamber  14 , a screen  80  is provided as a throttling device upstream of the outlet opening  56 ′ with respect to the stream  52  of suction gas and this screen leads to a drop in pressure downstream of the screen  80  when the reciprocating piston  24  carries out a suction intake movement with an increase in the size of the cylinder chamber  26  and so the static pressure P 1  in the area  54 ′ between the screen  80  and the inlet valve  32  drops for a short time during the suction intake movement  24  and, therefore, a static pressure P 1  is set, at least for a short time, which is lower than the pressure P 2  in the crankcase  10 , in particular in the collecting chamber  14 , and so during this time, during which the static pressure P 1  is lower than the static pressure P 2 , lubricant is drawn out of the collecting chamber  14  by suction via the lubricant suction conduit  60  when the surface level  20  is above the inlet opening  62 . 
     In all the cases, in which the static pressure P 1  in the conduit  48  is at an equally high pressure to the static pressure P 2  in the crankcase  10  or higher, no lubricant  16  will be drawn out of the collecting chamber  14  by suction but this does not represent any disadvantage since a temporary intake of lubricant by suction through the lubricant suction conduit  60  into the area  54 , which is repeated in each operating cycle, is already sufficient to maintain the surface level  20  of the lubricant bath  18  at an average with respect to time in the area of the inlet opening  62 . 
     In a fourth embodiment of a reciprocating piston compressor according to the invention, illustrated in  FIG. 5 , those parts which are identical to one of the preceding embodiments are likewise provided with the same reference numerals and so, with respect to the description thereof, reference can be made in full to the explanations concerning the preceding embodiments. 
     In this embodiment, as well, the outlet opening  56  is located at the valve plate  30 , namely in the area  54 ′ which is located between an adjustable throttling device  90  and the inlet valve  32 . 
     The throttling device  90  comprises a passage  92  which is adjustable with respect to its throttling effect for the stream  52  of suction gas with an adjustable throttle valve  94 , for example a throttle valve  94  pivotable about an axis  96 , wherein an actuating drive  98  is, for example, provided. 
     As a result, the same effect can, in principle, be achieved as with the screen  80  but with the difference that the throttling device  90  is adjustable with respect to its throttling effect on the stream  52  of suction gas as a result of rotation of the throttle valve  94  so that it is possible to adjust the pressure P 1 , namely in accordance with the stream  52  of suction gas, so that the static pressure P 1  drops, for example, during certain partial phases of the suction intake movement of the reciprocating piston  24 , to such an extent that this pressure is lower than the static pressure P 2  in the crankcase  10 , in particular in the collecting chamber  14 , and, therefore, it is possible to draw lubricant out of the collecting chamber  14  by suction and supply it to the stream  52  of suction gas for transporting further. 
     This solution has the advantage that, as a result of the throttle valve  94  being adjustable by means of the actuating drive  98  in accordance with the operating conditions of the reciprocating piston compressor, the periods of time, at which the static pressure P 1  in the conduit  48  is lower than the static pressure P 2  in the crankcase  10 , in particular in the collecting chamber  14  thereof, can be adjusted each time in adaptation to the stream  52  of suction gas. 
     The variation of the third embodiment described above therefore provides for the setting of the throttle valve  94  to remain constant over a plurality of operating cycles and, therefore, the setting can be brought about such that the static pressure P 1  drops at least temporarily to such an extent that lubricant  16  will be drawn in by suction via the lubricant suction conduit  60 . 
     Alternatively, it is, however, also conceivable to carry out the adjustment of the throttle valve  94  dynamically, i.e., for example, to adjust the throttle valve  94  to a specific value for the throttling of the stream  52  of suction gas during the course of each operating cycle in order to reduce the static pressure P 1  in the area  54 ′ for a specific length of time. 
     It is, however, also conceivable not to use the throttle valve  94  during each operating cycle for the throttling of the stream  52  of suction gas but rather, for example, to control the flow of the stream  52  of suction gas with the throttle valve  94  only during one or a few operating cycles and then to control the throttle valve  94  for a plurality of operating cycles such that throttling no longer takes place so that during periods of time corresponding to a great number of operating cycles no throttling whatsoever of the stream  52  of suction gas takes place by way of the throttle valve  94  in order not to impair the compressor capacity and throttling of the stream  52  of suction gas takes place with the throttle valve  94  only when a short-term impairment of the compressor capacity is accepted in order to draw lubricant out of the collecting chamber  14  by suction via the lubricant suction conduit  60  while, subsequently, the throttle valve  94  will be opened again for an appreciably long period of time in order to, on the other hand, have the full compressor capacity available.